Mechanical Bonds and Topological Effects in Radical Dimer Stabilization

While mechanical bonding stabilizes tetrathiafulvalene (TTF) radical dimers, the question arises: what role does topology play in catenanes containing TTF units? Here, we report how topology, together with mechanical bonding, in isomeric [3]- and doubly interlocked [2]catenanes controls the formation of TTF radical dimers within their structural frameworks, including a ring-in-ring complex (formed between an organoplatinum square and a {2+2} macrocyclic polyether containing two 1,5-dioxynaphthalene (DNP) and two TTF units) that is topologically isomeric with the doubly interlocked [2]catenane. The separate TTF units in the two {1+1} macrocycles (each containing also one DNP unit) of the isomeric [3]catenane exhibit slightly different redox properties compared with those in the {2+2} macrocycle present in the [2]catenane, while comparison with its topological isomer reveals substantially different redox behavior. Although the stabilities of the mixed-valence (TTF2)^(•+) dimers are similar in the two catenanes, the radical cationic (TTF^(•+))_2 dimer in the [2]catenane occurs only fleetingly compared with its prominent existence in the [3]catenane, while both dimers are absent altogether in the ring-in-ring complex. The electrochemical behavior of these three radically configurable isomers demonstrates that a fundamental relationship exists between topology and redox properties

Catenanes, rotaxanes and pretzelanes-template synthesis and chirality*

Abstract: Catenanes and Rotaxanes of the amide-type have been obtained in remarkable yields via supramolecular template syntheses. The amide-based structures can be designed by appropriate choice of building units. The regioselective synthesis of stable Catenanes and Rotaxanes of the amide type (cf. 4) can be prepared by using a nonionic supramolecular template effect. The regioselective synthesis of stable [2]catenane isomers allowed us to draw conclusions about their mechanism of formation [1]. AMIDE-BASED ROTAXANES Tetralactams of the type 1 form 'orthogonal key-lock-interactions' (cf. 3) with guest molecules containing amide units, which are mainly stabilized by H-bonds. The 'threading method' shown in scheme 1 allowed us to synthesize a number of rotaxanes with yields up to 50% A second method of forming rotaxanes is the 'slipping process' Evaluation of the deslipping kinetics showed a significant faster disassembling of the rotaxane 5 compared to 6, whereas the activation energy for the deslipping reaction was found to be of the same order. We attribute this remarkable fact to the lack of hydrogen bonds between wheel and hydrocarbon axle in rotaxane 5 which causes the wheel to strike more often against the stoppers than in rotaxane 6, and consequently the statistical probability for the wheel to slip over the hydrocarbon axle's stoppers is enhanced. The synthesis of rotaxanes 7-10 containing urea and carbamate units in the axle by a threadin