Dicobaltoctacarbonyl
Orange crystals
Fixed
1.73 g · cm -3 ( 18 ° C)
From 52 ° C decomposition
13 Pa (20 ° C)
Very poor in water
Risk
754 mg · kg -1 ( LD50, rat, oral)
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Dicobaltoctacarbonyl is a binuclear complex in which two cobalt nuclei are surrounded by eight carbonyl ligands.
Representation
The complex can be prepared by the reaction of the cobalt (II ) salts (such as cobalt ( II) acetate or cobalt (II) carbonate) be manufactured at a high carbon monoxide pressures. Often this reaction is performed in the presence of cyanide salts.
Properties
Dicobaltoctacarbonyl is an orange solid ( larger crystals are red ), which decomposes at 52 ° C to tetracobalt Co4 (CO) 12. At room temperature, the complex slowly decomposes to air with release of carbon monoxide.
The complex is in equilibrium between two structures, one of which consists of two trigonal- bipyramidal - coordinated cobalt nuclei with a bond between the cobalt atoms, the other consists of a bridged by two carbonyl complex. Here, the equilibrium is on the side of the bridged complex species. The bond length between the cobalt nuclei in the bridged complex is 252 pm, the Co -C bond to the terminal carbonyls is 180 pm to the bridging carbonyls 190 pm long.
Use
Dicobaltoctacarbonyl is needed in the Pauson -Khand reaction for the synthesis of cyclopentenones. This supplies by eliminating two Carbonyliganden the cobalt species which is used for adding to the used alkyne. The same applies to the Nicholas reaction is required to the same cobalt species.
Hydrogenation of the complex of the mononuclear complex HCo (CO) 4 forms
This complex is used as catalyst for the hydroformylation. Dicobaltoctacarbonyl thereby is reacted with hydrogen, so that Cobaltcarbonylhydrid formed as catalytically active species.
The industrial synthesis of the compound using phenylpyruvic acid as a catalyst in the double carbonylation of benzyl chloride by means of carbon monoxide and water.
By reduction with elemental alkali metals Co ( CO) 4 can - ions are formed.