Guanidines strike back: Exceptional Substrate Diversity in Oxygenation Reactions Catalyzed by a Bis(µ-oxo) Copper Complex.

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. We describe the synthesis and characterization 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 - ) via UV/Vis, Raman and XAS spectroscopy as well as cryo-UHR-ESI mass spectrometry, stabilized by the novel hybrid guanidine ligand 2-{2-((dimethylamino)methyl)phenyl}-1,1,3,3-tetramethylguanidine ( L1 ) . We highlight selective oxygenation of a plethora of phenolic substrates mediated by [ O1 ](PF 6 ) 2 , that results in mono- and bicyclic quinones and provides an attractive strategy on the route to design new phenazines . The selectivity is predictable 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 which goes far beyond the enzyme's scope.