No abstract

Ligating properties of a tetradentate ligand 2‐{bis[(3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)amino]methyl}tetrahydrofuran,H2L, with [O,O,N,O]‐donor atoms towards CuII and FeIII are described. The ligand H2L yields both mononuclear LFeIII(acac) (1) and dinuclear [L2FeIII2(μ‐OCH3)‐(μ‐OH)] (2), [L2FeIII2(μ‐C2O4)] (3) and [L2CuII2] (4) complexes, which were characterized by various physical techniques, including X‐ray diffraction, Mössbauer, electrochemical and magnetic susceptibility (2–290 K) measurements. That the electrochemical oxidations are ligand‐centered, i.e. formation of phenoxyl radicals from the coordinated phenolates, have been shown by voltammetric methods. Complexes 2–4 display antiferromagnetic exchange coupling of the neighbouring metal centers. Comparison of the evaluated weak exchange coupling constants (J) with the literature values leads to the conclusion that the angle Cu–O–Cu′ is not the only determinant for the nature of the exchange coupling and the capability of the bridging ligands as mediators for spin coupling in case of FeIII follows the order phenoxide ≈ methoxide > hydroxide. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

A tridentate benzoxazole-containing aminophenol ligand HL(BAP) was synthesized and complexed with Cu(II). The resulting Cu(II) complexes were characterized by X-ray, IR, UV-vis-NIR spectroscopies, and magnetic susceptibility studies, demonstrating that the ligand is oxidized to the o-iminosemiquinone form [L(BIS)](-) in the isolated complexes. L(BIS)Cu(II)Cl exhibits a distorted tetrahedral geometry, while L(BIS)Cu(II)OAc is square pyramidal. In both solid state structures the ligand is coordinated to Cu(II)via the benzoxazole, as well as the nitrogen and oxygen atoms from the o-iminosemiquinone moiety. The chloride, or acetate group occupies the fourth and/or fifth positions in L(BIS)Cu(II)Cl and L(BIS)Cu(II)OAc, respectively. Magnetic susceptibility measurements indicate that both complexes are diamagnetic due to antiferromagnetic coupling between the d(9) Cu(II) centre and iminosemiquinone ligand radical. Electrochemical studies of the complexes demonstrate both a quasi-reversible reduction and oxidation process for the Cu complexes. While L(BIS)Cu(II)X (X = Cl) is EPR-silent, chemical oxidation affords a species with an EPR signal consistent with ligand oxidation to form a d(9) Cu(II) iminoquinone species. In addition, chemical reduction results in a Cu(II) centre most likely bound to an amidophenoxide. Mild and efficient oxidation of alcohol substrates to the corresponding aldehydes was achieved with molecular oxygen as the oxidant and L(BIS)Cu(II)X-Cs2CO3 as the catalyst.

No abstract

No abstract

We aimed to immobilize a complex of iron(III) amine bis(phenolate) on silica‐coated magnetic nanoparticles as a new magnetically recoverable catalyst (Fe3O4@SiO2‐APTES‐FeLGDC). Both the chemical nature and the structure of catalyst were confirmed by using field‐emission transmission electron microscopy, field‐emission scanning electron microscopy, FTIR spectroscopy, thermogravimetric analysis, vibrating sample magnetometry, X‐ray photoelectron spectroscopy, XRD, atomic absorption spectroscopy, and elemental analysis. This sustainable catalyst leads to the efficient oxidation of a wide range of alcohols and sulfides with excellent conversion and selectivity under a mild conditions to their corresponding oxidized products, acids (or ketones) and sulfoxides, respectively. Furthermore, the stability of the structure and morphology of our efficient recyclable system was investigated, and all of the data proved that the complex was anchored firmly to the magnetite nanoparticles.

No abstract

Reaction of the noninnocent iminophenol‐iminopyridine hybrid ligand HLIPIP, where LIPIP denotes [2‐((E)‐{(E)‐2‐[(E)‐pyridin‐2‐ylmethyleneamino]benzylidene}amino)‐4,6‐di‐tert‐butylphenolate], with copper acetate afforded a copper complex, LAPIPCuII, in which one of the imine functional groups is oxidized to an amide during metal complexation. The new CuII complex is capable of catalyzing efficient aerobic alcohol oxidation under mild conditions. The crystal structure of LAPIPCuII exhibits a square‐planar geometry with the CuII center coordinated by three nitrogen atoms and one oxygen atom. Electrochemical studies were conducted to evaluate the redox‐active behavior of the complex, and the results showed a quasireversible reduction and a ligand‐based oxidation process. The neutral species of LAPIPCuII is EPR active, which is consistent with a paramagnetic electronic ground state (d9, S = 1/2), whereas the one‐electron oxidized complex was X‐band EPR silent. One‐electron chemical oxidation of LAPIPCuII gave a new species that can be attributed to a CuII‐phenoxyl radical complex. Based on EPR measurements in conjunction with density functional theory calculations, [LAPIPCuII]+ is proposed to have a triplet electronic ground state, exhibiting a weak ferromagnetic interaction between the CuII center and the coordinated phenoxyl radical.