Condensation of diphenylsilane diol through organostannoxane catalysis: a case study

Small amounts of [Ph 2 (OH)Sn] 2 CH 2 effectively catalyze the condensation of Ph 2 Si(OH) 2 to give cyclo-(Ph 2 SiO) 4 in good yield. The reaction proceeds under remarkably mild conditions. In contrast, the reaction of [Ph 2 (OH)Sn] 2 CH 2 with Ph 2 Si(OH) 2 in a stoichiometric ratio quantitatively gives the six-membered stannasiloxane ring cyclo-Ph 2 Si(OSnPh 2 ) 2 CH 2 (1). Compound 1 reacts slowly and irreversibly with Ph 2 Si(OH) 2 to provide the eight-membered stannasiloxane ring cyclo-O(Ph 2 SiOSnPh 2 ) 2 CH 2 (2) and [Ph 2 (OH)Sn] 2 CH 2 . The driving force for this reaction is attributed to the release of ring strain in 1. Condensation of [Ph 2 (OH)Sn] 2 CH 2 with diphenylsiloxanols HO(Ph 2 SiO) n H (n = 2-4), t-Bu 2 Si(OH) 2 , and t-Bu 2 Ge(OH) 2 , respectively, provides the metallastannoxane rings cyclo-O(Ph 2 SiOSnPh 2 ) 2 CH 2 (2), cyclo-Ph 2 Si(OSiPh 2 OSnPh 2 ) 2 CH 2 (3), cyclo-O(Ph 2 SiOPh 2 SiOSnPh 2 ) 2 CH 2 (4), cyclo-t-Bu 2 Si(OSnPh 2 ) 2 CH 2 (5), and cyclo-t-Bu 2 Ge(OSnPh 2 ) 2 CH 2 (6). The molecular structures of 2 and 5 were determined by X-ray diffraction.