Intramolecular Benzylic Hydroxylation by a {Cu₂O₂} Intermediate Leading to an Unusual Trinuclear Copper(II) Species

Dioxygen activation involving transition metal complexes, and its participation in substrate inert bond functionalizations, plays a crucial role in understanding the function of certain metalloenzymes as well as in the development of bioinspired catalysis. Here, we have described a unique module of side-on peroxo dicopper(II) formation using a tridentate alkyl amine ligand and its concomitant participation in benzylic hydroxylation of the internally tethered phenethyl moiety. Structural and spectroscopic characterization authenticates the unsymmetrical trinuclear copper (Cu₃) complex as a final product. Moreover, the EPR data and the magnetic moment calculation (1.89 B.M.) by the Evans method, together with spin density calculation (including broken symmetry treatments), collectively lead to the consideration of a spin 1/2 system for Cu^II ₃ species. The spectroscopic studies conducted at low temperatures, along with a series of controlled experiments and DFT-calculated transition state analysis, offer valuable insights into the mechanistic details of hydroxylation reaction.