Faster palladium-catalyzed arylation of simple arenes in the presence of a methylketone: beneficial effect of an a priori interfering solvent in C-H activation

The functionalization of simple arenes without coordinating directing groups is a challenge. Besides facing the task of cleaving the sluggish C-H bond, the process is hampered by the weak coordinating ability of the arene pi-system to the metal, which results in reactions that need a large excess of the reactant arene. Using a well-defined palladium complex with the ligand [2,2 '-bipyridin]-6(1H)-one, we have found that the use of a moderately coordinating solvent allows a decrease of the amount of arene used. Moreover, for the least coordinating arenes, the co-solvent produces a significant accelerating effect by altering the concentration and relative stability of relevant metal species in the catalytic cycle as well as the catalyst resting state. t-Butyl methyl ketone (pinacolone) is one of the most effective co-solvents: Even if the ketone C-H bond cleaves easily, the final products are determined by the reductive elimination step (the product-forming step) so the target biaryl products are selectively observed.

Automated summary

Functionalization of simple arenes is challenging, as it requires cleaving the sluggish C-H bond and overcoming the weak coordinating ability of the arene pi-system. Using a well-defined palladium complex with a specific ligand and a moderately coordinating solvent can decrease the amount of arene used, while a co-solvent like t-butyl methyl ketone can accelerate the reaction process by altering the concentration and stability of relevant metal species.