Photoinduced NO production from a mononuclear {MnNO}⁶ complex bearing a metal-diaryldisulphide ligand

A solution of six-coordinate [Mn(PS2)₂] (1) is inert towards nitric oxide (NO) at room temperature. In the presence of a proton source such as <i>p</i>-toluenesulfonic acid or perchloric acid, however, the treatment of 1 with NO in the dark leads to the formation of {MnNO}⁶ [Mn(NO)(SPS-SPS)] (2) with a metal-diaryldisulphide ligand, as confirmed by several spectroscopy investigations, including single-crystal X-ray diffraction. A possible pathway for the formation of 2 was determined through theoretical studies and involves the following: (i) the thiolato sulphur in 1 interacts with H⁺ to generate an intermediate [Mn(PS2)(PS2H)]⁺ (A) with an S⋯H interaction; (ii) the reaction of A with NO yields HNO and an Mn(IV)-bound-thiyl radical species (B); and (iii) the nucleophilicity of the thiyl radical B to an adjacent thiolato sulphur produces a five-coordinate Mn(III)-diaryldisulphide species (C), which reacts with the generated HNO to yield 2. Complex 2 is sensitive to visible light. When photolysis of 2 in solution is performed, complex 1 is regenerated and NO is released, which is related to metal-disulphide/metal-thiolate interconversion.