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Platinum Metals Rev., 2004, 48, (2), 71

Light-Driven Alkane Oxygenation by Ruthenium(II)

Photocatalysts can activate unreactive C-H bonds of complex saturated hydrocarbons, such as alkanes, to functionalise them: an important reaction in organic chemistry. The dissociation of a ligand often starts the reaction, catalysed by a transition metal complex. Ru(II) polypyridyl complexes take part in photosubstitution reactions, probably by excitation in the metal to ligand charge transfer (MLCT) region by dissociation.

Now, researchers from the Tokyo Metropolitan University, Japan, have developed, under visible light irradiation (> 385 nm), stereospecific and photoregulated catalytic alkane oxidation reactions using chloro(Me2SO)Ru(II) complexes with tris(2-pyridylmethyl)amine or its derivative in the presence of 2,6-dichloropyridine N-oxide (M. Yamaguchi, T. Kumano, D. Masui and T. Yamagishi, Chem. Commun., 2004, (7), 798–799). Excitation in the MLCT band selectively substituted the S-bound Me2SO ligand by a solvent molecule.

When adamantane, the most stable C10H16 isomer, was catalytically oxidised, 1-adamantanol and ada-mantane-1,3-diol were selectively formed in good yields. The Ru complex and irradiation were both necessary for oxidation to proceed; without irradiation the reaction diminished, but irradiation restored it. Thus the reaction is photoassisted, not photoinitiated. Irradiation may initiate the catalytic reaction and generate the active species for alkane oxidation.

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