Computational Study on Why and How of Nonconventional meta-C-H Arylation of Electron-Rich Arenes via Pd/Quinoxaline-based Ligand/Norbornene Cooperative Catalysis.

By performing DFT calculation, this work aims at understanding the nonconventional meta-CH arylation reaction of electronic-rich arenes with aryl iodide via a Pd/quinoxaline-based ligand/norbornene cooperative catalysis. The reaction is indicated to be initiated either from the ortho-C-H carbopalladation to give the meta-monoarylation product via a sequence of subsequent steps, including norbornene insertion, meta-CH activation, oxidative addition and reductive elimination via Pd(II)/Pd(IV)/Pd(II) redox cycle, norbornene extrusion, and protodepalladation, or from the para-C-H carbopalladation to form the meta-diarylation product via two sequential arylation processes following similar mechanisms. The initial carbopalladation process promoted by the ligand is characterized as the rate-determining step of the reaction. The calculated mechanism shows the distinct role of the norbornene as a transient mediator that enables the fi nal C-H arylation at the same meta-positions whatever the initial carbopalladation occurs at either ortho- or para-positons. The Pd/ligand/norbornene cooperative catalysis is essential for achieving the exclusive meta-selectivity of the CH arylation of electron-rich arenes.