Density Functional Theory Mechanistic Insight into the Base-Free Nickel-Catalyzed Suzuki-Miyaura Cross-Coupling of Acid Fluoride: Concerted versus Stepwise Transmetalation.

Density functional theory mechanistic study has been carried out to account for the base-free nickel-catalyzed Suzuki-Miyaura coupling of acid fluorides (ArC(O)F) with boronic acids (Ar'B(OH)2). After oxidative addition to break the C-F bond of acid fluoride, the resultant ArC(O)[Ni]F species undergoes transmetalation with Ar'B(OH)2 to give ArC(O)[Ni]Ar'. Subsequently, ArC(O)[Ni]Ar' can either undergo decarbonylation, finally leading to the coupling product (ArAr'), or reductive elimination to give ketone byproduct ArC(O)Ar'. The kinetic competition between the two pathways controls the chemoselectivity of the reaction, and transmetalation is the rate-determining step of the coupling. Importantly, it was found that transmetalation prefers a stepwise mechanism over a conventional concerted one. Detailed analyses indicate that the strong fluorophilicity of boron facilitates the base-free transmetalation and the coordination interaction between an oxygen atom of boronic acid and nickel gears the base-free transmetalation to undergo the stepwise pathway. The stepwise transmetalation mechanism also involves the nickel-catalyzed Suzuki-Miyaura coupling of aldehydes with ketone (PhC(O)CF3) as the transmetalation promoter.