Electrochemically Induced Dynamics of a Benzylic Amide [2]Catenane

The electrochemistry of a benzylic amide [2]catenane was investigated and compared to that of its topologically trivial components. The redox behavior of both the catenane and the uninterlocked macrocycle can be largely understood in terms of the electrochemistry of smaller molecular fragments and simple molecular orbital considerations that show that the electroactivity of the C=O groups is split into two sets of quasi-degenerate potentials separated by a substantial gap. A fast intermolecular reaction follows the reduction of the macrocycle and smaller fragments, consistent with the corresponding dimers containing a new C-C bond linking two reduced carbonyls. The cyclic voltammetric behavior of the catenane differs significantly from that of the macrocycle-a feature that must therefore be directly attributable to the mechanically interlocked molecular architecture of the catenane. In particular, an intramolecular reaction (irreversible in the CV time scale) occurs in the catenane, which is shown to be a function of temperature and scan rate. Simulation of the cyclic voltammograms shows that the intramolecular reaction occurs on a time scale wider than that of circumrotation of the two rings in the neutral molecule, thus excluding that cyclic voltammetry (CV) is monitoring the latter process. Both the analysis of the electrochemical data and semiempirical quantum chemical (MNDO) calculations would suggest that the electrochemically induced reaction in the catenane is the soldering of the two interlocked macrocycles: the formation of a C-C bond between two reduced carbonyl groups would thus prevent further rotation of the two interlocked rings.