High-Cluster (Cu₉) Cage Silsesquioxanes: Synthesis, Structure, and Catalytic Activity

Area of Science:

• Inorganic Chemistry
• Materials Science
• Catalysis

Background:

• Silsesquioxanes are versatile silicon-oxygen cage compounds with tunable properties.
• Metal-templated silsesquioxanes offer unique structural motifs and catalytic potential.
• Developing novel metallasilsesquioxanes with high nuclearity is an active area of research.

Purpose of the Study:

• To synthesize and characterize novel high-cluster (Cu9) cage phenylsilsesquioxanes.
• To investigate the influence of different ligands (phenanthroline and neocuproine) on the resulting metallasilsesquioxane structures.
• To evaluate the catalytic performance of the synthesized compounds in oxidation reactions.

Main Methods:

• Complexation of in situ Cu(II), Na-silsesquioxane species with phenanthroline and neocuproine.
• Single-crystal X-ray diffraction for structural elucidation of the metallasilsesquioxanes.
• Catalytic testing for oxidative amidation, alkane hydroperoxidation, and alcohol oxidation.

Main Results:

• Formation of an unprecedented Cu9Na6 cage phenylsilsesquioxane (1) using phenanthroline.
• Rearrangement into an anionic cage of Cu9Na4 nuclearity (2) in the presence of neocuproine, forming a specific ionic complex.
• Compound 1 demonstrated high catalytic activity in oxidative amidation of benzylic alcohol with low copper loading (100 ppm).
• Compound 1 also showed high activity in alkane hydroperoxidation and alcohol oxidation.

Conclusions:

• The study successfully synthesized novel high-cluster cage phenylsilsesquioxanes with distinct architectures.
• Ligand choice significantly impacts the nuclearity and structure of the resulting metallasilsesquioxanes.
• Compound 1 is a highly active and efficient catalyst for various oxidation reactions, highlighting its potential in sustainable chemistry.