@article{NollGrossShoyamaetal.2023,
  author    = {Noll, Niklas and Groß, Tobias and Shoyama, Kazutaka and Beuerle, Florian and W{\"u}rthner, Frank},
  title     = {Folding-Induced Promotion of Proton-Coupled Electron Transfers via Proximal Base for Light-Driven Water Oxidation},
  series = {Angewandte Chemie International Edition},
  volume    = {62},
  journal   = {Angewandte Chemie International Edition},
  number    = {7},
  doi       = {10.1002/anie.202217745},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312020},
  year      = {2023},
  abstract  = {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.},
  language  = {en}
}
@article{NollKrauseBeuerleetal.2022,
  author    = {Noll, Niklas and Krause, Ana-Maria and Beuerle, Florian and W{\"u}rthner, Frank},
  title     = {Enzyme-like water preorganization in a synthetic molecular cleft for homogeneous water oxidation catalysis},
  series = {Nature Catalysis},
  journal   = {Nature Catalysis},
  edition   = {accepted version},
  doi       = {10.1038/s41929-022-00843-x},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-302897},
  year      = {2022},
  abstract  = {Inspired by the proficiency of natural enzymes, mimicking of nanoenvironments for precise substrate preorganisation is a promising strategy in catalyst design. However, artificial examples of enzyme-like activation of H\(_2\)O molecules for the challenging oxidative water splitting reaction are hardly explored. Here, we introduce a mononuclear Ru(bda) complex (M1, bda: 2,2'-bipyridine-6,6'-dicarboxylate) equipped with a bipyridine-functionalized ligand to preorganize H\(_2\)O molecules in front of the metal center as in enzymatic clefts. The confined pocket of M1 accelerates chemically driven water oxidation at pH 1 by facilitating a water nucleophilic attack pathway with a remarkable turnover frequency of 140 s\(^{-1}\) that is comparable to the oxygen-evolving complex of photosystem II. Single crystal X-ray analysis of M1 under catalytic conditions allowed the observation of a 7th H\(_2\)O ligand directly coordinated to a RuIII center. Via a well-defined hydrogen-bonding network, another H\(_2\)O substrate is preorganized for the crucial O-O bond formation via nucleophilic attack.},
  language  = {en}
}
@article{WuerthnerNoll2021,
  author    = {W{\"u}rthner, Frank and Noll, Niklas},
  title     = {A Calix[4]arene-Based Cyclic Dinuclear Ruthenium Complex for Light-Driven Catalytic Water Oxidation},
  series = {Chemistry - A European Journal},
  volume    = {27},
  journal   = {Chemistry - A European Journal},
  number    = {1},
  doi       = {10.1002/chem.202004486},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-230030},
  pages     = {444-450},
  year      = {2021},
  abstract  = {A cyclic dinuclear ruthenium(bda) (bda: 2,2'-bipyridine-6,6'-dicarboxylate) complex equipped with oligo(ethylene glycol)-functionalized axial calix[4]arene ligands has been synthesized for homogenous catalytic water oxidation. This novel Ru(bda) macrocycle showed significantly increased catalytic activity in chemical and photocatalytic water oxidation compared to the archetype mononuclear reference [Ru(bda)(pic)\(_2\)]. Kinetic investigations, including kinetic isotope effect studies, disclosed a unimolecular water nucleophilic attack mechanism of this novel dinuclear water oxidation catalyst (WOC) under the involvement of the second coordination sphere. Photocatalytic water oxidation with this cyclic dinuclear Ru complex using [Ru(bpy)\(_3\)]Cl\(_2\) as a standard photosensitizer revealed a turnover frequency of 15.5 s\(^{-1}\) and a turnover number of 460. This so far highest photocatalytic performance reported for a Ru(bda) complex underlines the potential of this water-soluble WOC for artificial photosynthesis.},
  language  = {en}
}