Ligand effects in novel ruthenium-based ROMP catalysts bearing bidentate phosphines

Complexes of general formula [(Cy2P(CH2)(n)-PCy2)Ru(eta (3)-C4H7)(2)] (n = 1-3) are halide-free initiators for ring-opening metathesis polymerization (ROMP) of norbornene. The chain length of the chelating phosphine exhibits an effect on the polymer yield and the stereochemistry at the C=C double bo nd. Analysis of the resulting polymer by GPC and electron microscopy indica tes an initiation efficiency of approximately 10%. A mechanism for the form ation of the propagating species is proposed that involves merging of the t wo allyl moieties and cycloreversion of the resulting ruthenacyclobutane to give a carbene intermediate containing a cis-PRuP chelate ring.