Dimethyl ether of acyclic polyethers, Me (OCH 2 CH 2) n OMe, predominantly coordinated to MgX 2 in an ether solution of Grignard reagent and the MgX 2 adduct was removed as a precipitate. Consequently, an ethereal solution of pure R 2 Mg was obtained in reasonable yield. This method is more convenient than those known general.