An amino-linked nitrogen heterocyclic carbene (amino-NHC), 1-tBu, has been shown to mediate carbon-carbon coupling through the direct C-H functionalization of benzene and pyridine in the absence of a metal catalyst. Using EPR, the first spectroscopic evidence corroborating the single electron transfer mechanism for the metal-free carbon-carbon coupling manifold, as reported by others, is introduced.

Highlights  Subunit B (PmoB) of particulate methane monooxygenase (pMMO) is expressed in E. coli.  PmoB and its variants/mutants are expressed in the membranes as Cu I proteins.  The PmoB of pMMO contains a Cu I sponge with high reduction potentials for the Cu sites.  The PmoB proteins show evidence of a dinuclear copper site.  The PmoB-enriched E. coli membranes produce H 2 O 2 .

A study of the oxygen reduction reaction (ORR) on a screen printed carbon electrode surface mediated by the tricopper cluster complex Cu (7-N-Etppz(CH OH)) dispersed on electrochemically reduced carbon black, where 7-N-Etppz(CH OH) is the ligand 3,3'-(6-(hydroxymethyl)-1,4-diazepane-1,4-diyl)bis(1-(4-ethyl piperazin-1-yl)propan-2-ol), is described. Onset oxygen reduction potentials of about 0.92 V and about 0.77 V are observed at pH 13 and pH 7 vs. the reversible hydrogen electrode, which are comparable to the best values reported for any synthetic copper complex. Based on half-wave potentials (E ), the corresponding overpotentials are about 0.42 V and about 0.68 V, respectively. Kinetic studies indicate that the trinuclear copper catalyst can accomplish the 4 e reduction of O efficiently and the ORR is accompanied by the production of only small amounts of H O . The involvement of the copper triad in the O activation process is also verified.

The process of selective oxy-functionalization of hydrocarbons using peroxide, O 3 , H 2 O 2 , O 2 , and transition metals can be carried out by the reactive oxygen species such as hydroxyl/hydroperoxyl radical and/or metal oxygenated species generated in the catalytic reaction. Thus, a variety of mechanisms have been proposed for the selective catalytic oxidation of various hydrocarbons including light alkanes, olefins, and simple aromatics by the biological metalloproteins and their biomimetics either in their homogeneous or heterogeneous platforms. Most studies involving these metalloproteins are Fe or Cu monooxygenases. The pathways carried out by these metalloenzymes in the oxidation of C-H bonds invoke either radical reaction mechanisms including Fenton's chemistry and hydrogen atom transfer followed by radical rebound reaction mechanism or electrophilic oxygenation/O-atom transfer by metal-oxygen species. In this review, we discuss the metal oxide nano-catalysts obtained from metal salts/molecular precursors (M = Cu, Fe, and V) that can easily form in situ through the oxidation of substrates using H 2 O 2(aq) in CH 3 CN, and be facilely separated from the reaction mixtures as well as recycled for several times with comparable catalytic efficiency for the highly selective conversion from hydrocarbons including aromatics to oxygenates. The mechanistic insights revealed from the oxy-functionalization of simple aromatics mediated by the novel biomimetic metal oxide materials can pave the way toward developing facile, cost-effective, and highly efficient nano-catalysts for the selective partial oxidation of simple aromatics.

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