Photogeneration of a Phosphonium Alkylidene Olefin Metathesis Catalyst

Treatment of ruthenium carbide (H2IMes)(Cl)2(PCy3)RuC (1) with the photoacid generator (PAG) [Ph3S][OTf] (3) under 254 nm light results in a highly efficient catalyst for ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions. The reactions proceed via formation of the ruthenium phosphonium alkylidene complex [(H2IMes)(Cl)2RuC(H)PCy3][OTf] as the active catalytic species. In the case of ROMP of cycloalkenes, reactions do not require addition of PAG and protonation of 1 proceeds via allylic C–H bond activation of the substrate under UV light.