Ag(I)-Catalyzed C–H Activation: The Role of the Ag(I) Salt in Pd/Ag-Mediated C–H Arylation of Electron-Deficient Arenes

Abstract

ABSTRACT:The use of stoichiometric Ag(I)-salts as additives in Pd-catalyzed C-H functionalization reactions is widespread. It is commonly proposed that this additive acts as an oxidant or as a halide scavenger promoting Pd-catalyst turnover. We demonstrate that, contrary to current proposals, phosphine ligated Ag(I)-carboxylates can efficiently carry out C-H activation on electrondeficient arenes. We show through a combination of stoichiometric and kinetic studies that a (PPh 3 )Ag-carboxylate is responsible for the C-H activation step in the Pd-catalyzed arylation of Cr(CO) 3 -complexed fluorobenzene. Furthermore, the reaction rate is controlled by the rate of Ag(I)-C-H activation, leading to an order zero on the Pd-catalyst. H/D scrambling studies indicate that this Ag(I) complex can carry out C-H activation on a variety of aromatic compounds traditionally used in Pd/Ag-mediated C-H functionalization methodologies.

CH Activation as a Shortcut to Conjugated Polymer Synthesis

“…Recently, a PEPPSI‐type Pd catalyst was used to mediate a dual‐catalyst system involving a silver cocatalyst which exhibited chain‐growth behavior and yielded polymers with low molar‐mass dispersity . It was proposed that the reaction was more readily controlled in these conditions because the Ag catalyst is responsible for CH activation while the Pd complex catalyzes reductive elimination . In this study, a bulky carboxylate base was used to prevent coupling in the β‐position and pyridine was added to inhibit CH activation by the Pd catalyst ( Figure ).…”

C–H Bond Functionalization of 1,4‐Benzoquinone by Silver‐Mediated Regioselective Phosphination and Amination Reactions

“…Oxidants such as AgF, AgBF 4 , and Cu(OAc) 2 were ineffective in this reaction (entries 6-8). Recently, Larrosa [29] and Sanford [30] and their co-workers independently came to the same conclusion that Ag I is capable of activating the electron-deficient arene C-H bond through a concerted metalation/deprotonation (CMD) mechanism [31] when an appropriate base such as CO 3 2-, OAc -, or OPivis the counter ion to the silver salt. Although the capacity of Ag I to oxidize HQ intermediates to the corresponding BQ derivatives is known, its other roles have not yet been identified in this reaction.…”

A Direct Arylation‐Cyclisation Reaction for the Construction of Medium‐Sized Rings

“…[16] This investigation showedt hat the addition of PPh 3 increased the rate of the arylation reaction due to formation of ah igher concentrationo f (PPh 3 )Ag(O 2 CAd). Good yields were found for 6-and 8-membered rings (Scheme 2, 3ab and 3ae).S ubstrates with alkyl substituents on the core ring were also tested.…”