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[2,2′-Bipyridin]-6(1H)-one, a Truly Cooperating Ligand in the Palladium-Mediated C–H Activation Step: Experimental Evidence in the Direct C-3 Arylation of Pyridine
- Salamanca, Vanesa, Toledo, Alberto, Albéniz, Ana C.
- Journal of the American Chemical Society 2018 v.140 no.51 pp. 17851-17856
- aromatic hydrocarbons, arylation, carbon-hydrogen bond activation, catalytic activity, chemical bonding, ligands, palladium, pyridines
- The ligand [2,2′-bipyridin]-6(1H)-one (bipy-6-OH) has a strong accelerating effect on the Pd-catalyzed direct arylation of pyridine or arenes. The isolation of relevant intermediates and the study of their decomposition unequivocally show that the deprotonated coordinated ligand acts as a base and assists the cleavage of the C–H bond. Mechanistic work indicates that the direct arylation of pyridine with this ligand occurs through a Pd(0)/Pd(II) cycle. Because of this dual ligand–intramolecular base role, there is no need for an available coordination site on the metal for an external base, a difficulty encountered when chelating ligands are used in coupling reactions that involve a C–H cleavage step.