Multiple hindered rotators in a gyroscope-inspired tribenzylamine hemicryptophane.

Najat S Khan, Jose Manuel Perez-Aguilar, Tara Kaufmann, P Aru Hill, Olena Taratula, One-Sun Lee, Patrick J Carroll, Jeffery G Saven, Ivan J Dmochowski

Index: J. Org. Chem. 76(5) , 1418-24, (2011)

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Abstract

A gyroscope-inspired tribenzylamine hemicryptophane provides a vehicle for exploring the structure and properties of multiple p-phenylene rotators within one molecule. The hemicryptophane was synthesized in three steps in good overall yield using mild conditions. Three rotator-forming linkers were cyclized to form a rigid cyclotriveratrylene (CTV) stator framework, which was then closed with an amine. The gyroscope-like molecule was characterized by (1)H NMR and (13)C NMR spectroscopy, and the structure was solved by X-ray crystallography. The rigidity of the two-component CTV-trismethylamine stator was investigated by (1)H variable-temperature (VT) NMR experiments and molecular dynamics simulations. These techniques identified gyration of the three p-phenylene rotators on the millisecond time scale at -93 °C, with more dynamic but still hindered motion at room temperature (27 °C). The activation energy for the p-phenylene rotation was determined to be ~10 kcal mol(-1). Due to the propeller arrangement of the p-phenylenes, their rotation is hindered but not strongly correlated. The compact size, simple synthetic route, and molecular motions of this gyroscope-inspired tribenzylamine hemicryptophane make it an attractive starting point for controlling the direction and coupling of rotators within molecular systems.