Synthesis and structural elucidation of a rare example of a tris(amido) potassium magnesiate

An equimolar quantity of benzylpotassium and di-n-butylmagnesium were combined with three molar equivalents of diphenylamine in a solvent medium which consisted on THF, hexane and N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA). This mixture produces a rare example of a potassium tris(amido) magnesiate, namely (PMDETA)·K(μ-NPh2)Mg(THF)(NPh2)2 1. Complex 1 was characterized by X-ray crystallography and 1H and 13C NMR spectroscopy. The solid state structure of 1 (particularly the metals′ co-ordination spheres) differs considerably from that of previously characterized potassium magnesiates, presumably due to the less sterically demanding nature of the amido ligand employed in this study. The magnesium center is four-coordinate (usually three-coordinate in such ate systems) and as well as binding to three amido ligands, is coordinated to a THF molecule. Turning to the potassium center, it is bound to three N centers from the triamine PMDETA, only one amido group, and its coordination sphere is completed by a series of aryl-π contacts. The 1H NMR solution studies in C6D6 appear to show that the complex does not stay intact in arene but likely forms a solvent-separated species such as [K(C6D6)x]+[(THF)Mg(NPh2)3−].