Fluorinated Unsymmetrical N,N′-Diaryl Imidazolium Salts—New Functionalized NHC-Ligand Precursors

Article abstract of DOI:10.1002/chem.201700624

An efficient and scaled-up synthesis of the imidazol-2-ylidene-based unsymmetrical NHC precursors bearing the sterically demanding hexafluoroisopropylalkoxy group [(CF₃)₂(OR)C?] at the ortho position of the N-aryl substituent was dev

Full text of DOI:10.1002/chem.201700624

A Journal of
Accepted Article
Title: Fluorinated Unsymmetrical N,N'-Diaryl Imidazolium salts - new
functionalized NHC ligand precursors
Authors: Sergey N. Osipov, Maria A. Zotova, Salekh M. Masoud, Artur
K. Mailyan, Ivan V. Ananyev, Sergey E. Nefedov, Andrey F.
Asachenko, and Maxim A. Topchiy
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To be cited as: Chem. Eur. J. 10.1002/chem.201700624
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Fluorinated Unsymmetrical N,N’-Diaryl Imidazolium salts - new
functionalized NHC ligand precursors
Maxim A. Topchiy[a], Maria A. Zotova[a], Salekh M. Masoud[a], Artur K. Mailyan[a,b], Ivan V. Ananyev[a],
Sergey E. Nefedov[c], Andrey F. Asachenko[a] and Sergey N. Osipova*[a]
Abstract: An efficient and scaled-up synthesis of the imidazol-2-
ylidene-based unsymmetrical NHC precursors bearing sterically
demanding hexafluoroisopropylalkoxy-group [(CF3)2(OR)C-] in ortho-
position of N-aryl substituent was developed. The key step of the
method involved transformation of Mes-substituted oxazolinium
tetrafluoroborate salt via the reaction with the corresponding
binucleophilic fluoroalkyl substituted aniline. The subsequent post-
modification of the resulting hydroxyl-containing salt via simple one
step O-alkylation protocol provided access to a new family of
unsymmetrical fluorinated NHC precursors. The latter were further
successfully utilized for the preparation of several novel metal
complexes. The molecular structures of some NHC precursors and
their metal complexes have been unambiguously characterized by
single-crystal X-ray diffraction. A preliminary evaluation of catalytic
activity of palladium complexes was performed on Buchwald-Hartwig
amination reaction. As a result, two PEPPSI-type Pd-complexes
have demonstrated promising activity in alkane solvents.
In this context, the importance of unsymmetrical N-heterocyclic
carbenes (uNHCs) as ligands in metal catalysis is doubtless, as
desymmetrization allows for further fine-tuning. The introduction
of functionality, chelation, chirality, and shielding effects can
influence the catalyst stability, reactivity, and selectivity, thus
motivating the exploration of new tailor-made systems.[5]
Surprisingly, while a plenty of unsymmetrical saturated NHCs
(i.e. imidazolin-2-ylidenes) have been prepared, their
unsaturated analogues (i.e. imidazol-2-ylidenes) are still
essentially limited to unhindered N-substituent moieties,
obviously, due to a lack of synthetic procedures to access
imidazolium salts bearing two different sterically demanding
groups on the N-atoms.[6] As a consequence, only few examples
of the corresponding metal complexes have been described up
to date (Fig. 1). Therefore, given the above considerations,
convenient methodologies allowing practical synthesis of
unsymmetrical N,N’-disubstituted imidazolium salts bearing
hindered aryl groups remain highly desirable.
Introduction
N-Heterocyclic carbenes (NHCs) are important auxiliary ligands
in coordination and organometallic chemistry[1] due to the unique
electronic properties, namely high σ-basicity and low π-acidity,
that often induce enhanced activity in metal-catalyzed
processes,[2] such as C-C and C-N coupling reactions and olefin
metathesis. Imidazolium-derived NHCs with bulky N,N’-diaryl
substituents such as 1,3-dimesityl-2H-imidazol-2-ylidene (IMes)
and 1,3-bis(2,6-diisopropylphenyl)-2H-imidazol-2-ylidene (IPr)
are the most widely employed ligands in homogeneous catalysis.
They represent the ideal platform from which an optimization of
their electronic, steric, and asymmetric properties can be
anticipated. For instance, the outstanding results have been
recently obtained upon formal replacement of the 2,6-
diisopropylphenyl (Dipp) nitrogen substituents by bulkier, flexible
aryl groups[3] or by C2-symmetrical chiral aryl groups.[4]
Figure 1. Unsymmetrically N,N’-diarylsubstituted imidazole-based NHC metal
complexes.
On the other hand, fluorinated compounds have found
widespread applications in the pharmaceutical[7] and medicinal
chemistry[8] or crops[9] and material sciences.[10] Particular
attention is focused on CF3-containing compounds due to the
unique properties of CF3-group (e.g. high electronegativity, steric
hindrance, hydrophobic character), which can dramatically alter
the key physicochemical characteristics such as acidity/basicity
of neighbouring groups, H-bonding ability, electron density
distribution, or conformations to result in more desired properties,
e.g. such as increased lipophilicity or chemical stability.[11]
In the field of metal catalysis, the steric and electronic impact of
NHCs bearing N-fluoroaryl and N-fluoroalkyl groups on catalytic
properties of the corresponding complexes has been studied
mainly in metathesis and cross-coupling reactions.[12] Along with
notable catalytic activity the main advantages were connected
[a]
M.A. Topchiy, Dr. M.A. Zotova, S.M. Masoud, Dr. A.K. Mailyan, Dr.
I.V. Ananyev, Dr. A.F. Asachenko, Prof. Dr. S.N. Osipov
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian
Academy of Sciences
Vavilov str. 28, 119991, Moscow, Russia
E-mail: osipov@ineos.ac.ru
[b]
[c]
Department of Chemistry and Biochemistry
University of California, Santa Barbara, California 93106-9510
Prof. S.E. Nefedov
N. S. Kurnakov Institute of General and Inorganic Chemistry,
119991 Moscow, Leninskij pr. 31, Russia
with remarkable stability and enhanced solubility in common
[13]
Supporting information for this article is given via a link at the end of
the document.
solvents including supercritical CO2
as well as the possibility
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to utilize heavy fluorous separation techniques in the case of Results and Discussion
highly fluorinated N-alkyl chains.[14] One more advantage, found
by Grubbs and co-workers, is a rate acceleration in RCM of
diethyl diallylmalonate arising from a Ru···F interaction between
one ring of a N,N’-bis(2,6-difluorophenyl)imidazol-2-ylidene and
the metal center in the Grubbs II catalyst analogue.[15] This work
has been further extended with studies of synthesis and catalytic
activities of closely related saturated unsymmetrical
analogues.[16]
To the best of our knowledge there are no examples of
unsymmetrical N,N’-diaryl imidazole-based NHC ligands bearing
fluorinated functional groups on one of the N-aryl moiety in the
literature. Thus, taking into account all above reasons, the
development of new effective methods for the preparation of
such ligands, in particular sterically demanding ones, is of
current interest.
An access to unequally 1,3-diaryl-substituted NHCs is still
limited to trivial substitution patterns. In fact, the preparation of
their
corresponding imidazolium
salt
precursors
via
quarternization of N-aryl substituted imidazoles are mainly
restricted to simple aryl halides,[6d,f] hindered alkyl and aryl
halides are more problematic and often impracticable. In 2006
Fürstner et al. developed an original approach based on
heterocyclic interconversion of oxazolinium salts via the reaction
with the corresponding arylamines.[19] However only two
examples of N-Mes, N’-Dipp imidazolium salts were described.
Since that time, surprisingly a few examples of unequally 1,3-
diaryl-substituted imidazolium salts have been synthesized by
this method and utilized for the preparation of the corresponding
metal complexes.[5e, 20, 21] In the present work we for the first time
investigated the reaction of binucleophilic fluorinated arylamine 3
with mesityl-substituted oxazolinium salt 4 and synthesized the
new type of functionalized NHC precursors. The convenient
method for the preparation of 3 has been previously developed
by us from commercially available reagents [17] (Scheme 1).
Figure 2. Synthesis of unsymmetrical CF3-NHC metal complexes.
We have recently elaborated an access to unsymmetrical 1,3-
bis(aryl)-4,5-dihydroimidazolium
salts
bearing
the
Scheme 1. Synthesis of hydroxy-containing salt 5.
hexafluoroisopropylmethoxy group of N-aryl moiety (1, Fig. 2)
and have demonstrated their further potential to be used as the
precursors of the corresponding NHC ligands for the synthesis
of new family of metathesis catalysts.[17] Now we wish to report
on an efficient route to sterically demanding unsymmetrical 1,3-
Thus, we found that the reaction proceeds quite effectively in the
presence of Brönsted acid to give a mixture of the expected
hydroxyl-containing imidazolium salt
5 along with tricyclic
product 6 in a ratio of 10:1 respectively (determined by 19F NMR-
analysis). The formation of salt 6 can be rationalized by the
additional possibility for heterocyclization upon hydroxyl group
under the reaction conditions. Fortunately, we succeeded to
isolate the desired salt 5 in pure form by single crystallization
from CHCl3-ether solvent mixture. The procedure gives an
acceptable yield (57 %) even on ten-gram scale. The compound
6 was obtained by fractional crystallization of mother liquor. The
structures of 5 and 6 were fully characterized by standard
physicochemical methods of analysis and, in addition, structure
5 was confirmed by single-crystal X-Ray diffraction study (Fig. 3).
bis(aryl)-imidazolium
salts
comprising
hexafluoroisopropylalkoxy-group [(CF3)2(OR)C-] in ortho-position
of N-aryl substituent (2, Fig. 2) as well as their application for the
preparation of new metal complexes. The combination of two
bulky lipophilic CF3-groups with anionic alkoxy group could
generate a chelating ligand able to give rise to complexes with
increased stability, steric rigidity and enhanced solubility in
common organic solvents (or monomers).[18] In addition, the free
OH-group would provide unique possibility for further
functionalization of fluorinated NHC precursors opening the door
to a new way to tune these ligands and subsequently reactivity
of NHC-metal complexes. Here we also disclose the initial
testing on catalytic activity of some Pd-complexes.
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salt 5 with palladium (II) acetylacetonate took place only under
heating in dioxane to give a complicated mixture of products
along with palladium black. This result can be rationalized by the
possible formation of active Pd-cationic species under course of
reaction. Therefore, we envisioned that the addition of halogen
source could stabilize the palladium complex. Indeed, the
addition of equimolar amounts of sodium bromide or iodide into
the reaction mixture led to formation of OH-containing stable
complexes 8 and 9 in good yields (Scheme 3).
Figure 3. Molecular structure of salt 5. Displacement ellipsoids are drawn at a
30 % probability level.
First, in order to check the ability of 5 to act as the
corresponding NHC precursor, we performed its reaction with
Ag2O using the standard literature conditions. As a result, the
light- and air-stable dimeric Ag(I) complex 7 has been isolated
from the reaction mixture in low yield. Fortunately, the
application of improved protocol, recently published by Gimeno
and co-workers,[22] led to almost quantitative formation of 7
(Scheme 2). Its structure was fully confirmed by single-crystal X-
Ray diffraction study (Fig. 4).
It should be noted that the similar non-fluorinated silver
complexes with bidentate saturated (imidazoline-based) NHC
ligands have been previously described by Hoveyda et al.[23]
Scheme 3. Synthesis of Pd(acac) complexes 8 and 9.
The signal of carbene atom of 9 was unambiguously revealed by
2D NMR spectroscopy (see Supporting info). It was shifted into
upper field (149.7 ppm) due to the influence of iodine atom,
which is in the expected range for the similar Pd-complexes.[24]
In addition, the structure of 9 was confirmed by single-crystal X-
Ray analysis (Fig. 5).
Scheme 2. Preparation of binuclear complex 7.
Figure 4. Structure of binuclear complex 7. Thermal ellipsoids are drawn at
30% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths
(for one of two independent molecules): Ag1…Ag1A 2.8858(7)Å, Ag1-O1A
2.077(4)Å, Ag1-C1 2.074(6)Å, Ag1A-O1 2.098(4)Å, Ag1A-C1A 2.065(6)Å;
Ag1B…Ag1C 2.9135(8)Å, Ag1B-O1C 2.076(4)Å, Ag1C-O1B 2.103(4)Å, Ag1B-
C1B 2.054(6)Å, Ag1C -C1C 2.080(6)Å.
Figure 5. Molecular structure of complex 9. Thermal ellipsoids are drawn at
30% probability. Hydrogen C-H atoms are omitted for clarity.
We have also made several attempts to perform intermolecular
cyclization of 9 to get new complex with Pd-O covalent bond.
The reactions were run under basic condition (Cs2CO3 or DBU)
in anhydrous CH3CN at 80 C. However in all cases the starting
Pd-complex 9 was recovered from the reaction mixture.
Then, we turned our attention to the synthesis of palladium (II)
complexes bearing fluorinated bidentate NHC ligand. However
our first attempt failed. Thus, the reaction of tetrafluoroborate
o
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At the same time, the presence of free OH-group in imidazolium
salt 5 prompted us to study the feasibility of its direct
functionalization. Thus, the salt 5 was treated with three-fold
excess of potassium carbonate in the presence of two
equivalents of MeI at room temperature to afford the desired
methoxy derivative 10a in excellent yield (for X-ray structure of
10a see Supporting Info, Fig. 6). These conditions proved to be
optimal for other alkyl iodides (entrees 2-4, Table 1)
corresponding alkyl bromides were absolutely inactive under the
studied conditions.
The simple synthetic procedure, facile isolation and purification
of the final products (by single re-crystallization from toluene)
render this method suitable for scale-up synthesis of new family
of fluorinated unsymmetrical imidazolium salts 10 (see
Experimental Section).
Interestingly, that the replacement of K2CO3 for more active
Cs2CO3 leads to double alkylation product 11a comprising alkyl
groups upon oxygen of hexafluoroisopropoxy group and C2-
carbon of imidazolium ring (Scheme 4). It was confirmed by the
disappearance of characteristic proton signal at C2-imidazolium
atom and the occurrence of two additional signals of methyl
Table 1. Post-modification of imidazolium salt 5.
1
groups in H NMR spectra of 11a. The similar product 11b was
obtained when ethyl iodide was used as alkylating agent.
Entry
RHal
MeI
Product
10a
Yield[a], %
92
1
2
3
4
5
6
7
8
9
EtI
10b
10c
83
n-BuI
74
ICH2CO2Et
i-AmI
10d
10e
71
Scheme 4. Synthesis of double alkylated imidazolium salts.
69[b]
56[c]
75[c]
68[d,c]
0[d]
PhCH2Cl
AllCl
10f
Next, to evaluate the capability of imidazolium salts 10 to be
utilized as the corresponding carbene precursors for the
preparation of new NHC metal complexes, the free carbene
species was generated from methoxy derivative 10a. For this
10g
10h
10i
purpose, the latter has been initially transformed into
i-PrI
[25]
tetrafluoroborate salt via modified literature procedure
(see
-
Experimental Section). Then, the salt 10a (BF4 ) was
deprotonated with t-AmOK in THF, the resulting solution was
filtered out, THF was removed under reduced pressure and the
residue was immediately re-dissolved in d6-benzene for NMR
[a] Isolated yield. [b] Reactions were conducted at 60°C, [c] in the presence of
NaI, [d] Evolution of propylene was observed
1
analysis. Its H NMR-spectra displays the disappearance of the
low field C-2 proton at 9.57 ppm, which is consistent with the
formation of the normal C-2 NHC. The 13C NMR spectrum of the
NHC displays a broad resonance at 220.1 ppm for the carbene
center, which is in the expected range for aryl substituted
imidazolylidenes.[26]
Inspired by this result, we synthesized several new metal
complexes bearing unsymmetrical fluorinated NHC ligands
(Scheme 5). Thus, complex 12 was obtained in acceptable yield
(55%) by deprotonation of tetrafluoroborate salt 10a with
potassium tert-amylate in the presence of [RhCl(cod)]2. In
contrast, the preparation of complex 13 included the direct
reaction of iodide salt 10g with Pd(acac)2 following the recent
literature protocol.[27] Noteworthy, in our case the reaction
proceeded very quickly; the full conversion of starting material
was achieved in 20 min under heating in dioxane to give
excellent yield of 13.
Figure 6. Structure of salt 10a. Thermal ellipsoids are drawn at 30%
probability.
The only exception was found for isopropyl iodide; the propylene
gas evolution was observed during the reaction. In the case of
allyl chloride (entry 7) the addition of sodium iodide was required
for the successful formation of O-allylated product 10g. The
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Its reaction with free carbenes generated in situ from 10a,b, in
the same manner as 12, led to formation of desired complexes
in excellent yields. In addition, two-step protocol can be also
applied for the preparation of such pyridine containing
complexes. Thus, methoxy derivative 14 was synthesized in
moderate yield via the reaction of the corresponding free
carbene with bis(benzonitrile)palladium(II) followed by the
treatment of the intermediate complex with 3-chloropyridine
(Scheme 5). The all complexes obtained proved to be air- and
moisture-stable compounds and demonstrated remarkable
solubility in common organic solvents including hexanes. The
structures of 12, 13 and 14 have been fully confirmed by single-
crystal X-Ray diffraction studies (Fig. 7).
The structure of 14 was compared with known PEPPSI-IMes
[IMesPdCl2(3-Cl-Py)] complex.[29] The introduction of fluorinated
group into Mes-substituent leads to changes of bond length
values [Pd-Cl 2.356(2)Å, 2.339(2)Å; Pd-C1 1.954(8)Å; Pd-N3
2.099(8)Å in 14; Pd-Cl 2.298(1)Å, 2.290(1)Å; Pd-C1 1.962(3)Å;
Pd-N3 2.117(3)Å in PEPPSI-IMes] and angles Mes/C1N1N2
(81.1°, 71.8° in 14; 76.8°, 72.4° in PEPPSI-IMes), C1N1N2/3-Cl-
Py 61.2° and 62.6°; Cl1-Pd-Cl2/C1N1N2 25.2° and 23.5°; Cl1-
Pd-Cl2/3-Cl-Py 45.5° and 50.5o, respectively (Table 2.).
Scheme 5. Synthesis of (CF3)2(OR)C-containing complexes.
The complexes 14, 15 were obtained by one step procedure
based on the usage of bis(3-chloropyridine)palladium dichloride
complex [PdCl2(3-chloropyridine)2][28] as the palladium source.
12
13
14
Figure 7. Molecular structures of complexes 12, 13 and 14. Thermal ellipsoids are drawn at 30% probability.
Noteworthy, rather short contacts between oxygen of
Palladium-catalyzed cross-coupling reactions are widely
employed for construction of new carbon-carbon and carbon-
heteroatom bonds and have already gained an exclusive
importance for the production of compounds in the
pharmaceutical and fine chemical industries.[30] Keeping in mind
the previous reports by M. Organ’s and S. Nolan’s research
groups that PEPPSI (pyridine-enhanced pre-catalyst preparation,
stabilization, and initiation) complexes with bulky NHC ligands
are highly active and universal catalysts in many palladium-
catalyzed cross-coupling processes,[31] including Buchwald-
Hartwig reaction,[3d,32] we chose amination of bromobenzene by
morpholine as a model reaction for the initial estimation of the
catalytic activity of fluorinated PEPPSI-type catalysts 14 and 15.
(CF3)2(OR)C-group and imidazole atoms (O1…C1 2.949Å,
O1…N1 2.577Å, O1…N2 3.666Å) were detected, probably due
to steric and electronic factors (Table 3). Similar contacts were
also found for all complexes obtained including 9 despite the
presence of intramolecular hydrogen bond of OH-group with
oxygen of C=O group of acac ligand (О…О 2.649Å). The only
exception has been found in the case of salt 10a, in which iodide
anion has the contacts both with hydrogen of C1-H fragment
(I…C 3.565Å) and with C2-H hydrogen of imidazole rings (I…C
3.695Å) belonged to two different cations. As a result in this
case (CF3)2(OMe)C-group turns away from imidazole ring (see
Supporting Info, Fig. S49).
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Reactions were conducted in standard solvent dimethoxyethane
(DME) at 80°C as well as in heptane with 0.5 mol% catalyst
loading; potassium tert-butoxide was used as a base. All
reactions were performed in duplicate (Table 4).
6). The latter examples clearly show a potential of the catalysts
obtained to function in alkane solvents, which are the most
favorable for industrial application.[3g, 33]
Table 4. The catalytic activity of new Pd-complexes in Buchwald-Hartwig
Table 2. Selected geometric parameters of complexes obtained.
amination.
Angle
M-
C1,
[Å]
Angle
C2N2/-Mes
[°]
Com-
plex
M-Hal,
[Å]
plane
C2N2/sub
-Mes[°]
C1-N, [Å]
Entry
Catalyst
Solvent
DME
Yield[a], %
1.324(2);
1.328(2)
5
9
-
-
86.2
87.7
87.5
83.7
87.4
67.5
1
2
3
4
5
6
PEPPSI-IMES
32
49
51
28
59
58
2.5557
(7)
1.974
(6)
1.296(14);
1.403(14)
14
DME
15
DME
1.309(8);
1.352(8)
10a
-
-
PEPPSI-IMES
heptane
heptane
heptane
2.3753
(10)
2.4001
(9)
2.070
(3)
2.074
(4)
1.368(4);
1.369(4);
1.378(4);
1.362(4)
14
15
86.5;
74.8
72.2;
83.4
12[a]
2.5742
(3)
1.971
(2)
1.356(3);
1.362(3)
13
82.2
81.1
-
68.9
71.8
[a] isolated yield.
2.356
(2);
2.339
(2)
1.954
(8)
1.363(10);
1.367(10)
14
Conclusions
PEPPSI-
Mes[b]
2.298(1);
2.209(1)
1.962
(3)
1.352(5);
1.360(5)
76.8
72.4
We developed an efficient and scaled-up synthesis of imidazole-
based unsymmetrical NHC precursors bearing sterically
demanding hexafluoroisopropylalkoxy [(CF3)2(OR)C-] group in
ortho-position of N-aryl substituent. The method is based on
heterocyclic interconversion of Mes-substituted oxazolinium
tetrafluoroborate salt via the reaction with the corresponding
fluoroalkyl substituted aniline. The subsequent post-modification
of the resulting hydroxyl-containing salt lead to new family of
fluorinated NHC precursors. The latter were further successfully
utilized for the preparation of several novel metal complexes,
which exhibited remarkable stability and solubility in common
organic solvents including hexanes. An initial evaluation of
catalytic activity of palladium complexes obtained was
performed on Buchwald-Hartwig amination of bromobenzene
with morpholine as a model reaction. As a result, two PEPPSI-
type complexes revealed promising activity, approaching to the
known active catalysts with bulky NHC ligands. The facile
modification/functionalization of fluorinated NHC precursors via
elaborated O-alkylation protocol would allow for further fine
turning of these ligands and subsequently reactivity of NHC-
metal complexes. In addition, the remarkable solubility of
complexes would provide possibilities for the development of
new catalytic procedures in industrially important alkane
solvents. Studies of novel organometallic complexes of these
ligands with a variety of metals, including Ru, Cu, Ni and W are
in progress now.
[a] two independent molecules; [b] see ref.29
Table 3. Contacts between oxygen of (CF3)2(OR)C-group and imidazole
atoms.
Complex
C1, [Å]
3.085
3.051
-
N1, [Å]
2.566
2.753
-
N2, [Å]
3.627
3.644
-
5
9
10a
12[a]
13
3.121
3.218
2.949
2.642
2.617
2.557
3.804
3.856
3.666
14
Generally, the synthesized Pd-complexes demonstrated an
expected activity in DME. Thus, despite structural similarity to
symmetrical
PEPPSI-IMes
[N,N-bis(2,4,6-trimethylphenyl)
imidazol-2-ylidene] the 14 and 15 exhibited higher catalytic
activities in this model reaction. In addition, the remarkable
solubility found for new complexes, induced by the influence of
lipophilic fluorinated moiety, has allowed performing this reaction
in heptane to afford the product even in better yields (entries 5,
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C23H23BF10N2O (%): C, 50.76; H, 4.26; N, 5.15. Found: C, 50.68; H, 4.22;
N, 5.04.
Experimental Section
All solvents were freshly distilled from appropriate drying agents before
use. All other reagents were recrystallized or distilled as necessary.
Syntheses of metal complexes were performed under an argon
atmosphere using standard Schlenk technique. Analytical TLC was
performed with Merck silica gel 60 F254 plates. Visualization was
accomplished by UV light (254 and 366 nm), spraying by Ce(SO4)2
Silver complex 7. The mixture of 0.49 g (1 mmol) of imidazolium
chloride 5, 0.17 g (1 mmol) of silver nitrate and 0.69 g (5 mmol) of
potassium carbonate in 30 ml of dichloromethane was stirred for 2 days,
filtered through Celite and evaporated to dryness. Recrystallization of
resulting solid from heptane afforded 0.50 g (98 %) of the product as
white crystals. 1H NMR (d6-acetone, δ, ppm) 7.18 (s, 1H, HIm), 7.17 (s,
1H, HIm), 7.14 (s, 2H, HAr), 7.11 (s, 1H, HAr), 7.08 (s, 1H, HAr), 2.50 (s, 3H,
CH3), 2.35 (s, 3H, CH3), 2.09 (s, 3H, CH3), 1.91 (s, 3H, CH3), 1.51 (s, 3H,
solution in
5 % H2SO4 or KMnO4 solution in water. Column
chromatography was carried out using Merck silica gel 60 (230-400 mesh
ASTM) and ethyl acetate/petroleum ether or ethyl acetate/CH2Cl2 as
eluent. NMR spectra were recorded at room temperature on Bruker AV-
300, AV-400, AV-600 spectrometers operating at 300 MHz, 400 MHz and
1
CH3). 13C NMR (d6-acetone, δ, ppm) 183.0 (dd, JAg(109),C = 271.2 Hz,
1JAg(107),C = 236.2 Hz, NCN), 139.6 (Carom), 139.3 (Carom), 138.4 (Carom),
137.6 (Carom), 137.0 (Carom), 136.5 (Carom), 135.7 (Carom), 135.4 (Carom),
132.5 (Carom), 130.7 (Carom), 130.1 (Carom), 128.3 (Carom), 128.0 (Carom),
600 MHz for 1H; 101 and 151 MHz for 13C; 282 and 376 MHz and for 19
F
(CF3Cl as reference) and 121 MHz for 31P (85% H3PO4 as reference).
The chemical shifts are frequency referenced relative to the residual
undeuterated solvent peaks. 2-(2-Amino-3,5-dimethylphenyl)-1,1,1,3,3,3-
1
127.0 (q, JC,F = 296 Hz, CF3), 126.8 (Carom), 126.1 (qd, J = 293 Hz, 10
Hz, CF3), 126.0 (Carom), 121.4 (Carom), 121.3 (Carom), 88.8-87.8 [m,
C(CF3)2], 21.4 (CH3), 21.3 (CH3), 18.8 (CH3), 18.3 (CH3), 17.7 (CH3). 19F
NMR (d6-acetone, δ, ppm): -71.90 (br. s, CF3), -75.02 (q, J = 9.3 Hz, CF3).
Anal. Calcd for C46H44Ag2F12N4O2 (%): C, 48.95; H, 3.93; N, 4.96. Found:
C, 50.14; H, 4.11; N, 5.02.
hexafluoro-propan-2-ol 317, 5-acetoxy-3-mesityl-4,5-dihydrooxazol-3-ium
[34]
tetrafluoroborate 4[19] and PdCl2(3-ClPy)2
were synthesized according
to the literature procedures. All crystals suitable for X-Ray experiments
were obtained from the solvent mixture CH2Cl2/hexane (1:1) at -5о С.
Synthesis of palladium complex 8. The mixture of 0.15 g (0.276 mmol)
imidazolium tetrafluoroborate 5, 0.0763 g (0.251 mmol, 0.91 eq) of
Pd(acac)2 and 0.085 g (0.827 mmol, 3 eq) of sodium bromide were
dissolved in 5 ml of 1,4-dioxane. Reaction mixture was heated at 90°C
until TLC showed full conversion of starting Pd(acac)2 to product (4 h).
After cooling to room temperature the reaction mixture was evaporated in
vacuum, residue was dissolved in minimum amount of CH2Cl2 and
purified by flash chromatography using hexanes-CH2Cl2 (1:1) mixture.
Evaporation of resulting fractions yielded 0.140 g (75%) of pure product
as yellowish solid (m.p. 123-125 °C). 1H NMR (CDCl3, δ, ppm) 7.47 (s,
1H, HIm), 7.35 (s, 1H, HIm), 7.12 (s, 1H, HAr), 7.09-6.93 (m, 4H, HAr, OH),
5.24 [s, 1H, C(O)CH], 2.47 (s, 3H, CH3), 2.37 (s, 3H, CH3), 2.24 (s, 3H,
CH3), 2.23 (s, 3H, CH3), 2.11 (s, 3H, CH3), 1.90 [s, 3H, C(O)CH3], 1.86 [s,
3H, C(O)CH3]. 13C NMR (CDCl3, δ, ppm) 190.1 (C=O), 181.5 (C=O),
150.2 (NCN), 140.3 (CAr), 140.1 (CAr), 139.6 (CAr), 136.4 (CIm), 135.5
Synthesis of 5. A mixture of oxazolium tetrafluoroborate 4 (9.85 g, 29.4
mmol) and fluorinated aniline 3 (12.6 g, 44.0 mmol) in 100 ml of dry
toluene was stirred for 12 h at room temperature and then 6 ml of
HBF4·Et2O was added. The resulting suspension was heated at 80 °C
under stirring for 3 h, cooled to room temperature and evaporated to
dryness in vacuum. The oily residue was stirred with 150 ml of diethyl
ether until crystallization. Precipitate obtained was filtered, washed with
minimal volume of CHCl3 and dried in air to give 9.12 g (57 %) of beige
powder (m.p. 231-233 °C (dec.). 1H NMR (d6-DMSO, δ, ppm) 9.57 (s, 1H,
NCH-N), 8.86 (s, 1H, OH), 8.18 (s, 1H, NCH-C), 8.14 (s, 1H, NCH-C),
7.63 (s, 1H, HAr), 7.49 (s, 1H, HAr), 7.19 (s, 2H, HAr), 2.46 (s, 3H, CH3),
2.35 (s, 3H, CH3), 2.13 (s, 3H, CH3), 2.08 (s, 3H, CH3), 2.05 (s, 3H, CH3).
13C NMR (d6-DMSO, δ, ppm) 141.3 (NCN), 140.6 (Carom), 138.7 (Carom),
138.4 (Carom), 134.5 (Carom), 134.1 (Carom), 134.1 (Carom), 130.9 (Carom),
130.8 (Carom), 129.4 (Carom), 129.4 (Carom), 126.9 (Carom), 126.5 (Carom),
1
(CAr), 134.9 (CAr), 134.8 (CAr), 134.7 (CAr), 130.0 (CAr), 129.2 (CAr), 127.5
126.1 (Carom), 123.4 (Carom), 122.6 (q, JC,F = 289 Hz, CF3), 79.0 [m,
1
C(CF3)2], 20.9 (CH3), 20.6 (CH3), 17.2 (CH3), 17.2 (CH3), 17.0 (CH3). 19F
NMR (d6-DMSO, δ, ppm) -72.45 (q, J = 7.6 Hz, CF3), -73.12 (q, J = 7.7
Hz, CF3), -148.23 (s, BF4). Anal. Calcd for C23H23BF10N2O (%): C, 50.76;
H, 4.26; N, 5.15. Found: C, 50.64; H, 4.18; N, 5.08.
(CAr), 127.3 (CIm), 126.0 (d, J = 3 Hz, CAr), 124.3 (CAr), 123.5 (q, JC,F
=
1
291 Hz, CF3), 122.4 (q, JC,F = 287 Hz, CF3), 101.0 [C(O)CH], 81.0-79.5
[m, C(CF3)2], 28.0 [C(O)CH3], 25.4 [C(O)CH3], 21.6 (CH3), 21.3 (CH3),
20.1 (CH3), 19.4 (CH3), 17.8 (CH3). 19F NMR (CDCl3, δ, ppm) -69.60 (q, J
=
8.7 Hz, CF3), -76.16 (q, J = 8.4 Hz, CF3). Anal. Calcd for
C28H30BrF6N2O3Pd (%) C, 45.27; H, 4.07; N, 3.77. Found: C, 45.36; H,
4.19; N, 3.67.
Anion exchange. In order to exchange BF4 anion to Cl solution of 1.0 g
of imidazolium tetrafluoroborate 5 was dissolved in 20 ml of methanol,
filtered through a short pad (2 cm) of Amberlite® IRA-400(Cl). Ion
exchange resin was washed with additional volume of methanol.
Combined filtrate was concentrated in vacuum to give almost quantitative
yield of chloride salt of 5.
Synthesis of palladium complex 9. The mixture of 0.15 g (0.276 mmol)
of imidazolium tetrafluoroborate 5, 0.0763 g (0.251 mmol) of Pd(acac)2
and 0.1239 g (0.827 mmol) of sodium iodide were dissolved in 5 ml of
1,4-dioxane. Reaction mixture was heated at 90°C until TLC showed full
conversion of starting Pd(acac)2 to product (2 h). After cooling to room
temperature the reaction mixture was evaporated in vacuum, residue
was dissolved in minimum amount of CH2Cl2 and purified by flash
chromatography using hexanes-CH2Cl2 (1:1) mixture. Evaporation of
resulting fractions yielded 0.172 g (79%) of pure product as yellow solid
(m.p. 127-129 °C). 1H NMR (CDCl3, δ, ppm) 7.47 (s, 1H, HIm), 7.46 (s, 1H,
OH), 7.33 (s, 1H, HIm), 7.13 (s, 1H, HAr), 7.05 (s, 1H, HAr), 7.01 (s, 2H,
HAr), 5.25 [s, 1H, C(O)CH], 2.47 (s, 3H, CH3), 2.37 (s, 3H, CH3), 2.25 (s,
6H, CH3), 2.16 (s, 3H, CH3), 1.93 [s, 3H, C(O)CH3], 1.85 [s, 3H,
C(O)CH3]. 13C NMR (CDCl3, δ, ppm) 189.5 (C=O), 181.5 (C=O), 149.7
(NCN), 140.1 (CAr), 139.8 (CAr), 139.6 (CAr), 135.9 (CIm), 135.6 (CAr),
134.9 (CAr), 134.9 (CAr), 134.8 (CAr), 130.0 (CAr), 129.3 (CAr), 127.6 (CAr),
Imidazolinium tetrafluoroborate 6. Isolated as white crystals from
mother liquor remaining after filtration of 5 (see procedure above). Yield
5 %, M.p. 200-202 °C (dec.). 1H NMR (d6-acetone, δ, ppm) 9.63 (s, 1H,
NCH-N), 7.58 (s, 1H, HAr), 7.55 (s, 1H, HAr), 7.14 (s, 2H, HAr), 6.42 [d,
JH,H = 6.2 Hz, 1H, N(O)CH], 5.14 (dd, JH,H = 14.7, 6.5 Hz, 1H, NCH2),
4.69 (d, JH,H = 15.0 Hz, 1H, NCH2), 2.61 (s, 3H, CH3), 2.47 (s, 3H, CH3),
2.42 (s, 3H, CH3), 2.34 (s, 6H, CH3); 13C NMR (d6-acetone, δ, ppm) 159.0
(NCN), 142.1 (Carom), 140.1 (Carom), 136.6 (Carom), 136.3 (Carom), 133.1
1
(Carom), 130.9 (Carom), 130.2 (Carom), 126.5 (Carom), 123.1 (q, JC,F = 289
1
Hz, CF3), 122.5 (q, JC,F = 286 Hz, CF3), 117.8 (Carom), 86.9 [N(O)CH],
79.6-78.5 [m, C(CF3)2], 58.1 (NCH2), 21.2 (CH3), 21.0 (CH3), 17.5 (CH3),
17.3 (CH3), 17.1 (CH3); 19F NMR (d6-acetone, δ, ppm) -72.35 (q, J = 8.6
Hz, CF3), -76.45 (q, J = 8.6 Hz, CF3), -151.47 (s, BF4). Anal. Calcd for
1
127.4 (CIm), 126.1 (NCAr), 124.6 (NCAr), 123.5 (q, JC,F = 291 Hz, CF3),
1
122.4 (q, JC,F = 287 Hz, CF3), 100.6 [C(O)CH], 80.2 [m, C(CF3)2], 28.1
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10.1002/chem.201700624
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[C(O)CH3], 25.7 [C(O)CH3], 21.6 (CH3), 21.5 (CH3), 21.3 (CH3), 20.5
(CH3), 18.0 (CH3). 19F NMR (CDCl3, δ, ppm) -68.23 (s, CF3), -75.05 (s
CF3). Anal. Calcd for C28H30F6IN2O3Pd (%) C, 42.58; H, 3.83; N, 3.55.
Found: C, 42.39; H, 4.01; N, 3.61.
(CDCl3, δ, ppm) -67.52 (s, CF3), -71.68 (s, CF3). Anal. Calcd for
C25H27F6IN2O (%): C, 49.03; H, 4.44; N, 4.57. Found: C, 49.19; H, 4.31;
N, 4.48.
Imidazolium tetrafluoroborate 10b. Using procedure described for
compound 10a (BF4) the product 10b was isolated as white solid (m.p.
97-99 °C) in 97% yield. 1H NMR (CDCl3, δ, ppm) 9.08 (s, 1H, NCH-N),
7.57 (s, 1H, NCH-C), 7.55 (s, 1H, NCH-C), 7.47 (s, 1H, HAr), 7.40 (s, 1H,
HAr), 7.05 (s, 2H, HAr), 3.72 (m, 2H, OCH2), 2.48 (s, 3H, CH3), 2.36 (s, 3H,
CH3), 2.15 (s, 3H, CH3), 2.13 (s, 3H, CH3), 2.07 (s, 3H, CH3), 1.31 (t,
3JH,H = 7.0 Hz, 3H, CH2CH3). 13C NMR (CDCl3, δ, ppm) 142.5, NCN,
142.0 (Carom), 139.8 (Carom), 139.1 (Carom), 135.4 (Carom), 134.6 (Carom),
134.0 (Carom), 130.4 (Carom), 130.3 (Carom), 130.1 (Carom), 126.9 (Carom),
125.8 (Carom), 123.9 (Carom), 122.3 (q, 1JC,F = 291 Hz, CF3), 121.9 (q, 1JC,F
= 288 Hz, CF3), 83.3 [m, C(CF3)2], 63.7, (OCH2), 21.7 (CH3), 21.3 (CH3),
18.0 (CH3), 17.7 (CH3), 17.4 (CH3), 15.3(CH2CH3). 19F NMR (CDCl3, δ,
ppm), δ -67.82 (s, CF3), -71.92 (s, CF3), -152.88 (d, J = 20 Hz, BF4). Anal.
Calcd for C25H27BF10N2O (%) C, 52.47; H, 4.76; N, 4.89. Found C, 52.62;
H, 4.89; 4.75.
General procedure for O-aklylation of imidazolium salt 5. A mixture
of 0.272 g (0.5 mmol) of imidazolium tetrafluoroborate 5, 0.27 g (2 mmol)
of anhydrous K2CO3 and 2 mmol of methyliodide was dissolved in 2 ml of
CH3CN. Reaction mixture was stirred until TLC analysis (acetone)
showed absence of starting imidazolium salt (6 h). Reaction mixture was
concentrated in vacuum, residue triturated in dichloromethane and
filtered through Celite®. Resulting filtrate was evaporated to dryness.
Crystallization from 2 ml of toluene afforded 0.275 g (92 %) of pure O-
metylated imidazolium iodide 10a as a white solid (m.p. 128-130 °C). 1H
NMR (CDCl3, δ, ppm) 9.79 (s, 1H, NCH-N), 7.80 (s, 1H, NCH-C), 7.64 (s,
1H, NCH-C), 7.40 (s, 1H, HAr), 7.33 (s, 1H, HAr), 6.97 (s, 2H, HAr), 3.46 (s,
3H, OCH3), 2.40 (s, 3H, CH3), 2.28 (s, 3H, CH3), 2.14 (s, 3H, CH3), 2.07
(s, 3H, CH3), 2.05 (s, 3H, CH3). 13C NMR (CDCl3, δ, ppm) 142.1 (NCN),
141.6 (Carom), 138.9 (Carom), 138.4 (Carom), 135.2 (Carom), 134.2 (Carom),
133.8 (Carom), 130.1 (Carom), 129.9 (Carom), 129.6 (Carom), 127.0 (Carom),
125.0 (Carom), 124.0 (Carom), 122.0 (q, 1JC,F =292 Hz, CF3), 121.7 (q, 1JC,F
= 290 Hz, CF3), 83.7 [m, 2JC,F = 28 Hz, C(CF3)2], 56.7 (OCH3), 21.5 (CH3),
21.1 (CH3), 18.7 (CH3), 18.1 (CH3), 17.2 (CH3). 19F NMR (CDCl3, δ, ppm)
-66.80 (s, CF3), -68.57 (s, CF3). Anal. Calcd for C24H25F6IN2O (%): C,
48.17; H, 4.21; N, 4.68. Found: C, 47.98; H, 4.26; N, 4.45.
Imidazolium iodide 10c. Yield: 74% (m.p. 117-119 °C). 1H NMR (CDCl3,
δ, ppm) 10.06 (s, 1H, NCH-N), 7.61 (s, 1H, NCH-C), 7.58 (s, 1H, NCH-C),
7.54 (s, 1H, HAr), 7.38 (s, 1H, HAr), 7.02 (s, 1H, HAr), 7.02 (s, 1H, HAr),
3.69-3.53 (m, 2H, OCH2), 2.45 (s, 3H, CH3), 2.33 (s, 3H, CH3), 2.21 (s,
3H, CH3), 2.13 (s, 3H, CH3), 2.10 (s, 3H, CH3), 1.68-1.60 (m, 2H, CH2),
3
1.48-1.38 (m, 2H, CH2), 0.92 (t, JH,H = 7.4 Hz, 3H, CH3). 13C NMR
Scaled-up synthesis of 10a. A mixture of 6.0 g (11.0 mmol) of
imidazolium tetrafluoroborate 5, 6.1 g (44.0 mmol) of anhydrous K2CO3
and methyliodide (6.26 g, 44.0 mmol) was suspended in 50 ml of CH3CN.
Reaction mixture was vigorously stirred at room temperature overnight.
The solvent was removed under reduced pressure, and then the residue
was triturated in dichloromethane (50 ml) and filtered out through Celite®.
Resulting filtrate was evaporated to dryness. Crystallization from 25 ml of
toluene gave 5.93 g (90 %) of analytically pure 10a.
(CDCl3, δ, ppm) 142.4 (NCN), 141.8 (Carom), 139.1 (Carom), 135.5 (Carom),
134.4 (Carom), 133.9 (Carom), 130.4 (Carom), 130.3 (Carom), 130.2 (Carom),
130.1 (Carom), 129.7 (Carom), 126.8 (Carom), 125.6 (Carom), 124.0 (Carom),
122.1 (q, JC,F = 291 Hz, CF3), 121.7 (q, JC,F = 289 Hz, CF3), 83.5-82.4
[m, C(CF3)2], 67.2 (OCH2), 31.6 (CH2), 21.6 (CH3), 21.2 (CH3), 19.0 (CH2),
18.9 (CH3), 18.5 (CH3), 17.4 (CH3), 13.8 (CH2CH3). 19F NMR (CDCl3, δ,
ppm) -66.69 (s, CF3), -70.82 (s, CF3). Anal. Calcd for C27H31F6IN2O (%):
C, 50.64; H, 4.88; N, 4.37. Found: C, 50.26; H, 4.57; N, 4.30.
1
1
Synthesis of imidazolium tetrafluoroborate 10a. To the solution of
imidazolium iodide 10a (1.0 g, 1.67 mmol) in acetone (30 ml) sodium
tetrafluoroborate (0.733 g, 6.68 mmol) solution in water (30 ml) was
added. The resulting mixture was stirred for 10 min, concentrated in
vacuum approx. to 30 ml and extracted with dichloromethane (3x20 ml).
Organic extract was dried over MgSO4 and evaporated to dryness to give
Imidazolium iodide 10d. Yield: 71% (m.p. 121-123 °C). 1H NMR (CDCl3,
δ, ppm) 10.31 (s, 1H, NCH-N), 7.82 (s, 1H, NCH-C), 7.59 (s, 1H, NCH-C),
7.51 (s, 1H, HAr), 7.40 (s, 1H, HAr), 7.03 (s, 2H, HAr), 4.27 (dd, J = 66.9,
14.6 Hz, 2H, OCH2CO), 4.25-4.20 (m, 2H, OCH2CH3), 2.43 (s, 3H, CH3),
2.33 (s, 3H, CH3), 2.20 (s, 3H, CH3), 2.13 (s, 3H, CH3), 2.11 (s, 3H, CH3),
3
1.26 (t, JH,H = 7.1 Hz, 3H, CH2CH3). 13C NMR (CDCl3, δ, ppm) 167.2
1
0.92 g (98%) of white solid (m.p. 103-105 °C). H NMR (CDCl3, δ, ppm)
(C=O), 142.9 (NCN), 141.8 (Carom), 139.9 (Carom), 139.3 (Carom), 135.9
(Carom), 134.3 (Carom), 133.9 (Carom), 130.4 (Carom), 130.3 (Carom), 130.2
(Carom), 129.7 (Carom), 126.6 (Carom), 124.8 (Carom), 123.8 (Carom), 122.0 (d,
8.77 (s, 1H, NCH-N), 7.65 (s, 1H, NCH-C), 7.52 (s, 1H, NCH-C), 7.47 (s,
1H, HAr), 7.39 (s, 1H, HAr), 7.03 (s, 2H, HAr), 3.48 (s, 3H, OCH3), 2.46 (s,
3H, CH3), 2.35 (s, 3H, CH3), 2.25-1.91 (m, 9H, CH3). 13C NMR (CDCl3, δ,
ppm) 142.3 (NCN), 141.8 (Carom), 139.1 (Carom), 138.4 (Carom), 135.3
(Carom), 134.5 (Carom), 134.1 (Carom), 130.5 (Carom), 130.2 (Carom), 130.1
(Carom), 129.7 (Carom), 127.1 (Carom), 125.2 (Carom), 124.1 (Carom), 122.3 (q,
1
1JC,F = 290 Hz, CF3), 121.5 (d, JC,F = 289 Hz, CF3), 83.5 [m, C(CF3)2],
64.6 (OCH2CO), 61.9 (CH2CH3), 21.5 (CH3), 21.2 (CH3), 19.0 (CH3), 18.5
(CH3), 17.5 (CH3), 14.2 (CH2CH3). 19F NMR (CDCl3, δ, ppm) -67.04 (s,
CF3), -71.42 (s, CF3). Anal. Calcd for C27H29F6IN2O3 (%) C, 48.37; H,
4.36; N, 4.18. Found: C, 48.31; H, 4.59; N, 4.20.
1
1JC,F = 291 Hz, CF3), 122.0 (q, JC,F = 290 Hz, CF3), 84.0 [m, C(CF3)2],
56.4 (OCH3), 21.6 (CH3), 21.2 (CH3), 17.9 (CH3), 17.4 (CH3), 17.2 (CH3).
19F NMR (CDCl3, δ, ppm) -67.40 (s, CF3), -70.55 (s, CF3), -152.66 (m,
BF4). Anal. Calcd for C24H25BF10N2O (%) C, 51.63; H, 4.51; N, 5.02.
Found C, 51.73; H, 4.59; 5.15.
Imidazolium iodide 10e. Reaction was carried out at 60°C. Yield: 69%
(m.p. 134-135 °C). 1H NMR (CDCl3, δ, ppm) δ 9.94 (s, 1H, NCH-N), 7.61
(s, 2H, NCH-C), 7.52 (s, 1H, HAr), 7.36 (s, 1H, HAr), 7.00 (s, 2H, HAr),
3.74-3.52 (m, 2H, OCH2), 2.43 (s, 3H, CH3), 2.31 (s, 3H, CH3), 2.18 (s,
3H, CH3), 2.10 (s, 3H, CH3), 2.08 (s, 3H, CH3), 1.79-1.69 [m, 1H,
CH2CH(CH3)2], 1.60-1.48 (m, 2H, CH2CH2CH), 0.88 (d, 3JH,H = 6.3 Hz, 6H,
CH(CH3)2). 13C NMR (CDCl3, δ, ppm) δ 142.3 (NCN), 141.7 (Carom),
139.4 (Carom), 139.0 (Carom), 135.4 (Carom), 134.4 (Carom), 133.8 (Carom),
130.3 (Carom), 130.2 (Carom), 130.1 (Carom), 130.1 (Carom), 129.6 (Carom),
126.9 (Carom), 122.0 (q, JC,F = 291 Hz, CF3), 121.7 (q, JC,F = 289 Hz,
CF3), 83.6-82.3 [m, C(CF3)2], 65.9 (OCH2), 38.4 (CH2CH2CH), 24.6
[CH2CH(CH3)2], 22.54 [CH(CH3)2], 22.47 [CH(CH3)2], 21.5 (CH3), 21.1
(CH3), 18.9 (CH3), 18.4 (CH3), 17.4 (CH3). 19F NMR (CDCl3, δ, ppm) δ -
Imidazolium iodide 10b. Yield: 83% (m.p. 124-126 °C). 1H NMR (CDCl3,
δ, ppm), 9.91 (s, 1H, NCH-N), 7.62 (s, 2H, HIm), 7.50 (s, 1H, HAr), 7.34 (s,
1H, HAr), 6.98 (s, 2H, HAr), 3.76-3.54 (m, 2H, OCH2), 2.42 (s, 3H, CH3),
2.30 (s, 3H, CH3), 2.16 (s, 3H, CH3), 2.08 (s, 6H, CH3), 1.26 (t, 3JH,H = 7.0
Hz, 3H, CH2CH3). 13C NMR (CDCl3, δ, ppm) 142.3 (NCN), 141.7 (Carom),
139.4 (Carom), 139.0 (Carom), 135.4 (Carom), 134.3 (Carom), 133.8 (Carom),
130.3 (Carom), 130.2 (Carom), 130.1 (Carom), 129.9 (Carom), 129.6 (Carom),
126.9 (Carom), 125.7 (Carom), 122.1 (q, 1JC,F = 290 Hz, CF3), 121.7 (q, 1JC,F
= 289 Hz, CF3), 83.8-82.6 [m, C(CF3)2], 63.6 (OCH2), 21.6 (CH3), 21.1
(CH3), 18.8 (CH3), 18.4 (CH3), 17.4 (CH3), 15.2 (CH2CH3). 19F NMR
1
1
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10.1002/chem.201700624
Chemistry - A European Journal
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68.29 (s, CF3), -71.47 (s, CF3). Anal. Calcd for C28H33F6IN2O (%) C,
51.39; H, 5.08; N, 4.28. Found: C, 51.25; H, 5.19; N, 4.32.
(CAr), 133.8 (CAr), 130.6 (CAr), 130.3 (CAr), 129.7 (CIm), 129.6 (CAr), 129.4
(CAr), 126.2 (CIm), 125.9 (CAr), 123.9 (CAr), 122.24 (q, 1JC,F = 292 Hz, CF3),
1
2
122.17 (q, JC,F = 290 Hz, CF3), 83.3 [p, JC,F = 29 Hz, C(CF3)2], 57.0
(OCH3), 21.5 (CArH3), 21.1 (CArH3), 18.5 (CArH3), 18.0 (CArH3), 17.7
(CArH3), 10.8 (CImH3). 19F NMR (CDCl3, δ, ppm) -66.92 (s, CF3), -69.81 (s,
CF3). Anal. Calcd for C25H27F6IN2O (%) C, 49.03; H, 4.44; N, 4.57. Found
Imidazolium iodide 10f. 0.3 g (2 mmol) of NaI was added to a reaction
mixture. Yield: 56%. 1H NMR (CDCl3, δ, ppm) 10.09 (s, 1H, NCH-N), 7.62
(s, 1H, NCH-C), 7.53 (s, 1H, NCH-C), 7.40-7.28 (m, 6H, HAr), 6.99 (s, 1H,
HAr), 6.97 (s, 1H, HAr), 4.73 (q, J = 11.1 Hz, 2H, OCH2), 2.34 (s, 3H, CH3),
2.31 (s, 3H, CH3), 2.18 (s, 3H, CH3), 2.12 (s, 3H, CH3), 1.99 (s, 3H, CH3);
13C NMR (CDCl3, δ, ppm) 142.4 (NCN), 141.7 (Carom), 139.5 (Carom),
139.2 (Carom), 135.6 (Carom), 135.4 (Carom), 134.3 (Carom), 133.9 (Carom),
130.4 (Carom), 130.3 (Carom), 130.2 (Carom), 130.1 (Carom), 129.7 (Carom),
128.7 (Carom), 128.5 (Carom), 127.7 (Carom), 126.8 (Carom), 125.3 (Carom),
1
C, 49.13; H, 4.51; 4.65. Data for 11b: H NMR (CDCl3, δ, ppm) 7.88 (s,
1H, HIm), 7.83 (s, 1H, HIm), 7.60 (s, 1H, HAr), 7.47 (s, 1H, HAr), 7.092 (s,
1H, HAr), 7.085 (s, 1H, HAr), 3.86 (pent, J = 7.2 Hz, 1H, OCH2), 3.71 (pent,
J = 7.2 Hz, 1H, OCH2), 2.56 (m, 2H, CCH2), 2.49 (s, 3H, CH3), 2.37 (s,
3H, CH3), 2.15 (s, 3H, CH3), 2.10 (s, 3H, CH3), 2.05 (s, 3H, CH3), 1.31 (t,
3
J = 6.9 Hz, 3H, OCH2CH3), 0.83 (t, JH,H = 7.5 Hz, 3H, CCH2CH3). 13C
1
1
NMR (CDCl3, δ, ppm) 149.5 (NCN), 142.5 (CAr), 142.1 (CAr), 138.6 (CAr),
135.6 (CAr), 134.3 (CAr), 133.7 (CAr), 130.6 (CAr), 130.5 (CAr), 130.3 (br. s,
CIm), 129.9 (CAr), 129.2 (CAr), 126.57 (CIm), 126.55 (CAr), 124.5 (CAr),
123.7 (Carom), 122.1 (q, JC,F = 290 Hz, CF3), 121.7 (q, JC,F = 289 Hz,
CF3), 84.2–83.0 [m, C(CF3)2], 69.1 (OCH2), 21.4 (CH3), 21.2 (CH3), 19.0
(CH3), 18.4 (CH3), 17.3 (CH3); 19F NMR (CDCl3, δ, ppm) -67.55 (s, CF3), -
71.24 (s, CF3). Anal. Calcd for C30H29F6IN2O (%): C, 53.42; H, 4.33; N,
4.15. Found: C, 53.36; H, 4.34; N, 4.09.
1
1
122.3 (q, JC,F = 290 Hz, CF3), 121.9 (q, JC,F = 289 Hz, CF3), 83.2 [p,
2JC,F = 29 Hz, C(CF3)2], 64.4 (OCH2), 21.6 (CH3), 21.1 (CH3), 19.2
(CCH2), 18.7 (CH3), 18.3 (CH3), 17.5 (CH3), 15.5 (CH2CH3), 9.3
(CH2CH3). 19F NMR (CDCl3, δ, ppm) -68.40 (s, CF3), -69.62 (s, CF3).
Anal. Calcd for C27H31F6IN2O (%) C, 50.64; H, 4.88; N, 4.37. Found C,
50.73; H, 4.94; 4.35.
Imidazolium iodide 10g. 0.3 g (2 mmol) of NaI was added to a reaction
mixture. Yield: 75% (m.p. 109-111 °C). 1H NMR (CDCl3, δ, ppm) 10.34 (s,
1H, NCH-N), 7.59 (s, 1H, NCH-C), 7.56 (s, 1H, NCH-C), 7.48 (s, 1H, HAr),
7.41 (s, 1H, HAr), 7.05 (m, 2H, HAr), 5.92 (m, 1H, CH2CH=CH2), 5.45 (d, J
= 17.4 Hz, 1H, CH=CH2), 5.28 (d, J = 10.5 Hz, 1H, CH=CH2), 4.22 (m,
2H, OCH2), 2.45 (s, 3H, CH3), 2.35 (s, 3H, CH3), 2.25 (s, 3H, CH3), 2.17
(s, 3H, CH3), 2.13 (s, 3H, CH3). 13C NMR (CDCl3, δ, ppm) 142.5 (NCN),
141.8 (Carom), 139.7 (Carom), 139.2 (Carom), 135.6 (Carom), 134.4 (Carom),
133.8 (Carom), 131.8 (CH=CH2), 130.4 (Carom), 130.3 (Carom), 130.1 (Carom),
Generation of free carbene. A Schlenk flask, equipped with magnetic
stir bar, was charged with 70 mg (0.125 mmol, 1 eq) of imidazolium
tetrafluoroborate 10a, 5 ml of dry degassed THF and 0.09 ml of 1.7M
KOt-Am in toluene. The reaction mixture was allowed to stir for 30 min at
room temperature, and then THF was evaporated in vacuum. The solid
residue was triturated with 1 ml of dry C6D6, filtered and transferred to a J.
Young NMR tube. 1H NMR (C6D6, δ, ppm) 7.53 (s, 1H, HAr), 6.88-6.30 (m,
4H, HAr, HIm), 5.60 (br.s, 1H, HAr), 3.38 (s, 3H, OCH3), 2.14 (s, 9H, CH3),
2.00 (s, 3H, CH3), 1.92 (s, 3H, CH3). 13C NMR (C6D6, δ, ppm) 220.1 (d, J
= 3.9 Hz, NCN), 140.8 (Carom), 139.6 (Carom), 138.9 (Carom), 138.1 (Carom),
137.4 (Carom), 134.2 (Carom), 125.4 (Carom), 123.5 (q, 1JC,F = 292 Hz, CF3),
123.0 (q, 1JC,F = 289 Hz, CF3), 122.9 (Carom), 120.0 (Carom), 86.2-84.3 [m,
C(CF3)2], 56.2 (OCH3), 30.1 (CH3), 21.0 (CH3), 18.8 (CH3), 18.5 (CH3),
18.2 (CH3). 19F NMR (C6D6, δ, ppm) -66.93 (s, CF3), -69.96 (s, CF3).
129.7 (Carom), 126.8 (Carom), 125.4 (Carom), 123.9 (Carom), 122.1 (q, 1JC,F
=
290 Hz, CF3) , 121.8 (q, 1JC,F = 289 Hz, CF3), 118.4 (CH=CH2), 84.1-82.0
[m, C(CF3)2], 68.2 (OCH2), 21.5 (CH3), 21.2 (CH3), 19.0 (CH3), 18.5 (CH3),
17.5 (CH3). 19F NMR (CDCl3, δ, ppm) -67.70 (s, CF3), -71.48 (s, CF3).
Anal. Calcd for C26H27F6IN2O (%): C, 50.01; H, 4.36; N, 4.49. Found: C,
49.86; H, 4.26; N, 4.37.
Imidazolium iodide 10h. 0.3 g (2 mmol) of NaI was added to a reaction
mixture. Reaction was carried out at 60°C. Yield: 68% (m.p. 108-110°C).
1H NMR (CDCl3, δ, ppm) δ 10.05 (s, 1H, NCH-N), 7.59 (s, 2H, NCH-C),
7.56 (s, 1H, NCH-C), 7.56 (s, 1H, HAr), 7.36 (s, 1H, HAr), 7.00 (s, 2H, HAr),
5.09 (s, 1H, C=CH2), 4.95 (s, 1H, C=CH2), 4.08 (d, J = 12.0 Hz, 1H,
OCH2), 4.00 (d, J = 12.1 Hz, 1H, OCH2), 2.40 (s, 3H, CH3), 2.31 (s, 3H,
CH3), 2.19 (s, 3H, CH3), 2.11 (s, 3H, CH3), 2.08 (s, 3H, CH3), 1.75 [s, 3H,
C(=CH2)CH3]. 13C NMR (CDCl3, δ, ppm) δ 142.4 (NCN), 141.7 (Carom),
139.6 (Carom), 139.1 (Carom), 135.6 (Carom), 134.4 (Carom), 133.8 (Carom),
130.3 (Carom), 130.2 (Carom), 130.12 (Carom), 130.06 (C=CH2), 129.6
Synthesis of rhodium complex 12. A 20 ml Schlenk flask was charged
with 0.102 g (0.18 mmol) of imidazolium tetrafluoroborate 10a followed
by 10 ml of dry THF. Resulting suspension was degassed with Ar, cooled
to 0°C and 0.10 ml of 1.7M potassium tert-pentoxide solution in toluene
was added. Reaction mixture was stirred at ambient temperature for 30
min and resulting cloudy solution was added to solution of 0.0375 g (0.08
mmol) of chloro(1,5-cycloocta-diene)rhodium(I) dimer. Obtained yellow
solution was stirred overnight, and then opened to atmosphere; all
volatiles were removed in vacuum. Residue was dissolved in minimal
amount of CH2Cl2 and purified by flash chromatography using CH2Cl2 as
eluent, followed by 5:1 CH2Cl2-acetone mixture to yield 60 mg (55%) of
1
(Carom), 126.8 (Carom), 125.2 (Carom), 124.0 (Carom), 121.7 (q, JC,F = 290
1
Hz, CF3), 122.0 (q, JC,F = 290 Hz, CF3), 113.1 (C=CH2), 83.8-82.6 [m,
C(CF3)2], 70.4 (OCH2), 21.5 (CH3), 21.2 (CH3), 19.4 [C(=CH2)CH3], 18.9
(CH3), 18.5 (CH3), 17.4 (CH3). 19F NMR (CDCl3, δ, ppm) δ -68.30 (s, CF3),
-71.41 (s, CF3). Anal. Calcd for C27H29F6IN2O (%) C, 50.79; H, 4.58; N,
4.39. Found: C, 50.63; H, 4.70; N, 4.19.
1
product as yellow solid. H NMR (CDCl3, δ, ppm) 7.36 (s, 1H, HIm), 7.34
(s, 1H, HIm), 7.06 (s, 1H, HAr), 7.02 (s, 1H, HAr), 6.99 (s, 1H, HAr), 6.94 (s,
1H, HAr), 4.69-4.55 (m, 1H, HAr), 4.34 (q, J = 7.2, 6.7 Hz, 1H, CH2CH),
3.73-3.59 (m, 1H, CH2CH), 3.49 (s, 3H, OCH3), 3.25-3.14 (m, 1H,
CH2CH), 2.45 (s, 3H, CH3), 2.41 (s, 3H, CH3), 2.38 (s, 3H, CH3), 2.37 (s,
3H, CH3), 2.27 (s, 3H, CH3), 1.92-1.67 (m, 4H, CH2CH2), 1.63-1.35 (m,
Synthesis of imidazolium salts 11a,b. A mixture of imidazolium
tetrafluoroborate 5 (0.5 mmol), anhydrous Cs2CO3 (2 mmol) and MeI/or
EtI (2 mmol) was dissolved in 2 ml of CH3CN. The resulting suspension
was stirred until TLC analysis (acetone) showed absence of starting
imidazolium salt 5 (6 h). Reaction mixture was concentrated in vacuum,
residue dissolved in dichloromethane and filtered through Celite plug.
The filtrate was evaporated to dryness. Crystallization from 2 ml of
toluene afforded doubly alkylated imidazolium iodides 11a,b as a white
solids. Data for 11a: 1H NMR (CDCl3, δ, ppm) 7.94 (s, 1H, HIm), 7.88 (s,
1H, HIm), 7.52 (s, 1H, HAr), 7.47 (s, 1H, HAr), 7.09 (s, 2H, HAr), 3.62 (s, 3H,
OCH3), 2.48 (s, 3H, CH3), 2.36 (s, 3H, CH3), 2.12 (s, 3H, CH3), 2.11 (s,
3H, CH3), 2.08 (s, 3H, CH3), 2.04 (s, 3H, CH3). 13C NMR (CDCl3, δ, ppm)
146.0 (NCN), 142.3 (CAr), 142.0 (CAr), 138.3 (CAr), 135.5 (CAr), 134.3
1
4H, CH2CH2). 13C NMR (CDCl3, δ, ppm) 183.9 (d, JRh,C = 53 Hz, NCN),
141.7 (Carom), 138.7 (Carom), 138.5 (Carom), 138.2 (Carom), 136.6 (Carom),
134.4 (Carom), 134.1 (Carom), 129.8 (Carom), 128.4 (Carom), 127.2 (Carom),
125.7 (Carom), 124.0 (q, 1JC,F = 293 Hz, CF3), 123.8 (d, J = 3.8 Hz, Carom),
1
1
122.7 (Carom), 122.5 (q, JC,F = 293 Hz, CF3), 97.3 (d, JRh,C = 7.9 Hz,
1
2
CH2CH), 95.1 (d, JRh,C = 7.1 Hz, CH2CH), 84.2 [m, JC,F = 27 Hz,
C(CF3)2], 71.0 (d, 1JC,F = 15 Hz, CH2CH), 66.1 (d, 1JC,F = 14 Hz, CH2CH),
56.9 (OCH3), 34.2 (CH2), 31.3 (CH2), 29.9 (CH2), 27.1 (CH2), 21.5 (CH3),
21.3 (CH3), 20.9 (CH3), 20.2 (CH3), 18.9 (CH3). 19F NMR (CDCl3, δ, ppm)
This article is protected by copyright. All rights reserved.

10.1002/chem.201700624
Chemistry - A European Journal
FULL PAPER
-66.76 (s, CF3), -67.56 (s, CF3). HRMS m/z (ESI) calcd for
C32H36F6N2ORh [M-Cl]+: 681.1787, found 681.1781.
and 0.5 g (4.4 mmol) of 3-chloropyridine was added. Reaction mixture
was stirred overnight; all volatiles were removed in vacuum, purification
by flash chromatography using CH2Cl2 yielded 0.13 g (56%) of complex
14.
Synthesis of palladium complex 13. The mixture of 0.2 g (0.32 mmol)
of imidazolium iodide 10g and 0.0883 g (0.29 mmol) of Pd(acac)2 were
dissolved in 5 ml of 1,4-dioxane. Reaction mixture was heated at 90°C
until TLC showed full conversion of starting Pd(acac)2 to product (30 min).
After cooling to room temperature the reaction mixture was evaporated in
vacuum, residue was dissolved in minimum amount of EtOAc.
Purification by flash chromatography using 6:1 hexanes-EtOAc mixture
yielded 0.202 g (84%) of product as yellow solid (m.p. 156-158 °C, dec.).
1H NMR (CDCl3, δ, ppm) 7.54 (s, 1H, HIm), 7.26 (s, 1H, HIm) 7.06 (s, 1H,
HAr), 7.01 (s, 1H, HAr), 6.98 (s, 1H, HAr), 6.94 (s, 1H, HAr), 5.89-5.72 (m,
1H, CH=CH2), 5.25 (d, J = 17.4 Hz, 1H, CH=CH2), 5.16 (d, J = 10.5 Hz,
1H, CH=CH2), 5.06 [s, 1H, C(O)CH], 4.48-4.17 (m, 2H, OCH2), 2.41 (s,
3H, CH3), 2.37 (s, 3H, CH3), 2.34 (s, 3H, CH3), 2.30 (s, 3H, CH3), 2.10 (s,
3H, CH3), 1.78 [s, 3H, C(O)CH3], 1.75 [s, 3H, C(O)CH3]. 13C NMR (CDCl3,
δ, ppm) 186.6 (C=O), 183.4 (C=O), 154.9, (NCN), 141.9 (Carom), 139.6
(Carom), 139.2 (Carom), 136.2 (Carom), 135.9 (Carom), 135.7 (Carom), 135.7
(Carom), 135.5 (Carom), 135.4 (Carom), 134.8 (Carom), 134.5 (Carom), 133.2
(Carom), 129.7 (Carom), 129.0 (Carom), 126.4 (Carom), 126.1 (Carom), 123.5,
Palladium complex 15. Obtained by analogy with 14 using method A.
Yield: 85 % (m.p. 97-99 °C). 1H NMR (CDCl3, δ, ppm) 8.54 (d, JH,H = 2.3
Hz, 1H, HPy), 8.46 (dd, JH,H = 5.6, 1.4 Hz, 1H, HPy), 7.57-7.49 (m, 2H, HPy
,
HIm), 7.26 (s, 1H, HIm), 7.10-7.01 (m, 5H, HAr, HPy), 4.12 (m, 2H, CH2CH3),
2.45 (s, 3H, CH3), 2.43 (s, 3H, CH3), 2.42 (s, 3H, CH3), 2.37 (s, 3H, CH3),
2.16 (s, 3H, CH3), 1.09 (t, 3JH,H = 7.0 Hz, 3H, CH2CH3). 13C NMR (CDCl3,
δ, ppm) 152.0 (NCN), 150.7 (Carom), 149.7 (Carom), 139.2 (Carom), 139.0
(Carom), 137.5 (Carom), 136.2 (Carom), 135.9 (Carom), 135.8 (Carom), 135.2
(Carom), 133.9 (Carom), 129.7 (Carom), 129.6 (Carom), 128.1 (Carom), 126.9
(Carom), 126.3 (Carom), 124.4 (Carom), 123.3, 123.2 (q, 1JC,F = 293 Hz, CF3),
123.1 (q, 1JC,F = 293 Hz, CF3), 64.7 (OCH2), 21.6 (CH3), 21.3 (CH3), 20.5
(CH3), 19.8 (CH3), 19.7 (CH3), 15.8 (CH2CH3). 19F NMR (CDCl3, δ, ppm) -
65.25 (q, J = 6.5 Hz, CF3), -69.55 (q, J = 7.2 Hz, CF3). Anal. Calcd for
C30H31Cl3F6N3OPd (%): C, 46.41; H, 4.02; N, 5.41. Found: C, 46.28; H,
3.95; N, 5.21.
1
1
122.8 (q, JC,F = 292 Hz, CF3), 122.5 (q, JC,F = 291 Hz, CF3), 117.3
2
(CH=CH2), 99.6 (CH=CH2), 98.9 (CH=CH2), 83.9 [m, JC,F = 30 Hz,
Acknowledgements
C(CF3)2], 68.6 (OCH2), 27.2 [C(O)CH3], 27.0 [C(O)CH3], 25.5 [C(O)CH3],
25.1 [C(O)CH3], 21.5 (CH3), 21.2 (CH3), 20.2 (CH3), 19.3 (CH3), 18.9
(CH3). 19F NMR (CDCl3, δ, ppm) -67.23 (s, CF3), -69.00 (s, CF3). Anal.
Calcd for C31H34F6IN3OPd (%): C, 44.86; H, 4.13; N, 3.38. Found: C,
45.01; H, 3.99; N, 3.29.
This work was financially supported by the Russian Scientific
Foundation (grant RSF № 16-13-10364).
Keywords: N-Heterocyclic carbenes • unsymmetrical
Synthesis of palladium complex 14. Method A. A 20 ml Schlenk flask
was charged with 0.286 g (0.51 mmol) of imidazolium tetrafluoroborate
10a followed by 10 ml of dry THF. Resulting suspension was degassed
with Ar, cooled to 0°C and 0.3 ml of 1.7M potassium tert-pentoxide
solution in toluene was added. Reaction mixture was stirred at ambient
temperature for 30 min and resulting cloudy solution was added to
suspension of 0.198 g (0.49 mmol) of bis(3-chloropyridine)palladium
chloride. Obtained red solution was stirred overnight, and then opened to
atmosphere; all volatiles were removed in vacuum. Residue was
dissolved in minimal amount of CH2Cl2 and purification by flash
chromatography using CH2Cl2 as eluent yielded 0.35 g (90%) of yellow
powder (m.p. 141-143 °C). 1H NMR (CDCl3, δ, ppm) 8.53 (d, JH,H = 2.3
Hz, 1H, HPy), 8.45 (dd, JH,H = 5.6, 1.4 Hz, 1H, HPy), 7.54 (ddd, JH,H = 8.2,
2.2, 1.4 Hz, 1H, HPy), 7.48 (s, 1H, HIm), 7.26 (s, 1H, HIm), 7.10 – 7.00 (m,
5H, HAr, HPy), 3.66 (s, 3H, OCH3), 2.44 (s, 3H, CH3), 2.43 (s, 3H, CH3),
2.41 (s, 3H, CH3), 2.37 (s, 3H, CH3), 2.17 (s, 3H, CH3). 13C NMR (CDCl3,
δ, ppm) 151.7 (NCN), 150.7 (Carom), 149.7 (Carom), 141.4 (Carom), 139.2
(Carom), 139.0 (Carom), 137.4 (Carom), 136.2 (Carom), 135.7 (Carom), 135.7
(Carom), 135.2 (Carom), 133.9 (Carom), 132.0 (Carom), 129.7 (Carom), 129.6
(Carom), 127.7 (Carom), 126.6 (Carom), 125.1 (Carom), 124.4 (Carom), 123.7 (q,
imidazolium salts • fluorinated NHC ligands • metal catalysis
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1
1JC,F = 294 Hz, CF3), 123.2 (Carom), 122.9 (q, JC,F = 293 Hz, CF3), 83.6
2
[hept, JC,F = 28 Hz, C(CF3)2], 56.8 (OCH3), 21.7 (CH3), 21.3 (CH3), 20.4
(CH3), 19.6 (CH3), 19.6 (CH3). 19F NMR (CDCl3, δ, ppm) -66.34 (s, CF3), -
68.42 (s, CF3). Anal. Calcd for C29H29Cl3F6N3OPd (%): C, 45.69; H, 3.83;
N, 5.51. Found: C, 45.49; H, 3.93; N, 5.71. Method B. A 20 ml Schlenk
flask was charged with 0.172
g (0.31 mmol) of imidazolium
tetrafluoroborate 10a followed by 10 ml of dry THF. Resulting suspension
was degassed with Ar, cooled to 0°C and 0.17 ml of 1.7M potassium tert-
pentoxide solution in toluene was added. Reaction mixture was stirred at
ambient temperature for 30 min and resulting cloudy solution was added
to solution of 0.0985 g (0.26 mmol) of bis(benzonitrile)palladium chloride.
Obtained red solution was stirred overnight, all volatiles were removed in
vacuum. Residue was dissolved in minimal amount of CH2Cl2 and
purified by flash chromatography using CH2Cl2 as eluent. After
purification palladium complex was dissolved in 5 ml of dichloromethane
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10.1002/chem.201700624
Chemistry - A European Journal
FULL PAPER
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10.1002/chem.201700624
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
Layout 1:
FULL PAPER
Maxim A. Topchiy, Maria A. Zotova,
Salekh M. Masoud, Artur K. Mailyan,
Ivan V. Ananyev, Sergey E. Nefedov,
Andrey F. Asachenko, Sergey N.
Osipov*
Page No. – Page No.
An efficient and scaled-up synthesis of the imidazole-based unsymmetrical NHC
precursors bearing sterically demanding hexafluoroisopropylalkoxy-group
[(CF3)2(OR)C-] in ortho-position of N-aryl substituent is reported. The method
includes transformation of Mes-substituted oxazolinium tetrafluoroborate salt via the
reaction with the corresponding binucleophilic fluorinated aniline and subsequent O-
alkylation to access a new family of fluorinated NHC precursors.
Fluorinated Unsymmetrical N,N’-
Diaryl Imidazolium salts - new
functionalized NHC ligand precursors
This article is protected by copyright. All rights reserved.