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Papers by Dennis Pingen
Dalton Trans., 2016
A Ru-based half sandwich complex used in amine and alcohol racemization reactions was found to be... more A Ru-based half sandwich complex used in amine and alcohol racemization reactions was found to be active in the splitting of secondary amines to primary amines using NH3. Conversions up to 80% along with very high selectivities were achieved. However, after about 80% conversion the catalyst lost activity. Similar to Shvo's catalyst, the complex might deactivate under the influence of ammonia. It was revealed that not NH3 but mainly the primary amine is responsible for the deactivation.
Catal. Sci. Technol., 2014
Organometallics, 2014
ABSTRACT With RuHCl(CO)(PPh3)3 as the starting material, the complexes RuHCl(CO)(PPh3)(L) were pr... more ABSTRACT With RuHCl(CO)(PPh3)3 as the starting material, the complexes RuHCl(CO)(PPh3)(L) were prepared for L = Xantphos and closely related ligands. Their catalytic activity in the direct amination of cyclohexanol showed large differences depending on the different backbone structures. In those complexes the Xantphos-type ligand backbones are slightly bent and display fluxionality, studied by VT-NMR. This was assigned to the “flipping” of the backbone via the bridging atoms in the xanthene backbone. Via line shape analysis of the peaks, the Gibbs free energy of activation of the flipping movement was found to be around 56 kJ/mol in all cases. However, the activation enthalpy and entropy differed considerably. Employing RuCl2(PPh3)3 as the precursor resulted in the trans-coordinated complexes RuCl2(PPh3)(L) for L = Xantphos, Sixantphos. Fluxionality was no longer observed, due to the fact that in these complexes the O atom in the backbone also coordinates to the Ru.
Angewandte Chemie International Edition, 2010
Dalton Trans., 2016
A Ru-based half sandwich complex used in amine and alcohol racemization reactions was found to be... more A Ru-based half sandwich complex used in amine and alcohol racemization reactions was found to be active in the splitting of secondary amines to primary amines using NH3. Conversions up to 80% along with very high selectivities were achieved. However, after about 80% conversion the catalyst lost activity. Similar to Shvo's catalyst, the complex might deactivate under the influence of ammonia. It was revealed that not NH3 but mainly the primary amine is responsible for the deactivation.
Catal. Sci. Technol., 2014
Organometallics, 2014
ABSTRACT With RuHCl(CO)(PPh3)3 as the starting material, the complexes RuHCl(CO)(PPh3)(L) were pr... more ABSTRACT With RuHCl(CO)(PPh3)3 as the starting material, the complexes RuHCl(CO)(PPh3)(L) were prepared for L = Xantphos and closely related ligands. Their catalytic activity in the direct amination of cyclohexanol showed large differences depending on the different backbone structures. In those complexes the Xantphos-type ligand backbones are slightly bent and display fluxionality, studied by VT-NMR. This was assigned to the “flipping” of the backbone via the bridging atoms in the xanthene backbone. Via line shape analysis of the peaks, the Gibbs free energy of activation of the flipping movement was found to be around 56 kJ/mol in all cases. However, the activation enthalpy and entropy differed considerably. Employing RuCl2(PPh3)3 as the precursor resulted in the trans-coordinated complexes RuCl2(PPh3)(L) for L = Xantphos, Sixantphos. Fluxionality was no longer observed, due to the fact that in these complexes the O atom in the backbone also coordinates to the Ru.
Angewandte Chemie International Edition, 2010