title: Tunneling Effect That Changes the Reaction Pathway from Epoxidation to Hydroxylation in the Oxidation of Cyclohexene by a Compound I Model of Cytochrome P450.
abstract: The rate constants of the C═C epoxidation and the C-H hydroxylation (i.e., allylic C-H bond activation) in the oxidation of cyclohexene by a high-valent iron(IV)-oxo porphyrin π-cation radical complex, [(TMP•+)FeIV(O)(Cl)] (1, TMP = meso-tetramesitylporphyrin dianion), were determined at various temperatures by analyzing the overall rate constants and the products obtained in the cyclohexene oxidation by 1, leading us to conclude that reaction pathway changes from the C═C epoxidation to C-H hydroxylation by decreasing reaction temperature. When cyclohexene was replaced by deuterated cyclohexene (cyclohexene-d10), the epoxidation pathway dominated irrespective of the reaction temperature. The temperature dependence of the rate constant of the C-H hydroxylation pathway in the reactions of cyclohexene and cyclohexene-d10by 1 suggests that there is a significant tunneling effect on the hydrogen atom abstraction of allylic C-H bonds of cyclohexene by 1, leading us to propose that the tunneling effect is a determining factor for the switchover of the reaction pathway from the C═C epoxidation pathway to the C-H hydroxylation pathway by decreasing reaction temperature. By performing density functional theory (DFT) calculations, the reaction energy barriers of the C═C epoxidation and C-H bond activation reactions by 1 were found to be similar, supporting the notion that small environmental changes, such as the reaction temperature, can flip the preference for one reaction to another.
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
authors.forename: Ranjana
authors.initials: R
authors.lastname: Gupta
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.|State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences , Lanzhou 730000, China.
authors.forename: Xiao-Xi
authors.initials: XX
authors.lastname: Li
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
authors.forename: Kyung-Bin
authors.identifier: http://orcid.org/0000-0001-6586-983X
authors.initials: KB
authors.lastname: Cho
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
authors.forename: Mian
authors.initials: M
authors.lastname: Guo
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lee
authors.affiliation: State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences , Lanzhou 730000, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.|Faculty of Science and Engineering, Meijo University, SENTAN, Japan Science and Technology Agency (JST) , Nagoya, Aichi 468-8502, Japan.
authors.forename: Shunichi
authors.identifier: http://orcid.org/0000-0002-3559-4107
authors.initials: S
authors.lastname: Fukuzumi
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul 03760, Korea.|State Key Laboratory for Oxo Synthesis and Selective Oxidation, Suzhou Research Institute of LICP, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences , Lanzhou 730000, China.
authors.forename: Wonwoo
authors.identifier: http://orcid.org/0000-0001-8592-4867
authors.initials: W
authors.lastname: Nam