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.硫醇盐配合物[铂(II)(联吡啶)(N,S-氨基乙硫醇)]+Ch⁻（化合物1）会与单线态氧（singlet oxygen）发生分步反应，首先生成对应的亚磺酰基配合物[铂(II)(联吡啶)(N,S(=O)-氨基乙亚磺酰)]+（化合物2），随后以慢得多的反应速率生成对应的磺酰基配合物。与多数铂基二硫醇盐配合物不同，化合物1不会产生任何单线态氧，但其单线态氧清除速率常数（kT）可达3.2 × 10⁷ M⁻¹·s⁻¹，数值可观，其中约25%的kT值来源于化学反应过程。化合物1的反应行为与配合物铂(II)(联吡啶)(1,2-苯二硫醇盐)（化合物4）截然不同，后者可与1O2（既可来自外部敏化剂，也可通过自敏化途径）反应生成磺酰基配合物。这两种差异显著的反应路径暗示了不同的反应机理：化合物1与1O2的反应必然涉及O-O键断裂与分子间氧原子转移，而配合物4中的反应中间体则通过分子内过程裂解为磺酰基结构单元。