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Metal Complexes of Macrocyclic Ligands: Part XLVII - Copper(II) and Nickel(II) Complexes of 'trans'-Difunctionalized Tetraaza Macrocycles
Comparone, Antonio,Kaden, Thomas A.
, p. 1765 - 1772 (2007/10/03)
Reductive cleavage of the bis-aminal 1 of 1,4,8,11-tetraazacyclotetradecane allows a new synthesis of 1,8-dimethyl-1,4,8,11-tetraazacyclotetradecane (3), which is an ideal starting compound for preparing 'trans'-difunctionalized derivatives. Thus, 3 was reacted to give the macrocyclic diacetonitrile 5 and dipropanenitrile 9. These were reduced with Raney-Ni and H2 to the corresponding diamines 6 and 10, respectively. In addition, 5 was selectively hydrolysed to the diacetamide 7 and fully hydrolysed to the diacetic acid 8. The Cu2+ and Ni2+ complexes of these new ligands were prepared and their spectral and structural properties studied. Whereas 3 yielded square planar species, the functionalized derivatives gave penta- or hexacoordinate complexes. The ligands with amino groups in their side chains (6 and 10) formed square planar species at acidic pH (amino groups protonated), but pentacoordinate geometries resulted at alkaline pH, where one amino group underwent coordination. In contrast, the diacetic acid 8 gave distorted octahedral Cu2+ and Ni2+ complexes.
