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 initiators of the general formula Mo(CHR')(NAr)(OR)(2) with different substitution patterns was investigated. The influence of the ligands at the molybdenum 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 spectroscopy and size exclusion chromatography. The results clearly indicate that kinetics and mechanism of the metathesis reaction strongly depend on the structures of monomer and initiator. The use of partially fluorinated alkoxy ligands instead of aliphatic alkoxides leads to a change of the regiochemistry of the insertion. Ether functions in the monomer tend to slow the reaction, giving rise to polymers with a narrow molecular weight distribution probably due to coordination of the oxygen atom to the metal center.