Investigation of facet effects on the catalytic activity of Cu2O nanocrystals for efficient regioselective synthesis of 3,5-disubstituted isoxazoles

Abstract

Cubic, octahedral, and rhombic dodecahedral Cu2O nanocrystals bound by respectively {100}, {111}, and {110} facets were successfully employed to catalyze the [3 + 2] cycloaddition reaction for the regioselective synthesis of 3,5-disubstituted isoxazoles. Surfactant-free nanocrystals having the same total surface area were used for the catalysis. Strongly facet-dependent organocatalytic activity has been observed. Rhombic dodecahedra with fully exposed surface copper atoms on the (110) planes are the most efficient catalysts, followed by octahedra and the least active nanocubes. The particles are also recyclable catalysts. Cu2O rhombic dodecahedra were also used for the syntheses of 3,5-disubstituted isoxazoles from a wide variety of aromatic imidoyl chlorides and terminal alkynes in ethanol at 50 °C with excellent yields. Furthermore, a one-pot multi-component synthetic approach was demonstrated to form isoxazoles directly from readily available aldehyde precursors. This work clearly shows that precise facet engineering of Cu2O crystals can lead to significantly improved organocatalytic efficiency.

Facet‐Dependent Optical Properties Revealed through Investigation of Polyhedral Au–Cu2O and Bimetallic Core–Shell Nanocrystals

“…Previously, we demonstrated that Cu 2 O crystals display facet‐dependent electrical conductivity and photocatalytic activity, which involves charge carrier transport into and out of a Cu 2 O crystal through different facets or interfaces. Facet‐dependent organocatalytic properties of Cu 2 O crystals, on the other hand, are considered to be mainly surface‐related properties, because all surface facets exhibit some degrees of catalytic activity . The facet‐dependent optical responses arise in Au‐Cu 2 O crystals because of different degrees of band bending for different surface facets of Cu 2 O, such that different facets can be considered to consist of a thin surface layer with varying refractive indices to tune the plasmonic band positions of the gold cores.…”

Facet‐Controlled Synthetic Strategy of Cu2O‐Based Crystals for Catalysis and Sensing

“…It is noteworthy that, although high‐index facets that have high‐density atomic edges with corners and plentiful unsaturated active sites are promising for catalysis and sensing applications, those facets are often unstable, and hardly obtained by traditional chemical methods 17, 18, 19, 20, 21, 22, 23. Thus, the shape‐dependent catalysis and sensing behaviours is primarily focused on NCs enclosed by low‐index facets, especially the three basic facets (i. e., the {100}, {111}, and {110} facets) 6, 7, 8, 9, 12, 13, 14, 16, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34. For instance, by employing hydrofluoric acid as a capping agent (CA), H. G. Yang et al34 were the first to obtain uniform anatase TiO 2 single crystals with a high percentage (47%) of highly reactive {001} facets, which possessed promising applications in sensors, solar cells and photocatalysis.…”

“…In this context, the inexpensive, non‐toxic and abundantly available Cu 2 O nanomaterials, with unique optical and electrical properties,4, 9, 10, 53, 54, 55, 56, 57, 58 have recently aroused general attention, due to their outstanding morphology‐dependent applications in catalysis (gas oxidation,2, 3, 17, 59, 60, 61 CO 2 reduction,62, 63, 64, 65 organocatalysis,14, 24, 32, 40, 50, 66 electrocatalysis,28, 67, 68 and photocatalysis36, 44, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, sensing (gas sensors,8, 79, 80, 81, 82, 83 ion detection,29 and surface‐enhanced Raman scattering (SERS)84, 85, 86, 87, 88, 89, as adsorbents,7, 90 biotoxicity,26, 91, 92 as chemical templates35, 38, 45, 4...…”

Rhombic Dodecahedral Cu2O‐Catalysed Synthesis of Novel Alkenyl Pyrazoles

“…The morphology and structure of the sample were investigated by field emission scanning electron microscopy (FESEM) micrographs. As shown in Figure A and Figure B, the obtained Cu 2 O microcrystals exhibited uniform rhombic dodecahedra shapes with an average particle size of 0.66 µm, which is extremely important to serve as an excellent catalyst for many organic reactions , . To determine the chemical purity of the Cu 2 O microcrystals and identify the chemical state of Cu in the samples, XRD and XPS measurements were performed, respectively.…”

“…Cu‐based catalysts are used extensively in pyrazoles synthesis. Recently, Cu 2 O cubes, octahedra, and rhombic dodecahedra were employed as catalysts for the direct synthesis of 1,2,3‐triazoles, and 3,5‐disubstituted isoxazoles . And the results verified that rhombic dodecahedra are the most efficient catalysts giving excellent yields.…”