Cyclopentadienylcobalt dicarbonyl


Cyclopentadienylcobalt dicarbonyl is an organocobalt compound with formula Co2, abbreviated CpCo2. 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.

Preparation

CpCo2 was first reported in 1954 by Piper, Cotton, and Wilkinson 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 biscobalt at elevated temperature and pressures:
The compound is identified by strong bands in its IR spectrum at 2030 and 1960 cm-1.

Reactions

CpCo2 catalyzes the cyclotrimerization of alkynes. The catalytic cycle begins with dissociation of one CO ligand forming bis intermediate.
This reaction proceeds by formation of metal-alkyne complexes by dissociation of CO. Although monoalkyne complexes CpCo have not been isolated, their analogues, CpCo are made by the following reactions:
CpCo2 catalyzes the formation of pyridines from a mixture of alkynes and nitriles. Reduction of CpCo2 with sodium yields the dinuclear radical −, which reacts with alkyl halides to give the dialkyl complexes . Ketones are produced by carbonylation of these dialkyl complexes, regenerating CpCo2.

Related compounds

The pentamethylcyclopentadienyl analogue Cp*Co2 is well studied. The Rh and Ir analogues, CpRh2 and CpIr2, are also well known.