Influence of initiator and monomer structure on the polymerization of acetylene monomers using Schrock-type molybdenum carbenes

The polymerization of acetylene monomers using homogeneous Schrock-type ini tiators of the general formula Mo(CHR')(NAr)(OR)(2) with different substitu tion patterns was investigated. The influence of the ligands at the molybde num center and of donor functions at the beta-position with respect to the monomer's triple bond on the polymerization was studied by means of NMR spe ctroscopy and size exclusion chromatography. The results clearly indicate t hat kinetics and mechanism of the metathesis reaction strongly depend on th e structures of monomer and initiator. The use of partially fluorinated alk oxy ligands instead of aliphatic alkoxides leads to a change of the regioch emistry of the insertion. Ether functions in the monomer tend to slow the r eaction, giving rise to polymers with a narrow molecular weight distributio n probably due to coordination of the oxygen atom to the metal center.