Transition-metal-catalyzed hydrosilylation and hydroboration of terminal alkynes in ionic liquids

Several ionic liquids have been studied as solvents for transition metal catalyzed hydrosilylation and hydroboration of terminal alkynes. Speier's catalyst has been used. In general, reactions are much faster in methyltrioctyl ammonium triflimide and P-E vinylsilanes were selectively obtained and isolated in good to excellent yields simply by bulb to bulb distillation. The solution of catalyst in ionic liquid could then be reused several times without loss of activity showing that recycling is an easy process. Lewis acidic chloroaluminate melts could also catalyze the hydrosilylation leading to Z-vinylsilanes and to some extent to polymerization of the starting alkyne. Rhodium and nickel (II) catalyzed hydroboration of terminal alkynes with pinacolborane was also studied. Wilkinson's catalyst in 1-butyl-3-methyl imidazolium chlorozincate at 40degreesC was shown to be the combination of choice for this reaction leading quantitatively to vinylboronates in less than two hours. Recycling of the zincate solution of rhodium catalyst could be realized with some lost of catalyst activity but with a significant increase of the regioselectivity. Nickel (II) gave regioselective hydroboration.