Substituent effects on gas-phase homolytic Fe-O and Fe-S bond energies of m-G-C6H4OFe(CO)2(η5-C5H5) and m-G-C6H4SFe(CO)2(η5-C5H5) studied using Hartree-Fock and density functional theory methods

The thermochemistry of organometallic complexes in solution and in the gas phase has been an area of increasing research interest. In this paper, the Fe-O and Fe-S homolytic bond dissociation energies [H-homo(Fe-O)'s and H-homo(Fe-S)'s] of two series of meta-substituted phenoxydicarbonyl((5)-cyclopentadienyl) iron [m-G-C(6)H(4)OFp (1)] and (meta-substituted benzenethiolato)dicarbonyl((5)-cyclopentadienyl) iron [m-G-C(6)H(4)SFp (2)] were studied using Hartree-Fock and density functional theory methods with large basis sets. In this study, Fp is ((5)-C5H5)Fe(CO)(2), and G are NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2. The results show that Tao-Perdew-Staroverov-Scuseria and Minnesota 2006 functionals can provide the best price/performance ratio and accurate predictions of H-homo(Fe-O)'s and H-homo(Fe-S)'s. The polar effects of the meta substituents show that the dominant role to the magnitudes of H-homo(Fe-O)'s or H-homo(Fe-S)'s. sigma, sigma(c<bold>) values for meta substituents are all related to polar effects</bold>. Spin-delocalization effects of the meta substituents in H-homo(Fe-O)'s and H-homo(Fe-S)'s are small but not necessarily zero. Molecular effects rather than H-homo(Fe-O)'s and H-homo(Fe-S)'s are more suitable indexes for the overall substituent effects on H-homo(Fe-O)'s and H-homo(Fe-S)'s. The meta substituent effects of meta-electron-withdrawing groups on the Fe-S bonds are much stronger than those on the Fe-O bonds. For meta-electron-donating groups, the meta substituent effects have the comparable magnitudes between series 1 and 2. H-homo(Fe-O)'s (1) and H-homo(Fe-S)'s (2) conform to the captodative principle. Insight from this work may help the design of more effective catalytic processes. Copyright (c) 2015 John Wiley & Sons, Ltd.