Nitrogen-rich dendrimer-like hexamethylenetetramine grafted magnetite nanoreactor as sustainable next-generation materials for catalysis in organic reactions

Abstract

The Fe₃O₄@(TEA-HMTA)₂ magnetically retrievable nanoreactor developed in the present work has dendrimer-like branched architecture formed by grafting hexamethylenetetramine (HMTA) onto magnetite (Fe₃O₄) nanoparticles. This structure is synthesized through sequential reactions involving tris(2-bromoethyl)amine and HMTA with n-[3-(trimethoxysilyl)propyl]ethylenediamine-anchored Fe₃O₄ nanoparticles. The resulting nanoreactor offered abundant reactive sites and high nitrogen content in tertiary and quaternary amines, making it suitable for catalyzing the organic syntheses. The magnetic core of the nanoreactor allowed easy recovery, promoting sustainability in catalytic processes. The adaptability of the nanoreactor was demonstrated by its transformation into metallodendrimers (MDs) through selective loading of catalysts such as palladium, copper, or phosphomolybdic acid as representative examples. Its efficacy was validated in several reactions. In the aza-Michael addition, the nanoreactor achieved an 85 % yield with a turnover number (TON) of 21,546 and retained its reusability. The Cu-loaded variant gave a 90 % yield in the nitroaldol reaction with a TON of 4736, while the Pd-loaded system exhibited a 90 % yield in Heck coupling with a TON of 10,222 over four cycles. In ring-opening and phase-transfer reactions, moderate yields of 60 % and 55 % were achieved, with TONs of 789 and 6971, respectively. The magnetic nanoreactors exhibited the possibility of loading homogeneous catalysts with remarkable catalytic efficacy.