A Reusable CNT-Supported Single-Atom Iron Catalyst for the Highly Efficient Synthesis of C-N Bonds

C-N bond formation is regarded as a very useful and fundamental reaction for the synthesis of nitrogen-containing molecules in both organic and pharmaceutical chemistry. Noble-metal and homogeneous catalysts have frequently been used for C-N bond formation, however, these catalysts have a number of disadvantages, such as high cost, toxicity, and low atom economy. In this work, a low-toxic and cheap iron complex (iron ethylene-1,2-diamine) has been loaded onto carbon nanotubes (CNTs) to prepare a heterogeneous single-atom catalyst (SAC) named Fe-N-x/CNTs. We employed this SAC in the synthesis of C-N bonds for the first time. It was found that Fe-N-x/CNTs is an efficient catalyst for the synthesis of C-N bonds starting from aromatic amines and ketones. Its catalytic performance was excellent, giving yields of up to 96 %, six-fold higher than the yields obtained with noble-metal catalysts, such as AuCl3/CNTs and RhCl3/CNTs. The catalyst showed efficacy in the reactions of thirteen aromatic amine substrates, without the need for additives, and seventeen enaminones were obtained. High-angle annular dark-field scanning transmission electron microscopy in combination with X-ray absorption spectroscopy revealed that the iron species were well dispersed in the Fe-N-x/CNTs catalyst as single atoms and that Fe-N-x might be the catalytic active species. This Fe-N-x/CNTs catalyst has potential industrial applications as it could be cycled seven times without any significant loss of activity.