Highly Efficient and Selective Photocatalytic Oxidation of Sulfide by a Chromophore–Catalyst Dyad of Ruthenium-Based Complexes

Electronic
coupling across a bridging ligand between a chromophore and a catalyst
center has an important influence on biological and synthetic photocatalytic
processes. Structural and associated electronic modifications of ligands
may improve the efficiency of photocatalytic transformations of organic
substrates. Two ruthenium-based supramolecular assemblies based on
a chromophore–catalyst dyad containing a Ru–aqua complex
and its chloro form as the catalytic components were synthesized and
structurally characterized, and their spectroscopic and electrochemical
properties were investigated. Under visible light irradiation and
in the presence of [Co­(NH3)5Cl]­Cl2 as a sacrificial electron acceptor, both complexes exhibited good
photocatalytic activity toward oxidation of sulfide into the corresponding
sulfoxide with high efficiency and >99% product selectivity in
neutral aqueous solution. The Ru–aqua complex assembly was
more efficient than the chloro complex. Isotopic labeling experiments
using 18O-labeled water demonstrated the oxygen atom transfer
from the water to the organic substrate, likely through the formation
of an active intermediate, Ru­(IV)O.