Asymmetric synthesis of a chiral hetero-bidentate As-P ligand containing both As and P-stereogenic centres

Article abstract of DOI:10.1016/j.jorganchem.2008.07.029

The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]naphthalene as the chiral auxiliary has been used as the chiral template to promote the asymmetric cycloaddition reaction between phenyldivinylphosphine and 3,4-dimethyl-1-phenylarsole. The reaction was completed in 1 h at room temperature, with the formation of two isomeric cycloadducts in the ratio 1:3. The major phenylvinylphosphino-substituted asymmetrical hetero-bidentate arsanorbornene ligand with chirality residing on both As and P centers was obtained stereoselectively on the chiral palladium template in moderate yield. The chiral heterobidentate ligand was isolated in its enantiomerically pure form by removal of the chiral auxiliary using concentrated hydrochloric acid and subsequent cleavage from the neutral complex [(As-P)PdCl₂] by using potassium cyanide. Similar to the earlier reported analogous diphenylphosphino-substituted asymmetrical heterobidentate arsanorbornene (As-P) ligand, an arsenic elimination process was also found in the dichloro and dibromo palladium complex whereas the diiodo species did not show similar reactivity, but the corresponding η² diiodo complex could be obtained from the η² dibromo complex by treatment with sodium iodide.

Full text of DOI:10.1016/j.jorganchem.2008.07.029

Journal of Organometallic Chemistry 693 (2008) 3289–3294
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Asymmetric synthesis of a chiral hetero-bidentate As–P ligand containing both
As and P-stereogenic centres
*
Mengtao Ma, Sumod A. Pullarkat, Yongxin Li, Pak-Hing Leung
Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 June 2008
Received in revised form 21 July 2008
Accepted 23 July 2008
Available online 31 July 2008
The organopalladium complex containing ortho-metalated (S)-[1-(dimethylamino)ethyl]naphthalene as
the chiral auxiliary has been used as the chiral template to promote the asymmetric cycloaddition reac-
tion between phenyldivinylphosphine and 3,4-dimethyl-1-phenylarsole. The reaction was completed in
1 h at room temperature, with the formation of two isomeric cycloadducts in the ratio 1:3. The major
phenylvinylphosphino-substituted asymmetrical hetero-bidentate arsanorbornene ligand with chirality
residing on both As and P centers was obtained stereoselectively on the chiral palladium template in
moderate yield. The chiral heterobidentate ligand was isolated in its enantiomerically pure form by
removal of the chiral auxiliary using concentrated hydrochloric acid and subsequent cleavage from the
neutral complex [(As–P)PdCl2] by using potassium cyanide. Similar to the earlier reported analogous
diphenylphosphino-substituted asymmetrical heterobidentate arsanorbornene (As–P) ligand, an arsenic
elimination process was also found in the dichloro and dibromo palladium complex whereas the diiodo
Keywords:
Asymmetric Diels–Alder reaction
Chiral As–P Ligand
Palladium complex
species did not show similar reactivity, but the corresponding
g
2 diiodo complex could be obtained from
the g2 dibromo complex by treatment with sodium iodide.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
As part of our efforts to develop a more efficient procedure for
achieving asymmetric ligand transformation reactions such as
cycloaddition, hydroamination, hydrophosphination and hydroar-
sination, we have successfully employed an easily accessible
orthometallated chiral amine auxiliary as a chiral template to
achieve all the above goals with a wide variety of substrates [3].
We have also utilized this chiral template for the generation of
the As–P* [4] as well as As*–P [5] systems wherein the chirality re-
sides on either the phosphorus or arsenic centre as well as the car-
bon backbone. Interesting results including new insights into the
influence of trans ligand in a novel arsine elimination process ob-
served during the course of that study prompted us to attempt the
challenging task of simultaneous generation of P and As chiral cen-
ters in an asymmetric manner thus providing a pathway for the
development of a new class of compounds containing both As
and P chiral centers associated with various functionalities. To
our knowledge, no asymmetric synthesis involving the enantiose-
lective generation of both As and P chiral centers has been
reported in literature.
Optically active heterobidentate ligands bearing two or more
stereogenic centers offer enormous potential as chiral auxiliaries
in asymmetric synthesis. Their utility in such scenarios is attrib-
uted mainly to their ability to exercise stereoelectronic control
over the reactions of coordinated substrates. Although many re-
ports on such compounds containing two dissimilar asymmetric
donor atoms have been reported for chiral and non-chiral phos-
phine based ligands (mainly involving P and N/O/S) [1], a review
of literature reveals that very few studies involving development
of a heterobidentate As*–P* ligand system have been reported so
far. It is also noteworthy that the sole report on such a ligand sys-
tem utilized a method that involved multi-step separation and res-
olution of the antipodes by the method of metal complexation. For
example, the well known optical resolution of 1-(methylphenylar-
sino)-2-(methylphenylphosphino)benzene required the somewhat
difficult separation of the (R*, R*) and (R*, S*) diastereoisomers prior
to the individual resolution of the two racemic diasteoreoisomers
[2].
We herein report an efficient synthesis of a chiral heterobiden-
tate As*–P* ligand via metal template promoted cycloaddition
reaction between 3,4-dimethyl-1-phenylarsole (DMPA) and phen-
yldivinylphosphine. The norbornene based ligand system thus
obtained is also useful for the study of the intricacies of the stabil-
ity factors with respect to the As–C bond cleavage observed in our
earlier studies.
* Corresponding author. Tel.: +65 6316 8905; fax: +65 6316 6984.
E-mail address: pakhing@ntu.edu.sg (P.-H. Leung).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.07.029

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M. Ma et al. / Journal of Organometallic Chemistry 693 (2008) 3289–3294
2. Results and discussion
2.1. Metal template promoted asymmetric cycloaddition reaction
between phenyldivinylphosphine and 3,4-dimethyl-1-phenylarsole
In contrast to those reported for their phosphorus analogues [6],
cycloaddition reactions involving cyclic arsines are relatively rare
in the literature [7]. The few reports involving attempted cycload-
dition reactions of uncoordinated arsoles generally utilized high
temperature and produced a mixture of products with resultant
low yield [8]. We had earlier reported an alternative approach
wherein the coordinated arsole can be activated to undergo asym-
metric Diels–Alder reactions in the presence of a metal template.
The metal template served the dual role of reaction promoter as
well as chiral auxiliary during the course of the cycloaddition reac-
tion. Considering the efficacy of that procedure, we decided to uti-
lize the same methodology for the simultaneous generation of
phosphorus and arsenic chiral centers in this novel [4 + 2] cycload-
dition reaction between phenyldivinylphosphine and DMPA.
The cyclic arsine, DMPA, was coordinated regiospecifically to
(+)-1 to give monomeric neutral complex (+)-2 as stable yellow
Fig. 1. Molecular structure of complex (+)-2.
Table 1
Selected bond lengths (Å) and angles (deg) for (+)-2
Pd(1)–C(1)
Pd(1)–As(1)
As(1)–C(15)
As(1)–C(21)
C(16)–C(17)
C(17)–C(18)
C(1)–Pd(1)–N(1)
N(1)–Pd(1)–As(1)
N(1)–Pd(1)–Cl(1)
C(18)–As(1)–C(15)
C(18)–C(17)–C(16)
1.987(2)
2.359(1)
1.921(2)
1.946(2)
1.497(4)
1.338(3)
81.1(1)
175.8(1)
96.5(1)
87.4(1)
Pd(1)–N(1)
Pd(1)–Cl(1)
As(1)–C(18)
C(15)–C(16)
C(16)–C(19)
C(17)–C(20)
C(1)–Pd(1)–As(1)
C(1)–Pd(1)–Cl(1)
As(1)–Pd(1)–Cl(1)
C(15)–C(16)–C(17)
C(17)–C(18)–As(1)
2.128(2)
2.410(1)
1.906(2)
1.337(3)
1.501(4)
1.503(3)
95.4(1)
173.6(1)
87.2(1)
115.6(2)
111.3(2)
prisms in 64% isolated yield, [a] +259.1° (c 0.6, CH2Cl2) (Scheme
D
1). The regioselectivity and molecular structure of (+)-2 was con-
firmed by X-ray crystallography (Fig. 1). Selected bond lengths
and angles are listed in Table 1. As observed in other analogous ar-
sine complexes, the arsenic atom in DMPA is trans to the NMe2
group by virtue of the hard soft donor preference exhibited by
the chiral amine based auxiliary [4]. Treatment of the chloro com-
plex (+)-2 with silver perchlorate yielded the intermediate cationic
perchlorate species in essentially quantitative yield [9]. This highly
reactive species was not isolated and was treated directly with a
stoichiometric amount of phenyldivinylphosphine. The Diels–
Alder reaction was found to complete in an hour at room temper-
ature. Prior to purification, the 31P{1H} NMR spectrum of the crude
Diels–Alder reaction product in CDCl3 exhibited two singlets at d
49.0 and 48.6 in the ratio 1:3, respectively. The major diasteoreo-
mer (ꢀ)-3 could be separated by column chromatography as yel-
115.1(2)
was formed with the norbornene skeletal framework coordinated
to the Pd center through both As and P donors. The study also
confirmed that the absolute configurations of the five new chiral
centers formed at As(1), P(1), C(7), C(12) and C(14) are R, S, R, R
and S, respectively (Fig. 2). Selected bond lengths and angles are
listed in Table 2. In complex (ꢀ)-4 the geometry at Pd is slightly
distorted square-planar with angles at Pd in the ranges 82.7(1)–
95.8(1) and 171.6(1)–174.8(1)°, the smallest of these former bond
angles being associated with the bite of the novel As–P ligand.
The Pd–As [2.320(1) Å] and Pd–P [2.246(1) Å] distances are unex-
ceptional. The two Pd–Cl distances are similar [2.366(1) and
2.360(1) Å].
low solid in 56% yield, [
a
]
ꢀ40.0° (c 0.6, CH2Cl2). Attempts to
D
crystallize the complex as single crystals suitable for X-ray crystal-
lographic studies were unsuccessful. The chiral amine auxiliary on
(ꢀ)-3 could however be removed from metal complex chemoselec-
tively and efficiently using concentrated hydrochloric acid. The
resultant neutral dichloro complex (ꢀ)-4 was thus obtained as pale
yellow needles in 72% yield, [
a
]D ꢀ146.7° (c 0.6, CH2Cl2). The X-ray
structural analysis of (ꢀ)-4 confirmed that the desired cycloadduct
Ph
Me
Me
Me
Me
Pd
Me
Me
Me
Me
Ph
As
As
Cl
Cl
Me
N
Me
Me
N
N
+
AgClO4
Pd
Pd
Ph
-
1/2
ClO4
As
RT, 2h
PhP(CH=CH2)2
P
2
Ph
(+)-2
(+)-1
(−)-3
Me
Me
Ph
Ph
As
As
Cl
Cl
Conc.HCl
RT, 10min.
KCN
Ph
Me
Me
P
Pd
RT, 3min.
P
(−)-5
Ph
(−)-4
Scheme 1.

M. Ma et al. / Journal of Organometallic Chemistry 693 (2008) 3289–3294
3291
NMR spectrum of the crude product exhibited only one singlet at
d 46.5, which is attributed to the diastereomer that was not formed
in the original cycloaddition reaction (Scheme 2). The signal due to
the original major isomer was not detected thus confirming the
optical purity of the isolated ligand.
2.2. Arsenic elimination reaction
Recently, we have observed an interesting arsenic elimination
process with the similar heterobidentate arsanorbornene (As–P)
palladium complexes obtained from the cycloaddition reaction be-
tween DMPA and diphenylvinylphosphine. The trans ligand in
these complexes appeared to affect the rate of the elimination pro-
cess. These eliminations had led to the generation of an interesting
1-(diphenylphosphino)-3,4-dimethyl-2,4-cyclohexadiene ligand
which coordinated to Pd via its phosphorous donor and the g2
-
C–C bond. The present reaction allowed an opportunity to study
the various factors affecting this process in further detail as well
as the opportunity to develop such ligand systems further with
introduction of additional chirality on the phosphine donor atoms.
Previous work from our research group has given some indication
that a concerted mechanism exists wherein two As–C bonds in the
norbornene bridgehead system breaks along with the formation of
the
reactions.
Unlike in the case of our previous work, the complex (ꢀ)-4 was
g
2-Pd coordination during the course of such elimination
Fig. 2. Molecular structure of dichloro complex (ꢀ)-4.
found to convert with difficulty into the possible analogous retro-
diene complex 6 (Scheme 3). From the analysis of the 31P{1H} NMR
spectrum of (ꢀ)-4 in CDCl3, we found that its 31P{1H} NMR value
shifted from d 34.0 to 135.9 over a period of 17 days at room tem-
perature indicating the formation of complex 6. Further evidence
for the formation of the complex was obtained from the 1H NMR
spectrum in which we observed the two new hydrogen signals of
the retrodiene complex at d 5.6 (doublet) and 6.0 (singlet), respec-
tively. Another proof was obtained by the isolation of phenylarson-
ic acid from the reaction system which confirmed that the arsenic
elimination process has indeed occurred. The dichloro complex
(ꢀ)-4 was treated with potassium bromide for 10 min at room
temperature and the analogous dibromo complex (ꢀ)-7 was ob-
Table 2
Selected bond lengths (Å) and angles (deg) for (ꢀ)-4
Pd(1)–Cl(1)
Pd(1)–As(1)
As(1)–C(12)
P(1)–C(15)
C(7)–C(8)
C(8)–C(10)
C(12)–C(13)
C(15)–C(16)
P(1)–Pd(1)–As(1)
As(1)–Pd(1)–Cl(2)
As(1)–Pd(1)–Cl(1)
C(12)–As(1)–C(7)
C(8)–C(7)–C(14)
C(10)–C(8)–C(7)
C(13)–C(12)–As(1)
C(10)–C(12)–As(1)
C(7)–C(14)–P(1)
C(13)–C(14)–P(1)
2.366(1)
2.320(1)
1.971(4)
1.801(5)
1.521(6)
1.336(6)
1.548(7)
1.289(8)
82.7(1)
89.4(3)
174.8(1)
77.4(2)
111.9(3)
111.7(4)
98.9(3)
100.6(3)
107.3(3)
109.2(3)
Pd(1)–Cl(2)
Pd(1)–P(1)
As(1)–C(7)
P(1)–C(14)
C(7)–C(14)
C(10)–C(12)
C(13)–C(14)
2.360(1)
2.246(1)
1.974(4)
1.853(5)
1.556(6)
1.514(6)
1.554(6)
P(1)–Pd(1)–Cl(2)
P(1)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1)
C(14)–C(7)–As(1)
C(8)–C(7)–As(1)
C(8)–C(10)–C(12)
C(10)–C(12)–C(13)
C(12)–C(13)–C(14)
C(13)–C(14)–C(7)
171.6(1)
92.1(1)
95.8(1)
94.9(2)
tained as yellow solid in 90% yield, [
a
]
D
ꢀ146.7° (c 0.6, CH2Cl2).
100.9(3)
112.0(4)
107.4(4)
107.6(3)
106.2(3)
The 31P{1H} NMR spectrum exhibited only one signal at d 35.0 indi-
cating the absence of any side reaction. This complex was subse-
quently recrystallized with CHCl3–Et2O to give the product as
yellow needle crystals. The molecular structure of (ꢀ)-7 was con-
firmed by X-ray crystallography (Fig. 3). Selected bond lengths
and angles are listed in Table 3. Unfortunately, the arsenic elimina-
tion product arising from complex (ꢀ)-7, viz., complex 8, could not
be isolated by fractional crystallization or by column chromatogra-
phy using a wide range of solvent systems. Finally, the dichloro
complex (ꢀ)-4 was converted into the analogous diiodo derivative
(ꢀ)-9 by treatment of the dichloro complex with sodium iodide.
The diiodo complex was isolated as yellow solid in 95% yield,
Treatment of the dichloro complex (ꢀ)-4 with aqueous potas-
sium cyanide liberated the optically pure heterobidentate arsanor-
bornene ligand (ꢀ)-5 as a white solid in 91% yield, [
a
]
D
ꢀ40.8° (c
1.3, CH2Cl2). The 31P{1H} NMR spectrum of this liberated chiral free
ligand in CDCl3 exhibited a sharp singlet at d ꢀ13.3. Owing to the
configurational instability of the uncoordinated bridgehead arsenic
stereogenic center, the liberated ligand was re-coordinated imme-
diately to other selected metal ions. When (ꢀ)-5 was coordinated
to the enantiomeric bis(acetonitrile)[(R)-1-[1-(dimethylamino)-
ethyl]-2-naphthalenyl-C,N] palladium(II) perchlorate, the 31P{1H}
[
a
]
ꢀ97.8° (c 0.5, CH2Cl2). Similar to the reported analogous
D
diphenylphosphino-substituted asymmetrical heterobidentate
arsanorbornene complex [(As–P)PdI2], the arsenic elimination
reaction in this case did not occur when the diiodo complex
(ꢀ)-9 was dissolved in solution. On the contrary the complex
Me
Me Me
Me
Me Me
Ph
As
Ph
As
NCMe
NCMe
Me
N
Me
N
+
+
Ph
Me
Me
Pd
+
P
Pd
-
ClO4
P
-
−
(
)-5
ClO4
Ph
Scheme 2.

3292
M. Ma et al. / Journal of Organometallic Chemistry 693 (2008) 3289–3294
Me
Me
Me
Me
Ph
As
Cl
Cl
air
Cl
Cl
Pd
Ph
Pd
-PhAsO(OH)2
P
P
Ph
−
( )-4
6
Me
Me
Me
Me
Ph
As
Br
Br
air
Br
Br
Pd
Ph
Pd
-PhAsO(OH)2
P
P
Ph
8
−
( )-7
NaI
RT, 10 min.
Me
Me
Me
Ph
As
Me
I
I
I
I
Pd
Pd
X
P
P
Ph
Ph
−
( )-9
+
( )-10
Scheme 3.
Table 3
Selected bond lengths (Å) and angles (deg) for (ꢀ)-7
Pd(1)–Br(1)
Pd(1)–As(1)
As(1)–C(12)
P(1)–C(15)
C(7)–C(8)
C(8)–C(11)
C(12)–C(13)
C(15)–C(16)
P(1)–Pd(1)–As(1)
As(1)–Pd(1)–Br(1)
As(1)–Pd(1)–Br(2)
C(12)–As(1)–C(7)
C(8)–C(7)–C(14)
C(11)–C(8)–C(7)
C(13)–C(12)–As(1)
C(11)–C(12)–As(1)
C(12)–C(13)–C(14)
C(7)–C(14)–C(13)
2.481(1)
2.328(1)
1.973(4)
1.797(5)
1.528(6)
1.338(8)
1.556(7)
1.307(8)
82.8(1)
89.1(1)
175.4(1)
77.5(2)
107.4(4)
112.1(5)
94.8(3)
101.8(3)
106.0(4)
107.1(4)
Pd(1)–Br(2)
Pd(1)–P(1)
As(1)–C(7)
P(1)–C(13)
C(7)–C(14)
C(11)–C(12)
C(13)–C(14)
2.492(1)
2.256(1)
1.982(5)
1.853(5)
1.540(7)
1.513(7)
1.577(8)
P(1)–Pd(1)–Br(1)
P(1)–Pd(1)–Br(2)
Br(1)–Pd(1)–Br(2)
C(14)–C(7)–As(1)
C(8)–C(7)–As(1)
C(8)–C(11)–C(12)
C(11)–C(12)–C(13)
C(14)–C(13)–P(1)
C(12)–C(13)–P(1)
171.2(1)
92.8(1)
95.4(1)
99.4(3)
99.7(3)
111.7(4)
111.7(4)
110.0(3)
107.9(3)
phine and DMPA in our earlier studies. The reason can be attrib-
uted to the fact that the two As–C bonds [1.971(4) and
1.974(4) Å] within the arsanorbornene skeleton of (ꢀ)-4 are signif-
icantly symmetrical than that of the analogue [1.961(3) and
1.980(3) Å]. The deviance between the two As–C bond distances
in the latter (0.019 Å) is much bigger than that of the former
(0.003 Å), thus resulting in an enhanced configurational instability
in the analogue compared to that of (ꢀ)-4.
Fig. 3. Molecular structure of dibromo complex (ꢀ)-7.
decomposed rapidly in solution. But interestingly, the retrodiene
diiodo complex (+)-10 was subsequently obtained via an alternate
pathway. This involved treatment of complex 8 with sodium iodide
for 10 min at room temperature. The complex (+)-10 thus obtained
In conclusion, we have synthesized a new chiral heterobidentate
As–P ligand containing both As and P-stereogenic centers via a facile
metal template promoted cycloaddition reaction. This has provided
us with an avenue for the synthesis of a new class of heterobidentate
ligand system which can incorporate various functionalities. We
have also obtained a better understanding of the arsenic elimination
process occurring in such systems leading to the formation of the
novel chiral phosphine-olefin ligand. It needs to be noted that such
was isolated by column chromatography in 55% yield, [a]D +756.7°
(c 0.3, CH2Cl2). It is noteworthy that the rate of arsenic elimination
reaction in (ꢀ)-4 apparently decelerated relative to the analogous
complex obtained via cycloaddition between diphenylvinylphos-

M. Ma et al. / Journal of Organometallic Chemistry 693 (2008) 3289–3294
3293
chiral phosphine-olefin systems themselves are assuming impor-
tance as ‘‘spectator” ligands in catalysis [10].
sequently recrystallized from chloroform–diethyl ether as pale yel-
low needle crystals (ꢀ)-4 (0.13 g, 72%). [ D = ꢀ146.7° (c 0.6,
a
]
CH2Cl2). M.p.: 191–192 °C. Anal. Calc. for C22H24AsCl2PPd ꢂ CHCl3:
C, 40.0; H, 3.7. Found: C, 39.9; H, 3.6%. 31P{1H} NMR (CDCl3, d):
34.0. 1H NMR (CDCl3, d): 1.56 (s, 3H, @CCH3), 1.67 (d, 5JPH = 0.9 Hz,
3H, @CCH3), 2.12 (ddd, 3JHH = 21.6, 2JHH = 10.2 Hz, 3JHH = 3.1 Hz, 1H,
CHCH2), 2.68 (m, 1H, CHCH2), 2.78 (m, 1H, PCH), 2.86 (s, 1H, AsCH),
3. Experimental
Reactions involving air-sensitive compounds were performed
under an inert atmosphere of argon using standard Schlenk tech-
niques. Solvents were dried and freshly distilled according to stan-
dard procedures and degassed prior to use when necessary. The 1H
and 31P{1H} NMR spectra were recorded at 25 °C on Bruker Avance
300 and 400 spectrometers. Optical rotations were measured on
the specified solution in a 0.1 dm cell at 20 °C with a Perkin–Elmer
341 polarimeter. Elemental analysis was performed by the Ele-
mental Analysis Laboratory of the Division of Chemistry and Bio-
logical Chemistry at Nanyang Technological University. Melting
points are uncorrected.
3
3
3
3.54 (d, JHH = 3.0 Hz, 1H, AsCH), 6.22 (dd, JPH = 20.9, JHH
=
3
3
18.4 Hz, 1H, @CH2), 6.33 (dd, JPH = 31.4, JHH = 12.4 Hz,1H, @CH2),
6.83 (ddd, JPH = 23.0, JHH = 18.3, JHH = 12.4 Hz, 1H, @CH), 7.39–
2
3
3
8.11 (m, 10H, aromatics).
3.4. Liberation of the (As–P) ligand (ꢀ)-5
A solution of (ꢀ)-4 (0.10 g, 0.14 mmol) in dichloromethane
(20 mL) was stirred vigorously with a saturated aqueous solution
of potassium cyanide (1.0 g) for 3 min. The organic layer was sep-
arated, then washed with water (3 ꢁ 20 mL) and dried (MgSO4).
Upon removal of the solvent, the free ligand (ꢀ)-5 was obtained
Phenyldivinylphosphine [11], DMPA [12] and (+)-1 [13] were
prepared according to the literature procedures.
Caution! Perchlorate salts of metal complexes are potentially
explosive compounds and should be handled with care.
as an air-sensitive white solid (0.05 g, 91%). [
a]
D = ꢀ40.8° (c 1.3,
CH2Cl2). 31P{1H} NMR (CDCl3, d): ꢀ13.3.
3.1. Preparation of complex (+)-2
3.5. Preparation of the dibromo complex (ꢀ)-7
A mixture of DMPA (1.15 g, 4.95 mmol) and (+)-1 (1.68 g,
2.47 mmol) in dichloromethane (80 mL) was stirred at room
temperature for 2 h. The solvent was removed from the reaction
mixture, and the complex (+)-2 was isolated by column chroma-
tography on a silica column with dichloromethane–n-hexane to
give a yellow solid, which was recrystallized from chloroform–
n-hexane in the form of bright yellow prisms (1.81 g, 64%).
The solution of (ꢀ)-4 (0.07 g, 0.10 mmol) in dichloromethane
(50 mL) was added to potassium bromide (0.05 g) in acetone
(50 mL) and water (10 mL) and stirred vigorously for 10 min. The or-
ganic solvents were removed and the residue was extracted with
dichloromethane and water, dried with MgSO4, Removal of solvent
gave (ꢀ)-7 as a solid, which was then recrystallized from chloro-
form–diethyl ether to give the product as yellow needle crystals
[a]D = +259.1° (c 0.6, CH2Cl2). M.p.: 168–169 °C. Anal. Calc. for
C
26H29AsClNPd: C, 54.6; H, 5.1; N, 2.5. Found: C, 54.5; H, 4.9; N,
(0.07 g, 90%). [
a
]
D = ꢀ146.7° (c 0.6, CH2Cl2). M.p.: 188–189 °C. Anal.
3
2.6%. 1H NMR (CDCl3, d): 1.92 (d, JHH = 6.4 Hz, 3H, CHCH3), 2.08
Calc. for C22H24AsBr2PPdꢂCHCl3: C, 35.4; H, 3.2. Found: C, 35.9; H,
3.4%. 31P{1H} NMR (CD2Cl2, d): 35.0. 1H NMR (CD2Cl2, d): 1.47 (s,
(s, 3H, @CCH3), 2.11 (s, 3H, @CCH3), 2.88 (s, 3H, NCH3), 2.95 (s,
3H, NCH3), 4.35 (q, JHH = 6.4 Hz, 1H, CHCH3), 6.69 (s, 1H, AsCH),
6.97 (s, 1H, AsCH), 7.18–7.82 (m, 11H, aromatics).
3
5
3
3H, @CCH3), 1.65 (d, JPH = 1.0 Hz, 3H, @CCH3), 2.15 (ddd, JHH
=
22.3, 2JHH = 10.6 Hz, 3JHH = 3.3 Hz, 1H, CHCH2), 2.68 (m, 1H, CHCH2),
2.76 (m, 1H, PCH), 2.87 (s, 1H, AsCH), 3.59 (d, 3JHH = 3.2 Hz, 1H, AsCH),
6.17 (dd, 3JPH = 20.4, 3JHH = 18.5 Hz, 1H, @CH2), 6.33 (dd, 3JPH = 42.3,
3.2. Cycloaddition reaction: preparation of complex (ꢀ)-3
3JHH = 12.4 Hz,1H, @CH2), 6.92 (ddd, JPH = 23.8, JHH = 18.5, JHH
=
2
3
3
A solution of (+)-2 (0.67 g, 1.17 mmol) in dichloromethane
(60 mL) was stirred for 2 h in the presence of a solution of silver
perchlorate (0.39 g) in water (1 mL). The organic layer, after the re-
moval of AgCl then washed with water (3 ꢁ 60 mL), dried (MgSO4)
and subsequently treated with phenyldivinylphosphine (0.19 g,
1.17 mmol) at room temperature for 1 h. The solvent was removed
from the reaction mixture and the complex (ꢀ)-3 was isolated by
column chromatography on a silica column with dichlorometh-
12.4 Hz, 1H, @CH), 7.45–8.06 (m, 10H, aromatics).
3.6. Synthesis of the diiodo complex (ꢀ)-9
The solution of (ꢀ)-4 (0.05 g, 0.07 mmol) in dichloromethane
(30 mL) was mixed with sodium iodide (0.1 g) in acetone (30 mL)
and stirred vigorously for 10 min. The solvents were removed
and the residue was extracted with dichloromethane. The solvent
was removed from the reaction mixture and the complex (ꢀ)-9
was isolated by column chromatography on a silica column with
ane–diethyl ether, to give a yellow solid (0.52 g, 56%). [a] =
D
ꢀ40.0° (c 0.6, CH2Cl2). M.p.: 166–167 °C. Anal. Calc. for C36H40AsCl-
NO4PPd: C, 54.2; H, 5.0; N, 1.8. Found: C, 53.8; H, 5.2; N, 1.8%.
31P{1H} NMR (CDCl3, d): 48.6. 1H NMR (CDCl3, d): 1.33 (s, 3H,
dichloromethane, to give a yellow solid (0.05 g, 95%). [a] =
D
ꢀ97.8° (c 0.5, CH2Cl2). M.p.: 178–179 °C. Anal. Calc. for C22H24
-
3
AsI2PPd: C, 35.0; H, 3.2. Found: C, 34.6; H, 3.0%. 31P{1H} NMR
@CCH3), 1.64 (s, 3H, @CCH3), 1.95 (d, JHH = 6.1 Hz, 3H, CHCH3),
3
2
3
(CDCl3, d): 34.8. 1H NMR (CDCl3, d): 1.45 (s, 3H, @CCH3), 1.65 (d,
2.14 (ddd, JHH = 20.3, JHH = 9.8 Hz, JHH = 3.7 Hz, 1H, CHCH2),
2.61 (s, 1H, AsCH), 2.68 (m, 1H, CHCH2), 2.75 (s, 3H, NCH3), 2.85
3
2
5JPH = 0.8 Hz, 3H, @CCH3), 2.12 (ddd, JHH = 21.6, JHH = 9.6 Hz,
4
3JHH = 3.4 Hz, 1H, CHCH2), 2.61 (m, 1H, PCH), 2.78 (m, 1H, CHCH2),
(m, 1H, PCH), 2.89 (d, JPH = 2.6 Hz, 3H, NCH3), 3.77 (s, 1H, AsCH),
4.42 (qn, JHH = 4JPH = 5.9 Hz, 1H, CHCH3), 6.15 (dd, JPH = 21.9,
3
3
3
3
2.75 (d, JPH = 1.9 Hz, 1H, AsCH), 3.54 (d, JHH = 2.9 Hz, 1H, AsCH),
3JHH = 4.2 Hz, 1H, @CH2), 6.24 (dd, JPH = 34.7, JHH = 11.9 Hz,1H,
3
3
3
3
3
6.06 (dd, JPH = 19.0, JHH = 18.8 Hz, 1H, @CH2), 6.24 (dd, JPH
=
2
3
3
3
2
3
@CH2), 6.72 (ddd, JPH = 16.4, JHH = 12.0, JHH = 4.4 Hz, 1H, @CH),
40.7, JHH = 12.4 Hz,1H, @CH2), 7.05 (ddd, JPH = 24.3, JHH = 18.4,
3JHH = 12.4 Hz, 1H, @CH), 7.40–8.01 (m, 10H, aromatics).
6.80–8.15 (m, 16H, aromatics).
3.3. Removal of chiral auxiliary: synthesis of complex (ꢀ)-4
3.7. Arsenic-elimination reaction: isolation of complex (+)-10
The complex (ꢀ)-3 (0.21 g, 0.26 mmol) was dissolved in dichlo-
romethane (60 mL) and treated with excess concentrated hydro-
chloric acid (2 mL) at room temperature for 10 min. The mixture
was then washed with water (3 ꢁ 60 mL), dried (MgSO4), and sub-
The complex (ꢀ)-7 (0.01 g, 0.013 mmol) was dissolved in
dichloromethane (40 mL) and allowed to stir at room temperature
for 8 days. Then sodium iodide (0.05 g) in acetone (40 mL) was
added and stirred vigorously for 10 min. The solvents were

3294
M. Ma et al. / Journal of Organometallic Chemistry 693 (2008) 3289–3294
Table 4
Crystallographic data for complexes (+)-2, (ꢀ)-4 and (ꢀ)-7
(+)-2
(ꢀ)-4
(ꢀ)-7
Formula
Formula weight
Space group
Crystal system
a (Å)
C
26H29AsClNPd
C22H24AsCl2PPdꢂCHCl3
C22H24AsBr2PPdꢂCHCl3
572.27
690.97
779.89
P212121
Orthorhombic
9.0856(2)
11.1569(3)
23.3671(6)
2368.66(10)
4
P212121
P212121
Orthorhombic
10.1493(3)
15.0866(4)
17.9988(5)
2755.95(13)
4
Orthorhombic
10.2852(3)
14.9894(5)
18.0683(5)
2785.57(15)
4
b (Å)
c (Å)
V (Å3)
Z
T (K)
173(2)
1.605
0.71073
2.296
296(2)
1.665
0.71073
2.418
173(2)
1.860
0.71073
5.070
Dcalcd (g cmꢀ3
k (Å)
)
l
(mmꢀ1
)
F (000)
1152
1368
1512
Flack param
0.006(6)
0.0195
0.0438
ꢀ0.002(10)
0.016(8)
0.0374
0.0828
R1 (obs data)a
0.0351
wR2 (obs data)b
0.0846
P
P
a
R1
=
||Fo| ꢀ |Fc||/ |Fo|.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
P
2
2
wR2
¼
½wðF2o—F2c Þ ꢃ= ½wðFo2Þ ꢃ, wꢀ1
=
r
2(Fo)2 + (aP)2 + bP.
b
removed and the residue was extracted with dichloromethane. The
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a
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Acknowledgements
We thank Nanyang Technological University for support of this
research and for a scholarship to Ma M.T.