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Copper (1) complexes of the new tripodal ligands tris[2-( 1,4-diisopropylimidazolyl)]phosphine (PimiR2) and tris-[2-( 1 -isopropyl-4-terr-butylimidazolyl)]phosphine (PimiRJBu) have been prepared and characterized by 'H NMR and elemental analysis. The dioxygen reactivity of the pseudotetrahedral complexes [Cu(Pimik2)CH3CN]BF4 and [Cu(PimiRJBu)CH3CN]BF4 has been examined. The former complex forms a violet peroxo-dicopper(II) species upon reaction with dioxygen at low temperature; the electronic absorption spectrum (A = 343 nm, E = 19 500 M-' cm-I; ;1 = 549 nm, E = 790 M-I cm-l) and 0-0 stretching frequency (~( 0 -0 ) = 750 cm-l) of this adduct approximate those of oxyhemocyanin. Warming a mixture of the peroxide complex and triphenylphosphine to room temperature affords [Cu(PimiR2)PPh3]BF4 and produces no O-PPh3. In methanol at -78 OC, the peroxide complex is unreactive toward acid, carbon dioxide, 1 -hexene, and triphenylphosphine. Thermal decomposition of the dioxygen adduct in the presence of water yields a bis(hydroxide)-bridged dicopper(II) dimer, [Cu(PimiR2)]2(OH)2(BF4)2, which further reacts with atmospheric C02 to produce the carbonate-bridged complex [ C U ( P~~' "~) ]~C O~( B F~)~. X-ray crystallography has been used to characterize the carbonate complex. Crystal data: orthorhombic, space group Pbca, with a = 16.8705(17) A, b = 17.4731(14) A, c = 51.358(4) A, V = 15139.4(22) A3, and Z = 8. The structure of a prototypical mononuclear 5-coordinate complex, [Cu(PimiR2)-OAcIBF4, has also been determined. Crystal data: monoclinic, space group P21ln, with a = 9.657(3) A, b = 17.001(5) A, c = 24.642(6) A, p = 100.987(23)', V = 3971.4(19) A3, and Z = 4. The geometry about copper-(11) in both structures is approximately square pyramidal, indicating that PimiR2 can accommodate side-on binding of dioxygen to copper. The more sterically hindered copper(1) complex [Cu(PimiRJB")CH3CN]BF~ is inert to 0 2 , but it reacts readily with CO to form the isolable adduct [Cu(PimiRJBU)CO]BF4 with v(C0) = 2086 cm-I. In accord with its lack of dioxygen reactivity, [Cu(PimiRJBU)CH3CN]BF4 undergoes a quasi-reversible redox process at very high potential, with ,5112 (in CH3CN) of +1.08 V vs AglAgC1.

In analogous experiments we have found that aniline is also rapidly oxidized to the anilino radical by 0-The rate constant for reaction 2 was determined to be 1.6 X lo9 M-l ~e c -l .~ In the case of aniline abstraction of the "2, hydrogen atoms can contribute, but the very high value of the rate constant again suggests that 0may well oxidize the aniline directly by attack on the lone pair of electrons on the nitrogen atom. Further studies on these oxidation processes are in progress. (9) A rate constant of 2.4 X IO9 M i sec-' is calculated for reaction 2 by correcting the value measured previously (H. Christensen, Int. J. Radiat. Phys. Chem., 4, 31 1 (1972)) at pH 13.3 for the partial OH contribution. (1961). Models for Cytochrome P-450 Sir:Cytochrome P-450 oxygenases catalyze the hydroxylation of C-H bonds in metabolism, hormone regulation, and drug detoxification. These ubiquitous monohydroxylases contain a t their active site an oxygen binding hemoprotein referred to as P-450-a term derived from the anomalous Soret band of its ferrous carbonyl derivative. In higher organisms all cytochrome P-450's are membrane bound and are inactivated upon separation; however, Gunsalus2 has purified and extensively studied a soluble bacterial cytochrome P-45OCa, camphor hydroxylase. Four stages of P-450,,, have been characterized in the catalytic cycle (Scheme I):3 substrate-free low-spin (S = I/2) ferric 1, substrate-bound high-spin (S = 5/2) ferric 2,5 deoxy high-spin

The reaction of Cu(CH3CN)4BF4 with a range of imidazoles, pyrazoles, and pyridines yields two-coordinate copper(I) complexes of the form CuL2BF4. Two of those species, ligated by 1-methylpyrazole and 1,3,5-trimethylpyrazole, respectively, have been characterized by X-ray crystallography, and they both show an approximately linear N-Cu-N geometry with Cu-N bond lengths of 1.87 Á. The bis( 1-methylpyrazole) complex apparently forms dimeric units in the solid state with intermolecular distances of ca. 3.1 Á. The unhindered pyrazole and pyridine complexes react with carbon monoxide in solution to form presumed three-coordinate adducts, although the binding of CO is quite weak (P1;-2 > 1 atm). The imidazole and the hindered pyrazole and pyridine complexes are all inert toward reaction with carbon monoxide. A likely explanation for this observation is that steric effects prevent the increase in coordination number for the hindered species, and increased orbital overlap between the imidazole-nitrogen and copper(I) ion stabilizes the two-coordinate form for the imidazole-ligated species. Crystal data for Cu(MePz)2BF4: triclinic, a = 9.352 (4) k, b = 9.805 (4) A, c = 8.164 (3) A, a = 96.97 (3)°, ß = 109.15 (3)°, y = 62.40

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