New hybrid ligands containing combinations of pyrazole, pyridine, and imidazole have been prepared, and the reaction chemistry of their copper(1) derivatives has been studied. The dinucleating ligands provide three nitrogen donors to each metal ion, and each coordination unit is separated by a m-xylyl group. Except for the case where four of the donor groups are pyridyl, in which the xylyl spacer is hydroxylated, all of the complexes react via four-electron reduction of the dioxygen molecule to give bis(phydroxy)copper(Il) dimers.The crystal structure of deoxyHc**' shows a dinuclear site in which each copper ion is asymmetrically ligated by three histidyl-imidazole groups. The design and synthesis of ligands that might generate suitable mimics of this coordination environment, leading to modeling of the reaction chemistry of hemocyanin and the related enzyme tyrosinase, has therefore become the focus of much e f f~r t .~~~ ((DMP),)N6 (2),' and (Py,)N6 (3),8 which provide three nitrogen donors to each Cu ion, have been used to prepare biomimics of the type 111 copper protein sites. The differences in reactivity between those systems (vide infra)' have been difficult t o reconcile, especially in light of more recent results with Schiff-base ligands in which hydroxylation of the m-xylyl spacer appears t o be n~r m a t i v e .~ To continue exploring the chemistry of this type of binucleating ligand, we have synthesized and studied the reactivity of the new complexes C U~( L )~+ (L = 4-7) with the hope of observing reactivity patterns intermediate between those observed for the copper(1) complexes of ligands 1-3. In this paper, we compare the chemistry of the copper complexes of ligands 1-7.The ligand systems (Pz4)N6 1 2 3 4 5 X = 2-pyridyl Y = 1 -pyrazolyl 6 X = 2-pyridyl Y = 1 -(3,5dimethylpyrazolyl) 7 X = 2-pyridyl Y = 2-(Nmethylimidzolyl) Experimental SectionAll reagents and solvents were purchased from commercial sources and used as received unless noted otherwise. a.a'-Dihromo-m-xylene,'O

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