Hartree–Fock and density functional theory study of remote substituent effects on heterolytic Fe―C bond energies of p ‐G‐C 6 H 4 CH 2 Fe(CO) 2 (η 5 ‐C 5 H 5 ) and p ‐G‐C 6 H 4 (H)(CN)CFe(CO) 2 (η 5 ‐C 5 H 5 )

Knowledge of the strength of the metal–ligand 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(η 5 ‐cyclopentadienyl)iron, p ‐G‐C 6 H 4 CH 2 Fp [1, G = NO 2 , CN, COMe, CO 2 Me, CF 3 , Br, Cl, F, H, Me, MeO, NMe 2 ; Fp = (η 5 ‐C 5 H 5 )(CO) 2 Fe], and para‐substituted α‐cyanobenzyldicarbonyl(η 5 ‐cyclopentadienyl)iron, p ‐G‐PANFp [2, PAN = C 6 H 4 CH(CN)]. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of Δ H het (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 [ΔΔ H het (Fe―C)'s] of series 1 and 2 and the differences of acidic dissociation constants (Δ pK a ) of C―H bonds of p ‐G‐C 6 H 4 CH 3 and p ‐G‐C 6 H 4 CH 2 CN 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 ΔΔ H het (Fe―C)'s and the substituent σ 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 Δ H het (Fe―C)'s. ΔΔ H het (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 © 2011 John Wiley & Sons, Ltd.