| Cobalt tetracarbonyl hydride | |
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Other names
cobalt hydrocarbonyl |
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| Identifiers | |
| CAS number | 16842-03-8 = |
| PubChem | 61848 |
| Properties | |
| Molecular formula | C4HCoO4 |
| Molar mass | 171.98 g/mol |
| Appearance | Light yellow liquid |
| Melting point |
-33 °C, 240 K, -27 °F |
| Boiling point |
47 °C, 320 K, 117 °F |
| Solubility in water | Partially |
| Solubility | soluble in hexane, toluene, ethanol |
| Acidity (pKa) | 8.5 |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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.[1] Its main use is as a catalyst in hydroformylation.
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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.[2] The Co-CO and Co-H bond distances were determined by gas-phase electron diffraction to be 1.764 and 1.556 Å, respectively.[3]. 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.[4] HCo(CO)4 melts at -33 °C and above that temperature decomposes to Co2(CO)8 and H2.[1] 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.[5] These derivatives are generally less acidic than HCo(CO)4.[4]
Tetracarbonylhydrocobalt was first described by Hieber in the early 1930s.[6] 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.[2]
Since HCo(CO)4 decomposes so readily, it is usually generated in situ by hydrogenation of Co2(CO)8.[5]
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.[5]
Tetracarbonylhydridocobalt was the first transition metal hydride to be used in industry.[7] In 1940 it was discovered that it catalyzed the conversion of alkenes, CO, and H2 to aldehydes, a process known as hydroformylation (Oxo Reaction). Although it 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.[7]
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