Mechanistic Insights into the Initiation Step of the Base Promoted Direct C-H Arylation of Benzene in the Presence of Additive

The direct arylation of unactivated arenes is a very practical and highly convenient procedure for the construction of biaryl scaffolds. Recently, a direct arylation of unactivated benzene has been achieved in the presence of base (tBuOK or tBuONa) and organic additive such as 1,10-phenanthroline. However, details of intimate mechanism of reaction as well as the role of additive have remained elusive until date. The present work explores various mechanistic possibilities of the key electron transfer step of the reaction in order to identify a probable route for the initiation of phenyl radical from iodobenzene. A detailed DFT (M06-2X functional) investigation indicates that the reaction of additive and base can be crucial to generate an electron acceptordonor pair that can facilitate electron transfer mechanism. This computational model provides a satisfactory explanation for experimental observations, clearly defining the roles of additive and base in the reaction.