Theoretical Studies of C-H σ-Bond Activation and Related Reactions by Transition-Metal Complexes

Many σ-bond activation reactions are classified into two main categories, oxidative addition and metathesis, except for several examples. Important orbital interactions and electronic process in the oxidative addition are discussed first. Also, the characteristic features of the transition state are reviewed in several typical oxidative addition reactions of H2, CH4, SiH4, C2H6, and SiH3CH3. The significant differences in reactivity among C-H, Si-H, C-C, and C-B σ-bonds are discussed in terms of the orbital interaction in the transition state and the bond energy. Also, theoretical studies of the s-bond activation via metathesis are reviewed, in which the heterolytic C-H σ-bond activation of benzene and methane by palladium(II) formate complex and the homolytic Si-H σ-bond activation of silane by Cp2Zr(C2H4) and Cp2Zr(R1)(R2) (R1, R2=H, alkyl, or silyl) are mainly discussed to clarify the electronic process and the driving force. At the end of this chapter, several theoretical studies of transition-metal-catalyzed reactions via s-bond activation are presented as typical examples.