Study of the racemic and enantioselective hydrogenation of acetophenone and 3,4-dimethoxyacetophenone using platinum-based organotin catalysts

In this work, some results of the racemic and enantioselective hydrogenation of acetophenone and 3,4-dimethoxyacetophenone are presented. The employed catalysts were platinum-based modified with organotin precursors either chiral (Men3Sn-SnMen3) or achiral (SnBu4), and they were obtained via surface organometallic chemistry on metals (SOMC/M) techniques. The presence of organotin fragments on the catalyst surface inhibits the aromatic ring hydrogenation, leading to the hydrogenation of both acetophenone and 3,4-dimethoxyacetophenone to the corresponding alcohol with selectivity higher than 99%. With both substrates, a rate acceleration when changing from the achiral catalyst PtSn-OM to the chiral one, PtSn-OM* was observed. The presence of menthyl groups may be responsible for the rate acceleration in the key step of enantiodifferentiation. In the 3,4-dimethoxyacetophenone hydrogenation, 39% enantiomeric excess was obtained, with a selectivity of nearly 100%.