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 phosp horus with NaN(SiMe3)(2) (4) in the molar ratio of 1:1 in toluene lead s to the solvent-free sodium derivative 1a which forms a Na2P2-dimer i n solution and in the solid state. The coordinatively unsaturated Na c enters are each additionally bonded to a fluorine atom, so that a ladd er-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 derivativ e 1b is kinetically hampered and can only be achieved if 2 equiv of so dium amide 4 are employed. Excess 4 may be recovered by fractional cry stallization, from which its molecular Na3N3-trimer was isolated and s tructurally characterized for the first time. The unusual molecular po lymeric cesium phosphanide [Is(2)(F)Si-PCs(SiPr3i). 0.5THF] (2) was pr epared 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 di ffraction.