Cyclopentadienylcobalt dicarbonyl

Cyclopentadienylcobalt dicarbonyl
Cyclopentadienyl cobalt dicarbonyl
Identifiers
CAS number 12078025-0 YesY
Properties
Molecular 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, 251 K, -8 °F

Boiling point

139-140 °C (710 mmHg)
37-38.5 °C (2 mmHg)

Solubility in water Insoluble
Hazards
R-phrases R10 R23/24/25 R42/43 R53
S-phrases S23 S36/37 S45
 YesY dicarbonyl (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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 and it is best stored under nitrogen.[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:

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

Reactions

CpCo(CO)2 catalyzes the cyclotrimerization of alkynes.[3] The catalytic cycle begins with dissociation of one Co ligand forming bis(alkyne) intermediate.[4]

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

This reaction proceeds by coordination of one alkyne, followed by dissociation of the second CO. Although monoalkyne complexes CpCo(CO)(R1C2R2) have not been isolated, their analogs, CpCo(PPh3)(R1C2R2) are known. They are accessible, inter alia, by the following reactions:[4]

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.[4]

References

  1. ^ King, R.B.; Stone, F.G.A (1963). "Cyclopentadienyl Metal Carbonyls and Some Derivatives". Inorg. Synth. 7: 99. doi:10.1002/9780470132388.ch31. 
  2. ^ Piper, T.S.; Cotton, F.A.; Wilkinson, G. (1955). "Cyclopentadienyl-carbon monoxide and related compounds of some transitional metals.". Journal of Inorganic and Nuclear Chemistry 1 (3): 165. doi:10.1016/0022-1902(55)80053-X. 
  3. ^ Staeb, T.H.; Chavez, J.; Gleiter, R.; Nuber, Bernhard (2005). "The Role of [η2-Bis(tert-butylsulfonyl)acetylene](carbonyl)(η5-cyclopentadienyl) cobalt(I) as an Intermediate in the Alkyne Dimerisation". Eur. J. Inorg. Chem. 2005 (20): 4090. doi:10.1002/ejic.200500394. 
  4. ^ a b c Pauson, P.L. “Dicarbonyl(cyclopentadienyl)cobalt(I).” Encyclopedia of Reagents for Organic Synthesis. 2001. doi:10.1002/047084289X.rd078

Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • Alkyne trimerisation — An alkyne trimerisation reaction is a 2+2+2 cyclization reaction in which three alkyne molecules react to form an aromatic compound. The reaction is pseudo pericyclic since it has not been observed to occur without the assistance of metal… …   Wikipedia

  • 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… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”