DFT Studies on Transition Metal Mediated and Catalyzed C-C Formation Reaction

Theoretical studies on the mechanism of transition metal mediated and catalyzed C-C formation reactions involving CO2 activation and cycloaddition and cycloisomerization are reported in this thesis.;Part I: Theoretical studies of transition-metal mediated and catalyzed reactions involving CO2 have been reviewed in this chapter. Fundamental steps related to organometallic reactions of CO2 have been discussed, such as CO2 insertion into an M-R bond, CO2 insertion into an M-X bond, and oxidative coupling with unsaturated organic substrates.;Part II: The mechanism of copper-catalyzed hydrocarboxylation of alkynes using CO2 and hydrosilanes has been studied. In addition to hydrocarboxylation of alkynes, hydrosilylation of CO2 and silacarboxylation of alkynes have also been investigated and compared. Through the studies, we are able to understand the reason why only hydrocarboxylation of alkynes has been observed experimentally.;Part III: The reaction mechanism of dinuclear palladium(I) complexes containing two allyl bridging ligands with CO2 has been studied. The transformations of the first and second bridging allyl ligand to the bridging carboxylate ligands have been compared. It is found that the transformation of the first bridging allyl ligand is kinetically and thermodynamically favorable, while the transformation of the second ligand is thermodynamically and kinetically unfavorable.;Part IV: Gold-catalyzed cycloisomerization of 1,5-enynes has been investigated. How substituents influence the reaction paths in the cycloisomerization of 1,5-enynes catalyzed by AuCl and [AuL]+ (L = phosphine) has been examined and discussed.;Part V: The reaction mechanism of rhodium-mediated [3+2] cycloaddition reactions of diynes has been investigated. It was found that the regioselectivity in the reactions of unsymmetrical diynes is determined by the nucleophilicity of the distal alkyne carbon in a pseudo octahedral complex and the stability of a zwitterionic intermediate.