DFT Study of Electronic Properties of 3d Metal Complexes of σ-Geminal Diethynylethenes (gem-DEEs)

A density functional theory (DFT) analysis has been carried out to evaluate the structural and electronic properties of bimetallic compounds bridged by geminal diethynylethene (gem-DEE). Five stable equilibrium structures of the [M]-gem-DEE-[M] type ([M] = -M(H2PCH2CH2PH2)(2)Me) were obtained for the first-row transition metals, namely Ti, V, Cr, Fe, and Ni, using DFT at the B3LYP/LanL2DZ level. While the d orbitals in the Ti and Ni compounds exhibited minimal interactions with the gem-DEE-based orbitals, extensive interactions between the d(pi) orbitals and pi(DEE) orbitals were found for the V, Cr, and Fe compounds. A detailed natural bond orbital (NBO) analysis revealed that the electronic delocalization in [M]-gem-DEE-[M] is attributed to both the sigma orbitals along the DEE backbone and pi orbitals perpendicular to the DEE plane.