Control of Helical Structure in Random Copolymers of Chiral and Achiral Aryl Isocyanides Prepared with Palladium−Platinum μ-Ethynediyl Complexes

Abstract

Random copolymerization of aryl isocyanides possessing chiral and achiral alkoxycarbonyl groups at p- or m-positions was initiated with the Pd−Pt μ-ethynediyl complex to give in good yields the corresponding polymers with narrow polydispersity indexes. The selective formation of the one-handed helical structure in the resulting polymers was confirmed by the large values of specific rotation and the CD spectra showing the Cotton effect around 364 nm. The helical sense selectivity was strongly dependent on not only the contents of chiral monomers but also the structures of chiral and achiral monomers. Notably, inversion of helical sense was observed in random copolymers prepared from m-substituted chiral and p-substituted achiral aryl isocyanides depending on the content of the monomers. Those results were compared with a novel theory of the helical sense selective polymerization kinetics, which explained both strong dependence of the helical sense selectivity and weak dependence of the propagation reaction rate on the chiral monomer content.