Crystalline Metaphosphate Acid Salts: Synthesis in Organic Media, Structures, Hydrogen-Bonding Capability, and Implication of Superacidity.

Metaphosphate acids cannot be thoroughly studied in aqueous media because their acidity is leveled by the solvent, and the resulting metaphosphates are susceptible to acid-catalyzed hydrolysis. Exploration of metaphosphate acid chemistry has now been made possible with the development of a general synthetic method for organic media soluble metaphosphate acids. Protonation of the [PPN](+) salts ([PPN](+) = [N(PPh3)2](+)) of tri-, tetra-, and hexametaphosphates results in five new metaphosphate acids, [PPN]2[P3O9H] (2), [PPN]4[(P4O12)3H8] (3), [PPN]4[P6O18H2]·2H2O (4), [PPN]3[P6O18H3] (5), and [PPN]2[P6O18H2(H3O)2] (6), obtained in yields of 80, 71, 66, 88, and 76%, respectively. Additionally, our synthetic method can be extended to pyrophosphate to produce [PPN][P2O7H3] (7) in 77% yield. The structural configurations of these oxoacids are dictated by strong hydrogen bonds and the anticooperative effect. Intramolecular hydrogen bonds are observed in 2, 4, and 5 and the previously reported [PPN]2[P4O12H2] (1), while intermolecular hydrogen bonds are observed in 3, 6, and 7. The hydrogen bonds in 3-7 possess short distances and are classified as low-barrier hydrogen bonds. Gas-phase acidity computations reveal that the parent tri- and tetrametaphosphoric acids are superacids. Their remarkable acidity is attributable to the stabilization of their corresponding conjugate bases via intramolecular hydrogen bonding.

A family of cis-macrocyclic diphosphines: modular, stereoselective synthesis and application in catalytic CO2/ethylene coupling.

A family of cis-macrocyclic diphosphines was prepared in just three steps from white phosphorus and commercial materials using a modular synthetic approach. Alkylation of bicyclic diphosphane 3,4,8,9-tetramethyl-1,6-diphosphabicyclo(4.4.0)deca-3,8-diene, or P2(dmb)2, produced phosphino-phosphonium salts [R-P2(dmb)2]X, where R is methyl, benzyl and isobutyl, in yields of 90-96%. Treatment of these salts with organolithium or Grignard reagents yielded symmetric and unsymmetric macrocyclic diphosphines of the form cis-1-R-6-R'-3,4,8,9-tetramethyl-2,5,7,10-tetrahydro-1,6-DiPhospheCine, or R,R'-DPC, in which R' is methyl, cyclohexyl, phenyl or mesityl, in yields of 46-94%. Alternatively, symmetric diphosphine Cy2-DPC was synthesized in 74% yield from the dichlorodiphosphine Cl2P2(dmb)2. As a first application, these cis-macrocyclic diphosphines were used as ligands in the nickel-catalyzed synthesis of acrylate from CO2 and ethylene, for which they showed promising catalytic activity.