P-Amino-cyclopentadienylidene-phosphoranes versus P-cyclopentadienyl-iminophosphoranes—tautomeric protic forms of a new bidentate CpPNligand system

Abstract

The Staudinger reaction of cyclopentadienyl-phosphanes C₅H₅–PMe₂ (P1), C₅H₅–PPh₂ (P2), and C₅Me₄H–PMe₂ (P3) with azides Me₃SiN₃, 1-AdN₃ (Ad = 1-adamantyl) and DipN₃ (Dip = 2,6-diisopropylphenyl) has been studied. The nature of the products depends on the substituents at the C5 ring, at the phosphorus and nitrogen atoms: A series of new P-amino-cyclopentadienylidene-phosphoranes 2–6 was synthesized by reactions of P1–P3 with 1-AdN₃ (2–4) and DipN₃ (5, 6). In contrast, P-cyclopentadienyl-iminophosphoranes 1 and 7 were obtained as predominant tautomers by reaction of less CH-acidic P3 with less N-basic Me₃SiN₃ and DipN₃. Both tautomers are protonated forms of ambident, potentially chelating constrained-geometry ligands. The molecular structures of three members of this “CpPN” ligand family, 3, 4 and 6, are characterized by X-ray crystallography.