posted on 2016-02-21, 18:14authored byChong Tian, Wanli Nie, Maxim V. Borzov, Pengfei Su
Thermolysis of 1-ethyl-3-methyl-1H-imidazolium
tetrafluoroborate (1) and 1,3-dimethyl-1H-imidazolium hexafluorophosphate (3) under reduced pressure
eliminates HF to furnish the BF3 and PF5 adducts
of the corresponding Arduengo carbenes (2 and 4) in high yields. The intuitively anticipated imidazole N adducts
with BF3 and/or PF5 arising from elimination
of alkyl fluorides are not detected at all. These observations represent
the first examples of a direct bond rearrangement of the type [C–H]
+ E–F → [C–E] + H–F (E = B, P). DFT computational
studies suggest a single-step mechanism for the reaction 1 → 2 + HF. Lower yield thermolysis of a 1,2,3-trimethyl-1H-imidazolium hexafluorophosphate (11) into
[(1,3-dimethyl-1H-imidazolium-2-yl)methyl]pentafluorophosphate
(12) supports the generality of this transformation.