Theoretical study of stable silylenes and germylenes

Quantum chemical calculations at the semi-empirical, Hartree-Fock and correlated ab initio levels have been carried out to rationalize structure, bonding and reactivity of stable cyclic diaminosilylenes and -germylenes. Theory shows excellent agreement with experimental X-ray and electron diffraction data. The calculated thermochemical data provide a consistent description of chemical vapour deposition from a cyclogermylene precursor. Electronic stabilization via pπ–pπ delocaliiation is an important bonding feature in aminosubstituted silylenes and germylenes. The aminogermylenes have singlet ground states with the lowest triplet states at least 40 kcal/mol higher in energy. In contrast to the homologous aminocarbenes, aminosilylenes and -germylenes are thermodynamically stable with respect to their tetravalent isomers. Planar 2-germaimidazoles are predicted to be unstable. Theoretical data for four different types of Ge–N bonds are compared