A highly stereoselective synthesis of new styryl-π-conjugate organosilicon compounds

Article abstract of DOI:10.1016/j.tetlet.2014.03.119

This work describes very precise and controlled catalytic transformations as useful tools for the synthesis of new trans-π-conjugated molecular and macromolecular organosilicon compounds. Several distyryl-arenes were obtained efficiently via silylative coupling in high yields and with excellent selectivity for new E,E-bis(silyl)arenes.

Full text of DOI:10.1016/j.tetlet.2014.03.119

Tetrahedron Letters 55 (2014) 3055–3058
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A highly stereoselective synthesis of new styryl-
organosilicon compounds
p
-conjugate
a
a
a
b,
Mariusz Majchrzak a, , Milena Hybsz , Sylwia Kostera , Maciej Kubicki , Bogdan Marciniec
⇑
⇑
a Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznan, Poland
b Center of Advanced Technology, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
This work describes very precise and controlled catalytic transformations as useful tools for the synthesis
of new trans- -conjugated molecular and macromolecular organosilicon compounds. Several distyryl-
arenes were obtained efficiently via silylative coupling in high yields and with excellent selectivity for
Received 1 December 2013
Revised 13 March 2014
Accepted 27 March 2014
Available online 5 April 2014
p
new E,E-bis(silyl)arenes.
Ó 2014 Published by Elsevier Ltd.
Keywords:
Catalysis
Silylative coupling
Suzuki–Miyaura coupling
p-Conjugated compounds
Organosilicon compounds
The search for new, highly selective methods to synthesize lin-
ear and branched organosilicon compounds has generated signifi-
cant interest. Both molecular and macromolecular compounds
containing silylene–arylene fragments are synthesized via Würtz
polycondensation (using Grignard reagents)1,2 or by reactions cat-
alysed by transition metals, for instance: Sonogashira,1c Suzuki3 or
Heck.4
We have described the synthesis of polymers and copolymers
containing arylene–silylene–vinylene and arylene–silylene–vinyl-
ene–phenylene–vinylene units with divinylbenzene, respectively,
with well-defined structures.8–11
In this Letter, we present a highly efficient, stereoselective
method for the preparation of new
p-conjugated distyryl-arylene
silicon derivatives through silylative coupling catalysed by a
Silylative coupling (SC) has been developed in our group over
the last two decades. It is the reaction of olefins with vinyl-substi-
tuted organosilicon compounds, taking place in the presence of
complexes containing initially, or generating in situ, metal–hydro-
gen [M–H] and metal–silicon [M–Si] bonds.5 The process occurs via
cleavage of the @CASi bond in the vinylsilane and the CAH bond in
the olefin, and is catalysed by transition metal complexes [TM–H]
or silyl [TM–Si] ligands (silicometallics) (where TM = Ru, Rh, Ir,
Co).6,7
Silylative coupling appears to be a unique, effective and highly
regio- and stereoselective method for the functionalization of
molecular and macromolecular compounds that have one or a
few vinyl groups connected to the silicon atom. Without any doubt,
this reaction is a powerful and convenient tool for the synthesis of
well-defined ruthenium(II) complex.
The starting dienes were prepared in a highly efficient Suzuki–
Miyaura coupling reaction catalysed by the very active palladium
complex [Pd(g
2-dba)(PCy3)2] 1, as shown in Scheme 1.
Typically, the crude mixture was extracted with CH2Cl2/water
and a small amount of sodium chloride to disperse the slurry.
The mixture was then left over sodium sulfate for six hours.12 In
the next step, we used the obtained olefin for the silylative cou-
pling reaction. The catalytic process between distyrylarene and
trimethylvinylsilane was conducted following the original proce-
dure: [RuH(CO)Cl(PCy3)2]13 (catalyst 2), toluene, sealed ampoule,
argon atmosphere.
In order to optimize the reaction conditions with respect to
activity, selectivity, catalyst loading, time and temperature, the
model reaction between 4,4-divinyl-p-biphenyl and vinyltrimeth-
ylsilane (after redistillation) at different molar ratios (from 1:2 to
1:5), was studied (Scheme 2).14
unsaturated, highly p-conjugated compounds.
Since the reactive substrate contains a styryl group, the reaction
conditions were optimized to eliminate possible uncontrolled,
⇑
Corresponding authors. Tel.: +48 61 8291407; fax: +48 61 8291508.
E-mail addresses: mariusz.majchrzak@amu.edu.pl (M. Majchrzak), marcinb@
amu.edu.pl (B. Marciniec).
http://dx.doi.org/10.1016/j.tetlet.2014.03.119
0040-4039/Ó 2014 Published by Elsevier Ltd.

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M. Majchrzak et al. / Tetrahedron Letters 55 (2014) 3055–3058
Table 1
Br
[Pd] (0.5 mol%)
Optimization of the silylative coupling reaction conditionsa
OH
[Ar]
+
:
B
toluene, EtOH / Ar,
K2CO3 (2M solution)
80-85 oC, 6-9 h,
Entry Catalyst amountb (mol %) Temperature (°C) Time (h) Yieldc (%)
R
OH
76-99%
1
2
70
8
83
1 or 2.02
1
12
8
8
96
>99
65
90
70
Pd = Pd(dba)(PCy3)2; R = H2C=CH- or Br
Ar = 0, arene
2
1
12
8
12
8
24
8
24
8
74
95
>99
34, 4d
61, 10d
74
90
70
90
70
90
Scheme 1. Synthesis of distyrylarenes via Suzuki–Miyaura coupling.
3
4
0.5
radical polymerization. All the catalytic details are presented in
Table 1.
95
0.25
24, 8d
45, 14d
49
The search for the optimum combination of reaction conditions
established that the best conditions were an elevated temperature
(around 90 °C) with 2 or 1 mol % of catalyst 2 in a closed flask (the
ethylene elimination stage is irreversible7). The use of a higher
amount of ruthenium catalyst 2 reduced the reaction time to 8 h.
The use of the catalyst in a lower amount (0.25 mol %) gave a lower
yield of the desired product (yield 45% at 70 °C and 79% at 90 °C
after 24 h). We also used 2 mol % of catalyst 2 at 70 °C achieving
a very good yield of the order of 96% (GC–MS analysis) in a short
time (12 h).
The E-silyl by-product was identified on the basis of mass spec-
trometry. The reaction was carried out in the presence of 0.25 and
0.5 mol % of 2 in the ratio 1:2. Probably, a small amount of vinyltri-
methylsilane evaporated during the test. Therefore, we have iden-
tified mainly by-product and 23% of the desired product. These
reaction parameters have a significant impact on the total control
of the process.
The optimized conditions for the model reaction allowed us to
use the most effective catalytic system for selectively controlled
synthesis of a range of new bis(silyl)substituted distyrylarenes,
(Scheme 3).15
The silylative coupling of 1,4-di(styryl)benzene with vinyltri-
methylsilane (2.5 equiv) was accomplished following the well-
defined procedure: ruthenium catalyst [RuH(CO)Cl(PCy3)2] (2)
(1 mol % per olefin molecule), toluene, 90–95 °C for 10 h (up to
100% conversion of divinylarylene derivative), ‘Schlenk closed
24
8
24
79, 9d
a
b
c
[olefin]/[ViSi] = 1:2.5; closed system under Ar.
Per olefin molecule.
Determined by GC and GC–MS methods.
E-silyl by-product was observed.
d
system’ to give selectively one isomer of the E,E-bis[(dimethylsi-
lyl)vinylene]arenes in very good isolated yields 87–98%, except
for the thiophene derivative (55%). The 1H NMR spectrum of 4,4-
bis[(E)-2-(trimethylsilyl)vinyl]-p-terphenyl (4) (Fig. 1) testifies to
the formation of a clean, new organosilicon compound which
was isolated using simple and convenient flash filtration (glass fil-
ter/silica gel/Celite).
Signals A and B and their coupling constants (19.2 Hz) result
from typical E-isomer vinylene–silylene fragments between silicon
and the aromatic part. In addition, the X-ray crystallographic struc-
ture of new compound 8 was determined.16 As far as we are aware,
this is the first example of the crystallographic characterization of
this type of compound (Fig. 2).
The molecule of 8 is Ci-symmetrical, as it occupies a special
position in the space group P-1; the middle point of the central
phenyl ring lies in the inversion centre. As a consequence, the
two symmetry-related phenyl rings (C4–C9 and its counterpart)
Me Me
Si
[RuH] (0.25-1 mol%)
SiMe3
+
:
Me
Me
Me
toluene,Ar,
Si
Me
70-95 oC, 6-24 h,
1
2-5
3
- 2 H2C=CH2
E,E- >99%, GC–MS yield 99%
RuH = RuH(CO)Cl(PCy )2
3
+
Me Me
Si
Me
E-silyl by-product
Scheme 2. Stereocontrolled silylative coupling of 4,4-divinyl-p-biphenyl with vinyltrimethylsilane for the synthesis of novel compound 3.
Me
Si
Me
Me
[RuH] 1 (mol%)
SiMe3
2.5
[Ar]
+
Me
Si Me
Me
[Ar]
toluene, Ar,
90-95 oC, 10 h,
3-8
1
:
- 2 H2C=CH2
E,E- >99% (1H NMR)
yield up to 99% (GC–MS)
RuH = RuH(CO)Cl(PCy )2
3
F
F
98%
8
F
F
Ar = 0 or
S
93%
3
89%
4
92%
5
87%
6
55%
7
Scheme 3. Synthesis of new bis(trimethylsilyl)arenes.

M. Majchrzak et al. / Tetrahedron Letters 55 (2014) 3055–3058
3057
Figure 1. 1H NMR spectrum of 4 in CDCl3 at 25 °C.
Analysis of the proton spectrum confirmed the formation of an
oligomer made up of only trans-vinylene fragments in mers
‘–AB–AB–AB–AB–’ (coupling constants for the protons of the
AMe2SiAHC@CH-C< unit, JHH = 19.2 Hz and 18.6 Hz). Standard
analysis using high pressure gel permeation chromatography
(GPC) allowed the determination of the basic mass parameters
such as the numerical average molecular weight (Mn), average
molecular weight (Mw) and polydispersity (PDI) (Mw/Mn), which
due to the heterogeneous nature (‘ragged’) of the GPC curve
appeared in the following ranges: Mn = 1475–5952, Mw = 1491–
8702 for PDI = 1.03–1.46.
Figure 2. A perspective view of 8 together with the labelling scheme. The ellipsoids
are drawn at the 50% probability level, hydrogen atoms are shown as spheres with
arbitrary radii. The unlabelled part of the molecule is related with the labelled
section by the symmetry operation: Àx, Ày, Àz.
In conclusion, this is the first Letter of a highly selective method
are exactly coplanar, and form a dihedral angle of 51.63(18)° with
the plane of the central ring. The bond lengths and angles are quite
typical, the crystal structure almost exclusively being determined
by weak, largely non-specific van der Waals interactions and some
very weak CAHÁ Á ÁF contacts.
for the synthesis of new
p-conjugated, distyrylarylene molecular
organosilicon compounds 3–8. The reactions take place with high
yields and occur regio- and stereoselectively to give E,E-products.
An example synthesis of a new high trans-p-conjugated linear
copolymer 9 obtained via the silylative coupling is also disclosed.
In this way, several new
p-conjugated organosilicon com-
Further results on the use of these compounds for the synthesis
pounds 3–8 were synthesized with almost 100% selectivity (GC–
MS analysis). The above presented results on the synthesis of
molecular bis(silyl)arenes formed the basis for the synthesis of
an exemplary new arylene–vinylene–silylene copolymer 9. Due
to the low solubility of the anthracenyl derivative of the olefin,
the reaction was carried out as a 0.125 M solution instead of
0.5 M as before. In addition, the low concentration of the reagents
prevented the olefin from polymerizing. The reaction of copolycon-
densation was run according to Scheme 4.
of high-molecular weight
be reported in due course.
p-conjugated organic compounds will
Acknowledgment
We gratefully acknowledge financial support from the National
Science Centre (Poland) (Project ‘Maestro’ No. UMO-2011/0/A/ST5/
00472).
Me
Si
Me
Me
Si
Me
[RuH] (1 mol%)
+
:
toluene,Ar, 80-85 o
- n H2C=CH2
C
1
1
Me
Si
Me
Si
n
Me
Me
RuH = RuH(CO)Cl(PCy )2]
3
9
copolymer >99%, trans- >99%
Scheme 4. Copolycondensation reaction of 9,10-distyrylanthracene with 4,4-bis(dimethylvinylsilyl)biphenyl in the presence of catalyst 2.

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M. Majchrzak et al. / Tetrahedron Letters 55 (2014) 3055–3058
14. General procedure for the catalytic test of the silylative coupling: A 10 mL Schlenk
Supplementary data
system was charged under argon with distyrylarene (0.1 g, 4.85 Â 10À4 mol),
toluene (1.95 mL, 0.2 5 M solution of diene), vinyltrimethylsilane (an amount
depending on the [ViSi]/[olefin] ratio, 1:2, 1:2.5, 1:3, 1:4 and 1:5) and
[RuH(CO)Cl(PCy3)2] (2) (2, 1, 0.5 0.25 mol %, see details under Table 1). All
components were added under argon. The final mixture was heated to 70–
90 °C in an oil bath for 8–24 h. The reaction progress was monitored by TLC
(eluent/CH2Cl2/n-hexane: 1:3). Conversion of the substrate and reaction
selectivity were monitored by GC–MS chromatography. The final yields were
calculated on the basis of the 1H NMR spectra.
Supplementary data (general synthetic procedure for polycon-
densation; characterization of 3–9, analytical details: 1H NMR,
13C NMR, 29Si NMR, 19F NMR, MS, HRMS) associated with this arti-
cle can be found, in the online version, at http://dx.doi.org/
10.1016/j.tetlet.2014.03.119.
15. General procedure for the silylative cross-coupling:
A mixture consisting of
References and notes
distyrylarylene derivative (0.48 mmol), dry toluene (0.25–0.125 M, depending
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atmosphere in a 10 mL Schlenk glass reactor (closed system) equipped with
a stir bar and heated at 80–85°C for 20 h to complete the reaction (GC–MS
analysis). Then, after cooling to room temperature, the volume was reduced
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(eluent/CH2Cl2 in n-hexane = 0–20%, Rf = 0.24–0.46) to afford the analytically
pure products.
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= 107.150(5)°, b = 94.885(5)°,
= 103.533(5)°, V = 675.73(7) Å3, Z = 1,
dx = 1.23 g cmÀ3
CuK (k = 1.54178 Å), 5935 reflections measured, 2691
C28H30F4Si2;
´
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a
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D
q
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.
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