Synthesis, spectroscopic characterization and catalytic significance of Palladium(II) complexes derived from 1,1 bis(diphenylphosphinomethyl)ethane

Article abstract of DOI:10.1016/j.molstruc.2011.07.005

Two novel and neutral bidentate Palladium(II) complexes of the type, [PdX₂(dpme)] (X = Cl 1, OAc 2], have been synthesized from 1,1-bis(diphenylphosphinomethyl)ethene (dpme) ligand and characterized on the basis of elemental analyses, infrared, FAB-MS and ¹H-, ¹³C-, and ³¹P-NMR spectroscopy. The structure of 1 has been ascertained by single crystal X-ray crystallography and shows cis configuration in a square planar structure while the structural behavior of the dpme ligand through the formation of these complexes has been monitored by ³¹P{¹H} NMR and IR spectra. These Pd(II) complexes have shown a very significant catalytic role in Heck reaction giving high yield under mild condition.

Full text of DOI:10.1016/j.molstruc.2011.07.005

Journal of Molecular Structure 1002 (2011) 107–112
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic characterization and catalytic significance
of Palladium(II) complexes derived from 1,1 bis(diphenylphosphinomethyl)ethane
a
a
a
a
Ismail Warad a, , Mohammad Azam , Usama Karama , Saud Al-Resayes , Ahmed Aouissi ,
⇑
Belkheir Hammouti b
a Department of Chemistry, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
b LCAE-URAC18, Faculté des Sciences, Université Mohammed Ier B.P. 717, 60000 Oujda, Morocco
a r t i c l e i n f o
a b s t r a c t
Article history:
Two novel and neutral bidentate Palladium(II) complexes of the type, [PdX2(dpme)] (X = Cl 1, OAc 2],
have been synthesized from 1,1-bis(diphenylphosphinomethyl)ethene (dpme) ligand and characterized
on the basis of elemental analyses, infrared, FAB-MS and 1H-, 13C-, and 31P-NMR spectroscopy. The struc-
ture of 1 has been ascertained by single crystal X-ray crystallography and shows cis configuration in a
square planar structure while the structural behavior of the dpme ligand through the formation of these
complexes has been monitored by 31P{1H} NMR and IR spectra. These Pd(II) complexes have shown a very
significant catalytic role in Heck reaction giving high yield under mild condition.
Received 29 May 2011
Received in revised form 4 July 2011
Accepted 5 July 2011
Available online 23 July 2011
Keywords:
Pd(II) complexes
dpme ligands
Ó 2011 Elsevier B.V. All rights reserved.
Heck reaction
Single crystal structure
1. Introduction
heteroatom bond formation [9] and are now one of the most
valuable catalyzed reaction in organic synthesis [10–13]. In conti-
The coordination chemistry of phosphine ligands have played
an important role in the development and the structural design
of novel metal complexes and their applications in some of major
chemical reaction of homogeneous catalysis since 1960 [1]. Among
them, bidentate phosphines such as bis(diphenylphosphino)-
methane (dppm), 1,2 bis(diphenylphosphino)ethane, 1,3-bis(di-
phenylphosphino)propane (dppp) or ether–phosphine (PꢀO)
have received considerable attention because of their excellent
100% cis ligating properties to all most all transition metals [2,3].
Recently, the designs of conformationally rigid polyphosphine li-
gands for the coordination of late transition metals have been a
subject of much interest in organometallic chemistry and homoge-
neous catalysis. Indeed, decreasing the flexibility of the supporting
ligand decrease the number of the possible conformations of the
metal ligand assembly, thus leading to improved selectivity. Unlike
selectivity, the effect of the structural rigidity on the activity is un-
predictable as it mainly depends on the reaction under investiga-
tion rather than on the structural and conformational properties
of the metal diphosphine precursor [4–7]. Metal complexes con-
taining phosphorus ligands have always been important due to
their possible catalytic activity, and variety of them has been re-
ported [8]. Over the last 30 years, Palladium catalyzed coupling re-
actions have gained immense importance for the carbon-
nuation of our ongoing interest in chemistry of 1,1-bis(diphenyl-
phosphinomethyl)ethene (dpme) [14], Herein, we describe the
synthesis, structural characterization of Palladium(II) complexes
derived from 1,1-bis(diphenylphosphinomethyl)ethene and their
catalytic significance in Heck reaction.
2. Experimental
2.1. Materials, and instrumentations
All reactions were carried out in an inert atmosphere (argon) by
using standard high vacuum and Schlenk-line techniques unless
otherwise noted.
1,1-Bis(diphenylphosphinomethyl)ethene (dpme) was prepared
according to literature methods [14]. Ph3P, n-BuLi, H2C@(CH2Cl)2
and PdCl2(PhCN)2 and Pd(OAc)2 were available from Merck and
ChemPur, respectively, and used as received. Elemental analyses
were carried out on an Elementar Varrio EL analyzer. High-resolu-
tion 1H, 13C{1H}, DEPT 135, and 31P{1H} NMR spectra were recorded
on a Bruker DRX 250 spectrometer at 298 K. FT-IR and FAB-MS data
were obtained on a Bruker IFS 48 FT-IR spectrometer and Finnigan
711A (8 kV), modified by AMD and reported as mass/charge (m/z),
respectively. The analyses of the CAC coupling experiments were
performed on a GC 6000 Vega Gas 2 (Carlo Erba Instrument) with
a FID and capillary column PS 255 [20 m, carriergas, He(40 kPa), in-
tegrator3390A (HewlettPackard)].
⇑
Corresponding author. Tel./fax: +96 61 4675992.
E-mail address: warad@ksu.edu.sa (I. Warad).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.07.005

108
I. Warad et al. / Journal of Molecular Structure 1002 (2011) 107–112
Table 1
process samples were taken from the reaction mixture using syr-
Crystal data collection and refinement of 1.
inge to control the conversion. At the conclusion of the reaction,
the mixture was cooled, extracted with ethylacetate–hexane
(1:5), filtered through a pad of silica gel with copious washing, con-
centrated and purified by flash chromatography on silica gel. All
reactions were monitored by GC. The purity of the compounds
was checked by NMR.
Empirical formula
Molecular weight
Crystal color
Crystal description
Crystal system
Temperature (K)
Wavelength (Å)
Space group
C28 H26 Cl2 P2 Pd
601. 73
Yellow
Block
Monoclinic
293(2)
0.71073
P21/c
Unit cell dimension
2.4. Crystallography data collection and refinement of 1
a (Å)
b (Å)
c (Å)
11.194(2)
17.345(4)
13.8043(12)
90.00
92.114(15)
90.00
2678.6(8)
4
7.901–14.043
1216
The X-ray structure determination of 1 was performed on a
Bruker SMART diffractometer, using graphite monochromated Mo
a
(Å)
b (Å)
Ka radiation (k = 0.71069). The structure in P21/c space group
c
(Å)
was determined by direct method and refined by full matrix
least-square using SHELXL-97 program package. Data reduction
and cell refinement were performed by SAINT Program. All calcu-
lation was performed using the programs contained in the SHEL-
XL-97 packages [15]. Parameters associated with unit cell
dimensions, intensity data collection and refinement for the struc-
ture of 1 are given in Table 1.
Volume (Å3)
Z
Theta range for data collection (°)
F (0 0 0)
D (g cmÀ3
)
1.492
0.87369
0.98447
Date completeness
Absorption coefficient
l )
(mmÀ1
2.2. Synthesis of complexes, PdCl2[dpme] 1 and Pd(OAc)2[dpme] 2
3. Results and discussion
A solution of Pd(II) salt (0.26 mmol) dissolved in 15 ml dichloro-
methane was added in the 10 ml dichloromethane solution of
dpme ligand (0.26 mmol). The resultant reaction mixture was stir-
red for 10 min resulting a clear yellow colored solution. The result-
ing solution was kept for evaporation at room temperature leading
to the formation of yellow colored microcrystalline solid product
which on recrystallisation in dichloromethane yielded the yellow
crystals for complex 1 suitable for single crystal diffraction. No
The complexes, 1 and 2 have been synthesized by interacting
ligand, 1,1-bis(diphenylphosphinomethyl)ethane with Pd(II) ions
in 1:1 M ratio (Scheme 1). Both the isolated complexes are yellow
solids, stable at room temperature, soluble in chlorinated solvent
such as CH2Cl2, CHCl3 and insoluble in polar and non-polar solvent.
Formation of isolated complexes has been confirmed on the ba-
sis of characteristic bands in IR spectra, Uv–vis, elemental analysis,
resonance signals in 1H, 13 C and 31P NMR, molecular ion peak (m/z)
in FAB-MS and single crystal X-ray crystallography.
crystal for complex
diffraction.
2 was found suitable for single crystal
1: Yield: 88%, 31P{1H} NMR (CDCl3): d (ppm) 16.14 (s, 2P, dpme),
1H NMR (CDCl3): d (ppm) 2.93 (m, 4H, CH2P), 4.65 (s, 2H, H2C@C),
7.00–7.82 (m, 20H, PhAH), 13C NMR (CDCl3): d (ppm) 37.86, 38.11
(2d, 2C, PACH2), 115.55 (s, 1C, H2C@C), 128.66–133.55 (3 m, 20C,
PhAH), 135.53 (s, 1C, H2C@C), Anal. Found: C, 55.87; H, 4.32; Cl,
11.80%, Calculated, C, 55.79; H, 4.28; Cl, 11.73%.
2: Yield: 90%, 31P{1H} NMR (CDCl3): d (ppm) 17.22 (s, 2P, dpme),
1H NMR (CDCl3): d (ppm) 2.88 (m, 4H, CH2P), 3.72 (br, 3H, CH3O),
4.77 (s, 2H, H2C@C), 7.00–7.88 (m, 20H, PhAH), 13C NMR (CDCl3):
d (ppm) 39.21 (br, 2C, PCH2), 55.54 (s, 2C, CH3O), 117.21 (s, 1C,
H2C@C), 128.00–134.00 (3 m, 20C, PhAH), 136.34 (s, 1C, H2C@C).
Anal. Found: C, 59.25; H, 4.93%, Calculated, C, 59.17; H, 4.75%.
2.3. Heck reaction
Pd(II) salt (1.0 lmol), phenyl halide (1.0 mmol), metyl acrylate
(1.16 mol), Base (4 mmol), DMF (10 mL) were added to 100 ml
Schlenk tube and the reaction mixture was subjected to a freeze–
thaw cycle before it heated at 80 °C for 14 h. During the coupling
Fig. 1. IR spectra of: (a) PdCl2(PhCN)2 before addition of dpme ligand and (b) after
the addition to prepare 1.
PPh2
X
PdCl2(PhCN)2
or
PPh2
PPh2
CH2Cl2
Pd
+
RT
X
PPh2
Pd(OAc)2
X= Cl, OAc
Scheme 1. The synthetic route to prepare 1 and 2 complexes.

I. Warad et al. / Journal of Molecular Structure 1002 (2011) 107–112
109
Fig. 2. FAB-MS Spectrum of 2.
gion shows the bands at 212, 230, 250 nm assigned to
p –
p⁄
charge transfer transitions of the dpme ligand similar to the free
dpme ligand. A new band observed at 317 nm assignable d–d
electron transfer confirms the coordination of the dpme in 1.
(Fig. 3).
3.4. NMR spectra
3.4.1. 31P{1H} NMR
31P{1H} NMR spectra of complexes 1 and 2 exhibit singlets at
16.1 ppm and 17.3 ppm respectively, indicating that phosphorus
atom of phosphine groups of dpme ligand is coordinated to
Pd(II) to give chemically equivalent chelated complexes in
solution.
On addition of the PdCl2(PhCN)2 into the dpme ligand solution
in NMR tube, intensity of the free dpme 31P{1H} NMR signal is
gradually decreased while the intensity of complexed dpme
31P{1H} NMR signal is gradually increased simultaneously confirm-
ing metal–ligand molar ratio 1:1 (Fig. 4). Thus, on the basis of
31P{1H} NMR and UV–vis analyses, a square planar geometry has
been assigned around [PdCl2(dpme)] complex [16,18,19].
Fig. 3. Electronic spectra of free dpme ligand (A), and 1 (B), dissolved in CH2Cl2 at.
3.1. IR spectra
The IR spectra of the desired complexes showed characteristic
bands at 3265, 3190 cmÀ1, 2880, 2895 cmÀ1, 1108, 1115 cmÀ1
3.4.2. 1H and 13C{1H} NMR spectra
and 510, 512 cmÀ1 assigned to
t(C-HPh), t(C-H alph), t(C-P) and
The 1H and 13C{1H} NMR spectra of the complexes show charac-
teristic sets of signals attributed to the aliphatic and aromatic pro-
tons and carbons of dpme diphosphine ligand, [CH2P, H2C@C,
PhAH]. An addition signal has been recorded in 2 attributed to
CH3 of acetate group. The integral values of the 1H resonances
are in agreement with the compositions.
t
(Pd-P) for 1 and 2 respectively [16]. The carboxalyate bands in
complex 2 appeared at around 1550 cmÀ1 while the other bands
were found at their expected positions [17] (Fig. 1b). The fully ex-
change of PhCN in PdCl2(PhCN)2 (Scheme 1) was confirmed by the
disappearance of PhCN appearing at 2260 cmÀ1 (Fig. 1a).
3.2. Elemental analysis and FAB-MS
3.5. Crystallography of PdCl2(dpme) 1
The elemental analyses of these complexes are in a good agree-
ment with the proposed composition which is further confirmed
by molecular ion peaks of 1 and 2 observed at 601.2 and 648.1,
respectively.
The single crystal of 1 suitable for single crystal diffraction was
obtained as yellow block crystals by recrystallization in CH2Cl2
solution and crystallized as a monomeric square planar structure
(Fig. 5). This is the first time that molecular structure of
PdCl2(diphosphine) complex has been established by X-ray crys-
tallography using dpme ligand. Earlier, the structures of same
complexes using dpm, dpe, dpp have been reported [19]. The
coordination geometry of two phosphorus atoms of dpme ligand
and two chorine atoms coordinated to Pd(II) ion is a cis configu-
ration as required by the geometry of the bidentate chelating
diphosphine ligand. Bond distances and angles are given in
Table 2.
The FAB-MS of complex 2 shows molecular ion peak at 648.1 [M]+
corresponding to its molecular formula C32H32O4P2Pd. It also shows
a series of peaks at (m/z) 589.1 [M-OAc]+, 545.1 [M-OAc-Ac]+ 529.1
[M-2OAc]+, 457.1, corresponding to various fragments (Fig. 2).
3.3. Electronic spectra
The electronic absorption spectra of the complexes 1 and 2
show four intense bands between 200 and 400 nm. The UV re-

110
I. Warad et al. / Journal of Molecular Structure 1002 (2011) 107–112
3.6. Heck reaction
The Pd-catalyzed Heck reaction is an efficient way to prepare
organic derivatives, which are important chemicals for many appli-
cations viz., the Heck couplings of metyl acrylate with iodoben-
zene, bromobenzene, and chlorobenzene to cinnamate. The
reactions were performed with NEt3, K2CO3, KOH as a base in
DMF at 80 °C for 16 h (Scheme 2) (Table 3).
The choice of bases and solvents are usually important in
achieving an efficient cross coupling reaction. The widely used sol-
vents such as DMF, DMSO, toluene, dioxane, THF and CH3CN had
remarkable effects on the coupling reaction [20–23].
In general, all the catalysts studied exhibited a high degree of
activity, the expected product being obtained in high yield as in
Table 3. No product except cinnamate was observed. The Heck
reaction of iodobenzene with methylate in the presence of theses
complexes gave better yields under the studied conditions that
those of bromobenzene (Table 3, runs 1, 2, 4 and 5), as expected
no more than 5% coupling conversion was detected with chloro-
benzene (Table 3, runs 3 and 6). Less significant changes in the
activity of 1 and 2 was observed under identical Heck reaction
condition (Table 3, runs 1–6). Unfortunately, the catalysts are oxy-
gen sensitive and had to be kept under an inert atmosphere in or-
der to avoid deactivation and maintain its high activity, no
conversion was detected if non-degassed DMF served as solvent
(Table 3, run 7), therefore DMF was dried and deoxygenated prior
to use, and the reactions were kept under argon. By allowing oxy-
gen to enter the reaction Schlenk tube during reaction process, no
farther more conversion was observed even when reaction lifted
for 24 h.
Enhancements in activities were recorded in order KOH > K2CO3
ꢀ NEt3, respectively with the base strength (Table 3, run 1, 8 and
9). Control experiment indicate that the coupling reactions did
not occur in the absence of base (Table 3, run 10). These result
are in agreement with the previous studies [24,25].
Fig. 4. 31P{1H} NMR spectra at various [PdCl2(PhCN)2]/[dpme] mole ratios in CDCl3
at RT.
Fig. 5. ORTEP plots of 1 with thermal ellipsoids are drawn at the 50% probability.

I. Warad et al. / Journal of Molecular Structure 1002 (2011) 107–112
111
Table 2
Table 2 (continued)
Selected bond lengths (Å) and bond angles (°) of 1.
Bond lengths
Bond lengths
C(42)AC(41)AP(2)
C(43)AC(42)AC(41)
C(44)AC(43)AC(42)
C(43)AC(44)AC(45)
C(44)AC(45)AC(46)
C(41)AC(46)AC(45)
C(2)AC(1)AP(1)
C(4)AC(2)AC(1)
C(4)AC(2)AC(3)
C(1)AC(2)AC(3)
C(2)AC(3)AP(2)
121.7(2)
121.3(3)
119.5(3)
120.4(3)
120.9(3)
119.5(3)
111.91(17)
123.5(3)
122.0(3)
114.4(2)
111.71(16)
Pd(1)AP(2)
Pd(1)AP(1)
Pd(1)ACl(1)
Pd(1)ACl(1)
Pd(1)AC(l1)
P(1)AC(21)
P(1)AC(11)
P(1)AC(1)
2.2458(7)
2.2465(7)
2.3490(8)
2.3534(7)
2.3534(7)
1.811(3)
1.818(2)
1.834(2)
1.807(3)
1.816(2)
1.836(2)
1.377(4)
1.387(4)
1.394(4)
1.364(5)
1.373(5)
1.377(4)
1.382(4)
1.387(4)
1.390(5)
1.364(6)
1.358(6)
1.378(5)
1.380(4)
1.390(4)
1.356(5)
1.383(5)
1.496(4)
1.316(4)
P(2)AC(41)
P(2)AC(31)
P(2)AC(3)
C(11)AC(12)
C(11)AC(16)
C(12)AC(13)
C(13)AC(14)
C(14)AC(15)
C(15)AC(16)
C(21)AC(22)
C(21)AC(26)
C(22)AC(23)
C(23)AC(24)
C(24)AC(25)
C(25)AC(26)
C(31)AC(32)
C(31)AC(36)
C(44)AC(45)
C(45)AC(46)
C(1)AC(2)
Ph
1 or 2 / base
DMF at 80 oC
+
Ph-X
R
R
X = Cl, Br, I, R = CO2 Me
Scheme 2. The Heck coupling reaction of benzene halide with metyl acrylate to
prepare cinnamate.
Table 3
C(2)AC(4)
The Heck coupling reaction of benzene halaide with metyl acrylate.
Bond angles
P(2)APd(1)AP(1)
P(2)APd(1)ACl(2)
P(1)APd(1)ACl(2)
P(2)APd(1)AC(l1)
P(1)APd(1)AC(l1)
C(l2)APd(1)AC(l1)
C(21)AP(1)AC(11)
C(21)AP(1)AC(1)
C(11)AP(1)AC(1)
C(21)AP(1)APd(1)
C(11)AP(1)APd(1)
C(1)AP(1)APd(1)
C(41)AP(2)AC(31)
C(41)AP(2)AC(3)
C(31)AP(2)AC(3)
C(41)AP(2)APd(1)
C(31)AP(2)APd(1)
C(3)AP(2)APd(1)
C(12)AC(11)AC(16)
C(12)AC(11)AP(1)
C(16)AC(11)AP(1)
C(11)AC(12)AC(13)
C(14)AC(13)AC(12)
C(13)AC(14)AC(15)
C(14)AC(15)AC(16)
C(15)AC(16)AC(11)
C(22)AC(21)AC(26)
C(22)AC(21)AP(1)
C(26)AC(21)AP(1)
C(21)AC(22)AC(23)
C(24)AC(23)AC(22)
C(25)AC(24)AC(23)
C(24)AC(25)AC(26)
C(25)AC(26)AC(21)
C(32)AC(31)AC(36)
C(32)AC(31)AP(2)
C(36)AC(31)AP(2)
C(31)AC(32)AC(33)
C(34)AC(33)AC(32)
C(33)AC(34)AC(35)
C(34)AC(35)AC(36)
C(35)AC(36)AC(31)
C(46)AC(41)AC(42)
C(46)AC(41)AP(2)
96.82(2)
86.09(3)
176.45(2)
177.89(2)
85.24(3)
91.87(3)
108.58(12)
103.22(12)
103.66(12)
110.19(9)
112.57(9)
117.85(8)
109.48(12)
102.23(12)
101.81(11)
112.37(8)
111.90(8)
118.12(8)
118.9(2)
120.4(2)
120.7(2)
120.2(3)
120.2(3)
119.9(3)
120.3(3)
120.5(3)
118.7(3)
124.5(2)
116.8(2)
119.9(4)
120.0(4)
121.0(4)
119.5(4)
120.9(3)
119.2(2)
118.04(19)
122.7(2)
120.5(3)
120.0(3)
120.4(3)
120.3(3)
119.6(3)
118.3(2)
119.9(2)
Run
PhX
Complex
Base
Yielda
1
2
3
4
5
6
7
8
9
PhI
1
1
1
2
2
2
1
1
1
1
KOH
KOH
KOH
KOH
KOH
KOH
KOH
K2CO3
NEt3
–
>99
86
5
PhBr
PhCl
PhI
PhBr
PhCl
PhI
PhI
PhI
PhI
98
84
4
0b
75
73
0c
10
a
Reaction conditions: Pd(II) 1.0 lmol, phenyl halide 1 mmol, metyl acrylate
1.16 mmol, Base 4 mmol, in 10 mL DMF at 80 °C for 14 h, isolated yields are based
on phenyl halide, TON = 1000, all reactions were monitored by GC.
b
Non-degassed solvent was used,
No-base was added.
c
4. Conclusions
Two novel and neutral Palladium(II) complexes have been
prepared using 1,1-bis(diphenylphosphinomethyl)ethene (dpme)
ligand. The ligand exchange through these complexes have been
monitored by 31P{1H}-NMR and IR and characterized by elemental
analyses, infrared, FAB-MS and 1H-, 13C-, H, and 31P-NMR spectros-
copy data. Complex 1 was additionally characterized by X-ray
crystallography.
These complexes showed efficient catalytic activity under mild
basic conditions when subjected as catalysts to CAC Heck
cross coupling of metyl acrylate with phenyl halide to produce
cinnamate.
Supplementary material
Crystallographic data has been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication num-
ber CCDC 816387. Copies of this information may be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or

112
I. Warad et al. / Journal of Molecular Structure 1002 (2011) 107–112
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Acknowledgements
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Authors are thankful to the Deanship of Scientific Research,
King Saud University Riyadh for funding the work through the re-
search Project No. RGP-VPP-008.
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