Palladium catalysis in the synthesis of polyaniline-related materials

Abstract

The palladium-catalyzed aryl amination reaction, in conjunction with an orthogonal protective group scheme, forms the basis of two routes to oligoaniline precursors. One method consists of a bidirectional chain growth from a symmetric core piece, whereas the other involves a divergent-convergent synthesis of nonsymmetric fragments, followed by coupling to a symmetric core fragment. The oligoaniline precursors are soluble in a variety of common organic solvents, and are easily converted to the deprotected oligoanilines. The method allows the preparation of odd or even chain lengths, as long as a 24-mer, and the incorporation of a variety of functional groups. The effects of chain length and substitution upon oligomer behavior have been investigated by electronic absorption spectroscopy and cyclic voltammetry. Certain aspects of aryl amination methodology, arising from or applicable to the synthesis of polyaniline derivatives, are described. Commercially available benzophenone imine serves as a convenient ammonia equivalent in the palladiumcatalyzed amination of aryl halides and triflates. The chelating ligand bis[2-(diphenylphosphino) phenyl] ether (DPEphos), in combination with palladium acetate, forms a highly active catalyst system for the coupling of anilines with aryl bromides. A modification in the experimental procedure for aryl amination allows the use of palladium chloride, the least expensive compound of palladium, as the palladium source. A new copper-mediated method has been developed for the synthesis of 2- (di-tert-butylphosphino)biphenyl, a versatile ligand developed by Wolfe and Buchwald for palladium-catalyzed cross-coupling reactions, on multigram scale. The use cf this ligand in aryl amination reactions is described. The synthetic methods for the synthesis of oligoanilines have been modified to afford a wider variety of polyaniline-related materials. The preparation of ringsubstituted monomers for incorporation into internally functionalized oligoanilines is described. The synthesis of protected polyaniline derivatives by step-growth polymerization or copolymerization of suitable monomers has been achieved. A new analogue of polyaniline, a poly(aminophenothiazine), has also been synthesized by palladium catalysis.