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Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.7K
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.
2.7K
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

3.3K
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.
3.3K
Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.5K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
2.5K
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

4.1K
Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
4.1K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

4.5K
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...
4.5K
Reactivity of Enols01:18

Reactivity of Enols

4.5K
Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A carbonyl compound with an α hydrogen undergoes keto–enol tautomerism and remains in equilibrium with its tautomer, the enol form. Usually, the keto tautomer is present in a higher concentration than the enol tautomer due to the higher bond energy of C=O compared to C=C. Moreover, the direction of the keto–enol equilibrium is...
4.5K

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Related Experiment Video

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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex

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enantio-Enriched CPL-active helicene-bipyridine-rhenium complexes.

Nidal Saleh1, Monika Srebro, Thibault Reynaldo

  • 1Institut des Sciences Chimiques de Rennes, UMR 6226, Institut de Physique de Rennes, UMR 6251, Campus de Beaulieu, CNRS-Université de Rennes 1, 35042 Rennes Cedex, France. jeanne.crassous@univ-rennes1.fr.

Chemical Communications (Cambridge, England)
|February 4, 2015
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Summary

Researchers developed novel rhenium complexes with unique helical structures. These complexes are the first rhenium-based phosphors to demonstrate circularly polarized luminescence, impacting chiroptical and photophysical studies.

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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
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The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
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The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
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The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
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The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

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Area of Science:

  • Coordination Chemistry
  • Photophysics
  • Materials Science

Background:

  • Rhenium complexes are known for their photoluminescent properties.
  • Chiroptical materials are crucial for applications in optics and sensing.
  • Developing new phosphors with tailored properties remains an active research area.

Purpose of the Study:

  • To investigate the effect of incorporating a rhenium atom into extended helical π-conjugated bi-pyridine systems.
  • To explore the chiroptical and photophysical properties of these novel rhenium complexes.
  • To synthesize the first rhenium-based phosphors exhibiting circularly polarized luminescence.

Main Methods:

  • Synthesis of neutral and cationic rhenium-bi-pyridine complexes.
  • Characterization of structural, chiroptical, and photophysical properties.
  • Spectroscopic analysis to confirm luminescence and circular polarization.

Main Results:

  • Successful incorporation of rhenium into helical π-conjugated bi-pyridine systems.
  • Observation of significant impacts on chiroptical and photophysical properties.
  • Demonstration of circularly polarized luminescence from rhenium-based phosphors for the first time.

Conclusions:

  • The study presents novel rhenium complexes with tunable chiroptical and photophysical characteristics.
  • These findings open new avenues for developing advanced circularly polarized luminescence materials.
  • The synthesized complexes represent a significant advancement in rhenium-based phosphor technology.