Metal-free carbon dioxide reduction and acidic C–H activations using a frustrated Lewis pair

Activation of CO2 and acidic C–H bonds by the lutidine-tris(pentafluorophenyl)borane [Lut/B(C6F5)3] frustrated Lewis pair (FLP) are described (lutidine = 2,6-dimethylpyridine). Lut/B(C6F5)3 reacts with CO2 and H2 at ambient temperature and 4 atm of pressure to form the lutidinium boro-formate salt [LutH+][HC(O)OB(C6F5)3−]. This salt has been fully characterized including an X-ray crystal structure and independent synthesis from formic acid and Lut/B(C6F5)3. Attempts to activate a C–H bond in methane by Lut/B(C6F5)3, analogous to its heterolytic cleavage of H2, were unsuccessful, which are consistent with published calculations showing significant barriers to this reaction. Lut/B(C6F5)3 does react with more acidic C–H bonds, including acetone and nitroalkanes. With nitromethane, the boro-nitrone anion H2CNO2B(C6F5)3− is formed, as indicated by NMR and mass spectral analyses.