Cobalt tetracarbonyl hydride
Names | |
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Other names
cobalt hydrocarbonyl
tetracarbonylhydridocobalt Tetracarbonylhydrocobalt Hydrocobalt tetracarbonyl | |
Identifiers | |
3D model (
JSmol ) |
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ECHA InfoCard
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100.290.757 |
PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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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) | 1 (in water)[2] 8.3 (in acetonitrile)[3] |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards
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flammable, decomposes in air[1] |
NIOSH (US health exposure limits): | |
PEL (Permissible)
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none[1] |
REL (Recommended)
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TWA 0.1 mg/m3[1] |
IDLH (Immediate danger) |
N.D.[1] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cobalt tetracarbonyl hydride is an
Structure and properties
HCo(CO)4 adopts trigonal bipyramidal structure, with the hydride ligand occupying one of the axial positions, giving an overall symmetry of C3v. The three equatorial CO ligands are slightly bent out of the equatorial plane.[5] The Co–CO and Co–H bond distances were determined by gas-phase electron diffraction to be 1.764 and 1.556 Å, respectively.[6] Assuming the presence of a formal hydride ion, the oxidation state of cobalt in this compound is +1.
But unlike some other transition-metal hydrides complexes, HCo(CO)4 is highly acidic, with a pKa of 8.5.[7] 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.[8] These derivatives are generally less acidic than HCo(CO)4.[7]
Preparation
Tetracarbonylhydrocobalt was first described by Hieber in the early 1930s.
- 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.[8][10]
- 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.[8]
Applications
Tetracarbonylhydridocobalt was the first transition metal hydride to be used in industry.[11] 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).[12] 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 per year, roughly 2% of the total.[11]
References
- ^ a b c d e f g NIOSH Pocket Guide to Chemical Hazards. "#0148". National Institute for Occupational Safety and Health (NIOSH).
- OCLC 237142268.
- PMID 22175569.
- ISBN 0471936235.
- ^ ISBN 3527306730.
- .
- ^ PMID 22175569.
- ^ ISBN 9780080450476.
- .
- .
- ^ ISBN 3527306730.
- .