Copper catalyst paves new way to polyaniline

A copper catalyst with a bulky tris(pyrazolyl)borate ligand has been used in combination with hydrogen peroxide oxidant to synthesize the conducting polymer polyaniline under mild conditions (Chem. Commun. 2006, 976). The new synthesis, reported by H. V. Rasika Dias, Ronald L. Elsenbaumer, and coworkers at the University of Texas, Arlington, is a potentially cleaner and more efficient method to make the polymer. Polyaniline's broader use in optoelectronics and other devices has been hampered by its tricky synthesis. The polymer is commonly prepared by using stoichiometric amounts of the strong oxidant ammonium persulfate, (NH₄)₂S₂O₈, in conjunction with a strong mineral acid. Copper salts also have been used to make polyaniline, but they tend to overoxidize the polymer. Restricted access to the copper center of the tris(pyrazolyl)borate catalyst (shown, R is mesityl) allows better head-to-tail coupling of aniline dimers and limits cross-linking to provide good-quality polymer under less harsh conditions, Dias notes.