DOI RECORD
Scalable and Selective Homogeneous Hydrogenation of Adiponitrile to Hexamethylenediamine Using a Ru-Xantphos Catalyst
Abstract
Efficient and scalable hydrogenation of dinitriles to diamines is a significant challenge in industrial organic chemistry. This process typically requires harsh conditions and heterogeneous catalysts, which can lead to unwanted cyclization and dimerization side reactions. Herein, we present a highly efficient and selective homogeneous catalytic system for synthesizing hexamethylenediamine by hydrogenating adiponitrile. Using a robust ruthenium complex generated in situ from the readily available Ru(COD)Cl₂ and Xantphos ligand under mild, base-promoted conditions (15–40 bar H₂, 50 °C), the protocol achieves excellent conversion and selectivity toward the primary diamine. The practical viability of this catalytic system was demonstrated by successfully scaling up to a two-mol scale, yielding 172 g of hexamethylenediamine. Kinetic profiles and solvent screening highlight the importance of protic media and temperature optimization for reaction rates. Additionally, isolating and X-ray crystallographically characterizing an inactive bis-Xantphos ruthenium hydride complex provides key mechanistic insights into the catalyst deactivation pathway. This protocol offers a straightforward, economical strategy that can be extended to various aliphatic and aromatic nitriles.