Bis(o-phosphinophenyl)silane as a scaffold for dynamic behavior of H-Si and C-Si bonds with palladium(0)

Article abstract of DOI:10.1021/om900874p

Synthesis and structural analysis of an unprece-dented η²- Si-H complex of mononuclear Pd(0) was achieved utilizing bis(o-phosphinophenyl) silane as a PSiP pincer-type scaffold for the first time. This complex showed dynamic behavior in its reaction with an allene, involving a reversible oxidative addition/reductive elimination sequence of a C(sp³)-Si bond at room temperature. This system will be useful as a synthetic equivalent of highly reactive hydrido- and (σ-allyl)palladium species.

Full text of DOI:10.1021/om900874p

6636 Organometallics 2009, 28, 6636–6638
DOI: 10.1021/om900874p
Bis(o-phosphinophenyl)silane as a Scaffold for Dynamic Behavior
of H-Si and C-Si Bonds with Palladium(0)
Jun Takaya and Nobuharu Iwasawa*
Department of Chemistry, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8551, Japan
Received October 8, 2009
Summary: Synthesis and structural analysis of an unprece-
dented η2-Si-H complex of mononuclear Pd(0) was achieved
utilizing bis(o-phosphinophenyl)silane as a PSiP pincer-type
scaffold for the first time. This complex showed dynamic
behavior in its reaction with an allene, involving a rever-
sible oxidative addition/reductive elimination sequence of a
C(sp3)-Si bond at room temperature. This system will be
useful as a synthetic equivalent of highly reactive hydrido- and
(σ-allyl)palladium species.
Pd(0) complexes has been reported, even though these low-
valent metals are well recognized as practical catalysts for
various hydrosilylation reactions.3-5 Herein we report the
first synthesis and structural analysis of a η2-Si-H complex
of mononuclear Pd(0) and its dynamic behavior with an allene
through an oxidative addition/insertion/reductive elimination
sequence utilizing a PSiP pincer-type structure.
Our recent finding of the PSiP pincer-type palladium com-
plex catalyzed hydrocarboxylation of allenes under 1 atm of
CO2 prompted us to synthesize a possible key intermediate, the
silyl pincer-type palladium hydride A, for detailed mechanistic
studies.6 When bis(o-(diphenylphosphino)phenyl)methylsilane
(1)7 was treated with an equimolar amount of Pd(PPh3)4 in
THF at room temperature, the complex obtained was not the
expected palladium hydride A but the (η2-Si-H)Pd0 species 2
with a Si-H σ-bond coordinated to Pd(0) along with one
PPh3 and the two phosphorus atoms of 1 (Scheme 1, conditions
a). Complex 2 was also obtained in 86% yield by the reaction of
1 with CpPd(C3H5) in the presence of PPh3 (conditions b).
The ORTEP diagram of 2 is shown in Figure 1. The structure
around Pd is distorted tetrahedral, and the Si-H, Pd-H, and
The studies of η2-Si-H complexes have been attracting much
attention, since they can provide deeper mechanistic insight
into transition-metal-catalyzed silylation reactions involving
oxidative addition of the Si-H bond, in which such σ com-
plexes can be considered as “frozen intermediates”.1 However,
the synthesis and structural characterization of such η2-Si-H
metal complexes of the Ni triad remains mostly unexplored
because of their high reactivity toward oxidative addition to
give silyl metal hydride complexes (H-M-Si),2 and no
structural analysis of zerovalent, mononuclear η2-Si-H
*To whom correspondence should be addressed. E-mail: niwasawa@
chem.titech.ac.jp.
(1) (a) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151. (b) Crabtree,
R. H. Angew. Chem., Int. Ed. 1993, 32, 789. (c) Schneider, J. J. Angew. Chem.,
Int. Ed. 1996, 35, 1068. (d) Kubas, G. J. J. Organomet. Chem. 2001, 635, 37.
(e) Lin, Z. Chem. Soc. Rev. 2002, 31, 239.
˚
Pd-Si distances are 1.60(3), 1.67(3), and 2.4283(8) A, respec-
tively.8 The Si-H distance is obviously longer than that of the
˚
parent silane (∼1.5 A) but relatively shorter compared to typical
(2) For examples of oxidative addition of the H-Si bond to
group 10 metals to give silyl metal complexes, see: (a) Corey, J. Y.;
Braddock-Wilking, J. Chem. Rev. 1999, 99, 175 and references therein.
(b) Shimada, S.; Tanaka, M. Coord. Chem. Rev. 2006, 250, 991. (c) Iluc,
V. M.; Hillhouse, G. L. Tetrahedron 2006, 62, 7577. (d) Steinke, T.; Gemel,
C.; Cokoja, M.; Winter, M.; Fischer, R. A. Angew. Chem., Int. Ed. 2004, 43,
2299. (e) Boyle, R. C.; Pool, D.; Jacobsen, H.; Fink, M. J. J. Am. Chem. Soc.
2006, 128, 9054.
(6) Takaya, J.; Iwasawa, N. J. Am. Chem. Soc. 2008, 130, 15254.
(7) For the synthesis of 1 and 3, see: MacInnis, M. C.; MacLean,
D. F.; Lundgren, R. J.; McDonald, R.; Turculet, L. Organometallics
2007, 26, 6522.
(8) Synthesis of 2 by the reaction of 1 with Pd(PPh3)4: bis-
(o-(diphenylphosphino)phenyl)methylsilane (1; 113 mg, 0.199 mmol)
and Pd(PPh3)4 (230 mg, 0.199 mmol) were mixed in THF (10 mL), and
the mixture was stirred for 30 min at room temperature. After removal of
solvent under reduced pressure, the resulting solid was washed with ether
twice and recrystallized from THF-pentane at -30 °C to give the
(η2-Si-H)Pd0 complex 2 (131 mg, 0.140 mmol) as a pale yellow crystal-
line solid in 70% yield. IR (KBr): 3051, 1584, 1478, 1433, 1102, 1090
(3) Syntheses of η2-Si-H complexes stabilized by dinuclear struc-
tures involving Pt-Pt, Pt-Pd, and Pd-Pd have been reported:
(a) Auburn, M.; Ciriano, M.; Howard, J. A. K.; Murray, M.; Pugh,
N. J.; Spencer, J. L.; Stone, F. G. A.; Woodward, P. J. Chem. Soc.,
Dalton Trans. 1980, 659. (b) Kim, Y.-J.; Lee, S.-C.; Park, J.-I.; Osakada, K.;
Choi, J.-C.; Yamamoto, T. Organometallics 1998, 17, 4929. (c) Tanabe, M.;
Yamada, T.; Osakada, K. Organometallics 2003, 22, 2190. (d) Nakajima, S.;
Sumimoto, M.; Nakao, Y.; Sato, H.; Sakaki, S.; Osakada, K. Organometal-
lics 2005, 24, 4029. (e) White, C. P.; Braddock-Wilking, J.; Corey, J. Y.; Xu,
H.; Redekop, E.; Sedinkin, S.; Rath, N. P. Organometallics 2007, 26, 1996
and references therein. (f) Tanabe, M.; Ito, D.; Osakada, K. Organometallics
2008, 27, 2258 and references therein.
1
cm-1. H NMR (benzene-d6, 500 MHz, 300 K): δ 0.25 (1H, tdq, J =
34.9, 7.6, 2.3 Hz), 1.33 (3H, d, J = 2.3 Hz), 6.70-7.00 (27H, m), 7.10
(2H, t, J = 7.8 Hz), 7.28-7.33 (2H, m), 7.35-7.51 (10H, m), 7.94 (2H, d,
J = 7.4 Hz). 13C NMR (THF-d8, 125 MHz, 300 K): δ 5.8 (t, J = 7.6 Hz),
127.9, 128.2 (t, J = 8.6 Hz), 128.30 (t, J = 4.4 Hz), 128.33, 128.4 (t, J =
3.8 Hz), 128.5, 128.9, 129.1, 132.5, 132.9 (t, J = 7.0 Hz), 133.3 (t, J =
8.4 Hz), 133.7 (t, J = 12.1 Hz), 134.9 (d, J = 16.3 Hz), 139.0 (t, J =
3.8 Hz), 139.2 (t, J = 6.8 Hz), 140.6 (t, J = 13.3 Hz), 146.5 (td, J = 15.9,
8.6 Hz), 155.8 (td, J = 38.9, 8.4 Hz); 31P{1H} NMR (benzene-d6,
202 MHz, 300 K): δ 32.4 (1P, t, J = 8.1 Hz), 36.3 (2P, d, J = 8.1 Hz).
29Si NMR (THF-d8, 100 MHz): 300 K, δ -1.11 (br d, J = 77 Hz (1H
decoupled); brdd, J = 110, 77 Hz (non 1H decoupled)); 193 K, δ 3.01 (br
d, J = 81 Hz (1H-decoupled); br dd, J = 97, 81 Hz (non 1H decoupled)).
Anal. Calcd for C55H47P3PdSi: C, 70.62; H, 5.06. Found: C, 70.84; H,
5.32. Crystal data for 2: the hydrogen bound to Si was located in the final
difference map and refined isotropically, C55H47P3PdSi, fw = 935.33,
(4) The synthesis and X-ray analysis of a mononuclear η2-Si-H
complex of Ni(II) have been reported: (a) Chen, W.; Shimada, S.;
Tanaka, M.; Kobayashi, Y.; Saigo, K. J. Am. Chem. Soc. 2004, 126,
8072. Recently, Turculet and co-workers reported the synthesis of a η2-Si-H
coordinated Pt(0) complex, which was structurally identified by NMR, IR,
and low-resolution X-ray analysis; however, an exact X-ray structure analysis
was not reported: (b) Mitton, S. J.; McDonald, R.; Turculet, L. Organo-
metallics 2009, 28, 5122.
(5) (a) Ball, Z. T. In Comprehensive Organometallic Chemistry III;
Ojima, I., Ed.; Elsevier: Oxford, U.K., 2007; Vol. 10, p 789. (c) Makabe,
H.; Negishi, E.; In Organopalladium Chemistry; Negishi, E., Ed.; Wiley:
New York, 2002; Vol. 2, p 2789.
˚ ˚
monoclinic, space group P21/c, a = 16.617(6) A, b = 10.690(4) A, c =
3
25.340(8) A, β = 93.252(12)°, V = 4494(3) A , Z= 4, Dcalcd = 1.382 g/cm3,
temperature -123 °C, μ(MoKR) = 5.84 cm-1, R1 = 0.0326, wR2 = 0.0744
for 8418 reflections with I > 2σ(I).
˚
˚
r
pubs.acs.org/Organometallics
Published on Web 11/11/2009
2009 American Chemical Society

Communication
Scheme 1. Synthesis of (η2-Si-H)Pd0 Complex 2a
Organometallics, Vol. 28, No. 23, 2009 6637
Scheme 2. Catalytic Hydrocarboxylation of an Allene using 2
a Conditions: (a) 1.0 equiv of Pd(PPh3)4, THF, room temperature,
30 min; (b) 1.0 equiv of PPh3, 1.0 equiv of CpPd(C3H5), Et2O-THF,
room temperature, 20 min.
Scheme 3. Formation of 2 from PSiP Pincer-Type Pd(II)
Scheme 4. Reaction of (η2-Si-H)Pd0 2 with an Allene
Figure 1. ORTEP plot of 2 (disorder of one of the Ph rings on P2
was observed) at the 50% probability level (hydrogen atoms except
Si-Hare omitted for clarity). Selected bond lengths (A) and angles
(deg): Si-H, 1.60(3); Pd-H, 1.67(3); Pd-Si, 2.4283(8); Pd-P1,
2.4425(8); Pd-P2, 2.3776(8); Pd-P3, 2.4140(8); Si-H-Pd,
95.8(15); H-Pd-Si, 40.9(10); Pd-Si-H, 43.3(10); P1-Pd-P2,
109.63(3); P2-Pd-P3, 120.49(3); P3-Pd-P1, 104.59(3).
pincer palladium chloride 3 with LiBHEt3 in the presence of
1.0 equiv of PPh3 afforded 2in 90% yield (Scheme 3). Thus, 2and
Aappear to interconvert at room temperature, and the significant
point is that the reductive elimination (RE) of the Si-H bond to
give η2-Si-H complex 2 is more favorable than its reverse
pathway, even with the weak and easily cleaved Si-H bond. It
is likely that the PSiP linkage of A constrained by benzene rings
makes the pincer-type square planar structure rather strained,
thus facilitating reductive elimination and relatively stabilizing the
(η2-Si-H)Pd0 structure.
˚
values of previously reported η2-Si-H complexes (∼1.6-
1.9 A),1a,e suggesting weak back-donation from the metal center
˚
to the σ* orbital of the Si-H bond. The structure in solution was
confirmed to be the same (η2-Si-H)Pd0 by measurement of
various NMR spectra of 2 between 300 and 193 K. The H
1
NMR spectrum in benzene-d6 at 300 K exhibited an upfield shift of
the hydrogen atom on Si at 0.16 ppm, which is coupled with three
phosphorus atoms (td, JHP = 34.9, 7.6 Hz) and with the methyl
(10) Synthesis of 4: to a stirred solution of the (η2-Si-H)Pd0 complex
2 (94 mg, 0.10 mmol) in THF (1.0 mL) was added 3-methyl-1,2-
butadiene (20 μL, 0.20 mmol) at room temperature. The solution turned
red immediately and then yellow within 1 min. After 10 min, the solution
was layered with pentane and allowed to stand at -30 °C to give the
triphosphine Pd(0) complex 4 (72 mg, 0.072 mmol) in 72% yield, which
was suitable for X-ray analysis. The complex 4 exists as a mixture of two
conformational isomers in solution. IR (KBr): 3048, 1583, 1476, 1432,
847, 830 cm-1. 1H NMR (THF-d8, 500 MHz, 253 K): δ 0.30 (2.1H, s),
1.00 (0.9H, s), 1.02 (2.1H, s), 1.33 (0.9H, s), 1.49 (0.9H, s), 1.53 (2.1H, s),
1.97 (0.6H, d, J = 7.8 Hz), 2.69 (1.4H, d, J = 8.0 Hz), 4.74 (0.7H, t, J =
8.0 Hz), 4.87 (0.3H, t, J = 7.8 Hz), 6.52-6.56 (1.4H, m), 6.60-6.65
(0.6H, m), 6.82-7.22 (39H, m), 7.44 (1.4H, d, J = 7.4 Hz), 7.62 (0.6H, d,
J = 7.4 Hz). 13C NMR (THF-d8, 125 MHz, 253 K): δ 0.45, 3.44 (t, J =
10.3 Hz), 18.0, 18.1, 21.4, 22.2 (t, J = 10.6 Hz), 26.1, 26.6, 121.2, 121.9,
127.6, 127.8, 128.2 (t, J = 4.0 Hz), 128.3 (t, J = 4.0 Hz), 128.5-129.0
(m), 129.6, 130.0, 133.9, 134.0, 136.3-134.8 (m), 136.9 (t, J = 7.8 Hz),
137.4 (t, J = 7.8 Hz), 138.5 (t, J = 11.3 Hz), 138.9 (t, J = 11.3 Hz), 140.3
(t, J = 4.1 Hz), 140.5 (t, J = 4.0 Hz), 142.2 (t, J = 13.1 Hz), 142.9 (t, J =
12.8 Hz), 144.9 (t, J = 18.9 Hz), 145.1 (t, J = 18.9 Hz), 146.7-147.0 (m),
147.1-147.4 (m). 31P NMR (THF-d8, 102 MHz, 253 K): δ 17.0 (1.4P, d,
J = 82 Hz), 17.5 (0.6P, d, J = 82 Hz), 23.9 (0.7P, t, J = 82 Hz), 24.3
(0.3P, t, J = 82 Hz). 29Si{1H} NMR (THF-d8, 100 MHz, 253 K): δ -8.51
(t, J = 7.5 Hz). Anal. Calcd for C60H55P3PdSi: C, 71.81; H, 5.52. Found:
C, 71.80; H, 5.81. Crystal data for 4: C60H55P3PdSi, fw = 1003.44,
1
protons (q, JHH = 2.3 Hz, cf. JHH = 3.8 Hz in 1). The JHSi
coupling constant (JHSi = 110 Hz at 300 K, 97 Hz at 193 K) which
1
was observed by non H-decoupled 29Si NMR was larger than
typical values found for H-M-Si complexes (<∼20 Hz) but
significantly decreased from that of 1itself (JHSi = 204 Hz), clearly
1
supporting the η2-Si-H structure.9 This relatively larger JHSi
coupling constant suggests a weak interaction between the Pd(0)
and Si-H bond in solution, as was observed in the crystalline state.
This observation is in sharp contrast to the (η2-Si-H)NiII complex
reported by Shimada and Tanaka, which afforded a H-NiIV-Si
structure as the most stable form at 193 K in solution.4
This (η2-Si-H)Pd0 complex 2 was found to be an active
catalyst in the hydrocarboxylation of an allene under the reported
conditions as shown in Scheme 2,6 suggesting that 2 can function
as a synthetic equivalent of reactive palladium hydride intermedi-
ate A through dissociation of PPh3 and oxidative addition (OA)
of the Si-H bond in solution. Moreover, reduction of the PSiP
˚
˚
triclinic, space group P1, a = 12.462(3) A, b = 12.602(3) A, c =
˚
16.283(3) A, R = 78.139(9)°, β = 84.032(11)°, γ = 79.523(9)°, V =
1
3
(9) The JHSi coupling constants of (η2-Si-H)metal complexes are
2455.0(9) A , Z = 2, Dcalcd = 1.357 g/cm3, temperature -123 °C, μ(Mo
˚
usually in the range of 40-70 Hz.1,2a See also: Schubert, U.; Gilges, H.
Organometallics 1996, 15, 2373and references therein.
KR) = 5.40 cm-1, R1 = 0.0743, wR2 = 0.0712 for 2643 reflections with
I > 2σ(I).

6638 Organometallics, Vol. 28, No. 23, 2009
Takaya and Iwasawa
We next carried out the detailed investigation of each step
of the hydrocarboxylation of an allene using the (η2-Si-H)Pd0
complex 2 and found a facile dynamic behavior involving the
C(sp3)-Si bond, which is more robust and less reactive toward
oxidative addition with Pd(0) than the H-Si bond. Thus,
reaction of 2 with a stoichiometric amount of 3-methyl-1,
2-butadiene in benzene at room temperature immediately
afforded the tris(phosphine) Pd(0) complex 4, bearing an allylsi-
lane moiety, in 72% yield (Scheme 4). The structure of 4 was
determined by X-ray analysis, as depicted in Figure 2.10 The
reaction was thought to proceed through hydropalladation of
the allene with palladium hydride A generated in situ from 2 to
afford the PSiP pincer-type prenylpalladium complex B, fol-
lowed by reductive elimination of the C(sp3)-Si bond and
coordination of PPh3 to give 4. The prenylpalladium complex
B was prepared in situ by an independent route, including the
reaction of palladium chloride 3with prenylmagnesium chloride.
Addition of PPh3 to an equimolar amount of complex B resulted
in immediate reductive elimination to give complex 4.11,12
been recognized to be rather difficult and very few examples are
known,13-16 this system demonstrates the high utility of PSiP
pincer structures based on the bis(o-phosphinophenyl)silyl
ligand for efficient activation of the C-Si bond.
Scheme 5. Carboxylation of 4 via Oxidative Addition of a
C-Si Bond
Scheme 6. Equilibrium between 4 and B in the Presence
of Ni(cod)2
In conclusion, the synthesis of a (η2-Si-H)Pd0 complex and its
dynamic behavior through the reaction with an allene was dis-
closed, utilizing a bis(o-phosphinophenyl)silyl ligand as a PSiP
pincer-type scaffold. Facile, reversible oxidative addition/reductive
elimination of H-Si and C(sp3)-Si bonds with Pd(0) was
achieved in this system, leading to useful synthetic equivalents of
highly reactive hydrido- and (σ-allyl)palladium species. Studies on
the detailed mechanism of the dynamic behavior are in progress.
Acknowledgment. This research was partly supported
by a Grant-in-Aid for Scientific Research from the Min-
istry of Education, Culture, Sports, Science, and Tech-
nology of Japan. We thank Prof. Hidehiro Uekusa and
Ms. Sachiyo Kubo for performing X-ray analysis.
Supporting Information Available: Text and CIF files giving
preparative methods, spectral and analytical data, and crystallo-
graphic data for 2 and 4. This material is available free of charge via
the Internet at http://pubs.acs.org.
Figure 2. ORTEP plot of 4 at the 50% probability level
(hydrogen atoms except allylic protons are omitted for clarity).
Selected bond lengths (A) and angles (deg): Pd-P1, 2.288(3);
Pd-P2, 2.303(2); Pd-P3, 2.325(3); P1-Pd-P2, 123.02(10);
P2-Pd-P3, 115.68(10); P3-Pd-P1, 119.09(9).
˚
(13) Oxidative addition of the C(sp3)-Si bond has been mostly
limited to those in strained small rings, in dinuclear metal complexes,
and in systems that could be regarded as R- or β-carbon elimination:
(a) Tanaka, Y.; Yamashita, H.; Shimada, S.; Tanaka, M. Organo-
metallics 1997, 16, 3246. (b) Hendriksen, D. E.; Oswald, A. A.; Ansell,
G. B.; Leta, S.; Kastrup, R. V. Organometallics 1989, 8, 1153. (c) Thomson,
S. K.; Young, G. B. Organometallics 1989, 8, 2068. (d) Hofmann, P.; Heiss,
H.; Neiteler, P.; M€uller, G.; Lachmann, J. Angew. Chem., Int. Ed. 1990, 29,
880. (e) Koloski, T. S.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 1990,
112, 6405. (f) Shelby, Q. D.; Lin, W.; Girolami, G. S. Organometallics 1999,
18, 1904 and references therein. (g) Akita, M.; Hua, R.; Oku, T.; Tanaka, M.;
Moro-oka, Y. Organometallics 1996, 15, 4162. (h) Ong, C. M.; Burchell,
T. J.; Puddephatt, R. J. Organometallics 2004, 23, 1493.
More interestingly, when complex 4 was stirred under 1 atm
of CO2 in THF at room temperature for 24 h, allylation of CO2
proceeded to give 2,2-dimethyl-3-butenoic acid (5) in 45% yield
after acidic hydrolysis (Scheme 5). Regeneration of B from 4
was actually observed in the ratio 4:B = ca. 10:1 by 1H and 31
P
NMR when 2 equiv of Ni(cod)2 was added to a THF-d8
solution of 4 as a phosphine scavenger (Scheme 6). Thus, facile,
reversible oxidative addition and reductive elimination of an
C(sp3)-Si bond with Pd(0) was obviously realized at room
temperature. As oxidative addition of a C(sp3)-Si bond has
(14) For examples of allyl transfer to Pd(II) via transmetalation, see:
Denmark, S. E.; Werner, N. S. J. Am. Chem. Soc. 2008, 130, 16382 and
references therein.
(11) The preparation of B and its structural analysis by 1H, 31P, and
29Si NMR are described in the Supporting Information.
(15) For catalytic reactions via oxidative addition of a C(sp3)-Si
bond, see: (a) Takeyama, Y.; Nozaki, K.; Matsumoto, K.; Oshima, K.;
Utimoto, K. Bull. Chem. Soc. Jpn. 1991, 64, 1461. (b) Hirano, K.;
Yorimitsu, H.; Oshima, K. Org. Lett. 2008, 10, 2199. (c) Hirano, K.;
Yorimitsu, H.; Oshima, K. Chem. Commun. 2008, 3234. (d) Yamashita,
H.; Tanaka, M.; Honda, K. J. Am. Chem. Soc. 1995, 117, 8873. (e) Palmer,
W. S.; Woerpel, K. A. Organometallics 1997, 16, 4824.
(12) The formation of 4 from B apparently involves coupling of the two
ligands at the trans position of the square-planar complex. This type of reaction
is not common, and further computational studies on the mechanism are in
progress. For examples of coupling reactions involving sp3 carbon ligands at the
central atom of tridentate pincer ligands in Ni triad metal complexes, see: (a)
Albrecht, M.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2001,123, 7233. (b)
Madison, B. L.; Thyme, S. B.; Keene, S.; Williams, B. S. J. Am. Chem. Soc.
2007, 129, 9538. (c) Steinke, T.; Shaw, B. K.; Jong, H.; Patrick, B. O.; Fryzuk,
M. D.; Green, J. C. J. Am. Chem. Soc. 2009, 131, 10461. See also ref 4b.
(16) Duringthepreparationofthispaper, structuralrearrangementofNi
and Pd silyl pincer complexes that involves C(sp3)-Si and C(sp2)-Si bond
activation was reported by Turculet and co-workers: Milton, S. J.;
McDonald, R.; Turculet, L. Angew. Chem., Int. Ed. 2009, 48, 8568.