Photoswitchable Enantioselective and Helix‐Sense Controlled Living Polymerization

Abstract

AbstractA pair of enantiomeric photoswitchable PdII catalysts, alkyne‐PdII/LR−azo and alkyne‐PdII/LS−azo, were prepared via the coordination of alkyne‐PdII and azobenzene‐modified phosphine ligands LR−azo and LS−azo. Owing to the cis‐trans photoisomerization of the azobenzene moiety, alkyne‐PdII/LR−azo and alkyne‐PdII/LS−azo exhibited different polymerization activities, helix‐sense selectivities, and enantioselectivities during the polymerization of isocyanide monomers under irradiation of different wavelength lights. Furthermore, the achiral isocyanide monomer A‐1 could be polymerized efficiently using alkyne‐PdII/LR−azo under dark condition in a living/controlled manner. Further, it generated single right‐handed helical poly‐A‐1m(LR−azo), confirmed by the circular dichroism spectra and atomic force microscopy images. However, the polymerization of A‐1 almost could not be initiated under 420 nm light in identical conditions of dark condition. Moreover, the photoswitchable catalyst alkyne‐PdII/LR−azo exhibited high enantioselectivity for the polymerization of the racemates of L‐1 and D‐1, respectively. D‐1 was polymerized preferentially under dark condition with a D‐1/L‐1 rate ratio of 70, yielding single right‐handed polyisocyanides. Additionally, reversible enantioselectivity was observed under 420 nm light using alkyne‐PdII/LR−azo, and the calculated polymerization rate ratio of L‐1/D‐1 was 57 because of the isomerization of the azobenzene moiety of the catalyst. Furthermore, alkyne‐PdII/LS−azo showed opposite enantioselectivity and helix‐sense selectivity during the polymerization of the racemates of L‐1 and D‐1.