Palladium(II) complexes with hemilabile amphiphilic phosphines

Article abstract of DOI:10.1016/S0022-328X(01)00663-5

A series of trans-PdCl₂L₂ complexes were prepared and characterized with the following hemilabile amphiphilic phosphines: R-(C₆H₄)-(OCH₂CH₂) _n-PPh₂ {1 (R=tert-octyl, n=1), 2 (R=tert-octyl, n?=5), 3 (R=tert-octyl, n?=13), 4 (R=n-nonyl, n?=1.4), 5 (R=n-nonyl, n?=5), 6 (R=n-nonyl, n?=11)}, CH₃(OCH₂CH₂)₃PPh₂ (7), CH₃(OCH₂CH₂)₃PPhR (8, R=isopentyl) and HOCH₂CH₂(OCH₂CH₂)₂PPhR (9, R=n-octyl). The molecular structure of trans-PdCl₂(1)₂ was determined by X-ray crystallography. The reaction between the trans-PdCl₂L₂ complexes and Ag⁺ was studied by ³¹P-NMR spectroscopy. The formation of chelated P∩O species in tetrahydrofuran solution was observed in complexes with ligands 2, 3, 5, 6, 7, 8 and 9. However, with ligand 1 the formation of chelated species was only observed in the less coordinating solvent dichloromethane. This different behavior can be attributed to the electronic and steric effects of the aryl group bonded to the oxygen atom. Ligand 4 is a mixture of a molecule similar to 1 and molecules with more than one oxygen atom and thus displays both characteristics.

Full text of DOI:10.1016/S0022-328X(01)00663-5

Journal of Organometallic Chemistry 626 (2001) 139–144
www.elsevier.nl/locate/jorganchem
Palladium(II) complexes with hemilabile amphiphilic phosphines
Esteve Valls a, Joan Suades a,*, Rene´ Mathieu b, Joan F. Piniella c,
Angel Alvarez-Larena c
a Departament de Qu´ımica, Edifici C, Uni6ersitat Auto`noma de Barcelona, 08193 Bellaterra, Spain
b Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 Toulouse Cedex 4, France
c Departament de Geologia, Edifici C, Uni6ersitat Auto`noma de Barcelona, 08193 Bellaterra, Spain
Received 14 November 2000; accepted 3 January 2001
Abstract
A series of trans-PdCl2L2 complexes were prepared and characterized with the following hemilabile amphiphilic phosphines:
R-(C6H4)–(OCH2CH2)n–PPh2 {1 (R=tert-octyl, n=1), 2 (R=tert-octyl, n¯ =5), 3 (R=tert-octyl, n¯ =13), 4 (R=n-nonyl,
n¯ =1.4), 5 (R=n-nonyl, n¯ =5), 6 (R=n-nonyl, n¯ =11)}, CH3(OCH2CH2)3PPh2 (7), CH3(OCH2CH2)3PPhR (8, R=isopentyl)
and HOCH2CH2(OCH2CH2)2PPhR (9, R=n-octyl). The molecular structure of trans-PdCl2(1)2 was determined by X-ray
crystallography. The reaction between the trans-PdCl2L2 complexes and Ag+ was studied by 31P-NMR spectroscopy. The
formation of chelated PSO species in tetrahydrofuran solution was observed in complexes with ligands 2, 3, 5, 6, 7, 8 and 9.
However, with ligand 1 the formation of chelated species was only observed in the less coordinating solvent dichloromethane. This
different behavior can be attributed to the electronic and steric effects of the aryl group bonded to the oxygen atom. Ligand 4
is a mixture of a molecule similar to 1 and molecules with more than one oxygen atom and thus displays both characteristics.
© 2001 Elsevier Science B.V. All rights reserved.
Keywords: Palladium(II) complexes; Hemilabile amphiphilic phosphines; 31P-NMR spectroscopy
1. Introduction
yielding to supramolecular arrangements such as mi-
celles and vesicles [5]. These micro-heterogeneous sys-
tems are attractive for improving catalytic processes,
especially those working in two-phase systems due to
phase-transfer limitations [6]. This approach has been
recently utilized in the study of a catalytic reaction
accelerated by vesicle formation [7].
In a previous paper, we described the synthesis of a
new group of amphiphilic phosphines that feature the
combination of amphiphilic and hemilabile properties
[8] (Scheme 1). Ligands 1–9 were prepared straightfor-
wardly from polyethylene glycol monoalkylethers; com-
mon starting compounds since they are used extensively
as nonionic surfactants. In this paper, we report the
reactivity of ligands 1–9 (Scheme 1) towards Pd(II).
New data on the coordination chemistry of 1–9, thus
rounds out our previously reported results with Ru(II)
where various coordination modes such as monoden-
tate (P), bidentate (O, P) and tridentate (O, O, P) were
described [8].
The synthesis and study of new functionalized lig-
ands, which may improve certain properties in transi-
tion metal complexes, has become a central topic in
inorganic and organometallic chemistry. Functionalized
phosphine ligands exhibit a relevant position on this
subject since a broad range of groups may be anchored
to the phosphorus atom, leading to different functional-
ized phosphines, e.g. water-soluble [1], asymmetric [2],
hemilabile [3], etc. In this way, a new concept of
functionalized phosphines has emerged in recent years:
amphiphilic phosphines [4]. These ligands contain hy-
drophilic and hydrophobic groups in the same molecule
and can form metal complexes which can aggregate,
* Corresponding author. Tel.: +34-93-5812893; fax: +34-93-
5813101.
E-mail address: suades@cc.uab.es (J. Suades).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00663-5

140
E. Valls et al. / Journal of Organometallic Chemistry 626 (2001) 139–144
Scheme 1.
2. Results and discussion
signals assigned to cis-PdCl2L2 appeared between 17
and 19 ppm. This is consistent with the replacement of
an aryl group bonded to phosphorus by an alkyl group
in 8 and 9 with respect to 1–7. In addition, since
ligands 8 and 9 were obtained as racemic mixtures, the
31P-NMR spectra of their cis-PdCl2L2 complexes dis-
play the signals of the respective two diastereoisomers.
In previous studies with Ru(II) [8b], ligand 1 showed
a significantly different behavior from 2 to 6 since it is
the sole ligand that is not a mixture of molecules with
different ethoxylation grades and only one oxygen atom
is available for coordination. As mentioned above, after
reaction with PdCl2(COD) it was the only ligand that
led to the formation of a solid compound, which was
isolated and characterized as PdCl2(1)2 by the usual
analytical and spectroscopic methods. As noted above,
the trans-configuration is anticipated by 31P-NMR
spectroscopy and the 13C-NMR spectrum is also consis-
tent with this assignment. A signal at 26.5 ppm assigned
to the carbon atom of the methylene group bonded to
phosphorus is observed as a triplet. This splitting has
been previously described for the carbon atoms linked
to phosphorus in trans-PdX2P2 complexes and at-
tributed to the coupling of these carbon atoms to the
two virtually equivalent trans-phosphorus atoms
[10,12]. Single crystals of trans-PdCl2(1)2 were obtained
by recrystallization in acetone–ethanol and their struc-
ture was determined by X-ray analysis. A perspective
view of the molecule with the labelling scheme is shown
in Fig. 1. The palladium atom displays a square-planar
geometry with ligands in trans disposition, confirming
previous assignment from NMR data. Bond distances
and angles around the metal centre are similar to other
trans-PdCl2L2 complexes with monodentate phosphine
ligands [11,13]. The phenyl groups bonded to the phos-
phorus atoms are nearly eclipsed. This is evidenced by
2.1. Ligands
Ligands 1–6 were synthesized from commercial non-
ionic surfactants Igepal1 [9]. In accordance with the
nature of these starting nonionic surfactants, the lig-
ands were obtained as mixtures of compounds with the
same structure but with different ethoxylation grades
(Scheme 1). The only exception is 1, which was ob-
tained as a single compound because it crystallized
from the reaction mixture as a white solid. Ligands 7–9
were also achieved as single compounds because they
were prepared from pure Cl(CH2CH2O)3CH3 and
Cl(CH2CH2O)2CH2CH2OH.
2.2. PdCl2L2 complexes
The reaction of PdCl2(COD) with 2 moles of 1–9 in
dichloromethane yields orange solutions and except the
reaction with 1, no solids could be isolated. All the
31P-NMR spectra of the palladium complexes obtained
from ligands 1–7 display a main signal at 12.4–14.1
ppm and a very small peak at 24.5–26.8 ppm. The
upfield and major resonance is assigned to the trans-
PdCl2L2 isomer and the small and downfield resonance
to the cis-PdCl2L2 isomer. These assignments are con-
sistent with data reported previously for PdCl2L2 com-
plexes with monodentate phosphine ligands [9–11]. The
31P-NMR spectra of PdCl2(8)2 and PdCl2(9)2 display a
similar pattern but the resonances are upfield shifted.
Thus, the signals assigned to trans-PdCl2L2 are ob-
served at 10.0 (L=8) and 9.3 ppm (L=9) and the
1 These products are ethoxylated alkylphenols with different
ethoxylation grades.

E. Valls et al. / Journal of Organometallic Chemistry 626 (2001) 139–144
141
Fig. 1. View of the molecular structure of trans-PdCl2(1)2 together with the atomic numbering scheme.
Scheme 2.
neighboring molecule, and the shortest Me–Me dis-
tances are similar to those found in the above ruthe-
the small value of the C131–P1–P2–C231 torsion an-
gle (24.0(2)°) and it follows that the two tert-octylphe-
noxyethyl chains are close each other. This
arrangement could be explained by the trend of the
more hydrophobic parts of the molecule to be close
together, although other factors should also be consid-
ered. Thus, the Cl2 atom is located in a position near
the methylene groups bonded to the oxygen atoms. The
partial electrophylic character of these hydrogen atoms
,
nium complex (C–C=3.9–4.2 A).
2.3. Reacti6ity of PdCl2L2 complexes toward AgBF4
The results obtained in the above section are very
similar to those previously reported for phosphinoether
ligands like Ph2PCH2CH2OCH3 [11], which react with
PdCl2(COD) to form P-coordinated palladium com-
plexes. Likewise, these previous studies have shown
that the trans-PdCl2(PꢀO)2 complexes (PꢀO=P-co-
ordinated phosphinoether ligand) can lead to chelated
complexes [PdCl(PSO)(PꢀO)]+ and [Pd(PSO)2]2+
(PSO=chelated phosphinoether ligand) after abstrac-
tion of Cl− with Ag+. In order to find out if the
reported palladium complexes display a similar behav-
ior, their reaction with Ag+ was studied by 31P-NMR.
After addition of one equivalent of Ag+, PdCl2L2
complexes (L=2, 3, 5, 6 and 7) displayed a similar
behavior, which is consistent with previous work with
phosphinoethers. The main signal at 12.4–14.1 ppm of
the trans-PdCl2L2 complex faded and two broad bands
around 36 and 54 ppm appeared, which are respectively
assigned to the phosphorus atoms of the monodentate
and a 5-membered ring chelate ligands [11] (Scheme 2).
After addition of another equivalent of Ag+, a main
signal at 45–51 ppm was observed. This was assigned
to the bis(chelate) complex (Scheme 2). Since ligands 8
1
is shown by their position in the H-NMR spectrum
(4.19 ppm) and the existence of a hydrogen bond
between the Cl2 atom and the hydrogens of the methyl-
ene groups seems realistic2. Similarly, the presence of
another weak hydrogen bond between one oxygen atom
and one phenyl group can be proposed3. In a previous
paper [8b], we observed a particular molecular packing
of
a
ruthenium complex with the ligand
CH3(OCH2CH2)3PPhR (R=isopentyl) in such a way
that the hydrophobic isopentyl groups were close to-
gether. In the crystal structure of trans-PdCl2(1)2, each
tert-octyl group is close to a tert-octyl group of a
2
,
C132–H and C232–H: 0.97 A (hydrogen atoms placed in calcu-
,
,
,
lated positions). C132···Cl2: 3.478(5) A, H(C132)···Cl2: 2.74 A,
C132–H···Cl2: 133°; C232···Cl2: 3.658(5) A, H(C232)···Cl2: 2.94 A,
,
C232–H···Cl2: 131°.
3
,
C212–H: 0.93 A (hydrogen atom placed in calculated position).
,
,
C212···O233: 3.261(6) A, H···O233: 2.46 A, C212–H···O233: 144°.

142
E. Valls et al. / Journal of Organometallic Chemistry 626 (2001) 139–144
Scheme 3.
and 9 are racemic mixtures, the same reaction with
their PdCl2L2 complexes led to more complicated 31P-
NMR spectra. Nevertheless, after addition of two
equivalents of Ag+, two main signals in the 40–41 ppm
region were observed clearly. These are attributable to
the two diastereoisomers of the [Pd(PSO)2]2+
complexes.
ligands 2, 3, 5, 6 and 7, can chelate more easily.
Consequently, after addition of Ag+ to PdCl2(4)2 sig-
nals were observed in the 31P{1H}-NMR spectrum that
were similar to those obtained with 1, coexisting with
peaks observed in the analogous reaction with 2, 3, 5, 6
and 7.
As noted above, ligand 1 is substantially different
from the other ligands and shows a particular behavior.
Hence, although the 31P-NMR of a tetrahydrofuran
solution of PdCl2(1)2 is similar to those of the other
trans-PdCl2L2 complexes4, after addition of one equiva-
lent of Ag+, it evolved to a main signal at 12.6 ppm
and two small signals at 26.3 and 30.3 ppm with the
characteristic shape of an AB system (J=6.8 Hz).
After addition of a second equivalent of Ag+ the
spectrum changed to two signals at 23.9 and 34.6 ppm.
Since the bidentate coordination of 1 is hindered by
electronic and steric effects of the aryl group bonded to
the oxygen atom, these facts can be explained by the
replacement of a chloride ligand by a molecule of
tetrahydrofuran (Scheme 3). The substitution of a Cl−
by a molecule of tetrahydrofuran led to a compound
with two equivalent phosphorus atoms in the trans
isomer and non-equivalent phosphorus atoms in the cis
isomer. Nevertheless, when two equivalents of Ag+ are
added in a less coordinant solvent like dichloromethane
only a main signal at 48 ppm is observed, which is
concordant with the formation of a bis(chelate) com-
3. Experimental
3.1. General
All reactions were performed under nitrogen by stan-
dard Schlenk tube techniques. The NMR spectra were
recorded by the Servei de Ressona`ncia Magne`tica Nu-
clear de la Universitat Auto`noma de Barcelona on a
Bruker AC250 instrument. All chemical shift values are
given in ppm and are referenced with respect to residual
protons in the solvents for 1H spectra, to solvent signals
for 13C spectra and to external phosphoric acid for 31P
spectra.
Compounds 1–9 were prepared by published proce-
dures [8b]. Microanalyses were performed in Servei
d’Ana`lisi Qu´ımica de la Universitat Auto`noma de
Barcelona.
3.2. Synthesis of trans-PdCl2(1)2
plex [Pd(PSO)2]2+
.
A
solution of
1
(0.580 g, 1.4 mmol) in
Ligand 4 is a mixture that contains a compound
similar to 1, with the phenolic oxygen as the only
oxygen atom. However, this compound coexists with
other molecules with short polyether chains which, as
dichloromethane (10 ml) was added to a solution of
PdCl2(COD) (0.200 g, 0.7 mmol) in dichloromethane
(10 ml) at room temperature. The orange solution was
stirred for 2 h and evaporated to dryness subsequently.
The solid residue was recrystallized from acetone–etha-
nol at −18°C. The yellow crystals were collected,
washed in ethanol and dried in vacuo.
4 A main signal at 13.0 ppm assigned to trans-PdCl2(1)2 is observed
with only another small signal at 26.6 ppm assigned to the cis-
PdCl2(1)2 complex.

E. Valls et al. / Journal of Organometallic Chemistry 626 (2001) 139–144
143
Yield of trans-PdCl2(1)2, 56%. Anal. Calc. for
C56H70Cl2O2P2Pd: C, 66.30; H, 6.96. Found: C, 66.21;
H, 6.90. 31P{1H}-NMR (CDCl3): 13.0 (s, trans-
PdCl2(1)2), 26.6 (s, cis-PdCl2(1)2). 1H-NMR (CDCl3;
except phenyl resonances): 0.65 (s, (CH3)3), 1.26 (s,
(CH3)2), 1.62 (s, CH2, tert-octyl), 2.95 (m, CH2–P),
4.19 (m, CH2O). 13C{1H}-NMR (CDCl3; except phenyl
resonances): 26.5 (t, J=14.4 Hz, CH2P), 31.5 (s, CH3),
31.7 (s, CH3), 32.2 (s, CMe3), 37.8 (s, CMe2), 56.8 (s,
CH2, tert-octyl), 63.3 (b, CH2O).
speed 1.3–5.5°. Reflection ranges for the data collection
were 1BqB25°, −115h511, −185k519, 05
l520. Lp and empirical absorption corrections [14]
were applied, Tmin=0.922, Tmax=1.000. Unique reflec-
tions, 9244; 7483 with I\2|(I).
3.4.3. Structure solution and refinement
The structure was solved by direct methods (SHELXS
-
86) [15] and refined by full-matrix least-squares proce-
dures on F2 for all reflections (SHELXL-97) [16]. One
tert-octyl group showed structural disorder and it was
split. Final site occupation factors were 0.52/0.48. Dis-
ordered carbons were refined isotropically and geomet-
rical restraints were applied. The rest of non-hydrogen
atoms were refined anisotropically. Hydrogen atoms
were placed in calculated positions with isotropic dis-
placement factors 1.5 (methyl H) or 1.2 (the rest) times
the Ueq values of corresponding carbons. A total of 250
parameters were refined. The final weighting scheme
was w=1/[|2(Fo2)+(0.0845P)2+0.1521P] where P=
[max(F2o, 0)+2Fc2]/3. Final R(F) and Rw(F2) values
were 0.040 and 0.117 for reflections with I\2|(I).
3.3. Reacti6ity of 2–9 with PdCl2(COD)
In a representative procedure, a solution of ligand
(1.4 mmol) in dichloromethane (10 ml) was added to a
solution of PdCl2(COD) (0.200 g, 0.7 mmol) in
dichloromethane (10 ml) at room temperature. The
orange solution was stirred for 2 h and evaporated to
dryness yielding an orange oil. The 31P-NMR was
measured with a portion of this final oil.
Significant 31P{1H} (CDCl3) data:
2: {12.5 (s, main signal, trans-PdCl2(PꢀO)2), 24.8 (s,
cis-PdCl2(PꢀO)2)}
3: {12.7 (s, main signal, trans-PdCl2(PꢀO)2), 24.8 (s,
cis-PdCl2(PꢀO)2)}
3.5. Reacti6ity of PdCl2L2 (L=1–9) complexes toward
AgBF4
4: {13.8 (s, main signal, trans-PdCl2(PꢀO)2), 25.0–
25.2 (m, cis-PdCl2(PꢀO)2)}
5: {12.6 (s, main signal, trans-PdCl2(PꢀO)2), 25.0–
25.3 (m, cis-PdCl2(PꢀO)2)}
6: {12.5 (s, main signal, trans-PdCl2(PꢀO)2), 24.8–
26.3 (m, cis-PdCl2(PꢀO)2)}
7: {12.6 (s, main signal, trans-PdCl2(PꢀO)2), 24.8 (s,
cis–PdCl2(PꢀO)2)}
8: {10.0 (s, main signal, trans-PdCl2(PꢀO)2), 18.9 (s,
cis-PdCl2(PꢀO)2), 19.2 (s, cis-PdCl2(PꢀO)2)}
9: {9.3 (s, main signal, trans-PdCl2(PꢀO)2), 17.6 (s,
cis-PdCl2(PꢀO)2), 18.1 (s, cis-PdCl2(PꢀO)2)}
In a representative procedure, two aliquot parts of a
solution (0.5 ml) of the complex PdCl2L2 in tetrahydro-
furan (0.02 M) were placed in two NMR tubes. Next,
one equivalent of a AgBF4 solution in tetrahydrofuran
(0.43 M) was added to the first tube and two equiva-
lents to the second tube. The solid silver chloride was
allowed to sediment and the 31P{1H}-NMR of the
tetrahydrofuran solutions were recorded with an insert
tube of acetone-d6.
Significant 31P{1H}-NMR data:
1. After adding one equivalent of Ag+:
1: {12.6 (s); trans-PdCl(thf)(PꢀO)2}, {26.3 (d,
2JPP=6.8 Hz), 30.3 (d, 2JPP=6.8 Hz); cis-
PdCl(thf)(PꢀO)2}.
3.4. X-ray structure determination of trans-PdCl2(1)2
3.4.1. Crystal data
Suitable single crystals of the titled complex were
obtained by recrystallization in acetone–ethanol.
1 (spectrum recorded in CH2Cl2 with an insert of
acetone-d6): {33.3 (b, PꢀO), 44.2 (b, PSO)}
2: {36.0 (b, PꢀO), 54.0 (b, PSO)}
C56H70Cl2O2P2Pd,
Mr=1014.36.
Triclinic;
a=
3: {36.0 (b, PꢀO), 54.3 (b, PSO)}
4: {12.6 (s, PꢀO), 35.2 (b, PꢀO), 54.7 (b,
PSO)}
5: {36.0 (b, PꢀO), 51.0 (b, PSO)}
6: {36.5 (b, PꢀO), 54.5 (b, PSO)}
,
,
,
10.020(3) A, b=16.180(9) A, c=17.015(6) A, h=
77.39(4)°, i=78.39(3)°, k=82.66(4)°, V=2626.8(19)
3
,
A (by least-squares refinement on diffractometer an-
gles for 25 automatically centred reflections), space
group P1 (no. 2), Z=2, Dcalc=1.282 g cm−3. Yellow,
7: {37.5 (b, PꢀO), 55.0 (b, PSO)}
(
air-stable crystals, v (Mo–Ka)=0.56 mm−1
.
2. After adding two equivalents of Ag+:
1: {23.9 (s, trans-Pd(thf)2(PꢀO)2), 34.6 (b, cis-
Pd(thf)2(PꢀO)2)}.
3.4.2. Data collection and processing
Data were collected at room temperature on an
Enraf-Nonius CAD4 diffractometer using graphite-
1 (spectrum recorded in CH2Cl2 with an insert of
acetone-d6): {48.0 (s, PSO)}
,
monochromated Mo Ka radiation (u=0.71069 A) and
2: {46.5 (b, PSO)}
3: {46.6 (b, PSO)}
a ꢀ–2q scan, ꢀ scan width=0.80+0.35 tan q, ꢀ scan

144
E. Valls et al. / Journal of Organometallic Chemistry 626 (2001) 139–144
Mathieu, Organometallics 16 (1997) 1401. (c) E. Lindner, S.
4: {18–22 (m, PꢀO), 33.0 (s, PꢀO), 55.1 (s,
PSO)}
5: {35.9 (s, PꢀO, minor signal), 51.6 (b, PSO,
main signal)}
6: {36.0 (s, PꢀO, minor signal), 51.4 (b, PSO,
main signal)}
7: {50.8 (s, PSO)}
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9: {40.2 (s, PSO), 40.3 (s, PSO)}
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4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 151792 for compound trans-
PdCl2(1)2. Copies of this information may be obtained
from The Director, CCDC, 12 Union Road, Cam-
bridge, CB2 1EZ, UK (fax: +44-1233-336033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.
cam.ac.uk).
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Acknowledgements
We thank the DGICYT (Programa de Promocio´n
General del Conocimiento) for financial support.
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