金属イオン共役電子移動による高原子価金属オキソ錯体の水の酸化触媒活性制御

2014 Fiscal Year Annual Research Report

• Project/Area Number: 12J02902
• Research Institution: Osaka University
• Principal Investigator: 朴 ジュン 大阪大学, 大学院工学研究科, 特別研究員(PD)
• Keywords: Electron Transfer / Lewis Acid / Epoxidation / Unification

Outline of Annual Research Achievements

We report efficient epoxidation of styrene derivatives by a nonheme iron(IV)-oxo complex, [(N4Py)Fe^<IV>(O)]^<2+>(N4Py = N, N-bis(2-pyridylmethyl)-N- bis(2-pyridyl)methylamine) with trilflic acid (HOTf). No oxidation of styrene derivatives by [(N4Py)Fe^<IV>(O)]^<2+>(N4Py = N, N-bis(2-pyridylmethyl)-N-bis(2-pyridyl) methylamine) occurred in acetonitrile at 298 K, whereas efficient epoxidation of styrene derivatives was made possible by the presence of triflic acid (HOTf) via proton-coupled electron transfer (PCET) from styrene derivatives to the diprotonated species of [(N4Py)Fe^<IV>(O)]^<2+> with HOTf. Logarithms of the first-order rate constants of HOTf-promoted expoxidation of all styrene derivatives with [(N4Py)Fe^<IV>(O)]^<2+> and PCET from electron donors in the precursor complexes exhibit a remarkably unified correlation with the driving force of PCET in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes are taken into account. The same PCET driving force dependence is obtained for the first-order rate constants of HOTf-promoted oxygen atom transfer from thioanisols to [(N4Py)Fe^<IV>(O)]^<2+> and HOTf-promoted hydrogen atom transfer from toluene derivatives to [(N4Py)Fe^<IV>(O)]^<2+> in the precursor complexes. Thus, HOTf-promoted epoxidation of styrene derivatives by [(N4Py)Fe^<IV>(O)]^<2+> proceeds via the rate-determining electron transfer from styrene derivatives to the diprotonated species of [(N4Py)Fe^<IV>(O)]^<2+> as the case of HOTf-promoted oxygen atom transfer from thioanisols to [(N4Py)Fe^<IV>(O)]^<2+> and HOTf-promoted hydrogen atom transfer from toluene derivatives to [(N4Py)Fe^<IV>(O)]^<2+>.

Current Status of Research Progress

1: Research has progressed more than it was originally planned.

Reason

All of oxidation reaction which occur by electron transfer from organic substrates to nonheme iron(IV)-oxo in the presence of Lewis acid can be unified in Marcus theory. With Lewis and Bronsted acid, such as metal ion and HOTf, effect on oxidation reaction by non-heme iron(IV)-oxo well studied in our system.

Strategy for Future Research Activity

Lewis acids, such as redox inactive metal ion and proton, can promote oxidation reaction of organic substrate by nonheme iron(IV)-oxo complex via electron transfer. Huge enhancement came from precursor complex formation of metal ion-bounded or protomated nonheme iron(IV)-oxo and substrate. By using this super reactive species, the other oxidation reaction can be done which never has been studied by nonheme high-valent metal-oxo complex, not only with iron but also the other metals, Co, Cu, Cr and so on.