Leibniz Institute of Catalysis
Leibniz Institute of Catalysis
Brenna D.,University of Regensburg |
Villa M.,University of Regensburg |
Gieshoff T.N.,University of Regensburg |
Fischer F.,Johannes Kepler University |
And 4 more authors.
Angewandte Chemie - International Edition | Year: 2017
Catalyzing C−C bond-forming reactions with earth-abundant metals under mild conditions is at the heart of sustainable synthesis. The cyclotrimerization of alkynes is a valuable atom-efficient reaction in organic synthesis that is enabled by several metal catalysts, including iron. This study reports an effective iron-catalyzed cyclotrimerization for the regioselective synthesis of 1,2,4-substituted arenes (1 mol % catalyst, toluene, 20 °C, 5 min). A dual activation mechanism (substrate deprotonation, reductive elimination) renders the simple FeII precatalyst highly active in the absence of any reductant. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Perez-Ruiz R.,University of Cologne |
Fichtler R.,University of Cologne |
Diaz Miara Y.,University of Cologne |
Nicoul M.,University of Cologne |
And 6 more authors.
Journal of Fluorescence | Year: 2010
The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy. UV spectra in gas phase and DMSO solution were calculated by TD-DFT which revealed the existence of two low-energy excited singlet states with strong pH-sensitivity. © Springer Science+Business Media, LLC 2010.
Widmann D.,University of Ulm |
Krautsieder A.,University of Ulm |
Walter P.,University of Ulm |
Bruckner A.,Leibniz Institute of Catalysis |
Behm R.J.,University of Ulm
ACS Catalysis | Year: 2016
Despite enormous breakthroughs in our understanding of the reaction mechanism of the low-temperature CO oxidation on gold catalysts, in particular on Au/TiO2 and down to temperatures as low as -150 °C, there are still many contradictory proposals about the dominant reaction pathway. In this work, we will demonstrate that these discrepancies often originate from the rather different reaction conditions applied in numerous studies, most notably from different reaction temperatures. By combining temporal analysis of products reactor measurements with electron paramagnetic resonance spectroscopy, we will show that removal of TiO2 surface lattice oxygen from a Au/TiO2 catalyst upon exposure to CO (i) readily takes place at 120 °C, where it represents the active oxygen species for CO oxidation, (ii) is still possible at -20 °C, although much slower and to a much lower extent, and (iii) is completely inhibited at -90 °C. Consequences of these findings for our understanding of the dominant reaction pathway for the CO oxidation on Au/TiO2 catalysts, in particular its dependency on the reaction temperature, will be discussed. © 2016 American Chemical Society.
Desens W.,Leibniz Institute of Catalysis |
Werner T.,Leibniz Institute of Catalysis
Advanced Synthesis and Catalysis | Year: 2016
Concepts to facilitate the conversion of epoxides with carbon dioxide to the corresponding cyclic carbonates commonly focus on the activation of the epoxide. Herein we report a catalytic system which allows the simultaneous activation of carbon dioxide and the epoxide. This convergent activation concept is realized by combining a suitable carbene as catalyst for the carbon dioxide activation with a second catalytic system based on potassium iodide for epoxide activation. Initial experiments showed synergistic effects and thus proving the feasibility of this activation concept. Moreover a standard protocol was developed and the substrate scope under these conditions has been studied. Under mild and solvent-free conditions 14 epoxides could be converted. The respective cyclic carbonates were obtained in good to excellent yields with selectivities ≥ 99% after simple filtration. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Kulkarni S.J.,Indian Institute of Chemical Technology |
Rohitha C.N.,Indian Institute of Chemical Technology |
Narender N.,Indian Institute of Chemical Technology |
Koeckritz A.,Leibniz Institute of Catalysis
Journal of Porous Materials | Year: 2010
The in situ synthesis and encapsulation of metallo-octamethylcalix(4) pyrrole inside the pores of HMCM-41 catalyst is presented. The catalytic performance of the synthesized material was tested by the liquid phase oxidation of cyclohexene at room temperature using tert-butyl hydroperoxide as an oxidant. Similarly we have synthesized and encapsulated metallosalens in NaY zeolite and carried out the liquid phase oxidation of p-xylene at 100 °C using H2O2 as an oxidant. The central transition metal ions present in these two types of complexes were varied. The catalysts were characterized byXRD, IR spectra and thermal analysis. © 2009 Springer Science+Business Media, LLC.