Stepwise Sulfite Reduction on a Dinuclear Ruthenium Complex Leading to Hydrogen Sulfide

Sulfite reduction by dissimilatory sulfite reductases is a key process in the global sulfur cycle. Sulfite reductases catalyze the 6e^- reduction of SO₃^2- to H₂S using eight protons (SO₃^2- + 8H⁺ + 6e^- → H₂S + 3H₂O). However, detailed research into the reductive conversion of sulfite on transition-metal-based complexes remains unexplored. As part of our ongoing research into reproducing the function of reductases using dinuclear ruthenium complex {(TpRu)₂(μ-Cl)(μ-pz)} (Tp = HB(pyrazolyl)₃), we have targeted the function of sulfite reductase. The isolation of a key SO-bridged complex, followed by a sulfite-bridged complex, eventually resulted in a stepwise sulfite reduction. The reduction of a sulfite to a sulfur monoxide using 4H⁺ and 4e^-, which was followed by conversion of the sulfur monoxide to a disulfide with concomitant consumption of 2H⁺ and 2e^-, proceeded on the same platform. Finally, the production of H₂S from the disulfide-bridged complex was achieved.