Synthesis, characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

Article abstract of DOI:10.1002/aoc.3722

Although homogeneous catalysts provide high performance and selectivity, the difficulty of separation and recycling of these catalysts has bothered the scientific community worldwide. Therefore, the demand for heterogeneous catalysts that possess the advantages of homogeneous ones, with ease of separation and recyclability remains a topic of major impact. The oligomeric catalyst synthesized in this work was characterized using elemental analysis, Fourier transform infrared, ¹³C NMR, ²⁹Si NMR and energy-dispersive X-ray spectroscopies, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and Brunauer–Emmett–Teller analysis and compared to its homogeneous counterpart [W(CO)₃Br₂(ATC)] in the epoxidation of 1-octene, cyclooctene, (S)-limonene, cis-3-hexen-1-ol, trans-3-hexen-1-ol and styrene. The results showed that the percentage conversion for the homogeneous species [W(CO)₃Br₂(ATC)] was slightly higher than for the oligomeric catalyst (POSS-ATC-[W(CO)₃Br₂]). Furthermore, the selectivity for epoxide of the oligomeric catalyst was greater than that of the homogeneous catalyst by about 25% when (S)-limonene was used. Great conversions (yields) of products were obtained with a wide range of substrates and the catalyst was recycled many times without any substantial loss of its catalytic activity.

Full text of DOI:10.1002/aoc.3722

Received: 20 September 2016
DOI 10.1002/aoc.3722
Revised: 23 November 2016
Accepted: 29 November 2016
F U L L PA P E R
Synthesis, characterization and catalytic application of a new
organometallic oligomer based on polyhedral oligomeric
silsesquioxane
Eduardo Guimarães Vieira1 | Rafael Oliveira Silva1 | Enes Furlani Junior3 |
Newton Luiz Dias Filho1,2
1 Departamento de Física e Química, UNESP,
Although homogeneous catalysts provide high performance and selectivity, the dif-
ficulty of separation and recycling of these catalysts has bothered the scientific com-
munity worldwide. Therefore, the demand for heterogeneous catalysts that possess
the advantages of homogeneous ones, with ease of separation and recyclability
remains a topic of major impact. The oligomeric catalyst synthesized in this work
was characterized using elemental analysis, Fourier transform infrared, 13C NMR,
29Si NMR and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, thermo-
gravimetric analysis, scanning electron microscopy and Brunauer–Emmett–Teller
analysis and compared to its homogeneous counterpart [W(CO)3Br2(ATC)] in the
epoxidation of 1‐octene, cyclooctene, (S)‐limonene, cis‐3‐hexen‐1‐ol, trans‐3‐
hexen‐1‐ol and styrene. The results showed that the percentage conversion for the
homogeneous species [W(CO)3Br2(ATC)] was slightly higher than for the oligo-
meric catalyst (POSS‐ATC‐[W(CO)3Br2]). Furthermore, the selectivity for epoxide
of the oligomeric catalyst was greater than that of the homogeneous catalyst by about
25% when (S)‐limonene was used. Great conversions (yields) of products were
obtained with a wide range of substrates and the catalyst was recycled many times
without any substantial loss of its catalytic activity.
Universidade Estadual Paulista, Av. Brasil, 56‐
Centro, Caixa Postal 31, 15385‐000 Ilha Solteira,
São Paulo, Brazil
2 Universidade do Extremo Sul Catarinense, Av.
Universitaria, 1105, CP 3167, CEP88806‐000
Criciúma, Santa Catarina, Brazil
3 Departamento de Fitotecnia, Tecnologia de
Alimentos Sócio Economia, Faculdade de
Engenharia, UNESP, Universidade Estadual
Paulista, Campus de Ilha Solteira, São Paulo,
Brazil
Correspondence
N. L. Dias Filho and E. G. Vieira, Departamento
de Física e Química, UNESP – Universidade
Estadual Paulista, Av. Brasil, 56‐Centro, Caixa
Postal 31, 15385‐000 Ilha Solteira, São Paulo,
Brazil.
Email: nldias@unesc.net; eduardogv5007@gmail.
com
Funding information
FAPESP‐Fundação de Amparo à Pesquisa do
Estado de São Paulo, Grant/Award Number: 2013/
24602‐0 and 2014/05566‐5. CNPq‐Conselho
Nacional de Desenvolvimento Científico e
Tecnológico, Grant/Award Number: 306265/2013‐
3 and 448168/2014‐6.
KEYWORDS
catalysis, olefins, oligomer; organometallic catalyst
An oligomer is known as a molecule of intermediate relative
molecular mass, the structure of which essentially comprises
a small plurality of units derived, actually or conceptually,
from molecules of lower relative molecular mass.[1]
Recently, extensive research has been made into polyhedral
oligomeric silsesquioxane (POSS) due to its multidisciplin-
ary applications such as in column chromatography,[2,3]
adsorption,[4,5] separation and preconcentration[4,6] and het-
erogeneous catalysis.[7–12] POSS are nanoplatforms with
one to eight reactive or nonreactive organofunctional groups
(R) anchored to the eight possible vertices of the cubic
silsesquioxane. In a POSS, the cubic silica core is rigid ‘hard
particles’ with a diameter of 0.53 nm and a spherical radius
of 1–3 nm including peripheral organic units.[13,14] Reviews
of this field have been published by Unno et al.[15] and
Dudziec et al.[16]
POSS has been widely used to support transition metal
oxides for applications in catalytic epoxidation.[12,17,18] This
support is attractive for its high specific surface area,
mechanical stability and promotion of well‐dispersed active
sites. The epoxidation of organic substrates is especially
interesting because of the industrial importance of this type
of reaction, the products of which are widely used as starting
materials in the synthesis of many organic compounds.[19]
Transition metal complexes, such as those of tungsten and
molybdenum, are considered superior catalysts for the
Appl Organometal Chem. 2017;e3722.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3722

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VIEIRA ET AL.
selective epoxidation of olefins by alkyl hydroperox-
ides.[12,17,18] Molybdenum and tungsten[19] are well‐known
catalysts and have been widely investigated. In general, epox-
ides can be prepared by the reaction of olefins with tert‐butyl
hydroperoxide (TBHP), catalyzed by transition metal com-
plexes.[20,21] Many POSS catalysts have been employed in
epoxidation of olefins.[19] For example, Leng et al.[22]
employed a polyhedral oligomeric vinylsilsesquioxane as cat-
alyst for epoxidation of 1‐octene and the results showed a
conversion of 56% in a period of 6 h. In contrast, our catalyst
exhibits a better conversion (60%) in half the time. Leng
et al.[23] also achieved a conversion of 30% in the epoxidation
of styrene using a heterogeneous catalyst based on POSS‐
bridged oxomolybdenum in a period of 6 h and with a selec-
tivity of 83%. In the work reported here, a conversion of 68%
was obtained for the same substrate, and a selectivity of 100%
for a period of 2 h using the heterogeneous catalyst POSS‐
ATC‐W. Zhao et al.[24] investigated the catalytic activity of
POSS‐IM8‐PW in the epoxidation of cyclooctene in dichlo-
romethane. The results showed a conversion of approxi-
mately 55%. The catalyst used in the present work has
shown a superior conversion (72%) using the same solvent.
Dias Filho et al.[21] employed an oligosilsesquioxane cage
functionalized with molybdenum(II) for epoxidation of
cyclooctene and styrene in the presence of TBHP. The
results showed a conversion of 59% for cyclooctene and
36% for styrene. In short, the advantages of the newly
synthesized oligomeric material over those previously
reported in the literature consist of isolation of products
of high purity with excellent yields, good reaction times,
simple product separation procedure and reusability of the
catalyst.
1.2 | 1.2 Instrumentation
Fourier transform infrared (FT‐IR) spectral analyses were
conducted using a Nicolet 5DXB instrument. 13C NMR
and 29Si NMR analyses in the solid state were performed
with a Bruker Avance 400 spectrometer in the chemical
institute of Araraquara/SP. X‐ray diffraction (XRD) pat-
terns were obtained with a Rigaku Miniflex instrument,
operating at 30 kV and 15 mA using a nickel filter and
Cu radiation (Kα) with a wavelength of 1.5418 Å. Ther-
mogravimetric analysis (TGA) curves were obtained with
a SDT 2960 thermobalance. The temperature range was from
room temperature to 1252 K at a heating rate of 20 °C min−1
using air atmosphere to purge the system with a flow rate of
100 ml min−1. Scanning electron microscopy (SEM) images
were obtained using an EVO LS15 (Carl Zeiss) with speci-
mens coated with gold. Energy‐dispersive X‐ray spectroscopy
(EDS) was conducted with an Oxford Instruments Inca X‐act
with a resolution of 133 eV. Surface area was characterized
using the Brunauer–Emmett–Teller (BET) method through
N2 adsorption at 77 K.
The tungsten content was determined using inductively
coupled plasma with mass spectrometry (ICP‐MS; Thermo
Scientific Series X 2). For measurement, the tungsten catalyst
was added to a platinum crucible, followed by lithium
tetraborate. The lithium tetraborate and the sample were
homogenized and placed in a muffle furnace at a temperature
of 1000 °C. After the removal of the crucible from the muffle
furnace, the melted mass was dissolved in dilute nitric acid.
After complete solubilization, the volume was adjusted and
analyzed using ICP.
Analysis in the liquid state was not performed because the
samples were fully insoluble in various types of solvents.
Therefore, the main objective of the research reported here
was the synthesis and the catalytic application of a new oligo-
meric catalyst based on POSS (POSS‐ATC‐[W(CO)3Br2]) in
the epoxidation of olefins. Additionally, the work looked for
heterogeneous catalysts that combine the great selectivity and
other advantages of homogeneous catalysts, including greater
selectivity and yield. Octakis[(3‐amino‐1H‐1,2,4‐triazole‐5‐
carboxylic acid)propyl]octasilsesquioxane–[W(CO)3Br2] was
investigated as a catalyst in the epoxidation of 1‐octene,
cyclooctene, (S)‐limonene, cis‐3‐hexen‐1‐ol, trans‐3‐hexen‐
1‐ol and styrene.
1.3 | Synthesis of Oligomeric Catalyst: POSS‐ATC‐
[W(CO)3Br2]
In a flask containing 4 l of CH3OH, 225 ml of 3‐
chloropropyltriethoxysilane and 135 ml of HCl were added
under nitrogen atmosphere. The solution was vigorously
stirred and after 6 weeks the white solid that formed was
filtered, washed and dried. The resulting material, namely
octakis(3‐chloropropyl)octasilsesquioxane (POSS‐Cl), was
obtained in a yield of 41%.
Next, about 19.76 g (154.18 mmol) of ATC ligand, dur-
ing a period of 50 min, was added to a solution of POSS‐Cl
(10 g, 9.64 mmol) in dimethylformamide at a temperature
of 160 °C for 24 h. To precipitate the nanomaterial,
ethanol was added to the reaction. The white material was
filtered and washed with ethanol, resulting in a modified olig-
omer, namely octakis[(3‐amino‐1H‐1,2,4‐triazole‐5‐carbox-
ylic acid)propyl]octasilsesquioxane (POSS‐ATC), in 93%
yield. The resulting product was obtained after several
attempts.
1
| EXPERIMENTAL
1.1 | Materials
Chemicals were purchased from Sigma‐Aldrich. 3‐Amino‐
1H‐1,2,4‐triazole‐5‐carboxylic acid (ATC) was used as
received from Sigma‐Aldrich. All solvents used in this study
were previously purified, unless otherwise noted. The com-
plex [W(CO)3Br2(NCMe)2] was prepared according to litera-
ture methods, but with modifications.[25,26]

VIEIRA ET AL.
3 of 13
Next, a mixture of POSS‐ATC (2.5 g, 1.41 mmol) and
the amount of complex, the amount of adsorbent and the time
at 50 ml, 150 mg and 25 min, respectively.[27]
[W(CO)3Br2(NCMe)2] (5.75 g, 11.28 mmol) in ethanol
(50 ml) was stirred under reflux, in nitrogen flow, for over
12 h. Afterwards, the solvent was removed by filtration in
nitrogen atmosphere and the new organometallic catalyst
was washed four times with dichloromethane and ethanol,
and after drying afforded 2.1 g of POSS‐ATC‐[W(CO)3Br2]
(84% yield).
1.6 | Chromatography
Analyses were conducted with a GC–MS instrument
(Thermo Scientific) using a fused silica capillary column.
The carrier gas used was helium with a constant pressure
mode of 80 kPa. The heating ramp of the oven was pro-
grammed varying the temperature from 60 to 200 °C (held
for 3 min) at a rate of 30 °C min−1. Samples of 1.0 μl were
injected in a preheated inlet (250 °C) working in the splitless
mode. The mass spectrometer was operated in the full scan
mode in the range 30–350. The proportions between dibutyl
ether and olefins were calculated to analyze the conversion
percentages.
1.4 | 1.4 Synthesis of Homogeneous Species:
[W(CO)3Br2(ATC)]
A solution of [W(CO)3Br2(NCMe)2] (2 g, 3.92 mmol) was
added to a solution of ATC ligand (0.5 g, 3.92 mmol) in
heated ethanol (80 ml) in nitrogen flow. The reaction was
stirred for 8 h under reflux. Then the solvent was evapo-
rated in vacuo, giving a light yellow solid which was puri-
fied by washing with hexane and dried in vacuum (98%
yield).[12]
1.7 | Catalytic Studies
The oligomeric catalyst POSS‐ATC‐[W(CO)3Br2] was
investigated in the epoxidation of 1‐octene, cyclooctene,
limonene, cis‐3‐hexen‐1‐ol, trans‐3‐hexen‐1‐ol and sty-
rene, using TBHP as oxidant at 55 °C under air atmo-
sphere. The reactions were performed in a condenser
with magnetic stirring and, to prevent the evaporation of
the dichloromethane, a condenser was used.[12,21,27] In
each case, the container was loaded with the catalyst,
substrate and TBHP as oxidant in a ratio of 1:100:200
in mmol%.[12,21]
Catalysts: 0.137 mmol of POSS‐ATC‐[W(CO)3Br2]
(0.14 g) and [W(CO)3Br2(ATC)] (0.076 g). Substrates:
13.70 mmol of 1‐octene (1.53 g), cyclooctene (1.51 g), (S)‐
limonene (1.86 g), cis‐3‐hexen‐1‐ol (1.37 g), trans‐3‐hexen‐
1‐ol (1.37 g) and styrene (1.42 g). Dibutyl ether (internal
standard): the same amount in mmol of each olefin and
dichloromethane. Oxidant: 27.40 mmol of TBHP (5.0–
6.0 M in decane; 2.47 g).
The reactions were initiated with the addition of the
oxidant (TBHP). The samples were collected every
20 min during the first hour, then every two hours until
the eighth hour and the last after 24 h of reaction.[12,19,27]
To destroy the TBHP, a catalytic amount of manganese
dioxide was added.[12,21] TBHP decomposes spontaneously,
but very slowly, into water and oxygen gas. The manganese
dioxide acts as a catalyst for this reaction, increasing the
speed of decomposition of TBHP into tert‐butyl alcohol
and O2.[28,29] The resulting viscous material was separated
by filtration and a micro aliquot of the supernatant was
injected into a GC–MS instrument. The conversion of each
substrate was evaluated by formation of their respective
epoxides with GC–MS using previously developed
methods. Epoxidation test without a metal catalyst was
investigated and no catalytic activity was observed.[12,27]
The conversion rate after 24 h, turnover frequency (TOF)
after 20 min and selectivity for each detected product were
1.5 | Study of Immobilization of [W(CO)3Br2(NCMe)2]
on POSS‐ATC
1.5.1
| Effect of adsorbent dose
The dose of the adsorbent was studied by varying the mass
from 10 to 400 mg under nitrogen atmosphere and keeping
the concentration of organometallic complex fixed. The con-
tact time and temperature in 50 ml of the initial concentration
of 0.01 mol l−1 were 2 h and 25 °C, respectively, in ethanol
solution.
1.5.2
| Equilibrium time
The equilibrium times were studied using 150 mg
of POSS‐ATC at a temperature of 298 K and under
nitrogen atmosphere. The initial concentration of the
[W(CO)3Br2(NCMe)2] complex was 0.01 mol L−1 in etha-
nol and solution volume was 50 ml. The time intervals were
between 5 and 40 min, after which the material was filtered
and the concentration of tungsten in solution was determined.
1.5.3
| Isotherms of sorption
The maximum capacity of the POSS‐ATC adsorbent from
ethanolic solutions was investigated at 25 °C by batch immo-
bilization process under nitrogen atmosphere. An amount of
150 mg of adsorbent was added to 50 ml of solution with
various concentrations of [W(CO)3Br2(NCMe)2] complex
between 0.001 and 0.01 mol l−1. The previous tests showed
that the equilibrium was achieved rapidly, such as 25 min
for POSS‐ATC. The mixture was stirred for 30 min and then
the solids were filtered and the amount of tungsten was
analyzed using ICP‐MS.
1.5.4
| Thermodynamic parameters
Thermodynamic study was conducted at temperatures of 25
to 65 °C under nitrogen atmosphere, maintaining constant

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VIEIRA ET AL.
calculated. The same catalytic study was conducted for the
homogeneous species.
positions of the cube, the steric hindrance does not favor
multi‐alkylation. Moreover mono‐alkylation is favored by
the molar ratio of 16:1 between ligand and functionalized
cube. Even if it occurs, multi‐alkylation or esterification
to lesser extent does not affect the catalytic activity of
the catalyst.
2
| RESULTS AND DISCUSSION
Next, the modified oligomer POSS‐ATC was reacted
with the complex [W(CO)3Br2(NCMe)2] in a molar ratio of
1:8 giving a new oligomeric catalyst, namely POSS‐ATC‐
[W(CO)3Br2]. The synthesis of the heterogeneous catalyst is
shown in Scheme 1.
2.1 | Synthesis and Characterization of POSS‐ATC‐
[W(CO)3Br2] Oligomeric Catalyst
The oligomer POSS‐Cl was synthesized by the hydrolytic
condensation reaction of the 3‐chloropropyltriethoxysilane
monomer, where the reactions occur primarily with water
and subsequently between monomers. The hydrolysis reac-
tion of the alkoxides produces the monomer containing the
functional group (Si−OH), while the condensation reaction
of the Si−OH groups produces silicate bond (Si−O−Si)
and water and alcohol as byproducts.[30] Next, POSS‐Cl
was subsequently functionalized with ATC. As the alkyl
groups are anchored in the POSS support in fixed
POSS‐Cl. Si8O12C24H48Cl8 (1036.9 g mol−1). Calcd (%):
C, 27.77; H, 4.63; found (%): C, 27.56; H, 4.42.
POSS‐ATC. Si8O28C48H72N32 (1768.8 g mol−1). Calcd
(%): C, 32.56; N, 25.32; H, 4.07; found (%): C, 32.49; N,
24.95; H, 4.00%. Based on nitrogen elemental analysis, the
density of the organofunctionalization was calculated giving
a value of 4.45 mmol of (3‐amino‐1H‐1,2,4‐triazole‐5‐car-
boxylic acid)propyl groups per gram of POSS‐ATC
SCHEME 1 Synthesis route proposed for the oligomeric catalyst POSS‐ATC‐[W(CO)3Br2]

VIEIRA ET AL.
5 of 13
material, confirming that eight (3‐amino‐1H‐1,2,4‐triazole‐5‐
carboxylic acid)propyl arms are linked to the silsesquioxane
core.
1704 cm−1[31,33,34] suggests that the reaction between the
propyl chloride arm and ATC ligand occurs by NH2 group,
once the amine localized in the ring has a greater stabil-
ity.[12,21,31] The band of the CH2 aliphatic hydrocarbon is
observed in 2940 cm−1.[31–34] The band of Si−O−Si of the
POSS is slightly shifted from its initial value of 1108 to
1112 cm−1.[27–31]
POSS‐ATC‐[W(CO)3Br2].
Si8O37C57H72N32Br6W3
(3052 g mol−1). Calcd (%): C, 22.41; N, 14.67; H, 2.36; W,
18.08; found (%): C, 22.12; N, 14.37; H, 2.22; W, 17.93.
Based on nitrogen elemental analysis, the density of the
organofunctionalization was calculated giving a value of
2.56 mmol of (3‐amino‐1H‐1,2,4‐triazole‐5‐carboxylic acid)
propyl groups per gram of POSS‐ATC‐[W(CO)3Br2]
material. The catalyst material contained 17.93% of tungsten.
The FT‐IR spectrum of POSS‐Cl (Figure 1A) exhibits
the characteristic vibrational modes of the POSS cage,
namely the asymmetric Si−O−Si modes centered at
After the reaction with the organometallic complex, the
FT‐IR spectrum of POSS‐ATC‐[W(CO)3Br2] (Figure 1C)
shows three new peaks at 2092, 2021 and 1940 cm−1
which are assigned to C≡O stretching vibrations, proving
the coordination of [W(CO)3] to POSS‐ATC. The
presence of these bands is in agreement with the
literature.[12,23] The band of Si−O−Si of the POSS is
slightly shifted from its initial value of 1108 to
1108 cm−1 [27,30]
The presence of the propyl chain is
.
1124 cm−1 [27,30]
.
shown by the C−H modes at 3000 and 2954 cm−1, as
well as C−H deformation modes at 1458, 1436 and
In the 13C NMR solid‐state spectrum of POSS‐Cl
(Figure 2A), three peaks are observed at 10.76 (CH2−Si) (1),
27.14 (CH2−CH2Si) (2) and 48.30 ppm (CH2−Cl) (3), which
are allocated to the carbon of the propyl chain of the silylating
agent.[35–37]
1410 cm−1 [29,30]
at 698 cm−1 [31]
.
The C−Cl stretching mode is observed
.
The FT‐IR spectrum of POSS‐ATC (Figure 1B) shows a
peak at 1446 cm−1 which is assigned to single bond (C−N)
of the aromatic ring.[29] The band of the C═N group of the
Figure 2(B) shows the 13C NMR spectrum of POSS‐ATC,
and, as is evident, there is a shift of the first three peaks
(9.64 (CH2−Si) (1), 23.23 (CH2−CH2Si) (2) and 48.95 ppm
triazole ring is observed in 1600 cm−1 [31–34]
.
The presence
of the band of carbonyl (C═O) of carboxylic acid at
FIGURE
1
FT‐IR spectra of (A) POSS‐Cl, (B) POSS‐ATC and (C)
FIGURE 2 13C NMR spectra of (A) POSS‐Cl, (B) POSS‐ATC and (C)
POSS‐ATC‐[W(CO)3Br2]
oligomeric catalyst POSS‐ATC‐[W(CO)3Br2]

6 of 13
VIEIRA ET AL.
(CH2−N) (3)) when compared to POSS‐Cl precursor mate-
rial.[35–37] The signals in the regions 140.66 (4), 149.40 (5)
and 155.22 (6) ppm appear due to incorporation of ATC.
These signals are characteristic of ATC groups present in
the structure, confirming the modification of the surface
of the support.
After reaction with the [W(CO)3Br2(NCMe)2] complex,
the 13C NMR solid‐state spectrum of POSS‐ATC‐
[W(CO)3Br2] catalyst (Figure 2C) does not display the reso-
nance peak of the carbon atoms of the carbonyl groups due
to the absence of the proton.[12,38] However, there is a slight
shift of all peaks (8.94 (CH2−Si) (1), 21.55 (CH2−CH2Si)
(2), 45.53 (CH2−N) (3), 139.99 (4), 148.94 (5) and
154.20 ppm (6)) when compared to POSS‐Cl and POSS‐
ATC.
The 29Si NMR spectra of POSS‐Cl, POSS‐ATC and
POSS‐ATC‐[W(CO)3Br2] are shown in Figure 3. As can be
seen, a single resonance is observed in all cases. The peaks
at −68.50, −66.04 and −66.36 ppm, respectively, confirm
that the cage structure remains closed, even after several
reactions.[39,40]
According to Figure 4(A), the XRD pattern of POSS‐Cl
indicates a high crystallinity. On the other hand, the
FIGURE 4 XRD patterns of (A) POSS‐Cl, (B) POSS‐ATC and (C) POSS‐
ATC‐[W(CO)3Br2]
diffractogram of POSS‐ATC (Figure 4B) shows a high crys-
tallinity loss when compared to the precursor material, due to
the incorporation of the ATC ligand, indicating that there is a
higher ratio of organic groups than inorganic.
The XRD pattern of the oligomeric catalyst POSS‐ATC‐
[W(CO)3Br2] (Figure 4C) shows a high crystallinity loss
when compared to the free organometallic complex. Peaks
1 and 2 at 6.40° and 22.22° are due to the functionalization
of POSS‐Cl with ATC ligand. On the other hand, peaks 3
(21.84°), 4 (31.10°), 5 (38.30°), 6 (44.56°), 7 (50.16°)
and
8
(55.40°) appear after the reaction with
[W(CO)3Br2(NCMe)2]. These peaks confirm the incorpora-
tion of organometallic complex on the surface of the
oligomer.
In addition, the thermal properties of POSS‐Cl, POSS‐
ATC and POSS‐ATC‐[W(CO)3Br2] were also measured.
The TGA curves of the target compounds were obtained
under air atmosphere (Figure 5) and the thermal stability indi-
cated that the three compounds could be applied at a temper-
ature of about 200 °C.
FIGURE 3 29Si NMR spectra of (A) POSS‐Cl, (B) POSS‐ATC and (C)
POSS‐ATC‐[W(CO)3Br2]
As shown in Figure 5(A), the first mass loss of POSS‐Cl
occurs between 200 and 465 °C with a mass loss of 39.97%

VIEIRA ET AL.
7 of 13
for POSS‐ATC and POSS‐ATC‐[W(CO)3Br2] are 35.33 and
27.92%, respectively.
After the complete burning of the catalyst the amount of
resulting material is 34.76% referring to the inorganic part
of the POSS and of the tungsten oxide fragments formed.
This result is in accordance with elemental analysis of the
catalyst.
SEM images were obtained for each step of the prepara-
tion of the heterogeneous catalyst in order to investigate the
FIGURE 5 TGA curves of (A) POSS‐Cl, (B) POSS‐ATC and (C) POSS‐
ATC‐[W(CO)3Br2]
concerning the initial cleavage of the C−Cl and C−C
bonds.[41,42] The second mass loss is related to the degrada-
tion of the Si−C bond with a mass loss of 13.86%.[41,42] This
sequence of degradation may be due to low bond energies of
the corner groups of POSS‐Cl.[41,42] When the temperature is
below 200 °C, the TGA curve shows no substantial
modification.
Additionally, the TGA curves of POSS‐ATC and
POSS‐ATC‐[W(CO)3Br2] catalyst (Figure 5B and C) show
that the first mass loss occurs up to 100 °C related to the
loss of physisorbed water[43] with a mass loss of 6.83%
for POSS‐ATC and 6.03% for the catalyst. The second
mass loss of POSS‐ATC and heterogeneous POSS‐ATC‐
[W(CO)3Br2] catalyst is initiated from 100 to about
470 °C and is attributed to the decomposition of the
ATC groups. At this stage, the value of 34.10% for
POSS‐ATC and 31.29% for POSS‐ATC‐[W(CO)3Br2]
refer to the weight loss between 100 and 470 °C, showing
that the eight vertices of POSS are functionalized with
ATC.
The third mass loss occurs from 470 to about 550 °C. For
POSS‐ATC, this is related to the burning of the propyl chain,
whereas for the POSS‐ATC‐[W(CO)3Br2] catalyst it is
related to the degradation of the propyl chain together with
the organic groups of tungsten complex. The mass losses
FIGURE 6 SEM images of (A) POSS‐Cl, (B) POSS‐ATC and (C) POSS‐
ATC‐[W(CO)3Br2]

8 of 13
VIEIRA ET AL.
various morphologies. The SEM images of POSS‐Cl, POSS‐
ATC and POSS‐ATC‐[W(CO)3Br2] are shown in Figure 6.
The image of the heterogeneous catalyst (Figure 6C) presents
a more agglomerated surface than the precursor materials
POSS‐Cl (Figure 6A) and POSS‐ATC (Figure 6B).[44] This
can be beneficial when dealing with heterogeneous catalysts,
since it would facilitate their separation and recycling.
The EDS spectrum of POSS‐Cl (Figure 7A) shows the
peaks of the elements silicon, oxygen, carbon and
chlorine, demonstrating that the synthesis of the POSS‐Cl
precursor had been successful. In the EDS spectrum of
POSS‐ATC (Figure 7B), it is observed that the peak of
chlorine disappears, proving that all eight chlorine atoms
are replaced by ATC molecules. In the EDS spectrum of
POSS‐ATC‐[W(CO)3Br2] (Figure 7C), two peaks related to
tungsten and bromine derived from the tungsten complex
are noted. Furthermore, the peaks of silicon, oxygen, carbon
and nitrogen remain intact, proving the thermal and mechan-
ical stability of the precursor.
and POSS‐ATC‐[W(CO)3Br2] is not expected, since the
silsesquioxane core has a diameter of 0.53 nm and a spherical
radius of 1–3 nm containing peripheral organic units. The
low value of SBET of 80, 85 and 101 m2 g−1 for POSS‐Cl,
POSS‐ATC and POSS‐ATC‐[W(CO)3Br2], respectively,
could have been affected by the propensity of the particles
to form clusters.[45] All materials have a type IV isotherm
shape with H1 hysteresis,[45] typical of solids made up of
clusters of spherical particles of uniform size and shape. This
feature is fairly typical of mesoporous solids with pore
diameters in the range 2–50 nm. The absence of any micro-
pores, the calculated average pore diameter and the moder-
ately small SBET values are in agreement with these
observations.
2.2 | Synthesis and Characterization of Homogeneous
Species [W(CO)3Br2(ATC)]
The organometallic complex of tungsten ([W(CO)3Br2(NCMe)2])
is one of the most well‐known precursors due to the replacement
of nitriles with other ligands. The option for a certain ligand
must be done in order to achieve the desired properties, namely
the possibility of reacting with a given functional group. The
ATC ligand is a chemically interesting compound, because it
has coordinating functional groups as a nitrogen ligand that could
coordinate to [W(CO)3Br2(NCMe)2], affording a stable complex.
[W(CO)3Br2(ATC)]. WC6O5Br2N4H4 (555.84 g mol−1).
Calcd (%): C, 12.95; N, 10.07; H, 0.72; W, 33.07; found (%):
C, 12.79; N, 9.98; H, 0.67; W, 32.96. Nitrogen elemental anal-
ysis was conducted giving a value of 1.78 mmol of ATC
groups per gram of [W(CO)3Br2(ATC)] complex.
N = 9.98% indicates the replacement of the labile ligands
(NCMe) bound to the metal center by ATC ligand.
The superficial areas of POSS‐Cl, POSS‐ATC and POSS‐
ATC‐[W(CO)3Br2] were estimated using the BET method.
The relatively small value of SBET for POSS‐Cl, POSS‐ATC
The synthesis of homogeneous species [W(CO)3Br2(ATC)]
is proved by the presence of the bands of C≡O in the FT‐IR
spectrum, which appear at 2015, 1940 and 1868 cm−1, shifted
from their positions in the spectrum of precursor complex
(2094, 2032 and 1943 cm−1).[12,25] In addition, the bands at
1686 cm−1 (C═O), 1628 cm−1 (C═N), 1560 cm−1 (C−O)
and 1502 cm−1 (C−N) appear due to coordination of the com-
plex with ATC ligand. The characteristic bands of acetonitrile
are absent, confirming its replacement by ATC.[31,33,34]
SEM and EDS analyses were also carried out for the
homogeneous catalyst. A homogeneous surface without
clusters is observed in Figure 8(A). The EDS spectrum
(Figure 8B) shows exactly all elements involved in the
reaction, and a greater abundance of the elements carbon,
oxygen and nitrogen due to the incorporation of ATC ligand.
2.3 | Sorption Isotherms of Organometallic Complex
Preliminary tests showed that the system achieved equilib-
rium condition with 150 mg of oligomeric material (POSS‐
ATC) and a contact time of approximately 25 min for the
sorption of the tungsten complex for both atmospheres. The
FIGURE 7 EDS spectra of (A) POSS‐Cl, (B) POSS‐ATC and (C) POSS‐
ATC‐[W(CO)3Br2]

VIEIRA ET AL.
9 of 13
FIGURE 8 (A) SEM image and (B) EDS spectrum of [W(CO)3Br2(ATC)]
sorption rate of the functionalized oligomer was fast due to
the sorption sites being much more exposed on the surface
of this kind of material.
The adsorbent dosage for the immobilization of
[W(CO)3Br2(NCMe)2] in ethanol solution was investigated
for both atmospheres and the results are shown in Figure 9(A).
It is evident that the amount of organometallic complex uptake
increases from 0.28 mmol g−1 with 10 mg of adsorbent up to
0.97 mmol g−1 with 150 mg of adsorbent for the experiment
under nitrogen atmosphere and from 0.27 mmol g−1 with
10 mg of adsorbent up to 0.92 mmol g−1 with 150 mg of adsor-
bent for the experiment under air atmosphere. This
phenomenon is likely due to increased numbers of vacant
adsorption sites and increased surface area availability.[46–50]
When the amount of adsorbent is increased to 150/200 mg
for both atmospheres, the maximum adsorption is reached.
On the other hand, the immobilization capacity decreases as
the adsorbent dosage increases from 200 mg due to reduced
available surface area and reduced unoccupied active
sites.[46–48] Furthermore, large doses might result in adsorbent
aggregation.[46–48] In addition, high adsorbent dosages do not
enhance adsorption capacities. Similar results have been
reported in the literature.[46–49]
FIGURE 9 Comparison of immobilization of the [W(CO)3Br2(NCMe)2]
complex under nitrogen and air atmospheres: effect of (A) dose of
adsorbent, (B) time of contact, (C) sorption isotherms and (D) temperature in
ethanol solution
Figure 9(B) shows the effects of contact time on the sorp-
tion of the [W(CO)3Br2(NCMe)2] complex at 25 °C in

10 of 13
VIEIRA ET AL.
ethanol solution using POSS‐ATC. As can be seen, the equi-
librium time necessary for the immobilization of the complex
is 25 min for both atmospheres. The contact time has signif-
icant importance in immobilization studies. Rapid immobili-
zation of the complex and equilibrium in a short period
indicate the effectiveness of the oligomeric adsorbent.
Adsorption studies available in the literature show that the
uptake of adsorbate, although rapid at the initial stage,
becomes slower close to equilibrium.[51]
To investigate the sorption capacity, a range of
[W(CO)3Br2(NCMe)2] in ethanol solution was stirred for
30 min, using 150 mg of adsorbent at 25 °C. The maximum
sorption capacity of the [W(CO)3Br2(NCMe)2] complex using
POSS‐ATC is 1.0 mmol g−1. The sorption isotherm of the
metallic complex is presented in Figure 9(C). The highest
values of sorption of metallic complex provided by POSS‐
ATC could not be explained only by the porous structures of
the oligomer. The greater sorption of POSS‐ATC could be bet-
ter explained due to its larger degree of organofunctionalization.
To evaluate the influence of temperature on the
adsorption, experiments were performed at five different
temperatures (25, 35, 45, 55 and 65 °C). In Figure 9(D), the
adsorption process is slightly favored with increasing
temperature, which demonstrates that the adsorption of the
complex is an endothermic process. Increasing the tempera-
ture may increase the rate of diffusion of the adsorbate
molecules in the pores of the adsorbent particles and may
decrease the solution viscosity, thus increasing the adsorption
rate.[49]
where Nc is the concentration of solute remaining in solu-
tion after equilibrium is reached (mmol l−1); Nf is the amount
of solute adsorbed in the same condition (mmol g−1); Nfmax is
the maximum adsorption capacity in the monolayer; and b is
the equilibrium constant of the adsorption process.[53] The
linearization of the Langmuir model is obtained by plotting
Nc/Nf versus Nc.
Additionally, the Elovich model is the most appropriate to
define the kinetic data for both atmospheres. The high values
of the factor of determination indicate a kinetics of chemi-
sorption of the complex on the functionalized oligomer in
both atmospheres:
1
1
Nt ¼
þ
(2)
β lnðαβÞ β lnt
where α is the initial sorption rate constant (mmol min−1 g−1)
and the parameter β is related to the extent of surface
coverage and activation energy for chemisorption
(g mmol−1).[27]
The negative and positive values of ΔG, ΔH and ΔS
(Table 1) show a spontaneous nature, an endothermic process
and an increased randomness for both complexes, respec-
tively.[45] The temperatures of 25, 35, 45 and 55 °C show
the same behavior.
2.5 | Catalytic Activity
The activity of the oligomeric catalyst was investigated and
compared with that of its homogeneous counterpart for sev-
eral olefins. Figure 10 shows the conversion rate at various
time intervals for epoxidation of olefins 1‐octene (1‐ocy),
cyclooctene (Cy8), (S)‐limonene (S‐lim), cis‐3‐hexen‐1‐ol
(cis‐3), trans‐3‐hexen‐1‐ol (trans‐3) and styrene (Sty) in the
2.4 | Applications of isotherm models
From Figure 9(C) and (B) and using Equations (1) and (2) it
is possible to apply the isothermal and kinetic models of
Langmuir[4] and Elovich,[3,52] respectively. The theoretical
data for each model are listed in Table 1. The Langmuir
model emphasizes that the immobilization of the tungsten
complex is in monolayers and the anchoring of the complex
occurs through the atoms of nitrogen spread around the sur-
face of the functionalized oligomer. It is verified also that
the values of RL (Table 1) are smaller than 1 demonstrating
that the immobilization of the complex is favorable. The
Langmuir model can be expressed as
presence
of
the
POSS‐ATC‐[W(CO)3Br2)]
and
[W(CO)3Br2(ATC)]. The epoxidation of olefins using
POSS‐ATC‐[W(CO)3Br2)] (Figure 10A) shows that the max-
imum rate of conversion to epoxide is achieved in a short
period of time, i.e. 2 h for S‐lim, Cy8 and Sty, and about 4 h
for 1‐oct. However, cis‐3 and trans‐3 require a period of 6 to
8 h. Though the necessary period to produce the active species
is different in each case, analogous catalytic species can be
originated.[12,21,54]
Nc
Nc
1
The results presented in Table 2 show that the oligomeric
catalyst has a conversion and TOF slightly lower, but in
¼
þ
(1)
Nf Nmf ax Nmf axb
TABLE 1 Effects of immobilization for [W(CO)3Br2(NCMe)2] complex in ethanol solution onto POSS‐ATC: isotherms, kinetics and thermodynamics
Langmuir model
Elovich model
Thermodynamic parametersa
Nfexp
Nfmax
RL
α
β
ΔG
ΔS
ΔH
Atmosphere (mmol g−1
)
(mmol g−1
)
(l mmol−1
)
R2
(mmol min−1 g−1
)
(g mmol−1
)
R2
(kJ mol−1
)
(J mol−1 K−1
)
(kJ mol−1
)
Nitrogen
Air
1.00
0.96
0.96
0.93
0.013
0.010
0.992
0.990
5.42
4.13
1.57
1.43
0.999
0.995
−34.449
−33.172
102.117
98.321
66.220
60.457
aTemperature = 65 °C.

VIEIRA ET AL.
11 of 13
(a)
(a)
(b)
(b)
FIGURE 11 (A) Recycling and (B) selectivity studies performed over
POSS‐ATC‐[W(CO)3Br2] catalyst
FIGURE 10 Conversion yields versus time plots for six substrates using (A)
oligomeric catalyst and (B) homogeneous species
Table 3 shows the oxidation selectivity of the olefins 1‐
octene and (S)‐limonene. The four substrates cyclooctene,
cis‐3‐hexen‐1‐ol, trans‐3‐hexen‐1‐ol and styrene are selec-
tively oxidized to their epoxide without formation of diols
for both catalysts (oligomeric catalyst and homogeneous
species). However, in the oxidation of 1‐octene, two products
are detected, namely 1‐octanal and 1,2‐epoxyoctane.
[W(CO)3Br2(ATC)] has a high selectivity for formation of
generalare very similar to those of the homogeneous species
(Figure 10B), except for the oxidation of (S)‐limonene on
POSS‐ATC‐[W(CO)3Br2]. The unexpectedly better perfor-
mance of the oligomeric catalyst as compared to the homoge-
neous species in the case of (S)‐limonene conversion can be
attributed, at least partly, to its characteristic of being a
nanosized oligomeric catalyst, as well as to the nature of
the substrate.
TABLE 2 Conversions and TOFs for epoxidation of olefins promoted by POSS‐ATC‐[W(CO)3Br2] and [W(CO)3Br2(ATC)] in the presence of TBHP
Catalyst
Substrate
1‐Octene
Conversion (%)a
TOF (mol (mol W)−1 h−1
)
POSS‐ATC‐[W(CO)3Br2]
[W(CO)3Br2(ATC)]
60
65
72
85
76
70
22
46
26
40
68
76
121
144
142
150
154
133
79
POSS‐ATC‐[W(CO)3Br2]
[W(CO)3Br2(ATC)]
Cyclooctene
POSS‐ATC‐[W(CO)3Br2]
[W(CO)3Br2(ATC)]
(S)‐limonene
cis‐3‐Hexen‐1‐ol
trans‐3‐Hexen‐1‐ol
Styrene
POSS‐ATC‐[W(CO)3Br2]
[W(CO)3Br2(ATC)]
97
POSS‐ATC‐[W(CO)3Br2]
[W(CO)3Br2(ATC)]
87
94
POSS‐ATC‐[W(CO)3Br2]
[W(CO)3Br2(ATC)]
144
149
aConversion at 24 h.

12 of 13
VIEIRA ET AL.
TABLE 3 Selectivity in epoxidation of 1‐octene and (S)‐limonene
Catalyst Substrate 1‐Octanal (%) 1,2‐Epoxyoctane (%) Z‐lim‐Epox (%) E‐lim‐Epox (%) Z‐lim‐OH (%) E‐lim‐OH (%) Lim‐(OH)2 (%) Dioxide (%)
(1)a
(2)b
1‐Oct
4
96
88
12
(1)a
(2)b
(S)‐Lim
50
40
30
25
3
7
5
6
6
0
12
16
aPOSS‐ATC‐[W(CO)3Br2].
b[W(CO)3Br2(ATC)].
1,2‐epoxyoctane of 88%, versus 12% for the formation of
1‐octanal. On the other hand, POSS‐ATC‐[W(CO)3Br2]
increases the selectivity to 96% for epoxy against 4%
for 1‐octanal, but the conversion is 40%.
the percentage of tungsten leached out into the liquid mixture
during reactions. The tungsten loading after five reaction
cycles is about 97% of the starting value. The leaching of
some weakly anchored tungsten complex present in the orig-
inal catalyst may account for the initial low loss of activity.
Figure 11(B) shows the selectivity to epoxide versus the
number of cycles. The selectivity for cycles 1, 2 and 3 is
86, 82 and 82%, respectively, for Z‐lim‐Epox, E‐lim‐Epox
and dioxide. For the fourth cycle we can see that the selectiv-
ity presents a slight increase to 84% and to 87% for the fifth
cycle. Cycles 4 and 5 are selective only for the epoxides Z‐
and E‐lim‐Epox.
The epoxidation of (S)‐limonene results in the formation
of several products (Table 3) and six of them were identified
using GC–MS: isomers of (+)‐limonene‐1,2‐epoxide (Z‐lim‐
Epox and E‐lim‐Epox), isomers of cyclohexen‐1‐ol‐2‐
methyl‐5‐(1‐methylethenyl) (Z‐lim‐OH and E‐lim‐OH),
(1S,2S,4R)‐(+)‐limonene‐1,2‐diol (lim (OH)2) and dipentene
dioxide (dioxide).[55] As is evident, there is a strong selectiv-
ity for oxidation of the double bond between carbons, yield-
ing the Z‐lim‐Epox, E‐lim‐Epox and dioxide isomers.
[W(CO)3Br2(ATC)] shows a selectivity for epoxide of 65%
whereas for POSS‐ATC‐[W(CO)3Br2] this increases to 86%.
Table 4 compares other types of catalysts in the epoxida-
tion of olefins. As can be seen, POSS‐ATC‐[W(CO)3Br2] has
greater conversion capacity than the other catalysts, and a
similar value when compared with its homogeneous counter-
part. This is mainly attributed to the structural characteristics
of the oligomeric catalyst. POSS‐ATC is an exceptional che-
lating agent because of its high density of nitrogen ligands in
its surface, resulting in a substantial increase of immobiliza-
tion capacity of the tungsten complex. These advantages
make them favorable candidates for the immobilization of
the tungsten complex.
3
| CONCLUSIONS
One of the main reasons for supporting a homogeneous metal
complex on functionalized POSS is to improve the activity
and reusability of the catalyst. Therefore, in this work a
tungsten complex was immobilized on POSS‐ATC and its
structure was carefully characterized using elemental analy-
1
2
sis, FT‐IR, C NMR and Si NMR spectroscopies, XRD,
TGA, SEM, EDS and BET analysis. The sorption properties
of POSS functionalized with ATC showed them to be depen-
dent on the adsorbent dose, contact time, concentration and
temperature. This new oligomeric catalyst was applied as a
highly efficient catalyst for the selective oxidation of several
olefins to corresponding epoxides with TBHP. The main
advantages of this catalytic system are ease of preparation
and easy work‐up procedure. It can be recycled and reused
for at least five cycles without loss of activity. This heteroge-
neous catalyst exhibits similar conversions and better selec-
tivity to epoxide when compared to its homogeneous
counterpart.
Metal leaching studies were also performed by reusing
the recovered POSS‐ATC‐[W(CO)3Br2] in five cycles. After
the first cycle the solid was separated, washed with dichloro-
methane and dried at 60 °C for reuse; this was done at the end
of each cycle. As can be seen in Figure 11(A), there is a slight
reduction in the catalytic activity from the first to the second
cycle; however, the activities for the other cycles tend to
remain constant. ICP‐MS analysis was used to determine
ACKNOWLEDGMENTS
TABLE 4 Comparison of conversion capacity of POSS‐ATC‐[W(CO)3Br2]
E.G.V. thanks FAPESP‐Fundação de Amparo à Pesquisa do
Estado de São Paulo (grant no. 2014/05566‐5) for scholar-
ships awarded. N.L.D.F. is grateful for financial support by
the FAPESP‐Fundação de Amparo à Pesquisa do Estado de
São Paulo (grant no. 2013/24602‐0) and the CNPq‐Conselho
Nacional de Desenvolvimento Científico e Tecnológico
(grant no. 306265/2013‐3 and 448168/2014‐6). N.L.D.F.
and E.G.V. acknowledge Department of Plant Science, Food
with that of other catalysts
Catalyst
Olefin
Sty
Conversion (%)
Ref.
[22]
[56]
[14]
[56]
T8‐Pr‐DPA‐Mo
L@MCM‐41‐MnII
36
Sty
11.2
53.7
51.7
76/68
Cube‐C1
(S)‐lim
(S)‐lim
(S)‐lim/Sty
L@SBA‐15‐MnII
POSS‐ATC‐[W(CO)3Br2]
Present study

VIEIRA ET AL.
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How to cite this article: Vieira EG, Silva RO, Junior
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alytic application of a new organometallic oligomer
based on polyhedral oligomeric silsesquioxane. Appl
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