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 H-2 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 H-2, 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 H2C=NO2B(C6F5)(3) is formed, as indicated by NMR and mass spectral analyses. (C) 2010 Elsevier B.V. All rights reserved.