Singlet Oxygen Generation, Quenching and Reactivity with Metal Thiolates^†

Abstract

Metal thiolate complexes can act as photosensitizers for the generation of singlet oxygen, quenchers of singlet oxygen, and they may undergo chemical reactions with singlet oxygen leading to oxidized thiolate ligands. This review covers all of the chemical reactions of thiolate ligands with singlet oxygen (through early 2021). Since some of these reactions are selfsensitized photooxidations, singlet oxygen generation by metal complexes is also discussed. Mechanistic features such as the effects of protic vs. aprotic conditions are presented and compared with the comparatively well-understood photooxidation of organic sulfides. In general, the total rate of singlet oxygen removal correlates with the nucleophilicity of the thiolate ligand which in turn can be influenced by the metal. Some interesting patterns of reactivity have been noted as a result of this survey: Metal thiolate complexes bearing arylthiolate ligands appear to exclusively produce sulfinate (metal-bound sulfone) products upon reaction with singlet oxygen. In contrast, metal thiolate complexes bearing alkylthiolate ligands may produce sulfinate and/or sulfenate (metal-bound sulfoxide) products. Several mechanistic pathways have been proposed for these reactions, but the exact nature of any intermediates remains unknown at this time.

Fractional dependence of the free energy of activation on the driving force of charge transfer in the quenching of the excited states of substituted phenanthroline homoleptic ruthenium(ii) complexes in aqueous medium

“…It has also been reported that cyclometallated monocationic complexes of iridium(III) and platinum(II) are effective singlet oxygen photosensitizers. 67,68 Cyclometallated platinum(II) complexes, 69,70 were found to be efficient singlet oxygen photosensitizers. The photophysical properties and efficiency of singlet oxygen production photosensitized by thirty eight Re(I) complexes have been recently collected and singlet oxygen quantum yields were reported with the minimum value of 0.20 and highest value approaching unity.…”

Mechanism of Oxygen Quenching of the Excited States of Heteroleptic Chromium(III) Phenanthroline Derivatives

“…Studies on singlet oxygen photosensitization by coordination compounds are very limited in comparison with those reported for aromatic compounds. ,,, The majority of these studies have been concerned on the study of singlet oxygen generation photosensitized by ruthenium­(II) polypyridyl complexes in aqueous and nonaqueous media. − Photosensitization of singlet oxygen by metal complexes other than Ru­(II) has also been reported − using, for example, complexes of Pd­(II) and Pt­(II), − ,− Os­(II) with terpyridyl ligands, Au­(I), Ir­(III), ,, and Re­(I) …”

Singlet Oxygen's Potential Role as aNonoxidativeFacilitator of Disulfide S–S Bond Rotation†

“…Relatedly, peroxy intermediates arise in various photooxidation and regular oxidation reactions. These intermediates include R 2 C + OO − carbonyl oxide, RN + OO − nitrosooxide, R 2 NN + (=O)OO − nitrooxide, R 2 Si + OO − silanone oxide, R 2 S + OO − persulfoxide and R 2 Te + OO − pertelluroxide (14–25). Peroxy intermediates have been implicated in lowering the energy barrier for cis ‐ trans isomerization of alkene and polyene CC bonds (1).…”