Ion pairs of weakly coordinating cations and anions: Synthesis and application for sulfide to sulfoxide oxidations

Article abstract of DOI:10.5560/ZNB.2014-4165

A series of salts containing the weakly coordinating cations (WCC) 1-butyl-3-methylimidazolium ([Bmim]+), 1-butyl-2,3-dimethylimidazolium ([Bdmim]+), 1-dodecyl-3-methylimidazolium ([C12mim]+), tetrabutylphosphonium ([PBu₄]+), tributyltetradecyl

Full text of DOI:10.5560/ZNB.2014-4165

Ion Pairs of Weakly Coordinating Cations and Anions:
Synthesis and Application for Sulfide to Sulfoxide Oxidations
Bo Zhanga, Su Lia, Mirza Cokojaa, Eberhardt Herdtwecka, János Minkb,
Shu-Liang Zangc, Wolfgang A. Herrmanna, and Fritz E. Kühna
a
Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische
Universität München, Ernst-Otto-Fischer-Straße 1, D-85747 Garching bei München, Germany
Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian
b
Academy of Sciences, Budapest, H-1525 Hungary; Faculty of Information Technology,
University of Pannonia, Research Institute of Chemical and Process Engineering, Veszprém,
H-8201, Hungary
c
Department of Petroleum and Chemical Technology, Liaoning University of Petroleum and
Chemical Technology, Dandong Road, No. 1, 113001 Fushun, P. R. China; Institute of Rare
and Scattered Elements Chemistry, Liaoning University, Chongshan Middle Road No. 66,
110036 Shenyang, P. R. China
Reprint requests to Prof. Dr. F. E. Kühn. Tel: +49 89 289 13096. Fax: +49 89 289 13473.
E-mail: fritz.kuehn@ch.tum.de
Z. Naturforsch. 2014, 69b, 1149 – 1163 / DOI: 10.5560/ZNB.2014-4165
Received July 31, 2014
Dedicated to Professor Hubert Schmidbaur on the occasion of his 80th birthday
A series of salts containing the weakly coordinating cations (WCC) 1-butyl-3-methylimidazolium
([Bmim]+), 1-butyl-2,3-dimethylimidazolium ([Bdmim]+), 1-dodecyl-3-methylimidazolium
([C12mim]+), tetrabutylphosphonium ([PBu4]+), tributyltetradecylphosphonium ([P4,4,4,14]+),
tetrabutylammonium ([NBu4]+), and 1,1,3,3-tetramethylguanidium ([TMG]+) and fluorinated
tetraarylborate anions of the type [B(ArF)4] (ArF = C6F5, C6H3-3,5-(CF3)2) were synthesized
and characterized. The influence of cations and anions on the physical properties of the obtained
compounds was examined. In case of the compound [TMG][B(C6F5)4] hydrogen-fluorine contacts
between cation and anion are present in the solid state. Owing to H...F contacts between hydrogen
peroxide and the fluorine substituents of the anion and the resulting activation of H2O2 in solution,
the compound [P4,4,4,14][B(C6H3-3,5-(CF3)2)4] is applicable as an efficient mediator for the
oxidation of sulfides to sulfoxides.
Key words: Weakly Coordinating Anion, Hydrogen Peroxide, Oxidation, Sulfide, Sulfoxide
Introduction
different cations and anions [9 – 17]. It is therefore
not surprising that ILs play an important role in
The growing importance of environmental issues recent examinations aiming at “green” chemistry
for society and industry during the past few decades and applications in catalysis [3, 4, 7, 9, 18 – 23] The
has led to increasing attention to the need for more degree of ion pairing interactions and the size and
environmentally friendly and more sustainable tech- charge distribution of the ions influence the melting
nologies in chemical industry [1 – 8]. Minding this point, viscosity and conductivity [20, 24, 25]. The ion
background, ionic liquids (IL) have been regarded as pairing interactions can be ascribed to the strength
promising reaction media, as they are often non-toxic of different bonding types between the ions, mainly
and not volatile. Yet, most importantly, they can Coulomb forces and hydrogen contacts, which depend
be tailor-made to achieve desired properties, e. g. on the Lewis basicity of the anions [26 – 34]. For
high hydrophobicity and concomitant high polarity, this reason, ion pairs containing weakly coordinating
thus offering a large variety of compounds with cations (WCC; e. g. ammonium, phosphonium, pyri-
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1150
B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
dinium, imidazolium) and weakly coordinating anions studies [62, 64], some of the new WCCWCAs were
(WCA; e. g. [BF4]−, [PF6]−, [AlCl4]−, [CF3SO3]−, applied as mediators for the oxidation of sulfides to
[N{SO2(CF3)}2]−) are among the best studied IL sulfoxides. Oxidation of sulfur-containing compounds
systems [35, 36], as they exhibit weak Coulomb is of considerable current interest for industrial
(owing to charge delocalization) and weak hydrogen chemistry and petrochemistry [65 – 69].
bonding interactions [1 – 3]. For example, ILs con-
sisting of [Al(ORF)4]− (RF = C(CF3)3, C(H)(CF3)2, Results and Discussion
C(CH3)(CF3)2, C(Ph)(CF3)2) anions associated with
imidazolium cations have been described and ap-
Synthesis and characterization
plied as solvents for electrochemical and catalytic
The WCCWCAs were synthesized according to
applications [37 – 40]. Matsumoto et al. prepared and modified literature procedures [64]. They can be ac-
characterized low-melting and low-viscous ILs with cessed via salt metathesis from WCC-halide salts and
perfluoroalkyltrifluoroborates [41 – 44].
A compre- either lithium- or silver-WCAs, as shown in Scheme 1.
hensive examination of ionic compounds based on Li[B(C6F5)4] and Li[B{C6H3-3,5-(CF3)2}4] were syn-
carborane [45 – 47] or azolate [48, 49] anions was thesized according to literature procedures [64, 70].
also performed. However, in terms of anion stability, WCCWCAs 1a–7a and 1b–7b are obtained by the re-
it has been shown that weakly coordinating fluori- action of Li[B(C6F5)4] or Li[B{C6H3-3,5-(CF3)2}4]
nated tetraarylborate [B(ArF)4]− anions (ArF = C6F5, with WCC halides in dry CH2Cl2 under argon atmo-
-C6H3-3,5-(CF3)2) are much more stable than sphere with a reaction time of 2 h at room tempera-
the above mentioned anions [50 – 54]. Therefore, ture. After precipitation of the by-product and filtra-
[B(ArF)4]− anions are widely used as counterions tion of the product-containing supernatant, the solvent
for a plethora of cationic catalysts, e. g. for the is removed under vacuum. The remaining product is
polymerization of olefins [55 – 58].
washed with dry pentane, and dried under high vacu-
Recently it has been demonstrated that a re- um for one day. The yields of the purified products are
duced ion pairing interaction leads to an increased 55 – 62%. In order to increase the yield and reduce
nucleophilicity of perrhenate [59, 60] and polyoxo- the reaction time, Ag[B(C6F5)4] and Ag[B{C6H3-
molybdate [61, 62] anions, rendering anion-based 3,5-(CF3)2}4] have been selected as precursors for
activation of H2O2 and oxidation of olefins and the synthesis of the WCCWCAs. Ag[B(C6F5)4] and
sulfides possible. Additionally, the synthesis of Ag[B{C6H3-3,5-(CF3)2}4] were prepared according to
imidazolium salts containing the [B(C6F5)4]− an- literature procedures [71]
ion showing a weak cation-anion interaction was
The reaction is carried out under exclusion of light
reported [63]. The tetrafluoroborate anion is also at room temperature in dry CH2Cl2. The reaction mix-
capable of activating hydrogen peroxide by forming ture is stirred for 10 min, while the by-product precipi-
hydrogen bonds, which leads to the oxidation of tates. After filtration, the solvent is removed under high
sulfides [65]. These findings led to the idea of synthe- vacuum to obtain the raw product. This raw product is
sizing several different ionic compounds with weakly then washed with dry pentane and dried under vacu-
coordinating cations and fluoride-containing weakly um for one day. Typical yields of the pure products
coordinating anions (WCCWCA), and investigating are 85 – 95%. Hence, the best results are usually ob-
the relationship between the structure and the resulting tained with silver salts rather than lithium salts in dry
physical properties. In this work a series of WC- dichloromethane. All prepared WCCWCAs are stable
CWCAs, prepared by combining the organic cations to air and moisture. All synthesized compounds are
(1-butyl-3-methylimidazolium ([Bmim]+), 1-butyl- solid at room temperature, with the exception of 6a,
2,3-dimethylimidazolium ([Bdmim]+), 1-dodecyl- which is a pale-yellow liquid with a melting point of
3-methylimidazolium ([C12mim]+), tetrabutylphos- –39◦C (see Table 1). All salts display high solubility
phonium ([PBu4]+), tributyltetradecylphosphonium in water and polar organic solvents such as CH2Cl2,
([P4,4,4,14]+), tetrabutylammonium ([NBu4]+), and CH3CN and alcohols, but low solubility in n-hexane.
1,1,3,3-tetramethylguanidium ([TMG]+)) with two
The WCCWCAs 1a–7a and 1b–7b have been char-
different [B(ArF)4]− anions (ArF = C6F5, -C6H3- acterized by FT-IR, NMR spectroscopy and elemen-
3,5-(CF3)2) is described. In analogy to our previous tal analysis (see the Experimental Section). Melting
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B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
1151
Scheme 1. Synthesis of WCCWCA compounds 1a–7a and 1b–7b.
points (Tm) were determined by differential scanning and anion, which is known to have an influence on
calorimetry (DSC). The results are summarized in Ta- the melting point (see also the crystal structures be-
ble 1. Note that the melting points of WCCWCAs with low) [24 – 26, 74 – 76].
the [B{C6H3-3,5-(CF3)2}4] anion (1b–7b) are signif-
The thermal stability of compounds 1a–7a and
icantly lower than those with the [B(C6F5)4]− anion 1b–7b was determined by thermogravimetric analyses
(1a–7a), indicating that the size of the anion affects the (TGA), with isocratic heating at 10◦C min−1 under an
ion pairing and hence the long-range order [72]. The
nature of the cation, however, also influences the melt-
Table 1. Decomposition temperatures Td and melting points
Tm of the synthesized WCCWCAs.
+
ing point, as shown with the [P4,4,4,14
] cation, which
Td (◦C) Tm (◦C)
is giving rise to the long tetradecyl chain and hence, the
lowest melting points in the series of the synthesized
WCCWCAs, being –39◦C for 6a and 49◦C for 6b. In
contrast, WCCWCAs with cations of high Td symme-
try (4 and 5) lead to higher melting points. It is reported
that symmetry breaking in cations leads to lower melt-
ing points of ionic liquids [73]. Similarly, the melting
points of 2a and 2b decrease with increasing length of
the alkyl chain from butyl to dodecyl due to increas-
ing cation size and decreasing cation symmetry. Gen-
erally, WCCWCAs with cations exhibiting acidic pro-
tons (imidazolium, guanidinium) have higher melting
points than those with ammonium and phosphonium
cations, owing to hydrogen bonding between cation
Entry
1
2
3
4
5
6
7
Compound
[Bmim][B(C6F5)4] (1a)
[Bdmim][B(C6F5)4] (2a)
[C12mim][B(C6F5)4] (3a)
[NBu4][B(C6F5)4] (4a)
[PBu4][B(C6F5)4] (5a)
[P4,4,4,14][B(C6F5)4] (6a)
[TMG][B(C6F5)4] (7a)
245
270
287
220
330
337
255
260
255
284
238
300
318
250
145
151
120
159
114
−39a
152
106
91
73
92
121
49
156
8
9
[Bmim][B{C6H3-3,5-(CF3)2}4] (1b)
[Bdmim][B{C6H3-3,5-(CF3)2}4] (2b)
[C12mim][B{C6H3-3,5-(CF3)2}4] (3b)
[NBu4][B{C6H3-3,5-(CF3)2}4] (4b)
[PBu4][B{C6H3-3,5-(CF3)2}4] (5b)
[P4,4,4,14][B{C6H3-3,5-(CF3)2}4] (6b)
[TMG][B{C6H3-3,5-(CF3)2}4] (7b)
10
11
12
13
14
a
Glass transition temperature.
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1152
B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
inert argon atmosphere. All WCCWCAs are thermally
stable beyond 240◦C (Table 1). The decomposition
points also appear to mainly depend on the structure of
the anion. With longer alkyl substituents at the cation,
the decomposition temperature increases. Phospho-
nium WCCWCAs show higher thermal stability than
the corresponding imidazolium salts. Previous reports
have shown that salt compounds containing WCAs a
and b and cationic transition metal complexes usually
decompose below 200◦C [77 – 79], indicating that the
WCCWCAs display increased thermal stability.
Crystal structure analysis
Single crystals of 2b, 5a, 6b, and 7a were obtained
by slow diffusion of n-hexane into a dichloromethane
solution of the compounds at –10◦C. The diffraction
measurements were carried out at low temperatures
(between 100 and 200 K) in order to minimize rotation
of the CF3 groups and ensure the accuracy of the eval-
uation of intermolecular interactions involving F and H
atoms.
Fig. 1. (color online). ORTEP view of the solid-state structure
of compound 2b. Displacement ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clar-
ity. Atom colors: carbon: grey, nitrogen: blue, boron: pink,
fluorine: green.
by M. Bolte et al. [80]. The bond lengths and angles
Compound 2b crystallizes in the monoclinic space are listed in Table 2. H···F contacts between the ortho-
group P21/c with Z = 4 (Fig. 1). Noteworthy, there fluorine atoms and the γ- and δ-carbon atoms of the
are no significant cation-anion contacts, which is butyl substituents are visible.
giving rise to the substitution of a hydrogen atom
Compound 6b crystallizes in the triclinic space
¯
at the C2 ring position by a methyl group (c. f. group P1with Z = 2. The structure is shown in Fig. 3,
[Bmim][B(C6F5)4] (1a) [64]. This is in good agree- and the crystallographic data are summarized in the
ment to previous observations that hydrogen bonds be- Experimental Section. Interestingly, in comparison to
come less pronounced when the H atoms on the imida- compound 5a, there are significantly less H···F con-
zolium ring are replaced by alkyl groups [28].
tacts in compound 6b, which is most presumably
Compound 5a crystallizes in the orthorhombic a consequence of the steric repulsion of the tetrade-
space group Pca21 with two molecules per unit cell. cyl group and the different basicities of fluorine atoms
The asymmetric unit consists of two [PBu4]+ ions and in CF3 and C6F5 groups. The bond angle (C–B–C)min
two [B(C6F5)4]− ions (Fig. 2). Expectedly, the B–C (107.5(1)◦) is larger than that of other compounds
bond lengths (1.656(2) – 1.664(2) Å) are in a similar containing the [B(C6F5)4]− anion, probably due to
range as the B–C bond lengths (1.657(4) – 1.681(4) Å) the steric hindrance of the longer carbon chain of the
of the similar structure [NBu4][B(C6F5)4] described cation.
Table 2. Comparison of selected bond lengths (Å) and angles (deg).
Entry
Compound
Bond lengths (B–C)
(min–max) (Å)
Bond angles (C–B–C)
(min–max) (deg)
1
2
3
4
5
6
7
[Bmim][B(C6F5)4] (1a)
[Bdmim][B(C6F5)4] (2a)
[NBu4][B(C6F5)4] (4a)
[PBu,4][B(C6F5)4] (5a)
[TMG][B(C6F5)4] (7a)
1.652(2) – 1.655(2) [64]
1.653(3) – 1.659(3) [64]
1.657(4) – 1.681(14) [81]
1.656(2) – 1.664(2)
1.39(2) – 1.661(2)
1.635(2) – 1.640(2)
101.3(1) – 114.6(1) [64]
101.2 (1) – 114.2(2) [64]
100.5(2) – 115.5(2) [81]
101.4(1) – 115.6(1)
102.3(1) – 113.3(1)
101.9(2) – 122.7(1)
[Dbmim][B{C6H3-3,5-(CF3)2}4] (2b)
[P4,4,4,14][B{C6H3-3,5-(CF3)2}4] (6b)
1.649(2) – 1.65(2)
107.5(1) – 111.1(1)
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B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
1153
Fig. 2. (color online). ORTEP view of the solid-state structure of compound 5a. Displacement ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted for clarity. Atom colors: carbon: grey, phosphorus: orange, boron: pink,
fluorine: green.
Fig. 4. (color online). ORTEP view of the solid-state structure
of compound 7a. Displacement ellipsoids are drawn at a 50%
probability level. Atom colors: carbon: grey, nitrogen: blue,
boron: pink, fluorine: green.
Compound 7a crystallizes in the triclinic space
group P1 with Z = 2 (Fig. 4). It is noteworthy that
hydrogen atoms could be located in the difference
Fourier maps and are allowed to refine freely. In
the solid state, compound 7a exhibits a plethora of
Fig. 3. (color online). ORTEP view of the solid-state struc-
ture of compound 6b. Displacement ellipsoids are drawn
at a 50% probability level. Hydrogen atoms are omitted
for clarity. Atom colors: carbon: grey, phosphorus: orange,
boron: pink, fluorine: green.
¯
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B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
idation experiments, 6b was chosen as the medium
for the oxidation of sulfides to sulfoxides with H2O2
at room temperature (Scheme 2). A blank experiment
without oxidant was also investigated. No consider-
able oxidation was observed within 24 h, indicating
that the oxygen source for the synthesis of sulfoxide is
not air. Maximum yield is achieved after 4 h reaction
time, while the selectivity remains unchanged during
the whole reaction time.
To generalize the developed methodology, the ox-
idation of various sulfides with different substituents
was examined. The results are shown in Table 3. All
sulfides are effectively oxidized to the corresponding
sulfoxides in good to excellent yields using 35% aque-
ous hydrogen peroxide at room temperature. Interest-
ingly, dialkyl sulfides (entries 2, 3) are more active, af-
fording very high sulfoxide yields (within 3 h). Diaryl
sulfides (entries 1, 3 – 7) are less efficiently oxidized,
probably due to steric hindrance. The electronic nature
of the substituents has less influence on the yield and
selectivity of the sulfoxide products (entries 4 – 7) in
the oxidation of various phenyl-substituted sulfides to
Fig. 5. (color online). Illustration of hydrogen contacts (in red
color) of the fluoride groups of the [B(C6F5)4]− anion in 7a.
hydrogen-bonding interactions between the F atoms of the corresponding sulfoxides. It is important to note
[B(C6F5)4]− and the hydrogen atoms of the 1,1,3,3- that another useful feature of the presented protocol
tetramethylguanidinium (TMG) cation (Fig. 5). The
length of the hydrogen bonds is in the range of 2.357 to
2.650 Å, respectively, which is in the range of typical
H···F contacts [81 – 85]. The pronounced interactions
between cation and anion via hydrogen bonds may be
attributed to the relative acidity of the protons of the
TMG cation.
Oxidation of sulfides to sulfoxides mediated by
WCCWCAs
In analogy to the oxidation of sulfides to sulfox-
ides mediated by imidazolium tetrafluoroborates, the
oxidation of sulfides to sulfoxides was carried out us-
ing compounds 6a and 6b as reaction media, since
they exhibit the lowest melting points in the series of
all synthesized WCCWCAs. Oxidation of thioanisole
Fig. 6. Time-dependent yield (ꢀ) and selectivity (4) of
methyl phenyl sulfoxide.
with aqueous H2O2 as the oxidant was found to be
strongly solvent dependent (details concerning the re-
action details are given in the Experimental Section).
When using 6a as solvent, the sulfoxide yield is only
18% within 4 h with a selectivity of 90%. In an anal-
ogous experiment using 6b nearly quantitative conver-
sion and selectivity were obtained after the same reac-
Scheme 2. Oxidation of sulfides to sulfoxides mediated by
tion time (see Fig. 6). Therefore, for subsequent ox- WCCWCA 6b.
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B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
1155
Table 3. Oxidation of sulfides to sulfoxides with aqueous erolytic process involving nucleophilic attack of the
H2O2 mediated by WCCWCA 6ba.
sulfur on the oxygen atom [89]. This also explains why
R1
R2
Time
(h)
Yieldb Selectivityc
dialkyl sulfides are more easily oxidized than diaryl
sulfides. The efficiency of the described oxidizing sys-
tem can be explained by a specific feature of 6b, which
not only acts as solvent but also can be regarded as
a promoter of the organic reaction [65]. Because of
the electron-withdrawing character of the CF3 group,
a hydrogen bond between the fluoride substituents of
the [B{C6H3-3,5-(CF3)2}4]− anion in 6b and H2O2
or H2O is formed and prevents any further oxida-
tion to sulfone [90]. Furthermore, the [B{C6H3-3,5-
(CF3)2}4]− anion is more stable under oxidative con-
ditions than ionic liquids containing [BF4]− or [PF6]−
anions, which are sensitive to hydrolysis and release of
hydrofluoric acid [91 – 95].
Entry
(%)
(%)
1
2
3
4
5
6
7
Ph
Me
n-Butyl
Ph
Ph
Ph
Me
Me
n-Butyl
4
3
4
5
5
6
5
93
94
91
84
80
82
86
97
98
97
96
97
96
97
Ethyl
CH(CH3)2
CH2CH=CH2
CH2CH2OH
Ph
a
Reaction conditions: 0.5 mL 6b, 2 mmol substrate, 5 mmol H2O2
(30%) at 25 ◦C; b isolated yield after column chromatography; c de-
termined by GC-MS or 1H NMR spectroscopy of the crude reaction
mixture.
IR spectroscopy
In order to further study the interactions between
the WCCWCA 6b and H2O/H2O2 IR and NMR spec-
troscopy experiments were carried out. For an under-
standing of the hydrogen bonding to fluoride, D2O
was applied in the IR measurements. Figs. 8 and 9
show the IR spectra of the C–F stretching region of
6b in D2O and H2O2. The CF3 stretching modes are
very prominent in the infrared spectra. The local C3v
symmetry should produce only two bands; a higher
asymmetric (va) and lower symmetric (vs) stretching
Fig. 7. Oxidation of thioanisole with H2O2 in 6b at 25 ◦C
after five reaction cycles.
is that neither epoxidation of the double bond of allyl vibration. Instead, three pronounced bands at 1355,
phenyl sulfide (entry 6) nor oxidation of the hydroxy 1275 and 1119 cm−1 are observed. The first two bands
group (entry 7) is observed.
can be interpreted as individual localized CF stretch-
The advantage of this oxidation system is the recy- ing vibrations, showing different CF bond lengths. The
cling of the WCCWCA. After reaction completion, the broad band near 1119 cm−1 appears to be a symmet-
product is extracted with n-hexane-diethyl ether, and ric stretching mode of different, overlapping CF bands
subsequently, 6b is extracted with CH2Cl2. The ob- (v > v0 > v). This explanation is in agreement with
tained liquid is dried over anhydrous MgSO4 and then literature data on previously described organic CF3
dried under high vacuum. Five recycling tests were car- derivatives [96 – 104]. While v and v0 are not shifted,
ried out. The results are summarized in Fig. 7. No sig- new bands are formed in the region of the CF3 sym-
nificant loss of yield and selectivity was observed af- metric stretching mode (Fig. 8). The second deriva-
ter five runs of thioanisol oxidation. This system pro- tives of the original spectra are shown in Fig. 9. When
vides an advantage with respect to recycling and sta- adding D2O or H2O2 to 6b, two new bands at 1115
bility when compared to the other systems, which use and 1124 cm−1 or 1114 and 1123 cm−1 are formed,
organic solvents as media for the oxidation of sul- respectively. Furthermore, the development of a shoul-
fides [86 – 88].
der near 1085 cm−1 can be seen in Fig. 8, spectra 2a
Regarding the mechanism of this reaction, the in- and 3a. In Fig. 9, the band at 1085 cm−1 in 2b and 3b
teraction between the anion of 6b, H2O2 and H2O is getting stronger compared to the pure ionic liquid.
appears to be crucial. It is known that organic sul- These changes can be ascribed to a further distortion
fides are oxidized by hydrogen peroxide in a het- of the CF3 local symmetry from C3v to C1 leading to
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1156
B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
Fig. 8. C–F stretching region of neat 6b (1a,1b), a mixture of
6b and D2O (2a, 2b) and a mixture of 6b and H2O2 (3a, 3b).
Fig. 9. Second derivative of the C–F symmetric stretching
region of neat 6b (1b), a mixture of 6b and D2O (2b) and
the formation of new spectral features by weak coor- a mixture of 6b and H2O2 (3b). The derivative curves were
multiplied by a factor of 10.
dination, such as hydrogen bonding between F of the
ionic liquid and hydrogen from D2O or H2O2.
aqueous H2O2 is added the signal of the phosphorus
NMR spectroscopy
atom is shifted to 33.50 ppm, indicating no signifi-
cant changes of the chemical environment at the cen-
Approximate NMR shifts can be indicated for com- tral P atom. Based on the experimental and spectro-
pounds of a known structure and, vice versa, the ap- scopic findings described above, formation of hydro-
proximate coordination environment of unknown com- gen bonds between the CF3 groups of the [B{C6H3-
pounds can be predicted on the basis of chemical shift 3,5-(CF3)2}4]− anion of 6b and hydrogen peroxide
values [96]. Therefore, 11B, 19F and 31P NMR spec- lead to the activation of H2O2 and to the oxidation of
troscopy were performed to show hydrogen bonding sulfides to sulfoxides.
in neat 6b and in the presence of water or hydrogen
peroxide. The 11B NMR spectrum of 6b in deuter- Conclusion
ated DMSO shows one resonance at −6.58 ppm. Af-
ter adding water, the resonance is slightly shifted to
Ionic compounds containing imidazolium, tetra-
−6.84 ppm, and upon addition of aqueous H2O2 the butylammonium, tetraalkylphosphonium, and 1,1,3,3-
signal is shifted to –6.75 ppm (see Supporting Infor- tetramethylguanidium cations associated with
mation available online; see note at the end of the paper [B(ArF)4]− anions have been synthesized and
for availability). The 19F NMR spectrum of 6b shows characterized. The synthesis is facile, and the products
a signal at –59.55 ppm. When water is added the sig- are obtained in good yields. All salts exhibit high
nal shifts to –61.29 ppm or splits into two signals at thermal stability. It is shown that the [B(C6H3-3,5-
−60.64 and –61.23 ppm in the case of adding aqueous (CF3)2)4]− -containing salts 2b–5b display lower
H2O2 (see Supporting Information). The slight shift of melting points than the [B(C6F5)4]− -based salts. The
the CF3 signal points to a change in the chemical en- melting points of salts using tetrabutylammonium and
vironment of the fluorine atoms, pointing to a weak 1,1,3,3-tetramethylguanidium as cation are higher than
H–F interaction. Noteworthy, the signal splitting is not those of any other salts due to the highly symmetric
a consequence of the formation of BF3 or HF, which structure. Increasing the size of the ions has a crucial
would lead to a significantly different peak position. effect on the melting point. Variations of alkyl sub-
Additionally, the NMR shifts of the cation of 6b were stituents on the cation can also be used to fine-tune
also studied. While the 31P NMR spectrum of neat the melting point. In dependence of the structure of
6b exhibits one resonance at 34.95 ppm, upon addi- the cation, ion pairing via hydrogen-fluorine contacts
tion of water the signal moves to 33.43 ppm. When becomes increasingly relevant, which is particularly
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B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
1157
the case for 1,3-dialkylimidazolium and guanidinium (11.8 mL, 11.8 mmol) dissolved in diethyl ether (20 mL). Af-
ter 1 h, the resulting suspension was warmed slowly to room
temperature. The product Li[B(C6F5)4] or Li[B{C6H3-3,5-
(CF3)2}4] was separated by filtration, washed with pentane
for several times, and then dried under vacuum for one day.
Ag[B(C6F5)4] and Ag[B(C6H3-3,5-(CF3)2)4] were prepared
according to a previously published procedure [72].
cations. In the absence of such intramolecular interac-
tions the [B(ArF)4]− anion can also form H–F bonds
with water and hydrogen peroxide, respectively. This
leads to an activation of H2O2 and can be used to
mediate the oxidation of sulfides to sulfoxides.
General procedure for the synthesis of 1a–7a
Experimental Section
1 equiv. Li[B(C6F5)4] and 1 equiv. [WCC]X were
weighed in two different Schlenk tubes and dissolved in
CH2Cl2. The two solutions were mixed and stirred for 2 h
at room temperature, and then filtered. The solvent was re-
moved under high vacuum for 4 h. The product was washed
three times with dry n-hexane and then dried under vacuum
for one day.
General methods
All preparations and manipulation involving air-sensitive
materials were performed using standard Schlenk techniques
under argon atmosphere. Solvents were dried by standard
procedures (Et2O over Na/benzophenone; CH2Cl2 over
CaH2), distilled under argon and kept over 4 Å molecular
sieves. All chemicals were purchased from Acros Organics
or Aldrich and were of analytical grade. They were used as
received. NMR spectra were recorded on a Bruker Avance
DPX-400 instrument and referenced to the deuterated solvent
Improved procedure for the synthesis of 1a–7a
To a mixture of equimolar amounts of Ag[B(C6F5)4]
and [WCC]X dry CH2Cl2 (20 mL) was added. The mixture
was stirred under exclusion of light at room temperature for
10 min. The precipitate was removed by filtration, and the fil-
trate was dried for 4 h under high vacuum. The product was
washed several times with n-hexane and dried under vacuum
for one day.
in the case of the H NMR, C6F6 for 19F NMR, BF3·OEt2
1
for 11B NMR, and H3PO4 (85%) for 31P NMR spectra.
IR spectra were recorded on a Varian FTIR-670 spectrom-
eter, using a GladiATR accessory with a diamond ATR ele-
ment. Elemental analyses were obtained from the microan-
alytical laboratory at Technische Universität München. Cat-
alytic runs were monitored by GC methods on a Hewlett-
Packard instrument HP 5890 Series II equipped with a FID,
a Supelco column Alphadex 120 and a Hewlett-Packard in-
tegration unit HP 3396 Series II. Thermogravimetry analy-
sis (TGA) was conducted utilizing a Netzsch TG209 sys-
tem; typically about 10 mg of each sample was heated from
25 to 1000◦C at 10 K min−1. Differential scanning analysis
(DSC) was performed on a DSCQ2000 instrument (Waters)
Experimental data for 1a: Ag[B(C6F5)4] (0.787 g, 1 mmol),
[Bmim]Br (0.218 g, 1 mmol); isolated yield: 0.73 g (89%).
–
1H NMR ([D6]DMSO, 400 MHz, r. t., ppm): δ = 0.89
(t, 3H), 1.25 (m, 2H), 1.76 (m, 2H), 3.85 (s, 3H), 4.16
(t, 2H), 7.71 (m, 1H), 7.77 (m, 1H), 9.12 (s, 1H). – 19F
NMR ([D6]DMSO, 377 MHz, r. t., ppm): δ = −131.26
(s, 8F), −161.66 (t, 4F), −165.60 (t, 8F). – 11B NMR
([D6]DMSO, 128 MHz, r. t., ppm): δ = −16.7 (s). – IR
(cm−1): v = 480(w), 573 (w), 660 (m), 683 (m), 739 (m),
772 (m), 974 (vs), 1082 (vs), 1272 (m), 1373 (w), 1486 (vs),
1513 (s), 1642 (m), 1953 (w), 2159 (w), 2545 (vw). – Ele-
mental analysis for C32H14N2BF20 (%): calcd. C 46.91, H
1.97, N 3.42; found C 46.25, H 2.10, N 3.87.
in a temperature range from −150 to 200◦C at 10 K min−1
.
Melting points were measured by MPM-H2 melting point
meters. TLC was performed on silica gel 60F254 plates form
E. Merck. Silica gel (0.06 – 0.2 mm 60 Å) was used for col-
umn chromatography.
Synthesis of WCCWCAs
Experimental data for 2a: Ag[B(C6F5)4] (0.787 g, 1 mmol),
[Bdmim]Br (0.223 g, 1 mmol); isolated yield: 0.76 g (92%).
–
General procedures for the synthesis of Li[B(C6F5)4],
Li[B(C6H3-3,5-(CF3)2)4], Ag[B(C6F5)4], and
Ag[B(C6H3-3,5-(CF3)2)4]
1H NMR ([D6]DMSO, 400 MHz, r. t., ppm): δ = 0.89 (t,
3H), 1.27 (m, 2H), 1.68 (m, 2H), 2.58 (s, 3H), 3.75 (s,
3H), 4.11 (t, 2H), 7.61 (m, 1H), 7.64 (m, 1H). – 19F NMR
A 2.5 M solution of n-butyl lithium in hexane (17.82 mL) ([D6]DMSO, 377 MHz, r. t., ppm): δ = −132.42 (s, 8F),
was added slowly to
a
solution of bromopentafluo- −161.54 (t, 4F), −166.02 (t, 8F). – 11B NMR ([D6]DMSO,
robenzene (5 mL, 40 mmol) or 3,5-bis(trifluoromethyl)-5- 128 MHz, r. t., ppm): δ = −16.8 (s). – IR (cm−1): v = 477
bromobenzene (7 mL, 40 mmol) in a mixture of diethyl (vw), 573 (w), 621 (w), 659 (m), 683 (w), 830 (m), 957 (vs),
ether (40 mL) at −78◦C, and the mixture was stirred for 1081 (s), 1163 (m), 1274 (m), 1374 (w), 1458 (vs), 1512 (s),
1 h. This was followed by the dropwise addition of BCl3 1567 (w), 1592 (w), 1642 (m), 1957 (m), 2158 (m), 2547
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1158
B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
(w). – Elemental analysis for C33H17N2BF20 (%): calcd. C
47.56, H 2.18, N 3.36; found C 46.63, H 2.48, N 3.89.
–
31P NMR ([D6]DMSO, 162 MHz, r. t., ppm): δ = 33.77
(s). – IR (cm−1): v = 475 (vw), 573 (w), 602 (w), 610 (w),
660 (m), 683 (w), 726 (vw), 755 (m), 774 (vs), 909 (vw),
977 (vs), 1083 (vs), 1274 (m), 1373 (vw), 1461 (vs), 1512
(s), 1642 (m), 2857 (w), 2929 (w). – Elemental analysis for
C50H56BF20P (%): calcd. C 55.67, H 5.23; found C 55.66, H
5.96.
Experimental data for 3a: Ag[B(C6F5)4] (0.787 g, 1 mmol),
[C12mim]Br (0.331 g, 1 mmol); isolated yield: 0.87 g (93%).
–
1H NMR ([D6]DMSO, 400 MHz, r. t., ppm): δ = 0.78
(t, 3H), 1.20 (m, 18H), 1.75 (m, 2H), 3.83 (3H), 4.13(t,
2H), 7.68 (s, 1H), 7.73 (s, 1H), 9.09 (s, 1H). – 19F NMR
([D6]DMSO, 377 MHz, r. t., ppm): δ = −130.28(s, 8F),
−159.55 (t, 4F), −164.01 (t, 8F). – 11B NMR ([D6]DMSO,
128 MHz, r. t., ppm): δ = −16.51 (s). – IR (cm−1): v = 475
(vw), 573 (m), 610 (w), 623 (m), 660 (s), 682 (m),734 (w),
756 (m), 773 (m), 800 (vw), 831 (w), 976 (vs), 1080 (vs),
1165 (m), 1274 (m), 1461 (vs), 1514 (s), 1563 (w), 1589
(w), 1644 (m), 2856 (w), 2927 (w). – Elemental analysis for
C40H32N2BF20 (%): calcd. C 51.58, H 3.46, N 3.01; found
C 51.39, H 3.63, N 3.16.
Experimental data for 7a: Ag[B(C6F5)4] (0.787 g, 1 mmol),
[TMG]Cl (0.151 g, 1 mmol); isolated yield: 0.75 g (94%).
1
– H NMR ([D6]DMSO, 400 MHz, r. t., ppm): δ = 1.89 (s,
12H), 7.89 (s, 2H). – 19F NMR ([D6]DMSO, 377 MHz, r. t.,
ppm): δ = −130.32 (s, 8F), −159.30 (t, 4F), −163.91 (t, 8F).
–
11B NMR ([D6]DMSO, 128 MHz, r. t., ppm): δ = −16.49
(s). – IR (cm−1): v = 440 (w), 661 (s), 756 (w), 774 (m),
976 (vs), 1080 (s), 1276 (m), 1460 (vs), 1511 (s), 1628 (s),
1958 (w), 2158 (w), 3433 (vw). – Elemental analysis for
C29H14N3BF20 (%): calcd. C 43.80, H 1.77, N 5.28; found
C 43.52, H 1.86, N 5.38.
Experimental data for 4a: Ag[B(C6F5)4] (0.787 g, 1 mmol),
[NBu4]Br (0.322 g, 1 mmol); isolated yield: 0.86 g (93%). –
1H NMR (CDCl3, 400 MHz, r. t., ppm): δ = 0.97 (t, 12H),
1.25 (m, 8H), 1.53 (m, 8H), 3.05 (m, 8H). – 19F NMR
([D6]DMSO, 377 MHz, r. t., ppm): δ = −131.08 (s, 8F),
−160.51 (t, 4F), −161.40 (t, 8F). – 11B NMR ([D6]DMSO,
128 MHz, r. t., ppm): δ = −16.37 (s). – IR (cm−1): v = 476
(w), 574 (w), 660 (m), 682 (m), 773 (w), 977 (vs), 1085 (s),
1272 (m), 1461 (vs), 1513 (s), 1643 (w), 1960 (w), 2169 (w),
General procedure for the synthesis of 1b–7b
In a Schlenk flask, to a mixture of equimolar amounts
of Ag[B(C6H3-3,5-(CF3)2)4] and [WCC]X dry CH2Cl2
(20 mL) was added. The mixture was stirred under exclu-
sion of light at room temperature for 10 min. The precipitate
was removed by filtration, and the filtrate was dried in high
vacuum for 4 h. The product was washed several times with
n-hexane and dried under vacuum for one day.
2878 (w), 2963 (w). – Elemental analysis for C40H36BF20
N
(%): calcd. C 52.14, H 3.94, N 1.52; found C 51.07, H 4.10,
N 1.66.
Experimental data for 1b: Ag[B{C6H3-3,5-(CF3)2}4]
(0.971 g, 1 mmol), [C4mim]Br (0.218 g , 1 mmol); isolated
yield: 0.95 g (95%). – 1H NMR ([D6]DMSO, 400 MHz,
r. t., ppm): δ = 0.89 (t, 3H), 1.26 (m, 2H), 1.75 (m, 2H),
3.84 (s, 3H), 4.15 (t, 2H), 7.62 (m, 8H), 7.70 (m, 4H),
7.73 (m, 1H), 7.71 (m, 1H), 9.11 (s, 1H). – 19F NMR
Experimental data for 5a: Ag[B(C6F5)4] (0.787 g, 1 mmol),
[PBu4]Br (0.338 g, 1 mmol); isolated yield: 0.82 g (87%). –
1H NMR ([D6]DMSO, 400 MHz, r. t., ppm): δ = 0.86 (m,
12H), 1.38 (m, 16H), 2.14 (m, 8H). – 19F NMR ([D6]DMSO,
377 MHz, r. t., ppm): δ = −130.20(s, 8F), −159.07 (t, 4F),
−163.72(t, 8F). – 11B NMR ([D6]DMSO, 128 MHz, r. t.,
ppm): δ = −16.47 (s). – 31P NMR ([D6]DMSO, 162 MHz,
r. t., ppm): δ = 29.74 (s). – IR (cm−1): v = 574 (w), 660 (m),
683 (w), 755 (m), 772 (m), 906 (m), 975 (vs), 1082 (vs),
1273 (w), 1382 (vw), 1459 (vs), 1512 (s), 1642 (m), 1958
(vw), 2159 (vw), 2873 (w), 2932 (w), 2960 (w). – Elemen-
tal analysis for C40H36BF20P (%): calcd. C 51.19, H 3.87;
found C 50.27, H 4.03.
([D6]DMSO, 377 MHz, r. t., ppm): δ = −59.96 (s, 6F). – 11
B
NMR ([D6]DMSO, 128 MHz, r. t., ppm): δ = −6.58 (s). – IR
(cm−1): v = 448 (w), 621 (m), 669 (s), 712 (s), 743 (m), 837
(m), 887 (m), 1109 (vs), 1272 (vs), 1353 (s), 1568 (vw), 1608
(vw), 2961 (vw). – Elemental analysis for C40H28N2BF24
(%): calcd. C 47.88, H 2.81, N 2.79; found C 47.54, H 2.84,
N 3.08.
Experimental data for 2b: Ag[B{C6H3-3,5-(CF3)2}4]
(0.971 g, 1 mmol), [Bdmin]Br (0.223 g, 1 mmol); isolated
Experimental data for 6a: Ag[B(C6F5)4] (0.787 g, 1 mmol), yield: 0.97 g (95%). – 1H NMR ([D6]DMSO, 400 MHz,
[P4,4,4,14]Cl (0.434 g, 1 mmol); isolated yield: 0.92 g (85%). r. t., ppm): δ = 0.87 (t, 3H), 1.25 (m, 2H), 1.64 (m, 2H),
–
1H NMR ([D6]DMSO, 400 MHz, r. t., ppm): δ = 078 (t, 2.48 (s, 3H), 3.73 (s, 3H), 4.08 (t, 2H), 7.61 (m, 12H), 7.62
3H), 0.88 (t, 9H), 1.21 (m, 20H), 1.43 (m, 16H), 2.17 (m, (m, 2H). – 19F NMR ([D6]DMSO, 377 MHz, r. t., ppm):
8H). – 19F NMR ([D6]DMSO, 377 MHz, r. t., ppm): δ = δ = −59.55 (s, 6F). – 11B NMR ([D6]DMSO, 128 MHz, r. t.,
−130.23 (s, 8F), −160.21 (t, 4F), −164.35 (t, 8F,). – 11B ppm): δ = −6.59 (s). – IR (cm−1): v = 669 (vs), 715 (s), 742
NMR ([D6]DMSO, 128 MHz, r. t., ppm): δ = −16.51 (s). (m), 838 (m), 889 (s), 1115 (vs), 1274 (vs), 1352 (s), 1462
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B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
1159
(w), 1535 (vw), 2193 (w), 2959 (vw). – Elemental analy- 710 (s), 744 (vw), 838 (m), 887 (m), 934 (vw), 1001 (vw),
sis for C41H30N2BF24 (%): calcd. C48.40, H 2.97, N 2.75; 1112 (vs), 1161 (vs), 1274 (vs), 1351 (s), 1468 (w), 1608 (w),
found C 47.70, H 2.96, N 3.03.
2858 (w), 2927 (w). – Elemental analysis for C58H68BF24
(%): calcd. C 55.16, H 5.43; found C 55.79, H 5.81.
P
Experimental data for 3b: Ag[B{C6H3-3,5-(CF3)2}4]
(0.971 g, 1 mmol), [C12mim]Br (0.331 g, 1 mmol); isolated
yield: 1.03 g (93%). – 1H NMR ([D6]DMSO, 400 MHz, r. t.,
ppm): δ = 0.72 (t, 3H), 1.16 (m, 18H), 1.75 (m, 2H), 3.84
(3H), 4.13(t, 2H), 7.69 (m, 12H), 7.74 (s, 1H), 7.75 (s, 1H),
9.11 (s, 1H). – 19F NMR ([D6]DMSO, 377 MHz, r. t., ppm):
δ = −60.03 (s, 6F). – 11B NMR ([D6]DMSO, 128 MHz, r. t.,
ppm): δ = −6.54(s). – IR (cm−1): v = 446 (m), 580 (vw),
622 (w), 667 (s), 682 (m), 707(m), 715(m), 742 (w), 838(m),
888 (s), 899 (m), 949 (vw), 1114 (vs), 1158 (vs), 1272 (vs),
1353 (vs), 1466 (vw), 1570 (vw), 1610 (vw), 2860 (w), 2934
(w). – Elemental analysis for C48H44N2BF24 (%): calcd. C
51.68, H 3.98, N 2.51; found C 51.81, H 3.90, N 2.52.
Experimental data for 7b: Ag[B{C6H3-3,5-(CF3)2}4]
(0.971 g, 1 mmol), [TMG]Cl (0.151 g, 1 mmol); isolated
yield: 0.93 g (95%). – 1H NMR ([D6]DMSO, 400 MHz, r. t.,
ppm): δ = 2.86 (s, 12H), 7.66 (m, 12H), 7.80 (s, 2H). – 19
F
NMR ([D6]DMSO, 377 MHz, r. t., ppm): δ = −60.02 (s, 6F).
–
11B NMR ([D6]DMSO, 128 MHz, r. t., ppm): δ = −6.58
(s). – IR (cm−1): v = 449 (w), 669 (m), 709 (m), 837 (w), 885
(m), 1109 (vs), 1274 (vs), 1353 (s), 1415 (w), 1635 (m), 2210
(w), 2548 (vw). – Elemental analysis for C37H26N3BF24
(%): calcd. C 45.37, H 2.68, N 4.29; found C 45.20, H 2.72,
N 4.35.
Oxidation of sulfides to sulfoxides mediated by WCCWCA
6b
Experimental data for 4b: Ag[B{C6H3-3,5-(CF3)2}4]
(0.971 g, 1 mmol), [NBu4]Br (0.322 g, 1 mmol); isolated
yield: 1.04 g (94%). – 1H NMR ([D6]DMSO, 400 MHz, r. t.,
ppm): δ = 0.88 (t, 12H), 1.27 (m, 8H), 1.55 (m, 8H), 3.15
(m, 8H), 7.58 (m, 12H). – 19F NMR ([D6]DMSO, 377 MHz,
r. t., ppm): δ = −59.87 (s, 6F). – 11B NMR ([D6]DMSO,
128 MHz, r. t., ppm): δ = −6.81 (s). – IR (cm−1): v = 450
(vw), 670 (s), 712 (s), 799 (m), 838 (m), 889 (m), 1117 (vs),
1271 (vs), 1353 (s), 1470 (w), 1608 (vw), 2179 (w), 2964
(w). – Elemental analysis for C48H48NBF24 (%): calcd. C
52.14, H 4.38, N 1.27; found C 51.81, H 4.70, N 1.44.
Typical procedure for the oxidation of the sulfides in
[P4,4,4,14][B{C6H3-3,5-(CF3)2}4]: To a stirred solution of
the sulfide (2 mmol, 0.24 mL) in 6b (0.50 mL), an aque-
ous solution of hydrogen peroxide (30% in water) (0.51 mL,
5 mmol) was added in 2 to 3 portions at room temperature.
The progress of the reaction was followed by TLC. The
reaction mixture was extracted with n-hexane-diethyl ether
2:1 v/v (5 × 5 mL), and the extract was dried over anhy-
drous MgSO4. The crude product was obtained by rolling
evaporation and purified by column chromatography sepa-
ration (silica gel using n-hexane-ethyl acetate 90:10 v/v).
The yield and selectivity of methyl phenyl sulfoxide in ki-
netic and recycle experiments was calculated from calibra-
tion curves (r2 > 0.999) recorded using 3-methylanisole and
1,4-diacetylbenzene as internal standard. The WCCWCA
was extracted with CH2Cl2 and then treated with MnO2 to
destroy the excess peroxide. The obtained liquid was dried
over anhydrous MgSO4 and then dried for 4 h in vacuo at
50◦C to remove CH2Cl2. Fresh substrate and hydrogen per-
oxide were then added for a new reaction cycle. All products
were characterized by melting point, 1H NMR, 13C NMR
and IR spectroscopy (see the Supporting Information).
Experimental data for 5b: Ag[B{C6H3-3,5-(CF3)2}4]
(0.971 g, 1 mmol), [PBu4]Br (0.338 g, 1 mmol); isolated
yield: 1.02 g (91%). – 1H NMR ([D6]DMSO, 400 MHz, r. t.,
ppm): δ = 0.82 (m, 12H), 1.36 (m, 16H), 2.10 (m, 8H); 7.57
(m, 12H). – 19F NMR ([D6]DMSO, 377 MHz, r. t., ppm):
δ = −59.66 (s, 6F). – 11B NMR ([D6]DMSO, 128 MHz, r. t.,
ppm): δ = −6.59 (s). – 31P NMR ([D6]DMSO, 162 MHz,
r. t., ppm): δ = 33.76 (s). – IR (cm−1): v = 447 (vw), 667
(m), 712 (m), 837 (w), 886 (m), 1114 (vs), 1272 (vs), 1353
(s), 1465 (w), 1610 (vw), 2542 (vw), 2875 (vw), 2963 (vw).
– Elemental analysis for C48H48BF20P (%): calcd. C 51.35,
H 4.31; found: C 51.07, H 4.46.
Single-crystal X-ray structure determinations
Experimental data for 6b: Ag[B{C6H3-3,5-(CF3)2}4]
Data were collected on an X-ray single-crystal diffrac-
(0.971 g, 1 mmol), [P4,4,4,14]Cl (0.434 g, 1 mmol); isolated tometer equipped with a CCD detector (Bruker APEX II, κ-
yield: 1.15 g (91%). – 1H NMR ([D6]DMSO, 400 MHz, CCD), a rotating anode (Bruker AXS, FR591) with MoKα
r. t., ppm): δ = 0.73 (t, 3H), 0.84 (t, 9H), 1.16 (m, 20H), radiation (λ = 0.71073 Å), and a graphite monochromator
1.40 (m, 16H), 2.13 (m, 8H), 7.57 (m, 12H). – 19F NMR by using the SMART software package [105]. The measure-
([D6]DMSO, 377 MHz, r. t., ppm): δ = −59.55 (s, 6F). – 11
B
ments were performed on a single crystal coated with perflu-
NMR ([D6]DMSO, 128 MHz, r. t., ppm): δ = −6.58 (s). – orinated ether. The crystal was fixed on the top of a glass fiber
31P NMR ([D6]DMSO, 162 MHz, r. t., ppm): δ = 33.54 (s). – and transferred to the diffractometer. The crystal was frozen
IR (cm−1): v = 403 (w), 450 (w), 618 (vw), 669 (s), 681 (m), in a stream of cold nitrogen. A matrix scan was used to deter-
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1160
B. Zhang et al. · Ion Pairs of Weakly Coordinating Cations and Anions
mine the initial lattice parameters. Reflections were merged system: orthorhombic; space group: Pca21 (no. 29);
and corrected for Lorenz and polarization effects, scan speed, a = 18.9591(7), b = 22.2987(8), c = 19.2449(7) Å,
and background using SAINT [73]. Absorption corrections,
V
= 8136.0(5) Å3, Z = 8, λ(MoKα ) = 0.71073 Å,
including odd and even ordered spherical harmonics were µ = 0.2 mm−1, ρcalcd. = 1.53 g cm−3, T = 123(1) K,
performed using SADABS [106]. Space group assignments F(000) = 3808 e; θ-range = 0.91 – 25.40◦; data collected:
were based upon systematic absences, E statistics, and suc- 231060; independent data [Io > 2 σ(Io) / all data / Rint]:
cessful refinement of the structures. The structures were 14524 / 14933 / 0.036; data/restraints / parameters:
solved by Direct Methods with the aid of successive differ- 14933 / 1 / 1126; R1 [Io > 2 σ(Io) / all data]: 0.0245 /
ence Fourier maps and were refined against all data using 0.0257; wR2 [Io > 2 σ(Io) / all data]: 0.0667 / 0.0682;
WINGX [107] based on SIR92 [108]. If not mentioned oth- GOF = 1.046; ∆ρmax/min: 0.27 / −0.22 e Å−3
.
erwise, non-hydrogen atoms were refined with anisotropic
Single-crystal X-ray structure determination on compound
6b
displacement parameters. Methyl hydrogen atoms were re-
fined as part of rigid rotating groups, with C–H = 0.98 Å and
Uiso(H) = 1.5 ·Ueq(C). Other H atoms were placed in calcu-
lated positions and refined using a riding model, with methy-
lene and aromatic C–H distances of 0.99 and 0.95 Å, respec-
tively, and Uiso(H) = 1.2 ·Ueq(C). Full-matrix least-squares
refinements were carried out by minimizing Σw(Fo2 − Fc2)2
with the SHELXL-97 weighting scheme [109]. Neutral atom
scattering factors for all atoms and anomalous dispersion cor-
rections for the non-hydrogen atoms were taken from In-
ternational Tables for Crystallography [110]. Images of the
crystal structures were generated by PLATON [111].
CCDC 956714 (2b), 956711 (5a), 956712 (6b), and
956713 (7a) contain the supplementary crystallographic data
for this compound. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Crystal data: empirical formula: C58H68BF24P;
Mr = 1262.90; crystal color and shape: colorless frag-
ment, crystal dimensions: 0.56 × 0.59 × 0.59 mm3;
¯
crystal system: triclinic; space group: P1 (no. 2);
a = 12.9732(4),
α = 105.4144(14)◦, β = 97.8526(13)◦, γ = 97.5892(13)◦,
V = 3088.64(16) Å3,
Z = 2, λ(MoKα ) = 0.71073 Å,
µ = 0.2 mm−1 ρcalcd. = 1.36 g cm−3
T = 123(1) K,
b = 14.0401(4),
c = 18.0389(5) Å,
,
,
F(000) = 1304 e; θ-range = 1.19 – 25.43◦; data collected:
95414; independent data [Io > 2 σ (Io) / all data / Rint]:
10444 / 11372 / 0.030; data/restraints / parameters: 11372
/ 0 / 845; R1 [Io > 2σ (Io) / all data]: 0.0363 / 0.0399; wR2
[Io > 2 σ(Io) / all data]: 0.0889 / 0.0929; GOF = 1.015;
∆ρmax/min: 0.53 / −0.50 e Å−3
.
Single-crystal X-ray structure determination of compound
7a
Single-crystal X-ray structure determination of
compound 2b
Crystal data: empirical formula: C29H14BF20N3;
Mr = 795.24; crystal color and shape: colorless frag-
ment, crystal dimensions: 0.10 × 0.25 × 0.36 mm3;
Crystal data: empirical formula: C41H29BF24N2;
Mr = 1016.47; crystal color and shape: colorless block,
crystal dimensions: 0.38 × 0.51 × 0.51 mm3; crystal system:
monoclinic; space group: P21/c (no. 14); a = 20.1391(5),
b = 13.9355(3), c = 16.2559(4) Å, β = 111.2143(9)◦,
V = 4253.03(18) Å3, Z = 4, λ(MoKα ) = 0.71073 Å,
¯
crystal system: triclinic; space group: P1 (no. 2);
a = 8.1571(2), b = 12.7109(4), c = 14.5597(4) Å,
α = 89.4091(12)◦, β = 83.9006(12)◦, γ = 81.7908(12)◦,
V
= 1485.66(7) Å3, Z = 2, λ(MoKα ) = 0.71073 Å,
µ = 0.2 mm−1
, , T = 123(1) K,
ρcalcd. = 1.59 g cm−3
µ = 0.2 mm−1, ρcalcd. = 1.78 g cm−3, T = 123(1) K,
F(000) = 788 e; θ-range = 1.41 – 25.43◦; data collected:
51233; independent data [Io > 2 σ(Io) / all data / Rint]:
5014 / 5423 / 0.039; data/restraints / parameters: 5423 /
0 / 534; R1 [Io > 2 σ(Io) / all data]: 0.0296 / 0.0322; wR2
[Io > 2 σ(Io) / all data]: 0.0778 / 0.0808; GOF = 1.031;
F(000) = 2040 e; θ-range = 1.82 – 25.50◦; data collected:
133524; independent data [Io > 2 σ(Io) / all data / Rint]:
6806 / 7872 / 0.019; data/restraints / parameters: 7872 /
0 / 785; R1 [Io > 2 σ(Io) / all data]: 0.0396 / 0.0472; wR2
[Io > 2 σ(Io) / all data]: 0.0937 / 0.1006; GOF = 1.020;
∆ρmax/min: 0.47 / −0.43 e Å−3
.
∆ρmax/min: 0.29 / −0.19 e Å−3
.
Single-crystal X-ray structure determination of
compound 5a
Supporting information
Detailed information on all crystal structure determina-
Crystal data: empirical formula: C40H36BF20P; tions, spectroscopic data, and characterization of all sulfox-
Mr = 938.47; crystal color and shape: colorless frag- ides are given as Supporting Information (17 pages) available
ment, crystal dimensions: 0.48 × 0.56 × 0.61 mm3; crystal online (DOI: 10.5560/ZNB.2014-4165).
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Acknowledgement
Foundation of China (21071073) and the Cooperation
Project (21111130584) for financial support.
B. Z. and. S. L. thank the TUM Graduate School for
financial support. S.-L. Z. thanks the National Science
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