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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 Cyclopentadienyl can refer to *Cyclopentadienyl anion, or cyclopentadienide, **Cyclopentadienyl ligand *Cyclopentadienyl radical, • *Cyclopentadienyl cation, See also *Pentadienyl In organic chemistry, pentadienyl refers to the organic radic ...
ring that is bound in an η5-manner and two carbonyl ligands. The compound is soluble in common organic solvents.


Preparation

CpCo(CO)2 was first reported in 1954 by Piper, Cotton, and
Wilkinson Wilkinson may refer to: People * Wilkinson (surname), a surname (including a list of people with the name) Places in the United States * Wilkinson, Illinois * Wilkinson, Indiana, a town in Hancock County * Wilkinson, Minnesota * Wilkinson, Mis ...
who produced it by the reaction of cobalt carbonyl with
cyclopentadiene Cyclopentadiene is an organic compound with the chemical formula, formula C5H6.LeRoy H. Scharpen and Victor W. Laurie (1965): "Structure of cyclopentadiene". ''The Journal of Chemical Physics'', volume 43, issue 8, pages 2765-2766. It is often ab ...
. 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" The compound is identified by strong bands in its
IR spectrum Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...
at 2030 and 1960 cm−1.


Reactions

CpCo(CO)2 catalyzes the cyclotrimerization of alkynes. The catalytic cycle begins with dissociation of one CO ligand forming bis(alkyne) intermediate.Pauson, P.L. “Dicarbonyl(cyclopentadienyl)cobalt(I).” Encyclopedia of Reagents for Organic Synthesis. 2001. :CpCo(CO)2 + 2 R2C2 → CpCo(R2C2)2 + 2 CO This reaction proceeds by formation of
metal-alkyne complex 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. hydro ...
es 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: :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
nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix ''cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including met ...
s. Reduction of CpCo(CO)2 with sodium yields the dinuclear radical p2Co2(CO)2sup>−, which reacts with alkyl halides to give the dialkyl complexes p2Co2(CO)2R2 Ketones are produced by carbonylation of these dialkyl complexes, regenerating CpCo(CO)2.


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

{{cobalt compounds Cyclopentadienyl complexes Carbonyl complexes Organocobalt compounds Half sandwich compounds