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A Cu(I) fully fluorinated O-donor monodentate alkoxide complex, K[Cu(OC4F9)2], was previously shown to form a trinuclear copper–dioxygen species with a {Cu3(μ3-O)2} core, TOC4F9, upon reactivity with O2 at low temperature. Herein is reported a significantly expanded kinetic and mechanistic study of TOC4F9 formation using stopped-flow spectroscopy. The TOC4F9 complex performs catalytic oxidase conversion of hydroquinone (H2Q) to benzoquinone (Q). TOC4F9 also demonstrated hydroxylation of 2,4-di-tert-butylphenolate (DBP) to catecholate, making TOC4F9 the first trinuclear species to perform tyrosinase (both monooxygenase and oxidase) chemistry. Resonance Raman spectra were also obtained for TOC4F9, to our knowledge, the first such spectra for any T species. The mechanism and substrate reactivity of TOC4F9 are compared to those of its bidentate counterpart, TpinF, formed from K[Cu(pinF)(PR3)]. The monodentate derivative has both faster initial formation and more diverse substrate reactivity.

Chemistry - a European journal 26(34), 7556-7562 (2020). doi:10.1002/chem.202000664, The enzyme tyrosinase contains a reactive side‐on peroxo dicopper(II) center as catalytically active species in C−H oxygenation reactions. The tyrosinase activity of the isomeric bis($μ$‐oxo) dicopper(III) form has been discussed controversially. The synthesis of bis(μ‐oxo) dicopper(III) species [Cu$_2$($μ$‐O)$_2$(L1)$_2$](X)$_2$ ([O1](X)$_2$, X=PF$_6^−$, BF$_4^−$, OTf$^−$, ClO$_4^−$), stabilized by the new hybrid guanidine ligand 2‐{2‐((dimethylamino)methyl)phenyl}‐1,1,3,3‐tetramethylguanidine (L1), and its characterization by UV/Vis, Raman, and XAS spectroscopy, as well as cryo‐UHR‐ESI mass spectrometry, is described. We highlight selective oxygenation of a plethora of phenolic substrates mediated by [O1](PF$_6$)$_2$, which results in mono‐ and bicyclic quinones and provides an attractive strategy for designing new phenazines. The selectivity is predicted by using the Fukui function, which is hereby introduced into tyrosinase model chemistry. Our bioinspired catalysis harnesses molecular dioxygen for organic transformations and achieves a substrate diversity reaching far beyond the scope of the enzyme., Published by Wiley-VCH, Weinheim

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 SO(2)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.

CuI complexes of the form K[(R3P)Cu(pinF)], in which (pinF)2− is the bidentate, oxygen-donating ligand perfluoropinacolate, were synthesized and characterized. Low-temperature oxygenation of the K[(R3P)Cu(pinF)(PR3)] species resulted in a trisanionic bis(μ3-oxo) trinuclear copper(II,II,III) core characterized by UV/Vis spectroscopy (λmax [nm] = 330, 535, 630), cryospray-ionization mass spectrometry, and X-band electron paramagnetic resonance spectroscopy (derivative resonance at 3300 G, Δms=2 at 1500 G). The kinetic behavior of the trimeric {Cu3O2} species was quantified by stopped-flow spectroscopy and the associated electronic structures were investigated by DFT calculations. An asymmetric {Cu3O2} species, AsTpinF, which bears a structure similar to multicopper oxidases, forms prior to full formation of the symmetric trinuclear core, SyTpinF. The trimer catalytically oxidizes para-hydroquinone to benzoquinone (a form of oxidase chemistry).

A Cu(i) fully fluorinated O-donor monodentate alkoxide complex, K[Cu(OC4F9)2], was previously shown to form a trinuclear copper-dioxygen species with a {Cu3(μ3-O)2} core, TOC4F9, upon reactivity with O2 at low temperature. Herein is reported a significantly expanded kinetic and mechanistic study of TOC4F9 formation using stopped-flow spectroscopy. The TOC4F9 complex performs catalytic oxidase conversion of hydroquinone (H2Q) to benzoquinone (Q). TOC4F9 also demonstrated hydroxylation of 2,4-di-tert-butylphenolate (DBP) to catecholate, making TOC4F9 the first trinuclear species to perform tyrosinase (both monooxygenase and oxidase) chemistry. Resonance Raman spectra were also obtained for TOC4F9, to our knowledge, the first such spectra for any T species. The mechanism and substrate reactivity of TOC4F9 are compared to those of its bidentate counterpart, TpinF, formed from K[Cu(pinF)(PR3)]. The monodentate derivative has both faster initial formation and more diverse substrate reactivity.

Tyrosinase serves as archetype for nature’s solution to activate molecular oxygen and use it for mild and selective hydroxylation of phenols. In the last 30 years, a plethora of ligand systems has been used for the stabilization of model complexes. This module summarizes all functional models reported so far, which exert hydroxylation activity on exogenous substrates. The models are sorted according to the Cu 2 O 2 species they stabilize (viz, μ-η 2 :η 2 -peroxodicopper(II), bis(μ-oxo)dicopper(III) and trans -μ-1,2-peroxodicopper(II) species) and the reactivity they display, hence stoichiometric or catalytic. The fundamentals for the theoretical understanding of μ-η 2 :η 2 -peroxodicopper(II) and bis(μ-oxo)dicopper(III) cores are explained, and theoretical advancements on hydroxylation active model complexes are discussed.

Mono- and bis(guanidine) ligands stabilise bis-µ-oxido dicopper(III) complexes. Here, the formation of this complex has been investigated in detail using low temperature stopped-flow techniques for the monoguanidine 2-(3-(dimethylamino)propyl)-1,1,3,3-tetramethylguanidine (TMGdmap) and the related bis(guanidine) 1,3-bis(N,N,N',N'-tetramethylguanidino)propane (btmgp). Low temperature IR studies in solution support the formation of a bis-µ-oxido complex. For both systems, no intermediates could be detected on their way to the bis-µ-oxido complexes which is rationalised by extensive DFT calculations. In a first step, the oxygen reduction during the binding to the copper(I) complex to form a superoxido species is studied. In the second step, the full path from superoxido over trans-µ-peroxido to side-on-peroxido and finally bis-µ-oxido is modelled for singlet and triplet states. Hereby, a clear picture about the detailed reaction mechanism is gained which directly correlates with the observed activation enthalpies and reaction orders. The superoxido formation is rate-determining as pseudo-first order in copper(I) although the bis-µ-oxido formation is observed. The results illustrate the strength of density functional theory for the prediction of the reactivity of real-life systems.

Bis(pyrazolyl)methane ligands are excellent components of model complexes used to investigate the activity of the enzyme tyrosinase. Combining the N donors 3-tert-butylpyrazole and 1-methylimidazole results in a ligand that is capable of stabilising a (μ-η(2) :η(2) )-dicopper(II) core that resembles the active centre of tyrosinase. UV/Vis spectroscopy shows blueshifted UV bands in comparison to other known peroxo complexes, due to donor competition from different ligand substituents. This effect was investigated with the help of theoretical calculations, including DFT and natural transition orbital analysis. The peroxo complex acts as a catalyst capable of hydroxylating a variety of phenols by using oxygen. Catalytic conversion with the non-biological phenolic substrate 8-hydroxyquinoline resulted in remarkable turnover numbers. In stoichiometric reactions, substrate-binding kinetics was observed and the intrinsic hydroxylation constant, kox , was determined for five phenolates. It was found to be the fastest hydroxylation model system determined so far, reaching almost biological activity. Furthermore, Hammett analysis proved the electrophilic character of the reaction. This sheds light on the subtle role of donor strength and its influence on hydroxylation activity.

We synthesised and characterised four copper complexes (with copper in the oxidation states I and II) with the bis(pyrazolyl)methane ligands HC(3-tBuPz)2(Py) and HC(3-tBuPz)2(Qu). With the quinolinyl ligand (2-quinolinyl)bis(3-tert-butylpyrazolyl)methane [HC(3-tBuPz)2(Qu)] we obtained the tetrahedral monofacial complex [CuCl{HC(3-tBuPz)2(Qu)}] (C1) and with the pyridinyl ligand (2-pyridinyl)bis(3-tert-butylpyrazolyl)methane [HC(3-tBuPz)2(Py)] we obtained the three complexes [CuCl{HC(3-tBuPz)2(Py)}] (C2), [CuBr2{HC(3-tBuPz)2(Py)}] (C3) and [CuCl2{HC(3-tBuPz)2(Py)}] (C4), which are also monofacially coordinated. The mo

Tyrosinase model systems pinpoint pathways to translating Nature's synthetic abilities for useful synthetic catalysts. Mostly, they use N-donor ligands which mimic the histidine residues coordinating the two copper centres. Copper complexes with bis(pyrazolyl) methanes with pyridinyl or imidazolyl moieties are already reported as excellent tyrosinase models. Substitution of the pyridinyl donor results in the new ligand HC(3-tBuPz)(2)(4-CO2MePy) which stabilises a room-temperature stable mu-eta(2):eta(2)-peroxide dicopper(II) species upon oxygenation. It reveals highly efficient catalytic activity as it hydroxylates 8-hydroxyquinoline in high yields (TONs of up to 20) and much faster than all other model systems (max. conversion within 7.5 min). Stoichiometric reactions with para-substituted sodium phenolates show saturation kinetics which are nearly linear for electron-rich substrates. The resulting Hammett correlation proves the electrophilic aromatic substitution mechanism. Furthermore, density functional theory (DFT) calculations elucidate the influence of the substituent at the pyridinyl donor: the carboxymethyl group adjusts the basicity and nucleophilicity without additional steric demand. This substitution opens up new pathways in reactivity tuning.

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Anfang September fand an der RWTH Aachen das Bioanorganische Symposium 2016 mit 90 Teilnehmern statt. Die Mitglieder der DFG-geforderten Forschergruppe 1405 prasentierten in diesem Abschlusssymposium ihre neuesten Ergebnisse zum Thema Biological and Inorganic Charge Transfer Dynamics und diskutierten sie mit den neun eingeladenen Vortragenden aus aller Welt. Zur Forschergruppe gehoren insgesamt sieben Arbeitsgruppen von der RWTH Aachen, der Universitat Hamburg, dem Center of Free-Electron Laser Science (CFEL) und der Universitat Paderborn. Sie beschaftigt sich mit experimentellen und theoretischen Untersuchungen von Elektronen- und Charge-Transfer-Reaktionen. Etliche Wissenschaftler aus Deutschland nahmen teil und prasentierten neben 25 Vortragen 55 Poster.