Mechanism Of High Oxidation State Re (V) Catalytic Organic Reactions

The recent development of quantum computational methods provides powerful theoretical support for revealing the detailed mechanism of organic reactions. The thesis mainly concentrates on the mechanistic studies of high-valent transition metal Re(V) mediated organic reactions by using density functional theory calculation. The main contents include the following:Chapter1mainly reviews relevant primary steps in organometallic chemistry and the mechanism of hydrosilylation.Chapter2gives a brief introduction to main quantum computational methods.Chapter3and Chapter4describe the main research, which were accomplished during my Master’s Degree period.In Chapter3, we mainly concentrate on the theoretical studies on high-valent transition metal Re(V) catalyzed hydrosilylation reaction with carbonyls by using five different levels of functionals. On the basis of the comparison of energy of different pathways and the structural analysis of the important transition states and intermediates, we can finally conclude that the optimal pathway is ionic hydrogenation pathway. This complete catalytic cycle is proposed to involve three steps:the formation of cis η1-HSiMe3Re(V) adduct, the heterolytic cleavage of a Si-H bond through anti attack of carbonyls, and the hydride transfer step to give silyl ether and regenerate catalyst. This paper is published on Organometallics,2013,32:47.In Chapter4, with the aid of the classical DFT(B3LYP) calculations, we are able to study the mechanisms of activation reactions of CO catalyzed by two different high-valent transition metal Re(V) complexes. Through comparative analysis of potential energy surface, and the structural and electronic analysis of key intermediates and transition states, we find out that the mechanisms for activation of CO by these two Rhenium-oxo complexes are divergent. We believe that these reactivity preferences are greatly influenced by combination of the identity of the ligand and the rhenium-bonded X ligand.These studies show the effectiveness of quantum computational methods in mechanistic studies of transition metal complexes mediated organic reactions. They are able to provide information that is difficult to gain from experimental means, such as the structures and relative energies of critical intermediates and transition states.