Twin Triptycyl Spinning Tops: A Simple Case of Molecular Gearing with Dynamic <i>C</i><sub>2</sub> Symmetry

AbstractLithiation and subsequent oxidation of the recently described prototype molecular paddlewheel 9‐(2‐indenyl)triptycene (1) leads to the racemic dimer 2,2′‐bis(9‐triptycyl)‐1,1′‐biindenyl (4). In the solid state this very congested molecule adopts a conformation in which the two triptycenyl paddlewheel fragments are attached to the C2‐symmetric biindenyl core. However, the orientation of the triptycene blades, dictated by their size and shape, is gear‐like and breaks the nascent C2‐symmetry of the whole molecule. Nevertheless, effective C2‐symmetry is restored in solution when the triptycene paddlewheels, although apparently tightly interlocked, undergo rapid contra‐rotation on the NMR time‐scale. The analogous reaction of (2‐phenylindenyl)lithium (6), likewise yields racemic (RR/SS) 2,2′‐diphenyl‐1,1′‐biindenyl(7). Interestingly, although the treatment of 6 with a CuII salt leads to both rac‐7 and its diastereomer meso‐7, the reaction of 6 and 2‐phenylindenyl bromide furnishes selectively rac‐7. Overall, these data suggest that the oxidative dimerisation to yield racemic products occurs through a nucleophilic substitution mechanism. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Twin Triptycyl Spinning Tops: A Simple Case of Molecular Gearing with Dynamic C₂ Symmetry Journal Articles