Validation of the M-C/H-C bond enthalpy relationship through application of density functional theory

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 Delta H(M-C)(rel) with H-C bond enthalpies Delta H(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-Bu-3) (silox = OSitBu(3)) (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.