Molybdenum, carboxylate ligands

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). 

An isoelectronic nitrogen analogue of the carboxylate ligand [R C(NR)2, cf. R C02 ] has been successfully employed to prepare Mo2(amidinato)4 from both jV.A -diphenylbenzamidine and jV.jV -ditolylbenzamidine by reaction with molybdenum hexacarbonyl (84). 

Palladium-catalyzed carbonylation reactions with aryl halides are powerful methods of generating aromatic amides, hydrazides, esters and carboxylic acids [25]. We have previously reported the exploitation of Mo(CO)6 as a robust carbon monoxide-releasing reagent in palladium-catalyzed carbonylation reactions [26-29]. This stable and inexpensive solid delivers a fixed amount of carbon monoxide upon heating or by the addition of a competing molybdenum coordinating ligand (for example DBU). This allows for direct liberation of carbon monoxide in the reaction mixture without the need for external devices. 

Ccrvilla, A., Domenech, A., Llopis, E., Vicente, E, and Tamarit, R. 1994b. Molybdenum complexes with slcrically-hindcrcd thio-carboxylate ligands. Electrochemical properties of the anionic complex bis(2,2-diphenyl-2-mercaptoethanoate) dioxomolybdatefVI) in protic solvents. Inorganica ChimicaActa 221, 117-124. 

Molybdenum imido alkylidene complexes that contain bulky carboxylate ligands have been prepared and evaluated for the cyclopolymerizations of... 

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