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-C 6H4OFe(CO)2(η5-C 5H5) and p-G-C6H4SFe(CO) 2(η5-C5H5)
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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-C 5H5)Fe(CO)2, abbreviated as p-G-C 6H4OFp (1), where G-=-NO2, CN, COMe, CO 2Me, CF3, Br, Cl, F, H, Me, MeO, and NMe2] and para-substituted benzenethiolatodicarbonyl(η5-cyclopentadienyl) iron [p-G-C6H4S(η5-C5H 5)Fe(CO)2, abbreviated as p-G-C6H 4SFp (2)] complexes. The results show that BP86 and TPSSTPSS can provide the best price/performance ratio and more accurate predictions in the study of I?Hhet(Fe-O)'s and I?Hhet(Fe-S)'s. The excellent linear free-energy relations [r-=-0.99 (g, 1a), 1.00 (g, 2b)] among the I?I?Hhet (Fe-O)'s and I?pka's of O-H bonds of p-G-C6H4OH or I?I?Hhet(Fe-S) 's and I?pka'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 I?I?Hhet (Fe-O)'s or I?I?Hhet(Fe-S)'s and the substituent Ip- 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 I?Hhet(Fe-O)'s or I?Hhet(Fe-S)'s. I?I?Hhet(Fe-O)'s(g) (1) and I?I?H het(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.