The Grignard Reaction − Unraveling a Chemical Puzzle
| Autor: | Raphael Mathias Peltzer, Jürgen Gauss, Michele Cascella, Odile Eisenstein |
|---|---|
| Přispěvatelé: | Institut für Physikalische Chemie, Universität Mainz, Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier (ICGM ICMMM), Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Université Montpellier 1 (UM1)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut de Chimie du CNRS (INC) |
| Rok vydání: | 2020 |
| Předmět: |
Nucleophilic addition
010405 organic chemistry Schlenk equilibrium Radical Grignard reaction General Chemistry 010402 general chemistry 01 natural sciences Biochemistry Catalysis 0104 chemical sciences [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry chemistry.chemical_compound Colloid and Surface Chemistry Energy profile chemistry Nucleophile Fluorenone Computational chemistry [CHIM]Chemical Sciences [CHIM.COOR]Chemical Sciences/Coordination chemistry Reactivity (chemistry) ComputingMilieux_MISCELLANEOUS |
| Zdroj: | Journal of the American Chemical Society Journal of the American Chemical Society, American Chemical Society, 2020, 142 (6), pp.2984-2994. ⟨10.1021/jacs.9b11829⟩ |
| ISSN: | 0002-7863 1520-5126 |
| Popis: | More than 100 years since its discovery, the mechanism of the Grignard reaction remains unresolved. Ambiguities arise from the concomitant presence of multiple organomagnesium species and the competing mechanisms involving either nucleophilic addition or the formation of radical intermediates. To shed light on this topic, quantum-chemical calculations and ab initio molecular dynamics simulations are used to study the reaction of CH3MgCl in tetrahydrofuran with acetaldehyde and fluorenone as prototypical reagents. All organomagnesium species coexisting in solution due to the Schlenk equilibrium are found to be competent reagents for the nucleophilic pathway. The range of activation energies displayed by all of these compounds is relatively small. The most reactive species are a dinuclear Mg complex in which the substrate and the nucleophile initially bind to different Mg centers and the mononuclear dimethyl magnesium. The radical reaction, which requires the homolytic cleavage of the Mg-CH3 bond, cannot occur unless a substrate with a low-lying π*(CO) orbital coordinates the Mg center. This rationalizes why a radical mechanism is detected only in the presence of substrates with a low reduction potential. This feature, in turn, does not necessarily favor the nucleophilic addition, as shown for the reaction with fluorenone. The solvent needs to be considered as a reactant for both the nucleophilic and the radical reactions, and its dynamics is essential for representing the energy profile. The similar reactivity of several species in fast equilibrium implies that the reaction does not occur via a single process but by an ensemble of parallel reactions. |
| Databáze: | OpenAIRE |
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