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Hier werden aktuelle Publikationen vorgestellt. Die untergeordneten Seiten (s. Navigationsleiste auf der linken Seite) enthalten eine Liste aller Veröffentlichungen in Rückwärtschronologie.

Aggregation of mononuclear copper complexes by metal-oxidation-induced ligand deprotonation

Lupe

J. Gülzow, G. Hörner, E. Irran, A. Grohmann, Inorg. Chim. Acta 2017, DOI: 10.1016/j.ica.2017.08.017.

The coordination chemistry of the tetrapodal-pentadentate ligand L, which has a mixed N3O2 donor set, has been studied in the presence of copper(I) sources. The metal-to-ligand stoichiometry of the mononuclear copper(I) complexes resulting from 1:1 metal/ligand mixtures is markedly dependent on the character of the counter ion, giving 1:1 ([Cu(L)Cl]) and 1:2 complexes ([Cu(L)2](PF6)), with coordinating chloride and non-coordinating hexafluorophosphate, respectively. 1H NMR and UV-Vis spectroscopy and single crystal X-ray structure analysis reveal tetrahedral coordination in both cases, with the “soft” copper centre engaging only two pyridine donors out of the N3O2 donor set. Upon chemical oxidation of [Cu(L)2](PF6) with dioxygen or 3,5–di-tert-butyl-quinone, the same binuclear copper(II) complex [Cu2(L-H)2](PF6)2 is selectively formed, indicating metal-oxidation induced deprotonation of one ligand, extrusion of the second ligand and subsequent fusion of the coordination spheres via alkoxide bridges. Elongation along a Jahn-Teller active molecular axis in [Cu2(L-H)2]2+ is affected by the nature of the counter ion, giving N2O3 and N3O2 coordination patterns in the hexafluorophosphate and in the chloride salt, respectively. In addition to the oxidised complex, isolated in close-to-quantitative yield, catechol is identified as the only reduction product, indicating a 2e-/2H+ reduction of the quinone. Electron transfer from copper(I) to the chemical oxidant is suggested to steer the formation of base equivalents from O2 and Q, which then drive ligand deprotonation and complex nucleation.

Oxygen Delivery as a Limiting Factor in Modelling Dicopper(II) Oxidase Reactivity

Lupe

J. Gülzow, G. Hörner, P. Strauch, A. Stritt, E. Irran, A. Grohmann,
Chem. Eur. J.
2017, 23, 7009–7023.

Deprotonation of ligand-appended alkoxyl groups in mononuclear copper(II) complexes of N,O ligands L1 and L2, gave dinuclear complexes sharing symmetrical Cu2O2 cores. Molecular structures of these mono- and binuclear complexes have been characterized by XRD, and their electronic structures by UV/Vis, 1H NMR, EPR and DFT; moreover, catalytic performance as models of catechol oxidase was studied. The binuclear complexes with anti-ferromagnetically coupled copper(II) centers are moderately active in quinone formation from 3,5-di-tert-butyl-catechol under the established conditions of oxygen saturation, but are strongly activated when additional dioxygen is administered during catalytic turnover. This unforeseen and unprecedented effect is attributed to increased maximum reaction rates vmax, whereas the substrate affinity KM remains unaffected. Oxygen administration is capable of (partially) removing limitations to turnover caused by product inhibition. Because product inhibition is generally accepted to be a major limitation of catechol oxidase models, we think that our observations will be applicable more widely.

Controlled ligand distortion and its consequences for structure, symmetry, conformation and spin-state preferences of iron(II) complexes

Lupe

N. Kroll, K. Theilacker, M. Schoknecht, D. Baabe, D. Wiedemann, M. Kaupp, A. Grohmann, G. Hörner, Dalton Trans. 2015, 44, 19232–19247.

The ligand-field strength in metal complexes of polydentate ligands depends critically on how the ligand backbone places the donor atoms in three-dimensional space. Distortions from regular coordination geometries are often observed. In this work, we study the isolated effect of ligand-sphere distortion by means of two structurally related pentadentate ligands of identical donor set, in the solid state (X-ray diffraction, 57Fe-Mössbauer spectroscopy), in solution (NMR spectroscopy, UV/Vis spectroscopy, conductometry), and with quantum-chemical methods. Crystal structures of hexacoordinate iron(II) and nickel(II) complexes derived from the cyclic ligand L1 (6-methyl-6-(pyridin-2-yl)-1,4-bis(pyridin-2-ylmethyl)-1,4-diazepane) and its open-chain congener L2 (N1,N3,2-trimethyl-2-(pyridine-2-yl)-N1,N3-bis(pyridine-2-ylmethyl) propane-1,3-diamine) reveal distinctly different donor set distortions reflecting the differences in ligand topology. Distortion from regular octahedral geometry is minor for complexes of ligand L2, but becomes significant in the complexes of the cyclic ligand L1, where trans elongation of Fe−N bonds cannot be compensated by the rigid ligand backbone. This provokes trigonal twisting of the ligand field. This distortion causes the metal ion in complexes of L1 to experience a significantly weaker ligand field than in the complexes of L2, which are more regular. The reduced ligand-field strength in complexes of L1 translates into a marked preference for the electronic high-spin state, the emergence of conformational isomers, and massively enhanced lability with respect to ligand exchange and oxidation of the central ion. Accordingly, oxoiron(IV) species derived from L1 and L2 differ in their spectroscopic properties and their chemical reactivity.

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Leiter

Prof. Dr. Andreas Grohmann
Institut für Chemie
Sekr. C 2
Straße des 17. Juni 135
10623 Berlin
+49 30 314 79877
+49 30 314 22935

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Besuchsadresse

Prof. Dr. Andreas Grohmann
Bioanorganische Chemie
Institut für Chemie
Gebäude C
Raum C 107
Straße des 17. Juni 115
10623 Berlin