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

• Published in: Journal of organic chemistry Vol. 73; no. 7; pp. 2607 - 2620
• Main Authors: Kütt, Agnes, Movchun, Valeria, Rodima, Toomas, Dansauer, Timo, Rusanov, Eduard B, Leito, Ivo, Kaljurand, Ivari, Koppel, Juta, Pihl, Viljar, Koppel, Ivar, Ovsjannikov, Gea, Toom, Lauri, Mishima, Masaaki, Medebielle, Maurice, Lork, Enno, Röschenthaler, Gerd-Volker, Koppel, Ilmar A, Kolomeitsev, Alexander A
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 04.04.2008; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Computer Simulation; Crystallography, X-Ray; Electrons; Exact sciences and technology; Free radicals chemistry; Hydrocarbons, Fluorinated - chemical synthesis; Hydrocarbons, Fluorinated - chemistry; Hydrogen-Ion Concentration; Kinetics and mechanisms; Models, Chemical; Models, Molecular; Molecular Structure; Noncondensed benzenic compounds; Organic chemistry; Physical Sciences; Preparations and properties; Reactivity and mechanisms; Science & Technology; Stereoisomerism; ANIONS; HYDROGEN-BOND; CARBENES; ANILINES; REACTIVITY; GAS-PHASE ACIDITIES; DIMETHYL-SULFOXIDE; DERIVATIVES; TRIFLUOROMETHYLATION; Water; Phenolate; Molecular structure; Distortion; Anions; Carbene; Methyl sulfoxide; Functionalization; Steric effect; Reaction mechanism; Aromatic compound; Chemical synthesis; Solvent; Complexation; Toluene; Benzene derivatives; Theoretical study; Transition metal; Acidity; Aniline derivatives; Organic free radical; N,N-Dimethylformamide; Acetonitrile; Phenols; Superacid; Benzenic compound; Fluorine Organic compounds; Gas phase; Electron acceptor; Room temperature
• DOI: 10.1021/jo702513w
• ISSN: 0022-3263

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 (ΔG acid) and pK a 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.