I have been trying to alkylate one of my early transition metal-dichloride complexes. The alkylating reagent is benzyl magnesium chloride (as a 2M THF solution). In spite of all my attempts, I am unable to get rid of the free benzyl magnesium chloride peak at 2.75 ppm in my 1H NMR (C6D6 solvent). How does one commonly remove such impurities? Crystallization does not help!
Possibly you may add some SiMe3Cl. It could be more reactive towards BnMgCl than your metal-Bn bond. The resulting BnSime3 could be distilled off in vacuum. Seen somewhere in literature, although never tried by myself.
Add a few drops of 1,4-dioxane. It shifts the schlenk equilibrium to give Bn2Mg and MgCl2 which are very insoluble and then after removing all solvents under reduced pressure, your product can be extracted with aromatic or hydrocarbon solvent, depending on solubility.
Thank you both for the wonderful suggestions. I recently learned that this peak at 2.74 ppm corresponds to bibenzyl (C6H5CH2-CH2C6H5) and not free BnMgCl as I had assumed previously.
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