[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

Abstract

The ligand [2, 2'-bipyridin]-6(1H)-one (bipy-6-OH) has a strong accelerating effect in 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 of 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.

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

“…We showed before that this ligand enables the reaction for a few arenes as reactants and solvents. 14 We show now that these reactions can be carried out with a lower concentration of the arene, an important issue for less available substrates, and we have found an unprecedented accelerating effect upon the addition of a solvent such as pinacolone. This effect can be only be understood by looking into the mechanism aspects of the arylation reaction.…”

“…1, a). 14 This effect is also at play in the Pd-catalyzed functionalization of hydrocarbons with other pyridone derivatives as ligands, 15 and with the N-monoprotected aminoacid ligands (MPAA) extraordinarily developed by the group of J. -Q. Yu.…”

Deuterium Exchange between Arenes and Deuterated Solvents in the Absence of a Transition Metal: Synthesis of D‐Labeled Fluoroarenes

“…It is not accelerated in the presence of a transition metal such as palladium. The use of [Pd(bipy‐6‐OH)Br(C 6 F 5 )] (bipy‐6‐OH = [2,2'‐bipyridin]‐6( 1H )‐one), a complex that has proved to be active in the C‐H functionalization of arenes, has no effect on the deuteration rate. Pd/C, a form of palladium closer to a hypothetical contamination of the alkali carbonates, does not increase the deuteration rate either.…”

Regiocontrol in the oxidative Heck reaction of indole by ligand-enabled switch of the regioselectivity-determining step

“…Finally, we added [2,2 0 -bipyridin]-6(1H)-one (bipy-6-OH, L6), a ligand that was reported to remarkably accelerate the CMD process in palladium catalysis. 21 We intended to test the performance of these candidate ligands in the model oxidative Heck reaction of indole, with the hope that some of them could exhibit the desired C2-selectivity.…”