Synthesis and Structures of Low Valent Gallium (I)
Supported Organometallic Compounds and New
Organometallic Routes to Intermetallic Nickel-Gallium
Nanoparticles
Adinarayana Doddi
Ruhr-Universität Bochum
Bochum, November 2012
Synthesis and Structures of Low Valent Gallium (I) Supported
Organometallic Compounds and New Organometallic Routes
to Intermetallic Nickel-Gallium Nanoparticles DISSERTATION
Submitted by
Adinarayana Doddi (M.Sc Chemistry)
to obtain the doctorate Dr. rer. nat of the Faculty of Chemistry and
Biochemistry at the Ruhr University Bochum, Germany
Bochum, November 2012
(Andhra Pradesh, India)
i
The work described in this doctoral dissertation has been carried out under the guidance and
supervision of Prof. Dr. Roland A. Fischer at the Chair of Inorganic Chemistry-II,
Organometallics and Materials, Ruhr University Bochum, Germany between April-2009 to
September 2012.
1st Referee: Prof. Dr. Roland A. Fischer
2nd Referee: Prof. Dr. Nils Metzler-Nolte
Date of oral examination: 17.12.12
Herein, I declare that I have written this thesis independently and without unauthorised help.
Further, I assure that I have used no other sources, auxiliary means or quotes than those
stated. I further declare that I have not submitted this thesis in this or in a similar form to any
other university or college. Besides, I also declare that I have not already undertaken an
unsuccessful attempt to obtain a doctorate from another university or college.
Adinarayana Doddi
November 2012
ii
ACKNOWLEDGEMENTS
First of all, I wish to express my sincere thanks and gratitude to my supervisor Prof. Dr.
Roland A. Fischer for his constant encouragement, motivation, discussions and suggestions
during my stay. I am very much grateful to be part of organometallic subgroup and thanks
for providing excellent research fascilities. Thank you for keeping trust on me to work in
such a highly international student working group.
I am very much grateful to Dr. Christian Gemel who has been my side, whenever I go to
him; he has always been giving his suggestions and directions when I had some problems in
reactions and analysis of the spectra. Thank you so much Christian.
Sabine Pankau and Jacinta Essling: I thank Sabine and Jacinta for their wonderful help in
different administrative problems such as visa and private life in Bochum. Thanks for Sabine
for your help and advices.
I would like to thank my present and former organometallic sub-group colleagues; Dr.
Thomas Cadenbach, Dr. Timo Bollermann, Dr. Markus Halbherr, Mariusz Molon, Kerstin
Freitag, Arik Puls, Clarissa Kroll.
I express my sincere thanks to Dr. Ganesamoorthy Chelladuari and Dr. Ramasamy Pothiraja
for initial proof reading of this thesis.
I would like to thank Dr. Ganesan Prabushankar (IIT-Hyderabad) who introduced me to
Ga(DDP) chemistry for his guidance during the initial days of my Ph.D work, for the many
deep and fruitful discussions, as well as for the nice time spent in the lab including sharing a
hood.
I also would like to thank Dr. Mahmoud Ashour Sliem, who has been a very good friend and
always encouraging me when I lose motivation. Thank you Mahmoud. I would like to extend
my thanks to Dr. Suresh Babu Kalidindi for helpful suggestions as far as the Nanoparticle
work concerned as well as Mr. Christian Wiktor for TEM measurements of my samples.
I thank Dr. R. W. Siedel and Ms. Manueal Winter for their unique support for
crystallographic related work and spending lot of their time on solving single crystal X-ray
structures.
I thank Prof. Dr. rer. nat. Nils Metzler-Nolte for agreeing to act as second referee for my
thesis.
iii
I would like to extend my gratefulness to Prof. Dr. Gernot Frenking, Ms. C. Goedecke
(Philipps-Universität Marburg) for performing quantum chemical calculations.
Of course, I would like to thank all the group members of AC-II for the very nice and
friendly working atmosphere: Prof. Anjana Devi, Dr. Rochus Schmid, Dr. Harish Parala, Dr.
Radim Beránek, Frau Uschi Herrmann, Dr. Sareeya Bureekaew, Dr. Bo Liu, Dr. Saeed
Amirjalayer, Dr. Maike Müller, Dr. Tobias Thiede, Dr. Daniel Esken, Dr. Sudip
Chskraborty, Dr. Malte Hellwig, Mr. Michael Krasnopolski, Dr. Denise Zacher, Ke Xu. Kira
Khaletskaya, Dr. Sebastian Henke, Dr. Daniela Bekermann, Olesia Kozachuk, Sun Ja Kim,
Nagendra Babu Srinivasan, Manish Benerjee, Andrea Schneemann, Julian Schumann, Stefan
Cwik, Dr. Sandra Gonsalez-Gallardo, Dr. Eliza Gemel, Dr. Mikhail Meilikov, Dr. Andrian
Milanov, Dr. Xiaoning Zhang, Dr. Van-Son Dang, Daniel Peeters, Angélique Bétard, Min
Tu, Christoph Rösler, Hung Banh, Heike Gronau-Schmid and Dr. Nadia Gamel. My thanks
also go to Vanessa Gwildies for nice encouraging talks at times. I am highly thankful to Mr. Martin Gartmann who has been very helpful for me whenever I
need some help regarding NMR measurements as well as Mr. Hans-Jochen Hauswald for
questions concerning NMR spectroscopy related issues. I would like to extend my thanks to
Frau Karin Bartholomäus for performing micoranalysis of all my samples.
I am very much grateful to Prof. M. N. Sudheendra Rao (IIT-Madras) who has been a
constant source of encouragement and moral support.
I thank all my Indian friends in Bochum for the time that we spent together outside. My
apologies to the others who I have not mentioned by name, I am indebted to them for the
many ways they helped me.
Finally, I wish to express my deepest gratitude to my parents Nagabhushanam & Surya
Lakshmi who has been very supportive since my school days and also for always
encouraging me to go for higher studies. I would like to extend my thanks to my wife
Soujanya for her unconditional support and love.
iv
Dedicated to my parents
v
Table of Contents
1
Introduction……………………………………………………………………….
1.1
Introduction to Main-Group Chemistry……………………….……………. 1
1.1
1.2
1
Historic Milestones of Main-Group Organometallic Chemistry……
2
The Chemistry of Low Valent Group 13 Metals………..…….….…............
3
1.2.1
Synthesis of N-Heterocyclic Group 13 metal (I) Ligands
(NHE)…….......................................................................................... 8
1.3
1.2.2
Neutral Six-membered Heterocyclic Organyls................................... 10
1.2.3
Electronic Properties of Group 13 metal (I) Organyls as Ligands.....
11
1.2.4
Some Theoretical Aspects of free Heterocycles…………………….
13
A Brief Overview of Bonding and Electronic Properties in -Diketiminate
Gallium (I): A Carbene Analogue……………………..................................
1.3.1
15
Coordination Chemistry of Low Valent Group 13 Metal (I)
Organyls (ER) Towards Main-Group and Transition Metal
Fragments............................................................................................ 17
1.4
Reactivity of Ga(I) Heterocycles…………………………………….……...
1.5
Binary Intermetallic Compounds……………………………………..…….. 22
1.6
1.7
18
1.5.1
Intermetallic Compounds……………………………………….…... 22
1.5.2
Hume-Rothery Phases………………………………………….…… 23
1.5.3
Group 13 Elements Containing Intermetallics……………….……..
25
Synthetic Approaches to Metallic Nanoparticles…………………….……... 26
1.6.1
General Introduction………………………………………….…......
26
1.6.2
Synthesis of Metallic and Intermetallic Nanoparticles.......................
26
1.6.3
Existing Methods…………………………………………………....
26
1.6.4
Other Chemical Methods…………………………………….……...
27
Soft Chemical Synthesis of Intermetallic Nanoparticles: Hydrogenolysis of
Hydrocarbon Metal Complexes ……………….............................................
1.7.1
27
Soft Chemical Synthesis of M–E (E = Al and Ga) Nanoparticles….. 28
1.7.2 Applications of Nano Intermetallic Phases………………….…….... 30
1.8
Aims and Objectives of the Dissertation………………………….………...
30
1.9
References…………………………………………………………………..
33
vi
2
Synthesis and Characterization of Heteroleptic Platinum-GaR (R = DDP, 40
Cp*) Complexes………………………………….………………………………..
2.1
Introduction………………………………………………….……………… 41
2.2
Synthesis and Characterization of [(1,5-cod)(Cl)Pt{ClGa(DDP)}] (2) and
[(dcy)(Cl){PtClGa(DDP)}] (3)……………………...………….…………... 42
2.3
Single Crystal X-ray Analysis of [(1,5-cod)(Cl)Pt{ClGa(DDP)}] (2) and
[(dcy)(Cl)Pt{ClGa(DDP)}] (3)………………….…......................................
2.4
46
Synthesis of [(DDP)Ga(Me)(OTf)] (4)……………………….......…............ 49
2.4.1 Single Crystal X-ray Structure of [(DDP)Ga(Me)(OTf)] (4)……….
50
2.5
Synthesis of [(cod)(CH3)Pt{Ga(CH3)(DDP)}] (5).........................................
51
2.6
Synthesis of [(Cl3Ga)Pt(GaCp*)4] (6)………………………….……..…….
54
2.6.1
Single Crystal X-ray Structural Analysis of [(Cl3Ga)Pt(GaCp*)4]
(6)………………………….………………………………………... 55
2.7
3
References…………………………………………………………………... 57
PP Bond Activation of P4 Tetrahedron by Ga(DDP): Reactivity and
Coordination Chemistry of [(DDP)Ga(P4)] with Metal Carbonyls Mo(CO)6
and Fe2(CO)9……………………………………………………………………....
60
3.1
Introduction…………………………………………………………………. 61
3.2
Synthesis and Structural Characterization of [(DDP)Ga(P4)] (7)…………... 62
3.3
3.2.1
Synthesis of 7..…………..………………………..………………..
62
3.2.2
Molecular Structure of [(DDP)Ga(P4)] (7)………………………… 64
Synthesis and Structural Characterization of
[(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene (8)……………….…………….. 67
3.3.1
Synthesis of 8…..………..…………………………..……………..
3.3.2
Molecular Structure of
[(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene (8)………..…………...
3.4
69
Synthesis and Structural Characterization of
[(DDP)Ga(η2:1:1-P4){Fe(CO)4}] (9)………………………….……...……...
72
3.4.1
Synthesis of 9………………………………………………………
72
3.4.2
Molecular Structure of Compound [(DDP)Ga(η2:1:1-P4){Fe(CO)4}]
(9)………………………………......................................................
3.5
67
Reactivity of [(DDP)Ga(P4)] Towards Olefins: Attempted reactions to
vii
73
explore 7 as the phosphorus transfer reagent!................................................
3.6
4
75
References…………………………………………………………............... 76
Synthesis of Low Valent “Ge4” and “Ge2” Clusters Trapped by Low Valent
Ga(DDP): A -Bond Between two Ge–Ge Centers without a -Bond………...
79
4.1
Introduction…………………………………………………………………. 80
4.2
Synthesis of [Ge4{Ga(DDP)}2] (10)………………………………………...
81
Molecular structure of [Ge4{Ga(DDP)}2] (10)…………………….
84
Synthesis of [Ge2{Ga(DDP)}2] (11)………………………………………...
86
4.2.1
4.3
4.3.1
Single Crystal X-ray Structure of [Ge2{Ga(DDP)}2] (11)………… 90
4.3.2
Bonding Analysis of Ge2[Ga(DDP)]2 (11) by Quantum Chemical
Calculations………………………………....................................... 93
4.4
5
4.3.3
Electron Localization Function Calculations (ELF) for 11……......
98
4.3.4
Natural Bond Orbital Analysis (NBO) of 11....................................
99
References....................................................................................................... 102
Synthesis
and
Structural
Characterization
of
Ga(DDP)
Supported
Ruthenium and Copper Complexes: A Compound with a Perfect Linear
Ga-Cu-Ga bond……..…………………………………………..………………...
105
5.1
Introduction...................................................................................................
106
5.2
Synthesis of [{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}](12)………………………… 107
5.3
Molecular Structure of [{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}] (12)……………..
5.4
6
111
6
114
Synthesis of [(η -p-cymene)Ru(DDP)Ga)(µ-Cl){Ga(Cl)C29H41N2}] (13)..
5.5
Structure of [(η -p-cymene)Ru(DDP)Ga)(µ-Cl){Ga(Cl)C29H41N2}] (13)...
5.6
Reactivity of Ga(DDP) with Cu(II) and Cu(I) trifflates: First Dinuclear
5.7
109
6
Copper/Gallium complex with a Ga-Cu-Ga Linear Bond……......………..
117
5.6.1
Synthesis of [{(DDP)Ga}2Cu][OTf] (14)………………………….
118
5.6.2
Molecular Structure of Compound [{(DDP)Ga}2Cu][OTf] (14)….
119
References.....................................................................................................
122
Sterically Bulky N-heterocyclic Carbene Complexes of ZnCl2 and TiX4 (X =
F, Cl): Syntheses, Characterization and Reactivity…………… ………………
125
6.1
Introduction...................................................................................................
126
6.2
Synthesis of Mono NHC Derivative [Cl4TiC{N(2,6-iPr2C6H3)CH}2]
viii
(15)…………………………………………………………………………
6.2.1
127
X-ray Structural Analysis of [Cl4TiC{N(2,6-iPr2C6H3)CH}2]
(15)…................................................................................................ 128
6.3
Synthesis of Complex [TiCl4{C{N(2,6-iPr2C6H3)CH}2}2] (16)…………...
6.3.1
6.4
Molecular Structure of [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (17)…...
134
Synthesis of [HC{N(2,6-iPr2C6H3)CH}2]2[TiCl6] (18)………………….....
135
Molecular Structure of [HC{N(2,6-iPr2C6H3)CH}2]2[TiCl6] (18)…
136
6.5.1
6.6
i
Synthesis of [Cl2Zn-C{N(2,6- Pr2C6H3)CH}2] (19)………………………..
6.6.1
6.7
X-ray Structure of [TiCl4{C{N(2,6-iPr2C6H3)CH}2}2] (16)………. 131
Synthesis of Complex [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (17)……………. 132
6.4.1
6.5
130
Molecular Structure of [Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19)……. 138
Synthesis of [(CH3)2Zn{C{N(2,6-iPr2C6H3)CH}2}2] (20)…………………
6.7.1
137
139
Single Crystal X-ray Analysis of
[(CH3)2Zn{C{N(2,6-iPr2C6H3)CH}2}2] (20)……………………… 140
Reactivity of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] (15)……………….
6.8
6.8.1
141
Reactivity of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] with Dimethyl Zinc
(Me2Zn)……………………………………..................................... 141
6.9
Attempted
Synthesis
of
NHC
Stabilized
Titanium
and
Zinc
Clusters…………………………………………………………………….. 142
6.9.1
6.9.2
7
Reactivity of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] (15) with KC8.........
i
Reactivity of [Cl2Zn-C{N(2,6- Pr2C6H3)CH}2] (19) with KC8........
143
143
6.10
Reactivity Differences Between Ga(DDP) and IPr………………………... 144
6.11
References.....................................................................................................
146
Organometallic Synthesis of Nickel-Gallium Binary Intermetallic Alloy
Nanoparticles………………………………………………………………...........
7.1
7.2
149
Introduction and Goals…………………………………………………........ 150
7.1.1
Introduction....................................................................................... 150
7.1.2
Nickel-Metalloid Intermetallic Alloys………………………….....
150
7.1.3
Nickel-Gallium Phase Diagram…………………………………....
151
7.14
Goals.................................................................................................
152
Hydrogenolysis of [NiGaCp*(PMe3)3] and Characterization of Ni/Ga
nanoparticles (NP1)………………………………………………................
7.2.1
153
Synthesis of NP1............................................................................... 153
ix
7.3
7.2.2
X-ray Powder Diffraction Analysis of NP1……………………...... 154
7.2.3
Infrared Spectrum of NP1................................................................. 155
7.2.4
Transmission Electron Microscopy of NP1……………………….. 156
Cohydrogenolysis
of
[Ni(GaCp*)3(PCy3)]
and
[Ni(cod)2]
and
Characterization of Ni/Ga nanoparticles (NP2)………………...................... 157
7.4
7.3.2
X-ray Powder Diffraction Analysis of NP2……………………...... 157
7.3.3
Transmission Electron Microscopy of the Sample NP2…………...
158
Synthesis and Characterization of NiGa (1:1) Nanoalloy (NP3)…………… 159
7.4.1
Synthesis of NiGa nanopowder (NP3) from [Ni(cod)2] and
GaCp*……………………………………………...........................
160
7.4.2
X-ray Powder Diffraction Analysis of NP3…………………….....
160
7.4.3
Transmission Electron Microscopic Analysis of the Particle’s
Morphology……..…………………………………......................... 161
7.4.4
7.5
Infrared Spectrum of NP3………………..………………………... 163
Synthesis and Characterization of Intermetallic Crystalline Ni2Ga3 nano
powder (NP4)……………….………………………………………………. 163
7.5.1
Synthesis of NP4…………………………….…………………….. 163
7.5.2
X-ray Powder Diffraction Analysis of NP4……………….……..... 164
7.5.3
Transmission Electron Microscopic Analysis of the Particle’s
Morphology...……………………………………………………… 165
7.6
7.7
Synthesis of Intermetallic Ni3Ga Nanopowder (NP5)………..….................. 166
7.6.1
Synthesis of NP5…………..………………………………………. 166
7.6.2
X-ray Powder Diffraction Analysis of NP5………………..…….... 167
7.6.3
Infrared Spectrum of the Black Material (NP5)……………...…....
167
7.6.4
TEM Characterization of NP5…………………...…………….......
168
Synthesis and Characterization of the Colloidal Intermetallic NickelGallium Nanoparticles……………………………………………................
7.7.1
169
Intermetallic Ni-Ga Colloids from a Single Source Precursor
[NiGaCp*(PMe3)3] (NP6)……………………….………………….. 169
7.7.2
Infrared Spectrum of NP5…………………………………………... 170
7.7.3
Transmission Electron Microscopic Analysis of the Particle’s
Morphology……………….………………………………………...
7.7.4
171
Dynamic Light Scattering Analysis………………….……………... 172
x
7.8
Catalytic Activity of Nano Intermetallic Compounds NiGa, Ni2Ga3, Ni3Ga
and Hydrogenation of Olefin………………………………………………..
7.9
173
7.8.1
Cyclohexene Hydrogenation……………………………………… 173
7.8.2
Catalytic activity of Ni nanopowder……………………………… 174
7.8.3
Catalytic activity of NiGa (NP3) nanopowder…….…...................
7.8.4
Catalytic Activity of Ni2Ga3 nanopowder (NP4)………………..... 175
7.8.5
Catalytic activity of Ni3Ga nanopowder (NP5)……….…………..
175
176
References……………………………..……………………………………. 177
8
Summary and Outlook……………………………..……...................................... 179
9
Experimental Section…………………………………………..…………………
9.1
Materials and Methods………………………………………........................ 185
9.1.1
9.2
185
General Remarks………………………………………………….
185
Instrumental Details………………………………………………………..
186
9.2.1
Infrared Spectroscopy (IR)………………………………………..
186
9.2.2
Elemental Analysis and Atomic Absorption Spectroscopy
(AAS)............................................................................................... 186
9.2.3
Nuclear Magnetic Resonance Spectroscopy (NMR)…….………..
186
9.2.4
UV/Vis Spectroscopy…..………….……………………………...
187
9.2.5
Photoluminescence………………………………………………..
187
9.2.6
Single Crystal X-Ray Diffraction………………………………....
187
9.2.7
Mass Spectroscopy (MS)……………………………………….....
187
9.2.8
Melting Point Measurements……………………………………...
188
9.2.9
Working Procedure………………………………………………..
188
9.2.10
X-Ray Powder Diffraction………………………………………... 188
9.2.11
Instrumental Specifications……………………………………….
189
9.2.12
Transmission Electron Microscopy (TEM)…………………….....
189
9.2.13
Dynamic Light Scattering (DLS)…………………………………. 190
9.3
Syntheses of Starting Materials…….…………………………………….....
190
9.4
Syntheses of Compounds 1-21……………………………………………...
191
9.4.1
Synthesis of Ga(DDP) (1)………………………………….…….. 191
9.4.2
Preparation of [(cod)(Cl)Pt{ClGa(DDP)}] (2)................................
192
9.4.3
Preparation of [(dcy)(Cl)Pt{ClGa(DDP)}] (3)................................
193
xi
9.4.4
Synthesis of [(DDP)Ga(Me)(OTf)] (4)............................................ 194
9.4.5
Preparation of [(cod)(CH3)Pt{CH3Ga(DDP)}] (5)..........................
195
9.4.6
Preparation of [(Cl3Ga)Pt(GaCp*)4] (6).........................................
196
9.4.7
Preparation of [(DDP)Ga(P4)] (7).................................................... 196
9.4.8
Preparation of [(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene (8)........ 197
9.4.9
Preparation of [(DDP)Ga(η2:1:1-P4){Fe(CO)5}] (9)……………….
9.4.10
Preparation of [Ge4{Ga(DDP)}2] (10)……………………………. 198
9.4.11
Synthesis of [Ge2{Ga(DDP)}2] (11)……………………………....
199
9.4.12
Synthesis of [{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}] (12)……………….
200
9.4.13
Synthesis of [(η6-p-Cymene)RuCl]2 ……………………………… 201
9.4.14
Synthesis of
197
[(η6-p-cymene)Ru(DDP)Ga)(µ-Cl){Ga(Cl)C29H41N2}] (13)........... 201
9.4.15
Synthesis of [{(DDP)Ga}2Cu][OTf]·2C6H5F (14)……….………
i
203
9.4.16
Synthesis of [Cl4Ti-C{N(2,6-Pr 2C6H3)CH}2] (15)……….………
204
9.4.17
Synthesis of [Cl4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (16)…….………
205
9.4.18
Synthesis of [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (17)……….……..
205
9.4.19
Synthesis of [HC{N(2,6-iPr2C6H3)CH}2]2[TiCl6] (18)………….. . 206
9.4.20
Synthesis of [Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19)………………
207
9.4.21
Reaction of [IPr·TiCl4] Adduct with Me2Zn: Carbene Transfer …
208
9.4.22
Synthesis of [(CH3)2Zn{C{N(2,6-iPr2C6H3)CH}2}2] (20)………... 208
9.4.23
Synthesis of [(PCy3)·GeCl2] (21)..................................................... 209
9.4.24
Synthesis of Nanopowder (NP1)………………………………….
209
9.4.25
Synthesis of Nanopowder (NP2)………………………………….
209
9.4.26
Synthesis of NiGa Nanopowder (NP3)…………………………… 210
9.4.27
Synthesis of Ni2Ga3 Nanopowder (NP4)…………...……………..
210
9.4.28
Synthesis of Ni3Ga Nanopowder (NP5)…………………………..
211
9.4.29
Preparation of Nickel-Gallium Colloidal Nanoparticles (NP6)…..
211
9.4.30
Hydrogenation of cyclohexene with NiGa Nanopowder (NP3).…. 212
9.4.31
Hydrogenation of cyclohexene with Nanopowder (NP4)………… 212
9.4.32
Hydrogenation of cyclohexene with Ni3Ga Nanopowder (NP5)…. 213
9.4.33
Hydrogenation of cyclohexene with Ni Nanopowder…………….
213
9.5
Handling and Disposal of Solvents and Residual Wastes…………………..
213
9.6
References………………………………………………………………....... 215
xii
10
Crystallographic Tables………………………………………………….………. 216
11
Supporting Information…………….………………………………………..…... 221
12
Appendix…………………………………………………………………………..
223
12.1
List of Publications………………………………………………………… 223
12.2
Conference Presentations and Workshops…………………………………
12.3
Curriculum Vitae........................................................................................... 227
xiii
225
List of Abbreviations and Symbols
Aº
angstrom unit, 10-10 m
AAS
atomic absorption spectroscopy
Acac
acetylacetonate
AO
atomic orbital
Ar
argon
Av
average
br
broad
ºC
centigrade
Bu
butyl
t
Bu
tertiary butyl
cm-1
wave number
cod
cycloocta-1,5diene
cot
cyclooctatetraene
Cp*
pentamethylcyclopentadiene; C5Me5
Cp*H
1,3-pentamethylcyclopentadiene
Cy
cyclohexyl
d
doublet, day
DDP
2-diisopropylphenylamino-4-diisopropylphenylimino-2pentene
DFT
density functional theory
DLS
dynamic light scattering
EA
elemental analysis
e
electron
EDX
energy dispersive X-ray spectroscopy
Et
ethyl
eV
electron volt
FWHM
full widths at half maximum
h
hour
HDA
hexadecyamine
Hz
hertz, s-1
HOMO
highest occupied molecular orbital
xiv
IPr
[:C{[N(2,6-iPr2C6H3)]CH}2]
IR
infrared
J
coupling constant
K
Kelvin
L
ligand
LIFDI
liquid injection field desorption ionization
LUMO
lowest unoccupied molecular orbital
Me
methyl
min
minutes
m/z
mass/charge
m
multiplet
M
central metal atom in a compound
MO
molecular orbital
Mes
mesityl group
mg
milligrams
MP
melting point
MS
mass spectroscopy
NHC
N-heterocyclic carbene
NMR
nuclear magnetic resonance
nm
nanometer
NP
nanoparticle
OEt2
diethyl ether
OTf
trifflate anion (CF3SO3-)
i-Pr
isopropyl
Ph
phenyl
PPO
poly (phenylene oxide)
PXRD
powder X-ray diffraction
ppm
parts per million
R
alkyl or aryl group
RT
room temperature
s
singlet
t
triplet
s
septet
TEM
transmission electron microscopy
xv
THF or thf
tetrahydrofuran
TMS
tetramethylsilane
Tol-d8
toluene-d8
UV-Vis
ultraviolet-visible
X
halogen
Z
number of molecules in the unit cell

wavenumber

hapto

wavelength
μ
bridging
δ
chemical shift
xvi
Chapter 1
Introduction
Chapter 1
1. Introduction and Objectives
1.1 Introduction to Main-Group Chemistry
Main-group elements are the most
important elements in the periodic
table
consisting
of
metals,
metalloids and non-metals from s
and p-block elements. Since few
years, the research in this area had
led many fascinating discoveries of
elements, which have opened new
avenues in understanding of our fundamental concepts of bonding and structure. Many
unusual, unpredictable inventions took place in several years and the discoveries of many
scientists around the world came into the light and changed the features of main-group
chemistry. All these events and discoveries are now available in every standard inorganic
chemistry text-book. Furthermore, main-group chemistry made a deep impact on synthetic
inorganic and organometallic chemistry. Interestingly, heavier elements such as groups 1315 have various electronic attributes than the other lighter elements.
[1]
Since the last 40
years have witnessed few spectacular discoveries of main-group elements, and these were
highlighted in few review articles. [2-4]
As2O3 + 4 CH3COOK
" fuming liguid "
cacodyloxide [(CH3)2As]2O
First organometallic compound
Scheme 1.1: Preparation of the first organometallic arsenic compound. [5-6]
The very beginning of organometallic chemistry can be seen back from the discovery of first
organometallic arsenic compound, [(CH3)2As]2O (scheme 1.1). The first main-group
organometallic compound was discovered by a French chemist, Louis Claude Cadet de
1
Chapter 1
Introduction
Gassicourt in 1760. Cadet used the cobalt minerals that contain arsenic and treated with
potassium acetate to get a fuming liquid as shown in Scheme 1.1. [5-6] After it´s isolation, the
main-group organometallic chemistry has grown up with many intevestigations resulted
useful molecules from the reports of pioneering research work of well-known scientists
around the world. In this context, only few such milestones of main-group organometallic
chemistry are summarized as follows (Table 1.1).
1.1.1 Historic Milestones of Main-Group Organometallic Chemistry [5]
Table 1.1: Few examples of main-group organometallic compounds.
S. No
Year
Scientist(s)
Louis
1
Invention
Claude
1760 Cadet
de Cadet prepared the first organometallic compound
Gassicourt
Study of cacodyls compounds, which he named
“alkarsines”. The weakness of the As–As bond in
molecules of the type R2As-AsR2 leads to a profusion of
2
1840 R.W. Bunsen
derivatives such as (CH3)2AsCN, whose taste is checked
by Bunsen. [7-12]
C. J. Löwing
3
4
1852
&
First prepared diethyl lead (C2H5)2Pd from ethyl iodide
and Na /Pd alloy. In a similar manner they also obtained
M. E. Schweizer
(C2H5)2Sb and (C2H5)2Bi. [13-15
W. Hallwachs
Generated alkyl aluminum iodides. [16]
1859
&
2Al + 3 RI
R2AlI + RAlI2
A. Schafarik
C. Friedel
5
1863
&
Prepared organosilanes. [17-19]
SiCl4 + m/2 ZnR2
RmSiCl4-m + m/2 ZnCl2
J. M. Crafts
Developed a method for the synthesis of halide-free
6
7
1866 J. A. Wanklyn
1922
alkyl magnesium compounds. [20]
F. Midgley
Introduced Pd(C2H5)4 as an antiknock additive in
and T. A. Boyd
gasoline. [21]
Opened the field main-group element dimetallenes with
2
Chapter 1
8
1976 M. F. Lappert
Introduction
the
synthesis
of
[((CH3)3Si)2CH]2Sn=Sn[CH(Si(CH3)3)2]2. [22]
Reported
9
1981 R. West
a
first
stable
compound
with
Si=Si;
(Mes)2Si=Si(Mes)2. [23]
Synthesized tBu–CP, the first compound with a CP
10
1981 G. Becker
triple bond. [24]
11
1989 P. Jutzi
Preparation of Cp*2Si. [25]
Reported the synthesis of AlCl, which he used in the
12
1989 H. Schnökel
development of the organometallic chemistry of
monovalent aluminum, for example, [Cp*Al]4 (1991).
[26]
Reported the first germyne complex with a Mo–Ge
13
1996 P. P. Power
triple bond. [27]
The “C” atom in the ultimate ligand in organometallic
14
1997 C. C. Cummins
chemistry. [28]
Reported the salt Na2[ArGaGaAr] and postulates a
15
1997 G. M. Robinson
Ga–Ga triple bond for the diaryldigallyne anion.[29]
Fully characterized R–SiS–R, the first compound with
16
2005 A. Sekiguschi
a SiSi triple bond. [30]
Reported the first stable Mg (I) compound with Mg–Mg
17
2007 C. Jones
bonds. [31]
Reported a compound containing Si(0) with Si=Si;
18
2008 G. M. Robinson
(IPr)Si=Si(IPr). [32a]
Likewise, many more milestones of organometallic chemistry have been reported, but the
above-presented examples (taken from reference no.5) are only few of those which are more
relevant to the present discussion of this chapter.
1.2
The Chemistry of Low Valent Group 13 Metals
In the last two decades, many new exciting developments have taken place in the
chemistry of group 13 metals (Al to Tl) and this has led to the synthesis and isolation of
novel and unusual chemical species with implications for organometallic synthesis and the
3
Chapter 1
Introduction
development of materials with end use. [32b] The five elements in this group from boron to
thallium each has atoms whose electronic ground state has three valence electrons
(configuration of ns2np1). Table 1.2, depicts the general electronic configurations of all the
group-13 elements.
Table 1.2: Electronic configurations of the group 13 metals.
Group -13 metal
Symbol
Electronic
configuration
Boron
B
[He]2s22p1
Aluminum
Al
[Ne]3s23p1
Gallium
Ga
[Ar]3d104s2 4p1
Indium
In
[Kr]4d105s2 5p1
Thallium
Tl
[Xe]4f14 5d106s2 6p1
Figure 1.1: Schematic illustration of the condensation apparatus for the generation of
gaseous AlX high temperature species. Reprinted with permission from H. Schnöckel, H.
Köhnlein, Polyhedron. 2002, 21, 489-501. Copyright © 2002, Elsevier.
4
Chapter 1
Introduction
The most stable oxidation state of the group 13 metals is “+3” which is described in
the standared inorganic text-books.
[35]
However, since last three decades the low-valent
main-group chemistry has rapidly grown and had opened up new avenues. For instance,
Schnöckel and co-workers have developed a reactor (as shown in Figure 1.1) to produce
metastable Al(I) and Ga(I) mono halides, stabilized by the coordination of either Lewis basic
amine or ether such as [{MX(L)}n] (M=Al or Ga; X = Cl, Br or I; L= OR2 or NR3).
[35]
In
contrast to the low-valent group 13 halides of the heavier elements indium and thallium, the
respective Al(I)X and Ga(I)X (X = halide) species are generally unstable and transient at
room temperature, tend to disproportionate into other possible species. In other words, they
are unstable without some stabilizing “R” groups on the metal centre. In order to stabilize
such highly reactive and short-lived species, the most important requirement is to have a
suitable alkyl or aryl group on the low-valent metal center. This particular “R” group should
facilitate steric bulk at the same time electronically stabilizing species. In this regard, few
such sterically bulky ligands were found to be suitable and the species employed so far are i)
2,6-disubstituted aryl groups, ii) sterically pronounced alkyl and persilylated substituted
alkyl groups C(SiMe3)3, Si(tBu)3), tBu, and iii) cyclopentadienyl (Cp) groups including
C5(CH2Ph5), Cp* (pentamethylcyclopentadiene) and CpB. [35]
The important discovery in this area was reported by two synthetic strategies, which are
resulted from different routes. Paetzold and co-workers first time reported a Boron (I)
compound, [{BtBu}4][36], later Schnöckel and co-workers explored the synthesis of the first
Aluminum (I) compound, [AlCp*]4 by a metathetical exchange of chloride ion from [AlCl]
by [MgCp*2].[37] After their synthetic discovery, Linti and co-workers have shown similar
gallium containing clusters which were prepared from the metastable gallium(I) idodide,
“[GaI]” with some sterically bulky silylated reagents affords the tetragallane [R4Ga4I3]¯ and
gallium metal rich cluster, nonagallane [R6Ga9]- (R = Si(SiMe3)3).[38] Subsequently, Roesky
and co-workers successfully employed the reductive dehalogenation method to prepare
[AlCp*]4 from the reaction of [Cp*AlCl2] with potassium using the aromatic solvent such as
in toluene.
[39]
These authors have recently been adopted this synthetic strategy for the
reduction of aluminium diiodide derivative [(Me3Si)3CAlI2.THF] with Na/K alloy to afford
yet another aluminium cluster, [{AlC(SiMe3)3}4].
[40]
Jutzi and co-workers have also shown
that reductive dehalogenation of iodide derivative of gallium (III), [Cp*GaI2] with potassium
metal affords monovalent [GaCp*]6 in reasonably good yield from the use of ultrasonic
metal activation method.[41] By utilizing these two novel and reliable synthetic strategies,
5
Chapter 1
Introduction
many monovalent compounds containing Al, Ga, In, and Tl had been prepared. The
sterically bulky monovalent derivatives, AlCp* and GaCp* have been reported to contain
different compositions in solid and vapour state.
[35]
The oligomeric nature of [AlCp*]4 and
GaCp* is shown in Figure 1.2.
*Cp
Ga Cp*
Ga
*Cp Ga
Ga
Cp*
Ga
*Cp
Ga
Cp*
6 GaCp*
GaGa bond length
dGa-Ga : 4.073 Å
Cp*
Al
*Cp
*Cp
Al
Al

Al
4 AlCp*
Cp*
AlAl bond length
dAl-Al : 2.769 Å
Figure 1.2: Oligomeric nature of the low-valent [AlCp*]4 and [GaCp*]6 organyls. [35]
The single crystal X-ray structural analysis of the monovalent ECp* (E = Al to Tl) species
show interesting aggregates in the solid state with direct M–M bonds containing clusters
with the decoration of sterically bulky Cp* ligands on each metal centres. The molecular
structure of [AlCp*]4 is quite interesting in it’s solid state, which exhibits a tetrahedral “Al4”
core with the M–M distances of 2.769 Å.
[33, 34, 35, 40]
This indicates, that the interactions
between the AlCp* units in the cluster are slightly stronger than those in the metallic aluminum,
which is av. 2.86Å (see Table 1.3). This particular behavior of dissociation and association
mechanism is shown in Figure 1.2. According to Schnöckel and co-workers, the monomeric
units were observed only above the room temperature which was monitored by variable
temperature
27
Al NMR measurements. Whereas it’s gallium analogue, [GaCp*]
[35, 42]
forms
hexameric gallium cluster in the solid state and it is isomorphous to its indium analogue,
[Cp*In]6. [34, 35, 43] Due to very long gallium-gallium distances (dGa–Ga: 4.073 Å much longer
than in the metallic gallium; 2.45-3.07 Å) in GaCp*, the cluster arranges into a distorted
6
Chapter 1
Introduction
octahedral geometry. [35] These M–M distances are even longer than In–In interactions in its
indium analogue, [InCp*]6. This fact is further supported from the variable temperature 71GaNMR measurements and shows that when the temperature is changed no changes in the GaCp*
resonances were observed, which means that GaCp* does not undergo association or
dissociation equilibria (Fig. 1.2) in solution as it is for the case of AlCp*.
[33, 35]
Which means
that the lone-pairs of electrons on the gallium center are not favorably involving for the
oligomerization to occur as in the case of its analogue, AlCp* which is a tetramer. This is
because of the larger “inert-pair” effect expected for gallium over aluminum when we move
top to down in the group. [35]
Table 1.3: M–M bond distances in E(I)Cp* derivatives (E = Al, Ga, In and Tl).[80]
Compound, ECp*
E–E distance (Å)
E–E distance (bulk) (Å)
[AlCp*]4
a.v.2.77
2.86
[GaCp*]6
4.07
2.45 to 3.07
[InCp*]6
a.v. 3.95
3.36 and 3.39
[TlCp*]n
a.v. 6.41
3.36
and 3.43
Another interesting aspect of these compounds is the dimensions of GaCp* units which are
very much similar in its solid state as well as gas phase. Thus, the distance between the Ga
center to the Cp* centroid in both phases are the same (2.081 Å).
[34, 35]
From all these
observations, it was assumed that the monomeric units in the cluster are held by Van der
Waals interactions where the sterically bulky Cp* ligands are capping the whole cluster, but
not essentially the M–M bonds which is one of the important novel bonding modes which
helps the clusters stable. [35] Whereas, this particular bonding situation is different in case of
[AlCp*]4, where the tetrahedron unit is stabilized by electrons from the four two centred
three electron (2e3c) bonds as it is shown in Figure 1.2. Other important facets of these lowvalent organyls are having different aggregation modes in the solid state, but they vaporize
as monomeric unit which is useful to some extent in the MOCVD studies of these low-valent
organyls (GaCp* is found to have thermal stability upto 600 C).
7
[35, 41-43]
The average E–E
Chapter 1
Introduction
bond lengths of all these ECp* derivatives in the solid state as well as bulk are summarized
as shown in Table 1.3 for comparision.
1.2.1 Synthesis of N-Heterocyclic Group 13 metal (I) Ligands (NHE) [16, 48, 52]
R1
R N
R2
R1
N R
R
E
••
N
E
R1
R1
N R
R
R1
N
N
E
••
(A)
R
••
(C)
(B)
E = Group 13 element
R, R1, R2 = H, alkyl, aryl, etc.
Figure 1.3: Group 13 metal (I) incorporated in N, N-chelating ligands.
N
N
C
••
N
N
H
Ga
••
N
B
N H
••
Figure 1.4: Five-membered NHC and its analogues with group 13 metal (I) N-heterocycles.
After the successful isolation of the low-valent group 13 metal (I) organyls with aforementioned
ligands (such as 6 electron donor Cp* and other bulky silyl groups which have mostly yielded
oligomers at room temperature), a lot of interest has been devoted to the development of a new
class of ligands to stabilize similar metal (I) species with which the oligomerization of the group
13 metals can be prevented. In this regard, new N,N-cheating ligands with unsaturated backbone
were developed. These classes of ligands are shortly can be called as NHEs (N-heterocyclic
group 13 metal (I) ligands) and are regarded as heavy analogues of well known “Arduengo” type
8
Chapter 1
Introduction
N-heterocyclic carbenes. [48, 52] Figure 1.3 shows various NHE type compounds where the group
13 metal (I) is incorporated or stabilized by N,N-chelation to give new species in their
monomeric state and are stable at room temperature. Among these heterocycles the fivemembered heterocycles type B are described as the true valence electronic analogues of the
classical “Arduengo” type N-heterocyclic carbenes as depicted in Figure 1.4, whereas the other
two four- and six-membered heterocycles, with their singlet lone pairs, can be considered as
isolable with four and six membered N-heterocyclic carbenes. [48, 52]
NCy2
N
N
N
N
E
:
Ga
..
E = Ga, In and Tl
: Ga({ArNCH})-
: E(Giso)
R2
E
..
R1
R1
E:
R1
E = Al-Tl
N
E:
N
R1
R2
E = Ga, In and Tl
E(Mes*)
E = Al - Tl
[: E(DDP)]
R1 = iPr, R2 = iPr, tBu
Figure 1.5: Shows various low-valent group 13 metal (I) organyls. [80]
The chemistry of N, N-heterocycles of type A to C as ligands in organometallic and
coordination chemistry is still at the developing stage and is not as much as developed as the
group 14 N-heterocyclic analogues such as silylenes, germylene and stanylenes.
regard few working groups (Schnöckel,
[35]
Power
[50]
, Jutzi
[41]
, Uhl
[34]
[52]
and Roesky
In this
[49, 54a]
)
showed the preparation, stability and structures of various group 13 metal (I) ligands by using
sterically demanding groups such as guanidinates, bisimidinates
and 2,6-disubstituted aryl
groups., etc (Figure 1.5).[80] Now a day such low-valent sterically bulky ligands can be easily
synthesized in high purity which are stable at room temperature itself. In addition, the theoretical
9
Chapter 1
Introduction
aspects of all these reactive species have been well documented by various groups to explore
their electronic structures. [44-52]
Jones and co-workers in 2006 have reported the first example of a smallest and reactive
neutral gallylene ring, which is an analogue to the previously discussed heterocycles from a
salt metathesis reaction. According to their procedure, the four-membered N-heterocyclic
gallylene [:Ga(Giso)] can be made from the treatment of group 13 metal (I) halide with the
lithium guanidinate Li(Giso) (Giso- = [(Ar)NC(NCy2)N(Ar)] ¯) in toluene, which leads to the
formation of a sterically bulky [:Ga(Giso)] heterocycle. [53]
1.2.2 Neutral Six-membered Heterocyclic Organyls
Although the -diketinato and -enaminoketonato ligands are among the most
ubiquitous chelating systems in coordination chemistry, the isoelectronic -diketiminato
ligands have received wide-spread interest in recent times. This class of ligands were well
explored especially in the stabilization of new transition and main-group metals and their
applications.
[54]
One such very impressive example is the isolation of a first stable Mg (I)
dimer with a Mg–Mg bond. [31] Using such a ligand backbone (DDP or nacnac), Roesky and
co-workers reported Al(DDP) where the low-valent Al(I) is stabilized with -diketiminato
backbone.[54a] After its isolation other derivatives in the group such as Ga(DDP)
In(DDP)
[56]
and thallium(I) -diketiminates
[57]
[55]
,
were subsequently reported very much
similar to the Scheme 1.2.
Li(DipNacnac)
i) GaI
ii) Ks
N
Toluene, RT
N
Ga :
Scheme 1.2: Synthesis of Ga(DDP) by salt metathesis.
Heterocycle, Ga(DDP) was preparaed by salt metathesis of Li(DDP) with the metastable
“gallium iodide (GaI)”, whereas Al(DDP) was prepared by reducing the respective diiodide
10
Chapter 1
Introduction
[(DDP)AlI2] with potassium metal. [54a, 55] The reactive six-membered heterocycles, Al(DDP)
and Ga(DDP) are relatively stable compounds even at room-temperature in inert conditions
for several days. Whereas, the other remaining group 13 analogues, In(DDP) and Tl(DDP)
are difficult to handle at normal atmospheric conditions, because they were reported to be
light sensitive and fastely decompose in many aromatic solvents.
[56, 57]
In the following
sections more emphasis will be given on Ga(DDP), since the present work is focussed on it’s
reactivity aspects.
1.2.3 Electronic Properties of Group 13 metal (I) Organyls as Ligands [68]
The electronic structure and properties of a group 13 metal (I) centre is important to
understand at the fundamental point of view, because it gives an idea that how they interact
with transition or main-group metals in making complexes of general formula [LnM-(ER)] [
E = Al, Ga, In and Tl, R = sterically bulky ligand).[68] This particular bonding aspects have
been extensively reviewed by two groups namely, Cowley, [59] Frenking [58] and co-workers.
As shown in Figure 1.6, group 13 metal (I) centre exhibits a free lone-pair of electrons
(which are always available for the sigma coordination to the metal centres) situated in a orbital (HOMO) and two degenerate unoccupied p-orbitals (LUMO), which lie
perpendicular to the axis of the E–C bond.
[68]
In other words, the electronic state can be
described as a singlet state. Because of such electronic situation at the group 13 metal centre,
:EIR type ligands are isolable to the well-known “CO” and phosphines (PR3) which are
classical neutral ligands in the coordination and organometallic chemistry. Owing to this
analogy, one would expect similar reactions with :EIR as ligands involving different bonding
modes like phosphines (PR3) which also prefer the terminal and bridging coordination mode
when they react with transition and main-group organometallic fragments. [68]
px
R
*
py
E
O
C
Figure 1.6: Isolobale analogy between the low-valent :EIR and CO (E = Al, Ga, In and Tl).
11
Chapter 1
Introduction
Figure 1.7: Donor-acceptor bonding in complexes of type [LnM–ER]. Sterically bulky group
R contains the -electrons. Reprinted with permission from J. Uddin, G. Frenking, J. Am.
Chem. Soc. 2001, 123, 1683-1693. Copyright © 2001 American Chemical Society. [58]
In addition to the above, HOMO of :EIR interacts with the corresponding dz2 orbital
located on the transition metal centre, which results in the formation of a sigma-donation.
The free-electron pair on the metal (I) centre gradually becomes more inert with the increase
in the atomic number going down the group, from boron to thallium (BTl).
[68, 68b]
Moreover, the increase in s-character and expected “inert-pair” effect also contribute to this
aspect in dictating their reactivity and electronic property. As a result of the lone-pair effect
the M–E bond energy slowly decreases top to down in the group. Interestingly, besides the
sigma donor property, the other free unoccupied p-orbitals remain available for metal to
ligand back donation (MER donation).
[80]
This generally means that the electronic
(donating or withdrawing) properties of the “R” group as well as the group 13 metal (I)
center play a significant role in directing the acceptor property of the ligand when it is
coordinated with a transition metal centre. In other words, if the organic group (R) is a strong
-donor which strongly donates the electron density towards the unoccupied p-orbitals of
metal (I) centre (similar to Cp*), the -acceptance property will be decreased. It is also
proposed that the haptotropic shifts of 5 31 of Cp* ligand can improve the acceptance behaviour.[68] Moreover, the -acceptance property can be tuned at the group 13
metal center by employing weak -donor ligands such as the sterically over crowded phenyl
groups (e.g. Ar* = 2,6-(2,4,6-triisopropylphenyl)-phenyl).[68] Similar analogy can be applied
12
Chapter 1
Introduction
for sigma and -acceptance properties of sterically over-crowded Ga(DDP) which has a diketiminato ligand backbone. The sigma and pi-acceptance behaviour of Ga(DDP) is
discussed in the following sections. Figure 1.6 and 1.7 shows the orbital overview at both
group 13 and a transition metal center. It has been reported from the theoretical
investigations that the bond disscociation energies of complexes of the type, [TM–ER] are
high (as shown in Table 1.4) even for weak -donor ligands of group 13 metal centers (B >
Al > Ga ≈ In > Tl). [68b]
Table 1.4: Bond´s dissociation energies of Fe–E bond (kcal/mol) in the complexes of the
type, [(CO)4Fe–EIR]. [80, 68b]
Compound
B
Al
Ga
In
Tl
(CO)4Fe–ECp[58] 75.02
51.35
31.62
31.69
15.81
(CO)4Fe–Eph [58]
99.79
61.63
51.36
49.43
40.95
Ni(EMe3)4 [58]
79.70
53.24
40.66
43.44
27.00
1.2.4 Some Theoretical Aspects of free Heterocycles
Due to the difference in the ligand backbone between the :EICp* and heterocyclic
compounds showed in Figure 1.5, one would speculate that different electronic situations
exist at the coordinating atoms or group 13 metal (I) centers. It is clear that these inorganic
heterocycles possess a different steric, electronic backbone with N, N-chelation. In
particular, Schoeller and co-workers had shown the quantum chemical calculations on the
anionic heterocycles of the type, [:E{N(H)C(H)}2]−, (E = B to In).
[60]
Based on these
theoretical investigations all these inorganic N, N-chelation containing heterocycles should
exist as stable chemical entities and contains a sp-hybridized group 13 metal (I) centres as it
is depicted in Figure 1.5. Furthermore, (as in the case of NHCs) they also possess a singlet
lone-pair on the coordinating centre which is connected with its Highest Occupied Molecular
Orbitals and the p-orbitals at the metal(I) center lies perpendicular to the plane of the rings
are associated with the Lowest Unoccupied Molecular Orbitlas. Figure 1.8 shows the MO
bonding situation in four-membered gallylene, [:Ga(Giso)]. [53]
13
Chapter 1
Introduction
Figure 1.8: HUMO of one representative example in a four-memebered gallylene.
Figure 1.9: (According to Sundermann and co-workers) Electron Localization Function
plots of [{HC(CRNR)2}E], (E = B to In, R and R= H); the contour lines give the
increasing value for ELF in steps of 0.1 from 0.0 outside the molecules to 1.0 (high
localization) at the C–H and N–H bonds and at the lone-pairs; Reprinted with permission
from M. Reiher, A. Sundermann, Eur. J. Inorg. Chem. 2002, 1854-1863. Copyright 2002,
John Wiley & Sons, Ltd. [62]
14
Chapter 1
Introduction
The electronic and bonding situation of other group 13 six-membered rings such as
[:E{[N(R)C(R)]2CH}] (E =B to Tl; R= Me or C6H3iPr-2,6(Ar); R = H or Me) have also
been studied in recent years. Theoretical calculations carried out by Su,
[61]
Reiher
[62]
and
co-workers on such heterocycles had shown the electronic structure of -diketiminate
backbone containing group 13 metal (I) organyls and established that the metal centre (E =
Al to In) carries a partial positive charge (+), and N–E bonds exhibhit some ionic character.
In addition to this, electron localization function (ELF) calculations shows that the existence
of a lone-pair on the group 13 metal (I) centre which is a stereo chemically active pair on the
N, N-heterocycles (Figure 1.9). [60, 63, 80]
1.3
A Brief Overview of Bonding and Electronic Properties in -Diketiminate
Gallium (I): A Carbene Analogue [55, 64]
The sterically pronounced Ga(DDP) was first synthesized by Power and co-workers
in 2000
[55]
, from the salt metathesis reaction as shown in Scheme 1.2. The molecular
structure shown in Fig 1.10 exists as a monomeric in nature both in solid as well as in the
solution state at room temperature. In this compound, the Dipp (Dipp = 2,6diisopropylphenyl) ring planes are oriented at angles of 88.2 and 89.2 to each other and this
can be regarded as a bidentate ligand, [(NDippCMe)2CH]– is complexed with the “Ga+” ion.
Gallium (I) center in Ga(DDP) displays a “V” shaped two-coordinate geometry as shown in
the figure. The metal valence shell carries a lone pair, two bond and empty p-orbital which
are also very similar to its analogue GaCp*.
Figure 1.10: Molecular structure of Ga(DDP).[55, 64]
15
Chapter 1
Introduction
Table 1.5: (According to Power et al) Molecular orbital energies (kcal/mol) for the model
species [:E(DDP)] (E = Al or Ga) at 6-31G level. Reprinted with permission from N. J.
Hardman, A. D. Phillips, P. P. Power, ACS Symp. Ser. 2002, 822, 2-15. Copyright © 2002
American Chemical Society. [64]
Figure 1.11: Electron density surfaces and MO energies of [:Ga(DDP)]. Table and Figures
are reproduced with permission from N. J. Hardman, A. D. Phillips, P. P. Power, ACS Symp.
Ser. 2002, 822, 2-15. Copyright © 2002 American Chemical Society. [64]
16
Chapter 1
Introduction
According to Power and co-workers, the neutral six-membered gallium (I) heterocycle,
Ga(DDP) has the electronic structure quite similar to its Al(I) analogue, Al(DDP) and the
model species shows that although HOMO corresponds to gallium lone pair, the LUMO
does not involve the gallium p-orbital which is represented by LUMO+1. [60, 61, 64 and 65] There
is a large separation (Figure 1.11) of energy between these two levels, reveals the fact that
Ga(DDP) acts as a good -donor ligand but poor -acceptor property when it is coordinated
to a metal centre. For visual inspection, the molecular orbital diagrams and MO energies are
shown in Table 1.5 and Figure 1.11 respectively. [64]
1.3.1 Coordination Chemistry of Low Valent Group 13 Metal (I) Organyls (:EIR)
Towards Main-Group and Transition Metal Fragments
Based on the aforementioned works of the authors on the group 13 metal (I) organyls
highlight that they possess interesting bonding, structure and electronic properties which are
very well suitable for them to explore as effective ligands for making M–E type bonds.
Hence, the reactivity and the coordination chemistry of :EIR (E = Al, Ga, In and Tl) organyls
has been extensively studied towards main-group and transition metal fragments. Since these
organyls are isolable to CO, one would expect the similar reactivity and coordination modes
of CO when they interact with transition metal fragments such as terminal and bridging
modes.
Jutzi and co-workers first time examined their reactivity towards the classical CO
substitution reactions using pentamethylcyclopentadienylgallium (GaCp*) in transition metal
chemistry.
[66]
As it is shown in scheme 1.3, the reaction of iron nonacarbonyl with GaCp*
yields a mono nuclear complex, [(GaCp*)Fe(CO)4] through the elimination of pentacarbonyl
iron(0), Fe(CO)5, whereas the similar reaction with Ni(CO)4, yields a novel tetra nuclear
nickel cluster [Ni4(GaCp*)4(CO)6].[41] The donor-acceptor properties of ECp*(GaCp*,
AlCp* and InCp*) ligands in the formation of M–E bonds containing compounds have been
well explored in the stabilization of many unusual transition and main-group clusters
especially to give homoleptic complexes of the formula [M(ECp*)4] (M = Pd, Pt).[67] Many
such merits of these potent ligands have been extensively discussed in recent reviews by
various authors. [34, 35, 68]
Main-group and transition metal compounds and clusters resulted from these ligands
have given new insights into the bonding and novel structures. Many transition metal complexes
17
Chapter 1
Introduction
and clusters of type [LnM–(EIR)b] are in focus in last 10 years.
[51, 48, 70]
Another interesting
feature of these :ECp* ligands is that they are able to undergo bond activation reactions in few
transition metal complexes. For example, the reaction of AlCp* with [Ru(η4-cod)(η6-cot)]
gives a C–H activated compound with a “RuAl5” framework in which the two methyl groups
from two Cp* rings undergone C–H activation.[72-73]
CO
Fe2(CO)9
n-hexane
+
Ga
••
GaCp* + (CO)5Cr(C8H14)
- Fe(CO)5
OC Fe Ga
OC
CO
n-hexane
-cyclooctene
(CO)5CrGaCp*
C8H14 = ciscyclooctene
GaCp*
Ni
+ 4 GaCp*
n-hexane
-cod
Ni
*CpGa
GaCp*
GaCp*
GaCp*
Pt
+ 4 GaCp*
n-hexane
-cod
Pt
*CpGa
GaCp*
GaCp*
Scheme 1.3: Few examples of substitution reactions of GaCp*.
1.4
Reactivity of Ga (I) Heterocycles as Ligands [48, 52, 79]
The reactivity chemistry of :ECp* (E = Al, Ga, In and Tl) type ligands has been
deeply exploited so far in the coordination and organometallic chemistry. Whereas, the
reactivity studies of NHE type ligands is now started to develop to some extent towards
various main-group and transition metal fragments. [48] Very similar to ECp* ligands, NHEs
also undergo simple carbonyl (CO) or phosphine substitution reactions to afford the lowvalent M(0) type of complexes with M–E (E = Al, Ga and In) bonds.[48b] For example, Jones
18
Chapter 1
Introduction
and co-workers have studied the reactivity of recently developed neutral, four-membered
sterically encumbered, [:Ga(Giso)] with few group 10 metal (0) fragments to isolate homo or
heteroleptic complexes in which [:Ga(Giso)] acts as monodentate ligand in the formation of
M-Ga bonds.[48] The reaction of [:Ga(Giso)] with Pt(0) complex, [Pt(norbornene)3] gives a
homoleptic complex [Pt{Ga(Giso)}3], despite its steric bulk (unlike :ECp* type ligands).[74]
In addition, the crystallographic and theoretical studies performed on this compound
suggested that the covalent nature of Pt–Ga bonds possess a significant -character which is
a fundamentally interesting bonding aspect.[74] Another impressive example is the fivemembered heterocyclic gallylene [:Ga(Ar-DAB)]2[{K(18-crown-6)}2(μ-18-crown-6)] [ArDAB, (ArN=CH)2, Ar = 2,6-iPr2C6H3] which is an anionic ligand and NHC analogue system.
[75]
Due to its high reactivity, this ligand can easily undergo substitution and salt elimination
reactions with few main-group and transition metal organometallic fragments to give novel
complexes containing M–Ga bonds.
[76-77]
In addition; recent reports showed that NHE
ligands are also able to stabilize few f-block metals and demonstrated to give novel bonding
features with their unique reactivity. [78]
Among all the other Ga(I) heterocycles, Ga(DDP) (1) is the only six-membered gallium (I)
heterocycle which is so far been completely characterized and is a thermally stable
compound which is stable until 202-204 C.
[55, 64]
Among the all NHE type ligands, the
coordination chemistry of 1 has been considerably well developed than that of its DDP
analogue, Al(DDP).[80] In this regard, the low-valent Ga(DDP) has proven its potential to act
as relatively (compared to GaCp*) mild reactivity and reducing power for the reduction of
few metal salts to yield metal rich metalloid clusters with strong M–M bonding interactions.
Some aspects of its reactivity including few other organyls have been well documented in
recent years.
[51, 52, 68, 79]
Furthermore, Ga(DDP) undergoes typical classical organometallic
reactions such as oxidative insertion and reductive elimination.[80] Figure 1.12 shows the NX-N (X = Ga or C) angles in Ga(DDP) and N-heterocyclic carbene.
Figure 1.12: Representation of N-X-N (X = Ga and C) angles in Ga(DDP) and NHC.
19
Chapter 1
Introduction
Figure 1.13: Some bonding modes of Ga(DDP) (1)
Figure 1.13 shows different possible coordination modes of Ga(DDP) towards reactive metal
centers. It has been well established from many reports that the reactions of 1 with maingroup metal halides such as gallium trihalides, GaX3 does not lead to reduction reactions but
only yields the insertion of Ga(I) center into the M–X bonds (as shown in figure 1.13). [81] In
such reactions low-valent organyl 1 acting as a reducing agent, and when E is a metal, the
formed gallyl fragments [i. e., {-Ga(X)(DDP)}] have been found to be established as
reactive and unstable intermediates in the formation of more thermodynamically feasible
gallium (III) compounds, [X2GaIII(DDP)] (since “+ 3” is the most stable oxidation state of
Ga in group 13 metals). [68, 81b, 82] Moreover, the reducing character of heterocycle 1 has also
been demonstrated in the preparation of new complexes bearing gallium-mercury
gallium-lead
[83]
[83]
and
bonds which were structurally characterized in recent times. This gives the
novelty of 1 in making new Ga-M bonded systems. It was also shown recently that 1 can
stabilize novel coinage metal complexes of copper and gold similar to GaCp*. For example,
the dimeric copper (I) complex, [{Cu(X)[Ga(DDP)]}2] (X = O3SCF3, Br) which displayed
the shortest known Cu(I)···Cu(I) contact (2.277(3)Å) at least at the time of author’s
publication report.[68, 84] Figure 1.14 shows few coinage metal complexes bearing Ga(DDP)
and other gallium (I) ligands. Furthermore, many remarkable experimental results of
oxidative insertion and reductive elimination reactions involving Ga(DDP) is demonstrated
from the rhodium complex [Rh(PPh3)2(μ-Cl){Ga(DDP)}], which can be considered as an
intermediate obtained from the insertion of gallium (I) center of 1 into the Rhodium–
Chloride bond of famous Wilkinson’s catalyst. This product formation involves the
displacement of one triphenylphosphine ligand from the Rh center. [81b, 85]
20
Chapter 1
Introduction
I2
Ga
*CpGa
Au
GaCp*
Au
*CpGa
I2Ga
Au
Cp*
Ga
*CpGa
Ag
GaCp*
(OTf)
Ag
*CpGa
GaI2
GaCp*
O3SCF3
Ga
Cp*
GaCp*
R
R'
GaCp*
Ar
N
N
Ga
M
M
*CpGa
GaCp*
GaCp*
[X]
N
R'
N
R
Ar
M = Cu, Ag, Au; R = Mes, 2,6-iPr2C6H3; R' = H
M = Cu, R = C6H11, R' = Me
M = Ag, X = BPh4
M = Cu, X = BArF
BAF
N
L
Au
Ga
N
Sn
N
N
Cl
Ga
Au
N
Ga
Sn
N
S = THF; n = 0
L = PPh3, Ga(DDP)
Figure 1.14: Few examples of group 11 metal complexes supported by gallium-based
ligands.[85b]
The most impressive examples of Ga(DDP) chemistry so far are the reduction of main-group
metal salts to give high nuclearity metalloid clusters and the stabilization of heavier maingroup metal-metal multiple bonds.
[81b]
The reduction of simple group 14 metal salt such as
SnCl2 with Ga(DDP) gives highly metal-rich tin clusters, [{(DDP)ClGa}2Sn7] and
[{(DDP)ClGa}4Sn17] in moderately high yields (Figure 1.15).
[80]
Interestingly, the Sn–Sn
bond lengths in “Sn17” cluster are quite close to the a.v of 3.10Å in elemental grey tin (α-Sn,
diamond lattice).
[86]
In a similar manner, the reduction of bismuth (III) salts such as,
Bi(OSO2CF3)3 and Bi(OC6F5)3 with 1 have been found to give the dibismuthenes of the type,
[(RfO(DDP)Ga-Bi=Bi-Ga(DDP)(ORf)] (Rf = C6F5, SO2CF3,) with shortest Bi=Bi double
bonds at the time of publication (Scheme 1.4).
21
[87]
. These two synthetic procedures are
Chapter 1
Introduction
similar to the recently isolated silicon (0) derivatives (supported by NHC) reported by
Robinson and co-workers. [81b, 32]
[Sn7{ClGa(DDP)}2]
[Sn17{ClGa(DDP)}4]
Figure 1.15: Metalloid tin clusters stabilized by sterically crowded Ga(DDP). [80]
N
f
Bi(OR )3
+
2
N
Ga
PhF
N
Ga
ORf
N
Bi
Bi
ORf
Ga N
N
Scheme 1.4: Synthesis of [(RfO(DDP)Ga-Bi=Bi-Ga(DDP)(ORf)] (Rf = SO2CF3, C6F5).
1.5 Binary Intermetallic Compounds
1.5.1 Intermetallic compounds [88]
Intermetallic compounds are a fascinating group of materials consisting of a
homogeneous mixture of two or more metals with essentially metallic bonds. Their unique
physical and mechanical properties made them to occupy an intermediate position between
the pure metals and non-metals in the periodic table of elements. Intermetallic compound has
two different meanings; one is used in coordination chemistry to refer a coordination
compound which has two or more different metals in the complex. The second one is to refer
the solid-state phases involving only metals and exist as homogeneous. In contemporary
22
Chapter 1
Introduction
research, material scientists use this term exclusively to refer the solid-state phases of metals.
[88]
Intermetallic compounds (or intermetallic phases) can be shortly defined as materials
consisting of metals in approximately stoichiometric ratios. These normally crystallize other
than the constituent metals it contains and posses ordered crystal structures. These are further
separated by phase boundaries from individual metallic components. Another important
aspect of the intermetallic compounds is that their formulas or chemical composition can be
derived from the crystallographic data but not from the analytical data. [88c] It is a very wellknown fact that intermetallic materials are also established as metal alloys that are known
since ancient times. In this regard, the best example is the binary intermetallic “brass”. The
most important driving force in a binary intermetallic compound is the presence of attractive
forces between the unlike neighbor atoms. For example, if we consider an intermetallic
compound which has X-Y bonds, the strength these types of bonds is normally higher than
that of the X–X and Y–Y bonds that they replace on ordering.
[88d]
In addition, such an
ordered nature makes an intermetallic compound to exhibit attractive material properties
which have useful applications such as functional materials. [88d]
1.5.2 Hume-Rothery Phases [88, 90]
The first validated intermetallic compound CuZn alloy
(-brass) formation was reported by K. Karsten in 1839 in
Germany.[88b] Initial works on intermetallic compounds during
the first decades of this century were performed on phase
stability, phase equilibria to establish phase diagrams. Many
theories have been developed, in order to understand the
formation, stability of different intermetallic compounds or
alloys, which can form throughout the periodic table of
elements. In 1926, William Hume-Rothery whose portrait is shown in the figure (right) made
outstanding contributions to our understanding of a large number of intermetallic
compounds. Rothery pointed out that a great number of compounds, principally in the
systems of coinage metals such as Copper, Siliver and Gold with other elements could be
rationalized by considering the ratio of valence electrons to atoms in each compound.
Furthermore, there are three factors to be taken into account for the favorable formation of
an alloy which are the atomic size factor, electronegative and relative valency effects. [89, 90]
He has also postulated that the stability of solid-state structures depends on electron
23
Chapter 1
Introduction
properties of the constituent metals. This is indicated by the valence electron concentration,
(VEC = h) and this is defined as the number of valence electrons (electrons in the outer
shell) to the number of atoms in the unit cell (h= ne/na). Intermetallic compounds which
obey this electron concentration rule are generally called as Hume-Rothery phases or rather
electron compounds. These are mostly formed between the transition metal and main-group
13-15 elements. The meaning of VEC rule is depicted in Table 1.6 with few examples.
[68b,
100]
Table 1.6: VEC counts for Hume-Rothery rule.
Valence electrons
Element
3
Al, Ga and In
4
Si, Ge and Sn
1
Cu, Ag and Au
2
Mg, Zn, Cd and Hg
5
Sb
0
Other transition metals
According to Hume-Rothery rules the element combinations which have the same electron
concentration (h) crystallize in the same system. For example, the intermetallic compound
Cu5Cd8 [5 + 2 x 8 = 21, electron concentration h = 21/13] crystallizes in γ-phases (facecentered cubic lattice) and when the electron concentration (h) = 3/2, it crystallizes in βphases with a bcc lattice.[100] Whereas, when the electron concentration is (h =) 7/4 it adopts
in a hexagonal ε-phases as shown in Table 1.7.[100] Few other brass examples are
summarized in detail as shown in Table 1.7 describes the VEC rule and its applications to
determine the phase and corresponding structure. Furthermore, the Laves phases are also
considered as intermetallic phases that have the composition of AB2 and consisting of
alkaline earth and transition metals. German scientist, F. Laves in 1934, proposed the ratio of
atomic radii (rA /rB). All AB2 type structures of Laves phases exhibit closely related
structures. [88c] Furthermore, the Laves phases such as MgZn2 (as shown in Fig 1.16), MgNi2
and MgCu2 are few such examples of intermetallic binary systems. [100b, 101]
24
Chapter 1
Introduction
Table 1.7: General influence of the ratio of VEC at the crystal structure of the phase region
of Hume-Rothery alloys of CuxZn1-x (0  x  1)
Phase
Typical “x” range
VEC
Structure
Intermetallic
phase
α
0-0.38
1-1.38
fcc
Cu(Zn)

0.45-0.49
1.45-1.49
bcc
CuZn

0.58-0.66
1.58-1.66
cubic
Cu5Zn8

0.78-0.86
1.78-1.86
hcp
CuZn3
Figure 1.16: Unit cell of Laves phase with MgZn2 structure.
1.5.3 Group 13 Elements Containing Intermetallics
Although the entire group 13 metals form numerous alloys (i. e, metal alluminides
such as NiAl, Ni2Al3, Ni3Al) [103a], but the most emphasis is given for gallium metal and it´s
alloys. Gallium is one of the very low melting metal which melts at around room
temperature and melts in our hand itself. This is the second lowest melting solid after Hg in
the periodic table of elements and remains as a liquid at a quite long-range of temperatures.
Due to this nature gallium forms many useful materials, such as gallium arsenide (GaAs)
which is one of the very well known material being used in light emiting diods. [102] Like its
congener (Al), gallium readily alloys with most metals in the periodic table. This is possibly
due to its low-melting property. Gallium readily forms few binary intermetallic phases with
group 10 metals such as Ni, Pd and Pt. Of note, Nickel-Gallium binary intermetallic
[103b]
and
similarly, gallium also forms intermetallic compounds with Pd (i. e, GaPd2 and GaPd)
[104]
compounds such as NiGa, Ni2Ga3, Ni3Ga and Ni5Ga3 are well-studied phases
and Pt (i.e, GaPt and GaPt2).
[105, 106]
Noteworthy to mention that the intermetallic
25
Chapter 1
Introduction
compounds of gallium with metal Pu (PuGa, Pu3Ga and Pu6Ga) are found to have
applications in nuclear weapons. [107]
1.6
Synthetic Approaches to Metallic Nanoparticles
1.6.1 General Introduction
From the last few decades, a lot of research has been devoted for the synthesis of
nano-sized materials due to their applications in diverse fields.
[108]
The formation of metal
nanoparticles were first time observed 150 years ago from the initial experiments of Michal
Faraday on gold nanoparticles. In 1857, Michal Faraday first time reported his new
discoveries on the nano-meter scale metals in his classic paper, which is one of the popular
reports at that time of a scientific invention in the world history of nanomaterials. [109b] He
demonstrated the formation of colloidal gold nanoparticles by the reduction of
tetrachloroaurate [AuCl4] using phosphorus as the reducing agent.
[109]
In the following
sections few known synthetic methods for mono and intermetallic nanoparticles are
discussed briefly.
1.6.2 Synthesis of Metallic and Intermetallic Nanoparticles
1.6.3 Existing Methods
Chemical Method
M-atoms
Physical Method
aggregation of
metal atoms
Bulk metallic
powder
Metal precusor molecules
Figure 1.17: Schematic illustration of synthetic methods for metal nanoparticles. [108d-e]
26
Chapter 1
Introduction
In general metal and intermetallic nanoparticles can be prepared from two distinct methods,
namely physical and chemical methods as shown in Figure 1.17. There are few important
techniques for the synthesis of nanoparticles. For example, using vacuum, gas or condensed
phase processing. [110] Methods such as laser ablation, mechanical milling, sputtering are few
more examples. In such methods, a bulk solid is essentially broken into many small pieces in
case of physical methods (as depicted in Figure 1.17). For example, very recently, Shall and
co-workers showed the synthesis of few intermetallic nanoparticles of Nickel-Alluminide
(NiAl) and FeAl by laser ablation method by utilizing their pure metallic powders as metal
sources. [111]
1.6.4 Other Chemical Methods [108-112]
Few other chemical methods which are widely used for the preparation of mono and
intermetallic nanoparticles are briefly summarized as follows.
1)
Co-reduction of mixed metal ions [108d-e, 112]
For example, gold-platinum binary intermetallic nanoparticles can be produced from
the reduction of two corresponding metal salts such as HAuCl4 and H2PtCl6. [108e] The
reduction of metal salts with hydrazine is also a commonly employed method for the
preparation of intermetallic nanoparticles and their colloids as shown in Scheme 1.5.
The advantage of this method is the easy formation of dinitrogen (N2) which is the
driving force for these reactions. [112e-f]
MXn
+
M0 + n H-X + n N2 + n/2 H2
n N2 H 4
Scheme 1.5: Reduction of metal salts with hydrazine (X = NO3, SO4, Cl).
2)
Reduction of two organometallic complexes [113], 3) Reduction of metal ions [114] and
electrochemical synthesis,
[115]
thermal decompositon, microwave decomposition are
few other widely used methods. [125a]
1.7
Soft Chemical
Synthesis
of
Intermetallic
Nanoparticles:
Hydrogenolysis of Hydrocarbon Metal Complexes [117b]
From the last two decades, Chaudret and co-workers have first time developed a new
synthetic strategy for colloidal mono and bimetallic nanoparticles using the low-oxidation
state transition metal complexes which have only hydrocarbon ligands (olefins or other
27
Chapter 1
Introduction
hydrocarbon ligands) around the metal centres.[117b] Such kind of ligands supported metal
complexes were chosen because they can easily be cleaved off by hydrogen pressure at
rather mild experimental conditions (like low-temperature and pressure). Moreover, the
cleaved hydrocarbon species do not bind to the metal nanoparticle surface which allows the
precipitation of nanoparticles if there is no suitable surfactant present in the reaction
medium.
[116]
Quite recently, the same group has reported the synthesis of Ru nanoparticles
stabilized by NHCs (for example, sterically bulky IPr). These were synthesized by the
decomposition of one such ruthenium(0)-olefin complex, [(Ru(1,5-cod)(1,3,5-cot)] in a nonpolar solvent like pentane at RT using 3-4 bar hydrogen pressure in the presence of carbene
ligands as surfactant to stabilize the very small ruthenium nanoparticles. From this method
small size ruthenium nanoparticles (1.7  0.2 nm) were achieved and showed that they are
active in the hydrogenation of styrene.
[117]
The same method was extended for the
preparation of other intermetallic colloidal nanoparticles such as Ru1-xPtx,
NiFe
[120]
and Co1-xRux
[121]
[118]
CoFe,
[119]
by co-hydrogenolysis of their respective organometallic
complexes. More emphasis is given on this synthetic method since it was used for some part
of the thesis work.
1.7.1 Soft Chemical Synthesis of M–E (E = Al and Ga) Nanoparticles
Fischer and co-workers showed in the past that the use of highly sublimable
transition metal, group-13 metal-substituted alanes, gallanes and indanes of the general
formula [[LnM]3-xERx(Do)y] (E = Al, Ga, In; L = CO. Cp, Do = neutral O, N atom Lewis
base donor, x = 0–3 and y = 0–2) as single soruce precursors for the preparation intermetallic
materials.[70] These complexes were used as precursors for MOCVD and showed the
deposition of single-phase intermetallic thin films of -NiIn, PtGa2 and -Co0.35Ga0.65.
[70]
The most interesting driving force in such reactions is the flexible binding nature of Cp*
ligand on the group 13 metal (I) centers which facilitates it’s easy cleavage (as Cp*-H) in the
presence of (3-5 bar) H2 pressure. It indicates that these ligands are promising starting
materials to get access for the preparation of group 13 metal containing intermetallic
nanomaterials.
[68a]
In general the metal precursors containing substitutionally labile ligands
(preferably hydrocarbon ligands) with :ECp* in an inert solvent under hydrogen pressure
leads to the formation of corresponding nano intermetallic phases. Few such examples are
shown in Scheme 1.6. For example, highly hygroscopic Al nanoparticles can be prepared
from the decomposition of [AlCp*]4 in a high boiling organic solvent such as mesitylene at
28
Chapter 1
150 C.
[122]
Introduction
This example has demonstrated that the potential of using [AlCp*]4 for the
preparation of other nano intermetallic phases such as -CoAl and -NiAl. In this regard, the
first useful example is the soft chemical synthesis of Ni1-xAlx (0.09  x  0.05) by
hydrogynolysis of two metal precursors Ni(cod)2 with [AlCp*]4.
[123]
The treatment of an
equimolar amount of two metal precursors in mesitylene results in the formation of the
colloidal solution of the intermetallic -NiAl nanoparticles which were completely
characteriyed by PXRD and HRTEM. Figure 1.18 shows the HRTEM images of -NiAl
nanoparticles. In a similar manner, intermetallic -CoAl phase was prepared from the
respective organometallic precursors as shown in Scheme 1.6.
[124]
Thus, the soft chemical
syntheses enable to prepare Hume-Rothery type intermetallic phases in the nanometer scale
regime.
3 bar H2, 150 °C
1/4
H
Al(s)
+
Mesitylene, 30 min
Al
Ni
4
+
3 bar H2, 150 °C
1/4
Mesitylene, 4d
Al
4
3 bar H2, 150 °C
Co
+
-NiAl
1/4
-CoAl
Mesitylene, 48h
Al
4
Scheme 1.6: Preparation of different nano intermetallic phases using the low-valent
[AlCp*]4 as Al source.
29
Chapter 1
Introduction
Figure 1.18: TEM images of agglomerated nano -NiAl (left) NPs and zoom on a single
particle (right). Source; PhD thesis, M. Cokoja, Ruhr University Bochum, 2007. [117b]
1.7.2 Applications of Nano Intermetallic Phases
Bimetallic nanoparticles possess different and useful properties sometimes often
better than monometallic nanoparticles due to the composition of two different metals in a
particle. Their unique properties have made them to find enormous applications in diverse
fields, such as in material science and in nanocatalysis. The applications of bimetallic
nanoparticles have been extensively reviewed in a great deal in recent times. [125-129]
1.8 Aims and Objectives of the Dissertation
It is a very well-known fact that the ligand backbone or the steric bulk of a ligand plays a
crucial role in trapping and stabilizing unusual transition and main-group metal fragments.
Two such very spectacular examples appeared over 15 years that can be mentioned here are
the isolation of a stable compound with a five-fold bonding (quintuple bond)
[130]
between
the two Cr centres using a sterically bulky ligand Ar  [Ar  = C6H3-2,6(C6H3-2,6-iPr)], and
the isolation of a compound with a Si=Si trapped by NHC (IPr) ligands.[32] Similarly,
recently developed group 13 metal (I) organyls are found to be multitalented ligands to
various metal centres due to the presence of a lone pair of electrons on the metal (I) centre
which is always available for a strong -donation. As mentioned in the introduction section,
it could be summarized that the regimes of low-valent main-group organyls especially metal
(I) species contribute promising prospects to the fundamental understanding of structure and
bonding of metal complexes and also materials that were derived using such reactive
species.[68a] A variety of (organo) gallium (I) compounds are known till date, but only few of
30
Chapter 1
Introduction
them were explored as ligands in synthetic inorganic and organometallic chemistry to
systematically construct MM bonded molecular clusters and cages.[52] Although a multitude
of various complexes of type [LnM(ER)m] (M = main-group or transition metals), ER
=GaCp*, Al(DDP), Ga(DDP)] had already been realized to some extent when this work was
started
[80, 83, 86, 87]
the field was still pursued due to the various facets exhibited by the
novelty of complexes or clusters consisting of these ligands with some unusual bonding
modes (ME). Thus, the low-valent group 13 metal (I) organyls as ligands in organometallic
chemistry can thus be extended further to other organometallic fragments (main-group and
transition metals) to probe the possibility of synthesizing new molecules which may exhibit
novel bonding modes and new structures which are inaccessible so far.
The main goal of the thesis is to develop new synthetic procedures for novel molecules by
exploring the reactivity of mono-valent, sterically bulky and six-membered neutral Nheterocyclic carbene analogue Ga(DDP) (DDP = 2-{(2,6-diisopropylphenyl)amino}-4-{(2,6diisopropylphenyl)imino}-2-pentene, HC(CMeNC6H3-2,6-iPr2)2) towards various maingroup (P4, L·GeCl2, L = NHC or phosphine) and transition metal (Mo, Fe, Ru, Pd, Pt, and
Cu) organometallic fragments and address their reactivity and different coordination modes.
There are subtle differences in electronic situation at the Ga (I) centres in both Ga(DDP) and
GaCp*. As shown in Figure 1.19, the vacant p-orbital in Ga(DDP) is not being stabilized by
additional -electrons (as in the case of GaCp*, which is stabilized by 6 electron donor
backbone ligand Cp*). Due to which it leads to an increase in the electrophilicity of the Ga
centre in Ga(DDP) upon coordination with transition metals. This particular aspect can be
rationalized from the metal complexes consisting of Ga(DDP) and that can be able to be
compared with the chemistry of GaCp*. Furthermore, subtle reactivity differences between
these two sterically over-crowded metal (I) species can be addressed. [131]
Furthermore, the metal centre in Ga(DDP) is isolobal with the Arduengo type N-heterocyclic
carbenes (Figure 1.19). As shown in the figure, both Ga(DDP) and IPr (IPr = 1,3-bis(2,6diisopropylphenyl)imidazol-2-ylidene, [:C{[N(2,6-iPr2C6H3)]CH}2]) are Lewis bases and
possess almost similar electronic and steric situations at the ligator atoms. So one would
expect similar reactivity for IPr as it is for Ga(DDP) which is proven to be a potent ligand to
stabilize medium-size transition and main-group clusters.[68] To the best of our knowledge Nheterocyclic carbenes stabilized main-group and tranisiton metal clusters are very much
limited. For example, a neutral “Ga6” octahedron cluster, ([NHC:Ga{Ga4Mes4}Ga:NHC],
31
Chapter 1
Introduction
where NHC= :C{(i-Pr)NC(Me)}2 and Mes = 2,4,6-Me3C6H2).[132] Similarly, Whittlesey and
co-workers first time showed that a palladium cluster [Pd3(μ-SO2)3(NHC)3] (NHC = IMes,
1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene;
ylidene) stabilized by N-heterocyclic carbene.
[133]
IiPr2
=
1,3-bis-isopropylimidazol-2-
Thus, objectives of the thesis are also
devoted, some extent, to attempt for new NHC stabilized Ti and Zn complexes of the
anticipated clusters or molecular compounds of the type, [(NHC)nMm] which would be
similar to the well-known [(ER)nMm] (E = Al, Ga and In, R = Cp* or DDP) clusters by
reducing the corresponding metal halide NHC complexes such as [(IPr)MCln] (M = Ti and
Zn, n = 4 or 2). Besides, the reactivity differences of Ga(DDP) and IPr can be compared.
Figure 1.19: Similarities between Ga(DDP) and NHC.
In addition to the above goals, some part of the thesis is also oriented towards the question
that whether or not the new organometallic synthetic routes can be developed for the binary
intermetallic Nickel-Gallium (such as NiGa, Ni2Ga3 and Ni3Ga) nanopowders and colloidal
nanoparticles at relatively mild experimental conditions. As briefly discussed in the
introduction section, the use of low-valent group 13 metal (I), such as tetrameric [AlCp*]4
was proven to be a promising Al source to get access for the aluminium containing binary
alloy nanoparticles of -NiAl and CoAl intermetallic phases by wet chemical approach in
organic media.
[122-125]
With this motivation, few attempts are made to address the question
that the possibility of the preparation of those Ni-Ga nano intermetallic phases from the lowvalent GaCp*, nickel complexes containing GaCp* such as [NiGaCp*(PMe3)3],
[Ni(GaCp*)3(PCy3)] and Ni(cod)2 as single source precursors by soft chemical synthesis.
Moreover, the resulted nanophases can be tested for their catalytic activity. However, to the
best of our knowledge, such single source precursors have never been tested for the
preparation of Ni/Ga intermetallic compounds.
32
Chapter 1
Introduction
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Mosset, B. Chaudret, J. Phys. Chem. B. 1999, 103, 10098-10101. (b) F. Dassenoy, M.
J.Casanove, P. Lecante, C. Pan, K. Philippot, B. Chaudret, Phys. Rev. B: Condens.
Matter Mater. Phys. 2001, 63, 235407-235414.
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Chapter 1
Introduction
[119] C. Desvaux, C. Amiens, P. Fejes, P. Renaud, M. Respaud, P. Lecante, E. Snoeck, B.
Chaudret, Nat. Mater. 2005, 4, 750-753.
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M. Respaud, A. Serres, R. E. Benfield, C. Amiens, B. Chaudret, Faraday Discuss.
2004, 125, 265-278. (b) O. Margeat, D. Ciuculescu, P. Lecante, M. Respaud, C.
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Respaud, J. Phys. Chem. B. 2003, 107, 6997-7005.
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Appl. Chem. 2006, 78, 1667-1689. (c) C. Desvaux, F. Dumestre, C. Amiens, M.
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2009, 19, 3268-3275.
[126] G. A. Ozin, A. C. Arsenault, Nanochemistry, A Chemical Approach to
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[128] A. S. Edelstein, R. C. Cammarata. Nanomaterials: Synthesis, Properties and
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39
Syn. of PtGaR complexes and insertion reactions
Chapter 2
Chapter 2
Synthesis and Characterization of Heteroleptic Platinum-GaR (R = DDP,
Cp*) Complexes [a]
Abstract: The reactivity of low-valent gallium (I) organyls is investigated towards various
platinum (II) and Palladium (II) organometallic compounds. The sterically pronounced,
mono-valent group 13 bisimidinate gallium (I), Ga(DDP) (1) derivative (DDP = 2-{(2,6diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}-2-pentene,
HC(CMeNC6H3-
2,6-iPr2)2) with olefin supported group 10 complexes, such as [(diene)PtCl2] [diene = 1,5cyclooctadiene
(cod),
endo-dicyclopentadiene
(dcy)],
[(diene)PtMe2]and
[(cod)Pd(Me)(OTf)] (OTf = O3SCF3) are investigated. These reactions afford oxidative
insertion
products
[(cod)Pt(Cl){ClGa(DDP)}]
[(DDP)Ga(Me)(OTf)]
(4)
(2),
[(dcy)Pt(Cl){ClGa(DDP)}]
and [(cod)MePt{MeGa(DDP)]
(5)
in
moderate
(3),
yields.
Furthermore, the reaction of [Pt(cod)Cl2] with an excess of GaCp* in toluene yields a
complete substitution product [(Cl3Ga)Pt(GaCp*)4] (6) as an orange solid. Compounds 2–6
are completely characterized by elemental analysis, NMR (1H, 13C) spectroscopy and also by
single crystal X-ray structural analysis. The solid state molecular structures of complexes 2
and 3 reveal the oxidative insertion of Ga(DDP) into the Pt–Cl bond without altering the πcoordinated double bonds in the olefin ligand parts. Highly metal rich complex 6 represents
an example of a compound where a transition metal fragment and main-group metal gives a
Lewis acid-base adduct.
[a]
Some parts of this chapter are comprised in the publication; A. Doddi, C. Gemel, R.
W. Seidel, M. Winter, R. A. Fischer, J. Organomet. Chem. 2011, 696, 2635-2640.
Text and Figures are reproduced with permission. Copyright © 2011, Elsevier.
40
Syn. of PtGaR complexes and insertion reactions
Chapter 2
2.1
Introduction
Main-group and transition metal containing low valnet species is an exciting field of
research in the area of organometallic chemistry. After the isolation and structural
characterization of low-valent group 13 metal (I) chemical entities at room temperature, have
opened up new horizons in the history of main-group and transition metal organometallic
chemistry. The coordination chemistry of these sterically demanding :ER type of compounds
(E = Al, Ga, In; R = bulky alkyl, aryl, C5Me5 , etc.) as ligands to yield a variety of
intermetallic transition metal complexes of the kind [(LnM)a(ER)b] (a < b) is a continuously
expanding field of research. [1] Besides the fundamental interest in structure and bonding, the
chemistry of these complexes and clusters with unsupported M–E bonds is related to the
materials chemistry of the respective alloys or intermetallic compounds.
[1b-c]
Early work in
this direction targeted MOCVD of CoGa and related materials, [2a-b] more recent work deals
with soft chemical synthesis of MxEy alloy nanoparticles
colloids.
[2c]
[2c-e]
such as NiAl dispersed as
The substitution or the rearrangement of the labile ligands (i.e, CO, PR3 and
olefins) by ER has proven to be the most fruitful synthetic route for making a variety of such
homoleptic and heteroleptic complexes.
[1, 3]
Their reactivity and electronic properties are
comparable with the well known N-heterocyclic carbene (NHC) class of ligands. The NHC
analogous ER ligands are thus considered as strong σ-donors due to the presence of a sp2
hybridized lone pair on the main group metal (I) centre. However, there is a striking
difference between the behaviour of N-heterocyclic carbenes and :ER type highly reactive
ligands. In addition to its coordinating properties, :ER ligands exhibit strong reducing
properties and may also yield insertion compounds as intermediates when combined with
compounds exhibiting M–X bonds. Among these main-group metal–ligand species, the
neutral and bulky six-membered β-diketiminato derivatives [:E{[N(Ar)C(Me2)]2CH}; Ar =
C6H3iPr2-2,6; E = Al
[4]
, Ga
[5]
, In
[6]
, Tl
[7]
], abbreviated as E(DDP) [DDP = 2-{(2,6-
diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}-2-pentene],
are
of
special
interest due to the bulkiness which can be incorporated into their metal complexes. Another
NHC analogous anionic five-membered diazabutadienido ligand [:Ga{N(R)C(H)}2]- (R=tBu,
Ar)
[8]
and
recently
the
neutral
[:E{(Ar)NC(NCy2)N(Ar)}] (E=Ga, In and Tl)
years.
41
four-membered
[9]
guanidinate
ligands
have been developed during the last five
Syn. of PtGaR complexes and insertion reactions
Chapter 2
The chemistry of platinum gallyl complexes with these gallium (I) heterocyclic
ligands has been explored to some extent. Very recently the first homoleptic platinum(0)
complex, [Pt{Ga(Giso)}3] with the neutral four membered guanidinato gallium(I)
heterocycle [:Ga(Giso)] (Giso = {(2,6-iPr2C6H3)NC(NCy2)N(C6H3-2,6-iPr2)}, Cy =
cylohexyl) was reported by C. Jones and his coworkers, where they described particularly
short Pt–Ga (3-coordinate) bonds.
[10]
Likewise, few structurally interesting platinum
complexes have also been reported with the anionic gallium (I) heterocyle by the salt
elimination process. [11] Although the insertion chemistry of Ga(DDP) (1) has been explored
to some extent towards transition and main-group metal complexes (Figure 1) (i.e. the
insertion behavior of Ga(DDP) into the M–X ( M: Si, Sn, Ga, Hg, Zn, Pb, Rh, tBu, X:–Cl, –
O3SCF3) and also M–C (M = Ga) bonds)
[12-16]
, the same chemistry with olefin supported
platinum(II) chloro complexes is not explored. To the best of our knowledge, only a very
few Ga(DDP) containing platinum complexes have been reported in the literature so far. [17]
Following our previous work on the reactivity of zero valent, olefin supported platinum and
palladium complexes towards ER
[18-23]
, we got interested in comparing the reactions of 1
with olefin complexes of the group 10 metal centers Pt (II) and Pd(II). Herein, we report the
reactions of Ga(DDP) with the olefin supported complexes containing Pt–Cl and Pd–Me
bonds, such as [(diene)PtCl2] (diene=1,5-cyclooctadiene, endo-dicyclopetadiene) and
[(cod)PdMe(OTf)] in comparison to the reaction of [Pt(cod)2] with Ga(DDP) which yields a
bright orange complex [(1,3-cod)Pt{Ga(DDP)}2]. [17]
Unlike GaCp*, GaI(DDP) is less reducing and very bulky and thus likely not to yield
homoleptic complexes [Pt(Ga(DDP)n] (n  4) such as [Pt{Ga(Giso)}3]
[22]
[10]
or [Pt(GaCp*)4]
when combined with the selected olefin supported Pt(II) complexes, [(diene)PtCl2] (diene
= 1,5-cod, dcy)] and the Pd(II) complex [(1,5-cod)PdMe(OTf)]. These reactions afford the
new platinum complexes [(cod)Pt(Cl){ClGa(DDP)}] (2) and [(dcy)Pt(Cl){ClGa(DDP)}] (3)
as the insertion products of Gallium into the Pt–Cl bonds, while the palladium(II) complex is
reduced to Pd(0) and [(DDP)Ga(Me)(OTf)] (4) is obtained as the stoichiometric by-product.
2.2
Synthesis and Characterization of [(1,5-cod)(Cl)Pt{ClGa(DDP)}] (2)
and [(dcy)(Cl){PtClGa(DDP)}] (3)
Treatment of Ga(DDP) with the olefin supported Pt(II) complex, [(1,5-cod)PtCl2] in
toluene
at
room
temperature
yields
an
oxidative
insertion
product
[(cod)Pt(Cl){ClGa(DDP)}] (2) in 43% isolated yield as a pale yellow crystalline material.
42
Syn. of PtGaR complexes and insertion reactions
Chapter 2
The synthesis of 3 is shown in Scheme 2.1. In the same manner the reaction of Ga(DDP)
with [(dcy)PtCl2] yields yellow powder [(dcy)(Cl)Pt{ClGa(DDP)}] (3) in 28% yield
(Scheme 2.1).
Pt
Cl
N
+
Cl
Ga
Toluene
N
RT; 24h
N
N Ga
Cl
Cl
Pt
(2)
Cl
Pt
Cl
N
+
Ga
N
Toluene
RT; 20 h
N
N Ga Cl
Cl Pt
(3)
Scheme 2.1: Synthesis of [(cod)(Cl)Pt{ClGa(DDP)}] (2) and [(dcy)(Cl)Pt{ClGa(DDP)}] (3)
During these reactions, the initial colour of the reaction mixture (yellow) changed to orange
after 15 to 30 min of stirring at room temperature. The colour of the reaction mixture
gradually changes to brown as the final colour of the reaction mixture. Both two platinumgallyl complexes 2 and 3 are stable over several days in their solid–state at room temperature
under inert atmosphere (Argon), but prolonged storage in solution and solid–state leads to
slow decomposition with formation of a grey substance. They readily dissolve in common
organic solvents such as THF, benzene and toluene but are insoluble in non-polar solvents
such as n-hexane and pentane. Elemental analysis of both compounds are in good agreement
with
the
proposed
molecular
formulae
[(cod)(Cl)Pt{ClGa(DDP)}]
(2)
and
[(dcy)(Cl)Pt{ClGa(DDP)}] (3).
For the complete understanding and appreciation on the reactivity of Ga(DDP) in
similar reactions, few more experiments are performed using two fold excess of Ga(DDP)
for the possible isolation of Pt(0) complexes [Ptn{Ga(ddp)}m], since it is expected that ligand
43
Chapter 2
Syn. of PtGaR complexes and insertion reactions
1 can take up to two Cl– ligands from the Pt centre, and also by substituting cod; there by
leading to give gallium(III) derivative Cl2Ga(DDP) as an anticipated main by-product.
However, no such other products were isolated, except for 2 and 3 from their respective
reactions according to Scheme 2.1. The reaction of Ga(DDP) with [Pt(cod)2] has been
reported to give a bright orange Pt(0) complex [Pt(1,3-cod){Ga(DDP)}2] in hexane where
1,5-cod ligand in the complex undergone isomerisation, but in the present case no such
compounds were observed in the reaction mixture, but only the oxidative insertion of
Ga(DDP) into Pt–Cl bond has occurred. [17] This might be due to the fact that the steric bulk
of Ga(DDP) does not favour more substitution at the platinum centre unlike GaCp*, with
which a few homoleptic and heteroleptic complexes have been isolated with the metals
platinum and palladium. [22]
The 1H and 13C-NMR spectra of 2 and 3 exhibit the expected resonances for (DDP)
backbone of the ligand. These data are consistent with their proposed structures. The typical
1
H-NMR resonances [C6D6 for 2 and d8-THF for 3] for methine (γ-CH) protons of DDP
backbone in both 2 and 3 are observed as sharp singlets at δ; 4.94 and 5.15 ppm respectively
which are in the expected range when compared to the Ga(DDP) supported metal complexes.
[12-15]
The resonance due to the olefin protons of cod in 2 appears as two different broad
multiplets centred at δ; 4.53 and 5.52 ppm, associated with the NMR active
195
Pt satellites,
and whereas –CH– protons of isopropyl groups show two different overlapping septets
centred at δ; 3.80 and 3.89 ppm. The intensity of these two peaks exactly matches with the
expected four isopropyl protons in 2. The 2JPt-H couplings to these olefin protons (10 to 35
Hz) are considerably lower than those for [Cl2Pt(cod)] (2JPt-H = 65 Hz). [24] The
13
C-NMR
chemical shifts found for DDP and cod moieties fall in the expected range. Molecule 3
exhibits a non symmetric structure in solution at room temperature, which makes all protons
magnetically non-equivalent, due to which all resonances in 3 are assigned from the twodimensional nuclear magnetic resonance spectroscopy (Heteronuclear Multiple Bond
Coherence) spectrum.
44
Syn. of PtGaR complexes and insertion reactions
Chapter 2
Figure 2.1: 1H-NMR spectrum of compound 3 in C6D6 at room temperature
The structural complexity in the molecule 3 caused a few broad, partially overlapping
signals of (DDP) and dicyclopentadienyl ligands in the aliphatic region. The proton NMR
spectrum of 3 exhibits characteristic four septets of –CH– and eight sets of doublets
associated with four and eight non-equivalent isopropyl and methyl protons of this complex,
while the
13
C-NMR spectrum shows the expected twelve resonances of the corresponding
carbons. In contrast, 1H-NMR spectrum of 2 shows only 6 resonances (two septets and four
doublets) for the same protons, indicative of an over-all more symmetric structure in
solution. Furthermore, complex 3 exhibits the unequal nature of two CH3 protons on the
(DDP) ring which appear at δ; 1.77 and 1.74 ppm. 1H-NMR of 3 at room temperature also
exhibits four different broad olefin protons centred at δ; 7.88, 6.19, 4.87 and 4.17 ppm,
which are associated to the coupling with
corresponding
13
195
Pt nuclei and it is shown in Figure 2.1. The
C-NMR chemical shifts are assigned as δ; 139.4 and 132.6 ppm for the
olefin carbons of -C3=C4- and 85.2 and 83.1 for C1=C2 (atom labelling is shown in Figure
2.2 for
13
C-NMR). The methine (γ-C12) carbon in 3 resonates at δ; 100.4 ppm whereas the
same DDP carbon in 2 resonates at 99.4 ppm, which is slightly shifted to up field region.
The 13C-NMR spectrum of 3 also indicates the deshielding nature of imino carbons (-C=N-)
occurred in DDP ring (δ; 170.9 and 170.7ppm), when compared with the literature reported
45
Syn. of PtGaR complexes and insertion reactions
Chapter 2
complexes.
1
[17]
The structure and composition of 2 and 3 are consistent with the elemental,
H and 13C-NMR data.
2
9
5
7
20
1 17
8
10 18
6
4
19
16
3
22
24
Cl
Pt
21
25
N
Cl
Ga
23
11
26
27
14
38
39
N
37
28
33
34
29
32
30
31
12
13
35
15
36
3
Figure 2.2: All carbon atoms are labeled for the NMR assignment for complex 3.
2.3
Single Crystal X-ray Analysis of [(1,5-cod)(Cl)Pt{ClGa(DDP)}] (2)
and [(dcy)(Cl)Pt{ClGa(DDP)}] (3)
Figure 2.3: Molecular structure of compound 2 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level (Pt and
Ga). Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths
(Å) and angles (º): Pt(1)Ga(2) 2.417(16), Pt(1)C(5) 2.155(10), Pt(1)C(4) 2.211(12),
46
Chapter 2
Syn. of PtGaR complexes and insertion reactions
Pt(1)Cl(1) 2.362(3), Pt(1)C(8) 2.454(13), C(4)C(5) 1.385(15), C(1)C(8) 1.389(16),
Ga(2)Cl(2) 2.249(3), Ga(2)-N(2) 1.983(10), N(1)-Ga(2) 2.019(9), Cl(1)-Pt(1)-Ga(2)
85.5(8), Cl(2)-Ga(2)-Pt(1) 110.0(9), N(2)-Ga(2)-N(1) 97.2(4).
In order to characterise the platinum-gallium bonding, the solid state structures of 2
and 3 are unambiguously determined by the single crystal X-ray diffraction technique.
Perspective views of the molecular structures of 2, 3 with atom numbering schemes are
shown in Figures 2.3 and 2.4 respectively. Selected bond lengths and bond angles are given
at the corresponding figure footnotes. Single crystals suitable for X-ray structural
determination for compounds 2 and 3 were obtained as pale yellow crystals from saturated
toluene solutions at - 30 C.
Complex 2 crystallizes in the triclinic system with space group P-1 with a disordered solvent
molecule (toluene), whereas complex 3 crystallized with two solvent (toluene) molecules in
the monoclinic system space group P21/c. The solid state structures of 2 and 3 shows the
insertion of Ga(DDP) into the Pt–Cl bond. The molecular structure of complexes 2 and 3
depicts that the Pt centers are surrounded by Cl, Ga(DDP) and η4-coordinated 1,5cyclooctadiene (for 2) and η4-coordinated dicyclopentadiene (for 3) without altering the
olefin double bonds. In both compounds the Cl ligands are arranged in a trans orientation to
each other. The Pt–Ga bond distances in 2 and 3 are almost identical [Pt(1)–Ga(2) 2.417(2),
Pt(1)–Ga(2) 2.413(7) Å]. These bonds are considerably longer than Pt–Ga distances in the
homoleptic complex [Pt(GaCp*)4] (2.335(2) Å) or the terminal Pt–Ga distances in the
dimeric cluster [Pt2(GaCp*)5] (2.326(2) Å and 2.331(1) Å) [22], both featuring Ga(I) ligands.
A similar trend can be observed when platinum complexes containing cod and Ga(DDP) are
compared, for example [Pt(1,3-cod){Ga(DDP)}2] (Pt–Ga 2.346(1) and 2.342(1) Å)
[Pt{Ga{[N(Ar)C(H)2]}}2(cod)] (Pt–Ga 2.383(7) Å).
[11]
[17]
and
This elongation is expected because
of the tetra-coordinated Ga centre of 2 (and 3), as compared with the lower coordinate
gallium centers in the cited reference compounds.
47
Syn. of PtGaR complexes and insertion reactions
Chapter 2
Figure 2.4: Molecular structure of compound 3 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. The disorder in the dcy
carbons has been refined. Selected bond lengths (Å) and angles (º): Pt(1)Ga(2) 2.413(7),
Pt(1)C(31) 2.146(11), Pt(1)C(30) 2.161(11), Pt(1)C(39) 2.507(12), Pt(1)C(38)
2.576(10), Ga(1)Cl(2) 2.214(19), Pt(1)Cl(1) 2.320(2), Ga(1)N(1) 1.953(5), Ga(1)N(2)
1.962(6), C(30)C(31) 1.372(15), C(38)C(39) 1.459(15), Cl(1)-Pt(1)-Ga(1) 85.3(5), Cl(2)Ga(1)-Pt(1) 111.56(6), N(1)-Ga(1)-N(2) 96.3(2).
It is very well know that Pt–Ga bond lengths, and M–E bonds in general are quite
dependent on the type of ligand environment at both metal centers which influence
electronic and steric situations simultaneously. For example, the Pt–Ga distance of
[(Cy2PCH2CH2PCy2)Pt(GaR2)(R)] (R = CH2tBu, Cy = cyclohexyl), exhibiting a tricoordinate Ga centre, amounts to 2.438(1) Å.
[27]
The Pt–Cl bond distance in complex 2
[2.362(3) Å] shows a notable deviation when compared to the parent molecule [(1, 5cod)PtCl2] (av: Pt–Cl 2.257 Å).
[28, 29]
As it is observed in other Ga(DDP) supported metal
complexes, the bond angles in both compounds suggest that the gallium centre is shifted out
from the heterocyclic C3N2 plane after coordination with the platinum centre. The bite
angles of N-Ga-N in complexes 2 and 3 are 97.2(4)° [N(2)-Ga(2)-N(1)] and 96.3(2)° [N(1)Ga(1)-N(2)], respectively, which are significantly larger than the same observed in Ga(DDP)
48
Syn. of PtGaR complexes and insertion reactions
Chapter 2
(85.53(5)°).
[5]
In complex 2, the change in the bite angle is approximately 11.47°, whereas
in 3, it is 10.77° which lies in the range of those compounds previously reported.
[12d, 15, 30]
The Ga–N bond lengths are shortened considerably in comparison with the free ligand 1.
The average Ga–N bond distances in Ga(DDP) is reported as 2.054 Å, where as the average
Ga–N bond lengths in 2 and 3 are observed as 2.001 and 1.957 Å respectively. The increased
electrophilic nature of 1 upon insertion reaction and coordination to the platinum centre in 2
and 3, has resulted in the shortening of Ga–N bonds and elongation in N-Ga-N bite angles
relative to the free Ga(DDP). However, the structural features of the Ga(DDP) backbone in 2
and 3 are similar to those reported metal complexes containing this sterically crowded
ligand.
[15]
The oxidation states of Ga centers in 2 and 3 are not precisely discussed for
reasons we have extensively explained in numerous previous publications on similar
compounds. [12d, 31]
2.4
Synthesis of [(DDP)Ga(Me)(OTf)] (4)
The treatment of Ga(DDP) with [(cod)Pd(Me)(OTf)] affords a oxidized product
[(DDP)Ga(Me)(OTf)] (4) as a colorless solid in 33% isolated yield. The synthetic procedure
is shown in Scheme 2.2.
Pd
CH3
OTf
+
N
N
F-Benzol
Ga
- 40 C to RT
1h
N
Ga
N
CH3
OTf
Tf: triflate group
(4)
Scheme 2.2: Synthesis of [(DDP)Ga(Me)(OTf)] (4)
The formation of 4 involves the reduction of PdII to Pd0 followed by the concomitant
oxidation of group 13 metal GaI to GaIII by abstracting “CH3” and triflate groups from the
palladium centre. It appears that this reduction is quite fast and yields a black precipitate
within few minutes of reaction time presumably giving the insoluble palladium metal.
Compound 4 is sensitive to air and moisture and soluble in common organic solvents such as
49
Syn. of PtGaR complexes and insertion reactions
Chapter 2
benzene, toluene, fluorobenzene and THF. The 1H-NMR spectrum of 4 shows a sharp singlet
at δ; 1.57 ppm, corresponding to the presence of methyl protons of DDP ring. The –CH–
protons of isopropyl groups appear as broad resonances at 2.84 and 3.84 ppm. In addition to
the DDP ligand, the resonance associated with methyl protons of Ga–CH3 appears at δ; 0.46 ppm in 1H-NMR and that of the methyl carbon resonates at δ; - 13.8 ppm in 13C-NMR
spectrum.
[5, 25, 26]
The typical methine (γ-CH) carbon in DDP ring is slightly shifted to the
low field region (δ; 100.7 ppm) due to the presence of a more electron withdrawing triflate
group on the gallium (III) centre. It is noteworthy that the triflate carbon atom was not
observed in the 13C {1H} NMR spectroscopic times scale at room temperature measurement,
hence the existence of triflate group is confirmed from the infrared spectrum. A sharp
stretching frequency observed at 1013 cm-1 is assigned for the C–F bonds.
2.4.1 Single Crystal X-ray Structure of [(DDP)Ga(Me)(OTf)] (4)
Colorless crystals suitable for single crystal X-ray diffraction analysis are obtained
from concentrated toluene solution of 4 at - 30 C. X-ray crystallographic analysis carried
out on compound 4 resulted in poor crystallographic data and repeated trials to get good data
were failed due to the high sensitivity of the compound to moisture and air. Nevertheless, the
obtained crystallographic data for 4 is sufficient for the present structural discussion. The Xray data confirmed the presence of a tetra coordinated gallium (III) centre bearing one DDP
backbone and both, the triflate and methyl groups. These data match with the analytical and
spectroscopic characterization of 4. The molecular structure is shown in Figure 2.5 and the
important bond lengths and bond angles are shown as the figure foot notes. Compound 4
crystallizes in monoclinic, space group P2(1)/n. The most important bonding centers are the
GaO and GaC bonds. The bond lengths of these bonds [Ga(1)C(1) 1.922(3)Å) and
Ga(1)O(1) 1.985(2) Å)] are in the range of similar reported complexes.[26c] The slightly
longer GaO bond in 4 can be attributed to the higher (tetra) coordination of gallium metal
in this species. Furthermore the N(2)-Ga(1)-N(1) 99.46(12)º is considerably higher than
those complexes where gallium coordinates with transition metal centres. For example the
same bond angles in compounds 2 and 3 are observed as 97.2(4) º (N(2)-Ga(2)-N(1)) and
96.3(2) º (N(1)-Ga(1)-N(2)) respectively. The C3N2 backbone and phenyl groups are
arranged in coplanar as it is the case in Ga(DDP) supported complexes. Moreover the bond
angle of C(1)-Ga(1)-O(1) is observed as 105.11(13)º. The bond lengths and bond angles
50
Chapter 2
Syn. of PtGaR complexes and insertion reactions
indicate that the gallium (III) centre in 4 is in tetra coordinate state with distorted tetrahedral
gallium center. Figure 2.5: Molecular structure of compound 4 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Selected Bond lengths (Å)
and bond angles (°): Ga(1)N(2) 1.903(3), Ga(1)N(1) 1.910(2), Ga(1)C(1) 1.922(3),
Ga(1)O(1) 1.985(2), S(1)-O(3) 1.428(3), S(1)-O(2) 1.429(2), S(1)-O(1) 1.489(2), S(1)C(31) 1.824(4), N(1)-C(2) 1.345(4), N(1)-C(19) 1.451(4), F(1)-C(31) 1.326(5), N(2)-Ga(1)N(1) 99.46(12), N(2)-Ga(1)-C(1) 121.31(15), N(1)-Ga(1)-C(1) 125.79(13), N(2)-Ga(1)-O(1)
97.75(11), N(1)-Ga(1)-O(1) 102.68(10), C(1)-Ga(1)-O(1) 105.11(13), O(3)-S(1)-O(2)
117.98(13), O(3)-S(1)-O(1) 113.07(16), O(2)-S(1)-O(1) 113.57(12).
2.5
Synthesis of [(cod)(CH3)Pt{Ga(CH3)(DDP)}] (5)
The reaction between [(cod)Pt(Me)2] and Ga(DDP) in 1:1 molar ratio in toluene at
room temperature yields a pale yellow crystalline solid [(cod)(Me)PtGa(Me)(DDP)] (5) in
47% yield. The synthetic procedure for this compound is shown in Scheme 2.3. Compound 5
is stable under inert gas atmospheric conditions but slowly decomposes to grey solid after
prolonged storage even in inert atmosphere. It is highly soluble in common organic solvents
such as benzene, toluene and THF but sparingly soluble in n-hexane and pentane at room
temperature. The 1H-NMR of 5 in C6D6 measured at room temperature gives the expected
51
Syn. of PtGaR complexes and insertion reactions
Chapter 2
chemical shifts for the presence of COD and most importantly the PtMe and GaMe bonds.
Proton NMR spectrum shows two singlets at high field δ; 0.29 and - 0.31ppm are assigned
for the PtMe and GaMe groups respectively. As it is expected there are two different
septets associated to isopropyl protons are appeared in 1H-NMR at δ; 4.01 and 3.43 ppm
which are slightly shifted down field compared to the same protons in compounds 2 and 3,
but significantly shifted when comparison with the parent ligand Ga(DDP).[5] Whereas the
sharp singlet methine proton in 5 (δ; 4.71 ppm) is shifted to high field compared to the very
much similar complex 2.
Me
+
Pt
Me
N
N
Ga
Toluene
RT; 15h
N
N Ga
CH3 Pt
H3C
(5)
Scheme 2.3: Synthesis of [(cod)(CH3)Pt{Ga(CH3)(DDP)}] (5)
2.5.1 Single Crystal X-ray Structure of [(cod)(CH3)Pt{Ga(CH3)(DDP)}] (5)
Pale yellow single crystals suitable for X-ray diffraction analysis can be grown by
cooling over night the concentrated solution of 5 in toluene at - 30 ºC. Compound 5
crystallizes in orthorhombic, space group Pna2(1).The molecular structure of 5 is shown in
Figure 2.6 and the selected bond angles and bond lengths are shown at the figure foot note.
The molecular structure of 5 shows the two methyl groups one on each Pt and Ga centers are
arranged in a cis orientation, means same side to the PtGa bond unlike the chloride atoms
arranged in both complexes 2 and 3 which are in trans orientation. Whereas there is a certain
difference can be seen in case of bond angles of N-Ga-N for 5 and 2, this gives more
meaningful comparison since both complexes has same ligands [Ga(DDP) and cod] around
the platinum centers. The bond angle of N(2)-Ga(1)-N(1) (91.9(2)º) in 5 is substantially
lower than in 2 which is 97.2(4)º [N(2)-Ga(2)-N(1)]. This is almost 5.3º difference; could
have occurred due to the three dimensional arrangements of ligands around the metal
centers. The PtGa bond length in 5 [Pt(1)Ga(1) 2.4452(8)Å] is slightly longer than the
52
Chapter 2
Syn. of PtGaR complexes and insertion reactions
same in both complexes 2 [Pt(1)Ga(2) 2.417(16) Å] and 3 [Pt(1)Ga(2) 2.413(7)Å]. All the
important bond lengths and angles for compounds 2, 3 and 5 are summarized in Table 2.1.
Figure 2.6: Molecular structure of compound 5 in the solid state as determined by single
crystal X-ray diffraction. Ball and Stick model is shown. Hydrogen atoms and solvent
molecules are omitted for clarity. Selected Bond lengths (Å) and bond angles ():
Pt(1)Ga(1) 2.4452(8), Pt(1)C(33) 2.071(7), Pt(1)C(34) 2.212(6), Pt(1)C(36) 2.230(7),
Pt(1)C(38) 2.358(7), Pt(1)C(39) 2.443(8), Ga(1)C(1) 1.990(6), Ga(1)N(2) 2.027(5),
Ga(1)N(1) 2.031(5), C(39)C(38) 1.328(10), C(39)C(40) 1.532(11), C(1)-Ga(1)-N(2)
104.5(2), C(1)-Ga(1)-N(1) 107.7(2), N(2)-Ga(1)-N(1) 91.9(2), C(1)-Ga(1)-Pt(1) 126.03(19),
N(2)-Ga(1)-Pt(1)111.18(15), N(1)-Ga(1)-Pt(1) 110.12(14).
53
Syn. of PtGaR complexes and insertion reactions
Chapter 2
Table 2.1: Comparison of important bond lengths (Å) and angles (º) of 2, 3 and 5
Compound 2
Compound 3
Compound 5
Bond Length
Bond Length
Bond Length
(Or) Bond Angle
(Or) Bond
(Or) Bond Angle
Bond Type
Angle
2.6
Pt(1)Ga(1)
2.417(16)
2.413(7)
2.4452(8)
Ga(1)N(1)
1.983(10)
1.953(5)
2.031(5)
Ga(1)N(2)
2.019(9)
1.962(6)
2.027(5)
N(2)-Ga(1)-N(1)
97.2(4)
96.3(2)
91.9(2)
Synthesis of [(Cl3Ga)Pt(GaCp*)4] (6)
It is well known synthetic procedure that the reaction of [Pt(cod)2] with an excess of
GaCp* in n-hexane yields a monomeric homoleptic, tetrahedral Pt(0) cluster complex,
[Pt(GaCp*)4] as the solely product [22] where the GaCp* completely substitute the cod ligand
from the platinum center. Whereas the reaction of [Pt(cod)Cl2] with an access of GaCp* in
toluene at room temperature leads to the formation of a new platinum-gallane adduct
[Cl3GaPt(GaCp*)4] (6) as an orange solid product as shown in the Scheme 2.4.
Cl
Cl
Cl
Ga Ga
Pt
Cl
Cl
+ 6 Ga
Toluene
RT
24 h
- cod
Ga
Pt
Ga
Ga
(6)
Scheme 2.4: Synthesis of Lewis acid base adduct [(Cl3Ga)Pt(GaCp*)4] (6)
This reaction gives certain reactivity differences between the GaCP* and Ga(DDP).
As shown in Scheme 2.1, the reaction between [Pt(cod)2Cl2] and excess Ga(DDP) gives only
54
Syn. of PtGaR complexes and insertion reactions
Chapter 2
oxidatively inserted product [(1,5-cod)Pt(Cl){ClGa(DDP)}] (2), but there is no substitution
of the labile ligand cod has occurred. Whereas when the same reaction with GaCp* yields
the complete substitution of cod from the platinum center to give the metal rich PtGa5 core
containing low oxidation state compound 6 where the Pt is in zero oxidation state.
Compound 6 is stable for several days under inert gas argon atmosphere at - 30 C
but highly sensitive to moisture, air and is immediately decomposes upon exposure to the
normal atmospheric conditions. The 1H-NMR of this orange solid in C6D6 at room
temperature gives only one singlet for the Cp* methyl protons at δ; 1.94 ppm which is in the
range of similar reported compounds where as it is slightly shifted towards down-field when
compared with the [Pt(GaCp*)4]
[22]
(; 1.89 ppm). This is may be due to the highly acidic
Ga (III) center which could pull electrons from the Pt (0) center.
2.6.1 Single Crystal X-ray Structural Analysis of [(Cl3Ga)Pt(GaCp*)4] (6)
In order to characterize the Pt–Ga bonding, the solid-state structure of 6 was
unambiguously determined by the single-crystal X-ray diffraction technique. The
formulation of 6 was unequivocally determined from the X-ray data.
Figure 2.7: Molecular structure of compound 6 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Selected Bond lengths (Å)
and bond angles (): Pt1Ga3 2.3612(4), Pt1Ga2 2.3648(6), Pt1Ga4 2.3967(6), Pt1Ga5
55
Chapter 2
Syn. of PtGaR complexes and insertion reactions
2.4392(5). Ga5Cl1 2.2426(10), Ga5Cl1 2.2427(10), Ga5Cl2 2.2509(14), Cp*centroidGa(3) 1.610, Cp*centroid-Ga(2) 1.932, Cp*centroid-Ga(4) 1.610. Ga3-Pt1-Ga3 124.56(2),
Ga3-Pt1-Ga2 115.339(12), Ga3-Pt1-Ga2 115.338(12), Ga3-Pt1-Ga4 96.714(13), Ga3-Pt1Ga4 96.714(13), Ga2-Pt1-Ga4 98.51(2), Ga3-Pt1-Ga5 82.092(12) Ga3-Pt1-Ga5 82.092(12),
Ga2-Pt1-Ga5 84.133(19), Ga4-Pt1-Ga5 177.35(2).
Perspective views of the molecular structure with atom numbering schemes are
shown in Figures 2.7. Selected bond lengths and bond angles are given in figure footnotes.
Single crystals suitable for X-ray structural determination for compound 6 are grown as dark
orange crystals by cooling the saturated toluene at  30 ºC for one week. Compound 6
crystallizes in the orthorhobic, space group Pnma with two disordered solvent molecules.
The molecular structure of 6 reveals that the pentacoordinate platinum center. The Pt(0)
center is supported by four bulky GaCp* ligands and one Cl3Ga center. The bond angles and
bond lengths around the platinum center suggests that it has a distorted trigonal bipyramidal
molecular geometry with sterically over crowded ligands.
Among the four GaCp* ligands, three of them are lying in an equatorial positions where as
the other GaCp* and GaCl3 are in axial positions and trans to each other. Interestingly all the
three (equatorial) PtGaCp* bond lengths are same (av. PtGa 2.3636 Å) but the axial
PtGa bond length [Pt1Ga4 2.3967(6)] is slightly elongated compared to the equatorial
bonds as it is expected. The average bond lengths of PtGa of [Pt(GaCp*)4] moiety in 6 is
slightly elongated compared with the reported tetrahedral Pt(0) complex [Pt(GaCp*)4]
[22]
(2.335(2) Å). As it is expected the PtGa bond of PtGaCl3 in 6 is significantly elongated
from the normal PtGa bond lengths (Pt1Ga5 2.4392(5) Å) whereas this range is lies in the
similar reported Pt(0)·GaCl3 adducts such as in [(Cy3P)2PtGaCl3] (Pt1Ga1 2.4019(2)).[36]
The bond angle of Ga4-Pt1-Ga5 found to be 177.35(2) which is lower than the ideal Ga-PtGa bond angle of 180. Furthermore, the sum of bond angles around Pt center in the
equatorial plane is amounts to 355.74 which is slightly deviated from the ideal 360.
Compound 6 can be considered as a 1:1 Lewis acid-base adduct where a low valent
transition metal center acts as a mild nucleophilic center and main-group metal gallium acts
a electrophilic center similar to the reported examples of phosphine supported Pt(0)
analogous adducts with main-group metal(III) halides such as [(Cy3P)2Pt-AlCl3]
[(Cy3P)2Pt-GaCl3].
56
[37]
and
Chapter 2
Syn. of PtGaR complexes and insertion reactions
2.7
References
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C. Jones, D. P. Mills, R. P. Rose, A. Stasch. Dalton. Trans. 2008, 4395-4408.
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G. Prabusankar, C. Gemel, P. Parameswaran, C. Flener, G. Frenking, R. A. Fischer,
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Chapter 2
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(a) T. Cadenbach, C. Gemel, D. Zacher, R. A. Fischer, Angew. Chem. Int. Edit. 2008,
47, 3438-3441. (b) T. Cadenbach, C. Gemel, T. Bollermann, I. Fernandez, G.
Frenking, R. A. Fischer, Chem. Eur. J. 2008, 14, 10789-10796. (c) T. Bollermann,
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…………………………………………………………………………………………
59
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Chapter 3
PP Bond Activation of P4 Tetrahedron by Ga(DDP): Reactivity and
Coordination Chemistry of [(DDP)Ga(P4)] with Metal Carbonyls Mo(CO)6
and Fe2(CO)9 [b]
Abstract: The reactivity of Ga(DDP) (DDP = 2-Diiso-propylphenylamino-4-diisopropylphenylimino-2-pentene) towards the elemental white phosphorus (P4) is investigated
in detail. Reaction of Ga(DDP) with P4 tetrahedron in 1:1 ratio in toluene at room
temperature affords a novel [GaP4] cluster [(DDP)Ga(P4)] (7) by insertion of the Ga(I) center
at one of the six PP bonded edges of the P4 tetrahedron. Compound 7 is characterized by
1
H,
13
C, and
31
P NMR spectroscopy, elemental analysis, and single crystal X-ray structural
analysis. The solid state structure of molecule 7 reveals the first example of structurally
characterized GaP4 core stabilized by β-diketiminate ligand. Furthermore, the reactivity of
[(DDP)Ga(P4)] is explored towards few unsaturated organic substrates. The coordination
behavior of 7 is investigated towards metal carbonyls such as Mo(CO)6 and Fe2(CO)9. These
reactions have resulted in the formation of a bis-molybdenum pentacarbonyl adduct
[(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene
(8),
[(DDP)Ga(η2:1:1-P4){Fe(CO)5}]
(9)
respectively. These products represent a rare type of coordination mode of gallium metal
supported P4 butterfly structures.
[b] Some parts of this chapter are reported in the publication; Text and Figures are
reproduced with permission from G. Prabusankar, A. Doddi, C. Gemel, M. Winter,
R. A. Fischer, Inorg. Chem. 2010, 49, 7976-7980. Copyright © 2010 American
Chemical Society.
60
Chapter 3
3.1
Syn. of [(DDP)Ga(P4)] and its reactivity
Introduction
White phosphorus (P4) is readily available, and the most reactive allotrope of the
element. It is the classical starting material for the industrial preparation of numerous
organophosphorus derivatives. To meet the growing demand in phosphorus derivatives and
the increasingly stringent environmental regulations, new processes using white phosphorus
but avoiding chlorine are highly desirable. Thus, the interest in selective activation of a PP
bond in highly reactive white phosphorus is deeply rooted in phosphorus chemistry.
Phosphorus precursors of tailored reactivity are quite relevant for biological applications.[1]
Especially transition metal mediated PP bond activation has a promising future to produce
phosphorus transfer reagents for organic reactions, while this type of reaction is still at an
early stage of development with main group metals.[2-10]
Ar
Ar
N
P
P
N Al
Al N
P P
N
Ar
Ar
Ar = 2, 6-iPr2-C6H3
(Me3Si)3C
C(SiMe3)3
C(SiMe3)3
Ga Ga
P
Ga
P
P
P
C
A
Cp*
Al Cp*
*Cp
P
Al
P
Al
Al
P
Al
Cp*
P
*Cp Al
Cp*
Tl
Ar
P
Ar
Ar
P
P
P
Ar
Tl
Ar = 2, 6-iPr2-C6H3
D
B
Chart 3.1: Few examples of group 13 metal (I) organyls stabilized phosphorus- heterocycles
The main group metal mediated PP bond activation of the P4 tetrahedron can be
classified as either fragmentation or insertion of the P4 core by main group elements.
Fragmentation reactions are the most common pathways of P4 with main group precursors.
Recently G. Bertrand and co-workers have documented the fragmentation of P4 by an Nheterocyclic carbene (NHC) and related carbene ligands.[3b-d] A similar type of reaction is
observed with sigma donor low valent main group elements. For example, the reaction
61
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
between P4 and [(DDP)Al] (DDP = 2-Diiso-propylphenylamino-4-diiso-propylphenylimino2-pentene) resulted in the formation of [{(DDP)Al}2P4] (A) by the attack of two PP bonds
leading to double insertion.[4] Interestingly, the series of related carbenoid ER reactants, i.e.
[Cp*Al]4 (Cp* = C5Me5), [{(Me3Si)3C}Ga]4, and [ArTl]2 (Ar = C6H3(2,6-iPr2-C6H3)2) afford
[(Cp*Al)6P4] (B),[5] [{(Me3Si)3CGa}3P4] (C)[6] and [(ArP)2P2Tl2] (D)
[7]
respectively, by
dissipation of the P4 tetrahedron (chart 3.1). It is most often difficult to predict the fate of P4
in these reactions and random distribution of metal centers in the phosphorus core is
observed.
Interestingly, the P4 molecule also shows addition reactions with Lewis acids such as,
tBu3Ga, [8] or dissipation reactions with strong bases such as tBu3SiNa and [(Me3Si)3SiK][18crown-6].[9] However, stable molecules with single insertion of low valent main group
elements at P4 core are limited and such type of molecules can provide four naked
phosphorus centers for further reactions. The only reported example with a low valent main
group metal is a P4 unit supported by the NHC analog DDP”Si [DDP” = HC(CMeNC6H32,6-iPr2)(H2C=CNC6H3-2,6-iPr2)].[10]
The activation of P4 using gallium reagents was first investigated by A. R. Barron
and co-workers in 1991. The tBu and gallium addition of tBu3Ga into P4 led to the isolation
of [tBu2Ga{(P)(PtBu)(PGatBu)(P)}].[8] In contrast, the threefold insertion of gallium into
PP bond of P4 was observed when ¾ [{(Me3Si)3C}Ga]4 was treated with P4.[6] However, a
single or double insertion of a gallium center into P4 has not been reported yet. Since the
sterically encumbered Ga(DDP) is known to stabilize the unusual Zintl type group 14
clusters, [{(DDP)Ga(Cl)}4(Sn17)][13] and dibismuthenes, [{(DDP)Ga(ORf)}(Bi)]2 (Rf =
SO2CF3, C6F5),[14] one can anticipate a mild reaction between Ga(DDP) and white
phosphorus (P4).
3.2
Synthesis and Structural Characterization of [(DDP)Ga(P4)] (7)
3.2.1 Synthesis of 7
The reaction of white phosphorus (P4) with one equivalent of NHC analogue
Ga(DDP) in toluene at room temperature affords the formation of [(DDP)Ga(P4)] ( shown in
Scheme 3.1) with composition of [(DDP)Ga(P4)] as a solid product. Compound 7 is the first
example of a tetraphosphabicyclobutane molecule [(DDP)Ga(P4)] (7) which is supported by
a group 13 metal center. Bright yellow crystals of [(DDP)Ga(P4)] could be obtained in a
62
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
good yield (83%) when a solution of the crude product in a mixture of toluene and hexane
was cooled from room temperature to ‐ 30 °C and stored at this temperature for 12 h. It is
highly soluble in common organic solvents such as benzene, toluene and THF. Moreover, it
is stable both in solution as well as in the solid state at room temperature in an inert argon
atmosphere.
P
P
P
+
P
N
Ga
N
Toluene
N
RT, 1d
N
P
Ga
P
P
P
(7)
Scheme 3.1: Synthesis of [(DDP)Ga(P4)] (7) from the white phosphorus.
 (ppm)
Figure 3.1: 31P-NMR spectrum of [(DDP)Ga(P4)] (7) in C6D6 at room temperature.
63
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Compound [(DDP)Ga(P4)] has been characterized by
1
H,
13
C, and
31
P-NMR
spectroscopy, elemental analysis, and single crystal X-ray structural analysis. The 1H and
13
C-NMR spectra of [(DDP)Ga(P4)] exhibit the expected resonances for the (DDP) ligand,
well comparable with known metal complexes of Ga(DDP). The
31
P-NMR of compound
[(DDP)Ga(P4)] is useful in assigning the molecular composition as well as for the indication
of number of phosphorus atoms present in the molecule (Figure 3.1).
The 31P-NMR spectrum shows two sharp triplets at δ; +212.7 and -328.7 ppm which
indicates the presence of two kinds of phosphorus centers in the cluster. The signal at δ;
+212.7 ppm with a large coupling constant (1JP-P = 152 Hz) is assigned to the phosphorus
atoms linked to the gallium center directly. The same coupling constant is also observed for
the remaing two phosphorus atoms with a upfield chemical shift value at δ; -328.7 ppm. The
chemical shift value for PGa is nearly δ; 47-95 ppm downfield shifted, while that for P-PGa is δ; 110-122 ppm upfield shifted compared to the related compounds such as in
[(Cp”)2M(P4)] (Cp” = η5-1,3-tBu2-C5H3) [M = Zr (δ ; +166.1 & -206.5 ppm), Hf (δ ; +117.5
& -219.3 ppm)].15 Moreover, a considerable downfield shift of P-Ga (δ; 80 ppm) and P-P-Ga
(δ; 16 ppm) in [(DDP)Ga(P4)] are observed compared to [(DDP”)Si(P4)] (PSi, δ; 131.9 ppm
and P-P-Si, δ; -342.4 & -348.0 ppm), which is well acceptable since the electron
delocalization in C3N2Si and C3N2Ga back-bone are distinctly different.[10]
3.2.2 Molecular Structure of [(DDP)Ga(P4)] (7)
The bright yellow crystals of 7 suitable for X-ray structural analysis were obtained
from toluene and n-hexane solutions over a period of 12 h. Molecule 7 crystallizes in the
tetragonal space group, P43212 (Figure 3.2). Compound 7 can be regarded as a single
insertion product of [(DDP)Ga] into one of the PP bonds of a P4 tetrahedron. Therefore, the
molecular structure of [(DDP)Ga(P4)] is comparable with that of [(DDP”)Si(P4)].[10]
64
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Figure 3.2: Molecular structure of compound 7 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Important bond lengths (Å)
and angles (º): Ga(1)N(2) 1.907(6), Ga(1)N(1) 1.968(6), Ga(1)P(3) 2.340(2), Ga(1)P(1)
2.346(2), P(2)P(4) 2.154(3), P(2)P(3) 2.239(3), P(2)P(1) 2.242(3), P(3)P(4) 2.245(3),
P(4)P(1) 2.229(3), P(3)-P(2)-P(1) 90.14(11), P(4)-P(2)-P(1) 60.88(10), P(2)-P(3)-P(4)
57.41(10), P(2)-P(4)-P(1) 61.53(10), P(2)-P(4)-P(3) 61.15(10), P(1)-P(4)-P(3) 90.34(11),
P(4)-P(1)-P(2) 57.60(10), P(4)-P(2)-P(3) 61.44(10), P(2)-P(3)-Ga(1) 83.38(9), N(2)-Ga(1)N(1) 97.1(3), N(2)-Ga(1)-P(3) 119.03(19), N(1)-Ga(1)-P(3) 119.71(17), N(2)-Ga(1)-P(1)
115.82(18), N(1)-Ga(1)-P(1) 122.03(18), P(3)-Ga(1)-P(1) 85.21(8), P(4)-P(3)-Ga(1)
85.11(9), P(2)-P(1)-Ga(1) 83.17(9), P(4)-P(1)-Ga(1) 85.34(9).
The tetraphosphabicyclobutane fragment in [(DDP)Ga(P4)] shows a typical butterfly
shape structure. Atoms Ga(1), P(1) and P(3) are in the same plane, while the atoms P(2),
P(4) and the six membered GaN2C3 ring are perpendicular to the former plane. The GaP
bond distances in [(DDP)Ga(P4)] are almost equal within the range of the accuracy to the
measured data: 2.346(2) Å for Ga(1)P(1) and 2.340(2) Å for Ga(1)P(3). Consequently,
the remaining five PP bond distances are different and fall within the range of 2.154(3) to
2.245(3) Å. Although such types of bonding features were reported for [Cp*(CO)Co(P4)]
(CoP = 2.261(1) and 2.255(1) Å; PP range = 2.158(2) to 2.217(2) Å)[2j] and
65
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
[(DDP”)Si(P4)] (SiP = 2.250(1) and 2.246(1) Å; PP range = 2.159(2) to 2.235(2) Å),[10]
compound 6 draws near to the higher end of PP bond distances. The P(2)P(4) bond
distance in 6 is approximately 0.056(3)Å shorter than the PP bond distance found in P4
(2.21(2) Å), while P(2)P(3) (0.029 Å), P(2)P(1) (0.032 Å), P(3)P(4) (0.035 Å), and
P(4)P(1) (0.019 Å), are slightly elongated.[16] The P(1) and P(3) separation in 6 is 3.173(3)
Å, which is somewhat larger than that of [Cp*(CO)Co(P4)]
[2j]
(P···P = 2.606(1) Å) and
[(DDP”)Si(P4)] (P···P = 3.103 Å).[11] Furthermore, the value of the angle P(1)-Ga(1)-P(3) is
85.21(8)o, which compares with P-Si-P angle (87.32(5)o) of [(DDP”)Si(P4)].[11]
Figure 3.3: Molecular packing of [(DDP)Ga(P4)] (view along X-axis).
The widening of the P-P-P angles reveals the distorted tetrahedral geometry for the
phosphorus centers. The sum of P-P-P angle around P(2) (Σ P(2) = 212.46(10)o) and P(4)
(Σ P(4) = 213.02(10)o) and the sum of Ga-P-P and P-P-P angle around P(1) (Σ P(1) =
226.11(9)o) and P(3) (Σ P(3) = 225.9(9)o) are comparable. The P(2)-P(3)-P(4) bond in the
P4 core exhibits the lowest P-P-P angle (57.41(10)o), while the P(1)-P(4)-P(3) depicts the
66
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
highest angle (90.34(11)o). The shortening of the GaN bond [Ga(1)N(2) 1.907(6) and
Ga(1)N(1) 1.968(6) Å] and elongation of N(1)-Ga-N(2) angle (97.1(3)o) in [(DDP)Ga(P4)]
as compared to free Ga(DDP) (av. GaN = 2.0544 Å; N-Ga-N = 87.53 o) demonstrates the
increased electrophilic nature of Ga(DDP) upon coordination to the P4 moiety.[11] As shown
in the space-filling representation of compound 6 (Figure 3.3), the sterically crowded (DDP)
group effectively protects the extremely reactive P4 moiety of [(DDP)Ga(P4)] and thereby
prevents its oligomerization.
3.3
Synthesis and Structural Characterization of [(DDP)Ga(η2:1:1P4){Mo(CO)5}2]·2toluene (8)
3.3.1 Synthesis of 8
Furthermore, the coordinating ability of [(DDP)Ga(P4)] was investigated with
hexacarbonylmolybdenum. Treatment of Mo(CO)6 with [(DDP)Ga(P4)] in approximately 3:1
ratio in toluene at 80 C affords a bis-molybdenum pentacarbonyl adduct [(DDP)Ga(η2:1:1P4){Mo(CO)5}2]·2toluene as main product as pale yellow solid. Elimination of one carbonyl
group in Mo(CO)6 led to the formation of 8. The synthetic procedure for compound 8 is
shown in Scheme 3.2.
N
Ga
P CO CO
OC CO P
Mo P P Mo
OC
CO OC COCO
CO
N
N
N
P
Ga
P
P
P
+ 3 Mo(CO)6
Toluene
80  C
1d
(8)
Scheme 3.2: Synthesis of [(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene (8)
Pale yellow crystals of 8 are soluble in polar organic solvents and stable at room
temperature. Compound 8 is air and moisture sensitive compound and stable only under inert
atmosphere. It has been characterized by elemental analysis, IR, multinuclear NMR (1H, 13C,
and 31P) and single crystal X-ray diffraction technique. As indicated by elemental analysis, 8
has the composition of [(DDP)Ga(P4){Mo(CO)5}2]·2toluene (8) and is sufficiently pure to be
67
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
used directly for further characterization. IR spectroscopy confirms the presence of five
carbonyl bands (νCO; 2064(s), 1995(w), 1934(vs), 1912(vs), 1888(vs) cm-1), all attributable
to the Mo(CO)5 fragment.[17] The 13C-NMR spectrum of 8 in toluene-d8 shows only one peak
in the carbonyl region (δ; 204.8 ppm).
 (ppm)
Figure 3.4: 31P-NMR spectrum of [(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene in C6D6 at RT.
As it is shown in Figure 3.4, the 31P-NMR spectrum of 8 in C6D6 displays two triplets
at δ; -315.2 and 51.6 ppm. The triplet at δ; -315.2 ppm corresponds to the uncoordinated
phosphorus atoms, which is slightly shifted downfield with respect to 7 (13.5 ppm). The
lower field triplet at δ; 51.6 ppm can be attributed to the phosphorus atoms of [P-Mo(CO)5]
moiety and upon coordination, a very strong upfield shift (; 161.1 ppm) is observed.
Although compound 8 is isolated exclusively from this reaction, the
31
P NMR spectrum of
the mother liquor clearly indicates the presence of more than one complex with different
coordination modes of the phosphorus centers.
68
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
3.3.2 Molecular Structure of [(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene (8)
Compound 8 can be crystallized from the concentrated toluene solution layered with
n-hexane by cooling at  30 C. Pale yellow crystals can be grown in overnight. The
molecular structure of 8 is shown in Figures 3.5.
Figure 3.5: Molecular structure of compound 8 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Important bond lengths (Å)
and angles (º): Mo(2)P(1) 2.5458(8), P(4)–Mo(1) 2.5856(8), Ga(1)P(1) 2.3746(8),
Ga(1)P(4) 2.4051(8), Ga(1)N(2) 1.927(2), Ga(1)N(1) 1.931(2), P(4)P(3) 2.2163(11),
P(4)P(2) 2.2195(11), P(3)P(2) 2.1818(11), P(3)P(1) 2.2174(11), P(2)P(1) 2.2244(11),
N(2)-Ga(1)-N(1) 98.71(10), P(1)-Ga(1)-P(4) 79.03(3), P(3)-P(4)-P(2) 58.93(4), P(3)-P(4)Ga(1) 88.73(3), P(2)-P(4)-Ga(1) 88.12(3), P(3)-P(4)-Mo(1) 107.06(4), P(2)-P(4)-Mo(1)
107.85(4), Ga(1)-P(4)- Mo(1) 161.66(3), P(2)-P(3)-P(4) 60.61(4), P(2)-P(3)-P(1) 60.74(3),
P(4)-P(3)-P(1) 86.62(4), P(3)-P(2)-P(4) 60.47(4), P(3)-P(2)-P(1) 60.42(3), P(4)-P(2)-P(1)
86.38(4), P(3)-P(1)-P(2) 58.84(4), P(3)-P(1)-Ga(1) 89.48(3), P(2)-P(1)-Ga(1) 88.77(3), P(3)P(1)-Mo(2) 115.73(4), P(2)-P(1)-Mo(2) 116.61(4), Ga(1)-P(1)-Mo(2) 150.59(3).
Compound 8 crystallizes in monoclinic, space group P21/n with two solvent
molecules of toluene per asymmetric unit. 8 consists of a Ga, Mo and P based heteronuclear
69
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
[Ga(η2:1:1-P4)Mo2] core. Two [Mo(CO)5] fragments are attached to the phosphorus atoms of
7 in monodendate (η1) fashion. Interestingly, each [Mo(CO)5] fragment is tethered to the
phosphorus atoms that are linked to the gallium center which is a rather rare type of
coordination modes observed for metal complexes bearing a tetraphosphorus ligand.[2,17b,18]
However, the reaction of DDP”Si with [(NiDDP)2·toluene] or [(NiDDP’)2·toluene] (DDP’ =
2-Di-ethylphenylamino-4-diethylphenylimino-2-pentene) results in molecules consisting of a
[Si(μ,η2:2-P4)Ni] core similar to 8.[19a] The molybdenum center in 8 is in distorted octahedral
geometry, consisting of five CO ligands and one P atom. Interestingly, the Mo(CO)5
fragment prefers coordination at the more nucleophilic P centers despite the sterically less
favorable situation at this positions. Another interesting factor in 8 is the coordination mode
of the ligand [(DDP)Ga(P4)] to the molybdenum coordination sphere at axial position rather
than equatorial position which is sterically hindered site (Figure 3.6).
CO
OC
Mo
OC
CO
CO
P
P
Ga(DDP)
P
P
OC
Mo
OC
C
CO
O 1.142 Å
2.061 Å
(Mo-Cequi)
C 1.986 Å (Mo-C )
axial
O 1.152 Å
Figure 3.6: Different view of the complex 8 and shows the axial coordination of the P
centers of [(DDP)Ga(P4)] to Mo centers.
The MoP bond lengths (Mo(2)P(1), 2.5458(8) Å and Mo(1)P(4), 2.5856(8) Å) in 8 are
not equal and it is comparable with [Cp’Mo(CO)2(η3-P4){Cr(CO)5}4(H)] (Cp’ =
C5H4tBu).[17b] The Ga(1)P(1) distance (2.3746(8) Å) is distinctly shorter than that of
Ga(1)P(4) (2.4051(8) Å). The average GaP bond distances (2.3899(8) Å) in 8 is slightly
longer than the same bond distances of 7 (2.343(2) Å) (Figure 3.2). As shown in Figure3.2, a
negligible elongation of PP bond lengths with respect to 7 (except P(2)P(3)) is observed.
The PP bond distance of 8 falls in the range of 2.1818(11) to 2.2244(11) Å. The P(1)70
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Ga(1)-P(4) bond angle is 79.03(3)o, which is nearly 6o lower than 7 (P(1)-Ga(1)-P(3),
85.21(8)o). As expected, slight change in the bond angle of GaP4 core is observed in 8 as
compared to 7 (as shown in Figure 3.7). The central GaN2C3 ring atoms of Ga(DDP) are
essentially coplanar.
Figure 3.7: Selected bond lengths and angles comparison of GaP4 core in 7 (top) and 8
(bottom).
Moreover the bond lengths of all the CO groups are not same and carbonyl group which is
trans to the ligand has slightly higher bond distance [as it is shown in Figure 3.6] than the
other four carbonyl groups (av. 1.140 Å) in the molecule. Furthermore the MCaxial is shorter
than the MCequi. As a result, one can conclude that the trans ligand has some influence
which is a strong -donor in this case and facilitates the MC bond (M=C=O character)
strengthening by allowing unimpeded metal to CO pi-back bonding.
71
Chapter 3
3.4.
Syn. of [(DDP)Ga(P4)] and its reactivity
Synthesis and Structural Characterization of [(DDP)Ga(η2:1:1P4){Fe(CO)4}] (9)
3.4.1 Synthesis of 9
The coordination activity of compound 7 is further explored with diiron nona
carbonyl Fe2(CO)9. Treatment of [(DDP)Ga(P4)] with Fe2(CO)9 in 1:2 ratio in toluene at 70
C results in the formation of a mono coordinated complex [(DDP)Ga(η2:1:1-P4){Fe(CO)4}]
(9) as a brown solid as shown in Scheme 3.3.
CO
Fe CO
CO
P
P
OC
N
N
P
Ga
P
P
P
+ Fe2(CO)9
Toluene
N
70 C
20h
N
Ga
P
P
(9)
Scheme 3.3: Synthesis of [(DDP)Ga(η2:1:1-P4){Fe(CO)4}] (9) in toluene.
Compound 9 is stable under inert atmospheric conditions and soluble in benzene, toluene
and THF but insoluble in non polar organic solvents such as n-hexane and pentane. The 1HNMR of 9 in C6D6 gives the characteristic peaks such as the methine proton which appears at
; 5.08 ppm and the corresponding carbon center resonates at δ; 99.8 ppm. These chemical
shifts are slightly down field shifted when compared with the both compounds in 7 and 8 as
it is shown in Table 3.1. 13C NMR of 9 shows a very weak signal at ; 209.8 ppm which is
assigned for the FeCO moiety, this is in accordance with the complex [(DDP)GaFe(CO)4]
reported by Power and co-workers.
[19b]
The IR spectrum of 9 gives the characteristic three
sharp absorptions in the region of CO stretch (ν, cm-1; 2005, 1924, 1909, 1887) for
complexes of type LM(CO)4. The extra peak is probably due to the presence of minuet
quantities of the other isomer.
72
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Table 3.1: Comprises all the important proton chemical shifts for compounds 7, 8 and 9.
Nuclei
Compound 7
Compound 8
Compound 9
Chemical shift
Chemical shift
Chemical shift
δ (ppm)
δ (ppm)
δ (ppm)
-CH (1H)
4.58
4.50
5.08
-CH (13C)
96.1
98.3
99.8
(L)GaP4(ML1)n
-328.7 & 212.7
-315.2 & 51.6
……………
(31P)
3.4.2 Molecular Structure of Compound [(DDP)Ga(η2:1:1-P4){Fe(CO)4}] (9)
Single crystals suitable for X-ray analysis can be grown from the concentrated
toluene solution at - 30 ºC. Compound 9 crystallizes in monoclinic, space group P2(1)/n.
Figure 3.8: Molecular structure of compound 9 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Important bond lengths (Å)
and angles (º): Fe(1)P(2) 2.2465(10), Ga(1)N(1) 1.928(2), Ga(1)N(2) 1.929(2),
73
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Ga(1)P(1) 2.3616(9), Ga(1)P(2) 2.3956(8), Fe(1)C(37) 1.787(4), Fe(1)C(43) 1.800(4),
Fe(1)C(39) 1.804(3), Fe(1)C(41) 1.805(4), O(42)-C(41) 1.127(5), P(2)P(4) 2.2298(12),
P(2)P(3) 2.2348(12), P(1)P(4) 2.2031(12), P(1)P(3) 2.2082(12), P(4)P(3) 2.1918(15),
N(1)C(14) 1.335(3), N(1)-Ga(1)-N(2) 97.97(9), N(1)-Ga(1)-P(1) 118.54(7), N(2)-Ga(1)P(1) 121.03(7), P(4)-P(2)-P(3) 58.80(5), P(4)-P(2)-Fe(1) 122.25(4), P(3)-P(2)-Fe(1)
122.35(4), P(4)-P(2)-Ga(1) 88.32(4), N(1)-Ga(1)-P(1) 118.54(7), N(2)-Ga(1)-P(1) 121.03(7),
N(1)-Ga(1)-P(2) 120.40(7), N(2)-Ga(1)-P(2) 121.74(7), P(1)-Ga(1)-P(2) 78.93(3), Fe(1)P(2)-Ga(1) 144.08(4), C(41)-Fe(1)-P(2) 170.67(13).
The molecular structure of 9 is depicted in Figure 3.8 and the important bond lengths and
bond angles are shown at the foot note of the Figure 3.8. The molecular structure of 9 shows
the novel coordination mode of phosphorus atoms in [(DDP)Ga(P4)], where only one
phosphorus atom which is directly attached to the gallium center is coordinated to the
tetracarbonly iron (0) moiety (Fe(CO)4) in an unsymmetrical manner unlike in compound 8.
The FeP bond length [Fe(1)P(2) 2.2465(10)] in 9 is comparable with the FeP single bond
distacnces.[19c] The GaP distances are almost the same, but the average bond distances is
av.2.378 Å which is in the range of the same in complex 8 but significantly longer than in
the ligand 7 (2.343(2) Å) (Figure 3.2). Table 3.2 comprises the comparison of the most
important bond distances and IR frequencies.
Table 3.2: IR stretching frequencies and MP bond lengths of complexes 8 and 9
ν, CO stretching (cm-1)
Comp. no.
MP (Å)
8
2.5657 (av)
2.3895 (av)
2064, 1995, 1934, 1912, 1888
9
2.2465(10)
2.3786 (av)
2005, 1924, 1909, 1887
GaP (Å)
Molecular structure of 9 depicts that the p center form the ligand coordinates in an axial
fashion in the distorted trigonal pyramidal coordination sphere at the iron (0) center. The
bond angle between the ligating center (P) and the trans carbonyl [C(41)-Fe(1)-P(2)] is
observed as 170.67(13) which is lower than the ideal angle. More over the bond lengths of
all the CO groups are not the same, and the carbonyl group which is trans to the ligand has
the lower bond length [C(41) O(42) 1.127(5) Å] than the other three carbonyl groups (av.
1.151 Å). This means that metal to carbonyl [M(Fe)CO] more pi back bonding is favored.
74
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
This observation accounts for the fact that ligand 7 should act as a strong -donor and weak
pi-accepter.
3.5
Reactivity of [(DDP)Ga(P4)] Towards Olefins: Attempted reactions
to explore 7 as the phosphorus transfer reagent!
In general, the preparations of many organophosphorus compounds in industrial
process are involved in the past and in the present are based on the chlorination or
oxychlorination of white P4 to PCl3, PCl5, and POCl3. Using HCl or salt elimination
reactions, these compounds react to produce subsequent products such as phosphoric and
phosphonic acids and esters as well as organophosphorus derivatives of tri and pentavalent
phosphorus. To avoid these necessary steps needed so far and to achieve the criteria of more
sustainable and environmentally friendly processes, extreme efforts have been directed to
transfer white phosphorus directly to the desired industrial inorganic and organic phosphorus
containing products. These have been the goals of intensive academic as well as industrial
research in the periods of the 1970-80s by using main group elements and compounds to
transfer P4 directly to useful products. [20-24] However, the low selectivity and the problems in
the workup of the reaction mixtures usually obtained make these new processes noncompetitive with established industrial procedures. Nevertheless, exploration of such
reactions is of fundamental interest to test the possibility of making phosphorus containing
new products. With this background the reactivity of compound 7 was explored towards two
olefins (phenyl acetylene and styrene) to anticipate phosphorus transfer from compound 7!
as shown in Scheme 3.4.
The typical reactions were carried out in a Young NMR tube. The reaction of 7 with an
access of phenyl acetylene in Tol-d8 at room temperature showed no reaction. When the
temperature of the reaction was raised to 90 ºc for one day also did not yield any phosphorus
containing new products. These reactions were monitored by in situ
measurements. Interestingly, no other chemical shifts were found it its
31
31
P-NMR
P NMR spectrum
except the presence of starting material 7 even after long reaction periods. These results
show that the cluster 7 is highly stable and not reactive enough, means the cluster core GaP4
is very stable to break at least at the given experimental conditions.
75
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Ph
Ph
N
N
P
Ga
P
Tol-d8
90 C
P
No reaction
P
Tol-d8
90  C
No reaction
Scheme 3.4: Attempted reactions of 7 with olefins.
3.6
References
[1]
(a) Corbridge, D. E. C. Phosphorus-An Outline of its Chemistry, Biochemistry and
Technology, 5th ed., Elsevier, Amsterdam, 1995. (b) J. Emsley, the 13th Element:
The Sordid Tale of Murder, Fire, and Phosphorus, Wiley, New York, 2002.
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(a) M. Peruzzini, L. Gonsalvi, A. Romerosa, Chem. Soc. Rev. 2005, 34, 1038-1047.
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A. R. Fox, C. R. Clough, N. A. Piro, C. C. Cummins, Angew. Chem. Int. Ed. 2007,
46, 973-976. (d) J. S. Figueroa, C. C. Cummins, Dalton Trans. 2006, 2161-2168. (e)
N. A. Piro, J. S. Figueroa, J. T. McKellar, C. C. Cummins, Science. 2006, 313, 12761279. (f) C. C. Cummins, Angew. Chem. Int. Ed. 2006, 45, 862-870. (g) B. M.
Cossairt, N. A. Piro, C. C. Cummins, Chem. Rev. 2010, 110, 4164-4177. (h) J. S.
Figueroa, C. C. Cummins, Dalton Trans. 2006, 2161-2168. (i) C. C. Cummins,
Angew. Chem. Int. Ed. 2006, 45, 862-870. (j) O. J. Scherer, M. Swarowsky, G.
Wolmershäuser, Organometallics. 1989, 8, 841-842. (k) M. Caporali, L. Gonsalvi, A.
Rossin, M. Peruzzini, Chem. Rev. 2010, 110, 4178-4235.
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(a) M. H. Holthausen, J. J. Weigand, J. Am. Chem. Soc. 2009, 131, 14210-14211. (b)
J. D. Masuda, W. W. Schoeller, B. Donnadieu, G. Bertrand, J. Am. Chem. Soc. 2007,
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[4]
Y. Peng, H. Fan, H. Zhu, H. W. Roesky, J. Magull, C. E. Hughes, Angew. Chem.,
Int. Ed. 2004, 43, 3443-3445.
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Syn. of [(DDP)Ga(P4)] and its reactivity
C. Dohmeier, H. Schnöckel, C. Robl, U. Schneider, R. Ahlrichs, Angew. Chem., Int.
Ed. 1994, 33, 199-200.
[6]
W. Uhl, M. Benter, Chem. Commun. 1999, 771-772.
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A. R. Fox, R. J. Wright, E. Rivard, P. P. Power, Angew. Chem. Int. Ed. 2005, 44,
7729-7733.
[8]
M. B. Power, A. R. Barron, Angew. Chem. Int. Ed. 1991, 30, 1353-1354.
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For examples: (a) W. T. K. Chan, F. Garcίa, A. D. Hopkins, L. C. Martin, M.
McPartlin, D. S. Wright, Angew. Chem. Int. Ed. 2007, 46, 3084-3086. (b) H. W.
Lerner, M. Bolte, K. Karaghiosoff, M. Wagner, Organometallics 2004, 23, 60736076. (c) N. Wiberg, A. Wörner, K. Karaghiosoff, D. Fenske, Chem. Ber. 1997, 130,
135-140. (d) H. W. Lerner, M. Wagner, M. Bolte, Chem. Commun. 2003, 990-991.
(e) H. W. Lerner, G. Margraf, L. Kaufmann, J. W. Bats, M. Bolte, M. Wagner. Eur.
J. Inorg. Chem. 2005, 1932-1939. (e) N. Wiberg, A. Wörner, H. W. Lerner, K.
Karaghiosoff, H. Z. Noeth, Naturforsch. B, Chem. Sci. 1998, 53, 1004-1014.
[10]
Y. Xiong, S. Yao, M. Brym, M. Driess, Angew. Chem. Int. Ed. 2007, 46, 4511-4513.
[11]
N. J. Hardman, B. E. Eichler, P. P. Power, Chem. Commun. 2000, 1991-1992.
[12]
(a) G. M. Sheldrick, SHELXS-97, Program for the Solution of Crystal Structures,
Universität Göttingen, 1997. (b) G. M. Sheldrick, G. M. SHELXL-97, Program for
Crystal Structure Refinement, Universität Göttingen, 1997. (c) A. L. Spek, Acta
Cryst. Sect.A, 1990, 46, C34.
[13]
G. Prabusankar, A. Kempter, C. Gemel, M. K. Schröeter, R. A. Fischer, Angew.
Chem., Int. Ed. 2008, 47, 7234-7237.
[14]
G. Prabusankar, C. Gemel, P. Parameswaran, C. Flener, G. F. Frenking, R. A.
Fischer, Angew. Chem., Int. Ed. 2009, 48, 5526-5529.
[15]
O. J. Scherer, M. Swarowsky, H. Swarowsky, G. Wolmershäuser, Angew. Chem. Int.
Ed. 1988, 27, 694-695.
[16]
D. E. C. Corbridge, E. J. Lowe, Nature. 1952, 170, 629.
[17]
(a) O. S. Senturka, S. Serta, Ü. Özdemir,. Z. Naturforsch. 2003, 58b, 1124-1127. (b)
M. Scheer, U. Becker, P. Magull, Polyhedron 1998, 17, 1983-1989.
[18]
For examples: (a) M. Scheer, C. Troitzsch, P. G. Jones, Angew. Chem. Int. Ed. 1992,
31, 1377-1379. (b) D. N. Akbayeva, Russ. J. Coord. Chem. 2006, 32, 329-334. (c) D.
N. Akbayeva, O. J. Scherer, Z. Anorg. Allg. Chem. 2001, 627, 1429-1430. (d) M.
Scheer, U. Becker, E. Matern, Chem. Ber. 1996, 129, 721-124. (e) M. Scheer, M.
Dargatz, J. Organomet. Chem. 1992, 440, 327-333. (f) D. N. Akbayeva, Russ. J.
77
Chapter 3
Syn. of [(DDP)Ga(P4)] and its reactivity
Coord. Chem. 2007, 33, 661-668. (g) M. Scheer, U. Becker, J. Organomet. Chem.
1997, 545-546, 451-460. (h) M. Scheer, C. Troitzsch, L. Hilfert, M. Dargatz, E.
Kleinpeter, P. G. Jones, J. Sieler, Chem. Ber. 1995, 128, 251-257.
[19]
(a) Y. Xiong, S. Yao, E. Bill, M. Driess, Inorg. Chem. 2009, 48, 7522-7524. (b) N. J.
Hardman, R. J. Wright, A. D. Phillips, P. P. Power, J. Am. Chem. Soc. 2003, 125,
2667-2679. (c) K. Feldmann, R. Fröhlichc, J. J. Weigand, Chem. Commun., 2012,
48, 4296-4298.
[20]
S. Dapporto, S. Midollini, L. Sacconi, Angew. Chem., Int. Ed. Engl. 1979, 18, 469470.
[21]
M. Di Vaira, C. A. Ghilardi, S. Midollini, L. Sacconi, J. Am. Chem. Soc. 1978, 100,
2550-2551.
[22]
A. P. Ginsberg, W. E. Lindsell, J. Am. Chem. Soc. 1971, 93, 2082-2084.
[23]
O. J. Scherer, H. Sitzmann, G. Wolmersha¨user, Angew. Chem.,Int. Ed. Engl. 1985,
24, 351-353.
[24]
O. J. Scherer, T. Bru¨ck, Angew.Chem., Int. Ed. Engl. 1987, 26, 59-59.
78
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Chapter 4
Synthesis of Low Valent “Ge4” and “Ge2” Clusters Trapped by Low
Valent Ga(DDP): A -Bond Between two Ge–Ge Centers without a -Bond
[c]
Abstract: This chapter deals with the investigations resulted from the study of the
reactivity of Ga(DDP) with Lewis base supported germanium(II) chlorides. Reduction
reactions of a ligand stabilized (Lewis base) germanium dichlorides (IPr)·GeCl2 (IPr: 1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene)
and
(PCy3)·GeCl2
with
N-heterocyclic
I
carbene heavy analogue of low valent group 13 bulky carbenoid, Ga (DDP) have been
investigated. These reactions afford the group 13/14 element clusters [Ge4{Ga(DDP)}2] (10)
and
[Ge2{Ga(DDP)}2] (11) as an orange and red crystalline substances respectively.
Compounds 10 and 11 have a novel mixed metalloid Ga2Gen (n = 2 and 4) framework and
they are completely characterized by 1H,
13
C-NMR, LIFDI-MS and also with the single
crystal X-ray diffraction technique. The solid state structures of 10 and 11 reveals the first
structurally characterized Ga2Ge4 cluster with a puckered Ge4 core and a Ge2 dimer which
are stabilized by a low valent bulky β-diketiminate derivative of gallium (I) ligands. The Ge–
Ge and Ga–Ge bond lengths in 10 are in the range of 2.4533(16) and 2.5060(12) Å
respectively. The two germanium centers in 11 are separated by a distance of 2.8714(11) Å.
The quantum chemical calculations of compound 11 showed the presence of a -bond
between the two GeGe centers without a formal Ge–Ge -bond. Compound 11 is an
unusual example of a molecule where two heavy main group homo atoms are connected by a
-bond without -bond. The LIFDI-MS (Liquid Injection Field Desorption Ionization)
spectra show the isotopic parent ions are in full accordance with the proposed formulae of
compounds 10 and 11. In addition, LIFDI-MS spectroscopy proved to be a valuable tool for
in situ monitoring of the cluster formation reactions.
[c]
The results of this chapter are reported in the publication: Text and Figures are
reproduced with permission from; A. Doddi, C. Gemel, M. Winter, R. A. Fischer, C.
Goedecke, H. S. Rzepa, G. Frenking, Angew. Chem. Int. Ed. 2013, 52, 450-454. DOI:
10.1002/anie.201204440. Copyright © 2013 WILEY-VCH Verlag GmbH & Co.
KGaA, Weinheim.
79
Chapter 4
4.1
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Introduction
During the last two decades, group 13/14 metalloid cluster compounds have received
a widespread interest due to the formation of new compounds which are interesting at
fundamental point of view.
[1]
interesting class of compounds
recent years
Among the group 14 clusters, germanium compounds are
[2b, 2c]
and many synthetic procedures have been developed in
[2]
. Germanium is one of the well known elements in the periodic table of
elements which could form number of anionic clusters (Gen-m). Although the Zintle type
germanium clusters are known for long time but the ligand stabilized germanium clusters
were introduced in the late 1980s. Recently many such clusters of the formula (GeR)n have
been reported with different sterically demanding ligands. [3]
Bulky silyl groups are well known ligands for stabilizing many germanium clusters.
Very recently Schnepf and co-workers reported that the largest fullerene like metalloid
germanium cluster Ge14[Ge(SiMe3)3]5Li3(THF)6[4a] comprises a hollow arrangement of
polyhedron with 14 germanium atoms and similarly many such high nuclearity clusters with
different ligands are documented in the literature.[4] Wiberg and co-workers first time
reported a molecular germanium compound with a “Ge4” tetrahedron and structurally
characterized as Ge4((tBu)3Si)4.[4g] Several bulky ligands have been employed for the
isolation of such clusters, for example Power etal synthesized an orange crystalline Ge6Ar2'
(Ar' = C6H3-2, 6-Dipp2; Dipp = C6H3-2, 6-iPr2) where they employed sterically bulky
terphenyl ligand system for stabilizing the Ge6 cluster which has a distorted octahedron
germanium core.[5] To the best of our knowledge the mixed metalloid cluster compounds of
the heavier group 13/14 elements are very rare and interesting because they may have
interesting electronic, bonding and structural properties.[6] These findings are however
interesting to investigate the feasibility of sterically encumbered low valent Group 13
compounds for the trapping of germanium clusters. Very recently main-group clusters with
:E(I)R (E : Ga and Al, R: Cp*, DDP) type ligands
and
high-nuclearity
metalloid
tin
clusters
[7]
have been employed to isolate novel
such
as
[{(DDP)ClGa}2Sn7]
[{(DDP)ClGa}4Sn17] which are trapped by β-diketiminate Ga(DDP)
[8]
and
and multiple metal
bonds in case of bismuthenes Bi2L’2 (L’ = (DDP)XGa; X = Cl, CF3SO3).[9] These results
proved that Ga(DDP) is a potent ligand which can be used for reducing M+n to Ma ( n>a) on
the way for stabilizing medium to larger size clusters. Therefore, similar analogy can be
expanded for the isolation of heavier group 13/14 element clusters.
80
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Furthermore, in recent times much progress has been made in the field of low-valent
main group 13/15 compounds. The most impresive examples are the stabilization of maingroup diatomic allotropes. The disilicon molecule LSi=SiL (L = :C{N(2,6-Pri2C6H3)CH}2)
[10]
and the closely related species E2L2 (i.e. “Ge2”,[11] “P2”,[12] “As2”[13]) are the major
discoveries in recent years in the history of main group chemistry.[14] Even the most
intriguing di-carbon congeners C2L2 should be accessible, as is deduced from the quantum
chemical studies.[15] Usually such novel compounds are very labile, and the choice of the
right ligand system providing ideal steric as well as electronic properties is most crucial. One
concept, especially used by the groups of Robinson and Uhl, is the use of sterically crowded
N-heterocyclic carbenes (NHCs). N-heterocyclic carbenes (NHCs) turned out to be the key
for opening the door to this new chemistry, and their heavier main group 13/14 analogues
such as gallylenes (NHGa), silylenes (NHSi), germylenes (NHGe) etc., expand this library of
“multitalented” Lewis base ligands for stabilizing reactive species and unusual bonding
situations.[16] In particular the NHGa compound Ga(DDP) behaves as a potent trapping
ligand and a selective reducing agent as well. [17] This unique combination of properties has
been utilized for the synthesis of the metalloid tin clusters Sn7L’2, Sn17L’4[8] and the
bismuthenes Bi2L’2 (L’ = (DDP)XGa; X = Cl, CF3SO3).[9]
4.2
Synthesis of [Ge4{Ga(DDP)}2] (10)
At first the reactivity of Ga(DDP) with Dioxane.GeCl2 is investigated at ambient
conditions. Since most of the germanium clusters have been reported with the
Dioxane·GeCl2 complex as one of the germanium source, this observation prompted us to
study the possibility of isolation of germanium clusters with “ :E(I)R ” type ligands. But this
reaction in fluorobeneze at room temperature immediately yields a brown insoluble
precipitate with which complete characterization could not be done. Whereas when a ligand
stabilized L·GeCl2 (L: NHC (IPr), PCy3) is used the same reactions are found to undergo
very smoothly and clearly to give the germanium clusters.
The cluster 10 was synthesized from the reaction of a suitable N-heterocyclic carbene
stabilized germanium (II) precursor. The reduction of IPr·GeCl2
[11]
( IPr = 1,3-bis(2,6-di-
isopropylphenyl)-imidazol-2-ylidene) with excess of Ga(DDP) in 1:3 molar ratio in
fluorobenzene at room temperature affords 10 as an orange-red crystalline substance in about
10.7 % isolated yield (Scheme 4.1). This reaction proceeds smoothly from an initial pale
yellow to red, finally to dark brown-red without the formation of any insoluble solid during
81
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
the reaction course and at the end of the reaction period. The formation of anticipated byproduct, Cl2Ga(DDP) was also observed (Unit cell values by the single crystal X-ray
diffraction study), this observation gives an idea that, the redox reactivity of Ga(DDP) which
not only acts as a reducing agent but also simultaneously stabilizes the cluster atoms on its
coordination as shown in the scheme 4.1.
Ge
Cl
N
Ge
N
Cl
N
+ 3
N
Ga
PhF
RT, 4d
-Cl2Ga(DDP)
N
N
Ge
Ga
Ga
Ge
Ge
N
N
(10)
Scheme 4.1: Synthesis of [Ge4{Ga(DDP)}2] (10) in fluorobenze.
After work up of the reaction, an orange solid was got. Compound 10 is highly
soluble in common aromatic solvents such as benzene, toluene, and fluorobenzene and is
sparingly soluble in non polar solvents such as n-hexane and pentane. Compound 10 is stable
under inert atmosphere (Ar) for several days and slowly decomposes to pale yellow when it
is exposed to normal atmospheric conditions. Compound 10 is also characterized by solution
state NMR spectroscopy, LIFDI-MS (Liquid Injection Field Desorption Ionization) and
elemental analysis. In the 1H-NMR spectrum of 10, just one set of resonances for the ligands
Ga(DDP) is detected indicating that the two ligands are in the same chemical environment
and exhibits a symmetrical structure in solution at room temperature, which makes protons
of each functional groups are magnetically equivalent. These data is fully consistent with the
proposed molecular structure. The typical 1H-NMR resonance in C6D6 for methine (γ-CH)
protons of the (DDP) backbone is observed as a sharp singlet at δ; 4.85 ppm which is in the
expected range when compared to the similar Ga(DDP) supported main group metal
complexes
[9]
. Whereas the same methine carbon resonates at δ; 97.6 ppm in its
spectrum and are thus shifted up field compared to the parent ligand Ga(DDP)
13
[17]
C-NMR
and also
the same is true for the imino carbons (-C=N) in (DDP) ring (δ; 166.6 ppm), this is
presumably due to the electron drift towards the ligand part.
82
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
The LIFDI mass spectrum of compound 10 measured in toluene is very interesting. It shows
the 100% intensity of the expected molecular ion peak at [M]+ • (m/z) 1264.08 which is well
comparable with the computed isotopic distribution pattern (Figure 4.1) when the same
molecular formula is given. The absorption maximum of the UV/Vis spectrum in toluene is
detected at 391nm (Figure 4.2).
Figure 4.1: LIFDI-MS spectrum of crystals of [Ge4{Ga(DDP)}2] (10) measured in toluene.
Calculated isotope pattern for the molecular formula C58H82N4Ga2Ge4 (1265.184) for 10.
Figure 4.2: Left: UV/Vis spectrum of compound Ge4[Ga(DDP)]2 (10) in toluene as the
solvent. Right; UV/Vis and emission spectra of compound (10) measured in toluene.
83
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
4.2.1 Molecular structure of [Ge4{Ga(DDP)}2] (10)
Orange crystals suitable for X-ray analysis could be obtained by cooling the reaction
mixture at - 30 C for one week. Compound 10 crystallizes in the trigonal Space group
P3(1)21 with one disordered solvent molecule in the lattice. The molecular structure is
shown in Figure 4.3. Selected bond lengths and angles are shown at the figure 4.3 foot note
as well as in table 4.0. The structure of 10 is derived from a Ge4 tetrahedron by insertion of
Ga(DDP) into two opposite Ge–Ge edges. This structural motif is unknown for ligand
stabilized Zintl-like GenRm clusters (n  m; R = bulky aryl, silylamide, etc.).[18]
Figure 4.3: Molecular structure of compound 10 in the solid state as determined from single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å)
and angles (º): Ge(1)–Ge(1’) = 2.4551(8), Ge(1)–Ge(2) = 2.4623(6), Ge(2)–Ge(2’) =
2.4606(8), Ge(1)–Ga(1) = 2.5059(6), Ge(2)–Ga(1’) = 2.4755(6), Ga(1)–N(1) = 1.962(3),
Ga(1)–N(2) = 1.970(3), Ga(1)–Ge(2’) = 2.4755(6). Selected bond angles (): N(1)-Ga(1)N(2) 95.43(14), Ge(1’)-Ge(1)-Ge(2) = 73.761(16), Ge(1’)-Ge(1)-Ga(1) = 97.02(2), Ge(2)Ge(1)-Ga(1) = 90.10(2), N(1)-Ga(1)-N(2) = 95.43(13), N(1)-Ga(1)-Ge(2’) = 124.77(10),
84
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
N(2)-Ga(1)-Ge(2’) = 18.89(10), N(1)-Ga(1)-Ge(1) = 128.33(10), N(2)-Ga(1)-Ge(1) =
118.93(9), Ge(2’)-Ga(1)-Ge(1) = 72.659(17).
Molecular structure of compound 10 reveals the presence of a 2-fold axis of symmetry which
passes through the center of two Ge(1)–Ge(1’) and Ge2–Ge(2’) bonds in the cluster.
Furthermore, the molecular structure of 10 reveals that the puckered “Ge4” core is trapped by
two strongly coordinating gallium (I) ligands which are supported by sterically bulky βdiketiminato backbone.
N
N
Ga
Ge
Ge
Ge
Ge
Ga
N
N
Figure 4.4: Scheme of the metalloid core [Ga2Ge4] of 10 with two bulky capping (DDP)
moieties.
As shown in Figure 4.4, the core structure consists of a tetrhedro-tetragermanide Ge4 being
capped by two Ga(I) ligands on both edges of “Ge4” moeity, with a fold angle of av. 73.71 °
(Ge-Ge-Ge) which together form a {Ga2Ge4} cluster. To the best of our knowledge 10 is the
first structurally characterized group 13/14 neutral mixed metalloid cluster with a sixmembered ring consisting of Ga/Ge atoms exclusively.
[6]
Interestingly, the four Ge–Ge
bonds in 10, which only slightly vary around the average value of 2.459 Å and match with
the value of elemental germanium (2.45 Å).[19] Larger metalloid GenRm clusters (n  4; m 
n) exhibit longer Ge–Ge contacts, i.e. Ge6R2 (2.546(1)-2.886(2)Å; R = C6H3-2,6-Dipp2; Dipp
= C6H3-2,6-iPr2)[18a] and Ge8R6 (2.50 to 2.67Å; R = N(SiMe3)2).[18b] The structure of 10 can
be viewed as derived from an ideal Ge4 tetrahedron with two opposite edges being opened
by insertion of two carbenoid Ga(DDP) ligands in trans fashion which results in two long
Ge–Ge distances of 2.952 Å. Compound 10 may be compared with P4[Al(DDP)]2.[20] It was
described by an ionic bonding model as P44- butterfly shaped Zintl-anion coordinated by two
85
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
cationic [Al(DDP)]2+ units. If compound 10 is regarded as a similar contact ion pair of a
Ge44- anion and two [Ga(DDP)]2+ units, the very long Ge–Ge distances of 2.952 Å ought to
be treated as Ge–Ge bonding (the electron precise Ge44- Zintl ion is tetrahedral).
4.3
Synthesis of [Ge2{Ga(DDP)}2] (11)
After the isolation of compound 11 as a neutral Ge4 cluster stabilized by two
sterically bulky Ga(DDP) ligands, where Ga(DDP) acts as both reducing and stabilizing
ligand, this reaction prompted to study the possible isolation of other low coordinate
germanium fragments with Ga(DDP) but now in the presence of an external reducing agent
such as KC8. The reduction of phosphine supported (PCy3)GeCl2 adduct with KC8 in
presence of Ga(DDP) in THF at ambient temperature resulted in the formation of “Ge2”
dimer as compound 11 as the main reaction product including compound 10. Cluster 10 was
isolated (method-B) from the hexane extract of the reaction mixture, whereas the THF
solution of the reaction mixture affords 11 as a brown-red crystalline solid in 3.7 % yield.
Compound 11, surprisingly and unlike 10, is soluble in THF and has very poor solubility in
aromatic solvents such as benzene, toluene, and fluorobenzene and is insoluble in n-hexane
and pentane. Furthermore, once the compound 11 crystallized then its solubility is reduced.
Molecule 11 is highly moisture and air sensitive. Moreover, the red crystals of 11 straight
away decomposes to pale yellow amorphous solid when it is exposed to normal atmospheric
conditions, but are stable under inert argon atmosphere for about one week. Scheme 4.2
shows the typical synthetic procedure for the preparation of compound 11.
Cl
P Ge
N
+
Cl
N
Ga
KC8
N
THF
2h, RT
N
Ge
Ga
Ga
Ge
(11)
N
+ (10)
N
Scheme 4.2: Preparation of the dimer [Ge2{Ga(DDP)}2] (11)
Compound 11 has been characterized by solution NMR spectroscopy and LIFDI-MS
analysis. The 1H and 13C-NMR spectra of 11 in THF-d8 exhibit the expected resonances for
86
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
the (DDP) backbone. In the 1H-NMR spectrum of 11, just one set of resonances for the
ligands Ga(DDP) is detected as it is observed for cluster 10 which indicates the magnetically
equivalent protons with a symmetrical structure in solution at room temperature. The typical
γ-CH proton is observed as a sharp singlet at δ; 5.15 ppm which is almost equal to the same
observed for 10 but in THF-d8. All the chemical shifts observed in the 1H-NMR spectrum of
11 are assigned and there are no signals appear in the typical region of Ge–H groups (; 
3.92 and 8.0 ppm). The absence of GeH in 11 is further confirmed by the IR and Raman
spectra which do not provide any indications for the presence of terminal Ge–H moieties. [21] The molecular composition of 11 is further established by the mass spectral analysis. The
LIFDI mass spectrum measured in THF shows the expected molecular ion peak at [M]+
•
(m/z) 1120.3 which is well comparable with the computed isotopic pattern (as shown in
Figure 4.5) when the same molecular formula is given.
Figure 4.5: LIFDI-MS spectrum of red crystals of Ge2[Ga(DDP)]2 (11) measured in THF.
Top corner is for the calculated isotope pattern for the molecular formula C58H82N4Ga2Ge2
(1119.964) Ge2[Ga(DDP)]2 (11).
In order to completely understand the reaction course of the reduction of
(PCy3)GeCl2 with Ga(DDP) in presence of KC8, in situ LIFDI-MS measurements were
conducted by taking small and clear aliquots from the reaction mixture. These samples are
87
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
analyzed immediately taking out the aliquots from the Schlenk tube [since the compound is
highly sensitive to moisture and air; when these aliquots were allowed to stay more than 10
min the color of the sample changes to colorless]. In situ LIFDI-MS studies indicate that the
very quick formation of “Ge2” and “Ge4” clusters with in the short reaction periods (at 30
min; see Figure 4.6 and 12h; see Figure 4.7) of the reaction at room temperature. But the
presence of Ge2 cluster is not observed when the reaction mixture is allowed stirring for
longer reaction periods (more than one week). No other assignable clusters are observed in
the LIFDI-MS measurements. This aspect suggests that presumably the initially formed Ge2
cluster gradually grow up to Ge4 cluster by the inclusion of more germanium atoms in to the
cluster. One would believe that in the synthesis of 10 and 11, the stripping of stabilized
ligands [NHC (IPr) and phosphine (PCy3)] from the GeCl2 could have occurred in a
reductive elimination process there by the naked germanium atoms are released.
Simultaneously these intermediate species are trapped by the bulky Ga(DDP).
Figure 4.6: LIFDI-MS of an aliquot (reaction mixture) after 30 min stirring at RT.
Formation of compounds 10 and 11 is shown. Complete spectrum is not shown for clarity;
L: Ga(DDP).
88
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Figure 4.7: LIFDI-MS of the crude reaction mixture after 12h reaction period at RT.
Formation of compounds 10 and 11 is shown (L: Ga(DDP)).
For the deep understanding of this reaction few more reactions are conducted by changing
the solvent and in other relatively nonpolar solvents such as toluene and fluorobenze. In case
of toluene as the reaction solvent, even though 3 equivalents of KC8 is used and this reaction
was found to be very sluggish and no color change is observed until 3 days of the reaction
period at room temperature. This reaction gives Ge4 cluster (10) as the major product as
shown in Scheme 4.3. Whereas when the reaction was carried out in fluorobenze found to be
very fast similar to case of THF and isolated 11. The crystals isolated from fluorobenze
solution were found not having solvent molecules in the lattice, whereas in case of THF
compound 11 crystallizes with four THF molecules.
P Ge
Cl
Cl
+
N
Ga
3 KC8
Toluene
4d, RT
N
Ge4[Ga(DDP)]
(10)
Scheme 4.3: Alternative synthesis of compound 10 in toluene at room temperature
89
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
4.3.1 Single Crystal X-ray Structure of [Ge2{Ga(DDP)}2] (11)
Deep brown-red crystals of 11 suitable for single crystal X-ray diffraction analysis
could be obtained by cooling the dark brown-red reaction mixture after the filtration of
suspension. Single crystals shown in Figure 4.8 can be grown from cooling the concentrated
THF solution at - 30 C in 4-7 days. The molecular structure of compound 11 is shown in
Figure 4.9.
Figure 4.8: Dark brown-red crystals of compound 11 under the microscope.
Figure 4.9: Molecular structure of compound 11 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
90
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å)
and angles (º): Ge(1)–Ge(1’) = 2.8714(11) [2.911]; Ga(1)–Ge(1) = 2.4113(8) [2.467];
Ga(1)–Ge(1’) = 2.3899(8) [2.443] and Ga(1)–Ga(1’) = 3.848 [3.954]; Ga(1)-N(1) 1.967(4),
Ga(1)-N(2) 1.975(4), N(1)-C(13) 1.338(6), N(1)-C(1) 1.443(6), N(1)-Ga(1)-N(2) 94.04(17),
N(1)-Ga(1)-Ge(1) 122.40(12), N(2)-Ga(1)-Ge(1) 122.94(12), Ge(1)-Ga(1)-Ge(1’) = 73.46(3)
[72.7]; Ga(1)-Ge(1)-Ga(1’) = 106.54(3) [107.3] (The respective computational values for 11
at the BP86/SVP level of DFT theory are given in brackets).
Compound 11 crystallizes in the monoclinic space group C2/c. The solid state
structure of 11 reveals the presence of a center of symmetry. The planar, four-membered
“Ge2Ga2” rhombic ring of 11 exhibits two sets of equivalent Ga–Ge bonds of 2.3899(8) and
2.4113(8) Å which are shorter than in 10 (2.5059(6) and 2.4755(6) Å) as shown in figure
3.12. The distance Ge(1)–Ge(1’) of 2.8714(11) Å of 11 is much longer than the four Ge–Ge
bonds of 9 which only slightly vary around the average value of 2.459 Å. The elongation of
N(1)-Ga-N(2) angles (95.43(14)°) in 10 and 11 (94.04(17)°, as compared to the free
Ga(DDP) (N-Ga-N=87.53(5)°)[17], demonstrates the increased electrophilic nature of
Ga(DDP) upon coordination to the “Ge4” and “Ge2” moieties which are slightly lower than
those reported for the main group clusters with Ga(DDP).
[22]
This slight bite angel
difference in 10 and 11 indicates the more electrophlic nature of Ga(DDP) in 10 than in 11.
As shown in the space-filling representation of compound 11 (Figure 4.10), the sterically
over crowded (DDP) group effectively protects the unstable fragments. The bond lengths in
the four-membered ring are shown in Figure 4.11.
Figure 4.10: Space filling model of Ge2[Ga(DDP)]2 (10).
91
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Figure 4.11: Shows the parallelogram shaped [Ga2Ge2] frame-work core of the molecule 11
with Ga–Ge bond lengths (Å). All other organic groups are removed for clarity.
Table 4.0: Comparison of few selected bond lengths (Å) and Angles (°) for 10 and 11
Compound [Ge4{Ga(DDP)}2] (10)
Compound [Ge2{Ga(DDP)}2] (11)
Bond lengths
Bond type
Bond lengths
(Or) Bond angle
Bond type
(Or) Bond angle
Ge(1)–Ge(1’)
2.4551(8)
Ge(1)–Ge(1’)
2.8714(11)
Ge(1)–Ge(2)
2.4623(6)
Ga(1)–Ge(1)
2.4113(8)
Ge(2)–Ge(2’)
2.4606(8)
Ga(1)–Ge(1’)
2.3899(8)
Ge(1)–Ga(1)
2.5059(6)
Ga(1)–Ga(1’)
3.848
Ge(2)–Ga(1’)
2.4755(6)
Ga(1)-N(1)
1.967(4)
Ga(1)–N(1)
1.962(3)
Ga(1)-N(2)
1.975(4)
Ga(1)–N(2)
1.970(3)
N(1)-Ga(1)-N(2)
94.04(17)
Ga(1)–Ge(2’)
2.4755(6)
N(1)-Ga(1)-Ge(1)
122.40(12)
N(1)-Ga(1)-N(2)
95.43(14)
N(2)-Ga(1)-Ge(1)
122.94(12)
Ge(1’)-Ge(1)-Ge(2)
73.761(16)
Ge(1)-Ga(1)-Ge(1’)
73.46(3)
Ge(1’)-Ge(1)-Ga(1)
97.02(2)
Ga(1)-Ge(1)-Ga(1’)
106.54(3)
Ge(2)-Ge(1)-Ga(1)
90.10(2)
------
92
--------
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
4.3.2 Bonding Analysis of Ge2[Ga(DDP)]2 (11) by Quantum Chemical
Calculations [d]
The quantum chemical calculations on compound 11 were carried out in order to
analyze the electronic structure and the bonding situation in the molecule. The cyclic
structure of 11 is remarkably different from its NHC stabilized, chain like congeners L-E=EL with a distinct multiple bond situation between the main group elements (E = Si, Ge; L =
NHC).
[10, 11]
NHGa (N-heterocyclic gallylene) ligand prefers the bridging position in
contrast to the terminally bonded NHC (IPr) ligands. This is due to the fact that the NHC and
NHGa ligand properties are characteristically different which has interesting consequences
for the GeGe bond situation, as it is discussed in below section. Figure 4.12 shows the plot
of the relevant π-orbitals of NHGa and NHC ligands.
LUMO+1
ε = -0.04 eV
HOMO-1
ε = -0.20 eV
HOMO-3
ε = -0.29 eV
HOMO-4
ε = -0.34 eV
(a)
(b)
(c)
(d)
LUMO+1
ε = 0.01 eV
HOMO-1
ε = -0.21 eV
HOMO-2
ε = -0.27 eV
HOMO-3
ε = -0.38 eV
(e)
(f)
(g)
(h)
Figure 4.12: Plots of the relevant π-orbitals of NHGa (a - d, top row) and NHC (e - h,
bottom row). Note that models with all H-atom substituents at the C and N atoms of the
diketiminate fragment.
93
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Figure 4.12 displays the relevant occupied and vacant frontier MOs (Molecular
orbitals) of NHC and NHGa. The analysis of the calculated electronic structures of Nheterocyclic carbine (NHC) and N-heterocylcic gallylene (NHGa) reveals a striking
difference between the occupation of the formally vacant p(π) AOs (atomic orbitals) of the
donor atoms “C” and “Ga”, respectively. The p(π) AO of the C donor atom in NHC is
significantly occupied because of strong N(π)→C(π) donation. This is obvious by simple
visual inspection of the occupied π-orbitals HOMO-1 and HOMO-3. The Mulliken
population of the divalent C p(π) AO in NHC amounts to 0.69 eV. In contrast, the Ga p(π)
valence AO in NHGa is only weakly occupied (0.17 eV, according to the Mulliken
population). Figure 2 shows that the occupied π-orbitals of NHGa exhibit a small
contribution from the Ga p(π) AO only in the HOMO-1. This makes the Ga atom a strong πacceptor where the vacant p(π) AO of Ga interacts with the occupied orbitals of Ge2 in the
plane of the Ga2Ge2 moiety. Figure 4.12a shows that the LUMO+1 has a large coefficient at
the p(π) AO of Ga. The latter orbital is clearly lower in energy (ε = -0.04 eV) than the related
LUMO+1 of NHC (+ 0.01 eV, Figure 4.12e). The back donation Ga←GeGe→Ga
substantially weakens the Ge–Ge interactions and leads to a unique bonding situation in 11
which shall be discussed in the following section.
Figure 4.13: Optimized Structure of the dimer, Ge2[Ga(DDP)]2 (11) (BP86/def2-SVP).
Hydrogen atoms are omitted for clarity.
94
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
The optimized model structure 11M at the BP86/SVP level of theory (Figure 4.13,
11M contains CH3 groups at the N-atoms instead of the bulky aryl substituents in case of the
actual molecule 11). A comparison of the most important calculated bond lengths and bond
angles are summarized in Table 4.1. These values show a good agreement with the
experimental results of 11. The calculated Ga–Ge and Ga–N distances are slightly longer
than the experimental values. Intermolecular forces usually lead to shorten bond lengths,
which hold particularly for long and weak bonds.
[23]
The calculated transannular Ge–Ge
distance (2.911 Å) is also a bit longer than the measured data (2.871 Å).
Table 4.1: Comparison of the most important calculated bond lengths (Å) and bond angles
() with the experimental values for 11, computational values at the BP86/def2-SVP level of
theory.
11M (calc.)
11 (calc.)
11 (exp.)
Ge(1)-Ge(1’)
2.956
2.911
2.8714(11)
Ga(1)-Ge(1)
2.457
2.467
2.4113(8)
Ga(1)-Ge(1’)
2.444
2.443
2.3899(8)
Ge(1)-Ga(1)-Ge(1’)
74.2
72.7
73.46(3)
95
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Figure 4.14. Contour line diagram of the Laplacian distribution 2ρ(r) of 11M in the plane
of the four-membered ring. Solid lines indicate areas of charge concentration (2ρ(r) < 0)
while dotted lines show areas of charge depletion (2ρ(r) > 0). The thick solid lines
connecting the atomic nuclei are the bond paths. The thick solid lines separating the atomic
basins indicate the zero-flux surfaces crossing the molecular plane.
Figure 4.14 shows the Laplacian distribution 2ρ(r) of the electron density in the
plane of the “Ge2Ga2” ring of 11M. The contour line diagram shows four Ge–Ga bond paths
and one ring critical point but there is no Ge–Ge bond path. There are four small areas of
charge concentration (2ρ(r) < 0, solid lines) along the Ga–Ge bond paths which are on the
Ge side of the bond critical points. This is in agreement with the higher electronegativity of
Ge (2.0) compared to Ga (1.8). A striking aspect of the Laplacian distribution 2ρ(r) is the
absence of electron density at the Ge atoms which would come from σ lone-pair orbitals at
Ge. The latter were found in the Laplacian distribution 2ρ(r) of the electron density at the
low valent Si atoms in the four-membered ring of dimeric silaisonitrile (ArNSi:)2 (Ar = 2,6bis(2,4,6-triisopropylphenyl)-phenyl) which was recently reported by Roesky and coworkers where the two N atoms instead of Ga are bonded to Si centres.[24] It seems that the
bonding situation at the di-coordinated Ge atoms in 11M is quite different from that of the
96
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
di-coordinated Si atoms in Si2(NAr)2. In this compound the silicon atoms in the fourmembered ring are bonded to nitrogen atoms which have lone-pair π orbitals that can donate
electronic charge into the formally empty p(π) AOs of Si. Whereas the gallium atoms in
11M do not possess lone-pair π-orbitals which leads to a bonding situation at the dicoordinated Ge atoms that is quite different from that of the di-coordinated Si atoms in the
dimeric silaisonitrile Si2(NAr)2. This comes clearly to the fore when the relevant occupied
and vacant valence orbitals in the two compounds are compared with each other.
Figure 4.15 shows the shape of two occupied and two vacant orbitals of 11M which are
crucial for the discussion of the bonding situation. The complete set of occupied valence
orbitals is shown in the supplemental data for the thesis. The HOMO-1 and the LUMO of
11M are the plus and minus combination of the out-of-plane p() AOs of Ge where the
former orbital has small contributions at Ga. The shape of the HOMO-1 clearly identifies it
as transannular Ge–Ge π-bonding MO. The HOMO-2 and the LUMO+4 of 11M are the plus
and minus combination of the σ lone-pair orbitals at the Ge atoms. There is a striking
difference to the bonding situation in Si2(NAr)2, where the orbital analogous to the
LUMO+4 of 11 is occupied while the HOMO-1 is vacant.[24] The Ge2Ga2 ring in 11M has
only one occupied σ lone-pair MO which is the HOMO-2 while there are two occupied σ
lone-pair MOs at Si in Si2(NAr)2. This explains the emergence of charge concentration at Si
in the Laplacian distribution which comes from the σ lone-pair orbitals. There is no such
charge concentration at the Ge atoms which have only one-half lone-pair MO each. Instead
of a second occupied σ lone-pair MO there is the occupied Ge–Ge out-of-plane  HOMO-1
(Figure 4.15). Note that 11M may be regarded as hypoelectronic (12 valence electrons for
the Ge2Ga2 ring) with respect to the Si2(NAr)2 reference compound (16 valence electrons for
the Si2N2 ring). In spite of the difference between the occupation of the valence orbitals, both
compounds Si2(NAr)2 and 11M have electronic singlet ground states. Calculation of 11M in
the triplet state gave a structure which is 19.1 kcal/mol higher in energy than the singlet.
97
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
LUMO+4 (ε = -0.788 eV)
LUMO (ε = -1.983 eV)
HOMO-1 (ε = -3.704 eV)
HOMO-2 (ε = -4.509 eV)
Figure 4.15: Shows the shapes and eigenvalues ε of important vacant and occupied orbitals
of 11M which are relevant for the bonding situation
4.3.3 Electron Localization Function Calculations (ELF) for 11 [25]
This unusual bonding situation in compound 11 is further evidenced from the EFL
calculations as shown in Figure 4.16. Two trisynaptic areas are found which connect the
germanium atoms with gallium as shown in Figure 4.16. They truly represent the Ge–Ga σ
bonds of the “Ge2Ga2” ring. The most important result is the finding of two disynaptic basins
above and below the four-membered ring which feature the presence of Ge–Ge π bonding in
compound 11. In contrast, there is no disynaptic basin in the plane which would indicate a
Ge–Ge σ bond. Thus, the ELF calculations also suggest that 11M exhibits a Ge–Ge π bond
but no genuine Ge–Ge σ bond!
98
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Figure 4.16: Shows the ELF basins calculated for 11 using TopMod09 [g] (magenta
spheres, rwb97xd/6-311g (d,p) wave function) ; those surrounding the
Ge atoms
(highlighted with halos) are shown with basin electron integrations.
4.3.4 Natural Bond Orbital Analysis (NBO) of 11
The unusual bonding situation in 11M in terms of Ge–Ge π-bonding but no σ-bonding is
further supported by the NBO (Natural bond orbital analysis) analysis. Table 4.2 gives the
bonding orbitals and their occupation as well as the Wiberg bond indices (WBI). The NBO
results give four Ga–Ge σ bonds and four Ga–N σ bonds. The occupation of the natural
orbitals is close to a value of two, which is a normal value for a two-electron bond.
Furthermore, there is a Ge–Ge π bond which has also a rather high occupation of 1.795. Note
that the WBI value for the non polar Ge–Ge bond is very high while the WBI value for the
very polar Ga–N bonds is much smaller.
99
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Table 4.2: Natural orbital occupations for the bonds in the four-membered ring of 11M and
Wiberg bond indices WBI.
Bond Type
Atom(s)
Occ.
WBI
σ-bond
Ga1-Ge1
1.836
0.951
σ-bond
Ga1-Ge2
1.843
0.983
σ-bond
Ga2-Ge1
1.843
0.983
σ-bond
Ga2-Ge2
1.836
0.951
σ-bond
Ga1-N1
1.943
0.405
σ-bond
Ga2-N2
1.943
0.405
σ-bond
Ga2-N3
1.943
0.405
σ-bond
Ga2-N4
1.943
0.405
π-bond
Ge1-Ge2
1.761
1.203
Lone pair
Ge1
0.774
-
Lone pair
Ge2
0.774
-
The calculated value of 1.203 for the bond order indicates that the Ge–Ge π bond is
supported by some weak Ge–Ge σ bonding which comes from the small backside lobes of
the orbitals in the HOMO-2. The NBO analysis also gives one lone-pair orbital for each
germanium atom which, however, is occupied by only ~0.8 electrons. There is no genuine
Ge–Ge σ orbital in the NBO calculation. This unusual bonding situation in 11M is proved by
the AIM investigation, the shape analysis of the MOs and the ELF results is further
supported by the results of NBO calculations.
The best description of this bonding situation in terms of the Lewis formula concept features
equivalent mesomeric structures (Figure 4.17). Alternatively, the situation may be described
by two unpaired electrons at the germanium atoms possessing opposite spins which are
weakly coupled.
100
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
Figure 4.17: Schematic description of the bonding situation in the four-membered ring of 11
using two equivalent Lewis structures (above) or spin-coupled lone-electrons (below). The
formal negative charge at Ga which cancels with a positive charge at N has been omitted
because this is not relevant for the discussion.
101
Chapter 4
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
4.4
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Robinson, Chem. Eur. J. 2010, 16, 432-435.
[14]
(a) Y. Wang, G. H. Robinson, Dalton Trans. 2012, 41, 337-345. (b) Y. Wang, G. H.
Robinson, Chem. Commun. 2009, 5201-5213.
[15]
J. L. Dutton, D. J. D. Wilson, Angew. Chem. 2012, 124, 1506-1509; Angew. Chem.
Int. Ed. 2012, 51, 1477-1480.
[16]
M. Asay, C. Jones, M. Driess, Chem. Rev. 2011, 111, 354-396.
[17]
N. J. Hardman, B. E. Eichler, P. P. Power, Chem. Commun. 2000, 1991-1992.
[18]
(a) A. Schnepf, Eur. J. Inorg. Chem. 2008, 1007-1018. (b) A. Schnepf, Chem. Soc.
Rev. 2007, 36, 745–758. (c) A. Schnepf, Coord. Chem. Rev. 2006, 250, 2758-2770.
[19]
J. S. Kasper, S. M. Richards, Acta Cryst. 1964, 17, 752-755.
[20]
Y. Peng, H. Fan, H. Zhu, H. W. Roesky, J. Magull, C. E. Hughes. Angew. Chem.
2004, 116, 3525-3527, Angew. Chem. Int. Ed. 2004, 43, 3443-3445.
[21]
(a) K. C. Thimer, S. M. I. Al-Rafia, M. J. Ferguson, R. McDonald, E. Rivard, Chem.
Commun. 2009, 7119–7121. (b) S. L. Choong, W. D. Woodul, C. Schenk, A. Stasch,
A. F. Richards, C. Jones, Organometallics. 2011, 30, 5543-5550.
[22]
G. Prabusankar, A. Doddi, C. Gemel, M. Winter, R. A. Fischer, Inorg. Chem. 2010,
49, 7976-7980.
[23]
V. Jonas, G. Frenking, M. T. Reetz, J. Am. Chem. Soc. 1994, 116, 8741-8753.
[24]
R. S. Ghadwal, H. W. Roesky, K. Pröpper, B. Dittrich, S. Klein, G. Frenking, Angew.
Chem. 2011, 123, 5486-5490; Angew. Chem. Int. Ed. 2011, 50, 5374-5378.
[25]
A. D. Becke, K. E. Edgecombe, J. Chem. Phys. 1990, 92, 5397-5403.
103
Chapter 4
[26]
Ga(DDP) stabilized low-valent Ge4 and Ge2 clusters
(a) C. G. Davies, R. J. Gillespie, J. J. Park, J. Passmore, Inorg. Chem. 1971, 10,
2781-2785. (b) J. Passmore, G. Sutherland, T. Whidden, P. S. White, J. Chem. Soc.,
Chem. Commun. 1980, 289-290.
[27]
(a) Y. Canac, D. Bourissou, A. Bacareido, H. Gornitzka, W. W. Schoeller, G.
Bertrand, Science. 1998, 279, 2080-2082. (b) S. Yao, C. Milsmann, E. Bill, K.
Wieghardt, M. Driess, J. Am. Chem. Soc. 2008, 130, 13536-13537.
[d]
The theoretical part of work in this chapter has been resulted from the collaboration
work from Prof. Gernot Frenking group at Fachbereich Chemie, Philipps-Universität
Marburg, Hans-Meerwein-Strasse, D-35032 Marburg; ermany) and Dr. H. S. Rezpa,
Department of Chemistry, Imperial College, London (United Kingdom). Any
clarificartions can be directed to Prof. Gernot Frenking.
104
Chapter 5
Ga(DDP) supported Ru and Cu complexes
Chapter 5
Synthesis and Structural Characterization of Ga(DDP) Supported
Ruthenium and Copper Complexes: A Compound with a Perfect Linear
Ga-Cu-Ga bond.[e]
Abstract: Reactivity of Ga(DDP) with ruthenium and copper complexes are probed.
Reaction of low valent and sterically bulky Gallium (I), Ga(DDP) (1) (DDP = 2diisopropylphenylamino-4-diisopropylimino-2-pentene) Ga(DDP) with an equimolar amount
of Suzuki´s dimeric tetrahydrido bridged complex [Cp*Ru(μ-H)2]2 in toluene at 70 °C
affords exclusively Ga(DDP) bridged diruthenium complex [{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}]
(12) in moderately good yield. Whereas the reaction between Ga(DDP) and with [(η6-pcymene)RuCl2]2 in 5:1 equivalents in refluxing n-hexane yields a new cyclometallated
complex [(η6-p-cymene)Ru(DDP)Ga)(µ-Cl){Ga(Cl)C29H41N2}] (13) in a very low yield.
The red crystalline compound 12 contains a [Cp*Ru] dimer bridged by one Ga(DDP) and
two hydrido ligands with a Ga-Ru-Ru triangle. Gallium centre in 12 accommodates distorted
tetrahedral geometry. Compound 13 can be realized by C–H activation of one of the CH3
group in Ga(DDP) followed by intramolecular rearrangement. These new compounds are
fully characterized by NMR (1H, 13C), LIFDI-MS including single crystal X-ray diffraction
analysis. The structures and reactivity aspects are compared with GaCp* supported
ruthenium complexes.
In addition, further investigations on the reactivity of Ga(DDP) towards coinage metal
complexes are studied. The reduction of Cu(II) and Cu(I) trifflates (Cu(OTf)2, Cu(OTf) (Tf
=O2SCF3) with Ga(DDP) in 1:4 equivalents in fluorobenzene gives a linear and cationic
coinage metal complex [{(DDP)Ga}2Cu][OTf]·2C6H5F (14) in 53% isolated yield.
Compound 14 represents the first example of a linear copper (I) compound supported by the
group 13 metal (I) organly.
[e]
Some parts of these results are published in; G. Prabusankar, S. G. Gallardo, A.
Doddi, C. Gemel, M. Winter, R. A. Fischer, Eur. J. Inorg. Chem. 2010, 4415-4418.
Text and Figures are reproduced with permission. Copyright © 2010 WILEY-VCH
Verlag GmbH & Co. KGaA, Weinheim.
105
Chapter 5
5.1
Ga(DDP) supported Ru and Cu complexes
Introduction
Arduengo type N-heterocyclic carbene (NHC) supported ruthenium derivatives have
been extensively studied since such compounds exhibits as highly effective catalysts
particularly for the olefin metathesis reactions.[1, 5] This is probably of the most important
achievement of any other Metal–NHC complexes known to date. Notably, the ligand design
plays a very important role in the catalytic activities. This aspect has drawn the attention to
modify the NHC core or to introduce the analogous low valent molecular systems. Thus, the
heavier NHC analogue of N-heterocyclic group 13 metal(I) ligands (NHE), such as neutral
six-membered β-diketiminato complexes E(DDP) (DDP = HC(CMeNC6H3-2,6-iPr2)2) (E =
Al,[6] Ga,[7] (1) In,[8] Tl[9]), the neutral four-membered guanidinate complexes [Ga(Giso)]
[Giso = {(2,6-iPr2C6H3)NC(NCy2)N(C6H3-2,6-iPr2)}]
[10]
and the anionic five-membered
diazabutadienido complexes [Ga{N(R)C(H)}2] (R = tBu, Ar) were synthesized and
structurally characterized.[11] The reactivity and coordination chemistry of NHEs have been
studied in detail towards many main-group and transition metals.[12-21] Nevertheless, the
NHE stabilized ruthenium metal complexes are very much limited in recent times.
Chart 5.1: Few selected examples of M (I) (M= Al, Ga) organyls supported ruthenium
complexes.
106
Chapter 5
Ga(DDP) supported Ru and Cu complexes
Recently, the first NHE-ruthenium complex was reported by Jones and his co-workers with
ruthenium (0) carbonyl complex. The reaction of four membered gallium (I) heterocycle
[:E(Giso)] (E = Ga or In) with [Ru(CO)2(PPh3)3] affords the ruthenium(0) complexes
[Ru(CO)2(PPh3)2{E(Giso)}], where the [:E(Giso)] coordinated in a monodentate fashion by
exchanging one phosphine ligand.[22] This aspect also demonstrates the coordination power
of NHE type ligands to substitute strongly coordinating ligands such as phosphines. On other
hand, we had previously investigated the reactivity of GaCp* and AlCp* towards various
organoruthenium precursors including few polyhydride ruthenium complexes and isolated
new Ru–E (E= Al, Ga, In) type intermetallic compounds (as shown in Chart 5.1).
In this regard the most noteworthy examples are the C–C and C–H activation reactions.
The reaction of AlCp* with [Ru(η4-cod)(η6-cot)] [cod = 1,5-cyclooctadiene, cot = 1,3,5cyclooctatriene)] gave the C–H activated compound with a RuAl5 framework in which the
two methyl groups from two Cp* rings undergone C–H activation forming Ru-Al-CH2
bonds.[23-24] Whereas the reaction of GaCp* with [Ru(PPh3)3Cl2] showed the orthometallated
intermediate [RuCp*(H)(PPh3)(κ2-(C6H4)-PPh2)(GaCl2)]
[26]
with GaCp* with other metals are also reported].
[25]
[C–C bond activation reactions
However, these types of reactions are
not reported so far with the multitalented ligands NHE’s. [12, 21]
5.2
Synthesis of [{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}] (12)
Although several organo ruthenium derivatives supported by GaCp* known in the
literature
[27, 28]
, but the coordination chemistry of sterically crowded NHE ligands are
limited. The only known ruthenium (0) complex, [Ru(CO)2(PPh3)2{Ga(Giso)}] with four
membered heterocycle [Ga(Giso)] was derived from the phosphine ligand exchange
reaction.[22] Thus, the present work evidence for the substitution, rearrangement and C–H
activation reactions of Ga(DDP) ligand supported ruthenium metal complexes.
Treatment of Ga(DDP) with an equimolar amounts of [Cp*Ru(µ-H)2]2 in toluene at
70 °C affords red crystals of 12 exclusively in 53% isolated yield as shown in Scheme 5.1.
Complex 12 is stable under inert atmospheric conditions (Argon) for several days; however
it is thermally unstable and decomposes above 80 °C. It is sparingly soluble in common
organic solvents such as n-hexane and pentane but highly soluble in benzene, toluene, THF
and fluorobenzene. Analytically pure sample can be obtained by quickly washing the
107
Chapter 5
Ga(DDP) supported Ru and Cu complexes
crystals by cold dry pentane. Compound 12 has been characterized by IR, NMR and also by
single crystal X-ray diffraction techniques.
Ru
Ru
H
H
N
N
H
H
+
N
Toluene
Ga
70 oC, 5h
N
Ga
Ru
Ru
H
H
(12)
Scheme 5.1: Synthesis of compound 12 in toluene.
The typical absorption peak at 1553 cm-1 in IR spectrum of compound 12 reveals the
presence of bridging hydride ligands in the molecule. The proton NMR spectrum of 12
measured in C6D6 is quite informative for assigning the number of hydride ligands existing
around the ruthenium centres. A sharp resonance peak observed at δ; –14.91 ppm and its
intensity shows the presence of two magnetically equivalent hydrides at room-temperature as
shown in Figure 5.1. Interestingly, there is almost δ; –1.00 ppm change occurred which is
shifted high field compared to that of the same with the starting material [Cp*Ru(µ-H)2]2 (δ;
–13.99 ppm). [29]
The 1H and 13C NMR chemical shifts found for (DDP) and Cp* moieties fall in the expected
range. 1H-NMR spectrum shows the existence of two different isopropyl protons at δ; 4.15
and 3.52 ppm, which are shifted down field compared to the same in the parent starting
ligand Ga(DDP).[7] Furthermore, the LIFDI-MS of this sample measured in dry toluene
display its fragment ion at m/z 826.1 (100%) which corresponds to [M–Cp*] + •. It is worth to
mention that the similar reaction of [Cp*Ru(μ-H)2]2 and two equivalents of GaCp* gives
GaCp* inserted complex, [{Cp*Ru(μ-H)(H)(μ-GaCp*)}2] without losing the four hydrido
ligands.
[27]
Interestingly, when two equivalents of Ga(DDP) is used for the same reaction
by employing the same experimental conditions has also led to the formation of compound
12 (confirmed by in situ 1H-NMR spectrum) and this aspect points out that two Ga(DDP)
moieties possibly cannot be accommodated around the ruthenium centre by substituting all
hydrides from the ruthenium centre due to the steric restrictions of Ga(DDP) which is
108
Chapter 5
Ga(DDP) supported Ru and Cu complexes
relatively more than the GaCp* where more than one GaCp* can be coordinated to
ruthenium centres.
Figure 5.1: 1H-NMR spectrum of compound 12 in C6D6 at room temperature.
5.3
Molecular Structure of [{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}] (12)
To elucidate the nature of the Ru–Ga(DDP) bonding, the solid-state structure of 12
was unambiguously determined by single-crystal X-ray diffraction study. Single crystals
suitable for X-ray structural determination can be grown by cooling the solution of
toluene/n-hexane mixture of 12 at – 30 ºC. The X-ray structure with selected bond distances
and angles for 12 is shown in Figure 5.2 at the foot note.
Complex 12 crystallizes in the orthorhombic space group P22a. The molecular structure
shows that Ga(DDP) replaces the two hydride ligands without disturbing the dimeric
structure of [Cp*Ru(μ-H)2]2. 12 can be described as Cp*Ru dimer bridged by Ga(DDP) and
two hydrido ligands. The three metal centres Ru(1), Ga(1) and Ru(2) are in the triangle
shape. The plane defined by the Ru(1), Ga(1) and Ru(2) moiety and the (DDP) ring are lies
perfectly perpendicular to each other. The coordination environment around the each
ruthenium is completed by Cp*, bridging Ga(DDP), and hydrido ligands, that results the 18
valence electron ruthenium complex.
109
Chapter 5
Ga(DDP) supported Ru and Cu complexes
Figure 5.2: Molecular structure of compound 12 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Important bond lengths (Å)
and angles (º): Ru1–Ru2 2.5045(8), Ga1–Ru1 2.4294(11), Ga1–Ru2 2.5315(9), Ru(2)–Cp*
centroid 1.826, Ru(1)–Cp* centroid 1.827, Ga1–N2 2.001(6), Ga1–N1 2.050(5), N2-Ga1-N1
91.0(3), Ga1-Ru1-Ru2 61.72(3), N2-Ga1-Ru1 130.67(17), N1-Ga1-Ru1 130.0(2), N2-Ga1Ru2 123.51(16), N1-Ga1-Ru2 123.44(15), Ru1-Ga1-Ru2 60.60(3).
The Ru(1)–Ru(2) distance found in 12 is 2.5045(8) Å, which is slightly (0.0415Å)
elongated by the bridging bulky Ga(DDP) ligand compare to [Cp*Ru(μ-H)2]2][29] [2.463(1)
Å]. [Notably the Ru–Ru distance found in GaCp* bridged diruthenium complex,
[{Cp*Ru(μ-H)(H)(μ-GaCp*)}2][27] (3.254 Å) is about 23% longer (0.7495 Å) than 12. The
Ru–Ga bond lengths are not equal. The Ru(1)–Ga(1) bond length [2.4294(11) Å] is
relatively shorter than that of Ru(2)–Ga(1) [2.5315(9) Å]. This is in agreement with the bond
length
trends
observed
for
cymene)Ru}2(GaCp*)4(μ3-Cl)2][28]
the
known
[2.398(1)
ruthenium-gallium
and
2.486(1)Å],
complexes,
[{(η6-p-
[{Cp*Ru(μ-H)(H)(μ-
GaCp*)}2][27] (2.421(1) and 2.439(1)Å) and [{Cp*Ru}3(μ-H)5(μ3-GaCp*)] [2.4884(13),
2.6926(14), and 2.4736(13) Å] with GaCp* ligand is in bridging mode. The internal angles
[Ga(1)–Ru(1)-Ru(2) 61.72(3)o, Ru(1)-Ru(2)-Ga(1) 57.68(3)o, Ru(1)-Ga(1)–Ru(2), 60.63(4)o]
of Ru and Ga triangle core falls in the range close to the scalene triangle [ΣΔ = 180.03(3)o].
110
Chapter 5
Ga(DDP) supported Ru and Cu complexes
The geometry around gallium centre confirms the expected distorted tetrahedron geometry.
The metrics around gallium center [Ga(1)–N(2) 2.001(6) Å, Ga(1)–N(1) 2.050(5) Å; ∟NGa-N 91.0(3)o] are typical for the coordinating Ga(DDP) ligand.[7] The average distance of
Ru–Cp*centroid in 12 is ca.1.826 Å which is slightly shorter (ca. 0.023Å) compared with other
GaCp* supported ruthenium cluster [Cp*Ru(GaCp*)3]+[BPh4]- (Ru(1)–Cp*centroid 1.849 Å),
but it is significantly longer when compared with the similar hydrido complex [{Cp*Ru(µH)(H)(µ-GaCp*)}2] (Ru(1)–Cp*centr. 1.963Å)
[27]
whereas it is in the similar range as in
[Cp*Ru(GaCp*)3]+[Cp*GaCl3] − (Ru(1)–Cp*centroid 1.826Å).[28]
Furthermore, the reactivity of Ga(DDP) with other olefin supported Ru(0) precursor
[Ru(η4-cod)(η6-cot)] is studied. The reaction of [Ru(η4-cod)(η6-cot)] with an excess of
Ga(DDP) at room temperature shows that there is no reaction to isolate new products. When
the temperature of reaction mixture was raised to 70 °C for 15h in toluene, only un reacted
Ga(DDP) was isolated as a crystalline material (Scheme 5.2). Whereas the same reaction
with excess GaCp* yields an addition product [(η4-cod)(η4-cot)Ru(GaCp*)] where the
isomerization of cot ligand takes place from η6  η4.[23-24] This reaction gives an idea that
unlike GaCp*, Ga(DDP) is not reactive enough to substitute the olefin ligands from the
ruthenium(0) centre.
[Ru(4-cod)(6-cot)]
N
+
Ga
N
Toluene
70 oC
15h
No reaction
Scheme 5.2: Reaction between [Ru(η4-cod)(η6-cot)] and Ga(DDP).
5.4
Synthesis
of
[(η6-p-cymene)Ru(DDP)Ga)(µ-Cl){Ga(Cl)C29H41N2}]
(13)
The reactivity of Ga(DDP) with [(η6-p-cymene)RuCl2]2 in different solvents and in
different ratios has been studied as it is shown in the Scheme 5.3. The reaction of [(η6-pcymene)RuCl2]2 with two equivalents of Ga(DDP) in toluene at 60 °C has led to the
111
Chapter 5
Ga(DDP) supported Ru and Cu complexes
formation of a reduced Ru(I) dark red product [Cp*Ru(µ-Cl)]2
[30]
exclusively with the
formation of expected side product Cl2Ga(DDP) (confirmed by unit cell values) in 65%
yield.[31] According to the literature reports, compound [Cp*Ru(µ-Cl)]2 can also be
synthesized from the reduction of [(η6-p-cymene)RuCl2]2 with GaCp*
[28]
and also using Zn
metal as the reducing agent in relatively good yields. [31]
Treatment of [(η6-p-cymene)RuCl2]2 with five equivalents of Ga(DDP) in refluxing n-hexane
leads to the formation of cyclometallated product as an orange-brown complex 13 in very
low yield as depicted in the Scheme 5.3. Compound 13 is moisture sensitive and soluble in
aromatic solvents such as toluene, benzene and in THF. It is thermally stable under inert
atmosphere for several days. Compound 13 crystallizes along with the expected by-product
Cl2Ga(DDP) and excess Ga(DDP) in the reaction mixture. Analytically pure compound can
be got by manually separating the crystals of compound 13 by hand picking under
microscope in the glove box.
(1:1)
Toluene
60 oC, 3h
- Cl2Ga(DDP)
Cl
Ru
(a)
Ru
Cl
Ga(DDP)
Cl
Ru
Cl
Cl
Ru
Cl
N
Ga(DDP)
(1:5)
n-Hexane
Reflux, 5h
N
Ga
(b)
Cl H
Ru
Ga
Cl
H
N
HN
H
(13)
Scheme 5.3: Synthesis of compound 13.
The 1H and 13C-NMR of 13 are consistent with the proposed structure. The proton NMR of
13 measured in C6D6 contains the two different expected sharp singlets which are associated
with the methine protons in 13. Due to the unsymmetrical chemical composition of 13, the
presence of Ga(DDP) and open ring skeletons are assigned from the 2D NMR of the sample
112
Chapter 5
Ga(DDP) supported Ru and Cu complexes
13 measured at room temperature. Two sharp singlets observed at δ; 5.10, 4.37 ppm are
assigned to γ-CH in Ga(DDP) ring and for the open ring respectively. Same trend is also
observed in its 13C-NMR spectrum. Chemical shifts at δ; 99.0 and 95.3 ppm are associated
for these two carbons respectively. Due to the unsymmetrical nature of compound 13 gave
overlapped signals for the nine different isopropyl protons and also the various methyl
protons. The proton NMR of 13 clearly showed the presence of nine different isopropyl
protons [CH(Me)2] as septets as expected. Interestingly, the HMBC and 1H-1H-COSY
spectra of 13 showed the presence of two different diastreotopic protons (Ru–CH2) as broad
and weak signals at δ; 3.05 and 1.57 ppm (3JH-H = 11.8 HZ). The corresponding 13C-NMR of
this carbon is assigned as 23.4 ppm. This is in the similar range observed in the reported
ruthenium complexes such as in C–H activation of NHC ligand
[32]
and other phosphine
ligands supported ruthenium complexes, i. e. RuCl2[(2,6-Me2C6H3)PPh2]2, (δ; 3.81 to 3.37
ppm).
[33] 1
H-NMR also display the existence of N–H proton at δ = 6.48 ppm as a broad
signal. Moreover, the infrared spectrum of 13 is quite helpful in assigning the presence of N–
H bond. As secondary amines often show a single stretching band, a similar band is shown at
v = 3333 cm-1 as a very weak signal as shown in Figure 5.3. Furthermore, the LIFDI-MS of
13 measured in toluene displays the molecular ion peak m/z 1280.77 [M]
fragment ions m/z 1245.4 [M–Cl]+•, m/z 723 [M–Cl2Ga(DDP) ] + •.
tranmisttance (%)
1.0
-1
3333.4 cm
N-H stretching
0.9
C-H stretching
2200
2400
2600
2800
3000
3200
-1
Wave number (cm )
Figure 5.3: Infrared spectrum of compound 13 (as neat).
113
3400
+ •
and also its
Chapter 5
Ga(DDP) supported Ru and Cu complexes
The most interesting feature in the formation of 13 is the ring opening of the six membered
heterocyclic ring of Ga(DDP). The mechanism of the reaction is not known but one would
propose that after the insertion of two molecules of Ga(DDP) between the Ru–Cl bonds, C–
H activation could have occurred. Since one of the methyl group is held close to the
ruthenium center (intramolecular activation is favored entropically) activates C–H bond of
one of the CH3 group there by it forms a Ru–C bond by releasing one proton which
protonates one of the nitrogen in the DDP ring, which could induce the ring opening of
Ga(DDP) and then it rearranges to give more stable five membered cycloruthenated Ru-C-CN-Ga ring with the formation of a N–H bond. Similar C–H activation reactions were
reported in the past in complexes containing sterically crowded group 13 metal (I) organyls.
C–H activation of CH3 groups on AlCp* ligands in the homoleptic complexes such as
[Fe(AlCp*)5] and [Ru(AlCp*)5] have been reported.
[23, 24]
These results supports the
similarities between the low valent group 13 metal(I) ligands and N-heterocyclic carbenes
because similar C–H activation reactions were also reported within the N-heterocyclic
carbene supported ruthenium complexes where the CH3 groups in NHC ligands undergo C–
H activation.[34]
5.5
Structure
of
[(η6-p-cymene)Ru(DDP)Ga)(µ-Cl){Ga(Cl)C29H41N2}]
(13)
In order to elucidate the molecular structure of 13, single crystal X-ray diffraction
analysis is carried out. Single crystals suitable for X-ray structural determination can be
obtained by cooling the solution of 13 in n-hexane / toluene mixture at - 30 °C. The
molecular structure of 13 with some selected bond distances and angles are shown in Figure
5.4. Compound 13 crystallizes in triclinic, space group P-1. Complex 13 consists of a [(η6-pcymene)Ru] fragment with one bridging chlorine atom connecting two different gallium
centers. It is clearly shown in the molecular structure that there are two kinds of gallium
centers, one is Ga (1) from coordinated Ga(DDP) and other open ring Ga(2) centre. The Ru–
Ga bond lengths in 13 are almost equal in length although both gallium centers are having
different electronic and steric environment. The Ru(1)–Ga(1) (2.4250(4) Å) and Ru(1)–
Ga(2) (2.4039(4) Å) are comparable to that of the other dimeric ruthenium (I) complexes
reported with GaCp*. [27, 28]
114
Chapter 5
Ga(DDP) supported Ru and Cu complexes
Figure 5.4: Molecular structure of compound 13 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Important bond lengths (Å)
and angles (º): Ru(1)–C(30) 2.209(3), C30–C31 1.497(4), Ru(1)–Ga(2) 2.4039(4), Ru(1)–
Ga(1) 2.4250(4), Ru(1)–p-cymene centroid 1.722, Ga(1)–N(1) 2.004(2), Ga(1)–N(2)
2.018(2), Ga(1)–Cl(1) 2.5567(9), Ga(1)–Ga(2) 2.9813(5), Ga(2)–N(3) 2.021(2), Ga(2)–Cl(2)
2.2242(8), Ga(2)–Cl(1) 2.4381(8), C(59)-Ru(1)-C(30) 157.64(11), C(30)-Ru(1)-Ga(1)
88.08(8), Ga(2)-Ru(1)-Ga(1) 76.251(14), N(1)-Ga(1)-N(2) 92.87(10), N(1)-Ga(1)-Ru(1)
130.11(7), N(2)-Ga(1)-Ru(1) 130.72(7), N(1)-Ga(1)-Cl(1) 98.69(7), N(2)-Ga(1)-Cl(1)
92.82(7), Ru(1)-Ga(1)-Cl(1) 101.44(2), Ru(1)-Ga(1)-Ga(2) 51.555(11), Cl(1)-Ga(1)-Ga(2)
51.545(19), N(3)-Ga(2)-Ru(1) 99.07(7), Cl(2)-Ga(2)-Ru(1) 145.43(3), Ru(1)-Ga(2)-Cl(1)
105.61(2), N(3)-Ga(2)-Ga(1) 122.61(7), Ru(1)-Ga(2)-Ga(1) 52.195(11), Ga(2)-Cl(1)-Ga(1)
73.25(2), C(31)-C(30)-Ru(1) 116.41.
The Ruthenium-Carbon bond distance [Ru(1)–C(30), 2.209(3)Å] is found to be significantly
longer than the Ru=C double bond length [(P2C=d)Ru(H)(Cl), ca., Ru1A–C5A, 1.918(10),
(P2C=) = PCP pincer ligand containing a central carbene ligand] [35] but slightly longer than
the Ru–C single bond distance such as in [Ru(IEt2Me2)’(DMSO)3Cl] 2.130(2),Å
[Ru(IEt2Me2)’(CO)3Cl] 2.1656(17) Å]
[32]
and also longer than in the phosphine ligand
115
Chapter 5
Ga(DDP) supported Ru and Cu complexes
supported ruthenium complexes [i.e, [RuCl{(2-CH2-6-MeC6H3)PPh2}(CO)(2,6-Me2C6H3)PPh2)] 2.043(8)Å].[33-34] Furthermore, the Ru(1)–p-cymene centroid distance is found to be
1.722Å which is slightly smaller than in the similar GaCp* supported complex for example
the same in [(η6-p-cymene)Ru(GaCp*)2GaCl3] is shown to be 1.742 Å [28] The presence of a
weak bonding interaction between the two gallium [Ga(1)–Ga(2); 2.9813(5)Å] centers is
observed which is significantly longer than a typical Ga–Ga single bond [i.e. in
[(Me3Si)2CH]2Ga–Ga[CH-(SiMe3)2]2 ; Ga–Ga 2.541(1) Å]. [36-37]
The GaN and N-Ga-N bond lengths and angles in both 12 and 13 are comparable and lies
around in the Ga(DDP) supported metal complexes. The similarities and differences in bond
lengths and angles in compounds 12 and 13 are summarized in table 5.1.
Table 5.1: Summary of important bond lengths (Å) and bond angles (º) for 12 and 13
Compound
Compound
[{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}] (12)
[(η6-p-cymene)Ru(DDP)Ga)(µCl){Ga(Cl)C29H41N2}] (13)
Bond lengths
Bond type
Bond lengths
(Or) Bond angle
Bond type
(Or) Bond
angle
Ru1–Ru2
2.5045(8)
Ru(1)–Ga(2)
2.4039(4)
Ga1–Ru1
2.4294(11)
Ru(1)–Ga(1)
2.4250(4)
Ga1–Ru2
2.5315(9)
Ru(1)–p-cymene
centroid
1.722
Ru(2)–Cp* centroid
1.826
Ga(2)–Cl(2)
2.2242(8)
Ru(1)–Cp* centroid
1.827
Ga(2)–N(3)
2.021(2)
Ga1–N2
2.001(6)
Ga(1)–N(1)
2.004(2)
Ga1–N1
2.050(5)
Ga(1)–N(2)
2.018(2)
N2-Ga1-N1
91.0(3)
N(1)-Ga(1)-N(2)
92.87(10)
Ga1-Ru1-Ru2
61.72(3)
Ru(1)-Ga(1)-Ga(2)
51.555(11)
Ru1-Ga1-Ru2
60.60(3)
N(1)-Ga(1)-Ru(1)
130.11(7)
116
Chapter 5
5.6
Ga(DDP) supported Ru and Cu complexes
Reactivity of Ga(DDP) with Cu(II) and Cu(I) Triflates: First
Dinuclear Copper/Gallium complex with a Ga-Cu-Ga Linear Bond
The chemistry of coinage metal complexes has attracted a lot of interest in the past
few years, due to their interesting bonding, structural properties and diverse
applications.[38,39] Particularly, gold complexes bearing monodentate ancillary ligands such
as N-heterocyclic carbenes or phosphines have been in the focus of extensive research in
recent years, due to their application as homogeneous catalysts for organic synthesis,[39]
where the importance of cationic complexes has been highlighted.[39-46] Complexes of the d10
ions of the group 11 transition metals present variable coordination numbers. Cu(I) and
Ag(I) complexes most commonly exhibit coordination numbers three or four, while Au(I)
compounds are mostly linear, two-coordinate species. It has been suggested that this
difference may be ascribed to relativistic effects, which allow the efficient hybridization of s,
p and d orbitals of gold atoms.[48, 48] In 2004, the first examples of complexes containing
Au−Ga bonds were reported, namely the trinuclear cluster [Au3(µ-GaI2)3(Cp*Ga)5][49] and
the mononuclear, linear complexes [Ph3PAu−Ga(Cl)DDP] and [DDPGa−Au−Ga(Cl)DDP]
(DDP = [HC{(CMe)N(2,6-iPr2C6H3)}2]−).[50] Despite, the extensive work that has been done
on the study of the coordination chemistry of gallium-based ligands, only a handful of
complexes of the coinage metals have been isolated. Both neutral GaCp* and Ga(DDP), and
anionic [Ga{[N(Ar)C(H)]2}]− (Ar = 2,6-iPr2C6H3) ligands have been used to stabilize such
species.[51-53] All low-valent RGa compounds are strong -donors, but the nature of the R
groups influences their steric and π-acceptor properties strongly, leading to distinctly
different coordination behaviours. Therefore, the nature of the RGa−M (Cu, Ag, Au)
complexes characterized so far is very different from one another.
The coordination chemistry of Ga(DDP) in the isolation of cationic transition metal
complexes
has
limited
success.
Attempts
to
abstract
the
chlorine
atoms
of
[(Ph3P)2Rh{Ga(DDP)}(µ-Cl)] and [(COE)(benzene)Rh-{(DDP)GaCl}] with TlBArF (BArF =
B[3,5-(CF3)2C6H3]4) to produce the corresponding cationic species, did not lead to the
isolable stable products. However, their formation was confirmed by means of 1H-NMR
spectroscopy. Only the linear, symmetrical, cationic species [{(DDP)Ga}2Au][BArF] and
[{(DDP)GaTHF}2Au][BArF] have been fully characterized so far.
[51]
Variety of available
Cu(I) starting materials, allows to try the direct reaction of Ga(DDP) with metal salts
117
Chapter 5
Ga(DDP) supported Ru and Cu complexes
containing weakly coordinating anions, such as TfO−, BArF−, SbF6− and [Al(hfip)4]−, to
obtain the corresponding ionic complexes. As previously reported
[52]
, the nature of the
counter anion has a strong influence on the formation of desired complexes. Most of the
attempted reactions led to the decomposition products, as evidenced by the formation of
metallic films on the walls of the reaction flasks or precipitation of grey metallic solids.
However, the reaction of Cu(OTf)2 or Cu(OTf)·4CH3CN with Ga(DDP) gives the desired
product.
5.6.1 Synthesis of [{(DDP)Ga}2Cu][OTf] (14)
Reduction of Cu(OTf)2 with four equivalents of Ga(DDP) in fluorobenzene affords
the bimetallic complex 14 as colourless crystals in 53% yield (Scheme 5.4). Compound 14 is
stable under inert atmosphere for several days but prolonged storage gives a grey colour tint
which means the slow decomposition of compound occurs. 14 is highly soluble in polar
organic solvents such as THF and fluorobenzene but insoluble in n-hexane and pentane. The
1
H and
13
C{1H} NMR spectra in THF-d8 solution show signals associated to the (DDP)
backbone in the ligand part, it is in the expected range when compared to Ga(DDP)
supported metal complexes.[51, 54]
+
Cu(OTf)2
+ Ga(DDP)
or
Cu(OTf).4 CH3CN
N
PhF
60 °c, 1h
N
Ga
Cu
OTf = O2SCF3
N
Ga
(OTf)
N
(14)
Scheme 5.4: Synthesis of compound [{(DDP)Ga}2Cu][OTf] (14).
The 1H-NMR of 14 in THF-d8 shows the characteristic and sharp singlet peak for the
methane proton -CH is observed at ; 5.32 ppm and the corresponding carbon shows up at
; 100.6 ppm in its 13C NMR spectrum. Of note, the triflate carbon of the counter ion is not
observed in the
13
C{1H} NMR time scale which was measure at room temperature.
118
Chapter 5
Ga(DDP) supported Ru and Cu complexes
However, the 19F-NMR gives a sharp single signal at δ; – 80.5 ppm for the fluorine atoms of
the triflate group as shown in Figure 5.5. Moreover, the NMR spectra of 14 clearly indicate
that it is stable in solution for several hours. The infrared spectrum of compound 14 is very
much informative for assigning the trifflate group. The triflate stretching absorptions
(1261(s), 1230(m), 1163(m), 1015(s) cm-1) in the infrared spectrum suggests the presence of
non-coordinating triflate anion which acts as counter anion. [55]
 (ppm)
Figure 5.5: 19F NMR Spectrum of [{(DDP)Ga}2Cu][OTf] (14) in C6D6 at RT.
Interestingly, the treatment of Ga(DDP) now with copper(I) trifflate Cu(OTf)·4CH3CN in
2:1 molar ratio also gives the same complex [{(DDP)Ga}2Cu][OTf] (14) in better yield
(61%). In order to confirm the reproducibility the same reaction was carried out 3 days to
isolate 13 and prolonged reaction periods are found to give better yields. Besides, when
[Cu(cod)Cl]2 dimer is used as the copper source, the reaction immediately yields a insoluble
gray solid as the precipitate immediately after the addition of Ga(DDP) to the suspension
containing [Cu(cod)Cl]2 dimer in THF.
5.6.2 Molecular Structure of Compound [{(DDP)Ga}2Cu][OTf] (14)
Single crystal X-ray diffraction analysis on compound 14 was conducted to elucidate
the nature of the CuGa bonding situation. Single crystals suitable for X-ray structural
determination can be obtained from a fluorobenzene/hexane solution at - 30 oC over a period
119
Chapter 5
Ga(DDP) supported Ru and Cu complexes
of 1d. The X-ray structure, selected bond distances and selected bond angles for 14 are
shown in Figure 5.6. The compound 14 crystallizes in monoclinic, space group C2/m. The
solid state structure of 14 shows a linear Ga-Cu-Ga linkage (180.0(1)o) with a noncoordinating trifflate (OTf) group which acts as a counter anion. The Me2C3N2 backbone of
Ga(DDP) ligands are nearly coplanar to the Ga-Cu-Ga chain. The 2,6-iPr2-C6H3 groups
attached to the (DDP) nitrogen atoms lie perpendicular to the Me2C3N2 framework. It is
noteworthy, that there are a limited number of examples known for linear coordination
geometry around copper centres. [42] Furthermore, no linear copper compounds stabilized by
group 13 ligands have been reported so far. Hence, compound 14 represents the first
example of a linear copper (I) compound supported by sterically pronounced Ga(DDP)
ligand.
Figure 5.6: Molecular structure of compound 14 in the solid state as determined by single
crystal X-ray diffraction. Displacement ellipsoids are drawn at 50% probability level.
Hydrogen atoms and solvent molecules are omitted for clarity. Important bond lengths (Å)
and angles (º): GaCu, 2.3156(10); GaN, 1.931(6); Ga-Cu-Ga, 180.0(1); N-Ga-N, 94.8(3).
The GaCu bond distance is 2.3156(10) Å, which is remarkably shorter than the average
Ga−Cu distance found in the dimeric complexes sucs as [{(DDP)GaCu(OTf)}2] (av. 2.4605
Å), [Cu2(GaCp*)(µ-GaCp*)3Ga(OTf)3] (av. 2.412 Å) and [Cu2(GaCp*)3(µ-GaCp*)2][OTf]2
120
Chapter 5
Ga(DDP) supported Ru and Cu complexes
(av. 2.4189 Å).[54] While it is comparable with [LCuGaR] (2.3066(6) and 2.2807(5) Å with
R = {N(C6H3-2,6-iPr2)CH}2, L = {N(2,4,6-Me3-C6H2)CH}2C and L = {N(2,6-iPr2C6H3)CH}2C, respectively) and [Cu(GaCp*)4]+[BArF] (2.3517(5) and 2.3496(5) Å) (BArF =
B[3,5-(CF3)2C6H3]4).[53, 54] The coordination environment around gallium centers is satisfied
with Cu(I) and nitrogen atoms of DDP ligand. The GaN bond distances and N-Ga-N angles
of 14 is typical for Ga(DDP) supported metal complexes.[50]
121
Chapter 5
Ga(DDP) supported Ru and Cu complexes
5.7
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124
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
Chapter 6
Sterically Bulky N-heterocyclic Carbene Complexes of ZnCl2 and
TiX4 (X = F, Cl): Syntheses, Characterization and Reactivity [f]
Abstract: The synthesis and structural characterization of N-heterocyclic carbene
supported metal halide complexes are investigated. The treatment of the sterically
encumbered N-heterocyclic carbene IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2ylidene, [:C{[N(2,6-iPr2C6H3)]CH}2]) with the titanium tetrahalides, TiX4 (X = Cl, F) in
diethyl ether or THF affords the metal halide mono and bis-carbene complexes, [Cl4TiC{N(2,6-iPr2C6H3)CH}2] (15), [Cl4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (16), [F4Ti{C{N(2,6i
Pr2C6H3)CH}2}2] (17), and [HC{N(2,6-iPr2C6H3)CH}2]2[TiCl6] (18) at very mild
experimental conditions in moderately good yields. In addition the treatment of IPr with
zinc(II) chloride (ZnCl2) and Me2Zn room temperature yields mono NHC adducts [Cl2ZnC{N(2,6-iPr2C6H3)CH}2] (19) and [Me2Zn-C{N(2,6-iPr2C6H3)CH}2] (20) in moderately
good yields. The reduction of mono NHC metal halide adducts with KC8 is also studied.
Compounds 15–18 are fully characterized by elemental analysis, NMR spectroscopic
methods (1H,
13
C and
19
F-NMR) and X-ray single crystal structure determination.
Furthermore, the reaction of mono NHC adduct [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] (15) with
ZnMe2 yields monomeric [IPr·ZnCl2] (19), involving carbene and chloride ligands transfer
from Ti (IV) to Zn(II). The molecular structure of 15 reveals, the Ti–Ccarbene bond is
relatively shorter than the similar Ti (IV) NHC complexes and represents a strong bond. The
bis-carbene adduct 16 has a perfect linear Ccarbene–Ti–Ccarbene bond angle of 180° with a
distorted octahedral Ti (IV) center. X-ray diffraction study of 15, 16 and 17 showed a short
intra molecular Cl···Ccarbene contacts. Compound 18 displays a hydrogen bonding between the
solvent and the cationic part of the complex. Moreover, the reactivity differences of IPr and
its heavy analog Ga(DDP) are briefly discussed.
[f]
Few parts of these results are comprised in the publication: Text and Figures are
reproduced with permission from A. Doddi, C. Gemel, R. W. Seidel, M. Winter and
R. A. Fischer, Coordination Complexes of TiX4 (X = F, Cl) with Sterically Bulky Nheterocyclic Carbene: Syntheses, Characterization and Molecular Structures,
“Polyhedron”. 2013, 0(00), 00-00. DOI: 10.1016/j.poly.2012.06.067. In press.
Copyright © 2012, Elsevier
125
Chapter 6
6.1
NHC supported Zn and Ti complexes and their reactivity
Introduction
Carbon centre in a free N-heterocyclic carbene is in a six electron, divalent state
which may be linear or bent with no formal charge with sp2 hybridization. [1] The isolation of
a stable, crystalline and “bottleable” N-hetero cyclic carbene (NHC) was first time reported
by Arduengo and co-workers in 1991. [2] Since their discovery many new simple to sterically
bulky and highly stable NHCs were synthesized and structurally characterized in the past
two decades. This has led a spectacular explosion of interest in this type of heterocyclic
compounds.
[2d-i]
These nucleophilic carbenes are regarded as 2e Lewis bases and used as
ligands in organometallic chemistry extensively. [3] Due to the availability of one lone pair of
electrons on the two coordinate carbon centre allows them for strong coordination to a
transition-metal center.
[4]
They have been considered as strong sigma donors and weak pi-
acceptors in coordination and organometallic chemistry are concerned. Due to this property,
NHCs are considered as replacements to the well known phosphines in main-group as well
as transition metal complexes.
[5]
The remarkable properties of NHCs and their metal
complexes, they have been employed in different chemical fields and most prominently in
homogeneous catalysis.[6-8]
The rapid rise of organometallic chemistry in the second half of the 20th century is
closely related to the exploration of transition metal phosphine chemistry as well as the
development of new and sophisticated phosphines.
[9]
However, in the past two decades the
class of N-heterocyclic carbenes (NHCs) became increasingly important, especially due to
their large thermal and chemical stability.
[7]
NHC ligands are very strong ligands for many
metals in a wide range of oxidation states. Since NHCs are strong sigma donors and weak piacceptors they are considered as good (and thermally more robust) substitutes for phosphines
in many homogenous catalyst systems.[6,
7, 8]
Very recently for example, N-heterocyclic
carbene supported ZnX2 (X = Cl, CH3COO, PhCOO, and PhCH2COO) complexes have been
found to be active catalysts in the ring opening polymerization of caprolactone, and similar
Zn(II) NHC complexes were also found to have excellent catalytic properties in the synthesis
of polyurethanes. [10]
As for NHC adducts of high oxidation state metal centers, a very impressive recent
example is the bis(carbene) adduct of UCl4, [UCl4(IPr)2].
[11]
Also quite a number of NHC
adducts to early transition metal halides such as TiCl4 or TiCl3 have been reported.[12,
13]
Note worthy to mention that among all the so far reported N-heterocyclic carbenes in the
126
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
literature (simple to very bulky NHCs), the sterically bulky IPr is shown to be one of the
very well researched N-heterocyclic carbene in recent years in the stabilization of low-valent
main group metal species and proved that its steric and electronic properties well suits for
trapping some unusual and highly reactive main-group diatomic allotropes.[14] Recently, IPr
has been utilized in the stabilization of unusual metal-metal multiple bonds between the
main group metal species. [15, 16]
Group 13 metal (I) organyl Ga(DDP) is considered as the analogue of N-heterocyclic
carbenes. This is due to the fact that the carbon center in carbene is in two coordination state
with sp2 hybridized center. Similarly the coordinating “Ga” center in Ga(DDP) in divalent
with sp2 center and moreover they both exhibit similar electronic and steric considerations as
it is shown in Figure 6.1.
Figure 6.1: Isolobal nature of NHC and Ga(DDP).
6.2.
Synthesis of Mono NHC Derivative [Cl4TiC{N(2,6-iPr2C6H3)CH}2]
(15)
C
..
N
N
TiCl4
Ar
N
Et2O, 2d
- 78 oC to RT
N
Ar
Cl
Ti
Cl
Cl
(a)
Cl
(15)
Ar = 2,6-Diisopropylphenly
Scheme 6.1: Synthesis of mono NHC derivative [Cl4TiC{N(2,6-iPr2C6H3)CH}2] (15).
127
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
Treatment of IPr with TiCl4 in 1:1 molar ratio in Et2O or THF affords a mono NHC
adduct [Cl4TiC{N(2,6-iPr2C6H3)CH}2] (15) in 54% yield as a pale yellow crystalline solid as
it is shown in the Scheme 6.1. Compound 15 is highly sensitive to moisture and air when it
is exposed to normal atmospheric conditions but stable over several days under inert gas
glove box atmosphere. Prolonged storage in solution leads decomposition of the compounds
to give a white insoluble material which is probably TiO2. 15 is highly soluble in common
organic solvents such as benzene, THF and toluene but sparingly soluble in n-hexane and
pentane.
The 1H and 13C NMR spectra of compound 15 are consistent with the molecular structure in
the solid state and show only one set of resonances for the presence of carbene ligand (IPr).
1
H-NMR in C6D6 gives a well separated septet at δ; 3.21 ppm as it is expected for the
isopropyl protons from the carbene part. The carbene carbon in 15 appears in the 13C-NMR
spectrum at significantly lower field (δ; 188.8 ppm) with respect to the free IPr ligand, as it
is observed in other NHC–Ti complexes. [12a] This observation indicates that the lone pair of
electrons on carbene carbon are involved in the coordination with the highly acetic titanium
center. Elemental analysis of this substance supports to the given molecular formula.
6.2.1 X-ray Structural Analysis of [Cl4TiC{N(2,6-iPr2C6H3)CH}2] (15)
The molecular structure of compound 15 is analyzed by single crystal X-ray analysis.
Pale yellow single crystals suitable for X-ray analysis are grown from the concentrated
toluene solution by cooling at - 30 º C. The molecular structure of 15 is shown in Figure 6.2.
Compound 15 crystallizes in space group Orthorhombic, Pnma. The molecular structure is
shown in Figure 6.2. The selected bond lengths and bond angels are shown at the foot note
of the Figure 6.2. It shows that the Ti (IV) center is surrounded by one carbene carbon, four
chlorine centers with a slightly distorted trigonal bipyramidal coordination sphere. The more
electronegative Cl─ ligands are occupied at both axial positions; whereas the other two
chlorides and carbene carbon center are occupied at the equatorial position. The carbene
ligand occupies an equatorial position, which gives rises to an approximately C2v-symmetric
molecular structure of 15. In the crystal, the complex lies on a crystallographic mirror plane
perpendicular to [010]. The crystal structure of 15 2 C7H8 is isomorphous to the structure of
[SiBr4(IPr)] 2 C7H8.[17] The Ti1–C1 bond length is 15.198(6) Å, which lies in the range of
128
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
similar NHC supported Ti complexes.[12a and 13] The Ti1–Cl3 distance in the equatorial plane
is 2.210(1) Å, whereas the axial Ti1–Cl1 and Ti1–Cl2 bond lengths are 2.274(2) and
2.263(2) Å, respectively. The molecular structure of 15 clearly shows the two axial chlorido
ligands (Cl1 and Cl2) slightly tilted towards the carbene IPr, resulting in Cl···CNHC
interactions of ca. 2.91 and 3.01 Å. This can be attributed to weak Cl···CNHC interactions,
which can be also observed in related complexes and has been discussed in the literature in
some detail (Figure 6.3). [11, 12b and 18]
Figure 6.2: Partially labelled displacement ellipsoids plot (50 % probability level) of 15 in
the crystal of its toluene disolvate. Hydrogen atoms are omitted for clarity. Symmetry code:
(a) x, 0.5-y, z. Selected bond lengths (Å) and angles (°); Ti (1)–C(1) 2.198(6), Ti(1)–Cl(3)
2.2103(12), Ti(1)–Cl(2) 2.2631(18), Ti(1)–Cl(1) 2.2738(17), C(1)-Ti(1)-Cl(3) 123.54(4),
C(1)-Ti(1)-Cl(2) 84.97(14), Cl(3)-Ti(1)-Cl(2) 94.59(5).
129
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
Ar
Cl
N
Cl
Ti
C
Cl
N
Cl
Ar
Figure 6.3: Schematic representation of Cl···CNHC type non-bonding interactions in 15.
6.3
Synthesis of Complex [TiCl4{C{N(2,6-iPr2C6H3)CH}2}2] (16)
The reaction between two equivalents of IPr with one equivalent of titanium
tetrachloride, in diethyl ether at low temperature gives the bis-carbene complex
[TiCl4{C{N(2,6-iPr2C6H3)CH}2}2] (16). The synthetic procedure for the preparation of 16 is
shown in Scheme 6.2. The bis carbene adduct 16 is yellow in colour and highly sensitive to
moisture and air, immediately decomposes upon exposure to air, gives white solid, but stable
under inert gas atmosphere for several days.
0.5 TiCl4
C
..
N
N
Ar
Cl
N
Cl
Ar
N
Ti
N
Cl
Ar
Et2O, 60h
- 78 oC to RT
Cl
(b)
N
Ar
(16)
Ar = 2,6-Diisopropylphenly
Scheme 6.2: Synthesis of [TiCl4{C{N(2,6-iPr2C6H3)CH}2}2] (16)
Compound 16 is highly soluble in common organic solvents such as benzene, toluene and
THF, also sparingly soluble in non polar solvents such as n-hexane and pentane. The 1HNMR in C6D6 at room temperature gives only one set of protons due to the symmetry in the
molecule. A well separated septet is appeared at ; 3.14 ppm which is assigned for the
isopropyl protons and is slightly shifted up field when compared with the same in its mono
NHCTiCl4 derivative 15. Whereas the alkene protons in IPr (H-C=CH) appears at ; 6.42
ppm which is shifted up field in comparison with the same in 15. The elemental analysis of
this bright yellow substance supports the given molecular formula.
130
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
6.3.1 X-ray Structure of [TiCl4{C{N(2,6-iPr2C6H3)CH}2}2] (16)
Compound 16  6 C4H8O was crystallized from a concentrated THF solution at – 30
ºC as bright yellow blocks; Figure 6.4 depicts the molecular structure of 16 in the solid state.
Ti (IV) shows a distorted octahedral coordination sphere with four equatorial chlorido
ligands and two IPr ligands in axial positions. In the crystal, the complex sits on a
crystallographic twofold rotation axis with the direction [010], passing through the C1-TiC15 unit. The C1-Ti-C15 bond angle is thus 180°. The tilt angle between the mean planes of
the central five-mebered rings of the IPr ligands is ca. 83.4°. The molecular conformation of
the complex shows the approximate D2d symmetry. Similar to compound 15, considerable
Cl···CNHC interactions (Figure 6.5) are found in 16, as reflected by the two pairs of trans
chloride ligands being tilted towards the IPr ligand (dihedral angle Cl1-Cl2-Cl1a–Ti ca. 10.2
°), which is perpendicular to the Cl–Ti–Cl axis with short Cl···Ccarbene contacts of ca. 3.03
and 3.04 Å.
Figure 6.4: Partially labelled displacement ellipsoid plot (40 % probability level) of 16 in
the crystal of its THF hexa solvate. For the sake of clarity, hydrogen atoms and symmetrygenerated disorder of the IPr ligand carrying C1 are omitted. Symmetry code: (a) –x, y, 0.5z. Selected bond lengths (Å) and angles (°); Ti(1)–C(1) 2.317(5), Ti(1)–C(15) 2.318(5),
131
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
C(1)–N(1) 1.366(14), Ti(1)–Cl(2) 2.2791(11), Ti(1)–Cl(1) 2.2880(10), Cl(2)-Ti(1)-Cl(1)
90.91(4), Cl(2)-Ti(1)-C(1) 82.40(3), C(1)-Ti(1)-C(15) 180.0, Cl(1)-Ti(1)-C(15) 82.60(3),
Cl(2)-Ti(1)-C(15) 97.60(3).
Å 3.040 Å
3.028
Ar
Ar
Cl2 Cl3
N
N
Ti
N
N
Cl1 Cl4
Ar
Ar
(16)
180o
Figure 6.5: Schematic illustration of Cl···CNHC non bonding interactions in 16.
6.4.
Synthesis of Complex [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (17)
After the isolation of mono and bis-carbene TiCl4 complexes, similar reactions were
performed to explore the reactivity of IPr with titanium tetra fluoride. The bis-carbene
complex of titanium tetra fluoride [F4Ti(IPr)2] (17) is prepared by addition of one equivalent
of IPr to TiF4 in THF and is the sole isolable titanium containing product irrespective of
whether one or two molar equivalents of IPr are employed. The typical synthetic procedure
is shown in Scheme 6.3. Compound 17 is highly soluble in benzene, toluene but insoluble in
pentane and n-hexane.
C
..
N
N
Ar
N
TiF4
F
F
Ar
N
Ti
THF, 20h
- 78 oC to RT
N
Ar
F
F
N
Ar
(17)
Ar = 2,6-Diisopropylphenly
Scheme 6.3: Synthesis of [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (17).
132
(c)
Chapter 6
The 1H and
NHC supported Zn and Ti complexes and their reactivity
13
C-NMR spectra of 17 is consistent with the molecular structures in the solid
state and show only one set of resonances for the carbene ligand (IPr). The 1H-NMR of 17
shows a well separated septet at ; 2.78 ppm which is significantly up field shifted when
compared with the same in other complexes 15 and 16 and 17 (Table 6.1). The carbene
carbon in 17 appears in the
13
C-NMR spectrum at significantly lower field (δ; 188.8 ppm)
with respect to the free IPr ligand, as it is observed in other NHC–Ti complexes.
[11a]
similarly, the carbene carbon (Ti–Ccarbene) of 17 in C6D6 displays a well separated quintet
(2JC-F = 6.8 Hz) in the same region (δ; 188.5 ppm) as it is shown in Figure 6.6. The 19F-NMR
of 17 gives a single signal at δ; 169.7 ppm which is similar to the shift found for other
titanium fluoride NHC complexes (Figure 6.7). [12a]
Figure 6.6:13C-NMR spectrum of bis-carbene complex [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2]
(17) in C6D6 at room temperature. 133
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
Figure 6.7: 19F-NMR of compound [F4Ti{C{N(2,6-iPr2C6H3)CH2}}2] in C6D6 at RT (17). Table 6.1: Comparison of 1H and 13C-NMR shifts for compounds 15-17.
Compound 15
Compound 16
Compound 17
Chemical shifts in
Chemical shifts in
Chemical shifts in
 (ppm)
 (ppm)
 (ppm)
1
H
(CH(Me2)2
3.21
13
C
1
13
(Ti–Ccarbene)
H
(CH(Me2)2
C
(Ti–Ccarbene)
188.8
3.14
193.1
1
13
H
C
(CH(Me2)2 (Ti–Ccarbene)
2.78
188.5
6.4.1 Molecular Structure of [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (17)
Single crystals of 17 4.5 C4H8O suitable for X-ray measurement were grown from a
THF solution as colourless crystals. The molecular structure of 17 in the solid state is shown
in Figure 6.8. The molecular structure is very similar to that of the chloride analogue 16 and
is composed of an octahedrally surrounded titanium center with two trans IPr ligands. The
tilt angle between the mean planes of the five-membered rings of the IPr ligands is ca. 44.6°.
Thus, the molecule shows approximate D2 point symmetry in the crystal. In contrast to the
chlorido ligands in 16, the fluorido ligands in 17 do not show any interaction with the NHCcarbon atom, i.e. no notable distortion of the TiF4 plane is observed. The central TiF4 unit
134
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
shows, however, rotational disorder around the C-Ti-C axis. The Ti–C bond lengths in 16 are
virtually identical [Ti–C1: 2.263(3) and Ti1–C28: 2.261(3) Å]. The observed values are well
within the range of other NHC-titanium (IV) fluoride adducts but shorter than in 16. [12a]
Figure 6.8: Partially labelled displacement ellipsoid plot (40 % probability level) of 17 in
the crystal of its 4.5 THF solvate. The part of the disordered TiF4 unit with minor occupancy
in the crystal [43(1) %] is pale. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (°); Ti(1)–C(28) 2.261(3), Ti(1)–C(1) 2.263(3), Ti(1)–F(3) 1.801(4),
Ti(1)–F(1) 1.803(4), Ti(1)–F(2) 1.814(4), N(1)–C(1) 1.354(4), N(1)–C(2) 1.395(4), C(28)Ti(1)-C(1) 177.10(11), F(2)-Ti(1)-C(1) 91.82(16), F(3)-Ti(1)-C(28) 89.62(17), F(1)-Ti(1)C(28) 93.20(16), F(2)-Ti(1)-C(28) 87.22(17).
6.5
Synthesis of [HC{N(2,6-iPr2C6H3)CH}2]2[TiCl6] (18)
Treatment of IPr with titanium tetrachloride in diethyl ether in 1:1 ratio at -78 °C
gives the compound 18 as a white solid. The typical synthetic procedure is shown in the
Scheme 6.4. As shown in Scheme 6.4, shorter reaction periods gives the salt like compound
18, whereas the long reaction periods gives the mono N-heterocyclic carbene adduct
according to the Scheme 6.1. Compound 18 is stable in inert gas atmosphere and highly
soluble in THF, but in soluble in benzene, n-hexane and pentane. 1H-NMR of compound 18
135
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
in THF-d8 shows the presence of all the expected resonances. A sharp singlet appeared at δ;
10.0 ppm is assigned for the acidic proton from the imidazole ring in the protonated NHC.
The corresponding carbon resonates at δ; 221 ppm which is relatively down field shifted in
comparison with the compound [IPr·TiCl4]. Furthermore, alkene protons (H-C=C) resonates
at δ; 8.38 ppm. Elemental analysis of compound 18 supports the given molecular formula.
TiCl4
C
..
N
N
Ar
N
TiCl6
CH
N
2
Ar
Et2O, 15h
- 78 C to RT
(18)
Ar = 2,6-Diisopropylphenly Scheme 6.4: Synthesis of compound 18.
6.5.1 Molecular Structure of [HC{N(2,6-iPr2C6H3)CH}2]2[TiCl6] (18)
Single crystals suitable for X-ray analysis can be obtained by slowly cooling the
concentrated THF solution of 18 at – 30 C as colourless blocks. The molecular structure of
18 is depicted in Figure 6.9. Compound 18 crystallizes in the monoclinic space group C2/c
with four solvent molecules (THF) in the crystal lattice. The important bond length and bond
angles are given at the foot note of the Figure 6.9.
Table 6.2: Hydrogen bonding data of compound 18; distances in (Å), angles in (◦) [a]
D–H···A[a]
d (D–H)
d (H···A)
d (D···A)
<(D–H···A)
C(1) –H(1)…O(1)
0.95
2.26
3.161 (10)
159
[a] Symmetry transformations used to generate equivalent atoms: #1 -x, y, -z+1/2
An interesting structural feature of the compound 18 is that it exhibits an intermolecular
hydrogen bonding in the crystal between the hydrogen atom of the imidazolium cation and
oxygen of the solvent molecule THF (C–HO).
136
[12e, 12f]
Figure 6.9 is also depicts the
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
hydrogen bonding in the cationic part of the molecule. The details of this bonding geometry
are shown in table 6.2.
Figure 6.9: Molecular structure of compound 18. Anisotropic displacement parameters are
depicted at the 50% probability level. Hydrogen atoms and the solvent molecules are
removed for clarity. Selected bond lengths (Å): Ti(1)–Cl(3) 2.335(3), Ti(1)–Cl(2) 2.348(3),
Ti(1)–Cl(1)#1 2.351(3), Ti(1)–Cl(1) 2.351(3), N(1)–C(1) 1.331(8), N(1)–C(3), 1.359(9),
N(1)–C(4) 1.456(8), N(2)–C(1) 1.339(8), N(2)–C(2) 1.366(9), N(2)–C(16) 1.449(8), C(2)–
C(3) 1.366(9). Bond angles (°): N(1)-C(1)-N(2) 107.4(7), N(2)-C(2)-C(3) 105.7(7), N(1)C(3)-C(2) 107.8(7), C(5)-C(4)-C(9) 124.2(7). Symmetry transformations used to generate
equivalent atoms.
6.6
Synthesis of [Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19)
Treatment of IPr with ZnCl2 at room temperature in 1:1 ratio gives a 1:1 mono NHC adduct
[Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19) in 74% yield as a white powder. The typical synthetic
procedure is shown in Scheme 6.5. Compound 19 is highly soluble in benzene toluene and
THF but in soluble in non polar solvents such as n-hexane and pentane. 19 is highly stable
under inert gas atmospheric conditions.
137
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
THF
N
C:
N
+
ZnCl2
RT
24h
Cl
N
Zn
N
Cl
(19)
Scheme 6.5: Synthesis of [Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19).
6.6.1 Molecular Structure of [Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19)
Figure 6.10: Partially labelled displacement ellipsoid plot (40 % probability level) of the two
crystallographically distance molecules of 19 in the crystal of its THF disolvate. The
disordered parts of the ZnCl2 unit and the isopropyl group with minor occupancy in the
crystal [42(1) and 35.5(8) %, respectively] are shown in pale colour. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (°); Zn(1)–C(1) 2.046(4), Zn(2)–
C(32) 2.043(4), Zn(1)–O(1) 2.077(3), Zn(1)–Cl(2) 2.180(2), Zn(1)–Cl(1) 2.333(3), Zn(2)–
O(2) 2.109(3), Zn(2)–Cl(4) 2.2219(12), Zn(2)–Cl(3) 2.2532(13), C(1)-Zn(1)-O(1)
138
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
110.70(16), C(1)-Zn(1)-Cl(2) 119.81(14), O(1)-Zn(1)-Cl(2) 107.12(14), C(1)-Zn(1)-Cl(1)
106.84(14), O(1)-Zn(1)-Cl(1) 96.96(16), C(32)-Zn(2)-O(2) 110.54(16), C(32)-Zn(2)-Cl(4)
118.90(13).
Single crystals suitable for X-ray diffraction analysis can be obtained by cooling the
concentrated solution of 19 in THF at – 30 º C. Compound 19 crystallizes with two solvent
molecules in monoclinic space group P21. Figure 6.10 depicts the molecular structure of 19
in solid state. As shown in Figure 6.10, 19 2 C4H8O crystallizes with two molecules of 19 in
the asymmetric unit (Z’ = 2). In compound 19, Zn centre adopts a tetrahedral coordination
sphere, comprised of one IPr, two chlorido and one THF ligand. In the crystal, the molecule
containing Zn1 is affected by disorder of the ZnCl2 unit and one of the isopropyl groups of
the IPr ligands. The Zn1–C1 and Zn1–C32 bond lengths are 2.046(4) and 2.043(6) Å,
respectively, and lie well within the range of other NHC-Zn complexes.[10] The Zn1–O1 and
Zn2–O2 bond lengths exhibit values of 2.077(3) and 2.109(3) Å, respectively, and are
indicative for a comparably weak coordination of the THF molecule to the Zn(II) center.[10]
As is expected, the Zn2–Cl3 and Zn2–Cl4 distances of 2.253(1) and 2.222(1) Å,
respectively, are similar to the related complex [ZnCl2(NHC)(THF)] (NHC = 1,3bis(mesityl)-imidazol-2-ylidene) (average value 2.23 Å).[10]
6.7
Synthesis of [(CH3)2Zn{C{N(2,6-iPr2C6H3)CH}2}2] (20)
The reaction of IPr with an excess of Me2Zn in 1:3 molar ratio in toluene at
room temperature gives the expected N-heterocyclic carbene adduct [IPr·ZnMe2] in above
94% yield as a white powder. The synthetic procedure is shown in scheme 6.6. Compound
20 is highly soluble in aprotic solvents such as benzene, toluene and THF and is also
sparingly soluble in pentane and n-hexane at room temperature. The 1H-NMR of 20 in C6D6
gives all the expected chemical shifts which are associated with the presence of methyl
groups on the zinc center as well as the from the IPr moiety. A sharp singlet observed in high
field at δ; – 0.76 ppm is assigned for methyl protons bound to the Zn atoms (Zn–Me). The
carbon from the same group resonates at δ; – 8.0 ppm in its
13
C-NMR measured at room
temperature. The alkene protons (H-C=C) from the IPr resonates at δ; 6.53 ppm, which is
slightly down field shifted when compared the same with the similar adduct [IPr·ZnCl2]
from the present study (δ; 6.46 ppm).
139
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
N
C:
+
ZnMe2
N
Toluene
N
15h
RT
N
Me
Zn
Me
(20)
Scheme 6.6: Synthesis of [(CH3)2Zn{C{N(2,6-iPr2C6H3)CH}2}2] (20).
6.7.1 Single
i
Crystal
X-ray
Analysis
of
[(CH3)2Zn{C{N(2,6-
Pr2C6H3)CH}2}2] (20)
The dimethyl zinc-carbene adduct is a white solid and colorless single crystals which are
suitable for X-ray analysis can be obtained by cooling the saturated solution of 20 in toluene
at -30 ºC. Compound 20 crystallizes in monoclinic space group C2/c. The molecular
structure of 20 is shown in Figure 6.11.
Figure 6.11: Molecular structure of compound 20 in the solid state as determined by single
crystal X-ray diffraction. Hydrogen atoms and solvent molecules are omitted for clarity.
Important bond lengths (Å) and angles (º): Zn(1)C(1) 2.0029(19), Zn(1)C(1)a 2.0028(19),
140
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
Zn(1)C(2) 2.136(2), N(1)C(2) 1.358(2), N(1)C(3), 1.381(2), N(1)C(4), 1.448(2),
C(2)N(1)a 1.358(2), C(3)C(3)a 1.350(3), C(4)C(5) 1.395(2); C(1)a-Zn(1)-C(1)
128.03(12), C(1)a-Zn(1)-C(2) 115.99(6), C(1)-Zn(1)-C(2) 115.99(6), C(2)-N(1)-C(3)
111.99(14), C(2)-N(1)-C(4) 124.20(14), C(3)-N(1)-C(4) 123.80(14), N(1)-C(2)-N(1)a
103.2(2), N(1)-C(2)-Zn(1) 128.38(10), N(1)a-C(2)-Zn(1) 128.38(10), C(3)a-C(3)-N(1)
106.39(9), C(5)-C(4)-C(12) 123.49(15).
Compound 20 shows the zinc centre is in three coordinate state with one carbene carbon and
two methyl groups on it. The C3N2 and the phenyl groups are in coplanar. The observed
ZnCcarbene bond length (Zn(1)C(2) 2.136(2)Å) is slightly longer than in the similar diethyl
zinc-carbene adduct (carbene = 1,3-dimethylimidazole-2-ylidene, ZnCcarbene 209.6 (3)Å) as
the same in compound 19.[19] Another interesting feature in compound 20 is the both methyl
groups on the zinc centre are not in the same plane of imidazole-2-ylidene ring, but slightly
tilted above and below to this plan. The most important bond lengths and angles are given at
the foot note of the Figure 6.11.
6.8. Reactivity of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] (15)
6.8.1 Reactivity of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] with Dimethyl Zinc (Me2Zn).
N
Cl
Ti
N
Cl
Cl
Cl
4 ZnMe2
THF
o
- 55 C to RT
Cl
N
Zn
Carbene
transfer
N
Cl
O
(19)
Scheme 6.7: Carbene transfer from the titanium to Zinc centre.
After the isolation and complete characterization of mono NHC complex, [Cl4TiC{N(2,6-iPr2C6H3)CH}2] (15), few experiments were conducted to test the stability of IPr
coordinated titanium methyl complexes, the reaction of 15 with an excess of Me2Zn in THF
at - 55 ºC was investigated. However, this reaction does not lead to the expected tetramethy
141
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
titanium complex [TiMe4(IPr)], but results in the transfer of the IPr and two chlorido ligands
from the titanium to zinc, thereby leading to neutral complex [ZnCl2(IPr)] (19) in moderately
good yield around 50 %. The typical synthetic procedure of the carbene transfer reaction is
shown in Scheme 6.7.
The methylated titanium species most likely formed in the course of this reaction could
neither be observed nor identified, probably due to the rapid decomposition of already
existing NHC supported ZnCl2 adduct complexes.
[10]
After the formation of 19, it was also
shown from the independent synthesis by a direct reaction between the free carbene and
ZnCl2 in THF at room temperature. The carbene transfer reaction gives a new synthetic
pathway for the preparation of [ZnCl2(IPr)]. Similar tetrachloro N-heterocyclic carbene
adduct analog has been reported recently which acts as a carbene transfer reagent. The Nheterocyclic carbene adduct [(NHCMe)SiCl4] (NHCMe = 1,3-dimethylimidazolidin-2-ylidene)
is an efficient carbene transfer reagent to transfer carbene from the Si(IV) centre to Ni (II) or
Pd(II) centres to yield bis-carbene complexes treatment with the respective metal salts.[20]
6.9
Attempted Synthesis of NHC Stabilized Titanium and Zinc Clusters
N-heterocyclic carbenes (NHCs) offer an alternative ligand set to phosphines and
have found applications in many areas of contemporary organometallic chemistry, although
their use in metal cluster chemistry is still relatively limited. [21-26] Very recently, Whittlesey
and co-workers first time showed that the palladium N-heterocyclic carbene cluster
complexes [Pd3(μ-CO)3(NHC)3] and [Pd3(μ-SO2)3(NHC)3] (NHC = IMes, 1,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene; IiPr2 = 1,3-bis-isopropylimidazol-2-ylidene) where
palladium is in zero oxidation state. These clusters were synthesized by the KC8 reduction of
palladium (II) complex, trans-[Pd(NHC)2Cl2]. Moreover, Robinson, Uhl and their coworkers
have recently showed that N-heterocyclic carbenes can also be suitable ligand systems for
the stabilization of main group molecular diatomic allotropes, and clusters. The most
illustrious examples in this regard are the reduction of N-heterocyclic carbene stabilized
[IPrGeCl2]
[27]
and [IPrSiCl4]
[28]
with potassium graphite gives metal-metal multiple
bonded species, L-E=E-L (E= Ge, Si and L = IPr). By applying similar synthetic strategy,
few experiments were conducted to isolate anticipated molecular species such as
[(NHC)mTin] and [(NHC)mZnn].
142
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
6.9.1 Reactivity of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] (15) with KC8.
Treatment of [Cl4Ti-C{N(2,6-iPr2C6H3)CH}2] with KC8 at room temperature yields
decomposed products which could not be characterized and mostly yielded insoluble white
gray to black precipitates (Scheme 6.8). Even when the reactions were carried out at very
low temperatures also similar observations were drawn.
[IPr.TiCl4]
KC8
Benzene
No products could be isolated Scheme 6.8: Reduction of [IPrTiCl4] with KC8.
6.9.2 Reactivity of [Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19) with KC8
Treatment
i
of
zinc
(II)
N-heterocyclic
carbene
adduct
[Cl2Zn-C{N(2,6-
Pr2C6H3)CH}2] with an excess of KC8 in THF at room temperature yields NHC as the main
product as shown in the Scheme 6.9. The reaction pathway shows that Zn (II) center got
completely reduced to Zinc (0) and the cleavage of ZnC bond has taken place.
N
Cl
Zn
N
Cl
KC8
THF
O
N
N
(19)
Scheme 6.9: Reduction of [IPrZnCl2] with KC8.
143
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
6.10 Reactivity Differences Between Ga(DDP) and IPr
IPr
Ga(DDP)
Figure 6.12: Molecular structures of low-valent IPr (left) and Ga(DDP) (right).
As it is discussed in the aforementioned introduction, the sterically pronounced Nheterocyclic carbene (IPr) used for the present study and its heavy group 13 metal (I) analog
Ga(DDP) have almost similar steric and electronic environment around the coordinating or
donor centers “C” in carbene and “Ga” in Ga(DDP). Both coordinating centers are in low
(two) coordinate, low oxidation states as well as neutral species (Figure 6.12) with one lone
pair of electrons present on the carbon and gallium centers. Although both species exhibit
almost similar chemical environment around the coordinating center, but they have very
different reactivity towards metal centers (this particular aspect is also discussed in detail by
quantum chemical calculations as shown in chapter 4). The reactivity differences of IPr
ligand and its analogue Ga(DDP) towards ZnCl2 and ZnMe2 are summarized as case study
by comparing with the previously reported reactions of Ga(DDP) with ZnMe2 and ZnCl2. [29]
The reaction of Ga(DDP) with Me2Zn yields a insertion product [{(DDP)GaMe}2Zn]
as orange-red crystalline solid, whereas the similar reaction between IPr and Me2Zn yields a
simple N-heterocylcic carbene adduct [IPr·ZnMe2] where the zinc centre retains its “+2”
oxidation state. Whereas in the former case Zn (II) gets formally reduced to Zn (0) centre by
Ga(DDP) due to its insertion between the both ZnMe bonds, which is not seen in case of
IPr. Similarly, the reaction of Ga(DDP) with ZnCl2 gives a insertion product
[{(DDP)GaCl}ZnCl(THF)2] where Ga(DDP) inserts between one of the ZnCl bond, but
the same reaction with IPr gives the N-heterocyclic carbene adduct [IPrZnCl2]. Thus these
144
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
reactions highlights the reactivity differences and properties of Ga(DDP) and IPr, when they
are reacted with the same metal precursors. The main reactivity difference is due to the
ability of Ga(DDP) to reduce the metal centers by its redox activity thereby forming strong
MGa bonds, whereas IPr does not reduce the same metal centers, instead stabilizes to give
adducts with relatively weaker MC bonds. This is also due to the fact that Ga(DDP) is not
only a strong sigma donor but also good pi acceptor ligand, this particular behavior is useful
in forming or stabilizing strong MGa bonds, whereas N-heterocyclic carbenes are strong
sigma donors but weak pi acceptors due to the p(π) AO of the “C” donor atom in NHC is
significantly occupied because of strong N(π)→C(π) donation.
145
Chapter 6
NHC supported Zn and Ti complexes and their reactivity
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A. Kempter, Coordination chemistry of the low-valent group 13 NHC-analouge
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substitution reactions and cluster formation, PhD thesis, Ruhr University Bochum,
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148
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Chapter 7
Organometallic Synthesis of Nickel-Gallium Binary Intermetallic
Alloy Nanoparticles Abstract: Non-aqueous organometallic synthesis of various Nickel-Gallium alloy
nanoparticles is investigated and developed using organometallic preparative routes. The use
of
well
defined
Nickel-Gallium
phosphine
complexes
[NiGaCp*(PMe3)3]
and
[Ni(GaCp*)3(PCy3)] as single source precursors for the soft chemical synthesis of Ni/Ga
intermetallic phases is explored. The thermal hydrogenolysis of these precursors yields the
intermetallic Ni/Ga powders with a predominant formation of Ni2Ga3 as the crystalline
phase. Free standing Nickel-Gallium nanoparticles are also achieved in presence of
hexadecylamine (HDA) stabilizer. Furthermore, the individual metal precursors [Ni(cod)2]
and GaCp* are probed to selectively accomplish the series of NiGa, Ni2Ga3 and Ni3Ga nano
intermetallic phases. The catalytic activity of these nanoalloys is further investigated towards
a olefin hydrogenation.
149
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
7.1 Introduction and Goals
7.1.1 Introduction
The properties of metals, such as the catalytic activity, mechanical properties and
magnetism can be tuned by alloying with other suitable metals in a proper ratio. In such an
alloy the mutual influence of different neighboring atoms can lead to demonstrate different
properties over monometallic cluster systems.
[1a,b]
Bimetallic systems which are consisting
of group-13 metals are found to exhibhit interesting catalytic and magnetic properties which
are studied quite recently.
[1c-d]
In recent times many attempts have been made to prepare
gallium containing alloys in nanometer scale regime because it is expected that they possess
different properties compared to the same as a bulk material. In this regard two such very
well-known examples are the recently reported semiconductor material gallium-arsenide
and a novel nano structured, highly efficient heterogeneous catalyst Pd2Ga.[3,
4]
[2]
Very
recently, Armbrüster and co-workers described that the novelty of this intermetallic
compound, Pd2Ga as a high performance selectivity towards the semi-hydrogenation of
acetylene. This material has demonstrated to display five thousand fold more catalytic
activity than the bulk state of the same Pd2Ga model catalyst.
[3]
In addition, few other
Palladium/Gallium intermetallic compounds in different compositions such as Pd3Ga7, PdGa
are also found to act as highly effective hydrogenation catalysts.
[4]
Thus, these results
highlight the significant applications of gallium containing intermetallic main-group and
transition metal compounds as materials with unique properties especially as catalysts with
high performance.
7.1.2 Nickel-Metalloid Intermetallic Alloys
Group-13 metals Al, Ga and In readily form a number of different intermetallic
compounds with nickel in different compositions.
[5-11]
In general, the Nickel-Gallium
intermetallic systems are typically prepared by metallurgical process, such as arc melting
followed by annealing at high temperatures for several weeks by utilizing high purity
individual metals or reducing their corresponding metal salts.
[6, 12-19]
For example, various
Nickel-Gallium intermetallic phases can be made from the nitrate salts of Ni(NO3)2 and
Ga(NO3)3 by reducing them at very high temperatures (a.v 700 ºC) with pure H2 flow.
[20]
These kinds of routes apparantlay involve tedious experimental conditions and have some
disadvantages to get control over the reaction, size of those particles and the purity of the
150
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
desired materials. Thus, in such conditions there is a requirement to search for new
precursors and reliable preparative methods. One such efficient preparative method is the
recently developed soft chemical synthesis in organic solvent from the respective
organometallic complexes (described in detail in Chapter 1). [21]
The utilization of organometallic compounds in soft chemical synthesis of various metals
and intermetallic phases (alloys) is an intriguing field of research.
[1, 21]
The obtained
nanomaterials have wide-spread applications of fundamental and technological interest.
[22]
In this regard quite recently non-aqueous organometallic synthesis of nano-Cu colloids and
nano brass (α/β-CuZn) by the co-hydrogenolysis of suitable organometallic precursors as
metal sources has been reported.
[23, 24]
In particular it has been showed that the low-valent
[(AlCp*)4] is a reliable organometallic Al-source for obtaining aluminum nanoparticles as
well as the intermetallic Nickel-Aluminum (NixAly type) nano phases.[24]
7.1.3 Nickel-Gallium Phase Diagram
Figure 7.1 and Figure 7.2 depict the different intermetallic phases of Ni/Ga binary
alloys structures and the phase diagram respectively. It shows the existence of different solid
phases at different concentrations and temperatures.
Ni
Ga
NiGa
Ni3Ga
bcc CsCl type (B2)
fcc AuCu3 type (L12)
CN = 8
CN = 12 and 4
Ni2Ga3
Figure 7.1: Schematic illustration of Ni-Ga intermetallic phases.
151
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Figure 7.2: Nickel-Gallium Binary alloy phase diagram [25]
7.1.4 Goals
Synthetic Approach
Non-aqeous Organometallic Synthesis
Organometallic precursors
Decomposition
in presence
of a stabilizer
Decomposition
in absence
of a stabilizer
Alloy
NixGay
Chart 7.1: Chemical approach for the preparation of Ni-Ga nanoalloys.
152
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
The main objective of this part of work was to develop new and novel synthetic
routes for the bimetallic Nickel-Gallium nano intermetallic compounds using wet and soft
chemical approach in organic media. According to the phase diagram three simple
intermetallic compounds NiGa, Ni2Ga3 and Ni3Ga were chosen for the present study to
develop the possible organometallic routes to prepare these alloys in the nano scale regime
as nanopowders as well as colloidal nanoparticles. Such synthetic approach demands highly
pure metal precursors to produce nanoparticles upon reduction (hydrogenolysis) at relatively
mild experimental conditions. Chart 6.1 shows the employed synthetic approach for this
work. Although the organometallic syntheses of Nickel nanoparticles in an organic medium
are known in the literature, [21b and 21c] but there are no reports available on the soft chemical
synthesis
of
bimetallic
Nickel-Gallium
nano
intermetallic
compounds
utilizing
organometallic precursors so far. Recently developed both Nickel-Gallium metals containing
phosphine complexes [NiGaCp*(PMe3)3], and [Ni(GaCp*)3(PCy3)] are first time explored
for these decomposition studies.
[26a]
In addition, the individual precursors [Ni(cod)2] which
is the most commonly used staring material for nickel source for synthesis of molecular
complexes as well as Nickel nanoparticles. [27] Low-valent, GaCp* is explored to accomplish
the Nickel-Gallium nanoalloys for the first time. In addition, the catalytic activities of these
nanoalloys are studied for the hydrogenation of cyclohexene to cyclohexane.
7.2
Hydrogenolysis of [NiGaCp*(PMe3)3] and Characterization of Ni/Ga
Nanoparticles (NP1)
7.2.1 Synthesis
Single source organometallic precursor [NiGaCp*(PMe3)3] was chosen for the
decomposition studies with the aim of synthesizing intermetallic NiGa (1:1) phase, since this
precursor contains both desired metals (Ni and Ga) in 1:1 ratio, means upon decomposition
one would anticipate 1:1 intermetallic system. A yellow solution of the single source
precursor in n-decane (n-decane was selected because the thermo gravimetric analysis of the
precursor under N2 atmosphere showed the decomposition temperature at  210 C) was set
to 4 bar H2 pressure and heated at 185 ºC. The typical synthetic procedure is shown in
Scheme 7.1. After 10 min of stirring the solution color became brown to dark brown, and
then it gave black precipitate. The supernatant was filtered, and the residue was washed with
toluene and n-hexane.
153
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
GaCp*
Me3P
Ni
PMe3
PMe3
n-decane
4 bar H2
185 C
60 h
Black powder
(NP1)
Scheme 7.1: Hydrogenolysis of [NiGaCp*(PMe3)3] in n-decane.
7.2.2 X-ray Powder Diffraction Analysis of NP1
The powder X-ray diffraction pattern of NP1 is shown in Figure 6.3. The powder
pattern shows that it is crystalline in nature and closely matches with the Ni2Ga3 reported
phase (Hexagonal, space group, P-3m1). Although the expected phase is NiGa (1:1)
according to the single source precursor used, but the formation of 2:3 phase is observed.
This is possibly due to the fact that the remaining nickel is left over in the supernatant as the
nickel forms stable complexes with phosphines (Nickel has more affinity towards
phoshphines). This is further explained by the
31
P-NMR measurements of the dark brown
filtrate part which gave a single, not assignable resonance at δ; – 21.78 ppm which is not
corresponding to neither the free trimethly phosphine nor the staring material (; -5.6 ppm).
[26a]
The appearance of this new chemical shift supports the possible formation of new
[Ni(PR3)n] type of complexes in the reaction mixture during the decomposition processes,
thereby some part of Nickel might have left in the form of soluble Nickel complexes. [26b] In
addition, few high temperature experiments were conducted in order to see whether will
there be any phase transformations could occur. The DSC (Differential Scanning
Calorimetry) of the same sample measured from 30 to 1000 C showed no phase
transformation. Furthermore, the sample was annealed for 20 h at 300 C under the dynamic
vacuum (a.v.10-3 mbar). After annealing of the sample the same reflections got intensified
with a slight sharpening of the peaks observed when compared with the as-synthesized
sample as it is shown in the Figure 7.3. The average particle size according to the Scherrer´s
equation is calculated to be around 8-10 nm.
154
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Figure 7.3: X-ray powder diffraction pattern of Ni/Ga material (NP1). Reference data taken
from JCPDS no: [7-161].
7.2.3 Infrared Spectrum of NP1
The nature of the Ni/Ga sample NP1 was further examined by infrared spectroscopy.
As is shown in Figure 7.4, no considerable absorption bands were detected.
Figure 7.4: Infrared spectrum of the sample NP1 measured before and after annealing
.Measured as neat.
155
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
This observation supports that the material is most likely does not contain the organic
ligands around the particle surface which could not be detected from the IR spectrum and
one would predict that the material is mostly consisting of metallic powder. According to the
metal analysis by atomic absorption spectroscopy the powder contained 33.76 wt. % Ni and
58.75 wt. % Ga which is almost equal to the atomic ratio of 2:2.93 of Ni/Ga (Ni2Ga2.93,
Ni2Ga3 phase). Figure 7.4 shows that there is not much difference observed in the IR
spectra measured before and after the annealing of the sample NP1.
7.2.4 Transmission Electron Microscopy of NP1
In order to determine the particles morphology and the composition, transmission
electron microscopy measurements were performed on as-synthesized material.
Figure 7.5: TEM images of the material NP1. Left: BF-TEM of small agglomerated
particles. Right BF-TEM of large agglomerated particles. The particles are encased in an
unidentified matrix.
The bright field TEM image of this material is shown in Figure 7.5. The particles
exhibit no preferred size. The BF-TEM images show smaller particles (5-20 nm) as well as
the huge agglomerates (several hundred nanometers). The Energy-dispersive X-ray
spectroscopy (EDX) measurement indicates the presence of multiple intermetallic phases
with varying Ni to Ga ratios. To acquire EDX spectra, whole particle agglomerations were
illuminated, thus the calculated elemental compositions only reveal the average composition
156
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
of an agglomeration, not necessarily of the individual particles. The EDX analysis was
performed on several such agglomerations on the grid. The found ratios of Ni to Ga were
approximately 1:1, 2:3 and 1:2 (within the accuracy of the method of measurement), means
the material obtained is not completely phase pure, with only Ni2Ga3 as the crystalline phase
as it is supported by the powder X-ray diffraction data (Figure 7.3).
7.3
Cohydrogenolysis
of
[Ni(GaCp*)3(PCy3)]
and
[Ni(cod)2]
and
Characterization of Ni/Ga Nanoparticles (NP2)
7.3.1 Cohydrogenolysis of [Ni(GaCp*)3(PCy3)] and [Ni(cod)2]
In order to prepare the Ni2Ga3 phase, two different precursors were taken for the
decomposition reaction. Cohydrogenolysis of [Ni(cod)2] and [Ni(GaCp*)3(PCy3)]
[26]
in n-
decane at 4 bar H2 at 190 C in a Fischer-Porter bottle first gives a dark brown reaction
mixture, after 20 min heating at the same temperature gives a grey-black precipitate. The
amount of the precipitate grows with the reaction time. During the reaction a quick drop in
the hydrogen pressure was observed, indicates the decomposition of precursors could have
takes place by consuming the hydrogen gas. The reaction was carried out for 12 h at the
same temperature for the complete decomposition of the starting materials. The typical
decomposition reaction is shown in Scheme 7.2.
PCy3
*CpGa
Ni GaCp*
+
n-Decane
4bar H2
Ni
12h, 190 oC
GaCp*
Black powder
NP2
Scheme 7.2: Co-hydrogenolysis of two different precursors in n-decane
7.3.2 X-ray Powder Diffraction Analysis of NP2
The black powder material obtained according to Scheme 7.2 was analyzed by X-ray
powder diffraction analysis to determine the crystalline phase. Figure 7.6 shows the powder
pattern of the material NP2.
157
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Figure 7.6: Powder X-ray pattern for the material NP2. Reference data taken from ICSD: 103860 and the X-ray data was collected in a capillary mode.
As shown in Figure 7.6, the material has crystalline nature and the formation of Ni2Ga3
phase is observed and all the 2 (XRD reflections, 2θ/: 18.19 (0 0 1), 25.39 (1 0 0), 31.30 (1
0 1), 36.82 (0 0 2), 44.64 (2 -1 0), 45.23 (1 0 -2), 48.64 (2 -1 1), 52.26 (2 0 0), 55.69 (2 0 1),
56.45 (0 0 3), 59.30 (2 -1 2), 62.74 (1 0 3), 65.41 (2 0 2), 71.13 (3 -1 0), 73.99 (3 -1 1), 74.75
(2 -1 3)) reflections are closely matching with the reference powder data [ICSD: 103860].
7.3.3 Transmission Electron Microscopy of the Sample NP2
The BFTEM images of the dispersed powder in toluene shows the agglomerated
nanoparticles as it is in the case of NP1 sample (Figure 7.7). The EDX analysis of this
sample measured on few selected areas shows the presence of Ni and Ga in different ratios
also corresponding to the expected 2:3 phase as it is the crystalline phase. Although EDX
analysis of NP2 shows the presence of other phases (according to Ni to Ga ratio), but these
are not observed in the powder X-ray of NP2. This indicates that the material might contain
extra Ni or Ga in amorphous state which can’t be detected by PXRD. This aspect can be
rationalized in accordance with the 31P-NMR of the supernatant. As it is observed in case of
158
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
NP1, the 31P-NMR of the filtrate part showed a single sharp peak at ; 23.1ppm, which is not
corresponding to either the free tricyclohexyl phosphine or the staring material (; 87.4
ppm). [26a] The appearance of this new chemical shift supports the possible formation of new
[Ni(PR3)n] type of complexes in the reaction mixture during the decomposition processes,
thereby some part of Nickel might have left in the form of soluble Nickel complexes. [26b]
Figure 7.7: BFTEM image (left) and EDX (right) spectrum of material NP2.
Furthermore, AAS analysis showed that the atomic weight percentages for Ni 31.31
wt. % and Ga 52.14 wt. % which is corresponding to 2:2.81 ratio of Ni to Ga atomic
percentage. This gives the molecular composition of Ni2Ga2.81 which is almost near to the
expected Ni2Ga3 phase composition. Howere, EDX analysis indicates the material is not
phase pure, contains multi phases.
7.4
Synthesis and Characterization of NiGa (1:1) Nanoalloy (NP3)
Aforementioned results point out that both Nickel-Gallium metals containing single
source precursors which contain the phosphine ligands attached to Nickel center in
[NiGaCp*(PMe3)3] and [Ni(GaCp*)3(PCy3)] were found to be not a proper choice to achieve
the desired, phase pure Nickel-Gallium nanoalloys. Then the interest turned to use the
organometallic precursors which have no phosphine ligands around the metal centers. For
this purpose individual organometallic precursors [Ni(cod)2] and GaCp* were chosen for the
hydrogenolysis studies.
159
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
7.4.1 Synthesis of NiGa nanopowder (NP3) from [Ni(cod)2] and GaCp*
The co-hydrogenolysis of GaCp* and [Ni(cod)2] together with mesitylene in 1:1 ratio
under 4 bar H2 pressure leads to the formation of a dark-red solution in Fischer porter bottle,
which was stayed for 20-30 min (as shown in the Scheme 7.3). After 30 min of heating at
150 C, the color changes to dark brown and later formation of a black precipitate is
observed. After 2h heating, it becomes clear colorless solution with the formation of a black
precipitate. The suspension is stirred for another 1h for complete decomposition of the
precursors.
Ni
+
GaCp*
Mesitylene
4bar H2
o
3h, 150 C
Black powder
NiGa phase
(NP3)
Scheme 7.3: Co-hydrogenolysis of [Ni(cod)2] and GaCp* in mesitylene as the solvent.
The black solid material obtained was filtered and the colorless filtrate part was decanted off.
The black material obtained was washed several times thoroughly first with toluene, later
with n-hexane and dried under vacuum overnight to get a powdery black material.
7.4.2 X-ray Powder Diffraction Analysis of NP3
The black powder is characterized by means of powder XRD. The powder X-ray
pattern of NP3 black powder is very informative and shows the formation of phase pure
Ni1Ga1 (1:1) (Cubic, space group: Pm-3m, reference data taken from ICSD No: 103854).
The XRD pattern, shown in Figure 7.8, exhibits slightly broad peaks at (2 /º) = 31.44,
44.89, 55.74, 65.45, 74.20 and 82.65  which matches with the reference data but with
0.5-1.1 difference, shifted to low 2 reflections. This shift might have occurred due to the
fact that the synthetic procedure for the reported phases is entirely different in the present
organometallic routes. However, it can´t be excluded that the NiGa phase is stable
(according to the phase diagram) over more area of composition and temperature which may
have caused the deviation. Similar observations were reported in intermetallic compound
160
Chapter 7
ZnPd.
[31]
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
The average primary crystallite domain size is estimated to be 46 nm with the
Scherrer´r equation on the full widths at half maximum (FWHM) of the most intense
reflections 2 = 44.89 and 82.7. The preparation of NiGa phase was confirmed by repeating
the same reaction several times and confirmed by the PXRD reflections exhibited slight
shifts with the reported NiGa phase. The annealing of this sample at 300 ºC gives more sharp
peaks. The particle size calculated according to Scherrer’s equation shows no difference to
the sample before the annealing.
Intensity ( I )
----NiGa
20
30
40
50
60
70
80
90

Figure 7.8: Powder X-ray diffraction diagram of the NiGa nanopowder (NP3). Reference
data taken from ICSD No: 103854.
7.4.3 Transmission Electron Microscopic Analysis of the Particle’s Morphology
TEM images of the sample NP3 shows a nano crystalline material, which confirms
the particle size calculation from the powder X-ray diffraction data. Figure 7.9 shows a
HRTEM image of the NP3 powder, on the left square a magnification of the area labeled by
the white square is shown in the top right. An FFT analysis (bottom right) of this area shows
that a NiGa crystallite has been imaged in its [111] zone axis orientation.
161
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Figure 7.9: High resolution TEM images of the NiGa nanopowder. Close up of the particles
at Top (right). FFT of the crystallite shown in the top right corner.
The EDX analysis of the few selected areas on the TEM grid revealed an atomic Ni:Ga ratio
of 1.04:1, 1:1.02 and 1:1.01 within the accuracy of the method of measurement. Figure 7.10
shows the formation of NiGa (1:1) phase. The composition of this material was further
confirmed by the elemental analysis of the black material by Atomic Absorption
Spectroscopy. From the AAS analysis Ni and Ga atomic percentage were found to be 39.69
wt. % and 50.27 wt. %. This ratio is equal to the NiGa phase with 1:1.06 compositions.
120
GaL
100
Counts
80 NiK
NiK
GaK
60
Figure 7.10: Energy dispersive Xray (EDX) spectrum of the sample
NP3. 40
CuK
20
GaK
0
0
2
4
6
8
10
12
Energy (keV)
162
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
7.4.4 Infrared Spectrum of NP3
According to the AAS metal analysis and TEM-EDX data, it is established that the
material is phase pure which has the composition of almost 1:1 or sum formula of
Ni1.0Ga1.06. The infrared spectrum of NP3 exhibits almost no absorption as it is seen for
NP1and NP2 nanoparticles and shows almost like a straight line. No significant CH
stretching bands have been observed as shown in Figure 7.11. This evidences the more
Transimittance (%)
metallic nature of the material as a whole.
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm )
Figure 7.11: Infrared spectrum of the black material (NP3). The sample was measured as
neat.
7.5
Synthesis of and Characterization of Intermetallic Crystalline
Ni2Ga3 nano powder (NP4)
7.5.1 Synthesis of NP4
2
Ni
+
3 GaCp*
Mesitylene
4bar H2
24 h, 150 oC
Black Powder
Crystalline
Ni2Ga3 phase
(NP4)
Scheme 7.4: Co-hydrogenolysis of Ni(cod)2 and GaCp* in 2:3 ratio.
163
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
The cohydrogenolysis of Ni(cod)2 and GaCp* in 2:3 molar ratio in mesitylene at 150 C
yields a black powdery material as shown in the scheme 7.4. The initial color of the reaction
mixture slowly changed to dark-red to brown, and then it gave a black precipitate over a
period of 25 min heating at the same temperature. In contrast to the aforementioned reaction
(Scheme 7.4), a sudden drop of the H2 pressure was observed over a period of 1h heating.
This indicates the rapid decomposition of the precursors which utilizes the hydrogen gas.
Even after 24 h heating, no clear supernatant was observed, which remained as brown with
black precipitate. This is possibly due to the formation of some Nickel-Gallium metal rich
clusters.
7.5.2 X-ray Powder Diffraction Analysis of NP4
Figure 7.12: Powder X-ray pattern of NP4. Reference data taken from ICSD No: 103860.
After scrupulous washings and drying under vacuum, the powder X-ray of this
material was measured. Figure 7.12 shows the powder pattern of NP4 nanoalloy. The XRD
pattern shows the formation of Ni2Ga3 phase and the reflections are closely matches with the
reported data (reference data was taken from ICSD No: 103860). The reflections are broad.
From the FWHM of all the observed and most intense reflections the average particle size of
this sample is calculated to be 6-9 nm, which are in the range of particles obtained for
aforementioned material NP1.
164
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
7.5.3 Transmission Electron Microscopic Analysis of the Particle’s Morphology
Figure 7.13: BFTEM of the material NP4 obtained according to Scheme 6.5. The material is
visibly nanocrystalline. EDX of NP4 is also shown on the image.
TEM measurements were conducted on the material NP4. The BF-TEM image shows that
(Figure 7.13) the material is nano crystalline like NP1, NP2 and NP3 samples. The Ni:Ga
ratio, measured by EDX of different selected areas of the material was determined to be
almost 1:1, 2:3 and 1:2 of Ni to Ga ratios within the accuracy of the method. One such
example is shown in Figure 7.13. The powder X-ray diffraction analysis of this sample
showed crystalline Ni2Ga3 phase. This sample might also contain amorphous solids which
are not detectable in the powder X-ray pattern as it is shown in Figure 7.12. Furthermore, the
metal analysis by AAS method shows an atomic weight percentage of Ni 32.54 wt. % and
Ga 59.52 wt. % which reveals the 1:1.5 or 2:3 ratio of Ni/Ga phase, which corresponds to the
expected phase Ni2Ga3.
7.5.4 Infrared Spectrum of Nanopowder (NP4)
The infrared spectrum of the sample NP4 was measured and showed that there is almost
no absorption bands present in the material as it is evidenced from the Figure 7.14. The IR
165
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
spectrum of NP4 is very much similar to the material NP1 where Ni2Ga3 is formed as the
Transmittance (%)
major crystalline phase.
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm )
Figure 7.14: Infrared spectrum of the nanopowder (NP3). The sample was measured as neat.
7.6 Synthesis of Intermetallic Ni3Ga Nanopowder (NP5)
7.6.1 Synthesis of NP5
3
Ni
+
GaCp*
Mesitylene
4bar H2
Ni3Ga
6 h, 150 oC
( NP5 )
Black material
Scheme 7.5: Preparation of Ni3Ga nanoalloy from hydrogenolysis reaction
Cohydrogenolysis of GaCp* and Ni(cod)2 in 1:3 molar ratio in mesitylene under 4 bar
H2 pressure at 150 C also leads to the formation of dark brown solution which gives a black
precipitate after heating for 30 min. It is further heated for complete decomposition of the
precursors until the formation of a clear supernatant which is presumably due to the
166
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
complete decomposition of the organometallic precursors. The typical preparative method is
shown in Scheme 7.5.
I(a.u)
7.6.2 X-ray Powder Diffraction Analysis of NP5
Ni3Ga
20
30
40
50
2
60
70
80
90
Figure 7.15: Powder X-ray diffraction of the sample (NP5). Reference data was taken from
ICSD: 103856.
The PXRD pattern of NP5 is shown in Figure 7.15. The diffraction pattern confirms
that the obtained powder NP5 consists of Ni3Ga nanoparticles closely matches with the
reported Ni3Ga phase (reference data taken from ICSD: 1038569). The PXRD diagram of
sample NP5 shows that there are three major broad reflections can be seen at 2θ (deg) =
43.65 (111), 50.57 (200) and 74.60 (220). The crystallite domain size of these nanoparticles
are calculated from (FWHM) the Scherrer’s equation and shown to be small nanoparticles
(2-4 nm) from the most intense reflections 43.65 (111) and 74.60 (220). The particle size is
quite smaller than those observed in case of NP3 and NP4 nanoparticles.
7.6.3 Infrared Spectrum of the Black Material (NP5)
The IR spectrum of NP5 black powder indicates that there are no significant
absorptions as it is observed for both NiGa and Ni2Ga3 nanoalloys (Figure 7.16). This
spectrum indicates that the sample is completely metallic powder without any organics
around it.
167
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Tranmisttance (%)
Chapter 7
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm )
Figure 7.16: Infrared spectrum of NP5 nanopowder. The sample was measured as neat.
7.6.4 TEM Characterization of NP5
Figure 7.17: BFTEM image (left) and FFT (top right) and HRTEM (bottom right) of the
sample (NP5).
The black material obtained from the Scheme 7.3 was further characterized using
TEM-EDX measurements. The high resolution TEM image of this sample shows a nano
crystalline material (Figure 7.17). Although the Ni to Ga ratios derived from the EDX
measurements on few selected areas shows different ratios, but one selected area in image
revealed an atomic weight percentage of Ni 46.63 wt. % and Ga 15.26 wt. %, which
168
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
corresponds to the Ni:Ga ratio of 3.05:1, means the stoichiometry of the material could be
assigned as Ni3.05Ga1. The EDX spectrum of NP5 is shown in Fig 7.18. The composition of
this material was further confirmed by the elemental analysis of the black material by
Atomic Absorption Spectroscopy. From the AAS analysis Ni and Ga atomic percentages
were found to be 64.16 wt. % and 27.28 wt. %, respectively. This ratio corresponds to the
Nickel-Gallium phase with 3:1.17 compositions.
L
i
N
500

k
i
N
400

Counts
L
a
G
300

200
k
a
G



k
a
G
k
ki
uN
C
100

0
2
4
6
8
Energy (keV)
10
12
Figure 7.18: Energy dispersive X-ray (EDX) spectrum of the sample NP5.
7.7
Synthesis and Characterization of the Colloidal Intermetallic NickelGallium Nanoparticles
The results described above show the formation of Nickel-Gallium nanoalloys using
the pyrolysis of organometallic precursors. In all the above cases there is no stabilizer is used
and the agglomeration of particles is observed. The interest then turned to synthesis and
stabilization of such nano Nickel-Gallium particles as colloids using external capping agents
such as hexadecylamine (HDA), dodecanethiol and PPO.
7.7.1 Intermetallic Ni-Ga Colloids from a Single Source Precursor [NiGaCp*(PMe3)3]
(NP6)
The hydrogenolysis reactions of [NiGaCp*(PMe3)3] in presence of an excess of
dodecanthiol or PPO were resulted in the formation of a black amorphous precipitates within
the reaction periods of 10-15 mints heating, instead of giving colloidal solution. These
results showed that dodecanthiol and PPO are not suitable capping agents to stabilize the
169
Chapter 7
Ni/Ga
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
nanoparticles.
Whereas,
the
hydrogenolysis
of
single
source
precursor
[NiGaCp*(PMe3)3] in presence of excess (1:5 equivalents) of hexadecylamine in n-decane
did not yield any precipitates under similar experimental conditions. After hydrogenolysis, a
dark brown colloid was obtained. The nano particles were precipitated as a dark brown paste
like material by using dry methanol as the non-solvent which was further purified by
repeated washings with the methanol followed by centrifugation. The typical synthetic
procedure for these colloids is shown in Scheme 7.6. The paste like dark brown-black
material can be easily dispersed into the dry toluene which is stable towards precipitation for
several days even after exposing to moisture and air. The colloidal samples dispersed in
toluene different concentrations are shown in Figure 7.20.
GaCp*
Me3P
Ni
PMe3
PMe3
n-Decane
4 bar H2
HDA
185 C
15 h
Ni/Ga /HDA colloids
(NP6)
Scheme 7.6: Hydrogenolysis of [NiGaCp*(PMe3)3] in n-decane as the solvent.
In addition, the stability of these colloidal nanoparticles was examined by allowing them to
expose normal atmospheric conditions and found to be stable until several days and no color
change has been observed, but prolonged exposure leads to the formation of a black material,
which would have occurred oxidation of the nanoparticles.
7.7.2 Infrared Spectrum of NP5
The infrared spectrum of the paste like material (dried sample) is shown in the Figure
7.19 which is very much informative (top spectrum is colloidal material and the bottom is
HDA alone). The NH region (3300 cm-1) as well as the other peaks are slightly broadened
and indicate that HDA is not free in the colloid and is attached to the particle surface in order
to stabilize them.
170
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Figure 7.19: The infrared spectrum of the paste like material NP6 (top spectrum refers to the
colloid and bottom refers to the free HDA).
Figure 7.20: Vials containing the diluted solutions of
Nickel-Gallium colloid in dry toluene. Left: slow
dispersion in toluene.
7.7.3 Transmission Electron Microscopic Analysis of the Particle’s Morphology
Figure 7.21 shows the high resolution TEM image of the colloidal nanoparticles.
Analysis of the TEM images of the colloid dispersed in dry toluene revealed the free
standing nanoparticles without a definite shape. Figure 7.21 also shows the EDX spectrum of
the colloid and confirms the presence of Ni and Ga including the carbon content as it is
expected from the presence of the surfactant HDA. Furthermore, EDX analysis measured on
few areas of the sample indicates the ratios of Ni to Ga are in 1:1.019, 1:1.037, 1:1.45 and
1:0.6. The average particle’s size is found to be in the range of 15-18 nm (if the particles are
assumed as spherical in nature).
171
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
Cu
3000
2500
C
Counts
2000
1500
1000
Ga
500
Ni
0
0

Ga
Si
2
4
6
8
10
Energy (kev)
Figure 7.21: High resolution TEM image of the Nickel-Gallium colloidal solution of NP5
dispersed in toluene (left) and EDX spectrum of one of the measurement (right).
7.7.4 Dynamic Light Scattering Analysis
In order to confirm the dispersion of the prepared Nickel-Gallium nanoparticles from
the hydrogenolysis of a single source precursor [NiGaCp*(PMe3)3] in presence of
hexadecyleamine (HDA) as the surfactant, dynamic light scattering (DLS) was performed on
a highly diluted toluene suspension of the Ni/Ga nanoparticles.
Figure 7.22: A volume percentage distribution plot from DLS analysis of nano particles
dispersed in toluene at room temperature. A He-Ne gas laser was used ( = 635nm).
172
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
The paste like brown-black colloid obtained according to the Scheme 6.7, is highly
dispersible in toluene. For the DLS analysis the morphology of the particles is assumed to be
spherical. DLS measurements provide the mean hydrodynamic radii of the particles
including the organic shell capping agent, by fitting the experimentally observed auto
correlation function to a theoretical function that contains the diffusion coefficient D and
radius r. The DLS analysis of this sample is shown in Figure 7.22 which depicts the number
size distribution of the colloid. The number size displays only one major peak with the
distribution of 15-40 nm size particles. These are found to be slightly larger then the same
observed from the TEM measurements. The absence of any other peaks in the distributions
of Figure 7.22, suggests that the absence of agglomeration upon dilution.
7.8 Catalytic Activity of Nano Intermetallic Compounds NiGa, Ni2Ga3
Ni3Ga and Hydrogenation of Olefin
7.8.1 Cyclohexene Hydrogenation
Catalysis is one of the most important chemical applications of metal nanoparticles
and has been extensively studied. The catalytic activity of similar intermetallic alloy Nickelalluminide (NiAl) is reported to be a versatile reducing system, capable of conveniently
effecting many interesting transformations as heterogeneous catalyst.
[28-30]
As discussed in
the previous sections, the palladium-gallium intermetallic alloys are promising materials as a
selective catalyst for the semi-hydrogenation of acetylene and exhibit much higher
selectivity and stability than for a commercial elemental Pd reference catalyst. [3, 4] With this
background and in order to shine some light into the catalytic activities of these NickelGallium nano intermetallic phases some preliminary test reactions were conducted. All these
intermetallic phases can be regarded as main-group metal doped Nickel alloys in the forms
of NiGa (1:1), Ni2Ga3 (2:3) and Ni3Ga (3:1) bimetallic solid phases. Such nanomaterials
could offer different material, electronic properties than the elemental Ni catalyst. Due to the
change in the composition; solid state structures can exhibit different catalytic sites. This
kind of materials may also act as promising catalysts to achieve selectivity as in the case of
nano structured Pd2Ga intermetallic phase. [4]
These nano intermetallic compounds were tested for the olefin hydrogenation reactions. A
simple olefin cyclohexene was taken as a test case to study the catalytic activity. The typical
reactions were carried out in a high pressure Young NMR tube under the H2 pressure in
toluene-d8 as the reaction medium. In every case the NMR tube was first charged with ~ 22
173
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
mol % of the catalyst (NiGa, Ni2Ga3 or Ni3Ga) followed by tol-d8. To this suspension,
cyclohexene was added in glove box. The resultant black suspension was pressurized with 5
bar H2 gas. After the desired reaction periods, this suspension was filtered to get a clear
aliquot on which 1H-NMR measurements were conducted. Interestingly, in all the cases
(NiGa, Ni2Ga3 and Ni3Ga) hydrogenation of cyclohexene to cyclohexane has occurred as
shown in Figures 7.23 to 7.26. The 1H-NMR spectra in tol-d8 exhibits a sharp singlet at δ;
1.40 ppm, which is in agreement with the literature data for cyclohexane. The relative
percentage conversion of cyclohexene to cyclohexane has shown highest for “NiGa” phase
(85 %). Whereas for other two phases it is found to be 73 % (for Ni2Ga3 phase) and 31 %
(for Ni3Ga phase). Although similar experimental conditions were applied, among these
three phases NiGa (1:1) alloy is found to be more suitable for the better conversion of
cyclohexene to cyclohexane.
7.8.2 Catalytic activity of Ni nanopowder
Ni
nanopowder
Tol-d8
5 bar H2
12h at rt
12h at 100  C
Yield : 95 %
Figure 7.23: 1H‐NMR spectrum of cyclohexene when Ni nanopowder is used. (Conversion of
cyclohexene to cyclohexane).
174
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
7.8.3 Catalytic activity of NiGa (NP3) nanopowder
NiGa
Tol-d8
5 bar H2
12h at rt
12h at 100 °C
85 %
conversion
Figure 7.24: 1H-NMR spectrum of the filtrate part obtained after hydrogenation of
cyclohexene (NiGa as the catalyst).
7.8.4 Catalytic Activity of Ni2Ga3 nanopowder (NP4)
Ni2Ga3
Tol-d8
5 bar H2
12h at rt
12h at 100 ° C
Figure 7.25:
1
Conversion
73 %
H-NMR spectrum of the filtrate part obtained after hydrogenation of
cyclohexene (Ni2Ga3 as the catalyst).
175
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
7.8.5 Catalytic activity of Ni3Ga nanopowder (NP5)
Ni3Ga
Tol-d8
5 bar H2
12h at rt
12h at 100 °C
Figure 7.26:
1
Conversion: 31 %
H-NMR spectrum of the filtrate part obtained after the hydrogenation of
cyclohexene (Ni3Ga as the catalyst).
176
Chapter 7
Organomet. syn. routes to Ni/Ga intermetallic nanoparticles
7.9
References
[1]
(a) J. H. Sinfelt, J. Catal. 1973, 29, 308-315. (b) J. H. Sinfelt, Bimetallic Catalysts:
Discoveries, Concepts and Applications; Wiley: New York, 1983. (c) R. Ferrando, J.
Jellinek, R. L. Johnston, Chem. Rev. 2008, 108(3), 847-910. (d) M. Fatmi, M. A.
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178
Chapter 8
Summary and outlook
Chapter 8
8.0 Summary and Outlook [k]
The major work of this thesis deals with the reactivity studies of the sterically bulky group
13 metal (I) NHC analogue, Ga(DDP) towards various organometallic fragments. Its
reactivity has been discussed in detail and synthesized novel main-group and transition metal
compounds with their complete characterization. The most remarkable result is the isolation
of low valent and highy sensitive “Ge4 and Ge2” clusters trapped by the stericaly
overcrowded Ga(DDP). In addition, few IPr supported titanium; zinc complexes are
synthesized and completely characterized. The reactivity difference of Ga(DDP) and IPr are
discussed due to the similarities between them. Furthermore, the soft chemical
organometallic synthetic routes for Nickel-Gallium nano intermetallic compounds are shown
using the low-valent GaCp* as the Ga source. According to the efforts made to achieve the
intended goals and objectives of the thesis, the following conclusions can be drawn from
every chapter discussed on the previous sections.
Chapter 2
Synthesis and Characterization of Heteroleptic Platinum-GaR (R = DDP, Cp*)
Complexes
This part of thesis describe the reactivity and coordination chemistry of gallium (I)
organyls GaCp* and Ga(DDP) towards various Pt(II) and Pd(II) organometallic fragments.
Four new compounds containing Pt–Ga bonds are synthesized and structurally characterized,
which shows that Ga(DDP) selectively inserts into the Pt–Cl bonds of olefin ligands
supported platinum dihalide complexes [(1,5-cod)PtCl2] and [(dcy)PtCl2] to afford
exclusively products 2 and 3. Interestingly, unlike the GaCp*, Ga(DDP) does not reduce the
Pt(II) centre and trap the Pt(0) species by substituting the olefin ligands even when we used
excess equivalents of Ga(DDP) in the reaction.[17] In contrast, the reaction of Ga(DDP) with
Pd(II) precursor yields Pd(0) as precipitate and the oxidized gallium(III) product
[(DDP)Ga(Me)(OTf)] (4) as a colorless solid. This kind of reactivity is in accordance with
the steric bulk of Ga(DDP), which hinders the efficient trapping of Pd(0) as
[Pd{Ga(DDP)}n], the weaker coordination properties of the hard triflate at the soft Pd in
comparison to Cl and the well-known over-all enhanced susceptibility of organometallic
179
Chapter 8
Summary and outlook
Pd(II) complexes for reduction to Pd(0) in comparison to Pt(II). Whereas the reaction of
[Pt(cod)2Cl2] with GaCp* affords highly metal rich cluster containing [PtGa5] in which a
transition metal (0) main group metal (III) connected as a Lewis acid-base adduct
[Cl3Ga·Pt(GaCp*)4] (6) where the GaCp* completely substitute the olefin ligands on the
platinum centre. This aspect illustrates the main reactivity differences between GaCp* and
sterically bulky Ga(DDP) in stabilization of metal rich molecular clusters. The ambivalent
reactivity of Ga(DDP), depending on the transition metal centre and the ancillary ligands, i.e.
coordination, insertion and reduction, may allow the synthesis of unusual transition metal
compounds and clusters as reported recently with main group elements. [13, 14]
Chapter 3
PP Bond Activation of P4 Tetrahedron by Ga(DDP): Reactivity and Coordination
Chemistry of [(DDP)Ga(P4)] with Metal Carbonyls Mo(CO)6 and Fe2(CO)9 [L]
The results described in this chapter are dealt with the reactivity of Ga(DDP) with the
white Phosphorus. These results highlight the low valent main-group metal mediated
activation of white phosphorus and the reactivity, coordination chemistry of the resulted
cluster [(DDP)Ga(P4)] (7). Activation of a single P-P bond in white phosphorus (P4) by
Ga(DDP) led to the isolation of molecular gallium-tetraphosphabicyclopentane (7) with open
access to the phosphorus core and also demonstrates that the 2e donor Ga(DDP) is capabale
of stabilizing the elements clusters similar to other group-13 metal (I) organyls AlCp* and
Al(DDP). The butterfly shaped P4 unit coordinated to the Ga(DDP) framework is the first
example of a single insertion of monovalent group 13 element at the P4 tetrahedron. Further
reaction of [(DDP)Ga(P4)] with excess of Mo(CO)6 affords 8 consisting of a heteronuclear
[Ga(η2:1:1-P4)Mo2] core, which is an example for a rare coordination mode observed for
metal supported P4 molecules. In addition the reactivity of 7 was also studied which results
in the formation of a novel coordination mode of phosphorus atoms towards the simple
carbonyl substitution from the metal carbonyls. Compound 7 is highly stable and unreactive
towards olefins phenylacetylene and styrene. In nutshell, these results demonstrate the power
of carbonyl substitution reactions using the novel main group cluster [(DDP)Ga(P4)].
Furthermore, compound 7 acts as a strong -donor as phosphines and N-heterocyclic
carbenes does.
180
Chapter 8
Summary and outlook
Chapter 4
Synthesis of Low Valent “Ge4” and “Ge2” Clusters Trapped by Low Valent Ga(DDP):
A -Bond Between two Ge–Ge Centers without a -Bond
The results presented here show the great synthetic potential of Ga(DDP) as a trapping
reagent for the stabilization of low valent small germanium fragments which are not very
common. Compounds 10 and 11 have a unique Ga2Gen (n =2 and 4) frameworks which are
readily formed by the reduction of L·GeCl2 with Ga(DDP), shows the particular bifunctional
properties of Ga(DDP) as selective reducing and coordinative trapping agent. This synthetic
procedure may serve as an efficient traping of more such naked atoms in the cluster core.
LIFDI mass spectroscopy was sucessfully applied for the analysis of these air and moisture
sentive germanium-gallium clusters and altogether this technique has served as a reliable
tool for their analysis. The quantum chemical cacluations on compound 11 resulted
fascinating elctronic and bonding detials. The reactivity and bonding modes of both NHC
and NHGa ligands are discussed and showed that NHCs exclusively prefers the terminal
coordination to metal centers (due to storong sigma character with weak pi character) rather
than bridging mode. Whereas the NHGa prefers the bridging mode due to the high prefencity
of both pi and sigma character. The bonding analysis of 11M clearly rules out an ionic
description of Ge2[Ga(DPP)]2 (11) and provides an evidence for the covalent Ge–Ga
bonding. The most striking feature of 11 is the important transannular (Ge–Ge) single bond
interaction. The main difference in the bonding situation of the four-membered cyclic
moieties between 11M and Si2(NAr)2[11] is the absence of π lone-pair donation into the
group-14 atoms of the former molecule. Thus, compound 11 represents an unusual example
of a bonding situation where two (heavier) main group atoms are bonded in  fashion
without an additional  bond between them. Compound 11 is found to be the first example
of a compound where a molecule exhibits a π bond between two atoms without a σ bond. [26,
27]
Chapter 5
Synthesis and Structural Characterization of Ga(DDP) Supported Ruthenium and
Copper Complexes: A Compound with a Perfect Linear Ga-Cu-Ga bond
The low-valent Ga(DDP) reacts with the ruthenium derivatives to form the corresponding
Ru–Ga(DDP) bonded species. These results demonstrate that two hydrido ligands can be
181
Chapter 8
Summary and outlook
exchanged by Ga(DDP), which prefers a bridging coordination over the terminal
coordination to stabilize two Cp*Ru units as shown in compound 12. Furthermore, these
results shows that unlike GaCp* which yields gallium rich ruthenium complexes, the
sterically over crowded Ga(DDP) favor the substitution, rearrangement reactions to afford
stable products. The different reactivity aspects of Ga(DDP) with GaCp* are highlighted
toward the ruthenium and copper precursors. In addition reduction of copper (II) triflate
with an excess of Ga(DDP) affords the first copper(I) cationic complex 14 supported by a
main group metalloid ligand. Trifflate group is found to act as a non-coordinating species in
the formation of the complex. Compound 14 represents a first isolated compound with a
perfectly linear Ga-Cu-Ga bond where the d10 copper (I) centre is stabilized by two sterically
over crowded group 13 metal NHC analogue. Noteworthy, the cationic part of 14 can be
regarded as isostructural to N-heterocycylic carbene (NHC, NHC = N, N’-bis-(aryl)
imidazol-2-ylidene) stabilized copper (I) cationic complexes, [NHC-Cu-NHC]+[Anion]which are known to be potential catalysts for the hydrosilylation, carbonylation and coupling
reactions.[39]
Chapter 6
Sterically Bulky N-heterocyclic Carbene Complexes of ZnCl2 and TiX4 (X = F, Cl):
Syntheses, Characterization and Reactivity
The sterically pronounced N-heterocyclic carbene (IPr) smoothly reacts with the titanium
tetra halides and zinc (II) species (ZX2, X = Cl, Me) to give the respective mono and bis
metal-carbene adducts 15-20 which are structurally characterized. Although Ga(DDP) and
IPr has almost similar steric and electronic situation, but reactivity behavior of Ga(DDP) and
IPr are distinctly different, and showed that the former one undergoes insertion reactions
between the metal-halide or MC bonds due to its redox activity, whereas the IPr does not
give such insertion products instead it stabilizes the same species as N-heterocyclic carbene
adducts. These studies showed that the newly isolated N-heterocyclic carbene adduct
[IPr·TiCl4] undergoes carbene and chlorido transfer to the zinc center to afford another new
mono zinc-carbene adduct [IPr·ZnCl2]. Furthermore, the attempted reactions to isolate Nheterocyclic carbene (IPr) stabilized clusters or new organometallic complexes of titanium
and zinc metals were not successful at the given experimental conditions.
182
Chapter 8
Summary and outlook
Chapter 7
Organometallic Synthesis of Nickel-Gallium Binary Intermetallic Nanoparticles
A novel non-aqueous organometallic preparation of Nickel-Gallium nanoparticles is
presented, which is based on the co-hydrogenolysis of respective organometllic precursors in
mesitylene or n-decane solution at higher temperatures under the H2 pressure. The
preparative procedures employed in the present work for the intermetallic phases NiGa (1:1)
and Ni3Ga (3:1) are very much reliable to achieve almost pure crystalline composition as
nanointermetallics which is indicated by analytical techniques such as XRD, TEM-EDX and
AAS analysis. Whereas in case of Ni2Ga3 phase, although the powder X-ray pattern shows
the only crystalline phase but the EDX analysis of Ni to Ga ratios suggests the presence of
other phases in the material, which are not crystalline. In addition, both synthetic procedures
employed for the preparation of Ni2Ga3 phase were found not suitable to get phase pure
material. Furthermore, hexadecylamine was found to be a suitable surfactant than PPO and
dodecanthiol for the stabilization of Nickel-Gallium nanoparticles as colloids. In addition,
preliminary studies on the use of these series of nano intermetallics as heterogeneous
catalysts provided some insights that these materials could act as catalysts and showed that
the olefin (cyclohexene) undergos hydrogenation in presence of NiGa, Ni2Ga3 (impure) and
Ni3Ga nano intermetallic phases. In addition, in case of NiGa more conversion had observed
than the other two phases when similar experimental conditions were employed. However,
the presence of Nickel nanoparticles can’t be excluded because these materials may contain
the elemental nickel nanoparticles which also might be responsible for the conversion.
Outlook
It was shown that sterically over-crowded Ga(DDP) is a potent ligand to trap reactive
intermediates. In this context, the most interesting results are the isolation of low-valent,
Gen[Ga(DDP)]2 (n = 2 and 4) compounds. Among these two small clusters, the dimer (Ge2
cluster) possesses an entirely novel bonding mode and structure and is the first molecule to
be reported. Thus, similar synthetic strategy can be applied to reduce other group 13 and 14
metal salts with KC8 or with other mild reducing agents in presence of Ga(DDP) as well as
GaCp* which may result novel clusters. Such reactions can be monitored by LIFDI MS
analysis, which is proven to be a reliable analytical method to analyze sensitive clusters in
situ. Similar synthetic strategy can further be applied to the reduction of transition metal
183
Chapter 8
Summary and outlook
salts. Furthermore, more efforts should be devoted for the NHC stabilized transition metal
clusters by systematic studies not only from the reduction of NHC supported transition or
main-group metal salts but also reduction of few selected metal salts in presence of NHC
ligands. From the present studies, it can be concluded that it is advisable to use simple,
sterically not over crowded NHCs instead of using sterically bulky NHC ligands (like IPr
etc) as the steric bulk sometimes may not be favorable to isolate metal clusters due to the
effect of cone angle at the ligating center.
In case of nanoparticle work, these results encourage further research in the direction
of in-depth understanding of formation of the intermetallic phases and their material
properties such as magnetic property, which would help us to find out whether or not the
presence of extra elemental nickel nanoparticles could have also possibly responsible for the
catalytic activity. The catalytic activity of these nanoalloys shed light on the future
perspectives of in-depth understanding of these nano intermetallic phases to achieve more
selectivity in the functional group conversions or selective hydrogenation of mixture of
unsaturated substrates as it is shown for the similar group 13 metal containing alloys such as
Ni-Al or PdGa nanoalloy. In addition, experiments should be carried out by loading lower
amounts of catalyst and conduct the same experiments. Future work should also examine the
mechanic studies addressing the facts like how these bimetallic nanoparticles are working as
catalysts.
[k]
References are given according to their individual chapter´s references.
184
Chapter 9
Experimental section
Chapter 9
9. Experimental Section
This section summarizes the general working procedures used during the
experimental part of this dissertation work. It gives a brief description of the analytical
methods and instruments used for analyzing all new compounds and materials prepared. The
detailed synthetic procedures of the new complexes developed in this work are also
presented in this section.
9.1 Materials and Methods
9.1.1 General Remarks
Figure 9.1: Fischer-porter vessel used for high pressure hydrogenolysis reactions (left). High
pressure Young NMR tubes used for the hydrogenolysis reactions (right) as well as to
analyze the highly sensitive compounds.
All chemical reactions and experimental manipulations mentioned for this thesis work were
performed using standard Schlenk, vacuum-line and glove box techniques (Ar atmosphere;
H2O and O2 content < 1 ppm). In this method, the Argon gas was purified by passing
through molecular sieves and an activated copper catalyst. The Schlenk tubes used were
flame dried and the SiOH surfaces of the glass vessels were silylated by thoroughly
washing with boiling 1,1,1,3,3,3-hexamethyldisilaazane (99%) and subsequent evaporation
under vacuum to complete remove the traces of rhe silylation reagent. Reaction solvents
185
Chapter 9
Experimental section
such as cyclohexane, n-heptane, 1,4-dioxane, n-decane, mesitylene, dichloromethane and
fluorobenzene were dried by passing through a Schlenk frit filled with activated alumina
(chromatography grade, Merck) under Argon atmosphere. Alcoholic solvents such as
Methanol, ethanol were first refluxed over P2O5 followed by distillation. High boiling
solvents diglyme, mesitylene were dried over activated molecular sieve (3 Å) and degassed
several times. All other solvents used (toluene, THF, n-pentane, diethyl ether, n-hexane)
were dried, degassed and argon saturated by using a continuous solvent purification system
(MBraun; H2O content: ~ 1 ppm). The H2O content in all these purified reaction solvents
were checked using the Karl Fischer titration and made sure that the H2O content is
approximately below 10 ppm in each case. Low temperature experiments were conducted in
Dewar flasks using acetone/dry ice or isopropanol/dry ice baths at the desired temperatures.
9.2
Instrumental Details
9.2.1 Infrared Spectroscopy (IR)
Infrared spectra were measured using a Brukar Alpha-P FTIR spectrometer under
inert argon atmosphere in a glove box with ATR (Attenuated Total Reflectance).
9.2.2 Elemental Analysis and Atomic Absorption Spectroscopy (AAS)
Elemental analyses of the samples were measured at the Laboratory of Microanalysis
of the Ruhr University Bochum (CHNSO: Vario EL by Elementar Hanau; AAS: AAS 6
vario by Analytik Jena). The analysis for the metal content of Ga, Ni and Pt were undertaken
using a Vario 6 AAS instrument. The samples were dissolved in aqua regia or HCl and
H2SO4.
9.2.3 Nuclear Magnetic Resonance Spectroscopy (NMR) [1]
NMR spectra were recorded on a Bruker Avance DPX-250 spectrometer (1H,
250MHz;
13
C, 62.9 MHZ;
19
F, 235.3 MHz;
31
P, 101.3 MHz) and DRX 600MHz at Ruhr
University Bochum at 298K. Chemical shifts,  are described in parts per million (ppm),
downfield shifted from TMS, and are consecutively reported as position (δH or δC), relative
integral, multiplicity (s = singlet, d = doublet, sept = septet, m = multiplet, br =broad),
coupling constant (J in Hz), and assignment. Chemical shifts are given relative to
tetramethylsilane (TMS) and were referenced to the solvent resonances as internal standards.
186
Chapter 9
Experimental section
All the NMR spectra were analyzed using the software Mestric (version 4.7.0.0) or
MestReNova (version: 6.2.1-7569).
Solid State Nuclear Magnetic Resonance
The solid state MAS-NMR measurements were recorded by Mr. H. J. Hauswald on a
Bruker DSX 400 spectrometer with a magnetic field of 9 T. The samples were prepared in
2.5 and 4 mm ZrO2 rotors at 104.2 MHz (27Al) with a rotation frequency of 20 kHz, unless
otherwise stated.
9.2.4 UV / Vis Spectroscopy
UV/Vis spectra were measured on a Perkin-Elmer Lambda 9 UV/Vis/NIR
spectrophotometer.
9.2.5 Photoluminescence
The photoluminescence measurements were performed with a Jobin Yvon-Spex
FluoroMax2 Spectrometer.
9.2.6 Single Crystal X-Ray Diffraction
Single crystal X-ray diffraction studies were conducted using the instrument “Oxford
Xcalibur2 CCD/PD diffractometer using Mo-Kα radation (λ = 0.7107)”. The crystals used
were immediately coated with a perfluoropolyether, picked up with a glass fiber by seeing
under microscope, and immediately mounted in the cooled N2 stream of the diffractometer.
Absorption corrections were carried out semi-empirically using sadabs. The crystal
structures were solved by direct methods using SHELXS-97
97.
[3]
[2]
and refined with SHELXL-
Disordered solvent were removed from the diffraction data with the SQUEEZE
routine PLATON 1.13.
[4, 5]
For the detailed crystallographic data see the supplementary
section. All refinements were performed with the Full-matrix least-squares on F2 method
and all non hydrogen atoms were refined anisotropically.
9.2.7 Mass Spectroscopy (MS)
Mass spectra of few samples were measured on a Joel AccuTOF GCv spectrometer.
For few sensitive compounds LIFDI MS mass was used. Ionization method: LIFDI (Liquid
Injection Field Desorption Ionization). All mass spectra were analyzed using the
187
Chapter 9
Experimental section
MestRenova software programme. This is a very reliable MS technique through which
highly sensitive organometallic complexes cane be analyzed. In this method, a sample in
solution is aspirated into the spectrometer through a thin, fused silica capillary column. The,
the samples are deposited on the Field Desorption emitter for the analysis. Since the solid
samples are introduced as liquids (dissolved in a dry solvent such as toluene, THF) through a
capillary, this technique is called LIFDI-MS (Liquid Injection Field Desorption Ionization).
[6]
In all the cases dry toluene or THF has been used as the solvent for the desolution of the
sensitive complexes. The samples were prepared in glove box for the MS measurements and
immediately measured after taken out from the glove box.
9.2.8 Melting Point Measurements
The melting points of the compounds synthesized were measured in sealed capillaries
on Büchi (530) capillary apparatus and are reported uncorrected.
9.2.9 Working Procedure
The working procedure with the chemicals was developed according to the valid
legislation (in agreement with the dangerous material regulation). All the resulting work was
performed using appropriate protective clothing available in the laboratory. The used
solvents were collected in a properly labeled solvent waste can. The used Al2O3 and syringes
and needles were likewise added to the solid wastes in canisters.
9.2.10 X-Ray Powder Diffraction
X-ray powder diffraction method is a powerfull tool to analyze the crystalinity of
solid materials. This technique allows a phase analysis, lattice parameters. [4, 5, 6] Substance
identification can be analyzed by comparision with already reported plethora of compounds
deposited in the data base as ICSD or JCPDS. The principle behind this technique is based
on the irradiation of a powder (crystalline) by monochromatic X-ray photons and subsequent
elastic scattering of the photons as depicted in the Figure 9.2. The diffraction angles are
dependent on the material and are charactericstic of each crystalline plane. This relation is
described by Bragg´s Law. In Bragg equation, d is the distance between two lattice planes
(shown in the Eq. 9.1),  is the angle between the reflected lattice planes and λ refers to the
wavelength.
188
Chapter 9
Experimental section
n  = 2 d sin Equation 9.1: Bragg´s equation
Figure 9.2: Schematic illustration of Bragg´s diffraction of the X-rays on a plane of a
crystalline material.
Furthermore, the crystallite size can be roughly measured accordging to the Scherrer
equation (Equation 9.1), indicates the relfection width to the crystallite size.In Scherrer
equation “D” refers to the average crystallite size, K is a constant (for spherical shaped
particles it is considered as K ~ 1) and λ is the X-ray wavelength, β is the full width at half
maximum of a reflection and θ refers to the position of the reflection
D = /  Cos (
Equation 9.2: Scherrer equation
9.2.11 Instrument Specifications
The powder X-ray data for all the samples were measured on a D8-Advance-BrukerAXS-diffractometer (Cu-Kα-radiation: 1.54178 Å, scan step: 0.0141° 2θ, heating current: 30
mA, in Bragg-Brentano θ-2θ-geometry, using a Göbel mirror as monochromator and a
position sensitive detector. All the powder samples were prepared using the Lindemancapillaries in the glove box (diameter: 0.5, 0.7 or 1.0 mm). These were flame-sealed for the
measurements. The detector was calibrated to the reflections of crystalline α-Al2O3.
Measurements were done to collect the 2 range of 10-90.
9.2.12 Transmission Electron Microscopy (TEM) [7, 8]
189
Chapter 9
Experimental section
All the HR-TEM (High resolution TEM) measurements were carried out by Mr.
Christian Wiktor at University of Antwerp, Belgeium and all the TEM samples were
prepared as diluted solutions or suspensions in toluene and deposited on carbon coated
copper grids. BFTEM images were acquired on a Philips CM30 equipped with a Schottky
field emission source operated at 300 kV. Bright-field transmission electron microscopy
(TEM) and energy dispersive x-ray spectroscopy were carried out on a Philips CM20
microscope operated at 200 kV acceleration voltage. BFTEM and HRTEM images and
energy dispersive x-ray spectra were acquired on a Tecnai G2 microscope equipped with a
field-emission gun operated at 200 kV. Bright-field transmission electron microscopy (TEM)
and energy dispersive X-ray spectroscopy were carried out on a Hitachi H-8100 microscope
operated at 200 kV acceleration voltage.
9.2.13 Dynamic Light Scattering (DLS)
DLS is a very reliable technique through which the particle size distribution profle can
be calculated for a colloid or suspension dissolved in a solvent or polymer. This gives how
the particles are distributed in a given solution. The DLS measurements were made for few
samples on the fixed scattering angle Zetasizer Nano-S system (Malvern, UK) with a He-Ne
gas laser which has wavelength of λ = 635 nm. Typically, the samples were measured in
small cuvettes using highly diluted solutions (toluene was used for these measurements).The
Zetasizer Nano software was used for analyzed the obtained data.
9.3
Syntheses of Starting Materials
The syntheses of the starting compounds were performed using commercial available basis
chemicals. Thus, Ni(acac)2, DIBAH (Diisobutyl aluminum hydride), TiF4, TiCl4, ZnMe2,
ZnCl2, Cu(OTf), white P4, Potassium graphite (KC8), 2,6-Diisopropylaniline, 2,4pentanedione, gallium and [(dcy)PtCl2] are used as received without any further purification.
All other starting materials used in this study were synthesized accordingly to their literature
reported procedures with or without slightly modified methods.
Ga(DDP)[9]
[(1,5-cod)PtCl2][10]
[(1,5-cod)Pd(Me)(OTf)] [11]
[(IPr)GeCl2] [12]
190
Chapter 9
Experimental section
KC8 [13]
[(PCy3)GeCl2]
Cu(OTf)2.4CH3CN [14]
IPr (IPr = :C{[N(2,6-iPr2C6H3)]CH}2]) [15]
[Cp*Ru(μ-H)2]2 [16]
[(η6-p-cymene)RuCl2]2 [17]
[Ni(cod)2] [18]
[Ni(GaCp*)(PMe3)3] [19]
[Ni(GaCp*)3(PCy3)] [19]
GaCp* [20, 21]
9.4 Syntheses of Compounds 1-21
9.4.1 Synthesis of Ga(DDP) (1)
Although the synthesis of Ga(DDP) was reported by Power and co-workers but a slightly
modified synthetic procedure has been used for the synthesis of Ga(DDP) which was used
for this work. [9]
Synthesis of K(DDP):
Step 1
A big Schlenk tube was charged with H{(NDippCMe)2CH}[22] (20.50 g, 48.96 mmol) and
KH (2.55 g, 63.62 mmol). To this THF (170 mL) was added .The reaction mixture was
heated at reflux for 12h, and then filtered to remove the excess KH. The clear yellow filtrate
part was completely evaporated to remove the solvent and quickly washed with n-hexane
and dried under vacuum over night to get K(DDP) as a pale yellow solid. Yield obtained;
21.5 g (96% with respect to H{(NDippCMe)2CH}). The purity of this starting material is
sufficiently enough for the next step.
1
H-NMR (C6D6, 250 MHz): δ =7.19-7.17 (m, 4H, Ar CH), 7.08-7.02 (m, 2H, Ar-CH), 4.83
(s, 1H, γ-CH), 3.37 (sept, 4H, 3JH-H = 6.8Hz, CH(Me)2), 1.90 (s, 6H, CH(Me)2), 1.27 (d,
12H, 3JH-H = 6.9 Hz, CH3), 1.10 (d, 12H, 3JH-H = 6.8 Hz , CH(Me)2).
191
Chapter 9
Experimental section
Elemental analysis for C29H41N2K (M.W = 456.747 g/ mol); Calcd: C 76.25, H 9.04 and N
6.13, Found: C 76.75, H 8.74 and N 5.92.
Step 2:
Synthesis of GaI: A well flame dried Schlenk tube was charged with Ga (1.53 g, 21.9
mmol) and I2 (2.78 g, 21.9 mmol), dried for 5 mints under vacuum. Toluene (90 mL) was
added and the resultant suspension was sonicated under Ar atmosphere for 2h. During this
period, it gives “GaI” as a pale green suspension in toluene. [23]
Step 2:
K(DDP) ( 10.0g, 21.89 mmol) was added to the above “GaI” suspension in toluene (step 2)
in the glove box and stirred the reaction mixture for 3 days at room temperature. Then it was
filtered to get a brown-yellow filtrate (precipitate should be washed with toluene (3 x 20 mL)
for better yields). The resultant filtrate part was concentrated to 20 mL and stored in
refrigerator at - 30 C over night. The yellow block like crystals formed were quickly
washed with cold n-hexane and dried under vacuum to get Ga(DDP) as a crystalline
substance. Yield; 4.97 g (46% with respect to K(DDP)). Analytical data: 1H and 13C-NMR in
C6D6 matches with composition. [9]
9.4.2 Preparation of [(cod)(Cl)Pt{ClGa(DDP)}] (2)
To a stirred suspension of [(1,5-cod)PtCl2] (0.05 g, 0.133 mmol) in toluene (2 mL),
Ga(DDP) ( 0.065 g, 0.133 mmol) was added at room temperature. In few minutes the pale
yellow slurry became orange then to brown. The resultant reaction mixture was stirred for
24h and then filtered to remove the black solid. The filtrate was concentrated to half of its
volume and stored at - 30 C for one week to afford pale yellow needles of 2. These crystals
were filtered and quickly washed with n-hexane (2 x 2 mL) and dried in vacuo. Yield: 43%
(0.05 g, based on [(1,5-cod)PtCl2]). M. p: > 185 C (decomp).
1
H-NMR(C6D6, 250.1 MHz, ppm): δ = 7.16 - 7.14 (m, 6H, phenyl), 5.57 - 5.47 (m, 3JPt-H =
10 Hz, 2H, H-C=C, COD ), 4.94 (s, 1H, CH , Ga(DDP)), 4.66 - 4.36 (m, 3JPt-H = 35 Hz, 2H,
H-C=C, cod), 3.94 - 3.75 ( m, 4H, merged with each other CH(CH3)2), 1.62 (s, 6H, CH3),
1.58 - 1.52 (m, 12H, merged with CH(CH3)2 and 2H from H-C-C, cod) 1.34 - 1.27 (m, 4H,
H-C-C, cod), 1.23 (d, 3JH-H = 7 Hz, 6H, CH(CH3)2), merged with 2H from H-C-C, cod), 1.14
(d, 3JH-H = 6.5 Hz, 6H, CH(CH3)2).
192
Chapter 9
13
Experimental section
C-NMR (C6D6, 62.8952MHz): δ = 169.6 (C=N), 145.3 (C(Dipp)-N), 145.1 (C(Dipp)-N,
Dipp = 2, 6-diisopropylphenyl), 142.2 (o-C(Dipp)), 127.3 (m-C(Dipp)), 125.0 (m-C(Dipp)),
124.6 (p-C(Dipp)), 124.3 (p-C(Dipp)), 99.4 (γ-C), 77.6 (C=C; cod), 32.1 (C-C, cod], 28.8
(CHMe2), 28.5 (CHMe2), 26.5 (CMe), 25.8 (CMe), 25.2 (CHMe2), 25.1 (CHMe2), 25.0
(CHMe2), 24.1 (CHMe2) ppm.
IR (, cm-1): 2938(m), 2844(w), 1517(vs), 1449(m), 1424(m), 1371(vs), 1348(m), 1304(vs),
1252(m), 1242(s), 1165(s), 1091(w), 1048(w), 1010(s), 990(w), 931(w), 856(s), 787(vs),
749(vs), 703(w), 524(w), 437(s).
Anal. Calcd (%) for C37H53N2Cl2GaPt (861.53 g/mol): C, 51.58; H, 6.20; N, 3.25; found: C,
51.15; H, 6.67; N, 4.25.
9.4.3 Preparation of [(dcy)(Cl)Pt{ClGa(DDP)}] (3)
To a stirred solution of [(dcy)PtCl2] (0.08 g, 0.20 mmol) in toluene (4 mL), Ga(DDP) (0.097
g, 0.20 mmol) was added at room temperature. The colour of the reaction mixture turns pale
yellow to brown. The resultant reaction mixture was stirred for 20h and then filtered to
remove the insoluble black solid. The filtrate was concentrated to 2 mL and stored to - 30 C
for one week to afford pale yellow crystalline substance. Crystals formed were filtered,
quickly washed with n-hexane (2 x 3 mL) and dried in vacuum. Yield: 28% (0.05 g, based
on [(dcy)PtCl2]). M. p: > 180 C (decomp).
1
H-NMR (d8-THF, 600.13MHz): δ = 7.92 - 7.83 (m, 3JPt-H = 27 Hz, 1H, H-C4, dcy), 7.22 -
7.14 (m, 6H, aromatic protons, Ga(DDP)), 6.19 (br, 1H, H-C3, dcy), 5.15 (s, 1H, methine,
Ga(DDP)), 4.87 (m, 1H, H-C1, dcy), 4.10 - 4.23 (m, 1H from H-C4, and 1H from H-C34),
3.93 (sept, 1H, 3JH-H = 7 Hz, H-C37), 3.49 (sept, 1H, 3JH-H = 6.8 Hz, H-C18, Ga(DDP)), 3.34 3.38 (m, 1H from H-C9 and 1H from H-C29), 3.28 (br, 1H, H-C7, dcy), 2.86 (br, 1H, H-C6,
dcy), 2.59 - 2.62 (br, 1H, H-C8, dcy), 1.81 - 1.86 (m, 2H, H-C5, dcy), 1.77 (s, 3H, CH3, HC15, Ga(DDP)), 1.74 (s, 3H, H-C14, Ga(DDP)), 1.71 - 1.73 (m, 2H, H-C10, dcy), 1.59 (d, 3H,
3
JH-H = 6 Hz, H-C35, Ga(DDP)), 1.56 (d, 3H, 3JH-H = 6.4 Hz, H-C34, CHCH3), 1.32 (d, 3H, 3JH-
H
= 7 Hz, H-C39, CHCH3), 1.30 (d, 3H, 3JH-H = 6 Hz, H-C38, CHCH3), 1.23 (d, 3H, 3JH-H =
6.7 Hz, H-C17, CHCH3), 1.20 (d, 3H, 3JH-H = 7.4 Hz, H-C16, CHCH3), 1.12 (d, 3H, 3JH-H = 6
Hz, H-C26, CHCH3), 1.07 (d, 3H, 3JH-H = 6.5 Hz, H-C27, CHCH3) ppm.
193
Chapter 9
13
Experimental section
C-NMR (d8-THF, 150.90 MHz): δ = 170.9(C13-N, DDP), 170.7(C11-N, DDP),
146.3(C28(Dipp)-N), 146.1(C24(Dipp)-N), 145.6(o-C33(Dipp)), 145.4(o-C23(Dipp)), 142.6(oC29(Dipp)), 141.9(o-C19(Dipp)), 139.4(C4=C, dcy), 132.6(C3=C, dcy), 127.9(p-C31(Dipp)),
127.7(o-C21(Dipp)), 125.2(m-C30(Dipp)), 125.0(m-C32(Dipp)), 124.9(m-C22(Dipp)), 124.8
(m-C20(Dipp)), 100.4(γ-C12, Ga(DDP)), 85.2(C1=C, dcy), 83.2(C2=C, dcy), 59.1(C5, dcy),
57.5(C9, dcy), 52.7(C7, dcy), 48.0(C6, dcy), 43.5(C8, dcy), 33.8(C10-C=C, dcy),
29.6(C34H(CH3)2),
29.5(C37H(CH3)2),
29.4(C18H(CH3)2),
28.8(C25H(CH3)2),
27.8(C35H(CH3)2),
26.8(C36H(CH3)2),
25.7(C39H(CH3)2),
25.6(C38H(CH3)2),
25.4(C17H(CH3)2), 25.3(C16H(CH3)2), 25.2(C26H(CH3)2), 24.8(C27H(CH3)2, 24.6(C15-C),
24.3(C14-C) ppm.
IR (, cm-1, neat): 2939(s), 2901(w), 1517(vs), 1449(w), 1426(s), 1371(vs), 1305(vs),
1251(s), 1167(s), 1010(s), 929(s), 857(s),790(vs), 753(s), 728(vs).
Anal. Calcd (%) for C39H53Cl2N2GaPt (885.58 g/mol): C, 52.90; H, 6.03; N, 3.16; found: C,
53.50; H, 6.45; N, 2.93.
9.4.4 Synthesis of [(DDP)Ga(Me)(OTf)] (4)
Ga(DDP) (0.09 g, 0.184 mmol) in toluene (1 mL) was added to a Schlenk tube containing
[(cod)Pd(Me)(OTf)] (0.07 g, 0.184 mmol) in fluorobenzene (3 mL) at - 40 C. The resultant
reaction mixture was immediately turned to dark brown with formation of a grey-black solid.
It was slowly warmed to room temperature over a period of 30 min and stirred for another 30
min. The grey-black precipitate formed was filtered off and the filtrate was completely
evaporated under reduced pressure, dissolved in toluene (2 mL) and stored at - 30 C.
Colourless crystals formed in 3 days were filtered, quickly washed with n-hexane (2 x 4 mL)
and dried in vacuo. Yield: 33% (0.04 g, based on [(cod)Pd(Me)(OTf)] ). M.p: 169-171 C.
1
H-NMR (C6D6, 250 MHz): δ = 7.15 - 7.00 (m, 6H, Ar CH), 5.16 (s, 1H, γ-CH), 3.84 (broad,
2H, CH(Me)2), 2.84 (broad, 2H, CH(Me)2), 1.57 (s, 6H, CH3), 1.34 - 1.32 (broad, 12H,
CH(Me)2), 1.07-0.98 (broad, 12H, CH(Me)2), -0.46 (s, 3H, Ga-CH3) ppm.
13
C-NMR (C6D6, 62.8952 MHz) : δ = 172.1 (C=N), 146.4 (C(Dipp)-N), 145.4 (C(Dipp)-N),
143.1 (o-C(Dipp)), 139.2 (o-C(Dipp)), 124.1 (m-C(Dipp)), 125.5 (p-C(Dipp)), 100.7 (γ-C),
28.7 (CHMe2), 27.4 (CHMe2), 25.2 (CMe), 24.5 (CMe), 23.6 (CHMe2), -13.8 (Ga-CH3) ppm.
The 13C-NMR resonance of the triflate group could not be detected.
194
Chapter 9
Experimental section
IR (, cm-1): 2940(s), 2906(vw), 1507(vs), 1450(w), 1428(w), 1364(vs), 1335(w), 1306(vw),
1280(w), 1250(s), 1226(vs), 1193(vs), 1174(vs), 1090)w), 1013(vs), 994(vs), 938(w),
867(vw), 794(vs), 754(s), 624(vs), 514(vw), 497(vw), 447(w).
Anal. Calcd (%) for C31H44F3GaN2O3S (651.4862 g/mol). C, 57.15; H, 6.81; N, 4.30; S,
4.92; found: C, 55.91; H, 6.87; N, 4.03; S, 7.29.
9.4.5 Preparation of [(cod)(CH3)Pt{CH3Ga(DDP)}] (5)
To a stirred suspension of [(1,5-cod)Pt(CH3)2] (0.10 g, 0.290 mmol) in toluene (3 mL),
Ga(DDP) ( 0.146 g, 0.290 mmol) was added as such at room temperature. In few minutes the
pale yellow suspension became orange then to brown. The resultant reaction mixture was
stirred for 20h and then filtered to remove the black solid. The filtrate was concentrated to
half of its volume and stored at - 30 C for one week to afford pale yellow needles of 5.
These crystals were filtered and quickly washed with n-hexane (2 x 2 mL) and dried in
vacuum. Yield: 48% (0.120 g, based on [(1,5-cod)PtMe2]). M. p: > 177 C (decomp).
1
H-NMR(C6D6, 250.1 MHz, ppm): δ = 7.19 - 7.15 (m, 6H, phenyl), 5.47 - 5.35 (m, 3JPt-H =
13 Hz, 2H, H-C=C, COD ), 4.71 (s, 1H, -CH , Ga(DDP)), 4.43 - 4.21 (m, 3JPt-H = 26 Hz,
1H, H-C=C, COD), 4.01 (sept, 2H, 3JH-H = 6.3 Hz, 6H, CH(CH3)2, partially merged with one
COD protons), 3.81-3.78 (m, 1H, COD), 3.62-3.53 (m, 1H, COD, partially merged with
CH(CH3)2), 3.43 (sept, 2H, 3JH-H = 6.7 Hz, 6H, CH(CH3)2), 2.19-1.73 (m, COD), 1.61 (s, 6H,
CH3), 1.47-1.27 (m, 12H, CH(CH3)2 protons), 1.19 (d, 12H, 3JH-H = 7.1 Hz, CH(CH3)2
protons), 0.29 (s, 3H, PtMe), -0.31 (s, 3H, GaMe).
13
C-NMR (C6D6, 62.8952MHz): δ = 167.9 (C=N), 145.1(C(Dipp)-N), 144.2 (C(Dipp)-N,
Dipp = 2, 6-diisopropylphenyl), 143.28 (o-C(Dipp)), 143.0(o-C(Dipp)), 126.7 (m-C(Dipp)),
124.7 (m-C(Dipp)), 124.5 (p-C(Dipp)), 124.3 (p-C(Dipp)), 118.1 (p-C(Dipp), 97.9 (γ-CH),
84.2 (C=C; COD), 73.4 (C=C; COD), 32.1 (C-C, COD), 32.6 (C-C, COD), 28.4 (CHMe2),
28.2 (CHMe2), 27.2 (CMe), 26.2 (CMe), 25.9 (CHMe2), 25.6 (CHMe2), 25.4 (CHMe2), 24.9
(CHMe2), 24.7 (CHMe2), 24.1 (CHMe2), 23.6 (CHMe2), -10.1 (Ga-Me) ppm.
Anal. Calcd (%) for C39H59GaN2Pt (820.700 g/mol): C, 57.05; H, 7.24; N, 3.41; found: C,
57.43; H, 7.19; N, 3.31.
AAS; calcd (%); Ga 8.49 wt. %: found 8.88 wt. %.
195
Chapter 9
Experimental section
9.4.6 Preparation of [(Cl3Ga)Pt(GaCp*)4] (6)
To a stirred white slurry of [Pt(1,5-cod)Cl2] (0.05 g, 0.133 mmol) in toluene (4 mL), GaCp*
(0.160 g, 0.800 mmol) was added over a period of 5 min. Immediately the color of the
reaction mixture was changed to dark orange suspension and after its complete addition a
clear orange solution formed. It was continued further for 7 h. All the volatiles were
removed under reduced pressure; resultant oily mass was dissolved in minimum amount of
toluene and stored at - 30 C. Plate like yellow crystals formed were quickly washed with
cold n-hexane (2 x 3mL) and dried under vacuum to get compound 6. Yield obtained; 0.063
g, 39.6 %, based on the platinum source.
M. p; decomp: 198 °C.
1
H NMR (C6D6, 250 MHz, 25 °C): δ = 1.94 ppm.
IR (, cm-1, neat): 2929, 2888, 2844, 1438, 1403, 1374, 997, 835, 663, 577, 519.
Elemental analysis calcd (%) for C40H60Ga5Cl3Pt (1190.96 g/mol): C 40.33, H 5.07. Found:
C 43.2, H 4.77.
AAS: Calcd: Pt 16.35 wt. % and Ga 29.27 wt. %: Found: Pt 15.12 wt. % and Ga 29.06 wt.
%.
MS (EI, m/z): [M4GaCp*]+ : 374, [GaCp*]+: 204, [GaCp*Cl]+: 240.9. 9.4.7 Preparation of [(DDP)Ga(P4)] (7)
Toluene (1.5 mL) was added to a schlenk tube charged with Ga(DDP) (0.2 g, 0.41 mmol)
and P4 (0.026 g, 0.205) at room temperature under vigorous stirring. Slowly the P4 was
consumed within 15 min and the reaction mixture color changed from yellow to orange. The
clear orange solution was stirred for 24 h, volatiles were removed under vacuum, yellow
orange solid was dissolved in hexane/toluene mixture (2:1) under warm condition, filtered
and stored at - 30 C to afford bright yellow crystals of 7. Yield: 83% (0.106 g, based on P4).
Mp: 232-234 C.
1
H NMR (C6D6, 250 MHz):  = 7.17-7.04 (m, 6H, Ar CH), 4.58 (s, 1H, γ-CH), 3.19 (sept,
4H, CH(Me)2), 1.42 (s, 12H, CH3), 1.49 (d), 0.94 (d) (24H, CH(Me)2)ppm.
13
C NMR (C6D6, 62.8952 MHz): δ = 168.6 (C(Dipp)-N), 144.0 (CMe), 140.3 [o-C(Dipp)],
129.3 [p-C(Dipp)], 125.0 [m-C(Dipp)], 96.1 (γ-C), 29.4 (CHMe2), 25.3 (CHMe2), 25.2
196
Chapter 9
Experimental section
(CMe), 23.7 (CHMe2) ppm; 31P NMR (C6D6, 101.2545 MHz): δ = -328.7 (1JP-P = 152 Hz,
2P, P-P), 212.7 (1JP-P = 152 Hz, 2P, Ga-P).
Anal. Calcd (%) for C43H57GaN2P4 (795.56 g/mol): C, 64.92; H, 7.22; N, 3.52; found: C,
64.89; H, 7.17; N, 3.50.
9.4.8 Preparation of [(DDP)Ga(η2:1:1-P4){Mo(CO)5}2]·2toluene (8)
To a mixture of Mo(CO)6 (0.129 g, 0.490 mmol) and [(DDP)Ga(P4)] (0.1 g, 0.163 mmol),
dry toluene (4mL) was added, stirred for 5 min and heated at 80 C for one day. The
resultant brown solution was evaporated in order to remove all volatiles. The brown residue
was then redissolved in toluene (5mL), layered with hexane and placed at - 30 C for 1d to
give pale yellow crystals of compound 8. The crystals were washed with hexane (2 x 4 mL)
and dried under vacuum. Yield (0.070 g, 41%, based on (DDP)Ga(P4)). M. p: > 310 °C
(became black > 160 C).
1
H-NMR (Toluene-d8, 250 MHz):  = 7.19-6.99 (m, 6H, Ar CH), 4.50 (s, 1H, γ-CH), 3.09
(sept, 4H, CH(Me)2), 1.64 (d, 12H, CH(Me)2), 1.37 (s, 6H, CH3), 1.07 (d, 12H, CH(Me)2)
ppm.
13
C-NMR (Toluene-d8, 62.8952 MHz):  = 204.8 (Mo-CO), 170.55 (C(Dipp)-N), 143.7
(CMe), 138.7 [o-C(Dipp)], 137.9 [p-C(Dipp)], 128.2 [m-C(Dipp), overlapped with solvent
resonances], 98.3 (γ-CH), 29.5 (CHMe2), 26.5 (CHMe2), 24.8 (CMe), 23.8 (CHMe2) ppm.
31
P-NMR (C6D6, 101.2545 MHz):  = -315.2 (1JP-P =174 Hz, 2P, P-P), 51.6 (1JP-P = 175 Hz,
2P, Ga-P).
IR (, cm-1): 2966(w), 2929(w), 2871(w), 2064(s), 1995(w), 1934(vs), 1912(vs), 1888(vs),
1588(m), 1437(w), 1312(w), 1254(w), 1019(w), 871(w), 799(m), 789(m), 758(w), 600(vs),
581(vs), 559(w), 532(w), 442(w).
Anal. Calcd (%) for C53H57N2O10GaP4Mo2 (1267.53 g/mol): C, 50.22; H, 4.53; N, 2.21;
found C, 51.09; H, 4.99; N, 2.43.
9.4.9 Preparation of [(DDP)Ga(η2:1:1-P4){Fe(CO)5}] (9)
To a mixture of Fe2(CO)9 (0.071 g, 0.195 mmol) and [(DDP)Ga(P4)] (0.60 g, 0.098 mmol),
dry toluene (5 mL) was added. Immediately its color changed to green, and the resultant
197
Chapter 9
Experimental section
suspension was heated at 70 C for 20h. During this period the color of the reaction was
changed to dark brown. Then it was brought to room temperature, complete evaporated all
the volatiles under vacuum. The resultant brown solid got was extracted in to the toluene (6
mL) and concentrated to 3 mL, layered with n-hexane. After 3 days brown crystals have
appeared were filtered under argon and washed with n-hexane, dried under vacuum over
night to get analytically pure compound 9. Yield obtained; 0.037 (48 %) (With respect to
[(DDP)Ga(P4)]. M. P; decomp: > 214 C.
1
H-NMR (C6D6, 250 MHz):  = 7.24-7.10 (m, 6H, Ar CH), 5.08 (s, 1H, γ-CH), 3.00 (sept,
4H, CH(Me)2), 1.52 (s, 6H, CH(Me)2), 1.42 (d, 12H, CH3), 1.05 (d, 12H, CH(Me)2) ppm.
13
C-NMR (C6D6, 62.8952 MHz):  = 209.8 (very weak signal, Fe-CO), 169.55 (C(Dipp)-N),
143.9(CMe), 136.8[o-C(Dipp)], 135.5 [p-C(Dipp)], 128.7[m-C(Dipp), overlapped with
solvent resonances], 99.8(γ-CH), 28.2 (CHMe2), 25.4 (CHMe2), 22.4(CMe), 22.6 (CHMe2)
ppm.
IR (, cm-1): 2941(w), 2005 (s), 1924(s), 1909(vs), 1887(vs), 1524(s), 1450(w), 1426(w),
1364(w), 1350(w), 1305(w), 1249(w), 1015(w), 791(s), 622(vs).
Anal. Calcd (%) for C33H41FeGaN2O4P4 (779.15 g/mol): C, 50.86; H, 5.30; N, 3.59; found C,
50.98; H, 6.19; N, 3.47.
9.4.10 Preparation of [Ge4{Ga(DDP)}2] (10)
Method A
Fluorobenzene (20 mL) was added to a Schlenk containing IPrGeCl2 (0.400 g, 0.750 mmol)
and Ga(DDP) (1.090 g, 2.251mmol). The resultant pale yellow slurry slowly changed its
color to orange-red clear solution over a period of 15 min. This was then stirred at room
temperature for 12 days. The dark red solution was concentrated to 10 mL and added 35 mL
of n-hexane and allowed to settle some pale brown solid. The solid formed was removed by
filtration and the resultant red filtrate part was stored at - 30 C for 15 days. The orange-red
block crystals formed were filtered, quickly washed with n-hexanes (2 x 3 mL) and dried
under vacuum to get compound 10. Yield (0.102 g, 10.7 %, with respect to germanium
source). M. p: 274-276 C.
198
Chapter 9
Experimental section
1
H NMR (C6D6, 250 MHz, ppm): δ = 7.01-7.11 (m, 6H, Ph), 4.85(s, 1H, γ-CH), 3.24(sept,
3
JH-H = 6.7 Hz, 4H, CHMe2), 1.55 (overlapped singlet with doublet, 18H, CH3 and CHMe2),
1.03(d, 3JH-H = 6.9 Hz, 12H, CHMe2).
13
C {1H} NMR (C6D6, 62.8952 MHz, ppm): δ = 166.6 (C=N), 143.9 [p-C], 140.9 [o-
C(Dipp), Dipp = 2,6-Diisopropylphenyl], 127.1 [p-C(Dipp], 124.4 [m-C(Dipp], 97.6 (γ-C),
28.9 (CHMe2), 26.1 (CHMe2), 25.0 (CMe), 24.3 (CHMe2).
LIFDI-MS calcd for C58H82N4Ga2Ge4 [M] + (m/z) 1265.18464; Found 1265.0855.
IR (, cm-1): 2932(m), 2902(w), 2842(w), 1513(vs), 1449(w), 1424(m), 1371(vs), 1305(vs),
1279(w), 1249(vs), 1166(m), 1087(broad), 1005(broad), 930(m), 852(vs), 785(vs), 750(m),
699(w), 529(m), 491(w), 451(w), 439(m).
Elemental analysis calcd (%) for C58H82N4Ga2Ge4 (1265.1846 g/mol): C 55.06, H 6.53, N
4.43; found: C 53.31, H 6.45, N 3.64.
UV/Vis (toluene): λmax = 391 nm.
Method B:
A schlenk tube containing PCy3GeCl2 (1.50 g, 3.538 mmol), Ga(DDP) (1.7 g, 3.538 mmol)
and KC8 (0.95 g, 7.077 mmol) THF was added (50 mL) at room temperature and the
resultant slurry was stirred as such for 3d. The reaction mixture was allowed to stand for 2 h
to separate the brown-red solution from black solid, and then it was filtered to remove the
black-grey solid. This was then completely evaporated the solvent under vacuum and the
resultant brown-red oily mass was extracted with n-hexane (10 x 7 mL) till all extracts were
almost colorless. It was concentrated to 1/3rd of its volume and stored at room temperature
for one week. Dark orange-red crystals formed were filtered and quickly washed with nhexane (2 x 2mL) and dried under vacuum to obtain compound 10. Yield (0.052 g, 1.17%,
with respect to Ga(DDP)).
9.4.11 Synthesis of [Ge2{Ga(DDP)}2] (11)
A Schlenk tube containing (PCy3)·GeCl2 (0.300 g, 0.707 mmol), Ga(DDP) (0.344 g, 0.707
mmol mmol) and KC8 (0.192 g, 1.414 mmol), tetrahydrofuran was added (10 mL) at room
temperature and the resultant suspension was stirred for 2 h. After which the dark brown-red
supernatant was filtered, the volume was reduced in vacuum to approximately 4 mL. Placing
the solution at - 30 °C for 4 days afforded dark red-brown crystals of 11. These crystals were
199
Chapter 9
Experimental section
separated by filtration and quickly washed with n-hexane (2 x 5 mL) followed by benzene (2
x 4 mL) (Caution: Benzene is carcinogenic and care should be taken) till washings were
almost colorless and dried under reduced pressure at 0 ºC to obtain compound 11. Yield
(0.052 g, 6.5 %, with respect to Ga(DDP)).
M. p. 248–250 C.
1
H-NMR (THF-d8, 250 MHz, ppm): δ = 6.96-6.90 (m, 4H, Ar-H), 6.74-6.71 (m, 8H, Ph),
5.15 (s, 2H, γ-CH), 3.29 (Sept, 3JH-H = 6.8 Hz, 8H, CHMe2), 1.66 (s, 12H, C–CH3 ), 1.06 (d,
3
JH-H = 6.9 Hz, 24H, CHMe2), 0.59 (d, 3JH-H = 6.7 Hz, 24H, CHMe2).
13
C {1H}-NMR (THF-d8, 62.8952 MHz, ppm): δ = 170.0 (C=N), 145.4 [p-C], 144.2 [o-
C(Dipp), 129.2 [p-C(Dipp], 124.9 [m-C(Dipp], 124.7 [m-C(Dipp], (γ-CH, not visible due to
low concentration of the compound), 29.2 (CHMe2), 29.0 (CHMe2), 26.4 (CMe), 25.3
(CHMe2).
LIFDI-MS (in THF): Calculated for C58H82N4Ga2Ge2 (m/z) 1119.96; Found 1120.4 [M] + •.
Anal. calcd (%) for C58H82N4Ga2Ge2: C, 62.36; H, 7.34; N, 5.01. Found C, 61.49; H, 6.49;
N, 5.07.
UV/Vis (THF): λmax = 400 nm.
IR (, cm-1): 2935(s), 2901(w), 2842(w), 1539(s), 1514(vs), 1449(w), 1426(s), 1426(vs),
1306(vs), 1251(s), 1168(s), 1092(s), 1047(s), 1013(s), 928(s), 887(w), 852(w), 818(w),
787(vs), 750(vs), 526(w), 492(w), 440(w).
Note: Despite of several attempts solid state 69Ga and 73Ge NMR for compound 11 could not
be obtained due to its high sensitivity and instability.
9.4.12 Synthesis of [{Cp*Ru}2(μ-H)2{μ-Ga(DDP)}] (12)
Toluene (4 mL) was added to a mixture of [Cp*Ru(µ-H)2]2 (0.05 g, 0.105 mmol) and
Ga(DDP) (0.051 g, 0.105 mmol) under vigorous stirring at room temperature. The violet
reaction mixture was heated at 70 ºC for 5h. During which the reaction mixture color
changed from violet to red. The volatiles were removed under vacuum, washed with nhexane and dried for 1 h. The resultant red solid was nearly pure, which was further purified
by crystallization from toluene/n-hexane mixture at - 30 °C to yield red crystals of 12. Yield:
0.073g (73 % based on [Cp*Ru(µ-H)2]2).
200
Chapter 9
Experimental section
M. p: decomp. > 80 °C.
IR (, neat): 1554 (w,
1
Ru-(µ-H)-Ru)
cm-1.
H NMR (C6D6, 250 MHz): δ = 7.39-7.36 (m, 2H, Ar-H), 7.22-7.12 (m, 4H, Ar-H), 4.88 (s,
1H, γ-CH), 4.15 (sept, 2H, 3JH-H = 7.5 Hz, CH(Me)2), 3.52 (sept, 2H, 3JH-H = 6.8 Hz,
CH(Me)2), 1.95 (s, 15H, Ru-C5Me5), 1.88 (d, 6H, 3JH-H = 6.7 Hz, CH(Me)2), 1.65 (s, 6H,
C(Me)), 1.48 (s, 15H, Ru-C5Me5), 1.40 (d, 6H, 3JH-H = 6.6 Hz, CH(Me)2), 1.35 (d, 6H, 3JH-H
= 6.5 Hz, CH(Me)2), 1.18 (d, 6H, 3JH-H = 6.2 Hz, CH(Me)2), – 14.91 (s, 1H, Ru–H) ppm.
13
C NMR (C6D6, 62.8952 MHz): δ = 167.2 (C=N), 146.9 (CMe), 143.6 [C(Dipp)-N],
143.4[C(Dipp)-N],
126.6[o-C(Dipp)],
126.5[o-C(Dipp)],
124.5[p-C(Dipp)],
124.0[m-
C(Dipp)], 123.6[m-C(Dipp)], 98.8(γ-C), 83.8[Ru-C5Me5], 83.4[Ru-C5Me5], 29.0[CH(Me)2],
28.6[CH(Me)2],
28.5[CH(Me)2],
28.0[CH(Me)2],
27.6[CH(Me)2],
26.2[CH(Me)2],
25.6[CMe], 23.9 [CH(Me)2], 23.7[ CH(Me)2], 13.2 [Ru-C5Me5], 12.6 [Ru-C5Me5] ppm.
LIFDI MS: [M–Cp*] + •: 826.18 (100%).
Elemental analysis calcd (%) for C49H73Ru2GaN2 (962.31 g/mol): C 61.10, H 7.64, and N
2.91; Found: C 62.31, H 7.25, and N 3.45.
9.4.13 Synthesis of [(η6-p-Cymene)RuCl]2
Toluene (5 mL) was added to a Schlenk containing [(η6-p-Cymene)RuCl2]2 (0.05 g, 0.08
mmol) and Ga(DDP) (0.08 g, 0.160 mmol). The reaction mixture immediately became dark
brown-red; it was heated at 60 °C for 3 h. The black-grey precipitate formed was filtered off
and the filtrate part was concentrated to 1 mL and stored at - 30 °C. After one week dark red
crystals formed were filtered and quickly washed with n-hexanes to isolate compound [(η6-pCymene)RuCl]2. Yield (0.028 g, 65%, with respect to [(η6-p-Cymene)RuCl2]2. The
analytical and X-ray unit cell dimensions of these dark red crystals are same as reported for
the authenticated sample. [21]
9.4.14 Synthesis of [(η6-p-cymene)Ru(DDP)Ga)(µ-Cl){Ga(Cl)C29H41N2}]
(13)
Ga(DDP) (0.398 g, 0.816 mmol) was added as such to a stirred red suspension of [(η6-pCymene)RuCl2]2 (0.100 g, 0.163 mmol) in dry n-hexane (20 mL) at room temperature. The
resultant reaction mixture was slowly heated to reflux for 5 h, while it turned to clear brownred solution. After cooling to room temperature, all volatiles were removed under reduced
201
Chapter 9
Experimental section
pressure and the resultant brown-red solid was dissolved in minimum amount of n-hexane /
toluene (8 mL). This was then stored at - 30 °C for 2 weeks to isolate orange-brown crystals
of compound 13 which was co-crystallized with the byproduct Cl2Ga(DDP) and un reacted
Ga(DDP) (Note: these crystals were separated manually under microscope in a glove box).
Yield; 0.034 g (16 %, based on [(η6-p-Cymene)RuCl2]2) M. p: 210-212 °C.
1
H NMR (C6D6, 600 MHz): δ = 7.21-7.17 (m, 4H, Ar-H), 7.15-7.09 (m, 4H, Ar-H), 7.06-
6.99 (m, 4H, Ar-H), 6.31 (t, 1H, 3JH-H = 7.6 Hz, Ar-H), 6.29 (br, 1H, NH), 5.79 (d, 1H, 3JH-H
= 5.6 Hz , H3C-C6H4-iPr), 5.55 (br, 1H, H3C-C6H4-iPr), 5.10 (s, 1H, Ga(ddp)), 4.52 (d, 1H,
3
JH-H = 5.5 Hz, H3C-C6H4-iPr), 4.50 (d, 1H, 3JH-H = 5.6 Hz, H3C-C6H4-iPr), 4.37 (s, 1H, H-
C=C-), 4.03 (sept, 1H, 3JH-H = 6.9 Hz, CH(Me)2), 3.83 (sept, 1H, 3JH-H = 6.7 Hz, CH(Me)2),
3.54 (3JH-H = 6.6Hz, CH(Me)2), 3.33 (sept, 1H, 3JH-H = 6.8 Hz, CH(Me)2), 3.32 (sept, 1H,
3
JH-H = 6.9 Hz, CH(Me)2), 3.21 (sept, 1H, 3JH-H = 6.9 Hz, CH(Me)2), 3.13 (sept, 3JH-H = 6.8
Hz, CH(Me)2), 3JH-H = 6.9 Hz, CH(Me)2), 3.06 (br, 2JH-H = 13.1 Hz, Ru–CH2), 3.04 (sept,
1H, 3JH-H = 6.8 Hz, CH(Me)2), 1.82 (d, 6H, 3JH-H = 6.7 Hz, CH(CH3)2), 1.79 (d, 3H, 3JH-H =
6.4 Hz, H3C-C6H4-iPr), 1.65 (s, 3H, C-CH3), 1.61(s, 3H, C-CH3), 1.57 (br, 1H, , 2JH-H = 13.1
Hz, Ru–CH2), 1.51(d, 3H, 3JH-H = 6.5 Hz), 1.49-1.45(m, 9H, CH(CH3)2), 1.41 (d, 3H, 3JH-H
= 6.7 Hz , CH(CH3)2), 1.31(d, 3H, 3JH-H = 6.2 Hz, CH(CH3)2), (d, 3H, 3JH-H = 6.7 Hz,
CH(CH3)2), 1.28(d, 3H, 3JH-H = 6.8 Hz, CH(CH3)2), 1.20 (d, 3H, 3JH-H = 7.1 Hz, CH(CH3)2 ),
1.13(d, 3H, 3JH-H = 6.5 Hz, CH(CH3)2), 1.1(d, 3H, 3JH-H = 6.7 Hz, CH(CH3)2), 1.00(s, 3H, CCH3), 0.97-0.93(br, CH(CH3)2), 0.89-0.82(br, CH(CH3)2).
13
C-NMR (C6D6, 62.8952 MHz): δ = 197.0 (C=N), 167.2[-C(Me)=N, Ga(DDP)], 167.1[-
C(Me)=N, Ga(DDP)], 155.0[-C(Me)=C-N)], 147.8[N-C(Dipp), Ga(DDP)], 147.4[-NC(Dipp)], 146.6[HN-C(Dipp)], 146.4[o-C(Dipp), Ga(DDP)], 145.5[o-C(Dipp), Ga(DDP)],
145.1[o-C(Dipp), Ga(DDP)], 143.1[o-C(Dipp), Ga(DDP)], 142.9[o-C(Dipp), Ga(DDP)],
142.42[o-C(Dipp)], 142.4[o-C(Dipp)], 141.6 [o-C(Dipp)], 134.6 [o-C(Dipp)], 129.1 [pC(Dipp), Ga(DDP)], 127.2[p-C(Dipp), Ga(DDP)], 126.5[m-C(Dipp), Ga(DDP)], 125.8[mC(Dipp), Ga(DDP)], 125.5[m-C(Dipp), Ga(DDP)], 124.9[m-C(Dipp), Ga(DDP)], 124.6[pC(Dipp)], 124.0[p-C(Dipp)], 123.9 [m-C(Dipp)], 123.8[m-C(Dipp)], 123.3[m-C(Dipp)],
122.7[m-C(Dipp)], 99.0 [γ-CH], 95.3[-CH=C(Me)], 81.4[iPr-C-C4H4-C-CH3], 80.1[iPr-CC4H4-C-CH3], 79.8[iPr-C6H4-CH3], 79.5[iPr-C6H4-CH3], 73.9[iPr-C6H4-CH3], 34.9[(CH3)2C-
C6H4-CH3], 31.9[(CHMe2), Ga(DDP)], 31.2[CHMe2, Ga(DDP)], 29.5[(CHMe2), Ga(DDP)],
29.3[(CHMe2), Ga(DDP)], 29.0 [CHMe2)], 28.5[(CHMe2)], 28.0[(CHMe2)], 27.9[CHMe2],
202
Chapter 9
Experimental section
27.8[(CMe), Ga(DDP)], 27.7[(CMe), Ga(DDP)], 26.3[CMe], 25.8[(CHMe2), Ga(DDP)], 25.6
[(CHMe2), Ga(DDP)], 25.4[(CHMe2), Ga(DDP)], 25.3[(CHMe2), Ga(DDP)], 25.1[(CHMe2),
Ga(DDP)], 25.0[(CHMe2), Ga(DDP)], 24.9[(CHMe2), Ga(DDP)], 24.8[(CHMe2), Ga(DDP)],
24.6[CHMe2],
24.4[(CHMe2)],
23.8[CHMe2-C6H4-CH3],
24.3[(CHMe2)],
23.4[CHMe2-C6H4-CH3],
24.2[(CHMe2)],
23.4[Ru-CH2],
24.1[(CHMe2)],
22.2[CHMe2],
20.9[CHMe2], 18.7[CHMe2], 14.3[CHMe2-C6H4-CH3], 11.6 [CHMe2] ppm.
LIFDI-MS for C68H96Cl2Ga2N4Ru (1280.93 g / mol); 1280.77 [M]
+•
, and its fragment ions
m/z 1245.4 (100%) [M–Cl] + •, m/z 723 (40%) [M–Cl2Ga(DDP)] + •.
IR (, cm-1, neat) 3333(w, N–H), 2936(s), 2844(w), 1563(w), 1544(w), 1494(w), 1446(m),
1432(m), 1409((m), 1384(w),1371(w), 1294(w), 1248(vs), 1165(w), 1083(m), 1008(s),
846(w), 785(vs), 754(m), 701(w), 656(w), 631(w), 598(w), 494(w), 444(w), 430(w).
9.4.15 Synthesis of [{(DDP)Ga}2Cu][OTf]· 2C6H5F (14)
Method A
To a mixture of Ga(DDP) (0.1 g, 0.206 mmol) and Cu(OTf)2 (0.019 g, 0.052 mmol) was
added fluorobenzene (3 mL) under vigorous stirring at room temp. The clear pale yellow
solution was heated at 60 °C for 1 h, filtered, layered with hexane (2 mL) and stored at –30
°C for 24 h to afford colourless crystals of 14. Yield: 53% [based on Cu(OTf)].
Method B
Cu(OTf)·4CH3CN (0.05 g, 0.132 mmol) was added to a pale yellow solution of Ga(DDP)
(0.129 g, 0.265 mmol) in fluorobenzene (3 mL). The resultant slurry was heated at 60 °C for
1 h. The tan-colored insoluble solid formed was filtered off, and the colorless filtrate was
layered with hexane to isolate colorless crystals of 14 at - 30 °C over a period of one week.
Yield: 61% [based on Cu(OTf)·4CH3CN]. The samples used for elemental analysis and
spectroscopic characterization were washed with hexane and completely dried under
vacuum. This procedure removes all solvents from the synthesis, especially fluorobenzene.
1
H-NMR ([D8]THF, 250 MHz): δ = 7.30–7.07 (m, 12 H, Ar), 5.35 (s, 2 H, γ-CH), 2.92 (sept,
3
JH-H = 7Hz, 8 H, CHCH3), 1.73, 1.70 (s, 12 H, CCH3), 1.10 (d, 3JH-H = 6.5 Hz, 24 H,
CHCH3), 0.89 ppm (d, 3JH-H = 6.5 Hz, 24 H, CHCH3).
203
Chapter 9
13
Experimental section
C-NMR ([D8] THF, 62.9 MHz): δ = 168.2 (CN), 144.4 (Ar), 142.0 (Ar), 124.8 (Ar), 116.1,
115.7 (Ar), 100.7 (γ-CH), 28.8 (CHCH3) ppm. 19F NMR ([D8] THF, 235.3 MHz): δ = –80.5
ppm (OTf).
IR(, cm-1, neat ) = 2961 (w), 2869 (w), 1594 (s), 1528 (m), 1495 (m), 1460 (m), 1438 (m),
1360 (s), 1317 (s), 1261 (s), 1230 (m), 1199 (m), 1176 (m), 1163 (m), 1101 (w), 1055 (m),
1015 (s), 935 (w), 867 (w), 798 (s), 753 (m), 709 (w), 684 (w), 662 (vs), 632 (w), 572 (w),
531 (w), 516 (w), 498 (m), 439 (w), 403 (w) cm–1.
Anal. Calcd (%) for C59H82CuF3Ga2N4O3S (1187.36 without solvent): C 59.68, H 6.96, N
4.71, S 2.70; found C 59.54, H 6.05, N 4.48, S 2.88.
9.4.16 Synthesis of [Cl4Ti-C{N(2,6-Pri2C6H3)CH}2] (15)
IPr [IPr = :C{N(2,6-iPr2C6H3)CH}2] (0.614 g, 1.580 mmol) was dissolved in diethyl ether
(20 mL) and cooled to –78 °C (Acetone / Liq N2 bath). To this stirred suspension TiCl4
(0.300 g, 1.580 mmol) was slowly added through a syringe. The resultant suspension was
stirred for 2 days and during this time the temperature of the reaction slowly raised to room
temperature. Then it was filtered to remove the little brown solid and filtrate part was
completely evaporated under reduced pressure to remove the all volatiles, then it was
extracted with dry toluene (8 mL) and cooled to - 30 °C for 15 days to isolate a pale yellow
crystalline solid. Yield (0.170 g, 18.5%, with respect to TiCl4).
M. p: 218–220 C.
1
H-NMR (C6D6, 250 MHz, 25 °C): δ = 7.26-7.13 (m, 6H, Ar CH), 6.57 (s, 2H, -C=CH),
3.21 (sept, 4H, 3JH-H = 6.8 Hz, CH(Me)2), 1.52 (d, 3JH-H = 6.7 Hz , 12H, CH3), 1.01 (d, 3JH-H
= 6.7 Hz, 12H, CH3) ppm.
13
C-NMR (C6D6, 62.8952 MHz, 25 °C): δ = 188.8 (C–Ti), 146.9 (C=C), 133.2 (C(Dipp)-N),
131.8 (o-C(Dipp)), 124.6 (m-C(Dipp)), 123.6 (p-C(Dipp)), 29.4 (CHMe2), 26.8 (CHMe2),
22.2 (CHMe2).
IR (, cm-1, neat): 2939 (s), 2904 (w), 2846 (w), 1526 (s), 1449(s), 1375 (w), 1354 (w), 1318
(s), 1190 (s), 1173 (w), 1091 (s), 1050 (vs), 965 (w), 927 (w), 795 (vs), 746 (vs), 672(s), 509
(s), 430 (vs).
Elemental analysis calcd (%) for C27H36N2Cl4Ti (576.11g/mol): C 56.23, H 6.29, and N
4.86; found: C 56.13, H 7.14, and N 4.72.
204
Chapter 9
Experimental section
9.4.17 Synthesis of [Cl4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (16)
IPr (3.00 g, 7.726 mmol) was dissolved in diethyl ether (50 mL) and cooled to - 78 °C
(Acetone / Liq N2 bath). To this stirred suspension TiCl4 (0.732 g, 3.860 mmol) was slowly
added through a syringe. The resultant suspension was stirred for 60 h and during which the
temperature of the reaction slowly raised to room temperature. It was then evaporated under
vacuum to remove all volatiles and extracted with toluene (20 mL). This extract was cooled
to - 30 °C over night and the resultant brown solid formed was filtered off and the dark redbrown filtrate part was completely dried under vacuum and dissolved in THF (15 mL),
stored at - 30 °C for 3 days to isolate bright yellow block crystals. These were filtered and
quickly washed with n-hexane (5 x 3 mL) and dried under reduced pressure over night to get
compound 16. Yield (0.615 g, 16.4 %, with respect to TiCl4).
M. p: decomp at 162 °C and melted at 210 ºC.
1
H-NMR (C6D6, 250 MHz, 25 °C): δ = 7.23-7.12 (m, 6H, Ar-CH), 6.42 (s, 4H, -C=CH),
3.14 (sept, 8H, 3JH-H = 6.7 Hz, CH(Me)2), 1.41 (d, 3JH-H = 6.6 Hz , 24H, CH3), 0.98 (d, 3JH-H
= 6.8 Hz, 24H, CH3) ppm.
13
C-NMR (C6D6, 62.8952 MHz, 25 °C): δ = 193.1 (C–Ti), 146.4 (C=C), 137.3 (C(Dipp)-N),
129.3 (o-C(Dipp)), 123.5 (m-C(Dipp)), 122.5 (p-C(Dipp)), 28.8 (CHMe2), 26.3 (CHMe2),
23.1 (CHMe2).
IR (, cm-1, neat): 2939 (vs), 2905 (w), 2843 (w), 1520 (vw), 1451 (s), 1373 (s), 1350 (w),
1318 (s), 1226 (w), 1106 (w), 1091 (w), 1052 (s), 930 (s), 795 (vs), 750 (vs), 689 (s), 628
(w), 504 (w), 432 (w).
Elemental analysis calcd (%) for C54H72N4TiCl4 (966.854 g/mol): C 67.08, H 7.50 and N
5.79; found: C 66.47, H 7.90, and N 5.76.
9.4.18 Synthesis of [F4Ti{C{N(2,6-iPr2C6H3)CH}2}2] (17)
A solution of TiF4 (0.500 g, 4.036 mmol) in THF (10 mL) was added to a Schlenk flask
containing IPr [IPr =: C{N(2,6-iPr2C6H3)CH}2] (1.56 g, 4.036 mmol) in THF (15 mL) at - 78
°C while under stirring. This brown reaction mixture was stirred for additional one hour at 78 °C and then allowed to warm to room temperature under continuing stirring for 20 h and
finally filtered, concentrated to 20 mL and placed at - 30 °C. The colorless crystals formed in
overnight were filtered and washed with n-hexane (5 x 2 mL) and dried under reduced
205
Chapter 9
Experimental section
pressure for 10h. Upon storing the filtrate part at - 30 °C for 4 days gave second crop of
crystals. Yield (0.760 g, 21% with respect to TiF4).
M. p: at 237 °C decomposed to brown solid, then melted at 265 °C.
1
H-NMR (C6D6, 250 MHz, 25 °C): δ = 7.35-7.29 (2H, m, Ar CH), 7.13-7.18 (4H, m, Ar
CH), 6.34 (s, 2H, -C=CH), 2.78 (sept, 4H, 3JH-H = 6.6 Hz, CH(Me)2), 1.25 (d, 3JH-H = 6.6 Hz
, 12H, CH3), 1.07 (d, 3JH-H = 6.6 Hz, 12H, CH3) ppm.
13
C-NMR (C6D6, 62.8952 MHz, 25 °C): δ = 188.5 (quintet, 2JC-F = 6.8 Hz, C-Ti), 146.3
(C=C), 136.5 (C(Dipp)-N), 129.1 (o-C(Dipp)), 123.0 (m-C(Dipp)), 122.5 (p-C(Dipp)), 28.8
(CHMe2), 25.9(CHMe2), 22.9 (CHMe2).
19
F-NMR (C6D6, 235.357MHz): δ = 169.76 (s) ppm.
IR (, cm-1, neat): 2938 (s), 2904(w), 2845(w), 1526(w), 1445(s), 1388(w), 1374(w),
1352(w), 1319(s), 1265(w), 1246(w), 1193(w), 1171(s), 1096(s), 1051(s), 939 (w), 930(w),
794(vs),749(vs), 689(w), 673(s), 616(vs), 430(w).
Elemental analysis calcd (%) for C54H72N4F4Ti (901.103 g/mol): C 71.98, H 8.05 and N
6.21; found: C 71.92, H 6.25 and N 6.26.
9.4.19 Synthesis of [HC{N(2,6-iPr2C6H3)CH}2]2[TiCl6] (18)
IPr (2.046 g, 5.283 mmol) was dissolved in diethyl ether (60 mL) and cooled to - 78 °C
(Acetone / Liq N2 bath). To this stirred suspension TiCl4 (1.00 g, 5.272 mmol) was slowly
added through a syringe. The resultant suspension was stirred for 15 h and during this time
the temperature of the reaction slowly raised to room temperature. The resultant pale greenyellow slurry was dried under reduced pressure to remove the all volatiles, and extracted
with THF (15 mL) and concentrated to 6 mL. Placing this solution at - 30 °C for 3 days
afforded pale yellow to almost colorless crystalline solid. This was then filtered and dried
under reduced pressure over night to give compound 18. Yield (0.820 g, 15 %, with respect
to TiCl4).
M p: 92-94 C.
1
H-NMR (THF-d8, 250 MHz, 25 °C): δ = 10.01 ( N-CH-N, 1H), 8.38 (H-C=C, 2H), 7.58-
7.52 (m, Ar-H, 2H), 7.39-7.36 (m, Ar-H, 2H), 2.53 (sept, 3JH-H = 7 Hz, -CH(CH3)2, 4H), 1.24
(d, 3JH-H = 6.7 Hz, -CH(CH3)2, 12H), 1.16 (d, 3JH-H = 7 Hz, CH(CH3)2, 12H).
206
Chapter 9
13
Experimental section
C-NMR (THF-d8, 62.8952 MHz, 25 °C): δ = 221.8 (–N=C-H), 146.8 (C = C), 140.1
(C(Dipp)-N), 132.6 (C(Dipp)-N), 131.8 (o-C(Dipp)), 128.3 (m-C(Dipp)), 125.4 (p-C(Dipp)),
30.0 (CH(CH3)2), 26.5 (CH(CH3)2), 25.0 (CH(CH3)2), 24.2 (CH(CH3)2).
IR (, cm-1): 2939(vs), 2905(w), 2846 (w), 1522 (m), 1447 (s), 1375 (w), 1354 (w), 1319
(w), 1247 (w), 1241 (w), 1193 /m), 1093 (w), 1051 (s), 1019 (m), 900 (w), 797 (vs), 747
(vs), 673 (m), 534 (w), 517 (w), 431 (w), 415 (w).
Elemental analysis: Elemental analysis calcd (%) for C54H74N4TiCl6 (1039.775 g/mol). C
62.37, H 7.17, and N 5.38; found: C 56.89, H 7.32, and N 3.94.
9.4.20 Synthesis of [Cl2Zn-C{N(2,6-iPr2C6H3)CH}2] (19)
To a stirred suspension of anhydrous ZnCl2 (0.300 g, 2.202 mmol) in THF (8mL), IPr (0.855
g, 2.202 mmol) was added as such at room temperature. The resultant and almost clear
reaction mixture had become cloudy and the formation of a white precipitate was observed.
This was then stirred at room temperature for 24 h and filtered the white precipitate under
argon, washed with n-hexane (2 x 4 mL) and dried under vacuum over night to get
compound 19 as a free flowing powder. Yield: 225 mg. The filtrate part was evaporated
under reduced pressure, extracted with benzene and dried under vacuum to isolate another
batch of the compound 19. Overall yield of the reaction is 0.855 g (74%, with respect to
ZnCl2).
M. p: decomposed at 280 °C and melted at 300 ºC.
1
H-NMR (C6D6, 250 MHz, 25 °C): δ = 7.25-7.20 (m, 4H, Ar-CH), 7.13 (m, 2H, Ar- CH),
6.46 (s, 2H, -C=CH), 2.88 (sept, 4H, 3JH-H = 6.7 Hz, CH(Me)2), 1.54 (d, 3JH-H = 6.1 Hz ,
12H, CH3), 1.00 (d, 3JH-H = 6.7 Hz, 12H, CH3) ppm.
13
C-NMR (C6D6, 62.8952 MHz, 25 °C): δ = 176.4 (C–Zn), 146.2 (C=C), 134.6 (C(Dipp)-N),
130.8 (o-C(Dipp)), 124.5 (m-C(Dipp)), 124.2 (p-C(Dipp)), 29.0 (CHMe2), 26.1 (CHMe2),
23.4 (CHMe2) ppm.
IR (, cm-1, neat): 2937 (vs), 2906 (w), 2845 (w), 1581 (s), 1541 (s), 1456 (s), 1446 (w),
1261 (w), 1171 (w), 1110 (s), 1098 (w), 1035 (w), 941 (w), 927 (w), 793 (vs), 749 (vs), 695
(w), 629 (w), 451 (w).
Elemental analysis calcd (%) for C27H36N2Cl2Zn (524.88 g/mol): C 61.78, H 6.91 and N
5.33; found: C 61.23, H 7.11, and N 5.40.
207
Chapter 9
Experimental section
9.4.21 Reaction of [IPr·TiCl4] Adduct with Me2Zn: Carbene Transfer
IPr·TiCl4 (0.200 g, 0.3471 mmol) was dissolved in THF (7 mL), and cooled to - 55 °C. To
this yellow stirred solution Me2Zn (1.15 mL, 1.388 mL) was added in drop wise manner
through a syringe over a period of 5 min. The resultant orange-red reaction mixture was
stirred at this temperature for 30 min and then the cold bath was removed to warm up and it
was allowed stirring at room temperature for further 14.30 h. A white / brown solid formed
was filtered off and the filtrate part was layered with n-hexane, placed at - 30 °C for 3 days.
Once again the white solid with grey/brown substance formed was filtered and extracted
with hot benzene (2 x 4 mL) (Caution: Benzene is carcinogenic and care should be taken).
The colorless benzene extract was then completely evaporated to dryness under reduced
pressure to get analytically pure 19 as a white powder.
Yield: 98 mg (53 %).
1
H, 13C-NMR in C6D6 and all other characterization data is same as for compound 19.
9.4.22 Synthesis of [(CH3)2Zn{C{N(2,6-iPr2C6H3)CH}2}2] (20)
IPr (0.300 g, 0.772 mmol) was dissolved in toluene (8 mL) and stirred for 10 min. To this
stirred solution ZnMe2 (1.92 mL, 1.2M solution in toluene, 2.317 mmol) was added slowly
over a period of 5 min. The resultant clear colorless reaction mixture was stirred as such at
room temperature for 15h. Then the reaction mixture was filtered and completely evaporated
to dryness to get colorless solid. This was then dried under vacuum for 4h to get pure
complex 20 as a white solid. Yield (0.350 g, 94.5 %, with respect to IPr).
M. p: decomp.198 C.
1
H-NMR (C6D6, 250 MHz, 25 °C): δ = 7.29-7.26 (m, 2H, Ar-H), 7.19-7.14 (m, 4H, Ar-H),
2.89 (sept, 3JH-H = 6.3Hz, 4H, CH(Me)3), 6.53 (s, H-C=CH), 1.34 (d, 12H, 3JH-H = 6.3Hz,
CH(Me)3), 1.10 (d, 12H, 3JH-H = 6.3Hz, CH(Me)3), -0.76 (s, 6H, ZnMe) ppm.
13
C-NMR (C6D6, 62.8952 MHz, 25 °C): δ = 222.9 (ZnC), 145.7 (-C=C-), 136.1 ((C(Dipp)-
N), 130.8 (o-C(Dipp)), 124.2 (m-C(Dipp)), 123.0 (p-C(Dipp)), 28.8 (CHMe2), 24.7
CHMe2), 23.8 (CHMe2), -8.05 (ZnMe) ppm.
Elemental analysis calcd (%) for C29H42N2Zn (484.047 g/mol): C 71.95, H 8.74 and N 5.78;
Found; C 70.61, H 8.56 and N 5.96.
208
Chapter 9
Experimental section
9.4.23 Synthesis of (PCy3)·GeCl2 (21)
A Schlenk tube containing GeCl2.dioxane (1.00 g, 4.319 mmol) and PCy3 (1.20 g, 4.319
mmol)), benzene (12 mL) was added at room temperature. The resultant suspension changed
to clear colorless solution over a period of 10 min. After 15 mints stirring at RT, a white
precipitate formation observed. It was stirred as such for 12 h and then filtered the resultant
white precipitate, quickly washed with cold n-hexane (2 x 7 ml) and dried under vacuum.
Yield: 0.067g (36%).
Elemental analysis calcd (%) for C18H33PGeCl2 (423.94 g / mol): C 50.99, H 7.84; found: C
50.91, H 8.02. This material was used directly for the preparation of compound 11 without
further purification.
9.4.24 Synthesis of Nanopowder (NP1)
In a Fischer Porter bottle, 1.140 g of [Ni(GaCp*)(PMe3)3] (2.326 mmol) was taken and
dissolved in n-Decane (25 mL) and subsequently the Fischer Porter bottle was pressurised
with 4 bar H2 and placed into an oil bath which is pre-heated to 185 ºC. After 30 min of
stirring at this temperature the colour of the solution changed to dark brown with the slow
formation of black / brown precipitate. This mixture was further heated for 60h. After
cooling to room temperature, the suspension was taken into a Schlenk tube and centrifuged
to get the black precipitate, which was then washed with n-hexane (4 x 20 mL) till all
washing were colourless and dried in vacuum.
Yield: 250 mg (33 %, according to Ni2Ga3 phase).
AAS: Ni 33.76 wt. % and Ga 58.75 wt. %.
XRD reflections (2θ/): 25.33 (100), 31.27 (101), 45.11(102), 48.63 (111), 52.16 (200),
55.47 (201), 62.92 (103), 65.57 (202), 71.06 (210), 74.48 (113).
9.4.25 Synthesis of Nanopowder (NP2)
Fischer Porter bottle was charged with [Ni(GaCp*)3(PCy3)] (0.500 g, 0.524) mmol) and
[Ni(cod)2] (0.144 g, 0.524 mmol) and n-Decane (20 mL). Then the bottle was pressurized
with 4 bar of H2 and placed in an oil bath which was pre-heated to 190 ºC. After 15 min
reaction period its colour changed to dark brown and formation of black precipitate was
observed. In order to completely decompose the precursors, this was heated for 12h. After
cooling to room temperature the suspension was decanted into a Schlenk and centrifuged to
209
Chapter 9
Experimental section
get black precipitate and it was washed with n-hexane (30 x 3 mL), dried under vacuum.
Yield. 87 g (51%, according to N2Ga3 phase)
AAS: Ni, 31.31% and Ga, 52.14 %
XRD reflections (2θ/): 18.19 (0 0 1), 25.39 (1 0 0), 31.30 (1 0 1), 36.82 (0 0 2), 44.64 (2 -1
0), 45.23 (1 0 -2), 48.64 (2 -1 1), 52.26 (2 0 0), 55.69 (2 0 1), 56.45 (0 0 3), 59.30 (2 -1 2),
62.74 (1 0 3), 65.41 (2 0 2), 71.13 (3 -1 0), 73.99 (3 -1 1), 74.75 (2 -1 3).
9.4.26 Synthesis of NiGa Nanopowder (NP3)
In a Fischer-porter bottle, 0.400 g of [Ni(cod)2] (1.454 mmol) and 0.296 g of GaCp* (1.450
mmol) were dissolved in mesitylene (15 mL).The resultant yellow-orange solution was
degassed and set to 4bar H2. The bottle was then placed into a oil bath at 150 º C. After 10
min of heating the solution became dark red, and then slowly changed to dark brown after 20
min heating. After 30 min, a black precipitate started forming. The mixture was stirred for 3h
at the same temperature, where upon the solution became color less. After cooling to room
temperature (25 ºC), the colorless supernatant was decanted under argon and the black
material was washed several times with toluene (3 x 10 mL), followed by n-hexane (2 x 10
mL). The resultant material was dried under vacuum over night.
Yield: 0.184 g (100 %).
AAS: Ni 39.69 wt. % and Ga 50.27 wt. %.
XRD reflections (2θ/): 31.38, 44.85, 55.64, 64.45, 74.36, 82.66.
EDX analysis: Ni 38.59 %; Ga 38.30%.
9.4.27 Synthesis of Ni2Ga3 Nanopowder (NP4)
In a Fischer-porter bottle, 0.600 g of [Ni(cod)2] (2.181 mmol) and 0.667 g of GaCp* (3.272
mmol) were dissolved in mesitylene (30 mL).The resultant yellow-orange solution was
degassed and set to 4 bar H2. The bottle was then placed into a oil bath at 150 º C. The
resultant clear red reaction mixture became dark red, then to brown over a period of 15 mint
heating. After 30 min heating, there was a formation of black precipitate observed. During
the reaction there was huge drop in the hydrogen pressures had taken place. This was heated
until 24h, and cooled to the room temperature. The resultant suspension was filtered to
remove the supernatant to get the black precipitate. This was then washed several times with
toluene (3 x 20 mL), followed by n-hexane (2 x 20 mL) and dried under vacuum overnight.
Yield: 0.273 g (38 %, if the phase is assumed to be pure Ni2Ga3).
210
Chapter 9
Experimental section
AAS: Ni 32.54 wt. % and Ga 59.52 wt. %.
XRD reflections (2θ/): XRD reflections (2θ/): 18.19 (0 0 1), 25.39 (1 0 0), 31.30 (1 0 1),
36.82 (0 0 2), 44.64 (2 -1 0), 45.23 (1 0 -2), 48.64 (2 -1 1), 52.26 (2 0 0), 55.69 (2 0 1), 56.45
(0 0 3), 59.30 (2 -1 2), 62.74 (1 0 3), 65.41 (2 0 2), 71.13 (3 -1 0), 73.99 (3 -1 1), 74.75 (2 -1
3).
Calculated particles size according to Scherrer´s equation: 36 nm
9.4.28 Synthesis of Ni3Ga Nanopowder (NP5)
Samples of 0.404 g of [Ni(cod)2] (1.469 mmol) and 0.100 g of GaCp* (0.489 mmol) were
combined in a Fischer-porter bottle in mesitylene (20 mL). The resultant yellow reaction
mixture was degassed for 10 min at room temperature, set to 4 bar H2 pressure and placed
the Fischer-porter bottle in oil bath which is at 150 ºC. After 5min heating, the color of the
reaction mixture had changed to dark-brown, then after 15 min formation of a black
precipitate was observed. The mixture was stirred for 6 h at the same temperature, where
upon the solution became color less. After cooling to room temperature (25 ºC), the colorless
supernatant was decanted under argon and the black material was washed several times with
toluene (3 x 10 mL), followed by n-hexane (2 x 10 mL). Thereafter, the residual solvent and
hydrocarbon byproducts were removed in vacuum and the black residue was thoroughly
dried under vacuum over night.
Yield: 0.130 g (36 %).
AAS: Ni 64.16 wt. % and Ga 27.28 wt. %.
XRD reflections (2θ/): 43.68 (1 1 1), 50.52 (2 0 0), 74.62 (2 2 0).
EDX analysis: Ni 46.63 at. %, Ga 15.26 at. %.
Calculated particles size according to Scherrer´s equation: 24 nm
9.4.29 Preparation of Nickel-Gallium Colloidal Nanoparticles (NP6)
Fischer porter bottle was charged with [Ni(GaCp*)(PMe3)3] (0.500 g, 1.016 mmol) and
HDA (Hexadecylamine) (1.227 g, 5.052 mmol). To this reaction mixture n-Decane (20 mL)
was added. The resultant yellow reaction mixture was degassed for 15 min at room
temperature, set to 4 bar H2 pressure and placed the Fischer-porter bottle in oil bath which is
at 185 ºC. After 10 min of heating it became brown, then dark brown without the formation
of precipitate. This was then heated for 15 h at the same temperature. The resultant reaction
mixture was cooled to the room temperature and the dark brown solution was transferred
211
Chapter 9
Experimental section
into a Schlenk. To this dark brown colloid, dry ethanol (100 mL) was added and stirred for 2
h. The cloudy solution formed was centrifuged to get a dark brown semi-solid. This was then
washed with dry ethanol (2 x 20 mL) and dried under vacuum for 3 days.
Yield (35 mg).
IR (, cm-1, neat): 3245 (vw), 3115 (vw), 2935 (vs), 2894 (vs), 2826 (vs), 1588 (w), 1454
(w), 1397 (w), 1249 (vs), 1080 (s), 1008 (vs), 860 (w), 791(vs), 713 (w), 681 (w).
DLS (measured in dry toluene): 1240 nm (particle size).
9.4.30 Hydrogenation of cyclohexene with NiGa Nanopowder (NP3)
Young NMR tube was charged with 0.040 g (0.313 mmol) of NiGa nanopowder NP3,
cyclohexene (0.081 g, 0.987 mmol) in tolunene-d8 in glove box. The resultant suspension
was set for 5 bar H2, thereafter the NMR tube was kept for mechanical rotation for 12h at
room temperature. Then it was placed in an oil bath at 100 C for another 12h. The NMR
tube was transferred into the glove box. The NiGa particles were allowed to settle and the
colorless solution was removed with syringe for further analysis.
1
H-NMR (Tol-d8, 250.1MHz, 25 C):  = 1.40 ppm (s, 12H, cyclohexene, -CH2). Only
product chemical shifts are given. In situ NMR experiments were could not be performed
due to the magnetic property of these nano particles.
Percentage of conversion from cyclohexene to cyclohexane; 85 %
9.4.31 Hydrogenation of cyclohexene with Nanopowder (NP4)
Young NMR tube was charged with 0.040 g (0.122 mmol) of nanopowder NP4, cyclohexene
(0.081 g, 0.987 mmol) in tolunene-d8 in glove box. The resultant suspension was set for 5
bar H2, thereafter the NMR tube was kept for mechanical rotation for 12h at room
temperature. Then it was placed in an oil bath at 100 C for another 12h. The NMR tube was
transferred into the glove box. The black particles were allowed to settle and the colorless
solution was removed with syringe for further analysis.
1
H-NMR (Tol-d8, 250.1MHz, 25 C):  = 1.40 ppm (s, 12H, cyclohexene, -CH2). Only
product chemical shifts are given. In situ NMR experiments were could not be performed
due to the magnetic property of these nanoparticles.
Percentage of conversion from cyclohexene to cyclohexane; 73 %
212
Chapter 9
Experimental section
9.4.32 Hydrogenation of cyclohexene with Ni3Ga Nanopowder (NP5)
Young NMR tube was charged with 0.030 g (0.122 mmol) of nanopowder NP4, cyclohexene
(0.081 g, 0.987 mmol) in tolunene-d8 in glove box. The resultant suspension was set for 5
bar H2, thereafter the NMR tube was kept for mechanical rotation for 12h at room
temperature. Then it was placed in an oil bath at 100 C for another 12h. The NMR tube was
transferred into the glove box. The black particles were allowed to settle and the colorless
solution was removed with syringe for further analysis.
1
H-NMR (Tol-d8, 250.1MHz, 25 C):  = 1.40 ppm (s, 12H, cyclohexene, -CH2). Only
product chemical shifts are given. In situ NMR experiments were could not be performed
due to the magnetic property of these nanoparticles.
Percentage of conversion from cyclohexene to cyclohexane; 31 %
9.4.33 Hydrogenation of cyclohexene with Ni Nanopowder
Young NMR tube was charged with 0.020 g (0.34 mmol) of Ni nanopowder (prepared from
the hydrogenolysis of Ni(cod)2 with 4 bar H2 in mesitylene similar to NP3 synthesis),
cyclohexene (0.405 g, 4.93 mmol) in tolunene-d8 in glove box. The resultant suspension was
set for 5 bar H2, thereafter the NMR tube was kept for mechanical rotation for 12h at room
temperature. Then it was placed in an oil bath at 100 C for another 12h. The NMR tube was
transferred into the glove box. The black particles were allowed to settle and the colorless
solution was removed with for further analysis.
1
H-NMR (Tol-d8, 250.1MHz, 25 C):  = 1.41 ppm (s, 12H, cyclohexene, -CH2). Only
product chemical shifts are given. In situ NMR experiments were could not be performed
due to the magnetic property of these nanoparticles.
Percentage of conversion from cyclohexene to cyclohexane; 95 %
9.5. Handling and Disposal of Solvents and Residual Wastes
1. The recovered solvents were condensed into a liquid nitrogen cold-trap under vacuo
and collected in halogen-free or halogen-containing solvent containers, and stored for
disposal.
2. Sodium metal used for drying solvents was collected and reacted carefully with isopropanol and poured into the base-bath for cleaning glassware.
213
Chapter 9
Experimental section
3. Ethanol and acetone used for low temperature reactions for cold-baths (with solid
CO2 or liquid N2) were subsequently used for cleaning the glassware.
…………………………………………………………………………………………………………………….. 9.6
References
[1]
M. J. Duer (Ed.), Solid-State NMR, Blackwell Science, Oxford, 2002.
[2]
G. M. Sheldrick, SHELXS-97, Program for crystal structure solution, Universität
Göttingen; 1997.
[3]
G. M. Sheldrick, SHELXL-97, Program for crystal structure refinement, Universität
Göttingen, 1997.
[4]
A. L. Spek, Acta Crystallogr., Sect. A: Found. Crystallogr. 1990, 46, C34.
[5]
P. Van der Sluis, A. L. Spek, Acta Crystallogr. 1990, A46, 194-201.
[6]
http://linden-cms.de/
[7]
J. W. Niemantsverdriet, Spectroscopy in Catalysis, 2nd Ed., Wiley-VCH, New York,
2000.
[8]
E. Lifshin, in Characterisation of Materials – Materials Science and Technology,
Vol. 2a/2b (Eds.: R. W. Cahn, P. Haasen, E. J. Kramer), Wiley-VCH, New York,
2005.
[9]
N. J. Hardman, B. E. Eichler, P. P. Power, Chem. Commun. 2000, 1991-1992.
[10]
J. X. McDermott, J. F. White, G. M. Whitesides, J. Am. Chem. Soc. 1976, 98, 65216528.
[11]
P. Burger, J. M. Baumeister, J. Organomet. Chem. 1999, 575, 214 - 222.
[12]
A. Sidiropoulos, C. Jones, A. Stasch, S. Klein, G. Frenking, Angew. Chem. 2009,
121, 9881–9884; Angew. Chem. Int. Ed. 2009, 48, 9701-9704.
[13]
W. Uhlig, J. Organomet. Chem. 1996, 516, 147-154.
[14]
T. Bollermann, A. Puls, C. Gemel, T. Cadenbach, R. A. Fischer, Dalton Trans. 2009,
1372-1377.
[15]
L. Jafarpour, E. D. Stevens, S. P. Nolan, J. Organomet. Chem. 2000, 606, 49-54.
[16]
H. Suzuki, H. Omori, D. H. Lee, Y. Yoshlda, Y. Moro-oka, Organometallics. 1988,
7, 2243–2247.
[17]
S. B. Jensen, S. J. Rodger, M. D. Spicer, J. Organomet. Chem. 1998, 556, 151-158.
[18]
D. J. Krysan, P. B. Mackenzie, J. Org. Chem. 1990, 55, 4229-4230.
214
Chapter 9
[19]
Experimental section
M. Molon, T. Bollermann, C. Gemel, J. Schaumann, R. A. Fischer, Dalton Trans.
2011, 40, 10769-10774.
[20]
P. Jutzi, B. Neumann, G. Reumann and H. G. Stammler, Organometallics. 1998, 17,
1305-1314.
[21]
P. Jutzi and L. O. Schebaum, J. Organomet. Chem.2002, 654, 176-179.
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J. Feldman, S. J. McLain, A. Parthasarathy, W. J. Marshall, J. C. Calabrese, S. D.
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2763-2765.
215
Crystallographic data
10
Crystallographic Tables
Table 10.1
2
3
4
5
Empirical Formula
C44H61 Cl2GaN2Pt
C53H69Cl2GaN2Pt
C38H52F3GaN2O3S
C39 H59 GaN2 Pt
M.W (g /mol)
953.66
1069.81
743.60
820.69
Data / restraints /
6936 / 120 / 398
8538 / 42 / 483
4707 / 0 / 429
6627 / 13 / 400
Data coll, T, K
111(2)
110(2)
123(2) K
113(2)
Wavelength (Mo-Kα), Å
0.71073
0.71073
0.71073 A
0.71073
Crystal system,
Triclinic,
Monoclinic,
Monoclinic,
Orthorhombic,
P-1
P 21/c
P2(1)/n
Pna2(1)
a, Å
11.0869(12)
20.3741(11)
12.0867(7)
35.8034(16)
b, Å
12.4058(11)
18.3324(10)
12.7569(7)
9.7011(4)
c, Å
15.6409(16)
12.9208(7)
24.5174(16)
10.2689(4)
α, deg
88.722(8)
90.00
90
90
β, deg
79.674(9)
90.083(5)
90.261(8)
90
γ, deg
69.390(9)
90.00
90
90
V, A
1979.0(3)
4826.0(5)
3780.3(4)
3566.7(3)
Z, ρ (Calcd) Mg/m3
2, 1.600
4, 1.472
4, 1.307
4, 1.528
μ, mm-1
4.380
3.601
0.835
4.702
F(000)
964
2176
1568
1664
Crystal size, mm
0.35 x 0.30 x 0.25
0.31 x 0.10 x 0.07
0.46 x 0.25 x 0.20
θ range, deg
3.09 to 25.00
2.90 to 25.05
3.19 to 24.99
0.08 x 0.04 x
0.03
2.89 to 25.50
Reflections
collected/unique
12433 / 6936
[R(int) = 0.1060]
70499 /8538
[R(int) = 0.1515]
9235 / 4707 [R(int) =
0.0294]
Completeness to theta =
25.00,
Absorption correction
99.6%
99.8 %
70.7 %
40105 / 6627
[R(int)
=
0.0831]
99.8%
Empirical
Empirical
Empirical
Empirical
parameters
space group
3
Max.
and
min.
transmission
Goodness-of-fit on F2
0.4073 and 0.3094
0.7866 and 0.4015
0.8508 and 0.6999
0.860 and 0.790
0.683
0.950
0.989
1.079
Final
R
[I>2sigma(I)]
R1 = 0.0573,
wR2 = 0.0997
R1 = 0.0544,
wR2 = 0.1099
R1 = 0.0381
wR2 = 0.1007
R1 = 0.0367,
R1 = 0.1407,
wR2 = 0.1115
R1 = 0.0962,
wR2 = 0.1177
R1 = 0.0540
1.934 and -1.426
0.948 and -1.842
0.717 and -0.430
indices
R indices (all data)
Largest diff. peak and
hole, e.A-3
216
wR2 = 0.1054
wR2 = 0.0690
R1 = 0.0449,
wR2 = 0.0716
1.225 and -1.545
Crystallographic data
Table 10.2
6
7
8
9
Empirical Formula
C54H76Cl3Ga5Pt
C29 H41GaN2P4
C39H41GaMo2N2O10P4
C33H41FeGaN2O4P4
Molecular Weight
1375.19
611.24
1083.22
779.13
6614 / 161 / 354
6462 / 0 / 325
10628 / 0 / 513
7601 / 0 / 416
Data coll, T, K
110(2)
113(2) K
107(2)
113(2)
Wavelength (Mo-Kα),
0.71073
0.71073 A
0.71073
0.71073
Orthorhombic,
Tetragonal,
Monoclinic,
Monoclinic,
Pnma
P43212
P21/n
P2(1)/n
a, Å
20.1048(3)
19.9661(7)
13.8185(2)
11.313(2)
b, Å
24.4436(5)
19.9661(7)
11.1546(2)
20.410(4)
c, Å
11.5010(2)
18.6059(15)
39.2533(7)
19.139(4)
α, deg
90
90
90
90
β, deg
90
90
91.701(2)
101.96(3)
γ, deg
90
90
90
90
V, A
5651.98(17)
7417.2(7)
6047.82(18)
4323.0(15)
Z, ρ (Calcd) Mg/m3
4, 1.616
8, 1.095
4, 1.190
4, 1.197
μ, mm-1
4.990
0.932
0.997
1.139
F(000)
2736
2560
2176
1608
Crystal size, mm
0.55 x 0.14 x 0.04
0.21 x 0.09 x 0.07
0.17 x 0.15 x 0.12
0.38 x 0.17 x 0.12
θ range, deg
3.06 to 27.50
2.99 to 25.00
2.95 to 25.00
2.95 to 25.00
Reflections
collected/unique
72196 / 6614
14147 / 6462
67025 / 10628
15144 / 7601
(g /mol)
Data / restraints /
parameters
Å
Crystal system,
space group
3
[R(int) = 0.0561]
[R(int) = 0.0898]
[R(int) = 0.0292]
[R(int) = 0.0265]
99.7 %
99.5 %
99.8%
99.8 %
Empirical
Empirical
Empirical
Empirical
Max.
and
min.
transmission
Goodness-of-fit on F2
0.8254 and 0.1700
0.930 and 0.900
0.8897 and 0.8488
0.870 and 0.790
0.906
0.873
1.060
1.027
Final
R
[I>2sigma(I)]
R1 = 0.0266,
R1 = 0.0570,
R1 = 0.0303,
R1 = 0.0361,
wR2 = 0.0570
wR2 = 0.1330
wR2 = 0.0875
wR2 = 0.0961
R1 = 0.0447,
R1 = 0.0966,
R1 = 0.0382,
R1 = 0.0490,
wR2 = 0.0586
wR2 = 0.1400
wR2 = 0.0894
wR2 = 0.0996
1.259 and -0.787
1.275 and -0.421
0.482 and -0.395
0.555 and -0.351
Completeness to theta
= 25.00,
Absorption correction
indices
R indices (all data)
Largest diff. peak and
hole, e.A-3
217
Crystallographic data
Table 10.3
10
11
12
13
Empirical Formula
C64H87FGa2Ge4N4
C58H82Ga2Ge2N4
C56H79GaN2Ru2
C68H96Cl2Ga2N4Ru
M.W (g / mol)
1361.18
1119.90
1052.07
1280.90
Data / restraints /
6540 / 0 / 307
4869 / 0 / 303
8444 / 39 / 536
12093 / 0 / 716
Data coll, T, K
110(2) K
110(2)
110(2)
110(2) K
Wavelength (Mo-Kα),
0.71073 A
0.71073
0.71073
0.71073 A
Trigonal,
Monoclinic,
Orthorhombic,
Triclinic,
P3(1)21
C2/c
P2(1)2(1)2(1)
P-1
a, Å
19.5740(3)
24.2323(10)
14.0064(7)
13.7469(3)
b, Å
19.5740(3)
15.2254(8)
16.1944(8)
16.3086(4)
c, Å
15.2771(3)
15.0722(8)
22.4033(11)
17.7352(5)
α, deg
90
90
90
110.706(2)
β, deg
90
94.492(4)
90
109.472(2)
γ, deg
120
90
90
92.319(2
V, A
5069.10(15)
5543.8(5)
5081.64(4)
3449.57(15)
Z, ρ (Calcd) Mg/m3
3, 1.338
4, 1.342
4, 1.375
2, 1.233
μ, mm-1
2.583
2.075
1.150
1.108
F(000)
2094
2336
2192
1344
Crystal size, mm
0.20 x 0.18 x 0.12
0.06 x 0.06 x 0.04
0.20 x 0.15 x 0.10
0.10 x 0.10 x 0.06
θ range, deg
2.92 to 26.50
3.00 to 25.00
2.91 to 25.00
2.97 to 25.00
Reflections
collected/unique
10993 / 6540
30770 / 4869
17877 / 8444
21126 / 12093
[R(int) = 0.0203]
[R(int) = 0.1312]
[R(int) = 0.0800]
[R(int) = 0.0317]
99.6 %
99.9%
96.5
99.6
Empirical
Empirical
Empirical
Empirical
Max. and min.
transmission
Goodness-of-fit on F2
0.730 and 0.600
0.910 and 0.880
0.8937 and 0.8026
0.920 and 0.890
1.034
1.026
0.692
0.844
Final R indices
[I>2sigma(I)]
R1 = 0.0295,
R1 = 0.0564,
R1 = 0.0444,
R1 = 0.0322,
wR2 = 0.0812
wR2 = 0.1024
wR2 = 0.0609
wR2 = 0.0699
R1 = 0.0366,
R1 = 0.0954,
R1 = 0.0899,
R1 = 0.0552,
wR2 = 0.0820
wR2 = 0.1152
wR2 = 0.0.0675
wR2 = 0.0723
0.633 and-0.452
0.677 and -0.617
0 .790 and -0.476
0.732 and -0.412
parameters
Å
Crystal system,
space group
3
Completeness to theta
= 25.00,
Absorption correction
R indices (all data)
Largest diff. peak and
hole, e.A-3
218
Crystallographic data
Table 10.4
14
15

16
17
C54H72Cl4N4Ti  6
C4H8O
1399.48
C54H72F4N4Ti 
4.5 C4H8O
1225.52
Empirical Formula
C73H99CuF3Ga2N4O3S2
Molecular Weight
1404.66
C27H36Cl4N2Ti
C7H8
762.55
3321 / 0 / 160
5307 / 0 / 238
6912 / 249 / 614
12444 / 56 / 581
Data coll, T, K
112(2)
107(2)
108(2) K
108(2)
Wavelength (Mo-Kα),
0.71073
0.71073
0.71073 A
0.71073
Monoclinic,
C2/m
Orthorhombic,
Pnma
Monoclinic,
Monoclinic,
C 2/c
C 2/c
2
(g /mol)
Data / restraints /
parameters
Å
Crystal system,
space group
a, Å
19.6816(13)
16.1302(8)
24.456(4)
29.6180(14)
b, Å
18.2169(6)
14.7544(7)
15.6066(9)
12.6425(4)
c, Å
11.9282(8)
17.0220(6)
22.661(5)
39.7915(17)
α, deg
90
90
90
90
β, deg
121.448(9)
90
114.83(2)
108.210(5)
γ, deg
90
90
90
90
3648.5(4)
4051.1(3)
7849(2)
14153.5(10)
2, 1.279
4, 1.250
4, 1.184
8, 1.150
3
V, A
Z, ρ (Calcd) Mg/m3
μ, mm-1
1.133
0.505
0.296
0.180
F(000)
1478
1608
3016
5296
Crystal size, mm
0.30 x 0.28 x 0.25
0.12 x 0.12 x 0.10
0.20 x 0.13 x 0.09
2.88 to 29.01
2.79 to 25.00
0.16 x 0.12 x
0.09
2.89 to 25.00
6717 / 3321
88964 / 5307
62633 / 6912
83839 / 12444
[R(int) = 0.0217]
[R(int) = 0.0972]
[R(int) = 0.1249]
99.8%
99.8 %
99.9 %
[R(int)
0.1145]
99.8%
Empirical
Empirical
Empirical
Empirical
0.7648 and 0.7273
0.9512 and 0.9419
0.9738 and 0.9431
1.038
0.9840
0.9718
1.080
θ range, deg
3.00 to 25.00
Reflections
collected/unique
Completeness to theta
= 25.00,
Absorption correction
Max.
and
min.
transmission
Goodness-of-fit on F2
Final
R
[I>2sigma(I)]
indices
R indices (all data)
Largest diff. peak and
hole, e.A-3
1.089
1.081
=
and
R1 = 0.1035,
R1 = 0.0784,
R1 = 0.0694,
R1 = 0.0762,
wR2 = 0.3011
R1 = 0.1110,
wR2 = 0.3073
wR2 = 0.1992
R1 = 0.1172,
wR2 = 0.2182
wR2 = 0.1488
R1 = 0.1128, wR2 =
0.1714
wR2 = 0.1877
R1 = 0.1220,
wR2 = 0.2082
3.828 and -2.913
0.760 and -0.566
0.369 and -0.342
0.318
0.300
219
and
-
Crystallographic data
Table 10.5: a refinement method-Full-matrix least-squares on F2
18
19
20
C36H50N2Zn
Empirical Formula
C86H138Cl6N4O8Ti
Molecular Weight
1616.60
C31H44Cl2N2OZn
C4H8O
669.06
Data / restraints / parameters
7720 / 52 / 451
16717 / 15 / 784
3351 / 62 / 202
Data coll, T, K
108(2)
107(2) K
107(2)
Wavelength (Mo-Kα), Å
0.71073
0.71073 A
0.71073
Crystal system,
Monoclinic,
Monoclinic,
Monoclinic,
C 2/c
P 21
C2/c
a, Å
28.504(8)
13.2002(4)
21.6516(15)
b, Å
17.8876(14)
15.7288(5)
9.3679(4)
c, Å
20.12(3)
17.1657(5)
18.0659(12)
α, deg
90
90
90
β, deg
120.93(3)
91.147(3)
116.560(9)
γ, deg
90
90
90
V, A
8800(13)
3563.29(19)
3277.6(3)
Z, ρ (Calcd) Mg/m3
4, 1.220
4, 1.247
4, 1.168
μ, mm-1
0.334
0.871
0.774
F(000)
3480
1424
1240
Crystal size, mm
0.17 x 0.13 x 0.05
0.20 x 0.12 x 0.10
0.22 x 0.13 x 0.08
θ range, deg
2.93 to 25.00
2.81 to 29.06
2.93 to 26.37
Reflections collected/unique
56520 / 7720
54095 / 16717
17128 / 3351
[R(int) = 0.2883]
[R(int) = 0.0573]
[R(int) = 0.0413]
Completeness to theta =
25.00,
Absorption correction
99.8 %
99.8%
99.8%
Empirical
Empirical
Empirical
Max. and min. transmission
0.9835 and 0.9454
0.9180 and 0.8451
0.940 and 0.880
Goodness-of-fit on F2
1.023
1.048
1.066
R1 = 0.1089,
wR2 = 0.1806
R1 = 0.0635,
wR2 = 0.1489
R1 = 0.0342,
wR2 = 0.0856
R1 = 0.2390,
R1 = 0.0865,
R1 = 0.0439,
wR2 = 0.2364
wR2 = 0.1625
wR2 = 0.0901
2
576.15
(g /mol)
space group
3
Final
R
[I>2sigma(I)]
indices
R indices (all data)
Largest diff. peak and hole,
e.A-3
0.510 and -0.349
0.793 and -0.750
220
0.391 and -0.274
Supporting Information
11
SUPPROTING INFORMATION
11.1 Computational details for compound 11.
(Ga(DPP))2Ge2
1
2
Figure 11.1: (Ga(DPP))2Ge2 1 and model system 2.
LUMO
E = -0.0726
HOMO
E = -0.1322
HOMO-1
E = -0.1361
HOMO-2
E = -0.1657
221
Supporting Information
HOMO-3
E = -0.1761
HOMO-4
E = 0.1845
HOMO-5
E = -0.2316
Figure 11.2: Molecular orbitals of model system 2 (BP86/def2-SVP), orbital energies in
hartree.
Figure 11.3: HOMO-1 orbital of model system 2 (BP86/def2-SVP), E = -0.1361 a.u.; the
main atomic orbitals are the py orbital on atom Ge2 (coefficient: 0.335) and the py orbital on
atom Ge18 (coefficient: 0.335).
Figure 11.4: HOMO-2 orbital of model system 2 (BP86/def2-SVP), E = -0.1657 a.u.; the
main atomic orbitals are s orbitals on atoms Ge2 and Ge18, pz orbitals on atoms Ge2 and
Ge18, and s orbitals on atoms Ga1 and Ga17 (coefficients see table 3).
222
Appendix
12 Appendix
Several paragraphs (text) and figures, schemes of this thesis have already been published in
peer reviewed journals and are reproduced with permissions. References are given to
the Literature reports (chapter 1), figures and tables are also reproduced with
permissions and citations are given accordingly.
12.1
List of Publications
1.
A. Doddi, C. Gemel, M. Winter, R. A. Fischer, C. Goedecke, H. S. Rezpa, G.
Frenking. “Low Valent Ge2 and Ge4 Species Trapped by N-Heterocyclic Gallylene”
Angew. Chem. Int. Ed. 2013, 52, 450-454. DOI: 10.1002/anie.201204440. Angew.
Chem. 2013, 125, 468-472. Copyright © 2013 WILEY-VCH Verlag GmbH & Co.
KGaA, Weinheim. Reproduced with permission.
2.
A. Doddi, C. Gemel, R. W. Seidel, M. Winter, R. A. Fischer, “Coordination
Complexes of TiX4 (X = F, Cl) with Sterically Bulky N-heterocyclic Carbene:
Syntheses, Characterization and Molecular Structures”, Polyhedron. 2013, 0(00), 0000. DOI: 10.1016/j.poly.2012.06.067. Reproduced with permission, Copyright ©
2012, Elsevier. In press.
3.
A. Doddi, C. Gemel, R. W. Seidel, M. Winter, R. A. Fischer, “Synthesis and
Structure of New Compounds with Pt–Ga Bonds: Insertion of the bulky Gallium (I)
Bisimidinate Ga(DDP) into Pt–Cl bond”, J. Organomet. Chem. 2011, 696, 26352640. Reproduced with permission. Copyright © 2011, Elsevier.
4.
A. Doddi, G. Prabusankar, C. Gemel, M. Winter, R. A. Fischer, “N-Heterocyclic
Gallylene Supported Organoruthenium Derivatives: Synthesis, Structure and C–H
activation”.(Submitted to European Journal of Inorganic Chemistry).
5.
G. Prabusankar, A. Doddi, C. Gemel, M. Winter, R. A. Fischer, “P–P Bond
Activation of P4 Tetrahedron by Group 13 Carbenoid and its Bis Molybdenum
Pentacarbonyl Adduct”, Inorg. Chem. 2010, 49, 7976-7980. Reproduced with
permission. Copyright © 2010, American Chemical Society.
6.
G. Prabusankar, S. G. Gallardo, A. Doddi, C. Gemel, M. Winter, R. A. Fischer, “
Linear Coinage Metal Complexes Stabilized by a Group 13 Metalloid Ligand”, Eur.
223
Appendix
J. Inorg. Chem. 2010, 4415-4418. Reproduced with permission. Copyright © 2010
WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Manuscripts in preparation
7.
A. Doddi, C. Kroll, S. B. Kalidindi, C. Wiktor, R. A. Fischer, “Organometallic
Synthesis of NixGay Intermetallic Nanoparticles”. (Manuscript in preparation to
Journal of Materials Chemistry).
8.
A. Doddi, G. Prabusankar, C. Gemel, M. Winter, R. A. Fischer, “Schiff base
Supported Gallium (II) Dimer: Synthesis and Structure”. (Manuscript in preparation
to Journal of Organometallic Chemistry).
9.
A. Doddi, C. Gemel, R. W. Seidel, M. Winter and R. A. Fischer. “Synthesis and
Structural Characterization of RGa (R = DDP, Cp*) Supported New Platinum
Complexes”. (in preparation to ZAAC).
……………………………………………………………………………………………………………
Publications from previous work
1.
A. Doddi, J. V. Kingston, V. Ramkumar, Mika Suzuki, Masashi Hojo, M. N.
Sudheendra Rao, “Synthesis and Characterization of Dianionic hexacoordinate
Silicon (IV) Complexes of Substituted Catechols, Flavones and Fluorone: X-ray
Crystal
Structures
of
[(n-C3H7)2NH2)]2[(Cl4C6O2)3Si].3CH3CN
and
[(n-
C3H7)2NH2)]2[(Br4C6O2)3Si].2(CH3)2SO”, Phosphorus, Sulfur, and Silicon and the
Related Elements, 2012, 187 (3), 342-356.
2.
A. Luiz. T, A. Doddi, B. Varghese and M. N. S. Rao, “Synthesis and characterization
of aminophosphine derivatives of Molybdenum hexacarbonyl. X-ray structure
determination
of
Mo(CO)5(C5H10N)3P,
Mo(CO)5{Ph(OC4H8N)2P}
and
Mo(CO)5{Ph[(i-C3H7)2N][OC4H8N]P}”. Transition Met. Chem, 2008, 33 (6), 745750.
3.
J. Gopalakrishna, Varghese B, A. Doddi, M. N. S. Rao, “A new synthetic route
to cyclophosphadithiatriazenes: synthesis and X-ray structural characterization
the
first
of
spirocycle containing thiadiazaphosphetidine
and
phosphadithiatriazene heterocycles”. Appl. Organometal. Chem, 2006, 20 (12), 880885.
4.
A.
Luiz.
T,
A.
Doddi,
B.
Varghese
and
M.
N.
S.
Rao,
Dicyclohexylamino)(Phenyl)(Piperdino)phosphine”, Acta Cryst, 2007, E63, o3449.
224
“
Appendix
5.
A.
Doddi,
T.
A.
Luiz,
V.
Ramkumar,
M.
N.
S.
Rao,
“Cis-
bis[(benzyl)(methyl)(phenyl)phosphine]tetra(carbonyl)molybdenum(0) ”, Acta Cryst.
2007, E63, m 2727.
6.
P. Parthiban, M. Umamaheswari, A. Doddi, V. Ramkumar, S. Kabilan, “ r-2,c-6Bis(4-bromophenyl)-t-3,t-5-dimethyltetrahydropyran-4-one ”, Acta Cryst E, 2007,
E63, o4373.
7.
S. Ramachandran, P. Parthiban, A. Doddi, V. Ramkumar. S. Kabilan, “r-2,c-6Bis(m-fluorophenyl)t-3,t-5-dimethylpiperidin-4-one ”, Acta Cryst. 2007, E63, o4559.
Book Chapter
A. Doddi and M. N. S. Rao: Contributed to a book chapter in Titled “Experiments in
Green and Sustainable Chemistry” Edited by H. W. Roesky, D. K. Kennepohl, JeanMarie Lehn, WILEY-VCH, 2009: Title of the chapter; “Encapsulated silicon in
hypervalentcoordination-Synthesis and synthetic transformations”, p 149-157.
12.2
Conference presentations and workshops
1.
A. Doddi, S. B. Kalidindi, C. Wiktor, R. A. Fischer, “Organometallic preparation of
Nickel-Gallium Alloy Nanoparticles and their Colloids”. September-27, 3rd Junges
Chemie Symposium”–JCS Ruhr 2012, at Technical University of Dortmund,
Germany.
2.
A. Doddi, C. Gemel, M. Winter, R. A. Fischer, C. Goedecke, H. S. Rezpa, G.
Frenking. “Gallylene supported main-group clusters”. International Conference on
Organometallic Chemistry, XXV-ICOMC-2012, Lisbon, Portugal, 2-7th Sept 2012.
3.
A. Doddi, S. B. Kalidindi, C. Wiktor, R. A. Fischer, “Nanometallurgy in Organic
Solution: Organometallic Synthesis of Intermetallic Nickel-Gallium Nanoparticles”.
International Conference on Organometallic Chemistry, XXV-ICOMC-2012,
Lisbon, Portugal, 2-7th Sept 2012.
4.
A. Doddi, C. Gemel, M. Winter, G. Frenking, R. A. Fischer. “N-Heterocyclic
Carbene Analogue of Ga(I): A Versatile Ligand for Element-Cluster Stabilization”;
(MTIC-XIV, Modern Trends in Inorganic Chemistry), December 10-13, 2011 @
University of Hyderabad, India.
225
Appendix
5.
A. Doddi, C. Gemel, M. Winter, R. A. Fischer. “Carbene Like Low valent
[Ga(DDP)]: A Versatile Ligand for Reduction and Cluster Formation Reactions”.
September-22, 2nd Junges Chemie Symposium, University of Duisburg-Essen, 2011,
Germany.
6.
A. Doddi, C. Gemel, R. A. Fischer. “Activation, Reduction and Cluster formation
reactions with Low-valent N-heterocyclic carbene analogue of Gallium (I)
(GaDDP)”. September-9, 1st Junges Chemie Symposium”-JCS Ruhr 2010, Germany.
7.
A. Doddi, G. Prabusankar, C. Gemel, R. A. Fischer. “N-Heterocyclic Carbene
analogue of Ga(I): Reduction, Insertion and
Cluster formation”; (MTIC-XIII,
Modern Trends in Inorganic Chemistry), December 7-9, 2009 @ IISc–Bangalore,
India.
8.
A. Luiz. T, A. Doddi, B. Varghese and M. N. S. Rao. “Synthesis and X-ray
Structural Characterization of phosphine derivatives of Molybdenumhexacarbonyl”.
(MTIC-XII); December 6-8, 2007 @ IIT-Madras, India.
9.
A. Doddi, M. N. S. Rao, “Synthesis and Characterization of Dianionic
hexacoordinate Silicon (IV) Complexes of Substituted Catechols, flavones and
fluorone: X-ray crystal structures of [(n-C3H7)2NH2)]2[(Cl4C6O2)3Si]. 3CH3CN and
[(n-C3H7)2NH2)]2[(Br4C6O2)3Si]. 2(CH3)2SO. (MTIC-XII) ”, December 6-8, 2007 @
IIT-Madras, India.
10.
"Basic Scientific Presentation" for Doctoral Students, Ruhr-University Bochum
(11.03.2010 to 13.03.2010).
Oral Contributions
1.
“Organometallic preparation of Nickel-Gallium Alloy Nanoparticles and their
Colloids”. September-27, 3rd Junges Chemie Symposium”–JCS Ruhr 2012, at
Technical University of Dortmund, Germany.
2.
“Gallylene
Supported
Main-group
Clusters”.
International
Conference
on
Organometallic Chemistry, XXV-ICOMC-2012, Lisbon, Portugal, 2-7th Sept 2012.
(Oral flash presentation).
3.
“Low-Valent Gallium (I) NHC Analogue Stabilized Novel Main-Group Clusters”. At
2nd Junges Chemie Symposium, Duisburg-Essen, September-22, 2011, Germany.
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Appendix
Prizes and Awards
1. A. Doddi, C. Gemel, M. Winter, G. Frenking, R. A. Fischer. “N-Heterocyclic
Carbene Analogue of Ga(I): A Versatile Ligand for Element-Cluster Stabilization”;
(MTIC-XIV, Modern Trends in Inorganic Chemistry), December 10-13, 2011 @
University of Hyderabad, India. This poster has been selected for the best poster
award.
Curriculum Vitae
12.3
Personal Data
First Name
: Adinarayana
Family Name : Doddi
Nationality
: Indian
Date of Birth : August 28, 1981
Marital Status
: Married
Place of birth : Visakhapatnam; India
Educational qualifications and work experience
04/2009 to present
PhD in the research group of Prof. Dr. Roland A. Fischer, ACII, Faculty of Chemistry and Biochemistry, Ruhr-University
Bochum
03/2008-10/2008
Qualification thesis at Institute for Inorganic Chemistry
University of Bonn, Germany
06/2007-10/2007
Research Associate at Department of Chemistry
Indian Institute of Technology-Madras, Chennai, India
11/2005-12/2006
Junior Research Fellow, IIT-Madras, India
08/2004-10/2005
Research Project, IIT Madras, India
06/2002-07/2004
Master of Science (M. Sc) in Chemistry
Indian Institute of Technology Madras, Chennai, India
05/1998-05/2001
Bachelor of Science (B. Sc), A. M. A. L. College
Language Skills
English (Fluent), Telugu (Mother tongue); German (basic)
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