A straightforward zinc-catalysed reduction of sulfoxides to sulfides

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In the present study, the zinc-catalysed reduction of a variety of sulfoxides with silanes as reductant to the corresponding sulfide has been examined in detail. With the straightforward and commercially available zinc(II) triflate as pre-catalyst, excellent yields and chemoselectivities were feasible. After studying the reaction conditions and the scope and limitations several attempts were undertaken to shed light on the reaction mechanism.DFG, EXC 314, Unifying Concepts in Catalysi

Palladium-catalysed hydroxylation and alkoxylation

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The formation of oxygen–carbon bonds is one of the fundamental transformations in organic synthesis. In this regard the application of palladium-based catalysts has been extensively studied during recent years. Nowadays it is an established methodology and the success has been proven in manifold synthetic procedures. This tutorial review summarizes the advances on palladium-catalysed C–O bond formation, means hydroxylation and alkoxylation reactions.DFG, EXC 314, Unifying Concepts in Catalysi

Iron-catalyzed depolymerizations of end-of-life silicones with fatty alcohols

AbstractDuring the last decades, polymers became one of the major materials in our society and a future without polymers is hardly imaginable. However, as negative issue of this success enormous amount of end-of-life materials are accumulated, which are mainly treated by landfill storage, thermal recycling or down-cycling. On the other hand, feedstock recycling can be an interesting option to convert end-of-life polymers to high quality polymers, via depolymerization reactions to low-molecular weight building blocks and subsequent transformation via polymerization reactions. In this regard, we present herein the depolymerization of polysiloxanes (silicones) applying fatty alcohols as depolymerization reagents. In more detail, in the presence of catalytic amounts of simple iron salts, low-molecular weight products with the motif R(OSiMe2)mOR (R = alkyl, m = 1–2) were attained. Remarkably, the reaction of R(OSiMe2)mOR with water showed the formation of new cyclic siloxanes, which are useful starting materials for long-chain silicones, and the corresponding fatty alcohol as side product, which can be directly reused in subsequent depolymerization reactions. Importantly, a recycling of the silicones and a straightforward recycling of the depolymerization reagent are feasible

New Aspects in Homogeneous Hydrogenation – Development of Practical Rhodium Phosphine Catalysts and Environmentally Benign Iron Catalysts

This dissertation deals with the application of monodentate phosphine ligands in asymmetric hydrogenation of C-C double bonds. The usefulness of rhodium catalysts containing phosphines based on the 4,5-Dihydro-3H-dinaphtho[2,1-c;1´,2´-e]phosphepine scaffold was demonstrated in the reduction of various prochiral substrates, since excellent enantioselectivities up to 96% ee were achieved. Furthermore, the properties of iron-based catalysts were studied in the field of transfer hydrogenation. Here high catalyst activities up to 2500 h-1 were obtained in the reduction of ketones.Die vorliegende Dissertation beschäftigte sich mit der Anwendung von monodentaten Phosphinliganden in der asymmetrischen Hydrierung von C–C Doppelbindungen. Dabei konnte die Wirksamkeit von Rhodiumkatalysatoren, die Phosphinliganden mit der 4,5-Dihydro-3H-dinaphtho[2,1-c;1´,2´-e]phosphepin-Struktureinheit enthielten, gezeigt werden. Verschiedenste prochirale Substratklassen, wurden mit exzellenten Enantioselektivitäten von bis zu 96% ee zu den entsprechenden ungesättigten Derivaten reduziert. Ein zweiter Schwerpunkt der Arbeit lag in der Entwicklung neuartiger eisenbasierter Hydrierkatalysatoren und deren Anwendung in der Transferhydrierung von Ketonen, wobei Katalysatoraktivitäten von bis zu 2500 h-1 (TOF) erzielt werden konnten

Nitrous Oxide-dependent Iron-catalyzed Coupling Reactions of Grignard Reagents

The formation of carbon–carbon bonds is one of the fundamental transformations in chemistry. In this regard the application of palladium-based catalysts has been extensively investigated during recent years, but nowadays research focuses on iron catalysis, due to sustainability, costs and toxicity issues; hence numerous examples for iron-catalyzed cross-coupling reactions have been established, based on the coupling of electrophiles (R1-X, X = halide) with nucleophiles (R2-MgX). Only a small number of protocols deals with the iron-catalyzed oxidative coupling of nucleophiles (R1-MgX + R2-MgX) with the aid of oxidants (1,2-dihaloethanes). However, some issues arise with these oxidants; hence more recently the potential of the industrial waste product nitrous oxide (N2O) was investigated, because the unproblematic side product N2 is formed. Based on that, we demonstrate the catalytic potential of easily accessible iron complexes in the oxidative coupling of Grignard reagents. Importantly, nitrous oxide was essential to obtain yields up to >99% at mild conditions (e.g. 1 atm, ambient temperature) and low catalyst loadings (0.1 mol%) Excellent catalyst performance is realized with turnover numbers of up to 1000 and turnover frequencies of up to 12000 h–1. Moreover, a good functional group tolerance is observed (e.g. amide, ester, nitrile, alkene, alkyne). Afterwards the reaction of different Grignard reagents revealed interesting results with respect to the selectivity of cross-coupling product formation

Vorausschauende Restreichweitenberechnung in Elektrofahrzeugen - Senkung von Unsicherheiten und Reichweitenschwankungen durch rechtzeitige Berücksichtigung prädizierbarer Antriebs- und Nebenverbrauchseinflüsse

Die Einführung von Elektrofahrzeugen hat großen Einfluss auf die Senkung der $\text{CO}_2$-Flottendurchschnittswerte von Automobilherstellern. Um Elektrofahrzeuge wirtschaftlich für die breite Masse zugänglich zu machen, sind weitere Anstrengungen zur Senkung der Herstellungskosten und der Steigerung der Reichweite notwendig. Eine Möglichkeit zur Steigerung der im Alltag nutzbaren Reichweite liegt darin, die technisch realisierbare Reichweite durch eine nachvollziehbare und zuverlässige Restreichweitenanzeige für den Fahrer besser nutzbar zu machen. Die Funktionsweise historienbasierter Reichweitenalgorithmen wird diskutiert und es wird erläutert, weshalb diese aufgrund ihrer konzeptbedingten Einschränkungen für eine zuverlässige Reichweitenanzeige, insbesondere für eine konkrete Aussage über die Erreichbarkeit von Fahrzielen, ungeeignet sind. In dieser Arbeit werden Konzepte zur vorausschauenden Berechnung der Restreichweite und der verbleibenden Energiemenge am Zielort untersucht. Dazu werden Verfahren und Algorithmen zur Berechnung des Antriebsverbrauchs vorgestellt und durch Simulationen untersucht. Die eingesetzten rekursiven Verfahren der Regressionsanalyse sind rechnerisch effizient und erlauben eine schnelle und zuverlässige Prädiktion des Antriebsverbrauchs entlang der Strecke. Aufgrund ihrer Lernfähigkeit sind sie mit minimalem Applikationsaufwand für den Einsatz in einer Vielzahl von Derivaten geeignet. Voraussichtliche Reichweitenänderungen durch die Zustandsänderung von Nebenverbrauchern können rechnerisch effizient ermittelt werden. Durch die vorausschauende Restreichweitenberechnung konnte mit dem vorgestellten Verfahren eine verbesserte Genauigkeit der Reichweitenanzeige erzielt werden, die auf Basis objektiver Bewertungskriterien quantifiziert wurde. Auch Schwankungen in der Restreichweitenanzeige während der Fahrt konnten deutlich reduziert werden

A polymer analogous reaction for the formation of imidazolium and NHC based porous polymer networks

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.A polymer analogous reaction was carried out to generate a porous polymeric network with N-heterocyclic carbenes (NHC) in the polymer backbone. Using a stepwise approach, first a polyimine network is formed by polymerization of the tetrafunctional amine tetrakis(4-aminophenyl)methane. This polyimine network is converted in the second step into polyimidazolium chloride and finally to a polyNHC network. Furthermore a porous Cu(II)-coordinated polyNHC network can be generated. Supercritical drying generates polymer networks with high permanent surface areas and porosities which can be applied for different catalytic reactions. The catalytic properties were demonstrated for example in the activation of CO2 or in the deoxygenation of sulfoxides to the corresponding sulfides.BMBF, 01RC0901F, Dream Reactions - Stoffliche CO2-VerwertungDFG, EXC 314, Unifying Concepts in Catalysi

Dual functionality of formamidine polymers, as ligands and as bases, in ruthenium-catalysed hydrogen evolution from formic acid

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In the present study, the ruthenium-catalysed decomposition of formic acid to yield hydrogen has been examined. A ruthenium complex modified polyformamidine network was used as a solid catalyst. As a dual support the polyformamidine acts both as a ligand and as a base for the activation of formic acid.DFG, EXC 314, Unifying Concepts in Catalysi

Iron-catalyzed depolymerizations of end-of-life silicones with fatty alcohols

During the last decades, polymers became one of the major materials in our society and a future without polymers is hardly imaginable. However, as negative issue of this success enormous amount of end-of-life materials are accumulated, which are mainly treated by landfill storage, thermal recycling or down-cycling. On the other hand, feedstock recycling can be an interesting option to convert end-of-life polymers to high quality polymers, via depolymerization reactions to low-molecular weight building blocks and subsequent transformation via polymerization reactions. In this regard, we present herein the depolymerization of polysiloxanes (silicones) applying fatty alcohols as depolymerization reagents. In more detail, in the presence of catalytic amounts of simple iron salts, low-molecular weight products with the motif R(OSiMe2)mOR (R = alkyl, m = 1-2) were attained. Remarkably, the reaction of R(OSiMe2)mOR with water showed the formation of new cyclic siloxanes, which are useful starting materials for long-chain silicones, and the corresponding fatty alcohol as side product, which can be directly reused in subsequent depolymerization reactions. Importantly, a recycling of the silicones and a straightforward recycling of the depolymerization reagent are feasible. © 2015 Tomsk Polytechnic University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer review under responsibility of Tomsk Polytechnic University

Iron-based pre-catalyst supported on polyformamidine for C-C bond formation

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In the present study the incorporation of iron into an organic polymer, composed of formamidine subunits [R–N[double bond, length as m-dash]C(H)–NH–R], has been examined. The catalytic ability of the recyclable material was investigated in the iron-catalyzed formation of C–C bonds. After optimization of the reaction conditions, excellent yields and chemoselectivities were feasible.DFG, EXC 314, Unifying Concepts in Catalysi