Syntheses and catalytic activities of new metallodendritic catalysts

Article abstract of DOI:10.1039/c6nj01629d

This investigation presents the syntheses of new metallodendritic catalysts from a silsesquioxane core (Silsesq-PrNH₃⁺Cl^-) via a new route. For optimization of the syntheses of the catalysts, reaction times, thermodynamic effects, and the amounts of [Mo(η³-C₃H₅)Br(CO)₂(NCCH₃)₂] (1) and [Mo(CO)₃Br₂(NCCH₃)₂] (2) complexes fixed on the second-generation dendrimer (PDG2.0) were studied. After the optimization studies and with the objective of application in catalysis, the catalysts were prepared by reaction of PDG2.0 with the organometallic complexes and characterized by elemental analysis (CNH), FTIR, ¹³C and ²⁹Si NMR, XRD, TGA, SEM, EDS and BET. The metallodendritic catalysts were tested in the epoxidation of olefins and shown to be a vigorous catalyst with conversion rates between 76 and 97% for PDG2.0-[(Mo(η³-C₃H₅)(CO)₂Br)₈] and 30-80% for PDG2.0-[(Mo(CO)₃Br₂)₅], and a high selectivity in the formation of epoxides using tertbutyl hydroperoxide (TBHP) as an oxidant. The catalysts remain highly active after being used for at least 5 cycles. To the best of our knowledge, this study is the first to have reported the preparation of these new dendritic catalysts, as well as the catalytic comparison with their previous generations in the epoxidation of 1-octene, cyclooctene, (S)-limonene, cis-3-hexen-1-ol, trans-3-hexen-1-ol and styrene.

Full text of DOI:10.1039/c6nj01629d

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DOI: 10.1039/C6NJ01629D
New Journal of Chemistry
ARTICLE
Syntheses and catalytic activities of new metallodendritic
catalysts
Received 00th January 20xx,
Accepted 00th January 20xx
a*
a
b
Eduardo Guimarães Vieira, Rafael Oliveira Silva, Alexandre Gonçalves Dal-Bó, Tiago Elias Allievi
b
a,b**
Frizon and Newton Luiz Dias Filho
DOI: 10.1039/x0xx00000x
+
-
3
This investigation presents the syntheses of new metallodendritic catalysts from silsesquioxane core (Silsesq-PrNH Cl ) by
www.rsc.org/
a new route. For optimization of the syntheses of the catalysts, reaction times, thermodynamic effects, and the amounts
3
of [Mo(η -C
3
H
5
)Br(CO)
2
(NCCH
3
)
2
] (1) and [Mo(CO)
3
Br
2
(NCCH
3
2
) ] (2) complexes fixed on the second generation dendrimer
(PDG2.0) were studied. After the optimization studies and with the objective of application in catalysis, the catalysts were
prepared by reaction of the PDG2.0 with the organometallic complexes and characterized by elemental analysis (CNH),
1
3
29
FTIR, C and Si NMR, XRD, TGA, SEM, EDS and BET. The metallodendritic catalysts were tested in the epoxidation of
3
olefins and showed to be a vigorous catalyst with conversion rates between 76-97 % for PDG2.0-[(Mo(η -C
3
H
5
)(CO)
2
Br)
8
]
3 2 5
and 30-80 % for PDG2.0-[(Mo(CO) Br ) ], and a high selectivity in the formation of epoxides using tertbutyl hydroperoxide
(TBHP) as oxidant. The catalysts remain highly active after used for at least 5 cycles. To the best of our knowledge, this
study is the first that has reported the preparation of these new dendritic catalysts, as well as, the catalytic comparison
with their previous generations in epoxidation of the 1-octene, cyclooctene, (S)-limonene, cis-3-hexen-1-ol, trans-3-hexen-
1
-ol and styrene.
organometallic compounds based on molybdenum through its
1
. Introduction
1
5
terminal groups. The advantages of the dendrimers are
related, among other reasons, in the possibility of
combinations of different chemical species, such as the core,
branching and terminal groups. Various dendrimers have been
employed in catalytic epoxidation of olefins, such as S. Chavan
3
Molybdenum
)X(CO) (NCCH
and X = Br, Cl, I) have been the most regularly used transition
complexes
of
the
type
M(η -
C
3
H
5
2
3
)
2
] and [M(CO)
3
X
2
(NCCH
3 2
) ] (M = Mo or W
1
,2
metallic in academic and industrial applications
,4
for
3
1
6
epoxidation of olefins. The high demand for these types of
complexes is due to the lability of acetonitrile that can be
et al.
used benzimidazole-functionalized dendrons as
1
7
molybdenum supports, J.H. Noh et al. has employed colloidal
Pd and Pt nanoparticles synthesized by dendrimer templates,
5
-8
replaced by a large variety of ligands and supports, adding
new properties to the organometal material.
1
8
M. Peng et al. has synthesized a novel series of PAMAM
dendrimer-supported chiral salen Mn(III) complexes, M.A.
In recent years, there has been a growing interest in supported
organometallic compounds in different solid matrices for a
large variety of catalytic applications. One of them, if not the
main support which has a high compatibility for complexing of
1
9
Fardjahromi et al.
has synthesized Mn(III) salophen
supported on a nanosilica triazine dendrimer.
In this work, we present the syntheses and characterizations of
9
-14
organometallic compounds are the dendrimers.
two new metallodendritic catalysts from polyhedral oligomeric
3
silsesquioxane core PDG2.0-[(Mo(η -C
Dendrimers are well-suited hosts of organometal complex and
have the potential to combine the advantage of both
3
H
5
)(CO)
2
Br)
8
] (PDG2.0
-
Mo-(1)) and PDG2.0-[(Mo(CO)
3 2 5
Br ) ] (PDG2.0-Mo-(2)).
1
0
heterogeneous and homogeneous catalysts. Dendrimers
have hyperbranched structures which can interact with
To the best of our knowledge, this study is the first that has
reported the preparation of two new catalysts PDG2.0
3
-
-
[
(Mo(η -C
(Mo(CO)
3
H
5
)(CO)
2
Br)
8
]
(PDG2.0-Mo-(1)
)
and PDG2.0
[
3
2 5
Br ) ] (PDG2.0-Mo-(2)) and the catalytic comparison
with their previous generations in epoxidation of the 1-octene,
cyclooctene, (S)-limonene, cis-3-hexen-1-ol, trans-3-hexen-1-ol
and styrene. There are few works in the literature that have
reported the use of metallodendrimers in catalysis, and none
dealt with silsesquioxane core dendrimer and complexes of
This journal is © The Royal Society of Chemistry 20xx
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ARTICLE
New Journal of Chemistry
3
Mo(η -C
[
3
H
5
)Br(CO)
2
(NCCH
3
)
2
]
(1) or [Mo(CO)
3
Br
2
(NCCH
3
)
2
]
(2) Next, in a flask containing 200 ml of methanol under nitrogen
atmosphere, a suspension of 13 g of PDG0.5 and 14.72 ml of
ethylenediamine was stirred for 3 days at room temperature.
The product was obtained using a rotary evaporator heated to
on its surface.
2
. Experimental
5
0ºC, under vacuum. The product was separated and washed
with ethyl acetate until the recrystallization of PDG1.0
The PDG1.5 (10 g) was prepared from PDG1.0 described
The chemicals were purchased from Sigma-Aldrich and all previously, following the procedure similar to the preparation
solvents used in this study were previously purified, unless of PDG0.5
2
.1. General Procedures
.
.
3
otherwise indicated. The complexes of the type [Mo(η - The PDG2.0 (Figure 1A) (8 g) was prepared from PDG1.5
)Br(CO) (NCCH (1) and [Mo(CO) Br (NCCH (2) were described previously, following a procedure similar to the
prepared according to literature methods, but with preparation of PDG1.0
C
3
H
5
2
3
)
2
]
3
2
3 2
) ]
.
2
0,21
modifications.
The infrared analyses were obtained using a To a suspension of [Mo(CO) ] (10 g, 37.87 mmol) in 160 mL of
6
Nicolet 5DXB Instruments spectrometer. The analysis of dry CH CN under stirring and nitrogen atmosphere, allyl
3
1
3
29
nuclear magnetic resonance of C and Si were performed on bromide (13.44 mL, 79.52 mmol) was added. The colourless
a Bruker Avance 400 spectrometer in the chemical institute of mixture was refluxed for 10h, affording an orange staining
Araraquara/SP. The X-ray diffractograms were obtained by solution (shortly after the start of refluxing). At the end of 10
Ragaku Miniflex instrument, operating at 30 kV and 15 mA h, the solution was cooled with liquid nitrogen to precipitate
using nickel filter and Cu radiation (Ka) and a wavelength of the organometallic complex, next, the filtered solid was
1
.5418 angstrom. The images of electronic scanning washed with dichloromethane, dried, and stored in Schlenk
3
[Mo(η -
microscopy were taken in an EVO LS15 - Carl Zeiss and coated under
with gold. Energy dispersive spectroscopy (EDS). The EDS C H )Br(CO) (NCCH ) ] (1) with 97% yield.
nitrogen
atmosphere
giving
2
the
0,21
3
5
2
3 2
spectra were obtained by Oxford Instruments - Inca X-act with A suspension of [Mo(CO) ] (10.0 g, 37.87 mmol) was refluxed
6
resolution of 133 eV. The TG-DTA curves were obtained in a in purified acetonitrile (160 ml) under a nitrogen atmosphere
SDT 2960 thermobalance model. The temperature range was for 24 h. The resulting yellow solution was cooled to -20ºC
-
1
from room temperature to 1252 K at a heating flow 20ºC min
using air atmosphere to purge the system with a flow rate of added to the yellow solution resulting in immediate formation
1
using an ice bath and then Br (1.94 mL, 37.87 mmol) was
2
-1
00 ml min . Surface area was characterized by BET method of an orange-brown solution. The solution was allowed to
through N adsorption at 77 K. A Mass spectrometry with come to room temperature (25ºC) and stirred for 40 minutes.
inductively coupled plasma (ICP-MS-Series X 2 - Thermo The mixture was filtered under vacuum, thus obtaining a pure
2
Scientific) was used in this paper.
complex light brown coloration. The complex was stored in
Schlenk flask under vacuum and nitrogen and stored in a
desiccator under high vacuum giving the [Mo(CO) Br (NCCH ) ]
3
2
3 2
2
.2. Preparations
2
0,21
(
2) with 96 % yield.
PDG2.0 (3.0 g, 0.47 mmol) was added to a solution of (1) (1.66
g, 4.7 mmol) and to a solution of (2) (1.98 g, 4.7 mmol) in pure
ethanol (75 mL) under nitrogen, and both the systems were
stirred at 50ºC over 12 hours. The mixtures were filtered in
inert atmosphere and the two new catalysts were washed four
3
2
.2.1. Synthesis of heterogeneous catalysts PDG2.0-[(Mo(η -
)Br(CO) ] (PDG2.0-Mo-(1)) and PDG2.0-[(Mo(CO) Br
C
3
H
5
2
)
8
3
2 5
) ]
(
PDG2.0-Mo-(2)). The syntheses of all catalysts were
performed according to the immobilization studies presented
in Section 2.3.
times with dichloromethane and ethanol, dry and obtained
3
.78 g of PDG2.0-[(Mo(η -C H )Br(CO) ) ] (PDG2.0-Mo-(1)
The synthesis of the core of the dendrimer was performed
2
)
3
5
2 8
3
using 4000 mL of CH OH, 135 ml of HCl and 207 mL of 3-
(orange powder, 92.66 % yield), as illustrated in Figure 1B and
aminopropyltriethoxysilane in a 5000 mL reaction flask. The
solution was vigorously stirred and after 6 weeks the white
solid formed was filtered and washed. The solid phase formed
was separated by filtration and dried giving the Silsesq-
2
.56 g of PDG2.0-[(Mo(CO) Br ) ] (PDG2.0-Mo-(2)) (brown
2 5
3
powder, 85.33 % yield), as illustrated in Figure 1C.
+
-
3
PrNH Cl with 45 % yield.
Next, in a flask of 500 ml under an atmosphere of nitrogen, 15
-
+
3
g of Silsesq-PrNH Cl (material obtained in the previous step)
was added to a methanol solution containing 8.59 g of sodium
bicarbonate, the solution was stirred at room temperature for
48 hours. Then, to this reaction mixture, 99 ml of methyl
acrylate was added under constant magnetic stirring for 48
hours at 50ºC. After 48 hours, water was added to the
resulting suspension, affording the PDG0.5, the material was
filtered and washed successively with water resulting in a
pasty material.
Figure 1. PDG2.0 (A), PDG2.0-Mo-(1) (B) and PDG2.0-Mo-(2)
(C).
2
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ARTICLE
The syntheses of the catalysts of previous generations of both then every two hours until eight hours and the last in 24 hours
2
2,23
types were carried out similarly to PDG2.0-Mo-(1) and PDG2.0
-
-
of reaction.
To disable the oxidant agent was added
Mo-(2) and they have been named of PDG1.5-Mo-(1), PDG1.5
manganese dioxide in each collected sample. The resulting
Mo-(2), PDG1.0-Mo-(1), PDG1.0-Mo-(2), PDG0.5-Mo-(1) and suspensions were filtered and the resulting extract injected
PDG0.5-Mo-(2)
.
into the GC-MS system. The conversions of olefins, measures
by the formation of the corresponding epoxides, were
quantified through GC-MS. Epoxidation test without a metal
catalyst was investigated and no catalytic activity was
2.3. Optimization of the immobilization reaction
2
2,23
For optimization of the syntheses of two new catalysts,
reaction times, thermodynamic effects, and the amounts of
complexes fixed on the PDG2.0 were studied.
observed.
3
. Results and discussion
3
.1. PDG2.0-[(Mo(η -C
3
[
3
H
5
)Br(CO)
2
)
8
] (PDG2.0-Mo-(1)) and PDG2.0-
2
.3.1. Equilibrium time of the complexes. PDG2.0 was
(Mo(CO) Br ) ] (PDG2.0-Mo-(2))
3 2 5
thoroughly mixed into 50 mL of a solution containing each
-2
organometallic complex with concentration of 1 x 10 M in
ethanol and the contact time was varied from 5 to 40 min at
3
.1.1. Preparation of the metallodendritic catalysts. Firstly,
+
-
3
the neutralization of Silsesq-PrNH Cl was performed through
80 rpm.
+
-
3
the usual method by eluting the solution of Silsesq-PrNH Cl in
methanol across an ionic exchange column, however the yield
was very low.
2
.3.2. Isotherms of immobilization of the complexes. The
PDG2.0 was immersed in 50 mL of an ethanol solution
So it was decided to follow a new route. The development of
this route is associated with the neutralization of the precursor
material using a weak base, such as the sodium bicarbonate,
without the need of an ion-exchange resin.
-3
containing each complex of concentrations between 1.0 x 10
-2
to 1.0 x 10 M under agitation at 25 ± 0.2ºC. The quantity of
the Mo for each complex was determined by ICP-MS.
Excellent yield, reproducibility, easy manipulation and time
saving are some of the remarkable features of this method.
2
.3.3. Effect of temperature in the immobilization of the
complexes. The effects of temperature on the immobilization
efficiency were investigated for each complex of molybdenum
in the temperature range of 25-75ºC keeping constant the
concentrations of the complexes, the doses of adsorbent and
the contact times.
+
-
3
After the neutralization of the Silsesq-PrNH Cl core of the
dendrimer, the synthesis of dendrimer was finalized through
the Michael addition alternation with methyl acrylate and
excess of ethylenediamine by divergent method. The Michael
addition reactions are ideal for the synthesis of dendrimers
2
5
due to the low probability of secondary reactions. The
syntheses of the two new metallodendritic catalysts were
accomplished by the reaction of PDG2.0 obtained by Michael
addition with the complexes (1) and (2) in ethanol solution.
Because of the well-defined molecular architecture of
dendrimers, the catalyst localization can be placed at the
periphery or within of the dendrimer, at the core or more
seldom in the branches. However, the “dendrimer effect” has
been reported in the literature to explain phenomena that
arrive when the generation increases. In dendrimers with high
molecular weight, symmetrical geometry, and with reactive
2
.4. Chromatographic parameters
GC-MS analyses were performed by using a Thermo Scientific
gas chromatograph coupled to a mass selective detector
(
Thermo Scientific). The GC analyses were performed on a SPB-
(30 m × 0.25 mm × 0.25 μm film thickness) fused silica
capillary column.
1
2.4.1. Catalytic tests. PDG2.0-Mo-(1) and PDG2.0-Mo-(2) were
tested and compared with their previous generations in the
epoxidation of 1-octene (1-oct), cyclooctene (Cy8), (S)-
limonene (S-lim), cis-3-hexen-1-ol (cis-3), trans-3-hexen-1-ol
terminal groups (e.g. -NH
2
) the immobilization of the catalyst
9,12,18,19
on the surface of the material has been observed.
This
(
trans-3) and styrene (Sty), using tert-butyl hydroperoxide
TBHP) as oxidant. The catalytic epoxidations of the 1-octene,
may be due to strong steric hindrance and high reactivity of
the primary amines of the surface of the dendrimer. When the
steric hindrance and reactivity of the end groups is pierced by
catalyst, a high deactivation of catalytic activity has been
(
cyclooctene, (S)-limonene, cis-3-hexen-1-ol, trans-3-hexen-1-ol
and styrene were carried out at 328 K under a normal
atmosphere in a reaction vessel equipped with a magnetic
26
observed, as reported by Chow and Mak. Therefore, as this
2
2-24
stirrer and a condenser.
loaded with catalyst/substrate/oxidant in a ratio of 1:100:200
In each case, the vessel was
phenomenon of deactivation has not been observed for the
PDG2.0-Mo-(1) and PDG2.0-Mo-(2) catalysts, it is suggested
that the immobilization of the complexes occur on the surface
of the dendrimer as shown in Scheme 1.
(
mmol), dibutyl ether as internal standard (same amount of
2
2-24
the substrate) and dichloromethane.
The reactions were
initiated with the addition of the oxidant agent (TBHP). The
samples were collected every 20 minutes during the first hour,
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ARTICLE
New Journal of Chemistry
Scheme 1. Stages of preparation of the catalysts PDG2.0-Mo-(1) and PDG2.0-Mo-(2)
.
4
| J. Name., 2012, 00, 1-3
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3
.1.2. Characterization of the molybdenum complexes and The FTIR spectrum of PDG2.0-Mo-(1) catalyst (Figure 3A)
3
dendritic
MoC
, H 3.09 %, Mo 27.05 %; found C 29.99 %, N 7.72 %, H 3.02 %, stability of the material even after several steps of reaction.
catalysts.
3 5 2 3 2
[Mo(η -C H )Br(CO) (NCCH ) ]: shows the existence of peaks with different intensities. The
-1
9 2 2
H11BrO N (354.84 g/mol): calculated C 30.43 %, N 7.89 band in 1120 cm is assigned to Si-O-Si, this band proves the
%
-1
Mo 26.88 %. The resulting product contains 7.89 % nitrogen, Two strong absorptions centred at 1646 and 1552 cm are
signifying that two acetonitrile are bound to (1) complex. assigned to the C=O stretching (amide I) and N–H bending/C–N
Mo(CO) Br (NCCH ]: MoC Br (421.74 g/mol): stretching (amide II) vibrations of the PDG2.0-Mo-(1). The
calculated C 19.91 %, N 6.64 %, H 1.42 %, Mo 22.76 %; found C bands at 3425 and 3276 cm of primary amine, proves the
9.76 %, N 6.49 %, H 1.25 %, Mo 22.63 %. The resulting incorporation external with ethylenediamine. The stretching
2
9
[
3
2
3
)
2
7
O
3
2 2 6
N H
-
1
1
product contains 6.49 % nitrogen, proving the incorporation of
νC≡O vibrations appear as very intense absorptions at 1924 and
1826 cm , indicating the coordination of the [Mo(η -
31,32
-
1
3
acetonitrile on (2) complex.
3
PDG2.0-[(Mo(η -C
3
H
5
)Br(CO)
2
)
8
]:
Si
8
O
76
C
280
H
584
N
104Br
8
Mo
8
3 5 2
C H )Br(CO) ] fragment on dendrimer.
(7000 g/mol): calculated C 48.00 %, N 20.80 %, H 8.34 %, Mo The FTIR spectrum of PDG2.0-Mo-(2) catalyst (Figure 3B)
10.97 %; found C 47.55 %, N 20.52 %, H 8.16 %, Mo 10.85 %. shows the same peaks that the previous dendritic catalyst. The
The resulting product PDG2.0-Mo-(1) contained 10.85% of difference is related to the complex immobilized on its surface,
molybdenum. This value suggests that after reaction with the in which the fixing of the complex (2) results in the appearance
-
1
complex (1), eight units are bound to PDG2.0-Mo-(1)
PDG2.0-[(Mo(CO) Br ]: Si
.
of three peaks in the regions at 1936, 1888 and 1851 cm .
3
2
)
5
8
O
75
C
279
H
544
N
104Br10Mo
5
(8052
A
g/mol): calculated C 41.57 %, N 18.08 %, H 6.75 %, Mo 5.96 %;
found C 41.82 %, N 17.90 %, H 6.89 %, Mo 5.85 %. The
resulting catalyst has 5.85 % of molybdenum; this value
proposes that after reaction with (2), five units are fixed to the
PDG2.0-Mo-(2)
.
Si-O-Si
C-N
N-H
The FTIR spectrum of (1) complex (Figure 2A) exhibits two
-1
C
C
O
well-defined bands in the region of 1943 and 1851 cm
referring the bond carbon-oxygen (CO) and two small bands at
NH2
C=O
-1
2
319 and 2287 cm (NC) confirming the anchoring of the
2
B
7-30
acetonitrile molecule to complex.
O
A
Si-O-Si
C-N
N-H
N
C
C=O
NH2
4
000 3500 3000 2500 2000 1500 1000 500
-
Wavenumbers/cm
1
C
O
Figure 3. FTIR spectra of PDG2.0-Mo-(1) (A) and PDG2.0-Mo-
2) (B).
B
(
1
3
The C NMR solid-state spectrum of PDG2.0-Mo-(1) (Figure
A) three peaks are detected in 11.27 (CH -Si) (1), 21.22 (CH
CH Si) (2) and 34.73 ppm (CH -N) (3), which are allocated to
the carbon of the chain propyl of the silylating agent. The
peaks at 38.69 (N-CH -CH ) (4), 59.85 (N-CH -CH ) (5) and
74.32 (O-C=O) (6) regions appear due to the incorporation of
4
2
2
-
2
2
N
C
2
2
2
2
C
O
1
3
3
the two methyl acrylate molecules per nitrogen atoms. On
the other hand, the peaks in 53.66 (NH-CH -CH -NH ) (7) and
1.30 ppm (NH-CH -CH -NH ) (8) arose after the reaction with
4
000 3500 3000 2500 2000 1500 1000 500
-1
2
2
2
Wavenumbers/cm
5
2
33
2
2
3
Figure 2. FTIR spectra of the [Mo(η -C H )Br(CO) (NCCH ) ] (A) ethylenediamine. After the reaction with complex (1), the
3
5
2
3 2
and [Mo(CO) Br (NCCH ) ] (B) complexes.
3
spectrum of the new catalyst displays a peak at 73.63 ppm
2
3 2
which might be attributed to allyl groups of the complex (1)
The FTIR spectrum of (2) complex (Figure 2B) exhibits three immobilized on the dendrimer. Additionally, the resonances of
-
1
well-defined bands in the region of 2022, 1882 and 1834 cm
mentioning the interactions carbon-oxygen (CO) and two to the absence of allyl groups and of a proton bonded to
the carbonyl groups of the complex (2) are not apparent due
-1
32
intense bands at 2312 and 2279 cm (NC) confirming the carbonyl group.
attaching of the acetonitrile molecule to complex.
2
7-30
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2
9
In the Si spectra of PDG2.0-Mo-(1) and PDG2.0-Mo-(2) in After the reaction with the complexes (1) and (2) the X-ray
Figure 4B and Figure 5 respectively, a single resonance has spectra exhibited two major peaks at 8.6º and 22.6º (Figure
been observed, at -67.12 ppm for PDG2.0-Mo-(1) and -66.35 6C) for PDG2.0-Mo-(1) and at 9.02º and 22.50º (Figure 6D) for
ppm for PDG2.0-Mo-(2), which confirms that the cage PDG2.0-Mo-(2) catalyst. The appearance of the second peak
3
4,35
structure remains closed, even after several reactions.
for both catalysts confirms the incorporation of organometallic
complexes on the surface of the dendrimer.
A
4
A
B
7
3
6
8
5
1
2
9
0
10 20
30 40 50
60
0
10 20 30
40 50 60
C
D
4
00
300
200
100
-67.12
0
-100 -200
B
0
10 20
30 40 50
60
0
10 20 30
40 50 60
2
θ
2θ
Figure 6. X-ray diffractograms of the (1) (A) and (2) (B)
complexes; and of the PDG2.0-Mo-(1) (C) and PDG2.0-Mo-(2)
300 200 100
0
-100 -200 -300 -400 -500
(D) catalysts.
ppm
1
3
29
Figure 4. C NMR spectrum (A) and Si NMR spectrum (B) of the The two metallodendritic catalysts exhibit great thermal
PDG2.0-Mo-(1).
stability because of the existence of a silsesquioxane core. As
can be seen in Figure 7, the first mass loss for both catalysts
3
7
occurs until 120ºC concerning the loss of physisorbed water.
-66.35
The second mass loss of the catalysts PDG2.0-Mo-(1) and
PDG2.0-Mo-(2) is initiated from 150ºC to about 470ºC and
3
7
refers the decomposition of the dendrimers layers, where
firstly occurs the mass loss of the ethylenediamine groups (150
to 350°C) and next the loss of mass of the methyl acrylate
groups (250 to 470°C). The third mass loss occurs from 470ºC
to about 550ºC and is related the burning of the propyl amino
arm of the core POSS.
1
00
300 200 100
0
-100 -200 -300 -400 -500
PDG2.0-Mo-(1)
PDG2.0-Mo-(2)
ppm
80
2
9
Figure 5. Si NMR spectrum of the PDG2.0-Mo-(2).
60
40
20
0
According to Figures 6A and 6B the X-ray diffractograms of the
organometallic complexes have a high crystallinity. Already the
diffractograms of the catalysts PDG2.0-Mo-(1) and PDG2.0
-
Mo-(2) (Figure 6C and 6D) show a high crystallinity loss when
compared to organometallic complexes. Furthermore,
examining the diffractograms of the starting materials (Silsesq-
0
200
400
600
800
1000
+
-
Temperature (ºC)
3
PrNH Cl to PDG2.0) it was observed that for each new
generation of the dendrimer there was a loss of crystallinity, Figure 7. Thermogravimetric curves of the metallodentritic
resulting in a single main peak due to the incorporation of a catalysts.
large amount of organic groups (amorphous characteristic).
3
6
6
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The thermal stability indicated that both metallodendritic
catalysts from core silsesquioxane could be applied under the
temperature of about 200ºC. Similar occurrences were also
3
8-39
observed for other kinds of dendrimers.
After the
complete burn of PDG2.0-Mo-(1) the percentage of the
resulting material was 12.14 % referring to the inorganic part
of the core and of the immobilized complex. On the other
hand, the resulting percentage of the PDG2.0-Mo-(2) was 7.66
%. These results are in accordance with elemental analysis of
both catalysts.
Scanning electron micrographs (SEM) were performed in the
heterogeneous catalysts in order to detect differences in their
surfaces. The SEM images of PDG2.0-Mo-(1) and PDG2.0-Mo-
(2) are shown in Figure 8A and 8B. The spheres appearance
and size were similar to precursor materials, demonstrating
that the surface of the catalysts have good mechanical stability
4
0
and they were not destroyed during the whole reaction. The
surface of PDG2.0-Mo-(1) and PDG2.0-Mo-(2) have more
clusters than their starting materials. The EDS spectra of the
catalysts show exactly all elements involved in the reaction,
and a greater abundance of the elements carbon, oxygen,
nitrogen, bromine and molybdenum due to the incorporation
of methyl acrylate, ethylenediamine, (1) (Figure 8C) and (2)
(Figure 8D) on the POSS-Core.
The exact superficial areas of the PDG2.0-Mo-(1) and PDG2.0
-
Mo-(2) were estimated by BET method. The relatively small
value of the SBET for the PDG2.0-Mo-(1) and PDG2.0-Mo-(2) is
not expected, since that the silsesquioxane core has a
diameter of 0.53 nm and a spherical radius of 1-3 nm
Figure 8. SEM images and EDS spectra of PDG2.0-Mo-(1) (A and C)
and PDG2.0-Mo-(2) (B and D).
The amounts of adsorbents in the immobilizations of (1) and
4
1
containing peripheral organic units. The low value of the S
2
BET
(
2) in ethanol solutions were investigated and the results are
-1
2
-1
=
99 m g for the PDG2.0-Mo-(1) and SBET = 105 m g for the
PDG2.0-Mo-(2) could have been affected by the propensity of
shown in Figure 9A. It is obvious that the sorption balance
increases by increasing of the mass of adsorbent. This is due to
the fact that as the quantity of adsorbent increases there is an
increase in surface area and adsorption sites until the
adsorbed amount is correspondent to the quantity of
4
1
the particles to form clusters. Both catalysts have type IV
4
1
isotherm shape with H1 hysteresis, typical of solids made by
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
micropores, the calculated average pore diameter and the
moderately small SBET value are in arrangement with these
justifications.
42
unoccupied sites.
Figure 9B shows the effects of contact time for the
immobilization of (1) and (2) on the second generation
dendrimer at 25ºC in ethanol solution. The systems achieved
the equilibrium condition with a contact time of approximately
1
0 and 25 min for (1) and (2), respectively.
3
.2. Study of immobilization
The maximum sorption capacity values of the complexes (1)
-1
3
.2.1. Immobilization studies of the complexes [Mo(η -
and (2) using PDG2.0 were 1.19 mmol g for the complex (1)
3
C H )Br(CO) (NCCH ) ] (1) and [Mo(CO) Br (NCCH ) ] (2) on
-1
and 0.65 mmol g for the (2). The sorption isotherms of the
.
The immobilization studies of the organometallic metallic complexes are presented in Figure 9C. The values of
3
5
2
3 2
3
2
3 2
dendrimer
complexes were carried out to optimize the syntheses of the sorption of metallic complexes provided by PDG2.0 could be
catalysts and the results were expressed by the adsorption described by the porous structures of material and due to its
isotherm method.
bigger degree of functionalization.
Initially, some solvents were tested in the immobilization
processes, such as, methanol, ethanol, water, hexane and
dichloromethane. The ethanol showed the best behaviour.
Then, it was adopted as the medium to be used in
immobilization experiments.
To analyse the effect of temperature, the adsorption tests
were executed at six different temperatures (25, 35, 45, 55, 65
and 75ºC). In Figure 9D, the adsorption processes were
benefited with increasing temperature, which establishes that
the adsorption of the complexes are an endothermic
4
3
process.
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Table 1. Immobilization parameter: kinetics, isotherm and thermodynamics for (1) and (2) complexes in ethanol solutions onto PDG2.0
.
a
Langmuir model
Pseudo-second order model
Thermodynamic parameters
ΔG ΔS ΔH
(KJ/mol) (J/mol k ) (KJ/mol)
max
f
max
N
R
L
2
N
f
K
2
2
R
R
-1
-1
(
mmol/g) (L/mmol)
(mmol/g)
0.99
(min )
25.699
(1)
1
.09
0.010
0.980
0.990
-66.893
210.639 195.632
exp
f
N
mmol/g
.19
Freundlich model
Elovich model
β
(mmol/min g) (g/mmol)
20.427 8.189
1
n
mol/L) (mmol/g)
K
F
2
α
2
R
R
(
3
3.58 9.85
0.989
0.996
a
Langmuir model
Pseudo-second order model
Thermodynamic parameters
ΔG ΔS ΔH
(KJ/mol) (J/mol k ) (KJ/mol)
-45.880 140.219 111.111
max
max
Nf
RL
2
Nf
K2
(min )
6.221
2
R
R
-1
-1
(
mmol/g) (L/mmol)
(mmol/g)
0.53
(2)
0
.60
0.018
0.999
0.997
exp
f
N
mmol/g
.65
Freundlich model
Elovich model
β
(mmol/min g) (g/mmol)
8.328 3.258
0
n
K
F
2
α
2
R
R
(
mol/L) (mmol/g)
6.457 3.712
Temperature = 55ºC.
1
0.971
0.984
a
employed to describe heterogeneous systems and reversible
adsorption and is not restricted to the formation of
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
A
1.2
1.0
0.8
0.6
0.4
0.2
0.0
B
4
2,49
3
3
monolayers.
[
Mo(η -C H )Br(CO) (NCCH ) ]
[Mo(η -C H )Br(CO) (NCCH ) ]
3
5
2
3
2
3
5
2
3 2
[Mo(CO)
Br
(NCCH
)
]
[Mo(CO)
Br
(NCCH
)
]
3
2
3
2
3
2
3
2
Table 1 also shows the parameters of the kinetic models for
2
pseudo second order and Elovich models. R for Elovich and for
pseudo-second order are also very similar indicating that the
immobilization of the complex (1) and (2) may be described
by both models simultaneously. While the pseudo-second
order kinetic model is based on the assumption that
chemisorption is the rate determining step, the Elovich
model has been employed to describe the chemisorption
mechanism of the adsorbate on a solid surface without occur
0
50
100
150
200
250
0
5
10 15 20 25 30 35 40 45
Time (min.)
Adsorbent dose (mg)
1
1
1
0
0
0
0
0
.4
.2
.0
.8
.6
.4
.2
.0
C
1.6
D
1
.4
1.2
1.0
4
8-50
0
0
0
0
.8
.6
.4
.2
the desorption of the product.
also observed for other authors.
Similar occurrences were
37,42
3
3
[Mo(η -C H )Br(CO) (NCCH ) ]
3
5
2
3 2
[Mo(η -C
H
)Br(CO)
(NCCH
)
]
The negative and positive values of ΔG, ΔH and ΔS (Table 1,
Temperature = 55ºC) indicate a spontaneous nature, an
endothermic process and an increased randomness for both
complexes, respectively. The others temperatures showed the
3
5
2
3
2
[Mo(CO) Br (NCCH ) ]
3
2
3
2
[
Mo(CO) Br (NCCH ) ]
3 2 3 2
0.0
20
0
2
4
6
8
10
30
40
50
60
70
80
N (mmol/g)
Temperature (ºC)
c
Figure 9. Effect of dose of adsorbent (A), time of contact (B), same behaviour.
immobilization isotherms (C) and Effect of temperature (D) in
ethanol solution for (1) and (2) complexes using PDG2.0.
3.3. Activity catalytic
In temperatures above 60ºC there is a decrease in the The activities of two new catalysts PDG2.0-Mo-(1) and PD2.0
immobilization capacity of the complexes, which may be due Mo-(2) were compared with their previous generations
to the onset of degradation of organic groups. Immobilization PDG0.5-Mo-(1), PDG1.0-Mo-(1), PDG1.5-Mo-(1) and PDG0.5
experiments such as adsorbent dosage, equilibrium time and Mo-(2) PDG1.0-Mo-(2) PDG1.5-Mo-(2) respectively, in
immobilization isotherm has been studied to optimize the epoxidation of the 1-octene, cyclooctene, (S)-limonene, cis-3-
-
-
,
,
syntheses process of the new catalysts.
hexen-1-ol, trans-3-hexen-1-ol and styrene. The Figure 10
shows the kinetics of epoxidation of all olefins in the presence
3.2.1. Applications of isotherm models. From data of the of the eight new heterogeneous catalysts.
Figures 9B, 9C and 9D it was possible to apply three kinetics The epoxidation of olefins using heterogeneous catalyst
44,47
4
4-46
models,
three isotherm models
and thermodynamic PDG2.0-Mo-(1) in Figure 10A shows that the maximum
4
parameters, respectively.
8
conversion rate is achieved in a short period of time, i.e. 0.66
2
As seen from Table 1, the values of R (correlation coefficients) hour for Cy8 and Sty; 1 hour for 1-oct and S-lim. Though, cis-3
for Langmuir and Freundlich models in the immobilization of and trans-3 require a period of 2 hours. For PDG2.0-Mo-(2)
the complex (1) and (2) are very similar. The Langmuir model is catalyst (Figure 10B) the maximum conversion rate is
applicable to homogeneous adsorption, where the adsorption succeeded in 2 hours for Cy8 and Sty; 6 hours for 1-oct and S-
of each adsorbate molecule onto the surface has equal lim; and 8 hours for cis-3 and trans-3.
adsorption activation energy, while the Freundlich model is
8
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Figure 10. Epoxidation kinetics of each olefin using all catalysts.
The maximum conversion rate of dendrimers of previous Cyclooctene, cis-3-hexen-1-ol, trans-3-hexen-1-ol and styrene
generations functionalized with the complex (1) were analysed are selectively oxidized to their epoxide without formation of
and their epoxidation kinetics are depicted in Figures 10Aa, diols for all catalysts. However, in the epoxidation of the 1-
1
0Ab and 10Ac.
As can be seen in Figure 10Aa, the maximum conversion for octanaldehyde and 1-octene oxide.
PDG0.5-Mo-(1) occurred in 6 hours for all olefins; for PDG1.0 PDG2.0-Mo-(1) has a high selectivity for formation of 1-octene
octene are identified two products referred to as
-
Mo-(1) (Figure 10Ab) in 2 hours for Cy8 and Sty, 4 hours for 1- oxide, 99% versus 1% for the formation of octanaldehyde. For
oct, S-lim, cis-3 and trans-3; whereas the catalyst PDG1.5-Mo- PDG2.0-Mo-(2) the selectivity was 93% in epoxy against 7% for
(
1) (Figure 10Ac) exhibits a maximum conversion in 6 hours for octanaldehyde.
all olefins. Moreover, the catalysts PDG0.5-Mo-(1)
Lastly, the maximum conversion rate of dendrimers of PDG1.5-Mo-(1), PDG0.5-Mo-(2), PDG1.0-Mo-(2) and PDG1.5
generation 0.5
also examined and their epoxidation rates are illustrated in greater than their respective catalysts of last generation
Figures 10Ba, 10Bb and 10Bc. (PDG2.0-Mo-(1) and PDG2.0-Mo-(2)).
,
PDG1.0-Mo-(1)
,
-
,
1 and 1.5 modified with the complex (2) were Mo-(2) do not exhibit conversions, TOF(s) and selectivity
The Figure 10Ba shows that the maximum conversion for The epoxidation of (S)-limonene results in the formation of
PDG0.5-Mo-(2) happened in 8 hours for Cy8, Sty, 1-oct, S-lim numerous products (Table 3) and six of them were detected by
and 24 hours for cis-3 and trans-3; for PDG1.0-Mo-(2) (Figure GC-MS: Isomers of (+)-limonene-1,2-epoxide (Z-lim-Epox and
10Bb) in 6 hours for all olefins; however, the catalyst PDG1.5
-
E-lim-Epox), isomers of cyclohexen-1-ol-2-methyl-5-(1-
Mo-(2) (Figure 10Bc) reveals a maximum conversion in 8 hours methylethenyl) (Z-lim-OH and E-lim-OH), (1S,2S,4R) -(+)-
for all olefins. Though the required period to produce the Limonene-1,2-diol (lim(OH) ) and dipentene dioxide (dioxide).
2
active species is changed in each occasion, analogous catalytic This amount of products and by-products are due to the
3
1,32,51
species are possibly formed.
existence of double bonds between carbon in the structure of
The results of catalytic conversions are in Table 2. It is evident the (S)-limonene.
from initial certification of the table that the eight catalysts The S-lim has excellent conversion and TOF for the catalysts
present some catalytic activity in the epoxidation of 1-octene, that have the (1) complex onto its structure, such as PDG2.0
-
cyclooctene, (S)-limonene, cis-3-hexen-1-ol, trans-3-hexen-1-ol Mo-(1), PDG1.5-Mo-(1) and PDG1.0-Mo-(1). On the other
and styrene. PDG2.0-Mo-(1) was the best active catalyst with hand, the catalysts based on complex (2), do not exhibit
conversion between 76-97% and turnover frequencies (TOF / significant values, except for the PDG2.0-Mo-(2). PDG2.0-Mo-
-1
-1
-1
-1
mol molMo h ) between 180 to 260 mol molMo h . In (1) shows a selectivity for epoxide of 91 % whereas that their
contrast, PDG2.0-Mo-(2) has a good conversion and TOF only respective catalysts of previous generations have a selectivity
for styrene (Sty) and cyclooctene (Cy8), 80 % and 75 % of 80 %, 89 % and 67 % for PDG1.5-Mo-(1), PDG1.0-Mo-(1) and
-
1
-1
respectively, and TOF between 82 to 185 mol molMo h .
PDG0.5-Mo-(1), respectively. In contrast, PDG2.0-Mo-(2)
shows a selectivity for epoxide of 78 % though their
corresponding catalysts of previous generations have a
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Table 2. Conversions and Turnover Frequencies (TOF) for epoxidation of olefins in the presence of TBHP.
a
b
Catalytic precursor
PDG2.0-Mo-(1)
PDG1.5-Mo-(1)
PDG1.0-Mo-(1)
PDG0.5-Mo-(1)
PDG2.0-Mo-(2)
PDG1.5-Mo-(2)
PDG1.0-Mo-(2)
Substrate
Conversions (%)
TOF
92, 97, 90, 76, 80 and 94
60, 75, 55, 26, 30 and 70
75, 85, 70, 45, 53 and 79
20, 35, 15, 3, 6 and 30
40, 75, 50, 30, 35 and 80
20, 32, 21, 10, 16 and 40
28, 55, 33, 22, 25 and 65
11, 20, 13, 7, 7.5 and 25
260, 246, 200, 180, 192 and 240
99, 85, 65, 43, 66 and 100
220, 235, 195, 159, 161 and 200
61, 24, 37, 15, 21 and 36
1
-octene, Cyclooctene,
c
d
Limonene, Cis-3 , Trans-3
and Styrene
98, 179, 120, 82, 90 and 185
40, 75, 66, 15, 22 and 68
75, 140, 71, 56, 78 and 169
11, 22, 29, 2, 0 and 33
PDG0.5-Mo-(2)
a
b
-1 -1
c
d
Conversion at 24 h; In units of mol (mol of Mo) h ; cis-3-hexen-1-ol; Trans-3-hexen-1-ol.
Table 3. Selectivity in the Oxidation of 1-Octene and (S)-Limonene.
a
b
b
Z-Lim- E-Lim- Z-Lim- E-Lim-
Lim-
b
Catalysts
Subs .
Octanaldehyde
1-Octene oxide
b
b
b
b
b
Dioxide
Epox
Epox
OH
OH
(OH)
2
PDG2.0-Mo-(1)
PDG1.5-Mo-(1)
PDG1.0-Mo-(1)
PDG0.5-Mo-(1)
PDG2.0-Mo-(2)
PDG1.5-Mo-(2)
PDG1.0-Mo-(2)
PDG0.5-Mo-(2)
PDG2.0-Mo-(1)
PDG1.5-Mo-(1)
PDG1.0-Mo-(1)
PDG0.5-Mo-(1)
PDG2.0-Mo-(2)
PDG1.5-Mo-(2)
PDG1.0-Mo-(2)
PDG0.5-Mo-(2)
1-octene
1
99
80
90
60
93
75
82
50
20
10
40
7
25
18
50
(S)-limonene
60
38
45
26
40
30
33
20
25
30
36
25
32
22
27
15
4
3
6
2
6
4
8
5
5
4
7
6
12
8
8
4
3
15
10
12
10
30
10
7
16
6
26
15
18
5
11
10
a
b
Substrate; Percentage (%).
Table 4. Comparison of the conversion capacity of the
PDG2.0-Mo-(1) and PDG2.0-Mo-(2) with different dendritic
selectivity of 57 %, 71 % and 45 % for PDG1.5-Mo-(2), PDG1.0
-
Mo-(2) and PDG0.5-Mo-(2), respectively. As shown, the half
generation catalysts were less effective than the full
generation; it may be due to the different terminal groups. The
nitrogen atoms of the half generation dendrimers are within
the molecule, which may have caused the immobilization of
the complexes (1) and (2) within, and not on the surface of the
dendrimer. Consequently, the steric hindrance may be
affected the activities of the half generation catalysts. Mak and
catalysts.
a
Catalysts
Olefins
Conv.
Ref.
Sty
64.3
17
G5-OH(Pd )
80
b
PPCC-G1
cis-dioxo-Mo(VI)
1-Octene
cyclooctene
cyclohexene
Cy8/1-oct
Cy8
38
18
53
75
12.1
88/64
24
16
Mo-G
2
2
6
Chow demonstrated a sudden drop of the catalytic activity
as a bis(oxazoline)metal complex becomes buried within a
third-generation polyether dendrimer. Additionally, the
catalytic activity obtained with Meijer’s optically active amino-
alcohol dendrimers decreases to zero with the fifth
[
MoO L(EtOH)]
54
2
Complex (1)
Complex (2)
Present study
Present study
Present study
Present study
Cy8
19
5
2
PDG2.0-Mo-(1)
PDG2.0-Mo-(2)
Cy8/Sty
Cy8/Sty
97/94
75/80
generation.
Table 4 shows the comparison with other type of dendritic
catalysts in the epoxidation of olefins. As can be seen PDG2.0
-
a
b
Conversion (%); Determined by GC.
Mo-(1) and PDG2.0-Mo-(2) had higher convertion capacity
1
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than their corresponding complexes (1) and (2) and alternative The results of the characterization permitted to evidence that
catalysts. the syntheses of the PDG2.0-Mo-(1) and PDG2.0-Mo-(2)
This is mainly attributed to the structural characteristics of catalysts were efficacious.
PDG2.0-Mo-(1) and PDG2.0-Mo-(2). PDG2.0 is a unique The studies of immobilization of (1) and (2) complexes were
chelating agent because of its high density of nitrogen ligands necessary to optimize the syntheses of all catalysts.
and its dendritic structure, which can result in a substantial PDG2.0-Mo-(1) and PDG2.0-Mo-(2) show that the maximum
increase of immobilization capacity of the Mo-complexes. conversion was in a short period of time, 20 min and 2 hours,
These advantages make them promising candidates in the respectively for Cy8 and Sty olefins.
immobilization of the complexes (1) and (2)
.
PDG2.0-Mo-(1) was the best active catalyst in the conversion
-1
-1
of all olefins, 76-97 %, TOF of 180 to 260 mol molMo h and
.3.1. Leaching studies. Molybdenum leaching studies were selectivity to epoxide.
also executed in the catalysts recuperated PDG2.0-Mo-(1) and The catalysts PDG0.5-Mo-(1), PDG1.0-Mo-(1), PDG1.5-Mo-(1)
3
,
PDG2.0-Mo-(2) in five sequential reaction cycles. After the first PDG0.5-Mo-(2), PDG1.0-Mo-(2) and PDG1.5-Mo-(2) do not
cycle the solid was separated, washed with dichloromethane exhibit conversions, TOF(s) and selectivity greater than their
and dried at 50ºC for reuse, and it was done at the end of each respective catalysts of last generation (PDG2.0-Mo-(1) and
cycle. The catalytic activity decreased slightly from the first to PDG2.0-Mo-(2)).
the second cycle, but afterwards tended to continue constant The catalysts of the family of the complex (1) showed better
for both catalysts (Table 5).
performance than the catalysts of complex (2).
The catalysts of half generation exhibited a lower catalytic
activity that the full generations.
Table 5. Recycling studies performed over heterogeneous
The metallodendritic catalysts PDG2.0-Mo-(1) and PDG2.0-Mo
2) showed low leaching even after five cycles.
-
catalysts.
(
Catalyst
Cyclooctene
PDG2.0-Mo-(1)
Conversion (%)
Selectivity to epoxide (%)
a
a
a
a
a
1
2
3
4
5
º cycle
º cycle
º cycle
º cycle
º cycle
97
88
88
87
88
100
100
100
100
100
Acknowledgements
Eduardo G. Vieira thanks FAPESP-Fundação de Amparo à
Pesquisa do Estado de São Paulo (Grant no 2014/05566-5) for
scholarships awarded.
Catalyst
Styrene
Newton Luiz Dias Filho is grateful for the 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).
PDG2.0-Mo-(2)
Conversion (%)
Selectivity to epoxide (%)
b
1
2
3
4
5
º cycle
º cycle
º cycle
º cycle
º cycle
80
73
74
73
100
b
100
b
100
b
100
Newton Luiz Dias Filho and Eduardo G. Vieira acknowledge
Professor Enes Furlani Junior, of the Department of plant
science, food technology and social economy of Unesp-FEIS by
analysis of ICP-MS and GC-MS.
b
73
99
a
b
Epoxycyclooctane; styrene oxide.
ICP-MS analysis was used to determine the percentage of
molybdenum leached out into the liquid mixture during
reactions. The Mo loading of the (1) complex after five References
reaction cycles is at least 99 % of the starting value for the
PDG2.0-Mo-(1), whereas for PDG2.0-Mo-(2), the molybdenum
1
2
3
4
5
I. Honzícková, J. Honzícek, J. Vinklárek, Z. Padelková,
loading of the (2) complex was 96 %.
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present in the original catalyst may justify the initial low loss of
activity for both catalysts. FTIR analyses showed that both
complexes remain anchored on the surface of the dendrimer
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Table 4 also demonstrates the selectivity to epoxycyclooctane
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Metallodendritic catalysts showed high selectivity in the epoxidation of olefins even
after used for at least five cycles.