A Mechanically Interlocked Bundle

The prototype of an artificial molecular machine consisting of a tris- ammonium tricationic component in- terlocked with a tris(crown ether) com- ponent to form a molecular bundle with averaged C3v symmetry has been designed and synthesized.The system is based on noncovalent interactions, which include 1) N + H¥¥¥O hydrogen bonds; 2) CH¥¥¥O interactions be- tween the CH2NH2 + CH2 protons on three dibenzylammonium-ion-contain- ing arms, which are attached symmetri- cally to a benzenoid core, and three di- benzo(24)crown-8 macrorings fused onto a triphenylene core; and 3) p¥¥¥p stacking interactions between the aro- matic cores.The template-directed syn- thesis of the mechanically interlocked, triply threaded bundle involves post- assembly covalent modification, that is, the efficient conversion of three azide functions at the ends of the arms of the bound and threaded trication into bulky triazole stoppers, after 1,3-dipo- lar cycloaddition with di-tert-butylacet- ylenedicarboxylate to the extremely strong 1:1 adduct that is formed in di- chloromethane/acetonitrile (3:2), on account of a cluster effect associated with the paucivalent adduct.Evidence for the averaged C3v symmetry of the molecular bundle comes from absorp- tion and luminescence data, as well as from electrochemical experiments, 1 H NMR spectroscopy, and mass spec- trometry.The photophysical properties of the mechanically interlocked bundle are very similar to those of the super- bundle that precedes the formation of the bundle in the process of supra- molecular assistance to covalent syn- thesis.Although weak non-nucleophilic bases (e.g., nBu3N and iPr2NEt) fail to deprotonate the bundle, the strong tBuOK does, as indicated by both lumi- nescence and 1 H NMR spectroscopy. While deprotonation undoubtedly loos- ens up the interlocked structure of the molecular bundle by replacing relative- ly strong N + H¥¥¥O hydrogen bonds by much weaker NH¥¥¥O ones, the p¥¥¥p stacking interactions ensure that any structural changes are inconsequential, particularly when the temperature of the solution of the neutral molecular bundle in dichloromethane is cooled down to considerably below room tem- perature.