TRANSITION-METAL TEMPLATED FORMATION OF [2]-ROTAXANES AND [3]-ROTAXANES WITH PORPHYRINS AS STOPPERS

The transition metal-directed threading of a molecular fragment containing a central chelate and an end-attached gold(III) porphyrin into a presynthesized coordinating ring affords a general precursor to rotaxane-type structures. After threading, construction of the second porphyrin acting as an efficient stopper affords a copper(I)-complexed [2]-rotaxane as well as a novel compartmental [3]-rotaxane. The latter compound consists of a three-porphyrin-containing molecular fragment threaded through two 30-membered rings. Quantitative demetalation of the copper(I)-complexed [2]-rotaxane affords a free-ligand [2]-rotaxane. The two porphyrins are bulky enough to inhibit any process leading to separate fragments, the cycle and the thread. H-1 NMR spectroscopy demonstrates that upon decomplexation the [2]-rotaxane undergoes profound conformation changes. Recomplexation using zinc(II) regenerates an entwined and compact structure similar to that of the copper(I)-complexed [2]-rotaxane obtained in the template reaction.