Syntheses, solution multi-NMR characterization, and reactivities of [C 6F5Xe]+ salts of weakly coordinating borate anions, [BY4]- (Y = CF3, C6F 5, CN, or OTeF5</s

Article abstract of DOI:10.1021/ic7010138

New examples of [C₆F₅Xe]⁺ salts of the weakly coordinating anions [B(CF₃)₄]^_, [B(C₆F₅)₄]^-, [B(CN) ₄]^-, and [B(OTeF₅

Full text of DOI:10.1021/ic7010138

Inorg. Chem. 2007, 46, 9425−9437
Syntheses, Solution Multi-NMR Characterization, and Reactivities of
+
-
[C6F5Xe] Salts of Weakly Coordinating Borate Anions, [BY4] (Y
C6F5, CN, or OTeF5)
) CF3,
Karsten Koppe,†,‡ Vural Bilir,† Hermann-J. Frohn,*,† He´le`ne P. A. Mercier,‡ and Gary J. Schrobilgen*,‡
Anorganische Chemie, UniVersita¨t Duisburg-Essen, Lotharstrasse 1, D-47048 Duisburg, Germany,
and Department of Chemistry, McMaster UniVersity, Hamilton, Ontario L8S 4M1, Canada
Received May 24, 2007
New examples of [C6F5Xe]+ salts of the weakly coordinating anions [B(CF3)4]-, [B(C6F5)4]-, [B(CN)4]-, and
[B(OTeF5)4]- have been synthesized by metathesis reactions of [C6F5Xe][BF4] with the corresponding MI[BY4]
salts (MI
) K or Cs; Y ) CF3, C6F5, CN, or OTeF5). The salts were characterized in solution by multi-NMR
spectroscopy. Their stabilities in prototypic solvents (CH3CN and CH2Cl2) and decomposition products are reported.
The influence of the coordinating nature of [BY4]- on the decomposition rate of [C6F5Xe]+ as well as the presence
of the weakly nucleophilic [BF4]- ion has been studied. The electrophilic pentafluorophenylation of C6H5F by
[C6F5Xe][BY4] in solvents of different coordinating abilities (CH3CN and CH2Cl2) and the effects of stronger nucleophiles
(fluoride and water) on the pentafluorophenylation process have been investigated. Simulations of the 19F and
129Xe NMR spectra of [C6F5Xe]+ have provided the complete set of aryl 19F
and their relative signs. The 19F NMR parameters of the [C6F5Xe]+ cation in the present series of salts are shown
to reflect the relative degrees of cation solvent interactions.
− −
19F and 129Xe 19F coupling constants
−
Introduction
is a nucleophilic anion such as [C6F5CO2]-,6 Cl-,7 or F- 8,9
that forms a strong ion contact (donor-acceptor) interaction
with [RXe]+, leading to R-Xe-L molecules that possess
asymmetric 3c-4e bonds.
Presently, three types of organo groups, R, have been
shown to form organoxenonium salts, [RXe][A] (R ) aryl,1-5
alkenyl,10-13 and alkynyl14-16). The majority of the presently
known xenonium salts have an aryl group bonded to XeII.
The chemistry of xenon-carbon compounds was initiated
in 1989 when two independent investigations of the reaction
between XeF2 and B(C6F5)3 led to the syntheses and
characterizations of [C6F5Xe][(C6F5)nBF4-n] (n ) 1, 2, and
3) and the first documented example of a C-Xe bond.1-3
The development of xenon-carbon chemistry has been
previously reviewed.4,5 In the case of XeII-C compounds,
two classes of compounds are known; (1) [RXe][A], where
[A]- is a weakly coordinating anion in which the C-Xe bond
of the cation is a 2c-2e bond, and (2) R-Xe-L, where [L]-
(6) Frohn, H.-J.; Klose, A.; Henkel, G. Angew. Chem., Int. Ed. Engl. 1993,
32, 99-100.
(7) Frohn, H.-J.; Schroer, T.; Henkel, G. Angew. Chem., Int. Ed. 1999,
38, 2554-2556.
(8) Frohn, H.-J.; Theissen, M. Angew. Chem., Int. Ed. 2000, 39, 4591-
4593.
* To whom correspondence should be addressed. E-mail: h-j.frohn@
uni-due.de (H.-J.F.), schrobil@mcmaster.ca (G.J.S.).
†Universita¨t Duisburg-Essen.
(9) Maggiarosa, N.; Naumann, D.; Tyrra, W. Angew. Chem., Int. Ed. 2000,
39, 4588-4591.
(10) Frohn, H.-J.; Bardin, V. V. J. Chem. Soc., Chem. Commun. 1993,
1072-1074.
‡McMaster University.
(1) Naumann, D.; Tyrra, W. J. Chem. Soc., Chem. Commun. 1989, 47-
(11) Frohn, H.-J.; Bardin, V. V. Z. Anorg. Allg. Chem. 2003, 629, 2465-
50.
2469.
(2) Frohn, H.-J.; Jakobs, S. J. Chem. Soc., Chem. Commun. 1989, 625-
627.
(3) Frohn, H.-J.; Jakobs, S.; Henkel, G. Angew. Chem., Int. Ed. Engl.
1989, 28, 1506-1507.
(4) Frohn, H.-J.; Bardin, V. V. Organometallics 2001, 20, 4750-4762.
(5) Tyrra, W.; Naumann, D. Organoxenon Compounds. In Inorganic
Chemistry Highlights; Meyer, G., Naumann, D., Wesemann, L., Eds.;
Wiley-VCH: Weinheim, Germany, 2002; pp 297-317.
(12) Frohn, H.-J.; Adonin, N. Yu.; Bardin, V. V. Z. Anorg. Allg. Chem.
2003, 629, 2499-2508.
(13) Frohn, H.-J.; Bardin, V. V. MendeleeV Commun. 2007, 17, 137-138.
(14) Zhdankin, V. V.; Stang, P. J.; Zefirov, N. S. J. Chem. Soc., Chem.
Commun. 1992, 578-579.
(15) Frohn, H.-J.; Bardin, V. V. Chem. Commun. 2003, 2352-2353.
(16) Frohn, H.-J.; Bardin, V. V. Eur. J. Inorg. Chem. 2006, 19, 3948-
3953.
10.1021/ic7010138 CCC: $37.00
Published on Web 09/29/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 22, 2007 9425

Koppe et al.
[C6F5Xe][BF4] + MI[BY4] 20 to -40 °C8 [C6F5Xe][BY4] +
MI[BF4]V (2)
CH3CN
The syntheses of organoxenonium salts are generally carried
out under acidic conditions, which entail acid-assisted
fluorine/organo group substitution (xenodeborylation) starting
from XeF2 and an acidic borane, RBF2.
As a consequence of the electrophilic character of the
xenonium cation, the organo group bonded to XeII and the
counteranion must fulfill specific criteria: (1) the R group
and the counteranion of the [RXe]+ salt must be resistant to
oxidation by XeII, which can be achieved by use of electron-
withdrawing substituents such as F, Cl, CF3, or NO2, and
(2) the R group must resist the inductive effect of XeII in
the σ skeleton. The C6F5 group fulfills these criteria and
yields the most stable [RXe]+ salts. Moreover, the extended
π system of the C6F5 group, in combination with the electron-
poor nature of the carbon skeleton, results in sufficient
polarization of the [C6F5Xe]+ π system to develop a partial
negative charge on the ipso-carbon atom, which leads to
strengthening of the C-Xe bond by means of electrostatic
contributions.17
In order to meet criteria (1) and (2) and to arrive at
[C6F5Xe]+ salts having properties that approach those of the
[C6F5Xe]+ cation in the gas phase, a series of [C6F5Xe]+
salts of the weakly coordinating borate anions, [BY4]- (Y
) CF3, C6F5, CN, or OTeF5), have been synthesized and
their stabilities and reactivities have been investigated. The
detailed structures and bonding of the [C6F5Xe][BY4] (Y )
CF3, C6F5, or CN) salts will be described in a forthcoming
paper.
salts, [C6F5Xe][BY4] (Y ) CF3 or CN) and [C6F5XeNCCH3]-
[BY4] (Y ) C6F5), were obtained as pale-yellow solids, but
attempts to isolate solid [C6F5Xe][B(OTeF5)4] from CH3CN/
CH2Cl2, CH2Cl2, CH3CN/PFB, or PFB solutions failed
because the product separated as a yellow oil when the
solutions were cooled.
Thermoanalytical studies showed that the [B(C6F5)4]- and
[B(CF3)4]- salts have significantly lower thermal stabilities
in the solid state than the [B(CN)4]-, [BF4]-, and [AsF6]-
salts (Table 1). Both [C6F5Xe][BF4] and [C6F5Xe][AsF6] melt
without decomposition, whereas the [B(CN)4]-, [B(C6F5)4]-,
and [B(CF3)4]- salts decompose without melting.
The solubilities of [C6F5Xe][BF4] and [C6F5Xe][BY4] in
the weakly coordinating solvents, CH2Cl2, DCE, and PFB
as well as in CH3CN were determined to provide the
solubility database (Table S1) required for solution stability
studies (see Solution Stabilities of [C6F5Xe][BY4]). Among
the series of [C6F5Xe][BY4] salts discussed here, the solubil-
ity behavior of the [B(CN)4]- salt is most similar to that of
the [BF4]- salt. The solubility of [C6F5Xe][B(CN)4] is ∼4.3
mmol mL-1 in CH3CN at 20 °C compared with ∼4.8 mmol
mL-1 for the [BF4]- salt, whereas both salts are insoluble in
CH2Cl2, DCE, PFB, C6H5F, and SO2ClF. Salts having four
fluoroorganic groups in the anion such as [C6F5Xe][B(CF3)4]
and [C6F5XeNCCH3][B(C6F5)4] have satisfactory solubilities
in CH3CN and low solubilities in halogenated hydrocarbons.
Results and Discussion
The most efficient way to form a [C6F5Xe]+ salt, which
can serve as the starting material for other [C6F5Xe]+ salts
and is easy to handle at ambient temperature, is by means
of the xenodeborylation reaction of XeF2 with C6F5BF2
(eq 1).18 The reaction of equivalent amounts of XeF2 and
(b) Solution Stabilities of [C6F5Xe][BY4]; Solvent and
Counteranion Dependencies. The thermal stabilities of
[C6F5Xe][BY4] solutions were compared for different borate
salts in different solvent media at 20 °C. The [C6F5XeNCCH3]-
[B(C6F5)4] salt is highly unstable in CH2Cl2 at 20 °C;
consequently, this system was studied at -40 °C. When
possible, the stabilities of the [C6F5Xe][BY4] salts were
compared with that of [C6F5Xe][BF4] in the same solvent.
The extent of [C6F5Xe]+ conversion, expressed in mole
percent, was determined from the integrated 19F NMR
spectral intensities of [C6F5Xe]+ and the C6F5-containing
products. The reaction products are expressed in mole percent
of C6F5 products. These quantities and their corresponding
reaction times are provided in Table 2, with specific entries
from this table indicated in the ensuing discussion.
(i) [C6F5Xe][BF4]. The higher stabilities of [C6F5Xe]+ salts
in acidic media relative to basic media have been generally
recognized;18 however, rigorous comparisons of their relative
stabilities were not available. In the case of [C6F5Xe][BF4],
the cation does not undergo significant solvolysis in aHF at
-40 °C.
CH2Cl2
XeF2 + C6F5BF2
8 [C6F5Xe][BF4]
(1)
-50 °C
C6F5BF2 in CH2Cl2 at -50 °C yields pure [C6F5Xe][BF4] in
80-90% yield. The salt is a pale-yellow solid and is soluble
in CH3CN and anhydrous HF (aHF) but insoluble in the polar
and weakly coordinating solvents CH2Cl2, CF3CH2CF2CH3
(PFB), C6H5F, ClCH2CH2Cl (DCE), and SO2ClF.
[C6F5Xe]+ Salts with Weakly Coordinating [BY4]- (Y
) CF3, C6F5, CN, or OTeF5) Anions. (a) Syntheses by
Metathesis, Solid-State Stabilities, and Solubilities. Sat-
isfactory solubilities of the starting material, [C6F5Xe][BF4],
and the products, [C6F5Xe][BY4], in combination with the
low solubility of MI[BF4] (MI ) K or Cs) in CH3CN (5 mmol
L-1 at room temperature; negligible at -40 °C) made
CH3CN the preferred solvent for the metathesis reactions
described in eq 2 and allowed the preparation of the hitherto
unknown [C6F5Xe][BY4] salts and their isolation in nearly
quantitative yields (90-100%) and very high purities. The
Among the [C6F5Xe]+ salts examined in aprotic solvents
during this comparative study, [C6F5Xe][BF4] solutions in
CH3CN are the most stable and solutions of [C6F5Xe][BF4]
in aHF were found to be even more stable. After 54 days,
only 15% of [C6F5Xe]+ had decomposed to C6F6 in aHF
(entry 5b), whereas a comparable conversion was only
(17) Frohn, H.-J.; Klose, A.; Schroer, T.; Henkel, G.; Buss, V.; Opitz, D.;
Vahrenhorst, R. Inorg. Chem. 1998, 37, 4884-4890.
(18) Frohn, H.-J.; Franke, H.; Bardin, V. V. Z. Naturforsch. 1999, 54b,
1495-1498.
9426 Inorganic Chemistry, Vol. 46, No. 22, 2007

[C6F5Xe]+ Salts of Weakly Coordinating Borate Anions
Table 1. Melting Points and Decomposition Temperatures of
[C6F5Xe][BY4] (Y ) CF3, C6F5, or CN), [C6F5Xe][BF4], and
[C6F5Xe][AsF6]
Xe-C bond (eq 13), and electron transfer (eq 14)
to give the observed products (eq 15). Abstraction of [CF3]-
[C6F5Xe]+ + CH2Cl2 f [C6F5Xe-ClCH2Cl]+ f C6F5 +
•
mp, °C
decomp temp, °C
[C6F5Xe]+ salt
Tonset
Tmax
Tonset
Tmax
[Xe-ClCH2Cl]•+ (13)
[B(CF3)4]-
[B(C6F5)4]- a
[B(CN)4]-
[BF4]-
121.2
85.2
125.0
85.5
[XeClCH2Cl]•+ f Xe0 + [CH2Cl2]•+
f
152.2
156.6
159.2
154.8
180.5
182.7
79.5
109.8
85.8
CHCl2 + H+
(14)
•
[AsF6]-
112.2
solv
a This salt contains the [C6F5XeNCCH3]+ cation.
•
C6F5 + CH2Cl2 f C6F5Cl (C6F5H) +
achieved in CH3CN after 18 days and resulted in exclusive
formation of C6F5H (entry 5c). Although the HF molecule
can coordinate to the XeII center through fluorine, this
interaction is expected to be weaker than CH3CN coordina-
tion and leads to C6F6, Xe0, and [H(HF)n][BF4]. Thus, the
exclusive formation of C6F5H in CH3CN is consistent with
the initial coordination of CH3CN to the positively charged
xenon center and rapid homolytic cleavage of the Xe-C
bond (eqs 3-7). The absence of HF and C6F6 shows that
the main decomposition channel arose from CH3CN coor-
dination and not from [BF4]- coordination (eqs 8-11).
CH2Cl• (CHCl2 ) (15)
•
or F- from [B(CF3)4]- by “[C6F5]+” or [C6F5Xe]+ is ruled
out in CH3CN or CH2Cl2 solvents because neither C6F5CF3
nor C6F6 was detected. Clearly, [C6F5Xe][B(CF3)4] is sig-
nificantly more stable in PFB (entry 1c) than in CH2Cl2, with
a decomposition rate that is approximately one-fourth of that
in CH2Cl2. Two unidentified C6F5-containing products were
formed in PFB (total, ∼4 mol %) in addition to C6F6.
(iii) [C6F5XeNCCH3][B(C6F5)4]. The stabilities and
reaction pathways are markedly different in the case
of [C6F5XeNCCH3][B(C6F5)4]. Acetonitrile solutions of
[C6F5XeNCCH3][B(C6F5)4] were completely decomposed
after 20 days with the formation of C6F5H (85%) and (C6F5)2
(15%) (entry 2a). The stability of [C6F5XeNCCH3][B(C6F5)4]
in CH2Cl2 was strongly dependent on the temperature. At
20 °C, the salt completely decomposed in less than 20 min,
forming C6F5H (46%) and (C6F5)2 (9%), and the balance
(45%) was comprised of a mixture of [(C6F5)3BF]-, B(C6F5)3,
and [C6F5BF3]- (superimposed spectra prevented integration),
resulting from anion decomposition, whereas at -40 °C, only
4% of the cation was converted to C6F5H after 16 h (entry
2b). The stability of [C6F5XeNCCH3][B(C6F5)4] in DCE at
20 °C was significantly greater than that in CH2Cl2, with
only 85% of the cation consumed after 1 h, forming only
C6F5H (entry 2c). The solvent, CH2ClCH2Cl molecule [ꢀ )
10.7 (20 °C); IP ) 11.1 eV], is more polar than CH2Cl2 [ꢀ
) 8.9 (25 °C); IP ) 11.4 eV], and both solvents have
comparable ionization potentials (IPs).
[C6F5Xe]+ + CH3CN f [C6F5Xe-NCCH3]+ f C6F5 +
•
[Xe-NCCH3]•+ (3)
[XeNCCH3]•+ f Xe0 + [CH3CN]•+
(4)
(5)
(6)
(7)
[CH3CN]•+ f CH2CN• + H+
solv
C6F5 + CH3CN f C6F5H + •CH2CN
•
2•CH2CN f NCCH2CH2CN
[C6F5Xe]+ + [BF4]- f C6F5XeFBF3 / C6F5XeF + BF3 (8)
C6F5XeF f C6F6 + Xe
(9)
(10)
(11)
C6F5XeF f C6F5 + XeF•
•
XeF• + CH3CN f HF + Xe0 + •CH2CN
The higher polarity and coordinating ability of DCE
apparently hinders the interaction of [C6F5Xe]+, after elimi-
nation of CH3CN (eq 16), with nucleophilic sites of the
[B(C6F5)4]- anion and accounts for the absence of (C6F5)2
at 20 °C.
The formation of (C6F5)2 is clearly associated with the
[B(C6F5)4]- anion because none of the other [C6F5Xe][BY4]
salts considered in this study give rise to this product, which
most likely results from attack of [C6F5Xe]+ on the anion
(eq 17), with (C6F5)2 resulting from decomposition of the
intermediate, Xe(C6F5)2 (eq 18). In contrast with the revers-
ible step of Lewis acid elimination in eq 8, an irreversible
elimination of B(C6F5)3 is probable according to eq 17. The
dominant product deriving from intrinsically unstable
Xe(C6F5)2 is, however, C6F5H (eqs 19 and 20). The relative
(ii) [C6F5Xe][B(CF3)4]. The decomposition of [C6F5Xe]-
[B(CF3)4] was complete in CH3CN after 43 days, and C6F5H,
the only C6F5-containing product, and HF (56 mol % relative
to C6F5H) were the sole products (entry 1a), whereas in
CH2Cl2, 50% of the cation decomposed within 22 days,
forming C6F5Cl (80%) and C6F5H (20%) (entry 1b). De-
composition in CH3CN is likely initiated by coordination of
CH3CN, as previously described (eqs 3-6). The formation
of HF is indicative of anion decomposition according to eq
12.
H+solv/[B(CF3)4]- / (CF3)3BCF2 + HF
(12)
The weakly coordinating solvent, CH2Cl2, is capable of
coordinating to strong Lewis acid centers.19 Thus, the
decomposition sequence may be initiated by solvent coor-
dination to [C6F5Xe]+, subsequent homolytic cleavage of the
(19) Seggen, D. M. V.; Hurlburt, P. K.; Anderson, O. P.; Strauss, S. H.
Inorg. Chem. 1995, 34, 3453-3464.
Inorganic Chemistry, Vol. 46, No. 22, 2007 9427

Koppe et al.
Table 2. Solution Stabilities of [C6F5Xe][BY4] (Y ) CF3, C6F5, CN, or OTeF5) and [C6F5Xe][BF4] at 20 °C and Their C6F5-Containing Decomposition
Products
time,a
days
C6F5 products (mol %)c
derived from [C6F5Xe]+
entry
[C6F5Xe]+ salt
[B(CF3)4]-
solvent
% conversionb
1a
1b
1c
2a
2b
CH3CN
CH2Cl2
PFB
CH3CN
CH2Cl2
CH2Cl2
DCE
43
22
8
100
50
4
100
100
4
85
100
72
C6F5H (100)d
C6F5H (20), C6F5Cl (80)
C6F6 (6), C6F5X (31),e C6F5Y (63)f
C6F5H (85), (C6F5)2 (15)
C6F5H (46), (C6F5)2 (9), C6F5-B species (45)
C6F5H (100)
[B(C6F5)4]-g
20
0.010(3)
0.667(6) (-40 °C)
0.042(3)
2c
3a
4a
C6F5H (100)
[B(CN)4]-
CH3CN
CH3CN
71
C6F5H (100)h
[B(OTeF5)4]-
25
24
C6F5H (94), C6F5Z (6)i
and OTeF5 compds
4b
CH2Cl2
81
C6F5H (81), C6F5Cl (14), C6F5Z (5)j
and OTeF5 compds
5a
5b
5c
6a
6b
[BF4]-
CH3CN
aHF
CH3CN
CD3CN
CD2Cl2
58
54
18
2
79
15
15
100
100
C6F5H (100)
C6F6 (100)
C6F5H (100)
[B(CF3)4]- + [N(C4H9)4][BF4]k
C6F5H (∼100), C6F5D (traces)
18
C6F5H (64), C6F5D (18), C6F5Cl (18)
a The precision is (0.5 days for all entries except 2b and 2c, where the error on the last digit is indicated in parentheses. b Conversion of the [C6F5Xe]+
cation and relative molar amounts of C6F5-containing products are in mole percent. c The integrated intensities given in parentheses are relative to the total
C6F5-containing species in the sample. d HF (56). e Unknown product: δ(19F) ) -143.0 (o), -154.7 (p), -163.1 (m) ppm. f Unknown product: δ(19F) )
-143.1 (o), -155.2 (p), -162.5 (m) ppm. g This salt contains the [C6F5XeNCCH3]+ cation. h Unassigned singlets also occurred at -144.9 (0.10) and -181.3
(0.42) ppm. i Unknown C6F5 species: δ(19F) ) -138.1 (o), -151.0 (p), -161.3 (m) ppm; unassigned resonances also occurred at -130.6 and -136.7 ppm.
j Unknown C6F5 species: δ(19F) = -137.5 (o), -150.4 (p), -160.8 (m) ppm; unassigned resonances also occurred at -126.9 and -134.9 ppm. k Equimolar
amounts of [C6F5Xe][B(CF3)4] and [N(C4H9)4][BF4] were used.
ratios of C6F5H to (C6F5)2 in CH3CN and CH2Cl2 at 20 °C
are very similar, whereas C6F5H is formed exclusively in
DCE.
into account. In a weakly basic solvent such as CH2Cl2, the
radical lifetime is very short at low temperatures, and solvent
attack occurs with the exclusive formation of C6F5H.
(iv) [C6F5Xe][B(CN)4]. The decomposition rate of
[C6F5Xe][B(CN)4] in CH3CN at 20 °C (entry 3a) was among
the slowest encountered in this study and is similar to that
of the [BF4]- salt in CH3CN (entry 5a). After 71 days, the
cation had been consumed, with C6F5H being the only C6F5-
containing product. In addition, two unassigned singlets were
observed [δ(19F) ) -144.9 and -181.3 ppm].
(v) [C6F5Xe][B(OTeF5)4]. The stability of [C6F5Xe]-
[B(OTeF5)4] (entries 4a and 4b) was significantly greater than
that of [C6F5XeNCCH3][B(C6F5)4] (entries 2a and 2b),
especially in CH2Cl2. The conversion of [C6F5Xe][B(OTeF5)4]
was 72% (81%) in CH3CN (CH2Cl2) after 25 (24) days, with
94% (81%) C6F5H as the major product and 6% (5%) of an
unknown C6F5- compound as the minor product. In addition,
a significant amount of C6F5Cl (14%) was formed as a
decomposition product in a CH2Cl2 (eqs 13-15). The
decomposition pathway that led to C6F5H in CH3CN is
similar to that represented by eqs 3-6. The formation of
C6F5Cl can be explained by analogy with the decomposition
of [C6F5Xe][B(CF3)4] (eqs 13-15) in CH2Cl2. Low-intensity
overlapping AB4 patterns corresponding to different OTeF5-
containing species were also obtained in CH3CN and CH2Cl2.
(c) Reactions of [C6F5Xe][BY4] Salts with the π Nu-
cleophile, C6H5F. The reactions of [C6F5Xe][AsF6] with
monosubstituted benzenes, C6H5X (X ) CH3, F, CN, CF3,
or NO2; 1.0-1.7 equiv), in CH3CN at 20 °C have been
previously reported.22 In addition to isomeric mixtures of
the polyfluorobiphenyls, C6F5-C6H4X, traces or minor
amounts of C6F5H were obtained as products. Reaction rates
[C6F5XeNCCH3]+ / [C6F5Xe]+ + CH3CN
(16)
[C6F5Xe]+ + [B(C6F5)4]- f C6F5XeC6F5B(C6F5)3 f
Xe(C6F5)2 + B(C6F5)3 (17)
Xe(C6F5)2 f Xe0 + (C6F5)2
(18)
(19)
Xe(C6F5)2 f Xe0 + 2 C6F5
•
•
C6F5 + CH3CN (CH2Cl2) f C6F5H (C6F5H) +
•CH2CN (•CHCl2) (20)
The reaction pathway leading to (C6F5)2 is supported by
prior studies that have shown that, while the [B(C6F5)4]-
anion is generally classified as a weakly coordinating anion,
this anion, with relatively open tetrahedral geometry and rigid
C6F5 groups,1 highly electron-withdrawing substituents, and
decreased negative charge on the ipso-carbon atom, is still
susceptible to [C6F5]- abstraction by metal cation centers.20,21
The proposed intermediate, Xe(C6F5)2, is supported by its
independent synthesis and characterization.8,9 Acetonitrile
solutions of Xe(C6F5)2 have been shown to decompose within
24 h at -40 °C to mainly (C6F5)2 and trace amounts of
•
C6F5H.9 Under these conditions, the C6F5 radical does not
readily abstract an acidic hydrogen from a basic solvent such
as CH3CN, indicating that radical solvation as well as
•
resonance stabilization of the C6F5 radical must be taken
(20) Walker, D. A.; Woodman, T. J.; Hughes, D. L.; Bochmann, M.
Organometallics 2001, 20, 3772-3776.
(21) Bochmann, M.; Sarsfield, M. J. Organometallics 1998, 17, 5908-
5912.
(22) Bardin, V. V.; Frohn, H.-J.; Klose, A. J. Fluorine Chem. 1993, 64,
201-215.
9428 Inorganic Chemistry, Vol. 46, No. 22, 2007

[C6F5Xe]+ Salts of Weakly Coordinating Borate Anions
Table 3. Reactivities of [C6F5Xe][BY4] (Y ) CF3, C6F5, and CN), [C6F5Xe][BF4], and [C6F5Xe][AsF6] with C6H5F at 20 °C and Their
C6F5-Containing Reaction Products
time,a
days
equiv of
C6H5Fb
%
entry
[C6F5Xe]+ salt
[B(CF3)4]-
solvent
CH3CN
conversion
C6F5-C6H4Fc
C6F5H
C6F5X
1a
1b
2
5
100
100
89
100
100
100
100
82
100
100
100
100
96
31/29/38
33/30/37
32/30/37
33/30/37
33/30/37
32/30/38
32/30/38
18/19/22
33/30/37
10/8/12
32/30/38
32/30/38
32/30/38
32/30/38
9/9/13
0.010(3)
6
6
15
18
4
CH2Cl2
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH2Cl2
C6H5F
[B(C6F5)4]- d
[B(CN)4]-
[BF4]-
e2
3
20
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
}
}
[AsF6]-
[B(CF3)4]-
1.62(2)
1.2
64
100
41
31
[B(CF3)4]-
0.069(3)
<0.010(3)
0.250(6)
<0.017(3)
0.792(6)
0.017(3)
0.021(3)
<0.010(3)
[B(C6F5)4]- d
C6H5F
X ) C6F5 (39)
[BF4]- + H2Oe
[BF4]- + 20 H2Oe
[AsF6]- + H2Oe
[AsF6]- + 20 H2Oe
C6F5XeF
CH3CN
CH3CN
CH3CN
CH3CN
20
88
46
100
CH2Cl2, -40 °C
11
20
33
15
X ) Cl (36)
X ) C6F5 (5)
[B(C6F5)4]- d + [N(CH3)4]Ff
CH2Cl2, -55 °Cg
22/32/26
a The precision is (0.5 days for all entries except 1b and 5b-9b, where the error on the last digit is indicated in parentheses. b Prepared from freshly
distilled C6H5F that had been dried over P4O10. c The ratio of 2/3/4 isomers is given in mole percent. d This salt contains the [C6F5XeNCCH3]+ cation. e The
relative molar amounts of the [C6F5Xe]+ salt and H2O are indicated. f Equimolar amounts of [C6F5Xe][B(C6F5)4] and [N(CH3)4]F were used. g Both starting
materials were combined at -55 °C and allowed to warm to 20 °C.
were shown to decrease with an increase in the electron-
withdrawing character of X and varied from 1.25 to 42 h
for complete conversion of [C6F5Xe][AsF6].
In the present study, the effects of the counteranion and
the solvent (CH3CN or CH2Cl2) on the reaction rates of
[C6F5Xe]+ with C6H5F and on the product distributions as
well as the influences of water and fluoride ion as nucleo-
philes were investigated (Table 3). The specific entries cited
in the ensuing discussion appear in Table 3, unless otherwise
noted.
(i) Influences of the Counteranion and Solvent on the
Reactivity of [C6F5Xe]+ with C6H5F. The reaction of
[C6F5Xe][BY4] with rigorously dried C6H5F (20 equiv) in
CH3CN proceeded slowly. To exclude the possibility of large
uncertainties, a series of four identical experiments were
carried out for the slowest reaction of [C6F5Xe][BF4] with
C6H5F (20 equiv) in CH3CN at room temperature. The result
was comparable for all four experiments, ranging from 15
to 18 days for complete consumption of the [C6F5Xe]+ cation.
The conversion times are similar for [B(CF3)4]- (ca. 5
days, entry 1a), [B(C6F5)4]- (89% consumed after 6 days,
entry 2), and [B(CN)4]- (6 days, entry 3) but contrast with
that of the less reactive [BF4]- salt (15-18 days, entries 4a,b)
and the somewhat more reactive [AsF6]- salt (4 days, entry
5a) under the same conditions. In all cases, isomeric mixtures
of polyfluorobiphenyls, C6F5-C6H4F, were obtained in nearly
equimolar amounts of 2-, 3-, and 4-isomers, whereas C6F5H
was only detected (e2%) in the case of [C6F5XeNCCH3]-
[B(C6F5)4]. It is noteworthy that the single 4-position of
C6H5F is arylated twice as often as the two 2- and 3-positions
to give C6F5-C6H4F, which is likely a consequence of the
higher negative charge on carbon in the 4-position.
coordination of the π nucleophile, C6H5F, to the electrophilic
XeII center (eq 21), competing with solvent (cf. eq 3) and/or
counteranion coordination (cf. eqs 8 and 17), where all three
types of coordination serve to destabilize the C-Xe bond.
•
Following homolytic cleavage of the C-Xe bond, the C6F5
radical can combine, in a cage, with a C6H4F• radical, which
results from a one-electron transfer, and is accompanied by
the elimination of Xe0 and H+ from the intermediate radical
cation, [XeC6H5F]•+ (eq 22). The ability of C6H5F to
coordinate to [C6F5Xe]+ is enhanced when the coordinating
abilities of the [BY4]- anion and solvent are weaker. From
the reactivities of their [C6F5Xe]+ cations in CH3CN, it may
be concluded that the coordination abilities of the [BY4]-
anions increase in the order [B(CF3)4]- < [B(CN)4]-
[B(C6F5)4]- , [BF4]-.
<
[C6F5Xe]+ + C6H5F f [C6F5XeC6H5F]+
(21)
(22)
[C6F5XeC6H5F]+ f C6F5C6H4F + Xe0 + H+
solv
The reactivity of the [C6F5Xe]+ cation toward C6H5F (20
equiv) was significantly enhanced when the strongly coor-
dinating CH3CN solvent was replaced by the weakly
coordinating solvent, CH2Cl2. In CH2Cl2, [C6F5Xe][B(CF3)4]
was consumed in only 15 min (entry 1b), compared to 5
days in CH3CN (entry 1a), forming only C6F5-C6H4F. The
reaction proceeded more slowly in CH2Cl2 when only 1.2
equiv of C6H5F was used (82% conversion of [C6F5Xe]-
[B(CF3)4] after 1.62 days; entry 5b), showing that the reaction
is not initiated by CH2Cl2 coordination to the cation be-
cause C6F5H (41%) is formed and C6F5Cl is absent (eqs 23
and 24).
C6F5 + C6H5F f C6F5H + C6H4F•
(23)
(24)
•
The reaction rates with C6H5F are 4-8 times faster than
the decomposition rates of [C6F5Xe][BY4] salts in CH3CN
in the absence of C6H5F, where C6F5H was the only (Y )
CF3 or CN) or main (Y ) C6F5) reaction product (Table 2).
The experimental results are therefore consistent with
C6F5 + C6H4F• f C6F5-C6H4F
•
In contrast, only 50% of [C6F5Xe][B(CF3)4] reacted after 22
Inorganic Chemistry, Vol. 46, No. 22, 2007 9429

Koppe et al.
days in CH2Cl2 in the absence of C6H5F, yielding C6F5Cl as
the major product (80%) and C6F5H (20%) (Table 2, entry
1b). The rapid reaction of [C6F5Xe][A] with C6H5F in
CH2Cl2 and the dependence of the reaction rate on the C6H5F
concentration clearly demonstrate that the interaction of
[C6F5Xe]+ with the π nucleophile is favored in the presence
of a weakly coordinating anion and solvent. The [C6F5Xe]-
[B(CF3)4] and [C6F5XeNCCH3][B(C6F5)4] salts have solubili-
ties comparable to those of CH3CN in C6H5F and react
rapidly with neat C6H5F, whereas [C6F5Xe][B(CN)4],
[C6F5Xe][BF4], and [C6F5Xe][AsF6] are insoluble in C6H5F.
The [C6F5Xe]+ cation of [C6F5Xe][B(CF3)4] is completely
reacted within 100 min in C6H5F (64 equiv), exclusively
yielding an isomeric mixture of hexafluorobiphenyls (entry
6a), which supports the proposed reaction path (eqs 21 and
22). The reaction between [C6F5XeNCCH3][B(C6F5)4] and
C6H5F (100 equiv) proceeded more than 4 times faster, but
the product distribution differed. In addition to C6F5-C6H4F
(30%), C6F5H (31%), and (C6F5)2 (39%) were formed
(entry 6b). The latter product again supports attack by the
[C6F5Xe]+ cation at the nucleophilic ipso-carbon of the anion
(eqs 17 and 18) as a significant competing reaction path-
reactivities (cf. the reaction of C6F5XeF with C6H5F in CH2-
Cl2 discussed below). The C6F5 radical, resulting from the
•
[C6F5Xe]+ + H2O f [C6F5Xe-OH2]+ f C6F5XeOH +
H+
(25)
solv
C6F5XeOH f C6F5 + •XeOH
(26)
•
decomposition of C6F5XeOH (eq 26), may add preferentially
to C6H5F without attacking CH3CN. The C6F5-C6H4F
products, in the absence of C6F5H, agree with this interpreta-
tion.
In order to compare the relative influences of water and
fluoride ion, the reactivities of [C6F5XeNCCH3][B(C6F5)4]
in CH2Cl2 in the presence of both C6H5F and a “naked”
fluoride ion, [N(CH3)4]F, which yields C6F5XeF,8,23 were
also studied. As a result of the strong interaction between
[C6F5Xe]+ and F-, which leads to the 3c-4e-bonded
C6F5XeF molecule, C6H5F coordination to xenon is ex-
pected to be inhibited, so that the rate of C6F5-C6H4F form-
ation decreases. In order to test this hypothesis, C6F5XeF
was synthesized according to eq 27 using an alternative
method described in the Experimental Section that is based
on that originally developed by Frohn and Theissen.8
•
way, with the formation of C6F5H arising from C6F5 radical
attack on C6H5F (eq 23) or coordinated CH3CN (eqs 3-6).
(ii) Effects of H2O and F- on the Reactivity of
[C6F5Xe]+ with C6H5F. When the reactions of [C6F5Xe]-
[BY4] salts in CH3CN were initially carried out with freshly
distilled, but not rigorously dried C6H5F (1.2 equiv), the
reaction rates accelerated for the [BF4]-, [B(CF3)4]-, and
[AsF6]- salts but were less affected for the [B(C6F5)4]- salt.
In all cases, minor amounts of C6F5H were detected in
addition to C6F5-C6H4F.
In order to evaluate the influence of water on this reaction
in a controlled manner, the reactions of [C6F5Xe][BF4] and
[C6F5Xe][AsF6] with rigorously dried C6H5F (20 equiv) and
H2O (1 or 20 equiv) in CH3CN were investigated at 20 °C
(entries 7a-8b). A very pronounced effect of H2O on the
reaction rate was found, with the [BF4]- salt reacting slightly
faster than the [AsF6]- salt. In the presence of 1 equiv of
H2O, the [C6F5Xe]+ cation of the [AsF6]- salt was consumed
after only 19 h, and in the presence of 20 equiv of H2O, it
was consumed after only 25 min, or 60 and 950 times more
rapidly, respectively, than in the absence of H2O. The
distributions of C6F5-C6H4F isomers, the only C6F5-contain-
ing products, were not noticeably influenced by the presence
of H2O. The absence of C6F5H in experiments where H2O
was added confirms that C6F5H formed during the decom-
position of [C6F5Xe]+ salts in anhydrous CH3CN solvent
(Table 2) does not derive from fortuitous H2O that had
diffused through the walls of the FEP reaction vessels but
by hydrogen abstraction from the only hydrogen source
available, CH3CN.
[C6F5XeNCCH3][B(C6F5)4] +
CH2Cl2
[N(CH3)4]F
8 C6F5XeF + [N(CH3)4][B(C6F5)4]V +
-80 °C
CH3CN (27)
At -40 °C, 46% of C6F5XeF reacted in CH2Cl2 in the
presence of C6H5F (11 equiv) within 30 min, forming
C6F5Cl (36%), C6F5H (33%), and C6F5-C6H4F (31%) (entry
•
9a). The products, C6F5Cl and C6F5H, likely result from C6F5
radical attack on CH2Cl2 (eqs 13-15). A reaction mixture
consisting of [C6F5XeNCCH3][B(C6F5)4], C6H5F (20 equiv),
and [N(CH3)4]F (1 equiv) was combined in CH2Cl2 at -55
°C, and the mixture was warmed to 20 °C. The reaction was
complete within 15 min, yielding C6F5-C6H4F (80%),
(C6F5)2 (5%), and C6F5H (15%) (see Table 3, entry 9b).
Characterization of [C6F5Xe][BY4] (Y ) CF3, C6F5, CN,
or OTeF5) and [C6F5Xe][BF4] by Multi-NMR Spectros-
copy. Since the discovery of the [C6F5Xe]+ cation, NMR
data for [C6F5Xe]+ salts having different counteranions
such as [AsF6]-,17,24,25 [PF6]-,24 [SiF5]-,26 [BF4]-,18
[(C6F5)nBF4-n]-,1,2,25,27,28 [E(SO2CF3)n-1
]
(E ) O, N, and
-
C),24 and [HF2]- 29 have been reported.4,5 However, only two
of the six possible 19F-19F couplings in the aryl group have
(23) Frohn, H. -J.; Theissen, M. J. Fluorine Chem. 2004, 125, 981-988.
(24) Franke, H. Doctoral Dissertation, Gerhard-Mercator Universita¨t,
Duisburg, Germany, 2000.
(25) Schroer, T. Doctoral Dissertation, Gerhard-Mercator Universita¨t,
Duisburg, Germany, 1996.
(26) Scholten, T. Doctoral Dissertation, Gerhard-Mercator Universita¨t,
Duisburg, Germany, 1996.
(27) Jakobs, S. Doctoral Dissertation, Gerhard-Mercator Universita¨t, Duis-
burg, Germany, 1991.
Coordination of H2O to [C6F5Xe]+ and subsequent solvent-
assisted deprotonation to give the presently unknown
C6F5XeOH molecule (eq 25) as an unstable reaction inter-
mediate may account for the products and enhanced
(28) Klose, A. Doctoral Dissertation, Gerhard-Mercator Universita¨t, Duis-
burg, Germany, 1993.
(29) Frohn, H.-J.; Schroer, T. J. Fluorine Chem. 2001, 112, 259-264.
9430 Inorganic Chemistry, Vol. 46, No. 22, 2007

[C6F5Xe]+ Salts of Weakly Coordinating Borate Anions
been extracted from the 19F spectra in the course of these
fluorine-fluorine coupling constants of the C6F5 group (eqs
28-31)31,32 and were then manually iterated to give the best
spectral fits.
3
4
studies, namely, J(19Fo-19Fp) (J24) and J(19Fm-19Fp) (J34),
3
but all three possible 129Xe-19F couplings, J(19Fo-129Xe),
5
4J(19Fm-129Xe), and J(19Fp-129Xe), have been reported.1,2
J24 ) 0.471δ(19Fp) + 74.6 ) 8.24
J26 ) -0.396δ(19Fp) - 65.7 ) -9.9
J35 ) 0.164δ(19Fp) + 23.94 ) 0.83
J25 ) 0.091δ(19Fp) + 19.30 ) 6.5
(28)
(29)
(30)
(31)
Moreover, the relative signs of the reported couplings have
not been assigned. The availability of new [C6F5Xe][BY4]
(Y ) CF3, C6F5, CN, or OTeF5) salts that are soluble in
neutral polar solvents provided an opportunity to characterize
these salts by 19F, 11B, 13C, and 129Xe NMR spectroscopy
(Table 4) with the view to provide, for the first time, a com-
plete determination of the 19F and 129Xe NMR parameters
of the [C6F5Xe]+ cation and to correlate the nature of the
[C6F5Xe]+ cation-solvent interaction with its NMR para-
meters.
The signs of the coupling constants used for the simula-
tions are relative and have not been experimentally deter-
mined; however, extensive studies made on C6F5 deriva-
tives31,32 indicate that these signs are also the correct absolute
signs. The simulated spectra are in excellent agreement with
the experimental spectra, accounting for all of the observed
spectral features including asymmetries in the Fo and Fm
multiplets arising from second-order effects. All trends (i.e.,
relative magnitudes and relative signs of the J values) are in
agreement with those observed for C6F5I as well as for most
other C6F5 derivatives:31,32 (1) J23 (-20.2 Hz), J26 (-12.8
Hz), and J34 (-20.0 Hz) are of opposite sign to J24 (5.6 Hz)
and J25 (1.2 Hz), which is also observed for C6F5I (-22.7,
-4.9, -19.5, 2.1, and 7.2 Hz, respectively), (2) the J35
(0.4 Hz) coupling is also very small but slightly positive
(-1.2 Hz in C6F5I), and (3) the J34 and J23 couplings are
negative and similar in magnitude for both [C6F5Xe]+ and
C6F5I.
When [C6F5Xe]+ and isoelectronic C6F5I are compared,
it is noteworthy that, other than J23, the greatest differences
are observed for J couplings involving Fo, suggesting that
they are related to the proximity of the positively charged
xenon atom. The J26 coupling is significantly more negative
than that in C6F5I, but comparable negative values have been
observed for C6F5SO2Cl33,34 and C6F5NO2.31,32,35 The only
value that is markedly different is that of J25, which appears
to be among the smallest measured J25 couplings.
(b) Chemical Shift and Coupling Constant Trends. To
systematize the interpretation of chemical shift trends, a
model has been used in which the weakly coordinating anion
and the solvent compete for coordination to the positively
charged electrophilic XeII center of [C6F5Xe]+. Two sets of
conditions may be distinguished: (1) the anions are weakly
coordinating when compared with CH3CN and (2) both the
anion and the solvent are weakly coordinating.
In the first case, very similar 19F NMR chemical shifts
are obtained for [C6F5Xe][BY4], [C6F5Xe][BF4], and
[C6F5Xe][AsF6] when dissolved in CH3CN (Table 4). This
is consistent with [C6F5XeNCCH3]+ formation and counter-
(a) Simulation of [C6F5Xe]+ 19F and 129Xe NMR
Spectra. The 19F NMR spectra of [C6F5Xe][BY4] are well-
resolved at 7.0463 T, exhibiting complex multiplet structures
for the o- and m-C6F5 fluorine resonances and a triplet (J34)
of triplets (J24) for the p-C6F5 fluorine resonance (Figure 1).
All C6F5 resonances are accompanied by 129Xe satellites (I
) 1/2, 26.44%) arising from 3J(19Fo-129Xe), 4J(19Fm-129Xe),
and 5J(19Fp-129Xe) spin-spin couplings. The improved
resolution afforded in the present circumstances provided the
first fully resolved 129Xe NMR spectra of [C6F5Xe]+ (Figure
2), showing all of the expected 19F-129Xe spin-spin
couplings as a triplet (o) of triplets (m) of doublets (p).
3
5
The J(19Fo-129Xe) and J(19Fp-129Xe) spin-spin coupling
constants were found to be identical, within experimental
error, to those obtained in previous studies, whereas the
4J(19Fm-129Xe) coupling was found to be significantly smaller
(8.8 Hz) than that published earlier from 19F NMR spectra
(18.7-19.5 Hz).1-3
The present 19F and 129Xe NMR spectral simulations for
[C6F5Xe][B(CN)4] have yielded the first complete set of
J(19F-19F) couplings and assignments of their relative signs
for [C6F5Xe]+. The 19F and 129Xe NMR spectra of the
[B(CN)4]- salt in CH3CN solution were better resolved and
therefore were used for spectral simulations. The spectrum
of isoelectronic C6F5I was also compared and, in this case,
chemical shifts and J couplings were remeasured in CD3CN
at 24 °C and used for simulation of the 19F NMR spectrum.
The 19F ([C6F5Xe]+ and C6F5I) and 129Xe ([C6F5Xe]+) NMR
spectra were assigned and simulated using the multinuclear
NMR simulation program ISOTOPOMER.30 Spectra were
simulated using the natural abundances of the spin-1/2 nuclei
19F (100%) and 129Xe (26.44%). In the case of C6F5I,
complete quadrupolar collapse of the 127I-19F couplings
was assumed. Full spectral simulations were achieved under
C2V symmetry for both [C6F5Xe]+ and C6F5I. In the case of
[C6F5Xe]+, only the values of J24 and J34 were readily
available from the 19Fp multiplet, while 3J(129Xe-19Fo) (67.7
4
5
Hz), J(129Xe-19Fm) (8.8 Hz), and J(129Xe-19Fp) (3.7 Hz)
were obtained from the 129Xe NMR spectrum. Preliminary
values for J24, J26, J35, and J25 were calculated from empirical
relationships between δ(19Fp) ) -140.9 ppm and the
(31) Pushkina, L. N.; Stepanov, A. P.; Zhukov, V. S.; Naumov, A. D. J.
Org. Chem. USSR 1972, 8, 586-597.
(32) Pushkina, L. N.; Stepanov, A. P.; Zhukov, V. S.; Naumov, A. D. Org.
Magn. Reson. 1972, 4, 607-623.
(33) Bruce, M. I. J. Chem. Soc. A 1968, 1459-1464.
(34) Moniz, W. B.; Lustig, E.; Hanzen, E. A. J. Chem. Phys. 1969, 51,
4666-4669.
(30) Santry, D. P.; Mercier, H. P. A.; Schrobilgen, G. J. ISOTOPOMER,
A Multi-NMR Simulation Program, version 3.02NTF; Snowbird
Software, Inc.: Hamilton, Ontario, Canada, 2000.
(35) Fields, R.; Lee, J.; Mowthorpe, D. J. J. Chem. Soc. B 1968, 308-
312.
Inorganic Chemistry, Vol. 46, No. 22, 2007 9431

Koppe et al.
9432 Inorganic Chemistry, Vol. 46, No. 22, 2007

[C6F5Xe]+ Salts of Weakly Coordinating Borate Anions
anions that are less basic than CH3CN. Strong coordination
of the anion to the positively charged xenon center yields
asymmetric 3c-4e C-Xe-L bonds and results in more
shielded fluorine environments and larger coupling constants.
In the second case, only [C6F5Xe][B(CF3)4] has sufficient
stability and solubility in the weakly coordinating solvents
CH2Cl2 and PFB (stable at 20 °C for more than 3 and 5
days, respectively, contrasting with CH2Cl2 solutions of
[C6F5XeNCCH3][B(C6F5)4] and [C6F5Xe][B(OTeF5)4],
which must be maintained below -40 °C to avoid rapid
decomposition) to allow NMR studies in these media. A
comparison of the 19F NMR chemical shifts of [C6F5Xe]-
[B(CF3)4] in CH2Cl2, PFB, and CH3CN at 24 °C (Table 4)
shows that the fluorine resonances of the C6F5 group are
shifted to higher frequencies (deshielded) in CH2Cl2 (∼5 ppm
for Fm and Fp and ∼1.5 ppm for Fo) and PFB (∼2 ppm
for Fm and Fp and ∼0.5 ppm for Fo) relative to those in
CH3CN, consistent with a more weakly coordinated
[C6F5Xe]+ cation and significant polarization of the C6F5
group by XeII.
A more weakly coordinated [C6F5Xe]+ cation was also
achieved by dissolution of [C6F5Xe][BF4] in aHF. The 19F
NMR chemical shifts at -40 °C are similar to those obtained
for [C6F5Xe][B(CF3)4] in PFB at 24 °C (Table 4). Hydrogen
fluoride presumably solvates the anion, resulting in a much
larger [BF4‚(HF)n]- anion, which disperses the negative
charge over more than four fluorine atoms, rendering it less
basic. The [BF4‚(HF)n]- anion exhibits a broadened 1:1:1:1
quartet in the 19F NMR spectrum at -148.6 ppm and a
quintet splitting in the 11B NMR spectrum at -1.3 ppm that
1
arises from J(19F-11B) ) 11.5 Hz. The quartet in the 19F
NMR spectrum arises because the electric field gradient at
the quadrupolar 11B nucleus is nearly zero, and quadrupolar
relaxation is slow as a result of the highly symmetric ligand
environment and rapid dynamics of the solvation shell. The
1
overlapping equal-intensity septet arising from J(19F-10B)
was insufficiently resolved to provide a directly measured
value for this coupling constant (calcd, 3.9 Hz).
The 129Xe NMR chemical shifts of [C6F5Xe][BY4] and
[C6F5Xe][BF4] in CH3CN at 24 °C differ only slightly,
ranging from -3792.6 ([B(CN)4]-) to -3802.8 ppm ([BF4]-),
having spin-spin coupling constants of 3J(19Fo-129Xe)
4
) 66.6 ([BF4]-) to 67.6 Hz ([B(C6F5)4]-), J(19Fm-129Xe)
5
) 8.6 ([BF4]-) to 9.1 Hz ([B(C6F5)4]-), and J(19Fp-129Xe)
) 3.6 ([B(CF3)4]-) to 4.2 Hz ([BF4]-) (Table 4). The
temperature dependencies of the 129Xe NMR chemical
shifts of [C6F5Xe]+ salts are in good agreement with the
previously published results for [C6F5Xe][AsF6] in CD3CN/
C2H5CN (1:3, v/v) of -0.35 ppm K-1.36 The 129Xe NMR
chemical shifts of the [C6F5Xe][BY4] salts in CH3CN at -40
°C (-3772.2 to -3783.0 ppm) are only slightly shifted to
higher frequency when compared with that of C6F5XeF
(-3793.4 ppm) in CH2Cl2 at -40 °C. The chemical shifts
(36) Bardin, V. V.; Frohn, H.-J. Magn. Reson. Chem. 2006, 44, 648-
650.
(37) Bernhardt, E.; Henkel, G.; Willner, H.; Pawelke, G.; Bu¨rger, H.
Chem.sEur. J. 2001, 7, 4696-4705.
(38) Bernhardt, E.; Henkel, G.; Willner, H. Z. Anorg. Allg. Chem. 2000,
626, 560-568.
Inorganic Chemistry, Vol. 46, No. 22, 2007 9433

Koppe et al.
Figure 1. 19F NMR spectra (282.40 MHz) of the o-, p- and m-C6F5 fluorine resonances of the [C6F5Xe]+ cation in [C6F5Xe][B(CN)4] recorded in CH3CN
at 24 °C. Spectra were resolution-enhanced by Gaussian multiplication (a traces). The simulated spectra (b traces) are provided for comparison with the
lower traces depicting the subspectra, drawn to scale, that arise from 19F coupling to natural abundance (26.44%) 129Xe.
of the counteranions were not influenced by [C6F5XeNCCH3]+
formation and are very similar to those reported previously
for [B(CF3)4]-,37 [B(CN)4]-,38 and [B(C6F5)4]- 39 and are
therefore not discussed.
Generally, the nature of the counteranion influences the
3J(19Fo-129Xe) coupling constant, which is 68 ( 1 Hz for
[C6F5XeNCCH3]+ in the presence of weakly coordinating
[BY4]- anions and 70 and 73 Hz in the case of more
nucleophilic anions such as [SiF5]- 26 and [HF2]-,29 respec-
tively. The more strongly coordinating the anion is, the
greater the magnitude of the 3J(19Fo-129Xe) coupling, trend-
ing toward 80 Hz in C6F5XeF (CH2Cl2, -80 °C; see the
Experimental Section) and 94.2 Hz in C6F5XeCl (CH2Cl2,
-60 °C).7
by the metatheses of [C6F5Xe][BF4] and MI[BY4] salts,
showed no direct correlation between their decomposition
temperatures (neat or in solution) and the nucleophilicity of
the anion. The only salt in which CH3CN is coordinated to
the cation, [C6F5XeNCCH3][B(C6F5)4], was the least stable
among the [C6F5Xe]+ salts considered in both the solid state
and in weakly coordinating CH2Cl2 and strongly coordinating
CH3CN solvents.
In all cases except [B(C6F5)4]-, the only decomposition
product was C6F5H in CH3CN, whereas the decomposition
of [C6F5XeNCCH3][B(C6F5)4] in CH2Cl2 yielded significant
amounts of (C6F5)2, which resulted from cation attack at the
nucleophilic ipso-carbon of the anion. The decompositions
of [C6F5Xe][BY4] (Y ) CF3 or OTeF5) in CH2Cl2 result in
Conclusions
•
hydrogen and chlorine abstraction by the C6F5 radical,
The [C6F5Xe]+ salts of the weakly coordinating [BY4]-
(Y ) CF3, C6F5, CN, or OTeF5) anions, which were obtained
whereas [C6F5XeNCCH3][B(C6F5)4] also forms significant
quantities of (C6F5)2.
In general, [C6F5Xe][BY4] salts exhibited a range of
stabilities, which were not leveled by coordination of the
(39) Jutzi, P.; Mu¨ller, C.; Stammler, A.; Stammler, H.-G. Organometallics
2000, 19, 1442-1444.
9434 Inorganic Chemistry, Vol. 46, No. 22, 2007

[C6F5Xe]+ Salts of Weakly Coordinating Borate Anions
solvates the anion, resulting in a much larger [BF4‚(HF)n]-
anion, which disperses the negative charge over more than
four fluorine atoms, rendering it less basic. Simulations of
the 19F and 129Xe NMR spectra of [C6F5Xe]+ have provided
the complete set of aryl 19F-19F and 129Xe-19F coupling
constants and their relative signs, which are in accord with
those of isoelectronic C6F5I.
Experimental Section
Apparatus and Materials. Manipulations of volatile materials
were carried out on glass vacuum lines. Solid and moisture-
sensitive materials were handled inside a drybox (Fa. Braun, MB
100G, Ar atmosphere; H2O < 1 ppm). The reaction vessels,
constructed from 4.1-mm o.d. FEP tubing, were dried under
dynamic vacuum for several hours. Molecular sieves (Bayer AG,
3 Å) were washed with boiling water and predried at ∼80 °C,
followed by drying under vacuum (10-3 mbar) at 180 °C for 1 h
and at 340 °C for a further 4 h. Organic solvents were purified
and dried using standard literature methods.40 Acetonitrile (KMF
Laborchemie Handels GmbH; >99%) was refluxed with KMnO4
(5 g L-1 of CH3CN), distilled, repeatedly refluxed with P4O10 and
distilled until the P4O10 suspension was colorless. Finally, CH3CN
was distilled onto and stored over dry 3 Å molecular sieves.
Dichloromethane (Fluka, >99.9%; KMF, >99.9%), 1,1,1,3,3-
pentafluorobutane (Solvay, >99.5%), and 1,2-dichloroethane (Al-
drich, 99%) were refluxed with P4O10, distilled, and stored over
dry 3 Å molecular sieves. Two grades of C6H5F (Fluorochem Ltd.)
were used in this study: (1) redistilled C6H5F that had been stored
under argon and (2) C6H5F that had been freshly refluxed with
P4O10, distilled, and stored over 3 Å molecular sieves. Benzotri-
fluoride, C6H5CF3 (Aldrich; >99%, anhydrous), was stored over
dry 3 Å molecular sieves.
Sulfuryl chloride fluoride, SO2ClF (Allied Chemical), was
purified using the standard literature method.41 Anhydrous hydrogen
fluoride (Harshaw Chemical Co.) was purified by treatment with
fluorine gas as previously described42 and was then vacuum-distilled
into a dry Kel-F storage vessel equipped with a Kel-F valve and
stored at room temperature until used. Alternatively, HF (Solvay)
was dried electrochemically in a stainless steel cell using nickel
electrodes as previously described,43 transferred into a high-density
polyethylene, FEP, or PTFE storage vessel, and stored at -21 °C
until used.
Figure 2. 129Xe NMR spectrum (83.02 MHz) of the [C6F5Xe]+ cation in
[C6F5Xe][B(CN)4] recorded in CH3CN at 24 °C. The spectrum was
resolution-enhanced by Gaussian multiplication. The simulated spectrum
is provided for comparison (bottom trace).
nucleophile, CH3CN. Accordingly, the reactivities of
[C6F5Xe][BY4] with an excess of the π nucleophile, C6H5F,
differed in CH3CN. All reactions of [C6F5Xe][BY4] with
C6H5F proceeded significantly faster than their decomposi-
tions in the solvent alone. The reaction rates and product
distributions were dependent upon Y, the solvent, and the
presence of additional molecular (e.g., H2O) or anionic (e.g.,
F-) nucleophiles. The major products in all of these reactions
were isomeric mixtures of hexafluorobiphenyls, C6F5-
C6H4F. Their formation proceeded faster in weakly coordi-
nating CH2Cl2 than in strongly coordinating CH3CN. The
factors that influence the rates of pentafluorophenyl-
ation and the product distributions are in accord-
ance with the intermediate coordination of C6H5F at
[C6F5Xe]+ and the subsequent radical attack of C6H5F by
C6F5‚.
Samples for reactivity studies were contained in FEP vessels and
were stored at 20 °C (unless noted otherwise) inside a rigorously
dry, argon-flushed glass vessel to minimize diffusion of moisture
through their FEP walls and PTFE stoppers. Samples were shielded
from light and were periodically agitated. The reaction progress
was periodically monitored by 19F NMR spectroscopy at 24 °C.
Xenon difluoride was prepared by the thermal method described
in the literature.44 The starting materials, B(C6F5)345,46 (also see the
Supporting Information), Cs[B(C6F5)4]46 (also see the Supporting
The 19F NMR parameters of the [C6F5Xe]+ cation in the
present series of salts are shown to reflect the relative
degrees of cation-solvent interactions. The high-frequency
shifts of the 19F NMR resonances of [C6F5Xe]+ in CH2Cl2
and PFB are consistent with a more weakly coordinated
[C6F5Xe]+ cation and significant polarization of the C6F5
group by XeII relative to the 19F NMR chemical shifts
obtained for [C6F5Xe]+ in CH3CN solutions of [C6F5Xe]-
[BY4] (Y ) CF3, C6F5, CN, or OTeF5) and [C6F5Xe][BF4].
In the latter case, the enhanced shielding and narrow
chemical shift range are consistent with [C6F5XeNCCH3]+
formation. The 19F NMR chemical shifts of [C6F5Xe][BF4]
in aHF are similar to those obtained for [C6F5Xe][B(CF3)4]
in a PFB solution and are also indicative of a weakly
coordinated [C6F5Xe]+ cation. Hydrogen fluoride presumably
(40) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: Oxford, U.K., 1988.
(41) Schrobilgen, G. J.; Holloway, J. H.; Granger, P.; Brevard, C. Inorg.
Chem. 1978, 17, 980-987.
(42) Emara, A. A. A.; Schrobilgen, G. J. Inorg. Chem. 1992, 31, 1323-
1332.
(43) Ignate´v, N.; Sartori, P. J. Fluorine Chem. 2000, 103, 57-61.
(44) Mercier, H. P. A.; Sanders, J. C. P.; Schrobilgen, G. J.; Tsai, S. S.
Inorg. Chem. 1993, 32, 386-393.
(45) Massey, A. G.; Park, A. J.; Stone, F. G. A. Proc. Chem. Soc., London
1963, 212.
(46) Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 2, 245-
250.
Inorganic Chemistry, Vol. 46, No. 22, 2007 9435

Koppe et al.
Information), C6F5B(OH)2,47 K[C6F5BF3],48 C6F5BF2,48 B(OTeF5)3,49
Cs[B(OTeF5)4],49 and [C6F5Xe][BF4],18 were prepared as previously
described. Samples of K[B(CN)4]38 and MI[B(CF3)4] (MI ) K and
Cs)37 were obtained from Prof. Helge Willner (Bergische Universita¨t
Wuppertal, Wuppertal, Germany).
dried for several hours at temperatures not exceeding -50 °C. The
solid was further purified by washing with dry pentane at -60 °C.
The 19F and 129Xe NMR NMR parameters of C6F5XeF (CH2Cl2 at
-80 °C) prepared by the present method are in accordance with
the previously reported values.8 19F NMR: δ(19F) ) -2.8 ppm
1
[∆ν1/2 ) 129 Hz, J(19F-129Xe) ) 4016 Hz, XeF]; -129.6 ppm
Syntheses of [C6F5Xe][BY4] (Y ) CF3, C6F5, CN, or OTeF5).
Xenon difluoride (0.8734 g, 5.159 mmol) was suspended in cold
(-60 °C) CH2Cl2 (25 mL) in a 23-mm i.d. FEP reaction tube. A
freshly prepared C6F5BF2 (5.15 mmol) solution in CH2Cl2 (7 mL)
at -80 °C was transferred onto the XeF2 suspension with vigorous
stirring of the latter at -60 °C. After 15 min, the temperature was
raised to -40 °C. A pale-yellow solid precipitated. After 1.5 h of
additional stirring, the suspension was centrifuged at 20 °C and
the mother liquor was decanted. The near-white solid was dried
for 4 h under dynamic vacuum (10-2 mbar) at 20 °C, yielding
[C6F5Xe][BF4] (1.65 g, 4.28 mmol, 83% yield) in high purity.
[o-C6F5]; -147.0 ppm [3J(19F-19F)
) 20.1 Hz, p-C6F5];
-157.2 ppm [m-C6F5]. 129Xe NMR: δ(129Xe) ) -3793.4 ppm
[1J(19F-129Xe) ) 4016 Hz, XeF].
Reactivity Studies. Sample preparations are described below.
All samples were prepared in 4.1-mm o.d. FEP NMR/reaction tubes,
which were closed with PTFE stoppers. Samples were periodically
monitored by 19F NMR spectroscopy at 24 °C unless otherwise
indicated. Initial concentrations of [C6F5Xe]+ salts were 0.09-0.16
mol L-1
.
(a) Solubilities of [C6F5Xe][BY4] (Y ) CF3 or CN),
[C6F5XeNCCH3][B(C6F5)4], and [C6F5Xe][BF4] in Selected
Solvents. The solubilities of [C6F5Xe][BY4] salts were determined
in selected solvents (Table S1) prior to investigation of their solution
stabilities. Each salt was loaded into a reaction tube and suspended
in the solvent (CH3CN, CH2Cl2, DCE, PFB, SO2ClF, or C6H5F).
The saturated suspension was centrifuged, and the mother liquor
was decanted into a second reaction tube. The amount of dissolved
salt was determined by use of the internal quantitative standard for
integration, C6H5CF3.
The salts, [C6F5Xe][BY4] (Y ) CF3, C6F5, CN, or OTeF5) were
synthesized in CH3CN by metatheses of [C6F5Xe][BF4] (∼0.5
mmol) with equimolar amounts of either Cs[BY4] or K[BY4] at
-40 °C. Both reactants were separately dissolved in CH3CN (300
µL), and the solutions were combined at 20 °C. A pale-yellow
suspension resulted, which was stirred for 15 min, subsequently
cooled to -40 °C, and centrifuged. The mother liquor was
separated, and the solid, MI[BF4] (MI ) K or Cs), was washed
with cold (-40 °C) CH3CN (300 µL). Both CH3CN extracts were
combined and the solvent was subsequently removed under dynamic
vacuum, yielding the pale-yellow solids [C6F5Xe][B(CF3)4],
[C6F5XeNCCH3][B(C6F5)4], and [C6F5Xe][B(CN)4], which were
dried for several hours under dynamic vacuum (5 × 10-3 mbar) at
20 °C. Small amounts of MI[BF4] contaminants were removed from
[C6F5Xe][B(CF3)4] and [C6F5XeNCCH3][B(C6F5)4] by redissolving
each salt in CH2Cl2 followed by centrifugation. The supernatants
were removed and dried under dynamic vacuum (5 × 10-3 mbar)
at 24 and -50 °C, respectively, yielding products that were free of
[BF4]- in their 19F NMR spectra. It is important to note that
[C6F5Xe][B(CF3)4] tended to retain CH3CN even after pumping
under vacuum. It is only after repeated dissolutions (×5) in CH2Cl2
and evaporations under dynamic vacuum that [C6F5Xe][B(CF3)4]
(b) Stabilities of [C6F5Xe][BY4] (Y
) CF3 or CN),
[C6F5XeNCCH3][B(C6F5)4], and [C6F5Xe][BF4] in Solution.
Each [C6F5Xe][BY4] salt (25-50 mg) was loaded into a reaction
tube. The salts were dissolved in CH3CN (500 µL) or CH2Cl2 (500
µL), in the case of [C6F5Xe][B(CF3)4] and [C6F5XeNCCH3]-
[B(C6F5)4], outside the drybox under a blanket of argon.
(c) Influence of Equimolar Amounts of [N(C4H9)4][BF4] on
the Decomposition of [C6F5Xe][B(CF3)4] in CD2Cl2 and CD3CN.
Equimolar amounts of [C6F5Xe][B(CF3)4] (21.12 mg, 0.0361 mmol)
and [N(C4H9)4][BF4] (11.89 mg, 0.0361 mmol) were dissolved in
CD3CN (150 µL) in separate reaction tubes, and both solutions were
combined (Table 2, entry 6a).
Similarly, [C6F5Xe][B(CF3)4] (21.75 mg, 0.0372 mmol)
and [N(C4H9)4][BF4] (12.25 mg, 0.0372 mmol) were dissolved in
CD2Cl2 (150 µL) at 20 °C and combined (Table 2, entry 6b).
(d) Solvolytic Behavior of [C6F5Xe][BF4] in aHF. The salt,
[C6F5Xe][BF4] (39.00 mg, 0.1013 mmol), was loaded into a re-
action tube and dissolved in aHF (∼500 µL) at -40 °C (Table 2,
entry 5b).
1
was obtained free of CH3CN (monitored by Raman and H NMR
spectroscopies). When this procedure was applied to the salt
containing the [B(C6F5)4]- anion, [C6F5XeNCCH3][B(C6F5)4] was
obtained. The 1:1 stoichiometry of [C6F5Xe]+ to CH3CN was
confirmed by 1H/19F NMR spectroscopy using the quantitative
standard, C6H5CF3, for integration. All [C6F5Xe][BY4] salts were
obtained in essentially quantitative yields.
(e) Reactions of [C6F5Xe][BY4] (Y
) CF3 or CN),
[C6F5XeNCCH3][B(C6F5)4], [C6F5Xe][BF4], and [C6F5Xe][AsF6]
with the π Nucleophile, C6H5F. (i) Rigorously Dried C6H5F in
CH3CN. The salts [C6F5Xe][BF4] (1; 25.55 mg, 0.0663 mmol),
[C6F5XeNCCH3][B(C6F5)4] (2; 61.51 mg, 0.0604 mmol), [C6F5Xe]-
[B(CN)4] (3; 28.98 mg, 0.0701 mmol), [C6F5Xe][B(CF3)4]
(4; 34.88 mg, 0.0596 mmol), and [C6F5Xe][AsF6] (5; 30.93 mg,
0.0635 mmol) were loaded into separate reaction tubes and
dissolved in CH3CN (500 µL). Freshly dried and distilled C6H5F
(20 equiv) was added under argon to the pale-yellow [C6F5Xe]+
salt solutions: 125 µL (1; 128 mg, 1.33 mmol), 118 µL (2; 121
mg, 1.26 mmol); 130 µL (3; 133 mg, 1.38 mmol); 127 µL (4; 130
mg, 1.35 mmol); 112 µL (5; 115 mg, 1.20 mmol) (Table 3, entries
1a-5a).
AlternativeSynthesisofC6F5XeF.Inthedrybox,[C6F5XeNCCH3]-
[B(C6F5)4] (118.6 mg, 0.1165 mmol) was suspended in cold (-80
°C) CH2Cl2 (1000 µL). A solution of cold (-80 °C) CH2Cl2 (500
µL) and [N(CH3)4]F (13.59 mg, 0.1459 mmol) was added and
allowed to react for 1 h. A white suspension of [N(CH3)4][B(C6F5)4]
immediately formed. The suspension was centrifuged at -80 °C,
and the CH2Cl2 mother liquor was separated. The main product in
the mother liquor was C6F5XeF (75.1%) in addition to C6F5H
(4.0%), C6F5Cl (0.5%), [B(C6F5)4]- (9.7%), (C6F5)2 (2.0%), and
several other unidentified C6F5 compounds (8.7%). Methylene
chloride was then removed under vacuum (5 × 10-3 mbar) at
temperatures below -50 °C, and the resulting yellow solid was
(ii) C6H5F (20 equiv) and H2O (1 and 20 equiv) in CH3CN.
Two portions of the salts, 1 and 5 were loaded into separate reaction
tubes and dissolved in CH3CN (500 µL): 1a (31.66 mg, 0.0822
mmol), 5a (27.07 mg, 0.0556 mmol), 1b (30.13 mg, 0.0782 mmol),
and 5b (26.86 mg, 0.0551 mmol). Freshly dried and distilled C6H5F
(47) Frohn, H.-J.; Adonin, N. Y.; Bardin, V. V.; Starichenko, V. F. Z. Anorg.
Allg. Chem. 2002, 628, 2827-2833.
(48) Frohn, H.-J.; Franke, H.; Fritzen, P.; Bardin, V. V. J. Organomet.
Chem. 2000, 598, 127-135.
(49) Kropshofer, H.; Leitzke, O.; Peringer, P.; Sladky, F. Chem. Ber. 1981,
114, 2644-2648.
9436 Inorganic Chemistry, Vol. 46, No. 22, 2007

[C6F5Xe]+ Salts of Weakly Coordinating Borate Anions
(20 equiv) was added to the pale-yellow [C6F5Xe]+ salt solutions:
155 µL (1a; 158.7 mg, 1.651 mmol); 110 µL (5a; 112.6 mg, 1.172
mmol); 155 µL (1b; 158.7 mg, 1.651 mmol); 110.0 µL (5b; 112.6
mg, 1.172 mmol). This was followed by the addition of 1 or 20
equiv of triply distilled H2O: 1a (1.5 µL, 0.083 mmol); and 5a
(1.0 µL, 0.056 mmol); 1b (29 µL, 1.61 mmol) and 5b (20 µL, 1.11
mmol) (Table 3, entries 7a-8b).
(iii) C6H5F and Fluoride in CH2Cl2. In the drybox,
[C6F5XeNCCH3][B(C6F5)4] (26.04 mg, 0.0256 mmol) was loaded
into a reaction tube and suspended in cold (-55 °C) CH2Cl2 (1000
µL). Freshly dried and distilled C6H5F (45 µL, 45.9 mg, 0.478
mmol, 20 equiv) was added to the [C6F5XeNCCH3]+ salt suspen-
sion. The resulting solution was divided into two equal samples
(A and B), and a portion (250 µL, 0.015 mmol) of a solution of
[N(CH3)4]F (5.72 mg, 0.0614 mmol) in cold (-55 °C) CH2Cl2 (1000
µL) was added to sample A (Table 3, entry 9b). Sample B served
as a reference.
(iv) Reaction of C6F5XeF with C6H5F in CH2Cl2. Freshly
prepared C6F5XeF (16.3 mg, 0.0514 mmol) containing [N(CH3)4]-
[B(C6F5)4] (9%) as an impurity was loaded into a reaction tube
and dissolved in cold (-80 °C) CH2Cl2 (1200 µL). Freshly
dried and distilled C6H5F (50 µL, 51.2 mg, 0.533 mmol, 11 equiv)
was added to the pale-yellow solution at -80 °C. The solution
was warmed to -40 °C, stirred for 30 min, and periodically
monitored by 19F NMR spectroscopy at -40 °C (Table 3, entry
9a).
(13C), 14.6 (19F), and 8.5 (129Xe) µs. Line-broadening parameters
used in exponential multiplication of the free induction decays were
set equal to or less than their respective data-point resolutions or
the natural line widths of the resonances. All line-shape functions
were Lorentzian unless specified otherwise. In some cases, the free
induction decays were multiplied by Gaussian functions for
resolution enhancement on Fourier transformation. Spectra were
recorded using various memory sizes, optimal acquisition times,
and relaxation delays (0.5-2 s).
1
The H NMR chemical shifts were referenced with respect to
tetramethylsilane (TMS) using the chemical shifts for the solvents
CH2Cl2 (5.32 ppm) and CH3CN (1.95 ppm). The 13C NMR chemical
shifts were referenced with respect to TMS using the chemical
shifts for the solvents CH2Cl2 (53.5 ppm) and CH3CN (118.7 ppm).
The 19F NMR spectra were referenced with respect to CFCl3
using either the internal standards C6F6 (-162.9 ppm) or C6H5CF3
(-63.9 ppm) or externally to a neat CFCl3 reference sample at 24
°C. The 129Xe NMR spectra were directly referenced with respect
to neat liquid XeOF4 or indirectly by use of the secondary external
reference XeF2/CD3CN extrapolated to zero concentration, yielding
an XeF2 chemical shift of -1813.3 ppm with respect to external
XeOF4 at 24 °C.50 The 11B NMR spectra were referenced either to
an external BF3‚Et2O (neat) at 24 °C or to an external BF3‚Et2O/
CD3Cl solution (15% v/v) at 24 °C. A positive (negative) sign
denotes a chemical shift to high (low) frequency of the reference
compound.
(v) Reaction of [C6F5Xe][B(CF3)4] with C6H5F in CH2Cl2. Two
portions of salt 4, a (35.11 mg, 0.0600 mmol) and b (34.83 mg,
0.0595 mmol), were loaded into separate reaction tubes, and each
was dissolved in CH2Cl2 (500 µL). Freshly dried and distilled
C6H5F, 4a (20 equiv) and 4b (1.2 equiv) was added to the pale-
yellow [C6F5Xe]+ salt solutions: 4a, 113 µL (115.4 mg, 1.201
mmol); 4b, 6 µL (6.92 mg, 0.0720 mmol) (Table 3, entries 1b and
5b).
(vi) Reactions of [C6F5XeNCCH3][B(C6F5)4] and [C6F5Xe]-
[B(CF3)4] with Neat C6H5F. The salts 2 (45.0 mg, 0.0442 mmol)
and 4 (38.7 mg, 0.0661 mmol) were each loaded into a reaction
tube and dissolved in freshly dried and distilled C6H5F (400 µL,
4.2 mmol) (Table 3, entries 6a,b).
(b) Simulation of NMR Spectra. The 19F and 129Xe NMR
spectra of the [C6F5Xe]+ cation ([B(CN)4]- salt in CH3CN at 24 °C)
and C6F5I were simulated on a PC using the program ISOTO-
POMER.30 The program provides a full heteronuclear simulation
that takes into account second-order effects. Spectra in the present
study were not iterated.
Differential Scanning Calorimetry (DSC). Thermal analyses
were performed using previously described instrumentation and
procedures.51 Samples were typically 2-5 mg (4-40 µmol).
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council (NSERC) of Canada (G.J.S.)
and the Deutsche Forschungsgemeinschaft (DFG) and the
Fonds der Chemischen Industrie (H.-J.F.) for support in the
form of research grants and Prof. Helge Willner for providing
samples of MI[B(CF3)4] (MI ) K or Cs) and K[B(CN)4].
NMR Spectroscopy. (a) Instrumentation and Acquisition
Parameters. NMR samples were measured in 4.1-mm o.d. FEP
tubes placed inside a thin-walled precision glass NMR tube (Wilmad
537 PPT), which contained CD2Cl2 or CD3CN in the annular
space, or internally as dry solvents in precision glass NMR tubes
(Wilmad 528 PPT). Ambient and low-temperature NMR spectra
were recorded in the deuterium-locked mode on a Bruker
Avance 300 spectrometer equipped with a 7.0463 T cryo-
magnet. For low-temperature work, the NMR probe was cooled
using a nitrogen flow and a variable-temperature controller (BVT
3000).
Supporting Information Available: Solubilities of [C6F5Xe]-
[BY4] (Y ) CF3 or CN), [C6F5XeNCCH3][B(C6F5)4], and
[C6F5Xe][BF4] (Table S1) and solution decomposition rates and
products (20 °C) for [C6F5Xe][BY4] (Y ) CF3, CN, or OTeF5),
[C6F5XeNCCH3][B(C6F5)4], and [C6F5Xe][BF4] (Table S2), experi-
mental and simulated 19F NMR spectra of C6F5I (Figure S1), and
the syntheses of B(C6F5)3 and Cs[B(C6F5)4]. This material is
available free of charge via the Internet at http://pubs.acs.org.
The 1H and 19F NMR spectra were acquired using a 5 mm
1
combination H/19F probe operating at 300.14 and 282.40 MHz,
IC7010138
respectively. The 11B, 13C, and 129Xe NMR spectra were obtained
using a 5 mm broad-band inverse probe operating at 96.29, 75.47,
and 83.02 MHz, respectively. Pulse widths, corresponding to bulk
magnetization tip angles of ∼90°, were 11.9 (1H), 9.3 (11B), 8.0
(50) Schumacher, G. A.; Schrobilgen, G. J. Inorg. Chem. 1984, 23, 2923-
2929.
(51) NETZSCH, Proteus, Messung, version 4.2.1 ed.; Netzsch Gera¨tebau
GmbH: Selb, Germany, 2002.
Inorganic Chemistry, Vol. 46, No. 22, 2007 9437