Theoretical perspective on mononuclear copper‐oxygen mediated C–H and O–H activations:A comparison between biological and synthetic systems

Dioxygen activations constitute one of core issues in copper-dependent metalloenzymes. Upon O_(2) activation, copper-dependent metalloenzymes such as particulate methane monooxygenases(pM MOs), lytic polysaccharide monooxygenases(LPMOs) and binuclear copper enzymes PHM and DβM, are able to perform various challenging C–H bond activations. Meanwhile, various copper-oxygen core containing complexes have been synthetized to mimic the active species of metalloenzymes. Dioxygen activation by mononuclear copper active site may generate various copper-oxygen intermediates, including Cu(Ⅱ)-superoxo, Cu(Ⅱ)-hydroperoxo, Cu(Ⅱ)-oxyl as well as the Cu(Ⅲ)-hydroxide species. Intriguingly, all these species have been invoked as the potential active intermediates for C–H/O–H activations in either biological or synthetic systems. Due to the poor understanding on reactivities of copper-oxygen complex, the nature of active species in both biological and synthetic systems are highly controversial. In this account, we will compare the reactivities of various mononuclear copper-oxygen species between biological systems and the synthetic systems. The present study is expected to provide the consistent understanding on reactivities of various copper-oxygen active species in both biological and synthetic systems.

All-at-once arrangement of both oxygen atoms of dioxygen into aliphatic C(sp^(3))–C(sp^(3))bonds for hydroxyketone difunctionalization

Bothβ-andγ-hydroxyketone structures are important units in biologically active molecules,synthetic drugs and fine chemicals.Although there are some routes available for their manufacture from pre-functionalized groups on one or two matrix molecule(s),the approaches to simply and simultaneously deposit two oxygen atoms from dioxygen into two specific C(sp^(3))positions of pure saturated hydrocarbons have rarely succeeded because they are involved in the targeted activation of three inert C–Hσbonds all at once.Here,we show that a TiO_(2)-CH_(3)CN photocatalytic suspension system enables the insertion of dioxygen into one C(sp^(3))–C(sp^(3))bond of strained cycloparaffin derivatives,by which difunctionalized hydroxyketone products are obtained in a one-pot reaction.With the cleavage event to release strain as the directional driving force,as-designed photocatalytic reaction systems show 21 examples ofβ-hydroxyketone products with 31%–76%isolated yields for three-membered ring derivatives and 5 examples ofγ-hydroxyketone products with 30%–63%isolated yields for four-membered ring substrates.^(18)O isotopic labeling experiments using^(18)O2,Ti^(18)O_(2) and intentionally added H218O,respectively,indicated that both oxygen atoms of hydroxyketone products were exclusively from dioxygen,suggesting a previously unknown H^(+)/TiO_(2)-e−catalyzed arrangement pathway of the hydroperoxide intermediate to convert dioxygen into hydroxyketone units.

Synthesis and spectroscopic characterization of cobalt porphyrins and their catalytic activity towards dioxygen reduction

The synthesis and spectroscopic characterization of cobalt(Ⅱ) 5-(4-pyridyl)-10,15,20-triphe- nylporphyrin,cobalt(Ⅱ) 5-(4-N-hexadecylpyridiniumyl)-10,15,20-triphenylporphyrin bromide and cobalt(Ⅱ) 5-(2-aminophenyl)-10,15,20-triphenyl-porphyrin are reported.The corresponding copper and vanadyl derivatives ((TriP)Cu,[(hTriP)Cu]^+Br^- and [(hTriP)VO]^+Br^-) were also studied.Each metalloporphyrin was characterized by UV-visible,ESR and ~1H NMR spectroscopy.These me- talloporphyrins can be firmly adsorbed on the glassy carbon (GC) surface.The catalytic reduction of dioxygen at GC electrodes modified by these catalysts was studied by cyclic voltammetry (CV).The kinetic process of dioxygen reduction at the cobalt porphyrin-modified electrodes was studied with a rotating ring disk electrode.