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7.6.15.1 Method 1: Preparation from Grignard Reagents

DOI: 10.1055/sos-SD-007-00660

Zhang, J.-H.; Keh, C. C. K.; Li, C.-J.Science of Synthesis, (20047669.

In solution, a Schlenk equilibrium exists between a Grignard reagent and a diorganomagnesium, represented by Scheme 1. Displacement of the equilibrium to the right by selective precipitation of the magnesium halide provides a convenient synthetic method for diorganomagnesiums.[‌1‌] Various diorganomagnesium derivatives have been prepared by this method, and although solvents such as pyridine,[‌2‌] glymes,[‌3‌] and N,N,N,N-tetrameth­ylethylenediamine[‌4‌] are good precipitants for magnesium halides, only dioxane yields good results for a wide range of diorganomagnesiums.[‌5‌‌10‌] The addition of dioxane to a diethyl ether solution of a Grignard reagent precipitates insoluble complexes between magnesium halide and dioxane, which can be separated by filtration or centrifugation. This yields a clear solution of diorganomagnesium, which can be used directly or concentrated in vacuo to give the solid product. It should be noted that cyclic organomagnesium compounds are occasionally formed during the addition of dioxane to the Grignard reagent;[‌11‌] also diorganomagnesium may be coprecipitated, or traces of halide may remain in the diorganomagnesium solution. These factors should be considered if very pure products are required.

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