Polyhedron Vol. IO, No. I I, pp. 117%3176, 1991 Printed in Great Britain

0277-5387/91 $3.00+.00 0 1991 Pergamon Press plc

REACTIONS OF THE RUTHENJUM SILYLENE DERIVATIVE [(q”-C,Me,)(PMe,),RuSiPh,OVCMe)]BPh, WITH ALCOHOLS,

KETONES AND ACETIC ACID

CHENG ZHANG, STEVEN D. GRUMBINE and T. DON TILLEYt

Department of Chemistry, D-006, University of California at San Diego, La Jolla, CA 92093-0506, U.S.A.

Abstract-The cationic ruthenium silylene complex [Cp*(PMe,),RuSiPh,(NCMe)]+BPh,- (1, Cp* = $-CSMeS) reacts with alcohols (MeOH, EtOH and ‘BuOH) to produce the ruthenium acetonitrile complex [Cp*(PMe,),Ru(NCMe)]+BPh,- (2) and the corresponding alkoxysilanes HSiPh20R (R = Me, Et, ‘Bu). At low temperature (- 6O”C), an intermediate (3) was observed in the reaction involving ethanol (by ‘H NMR spectroscopy). This intermediate gives rise to a RuH hydride signal (6 11.08), which appears as a triplet

(‘JPR~H = 11 Hz). This species may therefore be cis-[Cp*(PMe,),Ru(H)SiPh,OEt]BPh,, however, the very low *JpRuH coupling constant suggests a structure involving an q2-H- SiPh,OEt ligand. The mechanism of these reactions is suggested to consist of dissociative loss of acetonitrile to produce the base-free silylene complex [Cp*(PMe3)2Ru=SiPh2]+, which adds alcohol across the double bond to form 3. The observed silane products are then formed via reductive elimination from ruthenium. The enolizable ketones MeCOMe and MeCOPh react with 1 in a similar fashion to give 2 and the silyl enol ethers HSiPh2 (OCR=CH2) (R = Me, Ph). Acetic acid reacts with 1 to afford 2 and HSiPh,(OOCMe).

Transition metal silylene complexes (L,M = SiR2) have been implicated in a number of processes involving metal-mediated transfer of silylene groups. I In particular, it appears that such species may be key intermediates in metal-catalysed Si-Si bond-forming reactions. 2-6 For example, (PEt3)2 PtCl, acts as a catalyst for redistributing the disilanes RMe,SiSiMe,H (R = H or Me) to a mixture of oligomers R(SiMe*),H (n = 1-6).6a Addition of diphenylacetylene to this reaction mix- ture resulted in trapping of SiMe, groups to form Me2Si(CPh=CPh),SiMe2. Based on these obser- vations, Yamamoto et al. proposed that an inter- mediate Pt=SiMe, complex was responsible for transfer of silylene groups.6b Recently, Zybill et al. have shown that the dimethylsilylene derivative (CO),FeSiMe,(HMPA) thermally decomposes to Fe,(CO),, and polysilane of low molecular weight.>”

Direct, conclusive evidence for participation of silylene complexes in reaction schemes awaits reac- tivity studies based on isolated, well-characterized examples. To date only a few transition metal silyl-

t Author to whom correspondence should be addressed.

ene complexes have been reported, and these all display coordination of a Lewis base to the silylene silicon atom. 7-9 Furthermore, very little has been re- ported regarding reactivity trends for these species. We have described the synthesis and characteriz- ation of a cationic ruthenium silylene complex, [Cp*(PMe3)2Ru=SiPh2(NCMe)]+BPh4- - CH2C12 (1, Cp* = $-&Me,), which is labile in solution and serves as a source of the base-free silylene species Cp*(PMe3)2Ru=SiPh2+.8b Here we describe reac- tivity studies of this complex, which involve transfer of the silylene group to alcohol, ketone and acetic acid substrates.

RESULTS AND DISCUSSION

Complex 1 exhibits very limited reactivity toward the aryl silanes PhSiH3, Ph2SiH2 and Ph$iH. Whereas Ph2SiH2 and Ph$iH do not react with 1 in dichloromethane over a 3-day period, PhSiH, reacts slowly with 1 over 1 week to produce a num- ber of unidentified products.

Addition of excess methanol, ethanol or tert- butanol to a dichloromethane solution of 1 results in immediate, quantitative (by ‘H NMR spec- troscopy) conversion to the ruthenium acetonitrile

1173

1174 CHENG ZHANG et al.

complex 2 and the corresponding alkoxysilanes mediate 3 decomposes to 2 and HSiPh,OEt (t,,2 at HSiPh*OR [eq. (1) R = Me, Et, or ‘Bu]. -40°C = 40 min).

ROH BPh4’ -

CH,CI,

BPhi + “\SiPh RO/

2 (1)

Ruthenium complex 2 was identified by comparison of ‘H and 3’P NMR data with an authentic sample, prepared from Cp*(PMe3)2RuC1 and AgBPh4 in acetonitrile.8b Spectroscopic characterization of the alkoxysilanes was also facilitated by independent syntheses. These HSiPh20R compounds were obtained in high yields by reaction of HSiPh$l with pyridine and the corresponding alcohol in diethyl ether. These reactions are related to the pre- viously reported conversion of 1 and water to 2 and Ph,Si(H)OSi(H)Ph2.8b

Variable temperature ‘H NMR spectroscopy showed that 1 and ethanol react in dichloro- methane-d, at -60°C to form an intermediate hydride complex 3. This species exhibits a triplet resonance at 6 - 11.08 in the ‘H NMR spectrum, characteristic for a ruthenium hydride complex with equivalent coupling to two phosphorous nuclei. However, the *JpRuH coupling constant appears to be too low (11 Hz) to be due to the silyl- hydrido complex @ans-[Cp*(PMe3)ZRu(H)SiPhz 0Et]BPh4, since the related alkyl-hydrido complex [Cp*(PMe,),Ru(H)Me]BF4 has a ‘JpRuH coupling constant of 41.8 Hz.” The low *JpRuH coupling con- stant for 3, and the equivalence of the phosphine ligands, is consistent with a structure involving an q2-silane ligand, [Cp*(PMeJ2Ru(n2-HSiPh20Et)] BPhl. Note that the related silyl complexes Cp*(PMe3)Ru(SiR3)2H [SiR3 = Si(OEt)3, SiPh,Cl and SiMe,OEt] also possess low ‘JpRuH coupling constants (3 Hz), suggesting the possibility of rl*- HSiR3 ligands. 8b Other n2-HSiRj complexes have been reported, ’ ’ and it has been observed that simi- lar dihydrogen complexes Cp(L)(L’)Ru(q2-H2)+ are relatively stable species. ’ * Unusually small 2JPMH coupling constants for the “hydride” atom(s) of both q2-H2 and q*-HSiR3 complexes have been observed. Note that for Cp(Me2PCH2CH2PMe2) RuH2+, ‘JpRuH = 31 Hz, whereas for Cp(Me2PCH2 CH2PMe2)Ru(q2-Hz)+, ‘JpRuH = 3.6 Hz.lZc As the reaction solution is warmed above -60°C inter-

Reactions of 1 with alcohols and ketones (uide infra) are severely inhibited by addition of aceto- nitrile, suggesting that reactions occur via initial loss of acetonitrile from 1. Indeed we have pre- viously shown that the lability of 1 in solution is due to rapid, dissociative loss of acetonitrile.8b The above experimental observations suggest the pro- posed mechanism shown in Scheme 1. Intermediate 4 was not detected, but it is presumed that coor- dination of alcohol to the silylene silicon atom pre- cedes Si-H bond formation. Migration of hydro- gen may then proceed via transfer to ruthenium, giving the observed [Cp*(PMe,),Ru(H)SiPh,OR]+ intermediate complex that decomposes to 2 and HSiPh20R by reductive elimination. A kinetic iso- tope effect, determined by use of a 1: 1 EtOH/EtOD mixture, was found to be kH/kD = 1.0. This neg- ligible ‘isotope effect suggests that a hydrogen migration step is not rate-limiting.

Silylene complex 1 also reacts with enolizable ketones over the course of ca 1 h to provide quan- titative yields (by ‘H NMR spectroscopy) of 2 and silyl enol ethers [eq. (2) R = Me, Ph].

0 CH,CI, [Cp’L2RuSiPh,(NCMe)]+BPh, + -

K Me R

1

R

’ H”--SiPhz 2+ c (2) II CH,

Under comparable conditions, no reaction of benzophenone occurred over 12 h. The silyl enol ethers were separated from the reaction mixtures by removal of volatiles under vacuum and extrac- tion with pentane. After filtration, removal of the pentane under reduced pressure afforded the pure silyl enol ethers as colourless oils in high yields. For these reactions, no intermediates could be observed

Reactions of [(q5-CsMe,)(PMe,),RuSiPh,(NCMe)]BPh, 1175

-NCMe +ROH Cp’L,RuSiPhp(NCMe) + _ Cp’L,Ru=SiPh2+ _ Cp’L,RuSiPh,(ROH)+

+NCMe -ROH

1 4

NCMe /

H Cp’L,Ru(NCMe)* + HSiPhPOR - Cp’L2Ru+-~iph OR

2 or Cp*L2Ru+<

SiPh,OR 2

3

Scheme 1. (L = PMe,.)

by variable temperature ‘H NMR spectroscopy, but we assume that coordination of substrate to the silylene ligand is a crucial step. In a similar process, reaction of 1 with acetic acid gives 2 and HSiPh,(OOCMe).

The reactions reported here involve transfer of a silylene fragment (SiPhJ from a metal centre to another molecule. In addition, it is interesting to note that the silicon-containing products are those that would be expected from reactions of alcohols, ketones and carboxylic acids with free silylenes. I3 However, reactions involving the ruthenium silylene derivative 1 appear to be mechanistically distinct, in that the metal centre plays an important role. It is clear that there is much to be learned about reactions of transition metal silylene com- plexes, and future reports will address additional features of this chemistry.

EXPERIMENTAL

Manipulations were carried out under inert atmospheres of nitrogen or argon using standard Schlenk line and glovebox techniques. Dry, oxygen- free solvents were employed throughout. IR spectra were recorded on a Perkin-Elmer 1330 infrared spectrometer. NMR spectra were recorded on a GE QE-300 instrument at 300 MHz (‘H) and 121.5 MHz (“P). Mass spectra were obtained with a Hewlett-Packard 5988-A mass spectrophotometer. Complexes 1, 8b 28b and Cp*(PMe,),RuCl’4 were prepared according to literature procedures.

Reactions of 1 with protic substrates

A representative procedure is given for the reac- tion with methanol. Methanol (4.4 x 10e3 cm3, 0.108 mmol) was added to a dichloromethane solu- tion (2 cm3) of 1 (0.100 g, 0.108 mmol). After stir- ring the solution for 0.5 h, the volatiles were removed under vacuum. The sticky solid was extracted with pentane (5 cm3) and volatiles were removed from this extract to afford an oily liquid.

The remaining solid was shown to be 2 by ‘H NMR spectroscopy. The oily liquid was identified as HSiPh,(OMe) (ca 96% pure), by comparison of spectroscopic properties with an independently prepared sample.

Independent syntheses of silanes

These syntheses were accomplished using the reaction of HSiPhCl with pyridine and the appro- priate protic reagent. A representative procedure is given for HSiPh,OMe. The silane HSiPh*Cl (2.0 cm3, 0.010 mol) and methanol (0.44 cm3, 0.012 mol) were combined with diethyl ether (40 cm3) in a flask. Pyridine (1.1 cm3, 0.012 mol) was then added by syringe, and the resulting solution was stirred for 2 h. The reaction mixture was filtered and the volatiles were removed from the solution containing the product. This afforded an oily liquid which was distilled in vacua (98”C, 0.01 torr) to obtain 2.0 cm3 of product (85% yield).

(i) HSiPh,OMe. ‘H NMR (23°C benzene-d,) : 6 3.37 (s, 3H, OMe), 5.60 (s, 1 H, SiH), 7.15 (m, 6 H, Ph), 7.63 (m, 4 H, Ph). MS (EI) : parent ion observed at m/z 214. IR (neat, CsI, cm- ‘) : 3065 m, 3046 m, 2995 w, 2932 m, 2830 mn, 2118 s (SiH), 1588 w, 1428s, 1182m, 1115s 1080s,840s,815s,762m, 735 s, 698 s, 678 w.

(ii) HSiPh*OEt. ‘H NMR (23°C benzene-d,) : 6 1.09 (t, J = 7 Hz, 3 H, CH2CH3), 3.69 (q, J = 7 Hz, 2 H, CH,CH,), 5.66 (s, 1 H, SiH), 7.16 (m, 6 H, Ph), 7.66 (m, 4 H, Ph). MS (EI) : parent ion observed at m/z 228. IR (neat, CsI, cm-‘): 3065 w, 3045 w, 2970 m, 2865 w, 2117 s, (SiH), 1587 w, 1427 s, 1388w, 116Ow, 1112s 1024w,949m,849s,815s, 730 s, 695 s.

(iii) HSiPh,O’Bu. ‘H NMR (23°C benzene-d,) : 6 1.34 (s, 9 H, OCMe,), 5.55 (s, 1 H, SiH), 7.40 (m, 6 H, Ph), 7.61 (m, 4 H, Ph). IR (neat, CsI, cm- ‘) : 2110 s (SiH).

(iv) HSiPh,(OCMe=CH,). ‘H NMR (23°C benzene-d,): 6 1.88 (s, 3 H, CH3), 4.12 (d, J= 1.5 Hz, 1 H, =CH2), 4.18 (d, J = 1.5 Hz, 1 H,==CH&

1176 CHENG ZHANG et al.

5.59 (s, 1 H, SiH), 7.44 (m, 6 H, Ph), 7.67 (m, 4 H, Ph). MS (EI): parent ion observed at m/z 240. IR (neat, 01, cm- ‘) : 2130 s (SiH).

(v) HSiPh,(OCPh=CHz). ‘H NMR (23”C, benzene-d,) : 6 4.53 (d, J = 2 Hz, 1 H, =CH,), 4.96 (d, J = 2 Hz, 1 H, =CHJ, 5.72 (s, 1 H, SiH), 7.59 (m, 5 H, Ph), 7.70 (m, 6 H, Ph), 7.95 (m, 4 H, Ph). MS (EI) : parent ion observed at m/z 302. IR (neat, CsI, cm-‘) : 2131 s (SiH).

(vi) HSiPh,OOCMe. ‘H NMR (23”C, benzene-

d,): 6 2.18 (s, 3 H, CHJ, 5.65 (s, 1 H, SiH), 7.41 (m, 6 H, Ph), 7.63 (m, 4 H, Ph). MS (EI) : parent ion observed at m/z 242. IR (neat, CsI, cm- ‘) ; 2964 w, 2944 w, 2910 w, 2168 m (SiH), 1725 s, 1588 w, 1426s, 1367s, 124Os, 112Os, 1015m,993m,820s, 733 m, 695 m.

NMR data for 3

‘H NMR (-SST, dichloromethane-d,): 6 -1l.l4(t, J= 11 Hz, 1 H,RuH), 1.11 (t, J= 7Hz, 3 H, CH,CH,), 1.39 (br, 18 H, PMe,), 1.51 (s, 15 H, CsA4es), 3.56 (q, J = 7 Hz, 2 H, CH,CH,), 6.86 (t, 8 Hz, 4 H, BPh), 7.02 (t, J = 8 Hz, BPh), 7.25 (br, 8 H, BPh), 7.41 (br, 10 H, SiPh). “P NMR (- 85”C, dichloromethane-d,) : 6 - 0.18.

Acknowledgements-Acknowledgement is made to the National Science Foundation for generous support of this work. T.D.T. thanks the Alfred P. Sloan Foundation for a research fellowship (1988-1990). We also thank Johnson Matthey Inc. for a loan of ruthenium tri- chloride.

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