Reactions of the hexachlorocyclodiphosphazane [MeNPCl3]2 with primary aromatic amines: formation of highly basic bisphosphinimines

Abstract

Reactions of hexachlorocyclodiphosphazane [MeNPCl₃]₂ with primary aromatic amines afforded the bisphosphinimine hydrochlorides [(RNH)₂(RN)PN(Me)P(NHMe)(NHR)₂]⁺ Cl^–(R = Ph 1, C₆H₄Me-4 2 or C₆H₄OMe-4 3). Dehydrochlorination of 2 and 3 by methanolic KOH yielded highly basic bisphosphinimines. [(RNH)₂(RN)PN(Me)P(NMe)(NHR)₂](R = C₆H₄Me-4 4 or C₆H₄OMe-4 5). Compounds 1–5 have been characterised by elemental analysis and IR and NMR (¹H, ¹³C, ³¹P) spectroscopy. The structure of 2 has been confirmed by single-crystal X-ray diffraction. The short P–N bond lengths and the conformations of the PN₄ units can be explained on the basis of cumulative negative hyperconjugative interactions between nitrogen lone pairs and adjacent P–N σ* orbitals. Ab initio calculations on the model phosphinimine (H₂N)₃PNH and its protonated form suggest that (amino)phosphinimines would be stronger bases compared to many organic bases such as guanidine.