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

Abstract

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 p-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.