A Ruthenium(III)-Oxyl Complex Bearing Strong Radical Character

Yoshihiro Shimoyama; Tomoya Ishizuka; Hiroaki Kotani; Yoshihito Shiota; Kazunari Yoshizawa; Kaoru Mieda; Takashi Ogura; Toshihiro Okajima; Shunsuke Nozawa; Takahiko Kojima

doi:10.1002/anie.201607861

A Ruthenium(III)-Oxyl Complex Bearing Strong Radical Character

Angew Chem Int Ed Engl. 2016 Nov 2;55(45):14041-14045. doi: 10.1002/anie.201607861. Epub 2016 Oct 6.

Affiliations

¹ Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8571, Japan.
² Institute for Materials Chemistry and Engineering, Kyushu University, Motooka, Nishi-Ku, Fukuoka, 819-0395, Japan.
³ Picobiology Institute, Graduate School of Life Science, University of Hyogo, RSC-UH Leading Program Center, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan.
⁴ Kyushu Synchrotron Light Research Center, 8-7 Yayoigaoka, Tosu, Saga, 841-0005, Japan.
⁵ Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan.
⁶ Department of Chemistry, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, 305-8571, Japan. kojima@chem.tsukuba.ac.jp.

PMID: 27709765
DOI: 10.1002/anie.201607861

Abstract

Proton-coupled electron-transfer oxidation of a Ru^II -OH₂ complex, having an N-heterocyclic carbene ligand, gives a Ru^III -O^. species, which has an electronically equivalent structure of the Ru^IV =O species, in an acidic aqueous solution. The Ru^III -O^. complex was characterized by spectroscopic methods and DFT calculations. The oxidation state of the Ru center was shown to be close to +3; the Ru-O bond showed a lower-energy Raman scattering at 732 cm^-1 and the Ru-O bond length was estimated to be 1.77(1) Å. The Ru^III -O^. complex exhibits high reactivity in substrate oxidation under catalytic conditions; particularly, benzaldehyde and the derivatives are oxidized to the corresponding benzoic acid through C-H abstraction from the formyl group by the Ru^III -O^. complex bearing a strong radical character as the active species.

Keywords: N-heterocyclic carbenes; catalysis; oxyl radicals; ruthenium; substrate oxidation.

Publication types

Research Support, Non-U.S. Gov't