Biomimetic Hydroxylation Catalysis Through Self‐Assembly of a Bis(pyrazolyl)methane Copper–Peroxo Complex

Wilfer, Claudia; Liebhäuser, Patricia; Erdmann, Hannes; Hoffmann, Alexander; Herres‐Pawlis, Sonja

doi:10.1002/ejic.201402957

Cited by 29 publications

(30 citation statements)

References 52 publications

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“…It should be noted that all attempts failed and yielded the experimentally found conformers. However, the observed pyrazolyl–imidazolyl coordination is not caused by steric hindrance of the large tert ‐butyl groups, since we already have structurally characterised comparable copper(II) halide complexes with the sterically similar ligand HC(3‐ t BuPz) 2 (Py) 19. We interpret this finding as an indication of the slightly stronger donor strength of imidazolyl groups, as already discussed by others 46–48.…”

Section: Resultssupporting

confidence: 79%

“…When both components are present, the P species does not appear, but the same catalytic hydroxylation reaction is observable by its strong quinone absorption as those observed when the components are added after P formation. This type of self‐assembly has been observed previously for related P species 19. 68 We also studied the potential influence of silver ions, but retrieving all AgCl by means of a syringe filter (0.45 μm) did not change the results.…”

Section: Resultssupporting

confidence: 67%

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Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex

Wilfer

Liebhäuser

Hoffmann

et al. 2015

Chemistry A European J

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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.

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Section: Resultssupporting

confidence: 79%

Section: Resultssupporting

confidence: 67%

Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex

Wilfer

Liebhäuser

Hoffmann

et al. 2015

Chemistry A European J

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“…The metal centre is coordinated by two chloride ions and all three N‐donor units of L . This coordination motif is comparable to the structure of [Cu{HC(3‐ t BuPz) 2 (Py)}Cl 2 ] ( CC1 ) where the pyridinyl moiety of the ligand is unsubstituted . In contrast, the reported complex CC2 ([Cu{HC(3‐ t BuPz) 2 (1‐MeIm)}Cl 2 ]), where the pyridinyl moiety is exchanged by a methylimidazolyl moiety, exhibits a tetra‐coordinated copper centre .…”

Section: Resultsmentioning

confidence: 50%

“…The same maximum value is obtained at room temperature, but then within 10 seconds. Remarkably, the catalytic reaction also proceeds when working under self‐assembly conditions at low and at room temperature, that is, injection of a copper precursor solution to an oxygenated phenol/NEt 3 solution . However, then no peroxide intermediate can be observed.…”

Section: Resultsmentioning

confidence: 99%

Record Broken: A Copper Peroxide Complex with Enhanced Stability and Faster Hydroxylation Catalysis

Liebhäuser

Keisers

Hoffmann

et al. 2017

Chemistry A European J

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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.

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“…[31] In contrast to catecholoxidase mimics,t yrosinase models require the addition of base. [15] Whereas originally an excess of triethylamine had to be employed to deprotonate phenolic substrates, [33,34] application of astoichiometric amount (or as light excess) of diamine ligand to achieve catalytic activity in these model systems has been shown only recently. [15] Whereas originally an excess of triethylamine had to be employed to deprotonate phenolic substrates, [33,34] application of astoichiometric amount (or as light excess) of diamine ligand to achieve catalytic activity in these model systems has been shown only recently.…”

Section: Methodsmentioning

confidence: 99%

Tyrosinase versus Catechol Oxidase: One Asparagine Makes the Difference

2016

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Tyrosinases mediate the ortho-hydroxylation and two-electron oxidation of monophenols to ortho-quinones. Catechol oxidases only catalyze the oxidation of diphenols. Although it is of significant interest, the origin of the functional discrimination between tyrosinases and catechol oxidases has been unclear. Recently, it has been postulated that a glutamate and an asparagine bind and activate a conserved water molecule towards deprotonation of monophenols. Here we demonstrate for the first time that a polyphenoloxidase, which exhibits only diphenolase activity, can be transformed to a tyrosinase by mutation to introduce an asparagine. The asparagine and a conserved glutamate are necessary to properly orient the conserved water in order to abstract a proton from the monophenol. These results provide direct evidence for the crucial importance of a proton shuttle for tyrosinase activity of type 3 copper proteins, allowing a consistent understanding of their different chemical reactivities.

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Biomimetic Hydroxylation Catalysis Through Self‐Assembly of a Bis(pyrazolyl)methane Copper–Peroxo Complex

Abstract: 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

Cited by 29 publications

References 52 publications

Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex

Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex

Record Broken: A Copper Peroxide Complex with Enhanced Stability and Faster Hydroxylation Catalysis

Tyrosinase versus Catechol Oxidase: One Asparagine Makes the Difference

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