RING SIZE, SUBSTITUENT, AND ANION EFFECTS ON THE KINETIC AND EQUILIBRIUM PROPERTIES OF COPPER(II) COMPLEXES WITH WATER-SOLUBLE MACROCYCLIC TETRATHIA ETHERS

The complete series of alcoholic derivatives for the 13- through 16-me mbered macrocyclic tetrathia ethers, in which a single -OH group is at tached to the central carbon of a trimethylene bridge, has now been sy nthesized. The derivatized ligands show a marked improvement in aqueou s solubility, permitting the measurement of both the Cu(II) complex st ability constants (K-CuIIL') and the corresponding formation (k(f)) an d dissociation (k(d)) rate constants in aqueous solution at 25 degrees C. Insofar as possible, the K-CuIIL', k(f), and k(d) values were dete rmined from independent measurements to assess the level of consistenc y between them. The (CuL)-L-II/I formal potentials for complexes of th e OH-substituted ligands have also been determined, permitting the cal culation of the stability constants for the (CuL)-L-I complexes. Excep t for the potential measurements, all values were determined in the pr esence of both 0.10 and 1.0 M perchlorate to assess the uniformity of anion adduct effects upon the various kinetic and thermodynamic values . All values for the alcoholic derivatives are compared to the corresp onding parameters determined previously for the unsubstituted macrocyc les-for which, due to solubility limitations, the formation kinetic da ta had to be extrapolated to aqueous conditions from measurements made in methanol-water mixtures. In general, the substitution of an -OH gr oup on the ligand backbone results in a 5-8-fold decrease in the k(f) values. This decrease in complex formation rate is attributed to the i nfluence of hydrogen bonding between the -OH group and the surrounding solvent molecules upon the preferred ligand conformation in water. Th e k(f) values for both series of ligands are consistent with a mechani sm in which the closure of the first chelate ring is the rate-determin ing step. The effect of -OH substitution upon the k(d) values is somew hat variable but tends to be less pronounced. The OH-substituted 14-me mbered macrocycle appears to be somewhat unique from the standpoint th at the Cu(II) complex is twice as stable as the unsubstituted analogue , whereas all other -OH derivatives show a decrease in (CuL)-L-II stab ility. Also included in the current study are measurements on the Cu(I I) complex formed with a water-soluble oxathiane derivative of the 12- membered macrocyclic tetrathia ether (oxathiane-[12]aneS(4)).