Dichotomous Si–H Bond Activation by Alkoxide and Alcohol in Base-Catalyzed Dehydrocoupling of Silanes
E.D. Voronova, Igor E. Golub, Alexander A. Pavlov, Natalia V. Belkova, Oleg A. Filippov, Lina M. Epstein, Elena S. Shubina
Abstract
The activation of silanes in dehydrogenative coupling with alcohols under general base catalysis was studied experimentally (using multinuclear NMR, IR, and UV–visible spectroscopies) and computationally (at DFT M06/6-311++G(d,p) theory level) on the example of Ph 4- n SiH n ( n = 1–3) interaction with (CF 3 ) 2 CHOH in the presence of Et 3 N. The effect of the phenyl groups’ number and H – substitution by the electron-withdrawing (CF 3 ) 2 CHO – group on Si–H bond hydricity (quantified as hydride-donating ability, HDA) and Lewis acidity of silicon atom (characterized by maxima of molecular electrostatic potential) was accessed. Our results show the coordination of Lewis base (Y = Me 3 N, ROH, OR – ) leads to the increased hydricity of pentacoordinate hypervalent Ph 4- n Si(Y)H n complexes and a decrease of the reaction barrier for H 2 release. The formation of tertiary complexes [Ph 4- n Si(Y)H n ]···HOR is a critical prerequisite for the dehydrocoupling with alkoxides being ideal activators. The latter can be external or internal, generated by in situ HOR deprotonation. The mutual effect of tetrel interaction and dihydrogen bonding in tertiary complexes (RO – )Ph 4- n SiH n ···HOR leads to dichotomous activation of Si–H bond promoting the proton–hydride transfer and H 2 release.