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.

Singlet oxygen production by a polypyridine ruthenium (II) complex with a perylene monoimide derivative: A strategy for photodynamic inactivation of Candida albicans

“…A variety of transition metal complexes have been studied as photosensitizers for singlet oxygen generation [2,[5][6][7][8]. Amongst these complexes, Ru(II)-polypiridyl complexes have been investigated due to their stability, inertness and biological activity [7][8][9][10].…”

“…Singlet oxygen ( 1 O 2 , 1 D g ), the lowest excited state of the dioxygen molecule, can be generated by photochemical and chemical processes [1][2][3][4][5][6]. The most common photochemical method involves energy transfer from a triplet excited photosensitizer ( 3 *PS).…”

“…The most common photochemical method involves energy transfer from a triplet excited photosensitizer ( 3 *PS). Many dyes, including some diimides [2][3][4] and metal complexes [3][4][5][6][7][8][9][10] can be used as photosensitizers for the production of 1…”

Synthesis of sulfur karrikin bioisosteres as potential neuroprotectives

“…An additive, HMDO applied together with Lawesson’s reagent improved significantly the yields of thiopyranthiones 6b , 15b , 16b over pyranthiones 6a , 15a , 16a . In contrast to previous reports on related systems [ 28 – 31 ], microwave heating did not improve the yields; therefore, conventional heating was used in our case.…”

“…In order to increase the selectivity and the yields, an improved procedure [ 28 ] has been tested. An additive, HMDO applied together with Lawesson’s reagent improved significantly the yields of thiopyranthiones 6b , 15b , 16b over pyranthiones 6a , 15a , 16a .…”