Palladium complexes with some phosphorus-sulfur ligands

Article abstract of DOI:10.1080/15533170600862432

The phosphorus-sulfur asymmetric ligands 2-(2-diphenylphosphinoethyl)- thiophene (P-S2), 2-(3-diphenylphosphinopropyl)thiophene (P-S3), and [2-[(methyl-thio)methyl]phenyl]diphenylbenzene (P-SM) have been synthesized and characterized by IR, ¹H-NMR, and ¹³C-NMR spectroscopy. Reaction of P-S2, P-S3 or P-SM with equimolar amount of dichlorobis(benzonitrile)palladium(II), [Pd(PhCN)Cl₂], gave the complexes [Pd(P-S2)Cl₂], [Pd(P-SM)Cl₂] and [Pd(P-S3)(μ-Cl)Cl]₂, respectively. However, reaction of P-S2 with [Pd(PhCN)Cl₂] in a molar ratio of 2:1 afforded the complex [Pd(P-S2)₂Cl₂]. The above complexes were characterized by microelemental analysis, IR, ¹H-NMR and ¹³C-NMR. Copyright

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Palladium Complexes with Some Phosphorus‐Sulfur
Ligands
Khalifah A. Salmeia a & Hamdallah A. Hodali a
a Department of Chemistry , University of Jordan , Amman, Jordan
Published online: 15 Feb 2007.
To cite this article: Khalifah A. Salmeia & Hamdallah A. Hodali (2006) Palladium Complexes with Some Phosphorus‐Sulfur
Ligands, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 36:7, 535-541
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Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 36:535–541, 2006
Copyright # 2006 Taylor & Francis Group, LLC
ISSN: 0094-5714 print/1532-2440 online
DOI: 10.1080/15533170600862432
Palladium Complexes with Some Phosphorus-Sulfur Ligands
Khalifah A. Salmeia and Hamdallah A. Hodali
Department of Chemistry, University of Jordan, Amman, Jordan
encourages the preparation of more ligands containing phos-
The phosphorus-sulfur asymmetric ligands 2-(2-diphenylphos- phorus and thiophene[5,11] and the use of their metal complexes
in variety of catalytic systems.[12,13] Herein, we report on the
preparation of palladium complexes with 2-[2-(diphenylpho-
phinoethyl)-thiophene (P-S2), 2-(3-diphenylphosphinopropyl)thio-
phene (P-S3), and [2-[(methyl-thio)methyl]phenyl]diphenylbenzene
1
(P-SM) have been synthesized and characterized by IR, H-NMR,
sphino)ethyl]thiophene (P-S2), 2-[3-(diphenylphosphino)pro-
pyl]thiophene (P-S3), and [2-[(methylthio)methyl]phenyl]
and 13C-NMR spectroscopy. Reaction of P-S2, P-S3 or P-SM with
equimolar amount of dichlorobis(benzonitrile)palladium(II),
[Pd(PhCN)Cl2], gave the complexes [Pd(P-S2)Cl2], [Pd(P-SM)Cl2] diphenylphosphine (P-SM). The complexes, [Pd(P-S2)nCl2]
(n ¼ 1, 2), [Pd(P-S3)(m-Cl)Cl]2, and [Pd(P-SM)Cl2] have
and [Pd(P-S3)(m-Cl)Cl]2, respectively. However, reaction of P-S2
with [Pd(PhCN)Cl2] in a molar ratio of 2:1 afforded the complex
[Pd(P-S2)2Cl2]. The above complexes were characterized by micro-
elemental analysis, IR, 1H-NMR and 13C-NMR.
been prepared and fully characterized by their microanaly
1
tical analysis, IR, H-NMR, and 13C-NMR spectroscopy.
EXPERIMENTAL
Keywords palladium complexes, phosphorus-sulfur ligands, asym-
All procedures were performed under an atmosphere of dry,
metric ligands, bidentate ligands
purified nitrogen using standard Schlenk techniques. Solvents
were distilled and dried by standard methods.[14] Thiophene,
1-bromo-3-chloropropane, thionyl chloride, 2-bromobenzyl
bromide, were purchased from Across. n-Butyllithium
INTRODUCTION
(1.55 M solution in hexane) and methanethiol were purchased
The asymmetric ligands (also called mixed-donor or hemi-
labile ligands) in general, and those withphosphorus and
sulfur donor centers, have received wide spread attention.[1,2]
On one hand, the phosphorus atom in this type of ligands
tends to stabilize metal ions in low oxidation state through its
effective p-back bonding,[3,4] and on the other hand, the
sulfur atom is weakly coordinated to the metal center and
thus facilitates the formation of a vacant coordination site.[5]
The combined effect of phosphorus and sulfur donor atoms
seems to be essential in homogeneous catalysis, since it stabil-
izes the catalytic intermediates in solution and allows organic
substrates to enter into the coordination sphere of the
metal.[6,7] Many palladium complexes with phosphino-
thioether ligands have been utilized in catalytic processes,
such as in photochemical carbonylation of benzene,[8]
polymerization of norbornene,[9] and arylation of olefin.[2,10]
Recently, asymmetric phosphorus-sulfur ligands involving
thiophene have been prepared and characterized.[5] The rela-
tively weak donor ability of the sulfur atom of thiophene
from Aldrich. Potassium diphenylphosphide (0.5 M solution in
THF) and palladium(II) chloride were purchased from Fluka.
Ethylene oxide was purchased from BDH. Benzonitrile was
purchased from Wardle Chemicals. Chlorodiphenylphosphine
was
purchased
from
PFALTZ
&
BAUER.
[PdCl2(PhCN)2][15] 2-(2-thienyl)ethanol,[16] 2-(3-chloropro-
pyl)thiophene,[11] and 2-bromo-1-[(methylthio)methyl]ben-
zene[17] were prepared following literature procedure. The IR
Spectra were recorded, as KBr discs, on a Nicolet Impact-
400 FT-IR spectrometer. The NMR spectra were recorded on
a Bruker DPX 300 MHz spectrometer using TMS as internal
reference. Melting points were determined with a Philip-
Harris melting point apparatus and are uncorrected. Microana-
lyses were performed by the Microanalytical Laboratories of
AL al-Bayt University, Jordan.
Preparation of Ligands
Preparation of 2-[2-(diphenylphosphino)ethyl]thiophene
(P-S2)
The above ligand was synthesized via the reaction of 2-(2-
chloroethyl)thiophene with potassium diphenylphosphide.
2-(2-chloroethyl)thiophene was prepared from 2-(2-thienyl)
ethanol[16] as in the following: A solution of 2-(2-thienyl)etha-
nol (10 g, 78 mmol) in dry benzene (50 mL) was introduced
Received 13 February, 2006; accepted 29 April, 2006.
Address correspondence to Hamdallah A. Hodali, Department of
Chemistry, University of Jordan, Amman 11942, Jordan. E-mail:
h-hodali@ju.edu.jo.
535

536
K. A. SALMEIA AND H. A. HODALI
into A 250 mL three-necked, round-bottomed flask equipped Preparation of [2-[(methylthio)methyl]phenyl]diphenylphosphine
with a nitrogen inlet, dropping funnel, and a condenser con- (P-SM)
nected to an oil bubbler. a solution of thionyl chloride
(11.4 mL, 156 mmol) in dry benzene (50 mL) was then
slowly added at 08C. After addition was complete
(ꢀ30 min), the solution was stirred at room temperature for
15 min, and then heated for 3 h at (50–608C). The solvent
was removed under reduced pressure, and the black residue
was vacuum distilled. The product was collected at 668C
and 7 mmHg as a pale yellow oil. Yield: 7.1 g (62%).
A
solution of 2-bromo-1-[(methylthio)methyl]benzene
(21.7 g, 0.1 mol) in dry diethyl ether (50 mL) was introduced
into a 250 mL three-necked, round-bottom flask equipped
with a nitrogen inlet, and a condenser connected to an oil
bubbler. The solution was cooled to 2658C and then a
solution of n-butyllithium (65 mL of 1.55 M) was slowly
added. After the addition was completed, the cooling bath
was removed, and the solution was stirred at room tempera-
ture for 4 h. Then, a solution of chlorodiphenylphosphine
(17.95 mL, 0.1 mol) in dry diethyl ether (20 mL) was
slowly added at 08C. After the addition was complete, the
reaction mixture was allowed to warm up to room tempera-
ture, and then refluxed for 1 h. Solvent was removed under
reduced pressure, and the residue was dissolved in diethyl
ether (100 mL). The ether solution was washed with distilled
water (2 ꢀ 100 mL). The ether layer was then dried over
anhydrous sodium sulfate over night. Ether was removed
from the filtrate under reduced pressure and the residue
was vacuum distilled. The product was collected at 2108C
and 5 mmHg as a pale yellow viscous oil. Yield: 13.0 g
(40%).
Preparation of (P-S2)
A solution of 2-(2-chloroethyl)thiophene (7.3 g, 0.05 mol)
in dry THF (50 mL) was introduced into a 250 mL three-
necked, round-bottomed flask equipped with a nitrogen inlet,
dropping funnel, and a condenser connected to an oil
bubbler. A solution of Potassium diphenylphosphide (100 mL
of 0.5 M, 0.05 mol) was then slowly added at 2458C. After
the addition was complete, the cooling bath was removed,
and the reaction mixture was stirred for 2 h at room tempera-
ture. The solvent was then removed under reduced pressure.
The residue was dissolved in diethyl ether (100 mL), washed
with distilled water (2 ꢀ 100 mL). The ether layer was then
dried over anhydrous sodium sulfate overnight. After filtration,
ether was removed under reduced pressure. The thick yellow
residue was dissolved in methanol (50 mL) with vigorous
stirring. The solution was stored at 08C overnight. The white
precipitate formed was filtered, washed three times with cold
methanol, and dried under vacuum at room temperature.
Yield: 10.0 g (71%).
Preparation of the Palladium Complexes
The complexes [Pd(P-S2)Cl2] (I), [Pd(P-S3)(m-Cl)Cl]2,
(II), and [Pd(P-SM)Cl2] (III), were prepared via the following
general procedure:
A sample of ligand (1.1 mmol) in benzene (20 mL) was
slowly added to a filtered solution of [PdCl2(PhCN)2]
(1.0 mmol) in benzene (30 mL). The solution was stirred
for 1 h at room temperature. During that time, the solution
changed color gradually. Solvent was removed under reduced
Preparation of 2-[3-(diphenylphosphino)propyl]
thiophene (P-S3)
The compound was prepared following literature pro- pressure until reaching a volume of about 10 mL. Upon
cedure[11] with slight modifications. A solution of 2-(3-chloro- addition of petroleum ether (boiling range of 40–608C), a pre-
propyl)thiophene (8.0 g, 0.05 mol) in dry THF (50 mL) was cipitate was separated, washed with petroleum ether (boiling
introduced into a 250 mL three-necked, round-bottomed flask range of 40–608C) and dried under vacuum at 508C.
equipped with a nitrogen inlet, dropping funnel, and a conden-
[Pd(P-S2)Cl2] (I): Yield: 0.39 g (82%); yellowish brown
ser connected to an oil bubbler. A solution of potassium diphe- solid; m.p: 215–218 (dec). Selected IR bands (KBr
nylphosphide (100 mL of 0.5 M, 0.05 mol) was then slowly pellet, cm21): 3074(m), 3057(m), 2918(m) and 2848(m)
added at 2458C. After the addition was complete, the (nC-H); 1102(s) (nP-Ph). Calcd. for [C18H17Cl2PPdS]
cooling bath was removed, and the reaction mixture was (473.69): C, 45.64; H, 3.62; S, 6.77. Found: C, 45.92; H,
stirred for 2 h at room temperature. Solvent was then 3.46; S, 6.68%.
removed under reduced pressure. The residue was dissolved
[Pd(P-S3)(m-Cl)Cl]2 (II): Yield: 0.45 g (92%); orange
in diethyl ether (100 mL), washed with distilled water solid; m.p: 225–227 (dec). Selected IR bands (KBr pellet,
(2 ꢀ 100 mL). The ether layer was then dried over anhydrous cm21): 3056(m), 2936(m) and 2896(m) (nC-H); 1102 (s)
sodium sulfate overnight. After filtration, ether was removed (nP-Ph). Calcd. for [C38H38Cl4P2Pd2S2] (975.44): C, 46.79;
under reduced pressure. The thick yellow residue was dis- H, 3.93; S, 6.57. Found: C, 46.23; H, 3.66; S, 5.51%.
solved in methanol (50 mL) with vigorous stirring. The
[Pd(P-SM)Cl2] (III): Yield: 0.36 (72%); yellow solid; m.p:
solution was stored at 08C overnight. The white precipitate 238–240 (dec). Selected IR bands (KBr pellet, cm21):
formed was filtered, washed three times with cold methanol, 3051(m), 2953(m), 2915(m), 2848(m) and 1250(s) (nC-H);
and dried under vacuum at room temperature. Yield: 14.3 g 1098(s) (P-Ph). Calcd. for [C20H19Cl2PPdS] (499.73): C,
(92%); m.p.: 65–678C, [literature[11], 90% yield].
48.07; H, 3.83; S, 6.42. Found: C, 48.21; H, 4.08; S, 6.82%.

PALLADIUM COMPLEXES WITH P AND S LIGANDS
537
Preparation of [Pd(P-S2)2Cl2] (IV)
singlet at d ¼ 2.76 (-CH2-OH), a triplet centered at d ¼ 3.03
(-CH2CH2OH), and another triplet centered at d ¼ 3.78
(-CH2CH2OH). The 13C NMR (75 MHz, CDCl3) spectrum
shows signals at d ¼ 33.3 (s,-CH2CH2OH, 1C), 63.4
(s,-CH2OH. 1C), 124.0 (s, C3, 1C), 125.6 (s, C4, 1C), 127.1
(s, C5, 1C) and 141.0 (s, C2, 1C).
A sample of a filtered solution of [PdCl2(PhCN)2 (0.59 g,
1.5 mmol) in benzene (30 mL) was slowly added to a
solution of P-S2 (0.977 g, 3.3 mmol) in benzene (20 mL).
The mixture was stirred for 1 h at room temperature. During
that time, solution changed color gradually from red-brown
to yellow with the formation of precipitate. Solvent was
removed under reduced pressure till a volume of about
10 mL. The yellow precipitate was collected, washed with pet-
roleum ether (boiling range of 40–608C) and dried under
vacuum at 508C. Yield: 1.0 g (87%). Selected IR bands (KBr
pellet, cm21): 3077(m), 3033(m), 2929(m), 2852(m), (nC-H);
1099(s) (P-Ph). Calcd. for [C36H34Cl2P2PdS2] (770.06):
C, 56.15; H, 4.45; S, 8.33. Found: C, 55.80; H, 4.37; S,
8.27%.
In the second step, 2-(2-thienyl)ethanol was reacted with
thionyl chloride to give 2-(2-chloroethyl)thiophene. The
product was collected as pale yellow liquid by vacuum distilla-
1
tion at 668C and 7 mmHg. The H-NMR (300 MHz, CDCl3)
spectrum of the product shows, in addition to thiophene
proton signals, two triplets centered at d ¼ 3.27 (-
CH2CH2Cl), and d ¼ 3.71 (-CH2CH2Cl). Comparing the IR
spectra of 2-(2-chloroethyl)thiophene and 2-(2-thienyl)ethanol
shows a disappearance of the absorption due to nO-H. Simi-
larly, the signal at d ¼ 2.76 due to OH proton in the 1H-
NMR spectrum of 2-(2-chloroethyl)thiophene has also been
disappeared.
RESULTS AND DISCUSSION
Preparation of the Ligands
Treatment of 2-(2-chloroethyl)thiophene with potassium
diphenylphosphide in dry THF affords 2-[2-(diphenylphosphi-
no)ethyl]thiophene (P-S2). The fine white precipitate was
filtered and recrystallized three times from methanol. The
product was fully characterized by its 1H-NMR, and 13C-
NMR spectroscopy (Table 1). The 1H-NMR spectrum
(300 MHz, CDCl3) of (P-S2) shows, a multiplet at d ¼ 7.31–
7.76 for the phenyl protons, a triplet centered at d ¼ 2.45
(-CH2CH2P-), and a quartet centered at d ¼ 2.95 (-CH2P-).
The three protons of thiophene appear as: two doublets
centered (at d ¼ 6.80 and d ¼ 7.12), and a triplet at
d ¼ 6.91. The 13C-NMR spectrum (75 MHz, CDCl3) of P-S2
Preparation of 2-[2-(diphenylphosphino)ethyl]thiophene
(P-S2)
The above ligand was prepared in three steps starting from
2-lithiothiophene. In the first step, 2-(2-thienyl)ethanol was
prepared following literature procedure[16] via bubbling of
ethylene oxide through a stirred THF solution containing
n-butyllithium and thiophene at 08C (Scheme 1). 2-(2-thienyl)
1
ethanol was isolated and characterized by IR, H-NMR and
13C-NMR spectroscopy (Table 1). In addition to the thiophene
ring vibrations, the IR spectrum of 2-(2-thienyl)ethanol shows
absorption due to yOH at 3349 cm21, indicating the insertion
of ethylene oxide. The 1H-NMR (300 MHz, CDCl3)
spectrum shows, in addition to the thiophene signals, a broad
1
shows d(Caliphatic): 26.5 (d, JC-P ¼ 19.5 Hz, 1C), and 30.5
2
(d, JC-P ¼ 12.8 Hz, 1C). d(Cthiophene): 123.3 (s, 1C), 124.2
3
(s, 1C), 126.85 (s, 1C), and 145.5 (d, JC-P ¼ 14.3 Hz, 1C).
d(Cphenyl): 138.2 (d, 1JC-P ¼ 12.8 Hz, 2C), 132.8
2
3
(d, JC-P ¼ 18.8 Hz, 4C), 128.6 (d, JC-P ¼ 3.3 Hz, 4C),
and 128.7 (s, 2C). The above 13C-NMR assignment were con-
firmed by running Dept-135 experiment that shows, the disap-
pearance of the two quaternary carbons (at d ¼ 138.2 ppm and
145.5 ppm). In Comparison with 2-(2-chloroethyl)thiophene,
the IR spectrum of P-S2 shows strong absorption at
1098 cm21due to n Ph-P.
Attempts to prepare 2-(2-chloroethyl)thiophene by the
addition of 1-bromo-2-chloroethane with a solution containing
n-butyllithium and thiophene at low temperature in dry THF
were unsuccessful (Scheme 1). Under these conditions,
1
2-butylthiophene was formed as evidenced by its H-NMR
spectrum and mass spectrometry. The 1H-NMR spectrum
(300 MHz, CDCl3) shows signals at d ¼ 0.97 (3H, t,
J ¼ 7.26, -CH2CH3), 1.42 (2H, m, J ¼ 7.5, -CH2CH2CH3),
1.70 (2H, q, J ¼ 7.4, -CH2CH2CH2-), 2.85 (2H, t, J ¼ 7.76,
C4H3S-CH2CH2-), 6.80 (1H, d, J3,4 ¼ 3.36, H-3), 6.93 (1H,
dd, J3,4 ¼ 3.59, J4,5 ¼ 5.09, H-4), and 7.12 (1H, d,
J4,5 ¼ 5.13, H-5). The mass spectrum shows the molecular
peak at (140 m/z).]
SCH. 1.

538
K. A. SALMEIA AND H. A. HODALI
TABLE 1
3
1H-NMR and C-NMR data of some starting materials, ligands and Pd-complexes
Compound
1H-NMR
3C-NMR
2-(2-chloroethyl)-thiophenea
3.27 (t, J ¼7.3 Hz, 2H) 3.71 (t, J ¼ 7.3 Hz, 2H),
6.88 (d, J ¼ 3.4 Hz, 1H), 6.95 (dd, J ¼ 3.4,
5.1 Hz, 1H), 7.14 (d, J ¼ 5.1 Hz, 1H)
2.45 (t, J ¼ 8.3 Hz, 2H), 2.95 (q, J ¼ 8.2 Hz, 2H),
6.80 (d, J ¼ 3.0 Hz, 1H), 6.91 (t, J ¼ 5.0 Hz,
1H), 6.80 (d, J ¼ 5.0 Hz, 1H), 7.75–7.34
(m, 10H).
33.4 (s), 44.9 (s); 124.4 (s), 126.0 (s, 1C),
127.1 (s), 140.3 (s).
P-S2a
26.5 (d, JC-P ¼ 19.5 Hz), 30.5 (d,
1
2JC-P ¼ 12.8 Hz), 123.3 (s), 124.2 (s),
3
126.9 (s), 128.6 (d, JC-P ¼ 3.3 Hz),
2
128.7 (s), 132.8 (d, JC-P ¼ 18.8 Hz),
1
138.2 (d, JC-P ¼ 12.8 Hz), 145.5
3
(d, JC-P ¼ 14.3 Hz).
P-S3a
1.81 (m, 2H), 2.09 (m, 2H), 2.94 (t, J ¼ 13.5 Hz,
2H), 6.75 (d, J ¼ 3.1 Hz, 1H), 7.10
(d, J ¼ 5.0 Hz, 1H), 6.89 (t, J ¼ 4.2 Hz, 1H),
7.76–7.31 (m, 10H)
27.3 (d, JC-P ¼ 11.5 Hz), 28.0
2
1
(d, JC-P ¼ 17.0 Hz), 31.2
3
(d, JC-P ¼ 13.5 Hz), 123.2 (s), 124.5
(s), 126.8 (s), 144.6 (s), 138.6
1
(d, JC-P ¼ 12.5 Hz), 132.8
2
(d, JC-P ¼ 18.3 Hz), 128.5
3
(d, JC-P ¼ 6.6 Hz), and 128.6 (s).
P-SMa
1.98 (s, 3H), 3.94 (d, J ¼ 1.5 Hz,2H), 7.46–6.91
15.4 (s), 36.9 (d, 3Jc-p ¼ 24.5 Hz), 128.6
3
(m, 14H).
(d, Jc-p ¼ 6.8 Hz), 128.7 (s), 129.1
3
(s), 129.6 (d, Jc-p ¼ 4.8 Hz), 132.0
3
(d, Jc-p ¼ 9.8 Hz),133.8
2
(d, Jc-p ¼ 19.5 Hz), 134.2 (s),
1
136.2 (d, Jc-p ¼ 13.6 Hz), 136.8
1
(d, Jc-p ¼ 10.2 Hz), 142.8
2
(d, Jc-p ¼ 24.5 Hz).
b
[Pd(P-S2)Cl2] (I)
2.88 (m, 2H), 2.74 (m, 2H). 6.86 (dd, J¼ 3.4,
5.1 Hz, 1H), 7.27 (dd, J¼ 1.1, 5.1 Hz, 1H), 6.80
(m, 1H), 7.81–7.48 (m, 10H)
24.7 (s), 30.0 (d, 2JC-P ¼ 34.5 Hz), 124.6
(s), 125.3 (s), 127.4 (s), 143.6
3
(d, JC-P ¼ 19.5 Hz), 129.7 (s), 129.1
2
(d, JC-P ¼ 11.3 Hz), 133.6
3
(d, JC-P ¼ 9.8 Hz), 132.0 (s).
a
2
[Pd(P-S3)(m-Cl)Cl]2 (II)
1.89 (m, 2H), 2.50 (m, 2H), 2.87 (t, J ¼ 7.2 Hz,
2H), 6.69 (d, J ¼ 2.8 Hz, 1H), 6.87
25.9 (s), 26.5 (d, JC-P ¼ 35.9 Hz), 30.5
3
(d, JC-P ¼ 17.5 Hz), 123.5 (s), 124.9
(dd, J ¼ 3.4, 5.1 Hz, 1H), 7.07 (d, J ¼ 5.1 Hz,
1H), 7.68–7.22 (m, 20H).
(s), 126.9 (s), 143.1 (s), 127.7 (s),
2
133.3 (d, JC-P ¼ 10.2 Hz), 128.8
3
(d, JC-P ¼ 11.9 Hz), 131.4 (s).
a
2
[Pd(P-SM)Cl2] (III)
2.45 (s, 3H), 3.45 (dd, JH-H¼ 13.6 Hz,
21.9 (s), 36.7 (d, 3Jc-p ¼ 11.4 Hz); 124.3
4JP-H¼ 2.7 Hz, 1H), 3.68 (dd, 2JH-H¼ 13.6 Hz,
4JP-H¼ 6.3 Hz, 1H), 6.79–7.72 (m, 14H).
(d, Jc-p ¼ 49.1 Hz), 125.1
1
1
(d, Jc-p ¼ 42.3 Hz), 125.9 (d,
1Jc-p ¼ 46.6 Hz), 128.9
2
(d, Jc-p ¼ 12.5 Hz), 129.3
3
(d, Jc-p ¼ 11.8 Hz), 130.0
3
(d, Jc-p ¼ 8.6 Hz), 132.3 (s), 134.7
2
(d, Jc-p ¼ 11.8 Hz, 4C), 134.9 (s),
2
137.7 (d, Jc-p ¼ 12.2 Hz),
132.3–132.6 (m).
1
aCDCl3 was used as a solvent for both H NMR (300 MHz) and 13C NMR (75 MHz).
1
bDMSO-d6 was used as a solvent for both H NMR (300 MHz) and 13C NMR (75 MHz).

PALLADIUM COMPLEXES WITH P AND S LIGANDS
539
Preparation of 2-[3-(diphenylphosphino)propyl]thiophene
(P-S3)
methyl]benzene was prepared via reaction of o-bromobenzyl
bromide with sodium methylsulfide solution in dry
ethanol.[17] The colorless, oily product was purified by
vacuum distillation at 108–1108C and 5 mmHg. The 1H-
NMR (300 MHz, CDCl3) spectrum of 2-bromo-1-
[(methylthio)methyl]benzene shows, a singlet at d ¼ 2.04
(-SCH3), a singlet at d ¼ 3.79 (ArCH2S-). The four protons
of the phenyl ring appear as: a two triplet centered (at
d ¼ 7.09 and d ¼ 7.25 ppm), and two doublets centered (at
d ¼ 7.33 and 7.55 ppm). The 13C NMR (75 MHz, CDCl3)
shows d(C aliphatic): 15.2 (s, 1C, -SCH3), 38.5 (s, 1C,
PhCH2S-); d(Cphenyl): 124.6 (s, 1C), 127.4 (s, 1C), 128.6
(s, 1C), 130.8 (s, 1C), 133.2 (s, 1C), 137.6 (s, 1C). Reaction
of 2-bromo-1-[(methylthio)methyl]benzene with n-butyl-
lithium followed by reaction with chlorodiphenylphosphine
affords a pale yellow viscous oil. A pure sample of ligand
(P-SM) was obtained by repeated vacuum distillation at
2108C and 5 mmHg.[18] The product was fully characterized
This ligand was prepared by the reaction of 1-bromo-3-
chloropropane with a solution containing n-butyllithium and
thiophene in dry THF[11] (Scheme 2). Then 2-(3-chloropro-
pyl)thiophene was collected as a pale yellow viscous liquid
and used without further purification. The 1H-NMR
(300 MHz, CDCl3) spectrum of this derivative shows, in
addition to the thiophene signals, a quintet centered at
d ¼ 2.12 (-CH2CH2CH2Cl), a triplet centered at d ¼ 3.02
(-CH2CH2CH2Cl), and
a
triplet centered at d ¼ 3.57
(-CH2Cl). The 13C NMR (75 MHz, CDCl3) shows d(Caliphatic):
26.9 (s, -CH2CH2CH2Cl), 34.3 (s, -CH2CH2CH2Cl), 43.9 (s,
-CH2CH2CH2Cl); d(Cthiophene): 123.5 (s, C3, 1C), 124.9
(s, C4, 1C), 126.9 (s, C5, 1C), 143.2 (s, C2, 1C). Treatment of
2-(3-chloropropyl)thiophene with potassium diphenylpho-
sphide in dry THF afforded the P-S3 ligand. The product was
collected and recrystallized several times from methanol. The
by H-NMR, and 13C-NMR spectroscopy (Table 1). The H-
NMR spectrum (300 MHz, CDCl3) of P-SM shows, in
addition to the phenyl protons signals (at d ¼ 6.91–
7.46 ppm), a singlet at d ¼ 1.98 (-SCH3), and a doublet
centered at d ¼ 3.94 (-CH2SCH3), which appeared due to
phosphorus-hydrogen coupling (J ¼ 1.5 Hz). The 13C-NMR
1
1
1
P-S3 ligand was fully characterized by its IR, H-NMR, and
1
13C-NMR spectroscopy. The H-NMR spectrum (300 MHz,
CDCl3) of P-S3 shows, in addition to the phenyl proton
signals, a multiplet centered at d ¼ 1.81 (-CH2CH2CH2P-), a
multiplet centered at d ¼ 2.09 (-CH2P-), and a triplet centered
at d ¼ 2.94 (-CH2CH2CH2P-). The three protons of thiophene
appear as: two doublets centered (at d ¼ 6.75, and d ¼ 7.10),
and a triplet centered (at d ¼ 6.89). The 13C-NMR spectrum
(75 MHz, CDCl3) of P-S3 shows d(Caliphatic): 28.0
spectrum (75 MHz, CDCl3) of P-SM shows signals at
3
D(Caliphatic): 15.4 (s, S-CH3, 1C), and 36.9 (d, Jc-p
¼
3
24.5 Hz, PhCH2–, 1C); d(Cphenyl): 128.6 (d, Jc-p ¼ 6.8 Hz,
3
1
2
1C), 128.7 (s, 1C), 129.1 (s, 2C), 129.6 (d, Jc-p ¼ 4.8 Hz,
(d, JC-P ¼ 17.0 Hz, 1C), 27.3 (d, JC-P ¼ 11.5 Hz, 1C), and
3
2
3
1C), 132.0 (d, Jc-p ¼ 9.8 Hz, 4C), 133.8 (d, Jc-p ¼ 19.5 Hz,
31.2 (d, JC-P ¼ 13.5 Hz, 1C); d(Cthiophene): 123.2 (s, 1C),
1
4C), 134.2 (s, 1C), 136.2 (d, Jc-p ¼ 13.6 Hz, 1C), 136.8
124.5 (s, 1C), 126.8 (s, 1C), and 144.6 (s, 1C). d(Cphenyl):
1
2
1
2
(d, Jc-p ¼ 10.2 Hz, 2C), and 142.8 (d, Jc-p ¼ 24.5 Hz, 1C).
The above 13C-NMR assignment were confirmed by running
a Dept-135 experiment that shows disappearance of the three
quaternary carbons (at d ¼ 136.2, 136.8, and 142.8 ppm). In
comparison with 2-bromo-1-[(methylthio)methyl)]benzene,
the IR spectra of P-SM shows, a vibration at 1119 cm21due
to nP-Ph.
138.6 (d, JC-P ¼ 12.5 Hz, 2C), 132.8 (d, JC-P ¼ 18.3 Hz,
3
4C), 128.5 (d, JC-P ¼ 6.6 Hz, 4C), and 128.6 (s, 2C). The
above 13C-NMR assignments were confirmed by a running
Dept-135 experiment that shows, disappearance of the two qua-
ternary carbons (at d ¼ 138.6 ppm, and 144.6 ppm). In compari-
son with 2-(3-chloropropyl)thiophene, the IR spectrum of P-S3
shows, a vibration at the 1120 cm21 due to nPh-P.
Preparation of [2-[(methylthio)methyl]phenyl]diphenylphosphine
(P-SM)
The P-SM ligand was prepared from o-bromobenzyl
bromide as shown in Scheme 3. 2-bromo-1-[(methylthio)-
SCH. 3.
SCH. 2.

540
K. A. SALMEIA AND H. A. HODALI
Preparation of the Palladium Complexes
spectrum (300 MHz, CDCl3) of II shows, in addition to the
phenyl proton signals, a multiplet centered at: d ¼ 1.89
(-CH2CH2CH2P-), d ¼ 2.50 (-CH2P-), and a triplet centered
at d ¼ 2.87 (-CH2CH2CH2P-). The signals of the thiophene
protons appear as doublets centered at d ¼ 6.69, and
d ¼ 7.07, and a doublet of doublet centered at d ¼ 6.87. The
13C-NMR spectrum (75 MHz, CDCl3) of II shows d(Caliphatic):
Preparation of [Pd(P-S2)Cl2] (I) and [Pd(P-S2)2Cl2] (IV)
Reaction of P-S2 with equimolar amount of
[Pd(PhCN)2Cl2] gave the complex [Pd(P-S2)Cl2] with P-S2
acting as a bidentate ligand. However, when the reaction was
conducted at a ligand-to-metal molar ratio of 2:1, the
complex [Pd (P-S2)2Cl2], was isolated with P-S2 acting as a
monodentate ligand. The 1H-NMR spectrum (300 MHz,
DMSO-d6) of [Pd(P-S2)Cl2] shows, in addition to the phenyl
proton signals at d ¼ 7.48–7.81, a multiplet at d ¼ 2.88
(-CH2CH2P-), and another multiplet at d ¼ 2.74 (-CH2P-).
The three protons of thiophene signals appear as: two doublet
of doublet centered at d ¼ 6.86 and 7.27, and a multiplet at
d ¼ 6.80. The 13C-NMR spectrum (75 MHz, DMSO-d6) of
[Pd(P-S2)Cl2] shows, d(Caliphatic): 24.7 (s, 1C), and 30.0
2
3
25.9 (s, 2C), 26.5 (d, JC-P ¼ 35.9 Hz, 2C), and 30.5 (d, JC-
¼ 17.5 Hz, 2C); d(Cthiophene): 123.5 (s, 2C), 124.9 (s, 2C),
P
126.9 (s, 2C), and 143.1 (s, 2C); d(Cphenyl): 127.7 (s, 4C),
2
3
133.3 (d, JC-P ¼ 10.2 Hz, 8C), 128.8 (d, JC-P ¼ 11.9 Hz,
8C), and 131.4 (s, 4C). Comparing the 13C-NMR spectrum of
[Pd(S-P3)Cl(m-Cl)]2 with that of the P-S3 ligand shows no
difference on the chemical shift of the thiophene ring
carbons, which is inconsistent with the ligand being coordi-
nated through the phosphorus atom only. The signal for
2
(d, JC-P ¼ 34.5 Hz, 1C), d(Cthiophene): 124.6 (s, 1C), 125.3
Cphenyl-P was shifted upfield upon coordination with the palla-
3
(s, 1C), 127.4 (s, 1C), and 143.6 (d, JC-P ¼ 19.5 Hz, 1C).
dium metal to 127.7 ppm and appeared as a singlet. Similarly,
the signal for CH2-P was shifted to upfield upon coordination
with the palladium metal to 26.5 ppm with an increase in J
value (J ¼ 35.9 Hz). The bidentate mode of bonding seems
to be unfavorable in case of the P-S3 ligand, probably due to
the 7-membered chelate ring that would form. Attempts to
obtain the palladium complex with the P-S3 ligand with
ligand-to-metal ratio of 2:1 were unsuccessful. This could be
due to the steric effect of the side arm containing thiophene
ring. In view of the above discussion the complex is believed
to have the dimeric structure shown in Figure 2.
2
d(Cphenyl): 129.7 (s, 2C), 129.1 (d, JC-P ¼ 11.3 Hz, 4C),
3
133.6 (d, JC-P ¼ 9.8 Hz, 4C), and 132.0 (s, 2C). The above
13C-NMR assignment were confirmed by running the Dept-
135 experiment that shows, disappearance of the two quatern-
ary carbons (at d ¼ 129.7 ppm and 143.6 ppm). In comparison
with the ligand (P-S2), the 13C-NMR spectrum of [Pd(P-
S2)Cl2] shows an upfield shifted of all carbons. For example,
the Cphenyl-P in the P-S2 ligand appears at 138.2 ppm as a
doublet with a coupling constant of 12.75 Hz, which shifts
upfield upon coordination with the palladium metal to
129.7 ppm. Unfortunately, the 1H-NMR and 13C-NMR
spectra of the complex [Pd(P-S2)2Cl2] were not informative
due to the extremely low solubility of the complex in most
deuterated solvents including DMSO-d6. The 2:1 ligand-to-
metal ratio for [Pd(P-S2)2Cl2] was confirmed only by the
result of its microelemental analysis. The proposed structures
of (I) and (IV) are shown in Figure 1.
Preparation of [Pd(P-SM)Cl2] (III)
Reaction of the P-SM ligand, with equimolar amount of
[Pd(PhCN)2Cl2] affords the complex III. This complex is
soluble in acetone, chloroform, and dichloromethane, and inso-
luble in petroleum ether, dioxane, and hexane. Microelemental
analysis for C, H, and S are inconsistent with the above formu-
lation of the complex. The 1H-NMR spectrum (300 MHz,
CDCl3) of [Pd(P-SM)Cl2] shows, in addition to the aromatic
proton signals at d ¼ 6.79-7.72, a singlet at d ¼ 2.45
(-SCH3), and two signals (doublet of doublet) at d ¼ 3.45
and 3.68 (-CH2SCH3). These two signals appear as doublet
of doublet due to phosphorus and geminal hydrogen
coupling. The non-equivalence of the methylene protons is
Preparation of [Pd(P-S3)Cl(m-Cl)]2 (II)
Reaction of the asymmetric ligand P-S3, with equimolar
amount of [Pd(PhCN)2Cl2] gave complex II. This palladium
complex is soluble in acetone, chloroform, and dichloro-
methane, and insoluble in petroleum ether, dioxane, and
hexane. Microelemental analysis for C, H, and S is inconsistent
with the above formation for the complex. The 1H-NMR
due to the rigid configuration of the ligand upon chelation[19]
.
The 13C-NMR spectrum (75 MHz, CDCl3) of [Pd(P-SM)Cl2]
FIG. 1. Proposed structures of [Pd(P-S2)Cl2] (I) and [Pd(P-S2)2Cl2] (IV).
FIG. 2. Proposed structure of [PdCl(m-Cl) (P-S3)]2.

PALLADIUM COMPLEXES WITH P AND S LIGANDS
541
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FIG. 3. Proposed structure of [Pd(P-SM)Cl2].
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1
1
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´
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Highly efficient and regioselective coupling of aryl halides to
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3
1C), 130.0 (d, Jc-p ¼ 8.6 Hz, 1C), 132.3 (s, 1C), 134.7
2
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2
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phene,
diphenylf5-[60-(diphenylphosphino)-20-pyridyl]-2-thie-
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