In Situ Formation of Cationic π-Allylpalladium Precatalysts in Alcoholic Solvents: Application to C–N Bond Formation
Résumé
We report an efficient Buchwald-Hartwig cross-coupling reaction in alcoholic solvents, in which low catalyst loading showed excellent performance for coupling aryl halides (I, Br, Cl) with a broad set of amines, amides, ureas, or carbamates under mild conditions. Mechanistically speaking, in protic and polar medium, extremely bulky biarylphosphine ligands interact with dimeric precatalyst [Pd(π-Rallyl)Cl]2 to form the corresponding cationic complexes [Pd(π-Rallyl)(L)]Cl in situ and spontaneously. The resulting precatalyst further evolves under basic conditions into the corresponding L-Pd(0) catalyst, which is commonly employed for cross-coupling reactions. This mechanistic study highlights the prominent role of alcoholic solvents for the formation of the active catalyst.
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