Oxidative cross-dehydrogenative coupling of amines and α-carbonyl aldehydes over heterogeneous Cu-MOF-74 catalyst: A ligand- and base-free approach

A crystalline porous metal-organic framework Cu-MOF-74 was synthesized and its properties were examined by a host of techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), atomic absorption spectrophotometry (AAS), and nitrogen physisorption measurements. The Cu-MOF-74 exhibited high activity in oxidative cross-dehydrogenative coupling of amines and α-carbonyl aldehydes to form α-ketoamides using air oxidant. High yields were achieved in the presence of a catalytic amount of the Cu-MOF without any added ligand and base. The activity of Cu-MOF-74 was showed to be higher than that of other frequently reported Cu-MOFs and comparable to common copper salts. Large pore aperture was proposed to strongly contribute to Cu-MOF-74 activity. Furthermore, leaching test indicated no contribution from homogeneous leached species and the catalyst could be recovered and reused several times without a significant degradation in catalytic activity.