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Related Concept Videos

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
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Aromatic Hydrocarbon Cations: Structural Overview01:18

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Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
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Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

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Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents
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Reversible C-C coupling in a uranium biheterocyclic complex.

Marisa J Monreal1, Paula L Diaconescu

  • 1Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.

Journal of the American Chemical Society
|April 6, 2010
PubMed
Summary

Scientists achieved C-C coupling of 1-methylbenzimidazole using a uranium complex. This reaction involves C-H activation and forms a reversible biheterocyclic product, confirmed by X-ray diffraction and NMR.

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Area of Science:

  • Organometallic Chemistry
  • Uranium Chemistry
  • Heterocyclic Chemistry

Background:

  • C-C coupling reactions are fundamental in organic synthesis.
  • Uranium complexes offer unique reactivity for challenging transformations.
  • 1-methylbenzimidazole is a relevant heterocyclic scaffold.

Purpose of the Study:

  • To investigate the C-C coupling of 1-methylbenzimidazole mediated by a uranium dibenzyl complex.
  • To elucidate the mechanism involving C-H activation and fragment coupling.
  • To characterize the resulting biheterocyclic product and assess the reaction's reversibility.

Main Methods:

  • Synthesis of a neutral uranium dibenzyl complex with a ferrocene 1,1'-diamide ligand.
  • X-ray diffraction (single-crystal and powder) for solid-state structure determination.
  • Variable-temperature NMR spectroscopy ((1)H and (2)H) and DFT calculations for solution studies and mechanistic insights.

Main Results:

  • Successful C-C coupling of two 1-methylbenzimidazole molecules was achieved.
  • The reaction proceeds via C-H activation and formation of a biheterocyclic moiety.
  • The solid-state structure confirmed the product's formation; solution studies revealed the coupling is reversible.

Conclusions:

  • A novel C-C coupling of 1-methylbenzimidazole has been demonstrated using a uranium complex.
  • The study provides insights into the mechanism of uranium-mediated C-H activation and coupling.
  • The reversible nature of the reaction opens avenues for further synthetic applications.