A wine red copper(II) complex of a tetradentate nitrogen donor showing two-electron oxidation. Generation of a copper(II)-phosphine bond.

Using the 1 : 2 condensate of benzil and 2-hydrazinopyridine as the ligand LH2(H: dissociable NH proton), the red complex Cu(LH2)(ClO4)2(1) was synthesized. The ligand also afforded the orange [Zn(LH2)(OH2)2](ClO4)2(2). The X-ray crystal structures of the ligand,1and2have been determined. The metals in1and2have octahedral N4O2environments.1is paramagnetic withμeffof one unpaired electron (1.63 μBand displays an axial EPR spectrum in the solid state with <g> = 2.07, characteristic of a (dx2−y2)1ground state (g|| > g⊥;A|| = 16 mT). In cyclic voltammetry,1displays a two-electron oxidation around 0.9 VversusNHE. The two-electron oxidized (coulometrically) solution of1(golden yellow) gives an EPR spectrum with <g> = 2.17 andg|| < g⊥. The reaction of PPh3with1yields the orange complex [Cu(LH2)(PPh3)](ClO4)2(4). With the assumed chemical formula, the effective magnetization of4corresponds to one electron. Its EPR spectrum in the solid state is isotropic withg = 2.07. Thisgvalue yields a theoreticalμeffof 1.80 μBat 298 K from Curie’s law, which matches very well with the experimental value of 1.89 μBat room temperature. Since single crystals of4could not be obtained, DFT calculations at the UBP86/6–311G(2d,p) level have been carried out and indicate that the cation in4is square pyramidal with the phosphine at the apex. The ease of the oxidation of the metal in1leads to the stabilization of the rare Cu(II)-P bond in4. [ABSTRACT FROM PUBLISHER]