Synthesis and Structure of the Small Superelectrophile [C2 (OH)2 Me2 ]2

The acid-activation of 1,2-dicarbonyl compounds plays a key role in a variety of electrophilic reactions, some of which are only accessible in superacidic media when a superelectrophilic dication is formed. To obtain structural and electronic information about these elusive species, the vicinal dication [C2 (OH)2 Me2 ]2+ is synthesized and characterized by Raman spectroscopy and X-ray diffraction. Since this superelectrophile could not be stabilized in convenient superacids, the usage of liquid SO2 turned out to be crucial. The experimental data are discussed together with quantum-chemical calculations on the B3LYP/aug-cc-pVTZ level of theory. Natural Bond Orbital (NBO) analyses quantify the superelectrophilic interactions found in the solid state.

On the Reaction of Phosphorous Acid with Superacids and the Crystal Structure of H(5)O(2)(+)SbF(6)(-) and Me(4)N(+)HPF(5)(-)

Phosphorous acid reacts with the superacidic system HF/SbF(5) with formation of HPF(4), water, and oxonium hexafluoroantimonate, which crystallizes as H(5)O(2)(+)SbF(6)(-) in the triclinic space group P&onemacr; with a = 6.492(6) Å, b = 7.469(8) Å, c = 8.095(6) Å, alpha = 116.17(7) degrees, beta = 93.90(7) degrees, and gamma = 112.34(7) degrees, with two formula units per unit cell. The unit cell contains two H(5)O(2)(+) ions of approximate symmetry C(2)(h)() with an intramolecular O.O distance of 2.418(8) or 2.40(1) Å, respectively. The reaction is discussed with regard to the formation of protonated species in various superacidic media. In addition the crystal structure of Me(4)N(+)HPF(5)(-) which is formed by the reaction of HPF(4) with Me(4)N(+)F(-) is reported. The salt crystallizes in the tetragonal space group P4/nmm with a = 8.564(5) Å and c = 5.687(2) Å, with two formula units per unit cell. The P-F distances of P-F(eq) = 1.595(6) Å and P-F(ax) = 1.594(9) Å for the psi-octahedral HPF(5)(-) show no significant interaction exercised by hydrogen on the cis- and trans-fluorine.