Wts. Huck et al., SYNTHESIS OF NEW MACROCYCLIC LIGANDS FOR HETERO-MULTINUCLEAR TRANSITION-METAL COMPLEXES, Recueil des travaux chimiques des Pays-Bas, 114(6), 1995, pp. 273-276
The [3 + 3] macrocyclic compounds 2a-2c were easily prepared by cycliz
ation of the dialdehyde 8 with the appropiate diamines in refluxing CH
3CN/MeOH (1/1), in the presence of Ba2+ as a template ion. These macro
cycles contain three salen units and are therefore, in combination wit
h the crown ether interior, potentially tetranucleating. The length of
the diamine bridge and the temperature at which the reaction is carri
ed out, appear to influence the size of the macrocycle formed. In this
way, the [4 + 4] macrocycle 2d could be formed selectively over the [
3 + 3] macrocycles by carrying out the reaction at room temperature.