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Photochemical activation of ruthenium(II)-pyridylamine complexes having a pyridine- N -oxide pendant toward oxygenation of organic substrates

Photochemical activation of ruthenium(II)-pyridylamine complexes having a pyridine- N -oxide pendant toward oxygenation of organic substrates
Kojima T.Nakayama K.Sakaguchi M.Ogura T.Ohkubo K.Fukuzumi S.
Ewha Authors
Shunichi Fukuzumi
Shunichi Fukuzumiscopus
Issue Date
Journal Title
Journal of the American Chemical Society
0002-7863JCR Link
vol. 133, no. 44, pp. 17901 - 17911
Ruthenium(II)-acetonitrile complexes having η 3-tris(2- pyridylmethyl)amine (TPA) with an uncoordinated pyridine ring and diimine such as 2,2′-bipyridine (bpy) and 2,2′-bipyrimidine (bpm), [Ru II(η 3-TPA)(diimine)(CH 3CN)] 2+, reacted with m-chloroperbenzoic acid to afford corresponding Ru(II)-acetonitrile complexes having an uncoordinated pyridine-N-oxide arm, [Ru II(η 3-TPA-O)(diimine)(CH 3CN)] 2+, with retention of the coordination environment. Photoirradiation of the acetonitrile complexes having diimine and the η 3-TPA with the uncoordinated pyridine-N-oxide arm afforded a mixture of [Ru II(TPA)(diimine)] 2+, intermediate-spin (S = 1) Ru(IV)-oxo complex with uncoordinated pyridine arm, and intermediate-spin Ru(IV)-oxo complex with uncoordinated pyridine-N-oxide arm. A Ru(II) complex bearing an oxygen-bound pyridine-N-oxide as a ligand and bpm as a diimine ligand was also obtained, and its crystal structure was determined by X-ray crystallography. Femtosecond laser flash photolysis of the isolated O-coordinated Ru(II)-pyridine-N-oxide complex has been investigated to reveal the photodynamics. The Ru(IV)-oxo complex with an uncoordinated pyridine moiety was alternatively prepared by reaction of the corresponding acetonitrile complex with 2,6-dichloropyridine-N-oxide (Cl 2py-O) to identify the Ru(IV)-oxo species. The formation of Ru(IV)-oxo complexes was concluded to proceed via intermolecular oxygen atom transfer from the uncoordinated pyridine-N-oxide to a Ru(II) center on the basis of the results of the reaction with Cl 2py-O and the concentration dependence of the consumption of the starting Ru(II) complexes having the uncoordinated pyridine-N-oxide moiety. Oxygenation reactions of organic substrates by [Ru II(η 3-TPA-O)(diimine)(CH 3CN)] 2+ were examined under irradiation (at 420 ± 5 nm) and showed selective allylic oxygenation of cyclohexene to give cyclohexen-1-ol and cyclohexen-1-one and cumene oxygenation to afford cumyl alcohol and acetophenone. © 2011 American Chemical Society.
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