Synthesis and conformational aspects of 20- and 40-membered macrocyclic mono and dinuclear uranyl complexes incorporating salen and (R)-BINOL units

20- and 40-membered macrocyclic mono and dinuclear uranyl complexes 11–13 incorporating salen and (R)-BINOL units have been designed and synthesized starting from 4-tert-butylphenol in eight steps. NMR measurements (COSY, NOESY/EXSY) indicate that such complexes in solution are involved in conformational equilibria, which for the 20-membered derivatives are observable already at room temperature (k1=300 s−1 at 300 K) and which are probably related to a flipping motion of salicylaldehyde units. T-ROESY experiments suggest that in solution, the dinuclear complexes do not assume structures wrapped around the metal ions.