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

Abstract

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)porphyrina- tozinc(II) faces linked by eight 1,4-bis(diphenylphosphino)- benzene pillars. The coordination preferences of the CuI 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 ZnII ions of the parallel porphyrins, whereas 4,4’-bipy exhibits weaker external coordi- nation 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)CuI}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.