yAu/SnO 2 (y = 1-5 wt%) and 1 wt% Pt-or Pd-doped 3Au/SnO 2 catalysts were prepared by the co-precipitation method. It is observed that the 3Au/SnO 2 catalyst showed the best performance (T 100% = 166°C). The pretreatment of 3Au/SnO 2 in CO obviously decreased the catalytic activity due to the reduction of oxidized gold species to metallic Au 0 . Pd-or Pt-doping to 3Au/SnO 2 brought about a significant enhancement in performance, with the T 100% value being 74 and 93°C, respectively. It is concluded that the oxidized gold species were more active than metallic Au 0 and the remarkable improvement in catalytic activity due to Pd or Pt doping was associated with the presence of strong interaction of Pd or Pt with Au.
Density functional theory (DFT) calculations have been carried out to study the mechanism of N-alkylation of primary and secondary arylamines with aldehydes and ketones under the catalysis of the Lewis acid B(C 6 F 5 ) 3 using silanes. The B(C 6 F 5 ) 3 -mediated reduction of organic substrates is usually reported under anhydrous conditions. It is noteworthy that Ingleson and co-workers have established that B(C 6 F 5 ) 3 could act as a water tolerant catalyst in N-alkylation of arylamines with aldehydes/ketones. Our DFT calculation results revealed that both Lewis acid B(C 6 F 5 ) 3 and water play important roles in the condensation of amine and aldehyde to generate an imine intermediate and in the subsequent reduction of imine to yield an amine product. In the condensation reaction, Brønsted acid B(C 6 F 5 ) 3 -H 2 O acts as the effective catalyst to promote the proton transfer process. The activation free energy barrier is calculated to be 21.1 kcal/ mol, which is 23.0 kcal/mol lower than that of the water-assisted condensation pathway. In the second stage of imine reduction, our DFT studies specifically show that a "one-pot" ionic outer-sphere S N 2@Si transition state is the favorable pathway, featuring the imine hydrate nucleophilically attacking the η 1 -silane boron adduct to activate silane, with an activation free energy barrier of 17.3 kcal/mol. With direct removal of silanol, a subsequent facile hydride transfer from the boronhydride anion [HB(C 6 F 5 ) 3 ] − to the protonated iminium ion generates the alkylated amine product.
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