Synthesis of a chiral palladacycle and its application in asymmetric hydrophosphanation reactions

Article abstract of DOI:10.1002/ejic.201000471

A novel amine ligand, 1-(2,5-dimethylphenyl)-N,N,2,2-tetramethylpropan- 1-amine, was synthesized in six steps from commercially available p-xylene. Direct ortho-palladation of this amine ligand proceeded readily to form the racemic dimeric complex. The pa

Full text of DOI:10.1002/ejic.201000471

FULL PAPER
DOI: 10.1002/ejic.201000471
Synthesis of a Chiral Palladacycle and Its Application in Asymmetric
Hydrophosphanation Reactions
Yi Ding,[a] Yi Zhang,[a] Yongxin Li,[a] Sumod A. Pullarkat,[a] Paul Andrews,[a] and
Pak-Hing Leung*[a]
Keywords: Asymmetric synthesis / Palladium / Chiral resolution / Phosphane ligands / Metallacycles
A novel amine ligand, 1-(2,5-dimethylphenyl)-N,N,2,2-tetra-
methylpropan-1-amine, was synthesized in six steps from
commercially available p-xylene. Direct ortho-palladation of
this amine ligand proceeded readily to form the racemic di-
meric complex. The palladacycle structure and ring confor-
mations of its triphenylphosphane derivative were thor-
oughly investigated by X-ray structural analysis in the solid
state and 2D 1H–1H ROESY NMR spectroscopy in solution.
This racemic palladacycle was efficiently resolved through
the formation of its (S)-prolinato derivatives and an efficient
separation of the resulting diastereomeric complexes was
achieved by slow crystallization with the use of different sol-
vent systems. The structure and absolute configuration of the
two optically resolved palladium complexes were deter-
mined by X-ray diffraction. Both the (R,R) and (S,S)-di-µ-
chlorido dimeric palladium complexes could be obtained
chemoselectively by treating the corresponding prolinato de-
rivatives with 1
M hydrochloric acid. The asymmetric hydro-
phosphanation reaction between diphenylphosphane and di-
ethyl acetylenedicarboxylate was promoted by this newly
synthesized palladacycle and resulted in the formation of a
single isomer according to the 31P NMR spectrum. The amine
auxiliary could be subsequently removed chemoselectively
from the palladium center by treatment with concentrated
HCl. An optically pure C2-symmetrical diphosphane ligand
containing two ester functional groups at the two chiral car-
bon stereogenic centers was prepared by ligand displace-
ment.
Introduction
The ortho-palladation of N-donor ligands has been ex-
tensively studied and has acquired great interest because of
the applications of palladacycles in many areas. Over the
past decades, chiral cyclopalladated amine complexes[1]
have generated interests for their many roles as resolving
agents for chiral ligands,[2] agents for NMR assignment of
unknown compound absolute configurations,[3] agents for
determination of optical purity of organic compounds,[4]
and chiral catalysts for asymmetric reactions.[5] In our
group, we have reported the application of ortho-palladated
dimethyl-[1-(α)-naphthyl]ethylamine complex (R)-1 (Fig-
ure 1) and its (S)-enantiomer as reaction promoters for
various asymmetric reactions including Diels–Alder and hy-
droamination reactions.[6]
To study the asymmetric synthesis of chiral diphospha-
nes through the addition of P–H bonds to unsaturated C–
C bonds, we have also applied chiral cyclopalladated amine
complex 1 in the synthesis of phosphane ligands in asym-
metric hydrophosphanation reactions.[7] Our previous stud-
ies on asymmetric reactions have given us insight into the
influence of the chiral amine auxiliary on the stereo- and
Figure 1. Stereochemical features of complexes (R)-1 and (R)-2.
regioselectivities observed. The unique stereochemical
feature of complex (R)-1 lays in the internal steric repulsion
between the methyl substituent on the stereogenic carbon
and its neighboring naphthylene proton H8. This particular
interaction confines the methyl group in the axial position,
and hence, the δ absolute conformation of the five-mem-
bered ring is fixed and not interconvertable in both the solid
state and in solution.[8] Due to this unique ring conforma-
tion, the chirality of the naphthylamine ring is transmitted
efficiently through its prochiral NMe groups onto the
neighboring coordination site. In pursuit of our interest in
the design of new chiral palladacycles[9] and to further im-
prove the stereoselectivity in asymmetric hydrophosphan-
ation reactions, novel palladacycle 2 was designed and syn-
thesized (Figure 1). Palladacycle 2 was designed to improve
three aspects: Firstly, the interaction between the aromatic
methyl group Me5 and the tert-butyl group would more
effectively lock the conformation of the five-membered pal-
View this journal online at
[a] Division of Chemistry and Biological Chemistry, School of
Physical and Mathematical Sciences, Nanyang Technological
University,
637371 Singapore
E-mail: pakhing@ntu.edu.sg
wileyonlinelibrary.com
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Y. Ding, Y. Zhang, Y. Li, S. A. Pullarkat, P. Andrews, P.-H. Leung
FULL PAPER
ladacycle in a fixed conformation in solution, hence locking palladation was observed when Pd(OAc)2 or Pd(NCMe)4-
the tert-butyl group in the axial position. Secondly, an ad- (ClO4)2/Et3N was employed as the palladation reagent.[9]
ditional methyl group Me2 was introduced on the aromatic
ring next to the Pd–C bond; through this introduction the
stereochemistry of the coordination site trans to the N do-
nor atom would be controlled more efficiently as compared
to palladacycle 1.[9a,9c,9h,9i] Thirdly, and most importantly,
the axially located tert-butyl group on the prochiral carbon
is expected to further enhance the interaction between itself
and the NMe groups, which would translate to a stronger
steric influence on the reaction site cis to the N donor atom.
To evaluate the above design rationale, target chiral cyclo-
palladated complex 2 was synthesized and its application in
asymmetric hydrophosphanation reactions was examined.
Racemic µ-chlorido dimer (Ϯ)-2 exists as a dynamic mix-
ture of two regioisomers interconverting in solution. This
fluxional behavior rendered characterization and confirm-
1
ation of the palladacycle difficult, as clustered H and 13C
NMR spectra were obtained. For example, the multiplet
1
resonance exhibited at δ = 1.64–1.69 ppm in the H NMR
spectrum, which is indicative of the tert-butyl group, sug-
gests the presence of preferential arrangements in solution
due to the variation in peak intensities. Several attempts
were made to crystallize the dimeric complex out fraction-
ally in a series of solvent systems. However, none of the
above attempts resulted in the formation of crystals that
were suitable for single-crystal X-ray crystallography. Thus,
racemic dimer (Ϯ)-2 was converted into its mononuclear
phosphane derivative (Ϯ)-10 by treatment with triphen-
ylphosphane. Reaction of complex (Ϯ)-2 with two molar
equivalents of triphenylphosphane in dichloromethane gave
a bright yellow solid that was slowly crystallized in dichlo-
romethane/hexane in 91.0% yield (Scheme 1). Through the
formation of phosphane derivative (Ϯ)-10, thorough exami-
nation of the chemical properties and structural characteri-
zation in both the solid state and solution became possible.
In the solid state, the structure of complex (Ϯ)-10 was
Results & Discussion
Synthesis and Characterization of ortho-Palladated
Complex (؎)-2
The preparation of ortho-palladated complex (Ϯ)-2 is il-
lustrated in Scheme 1. The first step involved a reaction be-
tween p-xylene 3 and isobutyryl chloride in the presence of
aluminum(III) chloride, which afforded ketone compound
4 in 93.0% yield. Further treatment of compound 4 with
iodomethane in sodium hydride led to the formation of the reaffirmed crystallographically. The single-crystal X-ray
tert-butyl group in compound 5.[10] Reduction of ketone 5 molecular structure and selected bond lengths and angles
by sodium borohydride in ethanol resulted in racemate are presented in Figure 2 and Table 1, respectively. In com-
alcohol (Ϯ)-6 in 87.5% yield. The alcohol was then con- plex (Ϯ)-10, the PPh3 group is located trans to the nitrogen
verted into azide (Ϯ)-7 in the presence of sodium azide and donor and the palladium center has a distorted square-
trifluoroacetic acid with a yield of 95.1%.[11] Reduction of planar coordination geometry. Analysis of the extent of the
compound (Ϯ)-7 by lithium aluminum hydride in dry THF tetrahedral distortion on the central Pd atom reveals that it
yielded amine compound (Ϯ)-8 in 85.4% yield, which was is located in a highly congested environment: the dihedral
subjected to subsequent methylation to form target N,N- angle between the {N1–Pd1–C1} and {Cl1–Pd1–P1} planes
dimethylamine ligand (Ϯ)-9 as an oil in 84.0% yield. The have a large value of 19.5°. The torsion angle P1–Pd1–C1–
molecular ion peak (ESI mode) of complex (Ϯ)-9 can be C2 is 52.0°, and such a twisting can be partially attributed
further observed at m/z = 220.2059 [M + H]+ by high-reso- to the repulsive interaction between the methyl spacer C3
lution mass spectrometry. N,N-Dimethylamine (Ϯ)-9 was and the phenyl group (C22–C27). The five-membered palla-
ortho-palladated to give racemic dimeric complex (Ϯ)-2 in dacycle, in this case, adopts a single conformation and the
67.9% yield by using Li2[PdCl4]/NaOAc as the palladation tert-butyl substituent attached to the α-carbon stereocenter
reagents. However, failure of amine (Ϯ)-9 to undergo ortho- remains axially located. The distance between C10 and C15
Scheme 1.
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A Chiral Palladacycle and Its Application in Asymmetric Hydrophosphanations
was found to be 3.060 Å, which is less than 3.4 Å, the sum the axial position. This conclusion can be inferred from the
of the van der Waals radii of the two atoms. This implies 4JP,H coupling constant of 5.2 Hz for the α-tert-butyl proton
1
that the bulky tert-butyl group must be projected away from and further confirmed by 2D H–1H ROESY NMR spec-
C15 to relieve steric repulsion in the crowded local environ- troscopy (Figure 3). In the NMR spectrum, the key
ment, which is the main driving force for this group to as- ROESY interaction is F, which demonstrates that the tert-
sume the axial position. Thus, the ring conformation is ef- butyl group exhibits a strong interaction only with the
fectively locked. Furthermore, the distance between C15 equatorial methyl substituent on the nitrogen atom. This
and Cl1 was found to be 3.190 Å, which is also smaller than interaction confirms that the methyl groups of the nitrogen
the van der Waals radii of the two atoms (3.5 Å). This is are fully fixed in position and that the ring is locked in
also indicative of a highly crowded localized environment, either the (S)λ or (R)δ conformation. Furthermore, the
which hence explains the stereochemical influence exhibited driving forces for the tert-butyl group to assume the axial
by the organopalladium complex as well as the regioselec- position can also be attributed to the repulsive interactions,
tivity observed.
(C) Me5–H7 and (G) Me5-tert-butyl. Other expected
ROESY interactions of NMe(eq)-NMe(ax) (E), tert-butyl-
H7 (D), Me5–H4 (H), and Me2–H3 (J) are also observed.
Interestingly, the interactions of tert-butyl-PPh3 (I) is also
observed, which indicates that through the introduction of
the bulky tert-butyl group, a steric effect will be experienced
when the reaction site trans to the nitrogen donor is coordi-
nated to a bulky group (for example, PPh3). The above
NMR spectroscopic investigations of complex (Ϯ)-10 in
solution indicates that the tert-butyl group is located in the
axial position and the interaction between the Me7 and
tert-butyl group can confine the five-membered organome-
tallic ring conformation and therefore λ and δ conforma-
tions are adopted in the (S) and (R) enantiomers, respec-
tively.
Figure 2. Molecular structure of complex (Ϯ)-10.
Table 1. Selected bond lengths [Å] and angles [°] for complex (Ϯ)-
10.
Pd1–C1
Pd1–P1
C1–Pd1–N1
N1–Pd1–P1
N1–Pd1–Cl1
C2–C1–Pd1
2.014(2)
2.275(5)
79.06(6)
166.0(5)
92.3(4)
Pd1–N1
Pd1–Cl1
C1–Pd1–P1
C1–Pd1–Cl1
P1–Pd1–Cl1
C8–C1–Pd1
2.145(2)
2.392(5)
101.8(5)
164.3(6)
89.8(2)
127.1(1)
112.6(1)
In solution, the NMR spectroscopic characterization of
this racemic palladacycle was achieved by a combination of
1
1H NMR and 2D H–1H ROESY NMR spectroscopy. In
CDCl3, the 31P NMR spectrum of complex (Ϯ)-10 shows
only a singlet resonance at δ = 30.0 ppm, indicating the
presence of a sole isomer in solution. Hence, in comparison
with dimeric complex (Ϯ)-2, mononuclear complex (Ϯ)-10
is more suitable for NMR spectroscopic studies. Further-
more, the absence of aliphatic protons in the triphenylphos-
phane ligand would not further contribute to the complex-
Figure 3. 2D 1H–1H ROESY NMR spectrum of complex (Ϯ)-10
in CDCl3. Refer to Scheme 1 for the numbered structure of com-
plex (Ϯ)-10. Selected ROESY interactions: (A) NMe(eq)–H7; (B)
NMe(ax)–H7; (C) H7–Me5; (D) H7–tert-butyl; (E) NMe(eq)–
NMe(ax); (F) NMe(eq)–tert-butyl; (G) Me5–tert-butyl; (H) Me5–
H4; (I) PPh3–tert-butyl; (J) Me2–H3.
1
ity of the aliphatic region of the H NMR spectrum. In the
1H NMR spectrum, the two N-methyl groups show charac-
teristic P–H couplings (J = 1.5 and 3.4 Hz). These JP,H cou-
plings confirm the trans relationship of the phosphorus
atom and the nitrogen donor, which could be observed and
justified by “transphobia”.[12]
Optical Resolution of Racemic Dimer (؎)-2
NMR study of racemic adduct (Ϯ)-10 has shown that in
The optical resolution of racemic dimeric complex (Ϯ)-2
solution the five-membered palladacycle exists in either the was achieved through the formation and separation of a
δ(R) or λ(S) conformation with the tert-butyl substituent in pair of diastereomeric (S)-prolinate derivatives (Scheme 2).
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Y. Ding, Y. Zhang, Y. Li, S. A. Pullarkat, P. Andrews, P.-H. Leung
FULL PAPER
By treating racemic dimeric complex (Ϯ)-2 with two molar
X-ray diffraction study of diastereomer (RC,SC,SN)-11
equivalents of sodium (S)-prolinate, the expected 1:1 mix- was carried out and there are three crystallographically dis-
ture of diastereomeric adducts (RC,SC,SN)-11 and tinguishable molecules in the unit cell with the same stereo-
1
(SC,SC,SN)-11 was formed and confirmed by the H NMR chemistry but with slightly different bond lengths and
spectroscopy.
angles. For clarity, only one of them (molecule A) is de-
picted in Figure 4. Selected bond lengths and angles are
provided in Table 2. The X-ray crystal structure revealed
the R absolute configuration of the stereocenter. The tert-
butyl group occupied the expected axial position and the
conformation of the five-membered palladacycle is δ. The
coordination geometry of the central palladium atom is in
a slightly distorted square plane. The dihedral angle be-
tween the planes N1–C1–Pd1 and O1–N2–Pd1 is 6.7°. Wor-
thy to note is that the two coordinated nitrogen atoms are
trans related, which is in contrast to the cis-(N,N)-relation-
ship for its α-methyl analogue.[9c] This phenomenon can be
attributed to severe intramolecular ligand–ligand interac-
tion arising from the presence of the bulky tert-butyl group
as compared to its α-methyl analogue. Consequently, less
steric interactions exist between the tert-butyl group and
the prolinato ligand when complex (RC,SC,SN)-11 adopts
the favorable trans-(N,N) arrangement.
Scheme 2.
Successful optical resolution was achieved by fractional
crystallization in dichloromethane/diethyl ether, affording
less-soluble diastereomer (SC,SC,SN)-11 in the form of yel-
low flakes with [α]D = +246 (c = 0.5, dichloromethane),
1
Ͼ99%de (according to H NMR spectroscopy). The dia-
Figure 4. Molecular structure of complex (RC,SC,SN)-11.
stereomerically enriched mother liquor allowed crystalli-
zation of remaining diastereomer (RC,SC,SN)-11 from chlo-
For diastereomer (SC,SC,SN)-11, yellow-colored crystals
roform/diethyl ether as pale-yellow feather-like crystals with suitable for X-ray crystallography were achieved from a
[α]D = –32 (c = 0.5, dichloromethane), Ͼ99%de (according dichloromethane/diethyl ether solution. There are two crys-
1
to H NMR spectroscopy). The absolute configurations of tallographically distinguishable molecules in the asymmetri-
both diastereomers were confirmed from X-ray single-crys- cal unit with the same stereochemistry but slightly different
tal diffractometry.
bond lengths and angles and only one of them (molecule A)
Table 2. Selected bond lengths [Å] and angles [°] for complex (RC,SC,SN)-11.
Molecule A
Molecule B
Molecule C
Pd1–C1
Pd1–N1
Pd1–N2
Pd1–O1
C1–Pd1–N1
C1–Pd1–N2
N1–Pd1–N2
C1–Pd1–O1
N1–Pd1–O1
N2–Pd1–O1
2.018(5)
2.062(5)
2.083(4)
2.136(4)
80.4(2)
106.1(2)
173.3(2)
174.6(2)
95.2(2)
Pd2–C21
Pd2–N3
Pd2–N4
Pd2–O3
C21–Pd2–N3
C21–Pd2–N4
N3–Pd2–N4
C21–Pd2–O3
N3–Pd2–O3
N4–Pd2–O3
2.009(6)
2.067(5)
2.071(5)
2.130(4)
81.0(2)
105.5(2)
173.4(2)
173.9(2)
95.0(2)
Pd3–C41
Pd3–N6
Pd3–N5
Pd3–O5
C41–Pd3–N6
C41–Pd3–N5
N6–Pd3–N5
C41–Pd3–O5
N6–Pd3–O5
N5–Pd3–O5
2.007(6)
2.072(5)
2.079(5)
2.112(4)
105.7(2)
81.8(2)
171.6(2)
174.4(2)
79.2(2)
78.3 (2)
78.4(2)
93.2(2)
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A Chiral Palladacycle and Its Application in Asymmetric Hydrophosphanations
is depicted in Figure 5, and selected bond lengths and
angles are provided in Table 3. The X-ray crystal structure
revealed the S absolute configuration of the carbon chiral
center, with the tert-butyl group in the axial position. All
the bond lengths and angles at the central palladium atoms
are within the normal ranges. Consistent with its α-methyl
counterpart, the two nitrogen atoms in each molecule are
trans-(N,N) related.[9c]
Scheme 3.
the chiral palladacycle to be determined. The molecular
structure and its numbering scheme are presented in Fig-
ure 6, whereas selected bond lengths and angles are given
in Table 4. The (R) absolute configuration of the optically
active palladacycle was confirmed from the Flack param-
eter of 0.001(16). X-ray analysis of complex (R)-12 revealed
that the tert-butyl group at the carbon center is in the axial
position. The geometry at palladium is in a distorted
square-planar with one molecule of water and one molecule
of acetonitrile coordinated cis and trans to the NMe2 group,
respectively. The dihedral angle between the planes N1–C1–
Pd1 and O1–N2–Pd1 is 5.7°.
Figure 5. Molecular structure of complex (SC,SC,SN)-11.
Table 3. Selected bond lengths [Å] and angles [°] for complex
(SC,SC,SN)-11.
Molecule A
Molecule B
Pd1–C1
Pd1–N1
Pd1–N2
Pd1–O1
C1–Pd1–N1
C1–Pd1–N2
N1–Pd1–N2
C1–Pd1–O1
N1–Pd1–O1
N2–Pd1–O1
2.022(7)
2.030(1)
2.065(1)
2.128(6)
81.2(4)
103.1(3)
173.4(3)
174.6(3)
94.0(3)
Pd2–C21
Pd2–N3
Pd2–N4
Pd2–O3
C21–Pd2–N3
C21–Pd2–N4
N3–Pd2–N4
C21–Pd2–O3
N3–Pd2–O3
N4–Pd2–O3
2.016(7)
2.044(1)
2.090(1)
2.116(5)
80.6(3)
102.0(3)
173.5(3)
175.8(3)
95.9(3)
Figure 6. Molecular structure of complex (R)-12.
81.5(3)
81.7(3)
Table 4. Selected bond lengths [Å] and angles [°] for complex (R)-
12.
Standard protonation of the auxiliary amino acid ligand
in complex (RC,SC,SN)-11 by 1  hydrochloric acid under
two-phase conditions readily yielded the enantiomerically
pure palladium complex dimer (R)-2. The other prolinate
derivative, (SC,SC,SN)-11, was converted into its respective
dichlorido dimer (S)-2 in a similar manner (Scheme 2). Un-
fortunately, both chiral dimeric palladium complexes, (R)-2
and (S)-2, could not be crystallized by using an array of
solvent systems. Thus, a conversion of dimeric complex (R)-
2 to its perchlorate salt derivative (R)-12, [α]D = –124 (c =
0.5, dichloromethane), by treatment with an excess amount
of silver perchlorate monohydrate in acetonitrile (Scheme 3)
circumvented this problem.
Pd1–C1
Pd1–N1
C1–Pd1–N2
N2–Pd1–N1
N2–Pd1–O1
C2–C1–Pd1
1.989(2)
2.052(1)
100.2(7)
176.1 (6)
85.3(6)
Pd1–N2
Pd1–O1
C1–Pd1–N1
C1–Pd1–O1
N1–Pd1–O1
C8–C1–Pd1
2.015(2)
2.207(2)
81.7(6)
173.3(7)
93.1(6)
127.5(1)
112.2(1)
Asymmetric Hydrophosphanation Reaction between
Diphenylphosphane and Diethyl Acetylenedicarboxylate
Promoted by Chiral Palladium Complex (R)-2
To evaluate the stereoselectivity of the new palladacycle,
A single crystal of complex (R)-12 suitable for X-ray the asymmetric hydrophosphanation reaction between di-
crystallography was obtained from a dichloromethane/hex- phenylphosphane and diethyl acetylenedicarboxylate pro-
ane solution, and it allowed the absolute configuration of moted by palladacycle (R)-2 was investigated.
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Y. Ding, Y. Zhang, Y. Li, S. A. Pullarkat, P. Andrews, P.-H. Leung
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As illustrated in Scheme 4, two equivalents of diphenyl-
phosphane ligand was allowed to coordinate to complex
(R)-12 in dichloromethane to yield complex (R)-13, the 31P
NMR spectrum of which showed a pair of doublets at δ =
–14.8 and 2.0 ppm (JP,P = 42.6 Hz). The hydrophosphan-
ation reaction between diphenylphosphane and diethyl ace-
tylenedicarboxylate was carried out at –78 °C in the pres-
ence of 20% equivalent of NEt3 in dichloromethane. The
reaction was monitored by 31P NMR spectroscopy and was
found to be complete in 12 h. The 31P NMR spectrum of
the reaction mixture in CDCl3 exhibited only one pair of
doublets and the resonances were observed at δ = 30.2 and
39.5 ppm (JP,P = 40.5 Hz). This indicated that only one iso-
mer was generated in the hydrophosphanation reaction.
However, the cationic product could not be crystallized
from a series of solvent systems. Hence a dichloromethane
solution of this complex was subsequently treated with con-
centrated HCl to remove the amine auxiliary, chemoselec-
tively giving dichlorido complex (S,S)-15, which was con-
firmed by X-ray analysis.
Figure 7. Molecular structure of complex (S,S)-15.
Table 5. Selected bond lengths [Å] and angles [°] for complex (S,S)-
15.
Molecule A
Molecule B
Pd1–P1A
Pd1–P1
Pd1–Cl1
Pd1–Cl1A
P1A–Pd1–P1
P1A–Pd1–Cl1
P1–Pd1–Cl1
P1A–Pd1–Cl1A
P1–Pd1–Cl1A
Cl1–Pd1–Cl1A
2.233(6)
2.233(6)
2.355(6)
2.355(6)
87.4(3)
173.6(2)
89.0(2)
89.0(2)
173.6(2)
95.1(3)
Pd2–P2
Pd2–P2A
Pd2–Cl2A
Pd2–Cl2
P2–Pd2–P2A
P2–Pd2–Cl2A
P2A–Pd2–Cl2A
P2–Pd2–Cl2
P2A–Pd2–Cl2
Cl2A–Pd2–Cl2
2.229(6)
2.229(6)
2.348(7)
2.348(7)
87.9(3)
176.3(2)
88.9(2)
88.9(2)
176.3(3)
94.5(3)
It needs to be noted that optically active diphosphane
ligand (S,S)-16 could be stereospecifically liberated from
complex (S,S)-15 by treating the dichlorido complex with
aqueous potassium cyanide, liberating compound (S,S)-16
as an air-sensitive ligand in 95.0% yield, [α]D = +280 (c =
0.5, dichloromethane), δ = –6.4 ppm (31P NMR, CDCl3).
The optical purity of free ligand (S,S)-16 was confirmed by
the quantitative recoordination of isomer (R,SS)-14 from
the liberated ligand and complex (R)-12 (Scheme 4). In
CDCl3, the 31P NMR spectrum of the crude product exhib-
ited only a pair of doublet signals at δ = 30.2 and 39.5 ppm
Scheme 4.
In CDCl3, dichlorido palladium complex (S,S)-15 exhib- (JP,P = 40.5 Hz). These signals are identical to those re-
ited a sharp singlet at δ = 57.7 ppm when monitored by 31
P
corded for sole diastereomer (R,SS)-14, which was gener-
NMR spectroscopy. Crystallization of the dichlorido com- ated directly from the asymmetric hydrophosphanation re-
plex from dichloromethane/diethyl ether resulted in the for- action. As a further test of the optical purity of the liber-
mation of light-yellow-colored crystals. The molecular ated ligand, liberated free ligand (S,S)-16 was recoordinated
structure and the absolute stereochemistry of complex to equally accessible isomer (S)-12. The 31P NMR spectrum
(S,S)-15 was determined by X-ray crystallography. There of the crude product in CDCl3 exhibited only a pair of dou-
were two crystallographically distinguishable molecules in blets at δ = 45.0 and 34.6 ppm (JP,P = 43.0 Hz). The chemi-
the asymmetrical unit with the same stereochemistry and cal shifts of these signals were different from the signals
only one of them is depicted in Figure 7. Selected bond for the sole product that was generated from the original
lengths and angles are given in Table 5. The absolute stereo- hydrophosphanation reaction. Hence, it could be confirmed
chemistry at C29 and C29A were established to be S and that liberated diphosphane (S,S)-16 is optically pure, and in
both the ester substituents on the chiral carbon centers were the asymmetric hydrophosphanation reaction only isomer
in the sterically favorable equatorial position as predicted.
(R,SS)-14 was generated in the presence of new chiral palla-
4432
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Eur. J. Inorg. Chem. 2010, 4427–4437

A Chiral Palladacycle and Its Application in Asymmetric Hydrophosphanations
The mixture was extracted with dichloromethane. The organic lay-
ers were combined, washed with H2O, and dried (MgSO4). Re-
dacycle (R)-2. When the widely used naphthylethylamine
auxiliary (R)-1 was employed for the asymmetric hydrophos-
phanation reaction between diphenylphosphane and di-
methyl acetylenedicarboxylate under the same reaction con-
dition, two diastereomers were formed in a 1:6 ratio.[7c]
moval of the solvent gave product 4 as a yellow oil (8.18 g, 93.0%).
IR (NaCl, neat): ν = 1782 cm–1. 1H NMR (400 MHz, CDCl ): δ =
˜
3
3
1.16 (d, JH,H = 6.8 Hz, 6 H, CHCH3), 2.35 (s, 3 H, aryl-CH3),
2.37 (s, 3 H, aryl-CH3), 3.30–3.37 (m, JH,H = 6.8 Hz, 1 H,
3
CHCH3), 7.10–7.15 (m, 2 H, aromatic protons), 7.29 (s, 1 H, aro-
matic proton) ppm. 13C NMR (100 MHz, CDCl3): δ = 18.55 (s,
CHCH3), 20.21 (s, C6H3CH3), 20.95 (s, C6H3CH3), 38.77 (s,
CHCH3), 127.91 (s, aryl-C), 131.26 (s, aryl-C), 131.47 (s, aryl-C),
134.17 (s, aryl-C), 135.00 (s, aryl-C), 138.68 (s, aryl-C), 209.53 (s,
C=O) ppm. HRMS (EI): calcd. for C12H16O 176.1196; found
176.1191.
Conclusions
In this article, novel palladacycle 2 was readily prepared
from p-xylene and then resolved through the separation of
its (S)-prolinate diastereomeric derivatives. The ability of
the newly synthesized palladacycle was demonstrated in the
preparation of a new diester-substituted diphosphane li-
gand through a chiral palladacycle (R)-12 promoted asym-
metric hydrophosphanation reaction, which proceeded with
excellent selectivity. The superiority of this chiral pallada-
cycle was similarly exhibited when it was used in the prepa-
ration of a range of chiral functionalized phosphanes.[13]
Further exploration of this novel palladacycle, for example
chiral catalysts for asymmetric reactions and resolving
agents for chiral ligands, is in progress in our laboratory.
1-(2,5-Dimethylphenyl)-2,2-dimethylpropan-1-one (5): A solution of
compound 4 (16.6 g, 94.4 mmol) in dry THF (100 mL) was added
dropwise to a 60% NaH (4.32 g, 108 mmol) solution in the same
solvent under an atmosphere of nitrogen, and the pale-yellow solu-
tion was heated at reflux for 1 h. The orange-brown solution was
cooled to room temperature and CH3I (15.0 mL, 188 mmol) was
added dropwise. The mixture was heated at 50 °C for 1 h then co-
oled to 0 °C. Ice water was added to quench the excess amount of
NaH, and the organic phase was extracted with diethyl ether,
washed with H2O, and dried (MgSO4). Removal of the solvent gave
product 5 as a yellow oil (13.9 g, (77.9%). IR (NaCl, neat): ν =
˜
1
1685 cm–1. H NMR (400 MHz, CDCl3): δ = 1.25 (s, 9 H, CCH3),
2.18 (s, 3 H, aryl-CH3), 2.31 (s, 3 H, aryl-CH3), 6.92 (s, 1 H, aro-
matic proton), 7.04–7.09 (m, 2 H, aromatic protons) ppm. 13C
NMR (100 MHz, CDCl3): δ = 19.33 (s, C6H3CH3), 21.10 (s,
C6H3CH3), 27.25 (s, COCCH3), 45.04 (s, COCCH3), 124.94 (s, aryl-
C), 129.25 (s, aryl-C), 130.58 (s, aryl-C), 134.33 (s, aryl-C), 140.99
(s, aryl-C), 215.19 (s, C=O) ppm. HRMS (ESI): calcd. for C13H19O
[M + H]+ 191.1436; found 191.1437.
Experimental Section
General: 1H and 13C NMR spectroscopy were performed with
Bruker Avance 300, 400, and 500 NMR spectrometers. Multiplici-
ties are given as: s (singlet); br. s (broad singlet), d (doublet), t
(triplet), q (quartet), dd (doublets of doublet), m (multiplet). The
number of protons (n) for a given resonance is indicated by n H.
Coupling constants are reported as a J value in Hz. Nuclear mag-
netic resonance spectra (1H NMR, 13C NMR) are reported as δ in
units of parts per million (ppm) downfield from SiMe4 (δ =
1-(2,5-Dimethylphenyl)-2,2-dimethylpropan-1-ol [(؎)-6]: A suspen-
sion of compound 5 (13.9 g, 73.5 mmol) in ethanol (100 mL) was
treated with NaBH4 (5.56 g, 147 mol) in the same solvent and al-
lowed to stir overnight at room temperature followed by treatment
with dilute NaOH solution. The resulting clear solution was con-
centrated under vacuum and extracted with dichloromethane. The
organic layers were combined, washed with H2O, and dried
(MgSO4). Removal of the solvent gave product (Ϯ)-6 as a yellow
0.0 ppm) and relative to the signal of [D]chloroform (δ
=
77.00 ppm, triplet). Unless stated otherwise, all NMR spectro-
scopic experiments were performed at room temperature (300 K).
Chemical shifts (δ) are reported in ppm relative to TMS, and refer-
enced to the chemical shifts of residual solvent resonances (1H and
13C NMR) or 85% H3PO4 (31P NMR). Mass spectra were recorded
with a Thermo Finnigan MAT 95 XP mass spectrometer in the EI
mode and a Waters Q-Tof Premimer Mass Spectrometer with ESI
mode. Infrared spectra were recorded with a Shimadzu IR Prestige-
21, either neat or in CHCl3. Melting points were determined with
oil (12.4 g, 87.5%). IR (NaCl, neat): ν = 3454 cm–1. 1H NMR
˜
(500 MHz, CDCl3): δ = 0.97 (s, 9 H, CCH3), 1.72 (s, 1 H, OH),
3
2.31 (s, 3 H, aryl-CH3), 2.33 (s, 3 H, aryl-CH3), 4.75 (d, JH,H
=
3
3.5 Hz, 1 H, CH), 6.98 (d, JH,H = 7.5 Hz, 1 H, aromatic proton),
7.02 (d, JH,H = 7.7 Hz, 1 H, aromatic proton), 7.29 (s, 1 H, aro-
3
a
SRS-Optimelt MPA-100 apparatus. Optical rotations were
matic proton) ppm. 13C NMR (75 MHz, CDCl3): δ = 20.00 (s,
C6H3CH3), 21.28 (s, C6H3CH3), 26.13 (s, CH3CCHOH), 36.89 (s,
CH3CCHOH), 76.75 (s, CH3CCHOH), 127.81 (s, aryl-C), 128.16
(s, aryl-C), 130.14 (s, aryl-C), 132.67 (s, aryl-C), 134.77 (s, aryl-C),
140.67 (s, aryl-C) ppm. HRMS (ESI): calcd. for C13H21O [M +
H]+ 192.1592; found 192.1603.
measured with a 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.
Caution: Perchlorate salts of metal complexes are potentially ex-
plosive compounds and should be handled with care.[14] Care
should be taken in handling highly toxic cyanide compounds and
azide compounds.
2-(1-Azido-2,2-dimethylpropyl)-1,4-dimethylbenzene [(؎)-7]: A mix-
ture of compound (Ϯ)-6 (5.80 g, 30.0 mmol) and sodium azide
(3.00 g, 45.0 mmol) in chloroform (30.0 mL) was cooled to below
0 °C. A solution of trifluoroacetic acid (18 mL) in chloroform
(15 mL) was added slowly. The mixture was left to stir overnight
at ambient temperature and a dilute NaOH solution was added to
pH 7. The organic layer was separated, washed with H2O, and
dried (MgSO4). Removal of the solvent gave product (Ϯ)-7 as a
1-Isobutyryl-2,5-dimethylbenzene (4): An isobutyryl chloride
(5.30 mL, 50.0 mmol) dichloromethane solution was added to a
suspension of anhydrous AlCl3 (7.34 g, 55.0 mmol) in the same sol-
vent (30 mL). A solution of p-xylene 3 (5.30 g, 50.0 mmol) was then
added dropwise to the mixture. The orange mixture was allowed to
stir at room temperature for 3 h and then poured into a mixture of
ice water and concentrated HCl (40 mL) and stirred for 10 min.
yellow oil (6.23 g, 95.1%). IR (NaCl, neat): ν = 2096 cm–1. 1H
˜
NMR (300 MHz, CDCl3): δ = 1.03 (s, 9 H, CCH3), 2.40 (s, 3 H,
aryl-CH3), 2.41 (s, 3 H, aryl-CH3), 4.70 (s, 1 H, CH), 7.05–7.13 (m,
Eur. J. Inorg. Chem. 2010, 4427–4437
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4433

Y. Ding, Y. Zhang, Y. Li, S. A. Pullarkat, P. Andrews, P.-H. Leung
FULL PAPER
2 H, aromatic protons), 7.22 (s, 1 H, aromatic proton) ppm. 13C
NMR (75 MHz, CDCl3): δ = 20.08 (s, C6H3CH3), 21.26 (s,
(s, 6 H), 2.51–2.57 (m, 12 H), 2.70–2.78 (m, 6 H), 3.48–3.50 (m, 2
H, CH), 6.58–6.66 (m, 4 H, aromatic protons) ppm. 13C NMR
C6H3CH3), 26.57 (s, CH3CCHN3), 37.01 (s, CH3CCHN3), 71.20 (s, (100 MHz, CDCl3): δ = 23.22 (s, CH3), 24.97 (s, CH3), 25.29 (s,
CH3CCHN3), 128.41 (s, aryl-C), 128.91 (s, aryl-C), 130.42 (s, aryl- CH3), 25.38 (s, CH3), 25.49 (s, CH3), 30.90 (s, CH3CCHN), 30.98
C), 133.22 (s, aryl-C), 135.09 (s, aryl-C), 136.00 (s, aryl-C) ppm. (s, CH3CCHN), 36.51 (s, CH3CCHN), 36.55 (s, CH3CCHN), 36.65
HRMS (EI): calcd. for C13H19 [M – N3] 175.1481; found 175.1477.
(s, CH3), 52.17 (s, CH3), 52.46 (s, CH3), 52.77 (s, CH3), 52.94 (s,
CH3), 56.12 (s, CH3), 56.17 (s, CH3), 56.33 (s, CH3), 87.99 (s, CH),
88.05 (s, CH), 126.64 (s, aryl-C), 126.75 (s, aryl-C), 127.96 (s, aryl-
C), 128.08 (s, aryl-C), 128.24 (s, aryl-C), 130.41 (s, aryl-C), 130.53
(s, aryl-C), 130.59 (s, aryl-C), 139.66 (s, aryl-C), 139.88 (s, aryl-C),
140.05 (s, aryl-C), 140.05 (s, aryl-C), 144.08 (s, aryl-C), 144.31 (s,
aryl-C), 144.55 (s, aryl-C), 148.61 (s, aryl-C), 148.65 (s, aryl-C),
148.70 (s, aryl-C) ppm.
1-(2,5-Dimethylphenyl)-2,2-dimethylpropan-1-amine [(؎)-8]: A solu-
tion of compound (Ϯ)-7 (5.30 g, 24.4 mmol) in dry THF (50 mL)
was added dropwise to a stirred solution of LAH (1.82 g,
48.0 mmol) in the same solvent (100 mL) at 0 °C. The reaction was
then heated to reflux for 3 h and then cooled to 0 °C. The excess
amount of LAH was quenched by consecutive addition of cold
ethyl acetate and ice water. The granular precipitate was removed
by filtration under vacuum and the filtrate was dried (MgSO4).
Removal of the solvent gave amine product (Ϯ)-8 as a light-yellow
(؎)-Chlorido{1-[1-(dimethylamino)-2,2-dimethylpropyl]-2,5-dimeth-
yl-6-phenyl-C,N}(triphenylphosphane-P)palladium(II) [(؎)-10]: A
dichloromethane solution of complex (Ϯ)-2 (0.184 g, 0.250 mmol)
and triphenylphosphane (0.131 g, 0.500 mmol) was stirred for 1 h
at room temperature and then concentrated to ca. 5 mL. The resi-
due liquid purified by column chromatography (silica gel, dichloro-
methane) to give a light-yellow powder that was recrystallized
(dichloromethane/hexane) to afford (Ϯ)-10 (0.28 g, 91.0%) as light-
yellow crystals. M.p. 170–172 °C (dec.). C33H39ClNPPd (621.15):
calcd. C 63.67, H 6.31, N 2.25; found C 63.95, H 6.31, N 2.53. IR
oil (3.98 g, 85.4%). IR (NaCl, neat): ν = 1215, 3447 cm–1. 1H NMR
˜
(300 MHz, CDCl3): δ = 1.01 (s, 9 H, CCH3), 1.51 (br. s, 2 H, NH),
2.37 (s, 6 H, aryl-CH3), 4.09 (s, 1 H, CH), 6.99 (dd, 4JH,H = 1.6 Hz,
3
3JH,H = 7.7 Hz, 1 H, aromatic proton), 7.05 (d, JH,H = 7.7 Hz, 1
H, aromatic proton), 7.31 (s, 1 H, aromatic proton) ppm. 13C NMR
(75 MHz, CDCl3): δ = 20.26 (s, C6H3CH3), 21.30 (s, C6H3CH3),
26.64 (s, CH3CCHN), 36.30 (s, CH3CCHN), 58.60 (s, CH3CCHN),
127.13 (s, aryl-C), 128.08 (s, aryl-C), 130.08 (s, aryl-C), 132.86 (s,
aryl-C), 134.63 (s, aryl-C), 142.30 (s, aryl-C) ppm. HRMS (ESI):
calcd. for C13H22N [M + H]+ 192.1752; found 192.1750.
(NaCl, CHCl ): ν = 1219 cm–1. 31P NMR (121 MHz, CDCl3): δ =
˜
3
30.0 (s) ppm. 1H NMR (500 MHz, CDCl3): δ = 1.46 (s, 9 H,
CCH3), 1.71 (s, 3 H, aryl-CH3), 2.30 (s, 3 H, aryl-CH3), 2.37 (s,
4
4JP,H = 1.5 Hz, 3 H, NCH3), 2.90 (d, JP,H = 3.4 Hz, 3 H, NCH3),
1-(2,5-Dimethylphenyl)-N,N,2,2-tetramethylpropan-1-amine [(؎)-9]:
A solution of compound (Ϯ)-8 (13.2 g, 69.1 mmol) in formic acid
(24 mL) was treated with formaldehyde (35 mL) at 0 °C. The reac-
tion mixture was heated to 100 °C for 6 h and then cooled to room
temperature. Concentrated HCl (10 mL) was added, and the mix-
ture was stirred for 15 min. After removal of the solvent under
vacuum, the sticky residual oil was treated with NaOH solution to
pH 14, and the liberated amine was extracted with dichlorometh-
ane. The organic layers were combined and dried (MgSO4). Re-
moval of the solvent gave product (Ϯ)-9 as a yellow oil (12.7 g,
3
5
3.60 (d, 4JP,H = 5.2 Hz, 1 H, CCH), 6.41 (dd, JH,H = 7.6 Hz, JP,H
3
= 1.4 Hz, 1 H, aromatic proton), 6.64 (d, JH,H = 7.6 Hz, 1 H,
aromatic proton), 7.20–8.00 (m, 15 H, aromatic protons) ppm. 13
NMR (125 MHz, CDCl3): δ = 23.46 (s, CH3), 27.75 (d, JC,P
C
=
10.8 Hz, CH3), 31.68 (s, NCHCCH3), 36.22 (s, NCHCCH3), 51.29
(d, JC,P = 1.4 Hz, CH3), 53.56 (d, JC,P = 2.7 Hz, CH3), 88.38 (d,
JC,P = 2.5 Hz, CH), 126.97 (s, aryl-C), 127.76 (br., aryl-C), 130.11
(br., aryl-C), 131.11 (s, aryl-C), 134.12 (br., aryl-C), 136.52 (br.,
aryl-C), 139.78 (d, JC,P = 5.3 Hz, aryl-C), 149.92 (d, JC,P = 1.3 Hz,
aryl-C), 158.70 (d, JC,P = 3.8 Hz, aryl-C) ppm. HRMS (ESI): calcd.
for C33H39NPPd [M – Cl]+ 586.1855; found 586.1874.
84.0%). IR (NaCl, neat): ν = 1215 cm–1. 1H NMR (300 MHz,
˜
CDCl3): δ = 1.06 (s, 9 H, CCH3), 2.30 (s, 6 H, NCH3), 2.34 (s, 3
H, aryl-CH3), 2.35 (s, 3 H, aryl-CH3), 3.56 (s, 1 H, CH), 6.98 (dd,
(SC,SC,SN)-Prolinato-{1-[1-(dimethylamino)-2,2-dimethylpropyl]-
2,5-dimethyl-6-phenyl-C,N}palladium(II) [(SC,SC,SN)-11]: A meth-
anol solution of sodium (S)-prolinate (0.83 g, 6.00 mmol) was
added to a suspension of racemic dimer (Ϯ)-2 (2.18 g, 3.00 mmol)
in the same solvent (30 mL). The mixture was stirred at room tem-
perature for 1 h, and the solvent was then removed under pressure.
The residue was dissolved in dichloromethane, washed with H2O,
and dried (MgSO4). Removal of the solvent gave a light yellow
solid that was dissolved in a minimum amount of dichloromethane.
Slow addition of diethyl ether resulted in the crystallization of less-
soluble diastereomer (SC,SC,SN)-11 as yellow needle-like crystals
(1.01 g, 77.0%). M.p. 185–187 °C (dec.). [α]D = +246, [α]578 = +256,
3
4JH,H = 1.3 Hz, JH,H = 7.7 Hz, 1 H, aromatic proton), 7.07 (d,
3JH,H = 7.7 Hz, 1 H, aromatic proton), 7.25 (s, 1 H, aromatic pro-
ton) ppm. 13C NMR (75 MHz, CDCl3): δ = 21.00 (s, C6H3CH3),
21.45 (s, C6H3CH3), 29.18 (s, CH3CCHN), 36.28 (s, CH3CCHN),
45.44 (s, CH3N), 71.68 (s, CH3CCHN), 126.92 (s, aryl-C), 129.37
(s, aryl-C), 130.25 (s, aryl-C), 134.07 (s, aryl-C), 134.26 (s, aryl-C),
137.94 (s, aryl-C) ppm. HRMS (ESI): calcd. for C15H26N [M +
H]+ 220.2065; found 220.2059.
(؎)-Di-µ-chloridobis{1-[1-(dimethylamino)-2,2-dimethylpropyl]-2,5-
dimethyl-6-phenyl-C,N}dipalladium(II) [(؎)-2]: A mixture of palla-
dium(II) chloride (10.3 g, 58.7 mmol) and lithium chloride (9.24 g,
220 mmol) in methanol (100 mL) was stirred at room temperature [α]546 = +292, [α]436 = +562, [α]365 = +890 (c = 0.5, dichlorometh-
for 3 h. Sodium acetate trihydrate (8.02 g, 59.0 mmol) was then dis-
solved into the solution followed by the addition of compound (Ϯ)-
9 (12.7 g, 58.0 mmol). The resulting mixture was stirred at room
temperature for 5 h and then filtered through Celite. The filtrate
was evaporated under vacuum, and the brown residue was dis-
solved in dichloromethane. The resulting solution was washed with
H2O, dried (MgSO4), and concentrated. The crude product was
purified by chromatography (silica gel; dichloromethane/hexane,
1:1) to afford the pure product (14.2 g, 67.9%). M.p. 129–130 °C
(dec.). C30H48Cl2N2Pd2 (720.46): calcd. C 50.01, H 6.72, N 3.89;
ane). C20H32N2O2Pd (438.15): calcd. C 54.73, H 7.35, N 6.38;
found C 54.75, H 7.79, N 6.42. IR (NaCl, CHCl ): ν = 1610, 1110,
˜
3
1182, 1219 cm–1. H NMR (500 MHz, CD2Cl2): δ = 1.51 (s, 9 H,
1
CCH3), 1.63–1.73 (m, 1 H, CHCH2), 1.96–2.04 (m, 1 H, CHCH2),
2.13–2.24 (m, 2 H, CH2CH2CH2), 2.29 (s, 3 H, aryl-CH3), 2.38 (s,
3 H, aryl-CH3), 2.56 [s, 3 H, NCH3(ax)], 2.82 [s, 3 H, NCH3(eq)],
3.19–3.31 (m, 2 H, NHCH, NHCH2), 3.56 (s, 1 H, CCH), 4.02–
4.07 (m, 1 H, NHCH2), 4.20 (br. s, 1 H, NH), 6.67–6.72 (m, 2 H,
aromatic protons) ppm. 13C NMR (100 MHz, CDCl3): δ = 22.79
(s, CH3), 23.78 (s, CH3), 25.03 (s, CH2), 29.75 (s, CH2), 30.09 (s,
CH3CCHN), 35.80 (s, CCH3), 50.70 (s, CH3), 53.26 (s, CH2), 55.12
found C 50.05, H 6.72, N 3.26. IR (NaCl, CHCl ): ν = 1217 cm–1.
˜
3
1H NMR (300 MHz, CDCl3): δ = 1.64–1.69 (m, 18 H, CCH3), 2.24 (s, CH3), 64.92 (s, NCH), 85.97 (s, COCH), 126.00 (s, aryl-C),
4434 Eur. J. Inorg. Chem. 2010, 4427–4437
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

A Chiral Palladacycle and Its Application in Asymmetric Hydrophosphanations
127.42 (s, aryl-C), 131.05 (s, aryl-C), 137.96 (s, aryl-C), 147.14 (s,
aryl-C), 149.51 (s, aryl-C), 180.17 (s, C=O) ppm. HRMS (ESI):
calcd. for C20H33N2O2Pd [M + H]+ 439.1577; found 439.1581.
42.25, H 6.05, N 5.80; found C 42.52, H 5.93, N 6.13. IR (NaCl,
1
CHCl ): ν = 2299, 3398 cm–1. H NMR (400 MHz, CD Cl ): δ =
˜
3
2
2
1.54 (s, 9 H, CCH3), 2.27 (s, 3 H, aryl-CH3), 2.39 (s, 6 H, aryl-
CH3, NCCH3), 2.61 [s, 3 H, NCH3(ax)], 2.77 [s, 3 H, NCH3(eq)],
3.06 (br. s, 2 H, OH2), 3.53 (s, 1 H, CCH), 6.78–6.89 (m, 2 H,
aromatic protons) ppm. 13C NMR (100 MHz, CD2Cl2): δ = 3.36
(s, CH3), 22.67 (s, CH3), 24.78 (s, CH3), 30.11 (s, NCHCCH3),
36.26 (s, NCHCCH3), 50.66 (s, CH3), 55.74 (s, CH3), 87.36 (s, CH),
122.55 (s, CN), 127.63 (s, aryl-C), 128.18 (s, aryl-C), 131.87 (s, aryl-
C), 137.92 (s, aryl-C), 140.97 (s, aryl-C), 148.56 (s, aryl-C) ppm.
HRMS (ESI): calcd. for C17H29N2OPd [M – ClO4]+ 383.1315;
found 383.1322.
(RC,SC,SN)-Prolinato-{1-[1-(dimethylamino)-2,2-dimethylpropyl]-
2,5-dimethyl-6-phenyl-C,N}palladium(II) [(RC,SC,SN)-11]: The
mother liquor of isomer (SC,SC,SN)-11 was evaporated to dryness,
and the residue was dissolved in a minimum amount of CHCl3.
The less-soluble diastereomer, (RC,SC,SN)-11, was crystallized by
slow addition of diethyl ether as pale-yellow feather-like crystals
(0.98 g, 75.0%). M.p.182–184 °C (dec.). [α]D = –32, [α]578 = –36,
[α]546 = –26, [α]436 = +22, [α]365 = +346 (c = 0.5, dichloromethane).
C20H32N2O2Pd (438.15): calcd. C 54.73, H 7.35, N 6.38; found C
54.75, H 7.79, N 6.42. IR (NaCl, CHCl ): ν = 1610, 1110, 1182,
˜
3
(S,S)-Dichlorido[diethyl-1,2-bis(diphenylphosphanyl)ethane Dicarb-
oxylate]palladium(II) [(S,S)-15]: A mixture of complex (R)-12
(0.10 g, 0.20 mmol) and diphenylphosphane (74.0 mg, 0.40 mmol)
in dichloromethane was stirred under an atmosphere of nitrogen at
room temperature for 1 h. A solution of diethyl acetylenedicarb-
oxylate (34.0 mg, 0.20 mmol) and triethylamine (4.0 mg,
0.04 mmol) in dichloromethane (5 mL) was added dropwise to the
reaction above, and the resulting mixture was stirred at –78 °C
overnight. After removal of the solvent, yellow-colored solid
(R,SS)-14 was obtained. [α]D = –22, [α]578 = –24, [α]546 = –26,
1219 cm–1. H NMR (500 MHz, CDCl3): δ = 1.47 (s, 9 H, CCH3),
1
1.70–1.87 (m, 3 H, CH2CH2CH2, NHCH2), 2.27 (s, 3 H, aryl-CH3),
2.34 (s, 3 H, aryl-CH3), 2.39–2.43 (m, 1 H, CHCH2), 2.64 [s, 3 H,
NCH3(ax)], 2.74 [s, 3 H, NCH3(eq)], 3.16–3.23 (m, 1 H, CHCH2),
3.52–3.53 (m, 1 H, NHCH2), 3.55 (s, 1 H, CCH), 3.80 (br. s, 1 H,
NH), 4.14–4.17 (m, 1 H, COCH), 6.67–6.71 (m, 2 H, aromatic
protons) ppm. 13C NMR (100 MHz, CDCl3): δ = 23.02 (CH2,
CH3), 24.43 (s, CH3), 28.90 (s, CH2), 30.33 (s, CH3CCHN), 36.23
(s, CCH3), 50.84 (s, CH2), 51.01 (s, CH3), 55.69 (s, CH3CCHN),
67.22 (s, CH), 86.06 (s, CH), 126.46 (s, aryl-C), 127.15 (s, aryl-C),
131.31 (s, aryl-C), 138.02 (s, aryl-C), 145.63 (s, aryl-C), 150.03 (s,
aryl-C), 177.80 (s, C=O) ppm. HRMS (ESI): calcd. for
C20H33N2O2Pd [M + H]+ 439.1577; found 439.1581.
[α]436 = –26 (c = 0.5, dichloromethane). IR (NaCl, CHCl ): ν =
˜
3
1377, 1724 cm–1. 31P NMR (121 MHz, CDCl3) δ = 39.5 (d, JP,P
=
40.5 Hz), 30.2 (d, JP,P = 40.5 Hz) ppm. 1H NMR (500 MHz
3
CDCl3): δ = 0.78 (t, JH,H = 7.1 Hz, 3 H, COOCH2CH3), 0.82 (t,
3JH,H = 7.1 Hz, 3 H, COOCH2CH3), 1.41 (s, 9 H, CCH3), 1.86 (s,
3 H, CH3), 2.25 (s, 3 H, CH3), 2.28 (s, 3 H, CH3), 2.73 (s, 3 H,
CH3), 3.49–3.55 (m, 1 H, PCH), 3.60–3.66 (m, 1 H, PCH), 3.69 (d,
4JP,H = 6.2 Hz, 1 H, NCH), 3.73–3.86 (m, 4 H, COOCH2CH3),
6.51–6.53 (m, 1 H, aromatic proton), 6.68 (d, 3JH,H = 7.7 Hz, 1 H,
(S)-Di-µ-chloridobis{1-[1-(dimethylamino)-2,2-dimethylpropyl]-2,5-
dimethyl-6-phenyl-C,N}dipalladium(II), (S)-2: A solution of dia-
stereomer (SC,SC,SN)-11 (1.01 g, 2.30 mmol) in dichloromethane
(15 mL) was treated with aqueous HCl (1 , 20 mL). After vigor-
ous stirring for 45 min, the organic layer was separated, washed
with H2O, and dried (MgSO4). Removal of the solvent and purifi-
cation by column chromatography (dichloromethane) gave the
product as a light yellow solid (0.78 g, 94.0%). [α]D = +210, [α]578
= +216, [α]546 = +228, (c = 0.5, dichloromethane). C30H48Cl2N2Pd2
(718.13): calcd. C 50.01, H 6.72, N 3.89; found C 50.26, H 6.25, N
aromatic proton), 7.18–8.20 (m, 20 H, aromatic protons) ppm. 13
C
NMR (100 MHz, CDCl3): δ = 13.39 (d, JC,P = 3.6 Hz, CH3), 14.12
(s, CH3), 22.64 (s, CH3), 23.78 (s, CH3), 29.55 (dd, JC,P = 3.6 Hz,
JC,P = 9.4 Hz, CH), 31.25 (s, CH3CCH), 35.48 (s, CH3CCH), 45.36
(dd, JC,P = 11.8 Hz, JC,P = 15.8 Hz, CH), 54.28 (d, JC,P = 4.1 Hz,
CH3), 56.98 (d, JC,P = 2.5 Hz, CH3), 62.21 (s, CH2), 62.74 (s, CH2),
91.00 (s, CH3CCH), 123.25, 123.86, 125.74 (d, JC,P = 3.7 Hz, aryl-
C), 126.23 (d, JC,P = 3.5 Hz, aryl-C), 127.40 (d, JC,P = 3.6 Hz, aryl-
C), 127.74 (d, JC,P = 7.0 Hz, aryl-C), 128.32 (d, JC,P = 11.1 Hz,
aryl-C), 128.43 (s, aryl-C), 128.54 (s, aryl-C), 128.59 (s, aryl-C),
128.67 (s, aryl-C), 128.84 (br., aryl-C), 128.94 (br., aryl-C), 130.54
4.16. IR (NaCl, CHCl ): ν = 1217 cm–1 1H NMR (400 MHz,
.
˜
3
CD2Cl2): δ = 1.65–1.67 (m, 18 H, CCH3), 2.22–2.23 (m, 6 H), 2.50–
2.56 (m, 12 H), 2.71–2.73 (m, 6 H), 3.47–3.49 (m, 2 H, CHCH3),
6.56–6.64 (m, 4 H, aromatic protons) ppm. 13C NMR (100 MHz,
CDCl3): δ = 23.00 (s, CH3), 24.75 (s, CH3), 25.27 (s, CH3), 30.76
(s, CH3), 36.34 (s, 1 C), 36.43 (s, 1 C), 52.25 (s, CH3), 52.56 (s,
CH3), 53.35 (s, CH3), 55.91 (s, CH3), 56.12 (s, CH3), 87.78 (s, CH),
126.43 (s, aryl-C), 126.55 (s, aryl-C), 127.75 (s, aryl-C), 128.03 (s,
aryl-C), 130.33 (s, aryl-C), 130.39 (s, aryl-C), 139.67 (s, aryl-C),
139.81 (s, aryl-C), 144.10 (s, aryl-C), 144.34 (s, aryl-C), 148.44 (s,
aryl-C), 148.49 (s, aryl-C) ppm. Optically pure (R)-2 was prepared
from (RC,SC,SN)-11 in a similar manner: [α]D = –208, [α]578 = –214,
[α]546 = –224 (c = 0.5, dichloromethane).
(d, JC,P = 10.9 Hz, aryl-C), 131.85 (br., aryl-C), 131.97 (d, JC,P
2.6 Hz, aryl-C), 132.04 (d, JC,P = 2.0 Hz, aryl-C), 132.23 (d, JC,P
6.6 Hz, aryl-C), 133.36 (d, JC,P = 1.9 Hz, aryl-C), 133.47 (d, JC,P
=
=
=
2.2 Hz, aryl-C), 134.81 (d, JC,P = 14.8 Hz, aryl-C), 136.32 (br., aryl-
C), 139.03 (dd, JC,P = 3.2 Hz, JC,P = 6.5 Hz, aryl-C), 149.10 (s,
aryl-C), 165.20 (d, JC,P = 7.5 Hz), 166.30 (d, JC,P = 7.3 Hz), 167.11
3
2
3
(dd, JC,P = 7.4 Hz, JC,P = 26.1 Hz, CO), 167.90 (dd, JC,P
=
2
5.6 Hz, JC,P = 19.2 Hz, CO) ppm. HRMS (ESI): calcd. for
C47H56NO4P2Pd [M – ClO4]+ 866.2719; found 866.2711. Concen-
trated hydrochloric acid (10 mL) was then added to complex
(R,SS)-14, and the mixture was stirred vigorously overnight. The
reaction mixture was washed with H2O, dried (MgSO4), and sub-
sequently crystallized from dichloromethane and diethyl ether to
give complex (S,S)-15 as yellow crystals (0.11 g, 74.0%). M.p. 251–
253 °C (dec). [α]436 = –138 (c = 0.5, dichloromethane). IR (NaCl,
(R)-{1-[1-(Dimethylamino)-2,2-dimethylpropyl]-2,5-dimethyl-6-
phenyl-C,N}palladium(II) Perchlorate [(R)-12]: Chiral palladium
complex (R)-2 (1.10 g, 1.53 mmol) was dissolved in acetonitrile
(20 mL) and AgClO4·H2O (1.38 g, 6.11 mmol). The mixture was
stirred vigorously in the dark at room temperature for 1 h. The
mixture was filtered through Celite (to remove AgCl), and the fil-
trate was concentrated under vacuum. The resulting residue was
dissolved in dichloromethane, washed with H2O, and dried
CHCl ): ν = 1730 cm–1. 31P NMR (121 MHz, CDCl3): δ = 57.3 (s)
˜
3
(MgSO4). Removal of the solvent gave (R)-12 (1.28 g, 87.0%) as ppm. 1H NMR (300 MHz CDCl3): δ = 0.91 (t, 3JH,H = 7.1 Hz, 6 H,
a yellow powder, and light-yellow crystals were formed by slow
evaporation of (R)-12 dichloromethane/hexane solution.
COOCH2CH3), 3.86–3.92 (m, 4 H, COOCH2CH3), 4.18 (d, 3JH,H
=
a
5.9 Hz, 2 H, PCHCOOCH2CH3), 7.53–7.94 (m, 20 H, aromatic
M.p.128–130 °C (dec). [α]D = –124, [α]578 = –128, [α]546 = –148 (c
protons) ppm. 13C NMR (100 MHz, CD2Cl2): δ = 13.28 (s, CH3),
= 0.5, dichloromethane). C17H29ClN2O5Pd (482.08): calcd. C
48.86 (t, JC,P = 22.3 Hz, CH), 62.34 (s, CH2), 123.62 (d, JC,P
=
Eur. J. Inorg. Chem. 2010, 4427–4437
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4435

Y. Ding, Y. Zhang, Y. Li, S. A. Pullarkat, P. Andrews, P.-H. Leung
Table 6. Crystallographic data for complexes (Ϯ)-10, (SC,SC,SN)-11, (RC,SC,SN)-11, (R)-12, and (S,S)-15.
FULL PAPER
(Ϯ)-10
(SC,SC,SN)-11
(RC,SC,SN)-11
(R)-12
(S,S)-15
Formula
C33H39ClNPPd
622.47
C20H32N2O2Pd
438.88
P21
monoclinic
13.4831(4)
10.5946(3)
15.1086(5)
2050.72(11)
4
C21H33Cl3N2O2Pd
558.24
C17H29ClN2O5Pd
483.27
C33H34Cl4O4P2Pd
804.74
C2
monoclinic
16.0113(4)
14.8142(4)
16.6228(5)
3551.99(17)
4
Formula weight
Space group
Crystal system
a [Å]
P212121
orthorhombic
10.6581(3)
15.7791(5)
17.6760(5)
2972.67(15)
4
P212121
orthorhombic
10.3779(3)
20.8123(8)
34.2018(12)
7387.2(4)
12
P212121
orthorhombic
8.4659(2)
10.7872(3)
22.7291(6)
2075.70(9)
4
b [Å]
c [Å]
V [Å3]
Z
T [K]
173(2)
1.391
0.71073
0.790
223(2)
1.421
0.71073
0.920
223(2)
1.506
0.71073
1.098
173(2)
1.546
0.71073
1.051
173(2)
1.505
0.71073
0.949
ρcalcd. [gcm–3]
λ [Å]
µ [mm–1]
Flack parameters
R1 (obsd. data)[a]
wR2 (obsd. data)[b]
0.044(14)
0.0165
0.0418
0.03(5)
0.0468
0.1229
0.04(3)
0.0467
0.1079
0.001(16)
0.0208
0.0508
–0.009(13)
0.0280
0.0661
2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = √{Σ[w(Fo – Fc ) ]}, w–1 = σ2(Fo2) + (aP)2 + bP.
2.0 Hz, aryl-C), 124.16 (d, JC,P = 2.0 Hz, aryl-C), 125.74 (d, JC,P
=
1.5 Hz, aryl-C), 126.34 (d, JC,P = 1.7 Hz, aryl-C), 128.55 (m, aryl-
C), 129.28 55 (m, aryl-C), 132.42 (s, CH3), 133.45 (m, aryl-C),
[1] a) J. Vicente, I. Saura-Llamas, M. G. Palin, P. G. Jones, J.
Chem. Soc., Dalton Trans. 1995, 2535–2540; b) J. Albert, J.
Granell, A. Luque, J. Minguez, R. Moragas, M. Font-Bardia,
X. Solans, J. Organomet. Chem. 1996, 522, 87–95; c) Y. Fu-
chita, K. Yoshinaga, Y. Ikeda, J. Kinoshita-Kawashima, J.
Chem. Soc., Dalton Trans. 1997, 2495–2500; d) V. V. Dunina,
L. G. KuzЈmina, M. Y. Kazakova, O. N. Gorunova, Y. K. Gri-
shin, E. I. Kazakova, Eur. J. Inorg. Chem. 1999, 1029–1039; e)
B. Calmuschi, U. Englert, Acta Crystallogr., Sect. C 2002, 58,
m545–m548; f) B. Calmuschi, A. Erik, U. Englert, Acta Crys-
tallogr., Sect. C 2004, 60, m320–m323; g) J. Vicente, I. Saura-
Llamas, D. Bautista, Organometallics 2005, 24, 6001–6004; h)
J. Vicente, I. Saura-Llamas, J.-A. Garcia-Lopez, B. Calmuschi-
Cula, D. Bautista, Organometallics 2007, 26, 2768–2776.
[2] For examples, see: a) S. Otsuka, A. Nakamura, T. Kano, K.
Tani, J. Am. Chem. Soc. 1971, 93, 4301–4303; b) K. Tani, L. D.
Brown, J. Ahmed, J. A. Ibers, M. Yokota, A. Nakamura, S.
Otsuka, M. Yokota, J. Am. Chem. Soc. 1977, 99, 7976–7886;
c) N. K. Roberts, S. B. Wild, J. Am. Chem. Soc. 1979, 101,
6254–6260; d) R. N. K. Roberts, S. B. Wild, J. Chem. Soc., Dal-
ton Trans. 1979, 2015–2021; e) D. G. Allen, G. M. McLaughlin,
G. B. Robertson, W. L. Steffen, G. Salem, S. B. Wild, Inorg.
Chem. 1982, 21, 1007–1014; f) S. Y. M. Chooi, S. Y. Siah, P.-H.
Leung, K. F. Mok, Inorg. Chem. 1993, 32, 4812–4818; g) V. V.
Dunina, E. B. Golovan, Tetrahedron: Asymmetry 1995, 6,
2747–2754; h) M. Pabel, A. C. Willis, S. B. Wild, Tetrahedron:
Asymmetry 1995, 6, 2369–2374; i) M. Pabel, A. C. Willis, S. B.
Wild, Inorg. Chem. 1996, 35, 1244–1249; j) A. Bader, M. Pabel,
A. C. Willis, S. B. Wild, Inorg. Chem. 1996, 35, 3874–3877; k)
J. Albert, J. M. Cadena, J. Granell, Tetrahedron: Asymmetry
1997, 8, 991–994; l) G. He, K. F. Mok, P.-H. Leung, Organome-
tallics 1999, 18, 4027–4031; m) J. Albert, J. M. Cadena, J.
Granell, G. Muller, J. I. Ordinas, D. Panyella, C. Puerta, C.
Sanudo, P. Valerga, Organometallics 1999, 18, 3511–3518; n) J.
Albert, J. M. Cadena, J. Granell, G. Muller, D. Panyella, C.
Sañudo, Eur. J. Inorg. Chem. 2000, 1283–1286; o) J. Albert,
J. M. Cadena, S. Delgado, J. Granell, J. Organomet. Chem.
2000, 603, 235–239; p) J. Albert, R. Bosque, J. M. Cadena, J. R.
Granell, G. Muller, J. I. Ordinas, Tetrahedron: Asymmetry
2000, 11, 3335–3343; q) E. Duran, E. Gordo, J. Granell, M.
Font-Bardia, X. Solans, D. Velasco, F. Lopez-Calahorra, Tetra-
hedron: Asymmetry 2001, 12, 1987–1997; r) S. Chatterjee,
M. D. George, G. Salem, A. C. Willis, J. Chem. Soc., Dalton
Trans. 2001, 1890–1896; s) J. Albert, R. Bosque, J. M. Cadena,
S. Delgado, J. Granell, G. Muller, J. I. Ordinas, M. F. Bardia,
X. Solans, Chem. Eur. J. 2002, 8, 2279–2287; t) J.-M. Camus,
P. Roy-Garcia, J. Andrieu, P. Richard, R. Poli, J. Organomet.
3
133.71 (s, CH3), 135.78 (m, aryl-C), 166.03 (dd, JC,P = 9.2 Hz,
2JC,P = 30.5 Hz, C=O) ppm.
Synthesis of (S,S)-16 by the Liberation of (S,S)-Diethyl-1,2-bis(di-
phenylphosphanyl)ethanedicarboxylate:
A solution of complex
(S,S)-15 (20.0 mg) in dichloromethane (20 mL) was stirred vigor-
ously with a saturated aqueous solution of KCN (0.50 g) for 1 h.
The colorless organic layer was separated, washed with H2O
(3ϫ20 mL), and dried (MgSO4). Upon removal of the solvent, a
white solid (14.0 mg, 95.0%) was obtained. [α]D = +280 (c = 0.5,
dichloromethane). 31P NMR (121 MHz, CDCl3): δ = –6.4 (s) ppm.
3
1H NMR (300 MHz, CDCl3): δ = 0.85 (t, JH,H = 7.1 Hz, 6 H,
3
COOCH2CH3), 3.41–3.58 (m, 4 H, COOCH2CH3), 3.88 (d, JH,H
= 4.1 Hz, 2 H, PCHCOOEt), 7.23–7.86 (m, 20 H, aromatic pro-
tons) ppm.
Crystal Structure Determination of (؎)-10, (SC,SC,SN)-11,
(RC,SC,SN)-11, (R)-12, and (S,S)-15: Crystal data for all five com-
plexes and a summary of the crystallographic analyses are given in
Table 6. Diffraction data were collected with a Bruker X8 CCD
diffractometer with Mo-Kα radiation (graphite monochromator).
SADABS absorption corrections were applied. All non-hydrogen
atoms were refined anisotropically, whereas 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.[15]
CCDC-728935 [for (Ϯ)-10], -728936 [for (S,S)-15], -728937 [for
(RC,SC,SN)-11], -728938 [for (R)-12], and -728939 [for (SC,SC,SN)-
11] contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Acknowledgments
We are grateful to Nanyang Technological University for support-
ing this research and for research scholarships to Y.D. and Y.Z. and
the exchange program (MChem Placement, School of Chemistry,
University of Southampton) for supporting P.A. to study in the
Division of Chemistry and Biological Chemistry, School of Physi-
cal and Mathematical Sciences, Nanyang Technological University.
4436
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 4427–4437

A Chiral Palladacycle and Its Application in Asymmetric Hydrophosphanations
Chem. 2005, 690, 1659–1668; u) J. Albert, J. Granell, G. Muller,
J. Organomet. Chem. 2006, 691, 2101–2106.
Y. Li, P.-H. Leung, J. Organomet. Chem. 2008, 693, 3289–3294;
f) M. Yuan, S. A. Pullarkat, C. H. Yeong, Y. Li, D. Krishnan,
P.-H. Leung, Dalton Trans. 2009, 3668–3670; g) S. A. Pullarkat,
K.-W. Tan, M. Ma, G.-K. Tan, L. L. Koh, J. J. Vittal, P.-H.
Leung, J. Organomet. Chem. 2006, 691, 3083–3088.
[3] For examples, see: a) S. B. Wild, Coord. Chem. Rev. 1997, 166,
291–311; b) S. Y. M. Chooi, P.-H. Leung, C. C. Lim, K. F.
Mok, G. H. Quek, K. Y. Sim, M. K. Tan, Tetrahedron: Asym-
metry 1992, 3, 529–532; c) C.-C. Lim, P.-H. Leung, K. Y. Sim,
Tetrahedron: Asymmetry 1994, 5, 1883–1886; d) V. V. Dunina,
E. B. Golovan, N. S. Gulyukina, A. V. Buyevich, Tetrahedron:
Asymmetry 1995, 6, 2731–2746; e) J. Albert, J. Granell, G.
Muller, D. Sainz, M. Font-Bardia, X. Solans, Tetrahedron:
Asymmetry 1995, 6, 325–328; f) Lopez, R. Bosque, D. Sainz,
X. Solans, M. Font-Bardia, Organometallics 1997, 16, 3261–
3266; g) V. V. Dunina, O. N. Gorunova, M. V. Livantsov, Y. K.
Grishin, Tetrahedron: Asymmetry 2000, 11, 2907–2916; h) F.
Levrat, H. Stoeckli-Evans, N. Engel, Tetrahedron: Asymmetry
2002, 13, 2335–2344; i) J. R. Moncarz, N. F. Laritcheva, D. S.
Glueck, J. Am. Chem. Soc. 2002, 124, 13356–13357.
[4] For examples, see: a) R. Schimdt, M. Cereghetti, B. Heiser, P.
Schonholzer, H. J. Hausen, Helv. Chim. Acta 1988, 71, 897–
929; b) R. Schimdt, J. Foricher, M. Cereghetti, P. Schonholzer,
Helv. Chim. Acta 1991, 74, 370–389; c) J. S. Giovanett, C. M.
Kelly, C. R. Landis, J. Am. Chem. Soc. 1993, 115, 4040–4057;
d) W. McFarlane, J. D. Swarbrick, J. I. Bookham, J. Chem.
Soc., Dalton Trans. 1998, 3233–3238; e) G. Uccello-Barretta,
R. Bernardini, R. Lazzaroni, P. Salvadori, Org. Lett. 2000, 2,
1795–1798.
[5] For examples, see: a) J. F. van Baar, J. M. Klerks, P. Overbosch,
D. J. Stufkens, K. Vrieze, J. Organomet. Chem. 1976, 112, 95–
103; b) Y. Yamamoto, H. Yamazaki, Inorg. Chim. Acta 1980,
41, 229–232; c) R. Navarro, E. P. Urriolabeitia, C. Cativiela,
M. D. Diaz-de-Villegas, M. P. Lopez, E. Alonso, J. Mol. Catal.
A 1996, 105, 111–116; d) J. M. Longmire, X. Zhang, M. Shang,
Organometallics 1998, 17, 4374–4379; e) M. A. Stark, C. J.
Richards, Tetrahedron Lett. 1997, 38, 5881–5884; f) J. Vicente,
I. Saura-Llamas, M. C. R. de Arellano, P. G. Jones, Organome-
tallics 1999, 18, 2683–2693; g) J. Vicente, I. Saura-Llamas, C.
Alcaraz, P. G. Jones, D. Bautisda, Organometallics 2002, 21,
3587–3595; h) W. E. Lindsell, D. D. Palmer, P. N. Preston,
G. M. Rosair, R. V. H. Jones, A. J. Whitton, Organometallics
2005, 24, 1119–1133.
[6] a) P.-H. Leung, Acc. Chem. Res. 2004, 37, 169–177 and refer-
ences cited therein; b) S.-K. Loh, G.-K. Tan, L. L. Koh, S.
Selvaratnam, P.-H. Leung, J. Organomet. Chem. 2005, 690,
4933–4938; c) S. A. Pullarkat, K.-W. Tan, M. Ma, G.-K. Tan,
L. L. Koh, J. J. Vittal, P.-H. Leung, J. Organomet. Chem. 2006,
691, 3083–3088; d) M. Ma, S. A. Pullarkat, Y. Li, P.-H. Leung,
Inorg. Chem. 2007, 46, 9488–9494; e) M. Ma, S. A. Pullarkat,
[7]
a) W.-C. Yeo, S. Y. Tee, H. B. Tan, G.-K. Tan, L. L. Koh, P.-
H. Leung, Inorg. Chem. 2004, 43, 8102–8109; b) S. A. Pullar-
kat, D. Yi, Y. Li, G.-K. Tan, P.-H. Leung, Inorg. Chem. 2006,
45, 7455–7463; c) L. Tang, Y. Zhang, L. Ding, Y. Li, K.-F.
Mok, W.-C. Yeo, P.-H. Leung, Tetrahedron Lett. 2007, 48, 33–
35; d) Y. Zhang, S. A. Pullarkat, Y. Li, P.-H. Leung, Inorg.
Chem. 2009, 48, 5535–5339; e) M. Yuan, S. A. Pullarkat, M.
Ma, Y. Zhang, Y. Huang, Y. Li, A. Goel, P.-H. Leung, Organo-
metallics 2009, 28, 780–786; f) F. Liu, S. A. Pullarkat, Y. Li, S.
Chen, M. Yuan, Y. Li, P.-H. Leung, Organometallics 2009, 28,
3941–3946.
[8]
[9]
B. H. Aw, S. Selvaratnam, P.-H. Leung, N. H. Rees, W. McFar-
lane, Tetrahedron: Asymmetry 1996, 7, 1753–1762.
a) Y. Li, K.-H. Ng, S. Selvaratnam, G.-K. Tan, J. J. Vittal, P.-
H. Leung, Organometallics 2003, 22, 834–842; b) J. K.-P. Ng,
G.-K. Tan, J. J. Vittal, P.-H. Leung, Inorg. Chem. 2003, 42,
7674–7682; c) Y. Li, S. Selvaratnam, J. J. Vittal, P.-H. Leung,
Inorg. Chem. 2003, 42, 3229–3236; d) J. K.-P. Ng, Y. Li, G.-K.
Tan, L.-L. Koh, J. J. Vittal, P.-H. Leung, Inorg. Chem. 2005,
44, 9874–9886; e) J. K.-P. Ng, S. Chen, Y. Li, G.-K. Tan, L.-L.
Koh, P.-H. Leung, Inorg. Chem. 2007, 46, 5100–5109; f) J. K.-
P. Ng, S. Chen, G.-K. Tan, P.-H. Leung, Eur. J. Inorg. Chem.
2007, 19, 3124–3134; g) J. K.-P. Ng, S. Chen, G.-K. Tan, P.-H.
Leung, Tetrahedron: Asymmetry 2007, 18, 1163–1169; h) Y.
Ding, Y. Li, Y. Zhang, S. A. Pullarkat, P.-H. Leung, Eur. J.
Inorg. Chem. 2008, 11, 1880–1891; i) Y. Ding, Y. Li, S. A. Pul-
larkat, S. L. Yap, P.-H. Leung, Eur. J. Inorg. Chem. 2009, 2,
267–276; j) Y. Ding, M. Chiang, S. A. Pullarkat, Y. Li, P.-H.
Leung, Organometallics 2009, 28, 4358–4370.
[10]
[11]
X. Jiang, C. Zhao, Y. Gong, Huaxue Xuebao 1988, 46, 900–
907.
D. Balderman, A. Kalir, Synthesis 1978, 24–26.
[12] a) J. Vicente, J. A. Abad, A. D. Frankland, M. C. R. Arellano,
Chem. Eur. J. 1999, 10, 3066–3075; b) J. Vicente, A. Arcas, D.
Bautista, P. G. Jones, Organometallics 1997, 16, 2127–2138.
[13] Y. Huang, S. A. Pullarkat, M. Yuan, Y. Ding, Y. Li, P.-H.
Leung, Organometallics 2010, 29, 536–542.
[14] W. C. Wolsey, J. Chem. Educ. 1973, 50, A335–A337.
[15] H. D. Flack, Acta Crystallogr., Sect. A 1983, 39, 876–881.
Received: April 28, 2010
Published Online: August 4, 2010
Eur. J. Inorg. Chem. 2010, 4427–4437
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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