Validation of the M−C/H−C Bond Enthalpy Relationship through Application of Density Functional Theory

Abstract

Density functional theory has been used to calculate H−C and M−C bond dissociation enthalpies in order to evaluate the feasibility of correlating relative M−C bond enthalpies ΔH(M−C)rel with H−C bond enthalpies ΔH(H−C) via computational methods. This approach has been tested against two experimental correlations:  a study of (a) Rh(H)(R)(Tp‘)(CNCH2CMe3) [R = hydrocarbyl, Tp‘ = HB(3,5-dimethylpyrazolyl)3] (Wick, D. D.; Jones, W. D. Organometallics 1999, 18, 495) and (b) Ti(R)(silox)2(NHSit-Bu3) (silox = OSit-Bu3) (Bennett, J. L.; Wolczanski, P. T. J. Am. Chem. Soc. 1997, 119, 10696). We show that the observation that M−C bond enthalpies increase more rapidly with different substituents than H−C bond enthalpies is reproduced by theory. Quantitative slopes of the correlation lines are reproduced within 4% of the experimental values with a B3PW91 functional and with very similar correlation coefficients. Absolute bond enthalpies are reproduced within 6% for H−C bonds, and relative bond enthalpies for M−C bonds are reproduced within 30 kJ mol-1 for Rh−C bonds and within 19 kJ mol-1 for Ti−C bonds. Values are also calculated with the BP86 functional