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 M_n 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.