Pseudorotaxanes and Rotaxanes Formed by Viologen Derivatives

<jats:title>Abstract</jats:title><jats:p>Dibenzyl‐4,4′‐bipyridinium (<jats:bold>BIPY<jats:sup>2+</jats:sup></jats:bold>) bis(hexafluorophosphate) and three of its derivatives – disubstituted at the <jats:italic>para</jats:italic> positions of the benzyl groups with CO<jats:sub>2</jats:sub>Me, F, and Me in turn – have been shown to form 1:1 complexes that are [2]pseudorotaxanes with dibenzo[24]crown‐8 (<jats:bold>DB24C8</jats:bold>), benzometaphenylene[25]crown‐8 (<jats:bold>BMP25C8</jats:bold>), and dipyrido[24]crown‐8 (<jats:bold>DP24C8</jats:bold>) in CD<jats:sub>3</jats:sub>CN solution by <jats:sup>1</jats:sup>H NMR spectroscopy and in one case in the solid state by X‐ray crystallography. Binding constants (<jats:italic>K</jats:italic><jats:sub>a</jats:sub>) for all of these 1:1 complexes, which were determined both (1) by isothermal titration calorimetry in MeCN solution and (2) by the <jats:sup>1</jats:sup>H NMR spectroscopic single‐point method in CD<jats:sub>3</jats:sub>CN solution, were found to be, on the average, an order of magnitude less than the <jats:italic>K</jats:italic><jats:sub>a</jats:sub> values obtained for <jats:bold>DB24C8</jats:bold> and <jats:bold>DP24C8</jats:bold> with dibenzylammonium (<jats:bold>DBA<jats:sup>+</jats:sup></jats:bold>) hexafluorophosphate and three of its derivatives, also disubstituted at the <jats:italic>para</jats:italic> positions of the benzyl groups with CO<jats:sub>2</jats:sub>Me, F and Me. In the case of <jats:bold>BMP25C8</jats:bold>, however, the <jats:italic>K</jats:italic><jats:sub>a</jats:sub> values with both categories (<jats:bold>BIPY<jats:sup>2+</jats:sup></jats:bold> and <jats:bold>DBA<jats:sup>+</jats:sup></jats:bold>) of guests are much of a muchness, being both small and error prone. The equilibrium thermodynamics for these small libraries of [2]pseudorotaxanes indicate that the best bistable [2]rotaxanes incorporating both <jats:bold>DBA<jats:sup>+</jats:sup></jats:bold> and <jats:bold>BIPY<jats:sup>2+</jats:sup></jats:bold> recognition sites are going to involve ester functions in their dumbbell components and will employ <jats:bold>DP24C8</jats:bold> or, failing that, <jats:bold>DB24C8</jats:bold> as the ring component. The <jats:bold>BIPY<jats:sup>2+</jats:sup></jats:bold>threads also directed the templated assembly of [2]rotaxanes incorporating the crown ethers (<jats:bold>DB24C8</jats:bold>, <jats:bold>DP24C8</jats:bold>, and <jats:bold>BMP25C8</jats:bold>) and triphenylphosphonium stoppers using the threading followed by stoppering approach. The rotaxanes were characterized in solution by <jats:sup>1</jats:sup>H NMR spectroscopy, and in one case, in the solid state by X‐ray crystallography.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)</jats:p>