Modular trimethylene-linked bisimidazol(in)ium salts

Article abstract of DOI:10.1055/s-0029-1218702

A short and modular synthesis of symmetrically and non-symmetrically substituted bisimidazolinylene N-heterocyclic carbene precursors is described. Two methods to establish dicopper(I) complexes of these compounds depending on the steric shielding of the

Full text of DOI:10.1055/s-0029-1218702

PAPER
1459
Modular Trimethylene-Linked Bisimidazol(in)ium Salts
Modular Trimethylene
i
-Linke
c
dBisimida
z
h
ol(in)ium Sa
a
lts el Bessel, Frank Rominger, Bernd F. Straub*
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
E-mail: straub@oci.uni-heidelberg.de
Received 20 November 2009; revised 12 February 2010
The general procedure for the preparation of NHC com-
plexes relies on simple ligand exchange. Therefore, syn-
thetic strategies leading to the corresponding highly
stabilized five-membered carbene rings as a discrete or a
transient species are in demand. In 2004, Marshall et al.
reported a suitable route to aryl-substituted, alkyl-linked
bisimidazolinium salts, but neither isolated nor character-
ized the free biscarbenes or metal complexes thereof.16 It
was reported that bisimidazolinium salts with 2,4,6-tri-
methylphenyl substituents form tetraaminoethene deriva-
tives after deprotonation. Only the deprotonation of a 2,6-
diisopropylphenyl-substituted bis-NHC precursor led to
an air-sensitive oil, which contained free carbene species
according to NMR data.
Abstract: A short and modular synthesis of symmetrically and non-
symmetrically substituted bisimidazolinylene N-heterocyclic car-
bene precursors is described. Two methods to establish dicopper(I)
complexes of these compounds depending on the steric shielding of
the carbene are reported.
Key words: alkylations, copper, carbene complexes, ligands, N-
heterocyclic carbenes
Wanzlick and Öfele published the first metal complexes
of N-heterocyclic carbenes (NHCs) more than 40 years
ago. However, it took nearly three decades until NHCs
were established in organometallic chemistry and cataly-
sis.1 The field remained more or less dormant until 1991,
when Arduengo and co-workers were able to isolate the
first NHC in substance.2 Nowadays, NHC complexes and
their catalytic activity have become an important area of
research.3,4
B
N
n N
N
N
N
N
R
R
A
n
N
N
M
M
M
R
R
homodinuclear,
symmetric
chelating,
The favorable stability of metal NHC complexes towards
heat, oxygen, and moisture represents a significant advan-
tage over the analogous phosphine-containing com-
pounds.5 Strong s-donating ability, wide functional group
compatibility, and the fact that they do not readily under-
go ligand dissociation, combine to make NHCs unique an-
cillary ligands. N-Heterocyclic carbenes are a good choice
not only for olefin metathesis reactions and aryl cross-
couplings, but also for polymerizations,6 hydrogenations,7
hydrosilylations,8 hydroborations,9 hydroformylations,10
allylic substitutions,11 cycloadditions (‘click’ chemis-
try),12 methenylations, and others.13
mononuclear, symmetric
D
C
N
N
N
N
N
N
N
N
R1
R2
R1
R2
n
n
M1
heterodinuclear,
different NHC ligands
M2
M
M
homodinuclear,
different NHC ligands
R, R1, R2 = aryl, alkyl
M, M1, M2 = transition-metal fragment
Figure 1 Examples of NHC metal complexes
We optimized this procedure and found a short, modular
route to symmetrically as well as non-symmetrically alkyl
and aryl substituted bis-NHC precursors and transition
metal complexes. Our procedure starts from the inexpen-
sive compounds 2-bromoethylamine hydrobromide and
an aniline derivative. In a simple SN2 reaction, N-aryleth-
ylenediamines 1a–c were obtained in good yields on the
gram scale (Scheme 1).
The literature comprises many examples of mononuclear
complexes of bidentate NHC ligands (type A) or bimolec-
ular NHC metal complexes.14 However, there is a growing
number of dinuclear bis-NHC complexes of late transition
metals of type B.15 We intended to prepare flexible and
stable homodinuclear complexes of nonchelating alky-
lene-linked bis-NHCs. Of particular interest are bis-NHC
precursor salts containing different heterocycles in one
molecule. They can provide different electronic and steric
coordination sites for homobimetallic complexes (type C)
and may prove to be helpful to rationally and specifically
prepare heterobimetallic bis-NHC complexes (type D)
(Figure 1).
Condensation of diamines 1 with triethyl orthoformate in
the presence of p-toluenesulfonic acid monohydrate gave
N-arylimidazolines 2a–c as nucleophilic building blocks
in good yields. Imidazolines 2 reacted with 0.5 equivalent
of 1,3-dibromopropane to give symmetrical bisimidazo-
linium dibromides 3, as depicted in Scheme 1. The molec-
ular structure of bis-NHC precursor 3a was confirmed by
X-ray crystallography (Figure 2).
SYNTHESIS 2010, No. 9, pp 1459–1466
Advanced online publication: 12.03.2010
DOI: 10.1055/s-0029-1218702; Art ID: T22509SS
x
x
.
x
x
.2
0
1
0
In some cases, exchange of counterions was beneficial to
improve the solubility of the bis-NHC precursors in a cer-
© Georg Thieme Verlag Stuttgart · New York

1460
M. Bessel et al.
PAPER
R1
R1
R1
Br(CH2)2NH2•HBr
toluene, 110 °C, 18 h
HC(OEt)3, PTSA
140 °C, 18 h
NH2
R1
N
N
R2
NH
NH2
R2
R1
2a–c 75–79%
R2
R1
1a–c 70–76%
R1
R1 X-ray (Figure 2)
1,3-dibromopropane
neat, 120 °C, 3 h
R1
N
N
N
N
N
N
2
R2
R2
R2
R1
2a,b
Br
R1
R1
Br
3a,b 90–92%
(a) R1 = i-Pr, R2 = H
(b) R1 = R2 = Me
(c) R1 = Me, R2 = H
Scheme 1 Synthesis of symmetric bis-NHC precursors
bis-NHC precursors. Unfortunately, both bromoalkyl
groups were found to react rapidly by stirring imidazoline
2a with a 10-fold excess of 1,3-dibromopropane in Et2O.
Therefore, monoimidazolinium salt 5a was obtained as a
6:1 mixture with 3a and could not be purified any further
(Scheme 3). Even though we were not able to obtain ana-
lytical data of pure 5a, we have proved its existence by the
X-ray structure depicted in Figure 3.
X-ray (Figure 3)
Br(CH2)3Br (10 equiv)
Br
N
N
N
N
Et2O, r.t., 18 h
Br
Figure 2 ORTEP plot of the molecular structure of bis-NHC pre-
cursor 3a. Bond lengths [Å]: C6–H6, 0.871; C6–N7, 1.307; C6–N10,
1.291; C9–N10, 1.469; C8–C9, 1.537; C8–N7, 1.482; H6–Br2, 2.786;
angles [°]: C8–N7–C31, 123.63; C8–N7–C31–C32, 86.26. Solvent
molecules have been omitted for clarity.
2a
5a (6:1 mixture with 3a)
2c (1.5 equiv)
neat, 90 °C, 3 h
X-ray (Figure 4)
N
N
N
N
Br
Br
N
N
N
N
6
(6:1 mixture with 3a)
Br
Br
Scheme 3 First attempt to synthesize non-symmetrically substitu-
3a
ted bis-NHC precursors
excess PTSA
CH2Cl2/H2O, r.t., 2 h
N
N
N
N
OTs
OTs
4
81% isolated
Scheme 2 Anion exchange on bis-NHC precursor 3a
tain solvent or tune coordination characteristics of the an-
ions referring to metals in later complexes. For example,
the bis-NHC dibromide 3a was converted into the ditosy-
late 4 by stirring a solution of 3a in CH2Cl2 with an excess
of an aqueous solution of p-toluenesulfonic acid monohy-
drate (Scheme 2). This procedure is widely used in ionic
liquid chemistry.
Figure 3 ORTEP plot of the molecular structure of 5a. Bond
lengths [Å]: C1–N5, 1.298; C1–N2, 1.309; N2–C3, 1.484; C3–C4,
1.533; C4–N5, 1.472; angles [°]: C3–N2–C31–C32, 118.93; N2–C3–
C4–N5, 12.12.
Reaction of monoimidazolinium salt 5a (as a 6:1 mixture
with 3a) with imidazoline 2c yielded the non-symmetri-
cally substituted bis-NHC precursor 6. Due to the contam-
ination of 5a with 3a, we were not able to obtain clean
Monoimidazolinium salts such as 5a are useful building
blocks for the synthesis of non-symmetrically substituted
Synthesis 2010, No. 9, 1459–1466 © Thieme Stuttgart · New York

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Modular Trimethylene-Linked Bisimidazol(in)ium Salts
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NHC precursor 8 (Scheme 5).18 Crystallization and purifi-
cation led to substances with varying chloride to bromide
ratios, as seen in Figure 5.
Figure 4 ORTEP plot of the molecular structure of 6. Bond lengths
[Å]: N92–C90, 1.315; C93–C96, 1.528; C90–N99, 1.278; C93–N92,
1.485; N99–C96, 1.493; angles [°]: N92–C93–C96–N99, 8.55;
C127–C126–N92–C90, 96.69; C110–C109–N82 –C80, 119.29. Sol-
vent molecules have been omitted for clarity.
Figure 5 ORTEP plot of the structure of mixed functional bis-NHC
precursor 8. Bond lengths [Å]: C1–N5, 1.295; C1–N2, 1.309; N2–C3,
1.473; C3–C4, 1.525; C6–N10, 1.322; C6–N7, 1.331; N7–C8, 1.383;
C8–C9, 1.340; C9–N10, 1.375; angles [°]: C8–N7–C41–C42, 118.45;
C3–N2–C21–C22, 118.05.
analytical data for 6. The structure of 6 is apparent from a
single-crystal X-ray structure analysis (Figure 4).
Using this modular approach, we tuned the properties of
bis-NHC precursors by the size of the substituent, the na-
ture of the NHC, the length and rigidity of the linker moi-
ety, and the counterion.
The reaction of imidazoline 2a with 1-bromo-3-chloro-
propane in refluxing Et2O afforded the monoimidazolini-
um salt 5b in moderate yield. The electrophilic building
block 5b reacted with 1-methylimidazoline (7), prepared
from commercially available N-methylethylenediamine
by condensation with N,N-dimethylformamide dimethyl
acetal as described by Cetinkaya et al.17 (Scheme 4), to
form the non-symmetrically substituted bis-NHC precur-
sor 9 (Scheme 5).
We developed two reliable pathways to dicopper(I) bis-
NHC complexes depending on the steric demand of the
aryl substituent of our bisimidazolinium salts 3a and 3b.
Deprotonation of the ligand precursor 3a with sodium
hexamethyldisilazide (NaHMDS) in anhydrous toluene in
the presence of a copper(I) salt led to complex 10 in mod-
erate yields (Scheme 6).
H
110 °C, 2 h
MeO
OMe
N
N
+
Me
Me NH
NH2
– 2 MeOH
– HNMe2
NMe2
7
81%
N
N
N
N
Scheme 4 Preparation of 1-methylimidazoline (7)
Br
Br
3a
Br(CH2)3Cl, Et2O
45 °C, 18 h
1. NaHMDS, toluene, r.t., 2 h
2. CuBrSMe2, r.t., 18 h
Cl
N
N
N
N
X-ray (Figure 6)
Br
5b 31%
2a
N
N
N
N
7 (1.5 equiv)
neat, 90 °C, 3 h
N-mesityl-
imidazole
neat, 3 h
100 °C
Cu
Br
Cu
Br
10 50%
N
N
N
N
Me
Cl
Br
Scheme 6 Synthesis of dicopper(I)-NHC complex 10 with sterical-
ly demanding diisopropylphenyl substituents
9
68%
N
X-ray (Figure 5)
N
After deprotonation with NaHMDS or DBU, bis-NHC
precursor 3b with its medium-sized substituents reacted
by intramolecular dimerization to form tetraaminoeth-
enes, as described by Marshall et al.16 These compounds
react with copper(I) salts by formation of black metal cop-
per precipitate. However, synthesis of dicopper(I) com-
plex 11 was achieved via transmetalation from an in situ
generated silver NHC species. It is well known that sil-
ver(I) NHC complexes easily transfer the ligand to other
metals and form silver halides or silver metal.19
N
N
Br
Cl
70%
8
Scheme 5 General approach to synthesize non-symmetrically sub-
stituted bis-NHC precursors
On the other hand, reaction of imidazolinium salt 5b with
N-mesitylimidazole yielded the mixed functional bis-
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1462
M. Bessel et al.
PAPER
Deprotonation of 3b was carried out in situ using Ag2O as
a base to form a labile and light-sensitive silver(I) NHC
species that was not isolated. This silver(I) NHC complex
reacted with copper(I) salts by transmetalation of the bis-
NHC ligand to form the desired homodinuclear dicop-
per(I) bis-NHC complex 11 (Scheme 7).
N
N
N
N
Br
Br
3b
1. Ag2O, CH2Cl2, r.t., 24 h
2. CuBrSMe2, r.t., 24 h
X-ray (Figure 7)
The general influence of the size of aryl groups in bis-
NHC-copper complexes 10 and 11 is depicted by X-ray
structure drawings in Figures 6 and 7.
N
N
N
N
Cu
Br
Cu
Br
Strong steric shielding by aryl groups leads to linearly co-
ordinated copper(I) in complex 10 in the solid state. With
decreasing bulk of the aryl groups, the NHC-copper(I)
bromide fragments form intermolecular coordination
bonds. This is displayed by Figure 7 showing complex 11
as a coordination polymer in the solid state. This fact
makes no statement regarding the behavior of the com-
plexes in solution. However, the influence of steric modi-
fications on the accessibility of the copper centers is
illustrated.
11 43%
Scheme 7 Synthetic approach to dicopper(I)-NHC complex 11 with
aryl groups of medium size
Starting materials were used as supplied by Acros Organics, Ald-
rich Chemical Company, and TCI without further purification. Re-
actions involving air-sensitive reagents were carried out in an
atmosphere of N2 or argon using standard Schlenk techniques. An-
hydrous solvents were dried in an MBraun MB SCS-800 solvent
purification system. NMR spectra were recorded using Bruker
ARX-250 and Bruker Avance 300 spectrometers. Chemical shifts
are reported in ppm relative to TMS and were determined by refer-
ence to the residual 1H or 13C solvent peaks. Melting points were de-
termined using a Gallenkamp hot-stage microscope and are
uncorrected.
Figure 6 ORTEP plot of the molecular structure of dicopper(I)
complex 10. Bond lengths [Å]: Cu1–Br1, 2.235; Cu1–C11, 1.887;
C13–C14, 1.516; C14–N15, 1.477; N12–C13, 1.468; C11–N15,
1.344; C11–N12, 1.340; angles [°]: Br1–Cu1–C11, 174.4; C32–C31–
N15–C11, 92.8; C31–N15–C11–Cu1, 0.1; N15–C11–Cu1–Br1,
170.6.
N-(2,6-Diisopropylphenyl)-1,2-diaminoethane (1a); Typical
Procedure
This synthesis was carried out according to the method of Marshall
et al.,16 but in a larger scale and with a more time-efficient workup
procedure. To a stirred solution of 2,6-diisopropylaniline (80.1 g,
0.452 mol) in toluene (500 mL) was added 2-bromoethylamine hy-
drobromide (46.4 g, 0.226 mol) and the mixture was heated under
reflux conditions for 18 h. The cooled suspension was poured into
aq 2 M KOH (500 mL) and stirred until the organic layer became a
homogeneous brown oil. The layers were separated and the aqueous
layer was extracted with Et2O (2 × 80 mL). All extracts were com-
bined, washed with brine (100 mL), dried (MgSO4), and filtered.
The filtrate was concentrated by rotary evaporation and the residual
brown oil was distilled in vacuum over a 15 cm Vigreux column to
give the diamine as a nearly colorless oil; yield: 34.9 g (70%,
0.158 mol); bp 106 °C/0.5 mbar; nD20 = 1.531.
1H NMR (300.131 MHz, CDCl3): d = 7.13 (m, 3 H, CHaryl), 3.37
(sept, 3JH,H = 6.8 Hz, 2 H, 2 × Me2CH), 2.99 (m, 4 H, NCH2), 1.28
[d, 3JH,H = 6.8 Hz, 12 H, 2 × (CH3)2CH].
13C{1H} NMR (75.47 MHz, CDCl3): d = 142.5 (Cipso-aryl), 123.6
(CHp-aryl), 123.6 (Co-aryl), 123.4 (CHm-aryl), 54.3 (NCH2), 42.5
(NCH2), 27.5 (Me2CH), 24.2 [(CH3)2CH].
MS (EI+): m/z (%) = 220.27 (20), 190.22 (100), 175.19 (20), 160.16
(20).
Anal. Calcd for C14H24N2 (220.27): C, 76.31; H, 10.98; N, 12.71.
Found: C, 76.12; H, 11.00; N, 12.67.
Figure 7 ORTEP plot of the molecular structure of 11 as coordina-
tion polymer in the solid state. The crystal quality was only sufficient
for constitutional evidence.
N-(2,4,6-Trimethylphenyl)-1,2-diaminoethane (1b)
Prepared analogously as described for 1a from 2,4,6-trimethyl-
aniline (80.1 g, 0.592 mol), 2-bromoethylamine hydrobromide
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PAPER
Modular Trimethylene-Linked Bisimidazol(in)ium Salts
1463
(60.6 g, 0.296 mol), and toluene (500 mL). A large amount of yel-
lowish precipitate occurred after a few hours of heating. The mix-
ture was worked up as above; colorless oil; yield: 40.1 g (76%,
0.225 mol); bp 84–92 °C/0.6 mbar; nD20 = 1.549.
1H NMR (250.133 MHz, CDCl3): d = 6.93 (s, 2 H, CHm-aryl), 6.85 (s,
3
3
1 H, NCHN), 4.07 (t, JH,H = 9.7 Hz, 2 H, NCH2), 3.57 (t, JH,H
=
9.7 Hz, 2 H, NCH2), 2.30 (s, 3 H, o-ArCH3), 2.24 (s, 6 H, 2 × p-
ArCH3).
1H NMR (300.131 MHz, CDCl3): d = 6.83 (s, 2 H, CHm-aryl), 2.97 (t,
13C{1H} NMR (75.47 MHz, CDCl3): d = 155.9 (NCHN), 137.3
(Cipso-aryl), 136.9 (Co-aryl), 134.8 (Cp-aryl), 129.3 (CHm-aryl), 55.3
(NCH2), 48.8 (NCH2), 20.9 (o-ArCH3), 18.1 (p-ArCH3).
3
3JH,H = 4.5 Hz, 2 H, NCH2), 2.89 (t, JH,H = 4.5 Hz, 2 H, NCH2),
2.29 (s, 6 H, 2 × o-ArCH3), 2.24 (s, 3 H, p-ArCH3).
13C{1H} NMR (75.47 MHz, CDCl3): d = 143.4 (Cipso-aryl), 131.0 (Cp-
aryl), 129.6 (Co-aryl), 129.3 (CHm-aryl), 51.1 (NCH2), 42.4 (NCH2),
20.4 (o-ArCH3), 18.2 (p-ArCH3).
MS (EI): m/z (%) = 188.20 (100), 148.13 (50), 132.1 (30).
Anal. Calcd for C12H16N2 (188.27): C, 76.55; H, 8.57; N, 14.88.
Found: C, 76.39; H, 8.54; N, 14.84.
MS (EI+): m/z (%) = 178.21 (30), 148.1 (100).
1-(2,6-Dimethylphenyl)-4,5-dihydro-1H-imidazole (2c)
Prepared analogously as described for 2a from 1c (26.0 g,
0.159 mol) and triethyl orthoformate (95 mL, 0.64 mol); colorless
crystals; yield: 22.1 g (79%, 0.127 mol); mp 64 °C.
Anal. Calcd for C11H18N2 (178.15): C, 74.11; H, 10.18; N, 15.71.
Found: C, 74.07; H, 10.26; N, 15.69.
N-(2,6-Dimethylphenyl)-1,2-diaminoethane (1c)
Prepared analogously as described for 1a from 2,6-trimethylaniline
(47.4 g, 0.391 mol), 2-bromoethylamine hydrobromide (40.0 g,
0.195 mol), and toluene (500 mL) to give the diamine 1c as a color-
less oil; yield: 23.1 g (72%, 0.141 mol); bp 78–84 °C/0.6 mbar;
nD20 = 1.556.
1H NMR (250.133 MHz, CDCl3): d = 7.09 (m, 3 H, CHaryl), 6.84 (s,
1 H, NCHN), 4.06 (t, 3JH,H = 10.2 Hz, 2 H, NCH2), 3.57 (t, 3JH,H
10.2 Hz, 2 H, NCH2), 2.26 (s, 6 H, 2 × o-ArCH3).
=
13C{1H} NMR (75.47 MHz, CDCl3): d = 155.4 (NCHN), 137.2
(Cipso-aryl), 136.8 (Co-aryl), 128.4 (CHp-aryl), 127.3 (CHm-aryl), 55.0
(NCH2), 48.4 (NCH2), 17.9 (o-ArCH3).
1H NMR (250.133 MHz, CDCl3): d = 6.97 (d, 3JH,H = 7.3 Hz, 2 H,
3
3
CHm-aryl), 6.80 (t, JH,H = 7.3 Hz, 1 H, CHp-aryl), 3.01 (t, JH,H
=
MS (EI+): m/z (%) = 174.19 (100), 146.16 (45), 134.16 (65).
3
5.2 Hz, 2 H, NCH2), 2.87 (t, JH,H = 5.2 Hz, 2 H, NCH2), 2.29 (s,
6 H, 2 × o-ArCH3).
Anal. Calcd for C12H16N2 (174.24): C, 75.82; H, 8.10; N, 16.08.
Found: C, 75.54; H, 8.10; N, 16.06.
13C{1H} NMR (75.47 MHz, CDCl3): d = 146.1 (Cipso-aryl), 129.5
(CHp-aryl), 128.7 (Co-aryl), 121.6 (CHm-aryl), 50.8 (NCH2), 42.4
(NCH2), 18.4 (ArCH3).
1,3-Propanediylbis-1-[3-(2,6-diisopropylphenyl)-4,5-dihydro-
1H-imidazolium] Dibromide (3a); Typical Procedure
MS (EI+): m/z (%) = 164.20 (40), 134.15 (100), 105.1 (30).
This synthesis was carried out according to the method of Marshall
et al.16 In a round-bottomed flask were heated 2a (20.3 g,
88.2 mmol) and 1,3-dibromopropane (8.76 g, 43.4 mmol) and the
mixture was stirred until a homogeneous mass was formed. After
some min at 100 °C, the mixture hardened to an orange glass. The
glass was heated for 2 h and then cooled to r.t. Then, the glass was
dissolved in CH2Cl2 (50 mL) and the crude product was precipitated
by adding Et2O. Filtration gave the product as a colorless solid,
which was recrystallized from CH2Cl2 and Et2O; yield: 26.0 g
(90%, 39.4 mmol). Crystals for X-ray structure determination were
collected from a CH2Cl2–Et2O solution at r.t.; mp 256 °C.
Anal. Calcd for C10H16N2 (164.13): C, 73.13; H, 9.82; N, 17.06.
Found: C, 72.72; H, 9.91; N, 17.05.
1-(2,6-Diisopropylphenyl)-4,5-dihydro-1H-imidazole (2a); Typ-
ical Procedure
This synthesis was carried out according to the method of Marshall
et al.,16 but in larger scale and with a more time-efficient workup
procedure. A solution of 1a (64.9 g, 0.294 mol) in triethyl orthofor-
mate (180 mL, 1.08 mol) and PTSA monohydrate (1.0 g) was heat-
ed over 18 h under reflux conditions. The cooled mixture was
dissolved in H2O (300 mL), extracted with Et2O (3 × 100 mL), and
the combined extracts were dried (MgSO4). After filtration and con-
centration by evaporation in vacuo, the orange crude product even-
tually crystallized. It was distilled in a Büchi glass oven (190 °C/
5 mbar) to yield the product as colorless crystals; yield: 54.1 g
(79%, 0.233 mol); mp 79 °C.
1H NMR (300.131 MHz, CDCl3): d = 9.63 (s, 2 H, NCHN), 7.33 (t,
3JH,H = 7.7 Hz, 2 H, CHp-aryl), 7.13 (d, 3JH,H = 7.7 Hz, 4 H, CHm-aryl),
3
3
4.52 (t, JH,H = 9.8 Hz, 4 H, NCH2), 4.34 (t, JH,H = 6.9 Hz, 4 H,
NCH2CH2), 4.15 (t, 3JH,H = 9.8 Hz, 4 H, NCH2), 2.90 (pseudo sept,
3JH,H = 6.8 Hz, 4 H, 4 × Me2CH), 2.38 (quint, JH,H = 6.9 Hz, 2 H,
3
3
CH2CH2CH2), 1.21 [d, JH,H = 6.8 Hz, 12 H, 2 × (CH3)2CH], 1.17
[d, 3JH,H = 6.8 Hz, 12 H, 2 × (CH3)2CH].
3
1H NMR (300.131 MHz, CDCl3): d = 7.31 (t, JH,H = 7.5 Hz, 1 H,
3
CHp-aryl), 7.19 (d, JH,H = 7.5 Hz, 2 H, CHm-aryl), 6.82 (s, 1 H,
13C{1H} NMR (75.47 MHz, CDCl3): d = 158.5 (NCHN), 146.4
(Co-aryl), 130.8 (CHp-aryl), 129.7 (Cipso-aryl), 124.7 (CHm-aryl), 53.2
(NCH2), 49.4 (NCH2), 45.3 (NCH2CH2), 28.5 (Me2CH), 25.0
[(CH3)2CH], 24.8 (CH2CH2CH2), 23.9 [(CH3)2CH].
NCHN), 4.08 (t, 3JH,H = 8.8 Hz, 2 H, NCH2), 3.58 (t, 3JH,H = 8.8 Hz,
2 H, NCH2), 3.11 (sept, 3JH,H = 7.5 Hz, 2 H, 2 × Me2CH), 1.22 [d,
3
3JH,H = 7.5 Hz, 6 H, (CH3)2CH], 1.19 [d, JH,H = 7.5 Hz, 6 H,
(CH3)2CH].
MS (FAB+): m/z (%) = 581.45 (50, [M – Br]+), 501.51 (50), 271.3
(100).
13C{1H} NMR (75.47 MHz, CDCl3): d = 156.1 (Cipso-aryl), 148.4
(CHp-aryl), 134.3 (NCHN), 128.6 (Co-aryl), 124.1 (CHm-aryl), 55.2
(NCH2), 51.6 (NCH2), 28.1 (Me2CH), 24.9 [(CH3)2CH], 24.1
[(CH3)2CH].
Anal. Calcd for C33H50Br2N4 (662.58) + CH2Cl2: C, 57.07; H, 7.29;
N, 7.95. Found: C, 57.07; H, 7.55; N, 8.00.
MS (EI+): m/z (%) = 230.25 (100), 215.22 (35), 186.18 (80).
Crystal Data and Structure Refinement for 3a20
Empirical formula C35.50H55Br2Cl5N4; crystal system: triclinic;
space group: P1; Z = 2; unit cell dimensions: a = 9.0161 Å,
a = 72.850°, b = 15.3247 Å, b = 83.340°, c = 16.4048(19) Å, g =
82.965°; goodness-of-fit on F2: 1.01; final R indices [I > 2s(I)]:
R1 = 0.049, wR2 = 0.109; largest difference peak and hole 1.20 and
–0.48 eÅ–3.
Anal. Calcd for C15H22N2 (230.35): C, 78.21; H, 9.63; N, 12.16.
Found: C, 78.25; H, 9.71; N, 11.92.
1-(2,4,6-Trimethylphenyl)-4,5-dihydro-1H-imidazole (2b)
Prepared analogously as described for 2a from 1b (78.0 g,
0.438 mol) and triethyl orthoformate (290 mL, 1.742 mol); color-
less crystals; yield: 65.1 g (79%, 0.346 mol); mp 76 °C.
Synthesis 2010, No. 9, 1459–1466 © Thieme Stuttgart · New York

1464
M. Bessel et al.
PAPER
1,3-Propanediylbis-1-[3-(2,4,6-trimethylphenyl)-4,5-dihydro-
1H-imidazolium] Dibromide (3b)
The procedure for the synthesis of 3a was followed using 2b
(16.3 g, 86.6 mmol) and 1,3-dibromopropane (8.7 g, 43.1 mmol);
white solid; yield: 23.1 g (92%, 39.9 mmol); mp 306 °C.
13C{1H} NMR (75.467 MHz, CDCl3): d = 158.7 (NCHN), 146.4
(Co-aryl), 130.9 (CHp-aryl), 129.7 (Cipso-aryl), 124.7 (CHm-aryl), 53.4
(NCH2), 49.1 (NCH2), 47.1 (NCH2CH2), 45.3 (CH2CH2Br), 29.9
(CH2CH2CH2), 28.6 (Me2CH), 25.0 [(CH3)2CH], 23.9 [(CH3)2CH].
MS (ESI+): m/z (%) = 351.14 (100, [M – Br]+).
1H NMR (300.131 MHz, CDCl3): d = 9.49 (s, 2 H, NCHN), 6.83 (s,
3
3
4 H, CHm-aryl), 4.46 (t, JH,H = 9.0 Hz, 4 H, NCH2), 4.25 (t, JH,H
=
Crystal Data and Structure Refinement for 5a20
3
6.1 Hz, 4 H, NCH2), 4.17 (t, JH,H = 9.0 Hz, 4 H, NCH2), 2.35
(quint, JH,H = 6.1 Hz, 2 H, CH2CH2CH2), 2.25 (s, 12 H, 4 × o-
ArCH3), 2.17 (s, 6 H, 2 × p-ArCH3).
Empirical formula C18H28Br2N2; crystal system: monoclinic; space
group: P21/n; Z = 4; unit cell dimensions: a = 14.4324 Å, a = 90°,
b = 9.0217 Å, b = 90.193°, c = 15.0491(19) Å, g = 90°; goodness-
of-fit on F2: 1.26; final R indices [I > 2s(I)]: R1 = 0.051, wR2 =
0.163; largest difference peak and hole 0.87 and –1.18 eÅ–3.
3
13C{1H} NMR (75.467 MHz, CDCl3): d = 158.8 (NCHN), 140.0
(Cipso-aryl), 135.1 (Co-aryl), 130.4 (Cp-aryl), 129.8 (CHm-aryl), 51.0
(NCH2), 49.2 (NCH2), 45.4 (NCH2CH2), 24.9 (CH2CH2CH2), 20.8
(o-ArCH3), 18.1 (p-ArCH3).
3-Chloropropyl-1-[3-(2,6-diisopropylphenyl)-4,5-dihydro-1H-
imidazolium] Bromide (5b)
MS (ESI+): m/z (%) = 499.23 (100, [M – Br]+).
To a stirred solution of 2a (4.0 g, 17 mmol) in Et2O (15 mL) was
added dropwise a solution of 1-bromo-3-chloropropane (2.7 g,
17 mmol) in Et2O (15 mL). The mixture was heated for 18 h at re-
flux. During reaction the product precipitated as a fine white solid.
After cooling to r.t., the precipitate was filtered off and recrystal-
lized from CH2Cl2 and Et2O; yield: 2.1 g (31%, 5.4 mmol); mp
174 °C.
1,3-Propanediylbis-1-[3-(2,6-diisopropylphenyl)-4,5-dihydro-
1H-imidazolium] Bis(p-toluenesulfonate) (4)
A solution of 3a (1.0 g, 1.5 mmol) in CH2Cl2 (20 mL) and a solution
of PTSA monohydrate (0.8 g, 4.6 mmol) in distilled H2O (20 mL)
were mixed and vigorously stirred for 1 h. Then the layers were sep-
arated, the organic layer was washed with H2O (20 mL), dried
(MgSO4), and filtered. The product was precipitated by dropwise
addition of Et2O to the filtrate. Recrystallization from CH2Cl2 and
Et2O afforded 4 as colorless crystals; yield: 1.0 g (81%, 1.2 mmol);
mp 218 °C.
1H NMR (300.131 MHz, CDCl3): d = 9.02 (s, 2 H, NCHN), 7.55 (d,
3JH,H = 5.0 Hz, 4 H, CHm-aryl), 7.37 (t, 3JH,H = 7.5 Hz, 2 H, CHp-aryl),
7.17 (d, 3JH,H = 7.5 Hz, 4 H, CHm-aryl), 6.98 (d, 3JH,H = 5.0 Hz, 4 H,
1H NMR (300.130 MHz, CDCl3): d = 9.53 (s, 1 H, NCHN), 7.43 (t,
3JH,H = 7.5 Hz, 1 H, CHp-aryl), 7.23 (d, 3JH,H = 7.5 Hz, 2 H, CHm-aryl),
3
3
4.44 (t, JH,H = 10.9 Hz, 2 H, NCH2), 4.29 (t, JH,H = 5.6 Hz, 2 H,
NCH2), 4.22 (t, 3JH,H = 10.9 Hz, 2 H, NCH2), 3.85 (t, 3JH,H = 5.6 Hz,
3
2 H, CH2CH2Cl), 2.95 (pseudo sept, JH,H = 6.8 Hz, 2 H, 2 ×
3
Me2CH), 2.33 (quint, JH,H = 5.6 Hz, 2 H, CH2CH2CH2), 1.26
[pseudo d, 3JH,H = 6.8 Hz, 12 H, 2 × (CH3)2CH].
13C{1H} NMR (75.475 MHz, CDCl3): d = 159.0 (NCHN), 146.6
(Co-aryl), 131.2 (CHp-aryl), 129.8 (Cipso-aryl), 125.0 (CHm-aryl), 53.4
(NCH2), 49.1 (NCH2), 46.6 (NCH2CH2), 42.3 (CH2CH2Cl), 29.4
(CH2CH2CH2), 28.8 (Me2CH), 25.2 [(CH3)2CH], 24.2 [(CH3)2CH].
3
3
CHo-aryl), 4.50 (t, JH,H = 10.0 Hz, 4 H, NCH2), 4.20 (t, JH,H
=
3
5.0 Hz, 4 H, NCH2), 4.10 (t, JH,H = 10.0 Hz, 4 H, NCH2), 2.87
(pseudo sept, 3JH,H = 5.0 Hz, 4 H, 4 × Me2CH), 2.57 (quint, 3JH,H
=
5.0 Hz, 2 H, CH2CH2CH2), 2.25 (s, 6 H, 2 × ArCH3, tosylate), 1.21
3
3
[d, JH,H = 5.0 Hz, 12 H, 2 × (CH3)2CH], 1.17 [d, JH,H = 5.0 Hz,
MS (ESI+): m/z (%) = 307.36 (100, [M – Br]+).
12 H, 2 × (CH3)2CH].
1,3-Propanediyl-1-[3-(2,6-dimethylphenyl)-4,5-dihydro-1H-
imidazolium]-1-[3-(2,6-diisopropylphenyl)-4,5-dihydro-1H-
imidazolium] Dibromide (6)
13C{1H} NMR (75.475 MHz, CDCl3): d = 155.0 (NCHN), 146.7
(Co-aryl), 143.5 (Cipso-aryl, tosylate), 139.1 (p-ArCH3), 130.9 (Cp-aryl),
130.1 (Cipso-aryl), 128.5 (CHo-aryl, tosylate), 125.7 (CHm-aryl, tosylate),
124.8 (CHm-aryl), 53.5 (NCH2), 49.2 (NCH2), 45.5 (NCH2CH2), 28.7
(Me2CH), 25.8 (CH2CH2CH2), 24.8 [(CH3)2CH], 24.1 [(CH3)2CH],
21.2 (ArCH3, tosylate).
A stirred mixture of 5a (0.4 g as a 6:1 mixture with 3a) and 2c
(0.65 g, 3.7 mmol)] was heated at 100 °C until a homogeneous mix-
ture was formed. After some min, the mixture hardened as an or-
ange glass. The glass was heated for 2 h and then cooled to r.t. Then,
the mixture was dissolved in CH2Cl2 (50 mL) and addition of Et2O
to the solution precipitated the crude product as a colorless solid.
The product contained 85% (determined by 1H NMR spectroscopy)
of the desired nonsymmetrically substituted bisimidazolinium salt 6
along with 15% of 3a. Crystals for X-ray structure determination
were collected from a CH2Cl2–Et2O solution at r.t.
MS (ESI+): m/z (%) = 673.5 (100, [M – OTs]+).
Anal. Calcd for C47H64N4O6S2 (845.17): C, 66.79; H, 7.63; N, 6.63.
Found: C, 66.74; H, 7.61; N, 6.60.
3-Bromopropyl-1-[3-(2,6-diisopropylphenyl)-4,5-dihydro-1H-
imidazolium] Bromide (5a)
1H NMR (300.130 MHz, CDCl3): d = 9.71 (s, 1 H, NCHNAryl),
To a stirred solution of 2a (2.0 g, 8.7 mmol) in Et2O (15 mL) was
added dropwise a solution of 1,3-dibromopropane (17.6 g,
87.0 mmol) in Et2O (15 mL). The mixture was heated for 18 h at re-
flux. During reaction the product precipitated as a fine white solid.
After cooling to r.t., the precipitate was filtered off and recrystal-
lized from CH2Cl2 and Et2O. The crude product contained 85% (de-
termined by 1H NMR spectroscopy) of the desired
monoimidazolinium salt 5a contaminated with 15% of 3a. All at-
tempts of purification were of no avail. Crystals for X-ray structure
determination were collected from a CH2Cl2–Et2O solution at r.t.
9.68 (s, 1 H, NCHNAryl), 7.42 [t, 3JH,H = 9.0 Hz, 1 H, CHp-aryl (di-
3
isopropylphenyl)], 7.25 [d, JH,H = 9.0 Hz, 2 H, CHm-aryl (diisopro-
pylphenyl)], 7.23 [t, 3JH,H = 6.0 Hz, 1 H, CHp-aryl (dimethylphenyl)],
3
7.11 [d, JH,H = 6.0 Hz, 2 H, CHm-aryl (dimethylphenyl)], 4.62–4.18
(m, 8 H, NCH2), 2.96 (sept, 3JH,H = 6.0 Hz, 2 H, 2 × Me2CH), 2.45
3
(quint, JH,H = 7.5 Hz, 2 H, CH2CH2CH2), 2.40 (s, 6 H, 2 × o-
ArCH3), 1.29 [pseudo t, 3JH,H = 6.0 Hz, 12 H, 2 × (CH3)2CH].
13C{1H} NMR (75.467 MHz, CDCl3): d = 158.9 (NCHN), 158.8
(NCHN), 146.6 (CHm-aryl), 135.6 (CHm-aryl), 133.1 (CHp-aryl), 131.3
(CHp-aryl), 130.1 (Cipso-aryl), 129.8 (Cipso-aryl), 129.4 (Co-aryl), 124.9
(Co-aryl), 53.4 (NCH2), 51.1 (NCH2), 49.5 (NCH2), 49.4 (NCH2),
45.6 (NCH2CH2), 45.5 (NCH2CH2), 28.8 (Me2CH), 25.2
[(CH3)2CH], 25.1 (CH2CH2CH2), 24.2 [(CH3)2CH], 18.4 (o-
ArCH3).
1H NMR (250.133 MHz, CDCl3): d = 9.49 (s, 1 H, NCHN), 7.43 (t,
3JH,H = 7.6 Hz, 1 H, CHp-aryl), 7.22 (d, 3JH,H = 7.6 Hz, 2 H, CHm-aryl),
4.46 (t, 3JH,H = 11.4 Hz, 2 H, NCH2), 4.25 (m, 4 H, NCH2), 3.64 (t,
3JH,H = 5.9 Hz, 2 H, CH2CH2Br), 2.95 (sept, 3JH,H = 6.9 Hz, 2 H, 2 ×
3
Me2CH), 2.40 (pseudo quint, JH,H = 6.3 Hz, 2 H, CH2CH2CH2),
1.26 [pseudo d, 3JH,H = 6.9 Hz, 12 H, 2 × (CH3)2CH].
MS (ESI+): m/z (%) = 525.36 (30, [M – Br]+), 223.17 (100, [M – 2
Br]2+).
Synthesis 2010, No. 9, 1459–1466 © Thieme Stuttgart · New York

PAPER
Modular Trimethylene-Linked Bisimidazol(in)ium Salts
1465
Crystal Data and Structure Refinement for 620
a = 90°, b = 6.5178 Å, b = 90.159°, c = 25.6265(19) Å, g = 90°;
goodness-of-fit on F2: 1.02; final R indices [I > 2s(I)]: R1 = 0.034,
wR2 = 0.075; largest difference peak and hole 0.39 and –0.20 eÅ–3.
Empirical formula C30.50H43.50Br2Cl4.50N4; crystal system: triclinic;
space group: P1, Z = 4; unit cell dimensions: a = 13.918 Å,
a = 105.722°, b = 16.3375 Å, b = 93.205°, c = 16.8897(19) Å, g =
90.619°; goodness-of-fit on F2: 1.06; final R indices [I > 2s(I)]:
R1 = 0.074, wR2 = 0.143; largest difference peak and hole 0.81 and
–0.70 eÅ–3.
1,3-Propanediyl-1-[3-methyl-4,5-dihydro-1H-imidazolium]-1-
[3-(2,6-diisopropylphenyl)-4,5-dihydro-1H-imidazolium] Bro-
mide Chloride (9)
A stirred mixture of 5b (1.5 g, 3.9 mmol) and 7 (0.45 g, 5.9 mmol)
was heated at 90 °C for 3 h, when the reagents first melted and then
formed a light orange glass. Once cooled to r.t., the crude product
was dissolved in EtOH (20 mL) and precipitated by the addition of
Et2O, decanted, and dried in vacuo. The resulting light yellow foam
was stirred for 24 h in a mixture of EtOAc (15 mL) and a few drops
of CH2Cl2 to afford the product as a colorless solid; yield: 1.2 g
(68%, 2.6 mmol); mp 141 °C.
1-Methyl-4,5-dihydro-1H-imidazole (7)
This synthesis was carried out according to the method of Cetinkaya
et al.18 In a round-bottomed flask equipped with a 15 cm Vigreux
column and distillation bridge N-methylethylenediamine (2.83 g,
38.1 mmol) was stirred with N,N-dimethylformamide dimethyl
acetal (5.1 g, 41 mmol) at 90 °C. The mixture was heated to 110 °C
for 1 h and then distilled to yield the product (178–180 °C/1 bar) as
a colorless oil; yield: 2.6 g (81%, 31 mmol). The product fraction
contained up to 15% of DMF and MeOH (determined by 1H NMR
spectroscopy) and was used without further purification.
1H NMR (300.130 MHz, CDCl3): d = 9.74 (s, 1 H, NCHNAryl),
9.60 (s, 1 H, NCHNCH3), 7.35 (t, 3JH,H = 7.8 Hz, 1 H, CHp-aryl), 7.15
3
3
(d, JH,H = 7.8 Hz, 2 H, CHm-aryl), 4.53 (t, JH,H = 10.5 Hz, 2 H,
NCH2CH2NAryl), 4.25–4.11 (m, 6 H, NCH2), 4.03–3.92 (m, 4 H,
1H NMR (250.134 MHz, CDCl3): d = 6.70 (s, 1 H, NCHN), 3.79 (t,
3
3
3JH,H = 9.6 Hz, 2 H, NCH2), 3.14 (t, JH,H = 9.6 Hz, 2 H, NCH2),
NCH2CH2NCH3), 3.28 (s, 3 H, NCH3), 2.90 (sept, JH,H = 6.6 Hz,
2 H, 2 × Me2CH), 2.28 (m, 2 H, CH2CH2CH2), 1.20 [d, JH,H
6.6 Hz, 12 H, 2 × (CH3)2CH].
3
2.80 (s, 3 H, NCH3).
13C{1H} NMR (75.47 MHz, CDCl3): d = 158.6 (NCHN), 55.4
(NCH2), 50.9 (CH3NCH2), 34.3 (NCH3).
MS (ESI+): m/z (%) = 410.40 (60, [M4 + DMF + H]+), 326.35 (100,
[M3 + DMF + H]+), 242.31 (70, [M2 + DMF + H]+), 85.21 (100, [M
+ H]+).
=
13C{1H} NMR (75.467 MHz, CDCl3): d = 159.8 (NCHNAryl),
158.9 (NCHNCH3), 146.9 (Co-aryl), 131.4 (CHp-aryl), 130.3 (Cipso-aryl),
125.2 (CHm-aryl), 54.0 (NCH2CH2NAryl), 51.3 (CH2N), 49.7
(NCH2), 49.7 (NCH2), 45.8 (AlkylNCH2CH2N), 45.4
(AlkylNCH2CH2N), 35.5 (NCH3), 29.1 (Me2CH), 25.5 [(CH3)2CH],
24.5 [(CH3)2CH].
1,3-Propanediyl-1-[3-(2,4,6-trimethylphenyl)imidazolium]-1-
[3-(2,6-diisopropylphenyl)-4,5-dihydro-1H-imidazolium] Bro-
mide Chloride (8)
MS (ESI+): m/z (%) = 435.39 (50, [M – Cl]+), 391.47 (20, [M –
Br]+), 178.47 (100, [M – Br – Cl]2+).
A mixture of 5b (0.35 g, 0.90 mmol) and N-mesitylimidazole
(0.19 g, 1.0 mmol) was heated at 100 °C for 3 h, when the reagents
first melted and then formed a light orange glass.10 After cooling to
r.t., the glass was dissolved in EtOH (10 mL) and precipitated by the
addition of Et2O, decanted, and dried in vacuo. The resulting light
yellow foam was stirred for 24 h in a mixture of EtOAc (15 mL) and
a few drops of CH2Cl2 to afford the product as colorless solid; yield:
0.36 mg (80%, 0.63 mmol). Crystals for X-ray structure determina-
tion were collected from a CH2Cl2–Et2O solution at r.t.; mp 266 °C.
Dicopper(I) Complex 10 Based on Ligand Precursor 3a
In an argon-filled Schlenk flask, 3a (0.20 g, 0.30 mmol) and NaH-
MDS (0.11 g, 0.60 mmol) were dissolved in anhyd toluene (5 mL)
and stirred at r.t. for 1 h. (CuBrSMe2)2 (0.13 g, 0.31 mmol) was add-
ed under argon to the light orange solution. The obtained yellowish
suspension was stirred for additional 24 h at r. t. During this time,
the mixture might change to a more gray color. It is recommended
to let the mixture react until the suspension had an orange color,
which might last up to 48 h. The solvent was removed in vacuo and
the slightly orange residue was stirred in anhyd CH2Cl2 (5 mL). The
suspension was filtered through a plug of Celite. Dropwise addition
of anhyd Et2O to the filtrate under vigorous stirring under argon pre-
cipitated the product as an off-white solid. Recrystallization from
CH2Cl2 and Et2O gave 10 as air-sensitive white or off-white solid;
yield: 0.11 g (50%, 0.14 mmol). Crystals for X-ray structure deter-
mination were collected from a CH2Cl2–Et2O solution at –50 °C;
mp 204 °C.
1H NMR (300.131 MHz, CDCl3): d = 10.22 [s, 1 H, NCHN (imida-
zole)], 9.51 (s, 1 H, NCHN), 8.49 [pseudo s, 1 H, NCHCHN (imi-
3
3
dazole)], 7.39 (t, JH,H = 7.5 Hz, 1 H, CHp-aryl), 7.19 (d, JH,H
=
7.5 Hz, 2 H, CHm-aryl), 7.05 [pseudo s, 1 H, NCHCHN (imidazole)],
6.97 [s, 2 H, CHm-aryl (mesityl)], 5.12 (t, 3JH,H = 7.5 Hz, 2 H, imida-
3
3
zole-CH2), 4.72 (t, JH,H = 12.0 Hz, 2 H, NCH2), 4.33 (t, JH,H
=
3
6.0 Hz, 2 H, imidazoline-CH2), 4.26 (t, JH,H = 12.0 Hz, 2 H,
NCH2), 2.99 (pseudo sept, JH,H = 7.0 Hz, 2 H, 2 × Me2CH), 2.72
3
(pseudo quint, 2 H, CH2CH2CH2), 2.31 (s, 3 H, p-ArylCH3), 2.03 (s,
6 H, o-ArCH3), 1.26 [d, 3JH,H = 7.0 Hz, 6 H, 2 × (CH3)2CH], 1.23 [d,
3JH,H = 7.0 Hz, 6 H, 2 × (CH3)2CH].
3
1H NMR (300.132 MHz, CDCl3): d = 6.87 (t, JH,H = 7.8 Hz, 2 H,
3
3
CHp-aryl), 6.71 (d, JH,H = 7.8 Hz, 4 H, CHm-aryl), 3.49 (t, JH,H
=
3
6.0 Hz, 4 H, NCH2), 3.41 (t, JH,H = 6.0 Hz, 4 H, NCH2), 3.35 (t,
13C{1H} NMR (75.467 MHz, CDCl3): d = 158.7 [NCHN (imidazo-
line)], 146.6 (Co-aryl (imidazoline)], 141.3 [(Cp-aryl (mesityl)], 137.5
[NCHN (imidazole)], 134.2 [Co-aryl (mesityl)], 131.1 [CHp-aryl (imi-
dazoline)], 130.7 [Cipso-aryl (mesityl)], 130.0 [CHm-aryl (mesityl)],
129.8 (Cipso-aryl (imidazoline)], 124.9 [CHm-aryl (imidazoline)], 124.4
(NCHCHN), 122.7 (NCHCHN), 53.6 (NCH2), 49.7 (NCH2), 47.2
[(imidazole) NCH2CH2], 45.6 [(imidazoline) NCH2CH2], 28.9
(CH2CH2CH2), 28.8 (Me2CH), 25.3 [(CH3)2CH], 25.2 [(CH3)2CH],
21.1 (p-ArCH3), 17.6 (o-ArCH3).
3JH,H = 4.5 Hz, 4 H, NCH2), 2.49 (pseudo sept, 3JH,H = 6.9 Hz, 4 H,
3
2 × Me2CH), 1.74 (quint, JH,H = 4.5 Hz, 2 H, CH2CH2CH2), 0.79
[d, JH,H = 6.9 Hz, 12 H, 2 × (CH3)2CH], 0.74 (d, JH,H = 6.9 Hz,
12 H, 2 × (CH3)2CH].
3
3
13C{1H} NMR (75.468 MHz, CDCl3–DMSO-d6): d = 200.2 (C–Cu),
145.8 (Co-aryl), 133.6 (Cipso-aryl), 128.3 (CHp-aryl), 123.3 (CHm-aryl),
52.7 (ArylNCH2), 48.1 (AlkylNCH2), 46.5 (NCH2CH2CH2), 27.1
(Me2CH), 26.2 (CH2CH2CH2), 24.2 [(CH3)2CH], 22.9 [(CH3)2CH].
MS (ESI+): m/z (%) = 539.4 (100, [M – Cl]+), 493.4 (20, [M – Br]+).
MS (ESI+): m/z (%) = 645.29 (100, [M – 2 Br + OH]+).
Anal. Calcd for C33H48Br2Cu2N4 (784.08): C, 50.32; H, 6.14; N,
7.11. Found: C, 49.92; H, 6.25; N, 6.92.
Crystal Data and Structure Refinement for 820
Empirical formula C30H42Br1.75Cl0.25N4; crystal system: monoclinic;
space group: P21/n; Z = 4; unit cell dimensions: a = 18.5166(14) Å,
Synthesis 2010, No. 9, 1459–1466 © Thieme Stuttgart · New York

1466
M. Bessel et al.
PAPER
N-Heterocyclic Carbenes in Synthesis; Wiley-VCH:
Crystal Data and Structure Refinement for 1020
Empirical formula C33H48Br2Cu2N4; crystal system: monoclinic;
space group: P21/c; Z = 4; unit cell dimensions: a = 13.4293 Å, a =
90°, b = 13.1184 Å, b = 103.461°, c = 21.2313(19) Å, g = 90°;
goodness-of-fit on F2: 1.10; final R indices [I > 2s(I)]: R1 = 0.044,
wR2 = 0.082; largest difference peak and hole 0.42 and –0.43 eÅ–3.
Weinheim, 2006. (h) Diéz-Gonzáles, S.; Marion, N.; Nolan,
S. P. Chem. Rev. 2009, 109, 3612.
(4) Reviews: (a) Herrmann, W. A. Angew. Chem. Int. Ed. 2002,
41, 1290. (b) Herrmann, W. A.; Köcher, C. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 2162. For reviews on other
applications of N-heterocyclic carbenes as reagents and
catalysts in organic synthesis, see: (c) Enders, D.; Gielen, H.
J. Organomet. Chem. 2001, 617-618, 70. (d) Enders, D.;
Balensiefer, T. Acc. Chem. Res. 2004, 37, 534.
(5) (a) Weskamp, T.; Schattenmann, W. C.; Spiegler, M.;
Herrmann, W. A. Angew. Chem. Int. Ed. 1998, 37, 2490.
(b) Herrmann, W. A.; Reisinger, C. P.; Spiegler, M.
J. Organomet. Chem. 1998, 557, 93. (c) Haung, J.; Nolan,
S. P. J. Am. Chem. Soc. 1999, 121, 9889.
(6) Buchowicz, W.; Koziol, A.; Jerzykiewicz, L. B.; Lis, T.;
Pasynkiewicz, S.; Pecherzewska, A.; Pietrzykowski, A.
J. Mol. Catal. A: Chem. 2006, 257, 118.
(7) Lee, H. M.; Jiang, T.; Stevens, E. D.; Nolan, S. P.
Organometallics 2001, 20, 1255.
Dicopper(I) Complex 11 Based on Ligand Precursor 3b
In an argon-filled Schlenk flask, 3b (0.20 g, 0.35 mmol) and Ag2O
(0.10 g, 0.43 mmol) were suspended in anhyd CH2Cl2 (5 mL). The
reaction mixture was stirred at r.t. for 24 h in the absence of light.
Then, (CuBrSMe2)2 (0.15 g, 0.36 mmol) was added under argon
and the mixture was stirred for 24 h at r.t. Then, the mixture was fil-
tered via Schlenk technique through a plug of Celite. After 1 h,
some more silver precipitated, which was removed by a second fil-
tration. Dropwise addition of anhyd Et2O to the slightly green fil-
trate precipitated the crude product as an air-sensitive greenish
solid. Recrystallization from CH2Cl2 and Et2O gave the product as
a white solid; yield: 0.10 g (43%, 0.15 mmol). Crystals for X-ray
structure determination were collected from a THF–Et2O solution at
r.t.; mp 153 °C.
(8) De Bo, G.; Berthon-Gelloz, G.; Tinant, B.; Marko, I. E.
Organometallics 2006, 25, 1881.
(9) Lillo, V.; Mata, J. A.; Segarra, A. M.; Peris, E.; Fernandez,
E. Chem. Commun. 2007, 2184.
(10) Bortenschlager, M.; Schuetz, J.; Von-Preysing, D.; Nuyken,
O.; Herrmann, W. A.; Weberskirch, R. J. Organomet. Chem.
2005, 690, 6233.
1H NMR (300.132 MHz, CDCl3): d = 6.88 (s, 4 H, CHm-aryl), 3.86
3
(pseudo s, 8 H, NCH2), 3.79 (t, JH,H = 7.8 Hz, 4 H, NCH2CH2),
2.25 (s, 6 H, 2 × p-ArCH3), 2.21(s, 12 H, 4 × o-ArCH3), 2.15 (quint,
3JH,H = 7.8 Hz, 2 H, CH2CH2CH2).
13C{1H} NMR (75.467 MHz, CDCl3): d = 201.8 (C–Cu), 138.5
(Cp-aryl), 135.6 (CHm-aryl), 135.0 (Cipso-aryl), 129.6 (Co-aryl), 51.2
(ArylNCH2), 49.1 (AlkylNCH2), 47.7 (NCH2CH2CH2), 27.5
(CH2CH2CH2), 21.0 (p-ArCH3), 18.3 (o-ArCH3).
(11) Tominaga, S.; Oi, Y.; Kato, T.; An, D. K.; Okamoto, S.
Tetrahedron Lett. 2004, 45, 5585.
(12) (a) Nolte, C.; Straub, B. F. Angew. Chem. Int. Ed. 2007, 46,
2101. (b) Díez-González, S.; Correa, A.; Cavallo, L.; Nolan,
S. P. Chem. Eur. J. 2006, 12, 7558.
(13) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248,
2247; and references cited therein.
MS (ESI+): m/z (%) = 561.25 (100, [M – 2 Br + OH]+).
Anal. Calcd for C27H36Br2Cu2N4 (703.50): C, 46.10; H, 5.16; N,
7.96. Found: C, 46.19; H, 5.25; N, 7.76.
(14) (a) Tulloch, A. A. D.; Danopoulos, A. A.; Kleinhenz, S.;
Light, M. E.; Hursthouse, M. B.; Eastham, G.
Crystal Data and Structure Refinement for 11
Empirical formula C27H36Br2Cu2N4; crystal system: monoclinic;
space group: P21/n; Z = 9; unit cell dimensions: a = 13.1062 Å, a =
90°, b = 33.1870 Å, b = 91.518°, c = 13.4956(19) Å, g = 90°; good-
ness-of-fit on F2: 1.76; final R indices [I > 2s(I)]: R1 = 0.154, wR2 =
0.351; largest difference peak and hole 2.42 and –1.34 eÅ–3.
Organometallics 2001, 20, 2027. (b) Yen, S. K.; Koh, L. L.;
Hahn, F. E.; Huynh, H. V.; Hor, T. S. A. Organometallics
2006, 25, 5105. (c) Eike, B.; Bauer, E. B.; Senthil Andavan,
G. T.; Hollis, T. K.; Rubio, R. J.; Cho, J.; Kuchenbeiser, G.
R.; Helgert, T. R.; Letko, C. S.; Tham, F. S. Org. Lett. 2008,
10, 1175. (d) Edworthy, I. S.; Blake, A. J.; Wilson, C.;
Arnold, P. L. Organometallics 2007, 26, 3684. (e) Larsen,
A. O.; Leu, W.; Nieto Oberhuber, C.; Campbell, J. E.;
Hoveyda, A. H. J. Am. Chem. Soc. 2004, 126, 11130.
(f) Mayr, M.; Wurst, K.; Ongania, K.-H.; Buchmeiser, M. R.
Chem. Eur. J. 2004, 10, 1256.
Acknowledgment
This work was supported by the DFG (Graduate College 850) and
the University of Heidelberg. We thank Dr. Jürgen Gross and co-
workers at the OCI, University of Heidelberg for mass spectra.
(15) Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109,
3677.
(16) Marshall, C.; Ward, M. F.; Skakle, J. M. Synthesis 2006,
1040.
(17) Cetinkaya, B.; Cetinkaya, E.; Alici, B. Heterocycles 1997,
45, 29.
(18) N-(2,4,6-Trimethylphenyl)imidazole was prepared as
described by: Arduengo, A.; Gentry, F.; Taverker, P.;
Simmons, H. US Patent 6177575, 2001; Chem. Abstr. 2001,
134, 115958.
(19) (a) Cooke, C. E.; Ramnial, T.; Jennings, M. C.; Pomeroya,
R. K.; Clyburne, J. A. C. Dalton Trans. 2007, 1755.
(b) Lin, I. J. B.; Vasam, C. S. Comments Inorg. Chem. 2004,
25, 75. (c) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005,
105, 3978.
(20) CCDC 768548–768552 contain the supplementary
crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
+44(1223)336033, E-mail: deposit@ccdc.cam.ac.uk].
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Synthesis 2010, No. 9, 1459–1466 © Thieme Stuttgart · New York