Palladium-Catalyzed Synthesis of Pure, Regiodefined Polymeric Triarylamines

Triarylamine polymers were prepared by palladium-catalyzed amination of aryl halides, and the electrochemical and magnetic properties of these materials were studied. Through a careful evaluation of the catalytic and polymer chemistry involved in this process, triarylamine polymers that are exclusively linear and free of phosphorus impurity in the polymer chain have been prepared. To suppress molecular weight-limiting side reactions from palladium-catalyzed poly(N-arylaniline) polymerizations, a number of phosphines were screened in reactions of small molecules to form triarylamines. Of these phosphines, tris(o-methoxymethylphenyl)phosphine (7) and tri(tert-butyl)phosphine (8) led to quantitative amination without ligand arylation, aryl bromide hydrodehalogenation, or exchange of phosphine aryl groups with the aryl bromide. When these phosphines were used in polymerizations, significant improvements in molecular weights were observed, but an additional molecular weight limiting side reaction, the formation of cyclic oligomers, was not affected. Strategies to minimize cyclizations that compete with chain growth were explored, including the use of oligomeric monomers that greatly reduced the formation of cyclic oligomers. A chromatographic method completely removed low molecular weight cyclic oligomers. A number of poly(N-arylaniline) derivatives with Mw values as high as 105 g/mol were synthesized by using the optimized palladium-catalyzed method, and the electronic and magnetic properties of these materials were investigated by cyclic voltammetry, magnetic susceptibility, and EPR spectroscopy.