The tetradentate ligand N,N‘-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-phenylenediamine, H4L1, has been prepared, and its square planar complexes [CuII(L3)] and [ZnII(L3)] have been synthesized from the reaction of H4L1 with [CuI(NCCH3)4](ClO4) or Zn(BF4)2·2H2O in methanol in the presence of air. The dianion (L3)2- represents the two-electron oxidized form of (L1)4-, namely N,N‘-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-diiminoquinone. Complexes [CuII(L3)]·CH3CN and [Zn(L3)]·CH3CN have been characterized by X-ray crystallography, EPR spectroscopy, and magnetochemistry; [CuII(L3)] has an S = 1/2 ground state, and [Zn(L3)] is diamagnetic. Cyclic voltammetry established that both complexes undergo two successive reversible one-electron oxidations and two successive reversible one-electron reductions. Thus, the coordinated ligand exists in five oxidation levels. The species [MII(L4)]PF6 (M = CuII, ZnII) and [MII(L5)](ClO4)2 (M = CuII, ZnII) have been isolated and characterized by UV/vis, EPR, and 1H NMR spectroscopy and by magnetic susceptibility measurements, where (L4)- represents the monoanion N-(3,5-di-tert-butyl-2-hydroxyphenyl)-N‘-(3,5-di-tert-butyl-2-phenoxyl)-1,2-diiminoquinone and (L5) is the neutral ligand N,N‘-bis(3,5-di-tert-butyl-2-phenoxyl)-1,2-diiminoquinone. Similarly, two complexes of the type [MII(L1H2)] (M = CuII, ZnII) have been isolated from the reaction of L1H4 with CuII(ClO4)2·6H2O or Zn(ClO4)2·6H2O under anaerobic conditions in the presence of NEt3. Complexes [CuII(L4)]PF6 and [Zn(L4)]PF6 selectively oxidize primary alcohols (including methanol and ethanol) in a stoichiometric fashion under anaerobic conditions, yielding the corresponding aldehydes and [MII(L2H2)]+ (M = CuII, ZnII), where (L2)3- is the trianionic form of N,N‘-bis(3,5-di-tert-butyl-2-hydroxyphenyl)-1,2-diiminosemiquinone. Since the latter reduced forms react rapidly with dioxygen with formation of [MII(L4)]+ (M = Cu, Zn) and 1 equiv of H2O2, these oxidized species are catalysts for the air oxidation of primary alcohols, including ethanol and methanol, with concomitant formation of H2O2 and aldehydes. The kinetics of the stoichiometric reactions and of the catalyses (initial rate method) have been measured. Large kinetic isotope effects show that H-abstraction from the α-carbon atom of a coordinated alcoholato ligand is the rate-determining step in all cases.

Primary alcohols such as ethanol or benzyl alcohol are selectively and catalytically oxidized by the mononuclear copper(II) radical complex 1-a functional model of the metalloenzyme galactose oxidase-with oxygen from air at 20°C to give the corresponding aldehydes and H2 O2 in about 60 % yield.

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The tridentate trianion of N,N-bis(2-hydroxy-di-3,5-tert-butylphenyl)amine, H(3)L(3), forms 1:1 and 2:1 complexes with di-, tri-, or tetravalent transition metal ions where it can exist in four oxidation levels (C(28)H(40)NO(2))(3)(-)(,2)(-)(,1)(-)(,0), which are herein designated as L(3), L(2), L(1), and L(0), respectively; (L(2))(2)(-) and (L(0))(0) are paramagnetic (S = (1)/(2)), whereas the other two are diamagnetic (S = 0). We have synthesized the complexes [Zn(L(2))(NEt(3))] (1), green [Zn(L(1))(2)] (2), and red [Zn(L(2))(L(0))] (3). Complexes 1, 2 (Girgis, A. Y.; Balch, A. L. Inorg. Chem. 1975, 14, 2724), and 3 have been characterized by X-ray crystallography: 1, orthorhombic, Iba2, a = 23.194(4) Å, b = 25.132(4) Å, c = 11.741(2) Å, V = 6844(2) Å(3), Z = 8; 2, orthorhombic, C222(1), a = 19.494(3) Å, b = 24.065(4) Å, c = 23.458(4) Å, V = 11004(3) Å(3), Z = 8; 3, triclinic, P&onemacr;, a = 11.677(2) Å, b = 12.192(2) Å, c = 20.522(3) Å, alpha = 83.68(2), beta = 74.37(2), gamma = 75.40(2)(o), V = 2720.0(8) Å(3), Z = 2. Complexes 1 and 3 are paramagnetic with one and two (uncoupled) unpaired electrons per zinc ion (3-290 K), respectively, whereas 2 is diamagnetic. Complexes 2 and 3 are shown to be ligand-based redox isomers. Red 3 converts into the green form 2 in tetrahydrofuran solution under anaerobic conditions via an intramolecular process (k = 0.7 x 10(-)(3) s(-)(1) at 23 degrees C; DeltaH() = 15.6 +/- 0.6 kcal mol(-)(1), DeltaS() = -20.4 +/- 1.8 cal mol(-)(1) K(-)(1)). The electronic structures of 1 and 3 have been investigated by X-band EPR and (1)H NMR spectroscopy. The electro-, spectroelectrochemistry, and magnetochemistry of all complexes are reported.

20 mJ pulse"1) and analyzed at 370 nm through a Schott glass filter WG 345. The sample solution was replaced after each shot.Conventional flash photolysis was carried out by means of an Applied Photophysic K-20 apparatus, using solutions ca. 10"5 M of the substrates 1 or 2 in the appropriate solvent in cylindrical tubes, analyzing at 370 nm through the above-mentioned filters. The optical path was 10 cm; the sample solution was replaced after each shot. The kinetic constants for the decay of the transients were obtained manually from oscilloscope traces.