Selective synthesis of primary amines by kinetic-based optimization of the ruthenium-Xantphos catalysed amination of alcohols with ammonia

Abstract

The selective synthesis of primary amines directly from several alcohols and ammonia using a homogeneous catalyst based on HRuCl(CO)(PPh3)3 and Xantphos is presented. The key to success was the detailed understanding of all mutually influencing parameters such as temperature, ammonia excess, and substrate concentration. These studies were supported by the determination of the kinetics, which allowed the reaction order to be calculated as 0.7. Furthermore, the kinetic model derived from the mechanism was confirmed. After measuring reaction profiles for all influencing parameters, optimized conditions were obtained, which finally allowed the amination of aliphatic, cyclic, as well as primary and secondary alcohols with selectivities to the desired primary amine exceeding 90 % at quantitative alcohol conversion with only minimal formation of the undesired secondary amines. Furthermore, the catalytic activity of the commercially available and robust Xantphos system was drastically improved, corresponding to a turnover frequency (TOF)>60 h−1 after 30 minutes and a turnover number (TON) of 120.