Steric Restraints in Redox‐Active Guanidine Ligands and Their Impact on Coordination Chemistry
Eliane Engels, Hanna Koepcke, Marko Lörsch, Patrick David Römgens, Anna Katharina Helm, Simone Leingang, Elisabeth Kaifer, Hans‐Jörg Himmel
TL;DR
Researchers synthesized new benzene ligands with guanidino groups and found that slight structural changes affect their ability to coordinate with metals.
Contribution
The first synthesis of cyclic diguanidino-benzene ligands and the discovery of structural parameters affecting coordination ability.
Findings
An ethylene bridge prevents coordination while maintaining basicity, similar to Huenig's base.
A propylene bridge restores coordination ability without losing nucleophilic properties.
Macrocyclic tetraguanidines were formed and analyzed for structural restraints.
Abstract
The introduction of redox‐active ligands into coordination compounds is attractive for a number of applications; intramolecular electron transfer between a redox‐active ligand and a metal is the basis for applications in switchable devices and advanced redox catalysis for multielectron substrate activations. A fine‐tuning of the properties of redox‐active ligands focusses on the redox potential and frontier orbital energies, as well as the steric demand and coordination mode. In this work, we report the first synthesis of new o‐diguanidino‐benzene ligands in which the two guanidino groups are connected through an alkyl chain of different length. The introduction of an ethylene bridge between the two guanidino groups turns a strongly coordinating ligand into a noncoordinating molecule, while keeping its strong Brønsted basicity. These features qualify the ethylene‐bridged compound as a…
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Taxonomy
TopicsMetal-Organic Frameworks: Synthesis and Applications · Metal complexes synthesis and properties · N-Heterocyclic Carbenes in Organic and Inorganic Chemistry