Pentakis(trifluoromethyl)phenyl, a Sterically Crowded and Electron-withdrawing Group: Synthesis and Acidity of Pentakis(trifluoromethyl)benzene, -toluene, -phenol, and -aniline

A general route to functionalized pentakis(trifluoromethyl)phenyl (C6(CF3)5) derivatives, promising building
blocks for designing novel stable carbenes, radical species, superacids, weakly coordinating anions and
other practically and theoretically useful species, is presented. This pertrifluoromethylation route proceeds
via conveniently pregenerated (trifluoromethyl)copper (CF3Cu) species in DMF, stabilized by addition
of 1,3-dimethyl-2-imidazolidinone (DMI). These species react with hexaiodobenzene at ambient temperature to give the potassium pentakis(trifluoromethyl)phenoxide along with hexakis(trifluoromethyl)benzene and pentakis(trifluoromethyl)benzene in a combined yield of 80%. A possible reaction pathway
explaining the formation of pentakis(trifluoromethyl)phenoxide is proposed. Pentakis(trifluoromethyl)phenol gives rise to easily functionalized pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)aniline. Pertrifluoromethylation of pentaiodochlorobenzene and pentaiodotoluene allows straightforward access to pentakis(trifluoromethyl)chlorobenzene and pentakis(trifluoromethyl)toluene, respectively. XRD structures of several C6(CF3)5 derivatives were determined and compared with the calculated
structures. Due to the steric crowding the aromatic rings in all C6(CF3)5 derivatives are significantly
distorted. The gas-phase acidities (ΔGacid) and pKa values in different solvents (acetonitrile (AN), DMSO,
water) for the title compounds and a number of related compounds have been measured. The origin of
the acidifying effect of the C6(CF3)5 group has been explored using the isodesmic reactions approach.