Ligand Effects in Novel Ruthenium-Based ROMP Catalysts Bearing Bidentate Phosphines

Abstract

Complexes of general formula [(Cy2P(CH2)nPCy2)Ru(η3-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 CC double bond. Analysis of the resulting polymer by GPC and electron microscopy indicates an initiation efficiency of approximately 10%. A mechanism for the formation of the propagating species is proposed that involves merging of the two allyl moieties and cycloreversion of the resulting ruthenacyclobutane to give a carbene intermediate containing a cis-PRuP chelate ring.