DFT study of Ni/NHC-catalyzed C-H alkylation of fluoroarenes with alkenes to synthesize fluorotetralins: mechanism, chemoselectivity of C-H vs. C-F bond activation, and regio- and enantioselectivities of C-H bond activation

Density functional theory calculations have been carried out to elucidate the mechanism, enantio-, regio-, and chemoselectivities, and the role of the NHC ligand in the Ni/NHC-catalyzed alkylation of fluoroarenes with alkenes, a new strategy that exclusively achieved enantio- and regioselective C-H activation over multiple C-F bonds (Angew. Chem., Int. Ed., 2019, 58, 13433-13437). The reaction is found to follow a concerted ligand-ligand hydrogen transfer (LLHT) mechanism instead of the stepwise oxidative addition/alkene insertion mechanism. The high R-enantioselectivity originates from the stronger agostic interaction in the R-configuration than that in the S-type enantiomer, the exclusive endo-regioselectivity is controlled by the stronger electrostatic force of the Ni(0) catalyst with the terminal carbon atom than that with the internal carbon atom in the alkene, and the excellent chemoselectivity of C-H activation over C-F activation is attributed to the more favorable concerted ligand-ligand hydrogen transfer (LLHT) mechanism of C-H activation than the stepwise mechanism of the C-F activation. The enhanced reactivity with the NHC ligand is attributed to the increase in the HOMO level of the catalyst via the highly electron-donating effect of the NHC ligand.