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Cyclopentadienylcobalt dicarbonyl
Chemical compound From Wikipedia, the free encyclopedia
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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 ring that is bound in an η5-manner and two carbonyl ligands. The compound is soluble in common organic solvents.[1]
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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]
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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]
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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
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