One-pot, in situ reductive catalytic approach for biomass furfural-based secondary amines at ambient conditions

Abstract

Biomass-based secondary amines are the versatile structural scaffolds of various drug molecules. This study reported a highly practical catalytic process for the room-temperature synthesis of renewable secondary amines from furfural (an inexpensive and readily available hemicellulose biomass-derived platform chemical) via one-pot, in situ reductive amination using an efficiently recyclable nanoalloy PdNi/Nb2O5 catalyst. The in situ hydrogenation of the imine intermediate obtained from the C-N coupling of furfural with benzylamine was carried out using a hydrogen donor, i.e., a mixture of readily available triethylsilane and methanol, which provides a valuable silyl ether product during the reaction as well. The synergy of PdNi nanoalloys and their strong interaction with shape-controlled Nb2O5 nanorods facilitated optimum amounts of active metal and redox sites, as elucidated by CO-chemisorption and H2-TPR studies, respectively. Controlled reactions confirm that metallic Pd facilitates hydrogen generation in situ from the hydrogen donor and the subsequent hydrogenation of the imine intermediate. The PdNi/Nb2O5 nanocatalyst (2 wt.% Pd and 3 wt.% Ni) gave a 97% yield of N-benzyl-1-(furan-2-yl)methanamine at room temperature. In contrast, only a 39% product yield was obtained over the Pd/Nb2O5 catalyst, whereas the Ni/Nb2O5 catalyst does not show any activity, confirming the significant role of the PdNi nanoalloy. The widespread substrate scope, gram-scale synthesis of secondary amines, robust structural stability of the PdNi/Nb2O5 nanocatalyst, and its excellent reusability even after 10 cycles confirmed the practical applicability of the developed catalytic methodology for producing furfural-based drug scaffolds at ambient conditions.