| Abstract
| - A series of newdioxocyclams with pendant phenol groups have been synthesized.Dioxocyclam derivatives deprotonate in a stepwise manner whencoordinated to cupric ions in aqueous solution. X-ray crystalstructure shows that the enolic tautomer of an amido group wascoordinated to the cupric ion. Ligands with bromo-substituentprobably form zwitterions near pH 9.4. While other ligands formordinary ampholytes near that pH. The pKaof the enolic tautomers are rather constant at 4.2−4.3 for all thecomplexes.
- A series of new dioxocyclams with pendant phenol groups has beensynthesized from coumarin 3-carboxylicester and linear polyamines in refluxing methanol/ethanol.Corresponding saturated cyclam derivatives wereobtained by B2 H6·THF reduction.Reaction of a dioxocylam derivative withCu(ClO4)2 in aqueous solutionyields a singly deprotonated dioxotetraamine copper(II) complex,whose X-ray crystal structure has shown thatthe enolic tautomer of an amido group was coordinated tocopper(II). X-ray crystal data for[C17H25N4O3Cu]ClO4·H2O: monoclinic, space groupP21/a, a =15.554(3) Å, b = 8.478(2) Å, c =17.250(3) Å, β = 111.4(1)°,V = 2117(1) Å3, Z = 4,Dc = 1.614 mg/mm3,F(000) = 1068, R = 0.040 andRw = 0.044. When coordinatedto copper(II), the amido group deprotonates withpKa = 4.3. Potentiometric,electrochemical, and EPR spectraldata of the complexes were studied. In the pH region 3−9, thesubstituent phenol does not coordinate to thecopper(II) ion; however, substituents do have some effect on theirCu(II)/Cu(III) potential and complex stability.In this study, we show that, besides doubly deprotonatedcopper(II) complexes, singly deprotonateddioxotetraaminecomplexes also exist both in aqueous solution and in the solid statewith considerable stability. The existence ofthe singly deprotonated dioxotetraamine copper(II) complexundoubtedly indicates that the complex deprotonatesstepwise and not simutaneous. This is a new conceptual discovery.The results provide us critical evidence fora discussion of the detailed mechanism of complex formation and aciddissociation.
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