Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles

Article abstract of DOI:10.1007/s00706-008-0932-2

Palladacycles of pyrido[1,2-a]quinoline complexes were synthesized via a one pot reaction of quinolines with XyNC (Xy = 2,6-Me ₂C ₆H₃) in the presence of Pd(dba)₂ (4:1). These palladacycles were also obtained via reaction of quinolines with Pd(dba) ₂ in the presence of PPh ₃ (1:2) in acetone to give the intermediate complexes of dinuclear palladaphosphaquinoline complexes. Dinuclear complexes were converted into palladacycles via reaction with XyNC in CH ₂Cl₂. The crystal structure of the dinuclear palladium complex was determined by X-ray diffraction studies.

Full text of DOI:10.1007/s00706-008-0932-2

Monatsh Chem 139, 1285–1297 (2008)
DOI 10.1007/s00706-008-0932-2
Printed in The Netherlands
Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles
Abdel-Sattar S. Hamad Elgazwy
Department of Chemistry, Faculty of Science, University of Ain Shams, Cairo, Egypt
Received 28 January 2008; Accepted 20 March 2008; Published online 16 June 2008
# Springer-Verlag 2008
Abstract Palladacycles of pyrido[1,2-a]quinoline
complexes were synthesized via a one pot reaction
of quinolines with XyNC (Xy ¼ 2,6-Me2C6H3) in the
presence of Pd(dba)2 (4:1). These palladacycles were
also obtained via reaction of quinolines with Pd(dba)2
in the presence of PPh3 (1:2) in acetone to give the
intermediate complexes of dinuclear palladaphospha-
quinoline complexes. Dinuclear complexes were con-
verted into palladacycles via reaction with XyNC
in CH2Cl2. The crystal structure of the dinuclear
palladium complex was determined by X-ray diffrac-
tion studies.
One of the most abundant classes of CPCs contains
a CN-type metallacycle. Several such CN-com-
plexes are derived from imines and other C¼N
bond-containing compounds, including quinolines.
On the basis of the position of the C¼N bond rela-
tive to the palladacycle, CPCs form either endo- or
exo-metallacycles (Fig. 1).
The vast majority of known imine-derived CPCs
contain endo-palladacycles with the C¼N bond be-
ing endo-cyclic. This preference of C¼N bond-con-
taining ligands for the formation of endo-palladacycles
is so strong that it has been referred to as the ‘‘endo
effect’’ [20, 21]. Exo-cyclopalladation of imines
can be achieved only when endo-metalation is im-
possible [21–25] or strongly disfavored [25–28]
for electronic or steric reasons. Thus far, there has
been no example of quinoline-derived endo-CPCs.
Palladacycles are widely applied also in organic syn-
thesis, organometallic catalysis, and new molecular
materials [29–39]. Among them, the best investigat-
ed palladacycles are five- or six-membered rings
fused with an aromatic ring, and the metalated car-
bon is usually an aromatic sp2 carbon [40–44]. For
this reason, there is a lot of interest in developing
new strategies for the straightforward synthesis of
substituted palladacycles. However, the above meth-
ods often suffer from one or more synthesis limita-
tions for large-scale preparation of cyclopalladated
complexes and six-membered palladacycles with
a metalated imine (C¼N–) sp2 carbon are rather
rare. During our ongoing investigations [45] into
the cyclopalladation reactions of quinolines and
Keywords Insertions; Metallacycles; Quinolines; Pallada-
cycles; Isonitrile.
Introduction
Palladacycles are one of the most important and
investigated classes of organometallic compounds
[1]. The importance of cyclopalladated compounds
(CPCs) is documented by the numerous articles pub-
lished each year on the subject [2–17]. After the dis-
covery of cyclopalladation by Cope and Siekman in
1965 [18], it has been believed that this reaction
could afford only five-membered metallacycles.
Meanwhile, palladacycles of different sizes have
been reported, including six-membered cycles [19].
Correspondence: Abdel-Sattar S. Hamad Elgazwy, Depart-
ment of Chemistry, Faculty of Science, University of Ain
Shams, Abbassia 11566, Cairo, Egypt. E-mail:elgazwy@
usa.com or aselgazwy@yahoo.com

1286
A.-S. S. Hamad Elgazwy
Pd2 dimers [Pd2(Ar–Cl)2(PPh3)2]. These dimers rep-
resent interesting precursors for the formation of
high nuclearity clusters. On the other hand, their
unsaturated electronic state, suggests that they may
readily react with organic fragments to form or-
ganometallic compounds. In this paper we report a
detailed study of their reactions with 2,6-dimethyl-
phenyl isonitrile (CNXy) (Xy ¼ 2,6-Me2C6H3).
Fig. 1 General structures of endo- and exo-palladcycles
Results and discussion
Knoevenagel condensation [58–67] of 2-chloro-3-
carbaldehyde-6-R-quinolines [R ¼ H (1a), R ¼OMe
(1b)] with acetophenone (2a) or 3,4,5-trimethoxy-
acetophenone (2b) in ethanol furnishes the enones
3a–3d in good yields (71–88%). Under an intert
atmosphere of nitrogen quinoline derivatives 3a–
3d react with [Pd(dba)2]( ¼ [Pd2(dba)3] ꢀ dba) [68]
in the presence of stoichiometric amounts of a neu-
tral ligand such as PPh3 furnishing the dinuclear
palladium complexes 4a–4d in good yields (62–
68%) via oxidative addition reaction. The reaction
mixture was analyzed by 31P-{1H} NMR spectros-
copy which showed the formation of different pro-
ducts. By careful recrystallization these products
were separated and characterized as dinuclear palla-
dium complexes 4a–4d (Scheme 1).
The reaction of chalcones 3a–3d with Pd(dba)2
and PPh3 in molar ratio (1:2:1) under N2 in degassed
acetone was expected to give the trans-complexes A
(Scheme 2). However, no trans mononuclear palla-
dium complexes (A or B) could be isolated, but
instead the only yellow solid isolated in pure form
contains the unexpected dinuclear palladium com-
plexes 4a–4d (Scheme 2). This is probably due to
the result of the interchange between the nitrogen
donor of the quinoline ring and the PPh3 ligand of
palladium, which is a very well-known process [69–
70]. It is believed that complexes A and B are inter-
mediates in the formation of complexes 4a–4d. This
suggests that the presence of PPh3 as a ligand could
be responsible for the interchange of the ligands, as
outlined in Scheme 2.
applications of their corresponding CPCs, chalcones
3a–3d were synthesized. In this paper, we report the
successful cyclopalladation of compounds 4a–4d
resulting in the formation of unique CPCs 5a–5d
containing an endo-palladacycle exhibiting a direct
Pd(II) sp2 carbon contact. Some of these reactions
involve ortho-functionalized aryl complexes that
after insertion of isocyanides give heterocycles in-
corporating the ortho group. A few examples of in-
sertion of isocyanides into other ortho-functionalized
arylpalladium (II) complexes leading to heterocyclic
compounds have been reported [46–48]. Thus, we
have prepared a chalcone by reacting 2-chloro-3-
quinolinecarboxaldehydes [R ¼ H (1a), R ¼OMe (1b)]
with acetophenone 2a or 3,4,5-trimethoxyacetophe-
none 2b. The interest of this subject has prompted
us to prepare arylpalladium complexes containing
ortho-functionalized aryl groups such as –CH¼
CHCO–C6H5– or CH¼CHCO–[C6H2–(OMe)3] as
well as cyclopalladated complexes. The trimethox-
ylaryl moiety is present in organic molecules of
pharmaceutical interest, for example the antileuke-
mic lactones steganacin and steganangin [49–52],
the antibacterial agent trimethoprim [53], or the cy-
totoxic colchicines [54]. The crystal structure of the
palladium complex 4d containing ꢀ,ꢁ-unsaturated
ketones has been determined and the structure shows
interesting features.
Recently, considerable interest has been shown
in palladium (II) dimers as possible intermediates
in catalytic systems for organic transformations.
Several compounds of this type containing a Pd–
Pd bond have been previously synthesized and their
reactivities studied [55–57]. Interestingly, the simple
CN bridged dimers 4a–4d have not been described
until recently. The reaction between [Pd2(dba)3]
(dba ¼ dibenzylideneacetone), PPh3, and the halo-
carbons Ar–Cl leads to the formation of the Pd1–
The complexes 4a–4d were confirmed by the ap-
pearance of one singlet signal at ꢂ ¼ 23.60, 23.63,
23.53, and 23.64 ppm in their 31P NMR spectrum
corresponding to an AB system. We believe that
this is due to the existence of complexes 4a–4d
in solution as a mixture of complexes derived
from two trans forms. The structure of compounds

Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles
1287
Scheme 1
Scheme 2
4a–4d was unambiguously assigned by comparison
with published NMR data and further proven by
us to place emphasis on these data. While this ob-
servation can be rationalized for 4a–4d, we were
surprised that the cyclopalladated 4a–4d showed
almost no change, in view of the angular distortion
involved in forming the six-membered ring. This
yellow product was characterized on the basis
of 31P-{1H} NMR, IR, and elemental analyses. A
single-crystal X-ray analysis of 4d is depicted in
Fig. 2.
1
X-ray crystallography (Fig. 2). The H NMR spec-
tra did not show the presence of impurities for all of
the complexes 4a–4d, even the quinoline fragments
show only slight variations when complexes 4a–4d
are compared. However, we feel that not enough
is known about the reactivity of Pd–C bonds of
quinoline palladium, through four bonds to permit

1288
A.-S. S. Hamad Elgazwy
Spectroscopic properties of arylpalladium complexes
4a–4d
The IR bands assignable to the ꢃ(C¼O), ꢃ(C¼N),
ꢃ(C¼C) mode in 4a–4d indicate the non-coordina-
tion of the carbonyl group of the ligand side chain
with these arylpalladium complexes. These bands ap-
pear in complex 4a at ꢃꢀ¼ 1677, 1665, 1575cmꢁ1, in
complex 4b slightly shorter at ꢃꢀ¼ 1664, 1622.0,
1610, 1580cmꢁ1, in complex 4c at ꢃꢀ¼ 1665, 1620,
1580cmꢁ1, and in 4d slightly shorter again at ꢃꢀ¼
1664, 1622, 1610, 1580 cmꢁ1 due to the extended con-
jugation of the side chain.
Scheme 3
We also investigated the reaction of chalcones 3a–
3d with isonitrile XyNC. Oxidative addition reaction
of halo quinolines 3a–3d with a mixture of Pd(dba)2
and XyNC in acetone takes place at room tempera-
ture and yielded the novel iminoacyl palladium com-
plexes of pyrido[1,2-a]quinoline 5a–5d (Scheme 1)
in moderate yields (46–51%). We believe that the
triinserted (C¼NXy) complex F (Scheme 3) could
be an intermediate and a nucleophilic attack of the
nitrogen of the primarily inserted isocyanide at the
metal center could give the five membered ring of G
as an intermediate too. This unstable complex could
then be attacked by the nitrogen of the quinoline ring
to give the pyrido[1,2-a]quinolines 5a–5d as the sta-
ble unexpected product (Schemes 1 and 2). A mech-
anistic proposal depicting the formation of desirable
product, including possible intermediates, is given in
Scheme 3.
The reactivity of the dinuclear palladium com-
plexes 4a–4d was examined towards bulky isocya-
nide XyNC depending on the nature of substitution,
ligands, and reaction conditions. The products ob-
tained are the result of mono-, di-, or tri-insertion
processes. The mono-inserted and di-inserted com-
plexes with XyNC in 1:1 or 1:2 molar ratios could
not be isolated and show an intractable mixture.
The IR bands assignable to the ꢃ(C¼O), ꢃ(C¼N),
and ꢃ(CꢂN) of pyrido[1,2-a]quinoline palladacycles
5a–5d appear with no significant differences to
the above complexes indicating that there is no cy-
clization of the carbonyl group in those complexes.
This suggests a little change in the carbonyl stretch-
ing frequency of 5a–5d due to complexation (see
Experimental section). The structure of compounds
5a–5d was unambiguously assigned by comparison
1
to published NMR data. The H NMR spectra of
complex 5a show three singlet signals at different
chemical shifts each corresponding to two methyl
groups appearing at ꢂ ¼ 2.30 (s, 6H, 2Me), 2.10 (s,
6H, 2Me), 1.55 (s, 6H, 2Me) ppm. There is one sin-
glet signal integrating for two methyl groups of co-
ordinated isocyanide (CNXy) appearing at ꢂ ¼ 2.20
(s, 6H, 2Me) ppm. The 1H NMR spectra of complex
5b show four singlet signals at different chemical
shifts each corresponding to two methyl groups ap-
pearing at ꢂ ¼ 2.31 (s, 6H, 2Me), 2.19 (s, 6H, 2Me),
2.09 (s, 6H, 2Me), 1.53 (s, 6H, 2Me) ppm. Two sin-
glet signals for the four methyl groups appear at
ꢂ ¼ 2.19 and 2.09 ppm, one of which for the inserted
XyNC, indicating the cis geometry and no free rota-
tion of the Xy groups. One of the two singlet signals
integrates for two methyl groups of the coordinated
isocyanide. This suggests a steric hindrance of the
rotation of three of the xylyl groups, while the fourth
one rotates freely. The rigidity of the palladacy-
cles was checked by variable temperature (ꢁ60 to
þ60ꢃC) 1H NMR experiments using the mononucle-
ar complexes in CDCl3. Minor changes in the mul-
tiplicities and resonance frequencies of the aromatic
protons in the spectra of 5a–5d over the studied
temperature range suggest that both endo pallada-
cycles in these complexes have a rigid conformation
in solution. The singlet signals integrating for two
Triple insertion of 2,6-dimethylphenylisocyanide
(XyNC) into 4a–4d complexes
The insertion reaction of excess XyNC into dinuclear
palladium complexes 4a–4d in a 8:1 molar ratio
for 16 h afforded tri-inserted palladacycles 5a–5d
in good yields (51–55%). These complexes resulted
from the insertion of XyNC into the sp2 carbon-pal-
ladium bond and the displacement of PPh3 by two
XyNC ligands. There is only one example of such a
complex type in literature, which has recently been
reported by Vicente et al. [71]. It is possible that free
PPh3 coordinates in that intermediate complexes,
forcing the insertion of the two isocyanide ligands.

Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles
1289
methyl groups of the coordinated 2,6-dimethylphe-
nyl isocyanides (CNXy) appearing at ꢂ ¼ 2.20 (5a),
2.19 (5b), 2.19 (5c), 2.18 (5d) ppm, due to the free
rotation of the 2,6-dimethylphenyl isocyanide, are
consistent with the results described more recently
by Vicente [71].
perature. The general view of this complex and at-
om-numbering scheme are presented in Fig. 2. The
complex adopts a transoid conformation and exists
as a palladium bridged dimer in endo-palladacycles.
The Pd(1)–Pd(2) bond length covers a range from
˚
2.562(5)–3.077(1) A. The longest Pd–Pd distance
between Pd(1) and Pd(2) is attributed to the report
of X-ray data for six-membered palladacycles, they
usually adopt a boat conformation in the solid state
[57]. This bond is bridged by two CN ligands and is
longer than the equivalent distance. From the molec-
ular structure, it is possible to see that a phosphine in
the structure stops the aggregation process at the
dinuclear stage. Unfortunately, it was impossible to
determine the endo palladacycles conformation in
complexes 4a–4d using NMR spectroscopy.
X-Ray crystal structure of the dinuclear complex 4d
To further confirm the structure of the product, a
yellow crystal of 4d suitable for X-ray analysis was
obtained from its solution in CH2Cl2 at room tem-
Taking into account that this structure is the first
example of a structurally characterized quinoline
derived CPC with a (sp2)C–Pd bond, it will be com-
pared with other known complexes of exo-imine N-
donor groups [72]. The coordination environment of
the palladium atom in complex 4d may be described
as square planar with very slight tetrahedral distor-
tion. The angle between the planes N–Pd–C and
P–Pd–N is equal to 2.9ꢃ. It is of note that an almost
ideal square planar geometry is a common feature in
pure heterocyclic six-membered –C¼N cyclopalla-
dated complexes, where the tetrahedral distortion
angles in complexes fall in the range 1.9–3.1ꢃ [73–
76]. Consequently, heterocyclic ortho-palladated deri-
vatives with pronounced flexibility allow for retention
of a square-planar configuration environment, which
is optimal for a d8-metal center such as Pd(II).
Fig. 2 Thermal ellipsoid plot (50% probability level and
˚
solvent omitted CH2Cl2) of 4d. Selected bond lengths (A)
and angles (deg): Pd(1)–C(1A)¼ 1.9911(17), Pd(1A)–
C(1) ¼ 2.0021(16), Pd(1A)–N(1A) ¼ 2.0855(14), Pd(1)–
P(1) ¼ 2.2905(5), Pd(1)–Cl(1) ¼ 2.3515(6), Pd(1)–Pd(1A)¼
The Pd–C bond distances of the iminoacyl ligands
decrease, in agreement with the decreasing electron
delocalization influence of the electron donating group
(OMe) located in the side chain position. Also, the Pd–
C bond distances of the iminoacyl ligands decrease,
in agreement with the trans influence of the ligand
located in the trans position with chloro ligand.
3.077(1),
Pd(1)–N(1) ¼ 2.4220(14),
Pd(1A)–P(1A)¼
2.481(7), Pd(1A)–Cl(1A) ¼ 2.3512(4), N(1)–C(1) ¼ 1.330(2),
N(1A)–C(1A)¼ 1.329(2), C(1A)–Pd(1)–N(1)¼ 82.25(6),
C(1A)–Pd(1)–P(1) ¼ 92.66(5), N(1)–Pd(1)–P(1) ¼ 174.53(4),
˚
Thus, these values are as follows (in A); Pd(1)–C(1)
C(1A)–Pd(1)–Cl(1) ¼ 173.99(5),
N(1)–Pd(1)–Cl(1) ¼
2.0021(16), Pd(1A)–C(1A) 1.9911(17). The Pd–C
bond length for complex 4d falls in the narrow ranges
reported for related CPCs with (sp2)C–Pd–Cl axes
92.30(4), P(1)–Pd(1)–Cl(1) ¼ 93.14(2), C(1A)–Pd(1)–
Pd(1A) ¼ 66.01(5), N(1)–Pd(1)–Pd(1A)¼ 63.12(4), P(1)–
Pd(1)–Pd(1A) ¼ 114.865(14),
Cl(1)–Pd(1)–Pd(1A) ¼
˚
(1.99–2.05 A), despite the expected difference in the
113.888(19), C(1)–Pd(1A)–N(1A) ¼ 84.88(6), C(1)–
Pd(1A)–P(1A) ¼ 93.35(5), N(1A)–Pd(1A)–P(1A) ¼ 175.15(4),
C(1A)–Pd(1)–Cl(1) ¼ 174.33(5), N(1A)–Pd(1A)–Cl(1A) ¼
90.20(4), P(1A)–Pd(1A)–Cl(1A) ¼ 91.91(2), C(1)–Pd(1A)–
Pd(1) ¼ 66.30(5), N(1A)–Pd(1A)–Pd(1) ¼ 63.27(4), P(1)–
Pd(1)–Pd(1A) ¼ 111.854(17), Cl(1)–Pd(1)–Pd(1A) ¼ 113.999
(18)
trans-influence of the quinoline ring and chloride
ligands. The Pd–Cl distances also allow us to
correlate shorter distances with greater delocaliza-
tion influence of side chain. Thus, the order is as
˚
follows Pd(1)–Cl(1) 2.3515(6)A, Pd(1A)–Cl(1A)

1290
A.-S. S. Hamad Elgazwy
Another structural peculiarity of complex 4d is
the nearly coplanar orientation of the trimethoxy-
phenyl ring and one of the PPh3 phenyl rings (A)
(Fig. 2) characterized by the torsion angle C1–
Pd(1A)–P(1A)–Cipso of ꢁ174.6ꢃ and an interplanar
angle between these two aromatic rings of 16.5ꢃ.
Non-covalent attractive interactions between ꢄ–ꢄ-
systems are invoked to account for stabilization and
orientation in many systems [90, 91]. In recent the-
oretical studies of intermolecular ꢄ–ꢄ-stacking in
simple arene dimers, three geometries are most
commonly discussed: sandwich (D6h), parallel-dis-
placed (C2h, ‘‘slipped sandwich’’), and T-shaped
(C2v, ‘‘point-to-face’’) [90–98]. In structure 4d, the
orientation of the 3,4,5-(MeO)–C6H2–CH¼CH–
CO– and P–PhA rings resembles the parallel-dis-
placed geometry of two arenes. The closest contact
Fig. 3 Structure conformations of half of the dinuclear
complex in X-ray structure of complex 4d (30% probability
ellipsoids)
˚
distance between the two aromatic rings is 3.5 A
(C51ꢀ ꢀ ꢀ C44A) (Fig. 4), which is in accord with exper-
˚
imental values of 3.3–3.5 A found to be the average
˚
2.3512(4) A. Similarly, the Pd–N bond length in com-
˚
plex 4d, Pd(1)–N(1) 2.1220(14) A, Pd(1A)–N(1A)
˚
2.0855(12) A, is longer than known examples of
˚
ortho-palladated derivatives (1.886–2.085 A), but is
between the normal values of 2.060–2.062 and
interplanar spacing in porphyrin aggregates [90]. For
comparison, a study of substituent effects on ꢄ–ꢄ-
interactions performed by Sinnokrot and Sherrill
˚
[91] found a vertical displacement of 3.6–3.8 A for
˚
2.142–2.188 A found for phosphane adducts of
a sandwich benzene-benzotrimethoxy dimer. Due to
the restricted geometry of the arene moieties in 4d,
ortho-palladated heterocycles with an endo C¼N
bond [77, 80]. Some elongation of the Pd–N bond
in the endo-adduct 4d compared to heterocyclic de-
rived endo-analogues may be explained as resulting
from less efficient palladium bonding with the imi-
no-donor group located in the endo-cyclic position,
due to the absence of intracyclic conjugation with
this double bond. This assumption can be supported
by similar values of Pd–N bond length (2.103–
˚
horizontal displacement of the two arenas is 1.39 A
(Figs. 2, 3; defined as the distance between the PhA-
˚
2.112 A) found for PPh3 derivatives of endo-cyclo-
palladated imines [81]. This shows the greater trans
influence of the C-donor iminoacyl ligand with re-
spect to the chloro ligand. Looking at these scales,
our proposal that the transphobia could be directly
related to the trans influence is reinforced [82, 83]
under this assumption; two ligands with great trans
influence will suffer a great transphobia.
The Pd–P bond length in complex 4d, Pd(1)–P(1)
˚
˚
2.2905(5) A, Pd(1A)–P(1A) 2.2481(7) A, is in good
˚
agreement with values (2.243–2.248 A) reported for
neutral exo-imine derivatives [81]. These values
fall within the ranges found previously for the neu-
tral PPh3 adducts of ortho-palladated heterocyclic of
Fig. 4 Structure of complex 4d with showing the interaction
of P–PhA and aromatic ring of trimethoxy aroyl. ꢄ–ꢄ-Stack-
ing interactions between two adjacent molecules in structure
4d. The distance between planes of P–PhA and ligand in
˚
endo-type (2.235–2.256 A) [84,85] and ortho-palla-
˚
dated arylamines (2.243–2.256 A) [86–89].
˚
adjacent aryl is 3.5 A

Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles
1291
Corthoꢁ1(!i1) and Pd–P–Cipso–Cortho-2(!i2), accord-
ing to the known equation !i ¼ (!i1 þ !i2 þ 180ꢃ)=2.
The torsion angle range of 0–90ꢃ is indicative of
the (P) propeller configuration, while the range 90–
180ꢃ corresponds to the (M) configuration. For
complex 4d, the angles !A–!B are equal to 90.3ꢃ,
141.0ꢃ, and 177.4ꢃ for PPh3 rings A(Cipso ¼ C41 or
C
C
41A), B(Cipso ¼ C21 or C21A), and C(Cipso ¼ C31 or
31A) (Fig. 5). These data allow us to describe the
Fig. 5 Possible chiral rotameric states (P) (a) and (M) (b) for
the Pd–PPh3 moiety derived from achiral C3-symmetric struc-
tures via the Ph-ring rotation around the P–Cipso bonds (c)
PPh3 conformation as an (M) propeller, distorted due
to interaction of ring A with the quinoline derivative
ligand.
centroid to C44A), which is slightly shorter than the
calculated horizontal displacements for benzene
˚
dimers (1.54–2.10 A) [91, 94–98]. Since the geo-
metric parameters of complex 4d are in good agree-
ment with both theoretical and experimental values
for systems with known ꢄ–ꢄ-interactions, one can
reasonably interpret the nearly coplanar orientation
of the two arene rings in complex 4d (Fig. 4) as due
to intramolecular ꢄ–ꢄ-interactions.
For comparison, the PPh3 ligands also adopt a
helical conformation in related phosphane adducts
and correspond to the (M) propeller configuration
of the phosphane ligand. In all reported X-ray data
for PPh3 derivatives of palladacycles [104] only two
P–Ph rings exist in the twisted state, while the third
P–Ph ring adopts a nearly parallel disposition, pre-
sumably due to secondary interactions that were not
investigated.
The stereochemistry of the coordinated PPh3 li-
gand in complex 4d is of special interest since its
propeller-like rotameric states can provide additional
chirality [99–102]. The Ph3P–M fragment remains
achiral only if all P–Ph rings are positioned either
parallel (‘‘parallel’’ conformation) or orthogonal
(‘‘orthogonal’’ conformation) to the C3 axis of the
PPh3 moiety (Fig. 5) [99–100]. Between the two ex-
tremes lie the rotameric states that result from syn-
chronous twisting of the three P–Ph rings (starting
from the orthogonal conformation) about the P–Cipso
axes [99–100]. Rotation can be either clockwise
or counterclockwise (Fig. 5), which generates the
chiral propeller-like configurations (P) and (M).
Unfortunately, studies of the influence of other chi-
rality elements on PPh3 stereochemistry have been
mainly restricted to cyclopentadienyl compounds
with planar chirality and an asymmetric metal center
[101–103]. Recently, a detailed analysis [104] of
available X-ray structure data for PPh3 derivatives
of C- and N-palladacycles has shown that the spir-
ality (helicity) of the phosphane ligand is dependent
upon both the palladacycle conformation and the
nature of the N-donor atom.
Conclusions
Despite the unfavorable combination of the reduced
propensity of (sp2)C–Cl bonds to be activated by
Pd(II) and the disadvantageous exo-position of the
C¼N bond in the target palladacycles, cyclopallada-
tion of quinoline derivatives was achieved using
palladium(II) dibenzylideneacetone as metallation
agent. This is the first example of direct cyclopalla-
dation of quinoline derivatives through the (sp2)C–
Cl and having an enone side chain group at position
3. Spectral investigations of the initial dimeric com-
plex and its dinuclear palladaphosphane derivatives
and X-ray diffraction study of an unusual pyrido[1,2-
a]quinoline palladaphosphane complex confirmed a
very high degree of cyclopalladated puckering and
its existence in both the crystal and solution states.
This conformation is fixed by the bicyclic structure
formed by cyclopalladated ring and the quinoline
ring. Peculiarities of the new cyclopalladated struc-
tures, such as its very pronounced twisting and high
conformational stability, create the best conditions
for efficient transmetallation transfer from the phos-
phane to other imine (XyNC) ligands in the palladi-
um environment. Further research into (sp2)C–Cl
activation toward formation of optically active CPCs
and their applications is ongoing at this time in our
laboratory.
The rotameric states of the aromatic rings in the
phosphane ligand (relative to the corresponding P–
Cipso bonds) in complex 4d were estimated using
averaged values of the pair of torsion angles that
include the ortho-Ph carbons, i.e., Pd–P–Cipso
–

1292
A.-S. S. Hamad Elgazwy
(2E)-3-(2-Chloroquinolin-3-yl)-1-(3,4,5-trimethoxyphenyl)-
prop-2-en-1-one (3c, C21H18ClNO4)
Experimental
Reactions were carried out without precautions to exclude
light, atmospheric oxygen, and moisture, unless otherwise
stated. Melting points were determined on a Reichert appara-
tus. Elemental analyses were carried out with a Carlo Erba
1106 microanalyzer results agreed favorably with IR calcu-
lated values. IR spectra were recorded on a Perkin-Elmer 16F
PC FT-IR spectrometer with Nujol mulls between polyethyl-
ene sheets or KBr pellets. NMR spectra were recorded on a
Bruker AC 200, Avance 300 or a Varian Unity 300 spectrom-
eter at room temperature unless otherwise stated. Chemical
shifts were referenced to TMS (1H and 13C(1H) and H3PO4
(31P). The NMR probe temperature was calibrated using eth-
ylene glycol 1H NMR standard methods. Chromatographic
separations were carried out by TLC on silica gel (70–230
mesh).
It was purified by column chromatography (n-hexane=Et2O
2=8, Rf ¼ 0.56) to yield 1.6 g 3c (74%). Yellow solid;
mp 148–150ꢃC; IR (Nujol): ꢃꢀ¼ 1664 (C¼O), 1646, 1580
1
(C¼N) cmꢁ1; H NMR (300 MHz, CDCl3): ꢂ ¼ 8.16 (s, 1H,
3
quin-H4), 8.11 (d, 1H, JHH ¼ 15.6Hz, CH¼CHCO) 8.06 (d,
3
3
1H, JHH ¼ 9.2Hz, quin-H8), 7.49 (d, 1H, JHH ¼ 15.8Hz,
4
CH¼CHCO) 7.42 (dd, 2H, JHH ¼ 9.2, 2.6 Hz, quin-H5, H7),
4
7.30 (s, 2H, Ar–H2), 7.14 (dd, 1H, JHH ¼ 9.2, 2.6 Hz, quin-
H6), 3.92 (s, 6H, 2OMe), 3.90 (s, 3H, OMe) ppm.
(2E)-3-(2-Chloro-6-methoxyquinolin-3-yl)-1-(3,4,5-
trimethoxyphenyl)prop-2-en-1-one (3d, C22H20ClNO5)
It was purified by column chromatography (n-hexane=Et2O
2=8, Rf ¼ 0.59) to yield 0.8 g 3d (72%). Yellow solid; mp
196–198ꢃC; IR (Nujol): ꢃꢀ¼ 1664 (C¼O), 1646, 1580 (C¼N)
1
cmꢁ1; H NMR (300 MHz, CDCl3): ꢂ ¼ 8.37 (s, 1H, quin-
3
Synthesis of chalcones 3a–3d: general method
H4), 8.15 (d, 1H, JHH ¼ 15.6 Hz, CH¼CHCO) 7.93 (d,
4
3
To a mixture of 0.59 g acetophenone (5 mmol) and 5 mmol
appropriate aromatic aldehydes in 25 cm3 oxygen-free eth-
anol was added 25 cm3 2 N NaOH solution in oxygen-free
distilled water with constant shaking of the reaction flask.
The reaction mixture was stirred for a specified period on a
magnetic stirrer and poured onto crushed ice. The solid
mass which separated was filtered off, washed with water,
and crystallized from a suitable solvent to give the desired
product. Purification by chromatography was performed
with silica gel.
1H, JHH ¼ 9.2 Hz, quin-H8), 7.49 (d, 1H, JHH ¼ 15.8Hz,
4
CH¼CHCO) 7.42 (dd, 1H, JHH ¼ 9.2, 2.8 Hz, quin-H7),
7.30 (s, 2H, Ar–H), 7.14 (d, 1H, 4JHH ¼ 2.8 Hz, quin-H5), 3.96
(s, 6H, 2OMe), 3.95 (s, 3H, OMe), 3.90 (s, 3H, OMe) ppm.
Synthesis of chalcone palladium complexes 4a–4d:
general method
A mixture of 216 mg [Pd(dba)2] (0.375 mmol), 195 mg PPh3
(0.75 mmol), and 0.375 mmol halochalcones 3a–3d was
stirred under N2 in 25cm3 dry acetone for 3–5 h at room
temperature. Then it was concentrated to ca. 2 cm3 and
25cm3 CH2Cl2 were added. The solution was passed through
a pad of silica gel:MgSO4 (3:1) in a fritted funnel. Then it was
evaporated under reduced pressure and 15cm3 Et2O were
added. The resulting solution was concentrated to ca. 2 cm3,
a mixture of the complex and dba was precipitated with
n-hexane. The suspension was stirred for 10min at RT. The
precipitate was collected by filtration, washed with 5 cm3
Et2O, and air-dried to give a yellow solid of 4a–4d.
(2E)-3-(2-Chloroquinolin-3-yl)-1-phenylprop-2-en-1-one
(3a, C18H12ClNO)
It was purified by column chromatography (n-hexane=Et2O
2=8, Rf ¼ 0.55) to yield 1.3 g 3a (88%). Yellow solid; mp
168–170ꢃC; IR (Nujol): ꢃꢀ¼ 1678 (C¼O), 1664, 1594, 1578
1
(C¼N) cmꢁ1; H NMR (400 MHz, CDCl3): ꢂ ¼ 8.16 (s, 1H,
quinoline-H4), 7.98–7.96 (d, 3H, 4JHH ¼ 9.26 Hz), 7.77–7.75
(d, 1H, 3JHH ¼ 8.2Hz) 7.69–7.64 (m, 1H), 7.58–7.49 (m, 3H),
7.46–7.42 (m, 3H) ppm.
Bis[(1E)-3-oxo-3-phenyl-1-propenyl(quinolin-2-yl)-
(triphenylphosphine)palladium(II) chloride]
(2E)-3-(2-Chloro-6-methoxy-quinolin-3-yl)-1-phenylprop-2-
en-1-one (3b, C19H14ClNO2)
(4a, C72H54N2O2Cl2Pd2P2)
It was purified by chromatography (CH2Cl2=Et2O 1=1,
Rf ¼ 0.44) to give 340mg 4a (68%). Yellow-orange powder;
mp 158–160ꢃC (dec); IR (Nujol): ꢃꢀ¼ 1677 (C¼O), 1665
It was purified by column chromatography (n-hexane=Et2O
2=8, Rf ¼ 0.52) to yield 1.15 g 3b (71%). Yellow solid;
mp 173–175ꢃC; IR (Nujol): ꢃꢀ¼ 1665 (C¼O), 1645, 1585
(C¼N), 1575 (C¼C) cmꢁ1
;
1H NMR (400MHz, CDCl3):
(C¼N) cmꢁ1
;
1H NMR (300 MHz, CDCl3): ꢂ ¼ 8.36
3
3
ꢂ ¼ 9.32 (s, 2H, quin-H4), 8.42 (d, 2H, JHH ¼ 9.3 Hz, quin-
(s, 1H, quinoline-H4), 8.14–8.09 (d, 1H, JHH ¼ 15.3Hz,
3
4
H8), 8.17 (d, 2H, JHH ¼ 15.5 Hz, CH¼CHCO–), 7.75 (15H,
CH¼CHCO) 7.93–7.90 (d, 1H, JHH ¼ 9.3 Hz, quinoline-
3
4
4
PPh3), 7.52 (dd, 2H, JHH ¼ 9.3 Hz, JHH ¼ 2.6 Hz, quin-H7),
7.22 (m, 18H, quin-H6, H5, and PPh3), 6.67 (d, 2H,
3JHH ¼ 15.5 Hz, CH¼CCO–), 6.66–6.43 (m, 10H, Ph–H)
ppm; 31P {1H} NMR (121MHz, CDCl3): ꢂ ¼ 23.60 ppm.
H8), 7.89–7.86 (d, 1H, JHH ¼ 9.3Hz, quinoline-H7), 7.73–
3
7.67 (d, 1H, JHH ¼ 15.3Hz, CH¼CHCO) 7.42–7.32 (m,
4H), 7.13–7.12 (d, 1H, J ¼ 2.7 Hz), 6.74–6.68 (d, 2H,
3JHH ¼ 7.8 Hz), 3.95 (s, 3H, OMe) ppm; 13C NMR (75 MHz,
CDCl3): ꢂ ¼ 190.6 (C¼O), 158.4 (quin-C6), 151.2 (quin-C2),
147.8 (quin-C8a), 143.8 (quin-CH¼CH), 137.6 (Ph–C1), 134.6
(quin-C4), 134.6 (Ph-C4), 131.0 (quin-C3), 129.7 (Ph–C2,6),
128.4 (CH¼CH–COPh), 128.1 (quin-C8), 127.2 (Ph-C3,5),
124.1 (quin-C4a), 118.4 (quin-C7), 105.1 (quin-C5), 55.5
(OMe) ppm.
Bis[(1E)-3-oxo-3-phenyl-1-propenyl(6-methoxyquinolin-
2-yl)(triphenylphosphine)palladium(II) chloride]
(4b, C74H58N2O4Cl2Pd2P2)
It was purified by chromatography (CH2Cl2=Et2O 1=1,
Rf ¼ 0.45) to give 339 mg 4b (65%). Yellow-orange powder;

Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles
1293
mp 162–164ꢃC (dec); IR (Nujol): ꢃꢀ¼ 1664, 1622 (C¼O),
NMR (125MHz, CDCl3): ꢂ ¼ 191.8 (C¼O), 165.9 (quin-
C6), 155.4 (quin-C4), 150.2 (Ph–C3,5), 148.5 (quin-C2),
146.8 (quin-CH¼CH), 145.5 (quin-C8a), 141.0 (Ph–C4),
136.4 (Ph–C1), 132.2 (P–Ph–C1), 130.6 (CH¼CH–COPh),
129.9 (quin-C8), 129.8 (P–Ph–C4), 129.7 (P–Ph–C2,6),
129.0 (quin-C3), 129.0 (quin-C4a), 127.9 (P–Ph–C3,5), 118.3
(quin-C7), 115.3 (quin-C5), 110.8 (Ph–C2,6), 57.5 (Ph–C4–
OMe), 57.2 (Ph–C3,5-OMe), 56.0 (quin-C6-OMe) ppm.
1610, 1580, 1572, 1538 (C¼N, C¼C) cmꢁ1
;
1H NMR
(400 MHz, CDCl3): ꢂ ¼ 9.38 (s, 2H, quin-H4), 8.51 (d, 2H,
3
3JHH ¼ 15.6Hz, CH¼CCO–), 8.15 (d, 2H, JHH ¼ 9.3 Hz,
quin-H8), 7.90–7.76 (m, 15H, PPh3), 7.59 (dd, 2H,
4
3JHH ¼ 9.3 Hz, JHH ¼ 2.6 Hz, quin-H7), 7.45–7.15 (m, 15H,
4
PPh3), 7.13 (d, 2H, JHH ¼ 2.6 Hz, quin-H5), 6.81 (d, 2H,
3JHH ¼ 15.6Hz, C¼CHCO–), 6.70–6.45 (m, 10H, 2Ph–H),
3.77 (s, 3H, OMe) ppm; 31P {1H} NMR (121MHz, CDCl3):
ꢂ ¼ 23.63 ppm; 13C NMR (125 MHz, CDCl3): ꢂ ¼ 193.6
(C¼O), 162.8 (quin-C6), 152.3 (quin-C2), 148.5 (quin-C8a),
142.8 (quin-CH¼CH), 138.2 (Ph–C1), 134.5 (Ph–C4), 134.3
(quin-C4), 132.1 (P–Ph–C1), 131.2 (quin-C3), 130.4 (P–Ph–
C4), 129.8 (quin-C8), 129.7 (Ph–C2,6), 129.4 (P–Ph–C2,6),
129.3 (CH¼CH–COPh), 129.2 (quin-C4a), 129.0 (Ph–C3,5),
128.8 (P–Ph–C3,5), 122.5 (quin-C7), 105.5 (quin-C5), 57.2
(OMe) ppm.
2,3,4-Tris(2,6-dimethylphenylimino)-5-(3-oxo-3-phenylprop-
enyl)-1,2,3,4-tetrahydropyrido[1,2-a]quinoline-1-(2,6-
dimethylphenylisocyano)palladium(II) chloride
(5a, C54H48N5OClPd)
Method A. Chalcone 3a (110mg, 0.375 mmol) was added to
a suspension of 300mg Pd(dba)2 (0.52 mmol) and 274 mg
XyNC (2.09 mmol) in 15 cm3 acetone under nitrogen. The
reaction mixture was stirred for 5 h at room temperature, then
evaporated under reduced pressure, and 25cm3 CH2Cl2 were
added. The resulting solution was passed through a pad of
silica gel:MgSO4 (3:1) in a fritted funnel. The resulting filtrate
was evaporated under reduced pressure and 15 cm3 Et2O were
added. The resulting solution was concentrated to 2 cm3, a
mixture of the complex and dba was precipitated with n-hex-
ane. The suspension was stirred for 10min at RT, filtered off,
washed with 5 cm3 Et2O, and air-dried to give 160 mg red
solid of palladacycle 5a (46%). Mp 182–184ꢃC (dec); IR
(Nujol): ꢃꢀ¼ 2180 (CꢂO), 1675 (C¼O), 1645, 1585, 1505
Bis[(1E)-3-oxo-3-(3,4,5-trimethoxyphenyl)-1-propenyl-
(quinolin-2-yl)(triphenylphosphine)palladium(II) chloride]
(4c, C78H66N2O8Cl2Pd2P2)
It was purified by chromatography (CH2Cl2=Et2O 1=1,
Rf ¼ 0.46) to give 398 mg 4c (67%). Yellow-orange powder;
mp 155–156ꢃC (dec); IR (Nujol): ꢃꢀ¼ 1663 (C¼O), 1620
(C¼N), 1580 (C¼C) cmꢁ1
;
1H NMR (400 MHz, CDCl3):
3
ꢂ ¼ 9.36 (d, 2H, JHH ¼ 9.3 Hz, quin-H8), 8.81–8.73 (d, 2H,
3JHH ¼ 8.7 Hz, quin-H5), 8.50–8.45 (d, 2H, JHH ¼ 15.6 Hz,
3
1
(C¼N) cmꢁ1; H NMR (200 MHz, CDCl3): ꢂ ¼ 9.27–9.24,
CH¼CHCO–), 8.38 (s, 2H, quin-H4), 8.18–8.12 (d, 2H,
3
3JHH ¼ 15.6Hz, CH¼CCO–), 7.94–7.91 (d, 2H, JHH
¼
3
(s, 1H, quin-H4), 8.72 (d, 1H, JHH ¼ 8.6 Hz, quin-H8),
3
8.57–8.50 (d, 1H, JHH ¼ 15.7 Hz, CH¼CCO–), 8.16 (d,
9.3 Hz, quin-H7), 7.85–7.54 (m, 15H, PPh3), 7.57–7.54 (dd,
3
3
3
4
1H, JHH ¼ 8.4 Hz, quin-H5), 7.99–7.94 (dd, 1H, JHH
¼
2H, JHH ¼ 6.4 Hz, JHH ¼ 2.7 Hz, quin-H6), 7.45–7.40 (m,
15H, PPh3), 7.03 (s, 4H, Ar–H), 3.95 (s, 6H, 2OMe) 3.91
(s, 12H, 4OMe) ppm; 31P {1H} NMR (121 MHz, CDCl3):
ꢂ ¼ 23.53 ppm; 13C NMR (125 MHz, CDCl3): ꢂ ¼ 190.6
(C¼O), 152.5 (quin-C2), 150.5 (Ph–C3,5), 149.0 (Ph–C4),
148.8 (quin-C4), 146.8 (quin-CH¼CH), 145.5 (quin-C8a),
135.2 (Ph–C1), 132.6 (P–Ph–C1), 130.8 (quin-C3), 130.3
(P–Ph–C4), 130.1 (CH¼CH–COPh), 129.9 (quin-C8), 129.6
(P–Ph–C2,6), 129.5 (quin-C5), 129.2 (quin-C4a), 128.9 (P–
Ph–C3,5), 128.8 (quin-C7), 127.5 (quin-C6), 110.2 (Ph–
C2,6), 57.0 (Ph–C3,5-OMe), 56.8 (Ph–C4-OMe) ppm.
8.6, 7.4 Hz, quin-H7), 7.80–7.65 (m, 12H), 7.56–7.51
3
(dd, 1H, JHH ¼ 8.4, 7.4 Hz, quin-H6), 6.98–6.91 (d, 1H,
3JHH ¼ 15.7 Hz, C¼CHCO–), 6.77–6.60 (s, 5H, Ph–H),
2.31 (s, 6H, 2Me), 2.20 (s, 6H, 2Me), 2.10 (s, 6H, 2Me),
1.55 (s, 6H, 2Me) ppm.
Method B. To a suspension of 0.158 g arylpalladium 4a
(0.12 mmol) in 15cm3 CH2Cl2 0.125 g XyNC (0.96 mmol)
were added. The suspension was stirred for 16h at room
temperature. The color changed from pale yellow into pale
red and then dark red during monitoring of the reaction. The
suspension was stirred for 5 h more at room temperature, then
evaporated under reduce pressure, and 25cm3 CH2Cl2 were
added. The resulting solution was passed through a pad of
silica gel:MgSO4 (3:1) in a fritted funnel. The resulting filtrate
was evaporated under reduced pressure and 15 cm3 Et2O were
added. The resulting solution was concentrated to 2 cm3,
a mixture of the complex and dba was precipitated with n-
hexane. The suspension was stirred for 10min at RT, filtered
off, washed with 5 cm3 Et2O, and air-dried to give 62mg red
solid of palladacycle 5b (55%).
Bis[(1E)-3-oxo-3-(3,4,5-trimethoxyphenyl)-1-propenyl-
(6-methoxyquinolin-2-yl)(triphenylphosphine)palladium(II)
chloride] (4d, C81H72N2O10Cl4Pd2P2)
It was purified by chromatography (CH2Cl2=Et2O 1=1,
Rf ¼ 0.43) to give 365 mg 4d (62%). Diffraction-quality crys-
tals were grown by slow diffusion of Et2O into a CH2Cl2
solution of 4d. Yellow-orange solid; mp 144–146ꢃC (dec);
IR (Nujol): ꢃꢀ¼ 1664, 1622 (C¼O), 1610, 1580 (C¼N,
1
C¼C) cmꢁ1; H NMR (200 MHz, CDCl3): ꢂ ¼ 9.39 (d, 2H,
3
4JHH ¼ 9.4 Hz, quin-H8), 8.51 (d, 2H, JHH ¼ 15.6 Hz,
2,3,4-Tris(2,6-dimethylphenylimino)-8-methoxy-5-(3-oxo-3-
phenylpropenyl)-1,2,3,4-tetrahydropyrido[1,2-a]quinoline-
1-(2,6-dimethylphenylisocyano)palladium(II) chloride
(5b, C55H50N5O2ClPd)
CH¼CCO–), 8.17–7.73 (m, 15H, PPh3 þ 2H of quin-H4),
4
7.62–7.56 (dd, 2H, JHH ¼ 2.6 Hz, quin-H5), 7.45–7.03 (m,
3
15H, PPh3 þ 2H of quin-H7), 6.84–6.76 (d, 2H, JHH
¼
15.6Hz, C¼CHCO–), 6.70 (s, 4H, Ar–H), 4.01 (s, 6H,
2OMe) 3.93 (s, 12H, 4OMe), 3.77 (s, 3H, OMe) ppm;
31P {1H} NMR (121 MHz, CDCl3): ꢂ ¼ 23.64 ppm; 13C
Method A. Chalcone 3b (252.5 mg, 0.78mmol) was added to
a suspension of 300mg Pd(dba)2 (0.52 mmol) and 274 mg

1294
A.-S. S. Hamad Elgazwy
XyNC (2.09 mmol) in 15 cm3 acetone under nitrogen. The
reaction mixture was stirred for 5 h at room temperature, then
evaporated under reduced pressure and 25cm3 CH2Cl2 were
added. The solution was passed through a pad of silica
gel:MgSO4 (3:1) in a fritted funnel. The resulting filtrate was
evaporated under reduced pressure and 15cm3 Et2O were
added. The resulting solution was concentrated to 2 cm3, a
mixture of the complex and dba was precipitated with n-hex-
ane. The suspension was stirred for 10 min at RT, filtered off,
washed with 5 cm3 Et2O, and air-dried to give 375mg red
solid of palladacycle 5b (51%). Mp 177–179ꢃC; IR (Nujol):
ꢃꢀ¼ 2185 (CꢂN), 1675 (C¼O), 1642, 1582, 1506 (C¼N)
C¼CHCO–), 6.77 (s, 2H, Ar–H), 3.91 (s, 6H, 2OMe), 3.87 (s,
3H, OMe), 2.30 (s, Me, 6H), 2.19 (s, 6H, 2Me), 2.08 (s, 6H,
2Me), 1.53 (s, 6H, 2Me) ppm.
Method B. To a suspension of 180 mg arylpalladium 4c
(0.12 mmol) in 15 cm3 CH2Cl2 125 mg XyNC (0.96 mmol)
were added. The suspension was stirred for 16h at room
temperature. The color changed from pale yellow into pale
red and then dark red during monitoring of the reaction mix-
ture. The suspension was stirred for 5 h more at room temper-
ature, then evaporated under reduced pressured and 25cm3
CH2Cl2 were added. The resulting solution was passed
through a pad of silica gel:MgSO4 (3:1) in a fritted funnel.
The resulting filtrate was evaporated under reduced pressure
and 15cm3 Et2O were added. The resulting solution was con-
centrated to 2 cm3, a mixture of the complex and dba was
precipitated with n-hexane. The suspension was stirred for
10 min at RT, filtered off, washed with 5 cm3 Et2O, and air-
dried to give 62 mg red solid of palladacycle 5c (51%).
1
3
cmꢁ1; H NMR (200MHz, CDCl3): ꢂ ¼ 9.24 (d, 1H, JHH
¼
¼
3
8.6 Hz, quin-H8), 8.72 (s, 1H, quin-H4), 8.51 (d, 2H, JHH
3
15.7Hz, CH¼CCO–), 8.16 (d, 1H, JHH ¼ 8.4Hz, quin-H5),
3
7.94 (dd, 1H, JHH ¼ 8.6, 8.4 Hz, quin-H7), 7.80–7.51 (m,
3
12H), 6.91 (d, 2H, JHH ¼ 15.7Hz, C¼CHCO–), 6.77–6.63
(m, 5H, Ph–H), 3.88 (s, 3H, OMe), 2.31 (s, Me, 6H), 2.19 (s,
6H, 2 Me), 2.09 (s, 6H, 2 Me) , 1.53 (s, 6H, 2 Me) ppm.
Method B. To a suspension of 166 mg arylpalladium 4b
(0.12 mmol) in 15 cm3 CH2Cl2 124 mg XyNC (0.96 mmol)
were added. The suspension was stirred for 16 h at room
temperature. The color changed from pale yellow into pale
red and then dark red during monitoring of the reaction. The
suspension was stirred for 5 h more at room temperature, then
evaporated under reduce pressure and 25 cm3 CH2Cl2 were
added. The resulting solution was passed through a pad of
silica gel:MgSO4 (3:1) in a fritted funnel. The resulting filtrate
was evaporated under reduced pressure and 15 cm3 Et2O were
added. The resulting solution was concentrated to 2 cm3, a
mixture of the complex and dba was precipitated with n-hex-
ane. The suspension was stirred for 10 min at RT, filtered off,
washed with 5 cm3 Et2O, and air-dried to give 59mg red solid
of palladacycle 5b (53%).
2,3,4-Tris(2,6-dimethylphenylimino)-8-methoxy-5-[3-oxo-3-
(3,4,5-trimethoxyphenyl)propenyl]-1,2,3,4-tetrahydropyrido-
[1,2-a]quinoline-1-(2,6-dimethylphenylisocyano)-
palladium(II) chloride (5d, C58H56N5O5ClPd)
Method A. Chalcone 3d (322.5 mg, 0.78mmol) was added to a
suspension of 300 mg Pd(dba)2 (0.52 mmol) and 274mg
XyNC (2.09 mmol) in 15 cm3 acetone under nitrogen. The
reaction mixture was stirred for 5 h at room temperature, then
evaporated under reduced pressure and 25cm3 CH2Cl2 were
added. The solution was passed through a pad of silica gel:
MgSO4 (3:1) in a fritted funnel. The resulting filtrate was
evaporated under reduced pressure and 15cm3 Et2O were
added. The resulting solution was concentrated to 2 cm3, a
mixture of the complex and dba was precipitated with n-hex-
ane. The suspension was stirred for 10min at RT, filtered off,
washed with 5 cm3 Et2O, and air-dried to give red solid of
palladacycle 5d which was purified by chromatography
(acetone:CH2Cl2 1:1, Rf ¼ 3.6). Yield: 385 mg (47%); mp
152–154ꢃC; IR (Nujol): ꢃꢀ¼ 2184, 1672 (CꢂN), 1640, 1582,
2,3,4-Tris(2,6-dimethylphenylimino)-5-[3-oxo-3-(3,4,5-tri-
methoxyphenyl)propenyl]-1,2,3,4-tetrahydropyrido
[1,2-a]quinoline-1-(2,6-dimethylphenylisocyano)
1
palladium(II) chloride (5c, C57H54N5O4ClPd)
1504 (C¼N); H NMR (200MHz, CDCl3): ꢂ ¼ 9.27 (d, 1H,
3JHH ¼ 8.6 Hz, quin-H8), 8.72 (s, 1H, quin-H4), 8.57 (d, 2H,
Method A. Chalcone 3c (144 mg, 0.375 mmol) was added to a
suspension of 300 mg Pd(dba)2 (0.52 mmol) and 274mg
XyNC (2.09 mmol) in 15 cm3 acetone under nitrogen. The
reaction mixture was stirred for 5 h more at room temperature,
then evaporated under reduce pressure and 25 cm3 CH2Cl2
were added. The solution was passed through a pad of silica
gel:MgSO4 (3:1) in a fritted funnel. The resulting filtrate was
evaporated under reduced pressure and 15cm3 Et2O were
added. The resulting solution was concentrated to 2 cm3, a
mixture of the complex and dba was precipitated with n-hex-
ane. The suspension was stirred for 10 min at RT, filtered off,
washed with 5 cm3 Et2O, and air-dried to give 180mg red
solid of palladacycle 5c (47%). Mp 173–175ꢃC (dec); IR
(Nujol): ꢃꢀ¼ 2185 (CꢂN), 1678 (C¼O), 1643, 1586, 1502
3JHH ¼ 15.7Hz, CH¼CCO–), 8.16–8.05 (s, 1H, quin-H5),
3
7.99–7.94 (d, 1H, JHH ¼ 8.6, quin-H7), 7.80–7.51 (m,
3
12H), 6.98–6.91 (d, 2H, JHH ¼ 15.7 Hz, C¼CHCO–), 6.77
(s, 2H, Ph–H), 3.96 (s, 3H, OMe), 3.91 (s, 6H, 2OMe), 3.87
(s, 3H, OMe), 2.30 (s, Me, 6H), 2.18 (s, 6H, 2 Me), 2.08 (s, 6H,
2Me), 1.52 (s, 6H, 2Me).
Method B. To a suspension of 187.8 mg arylpalladium
4d (0.12 mmol) in 15cm3 CH2Cl2 124 mg XyNC (0.96 mmol)
were added. The suspension was stirred for 16h at room
temperature. The color changed from pale yellow into pale
red and then dark red during monitoring of the reaction. The
suspension was stirred for 5 h more at room temperature, then
evaporated under reduce pressure and 25cm3 CH2Cl2 were
added. The resulting solution was passed through a pad of
silica gel:MgSO4 (3:1) in a fritted funnel. The resulting filtrate
was evaporated under reduced pressure and 15 cm3 Et2O were
added. The resulting solution was concentrated to 2 cm3, a
mixture of the complex and dba was precipitated with n-hex-
1
(C¼N) cmꢁ1; H NMR (200 MHz, CDCl3): ꢂ ¼ 9.29 (d, 1H,
3JHH ¼ 8.6 Hz, quin-H8), 8.72 (s, 1H, quin-H4), 8.53 (d, 2H,
3JHH ¼ 15.7Hz, CH¼CCO–), 8.16 (s, 1H, quin-H5), 7.97 (dd,
3
1H, JHH ¼ 8.7, 8.4 Hz, quin-H7), 7.80–7.66 (m, 12H), 7.54
(d, 1H, 3JHH ¼ 8.4 Hz, quin-H6), 6.95 (d, 2H, 3JHH ¼ 15.7 Hz,

Synthesis and characterization of pyrido[1,2-a]quinoline palladacycles
1295
ane. The suspension was stirred for 10 min at RT, filtered off,
washed with 5 cm3 Et2O, and air-dried to give 69mg red solid
of palladacycle 5d (55%).
scan mode for 4d. The structure was solved by the heavy
atom method and refined anisotropically on F2 with the pro-
¨
gram SHELXL-97 (G.M. Sheldrick, University of Gottingen,
Gemany). Hydrogen atoms were included using a riding mod-
el or rigid methyl groups. Disordered groups were refined
using appropriate systems of similarity restraints. Atomic
coordinates, bond lengths, bond angles, and thermal param-
eters have been deposited at the Cambridge Crystallographic
Data Centre (CCDC). These data can be obtained free
of charge via www.ccdc.cam.uk=conts=retrieving.html (or
from the CCDC, 12 Union Road, CambridgeCB2 1EZ, UK;
Fax: þ44 1223 336 033; or deposit@ccdc.cam.ac.uk). Any
request to the CCDC for data should quote the full literature
citation and CCDC reference number 680965.
X-Ray structure determination of dinuclear palladium(II)
complex 4d
Details of data collection and refinement are given in Table 1.
The crystal structure of 4d was determined by single crys-
tal X-ray diffraction. Measurements were recorded for 4d
on a Bruker SMART 1000 CCD, a Siemens P4 diffractometer
using monochromated Mo Kꢀ radiation in w-scan and f-
Table 1 Details of data collection and structure refinement
for the complex {Pd[6-OCH3–C9H4–CH¼CHCO–C6H2–
(3,4,5)–(OCH3)3]Cl (PPh3)}2 ꢀ CH2Cl2 (4d)
Acknowledgements
4d ꢀ CH2Cl2
C81H72Cl4N2O10P2Pd2
1650
166(2)
0.76274
Yellow rectangular prim
Triclinic
P-1
This work has been supported by Ministry of Education and
Science Spain and FEDER (EU). We thank Dr. Delia Bautista,
S.A.C.E. Universidad de Murcia, Apartado 4021, Murcia,
30071 Spain, for measurement of the X-ray crystallography.
Empirical formula
Formula weight
Temperature=K
˚
Wavelength=A
Crystal habit
Crystal system
Space group
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Unit cell dimensions
˚
a=A
˚
11.8585(11)
14.462(2)
18.822(3)
107.226(11)
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