Template synthesis of the macrobicyclic ligand 1,5,8,12,15-pentaazabicyclo[10.5.2]nonadecane: evidence for imidate and enamine intermediates stabilized by copper(II)

The pentadentate macrobicyclic ligand 1,5,8,12,15-pentaazabicyclo [10.5.2] nonadecane, in which 1,4,7-triazacyclononane and cyclam (1,4,8,11-tetraazacyclotetradecane) are «fused», has been synthesized. The reactions involve condensation of [N,N'-bis(aminopropyl)-1,4,7-triazacyclononane] copper(II), [Cu(L)] 2+ , with glyoxal followed by reduction and demetalation. This process represents one of the few successful ring-closure condensations of this type at a copper center. A detailed mechanism, involving two unusual intermediates that have been isolated and characterized, is provided