Tetracarbonylhydrocobalt
Encyclopedia
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. Its main use is as a catalyst in hydroformylation
.
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.. 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. HCo(CO)4 melts at -33 °C and above that temperature decomposes to Co2(CO)8 and H2. 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. These derivatives are generally less acidic than HCo(CO)4.
. It is prepared by reducing Co2(CO)8
with sodium amalgam or a similar reducing agent followed by acidification.
Since HCo(CO)4 decomposes so readily, it is usually generated in situ by hydrogenation
of Co2(CO)8.
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.
s, 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 Although it has since been largely superseded by rhodium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.
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
(CO)4. It is a yellow liquid that forms a colorless vapor and has an intolerable odor. Its main use is as a catalyst in hydroformylation
Hydroformylation
Hydroformylation, also known as oxo synthesis or oxo process, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group and a hydrogen atom to a carbon-carbon double bond...
.
Structure and properties
HCo(CO)4 is a trigonal bipyrimidal molecule. The hydride ligandLigand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
occupies one of the axial positions, thus the symmetry
Symmetry group
The symmetry group of an object is the group of all isometries under which it is invariant with composition as the operation...
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.. The oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
of cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
in this compound is -1.
Like some other metal carbonyl hydrides, HCo(CO)4 is acidic, with a pKa of 8.5. HCo(CO)4 melts at -33 °C and above that temperature decomposes to Co2(CO)8 and H2. It undergoes substitution by tertiary phosphines. For example, triphenylphosphine
Triphenylphosphine
Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...
gives HCo(CO)3PPh3 and HCo(CO)2(PPh3)2. These derivatives are more stable than HCo(CO)4 and are used industrially. These derivatives are generally less acidic than HCo(CO)4.
Preparation
Tetracarbonylhydrocobalt was first described by Hieber in the early 1930s. It was the second transition metal hydride to be discovered, after H2Fe(CO)4Iron tetracarbonyl hydride
Iron tetracarbonyl hydride is the organometallic compound with the formula H2Fe4. Also known as tetracarbonyldihydridoiron, or iron tetracarbonyldihydride, this compound was the first metal hydride discovered...
. It is prepared by reducing Co2(CO)8
Dicobalt octacarbonyl
Dicobalt octacarbonyl is the inorganic compound Co28. This metal carbonyl is a reagent and catalyst in organometallic chemistry and organic synthesis. It is used as a catalyst for hydroformylation, the conversion of alkenes to aldehydes....
with sodium amalgam or a similar reducing agent followed by acidification.
- 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
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
of Co2(CO)8.
- 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.
Applications
Tetracarbonylhydridocobalt was the first transition metal hydride to be used in industry. In 1940 it was discovered that it catalyzed the conversion of alkenes, CO, and H2 to aldehydeAldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
s, a process known as hydroformylation
Hydroformylation
Hydroformylation, also known as oxo synthesis or oxo process, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group and a hydrogen atom to a carbon-carbon double bond...
(Oxo Reaction). Although it has since been largely superseded by rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...
-based catalysts, the world output of C3-C18 aldehydes produced by tetracarbonylhydrocobalt catalysis is about 100,000 tons/year, roughly 2% of the total.