On the chloride lability in electron-rich second-generation ruthenium benzylidene complexes

A series of electron-rich second-generation cis-dichloro ruthenium aldehyde-chelating benzylidene complexes was prepared, characterized, and tested in typical ring-opening metathesis polymerization (ROMP) experiments. The benzylidene precursors were prepared via etherification of the hydroxyl group and vinylation at position 2 of 2-bromo-5-hydroxy-4-methoxybenzaldehyde. The corresponding ruthenium complexes were obtained from a carbene exchange reaction and were characterized by a cis-dichloro arrangement. A pronounced lability of the chloride ligand trans to the N-heterocyclic carbene ligand in methanol was observed and it was shown that this feature is responsible for a particularly slow ROMP in this solvent. [GRAPHICS] .