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

Abstract

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 (Delta Gacid) 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.

Density Functional Theory and Isodesmic Reaction Based Prediction of Four Stepwise Protonation Constants, as log KH(n), for Nitrilotriacetic Acid. The Importance of a Kind and Protonated Form of a Reference Molecule Used

“…To date, isodesmic reaction principles (where two structurally similar compounds were used, investigated and reference molecule) have been extensively utilized in the prediction of enthalpies of formation. [76][77][78][79][80][81][82][83][84] In some cases a reference molecule has been incorporated within TCs 1,[3][4][5][6][7] to eliminate uncertainties related to either The main challenge associated with the use of IRn, however, is the selection of appropriate reference molecule. 56,80 The ligand NTA can be seen as a set of 5 molecules that differ in (i) a number of protons (from 0 to 4), and (ii) charges on the molecule (from +1 to -3).…”

Boratabenzene Anions C5B(CN)6− and C5B(CF3)6− and the Superacidic Properties of their Conjugate Acids

“…[10] The CF 3 group is not as powerful an electron acceptor as CN as it is bulkier and has negligible basicity and coordinating ability. The immense acidity of the strongest neutral Brønsted acid that has ever been predicted [10] -CB 11 A C H T U N G T R E N N U N G (CF 3 ) 12 H with the gas-phase acidity below 200 kcal mol…”

“…Recently we carried out a study on synthesis and acidity of the compound family (CF 3 ) 5 C 6 X. [11] Included in the study was also C 6 A C H T U N G T R E N N U N G (CF 3 ) 6 , a compound isoelectronic to the C 5 …”

“…Pertrifluoro-methylation might work the same way as described in ref. [11]. Percyanation may be possible by the method outlined in ref.…”

Pentakis(trifluoromethyl)benzenediazonium Cation: A Useful Building Block for the Syntheis of Trifluoromethyl‐Substituted Derivatives

“…However, until now, only a few types of C 6 (CF 3 ) 5 derivatives have been prepared. [23] Herein, we present the synthesis of pentakis(trifluoromethyl)benzenediazonium cation (1 as a BF 4 À salt), which is expected to be a useful building block for obtaining different types of C 6 (CF 3 ) 5 compounds and makes this structural fragment more accessible for various applications. Pentakis(trifluoromethyl)phenol 4, -iodobenzene 5, -chlorobenzene 3, and -nitrobenzene 7, were obtained from their corresponding diazonium cations.…”