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

The thiolato complex [platinum­(II) (bipyridine)­(N,S-aminoethanethiolate)]+Ch– (1) undergoes sequential reactions with singlet oxygen to initially form the corresponding sulfenato complex [platinum­(II) (bipyridine)­(N,S(O)-aminoethansulfenate)]+ (2) followed by a much slower reaction to the corresponding sulfinato complex. In contrast with many platinum dithiolato complexes, 1 does not produce any singlet oxygen, but its rate constant for singlet oxygen removal (kT) is quite large (3.2 × 107 M–1 s–1) and chemical reaction accounts for ca. 25% of the value of kT. The behavior of 1 is strikingly different from that of the complex platinum­(II) (bipyridine)­(1,2-benzenditholate) (4). 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 1 with 1O2 must involve O–O bond cleavage and intermolecular oxygen atom transfer, while the reactive intermediate in complex 4 collapses intramolecularly to the sulfinato moiety.