Enantioselective imine hydrogenation with Ir diphosphine catalysts: fighting deactivation

While Ir diphosphine complexes are very active catalysts for the enantioselective hydrogenation of imines with good to excellent enantioselectivity, their deactivation is often a serious problem, leading to low catalyst productivity. Our study describes attempts to stabilize Ir catalysts with diop, bdpp and bppm ligands for the hydrogenation of different imines. The best results were obtained with complexes immobilised on silica gel and with bimetallic W-Ir and Mo-Ir complexes. In most cases, enantiomeric excesses as well as initial rates were only slightly affected while the stability of the catalysts was enhanced significantly.