Thioether S-ligation in a side-on mu-eta(2):eta(2)-peroxodicopper(II) complex

[(ANS)Cu-I(CH3CN)](+) reacts with O-2 giving [{(ANS)Cu-II}(2)(mu-eta(2):eta(2)-O-2(2-))](2+), nu(O-O) = 731 cm(-1), shown to possess S-thioether ligation, based on comparisons with analogues having all N-ligands or a -S(Ph) group. The finding is a rare occurrence and new for side-on O-2(2-) binding

Copper(I)/O(2)Chemistry with Imidazole Containing Tripodal Tetradentate Ligands Leading to mu-1,2-Peroxo-Dicopper(II) Species

Cuprous and cupric complexes with the new imidazolyl containing tripodal tetradentate ligands {L-MIm, (1H-imidazol-4-yl) -N,N-bis((pyridin-2-yl)methyl)methanamine, and L-EIm, 2-(1H-imidazol-4-yl)-N,N-bis((pyridin-2-yl)methyl)ethanamine}, have been investigated to probe differences in their chemistry, especially in copper(I)-dioxygen chemistry, compared to that already known for the pyridyl analogue TMPA, tris(2-pyridyl)methyl)amine. Infrared (IR) stretching frequencies obtained from carbon monoxide adducts of [(L-MIm)Cu-I](+) (1a) and [(L-EIm)Cu-I](+) (2a) show that the imidazolyl donor is stronger than its pyridyl analogue. Electrochemical data suggest differences in the binding constant of Cu-II to L-EIm compared to TMPA and L-MIm, reflecting geometric changes, Oxygenation of [(L-MIm)Cu-I](+) (1a) in 2-methyltetrahydrofuran (MeTHF) solvent at -128 degrees C leads to an intensely purple colored species with a UV-vis spectrum characteristic of an end-on bound peroxodicopper(II) complex [{(L-MIm)Cu-II}(2)(mu-1,2-O-2(2-))](2+) (1b(P)) {lambda(max)=528 nm}, very similar to the previously well characterized complex [{(TMPA)Cu-II}(2)(mu-1,2-O-2(2-))](2+) {lambda(max)=520 nm (epsilon=12 000 M-1 cm(-1)), in MeTHF; resonance Raman (rR) spectroscopy: nu(O-O)=832 (Delta(O-18(2))=-44) cm(-1)}. In the low-temperature oxygenation of 2a, benchtop (-128 degrees C) and stopped-flow (-90 degrees C) experiments reveal the formation of an initial superoxo-Cu(II) species [(L-EIm)Cu-II(O-2(center dot-))](+) (2b(S)), lambda(max)=431 nm in THF). This converts to the low-temperature stable peroxo complex [{(L-EIm)Cu-II}(2)(mu-1,2-O-2(2-))](2+) (2b(P)) {rR spectroscopy: nu(O-O)=822 (Delta(O-18(2))=-46) cm(-1)}. Complex 2b(P) possess distinctly reduced Cu-O and O-O stretching frequencies and a red-shifted UV-vis feature {to lambda(max)=535 nm (epsilon=11 000 M-1 cm(-1))} compared to the TMPA analogue due to a distortion from trigonal bipyramidal (TBP) to a square pyramidal ligand field. This distortion is supported by the structural characterization of related ligand-copper(II) complexes: A stable tetramer cluster complex [(mu(2)-LEIm-)(4)-(Cu-II)(4)](4+), obtained from thermal decomposition of 2b(P) (with formation of H2O2), also exhibits a distorted square pyramidal Cu(II) ion geometry as does the copper(II) complex [(L-EIm)Cu-II(CH3CN)](2+) (2c), characterized by X-ray crystallography and solution electron paramagnetic resonance (EPR) spectroscopy

Cu-ZSM-5 Zeolites for the Formation of Methanol from Methane and Oxygen: Probing the Active Sites and Spectator Species

A series of Cu-ZSM-5 zeolites was prepared by varying nature of the charge compensating cation, copper precursor, copper loading, and pH. The materials were tested for the oxidation of methane to methanol using oxygen. A linear relationship between the amount of methanol produced over Cu-ZSM-5 zeolites from methane and oxygen and a UV–Vis-NIR DRS charge transfer band at 22,700 cm−1 is reported irrespective of the synthesis route used. The absolute intensity of the 22,700 cm−1 band is always low, indicating a low number of active sites in the samples. In all studied Cu-ZSM-5 zeolites at least two copper species were present: (a) Cu–O clusters dispersed on the outer surface of ZSM-5 and (b) highly dispersed copper-oxo species inside the channels, a minority fraction in the sample. By relating catalytic activity to FT-IR data of adsorbed pivalonitrile, visualizing Cu–O particles on the outer surface of the zeolite, and subsequently adsorbed NO, indicative of the Cu–O species inside the zeolite channel, it was concluded that Cu–O species on the outer surface are not involved in the oxidation reaction, while copper inside the channels are responsible for the selective conversion of methane to methanol