The Syntheses of Carbocations by Use of the Noble-Gas Oxidant, [XeOTeF 5][Sb(OTeF5)6]: The Syntheses and Characterization of the CX3+ (X = Cl, Br, OTeF 5) and CBr(OTeF5)2+ Cations and Theoretical Studies of CX3+ and BX3 (X = F, Cl, Br, I, OTeF5)

Article abstract of DOI:10.1021/ja030649e

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(OTeF ₅)₂⁺, C(OTeF₅)₃ ⁺, and Br₂. The [XeOTeF₅][Sb(OTeF ₅)₆] salt was also found to react with BrOTeF₅ in SO₂ClF solvent at -78 °C to give the Br(OTeF₅) ₂⁺ cation. The CCl₃⁺, CBr ₃⁺, 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(OTeF ₅)₃⁺ cations have been determined in [CCl ₃][Sb(OTeF₅)₆], [CBr₃][Sb(OTeF ₅)₆]·SO₂ClF, and [C(OTeF ₅)₃][Sb(OTeF₅)₆]·3SO ₂ClF at -173 °C. The CCl₃⁺ and CBr ₃⁺ salts were stable at room temperature, whereas the CBr_n(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 CCl ₃ stretch. The energy-minimized geometries, natural charges, and natural bond orders of the CCl₃⁺, CBr₃ ⁺, Cl₃⁺, and C(OTeF₅) ₃⁺ cations and of the presently unknown CF ₃⁺ 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 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.

Full text of DOI:10.1021/ja030649e

Published on Web 04/10/2004
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
5
(X ) F, Cl, Br, I, OTeF )
‡
‡
,‡
H e´ l e` ne P. A. Mercier, Matthew D. Moran, Gary J. Schrobilgen,*
‡
§
Christoph Steinberg, and Reijo J. Suontamo
Contribution from the Department of Chemistry, McMaster UniVersity, Hamilton,
Ontario, L8S 4M1, Canada, and Department of Chemistry, UniVersity of JyV a¨ skyl a¨ ,
P.O. Box 35, FIN-40014 JyV a¨ skyl a¨ , Finland
Received December 5, 2003; Revised Manuscript Received February 3, 2004; E-mail: schrobil@mcmaster.ca
+
+
Abstract: The CCl
CBr at -78 °C in SO
BrOTeF
3
and CBr
3
cations have been synthesized by oxidation of a halide ligand of CCl
4
and
+
4
2
ClF solvent by use of [XeOTeF
5
][Sb(OTeF
. The [XeOTeF
5
)
6
]. The CBr
3
cation reacts further with
] salt was also found to
+
+
5
to give CBr(OTeF
5
)
2
, C(OTeF
)
5 3
, and Br
2
5
][Sb(OTeF
)
5 6
+
+
+
react with BrOTeF
5
in SO
2
ClF solvent at -78 °C to give the Br(OTeF
, and Br(OTeF
)
5 2
3 3
cation. The CCl , CBr , CBr-
+
+
+
(OTeF )
5 2
, C(OTeF
)
5 3
)
5 2
cations and C(OTeF
)
5 4
have been characterized in SO
2
ClF solution
by 13C and/or F NMR spectroscopy at -78 °C. The X-ray crystal structures of the CCl
19
+, CBr
]‚SO
salts were stable at room temperature,
3-n salts were stable at 0 °C for several hours. The cations were found to be
+
, and
3
3
+
C(OTeF
C(OTeF
whereas the CBr
trigonal planar about carbon, with the CCl
their carbon atoms and the fluorine atoms of the Sb(OTeF
interacts with an oxygen of each of two SO
cation. The solid-state Raman spectra of the Sb(OTeF
5
)
3
cations have been determined in [CCl
3
+
][Sb(OTeF
and CBr
3 3
5
+
)
6
], [CBr
3
][Sb(OTeF
5
)
6
2
ClF, and
[
)
5 3
][Sb(OTeF
5
)
6
]‚3SO
2
+
ClF at -173 °C. The CCl
n
(OTeF
5
)
+
+
3
3
and CBr cations showing no significant interactions between
-
+
5 6 5 3
) anions. In constrast, the C(OTeF ) cation
2
ClF molecules by coordination along the three-fold axis of the
-
+
+
5
)
6
salts of CCl
3
and CBr
3
have been obtained
+
and assigned with the aid of electronic structure calculations. The CCl
Cl/ Cl isotopic pattern for the symmetric CCl
and natural bond orders of the CCl
3
cation displays a well-resolved
35
37
3
stretch. The energy-minimized geometries, natural charges,
+
+, CI
+
+
3
, CBr
3
3
, and C(OTeF
)
5 3
cations and of the presently unknown
+
CF
3
cation have been calculated using HF and MP2 methods have been compared with those of the
). The 13C and B chemical shifts for CX
11
+
(X )
isoelectronic BX
Cl, Br, I) and BX
in terms of paramagnetic contributions and spin-orbit coupling.
3
molecules (X ) F, Cl, Br, I, and OTeF
5
3
3
(X ) F, Cl, Br, I) were calculated by the GIAO method, and their trends were assessed
spectrometry2 and by ion cyclotron resonance (ICR) mass
Introduction
3
+
spectrometry. The CCl3 cation has also been isolated in the
solid state by ultraviolet or microwave irradiation of CHCl3 and
trapping of the free ion in an argon matrix at 14 K,4 and by
co-deposition of CCl4 and SbF5 on a CsI window at 77 K
followed by warming to 150 K to produce [CCl3][Sb2F10Cl] in
Trihalomethyl cations, CX3+ (X ) Cl, Br, I), have been the
+
+
subject of considerable interest. The CCl3 and CBr3 cations
have been postulated as superelectrophilic intermediates that
catalyze efficient cracking, isomerization and oligomerization
of alkanes and cycloalkanes, and that facilitate the syntheses
,5
6
+
an SbF5 matrix. In all three studies, CCl3 was characterized
+
of carbocations by means of hydride abstraction by the CCl3
+
+
by infrared spectroscopy. The CBr3 and CI3 cations have been
more recently observed in the gas phase by ICR mass
spectrometry. The CF3 cation has been observed by mass
1
+
cation. The CCl3 cation, the first perhalomethyl cation to have
been reported, has been observed in the gas phase by mass
7
+
†
This work has been presented, in part, at (a) the 224th National Meeting
(1) Olah, G. A.; Rasul, G.; Yudin, A. K.; Burrichter, A.; Prakash, G. K. S.;
Chistyakov, A. L.; Stankevich, I. V.; Akhrem, I. S.; Gambaryan, N. P.;
Vol’pin, M. E. J. Am. Chem. Soc. 1996, 118, 1446 and references therein.
of the American Chemical Society, Neil Bartlett Symposium, Boston, MA,
August 14-18, 2002 (also see Dagani, R. Chem. Eng. News 2002, 80, 27),
b) the 16th Winter Fluorine Conference, St. Petersburg Beach, FL, January
(
(
(
2) Martin, R. H.; Lampe, F. W.; Taft, R. W. J. Am. Chem. Soc. 1966, 88,
353.
3) Lias, S. G.; Eyler, J. R.; Ausloos, P. Int. J. Mass Spectrom. Ion Phys. 1976,
9, 219.
(
1
1
2-17, 2003, and (c) the 225th National Meeting of the American Chemical
Society, Karl O. Christe Symposium, New Orleans, LA, March 23-27,
003.
1
2
4) Jacox, M. E.; Milligan, D. E. J. Chem. Phys. 1971, 54, 3935.
‡
Department of Chemistry, McMaster University.
Department of Chemistry, University of Jyv a¨ skyl a¨ .
(5) Jacox, M. E. Chem. Phys. 1976, 12, 51.
§
(6) Van cˇ ik, H.; Perca cˇ , K.; Sunko, D. E. J. Am. Chem. Soc. 1990, 112, 7418.
10.1021/ja030649e CCC: $27.50 © 2004 American Chemical Society
J. AM. CHEM. SOC. 2004, 126, 5533-5548
9
5533

A R T I C L E S
Mercier et al.
spectrometry2 and ICR mass spectrometry3 and was first
produced in the condensed state by photodecomposition of CF3X
gen- and oxygen-substituted carbocations. These include
+
22
+ 23
[
CF2-S-CF-S] , [(CH3)2CF] , [(m-CF3C6H4)(C6H5)-
8
+
(X ) Cl, Br, I, H) in argon matrices. The CF3 cation has also
+
23
+ 24
+ 25
+ 26
CF] , [CH3OCHF] , [(o-ClC6H4)(C6H5)CCl] , [ClCO] ,
Cl2CdNH2] , [ClBrCdNH2] , [CH3OCHCl] , [C(OH)2-
[HC(OH)2] , [(C6H5)C(-OCH2CH2O-)] , and
(CH3)C(-OC(CH3)2C(CH3)2O-)] . Until the present work,
the CI3 and C(OH)3 cations were the only perhalogen- and
peroxygen-substituted cations to have been characterized by
single-crystal X-ray diffraction.
been obtained by decomposition of an Ar/F3CNNCF3 mixture
+
27
+ 28
+ 24
[
at 14 K that had been co-deposited with microwave-excited neon
+
29,30
+ 31
+ 32
CH3] ,
[
9
atoms and by co-deposition of a Ne/CF4 mixture at 5 K with
+
33
microwave-excited neon atoms.10 Matrix-isolated CF3 , derived
+
+
+
in the aforementioned manners, was characterized by infrared
+
spectroscopy, and the vibrational assignments for CF3 have
1
4,20
been confirmed by ab initio calculations.11 The first syntheses
of long-lived perhalomethyl cations in solution were achieved
by the reactions of CX4 (X ) Cl, Br, I) with SbF5 in SO2ClF
Given the relative paucity of solid-state structural data for
trihalomethyl cations, electronic structure calculations have been
heavily relied upon for metric data and have been used to
account for the bonding and chemical properties of these cations.
The relative stabilities of the trihalomethyl cations have been
assessed in terms of relative degrees of σ and p(π) donation
1
2,13
solvent at -78 °C to give [CX3][SbnF5nX] (X ) Cl, Br, I).
13
All three cations were characterized by C NMR spectroscopy.
+
The CCl3 cation was also generated by reaction of CCl3C(O)Cl,
1
2,13
CCl3SO2Cl, or CCl3C(O)F with SbF5 in SO2ClF at -78 °C.
1
3,14,23,26,34-36
Similar attempts to prepare CF3+ by reaction of SbF5 with CF4,
from the halogen atom to the carbon center.
The
+
σ effect, from the perspective of the halogen atoms of CX3 ,
has been found to be strongly withdrawing in the case of fluorine
and weakly donating in the cases of chlorine, bromine, and
iodine (I > Br > Cl). Conversely, p(π) back-donation is very
weak for fluorine and stronger for the heavier halogens (I > Br
> Cl). Other properties also have been computed for the CX3
series, including C chemical shifts, fluoride ion affinities
(as measures of relative Lewis acidities), vibrational frequen-
CF3C(O)F, and CF3SO2Cl in SO2ClF at -78 °C were unsuc-
cessful and, in the cases of CF3C(O)F and CF3SO2Cl, yielded
CF4.12,13
+
The CI3 cation has been recently synthesized as the
[CI3][Al(OC(CF3)3)4] salt by the room-temperature abstraction
of iodide as AgI from CI4 in CH2Cl2 solution by use of [Ag]-
+
+
[
Al(OC(CF3)3)4] as the Ag ion source, and characterized by
1
3
37
14
X-ray crystallography.
14
+
Peralkoxymethyl cations, [C(OR)3] , have been extensively
studied and characterized in solution and were first generated
by alkylation of carbonic esters and by Meerwein’s method,
1
1
13,14,23,26,34-36
cies, and atomic charges.
15
16,17
While prior syntheses of long-lived perhalomethyl cations
have been achieved by halide ion abstraction by use of either a
which involves alkoxy group abstraction from an ortho ester
by BF3. Peralkoxymethyl cations, generated in acid solutions
from ortho esters or ketals, have been characterized by ultraviolet
+
strong Lewis acid or Ag (vide supra), no routes to such
carbocations through oxidative removal of a halogen bound to
carbon were known. Among the objectives of the present work
are to provide structural and spectroscopic data for the perha-
lomethyl cations and related OTeF5-substituted cations that, thus
far, have been lacking for these systems. The present paper
details an oxidative route to carbocations using the strongly
1
13
and infrared spectroscopy and by H and C NMR spectros-
copy.1 The trihydroxymethyl cation, C(OH)3 , was first gener-
8
+
ated by dissolution of M2CO3 (M ) Na, K), BaCO3, or NaHCO3
in FSO3H-SbF5-SO2 superacid solutions at -78 °C and
1
13
19
studied by H and C NMR spectroscopy. Prior to the present
+
+
5 5 6
oxidizing salt, [XeOTeF ][Sb(OTeF ) ], and represents an
work, the C(OH)3 cation was the only C(OX)3 cation to have
been isolated and studied in the solid state. The low-temperature
crystal structure of [C(OH)3][AsF6] and infrared and Raman
spectra of [C(OH)3][MF6] (M ) As, Sb) were obtained by the
low-temperature solvolysis of OC(OSiMe3)2 in the superacidic
interesting new application of noble-gas compounds to chemical
3
8-40
syntheses.
The present solution, solid-state, and computa-
(
(
(
(
22) Antel, J.; Klaus, H.; Jones, P. G.; Mews, R.; Sheldrick, G. M.; Waterfeld,
A. Chem. Ber. 1985, 118, 5006.
2
0
media HF/MF5. The salts were found to decompose quanti-
23) Christe, K. O.; Zhang, X.; Bau, R.; Hegge, J.; Olah, G. A.; Prakash, G. K.
S.; Sheehy, J. A. J. Am. Chem. Soc. 2000, 122, 481.
tatively to CO2 and [H3O][MF6] above -16 °C (M ) As) and
24) Minkwitz, R.; Reinemann, S.; Blecher, O.; Hartl, H.; Br u¨ dgam, I. Inorg.
Chem. 1999, 38, 844.
-
4 °C (M ) Sb).
While a considerable number of carbocation structures
25) Laube, T.; Bannwart, E.; Hollenstein, S. J. Am. Chem. Soc. 1993, 115,
1731.
2
1
have been determined by X-ray crystallography, rela-
tively few crystal structures have been determined for halo-
(26) Christe, K. O.; Hoge, B.; Boatz, J. A.; Prakash, G. K. S.; Olah, G. A.;
Sheehy, J. A. Inorg. Chem. 1999, 38, 3132.
(27) Minkwitz, R.; Meckstroth, W.; Preut, H. Z. Anorg. Allg. Chem. 1992, 617,
136.
(
7) Abboud, J.-L. M.; Casta n˜ o, O.; Herreros, M.; Elguero, J.; Jagerovic, N.;
Notario, R.; Sak, K. Int. J. Mass Spectrom. Ion Proc. 1998, 175, 35.
8) Prochaska, F. T.; Andrews, L. J. Am. Chem. Soc. 1978, 100, 2102.
9) Jacox, M. E. Chem. Phys. 1984, 83, 171.
(28) Minkwitz, R.; Meckstroth, W.; Preut, H. Z. Naturforsch., B: Chem. Sci.
1992, 48, 19.
(
(
(29) J o¨ nsson, P.-G.; Olovsson, I. Acta Crystallogr. 1968, B24, 559.
(30) Kvick, A° .; J o¨ nsson, P.-G.; Olovsson, I. Inorg. Chem. 1969, 8, 2775.
(31) Minkwitz, R.; Schneider, S.; Seifert, M. Z. Anorg. Allg. Chem. 1996, 622,
1404.
(
(
(
10) Forney, D.; Jacox, M. E.; Irikura, K. K. J. Chem. Phys. 1994, 101, 8290.
11) Maclagan, R. G. A. R. J. Mol. Struct. (THEOCHEM) 1991, 235, 21.
12) Olah, G. A.; Heiliger, L.; Prakash, G. K. S. J. Am. Chem. Soc. 1989, 111,
(32) Caira, M. R.; De Wet, J. F. Acta Crystallogr. 1981, B37, 709.
(33) Paulsen, H.; Dammeyer, R. Chem. Ber. 1973, 106, 2324.
(34) Frenking, G.; Fau, S.; Marchand, C. M.; Gr u¨ tzmacher, H. J. Am. Chem.
Soc. 1997, 119, 6648.
8
020.
13) Olah, G. A.; Rasul, G.; Heiliger, L.; Prakash, G. K. S. J. Am. Chem. Soc.
996, 118, 3580.
14) Krossing, I.; Bihlmeier, A.; Raabe, I.; Trapp, N. Angew. Chem., Int. Ed.
003, 42, 1531.
(
(
1
(35) Robinson, E. A.; Johnson, S. A.; Tang, T.-H.; Gillespie, R. J. Inorg. Chem.
1997, 36, 3022.
2
(
15) Klages, F.; Zange, E. Chem. Ber. 1959, 92, 1828.
16) Meerwein, H.; Bodenbenner, K.; Borner, P.; Kunert, F.; Wunderlich, H.
Ann. 1960, 632, 38.
(36) Robinson, E. A.; Heard, G. L.; Gillespie, R. J. J. Mol. Struct. 1999, 485-
(
486, 305.
(37) Kaupp, M.; Malkina, O. L.; Malkin, V. G. Chem. Phys. Lett. 1997, 265,
55.
(17) Meerwein, H.; Hederich, V.; Morschel, H.; Wunderlich, H. Ann. 1960, 635,
1
.
(38) Minkwitz, R.; B a¨ ck, B. In Inorganic Fluorine Chemistry, Toward the 21st
Century; Thrasher, J. S., Strauss, S. H., Eds.; ACS Symposium Series 555;
American Chemical Society: Washington, DC, 1994; Chapter 6, p 90.
(39) Brown, D. R.; Clegg, M. J.; Downs, A. J.; Fowler, R. C.; Minihan, A. R.;
Norris, J. R.; Stein, L. Inorg. Chem. 1992, 31, 5041.
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5534 J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004

Syntheses and Characterization of Carbocations
A R T I C L E S
Table 1. 13C and 19F NMR Parameters for C(OTeF5)4 and CBrn(OTeF5)3-n (n ) 0-3) and Products Resulting from the Reaction of
a
+
[
XeOTeF5][Sb(OTeF5)6] with CCl4 and CBr4
1
00 × (total satellite
chem shift (δ), ppmb
coupling constant, Hzb
intens/central peak intens)
c
13C
19F
19F
2
J( C−125Te)
13
2
J( F
19
− F
19
1
J( F
19
−125Te)
1
J( F
19
−125Te)
1
J( F
19
−123Te)
1
J( F
A
−123Te)
19
125Te
species
B
A
A
B
)
B
A
B
CCl3+
CBr3
d
237.1
209.7
201.1
187.6
168.8
115.8
+
d
+
+
d
d
e
CBr2(OTeF5)
CBr(OTeF5)2
C(OTeF5)3
C(OTeF5)4
Br(OTeF5)2
BrOTeF5
-19.9 -61.3
-24.4 -59.3
-31.6 -57.6
-41.5 -49.9
-24.4 -58.2
-53.8 -47.0
-54.0 -49.2
-42.6
156
4099
4029
4025
3758
4013
3786
3852
3563
162
164
180
164
180
178
4075
4012
3653
4047
3419
3474
3343
3337
3120
3324
3140
+
d
69
64
12 ( 1 (12.7)
16.9 ( 0.1 (16.8)
3029
3350
+
d
f
ClOTeF5
Sb(OTeF5)6
-
d
a
Nuclear magnetic resonance spectra were obtained for SO2ClF solutions at -80 °C (δ( F), 98.3 ppm; primary and secondary isotope shifts: ∆ F(16/18O),
19
2
19
1
19 32/34
2
19 35/37
Cl), 0.0085 ppm. b The symbols, FA and FB, denote equatorial and axial fluorine atoms, respectively.
0
.0428 ppm, ∆ F(
S), 0.0611 ppm, and ∆ F(
c
d
-
Ratios calculated from natural isotopic abundances are given in parentheses. The Sb(OTeF5)6 anion parameters apply to all carbocation salts and to the
+
-
e
Br(OTeF5)2 salt of Sb(OTeF5)6 ; also see ref 41. Predicted from pairwise additivity parameters as described in the Chemical Shifts and Coupling Constant
Trends section. See refs 42 and 43.
f
tional studies compliment previous solution 13C NMR studies
Coupling Constant Trends). The 19F NMR spectrum shows the
+
+
+ 12-14
-
41
of the CCl3 , CBr3 , and CI3
structure of the CI3 cation, which followed our preliminary
cations, as well as the X-ray
severe AB4 pattern that typifies the Sb(OTeF5)6 anion and a
+
14
45
well-resolved AB4 pattern for ClOTeF5 (Table 1).
accounts of the present work.†
The reaction of stoichiometric amounts of CBr4 with
[
XeOTeF5][Sb(OTeF5)6] in SO2ClF is initially rapid at -78 °C,
Results and Discussion
giving a deep red-brown solution which lightens to red-orange
Syntheses of [CCl3][Sb(OTeF5)6], [CBrn(OTeF5)3-n]-
over a period of several hours at ca. -50 °C. The color change
corresponds to the further reaction of the CBr3 cation with
+
[
Sb(OTeF5)6] (n ) 0, 1, 3), [Br(OTeF5)2][Sb(OTeF5)6], and
19
13
C(OTeF5)4 and Solution Characterization by F and
C
BrOTeF to produce Br and the mixed carbocations, CBr -
5
2
2
+
+
+
NMR Spectroscopy. The products of the reactions described
(OTeF ) , CBr(OTeF ) , and ultimately C(OTeF ) , according
5
5 2
5 3
1
3
below were initially characterized in SO2ClF solution by
C
to eqs 2-5, with the overall reaction being represented by eq
6.
1
9
and F NMR spectroscopy, and their NMR parameters are
provided in Table 1.
The synthesis and X-ray crystal structure of [XeOTeF5][Sb-
3[XeOTeF ][Sb(OTeF ) ] + 3CBr f
5
5 6
4
(
OTeF5)6]‚SO2ClF will be described in a forthcoming publica-
3
[CBr ][Sb(OTeF ) ] + 3BrOTeF + 3 Xe (2)
3 5 6 5
44
tion. Unlike that of its fluorine analogue, [XeF][SbF6], which
is insoluble in SO2ClF at room temperature, the solubility of
[CBr ][Sb(OTeF ) ] + BrOTeF f
3 5 6 5
[
XeOTeF5][Sb(OTeF5)6] in SO2ClF exceeds 2 M at -78 °C,
[
CBr (OTeF )][Sb(OTeF ) ] + Br (3)
2 5 5 6 2
forming an intense yellow solution. The salt rapidly oxidizes
stoichiometric amounts of CCl4 at -78 °C to yield clear,
colorless solutions of [CCl3][Sb(OTeF5)6] according to eq 1.
[
CBr (OTeF )][Sb(OTeF ) ] + BrOTeF f
2
5
5 6
5
[
CBr(OTeF ) ][Sb(OTeF ) ] + Br (4)
5 2 5 6 2
[
XeOTeF ][Sb(OTeF ) ] + CCl f
5 5 6 4
[
CCl ][Sb(OTeF ) ] + ClOTeF + Xe (1)
[CBr(OTeF ) ][Sb(OTeF ) ] + BrOTeF f
5 2 5 6 5
3
5 6
5
[
C(OTeF ) ][Sb(OTeF ) ] + Br (5)
5 3 5 6 2
Removal of SO2ClF and other volatile components under
vacuum between -78 and 0 °C gave colorless, crystalline [CCl3]-
3
[XeOTeF ][Sb(OTeF ) ] + 3CBr f
5 5 6 4
[Sb(OTeF5)6] (see X-ray Crystallography), which was found to
2
[CBr ][Sb(OTeF ) ] + [C(OTeF ) ][Sb(OTeF ) ] +
3 5 6 5 3 5 6
be stable indefinitely at room temperature.
The 13C NMR spectrum (SO2ClF solvent, -80 °C) of the
3
Br + 3 Xe (6)
2
products resulting from eq 1 give rise to a sharp singlet (237.1
Removal of SO2ClF and other volatile components under
vacuum between -78 and 0 °C resulted in a pale, yellow-orange
solid. The Raman spectra of the solid mixture showed that the
ppm) assigned to [CCl3][Sb(OTeF5)6], which is in agreement
1
2
13
with the previously reported value (236.3 ppm). The
C
+
chemical shift of CCl3 is significantly deshielded relative to
that of CCl4 [δ( C), 96.4 ppm; SO2ClF, -80 °C], which is
+
CBr3 salt was stable indefinitely at room temperature, whereas
1
3
+
the mixed CBrn(OTeF5)3-n salts were stable for several hours
consistent with carbocation formation (see Chemical Shift and
at 0 °C. The [CBr3][Sb(OTeF5)6] and [C(OTeF5)3][Sb(OTeF5)6]
salts have been characterized by single-crystal X-ray diffraction,
and Br2 was identified by determination of the unit cell
parameters from a single crystal at -173 °C (see Experimental
Section).
(
40) Frohn, H.-J.; Klose, A.; Henkel, G. GIT Fachz. Lab. 1993, 37, 752.
41) Mercier, H. P. A.; Sanders, J. C. P.; Schrobilgen, G. J. J. Am. Chem. Soc.
(
1
994, 116, 2921.
(
42) Seppelt, K. Chem. Ber. 1973, 106, 1920.
(
43) Gerken, M.; Kolb, P.; Wegner, A.; Mercier, H. P. A.; Borrmann, H.; Dixon,
D. A.; Schrobilgen, G. J. Inorg. Chem. 2000, 39, 2813.
44) Mercier, H. P. A.; Moran, M. D.; Sanders, J. C. P.; Schrobilgen, G. J.;
Suontamo, R. J. To be submitted for publication.
(
(45) Seppelt, K. Z. Anorg. Allg. Chem. 1973, 399, 65.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004 5535

A R T I C L E S
Mercier et al.
The 13C NMR spectrum of [CBr3][Sb(OTeF5)6] in SO2ClF
or F abstraction to form TeF6 [δ( F), -52.6 ppm; J( F-
-
19
1
19
1
25
1
19
123
at -80 °C gave rise to a singlet (209.7 ppm), in good agreement
Te), 3747 Hz; J( F- Te), 3095 Hz] according to eq 11.
The proposed species, Sb(OTeF5)5, which is known to be
unstable,
12
with the previously reported value (207 ppm). As in the case
+
13
+
49,50
of CCl3 , the C resonance of CBr3 is significantly deshielded
and F4TeOSb(OTeF5)5 have not been investigated
13
with respect to that of its parent molecule, CBr4 [δ( C), -29.7
ppm; SO2ClF, -80 °C], which is characteristic of carbocation
formation (see Chemical Shift and Coupling Constant Trends).
The F NMR spectrum shows a severe AB4 pattern corre-
sponding to the Sb(OTeF5)6 anion (Table 1), similar to that
obtained for [CCl3][Sb(OTeF5)6]. The 19F NMR spectrum of a
further in this study.
[
TeF ][Sb(OTeF ) ] f O(TeF ) + Sb(OTeF ) (10)
5 5 6 5 2 5 5
1
9
-
[TeF ][Sb(OTeF ) ] f TeF + F TeOSb(OTeF )
5 5
(11)
5
5 6
6
4
+
The formation of the C(OTeF5)3 cation was confirmed by
the presence of a
spectrum [ J( C- Te), 69 Hz]. The similar gyromagnetic
ratios of Te and Te and the low natural abundance of
Te (0.87%) relative to Te (6.99%) precluded the observation
of separate Te satellites because of overlap with the more
intense
intensities expected for coupling to
integrated satellite peak/central peak intensity ratios 0.111:1.000:
.123 in the C NMR spectrum were shown to be consistent
with the calculated satellite peak/central peak intensity ratios
.0001:0.0054:0.1268:1.0000:0.1268:0.0054:0.0001 expected for
a series of overlapping isotopomer subspectra that correspond
to three chemically equivalent tellurium atoms. Tellurium
satellites were not observed for CBr(OTeF5)2 , owing to the
low concentration of this species (10%).
sample of pure BrOTeF5 dissolved in SO2ClF at -80 °C (Table
) was also obtained and demonstrated that BrOTeF5, as
proposed in eq 2, was not present. The absence of BrOTeF5 is
consistent with the formation of mixed Br/OTeF5-substituted
methyl cations and the oxidation of BrOTeF5 by [XeOTeF5]-
Sb(OTeF5)6] to give the new Br(OTeF5)2+ cation (eq 7).
1
23/125
13
Te satellite doublet in the C NMR
1
2
13
125
51
1
23
125
123
-
1
25
1
23
[
1
25
Te satellites (ν1/2 ≈ 5 Hz). By combining the
1
23
125
Te and Te, the
[
XeOTeF ][Sb(OTeF ) ] + BrOTeF f
5
5 6
5
[
Br(OTeF ) ][Sb(OTeF ) ] + Xe (7)
5 2 5 6
13
0
The formation of Br(OTeF5)2+ was confirmed by reaction of
0
BrOTeF5 with [XeOTeF5][Sb(OTeF5)6] in SO2ClF at -78 °C
46
in a separate experiment.
5
2
The formation of the CBrn(OTeF5)3-n+ (n ) 1-3) cations
and their NMR assignments were confirmed by addition of
BrOTeF5 at -20 °C to the reaction products of eq 6, in a 3:1
molar ratio relative to the initial amounts of [XeOTeF5][Sb-
+
To compare the NMR parameters of C(OTeF5)3+ with those
of the unknown neutral parent, C(OTeF5)4, CBr4 was allowed
to react with a stoichiometric amount of BrOTeF5 at -78 °C
according to eq 12.
(
OTeF5)6] and CBr4. This resulted in increased amounts of the
OTeF5-containing carbocations and Br2 as outlined in eqs 3-5
13
(
Table 1). The C NMR spectrum indicated that a small quantity
of [CBr3][Sb(OTeF5)6] remained unreacted (7% based on
CBr + 4 BrOTeF f C(OTeF ) + 4 Br
(12)
The 13C NMR resonance of C(OTeF5)4 is a singlet at 115.8
4
5
5 4
2
integration of all 1 C resonances) with [C(OTeF5)3][Sb(OTeF5)6]
3
13
as the major product (70%; δ( C), 168.8 ppm). Of the mixed
+
OTeF5-substituted bromocations, CBrn(OTeF5)3-n (n ) 1, 2),
123/125
13
ppm, accompanied by
Te satellites. As expected, the C
+
13
only the CBr(OTeF5)2 cation was detected by C NMR
chemical shift of C(OTeF5)4 is significantly shielded with respect
1
3
13
spectroscopy (10%; δ( C), 187.6 ppm), while the C chemical
+
+
to that of the C(OTeF5)3 cation. As in the case of C(OTeF5)3 ,
+
shift of CBr2(OTeF5) was predicted by use of pairwise
the formation of C(OTeF5)4 was confirmed by the relative
13
additivity parameters (δ( C), 201.1 ppm; see Chemical Shift
123/125
intensities of the overlapping
Te satellites that arise from
and Coupling Constant Trends). A singlet was also observed
2
13
125
the natural abundance tellurium isotopomers [ J( C- Te), 64
1
3
(
13%; δ( C), 124.7 ppm) that is tentatively assigned to Od
53
Hz]. The integrated satellite peak/central peak area ratios of
13
C(OTeF5)2 based on the similarity of its C chemical shift to
that of OdCF2 (134.2 ppm) and may arise from the formal
loss of the TeF5 cation from C(OTeF5)3 , according to eq 8.
13
0
.168:1.000:0.170 in the C NMR spectrum confirm coupling
47
to four chemically equivalent tellurium atoms when compared
+
+
-6
with the calculated intensity ratios (3 × 10 : 0.0003:0.0107:
Alternatively, OdC(OTeF5)2 may prove to be unstable, decom-
-6
0
.1678:1.0000:0.1678:0.0107:0.0003:3 × 10 ).
1
3
48
19
posing to CO2 (δ( C), 124.2 ppm) and O(TeF5)2 [δ( FB),
41.4 ppm; FA was not observed because of overlap with FA
X-ray Crystal Structures of [CCl3][Sb(OTeF5)6], [CBr3]-
-
[
Sb(OTeF5)6]‚SO2ClF, and [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF.
Details of data collection parameters and other crystallographic
+
2
19
19
of C(OTeF5)3 ; J( FB- FA), 164 Hz] according to eq 9.
information are provided in Table 2. Bond lengths and bond
[
C(OTeF ) ][Sb(OTeF ) ] f
+
+
+
5
3
5 6
angles for the CCl3 , CBr3 , and C(OTeF5)3 cations are listed
in Table 3. Closest secondary contacts between the carbon and
halogen atoms of the cations and the fluorine atoms of the anion
or oxygen atoms of the SO2ClF solvent molecules are also given
OdC(OTeF ) + [TeF ][Sb(OTeF ) ] (8)
5
2
5
5 6
OdC(OTeF ) f CO + O(TeF )
5 2
(9)
5
2
2
The TeF5+ cation presumably was not observed because of its
(49) Lentz, D.; Seppelt, K. Z. Anorg. Allg. Chem. 1983, 502, 83.
(
50) Syvret, R. G.; Mitchell, K. M.; Sanders, J. C. P.; Schrobilgen, G. J. Inorg.
-
high electrophilicity, which could lead to OTeF5 abstraction
Chem. 1992, 31, 3381.
n
A
JAB ) (γ J
A′B/γA′), the calculated value for 1J( F-123Te) is 57
n
19
-
(51) Using
Hz.
from Sb(OTeF5)6 , forming O(TeF5)2 according to eq 10 and/
(
52) Sanders, J. C. P.; Schrobilgen, G. J. In Proceedings of the NATO AdVanced
(
46) Mercier, H. P. A.; Moran, M. D.; Schrobilgen, G. J.; Suontamo, R. J. To
Study Institute on Methodological Approach to Multinuclear NMR in
Liquids and Solids - Chemical Applications; Granger, P., Harris, R. K.,
Eds.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1988;
Vol. 322, pp 160-166.
be submitted for publication.
(47) Gombler, W. Spectrochim. Acta, Part A 1981, 37, 57.
48) Ettinger, R.; Blume, P.; Patterson, A.; Lauterbur, P. C. J. Magn. Reson.
(
(53) The calculated value for J( F-123Te) is 53 Hz; see ref 51.
1
19
1
972, 33, 1597.
5536 J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004

Syntheses and Characterization of Carbocations
A R T I C L E S
Table 2. Crystallographic Data for [CCl3][Sb(OTeF5)6], [CBr3][Sb(OTeF5)6]‚SO2ClF, and [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF
+
+
+
3
CCl
3
C(OTeF
5
)
3
CBr
chem formula
space group
a (Å)
b (Å)
c (Å)
CCl3F30O6SbTe6
P1h
CCl3F48O15S3SbTe9
P1h
CClBr3F31O8SSbTe6
P21/n
18.617(6)
9.935(3)
19.129(7)
90
90.781(7)
90
3538(4)
4
7694.40
3.611
-173
93.5
0.0621
0.1211
8.706(2)
9.181(2)
9.862(2)
104.111(5)
103.507(5)
98.851(5)
724.5(5)
1
1671.71
3.832
-173
73.7
10.082(4)
10.950(4)
24.572(10)
83.482(8)
81.679(7)
70.019(7)
2517(3)
2
5273.38
3.480
-173
61.7
R (deg)
â (deg)
γ (deg)
3
V (Å )
molecules/unit cell
-
1
mol wt (g mol
)
calcd density (g cm-3)
T (°C)
µ (cm-1)
a
R1
0.0355
0.0736
0.0668
0.1259
b
wR2
a
2
2 2
2 2 1/2
R1 is defined as Σ||Fo| - |Fc||/Σ|Fo| for I > 2σ(I); wR2 is defined as [Σ[w(Fo - Fc ) ]/Σw(Fo ) ] for I > 2σ(I).
in Table 3 together with important bond lengths and bond angles
for the Sb(OTeF5)6- anions and SO2ClF solvent molecules. A
complete list of bond lengths and bond angles for the
CFCl3 (1.75(1) Å)57 and CBr4 (1.91(4) Å)58 by ca. 0.15, 0.13,
and 0.10 Å, respectively, as expected for cations (see Compu-
tational Results for CX3 and BX3). In the case of the previously
+
-
Sb(OTeF5)6 anions and SO2ClF solvent molecules is also
reported structures of chloro- and bromo-substituted carboca-
provided (Supporting Information).
tions, the C-Cl or C-Br bond lengths are marginally longer
+
+
25
The present contribution reports the first crystal structures
than in CCl3 and CBr3 , i.e., [(o-ClC6H4)(C6H5)CCl][SbF6]
+
+
+
-
27
of the CCl3 , CBr3 , and C(OTeF5)3 cations. The Sb(OTeF5)6
(C-Cl, 1.668(8) Å), [Cl2CdNH2][SbCl6] (C-Cl, 1.663(6)-
anion, which has been described previously,41,54 is comprised
of a central antimony atom coordinated to six oxygen atoms,
and each of the six tellurium atoms is octahedrally coordinated
to one oxygen and five fluorine atoms so that the anion structure
can be described as an octahedron of octahedra. Bond angles
24
1.680(6) Å), [CH3OCHCl][SbF6] (C-Cl, 1.650(9) Å), and
28
[ClBrCdNH2][SbCl6] (C-Cl, 1.69(1); C-Br, 1.843(9) Å). In
+
+
the CCl3 and CBr3 salts, the shortest cation-anion C‚‚‚F
contacts are 2.962(9) Å and 3.09(2) Å, respectively, (cf. the
5
9
sum of the carbon and fluorine van der Waals radii, 3.10,
-
60
and bond lengths of the Sb(OTeF5)6 anions reported in the
present study are in good agreement with those reported in the
3.30 Å). These contacts approach the carbon at angles of 3°
(CCl3 ) and 8° (CBr3 ) with respect to the C3-axis. As well,
longer C‚‚‚F contacts (CCl3 , 3.464(9), 3.574(11), and 3.574-
+
+
5
4
54
+
crystal structures of [SbBr4][Sb(OTeF5)6], [SbCl4][Sb(OTeF5)6],
N(CH3)4][Sb(OTeF5)6],41 and [N(CH2CH3)4][Sb(OTeF5)6],41
+
[
(11) Å; CBr3 , 3.39(2) Å) approach above and below the CX3-
+
+
and therefore require no further comment. The SO2ClF solvent
molecules present in the structures of [CBr3][Sb(OTeF5)6]‚SO2-
ClF and [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF have the expected
pseudotetrahedral geometry, with the S-O, S-Cl, and S-F
bond lengths in agreement with those obtained from the X-ray
crystal structure of SO2ClF55 and require no further comment
plane at angles of 4, 13, and 37° (CCl3 ) and 8° (CBr3 ),
respectively. The bond length and bond angle trends are
consistent with the previously noted trend of decreasing contact
angle with decreasing contact distance in a number of carboca-
2
1
tion structures. The present structures indicate that the
Sb(OTeF5)6 anions are very weakly coordinated to the carbon
-
(
Table 3). There are no significant differences between the
centers. The occurrence of cation-anion contacts is a common
feature, and the present C‚‚‚F contact distances are comparable
to those observed in [CI3][Al(OC(CF3)3}4] (the shortest is 3.26
metric parameters of the two coordinated and one uncoordinated
SO2ClF molecule in the [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF
structure.
14
Å) and in [(m-CF3C6H4)(C6H5)CF][As2F11] (3.01(2) and 3.07-
2
3
(
a) [CCl3][Sb(OTeF5)6] and [CBr3][Sb(OTeF5)6]‚SO2ClF.
(2) Å). The chlorine and bromine atoms also interact with the
+
+
The trigonal planar CCl3 cation in [CCl3][Sb(OTeF5)6] is
positionally two-fold disordered about the crystallographic
inversion center (Figure 1), contrasting with the CBr3 cation
in [CBr3][Sb(OTeF5)6]‚SO2ClF which is not disordered (Figure
2
cally independent, and carbocation planarity is not imposed by
symmetry, with X-C-X bond angle sums of 360(1)°. The
C-Br bond lengths and Br-C-Br angles of CBr3 are all equal
within (3σ, giving the expected D3h symmetry. As a conse-
fluorine atoms of the anion and, in the case of the CBr3 salt,
with the oxygen atoms of SO2ClF (Cl‚‚‚F: 2.833(5)-3.022(5)
Å; Br‚‚‚F: 2.977(9)-3.301(11) Å; Br‚‚‚O: 2.778(13), 2.839-
(12) Å). These interactions are shorter than or are at the limit
of the sum of the halogen-fluorine(oxygen) van der Waals radii
+
). In both cases, the three halogen atoms are crystallographi-
5
9
60
59
60
59
(Cl‚‚‚F, 3.15, 3.22 Å; Br‚‚‚F, 3.30, 3.32 Å; Br‚‚‚O, 3.35,
6
0
3.37 Å) and are apparently a consequence of the positive
+
charges on the halogen atoms (see Computational Results for
+
CX3 and BX3). The Br‚‚‚O contacts, which occur with the
+
quence of the disorder, the CCl3 cation gives a slightly wider
range of bond lengths and angles, but displays essentially D3h
oxygen atoms of two SO2ClF solvent molecules, are shorter
+
than the secondary C‚‚‚F cation-anion contacts in the CCl3
symmetry in its crystal structure. The C-Cl and C-Br bond
lengths are found to be shorter than in CCl4 (1.751(13) Å),
5
6
(56) Cohen, S.; Powers, R.; Rudman, R. Acta Crystallogr. 1979, B35, 1670.
(
57) Cockcroft, J. K.; Fitch, A. N. Z. Kristallogr. 1994, 209, 488.
(
58) More, M.; Baert, F.; Lefebvre, J. Acta Crystallogr. 1977, B33, 3681.
(
54) Casteel, W. J.; Kolb, P.; LeBlond, N.; Mercier, H. P. A.; Schrobilgen, G.
J. Inorg. Chem. 1996, 35, 929.
(59) Pauling, L., The Nature of the Chemical Bond, 3rd ed.; Cornell University
Press: Ithaca, New York, 1960, 260.
(55) Mootz, D.; Merschenz-Quack, A. Acta Crystallogr. 1988, C44, 924.
(60) Bondi, A. J. Phys. Chem. 1964, 68, 441.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004 5537

A R T I C L E S
Mercier et al.
Table 3. Experimental Geometries in [CCl3][Sb(OTeF5)6], [CBr3][Sb(OTeF5)6]‚SO2ClF, and [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF
[CCl3][Sb(OTeF5)6]
bond lengths (Å)
bond angles (deg)
C(1)-Cl(1)
C(1)-Cl(2)
C(1)-Cl(3)
C(1)‚‚‚F(14A)
C(1)‚‚‚F(14)
C(1)‚‚‚F(8A)
C(1)‚‚‚F(2A)
1.672(11)
1.598(12)
1.592(13)
2.962(9) [3°]
Cl(1)-C(1)-Cl(2)
Cl(1)-C(1)-Cl(3)
Cl(2)-C(1)-Cl(3)
118.4(8)
118.7(7)
123.3(8)
a
3.464(9) [4°]a
a
3.574(11) [13°]
3.574(11) [37°]a
[CBr3[Sb(OTeF5)6]‚SO2ClF
bond lengths (Å)
bond angles (deg)
C(1)-Br(1)
C(1)-Br(2)
C(1)-Br(3)
C(1)‚‚‚F(44A)
C(1)‚‚‚F(24A)
1.851(16)
1.787(16)
Br(1)-C(1)-Br(2)
Br(1)-C(1)-Br(3)
Br(2)-C(1)-Br(3)
119.1(9)
117.9(9)
122.9(9)
1.783(16)
3.39(2) [8°]a
3.09(2) [8°]a
C(OTeF5)3[Sb(OTeF5)6]‚3SO2ClF
bond lengths (Å)
C(1)-O(1)
Te(1)-O(1)
Te(1)-F(1)
Te(1)-F(2)
Te(1)-F(3)
Te(1)-F(4)
Te(1)-F(5)
C(1)‚‚‚O(11)
1.313(16)
1.988(7)
1.816(6)
1.816(8)
1.801(8)
1.813(8)
1.814(8)
2.690(17) [1°]
C(1)-O(2)
1.279(13)
1.974(8)
1.798(8)
1.812(8)
1.810(7)
1.816(9)
C(1)-O(3)
1.258(15)
Te(2)-O(2)
Te(2)-F(6)
Te(2)-F(7)
Te(2)-F(8)
Te(2)-F(9)
Te(2)-F(10)
C(1)‚‚‚O(15A)
Te(3)-O(3)
Te(3)-F(11)
Te(3)-F(12)
Te(3)-F(13)
Te(3)-F(14)
Te(3)-F(15)
1.977(9)
1.819(8)
1.795(8)
1.820(6)
1.799(6)
1.809(8)
1.808(8)
a
2.738(18) [3°]a
bond angles (deg)
O(1)-C(1)-O(2)
C(1)-O(1)-Te(1)
O(1)-Te(1)-F(1)
O(1)-Te(1)-F(2)
O(1)-Te(1)-F(3)
O(1)-Te(1)-F(4)
O(1)-Te(1)-F(5)
F(1)-Te(1)-F(2)
F(1)-Te(1)-F(3)
F(1)-Te(1)-F(4)
F(1)-Te(1)-F(5)
F(2)-Te(1)-F(3)
F(2)-Te(1)-F(4)
F(2)-Te(1)-F(5)
F(3)-Te(1)-F(4)
F(3)-Te(1)-F(5)
F(4)-Te(1)-F(5)
119(1)
O(1)-C(1)-O(3)
C(1)-O(2)-Te(2)
O(2)-Te(2)-F(6)
O(2)-Te(2)-F(7)
O(2)-Te(2)-F(8)
O(2)-Te(2)-F(9)
O(2)-Te(2)-F(10)
F(6)-Te(2)-F(7)
F(6)-Te(2)-F(8)
F(6)-Te(2)-F(9)
F(6)-Te(2)-F(10)
F(7)-Te(2)-F(8)
F(7)-Te(2)-F(9)
F(7)-Te(2)-F(10)
F(8)-Te(2)-F(9)
F(8)-Te(2)-F(10)
F(9)-Te(2)-F(10)
119.8(9)
132.7(9)
176.2(4)
90.1(4)
89.9(4)
84.5(4)
85.3(4)
92.6(4)
92.8(4)
92.8(4)
92.0(4)
89.7(4)
90.2(4)
175.4(4)
174.4(4)
90.0(4)
89.6(4)
O(2)-C(1)-O(3)
121(1)
125.5(7)
176.8(4)
91.2(3)
84.2(3)
89.2(3)
86.0(3)
91.4(3)
93.9(3)
92.8(3)
91.4(3)
88.7(4)
89.7(4)
177.1(3)
173.2(3)
90.7(4)
90.6(4)
C(1)-O(3)-Te(3)
O(3)-Te(3)-F(11)
O(3)-Te(3)-F(12)
O(3)-Te(3)-F(13)
O(3)-Te(3)-F(14)
O(3)-Te(3)-F(15)
F(11)-Te(3)-F(12)
F(11)-Te(3)-F(13)
F(11)-Te(3)-F(14)
F(11)-Te(3)-F(15)
F(12)-Te(3)-F(13)
F(12)-Te(3)-F(14)
F(12)-Te(3)-F(15)
F(13)-Te(3)-F(14)
F(13)-Te(3)-F(15)
F(14)-Te(3)-F(15)
131.2(8)
174.6(3)
85.4(4)
91.8(4)
82.5(3)
89.1(4)
93.0(4)
93.3(3)
92.5(4)
92.7(4)
90.0(3)
90.9(3)
174.3(4)
174.1(4)
89.2(3)
89.6(3)
-
+
+
+
5 3
Sb(OTeF
5
)
6
CCl
3
salt
CBr
3
salt
C(OTeF ) salt
bond lengths (Å)
Sb-O
Te-O
Te-Fax
Te-Feq
1.951(3)-1.955(3)
1.844(4)-1.854(3)
1.834(3)-1.839(3)
1.819(3)-1.841(3)
1.936(10)-1.981(10)
1.819(10)-1.868(10)
1.833(9)-1.852(9)
1.807(10)-1.849(9)
1.934(9)-1.957(9)
1.832(9)-1.858(9)
1.819(8)-1.836(6)
1.809(7)-1.840(6)
bond angles (deg)
138.0(6)-140.7(6)
Sb-O-Te
SO
137.9(2)-138.2(2)
137.2(4)-139.3(4)
+
+
2
ClF
CBr
3
salt
C(OTeF
5
)
3
salt
bond lengths (Å)
1.404(13)-1.417(12)
1.533(10)
S-O
S-F
S-Cl
1.384(11)-1.407(9)
1.519(7)-1.520(10)
1.918(6)-1.951(6)
1.942(7)
bond angles (deg)
120.9(9)
109.9(6)-110.0(6)
107.0(8)-108.7(7)
97.8(5)
O-S-O
O-S-Cl
O-S-F
F-S-Cl
120.1(7)-122.3(8)
108.2(5)-111.7(6)
106.7(8)-109.4(6)
94.6(5)-99.7(4)
a
Values in square brackets represent the angles between the pseudo-C3-axis passing through carbon and the C‚‚‚F/C‚‚‚O trajectories.
5
538 J. AM. CHEM. SOC. VOL. 126, NO. 17, 2004
9

Syntheses and Characterization of Carbocations
A R T I C L E S
Figure 1. (a) Crystal structure of [CCl3][Sb(OTeF5)6]; thermal ellipsoids
are shown at the 50% probability level. (b) A view of the CCl3 cation
Figure 2. (a) Crystal structure of [CBr3][Sb(OTeF5)6]‚SO2ClF; thermal
+
+
ellipsoids are shown at the 50% probability level. (b) A view of the CBr3
showing the shortest contacts between carbon and the fluorine atoms of
the Sb(OTeF5)6 anion. (c) A view of the CCl3 cation, showing the two-
fold positional disorder around the crystallographic inversion center.
cation, showing the shortest contacts between carbon and the fluorine atoms
of the Sb(OTeF5)6 anion.
-
+
-
0
.149 Å, respectively. The C-O bond lengths are similar to
and CBr3+ salts and may be responsible for the absence of
disorder in the CBr3 structure.
+
20
+
those in C(OH)3 (1.231(4) Å), CH3C(OH)2 (1.265(6), 1.272-
+
2
9
30
+
(
6) Å; 1.261(7), 1.273(7) Å ), and HC(OH)2 (1.239(6),
.255(5) Å).31 As expected for a positively charged isoelectronic
species, the C-O bond lengths are shorter than the B-O bond
(b) [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF. The crystal struc-
1
ture of [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF consists of
-
Sb(OTeF5)6 anions that are well separated from the cations
6
1
lengths of B(OTeF5)3 (1.358(6) Å), and the C-O-Te bond
angles, which range from 125.7(7) to 132.4(9)°, are similar to
those in B(OTeF5)3 (132.3(4)°). The bond lengths and bond
angles in the OTeF5 groups are in good agreement with those
observed for the OTeF5 groups of the Sb(OTeF5)6 anion and
and the solvent molecules, while two of the three SO2ClF solvent
molecules are oxygen coordinated to the carbon atom of the
cation (Figure 3).
6
1
+
The C(OTeF5)3 cation is isoelectronic and isostructural with
-
61
the known B(OTeF5)3 molecule. To our knowledge, the
4
1,54
other OTeF5 derivatives
and require no further comment.
+
C(OTeF5)3 cation is only the second example of a trioxygen-
The C(OTeF5)3+ cation has two short C‚‚‚O contacts [2.690-
17) and 2.738(18) Å] with two SO2ClF solvent molecules
Figure 3, Table 3), which are both nearly perpendicular to the
substituted carbocation to have been isolated and characterized
in the solid state by X-ray crystallography, the first being the
(
(
-
AsF6 salt of the trigonal planar acidium ion of carbonic acid,
trigonal CO3 plane, approaching the carbon atoms at angles of
and 3° with respect to the pseudo-three-fold symmetry axis
+
20
+
C(OH)3 . The O-C-O angles of the C(OTeF5)3 cation are
equal, within (3σ, to the ideal 120° angle expected for a trigonal
1
of the cation. The contact distances are significantly shorter than
the sum of carbon and oxygen van der Waals radii (3.15,59 3.20
Å) and the C‚‚‚F contacts in [CCl3][Sb(OTeF5)6] and [CBr3]-
+
planar arrangement. Unlike B(OTeF5)3 and C(OH)3 , which
60
have BO3 and CO3 arrangements that are planar by symmetry
(
C3h point symmetry), the planarity of the CO3 moiety of
[
[
(
Sb(OTeF5)6]‚SO2ClF, but are similar to the C‚‚‚F contacts in
(CH3)2CF][AsF6] (2.66(1), 2.78(1) Å) and in [m-CF3C6H4)-
C6H5)CF][AsF6] (2.78(1), 2.79(1) Å). These interactions with
+
C(OTeF5)3 is not forced by symmetry, and the three OTeF5
groups bonded to the central carbon atom are crystallographi-
cally independent. Despite the low local crystallographic sym-
metry of C(OTeF5)3+ (C1), the conformational geometry of the
cation is very close to the optimized C3h gas-phase geometry
of this cation and the known solid-state6 and calculated gas-
6
2-64
the weak Lewis base, SO2ClF,
charge borne by the carbon atom and its substantial Lewis
acidity (see Computational Results for CX3 and BX3).
reflect the high positive
+
1
+
+
Raman Spectroscopy. (a) CCl3 and CBr3 . The vibrational
+
phase (see Computational Results for CX3 and BX3) geometries
+
+
modes of the CCl3 and CBr3 cations were assigned under
of B(OTeF5)3. The tellurium and axial fluorine atoms are slightly
out of plane and lie to one side of the CO3 plane by 0.087 and
(
62) Olah, G. A.; Donovan, D. J.; Lin, H. C. J. Am. Chem. Soc. 1976, 98, 2661.
63) Calves, J.-Y.; Gillespie, R. J. J. Am. Chem. Soc. 1977, 99, 1788.
(
(61) Sawyer, J. F.; Schrobilgen, G. J. Acta Crystallogr. 1982, B38, 1561.
(64) Olah, G. A.; Donovan, D. J. J. Am. Chem. Soc. 1978, 100, 5163.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004 5539

A R T I C L E S
Mercier et al.
-
mental Section). The frequency assignments for the Sb(OTeF5)6
+
anion and unreacted XeOTeF5 cation were made by compari-
son with those of [N(CH3)4][Sb(OTeF5)6] and [SbX4][Sb-
OTeF5)6] (X ) Cl, Br) and [XeOTeF5][AsF6] and [XeOTeF5]-
Sb(OTeF5)6]‚SO2ClF, respectively, and require no further
4
1
54
69
(
[
4
4
comment.
In the CCl4 system, two new bands were observed at 327
-
1
and 554 cm which were assigned to ν1(A1′) and ν4(E′) of
+
CCl3 , respectively, in excellent agreement with the calculated
frequencies and Raman intensities (Table 4). The high-resolution
Raman spectrum of [CCl3][Sb(OTeF5)6] reveals that the ν1(A1′)
band is split into four components that arise from the isoto-
3
5
+
35
37
+
35 37
+
37
+
pomers C Cl3 , C Cl2 Cl , C Cl Cl2 , and C Cl3 (Figure
). The intensities of the isotopomer bands are in excellent
agreement with the intensities calculated from the chlorine
4
35
37
natural isotopic abundances. The experimental Cl/ Cl isotopic
shifts are 5.0-5.3 cm and are in good agreement with the
calculated values (4.8-5.7 cm ) and are larger than the
experimental isotopic shifts of BCl3 (3.9-4.5 cm ) and CCl4
-
1
-
1
-1 67
-
1 70
(
3.2-3.6 cm ). The formally Raman-active ν3(E′) band was
not observed, in accord with the low Raman intensity calculated
for this band at all levels of theory and basis sets used in this
study (Table 4).
The low-temperature Raman spectrum resulting from the
reaction of CBr4 with a stoichiometric excess of [XeOTeF5]-
[
Sb(OTeF5)6] revealed new bands at 183.5, 187.0, and 321.4
-
1
-1
+
cm . The band at 321.4 cm is assigned to ν1(A1′) of CBr3
by comparison with the calculated value, 340 cm (MP2/cc-
pVTZ). The intense bands at 183.5 and 187.0 cm are assigned
to ν4(E′) of CBr3 . The splitting most likely arises from site
Figure 3. (a) Crystal structure of [C(OTeF5)3][Sb(OTeF5)6]‚3SO2ClF;
-
1
thermal ellipsoids are shown at the 50% probability level. (b) A view of
+
-1
the C(OTeF5)3 cation, showing the contacts between the carbon atom and
an oxygen atom from each of two SO2ClF molecules in the crystal lattice.
+
symmetry lowering of this doubly degenerate mode to produce
D3h symmetry and belong to the irreducible representation Γ )
A1′ + A2′′ + 2E′. A total of four fundamental vibrations are
expected, ν1(A1′), ν2(A2′′), ν3(E′), and ν4(E′), of which ν1(A1′),
ν3(E′), and ν4(E′) are Raman active and ν2(A2′′), ν3(E′), and
two Raman-active components. The assignment is supported
-1
by the calculated frequency of 186 cm (MP2/cc-pVTZ). As
+
in the case of CCl3 , the formally Raman-active ν3(E′) band of
+
+
CBr3 was not observed. Unlike CCl3 , where ν3(E′) is predicted
to be consistently weaker in intensity than ν4(E′), the relative
+
ν4(E′) are infrared active. The Raman assignments for the CCl3
+
and CBr3 cations were made by comparison with the calculated
+
Raman intensities of ν3(E′) and ν4(E′) of CBr3 , which are also
frequencies and Raman intensities (Table 4), which were carried
out at the MP2 level using the basis sets 6-31G(2d) and cc-
pVTZ. Calculated frequencies and Raman intensities at the HF
level (Table S1) can be found in the Supporting Information.
As a benchmark, the vibrational frequencies of CCl4 and CBr4
were also calculated with the same basis sets and at the same
levels of theory (Table S2).
predicted to be weak, are found to vary with the level of theory
and basis set used (Table 4) and are therefore difficult to
compare with the experimental Raman intensities. The experi-
+
mental vibrational frequencies of the CX3 cations are in general
found to be comparable to or lower than the calculated values,
a better fit being obtained for the MP2 frequencies (Table 4).
As expected from the observed and calculated C-X and B-X
+
The low-temperature, solid-state Raman spectra of the solids
resulting from the reactions of CCl4 and CBr4 with [XeOTeF5]-
bond lengths, all frequencies are higher for the CX3 cations
than for their BX analogues. The calculated values are also in
3
[
Sb(OTeF5)6] displayed large numbers of bands that could be
very good agreement with experimental infrared data obtained
-
+
+ 14
+ 10
+ 5
assigned to the Sb(OTeF5)6 anion, unreacted XeOTeF5 , and
CBr4 when an excess of CBr4 was used (Table S3). In the case
of CBr4, new bands were also observed in the S-F, S-O, and
C-O stretching regions, which are discussed in the following
section. Although the presence of Br2 could not be ascertained
because the expected bands at 296.5 and 302.5 cm for solid
Br2 overlapped with bands associated with Sb(OTeF5)6 or
unreacted XeOTeF5 , the presence of Br2 was confirmed by a
unit cell determination for solid Br2 at -173 °C (see Experi-
for CI3
(
and the matrix-isolated CF3
and CCl3 cations.
b) C(OTeF5)3+ and B(OTeF5)3. Although B(OTeF5)3 has
been known for some time and limited infrared data have been
71
previously reported, the Raman spectrum is now reported for
the first time (Table 5). The vibrational modes of B(OTeF5)3
were assigned under C3h symmetry and belong to the irreducible
representation Γ ) 11A′ + 9A′′ + 12E′ + 8E′′. A total of 40
fundamental bands are expected, of which the 31 A′, E′, and
E′′ modes are Raman active and the 23 A′′ and E′ modes are
-
1
68
-
+
(
65) Vanderryn, J. J. Chem. Phys. 1959, 30, 331.
(69) Fir, B. A.; Mercier, H. P. A.; Sanders, J. C. P.; Dixon, D. A.; Schrobilgen,
G. J. J. Fluorine Chem. 2001, 110, 89.
(70) Shurvell, H. F. Spectrochim. Acta, Part A 1971, 27, 2375.
(71) Kropshofer, H.; Leitzke, O.; Peringer, P.; Sladky, F. O. Chem. Ber. 1981,
114, 2644.
(
66) Anderson, T. F.; Lassettre, E. N.; Yost, D. M. J. Chem. Phys. 1936, 4,
7
03.
(
(
67) Clark, R. J. H.; Mitchell, P. D. J. Chem. Phys. 1972, 56, 2225.
68) Raman spectrum acquired on a sample of solid bromine at -150 °C.
5540 J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004

Syntheses and Characterization of Carbocations
A R T I C L E S
Table 4. Experimental and Calculated (MP2) Frequencies (cm- ), Raman Intensities and Assignments for CX3 and BX3 (X ) F, Cl, Br, I)
1
a
b
+
+
CF
3
BF
3
assgnts
expt c
6-31G(2d)
cc-pVTZ
expt d
6-31G(2d)
cc-pVTZ
ν1(A1′), νs(CF3)
ν2(A2′′), π(CF3)
ν3(E′), νas(CF3)
ν4(E′), δ(F-C-F)
1048(7)
843(0)
1692(<1)
595(1)
1072(7)
825(0)
1717(<0)
601(1)
888.0
691.5
1453.5
480.4
883(4)
723(0)
1475(<1)
491(<1)
895(4)
698(0)
1484(<1)
481(<1)
798.1
1662.4
+
CCl
3
BCl
3
assgnts
expt
6-31G(2d)
cc-pVTZ
expte
6-31G(2d)
cc-pVTZ
ν1(A1′), νs(CCl3)
ν2(A2′′), π(CCl3)
ν3(E′), νas(CCl3)
ν4(E′), δ(Cl-C-Cl)
554(28)f
559(18)
538(0)
1072(<1)
318(4)
568(17)
541(0)
1086(<1)
317(4)
467.3
447.3
931
477(9)
465(0)
970(<1)
257(3)
483(8)
465(0)
984(<1)
259(2)
i
-
g
h
1035, 1037
326.9(9)
254.5
187.0(12)
+
CBr
3
BBr
3
assgnts
expt
321.4(27)
6-31G(2d)
cc-pVTZ
exptj
6-31G(2d)
cc-pVTZ
ν1(A1′), νs(C-Br)
ν2(A2′′), π(C-Br3)
ν3(E′), νas(C-Br)
ν4(E′), δ(Br-C-Br)
341(13)
461(0)
932(3)
193(3)
340(13)
454(0)
931(2)
186(3)
279.6
377.3
794.4
153.4
292(7)
414(0)
849(<1)
155(1)
292(6)
401(0)
853(<1)
157(2)
i
183.5(15) 187.0(12)
+
CI
3
BI
3
assgnts
exptk
(SDB-)cc-pVTZ
exptj
(SDB-)cc-pVTZ
ν1(A1′), νs(CI3)
ν2(A2′′), π(CI3)
ν3(E′), νas(CI3)
ν4(E′), δ(I-C-I)
240(14)
384(0)
807(14)
127(3)
194.5
307.9
681
203(6)
336(0)
741(<1)
106(2)
i
339, w
739, vs
105.3
a
Values in parentheses denote experimental uncorrected relative Raman intensities (see Table S3 for anion frequencies and intensities) or calculated
4
-1
b
c
d
e
f
Raman intensities (in Å amu ). Frequencies have been calculated and assigned for D3h symmetry. From ref 10. From ref 64. From ref 65. The ν1
3
5
37
35
35
37
35 37
band is split as a result of the mass effect of the Cl and Cl isotopes: 554.1(100) (C Cl3), 549.1(96) (C Cl2 Cl), 544.1(32) (C Cl Cl2), and 538.8(3)
37
-1
g
i
(
C Cl3) cm ; the most intense band has been scaled to 100 (see Figure 4). From ref 6. h From ref 4 and ref 5. Observed as 2ν2(A2′′). j From ref 66.
k
From ref 14.
44
square brackets) SO2ClF: νasym(SO2), 1415, 1407 [1444, 1433,
-
1
-1
1
8
1
427] cm ; νsym(SO2), 1166 [1224, 1219] cm , and ν(SF),
-
1
19 [839] cm (Table S3). Although the bands at 1095 and
-
1
454 cm fall in the range of the calculated νsym(CO3) and
+
-1
νasym(CO3) frequencies for C(OTeF5)3 , 1165 and 1502 cm
(
HF/(SDB)-cc-pVTZ), they could not be definitively assigned
+
to the C(OTeF5)3 cation but could also be associated with the
mixed Br/OTeF5-substituted cations, CBr(OTeF5)2 and CBr2-
(
+
+
OTeF5) , formed in eqs 3-5.
Computational Results for CX3+ and BX3 (X ) F, Cl, Br,
I, OTeF5). Quantum mechanical ab initio calculations have been
+
6,12,14,34,37,72-79
previously reported for the isoelectronic CX3
14,34,80-85
and BX3,
(X ) F, Cl, Br, I) series and related isovalent
species such as AH2X , YH2X (X ) F, Cl, Br, I; A ) C, Si,
+
34
Ge, Sn, Pb; Y ) B, Al, Ga, In, Tl). While results are abundant
Figure 4. Expanded view of the symmetric ν1(A1′) stretching band of CCl3
in the Raman spectrum of [CCl3][Sb(OTeF5)6], showing the natural
abundance chlorine isotope shifts.
1
4,72,74-77,80-85
14,37,72,78-87
for species where X ) F
are relatively sparse for X ) Br,
or Cl,
they
12,14,37,72
or I.12,14,37
infrared active. The vibrational frequencies for C(OTeF5)3+ and
B(OTeF5)3 were calculated at the HF level using the (SDB)-
cc-pVTZ basis set. The assignments for B(OTeF5)3 were made
by comparison with the calculated frequencies and infrared and
Raman intensities, which are in agreement with the experimental
values (Table 5).
The low-temperature spectra resulting from the reaction of
CBr4 with a 2-fold molar excess of [XeOTeF5][Sb(OTeF5)6]
revealed new bands in the high-frequency stretching region. The
majority of these bands can be assigned to coordinated (see
X-ray Crystal Structures) and non-coordinated (frequencies in
(
72) Reynolds, C. H. J. Chem. Soc., Chem. Commun. 1991, 975.
(73) Dixon, D. A.; Feller, D.; Sandrone, G. J. Phys. Chem. A 1999, 103, 4744.
(
74) Ricca, A. J. Phys. Chem. A 1999, 103, 1876.
75) Hansel, A.; Scheiring, C.; Glantschnig, M.; Lindinger, W.; Ferguson, E.
E. J. Chem. Phys. 1998, 109, 1748.
(
(
76) Irikura, K. K. J. Am. Chem. Soc. 1999, 121, 7689.
(77) Basch, H.; Hoz, T.; Hoz, S. J. Phys. Chem. A 1999, 103, 6458.
(78) Rodriquez, C. F.; Bohme, D. K.; Hopkinson, A. C. J. Phys. Chem. 1996,
100, 2942.
(79) Robles, E. S. J.; Chen, P. J. Phys. Chem. 1994, 98, 6919.
(
80) Jonas, V.; Frenking, G.; Reetz, M. T. J. Am. Chem. Soc. 1994, 116, 8741.
81) Chandrakumar, K. R. S.; Pal, S. J. Phys. Chem. A 2002, 106, 11775.
(
(82) Rowsell, B. D.; Gillespie, R. J.; Heard, G. L. Inorg. Chem. 1999, 38, 4659.
(
(
83) Bauschlicher, C. W. J.; Ricca, A. J. Phys. Chem. A 1999, 103, 4313.
84) Fau, S.; Frenking, G. Mol. Phys. 1999, 96, 519.
(85) Brinck, T.; Murray, J. S.; Politzer, P. Inorg. Chem. 1993, 32, 2622.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004 5541

A R T I C L E S
Mercier et al.
Table 5. Calculated Vibrational Frequencies (cm-1) and Infrared
a
for the OTeF5 derivatives were only carried out at the HF level
+
and Raman Intensities for C(OTeF5)3 and B(OTeF5)3 and
Observed Vibrational Frequencies and Infrared and Raman
Intensities for B(OTeF5)3
(see Experimental Section) using the (SDB)-cc-pVTZ basis set.
The methods were benchmarked by calculating the vibrational
frequencies (Table S2), geometries (Table S4), and chemical
shifts of CX4 (see Chemical Shifts and Coupling Constant
+
C(OTeF
5
)
3
5 3
B(OTeF )
calcdb-d
calcdb-d
expt
Raman
expt
infrarede
assgnt
Trends) for which there are well-established experimental values.
(
C
3h
)
(C3h
)
(C3h)
+
(
a) Geometries. Geometry optimization using D3h (CX3 and
1
1
502 (0.2) [1266.5] 1297 (0.1) [1095.2]
165 (0.7) [i.a.] 1066 (3.5) [i.a.]
98 (i.a.) [316.7] 758 (i.a.) [484.5]
85 (0.1) [101.4] 754 (0.3) [272.7]
80 (0.1) [179.2] 770 (0.6) [92.4]
751 (0.2) [i.a.]
77 (i.a.) [133.6] 658 (i.a.) [2.7]
749 (1.5) [i.a.]
731 (21.1) [i.a.]
55 (2.0) [112.9] 716 (1.4) [78.8]
1330, s E′
A′
+
1050(6)
BX3), and C3h (C(OTeF5)3 , B(OTeF5)3) as the initial sym-
7
7
7
7
7
7
7
7
7
7
6
6
4
3
3
3
3
3
3
3
3
3
3
3
2
2
2
2
1
1
1
1
A′′
} 740, vs
E′
metries resulted in stationary points with all frequencies real.
+
All optimized metric parameters for CX3 and BX3 are listed
755(5)
E′
}
in Tables 6 and 7, respectively.
The HF and MP2 calculations give essentially the same results
79 (0.2) [i.a.]
E′′
A′′
A′
A′
77 (1.3) [i.a.]
64 (11.6) [i.a.]
732(5)
716(96)
+
+
+
for CCl3 , CBr3 , CI3 , and the isoelectronic BX3 molecules,
+
while for CF3 and BF3, the MP2 calculations predict slightly
longer bond lengths. The calculated bond lengths of CCl3 ,
725, vs E′
+
12 (32.9) [i.a.]
08 (0.3) [0.8]
82 (2.8) [i.a.]
80 (i.a.) [1.0]
48 (7.5) [i.a.]
88 (0.1) [98.4]
46 (0.1) [i.a.]
31 (0.0) [i.a.]
683 (17.3) [i.a.]
674 (1.2) [7.2]
660 (2.7) [i.a.]
626 (i.a.) [73.6]
474 (10.2) [i.a.]
430 (0.0) [125.3]
355 (0.1) [i.a.]
342 (0.0) [i.a.]
673(100)
702(16)
660(18)
A′
705, s E′
+
+
CBr3 , and CI3 are in good agreement with those obtained
from their X-ray crystal structures. The calculated bond lengths
for all BX3 molecules are also in good agreement with
experiment and the experimental bond length trends, C-X <
B-X, are reproduced for X ) Cl, Br, I.
E′′
615, m A′′
500(44)
A′
430, s E′
A′
338(7)
332(3)
E′′
A′′
A′
E′
E′
A′
E′′
E′
A′′
A′
E′
E′′
A′′
E′′
A′′
A′
28 (i.a.) [191.3] 337 (i.a.) [189.9]
The fully optimized (HF/(SDB)-cc-pVTZ) geometries of
+
25 (2.3) [i.a.]
25 (0.5) [5.1]
21 (0.6) [92.2]
17 (0.0) [i.a.]
11 (1.0) [i.a.]
328 (0.0) [i.a.]
332 (0.7) [46.7]
327 (0.1) [236.3]
315 (2.0) [i.a.]
327 (1.3) [i.a.]
C(OTeF5)3 and B(OTeF5)3 possess C3h symmetry (Figure 5),
325(15)
318(17)
with trigonal planar environments around the central carbon and
boron atoms. The calculated distances are in reasonable agree-
ment with the experimental ones, although they are all slightly
shorter. The calculated C-O-Te, B-O-Te, and OTeF5 group
angles are in good agreement with the observed angles. Overall,
the calculated geometries are in very good agreement with the
}
3
11(18)
}
08 (0.0) [293.9] 314 (0.3) [0.2]
03 (i.a.) [0.0]
60 (0.1) [i.a.]
54 (0.7) [0.3]
16 (0.2) [i.a.]
07 (i.a.) [0.0]
98 (0.0) [i.a.]
98 (i.a.) [0.0]
40 (0.3) [i.a.]
29 (0.1) [0.4]
319 (i.a.) [3.9]
256 (0.3) [i.a.]
247 (0.5) [11.7]
216 (0.0) [i.a.]
214 (i.a.) [0.1]
210 (0.0) [i.a.]
206 (i.a.) [0.6]
143 (0.2) [i.a.]
129 (0.1) [1.1]
77 (0.0) [i.a.]
63 (0.1) [i.a.]
29 (0.0) [0.1]
24 (i.a.) [0.1]
15 (i.a.) [0.0]
16 (0.2) [i.a.]
254(3)
246(7)
+
experimental geometries of the C(OTeF5)3 cation and B(OTeF5)3,
indicating that the two C‚‚‚O contacts with two SO2ClF solvent
molecules in the crystal lattice of [C(OTeF5)3][Sb(OTeF5)6]‚3SO2-
ClF do not have a significant effect on the structure of the cation
in the solid state (see X-ray Crystal Structures). Moreover, the
small distortions of the F-Te-F bond angles from 90° in
140(3)
E′
8
7
3
2
2
2
8 (0.1) [i.a.]
7 (0.1) [i.a.]
5 (0.0) [0.3]
8 (i.a.) [0.2]
0 (i.a.) [0.3]
0 (0.0) [i.a.]
71(5)
56(3)
A′
E′′
E′
A′′
A′′
E′′
+
C(OTeF5)3 and the near-regular OTeF5 groups observed for
B(OTeF5)3 are also reproduced by the calculations.
(b) Natural Bond Orbital (NBO) Analyses. Natural atomic
charges, Mayer natural atomic orbital valencies, and natural
1
59(2)
lattice
modes
+
atomic orbital bond orders between atoms in CX3 , CX4, and
9
8(2), 91(3)
}
BX3, calculated at the MP2 level of theory, are given in Table
84(5)
+
S5 and those calculated for C(OTeF5)3 and B(OTeF5)3, at the
a
HF/(SDB-)cc-pVTZ; calculated frequencies have been scaled by
multiplying the calculated frequencies by 0.890. Raman intensities, in Å
amu , are given in parentheses. Infrared intensities, in km mol , are
given in square brackets. The abbreviation, i.a., denotes an inactive mode.
Experimental values are from ref 70 (KBr, -195 °C). The abbreviations
denote very strong (vs), strong (s), and medium (m) infrared intensities.
HF level of theory, are given in Table 8. Natural atomic orbital
(NAO) populations (Table S6) are given in the Supporting
Information.
b
4
-
1
c
-1
d
e
(i) B-X/C-X σ- and π-Donations and Natural Atomic
Charges. Following previous approaches, bonding at the central
carbon and boron atoms was divided into σ- and π-donation,
and the values obtained agreed well with the previous values
and associated interpretations (see Tables 8 and S5).2
+
The series of trihalomethyl carbocations, CX3 , and boron
trihalides, BX3, (X ) F, Cl, Br, I) have been reinvestigated,
and the calculations have been extended to the related OTeF5
derivatives using all-electron correlation consistent (cc-pVTZ)
basis sets for all atoms other than tellurium and iodine, for which
semi-relativistic large core pseudopotential ((SDB)-cc-pVTZ)
basis sets were used. The geometric parameters and vibrational
frequencies (see Raman Spectroscopy) were calculated, and a
natural bond orbital (NBO) analysis was carried out at the HF
and MP2 levels of theory. Energies for the MP2-optimized
structures were calculated at the QCISD(T) level. Calculations
6,34
The NBO analyses for CX3+ and BX3 (X ) F or OTeF5)
were carried out at the same level of theory (HF/(SDB-)cc-
pVTZ; see Tables 8 and S6), so that both the carbocations and
neutral boron analogues could be compared. The π-donations
from the fluorine or from the oxygen atom of the OTeF5 ligand
+
to the central carbon or boron atom are similar for CX3 (0.15
for X ) F; 0.19 for X ) OTeF5), and BX3, (0.09 for X ) F or
OTeF5). In both cases, the σ-donation from the carbon or boron
atom to the ligand atom decreases when fluorine is replaced by
(
86) Hudgens, J. W.; Johnson, R. D. I.; Tsai, B. P.; Kafafi, S. A. J. Am. Chem.
Soc. 1990, 112, 5763.
+
the OTeF5 group. The charge on the carbon atom of C(OTeF5)3
+
(
87) Tachikawa, H. J. Phys. Chem. A 1997, 101, 7454.
(1.30) is lower than that on the carbon atom of CF3 (1.57),
5542 J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004

Syntheses and Characterization of Carbocations
A R T I C L E S
Table 6. Experimental and Calculated Geometries for CX3+ and BX3
+
CF
3
BF
3
6
-31G(2d)
cc-pVTZ
MP2
6-31G(2d)
cc-pVTZ
HF
MP2
HF
CCSD(T)
expta
HF
MP2
HF
MP2
CCSD(T)
C-F (Å)
F-C-F (deg)
F‚‚‚F (Å)
1.209
120
2.095
1.236
1.208
1.233
1.233
B-F (Å)
F-B-F (deg)
F‚‚‚F (Å)
1.30(2)
1.294
120
2.241
1.315
1.295
1.315
1.313
2.141
2.093
2.135
2.136
2.26(3)
2.277
2.243
2.277
2.274
+
CCl
-31G(2d)
MP2
3
BCl
3
6
cc-pVTZ
MP2
6-31G(2d)
cc-pVTZ
MP2
exptb
1.62(1)
HF
1.645
HF
CCSD(T)
exptc
1.75(2)
HF
MP2
HF
CCSD(T)
C-Cl (Å)
1.654 1.641 1.645
2.865 2.842 2.849
1.655
B-Cl (Å)
1.750 1.750 1.747 1.740
120
1.747
Cl-C-Cl (deg) 119.9(7) 120
Cl-B-Cl (deg)
Cl‚‚‚Cl (Å)
2.805(5) 2.848
2.866
Cl‚‚‚Cl (Å)
2.99(3)a 3.031 3.031 3.025 3.015
3.026
+
CBr
3
BBr
3
6
-31G(2d)
cc-pVTZ
MP2
6-31G(2d)
MP2 HF
cc-pVTZ
exptb
HF
MP2
HF
CCSD(T)
expt
HF
MP2
CCSD(T)
C-Br (Å)
1.81(2)
1.800 1.803 1.808 1.801
1.816
B-Br (Å)
Br-B-Br (deg)
Br‚‚‚Br (Å)
1.893(5)d 1.896 1.888 1.910 1.891
120
1.901
Br-C-Br (deg) 120.0(9) 120
Br‚‚‚Br (Å)
3.129(3) 3.117 3.123 3.132 3.120
3.145
3.25(3)a
3.284 3.270 3.308 3.275
3.293
+
CI
3
BI
3
(
SDB)-cc-pVTZ
(SDB)-cc-pVTZ
MP2
expte
HF
MP2
CCSD(T)
expt
HF
CCSD(T)
C-I (Å)
I-C-I (deg)
I‚‚‚ I (Å)
2.013(9)
120.0(5)
3.486(8)
2.001
3.466
1.990
2.007
B-I (Å)
I-B-I (deg)
I‚‚‚I (Å)
2.112(8)f
120.0(9)
3.659
2.117
120
3.667
2.092
2.105
f
3.447
3.477
3.624
3.646
a
From ref 87. b Average values, present work. c From ref 88. d From ref 89. e From ref 14. f From ref 90, the I‚‚‚I contact distance was calculated from
the published coordinates.
a
+
Table 7. Calculated and Experimental Geometries for C(OTeF5)3 and B(OTeF5)3
+
C(OTeF
5
)
3
(C3h
)
5 3
B(OTeF ) (C3h)
exptb
calcd
exptc
calcd
bond lengths (Å)d
C(1)-O(1)
Te(1)-O(1)
Te(1)-F(1)
Te(1)-F(2)
Te(1)-F(3)
1.28(3)
1.98(1)
1.81(1)
1.81(2)
1.81(2)
1.256
1.945
1.765
1.778
1.771
B(1)-O(1)
Te(1)-O(1)
Te(1)-F(1)
Te(1)-F(2)
Te(1)-F(3)
1.358(6)
1.874(6)
1.822(6)
1.809(4)
1.818(4)
1.354
1.833
1.785
1.790
1.785
+
C(OTeF
5
)
3
(C3h
)
5 3
B(OTeF ) (C3h)
exptb
calcd
exptc
calcd
bond angles (deg)d
135.27
C(1)-O(1)-Te(1)
O(1)-Te(1)-F(1)
O(1)-Te(1)-F(2)
O(1)-Te(1)-F(3)
F(1)-Te(1)-F(2)
F(1)-Te(1)-F(3)
F(2)-Te(1)-F(3)
F(2)-Te(1)-F(4)
F(2)-Te(1)-F(5)
129.8(1)
175.9(6)
90.2(9)
84.7(9)
92.6(9)
92.6(9)
89.9(9)
90.0(9)
174.8(9)
B(1)-O(1)-Te(1)
O(1)-Te(1)-F(1)
O(1)-Te(1)-F(2)
O(1)-Te(1)-F(3)
F(1)-Te(1)-F(2)
F(1)-Te(1)-F(3)
F(2)-Te(1)-F(3)
F(2)-Te(1)-F(4)
F(2)-Te(1)-F(5)
132.3(4)
178.0(3)
92.6(2)
137.32
180.00
91.88
89.56
89.12
89.44
89.87
90.12
178.56
180.00
88.43
85.50
92.75
93.32
89.76
89.68
173.92
88.8(2)
89.0(2)
90.2(2)
91.2(2)
a
HF/(SDB-)cc-pVTZ. b Experimental values are averaged values. c From ref 60. d The atom numbering scheme corresponds to that of the equivalently
+
labeled OTeF5 group of the C(OTeF5)3 cation in Figure 3, where F(1) is the axial fluorine and F(2-5) are the equatorial fluorines. In the calculated
structure, the F(2)/F(4) and the F(3)/F(5) pairs are related by symmetry.
and the overall charge of the OTeF5 group (-0.10) is somewhat
(ii) Mayer Bond Orders and Natural Atomic Orbital
Valencies for C(OTeF5)3 and B(OTeF5)3. The B-O bond
+
+
lower than that of fluorine in CF3 (-0.12). The lower positive
+
charge on the carbon atom of C(OTeF5)3 is consistent with
order and valencies at the boron and oxygen atoms are lower
92
+
the lower electronegativity of the OTeF5 group. In both
for B(OTeF5)3 than the corresponding values of C(OTeF5)3 ,
+
C(OTeF5)3 and B(OTeF5)3, the charges on the central atom
(
(
88) L e´ vy, H.; Brockway, L. O. J. Am. Chem. Soc. 1937, 59, 2085.
89) Spencer, C.; Lipscomb, W. N. J. Chem. Phys. 1958, 28, 355.
(90) Konaka, S.; Ito, T.; Morino, Y. Bull. Chem. Soc. Jpn. 1966, 39, 1146.
are lower and that on the ligand is more positive when compared
+
with the atomic charges of CF3 and BF3, respectively.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004 5543

A R T I C L E S
Mercier et al.
a
Table 8. Calculated Natural Atomic Charges, Mayer Bond
Orders, and Mayer Natural Atomic Orbital Valencies for
+
C(OTeF5)3 and B(OTeF5)3
+
(C3h)b
C(OTeF
5
)
3
charge
valency
bond order
C
O
Te
FA
FB
FB′
1.30
-0.86
4.07
-0.65
-0.67
-0.66
-0.10
3.04
1.33
3.19
0.53
0.49
0.51
C-O
1.01
0.45
0.56
0.54
0.55
Te-O
Te-FA
Te-FB
Te-FB′
overall OTeF5
pπ populations at C (O)
σ donation (π donation)c
0.56 (1.80)
0.28 (0.19)
+
CF
3
(D3h
)
charge
valency
bond order
0.89
C
F
1.57
-0.19
2.66
0.82
C-F
pπ populations at C (F)
σ donation (π donation)c
0.46 (1.83)
0.34 (0.15)
B(OTeF
5
)
3
(C3h)b
charge
valency
bond order
B
O
Te
FA
FB
FB′
1.45
-1.15
4.08
-0.68
-0.68
-0.68
-0.48
2.18
1.22
3.22
0.49
0.48
0.49
B-O
0.73
0.58
0.53
0.52
0.53
Te-O
Te-FA
Te-FB
Te-FB′
Figure 5. Experimental (left) and calculated (right) geometries for (a) the
+
C(OTeF5)3 cation and (b) the B(OTeF5)3 molecule (experimental structure
from ref 61).
overall OTeF5
indicating somewhat less double bond character. These observa-
tions are also reflected in the π donation which is lower for
BrO (0.09) than for CrO (0.19). At the HF level, the B-F
bond order and valencies at boron and fluorine are also lower
pπ populations at B (O)
σ donation (π donation)c
0.27 (1.88)
0.57 (0.09)
BF
3
(D3h
)
charge
valency
bond order
0.84
+
for BF3 than the corresponding values for CF3 . The difference
B
F
1.56
-0.52
2.53
0.80
B-F
between the valencies at boron in BF3 and in B(OTeF5)3 is 0.35,
which is almost the same as the difference between the valencies
pπ populations at B (F)
σ donation (π donation)c
0.26 (1.91)
0.61 (0.09)
+
+
at carbon in CF3 and in C(OTeF5)3 , 0.38. These trends
+
+
indicate that the electronic properties of C(OTeF5)3 /CF3 and
a
HF/(SDB-)cc-pVTZ. b The symbols, FA and FB/FB′ denote axial and
equatorial fluorine atoms, where FB and FB′ are nonequivalent under C3h
symmetry. c The value given is per bond; a negative sign indicates donation
in reversed order.
B(OTeF5)3/BF3 are similar.
Chemical Shift and Coupling Constant Trends. The 13C
+
+
chemical shifts of the CCl3 and CBr3 cations are significantly
deshielded with respect to their parent tetrahalomethanes (Table
2
µ
4µB
). The 13C resonance of CI3 has also been shown to be
+
o
1
-3
-3
σp ≈ -
[〈r 〉 P + 〈r 〉 D ]
(14)
( )(
)
np
i
nd
i
12,13
strongly deshielded with respect to CI4 (Table 9).
Electronic
4π ∆E
1
3
structure calculations (MP2/(SDB-)cc-pVTZ) reveal that the
C
where µ is the magnetic moment for a given nucleus, µ is the
Bohr magneton, ∆E is the mean excitation energy, 〈r 〉 and
np
o
B
-3
1
3
deshielding that results from carbocation formation, ∆δ( C),
parallels the decrease in the natural atomic charge on carbon
relative to the carbon charge in the tetrahalide (Table S5). This
-
3
〈r 〉 are the inverse cube roots of the mean expectation values
for the p and d orbital distances from the nucleus, and P and
D are the degrees of imbalance of valence electrons in p and d
orbitals, respectively. The approach, a one-center approximation,
is restricted to terms centered on the nucleus in question. As
the bond length contracts in going from the neutral halide (Table
S4) to the cation (Table 6), the mean expectation value of the
inverse cube of the 2p orbital radius of carbon in eq 14 is
expected to increase. The bond length contraction and con-
comitant increase in 〈r 〉2p results in a more negative para-
magnetic contribution to the overall nuclear magnetic shielding
term of carbon and, in turn, to a high-frequency C chemical
shift. Similar trends are noted for the isoelectronic boron
trihalides, BX3, and the tetrahaloborates, BX4 (X ) F, Cl,
nd
i
+
+
+
reduction in negative charge (CCl3 , 0.10; CBr3 , 0.10; CI3 ,
.26) does not, however, fully account for the extent of
deshielding, ∆δ( C) (CCl3 , +140.7 ppm; CBr3 , +239.4 ppm;
i
0
13
+
+
+
13
CI3 , +389.3 ppm), observed in the C NMR spectra. The
shielding changes can be rationalized in terms of the paramag-
p
netic shielding contribution (σ ) to the overall screening of the
1
3
C nucleus (σ) in the Ramsey equation (eq 13),
-
3
p
d
σ ) σ + σ
(13)
1
3
where σd is the diamagnetic shielding contribution. The
paramagnetic term in the Ramsey equation is negative and can
be interpreted in terms of the atom-in-a-molecule approach as
defined in eq 14,
9
4
-
9
7
Br, I).
There are significant discrepancies between the experimental
B and C NMR chemical shifts of BX3 and CX3 and those
1
1
13
+
(
91) Albert, B.; Schmitt, K. Z. Anorg. Allg. Chem. 2001, 627.
(
92) Birchall, T.; Myers, R. D.; de Waard, H.; Schrobilgen, G. J. Inorg. Chem.
(93) DeMarco, R. A.; Fox, W. B.; Moniz, W. B.; Sojka, S. A. J. Magn. Reson.
1975, 18, 522.
1
982, 21, 1068.
5544 J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004

Syntheses and Characterization of Carbocations
A R T I C L E S
a
+
Table 9. Experimental and Calculated Chemical Shifts for CX3 and BX3 (X ) F, Cl, Br, I, OTeF5) and CX4 (X ) F, Cl, Br, I)
13Cb
19Fc
expt
(150.7)f
6-31G(d)d,e
cc-pVTZd,e
expt
6-31G(d)d,e
cc-pVTZd,e
CF3+
-
155.5
249.8
304.9
154.5
254.8
312.8
436.4
-
32.1
32.9
+
d
g
CCl3
CBr3
237.1 (236.3)
+
d
g
209.7 (207)
+
h
g
CI3
97
(95)
13Cb
19Fc
exptd
SDB-cc-pVTZd,e
exptd
-57.6 (FA)
31.6 (FB)
SDB-cc-pVTZd,e
C(OTeF5)3+
168.8
139.5
-132.7 (FA)
-107.3 (FB)
-
13Cb
19Fc
expt
6-31G(d)d,e
cc-pVTZd,e
exptd
6-31G(d)d,e
cc-pVTZd,e
CF4
CCl4
CBr4
CI4
(119.9)i
119.6
132.1
139.1
-
123
137
142
93
-62.4
-88.8
-76.2
d
96.4
-29.7j
d
-292.3
11Bk
19Fc
exptl,m
-22.9
SDB-cc-pVTZd,e
exptm
SDB-cc-pVTZd,e
B(OTeF5)3
75.4
-48.2 (FA)
44.4 (FB)
-62.8 (FA)
-53.4 (FB)
-
11Bk
19Fc
exptn
6-31G(d)d,e
cc-pVTZd,e
expt
6-31G(d)d,e
cc-pVTZd,e
BF3
BCl3
BBr3
BI3
10.0
46.5
38.7
-7.9
30.8
73.1
92.8
24.0
68.8
73.1
-126.8o
-132.5
-125.6
-
-
-
117.8
a
+
Chemical shifts were calculated at the B3LYP/6-311G(d)//HF/6-31G(d) and B3LYP/(SDB-)cc-pVTZ//HF/(SDB-)cc-pVTZ levels for CX3 , CX4 and
BX3, and at the B3LYP/(SDB-)cc-pVTZ//HF/(SDB-)cc-pVTZ level for C(OTeF5)3 and B(OTeF5)3. b Referenced to TMS. c Referenced to CFCl3. Present
work. The predicted chemical shifts reported here have been obtained by subtracting their absolute values from that of their respective reference compound,
+
d
e
1
3
19
i.e., TMS ( C), 180.9969 ppm (Td, 6-311G*) and 181.2543 ppm (Td, (SDB-)cc-pVTZ); CFCl3 ( F), 167.9485 ppm (C3V, 6-311G*) and 183.9397 ppm (C3V,
1
1
f
13
(
SDB-)cc-pVTZ); F3BO(C2H5)2 ( B), 123.7710 ppm (C3V, 6-311G*) and 116.3587 ppm (C3V, cc-pVTZ). From ref 13. g From ref 12. h From ref 14. i
C
j
k
l
11
From ref 92. From ref 93. referenced to B(OCH3)3. The B chemical shift quoted in the literature (ref 70) was referenced to B(OCH3)3 and converted
to the B chemical shift referenced to F3BO(C2H5)2 by subtraction of 18.3 ppm. From ref 70. n The B spectra were recorded in methyl cyclohexane
1
1
m
11
o
at 33.5 °C (ref 94). From ref 95.
97
calculated by the GIAO method (B3LYP/(SDB-)cc-pVTZ) for
the heavier halides (Table 9). The calculated 11B and C NMR
chemical shifts show monotonic increases from BCl3 to BI3 and
versus halogen electronegativity for BX4, BX3,97 CX4,100 and
CX3
13
+ 13
are near linear for X ) Cl, Br, and I, it has been pointed
out that such trends are fortuitous, and are, in fact, attributable
to the SO coupling term. The B chemical shift of BF3 and
the predicted C chemical shift of CF3 cannot be understood
in terms of the high electronegativity of fluorine, nor can they
be understood in terms of the traditional notion that high
shielding arises from p(π) back-donation to the boron
carbon atom from the fluorine atoms. Electronic structure
+
+
37
11
from CCl3 to CI3 (inverse halogen effects), which contrast
with the observed trends of decreasing chemical shift upon
descending group 17 (Table 9). The calculated chemical shift
trends arise from larger paramagnetic contributions expected
for increasingly more covalent interactions between the central
atom and the halogen atom upon descending group 17. The
discrepancies between the calculated and experimental chemical
shifts, however, result from neglect of the effect of spin-orbit
1
3
+
101,102
or
1
2
calculations, however, reveal that the p(π) back-bonding
components in BF3 and CF3 are weakest among their respective
+
(
SO) coupling on the overall nuclear shielding, which is not
trihalide series (Table S5). Thus, the increased shieldings
experienced by the boron and carbon nuclei are actually the
normal behavior and arise from the highly ionic characters of
the B-F and C-F bonds, which lead to large ∆E values and
smaller paramagnetic contributions to their respective nuclear
shieldings (eq 14).
The 13C chemical shift of C(OTeF5)3+ (168.8 ppm) is in good
agreement with values reported for other peroxygen-substituted
9
8
taken into account by the original Ramsey equation. Spin-
orbit coupling causes a triplet excitation on the heavy atom,
which, in turn, is transmitted to a neighboring atom through
the bond. As previously shown, inclusion of the SO-correction
increases the shielding calculated for boron and carbon bonded
to bromine or iodine and results in good agreement with
3
7,99
1
1
13
99
observed B and C NMR chemical shifts for the BX3 and
CX3
+
37
11
13
series. Although plots of B and C chemical shifts
(
99) Kaupp, M. Relativistic Effects on NMR Chemical Shifts. In RelatiVistic
Electronic Structure Theory II: Applications; Schwerdtfeger, P., Ed;
Elsevier: Amsterdam, 2004. In press.
(
94) Lappert, M. F.; Litzow, M. R.; Pedley, J. B.; Tweedale, A. J. Chem. Soc.
A 1971, 2426.
(95) Branchadell, V.; Oliva, A. J. Mol. Struct. (THEOCHEM) 1991, 236, 75.
(96) Coyle, T. D.; Stone, F. G. A. J. Chem. Phys. 1960, 32, 1892.
(97) Hartman, S.; Schrobilgen, G. J. Inorg. Chem. 1972, 11, 940.
(98) Morishima, I.; Endo, K.; Yonezawa, T. J. Chem. Phys. 1973, 59, 3356.
(100) Malkin, V. G.; Malkina, O. L.; Salahub, D. R. Chem. Phys. Lett. 1996,
261, 335.
(101) Onak, T.; Landesman, H.; Williams, R. E.; Shapiro, I. J. Phys. Chem.
1959, 63, 1533.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004 5545

A R T I C L E S
carbocations (C(OH)3 , 166.8 ppm; C(OCH3)OH2 , 164.1
Mercier et al.
+
20
+
center, these observations are consistent with cation formation,
and the trends across the CBrn(OTeF5)3-n series can be
correlated with increasing covalent character of the C-O bond
1
9
+
ppm ). The experimental carbon deshielding relative to that of
1
3
C(OTeF5)4 (∆δ( C), 53.0 ppm) is consistent with cation
+
formation, and follows the trend predicted for CF3 /CF4 (∆δ-
with increasing bromine substitution.
1
3
(
C), 30.8 ppm). This result indicates that the C-O bonding
Conclusions
+
in C(OTeF5)3 is highly ionic, as expected from the estimated
9
2
high electronegativity of the -OTeF5 group (3.87), leading
to a small paramagnetic contribution to the overall nuclear
shielding and, thus, to a relatively shielded 13C nucleus. This
ionic character is supported by electronic structure calculations
The present study provides a new oxidative route to carboca-
tions and the first solid-state characterization of the previously
reported CCl and CBr3 cations as well as that of the novel
+
+
3
+
C(OTeF5)3 cation. The cations have been stabilized as salts of
(
HF/(SDB-)cc-pVTZ; vide supra) which show that the charge
the preformed, oxidatively resistant, and weakly coordinating
Sb(OTeF5)6 anion, which avoids the use of more strongly
coordinating anions derived from strong Lewis acid ligand
+
-
on the carbon of the C(OTeF5)3 cation (+1.30) is nearly equal
to that of CF3 (+1.37), which is consistent with the C NMR
empirically predicted (150.7 ppm) and calculated (167.9, 169.2
ppm; 154.5 ppm, this work) C chemical shifts for the CF3
cation.
+
13
13
acceptors, such as SbF . Despite their anticipated high electro-
5
1
3
13
+
philicity, these salts have appreciable stabilities at or near room
+
+
temperature. In addition, the CBr(OTeF5)2 and Br(OTeF )
5 2
1
3
+
13
The C resonance of CBr(OTeF5)2 was observed at 187.6
5 4
cations and C(OTeF ) have been characterized by C and/or
F NMR spectroscopy. NMR spectroscopy has also been used
+
19
ppm, but that of CBr2(OTeF5) was not observed. The chemical
shift of CBr2(OTeF5) was predicted from pairwise additivity
relationships (eq 15),9
+
to monitor carbocation formation, ligand substitution by means
of redox elimination, and decomposition pathways in these
systems.
7,103
δ )
∑ηi,j
(15)
X-ray crystallographic studies show, in all cases, that the
carbocation center is planar in the absence of symmetry
constraints imposed by the crystal lattice. Despite the strong
where ηi,j is a parameter associated with the carbon substituents
i and j and independent of all other substituents. The pairwise
additivity parameters ηBr,Br (69.9 ppm), ηOTeF ,OTeF (56.3 ppm),
and ηBr,OTeF (65.6 ppm) were evaluated from the experimental
chemical shifts of CBr3 , CBr(OTeF5)2 , and C(OTeF5)3 . In
+
Lewis acidities predicted for perhalomethyl cations, the CCl3
+
5
5
and CBr3 cations are well isolated in their respective crystal
5
lattices and possess only long secondary C‚‚‚F contacts to
+
+
+
-
fluorine atoms of the Sb(OTeF5)6 anion that do not significantly
+
this way, the chemical shift of CBr2(OTeF5) is predicted to
be 201.1 ppm from eq 16.
exceed the sum of the van der Waals radii of carbon and
fluorine. Secondary X‚‚‚F and X‚‚‚O (X ) Cl, Br) contacts that
are close to the sums of the van der Waals radii of the halogen
and an oxygen atom of cocrystallized SO2ClF or a fluorine atom
13
δ( C) ) η
+ 2ηBr,OTeF5
(16)
Br,Br
+
+
of the anion exist for CCl3 and CBr3 that are in accord with
the calculated positive charges on the halogen atoms of both
cations.
The 19F NMR data for CBrn(OTeF5)3-n+ are provided in
1
9
Table 1. Previous attempts have been made to correlate the
NMR trends observed for the OTeF5 group in different chemical
environments.4
F
Computational studies reproduce the experimental metric
5,104
The trends observed in the present study are
+
+
+
parameters of CCl3 , CBr3 , and C(OTeF5)3 , and the vibra-
1
9
in good agreement with the previously noted trends in
F
+
+
tional frequencies of CCl3 and CBr3 , and have been extended
to their -OTeF5 derivatives.
2
19
19
chemical shift and J( FA- FB); however, some significant
differences occur for OTeF5 bound to carbocation centers: (1)
The 19F chemical shifts of the equatorial fluorine environments
of CBrn(OTeF5)3-n have a substantially broader chemical shift
range (-31.6 to -19.9 ppm) than the axial fluorine environ-
ments (-61.3 to -57.6 ppm), contrasting with the ranges
Contrasting with the CCl3 and CBr3+ cations, the C(OTeF5)3+
cation possesses two short C‚‚‚O contacts to the oxygen atoms
of two weakly basic, cocrystallized SO2ClF molecules, which
is consistent with the high positive charge on carbon predicted
by electronic structure calculations, and which approximates the
+
+
19
19
observed for neutral ( FB, -56.6 to -36.7 ppm; FA, -54.6
+
positive charge calculated for the highly Lewis acidic CF3
104
to -27.8 ppm) OTeF5-substituted compounds.
(2) The
cation.
2
19
19
J( FA- FB) values range from 156 to 164 Hz, which is
significantly smaller than the previously observed range for
neutral and anionic species (175-195 Hz).1 Moreover, the
decrease in coupling in going from the neutral species to the
Experimental Section
04
Apparatus and Materials. Manipulations of volatile materials were
carried out on a glass vacuum line, while nonvolatile materials were
+
cation also holds for BrOTeF5 (180 Hz) and the Br(OTeF5)2
54
handled inside a drybox as previously described. All reaction vessels
1
19
123,125
1
19
cation (164 Hz). (3) The J( FA-
Te) and J( FB-
1
were fabricated from /
4
-in. o.d. FEP tubing, joined to Kel-F valves by
123,125
Te) couplings increase substantially in going from C(OTeF5)4
to C(OTeF5)3 , from CBr(OTeF5)2 to CBr2(OTeF5) , and from
BrOTeF5 to Br(OTeF5)2 (Table 1). Furthermore, the magnitude
means of compression fittings, and were dried under vacuum for several
hours prior to passivation with 1 atm of fluorine gas for 8-12 h. All
vacuum-line connections were made by use of /
+
+
+
+
1
4
-in. stainless steel
Cajon Ultratorr unions fitted with Viton O-rings. Sulfuryl chloride
fluoride, SO ClF, (Allied Chemical) was purified by use of the literature
method.1 Carbon tetrachloride (BDH Chemicals) was dried for several
days over CaH and distilled into a glass vessel fitted with a 4-mm J.
of the coupling increases to the greatest extent on going from
C(OTeF5)3 to CBr2(OTeF5) . Although there are no other
systematic studies involving OTeF5 ligands bound to a cation
+
+
2
05
2
(102) Good, C. D.; Ritter, D. M. J. Am. Chem. Soc. 1962, 84, 1162.
(103) Vladimiroff, T.; Malinowski, E. R. J. Chem. Phys. 1967, 46, 1830.
(104) Seppelt, K. Angew. Chem., Int. Ed. Engl. 1982, 21, 877.
(105) Schrobilgen, G. J.; Holloway, J. H.; Granger, P.; Brevard, C. Inorg. Chem.
1978, 17, 980.
5546 J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004

Syntheses and Characterization of Carbocations
A R T I C L E S
(270
Young glass/Teflon stopcock prior to use. Carbon tetrabromide
and allowed to react at -20 °C for ca. 3 h. In the case of CCl
Torr, 0.00337 g, 0.0219 mmol), SO ClF was vacuum distilled onto
[XeOTeF ][Sb(OTeF ] (0.04152 g, 0.02159 mmol), followed by
condensation of CCl onto the mixture at -196 °C.
(ii) C(OTeF ) . Inside the drybox, 0.05568 g (0.1679 mmol) of solid
4
(
Aldrich) was purified by sublimation at ca. 60 °C under dynamic
vacuum. The compound, BrOTeF , was prepared and purified as
previously described. The synthesis and structural characterization
of [XeOTeF ][Sb(OTeF ] will be described in a forthcoming publica-
tion. Because [XeOTeF ][Sb(OTeF ] undergoes decomposition at
2
5
5
5 6
)
4
3
4
5
5 6
)
5
4
4
4
5
5
)
6
CBr was transferred to an NMR tube, followed by removal from the
4
temperatures approaching ambient, the compound was manipulated
inside a drybox using low-temperature procedures as previously
drybox and connection to a glass vacuum line, where SO ClF solvent
(0.4-0.5 mL) was statically distilled under vacuum onto the solid at
2
1
06
described.
Raman Spectroscopy. (a) Raman Sample Preparation. (i) [CCl
Sb(OTeF ]. Inside the drybox, 0.07141 g (0.0371 mmol) of
XeOTeF ][Sb(OTeF ] at -120 °C was transferred by use of a
-78 °C. A stoichiometric amount of BrOTeF (0.21818 g, 0.6850
5
3
]-
mmol) was then vacuum distilled into the sample tube at -196 °C.
[
5
)
6
5 2 5 6 5
(iii) [Br(OTeF ) ][Sb(OTeF ) ]. Inside the drybox, [XeOTeF ][Sb-
[
5
5
)
6
(OTeF ] (0.10124 g, 0.05264 mmol) was transferred at -120 °C to
5 6
)
1
precooled syringe for solids into a 25-cm long /
4
-in. o.d. FEP reaction
an NMR sample tube kept at the same temperature. The sample was
vessel maintained at -120 °C. The cold reaction vessel was closed
with a Kel-F valve, and the contents were then removed from the
drybox, immediately placed in a -78 °C bath, and connected to a glass
removed from the drybox, immediately cooled to -78 °C, and
connected to a glass vacuum line, and 0.4-0.5 mL of SO
condensed onto the sample under static vacuum at -78 °C. A
stoichiometric excess of BrOTeF (0.02347 g, 0.0737 mmol) was then
2
ClF was
vacuum line, where SO
the reaction vessel under static vacuum at -196 °C. A stoichiometric
amount of CCl vapor (470 Torr, 0.00586 g, 0.0381 mmol) was
2
ClF solvent (ca 1.5 mL) was condensed into
5
vacuum distilled into the tube at -196 °C.
(b) NMR Intrumentation and Spectral Acquisition. Nuclear
4
measured into a calibrated bulb (1.488 mL) and then condensed into
the reactor under static vacuum at -196 °C. Warming to -78 °C
resulted in rapid reaction which was indicated by a color change from
a bright yellow to a colorless solution and by evolution of xenon gas.
The solvent was removed under vacuum at -78 °C, and the Raman
spectrum of the resulting white powder was acquired.
magnetic resonance spectra were recorded unlocked (field drift < 0.1
Hz h ) on a Bruker DRX-500 spectrometer equipped with an 11.744
T cryomagnet. For low-temperature work, the NMR probe was cooled
-
1
using a nitrogen flow and variable-temperature controller (BV-T 3000).
The 19F (13C) NMR spectra were obtained using a 5-mm combination
1H/19F (broad-band inverse) probe operating at 470.592 (125.758) MHz.
(
ii) [CBr
drybox, 0.06860 g (0.0357 mmol) of [XeOTeF
.01666 g (0.0503 mmol) of CBr
were loaded into a 1/
4
3
][Sb(OTeF
5
)
6
] and [C(OTeF
5
)
3
][Sb(OTeF
][Sb(OTeF
-in. o.d. FEP
5
)
6
]. Inside the
The spectra were recorded in 64 (32) K memories, with a spectral width
setting of 24 (38) kHz, yielding a data point resolution of 0.36 (1.15)
Hz/data point and acquisition times of 1.39 (0.436) s. A relaxation delay
of 0.1 (1-10) s was applied, and 2000 (1000-10000) transients were
typically accumulated using a pulse width of 2.5 (6) µs, corresponding
to a bulk magnetization tip angle, θ, of approximately 90°. A line-
broadening of 0.7 (5) Hz was used in the exponential multiplication of
5
5 6
) ] and
0
4
reaction vessel at -120 °C. The valved reaction vessel and contents
were then removed cold from the drybox and immediately placed in a
78 °C bath and connected to a glass vacuum line, where SO ClF
2
solvent (ca 1.5 mL) was condensed into the reactor under static vacuum.
Upon warming, the reaction proceeded rapidly at -78 °C to give xenon
gas and a red-brown solution, which changed over time (ca. 4-5 h) to
a red-orange solution. The solvent was removed under vacuum at -78
-
1
9
the free induction decays prior to Fourier transformation. The F and
13
C NMR spectra were referenced externally at 30 °C to samples of
neat CFCl and TMS, respectively. The chemical shift convention used
3
°
C, and the Raman spectrum of the resulting white powder was
is that a positive (negative) sign indicates a chemical shift to high (low)
frequency of the reference compound.
acquired.
(
b) Raman Instrumentation and Spectral Acquisition. The low-
X-ray Crystallography. (a) Crystal Growth of [CCl
(OTeF ], [CBr ][Sb(OTeF ]‚SO ClF, and [C(OTeF ][Sb(OTeF
3SO ClF. Crystals of [CCl ][Sb(OTeF ] were obtained by reaction
of ca. 0.2 g of [XeOTeF ][Sb(OTeF ] and a 2-fold molar excess of
CCl in 1.5 mL of SO ClF inside a T-shaped /
vessel. Crystals were grown by slow cooling of the reaction mixture
from -20 to -50 °C over a period of 6 h inside the vertical arm of the
reaction vessel. Colorless, plate-shaped crystals were isolated by
decanting the solvent into the horizontal arm, followed by drying under
3
][Sb-
temperature (-160 °C) Raman spectra of microcrystalline samples
5
)
6
3
5
)
6
2
5
)
3
5
)
6
]‚
resulting from the reaction of CCl
OTeF ] were recorded on a Bruker RFS 100 FT Raman spectrometer
using 1064-nm excitation and a resolution of 1 cm as previously
described. The spectra were recorded using a laser power of 300
mW and a total of 1200 scans.
4
and CBr
4
with [XeOTeF
5
][Sb-
2
3
5 6
)
(
)
5 6
5
5 6
)
-
1
1
4
2
4
-in. o.d. FEP reaction
1
06
Nuclear Magnetic Resonance Spectroscopy. (a) NMR Sample
Preparation. All NMR samples were prepared in 5-mm o.d. thin wall
precision glass NMR tubes (Wilmad) fused to /
glass tubing which were in turn attached to 4-mm J. Young Teflon
stopcocks by use of /
with Viton O-rings. The NMR tubes were then vacuum-dried for 8-12
h before use. Reactions between [XeOTeF ][Sb(OTeF ] and the
starting reagent(s) were carried out in SO ClF solvent at -78 °C for
ca. 2 h. The NMR tubes were then flame sealed under dynamic vacuum
at -196 °C and stored at the same temperature prior to acquisition of
the NMR spectra.
1
dynamic vacuum at -78 °C. The crystals were mounted as previously
4
-in. o.d. lengths of
described.1 Crystals of [CBr
06
][Sb(OTeF
ClF (colorless), and Br
crystals were grown and isolated in a manner analogous to that
described above for [CCl ][Sb(OTeF ]. Bromine was identified by
)
]‚SO
ClF (pale yellow),
3
5
6
2
1
[C(OTeF
5
)
3
][Sb(OTeF
5
)
6
]‚3SO
2
2
(red brown)
4
-in. stainless steel Cajon Ultratorr unions fitted
5 6
)
3
5 6
)
5
1
07,108
determination of the unit cell parameters
selected from the bulk sample.
at -173 °C for a crystal
2
(
b) Crystal Mounting and X-ray Data Collection. All crystals were
106
mounted at -100 ( 3 °C as previously described, and centered on
a P4 Siemens diffractometer, equipped with a Siemens SMART 1K
CCD area detector, controlled by SMART,1 and a rotating anode
emitting KR radiation monochromated (λ ) 0.71073 Å) by a graphite
crystal. Diffraction data collection (-173 °C) consisted of a full
ψ-rotation at ø ) 0° (using 1040 + 30) 0.3° frames, followed by a
series of short (100 frames) ω scans at various ψ and ø settings to fill
the gaps. The crystal-to-detector distance was 5.012 cm, and the data
(
i) [CX
amounts of solid [XeOTeF
and CBr (0.01091 g, 0.0329 mmol) were weighed into an NMR tube
in the drybox and transferred to a glass vacuum line, where 0.4-0.5
mL of SO ClF was vacuum distilled onto the mixture at -78 °C. To
enhance the yield of [C(OTeF ][Sb(OTeF ], BrOTeF was condensed
onto the sample of [CBr ][Sb(OTeF ] (see eqs 2-6) in a 3:1 mole
ratio based on initial amounts of [XeOTeF ][Sb(OTeF ] and CBr
3
][Sb(OTeF
5
)
6
] (X ) Cl, Br, OTeF
5
). Stoichiometric
09
5
][Sb(OTeF ] (0.04134 g, 0.0215 mmol)
5 6
)
4
2
)
5 3
)
5 6
5
3
5 6
)
5
5
)
6
4
(
107) Vonnegut, B.; Warren, B. E. J. Am. Chem. Soc. 1936, 58, 2459.
108) Powell, B. M.; Heal, K. M.; Torrie, B. H. Mol. Phys. 1984, 53, 929.
(
(
106) Gerken, M.; Dixon, D. A.; Schrobilgen, G. J. Inorg. Chem. 2000, 39,
(109) SMART, release 5.054, and SAINT, release 6.01; Siemens Energy and
4
244.
Automation Inc.; Madison, WI, 1999.
J. AM. CHEM. SOC.
9
VOL. 126, NO. 17, 2004 5547

A R T I C L E S
Mercier et al.
collection was carried out in a 512 × 512 pixel mode using 2 × 2
(d) and B3LYP/(SDB-)cc-pVTZ//HF/(SDB-)cc-pVTZ levels using
gauge-independent atomic orbital method (GIAO) as implemented in
Gaussian 98.
pixel binning. Processing of the raw data was completed using
109
SAINT+, which applied Lorentz and polarization corrections to three-
dimensionally integrated diffraction spots. The program SADABS1
was used for the scaling of diffraction data, the application of a decay
correction, and an empirical absorption correction on the basis of the
intensity ratios of redundant reflections.
10
Natural orbital analyses were performed using HF or MP2 densities
with the NBO program (versions 3.1 and 5.0).1 The use of a
pseudopotential basis set instead of an all-electron basis set was tested,
and the overall results did not differ significantly, as pointed out
13
c) Solution and Refinement of the Structure. The XPREP111
114
(
previously.
program was used to confirm the unit cell dimensions and the crystal
lattices. The solutions were obtained by direct methods, which located
Acknowledgment. This paper is dedicated to our friend and
colleague Professor Ronald J. Gillespie on the occasion of his
80th birthday and in recognition of his many outstanding
contributions across a broad spectrum of chemistry. We thank
the Natural Sciences and Engineering Research Council (NSERC)
of Canada for the award of a postgraduate scholarship (M.D.M.)
and for support in the form of a research grant (G.J.S.). We
also thank the Finnish IT Center for Science for the use of their
computing resources (R.J.S.) and Prof. K. O. Christe for helpful
discussions relating to the preparation of this manuscript.
-
+
the positions of the atoms defining the Sb(OTeF
5
)
6
anions, the CBr
3
+
+
and C(OTeF
)
5 3
2
cations and SO ClF molecules. In the case of the CCl
3
salt, the difference Fourier map was obtained after solutions by direct
+
methods revealed a trigonal planar CCl
3
cation positioned close to
the inversion center, which gave rise to a two-fold positional disorder.
+
The site occupancy factors of all the atoms defining the CCl
3
cation
were therefore set to 0.5. The final refinement was obtained by
introducing anisotropic thermal parameters and the recommended
weight for most of the atoms. The maximum electron densities in the
final difference Fourier map were located near the heavy atoms.
All calculations were performed using the SHELXTL-plus package1
for the structure determination and solution refinement and for the
molecular graphics.
11
Supporting Information Available: Experimental and cal-
+
culated Raman frequencies and intensities for CX3 and BX3
(X ) F, Cl, Br, I) at the HF and MP2 levels (Table S1).
Calculations. Electronic structure calculations were carried out at
the HF, MP2 (for geometry optimizations, Natural Bond Orbital
analysis, vibrational frequencies and intensities) and CCSD(T) (for
single-point energies at the MP2 geometries) levels of theory using
the program Gaussian-98 (version A-11).112 The standard all-electron
Experimental and calculated Raman frequencies and intensities
for CX4 (X ) F, Cl, Br, I) (Table S2). Raman frequencies and
assignments for [CCl3][Sb(OTeF5)6] and [CBr3][Sb(OTeF5)6]
and related species (Table S3). Experimental and calculated
geometrical parameters and NBO study for CX4 (X ) F, Cl,
Br, I) (Table S4). Calculated natural atomic charges, Mayer bond
6
-31G(2d) and cc-pVTZ basis sets as implemented in the Gaussian
program were utilized for all elements except Te and I, for which the
semirelativistic large core (RLC) pseudopotential basis set (SDB-)cc-
pVTZ was used. The combined use of cc-pVTZ and (SDB-)cc-pVTZ
basis sets is indicated as (SDB-)cc-pVTZ. Nuclear magnetic resonance
shielding tensors were calculated at the B3LYP/6-311G(d)//HF/6-31G-
+
orders, and Mayer natural atomic orbital valencies for CX ,
3
CX4, and BX3 (X ) F, Cl, Br, I) (Table S5). Valence NAO
+
populations for CX3 and BX3 (X ) F, Cl, Br, I, OTeF5) and
CX4 (X ) F, Cl, Br, I) (Table S6). The X-ray crystallographic
files in CIF format for the structure determinations of [CCl3]-
[Sb(OTeF5)6], [CBr3][Sb(OTeF5)6]‚SO2ClF, and [C(OTeF5)3]-
(
(
(
110) Sheldrick, G. M. SADABS (Siemens Area Detector Absorption Correc-
tions), personal communication, 1998.
111) SHELXTL-Plus, release 5.1; Siemens Analytical X-ray Instruments, Inc.:
Madison, WI, 1998.
[Sb(OTeF5)6]‚3SO2ClF. This material is available free of charge
112) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.;
Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.; Rag-
havachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul, A.
G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
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5548 J. AM. CHEM. SOC.
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