Regio- and stereoselective addition of sterically hindered silylboranes to terminal alkynes

Novel stable organosilylboranes possessing dimesityl groups attached to boron were synthesised. They gave an addition reaction with terminal acetylenic hydrocarbons in the presence of a transition metal complex. Thus, (diphenylmethylsilyl)dimesitylborane and (diphenyl-tert-butylsilyl)dimesitylborane reacted in good yields with phenylacetylene and alk-1-ynes in the presence of Pd2(dba)3(etpo)2 as a catalyst. The structures of the products were determined by NMR spectroscopy using INEPT techniques coupled to computational simulation. Various heteronuclear coupling constants and were determined for the first time in this series. The results showed that the dimesitylboryl group added to the terminal acetylenic carbon atom and the organosilyl group to the internal carbon atom, according to a regio- and stereoselective syn-addition.