Hartree-Fock and density functional theory study of remote substituent effects on heterolytic Fe-C bond energies of p-G-C6H4CH2Fe(CO)2(η5-C5H5) and p-G-C6H4(H)(CN)CFe(CO)2(η5-C5H5)

Knowledge of the strength of the metalligand bond breaking and formation is fundamental for an understanding of the thermodynamics underlying many important stoichiometric and catalytic organometallic reactions. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe-C bond energies of para-substituted benzyldicarbonyl(eta 5-cyclopentadienyl)iron, p-G-C6H4CH2Fp [1, G=NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, NMe2; Fp=(eta 5-C5H5)(CO)2Fe], and para-substituted alpha-cyanobenzyldicarbonyl(eta 5-cyclopentadienyl)iron, p-G-PANFp [2, PAN=C6H4CH(CN)]. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of Delta Hhet(Fe-C)'s. The good linear correlations [r=0.98 (g, 1a), 0.99 (g, 2b)] between the substituent effects of heterolytic Fe-C bond energies [Delta Delta Hhet(Fe-C)'s] of series 1 and 2 and the differences of acidic dissociation constants (Delta pKa) of C?H bonds of p-G-C6H4CH3 and p-G-C6H4CH2CN imply that the governing structural factors for these bond scissions are similar. And the excellent linear correlations [r=-1.00 (g, 1c), -0.99 (g, 2d)] between Delta Delta Hhet(Fe-C)'s and the substituent sigma p- constants show that these correlations are in accordance with Hammett linear free energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of Delta Hhet(Fe-C)'s. Delta Delta Hhet(Fe-C)'s(1, 2) follow the Capto-dative Principle. The detailed knowledge of the factors that determine the Fp?C bond strengths would greatly aid in understanding reactivity patterns in many processes. Copyright (C) 2011 John Wiley & Sons, Ltd.