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 pi delocalization of the lone pair on silylene onto the pi 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 a 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.