Glucose-based melanoidin-supported palladium single-atoms/clusters cocatalyst for site-selective cross-dehydrogenative coupling of two simple arenes

Abstract

The site-selective cross-dehydrogenative coupling (CDC) of two simple arenes is an ideal C–C bond-forming strategy to furnish structurally diverse molecules. In general, the site-selectivity represents the state-of-the-art approach in organic synthesis owing to the similar chemical BDE among C–H bonds of ∼100 kcal mol⁻¹. Here, we report a site-selective CDC of aromatic aldehydes and arenes enabled by heterogeneous glucose-based melanoidin-supported Pd single-atoms/clusters cocatalysts. The formation of an imine unit as a transient-directing group by using an amino acid or carbohydrazide can selectively activate either the C(sp²)–H or C(sp³)–H bond of substituted aromatic aldehydes, respectively. Multi-technique characterization data showed that a variety of groups, especially imine, in melanoidin coordinated with Pd to form a Pd single-atoms/clusters cocatalyst, and the good catalytic performance stems from the stable, low-coordinated and d-electron-deficient Pd (high-valent Pd) active sites. The heterogeneous catalyst could be efficiently reused, resulting in a cumulative TON of 48 after five runs, which is eight times higher than that of the analogous homogeneous palladium catalyst without the ligand.