A Heterogeneous cis-Dihydroxylation Catalyst with Stable, Site-Isolated Osmium-Diolate Reaction Centers This work was supported by the Belgian Federal Government in the frame of an Interuniversitary Attraction Pole on Supramolecular Catalysis. We are indebted to FWO for fellowships (A.S., D.D.V.) and for a research grant (D.D.V., F.V., P.A.J.)