Transition metal carbyne complex

Transition metal carbyne complexes are organometallic compounds with triple bond between carbon and the transition metal. They are also called metal alkylidynes—the carbon is a carbyne ligand. Such compounds are useful in organic synthesis of alkynes and nitriles. They have been the focus on much fundamental research.^[1]

Synthesis

Transition metal carbyne complexes are most common for the early transition metals, especially Nb, Ta, Mo, W, and Re.

The first example of a metal carbyne complex was prepared by Fischer school by treatment of Cr(CO)₅(C(OMe)Ph) with boron trichloride:

Cr(CO)₅(C(OMe)Ph) + BBr₃ → BrCr(CO)₄(CPh) + CO + BBr₂(OMe)

Many high valent carbyne complexes have since been prepared, often by dehydrohalogenation of carbene complexes. Alternatively, amino-substituted carbyne ligands sometime form upon protonation of electron-rich isonitrile complexes. Similarly, O-protonation of μ₃-CO ligands in clusters gives hydroxycarbyne complex.

Many cluster-bound carbyne complexes are known. These do not feature MC triple bonds, but the carbyne carbon is tetrahedral. One of the best known are the tricobalt derivatives, which are prepared from haloforms:^[2]

2 HCBr₃ + 9/2 Co₂(CO)₈ → 2 HCCo₃(CO)₉ + 18 CO + 3 CoBr₂

Structure

Metal carbyne complexes exist as monomers, with fairly linear M-C-R linkages. The carbyne ligand can also serve as a bridging ligand. Dimerization of metal carbynes affords dimetallacycobutadienes. The M-C distance is typically short.

Reactions and applications

Metal alkylidyne complexes have mainly been used for specialized reactions in the laboratory, the main used being alkyne metathesis.

Triply bridging carbynes are sometimes prepared by the condensation of terminal carbyne complexes with other metals.

References

1. ^ Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ISBN 978-3-29390-6.
2. ^ Dietmar Seyferth, Mara O. Nestle, John S. Hallgren "μ₃-Alkylidyne-Tris(Trigarbonylcobalt) Compounds: Organocobalt Cluster Complexes" Inorganic Syntheses, 1980, Volume 20, 224–226. doi:10.1002/9780470132517.ch52.