Electron Deficient Bridges Involving Silylenes: A Theoretical Study

Ab initio and density functional studies show that silylenes can form complexes with BH3 and the resultant complexes possess 3c-2e bridges. The complexation energy for the formation of the these H-bridged structures is in the range of 18-46 kcal/mol. The characteristics of the electron deficient bridges depend on the substituents attached to the silylenes. With an increase in the (pi)donating capacity of the substituents, the exothermicity of complex formation gets reduced but the kinetic stability of the H-bridged structures increase. The natural bond orbital analysis shows that all the H-bridged structures are associated with (sigma) B-H(right arrow)p Si second-order delocalization, which is responsible for the origin of the 3c-2e bonds. The complexation energies of the silylene-BH3 complexes have been shown to have a correlation to the singlet-triplet energy gaps of silylenes.