Chiral variation of a hybrid bis(carbene-amido) ligand system

Article abstract of DOI:10.1021/om100048d

A simple synthetic strategy starting from a chiral amino acid was used to prepare a unique chiral tetradentate hybrid dianionic bis(carbene-amido) ligand precursor, which was subsequently used for the generation of a chiral nickel complex.

Full text of DOI:10.1021/om100048d

2868 Organometallics 2010, 29, 2868–2873
DOI: 10.1021/om100048d
Chiral Variation of a Hybrid Bis(carbene-amido) Ligand System
Franc-ois Jean-Baptiste dit Dominique, Heinz Gornitzka,* and Catherine Hemmert*
CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, F-31077 Toulouse Cedex 4,
France, and Universiteꢀ de Toulouse, UPS, INP, LCC, F-31077 Toulouse, France
Received January 21, 2010
A simple synthetic strategy starting from a chiral amino acid was used to prepare a unique chiral
tetradentate hybrid dianionic bis(carbene-amido) ligand precursor, which was subsequently used for
the generation of a chiral nickel complex.
Introduction
carbene ligand precursors containing phosphine,2 pyridine,
pyrimidine, or amine,3 amido,4 alkoxy, aryloxy, phenoxyi-
mine, or enolate,5 and oxazoline6 donor functions have been
synthesized. Their reactions with various bases have produced
a new versatile class of hybrid, potentially hemilabile NHC
ligands, whereas some of their complexes have been applied in
valuable catalytic transformations.2f,g,3a,3e-3k,4d,4e,5b,5d,7
During the past few years, we have worked on tetradentate
ligands such as salens8 and more recently on hybrid N-func-
tionalized bis(NHC) systems.9 In this context, we recently
reported photoluminescent dinuclear bis(NHC) gold(I) and
gold(III) complexes, in which the two NHCs are functiona-
lized by alcohol pendant arms. During the course of these
syntheses, we became interested in potentially tetradentate
ligands incorporating easily deprotonatable donor func-
tions, susceptible to stabilize mononuclear complexes. The
In recent years, the development of bi- or polydentate ligand
precursors based on functionalized imidazolium salts incorpor-
ating more “classical heteroatom” donor(s) has attracted con-
siderable attention.1 In this context, heteroatom-functionalized
*To whom correspondence should be addressed. Fax:(þ33)561553003.
Tel:(þ33)561333187. E-mail: Catherine.Hemmert@lcc-toulouse.fr (C.
H.); Heinz.Gornitzka@lcc-toulouse.fr (H.G.).
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pubs.acs.org/Organometallics
Published on Web 06/11/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 13, 2010 2869
Scheme 1. Synthesis of Amide-Functionalized Bis-Imidazolium
Salts 3 and 4
Scheme 2. Synthesis of Complexes 5-8
Figure 1. Molecular structures (50% probability level for the
thermal ellipsoids) of complexes 5 (left) and 6 (right). Hydro-
gen atoms and anions have been omitted. Selected bond lengths
˚
(A) and angles (deg): for 5, Ni-C=1.867(3), Ni-N=1.936(2),
C-Ni-C = 99.2(2), C-Ni-N =87.7(2), N-Ni-N = 88.6(2);
for 6, Ni-C10 = 1.885(2), Ni-C16 = 1.886(2), Ni-N1 =
1.943(2), Ni-N6 = 1.932(2), C-Ni-C = 97.72(10), C10-
Ni-N1 = 86.66(9), C16-Ni-N6 = 88.19(9), N-Ni-N =
89.44(8).
chelating effect of tetradentate ligands is indeed prone to
enhance the robustness of the corresponding precatalysts
and to prevent catalyst decomposition under harsh reaction
conditions. Recently, Yagyu et al. reported the synthesis of a
dianionic tetradentate bis(carbene) ligand containing ary-
loxy moieties, a motif very similar to that for salen ligands.10
Salens and porphyrins represent the most famous examples
of dianionic tetradentate systems, particularly well-known
for applications in asymmetric catalysis.11 However, to date
no chiral equivalents of such ligands based on bis(carbene)
have been reported.
Scheme 3. Synthesis of Bis-Imidazolium Salts 13 and 14 and of
the Complexes 15 and 16
In the present report, we disclose the preparation of various
amido-functionalized bis-imidazolium salts, in which the two
imidazolium rings are held together by a flexibleC3chain, and
their subsequent complexation with Ni(II) and Pd(II) leading
to the first chiral archetype of this family.
Results and Discussion
The amide-functionalized bis-imidazolium salts 3 and 4
were obtained in quantitative yields by quaternization of 1 or
2
4d with 1/2 equiv of 1,3-dibromopropane (Scheme 1).
Lee et al. reported the successful synthesis of mononuclear
bis(bidentate) nickel(II) and palladium(II) complexes, invol-
ving amido-NHC ligands, via direct reaction between imi-
dazolium salts, NiCl2 or PdCl2, and K2CO3, in either DMF
or pyridine.4d,7g Following this procedure, the palladium(II)
and nickel(II) complexes 5-8 were prepared from equimolar
amounts of bis-imidazolium salts 3 or 4 with a slight excess of
K2CO3 as a base in dry DMF at 80 °C and isolated as yellow
solids (56-87%) (Scheme 2).
to the successful formation of tetradentate bis(amido-
carbene) complexes. In 13C NMR spectra of 5-8, the two
downfield quaternary signals have been unambiguously
attributed, using HMBC experiments, which enable the
assignments of the more upfield signals for the carbenic
carbons (161.2-162.2 ppm) and the more downfield ones
for the carbonyl carbons (166.6-170.2 ppm). These values
are in the range of those reported by Lee et al. for related
nickel(II) and palladium(II) complexes.4d,7g Elemental anal-
ysis and FAB-MS spectra of 5-8 are in agreement with
neutral monomeric species.
Single crystals of nickel(II) complexes were grown at room
temperature by slow evaporation of a methanol solution of
complex 5 or by slow diffusion of diethyl ether into a solution
of 6 in chloroform (Figure 1).
In further work, we became interested in a synthesis of the
corresponding chiral ligand system. For this purpose, an-
other strategy starting from amino acids was applied (see
Scheme 3). The sodium L-2-(1-imidazolyl)alkanoic acids 9
All the synthesized complexes are highly stable toward air
and moisture. For complexes 5-8, the most notable features
of the symmetrical H spectra are the absence of the reso-
nance for the imidazolium and the amide protons, attesting
1
(10) Yagyu, T.; Yano, K.; Kimata, T.; Jitsukawa, K. Organometallics
2009, 28, 2342.
(11) (a) Jacobsen, E. N.; Wu, M. H. In Catalytic Asymmetric Synth-
esis; Ojima, I., Ed.; Wiley-VCH: New York, 1993; pp 159-202. (b) Katsuki,
T. In Catalytic Asymmetric Synthesis; Ojima, I., Ed.; Wiley-VCH: New
York, 2000; pp 287-325. (c) Jacobsen; E. N.; Wu, M. H. In Comprehensive
Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.;
Springer: New York, 1999; pp 649-675.

2870 Organometallics, Vol. 29, No. 13, 2010
Jean-Baptiste dit Dominique et al.
Figure 3. Molecular structure (50% probability level for the
thermal ellipsoids) of complex 16. Only one of the two indepen-
dent molecules in the asymmetric unit is shown. Hydrogen
atoms and anions have been omitted. Selected bond lengths
Figure 2. Molecular structure (50% probability level for the
thermal ellipsoids) of the racemic complex 15. Hydrogen atoms
and anions have been omitted. Disorders of the parts concerning
the asymmetric carbon atoms are illustrated. Selected bond
lengths (A) and angles (deg): Ni-C = 1.886(2), Ni-N =
1.941(2); C-Ni-C = 98.11(9), C-Ni-N = 87.33(6), N-Ni-
N = 89.57(8).
˚
(A) and angles (deg): Ni-C14 = 1.887(4), Ni-C20 = 1.888(4),
˚
Ni-N1 = 1.928(4), Ni-N6 = 1.946(4); C-Ni-C = 97.0(2),
C14-Ni-N1 = 86.9(2), C20-Ni-N6 = 87.2(2), N-Ni-N =
89.8(2).
and 10 were prepared by a one-pot condensation strategy.12
A subsequent peptidic coupling between 9 and aniline or 10
and benzylamine, involving HOBT and EDC as coupling
agents, gave the corresponding imidazole precursors 11
and 12, respectively, obtained in moderate yields (44 and
27%). In order to verify if 13 conserved the stereochemical
information of the starting amino acid, the corresponding
system starting from a racemic mixture of the amino acid has
been prepared. Both 13 and the racemic proligand have
been studied by HPLC experiments using a chiral column
(Chirobiotic T), confirming that 13 is at 93% the desired
enantiomer. Very similar values obtained by the measure-
ments of optical rotations for the bis-imidazolium salts 13
and 14 confirmed also the formation of chiral proligands
([R]D20 = þ51.9° (13), þ53.2° (14)). The nickel complexes
were then generated by using the same protocol as described
above (albeit with pyridine as the solvent for 16), yielding
yellow powders (78% (15), 52% (16)).
The spectroscopic data of 16 are quite similar to those
of 5 and 6. Single crystals were obtained by slow diffu-
sion of diethyl ether into a solution of 16 in chloroform
(Figure 3).
All four complexes presented here are mononuclear neu-
tral species, in which the ligands are tetradentate. The two
carbenes and the two amido groups are in a cis disposition. In
all cases the Ni centers are distorted from the ideal square-
planar coordination geometry, with all four bond angles at
the metal center deviating significantly from 90°. The
C-Ni-C angles are larger than the N-Ni-N angles, mainly
due to the steric constraints imposed by the trimethylene
˚
chain. The Ni-C bonds (1.87-1.89 A) are shorter than the
˚
Ni-N bonds (1.94 A), as observed by Lee et al. for bis-
(amido-NHC) nickel complexes.13
Conclusion
Slow evaporation of a methanol solution of 15 gave single
crystals (Figure 2). The structure analysis revealed that the
racemization of the two stereogenic centers of the ligand
occurred during complexation, which is accompanied by a
In summary, we prepared new tetradentate NHC ligands
consisting of soft carbene and hard amido moieties, suitable
for the formation of air- and water-stable Pd(II) and Ni(II)
complexes. The structures of the square-pyramidal com-
plexes 5, 6, 15, and 16 were determined by single-crystal
X-ray diffraction. Furthermore, the nickel complex 16 re-
presents the first structurally characterized example of a
complex containing a chiral dianionic tetradentate bis-
(carbene) ligand.
20
dramatic decrease of RD ([R]D = þ8.5°) and important
changes in the spectroscopic data.13 This racemization is
probably due to the mobility of the H atoms on the asym-
metric carbons, under the drastic complexation conditions.
Attempts to obtain 15 in an enantiomerically pure form, by
lowering the temperature reaction (60 °C) or by using other
bases (pyridine or NHCO3) failed.
Experimental Section
In order to better protect the chiral centers, we choose a
non-racemizable system bearing a methyl and an isopro-
pyl group on the asymmetric carbon atoms (14), start-
ing from a disubstituted chiral amino acid. In that case,
the resulting nickel(II) complex must be optically pure,
which is also reflected in a very high [R]D20 value (þ85.8°).
Unless otherwise stated, all reactions were performed under
an atmosphere of argon using standard Schlenk techniques.
Solvents were freshly distilled from standard drying agents and
kept under argon. 2-(1H-imidazol-1-yl)-N-phenylacetamide
(1)14 and L-sodium 2-(1-imidazolyl)propanoic acid (9) were
prepared by following literature procedures.12 All other re-
agents were used as received from commercial suppliers. 1H
(250, 300, or 500 MHz) and 13C NMR (63, 75, or 125 MHz)
spectra were recorded at 298 K on Bruker ARX250, Bruker
DPX300, and Bruker AV500 spectrometers in DMSO-d6,
(12) Bao, W.; Wang, Z.; Li, Y. J. Org. Chem. 2003, 68, 591.
(13) In the 1H and 13C NMR data for 15, four distinct peaks for each
type of proton or carbon atom are observed. This is in agreement with a
racemization of the two asymmetric carbon centers, leading to two pairs
of enantiomers, where each one forms two types of conformers, which
interchange slowly relative to the NMR time scale. The presence of two
conformers for each diastereoisomer has been confirmed by NMR
ROESY analysis.
(14) Liao, C.-Y.; Chan, K.-T.; Zeng, J.-Y.; Hu, C.-H.; Tu, C.-Y.; Lee,
H. M. Organometallics 2007, 26, 1692.

Article
Organometallics, Vol. 29, No. 13, 2010 2871
CD3OD, and CDCl3 as solvents. Elemental analyses were
carried out by the “Service de Microanalyse du Laboratoire de
Chimie de Coordination” (Toulouse, France). Mass spectro-
metry analyses were performed on a Nermag R1010 apparatus
(FABþ/m-nitrobenzyl alcohol (MNBA) in DMSO) by the “Ser-
(2C, CIm), 122.2 (2C, CIm), 51.1 (2C, C6), 46.3 (2C, C2), 42.9 (2C,
C8), 30.0 (1C, C1). MS (FAB): m/z 551 [M - Br-]þ, 471 [M -
2Br- - Hþ]þ.
(2S)-2-(1H-Imidazol-1-yl)-N-phenylpropanamide (11). To a
solution of sodium (2S)-2-(1H-imidazol-1-yl)propanoate (0.486 g,
3.0 mmol) and N-methylmorpholine (1.011 g, 10 mmol) in dry
DMF (15 mL) was successively added EDC (0.767 g, 4.0 mmol),
HOBT (0.542 g, 4.0 mmol), and aniline (0.186 g, 2 mmol). The
resulting mixture was stirred at room temperature for 24 h, and
the solvent was completely removed under vacuum. The residue
was then extracted with dichloromethane (50 mL). The organic
phase was washed with a saturated NaHCO3 solution (75 mL)
and dried over Na2SO4. The crude product was further purified
by column chromatography (4/96 methanol/dichloromethane),
to give a hydroscopic white powder (0.190 g, 44%). Anal. Calcd
for C12H13N3O: C, 66.96; H, 6.09; N, 19.52. Found: C, 67.03; H,
6.15; N, 19.61. 1H NMR (250 MHz, DMSO-d6): δ 10.31 (bs, 1H,
NH), 7.75 (bs, 1H, H5), 7.60 (d, 2H, HAr, 3J = 8.0 Hz), 7.33 (t,
2H, HAr, 3J=7.8 Hz), 7.27 (bs, 1H, HIm), 7.09 (t, 1H, HAr, 3J=
7.5 Hz), 6.91 (bs, 1H, HIm), 5.11 (m, 1H, H6, 3J=7.0 Hz), 1.68
ꢀ
vice de Spectrometrie de Masse de Chimie UPS-CNRS”
(Toulouse, France). Optical rotations were measured with a
Perkin-Elmer 241 polarimeter.
Preparation of Amide-Functionalized Diimidazolium Salts.
N-Benzyl-2-(1H-imidazol-1-yl)acetamide (2). A mixture of imi-
dazole (1.02 g, 15.0 mmol) and 2-chloro-N-benzylacetamide
(0.567 g, 3.0 mmol) in toluene (10 mL) was heated to 110 °C
overnight. After cooling, the solvent was removed and the
residue was extracted with dichloromethane (15 mL). The
organic phase was washed with water (12 mL) and dried over
Na2SO4. After evaporation of the solvent and drying under
vacuum, 2 was obtained as a white solid (0.380 g, 60%). Anal.
Calcd for C12H13N3O: C, 66.96; H, 6.09; N, 19.52. Found: C,
66.65; H, 5.95; N, 19.35. 1H NMR (250 MHz, DMSO-d6): δ 8.64
(t, 1H, NH), 7.61 (s, 1H, H5), 7.32 (m, 5H, HAr), 7.13 (s, 1H,
3
(d, 3H, HMe, J = 7.2 Hz). 13C NMR (75 MHz, DMSO-d6):
δ 168.8 (2C, CdO), 139.0 (2C, CAr), 136.9 (2C, C5), 129.3 (4C,
CAr), 128.6 (4C, CAr), 124.3 (2C, CIm), 119.9 (2C, CAr), 118.9
(2C, CIm), 56.0 (2C, C6), 18.9 (1C, CMe). MS (FAB): m/z 216
[M þ Hþ]þ.
(2S)-N-Benzyl-2-(1H-imidazol-1-yl)-2,3-dimethylbutanamide
(12). A formaldehyde-water solution (36%, 0.142 g, 1.7 mmol)
and glyoxal water solution (32%, 0.38 g, 1.7 mmol) were added
in a 50 mL, three-necked flask provided with a stirrer and reflux
condenser. While the mixture was heated at 50 °C with stirring,
a mixture of (2S)-2-amino-2,3-dimethylbutyric acid (0.223 g,
1.7 mmol), ammonia solution (32%, 0.09 g, 1.7 mmol), and
sodium hydroxide solution (10%, 0.680 g, 1.7 mmol) was added
in small portions over 0.5 h. After the mixture was stirred for an
additional 4 h at 50 °C, acetone (20 mL) was added and the
solvents were removed under reduced pressure. The resulting
residue (10) was dried under vacuum. 1H NMR (250 MHz,
CD3OD): δ 7.94 (s, 1H, H5), 7.01 (s, 1H, H3), 6.97 (s, 1H, H4),
H
Im), 6.90 (s, 1H, HIm), 4.74 (s, 2H, H6), 4.32 (d, 2H, NCH2, 3J=
5.8 Hz). 13C NMR (63 MHz, DMSO-d6): δ 167.3 (1C, CdO),
139.4 (1C, C5), 138.6 (1C, CAr), 128.8 (2C, CAr), 128.5 (1C, CIm),
127.8 (2C, CAr), 127.4 (1C, CAr), 120.9 (1C, CIm), 49.1 (1C, C6),
42.8 (1C, NCH2). MS (FAB): m/z 216 [M þ Hþ]þ.
1,10-(1,3-Propanediyl)bis[3-(2-anilino-2-oxoethyl)-1H-imida-
zol-3-ium] Dibromide (3). A solution of 2-(1H-imidazol-1-yl)-N-
phenylacetamide (0.804 g, 4.0 mmol) and 1,3-dibromopropane
(0.203 mL, 2.0 mmol) in a mixture of acetonitrile and toluene
(2 mL/2 mL) was stirred at 100 °C overnight. After the mix-
ture was cooled to room temperature, the solvents were evapo-
rated. The product was dried under vacuum to afford 3 as a
white solid (1.208 g, 100%). Anal. Calcd for C25H28N6O2Br2: C,
49.69; H, 4.67; N, 13.91. Found: C, 49.65; H, 4.69; N, 13.93. 1H
NMR (250 MHz, DMSO-d6): δ 10.57 (bs, 2H, NH), 9.23 (s, 2H,
3
2.66 (m, 1H, CHMe2, J = 6.8 Hz), 1.69 (s, 3H, CH3), 0.94
(d, 3H, CH(CH3)2, 3J = 6.8 Hz), 0.76 (d, 3H, CH(CH3)2, 3J =
6.7 Hz).
To a solution of 10 (0.350 g, 1.7 mmol) and N-methylmorpho-
line (0.759 g, 7.5 mmol) in dry DMF (6 mL) were successively
added EDC (0.576 g, 3.0 mmol), HOBT (0.406 g, 3.0 mmol), and
benzylamine (0.348 g, 1.5 mmol). The solution was stirred at
room temperature for 24 h, and the solvent was completely
removed under vacuum. The residue was then extracted with
dichloromethane (50 mL). The organic phase was washed with a
saturated NaHCO3 solution (75 mL), separated, and dried with
anhydrous Na2SO4. The crude product was further purified by
column chromatography (4/96 methanol/dichloromethane) to
give a hygroscopic white powder (0.110 g, 27% yield). Anal.
Calcd for C16H21N3O: C, 70.82; H, 7.80; N, 15.49. Found: C,
70.47; H, 7.62; N, 15.61. 1H NMR (250 MHz, DMSO-d6): δ 8.36
(bs, 1H, NH), 7.74 (bs, 1H, H5), 7.27 (m, 6H, HAr and HIm), 6.91
H5), 7.85 (d, 2H, HIm, ,
3,4J = 1.7 Hz), 7.83 (d, 2H, HIm 3,4J =
1.5 Hz), 7.59 (d, 4H, H9, 3J=7.5 Hz), 7.35 (t, 4H, H10, 3J=7.5
Hz), 7.11 (t, 2H, H11, J = 7.5 Hz), 5.25 (s, 4H, H6), 4.34 (t,
3
4H, H2, J = 7.0 Hz), 2.46 (m, 2H, H1). 13C NMR (63 MHz,
3
DMSO-d6): δ 164.1 (2C, CdO), 138.7 (2C, C5), 138.2 (2C, C8),
129.5 (4C, C9 or 10), 124.8 (2C, CIm), 124.4 (2C, CIm), 122.2 (2C,
C11), 119.6 (4C, C9 or 10), 51.8 (2C, C6), 46.5 (2C, C2), 30.0
(1C, C1). MS (FAB): m/z 523 [M - Br-]þ and 443 [M -
2Br- - Hþ]þ.
3
1,10-(1,3-Propanediyl)bis{3-[(2-benzylamino)-2-oxoethyl]-1H-
imidazol-3-ium} Dibromide (4). A solution of N-benzyl-2-(1H-
imidazol-1-yl)acetamide (2; 0.364 g, 1.7 mmol) and 1,3-dibromo-
propane (0.086 mL, 0.84 mmol) in a mixture of acetonitrile and
toluene (1 mL/1 mL) was stirred at 100 °C overnight. After the
mixture was cooled to room temperature, the solvents were
evaporated. The product was dried under vacuum to afford 4 as
(bs, 1H, HIm), 4.27 (d, 2H, NCH2, J = 5.9 Hz), 2.70 (m, 1H,
CHMe2, 3J=6.7 Hz), 1.67 (s, 3H, HMe), 0.82 (d, 3H, CH(CH3)2,
3J=6.7 Hz), 0.62 (d, 3H, CH(CH3)2, 3J=6.7 Hz). 13C NMR (63
MHz, DMSO-d6): δ 171.5 (1C, C7), 139.7 (1C, C5), 136.2 (1C,
C
Ar), 128.7 (2C, CAr), 128.3 (1C, CIm), 127.5 (2C, CAr), 127.2
(1C, CAr), 118.7 (1C, CIm), 67.2 (1C, C6), 43.1 (1C, NCH2), 34.4
(1C, CH(CH3)2), 18.0 (1C, CMe), 16.9 (1C, CH(CH3)2), 16.7 (1C,
CH(CH3)2). MS (FAB): m/z 271 [M þ Hþ]þ.
a white solid (0.531 g, 100%). Anal. Calcd for C27H32N6O2Br2
3
1.6H2O: C, 49.04; H, 5.37; N, 12.71. Found: C, 49.07; H, 5.32; N,
12.70. 1H NMR (250 MHz, DMSO-d6): δ 9.24 (s, 2H, H5), 8.98
(pseudot, 2H, NH), 7.83 (bs, 2H, HIm), 7.79 (bs, 2H, HIm), 7.34
(m, 10H, HAr), 5.10 (s, 4H, H6), 4.36 (d, 4H, NCH2, 3J=5.8 Hz),
4.31 (t, 4H, H2, 3J = 7.0 Hz), 2.45 (m, 2H, H1). 13C NMR (75
MHz, DMSO-d6): δ 165.4 (2C, CdO), 139.0 (2C, C5), 138.1 (2C,
3,30-(1,3-Propanediyl)bis{1-[(1S)-2-anilino-1-methyl-2-oxoethyl]-
3H-imidazol-1-ium} Dibromide (13). A solution of 11 (0.260 g,
1.2 mmol) and 1,3-dibromopropane (0.121 g, 0.6 mmol) in
acetonitrile/toluene (0.5-0.5 mL) was stirred at 100 °C over-
night. After the mixture was cooled to room temperature, the
solvents were evaporated. The product was dried under vacuum
to afford the desired white solid (0.381 g, 100%). Anal. Calcd for
C
Ar), 128.8 (4C, CAr), 127.8 (4C, CAr), 127.5 (2C, CAr), 124.5

2872 Organometallics, Vol. 29, No. 13, 2010
Jean-Baptiste dit Dominique et al.
C27H32N6O2Br2 2H2O: C, 48.52; H, 5.43; N, 12.57. Found: C,
complex 6 was obtained as a yellow solid (0.510 g, 81%).
Crystals suitable for X-ray diffraction analysis were grown by
diffusion of diethyl ether into a solution of 6 in chloroform.
3
48.65; H, 4.91; N, 12.79. 1H NMR (300 MHz, DMSO-d6):
δ 10.57 (bs, 2H, NH), 9.45 (s, 2H, H5), 7.97 (bs, 2H, HIm),
7.86 (bs, 2H, HIm), 7.61 (d, 4H, HAr, 3J = 7.5 Hz), 7.35 (t, 4H,
Anal. Calcd for C27H28N6O2Ni 0.2CHCl3: C, 59.28; H, 5.16; N,
15.25. Found: C, 59.00; H, 5.07; N, 15.19. 1H NMR (250 MHz,
3
H
Ar, 3J = 7.5 Hz), 7.13 (t, 2H, HAr, 3J = 7.5 Hz), 5.41 (m, 2H,
H6), 4.31 (t, 4H, H2, 3J=7.0 Hz), 1.84 (d, 6H, HMe, 3J=7.1 Hz).
13C NMR (63 MHz, DMSO-d6): δ 167.1 (2C, C7), 138.6 (2C,
C5), 137.1 (2C, CAr), 129.4 (4C, CAr), 124.7 (2C, CIm), 123.2 (2C,
CD3OD): δ 7.35 (m, 10H, HAr), 7.26 (d, 2H, HIm
,
3,4J=1.8 Hz),
7.09 (d, 2H, HIm
,
3,4J=1.8 Hz), 4.79 (d, 2H, NCH2a, 2J=15.5
Hz), 4.01 (m, 4H, NCH2b and H2a), 3.63 (m, 4H, H6), 3.13 (m,
2H, H2b), 1.79 (m, 2H, H1). 13C NMR (63 MHz, CD3OD): δ
170.2 (2C, CdO), 161.2 (2C, C5), 142.6 (2C, CAr), 128.1 (4C,
C
Im), 122.3 (2C, CAr), 119.9 (4C, CAr), 58.8 (2C, C6), 46.6 (2C,
C2), 29.7 (1C, C1), 18.7 (2C, CMe). MS (FABþ): m/z 552 [M -
Br-]þ and 471 [M - 2Br- - Hþ]þ. [R]20D = þ51.9° (589 nm,
20 °C, 5.01 ꢀ 10-3 g/cm3 in MeOH, 10 cm path). HPLC
(Chirobiotic T, MeOH, 1 mL/min, UV): RT = 8.555 (93.74%,
UV 241.5 nm), 10.356 (6.26%, UV 240.4 nm); racemic
system RT = 8.583 (49.83%, UV 241.5 nm), 9.743 (47.81%,
UV 241.5 nm).
C
Ar), 127.7 (4C, CAr), 126.4 (2C, CAr), 123.5 (2C, CIm), 120.8
(2C, CIm), 54.0 (2C, C6), 48.3 (2C, NCH2), 44.0 (2C, C2), 31.5
(1C, C1). MS (FAB): m/z 527 [M þ Hþ]þ, 565 [M þ Kþ]þ.
Complex 7. A mixture of 3 (0.121 g, 0.2 mmol), K2CO3
(0.138 g, 1 mmol), and PdCl2(CH3CN)2 (0.052 g, 0.2 mmol) in
dry DMF (6 mL) was heated at 55 °C for 2 h and then at 80 °C
overnight. After it was cooled to room temperature, the solution
was filtered through a pad of Celite, and a yellow solid pre-
cipitated by addition of diethyl ether (60 mL). After filtration
and drying under vacuum, complex 7 was obtained as a yellow
solid (0.261 g, 79%). Anal. Calcd for C25H24N6O2Pd: C, 54.90;
H, 4.42; N, 15.37. Found: C, 54.76; H, 4.31; N, 15.26. 1H NMR
(500 MHz, DMSO-d6): δ 7.65 (d, 2H, H4, 3,4J=1.8 Hz), 7.42 (d,
2H, H3, 3,4J=1.8 Hz), 7.11 (d, 4H, HAr, 3J=7.4 Hz), 6.96 (t, 4H,
HAr, 3J = 7.4 Hz), 6.79 (t, 2H, HAr, 3J = 7.3 Hz), 4.93 (d, 2H,
H6a, 2J=14.1 Hz), 4.26 (d, 2H, H6b, 2J=14.2 Hz), 4.19 (m, 2H,
H2a), 3.58 (m, 2H, H2b), 1.92 (m, 2H, H1). 13C NMR (125 MHz,
DMSO-d6): δ 166.6 (2C, CdO), 162.1 (2C, C5), 148.4 (2C, CAr),
127.0 (4C, CAr), 126.2 (4C, CAr), 124.1 (2C, C4), 121.1 (2C, CAr),
119.6 (2C, C3), 58.0 (2C, C6), 45.0 (2C, C2), 32.5 (1C, C1). MS
(FAB): m/z 547 [M þ Hþ]þ.
3,30-(1,3-Propanediyl)bis(1-{(1S)-1-[(benzylamino)carbonyl]-
1,2-dimethylpropyl}-3H-imidazol-1-ium) Dibromide (14). A solu-
tion of 12 (0.110 g, 0.4 mmol) and 1,3-dibromopropane (0.041 g,
0.2 mmol) in acetonitrile/toluene (0.3-0.3 mL) was stirred at
100 °C overnight. After the mixture was cooled to room tem-
perature, the solvents were evaporated. The product was dried
under vacuum to afford the desired white solid (0.153 g, 100%).
Anal. Calcd for C35H48N6O2Br2 2H2O: C, 53.85; H, 6.71; N,
3
10.77. Found: C, 53.96; H, 6.41; N, 10.79. 1H NMR (250 MHz,
DMSO-d6): δ 9.51 (bs, 2H, H5), 8.87 (s, 2H, NH), 7.94 (bs, 2H,
HIm), 7.91 (bs, 2H, HIm), 7.28 (m, 10H, HAr), 4.31 (m, 8H, H2 and
NCH2), 2.70 (m, 2H, CH(CH3)2), 1.83 (d, 6H, HMe), 0.84 (d, 6H,
CH(CH3)2, 3J = 6.6 Hz), 0.75 (d, 6H, CH(CH3)2, 3J = 6.6 Hz).
13C NMR (75 MHz, DMSO-d6): δ 169.6 (2C, C7), 139.2 (2C,
CAr), 137.1 (2C, C5), 128.8 (4C, CAr), 127.8 (4C, CAr), 127.4 (2C,
CAr), 122.4 (2C, CIm), 122.2 (2C, CIm), 71.3 (2C, C6), 46.7 (2C,
NCH2), 43.5 (2C, C2), 34.8 (2C, CH(CH3)2), 30.1 (1C, C1), 17.5
(2C, CMe), 17.4 (2C, CH(CH3)2), 16.9 (2C, CH(CH3)2). MS
(FABþ): m/z 663 [M - Br-]þ and 583 [M - 2Br- - Hþ]þ.
[R]20D = þ53.2° (589 nm, 20 °C, 6.02 ꢀ 10-3 g/cm3 in MeOH,
10 cm path).
Complex 8. A mixture of 4 (0.127 g, 0.2 mmol), K2CO3 (0.138
g, 1 mmol), and PdCl2(CH3CN)2 (0.052 g, 0.2 mmol) in dry
DMF (6 mL) was heated at 55 °C for 2 h and then at 80 °C
overnight. After it was cooled to room temperature, the solution
was filtered through a pad of Celite, and a yellow solid pre-
cipitated by addition of diethyl ether (60 mL). After filtration
and drying under vacuum, complex 8 was obtained as a yellow
Synthesis of Complexes. Complex 5. A mixture of ligand
3 (0.604 g, 1.0 mmol), K2CO3 (0.690 g, 5 mmol), and NiCl2
(0.130 g, 1.0 mmol) in dry DMF (25 mL) was heated at 80 °C
overnight. After it was cooled to room temperature, the solution
was filtered through a pad of Celite; a yellow solid precipitated
by addition of diethyl ether (100 mL). After filtration, the preci-
pitate was dissolved in chloroform (100 mL) and the organic
layer was washed with water (50 mL). The water was extracted
twice with chloroform (50 mL), and the combined organic layers
were dried over Na2SO4. After removal of the solvent and drying
under vacuum, complex 5 was obtained as a yellow solid (0.434
g, 87%). Crystals suitable for X-ray diffraction analysis were
obtained by slow evaporation of a methanol solution of 5. Anal.
solid (0.065 g, 56%). Anal. Calcd for C27H28N6O2Pd H2O: C,
3
1
54.69; H, 5.10; N, 14.17. Found: C, 54.92; H, 4.82; N, 14.25. H
NMR (500 MHz, CD3OD): δ 7.32 (d, 2H, H4, 3,4J=1.9 Hz), 7.21
(m, 6H, HAr), 7.18(d, 2H, H3, 3,4J=1.9Hz), 7.10(m, 4H, HAr), 5.09
(d, 2H, NCH2a, 2J=14.6 Hz), 4.08 (m, 4H, H6b and H2a, 2J=14.8
Hz), 3.96 (d, 2H, NCH2b, 2J=14.5 Hz), 3.81 (d, 2H, H6a, 2J=14.8
Hz), 3.30 (m, 2H, H2b), 1.89 (m, 2H, H1). 13C NMR (125 MHz,
CD3OD): δ 169.7 (2C, CdO), 162.1 (2C, C5), 142.2 (2C, CAr), 128.0
(4C, CAr), 127.8 (4C, CAr), 126.1 (2C, CAr), 123.1 (2C, C4), 120.2
(2C, C3), 55.6 (2C, C6), 50.3 (2C, NCH2), 44.4 (2C, C2), 31.8 (1C,
C1). MS (FAB): m/z 575 [M þ Hþ]þ.
Complex 15. A mixture of ligand 13 (0.127 g, 0.2 mmol),
K2CO3 (0.138 g, 1 mmol), and NiCl2 (0.026 g, 0.2 mmol) in dry
DMF (6 mL) was heated at 80 °C overnight. After it was cooled
to room temperature, the solution was filtered through a pad of
Celite, and a yellow solid precipitated by addition of diethyl
ether (15 mL). After filtration, the precipitate was dissolved in
chloroform (20 mL) and the organic layer was washed with
water (15 mL). The water was washed twice with chloroform (15
mL), and the combined organic layers were dried over Na2SO4.
After removal of the solvent and drying under vacuum, complex
15 was obtained as a yellow solid (0.082 g, 78%). Crystals
suitable for X-ray diffraction analysis were obtained by slow
evaporation from a methanol solution of 15. Anal. Calcd for
Calcd for C25H24N6O2Ni 2H2O: C, 56.10; H, 5.27; N, 15.70.
3
Found: C, 55.85; H, 5.21; N, 15.71. 1H NMR (250 MHz,
DMSO-d6): δ 7.75 (d, 4H, HAr
HIm
3,4J=1.8 Hz), 7.28 (d, 2H, HIm
Ar, 3J = 7.3 Hz), 6.89 (t, 2H, HAr, 3J = 7.2 Hz), 5.19 (d, 2H,
,
3J = 7.5 Hz), 7.59 (d, 2H,
,
,
3,4J=1.8 Hz), 7.15 (t, 4H,
H
H6a, 2J=14.4 Hz), 4.11 (m, 4H, H6b and H2b), 3.43 (m, 2H, H2a),
1.82 (m, 2H, H1). 13C NMR (63 MHz, DMSO-d6): δ 166.6 (2C,
CdO), 161.8 (2C, C5), 148.1 (2C, CAr), 126.9 (4C, CAr), 126.6
(4C, CAr), 124.5 (2C, CIm), 121.9 (2C, CAr), 121.4 (2C, CIm), 56.7
(2C, C6), 44.6 (2C, C2), 36.3 (1C, C1). MS (FAB): m/z 499 [M þ
Hþ]þ, 537 [M þ Kþ]þ.
Complex 6. A mixture of 4 (0.630 g, 1.0 mmol), K2CO3
(0.690 g, 5 mmol), and NiCl2 (0.130 g, 1.0 mmol) in dry DMF
(25 mL) was heated at 80 °C overnight. After it was cooled to
room temperature, the solution was filtered through a pad of
Celite and the solvent was removed under vacuum. The residue
was dissolved in chloroform (100 mL) and was washed with
water (50 mL). The water was extracted twice with chloroform
(50 mL), and the combined organic layers were dried over
Na2SO4. After removal of the solvent and drying under vacuum,
C27H28N6O2Ni H2O: C, 59.47; H, 5.55; N, 15.41. Found: C,
3
59.31; H, 5.31; N, 15.27. Variable-temperature NMR experi-
ments have been carried out (in CD3OD between 223 and 323 K
and in DMSO-d6 between 298 and 363 K) to discard the
possibility of conformational equilibrium. For the strongly
affected methyl group on position 6, no fusion of the four
signals and no significant simplification of the spectra could
be observed. Only the room-temperature data are given here.

Article
Organometallics, Vol. 29, No. 13, 2010 2873
16 0.25CHCl3 0.5CH2Cl2 0.5Et2O 0.75H2O
Table 1. Crystal Data for 5, 6, 15, and 16
5 2MeOH
3
6 CHCl3 H2O
3
15 2MeOH
3
3
3
3
3
3
empirical formula
formula wt
temp (K)
C
563.30
173(2)
monoclinic
C2/c
14.774(1)
16.001(1)
12.392(1)
112.797(4)
2700.6(3)
4
1.385
0.763
1184
27H32N6NiO4
C28H31Cl3N6NiO3
664.65
193(2)
monoclinic
P21/c
10.5437(2)
14.9883(3)
19.1501(4)
100.537(1)
2975.3(1)
4
1.484
0.963
1376
C29H36N6NiO4
591.35
193(2)
monoclinic
C2/c
15.4796(4)
18.1846(4)
10.6625(2)
104.303(1)
2908.4(2)
4
1.351
0.712
1248
C37.75H51.75Cl1.75N6NiO3.25
762.35
193(2)
orthorhombic
P212121
14.9787(3)
cryst syst
space group
˚
a (A)
˚
b (A)
19.8518(4)
28.4798(6)
˚
c (A)
β (deg)
3
V (A )
˚
8468.6(3)
8
1.196
0.609
3232
0.6 ꢀ 0.4 ꢀ 0.3
5.12-25.35
89 914
15 341
0.0358
Z
F
calcd (Mg m-3
)
μ (mm-1
F(000)
)
cryst size (mm3)
0.1 ꢀ 0.1 ꢀ 0.1
5.13-25.35
11 542
2453
0.0989
0.4 ꢀ 0.2 ꢀ 0.2
1.96-26.85
28 389
6339
0.0392
0.4 ꢀ 0.4 ꢀ 0.3
5.11-26.37
10 994
2956
0.0217
θ range for data collecn (deg)
no. of rflns collected
no. of indep rflns
R(int)
max/min transmissn
no. of data/restraints/params
goodness of fit on F2
R1 (I > 2σ(I))
wR2 (I > 2σ(I))
R1 (all data)
0.9276/0.7153
2453/0/175
1.004
0.0443
0.0762
0.0836
0.0884
0.356/-0.360
0.8308/0.6994
6339/0/378
1.052
0.0394
0.1059
0.0563
0.1156
0.523/-0.462
0.8149/0.7639
2956/53/203
1.078
0.0298
0.0720
0.0328
0.0736
0.347/-0.261
0.8384/0.7114
15 341/572/1123
1.071
0.0541
0.1426
0.0781
0.1640
0.655/-0.390
wR2 (all data)
˚
-3
ΔFmax/min (e A
)
1H NMR (500 MHz, DMSO-d6): δ 7.85 (d, HAra, 3J=7 Hz), 7.65
(2C, CH(CH3)2), 16.01 (2C, CH(CH3)2), 15.06 (2C, CMe). MS
(FABþ): m/z 639 [M þ Hþ]þ. [R]20D = þ85.8° (589 nm, 20 °C,
8.00ꢀ10-3 g/cm3 in MeOH, 10 cm path).
(d, HArb’, 3J=6.9 Hz), 7.56 (d, H4b, 3,4J=1.6 Hz), 7.52 (bs, H4a),
7.49 (bs, H4a’), 7.47 (bs, H4b ), 7.34 (d, HAra’, 3J=7.4 Hz), 7.30
0
(d, H3, 3J=1.5 Hz), 7.17 (m, HArb and HAr), 7.06 (m, HAr), 6.91
Experimental Crystallographic Data for 5, 6, 15, and 16.
Details of the crystal data for all structures are presented in
Table 1. All data were collected at low temperatures using an oil-
coated shock-cooled crystal on a Bruker-AXS APEX2 diffracto-
0
0
(m, HAr), 5.81 (q, H6a ), 5.52 (q, H6b ), 4.47 (q, H6b), 4.40
(q, H6a), 4.10 (m, H2), 3.45 (m, H2), 3.37 (m, H2), 3.24
(m, H2), 3.10 (m, H2), 2.42 (d, HMeb, J = 7.2 Hz), 2.08 (d,
3
3
H
Mea, J=7.5 Hz), 1.78 (d, H1), 1.42 (d, HMea and HMeb ). 13C
meter with Mo KR radiation (λ = 0.710 73 A). The structures
˚
0
0
NMR (125 MHz, DMSO-d6): δ 170.3 (C7b), 170.0 (C7a), 169.5
were solved by direct methods,15 and all non-hydrogen atoms
were refined anisotropically using the least-squares method on
F2.16 A racemic disorder of the group concerning the asymmetric
carbon atom in 15 has been refined with the help of ADP and
distance restraints. Two molecules of compound 16 and some
partial occupied and disordered solvent molecules are present in
the independent unit of 16. Only one of the complexes shows
disorders of the phenyl rings. The ether molecule has been refined
on two positions, and a mixture of dichloromethane and tri-
chloromethane has been refined on the same position. As in 15,
all disorders could be refined with help of ADP and distance
restraints. With regard to 16, the absolute structure parameter
has been refined to -0.032(14).17 Crystallographic data in CIF
format for 5, 6, 15, and 16 are available in the Supporting
Information.
0
0
0
0
(C7a ), 168.7 (C7b ), 163.2 (C5b ), 162.8 (C5a ), 159.4 (C5a), 159.4
(C5b), 148.9 (CAr), 148.5 (2C, CAr), 148.3 (CAr), 148.0 (CAr),
0
129.0 (CArb), 128.3 (CAra ), 127.7 (CAra ), 127.0 (CArb ), 126.8
0
0
0
(CAra), 126.7 (CArb ), 126.5 (CAra), 126.1 (CArb), 124.0 (C4b),
0
123.7 (C4a), 123.4 (CArb), 122.5 (CAra), 122.3 (C3b), 122.2 (CAra ),
0
122.1 (CArb ), 122.0 (C3a), 121.1 (C3b ), 121.0 (C3a ), 120.7 (C4a ),
0
0
0
0
120.6 (C4b ), 62.9 (C6a), 62.8 (C6b), 58.9 (C6a ), 58.7 (C6b ), 45.1
0
0
0
(C2b), 44.9 (C2a), 44.8 (C2a ), 44.7 (C2b ), 32.3 (C1b ), 32.2 (C1a),
0
0
0
0
31.3 (C1b), 30.9 (C1a ), þ24.6 (CMeb), 24.3 (CMea), 14.4 (CMeb ),
þ þ
20
0
14.1 (CMea ). MS (FAB ): m/z 527 [M þ H ] . [R] D = þ8.5°
(589 nm, 20 °C, 5.31 ꢀ10-3 g/cm3 in MeOH, 10 cm path).
Complex 16. A mixture of 14 (0.270 g, 0.36 mmol), K2CO3
(0.250 g, 1.8 mmol), and NiCl2 (0.047 g, 0.36 mmol) in dry pyridine
(3 mL) was heated at 80 °C overnight. After the mixture was
cooled to room temperature, the solvent was removed under
vacuum. The residue was dissolved in dichloromethane (15 mL)
and was washed with water (15 mL). The water was washed twice
with chloroform (15 mL), and the combined organic layers were
dried over Na2SO4. After removal of the solvent, the crude solid
was washed with THF (10 mL). After drying under vacuum,
complex 16 was obtained as a yellow solid (0.120 g, 52%). Crystals
suitable for X-ray diffraction analysis were grown by diffusion of
diethyl ether into a solution of 16 in dichloromethane. Anal. Calcd
for C35H44N6O2Ni: C, 65.74; H, 6.94; N, 13.14. Found: C, 65.70;
H, 6.79; N, 13.13. 1H NMR (250 MHz, CDCl3): δ 7.17 (bs, 2H,
Acknowledgment. The CNRS and ECOS (C08E01) are
acknowledged for financial support. Dr. Guy Lavigne
(LCC CNRS-Toulouse) is acknowledged for fruitful dis-
cussions. Furthermore, we acknowledge Chantal Zedde
ꢀ
from the “Service de Chromatographie-Universite Paul
Sabatier” for her patience and the energy invested to find
the good conditions during the HPLC experiments for
compound 13.
H
Im), 7.04 (m, 10H, HAr), 6.80 (bs, 2H, HIm), 5.64 (m, 2H,
Supporting Information Available: Text giving additional
experimental details and CIF files giving crystallographic data
for 5, 6, 15, and 16. This material is available free of charge via
the Internet at http://pubs.acs.org.
CH(CH3)2, 3J = 5.5 Hz), 5.01 (d, 2H, NCH2a, 2J = 16 Hz), 3.99
(m, 2H, H2a), 3.90 (m, 2H, NCH2b, 2J = 15.9 Hz), 3.41 (m, 2H,
H2b), 1.73 (m, 2H, H1), 1.56 (s, 6H, HMe), 0.71 (m, 12H, CH-
(CH3)2). 13C NMR (75 MHz, CDCl3): δ 174.1 (2C, C7), 165.1 (2C,
C5), 143.3 (2C, CAr), 127.6 (4C, CAr), 126.0 (4C, CAr), 125.0 (2C,
(15) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(16) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(17) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
CAr), 121.9 (2C, CIm), 118.9 (2C, CIm), 71.0 (2C, C6), 49.7 (2C,
NCH2), 44.8 (2C, C2), 43.3 (2C, CH(CH3)2), 32.6 (1C, C1), 18.0