Molybdenum complexes three bridging ligands

A number of publications detail dimeric molybdenum(V) complexes with three bridging ligands. Thiolate-bridged, [Mo202(p-0)(p-SPh)2(S2CNMe2)2], is prepared upon addition of thiophenol to [Mo02(S2CNMe2)2] in methanol (Eq. 91), and contains a short metal-metal interaction [Mo—Mo 2.649(1) A]... 

Molybdenum imido alkylidene complexes have been prepared that contain bulky carboxylate ligands such as triphenylacetate [35]. Such species are isola-ble, perhaps in part because the carboxylate is bound to the metal in an r 2 fashion and the steric bulk prevents a carboxylate from bridging between metals. If carboxylates are counted as chelating three electron donors, and the linear imido ligand forms a pseudo triple bond to the metal, then bis(r 2-carboxylate) species are formally 18 electron complexes. They are poor catalysts for the metathesis of ordinary olefins, because the metal is electronically saturated unless one of the carboxylates slips to an ri1 coordination mode. However, they do react with terminal acetylenes of the propargylic type (see below). 

Sulfur dioxide is known to behave as an S—O bidentate to metal ions in low oxidation states, resulting in the formation of three-membered chelate rings. The structures of three such complexes of molybdenum have been described by Kubas and Ryan,including an unusual dinuclear complex in which the SO2 ligands bridge two Mo atoms. A closely related complex of Ru also has been characterized. This bonding form was discussed in relation to these structimes. 

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