Molybdenum complexes ligand-bridged carbonyls

A related reaction is shown for the molybdenum-niobium complex (equation 9). As described in a review by Horowitz and Shriver on bridging carbonyl ligands, this complex is a rare example of a structure containing terminal, bridging, and r-bridging CO ligands. All such complexes, of necessity, include metal-metal bonding. 

For mononuclear complexes, reactions at coordinated ligands is a topic of major study, and numerous reviews and even books have been written on this topic. At the time of writing this review, the authors could find no major review articles in this area for dinuclear compoimds. The best examples are probably those on the reactions of coordinated molybdenum sulfides discussed earlier. A related observation is the reaction of metal carbonyls with Lewis acids. It has been observed by Shriver and coworkers that carbonyl ligands bridging metal-metal bond atoms show increased tendency to coordinate Lewis acids (equation 96). 

A number of unusual structural features have been noted. The ruthenium porphyrin formed by reaction of triruthenium dodecacarbonyl with an N, AT-vinyl-bridged tetraphenylporphyrin involves disruption of a pyrrole C-N bond to give a product in which the ruthenium is bound to two pyrrole N atoms, the C and N atoms of the ruptured pyrrole ring, and two mutually cis carbonyl ligands. The remaining pyrrole N is uncoordinated.613 Mutually cis configurations have also been found for the dicarbonyl complex of molybdenum tetraphenylporphyrin and for some dinitrosyl porphyrins. 

Dithiocarbamates, in Ru and Os half-sandwiches, 6, 493 Dithiocarbenes, Pt complexes, 8, 439 Dithiocarboxy ligands, in molybdenum carbonyls, 5, 447 Dithiolate-bridged compounds in dinuclear iron compounds with Fe-Fe bonds, 6, 238 as iron-only hydrogenase biomimetic models, 6, 239 Dithiolate diamides, with Zr(IV), 4, 784 Dithiolene—uranium complexes, synthesis and characterization, 4, 212 Ditopic receptors, characteristics, 12, 489 Ditungsten complexes, associated reactions, 5, 748 Divinyllead diacetates... 

In addition to monocyclopentadienyl dimers, various molybdenocene derivatives can form dimers, as shown in equation (33). This is one example of a vast range of organic ligands that bridge metal-metal bonded complexes. Another example is one of the several products obtained by reaction of diphenylacetylene and molybdenum carbonyl (equation 34). 

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