Silver cluster-promoted heterogeneous copper catalyst for N-alkylation of amines with alcohols

A series of metal(M)-loaded Al2O3 catalysts (M/Al2O3) and bimetallic catalysts, CuxAg1-x/Al2O3 with different compositions, Cu0.95Ag0.05/MOx with different supports (MOx), and Cu0.95M'(0.05)/Al2O3 with different promoter (M'), were prepared by an impregnation method, followed by H-2-reduction at 600 degrees C. For the N-alkylation of amines with alcohols, Al2O3-supported copper-silver bimetallic catalysts with a Cu/Ag molar ratio of 95/5 (Cu0.95Ag0.05/Al2O3) was found to be the most effective heterogeneous catalyst. The alkylation of anilines and aliphatic amines with various alcohols (benzyl and aliphatic alcohols) was achieved with a small amount of the catalyst (1 mol%). Mechanistic studies show that the reaction proceeds through a hydrogen-borrowing mechanism initiated by alcohol dehydrogenation as the rate-limiting step. Structural studies indicate that small Ag nanoclusters are supported on Cu nanoparticles possibly through Ag-O-Cu bonds at the silver-copper boundary. This bimetallic structure can be crucial to an effective promotion of the alcohol dehydrogenation and hydride transfer to the imines.