Synthesis and solid state structures of sterically congested sodium and cesium silyl(fluorosily)phosphanide aggregates and structural characterization of the trimeric sodium bis(trimethylsilyl)amide

Metalation of the silyl(fluorosilyl)phosphane Is(2)(F)Si-PH(SiR3) (3a; Is = 2,4,6-triisopropylphenyl, R3Si = Me-2((PrMe2C)-Me-i)Si) at phosphorus with NaN(SiMe3)(2) (4) in the molar ratio of 1:1 in toluene leads to the solvent-free sodium derivative 1a which forms a Na2P2-dimer in solution and in the solid state. The coordinatively unsaturated Na centers are each additionally bonded to a fluorine atom, so that a ladder-like, puckered tricyclic F2Na2P2Si2 skeleton results as the central structural motif. The same conversion of 3a into 1a under less polar reaction conditions (hexane) and the complete conversion of the silyl(fluorosilyl)phosphane Is(2)(F)Si-PH(SiPr3i) (3b) into its Na derivative 1b is kinetically hampered and can only be achieved if 2 equiv of sodium amide 4 are employed. Excess 4 may be recovered by fractional crystallization, from which its molecular Na3N3-trimer was isolated and structurally characterized for the first time. The unusual molecular polymeric cesium phosphanide [Is(2)(F)Si-PCs(SiPr3i). 0.5THF] (2) was prepared by the metalation of 3a with elemental cesium in toluene in the presence of little THF. The structure of 2 was determined by X-ray diffraction.