Synthesis of dinuclear group 6 metal carbonyl complexes bridged by 4,4′-bipyrazole ligands

Abstract

A series of dinuclear group 6 metal carbonyl complexes containing 4,4′-bipyrazole ligands [(CO)5M (μ-dpz)M(CO)5)] have been synthesized by the photochemical reaction of 4,4′-bipyrazoles with M(CO)6 [M = Cr, Mo or W; dpz = 4,4′-bis-3,5-dimethylpyrazole; 4,4′-methylenebis(3,5-dimethylpyrazole)], and characterized by elemental analyses, i.r. and 1H-n.m.r. spectra. Their electrochemical behavior, investigated by cyclic voltammetry, indicates that all complexes exhibit one quasi-reversible redox peak owing to the presence of two equivalent M(CO)5 fragments. The crystal structure of (CO)5W(μ-dpz)W(CO)5 [dpz = 4,4′-methylenebis(3,5-dimethylpyrazole)] determined by X-ray diffraction, indicates that two W(CO)5 units are linked by the bridging bidentate ligand, and are located in a mutually cis-position. The molecules form a two-dimensional double-layer sheet by intermolecular hydrogen bonding interactions between the N—H groups and the oxygen atoms of metal carbonyls in the solid state.