Balancing between Heterogeneity and Reactivity in Porphyrin Chromium-Cobaltate Catalyzed Ring Expansion Carbonylation of Epoxide into β-Lactone

Article abstract of DOI:10.1021/acs.inorgchem.8b03361

The synthesis of a unique heterogeneous catalyst that combines the functionality of a homogeneous catalyst and the advantages of a heterogeneous catalytic process is a continuing goal in various industrially applicable reactions. Here, we report heterogenization of homogeneous catalyst for lactone production from epoxide carbonylation through a facile polymerization using Friedel-Crafts reaction. A correlation between reactivity and degree of heterogeneity has been deduced by synthesizing different sized polymeric catalysts. The partially polymerized catalyst showed a remarkable initial turnover frequency of 400 h^-1, and the fully polymerized catalyst displayed excellent selectivity during recycling with a total turnover number of 4100.

Full text of DOI:10.1021/acs.inorgchem.8b03361

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Balancing between Heterogeneity and Reactivity in Porphyrin
Chromium-Cobaltate Catalyzed Ring Expansion Carbonylation of
Epoxide into β‑Lactone
Senkuttuvan Rajendiran, Vinothkumar Ganesan, and Sungho Yoon*
Department of Applied Chemistry, Kookmin University, 861-1, Jeongneung-dong, Seongbuk-gu, Seoul 136-702, Republic of Korea
S
* Supporting Information
ABSTRACT: The synthesis of a unique heterogeneous catalyst that
combines the functionality of a homogeneous catalyst and the advantages
of a heterogeneous catalytic process is a continuing goal in various industrially
applicable reactions. Here, we report heterogenization of homogeneous
catalyst for lactone production from epoxide carbonylation through a facile
polymerization using Friedel−Crafts reaction. A correlation between
reactivity and degree of heterogeneity has been deduced by synthesizing
different sized polymeric catalysts. The partially polymerized catalyst showed
a remarkable initial turnover frequency of 400 h−1, and the fully polymerized
catalyst displayed excellent selectivity during recycling with a total turnover
number of 4100.
separation and catalyst recyclability. To this end, the search for
developing methods to heterogenize the highly active catalysts
is continuing. In this context, incorporation of active
homogeneous centers onto supporting materials inevitably
limits the amount of the active ion pair because of the steric
restriction of the supports, which results in reduced epoxide
carbonylation.20,21 Although, a recently developed Cr-MIL-101
supported heterogeneous catalyst possesses an active ion pair,
it shows moderate activity compared to any homogeneous
catalyst reported thus far.22 Therefore, to attain higher
reactivity, heterogenization of active homogeneous catalysts
such as [TPPCr][Co(CO)4] is expected to maintain their
active ion-pair centers in them.
In designing such an efficient heterogenization method, we
focused our attention to systematically heterogenize the active
homogeneous complex with the active centers intact using a
well-known Friedel−Crafts polymerization method. Herein,
the synthesis of chromium-cobaltate porphyrin organic
polymer with remarkable catalytic activity and high selectivity
toward epoxide carbonylation, which are comparable to the
performance of homogeneous catalyst, is reported. In addition,
one of the polymerized catalysts in the early period exhibits
high dispersibility in solution, which could enable it to be used
as a potential alternative for the homogeneous catalyst. The
synthesized recyclable heterogeneous catalyst maintained 95%
lactone selectivity in repeated cycles, demonstrating the
excellent stability of the catalyst.
INTRODUCTION
■
The efficient transformation of epoxide into β-lactone has
attracted considerable attention owing to its synthetic
significance in the production of acrylic acid,1 β-hydroxyacids,2
β-hydroxyester,3−8 succinic anhydride,9,10 and biodegradable
poly(β-hydroxybutyrate).11−14 Realizing the industrial impor-
tance of β-lactones, a number of homogeneous catalysts have
been reported for the conversion of epoxide into a
lactone.15−17 Among them, Coates et al. established that the
well-defined homogeneous bimetallic complex tetraphenylpor-
phyrin chromium tetracarbonyl cobaltate [TPPCr][Co(CO)4]
exhibited excellent conversion of epoxides to lactones, which is
the best catalyst to date for epoxide carbonylation. Moreover,
these bimetallic complexes demonstrated the necessity of
active ion pair for efficient carbonylation and gave important
mechanistic insights (Scheme 1).18,19 In addition, these studies
have received a great interest in commercial grounds.
In an industrial point of view, however, heterogeneous
catalytic systems are much desirable due to easy product
Scheme 1. Proposed Mechanism of Epoxide Carbonylation
to Lactone
Received: December 3, 2018
© XXXX American Chemical Society
A
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Scheme 2. A Schematic Representation of Polymerized Tetraphenylporphyrin Chromium-Cobaltate Complex
red line). Notably, the presence of a typical and well-known
porphyrin methyl cations peak in the near-IR region (Figure 1,
inset, red solid line) possibly demonstrates the generation of
intermediate carbocation during the Friedel−Crafts alkylation
in Scheme 2. The observation of this absorption band over the
reaction time affirms the continuous generation of a cationic
intermediate for the multiconnection of the [TPPCr]Cl methyl
linker to form a heterogeneous material. This result is in
agreement with the mechanistic explanation of Li et al. and
Tan et al., and also consistent with near-IR studies of other
carbocation results.24−27 As the reaction proceeds to the
completion, the observed peaks slowly diminish (solid black
line) due to the formation of methylene bridges between the
phenyl rings of the porphyrin polymers. It is worth to mention
here that the visually observed gradual color changes of
solution from reddish-orange to brown, which finally turned to
almost colorless with the black precipitate formation, reveals
the completion of heterogenization process.
RESULTS AND DISCUSSION
■
The porous porphyrin was synthesized through the knitting
strategy in which dimethoxymethane (DMM) was employed
as a cross-linker to combine the phenyl ring of porphyrins with
a methylene (−CH2−) bridge through the FeCl3 catalyzed
Friedel−Crafts alkylation at 80 °C (Scheme 2).23 The progress
of the reaction was monitored visually as well as by UV−visible
spectroscopy (Figure 1). After the addition of a linker, over the
reaction time, a typical sharp absorption band of metal-
loporphyrin undergoes a Soret shift from 448 to 454 nm (solid
To further deepen the understanding of the heterogenization
process, the catalyst was synthesized by varying the reaction
time (3, 6, 12, and 24 h) (Scheme 2). The resultant
precipitates were washed with water, THF, and diethyl ether
to obtain a porous organic polymer porphyrin chromium
chloride and are represented as POP-[TPPCr]Cl-3h (1), POP-
[TPPCr]Cl-6h (2), POP-[TPPCr]Cl-12h (3), and POP-
[TPPCr]Cl-24h (4), respectively.
The morphology of the resulting precipitates was analyzed
by scanning electron microscopy (SEM), and the results show
irregularly shaped particles for 1, 2, and 3 and partially
spherical particles for 4 (Figure 2). Particle size increased from
1 [>0.5 (10) μm] through to 3 [>1.2 (10) μm]. These
morphological changes indicate the continuous linkage of the
porphyrin unit to generate the connected oligomeric to
Figure 1. UV−visible spectra at different time intervals during the
reaction of TPPCrCl with DMM and FeCl3 in 1,2-dichloroethane
(DCE). (For clear representation, in the inset, we displayed the
intermediate cation peak in higher concentration.)
B
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dispersive X-ray (EDX) analysis demonstrates the presence
of Co ions throughout the samples. FTIR spectra showed a
CO stretching peak at 1875 cm−1 that further confirms the
exchanged Co(CO)4 ion in 5, 6, 7, and 8 (Figure S2).
Although this anion exchange reduces the surface area of the
catalyst to 45, 66, 186, and 306 m2 g−1, respectively (Figure
S7), the existence of porous channels is beneficial for mass
transfer of substrates to the active sites (Figure S8 and Table
S2). Further, the anion exchanged polymers show shifted Cr
binding energies in XPS measurements and the corresponding
cobalt ion peaks at 797.3 and 781.6 eV (Figure S9) are
precisely matched with the homogeneous [TPPCr][Co(CO)4]
complex. The Cr/Co contents in 5, 6, 7, and 8 were measured
using ICP-OES and were found to be 3.46/3.61, 4.01/3.89,
3.36/3.51, and 3.16/3.11 wt %, respectively.
All the data acquired from the structural characterization of
5, 6, 7, and 8 lead to performing carbonylation using propylene
oxide (PO) (less toxic than ethylene oxide) in ether solvent
(DME, which has been reported to be the best solvent for
carbonylation of an epoxide into lactone) at 60 °C under 6.0
MPa of CO; the results are summarized in Table 1. To
Figure 2. Scanning electron microscopic images of 1, 2, 3, and 4.
polymeric structures, which is consistent with the UV−visible
kinetic studies. The dispersion of different sized materials 1, 2,
3, and 4 was examined by absorption analysis (Figure S1).
These particles remained dispersed in the solution which
settles down at a different time interval (30, 26, 22, and 16
min), indicating the facile separation of the catalyst (Figure
S1).
Table 1. Carbonylation of PO Using Catalysts 5, 6, 7, and
8
a
b
c
entry
catalyst
PO (equiv) conversion (%) TOF (h−1
)
1
2
3
4
5
TPPCrCo(CO)4
2400
2400
2400
2400
2400
>99
92
75
56
43
530
400
300
180
120
5
6
7
8
The structural integrity of the polymeric materials was
initially assessed by Fourier transform infrared (FTIR)
spectroscopy. The FTIR spectra of 1, 2, 3, and 4 reveal a
weak signal of the methylene linker at around 2910−2980
cm−1 indicative of successful polymerization (Figure S2).23
Furthermore, a sharp peak at 1000 cm−1 confirms the presence
of Cr-porphyrin in the polymeric materials.28 X-ray photo-
electron spectroscopic (XPS) analysis of 1, 2, 3, and 4 shows
peaks at binding energies of 586.8 and 577 eV, which
correspond to Cr 2p1/2 and 2p3/2 in a porphyrin (Figure S3).
To understand the porosity of heterogenized porphyrins 1, 2,
3, and 4, nitrogen sorption experiments were measured at 77
K, and the result shows the surface area of 88, 129, 268, and
421 m2 g−1, respectively (Figure S4). The observed gradual
increase in surface area of the samples indicates that the
formed shorter polymeric chains rearranged themselves into a
dense packing arrangement, which reduces the pore volume,
resulting in the low surface area. In contrast, the growth of the
polymeric chain increased dramatically with the reaction time,
which hindered the arrangement of polymeric chains from
close packing. This resulted in increased pore volume and
thereby increasing the surface area for 4. In addition, the
Barrett−Joyner−Halenda (BJH) plot shows the presence of
mesopores in 1 and both micropores and mesopores in 2, 3,
and 4 samples (Figure S5 and Table S1).
Given the sufficient pore size in 1, 2, 3, and 4, endogenous
anion (Cl−) exchange was performed with freshly prepared
KCo(CO)4 at room temperature to form porous organic
polymer porphyrin chromium cobalt tetracarbonyl complexes
as a dark black solid and represented as POP-[TPPCr][Co-
(CO)4]-3h (5), POP-[TPPCr][Co(CO)4]-6h (6), POP-
[TPPCr][Co(CO)4]-12h (7), and POP-[TPPCr][Co-
(CO)4]-24h (8), respectively (Scheme 2). The SEM images
of the obtained black precipitates show no apparent changes in
morphology (Figure S6), and the corresponding energy-
a
Reaction performed in 2.5 mL of DME in a tube reactor pressurized
with 6.0 MPa of CO at room temperature and heated to 60 °C for 24
b
1
h. Determined by H NMR spectroscopy with naphthalene as an
c
internal standard. TOF for first 1 h.
demonstrate the validity of our heterogeneous reaction system,
epoxide carbonylation has been performed with previously
reported [TPPCr][Co(CO)4] catalyst in DME, at 60 °C under
6.0 MPa of CO, resulting in 99% conversion to β-
butyrolactone with a turnover number (TON) of 2400
(entry 1). This result encouraged us to evaluate the activity
of 5 with the same condition of entry 1, showing 92%
conversion of β-butyrolactone with the initial turnover
frequency (TOF) of 400 h−1 (entry 2). Even though the
catalyst 5 is in the beginning stage of heterogenization, it is
soluble in reaction condition which enables great interaction of
epoxide with Cr/Co centers, resulting in homogeneous catalyst
like activity. In similar condition, the other catalysts were
explored for PO carbonylation and found that 6, 7, and 8
showed conversion of 75, 56, and 42% with initial TOF of 300,
180, and 120 h−1 respectively (entries 3, 4, and 5). Although
decreased activity was observed, it is the highest TOF reported
to date than any other immobilized heterogeneous cata-
lyst.20−22 This reducing activity trend is explainable because
through the heterogenization process the catalyst behavior
would deviate from the homogeneous catalyst and shows
limited solubility with the substrate. The observed excellent
selectivity of the lactone indicates that the process of
heterogenization occurred by maintaining the bimetallic ion
pair as like homogeneous catalyst [TPPCr][Co(CO)4].
Further, the stability of 8 was examined by hot-filtration
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tests, and ICP-OES analysis of the filtrate shows no metal
content was leached.
The rate of PO carbonylation of catalysts 5, 6, 7, and 8 was
studied through kinetic experiments, and the products were
monitored by 1H NMR spectroscopy (Figure 4 and Table S4).
At least five cycles of PO carbonylation were performed to
investigate the stability of the catalysts 5, 6, 7, and 8. After the
initial run, catalysts were easily separated from the reaction
mixture by simple filtration and washed with DME for further
use. ICP-OES analysis of the separated precipitate demon-
strates that the ratio of Cr/Co was almost maintained for 7 and
8 (3.24/3.41 and 3.13/3.01 wt %), whereas those for 5 (3.12/
2.35) and 6 (3.89/3.03) showed a reduced Cr/Co content.
Since 5 demonstrates homogeneous catalyst characteristics, the
shortly formed polymers are dispersible in reaction condition
which undergoes dissociation easily.
The recovered catalyst was subjected to further four runs;
the overall activity of 7 and 8 was almost maintained (based on
cobalt wt %), whereas 5 and 6 showed reduced activity (Figure
3 and Table S3). This decreased activity is due to the partial
Figure 4. Kinetic study of β-butyrolactone formation with [TPPCr]-
[Co(CO)4], 5, 6, 7, and 8.
Initially, [TPPCr][Co(CO)4] shows complete conversion in
12 h with initial TOF of 530 h−1. Similarly, catalyst 5 attained
its full conversion in 16 h with an initial TOF of 400 h−1, and
the conversion rate almost maintained with the homogeneous
catalyst. However, in the case of 6, 7, and 8, the rate of
conversion of PO to lactone is gradually reduced compared to
[TPPCr][Co(CO)4], because the formed lactone is dispersed
and bound with an available catalytic center that reduces the
PO approach to the metal center which prolongs the reaction
to complete. These results indicate that the highly soluble form
of catalyst 5 exhibits a faster reaction rate than the fully
heterogenized catalyst 8. After endured the complete activity
and stability studies of 8 in batch-type reactions, this
heterogeneous catalyst was subjected to a three-phase
continuous process. A fixed bed reactor was packed with 8
in silicon carbide and pressurized with 2.0 MPa of CO at the
flow rate of 30 mL/min, and subjected to a flow of 0.5 M PO
in diethyl ether at 1.6 mL/h; β-butyrolactone was obtained
with the initial TOF of 17 h−1 and TON of 100 in 12 h (Figure
S10). It is noteworthy that this observed catalytic activity is the
highest for epoxide carbonylation in both batch type20,21 and
three-phase continuous reaction than any other modified
heterogeneous catalyst under similar condition.22
Figure 3. Recyclability of catalysts 5, 6, 7, and 8 under reaction
conditions of 60 °C and 6.0 MPa of CO. The 6th cycle represents
epoxide carbonylation performed with a regenerated catalyst. Dotted
line indicates the acetone formation during the recycle experiments.
solubility of the Cr part and rapid loss of Co ions from the
framework, which was confirmed by the ICP-OES analysis
(Cr/Co content 2.76/1.18 and 3.07/1.58 wt %). Notably,
upon recycling, the relative amounts of acetone were generated
(Table S3). To explore the possibility of replenishing the
cobalt content of the recycled catalysts, after the fifth run,
catalyst was separated and treated with freshly prepared
K[Co(CO)4] in THF for 24 h (see procedures in Supporting
Information) and Cr/Co content was analyzed by ICP-OES.
In the case of 5 and 6, the Cr/Co ratio was not retained as like
a fresh catalyst because this catalytic system partially lost its
cationic sites which limit the regeneration of the catalyst.
However, this partial regeneration did not limit the activity of
the catalyst. Moreover, it demonstrates that these catalysts are
superior to the homogeneous part. Further, PO carbonylation
was performed with the regenerated catalyst under the similar
conditions, resulting in the generation of β-butyrolactone (98%
and 99%) for 7 and 8 (Figure 3); however, for 5 and 6, the
conversion reached only 75% and 85%, respectively. Among
the developed catalysts, shortly polymerized 5 showed reduced
recyclability, whereas 8 maintained its overall activity with the
total TON of 4100 (five cycles) which is an attractive
heterogeneous catalyst for the large-scale production of
lactone.
CONCLUSION
■
We bridged homogeneous catalytic function with the benefits
of heterogeneous support through a direct knitting strategy
using the Friedel−Crafts alkylation method. The active
bimetallic ion-pair sites of the homogeneous complex was
maintained through the heterogenization. This study has
demonstrated the catalytic activity differences between partially
polymerized and fully heterogenized catalysts in comparison
with the homogeneous complex that is used for epoxide
carbonylation. The partially heterogenized catalysts were
highly dispersed in solution and displayed a comparable rate
of epoxide carbonylation as like a homogeneous catalyst. On
the other hand, fully heterogenized catalyst showed high
stability, activity, recyclability, and reusability. Moreover, these
catalytic studies have proven that this catalyst would be a
possible candidate for large-scale production.
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Synthesis of POP-[TPPCr]Cl-24h (4). To a solution of TPPCrCl
(0.2400 g, 0.3428 mmol) in DCE (10 mL), anhydrous FeCl3 (0.2224
g, 1.3712 mmol) and DMM (0.1043 g, 1.3718 mmol) were added in
room temperature. The greenish-brown solution was stirred at 80 °C
for 24 h and cooled to room temperature. The resulting black
precipitate was filtered and washed with water (2 × 100 mL), DMF
(50 mL), THF (50 mL), methanol (50 mL), acetonitrile (50 mL),
acetone (50 mL), dichloromethane (50 mL), and ether (50 mL). The
precipitate was further purified by a Soxhlet method with THF/
methanol (50/50 mL) and dried under vacuum at 60 °C for 24 h and
obtained as a black powder (Yield = 0.2219 g).
Synthesis of 5. In a glovebox, 1 (0.079 g) and KCo(CO)4 (0.4 g)
were dissolved in 10 mL of THF and stirred at room temperature for
24 h. The reaction mixture was filtered, and the precipitates are
washed with THF/diethyl ether (2/8) (2 × 10 mL) and pentane (10
mL). The resulting black precipitates was dried under vacuum for 16
h (Yield = 0.082 g).
Synthesis of 6. In a glovebox, KCo(CO)4 (0.4 g) dissolved in 10
mL of THF was added to 2 (0.2080 g) and stirred at room
temperature for 24 h. The reaction mixture was filtered, and the
precipitates are washed with THF/diethyl ether (2/8) (2 × 10 mL)
and pentane (10 mL). The resulting black precipitates were dried
under vacuum for 16 h (Yield = 0.214 g).
Synthesis of 7. In a glovebox, KCo(CO)4 (0.4 g) dissolved in 10
mL of THF was added to 3 (0.1864 g) and stirred at room
temperature for 24 h. The reaction mixture was filtered, and the
precipitates are washed with THF (10 mL), methanol (10 mL), and
pentane (10 mL). The resulting black precipitates were dried under
vacuum for 16 h (Yield = 0.195 g).
EXPERIMENTS
■
General Considerations and Physical Measurements. All
manipulations of air- and water-sensitive compounds were carried out
in the glovebox. All the chemicals purchased were of analytical grade
from Tokyo Chemical Industry and Sigma-Aldrich and were used as
received unless mentioned otherwise. Tetrahydrofuran was refluxed
over sodium/benzoquinone and distilled under a N2 atmosphere.
MeOH was refluxed over Mg/I and distilled under a N2 atmosphere.
PO and acetonitrile were distilled over calcium hydride under a N2
atmosphere. KCo(CO)4 was prepared by following reported
procedure.8 All new compounds were fully characterized by standard
spectroscopic techniques. Deuterated solvents were purchased from
Cambridge Isotope Laboratories, Inc., and used as received. NMR
spectra were recorded on a Bruker Advance IV (400 MHz) at 298 K,
and chemical shifts were referenced to the TMS peak. IR spectra were
collected on a Nicolet iS 50 (Thermo Fisher Scientific) spectrometer
using attenuated total reflection (ATR) techniques. Scanning electron
microscopy (SEM) and energy-dispersive spectroscopy (EDS) were
measured on a JEOL LTD (JAPAN) JEM-7610F operated at an
accelerating voltage of 15.0 kV. N2 adsorption/desorption was
measured at 77 K using an automated gas sorption system (Belsorp
II mini, BEL Japan, Inc.). Chromium and cobalt content in complexes
5, 6, 7, and 8 was determined using Inductively coupled plasma
optical emission spectroscopy (ICP-OES) (iCAP-Q, Thermo Fisher
Scientific) using a microwave assisted acid system (MARS6, CEM/
USA). X-ray photoelectron spectroscopy (XPS) analysis was
performed on an ESCA 2000 (VG Microtech) at a pressure of ∼3
× 10−9 mbar using Al Kα as the excitation source (hγ = 1486.6 eV)
with the concentric hemispherical analyzer. Research-grade carbon
monoxide was purchased from Sinyang Gas Company, Korea, with
99.995% purity used as received. All batch type carbonylation
reactions were performed in a 100 mL stainless steel (SS) tube reactor
and fitted with a pressure gauge and pressure release valve. Three-
phase continuous carbonylation was performed with a SS reactor. All
carbonylation reactions were set up and run in a well-ventilated fume
hood equipped with a carbon monoxide detector (see MSDS for
proper handling of CO). PO conversion, β-butyrolactone was
Synthesis of 8. In a glovebox, KCo(CO)4 (0.4 g) dissolved in 10
mL of THF was added to 4 (0.2219 g) and stirred at room
temperature for 24 h. The reaction mixture was filtered, and the
precipitates are washed with THF (10 mL), methanol (10 mL), and
pentane (10 mL). The resulting black precipitates were dried under
vacuum for 16 h (Yield = 0.236 g).
General Procedure for Epoxide Ring-Opening Carbon-
ylation into β-Lactone in Batch Type. A 100 mL SS tube reactor
was dried at 80 °C overnight and vacuumed for 4 h. In a glovebox, it
was equipped with a stir bar and charged with 5 (0.0091 g, 0.0056
mmol of cobalt) (PO: 0.7851 g, 13.5362 mmol), 6 (0.0085 g, 0.0056
mmol of cobalt) (PO: 0.7902 g, 13.6241 mmol), 7 (0.0121 g, 0.0072
mmol of cobalt) (PO: 1.0184 g, 17.5586 mmol), and 8 (0.0106 g,
0.0056 mmol of cobalt) (PO: 0.7821 g, 13.4844 mmol) in 2.5 mL of
dry DME. The reactor was taken out from the glovebox and
immediately cooled to 0 °C and purged with 0.5 MPa of CO. Then
the reactor was pressurized to 6.0 MPa of CO and heated to 60 °C for
24 h. After the reaction time, the reactor was cooled to 0 °C, and CO
gas was slowly released inside the hood. The crude sample was
weighed and dissolved in CDCl3, filtered through Celite, and washed
with CDCl3. The conversion was calculated using 1H NMR
spectroscopy with naphthalene as an internal standard.
General Procedure for Epoxide Ring-Opening Carbon-
ylation into β-Lactone in Three-Phase Continuous Reaction.
In a glovebox, the 0.038 g of 8 with ∼0.3218 g of silicon carbide
powder was mixed and the solid mixture was packed between two
quartz wool plugs in a SS tubing segment (OD - 9.55 mm, ID - 7.08
mm, wall thickness 1.23 mm). A thermocouple probe was mounted
downstream in direct contact with the middle of the catalyst bed for
accurate temperature maintenance. Remaining space was filled with
glass beads. Substrate 0.5 M PO in diethyl ether was charged into a 50
mL conical flask and sealed with an SS valve in the glovebox. The
packed tubing segment and liquid feed conical flask were transferred
from the glovebox. The catalyst was connected to the main heated
and liquid feeder connected to a precalibrated liquid delivery HPLC
pump (HKS 100) under a nitrogen atmosphere. The reactor was
pressurized with a mass flow controller (Brooks Instruments, 5850E
series) to 20 bar of CO using a back-pressure regulator (Tescom) and
allowed to stabilize to the flow rate of 30 mL/min of CO at the
desired temperature (75 °C for preheater to vaporize the substrate
and 60 °C for catalyst main heater). After pressurized the reactor
1
quantified by H NMR using naphthalene as an internal standard in
CDCl3.
Caution! Toxic chemical dicobaltoctacarbonyl and high pressured
carbon monoxide gas were used in the work.
Synthesis of POP-[TPPCr]Cl-3h (1). To a solution of TPPCrCl
(0.1321 g, 0.1897 mmol) in DCE (10 mL), anhydrous FeCl3 (0.1226
g, 0.7558 mmol) and DMM (0.0575g, 0.7567 mmol) were added in
room temperature. The greenish-brown solution was stirred at 80 °C
for 3 h and cooled to room temperature. The resulting reddish-brown
crude was quenched and washed with water (2 × 100 mL),
dichloromethane (2 × 50 mL), and diethyl ether (2 × 50 mL). The
precipitates were dissolved in THF (200 mL), all solvents were
removed, and the resultant was dried under vacuum at 60 °C for 24 h.
The black precipitates were soluble in THF (Yield = 0.079 g).
Synthesis of POP-[TPPCr]Cl-6h (2). To a solution of TPPCrCl
(0.2419 g, 0.1897 mmol) in DCE (10 mL), anhydrous FeCl3 (0.2246
g, 1.3858 mmol) and DMM (0.1104 g, 1.4546 mmol) were added in
room temperature. The greenish-brown solution was stirred at 80 °C
for 6 h and cooled to room temperature. The resulting reddish-brown
crude was quenched and washed with water (2 × 100 mL) and THF/
pentane (5/95) (50 mL), dichloromethane (2 × 50 mL), and diethyl
ether (2 × 50 mL), and dried under vacuum at 60 °C for 24 h. The
black precipitates were soluble in hot THF (Yield = 0.208 g).
Synthesis of POP-[TPPCr]Cl-12h (3). To a solution of TPPCrCl
(0.2065 g, 0.2954 mmol) in DCE (10 mL), anhydrous FeCl3 (0.1916
g, 1.1832 mmol) and DMM (0.090 g, 1.1816 mmol) were added in
room temperature. The greenish-brown solution was stirred at 80 °C
for 12 h and cooled to room temperature. The resulting crude was
quenched and washed with water (2 × 100 mL), THF (100 mL),
methanol (50 mL), diethyl ether (50 mL), and pentane (50 mL), and
dried under vacuum at 60 °C for 24 h. The black precipitates were
partly soluble in hot methanol (Yield = 0.1864 g).
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setup, begin the substrate flow rate of 1.6 mL/h to the preheater
section under CO atmosphere. Upon continuous flow of substrate
and CO flow, every 1 h time interval β-butyrolactone was collected
and weighed. The conversion was calculated using 1H NMR
spectroscopy with using naphthalene as an internal standard in
CDCl3.
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ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b03361.
1
Experimental details, H NMR, XPS, BET, UV−visible,
and FTIR analysis, SEM-images, and EDS mapping
(PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: yoona@kookmin.ac.kr.
■
ORCID
Senkuttuvan Rajendiran: 0000-0002-7335-2053
Sungho Yoon: 0000-0003-4521-2958
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledged financial support by the C1 Gas Refinery
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Science, ICT & Future
Planning (2018M3D3A1A01018006).
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