Selective Catalysts for the Homogeneous Semi-Hydrogenation

An efficient and highly selective semi-hydrogenation of terminal alkynes to alkenes using neutral dimeric rhodium(I) complexes of the type [Rh(mu-Cl)(PP)]2 is presented. Dehydroisophytol (DIP) was chosen as the alkyne for this study because of its high importance in the industrial production of synthetic vitamin E. Excellent selectivity of over 91% towards the alkene was achieved with known and new rhodium catalysts. No deactivation was observed for the [Rh(mu-Cl)(PP)]2 complexes and the molar Rh:DIP ratio could be increased to 1:20 000, and importantly, no reduction in selectivity was observed. The results presented open the door to the industrial application of homogeneous rhodium complexes in the semi-hydrogenation of terminal alkynes. image