Formation of hybrid guanidine-stabilized bis(μ-oxo)dicopper cores in solution: Electronic and steric perturbations.

A series of new hybrid peralkylated-amine-guanidine ligands based on a 1,3-propanediamine backbone and their Cu-O2 chemistry is reported. The copper(I) complexes react readily with O2 at low temperatures in aprotic solvents with weakly coordinating anions to form exclusively bis(μ-oxo) dicopper species (O). Variation of the substituents on each side of the hybrid bidentate ligand highlights that less sterically demanding amine and guanidine substituents increase not only the thermal stability of the formed O cores but enhance inner-sphere phenolate hydroxylation pathways. TD-DFT analysis on selected guanidine-amine O species suggest that the additional visible feature observed is a guanidine π*→ Cu2O2 LMCT, which appears along with the classic oxo-ζu*→Cu(III) and πζ*→ Cu(III) LMCT transitions.