Chiral cis-octahedral Grignard reagents

Three chiral cis-octahedral Grignard reagents have been synthesized and structurally characterized by X-ray diffraction methods. Crystals of cis-[(n-Pr)MgBr(dme)2] (1), cis-[(i-Pr)MgBr(dme)2] (2) and cis-[(allyl)MgBr(dme)2] (3) were prepared from neat 1,2-dimethoxyethane (DME) and are all racemic. Synthesis and structural characterization of trans-[MgBr2(tmeda)2] (4) and cis-[MgBr2(dme)2] (5) indicated that bidentate tertiary amino ligands may be less well suited for the preparation of cis-octahedral Grignard reagents. On the other hand, the crystal structures of cis-[MgBr2(trigly)] (6) and [Mg2(μ-Br)2(trigly)2][Mg2(μ-Me)2Br4] (7) {trigly=triglyme)}, suggest that the triglyme ligand may be ideally suited for this purpose.