Propeller rotation of aryl groups in triarylsilanes and triarylstannanes

Rotation of aryl groups was studied in eight systems with the general struc ture Ar3MX by changes in lineshapes as a function of temperature. Steric co nstraints were varied at each of the structural components (Ar, M, X). The barrier to rotation decreased as the central atom was changed from carbon t o silicon to tin. When the substituent X was large (allyl or Cl), buttressi ng by the meta methyls in duryl raised the barrier. For X = H, however, but tressing decreased the barrier. Copyright (C) 2001 John Wiley & Sons, Ltd.