NEW CHEMISTRY OF VANADIUM(II)

The synthetic routes to vanadium(II) complexes from metallic vanadium and from compounds in higher oxidation states, comprising both chemica l and electrochemical methods, are reviewed. The reduction of vanadium (III) chloride by Zn seems to be the simplest entry to useful starting materials such as trichlorohexakis(tetrahydrofuran)divanadium(1 +), d ichlorobis(tetramethylethylenediamine)vanadium and diiodotetrakis(tetr ahydrofuran)vanadium. The chemistry is not dominated by a single ligan d type, and O, N- and P-donors are all used. Few dinitrogen complexes of vanadium-(II) and -(III) have been reported and all contain bridgin g dinitrogen. The protonation of these compounds yields ammonia only f rom vanadium(II); the higher oxidation state regenerates dinitrogen. T he extensive chemistry of trinuclear vanadium(II) complexes now being revealed may also be relevant to vanadium(II)-catechol-methoxide nitro gen-fixing systems.