361 Journnl of Orgunometallic Chemisrry, 382 (1990) 361-373 Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands JOM 20446 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Regiochemical and mechanistic studies of the addition of tin hydride and oxide to substituted ketenes Azzam S. Hneihen, Joseph W. Bruno * Hall-Atwater Laboratories, Wesleyan University, Middletown, CT 06457 (U.S.A.) and John C. Huffman Molecular Structure Center, Indiana Unioersity, Bloomington, IN 47405 (U.S.A.) (Received August 7th, 1989) Abstract The reactions of aryl-substituted ketenes with tri-n-butyltin hydride give rise to O-bound tin enolates. With unsymmetrically-substituted methyl phenyl ketene this process exhibits little or no stereoselectivity. The kinetic mixture consists of virtually equal proportions of E and Z enolate isomers, which then equilibrates to a 71/29 Z/E mixture under thermodynamic control. Mechanistic studies are not consistent with either radical or polar mechanisms, and a concerted pathway with differential rates of bond formation is proposed. With dimethyl ketene a similar reaction gives a vinyl ester enolate, which presumably results from an initially-formed aldehyde enolate. Finally, the reaction of diphenyl ketene with tri-n-butyltin oxide results in a tin carboxylate which adopts a polymeric structure in the solid state. Introduction Ketenes are highly unsaturated molecules which serve as reactive substrates toward a variety of nucleophiles and ketenophiles [l]. These reactions can proceed with high levels of stereoselectivity, and result in carbonyl and/or cycloaddition products. Further, ketenes are currently thought to be intermediates in the Fischer-Tropsch synthesis of hydrocarbons from synthesis gas (CO/H,) mixtures [2]. Their formation is believed to involve the coupling of surface-bound methylene and carbon monoxide moieties [3], a process which has been amply modeled in homogeneous systems. Less is known, however, about the ultimate fate of the intermediate ketenes. Studies of their possible reduction pathways are thus im- portant, bearing on both synthetic and catalytic processes. One obvious means by which ketenes could be reduced is via insertion into a metal-hydride linkage. This process could exhibit a regiochemical preference for the 0022-328X/90/$03.50 0 1990 Elsevier Sequoia S.A.