Iron Nanoparticles Embedded in Graphitic Carbon Matrix as Heterogeneous Catalysts for the Oxidative C−N Coupling of Aromatic N−H Compounds and Amides

Abstract

AbstractFe or Co nanoparticles (NPs) and two nanoparticulate Fe‐Co alloys having different Fe/Co atomic ratio with average particle size ranging from 10.9 to 26.5 nm embedded in turbostratic graphitic carbon matrix have been prepared by pyrolysis at 900 °C under inert atmosphere of chitosan powders containing Fe2+ and Co2+ ions in various proportions. The resulting Fe/Co NP@C samples have been evaluated as heterogeneous catalysts for the oxidative C−N coupling of amides and aromatic N−H compounds. It was observed that sequential addition of two aliquots of tert‐butyl hydroperoxide (TBHP) in an excess of N,N‐dimethylacetamide (DMA) as solvent affords the corresponding coupling product in high yields, and the most efficient catalyst was Fe NP@C. Fe NP@C is reusable and exhibits a wide scope. The catalytic activity of Fe is supported by using highly pure Fe salt and by the observation that purposely addition of Cu2+ impurities even plays a detrimental effect on the catalytic activity. Mechanistic studies by quenching with 2,2,6,6‐tetramethylpiperidyl‐1‐oxyl (TEMPO) have shown that the amide radical is the key reaction intermediate, and the role of Fe NP@C is to generate the first radicals by TBHP decomposition.