NEW CAGE AND LINKED MACROCYCLIC SYSTEMS FOR METAL-ION AND SMALL-MOLECULE BINDING

Stepwise synthetic procedures have been developed for producing famili es of large cyclic ligand systems that include new oxygen-nitrogen don or cages as well as tri-linked macrocyclic species containing mixed ni trogen-sulfur donors. The crystal structure of a cage of the above typ e incorporating six phenoxy oxygens and two tribenzylamine (bridgehead ) nitrogens reveals that the nitrogens adopt exo-exo configurations. S emiempirical MO calculations have been employed to investigate the top ological rigidity of this hexabenzo cage relative to related aliphatic systems. The constraining of the bridgehead nitrogens (through the pr esence of tribenzylamine groups) has a significant effect on the overa ll flexibility of the system and appears to be largely responsible for inhibiting the inclusive coordination of metal ions by this cage. In contrast to the aliphatic 2,2,2-cryptand, which readily adopts an endo -endo arrangement, the present cage shows negligible affinity for sodi um ions - as judged from comparative sodium picrate extraction experim ents (water/chloroform). New 'super' cages related to the above system but incorporating three additional pyridyl nitrogens in their heteroa tom set have also been synthesised. Once again, the rigidity associate d with the tribenzylamine bridgeheads introduces a measure of preorgan isation into these cages. The X-ray structure of one system recrystall ised from benzene shows that a benzene guest is encapsulated centrally in the cavity, seemingly held in position by 'T' orientation pi-stack ing interactions. In deuterochloroform, this cage selectively binds ph loroglucinol although it also shows significant affinity for resorcino l. Two new tri-linked S2N2-donor macrocycles incorporating three 16-me mbered rings connected by spacer groups to a phloroglucinol 'core' hav e been synthesised. Using an NMR titration procedure, these systems ha ve been demonstrated to undergo stepwise interaction with silver(I), w ith the final product showing a 3:1(metal:ligand) stoichiometry.