General procedure for the synthesis of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine from 4,4'-dibromobiphenyl and 3-methyldiphenylamine: under argon protection, 3.0 g (30 mmol) of sodium tert-butoxide, 217 mg (0.5 mmol) of IPr-HCl (Compound No.1), 45 mg ( 0.2 mmol) palladium(II) acetate, 3.67 g (20 mmol) 3-methyldiphenylamine, 3.2 g (10 mmol) 4,4'-dibromobiphenyl, and 30 ml of toluene were added to a 50 ml three-necked flask fitted with a stirrer, a condenser tube, a thermometer, and a gas introduction tube. The reaction mixture was heated to 130°C in an oil bath and refluxed for 7 hours. Upon completion of the reaction, it was cooled to room temperature and allowed to stand overnight. Subsequently, 150 ml of dichloromethane was added to the reaction mixture and the insoluble material was removed by filtration. The filtrate was washed twice with 50 ml of water and then dried with 30 g of anhydrous sodium sulfate. After evaporation of the solvent, the crude product was obtained. The crude product was purified by column chromatography (using 150 g of Fuji Silicia's NH silica gel as the carrier and cyclohexane as the eluent) to give 4.4 g of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) in a final yield of 85.2%.
