Barium Templating Schiff-Base Lateral Macrobicycles
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Published on: June 5, 2021
David Esteban1, Daniel Bañobre, Rufina Bastida
1Departamento de Química Fundamental e Industrial, Universidade da Coruña, Campus da Zapateira s/n 15071 La Coruña, Spain, Departamento de Química Inorgánica, Universidad de Santiago, Avda. de las Ciencias s/n 15706, Santiago de Compostela, Spain, Chemistry Department, The University, Sheffield S3 7HF, U.K., and Servicios Xerais de Apoio á Investigación, Universidade da Coruña, Spain.
Abstract:
Schiff-base lateral macrobicycles containing two different binding units, a rigid and unsaturated N(2)X set (X: N, O) and a flexible and cyclic N(2)O(n)() set, linked by two aromatic bridges, have been prepared by reaction of the appropriate bibracchial diamines N,N'-bis(aminobenzyl)-diaza-crown and diformyl precursors in the presence of Ba(II) as templating agent. The expected cryptands do not form in the absence of the cation; the presence of this metal ion is necessary to orient the diamine precursor in a syn conformation. Comparison of the X-ray crystal structures of the barium complex of the bibracchial diamine N,N'-bis(2-aminobenzyl)-1,10-diaza-15-crown-5 and the barium complex of the cryptand derived from it incorporating a pyridine unit indicates that the encapsulation of the metal ion is clearly more effective in the case of the cryptand. The coordination of Ba(II) ion to the pyridine nitrogen atom promotes the displacement of the metal into the cavity of the cryptand as well as important changes in the conformation of the crown unit, although the fold of the pendant arms remains practically unchanged. The cryptands reported constitute the first example of a novel family of macrobicycles.
