Along the lines of the synthesis of Na2PO3F, our initial strategy involved the thermal reaction between NaH and Na3P3O9 (neat, 3:1 molar ratio) at 300 • C, and we were pleased to observe the formation of the desired phosphite by 31 P NMR spectroscopy. However, the presence of unreacted trimetaphosphate as the major phosphorus-containing species at the end of the reaction sequence pointed toward poor conversion. Additionally, the formation of an unusual phosphinophosphate, [H2P-OPO3] 2-, which is tentatively assigned based on data from NMR spectroscopy, suggested poor mixing of the solid reagents and high local concentrations of hydride, plausibly leading to overreduction.