@article{SchindlerMezaChinchaRothetal.2021,
  author    = {Schindler, Dorothee and Meza-Chincha, Anna-Lucia and Roth, Maximilian and W{\"u}rthner, Frank},
  title     = {Structure-Activity Relationship for Di- up to Tetranuclear Macrocyclic Ruthenium Catalysts in Homogeneous Water Oxidation},
  series = {Chemistry—A European Journal},
  volume    = {27},
  journal   = {Chemistry—A European Journal},
  number    = {68},
  doi       = {10.1002/chem.202100549},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256792},
  pages     = {16938-16946},
  year      = {2021},
  abstract  = {Two di- and tetranuclear Ru(bda) (bda: 2,2′-bipyridine-6,6′-dicarboxylate) macrocyclic complexes were synthesized and their catalytic activities in chemical and photochemical water oxidation investigated in a comparative manner to our previously reported trinuclear congener. Our studies have shown that the catalytic activities of this homologous series of multinuclear Ru(bda) macrocycles in homogeneous water oxidation are dependent on their size, exhibiting highest efficiencies for the largest tetranuclear catalyst. The turnover frequencies (TOFs) have increased from di- to tetranuclear macrocycles not only per catalyst molecule but more importantly also per Ru unit with TOF of 6 \(^{-1}\) to 8.7 \(^{-1}\) and 10.5 s\(^{-1}\) in chemical and 0.6 s\(^{-1}\) to 3.3 \(^{-1}\) and 5.8 \(^{-1}\) in photochemical water oxidation per Ru unit, respectively. Thus, for the first time, a clear structure-activity relationship could be established for this novel class of macrocyclic water oxidation catalysts.},
  language  = {en}
}
@article{SchlossarekStepanenkoBeuerleetal.2022,
  author    = {Schlossarek, Tim and Stepanenko, Vladimir and Beuerle, Florian and W{\"u}rthner, Frank},
  title     = {Self-assembled Ru(bda) Coordination Oligomers as Efficient Catalysts for Visible Light-Driven Water Oxidation in Pure Water},
  series = {Angewandte Chemie International Edition},
  volume    = {61},
  journal   = {Angewandte Chemie International Edition},
  number    = {52},
  doi       = {10.1002/anie.202211445},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312184},
  year      = {2022},
  abstract  = {Water-soluble multinuclear complexes based on ruthenium 2,2′-bipyridine-6,6′-dicarboxylate (bda) and ditopic bipyridine linker units are investigated in three-component visible light-driven water oxidation catalysis. Systematic studies revealed a strong enhancement of the catalytic efficiency in the absence of organic co-solvents and with increasing oligomer length. In-depth kinetic and morphological investigations suggest that the enhanced performance is induced by the self-assembly of linear Ru(bda) oligomers into aggregated superstructures. The obtained turnover frequencies (up to 14.9 s\(^{-1}\)) and turnover numbers (more than 1000) per ruthenium center are the highest reported so far for Ru(bda)-based photocatalytic water oxidation systems.},
  language  = {en}
}
@article{MezaChinchaLindnerSchindleretal.2020,
  author    = {Meza-Chincha, Ana-Lucia and Lindner, Joachim O. and Schindler, Dorothee and Schmidt, David and Krause, Ana-Maria and R{\"o}hr, Merle I. S. and Mitrić, Roland and W{\"u}rthner, Frank},
  title     = {Impact of substituents on molecular properties and catalytic activities of trinuclear Ru macrocycles in water oxidation},
  issn      = {2041-6539},
  doi       = {10.1039/d0sc01097a},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204653},
  year      = {2020},
  abstract  = {Herein we report a broad series of new trinuclear supramolecular Ru(bda) macrocycles bearing different substituents at the axial or equatorial ligands which enabled investigation of substituent effects on the catalytic activities in chemical and photocatalytic water oxidation. Our detailed investigations revealed that the activities of these functionalized macrocycles in water oxidation are significantly affected by the position at which the substituents were introduced. Interestingly, this effect could not be explained based on the redox properties of the catalysts since these are not markedly influenced by the functionalization of the ligands. Instead, detailed investigations by X-ray crystal structure analysis and theoretical simulations showed that conformational changes imparted by the substituents are responsible for the variation of catalytic activities of the Ru macrocycles. For the first time, macrocyclic structure of this class of water oxidation catalysts is unequivocally confirmed and experimental indication for a hydrogen-bonded water network present in the cavity of the macrocycles is provided by crystal structure analysis. We ascribe the high catalytic efficiency of our Ru(bda) macrocycles to cooperative proton abstractions facilitated by such a network of preorganized water molecules in their cavity, which is reminiscent of catalytic activities of enzymes at active sites.},
  language  = {en}
}
@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{SchindlerGil‐SepulcreLindneretal.2020,
  author    = {Schindler, Dorothee and Gil-Sepulcre, Marcos and Lindner, Joachim O. and Stepanenko, Vladimir and Moonshiram, Dooshaye and Llobet, Antoni and W{\"u}rthner, Frank},
  title     = {Efficient Electrochemical Water Oxidation by a Trinuclear Ru(bda) Macrocycle Immobilized on Multi-Walled Carbon Nanotube Electrodes},
  series = {Advanced Energy Materials},
  volume    = {10},
  journal   = {Advanced Energy Materials},
  number    = {43},
  doi       = {10.1002/aenm.202002329},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218381},
  year      = {2020},
  abstract  = {Catalytic water splitting is a viable process for the generation of renewable fuels. Here it is reported for the first time that a trinuclear supramolecular Ru(bda) (bda: 2,2′-bipyridine-6,6′-dicarboxylate) catalyst, anchored on multi-walled carbon nanotubes and subsequently immobilized on glassy carbon electrodes, shows outstanding performance in heterogeneous water oxidation. Activation of the catalyst on anodes by repetitive cyclic voltammetry (CV) scans results in a catalytic current density of 186 mA cm\(^{-2}\) at a potential of 1.45 V versus NHE. The activated catalyst performs water oxidation at an onset overpotential of 330 mV. The remarkably high stability of the hybrid anode is demonstrated by X-ray absorption spectroscopy and electrochemically, revealing the absence of any degradation after 1.8 million turnovers. Foot of the wave analysis of CV data of activated electrodes with different concentrations of catalyst indicates a monomolecular water nucleophilic attack mechanism with an apparent rate constant of TOFmax (turnover frequency) of 3200 s\(^{-1}\).},
  language  = {en}
}
@article{WuerthnerMezaChinchaSchindleretal.2021,
  author    = {W{\"u}rthner, Frank and Meza-Chincha, Ana-Lucia and Schindler, Dorothee and Natali, Mirco},
  title     = {Effects of Photosensitizers and Reaction Media on Light-Driven Water Oxidation with Trinuclear Ruthenium Macrocycles},
  series = {ChemPhotoChem},
  volume    = {5},
  journal   = {ChemPhotoChem},
  number    = {2},
  doi       = {10.1002/cptc.202000133},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-230116},
  pages     = {173-183},
  year      = {2021},
  abstract  = {Photocatalytic water oxidation is a promising process for the production of solar fuels and the elucidation of factors that influence this process is of high significance. Thus, we have studied in detail light-driven water oxidation with a trinuclear Ru(bda) (bda: 2,2'-bipyridine-6,6'-dicarboxylate) macrocycle MC3 and its highly water soluble derivative m-CH\(_2\)NMe\(_2\)-MC3 using a series of ruthenium tris(bipyridine) complexes as photosensitizers under varied reaction conditions. Our investigations showed that the catalytic activities of these Ru macrocycles are significantly affected by the choice of photosensitizer (PS) and reaction media, in addition to buffer concentration, light intensity and concentration of the sensitizer. Our steady-state and transient spectroscopic studies revealed that the photocatalytic performance of trinuclear Ru(bda) macrocycles is not limited by their intrinsic catalytic activities but rather by the efficiency of photogeneration of oxidant PS\(^+\) and its ability to act as an oxidizing agent to the catalysts as both are strongly dependent on the choice of photosensitizer and the amount of employed organic co-solvent.},
  language  = {en}
}
@article{KarakStepanenkoAddicoatetal.2022,
  author    = {Karak, Suvendu and Stepanenko, Vladimir and Addicoat, Matthew A. and Keßler, Philipp and Moser, Simon and Beuerle, Florian and W{\"u}rthner, Frank},
  title     = {A Covalent Organic Framework for Cooperative Water Oxidation},
  series = {Journal of the American Chemical Society},
  volume    = {144},
  journal   = {Journal of the American Chemical Society},
  number    = {38},
  issn      = {0002-7863},
  doi       = {10.1021/jacs.2c07282},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-287591},
  pages     = {17661-17670},
  year      = {2022},
  abstract  = {The future of water-derived hydrogen as the "sustainable energy source" straightaway bets on the success of the sluggish oxygen-generating half-reaction. The endeavor to emulate the natural photosystem II for efficient water oxidation has been extended across the spectrum of organic and inorganic combinations. However, the achievement has so far been restricted to homogeneous catalysts rather than their pristine heterogeneous forms. The poor structural understanding and control over the mechanistic pathway often impede the overall development. Herein, we have synthesized a highly crystalline covalent organic framework (COF) for chemical and photochemical water oxidation. The interpenetrated structure assures the catalyst stability, as the catalyst's performance remains unaltered after several cycles. This COF exhibits the highest ever accomplished catalytic activity for such an organometallic crystalline solid-state material where the rate of oxygen evolution is as high as ∼26,000 μmol L\(^{-1}\) s\(^{-1}\) (second-order rate constant k ≈ 1650 μmol L s\(^{-1}\) g\(^{-2}\)). The catalyst also proves its exceptional activity (k ≈ 1600 μmol L s\(^{-1}\) g\(^{-2}\)) during light-driven water oxidation under very dilute conditions. The cooperative interaction between metal centers in the crystalline network offers 20-30-fold superior activity during chemical as well as photocatalytic water oxidation as compared to its amorphous polymeric counterpart.},
  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}
}