A series of CuII and ZnII complexes with new ligands having either one or two substituted phenolates appended to the 1,4,7-triazacyclononane frame were prepared and characterized by optical absorption, EPR, NMR, and/or resonance Raman spectroscopy, cyclic voltammetry, and, in eight cases, X-ray crystallography. Features of the active site geometries of the CuII−tyrosinate forms of galactose and glyoxal oxidases (GAO and GLO) were modeled by these complexes, including the binding of a redox-active phenolate and an exogenous ligand (Cl-, CH3CO2-, or CH3CN) in a cis-equatorial position of a square pyramidal metal ion. The role of the unique ortho S−C covalent bond between a cysteine (C228) and the equatorial tyrosinate (Y272) in the proteins was probed through an examination of the optical absorption and electrochemical properties of sets of similar complexes comprised of phenolate ligands with differing ortho substituents, including thioether groups. The o-alkylthio unit influences the PhO- → CuII LMCT transition and the MII−phenolate/MII−phenoxyl radical redox potential, but to a relatively small degree. Electrochemical and chemical one-electron oxidations of the CuII and ZnII complexes of ligands having tert-butyl protecting groups on the phenolates yielded new species that were identified as novel MII−phenoxyl radical compounds analogous to the active CuII−tyrosyl radical forms of GAO and GLO. The MII−phenoxyl radical species were characterized by optical absorption, EPR, and resonance Raman spectroscopy, as well as by their stoichiometry of formation and chemical reduction. Notable features of the CuII−phenoxyl radical compounds that are similar to their protein counterparts include EPR silence indicative of magnetic coupling between the CuII ion and the bound radical, a band with λmax ≈ 410 nm (ε ≈ 3900 M-1 cm-1) in UV−vis spectra diagnostic for the phenoxyl radical, and a feature attributable to the phenoxyl radical C−O vibration (ν7a) in resonance Raman spectra. Similar Raman spectra and electrochemical behavior for the ZnII analogs, as well as an isotropic signal at g = 2.00 in their X-band EPR spectra, further corroborate the formulations of the MII−phenoxyl radical species.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A novel 3-coordinate Cu(I)-phenoxide complex with N-donor supporting ligation was structurally characterized and shown to be highly reactive towards dioxygen, similar to the reduced form of galactose oxidase.
The reactions of LCuCl (L = 2,4-bis((2,6-diisopropylphenyl)imido)pentane (LiPr), 2,4-bis((2,6-diisopropylphenyl)imido)-3-chloropentane (LCliPr)) with the phenolates TlOAr (Ar = C6H3Me2, C6H4OMe, C6H4tBu) and NaOC6H3(tBu)2 were explored. Novel three-coordinate Cu(II)−phenolates, LCuOAr, were isolated from the reactions with the thallium phenolates and were characterized by X-ray crystallography and spectroscopy (UV−vis, EPR). The complexes feature short Cu−O(phenolate) distances (average Cu−O = 1.81 Å) and, with one exception, irregular N−Cu−O(phenolate) angles that differ within each compound (15° < Δ < 28°, where Δ = ∠N1−Cu−O − ∠N2−Cu−O). The exception is LiPrCu(OC6H4tBu), for which X-ray structures at −100 and 25 °C differed due to an unusual reversible phase change with nonmerohedral twinning (2:1 ratio) in the low-temperature form. The high-temperature form has local C2v symmetry (Δ = 0°), and upon cooling below the phase transition temperature (−8 ± 5 °C) lateral movement of the phenolate ligand (Δ = 17.6°) and rotation of the phenolate plane by 10.7° occurs. Resonance Raman spectroscopic data acquired for LiPrCu(OC6H4tBu) corroborated assignment of phenolate → Cu(II) LMCT character in the UV−vis spectra. Cyclic voltammetry experiments (THF, 0.5 M NBu4PF6) revealed negative E1/2 values for the Cu(II)/Cu(I) couples relative to NHE, consistent with enhanced stabilization of the Cu(II) state by both the strongly electron donating β-diketiminate ligand and the phenolates. Although thermally stable, the Cu(II)−phenolates are unusually reactive with dioxygen, albeit to give product(s) that have yet to be identified. In the reaction of LiPrCuCl with NaOC6H3(tBu)2 no Cu(II)−phenolate was observed. Instead, a Cu(I) complex was generated quantitatively by trapping with added isocyanide, [LiPrCuNC(C6H3Me2)], along with 3,3',5,5'-tetra-tert-butyl-4,4'-dibenzoquinone and 2,6-di-tert-butylphenol in 27 ± 3% and 46 ± 6% yields, respectively, corresponding to the overall reaction 4LiPrCuIICl + 4NaOAr → 4LiPrCu(I) + 4NaCl + dibenzoquinone + 2(phenol).
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The reaction of 2,6-diisopropylaniline-based bis-imine ligands (4, 9) with M(CH2Ph)4 (M = Hf, Zr) led to formation of novel imino−amido tribenzyl complexes via migratory insertion of a benzyl group into a CN bond. Imino−amido complexes were found to undergo unprecedented dibenzyl elimination to form ene−diamido complexes. Imino−amido complexes were found to be active ethylene polymerization catalysts.
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