Remote substituent effects on gas‐phase homolytic Fe–O and Fe–S bond energies of p‐G‐C6H4OFe(CO)2(η5‐C5H5) and p‐G‐C6H4SFe(CO)2(η5‐C5H5) studied using Hartree–Fock and density functional theory methods

Abstract

Metal–ligand bond enthalpy data can afford invaluable insights into important reaction patterns in organometallic chemistry and catalysis. In this paper, the Fe–O and Fe–S homolytic bond dissociation energies [ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s] of two series of para‐substituted phenoxydicarbonyl(η5‐cyclopentadienyl) iron [p‐G‐C6H4OFp (1)] and (para‐substituted benzenethiolato)dicarbonyl(η5‐cyclopentadienyl) iron [p‐G‐C6H4SFp (2)] were studied using Hartree–Fock and density functional theory (DFT) methods with large basis sets. In this study, Fp is (η5‐C5H5)Fe(CO)2, and G are NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2. The results show that DFT methods can provide the best price/performance ratio and accurate predictions of ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s. The remote substituent effects on ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s [ΔΔHhomo(Fe–O)'s and ΔΔHhomo(Fe–S)'s] can also be satisfactorily predicted. The good correlations [r = 0.98 (g, 1), 0.98 (g, 2)] of ΔΔHhomo(Fe–O)'s and ΔΔHhomo(Fe–S)'s in series 1 and 2 with the substituent σp+ constants imply that the para‐substituent effects on ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. ΔΔHhomo(Fe–O)'s (1) and ΔΔHhomo(Fe–S)'s (2) conform to the captodative principle. Insight from this work may help the design of more effective catalytic processes. Copyright © 2013 John Wiley & Sons, Ltd.