Copper complexes with a hindered tris(pyrazolyl)borate ligand as synthetic models for the active sites of copper proteins.

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Abstracts

C(-)O7 COPPER COMPLEXES WITH A HINDERED TRIS(PYRAZOLYL)BORATE LIGAND AS SYNTHETIC MODELS FOR THE ACTIVE SITES OF COPPER PROTEINS.

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K. Fujisawa, S. Hikichi, Y. Mom-oka

Research Laboratory of Technology, 4259 Japan

of Resources Nagatsuta,

Utilization, Tokyo Institute Midori-ku, Yokohama 227,

The development of copper complexes with a hindered tris(pyrazolyl)borate as synthetic analogues for the active sites of copper proteins will be reviewed. A tripodal ligand, HB(3,5iPr2pz)g (hydrotris(3,5-diisopropyl-1-pyrazolyl)borate), has been successfully applied to prepare isolable transition metal complexes of unusual structure. The striking advantages of the ligand over conventionally known N3 donor ligands are 1) highly steric hindrance to prevent the formation of the bischelated species 2) shielding effect of the isopropyl groups to protect the coordination sphere against the ecompositions 3) highly solubility in non-coordinating solvents such as pentane. In particular, its rigidly but flexibly coordinating capability as a tripodal N3 ligand is suitable to mimic the coordination environment of the copper ions in hemocyanin which consist of three histidyl nitrogen atoms. We thus succeeded to prepare the first l~,-rl2:q2 peroxo dinuclear copper(I1) complex either by dioxygen addition to a copper(I) complex Cu(WB(3,5-iF’r2pz>:~) or by Hz02 reaction with a di-p-hydroxo copper-U1 t complex [Cu(HB(3,5- i P r;2pz)3)]2(0H)2 [l]. The entirely novel structure was established by X-ray crystallography. The remarkable physicochemical similarlities observed between the peroxo complex and oxyhemocyanin and oxytyrosinase led us to propose a new possibility that the peroxide ion in these proteins is also bound to the dicopper si.te in a p-q”:q” coordination The ligand also allowed us to synthesize and mode. structurally characterize a series of tetrahedral copper(II! complexes and the thiolato complex was found to closely mimic the spectroscopic characteristics of blue copper proteins [a]. 1. N. Kitajima, IS. Fujisawa, Y. Moro-oka, K. Toriumi, J. Am. C&n. SW, 111,8975 (1989). 2. N. Kitajima, K. Fujisawa, Y. More-oka, j: Am. Chem. SW., 112, 3210

11990).