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 SO to HS using eight protons (SO + 8H + 6e → HS + 3HO). 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)(μ-Cl)(μ-pz)} (Tp = HB(pyrazolyl)), 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 HS from the disulfide-bridged complex was achieved.