Synthesis and thermal reactivity of a Me₃N-stabilized cyclic (alkyl)(amino)oxophosphonium ion

Reaction of cyclic (alkyl)(amino)phosphorous chloride 3 with GaCl₃ followed by the treatment with Me₃NO afforded trimethylamine-stabilized oxophosphonium ion 5, which was fully characterized by NMR spectroscopy and X-ray diffraction analysis. Computational study using DFT calculations indicates that the incorporation of a carbon atom next to the P center accumulates electron density on the P center. Oxophosphonium ion 5 is air and moisture stable but undergoes thermal decomposition to afford a phosphorus oxychloride 7 as well as a few single crystals of the by-product 8. Reaction mechanisms for the formation of 7 and 8 may involve a Lewis base free oxophosphonium ion 6.