Strengthening of the C−F Bond in Fumaryl Fluoride with Superacids
Marie C. Bayer, Christoph Kremser, Christoph Jessen, Alexander Nitzer, Andreas Kornath
Abstract
Abstract The reaction of fumaryl fluoride with the superacidic solutions XF/MF 5 (X=H, D; M=As, Sb) results in the formation of the monoprotonated and diprotonated species, dependent on the stoichiometric ratio of the Lewis acid to fumaryl fluoride. The salts [C 4 H 3 F 2 O 2 ] + [MF 6 ] − (M=As, Sb) and [C 4 H 2 X 2 F 2 O 2 ] 2+ ([MF 6 ] − ) 2 (X=H, D; M=As, Sb) are the first examples with a protonated acyl fluoride moiety. They were characterized by low‐temperature vibrational spectroscopy. Low‐temperature NMR spectroscopy and single‐crystal X‐ray structure analyses were carried out for [C 4 H 3 F 2 O 2 ] + [SbF 6 ] − as well as for [C 4 H 4 F 2 O 2 ] 2+ ([MF 6 ] − ) 2 (M=As, Sb). The experimental results are discussed together with quantum chemical calculations of the cations [C 4 H 4 F 2 O 2 ⋅ 2 HF] 2+ and [C 4 H 3 F 2 O 2 ⋅ HF] + at the B3LYP/aug‐cc‐pVTZ level of theory. In addition, electrostatic potential (ESP) maps combined with natural population analysis (NPA) charges were calculated in order to investigate the electron distribution and the charge‐related properties of the diprotonated species. The C−F bond lengths in the protonated dication are considerably reduced on account of the +R effect.