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State Key Laboratory for Physical Chemistry of Solid Surface, Department of Chemistry, Xiamen University, China
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, MOE Laboratory for Computational Physical Science, Department of Chemistry, Fudan University, Shanghai, China
Org. Biomol. Chem., 2012,10, 9491-9500
22 Aug 2012,
11 Oct 2012
First published online
17 Oct 2012
Here we present a systematic theoretical investigation on the mechanisms of Grignard reagent formation (GRF) for CH3Cl reacting with Mg atom, Mg2 and a series of Mg clusters (Mg4–Mg20). Our calculations reveal that the ground state Mg atom is inactive under matrix condition, whereas it is active under metal vapor synthesis (MVS) conditions. On the other hand, the excited state Mg (3P) atom, as produced by laser-ablation, can react with CH3Cl barrierlessly, and hence is active under matrix condition. We predict that the bimagnesium Grignard reagent, though often proposed, can barely be observed experimentally, due to its high reactivity towards additional CH3Cl to produce more stable Grignard reagent dimer, and that the cluster Grignard reagent RMg4X possesses a flat Mg4 unit rather than a tetrahedral geometry. Our calculations further reveal that the radical pathway (T4) is prevalent on Mg, Mg2 and Mgn clusters of small size, while the no-radical pathway (T2), which starts at Mg4, becomes competitive with T4 as the cluster size increases. A structure–reactivity relationship between barrier heights and ionization potentials of Mgn is established. These findings not only resolve controversy in experiment and theory, but also provide insights which can be used in the design of effective synthesis approaches for the preparation of chiral Grignard reagents.
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Organic & Biomolecular Chemistry
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