Phosphane Complexes of Alkaline Earth Metals

Abstract

The reaction of lithium[bis(dimethylphosphanyl)(trimethyl-silyl)methanide] Li[(PMe2)2C(SiMe3)] with BeCl2 gave the homoleptic compound Be[(PMe2)2C(SiMe3)]2 (5) with four beryllium–phosphorus bonds constituting a distorted tetrahedron around the beryllium center. The reaction of MgCl2 with Li[(PMe2)2C(SiMe3)] resulted in the formation of the bis-chelate complex Mg[(PMe2)2C(SiMe3)]2 · 2 THF (7), where the distorted cis-octahedral magnesium center is additionally coordinated by two THF ligands. In the reaction of 7 with an additional equivalent of Li[C(PMe2)2(SiMe3)], THF is released and the magnesate anion {Mg[(PMe2)2C-(SiMe3)]3}– (8) was obtained. This compound is not only the first reported hexacoordinated magnesate, but also the first magnesium compound with six magnesium–phosphorus bonds. With CaCl2 and Li[C(PMe2)2(SiMe3)], a heptacoor-dinated complex Ca[(PMe2)2C(SiMe3)]2 · 3 THF (10) with three coordinating THF ligands was isolated. The complexes were characterized using 9Be{1H}-, 31P{1H}-, 1H-, 13C{1H}-NMR spectroscopy, and elemental analysis and by X-ray diffraction. The neutral compounds are highly soluble in nonpolar solvents.