Komplexe mit makrocyclischen Liganden, II. Zweischrittmechanismus bei der Komplexbildung von Cu2+ mit meso‐5,7,7,12,14,14‐Hexamethyl‐1,4,8,11‐tetraazacyclotetradecan

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Abstract
The complex formation between CuII and the title compound (tet a) is studied by spectrophotometry and pH‐stat techniques. Between pH 4 and 5,5 the reaction proceeds in two steps, the first giving a blue intermediate, Cu(teta)2+ (blue), exhibiting a broad absorption band at 620 nm. Titration with NaOH and the absorption spectrum suggest that, in the intermediate, CuII is coordinated to only two amino groups of the ligand. Both steps are slow compared to other complex formation reactions of CuII. The rate of the first step, in which Cu(tet a)2+ (blue) is formed, is given by v1 = k1 · [Cu2+] [(tet a) H]/[H+] with k1 = 2,7 · 10−6 s−1 at 40° and I = 0,1. In the second step the last two nitrogens of the quadridentate ligand are bound to CuII, giving the mauve end product. The rate of this step is given by v2 = k2 · [Cu(tet a)OH+ (blue)] [OH−] with k2 = 1,2 · 103 M−1 s−1 at 50° and I = 0,5.