Synthesis of Well-Defined Poly(2-alkoxypyridine-3,5-diyl) via Ni-Catalyst-Transfer Condensation Polymerization

Ni-catalyzed Kumada-Tamao coupling polymerization of S-bromo-3-chloromagnesio-2-(2-(2-methoxyethoxy)ethoxy)pyridine (1) was investigated. Monomer 1, which was obtained quantitatively by treatment of the corresponding bromoiodopyridine 3 with 1.0 equiv of (PrMgCl)-Pr-i at 0 degrees C, was polymerized with Ni(dppp)Cl-2 (dppp = 1,3-bis(diphenylphospino)propane)) in the presence of 2.0 equiv of LiCl in THF at room temperature to yield poly(2-(2-(2-methoxyethoxy)ethoxy)pyridine-3,5-diyl) (m-PMEEOPy) with narrow polydispersity. The M-n value was controlled by the feed ratio of the monomer precursor 3 to Ni(dppp)Cl-2. MALDI-TOF mass spectra showed that m-PMEEOPy uniformly had a bromine atom at one end and a hydrogen atom at the other. Both end groups could be converted to aryl groups by addition of an excess of aryl magnesium chloride to the reaction mixture after completion of the polymerization. These results indicate that the polymerization of 1 with Ni(dppp)Cl-2 involves the intramolecular catalyst-transfer polymerization mechanism.