Cu(I)-Based Metal–Organic Frameworks as Efficient and Recyclable Heterogeneous Catalysts for Aqueous-Medium C–H Oxidation

Abstract

The enantioselective transformation of ubiquitous C–H bonds into valuable C═O bonds offers an efficient synthetic approach to construct carbonyl functionalized molecules. However, the grand obstacles in the reaction are the selectivity issues and side reactions under the harsh reaction conditions. In order to overcome the limits, two Cu(I)-based MOFs {(NEt4)0.5[Cu3(TTPB)0.75(CN)0.5(H2O)]·H2O}n (1) and {[Cu2(TTPB)0.5]·DMF·2H2O}n (2) were synthesized (H4TTPB = 5,5′-(4′,5′-bis(4-(1H-tetrazol-5-yl)phenyl)-[1,1′:2′,1′′-terphenyl]-4,4′′-diyl) bis(1H-tetrazole)) under hydrothermal conditions with (triethylamine (TEA) and ethyldiisopropylamine (DIPEA) as structure-directing agents, respectively. Of these, 1 shows an anionic three-dimensional (3D) framework composed of two kinds of cagelike micropores with 7 × 17 Å and 10 × 17 Å, respectively. In comparison, 2 exhibits a 3D framework with open channels (14 × 8 Å). The stability studies showed that the crystallinity of 1 and 2 could remain in a series of organic solvents (ethanol, N,N-dimethylformamide, chloroform, dioxane, toluene) and acid and alkali aqueous solutions (pH = 1–13) at room temperature for 48 h. 1 and 2 with coordinatively unsaturated Cu(I) sites were applied as heterogeneous catalysts for the oxidation of arylacycloalkanes in aqueous medium and exhibited excellent catalytic activities, selectivities, and recyclabilities. Moreover, free-radical reaction mechanism and reversible valence-tautomeric conversions of central copper were confirmed during the process by control experiment.