1,4, 7-Triazacyclononane and N, N’, N”-trimethyl-1 “-trimethyl-1, 4, 7-triazacyclononane - two versatile macrocycles for the synthesis of monomeric and oligomeric metal complexes

Abstract

The tridentate, saturated macrocyclic ligand 1,4,7- triazacyclononane (L) forms stable pseudo-octahedral 2:1 com-plexes, ML2n+, with a large number of main group and transition metals in various and in some instance unusual oxidation states. In contrast, N, N’, N“-trimethyl-1,4,7-triazacyclononane (L' ‘) forms only 1:1 complexes, L'MXn (n= 1/2,3). In complexes of this type the macrocycles function as effective blocking group for three coordination sites of a given metal center. The reactivity of this center may then be exploited by its oxidation or reduction or, alternatively, the unidentate ligands X may be substituted or reactions occurring at the coordinated ligand X may be studied. LMX3 and L'MX3 complexes are useful starting materials for the syntheses of binuclear complexes, [LM(bridge)n Ml], containing a variety of bridging groups (02-, OH-, N3-; NCS-, [CrO4]2-, [MoO4]2-, R-CO2). In cases where M represents a paramagnetic transition metal center intramolecular spin exchange coupling phenomena are readily studied. The formation of oxo/hydroxo complexes of higher nuclearity (2–8) on hydrolysis of mononuclear LMX3 complexes has been observed: [([9]aneN3)4M406]4+ (M = Ti(IV), Mn(IV)) [([9]aneN3)6Fe8(μ-0)2 (μ-OH)12]8+, [([9]aneN3)3Cr3(OH)5]4+. Some of these species serve as model compounds for the active sites in metalloproteins which contain two or more metal ions per subunit. © 1988 IUPAC