Effects of ion association upon the solubilities of the cyclooctatetraene dianion

Abstract

The solubilities of disodium cyclooctatetraeneide and dipotassium cyclooctatetraeneide have been accurately determined in hexamethylphosphoramide (HMPA) and tetrahydrofuran (THF) as a function of temperature. For the THF systems the dianion was considered to exist as a quadruple ion (associated with two cations) as previously reported, and the enthalpies of solution were found to be 1.09 and 5.13 kcal/mol for the potassium and sodium salts, respectively. The fact that AH°of solution is positive indicates that the crystal lattice energies are larger than the solvation energies of the quadruple ions. In HMPA the dianion was considered to exist as a free ion. However, considerable curvature was observed in a plot of In Ksp vs. 1/RT. This curvature was attributed to the formation of ion pairs between the cyclooctatetraene (COT) dianion and one potassium cation. Addition of KI to solutions of the COT dianion and anion radical in HMPA shift the observed reverse disproportionation (comproportionation) equilibrium constant to smaller values confirming the formation of ion pairs. The sodium salt did not exhibit curvature in the van't Hoff plot, and the comproportionation equilibrium constant was invariant with the addition of NaClOs to solutions of the COT dianion and anion radical in HMPA.

The trindene trianion

“…That this product is a mixture of nearly statistical amounts of the two isomers, 16a and 16b, is indicated by its 1H NMR spectrum showing two methylene resonances, at 3.42 and 3.28, with similar intensities. The difference in the chemical shifts of these resonances is similar to the analogous difference in 4,7-dimethylindene (17),13 and accordingly the resonance at 3.42 CH,(S 2.34) CH,(S 2.23) 17 is assigned to the methylenes in 16b and to one of the methylenes in 16a, while that at 3.28 is assigned to the other two in 16a.14 With 3.5 equiv of n-butyllithium in tetrahydrofuran (THE) at -78 °C, the dihydro-1 //-trindenes (16) form the trianion 6, identified by its reaction with deuterated water (D30) giving back 16 (in 88% yield) with three deuterium atoms incorporated in the allylic positions. The number and location of the deuteriums were identified by the ratio of the intensities of the methylene and vinyl proton resonances, which in the precursor is 1.00 but in the deuterated product is 0.48 in one experiment and 0.49 in another.…”

Shining Light on Dinitrogen Cleavage: Structural Features, Redox Chemistry, and Photochemistry of the Key Intermediate Bridging Dinitrogen Complex

“…Moreover, a thermally stable, dicationic compound might be useful for the storage and in situ generation of 2. With isolated 2 in hand, the 2e oxidation was carried out by addition of 2 to a solution containing 2 equiv of [Cp 85 This reducing agent was desirable because it is soluble in THF 86,87 and has a sufficient reduction potential to carry out both reduction steps to form 2 while avoiding reduction of 2 to form 2 equiv of [88][89][90][91] Reduction of 2[B(Ar F ) 4 ] 2 by K 2 COT proceeds rapidly in THF solutions to form 2 as the only molybdenum-containing product (Scheme 2). Using this procedure, 2 may be obtained in 85% isolated yield, after separation from the K[B(Ar F ) 4 ] and COT byproducts.…”

Tris-[8]annulenyl Isocyanurate Trianion Triradical and Hexa-anion from the Alkali Metal Reduction of [8]Annulenyl Isocyanate

“…These results indicates that all three COT rings in 2 must have undergone the 2e – reduction resulting in the formation of the tris-[8]­annulenyl isocyanurate hexa-anion , 2 –6 . Although much of this salt had precipitated out of solution as a dark green solid, the partial solubility of 2 –6 was sufficient to obtain its NMR spectrum …”