Ag/Pd Cocatalyzed Direct Arylation of Fluoroarene Derivatives with Aryl Bromides.

Adyasha Panigrahi,Iñigo J Vitorica-Yrezabal,Daniel Whitaker,Igor Larrosa

doi:10.1021/acscatal.9b05334

Abstract

Diverse C–H functionalizations catalyzed by Pd employ Ag(I) salts added as halide abstractors or oxidants. Recent reports have shown that Ag can also perform the crucial C–H activation step in several of these functionalizations. However, all of these processes are limited by the wasteful requirement for (super)stoichiometric Ag(I) salts. Herein, we report the development of a Ag/Pd cocatalyzed direct arylation of (fluoroarene) chromium tricarbonyl complexes with bromoarenes. The small organic salt, NMe4OC(CF3)3, added as a halide abstractor, enables the use of a catalytic amount of Ag, reversing the rapid precipitation of AgBr. We have shown through H/D scrambling and kinetic studies that a (PR3)Ag-alkoxide is responsible for C–H activation, a departure from previous studies with Ag carboxylates. Furthermore, the construction of biaryls directly from the simple arene is achieved via a one-pot chromium tricarbonyl complexation/C–H arylation/decomplexation sequence using (pyrene)Cr(CO)3 as a Cr(CO)3 donor.

Highlights

In recent years, direct C−H arylation has become a versatile tool for the construction of biaryls
We have developed the first Ag/Pd cocatalyzed C−H arylation process. This catalytic system is capable of regioselective direct C−H arylation of fluoroarenes with bromoarenes using π-complexation to Cr(CO)[3] to enhance the fluoroarene reactivity
Key to developing this protocol was the identification of NMe4OC(CF3)[3] as a halide abstractor capable of removing Br from AgBr, to regenerate the catalytic Ag-species

Summary

Introduction

Direct C−H arylation has become a versatile tool for the construction of biaryls. In contrast to the mild conditions possible for C−H arylations using bis(aryliodonium) salts and iodoarenes as coupling partners,[9] the use of bromoarenes in Pd-catalyzed direct arylation reactions typically requires high temperature and electron-donating phosphine ligands to facilitate the more challenging oxidative addition step.[10] Intriguingly, Hartwig demonstrated that the electron-donating phosphine ligand inhibits the Pd(II)-mediated C−H activation step of simple arenes.[11] This presents a quandary for how to approach reaction design for direct arylation with bromoarenes, as any ligand used must strike a delicate balance between promoting oxidative addition and inhibiting C−H activation With this issue in mind, we envisaged that a cooperative bimetallic catalytic system, in which an electron-rich Pd undergoes oxidative addition and mediates C−C bond formation while another metal performs C−H activation, could provide a resourceful solution

Methods

Results

Conclusion