Dioxygen Activation by a Macrocyclic Copper Complex Leads to a Cu 2 O 2 Core with Unexpected Structure and Reactivity

We report the Cu I /O 2 chemistry of complexes derived from the macrocylic ligands 14‐TMC (1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane) and 12‐TMC (1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane). While [(14‐TMC)Cu I ] + is unreactive towards dioxygen, the smaller analog [(12‐TMC)Cu I (CH 3 CN)] + reacts with O 2 to give a side‐on bound peroxo‐dicopper(II) species ( S P), confirmed by spectroscopic and computational methods. Intriguingly, 12‐TMC as a N4 donor ligand generates S P species, thus in contrast with the previous observation that such species are generated by N2 and N3 ligands. In addition, the reactivity of this macrocyclic side‐on peroxo‐dicopper(II) differs from typical S P species, because it reacts only with acid to release H 2 O 2 , in contrast with the classic reactivity of Cu 2 O 2 cores. Kinetics and computations are consistent with a protonation mechanism whereby the TMC acts as a hemilabile ligand and shuttles H + to an isomerized peroxo core.