Silabenzene and disilabenzene complexes of ruthenium

Article abstract of DOI:10.1021/om000829m

The syntheses of sila- and disilabenzene complexes of Cp*Ru (Cp* = C₅Me₅) are described. Li[C₅H₅SiH(^tBu)] reacted with [Cp*RuCl]₄ to give the neutral silacyclohexadienyl complex Cp*Ru[η⁵-C₅H₅SiH(^tBu)] (2), characterized by NMR spectroscopy. Reaction of 2 with the Lewis acid B(C₆F₅)₃ gave the product of Si-H abstraction, [Cp*Ru(η⁶-C₅H₅Si^tBu)] [BH(C₆F₅)₃] (3). Complex 3 represents the first example of an isolated silabenzene complex. The characterization of 3 follows from ¹H, ¹³C, ²⁹Si, ¹⁹F, and ¹¹B NMR and IR spectroscopies. Finally, trans-1,4-dihydrohexamethyl-1,4-disilacyclohexa-2,5-diene reacted with Cp′(PMe₃)₂-RuCH₂SiMe₃ (Cp′ = C₅Me₄Et) to give Cp′(PMe₃)RuH(η²-hexamethyl-1,4-disilabenzene) (4), whose structure (by X-ray crystallography) may be described as a metallodisilanorbornadiene.

Full text of DOI:10.1021/om000829m

Organometallics 2001, 20, 1195-1203
1195
Sila ben zen e a n d Disila ben zen e Com p lexes of Ru th en iu m
J effrey M. Dysard and T. Don Tilley*
Department of Chemistry, University of California at Berkeley,
Berkeley, California 94720-1460
Tom K. Woo*
Department of Chemistry, The University of Western Ontario, London,
Ontario, Canada N6A 5B7
Received September 26, 2000
The syntheses of sila- and disilabenzene complexes of “Cp*Ru” (Cp* ) C5Me5) are described.
Li[C5H5SiH(tBu)] reacted with [Cp*RuCl]4 to give the neutral silacyclohexadienyl complex
Cp*Ru[η5-C5H5SiH(tBu)] (2), characterized by NMR spectroscopy. Reaction of 2 with the
Lewis acid B(C6F5)3 gave the product of Si-H abstraction, [Cp*Ru(η6-C5H5SitBu)][BH(C6F5)3]
(3). Complex 3 represents the first example of an isolated silabenzene complex. The
1
characterization of 3 follows from H, 13C, 29Si, 19F, and 11B NMR and IR spectroscopies.
Finally, trans-1,4-dihydrohexamethyl-1,4-disilacyclohexa-2,5-diene reacted with Cp′(PMe3)2-
RuCH2SiMe3 (Cp′ ) C5Me4Et) to give Cp′(PMe3)RuH(η2-hexamethyl-1,4-disilabenzene) (4),
whose structure (by X-ray crystallography) may be described as a metallodisilanorbornadiene.
In tr od u ction
solution and was stabilized by coordination of a Lewis
base to the silicon center.4 Only recently, Okazaki and
co-workers have succeeded in the synthesis of the first
stable examples of silabenzenoid compounds, as 2-si-
lanaphthalene and silabenzene derivatives.5 Both of
these compounds take advantage of an extremely bulky
substituent at silicon, 2,4,6-tris[bis(trimethylsilyl)m-
ethyl]phenyl (Tbt), to provide stability to the silaaro-
matic systems. Interestingly, these compounds have
been characterized both structurally and theoretically
as having full delocalization of their π-electrons.5 1,4-
Disilabenzene itself has been trapped in a frozen argon
matrix and characterized spectroscopically, and another
member of this series, hexamethyldisilabenzene, has
been generated photolytically and trapped with various
reagents.3d,e Very recently, a 1,4-disila(Dewar-benzene)
derivative has also been isolated.6
Silabenzenes have long been of interest as analogues
to benzene, the simplest 6π-electron aromatic system
of carbon.1 However, such species have been elusive,
although theory predicts significant aromatic character
for some silabenzenes, and both sila- and disilabenzene
have been observed in low-temperature matrices.1,2
Pioneering work by the groups of Barton and West in
the late 1970s to mid 1980s provided the first evidence
for the existence of potentially aromatic sila- and
disilabenzene derivatives.2,3 However, these π-systems
are extremely reactive and could only be isolated at
room temperature as products of dimerization or through
trapping experiments.2,3 In 1988 Ma¨rkl et al. reported
the synthesis of 2,6-bis(trimethylsilyl)-1,4-di-tert-butyl-
silabenzene, which was stable only below -100 °C in
Our work has shown that aromaticity in silacyclo-
pentadienyl (silolyl) anions is promoted by η5-coordina-
tion to transition metal fragments.7 Thus, it seemed that
η6-silabenzene complexes might be viable synthetic
targets and interesting new examples of π-delocalized
silaaromatic ligands. Some support for this notion came
from a literature report describing observation of the
(1) For reviews on silaaromatic compounds see: (a) Brook, A. G.;
Brook, M. A. Adv. Organomet. Chem. 1996, 39, 71. (b) Raabe, G.; Michl,
J . Chem. Rev. 1985, 85, 419. (c) Raabe, G.; Michl, J . In The Chemistry
of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley:
New York, 1989; p 1102. (d) Apeloig, Y. In The Chemistry of Organic
Silicon Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York,
1989; p 151. (e) Apeloig, Y.; Karni, M. In The Chemistry of Organic
Silicon Compounds; Part II; Rappoport, Z., Apeloig, Y., Eds.; Wiley:
New York, 1998; Vol. 2, Chapter 1.
(2) (a) Baldridge, K. K.; Uzan, O.; Martin, J . M. L. Organometallics
2000, 19, 1477. (b) Solouki, B.; Rosmus, P.; Bock, H.; Maier, G. Angew.
Chem., Int. Ed. Engl. 1980, 19, 51. (c) Maier, G.; Mihm, G.; Reisenauer,
H. P. Angew. Chem., Int. Ed. Engl. 1980, 19, 52. (d) Kreil, C. L.;
Chapman, O. L.; Burns, G. T.; Barton, T. J . J . Am. Chem. Soc. 1980,
102, 841. (e) Maier, G.; Mihm, G.; Reisenauer, H. P. Chem. Ber. 1982,
115, 801. (f) Maier, G.; Mihm, G.; Baumga¨rtner, R. O. W.; Reisenauer,
H. P. Chem. Ber. 1984, 117, 2337. (g) Maier, G.; Scho¨ttler, K.;
Reisenauer, H. P. Tetrahedron Lett. 1985, 26, 4079. (h) J utzi, P.; Meyer,
M.; Reisenauer, H. P.; Maier, G. Chem. Ber. 1989, 122, 1227.
(3) (a) Barton, T. J .; Banasiak, D. S. J . Am. Chem. Soc. 1977, 99,
5199. (b) Barton T. J .; Burns, G. T. J . Am. Chem. Soc. 1978, 100, 5246.
(c) Barton, T. J .; Vuper, M. J . Am. Chem. Soc. 1981, 103, 6788. (d)
Rich, J . D.; West, R. J . Am. Chem. Soc. 1982, 104, 6884. (e) Welsh, K.
M.; Rich, J . D.; West, R.; Michl, J . J . Organomet. Chem. 1987, 362,
105.
(4) Ma¨rkl, G.; Schlosser, W. Angew. Chem., Int. Ed. Engl. 1988, 27,
963.
(5) (a) Tokitoh, N.; Wakita, K.; Okazaki, R.; Nagase, S.; von R.
Schleyer, P.; J iao, H. J . Am. Chem. Soc. 1997, 119, 6951. (b) Wakita,
K.; Tokitoh, N.; Okazaki, R.; Nagase, S.; Schleyer, P. v. R.; J iao, H. J .
Am. Chem. Soc. 1999, 121, 11336. (c) Wakita, K.; Tokitoh, N.; Okazaki,
R.; Nagase, S. Angew. Chem., Int. Ed. 2000, 39, 634. (d) Wakita, K.;
Tokitoh, N.; Okazaki, R.; Takagi, N.; Nagase, S. J . Am. Chem. Soc.
2000, 122, 5648.
(6) Kabe, Y.; Ohkubo, K.; Ishikawa, H.; Ando, W. J . Am. Chem. Soc.
2000, 122, 3775.
(7) (a) Freeman, W. P.; Tilley, T. D.; Rheingold, A. L. J . Am. Chem.
Soc. 1994, 116, 8428. (b) Dysard, J . M.; Tilley, T. D. J . Am. Chem.
Soc. 1998, 120, 8245. (c) Dysard, J . M.; Tilley, T. D. J . Am. Chem. Soc.
2000, 122, 3097.
10.1021/om000829m CCC: $20.00 © 2001 American Chemical Society
Publication on Web 02/14/2001

1196 Organometallics, Vol. 20, No. 6, 2001
Dysard et al.
Li[C5H5SiH(tBu)].14 Reaction of this anion with either
1/4[Cp*RuCl]415 or 1/2[Cp*RuOMe]216 (tetrahydrofuran,
room temperature) resulted in formation of the ruthe-
nium silacyclohexadienyl complex Cp*Ru[η5-C5H5SiH-
(tBu)] (2), isolated in 45% yield as an orange microcrys-
talline solid upon crystallization from CH3CN (Scheme
1). This reaction proceeded in nearly quantitative yield
by 1H NMR spectroscopy (tetrahydrofuran-d8); thus the
low isolated yield of 2 is due to its high solubility in
various solvents (pentane, acetonitrile, diethyl ether,
tetrahydrofuran, and hexamethyldisiloxane). Interest-
ingly, only one isomer of 2 is formed in this reaction
(by 1H NMR spectroscopy). Presumably, this is the
isomer with the tert-butyl group exo to the metal center,
as the endo isomer would probably result in unfavorable
nonbonding contacts with the Cp* ligand.
Sch em e 1
Compound 2 was fully characterized, and the struc-
ture shown in Scheme 1 is based largely on NMR
spectroscopy. The 1H NMR spectrum of 2 exhibits
t
resonances for the Bu and Cp* groups at δ 0.85 and
1.69, respectively. The silacyclohexadienyl ring hydro-
gens resonate as multiplets at δ 1.88 (H1, H5) and 4.65
(H2, H3, and H4). These resonances are very similar to
those for the related silacyclohexadiene complex [Fe-
(η5-C5H5SiMe2)2] (δ 2.20, 4.85, and 4.97).17 In addition,
a resonance at δ 4.77 is assigned, based on a 1H, 29Si
HMQC experiment, as the silicon-bound hydrogen. The
[η6-4-cyclohexyl-1-methylsilabenzene]Fe radical cation
in the mass spectrum of [η5-4-cyclohexyl-1,1-dimethyl-
silacyclohexadienyl]Fe(CO)3+.8 Here we report the syn-
thesis and characterization of the first transition metal
silabenzene complex and a disilabenzene complex that
adopts a metallodisilanorbornadiene structure.
1
observed J SiH coupling constant (195 Hz) is similar to
Resu lts a n d Discu ssion
that for the free silane (191 Hz) but greater than that
for Li[C5H5SiH(tBu)] (150 Hz).14 The 13C NMR shifts for
the coordinated silacyclohexadienyl ring carbons of 2,
δ 33.0 (C1, C5), 82.7 (C3), and 91.8 (C2, C4), are similar
to corresponding values reported for [Fe(η5-C5H5SiMe2)2]
(δ 38.87, 78.54, and 94.47) and are also consistent with
shifts for the pentadienyl ligand in Cp*Ru(η5-pentadi-
enyl) (δ 42.5, 82.5, and 91.5).17,18 It is worth noting that
these 13C chemical shifts are quite different from those
in Li[C5H5SiH(tBu)] (δ 81.5 (C1, C5), 142.6 (C2, C4), and
92.4 (C3)).14 Also, the 29Si NMR spectrum of 2 exhibits
a resonance at δ -33.7, which is somewhat upfield
relative to the analogous 29Si shift of δ -16.2 for Li-
[C5H5SiH(tBu)].14 Finally, the IR spectrum for 2 contains
A Sila ben zen e Com p lex. The ruthenium-based
fragment Cp*Ru+ is known to bind strongly to six-
electron π-systems, and a number of complexes of the
type [Cp*Ru(η6-arene)]+ are known.9 Our synthetic
strategy therefore targeted the generation of an analo-
gous silabenzene complex, via abstraction of hydride
from silicon10 in an appropriate silacyclohexadiene
complex. A similar method for generating an η6-arene
ligand via dealkylation of coordinated η5-cyclohexadi-
enyl has been reported.11 Furthermore, it has recently
been shown that treatment of the related η5-cyclohexa-
dienyl complex Cp*Ru[η5-6-exo-methylcyclohexadienyl]
with various Lewis acids results in hydride abstraction
and formation of [Cp*Ru(η6-arene)]+ derivatives.12 For
the purpose of preparing a silacyclohexadienyl complex,
we prepared the silacyclohexadiene 1 in two steps from
C5H6SnBu2 according to literature procedures13 (Scheme
1).
a strong stretch for the Si-H bond at 2087 cm-1
.
Initial attempts to abstract hydride from 2 employed
the trityl reagent [Ph3C][B(C6F5)4], room temperature,
and various solvents (benzene, tetrahydrofuran, dichlo-
romethane). However, these reactions gave only mix-
tures of products containing species that could not be
identified. In contrast, 2 reacted cleanly with the highly
Lewis acidic borane B(C6F5)3 to give [Cp*Ru(η6-C5H5-
SitBu)][BH(C6F5)3] (3, Scheme 1).
Interestingly, the course of this reaction is highly
dependent on the solvent employed, as there is no
reaction in ethereal solvents (tetrahydrofuran, diethyl
ether). In benzene-d6 the reaction produced several
It was shown previously that 1 can be deprotonated
n
with BuLi to give the “nonclassical silabenzene anion”
(8) Ma¨rkl, G.; Soper, C.; Hofmeister, P.; Baier, H. J . Organomet.
Chem. 1979, 165, 399.
(9) Fagan, P. J .; Ward, M. D.; Calabrese, J . C. J . Am. Chem. Soc.
1989, 111, 1698.
(10) (a) Corey, J . Y. J . Am. Chem. Soc. 1975, 97, 3237. (b) Lambert,
J . B.; Zhang, S.; Stern, C. L.; Huffman, J . C. Science 1993, 260, 1917.
(11) (a) Rondon, D.; Chaudret, B.; He, X.-D.; Labroue, D. J . Am.
Chem. Soc. 1991, 113, 5671. (b) Urbanos, F.; Halcrow, M. A.; Fernan-
dez-Baeza, J .; Dahan, F.; Labroue, D.; Chaudret, B. J . Am. Chem. Soc.
1993, 115, 3484. (c) Chaudret, N. Bull. Soc. Chim. Fr. 1995, 132, 268.
(d) Chaudret, B.; Halcrow, M. A.; Urbanos, F. Organometallics 1993,
12, 955. (e) Masuda, K.; Ohkita, H.; Kurumatani, S.; Itoh, K. Orga-
nometallics 1993, 12, 2221. (f) Dimauro, P. T.; Wolczanski, P. T.
Polyhedron 1995, 1, 149.
(12) Older, C. M.; Stryker, J . M. J . Am. Chem. Soc. 2000, 122, 2784.
(13) (a) Ashe, A. J ., III; Shu, P. J . Am. Chem. Soc. 1971, 93, 1804.
(b) Verkruijsse, H. D.; Hasselaar, M. Synthesis 1979, 292. (c) Ashe, A.
J ., III; Chan, W.-T. J . Org. Chem. 1979, 44, 1409. (d) J utzi, P.;
Baumga¨rtner, J .; Schraut, W. J . Organomet. Chem. 1977, 132, 333.
(14) J utzi, P.; Meyer, M.; Rasika Dias, H. V.; Power, P. P. J . Am.
Chem. Soc. 1990, 112, 4841.
(15) Fagan, P. J .; Ward, M. D.; Caspar, J . V.; Calabrese, J . C.;
Krusic, P. J . J . Am. Chem. Soc. 1988, 110, 2981.
(16) (a) Koelle, U.; Kossakowski, J . J . Chem. Soc., Chem. Commun.
1988, 547. (b) Koelle, U.; Kossakowski, J . J . Organomet. Chem. 1989,
362, 383.
(17) J ohnson, B. F. G.; Martin, C. M.; Nowotny, M.; Palmer, W.;
Parsons, S. Chem. Commun. 1997, 977.
(18) Bosch, H. W.; Hund, H.-U.; Nietlispach, D.; Salzer, A. Orga-
nometallics 1992, 11, 2087.

Silabenzene and Disilabenzene Complexes of Ru
Organometallics, Vol. 20, No. 6, 2001 1197
Ta ble 1. Com p a r ison of Rin g Ca r bon 13C NMR
Sh iftsa
This resonance is shifted only slightly from that in 2 (δ
-33.7) and is quite upfield from the corresponding peak
in C5H5Si(Tbt) (δ 92.1).5c The three resonances observed
in the 19F NMR spectrum (δ -133.8, -156.0, and
-163.4) and the peak in the 11B NMR spectrum (δ 2.16)
are consistent with the presence of a borate anion.19
Although a B-H resonance could not be identified in
the 1H NMR spectrum of 3 (presumably due to the
quadrupolar boron nucleus), a B-H stretch was ob-
served in the IR spectrum at 2380 cm-1. Finally, the
cation in 3 was definitively identified by high-resolution
mass spectrometry (FAB).
Compound
Li[C5H5SiH(tBu)]14
C1, C5 C2, C4
C3
81.5
42.5
33.0
39.8
88.5
122.2
142.6
91.5
91.8
92.5
88.5
92.4
82.5
82.7
83.3
88.5
Cp*Ru(η5-pentadienyl)18
Cp*Ru[η5-C5H5SiH(tBu)] (2)
[Cp*Ru(η6-C5H5SitBu)][BH(C6F5)3] (3)
[Cp*Ru(η6-benzene)]OTf9
C5H5Si(Tbt)5c
143.4 116.1
a
Note: C1 and C5 are the carbons ortho to silicon in a ring, C2
and C4 are in the meta positions, and C3 is para to silicon. For
Cp*Ru(η5-pentadienyl), the labels refer to analogous carbon atoms
in the pentadienyl ligand.
A Disila ben zen e Com p lex. Given our success in
isolating η5-silacyclopentadienyl and η6-silabenzene com-
plexes of the Cp*Ru fragment, we envisioned the
stabilization of a 1,4-disilabenzene derivative by coor-
dination (Scheme 2). We have previously described the
synthesis of a range of ruthenium silyl complexes via
reaction of Cp*(PMe3)2RuCH2SiMe3 at elevated tem-
peratures with various hydrosilanes HSiX3. These reac-
tions proceed with loss of SiMe4 and formation of
Cp*(PMe3)2RuSiX3 complexes.20 It was therefore ex-
pected that Cp*(PMe3)2RuCH2SiMe3 would react with
the previously reported trans-1,4-dihydrohexamethyl-
1,4-disilacyclohexa-2,5-diene (Scheme 2)3d,e,21 to give
complex A upon loss of SiMe4. We hoped that further
heating would result in loss of the PMe3 ligands and
coordination of the diene portion of the disilacyclohexa-
diene ligand to then give complex B. This is supported
by the fact that heating Cp*(PMe3)2RuSi(CHdCH2)Ph2
in toluene results in formation of the silaallyl complex
Cp*(PMe3)Ru(η3-Ph2SiCHCH2).22 Reaction of B with
Ph3C+ or B(C6F5)3 was then expected to give the desired
η6-disilabenzene complex C.
products (by 1H NMR spectroscopy). However, addition
of tetrahydrofuran (0.35 mL of benzene and 0.10 mL of
tetrahydrofuran) to this mixture converted these prod-
ucts to 3 (84% yield by 1H NMR spectroscopy). Reaction
also took place in a benzene/THF mixture (90:10) to give
3 in 85% yield (by 1H NMR spectroscopy). Notably,
removal of solvent gave 3 as an impure tan foam which
did not contain THF (by 1H NMR spectroscopy). It would
therefore seem that the role of THF in this reaction is
to provide a more polar solvent mixture, which aids in
formation of the ion pair. In pure tetrahydrofuran,
however, formation of a strong adduct with the borane
appears to inhibit its reaction with the Si-H bond.
Complex 3 could not be isolated in pure form from other
Cp*-containing impurities, and thus, characterization
is based largely on spectroscopic methods.
The 1H NMR spectrum for 3 is quite revealing, in that
resonances for the silabenzene ring protons appear as
3
a doublet (C1, C5, 2.34 ppm, J HH ) 10 Hz), a triplet
3
(C3, 4.24 ppm, J HH ) 5 Hz), and a doublet of doublets
3
3
(C2, C4, 4.58 ppm, J HH ) 5 Hz, J HH ) 10 Hz). No
resonance for an Si-H bond was visible in the spectrum,
and its absence is further supported by the lack of J HH
coupling constants attributable to this group. The 13C
NMR spectrum exhibits new resonances for the sila-
benzene ring carbons (δ 39.8 (C1, C5), 83.3 (C3), and
92.5 (C2, C4)). Interestingly, these resonances are not
perturbed significantly from those in 2 (δ 33.0 (C1, C5),
82.7 (C3), and 91.8 (C2, C4)) and are also similar to
shifts for the related carbons in Cp*Ru(η5-pentadienyl)18
(δ 42.5 (C1, C5), 82.5 (C3), and 91.5 (C2, C4)). Further-
more, as expected,9 the 13C shifts for 3 are shifted
considerably upfield relative to those for the free sila-
benzene derivative C5H5Si(Tbt)5c (δ 122.2 (C1, C5), 116.1
(C3), and 143.4 (C2, C4)). The above comparisons (see
Table 1) suggest that the bonding of the silabenzene in
3 may best be described as an η5,η1-interaction (reso-
nance form 3b) with limited delocalization in the
silabenzene ligand, but the available data are somewhat
ambiguous given that the 13C shift for the coordinated
benzene ligand in Cp*Ru(η6-C6H6)+ is similar to those
for C2-4 in 3.
Heating Cp′(PMe3)2RuCH2SiMe3 (Cp′ ) C5Me4Et)
with trans-1,4-dihydrohexamethyl-1,4-disilacyclohexa-
2,5-diene in toluene at 90 °C for 12 h did not produce
B, but instead gave Cp′(PMe3)RuH(η2-hexamethyl-1,4-
disilabenzene) (4), isolated as a white crystalline solid
1
in 86% yield (Scheme 2). The H NMR spectrum of 4
exhibits a characteristic hydride peak at δ -12.55 with
a
2J PRuH coupling constant (34 Hz) typical for hydride
complexes of Cp(PR3)nRu and Cp*(PR3)nRu (n ) 1 or
2).23 In addition, there are two distinct resonances for
the inequivalent Si-Me groups at δ 0.63 (s) and 0.75
4
(d, J PH ) 1 Hz). Finally, two different peaks are
observed in the 29Si NMR spectrum of 4 at δ 44.0 (d,
2
2J PSi ) 22 Hz) and 31.5 (d, J PSi ) 7 Hz).
(19) (a) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015. (b) Kidd, R. G. In NMR of Newly Accessible Nuclei, Vol. 2;
Laszlo, P., Eds; Academic Press: New York, 1983; p 49.
(20) Straus, D. A.; Zhang, C.; Quimbita, G. E.; Grumbine, S. D.;
Heyn, R. H.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J . J . Am. Chem.
Soc. 1990, 112, 2673.
(21) (a) Welsh, K. M.; Corey, J . Y. Organometallics 1987, 6, 1393.
(b) Atwell, W.; Weyenberg, D. J . Am. Chem. Soc. 1968, 90, 3438.
(22) Goldman, E.; Tilley, T. D. Unpublished results.
(23) (a) Tilley, T. D.; Grubbs, R. H.; Bercaw, J . E. Organometallics
1984, 3, 274. (b) Campion, B. K.; Heyn, R. H.; Tilley, T. D. J . Chem.
Soc., Chem. Commun. 1988, 278. (c) Campion, B. K.; Heyn, R. H.;
Tilley, T. D. J . Am. Chem. Soc. 1988, 110, 7558. (d) Arligue, T.;
Chaudret, B.; J alon, F.; Lahoz, F. J . Chem. Soc., Chem. Commun. 1988,
998. (e) Suzuki, H.; Lee, D. H.; Oshima, N.; Moro-oda, Y. Organome-
tallics 1987, 6, 1569. (f) Davies, S. G.; Moon, S. D.; Simpson, S. J . J .
Chem. Soc., Chem. Commun. 1983, 1287. (g) Bruce, M. I.; Tomkins, I.
B.; Wong, F. S.; Skelton, B. W.; White, A. H. J . Chem. Soc., Dalton
Trans. 1982, 687. (h) Lehmkuhl, H.; Grundke, J .; Mynott, R. Chem.
Ber. 1983, 116, 159.
The proton-coupled 29Si INEPT spectrum of 3 displays
a resonance at δ -23.1 which exhibits no 1J SiH coupling.

1198 Organometallics, Vol. 20, No. 6, 2001
Dysard et al.
Sch em e 2
X-ray quality crystals of 4 were grown by slow cooling
of a concentrated toluene solution to -35 °C, and an
ORTEP diagram is shown in Figure 1. The PMe3 group
was disordered over two positions and was modeled as
two partial occupancy phosphorus and six partial oc-
cupancy carbon atoms (see Experimental Section for
details). This disorder prevented accurate location of the
hydride ligand. Complex 4 adopts a four-legged piano
stool geometry with the legs composed of the PMe3, H,
and η2-hexamethyl-1,4-disilabenzene ligands. Although
several complexes of the type Cp*(PMe3)RuH(SiR3)2
have been reported in the literature,20,24 4 represents
the first crystallographically characterized complex of
this type. The Ru-Si distances (2.430(1) and 2.430(2)
Å) fall in the high end of the range reported for Ru-Si
bonds (2.190-2.465 Å).22 The Me-Si-Si alignment in
4 is surprisingly linear (178°), and the angle between
the Si(1)-C(1)-C(2)-Si(2) and Si(1)-C(3)-C(4)-Si(2)
planes (71.66°) is rather acute. Finally, the sum of the
angles about Si(1) and Si(2) (321° and 330.9°, respec-
tively) reflects tetrahedral silicon centers.
Two resonance forms (4a and 4b) can be invoked to
describe the bonding in 4. At one extreme 4 can be
described as a metallodisilanorbornadiene complex pos-
sessing a Ru(IV) center bound to two silyl ligands which
do not interact (4a ). The other resonance structure (4b)
represents a Dewar-disilabenzene complex with a Si-
Si bond coordinated to ruthenium. Interestingly, the Si-
(1)-Si(2) distance (2.621(2) Å) is relatively short com-
pared to the same distance in other crystallographically
characterized examples of hexamethyldisilacyclohexa-
diene derivatives. For example, the corresponding dis-
tances in cis-bis(1,4-trimethylsilyl)-1,2,3,4,5,6-hexame-
possessing chelating disilyl ligands, such as trihydrido-
[bis(dimethylsilyl)benzene]bis(triphenylphosphine)-
iridium (3.150 Å)26 and (η4-cyclohexa-1,3-diene)(2-tert-
butyl-1,1,4,4-tetrafluoro-1,4-disilabutene)Fe(CO)2 (2.754(9)
Å).27 Moreover, the Si-Ru-Si angle in 4 (65.24(4)°) is
smaller than the corresponding values in the latter two
complexes (80.68(4)° and 73.1(3)°, respectively).26,27
The somewhat short Si-Si contact in 4 (2.621(2) Å)
suggests an interaction between the two silicon centers.
For comparison, it has been argued that in the dimers
[(PR3)2PtSiR2]2, the short Si-Si separation (2.55-2.65
Å) is consistent with a bonding interaction.28 However,
for related 1,3-cyclodisiloxanes (R2SiO)2 possessing short
Si-Si contacts (2.31-2.39 Å), it has been concluded on
a theoretical basis that the bonding is best described
as four equivalent, localized Si-O bonds with no ap-
preciable σ-bonding between the silicon atoms.29 Finally,
the length of the Si-Si separation in 4 compared to the
(26) Loza, M.; Faller, J . W.; Crabtree, R. H. Inorg. Chem. 1995, 34,
2937.
(27) Hseu, T.-H.; Lin, C.-H.; Lee, C.-Y.; Liu, C.-S. J . Chin. Chem.
Soc. 1989, 36, 91.
(28) (a) Michalczyk, M. J .; Recatto, C. A.; Calabrese, J . C.; Fink, M.
J . J . Am. Chem. Soc. 1992, 114, 7955. (b) Levchinsky, Y.; Rath, N.;
Braddock-Wilking, J . Organometallics 1999, 18, 2583. (c) Zarate, E.
A.; Tessier-Youngs, C. A.; Youngs, W. J . J . Am. Chem. Soc. 1988, 107,
4068. (d) Zarate, E. A.; Tessier-Youngs, C. A.; Youngs, W. J . J . Chem.
Soc., Chem. Commun. 1989, 577. (e) Anderson, a. B.; Shiller, P.; Zarate,
E. A.; Tessier-Youngs, C. A.; Youngs, W. J . Organometallics 1989, 8,
2320. (f) Liu, X.; Palacios, A. A.; Novoa, J . J .; Alvarez, S. Inorg. Chem.
1998, 37, 1202. (g) Aullo´n, G.; Alemany, P.; Alvarez, S. J . Organomet.
Chem. 1994, 478, 75. (h) Alemany, P.; Alvarez, S. Inorg. Chem. 1992,
31, 4266.
thyl-1,4-disilacyclohexa-2,5-diene and
a
1,4-disila-
barralene derivative (1,4-dimethyl-2,3,5,6,7,8-hexaphe-
nyl-1,4-disilabicyclo[2.2.2]octa-2,5,7-triene) are 3.405
and 2.93 Å, respectively.25 The Si-Si separation in 4 is
also short relative to analogous distances in complexes
(29) (a) Michalczyk, M. J .; Fink, M. J .; Haller, K. J .; West, R.; Michl,
J . Organometallics 1986, 5, 531. (b) Yokelson, H. B.; Millevolte, A. J .;
Adams, B. R.; West, R. J . Am. Chem. Soc. 1987, 109, 4116. (c) Fink,
M. J .; Haller, K. J .; West, R.; Michl, J . J . Am. Chem. Soc. 1984, 106,
822.
(24) Corey, J . Y.; Braddock-Wilking, J . Chem. Rev. 1999, 99, 175.
(25) (a) Rich, J . D.; Shafiee, F.; Haller, K. J .; Harsy, S. G.; West, R.
J . Organomet. Chem. 1984, 264, 61. (b) Sekiguchi, A.; Gillette, G. R.;
West, R. Organometallics 1988, 7, 1226.

Silabenzene and Disilabenzene Complexes of Ru
Organometallics, Vol. 20, No. 6, 2001 1199
Ta ble 2. Su m m a r y of Cr ysta llogr a p h ic Da ta
empirical formula
fw
RuSi2PC24H45
521.83
cryst color, habit
cryst dimens
cryst syst
white, platelike
0.32 × 0.18 × 0.05 mm
triclinic
cell determination (2θ range)
3050 (4.0-45.0°)
a ) 9.1338(8) Å
b ) 10.3057(9) Å
c ) 15.584(1) Å
R ) 96.093(2)°
â ) 91.242(2)°
γ ) 114.225(1)°
V ) 1326.8(2) Å3
P1h (#2)
lattice params
space group
Z
Dcalc
µ(Mo KR)
diffractometer
radiation
2
1.306 g/cm4
7.50 cm-1
Siemens SMART
Mo KR (λ ) 0.71069 Å)
graphite monochromated
-106 °C
ω (0.3° per frame)
total: 6011
temperature
scan type
no. of reflns measd
F igu r e 1. ORTEP diagram of Cp′(PMe3)RuH(η2-hexam-
ethyl-1,4-disilabenzene) (4).
unique: 4236 (Rint )0.014)
no. observations (I>3.00σ(I))
structure solution
refinement
residuals: R; Rw
max peak in final diff map
min peak in final diff map
3039
direct methods (SIR92)
full-matrix least-squares
0.035; 0.044
Si-Si bond distance in the known Dewar-disilabenzene
derivative 1,4-dimethyl-2,3,5,6-trimethylsilyl-1,4-disila-
Dewar-benzene (2.244(2) Å)6 suggests that there may
not be a strong bonding interaction between the two
silicon centers in 4. Given the data described above, it
was difficult to describe the bonding in 4. Thus, a
theoretical investigation was undertaken.
0.74 e/Å3
-0.49 e/Å3
Ta ble 3. Com p a r ison of Selected Geom etr ic
P a r a m eter s Der ived fr om th e Exp er im en ta l X-r a y
Str u ctu r e of 4 a n d th e Ca lcu la ted Mod el System , 5
parametera
X-ray structure calculated structure
Si-Si
2.62
2.43
2.28
1.92
65
2.66
2.46
2.28
1.95
65
The bonding in 4 has been examined within the
framework of molecular orbital theory with Kohn-
Sham density functional calculations. Calculations were
performed on the model system Cp(PH3)RuH(η2-hex-
amethyl-1,4-disilabenzene) (5), in which the Cp′ and
PMe3 ligands in 4 are replaced by Cp and PH3, respec-
tively. In 5, the six methyl substituents on the disila-
benzene fragment remain “intact”, as they are in 4. The
model system has been fully geometry optimized, pro-
viding a structure that preserves the important geo-
metric features observed in the X-ray structure of 4.
Most notably, the Si-Si bond is calculated to be 2.67
Å, which agrees well with the X-ray value of 2.62 Å.
The two Ru-Si bond distances, which are calculated to
be 2.45 Å, also agree well with the X-ray values of 2.43
Å. Other parameters, tabulated in Table 3, also show
that 5 is a reasonable model for 4.
Ru-Si (av)
P-Ru
Ru-Cp centroid
Si-Ru-Si angle
C(Me)-Si-Si angle (av)
178
177
a
Distances reported in angstroms, angles reported in degrees.
To examine the nature of the Ru-Si bonding in the
HOMO and HOMO-1 orbitals, we first studied the Si-
Si bonding in the isolated disilabenzene fragment frozen
in the geometry that it has in 5. The HOMO of this
“frozen” fragment, shown in Figure 2d, can be charac-
terized as a weak Si-Si σ-bonding orbital.30 The con-
tribution of this Si-Si bonding orbital to the Ru-Si
bonding in 5 can be assessed by constructing molecular
orbitals using a basis of orbitals from the free disila-
benzene and Cp(PH3)RuH fragments. By using this
procedure we can, in the framework of molecular orbital
theory, quantify the contribution of this Si-Si σ-bonding
orbital to the two Ru-Si bonding orbitals (HOMO and
HOMO-1 of 5). Shown on the left-hand side of Figure 3
are isosurface plots of the HOMO and HOMO-1 orbitals
of 5. On the right-hand side of Figure 3 are isosurface
plots of the three fragment orbitals which have coef-
ficients that are the largest in magnitude. The values
shown below these fragment orbitals are the molecular
orbital eigenvector coefficients. Both the HOMO and
HOMO-1 are primarily composed of a Ru d-based
Three molecular orbitals in 5 can be distinguished as
exhibiting Si-Ru bonding character. These are the
HOMO-5, HOMO, and HOMO-1 orbitals, which are
shown in Figure 2a, 2b, and 2c, respectively, as isosur-
face plots. HOMO-5 (Figure 2a) can be characterized as
a σ-type orbital which is bonding between the Ru and
each Si atom. Since there is a node between the two
Si-Si centers, there is no Si-Si orbital interaction
associated with this MO. Thus, the HOMO-5 orbital
provides a bonding picture suggestive of resonance
structure 4a . On the other hand, the HOMO and
HOMO-1 of 5 (Figure 2b and 2c) can be described as
C-C π-bonding orbitals with significant Ru-Si bonding
character. Since no orbital nodes exist between the Si-
Si atoms, these two orbitals are suggestive of a weak
Si-Si bond that is coordinating to the Ru center, as
depicted in resonance structure 4b.
(30) Full geometry optimization of hexamethyl-1,4-disilabenzene
gives a Dewer benzene structure with a Si-Si bond distance of 2.28
Å. This is in good agreement with the Si-Si bond distance of 2.24 Å
recently observed by Ando and co-workers for a similar 1,4-disilabezene
complex.6 The Cartesian coordinates of the optimized disilabenzene
complex is provided in the Supporting Information.

1200 Organometallics, Vol. 20, No. 6, 2001
Dysard et al.
F igu r e 2. Isosurface plots of the Kohn-Sham molecular orbitals of 5 (a-c) and the isolated disilabenzene fragment (d)
fixed in the geometry of 5. The molecular orbitals presented in a-c can be characterized as Si-Ru bonding orbitals. The
molecular orbital of the disilabenzene fragment shown in d is characterized as a Si-Si bonding orbital.
orbital, the Si-Si σ-bonding orbital of the disilabenzene
fragment previously shown in Figure 2d, and a CdC
π-bonding orbital of the disilabenzene fragment. This
analysis reveals that HOMO and HOMO-1 of 5 both
have significant contributions from the Si-Si σ-bonding
orbital of the disilabenzene fragment and that there is
constructive overlap between the Si-Si σ-bonding or-
bital and the d orbitals of the Ru center. We note that
the Si-Si σ-bonding orbital of the disilabenzene frag-
ment does not contribute significantly to any other
molecular orbitals in 5. Thus, it can be said that there
is a weak Si-Si σ-type interaction in 5 that contributes
to the bonding of the disilabenzene fragment to the Ru
center. Consistent with this, a Mayer bond order
calculation provided a Si-Si bond order of 0.17 and Ru-
Si bond orders of 0.53 and 0.48.
of the Si-Me bonds is converted to a cis geometry. In
fact, we had specifically employed the trans isomer of
hexamethyl-1,4-disilacyclohexadiene in the hope that
intramolecular oxidative addition of the second Si-H
bond would not interfere with coordination of the diene
portion of the molecule. By monitoring the reaction of
Cp′(PMe3)2RuCH2SiMe3 with trans-1,4-dihydrohexam-
ethyl-1,4-disilacyclohexa-2,5-diene in toluene-d8 at 90
°C, an intermediate (A) was observed to build up after
1
6 h (9% by H NMR spectroscopy). For intermediate A,
a resonance at δ 4.87 is attributed to the Si-H hydro-
gen, and a pseudodoublet at δ 1.18 is assigned to the
18 hydrogens of the PMe3 ligands. In addition, A
exhibits two resonances at δ 0.61 and 0.49 for the Si-
Me groups, and four resonances are observed for the
ring methyl groups of the disilacylohexadiene and Cp′
(δ 1.67, 1.72, 1.91, and 1.98) ligands. The 31P NMR
spectrum of A exhibits a singlet at δ -0.42 for the
equivalent PMe3 ligands.
A possible mechanism for the isomerization of A is
given in Scheme 3. Further heating of this complex
could result in loss of a PMe3 ligand from the Ru center
to generate a 16-electron intermediate. This species
could then undergo a reversible 1,2-methyl migration
From this analysis we conclude that the bonding in 5
(and by analogy also in 4) can be described as interme-
diate between the two extreme resonance forms 4a and
4b, such that it is a metallodisilanorbornadiene that
possesses a weak Si-Si σ-bond that participates in the
bonding to the Ru center.
Interestingly, the formation of 4 implies that a
rearrangement occurs in which the trans arrangement

Silabenzene and Disilabenzene Complexes of Ru
Organometallics, Vol. 20, No. 6, 2001 1201
F igu r e 3. Composition of HOMO and HOMO-1 orbitals of 5 in the basis of the disilabenzene fragment and Cp(PH3)RuH
fragment. Isosurface plots of the HOMO and HOMO-1 orbitals of 5 are shown with the three fragment orbitals which
have the largest contribution to each. The molecular orbital eigenvector coefficients are shown with each fragment orbital.
Sch em e 3
from silicon to Ru, to produce an 18-electron ruthenium
silylene complex (D, Scheme 3). Rotation about the
metal-silicon bond, followed by methyl migration back
to silicon, would result in a cis arrangement of the Si-
Me groups, and oxidative addition of the remaining
Si-H bond could produce 4. There is little precedent
for 1,2-methyl migrations of this sort, but an example
has been reported for a related Ir system.31 Further-
more, it is reasonable to expect that rotation about the
Ru-Si double bond would be facile given that hindered
rotation has not been observed for related species32 and
+
that calculations suggest that CpL2RudSiR2 silylene
complexes possess mainly dative Si-Ru σ-bonds with
little Ru-Si π-back-bonding.33 Finally, it is worth
(32) (a) Straus, D. A.; Grumbine, S. D.; Tilley, T. D. J . Am. Chem.
Soc. 1990, 112, 7801. (b) Grumbine, S. D.; Tilley, T. D.; Rheingold, A.
L. J . Am. Chem. Soc. 1993, 115, 358. (c) Grumbine, S. D.; Tilley, T.
D.; Rheingold, A. L.; Arnold, F. P. J . Am. Chem. Soc. 1993, 115, 7884.
(d) Grumbine, S. K.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L. J .
Am. Chem. Soc. 1994, 116, 5495. (e) Grumbine, S. K.; Mitchell, G. P.;
Straus, D. A.; Tilley, T. D. Organometallics 1998, 17, 5607.
(33) Arnold, F. P. Organometallics 1999, 18, 4800.
(31) (a) Burger, P.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115,
10462. (b) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J . Am. Chem. Soc.
2000, 122, 1816.

1202 Organometallics, Vol. 20, No. 6, 2001
Dysard et al.
[Cp*RuCl]4 (0.758 g, 0.69 mmol) in 100 mL of THF. This
reaction mixture was stirred for 30 min before the volatile
materials were removed under dynamic vacuum. The remain-
ing dark orange residue was extracted into acetonitrile (3 ×
20 mL). The combined extracts were concentrated to 20 mL
and cooled to -78 °C to give 2 as a dark orange powder in
mentioning that rotation about a Ru-Si double bond
has been invoked to explain the fluxional behavior
observed in alkoxy-bridged bis(silylene)ruthenium com-
plexes.34
Complex 4 is quite thermally stable, as heating a
concentrated toluene-d8 solution to 120 °C for several
days resulted in no detectable change. In addition, 4 did
not react with [Ph3C][B(C6F5)4] or B(C6F5)3 at room
temperature (benzene, toluene, tetrahydrofuran, dichlo-
romethane) or upon heating to 100 °C in toluene.
Finally, 4 did not react with BPh3 (as a phosphine
sponge) in toluene or cyclohexane, even upon heating
to reflux for 24 h.
1
45% yield (0.487 g, 1.26 mmol). H NMR (benzene-d6): δ 4.77
(br s, 1 H, SiH), 4.65 (m, 3 H, C5H5SiHtBu), 1.88 (m, 2 H, C5H5-
SiHtBu), 1.69 (s, 15 H, C5Me5), 0.85 (s, 9 H, SitBu). 13C{1H}
NMR (benzene-d6): δ 91.80 (s, C5H5SiHtBu) 88.85 (s, C5Me5),
82.74 (s, C5H5SiHtBu), 32.97 (s, C5H5SiHtBu), 29.80 (s, SiC-
Me3), 25.21 (s, SiCMe3), 11.37 (s, C5Me5). 29Si{1H} (benzene-
d6): δ -33.7 (s, C5H5SiHtBu). Anal. Calcd for C19H30RuSi: C,
58.88; H, 7.80. Found: C, 59.24; H, 7.60. IR: 2916 s, 2845 s,
2087 s (Si-H), 1465 m, 1456 m, 1380 m, 1310 m, 1027 w, 835
s, 800 m, 579 m. Mp: 82-85 °C.
Con clu d in g Rem a r k s
[Cp*Ru (η6-C5H5SitBu )][BH(C6F5)3] (3). Compound 2 (0.165
g, 0.43 mmol) and B(C6F5)3 (0.218 g, 0.43 mmol) were placed
together in a Schlenk tube. Benzene (30 mL) and THF (3 mL)
were then added to the flask, producing a light tan solution.
This solution was stirred for 30 min, after which time the
volatile materials were removed under dynamic vacuum. The
remaining residue was isolated, giving 3 (0.380 g) as a slightly
contaminated tan foam. This reaction was performed on an
NMR-tube reaction scale and checked by 1H NMR spectros-
copy, giving 3 in 84% yield (vs a 1,3,5-trimethoxybenzene
standard). 1H NMR (benzene-d6): δ 4.58 (dd, 3J HH ) 5 Hz, 3J HH
In this contribution we have described the first
examples of transition metal complexes containing
silabenzene and disilabenzene ligands. Abstraction of
a hydride from silicon is a viable route to complexes of
this type, and we have utilized this method in generat-
ing 1-tert-butylsilabenzene in the coordination sphere
of Cp*Ru. In addition, hexamethyl-1,4-disilabenzene has
been coordinated to Ru in an η2 fashion. Binding of the
disilabenzene in this manner seems to involve an
interesting rearrangement, which may occur via a
silylene intermediate. It is of course yet to be seen
whether a less saturated metal center might bind this
fragment in an η6 manner. η6-Coordination to a transi-
tion metal fragment lends further support to the notion
that silabenzene derivatives are at least to some degree
aromatic. These studies demonstrate that coordination
of silabenzenes to a transition metal fragment is a useful
way to stabilize these reactive species, and we are
currently exploring routes to complexes of various
silabenzenes in the hope of gaining a better understand-
ing of their coordination chemistry.
3
) 10 Hz, 2 H, C5H5SitBu), 4.24 (t, 1 H, J HH ) 5 Hz, C5H5Sit-
3
Bu), 2.34 (d, 2 H, J HH ) 10 Hz, C5H5SitBu), 1.63 (s, 15 H,
C5Me5), 1.33 (s, 9 H, SitBu). 13C{1H} NMR (benzene-d6): δ 92.45
(s, C5H5SitBu) 88.48 (s, C5Me5), 83.27 (s, C5H5SitBu), 39.82 (s,
C5H5SitBu), 30.35 (s, SiCMe3), 29.85 (s, SiCMe3), 11.34 (s,
C5Me5). 29Si{1H} (benzene-d6): δ -23.1 (s, C5H5SitBu). 11B
(160.5 MHz, benzene-d6, 25 °C): δ 2.16 (br s, HB(C6F5)3). 19F
3
(376.5 MHz, benzene-d6, 25 °C): δ -133.8 (d, o-F, J FF ) 22
3
3
Hz), -156.0 (t, p-F, J FF ) 21 Hz), -163.4 (dd, m-F, J FF ) 22
3
Hz, J FF ) 21 Hz). IR: 2380 s (B-H). HRMS (FAB) calcd for
C
19H29RuSi: 387.1082. Found: 387.1098.
Cp ′(P Me3)Ru H(η2-1,4-Si2C4Me6) (4). Cp′(PMe3)2RuCH2-
SiMe3 (0.357 g, 0.73 mmol) and trans-1,4-dihydrohexamethyl-
1,4-disilacyclohexa-2,5-diene (0.143 g, 0.73 mmol) were placed
in a 200 mL sealable reaction vessel. To this reaction flask
was added 75 mL of toluene. The flask was placed in an oil
bath, and the solution was heated to 90 °C for 12 h. During
this time the initial deep yellow solution turned colorless. After
this time the volatile materials were removed under dynamic
vacuum. The remaining white residue was dissolved in toluene
(10 mL), and the resulting solution was cooled to -35 °C,
giving 4 as white blocklike crystals in 86% yield (0.327 g, 0.63
Exp er im en ta l Section
All manipulations were performed under an argon atmo-
sphere using standard Schlenk techniques or a nitrogen-filled
glovebox. Dry, oxygen-free solvents were employed throughout.
Pentane, toluene, benzene, and diethyl ether were distilled
from sodium/benzophenone, whereas benzene-d6 and toluene-
d8 were distilled from Na/K alloy. The compounds [Cp*RuCl]4,15
C5H5SiHtBu,13 B(C6F5)3,35 Cp′(PMe3)2RuCH2SiMe3,20 and trans-
1,4-disilahexamethylcyclohexadiene3d,e,21 were prepared ac-
cording to literature procedures. NMR spectra were recorded
at 300 or 500 MHz (1H) with Bruker AMX-300 and DRX-500
spectrometers and at 125 MHz (13C{1H}), 202 MHz (31P{1H}),
or 99 MHz (29Si{1H}) with the DRX-500 spectrometer, at
ambient temperature unless otherwise noted. Elemental analy-
ses were performed by the microanalytical laboratory in the
College of Chemistry at the University of California, Berkeley.
IR samples of solid materials were prepared as KBr pellets.
All IR absorptions are reported in units of cm-1 and were
recorded with a Mattson Infinity 60 MI FTIR spectrometer.
Cp *Ru [η5-C5H5SiH(tBu )] (2). A 100 mL Schlenk tube was
charged with C5H5SiHtBu (0.425 g, 2.79 mmol) and 50 mL of
1
3
mmol). H NMR (benzene-d6): δ 2.08 (q, 2 H, J HH ) 7 Hz, C5-
Me4CH2CH3), 2.09, 2.02, 1.91, 1.90 (s, 12 H, SiC4Me4Si), 1.62,
2
1.61, 1.57, 1.57 (s, 12 H, C5Me4Et), 0.98 (d, 9 H, J PH ) 9 Hz,
PMe3), 0.84 (t, 3 H, 3J HH ) 7 Hz, C5Me4CH2CH3), 0.75 (d, 3 H,
4J PH ) 1 Hz, SiMe), 0.63 (s, 3 H, SiMe), -12.6 (d, 1 H, J PH
)
2
34 Hz, Ru-H). 13C{1H} NMR (benzene-d6): δ 166.79, 165.60,
2
164.60, 164.12 (s, SiC4Me4Si), 100.75 (d, 1 C, J PC ) 2 Hz, C5-
Me4Et), 95.80, 95.30, 94.71, 94.41 (d, 4 C, 2J PC ) 2 Hz, C5Me4-
Et), 25.01 (d, J PC ) 31 Hz, PMe3), 20.39, 18.54, 18.43, 16.95,
16.81, 15.61, 11.68, 11.67, 11.54, 11.47 (s, 10 C, SiC4Me4Si and
C5Me4Et), -0.43 (s, SiMe), -3.10 (d, J PC ) 1 Hz, SiMe). 29Si-
3
{1H} (benzene-d6): δ 44.0 (d, J PSi ) 22 Hz, silicon atom trans
2
to PMe3), 31.5 (d, J PSi ) 7 Hz, silicon atom cis to PMe3). 31P-
2
{1H} NMR (benzene-d6): δ 6.00 (s, PMe3) Anal. Calcd for
C
24H45PRuSi2: C, 55.24; H, 8.69. Found: C, 55.30; H, 8.72.
n
THF. BuLi (1.00 mL, 2.80 mmol) was added to this flask via
IR: 2890 s, 1949 s (Ru-H), 1451 s, 1364 m, 1297 m, 1277 m,
1240 m, 1162 w, 1024 w, 948 s, 848 w, 768 s, 710 m, 667 m.
Mp: 143-146 °C.
Cp′(P Me3)2Ru (MeSiC4Me4SiHMe). This complex was iden-
tified in the reaction solution (toluene-d8) of Cp′(PMe3)2RuCH2-
SiMe3 and trans-1,4-dihydrohexamethyl-1,4-disilacyclohexa-
2,5-diene (9% by 1H NMR spectroscopy). 1H NMR (benzene-
syringe, and the resulting reaction mixture was stirred for 30
min to give a dark orange solution. This solution was then
added to a 250 mL round-bottom Schlenk flask containing
(34) Wada, H.; Tobita, H.; Ogino, H. Chem. Lett. 1998, 993.
(35) (a) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2,
245. (b) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1966, 5, 218.

Silabenzene and Disilabenzene Complexes of Ru
Organometallics, Vol. 20, No. 6, 2001 1203
3
d6): δ 4.87 (s, 1 H, SiH), 2.15 (q, 2 H, J HH ) 7 Hz,
Perdew38,39 were utilized in conjunction with the LDA param-
etrization of Vosko, Wilk, and Nusair40 for the calculation of
both the energy and gradients. An uncontracted triple-ú basis
of Slater-type orbitals was employed for the 4s, 4p, 4d, 5s, and
5p valence shells of the Ru center and is designated as the IV
basis in ADF. For the main group elements, a double-ú basis
of Slater-type orbitals was employed for the ns and np valence
shells that were augmented with polarization functions and
are designated the III basis in ADF. Inner shells were treated
with the frozen core approximation. A spin-restricted formal-
ism was used for all calculations, and no symmetry constraints
were used during geometry optimizations. In ADF, the system
is built-up from fragments that can be either atomic fragments
or molecular fragments. The molecular orbital coefficients
provided correspond to the symmetrized fragment orbitals in
ADF. The molecular orbital eigenvector coefficients in this
basis provide a direct interpretation of the molecular orbitals
in terms of frontier orbital theory. Isosurface plots were created
by the ADFPLT program version 1.0 of J . Autschbach. For all
plots shown an isosurface value of (0.06 au was utilized.
Mayer bond order calculations were performed with a minimal
single-ú basis set.41
C5Me4CH2CH3), 1.98, 1.91 (s, 12 H, SiC4Me4Si), 1.72, 1.67 (s,
2
12 H, C5Me4Et), 1.18 (d, 18 H, J PH ) 9 Hz, PMe3), 1.85 (t, 3
H, 3J HH ) 7 Hz, C5Me4CH2CH3), 0.61 (s, 3 H, SiMe), 0.49 (d, 3
H, J PH ) 1 Hz, SiMe). 31P{1H} NMR (benzene-d6): δ -0.42
4
(s).
X-r a y Cr ysta llogr a p h y. White, platelike crystals were
obtained from a concentrated toluene solution at -35 °C. A
crystal of dimensions 0.32 × 0.18 × 0.05 mm was mounted on
a glass fiber using paratone N hydrocarbon oil. Data were
collected using a Siemens SMART diffractometer with a CCD
area detector. A preliminary orientation matrix and unit cell
parameters were determined by collecting 60 10-s frames,
followed by spot integration and least-squares refinement. A
hemisphere of data was collected using ω scans of 0.3°. Frame
data were integrated (XY spot spread ) 1.60°; Z spot spread
) 0.60°) using the program SAINT (SAX Area-Detector
Integration Program; V4.024; Siemens Industrial Automation,
Inc.: Madison, WI, 1995). An absorption correction was
performed using SADABS (Tmax ) 0.9766, Tmin ) 0.8770). The
6011 integrated reflections were averaged in point group -1
to give 4236 unique reflections (Rint ) 0.014), but only 3039
reflections were considered observed (I > 3.00σ(I)). No decay
correction was necessary. The space group was determined to
be P1h. The structure was solved using direct methods (SIR92)
and refined by full-matrix least-squares methods using teXsan
software. The non-hydrogen atoms that showed no disorder
were refined anisotropically. The PMe3 group bound to Ru was
disordered over two positions. This disorder was modeled using
two different, partial occupancy, PMe3 groups. Both P atoms
were modeled with anisotropic displacement parameters, and
all the carbons (C(22)-C(27)) were refined isotropically. The
occupancy of P(2) was constrained to be equal to the difference
of one and the occupancy of P(1), as were carbons 25, 26, and
27. Carbons 22, 23, and 24 were constrained to have the same
occupancy as P(1). The occupancy factor was refined to 58%
for P(1) and carbons 22, 23, and 24 and to 42% for P(2) and
carbons 25, 26, and 27. The number of variable parameters
was 260, giving a data/parameter ratio of 11.69. The maximum
and minimum peaks on the final difference Fourier map were
0.74 and -0.49 e/Å3, respectively. R ) 0.035, Rw ) 0.044, GOF
) 1.53. The crystallographic data are summarized in Table 2.
Com p u ta tion a l Deta ils. All Kohn-Sham density func-
tional theory calculations were performed with the ADF2000.01
quantum chemistry package.36 The gradient-corrected ex-
change functional of Becke37 and the correlation functional of
Ack n ow led gm en t is made to the National Science
Foundation for their generous support of this work. We
thank Dr. Fred Hollander for assistance with the X-ray
structure determination. We thank Professor Stella
Constas and the Compaq-Western Centre for Compu-
tational Research for use of computing facilities, and
Professor Yitzhak Apeloig (Technion) for useful discus-
sions.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal,
data collection, and refinement parameters, bond distances
and angles, and anisotropic displacement parameters for 4.
The Cartesian coordinates of the optimized geometry of the
model complex 5 and hexamethyl-1,4-disilabenzene. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM000829M
(37) Becke, A. Phys. Rev. A 1988, 38, 3098.
(38) Perdew, J . P. Phys. Rev. B 1986, 34, 7406.
(39) Perdew, J . P. Phys. Rev. B 1986, 33, 8822.
(40) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200.
(41) Mayer, I. Chem. Phys. Lett. 1983, 97, 270.
(36) Scientific Computing
& Modelling NV, V. U., Theoretical
Chemistry, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.