title: Ligand-based photooxidations of dithiomaltolato complexes of Ru(II) and Zn(II): photolytic CH activation and evidence of singlet oxygen generation and quenching.
abstract: 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(NH3)6](3+) and [Co(NH3)5Cl](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.
authors.affiliation: Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798, USA. Patrick_Farmer@baylor.edu.
authors.forename: Britain
authors.initials: B
authors.lastname: Bruner
authors.forename: Malin Backlund
authors.initials: MB
authors.lastname: Walker
authors.forename: Mukunda M
authors.initials: MM
authors.lastname: Ghimire
authors.forename: Dong
authors.initials: D
authors.lastname: Zhang
authors.forename: Matthias
authors.initials: M
authors.lastname: Selke
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Klausmeyer
authors.forename: Mohammad A
authors.initials: MA
authors.lastname: Omary
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Farmer
mesh_terms: D003460:Crystallization; D004563:Electrochemistry; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D010782:Photolysis; D017975:Ruthenium Compounds / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D008024:Ligands; D017975:Ruthenium Compounds; D017967:Zinc Compounds; D026082:Singlet Oxygen