Ligand-based photooxidations of dithiomaltolato complexes of Ru(ii) and Zn(ii): photolytic CH activation and evidence of singlet oxygen generation and quenchingThis paper is dedicated to the memory of Prof. Oussama El-Bjeirami, who contributed to this work.Electronic supplementary information (ESI) available: Including crystallographic data for Httma, 1H NMR comparison of compounds 1, 3 and 4, MS analysis of photolysis products, and steady state quenching and singlet oxygen quenching experiments

The complex [Ru(bpy) 2 (ttma)] + (bpy = 2,2′-bipyridine; ttma = 3-hydroxy-2-methyl-thiopyran-4-thionate, 1 , has previously been shown to undergo an unusual C-H activation of the dithiomaltolato ligand upon outer-sphere oxidation. The reaction generated alcohol and aldehyde products 2 and 3 from C-H oxidation of the pendant methyl group. In this report, we demonstrate that the same products are formed upon photolysis of 1 in presence of mild oxidants such as methyl viologen, [Ru(NH 3 ) 6 ] 3+ and [Co(NH 3 ) 5 Cl] 2+ , which do not oxidize 1 in the dark. This reactivity is engendered only upon excitation into an absorption band attributed to the ttma ligand. Analogous experiments with the homoleptic Zn(ttma) 2 , 4 , also result in reduction of electron acceptors upon excitation of the ttma absorption band. Complexes 1 and 4 exhibit short-lived visible fluorescence and long-lived near-infrared phosphorescence bands. Singlet oxygen is both generated and quenched during aerobic excitation of 1 or 4 , but is not involved in the C-H activation process. Unusual light induced C-H oxidation initiated by excitation into Ru-bound dithiomaltol ligand absorption.