Abstract
Abstract : Metal-metal bonds are found in alkoxides of molybdenum and tungsten when the metal atoms are in oxidation states 2 through 5. Metal-metal bonds may be locailized and multiple or single in order, or may be delocalized in cluster molecular orbitals. The structures of these metal alkoxides are quite different from those seen previously. Metal-metal bonds provide a reservoir of electrons for redox reactions: the reservoir may be tapped in oxidative- addition reactions and filled in reductive-eliminatin reactions. Alkoxide ligands may act as four or two electron donor ligands and may readily change between terminal and bridging sites. This allows for the facile interconnversion of saturated and unsaturated metal centers. As strong Pi-donor ligands, they can enhance backbonding to pi-acid ligands on the same metal. By pi-donating to vacant metal d orbitals, they may suppress metal-hydride abstraction from coordinated alkyl, alkylidene and alkylidyne ligands and they stabilize metals in high oxidation states. A variety of steric control can be engineered by choice of alkyl (RO0 groups and this may greatly influence structure, M-M bonding and reactivity of coordinated ligands.
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