Complexation of Methane and Chlorofluorocarbons by Cryptophane‐A in Organic Solution

Abstract

N R 2 hv + P=C-P, -5 I NR, NRz 10in place of diisopropylamino substituents.['] Compound 3 is a local minimum on the potential energy surface, but appeared to be 110 and 116 kJmol-' above 4, at the SCF and MP2 level, respectively. In the same way, 6 is 120 kJ mol-' above 7, which is 140 kJmol-' higher than 8. The surprising stabilities of 3, 6, and 7 are probably due to the presence of bulky substituents, since the tetracoordinate P-H ylide form better accommodates the steric hindrance than does the tricoordinate CH form. Lastly, the isomerization of 9 +lo is not surprising since phosphaalkene 10 was found to be 220 kJ mol-' lower in energy than 9. This work demonstrates the great potential of 1 as a building block for the synthesis of new metastable species, predicted by theory to be thermodynamically high in energy. Experimental Procedure 3:To a solution of 1 (1 mmol) in dichloromethane ( 5 mL) was added the equimolar amount of NaBF, at room temperature. After the solution had been stirred for 2 h, the solvent was removed under vacuum, and the residue was washed several times with Et,O. This afforded 3 as white powder (70%; m.p. J(P,H) = 4.0 and 17.3 Hz). 9.2 (dddq, J(P,P) = 32.9 Hz, J(P,F) =15.3 Hz, J(P,H) = 524.2 and 16.

Inclusion Complexes Oriented in Thermotropic Liquid-Crystalline Solvents Studied with Carbon-13 NMR

“…Moreover, the large stabilizing enthalpy of formation and large destabilizing entropy of formation (∆H=-34.3 kJ mol −1 and ∆S 0 =-67 J mol −1 K −1 , respectively [5]) determined previously for this complex suggest a highly rigid, "crystal-like" structure [7]. It has also been reported [7] that x-ray crystallographic studies of the analogous complex between chloroform and cryptophane-A6…”

“…The van der Waals volume of chloroform is ≈72Å 3 [5], whereas the corresponding cavity volume for cryptophane-A is ≈95…”

“…[1][2][3][4][5][6][7]). Correspondingly, there has been considerable interest in studying the structural and dynamical aspects of ligand binding in these systems.…”

“…1). The complexes between cryptophane-A and various guest species have been studied previously with NMR, including those between cryptophane-A and methane [5], chloroform [5,6], and xenon [7][8][9].…”

Strongly underestimated dispersion energy in cryptophanes and their complexes

“…By NMR studies it was shown that D 3 -symmetric cryptophane-A (D 3 -2, see Fig. 1) forms stable complexes with methane, chloroform and xenon 13,14 . Association constants were determined in 1,1,2,2-tetrachloroethane and amount to 130 M À 1 for methane and to 230 M À 1 for chloroform at 298 K (ref.…”