Fluorine-containing ionic liquids from N-alkylpyrrolidine and N-methylpiperidine and fluorinated acetylacetones: Low melting points and low viscosities

Article abstract of DOI:10.1002/ejic.200800448

A family of new fluorine-containing ionic liquids (3-14) was synthesized in high yield by the reaction of N-alkylpyrrolidine, N-methylpiperidine and fluorinated 1,3-diketones: 1,1,1,5,5,5-hexafluoroacetylacetone, 1,1,1-trifluoro-2,4-pentanedione and 4,4,4-trifluoro-1-phenyl-1,3-butanedione. Their properties, such as the phase-transition temperature, density, and viscosity, were determined. Most of them show relatively low melting points and low viscosities. The influence of fluorinated 1,3-diketonate anions and the structural variation in cyclic amine cations on the above physicochemical properties was examined. X-ray single-crystal diffraction analysis of compound 7 confirms the proton transfer from 4,4,4-trifluoro-1-phenyl-1,3-butanedione to N-butylpyrrolidine. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800448

FULL PAPER
DOI: 10.1002/ejic.200800448
Fluorine-Containing Ionic Liquids from N-Alkylpyrrolidine and
N-Methylpiperidine and Fluorinated Acetylacetones: Low Melting Points and
Low Viscosities
Xiaoju Li,[a] Zhuo Zeng,[a] Sonali Garg,[a] Brendan Twamley,[a] and Jean’ne M. Shreeve*[a]
Keywords: Ionic liquids / Fluorine / Cyclic amines / Low melting point / Low viscosity
A family of new fluorine-containing ionic liquids (3–14) was
synthesized in high yield by the reaction of N-alkylpyrrol-
idine, N-methylpiperidine and fluorinated 1,3-diketones:
1,1,1,5,5,5-hexafluoroacetylacetone, 1,1,1-trifluoro-2,4-pen-
ence of fluorinated 1,3-diketonate anions and the structural
variation in cyclic amine cations on the above physicochemi-
cal properties was examined. X-ray single-crystal diffraction
analysis of compound 7 confirms the proton transfer from
tanedione and 4,4,4-trifluoro-1-phenyl-1,3-butanedione. 4,4,4-trifluoro-1-phenyl-1,3-butanedione to N-butylpyrrol-
Their properties, such as the phase-transition temperature,
density, and viscosity, were determined. Most of them show
relatively low melting points and low viscosities. The influ-
idine.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
trialkylsulfonium cations[15] also led to numerous ionic li-
quids, which exhibit not only low melting points and low
viscosity but also other interesting physical properties ow-
ing to the presence of fluorine.
Introduction
Since the physical properties of ethylammonium nitrate
[(EtNH3)NO3] (m.p. 13–14 °C)[1] were reported, consider-
able effort has been devoted to the study of ionic liquids[2–3]
as well as to their green applications as solvents and ad-
vanced materials, and in separations.[4–7] Their unique
physicochemical properties, such as nonvolatility, non-
flammability, tunable polarity, water miscibility and wide
liquid range, can be easily modified to optimize the materi-
als for specific applications through variation and modifica-
tion of their cationic and/or anionic components.[8] How-
ever, their relatively high viscosity, as compared with com-
mon organic solvents, is one of the major barriers re-
stricting their practical applications, because high viscosity
usually results in low diffusion coefficients, slow mass trans-
fer, and low electric conductivity. Therefore, much interest
has been focused on the syntheses of ionic liquids with low
viscosity and low melting point or on methods to reduce
their viscosity.[9]
The combination of the 1-ethyl-3-methylimidazolium
(EMIM) cation and fluorine-containing anions produced
many promising ionic liquids possessing low melting points
and viscosities.[10–11] For example, the viscosities of [EM-
IM][F(HF)2.3] and [EMIM][TSAC] [TSAC = 2,2,2-tri-
fluoro-N-(trifluoromethylsulfonyl)acetamide] are 4.85 cP[12]
and 25 cP[13]at 25 °C, respectively. The combination of flu-
orine-containing anions with quaternary ammonium[14] and
Fluorinated 1,3-diketonates are promising anions in
ionic liquids,[3b,16,17] in which the strong electron-with-
drawing effect of the fluorinated moiety enhances the acid-
ity of the acetylacetone proton and the delocalization of the
negative charge which favors proton transfer to a Lewis
base with concomitant stabilization of the conjugate base.
1,3-Diketones exist as enol/keto tautomers with the equilib-
rium skewed toward the enolic form when the substituents
on the carbonyl carbon atoms are electron-withdrawing.
Thus, fluorinated 1,3-diketones can act as Brønsted acids
which offer an excellent choice for the anion of ionic liquids
leading to low viscosities.[16,18] In fact, the viscosity of trioc-
tylammonium hexafluoro-1,3-diketonate at 3.44 cP (25 °C)
is among the lowest reported for any ionic liquid.[16] By
taking advantage of 1,3-diketones as proton-transfer rea-
gents to form quaternary salts with a variety of amines, it
is possible to produce salts where an important feature of
the anion, perfluoroalkyl 1,3-diketonate, is introduced. As
is the case with the bis(trifluoromethanesulfonyl)amide
anion, there is considerable delocalization of the electron
cloud over the molecular backbone which may aid in reduc-
ing the degree of hydrogen bonding in these systems and
thus have impact on melting points and other physical
properties.[16,18] As a continuation of our research work in
fluorine-containing ionic liquids, we were interested in the
N-alkylpyrrolidines, which have generated some interesting
slightly viscous and highly conductive ionic liquids owing
to the existence of the related N-heterocyclic pyrrolidinium
[a] Department of Chemistry, University of Idaho,
Moscow, ID 83843-2343, USA
Fax: +1-208-885-9146
E-mail: jshreeve@uidaho.edu
Eur. J. Inorg. Chem. 2008, 3353–3358
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3353

X. Li, Z. Zeng, S. Garg, B. Twamley, J. M. Shreeve
FULL PAPER
core.[19] We now report the preparation and characteriza-
Summarized in Table 1 are the physical properties (melt-
tion of a range of new fluorine-containing ionic liquids ing point, glass transition temperature, viscosity and den-
from fluorinated 1,3-diketones and N-alkylpyrrolidines sity) of all the newly synthesized ionic liquids. Melting
with methyl, butyl, hexyl, and 4,4,4-trifluorobutyl substitu- points or glass transition temperatures of 3–14 were deter-
ents. In order to compare their physicochemical properties, mined by differential scanning calorimetry (DSC). The
ionic liquids formed from fluorinated 1,3-diketones and N- compounds 5, 6, 8, 9, and 14 are room-temperature ionic
methylpiperidine were also synthesized.
liquids with melting points below 0 °C, whereas 3, 4, 7, and
10–13 can also be classified as falling into the ionic liquid
class, because their melting points are below 100 °C. It
should be pointed out that, although the phase-transition
temperatures of the N-methylpyrrolidinium-based ionic li-
quids 3 (44 °C), 4 (36 °C) and 5 (–42 °C) are lower than
those of the analogous N-methylpiperidinium-based salts
12 (95 °C), 13 (59 °C) and 14 (–31 °C), the decrease in both
series is similar. The correlation between phase-transition
temperatures and alkyl substituents of cations is also clearly
observed in Table 1; e.g., with a constant fluorine-contain-
ing anion, an increase of length and flexibility of alkyl
groups on the cations resulted in lower phase-transition
temperatures in keeping with the alkyl-substituted imid-
azolium-based ionic liquids. For the 2a-based N-alkylpyrro-
lidinium ionic liquids, 3, 6 and 8, variation of N-substitu-
ents from methyl to butyl to hexyl, the melting points de-
Results and Discussion
Synthesis and Properties
Cations and/or anions with varying substituents have an
important effect on the chemical and physical properties of
ionic liquids; therefore, we chose the N-alkylpyrrolidines
1a–1d as proton acceptors and the three fluorinated 1,3-
diketones 1,1,1,5,5,5-hexafluoroacetylacetone (2a), 1,1,1-
trifluoro-2,4-pentanedione (2b), and 4,4,4-trifluoro-1-
phenyl-1,3-butanedione (2c) as proton donors. The syn-
thetic pathway leading to 3–11 is depicted in Scheme 1. The
reactants 1b, 1c and 1d were easily prepared by the alky-
lation reaction of pyrrolidine with 1-iodobutane, 1-bromo-
hexane and 1,1,1-trifluoro-4-iodobutane, respectively, in the
presence of dmf and aqueous NaOH solution. Subsequent
reactions with 2a–2c in acetonitrile gave rise to the target
ionic liquids. According to similar procedures, the N-meth-
ylpiperidinium-based liquids 12–14 were synthesized by the
reactions of N-methylpiperidine (1e) and 2a–2c.
Table 1. Physicochemical properties of ionic liquids.
[a]
Compound Tertiary Brønsted Tm
Tg[a]
Viscosity [cP][b]
Density[c]
amine acid (HY) [°C] [°C] 25 °C 50 °C 60 °C [g/cm3]
3
4
5
6
7
1a
1a
1a
1b
1b
1c
1c
1d
1d
2a
2b
2c
2a
2c
2a
2c
2a
2c
2a
2b
2c
44
36
1.45
1.31
1.22
1.25
1.08
1.21
1.16
1.48
1.35
1.44
1.23
1.21
All of the newly synthesized ionic liquids are miscible
–42 592.0 66.8 37.4
11.8 7.1 4.2
–5
67
with organic solvents ranging in polarity from hexane to
methanol. They were characterized by H and 19F NMR
1
8
9
–16 26.8
–53 346.3 52.7 29.8
spectroscopy and elemental analyses. For the ionic liquids
1
with the same anion, the H NMR spectroscopic data are
10
11
12
13
14
30
102
95
routine with minimal or no change in the chemical shifts
of the cationic pyrrolidine and piperidine parent rings. The
chemical shifts of the protons of –CH2–N– in both the par-
ent rings and the substituents were downfield compared to
those of their corresponding precursors 1a–1d; however, the
trend decreases when changing the anion from 1,1,1,5,5,5-
hexafluoroacetylacetone (2a) to 1,1,1-trifluoro-2,4-pentane-
1e[d]
1e[d]
1e[d]
59
–31
149.8 68.3
[a] Tm (melting point) and Tg (glass transformation temperature)
determined by DSC. [b] Viscosity for room-temperature ionic li-
quids, determined by MINIVIS II. [c] Density determined by
Micromeritics Accupyc 1330 gas pycnometer. [d] 1e, N-methyl-
dione (2b) to 4,4,4-trifluoro-1-phenyl-1,3-butanedione (2c). piperidine.
Scheme 1.
3354
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Eur. J. Inorg. Chem. 2008, 3353–3358

Fluorine-Containing Ionic Liquids: Low Melting Points and Low Viscosities
crease from 44 (3) to –5 (6) to –16 °C (8). This suggests is also lower than that of the piperidinium-based analogue
decreased packing efficiency in the crystal lattice as the 14 (149.8 cP at 50 °C, 68.3 cP at 60 °C).
alkyl groups are elongated. In the case of trifluorobutyl-
substituted liquids higher melting points are observed for
10 (30 °C) and 11 (102 °C) than those of butyl-substituted
6 (–5 °C) and 7 (67 °C).
Molecular Structure
Compound 7 is solid at room temperature. Crystals suit-
able for X-ray single crystal diffraction were obtained by
slow concentration of a hexane solution. The crystal data
and structural information are summarized in Table 2. The
asymmetric unit of 7 consists of one 1-butylpyrrolidinium
cation and one 4,4,4-trifluoro-1-phenyl-1,3-butanedionate
anion. One hydrogen atom of 4,4,4-trifluoro-1-phenyl-1,3-
butanedione was transferred to N(5) of 1-butyl-pyrrolidine
forming a six-membered hydrogen-bonded ring, which con-
firms that the fluorinated diketone can serve as a Brønsted
acid when reacting with cyclic tertiary amines. The hydro-
gen-bonding distances of N(5)–H(5)···O(2) and N(5)–H(5)···
O(1) are 2.759(1) Å and 2.767(1) Å, respectively (Figure 1).
The densities of 3–14 fall in the range from 1.08 to
1.48 gcm–3 (Table 1). Changing of the anion precursors
from 1,1,1,5,5,5-hexafluoroacetylacetone to 1,1,1-trifluoro-
2,4-pentanedione to 4,4,4-trifluoro-1-phenyl-1,3-butane-
dione results in the decrease of density in both pyrrolidin-
ium-based and piperidinium-based ionic liquids. Not sur-
prisingly, the densities of ionic liquids bearing fluoroalkyl
chains (10 and 11) are higher than those of their congeners
with non-fluoroalkyl chains (6 and 7). Thus, the presence
of alkyl and fluoroalkyl substituents has an important im-
pact on the physicochemical properties of these materials.
As expected, the viscosities of the room-temperature
ionic liquids 5, 6, 9 and 14 remarkably decrease with in-
creasing temperature. Ionic liquid 6, 1-butylpyrrolidinium
1,1,1,5,5,5-hexafluoroacetylacetonate has an interestingly
low viscosity (11.8 cP at 25 °C), which is considerably lower
than that of the N-methoxymethyl-N-methylpyrrolidinium
trifluoro(perfluoroethyl)borate (37 cP) reported earlier.[19]
Of the quaternary ammonium cations, N-alkyl-N-methyl-
pyrrolidinium salts have been shown to produce slightly vis-
cous ionic liquids due to the quasi-flat shape of the pyrrol-
idinium core.[20] This fact must arise because of the pro-
clivity of the 1,3-diketonate to delocalize the electron cloud
along the anion backbone. The viscosity of the pyrrolidin-
ium-based ionic liquid 5 (66.9 cP at 50 °C, 37.4 cP at 60 °C)
Table 2. Crystal data and structure refinement for compound 7.
Figure 1. Asymmetric unit of 7 with the thermal ellipsoids at a 30%
probability level; hydrogen bonding is indicated by dashed lines.
7
Empirical formula
Formula mass
Crystal size [mm]
Crystal system
Space group
a [Å]
C18H24F3NO2
343.38
0.40ϫ0.32ϫ0.21
monoclinic
P21/n
10.7435(7)
16.2935(10)
11.1612(7)
112.808(1)
1801.0(2)
4
1.266
0.102
90(2)
0.71073
26763
Conclusions
A series of new N-alkylpyrrolidinium-based and piperid-
inium-based ionic liquids with fluorine-containing 1,3-dike-
tonates as anions has been synthesized and characterized
successfully. The relationship between their structures,
phase-transition temperatures, densities and viscosities was
determined. Most of them have low melting points and low
viscosities. Fluorinated 1,3-diketonate anions are excellent
choices for the formation of slightly viscous ionic liquids
and provide a promising route for the design and synthesis
of new types of ionic liquids.
b [Å]
c [Å]
β [°]
V [Å3]
Z
Dcalcd. [gcm–3]
µ [mm–1]
T [K]
λ(Mo-Kα) [Å]
Reflections collected
Unique reflections
Rint
4132
0.0332
Parameters
221
1.035
0.0418
0.1051
0.0524
0.1125
0.334/–0.175
S on F2
R1 [IϾ2σ(I)][a]
wR2 [IϾ2σ(I)][b]
R1 (all data)[a]
wR2 (all data)[b]
∆ρmin/max [e/Å3]
Experimental Section
General Methods: All the reagents were available commercially and
1
were used as purchased. H and 19F NMR spectra were recorded
in CDCl3 with a 300 MHz spectrometer (Bruker AMX 300) op-
erating at 300 and 282 MHz, respectively by using CDCl3 as lock-
[a] R = ∑||Fo| – |Fc||/∑|Fo|. [b] wR = [∑w(Fo – Fc ) /∑w(Fo2)2]1/2
.
2
2 2
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3355

X. Li, Z. Zeng, S. Garg, B. Twamley, J. M. Shreeve
FULL PAPER
ing solvent. Chemical shifts are reported in ppm relative to CFCl3
(15 mL) were placed in a round flask and stirred at 25 °C for 24 h.
Then the solvent was removed, the residue was washed three times
with hexane (3 ϫ 5 mL), and dried under vacuum to give the pure
products 3–14.
1
for 19F and TMS for H NMR spectra. IR spectra were recorded
using KBr plates for neat liquids and KBr pellets for solids with
a BIORAD model 3000 FTS spectrometer. Differential scanning
calorimetry (DSC) measurements were performed by using a calo-
rimeter equipped with an Autocool accessory and calibrated with
indium. The following procedure was used in experiments for each
sample: cooling from 40 to –80 °C and heating to 400 °C at 10 °C/
min. The transition temperature, Tm, was taken at the onset of the
event. Density was measured at room temperature using a Micro-
meritics Accupyc 1330 gas pycnometer. Viscosity was obtained
with a MINIVIS II (Grabner Instruments). Elemental analyses
were determined with an Exeter CE-440 Elemental Analyzer.
1-Methylpyrrolidinium 1,1,1,5,5,5-Hexafluoroacetylacetonate (3):
White solid (0.28 g), yield 95%. IR: ν = 3048 (br.), 2835 (br.), 1668
˜
(vs), 1554 (vs), 1460 (s), 1254 (vs), 1192 (s), 1130 (s), 1009 (s), 942
(ms), 902 (w), 858 (w), 788 (s), 755 (m), 659 (ms), 572 (ms), 524
1
(w) cm–1. H NMR: δ = 11.37 (b, 1 H), 5.75 (s, 1 H), 3.93 (s, 2 H),
2.92 (s, 3 H), 2.79 (s, 2 H), 2.10 (m, 4 H) ppm. 19F NMR: δ = –76.9
(s, 6 F) ppm. C10H13F6NO2 (293.21): calcd. C 40.96, H 4.47, N
4.78; found C 40.74, H 4.42, N 4.71.
1-Methylpyrrolidinium 1,1,1-Trifluoro-2,4-pentanedionate (4): Semi-
X-ray Crystallography: Crystals of compound 7 were removed from
the flask, a suitable crystal was selected, attached to a glass fiber,
and data were collected at 90(2) K with a Bruker/Siemens SMART
APEX instrument (Mo-Kα radiation, λ = 0.71073 Å) equipped with
a Cryocool NeverIce low-temperature device. Data were measured
using ω-scans 0.3° per frame for 5 s, and a full sphere of data was
collected. A total of 2400 frames were collected with a final resolu-
tion of 0.77 Å. Cell parameters were retrieved by using SMART[21]
software and refined by using SAINTPlus[22] on all observed reflec-
tions. Data reduction and correction for Lp and decay were per-
formed by using the SAINTPlus software. Absorption corrections
were applied by using SADABS.[23] The structure was solved by
direct methods and refined by least-squares methods on F2 with
the SHELXTL program package.[24] The structure was solved in
the space group P21/n (# 14) by analysis of systematic absences. All
non-hydrogen atoms were refined anisotropically. Hydrogen atom
positions were refined by using a mixture of constrained and inde-
pendent [i.e. H(5)] parameters. No decomposition was observed
during data collection. Details of the data collection and refine-
ment are given in Table 2. CCDC-684761 for compound 7 contains
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
solid (0.22 g), yield 93%. IR: ν = 1643 (vs), 1460 (s), 1356 (s), 1273
˜
(vs), 1175 (m), 1124 (m), 999 (s), 932 (m), 878 (s), 837 (vs), 762 (s),
1
721 (s), 606 (w), 545 (vs), 449 (w) cm–1. H NMR: δ = 9.4 (br. s, 1
H), 5.53 (s, 1 H), 3.14 (t, J = 13.5 Hz, 4 H), 2.75 (s, 3 H), 1.93 (m, 7
H) ppm. 19F NMR: δ = –76.3 (s, 3 F) ppm. C10H16NO2F3 (239.23):
Elemental analysis was not possible because of the hygroscopic na-
ture of the salt.
1-Methylpyrrolidinium 4,4,4-Trifluoro-1-phenyl-1,3-butanedionate
(5): Yellow liquid (0.28 g); yield 93%. IR: ν = 2966 (br., s), 1970
˜
(w), 1681 (s), 1635 (vs), 1577 (m), 1522 (vs), 1274 (vs), 1176 (s),
1122 (s), 1072 (m), 935 (m), 758 (s), 709 (s), 626 (s), 569 (s), 407
1
(m) cm–1. H NMR: δ = 7.89 (d, J = 7.2 Hz, 2 H), 7.47–7.42 (m,
3 H), 6.33 (s, 1 H), 3.06–3.05 (m, 4 H), 2.73 (s, 3 H), 2.01–1.96 (m,
4 H) ppm. 19F NMR: δ = –76.2 (s, 3 F) ppm. C15H18F3NO2
(301.30): calcd. C 59.79, H 6.02, N 4.65; found C 58.92, H 5.81, N
4.34.
1-Butylpyrrolidinium 1,1,1,5,5,5-Hexafluoroacetylacetonate (6): Yel-
low liquid (0.30 g); yield 90%. IR: ν = 2968 (br., s), 2877 (s), 1668
˜
(vs), 1553 (vs), 1459 (s), 1386 (m), 1252 (vs), 1188 (s), 1079 (m),
941 (s), 906 (w), 825 (m), 787 (s), 748 (m), 659 (vs), 617 (w), 518
1
(vs), 504 (m) cm–1. H NMR: δ = 11.32 (br. s, 1 H), 5.74 (s, 1 H),
3.90 (s, 2 H), 3.10–3.04 (t, J = 18.0 Hz, 2 H), 2.75 (s, 2 H), 2.05
(m, 4 H), 1.67 (m, 2 H), 1.36 (m, 2 H), 0.92–0.88 (t, J = 15.0 Hz,
3 H) ppm. 19F NMR: δ = –76.2 (s, 3 F) ppm. C13H19F6NO2
(335.29): calcd. C 46.57, H 5.71, N 4.18; found C 45.68, H 5.62, N
4.33.
General Procedures for the Preparation of 1-Butyl-, 1-Hexyl-, and
1-(3,3,3-Trifluorobutyl)pyrrolidine (1b–1d): A mixture of pyrrolidine
(1.4 g, 20 mmol) and 35% aqueous NaOH (3.0 mL) in dmf (15 mL)
was stirred at 25 °C for 1 h. Then 1-iodobutane (4.8 g, 26 mmol)
for 1b, 1-bromohexane (4.3 g, 26 mmol) for 1c, and 1,1,1-trifluoro-
4-iodobutane for 1d (6.2 g, 26 mmol) was added slowly. The mix-
ture was stirred at 25 °C overnight. The resulting solution was
poured into H2O (15 mL), and extracted with ethyl acetate
(3ϫ10 mL). The combined organic layers were washed with H2O
(3ϫ10 mL), and dried with Na2SO4. After the solvents were re-
moved, the residue was purified by flash chromatography on silica
gel (70–230 mesh) to give 1b–1d.
1-Buthylpyrrolidinium
4,4,4-Trifluoro-1-phenyl-1,3-butanedionate
(7): White solid (0.32 g); yield 92%. IR: ν = 3049 (br., s), 2962 (s),
˜
1637 (vs), 1577 (m), 1509 (vs), 1354 (m), 1278 (s), 1238 (m), 1172
(s), 1126 (s), 1072 (m), 980 (w), 761 (vs), 854 (m), 713 (s), 624 (s),
1
579 (s), 519 (m), 478 (w) cm–1. H NMR: δ = 7.89 (d, J = 9.6 Hz,
2 H), 7.45 (m, 3 H), 6.43 (s, 3 H), 2.98 (s, 4 H), 2.81 (t, J = 58.5 Hz,
2 H), 1.94 (s, 4 H), 1.63 (m, 2 H), 1.35 (m, 2 H),092 (t, J = 14.7 Hz,
3 H) ppm. 19F NMR: δ = –76.1 (s, 3 F) ppm. C18H24F3NO2
(343.18): calcd. C 62.96, H 7.04, N 4.08; found C 62.58, H 7.16, N
4.15.
1-Butylpyrrolidine (1b): Yellow liquid (1.58 g), yield 62%. 1H
NMR: δ = 2.49 (m, 4 H), 2.43 (t, J = 10.7 Hz, 2 H), 1.76 (m, 4 H),
1.48 (m, 2 H), 1.33 (m, 2 H), 0.90 (t, J = 14.55 Hz, 3 H) ppm.
1-Hexylpyrrolidinium 1,1,1,5,5,5-Hexafluoroacetylacetonate (8):
Yellow liquid (0.33 g); yield 91%. IR: ν = 2936 (br., s), 2863 (bs),
˜
1-Hexylpyrrolidine (1c): Yellow liquid (2.14 g), yield 69%. 1H
NMR: δ = 2.48 (m, 4 H), 2.41 (t, J = 15.6 Hz, 2 H), 1.77 (m, 4 H),
1.34 (m, 8 H), 0.88 (t, J = 24.5 Hz, 3 H) ppm.
1668 (vs), 1553 (vs), 1459 (s), 1382 (m), 1251 (vs), 1188 (m), 1131
(m), 1080 (s), 941 (s), 788 (vs), 750 (s), 659 (vs), 574 (s), 524 (m)
1
cm–1. H NMR: δ = 5.73 (s, 1 H), 3.93 (s, 2 H), 3.11–3.06 (t, J =
1-(4,4,4-Trifluorobutyl)pyrrolidine (1d): Yellow liquid (2.83 g), yield
16.2 Hz, 2 H), 2.76 (s, 2 H), 2.06 (m, 4 H), 1.64 (m, 2 H), 1.26 (m,
6 H), 0.85 (t, J = 13.2 Hz, 3 H) ppm. 19F NMR: δ = –76.1 (s, 6 F)
ppm. C15H23F6NO2 (363.34): calcd. C 49.58, H 6.38, N 3.85; found
C 48.30, H 6.05, N 3.75.
1
78%. H NMR: δ = 2.48 (t, J = 11.9 Hz, 4 H), 2.16 (m, 2 H), 2.02
(m, 2 H), 1.76 (m, 4 H), 1.24 (t, J = 14.3 Hz, 2 H) ppm. 19F NMR:
δ = –66.9 (t, J = 23.1 Hz, 3 F) ppm.
General Procedure for the Preparation of 3–14: A mixture of N- 1-Hexylpyrrolidinium
4,4,4-Trifluoro-1-phenyl-1,3-butanedionate
alkylpyrrolidine (1.0 mmol) or N-methylpiperidinium (0.10 g,
(9): Yellow liquid (0.32 g); yield 86%. IR: ν = 3264 (br., s), 1963
˜
1.0 mmol), a fluorinated 1,3-diketone (1.0 mmol), and acetonitrile
(m), 1905 (m), 1818 (s), 1678 (m), 1634 (s), 1562 (s), 1273 (w), 1072
3356
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Eur. J. Inorg. Chem. 2008, 3353–3358

Fluorine-Containing Ionic Liquids: Low Melting Points and Low Viscosities
(s), 1020 (s), 935 (vs), 787 (s), 756 (vs), 705 (m), 629 (s), 569 (s)
1
cm–1. H NMR: δ = 7.87 (d, J = 9.6 Hz, 2 H), 7.46 (m, 3 H), 6.32 [1]
P. Walden, Bull. Acad. Imp. Sci. St.-Petersbourg 1914, 1800.
[2] a) T. Rüther, J. Huang, A. F. Hollenkamp, Chem. Commun.
2007, 5226–5228; b) T. Timofte, S. Pitula, A. Mudring, Inorg.
Chem. 2007, 46, 10938–10940; c) S. Z. E. Abedin, F. Enders,
Acc. Chem. Res. 2007, 40, 1106–1113; d) Y. R. Mirzaei, B.
Twamley, J. M. Shreeve, J. Org. Chem. 2002, 67, 9340–9345; e)
P. G. Jessop, D. J. Heldebrant, X. Li, C. A. Eckert, C. L. Liotta,
Nature 2005, 436, 1102–1102; f) H. Weingärtner, Angew. Chem.
Int. Ed. 2007, 46, 2–19.
[3] a) H. Xue, J. M. Shreeve, Eur. J. Inorg. Chem. 2005, 2573–2780;
b) H. Xue, R. Verma, J. M. Shreeve, J. Fluorine Chem. 2006,
127, 159–176.
[4] a) J. G. Huddleston, H. D. Willauer, R. P. Swatloski, A. E.
Visser, R. D. Rogers, Chem. Commun. 1998, 1765–1766; b)
R. E. Morris, Angew. Chem. Int. Ed. 2008, 47, 442–444; c) P. S.
Kulkarni, L. C. Branco, J. G. Crespo, C. A. M. Afonso, Chem.
Eur. J. 2007, 13, 8470–8477; d) H. Xue, B. Twamley, J. M.
Shreeve, Adv. Mater. 2005, 17, 2142–2146.
[5] M. A. B. H. Susan, A. Noda, S. Mitsushima, M. Watanabe,
Chem. Commun. 2003, 938–939.
[6] a) J. P. Belieres, D. Gervasio, C. A. Angell, Chem. Commun.
2006, 46, 4799–4801; b) T. Rüther, J. Huang, A. F. Hollenkamp,
Chem. Commun. 2007, 5226–5228.
[7] a) X. Han, D. W. Armstrong, Acc. Chem. Res. 2007, 40, 1079–
1086; b) C. Cadena, J. L. Anthony, J. K. Shah, T. I. Morrow,
J. F. Brennecke, E. J. Maginn, J. Am. Chem. Soc. 2004, 126,
5300–5308.
(s, 1 H), 3.89 (s, 2 H), 3.10 (t, J = 16.2 Hz, 2 H), 2.47 (s, 2 H), 1.99
(m, 4 H), 1.62 (m, 2 H), 1.28 (m, 6 H), 0.84 (t, J = 18.9 Hz) ppm.
19F NMR: δ = –76.2 (s, 3 F) ppm. C20H28F3NO2 (371.44): calcd.
C 64.67, H 7.60, N 3.77; found C 63.15, H 7.40, N 4.48.
1-Butyl-1-(4,4,4-trifluorobutyl)pyrrolidinium 1,1,1,5,5,5-Hexafluo-
roacetylacetonate (10): White solid (0.37 g); yield 95%. IR: ν =
˜
1669 (vs), 1549 (vs), 1456 (s), 1038 (m), 940 (ms), 838 (ms), 788 (s),
754 (s), 659 (vs), 574 (vs), 525 (m), 447 (m) cm–1. 1H NMR: δ =
11.34 (br. s, 1 H), 5.76 (s, 1 H), 3.94 (s, 2 H), 3.24 (t, J = 15.6 Hz,
2 H), 2.79 (s, 2 H), 2.12 (m, 8 H) ppm. 19F NMR: δ = –66.1 (t, J
= 21.2 Hz, 3 F), –77.0 (s, 3 F) ppm. C13H16F9NO2 (389.26): calcd.
C 40.11, H 4.14, N 3.60; found C 40.33, H 4.14, N 3.54.
1-Butyl-1-(4,4,4-trifluorobutyl)pyrrolidinium
4,4,4-Trifluoro-1-
phenyl-1,3-butanedionate (11): Colorless crystals (0.36 g); yield
92%. IR: ν = 3047 (br.), 1630 (br.), 1513 (s), 1280 (w), 1035 (s),
˜
978 (w), 850 (s), 800 (ms), 763 (vs), 713 (vs), 660 (ms), 569 (s), 524
(m), 465 (s) cm–1. 1H NMR: δ = 7.88 (d, J = 7.2 Hz, 2 H), 7.45
(m, 3 H), 6.41 (s, 1 H), 2.76 (m, 4 H), 2.18 (m, 6 H), 1.89 (m, 4 H)
ppm. 19F NMR: δ = –76.3 (s, 3 F), –66.2 (t, J = 22.0 Hz, 3 F) ppm.
C18H21F6NO2 (397.36): calcd. C 54.41, H 5.33, N 3.52; found C
53.91, H 5.26, N 3.90.
1-Methylpiperidinium 1,1,1,5,5,5-Hexafluoroacetylacetonate (12):
[8] a) Y. Xie, Z. Zhang, T. Jiang, J. He, B. Han, T. Wu, K. King,
Angew. Chem. Int. Ed. 2007, 46, 7255–7258; b) S. Luo, J. Li,
L. Zhang, H. Xu, J. P. Cheng, Chem. Eur. J. 2008, 14, 1273–
1281; c) Z. Fei, T. J. Geldbach, D. Zhao, P. J. Dyson, Chem.
Eur. J. 2006, 12, 2122–2130; d) P. Wassercheid, B. Drießen-
Hölscher, R. van Hal, H. C. Setffens, J. Zimmermann, Chem.
Commun. 2003, 2038–2039; e) G. Tao, L. He, W. Liu, L. Xu,
W. Xiong, T. Wang, Y. Kou, Green Chem. 2006, 8, 639–646.
White solid (0.29 g); yield 96%. IR: ν = 3024 (br., s), 2966 (s), 1666
˜
(vs), 1550 (vs), 1493 (m), 1458 (s), 1188 (s), 1130 (m), 997 (s), 974
(m), 860 (s), 788 (vs), 750 (s), 660 (vs), 572 (s), 524 (m), 461 (w),
1
414 (w) cm–1. H NMR: δ = 5.74 (s, 1 H), 3.66 (d, J = 11.4 Hz, 2
H), 2.77 (s, 3 H), 2.58 (s, 2 H), 1.89 (m, 2 H) ppm. 19F NMR: δ =
–76.9 (s, 6 F) ppm. 13C NMR: δ = 85.9, 55.6, 44.3, 22.8, 22.6, 21.5,
14.0 ppm. C11H15F6NO2 (307.23): calcd. C 43.00, H 4.92, N 4.56;
found C 42.80, H 4.87, N 4.55.
[9]
a) Y. Yoshida, K. Muroi, A. Otsuka, G. Saito, M. Takahashi,
T. Toko, Inorg. Chem. 2004, 43, 1458–1462; b) D. R. MacFar-
lane, J. Golding, S. Forsyth, M. Forsyth, G. B. Deacon, Chem.
Commun. 2001, 1430–1431.
1-Methylpiperidinium
1,1,1-Trifluoro-2,4-pentanedionate
(13):
White solid (0.23 g); yield 92%. IR: ν = 1688 (s), 1354 (s), 994 (s),
˜
983 (s), 938 (m), 836 (vs), 720 (vs), 605 (s), 563 (m), 547 (s), 515
(s), 461 (s), 441 (m), 413 (m) cm–1. 1H NMR: δ = 5.69 (s, 1 H),
2.94–2.87 (m, 4 H), 2.64 (s, 3 H), 1.97 (s, 3 H), 1.76 (m, J = 23.1 Hz,
4 H), 1.54–1.50 (m, J = 11.7 Hz, 2 H) ppm. 19F NMR: δ = –76.1
(s, 3 F) ppm. C11H18F3NO2 (253.26): calcd. C 52.17, H 7.16, N
5.53; found C 52.09, H 7.18, N 5.60.
[10]
a) A. A. Fannin, D. A. Floreali, L. A. King, J. S. Landers, B. J.
Piersma, D. J. Stech, R. L. Vaughan, J. S. Wilkes, J. L. Wil-
liams, J. Phys. Chem. 1984, 88, 2614–2621; b) P. Wang, S. M.
Zakeeruddin, R. Humprey-Bake, M. Grätzel, Chem. Mater.
2004, 16, 2694–2696; c) E. D. Bates, R. D. Mayton, I. Ntai,
J. H. Davis Jr, J. Am. Chem. Soc. 2002, 124, 926–927.
G. Law, P. R. Watson, Langmuir 2001, 17, 6138–6141.
R. Hagiwara, T. Hirashige, T. Tsuda, Y. Ito, J. Electrochem.
Soc. 2002, 149, D1.
H. Matsumoto, H. Kageyama, Y. Miyazaki, Chem. Commun.
2002, 1726–1727.
a) R. A. Olofson, R. V. Kendall, J. Org. Chem. 1970, 35, 2246–
2248; b) Z. B. Zhou, H. Matsumoto, K. Tatsumi, Chem. Lett.
2004, 33, 886–887.
[11]
[12]
1-Methylpiperidinium
4,4,4-Trifluoro-1-phenyl-1,3-butanedionate
(14): Yellow liquid (0.26 g); yield 84%. IR: ν = 3441 (br., s), 3264
˜
[13]
[14]
(s), 1909 (m), 1824 (m), 1676 (s), 1636 (vs), 1456 (m), 1278 (s), 1070
(s), 986 (m), 976 (s), 938 (s), 855 (vs), 783 (vs), 758 (s), 707 (s), 629
1
(vs), 563 (m) cm–1. H NMR: δ = 7.83 (d, J = 6.0 Hz, 2 H), 7.41–
7.35 (m, 3 H), 6.16 (s, 1 H), 3.04 (s, 4 H), 2.74 (s, 3 H), 1.82–1.77
(m, 2 H) ppm. 19F NMR: δ = –75.8 (s, 3 F) ppm. 13C NMR: δ =
187.3, 171.2 (q, J = 166.1 Hz), 140.8, 128.1, 126.9, 121.2 (q, J =
377.5 Hz), 89.2, 55.3, 44.2, 22.9, 21.6 ppm. C16H20F3NO2 (315.33):
calcd. C 60.94, H 6.39, N 4.44; found C 58.94, H 6.03, N 4.24.
[15]
[16]
D. Gerhard, S. C. Alpaslan, H. J. Gores, M. Uerdingen, P. Was-
serscheid, Chem. Commun. 2005, 5080–5082.
a) O. D. Gupta, B. Twamley, J. M. Shreeve, Tetrahedron Lett.
2004, 45, 1733–1736; b) O. D. Gupta, B. Twamley, J. M.
Shreeve, J. Fluorine Chem. 2005, 126, 1222–1229.
a) N. Lopez, T. E. Vos, A. M. Arif, W. W. Shum, J. C. Noveron,
J. S. Miller, Inorg. Chem. 2006, 45, 4325–4327; b) E. Colacio,
M. Ghazi, R. Kivekäs, M. Klinga, F. Lloret, J. M. Moreno,
Inorg. Chem. 2000, 39, 2770–2776; c) N. A. Bailey, D. E. Fen-
ton, M. V. Franklin, M. Hall, J. Chem. Soc., Dalton Trans.
1980, 984–990; d) S. Diezi, D. Ferri, A. Vargas, T. Mallat, A.
Baiker, J. Am. Chem. Soc. 2006, 128, 4048–4057.
O. D. Gupta, B. Twamley, J. M. Shreeve, J. Fluorine Chem.
2006, 127, 263–269.
[17]
Acknowledgments
The authors gratefully acknowledge the support of the Defense
Threat Reduction Agency (1-07-1-0024), the National Science
Foundation (CHE-0315275), and the Office of Naval Research
(N00014-06-1-1032). The Bruker (Siemens) SMART APEX dif-
fraction facility was established at the University of Idaho with the
assistance of the NSF-EPSCoR program and the M. J. Murdock
Charitable Trust, Vancouver, WA, USA.
[18]
[19]
Z. Zhou, H. Matsumoto, K. Tatsumi, Chem. Lett. 2004, 33,
1636–1637.
Eur. J. Inorg. Chem. 2008, 3353–3358
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3357

X. Li, Z. Zeng, S. Garg, B. Twamley, J. M. Shreeve
FULL PAPER
[20]
[23] SADABS, an empirical absorption correction program, v. 2004/
1, Bruker AXS Inc., Madison, WI, 2004.
[24] G. M. Sheldrick, SHELXTL, Structure Determination Software
Suite, v. 6.14, Bruker AXS Inc., Madison, WI, 2004.
Received: May 1, 2008
D. MacFarlane, P. Meakin, J. Sun, N. Amini, M. Forsyth, J.
Phys. Chem. B 1999, 103, 4164–4170.
[21] SMART, v. 5.632, Bruker AXS, Madison, WI, 2005.
[22] SAINTPlus, Data Reduction and Correction Program, v. 7.23a,
Bruker AXS, Madison, WI, 2004.
Published Online: June 19, 2008
3358
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3353–3358