@phdthesis{Roschmann2002,
  author    = {Roschmann, Konrad J.},
  title     = {Mn(salen)- und Fe(porph)-katalysierte enantioselektive Epoxidierungen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-1182584},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2002},
  abstract  = {Ziel der vorliegenden Arbeit war es zum einen, das Potential von chiralen Eisenporphyrin- und Mangansalen-Katalysatoren zur kinetischen Racematspaltung sekund{\"a}rer Allylalkohole durch asymmetrische Epoxidierung auszuloten. Zum anderen sollten Untersuchungen zum Mechanismus der Jacobsen-Katsuki-Epoxidierung durchgef{\"u}hrt werden; ein besonderes Augenmerk lag dabei auf der Fragestellung, welche Faktoren dazu f{\"u}hren, dass bei der Umsetzung von cis-Olefinen ein Gemisch aus cis- und trans-Epoxiden erhalten wird. Eine Auswahl arylsubstituierter Allylalkohole IIa-f wurde mit den Katalysatoren Ia und Ib,c und 0.8 bzw. 0.6 {\"A}quivalenten an Iodosobenzol als Sauerstoffdonor umgesetzt (Gl. I), wobei es zu einer kinetischen Racematspaltung kommt. Die Oxidation verl{\"a}uft f{\"u}r beide Katalysatorsysteme sowohl chemoselektiv (vorwiegend Epoxidierung) als auch diastereoselektiv (dr bis zu > 95:5). Als Hauptprodukte werden f{\"u}r die offenkettigen Allylalkohole IIa,e,f die threo-konfigurierten Epoxyalkohole III erhalten, w{\"a}hrend die cyclischen Allylakohole IIb-d die entsprechenden cis-Epoxyalkohole III lieferen. 1,1-Dimethyl-1,2-dihydro-2-naphthol (IIc) ist hierbei eine Ausnahme, da die CH-Oxidation dieses Substrats eine beachtliche Nebenreaktion darstellt. Der Hauptunterschied zwischen den Fe- und Mn-Katalysatoren liegt in der Enantioselektivit{\"a}t: W{\"a}hrend mit dem Fe(porph*)-Komplex Ia nur Selektivit{\"a}ten von maximal 43 Prozent ee (krel = 2.7) erzielt werden, erwiesen sich die Mn(salen*)-Komplexe Ib,c als geeignete Katalysatoren, mit denen ee-Werte von bis zu 80 Prozent (krel = 12.9) erreicht werden. Die in der kinetischen Racematspaltung erzielten Selektivit{\"a}ten k{\"o}nnen durch ein synergistisches Zusammenwirken von hydroxy-dirigierendem Effekt einerseits und sterischen Wechselwirkungen zwischen Substrat und Eisen-Komplex oder, im Falle des Mangan-Komplexes, Angriff des Olefins entlang der so genannten Katsuki-Trajektorie andererseits erkl{\"a}rt werden. Fazit: Die chiralen Mn(salen*)-Komplexe Ib,c sind wirkungsvolle Katalysatoren f{\"u}r die asymmetrische Epoxidierung racemischer sekund{\"a}rer Allylalkohole II. In exzellenten Chemo- und Diastereoselektivit{\"a}ten entstehen die entsprechenden Epoxyalkohole III mit ee-Werten bis zu 80 Prozent. Die zur{\"u}ckbleibenden Allylalkohole werden dabei bis zu 53 Prozent ee angereichert. Im Vergleich dazu weist der Eisenkomplex Ia eine ungleich geringere Enantioselektivit{\"a}t auf. Mechanistische Untersuchungen mit Vinylcyclopropan Va ergeben, dass die Jacobsen-Katsuki-Epoxidierung nicht {\"u}ber ein kationisches, sondern {\"u}ber ein radikalisches Intermediat abl{\"a}uft. Dies wird anhand von Produktstudien durch reversed phase-HPLC-Analytik belegt. In weitergehenden Untersuchungen mit cis-Stilben (Vb) und cis-\&\#61538;-Methylstyrol (Vc) als Sonden zur cis/trans-Isomerisierung wurde festgestellt, dass die Diastereoselektivit{\"a}t der Epoxidierung nicht nur vom Gegenion des Mangankatalysators Ib, sondern auch von der eingesetzten Sauerstoffquelle [OxD] abh{\"a}ngt. Daher musste der Katalysezyklus (Schema A) um eine diastereoselektivit{\"a}ts-bestimmende Gabelung erweitert werden: Das prim{\"a}r entstehende MnIII(OxD)-Addukt kann entweder unter Abspaltung der Fluchtgruppe zum etablierten MnV(oxo)-Komplex reagieren (Weg 1) oder direkt das Olefin epoxidieren (Weg 2). W{\"a}hrend die Sauerstoff{\"u}bertragung durch die Oxo-Spezies stufenweise {\"u}ber ein Radikalintermediat verl{\"a}uft und damit zu einer Mischung aus cis- und trans-Epoxid f{\"u}hrt, erfolgt der Lewis{\"a}ure-aktivierte Sauerstofftransfer konzertiert. Der Gegenion-Effekt auf die cis/trans-Isomerisierung erkl{\"a}rt sich dahingehend, dass die Natur des Anions (koordinierend oder nicht-koordinierend) die Lebensdauer des Radikalintermediats und/oder die Lage und Selektivit{\"a}t der Energiehyperfl{\"a}chen der verschiedenen Spinzust{\"a}nde des MnV(oxo)-Oxidans beeinflusst. Fazit: In der Jacobsen-Katsuki-Epoxidierung existiert neben dem etablierten MnV(oxo)-Oxidans zumindest noch ein weiteres; dabei handelt es sich um das MnIII(OxD)-Addukt, dessen Sauerstoff Lewiss{\"a}ure-aktiviert {\"u}bertragen wird. Ein unterschiedlicher Anteil der beiden Reaktionskan{\"a}le erkl{\"a}rt die Unterschiede im Ausmaß der cis/trans-Isomerisierung. Auch das Gegenion des Mangan-Komplexes Ib beeinflusst die cis/trans-Diastereoselektivit{\"a}t. Mit koordinierenden Gegenionen dominiert Isomerisierung zum trans-Epoxid, w{\"a}hrend nicht-koordinierende Gegenionen bevorzugt zum cis-Epoxid f{\"u}hren.},
  subject      = {Mangan},
  language  = {de}
}
@phdthesis{Kunz2018,
  author    = {Kunz, Valentin},
  title     = {Supramolecular Approaches for Water Oxidation Catalysis with Ruthenium Complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-154820},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {The catalytic splitting of water into its elements is an important reaction to establish hydrogen as a solar fuel. The bottle-neck of this process is considered to be the oxidative half reaction generating oxygen, and good catalysts are required to handle the complicated redox chemistry involved. As can be learned from nature, the incorporation of the catalytically active species into an appropriate matrix can help to improve the overall performance. Thus, the aim of the present thesis was to establish novel supramolecular approaches to improve water oxidation catalysis using the catalytically active {Ru(bda)} fragment as key motive (bda = 2,2'-bipyridine-6,6'-dicarboxylate). First, the synthesis of ruthenium catalysts gathering three {Ru(bda)} water oxidation subunits in a macrocyclic fashion is described. By using bridging bipyridine ligands of different lengths, metallosupramolecular macrocycles with distinct sizes have been obtained. Interestingly, an intermediate ring size has been proven to be optimal for the catalytic water oxidation. Detailed kinetic, spectroscopic, and theoretical studies helped to identify the reaction mechanism and to rationalize the different catalytic activities. Furthermore, solubilizing side chains have been introduced for the most active derivative to achieve full water solubility. Secondly, the {Ru(bda)} fragment was embedded into supramolecular aggregates to generate more stable catalytic systems compared to a homogeneous reference complex. Therefore, the catalyst fragment was equipped with axial perylene bisimide (PBI) ligands, which facilitate self-assembly. Moreover, the influence of the different accessible aggregate morphologies on the catalytic performance has been investigated.},
  subject      = {Ruthenium Komplexe},
  language  = {en}
}
@unpublished{LegarePranckeviciusBraunschweig2019,
  author    = {L{\´e}gar{\´e}, Marc-Andr{\´e} and Pranckevicius, Conor and Braunschweig, Holger},
  title     = {Metallomimetic Chemistry of Boron},
  series = {Chemical Reviews},
  journal   = {Chemical Reviews},
  doi       = {10.1021/acs.chemrev.8b00561},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-186317},
  year      = {2019},
  abstract  = {The study of main-group molecules that behave and react similarly to transition-metal (TM) complexes has attracted significant interest in recent decades. Most notably, the attractive idea of replacing the all-too-often rare and costly metals from catalysis has motivated efforts to develop main-group-element-mediated reactions. Main-group elements, however, lack the electronic flexibility of TM complexes that arises from combinations of empty and filled d orbitals and that seem ideally suited to bind and activate many substrates. In this review, we look at boron, an element that despite its nonmetal nature, low atomic weight, and relative redox staticity has achieved great milestones in terms of TM-like reactivity. We show how in interelement cooperative systems, diboron molecules, and hypovalent complexes the fifth element can acquire a truly metallomimetic character. As we discuss, this character is powerfully demonstrated by the reactivity of boron-based molecules with H2, CO, alkynes, alkenes and even with N2.},
  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{Lichtenberg2020,
  author    = {Lichtenberg, Crispin},
  title     = {Main-Group Metal Complexes in Selective Bond Formations Through Radical Pathways},
  series = {Chemistry - A European Journal},
  volume    = {26},
  journal   = {Chemistry - A European Journal},
  number    = {44},
  doi       = {10.1002/chem.202000194},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214758},
  pages     = {9674 -- 9687},
  year      = {2020},
  abstract  = {Recent years have witnessed remarkable advances in radical reactions involving main-group metal complexes. This includes the isolation and detailed characterization of main-group metal radical compounds, but also the generation of highly reactive persistent or transient radical species. A rich arsenal of methods has been established that allows control over and exploitation of their unusual reactivity patterns. Thus, main-group metal compounds have entered the field of selective bond formations in controlled radical reactions. Transformations that used to be the domain of late transition-metal compounds have been realized, and unusual selectivities, high activities, as well as remarkable functional-group tolerances have been reported. Recent findings demonstrate the potential of main-group metal compounds to become standard tools of synthetic chemistry, catalysis, and materials science, when operating through radical pathways.},
  language  = {en}
}
@phdthesis{MezaChincha2021,
  author    = {Meza Chincha, Ana Lucia},
  title     = {Catalytic Water Oxidation with Functionalized Ruthenium Macrocycles},
  doi       = {10.25972/OPUS-20962},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-209620},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {In light of the rapidly increasing global demand of energy and the negative effects of climate change, innovative solutions that allow an efficient transition to a carbon-neutral economy are urgently needed. In this context, artificial photosynthesis is emerging as a promising technology to enable the storage of the fluctuating energy of sunlight in chemical bonds of transportable "solar fuels". Thus, in recent years much efforts have been devoted to the development of robust water oxidation catalysts (WOCs) leading to the discovery of the highly reactive Ru(bda) (bda: 2,2'-bipyridine-6,6'-dicarboxylic acid) catalyst family. The aim of this thesis was the study of chemical and photocatalytic water oxidation with functionalized Ruthenium macrocycles to explore the impact of substituents on molecular properties and catalytic activities of trinuclear macrocyclic Ru(bda) catalysts. A further objective of this thesis comprises the elucidation of factors that influence the light-driven water oxidation process with this novel class of supramolecular WOCs.},
  subject      = {Rutheniumkomplexe},
  language  = {en}
}
@phdthesis{Schindler2022,
  author    = {Schindler, Dorothee},
  title     = {Water Oxidation with Multinuclear Ruthenium Catalysts},
  doi       = {10.25972/OPUS-23309},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-233093},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {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.},
  subject      = {Rutheniumkomplexe},
  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{RamlerSchwarzmannStoyetal.2022,
  author    = {Ramler, Jacqueline and Schwarzmann, Johannes and Stoy, Andreas and Lichtenberg, Crispin},
  title     = {Two Faces of the Bi-O Bond: Photochemically and Thermally Induced Dehydrocoupling for Si-O Bond Formation},
  series = {European Journal of Inorganic Chemistry},
  volume    = {2022},
  journal   = {European Journal of Inorganic Chemistry},
  number    = {7},
  doi       = {10.1002/ejic.202100934},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257428},
  year      = {2022},
  abstract  = {The diorgano(bismuth)alcoholate [Bi((C\(_{6}\)H\(_{4}\)CH\(_{2}\))\(_{2}\)S)OPh] (1-OPh) has been synthesized and fully characterized. Stoichiometric reactions, UV/Vis spectroscopy, and (TD-)DFT calculations suggest its susceptibility to homolytic and heterolytic Bi-O bond cleavage under given reaction conditions. Using the dehydrocoupling of silanes with either TEMPO or phenol as model reactions, the catalytic competency of 1-OPh has been investigated (TEMPO=(tetramethyl-piperidin-1-yl)-oxyl). Different reaction pathways can deliberately be addressed by applying photochemical or thermal reaction conditions and by choosing radical or closed-shell substrates (TEMPO vs. phenol). Applied analytical techniques include NMR, UV/Vis, and EPR spectroscopy, mass spectrometry, single-crystal X-ray diffraction analysis, and (TD)-DFT calculations.},
  language  = {en}
}
@article{ZhangFriedrichMarder2022,
  author    = {Zhang, Xiaolei and Friedrich, Alexandra and Marder, Todd B.},
  title     = {Copper-Catalyzed Borylation of Acyl Chlorides with an Alkoxy Diboron Reagent: A Facile Route to Acylboron Compounds},
  series = {Chemistry—A European Journal},
  volume    = {28},
  journal   = {Chemistry—A European Journal},
  number    = {42},
  doi       = {10.1002/chem.202201329},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318318},
  year      = {2022},
  abstract  = {Herein, the copper-catalyzed borylation of readily available acyl chlorides with bis(pinacolato)diboron, (B\(_{2}\)pin\(_{2}\)) or bis(neopentane glycolato)diboron (B\(_{2}\)neop\(_{2}\)) is reported, which provides stable potassium acyltrifluoroborates (KATs) in good yields from the acylboronate esters. A variety of functional groups are tolerated under the mild reaction conditions (room temperature) and substrates containing different carbon-skeletons, such as aryl, heteroaryl and primary, secondary, tertiary alkyl are applicable. Acyl N-methyliminodiacetic acid (MIDA) boronates can also been accessed by modification of the workup procedures. This process is scalable and also amenable to the late-stage conversion of carboxylic acid-containing drugs into their acylboron analogues, which have been challenging to prepare previously. A catalytic mechanism is proposed based on in situ monitoring of the reaction between p-toluoyl chloride and an NHC-copper(I) boryl complex as well as the isolation of an unusual lithium acylBpinOBpin compound as a key intermediate.},
  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}
}
@phdthesis{Herok2024,
  author    = {Herok, Christoph},
  title     = {Quantum Chemical Exploration of Potential Energy Surfaces: Reaction Cycles and Luminescence Phenomena},
  doi       = {10.25972/OPUS-35218},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-352185},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {This work aims at elucidating chemical processes involving homogeneous catalysis and photo-physical relaxation of excited molecules in the solid state. Furthermore, compounds with supposedly small singlet-triplet gaps and therefore biradicaloid character are investigated with respect to their electro-chemical behavior. The work on hydroboration catalysis via a reduced 9,10-diboraanthracene (DBA) was preformed in collaboration with the Wagner group in Frankfurt, more specifically Dr. Sven Prey, who performed all laboratory experiments. The investigation of delayed luminescence properties in arylboronic esters in their solid state was conducted in collaboration with the Marder group in W{\"u}rzburg. The author of this work took part in the synthesis of the investigated compounds while being supervised by Dr. Zhu Wu. The final project was a collaboration with the group of Anukul Jana from Hyderabad, India who provided the experimental data.},
  subject      = {Simulation},
  language  = {en}
}