Synthesis, characterization and structural studies of new palladium(II) complexes including non-symmetric phosphorus ylides

Article abstract of DOI:10.1016/j.ica.2010.07.072

The reaction of the non-symmetric phosphorus ylides, Ph ₂P(CH₂)_nPPh₂C(H)C(O)PhR [Y ₁-Y₄: n = 1, R = Cl, Br, NO₂, OCH₃ and Y₅-Y₈: n = 2, R = Cl, B

Full text of DOI:10.1016/j.ica.2010.07.072

Inorganica Chimica Acta 363 (2010) 3973–3980
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis, characterization and structural studies of new palladium(II)
complexes including non-symmetric phosphorus ylides
a
a
b
Seyyed Javad Sabounchei a, , Sepideh Samiee , Davood Nematollahi , Ali Naghipour ,
*
David Morales-Morales c,
**
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b Department of Chemistry, Faculty of Science, University of Ilam, Ilam 69315, Iran
c Instituto de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Circuito Exterior, Coyoacán, 04510, México D.F., Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 May 2010
Received in revised form 17 July 2010
Accepted 24 July 2010
Available online 30 July 2010
The reaction of the non-symmetric phosphorus ylides, Ph2P(CH2)nPPh2C(H)C(O)PhR [Y1–Y4: n = 1,
R = Cl, Br, NO2, OCH3 and Y5–Y8: n = 2, R = Cl, Br, NO, OCH3] with dichloro(1,5-cyclooctadiene)palla-
dium(II) in dichloromethane under mild conditions afford the monomeric P–C chelated complexes,
[(Y)PdCl2] (Y = Y1–Y8). These complexes were fully characterized by elemental analysis and spectro-
scopic techniques such as IR, 1H, 31P, and 13C NMR. In addition, the identity of complexes [(Y5)PdCl2]
(1b) and [(Y8)PdCl2] (4b) was unequivocally determined by single crystal X-diffraction techniques,
both structures consisting of six-membered rings formed by coordination of the ligands through
the phosphine group and the ylidic carbon atom to the metal center. The coordination geometry
around the Pd atoms in both these complexes be defined as slightly distorted square planar. Further-
more, their electrochemical behavior was also investigated by cyclic voltammeters, thus the cyclic
voltammetry of complex [(Y1)PdCl2], in dichloromethane solution with Pt electrode, shows that the
redox reaction of the pair Pd(II)/Pd(0) is irreversible with the cathodic peak potential at ꢀ1.08 V ver-
sus Ag wire.
Keywords:
Non-symmetric phosphorus ylides
Palladium(II) complexes
Crystal structure
Electrochemical studies
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
The bonding mode (d) had been previously observed for Pd(II),
Pt(II), Rh(I), Hg(II) [6–17] species. In addition, Rh(I) and Hg(II) were
Phosphorus ylides are a group of very interesting ligands in
organometallic chemistry, these compounds are also useful inter-
mediates in organic synthesis [1–4]. Much of the interest in the
coordination properties of resonance stabilized phosphorus ylides
stems from their coordination versatility due to the presence of
shown to exhibit the P-bonding mode (b) [10,15]. In this context,
we have now focused our attention in the study of the coordination
modes adopted by the resonance stabilized ylides when ligated to
Pd(II). The results of these studies including the full characteriza-
tion of the obtained complexes (performed by elemental analysis,
IR, multinuclear NMR techniques and electrochemical data) is
presented and discussed in this paper.
different functional groups in their molecular frame [5]. The a-keto
stabilized ylides derived from bisphosphines, viz., Ph2PCH2-
PPh2@C(H)C(O)R and Ph2PCH2CH2PPh2@C(H)C(O)R (R = Me, Ph or
OMe) [6] constitute an important class of hybrid ligands containing
both phosphine and ylide functionalities, and can exist in ylidic
and enolate forms. This versatility, has allowed the characteriza-
tion of coordinated ylides in different bonding modes: C-coordi-
2. Experimental
2.1. Materials
nated (through the C
a atom), O-bonded (through the carbonyl
O), P-bonded (through the P of the phosphine group), or even situ-
ations in which the same ylide shows a combination of bonding
modes. Different types of bonding are shown as depicted in Chart
1 for Ph2P(CH2)nPPh2C(H)C(O)PhR [see Chart 1].
All synthetic procedures were performed using standard
Schlenk tube techniques under dry nitrogen atmospheres. Starting
materials were purchased from commercial sources and used
without further purification. Solvents were dried according to the
methods given in the literature and purified under inert conditions
[18]. The starting material dichloro(1,5-cyclooctadiene)palla-
dium(II) complex, [PdCl2(COD)] was prepared according to the
published procedures [19].
* Corresponding author.
** Corresponding author. Tel.: +98 8118272072; fax: +98 8118273231.
E-mail addresses: jsabounchei@yahoo.co.uk (S.J. Sabounchei), damor@unam.mx
(D. Morales-Morales).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.07.072

3974
S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3973–3980
O
Ph2P
n(H2C)
CH
C
R
Ph2P
M
CH
Ph2P
Ph2P
C
O
R
CH
Ph2P
C
R
CH
Ph2P
Ph2P
C
O
R
n(H2C)
M
n(H2C)
n(H2C)
O
Ph2P
M
(c) O-bonding
(b) P-bonding
(a) C-bonding
CH
CH
Ph2P
n(H2C)
Ph2P
Ph2P
C
O
C
O
R
R
n(H2C)
M
Ph2P
M
(d) P, C-bonding, chelate
M
(e) P, O-bonding, chelate
CH
Ph2P
C
O
R
CH
Ph2P
Ph2P
C
O
R
n(H2C)
M
n(H2C)
Ph2P
M
M
(f) P, C-bonding, bridging
(g) P, O-bonding, bridging
Chart 1. The possible bonding modes of Ph2P(CH2)nPPh2C(H)C(O)C6H4R (n = 1, 2 and R = Cl, Br, OCH3, NO2) to metal M.
2.2. Physical measurements
2.3. Sample preparation
Melting points were measured on a SMPI apparatus and are
reported without correction. Elemental analysis was performed
using a Perkin–Elmer 2400 series analyzer. IR spectra were re-
corded on a Shimadzu 435-U-04 FT spectrophotometer from
KBr pellets. 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded
either on a 300 MHz Bruker and a 90 MHz Jeol spectrometer in
DMSO-d6 or CDCl3 as solvents at 25 °C. Cyclic voltammetry
was performed using an Autolab model PGSTAT 20 potentio-
stat/galvanostat. The working electrode used in the voltammetry
experiments was a Pt disc (2.2 mm diameter) and platinum wire
was used as the counter electrode. The working electrode poten-
tials were measured versus Ag wire (all electrodes from AZAR
Electrodes).
The ligands [Ph2PCH2PPh2C(H)C(O)C6H4R] (R = Cl (Y1), NO2 (Y3))
and [Ph2P(CH2)2PPh2C(H)C(O)C6H4NO2] (Y7) were prepared based
on the published methods [24,25].
2.3.1. Synthesis of ligands
2.3.1.1. Synthesis of [Ph2PCH2PPh2C(H)C(O)C6H4Br] (Y2). Bis(diphen-
ylphosphino)methane (dppm) (0.2 g, 0.52 mmol) was dissolved in
5 ml of chloroform and then a solution (5 ml, CHCl3) of 4-bromoph-
enacyl bromide (0.144 g, 0.52 mmol) was added dropwise. The
resulting reaction mixture was stirred for 2 h at room temperature.
Addition of 25 ml of diethyl ether, after the prescribed reaction
time caused the precipitation of the phosphonium salts. The result-
ing phosphonium salts (0.3 g, 0.45 mmol) were treated with tri-
ethyl amine (0.5 ml) in toluene (15 ml). The triethyl amine
hydrobromide produced was filtered off and the toluene layer con-
centrated to 5 ml which upon further addition of petroleum ether
(25 ml) results in the precipitation of the ligands as free-flowing
white solids. The product was collected and dried under vacuum.
Anal. Calc. for C33H27BrOP2: C, 68.17; H, 4.68. Found: C, 67.91; H,
4.52%. Yield: 0.205 g (78%), m.p. 153–155 °C. Selected IR absorp-
Suitable crystals for complexes 1b and 4b were obtained from
dimethylsulfoxide solution by slow evaporation of the solvent
and mounted in random orientation on glass fibers. The X-ray
intensity data were measured at 298 K on a Bruker SMART APEX
CCD-based three-circle X-ray diffractometer system using graphite
mono-chromated Mo K
a (k = 0.71073 Å) radiation. The crystal
structures were solved by direct methods and refined by using
SHELXS-97 and SHELXL-97 crystallographic software packages [20–
23]. All non-hydrogen atoms were refined anisotropically using
reflections I > 2r(I). Hydrogen atoms were located in ideal
positions.
tion in KBr (cmꢀ1): 1502 (
m
C@O). 1H NMR (CDCl3) dH (ppm): 3.63
2
2
(d, 2H, CH2, JPH = 14.15 Hz), 4.22 (d, 1H, CH, JPH = 23.56 Hz),
7.24–7.73 (m, 24H, Ph). 31P NMR (CDCl3) dP (ppm): ꢀ30.07 (d,
2
2
PPh2, JPP = 63.67 Hz), 11.39 (d, PCH, JPP = 62.98 Hz). 13C NMR

S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3973–3980
3975
1
(CDCl3) dC (ppm): 24.61 (dd, CH2, JPC = 56.22, 57.65 Hz), 50.51 (d,
treated with n-hexane (ca. 15 ml) to afford a yellow solid. The
product was collected and dried under vacuum. Anal. Calc. for
1
CH, JPC = 112.45 Hz), 123.62–140.12 (Ph), 183.58 (s, CO).
C33H27Cl3OP2Pd: C, 55.49; H, 3.81. Found: C, 56.01; H, 3.45%. Yield:
2.3.1.2. Synthesis of [Ph2PCH2PPh2C(H)C(O)C6H4OCH3] (Y4). A solu-
tion consisting of dppm (0.2 g, 0.52 mmol) and 4-methoxyphena-
cyl bromide (0.119 g, 0.52 mmol) in acetone was stirred at room
temperature for 4 h. The resulting white solid formed was filtered
off, and dried under reduced pressure. Further treatment with tri-
ethyl amine (0.5 ml) led to elimination of triethyl amine hydrobro-
mide, affording the free ligand Y4. White solid. Anal. Calc. for
0.288 g (81%), m.p. 201–203 °C. Selected IR absorption in KBr
(cmꢀ1): 1620 ( C@O). 1H NMR (DMSO-d6) dH (ppm): 4.86 (bt, CH2,
m
2JPH = 14.61 Hz), 5.98 (br, CH), 7.27–8.30 (m, 24H, Ph). 31P NMR
2
(DMSO-d6) dP (ppm): 26.96 (bd, PPh2, JPP = 49.53 Hz), 38.02 (d,
2
PCH, JPP = 46.01 Hz). 13C NMR (DMSO-d6) dC (ppm): 31.90 (br,
CH), 121.47–138.25 (Ph), 196.07 (s, CO), (CH2, was not seen).
C
34H30O2P2: C, 76.68; H, 5.68. Found: C, 76.49; H, 5.56%. Yield:
2.3.2.2. Data for [(Y2)PdCl2] (2a). This compound was prepared by a
similar procedure to that of complex (1a). Yellow solid. Anal. Calc.
for C33H27BrCl2OP2Pd: C, 52.24; H, 3.59. Found: C, 51.97; H, 3.38%.
Yield: 0.321 g (85%), m.p. 197–199 °C. Selected IR absorption in KBr
0.202 g (76%), m.p. 148–150 °C. Selected IR absorption in KBr
(cmꢀ1): 1507 ( C@O). 1H NMR (CDCl3) dH (ppm): 3.64 (d, 2H, CH2,
m
2JPH = 14.42 Hz), 3.79 (s, 3H, CH3); 4.24 (br, 1H, CH), 6.78–7.84
(m, 24H, Ph). 31P NMR (CDCl3) dP (ppm): ꢀ29.67 (d, PPh2,
(cmꢀ1): 1621 ( C@O). 1H NMR (DMSO-d6) dH (ppm): 4.76 (dd, CH2,
m
2JPP = 62.36 Hz), 11.15 (d, PCH, JPP = 62.36 Hz). 13C NMR (CDCl3)
2JPH = 12.27, 14.15 Hz), 5.99 (br, CH), 7.31–8.31 (m, 24H, Ph). 31P
2
1
2
dC (ppm): 24.87 (dd, CH2, JPC = 56.67, 56.82 Hz), 49.02 (d, CH,
NMR (DMSO-d6) dP (ppm): 26.86 (bd, PPh2, JPP = 47.79 Hz), 38.07
1JPC = 112.45 Hz), 55.30 (s, CH3), 112.86–137.71 (Ph), 160.72 (s,
COPh (i)), 184.61 (s, CO).
(d, PCH, JPP = 46.08 Hz). 13C NMR (DMSO-d6) dC (ppm): 22.54 (b,
2
CH2), 32.73 (d, CH, 2JPC = 57.75), 121.47–137.03 (Ph), 196.19 (s, CO).
2.3.1.3. Synthesis of [Ph2P(CH2)2PPh2C(H)C(O)C6H4Cl] (Y5) general
procedure. A solution consisting of bis(diphenylphosphino)ethane
(dppe) (0.398 g, 1 mmol) and 4-chlorophenacyl bromide (0.245 g,
1.05 mmol) in acetone was stirred at room temperature overnight.
The resulting solution was filtered off, and the precipitate obtained
washed with diethyl ether and dried. This product was further
treated with triethyl amine (0.5 ml) leading to the elimination of
triethyl amine hydrobromide, affording the free ligand Y5 as sole
product. White solid. Anal. Calc. for C34H29ClOP2: C, 74.11; H,
5.31. Found: C, 74.52; H, 5.23%. Yield: 0.208 g (76%), m.p. 142–
2.3.2.3. Data for [(Y3)PdCl2] (3a). This compound was prepared by a
similar procedure to that of complex (1a). Orange solid. Anal. Calc.
for C33H27Cl2N2O3P2Pd: C, 53.64; H, 3.68; N, 3.79. Found: C, 54.12;
H, 3.26; N, 3.64%. Yield: 0.287 g (78%), m.p. 230–232 °C. Selected IR
absorption in KBr (cmꢀ1): 1672 (
m
C@O). 1H NMR (DMSO-d6) dH
2
(ppm): 4.71 (dd, CH2, JPH = 12.90, 13.35 Hz), 6.09 (br, CH), 7.30–
8.29 (m, 24H, Ph). 31P NMR (DMSO-d6) dP (ppm): 26.87 (bd, PPh2,
2JPP = 45.57 Hz), 37.89 (d, PCH, JPP = 45.21 Hz). 13C NMR (DMSO-
2
2
d6) dC (ppm): 33.72 (d, CH, JPC = 54.74), 121.21–150.07 (Ph),
195.71 (s, CO), (CH2, was not seen).
144 °C. Selected IR absorption in KBr (cmꢀ1): 1579 ( C@O). 1H
m
NMR (CDCl3) dH (ppm): 2.17 (m, 2H, CH2), 2.77 (m, 2H, CH2),
2.3.2.4. Data for [(Y4)PdCl2] (4a). This compound was prepared by a
similar procedure to that of complex (1a). Yellow solid. Anal. Calc.
for C34H30Cl2O2P2Pd: C, 57.53; H, 4.26. Found: C, 57.89; H, 4.17%.
Yield: 0.284 g (80%), m.p. 270–272 °C. Selected IR absorption in
4.17 (br, 1H, CH), 7.32–7.84 (m, 24H, Ph). 31P NMR (CDCl3) dP
3
(ppm): ꢀ15.13 (d, PPh2, JPP = 46.13 Hz), 14.58 (d, PCH,
3JPP = 46.48 Hz). 13C NMR (CDCl3) dC (ppm): 20.53 (br, CH2), 47.37
1
(d, CH, JPC = 110.56 Hz), 126.05–139.56 (Ph), 183.91 (s, CO).
KBr (cmꢀ1): 1595 ( C@O). 1H NMR (DMSO-d6) dH (ppm): 3.79 (s,
m
CH3), 4.79 (b, CH2), 5.85 (br, CH), 6.86–8.29 (m, 24H, Ph). 31P
2
2.3.1.4. Data for [Ph2P(CH2)2PPh2C(H)C(O)C6H4Br] (Y6). The title
compound was prepared by a similar procedure to that of ligand
(Y5). White solid. Anal. Calc. for C34H29BrOP2: C, 68.58; H, 4.91.
Found: C, 68.10; H, 4.75%. Yield: 0.224 g (75%), m.p. 137–139 °C.
NMR (DMSO-d6) dP (ppm): 27.15 (bd, PPh2, JPP = 49.42 Hz), 38.27
2
(d, PCH, JPP = 48.37 Hz). 13C NMR (DMSO-d6) dC (ppm): 22.54 (b,
CH2), 32.83 (b, CH), 55.99 (s, CH3), 113.51–134.21 (Ph), 163.60 (s,
COPh (i)), 195.63 (s, CO), (CH2, was not seen).
Selected IR absorption in KBr (cmꢀ1): 1579 ( C@O). 1H NMR (CDCl3)
m
dH (ppm): 2.25 (m, 2H, CH2), 2.83 (m, 2H, CH2), 4.18 (br, 1H, CH),
2.3.2.5. Data for [(Y5)PdCl2] (1b). This compound was prepared by a
similar procedure to that of complex (1a). Yellow solid. Anal. Calc.
for C34H29Cl3OP2Pd: C, 56.07; H, 4.01. Found: C, 55.65; H, 4.32%.
Yield: 0.289 g (79%), m.p. 208–210 °C. Selected IR absorption in
7.07–7.86 (m, 24H, Ph). 31P NMR (CDCl3) dP(ppm): ꢀ15.17 (d,
3
3
PPh2, JPP = 46.34 Hz), 14.55 (d, PCH, JPP = 48.26 Hz). 13C NMR
1
(CDCl3) dC (ppm): 20.52 (br, CH2), 47.14 (d, CH, JPC = 113.50 Hz),
123.77–139.80 (Ph), 183.95 (s, CO).
KBr (cmꢀ1): 1624 ( C@O). 1H NMR (DMSO-d6) dH (ppm): 2.28 (b,
m
CH2, 2H merged with DMSO), 3.90 (m, CH2, 2H merged with resid-
2.3.1.5. Data for [Ph2P(CH2)2PPh2C(H)C(O)C6H4OCH3] (Y8). The title
compound was prepared by a similar procedure to that of ligand
(Y5). White solid. Anal. Calc. for C35H32O2P2: C, 76.91; H, 5.90.
Found: C, 77.03; H, 5.85%. Yield: 0.224 g (82%), m.p. 129–131 °C.
ual H2O), 6.15 (b, CH), 7.37–8.46 (m, 24H, Ph). 31P NMR (DMSO-d6)
2
dP (ppm): 22.82 (d, PCH, JPP = 23.46 Hz), 29.95 (b, PPh2). 13C NMR
(DMSO-d6) dC (ppm): 19.93 (b, CH2), 123.59–138.11 (Ph), 195.01 (s,
CO), (CH2, was not seen).
Selected IR absorption in KBr (cmꢀ1): 1603 ( C@O). 1H NMR (CDCl3)
m
dH (ppm): 2.27 (m, 2H, CH2), 2.87 (m, 2H, CH2), 3.84 (s, 3H, CH3),
2.3.2.6. Data for [(Y6)PdCl2] (2b). This compound was prepared by a
similar procedure to that of complex (1a). Yellow solid. Anal. Calc.
for C34H29BrCl2OP2Pd: C, 52.84; H, 3.78. Found: C, 52.46; H, 3.66%.
Yield: 0.321 g (83%), m.p. 214–216 °C. Selected IR absorption in KBr
1
4.18 (d, 1H, CH, JPH = 18.09 Hz), 6.86–8.01 (m, 24H, Ph). 31P NMR
3
(CDCl3) dP (ppm): ꢀ15.15 (d, PPh2, JPP = 47.53 Hz), 14.33 (d, PCH,
3JPP = 47.42 Hz). 13C NMR (CDCl3) dC (ppm): 20.80 (br, CH2), 46.28
1
(d, CH, JPC = 113.51 Hz), 113.10–137.37 (Ph), 160.84 (s, COPh (i)),
(cmꢀ1): 1625 ( C@O). 1H NMR (DMSO-d6) dH (ppm): 2.29 (b, CH2, 2H
m
185.04 (s, CO).
merged with DMSO), 3.90 (b, CH2, 2H merged with residual H2O),
6.16 (b, CH), 7.53–8.42 (m, 24H, Ph). 31P NMR (DMSO-d6) dP
(ppm): 22.77 (d, PCH, 2JPP = 21.97 Hz), 30.15 (bd, PPh2,
2JPP = 23.85 Hz). 13C NMR (DMSO-d6) dC (ppm): 19.46 (b, CH2),
122.96–137.32 (Ph), 19.16 (s, CO), (CH2, was not seen).
2.3.2. Synthesis of Pd(II) halide complexes
2.3.2.1. Synthesis of [(Y1)PdCl2] (1a) general procedure. To
[PdCl2(COD)] (0.142 g, 0.5 mmol) dichloromethane solution
(5 ml), a solution of Y1 (0.268 g, 0.5 mmol) (5 ml, CH2Cl2) was
added dropwise. The resulting solution was stirred for 1 h at room
temperature and then concentrated to a ca. 2 ml in volume and
a
2.3.2.7. Data for [(Y7)PdCl2] (3b). This compound was prepared by a
similar procedure to that of complex (1a). Orange solid. Anal. Calc.

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S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3973–3980
for C34H29Cl2NO3P2Pd: C, 55.27; H, 3.96; N, 1.90. Found: C, 55.83;
2.3.2.8. Data for [(Y8)PdCl2] (4b). This compound was prepared by a
similar procedure to that of complex (1a). Yellow solid. Anal. Calc.
for C35H32Cl2O2P2Pd: C, 58.07; H, 4.46. Found: C, 57.74; H, 4.15%.
Yield: 0.297 g (82%), m.p. 197–199 °C. Selected IR absorption in
H, 3.71; N, 1.73%. Yield: 0.326 g (77%), m.p. 190–192 °C. Selected
IR absorption in KBr (cmꢀ1): 1631 ( C@O). 1H NMR (DMSO-d6) dH
m
(ppm): 2.29 (b, CH2, 2H merged with DMSO), 3.90 (b, CH2, 2H
merged with residual H2O), 6.26 (b, CH), 7.58–8.51 (m, 24H, Ph).
KBr (cmꢀ1): 1622 ( C@O). 1H NMR (DMSO-d6) dH (ppm): 2.29 (b,
m
2
31P NMR (DMSO-d6) dP (ppm): 22.59 (d, PCH, JPP = 22.73 Hz),
CH2, 2H merged with DMSO), 3.90 (b, CH2, 2H merged with resid-
2
30.42 (bd, PPh2, JPP = 23.17 Hz). 13C NMR (DMSO-d6) dC (ppm):
ual H2O), 3.80 (s, 3H, CH3), 6.09 (b, CH), 6.83–8.49 (m, 24H, Ph). 31
P
2
19.73 (b, CH2), 123.39–149.90 (Ph), 194.62 (s, CO), (CH2, was not
seen).
NMR (DMSO-d6) dP (ppm): 22.78 (d, PCH, JPP = 22.80 Hz), 30.13
2
(bd, PPh2, JPP = 24.36 Hz). 13C NMR (DMSO-d6) dC (ppm): 19.68
PPh2
n = 1
CH
C
O
R
Ph2P
Pd
(1a): R = Cl
(2a): R = Br
(3a): R = NO2
(4a): R = OCH3
Cl
Cl
CH
Ph2P
Ph2P
C
O
R
+
- COD
n(H2C)
PdCl2(COD)
PPh2
CH
n = 2
R
C
Ph2P
Pd
(1b): R = Cl
(2b): R = Br
O
Cl
Cl
(3b): R = NO2
(4b): R = OCH3
Scheme 1. Synthetic route for preparation of Pd(II) complexes.
Fig. 1. ORTEP view of X-ray crystal structure of 1b. Hydrogen atoms and DMSO molecule are omitted for clarity.

S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3973–3980
3977
(b, CH2), 55.95 (s, CH3), 113.56–134.22 (Ph), 163.41 (s, COPh (i)),
194.87 (s, CO), (CH2, was not seen).
The 31P chemical shift values for the complexes appear to be
shifted downfield with respect to the parent ylide, also indicating
that coordination of the ylide has occurred. In the 31P NMR spectra
(DMSO-d6) the signal due to PCH appears as a broad doublet. The
significant downfield shift of this signal from that of the free ylide
is in agreement with the C-bonding of the ylides. The coordination
via the phosphine moiety is also clearly evidenced from the strong
downfield shifts of the signal due to PPh2 group when compared to
that of the same signal in the free ylides [13,14].
3. Results and discussion
3.1. Synthesis
The reactions of [PdCl2(COD)] with the non-symmetric phos-
phorus ylides Y1–Y8 in dichloromethane in a 1:1 molar ratio, at
room temperature afforded, in all cases the P–C chelated com-
plexes (see Scheme 1). These species being fairly soluble in haloge-
nated solvents such as dichloromethane and chloroform but
insoluble in non-polar solvents such as n-hexane.
In the 1H NMR spectra, the signals due to the methynic protons
for complexes are broad. Similar behavior was observed earlier in
the case of ylide complexes derived from PtCl2 [27]. The expected
lower shielding of both the 31P and 1H nuclei for the PC(H) group
upon complexation in the case of C-coordination was observed in
their corresponding spectra.
The most interesting features of the 13C spectra of the series of
complexes is the up-field shift of the signals due to the ylidic car-
bon. This up-field shift has been previously observed in the series
3.2. Spectroscopy
of compounds [PdCl (g
3-2-XC3H4) (C6H5)3PCHCOR] [X = H, CH3;
The
1500 cmꢀ1 in the parent ylides [24,25]. Coordination of the ylide
through carbon causes an increase in the (CO), while, when O-
coordination occurs, a lowering in the value of the (CO) would
m(CO), which is sensitive to complexation, occurs around
R = CH3, C6H5] and attributed to the change in hybridization of
the ylidic carbon [28]. Similar up-field shifts of about 2–3 ppm
with reference to the parent ylide have also been observed in the
case of the mercury derivative [(C6H5)3PC5H4HgI2]2 [29]. In this
case, the 13C shifts of the CO group in the complexes were found
around 190 ppm, compare to 180 ppm for the same carbon in the
m
m
be expected [26]. Thus the IR absorption bands for the complexes
at higher frequencies indicate that C-coordination has occurred
[13].
Fig. 2. ORTEP view of X-ray crystal structure of 4b. Hydrogen atoms and DMSO molecule are omitted for clarity.

3978
S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3973–3980
Table 1
Table 2
Crystal data and structure refinement for 1b and 4b.
Selected bond distances (Å) and angles (°) for 1b and 4b.
Compound
1b
4b
1b
4b
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
36H39Cl3O4P2PdS
C72H70Cl4O5P2Pd2S
1525.82
298(2)
Bond distances
Pd(1)–C(2)
Pd(1)–P(2)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
O(1)–C(1)
P(1)–C(2)
842.42
298(2)
0.71073
Monoclinic
P21/c
10.7800(10)
20.7278(19)
16.7468(15)
90
2.400(3)
2.2326(8)
2.3899(8)
2.3575(8)
1.219(3)
1.790(3)
1.828(3)
1.505(4)
2.114(3)
2.2207(11)
2.4080(11)
2.3450(11)
1.224(4)
1.784(4)
1.824(4)
0.71073
Triclinic
ꢀ
P1
12.1685(15)
16.705(2)
18.750(2)
67.081(2)
89.597(2)
85.940(2)
2
P(2)–C(4)
C(2)–C(1)
b (Å)
c (Å)
1.506(5)
a
(°)
Bond angles
b (°)
100.265(2)
90
4
C(2)–Pd(1)–P(2)
C(2)–Pd(1)–Cl(2)
P(2)–Pd(1)–Cl(2)
C(2)–Pd(1)–Cl(1)
P(2)–Pd(1)–Cl(1)
Cl(1)–Pd(1)–Cl(2)
93.25(8)
174.13(8)
89.12(3)
88.25(8)
176.74(3)
89.67(3)
94.52(11)
168.06(11)
88.17(4)
88.71(11)
168.04(4)
91.03(4)
c
(°)
Z
Absorption coefficient
0.903
0.836
(mmꢀ1
)
h Range for data collection (°) 1.58–25.36
Index ranges
1.68–25.33
ꢀ12 6 h 6 12
ꢀ24 6 k 6 24
ꢀ20 6 l 6 20
30105
6723 [Rint = 0.0534]
Integration
ꢀ14 6 h 6 14
ꢀ20 6 k 6 20
ꢀ22 6 l 6 22
29172
12760 [Rint = 0.0541]
Analytical
Reflections collected
Independent reflections
Absorption correction
Maximum and minimum
transmission
structures are shown in Figs. 1 and 2, respectively. Relevant param-
eters concerning data collection and refinement are given in Table
1 and selected bond distances and angles are collected in Table 2.
Fractional atomic coordinates and equivalent isotropic displace-
ment coefficients (Ueq) for the non-hydrogen atoms of the com-
plexes are available as Supplementary material.
0.8957 and 0.7850
0.9390 and 0.7619
Refinement method
Full-matrix least-
squares on F2
0.928
Full-matrix least-
squares on F2
0.886
Goodness-of-fit on F2
The X-ray analysis confirms unequivocally the P–C chelate
mode of coordination of the ligands, Ph2P(CH2)nPPh2C(H)-
C(O)C6H4R to the Pd atom in complexes 1b and 4b. The Pd atom
is surrounded by one P atom of the phosphine group, one ylidic
carbon and two chlorine atoms leading to a slightly distorted
square-planar geometry around the metal. The angles subtended
by the ligand at the Pd(II) centre in 1b vary from 88.25(8)° to
93.25(8)° (sum of the angles is 360.29) and 174.13(8)° to
176.74(3)° indicating the distortion from the square-planar envi-
ronment, whereas in 4b vary from 88.17(4)° to 94.52(11)° (sum
of the angles is 362.43) and 168.04(4)° to 168.06(11)° indicating
an even much distorted square-planar environment.
Final R indices [I > 2
r
(I)]
R1 = 0.0343,
wR2 = 0.0736
R1 = 0.0472,
wR2 = 0.0772
0.614 and ꢀ0.346
R1 = 0.0431,
wR2 = 0.0764
R1 = 0.0683,
wR2 = 0.0820
0.685 and ꢀ0.387
R indices (all data)
Largest difference in peak
and hole (e Åꢀ3
)
parent free ylides, indicating a much lower shielding of the carbon
of the CO group in these complexes. Thus, the spectral data indi-
cate the bidentate coordination of the ylides through both the
phosphine group and the ylidic carbon atom.
The two Pd–Cl distances in 1b (2.389(8) and 2.357(8) Å) and in
4b (2.4080(11) and 2.345(11) Å) are different, probably reflecting
slightly different trans effect of the phosphorus and ylidic carbon
atom. The Pd–C(ylide) bond lengths in these complexes
(2.100(3) Å (1b) and 2.114(3) (4b) Å) are similar to that found in
3.3. X-ray crystallography
Complexes 1b and 4b were recrystallized by slow evaporation
over several days from dimethylsulfoxide solutions. The molecular
15
18
AL4
5
-5
13
-15
AL3
-25
8
-1.9
-0.9
0.1
1.1
2.1
E/V vs. Ag wire
AL2
3
-2
AL1
CL1
-7
Starting Potential
-12
-17
-1.6
-1.1
-0.6
-0.1
0.4
0.9
1.4
1.9
E/V vs. Ag wire
Fig. 3. Cyclic voltammogram of 1 mM of Y1 in dichloromethane, containing 0.1 M tetra-n-butylammonium perchlorate (Bu4NClO4) as supporting electrolyte, at Pt electrode.
Sweeping direction: reduction of Y1 at the first stage and oxidation at the second stage. Scan rate: 100 mV sꢀ1; t = 25 °C. Vectors, show sweeping direction. Inset: cyclic
voltammogram of background at the same conditions.

S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3973–3980
3979
20
10
0
CL1
Starting Potential
-10
-20
-30
CM1
-1.6
-1.1
-0.6
-0.1
0.4
0.9
1.4
1.9
E/V vs. Ag wire
Fig. 4. Cyclic voltammogram of 1 mM of complex 2a in dichloromethane, containing 0.1 M tetra-n-butylammonium perchlorate (Bu4NClO4) as supporting electrolyte, at Pt
electrode. Sweeping direction: reduction of complex at the first stage and oxidation at the second stage. Scan rate: 100 mV sꢀ1; t = 25 °C.
[PdCl2{PPh2C(H)C(O)CH2PPh2C(H)}] (2.099(6) and 2.104(6) Å) [17].
The Pd(1)–P(2) bond lengths in 1b [2.232(8) Å] and in 4b
[2.220(11) Å] are comparable to analogous distances in diphos-
phine palladium complexes such as [PdCl2(dppe)] (dppe =
1,2-(diphenylphosphino)ethane)) [30], [PdCl2 (dppb)] (dppb = 1,4-
(diphenylphosphino)butane) [31].
The stabilized resonance structure for the parent ylide is de-
stroyed by the complex formation, thus the C(1)–C(2) bond length
in 1b (1.478(8) Å) and 4b (1.478(8) Å) are significantly longer than
the corresponding distance found in the similar non-coordinated
phosphoranes (1.404(3) Å [13] and 1.401(2) Å [32]). Likewise the
C(2)–P(1) bond length in a similar ylide is 1.705(2) Å [13], which
shows that the corresponding bond in 1b and 4b are considerably
elongated to 1.790(3) Å and 1.784(4) Å, respectively.
There are some examples of stable Pd(0) complexes; particularly
relevant is [Pd(L)2]0 (L = 1,2-bis(dimethylarsino)benzene), which
is adequately stable to be isolated as the solid [38]. These electro-
chemical data reconfirm complex formation between Pd(II) and Y1
and showed the presence of Pd(II) in complex 2a.
The overall two-electron reduction of the Pd(II) complexes is
expected to take place in separate one-electron steps [33–35]
and this might be achieved via manipulation of the thermodynam-
ics or electrode kinetics of one or both steps by correct choice of
the experimental conditions. In our experimental conditions,
Pd(I)-complex is unstable with respect to disproportionate [35].
Thus peak CM1 in Fig. 4 corresponds to a two-electron reduction
of Pd(II)-complex which is the consequence of the thermodynamic
instability of the intermediate one electron product in our experi-
mental conditions (Eq. (1)).
3.4. Electrochemical studies
2PdðIÞ ! PdðIIÞ þ Pdð0Þ
ð1Þ
The electrochemical behavior of Y1 and its Pd(II) complex, 2a,
was studied by cyclic voltammetry. Fig. 3 shows the cyclic voltam-
mogram obtained for 1 mM Y1 in dichloromethane, containing
0.2 M tetra-n-butylammonium perchlorate (Bu4NClO4) as support-
ing electrolyte recorded with a platinum electrode when reduction
of Y1 occurs at first stage. At this condition, voltammogram exhibit
a reduction peak CL1 and four anodic peaks (AL1, AL2, AL3 and AL4).
In addition, another anodic peak observed at ꢀ1.24 V which also
observed in cyclic voltammogram of background (dichlorometh-
ane/Bu4NClO4) (see Fig. 3).
The cyclic voltammogram of 1 mM solution of complex
[(Y1)PdCl2], in the same condition, showed that the electron trans-
fer was irreversible. At a scan rate of 100 mV/s, there was two
cathodic peaks, CL1, corresponding to the reduction of Y1 and CM1
at ꢀ1.08 V versus Ag wire, corresponding to the redox pair Pd(II)/
Pd(0). There is no anodic peak(s) observed on the reverse scan. This
behavior is similar to that reported previously by Champness et al.
[33], Batchelor et al. [34] and Downard et al. [35] in cyclic voltam-
metric study of various types of Pd(II)-complexes in aprotic sol-
vents. This irreversibility may be due to the reaction of a Pd(0)
complex with adventitious O2 or other components of the solution
[35].
4. Conclusion
The present study describes the very simple and efficient syn-
thesis and characterization of a series of P–C chelate Pd(II) com-
plexes. On the basis of the physicochemical and spectroscopic
data we have proposed that ligands employed herein exhibit a che-
late P–C coordination behavior to the metal center affording a five
or six-membered chelate rings. This coordination fashion has been
further confirmed by single crystal X-ray diffraction experiments
of complexes 1b and 4b. Additionally, electrochemical results
show the unstabilities of the Pd(I) and Pd(0) complexes which
are largely affected by the nature of ligand, solvent-impurities,
temperature and/or supporting electrolyte, whereas the divalent
complex will be relatively stabilized under the experimental condi-
tions employed.
Acknowledgements
We are highly grateful to Mr. Zebarjadian and Darvishi for
recording the NMR spectra. The authors thank Ms. R. Esmaili and
Mr. R. Farhadi for their invaluable support in electrochemistry
experiments. Ali Naghipour would like to thank ILAM University
Peak CM1 at ꢀ1.08 V versus Ag wire, can be assigned to the for-
mation of a Pd(0) center with coordination number between 2 and
4 (or to an equilibrium mixture of several Pd(0) species) [35–37].

3980
S.J. Sabounchei et al. / Inorganica Chimica Acta 363 (2010) 3973–3980
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Appendix A. Supplementary material
CCDC 754889 and 753846 contains the supplementary crystal-
lographic data for complexes 1b and 4b. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2010.07.072.
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