A dianionic bis-phosphorimidazolide has been reported by Wright and is facilely prepared by treatment of pyrophosphate with carbonyldimidazole (CDI) (Figure ). 17 This compound has been investigated for diphosphorylation activity, but imidazole groups are only moderate leaving groups. Nevertheless, the imidazole adduct reacts slowly with nucleoside monophosphates, a reaction that is greatly accelerated in the presence of promoters such as ZnCl2, to give symmetric dinucleoside tetraphosphates (Figure ). The only previous report of a neutral doubly zwitterionic adduct of P2O5 and an N-donor base is the pyridine adduct reported by Meisel, (5) generated by refluxing phosphorus pentoxide ((P2O5)∞) in pyridine (Figure ). However, this putative pyridine adduct was not characterized or investigated for phosphorylation reactivity. We therefore sought to characterize this pyridine adduct and adapt this synthetic method to 3. Notably, Wright patented their bisphosphorimidazolide compound and included the pyridine adduct, 5, as well as a proposed N-methylimidazole adduct in their application. However, they do not appear to have actually synthesized or explored the reactivity of either of Treating a mixture of 3 and 4 with methanol yields a mixture of 8 and 9. B. X-ray crystal structure of 7 with thermal ellipsoids set at 50% probability and cations omitted (red for oxygen, orange for phosphorus, blue for nitrogen, grey for carbon).