Highly Efficient Transition Metal-Catalyzed Reactions using Highly Electron-poor Arylphosphines bearing Fluoro-functional Groups

Abstract

We synthesized the novel electron-poor bidentate ligand (MeO-F₁₂-BIPHEP), which has 3,4,5-trifluorophenyl groups. The large ligand-acceleration effect (LAE) by MeO-F₁₂-BIPHEP was shown in the Rh-catalyzed asymmetric 1,4-addition of arylboronic acid to α,β-unsaturated ketone. The turnover frequency and the turnover number reached 53,000 h^-1 and 320,000 cycles, respectively. This large acceleration results from electron-poor nature of MeO-F₁₂-BIPHEP. However, highly electron-poor MeO-F₂₈-BIPHEP showed less catalytic activity for Rh-catalyzed asymmetric 1,4-addition, because of its large cone angle. To avoid steric bulkiness, we developed the MeO-BFPy-BIPHEP. It showed highly electron poor nature as well as MeO-F₂₈-BIPHEP, and had moderate bulkiness as well as MeO-F₁₂-BIPHEP. The MeO-BFPy-BIPHEP accelerated the Rh-catalyzed asymmetric arylation of N-Ts-imine. The turnover frequency was over 10,000 h^-1. In the metal-catalyzed reaction, such electron-poor phosphines accelerated transmetalation, migratory insertion, and reductive elimination steps.