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Abstract:
In enzymatic and synthetic catalytic oxidation, highly reactive iron–oxo intermediates play an important role as oxidants in the processes of hydroxylation, epoxidation, halogenation reactions, etc. Synthetic iron–oxo species also have the ability to catalyse chemo- or enantioselective reactions similar to enzymatic catalysis. In this context, a report on the [(PDP)FeII(CF3SO3)2)]/H2O2/AcOH system has gained attention as this activates the C=C bond of the alkene and has the catalytic ability to perform chemo- or enantioselective conversion of the alkenes. In this study, we have employed density functional methods for the formation of FeIV=O as well as FeV=O from O⋯O bond cleavage and also shown that the formation of FeV=O dominates over the corresponding FeIV=O species. In addition to having favourable formation energy, a lower barrier height was computed for the C=C bond activation of cis-2-butene in the S = 3/2 state in a concerted manner rather than forming a radical intermediate in a stepwise manner from the FeV=O unit. The concerted mechanism was found to be responsible for the chemo- and enantioselective product, which was also observed in the experimental findings. Furthermore, NCI plots also support the less steric interaction during the formation of FeV=O compared to FeIV=O species. Additionally, during the epoxidation reaction, these steric effects significantly contributed towards the concerted route over the stepwise pathway.
