Tris(imidazotyl) dicopper(I) complex and its reactivity to exert the catalytic oxidation of sterically hindered phenol substrates via a [Cu2O]2+ core

The Cu ion ligated with histidine residues is a common active site motif of various Cu-containing metalloenzymes exerting versatile catalytic oxidation reactions. Due to the scarcity of structurally characterized biomimetic binuclear Cu(I)-imidazolyl complexes, the bonding interactions between the Cu(I) center and imidazolyl donor ligands as well as their stoichiometric/catalytic oxidation reactivities remain relatively unexplored. In this study, we successfully synthesized a tris(imidazolyl) dicopper(I) complex [Cu-1(mu-bimeta)(3)Cul)[PF6](2) (1) characterized by single-crystal X-ray diffraction, cyclic voltammetry, and UV-vis absorption spectroscopy. The coordination environment around each Cu(I) center of complex 1 is best described as a regular trigonal geometry and the distance between two Cu(I) centers is similar to 3.0521(18) angstrom. From the O-2-/PhIO-titration reactions of complex 1, only 0.5 equiv. of O(2(g) )and one equiv. of PhlO are required to produce the corresponding oxygenated product complex 1(ox), respectively, exhibiting a distinct UV-vis absorption band at similar to 640 nm. From the characterization of ESI mass spectrometry, IR, UV-vis spectroscopy, and O-2-/PhIO-titration reactions, the molecular identity of complex ox is tentatively assigned as [Cu(mu-O)(p-bimeta)(3)Cu-](2)+, which is further corroborated by the spectroscopically calibrated DFT calculations. The oxidation reactivities of complex l(ox) were investigated using the well-understood sterically hindered phenol substrates DTBP and TBBP in both stoichiometric and catalytic fashions. In stoichiometric reactions, one equiv. of 1(ox) is capable of fully converting TBBP into TBOBF in the CH3CN solution at room temperature within 1 h. The optimized selectivity of catalytically oxidizing DTBP into TBOBF (>95% selectivity, similar to 100% conversion rate) could be achieved with a 10 mol% loading of complex 1(ox) using air as the oxidant. From the time-course product distributions of this catalyst system, similar to 40% of DTBP was converted into the corresponding TBBP product in the first 5 min. From 10 to 120 min, the oxidation of DTBP to TBBP and the oxidation of TBBP to TBOBF simultaneously proceeded, which was evidenced by the decrease of TBBP and the increase TBOBF.

Automated summary

A Cu(I) complex was successfully synthesized and characterized, showing a regular trigonal geometry around each Cu(I) center and efficient oxidation reactivity towards oxygen and PhlO. The molecular identity of the oxidized product was tentatively assigned, and the oxidation reactions of the complex with specific substrates were investigated both stoichiometrically and catalytically.