Dynamic Stereochemistry ofN-Phenyl-9-triptycylamine and ItsN-Alkyl Derivatives

In N-phenyl-9-triptycylamine (6), “gear rotation” (GR) and “isolated rotation” (IR) have almost the same free-energy barriers of ca. 45.2 kJ mol−1, while the nitrogen inversion is fast throughout the whole temperature range and thus the nitrogen is regarded as planar on the NMR timescale. In N-methyl-N-phenyl-9-triptycylamine (7), the internal motions are fast on the NMR time scale even at the lowest attainable temperature. In N-benzyl-N-phenyl-9-triptycylamine (8), the GR process has a free-energy barrier of ca. 36 kJ mol−1 and the passing of the benzyl group over an o-benzeno group has a higher barrier than GR. N-2-Biphenylyl-9-triptycylamine (9), which is obtained during the course of the synthesis of 6, shows a dynamic behavior presumably ascribable to GR with the free-energy barrier of 70 kJ mol−1.