Static and Dynamic Stereochemistry of Tris(9-triptycyl)stannane Derivatives

Abstract

Abstract Static and dynamic stereochemistry of several tris(9-triptycyl)stannane derivatives Tp3SnX (X = H, halogens, and alkyl groups) were studied. X-ray crystallography of the bromo and methyl compounds showed that the Sn atom was fundamentally tetrahedral and that the three Tp groups meshed with each other like bevel gears and formed a near-C3 chiral conformation. The rate constants for enantiomerization of the chiral conformation in solution could be obtained by the lineshape analysis of the aromatic proton signals, even when a direct probe for enantiomerization such as a benzyl group was absent. The energy barrier to enantiomerization decreased as the substituent X became bulkier, suggesting that the ground state is more destabilized than the transition state upon introduction of a bulkier group.