Remote substituent effects on gas‐phase homolytic Fe–O and Fe–S bond energies of <i>p</i>‐G‐C₆H₄OFe(CO)₂(<i>η</i>⁵‐C₅H₅) and <i>p</i>‐G‐C₆H₄SFe(CO)₂(<i>η</i>⁵‐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 [Δ H homo (Fe–O)'s and Δ H homo (Fe–S)'s] of two series of para‐substituted phenoxydicarbonyl( η 5 ‐cyclopentadienyl) iron [ p ‐G‐C 6 H 4 OFp ( 1 )] and (para‐substituted benzenethiolato)dicarbonyl( η 5 ‐cyclopentadienyl) iron [ p ‐G‐C 6 H 4 SFp ( 2 )] were studied using Hartree–Fock and density functional theory (DFT) methods with large basis sets. In this study, Fp is ( η 5 ‐C 5 H 5 )Fe(CO) 2 , and G are NO 2 , CN, COMe, CO 2 Me, CF 3 , Br, Cl, F, H, Me, MeO, and NMe 2 . The results show that DFT methods can provide the best price/performance ratio and accurate predictions of Δ H homo (Fe–O)'s and Δ H homo (Fe–S)'s. The remote substituent effects on Δ H homo (Fe–O)'s and Δ H homo (Fe–S)'s [ΔΔ H homo (Fe–O)'s and ΔΔ H homo (Fe–S)'s] can also be satisfactorily predicted. The good correlations [ r = 0.98 (g, 1), 0.98 (g, 2)] of ΔΔ H homo (Fe–O)'s and ΔΔ H homo (Fe–S)'s in series 1 and 2 with the substituent σ p + constants imply that the para‐substituent effects on Δ H homo (Fe–O)'s and Δ H homo (Fe–S)'s originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. ΔΔ H homo (Fe–O)'s ( 1 ) and ΔΔ 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 © 2013 John Wiley &amp; Sons, Ltd.