4-(Pentafluorosulfanyl)benzenediazonium Tetrafluoroborate: A Versatile Launch Pad for the Synthesis of Aromatic SF5 Compounds via Cross Coupling, Azo Coupling, Homocoupling, Dediazoniation, and Click Chemistry
Okazaki, T; Laali, KK; Bunge, SD; Adas, SK
The reagent 4-(pentafluorosulfanyl)benzenediazonium tetrafluoroborate (1) was synthesized and isolated as a stable salt for the first time; its application in a wide assortment of transformations was subsequently investigated. A series of novel SF5-bearing alkenes, alkynes, and biaryl derivatives were synthesized by employing Heck-Matsuda, Sonogashira, and Suzuki coupling protocols. Dediazoniation with TMSX (X = Hal; N-3; and CN) and NH4SCN in [BMIM][BF4] as solvent furnished the corresponding p-SF5-C6H4X derivatives. The azide derivative p-SF5-C6H4N3 entered into click chemistry with phenylacetylenes to furnish the corresponding triazoles. The 4,4-bis(pentafluorosulfanyl)biphenyl was synthesized by homo-coupling using Pd(OAc)(2). The corresponding azo compounds were obtained through azo-coupling with reactive aromatic nucleophiles (1,3-dimethoxybenzene, 1,3,5-trimethoxybenzene, 1,2,4-trimethoxybenzene, aniline and phenol). Fluorodediazoniation in [BMIM][PF6] and [BMIM][BF4] selectively furnished the fluoro derivative p-SF5-C6H4F. Dediazoniation in [BMIM][NTf2] gave p-SF5-C6H4OS(O)(CF3)=NSO2CF3 as the major and p-SF5-C6H4-NTf2 as the minor products. Homolytic dediazoniation in MeCN/NaI gave the unsymmetrical biaryls p-SF5-C6H4-Ar (ArH = mesitylene and p-xylene) along with p-SF5-C6H4I. Analysis of the dediazoniation product mixtures indicated that dediazoniation of p-SF5-C6H4N2+ BF4- in low nucleophilicity, highly ionizing, solvents (TfOH, TFE, HFIP, TFAH) is mainly heterolytic, while in MeOH it is mainly homolytic. The isodesmic reaction p-SF5-C6H4+ + R-C6H5SF5-C6H5 + p-R-C6H4+ (with R = NO2, CF3, H) was gauged by DFT at various levels and by PCM.