γ-Alumina-Supported Silver Cluster for N-Benzylation of Anilines with Alcohols

An alumina-supported silver cluster with a Lewis acidic cocatalyst (polyvalent metal salts, such as FeCl3 center dot 6H(2)O) acts as a heterogeneouos and recyclable catalyst for the direct N-alkylation of anilines with benzyl alcohols, which is driven by the borrowing hydrogen mechanism. Systematic studies on the effects of metal (Pt, Pd, Au, and Ag), silver particle size/support oxides (CeO2, ZrO2, Al2O3, SiO2), and Lewis acidic additives show four important factors required to achieve selective N-alkylation of anilines: 1) metal with a weak metal-hydrogen bond energy (ie., Ag), 2) smaller size of the silver cluster, 3) the support having both acidic and basic sites (ie., Al2O3), and 4) additives with high Lewis acidity (ie., Fe salt). Fundamental information will be useful for the rational design of platinum-group metal-free heterogeneous catalyts for environmentally benign C-N bond forming reactions.