CONFACIAL BIOCTAHEDRAL COMPLEXES OF MOLYBDENUM AND TUNGSTEN

The review deals with the chemistry of confacial bioctahedral or face- sharing bioctahedral (FBO) complexes of molybdenum and tungsten. As sh own in the first section on bonding complexes in which the metals are formally both in a +3 oxidation state are particularly stable owing to the optimal electronic configuration for the formation of metal-metal interactions. Hence the chemistry of such complexes is the most devel oped and is therefore most emphasized in the review. The fragment appr oach to bonding, introduced by Summerville and Hoffmann, is used to ex plain the structural features and reactivity of the FBO complexes. Tab ulated data on many of the known complexes are provided, organized by the oxidation states of molybdenum and tungsten respectively. A brief review of the synthetic approaches, especially to M(III)-M(III) system s, is followed by a more lengthy discussion of the reactivity patterns that are emerging. These include interconversion between FBO and othe r structural types, especially edge-sharing bioctahedral (EBO) complex es, ligand site exchange reactions and ligand displacement reactions. Some relatively recent chemistry involving reactions of the coordinate d ligands is then discussed, followed by a brief excursion into the kn own redox chemistry of the M(III)-M(III) systems which can lead to mix ed oxidation state complexes. Finally, the possibility of developing c atalytic uses for FBO complexes is suggested. The review cites ss refe rences to original papers and previous review articles. It deliberatel y avoids extensive discussion of aspects of the held which have been r eviewed elsewhere in recent years.