Selective Activation of Alcohols in the Presence of Reactive Amines over Intermetallic PdZn: Efficient Catalysis for Alcohol-Based N-Alkylation of Various Amines

Pd-based intermetallic compounds supported on Al2O3 (PdxMy/Al2O3) where M = Bi, Cu, Fe, Ga, In, Pb, Sn, or Zn) were prepared and tested as catalysts for the selective activation of alcohols in the presence of reactive amines, which is highly challenging and is the key strategy for alcohol-based N-alkylation of amines. Although the Pd/Al2O3 catalyst exhibited a high catalytic activity, undesired side reactions such as amine dimerization (via amine activation) and C-O bond scission occurred, resulting in a poor yield of the N-alkylation product. In contrast, the PdZn/Al2O3 catalyst acted as an efficient catalyst for this reaction, displaying high catalytic activities, selectivities, and atom efficiencies and a wide substrate scope. Detailed kinetic and computational studies revealed that the relative affinity of Pd for alcohol and amine drastically changes by the formation of a PdZn intermetallic phase. On monometallic Pd, the adsorption and activation of amines are preferred over those of alcohols in terms of thermodynamic and kinetic aspects, respectively. However, this trend is inverted on PdZn, allowing preferential adsorption and activation of alcohols and, hence, selective N-alkylation.