N-heterocyclic olefins as robust organocatalyst for the chemical conversion of carbon dioxide to value-added chemicals

Article abstract of DOI:10.1002/cssc.201600467

In this report, the activity of N-heterocyclic olefins (NHOs) as a newly emerging class of organocatalyst is investigated for the chemical fixation of carbon dioxide through reactions with aziridines to form oxazolidinones and the N-formylation of amines with polymethylhydrosiloxane (PMHS) or 9-borabicy-clo[3.3.1]nonane (9-BBN) as the reducing agent under mild conditions. The exocyclic carbon atoms of NHOs are highly nucleophilic owing to the electron-donating ability of the two nitrogen atoms. This high nucleophilicity of the NHOs activates CO₂ molecules to form zwitterionic NHO–carboxylate (NHO– CO₂) adducts, which are active in formylation reactions as well as the carboxylation of aziridines to oxazolidinones.

Full text of DOI:10.1002/cssc.201600467

DOI: 10.1002/cssc.201600467
Full Papers
N-Heterocyclic Olefins as Robust Organocatalyst for the
Chemical Conversion of Carbon Dioxide to Value-Added
Chemicals
Vitthal B. Saptal and Bhalchandra M. Bhanage*[a]
In this report, the activity of N-heterocyclic olefins (NHOs) as
a newly emerging class of organocatalyst is investigated for
the chemical fixation of carbon dioxide through reactions with
aziridines to form oxazolidinones and the N-formylation of
amines with polymethylhydrosiloxane (PMHS) or 9-borabicy-
clo[3.3.1]nonane (9-BBN) as the reducing agent under mild
conditions. The exocyclic carbon atoms of NHOs are highly nu-
cleophilic owing to the electron-donating ability of the two ni-
trogen atoms. This high nucleophilicity of the NHOs activates
CO2 molecules to form zwitterionic NHO–carboxylate (NHO–
CO2) adducts, which are active in formylation reactions as well
as the carboxylation of aziridines to oxazolidinones.
Introduction
N-Heterocyclic olefins (NHOs) represent a special new class of
organic ligand with strong donor characteristics. The NHOs
were first reported by Kuhn and co-workers in the 1990s.[1a]
These NHOs represent the cyclic derivatives of ketene aminals
(ene-1,1-diamines) and as a kind of ylidic olefin are extremely
polarized alkenes.[1] Owing to their inherent structural charac-
teristics, NHOs have received much attention recently. The exo-
cyclic carbon atoms of NHOs bear an extensive amount of
electron density, and the charge separation can be shown by
the resonance structure in Scheme 1b. The five-membered un-
saturated aromatic heterocyclic rings stabilize or effectively
capture the positive charge and maximize the electron density
at the terminal carbon atom of the olefins (exocyclic carbon
atom).
Scheme 1. (a) Typical procedure for NHO synthesis, (b) mesomeric structure
of NHO, (c) structure of NHO–CO2 adduct, and (d) NHO rhodium complex re-
ported by Fꢀrstner.[7]
Owing to their remarkable structures, NHOs were considered
as highly powerful nucleophiles and strong donor ligands com-
parable to N-heterocyclic carbenes (NHCs).[2] The structures of
NHOs closely resemble deoxy-Breslow intermediates, which are
projected to play a major role in NHC-based organocatalysis.[2l]
This extraordinary feature provides NHOs with remarkable
properties, a few of which have been utilized for the synthesis
of NHO–metal complexes,[3] the synthesis of NHO–CO2 ad-
ducts,[4,5] or in Diels–Alder reactions.[6] Amazingly, Fꢀrstner et al.
reported a very simple NHO complex also possesses more elec-
tron density at the metal center than typical NHC complexes.[7]
Recently, Rivard et al. demonstrated that NHOs act as strong
nucleophiles to stabilize GeH2 and SnH2 complexes.[8] Mayr and
co-workers demonstrated the olefinic carbon atoms of NHOs
are highly nucleophilic and have a tendency to attack benzhy-
drylium ions to yield azolium salts.[9] Ghadwal et al. reported
NHO-stabilized mono- and dicationic hydridoboron com-
pounds.[10] Tamm et al. demonstrated the treatment of NHOs
with B(C6F5)3 to afford classical or abnormal Lewis acid/base
adducts.[11] The combination of NHO ligands with metals result-
ed in superior activity in polymerization reactions.[12] Dove and
co-workers utilized NHOs as highly potent organocatalysts for
the polymerization of epoxides and synthesized poly(propy-
lene oxide) with a high turnover number (TON).[12b] In addition,
NHOs can react with kinetically stable CO2 to afford stable
zwitterionic NHO–CO2 adducts (Scheme 1c). These NHO–CO2
adducts show potential for CO2 capture and can quench reac-
tions for the synthesis of carbonates.[4,5] The cycloaddition re-
actions of CO2 with epoxides to synthesis cyclic carbonates
with NHOs as the catalysts were also established by Lu and co-
workers.[5a] Very recently, Chen et al. reported carbodicarbenes
(CDCs) or bent allenes analogous to NHOs as organocatalysts
[a] V. B. Saptal, Prof. B. M. Bhanage
Department of Chemistry, Institute of Chemical Technology
Matunga, Mumbai-400 019 (India)
Fax: (+91)22-33611020
E-mail: bm.bhanage@gmail.com
bm.bhanage@ictmumbai.edu.in
Supporting Information for this article can be found under http://
dx.doi.org/10.1002/cssc.201600467.
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for the reductive N-methylation of amines with CO2 and bo-
rane.[5c] Like NHOs, other strong Lewis bases, such as N-hetero-
cyclic carbenes,[5d] phosphorus ylides,[5e] and alkoxide-function-
alized imidazolium betaines,[5f] also form CO2 adducts readily,
and these adducts show high activity in the catalytic transfor-
mation of CO2.
Results and Discussion
A series of NHOs were synthesized from their precursor salts
by deprotonation with KH according to a previously reported
procedure (Figure 1 and Supporting Information, Sec-
Carbon dioxide contributes approximately 82% of total
greenhouse gases (GHGs), which are considered as the main
cause for global warming, and the climate change caused by
global warming is becoming one of the significant threats to
civilization in modern times.[13] Carbon dioxide contains carbon
in its highest oxidation state and is kinetically and thermody-
namically stable in nature. On the other hand, the chemical fix-
ation of CO2 into valuable chemicals is considered as a cutting-
edge sustainable-chemistry technology as CO2 is abundant,
cheap, and renewable and the process is environmentally
friendly.[14] The products derived from CO2 fixation provide
very important scaffolds for academic and industrial chemistry
such as methanol, formic acid, cyclic and acyclic carbonates,
polycarbonates, polyurethanes, and urea.[14] In some cases, CO2
can be used as a soft oxidant and promoter in catalysis.[14j]
Carbon capture and utilization (CCU) is also a hot research
topic.[14k]
Figure 1. Catalysts (NHOs) for the synthesis of oxazolidinones.
tion 2).[5,7,12] The resultant NHOs were obtained after simple fil-
tration and evaporation of the solvent and utilized for the cat-
alytic reactions without any further purification. These synthe-
sized NHOs were screened for the cycloaddition reaction of
CO2 with aziridines. Various aziridines were synthesized
through the previously reported method (Supporting Informa-
tion, Section 3).[17] To check the catalytic performance of the
synthesized NHOs, we chose 1-butyl-2-phenylaziridine as
a model substrate for the fixation of CO2 at room temperature.
Various reaction parameters such as time, catalyst, solvent ef-
fects, and CO2 pressure were studied (Table 1). Without the use
The cycloaddition reaction of CO2 with aziridines is the most
important and promising route for the transformation of CO2
into oxazolidinones through the formation of CÀN and CÀO
bonds, and this reaction is clean and atom-economical. The ox-
azolidinones are the most important heterocyclic ring system
and are used widely in chiral auxiliaries, antibacterial drugs,
and fine chemicals and as intermediates in pharmaceuticals.[15]
For the synthesis of oxazolidinones from CO2 and aziridines,
various homogeneous and heterogeneous catalytic systems
have been reported.[16] NHC-based catalysts are also highly
active for this reaction.[16b,c] Nevertheless, this reaction still has
disadvantages such as the use of solvents, metals, additives,
high temperature, or high pressure. Hence, there is an instant
need to develop an efficient catalytic protocol that operates
under mild reaction conditions. The NHO–CO2 adducts formed
from NHOs and CO2 are efficient CO2 carriers for CO2 fixation
through the nucleophilic addition of the CO2 unit to various
products.[5] This reactivity of NHOs towards CO2 encouraged us
to apply the CO2 fixation protocol to the synthesis of oxazolidi-
nones.
Table 1. Optimization of the oxazolidinone synthesis using a NHO cata-
lyst.[a]
Entry
Catalyst
Solvent
Conversion[b]
[%]
b/c[b]
TON
1
2
3
4
5
6
7
–
1
1
1
2
3
4
4
–
IPA
IPA
toluene
–
–
–
–
–
–
trace
75
72
93
95
96
99
58
trace
–
–
187
180
232
237
240
247
290
–
90:10
93:7
98:2
96:4
91:9
96:4
98:2
–
8[c]
9
Herein, we report the synthesis of various NHOs as organo-
catalysts and their use for the chemical fixation of CO2 through
cycloaddition reactions with aziridines to form oxazolidinones
as well as for the N-formylation of amines with polymethylhy-
drosiloxane (PMHS) and 9-borabicyclo[3.3.1]nonane (9-BBN) as
reducing agents. The reported NHOs can be synthesized readi-
ly and act as highly efficient organocatalysts for the synthesis
of oxazolidinones with high TONs and turnover frequencies
(TOFs). Additionally, the synthesized NHOs showed excellent
activities towards oxazolidinones under solvent-free and metal-
free conditions.
[a] Reaction conditions: aziridine (5 mmol), catalyst (0.02 mmol), CO2
(2 MPa), RT, 3 h. [b] Determined by GC and GC–MS. [c] Catalyst
(0.01 mmol).
of any NHO, a negligible amount of oxazolidinone was ob-
served (Table 1, entry 1). Then, to investigate the catalytic activ-
ity of the synthesized NHOs, we screened 1 as a catalyst for
the synthesis of the oxazolidinone and, to our delight, a good
yield and regioselectivity were observed with isopropyl alcohol
(IPA) as the solvent (Table 1, entry 2). Next, we studied the
effect of a nonpolar solvent such as toluene; a slightly de-
creased amount of oxazolidinone was observed (Table 1,
entry 3). In the next set of experiments, we performed the re-
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action under solvent-free conditions and, to our delight, an ex-
cellent yield of oxazolidinone was observed (Table 1, entry 4);
hence, we concluded that the use of a solvent is not necessary
for this reaction. The effects of various NHOs for the cycloaddi-
tion reaction were studied, and we observed that all the NHOs
were highly active for the synthesis of the oxazolidinone
(Table 1, entries 4–7). Notably, catalyst 4 provides an excellent
yield of the oxazolidinone at the room temperature with
a high TON (Table 1, entry 7). We also studied the effect of cat-
alyst loading and observed that the amount of catalyst also
plays an important role in the synthesis of oxazolidinones. As
the amount of NHO loading decreased, the yield of oxazolidi-
none also decreased (Table 1, entry 8). Without the use of sol-
vent and catalyst, a negligible amount of oxazolidinone was
noted (Table 1, entry 9). The effect of pressure on the synthesis
of the oxazolidinones also played an important role in the cy-
cloaddition reaction of aziridines with CO2 (Figure 2a). Among
the various pressures screened, we found that 2 MPa of CO2
pressure provides excellent yields of oxazolidinone, and as the
pressure decreased, the yield of oxazolidinone also decreased.
A kinetic study of the oxazolidinone synthesis showed that 3 h
was the optimum time to achieve the highest yield (Fig-
ure 2b). After the optimization of the reaction conditions, we
further extended this developed protocol for the synthesis of
various oxazolidinones (Table 2). Various kinds of aziridines
were reacted with CO2 to synthesize the oxazolidinones in the
Table 2. Scope of various oxazolidinones catalyzed by NHOs.[a]
Entry Aziridine
t
Conversion[b] b/c[b] TON[d] TOF
[h] [%]
[hÀ1
]
1
2
3
4
5
2
2
2
3
3
99
99
97
99
96
90:10 247
96:4 247
88:12 242
96:4 247
98:2 240
123
123
121
83
80
6
3
94
99:1 235
78
7
3
8
8
8
8
3
8
8
39
84
47
89
87
56
90
93
99:1
97
32
26
14
27
27
46
28
29
8[c]
99:1 210
98:2 117
97:3 222
96:4 217
99:1 140
99:1 225
96:4 232
9[c]
10[c]
11[c]
12
13[c]
14[c]
15[c]
8
88
98:2 220
27
[a] Reaction conditions: aziridine (5 mmol), CO2 (2 MPa), catalyst
(0.02 mmol), RT. [b] Determined by GC and GC–MS. [c] 608C, CO2 (4 MPa).
[d] TON: sum of moles of b and c produced per mole of catalyst, TOF:
sum of moles of b and c produced per mole of catalyst per hour.
presence of the NHO 4 as the catalyst owing to its high reac-
tivity. The developed NHO catalyst was extremely active and
provided the corresponding 5-aryl-2-oxazolidinones in good-
to-excellent yields with excellent regioselectivity. However, in-
creasing the steric hindrance of the R1 group of the aziridine
led to a lower yield of the desired product (Table 2, entry 7).
The steric hindrance could be overcome by increasing the
pressure of CO2 as well as by increasing the temperature of
Figure 2. (a) Effects of CO2 pressure and (b) reaction time on the synthesis of
oxazolidinone. Reaction conditions: aziridine (5 mmol), catalyst (0.02 mmol),
2 MPa, RT, 3 h.
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the reaction to obtain appreciable yields of the expected prod-
ucts (Table 2, entries 8–15). In the next set of experiments, we
reacted CO2 with various cyclic aziridines, including aliphatic as
well as aromatic substituents, in the presence of NHO 4 as the
catalyst, and good yields and selectivity towards the 5-aryl-2-
oxazolidinones were obtained (Table 2, entries 10–15). Interest-
ingly, this protocol provides high selectivity towards (b) 5-aryl-
2-oxazolidinones (more than 96%) over the 4-aryl-2-oxazolidi-
none (c).
and green alternative for the production of formamides.[18]
Recently, PMHS as an industrial waste product, was investigat-
ed as a hydrogen source for the formylation of amines
(Table 3).[18a] A literature survey revealed that NHC-based orga-
Table 3. Formylation reaction using NHO catalyst.[a]
A plausible reaction mechanism has been proposed for the
synthesis of oxazolidinones from CO2 and aziridines catalyzed
by NHOs (Scheme 2). The olefinic bond of the NHO catalyst
Entry
Catalyst
T
[8C]
Yield[b] [%]
PMHS/9-BBN
1
2
3
4
5
6
7
–
1
1
2
3
4
4
4
4
90
90
80
80
80
80
60
25
80
–
75/90
72/88
79/93
88/91
92/97
86/94
45/70
61/73
8
9[c]
[a] Reaction conditions: 1 (1 mmol), THF (3 mL), reducing agent (PMHS
2.3 mmol, 9-BBN 1.5 mmol), catalyst (5 mol%), 6 h, CO2 (2 MPa). [b] Deter-
mined by GC and GC–MS. [c] Catalyst (2 mol%).
nocatalysts are highly active for the silane activation owing to
their high nucleophilicity.[19] 9-BBN is also well-documented for
the reduction of CO2.[20] Thus, owing to the highly nucleophilic
nature of the synthesized NHOs, they were used for the formy-
lation of morpholine using PMHS or 9-BBN as the reducing
agent for CO2, and the results are listed in Table 3. Without the
use of any catalyst, no formylated product was observed using
both PMHS and 9-BBN as the reducing agent (Table 3, entry 1).
Various NHOs were tested for the formylation reaction, and
good-to-excellent yields of the product were noted (Table 3,
entries 2–9). Catalysts 2 and 3 produced good yields (Table 3,
entries 2–5), and catalyst 4 showed excellent activity for the
formylation reaction using PMHS and 9-BBN as the reducing
agents (Table 3, entry 6). Next, we studied the effect of temper-
ature on the reaction system; as the reaction temperature de-
creased, decreased formylation yields were noted (Table 3, en-
tries 6–8). At room temperature, moderate yields of formylated
product were still observed, and 9-BBN showed good reactivity
(Table 3, entry 8). Various amine substrates, including aliphatic,
aliphatic cyclic as well as aromatic amines, were well-tolerated
and provided good-to-excellent yields of the formylated prod-
ucts under the optimized reaction conditions (Table 4).
Scheme 2. Proposed reaction mechanism for the synthesis of oxazolidinones
using a NHO catalyst.
bearing the high nucleophilic character activates the CO2 mole-
cules to form a zwitterionic NHO–carboxylate (NHO–CO2)
adduct.[4,5] The NHO–CO2 adduct then assists the ring-opening
of the aziridine molecule to generate the anion. The CO2 mole-
cule then undergoes insertion with the anion of the amine
generated from the aziridine, followed by the cyclization of the
oxazolidinone. The above results indicate that the highly nucle-
ophilic character of the NHOs provides efficient catalytic activi-
ty towards the activation of the CO2 molecule by forming the
NHO-CO2 adduct, and this adduct plays the key role in the syn-
thesis of the oxazolidinones under very mild reaction condi-
tions.
Various amines were formylated by using PMHS and 9-BBN
as the reducing agent and NHO 4 as catalyst. Cyclic secondary
amines were highly reactive and provided excellent yields
(Table 4, entries 1–3 and 7). Primary aromatic amines such as
aniline also provided good yields of the formylated product
(Table 4, Entry 4). Simple aliphatic amines were slightly sluggish
towards the formylation reactions and provided the products
in moderate yields (Table 4, entries 5 and 6). A primary cyclic
aliphatic amine was also reactive and provided a good yield of
Encouraged by the successful results using NHOs as the cat-
alyst for the synthesis of oxazolidinones under ambient condi-
tions, we further explored the application of NHOs to the for-
mylation of amines using CO2 as the starting material to syn-
thesis formamides. Formamides are versatile chemicals and im-
portant intermediates that are commonly produced through
the formylation of amines. The use of CO2 instead of toxic CO
for the N-formylation reaction is considered to be an attractive
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adduct. This adduct would then be more reactive towards the
electropositive silane or borane centers and promote hydride
transfer to form the formoxysilane or formoxyborane inter-
mediate. The formoxysilane or formoxyborane then undergoes
nucleophilic attack by the amine molecule to form the formy-
lated product. For the synthesis of oxazolidinone as well as the
formylation reactions, the NHO 4 catalyst was highly active
and selective. This may be because the electronic effect of the
bulky isopropyl group stabilizes the NHO–CO2 adduct very ef-
fectively.
Table 4. Substrate study for the amine formylation reaction.[a]
Entry
Substrate
Product
Yield[b] [%]
PMHS/9-BBN
1
2
3
87/93
92/97
89/93
Conclusions
4
52/72
We have demonstrate catalytic processes promoted by robust
N-heterocyclic olefin (NHO) organocatalysts for the activation
of CO2 to synthesize oxazolidinones and for the N-formylation
of amines with polymethylhydrosiloxane (PMHS) and 9-borabi-
cyclo[3.3.1]nonane (9-BBN) as the reducing agent. The in situ
generated zwitterionic NHO–CO2 adduct plays the crucial role
for the activation of CO2. All of the reported NHOs can be syn-
thesized readily, show high activity, and provide excellent turn-
over numbers (TONs) and turnover frequencies (TOFs) with ex-
cellent regioselectivity towards 5-aryl-2-oxazolidinones under
very mild reaction conditions. This methodology also features
a simple and cost-effective process with low energy consump-
tion, and the complicated synthesis of expensive catalysts is
avoided. In addition, the cycloaddition reactions of aziridines
with CO2 proceed under solvent-free, transition-metal-free, and
additive-free conditions. Efforts are underway to further ex-
plore the NHO-based catalytic system.
5
6
7
72/78
71/80
83/91
8
9
88/96
55/78
10
11
12
ND
56/69
72/83[c]
Acknowledgements
83/91
V.B.S is greatly thankful to the University Grant Commission
(UGC), India for providing a Senior Research Fellowship (SRF).
[a] Reaction conditions: amine (1 mmol), THF (3 mL), reducing agent
(PMHS 2.5 mmol, 9-BBN 1.5 mmol), 4 (5 mol%), 6 h, CO2 (2 MPa), 808C;
ND not detected. [b] Determined by GC and GC–MS. [c] PMHS 6 mmol, 9-
BBN 6 mmol, CO2,(4 MPa) 1108C.
Keywords: carbon dioxide fixation · cycloaddition · nitrogen
heterocycles · organocatalysis · zwitterions
[1] a) N. Kuhn, H. Bohnen, J. Kreutzberg, D. Blꢂser, R. Boese, J. Chem. Soc.
Chem. Commun. 1993, 1136–1137; b) U. Gruseck, M. Heuschmann,
Chem. Ber. 1987, 120, 2053–2064; c) P. P. Ponti, J. C. Baldwin, W. C.
Kaska, Inorg. Chem. 1979, 18, 873–875; d) R. S. Ghadwal, S. O. Reich-
mann, F. Engelhardt, D. M. Andrada, G. Frenking, Chem. Commun. 2013,
49, 9440–9442; e) Y. Wang, M. Abraham, R. Gilliard, Jr., D. Sexton, P.
Wei, G. Robinson, Organometallics 2013, 32, 6639–6642;f) R. D. Crocker,
T. Nguyen, Chem. Eur. J. 2016, 22, 2208–2213.
[2] a) P. Jessop, T. Ikariya, R. Noyori, Chem. Rev. 1995, 95, 259–272; b) P.
Jessop, F. Joo, C. Tai, Coord. Chem. Rev. 2004, 248, 2425–2442; c) D.
Laitar, P. Mꢀller, J. Sadighi, J. Am. Chem. Soc. 2005, 127, 17196–17197;
d) G. Mꢃnard, D. Stephan, J. Am. Chem. Soc. 2010, 132, 1796–1797; e) G.
Mꢃnard, D. Stephan, Angew. Chem. Int. Ed. 2011, 50, 8396–8399;
Angew. Chem. 2011, 123, 8546–8549; f) S. Bontemps, L. Vendier, S.
Sabo-Etienne, Angew. Chem. Int. Ed. 2012, 51, 1671–1674; Angew.
Chem. 2012, 124, 1703–1706; g) M. Sgro, D. Stephan, Angew. Chem. Int.
Ed. 2012, 51, 11343–11345; Angew. Chem. 2012, 124, 11505–11507;
h) R. Dobrovetsky, D. Stephan, Angew. Chem. Int. Ed. 2013, 52, 2516–
2519; Angew. Chem. 2013, 125, 2576–2579; i) G. Mꢃnard, D. Stephan,
Dalton Trans. 2013, 42, 5447–5453; j) Y. Li, X. Fang, K. Junge, M. Beller,
Angew. Chem. Int. Ed. 2013, 52, 9568–9571; Angew. Chem. 2013, 125,
the formylated product (Table 4, entry 8). Then, we studied the
electronic effects of aromatic substituents on the formylation
reaction and noticed that electronic-donating substituents
such as methoxy groups are tolerated very well in the reaction
(Table 4, entry 9), whereas amines with electron-withdrawing
substituents such as nitro groups were not able to provide the
formylated product (Table 4, entry 10). The N-methylated prod-
uct was not observed even if the temperature and pressure
were increased (Table 4, entry 11). Benzylamine provided an ex-
cellent yield of the formylated amine of up to 91% (Table 4,
entry 12).
A tentative reaction mechanism has been proposed for the
N-formylation reaction of amines with CO2 with the NHO cata-
lytic system (Supporting Information, Section 4).[18–20] The
highly nucleophilic exocyclic carbon atom of the NHO mole-
cule activates the CO2 molecule to generate the NHO–CO2
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9747–9750; k) M. Hopkinson, C. Richter, M. Schedler, F. Glorius, Nature
2014, 510, 485–496; l) A. T. Biju, M. Padmanaban, N. E. Wurz, F. Glorius,
Angew. Chem. Int. Ed. 2011, 50, 8412–8415; Angew. Chem. 2011, 123,
8562–8565.
d) M. R. Barbachyn, C. W. Ford, Angew. Chem. Int. Ed. 2003, 42, 2010–
2023; Angew. Chem. 2003, 115, 2056–2070; e) A. R. Renslo, G. W. Luehr,
M. F. Gordeev, Bioorg. Med. Chem. 2006, 14, 4227–4240; f) T. A. Mukhtar,
G. D. Wright, Chem. Rev. 2005, 105, 529–542; g) J.-Y. Hu, J. Ma, Q.-G.
Zhu, Z.-F. Zhang, C.-Y. Wu, B.-X. Han, Angew. Chem. Int. Ed. 2015, 54,
5399–5403; Angew. Chem. 2015, 127, 5489–5493; h) A. W. Miller, S. T.
Nguyen, Org. Lett. 2004, 6, 2301–2304; i) M.-Y. Wang, Q.-W. Song, R. Ma,
J.-N. Xie, L.-N. He, Green Chem. 2016, 18, 282–287.
[3] a) N. Kuhn, H. Bohnen, D. Blꢂser, R. Boese, Chem. Ber. 1994, 127, 1405–
1407; b) H. Schumann, M. Glanz, J. Winterfeld, H. Hemling, N. Kuhn, H.
Bohnen, D. Blꢂser, R. Boese, J. Organomet. Chem. 1995, 493, C14;
c) S. M. Ibrahim Al-Rafia, A. C. Malcolm, S. K. Liew, M. J. Ferguson, R.
McDonald, E. Rivard, Chem. Commun. 2011, 47, 6987–6989; d) A.
GlÅckner, S. Kronig, T. Bannenberg, C. G. Daniliuc, P. G. Jones, M. Tamm,
J. Organomet. Chem. 2013, 723, 181–187; e) M. Iglesias, A. Iturmendi, P.
Miguel, V. Polo, J. Perez-Torrentea, L. Oro, Chem. Commun. 2015, 51,
12431; f) K. Powers, C. Hering-Junghans, R. McDonald, M. Ferguson, E.
Rivard, Polyhedron 2016, 108, 8–14.
[4] L. Dong, J. Wena, W. Li, Org. Biomol. Chem. 2015, 13, 8533.
[5] a) Y. Wang, Y. Wang, W. Zhang, X. Lu, J. Am. Chem. Soc. 2013, 135,
11996–12003; b) Y. Wang, D. Sun, H. Zhou, W. Zhang, X. Lu, Green
Chem. 2015, 17, 4009; c) W. Chen, J. Shen, T. Jurca, C. Peng, Y. Lin, Y.
Wang, W. Shih, G. Yap, T. Ong, Angew. Chem. Int. Ed. 2015, 54, 15207–
15212; Angew. Chem. 2015, 127, 15422–15427; d) H. Zhou, W.-Z. Zhang,
C.-H. Liu, J.-P. Qu, X.-B. Lu, J. Org. Chem. 2008, 73, 8039–8044; e) Y.-B.
Wang, D.-S. Sun, H. Zhou, W.-Z. Zhang, X.-B. Lu, Green Chem. 2014, 16,
2266; f) H. Zhou, G.-X. Wang, W.-Z. Zhang, X.-B. Lu, ACS Catal. 2015, 5,
6773–6779.
[16] a) Y. Takeda, H. Kawai, S. Minakata, Chem. Eur. J. 2013, 19, 13479–
13483; b) A. Ueno, Y. Kayaki, T. Ikariya, Green Chem. 2013, 15, 425–430;
c) J. Seayad, A. Seayad, J. Ng, C. Chai, ChemCatChem 2012, 4, 774–777;
d) M. Mikkelsen, M. Jorgensen, F. Krebs, Energy Environ. Sci. 2010, 3, 43–
81; e) Y. Du, A. Wu, L. Liu, N. He, J. Org. Chem. 2008, 73, 4709–4712;
f) R. A. Watile, D. B. Bagal, K. M. Deshmukh, K. P. Dhake, B. M. Bhanage, J.
Mol. Catal. A 2011, 351, 196–203; g) D. B. Nale, S. Rana, K. Parida, B. M.
Bhanage, Appl. Catal. A 2014, 469, 340–349; h) Z. Yang, Y. Li, Y. Wei, L.
He, Green Chem. 2011, 13, 2351; i) X. Lin, Z. Yang, L. He, Z. Yuan, Green
Chem. 2015, 17, 795–798; j) R. Watile, D. Bagal, Y. Patil, B. M. Bhanage,
Tetrahedron Lett. 2011, 52, 6383–6387.
[17] a) V. Saptal, D. B. Shinde, R. Banerjee, B. M. Bhanage, Catal. Sci. Technol.
2016, DOI: 10.1039/C6CY00362A; b) Y. Wu, L. N. He, Y. Du, J. Q. Wang,
C. X. Miao, W. Li, Tetrahedron 2009, 65, 6204–6210; c) C. Qi, J. Ye, W.
Zeng, H. Jiang, Adv. Synth. Catal. 2010, 352, 1925–1933; d) Z. Yang, L.
He, S. Y. Peng, A. Liu, Green Chem. 2010, 12, 1850–1954.
[6] U. Gruseck, M. Heuschmann, Tetrahedron Lett. 1987, 28, 6027–6030.
[7] A. Fꢀrstner, M. Alcarazo, R. Goddard, C. Lehmann, Angew. Chem. Int. Ed.
2008, 47, 3210–3214; Angew. Chem. 2008, 120, 3254–3258.
[8] S. Al-Rafia, A. Malcolm, S. Liew, M. Ferguson, R. McDonald, E. Rivard,
Chem. Commun. 2011, 47, 6987–6989.
[9] a) B. Maji, M. Horn, H. Mayr, Angew. Chem. Int. Ed. 2012, 51, 6231–6235;
Angew. Chem. 2012, 124, 6335–6339; b) B. Maji, M. Breugst, H. Mayr,
Angew. Chem. Int. Ed. 2011, 50, 6915–6919; Angew. Chem. 2011, 123,
7047–7052.
[18] a) O. Jacquet, C. Das Neves Gomes, M. Ephritikhine, T. Cantat, J. Am.
Chem. Soc. 2012, 134, 2934–2937; b) C. Das Neves Gomes, O. Jacquet,
C. Villiers, P. Thuery, M. Ephritikhine, T. Cantat, Angew. Chem. Int. Ed.
2012, 51, 187–190; Angew. Chem. 2012, 124, 191–194; c) X. J. Cui, Y.
Zhang, Y. Q. Deng, F. Shi, Chem. Commun. 2014, 50, 189–191; d) J. L.
Liu, C. K. Guo, Z. F. Zhang, T. Jiang, H. Z. Liu, J. L. Song, H. L. Fan, B. X.
Han, Chem. Commun. 2010, 46, 5770–5772; e) P. Munshi, D. J. Helde-
brant, E. P. McKoon, P. A. Kelly, C. C. Tai, P. G. Jessop, Tetrahedron Lett.
2003, 44, 2725–2727; f) S. Kumar, S. L. Jain, RSC Adv. 2014, 4, 64277–
64279; g) K. Motokura, N. Takahashi, D. Kashiwame, S. Yamaguchi, A.
Miyaji, T. Baba, Catal. Sci. Technol. 2013, 3, 2392–2396; h) L. Hao, Y.
Zhao, B. Yu, Z. Yang, H. Zhang, B. Han, X. Gao, Z. Liu, ACS Catal. 2015, 5,
4989–4993; i) C. Chong, R. Kinjo, Angew. Chem. Int. Ed. 2015, 54,
12116–12120; Angew. Chem. 2015, 127, 12284–12288; j) D. B. Nale,
B. M. Bhanage, Green Chem. 2015, 17, 2480; k) T. V. Q. Nguyen, W.-J. Yoo,
S. Kobayashi, Angew. Chem. Int. Ed. Angew.Chem. Int. Ed. 2015, 54,
9209–9212;l) L. Zhang, Z. Han, X. Zhao, Z. Wang, K. Ding, Angew. Chem.
Int. Ed. 2015, 54, 6186–6189; Angew. Chem. 2015, 127, 6284–6287;
m) S. Das, F. D. Bobbink, S. Bulut, M. Soudania, P. J. Dyson, Chem.
Commun. 2016, 52, 2497–2500.
[10] R. S. Ghadwal, C. J. Schꢀrmann, D. M. Andrada, G. Frenking, Dalton
Trans. 2015, 44, 14359.
[11] S. Kronig, P. Jones, M. Tamm, Eur. J. Inorg. Chem. 2013, 2301–2314.
[12] a) Y. Jia, Y. Wang, W. Ren, T. Xu, J. Wang, X. Lu, Macromolecules 2014, 47,
1966–1972; Y.-B. Jia, W.-M. Ren, S.-J. Liu, T. Xu, Y.-B. Wang, X.-B. Lu, ACS
Macro Lett. 2014, 3, 896–899; b) S. Naumann, A. Thomas, A. P. Dove,
Angew. Chem. Int. Ed. 2015, 54, 9550–9554; Angew. Chem. 2015, 127,
9686–9690; c) S. Naumann, A. W. Thomas, A. P. Dove, ACS Macro Lett.
2016, 5, 134–138.
[13] P. Nema, S. Nema, P. Roy, Renewable Sustainable Energy Rev. 2012, 16,
2329.
[14] a) Transformation and Utilization of Carbon Dioxide, Green Chemistry and
Sustainable Technology (Ed.: B. M. Bhanage, M. Arai), Springer, Berlin,
2014; b) M. Aresta, Carbon Dioxide as Chemical Feedstock, Wiley-VCH,
Weinheim, 2010; c) M. He, Y. Sun, B. Han, Angew. Chem. Int. Ed. 2013,
52, 9620–9633; Angew. Chem. 2013, 125, 9798–9812; d) B. M. Bhanage,
S. Fujita, Y. Ikushima, M. Arai, Green Chem. 2003, 5, 340–342; e) Y. P.
Patil, P. J. Tambade, S. R. Jagtap, B. M. Bhanage, J. Mol. Catal. A 2008,
289, 14–21; f) V. B. Saptal, B. M. Bhanage, ChemCatChem 2016, 8, 244–
250; g) B. M. Bhanage, S. Fujita, Y. Ikushima, M. Arai, Green Chem. 2004,
6, 78–80; h) Q. Liu, L. Wu, R. Jackstell, M. Beller, Nat. Commun. 2015, 6,
5933; i) V. B. Saptal, T. Sasaki, K. Harada, D. Nishio-Hamane, B. M. Bhan-
age, ChemSusChem 2016, 9, 644–650; j) M. B. Ansari, S.-E. Park, Energy
Environ. Sci. 2012, 5, 9419; k) N. von der Assen, P. Voll, M. Peters, A.
Bardow, Chem. Soc. Rev. 2014, 43, 7982.
[19] a) S. Riduan, Y. Zhang, J. Ying, Angew. Chem. Int. Ed. 2009, 48, 3322–
3325; Angew. Chem. 2009, 121, 3372–3375; S. N. Riduan, J. Y. Ying, Y.
Zhang, ChemCatChem 2013, 5, 1490–1496; b) S. Das, F. Bobbink, G.
Laurenczy, P. Dyson, Angew. Chem. Int. Ed. 2014, 53, 12876–12879;
Angew. Chem. 2014, 126, 13090–13093; c) O. Jacquet, C. Das Neves
Gomes, M. Ephritikhine, T. Cantat, ChemCatChem 2013, 5, 117–120.
[20] a) Y. Yang, M. Xu, D. Song, Chem. Commun. 2015, 51, 11293; b) T. Wang,
D. Stephan, Chem. Eur. J. 2014, 20, 3036–3039; c) Z. Lu, H. Hausmann,
S. Becker, H. Wegner, J. Am. Chem. Soc. 2015, 137, 5332–5335; d) E.
Blondiaux, J. Pouessel, T. Cantat, Angew. Chem. Int. Ed. 2014, 53, 12186–
12190; Angew. Chem. 2014, 126, 12382–12386; e) T. Wang, D. W. Ste-
phan, Chem. Commun. 2014, 50, 7007–7010.
[15] a) D. J. Ager, I. Prakash, D. R. Schaad, Aldrichimica Acta 1997, 30, 3–12;
b) D. A. Evans, J. S. Tedrow, J. T. Shaw, C. W. Downey, J. Am. Chem. Soc.
2002, 124, 392–393; c) G. Zappia, G. Cancelliere, E. Gacs-Baitz, G. Mon-
ache, D. Misiti, L. Nevola, B. Botta, Curr. Org. Synth. 2007, 4, 238–307;
Received: April 11, 2016
Revised: May 16, 2016
Published online on && &&, 0000
&
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
6
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPERS
NHO limits: N-Heterocyclic olefins
(NHOs) activate CO2 for the formation
of oxazolidinones from aziridines as well
as the N-formylation of amines with pol-
ymethylhydrosiloxane (PMHS) or 9-bora-
bicyclo[3.3.1]nonane (9-BBN) as the re-
ducing agent. These transformations
proceed under solvent-free and metal-
free mild conditions.
V. B. Saptal, B. M. Bhanage*
&& – &&
N-Heterocyclic Olefins as Robust
Organocatalyst for the Chemical
Conversion of Carbon Dioxide to
Value-Added Chemicals
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
7
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ