Unraveling the Electron Transfer Mechanism in the Reduction of Bis(µ‐Oxido) Dicopper Complexes

Tyrosinase is an oxygen‐activating enzyme and thus, functional model complexes are of high interest. The most prominent model complexes, the bis(µ‐oxido) as well as the µ‐η 2 :η 2 ‐peroxido dicopper species, show catalytic activity toward phenolic substrates. Herein, we present a kinetic and mechanistic study of the electron transfer reaction of reducing agents with two bis(µ‐oxido) dicopper complexes. As ligands, the bis(guanidine) 2‐(2‐(((bis(dimethylamino)methylene)‐amino)methyl)‐phenyl)‐1,1,3,3‐tetramethylguanidine (TMG 2 tol) and the hybrid guanidine 2‐(3‐(dimethylamino)propyl)‐1,1,3,3‐tetramethylguanidine (TMGdmap) were chosen since previous studies showed that the dicopper species with these ligands are relatively stable at −80°C and at the same time have a fast formation. We determine full kinetic and thermodynamic parameters of the electron transfer reaction. With the help of spectroscopic kinetic analysis, we show that the electron transfer step is a reaction containing two independent steps. Moreover, density functional theory studies reveal the intriguing electronic structure of the reduced Cu 2 O 2 complexes. This study highlights the ability of Cu 2 O 2 species to cope with reducing equivalents.