Electron Relay Boosts Ruthenium-Laccase System Photo-Epoxidation

We report here the light-driven oxidation of olefin to epoxide using a [Ru(bipyridine)₃]²⁺/laccase (Ru^II/LAC3)-based system, enhanced by the presence of methyl viologen (MV²⁺) as an electron relay. This approach leads to a fivefold increase in the conversion yield of sodium p-styrene sulfonate (pSS) oxidation (from 3% to 14% in the presence of MV²⁺), and favors chemoselectivity toward epoxidation. We demonstrate that laccase plays a crucial role in steering product selectivity, favoring epoxidation due to its ability to scavenge superoxide (O₂^•−). In contrast, in the absence of laccase, the reaction predominantly yields sodium p-benzaldehyde sulfonate (A) and the sodium α-hydroxyketone p-phenyl sulfonate (α-HK). Mechanistic insights, supported by reactive intermediate trapping, isotope labeling, and product distribution analysis, suggest a reaction pathway involving both molecular oxygen and water as the oxygen sources.