Solvent Effect on Palladium-Catalyzed Cross-Coupling Reactions and Implications on the Active Catalytic Species

摘要

One of the milestones in pushing the limits of the oxidative addition step in palladium-catalyzed cross-coupling reactions was the discovery that bulky phosphine ligands trigger unprecedented high reactivity in palladium catalysis. A variety of monodentate ligand systems were developed, for example PAdtBu2 (Ad = 1-adamantyl), ((Ph5C5)-(C5H4)Fe)PtBu2 ferrocenyl = (C5H5)(C5H4)Fe (Q-phos), PAd2nBu, and Buchwald's biaryl phosphine ligands. The groups of Nishiyama and Fu demonstrated the power of the bulky tri-tert-butylphosphine ligand, PtBu3. Fu and coworkers showed that a combination of [Pd2(dba)3] (dba = dibenzylideneacetone) and PtBu3 allows cross-coupling of aryl chlorides at room temperature. Experimental and theoretical mechanistic studies indicated that a monoligated palladium species would be the active catalyst in reactions of Pd and PtBu3.