Stepwise selective oxidation of tris(2-(diphenylphosphino)ethyl)phosphine on thiolato palladium(II) complexes

Article abstract of DOI:10.1016/j.ica.2003.11.041

One of the equatorially coordinated terminal phosphorus atoms of tris(2-(diphenylphosphino)ethyl)phosphine (pp₃) ligand on the five-coordinate trigonal-bipyramidal palladium(II) complex, [Pd(4-Cltp)(pp ₃)](BF₄) (4-Cltp = 4

Full text of DOI:10.1016/j.ica.2003.11.041

Inorganica Chimica Acta 357 (2004) 2191–2194
www.elsevier.com/locate/ica
Note
Stepwise selective oxidation of
tris(2-(diphenylphosphino)ethyl)phosphine on thiolato
palladium(II) complexes
a,
b
a
Sen-ichi Aizawa *, Tatsuya Kawamoto , Kenji Saito
a
Faculty of Engineering, Toyama University, 3190 Gofuku, Toyama 930-8555, Japan
b
Department of Chemistry, Graduate School of Science, Osaka University, 1-16 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
Received 22 September 2003; accepted 14 November 2003
Abstract
One of the equatorially coordinated terminal phosphorus atoms of tris(2-(diphenylphosphino)ethyl)phosphine (pp3) ligand on
the five-coordinate trigonal-bipyramidal palladium(II) complex, [Pd(4-Cltp)(pp3)](BF4) (4-Cltp ¼ 4-chlorothiophenolate), was
selectively oxidized by photolysis to form the four-coordinate square-planar complex. Further selective oxidation of another co-
ordinated terminal phosphorus atom proceeded quantitatively by the substitution reaction with 4-chlorothiophenolate. The solid
state structures of these stepwise-oxidized square-planar complexes were determined by X-ray crystal structure analyses, and the
structures of the starting trigonal-bipyramidal and the oxidized complexes in solution have been characterized by 31P NMR
spectroscopy.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Stepwise oxidation; Tetradentate phosphine ligands; Photolysis; Thiolato ligands; Trigonal-bipyramidal palladium(II) complexes
1. Introduction
bility of the two different coordination numbers, we have
investigated the selective oxidation reaction of one
phosphino group of the pp3 ligand on the five-coordinate
palladium(II) complex expecting that the oxidation is
terminated by forming the four-coordinate one. Fur-
thermore, we have examined the further oxidation of the
coordinated phosphino group on the square-planar
complex by the attack of the entering ligand. In this
work, we used 4-chlorothiophenolate (4-Cltp) as the
entering and bound X ligands because thiolates have
relatively strong p donating ability to dissociate the
neighboring coordinated phosphino group and the steric
and electronic effects of the entering and bound ligands
can be controlled by change in their substituent groups.
Selective chemical modification of compounds is one
of the important aims of the synthetic studies. Because
donor atoms, which are usually reactive sites, can be
protected by coordination to metal ions, the partial dis-
sociation of multidentate ligands in the intermediate or
under the equilibrium between two different coordina-
tion numbers can be quite useful for the selective modi-
fication. Recently, it was found that the palladium(II)
complexes with the tetradentate phosphine ligand, tris(2-
(diphenylphosphino)ethyl)phosphine (pp3), form the
stable five-coordinate trigonal-bipyramidal geometry,
[PdX(pp3)]2þ or þ (X ¼ halide ions [1], thiolates [2],
acetonitrile [3]), comparable to the four-coordinate
square-planar geometry with the terdentate phosphine
ligand, [PdX(p3)]2þ or þ, (p3 ¼ bis(2-(diphenylphosph-
ino)ethyl)phenylphosphine), with the same monodentate
ligands X [4,5]. Taking account of the comparable sta-
2. Experimental
2.1. Reagents
* Corresponding author. Tel./fax: +81-76-445-6980.
E-mail address: saizawa@eng.toyama-u.ac.jp (S.-i. Aizawa).
Chloroform (Wako, 1 pure) was dried over acti-
vated 4A Molecular Sieves. Tris(2-(diphenylphosphino)
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.11.041

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S. Aizawa et al. / Inorganica Chimica Acta 357 (2004) 2191–2194
ethyl)phosphine (pp3, Aldrich), tetrakis(acetonitrile)
palladium(II) tetrafluoroborate (Aldrich), and 4-chlo-
rothiophenol (H4-Cltp, Wako) were used for prepara-
tion of palladium(II) complexes without further
purification.
The sodium 4-chlorothiophenolate was prepared by
neutralization of acetonitrile solution of 4-chlorothi-
ophenol with 0.5 M aqueous NaOH under a nitrogen
atmosphere. The reaction solution was concentrated to
give the white salt. Anal. Calc. for C6H4NaSCl ꢀ 3H2O:
C, 32.66; H, 4.57; N, 0.00%. Found: C, 32.75; H, 4.25;
N, 0.00%. 1H NMR (CD3CN): d 6.80 and 7.20 (AB
system, J ¼ 8:4 Hz, Ph), 3.17 (s, H2O).
crystals. Yield: 0.070 g (69%). Anal. Calc. for C54H50-
O2P4S2Cl2Pd: C, 59.15; H, 4.60; N, 0.00%. Found: C,
58.98; H, 4.54; N, 0.00%. 31P{1H}NMR (CHCl3): d 32.1
(d, 2P, oxide), 58.0 (d, 1P, terminal), 67.5 (td, 1P, cen-
ter); JPðcenterÞ–PðoxideÞ ¼ 47:9 Hz, JPðcenterÞ–PðterminalÞ ¼ 12:7
1
Hz. It was confirmed by the H NMR measurements
that the diethylether in the crystals is volatile. UV–
Vis (in CHCl3): kmax/nm (log(e/molꢁ1 kg cmꢁ1)) 450
(3.66sh), 406 (3.71).
The single crystals of 3 were obtained by growing
the tiny crystals in the mother liquor under vapor of
diethylether.
2.3. X-ray structure analysis
2.2. Preparation of complexes
The crystal of complex 2 was sealed in a Lindemann
glass-capillary tube with the mother liquor and the
crystal of 3 was mounted on the glass fiber with epoxy.
The X-ray diffraction measurements were performed on
a Mac Science MXC3 diffractometer with Mo Ka ra-
diation. The unit-cell parameters and orientation matrix
were determined by a least-squares refinement of inde-
pendent 18 reflections collected in the ranges of
21:4° < 2h < 24:4° for 2 and 19:0° < 2h < 32:2° for 3,
respectively. Data collection was performed with the
h–2h scan mode with three standard reflections mea-
sured after every 100 scans, which showed no significant
decay. An empirical absorption (W scan) correction was
applied. The solution and refinement were carried out
using CRYSTAN-GM (version 6.3.3) [6]. The structures
were solved by direct methods using the programs of sir
92 [7]. All non-hydrogen atoms were refined anisotrop-
ically and hydrogen atoms were included in the calcu-
2.2.1. [Pd(4-Cltp)(pp3)](BF4) (1)
To a saturated solution of [Pd(pp3)](BF4)2 [3] (0.69 g,
0.73 mmol) in acetonitrile was added 4-chlorothiophe-
nol (0.11 g, 0.76 mmol) and the solution was neutralized
by adding 0.5 M aqueous NaOH. To the resultant deep
red solution was added ethanol and water to give red
crystals. The crystals were collected by filtration and air-
dried. Yield: 0.64 g (87%). Anal. Calc. for C48H46-
BF4P4SClPd: C, 57.22; H, 4.60; N, 0.00%. Found: C,
57.20; H, 4.56; N, 0.00%. 31P{1H}NMR (CHCl3): d 31.1
(d, 3P, terminal), 133.9 (q, 1P, center); JP–P ¼ 8:3 Hz.
UV–Vis (in CHCl3): kmax/nm(log(e/molꢁ1 kg cmꢁ1)) 541
(3.51), 430 (3.90sh).
2.2.2. [Pd(4-Cltp)(pp3O)](BF4) (2)
A red solution of 1 (0.11 g, 0.11 mmol) in acetonitrile
(1 dm3) was stirred under a luminescent lamp for five
days. The resultant yellow solution was concentrated to
ꢂ5 cm3. Yellow crystals were obtained by adding etha-
nol and water. Yield: 0.064 g (54%). Anal. Calc. for
C48H46BOF4P4SClPd ꢀ C2H5OH ꢀ H2O: C, 55.14; H,
4.99; N, 0.00%. Found: C, 54.88; H, 4.56; N, 0.00%.
31P{1H}NMR (CHCl3): d 32.3 (d, 2P, oxide), 47.6 (d,
ꢀ
lated positions (C–H ¼ 0.96 A). The atomic scattering
factors were taken from [8]. The crystallographic data
are summarized in Table 1.
2.4. Measurements
2P, terminal), 107.0 (dt, 1P, center); JPðcenterÞ–PðoxideÞ
¼
1
The 31P and H NMR spectra were recorded on a
33:1 Hz, JPðcenterÞ–PðterminalÞ ¼ 16:5 Hz. UV–Vis (in
CHCl3): kmax/nm (log(e/molꢁ1 kg cmꢁ1)) 431 (3.77), 360
(4.21sh).
JEOL JNM-A400 FT-NMR spectrometer. In order to
determine the chemical shifts of the 31P NMR, a 3 mm
o.d. NMR tube containing the sample solution was
coaxially mounted in a 5 mm o.d. NMR tube containing
deuterated water and phosphoric acid as a lock solvent
and a reference, respectively. The electronic absorption
spectra were recorded on a Perkin–Elmer Lambda 19
spectrophotometer. The reactions from 1 to 2 and from
2 to 3 were followed by the absorption and 31P NMR
spectral changes, and the wavelength of light for
irradiation experiments was controlled by the spectro-
photometer or sharp-cut filters, Shiguma-Koki SCF-
50S-52Y and UTF-50S-34U and 30U (transmission
k > 520, 340, and 300 nm, respectively).
The single crystals were obtained by recrystallization
from chloroform by adding ethanol and water.
2.2.3. [Pd(4-Cltp)2(pp3O2)] (3)
To a solution of 1 (0.094 g, 0.093 mmol) in acetoni-
trile (15 cm3) was added 4-chlorothiophenol (0.026 g,
0.18 mmol) and 0.5 M aqueous NaOH (0.35 cm3). The
deep red solution was stirred under a luminescent lamp
for several days to give the yellow solution that was then
concentrated to dryness. The obtained yellow solid was
dissolved in a minimum amount of chloroform and al-
lowed to stand under vapor of diethylether to give tiny

S. Aizawa et al. / Inorganica Chimica Acta 357 (2004) 2191–2194
2193
Table 1
Crystallographic data for 2 ꢀ C2H5OH ꢀ H2O and 3 ꢀ (C2H5)2O
Compound 2 ꢀ C2H5OH ꢀ H2O 3 ꢀ (C2H5)2O
Empirical formula C50H54BO3F4P4SClPd C58H60O3P4S2Cl2Pd
Formula weight
Temperature (K)
Crystal size (mm)
Crystal system
Space group
1087.62
298
1170.47
298
0.80 ꢃ 0.40 ꢃ 0.30
monoclinic
P21=a
31.25(2)
15.349(8)
10.64(2)
93.25(8)
5092(10)
4
0.60 ꢃ 0.15 ꢃ 0.15
triclinic
ꢁ
P1
ꢀ
a (A)
14.104(7)
16.861(5)
12.277(8)
95.63(4)
2775(2)
2
ꢀ
b (A)
ꢀ
c (A)
a (°)
V (A )
3
ꢀ
Z
Dcalc (g cmꢁ3
)
1.42
0.718
0.99, 0.116
1.40
0.648
0.086, 0.097
l (cmꢁ1
)
b
Ra,Rw
P
P
a R ¼ jjFoj ꢁ jFcjj= jFoj.
P
P
b Rw ¼ ½ wðjFoj ꢁ jFcjÞ = wjFoj ꢄ . w ¼ ðr2ðFoÞ þ 0:001Fo2Þꢁ1
.
2
2 1=2
Fig. 1. ORTEP diagram of complex cation of 2.
3. Results and discussion
The 31P NMR spectrum of 1 in chloroform (see
Section 2 and Scheme 1) exhibits two signals at 31.1 and
133.9 ppm with weak coupling to each other assigned to
the three equivalent terminal phosphorus atoms in the
equatorial position for the former and the central
phosphorus atom in the axial position for the latter in-
dicating the trigonal-bipyramidal geometry with C3
symmetry. The electronic absorption spectrum of 1 in
chloroform (see Section 2) is also consistent with the
five-coordinate trigonal-bipyramidal geometry showing
two d–d absorption bands in the visible region assigned
1
0
1
1
to the transitions from A1 to E0 and E00 [1,9]. These
NMR and absorption spectral behaviors are quite sim-
ilar to those of [Pd(pt)(pp3)](BF4) (pt ¼ 1-propanethi-
olate) [2]. The perspective views of the complex cation of
2 and complex molecule of 3 are displayed in Figs. 1 and
2, respectively. The complex 2 has the square-planar
structure where the dissociated terminal phosphorus
atom is oxidized. For the complex 3, the coordination of
another thiolate is accompanied by the oxidation of
another terminal phosphorus atom. The 31P NMR
spectra of 2 and 3 in chloroform (see Section 2 and
Scheme 2) are also consistent with the square-planar
Fig. 2. ORTEP diagram of 3.
structure in the crystal exhibiting three signals corre-
sponding to the oxidized free phosphorus atoms with
coupling to the central phosphorus atom (33.1 ppm for 2
and 32.1 ppm for 3) and the coordinated terminal and
central phosphorus atoms with coupling to each other
(47.6 and 107.0 ppm for 2 and 58.0 and 67.5 ppm for 3,
respectively).
It was confirmed by the 31P NMR and absorption
spectral measurements that the complex 1 was oxidized
to form the complex 2 quantitatively in acetonitrile on
exposure to visible light by using a luminescent lamp
O
P
P
P
P
hν
O2
P
P
Pd
P
P
P
Pd
Pd
2
P
RS
RS
P
P
SR
1
SR = 4-Cltp
Scheme 1. Oxidation reaction of 1 to 2.

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S. Aizawa et al. / Inorganica Chimica Acta 357 (2004) 2191–2194
In the case of the former reaction from 1 to 2, the
square-planar intermediate is readily formed on expo-
sure to visible light with wavelength in the lower-energy
O
O
O
P
P
P
-
SR
O
O2
P
P
P
P
d–d transition (from A1 to E0) region of 1, and once
the complex 2 is formed, neither further oxidation nor
reverse reaction is occurred by photolysis. This quanti-
tative reaction can be applied to the oxygen assay and
sensing system because this reaction is accompanied by
the distinct color change from red to yellow. Since we
found that the intermediates in Schemes 1 and 2 were
readily bridged to another metal ion to give the mixed-
metal bridged complexes with intended sequence of the
metal centers, the further investigation is in progress in
order to apply the bridging reaction to the synthesis of
the new mixed-metal catalysts with phosphine ligands.
P
1
0
1
P
P
P
Pd
Pd
2
Pd
RS
RS
RS
SR
P
SR
3
SR = 4-Cltp
Scheme 2. Oxidation reaction of 2 to 3.
Table 2
ꢀ
Selected bond distances (A) and angles (°) for 2 and 3
Pd1–S1
Pd1–P1
Pd1–P2
Pd1–P4
2.349(8)
2.302(8)
2.266(7)
2.322(7)
Pd1–S1
Pd1–S2
Pd1–P1
Pd1–P2
2.364(6)
2.361(6)
2.271(6)
2.277(5)
S1–Pd1–P1
S1–Pd1–P4
P1–Pd1–P2
P2–Pd1–P4
91.5(3)
100.3(3)
84.9(3)
82.3(3)
S1–Pd1–S2
S1–Pd1–P2
S2–Pd1–P1
P1–Pd1–P2
98.3(3)
88.9(2)
87.8(2)
85.0(2)
4. Supplementary material
Detailed crystallographic data in CIF format for
2 ꢀ C2H5OH ꢀ H2O and 3 ꢀ (C2H5)2O and 31P NMR
spectra for 1, 2, and 3 (Scheme 1) are available from the
author upon request.
with a sharp-cut filter SCF-50S-52Y (k > 520 nm) and
the spectrophotometer (irradiation k ¼ 535–540 nm) but
no reaction proceeded in the dark or in the deoxygen-
ated solution. Considering the complex 2 was similarly
formed in chloroform, which is non-coordinating sol-
vent, the selective oxidation of one terminal phosphorus
atom of pp3 proceeds via the photolysis of the coordi-
nated equatorial phosphorus atom of 1 followed by the
irreversible oxidation (Scheme 1). Further oxidation of 2
to 3 in acetonitrile did not proceed by photolysis, but
quantitatively by addition of excess sodium 4-chloro-
thiophenorate. It is possible that another terminal
phosphorus atom of 2 was dissociated by the substitu-
tion reaction with 4-chlorothiophenorate followed by
the irreversible oxidation to give 3 (Scheme 2). The bond
distance for the terminal phosphorus atom of 3 (Pd–
Acknowledgements
This work was supported by a grant from Kurita
Water and Environment Foundation and Grant-in-Aid
for Scientific Research (No. 15550104) from the Minis-
try of Education, Culture, Sports, Science and Tech-
nology of Japan.
References
[1] S. Aizawa, T. Iida, S. Funahashi, Inorg. Chem. 35 (1996) 5163.
[2] S. Aizawa, T. Iida, Y. Sone, T. Kawamoto, S. Funahashi, S.
Yamada, M. Nakamura, Bull. Chem. Soc. Jpn. 75 (2002) 91.
[3] S. Aizawa, S. Funahashi, Anal. Sci. 12 (1996) 27.
[4] S. Aizawa, Y. Sone, T. Kawamoto, S. Yamada, M. Nakamura,
Inorg. Chim. Acta 338 (2002) 235.
ꢀ
ꢀ
P1 ¼ 2.271 A) is obviously shorter than those of 2 (Pd–
ꢀ
P1 ¼ 2.302 A and Pd–P3 ¼ 2.322 A) due to the absence
of the trans influence of the phosphorus atoms and the
chelate strain of the terdentate ligand (Table 2). These
electronic and steric effects are probably the reasons why
further oxidation of 3 does not proceed even in the
presence of excess 4-chlorothiophenorate. From the fact
that such oxidation reactions were hardly observed for
the corresponding halo complexes [PdX(pp3)]X (X ¼
Clꢁ, Brꢁ, Iꢁ), such reactivity can be attributed to the
[5] D.L. DuBois, A. Miedaner, J. Am. Chem. Soc. 109 (1987) 133.
[6] Program for X-ray Crystal Structure Determination, MAC Sci-
ence, Yokohama, 1994.
[7] A. Altomare, G. Cascarano, C. Giacovarro, A. Guagliargi, J. Appl.
Crystallogr. 26 (1993) 343.
[8] International Tables for X-ray Crystallography, vol. IV, Kynoch,
Birmingham, AL, 1974.
[9] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed.,
Elsevier, Amsterdam, 1984 (Chapter 6).
1
electronic characteristics of thiolates.
1
Similar oxidation reactions of pp3 ligand were observed for
[Pd(SR)(pp3)]þ (SR ¼ thiophenolate and alkylthiolate derivatives).