Co2(CO)8 soaked in hexanes | |
Names | |
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IUPAC name Octacarbonyldicobalt(Co—Co) | |
Other names Cobalt carbonyl (2:8), di-mu-Carbonylhexacarbonyldicobalt, Cobalt octacarbonyl, Cobalt tetracarbonyl dimer, Dicobalt carbonyl, Octacarbonyldicobalt | |
Identifiers | |
3D model (JSmol) | |
ChemSpider | |
ECHA InfoCard | 100.030.454 |
EC Number |
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PubChem CID | |
RTECS number |
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UNII | |
UN number | 3281 |
CompTox Dashboard (EPA) | |
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Properties | |
Co2(CO)8 | |
Molar mass | 341.95 g/mol |
Appearance | red-orange crystals |
Density | 1.87 g/cm3 |
Melting point | 51 to 52 °C (124 to 126 °F; 324 to 325 K) |
Boiling point | 52 °C (126 °F; 325 K) decomposes |
insoluble | |
Vapor pressure | 0.7 mmHg (20 °C) [1] |
Structure | |
1.33 D (C2v isomer) 0 D (D3d isomer) | |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards | Potential carcinogen |
GHS labelling: | |
Danger | |
H251, H302, H304, H315, H317, H330, H351, H361, H412 | |
P201, P260, P273, P280, P304+P340+P310, P403+P233 | |
NFPA 704 (fire diamond) | |
Flash point | -23 °C (-9.4 °F) [1] |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 15 mg/kg (oral, rat) |
NIOSH (US health exposure limits): | |
PEL (Permissible) | none [1] |
REL (Recommended) | TWA 0.1 mg/m3 [1] |
IDLH (Immediate danger) | N.D. [1] |
Safety data sheet (SDS) | External SDS |
Related compounds | |
Related metal carbonyls | Iron pentacarbonyl Diiron nonacarbonyl Nickel tetracarbonyl |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Dicobalt octacarbonyl is an organocobalt compound with composition Co2(CO)8. This metal carbonyl is used as a reagent and catalyst in organometallic chemistry and organic synthesis, and is central to much known organocobalt chemistry. [2] [3] It is the parent member of a family of hydroformylation catalysts. [4] Each molecule consists of two cobalt atoms bound to eight carbon monoxide ligands, although multiple structural isomers are known. [5] Some of the carbonyl ligands are labile.
Dicobalt octacarbonyl an orange-colored, pyrophoric solid. [6] It is synthesised by the high pressure carbonylation of cobalt(II) salts: [6]
The preparation is often carried out in the presence of cyanide, converting the cobalt(II) salt into a pentacyanocobaltate(II) complex that reacts with carbon monoxide to yield K[Co(CO)4]. Acidification produces cobalt tetracarbonyl hydride, HCo(CO)4, which degrades near room temperature to dicobalt octacarbonyl and hydrogen. [3] [7] It can also be prepared by heating cobalt metal to above 250 °C in a stream of carbon monoxide gas at about 200 to 300 atm: [3]
It exist as a mixture of rapidly interconverting isomers. [2] [3] In solution, there are two isomers known that rapidly interconvert: [5]
The major isomer (on the left in the above equilibrium process) contains two bridging carbonyl ligands linking the cobalt centres and six terminal carbonyl ligands, three on each metal. [5] It can be summarised by the formula (CO)3Co(μ-CO)2Co(CO)3 and has C2v symmetry. This structure resembles diiron nonacarbonyl (Fe2(CO)9) but with one fewer bridging carbonyl. The Co–Co distance is 2.52 Å, and the Co–COterminal and Co–CObridge distances are 1.80 and 1.90 Å, respectively. [8] Analysis of the bonding suggests the absence of a direct cobalt–cobalt bond. [9]
The minor isomer has no bridging carbonyl ligands, but instead has a direct bond between the cobalt centres and eight terminal carbonyl ligands, four on each metal atom. [5] It can be summarised by the formula (CO)4Co-Co(CO)4 and has D4d symmetry. It features an unbridged cobalt–cobalt bond that is 2.70 Å in length in the solid structure when crystallized together with C60. [10]
Dicobalt octacarbonyl is reductively cleaved by alkali metals and related reagents, such as sodium amalgam. The resulting salts protonate to give tetracarbonyl cobalt hydride: [3]
Salts of this form are also intermediates in the cyanide synthesis pathway for dicobalt octacarbonyl. [7]
Halogens and related reagents cleave the Co–Co bond to give pentacoordinated halotetracarbonyls:
Cobalt tricarbonyl nitrosyl is produced by treatment of dicobalt octacarbonyl with nitric oxide:
The Nicholas reaction is a substitution reaction whereby an alkoxy group located on the α-carbon of an alkyne is replaced by another nucleophile. The alkyne reacts first with dicobalt octacarbonyl, from which is generated a stabilized propargylic cation that reacts with the incoming nucleophile and the product then forms by oxidative demetallation. [11] [12]
The Pauson–Khand reaction, [13] in which an alkyne, an alkene, and carbon monoxide cyclize to give a cyclopentenone, can be catalyzed by Co2(CO)8, [3] [14] though newer methods that are more efficient have since been developed: [15] [16]
Co2(CO)8 reacts with alkynes to form a stable covalent complex, which is useful as a protective group for the alkyne. This complex itself can also be used in the Pauson–Khand reaction. [13]
Intramolecular Pauson–Khand reactions, where the starting material contains both the alkene and alkyne moieties, are possible. In the asymmetric synthesis of the Lycopodium alkaloid huperzine-Q, Takayama and co-workers used an intramolecular Pauson–Khand reaction to cyclise an enyne containing a tert-butyldiphenylsilyl (TBDPS) protected primary alcohol. [17] The preparation of the cyclic siloxane moiety immediately prior to the introduction of the dicobalt octacarbonyl ensures that the product is formed with the desired conformation. [18]
Dicobalt octacarbonyl can catalyze alkyne trimerisation of diphenylacetylene and its derivatives to hexaphenylbenzenes. [19] Symmetrical diphenylacetylenes form 6-substituted hexaphenylbenzenes, while asymmetrical diphenylacetylenes form a mixture of two isomers. [20]
Hydrogenation of Co2(CO)8 produces cobalt tetracarbonyl hydride H[Co(CO)4]: [23]
This hydride is a catalyst for hydroformylation – the conversion of alkenes to aldehydes. [4] [23] The catalytic cycle for this hydroformylation is shown in the diagram. [4] [21] [22]
The CO ligands can be replaced with tertiary phosphine ligands to give Co2(CO)−8x(PR3)x. These bulky derivatives are more selective catalysts for hydroformylation reactions. [3] "Hard" Lewis bases, e.g. pyridine, cause disproportionation:
Heating causes decarbonylation and formation of tetracobalt dodecacarbonyl: [3] [24]
Like many metal carbonyls, dicobalt octacarbonyl abstracts halides from alkyl halides. Upon reaction with bromoform, it converts to methylidynetricobaltnonacarbonyl, HCCo3(CO)9, by a reaction that can be idealised as: [25]
Co2(CO)8 a volatile source of cobalt(0), is pyrophoric and releases carbon monoxide upon decomposition. [26] The National Institute for Occupational Safety and Health has recommended that workers should not be exposed to concentrations greater than 0.1 mg/m3 over an eight-hour time-weighted average, without the proper respiratory gear. [27]
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide, cyanide, or carbide, are generally considered to be organometallic as well. Some related compounds such as transition metal hydrides and metal phosphine complexes are often included in discussions of organometallic compounds, though strictly speaking, they are not necessarily organometallic. The related but distinct term "metalorganic compound" refers to metal-containing compounds lacking direct metal-carbon bonds but which contain organic ligands. Metal β-diketonates, alkoxides, dialkylamides, and metal phosphine complexes are representative members of this class. The field of organometallic chemistry combines aspects of traditional inorganic and organic chemistry.
Nickel carbonyl (IUPAC name: tetracarbonylnickel) is a nickel(0) organometallic compound with the formula Ni(CO)4. This colorless liquid is the principal carbonyl of nickel. It is an intermediate in the Mond process for producing very high-purity nickel and a reagent in organometallic chemistry, although the Mond Process has fallen out of common usage due to the health hazards in working with the compound. Nickel carbonyl is one of the most dangerous substances yet encountered in nickel chemistry due to its very high toxicity, compounded with high volatility and rapid skin absorption.
In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes from alkenes. This chemical reaction entails the net addition of a formyl group and a hydrogen atom to a carbon-carbon double bond. This process has undergone continuous growth since its invention: production capacity reached 6.6×106 tons in 1995. It is important because aldehydes are easily converted into many secondary products. For example, the resultant aldehydes are hydrogenated to alcohols that are converted to detergents. Hydroformylation is also used in speciality chemicals, relevant to the organic synthesis of fragrances and pharmaceuticals. The development of hydroformylation is one of the premier achievements of 20th-century industrial chemistry.
The Pauson–Khand (PK) reaction is a chemical reaction, described as a [2+2+1] cycloaddition. In it, an alkyne, an alkene and carbon monoxide combine into a α,β-cyclopentenone in the presence of a metal-carbonyl catalyst.
Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)6. This colorless solid, like its chromium, tungsten, and seaborgium analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero oxidation state.
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe chemistry. In the Mond process, nickel tetracarbonyl is used to produce pure nickel. In organometallic chemistry, metal carbonyls serve as precursors for the preparation of other organometallic complexes.
The Wulff–Dötz reaction (also known as the Dötz reaction or the benzannulation reaction of the Fischer carbene complexes) is the chemical reaction of an aromatic or vinylic alkoxy pentacarbonyl chromium carbene complex with an alkyne and carbon monoxide to give a Cr(CO)3-coordinated substituted phenol. Several reviews have been published. It is named after the German chemist Karl Heinz Dötz (b. 1943) and the American chemist William D. Wulff (b. 1949) at Michigan State University. The reaction was first discovered by Karl Dötz and was extensively developed by his group and W. Wulff's group. They subsequently share the name of the reaction.
The Nicholas reaction is an organic reaction where a dicobalt octacarbonyl-stabilized propargylic cation is reacted with a nucleophile. Oxidative demetallation gives the desired alkylated alkyne. It is named after Kenneth M. Nicholas.
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Cyclopentadienylcobalt dicarbonyl is an organocobalt compound with formula (C5H5)Co(CO)2, abbreviated CpCo(CO)2. It is an example of a half-sandwich complex. It is a dark red air sensitive liquid. This compound features one cyclopentadienyl ring that is bound in an η5-manner and two carbonyl ligands. The compound is soluble in common organic solvents.
Organocobalt chemistry is the chemistry of organometallic compounds containing a carbon to cobalt chemical bond. Organocobalt compounds are involved in several organic reactions and the important biomolecule vitamin B12 has a cobalt-carbon bond. Many organocobalt compounds exhibit useful catalytic properties, the preeminent example being dicobalt octacarbonyl.
Organoiron chemistry is the chemistry of iron compounds containing a carbon-to-iron chemical bond. Organoiron compounds are relevant in organic synthesis as reagents such as iron pentacarbonyl, diiron nonacarbonyl and disodium tetracarbonylferrate. Although iron is generally less active in many catalytic applications, it is less expensive and "greener" than other metals. Organoiron compounds feature a wide range of ligands that support the Fe-C bond; as with other organometals, these supporting ligands prominently include phosphines, carbon monoxide, and cyclopentadienyl, but hard ligands such as amines are employed as well.
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 (introduction of CO into inorganic compounds) reactions.
Iron tetracarbonyl dihydride is the organometallic compound with the formula H2Fe(CO)4. This compound was the first transition metal hydride discovered. The complex is stable at low temperatures but decomposes rapidly at temperatures above –20 °C.
A metal-phosphine complex is a coordination complex containing one or more phosphine ligands. Almost always, the phosphine is an organophosphine of the type R3P (R = alkyl, aryl). Metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh3)3Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0).
Cyclopentadienyliron dicarbonyl dimer is an organometallic compound with the formula [(η5-C5H5)Fe(CO)2]2, often abbreviated to Cp2Fe2(CO)4, [CpFe(CO)2]2 or even Fp2, with the colloquial name "fip dimer". It is a dark reddish-purple crystalline solid, which is readily soluble in moderately polar organic solvents such as chloroform and pyridine, but less soluble in carbon tetrachloride and carbon disulfide. Cp2Fe2(CO)4 is insoluble in but stable toward water. Cp2Fe2(CO)4 is reasonably stable to storage under air and serves as a convenient starting material for accessing other Fp (CpFe(CO)2) derivatives (described below).
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