A Copper Complex of a Noninnocent Iminophenol-Amidopyridine Hybrid Ligand: Synthesis,Characterization, and Aerobic Alcohol Oxidation

摘要

Reaction of the noninnocent iminophenol-iminopyridine hybrid ligand HLIPIP, where LIPIP denotes [2-((E)-{(E)-2-[(E)-pyridin-2-ylmethyleneamino]benzylidene}amino)-4,6-ditert-butylphenolate], with copper acetate afforded a copper complex, LAPIPCuII, in which one of the imine functional groups is oxidized to an amide during metal complexation. The new CuII complex is capable of catalyzing efficient aerobic alcohol oxidation under mild conditions. The crystal structure of LAPIPCuII exhibits a square-planar geometry with the CuII center coordinated by three nitrogen atoms and one oxygen atom. Electrochemical studies were conducted to evaluate the redox-active behavior of the complex, and the results showed a quasireversible reduction and a ligandbased oxidation process. The neutral species of LAPIPCuII is EPR active, which is consistent with a paramagnetic electronic ground state (d9, S = 1/2), whereas the one-electron oxidized complex was X-band EPR silent. One-electron chemical oxidation of LAPIPCuII gave a new species that can be attributed to a CuII-phenoxyl radical complex. Based on EPR measurements in conjunction with density functional theory calculations, [LAPIPCuII]+ is proposed to have a triplet electronic ground state, exhibiting a weak ferromagnetic interaction between the CuII center and the coordinated phenoxyl radical.