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 strength

A new donor group, triphenylphosphinimino, is described as a ligand in pentacoordinate siliconium halide dichelates, [XSiL₂] ⁺hal^-, where L is the bidentate ligand -OC(CH ₂Ph)=NN(=PPh₃)-, X = Me, C₆H₁₁, i-Bu, CH₂C1, 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.