Oxidative addition of a Si-C(sp) bond to ruthenium: Synthesis and reactivity of Ru(SiMe3)(C≡CSiMe3)(CO)(PtBu 2Me)2

Article abstract of DOI:10.1021/om9609776

Me₃SiC≡CSiMe₃ reacts with Ru(H)₂(CO)L₂ (L = P^tBu₂Me) to give Ru(SiMe₃)(CCSiMe₃)(CO)L₂, characterized by solution spectroscopic and single-crystal X-ray diffraction methods. The molecule is square-pyramidal with an apical SiMe₃ group and CO and CCSiMe₃ in mutually trans basal sites.

Full text of DOI:10.1021/om9609776

292
Organometallics 1997, 16, 292-293
Oxid a tive Ad d ition of a Si-C(sp ) Bon d to Ru th en iu m :
Syn th esis a n d Rea ctivity of
Ru (SiMe3)(CtCSiMe3)(CO)(P tBu 2Me)2
Dejian Huang, Richard H. Heyn, J ohn C. Bollinger, and Kenneth G. Caulton*
Department of Chemistry and Molecular Structure Center, Indiana University,
Bloomington, Indiana 47405-4001
Received November 14, 1996X
Summary: Me3SiCtCSiMe3 reacts with Ru(H)2(CO)L2
(L ) PtBu2Me) to give Ru(SiMe3)(CCSiMe3)(CO)L2,
characterized by solution spectroscopic and single-crystal
X-ray diffraction methods. The molecule is square-
pyramidal with an apical SiMe3 group and CO and
CCSiMe3 in mutually trans basal sites.
NMR signals, and a PMe 1H NMR virtual triplet
(indicating transoid phosphines). Particularly diagnos-
tic are two 13C NMR signals due to sp carbons, one of
which (CR) is a triplet (16.4 Hz) due to coupling to two
equivalent phosphorus nuclei. The fate of the two
hydride ligands is established to be H2, which is
scavenged by unreacted Ru(H)2(CO)L2 to give (eq 3) the
Examples of scission of Si-C bonds by transition
metals at 25 °C are rare but not unknown. Several
examples of an η2-Me3SiC2R complex of Rh have been
reported to show 1,2-silyl migration to form vinylidene
complexes,1 either thermally or photochemically (eq 1).
However, there are no experimental observations on the
mechanism of this migration. Vinylsilanes react with
certain metal hydrides to interchange hydride and silyl
groups (eq 2), by a mechanism proposed to involve
migration of a â-silyl substituent onto the transition
metal.2
1
broad hydride H NMR signals of fluxional Ru(H)2(H2)-
(CO)L2.3b Ru(H)2(H2)(CO)L2 loses H2 to re-form Ru(H)2-
(CO)L2. The fate of the H2 is 50% H2 gas. The other
50% H2 hydrogenates (see below) excess Me3SiCtCSiMe3
to form cis- and trans-(Me3Si)CHdCH(SiMe3), which
were identified by characteristic vinyl and trimethylsilyl
proton NMR signals. No intermediate is detected when
the reaction of eq 3 is monitored by 31P NMR spectros-
copy.
The crystal structure of this product (Figure 1),
crystallized from SiMe4, shows the molecule to have a
square-pyramidal structure with trans phosphines.5 The
silyl group occupies an apical position, showing that this
is a stronger σ donor ligand than the acetylide ligand,
which is in a basal site and trans to CO because this
facilitates a push-pull π-donation6 from the acetylide
filled π(CC) orbital. While the trimethylsilyl (cf. tertiary
alkyl) group occupies the more crowded apical site, its
Ru-Si distance (2.382(2)Å) is only modestly longer than
We report here several reactions involving unsatur-
ated ruthenium species in which a Me3Si-C(sp) bond
is cleaved, with addition of both Si and C to the
ruthenium center. Such an addition is unprecedented
on reaction with coordinatively unsaturated transition-
metal species.
7
that (2.331(2) Å) in RuH(SiHPh2)(CO)(PtBu2Me)2 and
(4) Ru (SiMe3)(CCSiMe3)(CO)L2 (L ) P tBu 2Me). A cold solution
of 0.22 mmol of Ru(H)2(CO)L2 was prepared and diluted with toluene
(5 mL). A cold toluene (5 mL) solution of Me3SiCCSiMe3 (0.05 mL, 0.22
mmol) was added to the red solution. After the mixture was stirred at
-75 °C for 3 h, the cold bath was removed and the solution evaporated
to dryness. Extraction of the red-orange residue with pentane (2 × 10
mL) and subsequent removal of the volatiles provided a sticky dark
red-orange solid. Purification by recrystallization from tetramethyl-
silane (-40 °C) provides dark red-orange crystals (40%). 1H NMR
(C6D6, 23 °C): δ 0.34 (s, 9H, SiCH3), 0.73 (s, 9H, SiCH3), 1.24
(overlapping t, J N ) 13 Hz, 36H, PCCH3), 1.59 (vt, N ) 5.1 Hz, 6H,
PCH3). 13C{1H} NMR (C6D6, 20 °C): δ 1.11 (s, SiC), 7.93 (t, J PC ) 9.1
Hz, PCH3), 13.6 (s, SiC), 30.2 (s, PCCH3), 31.6 (s, PCCH3), 35.33 (vt,
NPC ) 16.6 Hz, PCCH3), 35.7 (vt, NPC ) 16.5 Hz, PCCH3), 124.8 (s,
RuCC), 167.2 (t, J PC ) 16.4 Hz, RuCC), 203.5 (t, J PC ) 11.0 Hz, RuCO).
31P{1H} NMR (C6D6, 20 °C): δ 50.1. IR (C6D6, cm-1): νCC 2010, νCO
1902. Anal. Calcd for C27H60OP2RuSi2: C, 52.31; H, 9.75. Found: C,
52.70; H, 9.28.
Reaction of Ru(H)2(CO)L23a (L ) tBu2MeP) with excess
Me3SiCtCSiMe3 proceeds in toluene or cyclohexane to
give 90% Ru(SiMe3)(CCSiMe3)(CO)L2 (based on 31P
NMR).4 This molecule was characterized by two SiMe3
1H and 13C NMR signals, diastereotopic tBu H and 13C
1
X Abstract published in Advance ACS Abstracts, J anuary 15, 1997.
(1) (a) Bantel, H.; Powell, A. K.; Vahrenkamp, H. Chem. Ber. 1990,
123, 661. (b) Rappert, T.; Nu¨rnberg, O.; Werner, H. Organometallics
1993, 12, 1359. (c) Baum, M.; Windmu¨ller, B.; Werner, H. Z. Natur-
forsch. 1994, 49B, 859. (d) Werner, H.; Baum, M.; Schneider, D.;
Windmu¨ller, B. Organometallics 1994, 13, 1089.
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1995, 2003. (b) Wakatsuki, Y.; Yamazaki, H. J . Organomet. Chem.
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(3) (a) Heyn, R. H.; Macgregor, S. A.; Nadasdi, T. T.; Ogasawara,
M.; Eisenstein, O.; Caulton, K. G. Inorg. Chim. Acta, in press. (b)
Gusev, D. G.; Vymenits, A. B.; Bakhmutov, V. I. Inorg. Chem. 1992,
31, 1.
(5) Crystallographic data (-165 °C): a ) 11.168(2) Å, b ) 18.043-
(4) Å, c ) 17.746(4) Å, â ) 108.03(1)° with Z ) 4 in P21/n. R(F) )
0.0462 for 2823 observed (F > 4σ(F)) data.
(6) Caulton, K. G. New J . Chem. 1994, 18, 25.
S0276-7333(96)00977-6 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 3, 1997 293
The reactivity of Ru(SiMe3)(CCSiMe3)(CO)L2 observed
to date shows ready reductive elimination with re-
formation of the SisC bond. Slow reaction with CO over
12 h produces Ru(CO)3L2 and liberates alkyne, while
the complex reacts (70 °C, 12 h) in benzene under argon
to liberate alkyne and produce (η6-C6H6)Ru(CO)L and
equimolar L.10 If excess fluorobenzene is heated (70 °C,
12 h) with Ru(SiMe3)(CCSiMe3)(CO)L2 in benzene,
oxidative addition occurs exclusively to the ortho CsH
bond of C6H5F. Reaction of Ru(SiMe3)(CCSiMe3)(CO)-
L2 with 1 atm of H2 (excess) in benzene at 25 °C gives
Ru(H)2(H2)(CO)L2, which hydrogenates the liberated
Me3SiCCSiMe3 to cis- and trans-(Me3Si)HCdCH(SiMe3).
Reaction with equimolar Me3SiCtCH (70 °C, 20 min)
gives only partial consumption of Ru(SiMe3)(CCSiMe3)-
(CO)L2, with production of a trace of RuH(CCSiMe3)-
(CO)L2 along with the major products Ru(trans-CHdCH-
SiMe3)(CCSiMe3)(CO)L2 and Ru(CCSiMe3)2(CO)L2. The
last two are known reaction products of the former with
Me3SiCCH.12
F igu r e 1. ORTEP drawing of the non-hydrogen atoms of
Ru(SiMe3)(CCSiMe3)(CO)(PtBu2Me)2. Selected bond dis-
tances (Å) and angles (deg): Ru-C(26) ) 2.048(6), Ru-
C(32) ) 1.852(7), C(26)-C(27) ) 1.216(8); C(26)-Ru-C(32)
) 171.3(3), C(32)-Ru-Si ) 91.2(2), Ru-C(26)-C(27) )
176.0(6), Ru-C(32)-O(33) ) 174.0(6).
The majority of literature reports on transition-metal/
silicon chemistry involve migration of silicon from the
metal to carbon.13 Cleavage of SisC bonds with coor-
dination of SiR3 has been mainly limited to reports
which fail to account for the carbon fragment.14 How-
ever, an especially important exception is the oxidative
addition15 of both acetylide substituents of Me2Si(C2Ph)2
to L2Pt(C2H4)2 to give A. Two examples are known of
it shows no unusual Ru-Si-C angles (range 115.2(3)-
116.8(3)°). The most unusual feature of the structure
is the acute Si-Ru-C(CSiMe3) angle, 80.2(2)°. Al-
though the Si-C(CSiMe3) distance, 2.87 Å, is certainly
nonbonding (the C3 axis of the SiMe3 group also points
directly towards Ru), no comparably acute angle has
been observed in square-pyramidal d6 species.8 There
are no agostic interactions with ruthenium; the closest
t
hydrogen (from a Bu methyl) is 2.77 Å from the metal.
t
One Bu group from each phosphine projects below the
base of the square pyramid, and one methyl of the SiMe3
group eclipses the Ru-C-O bond. Consistent with the
presence of the bulky SiMe3 ligand, P-Ru-P is
uncharacteristically small (160.73(6)°).
SisC(sp3) cleavage under mild conditions.16,17 The
reactions reported here should allow for a more detailed
determination of whether SisC(sp) oxidative addition
always involves an intermediate η2-alkyne complex and
whether it responds to varying electron donation and
withdrawal in RC6H4CCsSiMe2(aryl) substrates, as
would be expected for an “oxidative” process.
There is supporting evidence that the SisC bond
cleavage is a redox process, requiring zerovalent Ru.
Some Ru(SiMe3)(CCSiMe3)(CO)L2 is formed by Mg
reduction of RuCl2(CO)L2 in THF in the presence of Me3-
SiCCSiMe3.9 Electron density at Ru is also implicated
as an important component of this reaction because
Ru(CO)2L2, with one more electron-withdrawing carbo-
nyl ligand than “Ru(CO)L2”, fails10 to react at all (not
even adduct formation) with Me3SiCCSiMe3 (although
it does oxidatively add the HsC bond of HsCCPh).
Ack n ow led gm en t. This work was supported by the
National Science Foundation. We also thank J ohnson
Matthey/Aesar for material support.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details for the reactions of Ru(SiMe3)(CCSiMe3)(CO)-
L2 and tables giving full crystallographic data, positional
parameters, and bond lengths and bond angles for Ru(SiMe3)-
(CCSiMe3)(CO)L2 (7 pages). Ordering information is given on
any current masthead page.
tBuCtCSiMe3
Ru(SiMe3)(CtCtBu)(CO)L2.11
also
reacts
similarly,
giving
(7) Heyn, R. H.; Huffman, J . C.; Caulton, K. G. New J . Chem. 1993,
17, 797-803.
OM9609776
(8) The H-Ir-C(ipso) angle is 78° in IrH(C6H5)Cl(PCy3)2: Werner,
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(9) This reaction, which might proceed through “Ru(CO)L2”, pro-
duces numerous other phosphorus-containing products, perhaps be-
cause the reduction in fact proceeds through a Ru(I) species.
(10) Ogasawara, M.; Macgregor, S. A.; Streib, W. E.; Folting, K.;
Eisenstein, O.; Caulton, K. G. J . Am. Chem. Soc. 1996, 118, 10189.
(11) Spectroscopic data of Ru(SiMe3)(CCtBu)(CO)L2. Anal. Calcd for
C28H60OP2RuSi: C, 55.57; H, 10.01. Found: C, 55.12; H, 9.74. 1H NMR
(C6D6, 20 °C): 1.61 (vt, N ) 6 Hz, 6H, PCH3), 1.38 (s, 9H, CC(CH3)3),
1.26 (vt, N ) 12.6 Hz, 18H, PC(CH3)3), 1.20 (vt, N ) 12.6 Hz, 18H,
P(CCH3)3), 0.74 (s, Si(CH3)3) ppm. 31P{1H} NMR (C6D6, 20 °C): 51.65
ppm. 13C{1H} NMR (C6D6, 20 °C): 203.6 (t, J PC ) 13 Hz, CO), 126.5
(s, CtBu), 126.0 (t, J PC ) 17 Hz, RusCCtBu), 35.7 (vt, N ) 16.2 Hz,
PsC(CH3)3), 35.4 (vt, N ) 16.2 Hz, PC(CH3)3), 32.2 (s, CC(CH3)3), 31.9
(s, PC(CH3)3), 30.4 (s, PC(CH3)3), 13.9 (s, Si(CH3)3), 7.7 (vt, N ) 9.5
(12) Pedersen, A.; Tilset, M.; Folting, K.; Caulton, K. G. Organo-
metallics 1995, 14, 875.
(13) (a) Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L.
J . Organometallics 1996, 15, 1793. (b) Braunstein, P.; Knorr, M. J .
Organomet. Chem. 1995, 500, 21. (c) Hikida, T.; Onitsuka, K.; Sono-
gashira, K.; Hayashi, T.; Ozawa, F. Chem. Lett. 1995, 985.
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1995, 14, 3855.
(15) Cirrano, M.; Howard, J . A. K.; Spencer, J . L.; Stone, F. G. A.;
Wadepohl, H. J . Chem. Soc., Dalton Trans 1979, 1749.
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Angew. Chem., Int. Ed. Engl. 1990, 29, 880.
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13, 2309. (b) Hua, R.; Akita, M.; Moro-oka, Y. J . Chem. Soc., Chem.
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Hz, PCH3) ppm. IR (C6D6): ν(CO) 1896, ν(CC) 2150 cm-1
.