Preparation and use of a chiral amine ruthenium hydrogenation catalyst supported on mesoporous silica

We report the synthesis and use of dichloro-(S)-6,6′-dimethyl-2,2′-diaminobiphenyl-ruthenium complex ((S)-MAB-Ru), an air-stable, highly active catalyst for the hydrogenation of α,β-unsaturated carboxylic acids at 25°C and 4.85atm hydrogen. The homogeneous hydrogenations of itaconic acid and α-acetamidocinnamic acid had yields above 97% in each case, and the enantiomeric excesses (e.e.) were 80 and 69.8% to the (R)-products, respectively. When we used (S)-MAB-Ru chemically bound to MCM-41, a mesoporous SiO2, the conversion of both acids was complete and both e.e. were practically 97%. The solid-bound catalyst was successfully reutilized in the hydrogenation of itaconic acid and the drop in asymmetric induction was only 3% after three runs. The fact that complexes containing chiral amine ligands provide such high yields and e.e. opens a potentially important area of research in the design of industrially relevant catalysts.