Interaction of Metal Complexes with G‐Quadruplexes

International audienc

CoIII and CuII complexes of reduced Schiff bases: Generation of phenoxyl radical species

International audienc

Co-II, Ni-II, Cu-II and Zn-II complexes of a bipyridine bis-phenol conjugate: Generation and properties of coordinated radical species

Four bis-phenolate complexes [(ZnL)-L-II], [(NiL)-L-II], [(CuL)-L-II] and [(CoL)-L-II] (where [H2L = 2,2'-[2,2'] bipyridinyl-6-yl-bis-4,6-di-tert-butylphenol] have been synthesized. The copper(II) and nickel(II) complexes have been characterized by X-ray diffraction, showing a metal ion within a square planar geometry, slightly distorted towards tetrahedral. The cyclic voltametry (CV) curve of [(ZnL)-L-II] consists of a single bi-electronic reversible wave at 0.06 V vs. Fc/Fc+. The electrochemically generated dication is a diradical species [(ZnL center dot center dot)-L-II](2+) that exhibits the typical phenoxyl pi-pi* band at 395 nm. It is EPR-silent due to magnetic interactions between the phenoxyl moieties. The CV curves of [(NiL)-L-II] and [(CuL)-L-II] exhibit two distinct ligand-centred one-electron oxidation waves. The first one is observed at E-1/2(1) = 0.38 and 0.40 V for the nickel and copper complex, respectively, and corresponds to the formation of M(II)-coordinated phenoxyl radicals. Accordingly, [(NiLS center dot)-L-II](+) exhibits a strong absorption band at 960 nm and an (S = 1/2) EPR signal centred at g(iso) = 2.02. [(CuLS center dot)-L-II](+) is EPR-silent, in agreement with a magnetic coupling between the metal and the radical spin. In contrast with the other complexes, [(CoL)-L-II] was found to react with dioxygen (mostly in the presence of pyridine), giving rise to a stable (S = 1/2) superoxo radical complex [(CoL)-L-III(Py)(O-2(center dot))]. One-electron oxidation of [(CoL)-L-II] at -0.01 V affords a diamagnetic cobalt(III) complex [(CoL)-L-III](+) that is inert towards O-2 binding, whereas two-electron oxidation leads to the paramagnetic phenoxyl radical species [(CoLS)-L-III](+) whose EPR spectrum features an (S = 1/2) signal at giso = 2.00

Mechanistic Insight on the Aerobic Oxidation of Alcohols by Trivalent Copper from DFT Calculations

International audienceDensity functional theory (DFT) calculations were carried out to elucidate the mechanism of alcohol oxidation by a Cu(III) anilidosalen complex. The study considered singlet, broken-symmetry singlet, and triplet states. During the first step the alcoholate binds to the copper, inducing valence tautomerism, transforming the Cu(III) complex into a Cu(II)-alkoxyradical adduct. Subsequently, an "aniline" ring abstracts a hydrogen from the substrate with a low barrier, yielding a Cu(I) aniline complex and the aldehyde, akin to galactose oxidase. Catalyst re-oxidation is coupled to dioxygen reduction. Initially, dioxygen is reduced by Cu(I) into superoxide, which binds to the metal. Protonation then yields either a Cu(II)-hydrosuperoxo or a Cu(III)-hydroperoxo adduct. Further protonation closes the catalytic cycle by releasing hydrogen peroxide.The alcoholate binds to the copper, transforming the Cu(III) complex into a broken symmetry Cu(II)-alkoxyradical adduct. Next, H-atom abstraction by the anilido moiety directly yields the reduced catalyst and the aldehyde. imag

Coordination chemistry of a redox non-innocent NHC bis(phenolate) pincer ligand with nickel(II)

International audienc

CoII, NiII, CuII and ZnII complexes of a bipyridine bis-phenol conjugate: Generation and properties of coordinated radical species

International audienc

Pseudo-Octahedral Schiff Base Nickel(II) Complexes: Does Single Oxidation Always Lead to the Nickel(III) Valence Tautomer?

International audienc

37Cl/35Cl and 13C/12C isotope effects on the fluorine shielding in several two-carbon chlorofluorocarbons

sotope effects on the chemical shift (IECS) of 19F bonded through two or three bonds to the isotopes 35Cl and 37Cl are reported for a wide range of two-carbon chlorofluorocarbons (and, for a few cases, with the isotopes 79Br and 81Br, for two-carbon bromofluorocarbons). These IECS through two bonds were found to range, for one chlorine atom, from -5.0 to -7.6 ppb for aliphatic compounds and from -4.5 to -6.4 ppb for olefinic compounds. The IECS through three bonds were found to be less than -1.15 ppb. No deviation from additivity was detected for the IECS when several equivalent chlorine atoms are present. The broadening of the 19F lines, due to scalar relaxation arising from 19F-37/35Cl spin-spin interactions, ranges from 0.32 to 2.50 Hz in our series and are related to the 2J(Cl, 19F)T1(Cl) term. IECS of 19F bonded through one or two bonds to the isotopes 13C and 12C are also reported for the same series. Several correlations, related to structural information, can be made and discussed between these IECS [13/12C IECS through two bonds as a function of 1J(13C, 19F) spin-spin coupling constants and 13/12C IECS as a function of 37/35Cl IECS]. 37/35Cl IECS can also be observed on 13C satellites of 19F spectra. For non-symmetrical compounds, the dependence of these signals on the 37/35Cl IECS is the same as that for the main 19F signal; however, for the centrosymmetrical compounds, the main 19F signal appears to be sensitive to all the chlorine atoms, whereas the 13C satellites seem to be sensitive only to the directly bonded chlorine

Unsymmetrical one-electron oxidized Ni(ii)–bis(salicylidene) complexes: a protonation-induced shift of the oxidation site

International audienc

X-Ray Structures of Copper(II) and Nickel(II) Radical Salen Complexes: The Preference of Galactose Oxidase for Copper(II)

International audienc