Chiral bisimidazolium salts derived from amino acids and their palladium(II)- and platinum(II)-biscarbene complexes

Article abstract of DOI:10.1016/j.jorganchem.2009.01.036

We report new chiral bisimidazolium salts synthesized from naturally occurring l-amino acids. They served as precursors for bidentate N-heterocyclic carbene metal complexes. The chiral imidazoles could be synthesized in good yields via a one-pot ring clos

Full text of DOI:10.1016/j.jorganchem.2009.01.036

Journal of Organometallic Chemistry 694 (2009) 1861–1868
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Journal of Organometallic Chemistry
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Chiral bisimidazolium salts derived from amino acids and their palladium(II)- and
platinum(II)-biscarbene complexes
1
*
Anke Meyer, Maria A. Taige , Thomas Strassner
Physikalische Organische Chemie, Technische Universität Dresden, Mommsenstrasse 13, 01062 Dresden, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
We report new chiral bisimidazolium salts synthesized from naturally occurring L-amino acids. They
Received 3 December 2008
Accepted 16 January 2009
Available online 25 February 2009
served as precursors for bidentate N-heterocyclic carbene metal complexes. The chiral imidazoles could
be synthesized in good yields via a one-pot ring closing reaction, followed by esterification. The methy-
lene bridged bisimidazolium iodide salts are accessible in moderate yields. Corresponding palladium(II)-
and platinum(II)-NHC complexes could be synthesized and fully characterized, but do not show optical
activity. We also report a solid state structure of one of the synthesized palladium(II) biscarbene com-
pounds derived from alanine.
Keywords:
Chiral bisimidazolium salts
Amino acids
N-heterocyclic carbene metal complexes
Palladium
Ó 2009 Elsevier B.V. All rights reserved.
Platinum
Solid state structure
1. Introduction
for the synthesis of chiral NHC-ligands, e.g. for oxazoline units
[20,28,47–51] (E). Some examples from each family (A–E) are gi-
N-heterocyclic carbenes are extraordinary stable ligands for
homogeneous transition metal catalysis, which has been reviewed
recently [1–9]. Especially bidentate or tridentate NHC-ligands have
shown their potential in many applications, for example C–C cou-
pling reactions [10–15] or CH activation [16,17]. The first chiral N-
heterocyclic carbene structures were published by Herrmann [18]
and Enders [19] in 1996. Structural concepts, known from efficient
stereodirecting phosphine ligands, were applied to N-heterocylic
carbenes together with newly developed structural motifs. Chiral
NHC-complexes have been used in different asymmetric catalytic
reactions, e.g. the hydrosilylation [20,21], the conjugate addition
of diethylzinc [22–25], hydrogenation [26–28] and the palla-
dium-catalyzed allylic alkylation [29,30]. A significant number of
selective catalysts based on N-heterocyclic carbene ligands were
published during the last years and quite recently reviewed [30–
35].
Some main concepts for ligand design have emerged. Gade and
Bellemin-Laponnaz distinguish between five families of chiral
N-heterocyclic carbene ligands [34], based on the type of chirality.
Ligands with centers of chirality within the N-substituents [29,36–
41] (A) or in the backbone of the heterocycle [42] (B), axial
[43,44] (C) and planar chirality [45,46] (D) have been published.
Fragments from the chiral pool, e.g. amino acids have been used
ven in Scheme 1.
We wanted to use the chiral pool in a different way by convert-
ing the naturally occurring amino acids to imidazoles, followed by
quaternization and deprotonation to yield new chiral metal–NHC
complexes with asymmetric centers near the carbene carbon. The
additional stability of bidentate ligands and their palladium(II)-
and platinum(II)-biscarbene complexes was described before
[17,52–62] and we therefore aimed at combining both concepts
by using methylene bridged bisimidazolium salts derived from
natural
L-amino acids as precursors for the metal complex synthe-
sis of palladium(II)- and platinum(II)-biscarbene complexes.
2. Results and discussion
2.1. Preparation of the chiral imidazoles 1a–j
It was shown by Bao that chiral imidazoles can be synthesized
starting from L-amino acids, which were converted to chiral ionic
liquids [63]. We modified the published procedure for the prepara-
tion of the imidazoles 1a–j (without previous esterification of the
L-amino acid) by substituting HCl/MeOH by SOCl2/ROH, which is
more convenient and turned out to be superior to the one-pot
imidazole synthesis [12,53] where glyoxal and paraformaldehyde
react with the amino acid ester hydrochloride in methanol
solution.
The synthesized chiral imidazoles 1a–j and the reaction condi-
tions are given in Scheme 2. The amino acids react with glyoxal,
* Corresponding author. Tel.: +49 351 46338571; fax: +49 351 46339679.
E-mail address: thomas.strassner@chemie.tu-dresden.de (T. Strassner).
1
X-ray analysis.
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.01.036

1862
A. Meyer et al. / Journal of Organometallic Chemistry 694 (2009) 1861–1868
iPr
vents at variable temperatures we found acetonitrile at
temperatures of 70–80 °C to be the best choice (Scheme 3).
Reaction of imidazoles 1a–h (derived from amino acids Ala, Val,
Leu, Ile, Phe) with diiodomethane lead to the corresponding opti-
cally active bisimidazolium salts 2a–h (Scheme 3). The analogous
bisimidazolium salts derived from the imidazoles 1i (Met) and 1j
(Asp) could not be isolated because of decomposition processes
during the reaction or workup.
N
N
N
N
Ph
N
N
iPr
BF4
BF4
N
Br
Pr
B
A
SiMe3
N
N
N
N
N
N
N
Fe
R
2 I
OH
2.3. Preparation of the metal biscarbene complexes
N
PF6
I
In situ deprotonation methods by palladium(II) acetate [58,67]
or platinum(II) acetylacetonate [53] have proven to be reliable syn-
thetic pathways for the synthesis of metal biscarbene complexes.
The reactions are carried out in DMSO with different temperature
settings. Similar to comparable systems it is necessary to increase
the temperature slowly during a couple of hours to avoid decom-
position of the ligand or precipitation of palladium/platinum black
[53,56]. The bisimidazolium salts 2a and 2d were tested in these
reactions (Scheme 4). Even after one week of drying under high
vacuum, complexes 3a and 3b (Ala) could be only isolated as
DMSO adducts, while the corresponding compounds 3c and 3d
do not contain DMSO.
C
D
N
O
O
O
N
n
N
N
N
R
N
N
N
Ar
R
R
X
O
R'
I
R
E OTf
Scheme 1. Examples for precursors of chiral N-heterocyclic carbene ligands.
Unfortunately the complexes do not show any optical activity in
dimethylsulfoxide or dimethylformamide solution. We suspect
that the basic conditions and the relatively high temperature are
responsible for the racemisation. We also tried other synthetic
routes and conditions to avoid the racemization, like the transmet-
allation by Ag2O [68] or other deprotonation reagents, which did
not lead to optically active palladium or platinum compounds. At-
tempts to synthesize the free carbene were not successful; they
lead to decomposition of the imidazolium salt.
glyoxal
CH O
2
NH , NaOH
3
O
O
O
1
1
2
R
R
R
1
SOCl
2
ONa
O
2
R
OH
1
N
N
water, 4 h 50 °C
R OH, 0 °C,
48 h rt
NH
2
N
N
1a-1j
2
1
2
1a:
1b:
1c:
1d:
1f:
Ala, R = CH , R = CH , 52%
Leu, R = CH CH(CH ) , R = CH , 71%
3
3
2
3 2
3
1
2
1
2
Ala, R = CH , R = CH CH , 29%
1g: Ile, R = CH(CH )CH CH , R = CH , 60%
3
2
3
3 2 3 3
1
2
1
2
1h:
1i:
1j:
Ala, R = CH , R = (CH ) CH , 63%
Phe, R = CH (C H ), R = CH , 36%
2 6 5 3
3
2 3
3
1
2
1
2
Val, R = CH(CH ) , R = CH , 62%
Met, R = (CH ) SCH , R = CH , 54%
3
2
3
2 2 3 3
1
2
1
2
1e: Val, R = CH(CH ) , R = CH CH , 25%
Asp, R = CH COOCH , R = CH , 31%
2 3 3
3
2
2
3
Scheme 2. Preparation and yields for the synthesis of imidazoles from amino acids.
2.4. NMR-analysis of the metal complexes
formaldehyde and ammonia in water at 50 °C under basic condi-
tions. For the necessary esterification we used thionyl chloride,
which is a reliable method for the preparation of amino acid esters
[64–66]. This strategy offers two possibilities to modify the prod-
uct by using different amino acids (R1) other than alanine (1a–c)
and valine (1d–e) and various alcohols (R2).
We thoroughly studied the NMR spectra of the metal–NHC
biscarbene complexes, which are relatively complex due to the dif-
ferent stereoisomers. Although (R,R) and (S,S) configuration can not
be distinguished in the NMR spectra they do show different signal
sets for the ‘‘dashed” (A) and the ‘‘dotted” (B) fragments of the
molecule (cf. Scheme 4). One example might be the Ccarbene shifts,
which were found at 150.80 and 152.36 ppm (3b) and at 150.80
and 151.62 ppm (3d).
2.2. Preparation of the chiral bisimidazolium salts 2a–h
For all metal complexes we observe different 1H- and 13C-sig-
nals for all atoms of the substituents at the nitrogen atoms and
for the imidazole core. For the methylene bridge of the platinum(II)
compounds 3b and 3d, a doublet of doublets is detected in the 1H
NMR spectrum, an effect well known from other platinum(II)
biscarbene complexes [52,53]. For the palladium(II) biscarbene
complexes 3a and 3c a singlet is observed for both hydrogen atoms
of the methylene bridge. The 13C NMR spectra of all complexes
(3a–d) show only one signal for the methylene bridge.
As we have been worried about the stability of the chiral center
we tried to keep the reaction temperatures as low as possible and
therefore chose diiodomethane for the preparation of the bisimi-
dazolium salts as the nucleophilic substitution reaction should
need less activation energy compared to dibromomethane. Initially
the substitution reaction was carried out in tetrahydrofuran at
100–130 °C according to known procedures [52], but the corre-
sponding products could not be isolated. By screening different sol-
O
B
A
R2
N
N
Pd(OAc) 2
or
N
N
N
N
1
2
R
R
CH I
R2
2
2
O
O
R2
R2
O
2
2
O
O
N
N
O
O
O
O
Pt(acac) 2
O
O
N
O
O
N
R
N
N
R
M
2
N
2 I
Δ
CH CN,
Δ
2 I
DMSO,
3
I
I
R1
R1
R1
R1
1
1
R
R
N
3a-3d
2a-2h
1
2
1
2
Ala, M = Pd, R1 = CH3, R2 = CH3, 39%
Ala, M = Pt, R1 = CH3, R2 = CH3, 45%
3a:
3b:
3c:
3d:
Ala, R = CH , R = CH 42%
Val, R = CH(CH ) , R = CH CH 32%
2a:
2b:
2c:
2d:
2e:
2f:
2g:
2h:
3
3,
3 2
2
3,
1
2
1
2
Ala, R = CH , R = CH CH 50%
Leu, R = CH CH(CH ) , R = CH 26%
3
2
3,
2 3 2 3,
Ala, R = CH , R = (CH ) CH 56%
Ile, R = CH(CH )CH CH , R = CH 34%
3 2 3 3,
Val, M = Pd, R1 = CH(CH3)2, R2 = CH3, 82%
Val, M = Pt, R 1 = CH(CH3)2, R2 = CH3, 30%
1
2
1
2
3
2
3
3,
1
2
1
2
Val, R = CH(CH ) , R = CH 44%
Phe, R = CH (C H ), R = CH 26%
3 2
3,
2 6 5 3,
Scheme 3. Preparation and yields of the bisimidazolium salts.
Scheme 4. Preparation of the metal carbene complexes.

A. Meyer et al. / Journal of Organometallic Chemistry 694 (2009) 1861–1868
1863
firmed as the metal complexes did not show any optical activity.
Additionally we report the solid state structure of 1,10-bis-[(1S)-
1-methoxycarbonyl-ethyl]-3,30-methylenediimidazoline-2,20-diy-
lidenepalladium(II) diiodide 3a. Different reaction conditions were
tested, but the chiral bisimidazolium salts could not be converted
into chiral metal complexes. Attempts to reduce the acidity of
the proton at the asymmetric carbon atom are under way and
seem to be necessary to succeed in making chiral complexes.
4. Experimental
4.1. General experimental methods
Platinum(II) acetylacetonate and palladium(II) acetate were
purchased from ACROS. All other chemicals and solvents were ob-
tained from common suppliers and used without further purifica-
tion. Melting points were measured with an Electrothermal IA9100
and were uncorrected. A Perkin Elmer polarimeter (model 341)
was used to prove the optical activity. Elemental analysis, mass
spectrometry as well as NMR spectrometry were performed by
our departmental analytical laboratory. Elemental analyses were
measured with an Eurovektor Hekatech EA-3000 Elemental Ana-
lyzer. The mass spectra were recorded with a Bruker Esquire mass
spectrometer, which is equipped with an ion trap detector. The
NMR spectra were measured with a Bruker AC 300 P NMR-spec-
trometer. 1H NMR spectra were recorded at 300.13 MHz and the
13C NMR spectra at 75.475 MHz. The solvent was used as internal
reference. The imidazoles 1a–j were prepared with some modifica-
tions according to known procedures [63,66].
Fig. 1. ORTEP plot of the solid state structure of compound 3a. Thermal ellipsoids
are drawn at the 50% probability level. Hydrogen atoms are plotted as balls of
arbitrary radii.
Table 1
Selected geometrical parameters of the solid state structure of 3a.
3aa
Pd(1)–C(1)
Pd(1)–C(5)
Pd(1)–I(1)
Pd(1)–I(2)
N(2)–C(4)–N(4)
C(1)–Pd(1)–C(5)
C(1)–Pd(1)–I(1)
I(1)–Pd(1)–I(2)
N(1)–C(1)–Pd(1)–I(1)
Pd(1)–C(1)–N(2)–C(4)
1.991(4)
1.998(4)
2.6649(4)
2.6516(5)
108.9(3)
83.98(17)
88.90(12)
93.35(14)
56.96(1)
ꢁ8.89(4)
4.2. Synthesis of the imidazoles
4.2.1. (S)-2-(1-Imidazolyl)-propionicacidmethylester 1a
A mixture of formaldehyde (37% solution in water, 17.12 mL,
0.22 mol formaldehyde) and glyoxal (40% solution in water,
a
Distances in angstroms (Å) and angles in degrees (°).
25.13 mL, 0.22 mol glyoxal) was heated to 50 °C. Meanwhile L-ala-
nine (20 g, 0.22 mol), sodium hydroxide (8.8 g, 0.22 mol) and
ammonia (25% solution in water, 16.47 mL, 0.22 mol ammonia)
were put together and water was added until all components were
dissolved. This solution was added dropwise to the formaldehyde
glyoxal mixture over 0.5 h. The reaction was stirred at 50 °C for
4 h. Afterwards the solvent was removed in vacuo.
The obtained solid was dissolved in methanol and cooled to
0 °C. Thionyl chloride (3.26 mL, 0.44 mol) was added slowly over
a period of 2 h, the mixture was then warmed up to room temper-
ature and stirred for 48 h. Removal of the solvent under reduced
pressure lead to an oily substance, which was treated with a satu-
rated sodium carbonate water solution to adjust the pH (8–9). The
product was extracted with ethyl acetate, the organic layer dried
with sodium sulfate and the solvent evaporated in vacuo. The
product was purified by column chromatography (ethyl acetate/
petroleum ether 4:1, silica gel 60G) to obtain an orange solid.
2.5. X-ray crystal structure of complex 3a
The solid state structure of the palladium complex 3a is given in
Fig. 1. The crystals were obtained by slow diffusion of methanol
into a DMSO solution of compound 3a. The substituents at the
imidazole have only a small effect on the geometry (Table 1) which
is in good agreement with the published solid state structure of
1,10-dimethyl-3,30-methylenediimidazoline-2,20-diylidenepalladi-
um(II) diiodide [69]. The major difference is the asymmetry of 3a,
which can e.g. be found in the bond lengths of the Pd–I bonds (Ta-
ble 1). The central six-membered ring of 3a shows the expected
boat conformation, which has already been observed for many
other palladium(II)- and platinum(II)-NHC bishalogene complexes
[12,52,53].
Yield: 17.46 g (52%). m.p. = 33 °C. ½a D25
ꢀ
= +8.3 (c = 0.09 mol/L, meth-
anol). 1H NMR (DMSO-d6): d 1.64 (d, J = 7.4 Hz, 3H, CH3), 3.68 (s,
3H, OCH3), 5.25 (q, J = 7.4 Hz, 1H, CH), 6.91 (s, 1H, NCHCHN), 7.24
(s, 1H, NCHCHN), 7.72 (s, 1H, NCHN) ppm. 13C NMR (DMSO-d6): d
17.95 (CH3), 52.49 (OCH3), 53.85 (CH), 118.52 (NCHCHN), 128.22
(NCHCHN), 136.88 (NCHN), 171.05 (CO) ppm. C7H10N2O2
(154.17): Calc.: C, 54.54; H, 6.54; N, 17.87. Found: C, 54.23; H,
6.54; N, 17.87%. MS (ESI): m/z = 154.9 [M+]. IR 3110, 3027, 2964,
3. Conclusion
Although we had been aware of the potential lability of the chi-
ral center we intended to create the chiral center as close as possi-
ble to the metal atom. A variety of natural L-amino acids could be
converted successfully to chiral imidazoles and the corresponding
chiral bisimidazolium salts. The new synthetic route offers the pos-
sibility for variation of the side chain R1 through the amino acid
and R2 by choice of the alcohol during the esterification. After
optimization of the temperature program we succeeded in the
synthesis of palladium(II)- and platinum(II) N-heterocyclic biscar-
bene complexes. Unfortunately, our initial concerns were con-
1728, 1246, 1073, 751, 661 cmꢁ1
.
4.2.2. (S)-2-(1-Imidazolyl)-propionicacidethylester 1b
The synthesis was performed following the procedure described
above for the preparation of 1a using 0.045 mol L-alanine (4 g) and

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A. Meyer et al. / Journal of Organometallic Chemistry 694 (2009) 1861–1868
ethanol in the esterification step. The product was obtained as a
7.32 (s, 1H, NCHCHN), 7.81 (s, 1H, NCHN) ppm. 13C NMR (DMSO-
d6): d 20.96 (CH3), 22.52 (CH3), 24.22 ((CH3)2CHCH2), 40.33 (CH2),
52.46 (OCH3), 56.79 (CH2CHCO), 118.63 (NCHCHN), 128.28
(NCHCHN), 137.34 (NCHN), 170.87 (CO) ppm. C10H16N2O2
(196.25): Calc.: C, 61.20; H, 8.22; N, 14.17. Found: C, 61.23; H,
8.33; N, 14.06%. MS (ESI): m/z = 196 [M+]. IR 2957, 1742, 1199,
yellow oil. Yield: 2.22 g (29%). ½a D25
ꢀ
= +12.5 (c = 0.09 mol/L, metha-
nol). 1H NMR (DMSO-d6): d 1.18 (t, J = 7.1 Hz, 3H, OCH2CH3), 1.64
(d, J = 7.3 Hz, 3H, CH3), 4.13 (q, J = 7.1 Hz, 2H, OCH2CH3), 5.21 (q,
J = 7.3 Hz, 1H, CH), 6.90 (s, 1H, NCHCHN), 7.23 (s, 1H, NCHCHN),
7.71 (s, 1H, NCHN) ppm. 13C NMR (DMSO-d6): d 13.89 (CH2CH3),
17.96 (CHCH3), 53.91 (CH), 61.23 (OCH2), 118.49 (NCHCHN),
128.15 (NCHCHN), 136.83 (NCHN), 170.52 (CO) ppm. C8H12N2O2
(168.20): Calc.: C, 57.13; H, 7.19; N, 16.66. Found: C, 57.22; H,
7.28; N, 16.76%. MS (ESI): m/z = 168 [M+]. IR 2986, 1736, 1192,
662 cmꢁ1
.
4.2.7. (2S,3S)-2-(1-Imidazolyl)-3-methylpentanoicacidmethylester 1g
The synthesis was performed following the procedure described
1089, 1017, 662 cmꢁ1
.
above for the preparation of 1a using 0.03 mol
The product was obtained as an orange oil. Yield: 3.56 g (60%).
= +13.2 (c = 0.08 mol/L, methanol). 1H NMR (DMSO-d6): d
L-isoleucine (4.00 g).
4.2.3. (S)-2-(1-Imidazolyl)-propionicacidbutylester 1c
The synthesis was performed following the procedure described
above for the preparation of 1a using 0.056 mol L-alanine (5 g) and
½ ꢀ
a 2D5
0.88 (t, J = 7.2 Hz, 3H, CH3CH2), 0.98 (d, J = 6.8 Hz, 3H, CH3CH),
1.01–1.19 (m, 2H, CH3CH2), 2.23–2.27 (m, 1H, CH3CH), 3.80 (s,
3H, CH3O), 4.93 (d, J = 9.4 Hz, 1H, CH3CH2CH(CH3)CH), 7.01 (s, 1H,
NCHCHN), 7.34 (s, 1H, NCHCHN), 7.82 (s, 1H, NCHN) ppm. 13C
NMR (DMSO-d6): d 10.47 (CH3CH2), 15.29 (CH3CH), 24.33 (CH2),
37.14 (CH3CH), 52.41 (OCH3), 63.52 (CH2CH(CH3)CH), 118.91
(NCHCHN), 128.42 (NCHCHN), 137.48 (NCHN), 170.29 (CO) ppm.
C10H16N2O2 (196.25): Calc.: C, 61.20; H, 8.22; N, 14.17. Found: C,
61.00; H, 8.35; N, 13.94%. MS (ESI): m/z = 196 [M+]. IR 2965,
butanol in the esterification step. The product was obtained as a
yellow oil. Yield: 6.94 g (63%). ½a D25
ꢀ
= +7.4 (c = 0.07 mol/L, metha-
nol). 1H NMR (DMSO-d6): d 0.86 (t, J = 7.4 Hz, 3H, O(CH2)3CH3),
1.21–1.33 (m, 2H, OCH2CH2CH2CH3), 1.49–1.58 (m, 2H,
OCH2CH2CH2CH3), 1.64 (d, J = 7.3 Hz, 3H, CH3), 4.08 (t, J = 6.5 Hz,
2H, OCH2), 5.12 (q, J = 7.3 Hz, 1H, CH), 6.89 (s, 1H, NCHCHN), 7.22
(s, 1H, NCHCHN), 7.70 (s, 1H, NCHN) ppm. 13C NMR (DMSO-d6): d
13.46 (CH2CH3), 17.89 (CHCH3), 18.41 (CH2), 29.96 (CH2), 53.92
(CH), 64.80 (OCH2), 118.47 (NCHCHN), 128.16 (NCHCHN), 136.85
(NCHN), 170.56 (CO) ppm. C10H16N2O2 (196.25): Calc.: C, 61.20;
H, 8.22; N, 14.27. Found: C, 61.17; H, 8.35; N, 14.29%. MS (ESI):
1742, 1198, 741, 662 cmꢁ1
.
4.2.8. (S)-2-(1-Imidazolyl)-3-phenylpropionicacidmethylester 1h
The synthesis was performed following the procedure described
above for the preparation of 1a using 0.03 mol L-phenylalanine
m/z = 197 [M+]. IR 2960, 1737, 1188, 1088, 662 cmꢁ1
.
(5.00 g). The product was obtained as a brown oil. Yield: 2.52 g
4.2.4. (S)-2-(1-Imidazolyl)-3-methylbutyricacidmethylester 1d
(36%). ½a 2D5
ꢀ
= ꢁ59.5 (c = 0.08 mol/L, methanol). 1H NMR (DMSO-
The synthesis was performed following the procedure described
d6): d 3.27–3.46 (m, 2H, CH2), 3.68 (s, 3H, OCH3), 5.39–5.44 (m,
1H, arom. CH), 6.83 (s, 1H, NCHCHN), 7.09–7.25 (m, 6H, NCHCHN,
arom. CH), 7.57 (s, 1H, NCHN) ppm. 13C NMR (DMSO-d6): d 37.48
(CH2), 52.56 (OCH3), 59.59 (CH), 118.67 (NCHCHN), 126.7 (CH),
128.09 (NCHCH), 128.24 (arom. CH), 128.75 (arom. CH), 136.25
(arom. C), 137.29 (NCHN), 170.06 (CO) ppm. C13H14N2O2
(230.27): Calc.: C, 67.81; H, 6.13; N, 12.17. Found: C, 67.19; H,
6.20; N, 11.79%. MS (ESI): m/z = 230 [M+]. IR 2954, 1740, 1172,
above for the preparation of 1a using 0.034 mol
The product was obtained as a yellow oil. Yield: 3.83 g (62%).
= +9.2 (c = 0.06 mol/L, methanol). 1H NMR (DMSO-d6): d 0.71
L-valine (3.98 g).
½ ꢀ
a 2D5
(d, J = 6.7 Hz, 3H, CH3), 0.91 (d, J = 6.7 Hz, 3H, CH3,), 2.30–2.42 (m,
1H, (CH3)2CH), 3.7 (s, 3H, OCH3), 4.8 (d, J = 9.1 Hz, 1H, (CH3)2CHCH),
6.92 (s, 1H, NCHCHN), 7.24 (s, 1H, NCHCHN), 7.71 (s, 1H, NCHN)
ppm. 13C NMR (DMSO-d6): d 18.11 (CH3), 18.89 (CH3), 31.16 (CH),
52.36 (OCH3), 64.52 (CH), 118.84 (NCHCHN), 128.34 (NCHCHN),
137.42 (NCHN), 170.14 (CO) ppm. C9H14N2O2 (182.22): Calc.: C,
59.32; H, 7.74; N, 15.37. Found: C, 59.54; H, 7.84; N, 15.40%. MS
745, 699, 660 cmꢁ1
.
4.2.9. (S)-2-(1-Imidazolyl)-4-methylsulfanylbutyricacidmethylester 1i
(ESI): m/z = 183 [M+]. IR 2967, 1741, 1199, 746, 662 cmꢁ1
.
The synthesis was performed following the procedure described
above for the preparation of 1a using 0.026 mol L-methionine
4.2.5. (S)-2-(1-Imidazolyl)-3-methylbutyricacidethylester 1e
(4.00 g). The product was obtained as a red-brown oil. Yield:
The synthesis was performed following the procedure described
above for the preparation of 1a using 0.034 mol -valine (3.98 g) as
3.11 g (54%). ½a 2D5
ꢀ
= ꢁ31.3 (c = 0.09 mol/L, methanol). 1H NMR
L
(DMSO-d6): d 2.02 (s, 3H, SCH3), 2.24–2.35 (m, 4H, CH2CH2), 3.68
(s, 3H, OCH3), 5.23 (t, J = 6.3 Hz, 1H, CH), 6.92 (s, 1H, NCHCHN),
7.25 (s, 1H, NCHCHN), 7.71 (s, 1H, NCHN) ppm. 13C NMR (DMSO-
d6): d 14.5 (SCH3), 29.26 (CH2), 31.1 (CH2), 52.65 (OCH3), 57.28
(CH), 118.67 (NCHCHN), 128.61 (NCHCHN), 137.52 (NCHN),
170.29 (CO) ppm. C9H14N2O2S (214.28): Calc.: C, 50.45; H, 6.59;
N, 13.07; S, 14.96. Found: C, 50.64; H, 6.76; N, 12.85; S, 14.33%.
well as ethanol in the esterification step. The product was obtained
as an orange oil. Yield: 1.65 g (25%). ½a D25
ꢀ
= +13.6 (c = 0.18 mol/L,
methanol). 1H NMR (DMSO-d6): d 0.78 (d, J = 6.7 Hz, 3H, CH3),
0.98 (d, J = 6.7 Hz, 3H, CH3), 1.28 (t, J = 7.1 Hz, 3H, OCH2CH3),
2.39–2.46 (m, 1H, (CH3)2CH), 4.18–4.30 (m, 2H, OCH2CH3), 4.83
(d, J = 9.1 Hz, 1H, (CH3)2CHCH), 6.99 (s, 1H, NCHCHN), 7.30 (s, 1H,
NCHCHN), 7.78 (s, 1H, NCHN) ppm. 13C NMR (DMSO-d6): d 13.90
(OCH2CH3), 18.12 (CH3), 18.87 (CH3), 31.22 ((CH3)2CH), 61.22
(CH2), 64.63 ((CH3)2CHCH), 118.84 (NCHCHN), 128.31 (NCHCHN),
137.41 (NCHN), 169.61 (CO) ppm. C10H16N2O2 (196.25): Calc.: C,
61.20; H, 8.22; N, 14.27. Found: C, 61.26; H, 8.26; N, 14.22%. MS
MS (ESI): m/z = 214 [M+]. IR 2918, 1740, 1229, 733, 661 cmꢁ1
.
4.2.10. (S)-2-(1-Imidazolyl)-succinicaciddimethylester 1j
The synthesis was performed following the procedure described
above for the preparation of 1a using 0.034 mol -aspartate
L
(ESI): m/z = 196 [M+]. IR 2968, 1737, 1187, 1020, 737, 662 cmꢁ1
.
(4.53 g). The product was obtained as a yellow oil. Yield: 2.25 g
(31%). ½a 2D5
ꢀ
= ꢁ8.9 (c = 0.06 mol/L, methanol). 1H NMR (DMSO-d6):
4.2.6. (S)-2-(1-Imidazolyl)-4-methylpentanoicacidmethylester 1f
d 3.12–3.33 (m, 2H, CH2), 3.59 (s, 3H, OCH3), 3.67 (s, 3H, OCH3),
5.49–5.54 (m, 1H, CH), 6.88 (s, 1H, NCHCHN), 7.24 (s, 1H,
NCHCHN), 7.73 (s, 1H, NCHN) ppm. 13C NMR (DMSO-d6): d 36.38
(CH2), 51.84 (OCH3), 52.79 (OCH3), 54.88 (CH), 118.68 (NCHCHN),
128.43 (NCHCHN), 137.54 (NCHN), 169.35 (CO), 170.01 (CO)
ppm. C9H12N2O4S (212.27): Calc.: C, 50.94; H, 5.70; N, 13.20.
Found: C, 50.93; H, 5.86; N, 13.07%. MS (ESI): m/z = 212 [M+]. IR
The synthesis was performed following the procedure described
above for the preparation of 1a using 0.03 mol -leucine (4.00 g).
The product was obtained as an orange oil. Yield: 4.15 g (71%).
= +1.7 (c = 0.06 mol/L, methanol). 1H NMR (DMSO-d6): d 0.90
L
½ ꢀ
a 2D5
(d, J = 6.6 Hz, 3H, CH3), 0.94 (d, J = 6.5 Hz, 3H, CH3), 1.11–1.30 (m,
1H, (CH3)2CH), 1.90–2.15 (m, 2H, CH2), 3.74 (s, 3H, OCH3), 5.20–
5.25 (m, J = 4.9 Hz, 1H, (CH3)2CHCH2CH), 6.97 (s, 1H, NCHCHN),
2956, 1730, 1167, 661 cmꢁ1
.

A. Meyer et al. / Journal of Organometallic Chemistry 694 (2009) 1861–1868
1865
4.3. Synthesis of the bisimidazolium salts
2H, (CH3)2CH), 3.78 (s, 6H, OCH3), 5.39 (d, J = 7.7 Hz, 2H,
(CH3)2CHCH), 6.74 (s, 2H, NCH2 N), 8.02 (s, 4H, NCHCHN), 8.11 (s,
2H, NCHN) ppm. 13C NMR (DMSO-d6): d 18.04 (CH3), 18.46 (CH3),
31.48 ((CH3)2CH), 53.25 (OCH3), 58.85 (NCH2N), 66.66 (CH),
121.94 (NCHCHN), 123.76 (NCHCHN), 138.17 (NCHN), 168.18
(CO) ppm. C19H30I2N4O4 (632.27): Calc.: C, 36.09; H, 4.78; N,
8.86. Found: C, 36.22; H, 4.58; N, 8.84%. IR 3051, 1741, 1158,
4.3.1. 1,10-Bis-[(S)-1-methoxycarbonylethyl]-3,30-
methylenediimidazolium diiodide 2a
The imidazole 1a (3.99 g, 0.026 mol), diiodomethane (1.04 mL,
0.013 mol) and 10 mL acetonitrile were added to a ACE pressure
tube. The reaction mixture was stirred for 12 h at 70 °C and 3 h
at 80 °C. The product was precipitated with diethyl ether and
washed with ethyl acetate. The product was obtained as a pale yel-
769, 633 cmꢁ1
.
low powder. Yield: 3.15 g (42%). ½a D25
ꢀ
= +2.6 (c = 0.02 mol/L, meth-
4.3.5. 1,10-Di-[(S)-1-ethoxycarbonyl-2-methylpropyl))-3,30-
methylenediimidazolium diiodide 2e
anol). m.p.: decomposition at 170.8 °C. 1H NMR (DMSO-d6): d 1.78
(d, J = 7.3 Hz, 6H, CH3), 3.75 (s, 6H, OCH3), 5.68 (q, J = 7.3 Hz, 2H,
CH), 6.73 (s, 2H, NCH2 N), 8.04 (s, 2H, NCHCHN), 8.08 (s, 2H,
NCHCHN), 9.59 (s, 2H, NCHN) ppm. 13C NMR (DMSO-d6): d 16.95
(CH3), 53.15 (OCH3), 57.08 (CH), 58.45 (NCH2N), 121.94 (NCHCHN),
122.53 (NCHCHN), 137.89 (NCHN), 168.89 (CO) ppm. C15H22 I2N4O4
(576.16): Calc.: C, 31.27; H, 3.85; N, 9.72. Found: C, 31.28; H, 3.71;
The imidazole 1e (0.65 g, 3.3 mmol), diiodomethane (0.13 mL,
1.7 mmol) and 5 mL acetonitrile were added to a ACE pressure
tube. The reaction mixture was stirred for 12 h at 70 °C and 8 h
at 80 °C. The product was precipitated with diethyl ether and
washed with ethyl acetate. The product was obtained as a pale yel-
low powder. Yield: 0.36 g (32%). m.p.: decomposition at 188 °C.
N, 9.82%. IR 3071, 1746, 1166, 761, 616 cmꢁ1
.
½
a 2D5
ꢀ
= ꢁ16.7 (c = 0.02 mol/L, methanol). 1H NMR (DMSO-d6): d
0.86 (d, J = 6.7 Hz, 6H, CH3CH), 0.97 (d, J = 6.7 Hz, 6H, CH3CH),
1.26 (t, J = 7.1 Hz, 6H, CH3CH2O) 2.43–2.52 (m, 2H, (CH3)2CH),
4.19–4.32 (m, 4H, OCH2CH3), 5.40 (d, J = 7.6 Hz, 2H, (CH3)2CHCH),
6.74 (s, 2H, NCH2N), 8.01 (s, 2H, NCHCHN), 8.12 (s, 2H, NCHCHN),
9.70 (s, 2H, NCHN) ppm. 13C NMR (DMSO-d6): d 13.86 (CH3CH),
17.95 (CH3CH), 18.36 (CH3CH2O), 31.44 ((CH3)2CH), 58.80 (NCH2N),
62.31 (CH3CH2O), 66.61 ((CH3)2CHCH), 121.85 (NCHCHN), 123.74
(NCHCHN), 138.07 (NCHN), 167.59 (CO) ppm. C21H34I2N4O4
(660.33): Calc.: C, 38.20; H, 5.19; N, 8.48. Found: C, 37.50; H,
4.3.2. 1,10-Bis-[(S)-1-ethoxycarbonylethyl]-3,30-
methylenediimidazolium diiodide 2b
The imidazole 1b (1.12 g, 6.7 mmol), diiodomethane (0.27 mL,
3.3 mmol) and 4 mL acetonitrile were added to a ACE pressure
tube. The reaction mixture was stirred for 12 h at 70 °C and 4 h
at 80 °C. The product was precipitated with diethyl ether and
washed with ethyl acetate. The product was obtained as a pale yel-
low powder. Yield: 1.01 g (50%). m.p.: decomposition at 107 °C.
½
a 2D5
ꢀ
= +3.7 (c = 0.01 mol/L, methanol). 1H NMR (DMSO-d6): d 1.23
4.99; N, 8.46%. IR 3026, 1732, 1199, 1158, 1017, 770 cmꢁ1
.
(t, J = 7.1 Hz, 6H, CH2CH3), 1.78 (d, J = 7.3 Hz, 6H, CHCH3), 4.11 (q,
J = 6.9 Hz, 4H, CH2CH3), 5.67 (q, J = 7.3 Hz, 2H, CHCH3), 6.75 (s,
2H, NCH2 N), 8.05 (s, 2H, NCHCHN), 8.08 (s, 2H, NCHCHN), 9.61
(s, 2H, NCHN) ppm. 13C NMR (DMSO-d6): d 13.83 (CH2CH3), 17.06
(CHCH3), 57.32 (CHCH3), 58.53 (NCH2N), 62.26 (CH2CH3), 121.98
(NCHCHN), 123.04 (NCHCHN), 137.97 (NCHN), 168.5 (CO) ppm.
C17H26I2N4O4 (604.22): Calc.: C, 33.79; H, 4.34; N, 9.27. Found: C,
4.3.6. 1,10-Bis-[(S)-1-methoxycarbonyl-3-methylbutyl]-3,30-
methylenediimidazolium diiodide 2f
The imidazole 1f (5.18 g, 0.026 mol), diiodomethane (1.05 mL,
0.013 mol) and 7 mL acetonitrile were added to a ACE pressure
tube. The reaction mixture was stirred for 48 h at 70 °C and 24 h
at 80 °C. The product was precipitated with diethyl ether and
washed with ethyl acetate. The product was obtained as a colorless
powder. Yield: 2.24 g (26%). m.p.: decomposition at 127 °C.
33.75; H, 4.37; N, 9.25%. IR 3072, 1747, 1165, 1014, 751, 615 cmꢁ1
.
4.3.3. 1,10-Bis-[(S)-1-butoxycarbonylethyl]-3,30-
methylenediimidazolium diiodide 2c
½
a 2D5 = +3.4 (c = 0.02 mol/L, methanol). 1H NMR (DMSO-d6): d 0.88
ꢀ
(d, J = 6.6 Hz, 6H, CH3), 0.92 (d, J = 6.5 Hz, 6H, CH3), 1.27–1.40 (m,
2H, (CH3)2CH), 1.99–2.13 (m, 4H, CH2), 3.76 (s, 6H, OCH3), 5.62–
5.67 (m, 2H, (CH3)2CHCH2CH), 6.74 (s, 2H, NCH2 N), 8.10 (s, 4H,
NCHCHN), 9.69 (s, 2H, NCHN) ppm. 13C NMR (DMSO-d6): d 21.04
(CH3), 22.28 (CH3), 24.10 ((CH3)2CH), 39.50 (CHCH2CH), 53.37
(OCH3), 58.92 (NCH2N), 60.00 ((CH3)2CHCH2CH), 122.32
(NCHCHN), 123.21 (NCHCHN), 138.25 (NCHN), 168.81 (CO) ppm.
C21H34I2N4O4 (660.33): Calc.: C, 38.20; H, 5.19; N, 8.48. Found: C,
38.09; H, 5.22; N, 8.51%. IR 3058, 2961, 1736, 1208, 1168, 764,
The imidazole 1c (2 g, 0.01 mol), diiodomethane (0.40 mL,
0.005 mol) and 4 mL acetonitrile were added to a ACE pressure
tube. The reaction mixture was stirred for 12 h at 70 °C and 4 h
at 80 °C. The product was precipitated with diethyl ether and
washed with ethyl acetate. The product was obtained as a pale yel-
low powder. Yield: 1.85 g (56%). m.p.: decomposition at 123.5 °C.
½
a 2D5 = +3.4 (c = 0.01 mol/L, methanol). 1H NMR (DMSO-d6): d 0.88
ꢀ
(t, J = 7.4 Hz, 6H, O(CH2)3CH3), 1.25–1.38 (m, 4H, OCH2CH2CH2CH3),
1.54–1.63 (m, 4H, OCH2CH2CH2CH3), 1.78 (d, J = 7.3 Hz, 6H, CH3),
4.09–5.64 (m, 4H, OCH2), 5.68 (q, J = 7.3 Hz, 2H, CH), 6.73 (s, 2H,
NCH2N), 8.05 (s, 4H, NCHCHN), 9.58 (s, 2H, NCHN) ppm. 13C NMR
(DMSO-d6): d 13.47 (CH2CH3), 17.06 (CHCH3), 18.44 (CH2), 29.86
(CH2), 57.24 (CH), 59.11 (NCH2N), 65.83 (OCH2), 122.00 (NCHCHN),
123.10 (NCHCHN), 138.00 (NCHN), 168.57 (CO) ppm. C21H34I2N4O4
(660.33): Calc.: C, 38.20; H, 5.19; N, 8.48. Found: C, 38.21; H, 5.22;
631 cmꢁ1
.
4.3.7. 1,10-Bis-[(1S,2S)-1-methoxycarbonyl-2-methylbutyl)]-3,30-
methylenediimidazolium diiodide 2g
The imidazole 1 g (1.94 g, 9.9 mmol), diiodomethane (0.39 mL,
4.9 mmol) and 6 mL acetonitrile were added to a ACE pressure
tube. The reaction mixture was stirred for 24 h at 70 °C and 3 h
at 80 °C. The product was precipitated with diethyl ether and
washed with ethyl acetate. The product was obtained as a pale yel-
low powder. Yield: 1.09 g (34%). m.p.: decomposition at 150 °C.
N, 8.41%. IR 2958, 1748, 1196, 1167, 731, 615 cmꢁ1
.
4.3.4. 1,10-Bis-[(S)-1-methoxycarbonyl-2-methylpropyl]-3,30-
methylenediimidazolium diiodide 2d
½
a 2D5 = +25.1 (c = 0.02 mol/L, methanol). 1H NMR (DMSO-d6): d
ꢀ
The imidazole 1d (3.66 g, 0.02 mol), diiodomethane (0.80 mL,
0.01 mol) and 5 mL acetonitrile were added to a ACE pressure tube.
The reaction mixture was stirred for 12 h at 70 °C and 0.5 h at
80 °C. The product was precipitated with diethyl ether and washed
with ethyl acetate. The product was obtained as a pale yellow pow-
0.85 (t, J = 7.5 Hz, 6H, CH3CH2), 0.94 (d, J = 6.8 Hz, 6H, CH3CH),
1.01–1.31 (m, 4H, CH3CH2), 2.20–2.28 (m, 2H, CH3CH), 3.79 (s,
6H, CH3O), 5.43 (d, J = 7.7 Hz, 2H, CH3CH2CH(CH3)CH), 6.73 (s, 2H,
NCH2N), 8.04 (s, 2H, NCHCHN), 8.12 (s, 2H, NCHCHN), 9.71 (s, 2H,
NCHN) ppm. 13C NMR (DMSO-d6):
d 10.73 (CH3CH2), 14.79
der. Yield: 2.78 g (44%). m.p.: decomposition at 167 °C. ½a D25
ꢀ
= +24.2
d 0.85 (d,
(CH3CH), 24.39 (CH2), 37.45 (CH3CH), 53.20 (OCH3), 58.79 (NCH2N),
65.85 (CH2CH(CH3)CH), 121.94 (NCHCHN), 123.69 (NCHCHN),
138.18 (NCHN), 168.17 (CO) ppm. C21H34N4O4I2 (660.33): Calc.:
(c = 0.01 mol/L, methanol). 1H NMR (DMSO-d6):
J = 6.7 Hz, 6H, CH3), 0.95 (d, J = 6.7 Hz, 6H, CH3), 2.39–2.51 (m,

1866
A. Meyer et al. / Journal of Organometallic Chemistry 694 (2009) 1861–1868
C, 38.20; H, 5.19; N, 8.48. Found: C, 38.23; H, 5.23; N, 8.43%. IR
3045, 2967, 1740, 1203, 1157, 766, 633 cmꢁ1
4.4.3. 1,10-Bis-(1-methoxycarbonyl-2-methylpropyl)-3,30-
.
methylenediimidazoline-2,20-diylidene-palladium(II) diiodide 3c
Palladium(II) acetate (0.071 g, 0.32 mmol) and 2d (0.2 g,
0.32 mmol) were dissolved in 5 mL dimethylsulfoxide. The mixture
was stirred for 1 h at 40 °C, 3 h at 60 °C, 4 h at 80 °C, 12 h at r.t. and
1 h at 100 °C. The dimethylsulfoxide was removed in vacuum and
the resulting solid was washed with cold tetrahydrofuran and
methanol. The product was obtained as a yellow powder. Yield:
0.192 g (82%). m.p.: decomposition at 240 °C. 1H NMR (DMSO-
d6): d 0.47 (d, J = 6.7 Hz, CH3), 0.72 (d, J = 6.5 Hz, CH3), 1.06 (d,
J = 6.5 Hz, CH3), 2.32–2.51 (m overlapped by DMSO-d6, (CH3)2CH)),
3.63 (s, OCCH3), 3.72 (s, OCCH3), 5.60–5.72 (br, (CH3)2CHCH), 5.85–
5.98 (br, (CH3)2CHCH), 6.36 (s, NCH2N), 7.48 (s, NCHCHN), 7.64 (s,
NCHCHN), 7.70–7.72 (m, NCHCHN) ppm. 13C NMR (DMSO-d6): d
18.41 (CH3), 18.79 (CH3), 19.05 (CH3), 19.10 (CH3), 30.20
((CH3)2CH), 31.11 ((CH3)2CH), 52.34 (OCCH3), 52.40 (OCCH3),
59.31 ((CH3)2CHCH), 62.82 (NCH2N), 120.94 (NCHCHN), 121.69
(NCHCHN), 121.96 (NCHCHN), 122.19 (NCHCHN), 169.10 (CO),
169.66 (CO) ppm. C19H28N4O4I2Pd (736.68): Calc.: C, 30.98; H,
3.83; N, 7.61. Found: C, 30.93; H, 3.48; N, 7.41%. IR 3163, 3127,
4.3.8. 1,10-Bis-[(S)-1-methoxycarbonyl-2-phenylethyl]-3,30-
methylenediimidazolium diiodide 2h
The imidazole 1 h (2 g, 8.7 mmol), diiodomethane (0.35 mL,
4.3 mmol) and 7 mL acetonitrile were added to a ACE pressure
tube. The reaction mixture was stirred for 12 h at 70 °C and 3 h
at 80 °C. The product was precipitated with diethyl ether and
washed with ethyl acetate. The product was obtained as a yellow
powder. Yield: 0.83 g (26%). m.p.: decomposition at 81 °C.
½
a 2D5
ꢀ
= ꢁ2.2 (c = 0.01 mol/L, methanol). 1H NMR (DMSO-d6): d
3.41–3.72 (m, 4H, CH2), 3.80 (s, 6H, OCH3), 5.98–6.05 (m, 2H,
CH), 6.57–6.60 (m, 2H, NCH2N), 7.10–7.22 (m, 10H, CH arom.),
7.72 (s, 1H, NCHCHN), 7.74 (s, 1H, NCHCHN), 8.05 (s, 2H, NCHCHN),
9.43 (s, 1H, NCHN), 9.46 (s, 1H, NCHN) ppm. 13C NMR (DMSO-d6): d
36.99 (CH2), 53.26 (OCH3), 58.29 (NCH2N), 62.39 (CH), 62.48 (CH),
121.60 (NCHCHN), 123.30 (NCHCHN), 123.40 (NCHCHN), 127.25
(CH arom.), 128.55 (CH arom.), 134.38 (C arom.), 137.87 (NCHN),
137.91 (NCHN), 167.65 (CO) ppm. C27H30I2N4O4 (728.36): Calc.:
C, 44.52; H, 4.15; N, 7.69. Found: C, 44.34; H, 4.04; N, 7.54%. IR
2969, 1739, 1458, 1414, 1201, 1168, 993, 799, 744, 727, 671 cmꢁ1
.
3059, 1742, 1158, 748, 701, 614 cmꢁ1
.
4.4.4. 1,10-Bis-(1-methoxycarbonyl-2-methylpropyl)-3,30-
methylenediimidazoline-2,20-diylidene-platinum(II) diiodide 3d
4.4. Synthesis of the metal carbene complexes
Platinum(II) acetylacetonate (0.062 g, 0.16 mmol) and 2d (0.1 g,
0.16 mmol) were dissolved in 6 mL dimethylsulfoxid. The mixture
was stirred for 2 h at 40 °C, 1.5 h at 60 °C, 1.5 h at 80 °C, 1 h at
100 °C, 12 h at r.t. and 1 h at 130 °C. The dimethylsulfoxide was re-
moved in vacuum and the resulting solid was washed with cold
tetrahydrofuran and methanol. The product was obtained as a yel-
low powder. Yield: 0.033 g (30%). m.p.: decomposition at 244 °C.
1H NMR (DMSO-d6): d 0.43 (d, J = 6.7 Hz, CH3), 0.70 (d, J = 6.7 Hz,
CH3), 1.05–1.10 (m, CH3), 2.29–2.31 (m, (CH3)2CH), 2.50–2.53 (m,
(CH3)2CH, overlapped by DMSO-d6), 3.62 (s, OCH3), 3.71 (s,
OCH3), 5.78 (d, J = 8 Hz, CH), 6.02–6.07 (m, NCH2N and CH), 6.17
(d, J = 13.2 Hz, NCH2N), 7.45–7.46 (m, NCHCHN), 7.60–7.63 (m,
NCHCHN) ppm. 13C NMR (DMSO-d6): d 18.36 (CH3), 18.64 (CH3),
18.85 (CH3), 18.97 (CH3), 29.87 ((CH3)2CH), 31.04 ((CH3)2CH),
52.09 (OCH3), 52.19 (OCH3), 62.13 (NCH2N), 65.70 (CH), 68.48
(CH), 120.26 (NCHCHN), 120.77 (NCHCHN), 120.90 (NCHCHN),
150.80 (NCN), 151.62 (NCN), 168.87 (CO), 169.41 (CO) ppm.
C19H28N4O4I2Pt (825.35): Calc.: C, 27.65; H, 3.42; N, 6.79. Found:
C, 27.44; H, 3.42; N, 6.53%. IR 2971, 1734, 1305, 1206, 729,
4.4.1. 1,10-Bis-(1-methoxycarbonylethyl)-3,30-
methylenediimidazoline-2,20-diylidenepalladium(II) diiodide 3a
Palladium(II) acetate (0.071 g, 0.32 mmol) and 2a (0.2 g,
0.32 mmol) were dissolved in 5 mL dimethylsulfoxide. The mixture
was stirred for 1 h at 40 °C, 3 h at 60 °C, 4 h at 80 °C, 12 h at r.t. and
1 h at 100 °C. After removal of the dimethylsulfoxide in vacuum,
the resulting solid was washed with cold tetrahydrofuran and
methanol. The product was obtained as a yellow powder. Yield:
0.093 g (39%). m.p.: decomposition at 250 °C. 1H NMR (DMSO-
d6): d 1.50 (d, J = 7.5 Hz, CH3), 1.69 (d, J = 7.1 Hz, CH3), 1.70 (d,
J = 7.4 Hz, CH3), 3.60 (s, OCCH3), 3.63 (s, OCCH3), 3.69 (s, OCCH3),
6.02 (br, CH3CH), 6.23 (br, CH3CH) 6.24 (br, CH3CH), 6.33 (s,
NCH2N), 7.54–7.58 (m, NCHCHN), 7.67–7.68 (m, NCHCHN) ppm.
13C NMR (DMSO-d6): d 16.28 (CH3), 16.91 (CH3), 18.59 (CH3),
52.57 (OCCH3), 52.60 (OCCH3), 52.75 (OCCH3), 58.78 (CH3CH),
62.86 (NCH2N), 119.90 (NCHCHN), 120.14 (NCHCHN), 120.92
(NCHCHN), 122.17 (NCHCHN), 122.44 (NCHCHN), 169.85 (CO),
.
169.88 (CO) 170.11 (CO) ppm. C15H20N4O4I2Pd 0.5 C2H6SO: Calc.:
C, 26.71; H, 3.22; N, 7.79; S, 2.23. Found: C, 26.94; H, 3.19; N, 7.52;
S, 2.11%. IR 3154, 3113, 2943, 1741, 1462, 1414, 1309, 1206, 1176,
680 cmꢁ1
.
1087, 980, 752, 678 cmꢁ1
.
4.5. Structure determination of compound 3a
4.4.2. 1,10-Bis-(1-methoxycarbonylethyl)-3,30-
Single crystals suitable for the X-ray diffraction study were
grown by condensing methanol into a solution of 3a in DMSO.
The crystal was stored under perfluorinated ether, transferred on
a glass capillary and fixed. Preliminary examination and data col-
lection were carried out on an area detecting system (kappa-
CCD; Nonius) at the window of a sealed X-ray tube (Nonius,
methylenediimidazoline-2,20-diylideneplatinum(II) diiodide 3b
Platinum(II) acetylacetonate (0.034 g, 0.087 mmol) and 2a
(0.05 g, 0.087 mmol) were dissolved in 3 mL dimethylsulfoxide.
The mixture was stirred for 3 h at 40 °C, 3 h at 60 °C, 1.5 h at
80 °C, 1 h at 100 °C, 12 h at rt and 1 h at 130 °C. The dimethylsulf-
oxide was removed in vacuum and the resulting solid was washed
with cold tetrahydrofuran and methanol. The product was ob-
tained as a yellow powder. Yield: 0.032 g (45%). m.p.: decomposi-
tion at 295 °C. 1H NMR (DMSO-d6): d 1.45 (d, J = 7.5 Hz, CH3), 1.71
(d, J = 7.4, CH3), 3.61 (s, OCH3), 3.69 (s, OCH3), 6.03–6.31 (m,
NCH2N, CH), 7.53–7.54 (m, NCHCHN), 7.60–7.62 (m, NCHCHN)
ppm. 13C NMR (DMSO-d6): d 16.15 (CH3), 18.31 (CH3), 52.56
(OCH3), 52.70 (OCH3), 57.91 (CH), 58.93 (CH), 62.30 (NCH2N),
119.39 (NCHCHN), 120.38 (NCHCHN), 121.07 (NCHCHN), 121.41
(NCHCHN), 150.80 (NCN), 152.36 (NCN), 169.71 (CO), 169.91 (CO)
FR590)
and
graphite-monochromated
Mo–K
radiation
a
(k = 0.71073 Å). The unit cell parameters were determined. Data
collection was performed at 198 K and all reflexes were integrated.
Raw data were corrected for Lorentz, polarization, decay and
absorption effects. The absorption correction was applied using
ꢀ
SADABS [70]. We used the non-chiral spacegroup P1 to solve the
structure because the twinned crystal could not be solved in the
chiral spacegroup P1. After merging the independent reflections
were used for all calculations. The structure was solved by a com-
bination of direct methods [71] and difference Fourier syntheses
[72]. All non-hydrogen atoms were refined with anisotropic dis-
placement parameters. All hydrogen atoms were calculated in
ideal positions using the SHELXL riding model. Full-matrix least-
.
ppm. C15H20N4O4I2Pt 0.65 C2H6SO: Calc.: C, 23.87; H, 2.94; N,
6.83; S, 2.54. Found: C, 23.81; H, 2.62; N, 6.64; S, 2.81%. IR 3155,
3114, 1742, 1207, 1088, 750, 683 cmꢁ1
.

A. Meyer et al. / Journal of Organometallic Chemistry 694 (2009) 1861–1868
1867
Table 2
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Crystallographic data for complex 3a.
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1483.
3a
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Measurement
Formula
M. Taige
C15H20I2N4O4Pd ꢂ C2H6OS
Formula weight
Color/shape
Crystal system
Space group
a (Å)
680.55
Yellow/plate
Triclinic
ꢀ
P1 (No. 2)
8.842(5)
9.594(6)
14.449(11)
75.077(5)
84.914(6)
78.492(5)
1159.66(13)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
qcalc (g/cm3)
1.949
3.486
644
l
(mmꢁ1
)
F(000)
Diffractometer
Temperature (K)
hmin/max (°)
Data collected (h, k, l)
Reflections integrated
Independent reflections (all data)
Observed reflections [I > 2
Parameter refined
Nonius kappa-CCD
198
2
3.21/26.00
10, 11, 17
25584
4552
4074
r
(I)]
239
R1 (observed/all data)
wR2 (observed/all data)
Goodness-of-fit
0.0317/0.0382
0.0741/0.0767
1.125
0.862/ꢁ1.149
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Residual electron density (e Åꢁ3
)
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1268.
squares refinements with 239 parameters were carried out by min-
imizing
P
2
wðF2o ꢁ F2c Þ with the SHELXL-97 weighting scheme and
stopped at shift/err <0.001. Details of the structure determination
are given in Table 2. Neutral-atom scattering factors for all atoms
and anomalous dispersion corrections for the non-hydrogen atoms
were taken from the International Tables for Crystallography [73]. All
calculations were performed with the programs COLLECT [74], DIRAX
[75], EVALCCD [76], SIR92 [71], SADABS [70], the SHELXL-97 package
[72,77] and ORTEP-III [78]. In addition, one molecule DMSO became
apparent in the final difference Fourier maps but the severe disor-
der could not be modeled properly. This problem was solved by
using the PLATON [79] calc squeeze procedure.
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Acknowledgement
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We are grateful to the ‘‘Evonik Degussa GmbH” for the generous
donation of various amino acids.
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