The Syntheses of Carbocations by Use of the Noble-Gas Oxidant, [XeOTeF<sub>5</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>]:  The Syntheses and Characterization of the CX<sub>3</sub><sup>+</sup> (X = Cl, Br, OTeF<sub>5</sub>) and CBr(OTeF<sub>5</sub>)<sub>2</sub><sup>+</sup> Cations and Theoretical Studies of CX<sub>3</sub><sup>+</sup> and BX<sub>3</sub> (X = F, Cl, Br, I, OTeF<sub>5</sub>)<sup>†</sup>

The CCl<sub>3</sub><sup>+</sup> and CBr<sub>3</sub><sup>+</sup> cations have been synthesized by oxidation of a halide ligand of CCl<sub>4</sub> and CBr<sub>4</sub> at −78 °C in SO<sub>2</sub>ClF solvent by use of [XeOTeF<sub>5</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>]. The CBr<sub>3</sub><sup>+</sup> cation reacts further with BrOTeF<sub>5</sub> to give CBr(OTeF<sub>5</sub>)<sub>2</sub><sup>+</sup>, C(OTeF<sub>5</sub>)<sub>3</sub><sup>+</sup>, and Br<sub>2</sub>. The [XeOTeF<sub>5</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>] salt was also found to react with BrOTeF<sub>5</sub> in SO<sub>2</sub>ClF solvent at −78 °C to give the Br(OTeF<sub>5</sub>)<sub>2</sub><sup>+</sup> cation. The CCl<sub>3</sub><sup>+</sup>, CBr<sub>3</sub><sup>+</sup>, CBr(OTeF<sub>5</sub>)<sub>2</sub><sup>+</sup>, C(OTeF<sub>5</sub>)<sub>3</sub><sup>+</sup>, and Br(OTeF<sub>5</sub>)<sub>2</sub><sup>+</sup> cations and C(OTeF<sub>5</sub>)<sub>4</sub> have been characterized in SO<sub>2</sub>ClF solution by <sup>13</sup>C and/or <sup>19</sup>F NMR spectroscopy at −78 °C. The X-ray crystal structures of the CCl<sub>3</sub><sup>+</sup>, CBr<sub>3</sub><sup>+</sup>, and C(OTeF<sub>5</sub>)<sub>3</sub><sup>+</sup> cations have been determined in [CCl<sub>3</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>], [CBr<sub>3</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>]·SO<sub>2</sub>ClF, and [C(OTeF<sub>5</sub>)<sub>3</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>]·3SO<sub>2</sub>ClF at −173 °C. The CCl<sub>3</sub><sup>+</sup> and CBr<sub>3</sub><sup>+</sup> salts were stable at room temperature, whereas the CBr<i><sub>n</sub></i>(OTeF<sub>5</sub>)<sub>3-<i>n</i></sub><sup>+</sup> salts were stable at 0 °C for several hours. The cations were found to be trigonal planar about carbon, with the CCl<sub>3</sub><sup>+</sup> and CBr<sub>3</sub><sup>+</sup> cations showing no significant interactions between their carbon atoms and the fluorine atoms of the Sb(OTeF<sub>5</sub>)<sub>6</sub><sup>-</sup> anions. In constrast, the C(OTeF<sub>5</sub>)<sub>3</sub><sup>+</sup> cation interacts with an oxygen of each of two SO<sub>2</sub>ClF molecules by coordination along the three-fold axis of the cation. The solid-state Raman spectra of the Sb(OTeF<sub>5</sub>)<sub>6</sub><sup>-</sup> salts of CCl<sub>3</sub><sup>+</sup> and CBr<sub>3</sub><sup>+</sup> have been obtained and assigned with the aid of electronic structure calculations. The CCl<sub>3</sub><sup>+</sup> cation displays a well-resolved <sup>35</sup>Cl/<sup>37</sup>Cl isotopic pattern for the symmetric CCl<sub>3</sub> stretch. The energy-minimized geometries, natural charges, and natural bond orders of the CCl<sub>3</sub><sup>+</sup>, CBr<sub>3</sub><sup>+</sup>, CI<sub>3</sub><sup>+</sup>, and C(OTeF<sub>5</sub>)<sub>3</sub><sup>+</sup> cations and of the presently unknown CF<sub>3</sub><sup>+</sup> cation have been calculated using HF and MP2 methods have been compared with those of the isoelectronic BX<sub>3</sub> molecules (X = F, Cl, Br, I, and OTeF<sub>5</sub>). The <sup>13</sup>C and <sup>11</sup>B chemical shifts for CX<sub>3</sub><sup>+</sup> (X = Cl, Br, I) and BX<sub>3</sub> (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.