Group 6 metal carbonyl complexes containing 3,5-dimethyl-4-ferrocenylmethylpyrazole: synthesis, structure and electrochemical properties

Abstract

Reaction of M(CO)6 with 3,5-dimethyl-4-ferrocenylmethylpyrazole under UV irradiation yields monosubstituted group 6 metal carbonyl complexes M(CO)5L (M = Cr, Mo or W; L = 3,5-dimethyl-4-ferrocenylmethylpyrazole). Their electrochemical behaviour, investigated by cyclic voltammetry, indicates that chromium and tungsten complexes exhibit two one-electron quasi-reversible couples corresponding to the ferrocenyl group and the chromium or tungsten centre, respectively, while the molybdenum complex has one quasi-reversible couple corresponding to the ferrocenyl group and one irreversible oxidation process for molybdenum. The crystal structure of W(CO)5L, determined by X-ray diffraction methods, shows that ferrocenylpyrazole acts as a monodentate ligand, and W is six-coordinate with quasi-octahedral coordination geometry. The complex is linked into a one-dimensional chain in the lattice through weak intermolecular hydrogen bonds with metal carbonyls acting as acceptors.