Stereochemical investigations of a novel class of chiral phosphapalladacycle complexes derived from 1-[(2,5-dimethyl)phenyl] ethyldiphenylphosphine

Article abstract of DOI:10.1021/ic0509579

The phosphapalladacycle derived from 1-(2′,5′-dimethylphenyl) ethyldiphenylphosphine has been prepared in the optically active and racemic forms. The phosphine was synthesized as a racemate by the treatment of 1-chloro-1-(2′,5′-dimethylphenyl)ethane with sodium diphenylphosphide in THF. The racemic phosphapalladacycle was subsequently obtained as the chloro-bridged dimer by the treatment of the phosphine with palladium(II) acetate followed by anion metathesis with lithium chloride. Alternatively, the phosphine could be optically resolved via metal complexation using (R,R)-bis(μ-chloro)bis{1-[1-(N,N-dimethylamino)ethyl]naphthyl-C ²,N}dipalladium(II) as the resolving agent. An efficient separation of the resulting diastereomeric complexes was achieved by silica gel chromatography. The obtained optically resolved diastereomers were next subject to chemoselective removal of the (R)-N,N-(dimethylamino)-1-(1-naphthyl) ethylaminate auxiliary by treatment with concentrated hydrochloric acid. This process yielded the binuclear dimer complexes containing the resolved η¹-P ligand. Cyclopalladation of the coordinated phosphine could next be performed by treatment of its η¹-P binuclear dimer with silver(I) hexafluorophosphate(V) in a dichloromethane/water mixture followed by treatment with lithium chloride, giving rise to a pair of optically pure enantiomeric dimers with [α]_D -322 and +319° in CH ₂Cl₂. Despite the possibilities of the phosphine to attain a five- membered structure by ortho-palladation or a six-membered ring formation by aliphatic C-H bond activation, only the former was observed. X-ray crystallographic data of the meso dimer and an acetylacetonate derivative indicated that the phosphapalladacycle α-C* methyl substituent was axially located. The 2-D ¹H-¹H ROESY spectrum of the acetylacetonate derivative further revealed that the phosphapalladacycle was conformationally rigid in CDCl₃.

Full text of DOI:10.1021/ic0509579

Inorg. Chem. 2005, 44, 9874−9886
Stereochemical Investigations of a Novel Class of Chiral
Phosphapalladacycle Complexes Derived from
1-[(2,5-Dimethyl)phenyl]ethyldiphenylphosphine
Joseph Kok-Peng Ng,† Yongxin Li,‡ Geok-Kheng Tan,† Lip-Lin Koh,† Jagadese J. Vittal,† and
Pak-Hing Leung*,‡
Department of Chemistry, National UniVersity of Singapore, Kent Ridge, Singapore 119260, and
DiVision of Chemistry and Biological Chemistry, Nanyang Technological UniVersity,
Singapore 637616
Received June 14, 2005
The phosphapalladacycle derived from 1-(2
optically active and racemic forms. The phosphine was synthesized as a racemate by the treatment of 1-chloro-
1-(2 ,5 -dimethylphenyl)ethane with sodium diphenylphosphide in THF. The racemic phosphapalladacycle was
′,5′-dimethylphenyl)ethyldiphenylphosphine has been prepared in the
′
′
subsequently obtained as the chloro-bridged dimer by the treatment of the phosphine with palladium(II) acetate
followed by anion metathesis with lithium chloride. Alternatively, the phosphine could be optically resolved via
1-[1-(N,N-dimethylamino)ethyl]naphthyl-C2,N
metal complexation using (R,R)-bis(µ-chloro)bis{ }dipalladium(II) as the
resolving agent. An efficient separation of the resulting diastereomeric complexes was achieved by silica gel
chromatography. The obtained optically resolved diastereomers were next subject to chemoselective removal of
the (R)-N,N-(dimethylamino)-1-(1-naphthyl)ethylaminate auxiliary by treatment with concentrated hydrochloric acid.
This process yielded the binuclear dimer complexes containing the resolved
coordinated phosphine could next be performed by treatment of its
hexafluorophosphate(V) in a dichloromethane/water mixture followed by treatment with lithium chloride, giving rise
to a pair of optically pure enantiomeric dimers with [R D 322 and 319 in CH2Cl2. Despite the possibilities of
the phosphine to attain a five- membered structure by ortho-palladation or a six-membered ring formation by aliphatic
H bond activation, only the former was observed. X-ray crystallographic data of the meso dimer and an
acetylacetonate derivative indicated that the phosphapalladacycle -C* methyl substituent was axially located. The
2-D 1H 1H ROESY spectrum of the acetylacetonate derivative further revealed that the phosphapalladacycle was
conformationally rigid in CDCl3.
η
η
1-P ligand. Cyclopalladation of the
1-P binuclear dimer with silver(I)
]
−
+
°
C
−
R
−
Introduction
remarkable class of stereoselective syntheses, giving rise to
molecular structures that could serve as intermediates to more
complex structures via additional synthetic procedures.
The use of chiral metal-ligand systems as promoters of
various asymmetric organic transformations has continued
to remain very significant in the field of synthetic chemistry.1
Among these, the chiral ligand bearing Lewis acid promoted
asymmetric Diels-Alder reaction2 constitutes an extremely
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* To whom correspondence should be addressed. E-mail:
pakhing@ntu.edu.sg.
† National University of Singapore.
‡ Nanyang Technological University.
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9874 Inorganic Chemistry, Vol. 44, No. 26, 2005
10.1021/ic0509579 CCC: $30.25
© 2005 American Chemical Society
Published on Web 11/24/2005

Chiral Phosphapalladacycle Complexes
Notably, we have been able to exploit the synthetic utility
of the asymmetric Diels-Alder reaction for the construction
of optically active exo-type diphosphines and functionalized
phosphines bearing the norbornene skeleton with high
stereoselectivities. These processes commonly employ the
optically active cyclopalladated N,N-(dimethylamino)-1-
(naphthyl)ethylaminate derivative 1 as a chiral auxiliary in
juncture onward could only proceed intermolecularly rather
than intramolecularly, which applies to the complex 1. As
such endo-cycloadditions take place at the domain adjacent
to and cis with respect to the Pd-C bond of the N,N-
(dimethylamino)-1-(naphthyl)ethylaminate palladacycle, one
may expect the aromatic H′ proton to be more influential
than the dimethylamino substituents in controlling the
stereochemical outcome of the reaction, since the reaction
site next to the dimethylamino group has been rendered
inactive by the presence of the Pd- Cl bond. It is therefore
conceivable that the intermolecular endo-cycloaddition has
proceeded with relatively low diastereoselectivity, after
taking into account the small size of the H′ proton. As a
consequence of its steric bulk deficiency, the proton alone
is usually ineffectual in conveying any stereochemical
information to the reaction site nearby.
the syntheses.3 The chiral-inducing ability of this type of
palladium(II) complex stems from the various features of
the five-membered palladacycle. These include the transmis-
sion of vital stereochemical information originating from the
conformationally robust palladacycle3a,g,4 by (i) the dimethyl-
amino group to neighboring coordination site on the Pd atom5
and (ii) the protruding aromatic proton H′ to the site adjacent
to the Pd-C bond.4e
Similar asymmetric endo-cycloadditions have also been
performed for the syntheses of optically active phosphanor-
bornene ligands.3a-d,i,6a,b By this approach, the originally
vacant site (from the ready release of the labile, ClO4- ligand)
in complex 1 can be made unavailable by the substitution
of a chloride ligand instead, in the form of the complex 2.
A solution to this deficiency was then provided by the
introduction of a bulkier spacer methyl group at position 5
on the aromatic ring. The design of this palladacycle complex
was aimed at enhancing the chiral-inducing potential of the
palladacycle to the reaction site adjacent to the Pd-C bond.
With a more pronounced steric bulk, this methyl substituent
was shown to exert a more significant influence than the
smaller H′ proton of the analogous N,N-(dimethylamino)-
1-(1-naphthyl)ethylaminate palladacycle. Indeed, the deriva-
tive 3 was found to be a more efficient chiral promoter for
the asymmetric [4 + 2] endo-cycloaddition involving ethyl
vinyl ketone as the dienophile.8
The above complexes 1-3 contain instances of cyclopal-
ladated ligands of the N-donor type,8,9 which represent the
most abundant type of palladacycles of other various ligating
heteroatom donors10 that are available. Truly, one can
Due to the thermodynamic and kinetic stability of the Pd-
Cl bond in the complex of this type,7 arriving dienophiles
become devoid of attachment to the reaction template like
they were once capable of as in the case of the perchlorato-
bound complex 1. The implication of this situation is that
any [4 + 2] cycloaddition that might take place from this
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Inorganic Chemistry, Vol. 44, No. 26, 2005 9875

Ng et al.
Scheme 1
appreciate the importance of cyclopalladated complexes by
a consideration of their very diverse applications.11 In line
with our continued interests of expanding the structural
diversities of this class of promising organopalladium
complexes8,9a,b,10o for the purpose of enhancing their efficien-
cies as promoters for various asymmetric transformations and
taking into consideration the above demonstrated potential
of the chiral aminate palladacycle 3, a modification of the
structure 3 could be made by the introduction of the
phosphine-based palladacycle 4, as an addition to this rare
class of P-donor palladacycles that have been prepared in
the optically active forms.10k-o
starting from the ketone 5. The product of a simple reduction
of the ketone 5 using sodium borohydride in ethanol was
obtained as a colorless oil after workup in an overall good
yield of 89.4%. The H NMR spectrum (CDCl3) of the
alcohol 6 exhibited a quartet and a doublet resonance at δ
In this paper, we report (a) the synthesis of the palladacycle
4 in the optically active form, followed by (b) a stereochem-
ical investigation of the chiral cyclic organopalladium
structure. In developing potential chiral Lewis acids for use
in future asymmetric transformations, stereochemical proper-
ties pertaining to these chiral inductors are fundamental and
therefore must be vigorously examined12 as an avoidance
against committing crucial misinterpretations that may further
propagate in subsequent research that are built on these
interpretations as foundations. Thus, it is in our opinion that
an emphasis be placed on point b above, prior to evaluating
the effectiveness of the target palladacycle in various
applications.
1
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Results and Discussions
Synthesis of the Phosphine Ligand and Its Cyclopal-
ladation. As illustrated in Scheme 1, the synthesis of the
key racemic phosphine ligand was accomplished in a
sequence of three standard functional group interconversions,
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9876 Inorganic Chemistry, Vol. 44, No. 26, 2005

Chiral Phosphapalladacycle Complexes
Figure 2. Molecular structure of complex meso-9.
Figure 1. 31P{1H} NMR spectra of (()-9 at 300 and 223 K.
Table 1. Selected Bond Lengths (Å) and Angles (deg) of meso-9
Pd(1)-C(1)
Pd(1)-Cl(1)
C(1)-C(6)
P(1)-C(9)
P(1)-C(16)
2.019(3) Pd(1)-P(1)
2.444(2) Pd(1)-Cl(1A)
1.402(4) C(6)-C(9)
1.848(3) C(9)-C(10)
1.823(3) P(1)-C(17)
2.217(2)
2.441(2)
1.517(4)
1.534(4)
1.825(3)
the methine proton and the protons of the methyl substituent
of the R- C* atom correspondingly. The two methyl groups
on the aromatic ring are revealed expectedly as two intense,
closely spaced individual three-proton singlets at δ 2.30 and
2.34.
C(1)-Pd(1)-P(1)
P(1)-Pd(1)-Cl(1)
Pd(1)-Cl(1)-Pd(1A)
C(1)-C(6)-C(9)
78.1(8)
102.9(1)
94.7(1)
C(1)-Pd(1)-Cl(1A)
96.5(1)
85.3(1)
119.3(2)
99.7(1)
Cl(1)-Pd(1)-Cl(1A)
Pd(1)-C(1)-C(6)
C(6)-C(9)-P(1)
116.7(2)
The intermediate 7 was obtained as a colorless liquid by
the chlorination of the alcohol 6 using the chlorinating agent
PCl3. Treatment of the alkyl chloride 7 with sodium
diphenylphosphide gave the racemic phosphine 8 as a viscous
and colorless oil in 98.0% yield. While the phosphine was
represented as a singlet at δ 3.5 in its 31P{1H} NMR spectrum
(CDCl3), the appearances of the expected 31P-1H spin-spin
couplings for the R-methyl (3JPH ) 14.5 Hz) and R-methine
of the cyclopalladated complex, which exists as a mixture
of six isomers in solution. These are the chiral anti-(R,R),
anti-(S,S), syn- (R,R), and syn-(S,S) as well as the achiral,
meso anti-(R,S) and syn-(R,S) isomers, in which both isomers
of the first two pairs of are enantiomeric and cannot be
distinguished from each other by routine NMR spectroscopy.
It is noteworthy that two modes of phosphapalladacycle
formation may be accomplished in this complex synthesis
(Scheme 2). In common with the general preference of
ligands to assume a five-membered ring when choices of
other ring sizes are available, the formation of a six-
membered ring 10 (path b) via the activation of the aliphatic
C-H bond of C(2) methyl group was not observed.
The X-ray crystallographic studies of the racemic dimer
9 reveal that the complex has crystallized in the meso, anti-
(S, R) form (Figure 2). Selected bond lengths and bond angles
are given in Table 1. The structure consists of two anti-
disposed mirror-image halves, and each half of the structure
represents an asymmetric unit. The central four-membered
{Pd2(µ-Cl)2} cycle forms a regular plane, and the Pd-C,
Pd-P, and Pd-Cl bond lengths fall in the expected range
of values for a similar phosphapalladacycle complexes.10l
In agreement with an anticipated steric effect presented
by the introduction of the spacer methyl group at the aromatic
1
(2JPH ) 7.2 Hz) protons were observed in the H NMR
spectrum (CDCl3). We may take note of the more efficient
coupling between the R-methyl protons and the attached 31
P
nucleus, despite the longer distance between these protons
and the 31P nucleus. Similar to its 1-(1-naphthyl)ethyldiphen-
ylphosphine analogue,10o the phosphine 8 is highly sensitive
to air.
The cyclopalladation process was carried out by the
treatment of the racemic phosphine with Pd(OAc)2, followed
by the in-situ chloride metathesis with LiCl to arrive at the
dimer 9 as yellow crystals in 77% yield. As shown in Figure
1, the racemic chloro dimer appeared as two broad, overlap-
ping singlets at δ 58.3 and 59.5 in its 31P{1H} NMR spectrum
(CDCl3) at 300 K. However, when the NMR sample was
cooled to 223 K, both peaks become resolved into four
singlets at δ 58.8, 59.7, 59.9, and 60.9 in unequal amounts.
These NMR signals are consistent with the nonchiral form
Scheme 2
Inorganic Chemistry, Vol. 44, No. 26, 2005 9877

Ng et al.
Scheme 3
C(2) atom, the palladium atom was noted to experience a
pronounced tetrahedral distortion, provided by the dihedral
angle of 23.7° between the P(1)-Pd(1)-C(1) and Cl(1)-
Pd(1)-Cl(1A) planes. As a comparison, a similar distortion
around the coordination environment of the palladium atom
in the chloro (S,S) dimer of the ortho-palladated 1-(1-
naphthyl)ethyldiphenylphosphine10o has been found to be
insignificant, at 2.5-2.7°. The distortion from planarity was
further indicated by the mean vertical displacement of 0.2459
Å for the five atoms from the mean coordination plane
(m.c.pl.). In addition, the torsion angle for the four atoms of
C(2)-C(1)-Pd(1)-Cl(1A) has been dramatically increased
from 9.5 to 19.3° to 55.7° involving these four similar atoms
for the previously reported analogous complex, in which a
spacer group was absent.10o Such a significant increment is
undoubtedly related to the need of minimizing the interligand
repulsions present between the bridging Cl(1A) atom and
the spacer methyl group at C(2) atom. The puckering of the
five-membered palladacycle ring is significant and is exem-
plified by the mean intrachelate torsion angle of 31.4° for
9878 Inorganic Chemistry, Vol. 44, No. 26, 2005

Chiral Phosphapalladacycle Complexes
the palladacycle ring. As such, the extent of ring puckering
is more severe for this system than those derived from the
ortho- palladated {1-(1-naphthyl)ethyl}diphenylphosphine
(16.7-21.0°) and {1-(1-naphthyl)ethyl}diphenylarsine (16.0-
20.3°) systems.10o The ring puckering generates diastereo-
topicity on both P-phenyl substituents; the chemical non-
equivalence between both phenyl rings is thus provided by
the positions of these phenyl rings with respect to the m.c.pl.
The {C(11-16)} phenyl ring is considered axial while the
{C(17-22)} phenyl ring is equatorial. These conclusions are
made on the basis of the angles between the P(1)-C(ipso
carbon atom) bond and the normal to the m.c.pl., in which
the values of 9.9 and 58.2° apply to the P(1)-C(16) and
P(1)-C(17) bonds, respectively. The C(9) and C(9A) atoms
hold opposite absolute configurations and hence opposite ring
conformations. The methyl substituents on both atoms were
noted to assume axial dispositions: the C(9)-C(10) bond
subtends an angle of 27.4° with respect to the normal to the
m.c.pl. The need to assume such a conformational state is
most probably associated with the necessity to avoid an
unfavorable steric repulsion between this methyl group and
the spacer methyl group on the aromatic C(5) atom, when it
is equatorially oriented instead. This can be supported by
the close proximity of 2.630 Å between the equatorially
disposed H(9) atom with the C(8) atom of the spacer methyl
substituent. The close approach of these two atoms is
significant when comparing the above distance with the sum
of the van der Waals radii of 3.0 Å for carbon and hydrogen
atoms.
Preparation of the Phosphapalladacycle in the Opti-
cally Active Form. In principle, the prepared racemic
phosphapalladacycle 9 may be optically resolved by the use
of suitable resolving agents such as amino acidate salts since
this method of obtaining the palladacycle in the optically
active forms has been documented.8,10k-l,9d,q However, the
attempted separation of the (S)-prolinate derivatives of 15
by fractional crystallization was rather unsuccessful and, at
best, afforded only partially resolved diastereomeric mixtures.
As such, we have performed, according to Scheme 3, an
effective optical resolution of the phosphine 8 by metal
coordination as a monodentate ligand, followed by a two-
step procedure to arrive at the optically active phosphapal-
ladacycle dimer 9. Thus, the treatment of the racemic
phosphine with the resolving agent (R,R)-11 led to the
expected formation of a pair of diastereomeric adducts (R,R)-
and (R,S)-12 in equal amounts. This was revealed from the
31P{1H} NMR spectrum (CDCl3) of the crude mixture, in
which the two diastereomers were presented as two clearly
well-separated peaks at δ 45.1 and 49.6 of equal integral
intensities. The initial separation of the two diastereomers
by fractional crystallization was unsuccessful as crystalliza-
tion could not be induced despite the use of an array of
solvent systems with different polarities. Nevertheless, the
neutral nature of these complexes has presented us with the
alternate option of diastereomer separation by column
chromatography. Thus, the 1:1 diasteromeric mixture was
slowly eluted through a silica gel column with hexanes/ethyl
acetate (4:1, v/v) as the mobile phase from which the two
Figure 3. Molecular structure of complex (R,S)-12.
Table 2. Selected Bond Lengths (Å) and Angles (deg) of (R,S)-12
Pd(1)-C(1)
Pd(1)-P(1)
N(1)-C(14)
N(1)-C(11)
P(1)-C(25)
C(15)-C(17)
1.944(3) Pd(1)-N(1)
2.245(1) Pd(1)-Cl(1)
1.470(4) N(1)-C(13)
1.503(4) P(1)-C(15)
1.828(4) P(1)-C(31)
1.511(4) C(17)-C(22)
2.152(3)
2.401(1)
1.481(4)
1.867(3)
1.823(3)
1.376(5)
C(1)-Pd(1)-N(1)
N(1)-Pd(1)-P(1)
N(1)-Pd(1)-Cl(1)
C(31)-P(1)-Pd(1)
C(15)-P(1)-Pd(1)
80.9(1)
170.8(1)
93.0(1)
115.2(1)
109.9(1)
C(1)-Pd(1)-P(1)
93.5(1)
169.7(1)
93.6(1)
C(1)-Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(1)
C(25)-P(1)-Pd(1) 112.8(1)
P(1)-C(15)-C(17) 113.8(2)
C(15)-C(17)-C(22) 119.1(3)
diastereomers were readily distinguished as two different
bands with different retention times. The fractions were
separately eluted and were further checked by 31P{1H} NMR
spectroscopy for their optical purities. In this manner, both
diastereomers were separated efficiently, and thus, the optical
purities were revealed by the appearance of only one peak
in the 31P{1H} NMR spectrum of each diastereomer. In its
optically pure form, the first eluted diastereomer, (R,S)-12,
was readily crystallized from ethyl acetate and hexanes as
yellow prisms in an overall yield of 83.6% with [R]D -135°
(CH2Cl2). The other diastereomer, (R,R)-12, was isolated as
an analytically pure amorphous yellow powder in 71.5%
yield with [R]D +98° (CH2Cl2).
The absolute (R,S) configuration of the diastereomer was
confirmed by the X-ray diffraction studies of the complex.
The complex exists as two independent molecules in the unit
cell, and both molecules are only slightly different in terms
of their geometric parameters. For clarity, only one of these
is presented (with the accompanying numbering scheme) in
Figure 3, and its selected bond lengths and bond angles are
given in Table 2. The tetrahedral distortion around the
palladium coordination environment is moderate and is
provided by the dihedral angle of 9.7° between the {N-
Pd-C} and {Cl-Pd-P} planes (and 10.8° for the other
molecule).
In accordance with Scheme 3, the next preparative step
toward the development of the ortho-palladated phosphapal-
ladacycle 9 in the optically active form proceeded with the
removal of the homochiral (R)-1-(1-naphthyl)ethylaminate
auxiliary by hydrolysis in concentrated HCl. The separate
transformations of (R,R)- and (R,S)-12 led to the binuclear
optical antipodes, (R,R)- and (S,S)-13, as analytically pure
Inorganic Chemistry, Vol. 44, No. 26, 2005 9879

Ng et al.
available coordination sites for C-H bond activation and
hence cyclopalladation.13 Electronically, the removal of
chloride ligands from the coordination sphere of the metal
center would also generate a stronger electrophile (Pd2+),
which is necessary for the crucial stage of the cyclopalla-
dation reaction, i.e., the presumable electrophilic attack on
the ortho-palladating aromatic ring.9f The cyclopalladation
process employed a two-phase reaction mixture comprising
a dichloromethane solution of the binuclear complex 13 and
aqueous AgPF6 in the absence of an external base. Upon
chloride abstraction and subsequent cyclopalladation, a
solvated ionic intermediate of the type 14 could be expected.
While this intermediate was not isolated, it was presented
from its 31P{1H} NMR spectrum (CDCl3) as a series of peaks
at δ 62 and a septet resonance at δ -144 corresponding to
the PF6- counterion. Thus, the conversion of the intermediate
species 14 to the dichloro dimer 9 was achieved by the
Figure 4. Molecular structure of complex (S,S)-13.
Table 3. Selected Bond Lengths (Å) and Angles (deg) of (S,S)-13
Pd(1)-P(1)
Pd(1)-Cl(1)
Pd(1)-Cl(3)
Pd(1)-Cl(4)
P(1)-C(9)
P(1)-C(11)
P(1)-C(17)
C(6)-C(9)
C(1)-C(6)
2.239(2) Pd(2)-P(2)
2.264(2) Pd(2)-Cl(2)
2.335(2) Pd(2)-Cl(4)
2.448(2) Pd(2)-Cl(3)
1.889(5) P(2)-C(31)
1.807(7) P(2)-C(33)
1.807(7) P(2)-C(39)
1.487(7) C(28)-C(31)
1.382(7) C(28)-C(23)
2.236(2)
2.274(2)
2.332(2)
2.409(2)
1.867(5)
1.821(7)
1.811(6)
1.536(6)
1.392(6)
P(1)-Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(3)
96.47(7)
88.1(1)
Cl(1)-Pd(1)-Cl(3) 175.2(1)
P(2)-Pd(2)-Cl(2)
94.07(7)
90.3(1)
174.2(1)
175.1(1)
90.2(1)
85.3(1)
94.7(1)
103.2(2)
109.9(2)
117.2(2)
111.2(3)
P(2)-Pd(2)-Cl(4)
Cl(2)-Pd(2)-Cl(4)
P(2)-Pd(2)-Cl(3)
Cl(2)-Pd(2)-Cl(3)
Cl(3)-Pd(2)-Cl(4)
Pd(2)-Cl(4)-Pd(1)
Pd(2)-P(2)-C(33)
Pd(2)-P(2)-C(39)
Pd(2)-P(2)-C(31)
P(2)-C(31)-C(28)
P(1)-Pd(1)-Cl(4)
Cl(1)-Pd(1)-Cl(4)
Cl(3)-Pd(1)-Cl(4)
Pd(1)-Cl(3)-Pd(2)
Pd(1)-P(1)-C(11)
Pd(1)-P(1)-C(17)
Pd(1)-P(1)-C(9)
P(1)-C(9)-C(6)
C(9)-C(6)-C(1)
172.3(1)
91.0(1)
84.4(1)
addition of LiCl to the reaction mixture. In this manner, the
targeted (R,R)- and (S,S)-9 enantiomers were obtained as
yellow amorphous solids with [R]D -322 and +319° (CH2-
Cl2) correspondingly. In solution, the optically active dimer
9 was revealed as a broad singlet only at δ 59.9 from its
31P{1H} NMR spectrum (CDCl3) at room temperature, which
represents a contrast to that of the racemate (Figure 1). The
spectroscopic appearance of the NMR signal was temperature
dependent: below 300 K, the broad resonance was resolved
into two singlets in ca. 1.5:1 ratio while the peak width was
observed to decrease upon heating, so that, at 328 K, the
signal was displayed as a sharp singlet. This behavior was
reversible and was correlated to the isomerism of the syn/
anti complexes in solution.
The fact that these phosphapalladacycle complexes were
prepared in the optically pure form was further established
by derivatizing the racemic and (R,R)- and (S,S)-9 dimers
to their corresponding (S)-prolinate derivatives 15. A pair
of E/Z regioisomers was generated from each optical antipode
of 9 because of the possibility of geometric isomerism arising
from the asymmetrical nature of the (S)-prolinate chelate
(Figure 5). The 31P{1H} spectra of these (S)-prolinate
derivatives are shown in Figure 6. From Figure 6a,b, the
optical purity of each enantiomer of 9 was readily confirmed
by the appearance of a pair of singlets corresponding to the
pair of E- and Z-regioisomers, whose formations were
specific to the enantiomeric form of the dimer 9. In fact, the
spectrum obtained from the racemate (Figure 6c) represents
a direct superimposition of the other two spectra.
95.6(1)
103.5(2)
109.6(2)
125.6(2)
116.8(3)
121.8(4)
C(31)-C(28)-C(23) 119.1(4)
red crystals in the respective yields of 92.1% and 99.4%,
respectively. Their enantiomeric relationship was established
from the opposite signs but nearly identical magnitudes of
the specific optical rotation measurements: [R]D +334° for
the former and -335° for the latter were recorded in CH2-
Cl2.
An X-ray diffraction study of the (S,S)-13 complex was
performed, whose molecular structure is presented in Figure
4, and its selected bond lengths and bond angles are provided
in Table 3. The structure reveals an anti geometrical isomer,
in which both phosphine ligands occupy two diagonally
opposite ends of the structure. The binuclear complex
consists of two crystallographically independent halves with
minor variations in the structural parameters. In contrast to
the situation in the ortho-palladated dimer 9, both palladium
atoms of (S,S)-13 are in essentially planar environments. This
is indicated by the dihedral angle between the planes
{P-Pd-terminal Cl} and {Cl(3)-Pd-Cl(4)} of 2.3-4.4°.
The central four-membered {Pd2(µ-Cl)2} ring is planar since
an angle of 0.9° was found between the {Cl(3)-Pd(1)-
Cl(4)} and {(Cl(3)-Pd(2)-Cl(4)} planes.
The cyclopalladation process comprised of the use of
excess AgPF6 as an agent for chloride abstraction from the
binuclear complex 13, in which the process should create
(13) Avshu, A.; O’Sullivan, R. D.; Parkins, A. W. J. Chem. Soc., Dalton.
Trans. 1983, 1619.
9880 Inorganic Chemistry, Vol. 44, No. 26, 2005

Chiral Phosphapalladacycle Complexes
Figure 5. The four diastereomers of 15.
Figure 7. 2D 1H-1H ROESY NMR spectrum (CDCl3) of (S)-16. Selected
NOE interactions: (A) (R-C*Me)-(C5-Me); (B) (C5-Me)-(R-C*H); (C)
(R-C*Me)-(R- C*H); (D) (acac-Me)-(acac-CH); (E) (acac-Me′)-(acac-
CH); (F) (C2-Me)-H3; (G) (C3-Me)-H4; (H) (R-C*H)-(ax ortho-PPh);
(I) (R-C*H)-(eq ortho-PPh); (J) (R-C*Me)-(eq ortho-PPh). Solvent
signals: 9, H2O; [, CH2Cl2; 0, CDCl3.
aliphatic groups, and the absence of any aromatic protons
within the acetylacetonate framework will therefore not
contribute to the complexity at the aromatic region of the
1H NMR spectrum. Most importantly, as the chelated
acetylacetonate ring is planar and is nonchiral, we may
therefore expect the observed phosphapalladacycle confor-
mational behavior to be intrinsic and not be imposed by that
of the adjacent â-diketonate chelate.
The H and H-1H ROESY NMR spectra of (S)-16 are
shown in Figure 7. The appearance of the three-proton singlet
resonance of the C(5)-methyl substituent immediately rules
out the six-membered phosphapalladacycle structure 10
(Scheme 2). This intense singlet resonance was differentiated
from the other three-proton singlet resonance attributed to
the C(2)-methyl substituent by its NOE signals with the
resonance of the R-methyl (interaction A) and methine
1
1
protons (interaction B) from the 2D H-1H ROESY NMR
1
Figure 6. Optical purity determinations of (R,R)- and (S,S)-9.
spectrum. The two aromatic H3 and H4 protons were
distinguished from each other by their selective NOE contacts
with either the C(2)- or C(5)-methyl protons (interactions F
and G).
Stereochemical Investigations of the Phosphapallada-
cycle. In solution, the 1H NMR spectroscopic characterization
of the chiral phosphapalladacycle was assisted by a combina-
tion of 1H{31P} and 2D 1H-1H ROESY NMR spectroscopy
experiments performed on the â-diketonate derivative (S)-
16, with [R]D +502° (CH2Cl2). This derivative was prepared
efficiently from the reaction between the (S,S)-9 dimer and
sodium acetylacetonate. The mononuclear complex is more
suitable for NMR spectroscopic studies of the organopalla-
dium ring on account of the improved spectral resolution of
the signals with respect to that from its parent dimer.
The conformational behavior of the five-membered phos-
phapalladacycle was deduced from NOE data obtained from
1
the H-1H ROESY NMR spectrum. The R- methine and
methyl protons exhibit characteristic NOE interactions with
the o- PPh2 protons that are key indications to the confor-
mational state of the phosphapalladacycle. These comprise
the existence of NOE contacts between the R-methine proton
and both sets of diastereotopic o-PPh protons (interactions
H and I) and the observed steric interaction between the
R-methyl substituent with only one set of the o-PPh protons
(interaction J). For the phosphapalladacycle with the (S)
1
Moreover, the simplicity of the H NMR spectroscopic
signals that are presented by the acetylacetonate ligand is
another attractive feature. It possesses only protons from
Inorganic Chemistry, Vol. 44, No. 26, 2005 9881

Ng et al.
Figure 9. Molecular structure of complex (S)-16.
Table 4. Selected Bond Lengths (Å) and Angles (deg) of (S)-16
Pd(1)-C(1)
Pd(1)-P(1)
P(1)-C(17)
P(1)-C(9)
C(1)-C(6)
2.019(3)
2.195(1)
1.819(3)
1.827(3)
1.412(5)
Pd(1)-O(1)
Pd(1)-O(2)
P(1)-C(11)
C(6)-C(9)
2.076(3)
2.100(3)
1.825(3)
1.507(4)
Figure 8. Sawhorse and Newman projections for the λ and δ conforma-
tions of the chiral five-membered phosphapalladacycle. (Curved arrows
denote possible NOE interactions.)
absolute configuration at the R-C* atom, an agreement with
such an observed NOE pattern can only be met by the λ
conformation in which the R-methyl substituent is axially
disposed. In accordance with the sawhorse and Newman
projections (viewed along the P-R*-C bond) illustrated in
Figure 8, the o-PPh protons which interact with both
R-methine and methyl protons must therefore belong to the
equatorially oriented phenyl ring of the phosphorus atom.
The other PPh ring must hence be axially oriented. For the
alternate unobserved δ conformation, it is the methyl
substituent that must display NOE contacts with both sets
of o-PPh protons. As such, the existence of the specific NOE
interactions between the R-methyl and only one set of o-PPh
protons therefore points to the conformational rigidity of the
phosphapalladacycle ring in solution.
The above NMR spectroscopic investigations of (S)-16 is
in agreement with the following prediction: By the alternate
adoption of the δ conformation in which the R-methine
proton and the methyl substituent have switched their
equatorial or axial orientations, a stronger and hence possibly
sterically undesired NOE contact would have developed
between the resulting equatorially disposed axial methyl
substituent and the C(5)-methyl substituent. It can be foreseen
that such a scenario would present a driving force against
adopting the diastereomeric δ(S) conformation.
In the solid state, the absolute stereochemistry of (S)-16
was investigated crystallographically. The X-ray molecular
structure and selected bond lengths and bond angles are
presented in Figure 9 and Table 4, respectively. The expected
absolute configuration on the phosphapalladacycle R-C*
stereogenic center was confirmed from the Flack parameter
of 0.03(3), and the geometrical structure of the complex in
the solid state resembled that in solution. Moreover, the
phosphapalladacycle structural characteristics of the â-
diketonate derivative (S)-16 are similar to those of the meso
dimer 9, the most important among these being the axial
C(1)-Pd(1)-O(1)
O(1)-Pd(1)-O(2)
O(1)-Pd(1)-P(1)
P(1)-C(9)-C(6)
Pd(1)-P(1)-C(9)
93.1(1)
88.7(1)
165.2(1)
101.1(2)
99.0(1)
C(1)-Pd(1)-O(2)
C(1)-Pd(1)-P(1)
O(2)-Pd(1)-P(1)
C(1)-C(6)-C(9)
Pd(1)-C(1)-C(6)
178.0(1)
77.9(1)
100.(1)
115.5(3)
119.0(2)
disposition of the R-C*Me substituent in the solid state. A
comparison of the molecular structures of these two com-
plexes points to the steric effect originating from the spacer
methyl group at the aromatic C(5) atom as the main factor
for the observed conformational state of the palladacycle.
This can be supported by the similar distance of 2.630-
2.663 Å separating the methyl C(8) and H(9) atoms. The
roles of the P-phenyl rings as the palladacycle conformation
lockers do not seem very significant. While the distances
between the H(9) atom and the nearest ortho protons of both
axial and equatorial P-phenyl substituents were found to be
2.347 and 3.658 Å correspondingly for the meso dimer 9;
these respective distances were observed to have fluctuated
to 3.347 and 2.458 Å for the â-diketonate derivative (S)-16.
Such variations in these distances are indicative of the freely
rotating behavior of the these phenyl rings about the P(1)-
C(ipso) bonds. The possibility of these phenyl substituents
to assume different rotameric states is further provided by a
consideration of the {axial P-phenyl ring/C(1-6)} and
{equatorial P-phenyl ring/C(1-6)} interplane angles. The
values were found to be variable by 10.1 and 111.7°
respectively when comparing these angles to those for meso-9
and (S)-16.
Currently, investigations concerning the synthetic applica-
tions of the enantiomeric form of the newly prepared
phosphapalladacycle are in progress.
Experimental Section
Reactions involving air-sensitive compounds were performed
under a positive pressure of argon. Routine 1H NMR spectra were
9882 Inorganic Chemistry, Vol. 44, No. 26, 2005

Chiral Phosphapalladacycle Complexes
recorded at 300 or 500 MHz on a Bruker ACF 300 or Bruker AMX
500 NMR spectrometer. All the 31P{1H} NMR spectra were
recorded at 120 or 202 MHz on the Bruker ACF 300 or Bruker
AMX 500 NMR spectrometer. The 13C NMR spectra were recorded
at 126 MHz on the Bruker AMX 500 spectrometer. The phase-
sensitive ROESY NMR experiment for (S)-16 was acquired into a
1024 × 512 matrix with a 250 ms spin locking time and a spin
lock field strength such that γB1/2π ) 5000 Hz and then
transformed into 1024 × 1024 points using a sine bell weighting
functions in both dimensions. Melting points were determined on
a Bu¨chi melting point B-545 apparatus and were uncorrected.
Optical rotations were measured on the specified solution in 1 or
0.1 dm cells at 25 °C with a Perkin-Elmer model 341 polarimeter.
Elemental analyses were performed by the Elemental Analysis
Laboratory of the Department of Chemistry at the National
University of Singapore. The starting materials 1-acetyl-2,5-
dimethylbenzene, 5,8 and the enantiomerically pure form of bis-
(µ-chloro)bis[(R)-1-[(dimethylamino)ethyl]naphthyl-C2,N]dipalladium-
(II), (R,R)-11,4a were prepared according to reported procedures.
(()-1-[(2,5-Dimethyl)-1-phenyl]ethanol, (()-6. A suspension
of NaBH4 (2.6 g, 68.42 mmol) in ethanol (70 mL) was added to an
ethanol solution (150 mL) of 1-acetyl-2,5-dimethylbenzene, 11 (5.07
g, 34.21 mmol). The mixture was stirred at room temperature for
24 h, followed by the addition of aqueous NaOH (70 mL, 3 wt
%/v) with rapid stirring for another 1 h. The solution was then
concentrated to a pale yellow oil and was extracted with dichlo-
romethane (3 × 50 mL). The organic extracts were combined, dried
with MgSO4, and filtered. The product was finally obtained as a
colorless liquid by distillation, bp 78-80 °C, 0.23 mmHg, 4.62 g
130.5 (aromatic), 132.1 (aromatic), 136.0 (aromatic), 140.2 (aro-
matic). EI MS: m/z 168 ([35Cl - M]+) and 170 ([37Cl - M]+) in
3:1 relative intensities.
{(()-1-[(2,5-Dimethyl)-1-phenyl]ethyl}diphenylphosphine, (()-
8. A freshly prepared THF solution (20 mL) of sodium diphen-
ylphosphide (22.55 mmol) was added dropwise to a solution of
racemic 1-chloro-1-(2,5-dimethylphenyl)ethane, (()-7 (3.80 g,
22.55 mmol), in THF (20 mL) with rapid stirring at room
temperature. The solvent was removed to give a white residue. Fresh
deoxygenated water (40 mL) was added with stirring, and the
mixture was extracted with dichloromethane (3 × 40 mL). The
combined organic extracts were dried by MgSO4, filtered, and
evaporated to give a colorless and air-sensitive liquid. The liquid
was further dried under vacuum at 60 °C until a very viscous and
1
colorless oil was obtained, 7.04 g (98.0%). H NMR (CDCl3): δ
3
3
1.34 (dd, 3H, JHH ) 7.2 Hz, JPH ) 14.5 Hz, PCHMe), 1.92 (s,
3
3H, aromatic Me), 2.32 (s, 3H, aromatic Me), 3.78 (dq, 1H, JHH
) JPH ) 7.2 Hz, PCHMe), 6.89-6.93 (m, 4H, aromatic protons),
2
7.04-7.17 (m, 3H, aromatic protons), 7.32 (br s, 1H, aromatic),
7.43-7.45 (m, 3H, aromatic), 7.63-7.69 (m, 2H, aromatic). 31P-
{1H} NMR (CDCl3): δ 3.5 (s).
1
3
(89.4% yield). H NMR (CDCl3): δ 1.46 (d, 3H, JHH ) 6.4 Hz,
(OH)CHMe), 2.30 (s, 3H, Me), 2.34 (s, 3H, Me), 5.11 (q, 1H, 3JHH
3
) 6.4 Hz, (OH)CHMe), 6.98 (d, 1H, JHH ) 7.6 Hz, aromatic),
Optical Resolution of {(()-1-[(2,5-Dimethyl)-1-phenyl]ethyl}-
diphenylphosphine. Isolation of Chloro{(R)-1-[1-(N,N-dimethyl-
amino)ethyl]naphthyl-C2,N}{(R/S)-{1-[(2,5-dimethyl)-1-phenyl]-
ethyl}diphenylphosphine}palladium(II), (R,R)- and (R,S)-12. A
dichloromethane solution (50 mL) of the freshly prepared racemic
{1-[(2,5-dimethyl)-1-phenyl]ethyl}diphenylphosphine, (()-8 (9.33
g, 29.29 mmol), was cannulated into a suspension of the resolving
agent (R,R)-11 (9.96 g, 14.65 mmol) in dichloromethane (150 mL)
with rapid stirring. The reaction mixture was allowed to stir for 30
min until the resolving agent had entirely dissolved. The mixture
was then evaporated to dryness under reduced pressure. At this
stage the 31P{1H} NMR (CDCl3) spectrum of the crude product
exhibited two singlets of ca. equal intensities at δ 45.1 and 49.6
indicating the formation of a 1:1 mixture of the two stereochemi-
cally nonequivalent (R,R) and (R,S) diastereomers. The diastereo-
meric mixture was redissolved in minimum amount of dichlo-
romethane and was separated using silica gel column chromatography
by using hexanes/ethyl acetate (4:1, v/v) as eluent, from which the
(R,S) diastereomer followed by the more polar (R,R) diastereomer
were eluted sequentially.
7.02 (d, 1H, 3JHH ) 7.6 Hz, aromatic), 7.33 (s, 1H, H6). 13C NMR
(126 MHz, CDCl3): δ 18.4 (s), 21.1 (s), 23.9 (s), 66.8 (s, (OH)-
CHMe), 125.1 (aromatic), 127.8 (aromatic), 130.3 (aromatic), 131.0
(aromatic), 135.8 (aromatic), 143.6 (aromatic). EI MS: m/z 150,
[M]+.
(()-1-Chloro-1-[(2,5-dimethyl)-1-phenyl]ethane, (()-7. A dichlo-
romethane solution (380 mL) of racemic 1-[(2,5-dimethyl)-1-
phenyl]ethanol, (()-6 (7.10 g, 47.3 mmol), was added with vigorous
stirring to PCl3 (39 g, 281 mmol) dissolved in the same solvent
(250 mL). The mixture was allowed to stir at room temperature
for 16 h. Water was then added dropwise to the mixture with stirring
(to hydrolyze the excess PCl3). The organic phase was separated,
washed with water (3 × 100 mL), dried with Na2SO4, and filtered.
The solvent was then removed, and the product was finally obtained
as a colorless liquid by distillation under reduced pressure, bp 62-
Chloro{(R)-1-[1-(N,N-dimethylamino)ethyl]naphthyl-C2,N}-
{(S)-{1-[(2,5-dimethyl)-1-phenyl]ethyl}diphenylphosphine}-
palladium(II), (R,S)-12. The optically pure (R,S)-12 diastereomer
was crystallized as yellow blocks from ethyl acetate/hexanes. Mp:
219-221 °C (dec). [R]D ) -135°, [R]578 ) -141°, [R]546 ) -159°,
and [R]436 ) -229° (c 1.0, CH2Cl2). Yield: 8.07 g (83.6%). Anal.
1
64 °C, 0.23 mmHg, 6.99 g (87.7% yield). H NMR (CDCl3): δ
Calcd for C36H39ClNPPd: C, 65.7; H, 6.0. Found: C, 65.8; H, 6.2.
3
3
1.87 (d, 3H, JHH ) 6.7 Hz, ClCHMe), 2.34 (s, 3H, Me), 2.37 (s,
1H NMR (CDCl3): δ 1.72 (s, 3H, C24-Me), 1.90 (dd, 3H, JHH
)
3H, Me), 5.33 (q, 1H, 3JHH ) 6.7 Hz, ClCHMe), 7.01 (d, 1H, 3JHH
7.2 Hz, JPH ) 19.0 Hz, PCHMe), 2.02 (s, 3H, C23-Me), 2.12 (d,
3
3
) 8.0 Hz, aromatic H), 7.04 (d, 1H, JHH ) 8.0 Hz, aromatic H),
3H, 3JHH ) 6.2 Hz, NCHMe), 2.77 (d, 3H, 4JPH ) 1.3 Hz, NMeax),
7.34 (s, 1H, H6). 13C NMR (126 MHz, CDCl3): δ 18.5 (s), 21.1
(s), 25.3 (s), 55.2 (s, ClCHMe), 126.4 (aromatic), 128.9 (aromatic),
3.07 (d, 3H, JPH ) 3.3 Hz, NMeeq), 4.36 (dq, 1H, JHH ) JPH )
4
3
4
3
2
6.2 Hz, NCHMe), 5.01 (dq, 1H, JHH ) 7.2 Hz, JPH ) 10.13 Hz,
Inorganic Chemistry, Vol. 44, No. 26, 2005 9883

Ng et al.
3
4
PCHMe), 5.96 (s, 1H, H22), 6.32 (dd, 1H, JHH ) 8.7 Hz, JPH
)
6.3 Hz, H2), 6.64 (d, 1H, 3JHH ) 8.7 Hz, H3), 6.89-6.94 (2 closely
spaced d, 2H, JHH ) 7.3 Hz, H19, H20), 7.12 (ddd, 2H, JHH
)
3
3
3JHH ) 7.6 Hz, JPH ) 1.8 Hz, m-PPh), 7.24-7.28 (m, 2H, H6,
4
p-PPh), 7.34-7.37 (m, 3H, H7, m-PPh), 7.48-7.52 (m, 4H, H5,
o-PPh, p-PPh), 7.68 (d, 1H, JHH ) 8.5 Hz, H8), 7.77 (dd, 2H,
3
3
1
3JHH ) 7.4 Hz, JPH ) 10.4 Hz, o-PPh). H NMR (CD2Cl2): δ
1.66 (s, 3H, C24-Me), 1.85 (dd, 3H, JHH ) 7.3 Hz, JPH ) 18.9
3
3
Hz, Ph2PCHMe), 2.00 (s, 3H, C23-Me), 2.08 (d, 3H, JHH ) 6.5
3
4
Hz, NMe2CHMe), 2.72 (d, 3H, JPH ) 1.7 Hz, NMeax), 3.03 (d,
4
3
4
3H, JPH ) 3.2 Hz, NMeeq), 4.35 (dq, 1H, JHH ) 6.5 Hz, JPH
)
3
2
6.1 Hz, NMe2CHMe), 4.94 (dq, 1H, JHH ) 7.3 Hz, JPH ) 10.4
Hz, Ph2PCHMe), 6.00 (s, 1H, H22), 6.32 (dd, 1H, JHH ) 8.5 Hz,
3
Attempts to crystallize the (R,R) diastereomer were unsuccessful
despite a range of solvent systems tried.
4JPH ) 6.2 Hz, H2), 6.64 (d, 1H, JHH ) 8.5 Hz, H3), 6.88-6.93
3
(m, 2H, H19, H20), 7.13 (ddd, 2H, 3JHH ) 7.9 Hz, 3JHH ) 7.90 Hz,
4JPH ) 2.1 Hz, m-PPh), 7.21-7.38 (m, 5H, H6, H7, m-PPh, p-PPh),
(R,R)-sym-Dichlorobis(µ-chloro)bis[{1-(2,5-dimethyl-1-phenyl)-
ethyl}diphenylphosphine]dipalladium(II), (R,R)-13. Concentrated
HCl (5.4 mL, 65.3 mmol) was added to an acetone solution (43
mL) of the complex (R,R)-12 (2.15 g, 3.26 mmol), and the mixture
was refluxed for 4 h. Water was then added to the cooled mixture
with stirring, and the resulting precipitate was then filtered out,
washed successively with water, dried, and redissolved in dichlo-
romethane (20 mL). The reddish solution was further washed with
water (3 × 20 mL), dried with MgSO4, and filtered. The solution
was then concentrated, and product was crystallized as small red
blocks from dichlromethane-hexanes, 1.49 g (92.1% yield). Mp:
196-200 °C (dec). [R]D: +334° (c 1.0, CH2Cl2). Anal. Calcd for
C44H46Cl4P2Pd2: C, 53.3; H, 4.7. Found: C, 53.6; H, 4.7. 1H NMR
7.45-7.55 (m, 4H, H5, o-PPh, p-PPh), 7.67 (d, 1H, JHH ) 8.5
3
Hz, H8), 7.78 (dtt, 2H, 3JHH ) 8.4 Hz, 4JHH ) 1.2 Hz, 3JPH ) 11.0
Hz, o-PPh). 31P{1H} NMR (CDCl3): δ 49.8 (s). 31P{1H} NMR
(CD2Cl2): δ 49.9 (s).
(CDCl3): δ 1.75 (s, 3H, C8-Me), 1.98 (dd, 3H, 3JHH ) 7.1 Hz, 3JPH
3
) 19.3 Hz, PCHMe), 2.00 (d, 3H, C7-Me), 4.64 (dq, 1H, JHH
)
7.1 Hz, JPH ) 12.3 Hz, PCHMe), 6.20 (s, 1H, H1), 6.88 (d, 1H,
2
3JHH ) 7.8 Hz, H4), 6.91 (d, 1H, JHH ) 7.76 Hz, H3), 7.34-7.39
3
(m, 4H, m-PPh + PPh aromatics), 7.52-7.57 (overlapping m, 4H,
3
3
p-PPh + PPh aromatics), 7.80 (dd, 2H, JHH ) 7.4 Hz, JPH
)
10.9 Hz, o-PPh). 31P{1H} NMR (CDCl3): δ 42.5 (s).
Chloro{(R)-1-[1-(N,N-dimethylamino)ethyl]naphthyl-C2,N}-
{(R)-{1-[(2,5-dimethyl)-1-phenyl]ethyl}diphenylphosphine}-
palladium(II), (R,R)-12. The solvents from the eluted optically
pure (R,R) diastereomer were evaporated to dryness in vacuo, and
the product was obtained as an amorphous yellow powder. Mp:
128-131 °C. [R]D ) +98°, [R]578 ) +104°, [R]546 ) +128°, and
[R]436 )397° (c 0.5, CH2Cl2). Yield: 6.90 g (71.5%). Anal. Calcd
1
for C36H39ClNPPd: C, 65.7; H, 6.0. Found: C, 65.9; H, 6.1. H
3
3
NMR (CDCl3): δ 1.56 (dd, 3H, JHH ) 7.5 Hz, JPH ) 17.6 Hz,
PCHMe), 1.95 (s, 3H, C23-Me), 2.11-2.12 (m, 6H, NCHMe,
C24-Me), 2.71 (d, 3H, 4JPH ) 1.2 Hz, NMeax), 2.99 (d, 3H, 4JPH
)
3
4
3.2 Hz, NMeeq), 4.35 (dq, 1H, JHH ) JPH ) 6.3 Hz, NCHMe),
4.40 (dq, 1H, JHH ) JPH ) 7.7 Hz, PCHMe), 6.11 (s, 1H, H22),
3
3
(S,S)-sym-Dichlorobis(µ-chloro)bis[{1-(2,5-dimethyl-1-phenyl)-
ethy}ldiphenylphosphine]dipalladium(II), (S,S)-13. Complex
(S,S)-13 was prepared as described above from the chromatographi-
cally pure (R,S)-12. Yield: 1.12 g (99.4%). Mp: 196-200 °C (dec).
[R]D: -335° (c 1.0, CH2Cl2). Anal. Calcd for C44H46Cl4P2Pd2: C,
53.3; H, 4.7. Found: C, 53.6; H, 4.6. 1H and 31P{1H} NMR (CDCl3)
were identical with those recorded for (R,R)-13.
6.87-6.91 (m, 2H, H2, H20), 6.99 (d, 1H, JHH ) 7.8 Hz, H19),
3
7.12 (d, 1H, 3JHH ) 8.6 Hz, H3), 7.26-7.46 (m, 8H, H6, H7, m-PPh2,
p-PPh2), 7.67-7.74 (m, 4H, H5, H8, o-PPh ), 7.77 (dd, 2H, 3JHH
)
7.5 Hz, JPH ) 10.9 Hz, o-PPh). 1H NMR (CD2Cl2): δ 1.53
3
(dd, 3H, 3JHH ) 7.3 Hz, 3JPH ) 17.5 Hz, Ph2PCHMe), 1.93 (s, 3H,
3
o-phenyl-Me), 2.10 (d, 3H, JHH ) 6.5 Hz, NMe2CHMe), 2.13
(s, 3H, p-phenyl-Me), 2.72 (d, 3H, JPH ) 1.7 Hz, NMeax), 3.03
(d, 3H, JPH ) 3.2 Hz, NMeeq), 4.34-4.41 (partially overlapped
4
(()-Bis(µ-chloro)bis{1-[1-(diphenylphosphino)ethyl]-3,6-di-
methylphenyl-C2,P}dipalladium(II), (()-9. A mixture of the
racemic phosphine (()-8 (7.04 g, 22.1 mmol) and palladium(II)
acetate (4.96 g, 22.1 mmol) in toluene (230 mL) was stirred at 50
°C for 10 h, after which a crude brown-black intermediate was
obtained upon removal of toluene under reduced pressure. The
mixture was dissolved in acetone (30 mL), and a methanol solution
(25 mL) of excess LiCl (3.8 g, 89.6 mmol) was added with vigorous
stirring for 4 h after which the black-green mixture was filtered
through Celite and then evaporated to dryness. The mixture was
washed with water (50 mL), extracted with dichloromethane (3 ×
4
3
4
3
m, 2H, JHH ) 6.5 Hz, JPH ) 6.5 Hz, NMe2CHMe; JHH ) 7.3
Hz, Ph2PCHMe), 6.23 (s, 1H, H22), 6.86 (dd, 1H, JHH ) 8.6 Hz,
3
4JPH ) 5.4 Hz, H2), 6.90 (d, 1H, 3JHH ) 7.6 Hz, H19), 7.00 (d, 1H,
3JHH ) 7.6 Hz, H20), 7.10 (d, 1H,3JHH ) 8.6 Hz, H3), 7.30-7.41
(m, 6H, H6, H7, m-PPh2), 7.43-7.50 (m, 2H, p-PPh2), 7.64-7.68
(m, 3H, H5, o-PPh), 7.73 (d, 1H, JHH ) 8.1 Hz, H8), 7.78 (ddd,
3
2H, JHH ) 8.6 Hz, JHH ) 0.9 Hz, JPH ) 11.0 Hz, o-PPh). 31P-
3
4
3
{1H} NMR (CDCl3): δ 45.2 (s). 31P{1H} NMR (CD2Cl2): δ 45.3
(s).
9884 Inorganic Chemistry, Vol. 44, No. 26, 2005

Chiral Phosphapalladacycle Complexes
Table 5. Crystallographic Data for Complexes of meso-9, (R,S)-12,
(S,S)-13, and (S)-16
50 mL), dried with MgSO4, and then filtered. The resulting orange
solution was then concentrated and purified by silica gel column
chromatography using chloroform-n-hexane as eluants, from which
the bright greenish yellow band was eluted and concentrated. The
complex (()-9 was crystallized from dichloromethane-hexane as
bright yellow prisms, 7.84 g (77.3% yield). Mp: 216-220 °C (dec).
Anal. Calcd for C44H44Cl2P2Pd2: C, 57.5; H, 4.8. Found: C, 57.4;
param
formula
meso-9
(R,S)-12
(S,S)-13
(S)-16
C
44H44Cl2P2Pd2
C
36H39ClNPPd C44H46Cl4P2Pd2
C
27H29O2PPd
Mr
918.43
P21/c
658.50
P21
991.35
P1
522.87
P21212
space group
cryst system
a/Å
monoclinic
12.649(11)
12.067(10)
13.869(13)
2023(3)
2
Monoclinic
11.789(1)
13.128(1)
21.367(1)
3305(1)
4
triclinic
8.790(1)
8.943(1)
15.387(1)
1048(1)
1
orthorhombic
9.5880(7)
26.560(2)
9.5467(7)
2431(1)
4
1
H, 5.2. H NMR (CDCl3, 2 sets of signals in ca. 1:1.5 ratio): δ
b/Å
3
3
c/Å
1.71 (dd, 3H, JHH ) 7.0 Hz, JPH ) 19.1 Hz, PCHMe of minor
isomer), 1.86 (dd, 3H, 3JHH ) 7.0 Hz, 3JPH ) 19.5 Hz, PCHMe of
major isomer), 2.24 (s, 3H, aromatic Me of minor isomer), 2.31 (s,
3H, aromatic Me of major isomer), 2.63 (s, 3H, aromatic Me of
minor isomer), 2.69 (s, 3H, aromatic Me of major isomer), 3.85
(m, 1H, PCHMe of both isomers), 6.60-6.69 (m, aromatic signals
of both isomers), 7.22-7.50 (m, aromatics of both isomers), 7.81-
7.92 (m, aromatic signals of both isomers). 31P{1H} NMR (CDCl3,
300 K): 2 signals in ca. 1:1.5 ratio, δ 58.3 (s), 59.5 (s). 31P{1H}
NMR (CDCl3, 223 K): 4 signals, δ 58.8 (s), 59.7 (s), 59.9 (s),
60.9 (s).
V/Å3
Z
T/K
223(2)
0.710 73
1.130
223(2)
0.710 73
0.715
0.0424
0.0773
-0.02(1)
223(2)
0.710 73
1.219
0.0374
0.0795
0.00(2)
295(2)
0.710 73
0.850
0.0449
0.0838
λ/Å
µ/mm-1
R1 (obsd data)a 0.0352
wR2 (obsd data)b 0.0794
Flack param
0.03(3)
2
2
2
a R1 ) Σ|Fo| - |Fc|/Σ|Fo|. b wR2 ) x{Σ[w(Fo - Fc )2]/Σ[w(Fo )2]},
w-1 ) σ2(Fo)2 + (aP)2 + bP.
(S,S)-9 was prepared as described above from (S,S)-13, 0.443 g
(56.6% yield). Mp: 148-150 °C (dec). [R]D: +319° (c 0.9, CH2-
Cl2). Anal. Calcd for C44H44Cl2P2Pd2: C, 57.5; H, 4.8. Found: C,
1
57.4; H, 4.8. H and 31P{1H} NMR (CDCl3) were identical with
those recorded for (R,R)-9.
(Acetylacetonato-O,O′){(S)-1-[1-(diphenylphosphino)ethyl]-
3,6-dimethylphenyl-C2,P}palladium(II), (S)-16. Sodium acetyl-
acetonate monohydrate (0.03 g, 0.2 mmol) was added to (S,S)-9
(0.110 g, 0.120 mmol) dissolved in acetone (5 mL) with rapid
stirring for 4 h at room temperature. The resulting suspension was
then filtered through a short plug of Celite, and the filtrate was
concentrated. Upon slow evaporation, the product was obtained
as pale yellow blocks, 0.087 g (69.2% yield). Mp: 149-150 °C.
(R,R)-Bis(µ-Chloro)bis{1-[1-(diphenylphosphino)ethyl]-3,6-
dimethylphenyl-C2,P}dipalladium(II), (R,R)-9. The complex
(R,R)-13 (0.64 g, 0.64 mmol) was dissolved in dichloromethane
(17 mL) to form a red solution. An aqueous solution (10 mL) of
excess AgPF6 (0.65 g, 2.58 mmol) was added to the red solution,
and the two-phase mixture was allowed to stir vigorously in the
dark for 16 h at room temperature. The reaction mixture was then
filtered through a plug of Celite to remove the precipitated AgCl
and Pd black. From the filtrate, the aqueous layer was separated
from the red dichloromethane layer, and the latter was washed
vigorously with water (3 × 50 mL). The combined organic extracts
were separated, evaporated to dryness in vacuo, and redissolved in
acetone (5 mL). A methanol solution (12 mL) of excess LiCl (1.0
g, 23.6 mmol) was next added to it with vigorous stirring at room
temperature for 24 h. The resulting bright yellow solution was
subsequently evaporated to dryness and was chromatographed on
a silica gel column using chloroform-n-hexane as eluants. A
greenish yellow band was eluted and evaporated to dryness in vacuo
to afford the product as a yellow amorphous powder. Attempts to
crystallize the product from a variety of solvents have been
unsuccessful, 0.46 g (76.9% yield). Mp: 146-149 °C (dec). [R]D:
-322° (c 0.5, CH2Cl2). Anal. Calcd for C44H44Cl2P2Pd2: C, 57.5;
[R]D ) +502°, [R]578 ) +531°, [R]546 ) +620°, and [R]436
)
+1333° (c 0.5, CH2Cl2). Anal. Calcd for C27H29O2PPd: C, 62.0;
H, 5.6. Found: C, 61.9; H, 5.6. 1H NMR (CDCl3): δ 1.66
3
3
(dd, 3H, JHH ) 7.0 Hz, JPH ) 19.2 Hz, Ph2CHMe), 1.97 (s, 3H,
acac-Me), 2.00 (s, 3H, acac-Me), 2.28 (s, 3H, C5-Me), 2.59 (s, 3H,
C2-Me), 3.87 (dq, 1H, 3JHH ) 7.0 Hz, 2JPH ) 13.2 Hz, Ph2CHMe),
5.39 (s, 1H, acac-CH), 6.96 (dd, 1H, 3JHH ) 7.6 Hz, JPH ) 1.2 Hz,
3
C4-H), 6.73 (d, 1H, JHH ) 7.6 Hz, C3-H), 7.20-7.23 (m, 2H,
m-PPhax), 7.26-7.30 (m, 1H, p-PPhax), 7.35-7.39 (m, 2H,
o-PPhax), 7.42-7.46 (m, 2H, m-PPheq), 7.48-7.52 (m, 1H,
p-PPheq), 7.93-7.97 (m, 2H, o-PPheq). 31P{1H} NMR (CDCl3): δ
53.7 (s).
1
H, 4.8. Found: C, 57.9; H, 5.0. H NMR (CDCl3): δ 1.72 (dd,
3H, 3JHH ) 6.9 Hz, 3JPH ) 19.3 Hz, PCHMe), 2.32 (s, 3H, C5-Me),
2.70 (s, 3H, C2-Me), 3.86 (dq, 1H, 3JHH ) 7.0 Hz, 3JPH ) 13.5 Hz,
PCHMe), 6.65 (d, 1H, 3JHH ) 7.4 Hz, H3), 6.69 (d, 1H, 3JHH ) 7.4
Crystal Structure Determination of meso-9, (R,S)-12, (S,S)-
13, and (S)-16. Crystal data for all four complexes and a summary
of the crystallographic analyses are given in Table 5. Diffraction
data were collected on a Siemens SMART CCD diffractometer with
Mo KR radiation (graphite monochromator) using ω-scans. SAD-
ABS absorption corrections were applied, and refinements by full-
matrix least squares were based on SHELXL 93.14 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were intro-
3
Hz, H4), 7.24-7.39 (m, 6H, m-PPh2, p-PPh2), 7.48 (ddd, 2H, JHH
) 7.9 Hz, 4JHH ) 1.4 Hz, 3JPH ) 11.4 Hz, o-PPhax), 7.90 (dd, 2H,
3JHH ) 7.8 Hz, 3JPH ) 10.6 Hz, o-PPheq). 31P{1H} NMR (CDCl3):
δ 59.9 (br s).
(S,S)-Bis(µ-chloro)bis{1-[1-(diphenylphosphino)ethyl]-3,6-
dimethylphenyl-C 2,P}dipalladium(II), (S,S)-9. The complex
Inorganic Chemistry, Vol. 44, No. 26, 2005 9885

Ng et al.
duced at fixed distance from carbon and nitrogen atoms and were
assigned fixed thermal parameters.
Supporting Information Available: For meso-9, (R,S)-12,
(S,S)-13, and (S)-16, tables of crystal data, data collection, solution
and refinement, final positional parameters, bond distances and
angles, thermal parameters of non-hydrogen atoms, and calculated
hydrogen parameters. This material is available free of charge via
the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the National
University of Singapore for support of this research and the
research scholarships to J.K.-P.N.
(14) Sheldrick, G. M. SHELXL 93, Program for Crystal Structure;
University of Gottingen: Gottingen, Germany, 1993.
IC0509579
9886 Inorganic Chemistry, Vol. 44, No. 26, 2005