N,N′-Di(alkyloxy)imidazolium Salts: New patent-free ionic liquids and NHC precatalysts

Article abstract of DOI:10.1515/znb-2007-0301

I-Hydroxyimidazole-3-oxides (2-H, 2-Me) were alkylated with (RO) ₂SO₂ (R = Me, Et) to give the new 1,3-di(alkyloxy) imidazolium cations which were isolated as hexafluorophosphates. Ion metathesis yielded new hydrophobic ionic liquids

Full text of DOI:10.1515/znb-2007-0301

N,N'-Di(alkyloxy)imidazolium Salts:
New Patent-free Ionic Liquids and NHC Precatalysts
Gerhard Lausa, Alexander Schwa¨rzlera,b, Philipp Schustera, Gino Bentivoglioa,
Michael Hummela, Klaus Wursta, Volker Kahlenbergc, Thomas Lo¨rtinga,
Johannes Schu¨tzd, Paul Peringera, Gu¨nther Bonnb, Gerhard Nauere, and
Herwig Schottenbergera
a Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck,
6020 Innsbruck, Austria
b Institute of Analytical Chemistry and Radiochemistry, University of Innsbruck,
6020 Innsbruck, Austria
c Institute of Mineralogy and Petrography, University of Innsbruck, 6020 Innsbruck, Austria
d Institute of Pharmacy, University of Innsbruck, 6020 Innsbruck, Austria
e ECHEM Competence Center of Applied Electrochemistry, Viktor-Kaplan-Straße 2,
2270 Wiener Neustadt, Austria
Reprint requests to Prof. Dr. Herwig Schottenberger. Fax: (+43) 512 507 2934.
E-mail: herwig.schottenberger@uibk.ac.at
Z. Naturforsch. 2007, 62b, 295 – 308; received December 7, 2006
Dedicated to Prof. Helgard G. Raubenheimer on the occasion of his 65th birthday
1-Hydroxyimidazole-3-oxides (2-H, 2-Me) were alkylated with (RO)2SO2 (R = Me, Et) to give the
new 1,3-di(alkyloxy)imidazolium cations which were isolated as hexafluorophosphates. Ion metathe-
sis yielded new hydrophobic ionic liquids (bis(trifluoromethanesulfonyl)imides, tris(pentafluoroeth-
yl)trifluorophosphates). Bromination afforded 2-bromo derivatives which were converted to Ni and
Pd N-heterocyclic carbene complexes by oxidative insertion. Fifteen crystal structures were deter-
mined by X-ray diffraction. The N-alkyloxy groups are twisted out of the imidazole ring plane and
adopt either syn or anti conformations in the solid state.
Key words: Carbene, Imidazolium Salt, Ionic Liquid, NHC, Nickel, Palladium
Introduction
organometallic ILs [9]. In particular, new hydropho-
bic ionic liquids, containing bis(trifluoromethanesulf-
onyl)imide (‘triflimide’) [10] or tris(pentafluoroethyl)
trifluorophosphate (‘FAP’) anions [11, 12], are promis-
ing reaction and extraction media.
Imidazoles and, in particular, imidazolium salts are
extremely important and versatile compounds. In re-
cent years, they have found manifold uses in the fields
of ionic liquids (ILs), as electrolytes, and as carbene
ligand precursors for transition metal complexes. As a
consequence, tremendous commercial interest in this
group of compounds has developed which is reflected
by the immense number of patents granted. Needless
to say that these patents exhibit varying degrees of in-
ventive ingenuity and originality.
On the other hand, imidazolium salts are easily con-
verted to N-heterocyclic carbenes (‘NHC’) [13 – 18]
which are valuable ligands for homogeneous catalysts
for cross-coupling reactions [19]. Typically, the con-
version to carbene complexes is effected either by met-
allation, especially lithiation, and subsequent transmet-
allation [20 – 22], or by oxidative insertion [23 – 26].
Therefore, imidazolium-based ILs could serve both
as solvents and catalysts [27 – 32]. A catalytically
active organometallic IL has been described previ-
ously [33].
Liquid imidazolium salts have been long known
[1 – 5] and praised for industrial applications due to
their low volatility, although their observed antiseptic
properties [1] and toxicity [6] make their postulated
environmental benignity appear questionable. Never-
In this work we present a new class of imidazolium
theless, their potential is huge, and exciting develop- salts and patent-free ionic liquids as well as 2-halogen
ments can be expected such as task-specific [7, 8] and derivatives thereof and derived NHC complexes.
0932–0776 / 07 / 0300–0295 $ 06.00 © 2007 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
Table 1. Conductivity σ and viscosity η of 1,3-dimethoxy-
imidazolium bis(trifluoromethanesulfonyl)imide (3b).
Results and Discussion
T [◦C] σ [mS cm−1] η [mPa s] T [◦C] σ [mS cm−1] η [mPa s]
1-Hydroxyimidazole-3-oxides 1 and 2 were readily
prepared [34, 35] and alkylated to give the not yet de-
scribed 1,3-di(alkyloxy)imidazoliumsalts which could
be conveniently purified by precipitation as hexaflu-
30
40
50
60
4.3
6.9
9.7
94.3
60.9
42.0
29.9
70
80
90
16.3
20.0
24.0
22.1
16.9
13.8
12.9
orophosphates from aqueous solution, as exemplified
by compounds 3a, 4a, and 5a (Scheme 1). These salts
were then transformed into new ILs by ion metathesis.
Thus, the hydrophobic triflimides 3b, 4b, 5b, and 6b
were obtained in high purity by reaction of the cor-
responding hexafluorophosphates with lithium triflim-
ide. Treatment of 3a and 4a with potassium FAP af-
forded the hydrophobic salts 3c and 4c containing the
FAP anion. Compound 4c was act◦ually crystalline but
with a melting point below 100 C still qualified as
an IL. These anions impart highly desirable proper-
ties on the ILs, such as low residual water content, hy-
drolytic and electrochemical stability, and low viscos-
ity. The IL 3b was subjected to more detailed investiga-
tion; it exhibited a relatively large electrochemical win-
dow (from −1.5 to +0.5 V versus Ag/AgCl by cyclic
voltammetry). Dynamic viscosity (η) and specific con-
ductivity (σ) data at different temperatures are sum-
marized in Table 1. For comparison, 1,3-diethylimid-
azolium triflimide feat◦ures an η of 35 cP and a σ
of 8.5 mS cm−1 at 20 C [10]. Thermal stability was
assessed by differential scanning calorimetry, and the
IL 3b was found to be stable up to 160 ◦C.
Furthermore, the triflimides are valuable intermedi-
ates for further ion exchange when other pathways are
not viable. Thus, sulfuric acid liberated from 3b the
corresponding amine and gave the water-soluble hy-
drogen sulfate which, in turn, could be converted to
the phenyltrifluoroboronate 3d and tert-butylethynyl-
trifluoroboronate 3e which also qualify as ILs. Anal-
ogous treatment of 3b with hydrobromic acid yielded
the bromide 3f which was transformed into the per-
chlorate 3g by the silver salt method.
The bromination of imidazolium cations reportedly
occurs in the 4,5-positions [36], but since bromina-
tion of 1-hydroxyimidazole-3-oxide gave the 2-bromo
derivative [37], we anticipated that in our case halo-
genation would also yield the 2-halogenoimidazo-
lium salts as functionalized building blocks for further
derivatization. Thus, addition of bromine to an aque-
ous solution of 1,3-dialkoxyimidazolium salts 3a or 5a
resulted at first in precipitation of an adduct of yet
unknown composition which upon further addition of
Scheme 1.
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297
bromine and sodium carbonate proceeded to give the
desired 2-bromoimidazolium salts 6a and 7a. The re-
action did not work well when acetate was used as a
buffer. The analogous reaction with iodine was not suc-
cessful, but iodination took place when iodine chloride
was used instead to afford the crystalline 2-iodo com-
pound 8. The novel azide 9 was obtained by reaction
of the bromo compound 6a with sodium azide. Aryl-
azides can act as ligands on their own in azido-metal
complexes or as sources of the nitrene fragment [38],
as precursors for iminophosphines [39] and iminoimi-
dazolines and derived complexes [40 – 42].
Unexpectedly, even the polar parent compound, 1-
hydroxyimidazole-3-oxide (1), liquefied on contact
with bis(trifluoromethanesulfonyl)amine to give the
Brønsted-acidic IL 1,3-dihydroxyimidazolium triflim-
ide (10), a novel protic hydrophobic IL. To mention
a discovery which is not exactly within the scope of
this paper but which we like to report anyway, we
found that the highly polar 1,3-diaminoimidazolium
chloride [43] also yielded a hydrophobic IL on con-
tact with lithium bis(trifluoromethanesulfonyl)imide.
Another fortunate observation in the course of this
work which we like to disclose here was that by
simple combination of commercially available solids,
i. e. 1-ethyl-3-methylimidazolium chloride and potas-
sium benzenetrifluoroboronate, a new IL was pro-
duced. It is also noteworthy that a few liquid 1-alkyl-
oxy-3-alkylimidazoliumsalts, e. g. 1-methoxy-3-meth-
ylimidazolium iodide, 1-ethoxy-3-methylimidazolium
tosylate, or 1-benzyloxy-3-butylimidazolium bromide,
have been observed earlier [44]. Finally, imidazo-
Scheme 2.
dently, the second carbene must originate from another
Ni(0)/Ni(II) oxidation cycle and replace a phosphine
molecule. Similar substitution of phosphine by NHC
has been observed in related Ni complexes [46]. Pre-
sumably, the electron-rich carbene further facilitates
the ligand exchange.
Reaction of Pd(tmdba)2 with the carbene-forming
lium-based ILs with alkyloxyalkyl substituents have oxidant 6a afforded the binuclear palladium com-
been reported [45] but, to the best of our knowledge, plex 12. Again, this dimer is not the primary product of
the present di(alkyloxy)imidazolium ions have not yet the insertion since four equivalents of 6a are required
been described, or claimed in the patent literature. In to contribute the necessary bromide ions. The fate of
preliminary experiments, we also looked at the pos- the other imidazolium units is unclear at this point. An
sible use of bulky silyloxy- and trityloxy-substituted analogous complex with 1,3-dialkylimidazolin-2-ylid-
imidazolium salts for the synthesis of free carbenes. ene ligands has been described previously [30].
These results will be communicated in due course.
In contrast, Ni(cod)2 in the presence of 1,2-bis(di-
Of course, the 2-bromoimidazoliumsalts lend them- phenylphosphino)ethane gave the expected product. In
selves to the construction of metal-NHC complexes by this case, it is likely that one cod ligand was replaced
oxidative addition to metal(0) precursors (Scheme 2). by the bidentate phosphine followed by oxidative addi-
Thus, Ni(cod)2 reacted with one equivalent of 6a in the tion of 6a, and the Ni-NHC complex 13 was obtained.
presence of two equivalents of triphenylphosphine[24] However, the compound Ni(dppe)Br2 was isolated as
to afford the mixed nickel(II) bis(carbene)/phosphine a byproduct and characterized by X-ray crystal struc-
complex 11. As a result of multiple ligand exchange, ture determination. Therefore, bromide/phosphine lig-
the reaction is obviously more complex than a sole and scrambling must have been involved as well. The
stoichiometric insertion of the cod/phosphine system structure of a CH2Cl2 solvate of this byproduct has
which would lead to a monocarbene species. Evi- been reported earlier [47].
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
Fig. 5. The molecular structure of the cation in 5a show-
ing the atom numbering scheme. Displacement ellipsoids are
drawn at the 50 % probability level.
Fig. 1. The molecular structure of the cation in 3a (syn con-
formation) showing the atom numbering scheme. Displace-
ment ellipsoids are drawn at the 50 % probability level.
Fig. 6. The molecular structure of the cation in 6a show-
ing the atom numbering scheme. Displacement ellipsoids are
drawn at the 50 % probability level.
Fig. 2. The molecular structure of the cation in 3a (anti con-
formation) showing the atom numbering scheme. Displace-
ment ellipsoids are drawn at the 50 % probability level.
Fig. 3. The molecular structure of the cation in 4a show-
ing the atom numbering scheme. Displacement ellipsoids are
drawn at the 50 % probability level.
Fig. 7. The molecular structure of the ionic components in 6b
showing the atom numbering scheme. Displacement ellip-
soids are drawn at the 50 % probability level.
Fig. 8. The molecular structure of the cation in 7b show-
ing the atom numbering scheme. Displacement ellipsoids are
drawn at the 50 % probability level.
Fig. 4. The molecular structure of the ionic components in 4c
showing part of the atom numbering scheme. Displacement
ellipsoids are drawn at the 50 % probability level.
be determined by X-ray diffraction. Key bond lengths
in 1,3-di(alkyloxy)imidazolium cations are: N–O typi-
˚
˚
cally 1.36 to 1.38 A, C1–N 1.32 to 1.33 A, C2–N 1.36
˚
˚
˚
The catalytic activity of these NHC complexes has to 1.37 A, C2–C3 1.33 to 1.36 A, C–Br 1.82 A. Typ-
yet to be tested.
Due to the high crystallinity of the complexes and
their precursors, a number of crystal structures could
ical values of N–C–N angles are around 105◦. Some
of these parameters are slightly different in the carbene
˚
˚
complexes: C1–N 1.32 to 1.35 A, C2–N 1.37 to 1.38 A,
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
299
Fig. 9. Packing diagram of the asymmetric unit of 8 at (a) r. t. and (b) at −40 ◦C.
N–C–N 101◦ (with Ni) and 103◦ (with Pd). The in the FAP salt 4c displayed again the syn geome-
tetrafluoroborate and FAP ions in 5c and 4c are disor- try (MeO-plane angles of 81.8◦ and 72.8◦) (Fig. 4).
dered, and the hexafluorophosphateions are disordered The 1,3-diethoxyimidazolium hexafluorophosphate 5a
in most of the structures. Interestingly, we observed also exhibited the syn conformation (CH2O-plane an-
two distinct conformations of the alkyloxy groups with gles of 84.0◦ and 78.7◦) (Fig. 5). The 2-bromo deriva-
respect to the imidazolium ring plane. They are twisted tive 6a crystallized as the anti conformer (MeO-plane
out of the plane in either syn or anti conformations. angles of 89.5◦ and 68.3◦) (Fig. 6). The related triflim-
We were fortunate to obtain single crystal data of two ide 6b showed two ion pairs in the asymmetric unit,
polymorphs of 1,3-dimethoxyimidazolium hexafluo- with both cations in anti orientation (MeO-plane an-
rophosphate 3a, one adopting the syn conformation gles of 81.4◦, 81.8◦, and 79.3◦, 87.3◦). The S–N bond
with MeO-plane angles of 79.9◦ and 82.6◦ (Fig. 1) and lengths are between 1.542 and 1.608 A. The S–N–
˚
the other anti with respective angles of 88.8◦ and 63.2◦ S angles are 124.5◦ and 124.9◦ (Fig. 7). In crystals
(Fig. 2). X-ray powder diffraction data of three batches of 2-bromo-1,3-diethoxyimidazolium bromide 7b the
of 3a confirmed the dominance of the syn conformer substituents are also anti oriented (CH2O-plane angles
in the bulk material, though in varying proportions. of 80.3◦ and 70.9◦) (Fig. 8). Surprisingly, a temper-
By temperature-dependent XRPD it was demonstrated ature dependence of the conformation was observed
that the conformation does not change between 173 in crystals of the 2-iodo compound 8. The asymme-
and 233 K (the temperatures at which the single crys- tric unit contains three cations, all of which adopt syn
tals were measured). The analogous 2-methyl com- conformations at 25 ◦C (MeO-plane angles in cation A:
pound 4a, however, occurred only in anti conforma- 88.9◦, 87.3◦; cation B: 85.2◦, 83.9◦; cation C: 88.2◦,
tion (MeO-plane angles of 82.0◦ and 85.2◦) (Fig. 3), 85.3◦) (Fig. 9a), whereas one of the cations◦(cation B)
since no phase transition between 133 and 273 K switches to an anti conformation at −40 C (MeO-
could be observed by DSC and XRPD. The cation plane angles in cation A: 87.6◦, 86.8◦; cation B: 85.1,
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
Fig. 10. The molecular structure of the cation in 9 show-
ing the atom numbering scheme. Displacement ellipsoids are
drawn at the 50 % probability level.
Fig. 12. The molecular structure of the dinuclear palladium-
carbene complex 12 showing part of the atom numbering
scheme. Displacement ellipsoids are drawn at the 50 % prob-
ability level. Hydrogen atoms and the solvent molecule are
omitted for clarity.
Fig. 11. The molecular structure of the cationic nickel-
carbene complex 11 showing part of the atom numbering
scheme. Displacement ellipsoids are drawn at the 50 % prob-
ability level. Hydrogen atoms and the anion are omitted for
clarity.
84.2◦; cation C: 88.3◦, 85.4◦) (Fig. 9b). In the crystal
structure of the azide 9, the C–N–N and N–N–N angles
have values of 115.8◦ and 170.3◦, the methoxy groups
are syn oriented (MeO-plane angles of 88.7◦ and 66.5◦)
(Fig. 10).
Fig. 13. The molecular structure of the cationic nickel-
carbene complex 13 showing part of the atom numbering
scheme. Displacement ellipsoids are drawn at the 50 % prob-
ability level. Hydrogen atoms and the anion are omitted for
clarity.
In the molecular structure of the Ni-NHC com-
plex 11, the carbene ligands occupy trans positions.
The square planar configuration around the central
Ni atom is noticeably distorted. Thus, the C–Ni–C
angle is 170.6◦ and P–Ni–Br is 173.3◦, whereas
both C–Ni–Br angles are 89.5◦, and C–Ni–P angles
are 90.0◦ and 92.1◦, respectively. The mean distances
in a dihedral angle between the two carbenes of 15.8◦.
˚
The Ni–C bond lengths are 1.899 and 1.893 A, Ni–P
˚
˚
is 2.181 A, and Ni–Br is 2.341 A. The methoxy groups
of the imidazolylidene rings adopt syn conformations
and are rotated out of the ring planes by 72.4◦, 89.9◦
and 75.6◦, 83.6◦, respectively (Fig. 11).
˚
of the ligands from the least-squares plane are 0.14 A
(carbene C atoms on one side, P and Br on the other
side of the plane). As in related complexes of this
type [48], the torsion angles between the ligand plane
In contrast, the µ-Br-bridged dimeric Pd-NHC com-
and the carbene planes are 81.8◦ and 82.4◦, resulting plex 12 possesses a center of inversion and, therefore,
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301
the four-membered Pd–Br–Pd–Br ring is perfectly pla- General procedure for the preparation of compounds 3a, 4a,
and 5a
nar. The Pd–Br–Pd and Br–Pd–Br angles within the
ring are 91.4◦ and 88.6◦, respectively. The Pd atoms
coordinate in square planar geometry with mean devia-
A mixture of dimethyl sulfate (15.2 mL, 0.16 mol)
and freshly prepared 1-hydroxyimidazole-3-oxide (8.0 g,
0.08 mol) was stirred at ambient temperature for 1 h. Then
NaHCO3 (6.7 g, 0.08 mol) was added and stirring was con-
tinued for 12 h. Addition of H2O (20 mL) and more stirring
yielded a clear solution to which NH4PF6 (13.0 g, 0.08 mol)
was added. The precipitate was ultrasonicated for 1 h, fil-
tered, and recrystallized from MeOH to give 3a as a col-
orless powder (16.0 g; 73 %). The compounds 4a (from 1-
hydroxy-2-methylimidazole-3-oxide), and 5a (using diethyl
sulfate) were prepared on a smaller scale with similar yields.
Crystals of the imidazolium hexafluorophosphates suitable
for X-ray diffraction studies were obtained by slow evapora-
tion of MeOH solutions.
˚
tions of the ligands from the plane of only 0.03 A. The
˚
˚
˚
Pd–C distance is 1.956 A, Pd–Br is 2.405 A, and the
Pd–µ-Br bond lengths are 2.450 and 2.516 A. The ring
plane and the ligand plane are slightly tilted by 0.92◦.
The imidazolylidene rings are almost perpendicular
to the molecular reference plane with a torsion angle
of 89.8◦. Again, the methoxy groups adopt syn con-
formations with out-of-plane angles of 80.1◦ and 85.0◦
(Fig. 12).
The Ni-NHC complex 13 again presents an approxi-
mately square planar environment around the Ni atom.
Distances to the coordinating ligands are Ni–C 1.893,
1,3-Dimethoxyimidazolium hexafluorophosphate (3a):
˚
Ni–Br 2.327, Ni–P 2.146 and 2.202 A. Mean devia-
m. p. 83 – 84 C. – 1H NMR (300 MHz, [D6]DMSO): δ =
◦
˚
tion from the ligand plane is 0.07 A, angles C–Ni–P1
4.26 (s, 6H), 8.29 (d, J = 2.1 Hz, 2H), 10.29 (t, J = 2.1 Hz,
1H). – IR (neat): ν = 3163, 1556, 1455, 1015, 944, 827, 718,
and Br–Ni–P2 are 173.3◦ and 175.6◦, respectively.
Other angles are C–Ni–Br 92.4◦, C–Ni–P2 91.8◦,
P1–Ni–Br 90.8◦, and the P–Ni–P bite angle of the
chelating dppe ligand is 85.3◦. The five-membered
chelate ring is nearest to a C7-envelope with
the C6 and C7 atoms lying out of the coordina-
706, 582, 555 cm−1
.
1,3-Dimethoxy-2-methylimidazolium
hexafluorophos-
phate (4a): m. p. 128 – 129 ◦C. – 1H NMR (300 MHz,
[D6]DMSO): δ = 2.59 (s, 3H), 4.16 (s, 6H), 8.19 (s, 2H). –
IR (neat): ν = 3155, 1595, 1460, 1444, 1117, 964, 944, 820,
733, 709, 650, 555 cm−1
.
˚
tion plane by 0.31 and 0.89 A. The torsion an-
1,3-Diethoxyimidazolium hexafluorophosphate (5a): m. p.
gle between the imidazolylidene ring and the lig-
and plane is 82.8◦, and the methoxy groups adopt a
syn orientation (MeO-plane angles 86.1◦ and 88.7◦)
(Fig. 13).
In summary, new imidazole-based ILs and NHC
complexes were prepared by facile and inexpensive
processes. The 1,3-di(alkyloxy)imidazoliumsalts open
a plethora of possibilities in the fields of IL research
and catalysis. Although the synthetic potential has not
yet been fully exploited and the experimental proce-
dures have not yet been fully optimized, it is clear
that a new chapter in imidazole chemistry has been
written.
◦
1
99 – 102 C. – H NMR (300 MHz, [D6]DMSO): δ = 1.32
(t, J = 7.0 Hz, 6H), 4.49 (q, J = 7.0 Hz, 4H), 8.26 (s, 2H),
10.26 (s, 1H). – 13C NMR (75 MHz, [D6]DMSO): δ =
13.0 (2C), 78.4 (2C), 117.9 (2C), 130.4. – IR (neat): ν =
3155, 1478, 1446, 1395, 1119, 1006, 810, 743, 726, 598,
554 cm−1
.
General procedure for the preparation of compounds 3b, 4b,
5b, and 6b
A mixture of 3a (11.0 g, 0.04 mol) and lithium bis
(trifluoromethanesulfonyl)imide (11.5 g, 0.04 mol) in H2O
(70 mL) was ultrasonicated for 1 h and then extracted with
CH2Cl2. The extract was dried with anhydrous Na2SO4
and filtered. After removal of the solvent the residue was
dried by means of a vacuum pump to yield 3b as a col-
orless oil (12.8 g; 78 %). The compounds 4b, 5b, and 6b
were prepared accordingly on a smaller scale with similar
yields.
Experimental Section
The starting 1-hydroxyimidazole-3-oxides 1 and 2 were
prepared according to [34]. The crystal structures were deter-
mined using Nonius KappaCCD and STOE IPDS 2 diffrac-
tometers. The experimental conditions and crystallographic
1,3-Dimethoxyimidazolium bis(trifluoromethanesulfonyl)
data are listed in Table 2. NMR spectra were recorded with imide (3b): n2D0 = 1.4240.
–
1H NMR (300 MHz,
Bruker AC 300 and Varian Unity 500 spectrometers. 1H and [D6]DMSO): δ = 4.25 (s, 6H), 8.28 (s, 2H), 10.29 (s, 1H). –
13C NMR spectra were referenced to internal TMS, whereas 13C NMR (75 MHz, [D6]DMSO): δ = 69.5 (2C), 117.1 (2C),
31P and 19F spectra were calibrated with external 85 % 119.6 (q, JC−F = 320 Hz, 2C), 129.5. – IR (neat): ν = 3138,
H3PO4 and CCl3F, respectively. IR spectra were obtained 1666, 1556, 1457, 1346, 1328, 1177, 1132, 1052, 1013, 943,
with a Nicolet 5700 FT instrument.
845, 789, 612, 569, 510 cm−1
.
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
α
ω
α
φ
ω
α
φ
α
α
ω
α
φ
σ
σ
∆ρ
µ
β
θ
∆ρ
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303
ω
α
φ
α
α
ω
α
φ
α
α
σ
σ
∆ρ
µ
α
β
γ
θ
∆ρ
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
Table 2 (continued).
Compound
CCDC no.
11
629565
12
629566
13
629567
Chemical formula
Mr
C
28H31BrF6N4NiO4P2
C10H16Br4N4O4Pd2·C4H10
O
C31H32BrF6N2NiO2P3
810.12
802.13
862.83
Crystal syst., space group
monoclinic, P21/n
12.2927(6)
18.5705(8)
14.8605(8)
93.707(4)
3385.3(3)
4
1.574
1.92
1624
monoclinic, C2/c
19.9922(3)
8.5719(3)
15.6670(6)
104.477(2)
2599.62(14)
4
2.205
7.561
1640
monoclinic, C2/c
34.2172(2)
9.1512(3)
23.0333(4)
105.637(2)
6945.4(3)
8
1.549
1.911
3280
˚
a [A]
˚
b [A]
˚
c [A]
β [deg]
3
˚
V [A ]
Z
Dx [g cm−3
]
µ [mm−1
]
F(000) [e]
Crystal form, color
Crystal size [mm3]
Diffractometer
plate, yellow-brown
0.36×0.26×0.10
STOE IPDS 2
Mo-Kα
prism, red
0.40×0.10×0.07
Nonius KappaCCD
MoKα
prism, yellow
0.4×0.35×0.08
Nonius KappaCCD
MoKα
Radiation type
Data collection method
Temperature [K]
θmax [deg]
h, k, l Ranges
Absorption correction
Measured reflections
Independent reflections
Observed reflections [I ≥ 2σ(I)]
Refinement on
rotation method
173(2)
24.7
14, 21, 17
multi-scan
20258
φ- and ω-scans
φ- and ω-scans
233(2)
233(2)
25.00
26.0
23, 10, −18 → 17
−42 → 39, 11, 28
none
7111
none
21029
5675 (Rint = 0.035)
4730
2288 (Rint = 0.0414)
1912
6807 (Rint = 0.0351)
5654
F2
F2
F2
Data, restraints, parameters
5675, 0, 419
R1 = 0.0406,
wR2 = 0.0839
R1 = 0.0542,
wR2 = 0.0884
1.06
2288, 0, 134
R1 = 0.0321,
wR2 = 0.0766
R1 = 0.0416,
wR2 = 0.0796
1.05
6807, 0, 454
R1 = 0.0343,
wR2 = 0.0806
R1 = 0.0459,
wR2 = 0.0853
1.03
R [F2 ≥ 2σ(F2)]
R (all data)
Goodness of fit
∆ρmax, ∆ρmin [e A
−3
˚
]
1.02, −0.30
0.87, −0.67
0.48, −0.37
1,3-Dimethoxy-2-methylimidazolium bis(trifluorometh- 118.3 (2C), 119.5 (q, JC−F = 322 Hz, 2C). – IR (neat): ν =
anesulfonyl)imide (4b): n2D0 = 1.4250. – 1H NMR (300 MHz, 3135, 1556, 1457, 1446, 1345, 1327, 1177, 1132, 1048, 937,
[D6]DMSO): δ = 2.62 (s, 3H), 4.19 (s, 6H), 8.22 (s, 2H). – 789, 739, 611, 600, 569, 510 cm−1
.
13C NMR (75 MHz, [D6]DMSO): δ = 7.6, 68.7 (2C), 115.6
(2C), 119.6 (q, JC−F = 320 Hz, 2C), 138.9. – IR (neat): ν =
General procedure for the preparation of compounds 3c and
4c
3153, 1594, 1460, 1434, 1389, 1347, 1180, 1133, 1052, 979,
957, 831, 741, 711, 603, 569, 505 cm−1
.
1,3-Diethoxyimidazolium bis(trifluoromethanesulfonyl)-
imide (5b): n2D0 = 1.4250. – 1H NMR (300 MHz, [D6]
DMSO): δ = 1.32 (t, J = 7.0 Hz, 6H), 4.49 (q, J = 7.0 Hz,
4H), 8.25 (d, J = 1.9 Hz, 2H), 10.26 (t, J = 1.9 Hz, 1H). –
13C NMR (75 MHz, [D6]DMSO): δ = 13.0 (2C), 78.4 (2C),
117.9 (2C), 119.6 (q, JC−F = 320 Hz, 2C), 130.4. – IR (neat):
ν = 3142, 1554, 1479, 1393, 1347, 1328, 1179, 1133, 1052,
A mixture of 3a (0.55 g, 0.002 mol) and potassium tris
(pentafluoroethyl)trifluorophosphate (0.97 g, 0.002 mol) in
H2O (5 mL) was ultrasonicated for 1 h and then extracted
with CH2Cl2. The extract was dried with anhydrous Na2SO4
and filtered. After removal of the solvent the residue was
dried by means of a vacuum pump to yield 3c as a colorless
oil (0.96 g; 84 %). The compound 4c (from 4a) was prepared
accordingly on a smaller scale with similar yield.
1006, 844, 789, 740, 611, 599, 569, 558, 509 cm−1
.
2-Bromo-1,3-dimethoxyimidazolium bis(trifluorometh-
1,3-Dimethoxyimidazolium tris(pentafluoroethyl)trifluor-
anesulfonyl)imide (6b): The triflimide crystallized from the ophosphate (3c): n2D0 = 1.3730. – 1H NMR (300 MHz,
biphasic mixture before extraction. Yield: 99 %. – nD20
=
[D6]DMSO): δ = 4.25 (s, 6H), 8.28 (d, J = 2.1 Hz, 2H),
1.4469 (subcooled melt). – M. p. 28 – 30 ◦C. – 1H NMR 10.32 (t, J = 2.1 Hz, 1H). – IR (neat): ν = 3165, 1556, 1459,
(300 MHz, [D6]DMSO): δ = 4.23 (s, 6H), 8.48 (s, 2H). – 1296, 1181, 1126, 1098, 1014, 961, 944, 803, 760, 712, 616,
13C NMR (75 MHz, [D6]DMSO): δ = 69.0 (2C), 116.9, 580 cm−1
.
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
305
1,3-Dimethoxy-2-methylimidazolium tris(pentafluoroeth- CH2Cl2. The organic layer was dried over Na2SO4 and the
yl)trifluorophosphate (4c): The FAP salt crystallized from solvent removed using a rotary evaporator. The product was
Et2O. M. p. 75 – 76 ◦C. – 1H NMR (300 MHz, [D6]DMSO): finally dried by means of a vacuum pump to give 3e as col-
δ = 2.63 (s, 3H), 4.20 (s, 6H), 8.23 (s, 2H). – 19F NMR orless crystals (140 mg, 23 %). M. p. 62 – 64 ◦C. – 1H NMR
(470 MHz, [D6]DMSO): δ = −42.5 (md, JF−P = 894 Hz, (300 MHz, [D6]DMSO): δ = 1.07 (s, 9H), 4.25 (s, 6H), 8.27
1F), −77.7 (m, 3F), −79.3 (m, 6F), −85.7 (md, JF−P
=
(d, J = 2.0 Hz), 10.24 (t, J = 2.0 Hz). – 13C NMR (75 MHz,
894 Hz, 2F), −113.8 (md, JF−P = 85 Hz, 2F), −114.3 (md, [D6]DMSO): δ = 26.9, 31.6 (3C), 69.6 (2C), 117.1 (2C),
JF−P = 99 Hz, 4F). – IR (neat): ν = 3168, 1462, 1294, 1210, 129.5. – IR (neat): ν = 3129, 2966, 1554, 1456, 1352, 1254,
1180, 1135, 1121, 1098, 954, 802, 762, 722, 617, 581, 531, 1195, 1142, 1043, 986, 939, 890, 816, 732, 703, 616, 581,
495 cm−1
.
506 cm−1
.
1,3-Dimethoxyimidazolium bromide (3f): A mixture of
the triflimide 3b (2.34 g, 5.7 mmol), aqueous HBr (47 %,
0.98 g, 5.7 mmol) and Et2O (5 mL) was stirred for 15 h
at r. t. Then, H2O was added, and the solution was repeat-
edly extracted with Et2O (8 × 10 mL). The aqueous phase
was taken to dryness to give the crude product 3f as a hygro-
scopic oil which was dried in vacuum. – 1H NMR (300 MHz,
[D6]DMSO): δ = 4.25 (s, 6H), 8.33 (d, J = 2.0 Hz, 2H), 10.38
(t, J = 2.0 Hz, 1H). – 13C NMR (75 MHz, [D6]DMSO): δ =
69.6 (2C), 117.1 (2C), 129.6. – IR (neat): ν = 3066, 2947,
Preparation of potassium (tert-butyl-ethynyl)trifluorobor-
onate: (3,3-Dimethyl-1-butynyl)di-(iso-propoxy)borane
(2.10 g, 10.0 mmol) was added dropwise to a solution of
KHF2 (4.60 g, 58.9 mmol) in H2O (12 mL). A white pre-
cipitate formed immediately. The suspension was stirred
for 15 min. The crude product was isolated by filtration,
washed with cold methanol, and recrystallized from CH3CN
(10 mL) to yield 1.57 g (84 %). – IR (neat): ν = 2969, 2869,
1456, 1223, 1066, 953, 890 cm−1
.
Solution of 1,3-dimethoxyimidazolium hydrogensulfate:
1,3-Dimethoxyimidazolium bis(trifluoromethylsulfonyl)imi-
de 3b (5.89 g, 14.4 mmol) and concentrated H2SO4 (5.5 mL)
were combined in a 50 mL flask. The evolving bis(trifluoro-
methylsulfonyl)amine was removed by vacuum distillation
1552, 1452, 1229, 1144, 1010, 939, 702, 580 cm−1
.
1,3-Dimethoxyimidazolium perchlorate (3g): AgClO4
(0.59 g, 2.9 mmol) was added to a solution of the crude bro-
mide 3f (0.60 g, 2.9 mmol) in H2O (15 mL), the mixture was
ultrasonicated and filtered. The filtrate was taken to dryness,
and the residue was recrystallized from MeOH to give 3g as a
colorless powder. M. p. 238 – 242 ◦C. – 1H NMR (300 MHz,
[D6]DMSO): δ = 4.24 (s, 6H), 8.29 (d, J = 2.0 Hz, 2H), 10.31
(t, J = 2.0 Hz, 1H). – 13C NMR (75 MHz, [D6]DMSO): δ =
69.6 (2C), 117.1 (2C), 129.6. – IR (neat): ν = 3163, 3143,
3122, 3042, 1555, 1469, 1073, 1010, 936, 773, 721, 705, 619,
◦
at 70 C. After several h the remaining solution was cooled
in an ice bath and H2O was added to a volume of 20 mL.
The resulting 0.72 M solution was used for further anion ex-
change.
1,3-Dimethoxyimidazolium phenyltrifluoroboronate (3d):
A portion of the above solution of 1,3-dimethoxyimidazo-
lium hydrogensulfate (5.0 mL, 3.6 mmol) was diluted with
H2O, and NaHCO3 (370 mg, 4.4 mmol) was added. After
gas evolution had ceased, potassium phenyltrifluoroboron-
ate [49 – 51] (760 mg, 4.1 mmol) was introduced. Complete
dissolution was achieved by ultrasonication. The resulting
aqueous solution was extracted with CH2Cl2. The organic
layer was dried over Na2SO4 and the solvent removed using
a rotary evaporator. The product was finally dried by means
of a vacuum pump to yield 3d as a colorless liquid (260 mg,
26 %). nD17 = 1.4809. – 1H NMR (300 MHz, [D6]DMSO):
δ = 4.23 (s, 6H), 7.08 (m, 3H), 7.33 (m, 2H), 8.25 (s, 2H),
10.25 (s, 1H). – 13C NMR (75 MHz, [D6]DMSO): δ = 69.5
(2C), 117.0 (2C), 125.0, 126.3 (2C), 129.5, 131.3 (2C). – IR
(neat): ν = 3127, 2953, 1554, 1453, 1351, 1191, 1137, 1058,
528, 516 cm−1
.
1,3-Diethoxyimidazolium tetrafluoroborate (5c): Potas-
sium imidazole-1,3-dioxide (2.61 g, 18.9 mmol; prepared
from 1 and KOMe in MeOH) was suspended in dry CH2Cl2
(15 mL). A solution of triethyloxonium tetrafluoroborate
(7.18 g, 37.8 mmol) in dry CH2Cl2 (40 mL) was added
dropwise. The mixture gradually turned yellow, and the sus-
pended reagent dissolved. Simultaneously, a voluminous pre-
cipitate was formed. The solid was removed by filtration, and
the solvent was evaporated to give 5c as a brown oil which
◦
crystallized on standing (3.76 g, 82 %). M. p. 40 – 46 C. –
1H NMR (300 MHz, [D6]DMSO): δ = 1.32 (t, J = 7.0 Hz,
6H), 4.49 (q, J = 7.0 Hz, 4H), 8.24 (d, J = 1.8 Hz, 2H), 10.24
(t, J = 1.8 Hz, 1H). – 13C NMR (75 MHz, [D6]DMSO): δ =
12.9 (2C), 78.3 (2C), 117.8 (2C), 130.3. – IR (neat): ν =
3146, 2992, 1555, 1477, 1393, 1049, 1005, 967, 856, 791,
1015, 938, 754, 706, 615, 597, 570, 512 cm−1
.
1,3-Dimethoxyimidazolium (tert-butyl-ethynyl)trifluoro-
boronate (3e): A portion of the above solution of 1,3-di-
methoxyimidazolium hydrogensulfate (3.0 mL, 2.2 mmol)
was diluted with H2O, and NaHCO3 (260 mg, 3.1 mmol)
was added. After gas evolution had ceased, potassium (tert-
butyl-ethynyl)trifluoroboronate (410 mg, 2.2 mmol) was in-
troduced. Complete dissolution was achieved by ultrasoni-
727, 596, 520 cm−1
.
General procedure for the preparation of compounds 6a and
7a
1,3-Dimethoxy-1H-imidazolium hexafluorophosphate 3a
cation. The resulting aqueous solution was extracted with (3.19 g, 11.7 mmol) was suspended in a mixture of H2O
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306
G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
(10 mL) and MeOH (5 mL). Bromine (0.60 mL, 11.7 mmol) (75 MHz, [D6]DMSO): δ = 68.9 (2C), 113.9 (2C), 132.0.
was added at once, and the mixture was stirred for 24 h. – IR (neat): ν = 3180, 3160, 2161, 1602, 1262, 1071, 825,
To the resulting yellow solution with a dark red precipitate 555 cm−1
.
Na2CO3 (1.23 g, 11.7 mmol) was added. Gas evolution was
observed. Subsequently, another equivalent of bromine was
added (0.60 mL) and stirring was continued for 24 h. Dur-
ing the first five minutes, more gas evolved and the red solid
dissolved. Simultaneously, a voluminous yellow precipitate
formed. The solid was filtered off, washed with H2O (10 mL)
and dissolved in hot MeOH (30 mL). The product was pre-
cipitated by addition of Et2O (250 mL) and collected by fil-
tration after cooling the suspension to −18 ◦C to yield 6a as
a white powder (3.1 g, 75 %). Compound 7a was prepared
accordingly from 5a on a smaller scale with similar yield.
A small amount of the related bromide 7b was isolated after
concentrating the aqueous filtrate and washing the resulting
precipitate repeatedly with H2O.
1,3-Dihydroxyimidazolium bis(trifluoromethanesulfonyl)
imide (10): 1-Hydroxyimidazole-3-oxide (1.50 g, 14.9
mmol) was added to bis(trifluoromethanesulfonyl)amine
(4.20 g, 14.9 mmol) in a Schlenk vessel. After stirring for 2 h,
the resulting liquid was filtered to give 10 as a colorless clear
liquid (5.6 g, 98 %). n2D0 = 1.4185. – 1H NMR (300 MHz,
[D6]DMSO): δ = 7.83 (2H, s), 9.73 (1H, s). – 13C NMR
(75 MHz, [D6]DMSO): δ = 118.4 (2C), 119.8 (2C, q, J =
322 Hz), 128.3. – IR (neat): ν = 3522, 3156, 1471, 1341,
1184, 1125, 1050, 1013, 792, 743, 727, 594, 569 cm−1
.
Bis(1,3-dimethoxyimidazolin-2-ylidene)(triphenylphos-
phine)bromonickel(II) hexafluorophosphate (11): A solution
of bis(cyclooctadiene)nickel(0) (113 mg, 0.41 mmol) and
triphenylphosphine (215 mg, 0.82 mmol) in dry THF was
stirred for 20 min at r. t. 2-Bromo-1,3-dimethoxyimidazo-
lium hexafluorophosphate (6a; 145 mg, 0.41 mmol) was
added and stirring was continued for 3 h. The yellow pre-
cipitate was collected by filtration, washed with Et2O and
dried in vacuum. It was redissolved in CH2Cl2, and sin-
gle crystals were grown by vapor diffusion with pentane.
M. p. 202 – 205 ◦C. – 1H NMR (300 MHz, [D6]DMSO): δ =
4.25 (s, 12H), 7.06 (s, 4H), 7.3 – 7.6 (m, 15H). – 31P NMR
(121 MHz, [D6]DMSO): δ = 22.0. – IR (neat): ν = 3168,
2-Bromo-1,3-dimethoxyimidazolium hexafluorophosphate
(6a): m. p. 148 – 149 ◦C. – 1H NMR (300 MHz, [D6]DMSO):
δ = 4.23 (s, 6H), 8.50 (s, 2H). – 13C NMR (75 MHz,
[D6]DMSO): δ = 69.0 (2C), 117.0, 118.3 (2C). – IR (neat):
ν = 3170, 3149, 1557, 1458, 1441, 1049, 941, 837, 733, 650,
556 cm−1
.
2-Bromo-1,3-diethoxyimidazolium hexafluorophosphate
◦
1
(7a): m. p. 84 – 86 C. – H NMR (300 MHz, [D6]DMSO):
δ = 1.36 (t, J = 7.0 Hz, 6H), 4.49 (q, J = 7.0 Hz, 4H), 8.47
(s, 2H). – IR (neat): ν = 3135, 3113, 1546, 1466, 1386,
2961, 1436, 1261, 1094, 1063, 836, 693, 557 cm−1
.
1345, 1108, 1044, 999, 852, 729, 615 cm−1
.
trans-[Bis(1,3-dimethoxyimidazolin-2-ylidene)]dibromo-
µ,µꢀ-dibromo-dipalladium(II) diethylether solvate (12):
2-Bromo-1,3-dimethoxyimidazolium hexafluorophosphate
6a (22 mg, 0.06 mmol) was added to a solution of bis-
(3, 5, 3ꢀ, 5ꢀ-tetramethoxydibenzylideneacetone) palladium(0)
(50 mg, 0.06 mmol) in CH2Cl2 (2 mL) under argon. The
mixture was stirred at r. t. overnight. The black precipitate
was removed by centrifugation, and the supernatant was
taken to dryness. The residue was extracted twice with Et2O
(2 × 1 mL) to remove the tmdba ligand. The remainder was
dissolved in CH2Cl2 (1 mL), and red crystals were grown
by vapor diffusion of Et2O. Yield: 10 mg (19 %). M. p.
106 – 110 ◦C (dec). – 1H NMR (300 MHz, [D6]DMSO): δ =
1.01 (t, J = 7.0 Hz, 6H), 3.28 (q, J = 7.0 Hz, 4H), 4.22 (s,
12H), 7.32 (s, 4H). – IR (neat): ν = 3151, 3119, 3078, 2968,
2937, 2859, 1594, 1557, 1446, 1432, 1149, 1113, 1030, 949,
2-Bromo-1,3-diethoxyimidazolium bromide (7b): m. p.
145 – 148 ◦C. – IR (neat): ν = 3016, 2994, 2963, 2888, 1552,
1472, 1387, 1115, 1039, 1006, 864, 777, 757, 637 cm−1
.
2-Iodo-1,3-dimethoxyimidazolium hexafluorophosphate
(8): A solution of ICl in CH2Cl2 (0.73 mL 1.0 M) was
added to a mixture of 3a (0.2 g, 0.7 mmol) in H2O (3 mL)
and CH2Cl2 (3 mL) which was stirred for 3 d at r. t. The
organic layer was separated and the solvent removed. The
residue was treated with Et2O to remove I2, then dissolved
in MeOH, and the product precipitated with Et2O. M. p.
148 – 150 ◦C. – 1H NMR (300 MHz, [D6]DMSO): δ = 4.19
(s, 6H), 8.44 (s, 2H). – 13C NMR (75 MHz, [D6]DMSO):
δ = 68.9 (2C), 117.0, 119.2 (2C). – IR (neat): ν = 3166,
3146, 1455, 1042, 945, 823, 732, 648, 557 cm−1
.
2-Azido-1,3-dimethoxyimidazolium hexafluorophosphate
(9): To a suspension of 2-bromo-1,3-dimethoxyimidazolium
hexafluorophosphate 6a (1.0 g, 2.8 mmol) in acetone (20 mL)
835, 719, 671, 613, 557 cm−1
[1,2-Bis(diphenylphosphino)ethane](1,3-dimethoxyimid-
.
was added NaN3 (0.18 g, 2.8 mmol). After stirring the re- azolin-2-ylidene)bromonickel(II) hexafluorophosphate (13):
action mixture for 72 h at r. t., a yellow solution with a A solution of bis(cyclooctadiene)nickel(0) (98 mg, 0.36
white precipitate was obtained. After addition of anhydrous mmol) and 1,2-bis(diphenylphosphino)ethane (142 mg,
Na2SO4 the solution was filtered and the solvent evaporated. 0.36 mmol) in dry THF was stirred for 20 min at r. t. 2-
The brown solid residue was recrystallized from MeOH Bromo-1,3-dimethoxyimidazolium hexafluorophosphate 6a
(2 mL) and washed with Et2O to yield 9 as colorless crys- (126 mg, 0.36 mmol) was added and stirring was contin-
tals (0.20 g, 22 %). M. p. 92 ◦C (dec). – 1H NMR (300 MHz, ued overnight. The yellow precipitate was removed by fil-
[D6]DMSO): δ = 4.22 (6H, s), 8.18 (2H, s). – 13C NMR tration and found to be Ni(dppe)Br2. Slow evaporation of
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G. Laus et al. · N,Nꢀ-Di(alkyloxy)imidazolium Salts
307
the filtrate yielded single crystals of complex 13. M. p. 228 – dried in vacuum. Yield: 7.28 g (56 %). – n2D0 = 1.4953. –
230 ◦C. – 1H NMR (300 MHz, [D8]THF): δ = 2.1 – 2.3 (m, 1H NMR (300 MHz, CD2Cl2): δ = 1.30 (t, J = 7.0 Hz, 3H),
2H), 2.5 – 2.8 (m, 2H), 4.05 (s, 6H), 7.13 (s, 2H), 7.3 – 7.9 3.59 (s, 3H), 3.90 (q, J = 7.0 Hz, 2H), 7.08 – 7.18 (m, 5H),
(m, 20H). – 31P NMR (121 MHz, [D8]THF): δ = 53.7 (d, 7.46 (d, J = 6.5 Hz, 2H), 8.33 (s, 1H). – 13C NMR (75 MHz,
JP−P = 58 Hz), 67.2 (d, JP−P = 58 Hz). – IR (neat): ν = [D6]DMSO): δ = 14.9, 35.6, 44.5, 121.8, 123.5, 126.0, 127.1
3150, 2962, 1437, 1260, 1099, 1019, 834, 754, 693, 556, 526, (2C), 131.5 (2C), 136.0, 148.7 (broad). – IR (neat): ν = 3154,
492 cm−1
.
3117, 3006, 1571, 1432, 1193, 1168, 945, 752, 707, 647, 621,
1-Ethyl-3-methylimidazolium phenyltrifluoroboronate: 1- 597 cm−1
Ethyl-3-methylimidazolium chloride (7.42 g, 50.6 mmol)
and potassium phenyltrifluoroboronate [49 – 51] (9.31 g,
.
Supplementary material
50.6 mmol) were dissolved in distilled water and the result-
ing mixture was stirred at r. t. for 2 h. Subsequently, this solu-
CCDC 629553 – 629567 contain the supplementary crys-
tion was extracted six times with small portions of CH2Cl2. tallographic data for this paper. These data can be obtained
The organic layer was dried over Na2SO4 and the solvent free of charge from The Cambridge Crystallographic Data
removed using a rotary evaporator. The product was finally Centre via www.ccdc.cam.ac.uk/data request/cif.
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