Platinum(II) complexes with amide-functionalized NHC ligands

Article abstract of DOI:10.1016/j.jorganchem.2012.05.019

We present the synthesis of neutral, amide-functionalized N-heterocyclic carbene (NHC) platinum(II) complexes with dianionic -N-C^NHC-C ^NHC-N- (NC^CN) tetradentate ligands. The imidazolium- and bisimidazolium bromide NHC lig

Full text of DOI:10.1016/j.jorganchem.2012.05.019

Journal of Organometallic Chemistry 713 (2012) 203e208
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Journal of Organometallic Chemistry
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Platinum(II) complexes with amide-functionalized NHC ligands
*
Yvonne Unger, Thomas Strassner
Technische Universität Dresden, Physikalische Organische Chemie, Bergstrasse 66, 01069 Dresden, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
We present the synthesis of neutral, amide-functionalized N-heterocyclic carbene (NHC) platinum(II)
complexes with dianionic eNeCNHCeCNHCeNe (NC*C*N) tetradentate ligands. The imidazolium- and
bisimidazolium bromide NHC ligand precursors with amide functionality in the side chain are reported
together with the corresponding biscarbene bromido complexes and, after deprotonation, of the neutral
NHC complexes without counterions. All compounds have been thoroughly characterized by standard
techniques.
Received 4 January 2012
Received in revised form
15 May 2012
Accepted 18 May 2012
Keywords:
NHC ligand
Ó 2012 Elsevier B.V. All rights reserved.
Platinum(II)NHC complexes
DFT calculations
2D-NMR
1. Introduction
fragments. While neutral eNeCNHCeCNHCeNe (NC*C*N) ligands
can be found in the literature, e.g. the tetradentate di(imidazol-2-
The interest in N-heterocyclic carbenes (NHCs) in the last
decade was mainly driven by new applications in homogeneous
catalysis [1e6]. We explored the additional stability of chelating
biscarbenes and synthesized different dihalogen complexes of
palladium(II) and platinum(II), which turned out to be very stable,
even in very acidic solutions [7e12].
ylidene) ligand (Fig. 2, IV) [38e40] or the dianionic C*NNC*
ligands (Fig. 2, V) [37,41] there have been (to the best of our
knowledge) no reports of di(imidazol-2-ylidene) ligands with
amide-functionalized side chains.
We herein describe the synthesis of platinum(II) complexes
with the new dianionic NeC*eC*eN tetradentate amide-
functionalized NHC ligands and their corresponding precursors.
Quite recently we and others found that they are also promising
ligands for the synthesis of blue phosphorescent platinum
compounds with interesting photophysical properties [13e16]. As
rigid structures promise better photophysical properties (due to
less geometrical changes between singlet and triplet state) we were
looking for tetradentate dianionic ligands based on N-heterocyclic
biscarbenes and explored different anionic side chains as it had
previously been shown for monodentate NHC ligands [5,17].
For the general structure shown in Fig.1 different Ag(I) and Au(I)
[18e21] as well as Ni(II) and Pd(II) complexes [16,22e37] are
known, but no homoleptic platinum(II) complexes have been
reported yet. Examples of previously reported complexes are given
in Fig. 1, e.g. the palladium complex I with one monodentate NHC
ligand [24] or the cis- (Fig. 1, II) and trans-isomers (Fig. 1, III) of
complexes with two bidentate ligands [23,25,27].
2. Results and discussion
The synthesis of the acetamide- or propionamide di(imidazol-2-
ylidene) platinum(II) dihalide complexes starts with the prepara-
tion of the corresponding chloroacetamides or -propionamides. 2-
chloro-N-phenylacetamide
1
[25]
and
2-chloro-N-(4-
methoxyphenyl)acetamide
2 as well as 3-chloro-N-phenyl-
propionamide 3 [42] and 3-chloro-N-(4-methoxyphenyl)-propio-
namide 4 were obtained in good yields by reaction of the
corresponding aniline with chloroacetyl chloride or chlor-
opropionyl chloride in the presence of triethylamine following
a literature procedure [25] (Scheme 1).
The chloroacetamides or -propionamides 1e4 react with imid-
azole in refluxing toluene to form the corresponding imidazolyla-
To exploit the well known additional stability of complexes with
methylene bridged NHCs [7,10] we also decided to introduce
cetamides
or
-propionamides
[25].
2-Imidazol-1-yl-N-
a
bridging methylene group between the two imidazolium
phenylacetamide 5 [25,44], 2-imidazol-1-yl-N-(4-methoxyphenyl)
acetamide 6 [43], 3-imidazol-1-yl-N-phenylpropionamide 7 [42]
and 3-imidazol-1-yl-N-(4-methoxyphenyl)-propionamide 8 were
obtained in moderate yields (Scheme 1).
* Corresponding author. Tel.: þ49 351 463 38571; fax: þ49 351 463 39679.
E-mail address: thomas.strassner@chemie.tu-dresden.de (T. Strassner).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.05.019

204
Y. Unger, T. Strassner / Journal of Organometallic Chemistry 713 (2012) 203e208
Fig. 1. Known structure-types of amide-functionalized NHC metal complexes with group 10 metals.
Reaction of 5e8 with dibromomethane yielded the corre-
deprotonation by a proton sponge e.g. 1,8-(dimethylamino)naph-
thalene [48,49], which only lead to the reisolation of the starting
material.
Exchange of the bromide ligands against non-coordinating
counterions followed by deprotonation with potassium carbonate
also did not result in the formation of the desired halide-free
complexes. We believe that the formation of the seven-
membered ring is sterically too unfavorable, why we only suc-
ceeded in synthesizing complexes 17 and 18.
In the context of this study the signal of the hydrogen atom at
the amide nitrogen was of special interest to us. Already in the 1H
NMR spectra of the bisimidazolium salts 9e12 and also in the
platinum(II) complexes 13e16 the proton is shifted to higher field
by more than 2 ppm compared to the imidazolylamides 5e8, in
agreement with an earlier publication which proposed the forma-
tion of a hydrogen bond between the halide atom and the hydrogen
atom at the amide nitrogen to be responsible for this shift [21]. This
implies that the amide fragment in complexes 13e16 should be
orientated toward the bromide ligands. The downfield shift of the
amide-NH is less pronounced (ca. 0.3 ppm) in 15 and 16 compared
to 13 and 14. For the para-methoxy substituted complexes 14 and
16 this signal is shifted downfield compared to the unsubstituted
complexes 13 and 15, which can be attributed to the electron
donating group (signal of amide proton: 13: 10.3 ppm,14: 10.1 ppm,
15: 10.0 ppm, 16: 9.8 ppm).
sponding bisimidazolium bromide salts 9e12 (Scheme 1). These
have been reacted with the basic metal precursor platinum(II)
acetylacetonate [7,8] in dimethylsulfoxide (DMSO) following
a temperature program for several hours (see Experimental details)
according to the method first described by Öfele [45e47]. The
platinum(II) complexes 13e16 could be synthesized in good yields
(Scheme 1).
Complexes 17 and 18 could be synthesized by reaction of 1,10-
methylene-bis(3-N-phenylacetamide-imidazol-2-ylidene)platinum-
(II) dibromide 13 and 1,10-methylene-bis(3-N-(4-methoxyphenyl)-
acetamide-imidazol-2-ylidene)platinum(II) dibromide 14 with
potassium carbonate in DMSO (Scheme 2).
Although the deprotonation of the amide by potassium
carbonate in dimethylsulfoxide and the synthesis of the corre-
sponding metal complex were successful for the shorter chain
lengths, we unfortunately were not able to make the corresponding
compounds with the longer alkyl chain from precursors 15 and 16.
Multiple unsuccessful attempts included changing the reaction
time and the use of different bases like cesium carbonate Cs2CO3,
potassium carbonate K2CO3 and lithium diisopropylamide (LDA). It
is well known that the protons of the NeCH2eN group between the
two imidazole heterocycles are acidic and susceptible to attack by
strong bases, therefore it is no surprise that in the case of the strong
base LDA, we did observe decomposition products. We also tried
3. Conclusion
2
We could synthesize and characterize new platinum(II)
complexes with NHC ligands carrying amide-functionalized side
chains. Next to platinum(II) biscarbene (C*eC*) complexes with
halide ligands we were also able to synthesize halide-free tethered
platinum(II) complexes with tetradentate NeC*eC*eN ligands by
deprotonation of the amide group.
N
N
N
N
N
N
O
R
R
N
N
N
N
2 X
M
M
N
O
N
4. Experimental
M = Ni, Pd
M = Ni, Pd
Solvents of 99.5% purity were used throughout this study. All
other chemicals, platinum(II) acetylacetonate and platinum(II)
chloride were obtained from common suppliers and used without
further purification. 1H and 13C NMR spectra were recorded with
IV
V
Fig. 2. NHC metal(II) complexes with tethered tetradentate ligand.

Y. Unger, T. Strassner / Journal of Organometallic Chemistry 713 (2012) 203e208
205
N
NH
R
O
R
NH2
R
O
O
toluene
reflux
Et3N
DCM
N
H
N n
+
Cl
N
H
n
n
Cl
Cl
N
1: n = 1, R = H (67%)
5: n = 1, R = H (42%)
6: n = 1, R = OMe (19%)
7: n = 2, R = H (19%)
8: n = 2, R = OMe (71%)
2: n = 1, R = OMe (97%)
3: n = 2, R = H (100%)
4: n = 2, R = OMe (92%)
CH2Br2
THF,
N
N
N
N
N
N
N
N
2 Br
n
Pt
Pt(acac)2
n
n
n
Br
Br
HN
O
O
NH
HN
O
O
NH
DMSO,
R
R
R
R
13: n = 1, R = H (65%)
9: n = 1, R = H (75%)
10: n = 1, R = OMe (61%)
11: n = 2, R = H (90%)
12: n = 2, R = OMe (71%)
14: n = 1, R = OMe (66%)
15: n = 2, R = H (51%)
16: n = 2, R = OMe (34%)
Scheme 1. Synthesis of acetamide- or propionamide di(imidazol-ylidene)platinum(II) dihalide complexes.
a Bruker AC 300 P or Bruker DRX 500 spectrometer. The spectra
were referenced internally to the references of the solvent (CDCl3,
DMSO). Elementary analyses were performed by the microanalyt-
ical laboratory at our institute using an Eurovektor Hekatech EA-
3000 Elemental Analyzer. The melting points were measured
with a Wagner&Munz PolyTherm A melting-point apparatus and
are uncorrected.
or chloropropionyl chloride were dissolved in dry dichloro-
methane. This solution was slowly added to the aniline solution at
0
allowed to slowly warm up to room temperature, extracted with
dichloromethane and washed with 2 M HCl. The organic phase was
separated from the aqueous phase and dried with anhydrous
MgSO4. Filtration and removal of the solvent under reduced pres-
sure gave the desired product.
ꢀC and the mixture was stirred at 0 ꢀC for 2 h. The solution was
4.1. Synthesis of chloroacetamides and -propionamides
4.1.2. 2-Chloro-N-phenylacetamide 1
Aniline (42.5 mmol, 3.958 g, 3.87 mL) reacts with triethylamine
(38.7 mmol, 3.916 g, 5.40 mL) in 15 mL dichloromethane and
4.1.1. General procedure
1 equiv aniline was slowly added to a dichloromethane solution
of 0.91 equiv triethylamine at 0 ꢀC. 1.18 equiv chloroacetyl chloride
Scheme 2. Synthesis of tethered di(imidazol-2-ylidene)platinum(II) complexes.

206
Y. Unger, T. Strassner / Journal of Organometallic Chemistry 713 (2012) 203e208
chloroacetyl chloride (50.26 mmol, 5.676 g, 4.0 mL) in 10 mL dry
dichloromethane.
NMR (CDCl3, 125.75 MHz):
125.2; 120.2; 120.0; 50.6 ppm.
d
¼ 164.7; 138.0; 136.8; 130.2; 129.1;
Yield: 4.818 g (66.8%). Mp: 125 ꢀC. 1H NMR (CDCl3, 300.13 MHz):
d
¼ 8.19 (s, 1H, NH); 7.48 (m, 2H, J ¼ 7.5 Hz, o-CH); 7.29 (m, 2H,
J ¼ 7.5 Hz, m-CH); 7.12 (m, 1H, J ¼ 7.4 Hz, p-CH); 4.12 (s, 2H, CH2)
ppm. 13C NMR (CDCl3, 75.475 MHz):
4.2.3. 2-Imidazol-1-yl-N-(4-methoxyphenyl)acetamide 6
Imidazole (64.0 mmol, 4.357 g) reacts with 2-chloro-N-(4-
methoxyphenyl)acetamide (12.8 mmol, 2.555 g) in 40 mL toluene.
Yield: 0.562 g (18.9%). Mp: 161.7 ꢀCe163.2 ꢀC. 1H NMR (CDCl3,
d
¼ 163.8; 136.6; 129.1; 125.3;
120.1; 42.9 ppm. Anal. Calcd for C8H8NOCl: C, 56.65; H, 4.75; N,
8.26%. Found: C, 56.42; H, 4.88; N, 8.10%.
300.13 MHz):
d
¼ 7.60 (s, 1H, NCHN); 7.25 (d, 2H, J ¼ 9.0 Hz, CH);
7.15 (s, 1H, NCHCHN); 7.05 (s, 1H, NH); 7.00 (s, 1H, NCHCHN); 6.74
4.1.3. 2-Chloro-N-(4-methoxyphenyl)acetamide 2
(d, 2H, J ¼ 9.1 Hz, CH); 4.74 (s, 2H, CH2); 3.71 (s, 3H, OCH3) ppm. 13
C
p-Anisidine (42.5 mmol, 5.234 g) reacts with triethylamine
(38.7 mmol, 3.916 g, 5.40 mL) in 15 mL dichloromethane and
chloroacetyl chloride (50.26 mmol, 5.676 g, 4.0 mL) in 10 mL dry
dichloromethane.
NMR (CDCl3, 75.475 MHz):
d
¼ 164.6; 157.1; 138.2; 131.0; 129.3;
122.1; 119.7; 114.3; 55.5; 50.5 ppm.
4.2.4. 3-Imidazol-1-yl-N-phenylpropionamide 7
Yield: 7.507 g (97.2%). Mp: 103 ꢀCe104 ꢀC. 1H NMR (CDCl3,
Imidazole (64.0 mmol, 4.357 g) reacts with 3-chloro-N-phe-
nylpropionamide (12.8 mmol, 2.351 g) in 40 mL toluene.
Yield: 0.522 g (18.9%). Mp: 139.8 ꢀC.1H NMR (CDCl3, 300.13 MHz):
300.13 MHz):
CH); 6.83e6.80 (dd, 2H, J ¼ 2.2 Hz, CH); 4.11 (s, 2H, CH2); 3.73 (s, 3H,
OCH3) ppm. 13C NMR (CDCl3, 75.475 MHz):
122.1; 114.2; 55.5; 42.8 ppm. Anal. Calcd for C9H10NO2Cl: C, 54.14;
H, 5.05; N, 7.02%. Found: C, 54.01; H, 5.16; N, 7.17%.
d
¼ 8.12 (bs, 1H, NH); 7.38e7.36 (dd, 2H, J ¼ 2.2 Hz,
d
¼ 163.7; 157.1; 129.7;
d
¼ 8.87 (s, 1H, NCHN); 7.45 (d, 2H, J ¼ 7.7 Hz, o-CH); 7.26 (t, 2H,
J ¼ 7.7 Hz, m-CH); 7.03 (t,1H, J ¼ 7.4 Hz, p-CH); 6.95 (s,1H, NCHCHN);
6.91 (s,1H, NCHCHN); 4.27 (t, 2H, J ¼ 6.4 Hz, NCH2CH2CO); 2.71 (t, 2H,
J ¼ 6.4 Hz, NCH2CH2CO); (NH not visible) ppm. 13C NMR (CDCl3,
4.1.4. 3-Chloro-N-phenylpropionamide 3
75.475 MHz):
d
¼ 168.0; 152.6; 138.0; 136.9; 134.1; 129.0; 124.4;
Aniline (42.5 mmol, 3.958 g, 3.87 mL) reacts with triethylamine
(38.7 mmol, 3.916 g, 5.40 mL) in 15 mL dichloromethane and 3-
chloropropionyl chloride (50.26 mmol, 6.382 g, 5.95 mL) in 10 mL
dry dichloromethane.
119.9; 43.0; 39.0 ppm. Anal. Calcd for C12H13N3O: C, 66.95; H, 6.09; N,
19.53%. Found: C, 66.68; H, 6.22; N, 19.37%.
4.2.5. 3-Imidazol-1-yl-N-(4-methoxyphenyl)propionamide 8
Imidazole (128 mmol, 8.714 g) reacts with 3-chloro-N-(4-
methoxyphenyl)propionamide(25.6mmol, 5.470 g)in80mLtoluene.
Yield: 7.532 g (100%). Mp: 90.8e91.5 ꢀC. 1H NMR (CDCl3,
300.13 MHz):
d
¼ 7.45 (d, 3H, J ¼ 7.8 Hz, o-CH, NH); 7.25 (t, 2H,
J ¼ 7.6 Hz, m-CH); 7.05 (t, 1H, J ¼ 7.4 Hz, p-CH); 3.80 (t, 2H,
Yield: 4.424
300.13 MHz):
g
(70.5%). Mp: 100.6 ꢀC. 1H NMR (CDCl3,
¼ 9.48 (s, 1H, NH); 7.35 (d, 2H, J ¼ 9.0 Hz, CH); 7.20
J ¼ 6.4 Hz, ClCH2CH2CO); 2.74 (t, 2H, J ¼ 6.4 Hz, ClCH2CH2CO) ppm.
d
13C NMR (CDCl3, 75.475 MHz):
40.4; 39.9 ppm.
d
¼ 167.8; 137.4; 129.0; 124.7; 120.1;
(s, 1H, NCHN); 6.88 (d, 2H, J ¼ 9.0 Hz, NCHCHN); 6.73 (d, 2H,
J ¼ 9.0 Hz, CH); 4.23 (t, 2H, J ¼ 6.2 Hz, NCH2CH2CO); 3.69 (s, 3H,
OCH3); 2.67 (t, 2H, J ¼ 6.4 Hz, NCH2CH2CO) ppm. 13C NMR (CDCl3,
4.1.5. 3-Chloro-N-(4-methoxyphenyl)propionamide 4
p-Anisidine (85 mmol, 10.469 g) reacts with triethylamine
(77.4 mmol, 7.832 g, 10.8 mL) in 30 mL dichloromethane and 3-
chloropropionyl chloride (100.52 mmol, 12.760 g, 11.9 mL) in
20 mL dry dichloromethane.
75.475 MHz):
d
¼ 168.0; 156.3; 136.8; 131.3; 128.6; 121.7; 119.7;
114.0; 55.4; 43.1; 38.5 ppm. Anal. Calcd for C13H15N3O2: C, 63.66; H,
6.17; N, 17.13%. Found: C, 63.19; H, 6.18; N, 16.82%.
4.3. Synthesis of the methylene-bisacetamide or propionamide-
imidazolium salts
Yield: 15.226 g (92.1%). Mp: 78.6 ꢀCe78.8 ꢀC. 1H NMR (CDCl3,
300.13 MHz):
d
¼ 7.83 (bs, 1H, NH); 7.36 (d, 2H, J ¼ 9.0 Hz, CH); 6.77
(d, 2H, J ¼ 9.0 Hz, CH); 3.80 (t, 2H, J ¼ 6.5 Hz, ClCH2CH2CO); 3.71 (s,
4.3.1. General procedure
3H, OCH3); 2.72 (t, 2H, J ¼ 6.5 Hz, ClCH2CH2CO) ppm. 13C NMR
2 equiv imidazoleamide or -propionamide and 1 equiv dibromo-
methane were dissolved in THF. The reaction mixture was heated at
110 ꢀC in a pressure tube. After cooling to room temperature the solid
formed was filtrated, washed with THF and dried under vacuum.
(CDCl3, 75.475 MHz):
d
¼ 167.8; 156.5; 130.7; 122.0; 114.0; 55.4;
39.1 ppm. Anal. Calcd for C10H12NO2Cl: C, 56.21; H, 5.66; N, 6.56%.
Found: C, 56.38; H, 5.82; N, 6.63%.
4.2. Synthesis of imidazolylacetamides and -propionamides
4.3.2. 1,10-Methylene-bis(3-N-phenylacetamide-1H-imidazolium)
dibromide 9
4.2.1. General procedure
2-Imidazol-1-yl-N-phenylacetamide (2.5 mmol, 0.500 g) and
dibromomethane (1.25 mmol, 0.216 g, 0.09 mL) were stirred in
5 mL THF at 110 ꢀC for 3 days.
A mixture of 5 equiv imidazole and 1 equiv 2-chloroacetamide
or 3-chloropropionamide was dissolved in toluene and heated at
110 ꢀC over night. After cooling to room temperature the solvent
was removed under vacuum. The residue was then extracted
with dichloromethane. The organic phase was washed with
water, separated and dried with anhydrous MgSO4. After filtration
and removal of the solvent under reduced pressure the product
was obtained.
Yield: 0.540 g (74.7%). Mp: 149.7 ꢀC. 1H NMR (d6-DMSO,
300.13 MHz):
d
¼ 10.69 (s, 2H, NH); 9.62 (s, 2H, NCHN); 8.13 (s, 2H,
NCHCHN); 7.93 (s, 2H, NCHCHN); 7.62 (d, 4H, J ¼ 7.6 Hz, o-CH); 7.36
(t, 4H, J ¼ 7.6 Hz, m-CH); 7.11 (t, 2H, J ¼ 7.4 Hz, p-CH); 6.89 (s, 2H,
NCH2N); 5.36 (s, 4H, NCH2CO) ppm. 13C NMR (d6-DMSO,
75.475 MHz):
d
¼ 163.3; 138.9; 138.2; 129.0; 125.0; 123.9; 121.5;
119.1; 58.3; 51.7 ppm. Anal. Calcd for C23H24N6O2Br2: C, 47.93; H,
4.20; N, 14.59%. Found: C, 47.79; H, 4.30; N, 14.32%.
4.2.2. 2-Imidazol-1-yl-N-phenylacetamide 5
Imidazole (70.0 mmol, 4.766 g) reacts with 2-chloro-N-phe-
nylacetamide (14.0 mmol, 2.374 g) in 40 mL toluene.
Yield: 1.174 g (41.7%). Mp: 130 ꢀC. 1H NMR (CDCl3, 300.13 MHz):
4.3.3. 1,10-Methylene-bis(3-N-(4-methoxyphenyl)-acetamide-1H-
imidazolium) dibromide 10
d
¼ 7.91 (s, 1H, NH); 7.55 (s, 1H, NCHN); 7.39 (d, 2H, J ¼ 7.7 Hz, o-
2-Imidazol-1-yl-N-(4-methoxyphenyl)acetamide (1.05 mmol,
0.243 g) and dibromomethane (0.53 mmol, 0.091 g, 0.04 mL) were
stirred in 3 mL THF at 110 ꢀC for 3 days.
CH); 7.25 (t, 2H, J ¼ 7.6 Hz, m-CH); 7.13 (s, 1H, NCHCHN); 7.06 (t, 1H,
J ¼ 7.4 Hz, p-CH); 7.01 (s, 1H, NCHCHN); 4.74 (s, 2H, CH2) ppm. 13
C

Y. Unger, T. Strassner / Journal of Organometallic Chemistry 713 (2012) 203e208
207
Yield: 0.205 g (60.8%). Mp: decomposition >292 ꢀC. 1H NMR (d6-
DMSO, 300.13 MHz):
4.4.3. 1,10-Methylene-bis(3-N-(4-methoxyphenyl)-acetamide-
d
¼ 10.57 (s, 2H, NH); 9.63 (s, 2H, NCHN); 8.14
imidazol-2-ylidene)platinum(II) dibromide 14
(s, 2H, NCHCHN); 7.92 (s, 2H, NCHCHN); 7.53 (d, 4H, J ¼ 7.1 Hz, CH);
6.92 (d, 6H, J ¼ 8.6 Hz, CH, NCH2N); 5.33 (s, 4H, NCH2CO); 3.73 (s,
1,10-Methylene-bis(3-N-(4-methoxyphenyl)-acetamide-1H-imi-
dazolium) dibromide (0.31 mmol, 0.200 g) and platinum(II) ace-
tylacetonate (0.31 mmol, 0.124 g) react in 4 mL DMSO.
6H, OCH3) ppm. 13C NMR (d6-DMSO, 75.475 MHz):
138.9; 131.3; 124.9; 121.5; 120.7; 114.1; 58.3; 55.2; 51.6 ppm. Anal.
Calcd for C23H24N6O2Br2: C, 47.18; H, 4.44; N, 13.21%. Found: C,
46.98; H, 4.31; N, 13.05%.
d
¼ 162.7; 155.6;
Yield: 0.170 g (66.1%). Mp: 347.6 ꢀC. 1H NMR (d6-DMSO,
300.13 MHz):
d
¼ 10.11 (s, 2H, NH); 7.58 (d, 2H, J ¼ 1.7 Hz, NCHCHN);
7.44 (d, 4H, J ¼ 8.9 Hz, CH); 7.36 (d, 2H, J ¼ 1.7 Hz, NCHCHN); 6.82
(d, 4H, J ¼ 9.0 Hz, CH); 6.20 (AB, 1H, J ¼ 13.2 Hz, NCH2N); 6.03
(AB, 1H, J ¼ 13.0 Hz, NCH2N); 5.57 (AB, 2H, J ¼ 16.6 Hz, NCH2CO);
5.08 (AB, 2H, J ¼ 16.7 Hz, NCH2CO); 3.69 (s, 6H, OCH3) ppm. 13C NMR
4.3.4. 1,10-Methylene-bis(3-N-phenylpropionamide-1H-imidazolium)
dibromide 11
3-Imidazol-1-yl-N-phenylpropionamide (2 mmol, 0.421 g) and
dibromomethane (1 mmol, 0.170 g, 0.07 mL) were stirred in 2 mL
THF at 110 ꢀC for 3 days.
(d6-DMSO, 75.475 MHz):
d
¼ 164.1; 155.1; 146.6; 132.0; 123.3;
120.5; 120.0; 113.8; 55.1; 52.6 ppm. Anal. Calcd for C25H26
N6O4PtBr2$1H2O: C, 35.43; H, 3.33; N, 9.92%. Found: C, 35.59; H,
3.16; N. 9.67%.
Yield: 0.542
500.15 MHz):
g
(89.7%). Mp: 161 ꢀC. 1H NMR (d6-DMSO,
¼ 10.25 (s, 2H, NH); 9.61 (s, 2H, NCHN); 8.05 (s, 2H,
d
NCHCHN); 7.92 (d, 2H, J ¼ 1.4 Hz, NCHCHN); 7.58 (d, 4H, J ¼ 7.7 Hz,
o-CH); 7.30 (t, 4H, J ¼ 7.9 Hz, m-CH); 7.04 (t, 2H, J ¼ 7.4 Hz, p-CH);
6.72 (s, 2H, NCH2N); 4.52 (t, 4H, J ¼ 6.1 Hz, NCH2CH2CO); 3.03 (t, 4H,
J ¼ 6.1 Hz, NCH2CH2CO) ppm. 13C NMR (d6-DMSO, 125.75 MHz):
4.4.4. 1,10-Methylene-bis(3-N-phenylpropionamide-imidazol-2-
ylidene)platinum(II) dibromide 15
1,10-Methylene-bis(3-N-phenylpropionamide-1H-imidazolium)
dibromide (0.41 mmol, 0.250 g) and platinum(II) acetylacetonate
(0.41 mmol, 0.163 g) react in 4 mL DMSO.
d
¼ 167.9; 138.8; 138.2; 128.7; 123.4; 122.0; 119.2; 58.0; 45.5;
35.6 ppm. Anal. Calcd for C25H28N6O2Br2: C, 49.68; H, 4.67; N,
13.91%. Found: C, 49.72; H, 4.89; N, 13.86%.
Yield: 0.168 g (51.4%). Mp: 293e305 ꢀC. 1H NMR (d6-DMSO,
300.13 MHz):
d
¼ 9.99 (s, 2H, NH); 7.53 (s, 2H, NCHCHN); 7.51 (d, 4H,
J ¼ 7.2 Hz, o-CH); 7.35 (s, 2H, NCHCHN); 7.26 (t, 4H, J ¼ 7.4 Hz, m-
CH); 7.02 (t, 2H, J ¼ 7.2 Hz, p-CH); 6.08 (AB, 1H, J ¼ 13.1 Hz, NCH2N);
6.00 (AB, 1H, J ¼ 13.1 Hz, NCH2N); 4.74e4.53 (m, 4H, J ¼ 13.3 Hz,
NCH2CH2CO); 3.02 (m, 4H, J ¼ 13.3 Hz, NCH2CH2CO) ppm.
4.3.5. 1,10-Methylene-bis(3-N-(4-methoxyphenyl)-propionamide-
1H-imidazolium) dibromide 12
3-Imidazol-1-yl-N-(4-methoxyphenyl)propionamide (1.75 mmol,
0.430 g) and dibromomethane (0.88 mmol, 0.153 g, 0.06 mL) were
stirred in 3 mL THF at 110 ꢀC for 2 days.
13C NMR (d6-DMSO, 75.475 MHz):
d
¼ 168.5; 145.2; 138.9;
128.7; 123.2; 121.5; 120.7; 119.2; 67.0; 45.8; 37.2 ppm. Anal. Calcd
for C25H26N6O2PtBr2: C, 37.65; H, 3.29; N,10.54%. Found: C, 37.56; H,
3.17; N, 10.45%.
Yield: 0.413 g (71.0%). Mp: 180.7 ꢀCe181.8 ꢀC. 1H NMR (d6-
DMSO, 500.15 MHz):
d
¼ 10.10 (s, 2H, NH); 9.60 (s, 2H, NCHN); 8.04
(s, 2H, NCHCHN); 7.91 (s, 2H, NCHCHN); 7.49 (d, 4H, J ¼ 8.3 Hz, CH);
6.88 (d, 4H, J ¼ 8.5 Hz, CH); 6.72 (s, 2H, NCH2N); 4.51 (t, 4H,
J ¼ 5.7 Hz, NCH2CH2CO); 3.72 (s, 6H, OCH3); 3.0 (t, 4H, J ¼ 5.7 Hz,
4.4.5. 1,10-Methylene-bis(3-N-(4-methoxyphenyl)-propionamide-
imidazol-2-ylidene)platinum(II) dibromide 16
NCH2CH2CO) ppm. 13C NMR (d6-DMSO, 125.75 MHz):
d
¼ 167.3;
1,10-Methylene-bis(3-N-(4-methoxyphenyl)-propionamide-1H-
imidazolium) dibromide (0.38 mmol, 0.250 g) and platinum(II)
acetylacetonate (0.38 mmol, 0.148 g) react in 4 mL DMSO. The solid
formed was washed twice with water, MeOH and THFewater
mixture.
155.3; 138.2; 131.9; 123.4; 122.0; 120.7; 113.8; 58.0; 55.2; 45.6;
35.4 ppm. Anal. Calcd for C27H32N6O4Br2: C, 48.81; H, 4.85; N,
12.65%. Found: C, 48.52; H, 4.73; N, 12.56%.
4.4. Synthesis of acetamide- or propionamide-imidazol-ylidene
platinum(II) dihalide complexes
Yield: 0.109 g (33.5%). Mp: 305.1 ꢀC. 1H NMR (d6-DMSO,
300.13 MHz):
d
¼ 9.84 (s, 2H, NH); 7.52 (d, 2H, J ¼ 2.0 Hz, NCHCHN);
7.42 (d, 4H, J ¼ 9.0 Hz, CH); 7.35 (d, 2H, J ¼ 1.9 Hz, NCHCHN); 6.83 (d,
4H, J ¼ 9.0 Hz, CH); 6.10 (AB, 1H, J ¼ 13.1 Hz, NCH2N); 5.99 (AB, 1H,
J ¼ 13.1 Hz, NCH2N); 4.77e4.70 (m, 2H, J ¼ 13.4 Hz, NCH2CH2CO);
4.59e4.51 (m, 2H, J ¼ 13.4 Hz, NCH2CH2CO); 2.99e2.93 (m, 4H,
4.4.1. General procedure
1 equiv bisimidazolium dibromide and 1 equiv platinum(II)
acetylacetonate were dissolved in DMSO. The reaction mixture was
stirred for 3 h at 60 ꢀC, at 80 ꢀC, and at 110 ꢀC. The solvent was
removed under reduced pressure to give a crude product, which for
purification was washed with water, MeOH and THF. The obtained
product was dried under vacuum.
NCH2CH2CO) ppm. 13C NMR (d6-DMSO, 75.475 MHz):
d
¼ 168.0;
155.2; 145.2; 132.0; 121.5; 120.8; 120.7; 113.8; 62.0; 55.1; 45.9;
37.1 ppm. Anal. Calcd for C27H30N6O4PtBr2$1H2O: C, 37.04; H, 3.68;
N, 9.60%. Found: C, 36.90; H, 3.42; N, 9.50%.
4.4.2. 1,10-Methylene-bis(3-N-phenylacetamide-imidazol-2-ylidene)
platinum(II) dibromide 13
4.5. Synthesis of acetamide-imidazol-ylidene platinum(II) complexes
1,10-Methylene-bis(3-N-phenylacetamide-1H-imidazolium) dibro-
mide (0.35 mmol, 0.200 g) and platinum(II) acetylacetonate
(0.35 mmol, 0.137 g) react in 4 mL DMSO.
4.5.1. 1,10-Methylene-bis(3-N-phenylacetamide-imidazol-2-ylidene)
platinum(II) 17
1,10-Methylene-bis(3-N-phenylacetamide-imidazoline-2-ylidene)-
platinum(II) dibromide (0.20 mmol, 0.155 g) and potassium carbonate
(0.40 mmol, 0.056 g) react in 4 mL DMSO. The reaction mixture was
stirred at 80 ꢀC for 8 h. The mixture was filtrated, the solvent removed
in vacuo and the crude product was washed with water. The obtained
product was dried in vacuo.
Yield: 0.174 g (64.6%). Mp: decomposition >350 ꢀC. 1H NMR (d6-
DMSO, 300.13 MHz):
d
¼ 10.25 (s, 2H, NH); 7.59 (d, 2H, J ¼ 1.6 Hz,
NCHCHN); 7.53 (d, 4H, J ¼ 7.9 Hz, o-CH); 7.37 (d, 2H, J ¼ 1.7 Hz,
NCHCHN); 7.26 (t, 4H, J ¼ 7.6 Hz, m-CH); 7.03 (t, 2H, J ¼ 7.3 Hz, p-
CH); 6.21 (AB, 1H, J ¼ 13.1 Hz, NCH2N); 6.04 (AB, 1H, J ¼ 13.1 Hz,
NCH2N); 5.55 (AB, 2H, J ¼ 16.7 Hz, NCH2CO); 5.15 (AB, 2H,
J ¼ 16.8 Hz, NCH2CO) ppm. 13C NMR (d6-DMSO, 75.475 MHz):
Yield: 0.093 g (76.5%). Mp: decomposition >365 ꢀC. 1H NMR (d6-
DMSO, 300.13 MHz):
d
¼ 7.60 (d, 2H, J ¼ 2.0 Hz, NCHCHN); 7.50 (d,
d
¼ 164.7; 146.6; 138.8; 128.7; 123.3; 123.2; 120.1; 118.9; 62.1;
2H, J ¼ 2.0 Hz, NCHCHN); 6.70 (t, 4H, J ¼ 8.9 Hz, o-CH); 6.66 (t, 4H,
J ¼ 8.9 Hz, m-CH); 6.63 (t, 2H, J ¼ 4.4 Hz, p-CH); 6.32 (s, 2H, NCH2N);
4.66 (s, 4H, NCH2CO) ppm. 13C NMR (d6-DMSO, 75.475 MHz):
52.6 ppm. Anal. Calcd for C23H22N6O2PtBr2$1H2O: C, 35.09; H, 3.07;
N, 10.67%. Found: C, 35.25; H, 2.84; N, 10.31%.

208
Y. Unger, T. Strassner / Journal of Organometallic Chemistry 713 (2012) 203e208
[15] Y. Unger, D. Meyer, O. Molt, C. Schildknecht, I. Munster, G. Wagenblast,
d
¼ 166.1; 149.0; 145.8; 126.8; 126.0; 121.5; 121.0; 120.3; 61.9;
T. Strassner, Angew. Chem. Int. Ed. Engl. 49 (2010) 10214.
[16] M.-H. Sie, Y.-H. Hsieh, Y.-H. Tsai, J.-R. Wu, S.-J. Chen, J.-H. Lii, H.-M. Lee,
Organometallics 29 (2010) 6473.
54.7 ppm. Anal. Calcd for C23H20N6O2Pt$0.3 DMSO$1H2O: C, 43.36;
H, 3.67; N,12.85; S,1.47%. Found: C, 43.34; H, 3.61; N,13.08; S,1.20%.
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2973.
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Chem. 692 (2007) 1672.
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R.B. Sunoj, P. Ghosh, Eur. J. Inorg. Chem. (2006) 2975.
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4153.
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(2010) 2868.
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Organometallics 26 (2007) 5826.
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(2009) 405.
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26 (2007) 1692.
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(2009) 6948.
4.5.2. 1,10-Methylene-bis(3-N-(4-methoxyphenyl)-acetamide-
imidazol-2-ylidene)platinum(II) 18
1,10-Methylene-bis(3-N-(4-methoxyphenyl)-acetamide-imida-
zoline-2-ylidene)-platinum(II) dibromide (0.18 mmol, 0.150 g) and
potassium carbonate (0.36 mmol, 0.050 g) react in 4 mL DMSO. The
reaction mixture was stirred at 80 ꢀC for 8 h. The mixture was fil-
trated, the solvent removed in vacuo and the crude product was
washed with water. The obtained product was dried in vacuo.
Yield: 0.075 g (57.3%). Mp: 255e266.9 ꢀC. 1H NMR (d6-DMSO,
300.13 MHz):
d
¼ 7.59 (d, 2H, J ¼ 1.9 Hz, NCHCHN); 7.48 (d, 2H,
J ¼ 1.9 Hz, NCHCHN); 6.52 (d, 4H, J ¼ 8.8 Hz, CH); 6.30 (s, 2H,
NCH2N); 6.28 (d, 4H, J ¼ 8.7 Hz, CH); 4.63 (s, 4H, NCH2CO); 3.66 (s,
6H, OCH3) ppm. 13C NMR (d6-DMSO, 75.475 MHz):
d
¼ 166.3; 154.4;
146.2; 142.1; 127.2; 120.9; 120.3; 111.5; 61.4; 54.9; 54.7 ppm. Anal.
Calcd for C25H24N6O4Pt$0.5KBr: C, 41.30; H, 3.33; N, 11.56%. Found:
C, 41.75; H, 3.94; N, 11.00%.
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Acknowledgment
[32] J.-Y. Lee, P.-Y. Cheng, Y.-H. Tsai, G.-R. Lin, S.-P. Liu, M.-H. Sie, H.M. Lee,
Organometallics 29 (2010) 3901.
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Dalton Trans. (2003) 699.
We are grateful for financial support by BASF SE and to the
Zentrum für Informationsdienste und Hochleistungsrechnen (ZIH,
TU Dresden) for the generous allocation of compute time.
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