Water-soluble salen–Pd complex as an efficient catalyst for Suzuki–Miyaura reaction of sterically hindered substrates in pure water

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Water-soluble 2N2O-salen ligands and their palladium complexes were synthesized and used as efficient catalysts for the Suzuki–Miyaura reactions in pure water. Notably, the reactions of substrates with sterically demanding ortho substituents (aryl bromides and/or arylboronic acids) proceed smoothly to generate corresponding products with moderate to high yields using 0.5 mol% (salph)Pd (salphN,N′-bis(4-SO3Na-salicylidene)-1,2-phenylenediamine) as the catalyst. Importantly, the catalytic system has the wide substrate scope and the high tolerance to various functional groups, including cyano, amino, nitro, methoxy, and acetyl. Moreover, the biaryl compounds were also obtained on a multi-gram scale by simple recrystallization with the system in the absence of any organic solvent, surfactant, or phase transfer agent and the catalyst was reused directly for the next cycle. Particularly, this protocol can be applied to synthesize aryl-substituted carbazolyl compounds.