Intermolecular highly regioselective hydroamination of alkenes with ligandless Platinum(II) catalysts in ionic solvents:: Activation role of n-Bu4PBr

The reaction of aniline with 1-hexene catalyzed by PtBr2 (0.3%) in the presence of n-Bu4PBr (65 equiv/Pt) at 150 degrees C affords the expected hydroamination products with a 95% Markovnikov regioselectivity (N-(2-hexyl)aniline). An activating role of n-Bu4PBr has been evidenced, which is due to the presence of the bromide ions. This accelerating effect is discussed in terms of increased basicity of the platinum center in a zwitterionic intermediate. The ligandless, inexpensive, and nontoxic PtBr2-n-Bu4PBr-H+ catalytic system allows reaching a TON = 243 after 96 h at 150 degrees C (70% yield, 95% Markovnikov regioselectivity). The same results are obtained for reactions performed in the air.