Selective Endo and Exo Binding of Mono- and Ditopic Ligands to a Rhomboidal Diporphyrin Prism

Copper(I) can preferentially form heteroleptic complexes containing two phosphine and two nitrogen donors due to steric factors. This preference was employed to direct the self-assembly of a porphyrin-faced rhomboidal prism having two parallel tetrakis(4-iminopyridyl)porphyrinatozinc(II) faces linked by eight 1,4-bis(diphenylphosphino)benzene pillars. The coordination preferences of the Cu-I ions and geometries of the ligands come together to generate a slipped-cofacial orientation of the porphyrinatozinc(II) faces. This orientation enables selective encapsulation of 3,3-bipyridine (bipy), which bridges the Zn-II ions of the parallel porphyrins, whereas 4,4-bipy exhibits weaker external coordination to the porphyrin faces. Reaction with 2,2-bipy, by contrast, results in the displacement of the tetratopic porphyrin ligand and formation of [{(2,2-bipy)Cu-I}(2)(diphosphine)(2)]. The differing strengths of interactions of bipyridine isomers with the system allows for a hierarchy to be deciphered, whereby 4,4-bipy may be displaced by 3,3-bipy, which in turn is displaced by 2,2-bipy.