Synthesis of highly substituted 2-13c-imidazolium salts and metal NHC complexes for the investigation of electronic unsymmetry by NMR

Article abstract of DOI:10.1055/s-0033-1338496

Complexes of unsymmetrically substituted N-heterocyclic carbenes with NMR-active metals (Ag, Hg, Pt) with or without a ¹³C-label in the 2-position were synthesized by aldimine cross coupling and analyzed with respect to the scalar couplings between the metal center or C2 and the other ring atoms. Georg Thieme Verlag Stuttgart. New York.

Full text of DOI:10.1055/s-0033-1338496

PAPER
▌2251
13
paper
Synthesis of Highly Substituted 2- C-Imidazolium Salts and Metal NHC
Complexes for the Investigation of Electronic Unsymmetry by NMR
Investigation of Electronic Unsymmetry by NMR
Jens Emsermann,a Anthony J. Arduengo, III,b Till Opatz*a
a
Institut für Organische Chemie, Johannes Gutenberg-Universität Mainz, Duesbergweg 10–14, 55128 Mainz, Germany
Fax +49(6131)3922338; E-mail: opatz@uni-mainz.de
b
Department of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, AL 35487-0336, USA
Received: 10.04.2013; Accepted after revision: 17.05.2013
are also potential probes for a broken symmetry. Since
there are no prior reports on the effects of broken symme-
try on the NMR-spectroscopic behavior of NHC–metal
complexes, we evaluated various NMR parameters for
their usefulness in this respect.
Abstract: Complexes of unsymmetrically substituted N-heterocy-
clic carbenes with NMR-active metals (Ag, Hg, Pt) with or without
a
13C-label in the 2-position were synthesized by aldimine cross
coupling and analyzed with respect to the scalar couplings between
the metal center or C2 and the other ring atoms.
Key words: N-heterocyclic carbenes, 13C labeling, NMR-active
metals, cross-coupling, spectroscopy
N
N
N
N
N-Heterocyclic carbenes, in particular those of the imid-
azole-2-ylidene type, have found widespread application
as ligands for numerous metals.1 The resulting complexes
exhibit high catalytic activity in Heck reactions,2–4
C(sp2)–C(sp2) couplings5 or olefin metathesis.6 Moreover,
imidazol-2-ylidenes themselves are active organocata-
lysts for Stetter-type umpolung processes, benzoin con-
densations, or intramolecular redox reactions.7,8
1
2
Figure 1 Some frequently used imidazol-2-ylidenes
While the electronic and steric properties of frequently
used 1,3-disubstituted imidazol-2-ylidenenes as ligands
like IMes 1 or IPr 2 (Figure 1) have been investigated in
some detail,9 the electronic consequences of unsymmetri-
cal substitution in this compound class are poorly under-
stood. This latter point is particularly important because
the high s-orbital character of the carbene center’s non-
bonding electrons frequently results in geometries in
which a coordinated metal center is substantially dis-
placed from the idealized imidazole axis of C2 symmetry
that passes through the carbene. Consider as examples the
following metal adducts and their distortions from the ide-
alized geometries: Ge 12°,10 Sb 19°,11 Yb 33°,12 Ba 30°,13
and B 12°.14 From the previous list of distortion examples,
it is evident that geometric distortions can occur both
within the plane of the imidazole (Ge, Sb, Yb) as well as
outside the plane. This present study focuses on effects of
in-plane distortions.
The aldimine cross-coupling reaction, i.e. the addition of
deprotonated α-aminonitriles 4 to aldimines 5 followed by
atmospheric oxidation of the resulting enediamines 6, per-
mits facile construction of diimines 7 with four variable
substituents.15 The latter compounds can be cyclized to
1,3,4,5-tetrasubstituted imidazolium chlorides 8 upon re-
action with a formaldehyde equivalent such as chloro-
methyl methyl ether (MOMCl) or paraformaldehyde in
the presence of hydrochloric acid (Scheme 1).16,17
A series of six aminonitriles 3a–f were synthesized by
Strecker reaction of the corresponding aldehydes and
amines with potassium cyanide in the presence of acetic
Table 1 Synthesis of α-Aminonitriles 3a–f by Strecker Reaction
KCN
AcOH
CN
O
R1
R1 NH2
+
R2
N
R2
H
H
3
As a result of steric or electronic differences between the
N-substituents, metal coordination will be permanently
distorted in complexes of unsymmetrical imidazol-2-yli-
denes in solution. To detect such time-averaged devia-
tions, scalar couplings from the metal to N1/N3 or C4/C5
can be analyzed that should respond to bending of the C2–
metal bond. Furthermore, intraresidual scalar couplings
R1
R2
Product
Yield (%)
mesityl
4-ClC6H4
4-FC6H4
4-FC6H4
4-FC6H4
4-FC6H4
4-FC6H4
3a
3b
3c
3d
3e
3f
54
66
74
17
65
45
CH2CH2Ph
CHPh2
1-adamantyl
Me
SYNTHESIS 2013, 45, 2251–2264
Advanced online publication: 09.07.2013
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1338496; Art ID: SS-2013-T0283-OP
© Georg Thieme Verlag Stuttgart · New York
i-Pr

2252
J. Emsermann et al.
PAPER
over, the corresponding products were difficult to purify
and were not further characterized.
Imidazolium salts 8, with a 13C label in the 2-position,
were obtained from compounds 7 by reaction with 13C-
paraformaldehyde and hydrochloric acid and purified by
column chromatography (Table 4).
N
N
C
CN
R2
KHMDS
NH
R1
R2
NH
R1
R2
NH
R1
THF
4
3
H
R1
R2
N
N
R4
R4
− CN−
R3
N
To prepare the mercury–NHC complexes, salts 8a, 8c,
and 8d were treated with mercury(II) acetate in tetrahy-
drofuran–dimethyl sulfoxide for 15 hours at room temper-
ature. After concentration in vacuo and purification by
column chromatography, the 2:1 carbene–Hg2+ complex-
es 9a–c were obtained in moderate to high yields as color-
less crystalline solids.9 The 2:1 carbene–Pt2+ complexes
were prepared from salts 8a and 8f via the silver(I) com-
plexes, which in turn were obtained by treating the imid-
azolium salts with silver(I) oxide in dichloromethane.19
Subsequent reaction with potassium tetrachloroplati-
nate(II) and purification by column chromatography gave
9g and 9h in 28% and 47% yield, respectively.20 Interest-
ingly, the 1:1 carbene–Ag1+ complex 9f was isolated when
the same procedure was applied to imidazolium salt 8e
(Table 5, Scheme 2).
5
R3
CN
R1
N
R3
HN R4
R1 NH
R2
R3
HN R4
R1 NH
R2
R3
N
R2
R4
6
R1
R2
N
R1
N
N
R4
(CH2O)n
O2
Cl−
N
R4
R3
R2
R3
HCl, dioxane
7
8
R1
R1
R2
R3
R2
Cl−
M2+
N
N
N
R4
N
R4
R3
Cl−
metal salt
9
R4
N+
13C
Scheme 1 Aldimine cross coupling via deprotonated α-aminonitriles
and preparation of imidazolium salts 8
R4
R3
R2
R3
R2
Ag2O (0.5 equiv)
N
13C Ag Cl
H
CH2Cl2,
r.t., 18 h
N
R1
Cl−
N
R1
9d–f
acid (Table 1). Their cross-coupling partners, aldimines 5,
were prepared by condensation of anilines and benzalde-
hyde derivatives (Table 2).
8a,c–f
K2PtCl4
CH2Cl2
r.t., 24 h
Hg(OAc)2
THF
DMSO (cat.)
r.t., 24 h
Table 2 Preparation of Aldimines 5
R4
R4
R4
R4
AcOH (cat.)
MgSO4
R3
R2
R3
R2
R3
R2
R3
R2
O
Cl−
Hg2+
Cl−
Cl
13C Pt
N
13C
N
R1
N
N
N
R4
R4 NH2
+
R3
N
13C
13C
R3
H
– H2O
N
R1
N
R1
N
R1
Cl
5
R3
R4
Product
Yield (%)
9a–c
9g,h
Scheme 2 Preparation of the 2-13C-labeled NHC metal complexes
4-ClC6H4
4-MeC6H4
5a
5b
5c
5d
83
73
63
72
4-EtOC6H4
4-MeOC6H4
2-Me-5-BrC6H3
Ph
Ph
Ph
For comparison of their NMR data with those of the un-
symmetrical compounds, the symmetrical tetrasubstituted
imidazolium salt 11 was prepared by condensation of ben-
zil with 4-ethoxyaniline to give diimine 10 and cyclization
of 10 with unlabeled paraformaldehyde. In analogy to the
preparation of compounds 9a and 9f, the 2:1 carbene–
Hg2+ complex 12 and the 1:1 carbene–Ag+ complex 13
were synthesized. The known 1:1 carbene–Hg2+ complex
14 of the IMes ligand was obtained according to a proce-
dure by Mohr et al. using IMes·HCl and tetramethylam-
monium chloride in combination with mercury(II) oxide
(Scheme 3).21
It had been observed that aldimines devoid of an aromatic
or electron-withdrawing N-substituent or with an enoliz-
able substituent R3 gave poor yields in the aldimine cross
coupling.18 The previously employed procedure involved
deprotonating substrates 3 with potassium hexamethyl-
disilazanide in tetrahydrofuran at –50 °C and adding the
electrophiles 5 after a deprotonation period of three min-
utes and warming the solution to –20 °C gradually over
100 minutes. Substitution of the argon atmosphere by air
effects the rapid oxidation of the intermediates 6 to
diimines 7 which, after aqueous workup, were purified by
preparative TLC (Table 3). Aminonitriles 3a, 3c, and 3d
gave low coupling yields due to the steric bulk of their N-
substituents. The same holds true for aldimine 5d. More-
First attempts to measure the three-bond couplings be-
tween 199Hg (I = ½, natural abundance 16.9%) and C4/C5
by 13C NMR in 12 were unsuccessful; no satellite signals
could be detected for their resonances, the intensity of
which is low due to their degree of substitution. The use
of the UDEFT technique, which enhances the signals of
quaternary carbons by an enhanced relaxation,22 did re-
Synthesis 2013, 45, 2251–2264
© Georg Thieme Verlag Stuttgart · New York

PAPER
Investigation of Electronic Unsymmetry by NMR
2253
Table 3 Aldimine Cross Coupling for the Preparation of Diimines 7
1) KHMDS
R4
R1
N
N
R4
R3
N
CN
2)
5
R1
R2
N
3) air
R2
R3
H
3
7
Aminonitrile
Aldimine
Product
Product
Yield (%)
N
N
3b
5a
7a
64
F
Cl
N
N
OEt
3b
5b
7b
42
F
N
N
N
N
N
N
3f
3e
3e
3e
3f
5a
5a
5b
5c
5c
7c
36
44
44
48
14
F
Cl
N
7d
F
Cl
Me
N
N
N
OEt
7e
F
Me
OMe
7f
F
OMe
7g
F
N
N
OMe
3b
5c
7h
28
F
veal the 199Hg satellites of the C2 resonance in 12 with a NHCs should give the same negative result; their reso-
very low intensity (1JC,Hg = 2715 Hz), but gave insuffi- nances are even lower in intensity due to the broken sym-
cient enhancement for the signals of C4 and C5. It became metry although the solubility of these complexes is higher
clear that complexes of the same type with unsymmetrical compared to their symmetrical counterparts. The silver
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2251–2264

2254
J. Emsermann et al.
PAPER
Table 4 Synthesis of the 13C-Labeled Imidazolium Salts 8
complexes 9f and 13 were investigated next and a better
signal intensity was expected, since silver only consists of
NMR active isotopes (107Ag, I = ½, natural abundance
51.8%; 109Ag, I = ½, natural abundance 48.2%) that have
similar gyromagnetic ratios. In the case of 9f however, the
C2 resonance was a very broad singlet. A similar observa-
tion has already been made by Wang and Lin who attrib-
uted it to fast dynamic equilibria between (NHC)AgCl
and [(NHC)2Ag]+.23 Bergbreiter and co-workers have
studied the concentration and temperature dependence of
the C2 resonances in 13C-labeled silver–NHC complexes
and found that dilution or lower temperature leads to a
slower exchange and makes the one-bond coupling from
107/109Ag to C2 visible.24 When the NMR sample of 9f
(0.13 M in CDCl3) was diluted to a concentration of 7.1
mM, a broad doublet (1JC,Ag = 252 Hz, see Supporting In-
formation) for C2 was found while the C4 and C5 reso-
nances did not change significantly, the former signal
R4
N
R4
R3
R2
Cl−
H
R3
R2
(
13CH2O)n
N
13C
N+
HCl, dioxane
THF
N
R1
R1
7
8
Diimine
Imidazolium salt
Product
Yield (%)
Cl
N
13C
N+
Cl−
H
7a
8a
75
F
2
being a doublet of JC,C = 1.7 Hz. This doublet splitting
was somewhat smaller than in the parent imidazolium salt
(2JC,C = 2.3 Hz). In the unlabeled complex 13, the C2 res-
onance was not visible and no coupling was observed for
the other ring carbons. In contrast to the Ag+ complexes,
the known 1:1 carbene–Hg2+ complex 14 showed an ap-
preciable NMR behavior with several coupling constants
Cl
N
7c
8b
87
79
13C
H
N+ Cl−
F
4
1
being easily visible (H4,5: JH,Hg = 23.8 Hz, C1: JC,Hg
=
3
2553.3 Hz, C4,5: JC,Hg = 74.9 Hz) without dilution both
Cl
in the UDEFT and the standard 1D 13C NMR spectrum.
We then turned to the 13C-labeled imidazolium salts 8, in
which the resonances of the carbons C4,5 and the nitro-
gens N1,3 should be split into doublets. Indeed, the 1JC,N
and 2JC,C couplings could be easily detected in the 1H,15N
HMBC, and 13C NMR spectra, respectively, and differed
in magnitude in agreement with the unsymmetrical substi-
tution. On the other hand, the results obtained with the
metal complexes 9a–f were less rewarding. The mercury
complexes 9a–c exclusively exhibited the very well visi-
ble one-bond coupling from 199Hg to the fully labeled 2-
position [1JC,Hg = 2850 Hz (9a), 2759 Hz (9b), 2845 Hz
(9c)]. The same was found for the platinum complexes 9g
and 9h, in which the satellites are more intense than in the
Hg complexes (195Pt, I = ½, natural abundance 33.8%).
Again, the one-bond coupling could be easily observed
[1JC,Pt = 943 Hz (9g), 943 Hz (9h)]. Surprisingly, none of
the metal complexes except for 9f exhibited a visible split-
ting of the resonances of C4 and C5. Their full width at
half maximum (FWHM) indicated that the formation of
the complexes had drastically reduced the two-bond cou-
plings to C2. In particular, the C4 resonances in the com-
plexes 9a, 9c, 9g, and 9h had linewidths at or below 1.5
Hz while the C5 resonances in 9a, 9c, and 9h were 2.6–
2.9 Hz wide. This is still significantly less that the widths
of the corresponding doublet signals in the respective im-
idazolium salts (Table 6).
N
7d
8c
13C
N+
H
Cl−
Me
F
OEt
N
7e
8d
83
13C
N+
H
Cl−
Me
F
OMe
N
7f
8e
89
13C
N+
H
Cl−
Me
F
OMe
N
13C
N+
H
Cl−
7h
8f
49
F
Unfortunately, no splitting of the N1 and N3 resonances
could be seen in 1H,15N HMBC spectra since the substitu-
tion of H2 by a metal removes the most intense cross
peaks. The multiple bond correlations from any side-chain
Synthesis 2013, 45, 2251–2264
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PAPER
Investigation of Electronic Unsymmetry by NMR
2255
OEt
OEt
NH2
toluene, (CH2O)n
r.t, 5 min
Cl−
EtO
OEt
N
DCE
72 h, 70 °C
O
Ph
N+
Ph
N
Ph
2
+
Ph
Ph
then: HCl, dioxane
r.t., 50 h
71%
66%
N
O
Ph
11
Ag2O (0.5 equiv)
CH2Cl2
r.t., 18 h
Hg(OAc)2, THF
EtO
DMSO (cat.)
r.t., 24 h
79%
10
57%
OEt
OEt EtO
HgO
(Me4N)Cl
Cl−
Hg2+
Cl−
Ph
Ph
Ph
Ph
Ph
N+
Cl
Hg
Cl
N
N
N
N
N
N
N
Ag
Cl
Cl−
CH2Cl2
r.t., 15 h
82%
N
N
Ph
OEt
OEt EtO
14
12
13
Scheme 3 Preparation of unlabeled symmetrical NHC–metal complexes
protons to the ring nitrogens in the unsymmetrical metal traresidual scalar couplings were observed in the 2-13C-la-
complexes 9 were too weak to be detected.
beled NHC precursors and responded to complexation of
a metal. Further investigations are required to assess the
usefulness of these parameters as probes for the analysis
of in-plane distortions in NHC metal complexes in solu-
tion.
In summary, no useful nontrivial metal-to-ligand cou-
plings could be measured in any of the investigated
1,3,4,5-tetrasubstituted imidazol-2-ylidene ligands due to
an unfavorable S/N ratio. In contrast, unsymmetrical in-
Table 5 Synthesis of the 13C-Labeled NHC Metal Complexes
Imidazolium salt
Product
Product
Yield (%)
F
F
Cl−
N
N
N
8a
9a
63
13C
Hg2+
Cl−
13C
N
Cl
F
Cl
F
Me
Me
Cl−
N
13C
N
N
Hg2+
Cl−
13C
N
8c
9b
(mixture)
Cl
F
Cl
F
Me
Me
Cl−
N
N
13C
N
Hg2+
Cl−
13C
N
8d
9c
46
OEt
EtO
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2251–2264

2256
J. Emsermann et al.
PAPER
Table 5 Synthesis of the 13C-Labeled NHC Metal Complexes (continued)
Imidazolium salt
Product
Product
Yield (%)
Cl
Cl
Cl
Pt
Cl
N
N
N
13C
13C
8a
9g
28a
N
F
F
F
F
Cl
N
N
47a
13C
N
Pt
Cl
13C
8f
9h
N
OMe
MeO
F
Me
N
13C
N
Ag
Cl
8e
9f
52a
OMe
a Over 2 steps.
Table 6 Coupling Constants in Metal Complexes 9a–c,g,h,f and Their Parent Imidazolium Salts 8a–f
Metal complex
δ (13C)
FWHM (Hz)
Salt
δ (13C)
1JCN (Hz)
2JCC (Hz)
9a
C4
C5
131.3
132.1
1.3
2.9
8a
131.5
130.5
N3 17.1
N1 17.2
2.2
3.3
a
9b
9c
9g
9h
9f
C4
C5
133.4–133.5
132.5
–
8c
8d
8a
8f
131.8
130.9
N3 17.0
N1 17.1
2.1
2.7
C4
C5
133.0
132.8
1.3
2.6
131.6
131.1
N3 17.2
N1 17.3
2.9
2.3
C4
C5
130.5
130.7
1.4
1.7
130.5
131.5
N3 17.1
N1 17.2
3.3
2.2
C4
C5
130.0
133.0
1.5
2.8
131.1
132.0
N3 16.9
N1 18.2
2.4
3.2
C4
C5
131.3
131.6
2.6b
1.1
8e
131.4
131.7
N3 18.0
N1 17.4
2.3
3.1
a FWHM could not be determined due to signal overlap.
b d, 2JCC = 1.7 Hz.
1H and 13C NMR spectra were recorded on a Bruker AC300,
Avance II-400 or Avance III-600 spectrometer, chemical shifts
were referenced to the residual solvent signal (CDCl3: δH = 7.26,
δC = 77.16; DMSO-d6: δH = 2.50, δC = 39.52).25 For ESI-MS analy-
ses, an Agilent Technologies 1200 series HPLC with a binary pump
system and a diode array detector in conjunction with a Bruker
LCD/MSD trap mass spectrometer was used. For ionization, an
electrospray ion source was employed. ESI-HRMS spectra were
measured on a Waters Q-TOF-Ultima 3 equipped with a dual inter-
face. FT-IR spectra were recorded on a Bruker Tensor 27 apparatus
using a diamond ATR unit. The melting points are determined with
a Krüss KSP1N semi-automatic apparatus. All reactions are carried
out in dried glassware and inert atmosphere (argon) in anhydrous
Synthesis 2013, 45, 2251–2264
© Georg Thieme Verlag Stuttgart · New York

PAPER
Investigation of Electronic Unsymmetry by NMR
2257
solvents. THF was freshly distilled over Na/benzophenone under
argon, CH2Cl2 was freshly distilled over CaH2 under argon.
(4-Fluorophenyl)(1-adamantylamino)acetonitrile (3d)
Prepared from 4-fluorobenzaldehyde (3.72 g, 30.0 mmol) and 1-ad-
amantylamine (4.54 g, 30.0 mmol) according to general procedure
A. Crystalline solid; yield: 1.43 g (17%); mp 109.6–110.1 °C,
Rf = 0.25 (cyclohexane–EtOAc, 10:1).
Aminonitriles 3a–f; General Procedure A (Table 1)
A soln of amine (60 mmol) in MeOH (10 mL) was added to a sus-
pension of KCN (120 mmol) and aldehyde (60 mmol) in MeOH
(90 mL) at 0 °C. AcOH (15 mL) in MeOH (10 mL) was then added
slowly. After stirring at r.t. for 18 h, sat. aq NaHCO3 (50 mL) was
added. After extraction with CH2Cl2 (50 mL), the organic layer was
washed with sat. aq NaHCO3 (20 mL) and dried (Na2SO4), and the
solvent was removed in vacuo. The crude product was recrystal-
lized (EtOH) to yield the aminonitriles 3a–f as crystalline solids.
IR (ATR): 2916, 2901, 2850, 1602, 1506, 1229, 1146, 707, 618, 504
cm–1.
1H NMR, HSQC, HMBC (400 MHz, CDCl3): δ = 7.51–7.47 (m, 2
H, FC6H4-H2,6), 7.09–7.04 (m, 2 H, FC6H4-H3,5), 4.81 (s, 1 H,
CHCN), 2.13 (br s, 3 H, CH), 1.81–1.62 (m, 12 H, CH2), 1.45 (br s,
1 H, NH).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 162.8 (d,
(4-Chlorophenyl)[(2,4,6-trimethylphenyl)amino]acetonitrile
(3a)
Prepared from 4-chlorobenzaldehyde (11.2 g, 79.7 mmol) and
2,4,6-trimethylaniline (10.8 g, 79.9 mmol) according to general
procedure A. Crystalline solid; yield: 12.3 g (54%); mp 99.5–100.5
°C, Rf = 0.33 (cyclohexane–EtOAc, 10:1).
4
1JCF = 247.9 Hz, FC6H4-C4), 133.1 (d, JCF = 3.4 Hz, FC6H4-C1),
3
129.0 (d, JCF = 8.3 Hz, 2 C, FC6H4-C2,6), 121.9 (CN), 115.9 (d,
2JCF = 21.8 Hz, 2 C, FC6H4-C3,5), 52.1 [C(CH2)3NH], 45.5
(CNCH), 43.1 (3 C, CH), 36.5 [3 C, C(CH2)3NH], 29.6 (3 C, CH2).
MS (ESI): m/z = 258.1 [M – CN]+.
HRMS (ESI): m/z [M – CN]+ calcd for C17H21NF: 258.1658; found:
258.1656.
IR (ATR): 2916, 1483, 1403, 1221, 1092, 1012, 934, 855, 751,
601 cm–1.
1H NMR, HSQC, HMBC (400 MHz, CDCl3): δ = 7.65–7.62 (m, 2
H, 4-ClC6H4-H2,6), 7.47–7.44 (m, 2 H, 4-ClC6H4-H3,5), 6.93 (s, 2
H, mesityl-H3,5), 5.07 (s, 1 H, CHCN), 2.35 (s, 6 H, mesityl-2,6-
CH3), 2.31 (s, 3 H, mesityl-4-CH3).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 139.0 (mesi-
tyl-C1), 135.3 (ClC6H4-C4), 134.0 (mesityl-C4), 133.4 (ClC6H4-
C1), 131.1 (2 C, mesityl-C2,6), 130.0 (2 C, mesityl-C3,5), 129.4 (2
C, ClC6H4-C3,5), 128.4 (2 C, ClC6H4-C2,6), 118.9 (CN), 53.0
(CNCH), 20.8 (mesityl-4-CH3), 18.2 (2 C, mesityl-2,6-CH3).
(4-Fluorophenyl)(methylamino)acetonitrile (3e)
Prepared from 4-fluorobenzaldehyde (7.45 g, 60.0 mmol) and 2 M
MeNH2 in MeOH (30.0 mL, 60.0 mmol) according to general pro-
cedure A. Colorless oil; yield: 6.40 g (65%); Rf = 0.16 (cyclohex-
ane–EtOAc, 20:1).
1H NMR (300 MHz, CDCl3): δ = 7.53–7.48 (m, 2 H), 7.12–7.07 (m,
2 H), 4.74 (s, 1 H, CHCN), 2.56 (s, 3 H, CH3).
1
13C NMR (75.5 MHz, CDCl3): δ = 163.1 (d, JCF = 248.7 Hz,
4
FC6H4-C4), 130.5 (d, JCF = 3.1 Hz, FC6H4-C1), 129.3 (d,
MS (ESI): m/z = 258.1 [M – CN]+.
HRMS (ESI): m/z [M – CN]+ calcd for C16H17N35Cl: 258.1050;
3JCF = 8.3 Hz, 2 C, FC6H4-C2,5), 118.5 (CN), 116.1 (d, 2JCF = 21.7
Hz, 2 C, FC6H4-C3,5), 55.5 (CHCN), 33.8 (CH3).
found: 258.1059.
(4-Fluorophenyl)(propan-2-ylamino)acetonitrile (3f)
Prepared from 4-fluorobenzaldehyde (7.45 g, 60.0 mmol) and
i-PrNH2 (3.55 g, 60.1 mmol) according to general procedure A.
Crystalline solid; yield: 5.11 g (45%); mp 69–69.1 °C; Rf = 0.13
(cyclohexane–EtOAc, 10:1).
Anal. Calcd for C17H17N2Cl: C, 71.70; H, 6.02; N, 9.84. Found: C,
71.43; H, 5.95; N, 9.59.
(4-Fluorophenyl)[(2-phenylethyl)amino]acetonitrile (3b)
Prepared from 4-fluorobenzaldehyde (7.45 g, 60.0 mmol) and
phenethylamine (7.27 g, 60.0 mmol) according to general proce-
dure A. Crystalline solid; yield: 10.1 g (66%); mp 71.1–71.5 °C,
Rf = 0.07 (cyclohexane–EtOAc, 10:1).
1H NMR (300 MHz, CDCl3): δ = 7.49–7.45 (m, 2 H), 7.34–7.30 (m,
2 H), 7.26–7.21 (m, 3 H), 7.11–7.05 (m, 2 H), 4.79 (br s, 1 H,
CHCN), 3.08–3.02 (m, 2 H, NHCH2), 2.88–2.82 (m, 2 H, PhCH2),
1.53 (br, 1 H, NH).
IR (ATR): 3316, 2974, 1602, 1511, 1382, 1219, 1167, 1139, 848,
789 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.53–7.48 (m, 2 H, FC6H4-H2,6),
7.11–7.06 (m, 2 H, FC6H4-H3,5), 4.76 (s, 1 H, CHCN), 3.20 [h,
J = 6.2 Hz, 1 H, CH(CH3)2], 1.42 (br s, 1 H, NH), 1.14 [d,
J = 6.2 Hz, 6 H, CH(CH3)2].
1
13C NMR (75.5 MHz, CDCl3): δ = 164.5 (d, JCF = 248.1 Hz,
1
13C NMR (75.5 MHz, CDCl3): δ = 163.0 (d, JCF = 248.2 Hz,
4
FC6H4-C4), 131.4 (d, JCF = 3.4 Hz, FC6H4-C1), 129.2 (d,
4
3JCF = 8.5 Hz,
2 C, FC6H4-C2,6), 119.1 (CN), 116.0 (d,
FC6H4-C4), 139.1 (Ph-C1), 130.6 (d, JCF = 3.3 Hz, FC6H4-C1),
129.1 (d, 3JCF = 8.5 Hz, 2 C, FC6H4-C2,5), 128.8 (2 C), 128.7 (2 C),
2JCF = 22.0 Hz, 2 C, FC6H4-C3,5), 51.7 (CHCN), 47.3 [CH(CH3)2],
2
126.6 (Ph-C4), 118.7 (CN), 115.9 (d, JCF = 21.8 Hz, 2 C, FC6H4-
23.7 (CH3), 21.5 (CH3).
MS (ESI): m/z = 192.9 [M + H]+.
C3,5), 53.7 (CNCH), 48.1 (CH2NH), 36.0 (PhCH2).
HRMS (ESI): m/z [M – CN]+ calcd for C10H13NF: 166.1032; found:
166.1024.
[(Diphenylmethyl)amino](4-fluorophenyl)acetonitrile (3c)
Prepared from 4-fluorobenzaldehyde (7.45 g, 60.0 mmol) and benz-
hydrylamine (11.0 g, 60.0 mmol) according to general procedure A.
Crystalline solid; yield: 13.9 g (74%); mp 88.9–89.6 °C, Rf = 0.32
(cyclohexane–EtOAc, 10:1).
1H NMR (300 MHz, CDCl3): δ = 7.61–7.53 (m, 4 H), 7.49–7.46 (m,
2 H), 7.43–7.38 (m, 2 H), 7.36–7.30 (m, 3 H), 7.28–7.25 (m, 1 H),
7.16–7.08 (m, 2 H), 5.26 (s, 1 H, CHCN), 4.60 (d, J = 12.3 Hz, 1 H,
NH), 2.17 (d, J = 12.3 Hz, 1 H, CHPh2).
N-(4-Chlorobenzylidene)-4-methylaniline (5a)
To a soln of 4-chlorobenzaldehyde (5.62 g, 40.0 mmol) and p-tolu-
idine (4.29 g, 40.0 mmol) in CH2Cl2 (30 mL) were added AcOH
(0.3 mL) and MgSO4 (6 g). After stirring for 18 h at 20 °C, the sus-
pension was filtered. The filtrate was washed with sat. aq NaHCO3
(10 mL) and dried (Na2SO4), and the solvent was removed in vacuo
to give pink-colored crystals; yield: 7.61 g (83%); mp 126.1–126.7
°C; Rf = 0.21 (cyclohexane–EtOAc, 15:1).
1
13C NMR (75.5 MHz, CDCl3): δ = 163.1 (d, JCF = 248.5 Hz,
FC6H4-C4), 142.7, 141.1, 130.9 (d, 4JCF = 3.1 Hz, FC6H4-C1), 129.2
(d, 3JCF = 8.5 Hz, 2 C, FC6H4-C2,5), 129.2 (2 C), 128.9 (2 C), 128.1,
127.9, 127.5 (2 C), 127.2 (2 C), 118.7 (CN), 116.1 (d,
2JCF = 21.9 Hz, 2 C, FC6H4-C3,5), 65.7 (CHPh2), 51.8 (CNCH).
1H NMR (300 MHz, CDCl3): δ = 8.43 (s, 1 H, NCH), 7.86–7.82 (m,
2 H), 7.47–7.42 (m, 2 H), 7.23–7.13 (m, 4 H), 2.38 (s, 3 H, CH3).
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2251–2264

2258
J. Emsermann et al.
PAPER
13C NMR (75.5 MHz, CDCl3): δ = 158.0 (NCH), 149.1 (MeC6H4-
C1), 137.2, 136.2, 134.9, 129.9 (2 C), 129.9 (2 C), 129.1 (2 C),
120.9 (2 C), 21.1 (CH3).
up to –20 °C over 100 min. The argon atmosphere was replaced by
air and the soln was allowed to warm up to r.t. After extraction with
EtOAc (30 mL), the organic layer was washed with brine (20 mL)
and dried (Na2SO4), and the solvent was removed in vacuo. The
products were purified by preparative TLC, but some minor impu-
rities were still evident. These impurities could be removed after
transformation to the imidazolium salts 8.
N-(4-Ethoxybenzylidene)aniline (5b)
To a soln of benzaldehyde (4.25 g, 40.0 mmol) and p-phenetidine
(5.49 g, 40.0 mmol) in CH2Cl2 (30 mL) were added AcOH
(0.3 mL) and MgSO4 (6 g) and the mixture was heated under reflux
for 4 h. The suspension was filtered, the filtrate was washed with
sat. aq NaHCO3 (10 mL) and dried (Na2SO4), and the solvent was
removed. The crude product was recrystallized (EtOH) to give 5b
as red-colored crystals; yield: 6.56 g (73%); mp 70.5–71.0 °C;
Rf = 0.19 (cyclohexane–EtOAc, 15:1).
1-(4-Chlorophenyl)-2-(4-fluorophenyl)-N1-(4-methylphenyl)-
N2-(2-phenylethyl)ethane-1,2-diimine (7a)
Prepared from aminonitrile 3b (853 mg, 3.35 mmol) and aldimine
5a (771 mg, 3.35 mmol) according to general procedure B; yellow
oil (1.42 g). A portion (329 mg) of the crude product was purified
by preparative TLC (silica gel, cyclohexane–EtOAc, 10:1) to give
7a as a yellow solid; yield: 223 mg (64%); mp 131.2–131.6 °C;
Rf = 0.41 (cyclohexane–EtOAc, 15:1).
1H NMR (300 MHz, CDCl3): δ = 8.49 (s, 1 H, NCH), 7.92–7.88 (m,
2 H), 7.49–7.45 (m, 3 H), 7.26–7.23 (m, 2 H), 6.95–6.92 (m, 2 H),
4.06 (q, J = 7.0 Hz, 2 H, OCH2CH3), 1.44 (t, J = 7.0 Hz, 3 H,
OCH2CH3).
13C NMR (75.5 MHz, CDCl3): δ = 158.4 (NCH), 157.8 (EtOC6H4-
C4), 144.8 (EtOC6H4-C1), 131.1 (Ph-C1), 128.8 (2 C), 128.7 (2 C),
122.3 (2 C), 115.0 (2 C, EtOC6H4-C3,5), 63.8 (CH2), 15.0 (CH3).
IR (ATR): 2922, 1589, 1504, 1232, 1154, 1092, 837, 751, 699, 550
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.75–7.71 (m, 2
H, FC6H4-H2,6), 7.60–7.57 (m, 2 H, Ph-H2,6), 7.33–7.31 (m, 2 H,
Ph-H3,5), 7.27–7.25 (m, 2 H, ClC6H4-H3,5), 7.24–7.22 (m, 1 H, Ph-
H4), 7.15–7.13 (m, 2 H, Cl-C6H4-H2,6), 7.06–7.01 (m, 2 H, FC6H4-
H3,5), 7.00–6.98 (m, 2 H, MeC6H4-H3,5), 6.76–6.73 (m, 2 H,
MeC6H4-H2,6), 3.62–3.49 (m, 2 H, NCH2), 3.01–2.82 (m, 2 H,
CH2Ph), 2.27 (s, 3 H, CH3).
N-(4-Methoxybenzylidene)aniline (5c)
To a soln of benzaldehyde (6.37 g, 60.0 mmol) and p-anisidine
(7.39 g, 60.0 mmol) in CH2Cl2 (50 mL) were added AcOH
(0.3 mL) and MgSO4 (20 g). After stirring for 72 h at 20 °C, the sus-
pension was filtered. The filtrate was washed with sat. aq NaHCO3
(10 mL) and dried (Na2SO4), and the solvent was removed in vacuo.
The crude product was recrystallized (EtOH) to give 5c as yellow-
ish crystals; yield: 7.98 g (63%); mp 70.4–70.8 °C; Rf = 0.17 (cyclo-
hexane–EtOAc, 15:1).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 164.2 (d,
1JCF = 251.0 Hz, FC6H4-C4), 163.4 (CNC6H4CH3), 163.2
(CNC2H4Ph), 146.8 (MeC6H4-C1), 140.1 (Ph-C1), 137.5 (ClC6H4-
C4), 135.1 (MeC6H4-C4), 134.5 (ClC6H4-C1), 133.2 (d,
3
4JCF = 3.1 Hz, FC6H4-C1), 129.6 (d, JCF = 8.8 Hz, 2 C, FC6H4-
1H NMR (300 MHz, CDCl3): δ = 8.49 (s, 1 H, NCH), 7.92–7.89 (m,
2 H), 7.50–7.45 (m, 3 H), 7.28–7.23 (m, 2 H), 6.98–6.92 (m, 2 H),
3.84 (s, 3 H, OCH3).
13C NMR (75.5 MHz, CDCl3): δ = 158.5 (NCH), 158.4 (MeOC6H4-
C4), 145.0, 136.5, 131.1 (Ph-C4), 128.8 (2 C), 128.7 (2 C), 122.3 (2
C), 114.5 (2 C), 55.6 (OCH3).
C2,6), 129.5 (2 C, MeC6H4-C3,5), 129.2 (2 C, Ph-C3,5), 129.1 (4 C,
ClC6H4-C2,6; Ph-C2,6), 128.4 (2 C, ClC6H4-C3,5), 126.2 (Ph-C4),
119.8 (2 C, MeC6H4-C2,6), 115.8 (d, 2JCF = 21.5 Hz, FC6H4-C3,5),
56.7 (NCH2), 37.2 (CH2Ph), 21.0 (CH3).
MS (ESI): m/z = 455.2 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C29H25N235ClF: 455.1690;
found: 455.1684.
N-(5-Bromo-2-methylbenzylidene)aniline (5d)
To a soln of benzaldehyde (2.45 g, 23.1 mmol) and 5-bromo-2-
methylaniline (4.30 g, 23.1 mmol) in CH2Cl2 (30 mL) were added
AcOH (0.3 mL) and MgSO4 (6 g) and the mixture was heated under
reflux for 4 h. The suspension was filtered, the filtrate was washed
with sat. aq NaHCO3 (10 mL) and dried (Na2SO4), and the solvent
was removed. The crude product was recrystallized (EtOH) to give
5d as yellowish crystals; yield: 4.56 g (72%); mp 82.1–82.5 °C;
Rf = 0.48 (cyclohexane–EtOAc, 15:1).
N2-(4-Ethoxyphenyl)-1-(4-fluorophenyl)-2-phenyl-N1-(2-phen-
ylethyl)ethane-1,2-diimine (7b)
Prepared from aminonitrile 3b (468 mg, 1.83 mmol) and aldimine
5b (414 mg, 1.83 mmol) according to general procedure B; orange
solid (764 mg). A portion (210 mg) of the crude product was puri-
fied by preparative TLC (silica gel, cyclohexane–EtOAc, 5:1) to
give 7b as a yellow solid; yield: 95.4 mg (42%); mp 107.1–107.5
°C; Rf = 0.25 (cyclohexane–EtOAc, 15:1).
IR (ATR): 2895, 1629, 1576, 1475, 1206, 890, 865, 813, 754, 691
cm–1.
1H NMR, COSY, HSQC, HMBC (400 MHz, CDCl3): δ = 8.34 (s, 1
H, NCH), 7.95–7.93 (m, 2 H, Ph-H2,6), 7.53–7.49 (m, 3 H, Ph-
H3,4,5), 7.28–7.26 (m, 1 H, BrMeC6H3-H6), 7.12–7.10 (m, 2 H,
BrMeC6H3-H3,4), 2.33 (s, 3 H, CH3).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 160.4 (NCH),
152.3 (BrMeC6H3-C1), 136.1 (Ph-C1), 131.7 (BrMeC6H3-C3),
131.7 (Ph-C4), 131.1 (BrMeC6H3-C4), 129.0 (2 C, Ph-C3,5), 128.9
(2 C, Ph-C2,6), 128.4 (BrMeC6H3-C6), 120.7 (BrMeC6H3-C3),
119.7 (BrMeC6H3-C2), 17.5 (CH3).
IR (ATR): 2924, 1599, 1502, 1447, 1244, 1152, 1047, 842, 753, 700
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.75–7.72 (m, 2
H, FC6H4-H2,6), 7.72–7.69 (m, 2 H, Ph-H2,6), 7.47–7.42 (m, 1 H,
Ph-H4), 7.38–7.34 (m, 2 H, Ph-H3,5), 7.28–7.20 (m, 3 H, C2H4Ph-
H3,4,5), 7.13–7.11 (m, 2 H, C2H4Ph-H2,6), 7.04–6.99 (m, 2 H,
FC6H4-H3,5), 6.84–6.81 (m, 2 H, EtOC6H4-H2,6), 6.72–6.68 (m, 2
H, EtOC6H4-H3,5), 3.96 (q, J = 7.0 Hz, 2 H, OCH2), 3.64–3.48 (m,
2 H, NCH2), 2.97–2.82 (m, 2 H, CH2Ph), 1.38 (t, J = 7.0 Hz, 3 H,
CH3).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 164.3 (d,
1JCF = 251.2 Hz, FC6H4-C4), 164.3 (CNC2H4Ph), 163.6
(CNC6H4OEt), 156.8 (EtOC6H4-C4), 142.5 (EtOC6H4-C1), 140.2
MS (ESI): m/z = 274.0 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C14H13N79Br: 274.0231;
4
(C2H4Ph-C1), 136.3 (Ph-C1), 133.3 (d, JCF = 3.1 Hz, FC6H4-C1),
found: 274.0235.
131.2 (Ph-C4), 129.6 (d, 3JCF = 8.7 Hz, 2 C, FC6H4-C2,6), 129.1 (2
C, C2H4Ph-C2,6), 129.0 (2 C, Ph-C3,5), 128.4 (2 C, C2H4Ph-C3,5),
127.7 (2 C, Ph-C2,6), 126.2 (C2H4Ph-C4), 121.9 (2 C, EtOC6H4-
Diimines 7a–h; General Procedure B (Table 3)
Prepared according a procedure of Kison and Opatz.26 To a stirred
soln of the aminonitrile 3 (1.68 mmol) in anhyd THF (1.5 mL) was
added a soln of KHMDS (1.85 mmol) in anhyd THF (2 mL) at –50
°C under argon. After 3 min a soln of aldimine 5 (1.68 mmol) in an-
hyd THF (1 mL) was added, and the mixture was allowed to warm
2
C2,6), 115.7 (d, JCF = 22.0 Hz, 2 C, FC6H4-C3,5), 114.6 (2 C,
EtOC6H4-C3,5), 63.6 (OCH2), 56.7 (NCH2), 37.1 (CH2Ph), 14.9
(CH3).
Synthesis 2013, 45, 2251–2264
© Georg Thieme Verlag Stuttgart · New York

PAPER
Investigation of Electronic Unsymmetry by NMR
2259
MS (ESI): m/z = 451.2 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C30H28FN2O: 451.2186;
a yellow oil; yield: 87.3 mg (44%); Rf = 0.30 (cyclohexane–EtOAc,
5:1).
found: 451.2193.
IR (ATR): 2979, 2360, 1600, 1504, 1242, 1155, 1047, 838, 693, 556
cm–1.
1-(4-Chlorophenyl)-2-(4-fluorophenyl)-N1-(4-methylphenyl)-
N2-(propan-2-yl)ethane-1,2-diimine (7c)
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.86–7.84 (m, 2
H, Ph-H2,6), 7.69–7.65 (m, 2 H, FC6H4-H2,6), 7.48–7.46 (m, 1 H,
Ph-H4), 7.45–7.41 (m, 2 H, Ph-H3,5), 7.01–6.96 (m, 2 H, FC6H4-
H3,5), 6.85–6.83 (m, 2 H, EtOC6H4-H2,6), 6.73–6.70 (m, 2 H,
EtOC6H4-H3,5), 3.94 (q, J = 7.0 Hz, 2 H, OCH2), 3.26 (s, 3 H,
NCH3), 1.36 (t, J = 7.0 Hz, 3 H, CH3).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 166.0
(CNCH3), 164.2 (d, 1JCF = 251.4 Hz, FC6H4-C4), 162.9
(CNC6H4OEt), 156.8 (EtOC6H4-C4), 142.5 (EtOC6H4-C1), 136.1
(Ph-C1), 133.2 (d, 4JCF = 3.2 Hz, FC6H4-C1), 131.4 (Ph-C4), 129.5
(d, 3JCF = 8.5 Hz, 2 C, FC6H4-C2,6), 129.1 (2 C, Ph-C3,5), 127.7 (2
C, Ph-C2,6), 121.6 (2 C, EtOC6H4-C2,6), 115.7 (d, 2JCF = 21.9 Hz,
2 C, FC6H4-C3,5), 114.6 (2 C, EtOC6H4-C3,5), 63.6 (OCH2), 42.3
(NCH3), 14.9 (CH3).
Prepared from aminonitrile 3f (368 mg, 1.68 mmol) and aldimine
5a (323 mg, 1.68 mmol) according to general procedure B; yellow
solid (657 mg). A portion (207 mg) of the crude product was puri-
fied by preparative TLC (silica gel, cyclohexane–t-BuOMe, 2:1) to
give 7c as a yellow oil; yield: 73.9 mg (36%); Rf = 0.37 (cyclohex-
ane–EtOAc, 15:1).
IR (ATR): 2966, 1589, 1504, 1233, 1154, 1093, 1011, 822, 733, 541
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.83–7.79 (m, 2
H, ClC6H4-H2,6), 7.77–7.73 (m, 2 H, FC6H4-H2,6), 7.39–7.37 (m,
2 H, MeC6H4-H3,5), 7.05–7.01 (m, 2 H, FC6H4-H3,5), 7.00–6.98
(m, 2 H, ClC6H4-H3,5), 6.78–6.76 (m, 2 H, MeC6H4-H2,6), 3.44 [h,
J = 6.2 Hz, 1 H, CH(CH3)2], 2.25 (s, 3 H, CH3), 0.99 [d, J = 6.2 Hz,
3 H, CH(CH3)2], 0.71 [d, J = 6.2 Hz, 3 H, CH(CH3)2].
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 164.2 (d,
1JCF = 251.3 Hz, FC6H4-C4), 162.8 (CNC6H4CH3), 159.8 (CNi-Pr),
146.8 (2 C, MeC6H4-C1, ClC6H4-C4), 135.3 (ClC6H4-C1), 135.2
MS (ESI): m/z = 361.2 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C23H22FN2O: 361.1716;
found: 361.1711.
1-(4-Fluorophenyl)-N2-(4-methoxyphenyl)-N1-methyl-2-phen-
ylethane-1,2-diimine (7f)
4
(MeC6H4-C4), 134.0 (d, JCF = 3.5 Hz, FC6H4-C1), 129.8 (d,
3JCF = 8.7 Hz, 2 C, FC6H4-C2,6), 129.4 (2 C, ClC6H4-C3,5), 129.4
Prepared from aminonitrile 3e (179 mg, 1.09 mmol) and aldimine
5c (231 mg, 1.09 mmol) according to general procedure B; yellow
oil (360 mg). A portion (185 mg) of the crude product was purified
by preparative TLC (silica gel, cyclohexane–EtOAc, 15:1) to give
7f as a yellow oil; yield: 91.6 mg (48%); Rf = 0.11 (cyclohexane–
EtOAc, 15:1).
(2 C, ClC6H4-C2,6), 129.1 (2 C, MeC6H4-C3,5), 120.4 (2 C,
MeC6H4-C2,6), 115.8 (d, JCF = 21.4 Hz, 2 C, FC6H4-C3,5), 54.7
[CH(CH3)2], 23.4 [2 C, CH(CH3)2], 21.0 (CH3).
MS (ESI): m/z = 393.1 [M + H]+.
2
HRMS (ESI): m/z [M + H]+ calcd for C24H2335ClFN2: 393.1534;
found: 393.1546.
IR (ATR): 2955, 1598, 1501, 1241, 1153, 1033, 832, 762, 693, 554
cm–1.
1-(4-Chlorophenyl)-2-(4-fluorophenyl)-N2-methyl-N1-(4-meth-
ylphenyl)ethane-1,2-diimine (7d)
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.86–7.84 (m, 2
H, Ph-H2,6), 7.69–7.65 (m, 2 H, FC6H4-H2,6), 7.47–7.45 (m, 1 H,
Ph-H4), 7.44–7.41 (m, 2 H, Ph-H3,5), 7.01–6.96 (m, 2 H, FC6H4-
H3,5), 6.86–6.83 (m, 2 H, MeOC6H4-H2,6), 6.73–6.71 (m, 2 H,
MeOC6H4-H3,5), 3.72 (s, 3 H, OCH3), 3.26 (s, 3 H, NCH3).
Prepared from aminonitrile 3e (192 mg, 1.17 mmol) and aldimine
5a (269 mg, 1.17 mmol) according to general procedure B; orange
solid (405 mg). A portion (170 mg) of the crude product was puri-
fied by preparative TLC (silica gel, toluene–EtOAc, 100:1) to give
7d as a yellow oil; yield: 78.2 mg (44%); Rf = 0.23 (cyclohexane–
EtOAc, 15:1).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 165.9
(CNCH3), 164.2 (d, 1JCF = 251.7 Hz, FC6H4-C4), 163.8
(CNC6H4OMe), 157.4 (MeOC6H4-C4), 142.7 (MeOC6H4-C1),
136.1 (Ph-C1), 133.2 (d, 4JCF = 3.3 Hz, FC6H4-C4), 131.4 (Ph-C4),
IR (ATR): 2918, 1590, 1504, 1229, 1156, 1089, 1011, 822, 732, 553
cm–1.
3
129.5 (d, JCF = 8.9 Hz, 2 C, FC6H4-C2,6), 129.1 (2 C, Ph-C3,5),
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.80–7.78 (m, 2
H, ClC6H4-H2,6), 7.66–7.62 (m, 2 H, FC6H4-H2,6), 7.42–7.40 (m,
2 H, ClC6H4-H3,5), 7.01–6.98 (m, 2 H, FC6H4-H3,5), 6.98–6.96 (m,
2 H, MeC6H4-H3,5), 6.73–6.71 (m, 2 H, MeC6H4-H2,6), 3.25 (s, 3
H, NCH3), 2.24 (s, 3 H, CH3).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 165.2
(CNCH3), 164.3 (d, 1JCF = 251.6 Hz, FC6H4-C4), 163.0
(CNC6H4CH3), 146.9 (MeC6H4-C1), 137.8 (ClC6H4-C4), 135.0
(MeC6H4-C4), 134.4 (ClC6H4-C1), 133.1 (d, 4JCF = 3.1 Hz, FC6H4-
C1), 129.5 (d, partly overlapping signals, 2 C, FC6H4-C2,6), 129.5
(2 C, ClC6H4-C3,5), 129.4 (2 C, MeC6H4-C3,5), 129.1 (2 C,
ClC6H4-C2,6), 119.6 (2 C, MeC6H4-C2,6), 115.8 (d, 2JCF = 22.0 Hz,
2 C, FC6H4-C3,5), 42.4 (NCH3), 21.0 (CH3).
127.7 (2 C, Ph-2,6), 121.6 (2 C, MeOC6H4-C2,6), 115.8 (d, 2 C,
2JCF = 21.7 Hz, FC6H4-C3,5), 114.1 (2 C, MeOC6H4-C3,5),
55.4 (OCH3), 42.3 (NCH3).
MS (ESI): m/z = 347.1 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C22H20FN2O: 347.1560;
found: 347.1573.
1-(4-Fluorophenyl)-N2-(4-methoxyphenyl)-2-phenyl-N1-(pro-
pan-2-yl)ethane-1,2-diimine (7g)
Prepared from aminonitrile 3f (323 mg, 1.68 mmol) and aldimine
5c (355 mg, 1.68 mmol) according to general procedure B; yellow
oil (590 mg). A portion (207 mg) of the crude product was purified
by preparative TLC (silica gel, cyclohexane–EtOAc, 5:1) to give 7g
as a yellow oil; yield: 28.8 mg (14%); Rf = 0.22 (cyclohexane–
EtOAc, 15:1).
MS (ESI): m/z = 365.1 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C22H1935ClFN2: 365.1221;
found: 365.1228.
IR (ATR): 2967, 1601, 1503, 1243, 1154, 1034, 832, 761, 692, 532
cm–1.
N2-(4-Ethoxyphenyl)-1-(4-fluorophenyl)-N1-methyl-2-phenyl-
ethane-1,2-diimine (7e)
Prepared from aminonitrile 3e (203 mg, 1.24 mmol) and aldimine
5b (279 mg, 1.24 mmol) according to general procedure B; orange
oil (375 mg). A portion (169 mg) of the crude product was purified
by preparative TLC (silica gel, toluene–EtOAc, 100:1) to give 7e as
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.86–7.83 (m, 2
H, Ph-H2,6), 7.78–7.75 (m, 2 H, FC6H4-H2,6), 7.47–7.44 (m, 1 H,
Ph-H4), 7.43–7.37 (m, 2 H, Ph-H3,5), 7.05–7.00 (m, 2 H, FC6H4-
H3,5), 6.91–6.87 (m, 2 H, MeOC6H4-H2,6), 6.74–6.72 (m, 2 H,
3
MeOC6H4-H3,5), 3.73 (s, 3 H, OCH3), 3.47 [h, J = 6.0 Hz, 1 H,
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2251–2264

2260
J. Emsermann et al.
PAPER
a
CH(CH3)2], 0.99 [d, 3J = 6.0 Hz, 3 H, CH(CH3)2 ], 0.71 [d,
MeC6H4-H2,3,5,6), 7.11–7.08 (m, 2 H, C2H4Ph-H2,6), 6.85–6.82
(m, 2 H, C2H4Ph-H3,5), 4.74–4.69 (m, 2 H, NCH2), 3.12 (t,
J = 7.5 Hz, 2 H, CH2Ph), 2.32 (s, 3 H, CH3).
b
3J = 6.0 Hz, 3 H, CH(CH3)2 ].
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 164.1 (d,
1JCF = 250.9 Hz, FC6H4-C4), 163.3 (CNC6H4OMe), 160.6 (CNi-
Pr), 157.6 (MeOC6H4-C4), 142.7 (MeOC6H4-C1), 137.0 (Ph-C1),
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 163.9 (d,
1JCF = 252.9 Hz, FC6H4-C4), 141.0 (MeC6H4-C4), 138.1 (C2),
136.4 (ClC6H4-C4), 136.2 (C2H4Ph-C1), 132.9 (d, 3JCF = 8.6 Hz, 2
C, FC6H4-C2,6), 131.6 (2 C, C2H4Ph-C3,5), 131.5 (d, 2JCC = 2.2 Hz,
4
134.1 (d, JCF = 3.3 Hz, FC6H4-C1), 131.2 (Ph-C4), 129.9 (d,
3JCF = 8.6 Hz, 2 C, FC6H4-C2,6), 128.9 (2 C, Ph-C3,5), 128.0 (2 C,
Ph-C2,6), 122.5 (2 C, MeOC6H4-C2,6), 115.8 (d, 2JCF = 21.8 Hz, 2
C, FC6H4-C3,5), 114.0 (2 C, MeOC6H4-C3,5), 55.5 (OCH3), 54.7
2
C4),130.8 (d, JCC2 = 2.9 Hz, MeC6H4-C1), 130.7 (2 C, MeC6H4-
C3,5), 130.5 (d, JCC = 3.3 Hz, C5), 129.3 (2 C, ClC6H4-C3,5),
129.2 (2 C, C2H4Ph-C2,6), 129.0 (2 C, ClC6H4-C2,6), 127.3
(C2H4Ph-C4), 125.6 (2 C, MeC6H4-C2,6), 123.3 (ClC6H4-C1),
a
b
[CH(CH3)2], 23.4 [CH(CH3)2 ], 23.3 [CH(CH3)2 ].
MS (ESI): m/z = 375.1 [M + H]+.
4
120.7 (d, JCF = 3.5 Hz, FC6H4-C1), 116.9 (d, 2JCF = 21.9 Hz, 2 C,
HRMS (ESI): m/z [M + H]+ calcd for C24H24FN2O: 375.1873;
FC6H4-C3,5), 49.1 (NCH2), 36.6 (CH2Ph), 21.3 (CH3).
found: 375.1863.
15N HMBC (60.8 MHz, CDCl3): δ = 184.8 (d, 1JNC = 17.2 Hz, N3),
181.7 (d, 1JNC = 17.1 Hz, N1).
1-(4-Fluorophenyl)-N2-(4-methoxyphenyl)-2-phenyl-N1-(2-phen-
ylethyl)ethane-1,2-diimine (7h)
MS (ESI): m/z = 468.2 [M]+.
HRMS (ESI): m/z [M]+ calcd for C2913CH2535ClFN2: 468.1723;
Prepared from aminonitrile 3b (427 mg, 1.68 mmol) and aldimine
5c (355 mg, 1.68 mmol) according to general procedure B; yellow
oil (669 mg). A portion (216 mg) of the crude product was purified
by preparative TLC (silica gel, cyclohexane–t-BuOMe, 2:1) to give
7h as a yellow oil; yield: 65.2 mg (28%); Rf = 0.17 (cyclohexane–
EtOAc, 15:1).
found: 468.1736.
5-(4-Chlorophenyl)-4-(4-fluorophenyl)-1-(4-methylphenyl)-3-
(propan-2-yl)(2-13C)-1H-imidazolium Chloride (8b)
Prepared from diimine 7c (67.0 mg, 0.171 mmol) according to gen-
eral procedure C. The crude product was purified by flash chroma-
tography (silica gel, CH2Cl2–MeOH, 10:1 to 4:1) to give 8b as a red
oil; yield: 65.3 mg (87%); Rf = 0.19 (CH2Cl2–MeOH, 8:1).
IR (ATR): 2928, 1560, 1502, 1243, 1154, 1032, 832, 751, 693, 550
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.73–7.70 (m, 2
H, FC6H4-H2,6), 7.69–7.67 (m, 2 H, Ph-H2,6), 7.46–7.42 (m, 1 H,
Ph-H4), 7.37–7.33 (m, 2 H, Ph-3,5), 7.24–7.23 (m, 2 H, C2H4Ph-
H3,5), 7.21–7.19 (m, 1 H, C2H4Ph-H4), 7.11–7.09 (m, 2 H, C2H4Ph-
H2,6), 7.03–6.99 (m, 2 H, FC6H4-H3,5), 6.83–6.80 (m, 2 H,
MeOC6H4-H2,6), 6.72–6.68 (m, 2 H, MeOC6H4-H3,5), 3.73 (s, 3 H,
OCH3), 3.63–3.47 (m, 2 H, NCH2), 2.95–2.81 (m, 2 H, CH2Ph).
IR (ATR): 2923, 1601, 1513, 1353, 1225, 1095, 1017, 818, 746, 512
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 10.78 (d,
1JCH = 223.4 Hz, 1 H, H2), 7.42–7.36 (m, 4 H, FC6H4-H2,6,
MeC6H4-H2,6), 7.20–7.15 (m, 6 H, FC6H4-H3,5, MeC6H4-H3,5, Cl-
C6H4-H3,5), 6.93–6.90 (m, 2 H, ClC6H4-H2,6), 4.54–4.46 [m, 1 H,
NCH(CH3)2], 2.33 (s, 3 H, CH3), 1.73 [d, J = 6.8 Hz, 6 H,
NCH(CH3)2].
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 164.3
(CNC2H4Ph), 164.2 (d, JCF = 251.3 Hz, FC6H4-C4), 163.8
1
(CNC6H4OMe), 157.4 (MeOC6H4-C4), 142.7 (MeOC6H4-C1),
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 164.0 (d,
140.2 (C2H4Ph-C1), 136.3 (Ph-C1), 133.3 (d, 4JCF = 3.1 Hz, FC6H4-
1JCF = 253.3 Hz, FC6H4-C4), 140.8 (MeC6H4-C4), 137.0 (MeC6H4-
3
C1), 131.3 (Ph-C4), 129.7 (d, JCF = 8.6 Hz, 2 C, FC6H4-C2,6),
3
C1), 136.6 (C2), 136.3 (ClC6H4-C4), 133.3 (d, JCF = 8.8 Hz, 2 C,
129.1 (2 C, C2H4Ph-C2,6), 129.0 (2 C, Ph-C3,5), 128.4 (2 C,
FC6H4-C2,6), 131.7 (2 C, ClC6H4-C3,5), 131.0–130.9 (partly over-
lapping signals, ClC6H4-C1, C4), 130.6 (2 C, MeC6H4-C3,5), 129.3
C2H4Ph-C3,5), 127.7 (2 C, Ph-C2,6), 126.2 (C2H4Ph-C4), 121.8 (2
2
C, MeOC6H4-C2,6), 115.8 (d, JCF = 22.0 Hz, 2 C, FC6H4-C3,5),
3
(2 C, ClC6H4-C2,6), 125.9 (d, JCC = 1.6 Hz, 2 C, MeC6H4-C2,6),
114.1 (2 C, MeOC6H4-C3,5), 56.7 (NCH2), 55.4 (OCH3), 37.2
(CH2Ph).
MS (ESI): m/z = 437.2 [M + H]+.
2
4
123.4 (d, JCC = 1.5 Hz, C5), 121.1 (dd, JCF = 3.4 Hz,
3JCC = 1.7 Hz, FC6H4-C1), 117.1 (d, JCF = 22.1 Hz, 2 C, FC6H4-
2
C3,5), 52.5 [d, 3JCC = 2.3 Hz, NCH(CH3)2], 23.1 [2 C, CH(CH3)2],
21.30 (CH3).
HRMS (ESI): m/z [M + H]+ calcd for C29H26FN2O: 437.2029;
found: 437.2045.
15N HMBC (60.8 MHz, CDCl3): δ = 196.5 (s, N1), 185.5 (s, N3).
MS (ESI): m/z = 406.1 [M]+.
HRMS (ESI): m/z [M]+ calcd for C2413CH2335ClFN2: 406.1568;
Imidazolium Salts 8a–f; General Procedure C (Table 4)
According a procedure of Noels et al.16 13C-Paraformaldehyde
(7.80 mg, 0.25 mmol) was dissolved in 4 M HCl in dioxane (75 μL,
0.30 mmol). In a separate flask the diimine 7 (0.20 mmol) was dis-
solved in anhyd THF (3 mL) and cooled to 0 °C. The acidic para-
formaldehyde soln was added slowly. After stirring at r.t. for 12 h,
the solvent removed in vacuo and the crude product was purified by
flash chromatography.
found: 406.1567.
5-(4-Chlorophenyl)-4-(4-fluorophenyl)-3-methyl-1-(4-methyl-
phenyl)(2-13C)-1H-imidazolium Chloride (8c)
Prepared from diimine 7d (57.7 mg, 0.158 mmol) according to gen-
eral procedure C. The crude product was purified by flash chroma-
tography (silica gel, CH2Cl2–MeOH, 10:1 to 4:1) to give 8c as a
yellowish oil; yield: 51.7 mg (79%); Rf = 0.17 (CH2Cl2–MeOH,
8:1).
5-(4-Chlorophenyl)-4-(4-fluorophenyl)-1-(4-methylphenyl)-3-
(2-phenylethyl)(2-13C)-1H-imidazolium Chloride (8a)
Prepared from diimine 7a (201 mg, 0.441 mmol) according to gen-
eral procedure C. The crude product was purified by flash chroma-
tography (silica gel, CH2Cl2–MeOH, 10:1) to give 8a as colorless
crystals; yield: 166 mg (75%); mp 100 °C (dec); Rf = 0.12 (CH2Cl2–
MeOH, 10:1).
IR (ATR): 2925, 1604, 1534, 1510, 1492, 1226, 1092, 819, 749, 532
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 10.70 (d,
1JCH = 225.7 Hz, 1 H, H2), 7.39–7.34 (m, 2 H, FC6H4-H2,6), 7.25–
7.23 (m, 2 H, MeC6H4-H2,6), 7.14–7.08 (m, 6 H, FC6H4-H3,5,
MeC6H4-H3,5, Cl-C6H4-H3,5), 6.91–6.87 (m, 2 H, ClC6H4-H2,6),
4.01 (d, 3JCH = 4.2 Hz, 3 H, NCH3), 2.29 (s, 3 H, CH3).
IR (ATR): 2923, 1513, 1491, 1228, 1096, 1016, 818, 745, 659, 532
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 10.85 (d,
1JCH = 224.7 Hz, 1 H, H2), 7.24–7.21 (m, 3 H, ClC6H4-H2,6,
C2H4Ph-H4), 7.18–7.11 (m, 10 H, ClC6H4-H3,5, FC6H4-H2,3,5,6,
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 163.8 (d,
1JCF = 252.6 Hz, FC6H4-C4), 140.7 (MeC6H4-C4), 138.3 (C2),
3
136.2 (ClC6H4-C4), 133.0 (d, JCF = 8.8 Hz, 2 C, FC6H4-C2,6),
Synthesis 2013, 45, 2251–2264
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Investigation of Electronic Unsymmetry by NMR
2261
2
131.8 (d, JCC = 2.1 Hz, C4), 131.7 (2 C, ClC6H4-C2,6), 130.9 (d,
2JCC = 2.7 Hz, C5), 130.6 (2 C, MeC6H4-C3,5), 130.5 (d,
2JCC = 3.1 Hz, MeC6H4-C1), 129.3 (2 C, ClC6H4-C3,5), 125.7 (d,
FC6H4-C1), 116.7 (d, 2JCF = 22.0 Hz, 2 C, FC6H4-C3,5), 115.0 (2 C,
MeOC6H4-C3,5), 55.6 (OCH3), 35.2 (d, 2JCC = 3.1 Hz, NCH3).
15N HMBC (60.8 MHz, CDCl3): δ = 183.9 (d, 1JNC = 17.4 Hz, N3),
3JCC = 1.7 Hz, 2 C, MeC6H4-C2,6), 123.4 (d, JCC = 1.6 Hz,
ClC6H4-C1), 120.6 (dd, JCF = 3.7 Hz, JCC = 1.4 Hz, FC6H4-C1),
116.8 (d, 2JCF = 22.1 Hz, 2 C, FC6H4-C3,5), 35.2 (d, 2JCC = 3.0 Hz,
NCH3), 21.2 (CH3).
3
170.5 (d, 1JNC = 18.0 Hz, N1).
4
3
MS (ESI): m/z = 360.1 [M]+.
HRMS (ESI): m/z [M]+ calcd for C2213CH20FN2O: 360.1593; found:
15N HMBC (60.8 MHz, CDCl3): δ = 184.2 (d, 1JNC = 17.1 Hz, N3),
360.1594.
171.4 (d, 1JNC = 17.0 Hz, N1).
4-(4-Fluorophenyl)-1-(4-methoxyphenyl)-5-phenyl-3-(2-phen-
ylethyl)(2-13C)-1H-imidazolium Chloride (8f)
MS (ESI): m/z = 378.1 [M]+.
Prepared from diimine 7h (61.5 mg, 0.141 mmol) according to gen-
eral procedure C. The crude product was purified by flash chroma-
tography (silica gel, CH2Cl2–MeOH, 10:1) to give 8f as a red oil;
yield: 33.9 mg (49%); Rf = 0.12 (CH2Cl2–MeOH, 10:1).
HRMS (ESI): m/z [M]+ calcd for C2213CH1935ClFN2: 378.1254;
found: 378.1258.
1-(4-Ethoxyphenyl)-4-(4-fluorophenyl)-3-methyl-5-phenyl(2-
13C)-1H-imidazolium Chloride (8d)
Prepared from diimine 7e (64.4 mg, 0.179 mmol) according to gen-
eral procedure C. The crude product was purified by flash chroma-
tography (silica gel, CH2Cl2–MeOH, 10:1 to 4:1) to give 8d as a red
oil; yield: 59.3 mg (83%); Rf = 0.19 (CH2Cl2–MeOH, 8:1).
IR (ATR): 2926, 1510, 1335, 1252, 1175, 1030, 838, 750, 699, 535
cm–1.
1H NMR, COSY, HSQC (600 MHz, CDCl3): δ = 10.34 (d,
1JCH = 224.6 Hz, 1 H, H2), 7.29–7.22 (m, 4 H, Ph-H4, C2H4Ph-
H3,4,5), 7.21–7.17 (m, 6 H, FC6H4-H2,6, Ph-H3,5, MeOC6H4-
H2,6), 7.13–7.10 (m, 2 H, FC6H4-H3,5), 7.07–7.06 (m, 2 H,
C2H4Ph-H2,6), 6.92–6.91 (m, 2 H, Ph-H2,6), 6.82–6.81 (m, 2 H,
MeOC6H4-H3,5), 4.62–4.59 (m, 2 H, NCH2), 3.76 (s, 3 H, OCH3),
3.07 (t, J = 7.4 Hz, 2 H, CH2Ph).
IR (ATR): 2982, 1607, 1536, 1510, 1225, 1175, 1043, 843, 699, 535
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 10.67 (d,
1JCH = 224.9 Hz, 1 H, H2), 7.34–7.30 (m, 2 H, FC6H4-H2,6), 7.25–
7.21 (m, 3 H, EtOC6H4-H2,6, Ph-H4), 7.16–7.12 (m, 2 H, Ph-H3,5),
7.09–7.05 (m, 2 H, FC6H4-H3,5), 6.92–6.90 (m, 2 H, Ph-H2,6),
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 163.9 (d,
1JCF = 252.7 Hz, FC6H4-C4), 160.7 (MeOC6H4-C4), 138.0 (C2),
3
6.79–6.75 (m, 2 H, EtOC6H4-H3,5), 4.04 (d, JCH = 4.0 Hz, 3 H,
3
136.2 (C2H4Ph-C1), 133.0 (d, JCF = 8.6 Hz, 2 C, FC6H4-C2,6),
NCH3), 3.92 (q, J = 7.0 Hz, 2 H, OCH2), 1.32 (t, J = 7.0 Hz, 3 H,
CH3).
132.0 (d, 2JCC = 3.2 Hz, C5), 131.1 (d, 2JCC = 2.4 Hz, C4), 130.5 (2
C, Ph-C2,6), 130.0 (Ph-C4), 129.1 (2 C, C2H4Ph-C2,6), 129.0 (2 C,
C2H4Ph-C3,5), 128.9 (2 C, Ph-C3,5), 127.4 (C2H4Ph-C4), 127.2 (d,
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 163.7 (d,
1JCF = 252.0 Hz, FC6H4-C4), 159.9 (EtOC6H4-C4), 138.1 (C2),
132.9 (d, 3JCF = 8.7 Hz, 2 C, FC6H4-C2,6), 131.6 (d, 2JCC = 2.9 Hz,
C4), 131.3 (d, 2JCC = 2.3 Hz, C5), 130.4 (2 C, Ph-C2,6), 129.8 (Ph-
C4), 128.8 (2 C, Ph-C3,5), 127.1 (d, 3JCC = 1.6 Hz, 2 C, EtOC6H4-
2
3JCC = 1.4 Hz, 2 C, MeOC6H4-C2,6), 126.2 (d, JCC = 2.9 Hz,
3
MeOC6H4-C1), 124.8 (d, JCC = 1.4 Hz, Ph-C1), 121.1 (dd,
3
2
4JCF = 3.5 Hz, JCC = 1.6 Hz, FC6H4-C1), 116.8 (d, JCF = 22.0 Hz,
2 C, FC6H4-C3,5), 115.1 (2 C, MeOC6H4-C3,5), 55.7 (OCH3), 49.2
(d, 2JCC = 2.3 Hz, NCH2), 36.4 (CH2Ph).
2
C2,6), 125.9 (d, JCC = 2.8 Hz, EtOC6H4-C1), 124.8 (d,
4
3
3JCC = 1.4 Hz, Ph-C1), 120.8 (dd, JCF = 3.4 Hz, JCC = 1.7 Hz,
FC6H4-C1), 116.6 (d, 2JCF = 22.0 Hz, 2 C, FC6H4-C3,5), 115.4 (2 C,
EtOC6H4-C3,5), 63.9 (OCH2), 35.1 (d, 2JCC = 3.3 Hz, NCH3), 14.6
(CH3).
15N HMBC (60.8 MHz, CDCl3): δ = 184.7 (d, 1JNC = 18.2 Hz, N3),
180.9 (d, 1JNC = 16.9 Hz, N1).
MS (ESI): m/z = 450.2 [M]+.
HRMS (ESI): m/z [M]+ calcd for C2913CH26FN2O: 450.2063; found:
15N HMBC (60.8 MHz, CDCl3): δ = 183.8 (d, 1JNC = 17.3 Hz, N3),
170.4 (d, 1JNC = 17.2 Hz, N1).
450.2074.
MS (ESI): m/z = 374.1 [M]+.
HRMS (ESI): m/z [M]+ calcd for C2313CH22FN2O: 374.1750; found:
Mercury Complexes 9a–c; General Procedure D (Table 5)
Prepared according to a procedure of Arduengo et al.9 To a soln of
imidazolium salt 8 (0.10 mmol) in anhyd THF (3 mL) were added
Hg(OAc)2 (50 μmol) and DMSO (1 drop). After stirring at r.t. for
15 h the solvent was removed in vacuo and the crude product was
purified by flash chromatography.
374.1758.
4-(4-Fluorophenyl)-1-(4-methoxyphenyl)-3-methyl-5-phenyl(2-
13C)-1H-imidazolium Chloride (8e)
Prepared from diimine 7f (72.5 mg, 0.209 mmol) according to gen-
eral procedure C. The crude product was purified by flash chroma-
tography (silica gel, CH2Cl2–MeOH, 10:1 to 4:1) to give 8e as a red
oil; yield: 70.2 mg (89%); Rf = 0.17 (CH2Cl2–MeOH, 8:1).
Bis[5-(4-chlorophenyl)-4-(4-fluorophenyl)-1-(4-methylphenyl)-
3-(2-phenylethyl)(2-13C)-1,3-dihydro-2H-imidazol-2-yli-
dene]mercury(II) Dichloride (9a)
Prepared from imidazolium salt 8a (61.3 mg, 0.122 mmol) accord-
ing to general procedure D. The crude product was purified by flash
chromatography (silica gel, CH2Cl2–MeOH, 8:1) to give 9a as a col-
orless solid; yield: 46.2 mg (63%); mp 150 °C (dec); Rf = 0.40
(CH2Cl2–MeOH, 8:1).
IR (ATR): 3009, 1607, 1510, 1252, 1175, 1029, 838, 699, 606, 535
cm–1.
1H NMR, COSY, HSQC (600 MHz, CDCl3): δ = 10.61 (d,
1JCH = 225.1 Hz, 1 H, H2), 7.35–7.33 (m, 2 H, FC6H4-H2,6), 7.29–
7.25 (m, 3 H, EtOC6H4-H2,6, Ph-H4), 7.19–7.16 (m, 2 H, Ph-H3,5),
7.12–7.09 (m, 2 H, FC6H4-H3,5), 6.95–6.93 (m, 2 H, Ph-H2,6),
IR (ATR): 2923, 1511, 1228, 1159, 1090, 1016, 819, 701, 621, 535
cm–1.
3
6.84–6.81 (m, 2 H, EtOC6H4-H3,5), 4.04 (d, JCH = 4.2 Hz, 3 H,
1H NMR, COSY, HSQC (600 MHz, CDCl3): δ = 7.33 (pseudo-d,
J = 8.0 Hz, 4 H, MeC6H4-H2,6), 7.11–7.08 (m, 10 H, FC6H4-H2,6,
C2H4Ph-H3,4,5), 7.06–7.04 (m, 8 H, FC6H4-H3,5, ClC6H4-H3,5),
6.98–6.96 (m, 4 H, C2H4Ph-H2,6), 6.93 (pseudo-d, J = 8.0 Hz, 4 H,
MeC6H4-H3,5), 6.69–6.67 (m, 4 H, ClC6H4-H2,6), 4.80 (br s, 4 H,
NCH2), 3.14–3.13 (m, 4 H, CH2Ph), 2.17 (s, 6 H, CH3).
NCH3), 3.75 (s, 3 H, OCH3).
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 163.8 (d,
1JCF = 252.3 Hz, FC6H4-C4), 160.6 (MeOC6H4-C4), 138.2 (C2),
133.0 (d, 3JCF = 8.7 Hz, 2 C, FC6H4-C2,6), 131.7 (d, 2JCC = 3.1 Hz,
C5), 131.4 (d, 2JCC = 2.3 Hz, C4), 130.4 (2 C, Ph-C2,6), 129.9 (Ph-
C4), 128.9 (2 C, Ph-C3,5), 127.2 (d, 3JCC = 1.7 Hz, 2 C, MeOC6H4-
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 177.0 (2 C, C2,
2
C2,6), 126.2 (d, JCC = 2.8 Hz, MeOC6H4-C1), 124.9 (d,
1JHgC = 2850 Hz), 163.5 (d, 1JCF = 251.5 Hz, 2 C, FC6H4-C4), 139.8
4
3
3JCC = 1.1 Hz, Ph-C1), 120.9 (dd, JCF = 3.4 Hz, JCC = 1.7 Hz,
© Georg Thieme Verlag Stuttgart · New York
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J. Emsermann et al.
PAPER
(2 C, MeC6H4-C4), 137.4 (2 C, C2H4Ph-C1), 135.4 (2 C, ClC6H4-
C4), 134.1 (2 C, MeC6H4-C1), 133.0 (d, 3JCF = 8.6 Hz, 4 C, FC6H4-
C2,6), 132.1 (2 C, C5), 131.5 (4 C, ClC6H4-C2,6), 131.3 (2 C, C4),
130.4 (4 C, MeC6H4-C3,5), 129.1 (4 C, C2H4Ph-C2,6), 128.9 (4 C,
ClC6H4-C3,5), 128.6 (4 C, C2H4Ph-C3,5), 127.0 (4 C, MeC6H4-
C2,6), 126.6 (2 C, C2H4Ph-C4), 124.8 (2 C, ClC6H4-C1), 122.5 (d,
orless solid; yield: 28.0 mg (46%); mp 170 °C (dec); Rf = 0.40
(CH2Cl2–MeOH, 8:1).
IR (ATR): 2982, 1511, 1395, 1247, 1160, 1041, 842, 786, 699,
538 cm–1.
1H NMR, COSY, HSQC (600 MHz, CDCl3): δ = 7.30–7.28 (m, 4
H, FC6H4-H2,6), 7.17–7.14 (m, 2 H, Ph-H4), 7.14–7.11 (m, 4 H,
EtOC6H4-H2,6), 7.07–7.03 (m, 8 H, Ph-H3,5, FC6H4-H3,5), 6.76–
6.74 (m, 4 H, Ph-H2,6), 6.55–6.54 (m, 4 H, EtOC6H4-H3,5), 4.18
(m, 6 H, NCH3), 3.90 (q, J = 7.0 Hz, 4 H, OCH2), 1.36 (t,
J = 7.0 Hz, 6 H, CH3).
2
4JCF = 3.6 Hz, 2 C, FC6H4-C1), 116.5 (d, JCF = 21.8 Hz, 4 C,
FC6H4-C3,5), 50.7 (2 C, NCH2), 36.7 (2 C, CH2Ph), 21.3 (2 C,
CH3).
MS (ESI): m/z = 1171.37 [M + Cl]+.
HRMS (ESI): m/z [M + Cl]+ calcd for C5813C2H4835Cl3F2198HgN4:
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 176.6 (2 C, C2,
1167.2647; found: 1167.2693.
1
1JHgC = 2845 Hz,), 163.5 (d, JCF = 251.9 Hz, 2 C, FC6H4-C4),
3
159.2 (2 C, EtOC6H4-C4), 133.1 (d, JCF = 8.6 Hz, 4 C, FC6H4-
Bis[5-(4-chlorophenyl)-4-(4-fluorophenyl)-3-methyl-1-(4-meth-
ylphenyl)(2-13C)-1,3-dihydro-2H-imidazol-2-ylidene]mercu-
ry(II) Dichloride (9b)
C2,6), 133.0 (2 C, C4), 132.8 (2 C, C5), 130.4 (4 C, Ph-C2,6), 129.2
(2 C, EtOC6H4-C1), 129.0 (2 C, Ph-C4), 128.5 (4 C, Ph-C3,5),
128.1 (4 C, EtOC6H4-C2,6), 126.6 (2 C, Ph-C1). 122.7 (d,
Prepared from imidazolium salt 8c (49.9 mg, 0.120 mmol) accord-
ing to general procedure D. The crude product was purified by flash
chromatography (silica gel, CH2Cl2–MeOH, 8:1) to give a mixture
of 9b and an unknown species (ratio 1:3 based on the assumption of
a monomeric structure for the contaminant) as a colorless solid;
yield: 53.3 mg (76%, based on the molecular weight of 9b); mp 180
°C (dec); Rf = 0.38 (CH2Cl2–MeOH, 8:1).
2
4JCF = 3.4 Hz, 2 C, FC6H4-C1), 116.4 (d, JCF = 21.9 Hz, 4 C,
FC6H4-C3,5), 115.0 (4 C, EtOC6H4-C3,5), 63.6 (2 C, OCH2), 37.5
(pseudo-t, 2 C, NCH3), 14.8 (2 C, CH3).
MS (ESI): m/z = 983.29 [M + Cl]+.
HRMS (ESI): m/z [M + Cl]+ calcd for C4613C2H42F2202HgN4O235Cl:
983.2738; found: 983.2735.
IR (ATR): 2923, 1511, 1228, 1159, 1090, 1016, 820, 623, 535, 504
cm–1.
1H NMR, COSY, HSQC (600 MHz, CDCl3): δ = 7.40–7.38 (m, 4
H, FC6H4-H2,6), 7.28–7.26 (m, 4 H, MeC6H4-H2,6); 7.04–6.99 (m,
12 H, FC6H4-H3,5, MeC6H4-H3,5, ClC6H4-H3,5), 6.83–6.82 (m, 4
H, ClC6H4-H2,6), 3.88–3.87 (m, 6 H, NCH3), 2.26 (s, 6 H, CH3).
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 175.4 (2 C, C2,
1JHgC = 2759 Hz), 163.6 (d, 1JCF = 251.2 Hz, 2 C, F-C6H4C4), 139.7
(2 C, MeC6H4-C4), 135.3 (2 C, ClC6H4-C4), 133.9 (2 C, MeC6H4-
C1), 133.5–133.4 (partly overlapping signals, 6 C, C4, FC6H4-
C2,6), 132.5 (2 C, C5), 132.1 (4 C, ClC6H4-C2,6), 130.4 (4 C,
MeC6H4-C3,5), 128.8 (4 C, ClC6H4-C3,5), 127.4 (4 C, MeC6H4-
C2,6), 125.2 (2 C, ClC6H4-C1), 122.5 (d, 4JCF = 3.5 Hz, 2 C, FC6H4-
C1), 116.3 (d, 2JCF = 22.2 Hz, 4 C, FC6H4-C3,5), 37.5 (2 C, NCH3),
21.4 (2 C, CH3).
Chloro[4-(4-fluorophenyl)-1-(4-methoxyphenyl)-3-methyl-5-
phenyl(2-13C)-1,3-dihydro-2H-imidazol-2-ylidene]silver(I) (9f)
Prepared according a procedure of Newman et al.19,20 To a soln of
imidazolium salt 8e (64.4 mg, 0.170 mmol) in anhyd CH2Cl2
(5 mL) was added Ag2O (19.7 mg, 85.0 μmol). After stirring in the
dark for 15 h at r.t., the soln was concentrated in vacuo. An excess
of Et2O (100 mL) was added and the silver–carbene complex 9f pre-
cipitated as a colorless solid (64.8 mg, 0.129 mmol). It was dis-
solved in anhyd CH2Cl2 (5 mL), K2PtCl4 (26.8 mg, 64.6 μmol) was
added and the soln was stirred for 24 h at r.t. The solvent was re-
moved and the crude product was dissolved in CH2Cl2 (0.5 mL). An
excess of cyclohexane (100 mL) was added and the silver–carbene
complex 9f, and not the platinum–carbene complex, precipitated as
a grey solid; yield: 42.9 mg (52%); Rf = 0.07 (CH2Cl2–MeOH,
10:1).
MS (ESI): m/z = 478.1 [M]2+.
HRMS (ESI): m/z [M]2+ calcd for C4413C2H3635Cl2F2198HgN4:
IR (ATR): 2936, 1511, 1300, 1250, 1159, 1030, 837, 780, 699, 538
cm–1.
1H NMR, COSY, HSQC (300 MHz, CDCl3): δ = 7.29–7.24 (m, 2
H, FC6H4-H6), 7.18–7.06 (m, 7 H, Ph-H3,4,5, FC6H4-H3,5,
MeOC6H4-H2,6), 6.88–6.84 (m, 2 H, Ph-H2,6), 6.83–6.80 (m, 2 H,
MeOC6H4-H2,6), 3.78 (s, 3 H, OCH3), 3.74 (d, 3JCH = 5.2 Hz, 3 H,
NCH3).
476.1010; found: 476.1017.
The unknown component gave a defined set of NMR signals and
exhibited an unusually large JHgC coupling constant of 3683 Hz.
Characteristic signals:
1H NMR, COSY, HSQC (600 MHz, CDCl3): δ = 7.36–7.33 (m, 2
H, FC6H4-H2,6), 7.23–7.22 (m, 2 H, MeC6H4-H2,6), 7.16–7.15 (m,
2 H, MeC6H4-H3,5), 7.12–7.08 (m, 4 H, FC6H4-H3,5, ClC6H4-
H3,5), 6.83–6.82 (m, 2 H, ClC6H4-H2,6), 4.13 (d, 3JCH = 4.9 Hz, 3
H, NCH3), 2.31 (s, 3 H, CH3).
1
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 180.5 (C2; this
signal splits to a doublet of 1J = 252 Hz at lower concentration, see
1
main text), 163.3 (d, JCF = 250.7 Hz, FC6H4-C4), 159.7
3
(MeOC6H4-C4), 132.7 (d, JCF = 8.5 Hz, 2 C, FC6H4-C2,6), 131.7
(MeOC6H4-C1), 131.6 (C5), 131.3 (d, 2JCC = 1.7 Hz, C4), 130.2 (2
C, Ph-C2,6), 128.7 (Ph-C4), 128.5 (2 C, Ph-C3,5), 128.1 (d,
3JCC = 2.3 Hz, 2 C, MeOC6H4-C2,6), 127.6 (Ph-C1), 123.9 (d,
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 173.5 (C, C2,
1JHgC = 3683 Hz), 163.7 (d, JCF = 251.2 Hz, FC6H4-C4), 140.6
1
2
4JCF = 3.6 Hz, FC6H4-C1), 116.4 (d, JCF = 22.0 Hz, 2 C, FC6H4-
(MeC6H4-C4), 135.6 (ClC6H4-C4), 134.0 (d, JCC = 5.2 Hz,
2
MeC6H4-C1), 133.5–133.4 (partly overlapping signals, C5), 133.1
C3,5), 114.7 (2 C, MeOC6H4-C3,5), 55.6 (OCH3), 37.7 (d,
3
2JCC = 11.9 Hz, NCH3).
(d, JCF = 8.8 Hz, 4 C, FC6H4-C2,6), 132.4 (C4), 131.6 (2 C,
ClC4H6-C2,6), 130.6 (2 C, MeC4H6-C3,5), 129.0 (2 C, ClC6H4-
MS (ESI): m/z = 825.21 [(NHC)2Ag]+.
HRMS (ESI): m/z [(NHC)2Ag]+ calcd for (C2213CH19FN2O)2107Ag:
C3,5), 127.2 (2 C, MeC6H4-C2,6), 125.0 (ClC6H4-C1), 122.4 (d,
4JCF = 3.3 Hz, FC6H4-C1), 116.7 (d, JCF = 21.9 Hz, 2 C, FC6H4-
2
C3,5), 37.9 (d, 2JCC = 6.3 Hz, NCH3), 21.4 (CH3).
825.2081; found: 825.2082.
Bis[1-(4-ethoxyphenyl)-4-(4-fluorophenyl)-3-methyl-5-phe-
nyl(2-13C)-1,3-dihydro-2H-imidazol-2-ylidene]mercury(II) Di-
chloride (9c)
Prepared from imidazolium salt 8d (57.1 mg, 0.139 mmol) accord-
ing to general procedure D. The crude product was purified by flash
chromatography (silica gel, CH2Cl2–MeOH, 8:1) to give 9c as a col-
Dichloro[bis[5-(4-chlorophenyl)-4-(4-fluorophenyl)-1-(4-meth-
ylphenyl)-3-(2-phenylethyl)(2-13C)-1,3-dihydro-2H-imidazol-2-
ylidene]]platinum(II) (9g)
Prepared according a procedure of Newman et al.19,20 To a soln of
imidazolium salt 8a (65.1 mg, 0.129 mmol) in anhyd CH2Cl2
(5 mL) was added Ag2O (16.6 mg, 71.6 μmol). After stirring in the
dark for 15 h at r.t., the soln was concentrated. An excess of Et2O
Synthesis 2013, 45, 2251–2264
© Georg Thieme Verlag Stuttgart · New York

PAPER
Investigation of Electronic Unsymmetry by NMR
2263
(100 mL) was added and the silver–carbene complex 9d precipitat-
ed as a colorless solid (29.3 mg, 47.9 μmol). It was dissolved in an-
hyd CH2Cl2 (5 mL), K2PtCl4 (9.90 mg, 23.9 μmol) was added, and
the soln was stirred for 24 h at r.t. The solvent was removed in vac-
uo and the crude product was purified by flash chromatography (sil-
ica gel, CH2Cl2–MeOH, 20:1 to 5:1) to give 9g as a colorless solid;
yield: 23.8 mg (28% over 2 steps); mp 290 °C (dec); Rf = 0.13
(CH2Cl2–MeOH, 10:1).
N1,N2-Bis(4-ethoxyphenyl)-1,2-diphenylethane-1,2-diimine (10)
Prepared according a procedure of Shimizu et al.27 A soln of benzil
(7.50 g, 35.7 mmol) and p-phenetidine (4.90 g, 35.7 mmol) in 1,2-
dichloroethane (70 mL) was stirred at 70 °C for 72 h. The soln was
filtered and the solvent was removed in vacuo. The crude product
was recrystallized (MeOH, 200 mL) to give 10 as yellow crystals;
yield: 10.4 g (66%); mp 149.1–149.3 °C; Rf = 0.32 (cyclohexane–
EtOAc, 10:1).
IR (ATR): 2979, 1608, 1502, 1243, 1116, 1047, 825, 767, 692, 545
cm–1.
IR (ATR): 2922, 1512, 1490, 1229, 1093, 837, 744, 698, 534, 505
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.89–7.87 (m, 4
H, Ph-H2,6), 7.43–7.34 (m, 6 H, Ph-H3,4,5), 6.72–6.68 (m, 4 H,
EtOC6H4-H2,6), 6.66–6.62 (m, 4 H, EtOC6H4-H3,5), 3.94 (q,
J = 7.0 Hz, 4 H, OCH2CH3), 1.37 (t, J = 7.0 Hz, 6 H, OCH2CH3).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 163.3 (2 C,
CN-C4H6OEt), 156.8 (2 C, EtOC6H4-C4), 142.4 (2 C, EtOC6H4-
C1), 137.5 (2 C, Ph-C1), 130.9 (2 C, Ph-C4), 128.8 (4 C, Ph-C3,5),
128.1 (4 C, Ph-C2,6), 122.2 (4 C, EtOC6H4-C2,6), 114.4 (4 C,
EtOC6H4-C3,5), 63.6 (2 C, OCH2CH3), 14.9 (2 C, OCH2CH3).
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.44–7.42 (m, 4
H, MeC6H4-H2,6), 7.24–7.23 (m, 6 H, C2H4Ph-H3,4,5), 7.01–6.96
(m, 12 H, C2H4Ph-H2,6, ClC6H4-H3,5, FC6H4-H3,5), 6.90–6.87 (m,
4 H, FC6H4-H2,6), 6.82–6.80 (m, 4 H, MeC6H4-H3,5), 6.67–6.65
(m, 4 H, ClC6H4-H2,6), 4.53–4.51 (m, 4 H, NCH2), 2.99 (t,
J = 7.6 Hz, 4 H, CH2Ph), 2.11 (s, 6 H, CH3).
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 167.8 (2 C, C2,
1
1JPtC = 943 Hz), 163.0 (d, JCF = 250.0 Hz, 2 C, FC6H4-C1), 138.9
(2 C, C2H4Ph-C1), 137.9 (2 C, MeC6H4-C4), 136.0 (2 C, MeC6H4-
C1), 134.1 (2 C, ClC6H4-C4), 132.8 (d, 3JCF = 8.2 Hz, 4 C, FC6H4-
C3,5), 131.5 (4 C, ClC6H4-C2,6), 130.7 (2 C, C5), 130.5 (2 C, C4),
129.4 (4 C, C2H4Ph-C2,6), 129.2 (4 C, MeC4H6-C3,5), 128.9 (4 C,
MeC4H6-C2,6), 128.6 (4 C, C2H4Ph-C3,5), 128.5 (4 C, ClC6H4-
C3,5), 126.7 (2 C, ClC6H4-C1), 126.5 (2 C, C2H4Ph-C4), 124.4 (d,
MS (ESI): m/z = 449.3 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C30H29N2O2: 449.2229; found:
449.2226.
1,3-Bis(4-ethoxyphenyl)-4,5-diphenyl-1H-imidazolium Chlo-
ride (11)
2
4JCF = 3.3 Hz, 2 C, FC6H4-C1), 116.0 (d, JCF = 21.8 Hz, 4 C,
Prepared according a procedure of Cowley et al.28 Paraformalde-
hyde (117 mg, 3.90 mmol) was dissolved in toluene (60 mL) under
heating. This soln was added to the diimine 10 (584 mg, 1.30 mmol)
under argon. After stirring at r.t. for 5 min, 4 M HCl in dioxane
(1.0 mL, 0.39 mmol) was added via cannula. After stirring at r.t for
50 h, the solvent was removed in vacuo and the crude product was
purified by flash chromatography (silica gel, CH2Cl2–MeOH, 6:1)
to give 11 as red solid; yield: 454 mg (71%); mp 70.0–70.5 °C;
Rf = 0.21 (CH2Cl2–MeOH, 8:1).
FC6H4-C3,5), 49.0 (2 C, NCH2), 36.6 (2 C, CH2Ph), 21.2 (2 C,
CH3).
MS (ESI): m/z = 1163.25 [M – Cl]+.
HRMS (ESI): m/z [M – Cl]+ calcd for C5813C2H4835Cl3F2N4194Pt:
1163.2606; found: 1163.2561.
Dichloro[bis[4-(4-fluorophenyl)-1-(4-methoxyphenyl)-5-phe-
nyl-3-(2-phenylethyl)(2-13C)-1,3-dihydro-2H-imidazol-2-yli-
dene]]platinum(II) (9h)
Prepared according a procedure of Newman et al.19,20 To a soln of
imidazolium salt 8f (29.8 mg, 61.3 μmol) in anhyd CH2Cl2 (5 mL)
was added Ag2O (7.1 mg, 31 μmol). After stirring in the dark for
15 h at r.t., the solvent was removed in vacuo to give the silver–car-
bene complex 9e as a red oil (34.9 mg, 58.9 μmol). It was dissolved
in anhyd CH2Cl2 (5 mL), K2PtCl4 (12.2 mg, 29.4 μmol) was added,
and the soln was stirred for 24 h at r.t. The solvent was removed in
vacuo and the crude product was purified by flash chromatography
(silica gel, CH2Cl2–MeOH, 10:1) to give 9h as a red solid; yield:
16.7 mg (47% over 2 steps); mp 284 °C (dec); Rf = 0.44 (cyclohex-
ane–EtOAc, 2:1).
IR (ATR): 2979, 1544, 1505, 1239, 1174, 1042, 841, 782, 697, 542
cm–1.
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 9.96 (s, 1 H, CH),
7.50–7.46 (m, 4 H, EtOC6H4-H2,6), 7.23–7.19 (m, 2 H, Ph-H4),
7.15–7.12 (m, 4 H, Ph-H3,5), 7.09–7.06 (m, 4 H, Ph-H2,6), 6.80–
6.76 (m, 4 H, EtOC6H4-H3,5), 3.89 (q, J = 7.0 Hz, 4 H, OCH2CH3),
1.28 (t, J = 7.0 Hz, 6 H, OCH2CH3).
13C NMR, HSQC, HMBC (100.6 MHz, CDCl3): δ = 160.0 (2 C,
EtOC6H4-C4), 136.7 (C2), 132.1 (2 C, C4,5), 130.8 (4 C, Ph-C2,6),
129.8 (2 C, Ph-C4), 128.6 (4 C, Ph-C3,5), 127.7 (4 C, EtOC6H4-
C2,6), 125.7 (2 C, EtOC6H4-C1), 124.8 (2 C, Ph-C1), 115.1 (4 C,
EtOC6H4-C3,5), 63.7 (2 C, OCH2CH3), 14.5 (2 C, OCH2CH3).
IR (ATR): 2923, 1511, 1447, 1247, 1158, 1028, 834, 749, 698, 535
cm–1.
MS (ESI): m/z = 461.2 [M]+.
HRMS (ESI): m/z [M]+ calcd for C31H29N2O2: 461.2229; found:
1H NMR, COSY, HSQC (400 MHz, CDCl3): δ = 7.48–7.46 (m, 4
H, MeOC6H4-H2,6), 7.27–7.23 (m, 6 H, C2H4Ph-H3,4,5), 7.11–
7.02 (m, 10 H, C2H4Ph-H2,6, Ph-H3,4,5), 7.02–6.96 (m, 8 H,
FC6H4-H2,3,5,6), 6.77–6.75 (m, 4 H, Ph-H2,6), 6.49–6.47 (m, 4 H,
MeOC6H4-H3,5), 4.62–4.59 (m, 4 H, NCH2), 3.49 (s, 6 H, OCH3),
3.05-3.02 (m, 4 H, CH2Ph).
461.2234.
Bis[1,3-bis(4-ethoxyphenyl)-4,5-diphenyl-1,3-dihydro-2H-im-
idazol-2-yliden]mercury(II) Dichloride (12)
Prepared according a procedure of Arduengo et al.9 To a soln of im-
idazolium salt 11 (77.9 mg, 0.157 mmol) in anhyd THF (1 mL) was
added Hg(OAc)2 (25.0 mg, 78.4 μmol) and DMSO (1 drop). After
stirring at r.t. for 15 h, the precipitate was filtered and washed with
THF (10 mL) to give 12 as a colorless solid; yield: 73.2 mg (79%);
mp 184 °C (dec); Rf = 0.48 (CH2Cl2–MeOH, 10:1).
13C NMR, HSQC, HMBC (75.5 MHz, CDCl3): δ = 167.5 (2 C, C2,
1
1JPtC = 943 Hz), 162.9 (d, JCF = 250.4 Hz, 2 C, FC6H4-C4), 158.9
(2 C, MeO-C6H4-C4), 139.0 (2 C, C2H4Ph-C1), 132.9 (d,
3JCF = 8.4 Hz, 4 C, FC6H4-C2,6), 132.0 (2 C, C5), 131.8 (2 C,
MeOC6H4-C1), 130.4 (4 C, Ph-C2,6), 130.2 (4 C, MeOC6H4-C2,6),
130.0 (2 C, C4), 129.4 (4 C, C2H4Ph-C2,6), 128.7 (4 C, Ph-C3,5),
128.1 (4 C, C2H4Ph-C3,5), 128.0 (2 C, Ph-C1), 128.0 (2 C, Ph-C4),
126.5 (2 C, C2H4Ph-C4), 124.8 (d, 4JCF = 3.4 Hz, 2 C, FC6H4-C1),
115.9 (d, 2JCF = 21.8 Hz, 4 C, FC6H4-C3,5), 113.5 (4 C, MeOC6H4-
C3,5), 55.3 (2 C, OCH3), 49.3 (2 C, NCH2), 36.8 (2 C, CH2Ph).
IR (ATR): 2981, 1606, 1508, 1244, 1172, 1045, 823, 786, 698,
554 cm–1.
1H NMR, COSY, HSQC (600 MHz, DMSO): δ = 7.33 (pseudo-d,
J = 8.7 Hz, 8 H, EtOC6H4-H2,6), 7.28–7.24 (m, 4 H, Ph-H4), 7.24–
7.20 (m, 8 H, Ph-H3,5), 7.10 (pseudo-d, J = 7.5 Hz, 8 H, Ph-H2,6),
6.74 (pseudo-d, J = 8.7 Hz, 8 H, EtOC6H4-H3,5), 4.03–3.98 (m, 8
H, OCH2CH3), 1.35 (t, J = 7.0 Hz, 12 H, OCH2CH3).
MS (ESI): m/z = 1185.38 [M + Na]+.
HRMS
(ESI):
m/z [M
+
Na]+
calcd
for
C5813C2H5035Cl2F2N4O2195PtNa: 1186.2891; found: 1186.2914.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2251–2264

2264
J. Emsermann et al.
PAPER
13C NMR, HSQC, HMBC (150.9 MHz, DMSO): δ = 175.4 (d,
1JHgC = 2715 Hz, 2 C, C2), 159.1 (4 C, EtOC6H4-C4), 133.6 (4 C,
Ph-C4), 130.8 (8C, Ph-C2,6), 129.5 (4 C, C4,5), 128.5 (8 C, Ph-
C3,5), 128.1 (8 C, EtO-C6H4-C2,6), 128.0 (4 C, EtOC6H4-C1),
126.1 (4 C, Ph-C1), 114.9 (8 C, EtOC6H4-C3,5), 63.5 (4 C,
OCH2CH3), 14.6 (4 C, OCH2CH3).
MS (ESI): m/z = 1157.39 [M – Cl]+.
HRMS (ESI): m/z [M – Cl]+ calcd for C62H5635Cl202HgN4O4:
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnoIufproi
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References
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1157.3696; found: 1157.3690.
[1,3-Bis(4-ethoxyphenyl)-4,5-diphenyl-1,3-dihydro-2H-imidaz-
ol-2-ylidene]silver(I) Chloride (13)
Prepared according a procedure of Newman et al.19 To a soln of im-
idazolium salt 11 (138 mg, 0.278 mmol) in anhyd CH2Cl2 (5 mL)
was added Ag2O (32.1 mg, 0.139 mmol). After stirring in the dark
for 15 h at r.t., the soln was concentrated in vacuo. An excess of
Et2O (100 mL) was added and 13 precipitated as a colorless solid;
yield: 94.1 mg (57%); mp 250 °C (dec); Rf = 0.09 (CH2Cl2–MeOH,
10:1).
IR (ATR): 2925, 1511, 1395, 1242, 1171, 1043, 921, 835, 696,
556 cm–1.
1H NMR, COSY. HSQC (600 MHz, CDCl3): δ = 7.26–7.22 (m, 2
H, Ph-4), 7.21–7.18 (m, 4 H, EtOC6H4-H2,6), 7.17–7.15 (m, 4 H,
Ph-H3,5), 6.96–6.95 (m, 4 H, Ph-H2,6), 6.84–6.82 (m, 4 H,
EtOC6H4-H3,5), 4.02 (q, J = 7.0 Hz, 4 H, OCH2CH3), 1.41 (t,
J = 7.0 Hz, 6 H, OCH2CH3).
(10) Arduengo, A. J.; Dias, H. V. R.; Calabrese, J. C.; Davidson,
F. Inorg. Chem. 1993, 32, 1541.
(11) Arduengo, I. I. I. A. J.; Krafczyk, R.; Schmutzler, R.;
Mahler, W.; Marshall, W. J. Z. Anorg. Allg. Chem. 1999,
625, 1813.
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McDonald, R.; Takats, J. J. Alloys Compd. 2006, 418, 184.
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Demtschuk, J. J. Organomet. Chem. 2001, 617–618, 588.
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G.; Jones, P. G.; Tamm, M. Chem. Eur. J. 2012, 18, 16938.
(15) Kison, C.; Meyer, N.; Opatz, T. Angew. Chem. Int. Ed. 2005,
44, 5662.
13C NMR, HSQC, HMBC (150.9 MHz, CDCl3): δ = 159.3 (2 C, Et-
C6H4-C4), 132.3 (2 C, C4, C5), 131.4 (2 C, EtOC6H4-C1), 130.6 (4
C, Ph-C2,6), 128.8 (2 C, Ph-C4), 128.6 (4 C, Ph-C3,5), 128.1 (4 C,
EtOC6H4-C2,6), 127.7 (2 C, Ph-C1), 115.2 (4 C, EtOC6H4-C3,5),
63.9 (2 C, OCH2CH3), 14.9 (2 C, OCH2CH3); C2 is not visible.
MS (ESI): m/z = 1027.34 [(NHC)2Ag]+.
HRMS (ESI): m/z [(NHC)2Ag]+ calcd for (C31H28N2O2)2107Ag:
1027.3352; found: 1027.3344.
(16) Delaude, L.; Szypa, M.; Demonceau, A.; Noels, A. F. Adv.
Synth. Catal. 2002, 344, 749.
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Goerlich, J. R.; Marshall, W. J.; Unverzagt, M. Tetrahedron
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(18) Kison, C.; Opatz, T. Synthesis 2006, 3727.
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[1,3-Bis(2,4,6-trimethylphenyl)-2,3-dihydro-2H-imidazol-2-yli-
dene]mercury(II) Dichloride (14)
Prepared according a procedure of Mohr et al.21 To a soln of
1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride (175 mg,
0.513 mmol) in CH2Cl2 (10 mL) was added HgO (108 mg,
0.514 mmol) and Me4NCl (56.4 mg, 0.51 mmol). After stirring at
r.t. for 15 h, the soln was passed through Celite, the solvent was re-
moved in vacuo, and the residue was washed with H2O (2 × 10 mL)
and Et2O (2 × 10 mL) to give 14 as a colorless solid; yield: 240 mg
(82%); mp 270 °C (dec); Rf = 0.09 (CH2Cl2–MeOH, 10:1).
1H NMR (300 MHz, CD2Cl2): δ = 7.50 (s, JHHg = 23.8 Hz, 2 H,
H4,5), 6.92 (s, 4 H, Mes-H3,5), 2.45 (s, 6 H, p-CH3), 1.81 (s, 12 H,
o-CH3).
4
13C NMR (75.5 MHz, CD2Cl2): δ = 179.8 (1JCHg = 2553.3 Hz, C1),
141.0 (Mes-C1), 135.0 (2 C, Mes-C2,6), 132.7 (Mes-C4), 129.9 (2
3
C, Mes-C3,5), 126.1 (2 C, JCHg = 74.9 Hz, C4,5), 21.4 (p-CH3),
17.5 (2 C, o-CH3).
(26) Kison, C.; Opatz, T. Synthesis 2006, 3727.
(27) Shimizu, M.; Kamei, M.; Fujisawa, T. Tetrahedron Lett.
1995, 36, 8607.
Acknowledgment
(28) Powell, A. B.; Bielawski, C. W.; Cowley, A. H. J. Am.
Chem. Soc. 2009, 131, 18232.
This work was supported by the Deutsche Forschungsgemeinschaft.
We are indebted to Dr. Johannes C. Liermann (University of Mainz)
and Prof. Christina M. Thiele (University of Darmstadt) for NMR
spectroscopy and helpful discussions.
Synthesis 2013, 45, 2251–2264
© Georg Thieme Verlag Stuttgart · New York