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

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.

钯（Palladium, Pd）催化的多样性C–H官能化（C–H functionalization）反应通常需添加银(I)（Silver(I), Ag(I)）盐作为卤离子提取剂（halide abstractor）或氧化剂。近期研究表明，在该类官能化反应中，银还可参与关键的C–H活化（C–H activation）步骤。然而，所有此类过程均受限于（超）化学计量比银(I)盐的高用量所带来的浪费问题。
本文报道了一种银/钯（Ag/Pd）共催化的（氟代芳烃）三羰基铬配合物与溴代芳烃的直接芳基化反应。作为卤离子提取剂添加的小型有机盐NMe4OC(CF3)3，可逆转溴化银的快速沉淀，从而实现银的催化量使用。
通过氢氘重排交换（H/D scrambling）实验与动力学研究，我们证实(PR3)银醇盐负责C–H活化步骤，这与此前针对银羧酸盐的研究结论存在显著差异。
此外，以（芘）三羰基铬[(pyrene)Cr(CO)3]作为三羰基铬给体，通过一锅法三羰基铬络合/C–H芳基化/脱络合串联反应，可直接由简单芳烃构建联芳烃骨架。