Effect of the Metal on Disulfide/Thiolate Interconversion: Manganese versus Cobalt

It has recently been proposed that disulfide/thiolate interconversion supported by transition-metal ions is involved in several relevant biological processes. In this context, the present contribution represents a unique investigation of the effect of the coordinated metal (M) on the M(n+)-disulfide/M((n+1)+)-thiolate switch properties. Like its isostructural Co(II)-based parent compound, Co(II)2SS (Angew. Chem. Int. Ed.- 2014, 53, 5318), the new dinuclear disulfide-bridged Mn(II) complex Mn(II)2SS can undergo an M(II)-disulfide/M(III)-thiolate interconversion, which leads to the first disulfide/thiolate switch based on Mn. The coordination of iodide to the metal ion stabilizes the oxidized form, as the disulfide is reduced to the thiolate. The reverse process, which involves the reduction of M(III) to M(II) with the concomitant oxidation of the thiolates, requires the release of iodide. The Mn(II)2SS complex slowly reacts with Bu4NI in CH2Cl2 to afford the mononuclear Mn(III)-thiolate complex Mn(III)I. The process is much slower (ca. 16 h) and much less efficient (ca. 30% yield) with respect to the instantaneous and quantitative conversion of Co(II)2SS into Co(III)I under similar conditions. This distinctive behavior can be rationalized by considering the different electrochemical properties of the involved Co and Mn complexes and the DFT-calculated driving force of the disulfide/thiolate conversion. For both Mn and Co systems, M(II)-disulfide/M(III)-thiolate interconversion is reversible. However, when the iodide is removed with Ag(+), the M(II)2SS complexes are regenerated, albeit much slower for Mn than for Co systems.