Assembly of [2 + 2] bimetallic macrocyclic complexes from bis(bipyridyl) ligands and metal ions

Abstract

Two new ligands L1 and L2, in which 6,6′-dimethyl-2,2′-bipyridyl groups are attached at the 6-position to 2,6-naphthalene or 2,7-pyrene via ether bridges, have been synthesised. In the presence of Cu1, L1 forms equal amounts of two [2 + 2] complexes [Cu2L12][PF6]2, which have been assigned tentatively to helical (1a) and non-helical (1b) forms. With ZnII, L1 forms two complexes [Zn2L12][CF3SO3] 4, tentatively assigned to the helical (3a) and non-helical (3b) forms, in the ratio ≈7:4. The relative populations of 3a and 3b are temperature and solvent dependent. Ligand L2 forms equal amounts of helical and non-helical complexes [Cu2L22][PF6]2 2a, 2b with CuI. However, in the presence of ZnII, L2 forms exclusively one complex, which has been assigned as the non-helical species [ZnL22][CF3SO3]4 4b, on the basis of NMR data. In this complex, the pyrene rings are rotating rapidly on the NMR time-scale at 300 K. Molecular modelling suggests that the size and interior of the cavities of these macrocycles are ideal for encapsulation of charged aromatic substrates. Show more