Video Experimental Relacionado
Updated: Jul 4, 2026
10:52
Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
Published on: July 27, 2022
Formación y reactividad de un radical persistente en un complejo de molibdeno dinuclear
Aaron M Appel1, Suh-Jane Lee, James A Franz
1Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA.
Journal of the American Chemical Society
|June 21, 2008
Resumen
Este estudio explora la reactividad de un complejo específico de molibdeno-azufre. Los investigadores determinaron la cinética de la abstracción del átomo de hidrógeno y la dimerización radical, revelando conocimientos sobre la química del molibdeno y el azufre.
Área de la Ciencia:
- Química organometálica Química orgánica de los metales.
- Coordinación Química de la Coordinación
- La cinética de la reacción.
Sus antecedentes:
- El enlace S-H en los complejos organo-molibdeno-azufre exhibe una reactividad única.
- Comprender la formación de radicales y la dimerización es crucial para las aplicaciones catalíticas.
Objetivo del estudio:
- Para investigar la cinética de abstracción del átomo de hidrógeno de Cp*Mo(mu-S) 2 ((mu-SMe) ((mu-SH) MoCp* (S4MeH).
- Para caracterizar el equilibrio de dimerización radical y la cinética del núcleo Mo2S4.
- Para dilucidar las vías de reacción que involucran complejos molibdeno-azufre.
Principales métodos:
- Estudios cinéticos dependientes de la temperatura de la abstracción del átomo de hidrógeno por el radical bencilo.
- Espectroscopia de resonancia paramagnética de electrones (EPR) para determinar las constantes de equilibrio radical-dimérico.
- Espectroscopia de Resonancia Magnética Nuclear (RMN) de temperatura variable 1H para estudiar la cinética de la disociación de dímeros.
- Cristalografía de rayos X para la determinación estructural de complejos clave.
Principales resultados:
- La abstracción del átomo de hidrógeno por el radical bencilo produjo una constante de velocidad de 1,3 x 10^6 M^-1 s^-1 a 25°C.
- El producto de terminación radical exclusivo fue el producto de terminación cruzada benzil (S4MeBz), consistente con el efecto radical persistente.
- El radical (S4Me*) se dimerizó reversiblemente para formar un complejo tetranuclear ((S4Me) 2) con una constante de equilibrio de 5,7 x 10^4 M^-1.
- La constante de la velocidad de disociación de dimeros fue de 1,1 x 10^3 s^-1, y la constante de la velocidad de dimerización radical se estimó en 6,5 x 10^7 M^-1 s^-1.
Conclusiones:
- El estudio proporciona una comprensión cinética y mecanicista completa de la reactividad del enlace S-H en el núcleo Mo2S4.
- La evidencia apoya una vía de adición/eliminación radical en el núcleo de Mo2S4.
- Los datos estructurales de los principales intermediarios y productos ofrecen información sobre el mecanismo de reacción.
Más Videos Relacionados
Videos de Conceptos Relacionados
01:11Radical Reactivity: Overview
Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...
01:10Radical Reactivity: Steric Effects
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic factors, steric factors also account...
Along with electronic factors, steric factors also account...
01:16Radical Reactivity: Nucleophilic Radicals
Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
01:33Radical Reactivity: Intramolecular vs Intermolecular
Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
01:20Radical Reactivity: Concentration Effects
In a radical reaction, the concentration of starting materials governs the selectivity of a radical. For example, the reaction between an alkyl halide and an alkene, in the presence of tin hydride and AIBN, begins with the generation of a tin radical. The generated radical then abstracts halogen from the alkyl halide, producing an alkyl radical. This alkyl radical can either react with tin hydride, yielding an alkane, or add to an alkene, generating a nitrile-stabilized radical, eventually...
00:47Radical Formation: Addition
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired...