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

Abstract

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.

Toward Understanding the Manipulation of Surface Acidity Behavior with Relativistic Effect for the Formation of C–N Bonds

“…This suggests that a satisfactory yield can be hardly achieved via merely strong dehydration capacity and the presence of an acid site. 19 Compared with the fully reported homogeneous catalysis process 20 shown in Table 4, given the exceptional selectivity and reasonable yield, ScTiTbAuAPO-5 exhibits immense advantages in terms of the green chemistry and the catalyst costs. Thus, ScTiTbAuAPO-5 is much more suitable for the continuous industrialized process.…”

A highly active and chemoselective homobimetallic ruthenium catalyst for one-pot reductive amination in water

“…13,14 Thus, the RA method has emerged as a very promising alternative using both homogeneous and heterogeneous catalysts based on Co, Rh, Ir, Fe, Ru, Ni, and Pd. 10,[22][23][24][25][26][27][28][29][30][31][32] Although the development of newer and more efficient RA catalysts is currently witnessing enormous activity, 33,34 there is ample scope for further improvements in all catalytic parameters, viz. catalyst load, overall yield, selectivity, TON, TOF, etc.…”

“…Collectively, high catalyst loading, harsher reaction conditions, use of organic solvents, use of hazardous H 2 as a hydrogen source, lack of chemoselectivity, low green metrics and sustainability still remain challenges for further develop-ment in this field. 14,33,[41][42][43][44] One way to tackle such a complex combination of challenges would be to design bimetallic (or multimetallic) catalyst systems that can operate in the aqueous medium and utilize formate buffer as a hydride source and still exhibit high selectivity for the secondary amine production via RA.…”