Five-co-ordinate silicon. Kinetics of the acid-catalysed hydrolysis of nitrilotriphenoxysilanes

Abstract

The hydrolysis of nitrilotriphenoxysilanes [(ntp)SiX, (1)] has been studied in water–dioxan mixtures at 27° in the presence of hydrochloric acid. The product of the reaction is the ligand nitrilotriphenol in all cases, but the mechanism is dependent on the substituent X. When X is Me, Ph or p-tolyl, the rate-determining step appears to involve breakage of a protonated Si–O bond. When X is Cl, reaction via the ion-pair [ntpSi⁺Cl^–] is proposed. The ion pair is considered to be stabilised by (p→d)π bonding in the siliconium ion since the analogous germanium compound, (ntp)GeCl, does not react by a similar ion-pair mechanism.