Studies of metaphosphate acids and metaphosphate anhydrides in aprotic media

Abstract

The chemistry of metaphosphate acids has historically been studied in aqueous media, where acid-catalyzed hydrolysis and solvent leveling effects of these strong acids have prevented their observations and rigorous characterization. Solubilization of tri-, tetra-, and hexametaphosphates in aprotic media using the IPPN + cation ([PPNI+ bis(triphenylphosphine)imninium) has revealed the rich acid chemistry of metaphosphates that has previously been elusive in aqueous media. Protonation of imetaphosphates in organic media has resulted in six metaphosphate acids. X-ray diffraction studies display that the structural configurations of metaphosphate acids are dictated by strong hydrogen bonding interactions. As a consequence of anti-cooperative effect, intramolecular hydrogen bonds are preferred at low degrees of protonation, and intermolecular hydrogen bonds are preferred at high degrees of protonation, resulting in oligomeric and polymeric structures. Because of the symmetry of the hydrogen bonds in metaphosphate acids, Low-Barrier Hydrogen Bonds (LBHB) are formed if the conformation of the metaphosphate ring allows. Metaphosphate anhydrides result from the dehydration of metaphosphate acids. They can undergo hydrolysis to regenerate metaphosphate acids, or alternatively alcoholysis to generate metaphosphate esters. Alcoholysis of metaphosphiate anhydrides presents a novel method to quantitatively phosphorylate organic substrates, of particular interest are substrates of biological significance such as nucleosides. The phosphorylating ability of metaphosphate anhydrides makes them promising candidates for biological phosphorylation.