Photogeneration of a Phosphonium Alkylidene Olefin Metathesis Catalyst

Treatment of ruthenium carbide (H(2)IMes)-(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 [(H(2)IMes)(Cl)(2)Ru=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.