Design, synthesis, and stereochemical evaluation of a novel chiral amine-palladacycle

Article abstract of DOI:10.1002/ejic.200701234

A novel chiral palladacycle containing ortho-metallated (±)-1-(3,6-dimethylnaphthalen-2-yl)-N,N-dimethylethylamine was designed and synthesized by a multi-step synthesis by using 2,7-dimethylnaphthalene as the starting material. The structure and palladacycle ring conformation of the triphenylphosphane derivative was investigated by X-ray structural analysis in the solid state and by 2D ROESY NMR spectroscopy in solution. Through a designed intramolecular steric interaction, the five-membered naphthylamine chelate can be locked into a fixed conformation, both in the solid state and in solution. The racemic cyclopalladated complex could be efficiently resolved through the formation of its (S)-prolinato and (S)-alaninato derivatives. The structure and absolute configuration of the two optically resolved palladium complexes were determined by X-ray diffraction. Both the (R,R) and (S,S)-di-μ-chlorido dimeric palladium complexes containing the resolved amine ligand was obtained chemoselectively by treating the corresponding prolinato and alaninato derivatives with 1 M hydrochloric acid. Despite the severe interchelate steric constraint within these new organopalladium complexes, the bulky monodentate ligand 3,4-dimethyl-1-phenylphosphole (dmpp) was able to split the chlorido bridges regiospecifically in the position trans to the NMe₂ group. With the new palladacycle used as the chiral template, the stereoselectivity of Diels-Alder cycloaddition between dmpp and ethyl vinyl ketone significantly improves relative to that of other analogue complexes. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701234

FULL PAPER
DOI: 10.1002/ejic.200701234
Design, Synthesis, and Stereochemical Evaluation of a Novel Chiral Amine–
Palladacycle
Yi Ding,[a] Yongxin Li,[a] Yi Zhang,[a] Sumod A. Pullarkat,[a] and Pak-Hing Leung*[a]
Keywords: Asymmetric synthesis / Palladacycles / Chiral resolution / Cycloaddition / X-ray diffraction
A novel chiral palladacycle containing ortho-metallated (Ϯ)-
1-(3,6-dimethylnaphthalen-2-yl)-N,N-dimethylethylamine
was designed and synthesized by a multi-step synthesis by
using 2,7-dimethylnaphthalene as the starting material. The
structure and palladacycle ring conformation of the tri-
phenylphosphane derivative was investigated by X-ray
structural analysis in the solid state and by 2D ROESY NMR
spectroscopy in solution. Through a designed intramolecular
steric interaction, the five-membered naphthylamine chelate
can be locked into a fixed conformation, both in the solid
state and in solution. The racemic cyclopalladated complex
could be efficiently resolved through the formation of its (S)-
prolinato and (S)-alaninato derivatives. The structure and ab-
solute configuration of the two optically resolved palladium
complexes were determined by X-ray diffraction. Both the
(R,R) and (S,S)-di-µ-chlorido dimeric palladium complexes
containing the resolved amine ligand was obtained chemose-
lectively by treating the corresponding prolinato and alanin-
ato derivatives with 1
M hydrochloric acid. Despite the severe
interchelate steric constraint within these new organopalla-
dium complexes, the bulky monodentate ligand 3,4-dimethyl-
1-phenylphosphole (dmpp) was able to split the chlorido
bridges regiospecifically in the position trans to the NMe2
group. With the new palladacycle used as the chiral tem-
plate, the stereoselectivity of Diels–Alder cycloaddition be-
tween dmpp and ethyl vinyl ketone significantly improves
relative to that of other analogue complexes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
Over the past decade, optically active organopalladium
compounds, especially those derived from metallated terti-
ary amines, have proven to be very useful reagents for many
synthetic applications. Such complexes have generated
interest for their many roles, as catalysts,[1] agents for the
determination of enantiomeric excess,[2] resolving agents,[3]
and stoichiometric agents for the syntheses of organic com-
pounds.[4]
We have been interested in the development of chiral or-
thopalladated complexes of substituted benzyl- [(S)-1] and
naphthylamines [(S)-2] (Figure 1).[4f] It has been proven that
(S)-2 is superior over (S)-1 in many applications.[5a,5b] The
organometallic ring in (S)-2 is kinetically and thermody-
namically stable. The intramolecular steric interaction be-
tween H8 and the methyl group at the stereogenic carbon
center confines the methyl group in the axial position and
hence locks the cyclopalladated ring into the non-intercon-
vertable λ conformation. On the other hand, the ring con-
formation of (S)-1 is not locked, and the puckered ring
adopts both the δ and λ conformations in the solid state
and (S)-1 undergoes rapid inversion in solution.[5]
Figure 1. Molecular design for complexes (S)-1, (S)-2, and (S)-5.
Recently, we utilized (S)-2 and its derivatives for the
asymmetric syntheses of a series of functionalized mono-
and diphosphanes.[4f–4i,6] Complex (S)-3 is generated from
the dimeric complex (S)-2 by the regiospecific cleavage reac-
tion with 3,4-dimethyl-1-phenylphosphole (dmpp). The Di-
els–Alder cycloadditions of this phosphole complex with a
series of dienophiles have been extensively studied. For ex-
ample, when (S)-3 was treated with ethyl vinyl ketone at
70 °C, two endo-cycloaddition products were obtained as a
1:1 diastereomeric mixture of complexes 4a and 4b
(Scheme 1).[6a] This experiment shows that the influence of
the chiral naphthylethylamine auxiliary on the reaction site
is insignificant. Evidently, in the transition state, the dmpp
[a] Division of Chemistry and Biological Chemistry, School of
Physical and Mathematical Sciences, Nanyang Technological
University,
637371 Singapore
E-mail: Pakhing@ntu.edu.sg
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Design, Synthesis and Stereochemistry of a Chiral Amine–Palladacycle
group enjoys a certain degree of free rotation around the ence on the coordination position trans to the N donor
P–Pd dative bond thus rendering poor stereoselectivity of atom. The application of this new chiral template in asym-
the reaction.
metric Diels–Alder reactions was examined.
Results and Discussion
Synthesis of the Palladium Complexes (؎)-5
As illustrated in Scheme 2, the disubstituted naphthalene
derivative 6[7] was acetylated with acetyl chloride in the
presence of aluminum chloride to give ketone 7 in 45%
yield. Reduction of 7 in ethanol by sodium borohydride
produced racemic alcohol (Ϯ)-8 in 95% yield, which was
then converted to chloride (Ϯ)-9 in 92% yield by treatment
with excess PCl3 in dichloromethane. Reaction between the
chloride (Ϯ)-9 and aqueous dimethylamine afforded the
target N,N-dimethylamine (Ϯ)-10 as a white powder in 88%
yield. The orthopalladation of (Ϯ)-10 could be achieved in
acetonitrile with [Pd(MeCN)4](ClO4)2 as the palladium
source in the presence of an equimolar amount of triethyl-
amine. Treatment of the reaction mixture with dilute HCl
gave (Ϯ)-5 in the form of yellow prisms in an 85% isolated
yield.
Scheme 1.
In several similar syntheses, the separation of the corre-
sponding two endo-diastereomeric products was somewhat
tedious and resulted in low yields of the target enantiomers
Stereochemical Investigation of the New Palladacycle
One of the major challenges in the structural design of
because of poor stereoselectivity. To improve the stereose- the auxiliary lies in the introduction of a sterically conges-
lectivity, we designed and synthesized a new chiral complex tive condition around the template site that is adjacent to
(S)-5 (Figure 1). We expect that (S)-5 will retain all the de- the protruding H3 atom. In order to establish a coordina-
sired stereoelectronic properties of the original naph- tion site that is able to accommodate a bulky monodentate
thylamine template; most importantly, the organometallic ligand in a regiospecific manner, (Ϯ)-5 was treated with tri-
ring conformation in (S)-5 can be locked in solution by the phenylphosphane. Interestingly, the bulky phosphane li-
interaction between Me12 and Me14 (Scheme 3). Further- gand splits the chlorido bridges of (Ϯ)-5 efficiently and gen-
more, the aromatic hydrogen atom H3 is introduced adja- erated the mononuclear complex (Ϯ)-11 as the sole product
cent to the Pd–C bond so as to exert stereochemical influ- in 93% yield (Scheme 3).
Scheme 2.
Eur. J. Inorg. Chem. 2008, 1880–1891
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FULL PAPER
Scheme 3.
The molecular structure of (Ϯ)-11 was studied by single-
crystal structural analysis (Figure 2), and the selected bond
lengths and angles are listed in Table 1. Complex (Ϯ)-11
adopts a distorted square-planar coordination geometry.
The strong steric repulsion between the PPh3 ligand and the
organometallic chelate results in the enlargement of the
bond angle C1–Pd1–P1 to 101.7(1)°. With these structural
features, the Pd–P bond would not be able to rotate freely,
as all the possible rotational motions are blocked by the
chlorido ligand and the projecting aromatic proton H3. It
is noteworthy that 5 adopts a molecular structure in which
the second aromatic ring of the naphthyl group is placed in
such a position so as to reduce such Pd–P bond rotations
in 11.[8c] Therefore, among the three P–Ph phenyl rings, the
C17–C22 ring experiences the most intramolecular ligand–
ligand repulsion. As a result, the bond angle Pd1–P1–C17
is enlarged to 117.9(1)°, which is larger than the two less-
affected angles, Pd1–P1–C23 and Pd1–P1–C29 [111.5(1)°
and 115.5(1)°]. Most importantly, the ligand–ligand repul-
sive interactions in complex (Ϯ)-11 also disturb the planar-
ity of the conjugated rings. Thus, the central ring (C1–C2–
C7–C8–C9–C10) and the adjacent projecting ring (C2–C7)
do not lie within the same plane, and the dihedral angle
between these two rings is 5.1°.
Figure 2. Molecular structure of (Ϯ)-11.
Table 1. Selected bond lengths [Å] and angles [°] for complex (Ϯ)-
11.
Pd1–C1
Pd1–P1
P1–C23
P1–C29
C1–Pd1–N1
N1–Pd1–P1
N1–Pd1–Cl1
2.048(3)
2.273(1)
1.823(4)
1.841(4)
80.0(1)
174.5(1)
91.0(1)
Pd1–N1
Pd1–Cl1
P1–C17
P1–Pd1–Cl1
C1–Pd1–P1
C1–Pd1–Cl1
2.128(3)
2.381(1)
1.827(4)
87.9(1)
101.7 (1)
169.4(1)
the absence of any aliphatic protons will therefore not con-
1
In spite of the severe steric repulsion observed in (Ϯ)-11, tribute to the complexity in the aliphatic region of the H
the regiochemistry of this complex remains unchanged in NMR spectrum.
1
solution. In CDCl3, the 31P NMR spectrum of the complex
In solution, the H NMR spectroscopic characterization
shows only one singlet resonance at δ = 30.9 ppm, which of (Ϯ)-11 was assisted by a combination of 1H and 2D 1H–
indicates the presence of a single species in solution. In the 1H ROESY NMR spectroscopy experiments. The confor-
corresponding 1H NMR spectrum, the two N-methyl mational behavior of the five-membered palladacycle was
groups show the characteristic P–H couplings (2.0 and deduced from NOE data obtained from the 2D 1H–1H
4
3.4 Hz). These J(P,H) couplings confirm the trans relation- ROESY NMR spectrum. The labeled structure and the 2D
ship of the phosphorus atom and the nitrogen donor, which 1H–1H ROESY NMR spectrum of (Ϯ)-11 in CDCl3 are
can be justified by the “transphobia”.[8a,8b] Here, the com- shown in Scheme 3 and Figure 3, respectively. In this spec-
plex does not undergo the possible ligand redistribution trum, strong NOE signals (A, B) for the interactions be-
process in solution to form the other possible regioisomer tween the α-methane proton H13 and the two NMe groups
that would be sterically more favorable.
are clearly recorded. On the other hand, the α-Me group
The mononuclear complex (Ϯ)-11 is more suitable for interacts strongly with the equatorially disposed NMe
NMR spectroscopic studies of the organopalladium ring group (C), but very weakly with the axially disposed group
conformation because of the improved spectral resolution (D). The driving force for Me14 to assume mainly an axial
of the signals with respect to that from its parent dimer, position, i.e. H13–Me12 (E) and Me14–Me12 (F) repulsive
which exists in solution as an equilibrium mixture of two interactions, is prominently reflected. Other expected NOE
regioisomers. Moreover, the simplicity of the 1H NMR contacts for H13–Me14(G) and Me16–Me15 (H) are also
spectroscopic signals that are presented by the tri- observed. This set of NOE interactions indicates that the
phenylphosphane ligand is another attractive feature. This Me14 group is located in the axial position and that the λ
ligand only possesses protons from aromatic groups, and and δ conformations are adopted in the (S) and (R)
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Design, Synthesis and Stereochemistry of a Chiral Amine–Palladacycle
1
Figure 3. 2D H–1H ROESY NMR spectrum of (Ϯ)-11 in CDCl3.
enantiomers, respectively. These spectroscopic results con-
The X-ray diffraction study of the diastereomer
firm that the five-membered palladacycle exists predomi- (SC,SC,SN)-12 was performed (Figure 4), and the selected
nantly in the δ(R) or λ(S) conformation in solution.
bond lengths and angles are provided in Table 2. The X-ray
crystallographic study reveals the S absolute configuration
of the α-carbon stereocenter. The α-methyl group occupies
the expected axial position, and the conformation of the
five-membered palladacycle is λ. This complex adopts a
trans-(N,N) arrangement, as observed in similar prolinato
complexes.[9] Distortion of the square-planar coordination
geometry about the palladium center is minimal. The di-
hedral angle between the two coordination planes
{Pd1C1N1} and {Pd1N2O1} is 10.2°. The bond lengths
around the central Pd atom are all in the normal range.
However, a slight widening of the angle C1–Pd1–N2
[102.2(6)°] is observed relative to that recorded in the proli-
nato derivative of (S)-1 [99.9(1)°]. This phenomenon can be
attributed to the presence of the spacer group, which im-
poses a repulsive force onto the adjacent pyrrolidine ring.
Consequently, the angle N1–Pd1–O1 is squeezed to 94.9(9)°
relative to 98.0(9)° for the prolinato derivative of (S)-1.[9]
The molecular structure and the absolute stereochemis-
try of (RC,SC)-13 were also investigated crystallographically.
Optical Resolution of the Dimeric Complex (؎)-5
The resolution of the racemic mixture of complex (Ϯ)-5
was performed by using sodium (S)-prolinate and sodium
(S)-alaninate as resolving reagents, as shown in
Scheme 4.[8c] The racemic dimer (Ϯ)-5 was first treated with
2 mol-equiv. sodium (S)-prolinate, and the formation of a
1:1 mixture of diastereomeric adducts, (RC,SC,SN)- and
1
(SC,SC,SN)-12, was detected by means of H NMR spec-
troscopy. A single crystallization from dichloromethane/
diethyl ether afforded the less soluble diastereomer
(SC,SC,SN)-12 in the form of pale-yellow flakes in 70%
1
yield and Ͼ99% de (according to the H NMR spectrum)
with a [α]D value of +331 (c = 0.5, CHCl3). The mother
liquor was treated with dilute hydrochloric acid, and the
resulting enantiomerically enriched dimer 5 was then
cleaved with sodium (S)-alaninate to form a mixture of
(RC,SC)-13 and (SC,SC)-13. The less soluble diastereomer
(RC,SC)-13 was crystallized as pale-yellow prisms from
chloroform/diethyl ether slowly in 75% yield and Ͼ99% de
1
Only one isomer was observed according to the H NMR
spectrum in CDCl3. Interestingly, two regioisomers, trans-
(N,N)-(RC,SC)-13 and cis-(N,N)-(RC,SC)-13, exist in the
asymmetric unit. The molecular structures and selected
1
(according to the H NMR spectrum) with a [α]D value of
–300 (c = 0.5, CHCl3).
Eur. J. Inorg. Chem. 2008, 1880–1891
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Y. Ding, Y. Li, Y. Zhang, S. A. Pullarkat, P.-H. Leung
FULL PAPER
Scheme 4.
Table 2. Selected bond lengths [Å] and angles [°] for complex
(SC,SC,SN)-12.
Pd1–C1
Pd1–N1
N1–C16
O1–C17
C1–Pd1–N1
N1–Pd1–O1
C1–Pd1–O1
2.000(2)
2.074(2)
1.485(3)
1.278(3)
81.3(1)
95.0(1)
176.3(1)
Pd1–O1
Pd1–N2
N2–C21
O2–C17
C1–Pd1–N2
N2–Pd1–O1
N1–Pd1–N2
2.103(1)
2.074(2)
1.496(3)
1.241(2)
102.3(1)
81.4(1)
169.3(1)
bond lengths and angles of both the trans- and cis isomers
are presented in Figures 5 and 6 as well as in Tables 3 and
4, respectively. These crystallographic studies reveal the R
absolute configuration of the chiral carbon center at C13
or C32. For trans-(N,N)-(RC,SC)-13, the coordination ge-
ometry of the central palladium atom is slightly distorted
square planar. The organopalladium five-membered ring
Figure 4. Molecular structure of (SC,SC,SN)-12.
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Design, Synthesis and Stereochemistry of a Chiral Amine–Palladacycle
adopts an envelop-like conformation in which the N3 atom Table 4. Selected bond lengths [Å] and angles [°] for complex (cis-
N,N)-(RC,SC)-13.
occupies the top point, which is 0.778 Å below the mean
plane of C32–C31–C20–Pd2. The torsion angle C35–N3–
C32–C33 was found to be –163.1°.
Pd1–C1
Pd1–N1
O1–C19
N1–C13
C1–Pd1–O1
O1–Pd1–N1
O1–Pd1–N2
2.017(7)
2.055(6)
1.280(8)
1.509(8)
101.0(2)
176.4(2)
79.8(2)
Pd1–O1
Pd1–N2
O2–C19
N2–C17
C1–Pd1–N1
C1–Pd1–N2
N1–Pd1–N2
2.043(5)
2.112(5)
1.225(8)
1.454(9)
81.4(3)
177.9(3)
97.7(2)
For the cis isomer, cis-(N,N)-(RC,SC)-13, the palladium
atom is located in a distorted square-planar coordination
sphere as expected. The bond lengths and angles around
Pd1 are comparable to those of similar complexes of palla-
dium(II), with the exception of the Pd1–N2 distance
[2.112(5) Å], which is significantly longer than the reported
values in the range 1.973–2.065 Å and also longer than the
Pd2–N4 distance of 2.069(6) Å for trans-(N,N)-(RC,SC)-
13.[9] Such lengthening of a bond is an expected result of
the large trans influence of the carbon donor atom of the
palladacycle. The tetrahedral distortion of the palladium
coordination environment is minimal, and the dihedral an-
gle between the two planes {Pd1N1C1} and {Pd1N2O1} is
3.1°.
The observation that there are two regioisomers in the
asymmetric unit for (RC,SC)-13 can be attributed to the less
severe intramolecular ligand–ligand interaction. In com-
parison with the prolinato ligand in (SC,SC,SN)-12, which
possesses a pyrrolidine ring, the alaninato ligand in com-
plex 13 does not have such a bulky group. Consequently,
less steric interactions exist between the alaninato resolving
unit and the amine auxiliary. The favorable steric environ-
ment in complex 13 allows the formation of both the trans
and cis isomers.
Figure 5. Molecular structure of (trans-N,N)-(RC,SC)-13.
Isolation of the Enantiomerically Pure Dimer 5
Treatment of (SC,SC,SN)-12 with dilute hydrochloric acid
gave the enantiomerically pure complex dimer (S)-5 in the
form of a yellow powder in 95% yield, with a [α]D value of
+476 (c = 1.0, CHCl3). Single crystals were obtained from
dicholoromethane/hexane. The solid-state structure of the
dimeric complex (S)-5 was determined by X-ray crystal-
lography. There are four crystallographically distinguishable
molecules in the asymmetrical unit with the same stereo-
chemistry but with slightly different bond lengths and
angles. For clarity, only one of the four (molecule A) is de-
picted in Figure 7. Selected bond lengths and angles are
listed in Table 5. The X-ray crystallographic study confirms
the S absolute configuration of the α-carbon stereocenter
of the palladacycle. There is a trans relationship between
the two nitrogen atoms and the two carbon donor atoms.
The bond lengths and angles around the palladium atoms
are within the normal range, and both palladium centers
have a distorted square planar geometry. It is noteworthy
that enantiomerically pure (R)-5 could be obtained from
(RC,SC)-13 with the same procedure, [α]D = –471 (c = 0.3,
CHCl3). In solution, an equilibrium between the two re-
Figure 6. Molecular structure of (cis-N,N)-(RC,SC)-13.
Table 3. Selected bond lengths [Å] and angles [°] for complex (trans-
N,N)-(RC,SC)-13.
Pd2–C20
Pd2–N4
O3–C36
N4–C37
C20–Pd2–N3
C20–Pd2–O3
N3–Pd2–O3
1.962(7)
2.069(6)
1.269(9)
1.486(8)
81.3(2)
174.6(3)
100.0(2)
Pd2–O3
Pd2–N3
N3–C35
2.149(5)
2.073(5)
1.477(1)
C20–Pd2–N4 99.1(2)
N4–Pd2–N3
N4–Pd2–O3
C36–O3–Pd2
170.5(2)
78.7(2)
112.1(5)
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Molecule D
FULL PAPER
Table 5. Selected bond lengths [Å] and angles [°] for complex(S)-5.
Molecule A
Molecule B
Molecule C
Pd1–C1
Pd1–N1
Pd1–Cl1
Pd1–Cl2
Pd2–C17
Pd2–N2
Pd2–Cl2
Pd2–Cl1
C1–Pd1–N1
C1–Pd1–Cl1
N1–Pd1–Cl1
C1–Pd1–Cl2
Cl1–Pd1–Cl2
C17–Pd2–N2
C17–Pd2–Cl2
C17–Pd2–Cl1
1.99(2)
2.069(2)
2.348(6)
2.458(6)
1.99(2)
2.077(2)
2.351(6)
2.470(6)
80.2(8)
99.2(6)
173.5(6)
176.4(7)
83.3(2)
80.0(9)
98.9(7)
173.7(7)
Pd3–C33
Pd3–N3
Pd3–Cl3
Pd3–Cl4
Pd4–C49
Pd4–N4
Pd4–Cl4
Pd4–Cl3
C33–Pd3–N3
C33–Pd3–Cl3
N3–Pd3–Cl3
C33–Pd3–Cl4
Cl3–Pd3–Cl4
C49–Pd4–N4
C49–Pd4–Cl4
C49–Pd4–Cl3
1.99(2)
2.066(2)
2.360(6)
2.469(6)
2.00(2)
2.07(2)
2.352(6)
2.470(6)
80.9(8)
99.2(7)
170.4(6)
177.4(7)
83.2(2)
80.6(9)
98.3(7)
178.3(7)
Pd5–C65
Pd5–N5
Pd5–Cl5
Pd5–Cl6
Pd6–C81
Pd6–N6
Pd6–Cl6
Pd6–Cl5
C65–Pd5–N5
C65–Pd5–Cl5
N5–Pd5–Cl5
C65–Pd5–Cl6
Cl5–Pd5–Cl6
C81–Pd6–N6
C81–Pd6–Cl6
C81–Pd6–Cl5
2.00(2)
Pd7–C97
Pd7–N7
Pd7–Cl7
Pd7–Cl8
Pd8–C113
Pd8–N8
Pd8–Cl7
Pd8–Cl8
C97–Pd7–N7
C97–Pd7–Cl8
N7–Pd7–Cl8
C97–Pd7–Cl7
Cl8–Pd7–Cl7
C113–Pd8–N8
C113–Pd8–Cl7
C113–Pd8–Cl8
2.00(2)
2.08(2)
2.446(6)
2.335(6)
2.00(2)
2.079(2)
2.347(6)
2.445(6)
81.0(9)
98.5(7)
175.1(6)
176.1(7)
83.9(2)
80.5(8)
98.6(7)
175.5(7)
2.065(2)
2.361(6)
2.467(7)
2.00(2)
2.071(2)
2.333(6)
2.457(6)
80.8(9)
100.9(6)
172.0(6)
175.9(6)
82.9(2)
81.2(9)
98.6(7)
176.9(7)
1
gioisomers was observed. The H NMR spectrum of (S)-5
in CDCl3 shows clearly two distinct pairs of CMe doublet
resonances at δ = 2.26 and 2.32 ppm (3JH,H = 6.3 Hz) in a
ratio of ca. 1:1 for the two regioisomers.
Figure 7. Molecular structure of (S)-5.
Asymmetric Diels–Alder Reaction Between (S)-14 and
Ethyl Vinyl Ketone
In order to evaluate the efficiency and stereoselectivity of
the new palladacycle 5, the asymmetric Diels–Alder reac-
tion between dmpp and ethyl vinyl ketone promoted by (S)-
5 was investigated (Scheme 5).
The cycloaddition reaction involves the synthesis of the
five-membered heterocycle dmpp complex (S)-14. The
structure of this key complex was investigated by X-ray
crystallography (Figure 8). Single crystals were obtained by
slow evaporation of a solution of dichloromethane and hex-
ane. Selected bond lengths and angles are given in Table 6.
The coordination geometry around the Pd center is dis-
torted square planar, and the phosphole is coordinated
trans to the amine nitrogen atom. The bond lengths and
angles around Pd1 atom are all comparable to those of
other dmpp complexes of α-arylalkylamine auxiliaries.[10]
The complex has a distorted square-planar coordination ge-
ometry, with a tetrahedral distortion angle of 8.5°. Due to
the fact that dmpp is smaller than PPh3, the angle C1–Pd1– Scheme 5.
1886
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1880–1891

Design, Synthesis and Stereochemistry of a Chiral Amine–Palladacycle
P1 [99.1(6)°] in (S)-14 is significantly smaller than the corre- +185. The molecular structure and the absolute stereo-
sponding angle observed in (Ϯ)-11 [117.9(6)°]. The dihedral chemistry of this major product were determined by X-ray
angle between the phenyl ring and the projecting aromatic structural analysis (Figure 9). Selected bond lengths and
ring in (S)-14 (4.9°) is also smaller than that observed in angles are given in Table 7. Structural investigations reveals
(Ϯ)-11 (5.1°]), which is consistent with this observation. that the complex is (SC,SP)-16, where the endo-cycloadduct,
The bond angles around P1 are significantly different. The trans to the NMe2 group, coordinates to the Pd atom as a
angle C20–P1–Pd1 [111.3(10)°] is significantly smaller than typical monodentate ligand through its bridgehead P donor
the angles C17–P1–Pd1 [122.7(1)°] and C23–P1–Pd1 atom. The absolute configurations of the four newly gener-
[117.6(1)°]. This difference can be attributed to the repulsive ated stereogenic centers P1, C17, C18, and C23 are S, S, R,
interactions between the coordinated dmpp group and the and S, respectively; the carbonyl group is oriented in the
“spacer” H3 (Figure 8). As expected, the five-membered endo position at C18. Interestingly, despite the same level
palladacycle adopts a λ configuration, in which the α- of asymmetric induction as that achieved previously,[8c] the
methyl group, Me14, is axially disposed.
geometry of the olefin upon approach is opposite as a
result of the steric effect of the newly introduced aromatic
ring.
Figure 8. Molecular structure of (S)-14.
Table 6. Selected bond lengths [Å] and angles [°] for complex (S)-
14.
Figure 9. Molecular structure of (SC,RP)-16.
Pd1–C1
Pd1–N1
N1–C16
P1–C17
C1–Pd1–N1
N1–Pd1–P1
N1–Pd1–Cl1
C16–N1–Pd1
2.035(3)
2.132(3)
1.487(4)
1.799(3)
80.1(1)
171.0(8)
93.1(8)
Pd1–P1
Pd1–Cl1
N1–C13
P1–C20
C1–Pd1–P1
C1–Pd1–Cl1
P1–Pd1–Cl1
C13–N1–Pd1
2.252(8)
2.412(7)
1.503(4)
1.797(3)
99.2(1)
172.6(1)
88.0(3)
Table 7. Selected bond lengths [Å] and angles [°] for complex
(SC,SP)-16.
Pd1–C1
Pd1–O1
C1–Pd1–N1
N1–Pd1–O1
N1–Pd1–P1
2.009(5)
2.180(4)
79.3(2)
Pd1–N1
Pd1–P1
C1–Pd1–O1
C1–Pd1–P1
O1–Pd1–P1
2.136(4)
2.260(1)
170.6(2)
95.5(1)
93.5(2)
115.9(2)
103.6(2)
169.1(1)
92.6(1)
When (S)-14 was treated with excess ethyl vinyl ketone
Treatment of (SC,SP)-16 with 1,2-bis(diphenylphos-
in chloroform at 50 °C, the reaction was found to be com- phanyl)ethane (dppe) gave the reported optically active li-
pleted in 2 d. The 31P NMR spectrum of the crude reaction gand (RP)-17.[6a] Conclusively, the P-chiral phosphanorbor-
mixture in CDCl3 exhibits two singlets at δ = 121.1 ppm nene (Rp)-17 was obtained as the major cycloaddition prod-
(major) and δ = 120.9 ppm (minor) in a ratio of 3.5:1, which uct when (S)-5 was used as the chiral auxiliary. The appar-
indicates that only two stereoisomeric cycloadducts, ent inversion of configuration at the stereogenic centers
(SC,SP)- and (SC,RP)-15, were generated from the reaction. during the liberation process is merely the consequence of
The products could not be crystallized from a variety of the Cahn–Ingold–Prelog sequence rules.[11]
solvents and were subsequently converted into the nitrato
It is important to note that when the more commonly
analogues, (SC,SP)- and (SC,RP)-16, by treatment with silver used chiral reaction promoter (S)-2 was employed for the
nitrate (Scheme 5). The 31P NMR spectrum of the resultant analogous Diels–Alder reaction between dmpp and ethyl
complex mixture shows two singlets at δ = 121.4 ppm vinyl ketone under similar reaction conditions, the cycload-
(major) and δ = 120.4 ppm (minor). The major isomer ducts were obtained in the ratio of 1.3:1.[4f] With the new
(SC,SP)-16 crystallized readily from ethyl acetate/diethyl complex (S)-5, however, the increased ratio (3.5:1) indicates
ether in the form of pale-yellow prisms with a [α]D value of that the stereoselectivity has been improved significantly.
Eur. J. Inorg. Chem. 2008, 1880–1891
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1887

Y. Ding, Y. Li, Y. Zhang, S. A. Pullarkat, P.-H. Leung
aromatic proton 8-H), 7.71 (s, 1 H, aromatic proton 1-H) ppm. 13
NMR (75 MHz, CDCl3): δ = 19.44 (s, CH3), 21.83 (s, CH3), 24.21
(s, CHCH3), 67.03 (s, COH), 123.10 (s, aryl-C), 125.91 (s, aryl-C),
127.58 (s, aryl-C), 127.66 (s, aryl-C), 127.89 (s, aryl-C), 130.57 (s,
aryl-C), 133.01 (s, aryl-C), 133.07 (s, aryl-C), 135.34 (s, aryl-C),
142.00 (s, aryl-C) ppm. GC-MS (M+): m/z (%) = 182.29 (100),
200.11 (51), 157.30 (70), 142.27 (28).
FULL PAPER
C
Thus, (S)-5 exerts a greater selectivity for this class of inter-
molecular cycloaddition reaction. Further exploration in
the applications of this class of orthometallated ligands is
in progress in our laboratory.
Experimental Section
2-(1-Chloridoethyl)-3,6-dimethylnaphthalene [(؎)-9]: A solution of
(Ϯ)-8 (1.0 g, 5.0 mmol) in CH2Cl2 (30 mL) was slowly added drop-
wise to a solution of PCl3 (3.0 g, 22 mmol) dissolved in the same
solvent (20 mL). The mixture was stirred overnight at room tem-
perature followed by addition of water. The organic layer was sepa-
rated, washed with water, and dried with Na2SO4. Removal of the
solvent gave the product as a white waxy solid. Yield: 1.0 g (92%).
Reactions involving air-sensitive compounds were performed under
a positive pressure of purified nitrogen using standard Schlenk
techniques. H NMR spectra were recorded on a Bruker Advance
1
DPX300 spectrometer at 300 MHz. 13C NMR spectra were re-
corded at 75 MHz or 100 MHz on a Bruker Advance DPX300 or
a Bruker Advance DPX400 spectrometer. The 31P NMR spectra
were recorded at 121 MHz on a Bruker Advance DPX300 spec-
trometer. Unless stated otherwise, all NMR spectroscopic experi-
ments were performed at room temperature (300 K). Chemical
shifts (δ) are reported in ppm relative to TMS and referenced to
the chemical shifts of residual solvent resonances (1H and 13C
NMR) or 85% H3PO4 (31P NMR). Mass spectra were recorded on
a Finnigan Trace GC Ultra instrument at 70 eV with EI mode.
Melting points were determined on a SRS-Optimelt MPA-100 ap-
paratus and were uncorrected. Optical rotations were measured on
the specified solution in a 0.1-dm cell at 20 °C with a Perkin–Elmer
model 341 polarimeter. Elemental analyses were performed by the
Elemental Analysis Laboratory of the Division of Chemistry and
Biological Chemistry at the Nanyang Technological University of
Singapore.
3
1H NMR (300 MHz, CDCl3): δ = 2.07 (d, JH,H = 6.8 Hz, 3 H,
CHCH3), 2.57 (s, 3 H, aryl-CH3), 2.64 (s, 3 H, aryl-CH3), 5.51 (q,
3
3JH,H = 6.8 Hz, 1 H, CHCH3), 7.33 (d, JH,H = 8.3 Hz, 1 H, aro-
matic proton 7-H), 7.57 (s, 1 H, aromatic proton 5-H), 7.59 (s, 1
3
H, aromatic proton 4-H), 7.79 (d, JH,H = 8.3 Hz, 1 H, aromatic
proton 8-H), 8.01 (s, 1 H, aromatic proton 1-H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 19.50 (s, CH3), 21.88 (s, CH3), 25.04 (s,
CHCH3), 55.55 (s, CHCH3), 124.79 (s, aryl-C), 125.92 (s, aryl-C),
127.78 (s, aryl-C), 127.90 (s, aryl-C), 128.25 (s, aryl-C), 130.38 (s,
aryl-C), 133.54 (s, aryl-C), 133.67 (s, aryl-C), 136.21 (s, aryl-C),
138.20 (s, aryl-C) ppm. GC-MS (M+): m/z (%) = 183.18 (100),
218.09 (20), 182.28 (55), 168.30 (50), 152.27 (10).
1-(3,6-Dimethylnaphthalen-2-yl)-N,N-dimethylethanamine [(؎)-10]:
A solution of 9 (2.18 g, 10 mmol) in CH2Cl2 was stirred vigorously
with an aqueous solution of dimethylamine (2 ) for 48 h. The sol-
vents were mostly removed, and the residue remained in some
CH2Cl2. The residue was washed with water and dried and the
solvents evaporated. The pure amine was obtained as a colorless
oil after column chromatography with ethyl acetate as the eluent.
Yield: 2.0 g (88%). 1H NMR (300 MHz, CDCl3): δ = 1.34 (d, 3JH,H
= 6.6 Hz, 3 H, CHCH3), 2.22 (s, 6 H, NCH3), 2.43 (s, 3 H, aryl-
1-(3,6-Dimethylnaphthalen-2-yl)ethanone (7): A solution of 2,7-di-
methylnaphthalene (6) (7.3 g, 46.8 mmol) in nitromethane
(100 mL) was added whilst stirring to a mixture of anhydrous AlCl3
(7.33 g, 55 mmol) and acetyl chloride (3.34 mL, 46.8 mmol) in ni-
tromethane (20 mL). The resultant red solution was stirred at room
temperature for 20 h and poured into a mixture of ice (50 g) and
conc. HCl (20 mL). After vigorous stirring for 30 min, the yellow-
ish organic layer was separated, washed with H2O, dried (Na2SO4),
and concentrated to dryness. The residue was passed through a
SiO2 column to give product 7 as a colorless solid. Yield: 4.16 g
(45%). M.p. 78–80 °C. C14H14O (198.26): C 84.81, H 7.12; found:
C 84.98, H 7.09. 1H NMR (300 MHz, CDCl3): δ = 2.51 (s, 3 H,
aryl-CH3), 2.65 (s, 3 H, aryl-CH3), 2.69 (s, 3 H, COCH3), 7.30 (d,
3
CH3), 2.47 (s, 3 H, aryl-CH3), 3.52 (q, JH,H = 6.5 Hz, 1 H,
CHCH3), 7.17 (d, 3JH,H = 8.3 Hz, 1 H, aromatic protons 7-H), 7.35
(s, 1 H, aromatic proton 5-H), 7.37 (s, 1 H, aromatic proton 4-H),
3
7.65 (d, JH,H = 8.3 Hz,1 H, aromatic proton 8-H), 7.82 (s, 1 H,
aromatic proton 1-H) ppm. 13C NMR (75 MHz, CDCl3): δ = 19.23
(s, CH3), 20.22 (s, CH3), 21.81 (s, CHCH3), 43.49 (s, NCH3), 61.75
(s, CHCH3), 124.96 (s, aryl-C), 125.83 (s, aryl-C), 127.38 (s, aryl-
C), 127.53 (s, aryl-C), 127.79 (s, aryl-C), 130.71 (s, aryl-C), 132.74
(s, aryl-C), 134.51 (s, aryl-C), 134.99 (s, aryl-C), 141.33 (s, aryl-C)
ppm. GC-MS (M+): m/z (%) = 212.38 (100), 182.32 (75), 227.12
(70), 168.25 (28), 153.18 (15).
3JH,H = 8.3 Hz, 1 H, aromatic proton 7-H), 7.52 (s, 1 H, aromatic
3
proton 5-H), 7.54 (m, 1 H, aromatic proton H4), 7.76 (d, JH,H
=
8.3 Hz, 1 H, aromatic proton H8), 8.20 (s, 1 H, aromatic proton 1-
H) ppm. 13C NMR (75 MHz, CDCl3): δ = 21.95 (s, CH3), 22.08 (s,
CH3), 29.32 (s, COCH3), 125.96 (s, aryl-C), 128.25 (s, aryl-C),
128.42 (s, aryl-C), 129.22 (s, aryl-C), 129.42 (s, aryl-C), 130.75 (s,
aryl-C), 134.81 (s, aryl-C), 135.10 (s, aryl-C), 135.28 (s, aryl-C),
138.37 (s, aryl-C), 201.24 (s, CO) ppm. GC-MS (M+): m/z (%) =
198.20 (90), 183.33 (100), 155.32(34).
(؎)-D-µ-Chloridobis{3-[1-(dimethylamino)ethyl]-2,7-dimethyl-4-naph-
thalenyl-C,N}dipalladium(II) [(؎)-5]: A mixture of trans-dichlorido-
bis(acetonitrile)palladium(II) (2.59 g, 10 mmol) and silver perchlo-
1-(3,6-Dimethylnaphthalen-2-yl)ethanol [(؎)-8]: To
5.05 mmol) in ethanol (20 mL) was added a solution of NaBH4
(0.38 g, 10.1 mmol) in ethanol (20 mL). The mixture was stirred at the filtrate was added dropwise into a mixture of N,N-dimethyl-1-
7
(1.0 g, rate (4.14 g, 20 mmol) in acetonitrile (30 mL) was stirred at room
temperature for 1 h. The precipitate (AgCl) was filtered out, and
room temperature for 24 h followed by treatment with dilute
NaOH (3%, 20 mL). The resulting solution was concentrated to
10 mL and extracted with CH2Cl2. The organic layers were com-
bined, washed with water, and dried with Na2SO4. Removal of the
solvent gave the product as a colorless oil. Yield: 0.96 g, (95%). 1H
(2,7-dimethylnaphthalen-5-yl)ethylamine (Ϯ)-10 (2.28 g, 10 mmol)
and triethylamine (1.01 g, 10 mmol) in dichloromethane (30 mL)
whilst stirring. The mixture was stirred at room temperature for
20 h and filtered through a Celite layer. The filtrate was evaporated,
and the residue was dissolved in dichloromethane (100 mL). Dilute
HCl (1 , 50 mL) was then added to the solution, and the mixture
3
NMR (300 MHz, CDCl3): δ = 1.34 (d, JH,H = 6.4 Hz, 3 H,
CHCH3), 2.26 (s, 3 H, aryl-CH3), 2.36 (s, 3 H, aryl-CH3), 2.61 (s, was stirred vigorously for 1 h. The organic layer was separated,
3
1 H, OH), 4.94 (q, 3JH,H = 6.2 Hz, 1 H, CHCH3), 7.10 (d, JH,H
=
washed with H2O, dried (Na2SO4), and concentrated to c.a. 10 mL.
Dilution of the solution with hexane caused the precipitation of
8.3 Hz, aromatic proton 7-H), 7.29 (s, 1 H, aromatic proton 5-H),
7.33 (s, 1 H, aromatic proton 4-H), 7.53 (d, JH,H = 8.3 Hz, 1 H, the racemic dimer as yellow prisms. Yield: 3.13 g, (85%). M.p. 150–
3
1888 Eur. J. Inorg. Chem. 2008, 1880–1891
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Design, Synthesis and Stereochemistry of a Chiral Amine–Palladacycle
152 °C (dec.). C32H40Cl2N2Pd2 (736.42): C 52.19, H 5.47, N 3.80; 124.49 (s, aryl-C), 126.69 (s, aryl-C), 127.74 (s, aryl-C), 129.46 (s,
1
found: C 52.52, H 5.34, N 3.59. H NMR (300 MHz, CDCl3): δ = aryl-C), 132.84 (s, aryl-C), 134.01 (s, aryl-C), 134.81 (s, aryl-C),
2.19–2.28 (m, 6 H, CH3), 2.26–2.42 (m, 12 H, CH3), 2.55–2.66 (m,
12 H, CH3), 3.56–3.70 (m, 2 H, CH CH3), 6.89–7.30 (m, 6 H, aro-
matic protons), 8.33–8.61 (m, 2 H, aromatic protons) ppm. 13C
NMR (100 MHz, CDCl3): δ = 21.61 (s, CH3), 21.20 (s, CH3), 21.28
(s, CH3), 22.53 (s, CH3), 22.60 (s, CHCH3), 22.69 (s, CHCH3),
49.17 (s, NCH3), 49.57 (s, NCH3), 49.72 (s, NCH3), 49.88 (s,
NCH3), 75.08 (s, CH3CH), 75.22 (s, CH3CH), 125.06 (s, aryl-C),
125.39 (s, aryl-C), 125.57 (s, aryl-C), 125.63 (s, aryl-C), 125.94 (s,
aryl-C), 128.74 (s, aryl-C), 128.79 (s, aryl-C), 130.35 (s, aryl-C),
130.46 (s, aryl-C), 132.58 (s, aryl-C), 132.76 (s, aryl-C), 133.95(s,
aryl-C), 134.03 (s, aryl-C), 144.08 (s, aryl-C), 144.39 (s, aryl-C),
147.04 (s, aryl-C), 147.20 (s, aryl-C), 147.37 (s, aryl-C) ppm.
147.93 (s, aryl-C), 148.58 (s, aryl-C), 181.25 (s, CO) ppm.
(RC,SC)-Alaninato-{3-[1-(dimethylamino)ethyl]-2,7-dimethyl-4-naph-
thalenyl-C,N}palladium(II) [(RC,SC)-13]: The previously described
mother liquor of (SC,SCSN)-12 was evaporated and treated with
aqueous HCl (1 , 30 mL) to afford a mixture of (Ϯ)-5 (2.00 g,
2.71 mmol). A solution of sodium alaninate (0.90 g, 8.13 mmol) in
CH3OH was added to the mixture of (Ϯ)-5, which was stirred at
room temperature for 1 h, and the solvent was removed under re-
duced pressure. The solution of the residue in CHCl3 (50 mL) was
washed with H2O, dried (Na2SO4), and diluted with diethyl ether.
The less soluble diastereomer (RC,SC)-13 crystallized slowly as
slightly yellowish crystals. Yield: 1.65 g (75%, based on half of the
dimer used), Ͼ99% de. M.p. 190–192 °C (dec.). [α]D = –300, [α]578
= –314, [α]546 = –364, [α]436 = –670, [α]365 = –1080 (c = 0.5, CHCl3).
C21H30N2O3Pd (464.87): C 54.25, H 6.50, N 6.03; found: C 54.47,
(؎)-Chlorido{3-[1-(dimethylamino)ethyl]-2,7-dimethyl-4-naphthal-
enyl-C,N}(triphenylphosphane-P)palladium(II) [(؎)-11]: To a solu-
tion of (Ϯ)-5 (0.184 g, 0.250 mmol) in dichloromethane (10 mL)
was added triphenylphosphane (0.131 g, 0.500 mmol) dissolved in
the same solvent (10 mL). The resulting solution was stirred for
30 min at room temperature and concentrated to ca 5 mL. Addition
of hexane to the solution caused the precipitation of the product as
yellow fluffy crystals. Yield: 0.29 g (93%). M.p. 200–202 °C (dec.).
C34H35ClNPPd (630.45): C 64.77, H 5.60, N 2.22; found: C 64.40,
H 5.42, N 2.22. 31P NMR (121 MHz, CDCl3): δ = 30.9 (s) ppm.
1
3
H 7.04, N 5.88. H NMR (300 MHz, CDCl3): δ = 1.62 (d, JH,H
=
6.9 Hz, 3 H, CHCH3), 2.01 (d, 3JH,H = 6.3 Hz, 3 H, CHCH3), 2.37
(s, 3 H, aryl-CH3), 2.46 (s, 3 H, aryl-CH3), 2.69 [s, 3 H, NCH3(ax)
3
], 2.75 [s, 3 H, NCH3(eq)], 3.34 (br. m, 2 H, NH), 3.75 (q, JH,H
=
3
6.3 Hz, 1 H, COCHCH3), 3.78 (q, JH,H = 6.3 Hz, 1 H, CHCH3),
3
7.17 (d, JH,H = 8.5 Hz, 1 H, aromatic proton 5-H), 7.19 (s, 1 H,
3
aromatic proton 1-H), 7.31 (d, JH,H = 8.5 Hz, 1 H, aromatic pro-
3
1H NMR (300 MHz, CDCl3): δ = 2.11 (d, JH,H = 6.4 Hz, 3 H,
ton 6-H), 7.43 (s, 1 H, aromatic proton 8-H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 20.58 (s, CH3), 21.09 (s, CH3), 21.39 (s,
CHCH3), 22.67 (s, CH-CH3), 48.06 (s, NCH3), 53.19 (s, NCH3),
56.27 (s, CH3CH), 74.14 (s, COCH), 124.79 (s, aryl-C), 127.06 (s,
aryl-C), 127.49 (s, aryl-C), 129.92 (s, aryl-C), 132.72 (s, aryl-C),
134.22 (s, aryl-C), 134.98 (s, aryl-C), 145.32 (s, aryl-C), 149.14 (s,
aryl-C), 179.31 (s, CO) ppm.
CHCH3), 2.17 (s, 3 H, aryl-CH3), 2.38 (s, 3 H, aryl-CH3), 2.50 (d,
4
4JP,H = 2.0 Hz, 3 H, NCH3), 2.90 (d, JP,H = 3.4 Hz, 3 H, NCH3),
4
3
4
3.76 (quint, JP,H = JH,H = 6.2 Hz, 1 H, CHCH3), 6.36 (dd, JH,H
3
= 1.3 Hz, JH,H = 8.5 Hz, 1 H, aromatic proton 6-H), 7.02–7.58
(m, 18 H, aromatic protons) ppm. 13C NMR (100 MHz, CDCl3):
δ = 20.90 (s, CH3), 21.01 (s, CH3), 21.14 (s, CHCH3), 49.07 (s,
3
3
NCH3), 50.75 (d, JC,P = 3.0 Hz, NCH3), 74.99 (d, JC,P = 3.3 Hz,
CH3CH), 124.55 (s, aryl-C), 125.13 (s, aryl-C), 125.31 (s, aryl-C),
(S)-Di-µ-chloridobis{3-[1-(dimethylamino)ethyl]-2,7-dimethyl-4-naph-
2
127.66 (d, JC,P = 14.7 Hz, aryl-C), 129.45 (s, aryl-C), 129.87 (d, thalenyl-C,N}dipalladium(II) [(S)-5]: A solution of the diastereomer
1
3JC,P = 2.3 Hz, aryl-C), 131.69 (d, JC,P = 47.2 Hz, aryl-C), 132.12
(SC,SC,SN)-12 (1.25 g, 2.81 mmol) in CH2Cl2 (20 mL) was treated
2
(d, JC,P = 11.4 Hz, aryl-C), 133.13 (s, aryl-C), 133.31 (s, aryl-C), with aqueous HCl (1 , 30 mL). After vigorous stirring for 30 min,
3
133.53 (d, 4JC,P = 4.1 Hz, aryl-C), 134.80 (d, JC,P = 11.1 Hz, aryl-
the organic layer was separated, washed with water, dried
(Na2SO4), and concentrated to dryness to afford an amorphous
yellow product. Yield: 1.0 g (97 %). M.p. 182–184 °C (dec.).
[α]D = +476, [α]578 = +485, [α]546 = +562 (c = 1.0, CHCl3).
C32H40Cl2N2Pd2 (736.42): C 52.19, H 5.47, N 3.80; found: C 52.52,
4
C), 147.86 (d, JC,P = 1.9 Hz, aryl-C), 156.53 (s, aryl-C) ppm.
(SC,SCSN)-Prolinato-{3-[1-(dimethylamino)ethyl]-2,7-dimethyl-4-
naphthalenyl-C,N}palladium(II) [(SC,SC,SN)-12]: To a suspension of
the racemic dimer (Ϯ)-5 (3.00 g, 4.07 mmol) in CH3OH (30 mL)
was added a solution of sodium prolinate (1.55 g, 11.3 mmol) dis-
solved in the same solvent (30 mL). The mixture was stirred at
room temperature for 1 h, and the solvent was removed under re-
duced pressure. The solution of the residue in CH2Cl2 (50 mL) was
washed with H2O, dried (Na2SO4), and diluted with diethyl ether.
The less soluble diastereomer (SC,SC,SN)-12 crystallized slowly as
slightly yellowish flakes. Yield: 1.32 g (73%, based on half of the
dimer used), Ͼ99 % de. M.p. 185–187 °C (dec.). [α]D = +331,
[α]578 = +350, [α]546 = +407, [α]436 = +827, [α]365 = +1697 (c = 0.5,
CHCl3). C22H30Cl2N2O2Pd (531.78): C 49.69, H 5.69, N 5.27;
1
3
H 5.34, N 3.59. H NMR (300 MHz, CDCl3): δ = 2.26 (d, JH,H
=
6.3 Hz, 3 H, CHCH3), 2.32 (d, 3JH,H = 6.3 Hz, 3 H, CHCH3), 2.36–
2.45 (m, 12 H), 2.63–2.76 (m, 12 H), 3.62–3.74 (m, 2 H, CHCH3),
6.93–7.33 (m, 6 H, aromatic protons), 8.36–8.64 (m, 2 H, aromatic
protons) ppm. 13C NMR (100 MHz, CDCl3): δ = 15.24 (s, CH3),
20.77 (s, CH3), 21.35 (s, CH3), 21.43 (s, CH3), 22.87 (s, CHCH3),
22.97 (s, CHCH3), 49.47 (s, NCH3), 50.25 (s, NCH3), 53.74 (s,
NCH3), 53.90 (s, NCH3), 75.45 (s, CH3CH), 75.64(s, CH3CH),
125.32 (s, aryl-C), 125.35 (s, aryl-C), 125.53 (s, aryl-C), 125.77 (s,
aryl-C), 125.92 (s, aryl-C), 126.25 (s, aryl-C), 128.82 (s, aryl-C),
128.88 (s, aryl-C), 130.43 (br. s, aryl-C), 130.57 (s, aryl-C), 132.80
(s, aryl-C), 133.03 (s, aryl-C), 134.20 (s, aryl-C), 134.32 (br. s, aryl-
C), 144.20 (s, aryl-C), 144.50 (s, aryl-C), 147.23 (s, aryl-C), 147.36
(s, aryl-C) ppm.
1
found: C 49.85, H 5.32, N 5.39. H NMR (300 MHz, CDCl3): δ =
3
1.55–1.64 (m, 1 H, CH), 1.92–2.03 (m, 1 H, CH), 2.07 (d, JH,H
=
6.2 Hz, 3 H, CHCH3), 2.34–2.37 (overlapping m, 2 H, CH2), 2.38
(s, 3 H, aryl-CH3), 2.46 (s, 3 H, aryl-CH3), 2.65 (s, 3 H, NCH3),
2.77 (s, 3 H, NCH3), 2.81–2.96 (m, 2 H, CH2), 3.66–3.72 (m, 1 H,
CH), 4.15 (q, 3JH,H = 7.9 Hz, 1 H, CHCH3), 4.50 (br. s, 1 H, NH),
The optically pure (R)-5 was prepared from (RC,SC)-13 in a similar
manner: [α]D = –471, [α]578 = –503, [α]546 = –564, [α]436 = –587,
[α]365 = –1187 (c = 0.3, CHCl3).
3
7.18 (s, 1 H, aromatic proton 8-H), 7.20 (d, JH,H = 8.5 Hz, 1 H,
aromatic proton 5-H), 7.41 (s, 1 H, aromatic proton 1-H), 7.65 (d,
3JH,H = 8.5 Hz, 1 H, aromatic proton 6-H) ppm. 13C NMR (S)-Chlorido{3-[1-(dimethylamino)ethyl]-2,7-dimethyl-4-naphthal-
(100 MHz, CDCl3): δ = 20.49 (s, CH3), 21.31 (s, CH3), 22.71 (s,
enyl-C,N}{3Ј,4Ј-dimethyl-1Ј-phenylphosphole-P}palladium(II) [(S)-
CHCH3), 25.24 (s, NCH3), 30.39 (s, NCH3), 48.17 (s, CH3CH), 14]: To a solution of (S)-5 (0.18 g, 0.25 mmol) in dichloromethane
53.01 (s, CH2), 53.25 (s, CH2), 66.03 (s, CH2), 74.04 (s, COCH), (10 mL) was added a solution of 3,4-dimethyl-1-phenylphosphole
Eur. J. Inorg. Chem. 2008, 1880–1891
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1889

Y. Ding, Y. Li, Y. Zhang, S. A. Pullarkat, P.-H. Leung
FULL PAPER
(dmpp) (0.10 g, 0.53 mmol) dissolved in the same solvent (5 mL).
The resulting yellow solution was stirred at room temperature for
1 h, and the solvent was removed under reduced pressure. The resi-
due solid was chromatographed on a silica gel column by using
dichloromethane/ethyl acetate (1:1, v/v) as the eluent to give a pale
yellow powder, which was recrystallized from dichloromethane/hex-
silica gel column by using ethyl acetate/dichloromethane (1:10,
v/v) as the eluent to give the diastereomeric mixture of (SC,SP)-
and (SC,RP)-16 as a yellow powder, which exhibited two 31P NMR
signals at δ = 121.4 (major) and 120.4 ppm (minor) in CDCl3.
Recrystallization of the mixture from ethyl acetate/diethyl ether
gave the major isomer (SC,SP)-16 as pale yellow prisms. Yield:
0.35 g (52.0%). [α]D = +185 (c = 0.5, CHCl3). M.p. 198–200 °C
(dec). C33H41N2O4PPd·H2O (685.10): C 57.85, H 6.33, N 4.09;
found: C 57.64, H 6.79, N 4.10. 31P NMR (121 MHz, CDCl3): δ =
ane as yellow prisms. Yield: 0.24 g (88.9%). [α]D = +875, [α]578
=
+920, [α]546 = +1090 (c = 0.5, CHCl3). M.p. 190–192 °C (dec).
C28H33ClNPPd (556.37): C 60.44, H 5.98, N 2.52; found: C 60.08,
H 6.40, N 2.52. 31P NMR (121 MHz, CDCl3): δ = 29.75 (s) ppm. 121.4 (s) ppm. H NMR (300 MHz, CDCl3): δ = 1.03 (t, JH,H
=
1
3
1H NMR (300 MHz, CDCl3): δ = 1.82 (s, 3 H, C=CCH3), 1.90 (d, 7.3 Hz, 3 H, CH2CH3), 1.19 (s, 3 H, C=CCH3), 1.25–1.32 (m, 1 H,
3JH,H = 6.4 Hz, 3 H, CHCH3), 1.95 (s, 3 H, C=CCH3), 2.40 (s, 6
Hexo), 1.52 (s, 3 H, C=CCH3), 1.58–1.74 (m, 1 H, PCHCH), 2.15
H, aryl-CH3), 2.54 [d, 4JP,H = 1.7 Hz, 3 H, NCH3(ax)], 2.84 [d, 4JP,H
(d, JH,H = 6.4 Hz, 3 H, CHCH3), 2.41 (s, 3 H, aryl-CH3), 2.50 (s,
3
3
4
= 3.4 Hz, 3 H, NCH3(eq)], 3.72 (quint, JH,H = 4JP,H = 6.3 Hz, 1 H, 3 H, aryl-CH3), 2.52 [d, JP,H = 1.5 Hz, 3 H, NCH3(ax)], 2.61–2.67
2
2
4
CH3CH), 5.61 (d, JP,H = 32.0 Hz, 1 H, C=CH), 6.75 (d, JP,H
=
(m, 2 H, CH2CH3), 2.67–2.71 (m, 1 H, Hendo), 2.73 [d, JP,H =
3
32.0 Hz, 1 H, C=CH), 6.76 (d, JH,H = 8.5 Hz, 1 H, aromatic pro-
3.3 Hz, 3 H, NCH3(eq)], 3.49–3.50 (m, 1 H, PCHCH2), 3.77 (quint,
4
ton 5-H), 7.19 (s, 1 H, aromatic proton 1-H), 7.37 (s, 1 H, aromatic
3JH,H = JP,H = 5.9 Hz, 1 H, CHCH3), 4.58 (m, 1 H, COCH), 7.02
3
3
proton 8-H), 7.40–7.45 (m, 3 H, p-Ph, 2 ϫ m-Ph), 7.60 (d, JH,H
=
(d, JH,H = 8.5 Hz, 1 H, aromatic proton 5-H), 7.23 (s, 1 H, aro-
3
8.5 Hz, 1 H, aromatic proton 6-H), 7.97–8.04 (m, 2 H, 2 ϫ o-Ph) matic proton 1-H), 7.40 (d, JH,H = 8.5 Hz, 1 H, aromatic protons
3
ppm. 13C NMR (100 MHz, CDCl3): δ = 16.86 (d, JC,P = 12.6 Hz,
6-H), 7.41 (s, 1 H, aromatic protons 8-H), 7.50–7.52 (m, 3 H, p-
3
C=CCH3), 17.48 (d, JC,P = 12.2 Hz, C=CCH3), 21.07 (s, CH3), Ph, 2 ϫ m-Ph), 7.64–7.70 (m, 2 H, 2 ϫ o-Ph) ppm. 13C NMR
22.45 (s, CH3), 27.60 (s CHCH3), 48.15 (s, NCH3), 50.36 (s, NCH3), (100 MHz, CDCl3): δ = 7.77 (s, CH3), 14.29 (s, CH3), 15.01 (s,
4
73.14 (d, JC,P = 3.1 Hz, CH3CH), 122.39 (s, aryl-C), 123.88 (s, CH3), 20.76 (s, CH3), 21.46 (s, CH3), 22.22 (s, CH3), 25.39 (d, 2JC,P
1
aryl-C), 125.44 (d, JC,P = 49.0 Hz, aryl-C), 126.49 (s, aryl-C), = 18.1 Hz, PCCH2), 34.76 (s, COCH2), 45.08 (s, NCH3), 48.10 (d,
1
2
126.71 (s, aryl-C), 127.40 (d, JC,P = 43.7 Hz, PC=C), 128.16 (d, 1JC,P = 31.6 Hz, PCCH2), 50.64 (d, JC,P = 22.7 Hz, PCCH), 51.15
2JC,P = 10.8 Hz, aryl-C), 129.14 (d, JC,P = 52 Hz, PC=C), 130.22 (s, NCH3), 52.74 (d, JC,P = 29.0 Hz, PCCH), 73.04 (s, CH3CH),
1
1
3
2
(s, aryl-C), 131.71 (s, aryl-C), 132.89 (s, aryl-C), 133.06 (d, JC,P
=
125.66 (d, JC,P = 17.4 Hz, aryl-C), 126.66 (s, aryl-C), 128.58 (d,
10.5 Hz, aryl-C), 133.12 (s, aryl-C), 140.73 (d, 4JC,P = 5.9 Hz, aryl- 3JC,P = 8.9 Hz, aryl-C), 130.54 (d, JC,P = 50.7 Hz, aryl-C), 130.34
1
2
2
C), 147.13 (s, aryl-C), 147.78 (d, JC,P = 10.0 Hz, PC=C), 150.93
(s, aryl-C), 153.36 (d, JC,P = 10.5 Hz, PC=C) ppm.
(s, aryl-C), 130.67 (s, aryl-C), 131.29 (s, aryl-C), 131.65 (d, JC,P =
12.3 Hz, C=C), 132.45 (d, 2JC,P = 8.9 Hz, C=C), 133.21 (s, aryl-C),
134.77 (s, aryl-C), 134.84 (s, aryl-C), 134.90 (s, aryl-C), 135.26 (s,
aryl-C), 146.33 (s, aryl-C), 148.89 (s, aryl-C) ppm.
2
Asymmetric Diels–Alder Reaction of (S)-14 and Ethyl Vinyl Ketone,
Synthesis of (SC,RP)-16 and (SC,SP)-16 and Isolation of (SC,SP)-16:
A mixture of the chlorido complex (S)-14 (0.56 g, 1.0 mmol) and
ethyl vinyl ketone (0.50 g, 6.0 mmol) in chloroform (10 mL) was
left at 50 °C for 2 d. The mixture was filtered through a layer of
Celite, and the solvent removed. The 31P NMR (CDCl3) spectrum
of the crude product showed signals at δ = 121.1, 120.9 ppm in a
ratio of 3.5: 1. This mixture in CH2Cl2 (5 mL) was stirred vigor-
ously with excess AgNO3 (0.50 g, 2.9 mmol) in water (5 mL) for
1 h in the dark. The precipitate (AgCl) was removed by filtration
through a layer of Celite, and the filtrate dried (MgSO4), and the
solvent removed. The crude product was chromatographed on a
Crystal Structure Determination of (؎)-11, (SC,SC,SN)-12, (RC,SC)-
13, (S)-5, (S)-14, and (SC,SP)-16: Crystal data for all six complexes
and a summary of the crystallographic analyses are given in
Table 8. Diffraction data were collected on a Bruker X8 CCD dif-
fractometer with Mo-Kα radiation (graphite monochromator). SA-
DABS absorption corrections were applied. All non-hydrogen
atoms were refined anisotropically, while the hydrogen atoms were
introduced at calculated positions and refined riding on their car-
rier atoms. The absolute configurations of the chiral complexes
were determined unambiguously by using the Flack parameter.[12]
Table 8. Crystallographic data for complexes (Ϯ)-11, (SC,SC,SN)-12, (RC,SC)-13, (S)-5, (S)-14, and (SC,SP)-16.
(Ϯ)-11
(SC,SC,SN)-12
(RC,SC)-13
(S)-5
(S)-14
(SC,SP)-16
Formula
C34H35ClNPPd
630.45
P21
monoclinic
11.0844(8)
8.2465(6)
16.3569(12)
1446.69(18)
2
C22H30Cl2N2O2Pd C21H30N2O3Pd
C33H42Cl4N2Pd2 C28H33ClNPPd
C33H41N2O4PPd
667.05
P212121
orthorhombic
11.0169(3)
14.3105(4)
20.2012(5)
3184.87(15)
4
Formula weight
Space group
Crystal system
a [Å]
531.78
464.87
C2
821.29
P21
556.37
P21
P212121
orthorhombic
8.9397(4)
11.3292(5)
23.2746(10)
2357.24(18)
4
monoclinic
26.346(3)
9.8051(13)
18.340(3)
4383.5(10)
8
monoclinic
15.6457(4)
24.4883(7)
19.2722(6)
7061.1(3)
8
monoclinic
11.7694(7)
8.3483(5)
13.2810(8)
1289.42(13)
2
b [Å]
c [Å]
V [Å3]
Z
T [K]
173(2)
1.447
0.71073(Mo)
0.813
–0.01(3)
0.0431
173(2)
1.498
0.71073(Mo)
1.034
–0.003(19)
0.0202
173(2)
1.409
0.71703(Mo)
0.868
–0.01(4)
0.0366
173(2)
1.545
0.71073(Mo)
1.346
–0.03(7)
0.0329
173(2)
1.433
0.71073(Mo)
0.901
–0.02(2)
0.0307
173(2)
1.391
0.71703(Mo)
0.671
0.01(3)
0.0443
0.0898
ρcalcd. [gcm–3]
λ [Å]
µ [mm–1]
Flack parameters
R1 (obsd. data)[a]
wR2 (obsd. data)[b] 0.1052
0.0582
0.0496
0.0772
0.0688
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = √{Σ[w(Fo – Fc ) ]}, w–1 = σ2(Fo2) + (aP)2 + bP.
2
2 2
1890
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1880–1891

Design, Synthesis and Stereochemistry of a Chiral Amine–Palladacycle
Bader, M. Pabel, A. C. Willis, S. B. Wild, Inorg. Chem. 1996,
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lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
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Acknowledgments
We are grateful to Nanyang Technological University for support-
ing this research and for the research scholarships to Y. D. and
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Received: November 19, 2007
Published Online: February 26, 2008
Eur. J. Inorg. Chem. 2008, 1880–1891
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1891