Reductive Amination Research Phase Hydrogenation Of Fast-moving Water

Amine is one of the most important compounds, which are widely found in natural products, agrochemicals and pharmaceuticals. Apart from extraction from natural products, the reduction of imines is one of the most efficient synthsis methods to access amine compounds. Imines, which are normally prepared from carbonyl compounds and amines, have limited stability. The direct coupling of carbonyl compounds and amines in the presence of a reducing agent is denoted as reductive amination (RA). RA alleviats the isolation of unstable imines; hence it has attracted much attention in recent years.Transition metal catalysis has played an important role in reduction reactions. For example, it has been used in hydrogenation and transfer hydrogenation of C=O and C=N bonds. However, RA reactions catalysed by transition metal catalysts are not many.Due to the enhance awareness of environmental protection, chemists are searching for green reagents and solvents to perfoming organic reactions. Water is the most widely reagent existing in Nature, as well as the greenest solvent. It is abundant, cheap and environmentally friendly. In addition, reactions under aqueous conditions might have different activity and selectivity patterns. Hence, a great deal of great effort has been made to develop aqueous organic reactions.In this thesis, we reported the reductive amination of ketones and aldehydes. The reaction is catalyzed by cyclometalated iridium complexes, using formate as hydrogen source under aqueous conditions.Firstly, the solution pH is found to be critical for high catalytic chemoselectivity and activity, with the best pH value being4.8. The best chemoselectivity of the reaction was obtained at this pH. Based on previous results, this thesis also discusses the reaction mechanism.Secondly, in comparison with that in organic solvents, the aqueous-phase reductive amination is faster. The substrate to catalyst ratio can be set as high as1x105, which is the highest S/C value ever reported in reductive amination of transfer hydrogenation reactions.Finally, the catalyst is easy to access and the reaction is operationally simple, allowing a wide range of ketones and aldehydes to react with various amines in high yields. The method developed in this thesis provides a rapid, efficient and environmental friendly new method for the synthesis of amines, one of the most useful compounds in our daily life.