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6. Kristalle züchten: zwischen Alchemie und Wissenschaft.

Author

Müßler, Mario, Pannwitz, Andrea, and Sorsche, Dieter

Subjects
INORGANIC chemistry, MOLECULAR structure, SINGLE crystals, NUCLEAR magnetic resonance spectroscopy, X-ray spectroscopy, COORDINATION polymers, POLYMERS
Abstract

Copyright of Nachrichten aus der Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Published
2023
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13. Red Light Absorption of [Re I (CO) 3 (α-diimine)Cl] Complexes through Extension of the 4,4′-Bipyrimidine Ligand's π-System.

Author

Meitinger, Nicolas, Mandal, Subrata, Sorsche, Dieter, Pannwitz, Andrea, and Rau, Sven

Subjects
LIGHT absorption, LIGANDS (Biochemistry), VISIBLE spectra, REDSHIFT, SINGLE crystals, METAL complexes, PYRIMIDINES
Abstract

Rhenium(I) complexes of type [Re(CO)3(NN)Cl] (NN = α-diimine) with MLCT absorption in the orange-red region of the visible spectrum have been synthesized and fully characterized, including single crystal X-ray diffraction on two complexes. The strong bathochromic shift of MLCT absorption was achieved through extension of the π-system of the electron-poor bidiazine ligand 4,4′-bipyrimidine by the addition of fused phenyl rings, resulting in 4,4′-biquinazoline. Furthermore, upon anionic cyclization of the twisted bidiazine, a new 4N-doped perylene ligand, namely, 1,3,10,12-tetraazaperylene, was obtained. Electrochemical characterization revealed a significant stabilization of the LUMO in this series, with the first reduction of the azaperylene found at E 1 / 2 (0 / −) = −1.131 V vs. Fc+/Fc, which is the most anodic half-wave potential observed for N-doped perylene derivatives so far. The low LUMO energies were directly correlated to the photophysical properties of the respective complexes, resulting in a strongly red-shifted MLCT absorption band in chloroform with a λmax = 586 nm and high extinction coefficients (ε586nm > 5000 M−1 cm−1) ranging above 700 nm in the case of the tetraazaperylene complex. Such low-energy MLCT absorption is highly unusual for Re(I) α-diimine complexes, for which these bands are typically found in the near UV. The reported 1,3,10,12-tetraazaperylene complex displayed the [Re(CO)3(α-diimine)Cl] complex with the strongest MLCT red shift ever reported. UV–Vis NIR spectroelectrochemical investigations gave further insights into the nature and stability of the reduced states. The electron-poor ligands explored herein open up a new path for designing metal complexes with strongly red-shifted absorption, thus enabling photocatalysis and photomedical applications with low-energy, tissue-penetrating red light in future. [ABSTRACT FROM AUTHOR]

Published
2023
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16. Silica Supported Organometallic IrIComplexes Enable Efficient Catalytic Methane Borylation

Author

Staples, Orion, Ferrandon, Magali S., Laurent, Guillaume P., Kanbur, Uddhav, Kropf, A. Jeremy, Gau, Michael R., Carroll, Patrick J., McCullough, Katherine, Sorsche, Dieter, Perras, Frédéric A., Delferro, Massimiliano, Kaphan, David M., and Mindiola, Daniel J.

Abstract

Catalytic C–H borylation is an attractive method for the conversion of the most abundant hydrocarbon, methane (CH4), to a mild nucleophilic building block. However, existing CH4borylation catalysts often suffer from low turnover numbers and conversions, which is hypothesized to result from inactive metal hydride agglomerates. Herein we report that the heterogenization of a bisphosphine molecular precatalyst, [(dmpe)Ir(cod)CH3], onto amorphous silica dramatically enhances its performance, yielding a catalyst that is 12-times more efficient than the current standard for CH4borylation. The catalyst affords over 2000 turnovers at 150 °C in 16 h with a selectivity of 91.5% for mono- vs diborylation. Higher catalyst loadings improve yield and selectivity for the monoborylated product (H3CBpin) with 82.8% yield and >99% selectivity being achieved with 1255 turnovers. X-ray absorption and dynamic nuclear polarization-enhanced solid-state NMR spectroscopic studies identify the supported precatalyst as an IrIspecies, and indicate that upon completion of catalysis, multinuclear Ir polyhydrides are not formed. This is consistent with the hypothesis that immobilization of the organometallic Ir species on a surface prevents bimolecular decomposition pathways. Immobilization of the homogeneous IrIfragment onto amorphous silica represents a unique and simple strategy to improve the TON and longevity of a CH4borylation catalyst.

Published
2023
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20. Unusual Dinitrogen Binding and Electron Storage in Dinuclear Iron Complexes

Author

Sorsche, Dieter, primary, Miehlich, Matthias E., additional, Searles, Keith, additional, Gouget, Guillaume, additional, Zolnhofer, Eva M., additional, Fortier, Skye, additional, Chen, Chun-Hsing, additional, Gau, Michael, additional, Carroll, Patrick J., additional, Murray, Christopher B., additional, Caulton, Kenneth G., additional, Khusniyarov, Marat M., additional, Meyer, Karsten, additional, and Mindiola, Daniel J., additional

Published
2020
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21. Beyond the First Coordination Sphere─Manipulating the Excited-State Landscape in Iron(II) Chromophores with Protons

Author

Witas, Kamil, Nair, Shruthi Santhosh, Maisuradze, Tamar, Zedler, Linda, Schmidt, Heiner, Garcia-Porta, Pablo, Rein, Alexandra Stefanie Jessica, Bolter, Tim, Rau, Sven, Kupfer, Stephan, Dietzek-Ivanšić, Benjamin, and Sorsche, Dieter U.

Abstract

Molecular transition metal chromophores play a central role in light harvesting and energy conversion. Recently, earth-abundant transition-metal-based chromophores have begun to challenge the dominance of platinum group metal complexes in this area. However, the development of new chromophores with optimized photophysical properties is still limited by a lack of synthetic methods, especially with respect to heteroleptic complexes with functional ligands. Here, we demonstrate a facile and efficient method for the combination of strong-field carbenes with the functional 2,2′-bibenzimidazole ligand in a heteroleptic iron(II) chromophore complex. Our approach yields two isomers that differ predominantly in their excited-state lifetimes based on the symmetry of the ligand field. Deprotonation of both isomers leads to a significant red-shift of the metal-to-ligand charge transfer (MLCT) absorption and a shortening of excited-state lifetimes. Femtosecond transient absorption spectroscopy in combination with quantum chemical simulations and resonance Raman spectroscopy reveals the complex relationship between protonation and photophysical properties. Protonation is found to tip the balance between MLCT and metal-centered (MC) excited states in favor of the former. This study showcases the first example of fine-tuning of the excited-state landscape in an iron(II) chromophore through second-sphere manipulations and provides a new perspective to the challenge of excited-state optimizations in 3d transition metal chromophores.

Published
2024
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27. Sterically confined second-sphere receptor chromophores for optical molecular recognition and photocatalysis

Author

Sorsche, Dieter, Rau, Sven, Beranek, Radim, and Plietker, Bernd

Subjects
DDC 540 / Chemistry & allied sciences, Chromophor, Photochemistry, ddc:540, Fotochemie, Anion, Fotophysik, Ruthenium
Abstract

The investigation of molecular processes and interactions through visible light is of fundamental importance for a wide range of technological and biological applications. The chromophores developed in this work have been used as luminescent sensors and light sensitizers for photocatalysis. A particular challenge is the optical detection of biologically abundant anions such as the halides. Simple inorganic ions are ubiquitously found in the environment, but they exhibit no visible interaction with light to be readily detected. A series of new ruthenium(II) chromophores with a hydrogen bond donating bibenzimidazole ligand have been developed in order to bind small ions and to signal the binding event through changes in their visible-light absorption and emission properties. Previous studies have shown that related complexes exhibit vivid color changes in the presence of basic anions as deprotonation strongly alters the electronic properties of these coordination compounds. Interaction with weakly basic anions through hydrogen bond interactions has been observed for example by NMR spectroscopy, the corresponding optical response however remained marginal. Progress has been reported upon introduction of substituents in a manner which defines a sterically confined pocket around the hydrogen bond donor functions. Using a versatile palladium(0) mediated synthetic procedure for variably substituted bibenzimidazole ligands, some new ruthenium(II) chromophores could be synthesized with well-defined binding pockets of varying size and flexibility. In particular, two complexes with anisyl substituents differ structurally only by four methyl groups which enforce a more rigid geometry of the respective binding pocket, whereas the flexible analogue exhibits rotational freedom. Remarkably, both new complexes show unprecedented optical sensitivity towards binding of the weakly basic halide ions chloride and bromide. Comparative investigations with an unsubstituted bibenzimidazole ruthenium(II) complex reveal that the pocket formation leads to dimming of the new chromophores, which is reversed upon anion binding with remarkable sensitivity towards chloride and bromide. These complexes hence represent a promising step forward for the detection of abundant, weakly basic, inorganic anions through optical events. One potential improvement beyond the reported anion studies is the synthetic achievement of a sensor with a macrocyclic binding pocket. An alternative chromophore unit for bibenzimidazole based sensors is based on the strongly luminescent properties of cyclometallated bis(phenylpyridine) iridium(III) complexes. In contrast to its ruthenium based analogue the new iridium(III) bibenzimidazole complex presented in this thesis exhibits vivid emission also in its deprotonated forms which potentially broadens the pH range for luminescence based recognition events. A combined ruthenium(II)/iridium(III) chromophore exhibits an appealing mixture of photophysical features of its subunits. This particular chromophore has hence been probed as sensitizer for light-driven catalysis and proved to be an interesting candidate for photocatalytic hydrogen production from an aqueous solution. For the purpose of detection of metal cations, a new phenanthroline based bridging ligand has been developed which exhibits a second diimine ligand function for 3d metal ion recognition. Due to the sterically demanding substitution pattern, regioselective synthesis of the respective iridium(III) chromophore has been achieved. Binding studies with nickel(II), zinc(II), and copper(I) reveal that only the latter was suitable to access the second binding sphere. The binding event is characterized by a vivid color change and darkening due to luminescence quenching. With respect to electrochemical measurements and in agreement with literature it is suggested that the selectivity for copper(I) potentially corresponds to a redox process which allows rearrangement and binding of the reduced diimine receptor sphere. In summary, chemically and structurally versatile new second-sphere receptors are presented in this thesis. The synthetic concepts allow a modular variation of photocenters and the corresponding photophysical properties, and binding modes for either anions or cations can be altered by the choice of bridging units. The reported supramolecular recognition and sensitization studies are promising and pave the way for the further development of molecular luminescent sensors with tunable selectivity and photochemistry.

Published
2016

30. Supramolecular activation of a molecular photocatalyst

Author

Pfeffer, Michael G., Pehlken, Christian, Staehle, Robert, Sorsche, Dieter, Streb, Carsten, and Rau, Sven

Subjects
ddc:540, Naturwissenschaftliche Fakultät
Abstract

The effects of the planar aromatic organic molecules anthracene and pyrene on the catalytic performance of the intramolecular hydrogen evolving photocatalyst [Ru(tbbpy)2(tpphz)PdCl2](PF6)2 functioning as a photocatalytic dyad have been studied. 1H-NMR studies on [Ru(tbbpy)2(tpphz)PdCl2](PF6)2 and [Ru(tbbpy)2(tpphz)](PF6)2 show a pronounced interaction of pyrene with the ruthenium complexes due to π–π-interactions. The solid state structure of [Ru(tbbpy)2(tpphz)PdCl2]2[Mo8O24] shows a pronounced π–π-stacking of the polyaromatic ligands. In addition, dimerization constants for the complexes and association constants between the complexes and pyrene were determined. Studies on the photocatalytic hydrogen production show a decreased induction phase and increased turn over frequencies during the initial phase of the catalysis in the presence of anthracene and pyrene utilising the catalyst [Ru(tbbpy)2(tpphz)PdCl2](PF6)2 irrespective of the nature of the polycyclic aromatic hydrocarbon.

Published
2014

36. Synthesis and characterization of an immobilizable photochemical molecular device for H-2-generation

Author

Braumueller, Markus, Schulz, Martin, Sorsche, Dieter, Pfeffer, Michael, Schaub, Markus, Popp, Juergen, Park, Byung-Wook, Hagfeldt, Anders, Dietzek, Benjamin, Rau, Sven, Braumueller, Markus, Schulz, Martin, Sorsche, Dieter, Pfeffer, Michael, Schaub, Markus, Popp, Juergen, Park, Byung-Wook, Hagfeldt, Anders, Dietzek, Benjamin, and Rau, Sven

Abstract

With [Ru-II(bpyMeP)(2)tpphzPtCl(2)](2+) (4) a molecular photocatalyst has been synthesized for visible-light-driven H-2-evolution. It contains the ligand bpyMeP (4,4'-bis(diethyl-(methylene)-phosphonate)-2,2'-bipyridine) with phosphate ester groups as precursors for the highly potent phosphonate anchoring groups, which can be utilized for immobilization of the catalyst on metal-oxide semiconductor surfaces. The synthesis was optimized with regard to high yields, bpyMeP was fully characterized and a solid-state structure could be obtained. Photophysical studies showed that the photophysical properties and the localization of the excited states are not altered compared to similar Ru-complexes without anchoring group precursors. (4) was even more active in homogenous catalysis experiments than [RuII(tbbpy)(2)tpphzPtCl(2)](2+) (6) with tbbpy (4,4'-bis(tbutyl)-2,2'-bipyridine) as peripheral ligands. After hydrolysis (4) was successfully immobilized on NiO, suggesting that an application in photoelectrosynthesis cells is feasible.

Published
2015
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49. Interaction of an Iridium(III)-Bibenzimidazole Complex with Anions - Implications for Luminescent Sensing.

Author

Rommel, Sebastian A., Sorsche, Dieter, Dixit, Apoorva, and Rau, Sven

Subjects
*IRIDIUM, *ANIONS, *DIAMINES, *HYDROGEN bonding, *NUCLEAR magnetic resonance, *EMISSION spectroscopy
Abstract

Iridium(III) complex [Ir(ppy)2(tmBBI-H2)](PF6) (IrBBI-H2) has been exploited as an anion receptor. In this complex, the cis-diamine function of the bibenzimidazole is coupled in such a way to the photophysics of the iridium metal core that the photophysics is influenced by hydrogen bonds in the ligand periphery. Systematic studies on the complex reveal that IrBBI-H2 is a convenient sensor for various anions under aerobic conditions and interacts with Cl-, Br-, I-, and HSO4- by forming hydrogen bonds. Whereas H2PO4- is only capable of mono-deprotonating IrBBI-H2, a stepwise process is operative when F- and OAc- are added: formation of the mono-deprotonated complex IrBBI-H with a low anion concentration, followed by the appearance of double-deprotonated complex IrBBI- in the presence of higher anion concentration. The interaction of various anions with IrBBI-H2 has been investigated by emission spectroscopy or NMR titration. According to the conditions chosen, strong binding interactions in the form of a 2:1 complex/anion ratio between the less basic anions and the complex, and a virtually stoichiometric reaction to their respective ion pairs, were observed. [ABSTRACT FROM AUTHOR]

Published
2016
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