Abstract: | The reactions of alkyn‐1‐yl(vinyl)silanes R2SiC?C‐Si(H)Me2]CH?CH2 R = Me (1a), Ph (1b)], Me2SiC?C‐Si(Br)Me2]CH?CH2 (2a), and of alkyn‐1‐yl(allyl)silanes R2SiC?C‐Si(H)Me2]CH2CH?CH2 (R = Me (3a), R = Ph (3b)] with 9‐borabicyclo3.3.1]nonane in a 1:1 ratio afford in high yield the 1‐silacyclopent‐2‐ene derivatives 4a, b and 5a, and the 1‐silacyclohex‐2‐ene derivatives 6a, b, respectively, all of which bear a functionally substituted silyl group in 2‐position and the boryl group in 3‐position. This is the result of selective intermolecular 1,2‐hydroboration of the vinyl or allyl group, followed by intramolecular 1,1‐organoboration of the alkynyl group. In the cases of 4a, b, potential electron‐deficient Si? H? B bridges are absent or extremely weak, whereas in 6a,b the existence of Si? H? B bridges is evident from the NMR spectroscopic data (1H, 11B, 13C and 29Si NMR). The molecular structure of 4b was determined by X‐ray analysis. Copyright © 2005 John Wiley & Sons, Ltd. |