Osmium pentacarbonyl

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.^[1]

Osmium pentacarbonyl

Identifiers
CAS Number	16406-49-8
3D model (JSmol)	Interactive image
ChemSpider	65793451
PubChem CID	10892861
CompTox Dashboard (EPA)	DTXSID901336738
InChI InChI=1S/5CO.Os/c5*1-2; Key: RLUHVGZGDXPTEM-UHFFFAOYSA-N
SMILES C(=O)=[Os](=C=O)(=C=O)(=C=O)=C=O
Properties
Chemical formula	C5O5Os
Molar mass	330.28 g·mol−1
Appearance	colorless liquid
Melting point	2–2.5 °C (35.6–36.5 °F; 275.1–275.6 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Reactions

Structure proposed for Os₂(CO)₉.^[2]

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:^[3]

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