Multicopper complexes and coordination polymers for mild oxidative functionalization of alkanes

Alkanes (main components of natural gas and oil) are rather inert compounds and their functionalization under mild conditions, toward the synthesis of added value organic products, constitutes a challenge to modern chemistry. A promising approach concerns the development of bioinspired metal complex catalysts which, with an appropriate oxidizing agent and under tuned reaction conditions, are capable of converting alkanes into valuable functionalized products. In view of the well recognized biological function of copper, which is present in the active sites of many oxidation enzymes including the multicopper particulate methane monooxygenase (pMMO), the current contribution summarizes recent advances in the oxidative functionalization of alkanes catalyzed by multicopper systems. The main types of polynuclear copper complexes and coordination polymers applied in homogeneous alkane transformations are classified, and the critical analysis of the most efficient catalytic systems in two different reactions is presented. These reactions include the mild oxidation of alkanes (typically cyclohexane as a model substrate) by hydrogen peroxide into alkyl hydroperoxides, alcohols, and ketones, as well as the hydrocarboxylation of gaseous and liquid Cn (n = 2–9) alkanes, by carbon monoxide, water, and potassium peroxodisulfate into the corresponding Cn+1 carboxylic acids. The important effects of various reaction parameters are highlighted and the preferable requirements for a prospective homogeneous Cu-based catalyst in oxidative transformations of alkanes are identified. Emphasis is given on the use of hydrosoluble copper catalysts with an N,O-environment, acid co-catalysts, H2O/MeCN mixed solvent, under mild reaction conditions.

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► Overview of main types of multicopper complexes and coordination polymers.
► Recent advances in Cu-catalyzed oxidation and hydrocarboxylation of alkanes.
► Critical analysis of the most efficient multicopper catalysts or catalyst precursors.
► Identification of preferable requirements for a Cu-based catalyst.
► Perspectives for further development of new alkane functionalization protocols.