Reactions of bis(alkynyl)silanes with HB(C6F5)2: Formation of boryl-substituted silacyclobutene derivatives

Treatment of R2Si(C C-SiMe3)(2) [ 1a (Me), 1b (Ph)] with HB(C6F5)(2) at low temperature (253 K (a), 273 K (b)) gives the -B(C6F5)(2) substituted silacyclobutene products (4a,b) under kinetic control. Upon warming to room temperature they disappear to form the thermodynamically favoured isomeric silole derivatives (2a,b). Similar treatment of Me2Si(C C-R-1)(2) [5a (R-1 = Ph), 5b (R-1 tert-butyl) with HB(C6F5)(2) at room temperature gave the stable -B(C6F5)(2) substituted silacyclobutene derivatives 6 and 7, respectively. Subsequent photolysis resulted in a Z- to E-isomerization of the substituted exocyclic C=C double bonds in these products. The silacyclobutene derivative E-6 was characterized by an X-ray crystal structure analysis. (C) 2010 Published by Elsevier B.V.