Construction of novel Mn-based metal–organic frameworks for regioselective cross-dehydrogenative coupling of coumarins and dimethylanilines

Abstract

Coumarin derivatives, especially C3-substituted coumarins, exhibit promising biological activities, but efficient and sustainable methods for their synthesis remain a challenge. This work reports the development of a novel manganese-based metal–organic framework (MOF), Mn-CDC (CDC = 9H-carbazole-2,7-dicarboxylate), as an effective catalyst for the regioselective C3 C–H functionalization of coumarins with N,N-dimethylanilines. Mn-CDC was characterized by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy. Under optimized conditions, Mn-CDC catalyzed the cross-dehydrogenative coupling of coumarins and N,N-dimethylanilines with yields up to 74%, demonstrating good tolerance to a wide range of substituents on both substrates. Compared with Mn-CDC, a bimetallic catalyst, Mn/Co-CDC, showed insufficient catalytic activity under similar reaction conditions. Mechanistic studies indicated that the reaction proceeded via a radical pathway, with Mn³⁺ playing a crucial role in the catalytic cycle. The catalyst retained 60% activity after five cycles, highlighting its potential for sustainable, recyclable catalysis. This work provided a promising strategy to construct porous crystalline materials for the synthesis of biologically active compounds.