Borane-catalyzed Si-H activation routes to polysilanes containing thiolato side chains

Article abstract of DOI:10.1021/om301246z

Dehydrocoupling and hydrosilation reactions of the Si-H bonds in poly(phenylsilane) catalyzed by B(C₆F₅)₃ allow the preparation of new polymers containing both Si-H and Si-SR side chains. This postpolymerization modification takes place without any observable competing Si-Si bond cleavage, unlike other Lewis acid, transition-metal, or radical mediated routes. The -SR-functionalized polymers have been characterized by GPC, IR, UV-vis, elemental analysis, and ¹H, ¹³C, and ²⁹Si NMR.

Full text of DOI:10.1021/om301246z

Communication
pubs.acs.org/Organometallics
Borane-Catalyzed Si−H Activation Routes to Polysilanes Containing
Thiolato Side Chains
Peter T. K. Lee, Miranda K. Skjel, and Lisa Rosenberg*
Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria, British Columbia, Canada V8W 3V6
S
* Supporting Information
ABSTRACT: Dehydrocoupling and hydrosilation reactions of the Si−H bonds in
poly(phenylsilane) catalyzed by B(C6F5)3 allow the preparation of new polymers
containing both Si−H and Si−SR side chains. This postpolymerization modification
takes place without any observable competing Si−Si bond cleavage, unlike other
Lewis acid, transition-metal, or radical mediated routes. The −SR-functionalized
polymers have been characterized by GPC, IR, UV−vis, elemental analysis, and 1H,
13C, and 29Si NMR.
olysilanes continue to be of interest for their intriguing
1
Pelectronic and optical properties, which arise from σ con-
jugation along their all-Si backbones.2 Practical application of
these intriguing materials in device technologies remains un-
developed, however, because of the facile oxidative and photo-
lytic degradation of the catenated silicon chains.1g,2b,3 Our interest
in designing more stable polysilane architectures has focused on
catalytic dehydrocoupling routes to oligo- and polysilanes that
contain Si−H bonds in the repeat units,4 on the premise that
the enormous, established arsenal of organic Si−H activation
chemistry5 could then be exploited in postpolymerization modi-
fication reactions. This would allow the introduction of con-
1
Figure 1. 500 MHz H NMR spectra for (a) the −SPrn modified
polymer, (b) the −STolp modified polymer, and (c) the parent
siderably more structural variety than is possible via the standard
reductive coupling routes to polysilanes.6 We are not the first to
poly(phenysilane), in d6-benzene. The • denotes residual C6D5H.
exploit this Si−H activation route to modified polysilanes,7 and
Si−Ph cleavage strategies have also been reported.8 However,
spectra (Figure 1), which show broad peaks (ω1/2 = 50−140 Hz)
the parent polysilanes are notoriously sensitive to Si−Si bond
cleavage under most conditions of modification,9 which can lead
to reduced molecular weights (MWs).10 For example, we found
that previously reported radical,7a−c titanocene,7g,h and platinic
acid mediated9 Si−H activation methods gave moderate to signi-
ficant Si−Si bond scission at poly(phenylsilane) (H−[Si(H)-
Ph]n−H) and even at more robust 1,2-dihydrodisilanes such as
sym-tetraphenyldisilane.11a,c However, we have found that hydro-
silation and heterodehydrocoupling reactions of disilanes medi-
ated by B(C6F5)312 proceed under mild conditions with absolute
chemoselectivity for Si−H versus Si−Si activation to give new
Si−O- and Si−S-containing substituents.11a,b In this communi-
cation we report the successful extension of this methodology
to chemoselective postpolymerization modification of poly-
(phenylsilane) to introduce thiolato side chains.
corresponding to the alkyl protons in these side chains, and
broadening and increased complexity in the aromatic region,
relative to the spectrum for the precursor poly(phenylsilane).
1
Integration of the alkyl and Si−H regions of the H NMR
spectra allows a crude estimation of the degree of Si−H
substitution: the modified polymers contain approximately
15−40% thiolato side chains.14 IR spectroscopy provides qualitative
confirmation of the partial replacement of Si−H bonds with Si−SR
fragments in the modified polysilanes: the intensity of the νSi−H band
at around 2100 cm−1 relative to the intensity of the νC−H band at
around 3000 cm−1 is diminished, relative to the spectrum for the
parent poly(phenylsilane). More critically, we observe weak
absorptions at approximately 490−500 cm−1 in spectra for the
SR-substituted polysilanes that are absent in spectra of the parent
polysilane. A similar low-frequency absorption was observed for
the S-substituted model disilane compound Ph2SiH-Si(STolp)Ph2
Addition of B(C6F5)3 to a mixture of poly(phenylsilane)13 and
either HSPrn or HSTolp in toluene caused immediate bubbling,
presumably due to evolution of hydrogen (Scheme 1, top).
The resulting modified polymers were isolated as white or off-white
solids, after trituration of the residues with either pentane or
hexanes. The incorporation of new n-propyl- or p-tolylthiolato
15,16
(Supporting Information). These are attributed to νSi−S
.
13C DEPT135 NMR also provides evidence for thiolato side-
chain incorporation in these modified polymers (Figure 2 and
Received: December 21, 2012
1
side chains in these polymers is evident from their H NMR
© XXXX American Chemical Society
A
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Organometallics
Communication
even with variation of the coupling constant and with long
acquisition times.
Scheme 1
Addition of B(C6F5)3 to a mixture of poly(phenylsilane) and
dark blue SCPh2 in toluene caused an immediate color
change to green (Scheme 1, bottom), corresponding to at least
partial reduction of the intensely colored thioketone via hydro-
silation. As for the dehydrocoupling products described above,
the resulting modified polymer was isolated as an off-white solid
after trituration of the green reaction residues with pentane.
Although its IR spectrum is consistent with partial replacement of
the Si−H bonds with SR fragments, this derivative proved more
1
difficult to analyze by H NMR, since the signal due to the
benzylic proton in the thiolato side chains overlaps with that due
to the residual Si−H bonds. This prevented us from estimating
the degree of Si−H substitution in the modified polymer. How-
ever, the overall broadening of peaks in this region and in the
aromatic region is consistent with a polymer structure relatively
similar to those obtained for the thiol dehydrocoupling derivatives
(Figure 4a). Although very weak,17 a broad signal for the benzylic
Figure 2. Alkyl region of the 75 MHz 13C DEPT135 NMR for (a) the
−SPrn modified polymer and (b) the −STolp modified polymer, in
d6-benzene.
Supporting Information). We see two distinct signals corre-
sponding to the CH2 groups α to sulfur in the n-propyl side
1
chains (confirmed by an H/13C HSQC experiment), which
suggests that two unique magnetic environments exist for the
SPrn groups along the modified chain and that the 13C chemical
shift difference falls off with distance from the Si−S bond. 29Si
DEPT90 NMR experiments (using 1JSi−H = 188 Hz) confirm the
persistence of unsubstituted Ph(H)Si repeat units in the back-
bone of the modified polymers (broad massif at −50 to −65 ppm
in Figure 3) and also apparently illustrate the presence of two
Figure 4. (a) 500 MHz 1H, (b) 75 MHz 13C DEPT135, and (c) 99 MHz
29Si DEPT90 NMR spectra of the −SCHPh2 modified polymer in
d6-benzene. The • denotes residual solvent proton signal, ⧧ denotes
△
diphenylmethane, and
denotes 1,1,2,2-tetraphenylethane.
carbon from the new side chains can be seen at ∼53 ppm in the
13C DEPT135 NMR (Figure 4b). Small, sharp signals in both the
1H and 13C NMR spectra of this polymer correspond to two side
products that result from “over-reduction” of the thiobenzo-
phenone in the borane-catalyzed hydrosilation reaction: diphenyl-
methane and 1,1,2,2-tetraphenylethane. We see these byproducts
even when the borane catalyst loading is reduced to 0.5%, at
which point the apparent degree of substitution of Si−H bonds is
very low. Analogous “CO to CH2” reduction chemistry has
previously been observed in B(C6F5)3-mediated reactions of
tertiary silane Si−H bonds with substrates containing carbonyl,
alcohol, and ether functionalities.18 Control reactions of
thiobenzophenone with PhSiH3, Ph2SiH2, and HPh2Si−SiPh2H
in the presence of borane catalyst show that a similar “over-
reduction” to diphenylmethane occurs rapidly and quantitatively
for the primary and secondary silanes, but not for the crowded
tertiary sym-disilane (Scheme 2).19 However, the disilane
hydrosilation product A does react rapidly with Ph2SiH2 in the
presence of borane to give diphenylmethane and the
Figure 3. 99 MHz 29Si DEPT90 NMR for (a) the −SPrn modified
polymer, (b) the −STolp modified polymer, and (c) the parent
poly(phenylsilane), in d6-benzene.
magnetically distinct thiolate-substituted end groups X−Si(H)SR,
where X = oligomer or polymer chains. These peaks between
−10 and −20 ppm have chemical shifts similar to peaks due to
the S-substituted silicons in our model disilanes (Supporting
Information) and are absent in the spectrum for the parent
poly(phenylsilane). Although long-range polarization transfer
3
experiments (29Si DEPT30, with JSi−H = 8 Hz corresponding
to the four Hortho protons on each SiPh2 unit) gave signals for
the quaternary, S-substituted silicons for samples of our model
disilane model compounds, Ph2SiH−SiPh2(SR) (Supporting
Information), similar experiments using the parent and modified
polymer samples (DEPT45 optimized for two Hortho protons on
each SiPh unit) showed no quaternary or tertiary silicon signals,
1
unsymmetric disilathiane B, as determined by H NMR (eq 1).
We conclude that the diphenylmethane observed in samples of
the hydrosilation-modified poly(phenylsilane) must be formed via
B
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Organometallics
Communication
Scheme 2
intramolecular “back-biting” reactions of unreacted end groups
−Si(Ph)H2 with internal −Si(Ph)(SCHPh2)−. This is consistent
with the drastically reduced intensity of signals due to −Si(Ph)-
(SCHPh2)H end groups from −10 to −20 ppm in 29Si DEPT90
spectra of samples of the thioketone-derivatized polymer (Figure
4c) and also with light-scattering MW data (vide infra) which are
too low to indicate intermolecular reactions leading to cross-linking.
Importantly, we see no evidence for Si−Si bond cleavage
reactions occurring during these polymer modifications. GC/
Figure 5. UV−visible absorption spectra of (i) the parent poly(phenylsilane)
and the (ii) −SPrn, (iii) −STolp, and (iv) −SCHPh2 modified polymers in
dichloromethane (0.1−0.3 mg/mL) at room temperature.
stored in the glovebox, again with no protection from ambient
light, show no degradation over months.
We are currently exploring the substrate scope for hetero-
dehydrocoupling and hydrosilation reactions of poly(phenylsilane)
using this mild and selective technique, with a view to introducing
a wider range of Si−element bonds including Si−O,22 Si−C,23 and
Si−N.24 These results, along with our exploration of the materials
properties of the resulting thin films, will be reported in due
course.
1
MS and H and 19F NMR analysis of the pentane or hexanes
washings of the crude polymers showed only B(C6F5)3, unreacted
sulfur substrate, or, in the case of the hydrosilation reaction,
diphenylmethane and 1,1,2,2-tetraphenylethaneno very low
MW silanes were detected, even at long GC elution times.20
MALS-GPC analysis (Table 1 and Supporting Information) shows
ASSOCIATED CONTENT
* Supporting Information
Text, figures, and a table giving experimental details and
selected spectroscopic and GPC data. This material is available
free of charge via the Internet at http://pubs.acs.org.
■
S
Table 1. Molecular Weight Data (in Da) Obtained from
Multi-Angle Light-Scattering (MALS) GPC for Multiple
Batches of Modified Polymers H−[SiHPh]n−[Si(SR)Ph)]m−H
a
SR
Mw
Mn
Mw/Mn
AUTHOR INFORMATION
Corresponding Author
*E-mail: lisarose@uvic.ca.
Notes
■
SCH2CH2CH3
SCH2CH2CH3
SC6H4CH3
6900 600
4500 100
5400 400
5000 <100
5100 100
5700 400
4000 300
2500 200
3400 200
3100 <100
2500 100
2600 300
1.7
1.8
1.6
1.6
2.0
2.2
b
SC6H4CH3
The authors declare no competing financial interest.
SCHPh2
SCHPh2
a
ACKNOWLEDGMENTS
Except where noted, the parent poly(phenylsilane) had Mw/Mn
■
(PDI) = 3500/2200 (1.6). Errors are standard deviations for triplicate
runs for each batch. The parent poly(phenylsilane) had Mw/Mn
(PDI) = 2600/1700 (1.5).
We thank the University of Victoria (Fellowship to P.T.K.L.)
and NSERC of Canada (Discovery Grant to L.R.) for funding,
the group of Derek Gates at UBC (Spencer Serin, Thomas
Hey, Paul Siu) for access to and training on their GPC
equipment, and Chris Barr for help with implementing NMR
experiments.
b
increased MWs for all three of the modified polymers. Slight
increases in polydispersity correspond to increases in intensity at
the higher rather than the low MW edge of the traces, which can
be attributed to a largely unchanged distribution of polymer back-
bones that has undergone nonuniform side-chain additions.
UV−vis absorptions of the modified polymers in solution
show bathochromic shifts relative to λmax ∼295 nm, observed
for the parent poly(phenylsilane) (Figure 5), consistent with
the (probably combined) effects of increased rigidity due to
replacement of Si−H groups with larger thiolate side chains
and the electronic contributions of the S heteroatoms on the
σ-conjugated polysilane backbone.2b Similar shifts were re-
ported by Waymouth7b and Shankar7d for Si−C and Si−O
modified poly(phenylsilanes). We have not yet investigated
with rigor the photostability of the new polymers but note that
spectra of NMR samples that are not protected from ambient
light remain unchanged over days to weeks.21 Also, solid samples
REFERENCES
■
(1) Recent reports include: (a) Klausen, R. S.; Widawsky, J. R.;
Steigerwald, M. L.; Venkataraman, L.; Nuckolls, C. J. Am. Chem. Soc.
2012, 134, 4541. (b) Wang, Q.; Lu, H.; Gai, L.; Chen, W.; Lai, G.; Li,
Z. Dyes Pigm. 2012, 94, 183. (c) Chung, W.; Shibaguchi, H.; Terao, K.;
Fujiki, M.; Naito, M. Macromolecules 2011, 44, 6568. (d) Feigl, A.;
Bockholt, A.; Weis, J.; Rieger, B. Adv. Polym. Sci. 2011, 235, 1.
(e) Nemec, H.; Kratochvilova, I.; Kuzel, P.; Sebera, J.; Kochalska, A.;
Nozar, J.; Nespurek, S. Phys. Chem. Chem. Phys. 2011, 13, 2850.
(f) Ostapenko, N.; Vodolazkyy, P.; Peckus, D.; Gulbinas, V.;
Moiseenko, V.; Surovtseva, N.; Suto, S.; Watanabe, A. Mol. Cryst.
Liq. Cryst. 2011, 536, 41. (g) Semenov, V. V. Russ. Chem. Rev. 2011,
80, 313. (h) Deepak; Banerjee, N.; Seki, S. J. Appl. Phys. 2010, 107,
124513/1. (i) Dostie, S.; Aktik, C.; Scarlete, M. Macromol. Containing
Met. Met.-Like Elem. 2010, 10, 205.
C
dx.doi.org/10.1021/om301246z | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Communication
(2) (a) Bande, A.; Michl, J. Chem. Eur. J. 2009, 15, 8504. (b) Miller,
R. D.; Michl, J. Chem. Rev. 1989, 89, 1359.
(3) (a) Hill, M. S. Struct. Bond. 2010, 136, 189. (b) Chatgilialoglu, C.;
Guerrini, A.; Lucarini, M.; Pedulli, G. F.; Carrozza, P.; Da Roit, G.;
Borzatta, V.; Lucchini, V. Organometallics 1998, 17, 2169.
procedure7b (see the Supporting Information). This method gives
mixtures of linear polysilane and cyclic oligomers.
(14) The breadth of signals in the 1H NMR spectra have not allowed
us to gauge whether the cyclic or linear portions of the polymer are
more highly substituted, but we are currently investigating the impact
of higher catalyst loadings on the overall degrees of Si−H substitution
in the modified polymers. The current reaction conditions (details in
the Supporting Information) were those established previously,11 using
catalyst loadings optimized for the modification of sym-tetraphenyldi-
silane, in which the Si−H bonds are quite sterically hindered. The
borane catalyst can be used in nonpolar hydrocarbons and
dichloromethane but not in strongly coordinating solvents; the
solubility of poly(phenylsilane) dictated our choice of toluene here.
Control reactions carried out on an NMR scale confirm that no Si−H
transformations occur in the absence of catalyst, even with heating up
to 70 °C.
(4) Corey, J. Y. Adv. Organomet. Chem. 2004, 51, 1.
(5) (a) Marciniec, B. Comprehensive Handbook on Hydrosilation;
Pergamon Press: Oxford, U.K., 1992. (b) Marciniec, B., Hydrosilation:
A Comprehensive Review on Recent Advances. Springer: 2008.
(6) Koe, J. Polym. Int. 2008, 58, 255.
(7) Waymouth prepared functionalized polysilanes by radical-
induced halogenation7a and hydrosilation reactions7b of Si−H bonds
in poly(arylsilanes). The latter method (∼10 mol % AIBN @ ≥90°
gives 50−90% substitution of Si−H bonds) serves as a benchmark for
the variety of polysilane derivatives it has been used to prepare (e.g.
refs 7c−e). Harrod7f and Woo7g,h both reported metallocene-catalyzed
dehydropolymerization reactions of arylsilanes in which heterodehy-
drocoupling of Si−H bonds with added alcohols or ammonia provides
one-pot routes to alkoxy- and amino-substituted poly(arylsilanes), and
Harrod reported the incorporation of pendant cyclohexyl groups when
using cyclohexene as a hydrogen acceptor during the titanocene-
mediated dehydropolymerization of phenylsilane.7i Tanaka used AlCl3-
catalyzed hydrosilation of alkynes and alkenes to modify oligosilanes
with Si−H repeat units.7j (a) Banovetz, J. P.; Hsiao, Y. L.; Waymouth,
R. M. J. Am. Chem. Soc. 1993, 115, 2540. (b) Hsiao, Y.-L.; Waymouth,
R. M. J. Am. Chem. Soc. 1994, 116, 9779. (c) Beach, J. V.; Loy, D. A.;
Hsiao, Y. L.; Waymouth, R. M. ACS Symp. Ser. 1995, 614, 355.
(d) Shankar, R.; Joshi, A. J. Organomet. Chem. 2006, 691, 3310.
(e) Shankar, R.; Shahi, V. J. Organomet. Chem. 2008, 693, 307. (f) Liu,
H. Q.; Harrod, J. F. Organometallics 1992, 11, 822. (g) Kim, B. H.;
Cho, M. S.; Kim, M. A.; Woo, H. G. J. Organomet. Chem. 2003, 685,
93. (h) Kim, B.-H.; Woo, H.-G. Adv. Organomet. Chem. 2005, 52, 143.
(i) Harrod, J. F. ACS Symp. Ser. 1988, 360, 89. (j) Kato, N.; Tamura,
Y.; Kashiwabara, T.; Sanji, T.; Tanaka, M. Organometallics 2010, 29,
5274.
(8) Stoichiometric modification of poly(methylphenylsilane) by
acetyl chloride/AlCl3 converts Si−Ph to reactive Si−Cl: (a) Tang,
H.; Liu, Y.; Huang, B.; Qin, J.; Fuentes-Hernandez, C.; Kippelen, B.;
Li, S.; Ye, C. J. Mater. Chem. 2005, 15, 778. (b) Herzog, U.; West, R.
Macromolecules 1999, 32, 2210. There is some debate over the
chemoselectivity of a comparable transformation (Si−Ph to Si−OTf)
using triflic acid: (c) Corey, J. Y.; Kraichely, D. M.; Huhmann, J. L.;
Braddock-Wilking, J.; Lindeberg, A. Organometallics 1995, 14, 2704.
(d) Uhlig, W. Prog. Polym. Sci. 2002, 27, 255.
(9) For example, Sacarescu has functionalized Si−H-containing
copolymers via platinic acid-catalyzed hydrosilation of alkenes9a but
notes facile competing chemical degradation at the Si−H-containing
repeat units in these polymers.9b,c (a) Sacarescu, L.; Ardeleanu, R.;
Sacarescu, G.; Simionescu, M. High Perform. Polym. 2007, 19, 510.
(b) Sacarescu, L.; Siokou, A.; Sacarescu, G.; Simionescu, M.;
Mangalagiu, I. Macromolecules 2008, 41, 1019. (c) Simionescu, M.;
Sacarescu, L.; Sacarescu, G. Des. Monomers Polym. 2012, 15, 127.
References 8a,b report Si−Si bond cleavage during AlCl3-mediated Si−
Ph modification chemistry. The sensitivity of Si−H units in
poly(hydrosilanes) to radical cleavage reactions has been described
by Chatgiliologlu.3b
(15) These correspond with νSi−S values previously reported for
disilthianes in the gas phase. Drake, J. E.; Glavincevski, B. M.;
Hemmings, R. T. Can. J. Chem. 1980, 58, 2161.
(16) Elemental analyses also confirm the presence of S in these
modified polymers (see the Supporting Information).
(17) The difficulty in observing the 13C signal due to the benzylic
carbon in the −SCHPh2 polymer can be rationalized on the basis of
poor polarization transfer from the single attached proton, relative to
the −CH3 in the −STolp polymer and the α-CH2 in the −SPrn
polymer, as well as the lower solubility of this polymer in d6-benzene
relative to the other polymers. In addition, we have determined that at
least some of the −SCHPh2 side chains in this polymer undergo a side
reaction in the presence of the borane catalyst (vide infra).
(18) See ref 12 and: (a) Bajracharya, G. B.; Nogami, T.; Jin, T.;
Matsuda, K.; Gevorgyan, V.; Yamamoto, Y. Synthesis 2004, 308.
(b) Gevorgyan, V.; Rubin, M.; Benson, S.; Liu, J.-X.; Yamamoto, Y. J.
Org. Chem. 2000, 65, 6179. These references do not, however, report
C−C bond coupling of liberated benzylic fragments to give 1,1,2,2-
tetraphenylethane, and we do not observe this product in control
reactions of the thioketone with discrete mono- and disilanes. We do
not yet understand why it forms in the polymer hydrosilation
reactions.
(19) This sensitivity of the rates of Si-H activation mediated by
B(C6F5)3 to increased steric hindrance at silicon is general11a,c,12 and
precludes a possible one-pot synthesis of the modified polymers
directly from phenylsilane and S-containing substrates using combined
Zr and borane catalysts: the Si−H bonds in phenylsilane react much
faster with S-substrates than those in the polymer, which competes
with the dehydropolymerization. A sequential, as opposed to
simultaneous, one-pot synthesisi.e. adding borane and S-substrate
directly to the already polymerized mixtureis an appealing
alternative but also presents challenges, since solvent must be added.
In solution, in the presence of Zr catalyst, the linear poly(phenylsilane)
chains undergo significant decomposition to cyclic oligomers.4
(20) The SPrn-modified polymer is slightly soluble in these nonpolar
1
organics. H NMR of these washings showed weak signals identical
with those for the bulk, isolated polymer.
(21) An exception is the −SPrn-modified polymer, for which NMR
samples eventually show small amounts of HSPrn attributable to the
hydrolysis of Si−S bonds by trace moisture.
(22) (a) Parks, D. J.; Piers, W. E. J. Am. Chem. Soc. 1996, 118, 9440.
(b) Blackwell, J. M.; Foster, K. L.; Beck, V. H.; Piers, W. E. J. Org.
Chem. 1999, 64, 4887.
(23) Rubin, M.; Schwier, T.; Gevorgyan, V. J. Org. Chem. 2002, 67,
1936.
(10) Little or no Si−Si bond cleavage (or diminished MWs) was
reported in refs 7b−e,7g,7h, and the modified polysilanes described in
refs 7b−e give GPC and UV−vis data consistent with reasonable
degrees of polymerization.
(11) (a) Harrison, D. J.; Edwards, D. R.; McDonald, R.; Rosenberg,
L. Dalton Trans. 2008, 3401. (b) Harrison, D. J.; McDonald, R.;
Rosenberg, L. Organometallics 2005, 24, 1398. (c) Harrison, D. J.
M.Sc. Thesis, University of Victoria, Victoria, British Columbia, 2005.
(12) Piers, W. E.; Marwitz, A. J. V.; Mercier, L. G. Inorg. Chem. 2011,
50, 12252.
(24) Blackwell, J. M.; Sonmor, E. R.; Scoccitti, T.; Piers, W. E. Org.
Lett. 2000, 2, 3921.
(13) We prepared the parent polymer by zirconocene-mediated
dehydrocoupling of phenylsilane,4 using a slightly modified literature
D
dx.doi.org/10.1021/om301246z | Organometallics XXXX, XXX, XXX−XXX