Highly Selective Synergistic N-Alkylation of Amines with ROH Catalyzed by Nickel–Ruthenium

Abstract

The synthesis of secondary amines through N-alkylation is particularly attractive. Conventional N-alkylation reactions usually provide undesired byproducts imines or/and tertiary amines, and discovery of high-selective transformations that can minimize byproducts remains a challenge. Herein, a reusable nickel–ruthenium catalyst Ni/Ru@SBA was developed exhibiting ideal selectivity toward N-monoalkylation of alcohols with amines, and no formation of byproducts imines or/and tertiary amines occurred. Mechanistic studies proved that the N-alkylation reaction is a reversible cascade mechanism. Based on the oxidation of alcohols to form aldehydes and the complex Ni/Ru@SBA[2H], what followed is the aldamine condensation into unstable intermediates which later obtained hydrogen from Ni/Ru@SBA[2H] to finally form secondary amines. The experimental reality is that solely with secondary amines under Ni/Ru@SBA in the presence of H2O, the formation of the original aldehydes/alcohols and amines took place, disclosing why ideal product yields could hardly be achieved in the presence of H2O. The Ni/Ru@SBA along with the developed process allows the production of diverse secondary amines with ideal selectivity.