DEHYDROGENATIVE SILATION, ISOMERIZATION AND THE CONTROL OF SYN-ADDITION VS ANTI-ADDITION IN THE HYDROSILATION OF ALKYNES

Alkyne hydrosilation has been examined in detail for the catalysts [IrH(H2O)(bq)L2]SbF6 (L = PPh3, bq = 7,8-benzoquinolinato) and RhCl(PPh3)3. Factors that favor the normal syn- or the unusual anti-silane addition to the alkynes are examined. Two other unusual products are noted: the dehydrogenative silation product RC=CSiR3, formed by beta-elimination in a vinylmetal intermediate and allylsilane products of vinylsilane isomerization. The iridium catalyst is advantageous in that it does not give fast vinylsilane isomerization, as does RhCl(PPh3)3, so allowing formation and isolation of the thermodynamically less stable cis-, rather than the more stable trans-vinylsilane isomer RCH=CH(SiR3').