Construction of an Active Copper Catalyst for Selective <i>N</i> -Monomethylation of Aliphatic Primary Amines via Surface <i>N</i> -Modification

Selective synthesis of N-monomethylamines from primary amines, especially aliphatic primary amines, remains challenging due to the more favored formation of N,N-dimethylamines. DFT study reveals that the N-modified Cu(111) surface using 1,10-phenanthroline (Phen) favors the selective N-monomethylation of aliphatic primary amine with HCHO and H2 by inhibiting the overmethylation side reaction. To prove this hypothesis, a N-modified heterogeneous Cu catalyst (N-CuAlOx) using 1,10-phenanthroline was synthesized, characterized, and tested. Up to 98% selectivity of N-monomethylation of aliphatic primary amines was obtained, which is higher than that of most homogeneous noble catalysts. Our system is the first one achieving such high selective conversion of aliphatic primary amines to the corresponding N-monomethylamines with over 80% yields without base additives and at temperatures lower than 200 °C.