Transition metal carbyne complex

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Transition metal carbyne complexes are

LUMO of the metal to create the σ-bond. The two π-bonds are formed when the two HOMO orbitals of the metal back-donate to the LUMO of the carbyne. 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.[3]

Synthesis

Transition metal carbyne complexes are most common for the early transition metals, especially niobium, tantalum, molybdenum, tungsten, and rhenium. They can also have low-valence metals as well as high-valence metals.

Protonation of a Re(I) vinylidene complex to give the corresponding cationic Re(V) carbyne derivative.

The first Fischer carbyne complex was reported in 1973.[4] Two years later in 1975, the first "Schrock carbyne" was reported.[5]

Many high-valent carbyne complexes have since been prepared, often by

vinylidene ligands also affords carbyne complexes.[3]

Bridging alkylidyne ligands in cluster compounds

methylidyne
ligand.

Some metal carbynes

dimerize to give dimetallacyclobutadienes. In these complexes, the carbyne ligand serves as a bridging ligand
.

Several cluster-bound carbyne complexes are known, typically with

haloforms:[6]

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

Structure

Structure of PhCW(OBu-t)3.[7]

Monomeric metal carbyne complexes exhibit fairly linear M–C–R linkages according to

infrared Spectroscopy, Raman spectroscopy.[10]
Bond lengths, bond angles and structures can be inferred from these and other analytical techniques.

Metal carbyne complexes also exhibit a large trans effect, where the ligand opposite the carbyne is typically labile.

Reactions and applications

Hexa(tert-butoxy)ditungsten(III) is a catalyst for alkyne metathesis.[11] The catalytic cycle involves an carbyne intermediate.[12]

Some carbyne complexes react with electrophiles at C-carbyne followed by association of the anion. The net reaction gives a transition metal carbene complex:

LnM≡CR + HX → Ln(X)M=CHR

These complexes can also undergo

photochemical reactions
.

In some carbyne complexes, coupling of the carbyne ligand to a

allyl.[13]

Main group analogue

A sulfur-based main group analog of a carbyne complex has been prepared by Seppalt and coworkers.[14] The compound, trifluoro(2,2,2-trifluoroethylidyne)-λ6-sulfurane, F3C–C≡SF3, prepared by dehydrofluorination of F3C–CH=SF4 or F3C–CH2–SF5, is an unstable gas that readily undergoes dimerization to form trans-(CF3)(SF3)C=C(CF3)(SF3) at above –50 °C.

Further reading

  • Mayr, A.; Bastos, C. M. (1992). Coupling Reactions of Terminal Two-Faced π Ligands and Related Cleavage Reactions. Progress in Inorganic Chemistry. Vol. 40. pp. 1–98.
    ISBN 9780470166413. {{cite book}}: |journal= ignored (help
    )

References

  1. PMID 35793547
    .
  2. ISBN 9780120311279. {{cite book}}: |journal= ignored (help
    )
  3. ^
    ISBN 978-3-527-29390-2
    .
  4. doi:10.1002/ange.19730851407
    .
  5. doi:10.1021/ja00843a072
    .
  6. ISBN 9780470132517. {{cite book}}: |journal= ignored (help
    )
  7. doi:10.1016/0022-328X(85)80338-7
    .
  8. ISBN 9780199342679
    .
  9. ISBN 9781118138076
    .
  10. ISBN 9789401047289
    .
  11. PMID 34519486
    .
  12. doi:10.1021/om00120a014
    .
  13. doi:10.1039/C39900000624
    .
  14. ISSN 0002-7863
    .
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