Polyhedral Cu₂O to Cu pseudomorphic conversion for stereoselective alkyne semihydrogenation

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Metal oxide nanoparticles are precursors for metal catalysts.
• Shape-controlled metal synthesis is crucial for catalytic applications.
• Selective semihydrogenation of alkynes remains a challenge.

Purpose of the Study:

• To develop a facile method for synthesizing shape-controlled copper crystals.
• To investigate the catalytic activity of these copper crystals in alkyne semihydrogenation.
• To explore the stereoselectivity of the semihydrogenation reaction.

Main Methods:

• Pseudomorphic conversion of copper(I) oxide (Cu2O) polyhedra to copper (Cu) crystals using ammonia borane reduction.
• Synthesis of various Cu2O shapes (cubes, octahedra, rhombic dodecahedra).
• Catalytic testing of Cu crystals in the semihydrogenation of diphenylacetylene and other alkynes.

Main Results:

• Cu2O polyhedra were rapidly converted to corresponding Cu crystals with nanoporous interiors.
• Cu rhombic dodecahedra exhibited complete stereoselectivity for (Z)-stilbene production from diphenylacetylene.
• Cu crystals demonstrated high selectivity for (Z)-alkenes in semihydrogenation reactions, outperforming CuCl2 and commercial Cu2O.
• Mechanistic studies indicated low alkene binding affinity on rhombic dodecahedra surfaces contributes to high selectivity.

Conclusions:

• Challenging polyhedral metal particles can be synthesized from metal oxide precursors.
• Shape-controlled copper crystals serve as efficient and selective green catalysts for (Z)-alkene synthesis.
• The low binding affinity of alkenes on specific copper crystal facets is key to achieving high stereoselectivity.