Borrowing Hydrogen Methodology in Deep Eutectic Solvents for Sustainable N-Alkylation of Amines Using Alcohols

The development of sustainable catalytic methodologies is a cornerstone of modern green chemistry. Among these, hydrogen borrowing has emerged as a particularly appealing strategy: it enables the use of alcohols as alkylating agents through a catalytic sequence of oxidation, condensation, and reduction, mediated by a suitable metal catalyst (Figure 1) [1,2]. Despite their synthetic utility, such transformations traditionally rely on rare and expensive transition metals and require harsh reaction conditions, which limit both their environmental compatibility and industrial scalability. Deep eutectic solvents (DESs) are increasingly recognized as green and versatile reaction media in both catalytic and stoichiometric chemistry. Formulated from biodegradable and renewable components, DESs offer tunable physicochemical properties, making them ideal for promoting and modulating catalytic transformations [3]. This project focuses on implementing hydrogen borrowing strategies for C–N bond formation, using alcohols and amines as in situ hydrogen donors, within DES-based reaction systems. By incorporating selected DESs this research seeks to overcome the drawbacks of traditional approaches, improving substrate scope, reaction efficiency, and selectivity under milder, more sustainable conditions. [4,5] An important feature of this approach is the ability to reuse both the catalyst and the hydrophobic DES medium without significant loss of activity. This reusing strategy not only circumvents the need for expensive and non-recyclable ligands, but also reduces the overall catalyst and reagent costs, while lowering waste generation. This reuse enhances the environmental and economic feasibility of the process, making it attractive for larger-scale and industrial applications. Placing this work in a broader context, the synergy between BH catalysis and DESs represents a step forward in developing inherently sustainable synthetic platforms. By reducing waste, eliminating hazardous solvents, and enabling the use of abundant catalysts, this methodology supports circular chemistry concepts and can be extended to other bond-forming reactions such as C–C and C–O couplings. Future challenges remain in expanding the mechanistic understanding of DES–catalyst–substrate interactions, scaling up these processes for industrial application, and designing task-specific DESs tailored to individual catalytic transformations. Addressing these challenges could open new frontiers in green catalysis, bridging the gap between academic innovation and sustainable manufacturing.