Cross-Linked Cyclodextrins Bimetallic Nanocatalysts: Applications in Microwave-Assisted Reductive Aminations

The optimization of sustainable protocols for reductive amination has been a lingering challenge in green synthesis. In this context, a comparative study of different metal-loaded cross-linked cyclodextrins (CDs) were examined for the microwave (MW)-assisted reductive amination of aldehydes and ketones using either H₂ or formic acid as a hydrogen source. The Pd/Cu heterogeneous nanocatalyst based on Pd (II) and Cu (I) salts embedded in a β-CD network was the most efficient in terms of yield and selectivity attained. In addition, the polymeric cross-linking avoided metal leaching, thus enhancing the process sustainability; good yields were realized using benzylamine under H₂. These interesting findings were then applied to the MW-assisted one-pot synthesis of secondary amines via a tandem reductive amination of benzaldehyde with nitroaromatics under H₂ pressure. The formation of a Cu_xPd_y alloy under reaction conditions was discerned, and a synergic effect due to the cooperation between Cu and Pd has been hypothesized. During the reaction, the system worked as a bifunctional nanocatalyst wherein the Pd sites facilitate the reduction of nitro compounds, while the Cu species promote the subsequent imine hydrogenation affording structurally diverse secondary amines with high yields. View Full-Text