Theoretical Insight into C(sp3)–F Bond Activations and Origins of Chemo- and Regioselectivities of “Tunable” Nickel-Mediated/-Catalyzed Couplings of 2-Trifluoromethyl-1-alkenes with Alkynes

Abstract

The mechanisms and chemo- and regioselectivities of divergent (Ni(cod)2/PCy3)-mediated/-catalyzed C(sp3)–F bond activation of 2-trifluoromethyl-1-alkenes (1) with alkynes (2) were investigated by density functional theory (DFT) calculations. The nickel-mediated/-catalyzed reaction involves sequential ligand exchange, alkene coordination, oxidative cyclization (1 + Ni(0) + 2), and first β-F(C(sp3)) elimination to give a common and requisite alkenylnickel(II) species, which bifurcates into either stoichiometric defluorinative [3 + 2] cycloaddition product 3 or catalytic defluorinative coupling products (nonmethylated 5, monomethylated 8, or trimethylated 9) depending on the absence and presence of additional reagents (Et3SiH, ZnMe2, and AlMe3). The Et3SiH-induced formation of 5 is found to be a result of facile metathesis relative to the 5-endo insertion leading to 3. Because of the presence of an F→Zn/Al interaction, ZnMe2/AlMe3 brings the methyl into defluorinative coupling products. In the stoichiometric...