Donor-Stabilized Silyl Cations. 10. Pentacoordinate Siliconium-Ion Salts with a Triphenylphosphinimino-N Ligand Group: Two-Bond P−N−Si Coupling as a Measure for Coordination Strength1

A new donor group, triphenylphosphinimino, is described as a ligand in pentacoordinate siliconium halide dichelates, [XSiL2]+hal-, where L is the bidentate ligand −OC(CH2Ph)NN(PPh3)−, X = Me, C6H11, i-Bu, CH2Cl, CHCl2, Cl, Br, and hal = Cl, Br. The complex 16 (X = Me, hal = Cl) was characterized by crystal structure analysis, and the others were characterized by NMR spectroscopy and elemental analysis. The phosphinimino ligand is a stronger donor than previously studied dimethylamino and isopropylidenimino ligands, causing all of the complexes to be pentacoordinate siliconium-halide salts in the crystal as well as in solution. Two-bond 31P−N−29Si coupling constants across the N→Si dative bond increase with increasing monodentate-ligand electron-withdrawing power and may serve as a criterion for coordination strength.