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Imide-Based Molten Salts As Solvents for Homogeneous Catalysis

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Imide-Based Molten Salts As Solvents for Homogeneous Catalysis Bis(trifluoromethylsulfonyl)imide-based Molten Salts as Solvents for homogeneous Catalysis Bis(trifluoromethylsulfonyl)imid-basierte Salzschmelzen als Lösungsmittel für homogene Katalyse Technische Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg zur Erlangung des Doktorgrades Dr.-Ing. vorgelegt von Marlene Scheuermeyer aus Erlangen i Als Dissertation genehmigt von der Technischen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg. Tag der mündlichen Prüfung: 15.6.2018 Vorsitzender des Promotionsorgans: Prof. Dr.-Ing. Reinhard Lerch Gutachter: Prof. Dr. Peter Wasserscheid Prof. Dr.-Ing. Andreas Paul Fröba ii Acknowledgements The results of this PhD thesis are based on my research carried out at the Institute of Chemical Reaction Engineering (Chemische Reaktionstechnik, CRT) at Friedrich-Alexander-Universität Erlangen- Nürnberg between 1.10.2013 and 31.3.2017. First and above all I would like to thank my supervisor Peter Wasserscheid, for the inspiring conversations and the guidance trough the time I spend at his chair. I greatly appreciate his trust and encouragement. He always could motivate me with his never dying enthusiasm and optimism. It wasn’t always simple but without him I would not have come this far. The financial support of the project “H2-SMS-CAT – Engineering of Supported Molten Salt Catalysts for Dehydrogenation Reactions and Hydrogen Production Technologies” within the program “ERC Advanced Grant” is gratefully acknowledged. Also I would like to thank Friederike Agel and the other group leaders of CRT for all the practical advice, the ideas and the assistance. In addition, a warm thank you goes to Peter Schulz who takes care that all GCs, especially the “Kleine Klaus” and the NMR do what they should, Nicola Taccardi for the ICP measurements, Dirk Lüdke for the XRD measurements, Christina Wronna for the elemental analysis and all the other staff at CRT especially the mechanical and electrical workshops and the secretary which makes the everyday work possible. I also would like to thank my supervisor at DTU during my short term scientific mission, Rolf W. Berg, for the help with the Raman measurements, for the wonderful time I had in Denmark and for all the scientific anecdotes. In addition I cannot thank Anders Riisager, Rasmus Fehrmann, Lotte Skafte Jespersen, Nanette Zahrtmann and all the other members of the group at DTU enough for the warm integration and the great time. I also would like to thank Irene Shim for her advice with the calculations. I would like to gratefully acknowledge my cooperation partners: Patrick Schreiber, Florian Maier and Hans-Peter Steinrück from the Chair of Physical Chemistry 2 in Erlangen for the XPS measurements. Florian Heym and Andreas Jess from the University of Bayreuth for support with the TG measurements and the group of James Davis, Jr. from the University of South Alabama for the synthesis of an interesting molten salt. I would like to thank all my colleagues at CRT for the wonderful time in the lab and after work; especially the fellows in my office. Even if I hated you guys sometimes, when you were discussing about acrylic acid for hours, days, months… I had a great time in the office, nice conversations and always open ears, good advice and help. It really helps to have so nice people around you every day. Also the boys from the third floor for all the wonderful sushi evenings when I couldn’t stop laughing. Johannes Schwegler for being the best lab buddy ever. Kaija Pohako-Esko for all the coffee breaks and wonderful time at our dancing lessons. Patrick, Holger, Christina, Julian and the other wonderful people who I just can’t name all here… I also would like to acknowledge my students, Dominic Hecht, Anja Goblirsch, Ying Zhou, Sebastian Raquet, and especially Peter Weißhaupt. iii There are some people outside of the institute who made my life so wonderful and helped me also through the hard times. Caspar and Claudia, Hanna, Max, Mario and Jana, Kerstin, thank you all so much for your friendship. And last but not least, I thank my family for the emotional support and always being there when I need them. iv Declaration I declare that the work presented within this PhD thesis, except where otherwise stated, is based on my own research carried out during my time at the Institute of Chemical Reaction Engineering (Chemische Reaktionstechnik CRT) at Friedrich-Alexander-Universität Erlangen-Nürnberg between 1.10.2013 and 31.3.2017. ___________________________ v Parts of this work have already been published M. Scheuermeyer, M. Kusche, F. Agel, P. Schreiber, F. Maier, H.-P. Steinrück, J.H. Davis, Jr., F. Heym, A. Jess, P. Wasserscheid: Thermally stable bis(trifluoromethylsulfonyl)imide salts and their mixtures, New J. Chem. 40 (2016) 7157-7161. M. Scheuermeyer, F. Agel, P. Wasserscheid: Thermally stable bis(trifluoromethylsulfonyl)imide salts and their mixtures, Poster presented at the Conference on Molten Salts and Ionic Liquids (EUCHEM), Vienna 3.-8.7.2016. M. Scheuermeyer, R.W. Berg, P. Wasserscheid: Raman spectroscopy and DFT calculations of bis(trifluoromethylsulfonyl)imide-based molten salts, Oral report given at the Conference on Molten Salts and Ionic Liquids (EUCHEM), Vienna 3.-8.7.2016. M. Schwarz, P. Bachmann, T. N. Silva, S. Mohr, M. Scheuermeyer, F. Späth, U. Bauer, F. Düll, J. Steinhauer, C. Hohner, T. Döpper, H. Noei, A. Stierle, C. Papp, H.-P. Steinrück, P. Wasserscheid, A. Görling, J. Libuda: Model Catalytic Studies of Novel Liquid Organic Hydrogen Carriers: Indole, Indoline and Octahydroindole on Pt(111), Chem. Eur. J. 23 (2017) 14806-14818. vi Abstract The work presented in this thesis can be divided in two parts. The first part covers the physico-chemical investigation of chosen molten salts, all based on the bis(trifluoromethylsulfonyl)imide anion, one of the most common anions in ionic liquids (ILs). The Cs[NTf2] and [PPh4][NTf2] molten salts were of special interest. With melting points of 125 and 134 °C, respectively, they cannot be defined as ionic liquids, but they are highly thermally stable. The high thermal stability makes these molten salts very interesting as solvents for reactions at higher temperatures (between 150 and 350 °C) where common ionic liquids already decompose. Also, binary mixtures of these salts were investigated and a eutectic mixture containing 32 mol% [PPh4][NTf2] with a melting point of 98 °C was found. The density and viscosity of the mixtures lie between the ones of the pure salts. The molten salts were further investigated with vibrational spectroscopy which was extended by DFT - calculations. The [NTf2] anions of both salts were found to be in cis conformation where both CF3 groups are on the same side of the S-N-S plane. With high temperature Raman spectroscopy and mass spectrometry investigations all volatile decomposition products after prolonged heating of the salts could be identified. In order to use the molten salts as solvents for homogeneous catalysis the solvation of transition metal bis(trifluoromethylsulfonyl)imide compounds with the general formula M(NTf2)2 was studied. Raman spectroscopy, powder X-ray diffraction and mass spectrometry lead to the conclusion Co(NTf2)2 in - [PPh4][NTf2] is octahedrally coordinated and the anion [Co(NTf2)3] is formed. The mixtures of metal compounds and molten salts were investigated regarding their melting points, viscosity and thermal stability. The second part of the thesis deals with the question if the molten salts can serve as solvents for homogeneous catalysis. Thus, the M(NTf2)2 compounds (with M = Mn, Co, Ni, Cu, Zn) were used as catalyst dissolved in the IL [PMeBu3][NTf2] for the Friedel-Crafts acylation of toluene with benzoylchloride. The yields of 4-methylbenzophenone were moderate and the catalyst was found to be not stable under reaction conditions. In the context of renewable energy the storage of excess energy in the form of hydrogen has recently received a great deal of interest. One very advantageous storage method for H2 is by covalently binding it to liquid organic hydrogen carriers (LOHC). In this thesis hydrogenation and dehydrogenation were tested with homogeneous Ir catalysts immobilized in a molten salt to realize a liquid-liquid biphasic reaction with the substrates residing in a second phase of extracting agent. The dehydrogenation of indoline to indole was optimized and the extracting agent diphenyl ether was superior to dibutyl ether due to the different solubilites of the substrates. Also, the molten salts with aromatic cations showed slightly higher activity. The most active catalyst was the commercially available Crabtree catalyst [Ir(cod)(Py)(PCy3)][PF6]. Also, Co(NTf2)2(PPh3)2 was found to be active in the dehydrogenation of indoline. The biphasic approach was extended to the homogeneous Ir catalyzed hydrogenation of indole, which was found to be rather slow. However, a one-pot pressure swing reversible hydrogenation- dehydrogenation of two LOHC pairs, namely indole/indoline and quinaldine/tetrahydroquinaldine was possible. This is the first example of an ultra-low temperature hydrogen battery. vii Deutsche Zusammenfassung Die hier präsentierte Arbeit kann in zwei Abschnitte geteilt werden. Der erste Teil beschäftigt sich mit der physiko-chemischen Untersuchung von einigen ausgesuchten Salzschmelzen, die alle das für ionische Flüssigkeit häufig verwendete Bis(trifluoromethylsulfonyl)imid-Anion gemeinsam haben. Dabei waren die Cs[NTf2] und [PPh4][NTf2] Salzschmelzen besonders interessant. Mit Schmelzpunkten von jeweils 125 und 134 °C fallen sie nicht mehr unter die Definition der ionischen Flüssigkeiten, allerdings sind sie sehr thermisch stabil. Diese hohe thermische Stabilität macht diese Salzschmelzen sehr interessant als Lösungsmittel für Reaktionen bei höheren Temperaturen (zwischen 150 und 350 °C), bei der herkömmliche ionische Flüssigkeiten sich bereits zersetzen. Außerdem wurden Mischungen der Salze untersucht und eine eutektische Mischung bestehend aus 32 mol% [PPh4][NTf2] und einem Schmelzpunkt von 98°C wurde gefunden. Die Dichte und die Viskosität der binären Mischungen liegen zwischen denen der reinen Salze.
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