Host - Guest Complexation. 36. Spherand and Lithium and Sodium Ion Complexation Rates and Equilibria

Article abstract of DOI:10.1021/ja00298a041

Thermodynamiic and kinetic parameters for complexation by three spherands of lithium and sodium picrates in CDCl3 are reported.The host are composed of the following units (Chart I) bonded to one another in 18-membered-ring systems: 2,6-disubstituted 4-methylanisyl (A); 2,6-disubstituted 4-methylanisyl deuterated in the methoxy group (Ad); 2,6-disubstituted 4-methylphenol (Ah); 2,6-disubstituted 4-methyl-1-allyloxybenzene (Aa); 2,6-disubstituted 4-methylphenyloxy (B); 1,3-phenylene (P); 1,2-cyclohexano(Cy); ethylene (E); methylene (M); oxygen (O); and nitrogen (N).The orders of the letters in the line formulas indicate the orders of attachment of the units in the cyclic or bicyclic hosts.In the polycyclic hosts, transannular B units serve as the bridgeheads linked through their oxygens to M3 or EOE units to transannular B units, at their 2-positions to A units, and at their 6-positions to either other B units (spherands) or to M units (hemispherands).In the cryptands, the nitrogen atoms act as bridgeheads.Chart II identifies the letters with the structures of the units and the structures and compound numbers with the line formulas.The hemispherands listed were useful in proving low, known concentrations of guests while the chorand listed was used for dissolving sodium and lithium picrates in CDCl3.The K_a and -ΔG^o values for 2 (2) binding sodium picrate were determined at 25 deg C in CDCl3 saturated with D2O by the direct picrate extraction method.The K_a values for A(AA)2A (1) and 2 (3) binding sodium picrate and for all three spherands binding lithium picrate could not be measured directly.Accordingly, values were obtained kinetically.Decomplexation rates for Ad(AdAd)2Ad (1d), 2 (2d), and 2 (3d) were prepared.With 1H NMR techniques at three temperatures in CDCl3 saturated at 25 deg C with D2O, the rate constants were determined for Li(1+) or Na(1+) transfering from nondeuterated to deuterated hosts.Because the reaction rate was comparable to rates of demethylation of the complex at high temperatures, only a maximum value could be placed on the rate constant for .Values for δH<*> and ΔS<*> for decomplexation were calculated, and decomplexation rate constants were extrapolated to 25 deg C.Rate constants for A(AA)2A (1), 2 (2) and 2 (3) complexing sodium picrate were determined at 25 deg C by following the 1H NMR changes as guest was transferred from B<(MOE)2O>B.NaPic (6.NaPic) to each of the three spherands.The complexation rate for complexing NaPic is much higher for 6 than for 1,2, or 3.The role of 6.NaPic was to provide a preequilibrium concentration of NaPic low enough to bring the complexation rate of the spherands onto the human time scale.The complexation rate constant of 1 with LiPic was determined by competition experiments between NaPic and LiPic, which were delivered in CDCl3 s