Structure, Bonding, and Tyrosinase-Like Reactivity of Copper Complexes Coordinated by Mononucleating Tridentate N−O−N Type Ligands

Copper complexes with mononucleating tridentate ligands of the N−O−N type, including 1,3‐bis(benzimidazol‐2‐yl)‐2‐oxapropane (bbmo), 1,3‐bis(N‐methylbenzimidazol‐2‐yl)‐2‐oxapropane (bbMemo), 1,3‐bis(N‐n‐propylbenzimidazol‐2‐yl)‐2‐oxapropane (bbPrmo), and 1,3‐bis(pyrid‐2‐yl)‐2‐oxapropane (bpmo), were tested for the oxygenation of phenols. Mixed ligand copper complexes of [Cu(N−O−N)(N−N)](ClO4)2, where N−N denotes 2,2′‐bipyridine (bipy), 1,10‐phenanthroline (phen), ethylenediamine (en), and/or N,N,N′,N′‐tetramethylethylenediammine (tmen), were prepared and characterized by elemental analyses, and electronic, vibrational, and epr spectroscopic measurements. The molecular structures of fac‐[Cu(bbMemo)(bipy)(H2O)](ClO4)2(H2O) (1a), fac‐[Cu(bbMemo)(phen)](ClO4)2(CH3CN) (4a), fac‐[Cu(bbPrmo)(phen)](ClO4)2 (5a), and fac‐[Cu(bpmo)(bipy)(ClO4)](ClO4) (7a) were determined by X‐ray diffraction methods. The structures of these complexes are square pyramids or elongated octahedra with the heterocycle nuclei forming the basal or equatorial planes. The terminal heterocycles of the facially coordinated tridentate ligands are nearly perpendicular to the basal or equatorial planes. Similar structures are proposed for the remaining complexes, based on spectroscopic data. Both stoichiometric and catalytic oxidation reactions of 2,4‐di‐tert‐butylphenol and 2,4‐di‐tert‐butylphenolate with dioxygen adducts of [Cu(bbPrmo)]+ at room temperature afforded 3,3′,5,5′‐tetra‐tert‐butyl‐2,2′‐biphenol and 3,5‐di‐tert‐butyl‐o‐quinone. Similar reactions with the dioxygen adduct of [Cu(bpmo)]+ yielded only 3,3′,5,5′‐tetra‐tert‐butyl‐2,2′‐biphenol. In light of the tyrosinase‐like reactivity, the possible intermediates, [(bbPrmo)2Cu2(μ‐η2:η2‐peroxo)]2+, [(bbPrmo)2Cu2(μ‐oxo)2]2+, and [(bpmo)2Cu2(μ‐oxo)2]2+ are proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)