Functionalized poly- and oligo-phenylenes: Variations on the Suzuki cross-coupling of functionalized aryl dibromides with the 1,3-propanediol diester of 2,5-dialkyl-1,4-phenylenediboronic acid

The synthesis of substituted poly(phenylene)s, in particular poly(1,4-phenylene)s, by palladium-catalyzed Suzuki coupling of the 1,3-propanediol diester of 2,5-dialkyl-1,4-phenylenediboronic acid with various aryl dibromides is described. Optimized reaction conditions for the polymerization of nitro group containing monomers were developed in this study. For example, poly(4,6-dinitro-2',5'-dihexyl-3,4'-biphenylylene) was obtained at 37 degrees C with the catalyst dichloro[1,1'-bis(diphenylphosphino)ferrocene]palladium(II) [PdCl2(dppf)] in THF and aqueous NaHCO3 in quantitative yield with a number average degree of polymerization of P-n = 27. These reaction conditions are among the mildest reported in the literature. Monomers, not only with the nitro group, but also with the following substituents were polymerized: fluoro, nitrile, N,N-dimethylamino, and trifluoromethyl. 2,5-Dibromopyridine was also used as monomer. The polymers gave M-n values of typically 3 - 7 kg/mol except for the nitrile-substituted polymer poly[(2,5-didodecyl-1,4-phenylene)-alt-(2-cyano-1,4-phenylene;3-cyano-1,4-phenylene)] which had a M-n = 87 kg/mol and P-n = 130. (C) 1997 Elsevier Science Ltd.