Five-coordinate rhenium(III)-thiolato complexes: The structure of [Re(SCH2PhOCH3)3(PPh3)2]

Article abstract of DOI:10.1016/S0020-1693(99)00143-7

A novel five-coordinate rhenium(III)-thiolato complex, Re(SCH₂C₆H₄OCH₃-p) ₃(PPh₃)₂ has been isolated during the reaction of trans-ReOCl₃(PPh₃)₂ with p-methoxybenzyl mercaptan. In the unexpected structure that was acquired, the central metal has undergone a reduction from Re(V) to Re(III). The five-coordinate Re(III) complex has been characterized by spectroscopic methods, elemental analysis and X-ray crystallography. X-ray crystallographic studies showed the coordination geometry around rhenium to be that of a trigonal bipyramid. The basal plane is defined by three sulfur atoms of the monodentate ligand, while the two apical positions are occupied by two phosphines of the precursor.

Full text of DOI:10.1016/S0020-1693(99)00143-7

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Inorganica Chimica Acta 290 (1999) 247–250
Note
Five-coordinate rhenium(III)-thiolato complexes: the structure of
[Re(SCH2PhOCH3)3(PPh3)2]
M.S. Papadopoulos a, P. Bouziotis a, I.C. Pirmettis a, C.P. Raptopoulou b, A. Terzis b,
E. Chiotellis a,*
a Institute of Radioisotopes-Radiodiagnostic Products, NCSR ‘Demokritos’, PO Box 60228, 15310, Aghia Paraske6i, Athens, Greece
b Institute of Materials Science, NCSR ‘Demokritos’, PO Box 60228, 15310, Aghia Paraske6i, Athens, Greece
Received 10 December 1998; accepted 9 March 1999
Abstract
A novel five-coordinate rhenium(III)-thiolato complex, Re(SCH2C6H4OCH3-p)3(PPh3)2 has been isolated during the reaction of
trans-ReOCl3(PPh3)2 with p-methoxybenzyl mercaptan. In the unexpected structure that was acquired, the central metal has
undergone a reduction from Re(V) to Re(III). The five-coordinate Re(III) complex has been characterized by spectroscopic
methods, elemental analysis and X-ray crystallography. X-ray crystallographic studies showed the coordination geometry around
rhenium to be that of a trigonal bipyramid. The basal plane is defined by three sulfur atoms of the monodentate ligand, while the
two apical positions are occupied by two phosphines of the precursor. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Rhenium complexes; Thiolato complexes; Five-coordinate complexes
1. Introduction
methoxybenzyl mercaptan, p-CH3OC6H4CH2SH. Sur-
prisingly, we obtained a complex with the unexpected
structure [Re(SCH2C6H4OCH3-p)3(PPh3)2], where the
central rhenium atom had undergone a reduction from
Re(V) to Re(III). So far, the acquisition of pentacoordi-
nate Re(III) complexes has been described in the litera-
ture only a few times [7,8]. The Re(III) products might
be thermodynamically more stable, thus more favorable
than the Re(V) products [9].
This report presents the complex [Re(SCH2C6H4-
OCH3-p)3(PPh3)2] as the major reaction product, while
among the minor products we can find the pentavalent
Re(V) anion [ReO(SCH2C6H4OCH3-p)4]−, where the
central metal is surrounded by four thiolato groups.
The coordination chemistry of technetium and rhe-
nium has attracted much attention due to the wide-
spread use of 99mTc in diagnostic imaging and 186Re
and 188Re in radiotherapy [1]. Rhenium is technetium’s
third row congener, thus exhibiting similar chemical
properties to technetium. Minor chemical differences
between complexes of these two isotopes can result in
different biological behavior. The most pronounced of
these is the redox potential of the central metal. Com-
plexes of rhenium are more difficult to reduce than the
analogous technetium complexes [2].
As part of our investigations into thiolato complexes
of rhenium, we have looked into the side products of
different reaction systems involving a variety of thiols
as coligands [3–6]. In the course of a systematic study,
we reacted trans-ReOCl3(PPh3)2 with an excess of p-
2. Experimental
2.1. Materials and methods
* Corresponding author. Tel.: +30-1-651 3793; fax: +30-1-654
3526.
IR spectra were recorded as KBr pellets in the range
4000–500 cm−1 on a Perkin-Elmer 1600 FT-IR spec-
E-mail address: mainathe@cyclades.nrcps.ariadne-t.gr (E. Chiotel-
lis)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00143-7

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M.S. Papadopoulos et al. / Inorganica Chimica Acta 290 (1999) 247–250
trophotometer and were referenced to polystyrene. Ele-
mental analyses were performed on a Perkin-Elmer
2400/II automatic analyzer.
All laboratory chemicals were reagent grade. The
p-methoxybenzyl mercaptan used as coligand was pur-
chased from Fluka. The ReOCl3(PPh3)2 precursor was
prepared according to literature [10].
Lorentz, polarization and absorption corrections were
applied using Crystal logic software.
Symmetry equivalent data were averaged with Rint
0.0568 to give 3926 independent reflections from a total
4068 collected. The structure was solved with SHELXS
=
-
86 [11] and refined by full-matrix least-squares tech-
niques on F2 with SHELXS-93 [12] using 3926 reflections
and refining 288 parameters. All hydrogen atoms of the
ligands (except those of the symmetric thiol) were intro-
duced at calculated positions as riding on bonded
atoms. All non-hydrogen atoms (except O2 and C38)
were refined anisotropically.
2.2. Synthesis of [Re(SCH2PhOCH3-p)3(PPh3)2]
2.2.1. Method A
To a stirred suspension of trichlorobis(triphenylphos-
phine)rhenium(V) oxide, ReOCl3(PPh3)2 (166 mg, 0.2
mmol) in methanol (10 ml), 1 M CH3COONa in
methanol was added. 123.2 mg of p-methoxybenzyl
mercaptan dissolved in dichloromethane (5 ml) were
added under stirring. The reactants are in a 1:4 molar
ratio, and were heated under reflux for approximately
1 h, after which the solution turned to a dark greenish-
brown color. After being cooled to room temperature,
water was added and the complex was extracted with
CH2Cl2. The organic extract was dried over MgSO4, the
volume of the solution was reduced to 10 ml and then
2–3 ml of methanol were added. Slow evaporation of
the solvents at room temperature afforded the major
product of the reaction, [Re(SCH2PhOCH3)3(PPh3)2],
as brown crystals. Yield 45%. Rf=0.80 (silica gel, 2/1/1
benzene/CH3CN/CHCl3). Anal. Calc. for C60H57O3P2-
S3Re: C, 61.53; H, 4.91; S, 8.20. Found: C, 61.50; H,
4.77; S, 7.76%.
The final values of R1, wR2 for observed data are
given in Table 1 and for all data they are 0.0940 and
0.1938, respectively. The maximum and minimum resid-
ual peaks in the final difference map were 2.595 and
−3
,
2.771 e A
in the vicinity of the heavy metal. The
largest shift/e.s.d in the final cycle was 0.147.
3. Results and discussion
trans-ReOCl3(PPh3)2 is one of the most versatile
precursor compounds in Re(V) chemistry [13]. Mild
reduction of monooxo Re(V) species leads to mono-
nuclear Re(III) with removal of terminal oxide. This
provides the usual synthetic route to octahedral com-
plexes of Re(III) [14]. A series of trans-octahedral
Re(III) complexes has recently been reported, which
can be useful precursors for the preparation of mixed-lig-
and complexes [15]. Another series of five-coordinate
rhenium(III) has been synthesized, starting from pre-re-
duced ReIIICl3(MeCN)(PPh3)2 by substitution reactions
with mixed bidentate and monodentate thiol ligands [7].
All attempts to obtain ReIIIP2S3 compounds starting
from Re(VII) or Re(V) precursors by reduction/substi-
2.2.2. Method B
Potassium perrhenate (19 mg), p-methoxybenzyl mer-
captan (50 mg) and triphenylphosphine (86.56 mg) were
refluxed in methanol, in a 1:5:5 molar ratio. After the
addition of excess SnCl2 (38 mg), the solution became a
light olive–green color, which eventually became dark
brown. The resulting suspension was filtered, in order
to eliminate the SnO2, and consequently allowed to
crystallize. Yield 40%.
Table 1
Summary of crystal, intensity collection and refinement data
Empirical formula
Formula weight
Temperature
C60H57O3P2ReS3
1170.46
298
2.3. X-ray crystallography
Wavelength
Space group
Mo Ka 0.71070
I2/a
The crystals of the complex were of poor quality and
the only reason for collecting data was to establish the
connectivity of the molecule. A brown crystal (0.10×
0.10×0.60 mm) was mounted in air on a Crystal Logic
Dual Goniometer diffractometer using graphite-
monochromated Mo radiation. Unit cell dimensions
were determined and refined by using the angular set-
tings of 25 automatically centered reflections in the
range 11B2qB23° and they appear in Table 1. Inten-
sity data were recorded using a q–2q to 2qmax=47 with
scan speed 2.2 min−1 and scan range 2.4+h1h2 separa-
tion. Three standard reflections monitored every 97
reflections showed less than 3% variation and no decay.
,
a (A)
17.88(1)
16.47(1)
18.48(1)
102.44(2)
5313(1)
4
1.463/1.44
2.510
2376
,
b (A)
,
c (A)
i (°)
V (°)
Z
D
calc/Dmeas (Mg m−3
)
Absorption coefficient v (mm−1
F(000)
)
Goodness-of-fit on F2
1.185
R indices [2747 reflections I\2|(I)]
R1=0.0659a,
wR2=0.1678b
a R1 based on F values.
b wR2 based on F2.

M.S. Papadopoulos et al. / Inorganica Chimica Acta 290 (1999) 247–250
249
Table 2
,
Selected bond distances (A) and angles (°) for 1
Re–P(1)
Re–S(1)
Re–S(2)
2.421(3)
2.256(3)
2.243(5)
S(2)–Re–S(1)
S(1)–Re–S(1%)a
S(2)–Re–P(1)
S(1)–Re–P(1)
S(1)–Re–P(1%)
P(1)–Re–P(1%)
119.4(1)
121.3(2)
89.6(1)
83.7(1)
96.7(1)
179.2(1)
a The primed atoms are generated by the symmetry operation:
1/2−x, y 1−z.
An ORTEP diagram of the complex is given in Fig. 1
and selected bond distances and angles are listed in
Table 2. The coordination sphere around rhenium is
comprised of three sulfur atoms of monodentate thiols
and two phosphorus atoms of triphenyl phosphines in a
trigonal bipyramidal geometry. The three sulfur atoms
define the basal plane of the trigonal bipyramid and the
two phosphines of the precursor occupy the apical
positions. There is a C2 symmetry axis passing through
Re, and atoms S(2) and C(38) of one of the thiol
ligands, and as a result, atoms C(31) and O(2) were
found disordered and refined with occupation factors
fixed at 10.50. The trigonal bipyramidal geometry of
rhenium is almost ideal (trigonality index, ~=0.96),
due to the symmetry of the molecule. The bond dis-
tances in the coordination sphere are consistent with
those found in other complexes [7,8,16]. The angles
between the atoms of the basal plane are close to the
ideal value of 120° (119.4(1)–121.3(2)°), while P(1)–
Re(1)–P(1%) is almost 180° (179.2(1)°).
Fig. 1. ORTEP diagram of [Re(SCH2C6H4OCH3-p)3(PPh3)2]. Atoms
are presented isotropically, labels of some symmetrical atoms and
H-atoms have been omitted for clarity.
tution reactions involving the above-mentioned thiol
ligands failed. Here we describe the successful synthesis
of a trigonal bipyramidal, five-coordinate Re(III) com-
plex, trans-ReIII(SCH2C6H4OCH3-p)3(PPh3)2, along
with its crystal structure. The complex resulted from the
in situ reduction of trans-ReVOCl3(PPh3)2 precursor in
the presence of an excess of p-methoxybenzyl mercap-
tan, p-CH3OC6H4CH2SH, in a neutral methanolic solu-
tion. The same complex was also formed by reacting
KReO4, p-methoxybenzyl mercaptan and triphenyl-
phosphine in the presence of stannous chloride.
TLC is used to monitor the reaction and check for
the existence of other products in the crude reaction
mixture. Another product of the above reaction is the
anion [ReVO(SCH2PhOCH3-p)4]−, which has been iso-
lated as the tetraphenylphosphonium salt [16].
4. Supplementary material
Tables of crystallographic data, fractional atomic
coordinates and anisotropic thermal parameters and a
full listing of bond distances and angles are available
upon request. A CIF in ASCII format is also available.
Acknowledgements
We are grateful to ATE (Agricultural Bank of
Greece) for financial support to A.T.
The infrared spectrum of trans-ReIII(SCH2C6H4-
OCH3-p)3(PPh3) is free of any IR band in the w(ReꢀO)
region, suggesting the absence of the ReꢀO core. The
PPh3 derivatives show a P-sensitive absorption at 1088
cm−1. Furthermore, the peaks found at 1247 and 816
cm−1 are indicative of the existence of the methoxyben-
zyl moiety.
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