Ulrich Herber

Formation of Novel Dinuclear Mixed-Valence Rhodium Complexes by Intramolecular Migration of a Chelating Ligand

Significantly different coordination spheres are displayed by the two central atoms of 2, the first representative of a novel type of mixed-valence dinuclear Rh0 -RhII compound, which was synthesized from the stibane-bridged complex 1. The Rh-Rh distance determined by an X-ray crystal structure analysis of 2 indicates a metal-metal interaction between the two metal centers.

Bildung neuartiger gemischtvalenter Rh0‐RhII‐Zweikernkomplexe durch intramolekulare Wanderung eines Chelatliganden

Unterschiedlich koordiniert sind die beiden Zentralatome in der ersten, ausgehend von dem Stiban-verbruckten Komplex 1 synthetisierten Verbindung 2 eines neuartigen Typs gemischtvalenter Rh0-RhII-Zweikernkomplexe. Zwischen den Metallzentren besteht dem kristallstrukturanalytisch ermittelten Rh-Rh-Abstand zufolge eine Metall-Metall-Wechselwirkung.

N-Donor Competition in Iron Bis(chelate) Bis(pyrazolyl)pyridinylmethane Complexes

Abstract We report on the synthesis and structural characterisation of the bis(chelate) bis(pyrazolyl) pyridinylmethane iron(II) complexes [Fe{HC(Pz)2(Py)}2][CF3CO2]2, [Fe{HC(3-iPrPz)(5- iPrPz)(Py)}2][CF3SO3]2 and [Fe{HC(3-iPrPz)(5-iPrPz)(Py)}2][FeBr4]Br·2C4H8O. During the synthesis of the latter ones, an isomerisation of the ligand is observed: the pyrazolyl substituent formally moves from the 3 to the 5 position. Since the donor competition between pyrazolyl and pyridinyl moieties is important for the coordination properties, we also studied the donor properties by density functional theory and natural bond orbital analysis (NBO). As a result, the pyridinyl donor is generally weaker than the pyrazolyl donor, but the pyrazolyl donor is heavily influenced by the alkyl substitution pattern. To confirm the low-spin state of the complexes, magnetic susceptibility measurements have been performed

Designed To React: Terminal Copper Nitrenes and Their Application in Catalytic C−H Aminations

Heteroscorpionate ligands of the bis(pyrazolyl)methane family have been applied in the stabilisation of terminal copper tosyl nitrenes. These species are highly active intermediates in the copper-catalysed direct C-H amination and nitrene transfer. Novel perfluoroalkyl-pyrazolyl- and pyridinyl-containing ligands were synthesized to coordinate to a reactive copper nitrene centre. Four distinct copper tosyl nitrenes were prepared at low temperatures by the reaction with SO2 tBuPhINTs and copper(I) acetonitrile complexes. Their stoichiometric reactivity has been elucidated regarding the imination of phosphines and the aziridination of styrenes. The formation and thermal decay of the copper nitrenes were investigated by UV/Vis spectroscopy of the highly coloured species. Additionally, the compounds were studied by cryo-UHR-ESI mass spectrometry and DFT calculations. In addition, a mild catalytic procedure has been developed where the copper nitrene precursors enable the C-H amination of cyclohexane and toluene and the aziridination of styrenes.