Facile synthesis of stereoregular helical poly(phenyl isocyanide)s and poly(3-hexylthiophene)-block-poly(phenyl isocyanide) copolymer using chiral π-allylnickel complexes as initiators

Abstract

Living polymerization of achiral phenyl isocyanide using a simply prepared chiral π-allylnickel complex as initiator was found to proceed in helix-sense-selective manner. The polymerization of achiral phenyl isocyanide, 4-isocyanobenzoyl-2-aminoisobutyric acid hexyl ester (1a) produced optically active helical poly-1am (L or D) whose chirality totally come from the helical conformation without containing any other chiral atoms. The monomer-structural effect on the helix-sense-selectivity was examined and indicated the long alkyl group in the monomer is not essential for the helix-sense-selective polymerization. The effect of chiral phosphine ligand was also investigated. The success of the helix-sense-selective polymerizations indicated the high activity of π-allylnickel complexes. Finally, polymerization of 2,5-dibromo-3-hexylthiophene (3HT) and subsequent addition of 1a in the presence of chiral π-allylnickel complex as a single catalyst afforded P3HTm-b-poly-1an with nonhelical P3HT and helical poly(phenyl isocyanide) (PPI) segments, which may be used as unique chiral organic materials in the future.