Cyclopentadienylcobalt dicarbonyl
Encyclopedia
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.
who produced it by the reaction of cobalt carbonyl with cyclopentadiene
. It is prepared commercially by the same method:
Alternatively, it is generated by the high pressure carbonylation
of bis(cyclopentadienyl)cobalt (cobaltocene
) at elevated temperature and pressures:
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:
CpCo(CO)2 catalyzes the formation of pyridine
s from a mixture of alkynes and nitrile
s. 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.
Cyclopentadienyl
In organic chemistry, cyclopentadienyl is a cyclic group of atoms with the formula C5H5. Cyclopentadienyl are closely related to cyclopentadiene. Cyclopentadienyl have five carbon atoms bonded together in a pentagonal planar ring, all five of which are bonded to individual hydrogen atoms...
ring that is bound in an η5
Hapticity
The term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...
-manner and two carbonyl ligands. The compound is soluble in common organic solvents and it is best stored under nitrogen.
Preparation
CpCo(CO)2 was first reported in 1954 by Piper, Cotton, and WilkinsonGeoffrey Wilkinson
Sir Geoffrey Wilkinson FRS was a Nobel laureate English chemist who pioneered inorganic chemistry and homogeneous transition metal catalysis.-Biography:...
who produced it by the reaction of cobalt carbonyl with cyclopentadiene
Cyclopentadiene
Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...
. 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
Carbonylation
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry.-Organic chemistry:...
of bis(cyclopentadienyl)cobalt (cobaltocene
Cobaltocene
Cobaltocene, known also as biscobalt or even "bis Cp cobalt", is an organocobalt compound with the formula Co2. It is a dark purple solid that sublimes readily slightly above room temperature. Cobaltocene was discovered shortly after ferrocene, the first metallocene...
) at elevated temperature and pressures:
- Co(C5H5)2 + 2 CO → C5H5Co(CO)2 + "C5H5"
Reactions
CpCo(CO)2 catalyzes the cyclotrimerization of alkynes. The catalytic cycle begins with dissociation of one Co ligand forming bis(alkyne) intermediate.- 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:
- 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 pyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
s from a mixture of alkynes and nitrile
Nitrile
A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
s. 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
Carbonylation
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry.-Organic chemistry:...
of these dialkyl complexes, regenerating CpCo(CO)2.