The knowledge of accurate
bond strengths is a fundamental basis for a proper analysis of chemical reaction mechanisms. Quantum chemical calculations at different levels of theory have been used to investigate heterolytic Fe–O and Fe–S
bond energies of (meta-substituted phenoxy)dicar
bonyl(η
5-cyclopentadienyl) iron [
m-G-C
6H
4OFp (
)] and (meta-substituted benzenethiolato)dicar
bonyl(η
5-cyclopentadienyl) iron [
m-G-C
6H
4SFp (
)] complexes. In this study, Fp is (η
5-C
5H
5)Fe(CO)
2, and G is NO
2, CN, COMe, CO
2Me, CF
3, Br, Cl, F, H, Me, MeO, and NMe
2. The results show that Tao–Perdew–Staroverov–Scuseria and Becke's power-series ansatz from 1997 with dispersion corrections functionals can provide the best price/performance ratio and accurate predictions of Δ
Hhet(Fe–O)'s and Δ
Hhet(Fe–S)'s. The excellent linear free energy relations [
r = 1.00 (g, 1e), 1.00 (g, 2b)] among the ΔΔ
Hhet (Fe–O)'s and δΔ
G0 of OH
bonds of
m-G-C
6H
4OH or ΔΔ
Hhet(Fe–S)'s and Δp
Ka's of SH
bonds of
m-G-C
6H
4SH imply that the governing structural factors for these
bond scissions are similar. And, the linear correlations [
r = −0.97 (g, 1 g), −0.97 (g, 2 h)] among the ΔΔ
Hhet (Fe–O)'s or ΔΔ
Hhet(Fe–S)'s and the substituent σ
m constants show that these correlations are in accordance with Hammett linear free energy relationships. The inductive effects of these substituents and the basis set effects influence the accuracy of Δ
Hhet(Fe–O)'s or Δ
Hhet(Fe–S)'s. The ΔΔ
Hhet(Fe–O)'s(g) (1) and ΔΔ
Hhet(Fe–S)'s(g)(2) follow the capto-dative Principle. The substituent effects on the Fe–O
bonds are much stronger than those on the less polar Fe–S
bonds. Insight from this work may help the design of more effective catalytic processes. Copyright