Remote substituent effects on homolytic Fe‐N bond energies of p‐G‐C₆H₄NHFe(CO)₂(η⁵‐C₅H₅) and p‐G‐C₆H₄(COMe)NFe(CO)₂(η⁵‐C₅H₅) studied using Hartree–Fock and density functional theory methods

Abstract

The nature and strength of metal-ligand bonds in organotransition-metal complexes is crucial to the understanding of organometallic reactions and catalysis. The Fe-N homolytic bond dissociation energies [ΔH homo (Fe-N)′s] of two series of para-substituted Fp anilines p-G-C 6 H 4 NHFp [1] and p-G-C 6 H 4 N(COMe)Fp [2] were studied using the Hartree-Fock (HF) and the density functional theory methods with large basis sets. In this study, Fp is (h 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 BP86 and TPSSTPSS can provide the best price/performance ratio and accurate predictions of ΔH homo (Fe-N)′s. B3LYP can also satisfactorily predict the a and remote substituent effects on ΔH homo (Fe-N)′s [ΔΔH homo (Fe-N)′s]. The good correlations [r = 0.96 (g, 1), 0.99(g, 2)] of ΔΔH homo (Fe-N)′s in series 1 and 2 with the substituent s p + constants imply that the para-substituent effects on ΔH homo (Fe-N)′s originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. ΔΔH homo (Fe-N)′s(1,2) conform to the captodative principle. Insight from this work may help the design of more effective catalytic processes.

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

“…Indeed, metal–ligand bond enthalpies can provide valuable information on metal–ligand bonding, can offer a deeper insight into known reaction pathways, and can aid in designing new transformations . Unfortunately, the experimental determination of metal–ligand bond dissociation energy (BDE) in organometallic complexes is often difficult . Density functional theory (DFT), however, has proven to be a powerful alternative in this effort, especially after the development of nonlocal and hybrid DFT methods.…”

“…However, there are scarce reports on the Fe–O and Fe–S bond energies in Fp compounds . In our laboratory, methods described by Venimadhavan et al ., Bordwell et al ., and Brauman for determining enthalpies of heterolysis (Δ H het ) and homolysis (Δ H homo ) for the cleavage of N–H, C–H, O–H, or C–S bonds were extended to the study of Fe–O and Fe–S σ‐bond energies through the reactions of para‐substituted phenoxide ions ( p ‐G‐C 6 H 4 O − ) or para‐substituted thiophenyl anions ( p ‐G‐C 6 H 4 S − ) with Fp + BF 4 − formed in solution.…”

Substituent effects on gas‐phase homolytic Fe–N bond energies of m‐G‐C6H4NHFe(CO)2(η5‐C5H5) and m‐G‐C6H4N(COMe)Fe(CO)2(η5‐C5H5) studied using density functional theory methods

“…It can be found that Δ H homo (Fe–N)'s from columns IV to V in series 1 are smaller than the corresponding Δ H homo (Fe–N)'s in series 2 , respectively. This results from the electron withdrawing effect of α‐COMe . They also have the comparable magnitudes with those in Fe(porphyrin)(NO) and Fe(porphyrin)(imidazole)(NO) whose Δ H homo (Fe–NO)'s are 35 and 36 kcal/mol calculated by DFT methods …”

“…In b , the Fe 1 –N 9 and N 9 –C 13 bond lengths and the ∠Fe 1 –N 9 –C 13 and ∠N 9 –Fe 1 –C 2 (88.0°) bond angles are different from the corresponding data in a notably. It results from the inductive effect and steric effect of α‐COMe on N 9 atom …”

“…The substituent effects on the Fe–N homolytic dissociation energies [Δ H homo (Fe–N)'s] of series 1 and 2 were also investigated in detail. We have known that the Fp–N BDEs of p ‐G‐C 6 H 4 NHFp and p ‐G‐C 6 H 4 N(COMe)Fp are reduced by para–electron‐donating groups (EDGs) but increased by para–electron‐withdrawing groups (EWGs) . Thus, it is interesting to know whether this also holds for the meta‐substituent effects on the Fp–N BDEs.…”