11 Chromium, molybdenum and tungsten

Abstract

In 2004, there were some important advances in the areas of catalysis and bioinorganic and organometallic chemistry. For example, for the very first time, antagonists molybdenum and copper in a heterometallic cluster ([S₂MoS₂CuS₂MoS₂]) were found in a novel protein which was isolated and purified from Desulfovibrio gigas, a sulfate reducing bacterium. A wide range of topics involving biomimetic complexes of chromium(III) and molybdenum(VI) were reported. The coordination chemistry of the antitumour metallocene molybdocene dichloride with biological ligands was also reported, along with the use of organomolybdenum complexes as lubricating oil antifriction additives. Also reported was the use of polyoxometallates of tungsten as effective photocatalysts for water purification by photo-destruction of pesticides. The first polyoxometallate polymer constructed by assembly of the heptamolybdic anion and copper coordination groups was another advance, along with the facile synthesis of Group 6 carbonyl complexes in a conventional microwave oven. Other interesting areas included the following: (i) use of (salen)Cr^IIIX as catalysts for the copolymerisation of carbon dioxide and epoxides; (ii) catalytic epoxidation of cyclohexene with molybdenum complexes; (iii) chromium monocyclopentadienyl complexes useful as olefin polymerisation catalysts; (iv) solvent-free ketone hydrogenations catalysed by molybdenum complexes; and (v) adducts of acetylene and dimethylacetylenedicarboxylate in sulfur-bridged incomplete cuboidal-type tungsten clusters. Also noteworthy was the micellar effect on the kinetics and mechanism of chromium(VI) oxidation of organic substrates.