Synthesis and characterisation of a novel chiral bidentate pyridine-N-heterocyclic carbene-based palladacycle

Article abstract of DOI:10.1002/ejic.200901142

A novel chiral six-membered bidentate pyridine-N-heterocyclic carbene palladacycle was prepared via optical resolution of the racemic palladacycle. This is the first successful demonstration of the synthesis of a chiral carbene palladacycle via fractional

Full text of DOI:10.1002/ejic.200901142

FULL PAPER
DOI: 10.1002/ejic.200901142
Synthesis and Characterisation of a Novel Chiral Bidentate
Pyridine-N-Heterocyclic Carbene-Based Palladacycle
[a]
[a]
[a]
[a]
[a]
Minyi Chiang, Yongxin Li, Deepa Krishnan, Pullarkat Sumod, Kim Hong Ng, and
Pak-Hing Leung*[
a]
Keywords: Carbene ligands / Nitrogen heterocycles / Palladium / Optical resolution
A novel chiral six-membered bidentate pyridine-N-hetero-
cyclic carbene palladacycle was prepared via optical resolu-
tion of the racemic palladacycle. This is the first successful
demonstration of the synthesis of a chiral carbene palladacy-
cle via fractional crystallization of its chiral amino acid deriv-
tallized out spontaneously. Optically active (R)- and (S)-
dichloropalladacycles can then be achieved by subsequent
cleavage of the chiral amino acid auxiliary in the presence
of aqueous HCl from their respective diastereomers. The ab-
solute configurations of both the (R)- and (S)-palladacycles
were determined by X-ray diffraction studies.
atives. Upon formation of (R
C
C C C
,S ) and (S ,S )-phenylalanate
derivatives, the (R ,S )-phenylalanate diastereomer crys-
C C
Introduction
knowledge, none of the above-mentioned pyridine-NHC
palladacycles exhibited any chirality in the carbon chelate
backbone.
Following the isolation of the stable carbene in crystal-
line form by Arduengo in 1991,[ the chemistry of N-het-
erocyclic carbenes (NHC) has experienced unprecedented
development. The popularity of NHC can be attributed to
the fact that both their electronic and steric properties can
be easily modified like phosphane ligands which have been
the ligand of choice in the field of organometallic catalysis.
Unlike phosphane ligands, NHCs are mainly σ donors and
weak π accepting ligands.[ Due to the strong metal–NHC
bond, NHC-based catalytic systems exhibit a high degree
of stability against heat, moisture and air during the course
of their synthetic applications. Therefore NHC have
emerged as a promising functional analogue to phosphanes
for the design of organometallic catalysts.[
1]
Realising that all the above-mentioned chiral palladium
complexes were achieved via manipulation of chiral amines
or other chiral starting materials and also due to the fact
that a literature search yielded no results on any chiral bi-
dentate pyridine-NHC palladacycle, we sought to achieve
the synthesis of such a palladium system by the optical res-
olution of a racemic palladium complex via diastereomeric
complex formation with chiral amino acids as the resolving
agent, since this is a common method employed in the syn-
2]
[9]
thesis of palladacycles. We envisaged that a more rigid
chiral chelating system would be more effective in con-
trolling the stereochemistry in an asymmetric reaction sce-
nario. We hereby present the synthesis, resolution and char-
acterisation of the first ever reported chiral NHC-pyridine
palladium bidentate complex.
3]
Recently, several groups have focused their efforts in the
development of hemilabile chelating NHC metallacycles
[
4]
like the S, N and O functionalized NHC bidentate ligands.
This trend can be attributed to the fact that through intro-
duction of the rigidity of a bidentate system and the options
of chirality on the chelate backbone, a more promising cata-
lyst can be developed.[ One of the most common variant is
the palladium system and these palladium complexes have
shown average to excellent ee values in a variety of asym-
Results and Discussion
5]
The synthesis of the new pyridine-functionalized imid-
azolium salt 3 was achieved by the initial reduction of the
commercially available 2-benzoylpyridine followed by halo-
genation to give 2-[chloro(phenyl)methyl]pyridine. Subse-
quent reaction of 2-[chloro(phenyl)methyl]pyridine with 1-
methylimidazole (Scheme 1) yielded the target imidazolium
[
6]
metric reactions. Pyridine-NHC chelating ligands are a
popular class of hemilabile ligands. These ligands are usu-
[
7]
ally coordinated to the palladium centre in a bidentate or
a tridentate fashion[ and display excellent catalytic ability
in C–C coupling reactions. However, to the best of our
8]
salt 3. The imidazolium salt 3 was then subjected to the
transmetalation method developed by Lin et al.
[10]
to give
the racemic palladacycle complex (Ϯ)-4. The silver complex
was generated in situ and its formation was confirmed by
the absence of the characteristic imidazolium proton peak
[
a] Division of Chemistry and Biological Chemistry, School of
Physical and Mathematical Sciences,
Nanyang Technological University, 637371 Singapore
E-mail: pakhing@ntu.edu.sg
1
at δ = 10.15 in H NMR spectroscopy. The crude silver
Eur. J. Inorg. Chem. 2010, 1413–1418
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M. Chiang, Y. Li, D. Krishnan, P. Sumod, K. H. Ng, P.-H. Leung
FULL PAPER
complex was filtered through a short plug of celite and was
immediately subjected to the proceeding step to yield com-
plex (Ϯ)-4 as yellow solid (Scheme 1). X-ray crystallography
grade single crystals of complex (Ϯ)-4 can be obtained via
slow diffusion of diethyl ether into a solution of complex
(Ϯ)-4 in methanol and dimethyl sulfoxide (DMSO). Race-
mic complex (Ϯ)-4 can then be resolved via the formation
of its diastereomeric derivatives with sodium-(S )-phenylal-
C
anate (Scheme 2). Complex (R ,S )-5 spontaneously crys-
C
C
tallized out from the reaction mixture and was isolated as
an off-white crystalline solid, leaving a (S ,S )-5-enriched
C
C
mother liquor. The diastereomeric derivatives were sub-
sequently treated with aqueous 1  HCl to give the optically
active complexes (R)-4 and (S)-4 respectively.
Scheme 2.
bon numbers that they are directly attached to in Figure 1),
it can be established that the six-membered ring remained
locked in the boat conformation with no rotational con-
formers present in room temperature.
Scheme 1.
The solubility of complex (Ϯ)-4 posed as the main chal-
lenge in the course of the synthesis. Complex (Ϯ)-4 was
found to be insoluble in an array of organic solvents like
CH Cl and CH Cl; sparingly soluble in more polar sol-
2
2
3
vents like tetrahydrofuran, acetonitrile and methanol; and
was only completely soluble in DMSO. Due to the poor
solubility of complex (Ϯ)-4, it is necessary to add a few
drops of DMSO to the methanol solution to enable com-
plex (Ϯ)-4 to be completely soluble in the solvent. The X-
ray diffraction study of complex (Ϯ)-4 was performed (Fig-
ure 1) and the selected bond lengths and angles are pro-
vided in Table 1. The X-ray diffraction study of complex
(Ϯ)-4 showed that the six-membered ring is in the boat con-
formation, with the Ph ring in the axial position. The con-
formation of complex (Ϯ)-4 in solution was determined by
1
1
2
D H- H ROESY NMR (Figure 2). The assignment of
proton signals was made by a combination of COSY and
HMQC. From the key correlations (A) and (B) observed in
1
1
2D
H- H ROESY NMR, namely between H5–H4 and
H5–H13 (protons were numbered in accordance to the car- Figure 1. Molecular structure of complex (Ϯ)-4.
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Eur. J. Inorg. Chem. 2010, 1413–1418

A Novel Chiral Bidentate NHC-Based Palladacycle
Table 1. Selected bond lengths selected bond lengths (Å) and angles
Off white crystals of diastereomer (R ,S )-5 suitable for
C C
(°) for racemic complex (Ϯ)-4.
X-ray crystallography were obtained by slow diffusion of
diethyl ether into a methanol/DMSO solution of complex
(R ,S )-5. The molecular structure of diastereomer
Pd(1)–C(1)
Pd(1)–Cl(2)
C(1)–Pd(1)–N(3) 86.2(9)
N(3)–Pd(1)–Cl(2) 173.7(6)
N(3)–Pd(1)–Cl(1) 91.3(6)
N(1)–C(1)–Pd(1) 133.8(2)
C(16)–N(3)–Pd(1) 119.7(16)
1.951(3)
2.310(7)
Pd(1)–N(3)
Pd(1)–Cl(1)
C(1)–Pd(1)–Cl(2) 90.8(7)
C(1)–Pd(1)–Cl(1) 176.6(7)
Cl(2)–Pd(1)–Cl(1) 91.8(3)
N(2)–C(1)–Pd(1)
C(12)–N(3)–Pd(1) 121.1(2)
2.055(2)
2.374(7)
C
C
(
R ,S )-5 is presented in Figure 3, selected bond lengths
C C
and bond angles are provided in Table 2. The X-ray crystal-
lographic study revealed the R absolute configuration of the
α-carbon stereocenter which was confirmed independently
120.8(2)
using (S )-phenylalanate as a reference point, as well as
C
based on the anomalous X-ray scattering method with the
Flack parameter of 0.003(18). The complex adopts a trans-
(N,N) arrangement, with the α-phenyl group (C7–C12) oc-
cupying the axial position. The tetrahedral distortion of the
palladium coordination environment is minimal, with an
angle of 5.5° between the {Pd(1)–C(16)–N(1)} and {Pd(1)–
N(4)–O(1)} planes.
Figure 2. ROESY NMR of complex (Ϯ)-4.
After screening through a range of amino acid salts in
different solvent systems, only sodium (S )-phenylalanate
C
was found to be an effective resolving agent for the resolu-
tion of complex (Ϯ)-4 in methanol. After the addition of 1
C C
Figure 3. Molecular structure of complex (R ,S )-5.
molar equivalent of sodium (S )-phenylalanate, the pro-
C
gress of the diastereomeric salt formation was monitored
by H NMR spectroscopy. The two resulting diastereomers
could not be separated and kept crystallizing out together
1
Table 2. Selected bond lengths (Å) and angles (°) for complex
,S )-5.
(
R
C
C
in several failed attempts at fractional crystallizations in dif- Pd(1)–C(16)
1.960(4)
2.028(3)
Pd(1)–N(1)
Pd(1)–O(1)
C(16)–Pd(1)–N(4) 99.01(17)
C(16)–Pd(1)–O(1) 176.3(2)
N(4)–Pd(1)–O(1)
N(3)–C(16)–Pd(1) 133.3(3)
C(5)–N(1)–Pd(1) 123.9(2)
2.027(3)
2.057(3)
Pd(1)–N(4)
ferent solvent system. The problem was circumnavigated by
changing the counter anion present in the diastereomeric
complexes. After switching the counter anion from chloride
C(16)–Pd(1)–N(1) 86.44(9)
N(1)–Pd(1)–N(4) 173.5(1)
N(1)–Pd(1)–O(1) 94.3(1)
80.5(6)
to nitrate, successful optical resolution of racemic complex N(2)–C(16)–Pd(1) 120.8(3)
C(1)–N(1)–Pd(1) 118.0(2)
(
Ϯ)-4 was achieved using sodium (S )-phenylalanate as the
C
auxiliary ligand (Scheme 2). Sequential treatment of com-
plex (Ϯ)-4 with two molar equivalent of silver nitrate and
Slow diffusion of diethyl ether into a methanol solution of
one molar equivalent of sodium (S )-phenylalanate resulted the resulting diastereomer (S ,S )-5-enriched mother liquid
C
C
C
in the formation of the expected 1:1 mixture of dia- allowed all of the remaining diastereomer (R ,S )-5 to crys-
C
C
stereomeric adducts (R ,S )-5 and (S ,S )-5 as evident tallize out. The resulting mother liquor comprised almost en-
C
C
C
C
from the presence of two distinct sets of proton resonances tirely of the other diastereomer (S ,S )-5 Ͼ 99% de (accord-
C
C
1
for each of the diastereomers. Fractional crystallization ing to the H NMR spectrum) with [α]4 = +42.1 (c = 0.5,
36
from methanol/diethyl ether afforded the less soluble dia- MeOH). Diastereomer (S ,S )-5 was subsequently isolated
C
C
stereomer (R ,S )-5 in the form of off-white crystalline so- as a light yellow colored solid in 67% yield. Compared to
C
C
1
lid in 70% yield and Ͼ 99% de (according to the H NMR (R ,S )-5, (S ,S )-5 displayed far superior solubility in an
C
C
C
C
spectrum) with [α]436 = +83.3 (c = 0.5, DMSO). In [D ]- array of solvents. Therefore, efforts to obtain X-ray grade
6
1
DMSO, the 500-MHz H NMR spectrum of complex crystals of (S ,S )-5 were unsuccessful. However, as demon-
C
C
(
R ,S )-5 at room temperature presents itself as a sole geo- strated below, an optically pure complex can be obtained
C C
metric isomer in solution, which was indicated by the pres- from the mother liquor (Ͼ 99% de) by the cleavage of the
ence of a solitary set of resonance observed for each chemi- chiral auxiliary phenylalanate ligand thereby leading to the
cally nonequivalent proton.
formation of the single crystals of the chiral complex (S)-4.
Eur. J. Inorg. Chem. 2010, 1413–1418
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M. Chiang, Y. Li, D. Krishnan, P. Sumod, K. H. Ng, P.-H. Leung
FULL PAPER
The optically active dichloro complex (R)-4 was obtained
by mixing a methanol solution of complex (R ,S )-5 with
C
C
1
 HCl and was isolated as a yellow powder in 51% yield
with [α]436 = –12.5 (c = 0.5, DMSO) (Scheme 2). Yellow
single crystals suitable for X-ray crystallography were ob-
tained from a solution of (R)-5 in methanol, DMSO and
diethyl ether and its molecular structure is depicted in Fig-
ure 4. The selected bond lengths and angles are listed in
Table 3. The X-ray crystallographic study confirmed the ex-
pected R absolute configuration of the α-phenyl stereocen-
ter of the palladacycle. The coordination sphere of the pal-
ladium center is in a distorted square-planar geometry, with
tetrahedral distortions of 1.5°.
Figure 5. Molecular structure of complex (S)-4.
C
Table 4. Selected bond lengths (Å) and angles (°) for complex (S )-
4.
Pd(1)–C(1)
Pd(1)–Cl(2)
C(1)–Pd(1)–N(1) 86.9(8)
N(1)–Pd(1)–Cl(2) 179.6(5)
N(1)–Pd(1)–Cl(1) 89.9(5)
N(3)–C(1)–Pd(1) 135.9(2)
C(12)–N(1)–Pd(1) 121.7(1)
1.984(2)
2.292(5)
Pd(1)–N(1)
Pd(1)–Cl(1)
C(1)–Pd(1)–Cl(2) 92.8(6)
C(1)–Pd(1)–Cl(1) 176.2(6)
Cl(2)–Pd(1)–Cl(1) 90.5(2)
N(2)–C(1)–Pd(1)
C(16)–N(1)–Pd(1) 118.9(1)
2.045(2)
2.357(5)
118.9(1)
Conclusions
In this paper, we have successfully demonstrated the via-
bility of synthesizing novel chiral bidentate NHC-based
palladacycles via efficient optical resolution of its dia-
stereomeric salts. Resolution of other hemilabile pallada-
cycles and catalytic applications of the synthesized chiral
palladacycles are currently in progress.
Figure 4. Molecular structure of complex (R)-4.
C
Table 3. Selected bond lengths (Å) and angles (°) for complex (R )-
4.
Pd(1)–C(1)
Pd(1)–Cl(2)
C(1)–Pd(1)–N(1) 87.0(7)
N(1)–Pd(1)–Cl(2) 179.5(5)
N(1)–Pd(1)–Cl(1) 89.9(5)
N(3)–C(1)–Pd(1) 136.1(2)
C(16)–N(1)–Pd(1) 118.7(1)
1.980(2)
2.292(5)
Pd(1)–N(1)
Pd(1)–Cl(1)
C(1)–Pd(1)–Cl(2) 92.7(6)
C(1)–Pd(1)–Cl(1) 176.4(6)
Cl(2)–Pd(1)–Cl(1) 90.5(2)
N(2)–C(1)–Pd(1)
C(12)–N(1)–Pd(1) 121.7(1)
2.045(2)
2.356(5)
Experimental Section
General: Reactions involving air-sensitive compounds were per-
formed under a positive pressure of purified nitrogen using stan-
dard Schlenk techniques. All the commercially available chemicals
and solvents were used without prior drying or purification. Phen-
118.9(1)
yl(pyridin-2-yl)methanol[ 1 and PdCl
11]
(NCMe)
[12]
were prepared
2
2
according to literature methods. Proton nuclear magnetic reso-
nance ( H NMR) and carbon nuclear magnetic resonance ( C
NMR) spectroscopy were performed on a Bruker Avance 300, 400
The enantiomerically pure palladacycle (S)-4 was pre-
pared from complex (S ,S )-5 in a similar manner: [α]
1
13
=
436
C
C
+
11.8 (c = 0.5, DMSO) (Scheme 2). Yellow colored single and 500 NMR spectrometers. Multiplicities were given as: s (sing-
crystals were obtained from a methanol, DMSO and diethyl let); b (broad singlet); d (doublet); t (triplet); q (quartet); dd (dou-
ether solution of complex (S)-4. The solid-state structure of
blets of doublet); m (multiplets) and etc. The number of protons
(
n) for a given resonance is indicated by nH. Coupling constants
the complex (S)-4 was determined by X-ray crystallography
refer to Figure 5). Selected bond lengths and angles are
are reported as a J value in Hz. Nuclear magnetic resonance spec-
(
1
tra ( H NMR) are reported as δ in units of parts per million (ppm)
listed in Table 4. The X-ray crystallographic study con-
firmed the S absolute configuration of the α-phenyl
stereocenter of the palladacycle. The Pd center experienced
a slight tetrahedral distortion and the dihedral angle be-
downfield from SiMe
4
(δ = 0.0 ppm), relative to the signal of
13
[D]chloroform (δ = 77.20, triplet) ( C NMR). Phase-sensitive
ROESY spectra were obtained with a Bruker AMX-500 spectrome-
ter and were acquired into a 1024X512 matrix with a 250 ms spin
tween the {N(1)–Pd(1)–C(1)} and {Cl(1)–Pd(1)–Cl(2)} pla- lock time and a spin lock field strength such that γB1/2π = 5000 Hz
nes was 1.9°. and then transformed into 1024ϫ1024 points by using a sine bell
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Eur. J. Inorg. Chem. 2010, 1413–1418

A Novel Chiral Bidentate NHC-Based Palladacycle
weighting function in both dimensions. Mass spectra were recorded
on a Thermo Finnigan MAT 95 XP Mass Spectrometer with EI
mode and Waters Q-Tof Premimer Mass Spectrometer with ESI
mode. Melting points were determined on SRS-Optimelt MPA-100
apparatus and were uncorrected. Optical rotations were measured
on the specified solution in 0.1-dm cell at 25 °C with a Perkin–
Elmer model 341 polarimeter. The Elemental Analysis Laboratory
of the Division of Chemistry and Biological Chemistry at the Nan-
yang Technological University of Singapore performed elemental
analyses.
16 2 3 4
C H16Cl N Pd·C H10O (501.77): calcd. C 47.87, H 5.22, N 8.37;
found C 48.06, H 5.69, N 8.38.
Optical Resolution of the Racemic Complex 4: To a suspension of
the racemic complex (2.45g, 5.7 mmol) in 20 mL of methanol,
AgNO
allowed to stir in the dark at room temperature for 3 h and was
filtered through celite. The filtrate was treated with sodium (S )-
3
(1.94 g, 11.4 mmol) was added. The reaction mixture was
C
phenylalanate (1.07 g, 5.7 mmol) in 100 mL of methanol. The reac-
tion mixture was stirred for 2 h and was concentrated to approxi-
mately 50 mL and was left to stand overnight. Complex (R
-[Chloro(phenyl)methyl]pyridine (2): Phenyl(pyridin-2-yl)methanol which precipitated out as off-white crystals the next day was iso-
1) (1.85 g, 10.5 mmol) and triethylamine (3.4 mL, 24.4 mmol) in
lated and washed with methanol.
C C
,S )-5
2
(
3
2 mL of dichloromethane was stirred in an ice bath. Methanesul-
Diastereomer (R ,S )-5: 1.2 g, 35%, [α]436 = +83.3 (c = 0.5,
DMSO); m.p. 189.5–190.2 °C (dec.). H NMR (500 MHz, DMSO):
δ = 2.61–2.65 (m, 1 H), 3.16 (d, JH,H = 5.2 Hz, 1 H), 3.50–3.52 (m,
C
C
fonyl chloride (1.2 mL, 15.8 mmol) was added dropwise to the stir-
ring solution. The reaction mixture was allowed to warm up slowly
to room temperature. The reaction mixture was left to stir over-
night and was then poured into a saturated aqueous NaHCO
tion. The aqueous layer was extracted with chloroform. The com-
bined organic layers were washed with H O, dried with anhydrous
MgSO and the solvents evaporated in vacuo to give a red liquid.
1
1
3
H), 3.82 (s, 3 H, CH ), 5.00 (d, JH,H = 9.6 Hz, 1 H), 5.98–6.01
3
solu-
(
(
m, 1 H), 6.94 (s, 1 H, arom. H), 6.96 (s, 1 H, arom. H), 7.15–7.23
m, 5 H, arom. H), 7.35–7.38 (m, 2 H, arom. H), 7.47–7.50 (m, 2
2
H, arom. H), 7.59 (d, JH,H = 1.8 Hz, 1 H, arom. H), 7.76–7.79 (m,
4
1
=
H, arom. H), 7.90 (d, JH,H = 1.8 Hz, 1 H, arom. H), 8.16 (d, JH,H
7.8 Hz, 1 H, arom. H), 8.33–8.36 (m, 1 H, arom. H), 8.71 (d,
The resultant red liquid was subjected to flash column chromatog-
raphy (ethyl acetate/hexanes = 1:4, v/v) to give a yellow oil 1.7 g,
1
3
JH,H = 4.7 Hz, 1 H, arom. H) ppm. C NMR (100 MHz, DMSO):
1
80%. H NMR (500 MHz, CDCl
3
): δ = 6.17 (s, 1 H, ClCH), 7.19–
δ = 37.26, 49.06, 62.71, 66.34, 123.58, 124.62, 126.61, 126.79,
7.22 (m, 1 H, arom. H), 7.26–7.36 (m, 3 H, arom. H), 7.47–7.56
1
1
27.08, 127.65, 128.55, 128.91, 129.29, 129.57, 129.78, 137.35,
39.71, 142.10, 151.70, 153.07, 154.77, 179.24 ppm. C25 Pd
(m, 3 H, arom. H), 7.69–7.72 (m, 1 H, arom. H), 8.57–8.58 [d,
25 5 5
H N O
13
J(H,H) = 4.0 Hz, 1 H, arom. H] ppm. C NMR (100 MHz,
CDCl ): δ = 64.58 (C-Cl), 122.11, 122.85, 127.81, 128.31, 128.67,
37.0, 139.96, 149.21, 159.71 ppm. HRMS (ESI) m/z: [M + H]+
calcd. for C12 10ClN 204.0580, found 204.0585.
(
581.09): calcd. C 51.60, H 4.33, N 12.03; found C 50.44, H 4.33,
3
N 12.05.
1
H
The mother liquor is enriched with the other diastereomer (S ,S )-
C
C
5.
1
(
-Methyl-3-[phenyl(pyridin-2-yl)methyl]-1H-imidazolium Chloride
3): 1-Methylimidazole (1.8 mL, 22.6 mmol) was added to a stirring
solution of compound 2 (4.35g, 21.3 mmol) in 50 mL of CH CN.
Diastereomer (S
MeOH); m.p. 189–190 °C (dec.). H NMR (400 MHz, MeOD): δ
= 2.56 (s, 2 H, CH ), 2.80–2.86 (m, 1 H), 3.13–3.17 (m, 1 H), 3.27–
3.29 (m, 1 H), 3.65 (s, 3 H, CH ), 7.07 (s, 1 H, arom. H), 7.09–7.33
(m, 11 H, arom. H), 7.56–7.59 (m, 1 H, arom. H), 7.68 (d, JH,H
C C
,S )-5: 1.1 g, 34%. [α]436 = +42.1 (c = 0.5,
1
3
The reaction mixture was heated at refluxing temperature for 48 h.
The reaction mixture was reduced in vacuo and the resulting oil
2
3
was stirred in diethyl ether. The diethyl ether layer was decanted to
=
1
give a pink oil 4.3 g, 70%. H NMR (400 MHz, CDCl
3
): δ = 4.01 7.7 Hz, 1 H, arom. H), 8.14–8.18 (m, 1 H, arom. H), 8.70 (d, JH,H
1
3
(
s, 3 H, CH
arom. H), 7.52 (s, 1 H, arom. H), 7.61–7.64 (m, 2 H, arom. H), 37.49, 40.62, 41.30, 63.24, 68.62, 124.35, 125.50, 127.27, 128.13,
.68–7.72 (m, 2 H, arom. H), 8.57 (d, JH,H = 4.5 Hz, 1 H, arom.
128.21, 128.27, 130.03, 130.42, 130.67, 138.36, 140.43, 142.90,
3
), 7.25–7.34 (m, 4 H, arom. H), 7.41–7.43 (m, 2 H, = 5.5 Hz, 1 H, arom. H) ppm. C NMR (100 MHz, MeOD): δ =
7
13
+
H), 10.15 (s, 1 H, carbenic proton) ppm. C NMR (100 MHz,
CDCl ): δ = 36.74 (N-CH
), 66.06 (N-C-Ph), 121.90, 122.87, for C25
23.95, 124.71, 129.07, 129.42, 129.56, 136.54, 137.82, 138.63,
49.60, 155.18 ppm. HRMS (ESI) m/z: [M – Cl]+ calcd. for
154.12, 156.39, 181.86 ppm. HRMS (ESI) m/z: [M–NO
3
]
calcd.
1
06
25 4 2
H N O
Pd 519.1012, found 519.1013.
3
3
1
1
[
Pd{1-methyl-3-{phenyl(pyridin-2-yl)methyl}-1H-(N-CH
3
)imid-
,S )-
C C
azolin-2-ylideneCl }] {(R)-4}: To a suspension of complex (R
2
C
16
H
16
N
3
250.1344, found 250.1345.
5
(0.50g, 0.86 mmol) in 50 mL of methanol, 1  HCl (aq) (4.3 mL,
Racemic
[Pd{1-methyl-3-{phenyl(pyridin-2-yl)methyl}-1H-imid-
4.3 mmol) was added. The reaction mixture was stirred vigorously
for approximately 1 hour and was concentrated down to give an
orange yellow solid. The solid was washed three times with copious
amount of methanol to give a pale yellow solid 0.2 g, 51%, [α]436
= –12.5 (c = 0.5, DMSO).
azolin-2-ylideneCl
2
}] (–)-4 and (+)-(4): To a solution of compound
(3.57g, 12.5 mmol) in 30 mL of dichloromethane, Ag O (1.59g,
.9 mmol) was added in the dark. The reaction mixture was allowed
3
6
2
to stir at room temperature for 12 hours and was filtered through
celite. A PdCl (NCMe) suspension (3.24g, 12.5 mmol in 100 mL
of CH CN) was added to the filtrate in the dark. The reaction
2
2
Similarly, complex (S)-4 was achieved using the same method from
3
complex (S
, S
C C
)-5 0.2 g, 50%. [α]436 = +11.8 (c = 0.5, DMSO).
mixture was then allowed to stir overnight at room temperature
and was filtered through a short plug of celite the next day. The
filtrate was reduced in vacuo to approximately 50 mL and diethyl
Crystal Structure Determinations of (؎)-4, (R
C
,S )-5, (R)-4, and
C
(S)-4: Crystal data for all 4 complexes and a summary of the crys-
ether (200 mL) was added which resulted in the precipitation of an
tallographic analyses are given in Table 5. Diffraction data were
1
orange-yellow solid 3.3 g, 61%; m.p. 249.2–249.8 °C (dec.).
NMR (400 MHz, DMSO): δ = 3.97 (s, 3 H, CH
H, arom. H), 7.62 (t, 1 H, arom. H), 7.84 (s, 1 H, arom. H), 8.02 were applied. All non-hydrogen atoms were refined anisotropically
H
collected on a Bruker X8 CCD diffractometer with Mo-K
α
radia-
3
), 7.33–7.47 (m, 6
tion (graphite monochromator). SADABS absorption corrections
(
J
d, JH,H = 7.6 Hz, 1 H, arom. H), 8.20 (t, 1 H, arom. H), 9.12 (d,
while hydrogen atoms were introduced at calculated positions and
refined riding on their carrier atoms. The absolute configurations
H,H = 5.6 Hz, 1 H, arom. H) ppm. 13C NMR (100 MHz, DMSO):
3
δ = 37.86 (N-CH ), 66.46 (N-C-Ph), 122.41, 124.11, 125.10, 126.34, of the chiral complexes were determined unambiguously using the
Flack parameter.[
13]
126.98, 128.29, 128.78, 138.19, 140.45, 150.37, 154.60, 155.10 ppm.
Eur. J. Inorg. Chem. 2010, 1413–1418
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1417

M. Chiang, Y. Li, D. Krishnan, P. Sumod, K. H. Ng, P.-H. Leung
FULL PAPER
Table 5. Crystallographic data for complexes (Ϯ)-4, (R
,S
C C
C
)-5, (Rc)-4 and (S )-4.
(Ϯ)-4
(R ,S )-5
C
C
(Rc)-4
(Sc)-4
Formula
Formula weight
Space group
Crystal system
a /Å
C
426.61
Pbca
orthorhombic
12.1801(5)
15.4613(7)
17.8198(7)
3355.8(2)
8
16
H
15Cl
2
N
3
Pd
C
581.90
P2(1)
monoclinic
9.3999(4)
10.6789(4)
11.9827(5)
1182.87(8)
2
25
H
25
N
5
O
5
Pd
C
426.61
16
H
15Cl
2
N
3
Pd
16 2 3
C H15Cl N Pd
426.61
P2(1)2(1)2(1)
orthorhombic
9.7816(3)
12.7776(3)
13.0825(4)
1635.12(8)
4
P2(1)2(1)2(1)
orthorhombic
9.7843(5)
12.7883(6)
13.0945(6)
1638.44(14)
4
b /Å
c /Å
V /Å
3
Z
T /K
ρ
223(2)
1.689
173(2)
1.634
173(2)
1.733
173(2)
1.729
calcd. /g cm–3
λ /Å
0.71073
1.423
0.71073
0.832
0.71073
1.460
0.71073
1.457
µ /mm–1
Flack parameter
0.003(18)
0.0265
0.0711
–0.01(2)
0.0290
0.0741
–0.008(19)
0.0234
0.0497
[
a]
R
wR
1
(obsd. data)
0.0393
0.0821
[
b]
2
(obsd. data)
= Σ||F | – |F
[a] R
1
o
|. [b] wR
2
= {Σ[w(F2
– F2
,S
)2]}/Σ[w(F2
o
2 1/2
) ] , w–1 = σ (F
2
2
) + (aP) + bP.
2
c
||/Σ|F
o
o
c
o
CCDC-755570 (for (Ϯ)-4), -755571 (for (R
C
C
)-5), -755572 (for
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Received: November 25, 2009
Published Online: February 12, 2010
1418
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 1413–1418