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Secondary Coordination Sphere Effects in Macrocycle-Embedded Mononuclear Ru(bda) Water Oxidation Catalysts
Gourab Das1, Daniel A P Friedewald1, Deqi Tang2
1Institut für Organische Chemie & Center for Nanosystems Chemistry (CNC), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
This study integrates ruthenium catalysts with different heterocycles in macrocycles, revealing how structural changes influence water oxidation mechanisms. The findings provide insights into optimizing photocatalytic water splitting for clean energy applications.
Area of Science:
- Inorganic Chemistry
- Photocatalysis
- Supramolecular Chemistry
Background:
- Ruthenium complexes with bda ligands are investigated for water oxidation.
- Macrocyclic structures incorporating heterocycles influence catalyst conformation.
- Understanding structure-activity relationships is crucial for efficient photocatalysis.
Purpose of the Study:
- To synthesize and characterize novel Ru(bda)-based macrocyclic catalysts.
- To investigate the impact of different heterocycles (dibenzofuran, dibenzothiophene, carbazole) on catalyst conformation and performance.
- To elucidate the mechanisms of photocatalytic water oxidation influenced by these structural modifications.
Main Methods:
- Synthesis of macrocyclic ligands and their complexation with Ru(bda).
- Structural characterization using NMR spectroscopy and single-crystal X-ray diffraction.
- Photocatalytic water oxidation studies, including kinetic isotope effect (H/D) measurements.
- Theoretical calculations to determine energy profiles and orientation effects.
Main Results:
- Three mononuclear Ru(bda)-based catalysts (1-3) with varying conformational preferences were synthesized.
- Noncovalent interactions (hydrogen and chalcogen bonds) dictate macrocycle conformation.
- Catalysts exhibited different water oxidation mechanisms: unimolecular (WNA) for dibenzothiophene/carbazole, and bimolecular (I2M) for dibenzofuran.
- Structure-property relationships were established, linking conformation to catalytic activity and mechanism.
Conclusions:
- The conformational preferences of macrocyclic ligands significantly influence the mechanism and rate of Ru-catalyzed water oxidation.
- Dibenzothiophene and carbazole moieties promote unimolecular pathways, while dibenzofuran favors bimolecular pathways.
- This work establishes a clear link between catalyst structure, secondary coordination sphere, and photocatalytic water oxidation efficiency.
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