Formation of new larger ring cyclic triphosphenium ions in solution – A 31P NMR study

In a notable extension of previous work, we have shown that several diphosphanes will form larger (7- or 8-membered ring) cyclic triphosphenium ions (CTIs) in solution by reaction with PX3 (X = Cl, Br or I), sometimes in the presence of SnCl2 or SnBr2. We have also formed new CTIs from two ferrocene derivatives. The ions are readily identifiable by 31P NMR solution-state spectroscopy, having large 1JP–P values between the middle ‘bare’ phosphorus atom PA and the outer phosphorus atoms PB (and PC where the outer groups are inequivalent). In addition, some data for known CTIs, but with different counter-ions, are presented. Three of the new CTIs have been successfully protonated, two by both AlCl3/tBuCl and triflic acid, and one via the triflic acid route only.