Iron(II)-templated synthesis of [3]rotaxanes by passing two threads through the same ring

The three-dimensional template effect of an octahedral iron(II) center has been exploited for threading two coordinating molecular units, each one is a bidentate 3.3'-biisoquinoline ligand bearing p-anisyl groups, through a coordinating 41-membered macrocycle containing the same endocyclic but nonstreically hindering chelate. The double threading process is driven by coordination of three bidentate ligands to the iron(II) center. By replacing the threads decorated with p-anisyl substituents by analogous long-chain ligands bearing appropriate end-functions (azide), the double threading process is as efficient as with the shorter (p-anisyl) chelates. An efficient quadruple end-functionalization reaction based on the copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition ("click" chemistry) affords the desired iron(II)-complexed two-string [3]rotaxane in excellent yield.