Cobalt-Catalyzed Synthesis of Unsymmetrically N, N-Disubstituted Formamides via Reductive Coupling of Primary Amines and Aldehydes with CO2 and H2

Article abstract of DOI:10.1021/acs.orglett.8b02384

Herein, a novel route to synthesize unsymmetrically N,N-disubstituted formamides is reported, which is achieved via reductive coupling of primary amine and aldehyde with CO₂/H₂ over a cobalt-based catalytic system composed of CoF₂, P(CH₂CH₂PPh₂)₃ and K₂CO₃. The mechanism investigation indicates that a secondary amine is formed via hydrogenation of the imine originated from aldehyde and primary amine, which further reacts with HCOOH generated from CO₂ hydrogenation, resulting in the formation of NNFA finally.

Full text of DOI:10.1021/acs.orglett.8b02384

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Cobalt-Catalyzed Synthesis of Unsymmetrically N,N‑Disubstituted
Formamides via Reductive Coupling of Primary Amines and
Aldehydes with CO2 and H2
Zhengang Ke,†,‡ Zhenzhen Yang,† Zhenghui Liu,†,‡ Bo Yu,† Yanfei Zhao,† Shien Guo,†,‡ Yunyan Wu,†,‡
and Zhimin Liu*,†,‡
†Beijing National Laboratory for Molecular Sciences, Key Laboratory of Colloid, Interface and Thermodynamics, CAS
Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing
100190, China
‡University of Chinese Academy of Sciences, Beijing 100049, China
S
* Supporting Information
ABSTRACT: Herein, a novel route to synthesize unsym-
metrically N,N-disubstituted formamides is reported, which is
achieved via reductive coupling of primary amine and
aldehyde with CO2/H2 over a cobalt-based catalytic system
composed of CoF2, P(CH2CH2PPh2)3 and K2CO3. The
mechanism investigation indicates that a secondary amine is
formed via hydrogenation of the imine originated from aldehyde and primary amine, which further reacts with HCOOH
generated from CO2 hydrogenation, resulting in the formation of NNFA finally.
pounds,45−47 and hydroformylation of olefin,48−50 and has
ince carbon dioxide (CO2) is nontoxic, abundant, and
Srenewable, its utilization has been given much attention
been widely applied in the organic synthesis. In our previous
work,51 we presented an efficient approach to synthesize
recently. In particular, as a C1 feedstock, CO2 has been widely
applied in the synthesis of chemicals1−3 and fuels,4−6 providing
unsymmetrical NNFAs via hydroamination of aldehyde and
various green synthetic routes. For example, N-formylation of
amines to formamides using CO2 as a formyl reagent has been
widely investigated in the presence of reductants, including H2,
hydrosilanes,7−14 and boranes.15−17 Although the utilization of
hydrosilanes and boranes could make the reaction proceed
under mild conditions, it suffers from poor atom economy and
production of organosilicone/organoborane wastes. The
reductive formylation of amines with CO2/H2 provides a
green strategy for the synthesis of formamides, because H2O is
the sole byproduct. Since the pioneering work of catalytic N-
formylation of amines with CO2/H2 over Raney nickel
catalyst,18 various noble metal catalysts, such as Rh,19
Ru,20−24 Pd,25−28 Ir,29,30 Au,31 and Pd−Au,32 have been
developed for the CO2-involved N-formylation of amines, with
a focus on achieving high reaction efficiency. Although the
noble-metal catalysts are effective for the N-formylation of
amines, their high costs hamper their industrial applications.
Recently, non-noble metal catalysts, including Mn-,33−35
Fe-,36,37 Co-,38,39 Ni-18 and Cu-based catalysts40−43 have
been presented for the N-formylation of amines with CO2/H2,
showing promising application potentials.
amine to unsymmetrical secondary amine, followed by
reductive N-formylation of this unsymmetrical secondary
amine with CO2 in the presence of phenylsilane, and a series
of unsymmetrical NNFAs were obtained via changing
aldehydes and amines. Compared to hydrosilanes, molecular
hydrogen is less expensive and more easily available, so it is
more interesting to use H2 as a reductant in the CO2-involved
reductive reactions. In particular, exploring inexpensive and
Earth-abundant metal catalysts to synthesize versatile unsym-
metrical NNFAs is of significance.
We are inspired by our previously reported work regarding
Co(BF4)2·6H2O/PP3/K2CO3 system-catalyzed methylation of
ketones with menthol.52 Herein, we present a highly efficient
cobalt-based catalytic system composed of CoF2, P-
(CH2CH2PPh2)3 (denoted as PP3) and K2CO3 for the
synthesis of unsymmetrically NNFAs via reductive coupling
of primary amine and aldehyde with CO2/H2. The optimized
reaction conditions were explored, and the scopes of aldehydes
and primary amines were also examined. It was demonstrated
that the catalytic system was very effective for this reaction at
140 °C, affording various unsymmetrical NNFAs in good to
excellent yields, together with good functional-group tolerance
and broad substrate scope.
Unsymmetrically N,N-disubstituted formamides (NNFAs)
are a class of chemicals with widespread applications in organic
and pharmaceutical synthesis, which are generally produced via
the formylation of N,N-disubstituted amines. Aldehyde is a
type of abundant and low-cost chemical that can be easily
obtained from natural products,44 biomass platform com-
Received: July 27, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b02384
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Hexylamine (1a) and cyclohexanecarboxaldehyde (1b) were
selected as model substrates of amine and aldehyde,
respectively, to explore the possibility to synthesize N-
cyclohexylmethyl-N-hexylformamide (1c) via the reductive
coupling of aldehyde and amine with CO2/H2. After screening
the catalytic system and reaction conditions (see Table 1, as
(BF4)2·6H2O, Co(acac)2, and Co2(CO)8 were examined, and
they were found to also be effective for this reaction, with most
of them showing high activity (Table 1, entries 9−14).
Fe(OAc)2, Ni(OAc)2·4H2O, and Cu(OAc)2·H2O were also
able to catalyze this reaction; however, they displayed much
lower activities, compared to most of the cobalt salts (Table 1,
entries 15−17). As is well-known, a base is usually needed in
the process catalytic hydrogenation of CO2 to HCOOH.
Besides K2CO3, other bases including KOH, tBuOK, K3PO4,
and Cs2CO3 were tested under the same other conditions
(Table 1, entry 1, 18−21), and K2CO3 showed the best
performance. The amounts of K2CO3 and PP3 also affected the
reductive coupling reaction (see Table S2 in the SI), and 1.5
equiv of K2CO3, together with 5 mol % of PP3, was appropriate
for the reaction to afford high product yield. In addition, the
solvents had significant influence (Table 1, entries 22−29).
Nonpolar solvents, e.g., n-heptane and toluene, almost
suppressed the reaction (Table 1, entries 23 and 24), and
weakly polar solvents such as THF, 1,4-dioxane, and CH3CN
afforded very low yield of 1c (Table 1, entries 25−27). Highly
polar aprotic solvents, such as EtOH, DMSO, and DMF,
showed better performances, affording a relatively high yield of
1c (Table 1, entries 1, 28, and 29). Other phosphine- or
nitrogen-containing ligands, instead of PP3, were tested in this
reaction, and it was indicated that they hardly showed any
activity (see Table S1 in the SI). This result suggests that PP3
played an important role in the reaction, which may chelate
with Co2+ to form active hydrogen complexes, thus enhancing
its catalytic activity.37,39
Based on the above results, the optimized reaction
conditions were obtained as listed in Scheme 1, under which
the generality of the reductive coupling of primary amines,
aldehydes with CO2 and H2, was investigated. First, using
aliphatic primary amines and aliphatic aldehydes as the
substrates, a series of unsymmetrical N-alkyl-N-alkylforma-
mides were obtained in high yields (see Scheme 1, 1c−22c).
For example, the coupling of 1b and various chain aliphatic
amines or cyclic aliphatic amines with CO2/H2 proceeded well,
giving good to excellent product yields (Scheme 1, 1c−11c,
76%−99%). Three isomers of butyl amines showed reactivity
in the following order: n-butylamine > iso-butylamine > tert-
butylamine, which may be due to the steric effect (Scheme 1,
2c−4c). As expected, the chain length of the chain amines
influenced their reactivity, and the product yields decreased
with the chain length (Scheme 1, 1c and 5c−8c). The tested
cyclic amines including c-hexylamine, c-pentylamine, and 1-
methylpiperidin-4-amine displayed high activity to react with
1b and CO2/H2, affording corresponding target products in
yields of 84%, 84%, and 78%, respectively (see Scheme 1, 9c−
11c). Cyclopentanecarbaldehyde as the aldehyde substrate
exhibited similar activity to 1b in this reductive coupling
reaction, affording corresponding NNFAs in high yields
(Scheme 1, 13c−22c).
Table 1. Reductive Coupling of Cyclohexanecarboxaldehyde
a
and n-Hexylamine with CO2 and H2
entry
1
2
catalyst
base
solvent
EtOH
yield (%)
CoF2
CoF2
CoF2
−
CoF2
CoF2
CoF2
CoF2
Co(ClO4)2·6H2O
Co(OAc)2·4H2O
CoBr2
Co(BF4)2·6H2O
Co(acac)3
Co2(CO)8
Cu(OAc)2·H2O
Ni(OAc)2·4H2O
Fe(OAc)2
CoF2
CoF2
CoF2
CoF2
CoF2
CoF2
CoF2
CoF2
CoF2
K2CO3
K2CO3
−
93
3
35
<1
75
7
b
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
CH2Cl2
toluene
n-heptane
THF
3
4
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
KOH
K3PO4
tBuOK
Cs2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
c
5
d
6
7
e
33
52
86
86
80
73
71
24
68
56
22
47
58
72
76
<1
6
f
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
7
13
13
23
60
70
1,4-dioxane
CH3CN
DMF
CoF2
CoF2
CoF2
DMSO
a
Reaction conditions: 1a (1.0 mmol), 1b (1.0 mmol); CoF2 (10
mol %), PP3 (5 mol %), base (1.5 mmol), solvent (3 mL), CO2 (3
1
MPa), H2 (3 MPa), 140 °C, 24 h, The yield was determined by H
NMR, calibrated using 1,1,2,2-tetrachloroethane as the internal
b
c
d
e
standard. Without PP3. 110 °C, 24 h. 90 °C, 24 h. CO2 (1
f
MPa), H2 (3 MPa). CO2 (3 MPa), H2 (1 MPa).
well as Tables S1 and S2 in the Supporting Information (SI)),
it was found that CoF2 combined with PP3 and K2CO3, was
very effective for catalyzing the reaction of 1a and 1b with
CO2/H2 at 140 °C, producing 1c in a high yield of 93% (see
Table 1, entry 1). Notably, CoF2, PP3, and K2CO3 were
necessary for a high yield of 1c, because the absence of any one
of them resulted in a remarkable decline in the yield of 1c (see
Table 1, entries 2−4). The influences of temperature and
pressure were explored, and it was demonstrated that a
temperature of 140 °C, together with an initial CO2 pressure of
3 MPa and H2 pressure of 3 MPa at room temperature was
appropriate (Table 1, entries 5−8). Other cobalt salts,
including Co(ClO4)2·6H2O, Co(OAc)2·4H2O, CoBr2, Co-
Encouraged by the above results, we extended the scopes of
amines and aldehydes to aromatic aldehydes and primary
amines with aromatic nucleus substituents (see Scheme 1,
23c−34c). First, the reaction of 1a and benzaldehyde with
CO2/H2 was performed, and a product yield of 77% was
obtained (Scheme 1, 23c). Next, more aromatic aldehydes
were examined, and it was indicated that all the reductive
coupling reactions proceeded well, producing target products
in moderate yields of 64%−80% (Scheme 1, 24c−27c). In
addition, other aromatic aldehydes, such as 5-methylfurfural, 4-
B
DOI: 10.1021/acs.orglett.8b02384
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Organic Letters
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To understand the reaction time to the effect of the
reductive coupling reaction of 1a and 1b with CO2/H2, the
kinetic study was performed under the optimized reaction
conditions (see Figure 1). At the beginning of the reaction, an
Scheme 1. Cobalt Catalytic Reductive Coupling Reaction of
Primary Amine and Aldehyde with CO2 and H2
a
Figure 1. Kinetic study of the reductive coupling of 1a and 1b with
CO2/H2. Reaction conditions: 1a (1.0 mmol), 1b (1.0 mmol); CoF2
(10 mol %), PP3 (5 mol %), K2CO3 (1.5 mmol), EtOH (3 mL), CO2
(3 MPa), H2 (3 MPa), 140 °C.
imine was immediately generated as 1a and 1b were mixed in
the absence of CO2/H2 in the reactor. After CO2 and H2 were
charged into the reactor and reacted under the reaction
conditions for 1 h, imine, (E)-1-cyclohexyl-N-hexylmethani-
mine, was not detectable, while unsymmetrical secondary
amine, N-(cyclohexylmethyl)hexan-1-amine, was detected
instead, suggesting that an amine was completely converted
to amine under the reaction conditions. Simultaneously,
HCOOH was detected in the reaction system, which may
originate from the CO2 hydrogenation over CoF2/PP3/
K2CO3.39 As the reaction proceeded, 1c was formed, and its
yield increased with reaction time, reaching 93% as the time
prolonged to 24 h; meanwhile, the amount of amine decreased
gradually and almost disappeared after 24 h. Notably, in the
reaction process, HCOOH was always detectable, and its
amount gradually accumulated, with 1.14 mmol of HCOOH
being obtained after 24 h. As known, the CO2 hydrogenation
to HCOOH is thermodynamically unfavorable, and a base is
usually required to promote this reaction. Considering that a
base (e.g., K2CO3) was necessary to obtain a high product
yield in the reductive coupling of aldehyde and amine with
CO2/H2, it is deduced that the base played the role in
promoting the formation of HCOOH from CO2 hydro-
genation under the experimental conditions. Although the
amount of HCOOH kept the concentration in the reaction
process relatively high, ammonium formate salt was not
detected; this implies that the dehydration between the
secondary amine and HCOOH may occur rapidly under the
reaction conditions.
To further reveal the mechanism of the reductive coupling
reaction, 13C-labeling isotope and control experiments were
performed (see Scheme 2). Using 13CO2 as a reactant in the
coupling reaction, N-13CHO group in 1c was detected (see
Scheme 2a, as well as Figure S1 in the SI), indicating that CO2
was the formyl source in the reductive coupling reaction. The
hydrogenation of CO2 was performed over the CoF2/PP3/
K2CO3 system in ethanol under the reaction conditions, and
HCOOH/KCOOH was obtained (Scheme 2b, as well as
Figure S2 in the SI), suggesting that this catalytic system was
effective for CO2 hydrogenation to HCOOH. The reaction of
1a and 1b with H2 over CoF2/PP3/K2CO3 produced N-
a
Reaction condition: amine (1.0 mmol), aldehyde (1.0 mmol), CoF2
(10 mol %), PP3 (5 mol %), K2CO3 (1.5 equiv), EtOH (3 mL), CO2
b
(3 MPa), H2 (3 MPa), 140 °C, 24 h. Isolated yield. The yield was
determined by 1H NMR, calibrated using 1,1,2,2-tetrachloroethane as
the internal standard.
pyridinecarboxaldehyde, and 2-benzofurancarboxaldehyde
were also suitable for the reductive coupling reaction, giving
high product yields (Scheme 1, 28c−30c). Interestingly,
phenylacetaldehyde also could react with n-hexylamine, giving
a product yield of 56% (Scheme 1, 31c). As for Aryl-CH2−
NH2, such as phenylmethanamine, 1-phenylethan-1-amine,
and furfurylamine, the reductive coupling reaction worked well
(see Scheme 1, 32c−34c). However, the reaction of aniline
and 1b with CO2 and H2 did not produce NNFA, while N-
(cyclohexylmethyl)aniline was obtained as the main product,
implying the formylation of N-cyclohexylaniline with CO2/H2
did not occur.
As known, it is difficult to keep an unsaturated bond (e.g.,
CC bond) unchanged in hydrogen atmosphere under
catalysis of transition-metal catalysts. Aldehydes with unsatu-
rated bonds were examined in this reductive coupling system.
It was indicated that the CoF2/PP3/K2CO3 catalytic system
was tolerable to the CC bond as citronellal or trans-
cinnamaldehyde were used as the substrates (Scheme 1, 35c−
39c).
C
DOI: 10.1021/acs.orglett.8b02384
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Organic Letters
Letter
Scheme 2. Control Experiments of the Reductive Coupling
Reaction
ASSOCIATED CONTENT
* Supporting Information
■
a
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b02384.
Experimental procedures, supplementary scheme and
figures, and NMR and MS spectra (PDF)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: liuzm@iccas.ac.cn.
ORCID
a
Reaction conditions: (a) 1a (1.0 mmol), 1b (1.0 mmol), CoF2 (10
mol %), PP3 (5 mol %), K2CO3 (1.5 mmol), EtOH (3 mL), 13CO2 (1
MPa), H2 (3 MPa); (b) CoF2 (10 mol %), PP3 (5 mol %), K2CO3
(1.5 mmol), EtOH (3 mL), CO2 (3 MPa), H2 (3 MPa) (the yield of
HCOOH was determined by 1H NMR, calibrated using 1,1,2,2-
tetrachloroethane as the internal standard); (c) 1a (1.0 mmol), 1b
(1.0 mmol), CoF2 (10 mol %), PP3 (5 mol %), K2CO3 (1.5 mmol),
EtOH (3 mL), CO2 (3 MPa), H2 (3 MPa); and (d) N,N-
dihexylamine (1.0 mmol), HCOOH (2.0 mmol). The liquid product
of was analyzed by GC-MS.
Zhimin Liu: 0000-0001-7953-7414
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the National Natural
Science Foundation of China (Grant No. 21533011), and
Chinese Academy of Sciences (Grant No. QYZDY-SSW-
SLH013).
(cyclohexylmethyl)hexan-1-amine in a yield of 99% (Scheme
2c, as well as Figure S3 in the SI), indicating that the CoF2/
PP3/K2CO3 catalytic syetem could catalyze the reduction of
the CN bond by H2. As is well known, amine can easily react
with HCOOH to form N-formamide, and this was verified in
Scheme 2d, as well as Figure S4 in the SI.
REFERENCES
■
(1) Artz, J.; Mu
̈
ller, T. E.; Thenert, K.; Kleinekorte, J.; Meys, R.;
Sternberg, A.; Bardow, A.; Leitner, W. Sustainable Conversion of
Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle
Assessment. Chem. Rev. 2018, 118, 434−504.
Based on the above experimental results and discussion, a
plausible reaction pathway is proposed as shown in Scheme 3.
(2) Sakakura, T.; Choi, J.-C.; Yasuda, H. Transformation of Carbon
Dioxide. Chem. Rev. 2007, 107, 2365−2387.
(3) Liu, Q.; Wu, L.; Jackstell, R.; Beller, M. Using carbon dioxide as
a building block in organic synthesis. Nat. Commun. 2015, 6, 5933.
(4) Wang, W.; Wang, S.; Ma, X.; Gong, J. Recent advances in
catalytic hydrogenation of carbon dioxide. Chem. Soc. Rev. 2011, 40,
3703−3727.
Scheme 3. Plausible Reaction Mechanism of the Reductive
Coupling of Primary Amine and Aldehyde with CO2 and H2
(5) Dorner, R. W.; Hardy, D. R.; Williams, F. W.; Willauer, H. D.
Heterogeneous catalytic CO2 conversion to value-added hydro-
carbons. Energy Environ. Sci. 2010, 3, 884−890.
(6) Qiao, J.; Liu, Y.; Hong, F.; Zhang, J. A review of catalysts for the
electroreduction of carbon dioxide to produce low-carbon fuels.
Chem. Soc. Rev. 2014, 43, 631−675.
(7) Xie, C.; Song, J.; Wu, H.; Zhou, B.; Wu, C.; Han, B. Natural
Product Glycine Betaine as an Efficient Catalyst for Transformation of
CO2 with Amines to Synthesize N-Substituted Compounds. ACS
Sustainable Chem. Eng. 2017, 5, 7086−7092.
(8) Luo, R.; Lin, X.; Chen, Y.; Zhang, W.; Zhou, X.; Ji, H.
Cooperative Catalytic Activation of Si−H Bonds: CO2-Based
Synthesis of Formamides from Amines and Hydrosilanes under
Mild Conditions. ChemSusChem 2017, 10, 1224−1232.
(9) Lu, Y.; Gao, Z.-H.; Chen, X.-Y.; Guo, J.; Liu, Z.; Dang, Y.; Ye, S.;
Wang, Z.-X. Formylation or methylation: what determines the
chemoselectivity of the reaction of amine, CO2, and hydrosilane
catalyzed by 1,3,2-diazaphospholene? Chem. Sci. 2017, 8, 7637−7650.
(10) Liu, X.-F.; Qiao, C.; Li, X.-Y.; He, L.-N. Carboxylate-promoted
reductive functionalization of CO2 with amine and hydrosilane under
mild conditions. Green Chem. 2017, 19, 1726.
At the beginning of the reaction, 1a rapidly reacts with 1b to
form imine (i1), which is further reduced to amine (i2) in the
presence of the CoF2/PP3/K2CO3 catalytic system. Mean-
while, CO2 is hydrogenated to form HCOOH, which
subsequently react with i2, resulting in the formation of 1c
finally.
In conclusion, a simple and clean route is presented to
synthesize unsymmetrical NNFAs via the reductive coupling of
primary amine and aldehyde with CO2/H2, which can be
realized over a Co-based catalytic system composing of CoF2/
PP3/K2CO3. This catalytic system allows wide scopes of
primary amine and aldehyde substrates, together with excellent
functional group tolerance, affording various unsymmetrical
NNFAs in good to excellent yields. This approach may have
promising application in the synthesis of NNFAs.
(11) Liu, X.-F.; Ma, R.; Qiao, C.; Cao, H.; He, L.-N. Fluoride-
Catalyzed Methylation of Amines by Reductive Functionalization of
CO2 with Hydrosilanes. Chem. - Eur. J. 2016, 22, 16489−16493.
(12) Nguyen, T. V. Q.; Yoo, W.-J.; Kobayashi, S. Effective
Formylation of Amines with Carbon Dioxide and Diphenylsilane
Catalyzed by Chelating bis(tzNHC) Rhodium Complexes. Angew.
Chem., Int. Ed. 2015, 54, 9209−9212.
(13) Chong, C. C.; Kinjo, R. Hydrophosphination of CO2 and
Subsequent Formate Transfer in the 1,3,2-Diazaphospholene-
D
DOI: 10.1021/acs.orglett.8b02384
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
̈
Catalyzed N-Formylation of Amines. Angew. Chem., Int. Ed. 2015, 54,
12116−12120.
(33) Bertini, F.; Glatz, M.; Gorgas, N.; Stoger, B.; Peruzzini, M.;
Veiros, L. F.; Kirchner, K.; Gonsalvi, L. Carbon dioxide hydrogenation
catalysed by well-defined Mn(I) PNP pincer hydride complexes.
Chem. Sci. 2017, 8, 5024−5029.
(14) Jacquet, O.; Das Neves Gomes, C.; Ephritikhine, M.; Cantat, T.
Recycling of Carbon and Silicon Wastes: Room Temperature
Formylation of N-H Bonds Using Carbon Dioxide and Polymethylhy-
drosiloxane. J. Am. Chem. Soc. 2012, 134, 2934−2937.
(15) Hao, L.; Zhang, H.; Luo, X.; Wu, C.; Zhao, Y.; Liu, X.; Gao, X.;
Chen, Y.; Liu, Z. Reductive formylation of amines with CO2 using
sodium borohydride: A catalyst-free route. J. CO2 Util. 2017, 22,
208−211.
(34) Kar, S.; Goeppert, A.; Kothandaraman, J.; Prakash, G. K. S.
Manganese-Catalyzed Sequential Hydrogenation of CO2 to Methanol
via Formamide. ACS Catal. 2017, 7, 6347−6351.
(35) Dubey, A.; Nencini, L.; Fayzullin, R. R.; Nervi, C.;
Khusnutdinova, J. R. Bio-Inspired Mn(I) Complexes for the
Hydrogenation of CO2 to Formate and Formamide. ACS Catal.
2017, 7, 3864−3868.
(36) Jayarathne, U.; Hazari, N.; Bernskoetter, W. H. Selective Iron-
Catalyzed N-Formylation of Amines using Dihydrogen and Carbon
Dioxide. ACS Catal. 2018, 8, 1338−1345.
(37) Federsel, C.; Boddien, A.; Jackstell, R.; Jennerjahn, R.; Dyson,
P. J.; Scopelliti, R.; Laurenczy, G.; Beller, M. A Well-Defined Iron
Catalyst for the Reduction of Bicarbonates and Carbon Dioxide to
Formates, Alkyl Formates, and Formamides. Angew. Chem., Int. Ed.
2010, 49, 9777−9780.
(38) Daw, P.; Chakraborty, S.; Leitus, G.; Diskin-Posner, Y.; Ben-
David, Y.; Milstein, D. Selective N-Formylation of Amines with H2
and CO2 Catalyzed by Cobalt Pincer Complexes. ACS Catal. 2017, 7,
2500−2504.
(39) Federsel, C.; Ziebart, C.; Jackstell, R.; Baumann, W.; Beller, M.
Catalytic Hydrogenation of Carbon Dioxide and Bicarbonates with a
Well-Defined Cobalt Dihydrogen Complex. Chem. - Eur. J. 2012, 18,
72−75.
(16) Blondiaux, E.; Pouessel, J.; Cantat, T. Carbon Dioxide
Reduction to Methylamines under Metal-Free Conditions. Angew.
Chem., Int. Ed. 2014, 53, 12186−12190.
(17) Shintani, R.; Nozaki, K. Copper-Catalyzed Hydroboration of
Carbon Dioxide. Organometallics 2013, 32, 2459−2462.
(18) Farlow, M. W.; Adkins, H. The Hydrogenation of Carbon
Dioxide and a Correction of the Reported Synthesis of Urethans. J.
Am. Chem. Soc. 1935, 57, 2222−2223.
(19) Haynes, P.; Slaugh, L. H.; Kohnle, J. F. Formamides from
carbon dioxide, amines and hydrogen in the presence of metal
complexes. Tetrahedron Lett. 1970, 11, 365−368.
(20) Jessop, P. G.; Hsiao, Y.; Ikariya, T.; Noyori, R. Catalytic
Production of Dimethylformamide from Supercritical Carbon
Dioxide. J. Am. Chem. Soc. 1994, 116, 8851−8852.
(21) Jessop, P. G.; Hsiao, Y.; Ikariya, T.; Noyori, R. Homogeneous
Catalysis in Supercritical Fluids: Hydrogenation of Supercritical
Carbon Dioxide to Formic Acid, Alkyl Formates, and Formamides. J.
Am. Chem. Soc. 1996, 118, 344−355.
(22) Rezayee, N. M.; Huff, C. A.; Sanford, M. S. Tandem Amine and
Ruthenium-Catalyzed Hydrogenation of CO2 to Methanol. J. Am.
Chem. Soc. 2015, 137, 1028−1031.
(23) Zhang, L.; Han, Z.; Zhao, X.; Wang, Z.; Ding, K. Highly
Efficient Ruthenium-Catalyzed N-Formylation of Amines with H2 and
CO2. Angew. Chem., Int. Ed. 2015, 54, 6186−6189.
(24) Schmid, L.; Schneider, M. S.; Engel, D.; Baiker, A. Formylation
with ″Supercritical″ CO2: Efficient Ruthenium-Catalyzed Synthesis of
N-Formylmorpholine. Catal. Lett. 2003, 88, 105−113.
(25) Kudo, K.; Phala, H.; Sugita, N.; Takezaki, Y. Synthesis of
dimethyl formamide from carbon dioxide, hydrogen and dimethyl
amine catalyzed by palladium (II) chloride. Chem. Lett. 1977, 6,
1495−1496.
(26) Cui, X.; Zhang, Y.; Deng, Y.; Shi, F. Amine formylation via
carbon dioxide recycling catalyzed by a simple and efficient
heterogeneous palladium catalyst. Chem. Commun. 2014, 50, 189−
191.
(27) Zhang, Y.; Wang, H.; Yuan, H.; Shi, F. Hydroxyl Group-
Regulated Active Nano-Pd/C Catalyst Generation via in Situ
Reduction of Pd(NH3)xCly/C for N-Formylation of Amines with
CO2/H2. ACS Sustainable Chem. Eng. 2017, 5, 5758−5765.
(28) Luo, X.; Zhang, H.; Ke, Z.; Wu, C.; Guo, S.; Wu, Y.; Yu, B.; Liu,
Z. N-doped carbon supported Pd catalysts for N-formylation of
amines with CO2/H2. Sci. China: Chem. 2018, 61, 725.
(29) Zhang, Y.; Dai, X.; Wang, H.; Shi, F. Catalytic Synthesis of
Formamides with Carbon Dioxide and Amines. Acta Phys.-Chim. Sin.
2018, 34, 845−857.
(30) Bi, Q.-Y.; Lin, J.-D.; Liu, Y.-M.; Xie, S.-H.; He, H.-Y.; Cao, Y.
Partially reduced iridium oxide clusters dispersed on titania as efficient
catalysts for facile synthesis of dimethylformamide from CO2, H2 and
dimethylamine. Chem. Commun. 2014, 50, 9138−9140.
(31) Mitsudome, T.; Urayama, T.; Fujita, S.; Maeno, Z.; Mizugaki,
T.; Jitsukawa, K.; Kaneda, K. A Titanium Dioxide Supported Gold
Nanoparticle Catalyst for the Selective N-Formylation of Function-
alized Amines with Carbon Dioxide and Hydrogen. ChemCatChem
2017, 9, 3632−3636.
(40) Liu, H.; Mei, Q.; Xu, Q.; Song, J.; Liu, H.; Han, B. Synthesis of
formamides containing unsaturated groups by N-formylation of
amines using CO2 with H2. Green Chem. 2017, 19, 196−201.
(41) Kumar, S.; Jain, S. L. An efficient copper catalyzed formylation
of amines utilizing CO2 and hydrogen. RSC Adv. 2014, 4, 64277−
64279.
(42) Liu, J.; Guo, C.; Zhang, Z.; Jiang, T.; Liu, H.; Song, J.; Fan, H.;
Han, B. Synthesis of dimethylformamide from CO2, H2 and
dimethylamine over Cu/ZnO. Chem. Commun. 2010, 46, 5770−5772.
̈
(43) Auer, S. M.; Gredig, S. V.; Koppel, R. A.; Baiker, A. Synthesis of
methylamines from CO2, H2 and NH3 over Cu-Mg-Al mixed oxides. J.
Mol. Catal. A: Chem. 1999, 141, 193−203.
(44) Mai, D. T.; Le, T. D.; Nguyen, T. P.; Phan, N. M.; Nguyen, H.
A.; Nguyen, T. T. P.; Tran, L. Q. A new aldehyde compound from the
fruit of Pandanus tectorius Parkinson ex Du Roi. Nat. Prod. Res. 2015,
29, 1437−1441.
(45) Besson, M.; Gallezot, P.; Pinel, C. Conversion of Biomass into
Chemicals over Metal Catalysts. Chem. Rev. 2014, 114, 1827−1870.
(46) Zhou, C.-H.; Xia, X.; Lin, C.-X.; Tong, D.-S.; Beltramini, J.
Catalytic conversion of lignocellulosic biomass to fine chemicals and
fuels. Chem. Soc. Rev. 2011, 40, 5588−5617.
(47) Bozell, J. J.; Petersen, G. R. Technology development for the
production of biobased products from biorefinery carbohydrates-the
US Department of Energy’s ″Top 10″ revisited. Green Chem. 2010,
12, 539−554.
(48) Wu, X.-F.; Fang, X.; Wu, L.; Jackstell, R.; Neumann, H.; Beller,
M. Transition-Metal-Catalyzed Carbonylation Reactions of Olefins
and Alkynes: A Personal Account. Acc. Chem. Res. 2014, 47, 1041−
1053.
̈
(49) Franke, R.; Selent, D.; Borner, A. Applied Hydroformylation.
Chem. Rev. 2012, 112, 5675−5732.
(50) Beller, M.; Cornils, B.; Frohning, C. D.; Kohlpaintner, C. W.
Progress in hydroformylation and carbonylation. J. Mol. Catal. A:
Chem. 1995, 104, 17−85.
(51) Ke, Z.; Hao, L.; Gao, X.; Zhang, H.; Zhao, Y.; Yu, B.; Yang, Z.;
Chen, Y.; Liu, Z. Reductive Coupling of CO2, Primary Amine, and
Aldehyde at Room Temperature: A Versatile Approach to Unsym-
metrically N,N-Disubstituted Formamides. Chem. - Eur. J. 2017, 23,
9721−9725.
(32) Ju, P.; Chen, J.; Chen, A.; Chen, L.; Yu, Y. N-Formylation of
Amines with CO2 and H2 Using Pd-Au Bimetallic Catalysts
Supported on Polyaniline-Functionalized Carbon Nanotubes. ACS
Sustainable Chem. Eng. 2017, 5, 2516−2528.
(52) Liu, Z.; Yang, Z.; Yu, X.; Zhang, H.; Yu, B.; Zhao, Y.; Liu, Z.
Methylation of C(sp3)-H/C(sp2)−H Bonds with Methanol Catalyzed
by Cobalt System. Org. Lett. 2017, 19, 5228−5231.
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DOI: 10.1021/acs.orglett.8b02384
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