Hydroboration of alkyn-1-yl(methyl)silanes bearing functional substituents at silicon

Alkyn-1-yl(methyl)silanes Me2(H)Si–CC–R (1), Me(H)(Cl)Si–CC–R (2) and Me2(Cl)Si–CC–R (3) [R=Bu (a), tBu (b), Ph (c), SiMe3 (d)] react with 9-borabicyclo[3.3.1]nonane (9-BBN) by 1,2-cis-hydroboration to give selectively (except of 3d) the alkenylsilanes 4 (from 1), 5 (from 2), and 6 (from 3), in which the boryl group has become attached to the carbon atom adjacent to the silyl group bearing functional substituents. In the case of 3d, a mixture consisting of the alkenes 6d and the isomers 7d, 8d and 9d is obtained. All products were characterised by NMR spectra (1H-, 11B-, 13C- and 29Si-NMR) in solution, and in the cases of 5c and 6c, the molecular structures in the solid state were determined by X-ray analysis.