Mechanistic Insights on the Challenging Trifluoromethylation of Ni(II)

While the transmetalation of Ni(II) intermediates constitutes a key elementary step, there are limited data and insights available on the precise underlying mechanism of transmetalation. This work describes our combined experimental and computational study of the mechanism of trifluoromethylation of LnNi(II)–F complexes and the origins of ligand effects in this process. Our studies reveal an ionic rebound mechanism to be favored in the trifluoromethylation with Me3SiCF3, in which fluoride abstraction from LnNi(II)–F by Me3SiCF3 takes place, followed by CF3 anion rebound from the intermediate ion pair. The steric shielding of the employed ligand controls accessibility, which was verified through the successful synthesis and isolation of a PMe3-bound Ni(II)−F3 complex. Alternative mechanisms of LnNi(II)−CF3 synthesis, e.g., via difluorocarbene insertion, were also studied, and although found to be feasible with the majority of ligands, alternative Ni–P insertions were seen for the sterically most demanding ligands.