Cyclopentadienylcobalt dicarbonyl

Cyclopentadienyl cobalt dicarbonyl

Identifiers
CAS Number	12078-25-0 N
3D model (JSmol)	Interactive image
ChemSpider	10158732 N
ECHA InfoCard	100.031.933
EC Number	235-139-8
PubChem CID	11986239
InChI InChI=1S/C5H5.2CO.Co/c1-2-4-5-3-1;2*1-2;/h1-5H;;;/q-1;;; N Key: AEVRNKXPLOTCBW-UHFFFAOYSA-N N InChI=1/C5H5.2CO.Co/c1-2-4-5-3-1;2*1-2;/h1-5H;;;/q-1;;; Key: AEVRNKXPLOTCBW-UHFFFAOYAD
SMILES [cH-]1cccc1.[O+]#C[Co-](C#[O+])
Properties
Chemical formula	CpCo(CO)2
Molar mass	180.05 g/mol
Appearance	Dark red to black liquid
Density	1.35 g/cm3
Melting point	−22 °C (−8 °F; 251 K)
Boiling point	139 to 140 °C (282 to 284 °F; 412 to 413 K) (710 mmHg) 37-38.5 °C (2 mmHg)
Solubility in water	Insoluble
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H226, H301, H311, H331, H334, H341, H351, H412
Flash point	26.7 °C (80.1 °F; 299.8 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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.^[1]

Preparation

CpCo(CO)₂ was first reported in 1954 by Piper, Cotton, and Wilkinson who produced it by the reaction of cobalt carbonyl with cyclopentadiene.^[2] It is prepared commercially by the same method:

Co₂(CO)₈ + 2 C₅H₆ → 2 C₅H₅Co(CO)₂ + H₂ + 4 CO

Alternatively, it is generated by the high pressure carbonylation of bis(cyclopentadienyl)cobalt (cobaltocene) at elevated temperature and pressures:^[1]

Co(C₅H₅)₂ + 2 CO → C₅H₅Co(CO)₂ + "C₅H₅"

The compound is identified by strong bands in its IR spectrum at 2030 and 1960 cm⁻¹.^[3]

Reactions

CpCo(CO)₂ catalyzes the cyclotrimerization of alkynes.^[4][5] The catalytic cycle begins with dissociation of one CO ligand forming bis(alkyne) intermediate.^[6]

CpCo(CO)₂ + 2 R₂C₂ → CpCo(R₂C₂)₂ + 2 CO

This reaction proceeds by formation of metal-alkyne complexes by dissociation of CO. Although monoalkyne complexes CpCo(CO)(R¹C₂R²) have not been isolated, their analogues, CpCo(PPh₃)(R¹C₂R²) are made by the following reactions:^[6]

CpCo(CO)₂ + PR₃ → CO + CpCo(CO)(PR₃)

CpCoL(PR₃) + R₂C₂ → L + CpCo(PR₃)(R₂C₂) (where L = CO or PR₃)

CpCo(CO)₂ catalyzes the formation of pyridines from a mixture of alkynes and nitriles. Reduction of CpCo(CO)₂ with sodium yields the dinuclear radical [Cp₂Co₂(CO)₂]⁻, which reacts with alkyl halides to give the dialkyl complexes [Cp₂Co₂(CO)₂R₂]. Ketones are produced by carbonylation of these dialkyl complexes, regenerating CpCo(CO)₂.^[6]

Related compounds

The pentamethylcyclopentadienyl analogue Cp*Co(CO)₂ (CAS RN#12129-77-0) is well studied. The Rh and Ir analogues, CpRh(CO)₂ (CAS RN#12192-97-1) and CpIr(CO)₂ (CAS RN#12192-96-0), are also well known.

References