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The reaction of 2 equiv of the bulky ligand N,N′-bis(3,5-di-tert-butylphenyl)-1,2-phenylenediamine, H2[3LPDI], excess triethylamine, and 1 equiv of M(CH3CO2)2•4H2O (M = Ni, Co) in the presence of air in CH3CN/CH2CI2 solution yields violet-black crystals of [NiII(3LISQ)2] CH3CN (1) or violet crystals of [Co(3L)2] (3). By using Pd(CH3CO2)2 as starting material, green-blue crystals of [PdII(3LISQ)2]•CH3CN (2) were obtained. Single-crystal X-ray crystallography revealed that 1 and 3 contain (pseudo)tetrahedral neutral molecules [M(3L)2] (M = Ni, Co) whereas in 2 nearly square planar, neutral molecules [PdII(3LISQ)2] are present. Temperature-dependent susceptibility measurements established that 1 and 2 are diamagnetic (S = O) whereas 3 is paramagnetic with an S = 3/2 ground state. It is shown that 1 contains two π radical benzosemiquinonate(1-)-type monoanions, ((3LISQ)1-•, Stad = ½), and a central Ni(II) ion (d8; S = 1) which are antiferromagnetically coupled yielding the observed St = 0 ground state. This result has been confirmed by broken symmetry DFT calculations of 1. In contrast, the St = 3/2 ground state of 3 is more difficult to understand: the two resonance structures [CoIII(3LISQ)(3LPDI)] ⃡ [CoII(3LPDI)(3LIBQ)] might be invoked (for tetrahedral [CoII(3LISQ)2] containing an SCo = 3/2 with two antiferromagnetically coupled π-radical ligands an St = ½ is anticipated). Complex 2 is diamagnetic (S = O) containing a PdII ion (d8, SPd = 0 in an almost square planar ligand field) and two antiferromagnetically coupled ligand radicals (Srad = ½). The electrochemistry and spectroelectrochemistry of 1, 2, and 3 have been studied, and electron-transfer series comprising the species [M(L)2]I (z = 2+, 1+, 0, 1-, 2-) have been established. All oxidations and reductions are ligand centered. [ABSTRACT FROM AUTHOR]

Examines the coordination chemistry of o-iminothiobenzosemiquinonate pi-radicals. Description of radical electronic structure; Protonation and oxidation levels of o-aminothiophenolate ligands; Characterization of metal complexes electron transfer series.

Seven new bis(o-iminosemiquinonato)copper(ll) complexes, 1-5, 1a, 1b, derived from differently substituted N-phenyl-2-aminophenol-based ligands, are described. Their crystal structures were determined by X-ray diffraction, and their electronic structures were established by various physical methods including electron paramagnetic resonance and variable- temperature (2-290 K) susceptibility measurements. Like complex 6, which was reported recently by us, all complexes exhibit an St = ½ ground state, based on the "isolated" copper(ll)-spin character resulting from the dominating antiferromagnetic spin coupling between the two radicals; the ground-state electronic configuration can thus be designated as (↑↑↓)[R-Cu-R]. In addition, broken spin symmetry density functional solutions have been obtained. From the set of unrestricted canonical Kohn-Sham orbitals, the magnetic orbitals have been identified. The identification procedure is based on the nonvanishing overlap integrals between the space parts of orbitals occupied by electrons of opposite spin. The theoretically determined magnetic orbitals support the spin configurations suggested by the experiments. Electrochemical measurements (cyclic voltammetry and square-wave voltammetry) indicate ligand-centered redox processes. Complex 1 is found to be the best catalyst among the Cu(Il) complexes for oxidation of primary alcohols with aerial oxygen as the sole oxidant to afford aldehydes under mild conditions. Thus, the function of the copper-containing enzyme Galactose Oxidase has been mimicked. Kinetic measurements in conjunction with electron paramagnetic resonance and electronic spectral studies have been used to decipher the catalytic oxidation process. A ligand-derived redox activity has been proposed as a mechanism for the aerial oxidation of primary alcohols. [ABSTRACT FROM AUTHOR]

Abstract: A tridentate redox-active ligand, based on 2-aminophenol, yields a manganese(IV) complex with an iminobenzosemiquinone radical, 1. The crystal structure of 1 was determined by X-ray diffraction and the electronic structure was established by various physical methods, including EPR and variable-temperature (2–290K) susceptibility measurements. The Mn(IV)-radical complex 1 catalyses the oxidation of primary amines with aerial oxygen as the sole oxidant to afford aldehydes under mild conditions to mimic the function of the copper-containing enzyme amine oxidases (CAO). Moreover, 1 is an efficient catalyst for the generation of phenoxazinone chromophore, thus models the catalytic function of the copper-containing enzyme phenoxazinone synthase (PHS). An ‘on–off’ mechanism of the radicals together with redox participation of the metal center is proposed for the catalytic oxidation processes. [Copyright &y& Elsevier]

A series of mononuclear square-based pyramidal complexes of iron containing two 1,2-diaryl-ethylene-1,2-dithiolate ligands in various oxidation levels has been synthesized. The reaction of the dinuclear species [FeIII2(¹L•)2(¹L)2]0, where (¹L)2- is the closed shell di-(4-tert-butylphenyl)-1,2-ethylenedithiolate dianion and (¹L•)1- is its one-electron-oxidized π-radical monoanion, with [N(n-Bu)4]CN in toluene yields dark green crystals of mononuclear [N(n-Bu)4]-[FeII(¹L•)2(CN)] (1). The oxidation of 1 with ferrocenium hexafluorophosphate yields blue [FeIII(¹L•)2(CN)] (1ox), and analogously, a reduction with [Cp2Co] yields [Cp2Co][N(n-Bu)4][FeII(¹L•)(¹L)(CN)] (1red); oxidation of the neutral dimer with iodine gives [FeIII(¹L•)21] (2). The dimer reacts with the phosphite P(OCH3)3 to yield [FeII(¹L•)2{P(OCH3)3}] (3), and [FeIII2(³L•)2(³L)2] reacts with P(OC6H5)3 to give [FeII(³L•)2{P(OC6H5)3}] (4), where (³L)2- represents 1,2-diphenyl-1,2-ethylenedithiolate(2-). Both 3 and 4 were electrochemically one-electron oxidized to the monocations 3ox and 4ox and reduced to the monoanions 3red and 4red. The structures of 1 and 4 have been determined by X-ray crystallography. All compounds have been studied by magnetic susceptibility measurements, X-band EPR, UV-vis, IR, and Mössbauer spectroscopies. The following five-coordinate chromophores have been identified: (a) [FeIII(L•)2X]n, X = CN-, l- (n = 0) (1ox, 2); X = P(OR)3 (n = 1+) )3ox 4ox) with St = 1/2, SFe = 3/2; (b) [FeII(L•)2X]n, X = CN-, (n = 1-) (1); X = P(OR)3 (n = 0) (3, 4) with St = SFe = 0; (c) [FeII(L•)(L)X]n ↔ [FeII(L)(L•)X]n, X = CN- (n = 2-) (1red); X = P(OR)3 (n = 1-) (3red, 4red) with St = 1/2, SFe = 0 (or 1). Complex 1ox displays spin crossover behavior: St = 1/2 ↔ St = 3/2 with intrinsic spin-state change SFe = 3/2 ↔ SFe = 5/2. The electronic structures of 1 and 1ox have been established by density functional theoretical calculations: [FeII(¹L•)2(CN)]1- (SFe = 0, St = 0) and [FeIII(¹L•)2(CN))0 (SFe = 3/2, St = 1/2). [ABSTRACT FROM AUTHOR]

Abstract: The synthesis and structure of an o-methylthio-phenol-imidazole, 2-(2′-(4′-tert-butyl-6′-methylsulfanyl)-hydroxyphenyl))-4,5-diphenyl-imidazole (MeSLH), is reported; X-ray crystallographic studies have shown that MeSLH involves an O–H···N+ hydrogen bond between the phenol and an imidazole nitrogen. MeSLH undergoes a reversible, one-electron, oxidation to form the radical cation [MeSLH] + the EPR spectrum of which is remarkably similar to that of Tyr272 in Cu-free, oxidized, apo-GO. Density Functional Theory calculations, have shown that the proton-transferred (R–O ···H–N+) form of [MeSLH] + has a spin density distribution – with a substantial delocalization of the unpaired electron spin density onto the ortho sulfur atom – and EPR properties that are in good agreement with those of Tyr272 in Cu-free, oxidized, apo-GO whereas the non-proton-transferred (R–O +–H···N) form does not. The results reported herein are a further demonstration of the influence of hydrogen bonding on the nature and properties of phenoxyl radicals and strongly suggest that the phenoxyl oxygen of Tyr272 in Cu-free, oxidized, apo-GO is involved in a O ···H–O/N hydrogen bond. [Copyright &y& Elsevier]

Four members of the electron-transfer series [Fe(NO)(S2C2R2)2]z (z = 1+, 0, 1-, 2-) have been isolated as solid materials (R = p-tolyl): [la](BF4), [1a]0, [Co(Cp)2][1a], and [Co(Cp)2]2[1a]. In addition, complexes [2a]0 (R = 4,4-diphenyl), [3a]0 (R = p-methoxyphenyl), [Et4N][4a] (R = phenyl), and [PPh4][5a] (R = -CN) have been synthesized and the members of each of their electron-transfer series electrochemically generated in CH2CI2 solution. All species have been characterized electro- and magnetochemically. Their electronic, Mössbauer, and electron paramagnetic resonance spectra as well as their infrared spectra have been recorded in order to elucidate the electronic structure of each member of the electron-transfer series. It is shown that the monocationic, neutral, and monoanionic species possess an {FeNO}6 (S = 0) moiety where the redox chemistry is sulfur ligand-based, (L)2-(L•)1-: [Fe(NO)(L•)2]+ (S = 0), [Fe(NO)(L•)(L)]0 ⃡ [Fe(NO)(L)(L•)]0 (S = 1/2), [Fe(NO)(L)2]¯ (S = 0). Further one-electron reduction generates a dianion with an {FeNO}7 (S = 1/2) unit and two fully reduced, diamagnetic dianions L2-: [Fe(NO)(L)2]2- (S = 1/2). [ABSTRACT FROM AUTHOR]

Investigates the electronic structure of bis(o-iminobenzosemiquinonato) metal complexes. Creation of physical oxidation states in transition-metal complexes containing radical ligands; Application of single-crystal X-ray crystallography; Measurement of square planar molecule complexes.