Condensation of Diphenylsilane Diol through Organostannoxane Catalysis:  A Case Study

Abstract

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), cycloPh 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.

The First Well-Defined Tellurastannoxanes: the X-ray Structure of trans-[(Bu3SnO)2{CH2(Ph2SnO)2}2Te]

“…[13] The identity of these species was unambiguously proven by 119 Sn and 125 Te NMR spectroscopy, although all attempts to isolate pure compounds from the mixtures failed. [16] The 125 Te NMR spectrum (CDCl 3 ) of compound 2 shows a signal at δ ϭ 726.1 with two 2 J( 125 TeϪOϪ 119 Sn) couplings of 397 and 355 Hz in the expected integral ratio. [14] The reaction of mer-[(Bu 3 SnO) 3 Te(OH) 3 ] (1) with two equivalents of (Ph 2 SnOH) 2 CH 2 [15] gave, with elimination of water and one equivalent of tributyltin hydroxide (Bu 3 SnOH), the spirocyclic tellurastannoxane derivative trans-[(Bu 3 SnO) 2 {CH 2 (Ph 2 SnO) 2 } 2 Te] (2) in good yields [Equation (2)].…”

Organotin catalysts in organosilicon chemistry

“…Studies by Beckmann and Jurkschat in the 1990s revealed the existence of transient Sn‐O‐Si systems along the reaction pathway that leads to Si‐O‐Si bonds, in a mechanism involving prior hydrolysis of the alkyltin carboxylate . The occurrence of stannasiloxanes after mixing organotin carboxylates and alkoxysilanes was well documented in the work of Nagy in the 1960s .…”

“…[7] The Sn-O-Si Bond Studies by Beckmann and Jurkschat in the 1990s revealed the existence of transient Sn-O-Si systems along the reaction pathway that leads to Si-O-Si bonds, in a mechanism involving prior hydrolysis of the alkyltin carboxylate. [8] The occurrence of stannasiloxanes after mixing organotin carboxylates and alkoxysilanes was well documented in the work of Nagy in the 1960s. [9] Further studies illustrated the feasibility of synthesizing stannasiloxanes from co-hydrolysis reactions of organotin chlorides with trialkylchlorosilanes, obtaining a series of compounds: {[R 2 (Me 3 SiO)Sn] 2 3 SiOH, which subsequently reacts with the organotin.…”

The First Well-Defined Tellurastannoxanes: the X-ray Structure oftrans-[(Bu3SnO)2{CH2(Ph2SnO)2}2Te]

“…It is interesting to note that the chemical shift for the (Ph 2 SnO) 2 CH 2 moiety at δ ϭ Ϫ40.2 is very close to that found for the cyclo-stannasiloxane tBu 2 Si(OSnPh 2 ) 2 CH 2 [δ( 119 Sn) ϭ Ϫ42.8], which also contains a (Ph 2 SnO) 2 CH 2 fragment incorporated into a six-membered ring. [16] The 125 Te NMR spectrum (CDCl 3 ) of compound 2 shows a signal at δ ϭ 726.1 with two 2 J( 125 TeϪOϪ 119 Sn) couplings of 397 and 355 Hz in the expected integral ratio. The number of signals in the 119 Sn NMR spectrum and the observed coupling patterns in both 119 Sn and 125 Te NMR spectroscopy confirms the coordination geometry of the tin atoms around the tellurium center.…”