A Structurally Characterized Cu Complex Supported by a Bis(anilido) Ligand and Its Oxidative Catalytic Activity.

Three copper(II) complexes of the (R,R)-N,N'-bis(3,5-di-tert-butyl-2-aminobenzylidene)-1,2-diaminocyclohexane ligand, namely [Cu( L)], [Cu( LH)] and [Cu( LH )] , were prepared and structurally characterized. In [Cu( LH )] the copper ion lies in an octahedral geometry with the aniline groups coordinated in equatorial positions. In [Cu( L)] the anilines are deprotonated (anilido moieties) and coordinated to an almost square-planar metal ion. Complex [Cu( L)] displays two oxidation waves at E =-0.14 V and E =0.36 V vs. Fc /Fc in CH Cl . Complex [Cu( LH )] displays an irreversible oxidation wave at high potential (1.21 V), but shows a readily accessible and reversible metal-centered reduction at E =-0.67 V (Cu /Cu redox couple). Oxidation of [Cu( L)] by AgSbF produces Cu( L), which was isolated as single crystals. X-ray structure analysis discloses a contraction of the coordination sphere by 0.05 Å upon oxidation, supporting a metal-centered process. Complex Cu( L) displays an intense NIR band at 1260 nm corresponding to an anilido-to-copper(III) charge transfer transition. This compound slowly evolves in CH Cl solution towards Cu( LH), which is a copper(II) complex comprised of both anilido and aniline groups coordinated to the metal center. The copper(III) complex Cu( L) is an efficient catalyst for benzyl alcohol oxidation, with 236 TON in 24 h at 298 K, without additives other than oxygen and a base.