Reactions of zwitterionic η2-(alkyn-1-yl-borate)alkenyltin compounds with Lewis bases

Wrackmeyer B.; Kehr G.; Willbold S.

Abstract

The different Lewis-acidic centres in the zwitterionic η2-(alkyn-1-yl-borate)alkenyltin compounds 1 and 2 react with Lewis bases (pyridine, N-Me-imidazole, trialkylphosphanes, fluoride). Depending on sterical and electronic conditions and on the nature of the Lewis base, either the boron, tin or carbon atom is involved in these reactions. Formation of borane adducts (3, 4, 7, 8, 17) is accompanied by migration of a boron-bonded alkynyl group to the tin atom. Coordination at the tin atom is weak (5, 6) except in the case of fluoride (10-12) and 2,2-bipyridyl (18). Phosphanes coordinate either to boron, to tin or to carbon. In the latter case, vinyl cationic fragments are stabilised (9, 19-22), which are believed to be important potential intermediates in the reversible rearrangement of 1-alkynyl-stannyl(boryl)alkenes 1′, 2′ into the zwitterionic η2-(alkyn-1-yl-borate)alkenyltin compounds 1 and 2, respectively. All new compounds were characterised by 1H-, 11B-, 13C-, 31P- and 119Sn-NMR. © 1999 Elsevier Science S.A.