A recyclable dendritic osmium catalyst for homogeneous dihydroxylation of olefins

A series of osmate (OsO(4)(2-)) core dendrimers was prepared by an ion-exchange technique through the mixing of K(2)OsO(4) and a bis(quaternary ammonium bromide) core dendrimer, which consisted of poly (benzyl ether) dendron. By employing an osmate core dendrimer as a homogeneous catalyst, dihydroxylation reactions of olefins proceeded rapidly, and the dendritic osmium catalyst was recovered by reprecipitation and then reused. Furthermore, a dendritic effect on the recyclability of a catalyst was observed. In the case of asymmetric dihydroxylation reactions, the corresponding diol was obtained in a high chemical yield with a fair enantiomeric excess (ee). In this case, not only the dendritic osmium catalyst but also the chiral ligand could be recovered by reprecipitation and reused efficiently up to five times. (C) 2010 Elsevier Ltd. All rights reserved.