Mechanistic study on the fluorination of K[B(CN)4] with ClF enabling the high yield and large scale synthesis of k[B(CF3) 4] and K[(CF3)3BCN]

Article abstract of DOI:10.1021/ic201319h

The fluorination of K[B(CN)₄] with ClF is studied by millimolar test reactions in aHF and CH₂Cl₂ solution and by subsequent identification of intermediates such as B-CF=NCl, B-CF ₂-NCl₂, and B-CF₃ species as well as NCl ₃ by ¹⁹F, ¹¹B NMR, and Raman spectroscopy, respectively. At first one cyano group of K[B(CN)₄] is converted fast into a CF₃ group, and with increasing fluorination the reaction becomes slower and several intermediates could be observed. On the basis of these results, a synthesis was developed for K[B(CF₃)₄] on a 0.2 molar scale by treatment of K[B(CN)₄] diluted in aHF with ClF. The course of the reactions was followed by (i) monitoring the vapor pressure inside the reactor, (ii) observing the heat dissipation during ClF uptake, and (iii) measuring the volume of the released nitrogen gas. Since the fluorination of the last cyano group proceeds very slowly, the selective synthesis of K[(CF₃)₃BCN] on a 0.2 molar scale is possible, as well. The analysis of the mechanisms, thermodynamics, and kinetics of the fluorination reactions is supported by density functional theory (DFT) calculations.

Full text of DOI:10.1021/ic201319h

ARTICLE
pubs.acs.org/IC
Mechanistic Study on the Fluorination of K[B(CN)4] with ClF
Enabling the High Yield and Large Scale Synthesis of K[B(CF3)4]
and K[(CF3)3BCN]
Eduard Bernhardt,*,† Maik Finze,‡ and Helge Willner*,†
†Fachbereich C ꢀ Anorganische Chemie, Bergische Universit€at Wuppertal, Gaußstraße 20, D-42097 Wuppertal, Germany
‡Institut f€ur Anorganische Chemie, Julius-Maximilians-Universit€at W€urzburg, Am Hubland, D-97074 W€urzburg, Germany
S Supporting Information
b
ABSTRACT: The fluorination of K[B(CN)4] with ClF is studied by millimolar test
reactions in aHF and CH2Cl2 solution and by subsequent identification of
intermediates such as BꢀCFdNCl, BꢀCF2ꢀNCl2, and BꢀCF3 species as well
as NCl3 by 19F, 11B NMR, and Raman spectroscopy, respectively. At first one cyano
group of K[B(CN)4] is converted fast into a CF3 group, and with increasing
fluorination the reaction becomes slower and several intermediates could be
observed. On the basis of these results, a synthesis was developed for K[B(CF3)4]
on a 0.2 molar scale by treatment of K[B(CN)4] diluted in aHF with ClF. The
course of the reactions was followed by (i) monitoring the vapor pressure inside the
reactor, (ii) observing the heat dissipation during ClF uptake, and (iii) measuring
the volume of the released nitrogen gas. Since the fluorination of the last cyano
group proceeds very slowly, the selective synthesis of K[(CF3)3BCN] on a 0.2
molar scale is possible, as well. The analysis of the mechanisms, thermodynamics,
and kinetics of the fluorination reactions is supported by density functional theory (DFT) calculations.
’ INTRODUCTION
of many (CF3)3B derivatives,3,6 for example, [(CF3)3BCPnic]ꢀ
(Pnic = N, P, As)15,16 and [(CF3)3BC(O)Hal]ꢀ (Hal = F,
Cl, Br, I).17
Since decades the development of weakly coordinating anions
remains a very important topic in inorganic and applied chemical
research.1 The title compound K[B(CF3)4] contains the very
promising weakly coordinating anion that can be used in
electrolytes, in dye-sensitized solar cells, in Li-ion batteries, in
ionic liquids, as counteranion for the stabilization of novel highly
electrophilic cations, with possible applications, for example,
in cationic catalysis. Simple M[B(CF3)4] salts with the single-
charged cations M+ = Li+, K+, Cs+, Ag+ have been synthesized
and fully characterized structurally and spectroscopically for the
first time only 10 years ago.2,3 It turned out that the highly
symmetric [B(CF3)4]ꢀ anion is most weakly coordinating, since
so far it is the only anion that stabilizes the [Ag(CO)4]+ cation2
and it exhibits the highest ν(NꢀH) vibrational frequency for the
Out of these derivatives the [(CF3)3BCN]ꢀ anion is of special
interest since its potential as building block, for example, in
ionic liquids [EMIM][(CF3)3BCN],18,19 as starting material for
the synthesis of novel weakly coordinating anions [(CF3)3-
BCNB(CF3)3]ꢀ,6 as part of Brønsted acids (CF3)3BCNH or
(CF3)3BCNH OEt2,6,18,20 and as ligand in transition metal
3 3 3
chemistry [Cp2ZrMe{NCB(CF3)3}] as well as [(PPh3)3RhNCB-
(CF3)3]6,18,21 has been demonstrated.3
The [B(CF3)4]ꢀ anion is accessible by fluorination of the
tetracyanoborate anion,22 [B(CN)4]ꢀ, with either ClF or ClF3.2
In contrast, related reactions of nitriles with chlorine fluorides
result in most cases in simple addition reactions to the RꢀCtN
triple bond yielding RꢀCF2ꢀNCl2 or RꢀCF2ꢀNFCl com-
pounds.23ꢀ26 So far, the formation of CH3ꢀCF3 as a side
product24 and in 45% yield25 has only been observed for the
fluorination of acetonitrile with ClF5 and ClF/F2, respectively.
There is only one further example known in which the fluorina-
tion with ClF results in the partial cleavage of CF2ꢀNCl2 bonds.26
In contrast, reactions with bromine trifluoride proceed under
complete cleavage of CtN triple bonds resulting in trifluoro-
methyl compounds,27,28 and iodine pentafluoride does not react
ion pair [(nC8H17)3NH]+ [B(CF3)4]ꢀ observed in CCl4
3 3 3
solution, indicating its extremely low basicity.4 The [B(CF3)4]ꢀ
anion is very redox stable,5 and it is stable against many highly
+ 8
reactive cations,3,6 for example, NO+,7 N5 , [H(OEt2)2]+,9
[Ph3C]+,9 [Cp2ZrMe]+,9 [Co(CO)5]+,10 [Co(CO)2(NO)2]+,10
and [C6F5Xe]+.11 In the presence of strong Lewis and Brønsted
acids the stability of the [B(CF3)4]ꢀ anion is limited.12 However,
this reactivity makes the [B(CF3)4]ꢀ anion a valuable starting
material for the preparation of a broad variety of derivatives of the
elusive free Lewis acid (CF3)3B3,12 since in concentrated sulfuric
acid the reactive boron carbonyl (CF3)3BCO is formed.13,14 This
boron carbonyl can be used as starting material for the synthesis
Received: June 20, 2011
Published: September 22, 2011
r
2011 American Chemical Society
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|

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ARTICLE
Figure 1. Stainless steel apparatus for the synthesis of K[B(CF3)4]: (a) capacitance manometer, (b) 16 mm flange with Cu gasket, (c) bellow valve with
6 mm fitting, (d) 5.6 L reactor, (e) Dewar vessel, (f) reaction mixture, and (g) stir bar. The photo shows the cooled reactor (middle) connected to the
cooled ClF cylinder (right).
with nitriles at all.28 Transition metal cyano complexes have
been converted into the corresponding trifluoromethyl com-
plexes by the reaction with ClF,29 similar to the synthesis of the
[B(CF3)4]ꢀ anion.
water. The reaction enthalpy for the fluorination of the tetra-
cyanoborate anion was estimated by the hypothetical model
reaction of HCN with ClF to result in HCF3, nitrogen, and
chlorine (eq 2) using experimental enthalpies of formation.31
The main obstacle for the further development of the chem-
istry of the [B(CF3)4]ꢀ anion is its availability in millimolar
quantities only.2 For this reason we have studied the course and
mechanism of the fluorination of K[B(CN)4] in detail and then
developed an improved and safe synthesis for K[B(CF3)4]
in high purity on a 0.2 molar scale, which is presented in
this contribution. Furthermore, it turned out that under con-
trolled conditions K[(CF3)3BCN] can be obtained in high yield,
which was previously only accessible in a multistep synthesis via
(CF3)3BCO.16,30
The reaction enthalpy of ꢀ2654.4 kJ molꢀ1 is in very good
agreement to the value derived for this model reaction from
density functional theory (DFT) calculations of ꢀ2613.2 kJ
molꢀ1. The synthesis of the [B(CF3)4]ꢀ anion is predicted to be
a little less exothermic: ꢀ2390.4 kJ molꢀ1 (eq 1). This high
reaction enthalpy shows the importance of controlling the
reaction conditions, which is easily accomplished with gaseous
ClF, to avoid overheating and, hence, BꢀC bond cleavage that
results in the formation of fluoroborate anions as side products.
Even at ꢀ78 °C the partially dissolved K[B(CN)4] in aHF
(vapor pressure <1 mbar) reacts with ClF very fast as monitored
by the pressure increase in the reactor (Figure 1). ClF at a
pressure of 10 to 20 mbar in the cold reactor is completely
consumed in large amount of aHF solution within a few seconds.
At the same time the dry ice in the cold bath evaporates faster
because of the exothermic reaction. After about 30 min one-third
of the required ClF is consumed, and the pressure increases to
approximately 20 mbar. During the addition of the second third
of ClF, heat release is still observed, and the pressure inside the
reactor increases to about 800 mbar within 1 h. To complete the
reaction, the reactor is warmed to room temperature overnight.
Subsequently the reactor is cooled to ꢀ78 °C again, all volatile
products (Cl2 and N2) are pumped off through a cold trap held at
ꢀ196 °C, and the N2 gas is collected at the exhaust of the pump.
The last third of ClF (in total ca. 15 equiv) is added to the
reaction mixture at ꢀ78 °C and subsequently the reactor is
’ RESULTS AND DISCUSSION
According to the original report,2 salts of the [B(CN)4]ꢀ
anion can be fluorinated in aHF with either ClF or ClF3 in
millimolar quantities. Attempts to scale up the reaction with ClF3
were found to be dangerous, because the highly exothermic
reaction is very difficult to control. The use of ClF in place of
ClF3 has the advantage that ClF is a gas under the reaction
conditions and, hence, the exothermic reaction in diluted aHF
solution is easier to control. The reaction setup is depicted in
Figure 1.
The reaction was found to proceed via 3 equiv of ClF per
cyano group according to eq 1.
K½BðCNÞ4ꢁ þ 12ClF f K½BðCF3Þ4ꢁ þ 2N2 þ 6Cl2
ð1Þ
The release of nitrogen was verified by cooling the reaction
mixture to ꢀ78 °C and pumping Cl2 and N2 gas through a cold
trap held at ꢀ196 °C. Only N2 leaves the exhaust tube of the
vacuum pump and is collected in a measuring glass filled with
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ARTICLE
Table 1. NMR Data of Borates Containing BꢀF, BꢀCN, BꢀCFNCl, BꢀCF2NCl2, BꢀCF3, BꢀCF2Cl, and BꢀCF2NClF Groups
Observed in Different Stages of the Reaction of K[B(CN)4] with ClF
anion
δ(11B) [ppm]
δ(19F) [ppm]
2J(19F,11B) [Hz]
4J(19F,19F) [Hz]
[B(CN)4]ꢀ
[B(CF3)(CN)3]ꢀ
[B(CF3)2(CN)2]ꢀ
[B(CF3)3(CN)]ꢀg
ꢀ38.6
ꢀ32.1
ꢀ26.6
ꢀ22.3
ꢀ19.0
ꢀ31.0
ꢀ24.8
ꢀ20.3
ꢀ33.1
ꢀ29.2
ꢀ17.4
ꢀ18.5
ꢀ13.7
ꢀ21.9
ꢀ25.7
ꢀ17.1
ꢀ20.0
ꢀ7.0
ꢀ67.0a
36.5
ꢀ65.3a
32.5
ꢀ63.9a
28.9
6.6
5.8
[B(CF3)4]ꢀh
ꢀ63.3a
25.9
[B(CF2NCl2)(CN)3]ꢀ
[B(CF2NCl2)2(CN)2]ꢀ
[B(CF2NCl2)3(CN)]ꢀ
[B(CFNCl)(CN)3]ꢀ
[B(CFNCl)2(CN)2]ꢀ
[B(CF3)3(CF2NCl2)]ꢀ
[B(CF3)3(CFNCl)]ꢀ
[B(CF2NCl2)2(CF2NClF)2]ꢀ
[B(CF3)2(CN)(CFNCl)]ꢀ
[B(CF3)(CN)2(CF2NCl2)]ꢀ
[B(CF3)3(CF2Cl)]ꢀ
[B(CF3)2(CF2Cl)CN]ꢀ
[BF(CF3)3]ꢀ
n.o.
29.7
ꢀ86.4b
26.1
ꢀ84.0b
22.9
n.o.
41.7
n.o.
30.0
ꢀ60.7a, ꢀ81.5b
ꢀ62.6a, ꢀ5.2c
ꢀ84.6b, ꢀ92.9d
ꢀ64.1a, ꢀ7.1c
ꢀ64.9a, ꢀ87.2b
ꢀ62.7a, ꢀ53.9e
ꢀ63.1a, ꢀ55.0e
ꢀ70.8a, ꢀ232.1f
25.3, 21.2
27.0, 28.8
23.3, 18.0
30.4, 33.5
32, 27
6.9
6.3
6.9
5.6
7.5
25.2, 20.7
28.3, 23.4
28.9, 58.4(1J)
6.6
6.8
5.1(3J)
a CF3. b CF2NCl2. c CFNCl. d CF2NClF. e CF2Cl. f BF. g [B(CF3)3(CN)]ꢀ: δ(13C, CF3) = 132.4 ppm, δ(13C, CN) = 127.5 ppm, 1J(11B,13C, CF3) = 76.3
Hz, 1J(11B,13C, CN) = 63.4 Hz, 1J(19F,13C) = 303.8 Hz, 1Δ19F(12/13C) = 0.1305 ppm, 2Δ19F(10/11B) = 0.009 ppm. h [B(CF3)4]ꢀ: δ(13C) = 133.0 ppm,
1J(11B,13C) = 73.4 Hz, 1J(19F,13C) = 304.4 Hz, 2J(19F,10B) = 8.7 Hz, 3J(19F,13C) = 3.9 Hz, 1Δ19F(12/13C) = 0.1314 ppm, 1Δ11B(12/13C) = 0.0035 ppm,
2Δ19F(10/11B) = 0.0111 ppm, 3Δ19F(12/13C) = 0.0011 ppm.
warmed to 30 °C for 15 h. Then the product is worked up and
isolated.
much lower compared to that of HF in aHF solution, the reaction
proceeds much slower in dichloromethane.
To gain a deeper insight into the course and the mechanism of
the reaction, fluorination experiments were conducted with (i) a
stoichiometrically deficient proportion of ClF at ꢀ78 °C with the
potassium salt in neat aHF and with (ii) an excess of ClF with the
tetrabutylammonium salt in dichloromethane in the presence of
potassium fluoride. From the NMR spectroscopic analyses (see
Table 1) it is evident that the transformation of the cyano groups to
trifluoromethyl groups proceeds in three steps: (i) the addition of
ClF results in BꢀCFdNCl species, (ii) the further addition of ClF
gives BꢀCF2ꢀNCl2 derivatives, and (iii) the cleavage of the CꢀN
bond with ClF results in BꢀCF3 species and NCl3. The formation
of NCl3 was unambiguously proven by Raman spectroscopy. NCl3
is unstable in the later stage of the reaction and decomposes to
elemental nitrogen and chlorine even at ꢀ78 °C.
A strong solvent effect was found for the CF2ꢀNCl2 bond
cleavage. In all reactions performed at ꢀ78 °C in aHF only small
amounts of BCF2ꢀNCl2 species were detected whereas in the
dichloromethane/KF system the main component is the
[B(CF2ꢀNCl2)3(CN)]ꢀ anion. This observation indirectly sup-
ports the results of the DFT calculations that predict a participa-
tion of HF and/or further ClF in the reaction.
Three of the cyano groups of the [B(CN)4]ꢀ anion undergo
fast addition of ClF in aHF and dichloromethane. The transfor-
mation of the fourth group is much slower and prolonged
reaction times and reaction temperatures of up to 30 °C are
necessary for a complete conversion of all four CN to CF3
groups. In aHF it was possible to selectively synthesize the
potassium salt of the [B(CF3)3(CN)]ꢀ anion that was previously
accessible via multistep protocols from (CF3)3BCO, only.16,30
Furthermore, it is possible to selectively prepare salts of the new,
unusual anion [B(CF2ꢀNCl2)3(CN)]ꢀ in CH2Cl2.
Calculations of transition states for the reaction of ClF with
CF2ꢀNCl2 groups resulting in CF3 groups and NCl3 ruled out a
concerted mechanism for the addition to and the cleavage of the
CꢀN single bond. On the basis of the calculations, an ionic transition
state according to eq 3 is involved in the CꢀN bond cleavage.q
It was found that all borates carrying ꢀCF2ꢀNCl2 or
ꢀCFdNCl groups are quite stable in neutral aqueous solution.
However, the ꢀCF2ꢀNCl2 group decomposes under basic or acidic
conditions, but ꢀCFdNCl is only acid sensitive. More work is
needed to isolate the new borates with ꢀCF2ꢀNCl2 or ꢀCFdNCl
groups in pure form and to explore their chemistry in detail.
q
½R3BꢀCF2ꢀNCl2ꢁꢀ þ ClF f f½R3BꢀCF2ꢀNþCl3
f ½R3BꢀCF3ꢁꢀ þ NCl3
Fꢀꢁꢀg
3 3 3
ð3Þ
The calculated activation barrier for this process of approximately
200 kJ molꢀ1 is too high for the observed reaction. However,
solvation of Fꢀ in the ionic transition state by at least 2 molecules of
either HF or ClF lowers the barrier to less than 50 kJ molꢀ1. In
dichloromethane the transition state needs to be stabilized via
solvation with ClF. Since (i) ClF is a less effective solvating agent
than HF and (ii) the concentration of ClF in dichloromethane is
’ CONCLUSION
Transformations of cyano groups into trifluoromethyl groups
with halogen fluorides, for example, ClF, ClF3, or BrF3, are of
broad interest in inorganic and organic chemistry. However, only
little is known on the mechanism of this reaction and, hence, the
insights into the addition reactions of chlorine monofluoride to
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ARTICLE
the [B(CN)4]ꢀ anion to result in ꢀCFdNCl and ꢀCF2ꢀNCl2
boron species and the subsequent cleavage of the CꢀN single
bond by ClF provide valuable information for the further devel-
opment of such reactions.
With the new synthesis of the K[B(CF3)4] and K[(CF3)3-
BCN] on a 0.2 molar scale using the readily available K[B(CN)4]
and chlorine monofluoride the borate anions are available in
larger quantities for the first time.2 This will enable the further
development of their chemistry and their use in various applica-
tions, for example, in coordination chemistry, for the stabilization
of highly reactive cations, and in ionic liquids.
mixture within 1 h. During this time the pressure inside the reactor
increased to about 800 mbar, and there was only little heat release. The
reactor was warmed overnight to room temperature and then cooled to
ꢀ78 °C again. Volatile Cl2 and N2 were slowly pumped off through a
cold trap held at ꢀ196 °C and at the end of the exhaust tube of the
vacuum pump 7.0 L of N2 were collected at room temperature in a
measuring glass (2 L, in 4 portions) filled with water. Subsequently the
cold reactor was filled with ClF (1 mol; in total 15 equivalents) within
1 h while the pressure increased to 900 mbar. The reactor was kept at
30 °C for 15 h and then cooled to ꢀ78 °C again. Volatile Cl2 and N2
were slowly pumped off through the cold trap held at ꢀ196 °C and at the
exhaust of the vacuum pump 3.5 L of N2 were collected. In total 10.5 L of
N2 (∼0.4 mol) had formed, which is in agreement to the stoichiometry
given in eq 1. All aHF was recovered in a 1.5 L steel storage vessel held at
ꢀ78 °C while stirring the solution under heating the reactor with warm
water to room temperature. After all aHF was transferred, the reactor
was evacuated for 20 min, the CF flange was opened, and the content
was worked up.
The raw product was washed out of the reactor using an aqueous
K2CO3 solution (50 g dissolved in 200 mL of H2O) and two portions of
water (100 mL). The collected aqueous washings were combined and
extracted with 3 portions of diethyl ether (200 + 100 + 100 mL). The
collected ethereal extracts were treated with K2CO3 to remove most of
the water. The ether solution was evaporated, and the solid residue was
treated at 80 °C with ultrasonic sound in a vacuum. The dry solid
product was crushed in a mortar, washed with CH2Cl2 and dried in a
vacuum. Yield: 62.3 g (96%, purity 99.0%; traces of K[(CF3)3BF]
(0.59%), K[(CF3)3BCN] (0.31%), K[(CF3)2BF2] (0.06%), and
K[(CF3)2B(CN)2] (0.01%)).
Preparation of K[(CF3)3BCN]. The procedure used for the
preparation of K[(CF3)3BCN] was similar to that described for the
synthesis of K[B(CF3)4]. In a typical run the reactor was charged with
K[B(CN)4] (30.8 g, 0.20 mol) and treated with ClF at ꢀ78 °C until
2 mol ClF were consumed. Subsequently the reaction mixture was stirred
for further 4 h at ꢀ78 °C to complete the reaction. Then all volatile
products (excess of ClF, Cl2 and N2) were pumped off through a trap
held at ꢀ196 °C. At the exhaust tube of the pump 5.8 L of N2 were
collected. To decompose all residual NCl3, the reaction mixture was
warmed to room temperature overnight. As expected, the volatile
products contained an additional amount of 1.5 L of N2 (in sum
∼0.3 mol). The isolation of the product was performed in analogy to that
of K[B(CF3)4]. Yield: 47.3 g (83%; composition: 76% K[(CF3)3BCN],
10% K[(CF3)2B(CN)2], 6% K[(CF3)3BCFNCl], 0.9% K[B(CF3)4],
0.3% [B(CF3)3(CF2Cl)]ꢀ, 0.1% K[(CF3)B(CN)3] and 6.7% other
complexes).
A portion of the raw product (2.18 g, containing 76% of K[B(CF3)3CN])
was dissolved in water (10 mL) and conc. HCl (10 mL), and the solution
was stirred for 5 min. Subsequently, a solution of [Me3NH]Cl (1.66 g,
17.4 mmol) in water (10 mL) was added to the solution of the raw
product. After 5 min of stirring, the suspension was filtered off and
washed with water (20 mL). The product was dissolved in acetonitrile
and transferred into a bulb. After evaporation of the acetonitrile at
the rotary evaporator and drying of the product in a vacuum 1.91 g
containing 89% of [Me3NH][B(CF3)3CN] and 9% of K[(CF3)2B(CN)2]
were obtained. The [Me3NH]+ salt can be converted with KOH
solution into the potassium salt, and the purification process can be
repeated.
’ EXPERIMENTAL SECTION
Caution! ClF3, ClF, and aHF are highly toxic and can cause severe
injuries via skin and eye contact or inhalation. Therefore all manipulations of
these chemicals have to be performed under a well-ventilated fume hood,
and wearing of protective gloves, an apron, and a head screen is strongly
recommended. Before starting the transfer of ClF3, ClF, or aHF, the
apparatus must be checked carefully for any leaks.
1
Materials and Apparatus. H, 11B, and 19F NMR spectra were
recorded at 25 °C in D2O or CD3CN solution on a Bruker DRX 400
spectrometer operating at 400.17 (1H), 128.39 (11B), 100.61 (13C), and
376.45 (19F) MHz. The NMR signals were referenced against Me4Si
(1H, 13C), BF3 OEt2 (11B), and CFCl3 (19F) as external standards. For
3
the determination of the relative amounts of borate anions that had
formed in the reactions only the 19F NMR data were used for the
integration, because the intensities of the 11B NMR signals in many cases
do not display the correct relative intensities. This effect in the 11B NMR
spectra is due to very long relaxation times of the [B(CF3)4]ꢀ and
[B(CN)4]ꢀ anions.14,16 In Table 1 the NMR spectroscopic data of all
anions that could be assigned in the spectra of the test reaction mixtures
and in the large scale syntheses are summarized. The assignments were
supported by calculated chemical shifts, which are listed in Table S1 in
the Supporting Information. Raman spectra were recorded at room
temperature on a Bruker EQUINOX 55 FT Raman spectrometer
(Bruker, Karlsruhe, Germany) using the 9394.8 cmꢀ1 excitation line
(100 mW) of an Nd/YAG laser. In the region of 3000ꢀ50 cmꢀ1 spectra
were recorded with a resolution of 2 cmꢀ1 by addition of 64 scans.
The syntheses were performed in a stainless steel reactor as depicted
in Figure 1. It consisted of a cylinder (o.d. 15 cm, height 32 cm, wall
thickness 4 mm, volume 5.6 L) equipped with 3 bellow valves (Swagelok
SS-4H), and a capacitance manometer (Setra 205ꢀ2, 0ꢀ3.5 bar)
connected via a 16 mm flange with a Cu gasket. The starting materials
K[B(CN)4]22 (donated by Merck KGaA, Darmstadt, Germany) and
ClF32 (commercially available from Ozark, U.S.A.) was synthesized
according to a literature procedure. aHF was donated by Solvay (Bad
Wimpfen) and ClF3 by Urenco (Gronau).
Preparation of K[B(CF3)4]. In a typical run the reactor was
charged via the CF 16 flange with K[B(CN)4] (30.8 g, 0.20 mol) and
a big magnetic stir bar and then evacuated via a 6 ꢂ 1 mm PFA tube for
several hours. The lower part of the reactor was cooled with an ethanol
bath at ꢀ20 °C, and liquid aHF (about 800 g) was introduced into the
reactor. While the suspension of K[B(CN)4] in aHF was stirred the
upper part of the reactor was cooled with dry ice to result in the
condensation of the refluxing aHF and to wash down the K[B(CN)4],
which possibly stuck at the upper part of the reactor. Subsequently, the
ethanol bath was cooled to ꢀ78 °C with dry ice and when the vapor
pressure of HF dropped below 2 mbar 54 g, 1 mol of ClF (the container
cooled to ꢀ78 °C) was introduced into the reactor within half an hour.
During the addition the pressure inside the reactor was checked and did
not exceed 20 mbar. All ClF was consumed with release of heat, as
evident from a faster evaporation of the dry ice in the cold bath. Another
portion of ClF (1 mol; in total 10 equiv) was added to the reaction
NMR Spectroscopic Study of the Reaction of K[B(CN)4]
with ClF in aHF. A 100 mL PFA reactor equipped with a magnetic
stirring bar was charged with K[B(CN)4] (160 mg, 1.0 mmol) and
anhydrous HF (10 mL). The reaction mixture was cooled to ꢀ78 °C and
ClF was added until its consumption declined. All highly volatile
materials (Cl2, N2, and ClF) were removed at ꢀ78 °C.
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Inorganic Chemistry
ARTICLE
A sample of the yellow suspension was cannula transferred at low
’ DEDICATION
temperature into a PFA inliner and studied at ꢀ70 and ꢀ60 °C by NMR
Dedicated to Prof. Dr. Felix Aubke on the occasion of his 80th
birthday.
spectroscopy. Only very broad signals were observed in the 11B and 19
F
NMR spectra. However, the formation of trifluoromethylborates was
evident from these spectra. Upon warming of the suspension inside the
PFA inliner the yellow solid liquefied at approximately ꢀ40 °C and
separated as a yellow phase at the bottom of the inliner (NCl3).
All volatiles of the reaction mixture in the PFA flask were removed in a
vacuum while warming up to room temperature. The solid yellow residue
was studied by NMR spectroscopy in CD3CN and by Raman spectroscopy
at room temperature. The Raman spectrum was dominated by strong
bands at 540, 351, and 260 cmꢀ1 that were assigned to NCl3,33 adsorbed
on the borate salts. A mixture of borate anions with CN, CF3, CF2ꢀNCl2,
and CFdNCl groups was observed by 11B and 19F NMR spectroscopy.
The main components of the mixture are the anions [(CF3)3BCN]ꢀ,
[(CF3)2B(CN)2]ꢀ, and [B(CF2NCl2)2(CN)2]ꢀ.
’ REFERENCES
(1) Beck, W.; S€unkel, K. Chem. Rev. 1988, 88, 1405–1421. Strauss,
S. H. Chem. Rev. 1993, 93, 927–942. Krossing, I.; Raabe, I. Angew. Chem.
2004, 116, 2116–2142. Angew. Chem., Int. Ed. 2004, 43, 2066–2090.
Reed, C. A. Acc. Chem. Res. 2010, 43, 121–128.
(2) Bernhardt, E.; Henkel, G.; Willner, H.; Pawelke, G.; B€urger, H.
Chem.—Eur. J. 2001, 7, 4696–4705.
(3) Finze, M.; Bernhardt, E.; Willner, H. Angew. Chem. 2007,
119, 9340–9357. Angew. Chem., Int. Ed. 2007, 46, 9180–9196.
(4) Bernhardt, E.; Berkei, M.; Willner, H. Z. Anorg. Allg. Chem. 2009,
635, 2009–2015.
NMR Spectroscopic Study of the Reaction of K[B(CN)4]
with ClF in CH2Cl2. A 100 mL PFA reactor equipped with a magnetic
stirring bar was charged with [nBu4N][B(CN)4] (300 mg, 0.8 mmol),
spray-dried KF (1.75 g, 30 mmol), and dichloromethane (20 mL). At
ꢀ78 °C ClF was added (12 g, 220 mmol) over 4 h. Then all volatiles
were removed under reduced pressure at low temperature. The remain-
ing white solid residue was studied by 11B and 19F NMR spectroscopy at
room temperature, and the data of the anions that could be assigned are
collected in Table 1. [nBu4N][B(CF2NCl2)3CN] is the main product of
the fluorination experiment (70%) followed by [nBu4N][B(CF3)4]
(15%), [nBu4N][B(CF2NCl2)2(CF2X)2] (X probably NClF) (5%),
and [nBu4N][B(CF3)3(CF2NCl2)] (4%).
(5) Schmidt, M.; K€uhner, A.; Willner, H.; Bernhardt, E. Merck
Patent GmbH EP1205480(A2), 2002.
(6) Finze, M. Ph.D. Thesis, University of Hannover, Hannover,
Germany, 2004.
(7) Bernhardt, E.; Finze, M.; Willner, H. Z. Anorg. Allg. Chem. 2006,
632, 248–250.
(8) Wilson, W. W.; Vij, A.; Vij, V.; Bernhardt, E.; Christe, K. O.
Chem.—Eur. J. 2003, 9, 2840–2844.
(9) Finze, M.; Bernhardt, E.; Berkei, M.; Willner, H.; Hung, J.;
Waymouth, R. M. Organometallics 2005, 24, 5103–5109.
(10) Bernhardt, E.; Finze, M.; Willner, H.; Lehmann, C. W.; Aubke,
F. Chem.—Eur. J. 2006, 12, 8276–8283.
(11) Koppe, K.; Bilir, V.; Frohn, H.-J.; Mercier, H. P. A.; Schrobilgen,
G. J. Inorg. Chem. 2007, 46, 9425–9437. Koppe, K.; Frohn, H.-J.;
Mercier, H. P. A.; Schrobilgen, G. J. Inorg. Chem. 2008, 47, 3205–3217.
(12) Finze, M.; Bernhardt, E.; Z€ahres, M.; Willner, H. Inorg. Chem.
2004, 43, 490–505.
(13) Terheiden, A.; Bernhardt, E.; Willner, H.; Aubke, F. Angew.
Chem. 2002, 114, 823–825. Angew. Chem., Int. Ed. 2002, 41, 799–801.
(14) Finze, M.; Bernhardt, E.; Terheiden, A.; Berkei, M.; Willner, H.;
Christen, D.; Oberhammer, H.; Aubke, F. J. Am. Chem. Soc. 2002, 124,
15385–15398.
DFT Calculations. DFT calculations34 were carried out using the
B3LYP method35 with the basis sets 6-311++G(d,p) as implemented in
the Gaussian 03 program suite.36 Diffuse functions were incorporated
because improved energies are obtained for anions.37 Frequency calcu-
lations were performed for all species, and all structures represent true
minima without imaginary frequencies on the respective hypersurface.
Transition states exhibit one imaginary frequency and IRC calculations
were performed to verify that the transition states connect the products
and reactants, respectively.38 All energies presented herein are zero point
corrected. For enthalpies and free energies the thermal contributions are
included for 298 K. DFT-GIAO39 NMR shielding constants σ(11B) and
σ(19F) were calculated at the B3LYP/6-311++G(d,p) level of theory.
(15) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Angew.
Chem. 2004, 116, 4253. Angew. Chem., Int. Ed. 2004, 43, 4160.
(16) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. J. Am.
Chem. Soc. 2005, 127, 10712–10722.
(17) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Angew.
Chem. 2003, 115, 1082. Angew. Chem., Int. Ed. 2003, 42, 1052. Finze, M.;
Bernhardt, E.; Willner, H.; Lehmann, C. W. Chem.—Eur. J. 2005, 11,
6653–6665.
(18) Finze, M.; Bernhardt, E.; Willner, H.; Ignatiev, N. V.; Welz-
Biermann, U. Merck Patent GmbH WO2006045405A1, 2006.
(19) Bernhardt, E.; Willner, H., unpublished results.
(20) K€utt, A.; Rodima, T.; Saame, J.; Raamat, E.; M€aemets, V.;
Kaljurand, I.; Koppel, I. A.; Garlyauskayte, R. Y.; Yagupolskii, Y. L.;
Yagupolskii, L. M.; Bernhardt, E.; Willner, H.; Leito, I. J. Org. Chem. 2011, 76,
391–395.
’ ASSOCIATED CONTENT
S
Supporting Information. A table containing calculated
b
19F and 11B NMR chemical shifts of borate anions containing
BꢀCN, BꢀCFNCl, BꢀCF2NCl2, BꢀCF3, BꢀCF2Cl, and
BꢀCF2NClF groups as well as 19F and 11B NMR spectra of
selected borate anions. This material is available free of charge via
the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
(21) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Orga-
nometallics 2006, 25, 3070–3075.
(22) Bernhardt, E.; Finze, M.; Willner, H. Z. Anorg. Allg. Chem. 2003,
Corresponding Author
*E-mail: edbern@uni-wuppertal.de (E.B.), willner@uni-wuppertal.
de (H.W.).
629, 1229–1234.
(23) Boguslavskaya, L. S. Usp. Khim. 1984, 53, 2024–2055. Russ.
Chem. Rev. 1984, 53, 1178–1194. Hynes, J. B.; Austin, T. E. Inorg. Chem.
1966, 5, 488–489. Young, D. E.; Anderson, L. R.; Fox, W. B. Chem.
Commun. 1970, 395.Young, D. E.; Anderson, L. R.; Fox, W. B.; 1972;
Sekiya, A.; DesMarteau, D. D. J. Am. Chem. Soc. 1979, 101, 7640–7641.
Thrasher, J. S.; Bauknight, C. W.; DesMarteau, D. D. Inorg. Chem. 1985,
24, 1598–1599. Marsden, H. M.; Shreeve, J. M. Inorg. Chem. 1987,
26, 169–172. Bauknight, C. W.; DesMarteau, D. D. J. Am. Chem. Soc.
1990, 112, 728–733. Zheng, Y. Y.; Patel, N. R.; Kirchmeier, R. L.;
Shreeve, J. M. Inorg. Chem. 1992, 31, 488–491.
’ ACKNOWLEDGMENT
This work was financial supported by the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen Industrie.
We appreciate Dr. J. Eicher (Solvay Fluor GmbH) for donating
aHF to us and Dr. N. Ignatiev (Merck KGaA) for donating
K[B(CN)4] to us.
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Inorganic Chemistry
ARTICLE
(24) Lustig, M. Inorg. Chem. 1967, 6, 1064–1065.
(25) Sekiya, A.; DesMarteau, D. D. Inorg. Chem. 1981, 20, 1–3.
(26) Foropoulos, J.; Shreeve, J. M. Inorg. Chem. 1991, 30, 2699–2701.
(27) Rozen, S. Acc. Chem. Res. 2005, 38, 803–812.Baker, M. T.;
Ruzicka, J. A.; 1997; Baker, M. T.; Ruzicka, J. A.; Tinker, J. H. J. Fluorine
Chem. 1999, 94, 123–126. Rozen, S.; Rechavi, D.; Hagooly, A. J. Fluorine
Chem. 2001, 111, 161–165.
(28) Stevens, T. E. J. Org. Chem. 1961, 26, 1627–1630.
(29) Bernhardt, E.; Finze, M.; Willner, H. J. Fluorine Chem. 2004,
125, 967–973. Balters, S.; Bernhardt, E.; Willner, H.; Berends, T. Z.
Anorg. Allg. Chem. 2004, 630, 257–267.
(30) Finze, M.; Bernhardt, E.; Willner, H.; Lehmann, C. W. Inorg.
Chem. 2006, 45, 669–678.
(31) Chase, M. W.; Davies, C. A.; Downey, J. R.; Frurip, D. J.;
McDonald, R. A.; Syverud, A. N. JANAF Thermochemical Tables, 3rd ed.;
American Chemical Society and American Institute of Physics for the
National Bureau of Standards: Washington, DC, 1986; Law, C.-K.;
Chien, S.-H.; Li, W.-K.; Cheung, Y.-S. J. Phys. Chem. A 2000,
106, 11271–11276. Csontos, J.; Rolik, Z.; Das, S.; Kallay, M. J. Phys.
Chem. A 2010, 114, 13093–13103.
(32) Handbuch der Pr€aparativen Anorganischen Chemie, Erster Band,
3rd ed.; Brauer, G., Ed.; Ferdinand Enke Verlag: Stuttgart, Germany,
1975. Schack, C. J.; Wilson, R. D. Synth. Inorg. Met.-Org. Chem. 1973,
3, 393–396.
(33) Schneider, S.; Gerken, M.; Haiges, R.; Schroer, T.; Boatz, J. A.;
Dixon, D. A.; Grant, D. J.; Christe, K. O. Inorg. Chem. 2007, 46, 93–102.
(34) Kohn, W.; Sham, L. J. Phys. Rev. A 1965, 140, 1133.
(35) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652. Becke, A. D.
Phys. Rev. A 1988, 38, 3098–3100. Lee, C.; Yang, W.; Parr, R. G. Phys.
Rev. B 1988, 37, 785–789.
(36) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Kudin, T. V. K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; ; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.;
Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, Revision D.01; Gaussian, Inc.: Wallingford, CT, 2004.
(37) Rienstra-Kiracofe, J. C.; Tschumper, G. S.; Schaefer, H. F., III;
Nandi, S.; Ellison, G. B. Chem. Rev. 2002, 102, 231.
(38) Gonzales, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90, 2154.
Gonzales, C.; Schlegel, H. B. J. Phys. Chem. 1990, 94, 5523.
(39) Wolinski, K.; Hinton, J. F.; Pulay, P. J. Am. Chem. Soc. 1990,
112, 8251.
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