18-Electron Ruthenium Phosphine Sulfonate Catalysts for Olefin Metathesis

The first instances of ruthenium alkylidene complexes based on chelating phosphine sulfonates are presented. Although these complexes are formally 18-electron complexes bearing cis phosphines and cis one-electron donors (sulfonates and chlorides), they are surprisingly active for ring-closing metathesis, cross-metathesis, and ring-opening metathesis polymerization, thus highlighting the unique potential of the sulfonate ligand in the design of a ruthenium metathesis catalyst.