Synthesis, spectroscopic study and X-ray crystal structure of
unsymmetrical bis(phosphine)-platinum
complex, ½PtCl2fg2-Ph2POCH2CH2NðCH3ÞPPh2
Maravanji S. Balakrishna
a
a,*
, Robert McDonald
b
Department of Chemistry, Indian Institute of Technology, Bombay 400 076, India
Department of Chemistry, University of Alberta, Edmonton, Canada T6G 2G2
b
Abstract
The bis(phosphine), Ph2 POCH2 CH2 NðCH3 ÞPPh2 (1) reacts with ½PtðCODÞCl2 to give seven-membered cis-chelated complex 2.
The complex was characterized by elemental analysis, IR, and NMR spectroscopic methods of which the 31 Pf1 Hg NMR data is very
informative and allows the direct measure of the P–P coupling through metal centers otherwise can not be seen in the free ligand as the
two phosphorus centers are five-bonds apart. The structure of the platinum(II) complex was determined by X-ray crystallography.
Keywords: Unsymmetrical bis(phosphine); Platinum complex; Through-metal coupling; Chelate
1. Introduction
We have been investigating the preparation, spectroscopic and structural studies, and transition metal
chemistry of a variety of phosphorus based acyclic [1]
and cyclic multi-dentate ligands [2] and also the functionalized [3] derivatives of bis(phosphines). The chemistry of this class of ligands is growing rapidly in recent
years because of their versatile coordination chemistry
[4] and their potential usefulness in catalytic applications
[5]. The platinum metal complexes containing unsymmetrical bisphosphines will be very useful in homogeneous catalysis as they cooperate more readily than the
symmetrical ones during oxidative addition reactions.
The ease with which the chelate ring opens, ultimately
decides the efficiency of that catalyst and the turn over
number. In addition, the ligands with asymmetric
phosphorus centers would be well suited for the study of
phosphorus–phosphorus coupling through the metal in
their chelate complexes. In this preliminary communication we describe the synthesis, spectral characterization, and X-ray structure of a platinum complex
containing
bis(phosphine)
ligand
N,O-bis(diphenylphosphino)-N-methylethanolamine.
2. Experimental
All manipulations were performed under rigorously
anaerobic conditions using Schlenk and vacuum line
techniques. Solvents were dried and distilled under the
nitrogen atmosphere prior to use. N-methylethanolamine
was obtained from Lancaster Synthesis, and used without
further purification; [Pt(COD)Cl2 ] [6] was prepared according to published procedures. The 1 H and 31 P NMR
spectra were recorded on a VXR 300S spectrometer operating at the appropriate frequencies using tetramethylsilane and 85% H3 PO4 as internal and external references,
respectively. Positive shifts lie downfield of the standard
in all cases. Microanalyses were performed on a Carlo
Erba (Thermoquest) model 1112 elemental analyser.
2.1. Synthesis of Ph2 POCH2 CH2 N ðCH3 ÞPPh2 ð1Þ
A solution of PPh2 Cl (14.5 g, 65.7 mmol) in dry diethyl ether (40 ml) was added with stirring to a solution
of N-methylethanolamine (4.93 g, 65.6 mmol) and
triethylamine (6.75 g, 66.7 mmol) at )10 °C also in di-
783
Table 1
Crystal data for ½PtCl2 fPh2 POðCH2 Þ2 NðCH3 ÞPPh2 g (2)
Formula
Formula weight
Crystal dimensions (mm)
Crystal system
Space group
Unit cell parametersa
)
a (A
)
b (A
)
c (A
a (deg)
b (deg)
c (deg)
3 )
V (A
Z
qcalcd ðg=cm3 Þ
l (mm1 )
Data collection 2h limit (°)
Reflections observed
Final R indices
Goodness-of-fit (S)
C27 H27 Cl2 NOP2 Pt
709.43
0:46 0:21 0:14
Triclinic
P1(No. 2)
9.4580 (4)
9.8528 (5)
14.5068 (6)
73.2880 (7)
77.9018 (9)
83.5843 (8)
1264.09 (10)
2
1.864
5.910
52.76
4655
R1 0.0225
wR2 0.0576
1.047
ethyl ether (75 ml). The stirring was continued for 3 h
and the solution was warmed to 0 °C and triethylamine
(6.75 g, 66.7 mmol) in dry diethyl ether (20 ml) was
added followed by the dropwise addition of PPh2 Cl
(14.5 g, 65.7 mmol) in a mixture of diethyl ether (60 ml)
and hexane (25 ml). Stirring was continued for 24 h at
room temperature. The reaction mixture was then filtered. The filtrate was passed through activated silica gel
and then through celite and the solvent was evaporated
under reduced pressure to give analytically pure product
of 1 as colorless oily liquid. Yield: (25 g, 56.4 mmol),
86%. Anal. Calc. for C27 H27 NOP2 : C, 73.13%; H,
6.13%; N, 3.15%. Found: C, 73.32%; H, 6.11%; N,
3.02%. 1 H NMR (CD2 Cl2 ): d 6.82–7.41 (20 H, m, phenyl), 3.28 (4 H, m, CH2 CH2 ); 2.44 (6 H, t, N-CH3 Þ.
31
Pf1 HgNMR (CD2 Cl2 ): d 114.3 (PO ), 58.6 (PN ), no JPP
was observed.
2.2. Synthesis of [PtCl2 fPh2 POCH2 CH2 N ðCH3 ÞPPh2 g]
A solution of Ph2 POCH2 CH2 NðCH3 ÞPPh2 (0.25 g,
0.6 mmol) in dry CH2 Cl2 (8 ml) was added dropwise to a
solution of [(COD)PtCl2 ] (0.22 g, 0.6 mmol) also in
CH2 Cl2 (10 ml). The reaction mixture was stirred at
room temperature for 2 h. The solution was concentrated to 6 ml, and then 2 ml of n-hexane was added.
Cooling this solution to 0 °C gave a colorless analytically pure crystalline product of 2 in 89% (0.35 g, 0.5
mmol) yield. m.p. 198–201 °C. Anal. Found: C, 45.58;
H, 3.81; N, 1.83. Calculated for C27 H27 Cl2 NOP2 Pt: C,
45.71%; H, 3.83%; N, 1.97%. 1 H NMR (CD2 Cl2 ): d
7.32–7.78 (20 H, m, phenyl), 3.82 (m), 4.22 (m) (4 H,
CH2 CH2 ), 2.70 (3 H, d, N-CH3 , 3 JPH 7.6 Hz). 31 Pf1gH
NMR(CD2 Cl2 ): d 76.7 (PO ), 62.3 (PN ), 2 JPPtP ¼
13:3 Hz; 1 JPtPðOÞ ¼ 4066:5 Hz; 1 JPtPðNÞ ¼ 3933 Hz.
2.3. Structure determination
) crysA colorless crystal of 2 ð0:46 0:21 0:14 A
tallized from CH2 Cl2 at 0 °C was mounted on Pyrex
filaments with epoxy resin. Unit cell dimensions were
determined from 25 well-centered reflections. Intensity
data were collected ()80 °C) with a Bruker P4/RA/
SMART 1000 CCD [7] diffractometer using graphite) radiation. The demonochromated MoKa (0.71073 A
tails of the crystal and data collection for 2:
) ¼ 9.4580
C27 H27 Cl2 NOP2 Pt, M ¼ 709:43, triclinic, a (A
Table 2
Selected bond distances and bond angles for ½PtCl2 fPh2 POCH2 CH2 NðCH3 ÞPPh2 g (2)
)
Bond distances (A
Pt–Cl(1)
Pt–Cl(2)
Pt–P(1)
Pt–P(2)
P(1)–O
P(1)–C1(1)
P(1)–C2(1)
Bond angles (°)
Cl(1)–Pt–Cl2
Cl(1)–Pt–P(1)
Cl(1)–Pt–P(2)
Cl(2)–Pt–P(1)
Cl(2)–Pt–P(2)
P(1)–Pt–P(2)
Pt–P(1)–O
Pt–P(1)–C(11)
Pt–P(1)–C(21)
O–P(1)–C(11)
O–P(1)–C(21)
C(11)–P(1)–C(21)
2.3381(9)
2.3645(7)
2.2153(9)
2.2379(7)
1.610(2)
1.815(3)
1.804(3)
87.84(3)
174.63(3)
93.52(3)
87.25(3)
172.23(3)
91.63(3)
116.92(9)
113.23(12)
114.80(11)
105.02(13)
98.88(13)
106.46(15)
P(2)–N
P(2)–C(31)
P(2)–C(41)
O–C(1)
N–C(2)
N–C(3)
C(1)–C(2)
Pt–P(2)–N
Pt–P(2)–C(31)
Pt–P(2)–C(41)
N–P(2)–C(31)
N–P(2)–C(41)
C(31)–P(2)–C(41)
P(1)–O–C(1)
P(2)–N–C(2)
P(2)–N–C(3)
C(2)–N–C(3)
O–C(1)–C(2)
N–C(2)–C(1)
1.660(3)
1.822(3)
1.819(3)
1.452(4)
1.464(4)
1.461(4)
1.507(5)
113.37(10)
107.30(9)
117.07(10)
111.19(15)
104.92(13)
102.50(15)
122.9(2)
120.7(2)
122.5(2)
115.7(2)
112.9(3)
114.1(3)
784
) ¼ 9.8528 (5) c (A
) ¼ 14.5068 (6), að°Þ ¼
(4) b (A
73.2880(7), 3 bð°Þ ¼ 77.9018(9), cð°Þ ¼ 83.5843 (8),
) ¼ 1264.09 (10), Tm (K) ¼ 293(2). Space
Z ¼ 2, V (A
group P1 (No. 2), D(calc) (g=cm3 Þ ¼ 1.864. l (MoKaÞ ¼ 5:910mm1 , reflections observed, 4655 (R
(int) ¼ 0.0348). The final R1 was 0.0225 (all data) and
wR2 ¼ 0:0576 (all data) (see Table 1). Periodic monitoring of check reflections showed stability of the intensity data. All calculations were performed with the
SHELXTL PLUS [8] program package. The data is
deposited in Cambridge Crystallographic Data Center
and the CCDC reference number is 150093. The structure was solved by direct methods [8] and refined by
using Shelex-93 software [9]. The non-hydrogen atoms
were geometrically fixed and allowed to refine using a
riding model. Absorption correction was employed
Gaussian integration (face-indexed). A perspective view
of 2 is illustrated in Fig. 2. Selected bond lengths and
angles are given in Table 2.
3. Results and discussion
N-methylethanolamine reacts with two moles of
chlorodiphenylphosphine in the presence of triethylamine to afford the unsymmetrical bisphosphine 1 in
good yield. The 31 P NMR spectrum of 1 shows two
single resonances at 114.3 and 58.6 ppm, respectively for
PO and PN centers and no phosphorus–phosphorus
coupling was observed. The reaction of N,O-bis(diphenylphosphino)-N-methylethanolamine (1) with 1:1
molar proportion of [Pt(COD)Cl2 ] in dichloromethane
Fig. 1.
31
affords the chelate complex 2 in good yield. The 31 P
NMR spectrum of the complex 2 is shown in Fig. 1. The
31
P NMR spectrum shows two doublets at 76.7 and 62.3
ppm, respectively for PO and PN centers with a 2 JPP
coupling of 13.3 Hz. The two phosphorus centers interact via through metal as they are only two bonds
apart. Both the phosphorus centers in complex 2 exhibit
1
JPtP coupling of 4066 and 3933 Hz, respectively.
The assignment of the chemical shifts are made in
comparison [1b,1c] with analogous complexes of N,
N 0 -bis(diphenylphosphino)-N ; N 0 -dialkyl/aryl-ethylenediamines. Usually the secondary amine derivatives of
phosphines are relatively shielded when compared to the
alcohol derivatives. This type of complexes gives the
actual magnitude of 2 JPP coupling that comes only by
through-metal interactions. Grim and co-workers, and
others have studied [10,11] the phosphorus–phosphorus
couplings in systems where the phosphorus centers interact via both the ligand backbone and through metal.
They have clearly mentioned about the through-metal
contribution towards the phosphorus–phosphorus couplings; yet, they were inconclusive about the amount of
contribution that actually comes via through–metal interactions. However, the present system can actually
assist in knowing the magnitude of through-metal couplings in related systems.
The structure of the platinum complex 2 has been
determined by single crystal X-ray diffraction studies.
Perspective view of the molecule and the numbering
scheme are shown in Fig. 2 with selected bond lengths
and bond angles in Table 2. The compound contains
the ligand chelating to platinum which, with the two
Pf1 HgNMR spectrum of ½PtCl2 fg2 -Ph2 POðCH2 Þ2 CH2 NðCH3 ÞPPh2 g, ppm vs 85% HPO4 .
785
Fig. 2. Perspective view of 2 showing the atom numbering scheme. Hydrogen atoms on phenyl groups are omitted for clarity.
chloride ligands gives an approximately square planar
geometry. The P(2)–N and P(1)–O distances are 1.660(3)
, respectively. The Pt–Cl and Pt–P disand 1.610(2) A
tances are within the range found previously for similar
complexes [1b,1c]. The slight differences observed may
result from packing or solid-state effects. The sum of the
angles at nitrogen is 359.3° and is virtually planar. The
Cl–Pt–Cl and P(1)–Pt–P(2) bond angles are 87.84 and
91.63°, respectively. Finally, the ligand backbone is in
the ‘‘lazy chair’’ conformation.
In summary, the unsymmetrical ligand and its platinum complex are synthesized in good yield. The platinum complex shows phosphorus–phosphorus coupling
which is not observed in the free ligand. Further, metal
chemistry and spectroscopic investigations of this and
related unsymmetrical ligands are under active investigation in our laboratory.
Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Center, CCDC no. 166571. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ
(fax: +44-1223-336033; E-mail: [email protected]
or interrefhttp://www.ccdc.cam.ac.ukurlhttp://www.ccdc.
cam.ac.uk).
Acknowledgements
We thank the Department of Science and Technology
(DST), India, for the financial support of the work done
at the Indian Institute of Technology, Bombay and the
University of Alberta, Edmonton, Canada for the support of the Diffractometer laboratory.
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