TEMPLATE SYNTHESIS OF A TETRAAZA MACROCYCLE WHICH INVOLVES BENZALDEHYDE RATHER THAN FORMALDEHYDE AS A BUILDING-BLOCK ISOLATION AND STRUCTURE DETERMINATION OF THE OPEN-CHAIN SCHIFF-BASE INTERMEDIATE COMPLEX

The classical formaldehyde building block has been replaced by the bul kier benzaldehyde in the Cu-II template synthesis of the cyclam-like t etraaza macrocycle of type 1, in which nitroethane operated as locking fragment. The synthetic pathway involves three distinct steps: (i) Sc hiff base condensation of the metal-free open-chain tetramine; (ii) Cu -II coordination and preorientation of the Schiff base; (iii) nucleoph ilic attack by the deprotonared nitroethane fragment and formation of the macrocyclic complex, Both the Schiff base Cu-II complex and the Cu -II macrocyclic complex were isolated in a crystalline form and their molecular structures were determined: eneamino)ethyl]-N'-[2-((Z)-benzy lideneamino)ethyl] propane-1,3-diamine}copper(II) nitrate: triclinic, space group P (1) over bar, with a = 12.296(5) Angstrom, b = 10.787(6) Angstrom, c = 10.547(7) Angstrom, V = 1161(1) Angstrom(3), and Z = 2 (R = 0.055, R(w) = 0.061); eny-1,4,8,11-tetraazacyclotetradecane]coppe r-(II)) perchlorate: monoclinic, space group P2(1)/n, with a = 15.246( 5) Angstrom, b = 23240(7) Angstrom, c = 8.540(4) Angstrom, V = 2980(2) Angstrom(3), and Z = 4 (R = 0.095, R(w) = 0.095). This allowed us to define mechanistic details of the macrocyclization process. It is sugg ested that the same three-step pathway takes place in the much easier and faster one-pot template syntheses of cyclam-like macrocyles, which involve formaldehyde as a building block.