| There are many examples in the literature of metal-alkyne complexes. The structures of these compounds range from mononuclear to polynuclear metal assemblies. Although these complexes are structurally well defined, there has been no definitive mechanistic study of metal-alkyne complexes. The goal of the research reported in this thesis was to examine the (mu)(,2)-(eta)('2) dinuclear alkyne complex with the objective of establishing the mechanistic features of reactions involving the acetylene ligand as in the hydrogenation and the acetylene exchange reactions.;In Chapter Two, the chemistry of dinuclear complexes of the specific type ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,4)(RC(,2)R) is presented. The hydrogenation of the acetylene (both stoichiometric and catalytic) as well as the alkyne exchange reaction are characterized. The new complex, ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,3)P(OCH(,3))(,3)(RC(,2)R) was prepared. Under catalytic hydrogenation conditions, this complex underwent a redistribution process to give the parent ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,4)(RC(,2)R) and a compound whose spectroscopic characteristics are consistent with ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,2){P(OCH(,3))(,3)}(,2). Mechanisms for both the alkyne hydrogenation and alkyne exchange reactions utilizing ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,4)(RC(,2)R) are proposed based on the experimental results. The mechanisms have, as their initial rate determining step, carbon monoxide ligand loss to generate ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,3)(RC(,2)R).;While investigating the reactions of the ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,4)(RC(,2)R) complexes, the bimetallacyclic species ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(C(,2)H(,5)C(,2)C(,2)H(,5))(,2) was prepared under photolytic conditions. Chapter Three presents the synthesis and characterization of this compound. In addition, the chemistry associated with the molybdenum-molybdenum triple bond is described. It was established that steric factors are responsible for the lack of reactivity of this complex with ligands other than the compact carbon monoxide and alkyl isocyanide ligands.;In Chapter Four, the chemistry of the ((eta)('5)-C(,5)H(,5))(,2)Ni(,2)(RC(,2)R) complexes associated with the alkyne ligand is presented. This type of dinuclear complex is formally similar to the ((eta)('5)-C(,5)H(,5))(,2)Mo(,2)(CO)(,4)(RC(,2)R) complexes. However, mechanistic pathways for the hydrogenation and alkyne exchange reactions were expected to be different in the dinulcear nickel-alkyne system as compared to that of the dinulcear molybdenum alkyne system because there is no easily dissociable ligand in the nickel complex. Based on the experimental results, a mechanism for the alkyne exchange reaction is proposed. This proposed mechanism involves fragmentation of the initial dinuclear metal alkyne compound to give mononuclear species.;The introduction comprehensively and critically evaluates the reported structural and chemical features of metal-alkyne adducts. Mechanistic schemes for alkyne hydrogenation and oligomerization are also examined. |
