C−I Selective Sonogashira and Heck Coupling Reactions Catalyzed by Aromatic Triangular Tri-palladium

Aromatic triangular tri-palladium cations 1–3, abbreviated as [Pd3]+, have shown interesting photoelectric properties, Lewis basic character, and excellent activities in catalytic hydrogenation. Herein, we report the highly efficient and C−I selective Sonogashira and Heck coupling reactions catalyzed by these tri-palladium complexes. Benefiting from the moderate C−I bond association energy, these tri-palladiums presented exclusive reactivities to aryl iodides over the brominated aromatics in coupling reactions. In the Sonogashira pathway, good to excellent isolated yields (71–95 %) were achieved. Gram-scale reaction reached 93 % of yield with palladium loading as few as 0.06 mol %. We also explored the electronic and steric effects for phenyl alkynes and aryl iodides including heteroaromatics like thiophene, pyridine, pyrazole, and pyrazine. Similarly, yields of 71–96 % were obtained for palladium loading of 1.5 mol% through catalyzed Heck coupling of aryl iodides and alkenes. The HRMS monitoring revealed that [Pd3]+ maintained as whole entity during the catalytic process due to its robusness.