Osmate

Osmate is a term used in inorganic chemistry to refer to salts and complexes that contain the oxido-osmium fragment, often associated with species derived from osmium tetroxide (OsO4). In common usage, osmate denotes OsO4-based salts such as potassium osmate, K2OsO4·2H2O, which act as precursors or sources of osmium in various oxidation states for chemical reactions.

One of the principal contexts for osmate chemistry is catalytic OsO4-catalyzed dihydroxylation of alkenes, known from the Upjohn dihydroxylation methodology. In these reactions, catalytic OsO4 is used with a stoichiometric co-oxidant to reoxidize the osmium center after it is reduced during the reaction. Osmate salts frequently serve as the practical Os source in such protocols, offering handling advantages compared with volatile OsO4 solutions.

Chemical properties of osmates reflect the presence of an oxido-osmium core, typically with osmium in high oxidation states bound to oxide ligands. In aqueous or hydrated forms, osmate salts are often coordinated with water and counterions, forming crystalline hydrates or solubilized species depending on the preparation.

Preparation methods for osmate salts involve oxidation and coordination processes that generate the Os–O framework and stabilize the salt with appropriate counterions. In practice, osmates are valued for delivering osmium in situ to catalytic cycles and stoichiometric oxidations, while allowing for easier handling than pure osmium tetroxide.

Safety considerations are important: osmium compounds can be toxic and irritant, with OsO4 vapors posing particular hazards. Proper fume hood use, protective equipment, and waste disposal procedures are essential.

See also: Osmium tetroxide, Upjohn dihydroxylation, Dihydroxylation, N-methylmorpholine N-oxide.