Dicobalt hexacarbonyl acetylene complex

Dicobalt hexacarbonyl acetylene complexes are a family of In organocobalt compounds with the formula Co₂(C₂R₂)(CO)₆. A large variety of R groups are tolerated. They are red compounds that are soluble in organic solvents. They arise from the reaction of alkynes and dicobalt octacarbonyl:^[1]

Co₂(CO)₈ + R₂C₂ → (R₂C₂)Co₂(CO)₆ + 2 CO

Structure of dicobalt hexacarbonyl adduct of 2-butyne.

According to X-ray crystallography, the two Co atoms and two alkyne carbons form the vertices of a distorted tetrahedron. The C-C distance for the bridging alkyne ligand is 1.33 Å, and the Co-Co distance is 2.47 Å. The (R₂C₂)Co₂(CO)₆ core has C_2v symmetry.^[2] The structure is related to that of methylidynetricobaltnonacarbonyl and tetracobalt dodecacarbonyl, which are also tetrahedranes.

These complexes are intermediates in the Pauson-Khand reaction.