An efficient synthesis of functional stilbenes in Hiyama coupling reaction catalysed by H-spirophosphorane palladium complex

Article abstract of DOI:10.1016/j.molcata.2011.09.025

An efficient Hiyama cross-coupling reaction of functionalised styrylsilanes with iodo- and bromobenzene has been performed using complex [PdCl ₂P(OCH₂CMe₂NH) OCH₂CMe ₂NH₂] as precatalyst. The styrylsilanes underwent cross-coupling reactions with excellent selectivity and yield, up to 99%, of the corresponding E-stilbenes. When (E)-[1-(4-bromophenyl)-2-(1,1,3,3,3- pentamethyldisiloxy)]ethene was used as a source of the silane, a homocoupling reaction took place and polymeric compound containing 0.77% of palladium in the form of Pd(0) nanoparticles was obtained. This material used as a catalyst made it possible to obtain 40% and 38% of the Hiyama cross-coupling product in two subsequent runs.

Full text of DOI:10.1016/j.molcata.2011.09.025

Journal of Molecular Catalysis A: Chemical 351 (2011) 128–135
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
An efficient synthesis of functional stilbenes in Hiyama coupling reaction
catalysed by H-spirophosphorane palladium complex
Anna Skarz˙ yn´ skaa,∗, Mariusz Majchrzakb, Anna M. Trzeciaka, Bogdan Marciniecb
a Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie Str., 50-383 Wrocław, Poland
b Department of Organometallic Chemistry, Faculty of Chemistry, 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:
Received 1 July 2011
Received in revised form
21 September 2011
Accepted 25 September 2011
Available online 1 October 2011
An efficient Hiyama cross-coupling reaction of functionalised styrylsilanes with iodo- and bromoben-
zene has been performed using complex [PdCl2P(OCH2CMe2NH) OCH2CMe2NH2] as precatalyst. The
styrylsilanes underwent cross-coupling reactions with excellent selectivity and yield, up to 99%, of
the corresponding E-stilbenes. When (E)-[1-(4-bromophenyl)-2-(1,1,3,3,3-pentamethyldisiloxy)]ethene
was used as a source of the silane, a homocoupling reaction took place and polymeric compound contain-
ing 0.77% of palladium in the form of Pd(0) nanoparticles was obtained. This material used as a catalyst
made it possible to obtain 40% and 38% of the Hiyama cross-coupling product in two subsequent runs.
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Cross-coupling
Hiyama coupling
Palladium catalyst
Stilbenes
Vinylsiloxanes
1. Introduction
synthesis of substituted E-stilbenes via Heck cross-coupling reac-
tion [14]. In order to compare both procedures, namely Heck
Stilbenes (1,2-diphenylethylenes) and their hydroxylated stil-
benoid derivatives, with ␲-electron conjugated systems, constitute
a class of compounds that have found an application in differ-
ent areas: chemistry, biology and physics [1]. Stilbene moieties
are recognised to exhibit anticancer, antibacterial, and fungistatic
activities [2–4]. Due to the extended ␲-system, they have found
an application in the manufacture of optoelectric and electronic
devices: dye lasers, solar cells, fluorescent sensors, light-emitting
diodes, scintillators, and others [5,6]. Some bioactive stilbene
derivatives (Resveratrol, Combretastatin A-4) might be naturally
obtainable through extraction from plant species; some need to be
synthetically obtained. Among several synthetic routes providing
substituted stilbenes, one must consider palladium-catalysed Heck
reaction of aryl halide (or triflate) with styrene [7]. The Hiyama cou-
pling presents an encouraging alternative route for the synthesis
of E-stilbenes (Scheme 1) [8], which can be considered environ-
mentally friendly taking into account the low toxicity of the silicon
derivatives used as substrates [9–13].
and Hiyama cross-coupling, we selected easily obtained complex
[PdCl2P(OCH2CMe2NH)OCH2CMe2NH2] [15] as a precatalyst. Here
we present an even more effective and stereoselective method of
synthesis of unsymmetrical E-stilbenes through the Hiyama cou-
pling (HC) of relevant styrylsilanes with iodo- and bromobenzene.
2. Experimental
2.1. Materials
1H NMR (500 or 400 MHz, 298 K), 13C NMR (126 or 100 MHz,
298 K) and 29Si NMR (75 MHz, 298 K) spectra were recorded on
a Bruker Avance 500 MHz or Varian XL 300 MHz spectrometer in
CDCl3 solution. Chemical shifts are reported as ı (in ppm) relative
to the residual solvent (CDCl3) peak for 1H, 13C and relative to TMS
for 29Si. Analytical gas chromatographic (GC) analyses for silyla-
tive coupling products were performed on a Varian Star 3400CX
with a DB-5 fused silica capillary column (30 m × 0.15 mm) and
TCD. Mass spectra of styrylsilanes were obtained by GC–MS anal-
ysis (Varian Saturn 2100T, equipped with a BD-5 capillary column
(30 m) and an ion trap detector. High-resolution mass spectroscopic
(HRMS) analyses were performed on an AMD-402 mass spectrom-
eter. Thin-layer chromatography (TLC) was done on plates coated
with 250 ␮m layer of silica gel (Aldrich and Merck), and column
chromatography was conducted with silica gel 60 (70–230 mesh,
During the course of our studies on the catalytic activity of
palladium complexes with H-spirophosphorane ligands, we have
developed a new efficient catalytic system for stereoselective
∗
Corresponding author. Tel.: +48 713757254.
E-mail address: zag@wchuwr.pl (A. Skarz˙ yn´ ska).
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.09.025

A. Skarz˙ yn´ska et al. / Journal of Molecular Catalysis A: Chemical 351 (2011) 128–135
129
[Si]
cat
cat
+
X
+
X
R
R
R
Hiyama coupling
Heck coupling
Scheme 1.
Fluka). Analytical gas chromatographic (GC) analyses for Hiyama
coupling products were performed on Hewlett Packard 5890 fitted
with a FID detector. Conversion of the substrates was calculated
using internal standard method. MS spectra were measured on an
ESI Finnigan Mat TSQ 700 instrument.
The chemicals were obtained from the following sources:
toluene, styrene, 4-methylstyrene, 4-methoxystyrene, 3-
methylstyrene, 4-chlorostyrene, 2-chlorostyrene, silica gel,
celite®, and copper (I) chloride were bought from Aldrich,
CDCl3 from Dr Glaser A.G. Basel, vinylpentamethyldisilox-
ane from Gelest. The complexes: [RuHCl(CO)(PPh3)3] and
[PdCl2P(OCH2CMe2NH)OCH2CMe2NH2] were prepared according
to the procedure described in the literature [15,16].
(E)-[1-(2-chlorophenyl)-2-(1,1,3,3,3-pentamethyldisiloxy)]ethene
(1c). bp 85–88 ◦C/0.7 mmHg, less-yellow liquid, yield 86%, purity
96.5%; 1H NMR(400 MHz, CDCl3) ı 0.17 (s, 9H, –Si(CH3)3), 0.28 (s,
6H, –Si(CH3)2–), 6.46 (d, 1H, JHH = 19.2 Hz, Si–HC CH–C6H4–Cl),
7.22 (t, 2H, –C6H4–Cl), 7.28 (d, 1H, JHH = 1.2 Hz, –C6H4–Cl), 7.39
(s, 1H, –C6H4–Cl), 7.40 (d, 1H, JHH = 19.6 Hz, Si–HC CH–C6H4–Cl),
7.64 (d, 1H, JHH = 1.2 Hz, –C6H4–Cl). 13C NMR (100 MHz, CDCl3)
ı 0.8, 2.0, 116.5, 126.7, 128.9, 129.7, 132.2, 133.3, 136.2, 139.9.
29Si NMR (79 MHz, CDCl3) ı −3.30, 8.71; HRMS (EI) m/z calcd for
C13H21ClOSi2: 284.08195; found 284.08190.
(E)-[1-(4-bromophenyl)-2-(1,1,3,3,3-
pentamethyldisiloxy)]ethene
(1d).
bp
104–108 ◦C/1 mmHg,
colourless liquid, yield 88%, purity >99%; 1H NMR (400 MHz,
CDCl3) ı 0.12 (s, 9H, –Si(CH3)3, 0.23 (s, 6H, –Si(CH3)2–), 6.41 (d,
1H, JHH = 19.5 Hz, Si–HC CH–C6H4–Br), 6.85 (d, 1H, JHH = 19.2 Hz,
Si–HC CH–C6H4–Br), 7.31 (d, 2H, JHH = 8.7 Hz, –C6H4–Br), 7.46 (d,
2H, JHH = 8.4 Hz, –C6H4–Br); 13C NMR (100 MHz, CDCl3) ı 0.9, 2.1,
121.9, 127.9, 129.7, 131.5, 137.0, 142.6; 29Si NMR (79 MHz, CDCl3)
ı −2.53, 9.29; HRMS (EI) m/z calcd for C13H21BrOSi2: 328.03143;
found 328.03138.
2.2. General procedure for synthesis of styrylsilanes
The syntheses via silylative cross-coupling were performed
under argon using [RuHCl(CO)(PPh3)2] as a catalyst. The reagents
and the solvent were distilled, dried and deoxygenated. The details
are presented below. The substrates were synthesised in a manner
similar to that reported previously [11a–b,17] with modifications
that made it possible to achieve a significant improvement in the
yield of the synthesis reaction. A toluene solution (25.4 mL, 1M)
of two reagents: vinylpentamethyldisiloxane (2.54 × 10−2 mol) and
styrene (3.05 × 10−2 mol) – ([ViSi]:[olefin] = 1:1.2) was placed in a
100 mL two-neck glass reactor with a magnetic stirring bar and
a condenser connected to a bubbler. Then, the reaction mixture
was stirred and heated to 110 ◦C under an argon flow. After 10 min,
the ruthenium complex (1 mol%) was added. The solution colour
changed from yellow to green and to yellow again. Next, more
than 5 min later, copper (I) chloride was added ([CuCl]:[Ru] = 3:1),
and substantial ethylene emission was observed. The synthesis pro-
cess was carried out for the next 8–14 h. Then, the solvent excess
was evaporated under vacuum. The crude product was separated
from the reaction mixture using ‘flash column’ system (glass filter
G3, silica gel, celite and membrane pomp) to remove residues of
ruthenium complex and copper. Finally, the pure compound was
obtained using the fraction distillation technique (yield 75–92%).
The degree of conversion was calculated by GC and GC–MS analy-
ses.
(E)-[1-(4-methylphenyl)-2-(1,1,3,3,3-
pentamethyldisiloxy)]ethene (1e). bp 98–101 ◦C/1 mmHg, colourless
liquid, yield 90%, purity 98%; 1H NMR(400 MHz, CDCl3) ı 0.16 (s,
9H, –Si(CH3)3), 0.25 (s, 6H, –Si(CH3)2–), 2.35 (s, 3H, –CH3), 6.51 (d,
1H, JHH = 19.2 Hz, Si–HC CH–C6H4–CH3), 6.94 (d, 1H, JHH = 19.2 Hz
Si–HC CH–C6H4–CH3), 7.23 (s, 2H, –C6H4–CH3), 7.25 (s, 2H,
–C6H4–CH3); 13C NMR (100 MHz, CDCl3) ı 0.8, 2.2, 21.5, 123.8,
127.2, 128.4, 128.9, 138.2, 144.2; 29Si NMR (79 MHz, CDCl3) ı
−3.07, 8.36; HRMS (EI) m/z calcd for C14H24OSi2: 264.13657;
found 264.13652.
(E)-[1-(3-methylphenyl)-2-(1,1,3,3,3-
pentamethyldisiloxy)]ethene (1f). bp 82–84 ◦C/0.7 mmHg, colourless
liquid, yield 91%, purity 98.5%; 1H NMR(400 MHz, CDCl3) ı 0.15
(s, 9H, –Si(CH3)3), 0.26 (s, 6H, –Si(CH3)2–), 2.39 (s, 3H, –CH3),
6.43 (d, 1H, JHH = 19.2 Hz, Si–HC CH–C6H4–CH3), 6.94 (d, 1H,
JHH = 19.2 Hz, Si–HC CH–C6H4–CH3), 7.11 (d, 1H, JHH = 7.2 Hz,
–C6H4–CH3), 7.24 (s, 1H, o-C6H4–CH3), 7.28 (s, 1H, –C6H4–CH3),
7.31 (s, 1H, –C6H4–CH3); 13C NMR (100 MHz, CDCl3) ı 0.8, 2.0, 22.7,
123.6, 127.2, 128.4, 128.4, 128.9, 138.0, 138.2, 144.2; 29Si NMR
(79 MHz, CDCl3) ı −3.09, 8.38; HRMS (EI) m/z calcd for C14H24OSi2:
264.13657; found 264.13654.
(E)-[1-(phenyl)-2-(1,1,3,3,3-pentamethyldisiloxane)]ethene (1a).
bp 78–81 ◦C/1 mmHg, colourless liquid, yield 92%, purity >99%;
1H NMR (400 MHz, CDCl3) ı 0.12 (s, 9H, –Si(CH3)3), 0.23 (s, 6H,
–Si(CH3)2–), 6.44 (d, 1H, JHH = 19.2 Hz, Si–CH CH–C6H5), 6.92 (d,
1H, JHH = 19.2 Hz, Si–HC CH–C6H5), 7.23–7.33 (m, 3H, 3,4-C6H5),
7.55 (d, 2H, JHH = 2.1 Hz, 2-C6H5); 13C NMR (100 MHz, CDCl3)
ı 0.9, 2.2, 127.0, 127.7, 128.4, 138.6, 139.6, 146.4; 29Si NMR
(79 MHz, CDCl3) ı −2.80, 8.82; HRMS (EI) m/z calcd for C13H22OSi2:
250.12092; found 250.12089.
(E)-[1-(4-methoxyphenyl)-2-(1,1,3,3,3-
pentamethyldisiloxy)]ethene
(1g).
bp
102–105 ◦C/1 mmHg,
colourless liquid, yield 89%, purity >99%; 1H NMR(400 MHz,
CDCl3) ı 0.15 (s, 9H, –Si(CH3)3), 0.25 (s, 6H, –Si(CH3)2–), 3.87 (s,
3H, –OCH3), 6.50 (d, 1H, JHH = 19.2 Hz, Si–HC CH–C6H4–OCH3),
6.97 (d, 1H, JHH = 19.2 Hz Si–HC CH–C6H4–OCH3), 6.93 (d, 2H,
JHH = 8.7 Hz, –C6H4–OCH3), 7.48 (d, 2H, JHH = 9.3 Hz, –C6H4–OCH3);
13C NMR (100 MHz, CDCl3) ı 0.9, 2.2, 55.3, 113.9, 127.8, 128.8,
132.2, 138.9, 144.9; 29Si NMR (79 MHz, CDCl3) ı −3.03, 8.35; HRMS
(EI) m/z calcd for C14H24O2Si2: 280.13148; founded 280.13145.
(E)-[1-(4-chlorophenyl)-2-(triethoxysilyl)]ethene
(1b).
bp
106–110 ◦C/1 mmHg, less-yellow liquid, yield 75%, purity 96%; 1H
NMR (400 MHz, CDCl3) ı 1.25 (t, 9H, –Si(OCH2CH3)3), 3.88 (q, 9H,
–Si(OCH2CH3)3), 6.14 (d, 1H, JHH = 19.5 Hz, Si–HC CH–C6H4–Cl),
7.15 (d, 1H, JHH = 19.5 Hz, Si–HC CH–C6H4–Cl), 7.30 (d, 2H,
JHH = 8.4 Hz, –C6H4–Cl), 7.40 (d, 2H, JHH = 8.4 Hz, –C6H4–Cl); 13C
NMR (100 MHz, CDCl3) ı 18.2, 58.6, 118.6, 127.9, 128.7, 134.4,
136.1, 147.6; 29Si NMR (79 MHz, CDCl3) ı −56.32; HRMS (EI) m/z
calcd for C14H21ClO3Si: 300.09485; found 300.09271.
2.3. Hiyama reaction procedure
The Hiyama reactions were carried out in a 50 mL Schlenk tube
equipped with a magnetic stirrer under nitrogen atmosphere. In
a typical experiment, the flask was charged with the reagents:
catalyst (1.31 × 10−5 mol), iodo- or bromobenzene PhX (X = I, Br)

130
A. Skarz˙ yn´ska et al. / Journal of Molecular Catalysis A: Chemical 351 (2011) 128–135
(1.31 × 10−3 mol), ArCH CH[Si] 1.44 × 10−3 mol in THF or DMF as
a solvent (2 mL) containing mesitylene as an internal standard.
An activator, [nBu4N]F (2.14 × 10−3 mol) was used as an additive.
The mixture was heated and stirred at 60 ◦C for 12 h (THF) or at
140 ◦C for 4 h (DMF). After that time, the reaction mixture was
cooled and the organic products were separated by extraction with
diethyl ether (3 times with 7 mL), washed with water, dried over
MgSO4, and analysed by GC–MS. The structures of the synthesised
(E)-stilbenes were confirmed by GC–MS and NMR spectroscopy,
matching data reported in the literature [18].
[RuHCl(CO)(PPh3)3]
CuCl
[Si]
[Si]
+
R
R
1
[Si] = SiMe2OSiMe3 or Si(OEt)3
R = H, Cl, Br, Me, OMe
Scheme 2.
3. Results and discussion
(E)-stilbene (2a). mp 119–120 ◦C (lit. 121 ◦C); 1H NMR (500 MHz,
CDCl3) ı 7.24 (s, 1H), 7.38 (t, J = 7.55 Hz, 1H), 7.48 (t, J = 8.42 Hz, 2H),
7.64 (d, J = 7.84 Hz, 2H); 13C NMR (126 MHz, CDCl3) ı 126.5, 127.6,
128.6, 128.7, 137.3; GC–MS: m/z (%) 180 (100), 179 (97), 178 (60),
165 (47), 152 (11), 89 (73), 76 (51).
3.1. Synthesis of styrylsilanes
In order to prepare the styrylsilanes to serve as substrates for
the Hiyama cross-coupling, silylative coupling of vinylsilanes with
substituted styrenes was used [11a,19]. Since an efficient protocol
for this reaction had been reported by some of us previously, we
utilised this route with slight modifications improving the yield
of the products. The reaction was carried out in the presence of
the ruthenium complex [RuHCl(CO)(PPh3)3] as a catalyst and CuCl
as a co-catalyst. The amount of olefin was reduced from three- or
five-fold molar excess to a nearly equimolar amount. The modified
protocol allowed us to suppress the undesired homocoupling
of vinylsilanes and resulted in improved yield of styrylsilanes.
As seen from Scheme 2, the procedure was applicable to styryl-
silanes bearing both electron-deficient as well as electron-rich
substituents on phenyl ring. Application of this catalytic system
effectively gives new useful reagents for Hiyama coupling: (E)-[1-
(2-chlorophenyl)-2-(1,1,3,3,3-pentamethyldisiloxy)]ethene (1c)
and (E)-[1-(3-methylphenyl)-2-(1,1,3,3,3-pentamethyldisiloxy)]
ethene (1f), which have, to our knowledge, not been reported
in the literature till now. The almost exclusive formation of
E-styrylsilanes was corroborated by means of NMR and HRMS
spectroscopic methods (see Section 2).
(E)-4-chlorostilbene (2b). mp 128–129 ◦C (lit. 128–129 ◦C); 1H
NMR (500 MHz, CDCl3) ı 6.98 (d, J = 4.35 Hz, 2H), 7.19 (t, J = 7.31 Hz,
1H), 7.24 (s, 1H), 7.25 (s, 1H), 7.29 (t, J = 7.87 Hz, 2H), 7.35 (d,
J = 8.52 Hz, 2H), 7.43 (d, J = 7.26 Hz, 2H); 13C NMR (126 MHz, CDCl3)
ı 126.6, 127.4, 127.7, 127.9, 128.7, 128.9, 129.3, 133.2, 135.9, 137.0;
GC–MS: m/z (%) 214 (89), 180 (17), 179 (98), 178 (100), 89 (58), 76
(51).
(E)-2-chlorostilbene (2c). mp 38–39 ◦C (lit. 39–40 ◦C); 1H NMR
(500 MHz, CDCl3) ı 6.99 (d, J = 16.3 Hz, 1H), 7.08 (td, J = 5.90 Hz, 1H),
7.15 (td, J = 6.98 Hz, 1H), 7.21 (tt, J = 7.39 Hz, 1H), 7.27–7.35 (m, 3H),
7.47–7.49 (m, 3H), 7.57 (dd, J = 6.19 Hz, 1H); 13C NMR (126 MHz,
CDCl3) ı 124.6, 126.4, 126.7, 126.8, 127.9, 128.4, 128.6, 129.7, 131.2,
133.3, 135.3, 136.9; GC–MS: m/z (%) 214 (43), 180(16), 179 (100),
178 (81), 89 (47), 76 (52).
(E)-4-bromostilbene (2d). mp 136–138 ◦C (lit. 136–137 ◦C); 1H
NMR (500 MHz, CDCl3) ı 6.94 (d, J = 16.3 Hz, 1H), 7.02 (d, J = 16.3 Hz,
1H), 7.17–7.30 (m, 5H), 7.39 (d, J = 8.49 Hz, 2H), 7.42 (d, J = 7.39 Hz,
2H); 13C NMR (126 MHz, CDCl3) ı 121.3, 126.5, 127.4, 127.8, 127.9,
128.7, 129.4, 131.8, 136.3, 136.9; GC–MS: m/z (%) 260 (57), 258 (56),
179 (58), 178 (100), 89 (32), 76 (25).
(E)-4-methylstilbene (2e). mp 118–119 ◦C (lit. 119–120 ◦C); 1H
NMR (500 MHz, CDCl3) ı 2.36 (s, 3H), 6.98 (s, 1H), 6.99 (s, 1H), 7.07
(d, J = 7.55 Hz, 2H), 7.16 (t, J = 7.09 Hz, 1H), 7.26 (t, J = 7.30 Hz, 2H),
7.32 (d, J = 7.36 Hz, 2H), 7.41 (d, J = 7.5 Hz, 2H); 13C NMR (126 MHz,
CDCl3) ı 21.28, 126.4, 126.5, 127.4, 127.8, 128.7, 129.4, 134.6, 137.5;
GC–MS: m/z (%) 194 (100), 193 (45), 179 (99), 76 (6).
3.2. Hiyama cross-coupling reaction
At the outset of our studies, we probed the Hiyama cou-
pling (HC) of styrylsilanes with iodobenzene under anaerobic
conditions in THF at 60 ◦C and [nBu4N]F as additive (Scheme 3).
The cross-coupling of 1-aryl-2-silylethenes with iodobenzene led
to the selective formation of corresponding stilbenes (Table 1).
The reactions proceeded with almost exclusive ipso substitu-
tion, in a highly stereospecific manner, to afford mainly coupling
products with an E configuration in good yields. The homo-
coupling product of iodobenzene, i.e. biaryl, was not observed.
When the same conditions were applied to the Hiyama coupling
with less reactive bromobenzene, no satisfactory results were
obtained. These outcomes prompted us to undertake the coupling
in more severe reaction conditions. In order to define the proper
reaction conditions, we initially studied the C–C coupling of (E)-
1-(4-chlorophenyl)-2-(triethoxysilyl)ethene as a model substrate.
Preliminary experiments were carried out at 120 ◦C over 4 h in the
(E)-3-methylstilbene (2f). mp 46–47 ◦C (lit. 48.6–49.2 ◦C); 1H
NMR (500 MHz, CDCl3) ı 2.28 (s, 3H), 6.97–6.99 (m, 3H), 7.15 (t,
J = 7.59 Hz, 2H), 7.21–7.27 (m, 4H), 7.41 (d, J = 7.80 Hz, 2H); 13C
NMR(126 MHz, CDCl3) ı 21.5, 123.7, 126.5, 127.2, 127.6, 128.4,
128.5, 128.6, 128.7, 128.9, 137.2, 137.4, 138.2; GC–MS: m/z (%) 194
(97), 193 (26), 179 (100), 178 (82), 76 (6).
(E)-4-methoxystilbene (2g). mp 134–135 ◦C (lit. 135–137 ◦C); 1
H
NMR (500 MHz, CDCl3) ı 3.74 (s, 3H), 6.81 (d, J = 8.78 Hz, 2H), 6.93
(m, 2H), 7.16 (t, J = 5.6 Hz, 1H), 7.26 (t, J = 7.51 Hz, 2H), 7.37 (d,
J = 8.75 Hz, 2H), 7.39 (d, J = 7.32 Hz, 2H); 13C NMR (126 MHz, CDCl3)
ı 55.3, 114.1, 126.2, 126.6, 127.2, 127.7, 128.2, 128.6, 130.1, 137.6,
159.3; GC–MS: m/z (%) 210 (100), 209 (14), 195 (15), 179 (10),
76 (4).
X
[Si]
[Pd]
[nBu4N]F
+
R
R
1
2
[Si] = SiMe2OSiMe3 or Si(OEt)3
R = H, Cl, Br, Me, OMe
X = I, Br
[Pd] = [PdCl2P(OCH2CMe2NH)OCH2CMe2NH2]
Scheme 3.

A. Skarz˙ yn´ska et al. / Journal of Molecular Catalysis A: Chemical 351 (2011) 128–135
131
Table 1
Product distribution in Hiyama coupling reactions of halobenzene and substituted styrylsilanes RC6H4CH CH[Si].
Entry
RC6H4CH CH[Si]
PhX
Conversion of PhX (%)
Yield (%) of E-stilbenes
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
1a C6H5CH CHSiMe2OSiMe3
1a C6H5CH CHSiMe2OSiMe3
1b 4-ClC6H4CH CHSi(OEt)3
1b 4-ClC6H4CH CHSi(OEt)3
PhIa
100
98
91
93
99
97
100
10
96
95
99
95
99
95
90
88
5
2a 98
2a 95
2b 90
2b 91
2c 97
2c 92
2d 99
–
2e 95
2e 92
2f 98
2f 91
2g 97
2g 93
2b 88
2b 87
2b 5
PhBrb
PhIa
PhBrb
PhIa
1c 2-ClC6H4CH CHSiMe2OSiMe3
1c 2-ClC6H4CH CHSiMe2OSiMe3
1d 4-BrC6H4CH CHSiMe2OSiMe3
1d 4-BrC6H4CH CHSiMe2OSiMe3
1e 4-MeC6H4CH CHSiMe2OSiMe3
1e 4-MeC6H4CH CHSiMe2OSiMe3
1f 3-MeC6H4CH CHSiMe2OSiMe3
1f 3-MeC6H4CH CHSiMe2OSiMe3
1g 4-OMeC6H4CH CHSiMe2OSiMe3
1g 4-OMeC6H4CH CHSiMe2OSiMe3
PhBrb
PhIa
PhBrb
PhIa
PhBrb
PhIa
PhBrb
PhIa
PhBrb
PhIa
*
1b 4-ClC6H4CH CHSi(OEt)3
1b 4-ClC6H4CH CHSi(OEt)3
PhIa
**
1b 4-ClC6H4CH CHSi(OEt)3
1b 4-ClC6H4CH CHSi(OEt)3
PhBrc
PhBrd
7
2b 7
[Pd catalyst] 1.31 × 10−5 mol; [nBu4N]F 2.14 × 10−3 mol; PhX (1.31 × 10−3 mol); RC6H4CH CH[Si] 1.44 × 10−3 mol; mesitylene as internal standard. The yields of compounds
are an average of at least two runs.
Entries 1–14, [Pd catalyst] = [PdCl2P(OCH2CMe2NH)OCH2CMe2NH2].
*
Entry 15 [Pd catalyst] = PdCl2.
**
Entry 16 [Pd catalyst] = Pd(OAc)2.
a
THF, 60 ◦C, 12 h.
b
DMF, 140 ◦C, 4 h.
c
Cs2CO3 as a base, DMF, 120 ◦C, 4 h.
d
NaOH as a base, DMF, 120 ◦C, 4 h.
Table 2
Product distribution in Hiyama coupling reactions of 4-OMeC6H4CH CH SiMe2OSiMe3 and halosubstituted methoxybenzenes.
Entry
RC6H4CH CH[Si]
PhX
Yield (%) of E-stilbenes*
1
2
3
4
5
4-OMeC6H4CH CHSiMe2OSiMe3
4-OMeC6H4CH CHSiMe2OSiMe3
4-OMeC6H4CH CHSiMe2OSiMe3
4-OMeC6H4CH CHSiMe2OSiMe3
4-OMeC6H4CH CHSiMe2OSiMe3
2-Iodoanisolea
4-Iodoanisolea
2-Bromoanisoleb
3-Bromoanisoleb
4-Bromoanisoleb
26
15
91
82
17
*
Yield of isolated product.
a
THF, 60 ◦C, 12 h.
DMF, 140 ◦C, 4 h.
b
presence of the [nBu4N]F, Cs2CO3 or NaOH. Tetrabutylammonium
fluoride appeared to be the most effective activator compared with
the two remaining bases. The yield of the reaction for cesium
carbonate or sodium hydroxide was very low (5–7%). Having opti-
mised the HC procedure, we were able to get almost exclusively
the E-isomer of 4-chlorostilbene with satisfactory yield. Other pal-
ladium sources, such as PdCl2 and Pd(OAc)2, were less effective than
complex [PdCl2P(OCH2CMe2NH)OCH2CMe2NH2] (entries 15 and
16 respectively). Subsequently, the Hiyama coupling (HC) of styryl-
silanes with bromobenzene (Scheme 3) was performed in DMF
under anaerobic conditions at 140 ◦C. To evaluate the effectiveness
of the catalytic system, substituted styrylsilanes incorporat-
ing electron-withdrawing or electron-donating groups were
tested.
It should be noted that the kind of substituent within the aro-
matic ring had no impact on the yield or the stereochemistry of the
stilbenes formed. The reactions of styrylsilanes having either an
electron-donating group in a para-position, i.e. (Me, OMe) (entries
9, 10 and 13, 14) or an electron withdrawing group, (Cl) (entries
3, 4), proceeded smoothly, with an excellent yield of the prod-
ucts, exceeded 90%. Similarly, no steric effect was observed. Both
small and sterically hindered styrylsilanes coupled effectively to
give substituted stilbenes. To extend the scope of the protocol,
we applied the optimum conditions to screen methoxy substi-
tuted halobenzenes. It was found that the catalytic system based on
bromosubstituted anisoles is more effective than iodosubstituted
one (Table 2).
To obtain mechanistic information about the system, the yield
of the product as a function of the time of the reaction of (E)-[1-
(4-methylphenyl)-2-(1,1,3,3,3-pentamethyldisiloxy)]ethene (1e)
with bromobenzene was studied. As shown in Fig. 1, the reaction
100
80
60
40
20
0
0
50
100
150
200
250
time (minutes)
Fig. 1. Reaction profile study of the Hijama cross-coupling of (E)-[1-(4-
methylphenyl)-2-(1,1,3,3,3-pentamethyldisiloxy)]ethene (1e) with bromobenzene
(solid line), and a poisoning test (dotted line) with Hg(0) added before reaction starts
(reaction conditions: DMF, 140 ◦C).

132
A. Skarz˙ yn´ska et al. / Journal of Molecular Catalysis A: Chemical 351 (2011) 128–135
Fig. 2. TEM micrograph and energy dispersive X-ray spectrum (with the use of Cu grid) of post reaction solution between (E)-[1-(4-methylphenyl)-2-(1,1,3,3,3-
pentamethyldisiloxy)] ethene (1e) and bromobenzene.
[Pd], [nBu4N]F
DMF, 140oC
n
SiMe2OSiMe3
Br
nBr
1d
Scheme 4.
starts immediately, over 70% yield of the relevant stilbene is
obtained within 15 min, and no induction period is observed. The
lack of an induction period as well as sigmoidal kinetics points to
the contribution of homogenous catalyst in catalytic process. This
supposition was confirmed by mercury poisoning test [20], which
was performed twice using 250 equivalents of mercury relative
to palladium. In the first case, mercury was added together with
the substrates, and in the second one, after 15 min of reaction. As
can be seen in Fig. 1, no suppression of the reaction course was
observed, as expected for the homogeneous catalyst.
Analysis of the post-reaction solution using TEM (transmission
electron microscopy) and EDS (energy dispersive X-ray spec-
troscopy) (Fig. 2) showed the presence of Pd(0) nanoparticles with
the mean size 6–7 nm. These nanoparticles were, most probably,
formed in the final stage of the catalytic process, when practically
all substrates had been used up.
Fig. 3. TEM micrograph of polycondensation product of (E)-[1-(4-bromophenyl)-2-(1,1,3,3,3-pentamethyldisiloxy)]ethene (1d) and the corresponding size histogram of
Pd(0) nanoparticles (70 Pd nanoparticles measured).

A. Skarz˙ yn´ska et al. / Journal of Molecular Catalysis A: Chemical 351 (2011) 128–135
133
298K
s.s.
s.s.
77 K
320 280 240
200 160 120 80
40
0
- 40 - 80
ppm
190
290
390
490 590
λ (nm)
690
790
890
Fig. 4. CPMAS spectrum of polycondensation product of (E)-[1-(4-bromophenyl)-2-
(1,1,3,3,3-pentamethyldisiloxy)]ethene made at r.t., s.s. denotes spinning sidebands.
Fig. 5. Photoluminescence spectra of the polymer measured at 298 and 77 K. The
excitation wavelength was 300 nm and 350 nm respectively. The emission peaks
occur at: (298) 517, 548 and 590 nm; (77 K) 526, 567, 616 nm.
3.3. Spectroscopic characterisation and catalytic activity of PPV
derivative
Interestingly, when (E)-[1-(4-bromophenyl)-2-(1,1,3,3,3-pen-
tamethyldisiloxy)]ethene (1d) was used as the substrate in
DMF at 140 ◦C, a mere 10% yield of stilbene was observed
in the process (Table 1, entry 8). Instead, a polymeric prod-
uct insoluble in dimethylformamide was formed in the system
quantitatively. According to ICP-MS analysis it contained 0.77%
of palladium. Actually, TEM analysis (Fig. 3) of the poly-
mer corroborated the presence of roughly spherical palladium
nanoparticles, mainly arranged in the form of agglomer-
in the system operating with Pd-PPV, again the mercury poisoning
test was performed. The addition of 250 equivalents of mercury rel-
ative to palladium together with substrates quenched the reaction;
only a residual amount of (E)-4-methoxystilbene was obtained.
These results suggest that most probably Pd(0) species in the form
of PdNPs trapped in PPV polymer are involved in the catalytic pro-
cess [21].
A Pd-PPV polymeric product, tentatively proposed as a mixture
of linear and branched poly(phenylene-vinylene) PPV polymers,
was also isolated in the absence of bromobenzene in the reaction
system, as a yellow-green precipitate (Scheme 4).
The Hiyama homocoupling of (E)-[1-(4-bromophenyl)-2-
(1,1,3,3,3-pentamethyldisiloxy)] ethene (1d) proceeded due
to the presence of a labile bromine substituent on the phenyl
ring. A similar homocoupling process giving a poly(phenylene-
vinylene) derivative with high yield and stereoselectivity has
been reported in the literature for 1,3-bis[(E)-4-bromostyryl]
ates, with an average size of
8
1.4 nm. We were curious
about the catalytic properties of the obtained polymer. The
Hiyama cross coupling of (E)-[1-(4-methoxyphenyl)-2-(1,1,3,3,3-
pentamethyldisiloxy)]ethene with bromobenzene catalysed by the
obtained polymer Pd-PPV (the ratio [Pd]:[PhBr] = 0.005:1) gave
40% yield of (E)-4-methoxystilbene. The Pd-PPV polymer separated
from the reaction mixture and used in the second run again pro-
duced 38% of stilbene. To identify the catalytically active species
Scheme 5. Possible mechanism of cross-coupling reactions.

134
A. Skarz˙ yn´ska et al. / Journal of Molecular Catalysis A: Chemical 351 (2011) 128–135
precatalyst is responsible for generation of Pd(0) nanoparticles
Heck reaction
Hiyama reaction
100
80
60
40
20
0
formed in situ in the system. Palladium nanoparticles are trapped
in PPV polymeric product contemporaneously generated follow-
ing the homocoupling reaction of bromosubstituted siloxane. The
mercury test and TEM studies performed suggest that these Pd
nanoparticles might be involved in the heterogenous catalytic
process of the Hiyama cross-coupling. The obtained polymeric
derivative of poly(phenylenevinylene) needs further examination,
but at the same time the presented simple catalytic methodology
open the window of opportunity to the application in e.g. LED
devices.
Acknowledgments
The authors would like to thank the Ministry of Science and
Higher Education (Grant No. N N204 028538) for financial support
of this research. The authors are grateful to Mr. Tomasz Borkowski
and Dr. Wojciech Gil and Dr. Andrzej Gniewek (Faculty of Chem-
istry, University of Wrocław) for XRD and TEM analyses, and Dr.
Paula Gawryszewska-Wilczyn´ ska and D.Sc. Mirosław Karbowiak
for making photoluminescence spectra.
Fig. 6. Yield of selected stilbenes obtained in Hiyama and Heck [14] reactions in
DMF at 140 ◦C.
tetramethyldisiloxane [22]. However, the authors did not men-
tioned the palladium species involved in polymer. The very
low solubility of PPV in most available solvents (e.g. in DMF
3 mg/100 ml) makes the structure of the polymer difficult to
establish unambiguously. Nevertheless, solid 13C NMR and the IR
spectra allowed us to propose the possible polymeric structure.
The cross-polarisation magic-angle spinning (CPMAS) spectrum
shown in Fig. 4 reveals signals attributed to the aromatic carbon
atoms at 126.18, 129.48, 132.80, 137.72 ppm as anticipated for the
structure of PPV [23].
The very strong absorptions in the IR spectrum at 837 and
966 cm−1 corresponding to phenylene and trans-vinylene C–H out-
of-plane bands point to the presence of E-vinylene fragments, as
does a weak band at 3021 cm−1 corresponding to trans-vinylene
C–H stretch [24–26]. The solid state reflectance spectra (mea-
sured at room temperature over 190−890 nm range) and emission
spectra are shown in Fig. 5. The features of reflectance spectrum
are analogous to those published before [27]. When exposed on
UV light, the polymer exhibits a green emission. In contrast to a
spectrum measured at room temperature with bands at 517, 548
and 590 nm, the emission spectrum measured at 77 K reveals well
resolved bands shifted to 526, 567, 616 nm [28,29].
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