Ortho-phosphite(PO33−): Mechanochemical Synthesis of a Missing Oxoanion and Precursor to Value-Added Organophosphorus Compounds

Abstract

Despite the ubiquity of the well-known phosphorus polyanion phosphite (HPO32−)[jls-end-space/], it appears to be the case that no simple salt of the corresponding conjugate base (PO33−[jls-end-space/], “ortho-phosphite”) has ever been reported. We report the synthesis and characterization of this elusive species as a major component of a mixture obtained upon mechanochemical reduction of condensed phosphates, as evidenced by solid-state 31P NMR and Raman spectroscopy as well as subsequent reactivity studies. To corroborate the 31P NMR spectroscopic assignment, we independently generated Na3PO3 and K3PO3 by deprotonation of Na2HPO3 with NaCH2SiMe3 and of K2HPO3 with KCH2Ph, respectively, providing an orthogonal route to PO33− salts whose spectroscopic signatures match those observed in the mixture obtained by mechanochemical reduction. We further found that ortho-phosphite can act as a precursor for various phosphorus chemicals, such as P(OSiMe3)3 (46%), which is already well established as a precursor to a plethora of useful organophosphorus compounds. Therefore, our results not only establish the first formal pathway from P(V) phosphate starting materials to P(OSiMe3)3 without the intermediacy of white phosphorus, but also open the door to a broad range of downstream transformations based on this sustainable pathway. Additionally, BaHPO3·H2O (66%), OP(OMe)2Me (DMMP), and OP(OBn)2Bn (DBBP) have been generated directly from ortho-phosphite, all traditionally synthesized from white phosphorus.