Tetramine complexes, macrocyclic

Formation and dissociation kinetics of nine Ni(II)-macrocyclic tetra-thiaether complexes (eight macrocyclic, one linear in acetonitrile) have been compared with those for Cu(II) analogues and for Ni(II) complexes with macrocylic tetramines (262). Whereas for the tetramine complexes conformational changes may be apparent in the kinetics this is not the case for the tetrathiaether complexes, where there is no kinetic evidence for slow conformational changes after initial bonding of the ligand to... 

S.3. Macrocyclic Ligands. In a similar way as for linear tetramines, complexes with macrocyclic ligands of the type 30 and 31 offer certain interesting stereochemical aspects. A considerable number of isomers is possible by the presence of the four... 

Cabbiness, D. K., Margerum, D. W, Macrocyclic effect on the stability of copper(ll) tetramine complexes. J. Am. Chem. 

The generality of the formaldehyde/nitroethane approach for macrocyclisation of linear tetramines has further been extended [178, 179]. By replacing nitroethane by a variety of other -C-H acids, such as 1-nitrododecane, 12-nitrododecanoic acid, 3-nitropropanoic acid, tetrahydro-2-(2 -nitroethoxy)-2H-pyran, l-nitro-3-(2-nitroethylbenzene), l-nitro-4-(2-nitroethylbenzene) and 2-phenylnitroethane, several macrocyclic tetramine complexes of the types [M(L143)] + and [M(L145)] + have been prepared (Eq. 2.86). 

Macrocyclic Ns complexes have been prepared from 2,6-diacetylpyridine and an appropriate tetramine using template methods. The crystal structures of two silver(I) complexes containing the ligands 3,2,3-N5 (58) and 2,3,2-Ns (59) have been determined.452,453... 

The tetraza macrocycle (150 LH4), with four ethanoate groups, is readily prepared by treatment of the cyclic tetramine with bromoethanoic acid.1101 Its complex [ZnLH2j utilizes two amino N atoms and two carboxylates as ligands. The fully deprotonated complex may be prepared in solution by treatment with NaOH. 

Examples of seven-coordination in pyridine-containing macrocycles have also been osberved. Thus the iron(TI) complexes [Fe(L)X,] xhLO (L = 126 X = halide or pseudohalide) are formed923 when the corresponding seven-coordinate iron(lll) complexes are reduced with aqueous sodium dithionite in the presence of excess NaX or by the direct template synthesis with 2,6-diacetylpyridine and the corresponding tetramine in the presence of iron(IJ). The triimine moiety gives rise to a strong... 

A second class of MRI contrast agents contains ligands that are derivatives of the macrocyclic tetramine, 1.4.7.10-tetraazacyclododecane (cyclen). Gadoterate (Dotarem, Gd-DOTA, Scheme 3, formula 5) was the first macrocyclic gadolinium complex which has entered the market. 

As far as quadridentate ligands are concerned, the easiest attainment of the Ni state, denoted by the less positive redox potential, is observed with the 14-membered macrocycle, 5, known as cyclam. Both contraction and expansion of tetramine ring atomicity, to 12 and to 16, respectively, makes the potential more positive, thus destabilizing Ni with respect to Ni Moreover, the isomeric 14-membered macrocycle, 6 (isocyclam) stabilizes the Ni state to a much lesser extent than cyclam. Notice that the two macrocyclic complexes simply differ in the sequence of the five-... 

Complexes of 14-membered macrocyclic tetramines (cyclams) and their use in medicine 04CSR246. 

According to the modular approach, components of the fluorosensor can be changed at will. For instance, it could be of some interest to replace the quad-ridentate receptors of systems 4 and 5 by their cyclic counterparts, to obtain 6 and 7 [8]. The reason of the interest is that, ceteris paribus, cyclic ligands form more stable metal complexes than their open-chain analogues (the thermodynamic macrocyclic effect [12]). The tetramine receptor in 6 has the skeleton of the classical 14-membered macrocycle cyclam, whereas the receptor subunit of 7 refers to the other well-known object of macrocyclic chemistry dioxocyclam. 

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