The Syntheses of Carbocations by Use of the Noble-Gas Oxidant, [XeOTeF_5][Sb(OTeF_5)_6]: The Syntheses and Characterization of the CX_3~+ (X = Cl, Br, OTeF_5) and CBr(OTeF_5)_2~+ Cations and Theoretical Studies of CX_3~+ and BX_3 (X = F, Cl, Br, I, O

摘要

The CCl_3~+ and CBr_3~+ cations have been synthesized by oxidation of a halide ligand of CCl4 and CBr4 at -78 ℃ in SO_2ClF solvent by use of [XeOTeF_5][Sb(OTeF_5)_6]. The CBr_3~+ cation reacts further with BrOTeF_5 to give CBr(OTeF_5)_2~+, C(OTeF_5)_3~+, and Br_2. The [XeOTeF_5][Sb(OTeF_5)_6] salt was also found to react with BrOTeF_5 in SO_2ClF solvent at -78 ℃ to give the Br(OTeF_5)_2~+ cation. The CCl_3~+, CBr_3~+, CBr(OTeF_5)_2~+, C(OTeF_5)_3~+, and Br(OTeF_5)_2~+ cations and C(OTeF_5)_4 have been characterized in SO_2ClF solution by 13C and/or 19F NMR spectroscopy at -78 ℃. The X-ray crystal structures of the CCl_3~+, CBr_3~+, and C(OTeF_5)_3~+ cations have been determined in [CCl_3][Sb(OTeF_5)_6], [CBr_3][Sb(OTeF_5)_6]·SO_2ClF, and [C(OTeF_5)_3][Sb(OTeF_5)_6]·3SO_2ClF at -173 ℃. The CCl_3~+ and CBr_3~+ salts were stable at room temperature, whereas the CBrn(OTeF_5)_(3-n)~+ salts were stable at 0 ℃ for several hours. The cations were found to be trigonal planar about carbon, with the CCl_3~+ and CBr_3~+ cations showing no significant interactions between their carbon atoms and the fluorine atoms of the Sb(OTeF_5)_6~- anions. In constrast, the C(OTeF_5)_3~+ cation interacts with an oxygen of each of two SO_2ClF molecules by coordination along the three-fold axis of the cation. The solid-state Raman spectra of the Sb(OTeF_5)_6~- salts of CCl_3~+ and CBr_3~+ have been obtained and assigned with the aid of electronic structure calculations. The CCl_3~+ cation displays a well-resolved ~(35)Cl/~(37)Cl isotopic pattern for the symmetric CCl_3 stretch. The energy-minimized geometries, natural charges, and natural bond orders of the CCl_3~+, CBr_3~+, CI_3~+, and C(OTeF_5)_3~+ cations and of the presently unknown CF_3~+ cation have been calculated using HF and MP_2 methods have been compared with those of the isoelectronic BX_3 molecules (X = F, Cl, Br, I, and OTeF_5). The ~(13)C and ~(11)B chemical shifts for CX_3~+ (X = Cl, Br, I) and BX_3 (X = F, Cl, Br, I) were calculated by the GIAO method, and their trends were assessed in terms of paramagnetic contributions and spin-orbit coupling.