The present work provides a comprehensive study of the efficient and environmentally friendly N-mono- methylation of amines using new caffeine-derived ruthenium–NHC complex as catalyst and methanol as a sustainable carbon source. N-methylation is a revolutionary strategy for amine functionalization that can improve the biological and chemical properties of life science molecules. This work focuses on the direct C–N formation and coupling reactions of amines and alcohols via hydrogen borrowing, demonstrating the advantages of methanol as a low-cost, low hazardous, and readily available methylating agent. The incorporation of N-heterocyclic carbenes (NHCs) into homogeneous catalysts is crucial to achieve high catalytic activity, stability, and selectivity. This method is particularly effective for selective N-mono-methylation of anilines, important reactions in the synthesis of chemicals and fine chemicals, providing acceptable catalytic results and preventing excessive alkylation. The use of bioavailable compounds, such as caffeine, is based on green chemistry principles and provides an attractive green synthetic method.

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