Issue 12, 2012
From the journal:

Chemical Science

Mechanistic insight into catalytic oxidations of organic compounds by ruthenium(iv)-oxo complexes with pyridylamine ligands†

Shingo Ohzu,a   Tomoya Ishizuka,a   Yuichirou Hirai,b   Hua Jiang,a   Miyuki Sakaguchi,c   Takashi Ogura,c   Shunichi Fukuzumi*bd  and  Takahiko Kojima*a  

* Corresponding authors

a Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571, Japan
E-mail: kojima@chem.tsukuba.ac.jp
Fax: +81-29-853-6503

b Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA, JST, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
E-mail: fukuzumi@chem.eng.osaka-u.ac.jp

c Graduate School of Life Science, University of Hyogo, Kouto, Hyogo 678-1297, Japan

d Department of Bioinsipired Science (WCU project), Ewha Womans University, Seoul 120-750, South Korea

Abstract

A series of Ru(IV)-oxo complexes (4–6) were synthesized from the corresponding Ru(II)-aqua complexes (1–3) and fully characterized by 1H NMR and resonance Raman spectroscopies, and ESI-MS spectrometry. Based on the diamagnetic character confirmed by the 1H NMR spectroscopy in D2O, the spin states of 5 and 6 were determined to be S = 0 in the d4 configuration, in sharp contrast to that of 4 being in the S = 1 spin state. The aqua-complexes 1–3 catalyzed oxidation of alcohols and olefins using (NH4)2[CeIV(NO3)6] (CAN) as an electron-transfer oxidant in acidic aqueous solutions. Comparison of the reactivity of electrochemically generated oxo-complexes (4–6) was made in the light of kinetic analyses for oxidation of 1-propanol and a water-soluble ethylbenzene derivative. The oxo complexes (4–6) exhibited no significant difference in the reactivity for the oxidation reactions, judging from the similar catalytic rates and the activation parameters. The slight difference observed in the reaction rates can be accounted for by the difference in the reduction potentials of the oxo-complexes, but the spin states of the oxo-complexes have hardly affected the reactivity. The activation parameters and the kinetic isotope effects (KIE) observed for the oxidation reactions of methanol indicate that the oxidation reactions of alcohols with the RuIV[double bond, length as m-dash]O complexes proceed via a concerted proton-coupled electron transfer mechanism.

Graphical abstract: Mechanistic insight into catalytic oxidations of organic compounds by ruthenium(iv)-oxo complexes with pyridylamine ligands

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DOI
https://doi.org/10.1039/C2SC21195E
Article type
Edge Article
Submitted
07 Aug 2012
Accepted
28 Aug 2012
First published
31 Aug 2012

Chem. Sci., 2012,3, 3421-3431

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Mechanistic insight into catalytic oxidations of organic compounds by ruthenium(IV)-oxo complexes with pyridylamine ligands

S. Ohzu, T. Ishizuka, Y. Hirai, H. Jiang, M. Sakaguchi, T. Ogura, S. Fukuzumi and T. Kojima, Chem. Sci., 2012, 3, 3421 DOI: 10.1039/C2SC21195E

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