Synthesis, crystal structure and electrochemical properties of carbonylchromium and tungsten complexes containing substituted pyrazole ligands

A series of carbonylchromium and tungsten complexes containing substituted pyrazole ligands, M(CO)(5)L, have been synthesized by the photochemical rea ctions of substituted pyrazoles with M(CO)(6) (M = Cr or W). Their electroc hemical behavior, investigated by cyclic voltammetry, indicates that the ch romium complexes exhibit one reversible or quasi-reversible couple correspo nding to a one-electron oxidation, whereas the tungsten complexes have one irreversible oxidation process. The crystal structure of W(CO)(5)L [L = 3(5 )-t-butylpyrazole] was determined by X-ray diffraction, indicating that 3(5 )-t-butylpyrazole is a monodentate ligand, and that the central metal is si x-coordinate with a quasi-octahedral coordination geometry. All new compoun ds were characterized by elemental analyses, i.r., H-1-n.m.r. and by C-13-n .m.r. in the case of the tungsten complexes.