Cobalt tetracarbonyl hydride
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| Names | |
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| Other names
cobalt hydrocarbonyl
tetracarbonylhydridocobalt Tetracarbonylhydrocobalt Hydrocobalt tetracarbonyl |
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| Identifiers | |
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PubChem CID
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| Properties | |
| C4HCoO4 | |
| Molar mass | 171.98 g/mol |
| Appearance | Light yellow liquid |
| Odor | offensive |
| Melting point | −33 °C (−27 °F; 240 K) |
| Boiling point | 47 °C (117 °F; 320 K) |
| 0.05% (20°C) | |
| Solubility | soluble in hexane, toluene, ethanol |
| Vapor pressure | >1 atm (20°C) |
| Acidity (pKa) | 8.5 |
| Hazards | |
| Main hazards | flammable, decomposes in air |
| US health exposure limits (NIOSH): | |
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PEL (Permissible)
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none |
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REL (Recommended)
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TWA 0.1 mg/m3 |
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IDLH (Immediate danger)
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N.D. |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Cobalt tetracarbonyl hydride is an organometallic compound with the formula HCo(CO)4. It is a volatile, yellow liquid that forms a colorless vapor and has an intolerable odor. The compound readily decomposes upon melt and in absentia of high CO partial pressures forms Co2(CO)8. Despite operational challenges associated with its handling, the compound has received considerable attention for its ability to function as a catalyst in hydroformylation. In this respect, HCo(CO)4 and related derivatives have received significant academic interest for their ability to mediate a variety of carbonylation reactions.
HCo(CO)4 adopts trigonal bipyrimidal structure with the equatorial CO ligands slightly bent out of the equatorial plane. The hydride ligand occupies one of the axial positions, thus the symmetry of the molecule is C3v. The Co–CO and Co–H bond distances were determined by gas-phase electron diffraction to be 1.764 and 1.556 Å, respectively. Assuming the presence of a formal hydride ion, the oxidation state of cobalt in this compound is +1.
Unlike some other transition-metal hydrides complexes, HCo(CO)4 is highly acidic, with a pKa of 8.5. It readily undergoes substitution by tertiary phosphines and other Lewis-bases. 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 to improve catalyst selectivity in hydroformylation. These derivatives are generally less acidic than HCo(CO)4.
Tetracarbonylhydrocobalt was first described by Hieber in the early 1930s. 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.
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