Intramolecular aromatic C-H bond activation by a silylene ligand in a methoxy-bridged bis(silylene)-ruthenium complex

Article abstract of DOI:10.1021/om970408d

When a solution of Cp(Ph₃P)Ru{SiMe₂?O-(Me)?SiMe₂} (1; Cp = η⁵-C₅H₅) and a two-electron-donating ligand L was heated at 130 °C, a C-H bond of a phenyl group was activated by the Ru=Si double bond, and the complexes CpLRuSiMe₂(o-C₆H₄PPh₂) (2a, L = PPTi₃; 2b, L = PMe₃; 2c, L = PEt₃ 2d, L = P(OMe)₃; 2e, L = ^tBuNC) were obtained. Heating 1 in the absence of a ligand at 130 °C gave CpRuSiMe₂(o-C₆H₄PPh₂)-(H)(SiMe ₂OMe) (3).

Full text of DOI:10.1021/om970408d

3870
Organometallics 1997, 16, 3870-3872
In tr a m olecu la r Ar om a tic C-H Bon d Activa tion by a
Silylen e Liga n d in a Meth oxy-Br id ged
Bis(silylen e)-Ru th en iu m Com p lex
Hiroaki Wada, Hiromi Tobita,* and Hiroshi Ogino*
Department of Chemistry, Graduate School of Science, Tohoku University,
Sendai 980-77, J apan
Received May 19, 1997X
Summary: When a solution of Cp(Ph3P)Ru{SiMe2‚‚‚O-
(Me)‚‚‚SiMe2} (1; Cp ) η5-C5H5) and a two-electron-
donating ligand L was heated at 130 °C, a CsH bond
of a phenyl group was activated by the RudSi double
bond, and the complexes CpLRuSiMe2(o-C6H4PPh2) (2a ,
L ) PPh3; 2b, L ) PMe3; 2c, L ) PEt3; 2d , L ) P(OMe)3;
2e, L ) tBuNC) were obtained. Heating 1 in the absence
of a ligand at 130 °C gave CpRuSiMe2(o-C6H4PPh2)-
(H)(SiMe2OMe) (3).
etc. and the intermolecular migration of substituents.11
We now report the first C-H bond activation by an
unsaturated metal-silicon bond, probably through aro-
matic electrophilic substitution induced by the electron-
deficient silylene ligand.
A benzene-d6 solution of the methoxy-bridged bis-
(silylene)-ruthenium complex Cp(Ph3P)Ru{SiMe2‚‚‚O-
(Me)‚‚‚SiMe2} (1; Cp ) η5-C5H5)1e and an excess of PPh3
in a thick-walled NMR tube was heated at 130 °C. After
60 h, the 1H NMR signals of complex 1 had almost
disappeared and those of HSiMe2OMe12 and the novel
complex 2a newly had appeared instead. The same
reaction was performed on a larger scale, and 2a was
isolated as air-stable yellow crystals in 34% yield (eq
1).13 Analogous reactions of 1 with PMe3, PEt3, P(OMe)3,
and CNtBu gave CpLRuSiMe2(o-C6H4PPh2) (2b, L )
PMe3, 75%; 2c, L ) PEt3, 54%; 2d , L ) P(OMe)3, 72%;
2e, L ) CNtBu, 39%).
The reactivity of the metal-silicon double bond of
transition-metal-silylene complexes has attracted much
attention. In this decade, a number of donor-stabilized1-5
and donor-free6 silylene complexes have been synthe-
sized and their reactivities examined. The electrophi-
licity of the silylene ligand has been demonstrated in
several reactions, including the addition of polar mol-
ecules such as water,4d,7 alcohols,1g,2e,7-10 ketones,2e,10
1
In the H NMR spectrum of complex 2a , two singlets
X Abstract published in Advance ACS Abstracts, August 1, 1997.
(1) (a) Ueno, K.; Tobita, H.; Shimoi, M.; Ogino, H. J . Am. Chem.
Soc. 1988, 110, 4092. (b) Tobita, H.; Ueno, K.; Shimoi, M.; Ogino, H.
J . Am. Chem. Soc. 1990, 112, 3415. (c) Koe, J . R.; Tobita, H.; Ogino,
H. Organometallics 1992, 11, 2479. (d) Takeuchi, T.; Tobita, H.; Ogino,
H. Organometallics 1991, 10, 835. (e) Ueno, K.; Ito, S.; Endo, K.;
Inomata, S.; Ogino, H. Organometallics 1994, 13, 3309. (f) Tobita, H.;
Wada, H.; Ueno, K.; Ogino, H. Organometallics 1994, 13, 2545. (g)
Kobayashi, H.; Ueno, K.; Ogino, H. Organometallics 1995, 14, 5490.
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669. (b) Zybill, C.; Mu¨ller, G. Organometallics 1988, 7, 1368. (c) Zybill,
C.; Willkinson, D. L.; Leis, C.; Mu¨ller, G. Angew. Chem., Int. Ed. Engl.
1989, 28, 203. (d) Probst, R.; Leis, C.; Gamper, S.; Herdtweck, E.; Zybill,
C.; Auner, N. Angew. Chem., Int. Ed. Engl. 1991, 30, 1132. (e) Leis,
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11, 514. (f) Handwerker, H.; Leis, C.; Gamper, S.; Zybill, C. Inorg.
Chim. Acta 1992, 198-200, 763.
assigned to two nonequivalent Si-Me groups were
observed at 0.54 and 0.94 ppm, and the signals in the
aromatic region were more complicated than those of
1. In the 13C NMR spectrum for 2a , 18 signals were
observed in the region of aromatic carbons. The 31P
NMR spectrum showed mutually coupled doublets at
(9) Handwerker, H.; Leis, C.; Probst, R.; Bissinger, P.; Grohmann,
A.; Kiprof, P.; Herdtweck, E.; Blu¨mel, J .; Auner, N.; Zybill, C.
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6951.
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Am. Chem. Soc. 1987, 109, 5872. (b) Straus, D. A.; Zhang, C.; Quinbita,
G. E.; Grumbine, S. D.; Heyn, R. H.; Tilley, T. D.; Rheingold, A. L.;
Geib, S. J . J . Am. Chem. Soc. 1990, 112, 2673.
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Ed. Engl., 1991, 30, 1130. (b) Corriu, R. J . P.; Lanneau, G. F.; Chauhan,
B. P. S. Organometallics 1993, 12, 2001. (c) Corriu, R. J . P.; Chauhan,
B. P. S.; Lanneau, G. F. Organometallics 1995, 14, 1646. (d) Chauhan,
B. P. S.; Corriu, R. J . P.; Lanneau, G. F.; Priou, C. Organometallics
1995, 14, 1657.
(5) (a) Horng, K. M.; Wang, S. L.; Liu, C. S. Organometallics 1991,
12, 631. (b) Woo, L. K.; Smith, D. A.; Young, V. G., J r. Organometallics
1991, 10, 3977. (c) J utzi, P.; Mo¨hrke, A. Angew. Chem., Int. Ed. Engl.
1990, 29, 893. (d) Bodensieck, U.; Braunstein, P.; Deck, W.; Faure, T.;
Knorr, M.; Stern, C. Angew. Chem., Int. Ed. Engl., 1994, 33, 2440. (e)
Nlate, S.; Herdtweck, E.; Fischer, R. Angew. Chem., Int. Ed. Engl.
1996, 35, 1861. (f) Braunstein, P.; Stern, C.; Strohmann, C.; Tong, N.
J . Chem. Soc., Chem. Commun. 1996, 2237.
(6) (a) Straus, D. A.; Grumbine, S. D.; Tilley, T. D. J . Am. Chem.
Soc. 1990, 112, 7801. (b) Leis, C.; Zybill, C.; Lachmann, J .; Mu¨ller, G.
Polyhedron 1991, 10, 1163. (c) Handwerker, H.; Paul, M.; Blu¨mel, J .;
Zybill, C. Angew. Chem., Int. Ed. Eng. 1993, 32, 1313. (d) Grumbine,
S. D.; Tilley, T. D.; Rheingold, A. L. J . Am. Chem. Soc. 1993, 115, 358.
(e) Grumbine, S. D.; Tilley, T. D.; Arnord, F. P.; Rheingold, A. L. J .
Am. Chem. Soc. 1994, 116, 5495. (f) Denk, M.; Hayashi, M. R.; West,
R. J . Chem. Soc., Chem. Commun. 1994, 33. (g) Grumbine, S. D.; Tilley,
T. D.; Arnord, F. P.; Rheingold, A. L. J . Am. Chem. Soc. 1993, 115,
7884.
(12) HSiMe2OMe was characterized by comparing its 1H, 13C, and
29Si NMR spectra with those of the authentic sample prepared by the
reaction of HSiMe2Cl and MeOH in the presence of (H2N)2CO.
(13) Preparation of 2a : toluene (2 mL) was transferred to a Pyrex
tube (10 mm o.d.) containing complex 1 (49.2 mg, 85.3 µmol) and PPh3
(23.4 mg, 89.5 µmol) by the trap-to-trap technique in a vacuum line,
and the tube was flame-sealed under high vacuum. After the mixture
was heated for 60 h at 130 °C, the tube was opened in a glovebox and
the solution was poured into a Schlenk tube. On removal of the solvent
in vacuo, an orange residue was obtained. Crystallization from
toluene-pentane gave 2a (21.5 mg, 28.8 µmol) as yellow crystals (yield
34%); mp 250 °C dec. Spectral data for 2a : 1H NMR (300 MHz, C6D6)
δ 0.54 (s, 3H, SiMe), 0.94 (s, 3H, SiMe), 4.58 (s, 5H, Cp), 6.71-7.88
(m, 29H, Ar); 13C NMR (75.5 MHz, C6D6) δ 9.0 (d, 2J C-P ) 4.5 Hz, SiMe),
2
2
11.6 (d, J C-P ) 1.0 Hz, SiMe), 83.7 (d, J C-P ) 1.8 Hz, Cp), 126.9 (d,
J C-P ) 5.8 Hz, Ar), 127.1 (br, Ar), 127.1 (d, J C-P ) 14.1 Hz, Ar), 127.5
(d, J C-P ) 12.5 Hz, Ar), 127.5 (br, Ar), 127.8 (d, J C-P ) 17.0 Hz, Ar),
128.7 (d, J C-P ) 2.2 Hz, Ar), 130.9 (d, J C-P ) 4.4 Hz, Ar), 131.8 (d,
J C-P ) 10.6 Hz, Ar), 132.2 (d, J C-P ) 23.4 Hz, Ar), 132.9 (br, Ar), 133.0
(d, J C-P ) 10.0 Hz, Ar), 134.0 (br, Ar), 135.3 (br, Ar), 138.3 (dd, J C-P
) 3.6, 36.6 Hz, Ar), 145.9 (dd, J C-P ) 1.6, 26.6 Hz, Ar), 146.5 (dd, J C-P
) 1.7, 40.0 Hz, Ar), 162.4 (dd, J C-P ) 1.3, 53.5 Hz, Ar); 29Si NMR (59.6
2
MHz, C6D6) δ 41.4 (dd, J Si-P ) 22.3, 24.5 Hz); 31P NMR (122 MHz,
2
2
C6D6) δ 60.5 (d, J P-P ) 29.5 Hz, PPh3), 83.4 (d, J P-P ) 29.5 Hz,
chelating P); IR (KBr pellet) 1477, 1430 (aromatic C-C stretch), 1086
(in-plane aromatic C-H bend), 785, 741, 721 (out-of-plane aromatic
C-H bend) cm-1; MS (FAB, m-nitrobenzyl alcohol, Xe) m/ z 741 (15,
M+), 691 (16, [Cp(Ph3P)2Ru]+), 626 (8.2, [(Ph3P)2Ru]+), 486 (48, M+
-
(7) Wada, H.; Tobita, H.; Ogino, H. Organometallics 1997, 16, 2200.
(8) Ueno, K.; Tobita, H.; Seki, S.; Ogino, H. Chem. Lett. 1993, 1723.
PPh3), 429 (100, [Cp(Ph3P)Ru]+). Anal. Calcd for C43H40
P2RuSi: C, 69.05; H, 5.40. Found: C, 69.22; H, 5.47.
-
S0276-7333(97)00408-1 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 18, 1997 3871
2
60.5 and 83.4 ppm (d, J P-P ) 29.5 Hz), the latter of
which can be assigned to the phosphorus atom in the
chelate ring on the basis of the general tendency of
downfield shift for the signals of phosphorus in 5-mem-
bered chelate phosphines.14 In the 29Si NMR spectrum,
only one signal was observed at 41.4 ppm as a doublet
of doublets (2J Si-P ) 22.3, 24.5 Hz).
The structure of 2b was unequivocally determined by
X-ray crystallography.15 The crystal contains the two
independent molecules A and B, but there is no essential
difference except their chirality. The ORTEP view of
molecule A is shown in Figure 1. The Ru-Si bond
lengths are 2.352(3) Å in molecule A and 2.354(3) Å in
molecule B. They are longer than those of bis(silylene)
complex 1 (2.290(5)-2.348(5) Å, average 2.326 Å)1f but
are relatively short among the values reported for Ru-
Si single-bond lengths (2.338-2.507 Å).16 This shorten-
ing of the Ru-Si bonds in 2b may be attributable to the
enhanced back-donation to the silyl group from the
electron-rich metal center due to the presence of two
phosphorus donors.
F igu r e 1. ORTEP diagram of Cp(Me3P)RuSiMe2(o-C6H4-
PPh2) (2b; molecule A). Selected bond lengths (Å) and
angles (deg): Ru(A)-Si(A) ) 2.352(3), Ru(A)-P(1A) )
2.238(3), Ru(A)-P(2A) ) 2.271(3), P(1A)-C(8A) ) 1.846-
(9), C(8A)-C(9A) ) 1.388(13), Si(A)-C(9A) ) 1.908(11);
P(1A)-Ru(A)-P(2A) ) 93.70(10), P(1A)-Ru(A)-Si(A) )
82.87(10), P(2A)-Ru(A)-Si(A) ) 89.79(10), Ru(A)-Si(A)-
C(9A) ) 108.1(3), Si(A)-C(9A)-C(8A) ) 116.6(7), P(1A)-
C(8A)-C(9A) ) 115.2(7), Ru(A)-P(1A)-C(8A) ) 114.5(7).
1
(83.4-85.1 ppm). In the H NMR spectrum, a doublet
assigned to a hydrido ligand was observed at -12.68
ppm (2J H-P ) 6.6 Hz) and also a singlet of a methoxy
(16) (a) Crozat, M. M.; Watkins, S. F. J . Chem. Soc., Dalton Trans.
1972, 2512. (b) Howard, J . A. K.; Knox, S. A. R.; Riera, V.; Sosinsky,
B. A.; Stone, F. G. A.; Woodward, P. J . Chem. Soc., Chem. Commun.
1974, 673. (c) Edwards, J . D.; Goddard, R.; Knox, S. A. R.; McKinney,
R. J .; Stone, F. G. A.; Woodward, P. J . Chem. Soc., Chem. Commun.
1975, 828. (d) Goddard, R.; Woodward, P. J . Chem. Soc., Dalton Trans.
1980, 559. (e) Brooks, A.; Howard, J .; Knox, S. A. R.; Riera, V.; Stone,
F. G. A.; Woodward, P. J . Chem. Soc., Chem. Commun. 1973, 727. (f)
Howard, J .; Woodward, P. J . Chem. Soc., Dalton Trans. 1975, 59. (g)
Harris, P. J .; Howard, J . A. K.; Knox, S. A. R.; McKinney, R. J .; Phillips,
R. P.; Stone, F. G. A.; Woodward, P. J . Chem. Soc., Dalton Trans. 1978,
403. (h) Einstein, F. W. B.; J ones, T. Inorg. Chem. 1982, 21, 987. (i)
Holmes-Smith, R. D.; Stobart, S. R.; Vefghi, R.; Zaworotko, M. J .;
J ochem, K.; Cameron, T. S. J . Chem. Soc., Dalton Trans. 1987, 969.
(j) Klein, H.-P.; Thewalt, U.; Herrmann, G.; Su¨ss-Fink, G.; Moinet, C.
J . Organomet. Chem. 1985, 286, 225. (k) Djurovich, P. I.; Carroll, P.
J .; Berry, D. H. Organometallics 1994, 13, 2551.
When a toluene solution of 1 is heated in the absence
of a ligand at 130 °C, complex 3, a structural isomer of
1 that is stable in the solid state, was isolated as a pale
brown powder in 78% yield (eq 2).17 In the 31P NMR
(17) Preparation of 3: Toluene (1.2 mL) was transferred to a Pyrex
tube (10 mm o.d.) containing complex 1 (113 mg, 196 µmol) by the
trap-to-trap technique in a vacuum line and the tube was flame-sealed
under high vacuum. After the mixture was heated for 47 h at 130 °C,
the tube was opened in a glovebox and the solution was poured into a
Schlenk tube. After removal of the solvent in vacuo, the brown, oily
residue was washed three times with pentane (0.5 mL × 3) at -60 °C
and dried under vacuum to afford 3 as a pale brown powder (88 mg,
153 µmol, yield 78%); mp 145 °C dec. Further purification was
performed by recrystallization from toluene-pentane. Spectral data
for 3: 1H NMR (300 MHz, C6D6) δ -12.68 (d, 2J H-P ) 6.6 Hz, 1H, RuH),
0.10 (s, 3H, SiMe), 0.18 (s, 3H, SiMe), 0.58 (s, 3H, SiMe), 0.97 (s, 3H,
SiMe), 3.05 (s, 3H, SiOMe), 4.72 (s, 5H, Cp), 6.86-7.88 (m, 14H, Ar);
2
13C NMR (75.5 MHz, C6D6) δ 9.8 (d, J C-P ) 1.3 Hz, chelating SiMe),
spectrum of 3, one singlet due to the phosphorus in the
chelate ring was observed at 78.5 ppm, which is at
slightly higher field than those of complexes 2a -e
9.9 (s, chelating SiMe), 10.3 (SiMe2OMe), 49.6 (SiMe2OMe), 85.1 (d,
2J C-P ) 1.9 Hz, Cp), 127.5 (d, J C-P ) 6.5 Hz, Ar), 127.7 (d, J C-P ) 28.7
Hz, Ar), 127.7 (d, J C-P ) 9.8 Hz, Ar), 128.1 (d, J C-P ) 5.9 Hz, Ar),
128.5 (d, J C-P ) 2.1 Hz, Ar), 129.2 (dd, J C-P ) 16.0 Hz, 2.2 Hz, Ar),
130.2 (d, J C-P ) 4.6 Hz, Ar), 132.0 (d, J C-P ) 22.6 Hz, Ar), 132.4 (d,
(14) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(15) Crystal data for 2b: formula C28H34P2RuSi, monoclinic, space
group C2 (variant of No. 5), a ) 29.227(11) Å, b ) 9.799(2) Å, c )
23.877(10) Å, â ) 127.73(3)°, V ) 5409(3) Å3, Z ) 8, dcalcd ) 1.38 g
cm-3. X-ray diffraction data were collected at room temperature on a
Rigaku AFC-6A diffractometer with graphite-monochromated Mo KR
radiation. Reflections (8334) with 3.52° < 2θ < 60.00° were collected
by the ω-scan technique. The structure was solved by heavy-atom
methods (SHELXS 86) and refined with full-matrix least squares using
individual anisotropic thermal parameters for non-hydrogen atoms.
The final R factor was 0.060 (Rw ) 0.131) for 8334 reflections with
|Fo| > 2σ(Fo).
J C-P ) 10.7 Hz, Ar), 134.3 (d, J C-P ) 10.5 Hz, Ar), 138.6 (d, J C-P )
43.1 Hz, Ar), 144.2 (d, J C-P ) 41.8 Hz, Ar), 146.2 (d, J C-P ) 54.9 Hz,
Ar), 156.8 (d, J C-P ) 50.0 Hz, Ar); 29Si NMR δ (59.6 MHz, C6D6) δ 35.2
2
2
(d, J Si-P ) 13.4 Hz, chelating Si), 54.0 (d, J Si-P ) 12.4 Hz, SiMe2-
OMe); 31P NMR δ (122 MHz, C6D6) 78.5 (s); IR (KBr pellet) 2081 (Ru-
H), 1479, 1433, 1232 (Si-Me), 1182, 1097 (Si-O-Me) cm-1; MS (FAB,
m-nitrobenzyl alcohol matrix, Xe) m/ z 576 (2.7, M+), 561 (6.4, M+
-
Me), 546 (5.6, M+ - 2Me), 503 (8.3, M+ - SiMe2 - Me), 487 (100, M+
- HSiMe2OMe), 472 (23, M+ - HSiMe2OMe - Me) 429 (3.9, [Cp-
(Ph3P)Ru]+). Anal. Calcd for C28H35O1PRuSi2: C, 58.40; H, 6.14.
Found: C, 58.65; H, 6.33.

3872 Organometallics, Vol. 16, No. 18, 1997
Communications
Sch em e 1
suggests that 3 is an intermediate in the formation of
complexes 2a -e.
A possible mechanism for formation of 2a -e from 1
and L is shown in Scheme 1. The four-membered
chelate ring in 1 opens at high temperature to generate
intermediate A, and the electron-deficient silicon atom
of the base-free silylene ligand electrophilically attacks
the ortho carbon of a phenyl group in the PPh3 ligands.
The proton on the ortho position subsequently migrates
to the electronegative ruthenium center to give 3. In
the presence of a two-electron donor L, intermediate B,
which is generated reversibly by reductive elimination
of HSiMe2OMe from 3, traps L to afford 2.
This is the first example of C-H bond activation by
a silylene complex.
group at 3.05 ppm. The 29Si NMR spectrum showed two
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research (No. 09440223)
from the Ministry of Education, Science, Sports and
Culture and a Kurata Research Grant from the Kurata
Foundation. We are grateful to Shin-Etsu Chemical Co.,
Ltd., and Dow Corning Toray Silicone Co., Ltd., for gifts
of silicon compounds.
doublets at 35.2 (2J Si-P ) 13.4 Hz) and 54.0 (2J Si-P
)
12.4 Hz) ppm, which demonstrate the existence of two
silyl ligands. Their Si-P coupling constants are very
similar to each other and also to that of trans-Cp-
(Ph3P)RuH(SiMe2OMe)2 (2J Si-P ) 11.6 Hz).7 This situ-
ation is in contrast to that of Cp(Ph3P)RuH(SiMe2-
2
OSiMe2), which has very different J Si-P values (7.0 and
19.0 Hz).7 These observations suggest that 3 adopts the
trans geometry.
Su p p or tin g In for m a tion Ava ila ble: Text and tables
giving synthetic procedures and characterization data for new
compounds and details of the X-ray structure determination
of 2b (16 pages). Ordering information is given on any current
masthead page.
When a benzene-d6 solution of complex 3 and PPh3
was heated in an NMR tube at 120 °C, 3 was consumed
within 3 days and complex 2a and HSiMe2OMe were
formed quantitatively (eq 3). This result strongly
OM970408D