Helix-Sense-Selective Polymerization of Achiral Phenylacetylenes with Two N-Alkylamide Groups to Generate the One-Handed Helical Polymers Stabilized by Intramolecular Hydrogen Bonds.

Abstract

In this study, we investigated the helix-sense-selective polymerizations of newly synthesized achiral phenylacetylenes having two N-alkylamide groups, such as 3,5-bis(dodecylamide)phenylacetylene (DAPA), 3,5-bis(octylamide)phenylacetylene (OAPA), and 3,5-bis(butylamide)phenylacetylene (BAPA), by using a chiral rhodium catalyst system ([Rh(nbd)Cl]2-(R)-(+)-1-phenylethylamine [(R)-PEA]). Poly(BAPA) was insoluble in any solvents. On the other hand, poly(DAPA) and poly(OAPA) were soluble in toluene, THF, and CHCl3, and the obtained polymers showed intense circular dichroism signals at the absorption region of the main chain in the UV-vis region. This result suggested those polymers were present in helical conformations with an excess of one-handed screw sense. The chiral helix structures of the formed polymers were stable in toluene at room temperature for a long time because of intramolecular hydrogen bonds. This result is the second example about polyacetylenes with one-handed helical conformation stabilized by intramolecular hydrogen bonds.