TY - JOUR
T1 - Tunneling Effect That Changes the Reaction Pathway from Epoxidation to Hydroxylation in the Oxidation of Cyclohexene by a Compound I Model of Cytochrome P450
AU - Gupta, Ranjana
AU - Li, Xiao Xi
AU - Cho, Kyung Bin
AU - Guo, Mian
AU - Lee, Yong Min
AU - Wang, Yong
AU - Fukuzumi, Shunichi
AU - Nam, Wonwoo
N1 - Funding Information:
The authors acknowledge financial support from the NRF of Korea through the CRI (NRF-2012R1A3A2048842 to W.N.), GRL (NRF-2010-00353 to W.N.) and MSIP (NRF-2013R1A1A2062737 to K.-B.C.) and from JSPS KAKENHI (No. 16H02268 to S.F.).
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/4/6
Y1 - 2017/4/6
N2 - The rate constants of the CC 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 CC 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-d10 by 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 CC 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 CC 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.
AB - The rate constants of the CC 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 CC 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-d10 by 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 CC 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 CC 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.
UR - http://www.scopus.com/inward/record.url?scp=85017001404&partnerID=8YFLogxK
U2 - 10.1021/acs.jpclett.7b00461
DO - 10.1021/acs.jpclett.7b00461
M3 - Article
C2 - 28301931
AN - SCOPUS:85017001404
SN - 1948-7185
VL - 8
SP - 1557
EP - 1561
JO - Journal of Physical Chemistry Letters
JF - Journal of Physical Chemistry Letters
IS - 7
ER -