Divalent E(0) compounds (E = Si-Sn)

Quantum-chemical calculations at the BP86/TZVPP level of theory have been carried out for compounds EL₂ for E = Si, Ge, Sn, where L is a five-membered cyclic ylidene or N-heterocyclic ylidene. The theoretical results provide evidence for the classification of the complexes as divalent E(0) compounds, where the bonding situation is best described in terms of donor-acceptor interactions between a bare atom E, which retains its valence electrons as two lone pairs, and two donor ligands L→E← L. The molecules are very strong donors, which may bind one or two Lewis acids. Divalent E(O) compounds have unusually high second proton affinities and they are strong o donor ligands. The calculations predict that complexes of EL ₂ with one or two BH₃ ligands are stable enough to become isolated in a condensed phase. It is also shown that the bond dissociation energies (BDEs) of transitionmetal complexes [(CO)₅WD] and [(CO) ₃NiD], where D = EL₂ are rather high. The BDE of some ligands D are higher than those of CO in the metal carbonyls.