Preparation of Amines: Reductive Amination of Aldehydes and Ketones
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
Nitriles to Amines: LiAlH4 Reduction
Reduction of Alkenes: Catalytic Hydrogenation
Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Preparation of Amines: Reduction of Amides and Nitriles
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Updated: May 14, 2026

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis
Published on: February 16, 2020
Qian Lei1, Yawen Wei, Dinesh Talwar
1Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, 710062, PR China.
This study introduces a new method for reductive amination that uses water as a solvent instead of traditional organic solvents. The method uses a cyclometallated iridium catalyst and formate as a hydrogen source. The researchers found that a pH of 4.8 is optimal for high catalytic activity and chemoselectivity. The reaction is faster in water than in organic solvents and allows for a higher substrate-to-catalyst ratio than previously reported. The method is practical and environmentally friendly, enabling the synthesis of a wide range of amine compounds in high yields.
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Area of Science:
Background:
Many chemical syntheses rely on organic solvents, which can be costly and environmentally harmful. Prior research has shown that transfer hydrogenation is an effective method for reductive amination, but most studies use non-aqueous systems. No prior work had resolved the optimal pH for high chemoselectivity and activity in aqueous reductive amination. This gap motivated the search for a more efficient and environmentally friendly approach. The researchers propose that using water as a solvent could reduce costs and environmental impact. However, the effectiveness of aqueous transfer hydrogenation for reductive amination remained unclear. The need for a catalyst that functions well in water was also unmet. This study addresses these uncertainties by exploring a new protocol.
Purpose Of The Study:
The aim of this study is to develop a reductive amination method that operates efficiently in water. The specific problem is the inefficiency and environmental drawbacks of traditional organic solvent-based reductive amination. The motivation is to create a more sustainable and practical synthesis route. The researchers propose that using a cyclometallated iridium catalyst and formate as a hydrogen source could achieve this goal. The study seeks to determine the optimal pH for high catalytic activity and chemoselectivity. It also aims to test the scalability of the reaction by increasing the substrate-to-catalyst ratio. The researchers propose that an aqueous system could offer faster reaction rates and higher yields. This approach could provide a practical alternative to current methods.
Main Methods:
The study uses cyclometallated iridium complexes as catalysts and formate as the hydrogen source. The reactions are carried out in an aqueous solution. The pH of the solution is systematically varied to determine its effect on catalytic activity and chemoselectivity. The best pH value is identified as 4.8. The researchers compare the reaction rates in aqueous and organic solvent systems. The substrate-to-catalyst ratio is tested up to 1×10⁵, which is the highest reported in reductive amination. A wide range of ketones and aldehydes are tested for compatibility with various amines. The yields of the resulting amine compounds are measured to assess the effectiveness of the method.
Main Results:
The highest catalytic activity and chemoselectivity are observed at pH 4.8. The reaction rate in aqueous solution is faster than in organic solvents. The substrate-to-catalyst ratio reaches 1×10⁵, which is the highest ever reported for reductive amination. The catalyst is accessible and the reaction is operationally simple. A wide range of ketones and aldehydes react successfully with various amines. The yields of the resulting amine compounds are high. The method is practical and environmentally friendly. These findings suggest that aqueous transfer hydrogenation is a viable alternative to traditional methods.
Conclusions:
The authors propose that the optimal pH for high catalytic activity and chemoselectivity is 4.8. The aqueous system allows for a higher substrate-to-catalyst ratio than previously reported. The reaction is faster in water than in organic solvents. The method is practical and environmentally friendly. The catalyst is easy to access and the reaction is operationally simple. A wide range of ketones and aldehydes can react with various amines in high yields. The protocol provides a new method for the synthesis of amine compounds. The authors suggest that this approach could be useful in industrial and academic settings.
The method achieves high yields of amine compounds using an aqueous system with a substrate-to-catalyst ratio of 1×10⁵.
Formate is used because it is a safe and environmentally friendly alternative to traditional hydrogen sources.
The authors propose that pH 4.8 is optimal for high catalytic activity and chemoselectivity in the aqueous system.
The aqueous system is faster and allows for a higher substrate-to-catalyst ratio than organic solvent methods.
A wide range of ketones and aldehydes can react with various amines to form amine compounds.
The authors propose that the method is environmentally friendly and practical for industrial use.