Less Symmetrical Dicopper( II ) Complexes as Catechol Oxidase Models—An Adjacent Thioether Group Increases Catecholase Activity

Three new unsymmetrical compartmental dinucleating ligands, 4‐bromo‐2‐(4‐methylpiperazin‐1‐ylmethyl)‐6‐[{2‐(1‐piperidyl)ethyl}aminomethyl]phenol (HL1), 4‐bromo‐2‐(4‐methylpiperazin‐1‐ylmethyl)‐6‐[{2‐(morpholin‐4‐yl)ethyl}aminomethyl]phenol (HL2), and 4‐bromo‐2‐(4‐methylpiperazin‐1‐ylmethyl)‐6‐[{2‐(thiomorpholin‐4‐yl)ethyl}aminomethyl]phenol (HL3), have been synthesized in order to model the active site of type 3 copper proteins. The dicopper( II ) complexes of these ligands give first hints about the influence of a thioether group close to the metal site. The bromophenol‐based ligands have one piperazine arm and one other bidentate arm in positions 2 and 6 of the phenolic ring, respectively. With each ligand a dinuclear copper( II ) complex was prepared and structurally characterized. The copper ions were found to have square pyramidal environments and a mixture of endogenous phenoxo and exogenous acetate bridging. The influence of a heteroatom in one arm of the ligand on catecholase activity and speciation in solution was studied by UV/Vis spectroscopy, ESI‐MS experiments and, DFT calculations.