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

Treatment of R2Si(Ctriple bond; length of mdashC-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(Ctriple bond; length of mdashC–R1)2 [5a (R1 = Ph), 5b (R1 = 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 Cdouble bond; length as m-dashC double bonds in these products. The silacyclobutene derivative E-6 was characterized by an X-ray crystal structure analysis.