J. Am. Chem. Soc. 1995,117, 10139-10140
10139
Catalytic Hydrosilation of Organic Esters Using Manganese Carbonyl Acetyl Complexes. (L)(CO)4MnC(O)CH, (L = CO, PPhJ) Zhibiao Mao, Brian T. Gregg, and Alan R. Cutler* Depnrtmenr of Ckemisrry Rensselner Polytechnic Institute Troy, New York 12180 Received Februnv 17. 1995 Revised Manuscripr Received A u g u r 15, 1995 Although the hydrosilation of ketones is catalyzed readily by a number of transitionmetal compounds,l organic esters have previously been regarded as inert.' Recently, Buchwald and co-workers established that catalytic quantities of the titanium complexes CpzTiClzh-BuLi or Ti(O-i-Pr)q and (EtO),SiH reduce esters to alcohols (after aqueous workup).? We now report that manganese acetyl complexes (L)(C0)4MnC(0)CH3 [L = PPhj, (1); CO, (2)] catalyze the hydrosilation of esters RC(=O)OR to give successively silyl acetal RCH(OSiR",)OR', then ether RCHzOR' or alkoxysilane products RCH,OSiR', and R'OSiR",.5 Addition of I .5-3.0 mol % of 1 to a ChDhsolution containing ethyl acetate and PhSiH3 exothermically transformed this ester within 15 min to ethyl ether (85%) and PhSiH(OEt)? (eq I)." 0
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.
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\om
.
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= ,PP",,IM,.MnC,O,C*r ICO,,M"CIOIC*>
The role of silyl acetal intermediates during catalytic ester hydrosilation was probed by switching to PhzSiH? and PhMe2SiH (eqs 2 and 3). Hydrosilation of CHICO2Et by Ph?SiHz (1.2 equiv) and 3% 1 (30 min) gave PhzSiH[OCH(CH?)OEt] (3) (95% NMR yield isolated, 81%) and Ph2SiH(OEt) (5%).& With 2.2 equiv of PhzSiHz, however, 3 smoothly converted to ether and (PhIHSi)20. Using 2 as the catalyst (1.2 equiv of PhzSiHz) again slowed the reaction (2.5 h to consume the ester) but also yielded a 2.1 mixture of 3 and PhzSi[OCH(CHz)OEt]z (4) (eq 2). Reaction of this mixture with 1.2 equiv of PhSiH? and fresh 2 for 2 h produced E t 2 0(88%) and the alkoxysilanes Ph2SiH(OEt) and PhSiH(OEt)2.
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lli
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,Co!,M"S,Ua*Ph ,h",
With the precatalyst 2. the slower reactions quantitatively gave Et20 after 1.5 h. Under similar conditions, the less effective Mn(C0)sCHz and Mn(C0)sBr catalysts converted CH?C02Et over 4 h to Et20 (85 and 55%). in addition to the silyl acetals PhSiH1-.,[OCH(CHi)OEt]., ( x = I , 2). In contrast, Mn(CO)s(SiMe2Ph). Mn(CO)s(SiHPh2), and Mn2(CO)tn were inactive. ( I 1 Reviews: (a) Ojims. 1. In The C b r m i . ~ rqf ~ O r p n i c Silicon C~~mporwr1.v: Patai. S.. Rappopon. 2.. Eds.: Wiley Interscience: New York. 1989: Part 2. Chapter 25. (h) Marciniec. B.; GuliRski, I . 1. O r ~ a n r ~ m e r . Clr~wn1993. 446. IS. (2) (a1 Ojima. I.: Kumagai. M.: Nsgai. Y. J. Oyq'onomer. C h m 1976. 111. 43. Ojima. I.: Kogurr. T.: Kumagai. M. J . O r i . Clwx. 1977. 42. 1671. (hl Metal halides under harsh or noncalalytic reaction conditions promote the hydrosiliition of esters: Coni". R. I. P.; Pen. R.: Reyt, C. T~,l,nlr
