Steric blocking of methyl bridging: The syntheses and X-ray crystal structures of a three-coordinate methyl magnesium complex and its THF adduct

Treatment of dimethylmagnesium with Ar'N = C(Bu-t)CHC(Bu-t)NHAr' (Ar' = 2,6 -diisopropylphenyl) in THF provides the beta -diketiminate complex [CH3Mg-( THF){eta (2)-(Ar'(NCBu)-Bu-t)(2)CH}]. The THF ligand may be removed from th is complex at 150 degreesC under vacuum to provide the three-coordinate com plex [CH3Mg{eta (2)-(Ar'(NCBu)-Bu-t)(2)CH}] Both species have been structur ally characterized by X-ray crystallography, which shows that the Mg-C bond decreases from 2.189(4) to 2.077(2) Angstrom on removal of the THF ligand, and this is accompanied by a change in magnesium coordination. geometry fr om distorted tetrahedral to trigonal planar.