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.

本文阐述了通往功能化五氟甲基苯基（C6(CF3)5）衍生物的一般途径，这些衍生物作为构建新型稳定碳烯、自由基物种、超强酸、弱配位阴离子及其他在实践和理论方面具有实用价值的物种的基石，展现出巨大的潜力。该五氟甲基化途径通过在DMF中预先生成的（三氟甲基）铜（CF3Cu）物种进行，该物种通过添加1,3-二甲基-2-咪唑啉酮（DMI）得以稳定。这些物种在常温下与六碘苯反应，可得到五氟甲基苯氧化钾，并伴随生成六氟甲基苯和五氟甲基苯，其总产率为80%。提出了一个可能的反应路径，以解释五氟甲基苯氧化物的形成。五氟甲基苯酚可转化为易于功能化的五氟甲基氯苯和五氟甲基苯胺。对五碘二氯苯和五碘甲苯的五氟甲基化，分别直接得到五氟甲基氯苯和五氟甲基甲苯。对若干C6(CF3)5衍生物的XRD结构进行了确定和比较，并与计算结构进行了对比。由于空间位阻效应，所有C6(CF3)5衍生物中的芳环均发生显著扭曲。在乙腈（AN）、二甲基亚砜（DMSO）、水等溶剂中，对标题化合物及其相关化合物的气相酸度（ΔGacid）和pKa值进行了测定。利用等量反应法探讨了C6(CF3)5基团酸性效应的起源。