TY  - JOUR
A1  - Kirchner, Philipp H.
A1  - Schramm, Louis
A1  - Ivanova, Svetlana
A1  - Shoyama, Kazutaka
A1  - Würthner, Frank
A1  - Beuerle, Florian
T1  - A water-stable boronate ester cage
JF  - Journal of the American Chemical Society
N2  - The reversible condensation of catechols and boronic acids to boronate esters is a paradigm reaction in dynamic covalent chemistry. However, facile backward hydrolysis is detrimental for stability and has so far prevented applications for boronate-based materials. Here, we introduce cubic boronate ester cages 6 derived from hexahydroxy tribenzotriquinacenes and phenylene diboronic acids with ortho-t-butyl substituents. Due to steric shielding, dynamic exchange at the Lewis acidic boron sites is feasible only under acid or base catalysis but fully prevented at neutral conditions. For the first time, boronate ester cages 6 tolerate substantial amounts of water or alcohols both in solution and solid state. The unprecedented applicability of these materials under ambient and aqueous conditions is showcased by efficient encapsulation and on-demand release of β-carotene dyes and heterogeneous water oxidation catalysis after the encapsulation of ruthenium catalysts.
KW  - absorption
KW  - hydrocarbons
KW  - materials
KW  - organic compounds
KW  - stability
KW  - boronate esters
Y1  - 2024
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-361245
SN  - 0002-7863
VL  - 146
IS  - 8
ER  - 
TY  - JOUR
A1  - Noll, Niklas
A1  - Groß, Tobias
A1  - Shoyama, Kazutaka
A1  - Beuerle, Florian
A1  - Würthner, Frank
T1  - Folding‐Induced Promotion of Proton‐Coupled Electron Transfers via Proximal Base for Light‐Driven Water Oxidation
JF  - Angewandte Chemie International Edition
N2  - Proton‐coupled electron‐transfer (PCET) processes play a key role in biocatalytic energy conversion and storage, for example, photosynthesis or nitrogen fixation. Here, we report a series of bipyridine‐containing di‐ to tetranuclear Ru(bda) macrocycles 2 C–4 C (bda: 2,2′‐bipyridine‐6,6′‐dicarboxylate) to promote O−O bond formation. In photocatalytic water oxidation under neutral conditions, all complexes 2 C–4 C prevail in a folded conformation that support the water nucleophilic attack (WNA) pathway with remarkable turnover frequencies of up to 15.5 s\(^{−1}\) per Ru unit respectively. Single‐crystal X‐ray analysis revealed an increased tendency for intramolecular π‐π stacking and preorganization of the proximal bases close to the active centers for the larger macrocycles. H/D kinetic isotope effect studies and electrochemical data demonstrate the key role of the proximal bipyridines as proton acceptors in lowering the activation barrier for the crucial nucleophilic attack of H\(_{2}\)O in the WNA mechanism.
KW  - artificial photosynthesis
KW  - folded macrocyles
KW  - homogeneous catalysis
KW  - photocatalysis
KW  - Ruthenium complexes
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-312020
VL  - 62
IS  - 7
ER  -