Chemistry of Bulky Alkoxide/Siloxide Complexes: Homogeneous Metal Oxides

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The focus of the proposed research is the synthesis and chemical reactions of metal compounds in which the metal is attached to several bulky groups which by steric crowding prevent the metal from making bonds to as many other atoms as it would if it could. The metal atoms in these so-called coordinatively unsaturated species are electron deficient, which causes them to manifest reactivities which are comparable to metal oxides. These compounds have been found to be capable of activating carbon monoxide and atmospheric oxygen, and their reactions are potentially of great importance in the synthesis of organic compounds and in providing a clearer understanding of heterogenous catalysis by metal oxides. A primary objective of the project is to elucidate the mechanisms of activation of small molecules by Zr and Ta complexes of tri-tertiary-butylmethoxide (tritox) and tri-tertiary-butylsiloxide (silox) ligands. Kinetic isotope effects and radical probes will be used to substantiate that the activation of dioxygen by a bis-tritoxZr complex is radical based. The cleavage of CO by tris(tritox)Ta will be studied as a model of the dissociative adsorption of CO, the initial step in Fischer-Tropsch synthesis. The details of the metal-hydride assisted cleavage of CO by dihydridobis(silox)Ta will be investigated as a unique example of a single sequence which involves a homogeneous Fischer-Tropsch reaction, CO reduction, deoxygenation and C-C bond formation.