Ligand Isomerization in Sulfur-Chelated Ruthenium Benzylidenes

cis-Dichloro−trans-dichloro isomerization was studied in sulfur-chelated ruthenium benzylidenes. The effect of solvents and additives on the isomerization process was analyzed. Notably, π-acid ligand molecules, dichloromethane, and polar solvents were found to significantly accelerate the isomerization rate. As expected, the cis−trans isomer equilibria had a strong effect on the olefin metathesis reactivity; the bulkier cis-dichloro catalysts, which show a larger amount of trans isomer in the equilibrium, were more reactive than their less bulky counterparts. This tendency was generally reversed in the isolated trans isomer series, where both steric factors and faster isomerization play a role in dictating the olefin metathesis reactivity. A better understanding of the trans−cis isomerization and the mechanism that governs reactivity in strongly chelated cis-dichloro ruthenium benzylidenes was obtained.