The critical review describes the known dicopper systems mediating the aromatic hydroxylation of monophenolic substrates. Such systems are of interest as structural and functional models of the type 3 copper enzyme tyrosinase, which catalyzes the ortho-hydroxylation of tyrosine to DOPA and the subsequent two-electron oxidation to dopaquinone. Small-molecule systems involving μ-η²:η² peroxo, bis-μ-oxo and trans-μ-1,2 peroxo dicopper cores are considered separately. These tyrosinase models are contrasted to copper-dioxygen systems inducing radical reactions, and the different mechanistic pathways are discussed. In addition to considering the stoichiometric conversion of phenolic substrates, the available catalytic systems are described. The second part of the review deals with tyrosinase. After an introduction on the occurrence and function of tyrosinases, several aspects of the chemical reactivity of this class of enzymes are described. The analogies between the small-molecule and the enzymatic system are considered, and the implications for the reaction pathway of tyrosinase are discussed (140 references).

Ready…︁ steady…︁ go! The copper(I) complex 1 not only catalyzes the oxygenation of di‐tert‐butylphenol (DTBP‐H) to di‐tert‐butylquinone (DTBQ) in a tyrosinase‐like fashion, but also allows the reactive cycle to be studied in a stepwise and controlled manner. This feature opens new insights into the individual stages of the tyrosinase reaction, phenol hydroxylation, and release of the product as quinone. The implications for the enzymatic reaction are discussed.

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Copper at work: The aliphatic ligand hydroxylation by a copper–oxygen center has been observed for the first time on a model system of the enzyme PHM (peptidylglycine‐α‐hydroxylating monooxygenase). This result is put in the context of the enzymatic mechanism, which presumably involves a high‐valent copper oxo unit (violet‐red) that hydroxylates the substrate (cyan).

Auf die Plätze, fertig, los! Der Kupfer(I)‐Komplex 1 katalysiert nicht nur die Oxygenierung von 2,4‐Di‐tert‐butylphenol 2 zum o‐Chinon 3 analog zur Tyrosinase, sondern ermöglicht auch, den Katalysezyklus schrittweise zu durchlaufen. Dies gibt neue Einblicke in die zwei Teile der Tyrosinasereaktion, Phenolhydroxylierung und Freisetzung des Produkts als Chinon. Die Bedeutung für die enzymatische Reaktion wird diskutiert.

A new tridentate N-donor ligand and its corresponding copper(i) complex have been synthesized to investigate the tyrosinase-like aromatic hydroxylation of an attached phenol. The results of the oxygenation reactions are compared to related systems having attached phenyl and catechol groups, respectively. The title complex is the first system mediating the monooxygenation of a phenol in the absence of an external base.

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Radicals in directed pathways: The μ‐η2:η2 peroxo CuII2 intermediate 1 shows a much faster benzylic ligand hydroxylation than systems without phenol. This novel reactivity can be further accelerated by addition of external H‐atom donors such as TEMPO‐H. The results imply initial H‐atom transfer leading to the formation of phenoxyl radicals. A highly reactive copper oxyl intermediate is then formed, which inserts oxygen into the benzylic CH bond.