Platinum-Imidazolyl Schiff Base Complexes Immobilized in Periodic Mesoporous Organosilica Frameworks as Catalysts for Hydrosilylation

Article abstract of DOI:10.1002/aoc.5697

An imidazolyl Schiff base-containing periodic mesoporous organosilica (PMO) was synthesized via co-condensation reactions between a newly prepared bis (imidazolyl)imine-bridged bis silane and tetraethyl orthosilicate in the presence of cetyltrimethyl ammonium bromide as a soft template. The resultant as-synthesized PMO was then employed as a solid support for platinum catalysts. This complex was fully characterized via various techniques including FTIR, solid-state¹³C NMR, and ²⁹Si-NMR spectroscopy, as well as N₂ adsorption/desorption analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods. In addition, the catalyst was proven to efficiently mediate hydrosilylation reactions between olefins and hydrosilanes, and it can be reused for at least five cycles without significant loss of activity.

Full text of DOI:10.1002/aoc.5697

Received: 16 December 2019
DOI: 10.1002/aoc.5697
Revised: 7 March 2020
Accepted: 9 March 2020
F U L L P A P E R
Platinum-Imidazolyl Schiff Base Complexes Immobilized in
Periodic Mesoporous Organosilica Frameworks as Catalysts
for Hydrosilylation
1
,2,3,4,5
1,2,3,4,5
1,2,5
Yingpeng Huo
| Jiwen Hu
| Yuanyuan Tu
|
1,2,5
1,2,5
1,2,5
1,2,5
Zhenzhu Huang
| Shudong Lin
| Yangfei Hu
| Chao Feng
1
Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou, 510650, P.R. China
The University of Chinese Academy of Sciences, Beijing, 100039, P.R. China
2
3
4
5
Guangdong Provincial Key Laboratory of Organic Polymer Materials for Electronics, 510650, P.R. China
CAS Engineering Laboratory for Special Fine Chemicals, 510650, P.R. China
CASH GCC (Nanxiong) Research Institute of New Materials Co., Ltd, 512400, P.R. China
Correspondence
Abstract
Prof. Dr. Jiwen Hu, Guangzhou Institute
of Chemistry, Chinese Academy of
Sciences. Guangzhou, P. R. China, 510650.
Email: hjw@gic.ac.cn
An imidazolyl Schiff base-containing periodic mesoporous organosilica (PMO)
was synthesized via co-condensation reactions between a newly prepared bis
(imidazolyl)imine-bridged bis silane and tetraethyl orthosilicate in the pres-
Funding information
National Natural Science Foundation of
China, Grant/Award Numbers: 21404121,
ence of cetyltrimethyl ammonium bromide as a soft template. The resultant as-
synthesized PMO was then employed as a solid support for platinum catalysts.
This complex was fully characterized via various techniques including FTIR,
21404122, 51173204, 51503124; Natural
13
29
Science Foundation of Guangdong
Province, Grant/Award Number:
solid-state C NMR, and
Si-NMR spectroscopy, as well as N2
adsorption/desorption analysis, X-ray diffraction (XRD), X-ray photoelectron
spectroscopy (XPS), scanning electron microscopy (SEM), and transmission
electron microscopy (TEM) methods. In addition, the catalyst was proven to
efficiently mediate hydrosilylation reactions between olefins and hydrosilanes,
and it can be reused for at least five cycles without significant loss of activity.
2
018A030313946; the Guangzhou
Industrial Technology Major Project,
Grant/Award Number: 201802010018; the
Innovative Talents Youth Program
(
Natural Science) in Universities of
Guangdong, Grant/Award Number:
017-GKQNCS113; the Production
2
Education Research Project in Guangdong
Province, Grant/Award Number:
K E Y W O R D S
hydrosilylation reactions, imidazolyl Schiff base, periodic mesoporous organosilica, platinum
catalysts
2015B090915004; the Science and
Technology Program of Guangzhou City,
Grant/Award Numbers: 201802010018
201904020019; the Sichuan Science and
Technology Project, Grant/Award
Number: 2019YFSY0011
[
2]
[3]
1
| INTRODUCTION
catalysts such as Speier's, Karstedt's, and later exam-
[
4]
ples of Marko's catalysts. However, homogeneous plati-
num catalysts generally suffer from various drawbacks
such as the formation of inactive aggregates, the need for
Hydrosilylation reactions between carbon–carbon double
bonds and hydrosilanes are one of the most important
reactions in silicon chemistry and in industry, particu-
larly with the frequent use of homogenous platinum
[1]
[5]
tedious complex separation procedures, and discolor-
ation of the final products, prompting the interest in
[
6]
Appl Organomet Chem. 2020;e5697.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 10
https://doi.org/10.1002/aoc.5697

2
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HUO ET AL.
developing heterogeneous platinum catalysts that can be
readily reused and recycled.
a building block to construct a novel periodic meso-
porous organosilica via co-condensation with TEOS.
While we are not aware of any reports on platinum-
imidazolyl Schiff base complexes immobilized in PMO
framworks, there have only been a few reports describing
the immobilization of platinum onto PMOs containing
[7]
Periodic mesoporous organosilicas (PMOs) are one of
the most widely investigated classes of inorganic–organic
[8]
hybrid materials. PMOs can be prepared via the con-
densation of bis-silane compounds ((R O) Si-R-Si-(OR ) ,
1
3
1 3
[
31,32]
[33]
where R1 = Me or Et), with or without tetraethyl
orthosilicate (TEOS), and thus a vast variety of organic
moieties can be uniformly incorporated into the frame-
bis (pyridine)
or imidazolyl ionic liquids.
The
platinum-imidazolyl Schiff base-containing PMO could
be then reduced by NaBH , thus endowing the resultant
4
[9]
works of these materials. Since the first report of PMOs
in 1999, numerous innovative examples of these materials
have been synthesized, bearing various R groups ranging
from simple ethylene, phenylene to hydrocarbons, hetero-
aromatic and metal complexes. Meanwhile, research on
the applications of such PMOs has been extended to many
fields such as adsorption, chemical separations, thin films,
PMO with a uniform dispersion of ultrafine platinum
nanoparticles (1–2 nm). Moreover, we also demonstrate
that both platinum-imidazolyl Schiff base complex-
containing and the platinum nanoparticle-containing
PMOs can efficiently mediate the hydrosilylation reac-
tions between olefins and hydrosilanes. In addition, the
platinum nanoparticle-containing PMOs exhibit desirable
recyclability, demonstrating the potential applicability of
these PMO materials in catalysis.
[10,11]
the biomedical sector, and especially catalysis.
The application of PMOs in catalysis is an attractive
theme, as functional PMOs with homogeneously distrib-
uted binding sites within the silica matrix can be obtained
through simple templated sol–gel processes via the careful
design of ligands containing organosilica precursors.
These PMOs are ideal solid supports for various metal
complexes and metal nanoparticles. Notably, they offer
distinct characteristics such as relatively short reactant dif-
fusion lengths and high accessibility to active sites, so that
active nanoparticles can be stabilized and uniformly dis-
2 | MATERIALS AND METHODS
2.1 | Reagents and chemicals
All of the reagents which were used in this research were
of analytical grade or better, unless stated otherwise. Sty-
rene, alpha-methylstyrene, triethoxy (vinyl)silane,
1-octadecene, 1-cyclooctene, allylbenzene, vinylpyridine,
allyl phenyl ether, methyl dimethoxy vinyl silane,
cinnamyl alcohol, norbornene, methallyl alcohol, oct-
[12]
persed, thus enhancing their catalytic activities.
Conse-
quently, the preparation of PMOs with suitable bridging
ligands in the pore walls to support metal complexes as
[13–17]
heterogenous catalysts has become a hot topic.
1-en-3-ol,
allyl
glycidyl
ether,
γ-aminopropyl
Nitrogen-containing heterocyclic Schiff bases repre-
sent a major class of polydentate ligands and fulfil impor-
triethoxysilane,
1H-imidazole-4-carbaldehyde,
diiodomethane, triethoxysilane and cesium carbonate
were purchased from Aladdin Industrial Corporation
(Shanghai, China). Ethanol, toluene, and hydrochloric
acid were purchased from Tianjin Fuyu Fine Chemical
Co., Ltd. (Tianjin, China). Lastly, CD OD and
chloroform-d (CDCl ) with TMS as an internal standard
[18,19]
tant applications in metal coordination.
Among
them, flexible imidazolyl Schiff bases have been widely
used in the synthesis of various metal (e.g., Cu, Fe, Zn,
Ru, etc.) complexes, most of which have been proven to
3
[20–26]
be efficient catalysts.
In fact, the imidazolyl moiety
3
itself is a fine chelating agent towards platinum due to
the electron donating N atoms on its rigid ring, and sev-
eral platinum-imidazolyl complexes have been reported
were purchased from J & K Co., Ltd. (Beijing, China).
[27–30]
in the literature.
When it is further converted into a
2.2 | Instruments
Schiff base, its chelating ability is further enhanced as the
number of donating atoms increase, thus increasing its
ability to form platinum complexes.
Inspired by these facts, we herein design for the first
time a novel bis (imidazolyl) Schiff base bridged bis-
silane compound (Scheme 1, compound 3), and use it as
NMR spectra of the hydrosilylation adducts were
recorded using a Bruker 400 MHz spectrometer. Solid-
13
29
state C and Si NMR spectra were recorded using a
Bruker 600 MHz spectrometer. X-ray powder diffraction
(XRD) data were collected using a RIGAKU SmartLab
diffractometer with Cu Ka radiation. Fourier-transform
infrared spectra were recorded with a Nicolet 6700 spec-
trophotometer. DR-UV–Vis spectra were obtained with a
Cary-300 Ultraviolet–visible spectrophotometer.
A
SCHEME 1 Synthetic route towards IMIS-PMO-Pt(0)
Thermo Scientific K-Alpha instrument was used to

HUO ET AL.
3 of 10
record the X-ray photoelectron spectra (XPS) of the cata-
lyst. Scanning electron microscopy (SEM) and energy dis-
persive spectroscopy (EDS) data were collected with a
Hitachi SU8010 system that was equipped with a HOR-
IBA EMAX ENERGY module. Meanwhile, N2
adsorption/desorption experiments were conducted using
a Micromeritics TriStar II 3flex Surface Area and Porosity
Instrument. The exact platinum contents in the catalysts
were analyzed with a HK-9600 inductively coupled
plasma (ICP) spectrometer. TEM images were obtained
with a JEM-2100F system.
2.5 | Preparation of IMIS-PMO
The imidazolyl Schiff base-containing periodic meso-
porous organosilica (IMIS-PMO) was synthesized via
surfactant-directed co-condensation as illustrated in
Scheme
1.
In
a
typical
trial,
hex-
adecyltrimethylammonium bromide (CTAB, 0.431 g,
1.08 mmol) was dissolved in 50 ml of an aqueous solution
containing 42.3 mg (1.06 mmol) of NaOH. The mixture
was magnetically stirred at a speed of 200 rpm and
ꢀ
heated to 50 C until the solution was clear. Subse-
quently, 2.10 g (10.0 mmol) of tetraethyl orthosilicate
(
TEOS) was slowly added to this solution. After 5 min, a
0
2
.3 | Preparation of 1,1 -
1 ml ethanol solution of 3 (containing 0.204 g, 1.00 mmol
of compound 3) was added dropwise to the reaction mix-
ture. After 4 hr of stirring at 50 C, the gel solution was
methylenebis(1H-imidazole-
-carbaldehyde) (2)
ꢀ
4
ꢀ
aged at 80 C for 24 hr. The pale yellow precipitate was
H-Imidazole-4-carbaldehyde (3.18 g, 33.1 mmol) was
placed in a 250 ml round-bottom flask and dissolved
in 80.0 ml of anhydrous ethanol. Subsequently,
diiodomethane (4.50 g, 16.8 mmol) and CsCO3
filtered, washed thoroughly with ethanol and deionized
water, and then dried under vacuum at 50 C for 10 hr.
ꢀ
Subsequently, CTAB was removed by refluxing the solid
ꢀ
product in 100 ml of ethanol at 80 C for 24 hr and then
(
12.4 g, 35.0 mmol) were added to the solution under
the product was filtrated, washed with ethanol, and dried
under vacuum at 50 C overnight, thus producing IMIS-
PMO.
ꢀ
magnetic stirring. The reaction was conducted under
reflux for 24 hr and monitored by thin-layer chroma-
tography (TLC). The mixture was then allowed to
cool to room temperature and the solvent was
removed via rotary-evaporation under vacuum. The
crude products were purified via silica gel chromatog-
raphy (eluent: dichloromethane-methanol = 10:1, v/v)
and 1.67 g of 2 (yield 48.7%) was thus obtained as
2.6 | Preparation of IMIS-PMO-PtCl2
IMIS-PMO (0.500 g) was dispersed in 50 ml of ethanol
via ultra-sonication. Subsequently, sodium tert-butoxide
1
13
light-yellow crystals. H NMR and C NMR spectra
of 2 are provided in Figures S1-S3 in the Supporting
Information (SI).
(0.112 g, 1.16 mmol) and
5 ml of a H PtCl .
2 6
H O/isopropanol solution (0.05 M) were added, and the
2
reaction was allowed to proceed for 6 hr at room temper-
ature. The resultant light yellow powder was filtered,
washed thoroughly with ethanol, and then dried under
vacuum at 50 C for 10 hr, giving 0.485 g IMI-PMO-
PtCl2.
0
2
.4 | Preparation of (N,N'E,N,N'E)-N,N -
0
ꢀ
(
(1,1 -methylenebis(1H-imidazole-4,1-diyl))
bis (methanyl ylidene)) bis (3 -
(
triethoxysilyl)propan-1-amine) (3)
0
Briefly, 0.102 g (0.500 mmol) of 1,1 -methylenebis(1H-
imidazole-4-carbaldehyde) (2) was dissolved in 2 ml of
methanol in a 10 ml round bottom flask. Under vigorous
stirring, 0.221 g (1.00 mmol) of γ-amino propyl
triethoxysilane was added dropwise into the flask. The
solution was stirred for 15 hr at room temperature and
the reaction was monitored by TLC. After the reaction
was complete (~100% conversion), the solvent was
removed from the reaction mixture via rotary-
evaporation under vacuum to yield the crude product 3.
2.7 | Preparation of IMIS-PMO-Pt(0)
The synthetic route of IMIS-PMO-Pt(0) was illustrated by
scheme 1. Typically, IMIS-PMO-PtCl (0.400 g) was dis-
2
persed in 50 mL of ethanol via ultra-sonication. This mix-
ꢀ
ture was then cooled to −5 C and 143 mg (3.78 mmol) of
NaBH was added while the solution was magnetically
4
ꢀ
stirred. The reaction was carried out at −5 C for 2 hr
and then allowed to proceed further at room temperature
for another 4 hr. The resultant pale black powder was fil-
tered, washed thoroughly with ethanol, dried under vac-
1
13
The H and C NMR spectra of 3 were recorded without
further purification with the use of MeOD as the solvent
ꢀ
uum at 50 C for 10 hr, thus giving 0.387 g IMI-PMO-
(Figures S4-S6 in the SI).
Pt(0).

4
of 10
HUO ET AL.
2
.8 | Hydrosilylation reactions
the binding effect between platinum and the N atom
on the imidazole ring.
1
3
The catalytic activity of IMIS-PMO-PtCl2 and IMIS-
PMO-Pt(0) were evaluated based on their ability to cata-
lyze a model hydrosilylation reaction between 1-octene
and triethoxylsilane. The reaction was performed in a
Further evidence could be found in the solid-state
C
29
and Si NMR spectra of IMIS-PMO. As shown in
13
Figure S9 (SI), the C NMR peaks at 164.9, 135.7, and
110.5 ppm corresponded to the imidazole imine moiety,
while the peaks at 42.2, 20.8 and 9.7 ppm represented the
2
5 mL round-bottom flask with a magnetic stirrer. Most
[
36,37]
commonly, 780 μL (5.00 mmol) of 1-octene and IMIS-
carbons in the propyl chain.
The peak at 61.4 ppm
PMO-PtCl /IMIS-PMO-Pt(0) were added into the flask
and stirred at 60 C for 0.5 hr, and then 925 μL
can be assigned to the -CH - between the two imidazole
2
2
ꢀ
ring and the peak at 191.5 ppm corresponded to the
C=N.
(5.00 mmol) of triethoxylsilane was added and the mix-
29
ture was subsequently stirred for 2–6 hr. The resulting
The Si NMR spectrum (Figure S10 in the SI) of
IMIS-PMO displayed three resonance peaks
1
mixture was analyzed via H NMR spectroscopy without
4
3
further purification.
corresponding to Q (Si (OSi) , δ = −89.3 ppm), Q
4
2
The recyclability of IMIS-PMO-Pt(0) was evaluated
in terms of the conversion performance obtained after
repeated use for several cycles. Briefly, 10.5 mg of the cat-
(Si (OSi) OH, δ = −80.5 ppm), and Q (Si (OSi) (OH) ,
δ = −71.5 ppm), as well as T signal (-CH -Si (OSi)(OH) )
at δ = −44.9 ppm, T signal (-CH -Si (OSi) (OH)) at
3
2
2
1
2
2
2
2
2
alyst that had been suspended in 2.34 ml (15.0 mmol) of
δ = −53.3 ppm and T3 signal (-CH -Si (OSi) ) at
2
3
ꢀ
[35]
n
1
2
-octene was first preheated at 60 C for 30 min, and then
.775 ml (15.0 mmol) of trimethoxylsilane was added
δ = −61.3 ppm.
The presence of the Q (n = 2–4)
peaks resulted from the self-condensation of TEOS.
n
before the reaction was allowed to proceed for another
Meanwhile, the appearance of the T (n = 1–3) peaks can
2
1
hr. The catalyst was then collected via centrifugation at
5000 rpm. The supernatant was poured out and then the
be attributed to the co-condensation between TEOS and
compound 3, which led to the covalent incorporation of
imidazole imine moieties into the silica network. How-
remaining catalyst was mixed with fresh 1-octene before
a second reaction cycle was conducted via the same pro-
cedure as mentioned above. The products obtained from
each cycle were subsequently analyzed via H NMR
spectroscopy.
2
3
ever, the T or T signals were relatively weaker than the
1
29
T in the Si Spectrum. This might be due to the compar-
atively slow stirring speed during the co-condensation
reaction between TEOS and compound 3, which may
have resulted in insufficient condensation between the
two hydrolyzed substrates.
1
3
3
| RESULTS AND DISCUSSION
.1 | Characterization of IMIS-PMO,
The immobilization of platinum into the IMIS-PMO
framework was then characterized by XPS. The XPS sur-
vey spectrum (Figure 1a) verified the presence of plati-
num within the resulting material. The Pt4f high-
IMIS-PMO-PtCl , and IMIS-PMO-Pt(0)
2
resolution XPS spectra of IMIS-PMO-PtCl (Figure 1b)
2
3
.1.1 | The composition of IMIS-PMO,
revealed two groups of peaks. These include relatively
strong peaks at 72.88 (Pt4f 7/2) and 76.08 eV (Pt4f 5/2),
which indicated that the platinum primarily existed as
IMIS-PMO-PtCl , and IMIS-PMO-Pt(0)
2
+2
[38]
The incorporation of the imidazole imine moiety within
the pore walls of the resulting PMO was demonstrated
by FTIR and solid-state NMR analysis. In the FTIR
spectra of IMIS-PMO, IMIS-PMO-PtCl , and IMIS-
PMO-Pt(0) (Figure S7 in the SI), the absorption bands
Pt in IMIS-PMO-PtCl2.
were observed at 75.38 (Pt4f 7/2) and 78.48 eV (Pt4f 5/2),
which implied that minority of the platinum
maintained its +4 valence form, in a similar manner as
In addition, weaker peaks
a
2
[39]
K PtCl after immobilization into the PMO structure.
2 6
−
1
at ~1062, 790, and 465 cm corresponded to the Si-O-
Si vibration.
However, after treatment with NaBH , all of the plati-
4
[34]
−1
The bands at 2934 and 1467 cm
num in the IMIS-PMO-PtCl2 framework had been
respectively corresponded to the stretching and bending
reduced to its zero valence form, as only a doublet at
[35]
vibrations of the -(CH ) - moieties.
The small bands
71.68 (Pt4f 7/2) and 74.78 eV (Pt4f 5/2) could be found in
2
3
−
1
[40]
in the spectrum of IMIS-PMO at 1498 cm represen-
this case (Figure 1c).
The slight shift in the binding
ted the skeleton vibration of the imidazole ring, while
energy can be attributed to the interaction between Pt
and N atoms or Pt and the C=N double bonds, which can
also be proven by the presence of the peak at 401.79 eV
in the N1s high-resolution XPS spectra of IMIS-PMO-
−1
those at 1336 and 1359 cm showed the bending vibra-
[36]
tions of C=N (Figure S8 in the SI),
and these three
peaks became weaker in the spectra of IMIS-PMO-
PtCl2 and IMIS-PMO-Pt(0), which might be due to
[
38]
Pt(0) (Figure 1d).

HUO ET AL.
5 of 10
FIGURE 1 XPS survey spectrum
of IMIS-PMO-Pt(0) (a). Also shown are
high-resolution Pt4f XPS spectra of
2
IMIS-PMO-PtCl (b) and IMIS-PMO-
Pt(0) (c) before use as catalysts as well
as the high-resolution N1s XPS
spectrum of IMIS-PMO-Pt(0) (d)
Lastly, the exact platinum content in IMIS-PMO-
Pt(0) was determined by ICP, and was found to be
5 nm and ended at over 20 nm, should be due to the
packing spaces between small particles with rough sur-
faces and generally small dimensions (about 100 to
150 nm in diameter, see Figure 3a). However, the true
inner pore structures could be clearly seen from the
TEM image of IMIS-PMO (Figure 3b), presenting uni-
form mesoporous channels (with diameter of 4~5 nm)
which were comparable to most periodic mesoporous
organosilica frameworks prepared using CTAB as a
7
.27 wt%. This value suggested that merely one quarter of
the IMIS moieties (probably those distributed on the
superficial layer of the pore walls) were chelated with
platinum, whilst almost three quarters of the IMIS units
were inaccessible in the PMO matrix (calculating method
see SI).
[
42]
template.
The well-ordered pore channels could also
3
.1.2 | Microstructure and surface
be proven by the low angle XRD pattern of IMIS-
morphology characterization of IMIS-PMO,
IMIS-PMO-PtCl , and IMIS-PMO-Pt(0)
PMO-Pt(0) and IMIS-PMO-PtCl , in which there were
2
o
peaks at
Figure S12, SI) .
The platinum distribution throughout the IMIS-PMO
2
theta
=
1.04 for (100) diffraction
2
(
The mesoporous microstructures of IMIS-PMO series
were demonstrated by N2 adsorption analysis
framework was also investigated via TEM methods. As
shown by the STEM image of IMIS-PMO-PtCl2
(Figure 3c), the Pt (II) complexes were uniformly
distributed throughout the silica matrix, mainly as
small nanoclusters with diameters of less than 1 nm.
In the case of IMIS-PMO-Pt(0), the larger
platinum(0) nanocrystals with diameters in the range of
1–2 nm could be clearly observed in the corresponding
TEM image (Figure 3d). Furthermore, the formation of
platinum(0) nanocrystals can be proven by the HRTEM
image (Figure 3e) of one of these platinum crystals show-
(Figure 2) and TEM characterization. The surface area
of each sample was calculated via the BET method
[41]
(See Table S1 in the SI).
The surface area of IMIS-
PMO series decreased drastically when the platinum
chloride was introduced into the matrix, and it further
diminished when the platinum was reduced to its
zero-valence state. The shape of the hysteresis loop
o
with p /p ranging from 0.45 to 0.95 indicated that
inkbottle-shape pore structures were presented inside
the materials, and the small distributions at around
[
43]
3
.8 nm of all three plots, which were calculated by
ing the lattice fringes,
and also by the XRD pattern of
BJH method using the adsorption curves in Figure 2b,
were artefacts of the closure of the hysteresis. The
broad peaks in Figure 2(b), which started from about
IMIS-PMO-Pt(0) (Figure S11 in the SI), in which four
diffraction peaks were identical to the characteristic dif-
[
44]
fraction lines of platinum crystals.

6
of 10
HUO ET AL.
FIGURE 2
N
2
adsorption/desorption isotherms (a) and
pore size distributions (b) of IMIS-
PMO, IMIS-PMO-PtCl
Pt(0)
2
, and IMIS-
FIGURE 3 SEM image of IMIS-
PMO (a), TEM image of IMIS-PMO
(b), STEM image of IMIS-PMO-PtCl
(c), TEM image of IMIS-PMO-Pt(0)
(d), and an HRTEM of platinum
2
nanoparticles in IMIS-PMO-Pt(0) (e)
3
.2 | Application of IMIS-PMO-Pt in
same reaction conditions as those employed for entry
2. Increasing the catalyst dosages resulted in a minor
increase in the conversion percentage (see entries 1 and
3).
hydrosilylation reactions
The performances of IMIS-PMO-PtCl and IMIS-PMO-
2
Pt(0) as catalysts for hydrosilylation reactions were evalu-
ated on account of their ability to mediate a model reac-
tion between 1-octene and triethoxylsilane (Scheme 2).
The influence of the catalyst dosage on the
hydrosilylation reaction was examined first. The results
are listed in Table 1 as entries 1–4, together with the
corresponding reaction conditions. In the case of IMIS-
The effect of the reaction time (Table 1, entries 4–8)
and reaction temperature (Table 1, entries 4, 8–11) on
hydrosilylation reactions that were mediated by IMIS-
PMO-Pt(0) were then studied. Samples were collected for
1H NMR analysis at 0, 0.5, 1, and 2 hr during the reaction
and the conversion rates of 1-octene at each interval were
then calculated. The conversion rate increased dramati-
cally as the reaction progressed, and it exceeded 99.0%
after 2 hr. The reaction could only be activated when the
PMO-PtCl , when 5 mmol of 1-octene was treated with
2
ꢀ
an equal amount of silane for 6 hr at 60 C, a 98.0% con-
1
ꢀ
version of 1-octene could be achieved (calculated by H
reaction temperature exceeded 60 C, and could not pro-
NMR) when 3.2 mg of this catalyst (0.0250 mol% of Pt,
see entry 2) was used. When 3.1 mg of IMIS-PMO-Pt(0)
ceed at low temperatures. Furthermore, it was found that
excellent regioselectivities were achieved through the 1H
NMR spectra of the final products in most cases, as no
alpha adducts could be found. Yet it has to be noted that
(0.0232 mol% of Pt) was used as a catalyst, the conversion
reached as high as 99.5% (Table 1, entry 4) under the

HUO ET AL.
7 of 10
SCHEME 2 Modeling
hydrosilylation reaction
TABLE 1
2
Data collected during various hydrosilylation tests with IMIS-PMO-PtCl and IMIS-PMO-Pt(0)
Catalyst
amount (mg)
Pt amount
(mmol)
Pt dosage
(mol%)
Temperature
( C)
Conversion
%
TOF
h
ꢀ
a
-1
entry catalyst
TON
1
2
3
4
5
6
7
8
9
1
1
IMIS-PMO-PtCl
IMIS-PMO-PtCl
2
2
30.1
3.2
30.2
3.1
3.1
3.1
3.1
3.1
3.0
3.2
3.1
0.0117
0.234
60 (6 h)
60 (6 h)
60 (6 h)
60 (6 h)
60 (0 h)
60 (0.5 h)
60 (1 h)
60 (2 h)
20 (2 h)
40 (2 h)
80 (2 h)
>99.5
98.0
>99.5
99.5
0
71
667
74
427
4000
442
4310
/
0.00125
0.0113
0.0250
0.226
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
IMIS-PMO-Pt(0)
0.00116
0.00116
0.00116
0.00116
0.00116
0.00112
0.00119
0.00116
0.0232
0.0232
0.0232
0.0232
0.0232
0.0224
0.0238
0.0232
718
/
35.5
94.8
>99.0
0
3060
4086
2160
/
1530
4086
4310
/
0
1
0
/
/
>99.5
2160
4310
a
Conditions: 1-Octene was mixed with a set amount of catalyst in a 25 ml flask and preheated at given temperature for 0.5 hr. Triethoxyl
hydrosilane was then added to the mixture and the reaction was allowed to proceed for another 2–4 hr. The conversion% were calculated via
1
3
H NMR characterization using CDCl as a solvent.
trace amount of 2-Octene and n-octane could also be
identified in the final products.The ability of IMIS-PMO-
Pt(0) to mediate hydrosilylation reactions involving vari-
ous substrates was then evaluated by using various
substituted olefins and styrenes. As can be seen in
Table 2, in most cases, IMIS-PMO-Pt(0) exhibited posi-
tive catalytic activity, and the impressive selectivity was
retained. In cases involving the olefins bearing a terminal
alkene such as 1-octene (Table 1, entry 9), 1-octadecene
(Table 2, entry 1), triethoxy (vinyl)silane (Table 2, entry
2), and (vinyloxy)benzene (Table 2, entry 9), all of the
conversion% were over 99%, which indicated that the cat-
alyst had high activity for hydrosilylation reactions.
When the olefins contained other functional groups,
moderate to high conversion percentages could also be
obtained (See Table 2, entries 3, 6, and 7). Meanwhile,
when the IMIS-PMO-Pt(0) was used to mediate the
hydrosilylation between styrene and triethoxysilane, the

8
of 10
HUO ET AL.
a
TABLE 2
Catalytic activity of IMIS-PMO-Pt(0) for the hydrosilylation of various olefins with triethoxysilane
Reaction
Selectivity
temperature
( C)
Reaction
time (hr)
(β−/α- adduct
percentage)
TOF
(h )
ꢀ
−1
Entry
Olefin
Silane
Conversion%
1
HSi
60
60
60
2
2
2
98.3
mainly
β-adduct
2118
2138
1959
b
(
OEt)
3
3
3
2
3
HSi
99.2
90.9
Only β-adduct
Only β-adduct
(
OEt)
HSi
(
OEt)
4
5
HSi
60
60
2
2
83.4
88.4
Only β-adduct
1797
1905
(
OEt)
3
3
HSi
5:1
(
OEt)
6
7
HSi
60
60
2
2
81.5
37.5
Only β-adduct
Only α-adduct
1756
808
(
OEt)
3
3
HSi
(
OEt)
8
9
HSi
60
60
2
2
42.9
Only β-adduct
Only β-adduct
924
(
OEt)
3
HSi
>99.5
2155
(
OEt)
3
1
0
HSi
60
2
41.2
Only β-adduct
888
(
OEt)
3
a
The platinum dosage was set at 0.0232 mol% (in comparison with moles of the olefin), while the olefin:silane molar ratio was 1:1.
No alpha adducts could be found, but trace amount of 2-octadecene and n-octadecane could possibly exit.
b
1
conversion could reach 80.1%, which was comparable to
H NMR data. As shown in entry 8, table 2, the conver-
sion% of 4-Phenyl but-1-ene was relatively low when cat-
alyzed by IMIS-PMO-Pt(0), comparing to that catalyzed
[45]
most catalysts reported in the literature.
In addition,
the β−/α- adduct percentage was ~ 5:1, according to the

HUO ET AL.
9 of 10
FIGURE 4 Recycling experiments
with IMIS-PMO-Pt(0) (a) and high-
resolution XPS spectra of Pt4f in IMIS-
PMO-Pt(0) after 5 cycles (b)
[
46]
by the Kardert's catalyst,
and this might be a result of
(2015B090915004), the Science and Technology Program
of Guangzhou City (201802010018, 201904020019), and
the Sichuan Science and Technology Project
(2019YFSY0011) for providing financial support. We are
also grateful for the support provided by the Innovative
Talents Youth Program (Natural Science) in Universities
of Guangdong (2017-GKQNCS113), and the Guangzhou
Industrial Technology Major Project (201802010018).
lower reaction temperature and shorter reaction time in
this research.
Finally, the recyclability of IMIS-PMO-Pt(0) was
also investigated. As shown in Figure 4a, the catalyst can
be used in five consecutive runs without exhibiting signif-
icant loss in activity. Yet according to the high-resolution
Pt4f XPS spectra of the catalyst after five reaction cycles
(Figure 4b), the platinum was oxidized to its +2 valence
state, and its catalytic activity toward hydrosilylation
reactions was still retained. We suspected that the cata-
lyst was gradually oxidized through the reaction proce-
dure, and further investigation into the catalytic
mechanism is still underway. In conclusion, the IMIS-
PMO-Pt(0) can be used as an efficient catalyst for
hydrosilylation reactions.
ORCID
Jiwen Hu https://orcid.org/0000-0002-8473-5797
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How to cite this article: Huo Y, Hu J, Tu Y, et al.
Platinum-Imidazolyl Schiff Base Complexes
Immobilized in Periodic Mesoporous Organosilica
Frameworks as Catalysts for Hydrosilylation. Appl
Organomet Chem. 2020;e5697. https://doi.org/10.
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1002/aoc.5697
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