TY - JOUR A1 - Würthner, Frank A1 - Meza-Chincha, Ana-Lucia A1 - Schindler, Dorothee A1 - Natali, Mirco T1 - Effects of Photosensitizers and Reaction Media on Light‐Driven Water Oxidation with Trinuclear Ruthenium Macrocycles JF - ChemPhotoChem N2 - 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. KW - photosenitizers KW - water oxidation KW - ruthenium complexes KW - macrocycles KW - trinuclear KW - homogenous catalysis KW - photocatalysis Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-230116 VL - 5 IS - 2 ER - TY - JOUR A1 - Schindler, Dorothee A1 - Meza-Chincha, Anna-Lucia A1 - Roth, Maximilian A1 - Würthner, Frank T1 - Structure-Activity Relationship for Di- up to Tetranuclear Macrocyclic Ruthenium Catalysts in Homogeneous Water Oxidation JF - Chemistry—A European Journal N2 - 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. KW - homogeneous catalysis KW - water oxidation KW - ruthenium catalysts KW - renewable fuels KW - metallomacrocycles Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256792 VL - 27 IS - 68 ER - TY - JOUR A1 - Schindler, Dorothee A1 - Gil‐Sepulcre, Marcos A1 - Lindner, Joachim O. A1 - Stepanenko, Vladimir A1 - Moonshiram, Dooshaye A1 - Llobet, Antoni A1 - Würthner, Frank T1 - Efficient Electrochemical Water Oxidation by a Trinuclear Ru(bda) Macrocycle Immobilized on Multi‐Walled Carbon Nanotube Electrodes JF - Advanced Energy Materials N2 - 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\(^{−1}\). KW - electrocatalysis KW - heterogeneous catalysis KW - renewable fuels KW - ruthenium bda complexes KW - water splitting Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218381 VL - 10 IS - 43 ER - TY - THES A1 - Schindler, Dorothee T1 - Water Oxidation with Multinuclear Ruthenium Catalysts T1 - Wasseroxidation mit mehrkernigen Ruthenium-Katalysatoren N2 - In terms of the need of environmentally benign renewable and storable energy sources, splitting of water into hydrogen and oxygen by using sunlight is a promising approach. Hereby, water oxidation catalysts (WOCs) are required to perform the water oxidation comprising the transfer of four electrons to provide the reducing equivalents for producing hydrogen. The class of Ru(bda) (bda = 2,2'-bipyridine-6,6'-dicarboxylate) catalysts has proven to be efficient for this reaction. In this thesis, ligand exchange processes in Ru(bda) complexes have been analyzed and the formation of multinuclear macrocyclic WOCs was studied. Based on the knowledge acquired by these studies, new multinuclear cyclic Ru(bda) complexes have been synthesized and their catalytic efficiencies in homogeneous water oxidation have been investigated. Going one step further for setting up functional devices, molecular WOCs have been immobilized on conducting or semiconducting supporting materials. Direct anchoring on carbon nanotubes generated a promising materials for further applications. N2 - Der Klimawandel als die gesellschaftliche Herausforderung des 21. Jahrhunderts ist der Allgemeinheit in den letzten Jahren insbesondere durch Aktivitäten der jüngeren Generation mehr und mehr ins Bewusstsein gerückt. Mit ihrem Engagement in Klimabewegungen machen sie auf die Dringlichkeit aufmerksam, fossile Brennstoffe als Hauptverursacher schädlicher Emissionen zu ersetzen. Angesichts des Bedarfs an umweltfreundlichen erneuerbaren und zugleich speicherbaren Energie¬quellen ist die Erzeugung von Wasserstoff unter Verwendung von Sonnenlicht zur Spaltung von Wasser in seine Bestandteile ein vielversprechender Ansatz (Kapitel 2.1). Die Wasser¬oxidationsreaktion, die die erforderlichen Reduktionsäquivalenten für die Umwandlung von Protonen in molekularen Wasserstoff liefert, umfasst jedoch einen herausfordernden Vier-Elektronen-Transferprozess, der robuste und effiziente Katalysatoren unverzichtbar macht (Kapitel 2.2). In den letzten Jahrzehnten durchgeführte ausführliche Untersuchungen an molekularen Wasser¬oxidations¬katalysatoren (WOCs, engl: water oxidation catalysts) haben gezeigt, dass Katalysatoren, die das katalytisch aktive Ru(bda) Fragment (bda: 2,2'-bipyridin-6,6'-dicarbonsäure) enthalten, eine hohe Effizienz in der Wasseroxidation aufweisen.[41] Basierend auf diesen Erkenntnissen entwickelten Würthner und Mitarbeiter einen supra-molekularen Ansatz, bei dem drei Ru(bda) Einheiten makrozyklisch organisiert werden.[42] Diese makrozyklischen Ru(bda) Komplexe zeigten außerordentlich hohe katalytische Aktivitäten mit bedeutend höherer Umsatzfrequenz (TOF, engl: turnover frequency) und Umsatzzahl (TON, engl: turnover number) sowie einer verbesserten Stabilität des Katalysators im Vergleich zur einkernigen Referenzverbindung Ru(bda)(pic)2.[40] Interessanter¬weise wurde heraus¬gefunden, dass vermutlich ein wasserstoffverbrücktes Wasser¬netzwerk in der Kavität des Makrozyklus für schnelle Protonen-gekoppelte Elektronen-Transfer-Schritte (PCET, engl: protonen-coupled electron transfer) und somit beschleunigte Reaktionsgeschwindigkeiten verantwortlich ist. Darüber hinaus belegten mechanistische Untersuchungen einen Wechsel des katalytischen Weges von einem bimolekularen I2M (Interaktion von zwei M-O Einheiten, engl: interaction of two M-O units) Mechanismus im einkernigen Ru(bda)pic2 Referenzkomplex zu einem mononuklearen WNA (nukleophiler Wasserangriff, engl: water nucleophiilic attack) Mechanismus im dreikernigen makro-zyklischen WOC MC3 (Kapitel 2.3), was letzteren besonders interessant für anwendungs-bezogene Untersuchungen macht. ... KW - Rutheniumkomplexe KW - catalysis KW - Wasser KW - Katalyse KW - Oxidation KW - metallosupramolecular chemistry KW - ruthenium complexes KW - water oxidation KW - Ruthenium Komplexe KW - Metallosupramolekulare Chemie KW - Wasseroxidation Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-233093 ER - TY - JOUR A1 - Meza-Chincha, Ana-Lucia A1 - Lindner, Joachim O. A1 - Schindler, Dorothee A1 - Schmidt, David A1 - Krause, Ana-Maria A1 - Röhr, Merle I. S. A1 - Mitrić, Roland A1 - Würthner, Frank T1 - Impact of substituents on molecular properties and catalytic activities of trinuclear Ru macrocycles in water oxidation N2 - 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. KW - water oxidation KW - self-assembly KW - solar fuels KW - supramolecular materials KW - catalysis Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-204653 UR - https://doi.org/10.1039/D0SC01097A SN - 2041-6539 ER -