METAL DERIVATIVES OF MOLECULAR-COMPOUNDS .7. BIS[1,2-BIS(DIMETHYLAMINO)ETHANE-N,N']LITHIUM DISILYLPHOSPHANIDE - SYNTHESIS AND STRUCTURE

Crystalline lithium phosphanides studied so far show a remarkably high diversity of structure types dependent on the ligands at lithium and the substituents at phosphorus. Bis[1,2-bis(dimethylamino)ethane-N,N']lithium disilylphosphanide (1) discussed here, belongs to the up to now small group of compounds which are ionic in the solid state. It is best prepared from silylphosphane by twofold lithiation with lithium dimethylphosphanide first and subsequent monosilylation with silyl trifluoromethanesulfonate, followed by complexation. As found by X-ray structure determination (wR = 0.038) on crystals obtained from diethyl ether {monoclinic; space group P2(1)/c; a = 897.8(1); b = 1673.6(2); c = 1 466.8(1) pm; beta = 90.73(1)-degrees at -100 +/- 3-degrees-C; Z = 4 formula units), the lithium cation is tetrahedrally coordinated by four nitrogen atoms of two 1,2-bis(dimethylamino)ethane molecules. Characteristic parameters of the disilylphosphanide anion are a shortened average P-Si bond length of 217 pm (standard value 225 pm) and a Si-P-Si angle of 92.3-degrees.