Structural, Chemical, and Theoretical Evidence for the Electrophilicity of the [C₆F₅Xe]⁺ Cation in [C₆F₅Xe][AsF₆]

Abstract

[C(6)F(5)Xe][AsF(6)] was prepared by metathesis from [C(6)F(5)Xe][(C(6)F(5))(2)BF(2)]. The thermal stability of the melt (</=125 degrees C) is surprisingly high. The decomposition products reveal the ability of the cation to effect electrophilic pentafluorophenylation. [C(6)F(5)Xe][AsF(6)] crystallizes in the triclinic system, space group P&onemacr;, with four molecules in the unit cell. Of these, two are symmetry independent with Xe-C distances of 2.079(6) and 2.082(5) Å, Xe-F distances (cation-anion contacts) of 2.714(5) and 2.672(5) Å, and C-Xe-F angles of 170.5(3) and 174.2(3) degrees, respectively. The relation between cations and anions is best described as an asymmetric hypervalent (3c-4e) bond. Temperature dependent (19)F NMR measurements reveal the occurrence of separated ions in solution, with [C(6)F(5)Xe](+) coordinated by a basic solvent molecule. Minimum energy geometries and charge distributions were calculated for [C(6)F(5)Xe](+), [C(6)H(5)Xe](+), [C(6)F(5)](+), [C(6)H(5)](+), [CF(3)Xe](+), [CH(3)Xe](+), [C(6)F(5)Ng](+) (Ng = Kr, Ar, Ne, He), and [C(6)F(5)Xe][AsF(6)] at the ab initio RHF/LANL2DZ level. According to these calculations, C-Ng cations with short C-Ng distances are stable when the natural charge of the noble gas carries the main part of the positive net-charge and the ipso-C atom is not positive. In [C(6)F(5)Xe](+), for example, 89% of the positive charge is concentrated on Xe.

Ab Initio Study of the Charge-Transfer Complex of Xenon and Dicarbon

“…On the other hand, the experimental CXe bond distances in the [C 6 F 5 Xe] + cation and in the (C 6 F 5 ) 2 Xe molecule from Xray diffraction are much shorter, viz. 208 pm and 235-239 pm, respectively (23,24).…”

The dependence on temperature and concentration of 129Xe NMR chemical shift values of organoxenon(II) salts [RXe][Y] and of the parent molecule XeF2

“…Salts (1), 16 (2), 17 (3), 18 (4), 19 (5), 7 and (6) 7 were prepared as described. All manipulations were performed in an FEP (block copolymer of tetrafluoroethylene and hexafluoropropylene) equipment under an atmosphere of dry argon.…”

C6F5XeCl and [(C6F5Xe)2Cl][AsF6]: The First Isolated and Unambiguously Characterized Xenon(II) Chlorine Compounds

“…[1,2] While there are a number of useful enantioselective routes to atropisomeric biaryls, [3] the enantioselective synthesis of non-biaryl atropisomers [4] is an unexplored area. Enantiomerically pure anilides have been derived from the chiral pool, [5,6] and other enantiomerically pure non-biaryl atropisomers have been resolvedÐclassically, [7,8] by chromatography on a chiral stationary phase, [9±11] or kinetically. [12,13] The only truly enantioselective synthesis of non-biaryl atropisomers is that of Koide and Uemura, [14] who used the desymmetrization of an arene ± tricarbonylchromium complex to make aromatic amides related to 1 (see Scheme 1) in enantiomerically pure form.…”

“…The dichloromethane molecules have no relevant contacts to 6. The [(C 6 F 5 Xe) 2 Cl] ion in 6´CH 2 Cl 2 shows no strong electrophile ± nucleophile interactions with the [AsF 6 ] À ionÐin contrast to the situations in 4 [8] and 2. [7] The cation in 6 consists of two C 6 F 5 Xe fragments bridged through a chloride ion.…”

“…The decomposition product contains 44 mol % C 6 F 5 Cl (expected: 50 mol %), 32 mol % C 6 F 6 , and 24 mol % 4 [Eq. (4), (5) [8] ].…”