Ring opening metathesis polymerization of methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate

Enantiomerically pure (1) and racemic (2) methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate were found to undergo ring opening metathesis polymerization reactions employing molybdenum alkylidene initiators of the type Mo(CH-t-Bu)(NAr)(OR)(2) (Ar = 2,6-C6H3-i-Pr-2; R = C(CH3)(3); C(CH3)(2)CF3; CCH3(CF3)(2)) in various aprotic solvents. Chain transfer by terminal olefins such as 1-octene leads to a decrease in molecular weights which can be correlated to the amount of chain transfer agent added. In this way oligomers can be prepared with lower initiator consumption. The presence of alkylidene signals in the H-1-NMR spectra and the possibility of chain transfer by acyclic olefins strongly confirm the assumption of a molybdenum alkylidene intermediate as a propagating species in a living polymerization. From the dramatic effect the presence of even small amounts of quinuclidine added as complexing agent has on the polymerization rate of (1) employing (III), we assume, that there is hardly any complexion of the initiator by the nitrogen of the monomer, otherwise the polymerization of (1) should be very slow or even impossible. The stereochemistry of the polymers can be correlated with the electron withdrawing effect of the initiator's alkoxide ligands. Fluorinated ligands at the initiator lead to polymers with increasing cis-vinylene content. There is no significant effect of the solvent's polarity on the stereochemistry of the resulting polymers.