Lewis Donor and Acceptor Interactions of Silylenes:  A Theoretical Study

Silylenes are known to show ambiphilic character. Ab initio study on (Lewis base)→H2Si coordination shows that the strength of the interaction depends mainly on two factors: (1) the nucleophilicity of the base and (2) the extent of π delocalization of the lone pair on silylene onto the π frame of the base. The stabilization energies due to the formation of H3N→SiH2, OC→SiH2, and HNC→SiH2 complexes at the G2 level are respectively 23.22, 20.84, and 29.59 kcal/mol. The base coordination triggers the nucleophilicity of silylenes, the strength of which is again dependent on the π interaction between the lone pair on Si and the Lewis base. The energy gains due to the formation of the LB→LA complexes (H3N)H2Si:→BH3, (OC)H2Si:→BH3, and (HNC)H2Si:→BH3 are 42.08, 24.65, and 29.16 kcal/mol, respectively, at the G2 level. The electrophilic nature of base-coordinated silylenes and the nucleophilicity of double-base-coordinated silylenes have been quantitatively estimated. Natural bond orbital (NBO) analysis and charge decomposition analysis (CDA) have been carried out to quantitatively estimate electron distribution.