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

摘要

Aromatic triangular tri-palladium cations 1-3, abbreviated as [Pd-3](+), 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 [Pd-3](+) maintained as whole entity during the catalytic process due to its robusness.

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