Alkoxycyanoborates: Metal salts and low-viscosity ionic liquids

Article abstract of DOI:10.1039/d0nj04950f

Syntheses of alkoxytricyanoborates and dialkoxydicyanoborates are described using different readily available boron-based starting compounds such as tetrahydrido-, tetrafluoro-, and tetraalkoxyborates, as well as trimethoxyborane and trimethylsilylcyanide as cyano sources. The salts obtained have been characterized by NMR and vibrational spectroscopy, elemental analysis, and DSC and DTA measurements. In addition to alkali metal salts, room temperature ionic liquids [EMIm][ROB(CN)3] (R = CH3, C2H5, CH2CF3) have been prepared. These ionic liquids exhibit very low melting points or glass transition temperatures, low viscosities, and high chemical, thermal, and electrochemical stabilities. The influence of alkyl chain length and the effect of partial fluorination of the alkoxy group on these properties have been elucidated. The advantageous physicochemical properties, in general, and in conjunction with the easy accessibility make alkoxytricyanoborate-ILs interesting compounds for potential applications in materials sciences. Furthermore, the Li salt of the [CH3OB(CN)3]- ions was prepared and found to provide a significantly higher solubility in propylene carbonate compared to lithium tetracyanoborate. Alkali metal salts Li[CH3OB(CN)3]·H2O, Na[CH3OB(CN)3]·H2O, K[CH3OB(CN)3], Na[C2H5OB(CN)3], and Na[CF3CH2OB(CN)3]·0.5H2O have been characterized by single-crystal X-ray diffraction. This journal is

Full text of DOI:10.1039/d0nj04950f

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Alkoxycyanoborates: metal salts and low-viscosity
ionic liquids†‡
Cite this:DOI: 10.1039/d0nj04950f
Nils Schopper,a Jan A. P. Sprenger,a Ludwig Zapf,a Guido J. Reiss,b
a
Nikolai V. Ignat’evac and Maik Finze
*
Syntheses of alkoxytricyanoborates and dialkoxydicyanoborates are described using different readily
available boron-based starting compounds such as tetrahydrido-, tetrafluoro-, and tetraalkoxyborates, as
well as trimethoxyborane and trimethylsilylcyanide as cyano sources. The salts obtained have been
characterized by NMR and vibrational spectroscopy, elemental analysis, and DSC and DTA measurements.
In addition to alkali metal salts, room temperature ionic liquids [EMIm][ROB(CN)3] (R = CH3, C2H5, CH2CF3)
have been prepared. These ionic liquids exhibit very low melting points or glass transition temperatures,
low viscosities, and high chemical, thermal, and electrochemical stabilities. The influence of alkyl chain
length and the effect of partial fluorination of the alkoxy group on these properties have been elucidated.
The advantageous physicochemical properties, in general, and in conjunction with the easy accessibility
make alkoxytricyanoborate-ILs interesting compounds for potential applications in materials sciences.
Furthermore, the Li salt of the [CH3OB(CN)3]À ions was prepared and found to provide a significantly
higher solubility in propylene carbonate compared to lithium tetracyanoborate. Alkali metal salts
Li[CH3OB(CN)3]ÁH2O, Na[CH3OB(CN)3]ÁH2O, K[CH3OB(CN)3], Na[C2H5OB(CN)3], and Na[CF3CH2OB(CN)3]Á
0.5H2O have been characterized by single-crystal X-ray diffraction.
Received 8th October 2020,
Accepted 24th November 2020
DOI: 10.1039/d0nj04950f
rsc.li/njc
stimulated the search for alternative anions in particular by mod-
ification of the parent tetrafluoroborate [BF4]À anion.
1. Introduction
In 1992 the first air and water stable room temperature ionic
The formal replacement of all four fluorine against cyano groups
liquid (RTIL), 1-ethyl-3-methylimidazolium tetrafluoroborate in [BF4]À leads to the tetracyanoborate anion [B(CN)4]À (TCB, Fig. 1)
([EMIm][BF4]), was described by Wilkes et al.1 This finding that was reported independently by Willner et al.6 and Kouvetakis
triggered intensive research in the field of ionic liquids, the et al.7 in 2000. The TCB anion is hydrolytically stable6,8 and in 2003
study of their physicochemical properties, and investigation of first TCB-ILs have been reported.5,9,10 TCB-ILs have superior proper-
possible practical applications in the fields of materials ties such as low viscosity and high specific conductivity in conjunc-
science, electrochemistry, and chemical engineering.2,3 Very tion with high electrochemical and thermal stability compared to
soon it turned out that tetrafluoroborate-ILs are not fully tetrafluoroborate-ILs.5,9,10 Therefore, they have been tested in many
hydrolytically stable4 and possess relatively high viscosity.5 different applications, in particular in electrochemical and opto-
These non-optimal properties of tetrafluoroborate-ILs have electronic devices,3,10 e.g. electrical storage devices, i.e. batteries,11
limited their practical applications, in particular, in electrochemical supercapacitors12,13 and dye-sensitized solar cells (DSSCs).13,14
devices. Thus, the demand for RTILs with improved properties
Later, it was found that ionic liquids based on mixed-substituted
cyanoborate anions often exhibit properties that are even superior
a
¨
¨
¨
Julius-Maximilians-Universitat Wurzburg, Institut fur Anorganische Chemie,
¨
Institut fur nachhaltige Chemie & Katalyse mit Bor (ICB), Am Hubland,
¨
97074 Wurzburg, Germany. E-mail: maik.finze@uni-wuerzburg.de
b
¨
¨
¨
Heinrich-Heine-Universitat Dusseldorf, Institut fur Anorganische Chemie und
¨
Strukturchemie, Lehrstuhl fur Material- und Strukturforschung,
¨
¨
Universitatsstraße 1, 40225 Dusseldorf, Germany
c Consultant, Merck KGaA, 64293 Darmstadt, Germany.
E-mail: nikolai.ignatiev@external.merckgroup.com
† Dedicated to Prof. Dr Todd B. Marder on the occasion of his 65th birthday and
for his outstanding contributions to organometallic and boron chemistry.
‡ Electronic supplementary information (ESI) available. CCDC 2033370 and
2035889–2035892. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/d0nj04950f
Fig. 1 Tricyanoborate anions [RB(CN)3]À (R
=
CN,5,9 H,15 F,5 Cl,18
that have been used for the design of very low-viscosity
perfluoroalkyl19,20 10
)
room temperature ionic liquids (RTILs) and the ions [B(CN)4]À (TCB) and
[BF(CN)3]À (MFB) in the crystals of their [CH3NH3]+ salts.17
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compared to those of the respective TCB-ILs.5,10 In particular,
mixed-substituted dicyano- and tricyanoborate anions are of inter-
est (Fig. 1), since these anions retain the hydrolytical and chemical
stability of the parent TCB anion, in general. Examples are the
cyanohydridoborate anions [BH(CN)3]À (MHB) and [BH2(CN)2]À
(DHB)15 and the cyanofluoroborate anions [BF(CN)3]À (MFB,
Fig. 1) and [BF2(CN)2]À (DFB).16,17 Most likely, the reduced sym-
metry of such mixed-substituted borate anions is the reason for the
improved properties of ILs based on them, such as lower viscosity
and higher conductivity.
À
Perfluoroalkyl(fluoro)cyanoborate anions [RFBFn(CN)3Àn
]
(RF = perfluoroalkyl, n = 0–2) are a further class of mixed-substituted
cyanoborate anions that provide access to low-viscosity RTILs with
high thermal, chemical, and electrochemical stabilities.19–21
À
Salts of the anions [RFBFn(CN)3Àn
]
(RF = perfluoroalkyl, n =
0–2) are conveniently accessible from the corresponding
perfluoroalkyltrifluoroborates22 using trimethylsilylcyanide
as the cyanide source.17,19,20,23
In addition to their use as components of ionic liquids,
cyanoborate anions are applied as counterions for metal ions24–26
and reactive nonmetal cations, e.g. the trityl ion, Ph3C+27 and the
oxonium ion, H3O+.10,26,28 Furthermore, cyanoborate anions serve
as versatile starting compounds for unprecedented and valuable
borate anions and boranes, e.g. the very weakly coordinating anion
[B(CF3)4]À,29 the carboxylatoborate anion [B{C(O)OH}4]À,30 the
anions [(CF3)3BCPnic]À (Pnic = N, P, As),31 the boron-centered
nucleophile B(CN)3 ,
2À 32 and the borane carbonyl (CF3)3BCO.33
All cyanoborate-ILs mentioned above show exceptional proper-
ties making them interesting materials for diverse applications.
However, there is still demand for cyanoborate anions having
similar advantageous, tunable properties that are very easily acces-
sible. In particular, for industrial applications, the aspect of avail-
ability is of outmost importance.
Here we report on a set of alkoxycyanoborate anions, which
have in part been previously mentioned in patent applications
by Lonza AG (Basel, Switzerland)34 and Merck KGaA (Darmstadt,
Germany).35 Structures of alkali metal salts of the anions
[ROB(CN)3]À (R = CH3, C2H5, CH2CF3) are discussed. Further-
Scheme 1 Syntheses of dialkoxydicyanoborates and alkoxytricyanoborates.
more, the syntheses and physicochemical properties of the are all cost-effective and readily available boron-containing com-
respective EMIm-ILs are described.
modities. In all cases trimethylsilylcyanide (TMSCN) served as a
cyanide source that was prepared also in situ from trimethylsilyl-
chloride and potassium or sodium cyanide.
Yields of up to 99% have been achieved, e.g. starting from
Li[BF4], TMSCN, and (CH3)3SiOCH3, surprisingly, even at room
temperature (Scheme 1). This latter reaction is noteworthy since
the well-known tricyanofluoroborate anion ([BF(CN)3]À, MFB) is
2. Results and discussion
Synthesis of alkoxycyanoborates Kt[(RO)xB(CN)4Àx] (x = 1, 2,
Kt = cation)
The different syntheses developed by us providing highly conveni- not formed under these reaction conditions (Scheme 1). Similarly,
ent access to dialkoxydicyanoborates and alkoxytricyanoborates Na[BF4] was converted into [ROB(CN)3]À (R = CH3, C2H5) in yields
are summarized in Scheme 1. Methoxy, ethoxy, and 1,1,1- of 74–76% (Scheme 1). The slightly higher yield starting from
trifluoroethoxy groups have been selected as substituents since we Li[BF4] instead of Na[BF4] may be attributed to the higher fluoride
are particularly interested in low-viscosity and highly conducting ion affinity of the Li+ cation, which results in a more efficient
RTILs for which ions with a low molecular weight are beneficial.36 replacement of fluorine against cyano and alkoxy groups at boron.
Tetrafluoroborates, tetraalkoxyborates, and tetrahydridobo- Furthermore, the higher solubility of Li[BF4] compared to Na[BF4]
rates have been successfully employed as starting compounds. might have a beneficial influence on the conversion, as well. A
Despite these easy-to-handle salts, trimethoxyborane (trimethyl similar beneficial effect of Li+ was reported by us earlier for the
borate) was used as a starting material, as well. These compounds conversion of tetrafluoroborates into tricyanofluoroborates.16
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Similar to tetrafluoroborates, tetraalkoxyborates were trans-
Paper
formed into the corresponding alkoxytricyanoborates in yields
of up to 92% (Scheme 1). In general, using tetraalkoxyborates
fortunately avoids the formation of trimethylsilylfluoride as a
toxic byproduct.
Tetrahydridoborates were converted into tetraalkoxyborates
in a first step, followed by the reaction with TMSCN to give
alkoxytricyanoborates (Scheme 1). Again, high yields have been
achieved (up to 91%). The application of trimethoxyborane as
the starting compound was demonstrated by its conversion into
alkoxytricyanoborates in a one pot reaction with sodium methoxide
and TMSCN (Scheme 1). A related synthesis for K[CH3OB(CN)3]
starting from trimethoxyborane was described in a patent applica-
tion filed by Lonza AG (Basel, Switzerland), earlier.34 However, KCN
and TMSCN in conjunction with trimethoxyborane were used in
the aforementioned patent and not NaOCH3 and TMSCN as
described herein.
Dialkoxydicyanoborates Na[(RO)2B(CN)2] (R = CH3, CF3CH2)
were selectively obtained via careful tuning of the reaction
conditions. The formation of Na[(CH3O)2B(CN)2] was achieved
by using two equivalents of TMSCN. The stronger electron-
withdrawing and slightly more sterically demanding 1,1,1-
trifluoroethoxy group results in a slower replacement against
a cyano group. Thus, the preparation of Na[(CF3CH2O)2B(CN)2]
was accomplished by simply lowering the reaction temperature to
room temperature compared to the synthesis of Na[CF3CH2OB(CN)3]
that was performed at 80 1C (Scheme 1).
Scheme 3 Metathesis reactions of alkali metal alkoxytricyanoborates.37
Alkoxytricyanoborates are stable in aqueous solution and
tolerate dilute basic and acidic conditions, as well. In contrast, NMR spectra of the EMIm-ILs are depicted. The 1H NMR
dialkoxydicyanoborates decompose in air.
signals of the methoxy group in [CH3OB(CN)3]À and of the
The protocols presented in Scheme 1 offer cost-efficient CH2 units in [C2H5OB(CN)3]À and [CF3CH2OB(CN)3]À show J
entries to alkoxytricyanoborates M[ROB(CN)3] (M = Na, K) using coupling to 11B as evident from the splitting of the signals
cheap and commercially available chemicals. Hence, these into quartets of lines with equal intensities. In cases of
borates are interesting reagents for further derivatizations, for [C2H5OB(CN)3]À and [CF3CH2OB(CN)3]À, additional couplings
instance for the conversion into tetracyanoborates (Scheme 2).37 to the CH3 and CF3 units are observed, respectively. Similarly,
Furthermore, these borates are valuable starting materials for the 13C NMR spectra provide clear evidence for the presence of
metatheses. In Scheme 3 the preparation of various organic salts the respective cyanoborate anions, e.g. by the signals of the
including EMIm- and BMPL-ILs with alkoxytricyanoborate anions cyano groups that show the splitting into quartets of equal
3
is presented. Both EMIm- and BMPL-ILs are hydrophobic and thus intensities due to the 1J coupling to 11B and, in addition, the 10
B
separate from aqueous solution during metathesis. The synthesis satellites that are septets of equal intensities (Fig. 2).
of Li[CH3OB(CN)3] starting from Na[CH3OB(CN)3] exemplifies the
The IR and Raman spectra of selected trimethoxyborates are
preparation of metal alkoxytricyanoborates via metathesis.
depicted in Fig. 3. In all Raman spectra, the strongest signal at
approximately 2206–2249 cmÀ1 refers to the CN stretching
mode. In contrast, in the IR spectrum the corresponding bands
are very weak and often their intensity is below the detection limit.
The IR spectra of Li[CH3OB(CN)3]ÁH2O and Li[CH3OB(CN)3] pro-
vide clear evidence for the effective removal of water upon drying
since the bands typical for water are fully absent in the spectrum
of Li[CH3OB(CN)3].
Spectroscopic characterization
The cyanoborates have been characterized by multinuclear
NMR and vibrational spectroscopy. In Fig. 2 the 1H and 13C
In Table 1 the band positions of the CN stretching modes of
selected alkali metal alkoxytricyanoborates and related cyano-
borates and their EMIm-ILs are listed. A comparison of n B
(CN) of the EMIm-ILs nicely demonstrates the decreasing
electron density at boron in the order [ROB(CN)3]À (R = CH3,
C2H5) o [CF3CH2OB(CN)3]À o [CF3B(CN)3]À E [B(CN)4]À,
which is in line to the calculated band positions at the
Scheme 2 Conversion of K[CH3OB(CN)3] into K[B(CN)4].37
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to be better donors or ligands in coordination chemistry than
perfluoroalkyltricyanoborates or the parent TCB ion, in general.
However, the difference should be rather small.
The wavenumber of n(CN) for the methoxytricyanoborates
decreases in the order Li+ 4 Na+ 4 K+ 4 [EMIm]+. So, a weaker
interaction of the cation with the cyanoborate anion results in a
lower wavenumber, which is a typical feature for cyanoboron
compounds as exemplified by a comparison to the literature
known TCB salts6,8,15 listed in Table 1.
Structural characterization
Crystals of three alkali metal salts of the methoxytricyanoborate
anions were characterized by single-crystal X-ray diffraction
(Fig. 4 and Table 2). Li[CH3OB(CN)3] and Na[CH3OB(CN)3]
crystallize with one water molecule per formula unit in the
monoclinic space group Cc with Z = 4 and in the triclinic space
%
group P1 with Z = 2, respectively. In contrast, the potassium salt
K[CH3OB(CN)3] crystallizes as anhydrous compounds in the
monoclinic space group C2/c with Z = 8. The lithium cation in
Li[CH3OB(CN)3]ÁH2O is coordinated by three N atoms and the
O atom of the water molecule resulting in a distorted tetra-
hedral arrangement. The sodium cation in Na[CH3OB(CN)3]ÁH2O
has a distorted octahedral coordination sphere composed of
four N atoms and two O atoms. The O atoms belong to water
molecules that are m2-coordinated to two Na atoms. Thus, the
O atom of the [CH3OB(CN)3]À anion is not coordinated to the
metal ion in M[CH3OB(CN)3]ÁH2O (M = Li, Na). The aqua
ligands in both salts are involved in OÁ Á ÁH–O hydrogen bonds
with the cyanoborate anions as depicted in Fig. 4.
Fig. 2 Sections of the 1H, 1H{19F}, and 1H{11B} NMR spectra of the OCHx
units (x = 2 or 3; top) and 13C{1H} NMR spectra of EMIm-alkoxytricyanoborates
in (CD3)2CO.
In K[CH3OB(CN)3] two crystallographically independent
potassium atoms are present that are located on special posi-
tions (Fig. 4). One K atom has a distorted octahedral environ-
ment with six N atoms in the coordination sphere. The second
K atom has the coordination number 8 and a strongly distorted
square antiprismatic geometry. The K atom is connected to six
N atoms, as well, and in addition to two O atoms. So, in
contrast to the lithium and sodium salt, the O atom of the
methoxytricyanoborate anion is involved in the coordination to
potassium.
Na[C2H5OB(CN)3] and Na[CF3CH2OB(CN)3]Á0.5H2O crystallize
%
in the triclinic space group P1 (Z = 2) and in the monoclinic space
group C2/c (Z = 8), respectively. The coordination sphere of the Na
atom in Na[C2H5OB(CN)3] is a distorted trigonal bipyramid with
four N atoms and one O atom. So, one of the cyano groups bridges
two Na atoms. In contrast, the sodium atom in the structure of the
partially fluorinated cyanoborate anion has a distorted octahedral
coordination sphere. Four N atoms, a single F atom of the CF3
group, and the O atom of the H2O solvate molecule are coordi-
nated to sodium. One of the N atoms and the O atom of water are
coordinated to two Na atoms.
Fig. 3 IR and Raman spectra of selected trimethoxytricyanoborates.
B3LYP/6-311++G(d,p) level of theory (Table 1). The decrease in
The bond parameters of the alkoxytricyanoborate anions are
electron density is attributed to the electronic properties of the listed in Table 2. The experimental and calculated bond lengths
substituent bonded to the B(CN)3 unit, e.g. alkoxy groups are and angles are very close. Furthermore, the bond parameters of
more electron rich than perfluoroalkyl or cyano groups. This the three closely related anions are very similar. Thus, most of
difference in electron density relates to the coordinative properties the differences of the experimental values are not significant
of the cyanoborate anions, thus, alkoxytricyanoborates are expected (43s). The calculated bond parameters of the non-fluorinated
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Table 1 Experimental (Raman) and calculated CN stretching band positions of alkoxytricyanoborates and selected related cyanoborates
Anion
Li+
Na+
K+
[EMIm]+
Calcda
[CH3OB(CN)3]À
[C2H5OB(CN)3]À
[CF3CH2OB(CN)3]À
[CF3B(CN)3]À
2249
n.d.b
n.d.
2224
2240/2228/2220
2236
2221
n.d.
2206
2207
2299
2299
n.d.
2211
2305
n.d.
n.d.
2237/223120
22336
2223c 20
222315
231420
231515
[B(CN)4]À
22638
22528
a
b
c
B3LYP/6-311++G(d,p), mean value where applicable. n.d. = not determined. IR.
Fig. 4 Crystal structures of Li[CH3OB(CN)3]ÁH2O, Na[CH3OB(CN)3]ÁH2O, K[CH3OB(CN)3], Na[C2H5OB(CN)3], and Na[CF3CH2OB(CN)3]Á0.5H2O.
Table 2 Selected experimental and calculateda bond lengths [Å] and angles [1] of alkoxytricyanoborate anionsb
Anion
Cation d(B–C)
d(B–O)
d(CRN)
d(O–C)
d(C–C)
,(C–B–C) ,(C–B–O) ,(B–CRN) ,(B–O–C)
[CH3OB(CN)3]À
Li+
Na+
K+
1.613(2)
1.449(2)
1.146(2)
1.441(2)
—
—
—
—
107.66(12) 111.21(13) 177.02(17)
107.38(8) 111.49(8) 178.84(11)
107.48(10) 111.39(10) 177.70(13)
115.55(12)
117.78(8)
116.80(10)
117.82
115.95(9)
118.32
1.6140(15) 1.4249(12) 1.1355(15) 1.4129(13)
1.6197(19) 1.4277(16) 1.1430(18) 1.4276(16)
B3LYP 1.6167
Na+
1.619(2)
B3LYP 1.6166
[CF3CH2OB(CN)3]À Na+
B3LYP 1.6104
1.4504
1.4314(14) 1.146(2)
1.4511 1.1570
1.1570
1.4080
1.435(2)
1.4117
108.11
110.81
178.20
178.59(12)
178.29
[C2H5OB(CN)3]À
1.5054(16) 106.59(10) 112.23(9)
1.5226
108.09
110.83
1.6143(17) 1.4509(15) 1.1447(15) 1.4149(13) 1.4973(18) 108.49(9)
1.4642 1.1565 1.3904 1.5167 108.64
110.41(9)
110.29
177.40(12)
177.91
115.39(8)
117.53
a
b
B3LYP/6-311++G(d,p). Mean value where applicable.
anions [ROB(CN)3]À (R = CH3, C2H5) are similar, as well. In and results in solid, anhydrous Li[CH3OB(CN)3], which is stable
contrast, small deviations are predicted for the partially fluori- up to 313 1C. At this temperature decomposition of the anion
nated analogue. The B–C and CRN distances are shorter while starts and gas evolution takes place. The IR spectrum of the gas
the d(B–O) distance is longer. These differences are attributed evolved corresponds to the spectrum of B(OCH3)3 with minor
to the less electron rich CF3CH2O group compared to its non- amounts of HCN (Fig. 5). The mass loss of 27.0% fits well to the
fluorinated counterparts. The shorter and thus stronger CRN mass loss calculated for trimethoxyborane of 23.9%. The black
bonds in [CF3CH2OB(CN)3]À are in agreement to the slightly solid residue in the crucible is hardly soluble in water and
higher wavenumber for n(CN) (Table 1). The short B–C bonds in insoluble in organic solvents. The 11B NMR spectrum of the
[CF3CH2OB(CN)3]À compared to [ROB(CN)3]À (R = CH3, C2H5) water extract shows a number of signals including a weak
indicate stronger B–C bonds.
signal that is assigned to the [B(CN)4]À ions.
The formation of B(OCH3)3 during decomposition of
Li[CH3OB(CN)3] may be rationalized by a dismutation initiated
Thermal properties
The thermal stability of the alkali metal salts and EMIm-ILs of by the Li+ cation that attacks the borate anion. In Scheme 4 the
selected alkoxytricyanoborates was studied by DTA and TG respective first step of this dismutation that results in a
measurements and the results are summarized in Table 3.
In Fig. 5 the TG and DTA curves for the decomposition of steps would yield the experimentally observed B(OCH3)3.
The sodium and potassium salts M[CH3OB(CN)3] (M = Na, K)
dimethoxyboron species is depicted. Further methoxy transfer
Li[CH3OB(CN)3]ÁH2O are depicted and the DSC curve is shown
in Fig. S2 (ESI‡). The hydrate melts at approximately 100 1C. exhibit similar thermal stabilities to the corresponding lithium
The melting process is followed by a loss in weight of 12.4% salt with decomposition temperatures of B310 and 304 1C.
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Table
3
Thermal properties of alkali metal salts and EMIm-ILs of
alkoxytricyanoboratesa
Salt
Tg [1C]
Tmp [1C]
Tdec [1C]
Li[CH3OB(CN)3]ÁH2Ob
Na[CH3OB(CN)3]ÁH2Od
K[CH3OB(CN)3]
n.o.c
n.o.
n.o.
n.o.
n.o.
À93
À86
À85
(58)b
298
242
320
265
n.o.
n.o.
À21
313
B310e
304
Na[C2H5OB(CN)3]
B340e
337
230
243
285
Na[CF3CH2OB(CN)3]Á0.5H2O f
[EMIm][CH3OB(CN)3]
[EMIm][C2H5OB(CN)3]
[EMIm][CF3CH2OB(CN)3]
a
Scheme 4 First step proposed for the dismutation of Li[CH3OB(CN)3].
Temperatures are onset values of the DSC measurements (plots of the
DSC curves are depicted in the ESI); Tdec = decomposition temperature;
Tmp = melting point; Tg = glass transition temperature; Tdec and Tmp
b
were confirmed visually. Li[CH3OB(CN)3]ÁH2O melts at 58 1C and
volatile decomposition products, all three sodium salts decompose
under loss of the respective borane B(OR)3 (R = CH3, C2H5, CF3CH2).
The three EMIm-ILs [EMIm][ROB(CN)3] (R = CH3, C2H5,
CF3CH2) are thermally very robust with decomposition tempera-
tures well above 200 1C (Table 3). The stability increases in the
order [EMIm][CH3OB(CN)3] (230 1C) o [EMIm][C2H5OB(CN)3]
(243 1C) o [EMIm][CF3CH2OB(CN)3] (285 1C).
loses water at 95 1C to give solid Li[CH3OB(CN)3] that decomposes at
c
d
313 1C (Fig. S2, ESI). n.o. = not observed. Loss of water starts at 44 1C
e
f
(Fig. S3, ESI). Decomposition starts during melting. Loss of water
starts at 86 1C. An irreversible phase transition is observed at 170 1C
(Fig. S10, ESI).
The EMIm-ILs decompose under release of the respective
trialkoxyborane as the main gaseous product, which is ratio-
nalized by dismutation reactions similar to the one depicted for
Li[CH3OB(CN)3] in Scheme 4. HCN was identified in the IR
spectra as a minor component. The significantly higher ther-
mal stability of [EMIm][CF3CH2OB(CN)3] is attributed to the
stronger electron withdrawing effect of the partially fluorinated
alkoxy group at boron that results in stronger bonds of boron to
its substituents, which is in line with the shorter and thus
stronger B–C bonds in the partially fluorinated anion (Table 2).
The electron density at oxygen in [CF3CH2OB(CN)3]À is lower
compared to its non-fluorinated counterparts [ROB(CN)3]À (R =
CH3, C2H5). Both, the stronger bonds of boron to its substituents
and the comparably low electron density at oxygen are expected
to result in an increase of the energy of the transition state of
dismutation reactions such as the one presented in Scheme 4.
The glass transition temperatures of the three EMIm-ILs are in
the range of À85 to À93 1C. Cold crystallization and melting were
observed for [EMIm][CF3CH2OB(CN)3] at À42 and À20 1C, only.
The DSC traces of the non-fluorinated ILs [EMIm][CH3OB(CN)3]
and [EMIm][C2H5OB(CN)3] do not show any crystallization.
Physicochemical properties of EMIm-ILs
Electrochemical properties. The three neat ionic liquids
[EMIm][ROB(CN)3] (R = CH3, C2H5, and CF3CH2) were studied
by cyclic voltammetry using a glassy carbon (GC) working
electrode (Fig. 6). All three RTILs are electrochemically surpris-
ingly stable with electrochemical windows of up to 4.4 V, which
are similar to related EMIm-cyanoborate-ILs, for example
Fig. 5 DTA (blue) and TG curve (green) of Li[CH3OB(CN)3]ÁH2O (bottom)
and IR spectra of H2O lost at 100 1C (onset) and of the volatile decomposi-
tion product B(OCH3)3 with traces of HCN (*) released at 309 1C (onset).
However, both salts M[CH3OB(CN)3] (M = Na, K) melt before [EMIm]TCB (DE = 4.4 V,15 Table 4). The oxidation of the
decomposition (Table 3) whereas Li[CH3OB(CN)3] remains different anions occurs at 1.8–2.0 V and reduction of the
solid until decomposition. In all cases, B(OCH3)3 is formed as [EMIm]+ cations at À2.4 V. Both electrochemical reductions
a gaseous decomposition product.
and oxidations proceed irreversibly.
The sodium salts of [ROB(CN)3]À (R = C2H5, CF3CH2) are
Density and viscosity. The dynamic viscosity (Z) and density
slightly more stable than Na[CH3OB(CN)3] (Table 3). According (r) of [EMIm][ROB(CN)3] (R = CH3, C2H5, and CF3CH2) was
to the TG measurements and the respective IR spectra of the determined using a rolling ball viscometer (Table 4). The density
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Fig. 6 Cyclic voltammograms of neat [EMIm][ROB(CN)3] (R = CH3, C2H5,
and CF3CH2) measured at 20 1C with a scan rate of 50 mV sÀ1 using a
glassy carbon working electrode.
of [EMIm][CH3OB(CN)3] and [EMIm][C2H5OB(CN)3] is almost
identical and similar to the one of [EMIm]TCB.15 As expected
from the data of our study on perfluoroalkyl(cyano)fluoroborate-
ILs,20 the introduction of fluorine into the alkyl chain of the
borate anion results in a significant increase in density of
[EMIm][CF3CH2OB(CN)3] (Table 4).
Surprisingly, [EMIm][CH3OB(CN)3] reveals a lower dynamic
viscosity than the well-established [EMIm]TCB15 (Table 4). An
increasing alkyl chain length of the alkoxy group results in an
increase in dynamic viscosity, which is in accordance with the
trend of higher viscosities of perfluoroalkylcyanoborates with longer
perfluoroalkyl chains.20 The dynamic viscosity of [EMIm][CF3-
Fig. 7 Temperature dependence of the dynamic viscosities (top) and
conductivities (bottom) of EMIm-ILs of [ROB(CN)3]À (R = CH3, C2H5, and
CF3CH2) and [B(CN)4]À.
CH2OB(CN)3] is slightly lower compared to [EMIm][C2H5OB(CN)3]. specific conductivity of 12.1 mS cmÀ1. This observation may
In spite of the increase of the anion mass, the electron withdrawing be rationalized by a stronger ion pairing or ion interaction in
effect of the trifluoromethyl group in CF3CH2O results in weaker [EMIm][CH3OB(CN)3] compared to [EMIm]TCB as evident from the
cation–anion interactions and thus leads to a lower viscosity. The ionicity,38 which is defined as the ratio of the molar conductivity
dynamic viscosity of all four ILs including [EMIm]TCB15 decreases based on impedance measurements Limp and the molar conduc-
with the increasing temperature as depicted in Fig. 7.
tivity derived from NMR diffusion coefficients LNMR (Fig. 8). Most
Specific conductivity and diffusivity. [EMIm][CH3OB(CN)3] likely, the methoxy group in [CH3OB(CN)3]À results in stronger
has the highest specific conductivity s (10.1 mS cmÀ1 at 20 1C) cation–anion interactions in [EMIm][CH3OB(CN)3] compared to
of the three alkoxytricyanoborate-ILs studied (Fig. 7 and [EMIm][B(CN)4], e.g. via hydrogen bonding between the [EMIm]+
Table 4). The specific conductivity of [EMIm][C2H5OB(CN)3] cation and the [CH3OB(CN)3]À ion. The ionicity further decreases in
and [EMIm][CF3CH2OB(CN)3] is very close as can be expected the order [EMIm][C2H5OB(CN)3] 4 [EMIm][CF3CH2OB(CN)3]. This
on the basis of the similar dynamic viscosities. Although behaviour may reflect an increase in ion pairing. So, the CF3 unit in
[EMIm][CH3OB(CN)3] reveals
a
slightly lower viscosity than [CF3CH2OB(CN)3]À may be involved in additional, weak hydrogen
[EMIm]TCB,15 the tetracyanoborate-IL possesses a slightly higher bonding to the [EMIm]+ ions.
Table 4 Selected physical and electrochemical propertiesa of [EMIm][ROB(CN)3] (R = CH3, C2H5, and CF3CH2) and [EMIm][B(CN)4] ([EMIm]TCB) at 20 1C
Limp
Z
r
c
D+
[mPa s] [g cmÀ3] [mol LÀ1] [10À11 m2
DÀ
s
LNMR
[cm2
S
]
Ec
Ea DE
Salt
s
À1] [10À11 m2
s
À1] [mS cmÀ1] [cm2 S molÀ1] molÀ1
I
[V] [V] [V] n2D0
[EMIm][CH3OB(CN)3]
[EMIm][C2H5OB(CN)3]
18.8
25.2
1.04
1.03
1.18
1.04
4.48
4.19
3.93
4.60
7.2
5.8
6.9
6.3
5.5
3.9
5.0
5.4
10.1
5.6
5.5
4.84
3.71
4.55
4.47
2.25
1.34
1.40
2.64
0.46 À2.4 1.9 4.3 1.450
0.36 À2.4 1.8 4.2 1.450
0.31 À2.4 2.0 4.4 1.422
0.59 À2.4 2.0 4.4 1.450
[EMIm][CF3CH2OB(CN)3] 24.4
[EMIm][B(CN)4]15
22.6
12.1
a
Dynamic viscosity Z; density r; concentration c; diffusion coefficients of cations (D+) and anions (DÀ); specific conductivity s measured via
impedance spectroscopy; molar conductivities calcd by LNMR = (D+ + DÀ)NAe2kÀ1TÀ1 and Limp = sMrÀ1; ionicity I = LimpLNMRÀ1; cathodic and
anodic limits Ec and Ea; electrochemical window DE = Ea À Ec.
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[EMIm]+ salts of the non-fluorinated ions [CH3OB(CN)3]À and
[C2H5OB(CN)3]À exhibit the same refractive index as [EMIm]TCB,5
whereas the value found for [EMIm][CF3CH2OB(CN)3] is lower,
which is typical for fluorine-containing ILs.5
Electrochemical properties of Li[CH3OB(CN)3]
The lithium salt Li[CH3OB(CN)3] is either accessible via direct
cyanation of Li[B(OCH3)4] or Li[BF4] (Scheme 1) or by salt
metathesis from Na[CH3OB(CN)3] (Scheme 3). The solubility of
Li[CH3OB(CN)3] in propylene carbonate (PC) at room tempera-
ture is 0.50 mol LÀ1, which is much higher than the solubility of
LiTCB of 0.10 mol LÀ1. The solution of Li[CH3OB(CN)3] in PC
possesses a large electrochemical window of ca. 5 V (Fig. 9).
The specific conductivity of this solution is 1.86 mS cmÀ1
at 20 1C and it increases with the increasing temperature and
reaches 4.67 mS cmÀ1 at 80 1C (Fig. 9).
Fig. 8 Ionicity of EMIm-ILs of [ROB(CN)3]À (R = CH3, C2H5, and CF3CH2)
and [B(CN)4]À.
The molar conductivities Limp and LNMR were determined at
20, 40, and 60 1C (Table S3 and Fig. S1 in the ESI‡) and both
Limp and LNMR increase with the increasing temperature.
Within the temperature range studied, LNMR reveals a stronger
increase with the increasing temperature than Limp and, thus,
the ionicity slightly decreases with the increasing temperature
(Fig. 8).
3. Conclusions
Alkali metal salts of alkoxytricyanoborate ions and dialkoxy-
dicyanoborate ions have become accessible using different com-
mercially available boron-based starting materials. In particular,
alkoxytricyanoborates exhibit high stabilities, which make them
interesting building blocks for material applications. Room
temperature ionic liquids with [EMIm]+ ions have been synthe-
sized via metathesis. These ILs possess low melting and low
viscous properties and they exhibit high specific conductivities
as well as high thermal, chemical, and electrochemical stabili-
ties. Thus, ILs based on these anions fulfill key requirements for
potential applications in electrochemical devices. In addition,
Li[CH3OB(CN)3] was prepared. This Li salt provides a 5-times
higher solubility in propylene carbonate than LiTCB and it
provides a decent conductivity. The high yield and easily scalable
syntheses of alkoxytricyanoborates combined with the interest-
ing properties of their salts make them promising alternatives to
tetracyanoborates.
Refractive indices. The refractive indices (n2D0) of the [EMIm]-
ILs depend on the number of fluorine atoms (Table 4). So, the
4. Experimental section
General
Reactions with air- and moisture-sensitive compounds were
performed in round-bottom flasks or glass tubes equipped with
¨
valves with PTFE stems (Rettberg, Gottingen) under argon using
Schlenk-line techniques. High pressure reactions (45 bar) were
conducted in a Carl Roth autoclave model I (working volume =
100 mL and inner volume = 135 mL). 1H, 11B, 13C, and 19F NMR
spectra were recorded at 25 1C in (CD3)2CO or CD3CN on a
Bruker Avance 500 NMR spectrometer. The NMR signals were
referenced against TMS (1H, 13C), BF3ÁOEt2 in CDCl3 with X(11B) =
32.083974 MHz, and CFCl3 with X(19F) = 94.094011 MHz as
external standard.39 1H and 13C chemical shifts were calibrated
against the residual solvent signal and the solvent signal, respec-
tively (d(1H): (CD3)(CD2H)CO 2.05 ppm, CD2HCN 1.94 ppm; d(13C):
(CD3)2CO 206.26 and 29.84 ppm, CD3CN 118.26 and 1.32 ppm).40
IR spectra were recorded at room temperature on a Bruker Alpha
Fig. 9 Cyclic voltammogram (20 1C; scan rate: 50 mV sÀ1, glassy carbon
working electrode, top) and temperature dependence of the conductivity
(bottom) of a saturated solution of Li[CH3OB(CN)3] in propylene carbonate
(0.50 mol LÀ1).
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spectrometer with an apodized resolution of 4 cmÀ1 in the 0.75H2O. Anal. calculated for C4H4.5BLiN3O1.75: C, 34.23%; H,
attenuated total reflection (ATR) mode in the region of 4000– 3.23%; N, 29.94%. Found: C, 34.72%; H, 3.09%; N, 31.25%.
500 cmÀ1 using a setup with a diamond crystal. Raman spectra
Method B
were recorded at room temperature with a MultiRAM FT-Raman
spectrometer using the 1064 nm excitation line of an Nd/YAG Li[BF4] (15.0 g, 160.0 mmol) was dissolved in a mixture of
laser on crystalline samples contained in melting point capil- TMSCN (120.0 mL, 956.2 mmol) and TMSOCH3 (150 mL,
laries in the region of 3500–100 cmÀ1. (À)-ESI mass spectra were 1092.3 mmol). The reaction mixture was stirred at room tem-
recorded on a Thermo Scientific Extractive Plus mass spectro- perature for 2 days. The resulting suspension was filtered, and
meter equipped with an Orbitrap mass analyser. Elemental the colorless solid was washed with CH2Cl2 (20 mL) and
analysis (C, H, N) was performed with an Elementar Varion dissolved in acetone (50 mL). CH2Cl2 (350 mL) was slowly
Micro Cube instrument. Thermal analyses were performed with added to give Li[CH3OB(CN)3] as a precipitate that was filtered
a DSC 204 F1 Phoenix (Netzsch) in the temperature range off and dried under vacuum. Yield: 20.1 g (158.5 mmol, 99%).
of À150 to 500 1C with a heating rate of 10 K minÀ1 and DTA
Method C
measurements were performed with a STA 449 F3 Perseus
(Netzsch), connected to an Alpha FTIR spectrometer (Bruker) Na[CH3OB(CN)3] (1.0 g, 7.0 mmol) was added to a solution of
for the analysis of the gaseous decomposition products, in the LiCl (296 mg, 7.0 mmol) in acetone (150 mL) under vigorous
temperature range of 30 to 500 1C with a heating rate of stirring. The precipitate (NaCl) was filtered off. The volume of
10 K minÀ1. The water content of the ILs was determined by the filtrate was reduced to approximately 5 mL with a rotary
Karl–Fischer titration with a Metrohm 831 KF Coulometer. The evaporator. Chloroform (100 mL) was added to give
water content of the ILs was o50 ppm. Viscosities and densi- Li[CH3OB(CN)3] as a precipitate that was filtered off and dried
ties were measured with a rolling-ball viscometer Lovis 2000 under vacuum. Yield: 874 mg (6.9 mmol, 99%).
ME combined with a DMA 4100 M density meter (Anton Paar) at
Sodium methoxytricyanoborate, Na[CH3OB(CN)3]. Method A
different angles and temperatures.
Na[B(OCH3)4] (3.0 g, 19.0 mmol) was mixed with TMSCN (100.0 mL,
796.8 mmol). The reaction mixture was stirred for 2 days at 60 1C.
Chemicals
Sodium and potassium tetraalkoxyborates were synthesized The excess of TMSCN and the byproduct TMSOMe was distilled off.
similar to a literature procedure for Na[B(OCH3)4]41 from The residue was dissolved in an aqueous solution of H2O2
Na[BH4] or K[BH4] and the corresponding alcohol (MeOH, (30% w/w, 20 mL), mixed with Na2CO3 (ca. 1 g) and stirred
EtOH, trifluoroethanol).42 Li[B(OCH3)4] was prepared from for 4 h. Subsequently, the mixture was treated with Na2S2O5. The
LiOCH3 and B(OCH3)3 in methanol.43 LiTCB was synthesized solution was extracted with THF (3 Â 20 mL). The combined THF
similar to a literature procedure.25
phases were dried with Na2CO3 (ca. 10 g), filtered and the solvent
Caution. Alkali metal cyanides and trimethylsilyl cyanides was evaporated under vacuum. The residue was dissolved in
are highly toxic. Peroxides are potentially hazardous. Thus, the acetone (5 mL). The addition of CH2Cl2 (100 mL) yielded colorless
decomposition of peroxides during the work-up procedures had to Na[CH3OB(CN)3] as a precipitate. The solid was filtered off and
be secured with Quantofix Peroxide 100 test sticks (Machery-Nagel). dried under vacuum. Yield: 2.5 g (17.5 mmol, 92%). 1H NMR
((CD3)2CO): d: 3.21 (q, J(11B,1H) = 3.8 Hz, OCH3, 3H). 13C NMR
3
((CD3)2CO): d: 128.50 (q, J(13C,11B) = 70.2 Hz, CN, 3C), 52.97 (qq,
Lithium methoxytricyanoborate, Li[CH3OB(CN)3]. Method A
1
A solution of Li[BF4] (15.0 g, 160.0 mmol) in acetonitrile (40 mL) 1J(13C,1H) = 139.6 Hz, 2J(13C,11B) E 1 Hz, 1C, OCH3). 11B NMR
was mixed with trimethylsilyl cyanide (TMSCN, 75.0 mL, ((CD3)2CO): d: À18.42 (q, 3J(11B,1H) = 3.8 Hz, 1B). (À)-ESI
597.6 mmol). Gas evolution (trimethylsilyl fluoride, TMSF) MS calculated for (C4H3BN3O)À: 120.0 (100%), 119.0 (25%),
was observed. After the gas evolution had ceased, trimethylm- 121.0 (6%). Found: 120.4 (100%), 119.4 (22%), 121.4 (5%).
etoxysilane (TMSOCH3, 25.0 mL, 182.1 mmol) was added. The Raman (cmÀ1): 2231, 2224, 2217 (n(CN)).
reaction mixture was stirred for 2 days at 40 1C. All volatiles
A sample of Na[CH3OB(CN)3] was crystallized from wet
were removed under vacuum. The residue was dissolved in acetone to give Na[B(CN)3OCH3]ÁH2O. Anal. calculated for
acetone (25 mL). Slow addition of CHCl3 (150 mL) resulted in C4H5BN3NaO2: C, 29.86%; H, 3.13%; N, 26.12%. Found: C,
Li[CH3OB(CN)3] as a precipitate, which was isolated by filtra- 29.94%; H, 2.79%; N, 26.22%.
tion and dried under vacuum. Yield: 20.2 g (159.3 mmol, 99%).
1H NMR ((CD3)2CO): d: 3.20 (q, 3J(11B,1H) = 4.1 Hz, 3H). 13C
Method B
NMR ((CD3)2CO): d: 128.56 (q, 1J(13C,11B) = 70.3 Hz, 3C, CN), Na[BH4] (10.0 g, 264.3 mmol) was slowly added to methanol
53.05 (qq, 1J(13C,1H) = 140.0 Hz, 2J(13C,11B) o 1 Hz, 1C, OCH3). (600 mL). After the exothermic reaction had stopped, the
11B NMR ((CD3)2CO): d: À18.42 (q, 3J(11B,1H) = 3.7 Hz, 1B). solution was evaporated using a rotary evaporator and the solid
Raman (cmÀ1): 2247, 2239 (n(CN)).
residue was dried under vacuum. The solid was dissolved in
Elemental analysis was performed on a material derived TMSCN (250 mL, 1992.0 mmol) and the reaction mixture was
from crystals of Li[CH3OB(CN)3]ÁH2O that have been briefly stirred for 5 days at 60 1C. Subsequently, all volatiles were
dried. Drying resulted in loss of part of the solvate molecules distilled off. The residue was treated with H2O2 (30% w/w,
and in salt of the approximate composition Li[CH3OB(CN)3]Á 25 mL) and mixed with Na2CO3 in portions (ca. 2 g). Na2S2O5
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1
2
was added to destroy the excess peroxide. The crude product 52.97 (qq, J(13C,1H) = 140.0 Hz, J(13C,11B) E 1 Hz, 1C, OCH3).
was extracted from the aqueous phase with THF (5 Â 100 mL). 11B NMR ((CD3)2CO): d: À18.44 (q, 3J(11B,1H) = 3.8 Hz, 1B).
The combined THF phases were dried with Na2CO3, filtered Raman (cmÀ1): 2227, 2220 (n(CN)).
and the solvent was removed under vacuum. The beige solid
residue was washed with CH2Cl2 (3 Â 50 mL) to result in
Tetraethylammonium methoxytricyanoborate,
[(C2H5)4N][CH3OB(CN)3]
a colourless solid that was dried under vacuum. Yield: 34.3 g
(240.0 mmol, 91%).
An aqueous solution of tetraethylammonium hydroxide (35% w/w,
20.2 g, 48.0 mmol) was added to Na[CH3OB(CN)3] (6.8 g,
Method C
NaOCH3 (1.0 g, 18.5 mmol) was suspended in acetonitrile 47.6 mmol) dissolved in distilled water (5 mL) under vigorous
(5 mL). B(OCH3)3 (1.9 g, 2.1 mL, 18.3 mmol) and TMSCN stirring. CH2Cl2 (50 mL) was added to the emulsion and the
(9.0 mL, 71.7 mmol) were added. The reaction mixture was organic phase was separated. The CH2Cl2 phase was subsequently
stirred for 4 days at 50 1C. Subsequently, all volatiles were washed with distilled water (3 Â 5 mL), dried with MgSO4, filtered,
removed under vacuum. The residue was treated with H2O2 and evaporated using a rotary evaporator. The residue was dried
(30% w/w, 10 mL) and mixed with Na2CO3 in portions (ca. 0.5 g). under fine vacuum at 60 1C. Yield: 10.0 g (40.0 mmol, 84%).
Excess H2O2 was destroyed with the addition of Na2S2O5. The 1H{11B} NMR ((CD3)2CO): d: 3.44 (q, 8H, CH2), 3.20 (s, 3H, OCH3),
crude product was extracted from the aqueous phase with THF 1.38 (tt, 3J(1H,1H) = 7.3 Hz, 12H, CH3). 13C{1H} NMR ((CD3)2CO): d:
(3 Â 50 mL). The combined THF phases were dried with Na2CO3, 128.74 (q, 1J(13C,11B) = 70.1 Hz, 3C, CN), 54.93 (q, 2J(13C,11B) E 1 Hz,
filtered and evaporated under vacuum to dryness. The beige 1C, OCH3), 53.02 (s, 4, CH2), 7.66 (s, 4C, CH3). 11B{1H} NMR
solid was washed with CH2Cl2 (50 mL) on a glass frit (D4) and ((CD3)2CO): d: À18.44 (s, 1B). Raman (cmÀ1): 2204, 2214 (n(CN)).
dried under vacuum. Yield: 1.8 g (12.6 mmol, 69%).
Tetrabutylammonium methoxytricyanoborate,
[(C4H9)4N][CH3OB(CN)3]. Method A
Method D
Na[BF4] (25.0 g, 227.6 mmol) was suspended in a mixture of
TMSCN (100 mL, 796.8 mmol) and TMSOCH3 (100 mL,
728.4 mmol). The mixture was heated to reflux for 2 d. All
volatiles were removed in a vacuum and the residue was
washed with CH2Cl2 (70 mL). The solid was dissolved in
acetonitrile (100 mL) and, after stirring for 5 min, insoluble
Na[BF4] was filtered off. The filtrate was evaporated to dryness
using a rotary evaporator, the residue was rinsed onto a glass
frit (D4) using dichloromethane (ca. 150 mL), and the solid was
subsequently dried under vacuum. Yield: 24.1 g (168.6 mmol,
74%). The crude material contained Na[BF4] (4%) and
Na[BF2(CN)2] (9%) as identified by 11B NMR spectroscopy.
A solution of Na[CH3OB(CN)3] (5.2 g, 36.4 mmol) in bidistilled
water (10 mL) was mixed with an aqueous solution of [Bu4N]OH
(40% w/w, 1.5 mol LÀ1, 25.0 mL, 38.3 mmol). CH2Cl2 (50 mL)
was added to the emulsion and stirred for 10 min. The CH2Cl2
phase was separated, washed with bidistilled water (3 Â 5 mL),
dried with MgSO4, and filtered. The solution was evaporated
using a rotary evaporator and the highly viscous liquid was
dried under vacuum. Yield: 11.6 g (32.0 mmol, 88%). Anal.
calculated for C20H39BN4O: C, 66.29%; H, 10.85%; N, 15.46%.
Found: C, 66.11%; H, 9.74%; N, 15.44%. 1H{11B} NMR
((CD3)2CO): d: 3.39 (m, 8H, CH2), 3.21 (s, 3H, OCH3), 1.80 (m, 8H,
CH2), 1.44 (m, 8H, CH2), 0.98 (t, 3J(1H,1H) = 7.4, 12H, CH3). 13C{1H}
NMR ((CD3)2CO): d: 128.84 (q, 1J(13C,11B) = 70.1 Hz, 3C, CN), 59.48
(t, 1J(15N,13C) = 2.9 Hz, 4C, NCH2), 53.04 (q, 2J(13C,11B) E 1 Hz, 1C,
OCH3), 24.47 (s, 4C, CH2), 20.42 (t, 4C, CH2), 13.88 (s, 4C, CH3).
11B{1H} NMR ((CD3)2CO): d: À18.44 (s, 1B). Raman (cmÀ1): 2202,
2212 (n(CN)).
Potassium methoxytricyanoborate, K[CH3OB(CN)3]
K[BH4] (10.0 g, 185.4 mmol) was slowly added to methanol
(500 mL). After the exothermic reaction had ceased, the reac-
tion mixture was refluxed for further 2 h. The resulting solution
was evaporated using a rotary evaporator and the colorless
K[B(OCH3)4] (11B NMR spectroscopy) was dried overnight under
vacuum. In a parallel reaction, NaCN (60.0 g, 1.22 mol) and
[EMIm]Cl (10 g, 68.2 mmol) were dissolved in acetonitrile
(20 mL) and TMSCl (140.0 mL, 1.103 mol) was added. The
suspension was stirred for 2 d at room temperature and
the formation of TMSCN was periodically checked by 13C NMR
spectroscopy. The freshly prepared TMSCN that still contained
some TMSCl was distilled at 150 1C to the colorless K[B(OCH3)4].
The resulting suspension was stirred at room temperature for 2 d.
All volatiles were removed under vacuum and the colorless residue
was rinsed onto a glass frit (D4) with CH2Cl2 (ca. 200 mL). Yield:
17.2 g (108.2 mmol, 58%). Anal. calculated for C4H3BKN3O: C,
30.22%; H, 1.90%; N, 26.43%. Found: C, 30.10%; H, 1.96%; N,
Method B
Na[B(OCH3)4] (300 mg, 1.90 mmol) was suspended in
(CH3)3SiCN (50.0 mL, 398.4 mmol). The reaction mixture was
stirred at 60 1C for 2 d. All volatiles were removed under
reduced pressure and the residue was dissolved in aqueous
H2O2 (15% w/w, 20 mL). K2CO3 was added to this solution, and
the mixture was stirred at 50 1C for 1 h. Tetrabutylammonium
bromide (806 mg, 2.50 mmol) was added and the resulting
emulsion was extracted with CH2Cl2 (3 Â 5 mL). The dichloro-
methane phase was separated, washed with distilled water
(3 Â 2 mL), dried with MgSO4, and evaporated to dryness under
vacuum to result in a highly viscous liquid. Yield: 600 mg
(1.66 mmol, 87%).
1
3
27.36%. H NMR ((CD3)2CO): d: 3.19 (q, J(11B,1H) = 3.8 Hz, 3H).
13C NMR ((CD3)2CO): d: 128.50 (q, J(13C,11B) = 70.2 Hz, 3C, CN),
1
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1-Ethyl-3-methylimidazolium methoxytricyanoborate,
[EMIm][CH3OB(CN)3]. Method A
off. The slimy residue was dissolved in an aqueous solution of
H2O2 (30% w/w, 15 mL) and treated with Na2CO3 (ca. 0.5 g). The
excess peroxide was destroyed with the addition of Na2S2O5.
The reaction mixture was extracted with THF (4 Â 50 mL) and
the combined THF phases were dried with Na2CO3, filtered,
and evaporated using a rotary evaporator. The residue was
dissolved in acetone and the product was precipitated by the
addition of a 1 : 1 mixture of CH2Cl2/CHCl3. Na[C2H5OB(CN)3]
was filtered off and dried under fine vacuum. Yield: 0.8 g
(5.1 mmol, 55%). Anal. calculated for C5H5BN3NaO: C,
38.27%; H, 3.21%; N, 26.78%. Found: C, 38.10%; H, 3.20%;
N, 27.33%. 1H NMR ((CD3)2CO): d: 3.42 (qq, 3J(1H,1H) = 7.0 Hz,
Na[CH3OB(CN)3] (8.0 g, 56.0 mmol) and [EMIm]Cl (8.2 g,
55.9 mmol) were dissolved in bidistilled water (10 mL) and stirred
vigorously for 15 min. CH2Cl2 (50 mL) was added and the emulsion
was stirred for another 15 min. The CH2Cl2 phase was separated,
washed with bidistilled water (3 Â 2 mL), dried with MgSO4, and
filtered. The solution was evaporated under vacuum and the ionic
liquid was dried under fine vacuum. Yield: 9.1 g (39.4 mmol, 70%).
Anal. calculated for C10H14BN5O: C, 51.98%; H, 6.11%; N, 30.31%.
Found: C, 51.35%; H, 6.35%; N, 30.76%. 1H{11B} NMR ((CD3)2CO):
d: 8.95 (s, 1H, CH), 7.72 (t, 3J(1H,1H) = 1.8 Hz, 1H, CH), 7.65
(t, 3J(1H,1H) = 1.7 Hz, 1H, CH), 4.38 (q, 3J(1H,1H) = 7.3 Hz, 2H, CH2),
3
3J(11B,1H) = 1.7 Hz, 2H, OCH2), 1.09 (t, J(1H,1H) = 7.0 Hz, 3H,
3
CH3). 13C{1H} NMR ((CD3)2CO): d: 128.82 (q, 1J(13C,11B) = 69.9 Hz,
4.04 (s, 3H, CH3), 3.19 (s, 3H, OCH3), 1.57 (t, J(1H,1H) = 7.3, 3H,
3
3C, CN), 61.12 (s, 1C, OCH2), 17.57 (q, J(13C,11B) = 3.2 Hz, 1C,
CH3). 13C{1H} NMR ((CD3)2CO): d: 136.91 (s, 1C, CH), 128.60
(q, 1J(13C,11B) = 70.0 Hz, 3C, CN), 124.69 (s, CH, 1C), 123.02
CH3). 11B NMR ((CD3)2CO): d: À18.99 (t, 3J(11B,1H) = 1.7 Hz, 1B).
(À)-ESI MS calculated for (C5H5BN3O)À: 134.1 (100%), 133.1
(24%). Found: 134.1 (100%), 133.3 (29%). Raman (cmÀ1): 2238,
2227, 2219 (n(CN)).
2
(s, 1C, CH), 52.98 (q, J(13C,11B) E 1 Hz, 1C, OCH3), 45.70 (s, 1C,
CH2), 36.61 (s, 1C, CH3), 15.49 (s, 1C, CH3). 11B{1H} NMR
((CD3)2CO): d: À18.48 (s, 1B). Raman (cmÀ1): 2205, 2214 (n(CN)).
Method B
Method B
Solutions of Li[CH3OB(CN)3] (2.25 g, 17.7 mmol) in bidistilled
water (10 mL) and [EMIm]Cl (2.80 g, 19.1 mmol) in bidistilled
water (10 mL) were combined and vigorously stirred for 15 min.
CH2Cl2 (100 mL) was added and the resulting emulsion was
stirred for 15 min. The CH2Cl2 phase was separated, washed
with bidistilled water (3 Â 5 mL), dried with MgSO4, and filtered.
The solution was evaporated under vacuum and the ionic liquid
was dried under a fine vacuum. Yield: 3.45 g (14.9 mmol, 84%).
Na[BH4] (10.0 g, 264.3 mmol) was added to ethanol (600 mL)
and the reaction mixture was refluxed for 12 h. Excess ethanol
was removed using a rotary evaporator at 70 1C to give
Na[B(OC2H5)4]. In a parallel reaction, NaCN (80.0 g, 1632.3 mmol)
and TMSCl (200.0 mL, 1.576 mol) were reacted for 2 d in
acetonitrile (25 mL) in the presence of NaI (10.0 g, 66.7 mmol)
to give a suspension containing TMSCN. The Na[B(OC2H5)4] was
added to this suspension. The reaction mixture was stirred for
6 d at 25 1C. All volatiles were removed under vacuum to give
a dark brown residue that was dissolved in H2O2 (30% w/w,
200 mL). Na2CO3 (ca. 5g) was added in portions and the reaction
mixture was stirred for 1 d at room temperature. The excess
peroxide was destroyed by the addition of Na2S2O5. The aqueous
phase was extracted with THF (5 Â 100 mL). The yellow THF
solution was dried with Na2CO3, filtered, and evaporated under
vacuum until dryness. The residue was dissolved in acetone at
60 1C and the product was precipitated by the addition of CH2Cl2
(300 mL). The yellowish solid was filtered off and dried under
fine vacuum. Yield: 37.3 g (237.7 mmol, 90%).
N-butyl-N-methylpyrrolidinium methoxytricyanoborate,
[BMPL][CH3OB(CN)3]
Na[CH3OB(CN)3] (6.0 g, 42.0 mmol) and [BMPL]Cl (7.5 g,
42.2 mmol) were dissolved in bidistilled water (10 mL) and
stirred for 10 min. The resulting emulsion was extracted with
CH2Cl2 (3 Â 20 mL). The combined organic phases were
washed with bidistilled water (3 Â 5 mL), dried with MgSO4,
filtered, and evaporated using a rotary evaporator. The ionic
liquid was dried under a fine vacuum at 60 1C. Yield: 9.1 g
(34.7 mmol, 83%). Anal. calculated for C13H23BN4O: C, 59.56%;
H, 8.84%; N, 21.37%. Found: C, 59.60%; H, 9.65%; N, 21.47%.
1H{11B} NMR ((CD3)2CO): d: 3.68 (m, 4H, CH2), 3.49 (m, 2H,
CH2), 3.22 (s, 3H, CH3), 3.20 (s, OCH3, 3H), 2.31 (m, 4H, CH2),
1.89 (m, 2H, CH2), 1.43 (m, 2H, CH2), 0.98 (t, 3J(1H,1H) = 7.4 Hz,
Method C
NaCN (3.0 g, 61.2 mmol) was suspended in a mixture of
acetonitrile (10 mL), (CH3)3SiCl (7.0 mL, 55.2 mmol), C2H5OH
(0.72 mL, 12.3 mmol), and a few drops of triethylamine. Na[BF4]
(0.78 g, 7.1 mmol) was subsequently added to this mixture, and
the reaction mixture was stirred at room temperature for 2 d.
The suspension was rendered alkaline with aqueous NaOH and
was evaporated to dryness. The residue was extracted with THF
(5 Â 5 mL), dried with MgSO4 and filtered. The THF phase was
evaporated to a residual volume of about 5 mL, and colorless
Na[C2H5OB(CN)3] was precipitated by the addition of CH2Cl2
(25 mL). The product was filtered off and dried under fine
vacuum. Yield: 0.85 g (5.4 mmol, 76%).
1
3H, CH3). 13C{1H} NMR ((CD3)2CO): d: 128.71 (q, J(13C,11B) =
70.1 Hz, 3C, CN), 65.20 (s, 2C, CH2), 65.00 (s, 1C, CH2), 53.04 (q,
2J(13C,11B) = 0.8 Hz, 1C, OCH3), 48.98 (s, 1C, CH3), 26.17 (s, 1C,
CH2), 22.23 (s, 2C, CH2), 20.30 (s, 1C, CH2), 13.64 (s, 1C, CH3).
11B{1H} NMR ((CD3)2CO): d: À18.44 (s, 1B). Raman (cmÀ1):
2204, 2214 (n(CN)).
Sodium ethoxytricyanoborate, Na[C2H5OB(CN)3]. Method A
Na[B(OC2H5)4] (2.0 g, 9.3 mmol) was suspended in TMSCN
(20.0 mL, 159.4 mmol) and stirred for 2 d at 60 1C. The excess
TMSCN and the byproduct trimethylethoxysilane were distilled
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3
Tetrabutylammonium ethoxytricyanoborate,
[(C2H5)4N][C2H5OB(CN)3]
1H NMR ((CD3)2CO): d: 3.80 (qq, J(19F,1H) = 9.1 Hz, J(11B,1H) =
2.0 Hz, 2H, OCH2). 13C{1H} NMR ((CD3)2CO): d: 127.47
(q, 1J(13C,11B) = 71.7 Hz, 3C, CN), 125.82 (qq, 1J(19F,13C) = 277.2 Hz,
3J(13C,11B) = 5.0 Hz, 1C, CF3), 64.21 (q, 2J(19F,13C) = 34.5 Hz, 1C,
Na[C2H5OB(CN)3] (5.0 g, 31.9 mmol) was dissolved in bidistilled
water (15 mL) and mixed with an aqueous solution of [nBu4-
N]OH (40% w/w, 1.5 mol LÀ1, 22.0 mL, 33.7 mmol). The
solution was extracted with CH2Cl2 (5 Â 50 mL). The combined
CH2Cl2 phases were washed with bidistilled water (3 Â 5 mL),
dried with MgSO4, and filtered. The solution was evaporated
under reduced pressure and the residue was dried under
vacuum. Yield: 10.9 g (29.0 mmol, 91%). Anal. calculated for
OCH2). 19F NMR ((CD3)2CO): d: À76.08 (t, J(19F,1H) = 8.8 Hz,
3
1H). 11B NMR ((CD3)2CO): d: À19.03 (t, 3J(11B,1H) = 2.0 Hz, 1B).
(À)-ESI MS calculated for (C5H2BF3N3O)À: 188.0 (100%), 187.0
(24%), 189.0 (7%). Found: 187.7 (100%), 186.7 (29%), 188.7
(10%). Raman (cmÀ1): 2236, 2228 (n(CN)).
Elemental analysis was performed on crystals of
Na[CF3CH2OB(CN)3]Á0.5H2O. Anal. calculated for C5H3BF3N3NaO1.5
:
C
21H25BN4O: C, 67.01%; H, 10.98%; N, 14.89%. Found: C,
66.63%; H, 12.34%; N, 13.78%. 1H{11}B NMR ((CD3)2CO): d:
C, 27.31%; H, 1.38%; N, 19.11%. Found: C, 27.09%; H, 1.29%; N,
18.77%.
3.42 (q, J(1H,1H) = 7.0 Hz, 2H, OCH2), 3.39 (m, 8H, CH2), 1.82
3
(m, 8H, CH2), 1.44 (m, 8H, CH2), 1.13 (t, 3J(1H,1H) = 7.0 Hz, 3H,
CH3), 0.99 (t, 3J(1H,1H) = 7.4 Hz, 12H, CH3). 13C{1H} NMR
((CD3)2CO): d: 129.01 (q, 1J(13C,11B) = 69.8 Hz, 3C, CN), 61.17
Method B
Na[B(OCH2CF3)4] (5.0 g, 11.63 mmol) was stirred in TMSCN
(20.0 mL, 159.4 mmol) for 17 h at 80 1C. The formation of a
colorless precipitate was observed. Subsequently, all volatiles
were removed under vacuum. The residue was dissolved in THF
(5 mL). The addition of CH2Cl2 resulted in the precipitation of a
colorless solid. Yield: 1.96 g (9.29 mmol, 80%).
(s, 1C, OCH2), 59.48 (t, J(15N,13C) = 2.9 Hz, 4C, NCH2), 24.47
1
(s, 4C, CH2), 20.39 (t, 4C, CH2), 17.78 (q, 3J(13C,11B) = 3.2 Hz, 1C,
CH3), 13.86 (s, 4C, CH3). 11B{1H} NMR ((CD3)2CO): d: À18.96
(s, 1B).
1-Ethyl-3-methylimidazolium ethoxytricyanoborate,
[EMIm][C2H5OB(CN)3]
Sodium bis(methoxy)dicyanoborate, Na[(CH3O)2B(CN)2]
TMSCN (1.0 mL, 7.97 mmol) was added to a suspension of
Na[B(OCH3)4] (592 mg, 3.75 mmol) in dry acetonitrile (30 mL)
and stirred for 12 h at room temperature. The stirring was
stopped, and the precipitant could settle. The clear liquid phase
was transferred into a second flask, all volatiles were removed
under reduced pressure, and the product was dried under a fine
vacuum. Yield: 440 mg (2.97 mmol, 79%). 1H NMR (CD3CN):
Na[C2H5OB(CN)3] (3.77 g, 24.0 mmol) was dissolved in bidistilled
water (15 mL) and mixed with a solution of [EMIm]Cl (3.69 g,
25.2 mmol) in bidistilled water (20 mL) under vigorous stirring.
CH2Cl2 (100 mL) was added and the resulting emulsion was
agitated for 15 min. The CH2Cl2 phase was separated, washed
with bidistilled water (3 Â 10 mL), dried with MgSO4, and
filtered. The solution was evaporated under reduced pressure
and the ionic liquid was dried under fine vacuum. Yield: 5.32 g
(21.7 mmol, 90%). Anal. calculated for C11H16BN5O: C, 53.91%;
H, 6.58%; N, 28.57%. Found: C, 53.45%; H, 6.87%; N, 27.81%.
1H{11B} NMR ((CD3)2CO): d: 8.97 (s, 1H, CH), 7.73 (t, 3J(1H,1H) =
1.8 Hz, 1H, CH), 7.66 (t, 3J(1H,1H) = 1.7 Hz, 1H, CH), 4.38
(q, 3J(1H,1H) = 7.3 Hz, 2H, CH2), 4.05 (s, 3H, CH3), 3.43
3
d: 3.21 (q, JB-H = 3.3 Hz, 6H) ppm. 1H{11B} NMR (CD3CN):
d: 3.21 (s, 6H). 13C NMR (CD3CN): d: 131.85 (q, 1J(13C,11B) = 68.4 Hz,
2C, CN), 50.91 (q, 3J(13C,1H) = 139.5 Hz, 2C, CH3). 11B NMR
(CD3CN): d: À5.40 (q, 3J(11B,1H) = 3.2 Hz, 1B).
Sodium bis(1,1,1-trifluoroethoxy)dicyanoborate,
Na[(CF3CH2O)2B(CN)2]. Method A
3
3
(q, J(1H,1H) = 7.0 Hz, 2H, OCH2), 1.57 (t, J(1H,1H) = 7.3 Hz,
Na[B(OCH2CF3)4] (2.0 g, 4.7 mmol) was stirred in TMSCN (20.0 mL,
159.4 mmol) for 2 d at room temperature. All volatiles were distilled
off and the colorless residue was dried under vacuum. The crude
product was dissolved in acetone (ca. 5 mL) and precipitated by the
addition of CHCl3 (50 mL). The solid was filtered off and dried
under fine vacuum. Yield: 1.2 g (4.2 mmol, 89%). 1H NMR
((CD3)2CO): d: 3.78 (qq, 3J(19F,1H) = 9.4 Hz, 3J(11B,1H) = 1.6 Hz,
3H, CH3), 1.10 (t, J(1H,1H) = 7.0 Hz, 3H, CH3). 13C{1H} NMR
3
((CD3)2CO): d: 137.00 (s, CH, 1C), 129.01 (q, J(13C,11B) = 69.8 Hz,
1
3C, CN), 124.76 (s, CH, 1C), 123.09 (s, CH, 1C), 61.17 (s, 1C, OCH2),
45.75 (s, CH2, 1C), 36.66 (s, 1C, CH3), 17.73 (q, 3J(13C,11B) = 3.2 Hz,
1C, CH3), 15.42 (s, 1C, CH3). 11B{1H} NMR ((CD3)2CO): d: À19.03
(s, 1B). Raman (cmÀ1): 2204, 2216 (n(CN)).
1
4H, OCH2).13C{1H} NMR ((CD3)2CO): d: 130.23 (q, J(13C,11B) =
73.8 Hz, 2C, CN), 126.40 (qq, 1J(19F,13C) = 280.9 Hz, 2J(13C,11B) =
Sodium trifluoroethoxytricyanoborate, Na[CF3CH2OB(CN)3].
Method A
2
4.4 Hz, 2C, CF3), 62.15 (q, J(19F,13C) = 34.1 Hz, 2C, OCH2). 11B
Na[B(OCH2CF3)4] (1.0 g, 2.33 mmol) was stirred in TMSCN (15.0 mL, NMR ((CD3)2CO): d = À6.67 (quin, J(11B,1H) = 1.5 Hz, 1B). 19F
119.5 mmol) for 2 d at 80 1C. All volatiles were removed under NMR ((CD3)2CO): d: À76.11 (t, 3J(19F,1H) = 9.3 Hz, 6F, CF3).
reduced pressure and the black residue was dissolved in an aqueous (À)-ESI MS calculated for (C5H2BF3N3O)À: 261.0 (100%), 260.0
solution of H2O2 (30% w/w, 20 mL). The solution was treated with (24%), 262.0 (7%). Found: 261.3 (100%), 260.3 (25%), 262.3 (1%).
Na2CO3 (ca. 0.5 g) in portions. The excess peroxide was destroyed Raman (cmÀ1): 2229, 2222, 2215 (n(CN)).
by the addition of Na2S2O5. The solution was extracted with THF
3
Method B
(3 Â 20 mL). The combined THF phases were dried with Na2CO3,
filtered, the solvent was removed under reduced pressure, and the Na[B(OCH2CF3)4] (15.0 g, 34.9 mmol) was stirred in TMSCN
solid was dried under fine vacuum. Yield: 443 mg (2.10 mmol, 90%). (45.0 mL, 358.6 mmol) for 2 d at room temperature. All volatiles
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were distilled off and the colorless residue was dried under and a Microcell HC set-up with a Eurotherm temperature con-
vacuum. The solid was redissolved in THF (10 mL) and pre- troller (rhd instruments). A 0.1 mL Pt-cell TSC-70 closed (rhd
cipitated by the addition of CH2Cl2 (200 mL). The product was instruments) served as a counter electrode and was equipped with
isolated by filtration and dried under fine vacuum. Yield: 8.0 g a glassy carbon working electrode (surface area: 3.14 Â 10À2 cm2).
(28.2 mmol, 81%).
Specific conductivities (s) were determined at different tempera-
tures (20, 40, 60, 70, and 80 1C) by impedance spectroscopy
from 500 Â 103 to 800 Hz. The cell constant was determined on a
1413 mS cmÀ1 conductivity solution HI 70031 (HANNA instru-
1-Ethyl-3-methylimidazolium trifluoroethoxytricyanoborate,
[EMIm][CF3CH2OB(CN)3]
Na[CF3CH2OB(CN)3] (1.50 g, 7.11 mmol) was dissolved in ments). Cyclic voltammetry was conducted at 20 1C with a scan
bidistilled water (10 mL) and mixed with a solution of [EMIm]Cl rate of 50 mV sÀ1 using the same set-up and an additional Ag/Ag+
(1.16 g, 7.91 mmol) in bidistilled water (10 mL). Dichloro- micro reference electrode (acetonitrile, rhd instruments).
methane (50 mL) was added to the reaction mixture and the
Single-crystal X-ray diffraction
emulsion was stirred for 15 min. The CH2Cl2 phase was
separated, washed with bidistilled water (3 Â 5 mL), dried with
MgSO4, and filtered. The solution was evaporated under
reduced pressure and the ionic liquid was dried under fine
vacuum. Yield: 1.93 g (6.45 mmol, 91%). Anal. calculated for
C11H13BF3N5O: C, 44.18%; H, 4.38%; N, 23.42%. Found: C,
Single-crystals of Li[CH3OB(CN)3]ÁH2O, K[CH3OB(CN)3],
Na[C2H5OB(CN)3], and Na[CF3CH2OB(CN)3]Á0.5H2O were stu-
died with a XtaLAB Synergy, Dualflex, HyPix diffractometer
equipped using Cu-Ka radiation (micro-focus sealed X-ray tube,
l = 1.54184 Å) and single-crystal of Na[CH3OB(CN)3]ÁH2O was
investigated using an Oxford Xcalibur equipped with an EOS
detector using Mo-Ka radiation (l = 0.71073 Å). All structures
were solved by direct methods,44,45 and refinements are based
on full-matrix least-squares calculations on F2.44,46 All non-
hydrogen atoms were refined anisotropically. The positions of
all H atoms were located from electron density difference maps.
In the final steps of the refinements, idealized bond lengths
and angles were introduced for most of the H atoms.
All calculations were performed with the ShelXle graphical
interface.47 Molecular structure diagrams were drawn with the
program Diamond 4.6.3.48 Experimental details, crystal data,
and the CCDC numbers are collected in Tables S4–S6 in the
ESI.‡
1
44.01%; H, 4.67%; N, 24.72%. H NMR ((CD3)2CO): d: 8.99 (s, 1H,
CH), 7.73 (t, 3J(1H,1H) = 1.8 Hz, 1H, CH), 7.66 (t, 3J(1H,1H) = 1.7 Hz,
1H, CH), 4.39 (q, 3J(1H,1H) = 7.3 Hz, 2H, CH2), 4.05 (s, 3H, CH3), 3.79
(qq, 3J(19F,1H) = 9.1 Hz, 3J(11B,1H) = 2.0 Hz, OCH2, 2H), 1.57
(t, 3J(1H,1H) = 7.3, 3H, CH3). 13C{1H} NMR ((CD3)2CO): d: 136.70 (s,
CH, 1C), 127.11 (q, 1J(13C,11B) = 71.7 Hz, 3C, CN), 124.45 (s, CH, 1C),
3
123.52 (qq, 1J(19F,13C) = 277.2 Hz, J(13C,11B) = 5.0 Hz, 1C, CF3),
122.78 (s, CH, 1C), 64.21 (q, 2J(19F,13C) = 34.5 Hz, 1C, OCH2), 45.45 (s,
CH2, 1C), 36.32 (s, 1C, CH3), 15.24 (s, 1C, CH3). 19F NMR ((CD3)2CO):
d: À75.96 (t, 3J(19F,1H) = 9.09 Hz, 1H). 11B NMR ((CD3)2CO): d: À19.07
(t, 3J(11B,1H) = 2.0 Hz, 1B). Raman (cmÀ1): 2211 (n(CN)).
1-Ethyl-3-methylimidazolium tetracyanoborate,
[EMIm][B(CN)4]
K[CH3OB(CN)3] (2.5 g, 15.72 mmol) was placed into an autoclave
and TMSCN (90.0 mL, 674.91 mmol) and TMSCl (10.0 mL,
79.16 mmol) were added. The reaction mixture was heated for
11 h to 250 1C while stirring. The maximum pressure was 70 bar.
After cooling to room temperature all volatiles were removed
under reduced pressure. The residue was dissolved in water
(50 mL). The suspension was treated with an aqueous solution
of H2O2 (30% w/w, 100 mL) and the pH was adjusted to about 3
by the addition of aqueous HCl (37% w/w). The mixture was
stirred overnight. All volatiles were removed using a rotary
evaporator (50 1C) and the residue was extracted with acetone
(30 mL). Acetone was removed using the rotary evaporator and
the residue was dissolved in water (10 mL) and treated with
[EMIm]CI (2.5 g, 11.17 mmol). The aqueous solution was
extracted with dichloromethane (20 mL) and the organic phase
was washed with bidistilled water (3 Â 1 mL). Subsequently,
dichloromethane was removed using the rotary evaporator and
the ionic liquid was dried under fine vacuum. Yield: 1.1 g
(4.87 mmol, 31%). The analytical data are consistent with those
reported earlier.15
DFT calculations
Density functional calculations (DFT)49 using the hybrid func-
tional B3LYP50 and Pople-type basis sets 6-311++G(d,p) were
performed with the Gaussian16 program suite.51 All structures
represent true minima with no imaginary frequency on the
respective hypersurface.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
Generous support by Merck KGaA (Darmstadt, Germany) is grate-
fully acknowledged. The authors are grateful to the Deutsche
Forschungsgemeinschaft (DFG, SPP 1708, FI 1628/4-2) for financial
support.
References
Electrochemical measurements
All electrochemical studies were performed on the neat ILs under
an argon atmosphere with a Metrohm PGSTAT30 potentiostat
1 J. S. Wilkes and M. J. Zaworotko, J. Chem. Soc., Chem.
Commun., 1992, 965–967.
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NJC
2 P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed., 2000, 13 K. Kawata, N. Ignatyev, M. Schulte and H. Yoshizaki, Merck
39, 3772–3789; Ionic Liquids in Synthesis, ed. P. Wasserscheid Pat., GmbH, WO2012041437, 2012.
and T. Welton, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 14 K. Kawata, H. Yoshizaki, H. Shinohara, P. Kirsch,
2nd edn, 2007; J. P. Hallett and T. Welton, Chem. Rev., 2011,
111, 3508–3576; T. Welton, Proc. R. Soc. London, Ser. A, 2015,
N. Ignatyev, W. R. Pitner and E. F. Aust, Merck Pat., GmbH,
WO2011085964, 2011.
471, 2015 0502; Electrochemical Aspects of Ionic Liquids, 15 L. A. Bischoff, M. Drisch, C. Kerpen, P. T. Hennig,
ed. H. Ohno, John Wiley & Sons, Inc., Hoboken, New Jersey,
USA, 2nd edn, 2011; M. Armand, F. Endres, D. R. MacFarlane,
H. Ohno and B. Scrosati, Nat. Mater., 2009, 8, 621–629;
J. Landmann, J. A. P. Sprenger, R. Bertermann, M. Gru¨ne,
Q. Yuan, J. Warneke, X.-B. Wang, N. V. Ignat’ev and
M. Finze, Chem. – Eur. J., 2019, 25, 3560–3574.
M. Kar, N. V. Plechkova, K. R. Seddon, J. M. Pringle and 16 J. A. P. Sprenger, J. Landmann, M. Drisch, N. Ignat’ev and
D. R. MacFarlane, Aust. J. Chem., 2019, 72, 3–10; R. D. Rogers
and K. R. Seddon, Science, 2003, 792, 792–793.
3 Z. Huang, S. Wang, R. D. Dewhurst, N. V. Ignat’ev, M. Finze
and H. Braunschweig, Angew. Chem., Int. Ed., 2020, 59,
8800–8816.
M. Finze, Inorg. Chem., 2015, 54, 3403–3412.
17 M. Drisch, L. A. Bischoff, J. A. P. Sprenger, P. T. Hennig,
R. Wirthensohn, S. Z. Konieczka, M. Hailmann,
N. V. Ignat’ev and M. Finze, Chem. – Eur. J., 2020, 26,
12794–12808.
4 M. G. Freire, C. M. S. S. Neves, I. M. Marrucho, 18 L. A. Bischoff, J. A. P. Sprenger, P. T. Hennig, N. V. Ignat’ev
J. A. P. Coutinho and A. M. Fernandes, J. Phys. Chem. A, and M. Finze, Z. Anorg. Allg. Chem., 2018, 644, 1285–1292.
2010, 114, 3744–3749; Z. Xue, in Encyclopedia of Ionic 19 N. Ignatyev, M. Schulte, J. Sprenger, M. Finze and W. Frank,
Liquids, ed. S. Zhang, Springer Nature Singapore Pte Ltd.,
2019, DOI: 10.1007/1978-1981-1010-6739-1006_1088-1001.
5 N. V. Ignat’ev, M. Finze, J. A. P. Sprenger, C. Kerpen,
E. Bernhardt and H. Willner, J. Fluorine Chem., 2015, 177,
46–54.
Merck Pat., GmbH, WO2011085966, 2011.
20 J. Landmann, J. A. P. Sprenger, P. T. Hennig, R. Bertermann,
M. Gru¨ne, F. Wu¨rthner, N. V. Ignat’ev and M. Finze, Chem. –
Eur. J., 2018, 24, 608–623.
21 K. Kawata, H. Yoshizaki, H. Shinohara, P. Kirsch,
N. Ignatyev, M. Schulte, J. Sprenger, M. Finze and
W. Frank, Merck Pat., GmbH, WO2011085965, 2011.
6 E. Bernhardt, G. Henkel and H. Willner, Z. Anorg. Allg.
Chem., 2000, 626, 560–568.
7 D. J. Williams, B. Pleune, J. Kouvetakis, M. D. Williams and 22 J. A. P. Sprenger, C. Kerpen, N. Ignat’ev and M. Finze,
R. A. Andersen, J. Am. Chem. Soc., 2000, 122, 7735–7741.
8 E. Bernhardt, M. Finze and H. Willner, Z. Anorg. Allg. Chem.,
2003, 629, 1229–1234.
J. Fluorine Chem., 2018, 206, 54–60; J. A. P. Sprenger,
M. Finze and N. Ignatyev, Merck Pat. GmbH,
WO2016074756, 2016.
9 U. Welz-Biermann, N. Ignatyev, E. Bernhardt, M. Finze and 23 J. A. P. Sprenger, M. Finze and N. Ignatiev, Julius-Maximilians-
¨
¨
H. Willner, Merck Pat., GmbH, WO2004072089, 2004.
10 N. V. Ignat’ev and M. Finze, Eur. J. Inorg. Chem., 2019,
3539–3560.
11 1. J. Zhang, R. E. Corman, J. K. Schuh, R. H. Ewoldt,
I. A. Shkrob and L. Zhang, J. Phys. Chem. C, 2018, 122,
8159–8172; A. Garsuch, D. M. Badine, K. Leitner,
L. H. S. Gasparotto, N. Borisenko, F. Endres, M. Vracar,
J. Janek and R. Oesten, Z. Phys. Chem., 2011, 226, 107–119;
Z. Liu, J. Chai, G. Xu, Q. Wang and G. Cui, Coord. Chem.
Rev., 2015, 292, 56–73; T. Romann, E. Anderson, P. Pikma,
Universitat Wurzburg, Merck Pat., GmbH, DE102015016400,
2017.
24 M. Berkei, E. Bernhardt, M. Schu¨rmann, M. Mehring and
H. Willner, Z. Anorg. Allg. Chem., 2002, 628, 1734–1740;
E. Bernhardt and H. Willner, Z. Anorg. Allg. Chem., 2009,
¨
635, 2511–2514; C. Nitschke and M. Kockerling, Inorg.
Chem., 2011, 50, 4313–4321; G. Kopplin, A. Bernsdorf and
M. Kockerling, Eur. J. Inorg. Chem., 2014, 319–325; F. Falk,
L. Herkert, L. Hackbarth, K. Mu¨ller-Buschbaum, M. Finze
¨
¨
and M. Kockerling, Z. Anorg. Allg. Chem., 2017, 643,
¨
H. Tamme, P. Moller and E. Lust, Electrochem. Commun.,
625–630; T. Ribbeck, S. H. Zottnick, C. Kerpen,
J. Landmann, N. V. Ignat’ev, K. Mu¨ller-Buschbaum and
M. Finze, Inorg. Chem., 2017, 56, 2278–2286.
2017, 74, 38–41; L. Yu and G. Z. Chen, Faraday Discuss.,
2016, 190, 231–240; A. Eilmes and P. Kubisiak, J. Phys.
Chem. B, 2015, 119, 11708–11720; H. Masuda, S. Mizutani, 25 T. Ku¨ppers, E. Bernhardt, H. Willner, H. W. Rohm and
¨
Y. Kawasoe, Y. Katsumata, M. Wilka and M. Friedrich, M. Kockerling, Inorg. Chem., 2005, 44, 1015–1022.
Lithium Energy and Power GmbH & Co. KG, EP3166169, 26 T. Ribbeck, C. Kerpen, C. Schmidle, F. Keppner, J. A. P. Sprenger,
2017; A. Kovacs, T. Alasaarela, D. Brown, D. Ruiz-Martinez,
M. Arrowsmith, H. Braunschweig, N. V. Ignat’ev and M. Finze,
´
J. M. Orts-Mateo and R. Gomez-Torregrosa, Broadbit Bat-
Inorg. Chem., 2019, 58, 16689–16702.
teries OY, WO2017055678, 2017; T. Hiasa, T. Odani and 27 M. Finze, E. Bernhardt, M. Berkei, H. Willner, J. Hung and
K.
Takeshi,
Tsubasa
Patent
Professional
Corp.,
R. M. Waymouth, Organometallics, 2005, 24, 5103–5109.
28 T. Ku¨ppers, E. Bernhardt, C. W. Lehmann and H. Willner,
Z. Anorg. Allg. Chem., 2007, 633, 1666–1672; C. Kerpen,
WO2018092468, 2018.
¨
12 H. Kurig, M. Vestli, A. Janes and E. Lust, Electrochem. Solid-State
Lett., 2011, 14, A120–A122; M. Sato and T. Isomura, Tokuyama
Corp., JP2018162169, 2018; N. Nagakura and M. Satou,
Tokuyama Corp., WO2017141806, 2017; N. Nagakura and
S. Yamaguchi, Tokuyama Corp., JP2018115122, 2018.
¨
J. A. P. Sprenger, L. Herkert, M. Schafer, L. A. Bischoff,
P. Zeides, M. Gru¨ne, R. Bertermann, F. A. Brede, K. Mu¨ller-
Buschbaum, N. V. Ignat’ev and M. Finze, Angew. Chem., Int.
Ed., 2017, 56, 2800–2804.
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2020

View Article Online
NJC
Paper
29 E. Bernhardt, G. Henkel, H. Willner, G. Pawelke and
F. Malberg, T. Welton and B. Kirchner, Phys. Chem. Chem. Phys.,
2014, 16, 16880–16890.
H. Bu¨rger, Chem.
–
Eur. J., 2001, 7, 4696–4705;
E. Bernhardt, M. Finze and H. Willner, Inorg. Chem., 2011, 39 R. K. Harris, E. D. Becker, S. M. Cabral de Menezes, R. Goodfellow
50, 10268–10273; M. Schmidt, A. Ku¨hner, H. Willner and
E. Bernhardt, Merck Pat. GmbH, EP1205480(A2), 2002.
30 E. Bernhardt, D. J. Brauer, M. Finze and H. Willner, Angew.
Chem., Int. Ed., 2006, 45, 6383–6386.
and P. Granger, Pure Appl. Chem., 2001, 73, 1795–1818.
40 G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb,
A. Nudelman, B. M. Stoltz, J. E. Bercaw and K. I. Goldberg,
Organometallics, 2010, 29, 2176–2179.
˜
´
31 M. Finze, E. Bernhardt, H. Willner and C. W. Lehmann, 41 A. G. Campana, N. Fuentes, E. Gomez-Bengoa, C. Mateo,
Angew. Chem., Int. Ed., 2004, 43, 4160–4163; M. Finze,
E. Bernhardt, H. Willner and C. W. Lehmann, J. Am. Chem.
Soc., 2005, 127, 10712–10722.
J. E. Oltra, A. M. Echavarren and J. M. Cuerva, J. Org. Chem.,
2007, 72, 8127–8130.
42 J. H. Golden, C. Schreier, B. Singaram and S. M. Williamson,
Inorg. Chem., 1992, 31, 1533–1535.
32 E. Bernhardt, V. Bernhardt-Pitchougina, H. Willner and
¨
¨
N. V. Ignatiev, Angew. Chem., Int. Ed., 2011, 50, 12085–12088; 43 R. Koster, Hoeben-Weyl, Organische Derivate der Borsauren,
J. Landmann, J. A. P. Sprenger, R. Bertermann, N. Ignat’ev, 1963, VI 2, 177–284.
V. Bernhardt-Pitchougina, E. Bernhardt, H. Willner and 44 G. M. Sheldrick, Acta Crystallogr., 2008, A64, 112–122.
M. Finze, Chem. Commun., 2015, 51, 4989–4992; 45 G. M. Sheldrick, SHELXS-97, Program for Crystal Structure
¨
¨
J. Landmann, F. Keppner, D. B. Hofmann, J. A. P. Sprenger,
Solution, Universitat Gottingen, 1997.
¨
M. Haring, S. H. Zottnick, K. Mu¨ller-Buschbaum, N. V. Ignat’ev 46 G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
¨ ¨
Refinement, Universitat Gottingen, 1997.
and M. Finze, Angew. Chem., Int. Ed., 2017, 56, 2795–2799;
J. Landmann, P. T. Hennig, N. V. Ignat’ev and M. Finze, Chem. 47 C. B. Hu¨bschle, G. M. Sheldrick and B. Dittrich, J. Appl.
Sci., 2017, 8, 5962–5968; J. Landmann, J. A. P. Sprenger, Crystallogr., 2011, 44, 1281–1284.
M. Hailmann, V. Bernhardt-Pitchougina, H. Willner, 48 K. Brandenburg, Diamond 4.6.3, Crystal Impact GbR, Bonn,
N. Ignat’ev, E. Bernhardt and M. Finze, Angew. Chem., Int.
Ed., 2015, 54, 11259–11264.
33 A. Terheiden, E. Bernhardt, H. Willner and F. Aubke, Angew.
Germany, 1997–2020.
49 W. Kohn and L. J. Sham, Phys. Rev. A: At., Mol., Opt. Phys.,
1965, 140, 1133–1138.
Chem., Int. Ed., 2002, 41, 799–801; M. Finze, E. Bernhardt, 50 A. D. Becke, Phys. Rev. A: At., Mol., Opt. Phys., 1988, 38,
A. Terheiden, M. Berkei, H. Willner, D. Christen,
H. Oberhammer and F. Aubke, J. Am. Chem. Soc., 2002,
124, 15385–15398.
3098–3100; A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652;
C. Lee, W. Yang and R. G. Parr, Phys. Rev. B: Condens. Matter
Mater. Phys., 1988, 37, 785–789.
¨
34 W. Wenger, C. Zur Taschler and A. G. Lonza, 51 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
WO2010086131, 2010.
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato,
A. V. Marenich, J. Bloino, B. G. Blanesko, R. Gomperts,
B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov,
J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini,
F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson,
D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng,
W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, K. Throssell, J. J. A. Montgomery,
J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd,
E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith,
R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell,
J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam,
M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin,
K. Morokuma, O. Farkas, J. B. Foresman and D. J. Fox, Gaussian
16, Revision A.03, Gaussian, Inc., Wallingford CT, USA, 2016.
35 N. Ignatyev, M. Schulte, K. Kawata, J. Sprenger, M. Finze and
W. Frank, Merck Pat. GmbH, WO2012041434, 2012.
36 P. Barthen, W. Frank and N. Ignatiev, Ionics, 2015, 21,
149–159.
37 J. A. P. Sprenger, M. Finze and N. Ignatyev, Merck Pat. GmbH,
WO2015185178, 2015.
38 H. Tokuda, K. Hayamizu, K. Ishii, M. A. B. H. Susan and
H. Watanabe, J. Phys. Chem. B, 2004, 108, 16593–16600;
H. Tokuda, K. Hayamizu, K. Ishii, M. A. B. H. Susan and
H. Watanabe, J. Phys. Chem. B, 2005, 109, 6103–6110;
H. Tokuda, K. Ishii, M. A. B. H. Susan, S. Tsuzuki,
K. Hayamizu and H. Watanabe, J. Phys. Chem. B, 2006,
110, 2833–2839; K. Ueno, H. Tokuda and M. Watanabe,
Phys. Chem. Chem. Phys., 2010, 12, 1649–1658; D. R. MacFarlane,
M. Forsyth, E. I. Izgorodina, A. P. Abbott, G. Annat and K. Fraser,
´
Phys. Chem. Chem. Phys., 2009, 11, 4962–4967; O. Holloczki,
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2020