Allyl-functionalised ionic liquids: Synthesis, characterisation, and reactivity

Article abstract of DOI:10.1002/hlca.200590046

The two known Me- and allyl-substituted 1H-imidazol-3-ium bromides 1 and 2, respectively, were converted to the corresponding BF₄^- and BPh₄^- salts 3-6 (Scheme 1). Compounds 3 and 4 were liquids at ambient temperature. Reaction of 1 or 2 with [PdCl₂] afforded the corresponding 2:1 imidazolium/metal complexes 7 and 8. The latter complex, melting at 58°, can be regarded as a 'true' ionic liquid. Attempts to polymerise 7 by radical promotion (AIBN) were unsuccessful, but resulted in the centrosymmetric 2:1 complex 9. The allyl group of 1 could be arylated (giving rise to 10) or hydrogenated (at 100 bar H₂ pressure). The solid-state structures of compounds 5-7 and 9 were solved by means of single-crystal X-ray analyses (Figs. 1-4).

Full text of DOI:10.1002/hlca.200590046

Helvetica Chimica Acta ± Vol. 88 (2005)
665
Allyl-Functionalised Ionic Liquids: Synthesis, Characterisation, and
Reactivity
by Dongbin Zhao, Zhaofu Fei, Tilmann J. Geldbach, Rosario Scopelliti, GaÂbor Laurenczy, and Paul J. Dyson*
Â
Â
Â
Ecole Polytechnique Federale de Lausanne (EPFL), Institut des Sciences et Ingenierie Chimiques,
CH-1015 Lausanne, Switzerland
(phone: ‡ 41-(0)21-6939854; fax: ‡ 41-(0)21-6939885; e-mail: paul.dyson@epfl.ch)
Â
Dedicated to Professor Andre E. Merbach on the occasion of his 65th birthday
The two known Me- and allyl-substituted 1H-imidazol-3-ium bromides 1 and 2, respectively, were
converted to the corresponding BFÀ4 and BPh4À salts 3 ± 6 (Scheme 1). Compounds 3 and 4 were liquids at
ambient temperature. Reaction of 1 or 2 with [PdCl2] afforded the corresponding 2 :1imidazolium/metal
complexes 7 and 8. The latter complex, melting at 588, can be regarded as a ꢀtrueꢁ ionic liquid. Attempts to
polymerise 7 by radical promotion (AIBN) were unsuccessful, but resulted in the centrosymmetric 2 :1complex
9. The allyl group of 1 could be arylated (giving rise to 10) or hydrogenated (at 100 bar H2 pressure). The solid-
state structures of compounds 5 ± 7 and 9 were solved by means of single-crystal X-ray analyses (Figs. 1 ± 4).
Introduction. ± Room-temperature ionic liquids have received considerable
attention as alternative solvents for a wide range of applications, in particular as
reaction media for homogeneous, heterogeneous, and enzymatic catalysis [1]. Ionic
liquids that incorporate functional groups are becoming more and more important,
since imparting specific chemical properties to the ionic liquid could lead to highly
specific roles in synthesis and catalysis unparalleled by more-generic systems. Only a
few ionic liquids with functional anions have been reported [2], whereas a large number
of ionic liquids with functional cations have been published, including alkenes [3 ± 5],
alkynes [6][7], amines [8], amides [9], ethers and alcohols [10], acids [11], fluorous
[12] and glycidyl [13] chains, nitriles [14], thiols [15 ± 17], and ferrocenyl groups [18].
Functionalised ionic liquids exhibit a range of physical and chemical properties that
are well-suited to specific applications. For example, ionic liquids incorporating the
O,O-diethylphosphonyl functionality have been evaluated as mechanical lubricants
[19], and ionic liquids with fluorous chains act as surfactants [12a]. Other applications
include the use of acid-functionalised ionic liquids in the acetalisation of aldehydes
[11e][20], and urea- and thiourea-functionalised ionic liquids to extract metal ions
from aqueous solution [21][22]. Thiol-functionalised ionic liquids have been shown to
stabilise gold and platinum nanoparticles [15][16], as have nitrile-functionalised ionic
liquids with palladium nanoparticles, which also exhibit catalytic activity in various
CÀC coupling reactions [14][23].
It is interesting to note that the first liquid alkene- or allyl-substituted1)
imidazolium salts were reported as early as 1971 [24]. However, at that time, the
1
)
Allyl ˆ prop-2-enyl.
ꢂ 2005 Verlag Helvetica Chimica Acta AG, Zürich

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liquid nature of these compounds was not appreciated and was, in part, attributed to
their deliquescent nature. As yet, no extensive study of ionic liquids bearing an alkene
functionality has been reported, although it has been shown that 1-allyl-3-methyl-
imidazolium chloride can be used as solvent for cellulose acetylation [25]. In addition, a
series of allyl-functionalised imidazolium halides were prepared, and their conductiv-
ities, viscosities, and thermal properties were investigated, indicating that the
introduction of an N-allyl group effectively suppresses crystallisation [26].
We have recently reported the synthesis of an ionic liquid comprised of a
functionalised fluoroborate anion and an alkene-substituted imidazolium cation [2g].
Here, we describe the synthesis and characterisation of a series of ionic liquids
incorporating the allyl functionality, together with some nascent reactions that they
undergo, indicating that these compounds are useful synthons to a wide range of other
functionalised ionic liquids.
Results and Discussion. ± Synthesis and Characterisation. The synthetic route used
to prepare the allyl-functionalised imidazolium salts 1 ± 8 is illustrated in Scheme 1. The
1-methyl- or 1-allyl-substituted 1H-imidazol-3-ium compounds 1 and 2, respectively,
‡
have been prepared previously [26]. Ion-exchange reaction of 1 or 2 with Na BFÀ4 and
‡
Na BPhÀ4 in acetone [27] afforded the salts 3 ± 6. Compound 3 can also be prepared by a
halide-free strategy (Method B in the Exper. Part) via methylation of 1-allylimidazole
‡
with trimethyloxonium tetrafluoroborate (Me3O BFÀ4 ) [28]. Salts 1 ± 4 are liquid at
room temperature, with low melting points; compounds 5 and 6 are solid at ambient
temperature. Presumably due to their higher symmetry, the melting points of the bis-
functionalised ionic liquids 2 and 4 are higher than those of the mono-functionalised
compounds 1 and 3, which is in keeping with previous observations [29].
Scheme 1
‡
‡
a) Allyl bromide (1equiv.), MeOH, r.t., 5 d. b) Na BF4À (1equiv.), acetone, r.t., 48 h. c) Na BPhÀ4 , acetone, r.t.,
48 h. d) [PdCl2] (0.5 equiv.), CH2Cl2, r.t., 2 d. e) AIBN, MeCN, 808, 1 0 h.

Helvetica Chimica Acta ± Vol. 88 (2005)
667
Salts 1 ± 6 were characterised by means of electrospray-ionisation mass spectrom-
1
etry (ESI-MS), IR, and H- and 13C-NMR spectroscopy. The positive-ion ESI mass
spectra of 1, 3 and 5, and of 2, 4, and 6 exhibited parent peaks at m/z 123 and 149,
‡
respectively, corresponding to the expected organic molecular ions (M ). In negative-
ion mode, the bromide, tetrafluoroborate, and tetraphenylborate counter-ions were
identified at m/z 79/81, 87, and 319, respectively. In keeping with previous observations
[14], aggregates composed of the anions and cations are present in more-concentrated
samples, but, upon dilution, essentially only the parent ions were observed with
significant relative intensities. The IR spectra of 3 ± 6 contained stretches between 3050
and 3100 cmÀ1 that correspond to ˆCÀH vibrations, and the CˆC stretch was observed
1
at ca. 1645 cmÀ1. The H- and 13C-NMR spectra of 3 ± 6 were as expected, with little
change in the spectra as the anion is varied.
In CH2Cl2 solution, [PdCl2] reacted with 2 equiv. of 1 or 2 to form the mixed-halide
complexes 7 or 8, respectively (Scheme 1). These complexes were isolated as dark-red
solids (at room temperature). They are air-stable, but slowly decompose in H2O and
alcoholic media. Both compounds are poorly soluble in chlorinated solvents such as
CHCl3 or CH2Cl2 , but are soluble in coordinating solvents such as MeCN. Complex 7
has a melting point of 1348. Complex 8, despite its higher molecular symmetry, already
melts at 588 and may, therefore, be a ꢀtrueꢁ ionic liquid ± based on the commonly
accepted definition [30]. The flexibility of the four allyl side chains probably contribute
to the low melting point of this compound.
The solid-state structures of compounds 5, 6, and 7 were established by means of
single-crystal X-ray analyses. Crystals suitable for X-ray diffraction were grown at
room temperature from acetone/H2O (for 5 and 6) or from MeCN/Et2O (for 7).
Representations of the structures are shown in Figs. 1 ± 3; key bond distances and
angles are provided in Table 1.
There is some conformational disorder in the allyl moieties of 5 and 7, both C(5)
and C(6) being distributed over two positions2). Furthermore, there is disorder in the
Fig. 1. X-Ray crystal structure of compound 5 (ORTEP plot; ellipsoids drawn at the 50% probability level)
2
)
Arbitrary atom numbering (see Fig. 1).

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Helvetica Chimica Acta ± Vol. 88 (2005)
Fig. 2. X-Ray crystal structure of compound 6 (ORTEP plot; ellipsoids drawn at the 50% probability level)
anion of 7, the position of the bromide being partially occupied by chloride (and vice
versa).
Comparable structures of allyl-imidazolium cations are known, and their bonding
parameters are similar to those observed in 5, 6, and 7 [31]. In all of these structures,
bond lengths and angles of the imidazolium ring are basically identical within
experimental error. The imidazolium ring is essentially planar, with no atom deviating
from the least-squares plane by more than 0.0062 Š. Even atoms C(4) and C(7) deviate
only slightly from that plane, except for compound 6. In the latter, the C(4)-atom lies
0.512 Š above the imidazolium plane. In 6, the two CˆC moieties display almost
identical bond distances: 1.301(2) and 1.303(2) Š, one of the double bonds being
basically parallel to, the other perpendicular to the imidazolium ring. In both
compounds 5 and 6, there is a weak CÀH ´´´ p contact between the acidic H(1)-atom
and the negative p-cloud of one of the rings of the [BPh4]À anion (H(1) ´´´ C(10) ± C(15)
centroids of 3.019 and 2.722 Š, resp.). Furthermore, in compound 5, there is weak p-
stacking interaction between the imidazolium and one Ph ring (centroid ± centroid
distance ˆ 3.77 Š).
In complex 7, the Pd-ion resides at a centre of inversion. The complex is square-
planar, with typical PdÀX (X ˆ Cl, Br) bond lengths and angles. The halide atoms are
involved in extensive H-bonding to symmetry-related cations (six close contacts
< 3 Š).

Helvetica Chimica Acta ± Vol. 88 (2005)
669
Fig. 3. X-Ray crystal structure of compound 7 (ORTEP plot; ellipsoids drawn at the 50% probability level). The
atoms marked with asterisks (*) are symmetry-related (À x, À y, À z ‡ 2).
Table 1. Key Bond Lengths (Š) and Angles (8) for Compounds 5 ± 7 and 9
5
6
7
9
C(1)ÀN(1)
C(1)ÀN(2)
C(2)ÀN(1)
C(3)ÀN(2)
C(2)ÀC(3)
N(1)ÀC(4)
N(2)ÀC(7)
C(5)ÀC(6)
C(8)ÀC(9)
PdÀN(1)
1.323(3)
1.328(2)
1.328(2)
1.374(2)
1.376(2)
1.343(2)
1.482(2)
1.470(2)
1.301(2)
1.303(2)
±
1.30(2)
1.35(2)
1.40(2)
1.39(2)
1.37(2)
1.48(2)
1.46(2)
)
1.325(3)
1.341(4)
1.379(4)
1.374(4)
1.351(4)
±
±
±
1.320(3)
1.378(3)
1.372(3)
1.337(3)
1.478(3)
1.466(3)
a
a
)
±
±
±
±
±
±
±
±
2.103(2)
2.4389(3)
±
106.4(2)
±
±
PdÀBr(1)
±
±
2.401(2)
2.350(3)
109(1)
)
±
PdÀCl(1)
N(1)ÀC(1)ÀN(2)
C(4)ÀC(5)ÀC(6)
C(7)ÀC(8)ÀC(9)
108.0(1)
123.4(2)
128.0(2)
a
a
)
±
a) Disordered.
Chemical Reactivity of Ionic Liquids. Attempts to polymerise the mono-function-
alised ionic liquids 1, 2, and 7 by means of a known free-radical-initiator procedure [32]
were unsuccessful. The reaction of 7 with ꢀ2,2'-azobis(isobutyronitrile)ꢁ (AIBN) in
refluxing MeCN led, after 10 h, to the formation of 9. The crystalline compound,
investigated by single-crystal X-ray diffraction, was identified as trans-palladium(II)-
bis(methylimidazole) dibromide (Fig. 4). The structure of the corresponding dichlor-
ide has been published previously [33]. Again, the Pd-atom resides at the centre of
symmetry and is almost perfectly square-planar, with N(1)ÀPd(1)ÀBr(1) angles of
89.92(7) and 90.08(7)8. The dihedral angle between the plane of the imidazole ring and
the square plane around Pd is 131.98. The PdÀN distance is slightly elongated (2.103(2)
vs. 2.011(4) Š) due to the higher electron density at Pd, arising from the less-

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Helvetica Chimica Acta ± Vol. 88 (2005)
Fig. 4. X-Ray crystal structure of the Pd complex 9 (ORTEP plot; ellipsoids drawn at the 50% probability level).
The atoms marked with asterisks (*) are symmetry-related (À x, À y ‡ 1, À z ‡ 1)
electronegative Br-atoms. All other bonding parameters are identical within exper-
imental error to those of the chloro analogue [33].
In the crystal, molecules of 9 form parallel stacks, the distance between the
molecules being 5.3852(5) Š (Fig. 5). There are no inter- or intramolecular H-bonds
below 3 Š to the Br-atoms. The relatively high melting point of 9, 2498, is, thus, a
reflection of Van der Waals and pÀp stacking interactions.
Fig. 5. Crystal packing in the Pd complex 9
Additional spectroscopic and analytical data of 9 were in full agreement with the
solid-state structure. The 1H-NMR spectrum of 9 showed the imidazolium H-atoms at
d(H) 8.14, 7.20, and 7.16, and the Me group at d(H) 3.72. The formation of 9
presumably results from radical reactions initiated by AIBN, which leads to the
elimination of the allyl group of 7.
Addition reactions to side chains of allyl-functionalised compounds represent an
important route to a wide range of novel, potential ionic-liquid imidazolium salts. To
illustrate the versatility of this approach, compound 1 was reacted with benzene in the

Helvetica Chimica Acta ± Vol. 88 (2005)
671
presence of trifluoromethanesulfonic acid (CF3SO3H; ꢀtriflic acidꢁ), following a
literature protocol [34]. This reaction afforded the adduct 10 (Scheme 2). The positive-
‡
and negative-ion ESI mass spectra of 10 showed parent peaks at m/z 201( M ) and 149
1
(CF3SOÀ3 ). The H-NMR spectrum exhibited a multiplet at d(H) 3.27 (benzylic H-
atom) and a doublet at 1.33 (3J ˆ 7.0 Hz, Me). In addition, characteristic resonances for
the Ph ring H-atoms were observed at d(H) 7.21± 7.34.
Scheme 2
Hydrogenation reactions in ionic liquids have been extensively investigated [35],
and the solubility of elemental H2 gas in various ionic liquids has been determined [36].
However, as far as we know, the hydrogenation of functionalised ionic liquids has not
been reported. Accordingly, we investigated the hydrogenation of 1 and 3 in the
presence of Wilkinsonꢁs catalyst. In the neat ionic liquid, no reaction was observed after
48 h according to NMR analysis. This is possibly due to suppression of the catalyst by
bromide present in 1 as the counter-ion or, in 3, as an impurity. However, other factors
cannot be fully ruled out. Inhibition or reduction of catalytic activity due to halide
contamination of ionic liquids has been noted previously [37]. Upon 50% dilution (v/v)
of 3 with CD3OD, and at a temperature of 608 and a pressure of 100 bar H2,
hydrogenation took place rapidly3). The high-pressure 13C-NMR spectra of the starting
material and the hydrogenated product, i.e., 3-butyl-1-methyl-1H-imidazol-3-ium
tetrafluoroborate (not shown), are depicted in Fig. 6. The resonances of 3 at d(C)
131.4 (d, ˆCH) and 121.6 (t, ˆCH2) were no longer present in the product; instead,
new aliphatic signals were observed at d(C) 23.4 (t, CH2) and 9.9 (q, Me).
Experimental Part
General. All chemicals were purchased from Acros and were used without further purification. Compounds
1 and 2 were prepared according to the literature [2g]. All reactions were performed under an inert atmosphere
of dry N2, using standard Schlenk techniques, in anh. solvents distilled immediately prior to use. IR Spectra were
recorded on a Perkin-Elmer FT-IR 2000 spectrophotometer; in cmÀ1. NMR spectra were recorded at 208 on a
Bruker DRX-400 spectrometer (100/400 MHz for 13C and 1H, resp.); chemical shifts d in ppm relative to SiMe4
(ˆ0 ppm) as external standard. Electrospray-ionisation (ESI) mass spectra were recorded on a ThermoFinni-
gan LCQ Deca-XP-Plus quadrupole ion-trap instrument on samples diluted with MeOH or H2O. Samples were
infused with a syringe pump directly into the source at a rate of 5 ml/min, and the spray voltage was set to 5 kV,
the capillary temp. being 508 [38]; ESI-MS signals are reported in m/z. Elemental analyses were carried out at
the EPFL, Switzerland.
1-Methyl-3-(prop-2-enyl)-1H-imidazol-3-ium Tetrafluoroborate (3). Method A. A suspension of 1 (6.09 g,
30 mmol) and Na BFÀ4 (3.62 g, 33 mmol) in acetone (80 ml) was stirred at r.t. for 48 h. The mixture was filtered,
‡
and the solvent was removed in vacuo: 5.86 g (93%) of 3. Pale-yellow, waxy solid. IR: 3155, 3117 (n(arom.
CÀH)); 3088 (n(ˆCÀH)), 2978 (n(aliph. CÀH)); 1599 (n(CˆC)). 1H-NMR ((D6)acetone): 9.04 (s, 1 H); 7.70
3
)
The half-life for the reduction was less than 1h under the conditions employed.

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Helvetica Chimica Acta ± Vol. 88 (2005)
Fig. 6. High-pressure 13C-NMR spectra (100 MHz) of a solution of compound 3 recorded a) before and b) after
hydrogenation at 100 bar H2 pressure (see Exper. Part)
(s, 1H); 7.65 ( s, 1H); 6.75 ( m, 1H); 5.85 ( s, 1H); 5.25 ( m, 2 H); 3.99 (s, 3 H). 13C-NMR ((D6)acetone)): 136.2;
‡
129.4; 124.3; 114.6; 114.4; 52.3; 35.7. ESI-MS (pos./neg.; H2O)4): 123 (M )/87 [BF4]À. Anal. calc. for
C7H11BF4N2 (209.98): C 40.03, H 5.28, N 13.34; found: C 40.02, H 5.25, N 13.26.
Method B. 1-(Prop-2-enyl)-1H-imidazole (5 ml) was added dropwise to a rapidly stirred suspension of
trimethyloxonium tetrafluoroborate (1equiv.) in hexane (20 ml) at À 788 over a period of 10 min. After the
initial vigorous gas evolution had ceased, the mixture was allowed to warm to r.t. The product was washed with
Et2O (3 Â 25 ml) and dried in vacuo to afford 3 quantitatively. IR: 3158, 3120, 3089, 2977, 1577. 1H-NMR
((D6)acetone): 8.64 (s, 1H); 7.47 ( s, 1H); 7.43 ( s, 1H); 6.02 ( m, 1H); 5.38 ( s, 1H); 4.78 ( m, 2 H); 3.93 (s, 3 H).
‡
13C-NMR ((D6)acetone)): 136.1; 130.6; 124.0; 122.6; 121.1; 51.5; 35.7. ESI-MS (pos./neg.; H2O)4): 123 (M )/87
[BF4]À. Anal. calc. for C7H11BF4N2 (209.98): C 40.03, H 5.28, N 13.34; found: C 40.10, H 5.26, N 13.41.
1,3-Bis(prop-2-enyl)-1H-imidazol-3-ium Tetrafluoroborate (4). A mixture of 2 (6.87 g, 30 mmol) and
‡
Na BFÀ4 (3.62 g, 33 mmol) in acetone (80 ml) was stirred at r.t. for 48 h. The resulting solid was filtered off, and
the solvent was removed in vacuo: 6.37 g (90%) of 4. Pale-yellow, waxy solid. IR: 3145, 3077, 2941, 2852, 1654.
1H-NMR ((D6)acetone): 9.18 (s, 1 H); 7.71 (s, 2 H); 6.18 (m, 2 H); 5.41( m, 4 H); 5.01( m, 4 H). 13C-NMR
‡
((D6)acetone): 136.2; 129.5; 123.4; 121.8; 52.2. ESI-MS (pos./neg.; H2O)4): 149 (M )/87 ([BF4]À). Anal. calc.
for C9H13BF4N2 (236.02): C 45.80, H 5.55, N 11.87; found: C 45.75, H 5.47, N 11.76.
1-Methyl-3-(prop-2-enyl)-1H-imidazol-3-ium Tetraphenylborate (5). A suspension of 1 (6.09 g, 30 mmol)
‡
and Na BPhÀ4 (11.29 g, 33 mmol) in acetone (80 ml) was stirred at r.t. for 48 h. The mixture was filtered, and
H2O (5 ml) was added to the filtrate, from which 5 crystallized over a period of 3 d: 11.8 g (89%). Colourless
crystals. M.p. 145.18. IR: 3137, 3082, 3053, 3033, 2999, 2945, 1599. 1H-NMR ((D6)acetone): 8.20 (s, 1 H); 7.48 (s,
2 H); 7.36 (t, 8 H); 6.93 (t, 8 H); 6.77 (t, 4 H); 6.02 (m, 1H); 5.37 ( m, 1H); 4.75 ( m, 2 H); 3.82
(s, 3 H). 13C-NMR ((D6)acetone): 164.8; 164.3; 163.8; 163.3; 136.4; 136.1; 131.0; 126.0; 125.2; 122.3; 121.4; 120.5;
‡
51.4; 35.9. ESI-MS (pos./neg.; H2O)4): 123 (M )/319 ([BPh4]À). Anal. calc. for C31H31N2B (442.40): C 84.16, H
7.06, N 6.33; found: C 85.30 H 7.10, N 6.26. X-Ray crystal structure: see Fig. 1 and Table 1.
1,3-Bis(prop-2-enyl)-1H-imidazol-3-ium Tetraphenylborate (6). A mixture of 2 (6.87 g, 30 mmol) and
‡
Na BPhÀ4 (11.29 g, 33 mmol) in acetone (80 ml) was stirred at r.t. for 48 h. The resulting solid was filtered off.
H2O (5 ml) was added to the filtrate, which led to crystallisation of 6 within 3 d: 12.4 g (88%). Colourless
‡
4
)
M Refers to the molecular ion of the cationic part (substituted imidazolium) of the salt.

Helvetica Chimica Acta ± Vol. 88 (2005)
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crystals. M.p. 170.28. IR: 3139, 3088, 2999, 2945, 1631. 1H-NMR ((D6)acetone): 8.17 (s, 1H); 7.41( s, 2 H); 7.38 (t,
8 H); 7.01( t, 8 H); 6.87 (t, 4 H); 5.98 (m, 1H); 5.37 ( m, 1H); 4.68 ( m, 2 H). 13C-NMR ((D6)acetone): 164.9;
164.2; 163.6; 163.3; 136.3; 135.9; 131.0; 124.8; 123.2; 122.3; 120.4; 120.1; 51.4. ESI-MS (pos./neg.; H2O)4): 149
‡
(M )/319 ([BPh4]À). Anal. Calc. for C33H33N2B (468.44): C 84.61, H 7.10, N 5.98; found: C 84.64, H 7.10, N 5.86.
X-Ray crystal structure: see Fig. 2 and Table 1.
Palladium Complex 7. To a soln. of 1 (406 mg, 1.0 mmol) in CH2Cl2 (5.0 ml) was added [PdCl2] (177 mg,
1.0 mmol). The mixture was stirred at r.t. for 2 d, during which time a dark-red suspension formed. The resulting
solid was collected by filtration, washed with CH2Cl2 (2 Â 2 ml), and dried in vacuo: 553 mg (95%) of 7. Dark-
red solid. M.p. 1348 (dec.). IR: 3138 (arom. CÀH); 3091, 3071 (ˆCÀH); 2973 (aliph. CÀH); 1632 (CˆC).
1H-NMR ((D6)DMSO): 9.16 (s, 1 H); 7.65 (m, 2 H); 5.91( m, 1H); 5.19 ( m, 1H); 4.77 ( m, 2 H); 3.78 (s, 3 H).
13C-NMR ((D6)-DMSO): 136.5; 132.1; 124.1; 121.7; 120.7; 51.4; 36.4. Anal. calc. for C14H22Br2Cl2N4Pd (583.49):
C 28.82, H 3.80, N 9.60; found: C 28.80, H 3.78, N 9.69. X-Ray crystal structure: see Fig. 3 and Table 1.
Palladium Complex 8. Prepared from 2 (458 mg, 1.0 mmol) and [PdCl2] (177 mg, 1.0 mmol) in analogy to 7.
Dark-red solid. Yield: 553 mg (95%). M.p. 588. IR: 3124 (arom. CÀH); 3091( ˆCÀH); 2981, 2960 (aliph.
CÀH); 1644 (CˆC). 1H-NMR ((D6)DMSO): 9.28 (s, 1H); 7.78 ( s, 2 H); 6.02 (m, 2 H); 5.35 (m, 4 H); 5.27 (m,
4 H). 13C-NMR ((D6)DMSO): 136.7; 132.2; 123.5; 122.1; 51.4. Anal. calc. for C18H26Br2Cl2N4Pd (635.56): C
34.02, H 4.12, N 8.81; found: C 34.08, H 4.18, N 8.79.
Palladium Complex 9. To a soln. of 7 (291.5 mg, 0.5 mmol) in MeCN (10 ml) was added ꢀ2,2'-
azobis(isobutyronitrile)ꢁ (AIBN; 2 mg), and the mixture was stirred at 808 for 10 h. Upon standing at r.t. for
24 h, orange cubic crystals of 9 formed, which were collected by filtration: 20 mg (9%). M.p. 2498 (dec.). IR:
3138 (arom. CÀH); 2951(aliph. C ÀH). 1H-NMR ((D6)DMSO): 8.14 (s, 1 H); 7.20 (s, 1 H); 7.16 (s, 1H); 3.72 ( s,
1H). 13C-NMR ((D6)DMSO): 137.7; 131.2; 124.2; 32.4. Anal. calc. for C8H12Br2N4Pd (430.44): C 22.32, H 2.81,
N 13.01; found: C 22.08, H 2.84, N 13.09. X-Ray crystal structure: see Figs. 4 and 5, and Table 1.
1-Methyl-3-(2-phenylpropyl)-1H-imidazol-3-ium Trifluoromethanesulfonate (10). To a suspension of 1
(2.03 g, 10 mmol) in benzene (20 ml) was added an excess of CF3SO3H (ꢀtriflic acidꢁ; 30 ml), and the mixture
was heated to reflux for 6 h. After cooling to 08, the mixture was neutralized (pH 7.1) with aq. 40% NaOH soln.,
and extracted with CH2Cl2 (3 Â 30 ml). The combined org. phases were washed with sat. aq. NH4Cl soln., dried
(MgSO4), and concentrated to afford 10: 0.8 g (22%). Pale-yellow liquid. IR: 3151 (arom. CÀH), 2969 (aliph.
CÀH), 1574; 1256, 1163, 1029. 1H-NMR (CD3CN): 8.32 (s, 1 H); 7.37 (s, 1 H); 7.35 (s, 1H); 7.30 ± 7.34 ( m, 2 H);
7.21± 7.27 ( m, 3 H); 4.25 ± 4.40 (m, 2 H); 3.76 (s, 3 H); 3.27 (m, 1 H); 1.32 (d, 3 H). 13C-NMR (CD3CN): 137.8;
124.8; 123.3; 123.1; 122.1; 119.4; 118.5; 51.5; 36.5; 31.8; 13.7. 19F-NMR (CD3CN): À 79.7. ESI-MS (pos./neg.;
‡
CH2Cl2)4): 201( M )/149 ([CF3SO3]À). Anal. calc. for C14H17F3N2O3S (350.58): C 47.99, H 4.89, N 7.99; found: C
47.68, H 5.00, N 7.89.
Hydrogenation Studied by High-Pressure NMR Spectroscopy. Samples were prepared under O2-free
conditions using Schlenk techniques. CD3OD was purchased from Cambridge Isotope Laboratories.
Hyrogenation reactions were carried out in situ in a medium-pressure sapphire NMR tube (10 mm) [39]
under 100 bar of H2 pressure. 13C-NMR Spectra were recorded on a Bruker DRX-400 spectrometer at 100 MHz.
X-Ray Crystal-Structure Analyses. Suitable crystals were obtained at ambient temperature from acetone/
H2O 10 :1 (for 5 and 6), from MeCN/Et2O 10 :1 (for 7), and from CH2Cl2 (for 9). The single crystals were
mounted on a KUMA KM4/Sapphire CCD diffractometer. Data reduction was performed with CrysAlis RED
[40]. Structure solution and refinement were performed with the SHELX97 software package [41], and
graphical representations of the structures were made with ORTEP32 [42]. Structures were solved by direct
methods and successive interpretation of the difference Fourier maps, followed by full-matrix least-squares
refinement (against F2). All non-H-atoms were refined anisotropically. H-atoms were placed in their
geometrically generated positions, and refined with a riding model. An adsorption correction (DELABS) was
applied for 7 and 9. In 5, atoms C(5) and C(6) were split over two positions, with an occupancy factor of 0.62(2)
for site A. In 7, only C(6) was split over two positions (occupancy factor 0.51(2) for site A). The disorder for both
Cl- and Br-atoms was solved for both positions, which led to the occupancy factor, followed by anisotropic
refinement. The crystallographic data have been deposited with the Cambridge Crystallographic Data Centre
(CCDC) as deposition numbers CCDC-257944 to -257947. Copies of the data can be obtained, free of charge, by
application to CCDC, 12 Union Road, Cambridge, CB21EZ, UK (fax: ‡ 44-1223-336033; e-mail: data_
request@ccdc.cam.ac.uk), or via the internet (http://www.ccdc.cam.ac.uk/products/csd/request). Details of the
structure determinations of compounds 5 ± 7 and 9 are summarised in Table 2.
We thank the Swiss National Science Foundation and EPFL for financial support.

674
Helvetica Chimica Acta ± Vol. 88 (2005)
Table 2. Crystallographic Data and Details of Structure Determinations
5
6
7
9
Formula
Mr
C31H31BN2
442.39
C33H33BN2
468.42
C14H22Br2Cl2N4Pd C8H12Br2N4Pd
583.48 430.44
Crystal size [mm]
T [K]
0.10 Â 0.15 Â 0.18 0.11 Â 0.14 Â 0.17 0.05 Â 0.10 Â 0.12 0.09 Â 0.10 Â 0.12
140
140
140
140
Crystal system
Space group
a [Š]
b [Š]
c [Š]
monoclinic
P 21/n
9.6409(8)
17.647(2)
15.3633(8)
90
monoclinic
P 21/n
10.8209(6)
17.478(1)
13.8763(9)
90
monoclinic
P 21/n
8.870(2)
12.110(4)
9.908(4)
90
monoclinic
P 21/c
5.3852(5)
11.815(1)
9.7595(8)
90
a [8]
b [8]
g [8]
V [Š3]
104.137(7)
90
2534.6(3)
4
90.804(5)
90
2624.2(3)
4
101.98(3)
90
1041.1(6)
2
98.139(7)
90
614.73(9)
2
Z
Density [Mg/m3]
V Range [8]
1.159
1.186
1.861
2.325
3.07 ꢀ Vꢀ 25.03
3.16 ꢀ Vꢀ 25.03
3.27 ꢀ Vꢀ 25.03
3.45 ꢀ Vꢀ 25.03
m [mmÀ1
]
0.067
0.068
4.989
7.983
Reflections measured
Goodness-of-fit on F2
14982
0.819
15423
0.918
6349
1.132
3355
1.135
Unique reflections [I > 2s(I)] 4250
4385
1844
1084
Rint
0.0607
0.0374
0.0422
0.0272
Final R1, wR2[I > 2s(I)]
R (all data)
Largest diff. peak and hole
0.0422, 0.0641
0.1285, 0.0810
0.146, À 0.170
0.0362, 0.0776
0.0627, 0.0852
0.157, À 0.226
0.0419, 0.1050
0.0542, 0.1133
1.082, À 0.563
0.0207, 0.0529
0.0215, 0.0533
0.418, À 0.711
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Received December 22, 2004