Search Results (5)

Two bis-ruthenium(II) complexes, namely N,N′-{5,17-diamino-4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene}-bis-[dichloro-(p-cymene)-ruthenium(II)] (1) and N,N′-{5,11-diamino-4(24),6(10),12(16), 18(22)-tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene}-bis-[dichloro-(p-cymene)-ruthenium(II)] (2) were synthesized and tested as catalysts in the N-alkylation of primary amines with arylmethyl alcohol using the green “hydrogen borrowing” methodology. The catalytic results were compared with those obtained when the N-{5-amino-4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentyl-resorcin[4]arene}-[dichloro-(p-cymene)-ruthenium(II)] (3) complex was employed as catalyst. The rate of the N-alkylation of aniline with benzyl alcohol increased in the order 3 < 1 ≪ 2, which highlights the importance of the relative positioning of the two metal centers on the upper rim of the resorcin[4]arene. Theoretical investigations suggest that the grafting of the two “RuCl₂(p-cymene)NH₂” moieties on two distal aromatic rings of the cavitand allows a cooperative effect between a ruthenium atom and the coordinated amine of the second metal center. Full article

The synthesis of primary amines via the reductive amination of alcohols involves a hydrogen-borrowing or hydrogen-transfer mechanism, which consists of three main steps: alcohol hydroxyl dehydrogenation, carbonyl imidization, and imine hydrogenation. Heterogeneous catalysts are widely used for this reaction because of their high performance and amenability to separation and reuse. However, the efficiency of reductive amination is limited by the dehydrogenation step, which is severely affected by the competitive adsorption of NH₃. We hope to improve the efficiency of reductive amination by increasing dehydrogenation efficiency. Therefore, in this overview, we introduce the research progress of alcohol reductive amination reaction catalyzed by heterogeneous metal catalysts, focusing on methods of enhancing dehydrogenation efficiency by screening the metal component and the acidity/alkalinity of the support. Finally, we propose some new strategies for the preparation of catalysts from the perspective of overcoming the competitive adsorption of NH₃ and speculate on the design and synthesis of novel catalysts with high performance in the future. Full article

Bio-based furanic oxygenates represent a well-known class of lignocellulosic biomass-derived platform molecules. In the presence of H₂ and different nitrogen sources, these versatile building blocks can be transformed into valuable amine compounds via reductive amination or hydrogen-borrowing amination mechanisms, yet they still face many challenges due to the co-existence of many side-reactions, such as direct hydrogenation, polymerization and cyclization. Hence, catalysts with specific structures and functions are required to achieve satisfactory yields of target amines. In recent years, heterogeneous catalytic synthesis of amines from bio-based furanic oxygenates has received extensive attention. In this review, we summarize and discuss the recent significant progress in the generation of useful amines from bio-based furanic oxygenates with H₂ and different nitrogen sources over heterogeneous catalysts, according to various raw materials and reaction pathways. The key factors affecting catalytic performances, such as active metals, supports, promoters, reaction solvents and conditions, as well as the possible reaction routes and catalytic reaction mechanisms are studied and discussed in depth. Special attention is paid to the structure–activity relationship, which would be helpful for the development of more efficient and stable heterogeneous catalysts. Moreover, the future research direction and development trend of the efficient synthesis for bio-based amines are prospected. Full article

In this review, we aim to give an overview of the use of the Borrowing Hydrogen (BH) methodology with bio-based alcohols. This methodology only forms water as a by-product, thus providing a sustainable way to amines, which have a large range of applications. This process is of particular interest when related to biomass due to the high abundance of alcohol functions in natural compounds. However, natural compounds often comprise multiple chemical functions that can change the reactivity of the substrate. This comprehensive review, comprising both homogeneous and heterogeneous catalysts, aims at summarizing the recent advancements in biomass amination for every class of substrate, highlighting the key parameters governing their reactivity and the remaining scientific hurdles. Even though most substrates have successfully been converted into the corresponding amines, reaction selectivity and functional group tolerance still need to be improved. Full article

Cobalt nanoparticles modified with N-doped hierarchical porous carbon derived from biomass are found to be a highly efficient, reusable heterogeneous catalyst for the coupling of nitroarenes with alcohols, selectively affording imines and amines via the borrowing hydrogen strategy for the first time. The product selectivity between imine and amine may be precisely tuned by simple alteration of the reaction conditions without changing the catalyst in one reaction system. In this study, a broad set of complex imines and amines was successfully synthesized in good to high yields with various functional groups tolerated for both nitroarenes and alcohols, highlighting the potentially practical utility of the protocol. This heterogeneous catalyst can be easily removed from the reaction medium by external magnet and can be reused at least four times without significant loss in activity and selectivity. Full article