Osmium pentacarbonyl explained

Osmium pentacarbonyl is the organoosmium compound with the formula Os(CO)₅. It is the simplest isolatable carbonyl complex of osmium. Osmium pentacarbonyl is a colorless volatile liquid that is obtained by treating solid triosmium dodecacarbonyl under 200 atmospheres of carbon monoxide at 280-290 °C. In contrast, also at 200 atm of CO, solid Ru₃(CO)₁₂ converts to Ru(CO)₅ at milder temperature of 160 °C.

Reactions

Samples of Os(CO)₅ convert back to the trioosmium cluster upon heating to 80 °C. The analogous conversion of Ru(CO)₅ back to Ru₃(CO)₁₂ occurs at room temperature.^[1] Chlorination of the pentacarbonyl gives a cationic pentacarbonyl complex:^[1]

Os(CO)₅ + Cl₂ → [Os(CO)₅Cl]⁺Cl⁻

Upon UV irradiation, hexane solutions of the pentacarbonyl react with ethylene to give mono-, di-, and trisubstituted derivatives:^[2]

Os(CO)₅ + nC₂H₄ → Os(CO)_5-n(C₂H₄)_n + nCO (n = 1,2,3)

Notes and References

1. 10.1021/om00077a026. Properties of the Pentacarbonyls of Ruthenium and Osmium. 1983. Rushman. Paul. Van Buuren. Gilbert N.. Shiralian. Mahmoud. Pomeroy. Roland K.. Organometallics. 2. 5. 693–694.
2. 10.1021/ja00241a075. Multisubstitution of Os(CO)₅ by ethylene: Isomeric Os(CO)₂(C₂H₄)₃ and a Derivative of Os(CO)(C₂H₄)₄. 1987. Kiel. Gong Yu. Takats. Josef. Grevels. Friedrich Wielhelm. Journal of the American Chemical Society. 109. 7. 2227–2229.