Synthesis of a poly(2-azanorbornene) with a high degree of cis-TT-stereoregularity and a regular secondary solution structure

Methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate (AzaN) was synthesized as a diastereomerically pure monomer and subsequently polymerized with the ruthenium-based M31® catalyst. The poly(2-azanorbornene)s with polymerization degrees in the range from 100 to 300 exhibited high degrees of cis-TT stereoregularity in contrast to previously reported poly(2-azanorbornene)s that were prepared with molybdenum-based catalysts and exhibited cis-HT and trans-HT stereoregularity. The formation of regular secondary structures in acetonitrile solution was verified by circular dichroism and AFM measurements and supported by theoretical calculations of a polymer model with eight repeating units. Of special note are the large diameters of the secondary structures that are indicative of a multiple-strand filament.