Mono-and bis(guanidine) ligands stabilise bis-μ-oxido dicopper(III) complexes. Here, the formation of these complexes has been investigated in detail by means of lowtemperature 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 bis-μ-oxido complexes. For both systems, no intermediates on the pathways to the bis-μ-oxido complexes could be detected; this has been explained through extensive DFT calculations. In the first step,

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.

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 [Cu2(μ‐O)2(L1)2](X)2 ([O1](X)2, X=PF6−, BF4−, OTf−, ClO4−), 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](PF6)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.

For the first time the formation and decay of the thermally very sensitive bis(μ-oxo)dicopper species was monitored at ambient temperature in a continuous flow setup and the rate constant of the decay was measured.

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) (4-CO MePy) which stabilises a room-temperature stable μ-η :η -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.

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

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 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.

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