Synthesis and characterization of novel five-membered palladacycles

Article abstract of DOI:10.1016/j.poly.2009.06.077

3-(2-Chloroquinolin-3-yl)-1,5-bis(3,4,5-trimethoxy-phenyl)-pentane-2,4-dione derivatives 3a-b were conveniently synthesized in excellent yields (82% each) by tandem Knoevenagel condensation reactions of 2-chloro-3-carbaldehyde-quinoline 1a-b with 3,4,5-tr

Full text of DOI:10.1016/j.poly.2009.06.077

Polyhedron 28 (2009) 3667–3674
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Polyhedron
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Synthesis and characterization of novel five-membered palladacycles
*
Abdel-Sattar S. Hamad Elgazwy
Department of Chemistry, Faculty of Science, Ain Shams University, Abbassia 11566, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
3-(2-Chloroquinolin-3-yl)-1,5-bis(3,4,5-trimethoxy-phenyl)-pentane-2,4-dione derivatives 3a–b were
conveniently synthesized in excellent yields (82% each) by tandem Knoevenagel condensation reactions
of 2-chloro-3-carbaldehyde-quinoline 1a–b with 3,4,5-trimethoxy acetophenone, followed by a base cat-
alyzed Michael addition, such as DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) with or without solvent. The
reactions of 3a–b with Pd(dba)2 in the presence of PPh3 (1:2) in degassed acetone provided the dinuclear
palladium complexes {Pd(C,N-2-C9H4N–CH–[–CH2CO(3,4,5-(OMe-)3–C6H2-]2–3-R-6)Cl(PPh3)}2 [(R = H
(4a), R = OMe (4b)] in moderate yields (38% and 43%), which in turn reacted with an excess of isonitrile
XyNC (Xy = 2,6-Me2C6H3) to give the corresponding palladacycles 5a–b in moderate yields (45% and 43%).
The palladacycles 5a–b were also obtained in similar yields (32% and 33%) via a one-pot oxidative addi-
tion reaction of 3a-b with isonitrile XyNC:Pd(dba)2 (4:1). The products were characterized by satisfactory
elemental analysis and spectral studies (IR, 1H, and 31P NMR). The crystal structure of 5a was determined
by X-ray crystallography diffraction studies.
Received 21 May 2009
Accepted 18 June 2009
Available online 3 July 2009
Dedicated to Professor Jose Jesus Vicente
Soler on the occasion of his 66th birthday.
Keywords:
Quinolines
Palladacycles
Arylpalladium complexes and isocyanides
Ó 2009 Published by Elsevier Ltd.
1. Introduction
2. Results and discussion
In an earlier paper, we reported on aryl palladium complexes
that are of interest as intermediates in important catalytic organic
syntheses [1–3]. Some of the catalytic reactions involve ortho-func-
tionalized aryl palladium(II) complexes, giving carbo- or heterocy-
cles in which the ortho group is not included. A few examples of
insertion of isocyanides into ortho-functionalized aryl palla-
dium(II) complexes leading to heterocyclic compounds have been
reported [3–14]. Thus we have prepared the dinuclear palla-
dium(II) complexes {Pd[C9H5–CH–[–CH2CO–C6H2–(OCH3)3]2–
(3,4,5)]Cl(PPh3)}2 4a and {Pd[6-CH3O–C9H4–CH–[–CH2CO–C6H2–
(OCH3)3]2–(3,4,5)]Cl(PPh3)}2 4b by reacting the prepared
compounds 3-(2-chloroquinolin-3-yl)-1,5-bis(3,4,5-trimethoxy-
phenyl)pentane-1,5-dione 3a and 3-(6-methoxy-2-chloroquino-
To investigate the role of the catalyst and the effect of grinding,
first the reaction of 2-chloro-3-carbaldehyde-6-R-quinolines [R = H
(1a), R = OMe (1b)], acetophenone and a catalytic amount of DBU
were ground together in a pestle and mortar at room temperature.
The reaction started immediately, usually with gentle heat produc-
tion, with the reaction mixture turning into a brownish viscous li-
quid, then to a thick brownish mass and finally to a free flowing
powder. Surprisingly, the reaction mixture turned into the desired
product within a short period of time. When DBU was used as a cat-
alyst in ethanol, stirring for 3 h at room temperature, the reaction
proceeded smoothly to afford (2Z)-3-(2-chloroquinolin-3-yl)-1-
(phenyl) prop-2-en-1-one in 65% yield [2]. The same result was ob-
tained without solvent after stirring for 3 h. Other solvents such as
chloroform, dichloromethane and methanol gave (2Z)-3-(2-chloro-
quinolin-3-yl)-1-(phenyl) prop-2-en-1-one with the same yield [2].
On the other hand, indication of softening for some seconds fol-
lowed by immediate hardening were visually observed only in the
syntheses with 2-chloro-3-carbaldehyde-6-methoxy-quinolines
(1b) with 3,4,5-trimethoxy acetophenone. Subsequently, the scope
of the Knoevenagel condensation of aldehydes with various active
methylene compounds catalyzed by DBU in grinding was investi-
gated. We found that the Knoevenagel condensation of aldehydes
with 3,4,5-trimethoxy acetophenones occurred easily in the pres-
ence of grinding to form the corresponding products. Both elec-
tron-rich and electron-deficient aldehydes worked well to give
the corresponding arylidene derivatives (2E)-3-(2-chloro-R-quino-
lin-3-yl)-1-(3,4,5-trimethoxyphenyl) prop-2-en-1-one [R = H (2a),
lin-3-yl)-1,5-bis(3,4,5-trimethoxyphenyl)pentane-1,5-dione
3b
with Pd(dba)2, in the presence of PPh3 (1:2). In this contribution
we present the synthesis and characterization of novel mono-
and dimeric palladacycles as well as their utility as precursors for
the synthesis of valuable organic products as the most outstanding
points. The sequence of the reactions led eventually to compounds
that could potentially possess pharmacological properties [3]. The
preparation of all the complexes were in one solvent (degassed
acetone). The crystal structure of complex 5a shows some interest-
ing features.
* Tel.: +20 22617 3044; fax: +20 24831836.
E-mail address: hamad@asunet.shams.eun.eg
0277-5387/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.poly.2009.06.077

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A.-S.S. Hamad Elgazwy / Polyhedron 28 (2009) 3667–3674
R = OMe, (2b)] in excellent yields (72–74%) [2]. Miscibility of DBU
with water makes the workup process quite easy as the catalyst
can be easily removed from product simply by washing the prod-
uct with water.
tion 3), affords the final product alkane–dione 3a–b. This mecha-
nism, as outlined in Scheme 2, is consistent with the mechanism
described as straight forward by Xu and co-workers [22].
Oxidative addition reactions of 3-(6-R-2-chloroquinolin-3-yl)-
1,5-bis(3,4,5-trimethoxyphenyl)pentane-1,5-dione [R = H (3a),
R = OMe (3b)] toward a stoichiometric amount of [Pd(dba)2]
(=[Pd2(dba)3].dba; dba = dibenzylideneacetone) [3,23,24] in the
presence of a neutral ligand such as PPh3 (1:2:1) under nitrogen
in degassed acetone gave the dimeric palladium complexes
Pd[C9H5–CH–[–CH2CO–C6H2–(OCH3)3]2–(3,4,5)]Cl(PPh3)}2 4a and
{Pd[6-CH3O–C9H4–CH–[–CH2CO–C6H2–(OCH3)3]2–(3,4,5)]Cl(PPh3)}2
4b in moderate yields (38% and 43%), through the coordination of
the quinolinyl nitrogen. Subsequently, the insertion reaction of 2,6-
dimethylphenyl isocyanide XyNC (Xy = 2,6-Me2C6H3) into dinucle-
ar complexes in CH2Cl2 at room temperature eventually forms the
mononuclear five-membered palladacycle complexes 5a–b in
moderate yields (32% and 45%). These five-membered palladacy-
cles 5a–b are also obtained in similar yields (33% and 43%) by
the direct oxidative addition of 3-(6-R-2-chloroquinolin-3-yl)-
1,5-bis(3,4,5-trimethoxyphenyl)pentane-1,5-dione [R = H (3a),
R = OMe (3b)] with Pd(dba)2 in the presence of a stoichiometric
amount of isonitrile XyNC in CH2Cl2 at room temperature, as de-
picted in Scheme 3.
The Knoevenagel condensation [15] reactions have been exten-
sively studied as an example of important carbon–carbon bond for-
mation. In this condensation reaction various catalysts are used,
such as (Te(IV)Cl4) [16], (ZnCl2) [17] and (KF-Al2O3) [18]. DBU
(1,8-diazabicyclo[5,4,0]undec-7-ene) has been widely used as a
catalyst in many reactions followed by Michael addition [19–21].
Thus the sequential condensation reactions are achieved in one
pot by the reaction of aldehydes 1a–b with the active methylene
compound 3,4,5-trimethoxy acetophenone in the presence of
DBU as a base catalyst, to afford arylidene derivatives, followed
by Michael addition to give d diketones 3a–b in good yields of
47–75% (Scheme 1).
The possible mechanism that could account for the formation of
d diketones 3a–b in these reactions of excess 3,4,5-trimethoxy ace-
tophenone with aromatic aldehydes 1 is as follows. First 1 is dehy-
drated on heating in the basic reaction medium to furnish the
highly electrophilic intermediate and thus yielding the corre-
sponding air stable
a,b-unsaturated quinoline [B]. The quinoline
intermediate [B] then undergoes competitive Michael addition by
the preformed carbanion [A]. The Michael type addition of the en-
one proceeds in a 1,4-fashion and results in an intermolecular
addition to give [C], which on hydrolysis during the reaction at re-
flux temperature under the action of a trace amount of water in the
reaction mixture, or during workup on a silica gel column (see Sec-
The intermediate species formed in the oxidative addition reac-
tion of 3a–b with Pd(dba)2/PPh3 to give 4a–b follow a very similar
pathway as previously described for related quinoline containing
palladacycles [3,25], and the structure of the dinuclear complex
obtained from the reaction of Pd(PPh3)4 and 2-bromopyridine,
OMe
OMe
OMe
MeO
OMe
MeO
OMe
O
MeO
OMe
O
Michael type
1,4- additions
O
N
O
R
R
CHO
Cl
R
OMe
OMe
DBU
Grinding
N
Cl
N
Cl
1a-b
2a-d
a) R = H
b) R = OMe
OMe
a) R = H
OR
3a-b
b) R = OMe
a) R = H
b) R = OMe
EtOH
NaOH (2N)
Stirred 1/2 h, 0oC
stirred 24 h, RT,
71-88%
Scheme 1.
MeO
MeO
OMe
OMe
MeO
OMe
O
O
[A]
H2C
CHO
Cl
O
OMe
+
O
N
DBU
- H
N
OMe
OMe
OMe
OMe
2
1
OMe
H
H2C
3
N
Cl
H
Cl
OMe
OMe
O
[B]
[A]
OMe
[C]
Scheme 2.

A.-S.S. Hamad Elgazwy / Polyhedron 28 (2009) 3667–3674
3669
Ar
OMe
OMe
OMe
O
R
Ar'
Ar = Ar' =
N
Cl
3a-b
a) R = H
b) R = OMe
Pd(dba)2
PPh3
acetone
XyNC (Isonitrile)
Pd(dba)2
acetone
H3C
Xy =
H3C
Ar
R
Ar'
Cl
Ar
N
XyNC
Cl Pd
XyNC
CNXy
R
N
Pd
Ar'
N
Ph3P
PPh3
XyNC (Excess)
CH2Cl2
PdN
Cl
Pd Cl
CNXy
+
N
N
Cl
Ar'
Xy
Pd
R
6
5a-b
a) R = H
b) R = OMe
Ar
XyNC
4a-b
a) R = H
b) R = OMe
Xy
Scheme 3.
determined by X-ray analysis, was shown to be trans(P,N)-bis-[bro-
mo(
-pyridyl-C2,N)(triphenylphosphine)palladium(II)], having an
approximate symmetry of C2 [26,27].
As far as we are aware, this is the first time these 3-substituted
dinuclear palladium complexes 4a–b and five-membered pallada-
cycles 5a–b have been synthesized. These complexes were con-
firmed by the appearance of one singlet signal in their 31P NMR
spectra. The reaction products were identified by comparison of
the 31P NMR spectra of the reaction mixture with those of related
reported complexes, which showed two AB resonance patterns in
mixture of Pd(dba)2 and 2,6-dimethylphenyl isocyanide XyNC
(Xy = 2,6-Me2C6H3) in a 1:4 molar ratio in degassed acetone at
RT, yielded the di-inserted iminoacyl palladium complexes 5a–b
in low yields (32%, 33%), and not the tri-inserted one due to the ste-
ric hindrance of the branched side chain. Instead of the required
4:1.5:1 molar ratios of reagents XyNC:3a–b:Pd(dba)2 for the for-
mation of 5a and 5b, 1:1.5:1 and 1:1:1 stoichiometric amounts
of these mixtures were used for both 5a and 5b, but unfortunately
it was not possible to isolate the inserted products. A mechanistic
proposal depicts the formation of possible intermediates and prod-
ucts consistent with literature data [3,28].
l
the case of R = H (4a) and R = OMe (4b) at
d 29.72 and
29.73 ppm. The 1H NMR spectra did not show the presence of
impurities for either of complexes 4a or 4b, although the quinoline
backbone shows slight variations when complexes 4a or 4b are
compared. However, we feel that not enough was known about
the palladium–carbon bonding of these complexes, through 4
bonds.
2.1.2. Reaction of [Pd2(quinoline-Cl)2(PPh3)2] 4a–b with XyNC
In order to study the possible aggregation to high nuclearity
clusters, the reactions between the dinuclear 4a–b and XyNC were
studied. The reactivity of the dinuclear palladium complexes 4a–b
towards the bulky isocyanide XyNC (Xy = 2,6-Me2C6H3) depends
on the nature of the ligands and on the reaction conditions. Thus
when the insertion reaction takes place in different molar ratios
of XyNC to complex, the inserted complexes obtained are the result
of a di-insertion processes. The mono-insertion of XyNC at 1:1 or
1:2 molar ratios were not isolated. The reaction of the dinuclear
palladium complexes 4a–b with 8 equiv. of XyNC at room temper-
ature with a longer reaction time (24 h) provided the inserted
products of the palladacycles 5a–b. Instead of the required 8:1
equivalents of XyNC:3a–b, stoichiometric amounts of 1:1, 2:1,
3:1, 4:1, 5:1 6:1 and 7:1 were used, but it was not possible to iso-
late complexes 5a–b in the case of the 1:1, 2:1, 3:1, 4:1 and 5:1
molar ratios. The inserted products are formed by the insertion
of XyNC into the Pd–C bond and the displacement of PPh3 by the
XyNC ligand. These kinds of complexes are very poorly represented
in the literature, the only examples being those recently prepared
by Vicente et al. [28], and suggest that the presence of PPh3 during
the insertion of XyNC into the dinuclear palladium complexes 4a–
b could be responsible for the change in reactivity of the interme-
diate complexes. It is possible that free PPh3 coordinates in the
intermediate complexes, forcing the insertion of the two isocya-
nide ligands. A mechanistic scheme depicting the formation of
the various products, including possible intermediates consistent
with literature data [3,28], is given in Scheme 4.
This promoted us to place an emphasis on these data. While this
observation can be rationalized for 4a–b, we were surprised that
the cyclopalladated product showed almost no change in view of
the angular distortion involved in forming the five-membered pal-
ladacycles. The IR (Nujol, cmÀ1) bands were assignable to
m(C@O),
m
(C@N) m(C@C) modes in 4a–b, and indicated the non-coordination
of the carbonyl group in these complexes. In complex 4a, IR bands
appear at 1672, 1618, 1581 cmÀ1 and for 4b these bands appear in
at slightly higher values at 1673, 1620, 1582 cmÀ1, respectively.
Complexes 4a–b show the strongest band in the IR spectrum at
ca. 1672 and 1673 cmÀ1, assignable to
m(C@O) of two ketonic
groups. These frequencies are similar to that observed in the start-
ing materials 2a–b or 3a–b, indicating that there is no coordination
of the ketonic group to the metal atom.
2.1. Reactions with XyNC (Xy = 2,6-Me2C6H3)
2.1.1. Reaction of the chloro-quinoline derivatives 3a–b with XyNC
Isocyanides behave in many respects like CO and can exhibit
terminal or bridging coordination modes. The oxidative addition
of 3-(6-R-2-chloroquinolin-3-yl)-1,5-bis(3,4,5-trimethoxyphenyl)-
pentane-1,5-dione R = H (3a), R = OMe (3b) (1.5 molar ratio) to a

3670
A.-S.S. Hamad Elgazwy / Polyhedron 28 (2009) 3667–3674
OMe
Ar
CNXy
Pd
O
R
XyN
Ar'
Ar'
Cl
OMe
Cl
Ar = Ar' =
2
N
Pd
Ar
OMe
PPh3
CNXy
8 XyNC
CH2Cl2
PPh3
Ph3P
N
PdN
Cl
H3C
N
Ar'
4a-b
R
Insertion
reaction
Xy =
R
Ar
a) R = H
b) R = OMe
Xy
Xy
H3C
Xy
Xy
N
N
Ar'
Ar'
2
N
N
Ar
Ar
CNXy
CNXy
Pd
Cl
N
Pd
Cl
5a-b
a) R = H
b) R = OMe
N
Ring closure
-PPh3
PPh3
R
R
Scheme 4.
Complex 5a was characterized by 1H NMR spectroscopy and
single-crystal X-ray diffraction studies. The 1H NMR spectra of
complexes 5a and 5b show three singlets, each corresponding to
a methyl group, two signals integrated to the four methyl groups
of the inserted Xy–N@C– indicate a cis geometry and no free rota-
tion of the Xy groups. Another one singlet signals integrates to two
methyl groups of equivalently coordinated isocyanide ligands. This
suggests a steric hindrance to rotation of two of the xylyl groups,
while the other three rotate freely. Thus the 1H NMR spectrum of
this reaction mixture in CDCl3 was recorded and was found to con-
tain three resonances at d 2.18, 2.08 and 1.53 ppm. These peaks are
assigned to the methyl protons adjacent to the phenyl ring on each
of XyNC, an immediate change of color from green to orange was
observed. The reaction was stirred for 2 hr and the 31P–{1H} NMR
spectrum was measured. The 31P–{1H} NMR spectrum showed only
one signal (chemical shift for the free phosphines) suggesting that
all the phosphines had been replaced by the XyNC groups. Hexane
was added to the reaction mixture and a dark yellow crystalline so-
lid precipitated. On the basis of the IR spectrum and elemental
analyses, the product obtained was formulated as [Pd2Cl2(XyNC)4].
This type of compound has been previously reported by Yamamoto
and Arima [31], and Balch and co-workers [32]. The structure of
the Pd(I) dimer 6 is similar to that of the few crystal structures re-
ported of related complexes, [Pd2(CNBut)4Cl2] contains two di-
rectly bonded Pd atoms, each having two coordinated
isocyanides in trans positions and a chloro ligand in the axial posi-
tion [33,34]. A different behavior was observed in the case of the
4a–b, as their reaction with XyNC (1:8 molar ratios) in CH2Cl2 gave
intractable mixtures. Workup of the mother liquors rendered a
mixture for which 1H NMR spectra showed the presence of the
Pd(I) dimer 6. During attempts at chromatographic separation,
the fraction at Rf = 0.4 was collected and extracted with acetone
to give a solution which was evaporated to dryness.
of the three different xylyl groups. The IR spectra (Nujol, cmÀ1
contain bands assignable to (C„N), (C@O) and (C@N) for 5a
and 5b, with no significances difference. In the case of 5a the bands
appear at (C„N) 2184, (C@O) 1702 and
(C@N) 1640 cmÀ1, but
in the case of 5b several bands appear in the (C„N) 2184, (C@O)
1710 and
(C@N) 1610 cmÀ1 region, which are probably attribut-
)
m
m
m
m
m
m
m
m
m
able to a solid state effect. This suggests little or no change in the
carbonyl stretching frequency due to complexation.
In addition, the transformation of 4a–b into 5a–b could be
achieved by reaction with an excess of XyNC. The Pd(I) dimer of
[Pd2Cl2(XyNC)4] 6 was obtained at room temperature after a long
reaction time. In the first case, the mixture decomposed to an ill-
defined mixture, while in the second, the palladium (I) complex
[Pd2Cl2(XyNC)4] 6 is formed.
2.1.4. X-ray crystal structure of {PdCl(2)–(C@N–Xy)2–(CN–Xy)–
C9H5N-(3)-CH)[CH2COC6H2–3,4,5-(OCH3)3]2} (5a)
To further confirm the structure of the product, the molecular
structure of red crystals of 5a. CH2Cl2 (Fig. 1) was determined by
X-ray analysis. The Pd–C bond distances of the iminoacyl ligands
decrease, in agreement with the electron delocalization influence
of the extended of electron donating group (3OMe), in complex
5a in agreement with the trans influence of the ligands, thus these
values are (in Å) Pd(1)–C(12) = 1.936(3), Pd–C(11) = 1.980(3). The
Pd(1)–Cl(1) distance is 2.4317(8) Å. Similarly, the Pd–N bond dis-
tance in complex 5a was compared, Pd(1)–N(1) 2.101(2) Å, show-
ing a greater trans influence of the chloro ligand with respect to the
carbon-donor iminoacyl ligand. Looking at these scales, our pro-
posal that transphobia could be directly related to the trans influ-
ence is reinforced [35] under this assumption; two ligands with a
great trans influence will suffer a great transphobia [36]. The
[Pd]–C@N–Xy bond distance of the iminoacyl ligands in complex
5a is N(2)–C(10) 1.267(4) Å, and N(3)–C(11) 1.257(4) Å for the
C@N distances corresponding to the inserted molecule of XyN@C
2.1.3. Preparation of [Pd2Cl2(XyNC)4] (6)
In addition, the transformation of [Pd2(Q-Cl)2(PPh3)2] 4a–b into
5a–b can be achieved by reaction with XyNC in a 1:4 molar ratio in
CH2Cl2, following the reported procedure [30]. 5a–b Could also be
prepared by oxidative addition of the corresponding 3-(6-R-2-
chloroquinolin-3-yl)-1,5-bis(3,4,5-trimethoxyphenyl)pentane-1,5-
dione [R = H (3a), R = OMe (3b)] to ‘‘Pd(dba)2” in the presence of
XyNC in acetone. In the first case, the mixture decomposed to an
ill-defined mixture, while in the second, the palladium (I) complex
[Pd2Cl2(CNXy)4] (6) formed in a yield of 58%. This complex has re-
cently been prepared by reacting [Pd2(í-Br)2(tBu3P)2] with XyNC
[29]. Our one-pot synthesis of complex 6 from ‘‘Pd(dba)2” and
3a–b is simpler and gives a similar yield. When a solution of
[Pd2(Q-Cl)2(PPh3)2] in CH2Cl2 was treated with eight equivalents

A.-S.S. Hamad Elgazwy / Polyhedron 28 (2009) 3667–3674
3671
Fig. 1. Thermal ellipsoid plot (50% probability level and solvent omitted) of 5a. Hydrogen atoms attached to N(20) have been displayed for clarity. Selected bond lengths (Å)
and angles (deg): Pd–C(12) = 1.936(3), Pd–C(11) = 1.980(3), Pd–N(1) = 2.101(2), Pd–Cl(1) = 2.4317(8), N(1)–C(1) = 1.338(4), N(1)–C(9) = 1.384(3), N(3)–C(11) = 1.257(4),
N(3)–C(31) = 1.430(4), N(2)–C(10) = 1.267(4), N(2)–C(21) = 1.432(3), N(4)–C(12) = 1.158(4), N(4)–C(41) = 1.402(4), C(11)–C(10) = 1.508(4), C(10)–C(1) = 1.499(4), C(12)–Pd–
C(11) = 92.45(11), C(12)–Pd–N(1) = 168.24(10), C(12)–Pd–Cl(1) = 89.77(8), C(11)–Pd–N(1) = 76.86(10), C(11)–Pd–Cl(1) = 176.63(8), N(1)–Pd–Cl(1) = 100.70(6), C(1)–N(1)–
C(9) = 119.8(2), C(1)–N(1)–Pd = 110.71(18), C(9)–N(1)–Pd = 128.70(19), C(11)–N(3)–C(31) = 119.7(2), C(10)–N(2)–C(21) = 123.0(2), C(12)–N(4)–C(41) = 170.1(3), N(1)–C(1)–
C(2) = 123.6(2), N(1)–C(1)–C(10) = 111.3(2), C(2)–C(1)–C(10) = 124.8(2), N(3)–C(11)–C(10) = 123.1(2), N(3)–C(11)–Pd = 133.5(2), C(10)–C(11)–Pd = 102.93(17), N(2)–C(10)–
C(1) = 122.0(3), C(1)–C(10)–C(11) = 109.8(2), N(2)–C(10)–C(11) = 128.1(2), C(10)–C(1)–C(2) = 124.8(2), N(4)–C(12)–Pd = 177.1(3).
and N(4)–C(12) 1.158(42) Å for the C@N distances corresponding
to the inserted molecule of XyNC. All these lengths are as expected
for a C@N bond [the mean value for C(aryl)–C@N–R distances is
1.432–1.382 Å] [34–37]. The (aryl)-C@N(–Xy)[Pd] distances corre-
sponding to the second inserted molecule of XyNC in complex 5a is
significantly lower than the other distances, N(2)–C(10) 1.267(4) Å
and N(1)–C(1) 1.338(4) Å, as a result of coordination of the nitro-
gen atom to Pd(II). This fact, and the angles around Pd, C(12)–
Pd–C(11) 92.45(11), C(12)–Pd–N(1) 168.24(10), C(11)–Pd–N(1)
76.86(10), C(12)–Pd–Cl(1) 89.77(8), C(11)–Pd–Cl(1)176.63(8) and
N(1)–Pd–Cl(1) 100.70(6)°, and the short C(1)–C(10) bond of
1.499(4) Å compared with C(10)–C(11) of 1.508(4) Å, suggest a
to TMS (1H and 13C) and H3PO4 31P). The NMR probe temperature
(
was calibrated using ethylene glycol 1H NMR standard methods.
Chromatographic separations were carried out by TLC on silica
gel (70–230 mesh).
3.1. General method for the synthesis of (2E)-3-(2-chloro-6-R-
quinolin-3-yl)-1-(3,4,5-trimethoxyphenyl) prop-2-en-1-one (R = H,
(2a), R = OMe, (2b))
To a mixture of acetophenone (0.005 mol) and the appropriate
aromatic aldehydes (0.005 mol) in oxygen-free ethanol (25 cm3)
was added a solution of sodium hydroxide (2 N, 25 cm3) in oxy-
gen-free distilled water with constant shaking of the reaction flask.
The reaction mixture was stirred for a specified period with a mag-
netic stirrer and poured onto crushed ice. The solid mass which
separated out was filtered, washed with water and crystallized
from a suitable solvent to give the desired product. Purification
by chromatography was performed with silica gel.
delocalization of
C(10)–C(1) angle of 122.0(3)°, and N(2)–C(10)–C(11) angle of
128.1(2)°. This points to a delocalization of electron density
p electron density as compared to the N(2)–
p
around C(10), the atoms being almost square planar. Crystals suit-
able for X-ray diffraction of compound 5a, light red in color and air
stable, were obtained by slow evaporation from a CH2Cl2/ether
solution; Diffraction-quality crystals were grown by slow diffusion
of Et2O into a CH2Cl2 solution of 5a. The structure is shown in Fig. 2
and reveals chains of molecules connected by hydrogen bonds.
Data were collected on an automatic diffractometer using the
parameters listed in Table 1.
3.1.1. Compound (2a)
This was purified by column chromatography, Silica gel (hex-
ane: Et2O 2:8) at Rf = 0.56 to isolate a yellow solid of 2a, yield,
1.6 g, 74%. M.p.: 148–150 °C. IR (Nujol, cmÀ1):
m
(C@O) 1664,
m
(C@N) 1646, 1580. 1H NMR (300 MHz, CDCl3) (d ppm): 8.16 (s,
3
1H, quin-H4), 8.11 (d, 1H, JHH = 15.6 Hz, CH@CHCO), 8.06 (d, 1H,
3. Experimental
3JHH = 9.2 Hz, quin-H8), 7.49 (d, 1H, JHH = 15.8 Hz, CH@CHCO),
3
4
4
7.42 (dd, 2H, JHH = 9.2 Hz and JHH = 2.6 Hz quin-H5, H7), 7.30 (s,
Reactions were carried out without precautions to exclude light,
atmospheric oxygen or moisture, unless otherwise stated. Melting
points were determined on a Reicher apparatus and are uncor-
rected. Elemental analyses were carried out with a Carlo Erba
1106 micro-analyzer. IR spectra were recorded on a Perkin–Elmer
16F P CFT-IR spectrometer with Nujol mulls between polyethylene
sheets or KBr pellets. NMR spectra were recorded in a Bruker AC
200, Avance 300 or a Varian Unity 300 spectrometer at room tem-
perature unless otherwise stated. Chemical shifts were referenced
4
2H, Ar–H2), 7.14 (dd, 1H, JHH = 9.2 and 2.6 Hz quin-H6), 3.92 (s,
6H, 2 OMe), 3.90 (s, 3H, OMe). Anal. Calc. for C21H18ClNO4
(383.8): C, 65.71; H, 4.73; N, 3.65. Found: C, 65.67; H, 4.47; N,
3.41%.
3.1.2. Compound (2b)
This was purified by column chromatography, silica gel (hex-
ane: Et2O 2:8) at Rf = 0.59, to isolate a yellow solid of 2b, yield,

3672
A.-S.S. Hamad Elgazwy / Polyhedron 28 (2009) 3667–3674
Fig. 2. Packing diagram of X-ray crystallographic structure of 5a, showing chains of molecules connected by hydrogen bonds (dashed lines). Only H atoms involved in
hydrogen bonds of H68B with O5 and H28A with O1 together with their neighbors are included in Table 2. View direction perpendicular to the xy-plane.
0.8 g, 72%. M.p.: 196–198 °C. IR (Nujol, cmÀ1):
(C@N) 1646, 1580.1H NMR (300 MHz, CDCl3) (d ppm): 8.37 (s,
m(C@O) 1664,
(413.9): C, 63.85; H, 4.87; N, 3.38. Found: C, 63.65; H, 4.86; N,
3.35%.
m
3
1H, quin-H4), 8.15 (d, 1H, JHH = 15.6 Hz, CH@CHCO), 7.93 (d, 1H
3
4JHH = 9.2 Hz, quin-H8), 7.49 (d, 1H, JHH = 15.8 Hz, CH@CHCO),
3.2. General procedure for the synthesis of 3-(6-R-2-chloroquinolin-3-
yl)-1,5-bis(3,4,5-trimethoxyphenyl)pentane-1,5-dione (R = H (3a),
R = OMe (3b))
4
7.42 (dd, 1H, JHH = 9.2 Hz and 2.8 Hz quin-H7), 7.30 (s, 2H, Ar–
4
H), 7.14 (d, 1H, JHH = 2.8 Hz quin-H5), 3.96 (s, 6H, 2 OMe), 3.95
(s, 3H, OMe), 3.90 (s, 3H, OMe). Anal. Calc. for C22H20ClNO5
3.2.1. General procedure method A
An equimolar quantity of the aldehydes 1a–b (1 mmol), and the
active methylene compounds 2 (2 mmol) were mixed thoroughly
and then 0.1 mmol of DBU was added. The reaction mixture was
ground in a mortar and pestle for 60 s to 5 min. for the appropriate
time, the reaction being monitored by TLC for completion of the
reaction. The reaction mixture was treated with cold water and
the product was filtered, dried, and the crude compounds were
recrystallized from a mixture of ethanol and water to get the de-
sired compound in the pure form (3a–b) in excellent yields (82%
and 84%).
Table 1
Crystal data and structure refinement of complex 5a.
Identification code
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Crystal habit
Space group
Unit cell dimensions
a (Å)
5a
C
59H59ClN4O8Pd
1093.95
100(2)
0.71073
triclinic
red tablet
ꢀ
P1
11.1555(7)
14.8389(10)
16.7839(11)
3.2.2. General procedure method B
b (Å)
c (Å)
A
solution of 2-chloro-3-quinoline carboxaldehyde 1a–b
(0.005 mol) in ethanol (25 ml) was added dropwise to a solution
of 3,4,5-trimethoxyacetophenone (1.00 g, 0.005 mol) in NaOH
(2 N, 25 ml) solution at 0 °C then the mixture was stirred for 24 h
at RT. The precipitate was filtered and the solid washed 3 times
with ethanol/water (1:1 ratio, 25 ml) to give a solid which was
air-dried.
a
b (°)
(°)
105.8520(10)
100.1800(10)
96.8170(10)
2589.4(3)
2
1.403
0.471
1136
c
(°)
V (Å3)
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mmÀ1
F(0 0 0)
)
Crystal size (mm3)
0.28 Â 0.13 Â 0.10
1.63 to 27.10
À14 6 h 6 14, À18 6 k 6 19,
À21 6 l 6 21
3.2.3. Compound 3a
h Range for data collection (°)
Index ranges
The solid product was purified by column chromatography
using silica gel (hexane:Et2O 2:8 or hexane:CH2Cl2 1:5) to give
3a as a yellow solid. Yield, 2.4 g, 81%. M.p.: 158–160 °C. IR (Nujol,
Reflections collected
29 264
Independent reflections
Completeness to theta = 26.00°
Absorption correction
Max. and min. transmission
Refinement method
11 163 [Rint = 0.0331]
99.4%
semi-empirical from equivalents
0.9545 and 0.8795
full-matrix least-squares on F2
11 163/52/670
1.076
Table 2
Hydrogen bonds (Å and °).
Data/restraints/parameters
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
<(DHA)
Goodness-of-fit on F2
C(68)–H(68B)Á Á ÁO(5)#1
C(28)–H(28A)Á Á ÁO(1)#2
0.98
0.98
2.40
2.40
3.275(5)
3.352(3)
147.7
162.6
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0493, wR2 = 0.1154
R1 = 0.0593, wR2 = 0.1197
1.941 and À0.781
Largest difference in peak and hole
Symmetry transformations used to generate equivalent atoms: #1 x À 1, y, z À 1; #2
Àx + 2, Ày + 2, Àz + 1.
(e Å3)

A.-S.S. Hamad Elgazwy / Polyhedron 28 (2009) 3667–3674
3673
cmÀ1):
m
(C@O) 1748,
m
(C@O) 1672,
m
(C@N) 1580, 1504. 1H NMR
3.4. General procedure for the synthesis of (1Z,2Z)-N-(2,6-
dimethylphenyl)-2-(2,6-dimethylphenylimino)-7-R-2-{3-[-1,5-
bis(3,4,5-trimethoxyphenyl)-1,5-dioxopenta-3-nyl]quinolin-2-
yl}ethanimidoyl palladium cyanidous chloride ([R = H, (5a), R = OMe,
(5b)]
(200 MHz, CDCl3) (d ppm): 8.16 (s,1H, Quino-H8), 8.00–7.96 (d,
4
3
1H JHH = 8.4 Hz, Quino-H4), 7.87–7.77 (d, 1H, JHH = 8.4 Hz, Qui-
3
no-H5), 7.73–7.65 (t, 1H, JHH = 7.2 Hz, Quino-H6), 7.57-7.46 (d,
3
1H, JHH = 7.2 Hz, Quino-H7), 7.25 (m, 4H), 3.91–3.90 (s, 18H,
3
6OMe), 3.80–3.71 [(d, 4H, JHH = 6.8 Hz, 2(–CH2–)], 3.61–3.46
(quintet, 1H, JHH = 6.8 Hz, –CH2–CH–CH2–). Anal. Calc. for
3
3.4.1. General procedure method A
C32H32NO8Cl (594.06): C, 64.70; H, 5.43; N, 2.36. Found: C, 64.72;
H, 5.47; N, 2.41%.
Chloro-quinoline derivatives 3a–b (0.78 mmol) were added un-
der nitrogen to a suspension of ‘‘Pd(dba)2” (300 mg, 0.52 mmol)
and XyNC (274 mg, 2.09 mmol) in acetone (15 ml). The suspension
was stirred for 5 h at room temperature. After this time the workup
is carried out in air. The solvents were evaporated, the residue was
extracted with CH2Cl2, and the extract filtrate was filtered over
anhydrous MgSO4/silica gel (1:3).The resulting red solution was
evaporated and the residue was triturated with Et2O (15 cm3).
The precipitate was filtered, washed with Et2O (2 Â 5 cm3), and
air-dried, giving deep red compounds 5a–b, in yields 275 mg,
32% and 295 mg, 33%, respectively.
3.2.4. Compound 3b
The solid product was purified by column chromatography
using silica gel (hexane:Et2O 2:8 or hexane:CH2Cl2 1:5) to give
3b as a yellow solid. Yield 2.6 g, 83%. M.p.: 204–206 °C. IR (Nujol,
cmÀ1):
m
(C@O)1748,
m(C@O)1674, m
(C@N)1582, 1505. 1H NMR
(200 MHz, CDCl3) (d ppm): 8.37 (s,1H, Quino-H8), 8.06–7.99 (d,
4
3
1H JHH = 9.4 Hz, Quino-H4), 7.88À7.77 (dd, 1H, JHH = 9.2 and
4
2.6 Hz, Quino-H5), 7.77–7.57 (d, 1H, JHH = 2.6 Hz, Quino-H7), 7.25
(m, 4H), 3.962 (s, 3H, OMe), 3.91–3.90 (s, 18H, 6OMe), 3.80–3.71
[(d, 4H, 3JHH = 6.8 Hz, 2(–CH2–)], 3.61–3.46 (quintet, 1H,
3.4.2. General procedure method B
3JHH = 6.8 Hz, –CH2–CH–CH2–). Anal.
Calc. for C33H34NO9Cl
XyNC (125 mg, 0.96 mmol) was added to a suspension of 4a–
b (0.12 mmol) in CH2Cl2 (15 ml). The suspension was stirred for
16 hrs at room temperature. The color changed from pale yel-
low to pale red and then dark red on monitoring the reaction
mixture. After this time the workup was carried out in air.
The solvents was filtered over anhydrous MgSO4/silica gel
(1:3). The resulting red solution was evaporated and the residue
was triturated with Et2O (15 cm3). The precipitate was filtered,
washed with Et2O (2 Â 5 cm3), and air-dried, giving deep red
compounds 5a–b, in yields 60 mg, 45% and 59 mg, 43%,
respectively.
(624.077): C, 63.51; H, 5.49; N, 2.24. Found: C, 63.65; H, 5.47; N,
2.39%.
3.3. General procedure for the synthesis of {Pd[6-R-C9H4–CH–[–CH2
CO–C6H2–(OCH3)3]2–(3,4,5)]Cl(PPh3)}2 [R = H, (4a) and [R = OMe,
(4b)]
[Pd(dba)2] (216 mg, 0.375 mmol), PPh3 (197 mg, 0.75 mmol)
and chloroquinoline derivatives of 3a–b (0.375 mmol) were mixed
under N2 in dry acetone (25 ml) and allowed to react with stirring
at room temperature for 6 hrs. After evaporation of the solvent and
extraction of the residue with CH2Cl2 (15 + 2 Â 5 ml), the combined
organic solution was filtered over silica gel/MgSO4 (3:1). The
resulting solution was concentrated (2 ml), and a mixture of the
complex and dba was precipitated with n-hexane. Purification by
chromatography through silica gel with CH2Cl2 gave 4a or 4b as
a yellow powder.
3.4.3. {PdCl(2)–(C@N–Xy)2–(CN–Xy)–C9H5N–(3)–CH)[CH2COC6H2–
3,4,5-(OCH3)3]2} (5a)
The solid red compound was purified by chromatography using
silica gel (acetone/hexane; 9:1). TLC: Rf = 0.88; Yield: 275 mg, 32%.
Diffraction-quality crystals were grown by slow diffusion of Et2O
into a CH2Cl2 solution of 5a. M.p.: 139–140 °C. IR (Nujol, cmÀ1):
m
(C„N) 2184,
m
(C@O)1672,
m
(C@N) 1640, 1582, 1504. 1H NMR
3
3.3.1. Complex (4a)
(200 MHz, CDCl3) (d ppm): 9.27À9.24 (d,1H, JHH = 8.4 Hz, Quino-
Diffraction- quality crystals were grown by slow diffusion of
Et2O into a CH2Cl2 solution of 4a. Yield: 274 mg, 38%. M.p.;
H8), 8.72 (s, 1H, Quino-H4), 8.16 (s, 1H, Ar–H), 7.99–7.94 (t, 2H,
3JHH = 8.4 Hz), 7.87–7.85 (t, 1H, JHH = 6.9 Hz), 7.80–7.77 (d, 1H,
3
210 °C dec., yellow solid. IR (Nujol, cmÀ1);
m
(C@O) 1672.2,
3JHH = 8.4 Hz, Quino-H7), 7.73–7.66 (m, 2H), 7.56–7.51 (t, 1H,
3JHH = 8.4 Hz, Quino-H6), 7.25–7.24 (s, 4H), 7.17–7.11 (t, 1H,
m
(C@N) 1618,
m
(C@C 1580.9. 1H NMR (200 MHz, CDCl3) (d ppm):
4
3
8.16 (s,2H, Quino-H8), 8.00-7.96 (d, 2H, JHH = 8.4 Hz, Quino-H4),
7.81–7.77 (d, 2H, 3JHH = 8.2 Hz, Quino-H5), 7.72–7.62 (m, 17H, Qui-
no-H6 + PPh3), 7.60–7.35 (m, 17H, Quino-H7 + PPh3), 7.25 [m, 8H,
(MeO)3–C6H2], 3.91 (s, 24H, 8OMe), 3.90 (s, 12H, 4OMe), 3.69–
3.66 (d, 8H, 4JHH = 6.8 Hz, CH–CH2–), 3.61–3.54 (t, 2H, 4JHH = 6.8 Hz
–CH–). 31P {1H} NMR (121 MHz, CDCl3) (d ppm): 29.72. Anal. Calc.
for C100H94N2O16Cl2Pd2P2 (1925.544): C, 62.38; H, 4.92; N, 1.45.
Found; C, 62.27; H, 4.83; N, 1.45%.
3JHH = 7.8 Hz), 6.99–6.97 (d, 2H, JHH = 7.5 Hz), 6.93–6.90 (d, 2H,
3JHH = 7.5 Hz), 6.85–6.80 (d, 1H, JHH = 6.6 Hz), 6.72–6.65 (t, 2H,
3
3JHH = 6.9 Hz), 6.62–6.60 (d, 1H, JHH = 6.6 Hz), 3.91(s, 6H, 2OMe),
3
3.90 (s, 3H, OMe), 3.89 (s, 3H, OMe), 3.87 (s, 6H, 2OMe), 2.18 (s,
6H, 2 Me), 2.08 (s, 6H, 2 Me), 1.52 (s, 6H, 2 Me). Anal. Calc. for
C59H59N4O8ClPd (1093.995): C, 64.77; H, 5.44; N, 5.12. Found: C,
64.75; H, 5.45; N, 5.10%.
3.4.4. {PdCl(2)–(C@N–Xy)2–(CN–Xy)–6-OMe–C9H4N–(3)-
CH)[CH2COC6H2–3,4,5-(OCH3)3]2} (5b)
3.3.2. Complex (4b)
Diffraction-quality crystals were grown by slow diffusion of
Et2O into a CH2Cl2 solution of 4b. Yield: 320 mg, 43%. M.p.:
The solid red compound was purified by chromatography using
silica gel (acetone); the fraction at Rf = 0.66 was collected and ex-
tracted to give a solution which was evaporated to dryness. Yield:
222 °C dec., yellow solid. IR (Nujol, cmÀ1);
m
(C@O) 1673,
m(C@N)
1620,
m
(C@C) 1582. 1H NMR (200 MHz, CDCl3) (d ppm): 8.16
295 mg, 33%. M.p.: 142–144 °C. IR (Nujol, cmÀ1):
m(C„N) 2184,
4
(s,2H, Quino-H8), 8.08–7.966 (d, 2H JHH = 8.4 Hz, Quino-H4),
7.81–7.77 (d, 2H, JHH = 8.4 Hz, Quino-H5), 7.72–7.62 (m, 15H,
m
(C@O) 1710, 1664,
m
(C@N) 1610, 1580, 1498. 1H NMR
3
3
(200 MHz, CDCl3) (d ppm): 8.65 (d,1H, JHH = 8.4 Hz, Quino-H8),
8.39 (s, 1H, Quino-H5), 8.19 (s, 1H) 8.11–8.07 (d,1H, JHH = 8.4 Hz,
Quino-H7), 7.95–7.90 (d, 2H, JHH = 9.2 Hz), 7.54 (s, 2H), 7.46–
3
PPh3), 7.60–7.35 (m, 17H, Quino-H7+PPh3), 7.25 [m, 8H, (MeO)3–
3
C6H2], 3.91 (s, 24H, 8OMe), 3.90 (s, 12H, 4OMe), 3.89 (s, 6H,
4
2OMe), 3.69–3.66 (d, 8H, JHH = 6.8 Hz, CH–CH2–), 3.61–3.54 (t,
7.43 (m, 2H), 7.40–7.37 (m, 1H), 7.31 (s, 4H), 7.17–7.12 (m, 3H),
7.08–7.04 (m, 2H), 7.00–698 (m, 2H), 6.90 (s 2H), 6.83 (s, 2H),
3.96 (s, 6H, 2OMe), 3.90 (s, 12H, 4OMe), 3.82 (s, 3H, OMe), 2.58
(s, 3H, Me), 2.51 (s, 3H, Me), 2.32 (s, 3H, Me), 2.18 (s, 6H, 2 Me),
4
2H, JHH = 6.8 Hz –CH–). 31P {1H} NMR (121 MHz, CDCl3) (d ppm):
29.73. Anal. Calc. for C101H96N2O17Cl2Pd2P2 (1955.54): C, 62.03;
H, 4.95; N, 1.43. Found; C, 62.02; H, 4.89; N, 1.42%.

3674
A.-S.S. Hamad Elgazwy / Polyhedron 28 (2009) 3667–3674
2.02 (s, 3H, Me), 1.52 (s, 6H, 2 Me). Anal. Calc. for C60H61N4O9ClPd
(1124.021): C, 64.11; H, 5.47; N, 4.98. Found: C, 64.10; H, 5.47; N,
4.92%.
Acknowledgments
This work has been supported by the Ministry of Education &
Science Spain and FEDER (EU) during the sabbatical leave of the
author as a visiting professor. The author wishes to thank Professor
Peter G. Jones, Institut für Anorganische und Analytische Chemie
der Technischen Universität, Postfach 3329, 38023 Braunschweig,
Germany and Dr. Dalia Bautista, S.A.C.E. Universidad de Murcia,
Apartado 4021, Murcia, 30071 Spain for the single-crystal X-ray
crystallography measurements.
3.4.5. Synthesis of [Pd2Cl2(CNXy)4] (6)
This compound was prepared by following the procedure meth-
od A described for 5a–b, from ‘‘Pd(dba)2” (300 mg, 0.52 mmol),
XyNC (274 mg, 2.09 mmol) and the chloro-quinoline derivatives
3a–b (0.78 mmol). In this case, the isolated yellow solid is identi-
fied as 6, which had previously been described [37]. The fraction
at Rf = 0.4 was collected and extracted with acetone to give a solu-
tion which was evaporated to dryness.
References
Yield: 366 mg, 58%. 1H NMR (300 MHz, CDCl3) (d ppm) 7.25–
7.09 (m, 12H), 2.52 (s, Me, 24H). 13C NMR (50 MHz, CDCl3) (d
ppm): 142.9 (C„N), 135.6 (CMe), 129.8 (CH), 128.0 (CH), 126.4
(CNC), 19.1 (Me). Anal. Calc. for C36H36N4Cl2Pd2 (808.44): C,
53.48; H, 4.49; N, 6.93. Found: C, 53.40; H, 4.37; N, 6.72%.
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a and
a
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Supplementary data
CCDC 715598 contains the supplementary crystallographic data
for 5a. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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University of Gottingen, Germany, 1997.