Insight into highly selective photocatalytic oxidation of alcohols by a new trinuclear ruthenium complex with visible light

A new ligand bearing two tpy moieties and one bpy unit (tpy = 2,2':6',2''-terpyridine; bpy = 2,2'-bipyridine) linked by carbon-carbon single bonds and its corresponding trinuclear ruthenium complex were readily synthesized in high yield, and characterized by (1)H NMR spectroscopy, high-resolution electrospray ionization mass spectrometry (HR-ESI/MS) and elemental analysis. The ruthenium complex exhibited moderate catalytic activity towards selective oxidation of alcohols in water with visible light under an air atmosphere. Investigations of UV/vis spectra, electrochemistry and ESI/MS suggested that the catalytic cycle involves two processes, Ru(c)(II)-OH2/Ru(c)(III)-OH and Ru(c)(III)-OH/Ru(c)(IV)=O. The effective electron transfer from the excited state *[Ru(tpy)2](2+) to [Co(NH3)5Cl]Cl2 is proposed to be responsible for the good activities of this visible-light-driven system under an air atmosphere.