Organoselenium ligand-stabilized copper nanoparticles: Development of a magnetically separable catalytic system for efficient, room temperature and aqueous phase reduction of nitroarenes

Herein, we report the synthesis of a novel selenoether ligand L1 (pyren-1-yl-CH2-NH-CH2-CH2-SePh) and the first example of organoselenium compound stabilized-copper nanoparticles (NPs) with long term stability. Such stabilized nanoparticles (NPs) have been immobilised non-covalently on a chitosan-layered magnetic support to obtain Fe3O4@CS@L1-stabilized-CuNPs, characterized very well by various techniques. It has been explored as an extremely efficient and recyclable catalytic system for cost effective and green borohydride reduction reactions of a variety of nitroarenes (4-nitrophenol, nitrobenzene, 2-nitrophenol, 4-nitroaniline, 2-nitroaniline, 4-nitrotoluene, 1-chloro-4-nitrobenzene and 4-nitroanisole) in an eco-friendly solvent i.e. water at room temperature with ≥99% conversions into aminoarenes in very short reaction times. Additional advantages, offered by the catalyst, are its magnetic separability and recyclability. A very high value of rate constant (0.350 per minute) and a very low value (31.7 KJ per mol) of activation energy (Ea) have been found. Catalyst is very robust and does not let the copper species and ligand leach into the solution during the course of reduction reaction. Kinetics and Hammett plot of the catalytic reaction have been studied. It appears that the catalysis proceeds via a cationic transition state.