Living Coordination Polymerization of Alkoxyallenes by π-Allylnickel Catalyst. 2. Effect of Anionic Ligands on Polymerization Behavior and Polymer Structure

The coordination polymerization of ( n -octyloxy)allene ( 2 ) was carried out by π-allylnickel catalysts possessing various carboxylate ligands ( 1a − 1c ). The electronic character of the carboxylate ligand strongly influences the polymerization. Electron-withdrawing groups provide a living system that produces polymers with well-defined molecular weights and narrow molecular weight distributions in high yields. Without electron-withdrawing substituents, the reaction produces oligomeric byproducts. The ratio of 1,2- to 2,3-polymerization unit in the polymer increased with the electron-withdrawing character of carboxylate ligands. π-Allylnickel catalysts bearing halide ligands ( 1d, 1e, and 1f /Na 2 S 2 O 3 ) also gave polymers from 2 in high yields, in which the polymerization rate, the microstructure, and the molecular weight distributions ( M w / M n ) of polymers were dependent upon the specific halide. The catalyst with chloride ( 1d ) afforded a polymer with narrow M w / M n (1.03), possessing the ratio of 1,2- to 2,3-polymerization unit of 6:94, whereas with iodide ( 1f /Na 2 S 2 O 3 ), the polymerization took place much faster to give a polymer (1,2-:2,3-polymerization unit = 16:84) with a little broader M w / M n (1.10).