The First Platinum-Catalyzed Hydroamination of Ethylene

The platinum-catalyzed hydroamination of ethylene with aniline is reported for the first time. Using PtBr2 as a catalyst precursor in n-Bu4PBr under 25 bar of ethylene pressure affords N-ethylaniline with 80 turnovers after 10 h at 150 °C. The reaction simultaneously produces 2-methylquinoline in ca. 10 cycles. The catalytic activity is slightly improved by increasing the reaction temperature or the ethylene pressure and strongly depends on the aniline/platinum ratio. The beneficial effects of added P(OMe)3 (2 equiv/PtBr2) or of a proton source (3 equiv/PtBr2) have also been pointed out. A gradual poisoning by N-ethylaniline has been observed, which could be minimized by using biphasic systems. The best result for the hydroamination with aniline (TON = 145 after 10 h at 150 °C) has been obtained in a biphasic system (n-Bu4PBr/decane) in the presence of C6H5NH3 + (3 equiv/PtBr2). The basicity of the arylamine has been shown to play an important role: the lower the basicity, the higher the TON. Thus, the hydroamination of ethylene with the weakly basic 2-chloroaniline in the presence of the PtBr2/H+ catalytic system (0.3% mol) for 72 h at 150 °C yields N-ethyl-2-chloroaniline as the sole reaction product (70% yield based on the amine charged) with TON = 250. When conducted with 1% of the above catalytic system, the reaction resulted in nearly quantitative conversion of 2-chloroaniline.