1,1‐Organoboration of silylethynyltin compounds studied by multinuclear magnetic resonance spectroscopy: isomerization at the CC bonds and electron‐deficient SiHB bridges

1,1‐Organoboration, using triethyl‐, triallyl‐ and triphenyl‐borane (BEt 3 , BAll 3 , BPh 3 ), of dimethysilylethynyl(trimethyl)stannane, Me 3 SnCCSi(H)Me 2 ( 1 ), affords alkenes bearing three different organometallic groups at the CC bond. For BEt 3 and BPh 3 , the first products are the alkenes 4 with boryl and stannyl groups in cis‐positions. These rearrange by consecutive 1,1‐deorganoboration and 1,1‐organoboration into the isomers 5 as the final products, where boryl and silyl groups are in cis‐positions linked by an electron‐deficient SiHB bridge. 1,1‐Ethylboration of bis(dimethylsilylethynyl)dimethylstannane, Me 2 Sn[CCSi(H)Me 2 ] 2 ( 2 ), leads to the stannacyclopentadiene 6 along with non‐cyclic di(alkenyl)tin compounds 7 and 8 . 1,1‐Ethylboration of ethynyl(trimethylstannylethynyl)methylsilane, Me(H)Si(CCSnMe 3 )CCH ( 3 ), leads selectively to a new silacyclopentadiene 13 as the final product. The reactions were monitored and the products were characterized by multinuclear magnetic resonance spectroscopy ( 1 H, 11 B, 13 C, 29 Si and 119 Sn NMR). Copyright © 2005 John Wiley & Sons, Ltd.