Porous Organic Polymers with Built-in N-Heterocyclic Carbenes: Selective and Efficient Heterogeneous Catalyst for the Reductive N-Formylation of Amines with CO2

Article abstract of DOI:10.1002/chem.201803364

A series of porous organic polymers (POPs) based on N-heterocyclic carbene (NHC) building blocks has been prepared through an octacarbonyldicobalt complex [Co₂(CO)₈]-catalyzed trimerization of terminal alkyne groups. By changing the monomer ratio in the copolymerization, cross-linked POPs with tunable surface areas of 485–731 m² g^?1 and pore volumes of 0.31–0.51 cm³ g^?1 were easily prepared. Compared with the analogues homogeneous NHC (SIPr) catalysts, the POPs exhibited an enhanced catalytic activity and high selectivity in the reductive functionalization of CO₂ with amines. The extraordinary performance of the sample could be attributed to the combination of the gas enrichment (or storage) effect, enhanced in-pore concentrations of other substrates, and advantageous micropore structures of the porous polymers. Meanwhile, these catalysts can easily be separated and recycled from the reaction systems with only a slight loss of activity. This excellent catalytic performance and facile recycling of heterogeneous catalysts make them very attractive. These NHC-containing POPs may provide a new platform for catalytic transformations of CO₂.

Full text of DOI:10.1002/chem.201803364

A Journal of
Accepted Article
Title: Porous Organic Polymers with Built-in N-Heterocyclic Carbenes:
Selective and Efficient Heterogeneous Catalyst for the Reductive
N-formylation of Amines with CO2
Authors: Hui Lv, Wenlong Wang, and Fuwei Li
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201803364
Link to VoR: http://dx.doi.org/10.1002/chem.201803364
Supported by

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
Porous Organic Polymers with Built-in N-Heterocyclic Carbenes:
Selective and Efficient Heterogeneous Catalyst for the Reductive
N-formylation of Amines with CO2
Hui Lv,[b] Wenlong Wang*[a], and Fuwei Li *[b]
Abstract: A series of porous organic polymers (POPs) based on N-
heterocyclic carbene (NHC) building blocks have been prepared via
the octacarbonyldicobalt complex (Co2(CO)8)-catalyzed trimerization
of terminal alkyne groups. By changing the monomer ratio in the
copolymerization, cross-linked POPs with tunable surface areas of
485 to 731 m2/g and pore volumes of 0.31 to 0.51 cm3/g were easily
prepared. Compared with the analogues homogeneous NHC (SIPr)
catalysts, the POPs exhibited enhanced catalytic activity and high
selectivity in the reductive functionalization of CO2 with amines. The
extraordinary performance of the sample could be attributed to the
combination of the gas enrichment (or storage) effect, enhanced in-
pore concentrations of other substrates and advantageous micropore
structures of the porous polymers. Meanwhile, these catalysts can
easily be separated and recycled from the reaction systems with only
a slight loss of activity. This excellent catalytic performance and facile
recycling of heterogeneous catalysts make them very attractive.
These NHC-containing POPs may provide new platforms for catalytic
transformations of CO2.
Particularly, in regard to NHCs catalysts, an excellent yield (99%)
of N-formylated morpholine can be obtained by using 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidine (IPr) as the catalyst, however,
the analogue of IPr, namely, 1,3-bis(2,6-diisopropyl)phenyl-4,5-
dihydroimidazol-2-ylidene (SIPr), only gave 24% yield with 5.0
mol% catalyst loading under the same reaction conditions.[22]
Notably, the selectivity problem (especially for aromatic
substrates with primary amine) that resulted in the double
formylation side reaction has not been effectively solved in the
majority of homogeneous catalytic systems. Moreover, although
significant advances have been achieved in these homogeneous
catalysts, the development of efficient reusable heterogeneous
catalyst is still highly desirable considering their complicated
synthesis and intricate recycling problems associated with
homogeneous catalysts.[13] This work is aimed at providing a
reusable and highly selective SIPr-based heterogeneous catalyst
for the reductive mono-N-formylation of amine with CO2.
Porous organic polymers (POPs), a class of highly cross-linked
amorphous polymers prepared through the direct assembly of
several organic building blocks using stable covalent organic
bonds, can provide chemically and thermally stable materials with
both high surface areas and a wide range of attractive chemical
functionalities.[14] In addition to broad applicability in gas sorption
and separation fields,[15] they have recently emerged as a new
kind of material with promise in heterogeneous catalysis,
especially for reaction involving gas because of their gas
enrichment capacity.[16] In addition to the built-in catalytic sites,
the unique micropore structural environments will exhibit a
confinement effect in some catalytic reactions,[14f, 14h, 15d, 16i] which
may either improve the product selectivity by favoring the main
reaction pathway through chemical size selection, or enhance the
catalytic activity through sequestering/confining the reaction
substrate in the nanometer-sized pores and then increasing their
concentration around the catalytic sites to a level greater than that
in solution.
Introduction
Carbon dioxide (CO2) is an abundant, economical and renewable
C1 building block and is an alternative to petrochemistry for the
production of chemicals.[1] Among the reported chemical
syntheses involving CO2, the reductive N-formylation of amines
with CO2 is a promising route for the synthesis of formamides,
which are widely used as solvents and key intermediates in
organic syntheses and industry.[2] In addition to metal-based
homogeneous catalysts, including those derived from Rh,[3] Ru,[4]
Cu,[5] Co,[6] and Zn,[7] metal-free catalyst systems, such as N-
heterocyclic carbenes (NHCs),[8] N-heterocyclic olefins (NHOs),[9]
1,3,2-diazaphospholene (NHP-H),[10] ionic liquids (ILs),[11] and
organic bases,[2f, 12] have been developed as efficient alternatives.
As mentioned before, Cantat and coworkers found that SIPr
was much less reactive toward the N-formylation than its
analogue, IPr; unfortunately, the latter showed poor selectivity
with the standard aniline giving a 35%/31% yield ratio of mono-
formylation/double-formylation products, and their investigations
also revealed that increasing the steric hinderance of the aryl
amine could significantly improve the mono-formylation selectivity,
[a]
Dr. W. Wang
School of Environment and Civil Engineering
Dongguan University of Technology
No.1, Daxue Rd., Songshan Lake, Dongguan, Guangdong Province,
P. R. China
E-mail: wangwl@dgut.edu.cn
but 4%-11% of the double-formylation products were still
[b]
H. Lv, Prof. Dr. F. Li
17]
produced.[8a] Based on DFT calculations[8b,
and the
State Key Laboratory for Oxo Synthesis and Selective Oxidation
Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences
No.18，Tianshui Middle Road，Lanzhou，P. R. China
E-mail: fuweili@licp.cas.cn
corresponding experimental results with NHCs as the catalyst, it
could be envisioned that the double formylation originated from
the further activation of the N-H of the amide of the generated
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
Scheme 1. Synthesis of SIPr·HCl-incorporated POPs A1B1, A2B1, and A3B1 using cobalt-catalyzed acetylene trimerization reaction.
[NHCH]+[carbamate]– intermediate by the second NHC in the
homogeneous reaction system.[17] Therefore, the development of
a functional POP with NHC catalytic sites built in to the rigid
catalyst and at suitable distances from each other to prevent the
formation
of
undesirable
‘[NHCH]+[carbamate]–—NHC’
intermediate might prevent formation of the double N-formylation
product. Further, we expected the catalytic activity might also be
improved due to the substrate sequestering/confining effects. As
part of our continuing studies on the development of recyclable N-
heterocyclic carbene-based catalysts,[14f, 18] herein, we report the
synthesis of a series of POPs catalysts with built-in NHC
precursors
(SIPr·HCl)
via
the
(Co2(CO)8)-catalyzed
trimerization[19] of terminal alkyne groups at the para-position of
benzene rings without influencing the steric and electronic
properties of SIPr (Scheme 1); as expected, they showed
enhanced catalytic activity and selectivity in the N-formylation of
a wide range of amine compounds with CO2 and silane and could
be stably recycled and reused for five runs without loss of activity.
Figure 1. Comparison of the FT-IR spectra of monomer A, monomer B, and
POPs
Results and Discussion
First, FT-IR (Figure 1) and solid-state NMR spectra (Figure 2)
were collected to confirm the structures of the synthesized A1B1,
A2B1 and A3B1 POPs. Their spectra were consistent with a high
degree of trimerization of the terminal alkynes of A and B,
because the C-H stretching peak of the C≡C-H group between
3000-3300 cm-1 and the C-C stretching peak of the -C≡C- group
at approximately 2200 cm-1 are absent in all the IR spectra. This
result suggests that the alkyne groups in the starting materials
were converted to benzene rings in the POPs. The representative
solid-state NMR spectrum of A1B1 is shown in Figure 2, and the
peaks at 25 and 28 ppm correspond to the carbon atom of the –
CH3 group and the tertiary carbon atom of the –CH(CH3)2 group,
respectively. The signals from 40-55 ppm are attributed to the
secondary carbon (-CH2) and the quaternary carbon atom
connected to the phenyl group (Ar-C) of adamantane. The peaks
between 120-160 ppm are from the aromatic groups.
Figure 2. Representative solid-state NMR spectrum of POP A1B1.
In exploring the use of POPs with built-in NHC precursors for
the catalytic formylation of amines with CO2, we sought to
investigate how the micropore environment affects the reaction
activity; therefore, three POPs with different monomer ratios were
synthesized via the same procedures. The N2 adsorption and
desorption isotherms of A1B1, A2B1 and A3B1 are shown in Figure
3a. The nitrogen sorption of these three POPs displayed a
combination of type I and type II sorption isotherm curves along
with a large adsorption at low pressure (P/P0 < 0.1), which is
indicative of the coexistence of micro- and mesopores in the
framework. Compared with A3B1 (SBET = 485 m2/g) and A2B1 (SBET
This article is protected by copyright. All rights reserved.

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
= 525 m2/g), A1B1 has the greatest surface area (SBET = 731 m2/g),
and this is mainly because of the high ratio of the tetrahedral
alkyne monomer B. The large and rigid monomer B with its four
alkyne groups stretching to four sides in a tetrahedral way can
expand the pore volume, and further generate a hierarchical pore
structure, which is very beneficial for the diffusion and mass
transfer process. From the relative BET-derived pore size
distribution plots (Figure 3b), we can conclude that these three
POPs have almost the same pore size distribution but different
pore volumes. The results of the BET surface areas and pore
volumes are listed in Table 1.
in the nanopores of these materials. This direct observation of
CO2 uptake shows that this kind of POP is very attractive for
catalytic transformations involving CO2. The order of catalytic
activities of three POPs AxBy is A1B1 > A2B1 > A3B1 (refer to Table
2), which is consistent to their CO2 absorption capacity order A1B1
≈ A2B1 > A3B1. This difference of catalytic activity correlates well
with the gas enrichment (or storage) effect.
(a)
Figure 4. CO2 adsorption isotherms at 273 K for A1B1, A2B1 and A3B1.
Table 2. Catalytic performances in different reaction systems.[a]
(b)
Entry
Catalyst
Loading[b]
(mol%)
Base
(mol%)
Yield[c] (%)
1
2
A1B1
A2B1
2
2
2
–
2
–
2
2
2
2
2
2
2
2
–
–
–
2
2
2
98
89
86
37
22
0
3
A3B1
Figure 3. (a) Nitrogen isotherms measured at 77 K for POPs A1B1, A2B1 and
A3B1. (b) pore size distribution plots for A1B1, A2B1 and A3B1 caculated by NLDFT
method.
4
–
5
A1B1
Table 1. Pore and surface properties of POPs with built-in NHC precursors.
6
–
Entry
POP
BET surface
area (m2/g)
Total pore volume
(cm3/g)
7
(A-CO2)1B1
A
50
42
60
16
8
1
2
3
A1B1
A2B1
A3B1
731
525
485
0.51
0.34
0.31
9
SIPr·HCl
SIPr-CO2
10
[a] Reaction conditions: morpholine (0.5 mmol), phenylsilane (0.75 mmol),
dry THF (2 mL), CO2 (4 atm) room temperature, 24 h. [b] Equivalent to the
amount of SIPr. [c] GC yield using n-hexadecane as an internal standard.
In addition, the CO2 sorption isotherms for the three samples at
273 K are presented in Figure 4. No saturation was observed for
any of the three POPs in the 900 mmHg range, which suggests
higher CO2 absorption capacities can be achieved at higher
pressures. POPs A1B1, A2B1 and A3B1 exhibited CO2 uptakes of
36, 34 and 28 cm3/g, respectively. Compared with the difference
between the BET surface areas of the three POPs from the N2
adsorption experiments, the gap in the CO2 absorption capacity
is narrower, and this is probably because of the enhanced
interactions between the N atoms of the imidazole ring and CO2
To begin with the catalytic investigation, we explored the
possibility of using morpholine as the substrate in
a
heterogeneous system. Morpholine (0.5 mmol), CO2 (4 atm),
PhSiH3 (0.75 mmol), NaHMDS (2 mol%) and A1B1 (10 mg,
equivalent to 2 mol% SIPr, as a catalyst) were loaded into a
stainless-steel autoclave and stirred at room temperature for 24
h. As a result, the corresponding N-formylmorpholine was
This article is protected by copyright. All rights reserved.

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
obtained in 98% GC yield (Table 2, entry 1). For comparison, we
then investigated A2B1 and A3B1 as catalysts (2 mol% loading and
4 atm of CO2), and slightly lower yields were obtained (89% and
86%, Table 2, entries 2 and 3). This is possibly because of the
lower surface areas and pore volumes of A2B1 and A3B1
compared with A1B1; moreover, the higher proportion of
hydrophobic adamantane moieties in A1B1 could further enhance
the solvophobic encapsulation ability of the hydrophobic substrate
in polar media, increasing the catalyst efficiency.
Control experiments showed that only 37% yield was obtained
(Table 2, entry 4) when catalyst was removed from the reaction
system; when base was removed from the catalytic system, only
22% yield was achieved (Table 2, entry 5); Further control
experiments showed that this reaction did not occur in the
absence of both the catalysts and base (Table 2, entry 6). These
three results suggest that the catalyst[11a] and base[2f] both can
catalyze this reaction. It is worth noting that when the NHC·HCl-
built-in POP was treated with an equivalent of base (NaHMDS),
free N-heterocyclic carbene is immediately generated, and the
carbene-based activation mode was more reasonable
according to literature reports.[8b, 8c, 17] Scheme 2 shows the three
most likely activation modes for such N-formylation with a
carbene-based catalyst. According to the results of the DFT
calculations reported by Li’s group,[17] activation mode I, i.e.,
[NHCH]+[carbamate]– (generated through a carbene process),
was the most favorable species based on free energy; and in the
activation mode II, the free energies of the NHC-CO2 adduct and
its subsequent transition state with silanes were higher than that
of the [NHCH]+[carbamate]– process. Therefore, the formation of
an NHC-CO2 species was theoretically unfavorable in this
reaction. To confirm this theoretical prediction, porous polymeric
materials (A-CO2)1B1 and molecular SIPr-CO2 were prepared
(Supporting Information), and their catalytic efficiencies were
investigated (2 mol% loading and 4 atm of CO2). Only 50% and
16% yields were obtained (Table 2, entries 7 and 10), which
proved the rationality of activation mode I. In addition, the catalytic
activity of their homogeneous counterparts (A and SIPr·HCl) were
tested for comparison with the newly synthesized heterogeneous
catalyst, which exhibited much lower yields (42% and 60%,
respectively) than that of the heterogeneous catalysts. The
heterogeneous samples’ (POPs) extraordinary performance
could be attributed to the combination of the gas enrichment (or
storage) effect and enhanced in-pore concentrations of other
substrates in the porous polymers.
Scheme 2. Three activation modes through carbene process.
A favorable feature of the catalytic system that caught our
attention was the precipitation of the POP catalysts from the
mixture. Thus, we investigated the possibility of recycling and
reusing catalyst A1B1. After the reaction, the catalyst was
collected by centrifugation and then reused for another round of
the N-formylation reaction. To better test the stability of catalyst
A1B1, a recycling experiment was conducted by increasing the
level of the alkyne substrate to 1.0 mmol with 1 mol% of A1B1 to
achieve an approximate ~60% yield of morpholine-4-
carbaldehyde (Figure 5). Recycling catalyst A1B1 over four runs
did not result in a loss of activity. We have supplemented the hot
filtration experiment in the recyclability test. Under the same
reaction condition as illustrated in Figure 5, after 24 hour’s
reaction (GC yield was 63%), the catalyst was filtrated off, the
filtrate was continued to react for another 24 hours, and the GC
yield was 65%, which indicated the heterogeneous nature of the
catalyst.
Figure 5. Recyclability test of A1B1 in the model reaction of the N-formylation of
morpholine: morpholine (1.0 mmol), phenylsilane (1.5 mmol), A1B1 (1 mol%),
dry THF (4 mL), room temperature, 24 h; GC yield using n-hexadecane as an
internal standard.
This article is protected by copyright. All rights reserved.

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
Subsequently, we examined the scope of this catalytic system.
As shown in Figure 6, only one product was obtained for all
substrates (selectivity >99%, moderate to good isolated yields)
when using POP A1B1 as the catalyst. To further compare this
unique selectivity of the POP catalysts, the homogeneous catalyst
counterpart (SIPr∙HCl) was tested by using the same aniline
derivatives. As depicted in Figure 6, substantial amounts of the
bis-formylanilines (5f’-5l’) were isolated, which indicated the poor
selectivity of the homogeneous counterpart. The surprising
selectivity of the POP catalysts could probably be attributed to the
confinement effects of the unique micropore environment in the
POP catalysts, which prohibited the formation of large-size
intermediates of the bis-formylanilines; it is also possible that the
rigid micro-environment hindered the double-site activation mode
(Figure 7), severely limiting the formation of bis-formylanilines,
which easily can be realized in the homogeneous process. In
addition, aliphatic secondary amines, such as morpholine,
dibutylamine, 1,2,3,4-tetrahydroisoquinoline and dibenzylamine,
were converted to their formamides (5a-5e) in high isolated yields
after 24 h at room temperature under 4 atm of CO2. An electron-
donating group (p-methoxy, 5k, 64% yield) and an electron-
withdrawing group (p-Cl, 5h, 65% yield) did not have obvious
influences on the conversions observed for the aniline derivatives.
Increasing the steric congestion around the phenyl ring did not
deactivate the anilines, and 2,4,6-trimethylaniline was formylated
in 61% yield (5i), and 2,6-diisopropylaniline was obtained with a
Figure 6. Scope of the catalytic formylation of N-H bonds using CO2 and PhSiH3. Reaction conditions: amine substrate 0.5 mmol, CO2 4 atm, PhSiH3 0.75 mmol,
catalyst 2-20 mol%, NaHMDS 2-20 mol%, THF 2 mL, room temperature, 24 h. [a]10 mg of polymeric catalyst (equivalent to 2 mol% of the imidazolium salts), 2
mol% NaHMDS. [b] 25 mg of polymeric catalyst (equivalent to 5 mol% of the imidazolium salts), 5 mol% NaHMDS. [c] 20 mol% catalyst. [d]10 mol% catalyst. All
yields are isolated yields and are the average of two runs, except for 5a and 5b, which were analyzed by GC.
slightly higher yield of 70% (5l). Other non-substituted anilines,
phenylamine (5f, 70% yield) and naphthalen-1-amine (5g, 75%
yield), all performed well under the heterogeneous catalytic
system. In addition, it is worth noting that not only the compelling
selectivity advantage but also the enhanced heterogeneous
catalytic activity for all the investigated substrates were due to the
micropore structure of our NHC-based POP catalysts, which
This article is protected by copyright. All rights reserved.

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
possessed both the substrate enrichment and confinement
effects.
of Et2O and then recrystallized from CH2Cl2/n-pentane to give 2.25 g of
white solid A (84% yield based on 3). Its molecular structure was confirmed
by Single-crystal X-ray diffraction analysis, which showed the expected
structural motif with terminal alkyne substituents (Figure 8, CCDC
1469334).
Scheme 3. Synthesis of acetylene-functionalized SIPr·HCl
Figure 7. Proposed rigid micropore environment.
Conclusions
In summary, POPs materials based on NHC building blocks with
tunable surface areas and pore volumes have been prepared via
the Co2(CO)8-catalyzed trimerization reaction of terminal alkyne
groups. Notably, compared with their homogeneous counterparts,
the heterogeneous POP catalyst A1B1 displayed enhanced
activity and extremely high selectivity. This improved activity
could be attributed to the enrichment of reactants, and the
extremely high selectivity (> 99%) could probably be attributed to
the confinement effect that was posed to occur in the favorable
micropore environments, which prohibited the formation of the
large-size intermediates of bis-formylanilines or hindered the
double site activation mode. In addition, the POPs catalyst A1B1
has good substrates tolerance and could be reused at least four
times without a loss of activity. These unique characteristics
clearly indicate that this kind of POP catalyst with built-in NHCs
could provide a new platform for the exploration of catalytic
transformation of CO2 and other poorly selective catalytic
reactions.[14h, 20]
Figure 8. Crystal structure of monomer A. Displacement ellipsoids are set at
30% probability, and H atoms have been omitted for clarity.
Synthesis of SIPr-Built-in POP catalysts. The SIPr·HCl-built-in
polymeric organic polymer catalyst could be readily prepared from the Co-
catalyzed intermolecular alkyne trimerization of ac-SIPr·HCl (A) and
1,3,5,7-tetrakis(4-ethynylphenyl)adamantine (B). Monomer
B
was
selected as a three-dimensional connector and synthesized according to
the reported procedures.[21] To tune the physical properties of these POPs,
different monomer ratios (A:B = 1:1, 2:1 and 3:1) were selected for the co-
polymerization to provide the corresponding SIPr-built-in POP catalysts,
which were named AxBy according to the monomer ratio (Scheme 1). The
following is a typical procedure for the preparation of A1B1: in an argon-
filled glovebox, a 20 mL vial equipped with a magnetic stir bar was charged
with monomers A (80 mg, 0.17 mmol) and B (90 mg, 0.17 mmol). This
mixture was dissolved in dry 1,4-dioxane (6 mL), and then, Co2(CO)8 (30
mg, 0.09 mmol) was added. The solution was stirred for 5 min prior to
being sealed. The reaction mixture was then stirred at 115 ℃ for 3 h, during
which a black precipitate was generated. After cooling the reaction mixture
to room temperature, the vial was opened, and the precipitate was isolated
by filtration, washed with H2O (50 mL), and stirred in concentrated
aqueous HCl (15 mL) for 1 h. The remaining black polymer was isolated
by filtration, washed with H2O (50 mL) and MeOH (50 mL), and then
refluxed in CH2Cl2 in a Soxhlet extractor for 3 days. The resultant material
(167 mg, 98% yield based on all monomers mass) was dried under a
dynamic vacuum for 24 h at 60 °C. The A2B1 and A3B1 POP catalysts could
be prepared in near quantitative yields following the above procedure by
changing the corresponding A/B ratio.
Experimental Section
Synthesis of Acetylene-Functionalized SIPr·HCl. The synthetic route for
the preparation of the acetylene-functionalized N-heterocyclic carbene
precursor building block, ac-SIPr·HCl (A), is shown in Scheme 3.
Diiododiamine
1
(4.47 g, 7.0 mmol) was reacted with
trimethylsilylacetylene via a Pd-catalyzed Sonogashira coupling and
subsequent treated with KF to give alkyne-functionalized diamine 3 (2.34
g, 5.46 mmol) in 78% yield over two steps. Intermediate 3 (2.34 g, 5.46
mmol) was treated with excess of ethanolic HCl (approximately 3 equiv,
freshly prepared by the cautious addition of 1.6 mL of acetyl chloride to 15
mL of absolute ethanol). After 30 min of vigorous stirring, the solution was
filtrated, and the solid was washed with cold ethanol to give double
chlorhydrate 3·2HCl, which was then refluxed in 70 mL of a 1/1
HC(OEt)3/EtOH mixture for 2 h. After the reaction mixture was cooled to
room temperature and evaporated, the residue was triturated with 50 mL
Representative Procedure for the Catalytic Formylation of an
Amine with CO2. In a typical experiment, morpholine (0.5 mmol, 44 mg),
phenylsilane (0.75 mmol, 81 mg), catalyst A1B1 (2 mol%, 10 mg), NaHMDS
(2 mol%, 9 mg) and 2 mL of dry THF were loaded in a 5 mL ampoule vial
equipped with a magnetic stir bar under an argon atmosphere. Then, the
vial was transferred to a 100 mL stainless steel autoclave, sealed and
This article is protected by copyright. All rights reserved.

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
pressurized with 4.0 atm of CO2 after being purged three times with pure
CO2. Then, the reactor was stirred at room temperature for 24 h. After the
reaction, the excess CO2 was discharged, and the reaction mixture was
analyzed by gas chromatography (GC), which indicated a 98% yield of N-
formylmorpholine (n-hexadecane was used as an internal standard).
Keywords: N-heterocyclic carbene • porous organic polymer •
carbon dioxide • formylation • heterogenized catalyst
[1]
a) D. B. Dell'Amico, F. Calderazzo, L. Labella, F. Marchetti, G. A.
Pampaloni, Chem. Rev. 2003, 103, 3857-3898; b) D. J. Darensbourg,
Chem. Rev. 2007, 107, 2388-2410; c) M. He, Y. Sun, B. Han, Angew.
Chem. Int. Ed. 2013, 52, 9620-9633; d) K. Huang, C.-L. Sun, Z.-J. Shi,
Chem. Soc. Rev. 2011, 40, 2435-2452; e) T. Sakakura, J.-C. Choi, H.
Yasuda, Chem. Rev. 2007, 107, 2365-2387.
[14] a) P. Kaur, J. T. Hupp, S. T. Nguyen, ACS Catal. 2011, 1, 819-835; b) N.
B. McKeown, P. M. Budd, Chem. Soc. Rev. 2006, 35, 675-683; c) Q. Sun,
Z. Dai, X. Meng, F.-S. Xiao, Chem. Soc. Rev. 2015, 44, 6018-6034; d) A.
I. Cooper, Adv. Mater. 2009, 21, 1291-1295; e) T. Ben, H. Ren, S. Ma,
D. Cao, J. Lan, X. Jing, C. Wang, J. Xu, F. Deng, J. M. Simmons, Angew.
Chem. Int. Ed. 2009, 48, 9457-9460; f) W. Wang, A. Zheng, P. Zhao, C.
Xia, F. Li, ACS Catal. 2014, 4, 321-327; g) R. S. Sprick, J.-X. Jiang, B.
Bonillo, S. Ren, T. Ratvijitvech, P. Guiglion, M. A. Zwijnenburg, D. J.
Adams, A. I. Cooper, J. Am. Chem. Soc. 2015, 137, 3265-3270; h) Y.-B.
Zhou, Y.-Q. Wang, L.-C. Ning, Z.-C. Ding, W. Wang, C.-K. Ding, R.-H. Li,
J.-J. Chen, X. Lu, Y.-J. Ding, Z.-P. Zhan, J. Am. Chem. Soc. 2017, 139,
3966-3969; i) Y. Zhang, S. Wei, F. Liu, Y. Du, S. Liu, Y. Ji, T. Yokoi, T.
Tatsumi, F.-S. Xiao, Nano Today, 2009, 4, 135-142.
[2]
a) T. G. Ostapowicz, M. Schmitz, M. Krystof, J. Klankermayer, W. Leitner,
Angew. Chem. Int. Ed. 2013, 52, 12119-12123; b) T. T. Metsänen, M.
Oestreich, Organometallics, 2015, 34, 543-546; c) P. G. Jessop, Y. Hsiao,
T. Ikariya, R. Noyori, J. Am. Chem. Soc. 1994, 116, 8851-8852. d) P. G.
Jessop, Y. Hsiao, T. Ikariya, R. Noyori, J. Am. Chem. Soc. 1996, 118,
344-355. e) Y. Li, X. Fang, K. Junge, M. Beller, Angew. Chem. Int. Ed.
2013, 52, 9568-9571; f) C. Das Neves Gomes, O. Jacquet, C. Villiers, P.
Thuéry, M. Ephritikhine, T. Cantat, Angew. Chem. Int. Ed. 2011, 51, 187-
190; g) Y. Zhao, B. Yu, Z. Yang, H. Zhang, L. Hao, X. Gao, Z. Liu, Angew.
Chem. Int. Ed. 2014, 53, 5922-5925; h) J. Klankermayer, S. Wesselbaum,
K. Beydoun, W. Leitner, Angew. Chem. Int. Ed. 2016, 55, 7296-7343; i)
A. Tlili, E. Blondiaux, X. Frogneux, T. Cantat, Green Chem. 2015, 17,
157-168.
[15] a) X. Zou, G. Zhu, Adv. Mater. 2018, 30, DOI: 10.1002/adma.201700750;
b) J.-X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell, H. Niu, C.
Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y. Z. Khimyak, Angew. Chem.
Int. Ed. 2007, 46, 8574-8578.
[16] a) L. Chen, Y. Honsho, S. Seki, D. Jiang, J. Am. Chem. Soc. 2010, 132,
6742-6748; b) Q. Sun, Z. Dai, X. Liu, N. Sheng, F. Deng, X. Meng, F.-S.
Xiao, J. Am. Chem. Soc. 2015, 137, 5204-5209; c) W. Wang, C. Li, L.
Yan, Y. Wang, M. Jiang, Y. Ding, ACS Catal. 2016, 6, 6091-6100; d) Q.
Sun, M. Jiang, Z. Shen, Y. Jin, S. Pan, L. Wang, X. Meng, W. Chen, Y.
Ding, J. Li, F.-S. Xiao, Chem. Commun. 2014, 50, 11844-11847; e) W.
Wang, Y. Wang, C. Li, L. Yan, M. Jiang, Y. Ding, ACS Sustainable Chem.
Eng. 2017, 5, 4523-4528; f) X. Chen, H. Zhu, W. Wang, H. Du, T. Wang,
L. Yan, X. Hu, Y. Ding, ChemSusChem, 2016, 9, 2451-2459; g) C. Li, L.
Yan, L. Lu, K. Xiong, W. Wang, M. Jiang, J. Liu, X. Song, Z. Zhan, Z.
Jiang, Y. Ding, Green Chem. 2016, 18, 2995-3005; h) C. Li, K. Sun, W.
Wang, L. Yan, X. Sun, Y. Wang, K. Xiong, Z. Zhan, Z. Jiang, Y. Ding, J.
Catal. 2017, 353, 123-132; i) T. Wang, W. Wang, Y. Lyu, K. Xiong, C. Li,
H. Zhang, Z. Zhan, Z. Jiang, Y. Ding, Chin. J. Catal. 2017, 38, 691-698.
[17] Q. Zhou, Y. Li, J. Am. Chem. Soc. 2015, 137, 10182-10189.
[3]
[4]
V. Q. Nguyen Thanh, W. J. Yoo, S. Kobayashi, Angew. Chem. Int. Ed.
2015, 54, 9209-9212.
a) O. Krocher, R. A. Koppel, A. Baiker, Chem. Commun. 1997, 453-454;
b) L. Zhang, Z. Han, X. Zhao, Z. Wang, K. Ding, Angew. Chem. Int. Ed.
2015, 54, 6186-6189.
[5]
a) H. Liu, Q. Mei, Q. Xu, J. Song, H. Liu, B. Han, Green Chem. 2017, 19,
196-201; b) K. Motokura, N. Takahashi, D. Kashiwame, S. Yamaguchi,
A. Miyaji, T. Baba, Catal. Sci. Technol. 2013, 3, 2392-2396.
P. Daw, S. Chakraborty, G. Leitus, Y. Diskin-Posner, Y. Ben-David, D.
Milstein, ACS Catal. 2017, 7, 2500-2504.
[6]
[7]
[8]
R. Luo, X. Lin, Y. Chen, W. Zhang, X. Zhang, H. Ji, ChemSusChem,
2016, 10, 1224-1232.
a) O. Jacquet, C. Das Neves, Gomes, M. Ephritikhine, T. Cantat, J. Am.
Chem. Soc. 2012, 134, 2934-2937; b) F. Huang, G. Lu, L. Zhao, H. Li,
Z.-X. Wang, J. Am. Chem. Soc. 2010, 132, 12388-12396; c) S. N. Riduan,
Y. Zhang, Y. Ying Jackie, Angew. Chem. Int. Ed. 2009, 48, 3322-3325.
B. Saptal Vitthal, M. Bhanage Bhalchandra, ChemSusChem, 2016, 9,
1980-1985.
[18]
a) W. Wang, G. Zhang, R. Lang, C. Xia, F. Li, Green Chem. 2013, 15,
635-640; b) W. Wang, J. Wu, C. Xia, F. Li, Green Chem. 2011, 13, 3440-
3445; c) G. Zhang, R. Lang, W. Wang, H. Lv, L. Zhao, C. Xia, F. Li, Adv.
Synth. Catal. 2015, 357, 917-922; d) W. Wang, L. Zhao, H. Lv, G. Zhang,
C. Xia, F. E. Hahn, F. Li, Angew. Chem. Int. Ed. 2016, 55, 7665-7670; e)
W. Wang, L. Cui, P. Sun, L. Shi, C. Yue, F. Li, Chem. Rev. 2018, DOI:
10.1021/acs.chemrev.8b00057.
[9]
[10] C. Chong Che, R. Kinjo, Angew. Chem. Int. Ed. 2015, 54, 12116-12120.
[11] a) L. Hao, Y. Zhao, B. Yu, Z. Yang, H. Zhang, B. Han, X. Gao, Z. Liu,
ACS Catal. 2015, 5, 4989-4993; b) Z. Ke, L. Hao, X. Gao, H. Zhang, Y.
Zhao, B. Yu, Z. Yang, Y. Chen, Z. Liu, Chem. – Eur. J. 2017, 23, 9721-
9725; c) X.-Y. Li, S.-S. Zheng, X.-F. Liu, Z.-W. Yang, T.-Y. Tan, A. Yu,
[19] a) R. K. Totten, Y.-S. Kim, M. H. Weston, O. K. Farha, J. T. Hupp, S. T.
Nguyen, J. Am. Chem. Soc. 2013, 135, 11720-11723; b) Z. Xie, C. Wang,
K. E. deKrafft, W. Lin, J. Am. Chem. Soc. 2011, 133, 2056-2059.
[20] W. Tong, W.-H. Li, Y. He, Z.-Y. Mo, H.-T. Tang, H.-S. Wang, Y.-M. Pan,
Org. Lett. 2018, 20, 2494-2498.
L.-N.
He,
ACS
Sustainable
Chem.
Eng.
DOI:
10.1021/acssuschemeng.8b02352
[12] B. Zhang, G. Du, W. Hang, S. Wang, C. Xi, Eur. J. Org. Chem. 2018,
1739-1743.
[21] E. Galoppini, R. Gilardi, Chem. Commun. 1999, 173-174.
[13] D. J. Cole-Hamilton, Science, 2010, 327, 41-42.
This article is protected by copyright. All rights reserved.

10.1002/chem.201803364
Chemistry - A European Journal
FULL PAPER
Table of Contents
FULL PAPER
Porous organic polymers with built-in
Hui Lv, Wenlong Wang*, Fuwei Li*
N-heterocyclic
carbenes
were
Page No. – Page No.
prepared and used as a selective and
efficient heterogeneous catalyst for the
reductive N-formylation of amine with
CO2. The improved performance could
be attributed to the unique micropore
structure of the POPs catalysts.
Porous Organic Polymers with Built-
in N-Heterocyclic Carbenes: Selective
and Efficient Heterogeneous Catalyst
for the Reductive N-formylation of
Amines with CO2
√ High selectivity > 99%
√ recyclable
√ NHC-built-in POPs
This article is protected by copyright. All rights reserved.