Structural Characterization of the [CuOR]2+ Core.

Formal Cu(III) complexes bearing an oxygen-based auxiliary ligand ([CuOR]2+, R = H or CH2CF3) were stabilized by modulating the donor character of supporting ligand LY (LY = 4-Y, N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Y = H or OMe) and/or the basicity of the auxiliary ligand, enabling the first characterization of these typically highly reactive cores by NMR spectroscopy and X-ray crystallography. Enhanced lifetimes in solution and slowed rates of PCET with a phenol substrate were observed. NMR spectra corroborate the S = 0 ground states of the complexes, and X-ray structures reveal shortened Cu-ligand bond distances that match well with theory.