Steric Blocking of Methyl Bridging: The Syntheses and X-ray Crystal Structures of a Three-Coordinate Methyl Magnesium Complex and Its THF Adduct

Abstract

Treatment of dimethylmagnesium with Ar‘NC(tBu)CHC(tBu)NHAr‘ (Ar‘ = 2,6-diisopropylphenyl) in THF provides the β-diketiminate complex [CH3Mg(THF){η2-(Ar‘NCtBu)2CH}]. The THF ligand may be removed from this complex at 150 °C under vacuum to provide the three-coordinate complex [CH3Mg{η2-(Ar‘NCtBu)2CH}]. Both species have been structurally characterized by X-ray crystallography, which shows that the Mg−C bond decreases from 2.189(4) to 2.077(2) Å on removal of the THF ligand, and this is accompanied by a change in magnesium coordination geometry from distorted tetrahedral to trigonal planar.