Arene-Metal Dimer Complexes (C6H6)2V2 and (C6H6)V2; Experiment and Xα Theory. 3

Article abstract of DOI:10.1021/j100398a010

V atoms have been shown in a previous paper (part 1) to react with one or two benzene rings in rare gas matrices to form the respective half-sandwich, (C6H6)V, or the bis(benzene)vanadium complex, (C6H6)2V, depending on the relative concentrations of the various components.In this study, at higher V atom loadings, the corresponding binuclear complexes (C6H6)V2 and (C6H6)2V2 are identified from a combination of a kinetic analysis and V atom concentration study, the results of thermal annealing, and the outcome of V and Cr atom depositions into low-temperature methylcyclohexane solutions of bis(toluene)M (M=V,Cr).Xα-SW calculations were undertaken to provide a qualitative insight into modes of bonding in metal dimer arene molecules.Simplified half-sandwich models were utilized in C_6v and C_2v symmetry, as implied by stable, known structural analogues.In both cases the molecular orbital divided neatly into three types.The first type related essentially to the benzene ligand itself.The second type was characterized by uniquely metal-metal bonding interactions.These interactions established a basis for inferring metal localized excitations as being at the origin of the electronic absorption spectra seen red-shifted from the main MLCT band.The third type detailed the metal-ligand bonding interactions.The C_6v structure showed bonding interactions similar to those of the mono(benzene)vanadium half-sandwich.The C_2v molecule showed features in common with metal atoms interacting with a benzene ring which can show latent allyl-like character.The relevance of such a structure to known vanadium dimer molecules incorporating a single fluxional benzene ring is indicated.