Ditopic Hexadentate Ligands with a Central Dihydrobenzo-diimidazole Unit Forming a [2x2] Zn4 Grid Complex

Abstract

A family of ditopic hexadentate ligands based on the parent compound 2,6-bis(6-(pyrazol-1-yl)pyridin-2-yl)-1,5-dihydrobenzo[1,2-d:4,5-d’]diimidazole (L) was developed and synthesized by using a straightforward condensation reaction, which forms the interlinking central benzo[1,2-d:4,5-d’]diimidazole bridge in the ligand backbone. The two secondary amine groups of the benzodiimidazole unit tautomerize and allow the formation of two tauto-conformers, which upon treatment with metal salts forms different isomeric coordination complexes. Here we report six new derivatives (1–6) that can tautomerize (varying the pyrazolylpyridine part) and 14 derivatives (7–13) with different alkyl and benzyl substitution on secondary amino groups (of L) that prevent the tautomerization. This way, it is possible to study the properties of isomeric coordination complexes and their intrinsic cooperativity by the example of [2x2] grid complexes in the future. A [2x2] Zn4 complex of the ligand L was synthesized and structurally characterized.