N-Alkylation of substituted alcohols through self-supported mesoporous CuMn2O4

Abstract

N-Alkylation of alcohols by hydrogen transfer is a green and atomically economical method for the preparation of amines; however, most of the reported catalysts are noble metal and homogeneous catalysts. Essentially, heterogeneous catalysts with the stable co-existence of multiple valence metals are difficult to prepare. In this study, we designed mixed-metal oxide (MMO) CuMn₂O₄ with a self-supported mesoporous structure as a catalyst for the reactions of substituted alcohols and benzenesulfonamides/anilines. It possessed a high catalytic activity in the hydrogen transfer reaction, which can be mainly attributed to the Jahn–Teller effect and the unique electronic states of copper and manganese ions for their variable values and complex coordination status in the MMO material. Furthermore, the self-supported CuMn₂O₄ catalyst with the advantages of high surface area and large particle size, benefitted the adsorption–desorption of hydrogen over active sites, which established a 30% higher yield in the N-alkylation reaction as compared with its bulk alternative. Therefore, the active compositions with variable values and the unique mesoporous structure of CuMn₂O₄ were the combined reasons for the efficient hydrogen transfer and further N-alkylation reaction. Extensive substrates, such as, sulfonamides and alcohols, including electron-donating and electron-withdrawing substituents on benzyl alcohols and benzene sulfonamides were tried and were well-tolerated to achieve high yields, suggesting that the self-supported CuMn₂O₄ possesses excellent catalytic activity and broad universality.