Dicobalt octacarbonyl

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Dicobalt octacarbonyl
Dicobalt-octacarbonyl-C2v-bridged-from-xtal-1983-3D-balls-A.png
Dicobalt octacarbonyl.png
Co2(CO)8 soaked in hexanes
Names
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 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-514-0
PubChem CID
RTECS number
  • GG0300000
UNII
UN number 3281
  • InChI=1S/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2 Yes check.svgY
    Key: MQIKJSYMMJWAMP-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/8CO.2Co/c8*1-2;;/q;;;;;;;;2*+2
    Key: MQIKJSYMMJWAMP-UHFFFAOYAG
  • O=C=[Co]1(=C=O)(=C=O)C(=O)[Co](=C=O)(=C=O)(=C=O)C1=O
  • O=C=[Co-4](=C=O)(=C=O)(=C=O)[Co-4](=C=O)(=C=O)(=C=O)=C=O
Properties
Co2(CO)8
Molar mass 341.95 g/mol
Appearancered-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:
GHS-pictogram-flamme.svg GHS-pictogram-skull.svg GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg
Danger
H251, H302, H304, H315, H317, H330, H351, H361, H412
P201, P260, P273, P280, P304+P340+P310, P403+P233
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
4
3
1
Flash point -23 °C (-9.4 °F) [1]
Lethal dose or concentration (LD, LC):
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).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

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.

Contents

Synthesis, structure, properties

Dicobalt octacarbonyl an orange-colored, pyrophoric solid. [6] It is synthesised by the high pressure carbonylation of cobalt(II) salts: [6]

2 (CH3COO)2Co + 8 CO + 2 H2 → Co2(CO)8 + 4 CH3COOH

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]

2 Co + 8 CO → Co2(CO)8

It exist as a mixture of rapidly interconverting isomers. [2] [3] In solution, there are two isomers known that rapidly interconvert: [5]

Co2(CO)8NoCo-Co.png

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 cobaltcobalt 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 cobaltcobalt bond that is 2.70 Å in length in the solid structure when crystallized together with C60. [10]

Reactions

Reduction

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]

Co2(CO)8 + 2 Na → 2 Na[Co(CO)4]
Na[Co(CO)4] + H+ → H[Co(CO)4] + Na+

Salts of this form are also intermediates in the cyanide synthesis pathway for dicobalt octacarbonyl. [7]

Reactions with electrophiles

Halogens and related reagents cleave the Co–Co bond to give pentacoordinated halotetracarbonyls:

Co2(CO)8 + Br2 → 2 Br[Co(CO)4]

Cobalt tricarbonyl nitrosyl is produced by treatment of dicobalt octacarbonyl with nitric oxide:

Co2(CO)8 + 2 NO → 2 Co(CO)3NO + 2 CO

Reactions with alkynes

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 Nicholas reaction Nicholas Reaction Scheme.png
The Nicholas reaction

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]

Pauson Khand reaction original.svg

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]

Pauson-Khand reaction in synthesis of huperzine-Q.jpg

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]

Symmetric diphenylacetylene cyclotrimerization using dicobalt octacarbonyl Diphenylacetylene cyclotrimerization symmetrical.png
Symmetric diphenylacetylene cyclotrimerization using dicobalt octacarbonyl
Asymmetric diphenylacetylene cyclotrimerization using dicobalt octacarbonyl Diphenylacetylene cyclotrimerization asymmetrical.png
Asymmetric diphenylacetylene cyclotrimerization using dicobalt octacarbonyl

Hydroformylation

Catalytic cycle for the hydroformylation of a terminal alkene (
RCH=CH2) to an aldehyde (
RCH2CH2CHO):
Carbon monoxide dissociates from cobalt tetracarbonyl hydride to form the active catalyst,
HCo(CO)3
The cobalt centre p bonds to the alkene
The alkene ligand inserts into the cobalt-hydride bond
An additional carbonyl ligand coordinates
A carbonyl ligand migrates into the cobalt-alkyl bond
Dihydrogen adds to the acyl complex
The dihidrydo complex eliminates the aldehyde product, regenerating the catalyst
An unproductive and reversible side reaction Hydroformylation Mechanism V.1.svg
Catalytic cycle for the hydroformylation of a terminal alkene (RCH=CH2) to an aldehyde (RCH2CH2CHO):
  1. Carbon monoxide dissociates from cobalt tetracarbonyl hydride to form the active catalyst, HCo(CO)3
  2. The cobalt centre π bonds to the alkene
  3. The alkene ligand inserts into the cobalthydride bond
  4. An additional carbonyl ligand coordinates
  5. A carbonyl ligand migrates into the cobaltalkyl bond
  6. Dihydrogen adds to the acyl complex
  7. The dihidrydo complex eliminates the aldehyde product, regenerating the catalyst
  8. An unproductive and reversible side reaction

Hydrogenation of Co2(CO)8 produces cobalt tetracarbonyl hydride H[Co(CO)4]: [23]

Co2(CO)8 + H2 → 2 H[Co(CO)4]

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]

Substitution reactions

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:

12 C5H5N + 3 Co2(CO)8 → 2 [Co(C5H5N)6][Co(CO)4]2 + 8 CO

Conversion to higher carbonyls

Methylidynetricobaltnonacarbonyl,
HCCo3(CO)9, an organocobalt cluster compound structurally related to tetracobalt dodecacarbonyl HCCo3(CO)9.png
Methylidynetricobaltnonacarbonyl, HCCo3(CO)9, an organocobalt cluster compound structurally related to tetracobalt dodecacarbonyl

Heating causes decarbonylation and formation of tetracobalt dodecacarbonyl: [3] [24]

2 Co2(CO)8 → Co4(CO)12 + 4 CO

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]

9 Co2(CO)8 + 4 CHBr3 → 4 HCCo3(CO)9 + 36 CO + 6 CoBr2

Safety

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]

Related Research Articles

<span class="mw-page-title-main">Organometallic chemistry</span> Study of organic compounds containing metal(s)

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.

<span class="mw-page-title-main">Nickel tetracarbonyl</span> Chemical compound

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.

<span class="mw-page-title-main">Pauson–Khand reaction</span> Chemical reaction

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.

<span class="mw-page-title-main">Molybdenum hexacarbonyl</span> Chemical compound

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.

<span class="mw-page-title-main">Metal carbonyl</span> Coordination complexes of transition metals with carbon monoxide ligands

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.

<span class="mw-page-title-main">Tetrarhodium dodecacarbonyl</span> Chemical compound

Tetrarhodium dodecacarbonyl is the chemical compound with the formula Rh4(CO)12. This dark-red crystalline solid is the smallest binary rhodium carbonyl that can be handled as a solid under ambient conditions. It is used as a catalyst in organic synthesis.

<span class="mw-page-title-main">Cyclopentadienylcobalt dicarbonyl</span> Chemical compound

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.

<span class="mw-page-title-main">Organocobalt chemistry</span> Chemistry of compounds with a carbon to cobalt bond

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.

<span class="mw-page-title-main">Cobalt tetracarbonyl hydride</span> Chemical compound

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.

<span class="mw-page-title-main">Iron tetracarbonyl dihydride</span> Chemical compound

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.

<span class="mw-page-title-main">Metal-phosphine complex</span>

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).

<span class="mw-page-title-main">Cyclopentadienyliron dicarbonyl dimer</span> Chemical compound

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).

<span class="mw-page-title-main">Metal carbonyl hydride</span>

Metal carbonyl hydrides are complexes of transition metals with carbon monoxide and hydride as ligands. These complexes are useful in organic synthesis as catalysts in homogeneous catalysis, such as hydroformylation.

In organometallic chemistry, a transition metal alkyne complex is a coordination compound containing one or more alkyne ligands. Such compounds are intermediates in many catalytic reactions that convert alkynes to other organic products, e.g. hydrogenation and trimerization.

<span class="mw-page-title-main">Methylidynetricobaltnonacarbonyl</span> Chemical compound

Methylidynetricobaltnonacarbonyl is an organometallic cobalt cluster with the chemical formula Co3(CO)9CH that contains a metal carbonyl core with the methylidyne ligand, first discovered in the late 1950s. A variety of substituents can be added to the methylidyne group to form derivatives of the parent compound that have unique spectroscopic properties and reactivity. This page will explore the discovery and synthesis of methylidynetricobaltnonacarbonyl, the structure and bonding of the parent compound, as well as some examples reactivity and catalysis with the cluster.

<span class="mw-page-title-main">Dicobalt hexacarbonyl acetylene complex</span>

Dicobalt hexacarbonyl acetylene complexes are a family of In organocobalt compounds with the formula Co2(C2R2)(CO)6. A large variety of R groups are tolerated. They are red compounds that are soluble in organic solvents. They arise from the reaction of alkynes and dicobalt octacarbonyl:

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