| Abstract
| - [MII(bpy)(LAP-H)] and [MII(bpy)(LISQ)]PF6 (M = Pd, Pt), where (LAP-H)2- and (LISQ)1- are the doubly deprotonated diainon and the monoanionic o-iminobenzosemiquinonate π radical form of 2-anilino-4,6-di-tert-butylphenyl, respectively, have been synthesized and characterized by X-ray crystallography. The one-electron oxidation from the neutral to their monocationic complexes is ligand-centered. Diamagnetic [Pt(LISQ)2] has also been prepared, and its one-electron oxidized and reduced forms have been characterized by EPR spectroscopy. The EPR spectra are interpreted by using an MO model.
- From the reaction mixture of [MII(bpy)Cl2], the ligand 2-anilino-4,6-di-tert-butylphenol, H[LAP], and 2 equiv of a base(NaOCH3) in CH3CN under anaerobic conditions were obtained the blue-green neutral complexes [MII(LAP-H)(bpy)](M = Pd (1), Pt (2)). (LAP-H)2- represents the o-amidophenolato dianion, (LAP)1- is the o-aminophenolate(1−),(LISQ)1- is its one-electron-oxidized, π-radical o-iminobenzosemiquinonate(1−), and (LIBQ)0 is the neutral quinone.Complexes 1 and 2 can be oxidized by ferrocenium hexafluorophosphate, yielding the paramagnetic salts[MII(LISQ)(bpy)]PF6 (S = 1/2) (M = Pd (1a), Pt (2a)). The reaction of PtCl2, 2 equiv of H[LAP], and 4 equiv of basein CH3CN in the presence of air yields diamagnetic [Pt(LISQ)2] (3), which is shown to possess an electronic structurethat is best described as a singlet diradical. Complexes 1, 1a, 2, 2a, and 3 have been structurally characterizedby X-ray crystallography at 100 K. It is clearly established that O,N-coordinated (LAP-H)2- ligands have a distinctlydifferent structure than the corresponding O,N-coordinated (LISQ)1- radicals. It is therefore possible to unambiguouslyassign the protonation and oxidation level of o-aminophenol derived ligands in coordination compounds. All complexeshave been investigated by cyclic voltammetry, spectroelectrochemistry, EPR, and UV−vis spectroscopy. Complexes1 and 2 can be reversibly oxidized to the [MII(LISQ)(bpy)]+ and [MII(LIBQ)(pby)]2+ mono- and dications, respectively,and reduced to the [M(LAP-H)(bpy•)]- anion, where (bpy•)1- is the radical anion of 2,2‘-bipyridine. Complex 3exhibits four reversible one-electron-transfer waves (two oxidations and two reductions) which are all shown to beligand centered. The EPR spectra of the one-electron-reduced species [Pt(LAP-H)(LISQ)]- (S = 1/2) and of theone-electron-oxidized species [Pt(LISQ)(LIBQ)]+ (S = 1/2) in CH2Cl2 solutions have been recorded. To gain a betterunderstanding of the electronic structure of 3 and its monooxidized and reduced forms, relativistic DFT calculationshave been carried out. Magnetic coupling parameters and hyperfine couplings were calculated and found to be invery good agreement with experiment. It is shown that both the one-electron oxidation and reduction of 3 areligand centered. A simple MO model is developed in order to understand the EPR properties of the monocationand monoanion of 3.
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