Recyclable Mn₂O₃@SiO₂ Nanocatalyst for Selective Mono-N-alkylation of Amines Utilizing a Borrowing-Hydrogen Approach

Amines are structural motifs that are found naturally in a wide variety of products and are used as fundamental building blocks in the production of pharmaceuticals and agrochemicals. The creation of C-N bonds has evolved; among many synthetic approaches, the utilization of the hydrogen-borrowing strategy has emerged as a green, atom-economical, and sustainable approach. This approach involves the N-alkylation of amines through the utilization of renewable alcohols as an alkylation source. In spite of the fact that there are a great number of heterogeneous catalysts based on nonnoble metals, the creation of systems that are highly active, stable, and recyclable continues to be a persistent challenge. In this article, we present the synthesis and catalytic application of a highly air-stable Mn₂O₃@SiO₂ nanocomposite for the selective mono-N-alkylation of amines with alcohols, without any solvent, under a neat condition. Using the hydrogen-borrowing pathway, the catalyst effectively supports the alkylation reaction, which results in an excellent yield of N-alkylated products (up to 97%) within a period of 6 h. There was a demonstration of a broad substrate scope, which included a variety of functional groups and intermediates of amines that are relevant to the pharmaceutical industry. A comprehensive characterization of the nanocatalyst was carried out by employing techniques such as XRD, FT-IR, TGA, XPS, FE-SEM, TEM, and BET. The catalyst demonstrated outstanding reusability, as it maintained its activity over six successive catalytic cycles without suffering a substantial decline in performance. Control experiments were carried out to provide a mechanistic understanding, which supported the hypothesis of a borrowing-hydrogen pathway. The overall purpose of this protocol is to demonstrate a Mn₂O₃@SiO₂ nanocatalytic system that is resilient, efficient, and recyclable for the purpose of achieving sustainable N-alkylation reactions.