Dihydrogen tetrametaphosphate, [P4O12H2]2-: synthesis, solubilization in organic media, preparation of its anhydride [P4O11]2- and acidic methyl ester, and conversion to tetrametaphosphate metal complexes via protonolysis.

Dihydrogen tetrametaphosphate [P4O12H2](2-) (1) can now be synthesized and isolated as its PPN salt ([PPN](+) = [N(PPh3)2](+)) via treatment of [PPN]4[P4O12] with trifluoroacetic anhydride in wet acetone; this simple procedure affords the oxoacid salt in 94% yield. A pKa of 15.83 ± 0.11 in acetonitrile was determined. [P4O12H2](2-) reacts with the dehydrating agent N,N'-dicyclohexylcarbodiimide to afford tetrametaphosphate anhydride [P4O11](2-) (2) in 82% yield, also as the PPN salt. From 2 a monohydrogen tetrametaphosphate ester [P4O10(OH)(OMe)](2-) (3, 96%) was derived by addition of methanol, illustrating that 2 can function as a reagent for chemical phosphorylation. Addition of water to 2 regenerates 1 quantitatively. Deprotonation of 1 by metal amides in the +2 oxidation state led to the unconventional monomeric tin(II) κ(4) tetrametaphosphate [Sn(P4O12)](2-) (4, 78%, a molecular analog of SnO) and binary dimeric chromium(II) bis(μ2,κ(2),κ(2)) derivative [Cr2(P4O12)2](4-) (5, 82%). Structural data stemming from single-crystal X-ray diffraction studies for the PPN salts of anions 1-5 are also reported.