Osmates dioxo

Organoiron, 1181 Organoiron(I) complexes, 1203 Orthoperrhenates, 198 Osmates dioxo, 581 fluorohalo, 610 Osmium... 

Many osmyl complexes with group VI ligands have been reported. The purple diamagnetic potassium osmate K2[0s(0H)4(0)2] is the best known and is a useful starting material for the preparation of other osmyl or osmium complexes. It is best prepared from the reaction of 0s04 with excess KOH. The X-ray crystal structure of K2[0s(0H)4(0)2] shows that the complex has the trans-dioxo unit, with a d(0s=0) of 1.77 A and a 0=0s=0 angle of 180° (238,239). The acid dissociation constants of H2[0s02(0H)4] have been determined. 

Jacobs and coworkers published a completely different type of heterogeneous osmium catalyst. Their approach is based on two details from the mechanism of the ds-dihydroxylation (1) tetrasubstituted olefins are smoothly osmylated to an osmate(VI) ester, but these esters are not hydrolyzed under mild conditions, and (2) an Os monodiolate complex can be reoxidized to ds-dioxo Os without release of the diol subsequent addition of a second olefin results in an Os bisdiolate complex. These two properties make it possible to immobihze a catalytically active osmium compound by the addition of OSO4 to a tetrasubstituted olefin that is covalently linked to a silica support The tetrasubstituted diolate ester which is formed at one side of the Os atom is stable, and keeps the catalyst fixed on the support material. The catalytic reaction can take place at the free coordination sites of Os (Scheme 1.12) [40]. 

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