PREPARATIONS, STRUCTURES, AND PROPERTIES OF COPPER(II) COMPLEXES WITHA NEW TRIPODAL TETRADENTATE LIGAND, IDYLMETHYL)BIS(6-PIVALAMIDO-2-PYRIDYLMETHYL)AMINE, AND REACTIVITIES OF THE CU(I) COMPLEX WITH DIOXYGEN

Copper complexes of a tripodal tetradentate ligand, ridylmethyl)bis(6- pivalamido-2-pyridylmethyl)amine (Hbppa), have been prepared as a mode l of metal centers of mononuclear copper enzymes; their structures and properties have been examined together with those having several seco ndary ligands by electronic absorption, ESR and FAB mass spectral, cyc lic voltammetric, and X-ray diffraction methods. The complexes, [Cu(Hb ppa)](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 E SR 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 r edox potentials of [Cu(Hbppa)Cl]Cl in MeCN, THE MeOH, and CH2Cl2 showe d 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 Et CN at -78 degrees C, resulted in a graduate absorption spectral change with two well-separated absorption maxima at 665 (epsilon = 162 M-1 c m(-1)) and 837 nm (epsilon = 305 M-1 cm(-1)) and an intense band at 37 5 nm (epsilon = 641 M-1 cm(-1)) as a shoulder. Simultaneous ESR experi ments of the same complex solution exhibited a silent spectrum, indica ting 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 (eps ilon = 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)](-) spe cies, 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 anal yzed by GC and HPLC.