Reusable, Highly Active Heterogeneous Palladium Catalyst by Convenient Self-Encapsulation Cross-Linking Polymerization for Multiple Carbon-Carbon Cross-Coupling Reactions at ppm to ppb Palladium Loadings

摘要

Designing reusable high-performance heterogeneous palladium (Pd) catalysts via convenient, economic synthesis is of great importance to the industrial applications of various carbon-carbon cross-coupling reactions. We demonstrate herein a convenient one-pot self-encapsulation synthesis of a heterogeneous Pd catalyst [Pd@PDEB, PDEB = poly(1,3-diethynylbenzene)] directly from commercially available, economic precursors. In the synthesis, the formation of the cross-linked polymer networks and Pd encapsulation are accomplished simultaneously, turning a homogeneous Pd polymerization catalyst into the heterogeneous cross-coupling catalyst. As a unique, practical heterogeneous catalyst, Pd@PDEB shows remarkably high activity, high reusability, and high versatility towards at least four types of cross-coupling reactions (Suzuki-Miyaura, Stille, allylic arylation, and Mizoroki-Heck reactions) with even difficult rcactants (aryl chlorides and heteroaryl halides) under aerobic conditions with Pd loadings down to ppm or even ppb levels. Evidences from hot filtration and 3-phase tests demonstrate the heterogeneous nature of the catalyst with very low Pd leaching and negligible contributions of leached homogeneous Pd species towards the coupling reactions.