title: Syntheses and electronic structures of one-electron-oxidized group 10 metal(II)-(disalicylidene)diamine complexes (metal = Ni, Pd, Pt).
abstract: 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.
authors.affiliation: Institute for Materials Chemistry and Engineering, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan. yshima@ms.ifoc.kyushu-u.ac.jp
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Shimazaki
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Yajima
authors.forename: Fumito
authors.initials: F
authors.lastname: Tani
authors.forename: Satoru
authors.initials: S
authors.lastname: Karasawa
authors.forename: Koichi
authors.initials: K
authors.lastname: Fukui
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Naruta
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamauchi
mesh_terms: D004563:Electrochemistry; D004566:Electrodes; D004583:Electrons; D005029:Ethylenediamines / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D008752:Methylene Chloride / Q000737:chemistry; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry; D010984:Platinum / Q000737:chemistry; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D005029:Ethylenediamines; D005609:Free Radicals; D008670:Metals; D009942:Organometallic Compounds; D010984:Platinum; D008752:Methylene Chloride; D010165:Palladium; C031234:ethylenediamine; D009532:Nickel