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

Abstract

[EN] Fe 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 degrees C under inert atmosphere of chitosan powders containing Fe2+ and Co2+ ions in various proportions. The resulting Fe/CoNP@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 FeNP@C. FeNP@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 FeNP@C is to generate the first radicals by TBHP decomposition.