Dicobalt octacarbonyl

Dicobalt octacarbonyl
Dicobalt octacarbonyl Dicobalt octacarbonyl
General
Systematic name	Dicobalt octacarbonyl
Other names	Cobalt carbonyl Octacarbonyldicobalt
Molecular formula	Co2CO8
SMILES	?
Molar mass	341.95 g/mol
Appearance	red-orange crystals when pure
CAS number	[10210-68-1]
Properties
Density and phase	ca. 2 g/cm3
Solubility in water	insoluble
Other solvents	Benzene, THF
Melting point	51–52 °C
Boiling point	sublimes > 40 °C (vacuum)
Structure
Dipole moment	0 D
Hazards
MSDS	External MSDS
Main hazards	CO source pyrophoric
Flash point	? °C
R/S statement	R: 11-22-40-43-48/ 20-52/53-62 S: 36/37-61
RTECS number	GG0300000
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Related compounds	Ni(CO)4 Fe3(CO)12 Fe2(CO)9, Co4(CO)12
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Dicobalt octacarbonyl is the chemical compound Co₂(CO)₈. This metal carbonyl is a versatile reagent in organometallic chemistry and organic synthesis. It continues to be used as a catalyst for hydroformylation catalysis.

Synthesis

The high pressure reaction of cobalt(II) salts with CO, often in the presence of cyanide, affords this compound.

Structure

Co₂(CO)₈ is the most structurally complex of the binary metal carbonyls because it exists in two isomers. These isomers rapidly interconvert. The minor isomer has no bridging CO ligands, it is described (CO)₄Co-Co(CO)₄. The major isomer contains two bridging CO ligand and is described as (CO)₃Co(μ-CO)₂Co(CO)₃.

Reactions

• The characteristic reaction of this species entails its hydrogenation:

Co₂(CO)₈ + H₂ → 2 HCo(CO)₄

This hydride is the active agent in hydroformylation. It adds to alkenes to give an alkylCo(CO)₄ product that then proceeds to insert CO and undergo hydrogenolysis to affort the aldehyde.

• Reduction of Co₂(CO)₈ gives the conjugate base of HCo(CO)₄:

Co₂(CO)₈ + 2 Na → 2 NaCo(CO)₄

• The CO ligands can be replaced with tertiaryphosphine ligands to give Co₂(CO)_8-x(PR₃)_x. These bulky derivatives are more selective catalysts for hydroformylation reactions.
• Co₂(CO)₈ catalyzes the Pauson–Khand reaction of an alkyne, an alkene, and CO to give a cyclopentenone.
• Lewis bases cause disproportionation:

6 pyridine + 1.5 Co₂(CO)₈ → [Co(pyridine)₆][Co(CO)₄]₂ + 4 CO

• Heating causes decarbonylation and formation of the tetrahedral cluster Co₄(CO)₁₂.

Safety

Co₂(CO)₈ is a volatile source of cobalt; it releases carbon monoxide upon decomposition. This is one of the more reactive binary metal carbonyls, and some samples will contain pyrophoric particles of cobalt that can inflame in air. Samples are refrigerated during storage.

See also

• Nicholas reaction