Fast Living Polymerization of Challenging Aryl Isocyanides Using an Air-Stable Bisphosphine-Chelated Nickel(II) Initiator

Here we report a highly efficient living polymerization of challenging electron-rich or sterically hindered aryl isocyanides using an air-stable, but highly active, bisphosphine-chelated nickel(II) complex. Initially, the living character was examined by screening various Ni(II) complexes, and we identified o-Tol(dppe)NiCl as an excellent initiator for the living polymerization of aryl isocyanides. On the basis of chain extension experiments and in situ 31P NMR spectroscopy, we concluded that the high stability of the propagating species due to the tightly bound chelating ligand was crucial for successful living polymerizations. Not only reactive electron-poor aryl isocyanides but also more challenging electron-rich or sterically hindered aryl isocyanides underwent fast living polymerizations to give polymers having controlled Mn with narrow dispersity. In addition, we confirmed that the electronic character of the monomer significantly affected the polymerization efficiency by comparing the polymerization of 4-octyloxyphenyl isocyanide and 3-octyloxyphenyl isocyanide, which have the same substituents at different positions on the phenyl ring. Furthermore, ABCDE pentablock copolymer containing various substituents was efficiently synthesized in only 1 min.