The neutral and one-electron oxidized Cu(II) six-membered chelate 1,3-Salcn (1,3-Salcn = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,3-cyclohexanediamine) complexes have been investigated and compared with the five-membered chelate 1,2-Salcn (N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) complexes. Cyclic voltammetry of Cu(1,3-Salcn) showed two reversible redox waves at 0.48 and 0.68 V, which are only 0.03 V higher than those of Cu(1,2-Salcn). Reaction of Cu(1,3-Salcn) with 1 equiv of AgSbF6 afforded the oxidized complex which exists as a ligand-based radical species in solution and in the solid state. The X-ray crystal structure of the oxidized complex, [Cu(1,3-Salcn)]SbF6, exhibited an asymmetric metal binding environment with a longer Cu-O bond and quinoid distortion in the phenolate moiety on one side, demonstrating at least partial ligand radical localization in the solid state. The ligand oxidation is also supported by XPS and temperature dependent magnetic susceptibility. The electronic structure of the [Cu(1,3-Salcn)](+) complex was further probed by UV-vis-NIR, resonance Raman, and electron paramagnetic resonance (EPR) measurements, and by theoretical calculations, indicating that the phenoxyl radical electron is relatively localized on one phenolate moiety in the molecule. The reactivity of [Cu(1,3-Salcn)](+) with benzyl alcohol was also studied. Quantitative conversion of benzyl alcohol to benzaldehyde was observed, with a faster reaction rate in comparison with [Cu(1,2-Salcn)](+). The kinetic isotope effect (KIE = k(H)/k(D)) of benzyl alcohol oxidation by [Cu(1,3-Salcn)](+) was estimated to be 13, which is smaller than the value reported for [Cu(1,2-Salcn)](+). The activation energy difference between [Cu(1,2-Salcn)](+) and [Cu(1,3-Salcn)](+) was in good agreement with the energy calculated from KIE. This correlation suggests that the Cu(II)-phenoxyl radical species, characterized for [Cu(1,2-salcn)](+) is more reactive for hydrogen abstraction from benzyl alcohol in comparison to the 1:1 mixture of Cu(III)-phenolate and Cu(II)-phenoxyl radical species, [Cu(1,2-Salcn)](+). Thus, the Cu(II)-phenoxyl radical species accelerates benzyl alcohol oxidation in comparison with the Cu(III)-phenolate ground state complex, in spite of the similar activated intermediate and oxidation pathway.

Group 10 metal(II) complexes of H2tbu-salen (H2tbu-salen = N,N'-bis(3',5'-di-tert-butylsalicylidene)ethylenediamine) and H2tbu-salcn (H2tbu-salcn = N,N'-bis(3',5'-di-tert-butylsalicylidene)-1,2-cyclohexanediamine) containing two 2,4-di(tert-butyl)phenol moieties, [Ni(tbu-salen)] (1a), [Ni(tbu-salcn)] (1b), [Pd(tbu-salen)] (2a), [Pd(tbu-salcn)] (2b), and [Pt(tbu-salen)] (3), were prepared and structurally characterized by X-ray diffraction, and the electronic structures of their one-electron-oxidized species were established by spectroscopic and electrochemical methods. All the complexes have a mononuclear structure with two phenolate oxygens coordinated in a very similar square-planar geometry. These complexes exhibited similar absorption spectra in CH2Cl2, indicating that they all have a similar structure in solution. Cyclic voltammograms of the complexes showed a quasi-reversible redox wave at E1/2 = 0.82-1.05 V (vs Ag/AgCl), corresponding to formation of the relatively stable one-electron-oxidized species. The electrochemically oxidized or Ce(IV)-oxidized species of 1a, 2a, and 3 displayed a first-order decay with a half-life of 83, 20, and 148 min at -20 degrees C, respectively. Ni(II) complexes 1a and 1b were converted to the phenoxyl radicals upon one-electron oxidation in CH2Cl2 above -80 degrees C and to the Ni(III)-phenolate species below -120 degrees C. The temperature-dependent conversion was reversible with the Ni(III)-phenolate ground state and was found to be a valence tautomerism governed by the solvent. One-electron-oxidized 1b was isolated as [Ni(tbu-salcn)]NO3 (4) having the Ni(II)-phenoxyl radical ground state. One-electron-oxidized species of the Pd(II) complexes 2a and 2b were different from those of the Ni(II) complexes, the Pd(II)-phenoxyl radical species being the ground state in CH2Cl2 in the range 5-300 K. The one-electron-oxidized form of 2b, [Pd(tbu-salcn)]NO3 (5), which was isolated as a dark green powder, was found to be a Pd(II)-phenoxyl radical complex. On the other hand, the ESR spectrum of the one-electron-oxidized species of Pt(II) complex 3 exhibited a temperature-independent large g anisotropy in CH2Cl2 below -80 degrees C, while its resonance Raman spectrum at -60 degrees C displayed nu8a of the phenoxyl radical band at 1600 cm-1. These results indicated that the ground state of the Pt(II)-phenoxyl radical species has a large distribution of the radical electron spin at the Pt center. One-electron oxidation of 3 gave [Pt(tbu-salen)]NO3 (6) as a solid, where the oxidation state of the Pt center was determined to be ca. +2.5 from the XPS and XANES measurements.

A stable bridge: A peroxo‐bridged Fe–O2–Cu complex (see picture) was synthesized and isolated as crystals. The X‐ray structure analysis revealed that the Fe–O2–Cu moiety has a μ‐η2:η1 coordination mode; a peroxo ligand is bound to Fe in a side‐on fashion with only one oxygen atom of the peroxide bound to Cu. The two metal ions (high‐spin FeIII and CuII) were strongly coupled in an antiferromagnetic fashion, thus resulting in a total spin of S=2.