Theoretical prediction of O–H, Si–H, and Si–C σ-bond activation reactions by titanium(IV)–imido complex

Abstract

The O–H σ-bond activation of methanol, the Si–H σ-bond activation of silane, and the Si–C σ-bond activation of methylsilane by titanium(IV)–imido complex (Me3SiO)2Ti(NSiMe3) were theoretically investigated with DFT and MP2 to MP4(SDQ) methods. The O–H σ-bond activation of methanol occurs with small activation barrier (Ea) of 7.1 (14.6) kcal/mol and large exothermicity (Eexo) of 65.8 (61.4) kcal/mol to afford (Me3SiO)2Ti(OCH3)[NH(SiMe3)], indicating that the O–H σ-bond activation occurs easier than the C–H σ-bond activation (Ea = 14.6 (21.5) kcal/mol and Eexo = 22.7 (16.5) kcal/mol), where DFT- and MP4(SDQ)-calculated values are presented without and in parenthesis hereafter. Though the OCH3 group becomes anionic and the H atom becomes proton-like in this activation reaction, population changes more moderately occur than those of the C–H σ-bond activation. This is because the H–OCH3 bond is already polarized in methanol. In the Si–H σ-bond activation, two reaction courses were investigated; in one course, the product is (Me3SiO)2Ti(SiH3)[NH(SiMe3)] in which the H atom and the SiH3 group are bound to the N atom and the Ti center, respectively, while in the other course the product is (Me3SiO)2Ti(H)[N(SiH3)(SiMe3)] in which the H atom and the SiH3 group are bound to the Ti center and the imido N atom, respectively. Though the former reaction occurs with small Ea value and large exothermicity, the latter reaction occurs easier with further smaller Ea value of 2.6 (4.3) kcal/mol and larger Eexo value of 32.5 (34.1) kcal/mol than those of the former reaction. This is because the Ti–H bond energy is much larger than the Ti–SiH3 one. The Si–C σ-bond activation occurs with moderate activation barrier of 19.1 (18.6) kcal/mol and considerably large exothermicity of 33.9 (37.7) kcal/mol. Based on these results, we wish to propose the theoretical prediction that the titanium(IV)–imido complex is useful for O–H, Si–H, and Si–C σ-bond activation reactions.