Thermochemistry of sulfide and thiolato derivatives of iron carbonyl, and the strengths of the iron—sulfur bonds

J of Physical Organic Chem

Wang

et al. 2015

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 [ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s] of two series of meta‐substituted phenoxydicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4OFp (1)] and (meta‐substituted benzenethiolato)dicarbonyl(η5‐cyclopentadienyl) iron [m‐G‐C6H4SFp (2)] were studied using Hartree–Fock and density functional theory 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 Tao–Perdew–Staroverov–Scuseria and Minnesota 2006 functionals can provide the best price/performance ratio and accurate predictions of ΔHhomo(Fe–O)'s and ΔHhomo(Fe–S)'s. The polar effects of the meta substituents show that the dominant role to the magnitudes of ΔΔHhomo(Fe–O)'s or ΔΔHhomo(Fe–S)'s. σα·, σc· values for meta substituents are all related to polar effects. Spin‐delocalization effects of the meta substituents in ΔΔHhomo(Fe–O)'s and ΔΔHhomo(Fe–S)'s are small but not necessarily zero. Molecular effects rather than ΔΔHhomo(Fe–O)'s and ΔΔHhomo(Fe–S)'s are more suitable indexes for the overall substituent effects on ΔHhomo(Fe–O)'s and ΔHhomo(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. 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 © 2015 John Wiley & Sons, Ltd.

Section: Resultsmentioning

confidence: 84%

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

J of Physical Organic Chem

Wang

et al. 2015

“…In addition, Δ H homo (Fe–O)'s are larger than those in Fe‐porphyrin(O 2 ) and Fe‐porphyrin(imidazole)(O 2 ), whose Δ H homo (Fe–O)'s are 9 and 15 kcal/mol, calculated by DFT methods . Δ H homo (Fe–S)'s have comparable magnitudes with those of S 2 Fe 2 (CO) 6 , S 2 Fe 3 (CO) 9 , (SCH 3 ) 2 Fe 2 (CO) 6 , and (SC 2 H 5 ) 2 Fe 2 (CO) 6 whose Δ H homo (Fe–S)'s are 41.83, 41.11, 46.61, and 46.37 kcal/mol, respectively, calculated by drop microcalorimetric methods …”

Section: Resultsmentioning

confidence: 86%

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

J of Physical Organic Chem

Dong

et al. 2013

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 [ΔH homo (Fe-O)'s and ΔH homo (Fe-S)'s] of two series of para-substituted phenoxydicarbonyl(h 5 -cyclopentadienyl) iron [p-G-C 6 H 4 OFp (1)] and (para-substituted benzenethiolato)dicarbonyl(h 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 (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 DFT methods can provide the best price/performance ratio and accurate predictions of ΔH homo (Fe-O)'s and ΔH homo (Fe-S)'s. The remote substituent effects on ΔH homo (Fe-O)'s and ΔH homo (Fe-S)'s [ΔΔH homo (Fe-O)'s and ΔΔH homo (Fe-S)'s] can also be satisfactorily predicted. The good correlations [r = 0.98 (g, 1), 0.98 (g, 2)] of ΔΔH homo (Fe-O)'s and ΔΔH homo (Fe-S)'s in series 1 and 2 with the substituent s p + constants imply that the para-substituent effects on ΔH homo (Fe-O)'s and ΔH homo (Fe-S)'s originate mainly from polar effects, but those on radical stability originate from both spin delocalization and polar effects. ΔΔH homo (Fe-O)'s (1) and ΔΔH homo (Fe-S)'s (2) conform to the captodative principle. Insight from this work may help the design of more effective catalytic processes.

“…For example, Δ H homo (Fe–O)'s are larger than those in FePorphyrin(O 2 ) and FePorphyrin(imidazole)(O 2 ) whose Δ H homo (Fe–O)'s are 9 and 15 kcal/mol calculated by DFT methods . Δ H homo (Fe–S)'s have the comparable magnitudes with those in S 2 Fe 2 (CO) 6 , S 2 Fe 3 (CO) 9 , (SCH 3 ) 2 Fe 2 (CO) 6 , and (SC 2 H 5 ) 2 Fe 2 (CO) 6 whose Δ H homo (Fe–S)'s are 41.83, 41.11, 46.61, and 46.37 kcal/mol calculated by drop‐microcalorimetric methods . Because the superiority of using nonhybrid functionals (e.g., BP86 and TPSSTPSS) in handling Co‐C BDEs is confirmed, we conclude that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of Δ H het (Fe–O)'s and Δ H het (Fe–S)'s …”

Section: Resultsmentioning

confidence: 87%

Hartree-Fock and density functional theory study of remote substituent effects on gas-phase heterolytic Fe-O and Fe-S bond energies of p -G-C₆ H₄ OFe(CO)₂ (η ⁵ -C₅ H₅ ) and p -G-C₆ H₄ SFe(CO)₂ (η ⁵ -C₅ H₅ )

Han

et al. 2013

J. Phys. Org. Chem.

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 para‐substituted phenoxydicarbonyl(η5‐cyclopentadienyl) iron [p‐G‐C6H4O(η5‐C5H5)Fe(CO)2, abbreviated as p‐G‐C6H4OFp (1), where G = NO2, CN, COMe, CO2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2] and para‐substituted benzenethiolatodicarbonyl(η5‐cyclopentadienyl) iron [p‐G‐C6H4S(η5‐C5H5)Fe(CO)2, abbreviated as p‐G‐C6H4SFp (2)] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of ΔHhet(Fe–O)'s and ΔHhet(Fe–S)'s. The excellent linear free‐energy relations [r = 0.99 (g, 1a), 1.00 (g, 2b)] among the ΔΔHhet (Fe–O)'s and Δpka's of O–H bonds of p‐G‐C6H4OH or ΔΔHhet(Fe‐S)'s and Δpka's of S–H bonds of p‐G‐C6H4SH imply that the governing structural factors for these bond scissions are similar. And the linear correlations [r = −0.99 (g, 1g), −0.98 (g, 2h)] among the ΔΔHhet (Fe‐O)'s or ΔΔHhet(Fe‐S)'s and the substituent σp− constants show that these correlations are in accordance with Hammett linear free‐energy relationships. The polar effects of these substituents and the basis set effects influence the accuracy of ΔHhet(Fe–O)'s or ΔHhet(Fe–S)'s. ΔΔHhet(Fe–O)'s(g) (1) and ΔΔHhet(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 © 2013 John Wiley & Sons, Ltd.