jo0515430_si_001.pdf (34.63 kB)
Inherently Chiral Uranyl-Salophen Macrocycles: Computer-Aided Design and Resolution
journal contribution
posted on 2005-11-25, 00:00 authored by Antonella Dalla Cort, Luigi Mandolini, Chiara Pasquini, Luca SchiaffinoA flipping motion rapidly inverts the bent structure of uranyl-salophen compounds and, consequently, causes fast enantiomerization of nonsymmetrically substituted derivatives. This process
has been previously slowed by introducing bulky substituents in the imine bond region. Since the
resulting complexes dissociate upon chromatographic treatment, an alternative approach to the
design and synthesis of robust, nonflipping uranyl-salophen compounds is here described. Such an
approach is based on the idea that the flipping motion would be blocked by connecting the para
positions with respect to the phenoxide oxygens by means of polymethylene bridges of suitable
length. Analysis of a number of uranyl-salophen compounds by molecular mechanics, while showing
that bulky substituents in the imine bond region cause severe distortions of the ligand backbone,
suggested that the best chain lengths are those that fit the gap between the phenoxide rings without
altering the natural geometry of the parent uranyl-salophen compound. Calculations showed that
such chains are those composed of 12 and 13 methylene units. Accordingly, chiral uranyl-salophen
macrocycles bridged with 12- and 13-methylene chains were synthesized in fairly good yields and
resolved by chiral HPLC.