Synthesis and Solid State Structures of Sterically Congested Sodium and Cesium Silyl(fluorosilyl)phosphanide Aggregates and Structural Characterization of the Trimeric Sodium Bis(trimethylsilyl)amide

Abstract

Metalation of the silyl(fluorosilyl)phosphane Is 2 (F)Si−PH(SiR 3 ) ( 3a; Is = 2,4,6-triisopropylphenyl, R 3 Si = Me 2 (Pr i Me 2 C)Si) at phosphorus with NaN(SiMe 3 ) 2 ( 4 ) in the molar ratio of 1:1 in toluene leads to the solvent-free sodium derivative 1a which forms a Na 2 P 2 -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 F 2 Na 2 P 2 Si 2 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(SiPr i 3 ) ( 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 Na 3 N 3 -trimer was isolated and structurally characterized for the first time. The unusual molecular polymeric cesium phosphanide [Is 2 (F)Si−PCs(SiPr i 3 )·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.