Rhenium‐Loaded TiO₂: A Highly Versatile and Chemoselective Catalyst for the Hydrogenation of Carboxylic Acid Derivatives and the N‐Methylation of Amines Using H₂ and CO₂

Abstract

Herein, we report a heterogeneous TiO -supported Re catalyst (Re/TiO ) that promotes various selective hydrogenation reactions, which includes the hydrogenation of esters to alcohols, the hydrogenation of amides to amines, and the N-methylation of amines, by using H and CO . Initially, Re/TiO was evaluated in the context of the selective hydrogenation of 3-phenylpropionic acid methyl ester to afford 3-phenylpropanol (pH2 =5 MPa, T=180 °C), which revealed a superior performance over other catalysts that we tested in this study. In contrast to other typical heterogeneous catalysts, hydrogenation reactions with Re/TiO did not produce dearomatized byproducts. DFT studies suggested that the high selectivity for the formation of alcohols in favor of the hydrogenation of aromatic rings is ascribed to the higher affinity of Re towards the COOCH group than to the benzene ring. Moreover, Re/TiO showed a wide substrate scope for the hydrogenation reaction (19 examples). Subsequently, this Re/TiO catalyst was applied to the hydrogenation of amides, the N-methylation of amines, and the N-alkylation of amines with carboxylic acids or esters.

Selective Transformations of Triglycerides into Fatty Amines, Amides, and Nitriles by using Heterogeneous Catalysis

“…It is noteworthy that the thus‐obtained fatty amines are an important class of chemicals for the industrial production of surfactants, germicides, and softeners. Although the reductive amination of relatively reactive carbonyl compounds such as ketones and aldehydes into amines has been studied extensively, reports on the reductive amination of carboxylic acids and esters including triglycerides remain relatively rare . Our heterogeneous catalytic system using NH 3 as a nitrogen source and H 2 does not require any additives and could thus serve as an effective method for the direct transformation of triglycerides into fatty amines.…”

“…The alarming predictions of the rapid depletion of fossil‐fuel resources have inspired researchers to develop alternative technologies that exploit renewable energy sources . Many studies have focused on the conversion of lignocellulosic biomass and triglycerides into various platforms of value‐added chemicals . Industrially, triglycerides in oils and fats have been used as feedstocks for the synthesis of fatty amines, amides, nitriles, and alcohols, which in turn are used for the production of surfactants, polymers, and other useful commodity chemicals …”

The Catalytic Reduction of Carboxylic Acid Derivatives and CO2 by Metal Nanoparticles on Lewis‐Acidic Supports

“…It should be noted here that this heterogeneous catalytic system does not produce any dearomatized byproducts, despite the difficulty of hydrogenating the COOH group. Furthermore, Re/TiO 2 promotes various selective hydrogenation reactions of other carboxylic acid derivatives and CO 2 , e. g. the hydrogenation of esters to alcohols, the hydrogenation of amides to amines, and the N ‐methylation of amines using H 2 and CO 2 . Moreover, Re/TiO 2 promotes the N ‐alkylation of amines with carboxylic acids or esters in the presence of H 2 …”

Synthesis of Quinolines Through Acceptorless Dehydrogenative Coupling Catalyzed by Rhenium PN(H)P Complexes

“…[19] Studies on manganese catalysis for (de)-hydrogenation reactions have increased exponentially over the last two years. [22] Recently,w eh ave developed as eries of rheniumc omplexes with tridentate PN(H)P ligands (Scheme 1, A-E), which were efficiently employed in the hydrogenationo fc arbonyl derivatives [23] and the mono-N-methylation of anilinesw ith methanol as C1 source. [21] In contrast, hydrogen auto-transfer reactions catalyzed by rhenium are still quite rare.…”