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

Molecules. 2020 Jan 19;25(2):410. doi: 10.3390/molecules25020410.

Abstract

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 CuxPdy 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.

Keywords: bimetallic nanocatalyst; heterogeneous catalysis; microwaves; one-pot reductive amination; sustainable protocols.

MeSH terms

  • Amination
  • Amines / chemistry
  • Benzaldehydes / chemistry
  • Catalysis
  • Copper / chemistry
  • Cross-Linking Reagents / chemistry*
  • Cyclodextrins / chemistry*
  • Metals / chemistry*
  • Microwaves*
  • Nanoparticles / chemistry*
  • Palladium / chemistry
  • beta-Cyclodextrins / chemistry

Substances

  • Amines
  • Benzaldehydes
  • Cross-Linking Reagents
  • Cyclodextrins
  • Metals
  • beta-Cyclodextrins
  • Palladium
  • Copper
  • betadex
  • benzaldehyde