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The synthesis and coordination chemistry of two novel ligands, 2,6,9,12,16-pentaaza[17]metacyclophane (L1) and 2,6,9,12,16-pentaaza[17]paracyclophane (L2), is described. Potentiometric studies indicate that L1 and L2 form a variety of mononuclear complexes the stability constants of which reveal a change in the denticity of the ligand when moving from L1 to L2, a behaviour that can be qualitatively explained by the inability of the paracyclophanes to simultaneously use both benzylic nitrogen atoms for coordination to a single metal centre. In contrast, the formation of dinuclear hydroxylated complexes is more favoured for the paraL2 ligand. DFT calculations have been carried out to compare the geometries and relative energies of isomeric forms of the [CuL]2+ complexes of L1 and L2 in which the cyclophane acts either as tri- or tetradentate. The results indicate that the energy cost associated with a change in the coordination mode of the cyclophane from tri- to tetradentate is moderate for both ligands so that the actual coordination mode can be determined not only by the characteristics of the first coordination sphere but also by the specific interactions with additional nearby water molecules. The kinetics of the acid promoted decomposition of the mono- and dinuclear CuII complexes of both cyclophanes have also been studied. For both ligands, dinuclear complexes convert rapidly to mononuclear species upon addition of excess acid, the release of the first metal ion occurring within the mixing time of the stopped-flow instrument. Decomposition of the mononuclear [CuL2]2+ and [CuHL2]3+ species occurs with the same kinetics, thus showing that protonation of [CuL2]2+ occurs at an uncoordinated amine group. In contrast, the [CuL1]2+ and [CuHL1]3+ species show different decomposition kinetics indicating the existence of significant structural reorganisation upon protonation of the [CuL1]2+ species. The interaction of AMP with the protonated forms of the cyclophanes and the formation of mixed complexes in the systems Cu–L1-AMP, Cu–L2-AMP, and Cu–L3-AMP, where L3 is the related pyridinophane containing the same polyamine chain and 2,6-dimethylpyridine as a spacer, is also reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The o-B232, m-B232 and p-B232 cyclophanes result from attaching the terminal amine groups of 1,4,8,11-tetraazaundecane (232) to the benzylic carbons of the corresponding o-, m- or p-xylanes. The cavity size of these cyclophanes changes moderately as a consequence of the substitution at the aromatic ring. The effects caused by these changes on the equilibrium constants for protonation and CuII complex formation of the cyclophanes are analyzed and compared with those of the noncyclic 232 polyamine. All three cyclophanes form mononuclear complexes, but only o-B232 is able to coordinate to CuII through the four amine groups simultaneously, whereas m-B232 and p-B232 can only use three nitrogen donors. The larger cavity and higher flexibility of the latter two cyclophanes allow them to form stable dinuclear CuII complexes. The kinetics of the acid-promoted dissociation of CuII from its mono- and dinuclear complexes has also been studied and the results indicate the existence of large differences in the kinetic properties for the complexes with these three closely related ligands. Whereas the mononuclear m-B232 and p-B232 complexes decompose with very similar kinetic behaviour to that of the Cu(232)2+ complex, the lability of the Cu–N bonds is largely reduced in the Cu(o-B232)2+ complex, and this leads to slower decomposition and even to a different rate law for this complex. The dinuclear complexes are not formed with o-B232, and very different decomposition kinetics is observed for the complexes formed by m-B232 and p-B232. In the case of m-B232, the two metal ions are situated very close to each other, which causes a rapid release of one of them upon reaction with acid. In contrast, the larger size of p-B232 allows it to accommodate two metal ions without important electrostatic or steric interactions so that they are released with statistically controlled kinetics.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

An aza-terpyridinophane receptor containing the polyamine 4,7,10,13-tetraazahexadecane-1,16-diamine linked through methylene groups to the 5,5″ positions of a terpyridine unit has been prepared and characterized (L). The acid-base behaviour, CuII speciation and ability to form ternary complexes (CuII-L-carbonate) have been explored by potentiometric titrations in 0.15 M NaClO4 and by UV/Vis and paramagnetic NMR spectroscopy. Comparisons are made with a previously reported terpyridinophane containing the polyamine 4,7,10-triazatridecane-1,13-diamine (L1). For this latter receptor, reductive coupling between indigo and carbon dioxide at indigo-modified electrodes produces carboxylated derivatives via a solid-state reaction under electrochemical activation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)