Osmium Catalysts

Osmium is one of the members of the platinum group metal, with a symbol Os and atomic number 76. The bulk metallic osmium is very stable in the air, but the powdery osmium is easily oxidized, which reacts easily with oxygen at room temperature to form osmium oxide (OsO₂), and this reaction produces a volatile and highly toxic OsO₄ when heated.

Applications:

Since its oxide is not only toxic, but also volatile, osmium is rarely used in the form of its oxide. It is currently widely used as an anti-wear material, an oxidizing agent and a clinical anticancer drug in the form of simple substance, alloy and metal salt. Osmium sometimes can play a role of a catalyst in industry. When the synthetic ammonia reaction, hydrogenation reaction and dihydroxylation reaction are carried out using osmium compounds as the catalysts, a higher conversion rate can be obtained at a relatively mild temperature.

• Synthetic ammonia reaction: The synthetic ammonia industry occupies an important position in the basic chemical industry and has a wide range of applications. Haber, the winner of Nobel Prize, first proposed the use of Os as a catalyst to prepare NH₃, which was of great significance. At that time, this method had high productivity and good economic benefits.

Figure 1. The schematic of synthetic ammonia reaction.

• Hydrogenation reaction: In hydrogenation, Os compounds can be used as an excellent catalyst to catalyze reactions such as hydroformylation of olefins, hydrogenation and transfer-hydrogenation of ketones, hydrogenation of esters. For example, the combination of Os₃(CO)₁₂ and an imidazolyl-substituted phosphine ligand can catalyze n-selective (up to 99%) hydroformylation of various aliphatic and functional olefins, the yield of which usually is up to 64-87%.

Figure 2. The reaction schematic of osmium-catalyzed hydroformylation.

• Dihydroxylation reaction: K₂[OsO₂(OH)₄] has a good catalytic effect on the synthesis of 1,2-diols and diol derivatives, and the main body of the reaction is a double-build olefin.

Figure 3. The reaction schematic of osmium-catalyzed dihydroxylation.

References

1. L. Wu, Q. Liu, A. Spannenberg, R. Jackstell, M. Beller, (2015). 'Highly regioselective osmium-catalyzed hydroformylation'. Chem. Commun. 51,3080-3082.
2. D. Spasyuk, S. Smith, D. G. Gusev, (2012). 'Highly regioselective osmium-catalyzed hydroformylation'. Angew. Chem. Int. Ed. 51, 2772-2775.
3. Arblaster, J. W. (1989). 'Densities of osmium and iridium: recalculations based upon a review of the latest crystallographic data'. Platinum Metals Review. 33 (1): 14-16.