Palladium and platinum catalyzed hydroselenation of alkynes: Se-H vs Se-Se addition to CC bond

A mechanistic study of the hydroselenation of alkynes catalyzed by Pd(PPh3)(4) and Pt(PPh3)(4) has shown that the palladium complex gives products of both Se-H and Se-Se bond addition to the triple bond of alkynes, while the platinum complex selectively catalyzes Se-H bond addition. The key intermediate of PhSeH addition to the metal center, namely Pt(H)(SePh)(PPh3)(2), was detected by H-1-NMR spectroscopy. The analogous palladium complex rapidly decomposes with evolution of molecular hydrogen. A convenient method was developed for the preparation of Markovnikov hydroselenation products H2C=C(ScPh)R, and the scope of this reaction was investigated. The first X-ray structure of the Markovnikov product H2C=C(SePh)CH2N+HMe2-HOOCCOO- is reported. (C) 2003 Elsevier B.V. All rights reserved.