Cobalt tetracarbonyl hydride
 |
|
| Names | |
|---|---|
| Other names
cobalt hydrocarbonyl
tetracarbonylhydridocobalt Tetracarbonylhydrocobalt Hydrocobalt tetracarbonyl |
|
| Identifiers | |
16842-03-8  = |
|
| PubChem | 61848 |
| Properties | |
| C4HCoO4 | |
| Molar mass | 171.98 g/mol |
| Appearance | Light yellow liquid |
| Odor | offensive[1] |
| Melting point | −33 °C (−27 °F; 240 K) |
| Boiling point | 47 °C (117 °F; 320 K) |
| 0.05% (20°C)[1] | |
| Solubility | soluble in hexane, toluene, ethanol |
| Vapor pressure | >1 atm (20°C)[1] |
| Acidity (pKa) | 8.5 |
| Vapor pressure | {{{value}}} |
|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
|
 verify (what is  ?) |
|
| Infobox references | |
Cobalt tetracarbonyl hydride is the organometallic compound with the formula HCo(CO)4. It is a yellow liquid that forms a colorless vapor and has an intolerable odor.[2] Its main use is as a catalyst in hydroformylation.
Structure and properties
4-3D-balls.png)
HCo(CO)4 is a trigonal bipyrimidal molecule. The hydride ligand occupies one of the axial positions, thus the symmetry of the molecule is C3v.[3] The Co-CO and Co-H bond distances were determined by gas-phase electron diffraction to be 1.764 and 1.556 Å, respectively.[4] Assuming the presence of a formal hydride ion, the oxidation state of cobalt in this compound is +1.
Like some other metal carbonyl hydrides, HCo(CO)4 is acidic, with a pKa of 8.5.[5] HCo(CO)4 melts at -33 °C and above that temperature decomposes to Co2(CO)8 and H2.[2] It undergoes substitution by tertiary phosphines. For example, triphenylphosphine gives HCo(CO)3PPh3 and HCo(CO)2(PPh3)2. These derivatives are more stable than HCo(CO)4 and are used industrially.[6] These derivatives are generally less acidic than HCo(CO)4.[5]
Preparation
Tetracarbonylhydrocobalt was first described by Hieber in the early 1930s.[7] It was the second transition metal hydride to be discovered, after H2Fe(CO)4. It is prepared by reducing Co2(CO)8 with sodium amalgam or a similar reducing agent followed by acidification.[3]
- Co2(CO)8 + 2 Na → 2 NaCo(CO)4
- NaCo(CO)4 + H+ → HCo(CO)4 + Na+
Since HCo(CO)4 decomposes so readily, it is usually generated in situ by hydrogenation of Co2(CO)8.[6]
- Co2(CO)8 + H2 ⇌ 2 HCo(CO)4
The thermodynamic parameters for the equilibrium reaction were determined by infrared spectroscopy to be ΔH = 4.054 kcal mol−1, ΔS = -3.067 cal mol−1 K−1.[6]
Applications
Tetracarbonylhydridocobalt was the first transition metal hydride to be used in industry.[8] In 1953 evidence was disclosed that it is the active catalyst for the conversion of alkenes, CO, and H2 to aldehydes, a process known as hydroformylation (Oxo Reaction).[9] Although the use of cobalt-based hydroformylation has since been largely superseded by rhodium-based catalysts, the world output of C3-C18 aldehydes produced by tetracarbonylhydrocobalt catalysis is about 100,000 tons/year, roughly 2% of the total.[8]
References
- ↑ 1.0 1.1 1.2 Cite error: Invalid
<ref>tag; no text was provided for refs namedPGCH - ↑ 2.0 2.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 6.0 6.1 6.2 M. Pfeffer, M. Grellier "Cobalt Organometallics" in Comprehensive Organometallic Chemistry III, 2007, Elsevier.doi:10.1016/B0-08-045047-4/00096-0
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 8.0 8.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ I. Wender , H. W. Sternberg , M. Orchin "Evidence for Cobalt Hydrocarbonyl as the Hydroformylation Catalyst" J. Am. Chem. Soc., 1953, vol. 75, pp 3041–3042. doi:10.1021/ja01108a528
