A novel organometallic route to phenylethenyl-modified polysiloxanes

Article abstract of DOI:10.1039/b413474e

We have synthesized a series of cyclic and linear siloxane materials with phenylethenyl substituents via transition metal complex-catalyzed coupling of the respective vinylsiloxane systems with styrene and α-methylstyrene. It has been shown that the non-carbene metal catalysts [RuCl(H)(CO)(PPh ₃)₃] and [RuCl(SiMe₃)(CO)(PPh₃) ₂] are the most effective ones, pointing to a silylative coupling pathway as the most plausible mechanistic route. The process was studied in the presence of a series of catalysts and styrene polymerization inhibitors under different reaction conditions, leading to useful silicone materials characterized by high refractive index values ranging from 1.51 to 1.59 due to strong π-conjugation in side chain substituents.

Full text of DOI:10.1039/b413474e

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www.rsc.org/materials | Journal of Materials Chemistry
A novel organometallic route to phenylethenyl-modified polysiloxanes
a
Tomasz Ganicz, Anna Kowalewska, Włodzimierz A. Stanczyk,* Matthew Butts, Susan A. Nye and
a
a
b
b
´
Slawomir Rubinsztajnc
Received 2nd September 2004, Accepted 1st November 2004
First published as an Advance Article on the web 19th November 2004
DOI: 10.1039/b413474e
We have synthesized a series of cyclic and linear siloxane materials with phenylethenyl
substituents via transition metal complex-catalyzed coupling of the respective vinylsiloxane
systems with styrene and a-methylstyrene. It has been shown that the non-carbene metal catalysts
[RuCl(H)(CO)(PPh3)3] and [RuCl(SiMe3)(CO)(PPh3)2] are the most effective ones, pointing to a
silylative coupling pathway as the most plausible mechanistic route. The process was studied in
the presence of a series of catalysts and styrene polymerization inhibitors under different reaction
conditions, leading to useful silicone materials characterized by high refractive index values
ranging from 1.51 to 1.59 due to strong p-conjugation in side chain substituents.
approach provides a new modification route, alternative to
Introduction
hydrosilylation, for synthesis of phenylethenyl substituted
In recent years there has been a growing demand for materials
siloxanes.
with properties which can not be provided by conventional
polymers. Numerous specialty polymers can be utilized in such
Experimental
areas as interpenetrating polymer networks, thermally and
chemically resistant materials, nonlinear optical materials,
polymer liquid crystals and p-conjugated systems.1–3 Within
these, organometallic polymers are investigated extensively as
Chemicals and procedures
Poly(dimethylsiloxane-co-methylvinylsiloxane)s were made
from octamethylcyclotetrasiloxane (D4, ABCR) and tetra-
Me,Vi
methyltetravinylcyclotetrasiloxane (D4
their properties arise from both inorganic and organic com-
,
ABCR) with
ponents. Several authors have proven the utility of organosi-
licon polymers containing Si–O, Si–C and Si–N monomeric
units, due to their thermal and optical behaviour.4,5 For
example, the syntheses of structurally diverse polymeric and
oligomeric liquid crystal systems through new metal catalyzed
metathesis or silylative coupling routes have been reported.6–10
There is an industrial demand for materials in personal care
applications which have high refractive indices (RI), and
silylative coupling routes offer the possibility of developing
new materials or new methods to meet these needs. Aryl-
substituted silicone fluids, typically made by hydrosilation of
phenylacetylenes by Si–H substrates, are widely known as high
RI materials.11–13
hexamethyldisiloxane (MM, Aldrich) or octamethyltrisiloxane
(MD2M, GE) as chain terminating agents by ionic copoly-
merization (described below for
a
standard process).16
Clearly, both catalytic processes mentioned above can be
developed into efficient synthetic methods for useful siloxane
materials bearing phenylethenyl groups, which due to the
electron conjugation impart high refractive indices. These
processes could thus provide an alternative route to similar
systems commonly prepared by hydrosilation. Both metathesis
and silylative coupling lead to the same product, but of course
differ mechanistically. Whereas metathesis involves CLC bond
cleavage, silylative coupling occurs via LC–Si and LC–H bond
breaking (Scheme 1), as shown in earlier work on simple
deuterium labelled vinylsilanes.14,15
Scheme 1 Metathesis and silylative coupling routes.
In this work, vinyl containing siloxanes, both linear (I) and
cyclic (II) as well as diethoxysilane (III) (Scheme 2), were
studied in coupling processes with styrene and a-methyl-
styrene, leading to fluids with high refractive indices. Such an
Scheme 2 Vinyl containing siloxanes (I, II, III).
J. Mater. Chem., 2005, 15, 611–619 | 611
*was@bilbo.cbmm.lodz.pl
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a-Methylstyrene (Merck), styrene (Merck), toluene (POCh),
hydroquinone (Aldrich), 4-tert-butylcatechol (Aldrich),
2,6-di-tert-butyl-4-methylphenol (BHT, Aldrich), [RuCl2-
source of dimethylsiloxane monomeric units instead of D4.
Experimental details are summarized in Table 1.
(PPh3)3]
[RuCl2(LCHPh)(PCy3)2] (Strem) and [{(i-Pr)2C6H3NL}-
Mo(LCHCMe2Ph)(biphen)] (biphen 3,39-di-tert-butyl-
(Aldrich),
[RuCl(H)(CO)PPh3]
(Aldrich),
Silylative coupling of copolysiloxane of average structure
[Me3SiO(MeViSiO)53%(Me2SiO)47%SiMe3; Mn 5 1250] with
styrene, representative procedure
5
5,59,6,69-tetramethyl-1,19-biphenyl-2,29-diolate, Strem) were
used as supplied, whereas [RuCl(SiMe3)(CO)(PPh3)2]17 and
[Ru(OAc)H(CO)(PPh3)2]18 were prepared according to litera-
ture methods. Tris(hydroxymethyl)phosphine (Aldrich) was
used to remove ruthenium complexes from final products.19
1H, 13C, and 29Si (INEPT) NMR measurements were
performed on either a Bruker AC 200 MHz or a Bruker
DRX 500 MHz instrument. Size exclusion chromatography
(SEC) was performed on a Wyatt Optilab 903 apparatus using
two columns (TSK G4000HLX and G2000HLX) in a series
with CH2Cl2 as the eluent. The instrument was calibrated
using polystyrene standards. GC-MS analyses were run on a
Thermo-Quest apparatus, while the spectra recorded by the
MALDI-TOF technique were performed on a Voyager-Elite
Perceptive Biosystems spectrometer.
Copolysiloxane (100 g, 0.66 mol of –[–SiMeViO–]– mono-
meric units), styrene (137.4 g, 151 mL, 1.32 mol),
[RuCl(H)(CO)(PPh3)3] (4.71 g, 0.005 mol) and an inhibitor
(BHT, 0.29 g, 1.3. 6 1023 mol) were stirred under argon at
100 uC for 191 h. After that time the conversion, as measured
by 1H NMR spectroscopy, was 90%. The polymer was
precipitated with MeOH (2 L) and then taken up in pentane,
filtered and dried under vacuum for
4 days at room
temperature. Styryl modified polysiloxane Me3SiO-
[SiMe(CHLCH–Ph)O]48%[SiMeViO]4%[SiMe2O]47%SiMe3 was
obtained. Yield 115 g (77%); H NMR (CDCl3, ppm) d: 0.05–
1
0.25 (m, –Me2SiO–), 0.25–0.45 (m, –MeSiO–), 6.25–6.60 (d of
m, SiCHLCHPh, JCHLCH 5 19.2 Hz), 6.95–7.25 (d of m,
SiCHLCHPh, JCHLCH 5 19.2 Hz), 7.25–7.70 (m, Ph); 13C
NMR (CDCl3, ppm) d: (20.05)–(0.03) (–MeSiO–), 0.09–1.65
(–Me2SiO–), 1.70–2.25 (Me3Si end groups), 125.5–126.5
(SiCHLCHPh), 126.6–128.5 (aromatic CH), 137.5–138.5 (aro-
matic Cq), 145–146 (SiCHLCHPh); 29Si NMR (CDCl3,
Cr(acac)3, ppm) d: (234.5)–(229.2) [SiMe(CHLCHPh)O] (in
sequences of monomeric units), (222.1)–(217.9) (SiMe2O in
sequences of monomeric units), 7.8–9.4 (Me3SiO in sequences
of monomeric units), SEC (THF): Mn 5 1050; Mw/Mn 5 1.6.
Synthesis of poly(dimethylsiloxane-co-methylvinylsiloxane)s,
representative procedure
A typical base catalyzed equilibration procedure was as
Vi,Me
follows: D4
(100 g, 1.16 mol of –SiMeViO– monomeric
units), D4 (43 g, 0.58 mol of –SiMe2O– monomeric units) and
MD2M (72 g, 0.232 mol) were stirred under nitrogen at 130 uC
for 1 hour. At this time potassium silanolate (0.05 g, freshly
made from octamethylcyclotetrasiloxane and KOH) was
added, and the reaction mixture was stirred at 130 uC for
6 hours. It was then cooled to room temperature and
neutralized with concentrated acetic acid to stop the equilibra-
tion. The resulting polymer was washed three times with
MeOH (100 mL) and the volatile components were removed
under vacuum (1 mmHg, 100 uC, 12 hours). Yield 155 g (72%);
1H NMR (CDCl3, ppm) d: 0.09 (s, 6H, –Me2SiO–), 0.16 (s, 3H,
–MeViSiO–), 5.73–6.11 (m, 3H, –MeViSiO–); 13C NMR
(CDCl3, ppm) d: 20.65 (–MeViSiO–), 1.05 (–Me2SiO–),
133.0 (LCH2), 136.9 (LCH); 29Si NMR (CDCl3, Cr(acac)3,
ppm) d: 20.34 (–MeViSiO–), 220.5 (–Me2SiO–), 8.50 (Me3Si
end groups); SEC (THF) Mn 5 1250, Mw/Mn 5 1.3.
Silylative coupling of tetramethyltetravinylcyclotetrasiloxane
(D4Vi,Me) with styrene, representative procedure
D4Vi,Me (100 g, 1.36 mol [–SiMeViO–] molecular units), styrene
(181.2 g, 1.74 mol), toluene (80 mL), [RuCl(H)(CO)(PPh3)3]
(5 g, 5.1 6 1023 mol) and hydroquinone (0.83 g, 7.5 6
1023 mol) were stirred under argon at 100 uC for 96 h. Then
MeOH (300 mL) was added in order to precipitate poly-
styrene. The mixture was filtered and the volatile materials
were removed under reduced pressure. The resulting oily,
opaque, green residue was washed with 300 mL of MeOH,
filtered and dried under vacuum again. The greenish product
was dissolved in 300 mL of pentane and left in a refrigerator
for 12 h. It was filtered cold and the pentane was evaporated.
The transparent, brownish, oily residue was dissolved again in
pentane, kept in a refrigerator for 3 h, filtered, evaporated and
In the case of acid catalyzed processes, H2SO4 (0.6 mL) or
CF3COOH (0.15 mL) were used. Occasionally, D3 served as a
Table 1 Equilibration process parameters
Molar ratio of organosilicon substrates
Me,Vi
D4
D3
D4
MM
MD2M
Catalyst
Mn
Mw/Mn
–MeViSiO– m.u. (%)
Reaction time/h
1
1
1
1
1
1
1
a
—
—
3.40
0.55
—
0.50
0.50
—
0.10
—
0.20
0.20
—
—
0.10
—
H2SO4
H2SO4
H2SO4
CF3COOH
[KO(SiMe2O)xK]
[KO(SiMe2O)xK]
[KO(SiMe2O)xK]
4060
9450
3280
5000
2670
1740
3200
4.00
3.95
1.36
1.29
1.12
1.13
1.10
53
52
50
67
56
65
65
72
96
24
240
7
—
—
0.50
0.50
0.50
0.15
0.20
0.10
—
—
—
—
7
7
Me,Vi
D4
– tetramethyltetravinylcyclotetrasiloxane, D3 – hexamethylcyclotrisiloxane, D4 – octamethylcyclotetrasiloxane, MM – hexamethyl-
b
disiloxane, MD2M – decamethyltetrasiloxane. Synthesis of poly(dimethylsiloxane-co-methylvinylsiloxane)s.
612 | J. Mater. Chem., 2005, 15, 611–619
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Vi,Me
Fig. 1 GC/MS analysis of silylative coupling products of D4
and styrene.
dried under vacuum for 12 h, at 100 uC. Yield 104.5 g (43%).
1H NMR (CDCl3, ppm) d: 0.12–0.15 (m, 3H, MeSiViO), 0.15–
0.25 (m, 3H, MeSiCHLCHPh), 5.70–6.05 (m, 3H, unreacted
Vi), 6.25–6.5 (m, 1H SiCHLCHPh, JCHLCH 5 18.9 Hz), 6.90–
7.1 (m, 1H, SiCHLCHPh, JCHLCH 5 18.9 Hz), 7.20–7.50 (m,
Ph). 13C NMR (CDCl3, ppm) d: (21.1)–(20.8) (–MeSiO–),
0.46–1.1 (–Me2SiO–), 125.0–125.6 (SiCHLCHPh), 128.0–128.5
(aromatic CH), 133.5–135.7 (aromatic Cq), 145.3–148.7
(SiCHLCHPh); 29Si NMR (CDCl3, Cr(acac)3, ppm) d:
(222.5)–(220.7) [MeSi(CHLCHPh)O]– (in sequences of
monomeric units).
presence of [RuCl(H)(CO)(PPh3)3] (10.9 g, 0.011 mol). Pro-
gress of coupling was followed by 1H NMR spectroscopy. The
reaction was stopped after 96 h (52% conversion of vinyl
groups). At this stage the reaction mixture was cooled to room
temperature and 10 mL of MeOH was added in order to
deactivate the catalyst. The solvent was evaporated leaving a
green oily liquid. This liquid was dissolved in pentane (200 mL)
and then left in
a refrigerator overnight, filtered and
evaporated giving 105 g of the cyclic siloxanes. Yield 179.7 g
(69%). 1H NMR (CDCl3, ppm) d: 0.12–0.15 (m, 3H,
MeSiViO), 0.15–0.25 (m, 3H, MeSiCHLC(Me)Ph), 2.18 (s,
3H, MeSiCHLC(Me)Ph), 5.80–6.10 (m, 3H, unreacted Vi),
6.45–6.60 (m, 1H, SiCHL), 7.30–7.55 (m, 5H, Ph). 13C
NMR (CDCl3, ppm) d: (20.8)–(20.4) (–MeSiO–), 1.1–1.3
(–Me2SiO–), 18.4–18.9 (MeSiCHLC(Me)Ph), 128.7–129.8
(aromatic CH), 133.4–136.0 (aromatic Cq), 148.5–149.3
(SiCHLCHPh). 29Si NMR (CDCl3, Cr(acac)3, ppm) d:
(223.5)–(222.4) [SiMe(CHLCMePh)O] (in sequences of
monomeric units).
Proportions of monomeric units (1H NMR): 47% of
–[MeSiCHLCHPhO]– and 53% of –[MeSiViO]–; SEC
(CH2Cl2): Mn 5 450, Mw/Mn 5 1.24; EI GC/MS (Fig. 1)
(m/z): A [Si(Me)(Vi)O]4 (retention time 8.56 min) 329 (M+
2
Me, 60%), 317 (M+ 2 Vi, 22%), 302 (M+ 2 Me 2 Vi, 28%),
275 (M+ 2 Me 2 2Vi, 50%) ; B [Si(Me)(Vi)O]3[Si(Me)-
(CHLCHPh)O] (retention times 12.24, 12.30, 12.36 min) 420
(M+, 1%), 405 (M+ 2 Me, 5%), 317 (M+ 2 CHLCHPh, 4%),
302 (M+ 2 CHLCHPh 2 Me, 6%), 275 (M+ 2 CHLCHPh 2
Me 2 Vi, 100%); C [Si(Me)(Vi)O]2[Si(Me)(CHLCHPh)O]2
(retention time 15.68 min) 496 (M+, 10%), 481 (M+ 2 Me, 2%),
393 (M+ 2 CHLCHPh, 50%), 378 (M+ 2 CHLCHPh 2 Me,
35%), 290 (M+ 2 2CHLCHPh, 50%), 275 (M+ 2 Me 2
2CHLCHPh, 72%); D [Si(Me)(Vi)O][Si(Me)(CHLCHPh)O]3
Proportions of monomeric units (1H NMR): 52% of
–{MeSi[CHLC(Me)Ph]O}– and 48% of –[MeSiViO]–; SEC
(CH2Cl2): Mn 5 500, Mw/Mn 5 1.28.
MeViSi(OEt)2
Two methods were used. (A): A THF solution of EtONa was
prepared by allowing sodium metal (12.5 g, 0.54 mol) to react
with ethanol (43.2 g, 0.94 mol) in THF (160 mL). The reaction
was carried out at room temperature for 20 h. Then MeViSiCl2
was added dropwise to the solution, and the reaction mixture
was stirred for 4 h. The solution was diluted with pentane
(300 mL) and washed with ice water. The organic layer
(pH 5 7) was separated and dried over MgSO4. The solvent
(retention times 18.16, 18.66 min) 572 (M+,1%), 366 (M+
2CHLCHPh, 3%), 351 (M+ 2 Me 2 2CHLCHPh, 4%).
2
Silylative coupling of tetramethyltetravinylcyclotetrasiloxane
Vi,Me
D4
with a-methylstyrene, representative procedure
Vi,Me
D4 (99.7 g, 0.34 mol) and a-methylstyrene (274 g,
2.32 mol) were stirred in toluene (100 mL) at 100 uC, in the
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was evaporated and the product was distilled at reduced
pressure to give 12.6 g (34%) of MeViSi(OEt)2. B.p. 40 uC at
1
20 mmHg (lit.:20 133–134 uC/760 mmHg). H NMR (CDCl3,
ppm) d: 0.15 (s, 3H, Me); 1.18 (t, 3H, OCH2CH3, JH–H
5
7.0 Hz); 3.47 (q, 2H, OCH2CH3, JH–H 5 7.0 Hz); 5.97 (m, 3H,
CHLCH2); 13C NMR (CDCl3, ppm) d: 24.78 (Me); 18.23
(OCH2CH3), 58.19 (OCH2CH3), 133.72 (CHLCH2), 135.01
(CHLCH2); 29Si NMR (CDCl3, Cr(acac)3, ppm) d: 218.6; GC-
MS (EI): 159 (M+ 2 H, 10%), 145 (M+ 2 Me, 100%), 115
(28%), 101 (36%), 89 (37%), 61 (34%), 45 (42%).
(B): A mixture of EtOH (200 mL, 3.42 mol) and pyridine
(277 mL, 3.43 mol) was added dropwise to a stirred solution of
Cl2SiMeVi (211 mL, 1.62 mol) in dry pentane (1200 mL). The
temperature was kept in the range of 15–20 uC. After the
addition was completed, the reaction mixture was stirred
for 4 hours at room temperature and left overnight. Then,
pyridine hydrochloride was filtered off, the solution was
concentrated and distilled (133 uC at 760 mmHg) to give
MeViSi(OEt)2. Yield 114.5 g (65%).
Scheme 3 Z and E isomers of Me(EtO)2SiCHLCHSi(OEt)2Me.
SiCHLCHPh resonances for sequences of monomeric units),
7.35–7.7 (m, Ph); 13C NMR (CDCl3, ppm) d: (20.4)–(0.2)
(–MeViSiO–), (0.08)–(1.3) (–Me2SiO–), (1.7)–(2.0) (Me3Si end
groups), (125.0)–(126.0) (SiCHLCHPh), (126.6)–(128.5) (aro-
matic CH), (138.0)–(138.5) (aromatic Cq), (145.5)–(146.5)
(SiCHLCHPh); 29Si NMR (CDCl3, Cr(acac)3, ppm) d:
(233.2)–(230.6) ([SiMe(CHLCHPh)O] in sequences of mono-
meric units), (223.1)–(217.8) (SiMe2O in sequences of
monomeric units), 7.6–8.7 (Me3SiO in sequences of monomeric
units) (Fig. 2).
Me(EtO)2SiCHLCHPh
Me(EtO)2SiVi (150 mL, 0.8 mol) and styrene (370 mL, 3.23 mol)
were stirred in the presence of [RuCl(H)(CO)(PPh3)3] (4.66 g,
4.9 mmol) at 100 uC for 190 h. The reaction was monitored
by GLC. Polystyrene (182 g, no inhibitor was used) was
precipitated in pentane and the cross-coupled product
[Me(EtO)2SiCHLCHPh] was purified by distillation (60 uC at
1
0.2 mmHg) giving 163.5 g (86%). H NMR (CDCl3, ppm) d:
0.32 (s, 3H, Me), 1.29 (t, 3H, CH2CH3, JCH–CH 5 7.1 Hz), 3.86
(q, 2H, CH2CH3, JCH–CH 5 7.1 Hz), 6.35 (d, 1H, Si–CHL,
JCHLCH 5 19.3), 7.15 (d, 1H, LCHPh, JCHLCH 5 19.3), 7.25–
7.50 (m, 5H, Ph); 13C NMR (CDCl3, ppm) d: 24.58 (Me),
17.84 (CH2CH3), 57.82 (CH2CH3), 122.03 (SiCHL), 126.29–
128.14 (CH, Ph), 137.37 (Cq, Ph ); 147.00 (LCHPh); 29Si NMR
(CDCl3, Cr(acac)3, ppm) d: 217.6; MS (EI): 236 (M+, 10%),
221% (M+ 2 Me, 60%), 177 (50%), 147 (85%), 131 (100%), 117
(50%), 105 (45%), 77 (75%), 61 (50%), 45 (70%).
Results and discussion
The functionalization of silicones was studied focusing on the
coupling of styrene and a-methylstyrene with both linear (I)
and cyclic siloxanes (II) (Scheme 2). The corresponding
monomer, diethoxy(methyl)(phenylethenyl)silane, was also
made by the same route in order to check the efficiency of
the synthetic approach in a more straightforward manner
(Scheme 4).
Side products of the homocoupling of Me(EtO)2SiCHLCH2
High refractive index optical fluid applications require that
the viscosity of the material be limited,21,22 thus the highest
value of Mn of the starting linear siloxanes used was y3200
daltons. However, conditions of acid and base catalysed
(y10%) were
Z
and
E stereoisomers of Me(EtO)2-
SiCHLCHSi(OEt)2Me in a ratio 2 : 1 (GC) as determined by
GC/MS analyses of the reaction mixture. In EI ionization
mode, both isomers showed the same fragmentation pattern
with M+ 2 Me at 277. The two isomers could be differentiated
by CI (isobutene), since they gave different principal peaks viz.
Me(EtO)2SiCHLCHSi(OEt)2Me (Z): 247 (M + H 2 EtOH)
and Me(EtO)2CHLCH(OEt)2Me (E): 293 (M + H) (Scheme 3).
equilibration
of
tetramethyltetravinylcyclotetrasiloxane
(D4Me,Vi) with hexamethylcyclotrisiloxane (D3) or octamethyl-
cyclotetrasiloxane (D4), in the presence of end blockers such
as hexamethyldisiloxane (MM) or decamethyltetrasiloxane
(MD2M), can be adjusted to give linear products of various
chain lengths (see Experimental section and Table 1).
Co-hydrolysis of Me(EtO)2SiCHLCHPh with Me2Si(OEt)2
Initial experiments performed with ruthenium and molyb-
denum complexes (Table 2) allowed for a comparative
evaluation of catalytic activity of the respective organometallic
compounds. Additionally, they also provided an opportunity
to evaluate the likelihood or effectiveness of the two possible
mechanistic pathways leading to the final phenylethenyl
substituted siloxanes (using catalysts known to promote either
metathetical or silylative coupling). Considering the final
material, from the practical point of view it did not matter,
of course, which of the two processes prevailed as in both
couplings the desired copolymers bearing variable amounts of
Me(EtO)2SiCHLCHPh (96.6 g, 0.41 mol), (EtO)2SiMe2
(26.64 g, 0.18 mol), Me3SiCl (23.8 g, 0.22 mol) and water
(78 mL, 4.33 mol) were stirred in diethyl ether (250 mL) for
100 h at room temperature. The organic phase was separated,
washed with water until pH 7 was achieved and dried over
MgSO4. The solvent was evaporated yielding 96 g (97%) of a
pale yellow viscous liquid.
1H NMR (CDCl3, ppm) d: 0.2–0.6 (m, MeSi resonances for
sequences of monomeric units), 6.4–6.6 (m, SiCHLCHPh
resonances for sequences of monomeric units), 7.1–7.3 (m,
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Fig. 2 1H NMR spectrum of co-hydrolysis product of Me(EtO)2SiCHLCHPh and Me2Si(OEt)2.
and type of solvent present on the course of the reaction, as
well as the extent of polystyrene production. Polystyrene is
often formed in this type of reaction as a byproduct via,
presumably, free radical polymerization (strong EPR signals
were reported, for example, in reaction systems containing
[RuCl2(PCy3)2(LCHPh)]23).
Results obtained for the coupling of linear polymethyl-
vinylsiloxane (Mn 5 3200, IP 5 1.1) with styrene (Table 2)
show the effects of process variables and type of catalyst on
the progress of the reaction. The first six entries refer to the
use of the metallacarbene complexes benzylidene-bis(tricyclo-
hexylphosphine)dichlororuthenium
and
2,6-diisopropyl-
Scheme 4 Synthesis of phenylethenyl-modified siloxanes—an alter-
phenylimidoneophylidene-(racemic BIPHEN)-molybdenum,
for reactions run in both CH2Cl2 and toluene. In each
native route.
case,
a very small extent of coupling (via metathesis)
phenylethenyl groups are being formed. However, it was
important to understand the effect of key variables such as the
type of catalyst, catalyst concentration, styrene concentration
was observed together with a large amount of polystyrene,
even in the presence of hydroquinone as a free radical
quencher.
Table 2 Coupling of linear poly(dimethylsiloxane-co-methylvinylsiloxane) (65% of –MeViSiO– m.u., Mn 5 3200) with styrenes
Styrene molar
excess per
–MeViSiO–
m.u. (%)
Catalysta
(%wt)
Reaction
time/h
Molar content
of PSb (%)
Inhibitorb (%wt)
T/uC
Solvent
Coupling (%)
45
1
2
–CHLCH2
0
I (2)
I (2)
—
—
50
50
40 CH2Cl2
40 CH2Cl2
100 toluene
100 toluene
100 toluene
40 CH2Cl2
110 n-decane
110 PhCl
100 toluene
100 toluene
100 toluene
100 toluene
100 toluene
100 toluene
100 toluene
100 toluene
6
6
45
18c
35
28
—
7
19
25
1
0
0
0
38
0
8
28
3
4
5
6
7
8
9
10
11
12
13
14
15
16
a
0
0
0
0
0
0
0
0
0
0
0
0
I (2)
I (2)
—
50
48
12
48
96
48
72
48
144
92
102
20
92
96
93
QUIN (0.2)
—
—
—
—
CAT (0.5)
CAT (0.5)
BHT (0.5)
QUIN (0.5)
QUIN (0.5)
BHT (0.5)
—
100
100
100
50
50
100
50
100
100
100
100
100
100
20
gel formation
II (1.5)
II (1.5)
III (2)
III (2)
III (2)
III (2)
III (2)
III (2)
IV (2)
V (2)
36
58
36
30
72
86
100
0
95
70
0
–C(CH3)LCH2
–CHLCH2
III (2)
VI (1)
—
—
—
I – (Grubbs catalyst) benzylidene-bis(tricyclohexylphosphine)dichlororuthenium; II – (Schrock’s catalyst) 2,6-diisopropylphenylimidone-
phenylidene-(racemic BIPHEN)molybdenum, III – RuCl(H)(CO)(PPh3)3; IV – Ru(OAc)H(CO)PPh3)2; V – RuCl(SiMe3)(CO)(PPh3)2, VI –
RuCl2(PPh3)3. QUIN – hydroquinone; CAT – 4-tert-butylcatechol; BHT – 2,6-di-tert-butyl-4-methylphenyl; PS – polystyrene. Drop-wise
b
c
addition of styrene (5 h).
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Among ruthenium complexes reported to promote silylative
coupling, the effectiveness increased in the following order:
[RuCl2(PPh3)3] y [Ru(OAc)(H)(CO)(PPh3)2] % [RuCl(H)-
(CO)(PPh3)3] y [RuCl(SiMe3)(CO)(PPh3)2]. Although the
reactions involving styrene and the cyclic siloxane, polystyrene
was formed even in the presence of each of the three inhibitors.
However, the homopolymer was easily removed from the
mixture of phenylethenylated cyclosiloxanes upon the addition
of methanol and subsequent filtration.
catalytic
efficiencies
of
[RuCl(H)(CO)(PPh3)3]
and
[RuCl(SiMe3)(CO)(PPh3)2] were comparable, the latter was
much less stable, so further experiments with other silicon
substrates were carried out in the presence of
[RuCl(H)(CO)(PPh3)3].
In experiments with cyclic silicone substrate, 100% conver-
sion was not reached, and conversions were lower with
a-methylstyrene than with styrene. Byproducts included a
mixture of cyclic derivatives from which the desired product
could be isolated by chromatography. It was found, in
reactions in which inhibitor was used, that the coupling
yield could be improved under certain reaction conditions
Our observations seem contrary, in two aspects, to previous
reports concerning analogous processes with simple, non-
polymeric vinylsilanes. First, successful coupling between
vinyltriethoxysilane and styrene was reported in the presence
of [RuCl2(PPh3)3].24 [Ru(OAc)(H)(CO)(PPh3)2] was also
found to be effective in silylative coupling polycondensation
of dimethyl(p-vinylphenyl)vinylsilane.25 In our work, both
complexes turned out to be inactive as silylative coupling
catalysts. Moreover, in all reactions, where styrene was one of
the substrates, significant amounts of polystyrene were always
found. To our surprise this has not been reported earlier.14
Importantly, formation of large amounts of polystyrene can be
avoided by the use of free radical quenchers such as
hydroquinone, 4-tert-butylcatechol or 2,6-di-tert-butyl-4-
methylphenol (entries 9–14, Table 2), except in the case of
[Ru(OAc)(H)(CO)(PPh3)3], which, as mentioned, was totally
ineffective in catalyzing the silylative cross coupling reaction
under the studied conditions. The optimum conditions found
for the linear polymethylvinylsiloxane functionalization
included 100% molar excess of styrene, a level which raises
the importance of adding a radical quencher to the reaction.
The only other way of avoiding formation of the polyolefin as
a side product is to perform the cross coupling of poly-
methylvinylsiloxane with a-methylstyrene. With a-methyl-
styrene, the equilibrium between monomer and polymer
favors the monomer under typical reaction conditions due to
steric hindrance. However, the relevant coupling yield was
lower than in the case of unsubstituted styrene (entry 15,
Table 2). The same picture is valid for silylative coupling of
tetramethyltetravinylcyclotetrasiloxane with styrenes (Table 3),
i.e. the yields are lower for a-methylstyrene (entries 1–4)
compared to those with unsubstituted styrene (entries 5–8).
Although no homopolymerization occurred in the case of
a-methylstyrene coupling even in the absence of added
inhibitor(s), it was found that the addition of BHT, hydro-
quinone or 4-tert-butylcatechol led to an increase in the
coupling yield (e.g. y20% in the presence of BHT). In
(see, for example, entry 6 in Table 3, where 90% conversion
Me,Vi
was obtained). The coupling products of D4
and styrenes
were mono-, di-, tri-, and presumably tetra-substituted
cyclic siloxanes. The latter could not be resolved by GC
under the conditions used. In the case of monophenylethenyl
derivatives, three isomers are evident in the GC/MS
spectra (Fig. 1, retention times 12.24, 12.30 and 12.35 min).
They were assumed to be Z and E isomers containing
–[PhCHLCHSi(Me)O]– monomeric units as well as a product
of styrene coupling via a-C–H bond cleavage, leading to
a-phenylethenyl-substituted cyclosiloxane with a [CH2LC(Ph)–]
side group.
The presence of the third isomer as well as low effectiveness
of metallacarbene type catalysts (Table 2) point clearly to the
silylative coupling process as an efficient pathway in reactions
of vinylsiloxanes with styrenes. Although no kinetic data were
collected for these reactions, as mechanistic studies were
not the primary objective of this work, it seems justified to
adapt the mechanism suggested first by Wakatsuki et al.26 for
coupling of low molecular species catalysed by ruthenium
complexes (Scheme 5).
Higher substituted cyclosiloxanes can be seen as broadened
signals in the range of 15.68–16.47 min and 17.72–18.66 min in
the GC plot shown in Fig. 1. Their respective EI MS spectra
correspond to di- and tri-substituted cyclosiloxanes. In all
cases,
unreacted
tetramethyltetravinylcyclotetrasiloxane
appears as well (not marked on GC plot) having a retention
time of y8.50 min. These results suggest that under such
reaction conditions, only silylative coupling occurred. Linear
polymers resulting from ring-opening processes were not
detected.
An alternative synthesis of phenylethenylsiloxanes involved
a sort of reverse sequence of reactions (Scheme 4). The difunc-
tional monomer methylvinyldichlorosilane was ethoxylated to
Me,Vi
Table 3 Coupling of D4
with styrenes {[RuCl(H)(CO)(PPh3)3], 100 uC, toluene}
Styrene molar excess
per –MeViSiO–
m.u. (%)
Molar
content
of PS (%)
RuCl(H)(CO)(PPh3)3
(%wt)
Inhibitor
(%wt)
Reaction
time/h
Coupling
(%)
1
2
3
4
5
6
7
8
–C(CH3)LCH2
1.50
1.50
1.50
1.50
1.50
1.50
0.44
1.50
—
100
100
100
100
50
100
100
100
96
96
120
48
96
48
96
96
39
47
61
31
63
90
68
46
0
0
0
0
BHT (0.3)
BHT (0.3)
CAT (0.3)
QUIN (0.1)
QUIN (0.5)
QUIN (0.3)
CAT (0.5)
0
0
0
–CHLCH2
0
0
0
17
18
21
9
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Scheme 5 Mechanism of silylative coupling in the presence of ruthenium complex.
give the corresponding diethoxy derivative. Subsequent
silylative coupling of this monomer with styrene yielded
Me(EtO)2SiCHLCHPh, a suitable source of phenylethenyl
containing monomeric units for hydrolytic polycondensation
reactions. The ethoxylation reaction gave higher yields
when carried out with ethanol in the presence of pyridine as
the HCl acceptor. Silylative coupling with styrene, in the
presence of [RuCl(H)(CO)(PPh3)3] (Table 4), gave three
products. They were the (E) and (Z) isomers of
Me(EtO)2SiCHLCHSi(OEt)2Me, formed in a relatively small
amount as a result of homo-coupling of vinylsilane, and the
expected cross-coupling product Me(EtO)2SiCHLCHPh (E).
Use of the alternative catalyst [RuCl(SiMe3)(CO)(PPh3)2] led
to a higher amount of homo-coupled products, however when
the reaction was carried out with large excess of styrene (as a
reactant and diluent), 99% of methyl(phenylethenyl)diethoxy-
silane was obtained. The small amount of isomeric substituted
ethenes were separated from the desired product by distilla-
tion, because in the subsequent hydrolytic condensation
reaction their presence could lead to highly cross-linked
siloxane products. Attempts to obtain the corresponding
a-methylstyryl derivative by the same route failed. The only
products, independent of the type of ruthenium catalyst used,
were the two isomers of methylvinyldiethoxysilane resulting
from homocoupling.
Hydrolysis of methyl(phenylethenyl)diethoxysilane and its
co-hydrolysis with dimethyldiethoxysilane were carried out
under variable reaction conditions: concentration of water,
base or acid catalysts, temperature and solvent. The results,
summarized in Table 5, show that the hydrolytic condensation
can be carried out under both acid and base catalyzed
conditions. At low concentration of water (y0.5 mol per
1 mol of diethoxysilane) the process led to formation of a
dimer [Me(EtO)(PhCHLCH)Si]2O. When an excess of water
was used, the molecular weights of the oligomeric products
were rather low and independent of the ratio [monomer]/[H2O]
in the studied range. Progress of hydrolysis was followed by
monitoring the relative intensities of the CH3–Si/CH3CH2O
Table 4 Coupling of Me(EtO)2SiCHLCH2 with styrene
Coupling productsa (%)
Styrene molar excess (%)
Catalyst (%wt)
Solvent
Reaction time/h
A
B
C
3
10
400
400
RuCl(H)(CO)(PPh3)3 (2)
RuCl(SiMe3)(CO)(PPh3)2 (2)
RuCl(H)(CO)(PPh3)3 (1.5)
RuCl(H)(CO)(PPh3)3 (1)
toluene
toluene
toluene
—
19
21
90
90
11
5
1
0.5
7
3
1
0.5
75
89
98
99
a
A – Me(EtO)2SiCHLCHSi(OEt)2Me (Z); B – Me(EtO)2SiCHLCHSi(OEt)2Me (E); C – Me(EtO)2SiCHLCHPh (E).
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Table 5 Hydrolytic oligomerization of Me(EtO)2SiCHLCHPh
SMe/CH3CH2O
(1H NMR)a
SMe/–CHL
(1H NMR)a
[Me(EtO)2SiCHL [Me2Si(OEt)2]/ [H2O]/
[Catalyst]/
mol L21 mol L21
Reaction
Solvent T/uC time/h
CHPh]/mol L21
mol L21
Mn Mw/Mn
A
B
A
B
0.80
0.79
2.70
2.90
0.86
a
—
—
—
—
0.37
b
0.40
0.40
2.60
5.80
8.95
H2SiO4 (0.001) Et2O
Me3SiCl (0.31) Et2O
Me3SiCl (1.08) toluene
KOH (0.004) toluene
Me3SiCl (0.46) Et2O
20
20
70
70
20
24
24
165
115
100
—
—
0.5
1.1
1.1
0.5
1.0
15.4
36.4
3.1
2.8
246.6
3.0
6.5
6.6
3.0
7.9
10.3
37.1
3.3
290 1.6
640 1.9
613 1.8
260 1.7
10.4
9.6
A – before reaction. B – after reaction.
1
resonances in the H NMR spectrum (at 0.32 and 1.29 ppm,
respectively), and the structures of products were determined
from the ratios of the CH3–Si/Ph–CHL resonances (at 0.32
and 7.15 ppm). The degree of hydrolysis was larger in acid
catalyzed reactions. H2SO4 was found to be more efficient than
HCl generated from Me3SiCl. The conversion of ethoxy
coupling. This side reaction of radical styrene polymerization
can be limited or avoided by the use of such quenchers
as hydroquinone, 4-tert-butylcatechol or 2,6-di-tert-butyl-4-
methylphenol. It was also noted that the addition of radical
quenchers increases the yield of coupling presumably limiting
the decay of the active ruthenium species.
groups increased
a lot on increasing the ratio [H2O]/
[CH3CH2O–] (Table 5, entry 5; co-hydrolysis). However, acid
catalysts apparently cleave off phenylethenyl groups in the
condensation products. The ratio of CH3–Si/Ph–CHL was
higher than the theoretical value, and increased with the
amount of acid used. The exception is hydrolytic co-
polycondensation of methyl(phenylethenyl)diethoxysilane with
dimethyldiethoxysilane, again carried out with an excess of
water. Apparently the strength and molar concentration of an
acid is more important in the studied system than the ratio of
[–CHLCHPh]/[acid].
Acknowledgements
This work was supported by GE Silicones, General Electric
Company, and by KBN Polish State Committee for Research,
Grant PBZ-KBN/01/CD/00.
Tomasz Ganicz,a Anna Kowalewska,a Włodzimierz A. Stanczyk,*
a
´
Matthew Butts,b Susan A. Nyeb and Slawomir Rubinsztajnc
aCentre of Molecular and Macromolecular Studies, Polish Academy of
Sciences, Sienkiewicza 112, 90-363 Ło´dz´, Poland.
E-mail: was@bilbo.cbmm.lodz.pl
bGE Global Research, One Research Circle, Niskayuna, NY 12309, USA
cGE Silicones, 260 Hudson River Road, Waterford, NY 12188, USA
Conclusions
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In this work we have presented a novel approach to the
synthesis of oligo- and polysiloxanes bearing p-conjugated
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ruthenium complexes yielding a cost effective alternative to the
hydrosilylation pathway. The products exhibit refractive
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