Preparations, structures, and properties of copper(II) complexes with a new tripodal tetradentate ligand, N-(2-pyridylmethyl)bis(6-pivalamido-2-pyridylmethyl)amine, and reactivities of the Cu(I) complex with dioxygen

Copper complexes of a tripodal tetradentate ligand, N-(2-pyridylmethyl)bis(6-pivalamido-2-pyridylmethyl)amine (Hbppa), have been prepared as a model of metal centers of mononuclear copper enzymes; their structures and properties have been examined together with those having several secondary ligands by electronic absorption, ESR and FAB mass spectral, cyclic voltammetric, and X-ray diffraction methods. The complexes, [Cu(Hbppa)](ClO4)(2) and [Cu(Hbppa)(N-3)]-ClO4 H2O, were obtained as single crystals, whose crystal structures revealed square-planar and trigonal-bipyramidal geometries, respectively. The electronic absorption and ESR spectra for the Cu-II(Hbppa)-X systems (X = no, Cl-, Br-, I-, N-3(-), and CH3COO-) allowed us to conclude that the complexes form several coordination geometries, such as square-planar, square-pyramidal, and trigonal-bipyramidal, depending upon the solvents (MeOH, MeCN). The redox potentials of [Cu(Hbppa)Cl]Cl in MeCN, THE MeOH, and CH2Cl2 showed quasi-reversible Cu-I/Cu-II couples in the range of -0.056-+0.085 V vs. Ag/AgCl at room temperature. The addition of dioxygen to the Cu(I)-Hbppa, which was prepared from [Cu(MeCN)(4)]PF6 and Hbppa (1:1) in EtCN at -78 degrees C, resulted in a graduate absorption spectral change with two well-separated absorption maxima at 665 (epsilon = 162 M-1 cm(-1)) and 837 nm (epsilon = 305 M-1 cm(-1)) and an intense band at 375 nm (epsilon = 641 M-1 cm(-1)) as a shoulder. Simultaneous ESR experiments of the same complex solution exhibited a silent spectrum, indicating that the complex is diamagnetic. A similar electronic absorption spectral change was observed in MeOH with absorption peaks at 387 nm (epsilon = 843 M-1 cm(-1)), 640 (epsilon = 183 M-1 cm(-1)) and 828 (epsilon = 289 M-1 cm(-1)), although the ESR spectrum did not continue to be completely silent, increasing the temperature of the solution up to room temperature demonstrated the formation of [Cu(Hbppa)(OH)](-) species, whose X-ray structure was [Cu(Hbppa)(OH)]PF6 . H2O. The reaction of the [Cu(Hbppa)]ClO4-sodium benzoylformate system with dioxygen in DMF resulted in production of carbon dioxide and benzoic acid, as analyzed by GC and HPLC.