Mixed-Ligand Approach to Palladium-Catalyzed Direct Arylation of Heteroarenes with Aryl Chlorides: Controlling Reactivity of Catalytic Intermediates via Dynamic Ligand Exchange

Homogeneous catalysis using transition metal complexes typically employs a single supporting ligand, which can prove inadequate for diverse requirements at different steps of the catalytic cycle. To navigate this inadequacy, researchers are exploring a mixed-ligand approach, which involves the sequential interaction of two distinct ligands with the metal, fostering various product-forming steps within the same catalytic cycle. Herein, we introduce the successful application of this mixed-ligand approach to the palladium-catalyzed direct arylation of heteroarenes with aryl halides. The key to this success is the use of XPhos and P­(2-MeOC6H4)3 (L1) as supporting ligands. This mixed-ligand catalyst facilitates direct arylation with readily available but less reactive aryl chloride, yielding the coupling products in high yield (up to >99%). Moreover, the catalyst enables sequential reactions that leverage the differential reactivity between C–Cl and C–Br bonds, producing π-extended small molecules in a one-pot synthesis. The catalyst also proves effective in direct arylation polymerization (DArP) with dichloroarenes, yielding π-conjugated polymers with well-controlled structures and high molecular weights (M n up to 191000). Our mechanistic investigations into the mixed-ligand catalyst highlight that XPhos and L1 contribute to activating the C–Cl bond in aryl chlorides and the C–H bonds in heteroarenes, respectively.