Evaluation of Aromatic Amination Catalyzed by Palladium on Carbon: A Practical Synthesis of Triarylamines

Abstract

AbstractA heterogeneous palladium on carbon (Pd/C)‐catalyzed coupling between amines and aromatic halides including aromatic chlorides has been achieved using sodium tert‐butoxide (NaO‐t‐Bu) and 1,1′‐bis(diphenylphosphino)ferrocene (dppf) as a ligand in cyclopentyl methyl ether (CPME). The use of potassium tert‐butoxide (KO‐t‐Bu) in place of NaO‐t‐Bu brought about the benzyne‐mediated aromatic amination even without Pd/C and dppf, giving a mixture of regioisomers when 4‐substituted bromobenzenes were employed as the substrate. The combination of Pd/C, dppf, NaO‐t‐Bu could be utilized for the syntheses of a broad range of triarylamines by replacing CPME with mesitylene which can provide a higher reaction temperature. The Pd/C could be quantitatively recovered and reused until at least the fourth cycle without any loss in catalytic activity. The quite low leaching of palladium (<1.1%) was demonstrated by an inductively coupled plasma‐atomic emission spectrometric analysis.