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.