Half-Sandwich Ru(II) Complexes with N,O-Chelate Ligands: Diverse Catalytic Activity for Amine Synthesis in Water

Abstract

Several types of β-ketoamino based N,O-coordinate halfsandwich ruthenium complexes have been synthesized in moderate to good yields. The stable ruthenium complexes displayed good and diverse catalytic efficiency in reductive amination between aldehydes and amines in aqueous solution. The method gave a facile route for one-pot synthesis of diverse complicated amines with a low catalyst loading by using cheap and less-toxic HCOOH or clean H 2 as hydrogen source. Catalyst Ru1 showed the highest catalytic activity of 190 h −1 TOF value in the reductive amination reaction of benzaldehyde with aniline. The corresponding amine products were furnished in excellent yields under the standard catalysis system. The efficient and diverse catalytic activity, broad substance scope, mild conditions, and environmentally benign solvent made this system potentially applicable in industrial production. Ruthenium complexes were characterized using NMR, elemental analysis, and IR techniques to confirm their structure.

Ligand-Controlled Ruthenium-Catalyzed Borrowing-Hydrogen and Interrupted-Borrowing-Hydrogen Methodologies: Functionalization of Ketones Using Methanol as a C1 Source

“…On the basis of these experiments, we propose a plausible reaction mechanism as shown in Scheme . Although the exact reason behind the ligand-controlled selectivity is not known, as noticed in other complexes, the electronic effect of the cationic N,N–Ru catalyst having a neutral donor ligand plays a crucial role for the formation of the α,β-unsaturated ketone by liberating H 2 gas without reversible hydrogenation.…”

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

“…The Ru-N bond lengths (2.108 for Ru1 and 2.107 Å for Ru2) as well as Ru-O bond distances (2.047 for Ru1 and for Ru2 for 2.056 Å) are comparable to those reported in the literature. 41 The torsional angle in homobimetallic Ru1 is found to be 179.9°which is linear. Selected bond lengths and bond angles for both complexes are listed in Tables S6 and S7.…”

“…22,36 However, to date there are only a few examples of selective RA catalysts in the literature which employ water as the reaction medium or do not use H 2 as a hydride source. [38][39][40][41] These examples use formic acid/formate buffer as an alternative hydride source since it is mild, selective, and less hazardous. 24,41,42 Moreover, reactions performed in organic solvents generally employ H 2 , 37 while formate buffer is the preferred hydrogen source in the aqueous medium for better miscibility and homogeneity.…”

“…[38][39][40][41] These examples use formic acid/formate buffer as an alternative hydride source since it is mild, selective, and less hazardous. 24,41,42 Moreover, reactions performed in organic solvents generally employ H 2 , 37 while formate buffer is the preferred hydrogen source in the aqueous medium for better miscibility and homogeneity. This system also offers new reactivity and selectivity.…”

“…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.…”