Synthetic and structural studies on pentafluorobenzylated imidazole systems

Synthetic and structural studies on pentafluorobenzylated imidazole

systems

1

‡

1‡

1

Martin Lampl , Inge Schlapp-Hackl , Klaus Wurst , Thomas Gelbrich , Holger Kopacka ,

1

Thomas Müller , Christoph Kreutz , Benjamin Naier , Gabriel Julian Partl *, Volker

2

3

1

Kahlenberg , Hassan Amer , Markus Bacher , Thomas Rosenau , Hubert Huppertz , and

Herwig Schottenberger¹

¹University of Innsbruck, Faculty of Chemistry and Pharmacy, Innrain 80-82, 6020 Innsbruck, Austria.

²University of Innsbruck, Institute of Mineralogy and Petrography, Innrain 52, 6020 Innsbruck, Austria.

³University of Natural Resources and Life Sciences, Department of Chemistry, Division of Chemistry of Renewable Resources,

Konrad-Lorenz-Straße 24, 3430 Tulln, Austria.

‡

These authors contributed equally.

*Corresponding author; E-mail: gabriel.partl@uibk.ac.at.

Graphical abstract

Highlights:



Synthesis of different amphiphilic compounds via well-known S- and/or N- alkylation routes.

Characterisation of several pentafluorobenzylated imidazole compounds and their reaction

intermediates by single crystal analysis, IR- and NMR-spectroscopy, and mass spectrometry.

Performance of surface tension experiments for key substances.



Functionalisation of the pentafluorobenzyl subunit using azide, and thermochemical

investigations of the product (TGA/DSC).



Investigation of Staudinger and copper-catalysed azide-alkyne cycloaddition reactions with

azide derivative.

ABSTRACT

Quaternization of common N-functionalized imidazoles (vinyl-, allyl-, propargyl-) with

pentafluorobenzyl bromide afforded the respective series of differently substituted imidazolium salts.

Likewise, chemospecific S- and N-alkylation of the commercial medicinal drug methimazole

(1-methyl-3H-imidazole-2-thione) and its vinylated relative 1-vinyl-3H-imidazole-2-thione yielded

N,S-bis(pentafluorobenzyl)-2-mercaptoimidazole derivatives.

In order to illustrate the proven feasibility of perfluorophenyl moieties to undergo further nucleophilic

aromatic substitution, one member of this newly conceived family of fluorinated salts was converted

to the 4-azido derivative, namely 3-(4-azido-2,3,5,6-tetrafluorobenzyl)-1-vinylimidazolium bromide.

Staudinger and copper-catalyzed azide-alkyne cycloaddition reactions were performed as well in an

initial investigation into azide follow-up chemistry. All target compounds, including new

intermediates, were characterized by routine spectroscopy and mass spectrometry. Additionally, X-

ray single crystal structure determinations were performed for 14 substances.

Surfactant properties were investigated for selected representatives through surface tension

measurements. Lastly, the thermal stability of the azido compound was evaluated by thermoanalysis

(TGA /DSC).

Keywords: pentafluorobenzyl imidazoles; crystal structure analysis; surface tension; nucleophilic

aromatic azidation, Staudinger reaction, CuAAC click reaction

1

. INTRODUCTION

Ever since Heinrich Debus discovered glyoxaline (imidazole) in 1858,[1] the scientific world

continues to be intrigued by this simple aromatic heterocycle, an amphoteric molecule frequently

referred to as “organic water”. Like imidazole itself, which is a natural product occurring in edible

lentils,[2] countless derivatives have been identified as active principles of medicinal and biological

relevance. Due to their exceptional chemical tailorability, azolium heterocycles, including

polymerizable ones, have conquered many different technical fields [3] and applications spanning

from cosmetic hair care [4] to electrochemical processes.[5]

In the closely interrelated areas of N-heterocyclic carbene (NHC) complexes and imidazole-based

ionic liquid (IL) chemistry, materials science and catalysis are continuously advancing.[6-13] In

particular, azolium compounds bearing unsaturated side chains, such as 1-allyl-, 1-vinyl- or

1

-propargylimidazole, had a profound impact.[4,5,14]

As is generally known, the incorporation of perfluoroalkyl or (perfluoroalkyl)alkyl moieties results

in physicochemical properties that significantly differ from those of their respective hydrocarbon

parent structures. Perfluoroalkyl and (perfluoroalkyl)alkyl compounds are famous for their water

and/or oil repellency, thermal stability, oxygen affinity, and surfactant properties.[15-17]

In contrast, the formally related perfluoroaryl or (perfluoroaryl)alkyl groups are not necessarily linked

to high surface activity. However, Broniatowski & Dynarowicz-Łatka [18] recently reported on non-

ionic surfactants based on a perfluorobenzyl system. In the same vein, we set out to conduct an

investigation focused on the combination of hydrophobic, lipophilic (perfluoroaryl)alkyl moieties

with several polar, hydrophilic imidazolium cores.

2

. RESULTS AND DISCUSSION

.1 Synthetic considerations

Quaternization of amine or imine systems is mainly achieved by the well-known Menshutkin

reaction,[19,20] yielding N-quaternized organic cations. In comparison to standard N-alkylation

reactions, perfluoralkyl and (perfluoroalkyl)alkyl halides of the types Rf

significantly decreased propensity towards S 2 reactions due to the electron withdrawing effect of

the fluorine atoms, rendering the terminal halide a bad leaving group.[21] The introduction of an

ethylene spacer to Rf X compounds, giving reactants of the type Rf CH CH X, mitigates this

deactivating effect and allows for S 2-typical use as alkylating agent.[10]

n

X and Rf

n

CH X show a

2

N

n

2

N

However, quaternization reactions of amines or imines with such 1H,1H,2H,2H-perfluoroalkyl

halides may be rivalled by base-promoted elimination reactions and might predominantly result in

1

H,1H,2H,2H-perfluoroalk-1-enes and ammonium or iminium halides.[22,23] In contrast, no

eliminative side reactions are to be expected for the highly reactive and commercially available

2

,3,4,5,6-pentafluorobenzyl bromide (PFB-Br).

In analogy to our previous efforts in the field of (perfluoroalkyl)alkylimidazolium salts,[9] we again

chose the affordable medical drug methimazole (1-methyl-3H-imidazole-2-thione) as starting

material. As MacFarlane and co-workers have shown, methimazole regioselectively reacts with alkyl

halides via S-alkylation to the respective 2-alkylmercaptoimidazolium halides.[12-13] Accordingly,

the alkylation of methimazole with PFB-Br leads to the formation of 1-methyl-2-[(2,3,4,5,6-

pentafluorobenzyl)thio]-3H-imidazolium bromide (2). This substance was one of many compounds

tested for antimicrobial behaviour, but no further analytical characterization (e.g. NMR spectroscopy,

X-ray diffraction) has been reported.[24] Deprotonation of 2, resulting in compound 3, and

subsequent N-functionalization affords the doubly alkylated S,N-bis(pentafluorobenzyl) salt 4 in high

yields (Scheme 1).

Scheme 1. Synthetic approaches to multiply functionalized pentafluorobenzylated imidazole systems. (a) PFB-Br, MeCN;

i

(

b) NaHCO

3

, MeOH; (c) PFB-Br, MeCN; (d) Pr-MgCl, S

8

, THF, HCl/H

2 8 3

O; (e) PFB-Br, MeCN; (f) S , NEt , pyridine; (g) PFB-Br,

MeCN; (h) NaN

3

, CaBr

2

, MeCN; (i) PFB-Br (2 equiv.), NaHCO

3

, MeCN; (j) PFB-Br, MeCN; (k) PFB-Br, MeCN.

In recent literature,[25-27] the N,N-bispentafluorobenzylated imidazolium salt 14 [1356845-03-8]

has proven to be a valuable precursor in the synthesis of palladium or rhodium NHC complexes for

catalytic purposes or the fabrication of perrhenate salts. A new preparative strategy was conceived,

and 14 was obtained in excellent yields via a one-pot reaction of imidazole with a mild base and PFB-

Br (2 equiv.).

According to a procedure published by Vereshchagin et al. (2006) [28] and Wang et al. (2016),[29]

propargyl imidazole (17) was synthesised from imidazole and propargyl bromide in the presence of

KOH under mild conditions. Inspired by this work, both 1-propargyl- and 1-allylimidazole were

functionalized as well, resulting in their respective N-pentafluorobenzyl salts 16 and 18.

In order to access the doubly N- and S-pentafluorobenzylated vinylimidazolium bromide 9, two

different routes, starting with vinylimidazole, are viable. The first route begins with the thionation of

vinylimidazole using a published procedure.[30] S-Pentafluorobenzylation of 6 resulted in the

hydrobromide salt 7, which was neutralized to give 8. The second route comprises

N-pentafluorobenzylation of vinylimidazole,[31] yielding compound 10, followed by thionation at

position 2, in turn forming the thione 11. Subsequent alkylation of 8 or 11 afforded the

S,N-bis(pentafluorobenzyl)ated compound 9 in comparatively low yields. In search of a reason for

such poor conversions, we found that the S-pentafluorobenzyl moiety of 9 exhibits a certain instability

in solution and is readily attacked by nucleophiles. It is likely that, at elevated temperatures or long

reaction times, even bad nucleophiles such as bromide, suffice to abstract the S-pentafluorobenzyl

group, thus reversing the desired reaction.

1

The aforementioned peculiarity was confirmed by H-NMR experiments (Figure 1). In the presence

of moderately nucleophilic pyridine, 9 reacts to the thione 11, and the respective

pentafluorobenzylated pyridinium salt is formed to the same extent. The first two NMR spectra

display the proton signals of 9 before (A) and directly after (B) the addition of pyridine. After 24

hours at room temperature, the spectrum exhibits additional peaks at 9.17, 8.70, 8.23 and 6.18 ppm,

corresponding to the newly formed pyridinium salt, whereas the peaks at 4.96, 5.30, 5.49, 7.27 – 7.42

and 7.64 ppm belong to thione 11. Approximately 30 % of 9 are still left in the sample (C). After 12

1

days at room temperature, the S-pentafluorobenzyl moiety was fully transferred to pyridine. The H-

NMR spectrum shows only the signals of the thione 11, the pyridinium salt and an excess of pyridine

(D). The reference spectra of the thione 11 and the pure pyridinium salt, obtained via equimolar

reaction of pyridine with PFB-Br at room temperature overnight, are shown in E and F, respectively.

Similar findings in recent literature regarding thioimidazolium ionic liquids [32] suggest that S-

alkylated thioimidazolium salts may, generally, react as alkylating agents.

Figure 1. Transfer of the S-pentafluorobenzyl moiety from the both N- and S-pentafluorobenzylated salt 9 to pyridine, forming the N-

pentafluorobenzylated vinylimidazolinethione 11 and N-pentafluorobenzylated pyridinium bromide.

Furthermore, conversion of the pentafluorobenzyl moiety into a 4-azidotetrafluorobenzyl group via

well-established S Ar reactions,[33-37] forming compound 12, underline their synthetic modularity

Scheme 1). The thermal properties of the introduced azide functionality were characterized by DSC

N

(

and TGA analysis (Figure 2). Thermal decomposition of 12 starts at approximately 125 °C and

undergoes an apparent interconnected two-step process (125 ‒ 159 °C, 159 ‒ 180 °C), followed by

continuous mass loss. This result is in accordance with the DSC analysis, in which a single exothermic

event peaking at around 159 °C occurs, thus reflecting the onset of rapid decomposition typically

observed in azide-containing energetic compounds. Considering the two steps observed in the TGA

curve and the corresponding mass loss, there is evidently a more complex degradation-polymerisation

cascade involved than the mere elimination of N .[38-40]

2

Figure 2. TG, DTG and DSC analyses of azide compound 12.

The implementation of an azide moiety opens up a plethora of further derivation options, two of

which were explored, namely a Staudinger reaction and a copper-catalysed azide-alkyne

cycloaddition (CuAAC) (Scheme 2).[34,35,41,42] Addition of triphenylphosphine to a solution of 12

results in the formation of the corresponding phosphazene 19, which proved to be rather stable against

hydrolysis.

The CuAAC reaction was performed using reactants 12 and 18, yielding triazole 20. Of course, these

model reactions should be understood as proof of principle and merely aim to illustrate the rich

follow-up chemistry that was made accessible through azidation of the pentafluorophenyl moiety.

3 4 2

Scheme 2. Representative follow-up chemistry based on azide intermediate 12. (l) PPh , MeCN; (m) 1. CuSO · 5 H O (cat.), sodium

i

2 4 6 2

ascorbate (0.2 equiv.), PrOH / H O 2:1, 2. (NH )PF , H O.

2

.2 Structural analyses

All investigated substances were found to crystallize readily, thus enabling the structure

determination of 2 ‒ 4, 7, 8, 9 · CHCl , 10 · 2 H O, 11, 12, 14, 16, 18, 19 · CH CN· 0.22 H O and

0 (Scheme 1 and 2) from single-crystal X-ray data (see Table S1 and Figures S1 ‒ S14 in section 2

3

2

3

2

of the supporting information). The bond distances and angles observed for these compounds do not

exhibit any uncommon features. The bromide salts 2 and 7, whose cations differ only in their N-1

substituent (Me or vinyl), are isostructural (Figure 3). The corresponding XPac comparison [43] of

the cation packing gives a dissimilarity index [44] of 5.4 (for details, see section 3 of the supporting

information).

Figure 3. Molecular packing of 2 and 7, viewed along the respective b axis in the crystal structures, illustrating their isostructural

‒

relationship. Cations and Br are connected by an N‒H···O bond. H atoms not involved in H-bonds are omitted for clarity.

Variations in molecular conformation can be rationalized in terms of the

-[(pentafluorobenzyl)thio]imidazole fragment I (Figure 4a) present in compounds 2 ‒ 4 and 7 ‒ 9 or

the 1-(pentafluorobenzyl)imidazole fragment II, which is found in 4, 14, 16, 18 and 9 ‒ 12 (Figure

b). In the first set, the molecular geometry of the isostructural analogues of 2 and 7 differs from that

2

4

of 8 in a 180° rotation about the central S‒C(benzyl) bond. By contrast, the imidazole ring of

compound 3 is approximately coplanar with the C‒S‒C‒C fragment linking the imidazole and phenyl

rings. 4 and 9 are close chemical analogues displaying very similar type-I geometries but

fundamentally different type-II-conformations. As a result, the two phenyl rings of 4 are almost

parallel, while those of 9 form a 54° angle. Fragment II occurs in a range of conformations in which

the angle formed by the planes of the imidazole and phenyl rings range between 59° (in 4) and 82°

(in 11). Compounds 2 and 7 display the expected intermolecular (imidazole) N‒H···Br bond.

Figure 4. Comparison of molecular geometries. a) Overlay of 2-[(pentafluorobenzyl)thio]imidazole fragments I present in compounds

, 3, 4, 7, 8 and 9, obtained by least-squares fitting a rigid fragment composed of the imidazole ring, the S atom of the thio substituent

and a C atom of either the Me or vinyl substituent. b) Overlay of 1-(pentafluorobenzyl)imidazole fragments II present in compounds

, 14, 16, 18 and 9 ‒ 12, obtained by least-squares fitting a rigid fragment composed of the imidazole ring and the first C atom of the

2

4

pentafluorobenzyl group. Fitted fragments are shown in balls and sticks style, F and H atoms are omitted for clarity. Only one of two

independent cations of 18 is shown.

‒

In the dihydrate 10 · 2H

2

O, water molecules (w1, w2) and Br anions are linked into a (w2)O‒

H···O(w1) and (w1)O‒H···Br-bonded chain structure, which propagates parallel to the a axis

Figure 5). This chain can be described as an …ABAB… sequence of two types of symmetrical,

(

vertex-sharing rings, each having the graph set symbol R²

(8).[45] Ring type A is formed by two w1

4

‒

water molecules and two Br anions, with each of the former donating an H bond to each of the latter.

Moreover, each water molecule w1 also belongs to a homodromic ring of type B within which it

accepts an H-bond from each of two w2 water molecules.

The asymmetric unit of the acetonitrile solvate 19 · CH

3

CN · 0.22 H O contains two units of 19, two

2

solvent molecules and additionally one partially occupied water site with an occupancy of 0.44(1).

The vacancy/occupation of the water site is correlated with the adoption of two alternative positions

-

by one Br ion. The presence of water in this crystal structure was confirmed via Karl-Fischer titration.

The quality of diffraction data of 20 was negatively affected by multiple twinning. However, the

obtained molecular structure is consistent with expected geometrical features (see Figure 6).

Figure 5. Packing of cations and an H-bonded homodromic chain propagating parallel to the a axis in the structure of 10 · 2H

2

O.

2

The O‒H···Br and O‒H···O bonded chain displays two types of R

4

(8) ring with ring A being composed of two water molecules and

two bromide ions and ring B connecting four water molecules.

Figure 6. Molecular structure of 20 showing the atom labels and non-H-atoms with displacement ellipsoids drawn at the 50%

probability level. The PF -anions were omitted.

6

2

.3 Surface tension experiments

In order to assess whether pentafluorobenzylated imidazolium salts display any appreciable surface

activity, aqueous surface tension measurements were conducted. While it was deemed unlikely that

their surfactancy is in the same order of magnitude as for (perfluoroalkyl)alkyl imidazolium salts,[9]

these compounds still contain the key moieties often employed in surfactant design: a hydrophobic

(perfluorophenyl) part and a hydrophilic (imidazolium) counterpart. In the measured concentration

range, the compounds 4, 7 and 18 reduced aqueous surface tension values the most (Figure 7) but did

not influence it to the same extent as commercial (fluoro)surfactants.[46] In case of compound 18, a

concentration of 43.6 mmol/L led to a value of 59.0 mN/m. Only the generation of a saturated solution

c = 164 mmol/L) helped to bring the surface tension down to 49.0 mN/m (Table 1). Concentrated

(

solutions of the other tested substances, namely the S-alkylated compound 2, the doubly N-alkylated

salt 14 and the N-alkylated compounds 10 and 16, hardly influenced the average surface tension or

even did not affect it at all. Consequently, their measurements were not included in the graph.

2

Conclusively, these findings further emphasize that sp -hybridized perfluorophenyl groups contribute

3

far less to aqueous surfactancy than sp perfluoroalkyl substituents.

Figure 7. Surface tension data of selected compounds (–■– compound 4, –■– compound 7, –▲– compound 18).

3

. CONCLUSION

A series of pentafluorobenzylated imidazole compounds has been conceived and prepared in order to

evaluate their synthetic accessibility, stability, structural features and surfactancy. Simple aromatic

nucleophilic substitution at the pentafluorophenyl subunit by azide [33] yielded the p-substituted

derivative (12) almost quantitatively. Through this, new avenues of follow up derivations have been

opened and were exemplified by a Staudinger as well as a CuAAC reaction.[34,35,41,42] In

conclusion, the molecular assemblies of allyl, vinyl, or propargyl side chains paired with

functionalized pentafluorobenzyl groups allow access to a plethora of application-tailorable materials

such as functional ionic liquids and related salts, polyelectrolytes,[47-52] or nitrene-mediated

covalent grafts.[53,54]

4

. EXPERIMENTAL

Reagents and solvents were purchased from commercial suppliers and used without further

purification. Propargylimidazole (17) [28,29] and 1-vinyl-4-imidazoline-2-thione (6) [30] were

1

13

prepared according to published procedures. H and C NMR spectra were recorded on a Bruker

1

9

Avance DPX 300, F spectra with a Bruker 600 MHz Avance II+ spectrometer and analyzed using

the MestReNova software (version 9.0.1).[55] IR spectra were obtained with a Bruker ALPHA

Platinum FT-ATR instrument and analyzed with the Bruker Opus software (version 7.2).[56] Mass

spectrometry was performed on a Thermo Finnigan Q Exactive Orbitrap spectrometer and melting

points were determined on a Leica Galen III Kofler microscope. Thermogravimetric measurements

were carried out on a Netzsch TG209 F1 analyzer. 8-12 mg of the sample was heated in an atmosphere

of nitrogen from room temperature to 900 °C at a rate of 20 °C/min with a flow rate of 30 mL/min.

DSC measurements were performed on a Netzsch DSC 200 F3 Maia differential scanning

calorimeter. 3-5 mg of the sample was weighed into a standard 40 µL aluminum crucible, which was

sealed afterwards. The lid was pricked prior to measurement allowing evaporation of volatile

substances. The sample was subjected to a temperature range between −55 and 200 °C with a heating

rate of 5 °C/min. Dry nitrogen was used as the purge gas (purge: 10 mL/min). Thermogravimetric

analyses (TGA, DTG) and differential scanning calorimetry (DSC) scans were recorded and analyzed

by the Netzsch Proteus software (version 6.1.0). Surface tension measurements were carried out on a

Krüss (DSA25E) drop shape analyzer. At a temperature of 25 °C at the tip of a needle (1.83 mm

external diameter), a suspended drop of a liquid is generated, pictures were recorded by an Allied

Vision camera (GuppyPro) and the surface tension calculated via Krüss Advance software (Version

1

.6-03) using the Young-Laplace method. Diffraction intensity data were recorded with a Bruker D8

Quest Photon 100 diffractometer using MoKα (λ = 0.7107 Å) radiation. The crystal structures were

solved using Direct Methods and refined by full-matrix least-squares techniques.[57,58] The

structures were visualized and the distances and angles calculated with the programs Ortep-3 [59]

and Mercury.[60] CCDC 1856823‒34, 1882203 and 1882204 contain the supplementary

crystallographic data for this paper, which can be obtained free of charge from the Cambridge

Crystallographic Data Centre (www.ccdc.cam.ac.uk/data_request/cif).

4

.1 1-Methyl-2-[(2,3,4,5,6-pentafluorobenzyl)thio]-3H-imidazolium bromide (2)

1

-Methyl-4-imidazoline-2-thione (1; 1.0 g, 8.8 mmol) was dissolved in anhydrous acetonitrile

(10 mL). 2,3,4,5,6-pentafluorobenzyl bromide (1.4 mL, 1.05 equiv., 9.3 mmol) was added and the

mixture was stirred for 24 h under argon at room temperature, forming a white precipitate.

Subsequently, diethyl ether (5 mL) was added and the mixture was cooled to -24 °C. Immediately

after, the product was filtered off, washed twice with diethyl ether (2 × 10 mL) and dried under

reduced pressure, yielding 3.2 g (97 %) of 1-methyl-2-[(2,3,4,5,6-pentafluorobenzyl)thio]-3H-

imidazolium bromide (2) as a white powder. Single-crystals were obtained by diffusion of Et O into

2

1

a methanolic solution of 2. M.p. 175 °C (dec.). – H NMR (300 MHz, (CD

3

2

) SO): δ 3.83 (s, 3H,

1

3

MeH), 4.42 (s, 2H, N-BnH), 7.83 (d, J = 2.0 Hz, 1H, ImH), 7.97 (d, J = 2.0 Hz, 1H, ImH) ppm. – C

NMR (75 MHz, (CD

3

)

2

SO): δ 26.3 (N-BnC), 35.2 (MeC), 110.6-111.3 (m, BnC), 121.9 (ImC), 126.4

(

ImC), 135.0 – 135.7 (m, BnC), 136.7 (ImC), 138.3 – 139.3 (m, BnC), 141.7 – 142.2 (m, BnC), 142.5

1

9

–

143.0 (m, BnC), 145.8 – 146.3 (m, BnC) ppm. – F NMR (376 MHz, (CD

m, BnF), -154.7 (t, J = 22.3 Hz, BnF), -143.9 – -143.8 (m, BnF) ppm. – FT-IR (ATR): ν 3154 (w),

088 (w), 2919 (w), 2873 (w) (νCH), 2649 (br, νNH), 1738 (w), 1703 (w), 1659 (w), 1571 (w), 1527

m), 1504 (s), 1480 (m) (νC=N, νC=C), 1296 (m), 1131 (m) (νCF), 994 (s), 964 (s), 918 (m), 885 (m),

3

)

2

SO): δ -162.3 – -162.1

(

3

(

-1

+

7

75 (s) (δ

o

CH), 676 (m), 644 (m) (νCS) cm . – HRMS (ESI pos.): calcd. m/z [M ] = 295.0323, found

m/z [C11

H

8

F

5

N

2

S⁺] = 295.0307.

4

.2 1-Methyl-2-[(2,3,4,5,6-pentafluorobenzyl)thio]imidazole (3)

To a solution of 1-methyl-2-[(2,3,4,5,6-pentafluorobenzyl)thio]-3H-imidazolium bromide (2;

50 mg, 1.7 mmol) in methanol (3 mL), sodium hydrogen carbonate (161 mg, 1.1 equiv., 1.9 mmol)

6

was added. The mixture was stirred under argon at room temperature for 17 h. Afterwards, diethyl

ether (10 ml) was added, the white precipitate removed by filtration and the filtrate concentrated under

reduced pressure. The resulting colorless liquid was dried in vacuo, which led to its crystallization.

1

Yield: 499 mg (98 %). M.p. 34 – 35 °C. – H NMR (300 MHz, (CD

3

)

2

SO): δ 3.58 (s, 3H, MeH), 4.17

SO): δ 25.5

N-BnC), 33.1 (MeC), 111.9 – 112.8 (m, BnC), 124.5 (ImC), 129.3 (ImC), 134.5 – 135.5 (m, BnC),

1

3

(

s, 2H, N-BnH), 6.94 (s, 1H, ImH), 7.31 (s, 1H, ImH) ppm. – C NMR (75 MHz, (CD

)

3 2

(

1

36.8 (ImC), 137.4 – 139.0 (m, BnC), 140.8 – 141.9 (m, BnC), 142.3 – 143.1 (m, BnC), 145.4 –

1

9

46.4 (m, BnC) ppm. – F NMR (376 MHz, (CD

3

2

) SO): δ -163.3 – -163.1 (m, BnF), -156.0 (t,

J = 21.7 Hz, BnF), -143.7 – -143.6 (m, BnF) ppm. – FT-IR (ATR): ν 3115 (w), 2994 (w), 2952 (w)

(νCH), 1657 (m), 1521 (m), 1500 (s), 1463 (m) (νC=N, νC=C), 1275 (m), 1121 (s) (νCF), 983 (s),

-1

9

68 (s), 913 (m), 889 (m), 728 (s), 677 (m) (δ CH), 645 (m) (νCS) cm . – HRMS (ESI pos.): calcd.

o

+

m/z [M + H ] = 295.0323, found m/z [C11

H

7

F

5

N S + H ] = 295.0302, calcd. m/z [M + Na ] =

2

+

3

17.0142, found m/z [C11

H

7

F

5

N

2

S + Na ] = 317.0119.

4

.3 3-Methyl-1-(2,3,4,5,6-pentafluorobenzyl)-2-[(2,3,4,5,6-pentafluorobenzyl)thio]-

imidazolium bromide (4)

(a) To a solution of 1-methyl-4-imidazoline-2-thione (1; 250 mg, 2.2 mmol) in anhydrous acetonitrile

(2 mL), 2,3,4,5,6-pentafluorobenzyl bromide (728 µL, 2.2 equiv., 4.8 mmol) was added. The mixture

was stirred for 24 h under argon at room temperature. Next, sodium hydrogen carbonate (220 mg,

.2 equiv., 2.6 mmol) and anhydrous acetonitrile were added and stirring was continued for 4 days.

1

Afterwards, acetone (5 mL) was added, the solids were removed by filtration and the solvent was

removed under reduced pressure. The crude product was dissolved in acetone (2 mL) and

reprecipitated via the addition of diethyl ether (10 mL), filtered and dried in vacuo, yielding 1.1 g

(

92

imidazolium bromide (4) as a white powder.

b) To a solution of 1-methyl-2-[(2,3,4,5,6-pentafluorobenzyl)thio]imidazole (3, 499 mg, 1.7 mmol)

%)

of

3-methyl-1-(2,3,4,5,6-pentafluorobenzyl)-2-[(2,3,4,5,6-pentafluorobenzyl)thio]-

(

in anhydrous acetonitrile (1 mL), 2,3,4,5,6-pentafluorobenzyl bromide (282 µL, 1.1 equiv., 1.9 mmol)

was added. The solution was stirred under argon at room temperature for 6 d, forming a white

precipitate. Diethyl ether (5 mL) was added for complete precipitation. The product was filtered,

washed with diethyl ether (2 × 2 mL) and dried in vacuo, yielding 920 mg (98 %).

Single-crystals of 4 were obtained by diffusion of Et

2

O into a solution of 4 in acetonitrile. M.p.

1

09.5 °C (dec.). – H NMR (300 MHz, Methanol-d

4

): δ 3.97 (s, 3H, MeH), 4.40 – 4.47 (m, 2H, N-

13

BnH), 5.65 (s, 2H, S-BnH), 7.94 – 7.98 (m, 2H, ImH) ppm. – C NMR (75 MHz, Methanol-d

4

):

δ 27.4 (N-BnC), 37.5 (MeC), 42.5 (S-BnC), 108.6 – 109.3 (m, BnC), 111.1 – 111.7 (m, BnC), 126.6

(

ImC), 127.8 (ImC), 137.3 – 137.9 (m, BnC), 140.8 (ImC), 140.6 – 141.2 (m, BnC), 141.4 – 141.7

m, BnC), 141.9 – 142.4 (m, BnC), 144.7 – 145.1 (m, BnC), 145.4 – 145.8 (m, BnC), 147.9 – 148.4

1

9

m, BnC), 148.7 – 149.1 (m, BnC) ppm. – F NMR (376 MHz, Methanol-d ): δ -163.7 – -163.6 (m,

4

BnF), -163.4 – -163.2 (m, BnF), -155.1 (t, J = 19.9 Hz, BnF), -154.2 – -154.1 (m, BnF), -145.3 – -

1

2

45.2 (m, BnF), -142.3 – -142.2 (m, BnF) ppm. – FT-IR (ATR): ν 3151 (w), 3092 (w), 3020 (w),

997 (w), 2969 (w), 2922 (w) (νCH), 1657 (m), 1564 (w), 1529 (m), 1500 (s) (νC=N, νC=C), 1428

(

m), 1247 (m), 1133 (m) (ν CF), 1013 (m), 989 (s) (δ

i

o

CH), 969 (s), 910 (m), 787 (m) (δ CH), 697

-1

+

(

m), 637 (m) (νCS) cm . – HRMS (ESI pos.): calcd. m/z [M ] = 475.0321, found m/z [C18

H

9

F

10

N

2

S ]

=

475.0265.

4

.4 1-Vinyl-4-imidazoline-2-thione (6) [1146852-33-6] (according to [30])

-Vinylimidazole (5; 7.5 g, 79.7 mmol) was dissolved in anhydrous tetrahydrofuran (THF; 60 mL)

1

and cooled in an ice bath. Isopropylmagnesium chloride solution (42 mL, 2 M in THF, 1.05 equiv.,

4.0 mmol) was added and the mixture was stirred at room temperature under an argon atmosphere

for 2 d. Then, elemental sulfur (S , 2.7 g, 1.05 equiv., 84.2 mmol) was added to the solution and

8

stirring was continued at room temperature for 24 h. Next, water (25 mL) was added and the mixture

was acidified with HCl (50 mL, 1 M, 50.0 mmol). The mixture was extracted with chloroform (3 ×

1

00 mL) and the combined organic layers were washed with brine (100 mL). The solvent was

removed under reduced pressure, yielding 7.5 g (74 %) of 1-vinyl-4-imidazoline-2-thione (6) as an

1

off-white solid. M.p. 143-144 °C. – H NMR (300 MHz, (CD

3

2

) SO): δ 4.92 (dd, J = 9.0, 1.1 Hz, 1H,

VinH), 5.43 (dd, J = 16.1, 1.2 Hz, 1H, VinH), 7.04 (t, J = 2.5 Hz, 1H, ImH), 7.38 (dd, J = 16.1, 9.1

13

Hz, 1H, VinH), 7.53 (t, J = 2.2 Hz, 1H, ImH), 12.35 (br s, 1H, N-H) ppm. – C NMR (75 MHz,

(

CD

3

)

2

SO): δ 100.9 (VinC), 113.8 (ImC), 116.3 (ImC), 129.0 (VinC), 161.8 (ImC) ppm. – FT-IR

(ATR): ν 3120 (m), 3018 (m), 2916 (w), 2704 (w) (νCH, νNH), 1646 (m), 1570 (m), 1463 (s), 1415

(m) (νC=N, νC=C), 1286 (m), 1269 (s), 1245 (m) (νC=S), 961 (m), 877 (m), 775 (m), 745 (s), 684

-

1

(

m), 653 (m) (δ CH) cm .

o

4

.5 2-[(2,3,4,5,6-Pentafluorobenzyl)thio]-1-vinyl-3H-imidazolium bromide (7)

To a solution of 1-vinyl-4-imidazoline-2-thione (6; 500 mg, 4.0 mmol) in anhydrous acetonitrile

10 mL), 2,3,4,5,6-pentafluorobenzyl bromide (634 µL, 1.05 equiv., 4.2 mmol) was added. The

(

mixture was stirred under inert gas at room temperature for 2 d, forming a white precipitate. Then,

diethyl ether (20 mL) was added and the mixture was cooled to -24 °C in order to complete

precipitation. The white crystalline product was filtered off, washed with diethyl ether (2 × 5 mL)

and dried, yielding 1.4 g (93 %) of 2-[(2,3,4,5,6-pentafluorobenzyl)thio]-1-vinyl-3H-imidazolium

bromide (7). Single-crystals were obtained by diffusion of Et O into a methanolic solution of 7. M.p.

2

1

72 °C (dec.). – H NMR (300 MHz, (CD

3

) SO): δ 4.35 (s, 2H, S-BnH), 5.35 (dd, J = 8.8, 2.0 Hz,

2

H, VinH), 5.89 (dd, J = 15.4, 2.0 Hz, 1H, VinH), 7.26 (dd, J = 15.5, 8.8 Hz, 1H, VinH), 7.81 (d,

13

J = 2.0 Hz, 1H, ImH), 8.32 (d, J = 2.0 Hz, 1H, ImH), 10.76 (br s, 1H, N-H) ppm. – C NMR (75

MHz, (CD SO): δ 26.7 (S-BnC), 109.5 (VinC), 110.6 – 111.4 (m, BnC), 121.2 (ImC), 124.2 (ImC),

27.6 (VinC), 135.0 – 135.6 (m, BnC), 136.8 (ImC), 138.3 – 138.9 (m, BnC), 141.7 – 142.2 (m,

)

3 2

1

19

BnC), 142.5 – 143.0 (m, BnC), 145.8 – 146.3 (m, BnC) ppm. – F NMR (376 MHz, (CD

62.4 – -162.2 (m, BnF), -155.0 (t, J = 22.3 Hz, BnF), -143.8 – -143.6 (m, BnF) ppm. – FT-IR (ATR):

ν 3160 (w), 3085 (w), 2988 (w), 2935 (w), 2906 (w) (νCH), 2653 (br m) (νNH), 1738 (w), 1705 (w),

3

)

2

SO): δ -

1

9

657 (w), 1646 (w), 1568 (w), 1525 (m), 1503 (s), 1468 (s) (νC=N, νC=C), 1313 (m), 1131 (m) (νCF),

-1

96 (s), 965 (s), 931 (s), 915 (m), 885 (m), 770 (s), 660 (m), 643 (m) (νCS, δCH) cm . – HRMS (ESI

+

N

S⁺] = 307.0302.

pos.): calcd. m/z [M ] = 307.0323, found m/z [C12H8F

5

2

4

.6 2-[(2,3,4,5,6-Pentafluorobenzyl)thio]-1-vinylimidazole (8)

To 2-[(2,3,4,5,6-pentafluorobenzyl)thio]-1-vinyl-3H-imidazolium bromide (7; 600 mg, 1.5 mmol)

and sodium hydrogen carbonate (145 mg, 1.1 equiv., 1.7 mmol), methanol (3 mL) was added and the

mixture stirred under inert gas at room temperature for 1d. Next, diethyl ether (10 mL) was added,

the precipitate removed by filtration and the filtrate concentrated under reduced pressure. The

colorless residue was dissolved in heptane (1 mL) and slowly cooled to -24 °C, which led to phase

separation and crystallization. The heptane layer was removed and the product was dried in vacuo,

yielding 334 mg (96 %) of 2-[(2,3,4,5,6-pentafluorobenzyl)thio]-1-vinylimidazole (8) as a white

1

crystalline solid. M.p. 33 – 34 °C. – H NMR (300 MHz, (CD

3

2

) SO): δ 4.18 (s, 2H, S-BnH), 4.91 (dt,

J = 8.8, 1.1 Hz, 1H, VinH), 5.47 (dt, J = 15.7, 1.0 Hz, 1H, VinH), 7.02 – 7.14 (m, 2H, VinH and

1

3

ImH), 7.82 (d, J = 1.6 Hz, 1H, ImH) ppm. – C NMR (75 MHz, (CD

3

2

) SO): δ 25.9 (S-BnC), 102.7

(VinC), 111.7 – 112.5 (m, BnC), 119.2 (ImC), 128.3 (ImC), 130.8 (VinC), 134.8 – 135.5 (m, BnC),

1

37.1 (ImC), 137.8 – 138.8 (m, BnC), 141.2 – 141.8 (m, BnC), 142.5 – 143.1 (m, BnC), 145.7 –

1

9

1

46.4 (m, BnC) ppm. – F NMR (376 MHz, (CD

J = 21.9 Hz, BnF), -143.6 – -143.4 (m, BnF) ppm. – FT-IR (ATR): ν 3157 (w), 3124 (w), 3097 (w),

979 (w), 2934 (w) (νCH), 1729 (w), 1647 (m), 1580 (w), 1500 (s), 1438 (s) (νC=N, νC=C), 1273

3

) SO): δ -163.3 – -163.1 (m, BnF), -156.2 (t,

2

-1

(

s), 1125 (m), 1106 (m) (νCF), 991 (s), 959 (s), 869 (s), 745 (s) (δ

o

CH), 676 (m), 644 (m) (νCS) cm .

+

–

HRMS (ESI pos.): calcd. m/z [M + H ] = 307.0323, found m/z [C12

H F

7 5

N

2

S + H ] = 307.0301,

+

calcd. m/z [M + Na ] = 329.0142, found m/z [C12

H

7

F

5

N S + Na ] = 329.0119.

2

4

.7 3-(2,3,4,5,6-Pentafluorobenzyl)-2-[(2,3,4,5,6-pentafluorobenzyl)thio]-1-vinylimidazolium

bromide (9)

a) 2,3,4,5,6-Pentafluorobenzyl bromide (176 µL, 2.0 equiv., 1.2 mmol) was added to a solution of

-[(2,3,4,5,6-pentafluorobenzyl)thio]-1-vinylimidazole (8, 178 mg, 0.58 mmol) in anhydrous

(

2

acetonitrile (1 mL). The solution was concentrated under reduced pressure after stirring at 50 °C

under inert gas for 1.5 d. Finally, diethyl ether (10 mL) was added and the precipitate was isolated by

filtration, washed with diethyl ether (2 × 5 mL) and dried in vacuo, yielding 330 mg (38 %) of

3

-(2,3,4,5,6-pentafluorobenzyl)-2-[(2,3,4,5,6-pentafluorobenzyl)thio]-1-vinylimidazolium bromide

(9) as a white powder.

(b) 2,3,4,5,6-Pentafluorobenzyl bromide (127 µL, 1.2 equiv., 0.84 mmol) was added to 3-(2,3,4,5,6-

pentafluorobenzyl)-1-vinylimidazoline-2-thione (11, 215 mg, 0.70 mmol) in anhydrous diethyl ether

4 mL). The mixture was stirred under argon atmosphere at room temperature for 24 h. Then, the

(

resulting precipitate was filtered, washed with diethyl ether (2 × 5 mL) and dried under reduced

pressure, yielding 120 mg (30 %) of 9.

Single-crystals were obtained by crystallization from slow evaporation of a solution of 9 in

chloroform. M.p. 108 °C (dec.). The substance decomposes in solution over time, resulting in

1

13

additional peaks in the H- and C-NMR spectra, assignable to compound 11 and other by-products.

19

1

Due to the decomposition, no F-spectrum was recorded. – H NMR (300 MHz, (CD

3

2

) SO): δ 4.36

(s, 2H, S-BnH), 5.46 (dd, J = 8.7, 2.3 Hz, 1H, VinH), 5.66 (s, 2H, N-BnH), 6.04 (dd, J = 15.3, 2.3 Hz,

1

H, VinH), 7.20 (dd, J = 15.3, 8.7 Hz, 1H, VinH), 8.28 (d, J = 2.2 Hz, 1H, ImH), 8.58 (d, J = 2.3 Hz,

1

3

H, ImH) ppm. – C NMR (75 MHz, (CD

3

2

) SO): δ 26.2 (S-BnC), 40.9 (N-BnC), 111.3 (VinC), 121.1

(

ImC), 126.5 (ImC), 127.7 (VinC), 138.5 (ImC) ppm (Quaternary C-atoms of the benzyl ring were

not observed due to low concentration). – FT-IR (ATR): ν 3094 (w), 3026 (w), 2947 (w) (νCH), 1658

w), 1644 (w), 1546 (w), 1519 (s), 1505 (s) (νC=N, νC=C), 1456 (w), 1401 (w), 1312 (w) (δSCH ),

CH), 716 (w), 693

(

2

1

226 (w), 1130 (m) (νCF), 1042 (m) (δ

i

CH), 995 (m), 969 (s), 930 (m), 811 (m) (δ

o

-1

+

(

w), 648 (w) (νCS) cm . – HRMS (ESI pos.): calcd. m/z [M ] = 487.0321, found m/z [C19

H

9

F

10

N S ]

2

=

487.0277.

4

.8 3-(2,3,4,5,6-Pentafluorobenzyl)-1-vinylimidazolium bromide (10)

To a cooled (ice-bath) solution of 1-vinylimidazole (5; 2.0 g, 21.3 mmol) in anhydrous acetonitrile

10 mL), 2,3,4,5,6-pentafluorobenzyl bromide (3.4 mL, 1.05 equiv., 22.5 mmol) was added. The

(

mixture was allowed to warm up to room temperature and was stirred under inert gas for 2 d. Diethyl

ether (50 mL) was added and the product precipitated by storing at -24 °C. The solid was filtered off,

washed with diethyl ether (2 × 20 mL) and dried, yielding 7.4 g (99 %) of 3-(2,3,4,5,6-

pentafluorobenzyl)-1-vinylimidazolium bromide (10) as a white product. Single-crystals of the

dihydrate were obtained by diffusion of Et

– ¹

H NMR (300 MHz, (CD SO): δ 5.44 (dd, J = 8.8, 2.5 Hz, 1H, VinH), 5.72 (s, 2H, N-BnH), 6.08

dd, J = 15.7, 2.5 Hz, 1H, VinH), 7.38 (dd, J = 15.6, 8.8 Hz, 1H, VinH), 8.03 (t, J = 1.9 Hz, 1H, ImH),

2

O into a methanolic solution of 10. M.p. 114.5 – 116 °C.

)

3 2

(

1

3

8

.39 (t, J = 1.9 Hz, 1H, ImH), 9.82 (s, 1H, ImH) ppm. – C NMR (75 MHz, (CD

3

2

) SO): δ 40.3

(N-BnC), 107.5 – 108.2 (m, BnC), 109.2 (VinC), 119.3 (ImC), 123.5 (ImC), 128.6 (VinC), 135.1 –

1

35.8 (m, BnC), 136.1 (ImC), 138.3 – 139.2 (m, BnC), 139.3 – 140.1 (m, BnC), 142.6 – 143.4 (m,

1

9

BnC), 143.4 – 143.9 (m, BnC), 146.6 – 147.3 (m, BnC) ppm. – F NMR (376 MHz, (CD

62.0– -161.8 (m, BnF), -153.2 (t, J = 22.0 Hz, BnF), -140.9 – -140.7 (m, BnF) ppm. – IR (ATR):

ν 3117 (w), 3093 (w), 3063 (w), 3033 (w), 2985 (w), 2951 (w), 2898 (w) (νCH), 1655 (m), 1566 (m),

544 (m), 1529 (s), 1507 (s) (νC=N, νC=C), 1170 (s), 1134 (s) (νCF), 1037 (s), 1017 (m) (δ CH), 969

CH) cm . – HRMS (ESI pos.): calcd. m/z [M ] = 275.0602,

3

)

2

SO): δ -

1

i

-1

+

(s), 924 (s), 849 (m), 785 (m), 673 (s) (δ

o

found m/z [C12

H

8

F

5

N

⁺] = 275.0583.

2

4

.9 3-(2,3,4,5,6-Pentafluorobenzyl)-1-vinylimidazoline-2-thione (11)

To 3-(2,3,4,5,6-pentafluorobenzyl)-1-vinylimidazolium bromide (10; 1.0 g, 2.8 mmol) and elemental

sulfur (91 mg, 1.0 equiv.,2.8 mmol), pyridine (3 mL) and trimethylamine (311 mg, 1.1 equiv.,

3

.1 mmol) were added. The mixture was stirred at 70 °C under inert gas for 2 h. After cooling to room

temperature, activated charcoal was added to remove discoloration. Then, the mixture was filtered

and washed with pyridine (2 mL). Water (8 mL) was added, forming an off-white precipitate. The

mixture was cooled to 4 °C in order to complete precipitation. Finally, the precipitate was filtered off,

washed with ice-cold water (2 × 5 mL) and dried under reduced pressure, yielding 695 mg (81 %) of

3

-(2,3,4,5,6-pentafluorobenzyl)-1-vinylimidazoline-2-thione (11). Single-crystals were obtained

1

from slow evaporation of a solution of 11 in methanol/water. M.p. 99 – 100 °C. – H NMR (300

MHz, (CD

.5 Hz, 1H, VinH), 7.27 – 7.42 (m, 2H, VinH and ImH), 7.64 (d, J = 2.7 Hz, 1H, ImH) ppm. – C

NMR (75 MHz, (CD SO): δ 101.6 (VinC), 109.2 – 109.8 (m, BnC), 113.3 (ImC), 119.5 (ImC),

29.4 (VinC), 135.0 – 135.6 (m, BnC), 138.3 – 138.6 (m, BnC), 138.7 – 139.0 (m, BnC), 141.8 –

42.4 (m, BnC), 143.1 – 143.6 (m, BnC), 146.3 – 147.0 (m, BnC), 162.4 (ImC) ppm (N-BnC hidden

3

2

) SO): δ 4.96 (dd, J = 9.1, 1.5 Hz, 1H, VinH), 5.30 (s, 2H, N-BnH), 5.49 (dd, J = 16.1,

1

3

1

)

3 2

1

9

by solvent). – F NMR (376 MHz, (CD

3

2

) SO): δ -164.6– -161.5 (m, BnF), -154.7 (t, J = 22.4 Hz,

BnF), -142.6 – -139.5 (m, BnF) ppm. – FT-IR (ATR): ν 3170 (w), 3135 (w), 3109 (w), 2992 (w),

976 (w), 2943 (w) (νCH), 1655 (w), 1640 (m), 1524 (m), 1500 (s), 1454 (m) (νC=N, νC=C), 1420

m), 1403 (s), 1371 (m), 1301 (m), 1246 (m) (νC=S), 1200 (m), 1128 (m) (νCF), 1067 (m), 1012 (m),

2

(

1

6

000 (m) (δ CH), 967 (m), 958 (m), 923 (m), 890 (m), 803 (m), 727 (m), 714 (m), 703 (m), 683 (m),

i

-1

+

67 (m) (δ

o

CH) cm . – HRMS (ESI pos.): calcd. m/z [M + H ] = 307.0323, found m/z [C12

H

7

F

5

2

N S

+

H ] = 307.0309.

4

.10 3-(4-Azido-2,3,5,6-tetrafluorobenzyl)-1-vinylimidazolium bromide (12)

An Ar-purged Schlenk round-bottom flask was charged with 1-(2,3,4,5,6-pentafluorobenzyl)-3-

vinylimidazolium bromide (10, 1.4 g, 4.0 mmol), dissolved in acetonitrile (150 ml). Then, sodium

azide (390 mg, 1.5 equiv, 6.0 mmol) and calcium bromide (601 mg, 0.75 equiv, 3.0 mmol) were

added and the reaction mixture was stirred under reflux protected from light and air for 5 d (Warning:

It is advised to comply with the described conditions to avoid multiple fluorine substitution and thus

the formation of explosive side products [37]). The solids were removed by filtration and the solvent

was evaporated. The crude product was taken up in acetonitrile and filtered a second time. The filtrate

was overlaid with diethyl ether (300 ml) and cooled to -20 °C overnight. The product was separated

from the solvents and by-products by filtration. Last traces of contaminants were removed by a second

precipitation in a mixture of methylene chloride / n-hexane (1:7). Finally, the desired product was

filtered off and washed with diethyl ether and n-hexane, yielding a yellow solid 1.3 g (87 %). Single-

crystals were obtained by slow evaporation of a solution of 12 in methylene chloride covered with n-

1

hexane or n-heptane. M.p. 128 °C (dec.). – H NMR (300 MHz, MeOH-d4): δ 5.48 (dd, J = 8.7,

2

8

.7 Hz, 1H, N-BnH), 5.66 (s, 2H, N-BnH), 5.95 (dd, J = 15.6, 2.8 Hz, 1H, VinH), 7.25 (dd, J = 15.6,

1

3

.7 Hz, 1H, VinH), 7.80 (d, J = 2.3 Hz, 1H, ImH), 8.07 (d, J = 2.2 Hz, 1H, ImH) ppm. – C NMR

(75 MHz, MeOH-d4): δ 42.0 (N-BnC), 108.3 – 108.8 (m, BnC), 110.8 (VinC), 121.4 (ImC), 121.9

1

9

(

ImC), 124.7 (ImC), 129.8 (VinC) ppm. F NMR (376 MHz, Acetone-d6): δ -152.9 – -152.8 (m,

BnF), -143.7 – -1143.5 (m, BnF) ppm. – FT-IR (ATR): ν 3120, 3080, 2975, 2948, 2920, 2816 (νCH),

2

9

179, 2162, 2120 (νN=N), 1652, 1567, 1550 (νC=C, νC=N),1491, 1225 (νCF), 1164, 1019 (δ

i

CH),

CH) cm – HRMS (ESI pos): calcd. m/z [M ] = 298.0710, found m/z

⁺] = 298.0696.

-1

+

43, 922, 786, 662 (δ

o

[

C

12

H

8

F

4

N

5

4

.11 1,3-Bis(2,3,4,5,6-pentafluorobenzyl)imidazolium bromide (14)

To a solution of imidazole (13; 475 mg, 7.0 mmol) in anhydrous acetonitrile (10 mL), sodium

hydrogen carbonate (685 mg, 1.2 equiv., 8.2 mmol) and 2,3,4,5,6-pentafluorobenzyl bromide

(

2.2 mL, 2.1 equiv., 14.6 mmol) were added. The mixture was stirred under argon at room temperature

for 5 d. After filtration, the solvent was removed under reduced pressure, yielding 2.9 g (81 %) of

,3-bis(2,3,4,5,6-pentafluorobenzyl)imidazolium bromide (14) as a white powder. Single-crystals

1

were obtained by diffusion of Et

NMR (300 MHz, (CD SO): δ 5.70 (s, 4H, N-BnH), 7.89 (d, J = 1.6 Hz, 2H, ImH), 9.63 (s, 1H,

ImH) ppm. – C NMR (75 MHz, (CD SO): δ 40.3 (N-BnC), 107.2 – 108.6 (m, BnC), 123.0 (ImC),

35.2 – 135.8 (m, BnC), 137.6 (ImC), 138.4 – 139.1 (m, BnC), 139.3 – 139.9 (m, BnC), 142.7 –

2

O into a methanolic solution of 14. M.p. 184.5 – 185.0 °C. – H

)

3 2

13

)

3 2

1

19

43.3 (m, BnC), 143.3 – 143.9 (m, BnC), 146.5 – 147.2 (m, BnC) ppm. – F NMR (376 MHz,

SO): δ -162.0 – -161.7 (m, BnF), -152.9 (t, J = 21.9 Hz, BnF), -141.2 – -141.0 (m, BnF) ppm.

(CD

)

3 2

–

1

FT-IR (ATR): ν 3185 (w), 3059 (m), 2980 (w), 2955 (m), 2919 (w), 2871 (w) (νCH), 1761 (w),

656 (w), 1631 (w), 1578 (w), 1563 (w), 1525 (m), 1502 (s) (νC=N, νC=C), 1174 (m), 1129 (m)

-1

(

νCF), 1031 (m), 1020 (s) (δ

i

CH), 968 (m), 931 (s), 799 (m) (δ

o

CH) cm . – HRMS (ESI pos.): calcd.

+

⁺] = 429.0409.

m/z [M ] = 429.0444, found m/z [C17

H

7

F

10

N

2

4

.12 3-Allyl-1-(2,3,4,5,6-pentafluorobenzyl)imidazolium bromide (16)

To a solution of 1-allylimidazole (15; 420 mg,3.9 mmol) in acetonitrile (anhydrous, 5 mL)

,3,4,5,6-pentafluorobenzyl bromide (580 µL, 0.99 equiv., 3.8 mmol) was added. The mixture was

2

refluxed under inert gas for 2 d. After cooling to room temperature, diethyl ether (20 mL) was added

and the mixture stored at -24 °C for a few hours. After filtration of the cold mixture, the product was

washed with diethyl ether (2 × 10 mL) and dried, yielding 1.3 g (93 %) of 3-allyl-1-(2,3,4,5,6-

pentafluorobenzyl)imidazolium bromide (16) as a white crystalline solid. Single-crystals were

1

obtained by diffusion of Et

CD

J = 10.2, 1.3 Hz, 1H, AllH), 5.68 (s, 2H, N-BnH), 6.05 (ddt, J = 16.4, 10.3, 6.0 Hz, 1H, AllH), 7.84

2

O into a solution in acetonitrile. M.p. 108 – 109°C. – H NMR (300 MHz,

(

3

2

) SO): δ 4.88 (dt, J = 6.0, 1.5 Hz, 2H, AllH), 5.30 (dd, J = 17.1, 1.5 Hz, 1H, AllH), 5.36 (dd,

1

3

(

dt, J = 11.4, 1.9 Hz, 2H, ImH), 9.41 (s, 1H, ImH) ppm. – C NMR (75 MHz, (CD

3

2

) SO): δ 51.0

(AllC), 107.7 – 108.5 (m, BnC), 120.3 (AllC), 122.8 (AllC), 122.9 (ImC), 131.6 (ImC), 135.3 – 135.8

(m, BnC), 136.8 (ImC), 138.5 – 139.1 (m, BnC), 139.4 – 139.8 (m, BnC), 142.7 – 143.1 (m, BnC),

19

1

43.3 – 143.9 (m, BnC), 146.5 – 147.1 (m, BnC) ppm (N-BnC hidden by solvent peak). – F NMR

SO): δ -161.8 – -161.7 (m, BnF), -153.0 (t, J = 22.0 Hz, BnF), -141.3 – -141.2 (m,

BnF) ppm. – FT-IR (ATR): ν 3177 (w), 3128 (w), 3065 (m), 3972 (m), 2862 (w) (νCH), 1754 (w),

660 (m), 1634(w), 1569 (m), 1524 (s), 1502 (s) (νC=N, νC=C),1453 (m), 1420 (m), 1349 (m), 1305

(376 MHz, (CD

)

3 2

1

-1

(

m), 1175 (s), 1129 (s) (νCF), 1028 (s), 970 (s) (δ

i

CH), 945 (s), 931 (s), 762 (s), 655 (s) (δ

o

CH) cm .

+

⁺] = 289.0739.

–

HRMS (ESI pos.): calcd. m/z [M ] = 289.0759, found m/z [C13

H

10

F

5

N

2

4

.13 1-Propargylimidazole (17) [18994-77-9] (modified procedure according to [28, 29])

Imidazole (13; 8.3 g, 122 mmol) was added to a solution of KOH (15.2 g, 270.9 mmol) in water

24 mL) and combined with acetone (75 mL) under vigorous stirring. After 20 min the mixture was

(

cooled in an ice-NaCl-bath, then propargyl bromide (9.6 mL, 1.04 equiv., 127 mmol) was added

dropwise. After stirring for 1 h, the biphasic mixture was allowed to warm to room temperature and

stirred for another 1.5 h. The organic layer was separated and the aqueous layer was extracted with

chloroform (3 × 50 ml). The solvents of the combined organic layers were removed by evaporation

under reduced pressure. The product was purified by silica gel flash column chromatography

1

(

petroleum ether/EtOAc 2/1), yielding 6.8 g (52 %) of 1-propargylimidazole (17). – H NMR (300

MHz, (CD

Hz, 1H, ImH), 7.21 (t, J = 1.3 Hz, 1H, ImH), 7.70 (s, 1H, ImH) ppm. – C NMR (75 MHz,

CD SO): δ 35.4 (PpgC), 76.1 (PpgC), 78.7 (Ppg C), 119.3 (ImC), 128.7 (ImC), 137.0 (ImC) ppm.

FT-IR (ATR): ν 3289 (m), 3113 (m), 2960 (w), 2927 (w), 2120 (w) (νCH), 1504 (s) (νC=N, νC=C),

281 (m), 1228 (s) (νCH), 1107 (m), 1074 (s) (δ CH), 906 (m), 818 (m), 732 (s), 658 (s), 612 (s)

3

2

) SO): δ 3.50 (t, J = 2.6 Hz, 1H, PpgH), 4.93 (d, J = 2.6 Hz, 2H, PpgH), 6.94 (t, J = 1.3

13

(

)

3 2

–

1

i

-1

(

δ CH) cm .

o

4

2

1

.14 1-(2,3,4,5,6-pentafluorobenzyl)-3-propargylimidazolium bromide (18)

,3,4,5,6-Pentafluorobenzyl bromide (392 µL, 1.1 equiv., 2.6 mmol) was added to a solution of

-propargylimidazole (17; 250 mg, 2.4 mmol) in anhydrous acetonitrile (3 mL). The mixture was

stirred under argon at room temperature for 3 d. Diethyl ether (10 mL) was added and the white

precipitate was filtered, washed with ether (2 × 5 mL) and dried under reduced pressure, yielding

8

32 mg (96 %) of 1-(2,3,4,5,6-pentafluorobenzyl)-3-propargylimidazolium bromide (18) as a white

crystalline solid. Single-crystals of 18 were obtained by diffusion of Et O into a solution in

2

1

acetonitrile. M.p. 124 – 125 °C. – H NMR (300 MHz, (CD

3

2

) SO): δ 3.87 (t, J = 2.5 Hz, 1H, PpgH),

5

.26 (d, J = 2.6 Hz, 2H, PpgH), 5.72 (s, 2H, N-BnH), 7.89 (dt, J = 9.4, 1.9 Hz, 2H, ImH), 9.52 (s, 1H,

1

3

ImH) ppm. – C NMR (75 MHz, (CD

3

)

2

SO): δ 38.8 (PpgC), 40.2 (N-BnC), 75.9(PpgC), 79.1 (PpgC),

07.7 – 108.4 (m, BnC), 122.6 (ImC), 123.1 (ImC), 135.1 – 135.8 (m, BnC), 136.9 (ImC), 138.4 –

39.1 (m, BnC), 139.3 – 139.9 (m, BnC), 142.6 – 143.3 (m, BnC), 143.3 – 143.9 (m, BnC), 146.6 –

1

9

47.2 (m, BnC) ppm. – F NMR (376 MHz, (CD

3

) SO): δ -161.9 – -161.7 (m, BnF), -153.0 (t,

2

J = 22.2 Hz, BnF), -141.2 – -141.1 (m, BnF) ppm. – FT-IR (ATR): ν 3164 (w), 3122 (m), 3050 (m),

017 (m), 2918 (w), 2843 (w), 2116 (w) (νCH), 1749 (w), 1660 (m), 1569 (m), 1525 (s), 1505 (s)

νC=N, νC=C), 1173 (s), 1124 (s) (νCF), 1040 (s), 1029 (s) (δ CH), 960 (s), 911 (s), 788 (m), 760 (s),

CH) cm . – HRMS (ESI pos.): calcd. m/z [M ] = 287.0602, found m/z [C13

⁺] =

3

(

i

-1

+

6

2

60 (s) (δ

o

H

8

F

5

N

2

87.0582.

4

.15 3-{2,3,5,6-Tetrafluoro-4-[(triphenylphosphoranylidene)amino]benzyl}-1-vinyl-

imidazolium bromide (19)

-(4-Azido-2,3,5,6-tetrafluorobenzyl)-1-vinylimidazolium bromide (12; 100 mg, 0.26 mmol) and

3

triphenylphosphine (70 mg, 1.03 equiv., 0.27 mmol) were dissolved in acetonitrile (3 ml) and stirred

under an argon atmosphere at room temperature for 3 d. Via addition of diethyl ether (10 ml), the

desired product precipitated. The solid was collected and dried under reduced pressure, yielding

1

38 mg (85 %) of 3-{2,3,5,6-tetrafluoro-4-[(triphenylphosphoranylidene)amino]benzyl}-1-

vinylimidazolium bromide (19) as a pale yellow solid. Single-crystals of the acetonitrile/water adduct

were obtained by diffusion of diethyl ether into a solution of 19 in acetonitrile. M.p. 216 – 219 °C

1

(

dec). – H NMR (300 MHz, (CD

3

2

) SO): δ 5.41 (dd, J = 8.7, 2.4 Hz, 1H, VinH), 5.46 (s, 2H, N-BnH),

5

.98 (dd, J = 15.7, 2.5 Hz, 1H, VinH), 7.27 (dd, J = 15.7, 8.8 Hz, 1H, VinH), 7.52 – 7.81 (m, 15H,

1

3

PhH), 7.91 (s, 1H, ImH), 8.24 (s, 1H, ImH), 9.52 (s, 1H, ImH) ppm. – C NMR (75 MHz, (CD

δ 40.7 (N-BnC), 97.07 – 97.8 (m, BnC), 108.9 (VinC), 119.2 (ImC), 123.3 (ImC), 128.7 (VinC),

29.0 (d, J = 12.4 Hz, PhC), 130.2 (d, J = 102.9 Hz, PhC), 131.8 (d, J = 10.1 Hz, PhC), 132.4 (ImC)

d, J = 2.9 Hz, PhC), 135.7 (ImC), 139.4 – 140.4 (m, BnC), 142.8 – 144.2 (m, BnC), 146.7 – 147.4

3

) SO):

2

1

(

1

9

m, BnC) ppm. – F NMR (376 MHz, (CD

3

) SO): δ -153.0 – -152.9 (m, BnF), -146.8 – -146.7 (m,

2

BnF) ppm. – FT-IR (ATR): ν 3400 (br w) (water), 3038 (w), 2987 (w) (νCH), 1648 (m), 1527 (s),

486 (s), 1435 (m) (νC=C, νC=N, νN=P), 1223 (s), 1159 (m), 1110 (m) (νCF, νPPh), 1027 (m), 1008

1

(

m), 965 (w), 910 (m), 876 (w), 853 (w) (δ

i

CH), 763 (m), 719 (s), 694 (s), 675 (m) (δ CH), 626 (m),

o

–

1

+

5

98 (w), 560 (m), 529 (s) (δoop/ipring) cm . – HRMS (ESI pos.): calcd. m/z [M ] = 532.1560, found

m/z [C30

H

23

F

4

N

P⁺] = 532.1551.

3

4

.16 1-(2,3,4,5,6-Pentafluorobenzyl)-3-[(1-{2,3,5,6-tetrafluoro-4-[(3-vinylimidazolium-1-yl)-

methyl]phenyl}-1,2,3-triazol-4-yl]methyl]imidazolium bis(hexafluoridophosphate) (20)

-(2,3,4,5,6-pentafluorobenzyl)-3-propargylimidazolium bromide (18; 100 mg, 0.27 mmol) and 3-(4-

1

azido-2,3,5,6-tetrafluorobenzyl)-1-vinylimidazolium bromide (12; 103 mg, 1.0 equiv., 0.27 mmol)

were dissolved in an isopropanol/water 2:1 mixture (4.5 ml). Copper(II) sulfate pentahydrate (5 mg,

0

.07 equiv.) and sodium ascorbate (12 mg, 0.22 equiv.) were added and the mixture was stirred under

an argon atmosphere at room temperature for 4 days. Then, the solvents were removed under reduced

pressure. After re-dissolving the residue in water (2 ml), a solution of ammonium

hexafluorophosphate in water (1 ml) was added. The precipitate was collected by filtration and dried

in vacuo, yielding 188 mg (79 %) of the crude 1-(2,3,4,5,6-pentafluorobenzyl)-3-((1-(2,3,5,6-

tetrafluoro-4-((3-vinylimidazolium-1-yl)-methyl)-phenyl)-1,2,3-triazol-4-yl)methyl)-imidazolium

bis(hexafluoridophosphate) (20) as a pale yellow solid. Single-crystals were obtained by diffusion of

1

diethyl ether into a solution of 20 dissolved in acetonitrile. M.p. 202 – 204 °C (dec.) – H NMR (300

MHz, (CD

.79 (s, 2H, CH2), 6.00 (dd, J = 15.6, 2.5 Hz, 1H, VinH), 7.31 (dd, J = 15.6, 8.8 Hz, 1H, VinH), 7.83

t, J = 1.7 Hz, ImH), 7.90 (t, J = 1.8 Hz, ImH), 7.99 (t, J = 1.9 Hz, ImH), 8.26 (t, J = 1.9 Hz, ImH),

3

2

) SO): δ 5.47 (dd, J = 8.7, 2.5 Hz, 1H, VinH), 5.69 (s, 2H, N-BnH), 5.71 (s, 2H, N-BnH),

5

(

13

8

.78 (s, 1H, TrH), 9.49 (s, 1H, ImH), 9.59 (s, 1H, ImH) ppm. – C NMR (75 MHz, (CD

), 43.5 (N-BnC), 107.7 – 108.5 (m, BnC), 109.4 (VinC) , 114.1 – 114.8 (m, BnC), 116.8 – 117.3

m, BnC), 119.3 (ImC), 123.1 (ImC), 123.8 (ImC), 127.4 (TrC) , 128.7 (VinC), 135.2 – 135.9 (m,

3

) SO): δ 40.5

2

(CH

2

(

BnC), 136.4 (ImC), 137.3 (ImC), 138.3 – 139.2 (m), 139.3 – 139.8 (m), 141.4 (TrC), 142.6 – 143.2

m), 143.2 – 143.9 (m), 146.6 – 147.2 (m)ppm. (One of the benzylic CH is hidden by solvent peak,

SO): δ -161.8 – -161.6 (m, BnF), -152.8 (t,

J = 22.2 Hz, BnF), -147.3 – -147.1 (m, BnF), -141.4 – -141.2 (m, BnF), -139.8 – -139.7 (m, BnF), -

(

2

1

9

see C,H-HETCORR). – F NMR (376 MHz, (CD

)

3 2

7

1

0.3 (d, J = 710.0 Hz, PF

^-) ppm. – FT-IR (ATR): ν 3161 (w) (νCH), 1661 (w), 1559 (w), 1506 (m),

6

453 (w) (νC=C, νC=N, νN=N), 1162 (m), 1129 (m) (νCF), 1038 (m), 1017 (m), 970 (w), 920 (m)

^-), 740 (m), 680 (m), 654 (m) (δ

CH), 556 (s) (δoop/ipring) cm . – HRMS (ESI

–1

(δ

i

CH), 824 (s) (PF

6

o

+

N

P⁺] = 730.0943.

pos.): calcd. m/z [M ] = 730.0960, found m/z [C25

H

16

F

15

7

Statement of significance:

In order to further explore the applicative potential of imidazoles with novel substitution patterns,

several polymerisable and pentafluorobenzylated derivatives thereof were synthesised and

thoroughly characterised. Via well-established thionation to S-nucleophilic imidazolinethiones, the

incorporation of a second side-chain was achieved. Even further derivatisation options were

demonstrated through nucleophilic aromatic substitution at the pentafluorophenyl moiety. This

remarkably versatile family of fluorinated imidazoles may be chemically tailored to numerous

applications, amongst which are e.g. N-heterocyclic carbene pre-catalysts, energetic materials,

polyelectrolytes and ionic liquids

ACKNOWLEDGEMENTS

This work was supported by the Austria Wirtschaftsservice (aws) under grant number P1621682. The

authors are grateful to Andreas Feichtner for technical assistance.

Declarations of interest: none.

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Table 1. Minimal aqueous surface tension values at a given concentration for compounds 2, 4, 7, 10, 14, 16 and 18.

Concentration

Min. Surface Tension

[mN/m]

Compound

[

mmol/L]

2

4

7

133.3

25.70

21.54

169.4

197.9

136.8

163.8

67.66 ± 0.11

45.53 ± 0.13

46.94 ± 0.10

62.08 ± 0.09

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1

0

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6

8

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Synthetic and structural studies on pentafluorobenzylated imidazole systems

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