Heteroleptic Ligation by an endo-Functionalized Cage

A conceptual approach for the synthesis of quasi-heteroleptic complexes with properly endo-functionalized cages as ligands is presented. The cage ligand reported here is of a covalent organic nature, it has been synthesized via a dynamic combinatorial chemistry approach, making use of a masked amine. Inspired by enzymatic active sites, the described system bears one carboxylate and two imidazole moieties as independent ligating units through which it is able to coordinate to transition metals. Analysis of the iron(II) complex in solution and the solid state validates the structure and shows that no undesired but commonly observed dimerization process takes place. The solid-state structure shows a five-coordinate metal center with the carboxylate bidentately bound to iron, which makes Fe@2 an unprecedentedly detailed structural model complex for this kind of non-heme iron oxygenases. As, as confirmed by the crystal structure, sufficient space for other organic ligands is available, the biologically relevant ligand alpha-ketoglutarate is implemented. We observe biomimetic reaction behavior towards dioxygen that opens studies investigating Fe@2 as a functional model complex.

Automated summary

A conceptual approach for the synthesis of quasi-heteroleptic complexes with properly endo-functionalized cages as ligands is introduced. The synthesized cage ligand, inspired by enzymatic active sites, has a covalent organic nature and demonstrates unique coordination properties to transition metals. Analysis of the iron(II) complex in both solution and solid state confirms the structure and lack of undesired dimerization, making Fe@2 a detailed structural model complex for non-heme iron oxygenases.