Synthesis and electronic properties of
new organic materials
––––––––––––––––––––––––––––––––
Synthese und elektronische
Eigenschaften von neuen organischen
Materialien
Der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität
Erlangen-Nürnberg
zur Erlangung des Doktorgrades Dr. rer. nat.
vorgelegt von
Anna Chiara Sale
aus Bitti
Als Dissertation genehmigt
von der Naturwissenschaftlichen Fakultät
der Friedrich-Alexander-Universität Erlangen-Nürnberg
Tag der mündlichen Prüfung: 7/05/2015
Vorsitzender des Promotionsorgans:
Prof. Dr. Jörn Wilms
Gutachter:
Prof. Dr. Rik R. Tykwinski
Gutachter:
Prof. Dr. Norbert Jux
Die vorliegende Arbeit entstand in der Zeit von März 2012 bis Februar 2015 am Institut für
Organische Chemie (Lehrstuhl I) der Friedrich-Alexander-Universität (FAU) ErlangenNürnberg.
Pro sa vamiglia mea e Giovanni.
Per la mia famiglia e Giovanni.
„La più bella e profonda emozione che possiamo provare è il senso del mistero; sta
qui il seme di ogni arte, di ogni vera scienza“
A. Einstein
Zusammenfassung
Diese Arbeit basiert auf des Untersuchung an polyzyklischen aromatischen Kohlenwasserstoffen
(PAH). Der erste Teil dieser Arbeit befasst sich mit den elektrochemischen Untersuchungen von
PAH: Pentacenderivate sowie verschiedene kationische Triangulene und Heterotriangulene wurden
durch Cyclovoltammetrie analysiert. Der zweite Teil dieser Arbeit konzentriert sich auf die
Synthese arylsubstituierte, Benzolderivate und ihrer Anwendung in der Diels-Alder Reaktion, um
Bausteine für PAH herzuskellen. In diesem Zusammenhang werden Triine mit verschiedenen
Endgruppen synthetisiert, in einer Diels-Alder Reaktion mit Tetraphenylcyclopentadienon
umgesetzt und anschließend in Desilylierungs und Homokupplungs Reaktionen weiter verwendet.
Die Diels-Alder-Cycloadditionen werden entweder unter thermischen Bedingungen oder
Mikrowellenbestrahlung durchgeführt.
Kapitel 1 der vorliegenden Dissertation gibt einen Einblick in kohlenstoffreichen Materialien mit
Schwerpunkt auf PAH. Zudem wird ein Überblick über die Analysemethode Cyclovoltammetrie
und ihre Verwendung bei mehreren Klassen von PAH gegeben: Pentacen-Derivate, kationische
Triangulene und Heterotriangulene. Abschließend werden allgemeine Synthesevorschiften für
Triine im Zusammenhang mit der Reaktivität von Polyinen diskutiert.
Kapitel 2 zeigt die Synthese und die elektrochemischen Eigenschaften von arylsubstituierten
Pentacenen.
Ihre
relativen
HOMO-LUMO
Bandlücken
werden
im
Kontext
ähnlicher
literaturbekannter Verbindungen untersucht.
Kapitel 3 beschreibt die Synthese und die elektrochemischen Eigenschaften der TriangulenDerivate. Der erste Teil des Kapitels konzentriert sich auf die Cyclovoltammetrie von kationischen
Triangulenen und deren Helicen-Vorstufen im Vergleich mit dem aktuellen Literatur. Der zweite
Teil des Kapitels beschäftigt sich mit der Cyclovoltammetrie von Heterotriangulen Derivaten.
Kapitel 4 beschreibt die Synthesen verschiedener substituierter Triine. Diese werden in einer DielsAlder-Cycloaddition, sowohl unter konventionellem Heizen als such unter Mikrowellenbestrahlung,
durchgeführt. Tetraphenylcyclopentadienon reagiert als Dien mit den entsprechenden Triinen zu
Tetraphenyl-substituierten Benzolderivaten. Hieraus sind durch eine Abfolge von Desilylierungs
und Homokupplungs Reaktionen Dimere erhalten wurden. Monomere und Dimere sind durch UVvis Spektroskopie, Cyclovoltammetrie und Röntgenkristallographie charakterisiert wurden.
Kapitel 5 beinhaltet die experimentellen Vorschriften und Daten der Vorstufen und der
Zielmoleküle. In Kapitel 6 sind die 1H und 13C NMR Spektren zu finden.
Abstract
The work described in this thesis is focused on the investigation of polycyclic aromatic
hydrocarbons (PAHs). The first topic concerns the electrochemical investigation of PAHs.
Pentacene derivatives as well as various cationic triangulenes and heterotriangulenes are analyzed
by cyclic voltammetry. The second topic of the thesis is related to the use of the Diels-Alder
reaction to obtain aryl substituted benzene derivatives, which might be utilized as precursors for the
assembly of PAH. In this context, different end-capped triynes are synthesized as building blocks
that are used in Diels-Alder reactions with tetraphenylcyclopentadienone. The Diels-Alder
cycloadditions are performed under either thermal conditions or microwave irradiation. Selected
Diels-Alder products are taken on to a sequence of desilylation and homocoupling reactions.
Chapter 1 introduces carbon-rich materials with the focus on PAHs. This includes an overview
about the cyclic voltammetry analysis of several class of PAHs is then presented: pentacene
derivatives, cationic triangulenes, and heterotriangulene. Finally, general protocols to synthesize
triynes are discussed, together with some example of polyynes reactivity.
Chapter 2 presents the synthesis and electrochemical investigation of aryl substituted pentacenes
and the relative HOMO-LUMO gaps are investigated. The results are compared to those obtained
for similar compounds reported in literature.
Chapter 3 describes the synthesis and electrochemical properties of triangulene derivatives. The
first part of the chapter is focused on the cyclic voltammetry of cationic triangulenes and their
helicene precursors. The results are compared to those obtained for similar compounds known in
literature. The second part of the chapter deals with the cyclic voltammetry of heterotriangulene
derivatives, and the results are compared to those reported for similar compounds.
Chapter 4 describes the synthesis of different substituted triynes. The resulting triynes are taken on
to a Diels-Alder cycloaddition reaction which is performed under conventional heating as well as
under microwave irradiation. Tetraphenylcyclopentadienone is used as the diene in the Diels-Alder
reactions, and this overall reaction results in the construction of tetraphenyl-substituted benzene
derivatives. Selected products of these Diels-Alder reactions are taken on to a sequence of
desilylation and homocoupling reactions to provide dimers. Selected monomers and dimers have
been analyzed by UV-vis spectroscopy, cyclic voltammetry, and X-ray crystallography.
Chapter 5 includes experimental data of the precursors and target compounds, and a description of
instruments and methods is provided. Chapter 6 presents an appendix containing the 1H and
NMR spectra of selected compounds.
13
C
List of Symbols
Å
Angström
δ
chemical shift (NMR)
ε
molar extinction coefficient
Δ
heat
λ
wavelength
λmax
wavelength of lowest energy absorption
μ
micro
J
Coupling constant (NMR)
List of Abbreviations
ACN
acetonitrile
APPI
atmospheric pressure photoionization
aq
aqueous
Ar
aryl
Bu
n-butyl
calcd
calculated
CCDC
Cambridge Crystallographic Data Centre
cm
centimeter(s)
cmpd
compound
CV
cyclic voltammetry
d
doublet (NMR)
d
day(s)
deg
degree(s)
decomp
decomposition
DMF
N, N-dimethylformamide
D-π-A
donor-π-acceptor
E
electrochemical potential
E½
electrochemical half-wave potential
EA
elemental analysis
Egap, el
electrochemical band gap energy
ESI
electrospray ionization
Et
ethyl
EtOAc
ethyl acetate
equiv
equivalent(s)
eV
electron volt(s)
FBW
Fritsch-Buttenberg-Wiechell
Fc/Fc+
ferrocene/ferrocenium
g
gram(s)
h
hour(s)
HOMO
highest occupied molecular orbital
HRMS
high resolution mass spectrometry
Hz
Hertz
i
iso
IR
infrared
irrev
irreversible
L
liter(s)
LUMO
lowest unoccupied molecular orbital
m
multiplet (NMR)
m
medium (IR)
m
meta
M
formula weight
m
molar
LDI
laser desorption ionization
Me
methyl
mg
milligram(s)
MHz
megaHertz
Min
minute(s)
mL
milliliter(s)
mmol
millimole(s)
mol
mole(s)
Mp
melting point
MS
mass spectrometry
mV
millivolt(s)
mw
microwave
m/z
mass-to-charge ratio
n-BuLi
n-butyllithium
NIR
near-infrared
nm
nanometer(s)
NMP
n-methyl-2-pyrrolidone
NMR
nuclear magnetic resonance
o
ortho
o-DCB
1,2-dichlorobenzene
OFET
organic field effect transistor
p
para
PAH
polycyclic aromatic hydrocarbon
PCC
pyridinium chlorochromate
Ph
phenyl
ppm
parts per million
Pr
propyl
q
quartet (NMR)
quant
quantitative
Rf
retention factor
ref
reference
rt
room temperature
s
singlet (NMR)
s
strong (IR)
s
second(s)
satd
saturated
sev
several
Sub
suberyl
t
triplet (NMR)
t
tertiary
TBAF
tetrabutyl ammonium fluoride
TCNE
tetracyanoethylene
temp
temperature
TES
triethylisilyl
THF
tetrahydrofuran
TIPS
triisopropylsilyl
TIPS-pc
6,13-bis(triisopropylsilylethynyl)pentacene
TLC
thin layer chromatography
TMEDA
N,N,Nʹ′,Nʹ′-tetramethylethylenediamine
TMS
trimethylsilyl
TOF
time-of-flight
TPCPD
tetraphenylcyclopentadienone
Tr*
tris(3,5-di-t-butylphenyl)methyl
TTF
tetrathiafulvalene
UV
ultraviolet
vis
visible
vw
very weak (IR)
w
weak (IR)
V
volt
Table of Contents
Chapter 1. Introduction........................................................................................................... 1
1.1
Carbon-rich compounds and polycylic aromatic hydrocarbons (PAHs) ..................... 1
1.2
Acenes and pentacene .................................................................................................. 3
1.3
Triangulenes as a class of PAH ................................................................................... 7
1.3.1
Cationic triangulenes............................................................................................ 8
1.3.2
Heterotriangulenes ............................................................................................... 9
1.4
Polyynes and acetylenes as possible start point to assembly PAHs .......................... 12
1.4.1
Synthesis of triynes ............................................................................................ 12
1.4.2
Reactivity of monoynes and polyynes ............................................................... 14
1.5
Conclusion and motivation ........................................................................................ 17
1.6
References .................................................................................................................. 18
Chapter 2. Electrochemical investigation of new aryl substituted pentacenes ............... 22
2.1
Introduction ................................................................................................................ 22
2.2
Synthesis of aryl substituted pentacenes .................................................................... 24
2.3
Electrochemical investigation of aryl substituted pentacenes ................................... 26
2.4
Conclusion ................................................................................................................. 33
2.5
References .................................................................................................................. 33
Chapter 3. Electrochemical investigation of new dyes based on functionalized
triangulenes…………………………………………………………………………………..35
3.1
Introduction ................................................................................................................ 35
3.2
Electrochemical investigation of new dyes based on functionalized cationic
triangulenes ……………… ...................................................................................... 36
3.2.1
Synthesis of cationic triangulenes ...................................................................... 36
3.2.2
Electrochemical investigation of new cationic triangulenes and relative
helicene precursors ............................................................................................ 37
3.3
Electrochemical investigation of push-pull system based on
functionalized heterotriangulenes......................................................................................... 43
3.3.1
Synthesis of new functionalized heterotriangulenes .......................................... 43
3.3.2
Electrochemical investigation of new functionalized heterotriangulenes.......... 44
3.4
Conclusion ................................................................................................................. 50
3.5
References .................................................................................................................. 50
Chapter 4. Diels-Alder cycloaddition of tetraphenylcyclopentadienone and
1,3,5-hexatriynes……………………………………………………………………………...52
4.1
Introduction ................................................................................................................ 52
4.2
Synthesis of triynes……………………………………………………………….....54
4.3
Diels-Alder cycloaddition of tetraphenylcyclopentadienone (TPCPD)
and 1,3,5-hexatriynes under conventional heating………………………………….60
4.4
Diels-Alder cycloaddition of tetraphenylcyclopentadienone (TPCPD)
and 1,3,5-hexatriynes under microwave irradiation……………………………………….63
4.5
Desilylation and homocoupling reaction toward the formation of the dimers .......... 68
4.6
UV-vis spectroscopy, cyclic voltammetry, and X-ray crystallography ..................... 71
4.7
Attempts to synthesize PAH derivatives via Scholl cyclodehydrogenation .............. 79
4.8
Conclusion ................................................................................................................. 80
4.9
References .................................................................................................................. 81
Chapter 5. Experimental section .......................................................................................... 83
5.1
General data ............................................................................................................... 83
5.2
Synthesis of known compounds ................................................................................ 84
5.3
Synthesis of new compounds ..................................................................................... 91
5.4
References ................................................................................................................ 106
Chapter 6. Appendix ........................................................................................................ 108
Chapter 1: Introduction
Chapter 1: Introduction
1.1.1 Carbon-rich compounds and polycyclic aromatic hydrocarbons (PAHs)
In recent years, many efforts have been directed to the investigation of carbon richcompounds such as graphite, graphene, diamond, fullerenes, carbon nanotubes, and PAHs.1
Carbon rich materials have been incorporated into electronic devices such as OLEDs, FETs,
and organic solar cells. 1,2,3 Within the general class of carbon-rich compounds, polycyclic
aromatic hydrocarbons (PAHs) are member of this class and composed of hydrogen and carbon
atoms with multiple aromatic rings. Examples of PAH molecules are shown in Figure 1.1
(1.1−1.6). PAHs have been intensely investigated, especially in the field of organic chemistry,
material science, and astronomy because they display interesting mechanical, electronic, and
optical properties. 4,5 Clar and Scholl are often referred as the pioneers of the synthesis of
PAHs. 6,7,8
1.1
1.5
1.2
1.3
1.4
1.6
Figure 1.1. Examples of common PAHs: hexa-peri-hexabenzocoronene 1.1, pyrene 1.2, pentacene 1.3,
tribenzopentaphene 1.4, phenanthrene 1.5, and ovalene 1.6.
The material graphene can be defined as the homologue of molecular polycyclic aromatic
hydrocarbon of quasi-infinite size. 9 Since the first reported production in 2004, 10 an increasing
number of chemical and physical protocols have been developed to produce graphene.3,11,12,13
Graphene shows interesting and unique properties such as high electron mobility, 14 thermal
1
Chapter 1: Introduction
conductivity, 15 optical transmittance, and electrical conductivity. 16 Due to these, and other,
interesting properties research on graphene has focused on possible applications such as in field
effect transistors, sensors, transparent conductive films, and as electrodes for clean energy
devices. 17
Considering the potential application of PAHs reported in recent years,3,18 research efforts have
been focused on the investigation of specific PAH such as acenes 19 and triangulenes. 20 Acenes
describe a class of molecules that contain only linearly fused benzene rings, while triangulenes are
defined as alternant polycyclic aromatic hydrocarbons with zigzag edges (triangular structure). As a
part of the synthesis of new PAHs, new methodologies have been accomplished based on the use
acetylene chemistry.2,21 The alkyne functionality is an attractive entry point to synthesize PAHs due
to its high-carbon content and the possibility of modular assembly via the Diels-Alder reaction,
cyclodehydrogenation, and cross-coupling chemistry leading to a rapid construction of PAH.
Several examples are reported in the literature describing the use of functionalized alkynes to
construct PAH moieties via phenyl-substituted benzene derivatives. 22
In general, rather detailed knowledge about the electronic properties of conjugated molecules is
required in order to consider the compounds for incorporation into devices. Related to this,
electrochemical techniques, and especially cyclic voltammetry, can play a significant role for
understanding the electronic properties of organic compounds. With cyclic voltammetry, for
example, it is possible to investigate the HOMO and LUMO energy levels, as well as the
HOMO−LUMO gap, which are both fundamental parameters for evaluating organic compounds in
devices.
The first goal of the thesis is to investigate the electronic properties of new pentacene and
triangulene derivatives by cyclic voltammetry. Thus, the following introduction provides an
overview about the use of cyclic voltammetry to study selected classes of PAH including
pentacenes and triangulenes. The second goal of the thesis is to synthesize triynes and explore the
reactivity of this class of compounds in Diels-Alder reactions with tetraphenylcyclopentadienone to
obtain tetraphenylbenzene derivatives that might be used as precursors for PAH. Such arylsubstituted benzene have been used in opto-electronic devices and supramolecular assembly
materials. 23,24,25
Thus, the introduction section also provides a brief overview of synthetic protocols described in
literature for the synthesis of triynes, as well as a general overview of reactivity of monoynes and
polyynes that might be used for the formation of PAH.
2
Chapter 1: Introduction
1.2
Acenes and pentacenes
Acenes are polycyclic aromatic hydrocarbons that contain linearly fused benzene rings
(Figure 1.2). Acenes have been often investigated as organic semiconductors.19 Within the class of
acenes, pentacene 1.3 has been particularly well studied and shows interesting optoelectronic
properties. It has, for example, already been used as p-type material in organic solar cells combined
with fullerene as n-type semiconductor. 26
Pentacene 1.3 was first synthesized by Clar in 1930 (Figure 1.2).7,27 More recently, the purpose to
understand the potential use of 1.3 in organic devices, the opto-electronic properties were analyzed
for comparison with the results obtained for other PAH. The electrochemical properties of
pentacene 1.3 were investigated using voltammetry experiments. Pentacene 1.3 displays an
oxidation event at 0.3 V, and a reduction process at −1.8 V (calculated vs Fc/Fc+ in odichlorobenzene). Both processes are reversible and the electrochemical HOMO−LUMO gap of 1.3
is thus 2.1 eV. 28
4
5
6
7
8
1
14
13
12
11
3
2
n
9
10
1.3
Figure 1.2. General structure of acenes and unsubstituted pentacene (1.3) with atomic labelling.
Unfortunately, pentacene exhibits poor solubility in common organic solvents and is rather unstable
under ambient conditions. The most reactive regions of the pentacene framework are usually the 6and 13-positions, and these are the preferential location for photo-oxidation and Diels−Alder
reactions. In order to tune solubility, stability, electronic, and optical properties of 1.3, research has
focused on the synthesis of pentacene derivatives through introducing substituents to the acene
framework. Pentacene derivatives also display significant charge-transport ability, strong absorption
in UV-vis region, stability under ambient conditions, and processability. 29,30 Two main strategies to
functionalize pentacenes have been adopted: 1) blocking the 6- and 13-positions with substituents
2) appending electron-withdrawing groups substituents at 2,3,9,10-positions.
Pentacenes functionalized in 2,3,9,10-positions of the pentacene core with donor groups such as in
2,3,9,10-tetramethylpentacene 1.7 are also reported. Pentacene 1.7 shows more solubility in
common organic solvents compared to 1.3. Concerning the electronic properties, the presence of
3
Chapter 1: Introduction
methyl groups increased slightly the HOMO energy level (−4.41 eV) compared to unsubstituted
pentacene 1.3 (−4.49 eV, Figure 1.3). 31
1.7
Figure 1.3 Pentacene 1.7 investigated by Meng and coworkers.31
One of the goals of acene research is to change the electronic properties of derivatives of 1.3
through the synthetic design of compounds with smaller HOMO−LUMO gaps, while maintaining
stability under ambient conditions. Several relevant studies are provided by Miller and coworkers. 32
They have investigated the stability of different aryl substituted pentacene 1.8−1.12 (Figure 1.4),
and they have reported on the influence of substituents on the values of the HOMO−LUMO gaps. It
has been demonstrated that the steric hinderance associated with aryl substituents marginally affects
the electrochemical HOMO−LUMO gap, namely pentacenes with 2,6-dimethyl or 2.6-diethyl
substitution (1.9 and 1.8, respectively) are somewhat more difficult to reduce and oxidize than
phenylated 1.10 (Figure 1.4) where the HOMO−LUMO gap values are 2.01 eV, 2.04 eV, and 1.92
eV. The aryl substituted pentacenes 1.8−1.12 are only partially conjugated to the pentacene ring
because of the orthogonal orientation of the aryl rings. As a result, significant differences in the
series of pentacenes 1.8−1.12 are not observed in terms of electronic absorption as demonstrated by
the λmax value of 601 nm for 1.8, 604 nm for 1.9, and 605 nm for 1.10. All analyzed compounds
(1.8−1.12) show an optical HOMO−LUMO gap in the range of 1.92 to 2.04 eV, which is similar to
that defined by the cyclic voltammetry experiments and smaller compared to 1.3 (2.1 eV).
With respect to stability, the authors show that the inclusion of electron-withdrawing group at the
2,3,9,10-position as in 1.11 leads to a longer-lived species compared to 1.9. The opposite effect is
observed with the inclusion of electron-donating groups, tetra-donor 1.12 is less stable compared to
1.10.
4
Chapter 1: Introduction
1.8 (2.04 eV)
1.9 (2.01 eV)
1.10 (1.92 eV)
Cl
Cl
O
O
Cl
Cl
O
O
1.11 (1.97 eV)
1.12 (1.94 eV)
Figure 1.4 Aryl substituted pentacenes 1.8−1.12 with their relatives electrochemical HOMO−LUMO gaps shown in
parenthesis studied by Miller and coworkers.32
The most relevant contributions to pentacene chemistry have been provided by Anthony and
coworkers who synthetized 1.13, so called TIPS-pentacene (TIPS-pc, Figure 1.5). 33 Compared to
1.3, TIPS-pc shows excellent solubility in many organic solvents, and it is also reasonably stable
under ambient conditions in the presence of air, light, and water. Compound 1.13 has been studied
electrochemically by cyclic voltammetry and displays two oxidation (0.39 V and 0.99 V) and one
reduction potential (−1.52 V); all three of which are reversible. Thus, 1.13 shows a smaller HOMOLUMO gap (electrochemical 1.91 eV, optical 1.84 eV) compared to unsubstituted pentacene 1.3
(2.1 eV). The change of the HOMO−LUMO gap is ascribed to a decrease of the LUMO energy
value because of extended conjugation from the silylethynyl groups, and to the increased
electronegativity of sp-hybridized carbons of the ethynyl moieties. 34
5
Chapter 1: Introduction
Sii-Pr3
Sii-Pr3
1.13
Figure 1.5. Pentacene 1.13 synthesized by Anthony.33
To extend the π-system of 1.13 toward improving device characteristics, a new pentacene derivative
with additional donor substituents at the 2,3,9,10-positions (1.14) has been explored. The additional
alkyl groups appended to the framework of 1.14 result in a decrease in the oxidation potential to
0.69 V for 1.14 compared to 0.85 V observed for 1.13. Pentacene 1.15 has also been assembled in
which ethynyl groups have been inserted at the 2,3,6,9,10,13-positions of the pentacene skeleton
(Figure 1.6). Compound 1.15 shows even a smaller HOMO−LUMO gap (1.74 eV) compared to
1.13 (1.91 eV). 35,36
SiMe3
Sii-Pr3
H17C8
C8H17
H17C8
C8H17
Me3Si
SiMe3
Me3Si
SiMe3
SiMe3
Sii-Pr3
1.14
1.15
Figure 1.6. Pentacenes 1.14 studied by Wudl and 1.15 investigated by Neckers.35,36
For incorporating organic compound into devices based on light absorption, such as solar cells, the
compound should ideally possess a significant absorption in the range of 350 to 525 nm. While
pentacene 1.13 has a reasonably small HOMO−LUMO gap, it is transparent in the region of
350−525 nm. As a result, efforts have been directed on the synthesis of other pentacene derivatives
in which the absorption is shifted into the visible region. For example, Tykwinski and coworkers
have reported about pentacenes derivatives 1.16a−f with a TIPS ethynyl group attached to the 6position that helps to maintain the solubility, and with a PAH moiety appended to the 13-position
through an ethynyl spacer (Figure 1.7). The result of this substitution pattern is a chromophore with
6
Chapter 1: Introduction
extended conjugation and absorption in the range of 300 to 475 nm. 37 The electronic aspects of
these derivatives have been examined by CV. Derivatives 1.16a−f show one oxidation and two
reduction processes and all three events are reversible. Compounds 1.16c and 1.16f show a second
oxidation potentials which is reversible. Both the reduction and oxidation potentials become easier
as the size of the pendent PAH increased, and the electrochemical HOMO−LUMO gaps decrease
from 1.83 eV for 1.16a to 1.81 eV for 1.16b to 1.71 eV for 1.16c.
Sii-Pr3
Ar
Ar =
1.16a
1.16b
1.16c
1.16d
1.16e
1.16f
Figure 1.7. Pentacenes derivatives 1.16a−f reported by Tykwinski and coworkers.37
1.3 Triangulenes as a class of PAH
Triangulenes are defined as alternant polycyclic aromatic hydrocarbons with zigzag edges
that result in a triangular structure (Figure 1.8). All the attempts to synthesize the parent triangulene
1.17 have failed so far because the structure is highly reactive due to the biradical nature in the
ground state.20 As a result of the instability, triangulene derivatives such as cationic triangulenes and
heterotriangulenes have been investigated. 38,39 The functionalization of triangulenes is based on
three different key points. Region X is defined by the 4-, 8- and 12-positions and with variation of
the structure of this region, the electronic demands can be regulated by insertion of for example O
or N atoms (Figure 1.8). Substitution in region Y (radial and flanking) can modify the symmetry of
1.17 while variation at the central Z position can be used to vary the solubility through the
incorporation of heteroatoms such as N, B or P. 40
7
Chapter 1: Introduction
Y
2
a)
b)
X: controls electronic demand, could be O or N
Y: controls symmetry, could be alkyl or aryl moieties
Z: controls solubility, could be N, P or B.
3
1
X
4
12
X
Z
5
11
X
6
10
9
8
7
radial Y
flanking Y
1.17
Figure 1.8. Triangulene structure: 1.17 with atoms labeling and with definition of positions X, Y, and Z.
1.3.1 Cationic triangulenes
Cationic triangulenes have attractive absorption and emission properties due to rigid planar
structure. They also show good stability, which is often also observed also in strongly basic
solutions. 41 Cationic triangulenes are also important in the field of biology, and there are examples
of the interaction of cationic triangulenes with DNA sequences as intercalating agents. 42
The study of cationic triangulenes in basic solutions is particularly interesting because the stability
of these compounds could make them potential candidates for the use in phase transfer catalysis.41
The stability of cationic triangulenes in basic solution is related to the resistance to nucleophilic
attack of water and the hydroxide anion. This resistance is expressed by the pKR+ values of these
compounds. A pKR+ is defined by the equilibrium between the cationic species and their
corresponding carbinols. HX is an acidity function characteristic for the cation/carbinol equilibrium
and the solvent system (Figure 1.9).41
R 3C + + H 2O
pKR+ = HX + log
R3COH + H+
+
[R3C ]
[R3COH]
Figure 1.9. Definition of pKR+.
Cationic triangulenes are also important molecules because of their self-assembly properties,
especially aggregation. 43,44 It has been demonstrated that the delocalization of the positive charge of
a cationic triangulene through the molecule strongly affects the aggregation in the solid state, and
also the
nature of the negative counterions has a noticeable influence on the photophysical
properties in solution and in condensed state.41
8
Chapter 1: Introduction
The first triangulenium salt 1.18 was synthesized in 1963 by Martin and Smith (Figure 1.10).38
Laursen and Krebs synthesized the triazatriangulenium 1.19a
45
that is considered more
thermodynamically stable compared to 1.18 (Figure 1.10). Compound 1.19a displays a pKR+ value
of 23.7 compared to 1.18 that shows pKR+ = 9.1. As a consequence of the bigger pKR value, 1.19a
is more stable than 1.18. Related to the applications of cationic triangulenes as organic electronic
materials, investigation of stability and the properties by cyclic voltammetry plays a significant role
for understanding this class of compounds. Different atoms or substitution in the X-positions of the
triangulene core of 1.17 have been incorporated and the products then explored by cyclic
voltammetry, such as in the cationic triangulenes 1.18−1.21 by Lacour and coworkers (Figure
1.10).41 The electrochemical results demonstrated that with increasing of the numbers of N rather
than of O-atoms, oxidation is easier and the reduction more difficult in the series 1.18 →1.20
→1.21 →1.19b. Specifically, an oxidation event is not observable for 1.18 and 1.20, while the
oxidation potential decreases from 1.40 V for 1.21 to 1.20 V for 1.19b demonstrating the better
donor ability of N-atoms compared to O-atoms which stabilizes the positive charge. A reduction
process is observed for all the compounds with increasing values from −0.39 V for 1.18, to −0.5 V
for 1.20, to −0.85 V for 1.21, and −1.40 for 1.19b.
R
N
O
O
O
BF41.18
R
N
C 3H 7
N
CH3
N
N
O
R
O
N
O
BF4-
X1.19a R = CH3, X = PF61.20
1.19b R = C8H17, X = BF4-
C 3H 7
BF41.21
Figure 1.10. Triangulenium salts 1.18−1.21 reported in literature.
1.3.2 Heterotriangulenes
A second class of triangulenes, the so called heterotriangulenes, includes derivatives in
which the carbon atom at the central core of triangulene structure is replaced with, boron, 46
phosphorous, 47 or nitrogen atom.39 Heterotriangulenes are simple and attractive building blocks for
functional organic materials such as n-type semiconductors. 48 Examples of heterotriangulenes have
been also reported in which the framework has been appropriately functionalized to serve as a push9
Chapter 1: Introduction
pull dye where the planarity of the heterotriangulene framework can avoid phenomenon of the
charge recombination. 49
The first nitrogen-doped heterotriangulenes 1.22 and 1.23 have been synthesized by Hellwinkel and
Melan (Figure 1.11).39,50,51 Compound 1.22 displays n-type semiconductor behavior 52 because of
the carbonyl groups that reduce the electron density in the core. Unfortunately, the properties of
1.22 could not be investigated by cyclic voltammetry because of the poor solubility of 1.22 in
common organic solvents. 53 The dimethylmethylene bridges of 1.23 increase the solubility in
comparison to 1.22, but unfortunately, these groups also destroy the intermolecular charge transfer
interactions. Compound 1.23 has been analyzed by cyclic voltammetry and shows a reversible
oxidation event at 0.34 V vs Fc/Fc+. 54
O
O
N
N
O
1.22
1.23
Figure 1.11. Heterotriangulenes reported by Melan and Hellwinkel.39,50,51
With the purpose to obtain π-expanded heterotriangulenes compared to 1.23, heterotriangulenes
with substituents in the X and Y-positions 1.24a,b have been synthesized (Figure 1.12). 55
Electrochemical investigations by cyclic voltammetry for 1.24a and 1.24b show a reversible
oxidation process at 0.40 V for 1.24a and 0.39 V for 1.24b, as well as irreversible reduction
processes that occur at −2.49 V for 1.24a and −2.15 for 1.24b.
C6F5
Ar
Ar
Ar
Ar
N
C6F5
F5C6
Ar
Ar
1.24a Ar = Ph
1.24b Ar = 2-naphthyl
Figure 1.12 Heterotriangulenes 1.24a-b reported by Chou and coworkers.55
Several heterotriangulenes with substituents in the Y-positions have been reported (1.25a−d), 56 and
these molecules are designed in order to expand the π-system of triangulene 1.22 and to increase the
solubility compared to 1.21 (Figure 1.13). Compounds 1.25a−d have been investigated by cyclic
10
Chapter 1: Introduction
voltammetry, and all derivatives except 1.25b display two reduction processes ascribed to the
triangulene core (Figure 1.13). The inclusion of electron-withdrawing groups as substituents in
1.25b, 1.25c, 1.25d facilitate the first electron uptake, and the reduction for 1.25a the reduction is
shifted cathodically due the directly linked of the alkyl substituent to the heterotriangulene core.
Compound 1.25b shows an irreversible oxidation ascribed to the 3,5−bis(dodecyloxy)phenyl donor
moiety.
R
O
O
N
R
R
O
1.25a R = C12H25
OC12H25
1.25b R =
OC12H25
1.25c R =
C12H25
1.25d R =
Sii-Pr3
Figure 1.13. Heterotriangulenes 1.25a−d reported in literature.56
Ko and coworkers have reported heterotriangulenes 1.26a−c and their potential use as push-pull
dyes where the donor moiety is represented by the heterotriangulene skeleton 1.23 and the acceptor
linked to the core by thiophene units (Figure 1.14).49 Cyclic voltammetry measurements show a
quasi-reversible couples process for each of the three molecules, with oxidation potentials of 1.07 V
(1.26a), 1.00 V (1.26b), and 1.01 V (1.26c). Theoretical calculations have shown to determine the
HOMO and LUMO energy levels and have been demonstrated that is possible to effect a
photoinduced electronic transfer from 1.26a−c to the conduction band of the device.
11
Chapter 1: Introduction
R1
N
R2
R1
1.26a R1 = H
1.26b R1 = OC6H13 R2 =
1.26c R1 = OC9H19
S
S
CN
COOH
Figure 1.14. Heterotriangulenes derivatives 1.26a−c synthesized by Ko and coworkers.49
1.4
Polyynes and acetylenes as possible starting point to assemble PAHs
1.4.1 Synthesis of triynes
Triynes are compounds with series of three alternating of single and triple bonds, and these
molecules belong to the class of compounds broadly described as polyynes. Due to their unique
array of sp-hybridized carbon atoms, polyynes display interesting optoelectronic properties and are
potentially suitable for incorporation into organic electronic devices. 57,58
There are a variety of ways to synthesize triynes. Cadiot and Chodkiewicz have reported a crosscoupling reaction to obtain unsymmetrical triynes (Scheme 1.1a) in which the terminal diyne is
reacted with a bromoalkyne derivative. This reaction can be complicated by the side reaction that
involves that homocoupling reaction of the alkynyl halide, which leads to a mixture of products that
can be difficult to separate. A version of this protocol using Pd as a catalyst has also been reported
(Scheme 1.1b). 59,60
a)
R
H +
Br
R
CuCl, NH2OH HCl
R
R
R
R
EtNH2, MeOH, N2
b)
R
H +
Br
R
PdCl2(PPh3)2, CuI
i-Pr2NH, THF
Scheme 1.1. Cadiot-Chodkiewicz cross coupling.59,60
12
Chapter 1: Introduction
Tobe and coworkers have reported the synthesis of triynes 1.27a,b (Scheme 1.2).
Dialkynylmethylenebicyclo-[4.3.1]deca-1,3,5-triene derivatives that is irradiated with UV light (254
nm) to induce an electrocyclic ring closure followed by the [2+1] cheletropic fragmentation.
Finally, FBW rearrangement reaction of the intermediate alkylidene carbyne affords triynes
1.27a,b.61
hv (254 nm)
R
R
R
−
R
R
1.27a R = SiMe3 (43%)
1.27b R = Ph
(37%)
R
Scheme 1.2. Synthesis of polyynes 1.27a−c reported by Tobe and coworkers.61
A synthesis of triynes 1.27a,b and 1.28a,b using a solution spray flash vacuum pyrolysis (SS-VP)
has been reported starting from 3-cyclobutene-1,2-diones (Scheme 1.3). The starting material is
introduced into a quartz tube under vacuum (1−2 torr) which leads to fragmentation and affords
1.27a,b and 1.28a,b. This technique can be efficient for compound that are thermally stable and
non-volatile. 62
O
O
SS-FVP
R
R
650 °C
R
R
1.27a R = SiMe3 (99%)
1.27b R = Ph (97%)
1.28a R = SiMe2t-Bu (99%)
1.28b R = Sii-Pr3 (95%)
62
Scheme 1.3. Synthesis of triynes 1.27a,b and 1.28a,b proposed by Diederich and coworkers.
Tykwinski and coworkers have described a procedure to synthesize symmetrical triynes (Route B)
1.27a, 1.28b, and 1.29a−c as well as unsymmetrical triynes (Route A) 1.30a−e (Scheme 1.4). The
steps of this synthetic protocol are based on a sequence involving alcohol formation followed by
oxidation and dibromoolefination that leads to the triynes 1.27a, 1.28b, 1.29a−c, 1.30a−e. via FBW
rearrangement. 63, 64, 65
13
Chapter 1: Introduction
ROUTE A: R1 ≠ R2
R1
H
ROUTE B: R1 = R2
1. n-BuLi
Et2O, -78 °C
2.
1. n-BuLi
Et2O, -78 °C
OH
O
R1
R2
H
H
R2
R2
H
2. O
OEt
PCC
CH2Cl2
rt
O
R1
R2
CBr4, PPh3
CH2Cl2
rt
Br
Br
n-BuLi, hexanes
-78 °C
R1
1.28b R1 = R2 Sii-Pr3
1.27a R1 = R2 SiMe3
1.29a R1 = R2 n-Bu
1.29b R1 = R2 n-octyl
1.29c R1 = R2 2-thienyl
70%
50%
80%
66%
64%
R2
R1
R2
1.28b, 1.27a, 1.29a-c
1.30a-e
1.30a R1 = SiMe3,
R2 = Sii-Pr3
1.30b R1 = 1-naphthyl, R2 = SiMe3
1.30c R1 = 1-naphthyl, R2 = Sii-Pr3
1.30d R1 = SiMe3,
R2 = n-Bu
2
1
1.30e R = SiMe3, R = Sii-Pr3
61%
70%
62%
82%
61%
Scheme 1.4. Synthetic route to obtain triynes 1.28b, 1.27a, 1.29a−c, and 1.30a−e as reported by Tykwinski and
coworkers.63,64,65
1.4.2 Reactivity of monoynes and polyynes
Many groups have focused research on the synthesis of long polyynes, but the reactivity of
the polyyne products remains an undeveloped area. In one of the most useful examples reported to
date Diederich and coworkers describe the reaction of electron rich tetrayne 1.31, with
tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) to obtain a push-pull nonplanar molecule
14
Chapter 1: Introduction
1.32 (Scheme 1.5). In this sequential, but one pot reaction, TCNE is used to generate the acceptor
groups and TTF donating units of the product 1.32. 66 The selectivity of this reaction is based on pielectron density resulting from the divergent endgroups.
Me2N
1.31
S
CN
S
CN
NC
S
S
CN
CH2Cl2/ACN
50 °C
NC
Me2N
NC
CN S
CN S
CN S
S NC
S NC
CN
S
S
S
1.32 (21%)
Scheme 1.5. Reaction of polyyne 1.31 to obtain push-pull chromophore 1.32 as reported by Diederich and coworkers.66
White and coworkers reported a synthetic procedure where the central triple bond of the triyne 1.33
reacts with Co2(CO)6L2 (L2 = CO) to afford 1.34 (Scheme 1.7). 67
Ph3P Ru
PPh3
L2 = CO
Ru
PPh3
Ph3P
Co2(CO)6L2
PPh3
Ru PPh
3
Ph3P PPh3
Ru
MeOH,CH2Cl2
30 min
1.33
C
L(OC)2Co
C
Co(CO)2L
1.34 (56%)
Scheme 1.7. Reaction of triyne 1.33 with a cobalt complex to afford 1.34, as reported by White and coworkers.67
Another interesting reactivity pattern of polyynes concern the cycloaddition reaction of an azide, the
so called Huisgen reaction. Walton and coworkers have developed a procedure in which the thermal
reaction of benzyl azide with a silyl endcapped triyne (1.27a) affords the regioselective formation
of the triazole product 1.35 (Scheme 1.8). In this case, the reaction regioselectivity is ascribed to
orbital control via π−donation from the alkynyl system to silicon. 68
15
Chapter 1: Introduction
O 2N
O 2N
N3
Me3Si
SiMe3
N N
N
Me3Si
xylenes, reflux
Me3Si
1.27a
1.35 (43%)
Scheme 1.8. Reaction of triyne 1.27a with benzyl azide to afford 1.35 as reported by Walton and coworkers.68
Tykwinski and coworkers have used a copper catalyzed variation of the Huisgen reaction to obtain
triazoles using triynes 1.36a−d (Scheme 1.9). It was demonstrated that the reaction is regioselective
with the attack of benzylazide at the terminal acetylenic bond (Scheme 1.9) 69 to afford 1.37a−d.
Others groups have also followed this protocol with polyynes. 70,71,72
N3
R
R
H
N N
N
CuSO4 5H2O
ascorbic acid,
DMF, rt
1.37a R = Bu (71%)
1.37b R = Ph ( 68%)
1.36a
1.36b
1.36c
1.36d
1.37c R =
OMe (82%)
1.37d R =
t−Bu (73%)
Scheme 1.9. Reaction of triynes 1.36a−d using benzylazide to obtain 1.37a−d as reported by Tykwinski and
coworkers.69
Müllen and coworkers have utilized a Diels-Alder reaction using aryl acetylene 1.38 as dienophile
and tetraphenylcyclopentadienone (TPCPD) as diene to obtain hexaphenylbenzene 1.39 (Scheme
1.10).22 This reaction is versatile and has been used to assembly numerous carbon rich frameworks,
often on the way to some of the largest PAHs to be synthesized with a defined structure. 73,74
16
Chapter 1: Introduction
Br
Br
O
Ph2O
+
94 h, 250 °C
1.38
1.39 (85%)
TPCBD
Scheme 1.10. Diels−Αlder reaction reported by Müllen and coworkers to obtain 1.39.22
1.5 Conclusion and motivation
In this chapter an overview describing the electrochemical properties of PAH, the synthesis of
triynes, and reactivity of poly- and monoyne compounds has been presented. Within the class of
PAH, selected pentacene derivatives known in literature have been discussed. Functionalization of
pentacene by varying the nature, positions, and type of substituents, allows to change the
optoelectronic properties with the purpose to decrease the ΗΟΜΟ−LUΜΟ gap to better apply in
organic electronic devices. A second class of PAH molecules that has been presented are the
cationic triangulenes. These molecules show strong stability, planarity, and fluorescent properties.
Different functionalization with acceptors moieties suggested by Ko and coworkers is a fascinating
topic due to the potential use of heterotriangulene in push-pull chromophores where the
heterotriangulene functionalized with dimethyl substituents in X-positions is used as donating unit.
An overview about the synthesis of triynes that have been reported in literature has been presented.
In general for polyynes compounds, research has been focused on the development of synthetic
methods, but the reactivity is not fully explored. It is known that polyynes can react with metals
such as cobalt and another reactivity pattern concerns the cycloaddition reaction. Trends for these
additions, however, are not fully understood.
The first goal of this thesis work was the investigation by cyclic voltammetry of the electronic
properties and electrochemical HOMO−LUMO gaps of new pentacene derivatives with different
substitutions in 6- and 13-positions synthesized by my colleague Andreas Waterloo. These studies
further on understanding of the possible use of these new compounds in electronic devices. This
topic is going to be discussed in Chapter 2.
17
Chapter 1: Introduction
A second goal of this thesis work was the investigation of the electrochemical properties by cyclic
voltammetry of new cationic triangulenes and their helicene precursors with the purpose to
understand the relative changes in terms of electronic properties. The synthesis of these compounds
was conducted by Agnes Uhl in the groups of Prof. Dr. Jürgen Schatz. The third goal of the project
was to investigate the electronic properties of new heterotriangulene derivatives synthesized by my
colleague Ute Meinhardt in the Dr. Milan Kivala group with the final goal to explore the push-pull
device behavior of this new compounds. These topics are discussed in Chapter 3.
The Diels-Alder reaction with monoyne reported by Müllen (Scheme 1.10) offered a start point to
explore the reactivity of triynes in Diels-Alder reactions and this topic is going to be discussed in
Chapter 4. The first goal of the project was to synthesize triynes with different end-groups and then
investigate the regioselectivity of the Diels-Alder reactions, ascribed to electronic and steric
influences resulting from different end-capped triynes. The relative results of these cycloaddition
reaction on subsequent optimized under microwave irradiations. With different Diels-Alder adducts
in hand, the third focus dimers, that together with the Diels-Alder products, might be used as
precursors to make PAHs. The properties of these new compounds were investigated by NMR, IR,
UV-vis spectroscopy, MS spectrometry, cyclic voltammetry, and crystallographic analysis.
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A. L. K. Shun, E. T. Chernick, S. Eisler, R. R. Tykwinski. J. Org. Chem, 2003, 68,
339−1347.
64.
S. Eisler, N. Chahal, R. McDonald, R. R. Tykwinski, Chem. Eur. J. 2003, 9, 2542−2550.
65.
Y. Morisaki, T. Luu, R.R. Tykwinski, Org. Lett. 2006, 8, 689−692.
66.
M. Kivala, F. Diederich, Acc. Chem. Res. 2009, 42, 235−248.
67.
M. I. Bruce, B. D, Kelly, B. W, A. H, White, J. Organomet. Chem. 2000, 604, 150−156.
68.
R. M. Bettinson, P. B. Hitchcock, D. R. M. Walton, J. Organomet. Chem. 1988, 341,
247−254.
69.
T. Luu, R. McDonald, R. R, Tykwinski, Org. Lett. 2006, 8, 6035−6038.
70.
K. West, L. N. Hayward, A. S. Batsanov, M. R. Bryce, Eur. J. Org. Chem. 2008, 30,
5093−5098.
71.
S. Gauthier, N. Weisbach, N. Bhuvanesh, J. A. Gladysz, Organomet 2009, 28, 5597−5599.
72.
C. Ross, K. Scherlach, F. Kloss, C. Hertweck, Angew. Chem. Int. Ed. 2014, 53, 7794−7798.
73.
S. Yang, R. E. Bachman, X. Feng, K. Müllen, Acc. Chem. Res. 2013, 46, 116−128.
74.
L. Chen, Y. Hernandez, X. Feng, K. Müllen, Angew. Chem. Int. Ed. 2012, 51, 7640−7654.
21
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
Chapter 2: Electrochemical investigation of new aryl substituted pentacenes †
2.1
Introduction
Pentacene shows interesting optoelectronic properties and it has been already used, for
example, in organic solar cells as p-type semiconductor. 1 Unfortunately, unsubstituted pentacene
(1.3, Figure 2.1a) shows poor solubility in common organic solvents and is unstable under ambient
conditions. 2 As a result of the insolubility and instability, efforts have been directed to the
functionalization of pentacene, especially at the 6- and 13-positions to change the opto-electronic
properties with the final purpose to incorporate pentacene derivatives into devices. Pentacene
derivatives have been already utilized in FET devices. 3
Miller and coworkers have reported aryl substituted pentacenes (Figure 2.1b) where the aryl
moieties were linked directly to the pentacene core at 6- and 13-positions, and they have
investigated the electronic properties of these compounds by cyclic voltammetry. 4 It has been found
that the HOMO−LUMO gap values are not dramatically affected by different aryl substituents
appended at the pentacene moiety as a result of the lack of coplanarity between the aryl and the
pentacene skeleton that limits the conjugation.
Anthony and coworkers have reported the synthesis of 6,13-bis(triisopropylsilylethynyl)pentacene
(1.13, Figure 2.1c) in which both solubility and stability are increased compared to unsubstituted
pentacene. 5 With the purpose to incorporate pentacene derivatives into organic devices based on
light absorption such as solar cells, Tykwinski and coworkers have reported the synthesis of
pentacene derivatives with a TIPS-ethynyl group attached to 13-position to help maintain the
solubility, and with a PAH moiety appended to the 6-position via an ethynyl spacer that extends the
conjugation
and
the
absorption
in
the
range
of
300
to
475
nm
compared
to
6,13−bis(triisopropylsilylethynyl)pentacene (Figure 2.1d). 6
†
A version of this chapter has been published: Andreas R. Waterloo, Anna−Chiara Sale, Dan Lehnherr, Frank Hampel,
Rik R. Tykwinski, Beilstein J. Org. Chem. 2014, 10, 1692–1705, doi:10.3762/bjoc.10.178.
22
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
Previous work
a)
b)
c)
d)
Sii-Pr3
SiR3
Sii-Pr3
Ar
Ar
1.3
Ar
1.13
This work
e)
SiR3
Ar
Figure 2.1. a-d) Examples of common pentacenes reported in literature and e) aryl substituted pentacene derivatives
explored in this work.
With this knowledge in hand, the goal of the current project was to analyze different pentacene
derivatives with silyl ethynyl moieties appended at 6-position and with aryl substituents linked
directly to the 13-position of the pentacene moiety (Figure 2.1e). Specifically, the solution state
properties of the pentacenes have been explored by analysis of the redox behavior and the influence
of different aryl substituents linked to the pentacene core on the HOMO−LUMO gap. The obtained
results are compared to those for a selection of similar compounds known in literature.
23
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
2.2
Synthesis of aryl substituted pentacenes ‡
The synthesis of aryl substituted pentacenes started from the known pentacenequinone
derivatives 2.1a and 2.1b, formed via the addition of an acetylide to pentacenequinone (Scheme
2.1). 7,8,9,10 With these two ketones in hand (2.1a and 2.1b), a second nucleophilic addition was
initiated. Thus, commercially available aryl halides dissolved in dry THF were subjected to lithium
halogen exchange at −78 °C using n-BuLi. A substoichiometric amount of n-BuLi was used in each
case to ensure complete consumption of the n-BuLi through Li-halogen exchanged and thus avoid
the possibility of competitive addition of the nucleophilic butyl anion to the ketone group of either
2.1a or 2.1b. After reaction with the appropriate aryl lithium species, the reaction was quenched
with a proton source, and the resulting diol intermediates 2.2a–h were carried on directly to
reductive aromatization with SnCl2/H2SO4 without further purification, ultimately yielding
pentacene products 2.3a–h While the isolation and characterization of diol products resulting from
nucleophilic additions to pentacene quinone can typically be isolated and characterized, 11 previous
work has shown that aromatized products were more easily purified by column chromatography and
recrystallization in the last reaction step. Thus, it was deemed procedurally more efficient to
eliminate the intermediate purification step. Once formed, pentacenes 2.3a−h were obtained in
moderate yields over two steps, as deep-blue solids.
‡
The synthesis of the compounds 2.3a−k was performed by the Tykwinski group member Andreas Waterloo, but for
reasons of clarity and comprehensibility, it is discussed in this chapter.
24
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
O
Ar
Ar M
Ar
OH
M = Li or MgBr
SnCl2 2H2O
THF, rt, 16−18 h
OH
H2SO4, THF
rt, 6 h
OH
R
R
R
2.2a−i
2.1a R = Sii−Pr3
2.1b R = SiEt3
2.3a−i
I
O
O
Ar =
O
S
a R = Sii−Pr3
51%
b R = Sii−Pr3
25%
c R = Sii−Pr3
51%
d R = SiEt3
8%
e R = Sii−Pr3
21%
f R = Sii−Pr3
60%
g R = Sii−Pr3
58%
h R = Sii−Pr3
45%
i R = Sii−Pr3
25%
Scheme 2.1. Synthesis of unsymmetrical pentacenes 2.3a-i by nucleophilic addition reactions.
To expand the π−system in a linear fashion along the short molecular axis of the pentacene core, the
general procedure described above was changed slightly, and ketone 2.1a was treated with a
solution of biphenyl-magnesium bromide in THF. After workup and isolation of the intermediate
diol 2.2i, reductive aromatization gave pentacene 2.3i in moderate yield over the two steps.
Elaborating on the general idea of lateral functionalization, iodoaryl pentacene 2.3h offered an
opportunity to vary the pendent substituent via a Pd-catalyzed cross-coupling protocol (Scheme
2.2). Thus, pentacene 2.3h was treated under Suzuki-Miyaura coupling conditions with arylboronic
acids, and the desired pentacenes 2.3j–k were obtained in yields of 92 and 68%, respectively.
Notably, anthracenyl substituted pentacene 2.3k was the least stable of all derivatives 2.3a−k. It
slowly decomposed in solution when exposed to ambient laboratory conditions and was unstable
toward silica gel chromatography, but it could be purified by recrystallization from a mixture of
MeOH and acetone.
25
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
I
Ar
Ar B(OH)2
Pd(PPh3)2Cl2, Na2CO3
reflux, 2-4 h
Sii-Pr3
Sii-Pr3
2.3h
Ar =
2.3j 92%
2.3k 68%
Scheme 2.2. Functionalization of iodoaryl pentacene 2.3h using the Suzuki cross-coupling reaction.
2.2.
Electrochemical investigation of aryl substituted pentacenes
Pentacene derivatives 2.3a−k were analyzed by cyclic voltammetry and the results are
summarized in Table 2.1. The corresponding cyclic voltammetry plots of compounds 2.3a−k are
shown in Figure 2.2. Aryl substituted pentacenes 2.3a−k each show a one reversible oxidation
event in the range of 0.30 to 0.37 V, and a second quasi-reversible oxidation process in the range of
0.80 to 0.99 V. There is, unfortunately, no clear trend observed for the oxidation potentials based on
the substitution pattern of the aryl-moieties, although both oxidation events appear somewhat easier
for pentacene 2.3g (0.30 V and 0.80 V, Table 2.1, entry 7) as a result of the two electron donating
methoxy groups attached to the pendent phenyl ring.
Aryl-substituted pentacenes 2.3a−k each show one reversible reduction event in a rather narrow
range of –1.59 to –1.68 V. Similar to that observed for the oxidation potentials, there is no obvious
trend that can be identified in the reduction potentials based on substitution pattern, aside from the
observation that the silyl substituent might have a slight impact on reduction: 2.3d (−1.68 V, Table
2.1, entry 4) is slightly harder to reduce than 2.3c (−1.65 V, Table 2.1, entry 3), and the reduction of
thienyl derivative 2.3e (–1.59 V, Table 2.1, entry 5) stands out as lower than the others. The
electrochemical HOMO−LUMO gap values range between 1.94−2.02 eV. The thienyl derivative
2.3e displays the smallest HOMO−LUMO gap (1.94 eV, Table 2.1, entry 5) compared to the other
pentacene in the series.
26
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
Table 2.1. Cyclic voltammetry results of aryl-substituted pentacenes 2.3a−k.
[a]
R1
R2
Entry Compound
R1
E½ox1 [V] E½ox2 [V] E½red1 [V] Egap,el [eV][b]
R2
1
2.3a
Sii-Pr3
0.34
0.87
–1.63
1.97
2
2.3b
Sii-Pr3
0.37
0.99
–1.61
1.98
3
2.3c
Sii-Pr3
0.36
0.93
–1.65
2.01
4
2.3d
SiEt3
0.32
0.91
–1.68
2.00
5
2.3e
Sii-Pr3
0.35
0.87
–1.59
1.94
6
2.3f
Sii-Pr3
0.32
0.87
–1.68
2.00
7
2.3g
Sii-Pr3
O
0.30
0.80
–1.67
1.97
8
2.3h
Sii-Pr3
I
0.34
0.87
–1.65
1.99
9
2.3i
Sii-Pr3
0.32
0.87
–1.66
1.98
10
2.3j
Sii-Pr3
0.32
0.93
–1.67
1.99
11
2.3k
Sii-Pr3
0.35
0.88
–1.67
2.02
S
O
O
[a]
Cyclic voltammetry was performed in CH2Cl2 solutions (1.5 mM) containing 0.1 M n-Bu4NPF6 as supporting
electrolyte at a scan rate of 0.15 V s−1. Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode,
and Pt working electrode. The potential values (E½) were calculated using the following equation E½ =
(Ered + Eox)/2, where Ered and Eox correspond to the cathodic and anodic peak potentials, respectively. Potentials
are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal standard.
HOMO−LUMO gaps determined by Egap,el = Eox1 – Ered1.
27
[b]
Electrochemical
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
2.3a
2.3b
2.3c
2.3d
2.3e
2.3f
28
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
2.3g
2.3h
2.3i
2.3j
2.3k
Figure 2.2.Cyclic voltammetry plots of 2.3a−k.
29
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
The results obtained for pentacenes 2.3a−c are compared to those obtained for similar compounds
reported in literature: 1.16a, 1.16b, and 1.16c (Table 2.2, entries 1−3).6 For pentacenes 1.16a−c the
pendant aryl groups are linked through an ethynyl spacer at the pentacene core that allows
electronic communication between the aryl group and the pentacene skeleton. Compounds 2.3a−c
display one reversible and a second quasi-reversible oxidation processes 0.34 V and 0.87 V for
2.3a, 0.37 V and 0.99 V for 2.3b, and 0.36 V and 0.93 V for 2.3c, while 1.16a−c display only one
reversible oxidation event that is 0.39 V for 1.16a and 1.16b, and 0.33 V for 1.16f. (Table 2.2,
entries 1−3). Compounds 2.3a−c display one reversible reduction process that is −1.63 V for 2.3a,
−1.61 V for 2.3b, and −1.65 V for 2.3c, while 1.16a−c display two reversible reduction events:
−1.44 V and −1.90 V for 1.16a, −1.42 V and −1.86 V for 1.16b, and −1.38 V and −1.77 V for 1.16c
(Table 2.2, entries 1−3). Compounds 1.16a, 1.16b, and 1.16c are easier to reduce compared to the
series 2.3a−c. Compounds 2.3a−c show larger HOMO−LUMO gaps in the range of 1.97 to 2.10 eV
compared to the compounds 1.16a−c with HOMO−LUMO gaps in the range of 1.71 to 1.83 eV.
This behavior can be explained with the incorporation of the ethynyl space in 1.16a−c that allows
for electronic communication between the pendant substituents and the pentacene moiety resulting
in smaller HOMO−LUMO gaps for 1.16a−c compared to the series 2.3a−c.
The cyclic voltammetry results of the series 2.3a−k are also compared to the literature known
pentacene 1.135 (Table 2.2, entry 4). Pentacene derivatives 1.13 displays two oxidation processes at
0.39 V and 0.99 V (Table 2.2, entry 4). The first oxidation step is similar to 1.16a−b. Thus,
compound 1.13 is slightly harder to oxidize than 2.3a−k where the values range from 0.30 to 0.37 V
for the first oxidation process and from 0.80 to 0.99 V for the second one (Table 2.1, entries 1−11).
Pentacenes 2.3a−k and 1.13 display one reversible reduction process that for 1.13 (−1.52 V) is
easier than for 2.3a−k (−1.59 V to −1.68 V). The HOMO−LUMO gaps is marginally smaller for
1.13 (1.91 eV) compared to the series 2.3a−k where the values range between 1.94 to 2.02 eV
(Table 2.1, entries 1−11).
The cyclic voltammetry results of the series 2.3a−k are also compared to the literature known
pentacene 1.10 where the aryl rings are linked directly to the pentacene skeleton in 6- and 13positions (Table 2.2, entry 5).4 Compound 1.10 display an oxidation event (0.23 V) and appears to
be easier to oxidize than 2.3a−k. Pentacene 1.10 appears to be harder to reduce (−1.85 V) compared
to the series 2.3a−k (−1.59 V to −1.68 V, Table 2.1, entries 1−11). The HOMO−LUMO gaps is
30
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
larger for 1.10 (2.08 eV) compared to the series 2.3a−k where the values range between 1.94 to
2.02 eV (Table 2.1, entries 1−11) as a result of orthogonal orientation of the aryls with the
pentacene skeleton that limits the conjugation.
The range of oxidation potentials within 1.10, 1.13, 1.16a−c, (Table 2.2, entries 1−4) , and 2.3a−k,
is, however, quite narrow, suggesting that the pendent substituent offers little influence on the
HOMO level. On the other hand, there is a marked difference in the observed reduction potentials.
The reduction of 1.13 falls at approximately a midpoint between the two other classes 2.3a−k and
1.16a,c,f suggesting that the biggest influence of the pendent substituent appears to be related to the
energy of the LUMO.
31
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
Table 2.2. Cyclic voltammetry results of 1.10, 1.13, 1.16a, 1.16b, and 1.16c.4,5,6
Sii-Pr3
Sii-Pr3
Ar
Sii-Pr3
1.13
1.16a
1.16b
1.16c
Ar =
a
Entry Compound
[a]
1.10
c
b
E½ox1
E½ox2
E½red1
E½red2
Egap,el
[V]
[V]
[V]
[V]
[eV][e]
1
1.16a[a]
0.39
–
−1.44
−1.90
1.83
2
1.16b[a]
0.39
–
−1.42
−1.86
1.81
3
1.16c[a][b]
0.33
–
−1.38
−1.77
1.71
4
1.13[c]
0.39
0.99
–1.52
−
1.91
5
1.10[d]
0.23
−
−1.85
−
2.08
Cyclic voltammetry was performed in benzene/ACN (3:1 v/v) solutions containing 0.1 M n-Bu4NPF6 as
support electrolyte at a scan rate of 0.15 V s−1. Pt wire was used as counter electrode, Ag/AgCl as reference
electrode, and Pt as working electrode. The potential values (E½) were calculated using the following
equation E½ = (Ered + Eox)/2, where Ered and Eox correspond to the cathodic and anodic peak potentials,
respectively vs Fc/Fc+.
[b]
Measurement performed at scan rate of 0.2 V s−1.
6 [c]
Cyclic voltammetry was
performed in CH2Cl2 solutions (1.5 mM) containing 0.1 M n-Bu4NPF6 as supporting electrolyte at a scan
rate of 0.15 V s−1. Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode, and Pt working
electrode. Potentials are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal
standard.
5 [d]
In the reference E½ values are recorded vs Ag/Ag+ in CH2Cl2 using n-Bu4NPF6 as support
4
electrolyte. In this table E½ values have been converted vs Fc/Fc+.
gaps determined by Egap,el = Eox1 – Ered1.
32
[e]
Electrochemical HOMO−LUMO
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
2.4
Conclusion
A series of 11 aryl substituted pentacenes with silylethynyl moieties appended at 6- position
and with aryl substituents linked directly to the 13-position of the pentacene skeleton have been
investigated by cyclic voltammetry. The results obtained reveal that electronic communication
between the pentacene core and the different aryl substituents is limited, as a result of the
orthogonal orientation of the pentacene backbone and the pendent aryl moieties. Thus, these results
show that the nature of the aryl substituent does not change the electronic properties of the
pentacene skeleton itself. The range of oxidation potentials suggest that the pendent aryl substituent
offers a minimal influence on the HOMO level. Comparing the results with those obtained for
similar compounds known in literature it is evident that the biggest influence of the pendent
substituent appears to be related to the energy of the LUMO.
2.5
References
1.
J. E. Anthony, Chem. Rev. 2006, 106, 5028−5048.
2.
A. R. Waterloo, A. C. Sale, D. Lehnherr, F. Hampel, R. R. Tykwinski, Beilstein J. Org
Chem. 2014, 10, 1692–1705.
3.
H. Meng, M. Bendikov, G. Mitchell, R. Helgeson, F. Wudl, Z. Bao, T. Siegrist, C. Kloc,
C.H. Chen, Adv. Mater. 2003, 15, 1090−1093.
4.
I. Kaur, W. Jia, R. P. Kopreski, S. Selvarasah, M. R. Dokmeci, C. Pramanik, N. E. McGruer,
G. P. Miller, J. Am. Chem. Soc. 2008, 48, 16274−16286.
5.
J. E. Anthony, J. S. Brooks, D. L. Eaton, S. R. Parkin, J. Am. Chem. Soc. 2001, 123,
9482−9483.
6.
D. Lehnherr, A. H. Murray, R. McDonald, M. J. Ferguson, R. R. Tykwinski, Chem. Eur. J.
2009, 15, 12580−12584.
7.
D. Lehnherr, R. McDonald, R. R. Tykwinski, Org. Lett. 2008, 10, 4163−4166.
33
Chapter 2: Electrochemical investigation of new aryl substituted
pentacenes
8.
A. R. Waterloo, S. Kunakom, F. Hampel, R. R. Tykwinski, Macromol. Chem. Phys. 2012,
213, 1020–1032.
9.
A. Boudebous, E. C. Constable, C. E. Housecroft, M. Neuburger, S. Schaffner,
Acta
Crystallogr. Sect. C 2006, 62, 243–245.
10.
N. Vets, M. Smet, W. Dehaen, Synlett 2005, 217–222.
11.
S. Li, L. Zhou, K. Nakajima, K. I. Kanno, T. Takahashi, Chem. Asian J. 2010, 5,
1620−1626.
34
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
Chapter 3: Electrochemical investigation of new dyes based on functionalized
triangulenes
3.1
Introduction
Triangulene derivatives such as cationic triangulenes and heterotriangulenes have been
intensely investigated. 1,2,3 Cationic triangulenes display high stability in strongly basic solution
making them potential candidates for use in phase transfer catalysis. 4 In addition, cationic
triangulenes have raised interest due to their function of fluorescent dyes, offering applications as
stains to image biological system 5 and as sensing events. 6 In the solid state, cationic triangulenes
display self-assembly properties, and the corresponding potential applications have been
investigated in the fields of nano and materials science. 7,8 The influence of counterions on the
photophysical properties in solution and in the solid state is also an issue of great importance.4
Heterotriangulenes, with nitrogen in the central position of the triangulene structure, have attracted
attention for their potential use as n-type semiconductors. 9 Ko and coworkers have reported
examples of heterotriangulenes as possible candidates for new organic sensitizers, which consist in
a D-π-A feature. The planar heterotriangulene with methyl substituents in X-positions is used as
donor unit and the electron acceptor moieties are alkyl groups connected at the core in Y-position
by a π-conjugated bridge that consist of thiophene units. 10 Harima and coworkers reported new
organic sensitizers where pyridine ligands represent the acceptors and the anchoring moieties of the
D-π-A dye. 11
The first goal of this project was to investigate by cyclic voltammetry of different functionalized
cationic triangulenes and their helicene precursors with the purpose to understand the influence of
substituents and counterions on the electronic properties. The results are also compared to those
obtained for similar compounds reported in literature.
The second goal of this project was to analyze the electrochemical properties by cyclic voltammetry
of new donor-acceptor push-pull dyes where the donor units are represented by heterotriangulenes
with dimethylmethylene groups attached to the X-positions of the heterotriangulenes core and the
35
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
acceptor moieties are pyridine ligands connected to the heterotriangulene core in Y-positions. The
results are also compared to those obtained for similar push-pull systems known in literature.
3.2
Electrochemical investigations of new dyes based on functionalized cationic
triangulenes
3.2.1 Synthesis of cationic triangulenes †
Compound 3.1 (1 equiv) known in literature 12 was diluted in NMP, n-dodecylamine (2.1
equiv) was added and the mixture was stirred at rt for 20 h (Scheme 3.1). After dilution with KPF6
and work up, 3.2 was isolated in 48% yield. Compound 3.3 was synthesized from compound 3.2
that was stirred at 120 °C for 45 min and after work up led to 3.3 in 73%. Compound 3.4 was
isolated from compound 3.3 that after stirring at 180 °C for 3 d led to 3.4 in 47% yield. Compound
3.1 (1 equiv) was diluted in NMP, n-octylamine (47 equiv) was added and the mixture was stirred at
110 °C for 3 d. After dilution with KPF6 and work up, 3.5 was isolated in 56% yield. Compound 3.1
(1 equiv) was diluted in NMP, n-hexylamine (47 equiv) was added and the mixture was stirred at
110 °C for 24 h. After dilution with H2O and work up, 3.6 was isolated in 49% yield.
†
The synthesis of the compounds was performed by Agnes Uhl from the Prof. Dr. Jürgen Schatz group.
The synthetic protocol is mentioned in this thesis for reasons of clarity and comprehension.
36
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
O
O
O
O
BF4
NMP
H25C12NH2
O
O
rt, 20 h
KPF6, H2O
N
C12H25 NMP
H25C12NH2
PF6
120 °C, 45 min
KPF6, H2O
O
O
C12H25
PF6
N
OO
OO
N
C12H25
3.1
3.2 (48%)
NMP
H13C6NH2
180 °C, 24 h
3.3 (73%)
NMP
H8C17NH2
110 °C, 3 d
H17C8
NMP
H25C12NH2
180 °C, 3 d
KPF6, H2O
N
N
C8H17
PF6
H13 C6
N
N
C6H13
BF4
N
H25 C12
N
N
N
PF6
C8H17
3.5 (56%)
C6H13
C12H25
N
C12H25
3.6 (49%)
3.4 (47%)
Scheme 3.1. Synthesis of cationic triangulenes 3.2−3.6.
3.2.2 Electrochemical investigation of new cationic triangulenes and relative
helicenes precursors
Electrochemical investigation by cyclic voltammetry has been performed for compounds 3.2−3.6
and the results are summarized in Table 3.1. The cyclic voltammetry plots of 3.2−3.6 are shown in
Figure 3.1. Compounds 3.2−3.6 show a first reduction event which appears to be reversible for 3.2
(−1.15 V) and 3.3 (−1.30 V). The first reduction wave is irreversible for 3.4 and 3.5 (−1.43 V) and
3.6 (−1.44 V). In addition to the first reduction process, compound 3.4−3.6 display a second
reversible reduction event and relevant differences within the potentials are not observed in the
series: −1.70 V for 3.4 and as well as 3.5, and −1.69 V for 3.6. The first reduction process becomes
more difficult within the series 3.2 (−1.15 V) → 3.3 (−1.30 V) → 3.4 (−1.43 V). This trend can be
explained by the replacement of methoxy groups with bridging N-alkyl moieties in the X-position
that decrease the electron accepting ability of the cationic ring system and, consequently, makes the
37
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
compounds more difficult to reduce. Furthermore, triangulene 3.4 is planar and this facilitates
stabilization of the cationic ring system via electron donation from the amine substituents compared
to the helicene precursors 3.2 and 3.3. Thus, 3.4 is more difficult to reduce (−1.43 V) compared to
3.2 and 3.3. Compounds 3.3−3.6 (Table 3.1, entries 2−5) show a reversible oxidation process at
0.96−0.99 V, while 3.2 (Table 3.1 entry 1) does not displays any oxidation potential. As expected,
the oxidation process becomes slightly easier with the introduction of more N-alkyl moieties in xposition that stabilize the positive charge in the heterotriangulenes ring as in the series 3.2 → 3.3 →
3.4.
The trend of the oxidation and reduction values observed within the series 3.2−3.4 suggests that the
replacement of the methoxy groups with N-alkyl moieties in X-positions of the triangulene ring has
a slight impact on the oxidation potential and, thus, on the HOMO energy level, while a marked
difference is observed in the reduction potentials that suggests that the biggest influence of the Nalkyl substituents appears to be related to the energy of the LUMO.
38
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
Table 3.1. Cyclic voltammetry results of 3.2−3.6[a]
O
O
N
C12H25
O
O
N
PF6
OO
3.2
H17C8
N
N
C12H25 H25C12
C8H17 H13C6
N
C12H25
C12H25
3.3
3.4
N
N
N
C8H17
C6H13
3.5
[a]
C6H13
BF4
N
Compound
C12H25
PF6
N
PF6
Entry
N
N
PF6
3.6
E½ox
Ered1
E½red2
[V]
[V]
[V]
1
3.2
−
−1.15[b]
−
2
3.3
0.99
−1.30[b]
−
3
3.4
0.96
−1.43
−1.70
4
3.5
0.97
−1.43
−1.70
5
3.6
0.96
−1.44
−1.69
Cyclic voltammetry was performed in CH2Cl2 solutions (1 mM) containing 0.1 M n-Bu4NPF6 as
supporting electrolyte at a scan rate of 0.15 V s−1. Pt wire was used as counter electrode, Ag/AgNO3 as
reference electrode and Pt as working electrode. The potential values (E½) were calculated using the
following equation E½ = (Ered + Eox)/2, where Ered and Eox correspond to the cathodic and anodic peak
potentials, respectively. Potentials are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as
an internal standard.
[b]
The reduction process is reversible. As a result, the reduction value is
determined by the equation previously mentioned to calculate E½.
39
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
3.2
3.3
3.4
3.5
3.6
Figure 3.1. Cyclic voltammetry plots of 3.2−3.6.
40
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
The electrochemical results of 3.2−3.6 are compared to those obtained for similar compounds
known in literature 1.19b, 1.20, 1.21,4,13 and 3.74,14 (Table 3.2, entries 1−4). Comparison of 1.19b
and 3.5 where the only difference between the compounds is attributed to the nature of the
counterions is observed that for the tetrafluoroborate triangulenium salt 3.5 the reversible oxidation
event (0.97 V) is more difficult compared to that for the hexafluorophosphate triangulenium salt
1.19b (0.82 V). Compounds 3.5 shows two reduction events, while 1.19b displays one reversible
reduction wave. The reductions events appears to be easier for 3.5 compared to 1.19b: −1.43 V and
−1.70 V for 3.5, and −1.78 V for 1.19b. Comparison of 3.3 to the similar compound 3.7 where the
difference between the compounds is only attribute to the length of the alkyl moieties attached to Natom in X-position is observed that 3.3 with dodecyl substituents shows one reversible oxidation
process (0.99 V) and one reversible reduction event (−1.30 V). Compound 3.7 with propyl groups
displays two oxidation processes: the first is reversible (0.94 V) and the second is irreversible (1.72
V). In addition, 3.7 exhibits also two reduction processes: the first is reversible (−1.16 V) and the
second one is irreversible (−2.08 V). In general, it is observed that compound 3.3 is slightly more
difficult to oxidize and easier to reduce compared to 3.7. The series of triangulenes 1.19b−1.21 and
3.2−3.4 show the same general trend for potentials values: with the replacement of O-atoms as in
the series 1.20 → 1.21 → 1.19b or methoxy groups as in the series 3.2 → 3.3 → 3.4 by more Nalkyl substituents in X-position the oxidation becomes easier and the reduction more difficult. This
confirms that N-atoms as well as planarization stabilize the positive charge, and thus the triangulene
ring. Beside these considerations, in general small differences within potentials values of 3.2−3.6
(Table 3.1 entries 1−5) and 1.19b, 1.20, 1.21, 1.37 (Table 3.1, entries 1−4) can be also attributed to
the different conditions used for the measurements.
41
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
Table 3.2. Cyclic voltammetry results of 1.19b, 1.20, 1.21, 1.37.4,13,14[a]
CH3
N
C8H17
N
H17C8
N
N
C8H17
C 3H 7
N
O
O
1.19b
Entry
[a]
Compound
N
O
-
BF4
BF4-
OO
C 3H 7
-
H7 C3
N
N
BF4
3.7
1.21
1.20
C 3H 7
BF4
E½ox1
Eox2
E½red1
Ered2
[V]
[V]
[V]
[V]
1
1.19b
0.82
−
−1.78
−
2
1.20
−
−
−0.88
−
3
1.21
1.02
−
−1.23
−
4
3.7
0.94
1.72
−1.16
−2.08
Cyclic voltammetry was performed in ACN solutions containing 0.1 M n-Bu4NBF4 as supporting
electrolyte at a scan rate of 0.1 V s−1 vs SCE.
Fc/Fc+ as described in ref.
4,13,14
In this table, the potential values have been converted vs
15
42
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
3.3
Electrochemical investigation of push-pull systems based on functionalized
heterotriangulenes
3.3.1 Synthesis of new functionalized heterotriangulenes ‡
The brominated starting material 3.8−3.10 were synthesized according to literature 16 and
undergoes a palladium-catalyzed Suzuki-Miyaura coupling reaction resulting in the desired dyes
3.11−3.13 (Scheme 3.2). The brominated compound 3.8 and 4-pyridineboronic acid (1 equiv) and
[Pd(PPh3)4] as a catalyst in toluene and methanol was heated under microwave irradiations to 120
°C for 9 h to afford 3.11 in 55% yield. 17 Compound 3.12 was synthesized according to the
analogous protocol using compound 3.9 and 4-pyridineboronic acid (2 equiv) that after 27 h led to
3.12 in 81% yield. The procedure was applied to synthesize 3.13 from 3.10 and 4-pyridineboronic
acid (3 equiv) giving 3.13 after 20 h in 86% yield.
‡
The synthesis of the compounds was performed by Ute Meinhardt from the Dr. Milan Kivala group. The synthetic
protocol is mentioned in this thesis for reasons of clarity and comprehension.
43
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
N
Br
+
N
N
B(OH)2
[Pd(PPh3)4]
2 M K2CO3
N
toluene/EtOH (2:1)
mw 120 °C, 9 h
3.8
3.11 (55%)
+ 2 N
N
Br
B(OH)2
Br
[Pd(PPh3)4]
2 M K2CO3
N
toluene/EtOH (2:1)
mw 120 °C, 27 h
N
3.9
N
3.12 (81%)
N
Br
+ 3 N
N
Br
B(OH)2
Br
[Pd(PPh3)4]
2 M K2CO3
N
toluene/EtOH (2:1)
mw 120 °C, 20 h
N
3.10
N
3.13 (86%)
Scheme 3.2 Syntheses of heterotriangulenes 3.11−3.13.
3.3.2 Electrochemical investigation of new functionalized heterotriangulenes
Electrochemical investigation by cyclic voltammetry has been performed for compounds
1.23, and 3.11−3.13 and the results are summarized in Table 3.3. All the heterotriangulenes 1.23,
3.11−3.13 display one reversible oxidation process. The oxidation potentials values increase within
the series 1.23 (0.36 V) → 3.11 (0.42 V) → 3.12 (0.50 V) → 3.13 (0.56 V). The trend can be
explained by the electron withdrawing nature of the pyridyl groups: with the increasing number of
pyridyl moieties attached to the heterotriangulene scaffold, the oxidation becomes more difficult.
The corresponding HOMO energy level decreases: −5.16 eV for 1.23, −5.22 eV for 3.11, −5.30 eV
for 3.12, −5.36 eV for 3.13. The compound analyzed 1.23, 3.11−3.13 show an irreversible reduction
event that is not expected. The irreversible reduction process becomes easier in the series 1.23
44
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
(−1.80 V) → 3.11 (−1.78 V) → 3.12 (−1.72 V) → 3.13 (−1.58 V). The cyclic voltammetry results
known in literature for 1.23 18 do not report any reduction wave, and similar compound of 3.11−3.13
do not mention reduction events. 19,20 Compounds 1.23, 3.11−3.13 have been analyzed by NMR,
MS, EA, and IR that establish compounds high purity except for traces of water. Considering the
blank recorded before the analysis, impurities derived from the solvent, ferrocene, and the support
electrolyte can be excluded. The first hypothesis considered to explain the unexpected reduction
waves was the presence of oxygen, but the solutions were degased before each analysis with
nitrogen for 25 min and the flow of the gas was maintained into the cell during the analysis.
Furthermore, with the presence of oxygen it is typically observed an anodic peak in the region of −1
V 21, which in this case it is not visible. The reduction of water21 could be possible due to the
presence of water proven by compounds characterization. Considering also that the reduction waves
are much smaller compared to the peaks of the reversible oxidation events shown for all the
compounds 1.23 and 3.11−3.13, the most likely hypothesis comes from the interaction of water with
each compound. The interaction of water with each compound might shift the reduction event of the
water leading to the observed trend of the reduction values for 1.23 and 3.11−3.13.
45
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
Table 3.3. Cyclic voltammetry results of compound 1.23, 3.11−3.13
N
N
N
N
N
N
N
N
N
1.23
3.11
Entry
[a]
Compound
N
3.13
3.12
E½ox[a]
Ered[a]
EHOMO[b]
[V]
[V]
[eV]
1
1.23
0.36
−1.80
−5.16
2
3.11
0.42
−1.78
−5.22
3
3.12
0.50
−1.72
−5.30
4
3.13
0.56
−1.58
−5.36
Cyclic voltammetry was performed in CH2Cl2 solutions (1.5 mM) containing 0.1 M n-
Bu4NPF6 as supporting electrolyte at a scan rate of 0.15 V s−1. Pt wire was used as counter
electrode, Ag/AgNO3 as reference electrode, and Pt as working electrode. The potential
values (E½) were calculated using the following equation E½ = (Ered + Eox)/2, where
Ered and Eox correspond to the cathodic and anodic peak potentials, respectively. Potentials
are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal standard.
[b]
For the HOMO levels valuation the formula EHOMO = −(E½ox + 4.8 eV) is applied as
described in ref. 22
46
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
1.23
3.11
3.12
3.13
Figure 3.2. Cyclic voltammetry plots of compounds 1.23 and 3.11−3.13.
Comparing literature results of heterotriangulenes reported by Ko and coworkers10 1.26a-c (Table
3.4), it is observed that in the heterotriangulenes analyzed 3.11−3.13 (Table 3.3). The oxidation
process is easier compared to the series 1.26a−c: 1.07 V for 1.26a, 1.00 V for 1.26b, 1.01 V for
1.26c, while in 3.11−3.13, the oxidation potentials values range from 0.42 to 0.56 V. This is not
surprising, given the presence of the strong accepting groups of 1.26a−c. In 1.26a−c, reduction
events are not observed, while for the series 3.11−3.13, one irreversible reduction process that range
from −1.78 to −1.80 V is found.
47
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
Table 3.4. Cyclic voltammetry results of heterotriangulenes 1.26a−c reported by Ko and coworkers.10[a]
R2
N
R1
R2
1.26a R1 = H
1.26b R1 = OC6H13 R2 =
1.26c R1 = OC9H19
S
S
CN
COOH
[a]
Entry
Compound
E½ox [V]
1
1.26a
1.07
2
1.26b
1.00
3
1.26c
1.01
Redox potential were measured in ACN with 0.1 M (n-C4H9)4NPF6
with a scan rate of 0.05 V s−1 vs Fc/Fc+ as described in ref.10
The compounds 1.23, 3.11−3.13 (Table 3.3) are also compared to the dyes 3.14−3.19 reported in
literature (Table 3.5).11 The sensitizers 3.14−3.19 are reported due to common use of the pyridyl
groups as acceptor moieties as in 1.23, 3.11−3.13. Compounds 3.11, 3.12, 3.13 display a more
difficult oxidation process that range of 0.42 to 0.56 V compared to 3.14−3.19 where the values
range of 0.34 to 0.39 V.
48
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
Table 3.5. Cyclic voltammetry results of dyes 3.14−3.19 reported by Harima and coworkers.11
N
N
N
S
N
N
R
N
R
3.16 R = H
3.17 R = n-butyl
3.14 R = H
3.15 R = n-butyl
N
S
N
N
N
N
N
6
HOOC
HOOC
3.18
[a]
6
3.19
Entry
Compound
E½ ox[V][a]
1
3.14
0.34
2
3.15
0.39
3
3.16
0.30
4
3.17
0.34
5
3.18
0.38
6
3.19
0.34
The redox potentials were measured using 0.1 M Bu4NClO4 in
CH2Cl2, FC/FC+ is used as internal standard as described in ref.11
The results obtained for 1.23 have been compared to those reported of triphenylamine (TPA).18
Compound 1.23 shows a reversible oxidation process (0.36 V) that is easier compared to that
reported for TPA (0.54 V, vs Fc/Fc+ measured by square wave voltammetry), as a result of the
increase of the planarity in 1.23.
49
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
3.4
Conclusion
Cyclic voltammetry has been performed for cationic triangulenes and helicene precursors
and the results are compared to those obtained for similar compounds reported in literature. In
general, it is observed that the cationic triangulenes gain less accepting ability with the replacement
of methoxy groups in X-positions by N-alkyl moieties that stabilize the positive charge and by
increasing of the planarity. The trend of the oxidation and reduction values observed with the
replacement of the methoxy groups with N-alkyl moieties in X-positions of the triangulene ring has
a slight impact on the oxidation potential, and thus on the HOMO energy level, while a marked
difference is observed within the reduction potentials that suggests that the biggest influence of the
N-alkyl substituents appears to be related to the energy of the LUMO. The length of the alkyl
substituents attached to N-atoms has only a slight impact on the reduction and oxidation potentials.
Comparing the results in literature might be assumed that the nature of the counterions influence the
redox properties of the cationic triangulenes: in the tetrafluoroborate triangulenium the oxidation
appears to be more difficult while the reduction process is easier compared to the similar
hexafluorophospate triangulenium.
Electrochemical
investigations
have
been
conducted
for
new
heterotriangulenes.
The
electrochemical results demonstrated that the oxidation potential becomes more difficult by the
attachment of more pyridyl groups with subsequent reduction of HOMO energy levels.
3.5
References
1.
J. C. Martin, R. G. Smith, J. Am. Chem. Soc. 1964, 86, 2252−2256.
2.
D. Hellwinkel, M. Melan, Chem. Ber. 1971, 104, 1001−10016.
3.
D. Hellwinkel, A. Wiel, G. Sattler, B. Nuber, Angew. Chem. Int. Ed. 1990, 29, 689−692.
4.
J. Bosson, J. Gouin, J. Lacour, Chem. Soc. Rev. 2014, 43, 2824−2840.
5.
P. Dedecker, C. Flors, J. I. Hotta, I-H Uji, J. Hofkens, Angew. Chem. Int. Ed. 2007, 46,
8330−8332.
50
Chapter 3: Electrochemical investigation of new dyes based on
functionalized triangulenes
6.
M. Amelia, A. Lavie-Cambot, N. D. McClenaghan, A. Credi, Chem. Commun. 2011, 47,
325−327.
7.
C. Nicolas, J. Lacour, Org. Lett. 2006, 8, 4343−4346.
8.
O. Kel, A. Fürstenberg, N. Mehanna, C. Nicolas, B. Laleu, M. Hammarson, B. Albinsson, J.
Lacour, E. Vauthey, Chem. Eur. J. 2013, 19, 7173−7180.
9.
H. Q. Zhang, S. M. Wang, Y. Q. Li, B. Zhang, C. X. Du, X. J. Wan, Y. S. Chen,
Tetrahedron 2009, 65, 4455−4463.
10.
K. Do, D. Kim, N. Cho, S. Paek, K. Song, J. Ko, Org. Lett. 2012, 14, 222–225.
11.
Y. Ooyama, T. Nagano, S. Inoue, I. Imae, K. Komaguchi, J. Ohshita, Y. Harima, Chem.
Eur. J. 2011, 17, 14837–14843.
12.
Bo W. Laursen, F. Krebs, Chem. Eur. J. 2001, 7, 1773−1783.
13.
S. Dileesh, K. R. Gopidas, J. Photochem. Photobiol. A. 2004, 162, 115−120.
14.
B. W. Laursen, PhD thesis, University of Copenhaghen (Risø), 2001.
15.
V. V. Pavlishchuk, A. W. Addison, Inorg. Chim. Acta. 2000, 298, 97−102.
16.
Z. Fang, T. L. Teo, L. Cai, Y. H. Lai, A. Samoc, M. Samoc, Org. Lett. 2009, 11, 1−4.
17.
L. Arnold, H. Norouzi-Arasi, M. Wagner, V. Enkelmann, K. Müllen, Chem. Commun. 2011,
47, 970–972.
18.
J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bässler, M. Porsch, J. Daub, Adv.
Mater. 1995, 7, 551−554
19.
C. Hua, P. Turner, D. M. D’Alessandro, Dalton Trans. 2013, 42, 6310−6313.
20.
G. Casalbore-Miceli, A. Degli Espositi, V. Fattori, G. Marconi, C. Sabatini, Phys. Chem.
Chem. Phys. 2004, 6, 3092−3096.
21.
J. J. Van Benschoten, J. Y. Lewis, W. R. Heineman, D. A. Roston, P. T. Kissinger, J. Chem.
Ed. 1983, 60, 772−776
51
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5hexatriynes
4.1.
Introduction
Polycyclic aromatic hydrocarbons such as hexa-peri-hexabenzocoronene (HBC) and
tribenzopentaphene (TBP) derivatives have been intensely investigated especially in the field of
organic chemistry and material science because they display interesting electronic and optical
properties. 1 Many examples are reported in literature where HBC and TBP derivatives are
synthesized via the Scholl cyclodehydrogenation reaction from aryl-substituted benzene derivatives.
For example, Müllen and coworkers have reported the synthesis of HBC from hexaphenylbenzene, 2
and Jenny and coworkers have used the same protocol for the synthesis of TBP from
tetraphenylbenzene derivatives as precursors to the Scholl reaction. 3 Aryl-substituted benzene
derivatives are also interesting for the potential application in opto-electronic devices and
supramolecular assembly materials. 4,5,6 In this context, alkynes are suitable start point for the
preparation
of
aryl-substituted
benzene
derivatives
via
Diels-Alder
reaction
using
tetraphenylcyclopentadienone (TPCPD) as diene. 7 Diels-Alder reactions have been intensely
studied under conventional heating and since the development of microwave chemistry in 1986, the
Diels-Alder reactions have also been optimized under microwave irradiations. 8,9,10
Microwave chemistry used for Diels-Alder reaction serves to decrease the reaction time, from
weeks to days or from hours to minutes, also providing increased reaction yields. 11 Classical
heating of a reaction mixture is less efficient than microwave heating because it results in localized
“hot spot”, so-called “wall effects” that can lead to the formation of side products because the
thermal energy is transferred inward from the surface of the reaction vessel (Figure 4.1). In contrast
to conventional thermal conditions, microwave heating is essentially instantaneous, rapid, and
uniform throughout the entire sample.
52
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Figure 4.1. Distribution of the heating a) under microwave irradiations b) under conventional heating showing the wall
effect. Picture adapted with the permission of Pelle Lidstrom (Biotage).
In this chapter, Diels-Alder cycloaddition reactions of tetraphenylcyclopentadienone (TPCPD) with
a series of 1,3,5-hexatriynes are described, in order to explore the chemical reactivity of triynes
under these cycloaddition reaction. Different end-capped triynes used for the Diels-Alder reactions
are synthesized according to the protocols reported by Tykwinski and coworkers. 12,13,14,15 The
Diels-Alder reactions have been initially conducted under conventional thermal heating and then
optimized under microwave irradiation. The tetraphenylbenzene derivatives obtained from DielsAlder reactions have been analyzed by UV-vis spectroscopy, cyclic voltammetry, and in some cases
by X-ray crystallography. Selected Diels-Alder products have been then taken on to a sequence of
desilylation and homocoupling reactions, and the obtained dimers have been investigated by UV-vis
spectroscopy, and cyclic voltammetry.
53
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
4.2.
Synthesis of triynes
Triyne 1.30a was synthesized according to the procedure reported in literature (Scheme
4.1).13 Reaction of lithiated TMS-acetylene and aldehyde 4.1 resulted in the formation of alcohol
4.2 in 90%. The following reaction was an oxidation using pyridinium chlorochromate to afford the
ketone 4.3 in 98% yield, and subsequent dibromoolefination of 4.3 led to 4.4 in 67% yield. A FBW
rearrangement reaction of 4.4 afforded triyne 1.30a in 68% yield.
Me3Si
H
1. n-BuLi
Et2O -78 °C
PCC
CH2Cl2
OH
O
rt, 24 h
2.
O
Me3Si
H
Sii-Pr3
Me3Si
4.2 (90%)
Sii-Pr3
4.3 (98%)
Sii-Pr3
4.1
CBr4, PPh3
CH2Cl2
rt, 24 h
n-BuLi, hexanes
from - 78 °C to -10 °C
Me3Si
Br
Br
Sii-Pr3
Me3Si
1.30a (68%)
Sii-Pr3
4.4 (67%)
13
Scheme 4.1. Synthesis of triyne 1.30a.
Friedel-Crafts acylation of p-methoxy benzoylchloride with 1,4-bis(trimethylsilyl)buta-1,3-diyne
afforded the ketone 4.5 in quantitative yield, after work-up and passing the reaction solution
through a plug of silica gel (Scheme 4.2). Dibromoolefination of 4.5 led to 4.6 in 61% yield and a
FBW rearrangement resulted in the formation of triyne 4.7 in 87% yield.15
54
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
AlCl3
O
SiMe3
Cl
O
SiMe3
0 °C, CH2Cl2, 2 h
MeO
MeO
SiMe3
4.5 (100%)
CBr4, PPh3
CH2Cl2
rt, 24 h
Br
Br
n−BuLi, hexanes
MeO
SiMe3
from − 78 °C to −10 °C
MeO
4.6 (61%)
4.7 (87%)
SiMe3
Scheme 4.2. Synthesis of triyne 4.7.15
Precursor compounds 4.8a-4.12a were synthesized using routes previously reported. 16,17 The
crosscoupling reaction of n-butyl-1-bromobenzene and TMS-acetylene under Sonogashira coupling
conditions was stirred at 50 °C for 3 d (Scheme 4.3). After cooling the reaction to room
temperature, work-up, and purification, compound 4.8a was obtained in 81% yield. Desilylation
reaction of 4.8a afforded the terminal acetylene 4.9a in 86% yield. Attempts to synthesize the
alcohol 4.10a using n-BuLi to form the correspondent acetylide followed by the addition of ethyl
formate were unsuccessful. The reaction to obtain 4.10a from 4.9a using Grignard reagent MeMgBr
or EtMgBr instead of n-BuLi to generate the acetylide was successful, and the alcohol 4.10a was
obtained in 67% yield after work up and column chromatography. The oxidation of 4.10a using
pyridinium chlorochromate afforded ketone 4.11a in 76% yield, and the subsequent
dibromoolefination reaction of 4.11a led to 4.12a in 78% yield. FBW rearrangement reaction of
4.12a resulted in the formation of triyne 4.13a in 90% yield.14
55
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
[Pd(PPh3)2Cl2]
HNi-Pr2, CuI
H
Me3Si
R X
K2CO3
THF/MeOH
R
SiMe3
THF
R
4.9a (86%)
4.9b (78%)
4.8a (81%)
4.8b (100%)
a: X = Br, R =
H
rt, 5 h
1. MeMgBr
THF, 50 °C
Bu
2 O
b: X = I, R =
Br
Br
R
H
OMe
R
R
R
4.11a (76%)
4.11b (81%)
4.12a (78%)
4.12b (73%)
OH
PCC
CH2Cl2
O
CBr4, PPh3
CH2Cl2
OEt
rt
R
R
4.10a (67%)
4.10b (80%)
n-BuLi,
hexanes or toluene
from - 78 °C to -10 °C
R
R
4.13a (90%)
4.13b
Scheme 4.3. Synthesis of triynes 4.13a and 4.13b.16,17
The crosscoupling reaction of p-iodoanisole and TMS-acetylene under Sonogashira coupling
conditions was stirred at rt for 24 h (Scheme 4.3).16 After work-up and purification, compound 4.8b
was isolated in quantitative yield. Desilylation of 4.8b afforded the terminal acetylene 4.9b in 78%
yield.16 Alcohol 4.10b was isolated from the reaction of 4.9b in 80% yield after work-up and
purification. The oxidation of 4.10b using pyridinium chlorochromate afforded ketone 4.11b in
81% yield, and subsequent dibromoolefination of 4.11b led to 4.12b in 73% yield. The FBW
rearrangement reaction of 4.12b was performed in toluene to increase the solubility of the precursor
4.12b, which is insoluble in hexanes. Thus, the reaction resulted in the formation of impure triyne
4.13b.
56
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
After work-up, from FBW rearrangement of 4.12b to obtain 4.13b two fractions were isolated
(fraction A and fraction B). In Figure 4.2 the 1H NMR spectrum of fraction A measured in THF-d8
is shown. The 1H NMR spectrum suggested the existence of triyne 4.13b in both fractions. Fraction
A gave a solid that was insoluble in hexanes and CDCl3, and fraction B showed solubility in
hexanes and CDCl3. The spectrum suggests the formation of product 4.13b, but reveals also
impurities based on signals in the aromatic region around 8 ppm and in the aliphatic region at 2.6
ppm (red boxes in Figure 4.2) ascribed to unknown impurities. The 13C NMR spectrum measured in
THF-d8 in Figure 4.3 also suggests the formation of the desired product 4.13b based on the
acetylenic signals at: 79.8 ppm, 73.9 ppm, and 66.9 ppm (green crosses in Figure 4.3), but revealed
also the presence of impurities in the range of 31-35 ppm and in the aromatic region around
124-132 ppm and 135 ppm (signals of impurities are shown in the red boxes in Figure 4.3).
Figure 4.2. 1H NMR spectrum in THF-d8 of fraction A containing product 4.13b and impurities highlighted in red
boxes.
57
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Figure 4.3.
13
C NMR spectrum of fraction A in THF-d8 containing 4.13b showing acetylenic signals in the green
crosses and impurities highlighted in red boxes.
The
13
C NMR spectrum of fraction B shows a mixture of 4.12b and 4.13b (Figure 4.4). The
acetylenic signals ascribed to the desired product 4.13b are found at 66.3 ppm, 73.5 ppm, 78.6 ppm
(green crosses in Figure 4.4) and the acetylenic signals attributed to the starting material 4.12b are
visible at 85.1 ppm and 95.8 ppm (red boxes in Figure 4.4). Signals were also observed attributed to
both substrate 4.12b and triyne 4.13b in the aromatic region. The formation of the triyne 4.13b is
also confirmed by APPI HRMS by the signal attributed to 4.13b (m/z calculated for C20H14O2 (M+)
286.09883, found 286.0996, Figure 4.5).
58
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Figure 4.4.
13
C NMR spectrum of fraction B in CDCl3 containing 4.12b (acetylenic in red boxes signals) and 4.13b
(acetylenic green crosses).
59
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Figure 4.5. APPI HRMS expansion of the region that can be assigned to (M+) of 4.13b.
4.3. Diels-Alder cycloaddition of tetraphenylcyclopentadienone (TPCPD) and
1,3,5-hexatriynes under conventional heating
The Diels-Alder reactions with TPCPD were performed for triynes 1.27a, 1.28a, 1.30a, and
4.14a (Scheme 4.4) using thermal heating of the reaction mixture. In principal, three different
regioisomers A, B, C might be obtained depending on reaction regioselectivity for the bond
a, b, or a' of the triyne. The reactions was regioselective leading preferentially to the regioisomer A
ascribed to the reaction of TPCPD with the central triple bond β of the triyne.
Triyne 4.14a (1 equiv) and TPCPD (1 equiv) were dissolved in dry xylenes, and the mixture was
heated to 140 °C for 93 h. Solvent was removed in vacuo, and purification by flash chromatography
afforded the pure product 4.15a in 49% yield (Table 4.1, entry 1). Triyne 1.30a (1 equiv) and
TPCPD (1 equiv) were dissolved in dry xylenes and the mixture was heated to 140 °C for 95 h. The
reaction mixture was cooled to rt, solvent was removed in vacuo, and purification by flash
chromatography afforded the pure product 4.15b in 70% yield (Table 4.1, entry 2). Triyne 1.28b (1
equiv) and TPCPD (1 equiv) were dissolved in dry xylenes, and the mixture was heated to 140 °C
for 97 h. The solvent was removed in vacuo and purification by flash chromatography afforded the
pure product 4.15c in 58% yield (Table 4.1, entry 3). Triyne 1.27a (1 equiv) and TPCPD (1 equiv)
60
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
were dissolved in dry xylenes and the mixture was heated to 140 °C for 67 h. After solvent removal
and purification by flash chromatography, the pure products 4.15d was isolated in 78% yield
(Table 4.1, entry 4).
The formation of regioisomer A and the associated yield can be explained to some extent by steric
effects and increased donor nature ascribed to the end group. Considering the triynes substituted
with two trialkylsilyl groups 1.27a, 1.28b, and 1.30a; increasing the steric hindrance of the
endgroups, the yields decrease in the series 4.15d 78% (Table 4.1, entry 4) → 4.15b 70% (Table
4.1, entry 2) → 4.15c 58% (Table 4.1, entry 3). Compound 4.15a is isolated in the lowest yield,
perhaps due to the lack of steric shielding from the phenyl substituents 7 that lead to less selectivity
for the central triple bond β.
Thus, with conventional thermal heating the Diels-Alder reaction of TPCPD with different endcapped triynes is possible, leading predominantly to a reaction at the central acetylenic bond to give
regioisomer A. The required reaction time, however, is long with 67-97 h, and the yields are
moderate to good (49-78%).
61
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
R1
a
b
R1
a'
TPCPD
R2
R1
+
xylenes
140 °C, 67−97 h
R2
R2
A
4.15a R1 = SiEt3, R2 =
4.14a R1 = SiEt3, R2 =
R1
B
+
R2
R1
R2
= Sii−Pr3
= SiMe3,
4.15b
4.15c R1 = R2 = Sii−Pr3
4.15d R1 = R2 = SiMe3
= Sii−Pr3
= SiMe3,
1.30a
1.28b R1 = R2 = Sii−Pr3
1.27a R1 = R2 = SiMe3
R1
R2
C
Scheme 4.4. Diels-Alder reactions performed under thermal heating to give 4.15a-d.
Table 4.1. Diels-Alder reactions performed under thermal heating afforded 4.15a-d. 18[a]
Entry
Triyne
Product
Time (h)
Yield
Regioisomer A
[a]
1
4.14a[b]†
4.15a
93
49%
2
1.30a
4.15b
95
70%
3
1.28b[b]
4.15c
97
58%
4
1.27a[c]
4.15d
67
78%
Reactions were performed with TPCPD (1 equiv) and triyne (1 equiv) in dry
xylenes under heating to reflux for individual time.
[b]
Triyne 4.14a was
synthesized from a dibromo-precursor provided by a group member.
[c]
Triyne
1.27a was synthesized by a group member according to literature procedure.
†
This reaction was already investigated. Studies related to the formation of the three regioisomers over the time were
conducted. For more details see: Michael Vogl, Bachelorarbeit, Universität Erlangen-Nürnberg, 2010.
62
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
4.4.
Diels-Alder cycloaddition of TPCPD and 1,3,5-hexatriynes under microwave
irradiation
After the investigation of the Diels-Alder reactions under thermal conditions, the DielsAlder reactions were performed under microwave irradiation with two different conditions (Scheme
4.5, Table 4.2). Triyne 4.14a (1 equiv) and TPCPD (1 equiv) were dissolved in dry xylenes. The
mixture was heated under microwave irradiation to 210 °C for 1.5 h. After solvent removal and
purification by column chromatography, 4.15a was isolated in 61% yield (Table 4.2 entry 1,
Condition A). This reaction was repeated under microwave irradiations heating triyne 4.14a (1
equiv) and TPCPD (1 equiv) to 250 °C for 1 h. After solvent removal and purification by column
chromatography, 4.15a was isolated in a significantly higher yield of 95% (Table 4.2, entry 1,
Condition B). Triyne 1.28b (1 equiv) and TPCPD (1 equiv) in o-dichlorobenzene were then tested
toward synthesis of 4.15b and also gave good yields using Condition B (Table 4.2, entry 3)
establishing that the slightly higher temperature was indeed beneficial
Using Condition B, triyne 1.30a (1 equiv.) and TPCPD (1 equiv.) were dissolved in dry odichlorobenzene and were used to synthesize 4.15d which was isolated in 92% yield (table 4.2,
entry 4, Condition B).
The Diels-Alder reactions to obtain 4.15a, 4.15c, and 4.15d were performed using a Cem
microwave and the selected solvent xylenes worked well for both Condition A and B (Table 4.2
entries 1, 3, and 4). When the same reaction condition were utilized to obtain 4.15b using Biotage
microwave, the reaction did not reach the desired temperature (250 °C) leading to an explosion of
the vial inside the vial cavity. The problem was not related to high pressure, but to a different
physical set-up of Biotage microwave compared to Cem microwave including different vial
materials, and it was expected that the low absorber power of xylenes also played a role.
Considering the better ability of o-dichlorobenzene to absorb microwave irradiations compared to
xylenes and furthermore that is a common solvent utilized in Diels-Alder reactions 19, Diels-Alder
reactions to obtain 4.15b, 4.15e, 4.15f were performed with Biotage microwave using odichlorobenzene. (Table 4.2 entries 2, 5, and 6).
In general, the ability of the solvent to convert electromagnetic energy into heat at a given
frequency and temperature is determined by the following equation:
63
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
tan δ = ε”/ ε’
where the tan δ (loss tangent, the dissipation factor of how efficiently microwave energy is
converted into thermal energy) is a function of ε’’ (dielectric loss factor which represent the amount
of input microwave energy that is lost to the sample by being dissipate as heat), and ε’ (dielectric
constant or relative permittivity which represents the ability of a dielectric material to store electric
potential energy under the influence of an electric field). If tan δ > 0.5, the solvent is classified as a
high mw absorber, if 0.1 < tan δ < 0.5, the solvent is considered medium mw absorber (e. g odichlorobenzene, tan δ = 0.280), and tan δ < 0.1, the solvent is considered low mw absorber (e. g oxylene shows tan δ = 0.018) .
Triyne 4.7 (1 equiv.) and TPCPD (1 equiv.) were dissolved in dry o-dichlorobenzene and were used
to synthesize 4.15e according to Condition B and 4.15e was isolated in 72% yield (Table 4.2, entry
5). Triyne 4.13a (1 equiv.) and TPCPD (1 equiv.) were dissolved in dry o-dichlorobenzene and
were used to synthesize 4.15f according to Condition B, and 4.15f was isolated in 57% yield (Table
4.2, entry 6, Procedure B).
The Diels-Alder reactions were optimized under microwave irradiation (Table 4.2) decreasing the
reaction time from 67-97 h under thermal condition to 1 h under mw irradiation. As for Diels-Alder
reactions under thermal heating, reactions under mw irradiation lead preferentially to the
regioisomer A derived from the reaction of TPCPD to the central triple bond β. The yields of 4.15a
range from 85 to 95% under microwave irradiation using Condition B compared to the thermal
heating where the yields values range from 49 to 78%. With the inclusion of more electron-donating
ability or decreasing steric hindrance of end-groups, the yield is decreased (72% for 4.15e and 57%
for 4.15f) compared to the series 4.15b-d (88%, 85%, and 92%, respectively). The slight decrease
of the yield from 72% for 4.15e to 57% for 4.15f might also be explained by the steric hindrance of
end-groups in 4.13a compared to 4.7 that lead to less selectivity for the central triple bond β.
64
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
R1
α
α'
β
R1
Condition A or
R2
Condition β
R2
A
4.15α R1 = SiEt3, R2 =
4.14α R1 = SiEt3, R2 =
4.15β R1 = SiMe3, R2 = Sii-Pr3,
1.30α R1 = SiMe3, R2 = Sii-Pr3,
1.28β R1 = R2 = Sii-Pr3
1.27α R1 = R2 = SiMe3
4.7 R1 = SiMe3, R2 =
4.15c R1 = R2 = Sii-Pr3
4.15d R1 = R2 = SiMe3
4.15e R1 = SiMe3, R2 =
OMe
4.13α R1 = R2 =
4.15f R1 = R2 =
Bu
OMe
Bu
Scheme 4.5. Diels-Alder reactions under microwave irradiation giving 4.15a-f.
Table 4.2. Diels-Alder reactions under microwave irradiation afforded 4.15a-f.
[a]
Products Condition A[a] Condition B[b]
Entry
Triyne
1
4.14[d]
4.15a
61% [e]
95% [e]
2
1.30a
4.15b
-
88% [f]
3
1.28b[c]
4.15c
79% [e]
85% [e]
4
1.27[d]
4.15d
-
92% [e]
5
4.7
4.15e
-
72% [f]
6
4.13a
4.15f
-
57% [f]
Condition A: mw 210 °C, 1.5 h.
[b]
Condition B: mw 250 °C, 1 h.
synthesized from dibromo-precursor provided by a group member.
synthesized by a group member.
Cem microwave.
18 [f]
[e]
[c]
[d]
Triyne
Triyne
Reaction was carried out using dry xylenes with
Reaction performed using o-DCB using Biotage microwave.
The Diels-Alder reaction of triynes 4.16a,b and TPCPD was also explored under microwave
irradiation at 250 °C for 1 h (Scheme 4.6). All reaction resulted in a mixture of regioisomer A,
65
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
regioisomer B, and regioisomer C 4.17a,b, 4.18a,b, and 4.19a,b, respectively. It was not possible to
separate the regioisomers, but evidence for formation of regioisomer A, B, and C was provided by
mass spectroscopy.
Tr*
a
b
Tr*
a'
TPCPD
+
R
Tr*
4.16a,b
xylenes or o-DCB
mw, 250 °C, 1 h
R
R
A
4.17a,b
Tr* =
B
4.18a,b
+
a R = Sii-Pr3
b R = CH3
Tr*
R
C
4.19a,b
Scheme 4.6. Diels-Alder reaction of 4.16a,b.
The ESI HRMS analysis confirmed that the Diels-Alder reaction of 4.16a and TPCPD was
successful because a signal that can be ascribed to 4.17a, 4.18a, or 4.19a was observed at m/z
calculated for C86H104NaSi ([M + Na]+) 1187.77568, found 1187.77995.
66
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Figure 4.6. Expansion of ESI HRMS signals that can be assigned to 4.17a, 4.18a, and 4.19a ([M + Na]+).
The APPI HRMS analysis confirmed that the Diels-Alder reaction of 4.16b and TPCPD was
successful because was observed the signals that can be assigned to Diels-Alder products 4.17b,
4.18b, or 4.19b at m/z calculated for C78H86 (M+) 1022.67241, found 1022.67240, Figure 4.7.
Figure 4.7. Expansion of APPI HRMS signals that can be assigned to 4.17b, 4.18b, and 4.19b (M+).
67
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
4.5 Desilylation and homocoupling reactions toward the formation of the dimers.
The desilylation of tetraphenylbenzene derivatives 4.15a-e was explored with two
different methods (Table 4.3 entries 1-5). Desilylation of 4.15a using KOH was attempted, but
the reaction did not lead to a complete conversion to 4.20a after stirring for 24 h. The reaction
led to a mixture of 4.15a and 4.20a that was difficult to separate. As a consequence, compound
4.15a (1 equiv) in dry THF was cooled to 0 °C, and TBAF (4 equiv) was added. The mixture
was allowed to reach rt and then stirred for 3 h. After work-up, the resulting solid was purified
by a short column chromatography to afford 4.20a in 72% yield (Table 4.3, entry 1).
Desilylation of compound 4.15b (1 equiv), however, could be accomplished using KOH (3
equiv) in THF and MeOH (2:1 v/v) at rt for 5 h. After work up, the solid was purified by a
short column chromatography to afford 4.20b in 93% yield (Table 4.3, entry 2). Compound
4.15c (1 equiv) was desilylated according to the protocol using TBAF (4 equiv) and after 5 h of
stirring and work up, 4.20c was isolated in 61% yield (Table 4.3, entry 3). Reaction to 4.20c
was attempted using KOH, but did not lead to a complete conversion after 24 h. Rather, the
reaction led to a mixture of 4.15d and the product ascribed to the removal of one TMS group.
Desilylation of 4.15d and TBAF (3 equiv) generates 4.20c in 88% yield after work-up and
purification (Table 4.3, entry 4). Finally, compound 4.20e was synthesized from 4.15e using
KOH (3 equiv) After stirring for 2 h and work up, 4.20e was isolated in quantitative yield
(Table 4.3, entry 5).
68
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
R1
H
R2
R3
4.15a: R1 = SiEt3, R2 =
4.20a R3 =
4.15b: R1 = SiMe3, R2 = Sii-Pr3,
4.15c: R1 = R2 = Sii-Pr3
4.15d: R1 = R2 = SiMe3
4.15e: R1 = SiMe3, R2 =
4.20b R3 = Sii-Pr3
4.20c R3 = H
4.20e R3 =
OMe
OMe
Scheme 4.7. Desilylation reactions of 4.20a-e.a
Table 4.3. Desilylation reactions of 4.20a-e.
Entry
Substrate TBAF[a] KOH[b]
(equiv) (equiv)
[a]
Time
Products Yield
(h)
1
4.15a 20
4
-
3h
4.20a
72%
2
4.15b
-
3
5h
4.20b
93%
3
4.15c
4
-
5h
4.20c
61%
4
4.15d
3
-
3h
4.20c
88%
5
4.15e
-
3
2h
4.20e
100%
Desilylation using: substrate (1 equiv), TBAF and THF at rt for 3-5 h.
[b]
Desilylation using substrate (1 equiv) with KOH and THF/MeOH (2:1 v/v) ar rt for
2-5 h.
With terminal alkynes 4.20a, 4.20c and 4.20e in hand, Cu-catalyzed reactions were explored.
Compound 4.20a was subjected to homocoupling under Hay conditions: 21 CuCl (2.5 equiv) and
TMEDA (5 equiv.) in CH2Cl2 were kept in the ultrasonic bath for 20 min (Scheme 4.8). Then,
4.20a (1 equiv) was added. CH2Cl2 was evaporated and replaced by toluene, and the mixture was
69
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
heated to 100 °C for 2 h. After work-up, purification by column chromatography gave 4.21a in 32%
as a yellow solid. It was clear, however, that the reaction was not completed and unreacted 4.20a
(Table 4.4, entry 1, Procedure A) remained. Due to the low yield of 4.21a utilizing Hay conditions,
the homocoupling was repeated using Pd as catalyst: 22,23 Specifically, to a mixture of
[PdCl2(PPh3)2] (0.04 equiv), CuI (0.05 equiv), and dry i-Pr2NH (2.4 equiv) was added 4.20a (1
equiv) in dry THF. Ethyl bromoacetate (1 equiv) was added, and the mixture was stirred at rt under
N2 atmosphere for 24 h. After work-up and purification by column chromatography, 4.21a was
isolated in 66% yield. (Table 4.4, entry 1, Procedure B). Thus, it appeared that the homocoupling
reaction under Pd-catalysis increased the yield. Compound 4.20b under Hay conditions led to 4.21b
in 23% yield. The reaction was not complete and unreacted substrate 4.20b (Table 4.4, entry 2,
Procedure A) was again observed. As a result of the low yield of 4.21b under Hay conditions, the
homocoupling using Pd-catalysis was applied for 4.20b leading to 4.21b in 52% yield (Table 4.4,
entry 2, Procedure B). Finally, compound 4.21e was synthesized from 4.20e under Hay conditions,
but the reaction failed to proceed to completion. Compound 4.21e was isolated in 45% (Table 4.4,
entry 3, Procedure A). Homocoupling using Pd-catalysis gave 4.21e in 85% yield (Table 4.4, entry
2, Procedure B).
70
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
R1
H
R1
R1
4.20a R1 =
4.21a R1 =
4.20b R1 = Sii-Pr3
4.21b R1 = Sii-Pr3
4.20e R1 =
OMe
4.21e R1 =
OMe
Scheme 4.8. Homocoupling condition used to synthesize 4.21a,b,e.
Table 4.4. Homocoupling reactions of 4.20a, 4.20b, and 4.20e to give 4.21a,b,e.
Procedure A [a]20 Procedure B [b]
Entry
Substrate
Product
1
4.20a
4.21a
32%
66%
2
4.20b
4.21b
23%
52%
3
4.20e
4.21e
45%
85%
[a]
Terminal acetylene (1 equiv), CuCl (2.5 equiv), TMEDA (5 equiv), toluene, 100 °C, 2
h.
[b]
Terminal acetylene (1 equiv), [Pd(PPh3)2Cl2] (0.04 equiv), CuI (0.05 equiv), HNi-
Pr2 (2.4 equiv), THF, ethyl bromoacetate (1 equiv) , rt, 24 h.
4.6
UV-vis spectroscopy, cyclic voltammetry, and X-ray crystallography
Figure 4.8a shows the structure of 4.15a-f and 4.20c with the corresponding λmax values
summarized in parenthesis and Figure 4.8b shows the corresponding UV-vis spectra of 4.15a-f and
4.20c. In the series of 4.15b-d the λmax values are approximately the same with values of 297 nm
for 4.15b and 4.15c and 294 nm for 4.15d. ε values increase in the series 4.15d → 4.15c → 4.15b,
and also in the series 4.15e → 4.15a. In comparison to 4.15a, 4.15b-d, and 4.15e-f is shown a red
71
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
shift of λmax due to the extended conjugation through the aryl groups. Compound 4.20c shows a λmax
of 278 nm which is blue shifted relative to all other derivatives as a result of decreased conjugation
and loss of the tri-alkylsilyl groups.
72
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
a)
SiEt3
4.15a (λmax = 328 nm)
Sii-Pr3
Sii-Pr3
SiMe3
SiMe3
Sii-Pr3
SiMe3
4.15b (λmax = 297 nm)
4.15c (λmax = 297 nm)
4.15d (λmax = 294 nm)
Bu
OMe
H
H
SiMe3
Bu
4.15e(λmax = 340 nm)
4.15f (λmax = 352 nm)
4.20c (λmax = 278 nm)
b)
Figure 4.8 a) Structures of 4.15a-f and 4.20c with correspondent λmax values in parenthesis. b) UV-vis absorption
spectra of 4.15a-f and 4.20c measured in CH2Cl2.
Figure 4.9a shows the structure of 4.15a,b,e and 4.21a,b,e with the correspondent λmax values
obtained summarized in parenthesis. Figure 4.9b show the UV-vis spectra of 4.15a,b,e and
4.21a,b,e The λmax values of the dimers 4.21a,b,e are red shifted compared the corresponding
precursors 4.15a,b,e and this fact is ascribed to the increasing conjugation in the dimers 4.21a,b,e.
73
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
The red shifts observed from the Diels-Alder precursors to the corresponding dimers are: 58 nm
from 4.15a to 4.21a, 70 nm from 4.15b to 4.21b, and 54 nm from 4.15e to 4.21e. ε values decrease
in the series 4.21e → 4.21a; the reason of this behaviour is not been investigated yet.
74
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
a)
OMe
Sii-Pr3
SiEt3
4.15a (λmax = 328 nm)
SiMe3
SiMe3
4.15b (λmax = 297 nm)
4.15e (λmax = 340 nm)
OMe
4.21a (λmax = 386 nm)
Sii-Pr3
i-Pr3Si
MeO
4.21b (λmax = 367 nm)
4.21e (λmax = 394 nm)
b)
Figure 4.9. a) Structures of 4.15a,b,e and 4.21a,b,e with correspondent λmax values in parenthesis. b) UV-vis absorption
spectra of 4.15a,b,e and 4.21a,b,e measured in CH2Cl2.
75
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Electrochemical analysis were conducted by cyclic voltammetry for compounds 4.15e-f, 4.20c and
4.21a,b,e, but the compounds do not show any redox event. The redox behavior it is surprising for
compounds 4.15e and 4.21e due to the fact that in literature is known a similar compounds 4.22
which exhibit oxidation events (Figure 4.10) 24. The reason why the compounds analyzed do not
display redox events are not known yet.
OMe
OMe
OMe
i-Pr3Si
SiMe3
Me3Si
OMe
4.22
4.15e
MeO
4.21e
Figure 4.10. Molecular structure of 4.15e, 4.21e, and 4.22.24
Aryl substituents in tetraphenylbenzene are not constrained by additional bonding in the plane of
the aromatic core, and, thus, the phenyl substituents display a twisted angle with respect to the
central benzene core. As a consequence, tetraphenyl-benzene derivatives display complex non
planar topologies,
25
and the conjugation between the phenyl moieties and the central benzene ring
could be limited. 26,27
Compound 4.20c was analyzed by X-ray crystallography and the solid state torsion angles are
compared to un-substituted tetraphenylbenzene (TPB) known in literature.5 Single crystals of 4.20c
were obtained by slow evaporation of a CDCl3 solution at rt. Considering the structures of 4.20c
(Figure 4.11a) and TPB (Figure 4.11b), TPB displays C2 symmetry, while 4.20c does not. The
phenyl substituents in 4.20c are more twisted with respect to the central benzene ring than those in
TPB. The torsion angles of 4.20c range from 63.6(4)° to 67.6(5)° (Table 4.5, entries 3-6), while
those in TPB range from 68.1(2)° to 68.8(2)° (Table 4.6, entries 1-2).
76
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
a)
b)
Figure 4.11. X-ray crystallographic structure of a) 4.20c. b) TPB.
Table 4.5. Torsion angles of phenyl substituents and the central benzene ring of 4.20c.
Entry
Carbon atoms
Torsion angle °
1
C12
C13
C21
C22
76.9(4)
2
C14
C13
C21
C26
78.5(4)
3
C13
C14
C31
C32
67.6(5)
4
C15
C14
C31
C36
63.6(4)
5
C14
C15
C41
C42
66.0(5)
6
C16
C15
C41
C46
64.3(4)
7
C15
C16
C61
C62
66.7(4)
8
C11
C16
C61
C66
73.2(4)
77
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Table 4.6. Torsion angles of phenyl substituents and the central benzene ring of TPB.
Entry
Carbon atoms
Torsion angle °
1
C5
C1
C2
C2’
68.1(2)
2
C9
C1
C2
C4
68.8(2)
3
C6
C3
C4
C2
51.5(5)
4
C11
C3
C4
C7
47.6(2)
A single crystal of 4.15c suitable for X-ray crystallographic analysis was obtained by slow
evaporation of a CDCl3 solution at rt. The solid state structure with selected carbon atoms labels of
4.15c is shown in Figure 4.12a. Two unique molecules are found in the unit cell: molecule A and
molecule B. Both molecules were analyzed in terms of torsion angles of the phenyl substituents to
the central benzene rings. The results for molecule A and B are shown in Table 4.7. The molecules
show different torsion angles, but the differences are small. Overall the angles vary from 62.0 °
(C35a-C34A-C51A-C52A) to 81.6 ° (C31A.C36A-C71A-C72A) for molecule B, while the angles
vary from 63.9 ° (C35B-C34B-C51B-C52B) to 73.2 ° (C31B.C36B-C71B-C72B) for molecule A.
Figure 4.12. a) X-ray crystallographic structure of 4.15c with selected label atoms.
78
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Table 4.7. Torsion angles of aryls substituent with the central benzene rings of 4.15c
Entry
Carbon atoms
Torsion angle °
Torsion angle °
Molecule A
Molecule B
1
C32
C33
C41
C42
68.7 (4)
69.0 (4)
2
C34
C33
C41
C46
68.9 (4)
72.1 (4)
3
C33
C34
C51
C56
66.0 (4)
64.7 (4)
4
C35
C34
C51
C52
63.9 (4)
62.0 (4)
5
C34
C35
C61
C66
67.4 (4)
64.4 (4)
6
C36
C35
C61
C62
68.4 (4)
69.2 (4)
7
C35
C36
C71
C76
70.7 (4)
79.9 (4)
8
C31
C36
C71
C72
73.2 (4)
81.6 (4)
4.7
Attempts to synthesize PAH derivatives via Scholl cyclodehydrogenation
Considering the procedure known in literature to synthesize PAH from phenyl-substituted
benzenes via the Scholl reaction,2 the same protocol was applied for compounds 4.15c, 4.21a, and
4.21b, but attempts to obtain the desired products, however, failed (Scheme 4.9). For all three cases,
products derived from partial cyclization were observed. For the reaction of 4.21a and 4.21b,
remaining starting material was also visible in the 1H NMR spectra. Due to time constraints, other
cyclodehydrogenation protocols were not tried.
79
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
Sii-Pr3
Sii-Pr3
FeCl3, CH3NO2
CH2Cl2
Sii-Pr3
Sii-Pr3
4.15c
R
R
FeCl3, CH3NO2
CH2Cl2
R
R
4.21a R =
4.21b R = Sii-Pr3
Scheme 4.9. Attempts to synthesize PAHs via the Scholl reaction.
4.8
Conclusions
The Diels-Alder reaction of TPCPD and different triynes has been investigated. The DielsAlder reactions shows regioselectivity with the preferential reaction of TBCPD at the central triple
bond of the triynes. The Diels-Alder reaction was optimized under microwave irradiation resulting
in the decrease of the reaction time and increase of the yield compared to the analogous Diels-Alder
reaction conducted under thermal conditions. Selected Diels-Alder products have been taken on to a
sequence of desilylation and homocoupling reactions to form dimeric derivatives. The
homocoupling reaction has been optimized using Pd(PPh3)2Cl2 as a catalyst and the reaction results
in an increase of the yield compared to those obtained with Hay homocoupling using Cu(I). The
properties of obtained products have been explored using UV-vis spectroscopy, cyclic voltammetry,
and in two cases X-ray crystallography. The dimers show a red shift of λmax compared to the
80
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
corresponding monomeric precursors ascribed to the increasing conjugation in the dimers compared
to the precursors.
4.9
References
1.
X. Feng, W. Pisula, K. Müllen, Pure Appl. Chem. 2009, 81, 2203-2224.
2.
R. Liu, D. Wu, X. Feng, K. Müllen, J. Am. Chem. Soc. 2011, 133, 15221-15223.
3.
B. Alameddine, S. M. Caba, M. Schindler, T. A. Jenny, Synthesis 2012, 44, 1928-1934.
4.
A. J. Berresheim, M. Müller, K. Müllen, Chem. Rev. 1999, 99, 1747-1786.
5.
H. Wang, Y. Liang, H. Xie, L. Feng, H. Lu, S. Feng, J. Mater. Chem. 2014, 2, 5601-5606.
6.
M. D. Watson, A. Fechtenkötter, K. Müllen, Chem. Rev. 2001, 101, 1267-1300.
7.
C. Kübel, S. L. Chen, K. Müllen, Macromolecules 1998, 31, 6014-6021.
8.
R. Gedye, F. Smith, K. Westaway, H. Ali, L. Baldisera, Tetrahedron Lett. 1986, 27,
279-282.
9.
R. J. Giguere, T. L. Bray, S. M. Duncan, G. Majetich, Tetrahedron Lett. 1986, 27,
4945-4948.
10.
A. Loupy, F. Maurel, A. Sabatié-Gogovà, Tetrahedron 2004, 60, 1683-1691.
11.
W. D. Shipe, S. E. Wolkenberg, C. W. Lindsley, Drug Discov. Today Technol. 2005, 2,
155-161.
12.
A. L. K. Shi Shun, E. T. Chernick, S. Eisler, R. R. Tykwinski, J. Org. Chem. 2003, 68,
1339-1347.
13.
S. Eisler, N. Chahal, R. McDonald, R. R. Tykwinski. Chem. Eur. J. 2003, 9, 2542-2550.
14.
Y. Morisaki, T. Luu, R. R. Tykwinski, Org. Lett. 2006, 8, 689-692.
15.
T. Luu, E. Elliott, A. D. Slepkov, S. Eisler, R. McDonald, F. A. Hegmann, R. R Tykwinski,
Org. Lett. 2005, 7, 51-54.
16.
I. Van Overmeire, S. A. Boldin, K. Venkataraman, R. Zisling, S. D. Jonghe, S. Van
Calenbergh, D. De Keukeleire, A. H. Futerman, P. Herdewijn, J. Med. Chem. 2000, 43,
4189-4199.
17.
A. Auffrant, F. Diederich, Helv. Chim. Acta 2004, 87, 3085-3105.
81
Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone
and 1,3,5-hexatriynes
18.
Initial
reactions were carried out during the master thesis, but all the products were
completely characterized during the PhD work.
19.
N. Kaval, W. Dehaen, C. O. Kappe, E. Van der Eycken, Org. Biomol. Chem. 2004, 2,
154-156.
20.
This reaction was already investigated. For more details see: Michael Vogl, Bachelorarbeit,
Universität Erlangen-Nürnberg, 2010.
21.
A. S. Hay, J. Org. Chem. 1962, 27, 3320-3321.
22.
A. Lei, M. Srivastava, X. Zhang, J. Org. Chem. 2002, 67, 1969-1971.
23.
W. A. Chalifoux, M. J. Ferguson, R. R. Tykwinski, Eur. J. Org. Chem. 2007, 1001-1006.
24.
J. P. Gisselbrecht, N. N. P. Moonen, C. Boudon, M. B. Nielsen, F. Diederich, M. Gross,
Eur. J. Org. Chem. 2004, 2959-2972.
25.
E. Gagnon, T. Maris, P. M. Arseneault, K. E. Maly, J. D. Wuest, Cryst. Growth Des. 2009,
10, 648-657.
26.
I. Y. Wu, J. T. Lin, Y. T. Tao, E. Balasubramanian, Adv. Mater. 2000, 12, 668-669.
27.
R. N. Bera, N. Cumpstey, P. L. Burn, I. D. W. Samuel, Adv. Funct. Mater. 2007, 17,
1149-1152.
82
Chapter 5: Experimental section
Chapter 5: Experimental section
5.1
General data
Reagents were purchased reagent grade from commercial suppliers and used without further
purification. THF and Et2O were distilled from sodium/benzophenone, CH2Cl2 was distilled from
CaH2, hexanes, toluene, and xylenes from sodium, and i-Pr2NH was distilled from CaCl2. MgSO4
and Na2SO4 were used as standard drying reagents after aqueous work-up. TLC analyses were
carried out on TLC plates from Macherey-Nagel (ALUGRAM® SIL G/UV254) and visualized via
UV-light (264/364 nm) or standard coloring reagents. Column chromatography was performed
using Silica Gel 60M (Merck).
1
H and 13C NMR spectra were recorded on a Bruker Avance 300 operating at 300 MHz (1H NMR)
and 75 MHz (13C NMR), a Bruker Avance 400 operating at 400 MHz (1H NMR) and 100 MHz (13C
NMR), or a Jeol Alpha 500 operating at 500 MHz (1H NMR) and 126 Hz (13C NMR). NMR spectra
were referenced to the residual solvent signal (1H: CDCl3, 7.24 ppm;
THFD8, 3.58 ppm, 1.73 ppm;
13
13
C: CDCl3, 77.0 ppm; 1H:
C: THDD8, 67.4 ppm, 25.2 ppm) and recorded at ambient probe
temperature. Coupling constants are reported as observed (±0.5 Hz).
Mass spectra were obtained from a Bruker 9.4T Apex-Qe FTICR (MALDI, Matrix: DCTB),
Agilent Technologies 6220 TOF (ESI), Bruker micro TOF II focus, and Bruker maxis 4G (APPI,
ESI, in CH2Cl2) instruments.
IR spectra were recorded on a Varian 660-IR spectrometer as solids in ATR-mode.
UV-vis spectroscopic measurements were carried out on a Varian Cary 5000 UV-vis-NIR
spectrophotometer.
Melting points were measured with an Electrothermal 9100 instrument.
Crystallographic data for unpublished compounds are available from the X-ray Crystallographic
Laboratory, Institute for Organic Chemistry, Universität Erlangen-Nürnberg.
Reactions under microwave were performed using a Synthesis Cem microwave or Biotage Initiator
microwave.
Cyclic voltammetry was performed using BAS CV 50 W VERSION 2 instrument. Three electrodes
compartment was used: Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode,
83
Chapter 5: Experimental section
and Pt as working electrode. The reference electrode Ag/AgNO3 contains a solution of 0.001 M of
AgNO3, 0.1 M of n-Bu4NPF6 in ACN. The reference electrode was stored in a solution containing
0.1 M n-Bu4NPF6 in ACN. n-Bu4NPF6, commercial available in 99% for analytical purpose, it was
used as the supporting electrolyte without further purification. Ferrocene was used as internal
standard. Before each analysis, the solutions were stirred and degassed with a constant flow of
nitrogen for 25 min and during the measurement, the flow of nitrogen was maintain in the cell. The
solvent used was fresh distilled CH2Cl2.
5.2
Synthesis of known compounds
O
H
Sii-Pr3
4.1
Compound 4.1. 1 To a solution of triisopropylsilyl acetylene (5.1 g, 6.1 mL, 27 mmol) in dry Et2O
(50 mL) at –78 °C was slowly added n-BuLi (2.5 M in hexanes, 11 mL, 27 mmol). The solution
was stirred for 30 min, and dry DMF (2.5 g, 2.7 mL, 34 mmol) was added via a syringe. The
cooling bath was removed and the reaction was allowed to reach rt. The solution was poured into a
mixture of ice (50 mL) and HCl (1.0 M, 50 mL). The layers were separated, and the organic phase
was washed sequentially with sat. aq. NaHCO3 (2 x 50 mL), sat. aq. NaCl (2 x 50 mL), dried
(MgSO4), and filtered. The solvent was removed in vacuum, and the crude product was filtered
through a short silica gel plug with hexanes. After removal of the solvent, 4.1 (4.1 g, 73%) was
obtained as a clear colorless liquid. Spectral and physical data were consistent with those reported. 2
84
Chapter 5: Experimental section
OH
Me3Si
Sii-Pr3
4.2
Compound 4.2. 3 To a solution of trimethylsilylacetylene (1.95 g, 2.7 mL, 20 mmol) in dry THF (60
mL) at –78 °C was slowly added n-BuLi (2.5 M in hexanes, 7.6 mL, 20.1 mmol). The reaction
mixture was stirred for 1 h and the aldehyde 4.1 (4.1 g, 20 mmol), dissolved in dry THF (10 mL),
was slowly added over 5 min. The reaction mixture was allowed to warm to rt. After stirring for 3.5
h, sat. aq. NH4Cl (25 mL) and Et2O (25 mL) were added and the layers were separated. The organic
layer was washed with sat. aq. NH4Cl (3 x 25 mL), dried (MgSO4), filtered, and the solvent
removed in vacuum. The crude product was purified by column chromatography (silica gel,
hexanes/ethyl acetate 10:1) and 4.2 (5.1 g, 83%) was obtained as a yellow oil. Spectral and physical
data were consistent with those reported. 4
O
Me3Si
Sii-Pr3
4.3
Compound 4.3 was synthesized according to literature3 and was isolated in 98% yield (3.9 g).
Spectral and physical data were consistent with those reported. 5
Br
Me3Si
Br
Sii-Pr3
4.4
Compound 4.4 was synthesized according to literature3 and was isolated in 67% yield (2.1 g).
Spectral and physical data were consistent with those reported.5
85
Chapter 5: Experimental section
Me3Si
Sii-Pr3
1.30a
Compound 1.30a was synthesized according to literature3 and was isolated in 68% yield (2.3 g).
Spectral and physical data were consistent with those reported. 6
O
MeO
SiMe3
4.5
Compound 4.5 was synthesized according to literature 7 and was isolated in 100% (4.14 g) yield.
Spectral and physical data were consistent with those reported.7
Br
Br
MeO
SiMe3
4.6
Compound 4.6 was synthesized according to literature3 and was isolated in 61% (4.1 g) yield.
Spectral and physical data were consistent with those reported.3
86
Chapter 5: Experimental section
MeO
SiMe3
4.7
Compound 4.7 was synthesized according to literature 8 and was isolated in 87% (0.81 g) yield.
Spectral and physical data were consistent with those reported.8
SiMe3
4.8a
Compound 4.8. 9 To a solution of 4-bromobutylbenzene (3.8 ml, 6.0 g, 28 mmol) in dry i-Pr2NH
(12 ml) were added PdCl2(PPh3)2 (0.21 g, 0.28 mmol), CuI (0.053 g, 0.28 mmol) and
trimethylsilylacetylene (9 mL, 63 mmol). After stirring for two days at 50 °C, the volatiles were
removed in vacuum and the residue was dissolved in CH2Cl2 (10 mL). The organic layer was
washed with sat aq. solution of NaCl (10 mL), H2O (10 mL), and dried over Na2SO4. The pure
product was obtained after a column chromatography using hexanes. The reaction afforded the pure
product 4.8a (5.2 g, 81%) as a light yellow oil. Spectral and physical data were consistent with
those reported.9
H
4.9a
Compound 4.9. 10 To a solution of 4.8a (1.7 g, 8.3 mmol) in MeOH/ THF (30 mL, 1:5 v/v) was
added KOH (2.3 g, 42 mmol). The mixture was stirred at rt overnight, and the solvent was removed
87
Chapter 5: Experimental section
by rotary evaporation. The residue was diluted with EtOAc (15 mL) and sequentially washed with
HCl (aq. 10%, 10 mL) and NaCl (10 mL). The organic layer was dried over MgSO4, concentrated
under vacuum and purified by column chromatography (hexanes/CH2Cl2, 9:1) to afford 4.9a (0.7 g,
86%) as a brown-yellow oil. Spectral and physical data were consistent with those reported.10,11
MeO
SiMe3
4.8b
Compound 4.8b.12 To a solution of 4-iodoanisole (4.9 g, 21 mmol) in dry i-Pr2NH (55 ml) were
added PdCl2(PPh3)2 (0.15 g, 0.21 mmol), CuI (0.040 g, 0.21 mmol) and trimethylsilylacetylene (9.0
mL, 63 mmol). After stirring overnight at room temperature, the volatiles were removed in vacuum
and the residue was dissolved in CH2Cl2. The organic layers was washed with sat aq. Solution of
NaCl (15 mL), H2O (15 mL) and dried over Na2SO4. The pure product 4.8b (4.3 g, 100%) was
isolated after a column chromatography (hexane/CH2Cl2, 10:1). Spectral and physical data were
consistent with those reported.12
H
MeO
4.9b
Compound 4.9b.12 To a solution of 4.8b (4.4 g, 21 mmol) in MeOH/THF (42 mL, 1:5 v/v) was
added K2CO3 (5.9 g, 43 mmol). The mixture was stirred for 2 h, and the reaction solvent was
removed by rotary evaporation. The residue was diluted with EtOAc (15 mL) and sequentially
washed with HCl (30%, 15 mL), and NaCl (15 mL). The organic layer was dried over MgSO4,
concentrated under vacuum to afford 4.9b (2.2 g, 78%) as a colorless oil. Spectral and physical data
were consistent with those reported.12
88
Chapter 5: Experimental section
OH
OMe
MeO
4.10b
Compound 4.10b was synthesized according to literature 13 and was isolated in 80% (0.73 g) yield.
Spectral and physical data were consistent with those reported.13
O
MeO
OMe
4.11b
Compound 4.11b.13 To a solution of 4.10b (0.73 g, 2.5 mmol) in CH2Cl2 (22 mL) were added
PCC (0.78 g, 3.6 mmol), celite (0.74 g), and molecular sieves (4 Å, 0.74 g). After 24 h, the reaction
mixture was passed through a plug of silica gel using CH2Cl2 (50 mL) to remove the chromium
waste. After solvent removal 4.11b (0.59 g, 81%) was obtained as an orange solid. Spectral and
physical data were consistent with those reported.13
89
Chapter 5: Experimental section
Br
Br
MeO
OMe
4.12b
Compound 4.12b.13 To a solution of CBr4 (9.5 g, 28 mmol) and PPh3 (15 g, 56 mmol) in dry
CH2Cl2 (24 mL) at rt was slowly added a solution of 4.11b (0.61 g, 21 mmol) in dry CH2Cl2 (3
mL). After stirring for 3 d, the solvent was reduced, and hexanes (10 mL)was added. The
inhomogeneous mixture was passed through a plug of silica gel (hexanes, 20 mL). After solvent
removal, 4.12b was obtained (0.68 g, 73%) as a yellow solid. Spectral and physical data were
consistent with those reported.13
5.3
Synthesis of new compounds
OH
Bu
Bu
4.10a
Compound 4.10a. MeMgBr (1 M in THF, 0.95 mL, 2.8 mmol) was added to 4.9a (0.49 g, 2.6
mmol) in dry THF (4 mL) and the mixture was heated to 50 °C for 2 h. After cooling to 0 °C, ethyl
formate (0.092 g, 1.2 mmol, 0.10 mL) was added and the solution was stirred at rt for 5 h. The
mixture was quenched with sat. aq NH4Cl (2 x 10 mL), and the organic phase was extracted with
Et2O (10 mL), washed with sat. aq. NaCl (10 mL), H2O (10 mL), and dried (MgSO4). After
purification by column chromatography (hexanes/CH2Cl2 2:4), 4.10a (0.30 g, 67%) was obtained as
a light yellow solid. Rf = 0.56 (hexanes/CH2Cl2 2:4). Mp = 85 °C. IR (ATR) 3372 (w), 3024 (vw),
2958 (w), 2925 (m), 2853 (w), 2229 (w), 1604 (m), 1505 (w), 1455 (w), 1410 (w), 1296 (m). 1H
90
Chapter 5: Experimental section
NMR (300 MHz, CDCl3) δ 7.41 (d, J = 8.2 Hz, 4H), 7.11 (d, J = 8.1 Hz, 4H), 5.61 (s, 1H), 2.86 (bs,
1H), 2.6 (t, J = 7.7 Hz, 4H), 1.61−1.54 (m, 4H), 1.38−1.30 (m, 4H), 0.93 (t, J = 7.3 Hz, 6H). 13C
NMR (75.5 MHz, CDCl3) δ 143.8, 131.7, 128.3, 119.1, 85.5, 84.6, 53.2, 35.5, 33.2, 22.2, 13.8. LDI
TOF m/z 344 (M+, 20), 327 ([M − OH]+, 100).
O
Bu
Bu
4.11a
Compound 4.11a. To a solution of 4.10a (0.30 g, 0.86 mmol) in CH2Cl2 (8 mL) was added PCC
(0.27 g, 1.3 mmol), celite (0.26 g), and molecular sieves (4 Å, 0.26 g). After 24 h, the reaction
mixture was passed through a plug of silica gel using CH2Cl2 (15 mL) to remove the chromium
waste. After solvent removal and purification by column chromatography (silica gel,
hexanes/CH2Cl2 3:2), 4.11a (0.20 g, 67%) was obtained as a light yellow oil. Rf = 0.52
(hexanes/CH2Cl2 3:2). IR (ATR) 3199 (vw), 3029 (vw), 2951 (m), 2926 (m), 2857 (m), 2206 (s),
2179 (s), 1600 (s), 1505 (m), 1302 (s), 1091 (s). 1H NMR (300 MHz, CDCl3) δ 7.53 (d, J = 8.1 Hz,
4H), 7.19 (d, J = 8.1 Hz, 4H), 2.62 (t, J = 7.7 Hz, 4H), 1.61−1.53 (m, 4H); 1.38−1.24 (m, 4H), 0.64
(t, J = 7.3 Hz, 6H). 13C NMR (75.5 MHz, CDCl3) δ 160.7, 146.8, 133.3, 128.7, 116.5, 92.1, 89.4,
35.7, 33.0, 22.2, 13.8. LDI TOF m/z 343 ([M + H]+).
91
Chapter 5: Experimental section
Br
Br
Bu
Bu
4.12a
Compound 4.12a. To a solution of CBr4 (0.11 g, 0.33 mmol) and PPh3 (0.18 g, 0.67 mmol) in dry
CH2Cl2 (4 mL) at rt was slowly added a solution of 4.11a (0.086 g, 0.25 mmol) in dry CH2Cl2 (0.4
mL). After stirring overnight, the solvent was reduced and hexanes added. The inhomogeneous
mixture was passed through a plug of silica gel (hexanes, 15 mL). After solvent removal, 4.12a
(0.097 g, 78%) was obtained as a light yellow oil. Rf = 0.7 (hexanes). IR (ATR) 3026 (vw), 2947
(m), 2924 (m), 2854 (m), 2264 (vw), 2195 (s), 1605 (m), 1509 (s), 1458 (m). 1H NMR (300 MHz,
CDCl3) δ 7.46 (d, J = 8.1 Hz, 4H), 7.15 (d, J = 8.1 Hz, 4H), 2.61 (t, J = 7.7 Hz, 4H), 1.62−1.54 (m,
4H); 1.39−1.27 (m, 4H), 0.93 (t, J = 7.3 Hz, 6H). 13C NMR (75.5 MHz, CDCl3) δ 144.4, 131.6,
128.5, 119.3, 114.5, 106.8, 96.0, 85.6, 35.7, 33.3, 22.3, 13.9. APPI HRMS m/z calcd for C26H2679Br2
(M+): 496.0396; found: 496.0398.
Bu
Bu
4.13a
Compound 4.13a. A solution of 4.12a (95 mg, 0.19 mmol) in hexanes (1 mL) was cooled to –78
°C. n-BuLi (1.6 M in hexane, 0.14 mL, 0.23 mmol) was slowly added over a period of ca. 2 min.
After 10 min, the reaction was warmed to approximately –10 °C and was stirred for 2 h. The
mixture was quenched via the addition of sat. aq. NH4Cl (1 mL). Et2O (1 mL) was added, the
organic layer was separated, washed with sat. aq. NH4Cl (2 × 1 mL), dried (MgSO4), filtered, and
the solvent was removed in vacuum. After the crude mixture was passed through a plug of silica gel
to remove baseline material, 4.13a (58 mg, 90%) was obtained as a light yellow solid. Rf = 0.2
(hexanes). Mp = 72 °C. IR (ATR) 2956 (m), 2925 (s), 2854 (m), 1457 (m). 1H NMR (300 MHz,
92
Chapter 5: Experimental section
CDCl3) δ 7.41 (d, J = 8.1 Hz, 4H), 7.15 (d, J = 8.1 Hz, 4H), 2.6 (t, J = 7.6 Hz, 4H), 1.62−1.52 (m,
4H), 1.39−1.27 (m, 4H), 0.93 (t, J = 7.3 Hz, 6H). 13C NMR (75.5 MHz, CDCl3) δ 145.1, 132.9,
128.6, 118.0, 78.8, 73.9, 66.4, 35.7, 33.2, 22.3, 13.9. APPI HRMS m/z calcd for C26H27 ([M + H]+):
339.2107; found: 339.2105.
SiEt3
4.15a
Compound 4.15a. Thermal reaction: Triyne 4.14a (0.48 g, 1.9 mmol) and TPCBD (0.71 g, 1.9
mmol) were dissolved in dry xylenes (10 mL). The mixture was heated to reflux at 140 °C for 97 h.
After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1),
4.15a (0.56 g, 49%) was obtained as a colorless solid.
Microwave at 210 °C: Triyne 4.14a (0.10 g, 0.38 mmol) and TPCBD (0.15 mg, 0.38 mmol) were
dissolved in dry xylenes (4 mL). The mixture was heated under microwave irradiation at 210 °C for
1.5 h. After solvent removal and purification by column chromatography (silica gel,
hexanes/CH2Cl2 5:1), 4.15a (0.14 g, 61%) was obtained as a colorless solid.
Microwave at 250 °C: Triyne 4.14a (48 mg, 0.18 mmol) and TPCBD (70 mg, 0.18 mmol) were
dissolved in dry xylenes (1.7 mL). The mixture was heated under microwave irradiation to 250 °C
for 1 h. After solvent removal and purification by column chromatography (silica gel,
hexanes/CH2Cl2 5:1), 4.15a (11 mg, 95%) was obtained as a colorless solid. Rf = 0.2
(hexanes/CH2Cl2 5:1). Mp = 206 °C. IR (ATR) 3055 (vw), 2951 (w) , 2872 (w), 2141 (w), 1598
(w), 1491 (w), 1441 (m), 1401 (m) cm–1. UV-vis (CH2Cl2) λmax (ε) 328 (30500), 312 (36100), 272
(71700). 1H NMR (300 MHz, CDCl3) δ 7.20–7.09 (m, 15H), 6.84–6.73 (m, 10H), 0.81 (t, J = 7.8
Hz, 9H), 0.46 (q, J = 7.2 Hz, 6H).
13
C NMR (75.5 MHz, CDCl3) δ 144.2, 143.6, 141.1, 141.0,
140.0, 139.8, 139.4, 131.4, 131.2, 131.0, 130.6, 130.4, 127.9, 127.1, 126.70, 126.68, 126.44,
93
Chapter 5: Experimental section
126.40, 126.0, 125.7, 125.6, 125.3, 124.8, 123.6, 104.2, 100.4, 97.1, 88.8, 7.4, 4.3 (two signals are
coincident or not observed) ESI HRMS m/z calcd for C46H40Si (M+): 620.2894; found: 620.2906,
([M + Na]+): 643.2795; found: 643.2792.
SiMe3
Sii-Pr3
4.15b
Compound 4.15b. Thermal reaction: Triyne 1.30a (0.55 g, 1.8 mmol) and TPCBD (0.70 g, 1.8
mmol) were dissolved in dry xylenes (27 mL). The mixture was heated to reflux at 140 °C for 95 h.
After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1)
4.15b (0.83 g, 70%) was obtained as a colorless solid.
Microwave at 250 °C: Triyne 1.30a (0.10 g, 0.33 mmol) and TPCBD (0.13 g, 0.33 mmol) were
dissolved in dry o-dichlorobenzene (3.7 mL). The mixture was heated under microwave irradiation
at 250 °C for 1 h. After solvent removal and purification by column chromatography (silica gel,
hexanes/CH2Cl2 5:1), 4.15b (0.19 g, 88%) was isolated as a colorless solid. Rf = 0.3
(hexanes/CH2Cl2 5:1). Mp = 174 °C. IR (CDCl3 cast): 3076 (vw), 3055 (vw), 3024 (vw), 2941 (m),
2862 (m), 2150 (m), 1247 (m) cm–1. UV-vis (CH2Cl2) λmax (ε) 297 (21300), 260 (54900). 1H NMR
(300 MHz, CDCl3) δ 7.12–7.05 (m, 10H), 6.83–6.78 (m, 6H), 6.72–6.67 (m, 4H), 1.02−0.92 (m,
21H), 0.08 (s, 9H). 13C NMR (75.5 MHz, CDCl3) δ 144.6, 144.1, 141.3, 141.1, 140.0, 139.9, 139.4,
139.3, 130.9, 130.4, 130.3, 127.2, 127.1, 126.64, 126.62, 126.4, 126.3, 125.6, 125.2, 124.7, 104.5,
103.5, 102.8, 99.3, 97.3, 18.6, 11.1, –0.4. ESI HRMS m/z calcd for C46H50Si2Na ([M + Na]+):
681.3343; found: 681.3352.
94
Chapter 5: Experimental section
Sii-Pr3
Sii-Pr3
4.15c
Compound 4.15c. Thermal reaction: Triyne 1.28b (0.20 g, 0.52 mmol) and TPCBD (0.20 g, 0.52
mmol) were dissolved in dry xylenes (7 mL). The mixture was heated to reflux at 140 °C for 97 h.
After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1)
4.15c (0.22 g, 58%) was obtained as a colorless solid.
Microwave at 210 °C: Triyne 1.28b (0.10 g, 0.26 mmol) and TPCBD (0.099 g, 0.26 mmol) were
dissolved in dry xylenes (4 mL). The mixture was heated under microwave irradiation at 210 °C for
1.5 h. After solvent removal and purification by column chromatography (silica gel,
hexanes/CH2Cl2 5:1), 4.15c (0.15 g, 79%) was obtained as a colorless solid.
Microwave at 250 °C: Triyne 1.28b (0.10 g, 0.26 mmol) and TPCBD (0.10 g, 0.26 mmol) were
dissolved in dry xylenes (4.1 mL). The mixture was heated under microwave irradiation at 250 °C
for 1 h. After solvent removal and purification by column chromatography (silica gel,
hexanes/CH2Cl2 5:1), 4.15c (0.17 mg, 85%) was obtained as a colorless solid. Rf = 0.2
(hexanes/CH2Cl2 5:1). Mp = 235 °C. IR (CDCl3 cast): 3080 (vw), 3057 (vw), 3026 (wv), 2941 (s),
2890 (m), 2864 (s), 2145 (w), 1602 (w), 1462 (m) cm–1. UV-vis (CH2Cl2) λmax (ε) 297 (19000), 260
(48300), 227 (20200). 1H NMR (300 MHz, CDCl3) δ 7.12–7.02 (m, 10H), 6.81–6.76 (m, 6H), 6.68–
6.64 (m, 4H), 0.91–0.85 (m, 42H).
13
C NMR (75.5 MHz, CDCl3) δ 144.7, 141.3, 140.1, 139.5,
130.9, 130.4, 127.3, 126.6, 126.4, 125.5, 124.8, 104.6, 99.6, 18.6, 11.3. LDI TOF m/z 766 ([M +
Na]+, 100).
95
Chapter 5: Experimental section
Single crystals suitable for X-ray crystallographic analysis were crystallized from CDCl3.
C52H62Si2, Fw = 743.20; crystal dimension 0.5135 x 0.1863 x 0.0598 mm3; triclinic system; space
group P-1: a = 13.6637(5) Å, b = 19.1001(5) Å, c = 19.4906(7) Å, α β = 102.853 (3)°, β V =
4599.5(3) Å3, Z = 4, ρcalcd = 1.073 mg mm–3; µ(CuKα) = 0.927 mm–1; T = 173.00(10) K; 2θ max =
125.62°; total data collected = 21646; R1 = 0.0776 [11216 independent reflections with [I≥ 2σ(I)];
wR2 = 0.2387 for 13963 data, 1019 variables, and 10 restraints, largest difference, peak and hole =
1.43 and –0.47 e Å–3. The crystal showed disorder that was resolved to the following occupation
factors: C15/15’ = 70:30%, C17/C17’/C19/C19’ = 32:68%, C5a/C5a’/C6a/C6a’ = 60:40%,
C21/C21’/ C22/C22’ = 33:67 %, C13a/C13 = 50:50%.
SiMe3
SiMe3
4.15d
Compound 4.15d. Thermal reaction: Triyne 1.27a (0.11 g, 0.46 mmol) and TPCBD (0.18 g, 0.46
mmol) were dissolved in dry xylenes (4 mL). The mixture was heated to reflux at 140 °C for 67 h.
After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1),
4.15d (0.21 g, 78%) was obtained as a colorless solid.
Microwave at 250 °C: Triyne 1.27a (0.11 g, 0.46 mmol) and TPCBD (0.18 g, 0.46 mmol) were
dissolved in dry xylenes (3.6 mL). The mixture was heated under microwave irradiation at 250 °C
for 1 h. After solvent removal and purification by column chromatography (silica gel,
hexanes/CH2Cl2 5:1), 4.15d (0.25 g, 93%) was isolated as a colorless solid. Rf = 0.2
(hexanes/CH2Cl2 5:1). Mp = 235 °C. IR (ATR) 3078 (vw), 3058 (vw) , 3026 (vw), 2959 (m), 2898
(vw), 2158 (w), 1601 (vw), 1497 (vw), 1443 (w), 1404 (m), 1288 (w), 1249 (s), 1072 (w), 1027 (m)
96
Chapter 5: Experimental section
cm–1. UV-vis (CH2Cl2) λmax (ε) 294 (17000), 259 (42100). 1H NMR (300 MHz, CDCl3) δ 7.09–6.82
(m, 10H), 6.81–6.69 (m, 10H), 0.01 (s, 18H). 13C NMR (75.5 MHz, CDCl3) δ 144.0, 141.1, 139.7,
139.3, 131.0, 130.4, 127.0, 126.7, 126.3, 125.7, 125.0, 103.0, 102.8, 0.4. ESI HRMS m/z calcd for
C40H38Si2Na ([M + Na]+): 597.2404; found: 597.2423.
OMe
SiMe3
4.15e
Compound 4.15e. Microwave at 250 °C: Triyne 4.7 (30 mg, 0.12 mmol) and TPCBD (46 mg,
0.12 mmol) were dissolved in dry o-dichlorobenzene (3 mL). The mixture was heated under
microwave irradiation at 250 °C for 1 h. After solvent removal and purification by column
chromatography (silica gel, hexanes/CH2Cl2 8:3), 4.15e (52 mg, 72%) was isolated as a light
orange solid. Rf = 0.41 (hexanes/CH2Cl2 8:3). Mp = 168 °C. IR (ATR) 3054 (vw), 3026 (vw) , 2954
(vw), 1603 (m), 1508 (m), 1441 (w), 1288 (w), 1245 (m), 1165 (w), 1027 (m) cm–1. UV-vis
(CH2Cl2) λmax (ε) 340 (19200), 322 (23600), 277 (38300), 230 (25800). 1H NMR (300 MHz, CDCl3)
δ 7.19–7.08 (m, 12H), 6.84–6.74 (m, 12H), 3.75 (s, 3H), 0.05 (s, 9H). 13C NMR (75.5 MHz, CDCl3)
δ 159.5, 144.1, 142.9, 141.1, 140.5, 140.0, 139.8, 139.4, 132.9, 131.1, 131.0, 130.7, 130.5, 127.1,
127.0, 126.7, 126.4, 126.3, 125.6, 125.5, 124.5, 115.8, 113.7, 103.5, 102.5, 97.3, 87.5, 55.2, 0.3
(one signal coincident or not observed). LDI TOF m/z 608 (M+, 100). ESI HRMS m/z calcd for
C44H37OSi ([M + H]+): 609.2608; found: 609.2625.
97
Chapter 5: Experimental section
Bu
Bu
4.15f
Compound 4.15f. Microwave at 250 °C. Triyne 4.13a (3.1 mg, 0.093 mmol) and TPCBD (3.6 mg,
0.093 mmol) were dissolved in dry o-dichlorobenzene (1 mL). The mixture was heated under
microwave irradiation at 250 °C for 1 h. After solvent removal and purification by column
chromatography (silica gel, hexanes/CH2Cl2 4:1) 4.15f (3.7 mg, 57%) was obtained as a light
orange solid. Rf = 0.48 (hexanes/CH2Cl2 4:1). Mp = 174 °C. IR (ATR) 3059 (w), 3026 (w), 2954
(w), 2925 (m), 2855 (m), 1601 (w), 1510 (m), 1459 (m), 1405 (m), 1071 (m), 1022 (m) cm–1. UVvis (CH2Cl2) λmax (ε) 352 (16400), 330 (26600), 300 (62700), 277 (32500). 1H NMR (300 MHz,
CDCl3) δ 7.21–7.00 (m, 18H), 6.86–6.76 (m, 10H), 2.54 (t, J = 7.6 Hz, 4H), 1.58−1.49 (m, 4H);
1.36−1.34 (m, 4H), 1.29 (t, J = 7 Hz, 6H).
C NMR (75.5 MHz, CDCl3) δ 143.3, 143.2, 140.8,
13
140.0, 139.5, 131.3, 131.1, 130.71, 127.1, 126.7, 126.4, 125.6, 125.1, 120.8, 97.3, 88.30, 35.6, 33.3,
22.2, 13.9 (one signal coincident or not observed). APPI HRMS m/z calcd for C54H46 (M +):
694.3594; found: 694.3606.
98
Chapter 5: Experimental section
H
4.20a
Compound 4.20a. Compound 4.15a (96 mg, 0.15 mmol) in THF (10 mL) was cooled to 0 °C and
TBAF (1 M. 0.16 g, 0.60 mmol, 0.60 mL) was added. The mixture was allowed to reach rt and was
stirred for 3 h, diluted with Et2O (10 mL), washed with sat. aq. NH4Cl (2 x 10 mL), sat. aq. NaCl
(10 mL), H2O (10 mL), dried (MgSO4), filtered, and concentrated under vacuum. The resulting
solid was purified by passing through a short column (silica gel, hexanes/CH2Cl2 1:1) to afford
4.20a (56 mg, 72%) as a colorless solid. Rf = 0.5 (hexanes/CH2Cl2 1:1). Mp = 201 °C (decomp). IR
(ATR) 3288 (m), 3024 (m), 2920 (m), 2851 (m), 2141 (w), 1441 (m), 1441 (m) cm–1. 1H NMR (300
MHz, CDCl3) δ 7.24–7.02 (m, 10H), 6.88–6.79 (m, 15H), 3.28 (s, 1H).
13
C NMR (75.5 MHz,
CDCl3) δ 145.0, 143.5, 141.6, 141.2, 139.8, 139.5, 139.2, 131.5, 131.0, 131.0, 130.6, 130.4, 128.2,
128.1, 127.20, 127.15, 126.7, 126.64, 126.57, 126.1, 125.74, 125.70, 123.4, 97.2, 88.5, 84.7, 81.9 (3
signals coincident). LDI TOF m/z 506 (M+, 100).
99
Chapter 5: Experimental section
H
Sii-Pr3
4.20b
Compound 4.20b. Compound 4.15b (0.14 g, 0.21 mmol) and KOH (33 mg, 0.63 mmol) were
dissolved in THF (2 mL) and MeOH (1 mL). The mixture was stirred at rt for 5 h. Satd. aq. NH4Cl
(3 mL) and CH2Cl2 (3 mL) were added, the organic layer separated, washed with satd. aq. NH4Cl (3
mL), satd. aq. NaCl (3 mL), H2O (3 mL), dried (MgSO4), filtered, and the solvent removed in
vacuum. Purification by column chromatography (silica gel, hexanes/CH2Cl2 4:1) afforded 4.20b
(0.11 g, 93%) as a colorless solid. Rf = 0.52 (hexanes/CH2Cl2 4:1). Mp = 172 °C. IR (CDCl3 cast):
3302 (m), 3081 (vw), 3056 (vw), 3025 (vw), 2941 (m), 2889 (w), 2862 (m), 2156 (w), 1601 (w),
1462 (m), 1442 (m), 1403 (m) 1246 (w) cm–1. 1H NMR (300 MHz, CDCl3) δ 7.16–7.07 (m, 10H),
6.84–6.73 (m, 6H), 6.72–6.69 (m, 4H), 3.11 (s, 1H), 0.93 (s, 21H). 13C NMR (75.5 MHz, CDCl3) δ
144.0, 143.9, 141.6, 141.1, 139.7, 139.6, 139.2, 131.1, 130.94, 130.89, 130.6, 130.4,127.3, 127.23,
127.17, 126.70, 126.68, 126.60, 126.5, 126.2, 125.7, 124.3, 104.4, 99.7, 84.8, 82.0, 18.5, 11.1 (two
signals are coincident). LDI TOF m/z 609 ([M + Na]+ 30).
100
Chapter 5: Experimental section
H
H
4.20c
Compound 4.20c. Compound 4.15d (0.11 g, 0.17 mmol) in THF (10 mL) was cooled to 0 °C and
TBAF (1 M, 30 mg, 0.43 mmol, 0.43 mL) was added. The mixture was allowed to reach rt and was
stirred for 3 h, diluted with Et2O (10 mL), washed with sat. aq. NH4Cl (2 x 10 mL), sat. aq. NaCl
(10 mL), H2O (10 mL), dried (MgSO4), filtered, and concentrated under vacuum. The resulting
solid was purified by passing through a short column (silica gel, hexanes/ CH2Cl2 2:1) to afford
4.20c (66 mg, 88%,) as a colorless solid. Rf = 0.54 (hexanes/CH2Cl2 2:1). Mp = 197 °C. IR (CDCl3
cast): 3289 (m), 3081 (vw), 3056 (w), 3024 (w), 2923 (w), 2852 (w), 2244 (w), 1602 (w), 1496 (m),
1443 (m), 1072 (m), 1026 (m) cm–1. UV-vis (CH2Cl2) λmax (ε) 278 (18400), 252 (37500). 1H NMR
(300 MHz, CDCl3) δ 7.14–7,12 (m, 10H), 6.85−6.81 (m, 4H), 6.72–6.69 (m, 4H), 3.20 (s, 2H). 13C
NMR (75.5 MHz, CDCl3) δ 144.1, 141.7, 139.9, 139.0, 130.9, 130.3, 127.2, 126.8, 126.7, 125.8,
124.6, 84.8, 81.6. APPI HRMS m/z calcd for C34H22 (M+): 430.1716; found: 430.1719.
Single crystals suitable for X-ray crystallographic analysis were crystallized from CDCl3. C34H22,
Fw = 430.52; crystal dimension 0.18 x 0.14 x 0.06 mm3; trigonal system; space group P32, a =
11.8722(3) Å, b = 11.8722(3) Å, c = 14.6199(5) Å, V = 1784.57(8) Å3, Z = 3, ρcalcd = 1.202 mg
mm–3; µ(CuKα) = 0.516 mm–1; T = 173.05(10) K; 2θ max = 140.92°; total data collected = 7175;
R1 = 0.0520 [3876 independent reflections with [I≥ 2σ(I)]; wR2 = 0.1344 for 4392 data, 308
variables, and 1 restraint, largest difference, peak and hole = 0.17 and –0.18 e Å–3.
101
Chapter 5: Experimental section
OMe
H
4.20e
Compound 4.20e. A mixture of compound 4.15e (83 mg, 0.14 mmol) and KOH (30 mg, 0.41
mmol) in THF (3.1 mL) and MeOH (1.5 mL) was stirred at rt for 2 h. The mixture was diluted with
CH2Cl2, washed with sat. aq. NH4Cl (2 x 4 mL), sat. aq. NaCl (4 mL), H2O (4 mL), dried (MgSO4),
filtered, and concentrated under vacuo. The resulting solid was purified by passing through a short
column (silica gel, hexanes/ CH2Cl2 2:1) to afford 4.20e (75 mg, 100%,) as a light yellow solid. Rf =
0.5 (hexanes/CH2Cl2 2:1). Mp = 204 °C. IR (ATR) 3284 (w), 3024 (vw), 2928 (vw), 2208 (w),
1602 (m), 1507 (m), 1440 (m). 1H NMR (300 MHz, CDCl3) δ 7.19–7.06 (m, 12H), 6.84–6.73 (m,
12H), 3.75 (s, 3H), 3.23 (s, 1H). 13C NMR (75.5 MHz, CDCl3) δ 159.6, 143.9, 143.1, 142.9, 141.5,
141.1, 140.7, 140.0, 139.6, 139.3, 133.0, 131.1, 131.0, 130.7, 130.4, 127.2, 127.1, 126.7, 126.6,
126.5, 125.72, 125.67, 123.3, 115.6, 113.8, 97.5, 87.4, 84.5, 82.0, 55.2. APPI HRMS m/z calcd for
C41H28O (M+): 536.2135; found: 536.2146.
102
Chapter 5: Experimental section
4.21a
Compound 4.21a. Homocoupling reaction under Hay condition. CuCl (17 mg, 0.17 mmol) and
TMEDA (50 μL, 39 mg, 0.33 mmol) in CH2Cl2 (1.3 mL) were kept in the ultrasonic bath for 20
min. Then, 4.20a (34 mg, 0.067 mmol) was added. CH2Cl2 was evaporated and replaced by toluene
(1.3 mL) and the mixture was heated at 100 °C for 2 h. The reaction mixture was washed with sat.
aq. NH4Cl (2 x 2 mL), NaCl (2 mL), dried (MgSO4), and filtered. After solvent removal and
purification by column chromatography (silica gel, hexanes/ CH2Cl2 1:1), 4.21a was obtained (11
mg, 32%) as a yellow solid.
Pd homocoupling reaction. To a mixture of [PdCl2(PPh3)2] (1.1 mg, 0.0016 mmol), CuI (0.34 mg,
0.066 mmol), and dry i-Pr2NH (15 μL) was added 4.20a (24 mg, 0.45 mmol) in dry THF (0.57
mL). Ethyl bromoacetate (5.1 μL, 0.46 mmol) was added, and the mixture was stirred at rt under N2
atmosphere for 24 h. H2O (2 mL) was added, and the resulting mixture extracted with CH2Cl2 (2
mL). The organic layer was washed with sat. aq. NaCl (2 x 2 mL), dried (MgSO4), and filtered. The
resulting solution was concentrated under vacuum. After purification by column chromatography
(silica gel, hexanes/CH2Cl2 1:1), 4.21a was obtained (15 mg, 66%,) as a yellow solid. Rf = 0.5
(hexanes/CH2Cl2 1:1). Mp = 324 °C. IR (ATR) 3053 (w), 3024 (vw), 2961 (w), 2921 (w), 1489 (m)
cm–1. UV-vis (CH2Cl2) λmax (ε) 386 (5600), 356 (10600), 290 (33600), 226 (27400). 1H NMR (300
MHz, CDCl3) δ 7.23–7.06 (m, 30H), 7.05–6.7 (m, 20H).
13
C NMR (75.5 MHz, CDCl3) δ 144.5,
143.5, 142.0, 141.2, 139.8, 139.4, 139.3, 139.2, 131.9, 131.3, 131.2, 130.8, 130.6, 129.5, 128.6,
128.3, 128.2, 127.43, 127.37, 127.0, 126.8, 126.01, 125.97, 125.8, 124.2, 123.3, 98.1, 88.3, 81.7,
81.6. LDI TOF m/z 1010 (M+, 65).
103
Chapter 5: Experimental section
Sii-Pr3
i-Pr3Si
4.21b
Compound 4.21b. Homocoupling reaction under Hay condition. CuCl (17 mg, 0.17 mmol) and
TMEDA (5.1 μL, 40 mg, 0.35 mmol) in CH2Cl2 (1.8 mL), were kept in the ultrasonic bath for 20
min. Then, 4.20b (41 mg, 0.069 mmol) was added. CH2Cl2 was evaporated and replaced by toluene
(1.8 mL) and the mixture was heated at 100 °C for 2 h. The reaction mixture was cooled and
washed with sat. aq. NH4Cl (2 x 2 mL), NaCl (2 mL), dried (MgSO4), and filtered. After solvent
removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 4:1) 4.21b (9.2
mg, 23%) was obtained as a yellow solid.
Pd homocoupling reaction. To a mixture of [PdCl2(PPh3)2] (2.9 mg, 0.0041 mmol), CuI (11 mg,
0.0046 mmol), and dry i-Pr2NH (36 μL) was added 4.20b (66 mg, 0.11 mmol) in dry THF (1.4
mL). Ethyl bromoacetate (14 μL, 0.12 mmol) was added, and the mixture was stirred at rt under N2
atmosphere for 24 h. H2O (2 mL) was added, and the resulting mixture was extracted with CH2Cl2
(2 mL). The organic layer was washed with sat. aq. NaCl (2 x 2 mL), dried (MgSO4), and filtered.
The resulting solution was concentrated under vacuum. After purification by column
chromatography (silica gel, hexanes/CH2Cl2 4:1), 4.21b (34 mg, 52%) was obtained as a yellow
solid. Rf = 0.33 (hexanes/CH2Cl2 4:1). Mp = 178 °C. IR (ATR) 3082 (vw), 3056 (vw), 3025 (vw),
2940 (m), 2924 (vw), 2862 (m), 2154 (w), 1601 (m), 1498(m), 1461 (m), 1443 (m), 1388 (m). UVvis (CH2Cl2) λmax (ε) 367 (5200), 344 (14900), 322 (30500), 307 (38300), 270 (87000), 229
(40900). 1H NMR (300 MHz, CDCl3) δ 7.13–7.02 (m, 20H), 6.83–6.79 (m, 12H), 6.71–6.65 (m,
8H), 0.92−0.89 (m, 42H). 13C NMR (75.5 MHz, CDCl3) δ 144.4, 144.0, 141.6, 141.0, 140.4, 139.6,
139.3, 139.2, 139.0, 138.3, 131.0, 130.9, 130.42, 130.37, 127.2, 127.1, 126.69, 126.65, 126.4,
104
Chapter 5: Experimental section
126.3, 125.6, 124.5, 104.1, 100.1, 81.7, 81.2, 18.6, 11.1. ESI HRMS m/z calcd for C86H82Si2Na ([M
+ Na]+): 1193.5847; found: 1193.5829.
OMe
MeO
4.21e
Compound 4.21e. Homocoupling reaction under Hay condition. CuCl (13 mg, 0.13 mmol) and
TMEDA (37 μL, 29 mg, 0.25 mmol) in CH2Cl2 (1.9 mL) were kept in the ultrasonic bath for 20
min. Then, 4.20e (27 mg, 0.050 mmol) was added. CH2Cl2 was evaporated and replaced by toluene
(1.9 mL) and the mixture was heated at 100 °C for 2 h. The reaction mixture was washed with sat.
aq. NH4Cl (2 x 2 mL), NaCl (2 mL), dried (MgSO4), and filtered. After solvent removal and
purification by column chromatography (silica gel, hexanes/ CH2Cl2 1:1), 4.21e (12 mg, 45%) was
obtained as a yellow solid.
Pd homocoupling reaction. To a mixture of [PdCl2(PPh3)2] (4.1 mg, 0.0058 mmol), CuI (1.2 mg,
0.064 mmol), and dry i-Pr2NH (0.053 mL) was added 4.20e (85 mg, 0.16 mmol) in dry THF (2.1
mL). Ethyl bromoacetate (17 μL, 0.16 mmol) was added, and the mixture was stirred at rt under N2
atmosphere for 24 h. H2O (3 mL) was added, and the resulting mixture extracted with CH2Cl2 (3
mL). The organic layer was washed with sat. aq. NaCl (2 x 2 mL), dried (MgSO4), and filtered. The
resulting solution was concentrated under vacuum. After purification by column chromatography
(silica gel, hexanes/CH2Cl2 1:1), 4.21e (70 mg, 82%) was obtained as a yellow solid. Rf = 0.75
(hexane/CH2Cl2 1:1). Mp = 329 °C (decomp). IR (ATR) 3055 (vw), 3025 (vw), 2956 (vw), 2924
(vw), 2849 (vw), 2833 (vw), 2209 (w), 1604 (m), 1509 (m), 1441 (w), 1398 (w), 1292 (m), 1249
105
Chapter 5: Experimental section
(m), 1167 (w), 1071 (w), 1027 (m) cm–1. UV-vis (CH2Cl2) λmax (ε) 394 (3400), 358 (15700), 316
(37900), 294 (41800), 227 (37100). 1H NMR (300 MHz, CDCl3) δ 7.15–6.98 (m, 24H), 6.95–6.57
(m, 24H), 3.66 (s, 6H).
C NMR (75.5 MHz, CDCl3) δ 159.5, 144.7, 144.2, 142.9, 141.7, 140.6,
13
139.8, 139.3, 139.1, 138.0, 133.2, 131.1, 131.0 130.7, 130.4, 129.9, 128.0, 127.2, 127.1, 126.5,
125.73, 125.69, 124.3 123.6, 115.3, 113.7, 98.2, 87.1, 81.7, 81.4, 55.1. APPI HRMS m/z calcd for
C82H54O2 (M+): 1070.4118; found: 1070.4121.
5.4
References
1.
O. Robles, F. E. McDonald, Org. Lett. 2008, 10, 1811−1814.
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H. Lütjens, S. Nowotny, P. Knochel, Tetrahedron: Asymmetry, 1995, 6, 2675−2678.
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A. M. Boldi, J. Anthony, C. B. Knobler, F. Diederich, Angew. Chem. Int. Ed. 1992, 31,
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Chapter 5: Experimental section
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I. Van Overmeire, S. A. Boldin, K. Venkataraman, R. Zisling, S. D. Jonghe, S. Van
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107
6: Appendix
Figure 6.1. 1H NMR spectrum of 4.10a.
Figure 6.2. 13C NMR spectrum of 4.10a.
108
6: Appendix
Figure 6.3. 1H NMR spectrum of 4.11a.
Figure 6.4. 13C NMR spectrum of 4.11a.
109
6: Appendix
Figure 6.5. 1H NMR spectrum of 4.12a.
Figure 6.6. 13C NMR spectrum of 4.12a.
110
6: Appendix
Figure 6.7. 1H NMR spectrum of 4.13a.
Figure 6.8. 13C NMR spectrum of 4.13a.
111
6: Appendix
Figure 6.9. 1H NMR spectrum of 4.15a.
Figure 6.10. 13C NMR spectrum of 4.15a.
112
6: Appendix
Figure 6.11. 1H NMR spectrum of 4.15b.
Figure 6.12. 13C NMR spectrum of 4.15b.
113
6: Appendix
Figure 6.13. 1H NMR spectrum of 4.15c.
Figure 6.14. 13C NMR spectrum of 4.15c.
114
6: Appendix
Figure 6.15. 1H NMR spectrum of 4.15d
Figure 6.16. 13C NMR spectrum of 4.15d.
115
6: Appendix
Figure 6.17. 1H NMR spectrum of 4.15e.
Figure 6.18. 13C NMR spectrum of 4.15e.
116
6: Appendix
Figure 6.19. 1H NMR spectrum of 4.15f.
Figure 6.20. 13C NMR spectrum of 4.15f.
117
6: Appendix
Figure 6.21. 1H NMR spectrum of 4.20a.
Figure 6.22. 13C NMR spectrum of 4.20a.
118
6: Appendix
Figure 6.23. 1H NMR spectrum of 4.20b.
Figure 6.24. 13C NMR spectrum of 4.20b.
119
6: Appendix
Figure 6.25. 1H NMR spectrum of 4.20c.
Figure 6.26. 13C NMR spectrum of 4.20c.
120
6: Appendix
Figure 6.27. 1H NMR spectrum of 4.20e.
Figure 6.28. 13C NMR spectrum of 4.20e.
121
6: Appendix
Figure 6.29. 1H NMR spectrum of 4.21a.
Figure 6.30. 13C NMR spectrum of 4.21a.
122
6: Appendix
Figure 6.31. 1H NMR spectrum of 4.21b.
Figure 6.32. 13C NMR spectrum of 4.21b.
123
6: Appendix
Figure 6.33. 1H NMR spectrum of 4.21e.
Figure 6.34. 13C NMR spectrum of 4.21e.
124
6: Appendix
125