The First Stable Copper( III ) Complex Containing Aliphatic Thiolates as Ligands: Structural and Spectroscopic Evidence for CuII and CuIII Ions in Complexes with Square‐Planar CuN2S2 Coordination Environments

Although it was once deemed a nearly impossible task (since CuII centers are generally readily reduced by thiolates), authentic CuII and CuIII complexes with aliphatic thiolates in the metal coordination sphere have been synthesized. The unusual pair of squareplanar complexes (NEt4)2[Cu(phmi)] · H2O and (PPh4)[Cu(phmi)] (the anion is depicted on the right) displays the lowest known redox potential ever recorded for a CuIII/CuII redox couple and has been completely characterized. H4phmi = N, N′-1,2-phenylenebis(2-mercapto-2-methylpropionamide).