Synthesis and complexation studies of cyclohexane-based tripodands

The present work has been concerned with the design and synthesis of cyclohexane-based polypodands and physico-chemical studies of the corresponding podates formed by complexation of alkali metal ions. Of particular interest has been the drastic conformational biasing of the back-bone ligand structure which is associated with the complexation process. A number of new tripodand ligands (11, 12, 13, 15, & 17) have been synthesized. The methodology central to these syntheses has been the alkylation of the cyclohexanetriol with the podal tosylates (or alkyl halide). Some of the final synthetic targets were arrived at by subsequent functional group conversions.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). \sp1H and \sp{13}C NMR studies were conducted to determine the ability of these ligands to complex NaBPh\sb4 (as well as some other metal salts) in CDCl\sb3. The relative complex stability constants for some of these ligands (with NaBPh\sb4 in CDCl\sb3) were determined by \sp{13}C NMR competition studies and compared. Complexation constants for 11 and 3 with NaPBh\sb4 in acetone-d\sb6 were obtained by \sp{13}C NMR Titrations. \sp{13}C-T\sb1 relaxation times were used to study the motional dynamics of uncomplexed and Na\sp{+}-complexed 3 in CDCl\sb3. In general, the complexation of cyclohexane-base tripodands involves a relatively well defined reorientation of ligand to a complex conformation having a cavity with convergent binding sites. Complexation of sodium by 3 in CDCl\sb3 involves an induced cyclohexane ring inversion that organizes the oxygen donor sites in the podal groups. Hexacoordination with the sodium cation removes conformational flexibility. The overall molecular reorientational mobility of the ligand increases upon complex formation and has been rationalized in terms of a compact spherical complex geometry that rotates freely in solution