Chromium-Based Metal–Organic Framework MIL-101 Decorated with CdS Quantum Dots for the Photocatalytic Synthesis of Imines

Imine and its derivatives, serving as vital intermediates to construct N-containing heterocyclic compounds, are the highly desired products for fine chemical industry and pharmaceutical industry. With visible light as environmental-benign energy sources, imines are generally synthesized with coupling of amines and alcohols or oxidative self-coupling of amines. However, the coupling of amines and alcohols strategy is usually catalyzed by noble metal catalyst, and the yield of imines is still far from satisfactory owing to the formation of overhydrogenation byproducts. Meanwhile, oxidation self-coupling of amines cannot meet the requirement for the synthesis of asymmetrical substituted imines. In this work, CdS quantum dots decorated MIL-101 catalysts have been constructed as versatile catalysts for photocatalytic synthesis of imines with two different strategies at low temperature (ice bath). Strong interactions between CdS quantum dots and MIL-101 carrier are observed by Raman and UV–Vis DRS measurement results. By taking the combined advantages of CdS quantum dots and MIL-101 materials, CdS@MIL-101 multifunctional catalyst is not only feasible to the photocatalytic coupling of amines and alcohols to synthesize imines under N2 or air atmosphere but also highly active for the oxidative self-coupling of benzylamine derivatives for the synthesis of imines with air as photo-oxidant. Noteworthy, the two photocatalytic synthesis strategies provide an ultra-high selectivity for imine products.