Nucleophilic aromatic substitution with 2,3-dihydro-1,3-diisopropyl- 4,5-dimethylimidazol-2-ylidene

Article abstract of DOI:10.1515/znb-2009-1010

2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (1) reacts with an excess of hexafluorobenzene in the presence of boron trifluoride diethyletherate to give 1,3-diisopropyl-4,5- dimethyl-2-(perfluorophenyl) imidazolium tetrafluoroborate (2). Sol

Full text of DOI:10.1515/znb-2009-1010

Nucleophilic Aromatic Substitution with 2,3-Dihydro-1,3-diisopropyl-
4,5-dimethylimidazol-2-ylidene
Eyad Mallaha, Norbert Kuhna, Ca¨cilia Maichle-Mo¨ßmera, Manfred Steimanna,
Markus Stro¨belea, and Klaus-Peter Zellerb
a Institut fu¨r Anorganische Chemie der Universita¨t Tu¨bingen, Auf der Morgenstelle 18,
D-72076 Tu¨bingen, Germany
b Institut fu¨r Organische Chemie der Universita¨t Tu¨bingen, Auf der Morgenstelle 18,
D-72076 Tu¨bingen, Germany
Reprint requests to Prof. Dr. N. Kuhn. E-mail: norbert.kuhn@uni-tuebingen.de or
Prof. Dr. K.-P. Zeller. E-mail: kpz@uni-tuebingen.de
Z. Naturforsch. 2009, 64b, 1176 – 1182; received June 13, 2009
Dedicated to Professor Ekkehard Lindner on the occasion of his 75th birthday
2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (1) reacts with an excess of hexa-
fluorobenzene in the presence of boron trifluoride diethyletherate to give 1,3-diisopropyl-4,5-
dimethyl-2-(perfluorophenyl)imidazolium tetrafluoroborate (2). Solutions of 2 exhibit an equilib-
rium consisting also of hexafluorobenzene and 2,2ꢀ-(perfluoro-1,4-phenylene)bis(1,3-diisopropyl-
4,5-dimethylimidazolium)bis(tetrafluoroborate) (3) which is obtained from 1 and hexafluoroben-
zene in the ratio 2 : 1 on a preparative scale. Similar to 2, 2-(4-cyano-2,3,5,6-tetrafluorophenyl)-1,3-
diisopropyl-4,5-dimethylimidazolium tetrafluoroborate (4), 2-(2,4-dicyano-2,5,6-trifluorophenyl)-
1,3-diisopropyl-4,5-dimethylimidazolium tetrafluoroborate (5), and 2-(4,6-difluoro-1,3,5-triazin-2-
yl)-1,3-diisopropyl-4,5-dimethylimidazolium tetrafluoroborate (6) are obtained from 1 and perfluo-
robenzonitrile, 1,3-dicyano-2,4,5,6-tetrafluorobenzene, and 2,4,6-trifluoro-1,3,5-triazin, respectively.
The FAB mass spectra of compounds 2 – 6 and the results of the crystal structure analyses of com-
pounds 2 – 4 are discussed.
Key words: Carbenes, Heterocycles, Fluorine, Nucleophilic Aromatic Substitutions,
Mass Spectrometry, Crystal Structure
Introduction
now on our results of the reactions of nucleophilic car-
benes with perfluorinated arenes.
Starting with the pioneering work of Meisen-
heimer [1], the addition-elimination mechanism of the
nucleophilic aromatic substitution has found continu-
ous interest [2]. More recently, this type of reaction
has been extended to perfluorinated arenes predom-
inantly by reactions with anionic nucleophiles [3, 4].
Results and Discussion
Reaction of 2,3-dihydro-1,3-diisopropyl-4,5-dimethyl-
imidazol-2-ylidene with fluorinated arenes
2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-
Much less is known on the substitution of fluoride by 2-ylidene (1) undergoes nucleophilic aromatic
neutral nucleophiles such as amines [5] and in situ pre- substitution with fluorinated arenes in diethyl ether
pared nucleophilic carbenes [6].
to yield imidazolium compounds (Scheme 1). Appar-
Stable heterocyclic carbenes have been in the center ently, owing to the nucleophilic character of fluoride
of interest as strong nucleophiles [7] beginning with in organic solvents, equilibria are formed which need
their synthesis about 20 years ago [8, 9]. To the best the addition of boron trifluoride to generate stable
of our knowledge, their reaction with pentafluoropyri- salts. To avoid the formation of carbene adducts [11],
dine [10] is a single example of nucleophilic aromatic BF3 diethyletherate should not be in contact with the
substitution with these carbenes.
unreacted carbene.
We have become interested in the synthesis of
With hexafluorobenzene, the pentafluorophenylim-
perfluoroaryl-substituted imidazolium salts and report idazolium salt 2 is formed as the initial product.
c
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E. Mallah et al. · Nucleophilic Aromatic Substitution with 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene 1177
F
F
F
F
N
N
N
N
.
BF3 Et2O
–
F
BF4
F
F
+
F
F
F
F
2
1
F
F
F
F
+ 1/
.
N
N
N
BF3 Et2O
–
(BF4
)
2
N
Scheme 1.
3
BF4
BF3
+
F–
–
F
F
F
N F
N
F
F
N
N
N
N
+ C6F6
+ BF3
F
F
F
F
F
–
2
+ BF3
BF4
F
F
F
F
N
+ C6F6
+ BF3
N
N
+ 2
N
3
F
–
BF4
Scheme 2.
Apparently, the fluorinated arene ring is activated preferred over substitution of cyanide. The 6-position
towards nucleophilic aromatic substitution by intro- is attacked regioselectively resulting in the formation
duction of the electron-withdrawing heterocyclic sub- of the 2,4-dicyano-3,5,6-trifluorophenylimidazolium
stituent. To avoid the formation of the dicationic salt 3, salt 5. This reflects the superior quality of ortho/para-
an excess of hexafluorobenzeneis needed. On standing placed cyano groups to stabilize the negative charge
of 2 in solution for some hours, the formation of 3 and in the intermediate Meisenheimer complexes. Surpris-
hexafluorobenzene is detected. This dismutation reac- ingly, only mono-substitution of fluoride is observed
tion is an experimental proof for the reversibility of the with s-trifluorotriazin to give the salt 6 (Scheme 3).
formation of the Meisenheimer complex. The regen-
The imidazolium salts 2 – 6, obtained as stable col-
erated carbene is trapped by excess 2 with the forma- orless crystals in good yield, have been characterized
tion of 3 (Scheme 2). Using stoichiometric amounts by elemental analysis and NMR spectroscopy (see Ex-
of the carbene and hexafluorobenzene (2 : 1), 3 is pre- perimental Section).
pared easily on a preparative scale.
Crystal structure analyses
In pentafluorobenzonitrile, 1 attacks the 4-position
selectively to give the 4-cyano-2,3,5,6-tetrafluoro-
Because of the limited information to be drawn from
phenylimidazolium salt 4. Similarly in 1,3-dicyano- the (in part) complicated 13C and 19F NMR spectra,
2,4,5,6-tetrafluorobenzene, substitution of fluoride is we have determined the crystal structures of the salts 2,
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1178 E. Mallah et al. · Nucleophilic Aromatic Substitution with 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene
Table 1. Crystal data and structure refinement for C17H20BF9N2 (2), C32H46B2F12N6 (3 · 2CH3CN), C18H20F4N3BF4
(4 · CH3CN).
2
3 · 2CH3CN
4 · CH3CN
Empirical formula
Formula weight
Temperature, K
C17H23BF9N2
434.16
210(2)
C32H46B2F12N6
C20H23BF8N4
482.23
764.37
173(2)
173(2)
˚
λ, A
0.71073
Crystal system
Space group
monoclinic
P21/n
monoclinic
P21/c
14.185(2)
7.154(1)
23.128(3)
125.43(1)
1912.3(4)
4
orthorhombic
P212121
1122.1(1)
1122.1(1)
1837.1(2)
90
2313.2(3)
4
1.385
˚
a, A
11.003(2)
10.721(1)
16.841(3)
101.03(2)
1949.9(5)
4
1.479
0.147
888
˚
b, A
˚
c, A
β, deg
3
˚
Volume, A
Z
Dcalcd, g cm−3
1.327
0.120
796
µ (MoKα ), mm−1
F(000), e
0.128
992
θ, deg
Refls. coll.
2.44 – 25.95
21093
2.87 – 25.94
20505
5.74 – 26.36
32539
Refls. indep.
3786
3677
4660
Refinement method
Param. refined
Full-matrix least-squares on F2
328
342
0.980
0.0494 / 0.1353
0.0650 / 0.1424
+0.654 / −0.394
337
1.157
0.0719 / 0.1259
0.0916 / 0.1332
+0.242 / −0.200
Goodness-of-fit on F2
Final R1/wR2[I ≥ 2σ(I)]
Final R1/wR2 (all data)
0.894
0.0531 / 0.1340
0.0744 / 0.1443
+0.433 / −0.281
−3
˚
∆ρfin (max / min), e A
Fig. 1. View of the ion pair of C17H23BF9N2 (2) in the crys-
tal.
Scheme 3.
is near by perpendicular (2: 63(1)◦; 3 · 2CH3CN:
68(1)◦; 4 · CH3CN: 73.0(1)◦). In the six-membered
rings, the C–C bond lengths [2: 1.370(3)– 1.396(3);
3 · 2CH3CN, and 4 · CH3CN (Table 1, Figs. 1 – 3).
The central C–C bonds connecting the five- and six-
membered rings [2: 1.473(2); 3 · 2CH3CN: 1.476(2);
3 · 2CH3CN:
1.376(3)– 1.389(3);
˚
4 · CH3CN:
˚
1.364(5)– 1.393(5) A] and C–F bond lengths [2:
1.330(3)– 1.338(2); 3 · 2CH3CN: 1.335(2)– 1.337(2);
4 · CH3CN: 1.471(5) A] are at the short end of the
range observed for C(sp2)–C(sp2) single bonds [12].
The relative orientation of the rings inside the cations
˚
4 · CH3CN: 1.329(4)– 1.343(4) A] are as expected,
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E. Mallah et al. · Nucleophilic Aromatic Substitution with 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene 1179
˚
˚
Table 2. Selected bond lengths (A) and angles (deg) for Table 4. Selected bond lengths (A) and angles (deg) for
C17H23BF9N2 (2).
C20H23BF8N4 (4 · CH3CN).
C(1)–C(6)
C(1)–C(2)
C(1)–C(7)
C(2)–F(1)
C(2)–C(3)
C(3)–F(2)
C(3)–C(4)
C(4)–F(3)
C(4)–C(5)
C(5)–F(4)
C(5)–C(6)
C(6)–F(5)
C(7)–N(1)
C(7)–N(2)
N(1)–C(8)
C(8)–C(9)
C(9)–N(2)
1.387(3)
C(6)–C(1)–C(2)
C(6)–C(1)–C(7)
C(2)–C(1)–C(7)
C(3)–C(2)–C(1)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(6)–C(5)–C(4)
C(5)–C(6)–C(1)
N(1)–C(7)–N(2)
C(7)–N(1)–C(8)
C(9)–C(8)–N(1)
C(8)–C(9)–N(2)
C(7)–N(2)–C(9)
C(7)–N(2)–C(9)
117.5(2)
122.0(2)
120.5(2)
121.5(2)
119.3(2)
120.8(2)
119.2(2)
121.7(2)
108.9(2)
108.3(2)
107.2(2)
107.5(2)
108.1(2)
108.1(2)
C(1)–N(2)
C(1)–N(5)
C(1)–C(11)
C(3)–C(4)
C(3)–N(2)
1.331(4)
1.336(4)
1.471(5)
1.350(5)
1.389(4)
1.384(5)
1.382(5)
1.393(5)
1.341(4)
1.369(5)
1.329(4)
1.393(5)
1.383(5)
1.433(5)
1.342(4)
1.364(5)
1.343(4)
N(2)–C(1)–N(5)
109.1(3)
125.0(3)
125.7(3)
106.9(3)
107.7(3)
117.8(3)
122.1(3)
120.1(3)
121.5(3)
120.0(3)
118.7(3)
120.5(4)
120.7(3)
120.7(3)
121.1(3)
1.396(3)
1.473(2)
1.335(2)
1.370(3)
1.330(3)
1.376(3)
1.331(2)
1.378(3)
1.332(3)
1.371(3)
1.338(2)
1.340(2)
1.348(2)
1.389(2)
1.359(3)
1.384(2)
N(2)–C(1)–C(11)
N(5)–C(1)–C(11)
C(4)–C(3)–N(2)
C(3)–C(4)–N(5)
C(4)–N(5)
C(12)–C(11)–C(16)
C(12)–C(11)–C(1)
C(16)–C(11)–C(1)
C(13)–C(12)–C(11)
C(12)–C(13)–C(14)
C(15)–C(14)–C(13)
C(15)–C(14)–C(131)
C(13)–C(14)–C(131)
C(16)–C(15)–C(14)
C(15)–C(16)–C(11)
C(11)–C(12)
C(11)–C(16)
C(12)–F(16)
C(12)–C(13)
C(13)–F(13)
C(13)–C(14)
C(14)–C(15)
C(14)–C(131)
C(15)–F(14)
C(15)–C(16)
C(16)–F(15)
N(131)–C(131)–C(14) 178.8(5)
C(1)–N(2)–C(3)
C(1)–N(5)–C(4)
108.2(3)
108.1(3)
C(131)–N(131) 1.135(5)
˚
Table 3. Selected bond lengths (A) and angles (deg) for
C32H46B2F12N6 (3 · 2CH3CN)a.
C(1)–C(2)
C(1)–C(3)
C(1)–C(4)
C(2)–F(1)
C(2)–C(3)#1
C(3)–F(2)
C(4)–N(2)
C(4)–N(1)
N(1)–C(5)
C(5)–C(6)
C(6)–N(2)
1.380(2)
1.389(3)
1.476(2)
1.335(2)
1.376(3)
1.337(2)
1.335(2)
1.340(2)
1.388(2)
1.356(3)
1.382(3)
C(2)–C(1)–C(3)
C(2)–C(1)–C(4)
C(3)–C(1)–C(4)
C(3)#1–C(2)–C(1)
C(2)#1–C(3)–C(1)
N(2)–C(4)–N(1)
N(2)–C(4)–C(1)
N(1)–C(4)–C(1)
C(4)–N(1)–C(5)
C(6)–C(5)–N(1)
C(5)–C(6)–N(2)
C(4)–N(2)–C(6)
115.9(2)
121.7(2)
122.4(2)
122.1(2)
122.0(2)
108.8(2)
126.2(2)
125.0(2)
108.4(2)
106.8(2)
107.6(2)
108.4(2)
a
Symmetry transformation used to generate equivalent atoms:
#1 1−x, 1−y, 1−z.
as are the geometric parameters of the imidazolium
fragments [7]. For individual bond lengths and angles
see Tables 2 – 4. The structures of the cations in the
salts 5 and 6 have also been confirmed by preliminary
data of single crystal structure analyses.
FAB mass spectra
The imidazolium tetrafluoroborate 2 dissolved in a
m-nitrobenzylic alcohol matrix exhibits an abundant
ion at m/z = 347 (rel. int. 100 %) in the FAB spec-
trum. This ion represents the imidazolium cation. The
successive elimination of propene from the isopropyl
Fig. 2. View of the ion triple of C32H46B2F12N6
(3 · 2CH3CN) in the crystal.
substituents results in two fragments of minor intensi- The ion at 595 corresponds to an ion pair composed
ties at m/z = 305 (15%) and m/z = 263 (22 %). Com- of the dication and one tetrafluoroborate anion. This is
pound 3, containing a bis-imidazolium dication, shows substantiated by the appearance of a satellite peak at
a relatively weak signal for the doubly charged species 594 for the contribution of the 10B isotope (∼ 20 %).
at m/z = 254 (10 %). The FAB mass spectrum is dom- The base peak at m/z = 465 is generated by internal
inated by peaks at m/z = 595 (48%) and 465 (100%). dealkylation of the dicationic subunit of the m/z = 595
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1180 E. Mallah et al. · Nucleophilic Aromatic Substitution with 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene
Fig. 3. View of the ion pair of C20H23BF8N4
(4 · CH3CN) in the crystal.
At first glance, the FAB spectrum of the monosubsti-
tution product of trifluoro-1,3,5-triazine (compound 6)
looks rather confusing. Apart from the expected peak
for the corresponding imidazolium cation at m/z = 296
(28 %) a peak at m/z = 429 (46 %) appears when the
measurement is performed with m-nitrobenzylic alco-
hol as matrix material (Scheme 5). The formation of
Scheme 4.
this cation can be rationalized by nucleophilic dis-
placement of fluorine in 6 by an m-nitrobenzyloxy
group of the matrix yielding the cationic species a.
When the matrix glycerol (containing traces of water)
is offered as a potential nucleophile, peak a is shifted
to m/z = 368 (b) and 294 (c). Ions b and c are the sub-
stitution products obtained by attack of glycerol and
water, respectively, on the imidazolium salt 6 prior to
the transfer of ions from the matrix into the gas phase.
The FAB spectrum of 6, measured in glycerol, ex-
hibits a further peak at m/z = 181. Depending on the
Scheme 5.
experimental conditions of the FAB experiment, this
ion according to Scheme 4. This fragmentation process
peak can become the base peak. The only reasonable
cancels one positive and the negative charge of the ion
structure to describe this ion is the 1,4-diisopropyl-
pair and yields a singly charged cation. Subsequent ex-
2,3-dimethyl-imidazolium ion d. Its formation would
pulsion of up to three propene molecules is responsible
require the reductive elimination of the 2,4-difluoro-
for the formation of ions at m/z = 423 (6 %), 361 (10 %)
1,3,5-triazinyl substituent in 6. Tentatively, we suggest
and 339 (8 %).
that the secondary carbinol function of glycerol trans-
fers a hydride to the C2-position of 6.
The imidazolium salts 4 and 5 behave like com-
pound 2 in the FAB experiment and yield intense im-
idazolium cation peaks at m/z = 354 (100 %) and 361
(100 %), respectively, followed by fragments of minor
Experimental Section
intensity for the loss of one and two propenes (4: m/z =
312, 270; 5: m/z = 319, 277).
FAB mass spectra (positive mode): The FAB spectra
were recorded on a TSQ 70 quadrupol mass spectrometer
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E. Mallah et al. · Nucleophilic Aromatic Substitution with 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene 1181
with xenon atoms as bombarding particles (kinetic energy
ca. 8 keV). Unless otherwise stated, m-nitrobenzyl alcohol
was used as matrix material at an ion source temperature of
ca. 50 ◦C. For results see text.
All experiments were performed in purified solvents un-
der argon. 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimid-
azol-2-ylidene (1) was obtained according to a published pro-
cedure [9].
CCDC 737798 (2), CCDC 737799 (3 · 2CH3CN) and
CCDC 737800 (4 · CH3CN) contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data request/cif.
C H BF N (4)
18 20 8 3
To a solution of 2,3-dihydro-1,3-diisopropyl-4,5-dimeth-
ylimidazol-2-ylidene (1, 0.370 g, 2.05 mmol) in 35 mL of
diethyl ether, pentafluorobenzonitrile (0.246 mL, 2.04 mmol)
was added at −70 ◦C. The mixture was stirred for 12 h at r. t.,
and trifluoroborane diethyletherate (0.260 mL, 2.24 mmol)
was added dropwise. After stirring for further 4 h at r. t.,
the resulting precipitate was isolated, washed with diethyl
ether, and dried in vacuo. Yield after recrystallization from
acetonitrile/diethyl ether: 0.780 g (86 %), colorless plates. –
1H NMR (CD3CN): δ = 1.52 (d, 12 H, 1,3-CHMe2, 3J =
6.7 Hz), 2.55 (s, 6 H, 4,5-Me), 4.57 (sept, 2 H, CHMe2). –
11B NMR (CD3CN, BF3 · Et2O ext.): δ = −1.33. – 13C NMR
(CD3CN): δ = 9.3 (4,5-Me), 20.0 (1,3-CHMe2), 53.1 (1,3-
CHMe2), 106.6 – 149.3 (m, CPh),108.6 (CN), 128.6 (CIm2),
130.8 (CIm4,5). – 19F NMR (CD3CN), CCl3F ext.): δ =
−152.2 (BF4), −130.0, −133.1 (2,6-F, 3,5-F). – Elemental
analysis for C18H20BF8N3 (441.17): calcd. C 49.00, H 4.57,
N 9.52; found C 49.48, H 4.60, N 9.89.
C
H BF N (2)
17 20 9 2
2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-
ylidene (1, 0.460 g, 2.55 mmol) was added to a solution
of hexafluorobenzene (2.00 mL, 17.33 mmol) in 35 mL
of diethyl ether at −70 ◦C. The mixture was stirred for
12 h at r. t., and trifluoroborane diethyletherate (0.32 mL,
2.77 mmol) was added dropwise. After stirring for further
4 h at r. t., the resulting precipitate was isolated, washed
with diethyl ether, and dried in vacuo. Yield after recrys-
tallization from acetonitrile/diethyl ether: 0.860 g (78 %),
colorless plates. – 1H NMR (CD3CN): δ = 1.36 (d, 12
H, 1,3-CHMe2, 3J = 6.6 Hz), 2.33 (s, 6 H, 4,5-Me), 4.37
(sept, 2 H, CHMe2). – 11B NMR (CD3CN, BF3 · Et2O
ext.): δ = −1.38. – 19F NMR (CD3CN, CCl3F ext.): δ =
−152.1 (BF4), −135.7, −147.0, −159.8 (2,6-F, 3,5-F,
4-F). – Elemental analysis for C17H20BF9N2 (434.15):
calcd. C 47.03, H 4.64, N 6.45; found C 47.03, H 4.81,
N 5.76.
C
H
19 20
BF N (5)
7 4
To
a solution of 2,3-dihydro-1,3-diisopropyl-4,5-di-
methylimidazol-2-ylidene (1, 0.461 g, 2.56 mmol) in
35 mL of diethyl ether, tetrafluoroisophtalonitrile (0.511 g,
2.55 mmol) was added at −70 ◦C. The mixture was stirred for
12 h at r. t., and trifluoroborane diethyletherate (0.323 mL,
2.79 mmol) was added dropwise. After stirring for further
4 h at r. t., the resulting precipitate was isolated, washed
with diethyl ether, and dried in vacuo. Yield after recrys-
tallization from acetonitrile/diethyl ether: 0.980 g (86 %),
colorless crystals. – 1H NMR (CD3CN): δ = 1.37 (d, 12
H, 1,3-CHMe2, 3J = 6.7 Hz, 2.37 (s, 6 H, 4,5-Me), 4.33
(sept, 2 H, CHMe2). – 11B NMR (CD3CN, BF3 · Et2O
ext.): δ = −1.34. – 13C NMR (CD3CN): δ = 9.5 (4,5-
Me), 20.2 (1,3-CHMe2), 53.6 (1,3-CHMe2), 99.7 – 162.1 (m,
CPh), 106.0, 108.9 (CN),; 127.4 (CIm2), 131.2 (CIm4,5). –
19F NMR (CD3CN), CCl3F ext.): δ = −152.4 (BF4), −99.3,
−112.1, −129.5 (2-F, 3-F, 5-F). – Elemental analysis for
C19H20BF7N4 (448.18): calcd. C 50.92, H 4.50, N 12.50;
found C 50.60, H 4.48, N 11.63.
C
H
28 40
B F N (3)
2 12 4
To
a solution of 2,3-dihydro-1,3-diisopropyl-4,5-di-
methylimidazol-2-ylidene (1, 0.490 g, 2.72 mmol) in 35 mL
of diethyl ether, hexafluorobenzene (0.157 mL, 1.36 mmol)
was added at −70 ◦C. The mixture was stirred for 12 h at r. t.,
and trifluoroborane diethyletherate (0.172 mL, 1.36 mmol)
was added dropwise. After stirring for further 4 h at r. t.,
the resulting precipitate was isolated, washed with diethyl
ether, and dried in vacuo. Yield after recrystallization from
acetonitrile/diethyl ether: 0.928 g (56 %), colorless nee-
dles. – 1H NMR (CD2Cl2): δ = 1.52 (d, 12 H, 1,3-
C
H BF N (6)
14 20 6 5
To a solution of 2,3-dihydro-1,3-diisopropyl-4,5-dimeth-
CHMe2, 3J = 6.7 Hz), 2.41 (s, 6 H, 4,5-Me), 4.61 (sept, 2 ylimidazol-2-ylidene (1, 0.475 g, 2.63 mmol) in 35 mL of
H, CHMe2). – 11B NMR (CD2Cl2, BF3 · Et2O ext.): δ = diethyl ether, cyanuric trifluoride (0.22 mL, 2.61 mmol) was
−1.41. – 13C NMR (CD2Cl2): δ = 9.0 (4,5-Me), 19.3 (1,3- added at −70 ◦C. The mixture was stirred for 12 h at r. t., and
CHMe2), 52.9 (1,3-CHMe2), 106.4 – 145.6 (m, CPh), 126.2 trifluoroborane diethyletherate (0.334 mL, 2.91 mmol) was
(CIm2), 129.1 (CIm4,5). – 19F NMR (CD2Cl2, CCl3F ext.): added dropwise. After stirring for further 4 h at r. t., the re-
δ = −153.4 (BF4), −132.0 (2,3,5,6-F). – Elemental anal- sulting precipitate was isolated, washed with diethyl ether,
ysis for C28H40B2F12N4 (682.20): calcd. C 49.29, H 5.91, and dried in vacuo. Yield after recrystallization from ace-
N 8.21; found C 49.19, H 6.24, N 7.84.
tonitrile/diethyl ether: 0.850 g (85 %), colorless needles. –
Unauthenticated
Download Date | 10/7/15 9:23 AM

1182 E. Mallah et al. · Nucleophilic Aromatic Substitution with 2,3-Dihydro-1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene
1H NMR (CD3CN): δ = 1.42 (d, 12 H, 1,3-CHMe2, 3J = CCl3F ext.): δ = −152.1 (BF4), −33.5 (3,5-F). – Elemental
6.7 Hz), 2.32 (s, 6 H, 4,5-Me), 4.80 (sept, 2 H, CHMe2). – analysis for C14H20BF6N5 (383.14): calcd. C 43.89, H 4.26,
11B NMR (CD3CN, BF3 · Et2O ext.): δ = −1.34. – 13C NMR N 18.18; found C 43.93, H 5.60, N 18.04.
(CD3CN): δ = 9.7 (4,5-Me), 19.9 (1,3-CHMe2), 53.0 (1,3-
Acknowledgement
CHMe2), 129.1 (CIm2), 130.8 (CIm4,5), 167.1 (t, Ctriaz2, 3J =
6.9 Hz), 170.6 – 172.9 (m, Ctriaz 4,6). – 19F NMR (CD3CN),
We are indebted to Dr. P. Haiß for his skillful assistance.
z
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Unauthenticated
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