Sequential Photooxidation of a Pt(II) (Diimine)cysteamine Complex: Intermolecular Oxygen Atom Transfer versus Sulfinate Formation

The thiolato complex [platinum­(II) (bipyridine)­(<i>N</i>,<i>S</i>-aminoethanethiolate)]⁺Ch^– (<b>1</b>) undergoes sequential reactions with singlet oxygen to initially form the corresponding sulfenato complex [platinum­(II) (bipyridine)­(<i>N</i>,<i>S</i>(O)-aminoethansulfenate)]⁺ (<b>2</b>) followed by a much slower reaction to the corresponding sulfinato complex. In contrast with many platinum dithiolato complexes, <b>1</b> does not produce any singlet oxygen, but its rate constant for singlet oxygen removal (<i>k</i>_T) is quite large (3.2 × 10⁷ M^–1 s^–1) and chemical reaction accounts for ca. 25% of the value of <i>k</i>_T. The behavior of <b>1</b> is strikingly different from that of the complex platinum­(II) (bipyridine)­(1,2-benzenditholate) (<b>4</b>). The latter complex reacts with ¹O₂ (either from an external sensitizer or via a self-sensitized pathway) to form a sulfinato complex. These two very different reactivity pathways imply different mechanistic pathways: The reaction of <b>1</b> with ¹O₂ must involve O–O bond cleavage and intermolecular oxygen atom transfer, while the reactive intermediate in complex <b>4</b> collapses intramolecularly to the sulfinato moiety