The Syntheses of Carbocations by Use of the Noble-Gas Oxidant, [XeOTeF5][Sb(OTeF5)6]: The Syntheses and Characterization of the CX3+ (X = Cl, Br, OTeF5) and CBr(OTeF5)2+ Cations and Theoretical Studies of CX3+ and BX3 (X = F, Cl, Br, I, OTeF5)†
2004-05-05T00:00:00Z (GMT) by
The CCl3+ and CBr3+ cations have been synthesized by oxidation of a halide ligand of CCl4 and CBr4 at −78 °C in SO2ClF solvent by use of [XeOTeF5][Sb(OTeF5)6]. The CBr3+ cation reacts further with BrOTeF5 to give CBr(OTeF5)2+, C(OTeF5)3+, and Br2. The [XeOTeF5][Sb(OTeF5)6] salt was also found to react with BrOTeF5 in SO2ClF solvent at −78 °C to give the Br(OTeF5)2+ cation. The CCl3+, CBr3+, CBr(OTeF5)2+, C(OTeF5)3+, and Br(OTeF5)2+ cations and C(OTeF5)4 have been characterized in SO2ClF solution by 13C and/or 19F NMR spectroscopy at −78 °C. The X-ray crystal structures of the CCl3+, CBr3+, and C(OTeF5)3+ cations have been determined in [CCl3][Sb(OTeF5)6], [CBr3][Sb(OTeF5)6]·SO2ClF, and [C(OTeF5)3][Sb(OTeF5)6]·3SO2ClF at −173 °C. The CCl3+ and CBr3+ salts were stable at room temperature, whereas the CBrn(OTeF5)3-n+ salts were stable at 0 °C for several hours. The cations were found to be trigonal planar about carbon, with the CCl3+ and CBr3+ cations showing no significant interactions between their carbon atoms and the fluorine atoms of the Sb(OTeF5)6- anions. In constrast, the C(OTeF5)3+ cation interacts with an oxygen of each of two SO2ClF molecules by coordination along the three-fold axis of the cation. The solid-state Raman spectra of the Sb(OTeF5)6- salts of CCl3+ and CBr3+ have been obtained and assigned with the aid of electronic structure calculations. The CCl3+ cation displays a well-resolved 35Cl/37Cl isotopic pattern for the symmetric CCl3 stretch. The energy-minimized geometries, natural charges, and natural bond orders of the CCl3+, CBr3+, CI3+, and C(OTeF5)3+ cations and of the presently unknown CF3+ cation have been calculated using HF and MP2 methods have been compared with those of the isoelectronic BX3 molecules (X = F, Cl, Br, I, and OTeF5). The 13C and 11B chemical shifts for CX3+ (X = Cl, Br, I) and BX3 (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.