Highly Selective Synergistic N-Alkylation of Amines with ROH Catalyzed by Nickel–Ruthenium
Lan Wang, Xinchun Jv, Ruke Wang, Linzheng Ma, Jing Liu, Jifu Sun, Ting Shi, Lanmei Zhao, Xuekai Zhang, Bo Wang
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.