Coordinatively unsaturated Ru(II) species Ru(xantsil)(CO): A new active catalyst for oligomerization/deoligomerization of HSiMe2SiMe3 [xantsil = (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)]. Isolation of a stabilized form of the silyl(silylene) intermediates

Article abstract of DOI:10.1246/cl.2002.406

Ru(xantsil)(CO)(η⁶-C₆H₅CH₃) (1) was found to be a catalyst for the oligomerization/deoligomerization of HSiMe₂SiMe₃ to give H(SiMe₂)_nMe (n = 1-8). A possible mechanism involving a silyl(silylene) intermediate was strongly supported by the isolation of its stabilized form, i.e., alkoxy-bridged bis(silylene) complex which was characterized by X-ray crystal structure analysis.

Full text of DOI:10.1246/cl.2002.406

406
Chemistry Letters 2002
Coordinatively Unsaturated Ru(II) Species Ru(xantsil)(CO):
A New Active Catalyst for Oligomerization/Deoligomerization of HSiMe2SiMe3
[xantsil ¼ ð9,9-Dimethylxanthene-4,5-diylÞbisðdimethylsilylÞ].
Isolation of a Stabilized Form of the Silyl(silylene) Intermediates
Jim Josephus G. Minglana, Masaaki Okazaki, Hiromi Tobita,ꢀ and Hiroshi Ogino
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578
(Received December 5, 2001; CL-011230)
Ru(xantsil)(CO)(ꢀ6-C6H5CH3) (1) was found to be a catalyst
temperature to give H(SiMe2)nMe (n ¼ 1{5) after 2 days reaction
with the molar ratios of 81 ðn ¼ 1Þ : 56 ðn ¼ 2Þ : 11 ðn ¼ 3Þ :
3 ðn ¼ 4Þ : 1 ðn ¼ 5Þ based on the peak areas of the GC(FID). The
products were confirmed by 1H NMR and GC-Mass spectroscopy
(eq 1). When the reaction was carried out at 90 ꢁC for 2 days,
formation of products with n up to 8 was observed with the molar
ratios of 346 ðn ¼ 1Þ : 96 ðn ¼ 2Þ : 82 ðn ¼ 3Þ : 64 ðn ¼ 4Þ : 35
ðn ¼ 5Þ : 13 ðn ¼ 6Þ : 4 ðn ¼ 7Þ : 1 ðn ¼ 8Þ (eq 1).
for the oligomerization/deoligomerization of HSiMe2SiMe3 to give
H(SiMe2)nMe (n ¼ 1{8). A possible mechanism involving a
silyl(silylene) intermediate was strongly supported by the isolation
of its stabilized form, i.e., alkoxy-bridged bis(silylene) complex
which was characterized by X-ray crystal structure analysis.
Transition-metal chloro complexes such as RhCl(PR3)3,
IrCl(CO)(PR3)2, RuCl2(PR3)3, and MCl2(PR3)2 (M¼Pd, Pt) have
been widely employed as active homogeneous catalysts for the
various transformation reactions of organic compounds.1 Recently,
our study2 has been focused on the exceptionally strong ꢁ-donor
character and high trans influencing ability of silyl ligands.3
Introduction of a silyl ligand instead of the chloro ligand could
enhance or change the reactivity and catalytic performance of
transition metal complexes. However, facile elimination of silyl
ligands from the metal center has retarded the progress of such
application.4 To avoid this drawback of silyl ligands, we designed a
chelate ligand ‘‘xantsil’’ [xantsil ¼ ð9,9-dimethylxanthene-4,5-
diylÞbisðdimethylsilylÞ]. Because of the rigid backbone of the
xanthene core and electron-releasing character of silyl groups,
xantsil can be an ideal supporting ligand for coordinatively
unsaturated transition-metal complexes. In a previous paper, we
reported the synthesis and structure of a bis(silyl) chelate-type
Ru(II) complex Ru(xantsil)(CO)(ꢀ6-C6H5CH3) (1) which under-
goes extremely fast arene exchange at room temperature.5 This
observation implies that 1 can be formally a source of either 12- or
14-electron, coordinatively unsaturated species ‘‘Ru(xantsil)(CO)’’
depending on the mode of coordination of the xantsil ligand (Figure
1). We report here that Ru(xantsil)(CO)(ꢀ6-C6H5CH3) (1) can
mediate the catalytic oligomerization/deoligomerization of
HSiMe2SiMe3 to give H(SiMe2)nMe (n ¼ 1{8). We also succeeded
in the isolation of the stabilized form of a silyl(silylene) complex
which have been believed so far as a key intermediate in the
catalytic oligomerization of hydrosilanes.
A plausible mechanism for the ruthenium-mediated oligomer-
ization/deoligomerization is illustrated in Scheme 1.
Scheme 1. A plausible mechanism for the Ru(II) mediated oligomeriza-
tion/deoligomerization of hydrodisilane.
The reaction could proceed via repeated oxidative additions of
Si-H, 1,2-silyl migration,6 and reductive elimination processes. The
silyl(silylene) intermediates can be indirectly confirmed by
replacing a methyl group of the disilane with a tBuO group. When
1 was allowed to react with a stoichiometric amount of
HSiMe2SiMe2OtBu at room temperature, a bis(silylene) rutheniu-
m(IV) complex 2 was formed almost quantitatively (eq 2). Workup
of the resulting solution and crystallization from toluene afforded
colorless needles of 2 (84%).7 The elemental analysis and mass
spectral data are consistent with the formula of 2.
Figure 1. Coordination modes of xantsil.
The ruthenium(II) xantsil complex 1 (0.1 mol%) catalyzed the
oligomerization/deoligomerization of HSiMe2SiMe3 at room
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
407
Ru1-Si4 angle. The NOESY spectrum also shows the intramole-
cular exchange process of the methyl groups on the silylene ligands.
The dynamic process could involve the cleavage of a Si-O bond
followed by rotation of the resulting donor-free silylene moiety
about the Ru¼Si double bond to interchange the methyl group
environments. This mechanism is essentially the same as those of
the exchange of Si-Me groups in CpðCOÞ WfSiMe2 Á Á Á Do Á Á Á
SiMe2g (Do¼OMe, NEt2)9 and CpꢀðMe3PÞ2RufSiMe2 Á Á Á OR Á Á Á
SiMe2g (R¼Me, tBu).10 In the 29Si{1Hg NMR spectrum, the signal
of two silylene ligands appeared equivalently at 107.6 ppm, which is
shifted significantlyto downfieldfrom thatof thexantsil silylgroups
(15.4 ppm). The 29Si chemical shift of silylene ligands is
characteristic of base-stabilized silylene complexes.
The structure of 2 was unequivocally determined by the X-ray
crystal structure analysis.8 The crystal contains two independent
molecules, but there is no essential difference. The ORTEP view of
one of them is shown in Figure 2. Although the hydrido ligand could
not be located crystallographically, NMR data clearly indicates its
existence. It might be found along the unusually widened Si3-Ru1-
Si4 angle (119.4(1) ꢁ). Thus, 2 takes a distorted seven-coordinate
pentagonal bipyramid with the nearly planar arrangement of all four
silicon atoms with ruthenium (mean deviation from the least square
Disproportionation of pentamethyldisilane has been reported
by Yamamoto et al. in which a catalytic amount of (Et3P)2PtCl2 was
employed.11 The reaction requires relatively severe conditions and
proceeds at 90 ꢁC (18 h) to give H(SiMe2)nMe (n ¼ 1{6).
This paper demonstrated that our bis(silyl)ruthenium complex
1 generates a 12- or 14-electron coordinatively unsaturated A or B
species and works as an active catalyst for the metal-mediated
oligomerization/deoligomerization of hydrodisilanes. Over the past
few decades, silyl(silylene) complexes have been postulated in the
metal-mediated oligomerization of hydrosilanes and hydrodisi-
lanes. In this paper, we offered a convincing evidence in support of
the existence of silyl(silylene) complexes in the catalytic reaction.
ꢀ
Si4 plane: 0.0161 A). The bond lengths of Ru-Si (silylene) (ave.
ꢀ
2.399 A) are shorter than those of Ru-Si (silyl) (ave. 2.434 A) but
ꢀ
ꢀ
about 0.09 A longer than those of the previously reported ruthenium
bis(silylene) complexes, probably due to the trans-influence of the
ꢀ
silyl ligands. The length between Ru1 and O2 is 2.289(8) A,
References and Notes
1
2
a) R. H. Crabtree, ‘‘The Organometallic Chemistry of the Transition Metals,’’ 2nd
ed., John Wiley & Sons, New York (1994). b) A. Yamamoto, ‘‘Organotransition
Metal Chemistry,’’ John Wiley & Sons, New York (1986).
a) M. Okazaki, H. Tobita, and H. Ogino, Organometallics, 15, 2790 (1996). b) M.
Okazaki, H. Tobita, and H. Ogino, Chem. Lett., 1997, 437. c) M. Okazaki, H.
Tobita, and H. Ogino, J. Chem. Soc., Dalton Trans., 1997, 3531. d) M. Okazaki, H.
Tobita, and H. Ogino, Chem. Lett., 1998, 69. e) M. Okazaki, S. Ohshitanai, H.
Tobita, and H. Ogino, Chem. Lett., 2001, 952. f) M. Okazaki, S. Ohshitanai, M.
Iwata, H. Tobita, and H. Ogino, Coord. Chem. Rev., in press.
indicating the coordination of the oxygen atom O2 to the ruthenium
center to satisfy the 18-electron rule. Thus, the xantsil works as a
tridentate ligand.
3
4
a) J. Chatt, C. Eaborn, and S. Ibekwe, J. Chem. Soc., Chem. Commun., 1966, 700.
b) R. McWeeny, R. Mason, and A. D. C. Towl, Discuss. Faraday Soc., 47, 20
(1969). c) R. N. Haszeldine, R. V. Parish, and J. H. Setchfield, J. Organomet.
Chem., 57, 279 (1973).
T. D. Tilley, ‘‘The Chemistry of Organic Silicon Compounds,’’ ed. by S. Patai and
Z. Rappoport, Wiley, New York (1989), p 1415.
5H. Tobita, K. Hasegawa, J. J. G. Minglana, L.-S. Luh, M. Okazaki, and H. Ogino,
Organometallics, 18, 2058 (1999).
6
7
a) K. H. Pannell, J. Cervantes, C. Hernandez, J. Cassias, and S. Vincenti,
Organometallics, 5, 1056 (1986). b) H. Tobita, K. Ueno, and H. Ogino, Chem.
Lett., 1986, 1777.
Data for 2: 1H NMR (CD2Cl2) ꢂ À 2:23 (s, 1H, RuH), 0.13 (s, 6H, SiMeB), 0.59 (s,
6H, SiMeD), 0.62 (s, 6H, SiMeE), 0.88 (s, 6H, SiMeC), 1.24 (s, 3H, 9-MeF), 1.38 (s,
G
9H, tBu), 1.75(s, 3H, 9-Me Þ, 7.12, 7.23, 7.48 (m, 6H, Ar). 13C{1Hg NMR
(CD2Cl2) 6.2, 7.2, 10.0, 14.0 (SiMe), 22.6 (OCMe3Þ, 30.7, 30.9 (9-Me), 35.8 (C-
Me2Þ, 92.3 (OCMe3Þ, 123.5, 124.9, 130.7, 134.4, 136.0, 161.9 (Ar), 204.2 (CO).
29Si{1Hg NMR (CD2Cl2) 15.4 (xantsil Si), 107.6 (silylene Si), IR (KBr pellet)
1923 cmÀ1 (ꢃCO), Mass (EI, 70 eV) m=z 587 (Mþ-tBu, 26), 513 (Mþ-tBu-
Me2SiO, 41), 325(100). Anal. Calcd for C 28H46RuO3Si4: C, 52.21; H, 7.20%.
Found: C, 51.71; H, 7.16%.
ꢀ
Figure 2. ORTEP drawing of 2. Selected bond lengths (A) and
angles (ꢁ): Ru1-Si1 2.395(4), Ru1-Si2 2.402(4), Ru1-Si3
2.443(4), Ru1-Si4 2.424(4), Ru1-C51.79(1), Ru1-O2 2.289(8),
Si1-O1 1.813(9), Si2-O1 1.827(9), O1-C1 1.52(1), Si1-Ru1-Si2
67.9(1), Si3-Ru1-Si4 119.4(1), O2-Ru1-C5175.2(6).
8
Crystallographic data for 2: C28H46O3RuSi4, M ¼ 644:08, monoclinic, space
ꢁ
ꢀ
ꢀ
ꢀ
group P21, a ¼ 18:216ð3Þ A, b ¼ 9:634ð1Þ A, c ¼ 19:327ð2Þ A, ꢄ ¼ 109:647ð6Þ ,
The NMR spectroscopic data of 2 are consistent with the crystal
structure. The 1H NMR spectrum of 2 shows a singlet at À2:23 ppm
assignable to Ru-H. Four singlet signals of the methyl groups appear
at 0.13 (6H), 0.59 (6H), 0.62 (6H), and 0.88 (6H) which are assigned
to SiMeB, SiMeD, SiMeE, and SiMeC, respectively (see eq 2). The
signals of two 9-Me groups on xantsil appear inequivalently at 1.24
ꢀ 3
V ¼ 3194:2ð7Þ A , T ¼ À123 ꢁC, Z ¼ 4, Dc ¼ 1:339 g cmÀ3, ꢅðMo-KꢆÞ ¼
6:67 cmÀ1, R1 ¼ 0:075 (I > 2ꢁ (I)), R ¼ 0:114, Rw ¼ 0:216 (all data). Crystal-
lographic data reported in this paper have been deposited with Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC-177653.
Copies of the data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
G
(9-MeFÞ and 1.75(9-Me Þ. These assignments are established by
9
K. Ueno, A. Masuko, and H. Ogino, Organometallics, 16, 5023 (1997). K. Ueno,
A. Masuko, and H. Ogino, Organometallics, 18, 2694 (1999).
the NOESY technique. In the two-dimensional NOESY spectrum, a
correlation peak is present between Ru-H and SiMeE resonances,
indicating that the hydrido hydrogen atom is located along the Si3-
10 H. Wada, H. Tobita, and H. Ogino, Chem. Lett., 1998, 993.
11 K. Yamamoto, H. Okinoshima, and M. Kumada, J. Organomet. Chem., 23, C7
(1970).