C-H Arylation of Phenanthrene with Trimethylphenylsilane by Pd/o-Chloranil Catalysis: Computational Studies on the Mechanism, Regioselectivity, and Role of o-Chloranil.

The transition-metal-catalyzed C-H arylation of aromatic hydrocarbons represents a useful and ideal method for the production of biaryls and multiarylated aromatic compounds. We have previously reported the palladium-catalyzed direct C-H arylation of polycyclic aromatic hydrocarbons, such as phenanthrene, pyrene, and corannulene with various organosilicon, -borane, and -germanium compounds. In these reactions, o-chloranil proved to be an essential and unique promoter (stoichiometrically as an oxidant) and arylation occurred exclusively at the K-region. Herein, we report our mechanistic investigation of Pd/o-chloranil catalysis in C-H arylation of phenanthrene with trimethylphenylsilane by computational calculations. The results revealed that C-H arylation occurs through a sequence of transmetalation, carbometalation, and trans-ß-hydrogen elimination steps. In addition, the triple role of o-chloranil as a ligand, oxidant, and base is also elucidated.