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 L-Y (L-Y = 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.