Formation of the O−O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High‐valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O−O bond in solution, from non‐heme, N5‐coordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once meta‐chloroperbenzoic acid is administered in excess. Oxygen‐isotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT (hydrogen atom transfer)‐initiated free‐radical pathways of the peroxides, which are typical of catalase‐like reactivity, and iron‐borne O−O coupling, which is unprecedented for non‐heme/peroxide systems. Interpretation in terms of [FeIV(O)] and [FeV(O)] being the resting and active principles of the O−O coupling, respectively, concurs with fundamental mechanistic ideas of (electro‐) chemical O−O coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting.
Copper oxide catalysts supported on nanostructured silica SBA‐15 were synthesized with varying copper loadings in a range from 1.1 to 19.4 wt.%. Catalysts were structurally characterized by N2 physisorption, X‐ray diffraction and ex situ as well as in situ diffuse reflectance UV‐Vis spectroscopy. Copper oxide species contained Cu2+ in an octahedral configuration with a tetragonal distortion. Increasing the copper loading resulted in a decreasing optical band gap, which is associated with a growing particle size. Additionally, CuO/SBA‐15 samples were examined by temperature‐programmed reduction confirming a narrow particle size distribution. Structural evolution and catalytic activity were investigated during selective oxidation of propene focusing on product distribution of nucleophilic and electrophilic oxidation. Catalytic testing was carried out using an on‐line GC and MS coupled to a laboratory fixed‐bed reactor. All catalysts selectively oxidized propene to acrolein and propylene oxide (PO). With time on stream activity decreased while selectivity towards acrolein and PO increased. While selectivity towards PO increased with copper loading and, hence, copper oxide particle size, selectivity towards acrolein was largely independent of copper loading.
Formation of the OÀOb ond is considered the Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.org/10.
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