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We report the chelation-assisted oxidative CH2 extrusion from a PtII-coordinated dipyridylmethane, resulting in the formation of a 2,2′-bipyridyl ligand. This unusual one-pot reaction (solvent: dimethylformamide, DMF), which is quantitative, proceeds in air at mildly elevated temperature, with CH2 → C=O conversion, decarbonylation, and ipso-ipso C–C coupling of the two pyridyl residues ("fragment coupling"). It constitutes, in effect, a chelate ring contraction by one member. [ABSTRACT FROM AUTHOR]

Formation of the O−O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High‐valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O−O bond in solution, from non‐heme, N5‐coordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once meta‐chloroperbenzoic acid is administered in excess. Oxygen‐isotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT (hydrogen atom transfer)‐initiated free‐radical pathways of the peroxides, which are typical of catalase‐like reactivity, and iron‐borne O−O coupling, which is unprecedented for non‐heme/peroxide systems. Interpretation in terms of [FeIV(O)] and [FeV(O)] being the resting and active principles of the O−O coupling, respectively, concurs with fundamental mechanistic ideas of (electro‐) chemical O−O coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting. [ABSTRACT FROM AUTHOR]

Three copper(II) complexes of a series of bidentate dipyridylmethane ligands, as well as their structurally related platinum(II) analogues, have been synthesised and fully characterised to evaluate their coordination chemistry and antiproliferative properties. New crystal structures of the complexes L³CuCl2, L²PtCl² and L³PtCl², where L², L³ have one and two methyl substituents on the bridgehead carbon atom between the coordinated pyridine ligands, respectively, were obtained The in vitro cytotoxicity of the free ligands and their corresponding platinum and copper complexes was evaluated in the cisplatin-sensitive ovarian teratocarcinoma cell line CH1/PA1, as well as in rather cisplatin-insensitive colon (SW480) and lung (A549) carcinoma cells, using the MTT assay. All six complexes showed higher cytotoxicity than the ligands L¹-L³ alone, giving IC50 values in the low micromolar range. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Oxidation of catechol to quinone facilitated by dicopper‐dependent oxidases is vital in plant defense. One of the most striking manifestations is the browning of sliced or injured fruit (painting by Gabriele Endres). Our modeling of enzyme action with a new set of synthetic dicopper(II) complexes revealed a massive increase in catalytic turnover if dioxygen‐saturated solutions are periodically treated with additional dioxygen. This effect of oxygen administration has heretofore gone unnoticed. Thus, kinetics modeling should also take into account the amplifying effect of mass transport from bubbles. More information can be found in the Full Paper by G. Hörner and A. Grohmann et al. on page 7009. [ABSTRACT FROM AUTHOR]

Formation of the O-O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High-valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O-O bond in solution, from non-heme, N 5 -coordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once meta-chloroperbenzoic acid is administered in excess. Oxygen-isotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT (hydrogen atom transfer)-initiated free-radical pathways of the peroxides, which are typical of catalase-like reactivity, and iron-borne O-O coupling, which is unprecedented for non-heme/peroxide systems. Interpretation in terms of [Fe IV (O)] and [Fe V (O)] being the resting and active principles of the O-O coupling, respectively, concurs with fundamental mechanistic ideas of (electro-) chemical O-O coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)