Ruthenium N‐Heterocyclic Carbene Complexes for Chemoselective Reduction of Imines and Reductive Amination of Aldehydes and Ketones

• Published in: European journal of inorganic chemistry 2020-06, Vol.2020 (24), p.2372-2379
• Main Authors: Kathuria, Lakshay, Samuelson, Ashoka G.
• Format: Article
• Language: English
• Subjects: Aldehydes; Amines; Anaerobic conditions; Carbene ligands; Catalysts; Half‐sandwich complexes; Homogeneous catalysis; Imines; Inorganic chemistry; Ketones; Reduction; Room temperature; Ruthenium
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202000069

Chemoselective reduction of imines to secondary amines is catalyzed efficiently by tethered and untethered, half‐sandwich ruthenium N‐heterocyclic carbene (NHC) complexes at room temperature. The untethered Ru‐NHC complexes are more efficient as catalysts for the reduction of aldimines and ketimines than the tethered complexes. Using the best untethered complex as a catalyst, electronic and steric demands on the reaction was probed using a series of imines. Chemoselectivity of the catalyst towards imine reduction was tested by performing inter and intramolecular competitive reactions in a variety of ways. The catalyst exhibits a very high TON and TOF under anaerobic conditions. An efficient reduction of imines carried out by the untethered and arene‐tethered Ru‐NHC complexes was studied under hydrosilylation reaction conditions. The reduction of imines was chemoselective in nature, proven by several competitive reactions. A quick reduction of the imines by these Ru‐NHC complexes points to their high TON and TOF. The amines could also be synthesized by these complexes by reducing the in situ formed imines.