Design and synthesis of binucleating macrocyclic clefts derived from Schiff-base calixpyrroles

The syntheses, characterisation and complexation reactions of a series of binucleating Schiff-base calix-pyrrole macrocycles are described. The acid-templated [2+2] condensations between meso-disubstituted diformyldipyrromethanes and o-phenylenediamines generate the Schiff-base pyrrolic macrocycles H4L1 to H4L6 upon basic workup. The single-crystal X-ray structures of both H4L3 center dot 2 EtOH and H4L6 center dot H2O confirm that [2+2] cyclisation has occurred, with either EtOH or 11,0 hydrogen-bonded within the macrocyclic cleft. A series of complexation reactions generate the dipalladiurn [Pd-2(L)] (L = L-1 to L-5), dinickel [Ni-2(L-1)] and dicopper [Cu-2(L)] (L = L-1 to L 3) complexes. All of these complexes have been structurally characterised in the solid state and are found to adopt wedged structures that are enforced by the rigidity of the aryl backbone to give a cleft reminiscent of the structures of Pacman porphyrins. The binuclear nickel complexes [Ni-2(mu-OMe)(2)Cl-2(HOMe)(2)(H4L1)] and [Ni-2(mu- OH)(2)Cl-2(HOMe)(H4L5)] have also been prepared, although in these cases the solid-state structures show that the macrocyclic ligand remains protonated at the pyrrolic nitrogen atoms, and the Ni-II cations are therefore co-ordinated by the imine nitrogen atoms only to give an open conformation for the complex. The dicopper complex [Cu-2(L-3)] was crystallised in the presence of pyridine to form the adduct [Cu-2(py)(L-3)], in which, in the solid state, the pyridine ligand is bound within the binuclear molecular cleft. Reaction between H4L1 and [Mn(thf){N(SiMe3)(2)}(2)] results in clean formation of the dimanganese complex [Mn-2(L-1)], which, upon crystallisation, formed the mixed-valent complex [Mn-2(mu-OH)(L-1)] in which the hydroxo ligand bridges the metal centres within the molecular cleft.