Selectivity tunable iron nanoparticles from lignocellulosic components for the reductive amination of carbonyl compounds towards switchable products

Abstract

Various kinds of functional amines have been well synthesized by the reductive amination of carbonyl compounds for high-value pharmaceuticals, but they often suffer from complicated processes and low efficiency. In this study, we developed a facile strategy to achieve product diversity using iron-based nanoparticles, whose catalytic selectivity can be particularly controlled via specific combinations of active metals and carbonaceous matrixes in a simple way; over these catalysts, the main products completely switched from primary amines (>91.2%) to secondary imines (>92.3%) in a one-pot process, in accordance with the observed changes in chemical states (Fe⁰ to Fe_xO_y), particle size (9.3 to 63.2 nm), surface acidity (42.4 to 195.7 μmol g⁻¹), and porosity (388.5 to 14.4 m² g⁻¹). By further analyzing the differences in reaction routes, the dehydration of nucleophilic amines with excess aldehydes was found to be the crucial step, accelerating the chemical equilibrium turned towards secondary imines. In addition, a wide range of substrates (>15 examples) were well tolerated by the prepared catalysts resulting in good to excellent yields (67.7–96.3%), and the catalytic stability was proven to be standard satisfactorily even after reusing up to five times, which was superior to commercial catalysts with noble or transition metals. More surprisingly, the magnetic properties exhibited by the iron cores allowed easy separation from aqueous systems. Overall, this strategy provides an applicable approach for the preparation of simple but highly efficient catalysts for switchable amination, which fills the knowledge gap on catalytic selectivity and exerts a positive impact on the industrial application.