Dicobalt hexacarbonyl acetylene complex

Structure of dicobalt hexacarbonyl adduct of 2-butyne.

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

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.

References

1. Greenfield, Harold; Sternberg, Heinz W.; Friedel, Robert A.; Wotiz, John H.; Markby, Raymond; Wender, Irving (1956). "Acetylenic Dicobalt Hexacarbonyls. Organometallic Compounds Derived from Alkynes and Dicobalt Octacarbonyl1,2". Journal of the American Chemical Society. 78: 120–124. doi:10.1021/ja01582a036.
2. d'Agostino, Michael F.; Frampton, Christopher S.; McGlinchey, Michael J. (1990). "Diastereoselective Ligand and Vertex Substitutions in Bimetallic Bridged Alkyne Clusters: X-Ray Crystal Structure of .mu.2-(endo-2-Propynylborneol)hexacarbonyldicobalt". Organometallics. 9 (11): 2972–2984. doi:10.1021/om00161a029.