Cleavage and Formation of Carbon-Carbon Bonds by Transition Metal Complexes

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The long term objective of this project in the Inorganic, Bioinorganic and Organometallic Chemistry Program is to achieve greater understanding of how transition metal compounds can effect the cleavage and formation of carbon-carbon bonds. Such reactions are among the most important in chemistry and are involved in industrial processes such as reforming gasoline to upgrade the octane number. The overall strategy of the project is to isolate and model the individual steps of organic transformations involving C-C bond forming or cleavage as effected both stoichiometrically and catalytically by transition metal reagents. Emphasis will be placed on compounds with cyclopropenyl, cyclopropene and vinylcylclopropene ligands. Reactions of perfluorocyclopropene with transition metal centers will serve as a model for the C-C bond cleavage reaction, with oxidative addition of the C-C bond providing a route to metallacyclobutene complexes. The mechanism of transformation of 3-vinyl-1-cyclopropenes into 1,3-cyclopentadienes, or into eta-5-cyclopentadienyl(hydrido) metal complexes, are of particular interest since sequential C-C bond cleavage and C-C bond formation steps are involved. For some Rh- and Ir-promoted reactions intermediates can be isolated, and the structures of these intermediates demonstrate that the mechanism for opening the cyclopropene ring is more complicated than for simpler cyclopropenes, and cannot involve a "simple" oxidative insertion of the metal into the C-C bond. Reactions of selectively isotopically labelled precursors will be used to map the course of the novel skeletal rearrangements, corresponding to previously unknown organometallic transformations, which occur during the ring opening reactions. Isotopically labeled precursors will be used also to further elucidate the mechanism of the C-C bond forming reaction whereby 1,2,3,5-eta-pentadienediyl and 1,5-eta-pentadienediyl- (1-metallacyclohexa-2,4-diene) complexes of Rh(III) and Ir(III) undergo conversion to eta-5-cyclopentadienyl(hydrido) metal compounds.