Preparation and characterization of organotin-oxomolybdate coordination polymers and their use in sulfoxidation catalysis

Article abstract of DOI:10.1002/chem.200204399

The organotin-oxomolybdates [(R₃Sn)₂MoO₄]·n H₂O (R = methyl, n-butyl, cyclohexyl, phenyl, benzyl) have been prepared and tested as catalysts for the oxidation of benzothiophene with aqueous hydrogen peroxide, at 35°C and atmospheric pressure. In all cases, the 1,1-dioxide was the only observed product. The kinetic profiles depend on the nature of the tin-bound R group and also on the addition of a cosolvent. For the tribenzyltin derivative, the apparent activation energies for sulfoxidation as a function of the cosolvent are in the order 1,2-dichloroethane (5 kcalmol^-1) < ethanol < acetonitrile < water (27 kcalmol^-1). The solid could be recovered by centrifugation from the three-phase (solid-liquid-liquid) system containing 1,2-dichloroethane. The catalyst was reused in a second reaction cycle with no significant loss of activity. Increasing the oxidant/substrate ratio from 2:1 to 6:1 allows the corresponding sulfone to be obtained in quantitative yield within 24 h. Changing the nature of the tin-bound R group in the catalyst precursors modifies their physical properties and hence their catalytic performance. The variation in hydrophobic/hydrophilic character is important, since the Me, nBu and Cy derivatives crystallize as anhydrous compounds, whereas the other two derivatives are hydrates. The polymers also have different structures, as evidenced by X-ray powder diffraction. Mo K-edge and Sn K-edge EXAFS spectroscopy confirmed that the structures arise from the self-assembly of tetrahedral [MoO₄]^2- subunits and [R₃Sn]⁺ spacers. The Mo ... Sn separation in the trimethyltin derivative is a uniform 3.84 A. By contrast, the EXAFS results revealed the coexistence of short (3.67 - 3.79 A) and long (3.93 - 4.07 A) Mo ... Sn separations in the other coordination polymers. The catalyst precursors were also characterized in the solid state by thermogravimetric analysis, FTIR, and Raman spectroscopy, and MAS NMR (¹³C, ¹¹⁹Sn) spectroscopy.

Full text of DOI:10.1002/chem.200204399

I. S. GonÁalves et al.
Chem. Eur. J. 2003, 9, 2685 ± 2695
DOI: 10.1002/chem.200204399
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2685

FULL PAPER
Preparation and Characterization of Organotin ± Oxomolybdate Coordination
Polymers and Their Use in Sulfoxidation Catalysis
[
a]
[b]
[b]
[b]
Marta Abrantes, Anabela A. Valente, Martyn Pillinger, IsabelS. GonÁa lv es,*
[
b]
[a]
Jo aƒ o Rocha, and Carlos C. Rom aƒ o*
Abstract: The organotin ± oxomolyb-
dates [(R Sn) MoO ] ¥ nH O
(R ˆ
liquid) system containing 1,2-dichloro-
ethane. The catalyst was reused in a
second reaction cycle withno significant
loss of activity. Increasing the oxidant/
substrate ratio from 2:1 to 6:1 allows the
corresponding sulfone to be obtained in
quantitative yield within 24 h. Changing
the nature of the tin-bound R group in
the catalyst precursors modifies their
physical properties and hence their cat-
alytic performance. The variation in
hydrophobic/hydrophilic character is
important, since the Me, nBu and Cy
derivatives crystallize as anhydrous
compounds, whereas the other two de-
rivatives are hydrates. The polymers also
have different structures, as evidenced
by X-ray powder diffraction. Mo K-edge
and Sn K-edge EXAFS spectroscopy
confirmed that the structures arise
from the self-assembly of tetrahedral
3
2
4
2
methyl, n-butyl, cyclohexyl, phenyl, ben-
zyl) have been prepared and tested as
catalysts for the oxidation of benzothio-
phene with aqueous hydrogen peroxide,
at 358C and atmospheric pressure. In
all cases, the 1,1-dioxide was the only
observed product. The kinetic profiles
depend on the nature of the tin-bound R
group and also on the addition of a co-
solvent. For the tribenzyltin derivative,
the apparent activation energies for
sulfoxidation as a function of the co-
solvent are in the order 1,2-dichloro-
2À
‡
[MoO4] subunits and [R Sn] spacers.
3
The Mo ¥¥¥ Sn separation in the trimeth-
yltin derivative is a uniform 3.84 ä. By
contrast, the EXAFS results revealed
the coexistence of short (3.67 ± 3.79 ä)
and long (3.93 ± 4.07 ä) Mo ¥¥¥ Sn sepa-
rations in the other coordination poly-
mers. The catalyst precursors were also
characterized in the solid state by ther-
mogravimetric analysis, FTIR, and
Raman spectroscopy, and MAS NMR
À1
ethane (5 kcalmol ) < ethanol < aceto-
Keywords: EXAFS spectroscopy ¥
À1
nitrile < water (27 kcalmol ). The solid
molybdenum
¥
polymerization
¥
could be recovered by centrifugation
from the three-phase (solid ± liquid ±
sulfoxidation ¥ tin
1
3
119
( C, Sn) spectroscopy.
Introduction
temperatures and pressures required, the high hydrogen
consumption, and the difficulty in removing certain refractory
In NorthAmerica and Europe, the acceptable levels of sulfur
in liquid hydrocarbon fuels are continually on the decrease,
driven in part by the need to limit emissions of the oxides of
sulfur which lead to acid rain, atmospheric ozone, and smog.[1]
New, highly efficient and cost-effective desulfurization tech-
nologies are therefore required. Existing catalytic hydro-
desulfurization processes are problematic because of the high
sulfides such as benzothiophene, dibenzothiophene, and 4,6-
dimethyldibenzothiophene.[
1, 2]
To eliminate undesirable sul-
fur compounds or to convert them into more innocuous forms,
various nonconventional processes have been employed or
are being investigated, suchas p hy sical extraction witha
liquid, selective adsorption on zeolites, and liquid-phase
oxidative desulfurization.[ In the last case, various types of
oxidants are used, including hydrogen peroxide, ozone,
tBuOOH, oxygen, and peracids. The liquid oxidation process
withH O produces sulfoxides (1-oxides) and sulfones (1,1-
3]
[
a] Prof. Dr. C. C. Rom aƒ o, Dipl.-Chem. M. Abrantes
Instituto de Tecnologia QuÌmica e Biol o¬ gica
da Universidade Nova de Lisboa
2
2
dioxides) that can be separated physically and processed
downstream (sulfones can, for example, be used as surfac-
tants). Near-atmospheric pressures and mild temperatures are
used, and there is no need for hydrogen. Furthermore, H O is
Quinta do Marqu e√ s, 2781-901 Oeiras (Portugal)
Fax : (‡351)21-4411277
E-mail: ccr@itqb.unl.pt
[
b] Prof. Dr. I. S. GonÁalves, Dr. A. A. Valente, Dr. M. Pillinger,
Prof. Dr. J. Rocha
2
2
economically attractive and eco-compatible as the oxidant,
since water is the only chemical by-product formed from its
decomposition during oxidative transformations. The oxida-
Department of Chemistry, CICECO
University of Aveiro, 3810-193 Aveiro (Portugal)
E-mail: igoncalves@dq.ua.pt
tion of thiophene derivatives with H O is known to take place
over a limited range of metal-containing catalyst systems, such
Supporting information for this article is available on the WWW under
http://www.wiley-vch.de/home/chemistry/ or from the author.
2
2
2686
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/chem.200204399
Chem. Eur. J. 2003, 9, 2685 ± 2695

Organotin ± Oxomolybdate Coordination Polymers
2685±2695
as methyltrioxorhenium(vii),[4] polyoxometalates, and tita-
[5]
Elemental analysis repeatedly indicated that 1 ± 3 are
anhydrous compounds (n ˆ 0), whereas 4 and 5 contain
approximately two and four water molecules per formula
unit, respectively. Thermogravimetric analysis (TGA) meas-
urements under N2 provided supporting evidence for the
nium-containing molecular sieves.[
6]
Recently, we found that organotin ± oxometalate coordina-
tion polymers [(nBu Sn) MO ] (M ˆ Mo, W) exhibit good
3
2
4
catalytic activity for H O -based oxidations (epoxidation of
2
2
olefins) at room temperature and atmospheric pressure.[
7]
presence of nonremovable H O molecules in 4 and 5 (at least
2
With appropriate adjustment of the reaction conditions these
materials become insoluble and act as heterogeneous cata-
lysts, which are easily separated from the reaction products by
centrifuging and can be reused without significant loss of
activity. The tri-n-butyltin derivatives belong to a wider family
of materials,[ general formula [(R E) MO ] (R ˆ Me, Et, nPr,
after prolonged drying in vacuo at room temperature). Thus,
upon heating, the weight of compounds 1 ± 3 remains constant
from 258C to at least 1008C (1508C for 3). Compound 4,
however, loses 1.7% of its initial weight in the temperature
range 25 ± 1008C. The tribenzyltin derivative 5 starts to melt at
858C and then produces a foam at 1088C. A steady mass loss
of 6.5% occurs between 25 and 1258C; this is consistent with
8]
3
2
4
nBu, Ph; E ˆ Sn, Pb; M ˆ Mo, W). These compounds are
accessible by precipitation from aqueous solution, using the
starting materials R ECl and NaMO ¥ 2H O. Apart from the
the presence of four H O molecules per formula unit. Upon
2
further heating, decomposition starts at about 1508C and
38% weight loss takes place up to 2758C. The thermal
behavior of 5 is quite different from that of 1 ± 4, which tend to
melt and decompose above 2008C (Table 1).
3
4
2
trimethyltin ± oxomolybdate analogue, which was character-
ized by single-crystal X-ray diffraction, the organotin ± oxo-
metalate materials have not yet been characterized in detail.
[
(Me Sn) MoO ] has a layered structure built up of tetrahe-
The identity and purity of the trimethyltin derivative 1 were
confirmed by comparison of experimental and calculated
X-ray powder diffraction (XRPD) patterns (see Supporting
Information). Compounds 2, 3, and 5 give rise to XRPD
patterns consisting of relatively sharp reflections, indicating a
polycrystalline nature (see Supporting Information). The
patterns are quite different from that of 1, suggesting that
the tin-bound R group exerts a considerable structure-
directing influence, as observed previously for coordination
3
2
4
dral MoO4 and trigonal-bipyramidal Me SnO units (with
3
2
shared oxygen atoms).[ It is surprising that the catalytic
properties of these polymers have not been investigated
seriously. Encouraged by our recent findings witht he tri- n-
butyltin derivative, we now report on the oxidation of
benzothiophene, chosen as a model substrate, by aqueous
8]
H O2 in the presence of the organotin ± oxomolybdates
[
(
and we have studied the influence of the nature of the solvent,
the tin-bound R group, the reaction temperature, and the
oxidant concentration on the catalytic reaction.
2
(R Sn) MoO ] [R ˆ Me, nBu, cyclohexyl (Cy), Ph, benzyl
3
2
4
[9]
Bz)]. The precursors have been characterized extensively,
polymers [(R Sn) Rh(SCN) ] (R ˆ Me, Et, nPr, nBu).
3
3
6
Compound 4 has poor long-range order, as evidenced by the
presence of only very broad, weak reflections in the XRPD
pattern at d spacings of 11.00, 5.40, 4.30, 3.17, and 1.99 ä.
The X-ray structure of the trimethyltin derivative 1 predicts
an asymmetric unit withone type of Me Sn environment, in
3
1
19
accordance with which in the Sn CP MAS NMR spectrum
of 1 one fairly sharp singlet at d ˆ 47.9 ppm is observed. This
chemical shift is compatible with the crystallographically
Results and Discussion
Synthesis and characterization of catalyst precursors:
The organotin ± oxomolybdates [(R Sn) MoO ] ¥ nH O
determined trigonal-bipyramidal trans-Me
3
SnO
configura-
2
3
2
4
2
tion.[ In agreement withthe
10]
13
C CP MAS NMR spectrum
were obtained as analytically pure precipitates by addition
of a saturated aqueous solution of Na MoO ¥ 2H O to a
[8]
reported by Behrens et al., that of 1 shows only one
symmetric signal at room temperature (d ˆ 3.80 ppm), despite
there being two nonequivalent methyl carbon atoms in the
2
4
2
solution/suspension of R SnCl in either water (1, 2) or acetone
3
(
3 ± 5) at room temperature [Eq. (1), in which R ˆ Me (1),
nBu (2), Cy (3), Ph( 4), Bz (5)].
asymmetric unit. Therefore the Me Sn groups must rotate
3
freely about the O-Sn-O axes on the NMR timescale.
Compounds 2 ± 5 were also characterized by C and 119Sn
[8]
13
CP MAS NMR spectroscopy. The tricyclohexyltin derivative
1
3
3
gives rise to several sharp or broad overlapping C signals in
[11]
the expected range for Cy Sn species. Compound 4 exhibits
3
Table 1. Thermogravimetric, 119Sn CP MAS NMR, FTIR, and FT Raman data of the compounds [(R
MoO
] ¥ nH
3
Sn)
2
4
2
2 4 2
O (1 ± 5) and Na MoO ¥ 2H O.
À1
n(MoO) and d(MoO) [cm
]
Compound
DTGmax [8C]
d(119Sn)
IR
Raman
1
2
3
4
5
(R ˆ Me)
(R ˆ nBu)
(R ˆ Cy)
(R ˆ Ph)
(R ˆ Bz)
297
287
262[
293[
197[
±
47.9
17.9, 20.3
856
810
941, 800
814
835
901, 869, 822
917, 867, 348, 311
924, 860, 308
940, 925, 856, 318
935, 864, 309
933, 863, 317
896, 834, 842, 807, 327, 285
[
a]
b]
À 96.7
c]
[d]
±
e]
[f]
À 67.0, À85.9, À112.6
Na
2
MoO
4
Á2H
2
O
±
[
a] See ref. [7]. [b] Starts to melt at 2158C and decomposes to an orange product. [c] Decomposes to a blue-green product. [d] No resolved signals were
observed. [e] Starts to melt at 858C, foams at 1088C. [f] Spectrum acquired with20000 scans (ca. 22 h) .
Chem. Eur. J. 2003, 9, 2685 ± 2695
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2687

I. S. GonÁalves et al.
FULL PAPER
three resonances at d ˆ 141.9, 136.1, and 128.2 ppm, attributed
to the phenyl carbon atoms. Two resonance ranges are in
evidence for the tribenzyltin derivative 5, at d ˆ 26.8 ± 30.2
and 123.4 ± 141.6 ppm, attributed to the methylene carbon and
observations also apply to 2 ± 5. The main differences are that
the IR-active nasym mode for 2 ± 5 is observed at slightly lower
À1
frequency (800 ± 835 cm ), and the Raman-active n mode
sym
À1
at higher frequency (924 ± 940 cm ). Hardcastle and Wachs
[7]
phenyl carbon atoms, respectively. As reported previously,
found the correlation between the Raman scattering frequen-
the 1 Sn CP MAS NMR spectrum of 2 shows two very close
singlets, suggesting the presence of two slightly nonequivalent
sites in the asymmetric units (Table 1). Compound 3, however,
exhibits only one 1 Sn resonance, indicating the presence of a
relatively simple asymmetric unit containing only one type of
19
cies of MoÀO bonds and their respective bond lengths in
molybdenum oxide compounds[ to be given by Equa-
15]
tion (2).
19
n ˆ 32895exp(À2.073r)
(2)
tin atom. The chemical shift value is consistent with the
presence of a five-coordinate tin atom.[
11, 12]
For the triphe-
The standard deviation associated with the calculation of a
nyltin derivative 4 no resolved signals were observed,
stretching frequency from an MoÀO bond lengthwas
À1
presumably because of its low crystallinity. The tribenzyltin
Æ25 cm . In 1 ± 5, the average MoÀO bond lengthis 1.77 ä
1
19
derivative 5 gave a complicated Sn CP MAS NMR spec-
trum composed of three resolved signals at d ˆ À67.0, À85.9,
and À112.6 ppm. These are shifted markedly upfield relative
by X-ray diffraction for 1 or EXAFS for 2 ± 5 (see below), and
À1
inserting this value in Equation (2) gives a value of 839 cm
for the nsym mode. This is close to the estimate by Hardcastle
1
19
to the characteristic d( Sn) values for four-coordinate
tribenzyltin compounds (‡55 to À25 ppm), and are in the
range typical for five-coordinate compounds.[ The presence
of a fourthsignal was also indicated, but it was impossible to
decide between lines at d ˆ À115 and À154 ppm because of
the overlapping of peaks and the complex spinning sideband
pattern.
and Wachs for the stretching frequency of a perfect MoO4
À1 [15]
tetrahedron (858 cm ). The observed symmetric stretches
13]
for Na MoO ¥ 2H O and 1 ± 5 are considerably higher than
2
4
2
these calculated values, indicating the presence of distorted
[15, 16]
MoO tetrahedra.
Accordingly, the vibrational spectra of
4
Na MoO ¥ 2H O indicate a lowering of the symmetry of the
2
4
2
2
À
[16]
[MoO4] oxoanion. It is surprising that the spectra of 1 ± 5
do not follow this trend. A possible exception is 3, which
Table 1 summarizes the observed MoÀO vibrational fre-
À1
quencies for 1 ± 5. The FTIR spectrum of 1 presents a very
shows a weak band at 940 cm in the FTIR spectrum. This
À1
strong band at 856 cm , which is assigned to the asymmetric
may be attributed to the nsym mode that has become IR-active
because of a reduction of symmetry from Td.
2À
stretchof t he [MoO 4] oxoanion. In the Raman spectrum,
À1
this mode is observed with medium intensity at 867 cm .
Mo K-edge and Sn K-edge extended X-ray absorption fine
structure (EXAFS) studies were carried out for 1 ± 5 to obtain
more detailed structural information on the average local
environments of molybdenum and tin. The X-ray crystal
structure of 1 is known and therefore it serves as a good model
À1
The Raman spectrum also contains a strong band at 917 cm
for the symmetric stretch and bands at lower wavenumbers
À1
(
348 and 311 cm ) for the bending modes. The n and
d(MoÀO) vibrational frequencies for 1 are weakly shifted in
[8]
[8]
comparison witht ho se of Na MoO ¥ 2H O (Table 1). De-
compound. The room-temperature Mo K-edge EXAFS of 1
2
4
2
spite the local D2d symmetry of eachMo(OSn) 4 fragment, the
was fitted by a model comprising four oxygen atoms at 1.77 ä
(Table 2; Figure 1). The refined coordination number (CN)
and distance match the X-ray crystallographic values very
observed vibrational spectrum of the MoO unit follows the
4
selection rules for Td symmetry.[
8, 14]
On the whole, these
Table 2. Mo K-edge and Sn K-edge EXAFS-derived structural parameters for [(Me
3
Sn)
2
MoO
4
] (1).[a]
CN[b]
r [ä]
2s [ä]
2
2[c]
E
f
[eV][d]
R [%][e]
Edge
T [K]
Fit
Atom
Mo K
298
A1
B1
O
O
Sn
O
Sn
O
Sn
Mo
C
4.0(2)
4.0(2)
2.0(4)
4.0(2)
4.0
4.0(2)
4.0
8.0(50)
3.0(5)
2.0(4)
2.0
1.768(2)
1.761(2)
3.824(3)
1.763(2)
3.829(3)
1.763(2)
3.829(3)
7.391(22)
2.131(7)
2.252(8)
3.831(3)
5.601(17)
7.469(6)
0.0032(2)
0.0028(2)
0.0045(4)
0.0028(2)
0.0064(3)
0.0028(2)
0.0064(3)
0.0139(37)
0.0061(8)
0.0062(11)
0.0056(4)
0.0165(30)
0.0079(7)
1.3(5)
2.5(5)
28.0
30.3
3
0
B2[f]
B3[f]
1.8(5)
1.8(5)
27.9
27.6
Sn K
30
C1[g]
À 9.6(7)
46.7
O
Mo
Sn
Sn
4.0(40)
8.0(30)
[
a] Coordination shells and mean interatomic distances [ä] for [(Me
3
2 4
Sn) MoO ], calculated from the crystal structure(ref. [8]) using the program SEXIE
(
7
see ref. [17]) (central atom in italics, coordination number in parentheses): Mo¥¥¥Oˆ1.770 (4), Mo¥¥¥Snˆ3.839 (4) (Mo-O-Snˆ143.68), Mo¥¥¥Mo
.390 (4), Mo¥¥¥Mo 7.466 (4); Sn¥¥¥Cˆ2.095 (2), Sn¥¥¥Cˆ2.148 (1), Sn¥¥¥Oˆ2.269 (2), Sn¥¥¥Moˆ3.839 (2), Sn¥¥¥Snˆ5.626 (4), Sn¥¥¥Snˆ7.390 (4),
Sn¥¥¥Snˆ7.463 (4). Maximum deviation for considering atoms to be in a common shellˆ0.01 ä. [b] CNˆcoordination number. Values in parentheses are
statistical errors generated in EXCURVE. The true errors in coordination numbers are likely to be of the order of 20%, and those for the interatomic
distances ca. 1.5% (see Ref. [18]). [c] Debye ± Waller factor; sˆroot-mean-square internuclear separation. [d] E
f
ˆedge position (Fermi energy), relative to
ÀS ]k dk/[S ]k dk)Â100%. [f] Multiple scattering calculation for Mo-O-Sn: Mo-O-Snˆ143.7(13)8; maximum
pathlengthˆ10 ä; maximum order of scatteringˆ3; paths consideredˆMo-O-Sn-Mo, Mo-O-Sn-O-Mo. [g] Multiple scattering calculation for Sn-O-Mo: Sn-
„
theory
exptl
3
exptl
3
calculated vacuum zero. [e] Rˆ( [S
2688
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 2685 ± 2695

Organotin ± Oxomolybdate Coordination Polymers
2685±2695
fit R factor decreased to 27.9% and the refined structural
parameters, including the Mo-O-Sn angle (143.7(13)8), are in
excellent agreement witht eh X-ray diffraction results. A
slight improvement in the overall fit was obtained by addition
of eight Mo atoms at 7.4 ä (fit B3; the crystal structure
predicts four Mo at 7.39 ä and four Mo at 7.47 ä). Not
surprisingly, there are large statistical errors in the refined
structural parameters for this distant third shell.
The low-temperature Sn K-edge EXAFS of 1 turned out to
be very complex and it was difficult to obtain a good fit, even
with the five-shell model described in Table 2 (Figure 1).
Nevertheless there is excellent agreement (to 1% or less)
between the EXAFS-derived interatomic distances and the
single-crystal X-ray values. Once again, multiple scattering
was included for the Sn-O-Mo unit (Sn-O-Mo ˆ 144.1(9)8).
Overall the results are consistent with the presence of trans-
R SnO units withtrigonal-bipyramidal geometry. A crucial
3
2
finding is that analysis of both the Mo K-edge and Sn K-edge
data gives the same value for the closest Mo ¥¥¥ Sn interaction
(
3.83 ä).
The Mo K-edge and Sn K-edge EXAFS analysis results for
3
± 5 are detailed in Tables 3 ± 5, and Figure 2 illustrates results
for compound 4 (other spectra are given in the Supporting
information; see also ref. [7] for results concerning 2). A few
general comments apply to the Mo K-edge EXAFS-derived
structural parameters for all compounds 2 ± 5. The first shell
always fits very well as four oxygen atoms at 1.763 ± 1.768 ä.
This shell is very well defined, characterized by low Debye ±
3
Figure 1. k -weighted EXAFS and Fourier transforms of [(Me
(
3
Sn)
2
MoO
4
]
1): a) Mo K-edge at 298 K; b) Mo K-edge at 30 K; c) Sn K-edge at 30 K.
The solid lines represent the experimental data and the broken lines show
fits using parameters given in Table 2 (fits A1, B2, and C1).
2
Waller factors in the range 0.002 ± 0.006 ä . Molybdenum is
present in all five coordination polymers as tetrahedral
3 2 4
Table 3. Mo K-edge and Sn K-edge EXAFS-derived structural parameters for [(Cy Sn) MoO ] (3).
well (see the footnote in Table 2).
According to the crystal structure,
there is only one type of molybde-
num atom in the asymmetric unit.
The second coordination shell for
this atom consists of four tin atoms
at the mean distance of 3.84 ä.
However, the Fourier transform
2
2
Edge
T [K]
Fit
Atom
CN
r [ä]
2s [ä]
E
f
[eV]
R [%]
Mo K
298
A1
A2
O
O
Sn
O
Sn
O
O
Sn
O
Sn
C
C
C
C
C
Mo
C
C
Mo
C
C
4.0(1)
4.0(1)
0.7(4)
4.0(1)
0.5(4)
4.0(1)
4.0(1)
1.0(4)
4.0(1)
0.6(3)
4.7(2)
4.6(7)
2.5(7)
4.7(2)
4.4(7)
0.5(3)
4.7(2)
4.4(7)
0.5(4)
4.6(2)
5.5(6)
4.0(10)
4.6(2)
5.4(6)
0.8(5)
4.6(2)
5.4(6)
0.8(4)
1.768(2)
1.768(2)
3.677(10)
1.768(2)
3.925(12)
1.768(2)
1.768(2)
3.698(8)
1.768(2)
3.999(9)
2.156(2)
3.083(8)
3.544(10)
2.156(2)
3.083(8)
3.670(10)
2.156(2)
3.083(8)
3.991(32)
2.156(2)
3.081(5)
3.544(12)
2.156(2)
3.081(5)
3.695(12)
2.156(2)
3.080(5)
3.992(10)
0.0057(2)
0.0056(2)
0.0(4)
0.0(4)
26.3
24.4
0.0095(16)
0.0057(2)
0.0076(18)
0.0044(2)
0.0044(2)
0.0100(13)
0.0044(2)
0.0063(13)
0.0090(4)
0.0133(16)
0.0067(18)
0.0090(4)
0.0125(16)
0.0108(17)
0.0090(4)
0.0126(17)
0.0179(61)
0.0071(4)
0.0084(9)
0.0108(24)
0.0072(4)
0.0081(9)
0.0141(21)
0.0071(4)
0.0082(9)
0.0109(16)
A3
0.1(4)
25.2
30
B1
B2
0.3(4)
0.2(4)
25.7
23.3
(
FT) of the room-temperature Mo
B3
0.3(4)
23.8
24.8
K-edge EXAFS of 1 does not
indicate a well-defined second shell
close to 4 ä (Figure 1). Cooling the
sample down to 30 K had a dra-
matic effect, leading to the appear-
ance of a new intense peak in the
FT just below 4 ä (Figure 1). Fit-
ting this shell as tin with single
scattering calculations gave a rea-
Sn K
298
C1[a]
À 8.6(3)
À 8.6(3)
À 8.6(3)
À 8.2(4)
À 8.3(4)
À 8.1(4)
C2
25.5
26.8
28.0
28.6
28.5
C3
30
D1[a]
D2
D3
sonable
.824(3) ä, fit B1 in Table 2), but
the refined coordination number of
.0(4) is much lower than the
result
(Mo ¥¥¥ Sn ˆ
3
C
C
C
Mo
C
2
expected value of 4.0. A much
better result was obtained upon
inclusion of multiple scattering for
the Mo-O-Sn unit (fit B2 in Ta-
ble 2; Figure 1). The goodness-of-
C
Mo
[a] Two-shell fits (carbon atoms at 2.16 and 3.08 ä) to the room-temperature and low-temperature Sn K-edge
EXAFS data gave R factors of 27.3% and 30.9%, respectively.
Chem. Eur. J. 2003, 9, 2685 ± 2695
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2689

I. S. GonÁalves et al.
FULL PAPER
Table 4. Mo K-edge and Sn K-edge EXAFS-derived structural parameters for
Table 5. Mo K-edge and Sn K-edge EXAFS-derived structural parameters for
[
(Ph
3
Sn)
2
MoO
4
] ¥ 2H
2
O (4).
[(Bz
3
Sn)
2
MoO
4
] ¥ 4H
2
O (5).
2
2
2
2
Edge T [K] Fit
Atom CN
r [ä]
2s [ä]
E
f
[eV]
R [%]
Edge T [K] Fit
Atom CN
r [ä]
2s [ä]
E
f
[eV] R [%]
Mo K 298
Sn K 298
A1
A2
O
O
Sn
O
Sn
C
C
C
C
C
C
C
C
Mo
C
C
C
C
Mo
C
4.0(1) 1.767(2)
4.0(1) 1.767(2)
1.0(6) 3.752(14) 0.0127(23)
4.0(1) 1.766(2) 0.0041(2)
1.0(6) 4.041(13) 0.0110(21)
0.0041(2)
0.0041(2)
0.4(4) 26.2
0.3(4) 25.3
Mo K 298
A1
A2
O
O
Sn
O
Sn
O
O
Sn
O
Sn
C
C
C
Mo
C
C
C
Mo
C
C
C
Mo
4.0(1) 1.765(2) 0.0043(2)
4.0(1) 1.765(2) 0.0043(2)
0.5(4) 3.735(12) 0.0082(19)
4.0(1) 1.764(1) 0.0043(2)
1.0(6) 3.996(13) 0.0120(22)
4.0(1) 1.764(1) 0.0035(2)
4.0(1) 1.764(1) 0.0035(2)
0.5(4) 3.653(24) 0.0124(41)
4.0(1) 1.764(1) 0.0035(2)
1.4(6) 3.938(8) 0.0111(13)
5.0(2) 2.152(2) 0.0090(4)
3.0(15) 2.999(30) 0.0382(107)
2.5(10) 3.512(13) 0.0084(29)
0.4(3) 3.726(14) 0.0104(25)
5.0(2) 2.152(2) 0.0090(4)
3.0(15) 2.998(29) 0.0379(104)
2.5(10) 3.539(13) 0.0090(26)
0.4(3) 3.992(12) 0.0089(19)
5.0(2) 2.158(2) 0.0082(4)
3.0(10) 3.035(19) 0.0213(52)
3.0(9) 3.524(10) 0.0069(18)
0.5(2) 3.941(7) 0.0064(11)
0.1(4) 23.7
0.1(4) 22.9
A3
0.6(4) 25.1
A3
0.2(4) 22.8
B1[a]
3.0
2.123(3)
0.0048(5)
0.0104(15)
À 7.6(6) 37.1
30
B1
B2
0.3(4) 23.7
0.2(4) 23.1
6.0(8) 3.071(8)
6.0
3.0
3.0
4.414(14) 0.0030(27)
4.912(20) 0.0076(40)
2.123(3)
B3
0.3(4) 21.3
B2[a]
B3[a]
B4[b]
0.0048(5)
0.0104(14)
À 7.5(6) 35.2
6.0(8) 3.070(8)
Sn K 298
C1[a]
À 7.0(3) 24.0
À 7.0(3) 23.9
À 6.4(4) 25.5
6.0
3.0
4.410(14) 0.0028(27)
4.910(19) 0.0073(38)
1.0(6) 3.731(18) 0.0168(33)
3.0
2.123(3)
0.0048(5)
0.0104(14)
À 7.7(6) 34.9
À 8.4(6) 38.2
C2
6.0(8) 3.072(8)
6.0
3.0
4.408(22) 0.0073(48)
4.906(21) 0.0083(41)
1.0(7) 4.027(15) 0.0132(27)
30
D1[b]
3.0
6.0
6.0
3.0
2.125(3)
3.067(8)
4.412(16) 0.0116(39)
4.923(26) 0.0104(56)
0.0050(5)
0.0122(14)
C
C
C
[
a] The R factor decreased from 29.4% to 27.2% upon addition of the second
[
a] Multiple scattering calculation for SnÀC1 ¥¥¥ C4: SnÀC ¥¥¥ C ˆ 1808; maximum
C shell at 3.00 ä, and from 27.2% to 24.9% upon addition of the third C shell at
3.51 ä. [b] The R factor decreased from 35.2% to 32.8% upon addition of the
second C shell at 3.04 ä, and from 32.8% to 29.8% upon addition of the third
C shell at 3.52 ä.
pathlength ˆ 10 ä; maximum order of scattering ˆ 3; paths considered ˆ Sn-C1-
C4-Sn, Sn-C1-C4-C1-Sn. Multiple scattering calculation for Sn ¥¥¥ C2ÀC3: Sn ¥¥¥
CÀC ˆ 158(7)8; maximum pathlength ˆ 10 ä; maximum order of scattering ˆ 3;
paths considered ˆ Sn-C2-C3-Sn, Sn-C2-C3-C2-Sn. [b] A full multiple scattering
calculation was performed, using a cluster with D3h point group symmetry
generated from the four-shell model. Spherical polar coordinates for shells 1 ± 4
2
À
[
MoO4] units. As described above, eachMo atom in 1 has
were q
between the principal axis (z axis) and the line from the central atom to the
atom(s) in shell i, and f is the angle between an atom in shell i and the x axis].
1
ˆ 908, q
2
ˆ 66.48, q
3
ˆ 73.28, q
4
ˆ 908, and f(1±4) ˆ 08 [q
i
is the angle
four tin neighbors at 3.83 ä. Compounds 2 ± 5 are different in
that it is generally possible to fit shells for tin at two different
distances, slightly shorter (3.65 ± 3.79 ä) and slightly longer
i
Maximum pathlength ˆ 10 ä; maximum order of scattering ˆ 3; paths consid-
ered ˆ Sn-C1-Sn-C1-Sn, Sn-C1-C1''-Sn, Sn-C1-C2-Sn, Sn-C1-C2-C1-Sn, Sn-C2-
C1-C2-Sn, Sn-C1-C2''-Sn, Sn-C1-C3-Sn, Sn-C1-C3-C1-Sn, Sn-C1-C4-Sn, Sn-C1-
C4-C1-Sn, Sn-C2-C2'-Sn, Sn-C2-C3-Sn, Sn-C2-C3-C2-Sn (C'' indicates C atom in
different phenyl ring; C' indicates equivalent C atom in the same phenyl ring).
(
1
3.93 ± 4.07 ä) than the corresponding Mo ¥¥¥ Sn interaction in
. The addition of these shells brings about relatively small
improvements in the overall fits, and there are large statistical
errors in the refined structural parameters, in particular the
coordination numbers, which are lower than expected and do
not seem to be consistent witht eh presence of four tin
neighbors. However, considerable caution must be attached
to the accuracy of these results, partly because of the large
statistical errors, and also because the refinement of coordi-
nation numbers and Debye ± Waller factors simultaneously
does not always give reliable results, owing to the high
correlation of the two parameters. Measuring the Mo K-edge
EXAFS spectra of 3 and 5 at low temperature (30 K) did not
result in a marked improvement in the definition of the Mo ¥¥¥
Sn interaction, unlike that seen for 1, although there were
slight reductions in the statistical errors with a concomitant
increase in the refined coordination numbers (Tables 3 and 5).
As described previously, the room-temperature Sn K-edge
EXAFS of 2 could be fitted by a two-shell model composed of
.5 carbon atoms at 2.14 ä and 2.0 oxygen atoms at 2.26 ä.[
7]
3
These distances are very similar to those for 1 and, therefore,
support the presence of trigonal-bipyramidal R SnO units
3
2
(
withs ha red oxygen atoms). By contrast, for 3 ± 5 it was not
possible to fit two separate shells for the first coordination
sphere (Tables 3 ± 5). Instead, only one carbon shell was fitted
at 2.12 ± 2.16 ä withoptimum coordination numbers in the
range 4.3 ± 5.0. The coordination number values nevertheless
3
Figure 2. a) Mo K-edge and b) Sn K-edge k -weighted EXAFS and
3 2 4 2
Fourier transforms of [(Ph Sn) MoO ] ¥ 2H O (4). The solid lines represent
the experimental data, measured at room temperature, and the broken
lines show fits using parameters given in Table 4 (fits A2 and B2).
2690
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Chem. Eur. J. 2003, 9, 2685 ± 2695

Organotin ± Oxomolybdate Coordination Polymers
2685±2695
suggest the presence of five-coordinate tin environments, in
shell is similar to that reported for tribenzyltin chloride.[20]
According to the X-ray crystal structure of this compound, the
next shell of carbon atoms after that at 3.03 ä is at 3.69 ä
(CN ˆ 3). Therefore, once again, the 3.5 ä shell for 5 seems
rather short to be assigned to CH carbon atoms of the phenyl
groups.
1
19
agreement withthe
Sn NMR results. That separate shells
for carbon and oxygen cannot be fitted is probably due to the
similarity of the two elements as backscatterers, and the close
proximity of the two shells. The presence of multiple tin
environments (especially for 4 and 5) also complicates the
analysis. As found for the Mo K-edge data, the FTs of the Sn
K-edge EXAFS of 2 ± 5 indicate the presence of shells around
The room-temperature Sn K-edge EXAFS and FT for
compound 4 are shown in Figure 2. The data were initially
modeled withfour carbon shells at 2.12, 3.07, 4.41, and 4.91 ä
(fit B1, Table 4). Although the best value for the coordination
number of the first shell was 4.3(2), this was fixed at 3.0 so that
multiple scattering could be included in the calculations for
the linear SnÀC ¥¥¥ C unit (2.12 and 4.91 ä, SnÀC ¥¥¥ C ˆ 1808).
4
ä. Indeed, it is possible to fit shells for molybdenum at two
different distances, slightly shorter (3.67 ± 3.76 ä) and slightly
longer (3.94 ± 4.07 ä) than the corresponding Sn ¥¥¥ Mo inter-
action in 1 (3.83 ä). The addition of each shell generally
produced statistically significant improvements in the overall
fits and the refined Sn ¥¥¥ Mo distances correlate remarkably
well (to within Æ0.01 ä in most cases) witht eh values
obtained from the Mo K-edge EXAFS data. This confirms
quite strongly the coexistence of short (3.65 ± 3.79 ä) and long
A separate unit was also defined for the other two carbon
atoms (3.07 and 4.41 ä, Sn ¥¥¥ CÀC ˆ 1588). The refined Sn ¥¥¥
C distances are in the expected range for triphenyltin
species.[ Satisfactory fitting of the two shells at 4.41 and
4.91 ä could not be achieved without multiple scattering
included. The EXAFS fits were further improved by addition
of shells for molybdenum at either 3.73 (fit B2) or 4.03 ä
21]
(
3.93 ± 4.07 ä) Mo ¥¥¥ Sn interactions in the organotin ± oxo-
molybdate coordination polymers 2 ± 5 (Figure 3). A referee
(
fit B3). Returning to the four-shell model, as an alternative to
defining two separate units for the multiple scattering
calculations, a full multiple scattering calculation by using
the so-called cluster method was achieved by starting with the
four-shell model described above and in Table 4. For each
shell, the position of one particular atom was defined by
spherical polar coordinates q and f, values for which were
determined from the above unit-method theoretical fits
Figure 3. Summary of the EXAFS-derived structural information for the
organotin ± oxomolybdates 2 ± 5. Th e SnÀO distance could be determined
(
Table 4). A D3h symmetry operation was then performed to
generate the complete cluster. The structural parameters
Debye ± Waller factors, interatomic distances, and E ) were
only for the tri-n-butyltin derivative 2.
(
f
suggested that, for the hydrated compounds 4 and 5, insertion
of water into SnÀO bonds to give nonlinear fragments of the
then refined with multiple scattering calculated for paths
between all atoms, including those through the central atom
(up to a maximum pathlength of 10 ä). The final cluster is
represented in Figure 4. The interatomic distances are rea-
sonable, including the calculated CÀC bond lengths for the
type SnO(H)H ¥¥¥ OMo may be possible. However, there is no
convincing evidence for this from the EXAFS data. In
particular, the Mo and Sn K-edge EXAFS results concerning
the nonbonded Sn ¥¥¥ Mo interactions for the anhydrous
compounds 2 ± 3 are not very different from those of the
hydrated compounds 4 ± 5.
aromatic rings (1.4 ä). However, the overall fit, as judged by
the R factor, is not better than that achieved using the simple
(and computationally muchfaster) unit met ho d.
For the Sn K-edge EXAFS of 3, a shell for carbon atoms at
3.08 ä could be fitted in addition to the shells described above
(
Table 3). The best coordination number for this shell was
about 4.5 for the room-temperature data, rising to 5.5 for the
low-temperature data. This is consistent with the presence of
tricyclohexyltin environments. The Sn ¥¥¥ C distance seems
reasonable when compared with that reported for trans-
dichlorotricyclohexylarsenic(v), [AsCl (C H ) ] (As ¥¥¥ C ˆ
2
6
11 3
[
19]
2
.84 ± 2.99 ä; AsÀC ˆ 1.99 ä). The FTs of the Sn K-edge
EXAFS of 3 recorded at different temperatures indicate the
presence of an additional shell at about 3.5 ä. This was best
fitted as either 2.5 (298 K, fit C1) or 4 (30 K, fit D1) carbon
atoms at 3.54 ä. However, this distance does not seem
plausible, considering that the X-ray crystal structure of the
[
AsCl (C H ) ] mentioned above reveals the next significant
2 6 11 3
shell of carbon atoms after those at 2.84 ± 2.99 ä to be at
.26 ± 4.33 ä. At present, we are unable to offer an attribution
4
for this shell. Curiously, the same shell is also in evidence for
the tribenzyltin derivative 5, in addition to a shell of three
carbon atoms at 3.0 ä (Table 5). The distance for the latter
Figure 4. Representation of the final cluster with D3h symmetry used to
model the room-temperature Sn K-edge EXAFS of 4 withfull multiple
scattering included in the calculations (fit B4, Table 4).
Chem. Eur. J. 2003, 9, 2685 ± 2695
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2691

I. S. GonÁalves et al.
FULL PAPER
Sulfoxidation catalysis in the presence of 1 ± 5: The oxidation
of benzothiophene was carried out with aqueous hydrogen
peroxide in the presence of compounds 1 ± 5 at 358C and
atmospheric pressure, with water, acetonitrile, ethanol, or 1,2-
dichloroethane as additional co-solvent (substrate/oxidant/
catalyst ˆ 100:200:1). Control experiments showed that ben-
zothiophene oxidation did not take place to a measurable
extent in the absence of 1 ± 5. In the most favorable case (2 as
catalyst precursor and 1,2-dichloroethane as co-solvent),
conversion of benzothiophene reached 57% within one hour
1 ± 3 appear to dissolve slightly during the reaction, and
compounds 4 and 5 are even more soluble. In the ethanol-
containing system, the trimethyltin derivative is soluble,
whereas the other compounds exhibit poor or only partial
solubility. 1,2-Dichloroethane dissolves the substrate, but is
immiscible with the hydrogen peroxide solution, leading to
the formation of two liquid phases. For this system, 1 is very
soluble, 2 and 3 only partially so, and 4 and 5 are insoluble.
The turnover frequencies of benzothiophene conversion at
358C (calculated for the first 2 h of reaction) vary according to
the type of co-solvent and generally increase in the order
(
Figure 5). The nature of the additional solvent has an
water< acetonitrile < ethanol < 1,2-dichloroethane
(Fig-
ure 6). This trend parallels the decrease in solvent polarity,
as indicated by the dielectric constants (e) at 258C: water
Figure 6. Turnover frequencies of benzothiophene conversion at 358C
(
calculated for the first 2 h of reaction) for the different catalyst precursors,
in different co-solvents.
Figure 5. Kinetics of benzothiophene oxidation with aqueous H
2 2
O at
3
(
58C in the presence of the organotin ± oxomolybdates 1 (‡), 2 (
&
), 3 (~), 4
(
80.10) > acetonitrile (35.94) > ethanol (24.55) > 1,2-dichloro-
ethane (10.42). In water, long induction periods (up to
00 min) are observed, which become shorter for acetonitrile
and ethanol and are not observed for 1,2-dichloroethane
except for 1). This phenomenon may be related to the
Â) and 5 (*), using a) water, b) acetonitrile, c) ethanol, or d) 1,2-dichloro-
ethane as co-solvent. Molar ratio substrate/oxidant/catalyst ˆ 100:200:1.
1
important effect on yields and reaction kinetics, although this
effect is strongly dependent on the catalyst type (Figure 5).
Regardless of the type of catalyst precursor or additional
solvent, the reactions were highly selective and led directly to
the sulfone (1,1-dioxide), even for low levels of substrate
conversion [Eq. (3)]. Only traces of sulfoxides were found
among the oxidation products.
(
different coordinating powers of the solvent molecules. Thus,
H O and MeCN may compete withperoxide molecules for
coordination to the Lewis acidic Mo center. This will clearly
have a detrimental effect if, as is the case for H O -based
epoxidations of olefins withMo complexes, coordination of
the oxidant to the metal center is necessary to generate an
electrophilic oxygen atom.[
2
VI
2
2
VI
22, 23]
Nucleophilic attack of the
electron-rich sulfur atom of the substrate on the peroxidic
oxygen atom of the intermediate species may then take place,
yielding the sulfoxide, which may subsequently be oxidized to
the corresponding sulfone.[
23±25]
Relative to H O and MeCN,
2
alcohols are relatively weak ligands and, therefore, may
compete less witht he oxidant for coordination to molybde-
num, resulting in a higher initial activity. The use of a
noncoordinating solvent, namely 1,2-dichloroethane, facili-
tates achievement of the highest initial oxidation rates.
When 1,2-dichloroethane is used as the co-solvent, the
initial sulfoxidation rates increase in the order 4 < 5 < 3 < 2.
However, as noted above, the polymers 2 and 3 partially
dissolve in this system and the catalysis could be homoge-
neous. In terms of ease of catalyst separation from the
Some properties of the different catalyst systems need to be
borne in mind when interpreting the oxidation results. With
water as the only solvent, two liquid phases are present as
benzothiophene is insoluble in water. For this system it was
noted that the catalyst precursors 4 and 5 dissolve readily,
whereas 1 ± 3 are insoluble (forming solid ± liquid ± liquid (S ±
L ± L) systems). Acetonitrile and ethanol are fully miscible
with the substrate and the hydrogen peroxide solution,
forming a single liquid phase. With acetonitrile, the polymers
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Chem. Eur. J. 2003, 9, 2685 ± 2695

Organotin ± Oxomolybdate Coordination Polymers
2685±2695
reaction products, the system that includes the tribenzyltin
derivative 5, which gives practically the same benzothiophene
conversion after 6.5 h(approximately 60%), is a more
attractive alternative, since for this system the solid catalyst
could be separated easily from the liquid phase by centrifug-
ing. After being washed thoroughly with 1,2-dichloroethane,
the solid was reused in a second reaction cycle. Benzothio-
phene conversion after 7 h was 57%, compared with 60%
obtained witht he freshcatalyst, indicating no significant loss
of activity. When the reaction is carried out without substrate,
with 5 and 1,2-dichloroethane as co-solvent at 358C, the
nonproductive decomposition of H O measured after 4 his
2
2
approximately 10%. In all the above experiments the total
amount of peroxide was added at the beginning and the H O /
benzothiophene molar ratio was 2:1. A three-fold increase in
this ratio does not change product selectivity, but raises
conversion in increments which increase with the reaction
time (Figure 7). A further increase in this ratio to 10:1 leads to
2
2
Figure 8. Apparent activation energy of benzothiophene oxidation in the
presence of [(Bz Sn) MoO ] ¥ 4H O (5), using different co-solvents.
3 2 4 2
explanation for the poor performance is that diffusion of
substrate and/or oxidant molecules between the layers is
hindered by the hydrophobic character of the interlamellar
space. The systems containing 2 and 3 may exhibit an
induction period for the same reason, but in these cases the
bulkier n-butyl and cyclohexyl groups probably give rise to a
more open structure, thereby facilitating eventual intercala-
tion of reactant molecules. This might be a better explanation
for the induction periods observed in the presence of water,
acetonitrile, or ethanol (instead of with the competing
influence of coordinating solvent molecules). Thus, the
polymers 4 and 5 crystallize as hydrated compounds and
mass transfer of reactants in the presence of polar solvents
may not be so limiting, resulting in higher initial sulfoxidation
activities. The kinetic curves demonstrate that, for a given co-
solvent, differences in activity are concentrated in the first
1
± 2 h of reaction, after which the observed reaction rates are
comparable for all the compounds 2 ± 5. The trimethyltin
derivative 1 in the presence of 1,2-dichloroethane exhibits a
very long induction period of 6 h, after which benzothiophene
conversion increases to 46% after reaction for 24 h. As
mentioned above, 1 immediately starts to dissolve in this
reaction mixture. The long induction period may be associ-
ated witht eh formation of catalytically active species in
solution.
Figure 7. Effect of oxidant concentration on benzothiophene oxidation at
3
58C in the presence of [(Bz
3
Sn)
2 4 2
MoO ] ¥ 4H O (5), with1,2-dic hl oro-
2 2
ethane as co-solvent: Initial H O
/substrate molar ratio ˆ 2:1 (*), 6:1 (~)
and 10:1 (Â).
a slight decrease in benzothiophene conversion. After reac-
tion for 24 ht he sulfone is obtained in quantitative yield.
Apparent activation energies of sulfoxidation for the catalyst
systems involving 5 were determined in the temperature range
Concluding Remarks
35 ± 658C (Figure 8). Higher reaction temperatures improved
In this work, the [(R Sn) MoO ] family of compounds has
3
2
4
benzothiophene conversion without affecting selectivity. In
accordance witht he above observations on use of different
solvents, the activation energy of sulfoxidation increased from
been extended to include novel tricyclohexyltin and triben-
zyltin derivatives. The physicochemical characterization of
these compounds, and also of those with R ˆ n-butyl and
phenyl, points to the formation of coordination polymers in
À1
À1
5
kcalmol with 1,2-dichloroethane to 27 kcalmol with
water.
The catalyst systems containing the derivatives 1 ± 3 gen-
erally exhibit similar kinetic profiles for a given co-solvent
Figure 5). However, anomalous behavior is exhibited by 1 in
2À
the solid state, in which tetrahedral [MoO ] subunits are
4
‡
linked through [R Sn] spacers. These compounds are inter-
3
esting candidates as catalysts or catalyst precursors for
oxidation reactions. We have shown that benzothiophene
can be oxidized selectively to the corresponding sulfone with
aqueous hydrogen peroxide. The catalysis results depend on
the complex interplay between various factors, such as the
addition of co-solvents and the hydrophobic/hydrophilic
(
the presence of water as only solvent (S ± L ± L system), for
which no conversion of benzothiophene was observed. As
described above, the polymers 1 ± 3 crystallize as anhydrous
compounds. Given that 1 has a layered structure, a possible
Chem. Eur. J. 2003, 9, 2685 ± 2695
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2693

I. S. GonÁalves et al.
FULL PAPER
properties of the starting polymers. Changing the nature and
size of the tin-bound R groups influences catalytic perform-
ance, by inducing structural changes and modifying the
surface polarity/polarizability of the compounds. Future work
will center on the application of the sulfoxidation reaction
with hy drogen peroxide to remove sulfur from petroleum
products.
Preparation of [(Cy
O (0.72 g, 3 mmol) in water (4.5 mL) was added dropwise withstirring
to a mixture of Cy SnCl (2.40 g, 6 mmol) in acetone (40 mL). A colorless
precipitate was formed immediately and stirring was continued for 5 min.
The precipitate was filtered, then washed thoroughly with water and cold
acetone. The compound dried spontaneously overnight at room temper-
ature and was dried further under vacuum. Yield: 80% (2.14 g); IR (KBr):
3 2 4 2 4
Sn) MoO ] (3): A saturated solution of Na MoO ¥
2
H
2
3
nÄ ˆ 2918 (vs), 2846 (s), 1444 (s), 1259 (m), 1171 (m), 991 (m), 941 (w), 881
À1
(
(
m), 843 (m), 800 (vs), 661 cm (m); Raman: nÄ ˆ 2928 (vs), 2847 (vs), 1439
m), 1339 (w), 1295 (w), 1269 (w), 1258 (w), 1172 (m), 1080 (w), 1042 (w),
1
022 (m), 992 (w), 940 (m), 925 (w), 880 (m), 856 (w), 842 (m), 806 (m), 649
À1
13
(
s), 487 (w), 419 (w), 318 (w), 298 (w), 239 (w), 189 (s), 88 cm (w);
CP MAS NMR (8 kHz, 258C): d ˆ 37.2, 35.9, 34.3, 32.9, 31.8, 29.8, 29.6, 29.4,
8.1, 27.5, 26.3 ppm; elemental analysis calcd (%) for C36 MoSn
890.20): C 48.57, H 6.79; found C 48.68, H 7.13.
Preparation of [(Ph Sn) MoO ] ¥ 2H (4):
Na MoO ¥ 2H O (1.21 g, 5 mmol) in water (7.5 mL) was added dropwise
C
2
(
H
60
O
4
2
ExperimentalSection
Microanalyses were performed at the ITQB, Oeiras (C. Almeida).
Thermogravimetric analysis studies were performed using a Mettler
TA3000 system at a heating rate of 58Cmin under nitrogen. Powder
3
2
4
2
O
A saturated solution of
2
4
2
À1
withstirring to a solution of Ph SnCl (3.85 g, 10 mmol) in acetone (18 mL).
The colorless precipitate that was formed immediately was isolated,
3
XRD data were collected on a Philips X×pert diffractometer with CuKa
radiation filtered by Ni. Infrared spectra were recorded in the range 400 ±
washed, and dried as for 3, above. Yield: 85% (3.58 g); IR (KBr): nÄ ˆ 3066
À1
(m), 3047 (m), 1955 (w), 1882 (w), 1819 (w), 1479 (m), 1429 (s), 1076 (m),
4
000 cm on a Unican Mattson Mod 7000 FTIR spectrometer withKBr
À1
pellets. Raman spectra were recorded on a Bruker RFS 100/S FT Raman
spectrometer using 1064 nm excitation of the Nd/YAG laser. Room-
999 (m), 812 (vs), 727 (s), 696 (s), 453 cm (s); Raman: nÄ ˆ 3139 (vw), 3051
(s), 1580 (m), 1481 (w), 1431 (w), 1332 (w), 1192 (w), 1158 (w), 1023 (m),
1002 (vs), 935 (m), 864 (m), 655 (m), 618 (w), 309 (m), 275 (w), 213 (s),
temperature 13C and Sn NMR spectra were recorded in the solid state at
119
À1
13
1
00.62 and 149.21 MHz, respectively, on a Bruker Avance 400(9.4 T)
100 cm
(s);
C
CP MAS NMR (8 kHz, 258C): d ˆ 141.9, 136.1,
1
3
1
128.2 ppm; elemental analysis calcd (%) for C H O MoSn (895.99): C
spectrometer. C CP MAS NMR spectra were recorded witha 4.5 ms H
36 34
6
2
9
08 pulse, 2 ms contact time, a spinning rate of 8 kHz, and 4 s recycle delays.
Sn CP MAS NMR spectra were recorded witha 3.5 ms H 908 pulse, 3 ms
48.26, H 3.81; found: C 47.77, H 3.52.
1
19
1
Preparation of [(Bz Sn) MoO ] ¥ 4H O (5): A saturated solution of
3
2
4
2
contact time, a spinning rate of 6 ± 10 kHz and 4 s recycle delays. For 5, one
2 4 2
Na MoO ¥ 2H O (0.72 g, 3 mmol) in water (4.5 mL) was added dropwise
1
19
Sn MAS NMR spectrum was also recorded, using a spinning rate of
5 kHz and 40 s recycle delays (4050 scans). Chemical shift references were
withstirring to a solution of Bz SnCl (2.56 g, 6 mmol) in acetone (36 mL).
3
1
A colorless precipitate that was formed immediately quickly redissolved.
1
3
119
SiMe
4
and SnMe
4
.
C and Sn NMR spectra were also recorded in the
The acetone was evaporated to give a colorless elastic solid suspended in
the aqueous phase. After treatment with ultrasound, the white powder
obtained was filtered and washed with cold acetone. The compound was
left to dry overnight at room temperature and turned pale yellow upon
further drying in vacuo (drying at higher temperatures degrades the
product). Yield: 72% (2.19 g); IR (KBr): nÄ ˆ 3078 (w), 3057 (m), 3020 (m),
2920 (w), 1637 (m), 1597 (s), 1491 (vs), 1452 (s), 1402 (m), 1207 (m), 1108
(w), 1055 (m), 1030 (m), 872 (m), 835 (vs), 798 (m), 758 (vs), 727 (s), 708
solid state at 125.76 and 186.50 MHz, respectively, on a Bruker Avance 500
spectrometer.
Mo K-edge and Sn K-edge X-ray absorption spectra were measured at
room temperature or approximately 30 K (in an Oxford Instruments
cryostat filled withHe exc ha nge gas) in transmission mode on beamline
BM29 at the ESRF (Grenoble),[ operating at 6 GeV in ³
26]
2
3
filling mode
with typical currents of 170 ± 200 mA. The one scan that was performed for
each sample was set up to record the pre-edge in 5 eV steps and the post-
À1
(vs), 696 (vs), 619 (w), 551 (w), 451 cm (m); Raman: nÄ ˆ 3156 (w), 3057
À1
(s), 2974 (w), 2929 (w), 1599 (s), 1581 (w), 1492 (w), 1452 (w), 1407 (w),
1335 (vw), 1209v (s), 1155 (m), 1121 (s), 1107 (s), 1031 (m), 1001 (vs), 933
(m), 863 (w), 800 (w), 621 (w), 582 (w), 563 (s), 435 (s), 317 (m), 225 (m),
edge region in 0.025 ± 0.05 ä steps, giving a total acquisition time of
approximately 45 min per scan. The order-sorting double Si(311) crystal
monochromator was detuned by 40% to ensure harmonic rejection. Solid
samples were diluted withBN and pressed into 13 mm pellets. Ionization
À1
13
203 (m), 114 cm (s); C CP MAS NMR (8 kHz, 258C): d ˆ 141.6, 140.1,
chamber detectors were filled with Kr to give 30% absorbing I
o
(incidence)
139.3, 137.6, 128.6, 125.7, 125.0, 124.2, 123.4 (all phenyl C), 30.2, 28.6,
and 70% absorbing I (transmission). The programs EXCALIB and
t
26.8 ppm (all CH
2 50 8 2
); elemental analysis calcd (%) for C42H O MoSn
EXBACK (SRS Daresbury Laboratory, UK) were used in the usual
manner for calibration and background subtraction of the raw data.
EXAFS curve-fitting analyses, by least-squares refinement of the non-
(1016.18): C 49.64, H 4.96; found: C 49.13, H 4.40.
Catalytic sulfoxidation in the presence of 1 ± 5: Catalytic oxidation of
benzothiophene was performed under air (atmospheric pressure) in a
reaction vessel equipped witha magnetic stirrer, immersed in a t he rmo-
stated oil bathat 35 8C. The catalyst/substrate molar ratio was 1% (36 mmol
coordination polymer/3.6 mmol benzothiophene) and the benzothiophene/
hydrogen peroxide (30% aqueous) molar ratio was 0.5:1, with 4 mL
solvent. Samples were withdrawn periodically and analyzed in a gas
chromatograph (Varian 3800) equipped with a capillary column (SPB-5,
20 m  0.25 mm  0.25 mm) and a flame ionization detector. The substrate
was quantified by using a calibration curve and undecane as internal
standard (added after the reaction). Hydrogen peroxide was quantified by
standard iodometric titration.
3
Fourier filtered k -weighted EXAFS data, were carried out with the
[
27]
program EXCURVE (EXCURV98 version ) by using fast curved wave
[
28]
theory.
Phase shifts were obtained within this program by ab-initio
calculations based on the Hedin Lundqvist/von Barth scheme. Unless
otherwise stated, the calculations were performed with single scattering
only.
The precursors Na
2 4 2 3 3
MoO ¥ 2H O, Me SnCl, and Ph SnCl were obtained
from Aldrichand recrystallized before use. Literature met ho ds were used
[
29]
[30]
to prepare Bz
(nBu Sn) MoO
Preparation of [(Me
O (1.21 g, 5 mmol) in water (7.0 mL) was added dropwise withstirring
to a solution of Me SnCl (1.99 g, 10 mmol) in water (5.0 mL). A colorless
3
SnCl
] (2) was prepared as described previously.
Sn) MoO ] (1): A saturated solution of Na
and Cy
3
SnCl.
The tri-n-butyltin(iv) derivative
[7, 8]
[
3
2
4
3
2
4
2 4
MoO ¥
2
H
2
3
precipitate was formed immediately and stirring was continued for 5 min.
The precipitate was filtered, washed thoroughly with water, and air-dried at
Acknowledgement
1
1
5
9
1
008C overnight. Yield: 86% (2.09 g); IR (KBr): nÄ ˆ 2997 (m), 2920 (s),
749 (w), 1707 (w), 1400 (m), 1261 (w), 1195 (w), 1190 (s), 856 (vs), 725 (vs),
This work was mainly funded by FCT, POCTI and PRAXIS XXI
(including a Ph.D. grant to M.A. and postdoctoral grants to A.A.V. and
M.P.). We acknowledge the European Synchrotron Radiation Facility for
provision of synchrotron radiation facilities and we thank Stuart Ansell for
assistance in using beamline BM29. Cl a¬ udia Morais and Paula Esculcas are
thanked for assistance with the NMR experiments.
À1
55 cm (vs; nas SnÀC); Raman: nÄ ˆ 3001 (w), 2924 (s), 1214 (m), 1188 (w),
17 (s), 867 (m), 555 (s; nas SnÀC), 525 (vs; n SnÀC), 348 (w), 311 (w),
s
À1
13
42 cm (s); C CP MAS NMR (8 kHz, 258C): d ˆ 3.8 ppm; elemental
MoSn (487.53): C 14.78, H 3.72; found: C
analysis calcd (%) for C
4.66, H 3.65.
6
H
18
O
4
2
1
2694
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 2685 ± 2695

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2685±2695
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Received: September 6, 2002 [F4399]
Chem. Eur. J. 2003, 9, 2685 ± 2695
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2695