Tricopper Helicates

Tricopper helicates could also be synthesized using a simple modification of the dicopper helicate preparation [28]. When three equivalents of copper(I) were employed and 8-aminoquinoline was used in place of an aniline, tricopper double-helicate 4 was formed as the unique product (Scheme 1.6). 

This concept may also be extended to polynuclear helicates [38]. When 2-amino-quinoline and 4-chloroaniline were mixed with the phenanthroline dialdehyde shown in Scheme 1.10, a dynamic library of potential ligands was observed to form. The addition of copper(I) causes this library to collapse, generating only dicopper and tricopper helicates. As in the mononuclear case of Scheme 1.9, the driving force behind this selectivity appeared to be the formation of structures in which all ligand and metal valences are satisfied. The use of supramolecular (coordination) chemistry to drive the covalent reconfiguration of intraligand bonds thus... 

The preparation of structure 10, shown in Scheme 1.11, requires a different kind of selectivity in the choice of ligand subcomponents. Whereas during the simultaneous formation of dicopper and tricopper helicates (Scheme 1.10) all mixed ligands were eliminated from the dynamic library initially formed, in Scheme 1.11 the mixed ligand forms the unique structure selected during equilibration [39]. 

This differential selectivity results from the differing numbers of donor atoms offered by the two dialdehydes upon which these structures are based. Phenanth-roline dicarbaldehyde readily lends itself to the construction of a set of homo-ligands bearing a number of donor atoms divisible by 4, matching the coordination preference of copper(I), as seen in the dicopper and tricopper helicate structures discussed earlier. 

Scheme 1.10 Simultaneous preparation of dicopper and tricopper helicates from a dynamic library of ligands.

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