Osmium pentacarbonyl
{{Chembox
| ImageFile = Os(CO)5.svg
| ImageSize = 122
| ImageAlt =
| IUPACName =
| OtherNames =
|Section1={{Chembox Identifiers
| CASNo = 16406-49-8
| ChemSpiderID = 65793451
| PubChem = 10892861
| SMILES = C(=O)=[Os](=C=O)(=C=O)(=C=O)=C=O
| StdInChI = 1S/5CO.Os/c5*1-2;
| StdInChIKey = RLUHVGZGDXPTEM-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
| C=5|O=5|Os=1
| MolarMass =
| Appearance = colorless liquid
| Density =
| MeltingPtC = 2-2.5
| BoilingPt =
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|Section3={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt = }}
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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.{{cite journal |doi=10.1021/om00077a026|title=Properties of the Pentacarbonyls of Ruthenium and Osmium|year=1983|last1=Rushman|first1=Paul|last2=Van Buuren|first2=Gilbert N.|last3=Shiralian|first3=Mahmoud|last4=Pomeroy|first4=Roland K.|journal=Organometallics|volume=2|issue=5|pages=693–694}}
Chlorination of the pentacarbonyl gives a cationic pentacarbonyl complex:
: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:{{cite journal |doi=10.1021/ja00241a075|title=Multisubstitution of Os(CO)5 by ethylene: Isomeric Os(CO)2(C2H4)3 and a Derivative of Os(CO)(C2H4)4|year=1987|last1=Kiel|first1=Gong Yu|last2=Takats|first2=Josef|last3=Grevels|first3=Friedrich Wielhelm|journal=Journal of the American Chemical Society|volume=109|issue=7|pages=2227–2229}}
:Os(CO)5 + n{{nbsp}}C2H4 → Os(CO)5-n(C2H4)n + n{{nbsp}}CO (n = 1,2,3)