Ligand-free Pd-Catalyzed C-N Coupling of Diphenylamine and Aryl Halides under Air

Triphenylamine derivatives are extensively used as a number of organic dyes, drugs, intermediates, dye-sensitized solar cells (DSSCs) and organic electroluminescence materials. It is valuable to discover a new synthetic method of triphenylamines with mild reaction conditions, easy-operation, and cheap starting materials. During our research of C-H bond activation, accidentally we found palladium acetate accomplished the C-N cross coupling of diphenylamine and 4-nitrobromobenzene under air. This discovery meets one of hot research topics of modern organic chemistry, that is, transition-metal-catalyzed reactions which must operate under inert atmosphere in the traditional procedures now can be performed under air. Consequently, ligand-free Pd(OAc)(2)-catalyzed C-N cross coupling of diphenylamines and aryl halides under air for synthesis of triphenylamines was studied in details. The effect of catalyst loading, base, additives, solvents and reaction time on this transformation was investigated. The optimized conditions were as follows: Pd(OAc)(2) (3 mol%), K2CO3 (1.5 equiv.), heated at 90 degrees C in DMSO under air. Electron-withdrawing group of phenyl bromides and electron-donating group of diphenylamine benefit the coupling reaction, and among them, 4-nitrotriphenylamine gave yield up to 93%. Compared with traditional methods, the reactions were conducted under air and mild conditions in absence of ligand, that is, anhydrous and oxygen-free conditions are not required, and operation is extremely easy.