Tungstate catalysis: Pressure-switched 2- and 6-electron reductive functionalization of CO2 with amines and phenylsilane

Article abstract of DOI:10.1039/c7gc03416d

An efficient and environmentally benign tungstate catalyst for reductive functionalization of CO₂ with amines and phenylsilane was developed. By simply varying the pressure, 2-electron or 6-electron reduction of CO₂ was successfully achieved with simultaneous C-N bond formation, thus leading to the formation of formamides and methylamines, respectively. That is, secondary and primary amines furnished the corresponding methylamines or dimethylamines in excellent yields under atmospheric pressure of CO₂, while various formamides were formed in yields ranging from 52% to 98% when increasing the CO₂ pressure to 2 MPa. ¹H NMR studies and control experiments demonstrate that N-formylation proceeds through the formation of silyl formate, while N-methylation proceeds through an aminal intermediate generated by 4-electron reduction of CO₂.

Full text of DOI:10.1039/c7gc03416d

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: M. Wang, N.
Wang, X. Liu, C. Qiao and L. He, Green Chem., 2018, DOI: 10.1039/C7GC03416D.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 7
View Article Online
DOI: 10.1039/C7GC03416D
Green Chemistry
ARTICLE
Tungstate catalysis: pressure-switched 2- and 6- electron reductive
functionalization of CO2 with amines and phenylsilane †
Received 00th January 20xx,
Accepted 00th January 20xx
Mei-Yan Wang, Ning Wang, Xiao-Fang Liu, Chang Qiao and Liang-Nian He*
An efficient and environmentally benign tungstate catalysis for reductive functionalization of CO2 with amines and
phenylsilane was developed. By simply varying the pressure, 2-electron or 6-electron reduction of CO2 successfully
approached with simultaneous C-N bond formation, thus leading to the formation of formamides and methylamines,
respectively. That is, secondary and primary amines furnished the corresponding methylamines or dimethylamines in
excellent yields under atmospheric pressure of CO2, while various formamides were formed in yields ranging from 52% to
98% when increasing the CO2 pressure to 2 MPa. 1H NMR studies and control experiments demonstrate that the N-
formylation undergoes the formation of silyl formate while the N-methylation proceeds through an aminal intermediate
generated by 4-electron reduction of CO2.
DOI: 10.1039/x0xx00000x
www.rsc.org/
17
organic superbases,4b,
carbene,18 1,3,2-diazaphospholene,19
B(C6F5)3,20 cesium formate,21 ionic liquids,22 -valerolactone,23
γ
Introduction
DMSO24 as well as DMF25 have also been a research hotspot.
In 2014, Cantat et al. described the temperature-tuned reductive
functionalization of CO2 with amine catalyzed by Fe(acac)2 in
CO2 has been attracting much attention as an abundant,
nontoxic and renewable C1 building block.1 Many procedures
have been developed towards cost-effective chemical fixation
of CO2 to value-added chemicals via the construction of C–C,
C–N and C–O bond.2 In most of these processes, CO2 is only
functionalized but there is no reduction of the carbon atom and
therefore no significant energy storage. On the other hand,
extensive research efforts have also been devoted to CO2
reduction, which can achieve energy-related molecules such as
formic acid, methanol, methane or light alkanes.3 Even so, the
scope of chemicals directly available from CO2 remains very
narrow. To further expand the scope of CO2 recycling, novel
processes for CO2 conversion that combine both reduction of
CO2 and the formation of C–C, C–N or C–O bond, namely
reductive functionalization of CO2 by Cantat et al., were
explored.4 Notably, using amine as the functionalizing reagent,
the reductive functionalization of CO2 can output formamide
and methylamine derivatives, which are widely applied as
important solvent and intermediates in organic synthesis and
material science.5
combination
with
tris[2-(diphenylphosphino)ethyl]-
phosphine.10b Although the chemoselectivity is moderate, this
work represents the first example for reductive
functionalization of CO2 to respectively obtain methylamines
and formamides. By tuning the temperature, Dyson et al. also
realized the selective fixation of CO2 onto amines.18c Changing
both the temperature and the type of hydrosilane, the
methylation and formylation can proceed as well with Cs2CO3
N-
26
or TBAF27 as a catalyst. Recently, our group has achieved the
betaine-catalyzed hierarchical reduction of CO2 with amine and
hydrosilane by tuning the reaction temperature and the CO2
amount, giving products with various energy contents i.e.
formamide, aminal and methylamine.28 In spite of the above
few examples for selectively reductive functionalization of CO2
with amine, exploring catalytic system with distinctive
conditions to respectively form methylamine and formamide
appears to be pregnant. Especially, through regulating single
variable of reaction conditions, e.g. CO2 pressure, to control the
chemoselectivity would be interesting and challenging.
Among
the
established
methods
of
reductive
functionalization of CO2 with amine, transition metal catalytic
systems such as Ru,6 Rh,7 Re,8 Ir,9 Fe,10 Ni,11 Cu,12 Zn,13 Pd,14
Au15 and Pt16 have been employed using hydrosilane,
hydroborane or hydrogen as reductant. Organocatalysis such as
On the other hand, the oxygen atoms of tungstate have a high
charge density,29 we speculated the tungstate anion could
facilitate the hydrosilylation of CO2 via interacting with the Si
atom of hydrosilane to promote hydride transfer from
hydrosilane to CO2. In addition, the CO2 pressure may
influence the reductive level associated with CO2
30
hydrosilylation.28,
Understandably, high CO2 pressure
represents a high molar fraction of CO2, thus the hydrosilane
can be rapidly consumed up, thus the further reduction is
suppressed and terminated in the initial stage of forming silyl
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 7
View Article Online
DOI: 10.1039/C7GC03416D
ARTICLE
Journal Name
Table 1 Optimization for the selectively reductive functionalization of CO2 with 1a.a
formate. While a decrease in CO2 pressure may lower the
reaction rate of hydrosilane with CO2, thereby leading to further
reduction of the silyl formate by hydrosilane to bis(silyl)acetal
or silylmethoxide.31 As
a result, various products e.g.
formamide, aminal and methylamine may be generated in the
presence of an amine,7b, 21, 27, 28, 32 thus achieving selectively
reductive functionalization of CO2. Herein, we developed an
intriguing method using tungstate i.e. K2WO4 as efficient
catalyst for the 2-electron or 6-electron reduction of CO2 along
with C-N bond formation in the presence of amine and
phenylsilane (PhSiH3). Only by varying the CO2 pressure,
methylamine and formamide derivatives were attained
respectively, as shown in Scheme 1.
Yield of
Yield of
Entry
Cat./(mol%)
Conv./%b
2a/%b
–
3a/%b
1
2
3
–
0
0
0
–
0
0
Na3PW12O40(10)
Na6SiW12O40(10)
Na4SiW10O32(10)
Na2WO4(10)
K2WO4(10)
Li2WO4(10)
NiWO4(10)
0
0
4
11
>99
>99
6
0
7
5
90
99
0
7
6
0
7
5
8
0
0
0
9
CoWO4(10)
K2WO4(7.5)
K2WO4(5)
7
0
5
10
11
12
13c
14d
>99
>99
92
>99
>99
97
90
53
7
trace
8
K2WO4(2.5)
K2WO4(7.5)
K2WO4(7.5)
33
93
95
Scheme 1 Pressure-switched reductive functionalization of CO2 to respectively
form methylamine and formamide.
trace
a Reaction conditions: 1a (0.0535 g, 0.5 mmol), catalyst, PhSiH3 (248 ꢁL, 2
mmol), 1 bar CO2, CH3CN (2 mL), 70 K, 12 h. b Determined by GC using
Results and Discussion
d
1,3,5-trimethyoxybenzene as an internal standard. c 1.5 MPa CO2. 2 MPa
The experiment was initially explored at atmospheric pressure
CO2.
of CO2 using
N-methylaniline 1a as the substrate and 4
equivalents of PhSiH3 (relative to 1a) as the reductant in
acetonitrile. The reaction could hardly proceed without any
catalyst (Table 1, entry 1). Then several representative sodium
polyoxometalates and sodium tungstate were primarily
high chemoselectivity, even decreasing the amount of PhSiH3
to 1.5 mmol (Table S1, entries 10, 11, ESI†). While, inadequate
amount of PhSiH3 caused tremendous decrease in both yield
and the product selectivity (Table S1, entries 12, 13, ESI†),
perhaps because only one hydride of PhSiH3 plays the role in
reduction.
screened (entries 2-5). The methylated product i.e.
dimethylaniline (2a) was obtained in 90% yield along with
small amount of -methyl-formanilide (3a) when using sodium
N,Nꢀ
N
Having in hand the protocol for this kind of reductive
tungstate as catalyst, indicating that tungstate with a stronger
basicity29 is more efficient for the reductive functionalization of
functionalization of CO2, the generality of the
N-methylation
was firstly examined with 7.5 mol% of K2WO4 and 3
CO2 to methylamine (hereafter referred to as
N
-methylation)
o
equivalents of PhSiH3 in acetonitrile under 1 bar CO2 at 70 C
(entry 5 vs. 2-4). Then various tungstates with different counter
cations were further investigated (entries 6-9), of which
potassium tungstate (K2WO4) exhibited excellent catalytic
for 12 h, as shown in Table 2. Most of aromatic, heteroaromatic
and aliphatic amines were successfully methylated in excellent
yields. The para-substituted
electron donating or weak electron withdrawing groups are
active to produce the corresponding -dimethylanilines in
over 90% yields (entries 1-4). -alkyl anilines could be also
converted to methylamines efficiently (entries 5-8).
Particularly, -allyl aniline delivered -allyl- -methylaniline
N-methylanilines with either
activity towards the
N-methylation. This result illustrates that
the counter cation with lower electronegativity is more
favourable for the tungstate catalysis. Yields over 90% can still
be obtained when the amount of K2WO4 was reduced to 7.5
mol% (relative to 1a, entry 10). Further reducing the dosage of
K2WO4 gave a good conversion of 1a but caused a decrease in
the product selectivity (entries 11, 12). Subsequently, we tried
to validate our hypothesis that the reductive functionalization of
CO2 could be switched by adjusting the CO2 pressure on basis
of the methylated conditions. Delightedly, the formylated
product 3a was generated in 93% yield along with trace of 2a in
1.5 MPa CO2 (entry 13). Further raising the pressure of CO2 to
2 MPa, 3a was exclusively obtained in 95% yield (entry 14).
In addition, we also found that PhSiH3 was a more active
reductant than other hydrosilanes e.g. PMHS, Ph2SiH2 or
(EtO)3SiH (Table S1, entry 9 vs. 1-8, ESI†). The discriminatory
activity of various hydrosilanes may be ascribed to the different
N,N
N
N
N
N
without the reduction of the unsaturated bond (entry 5). This
catalysis also worked effectively with heterocyclic amines such
as 1,2,3,4-tetrahydroquinoline and morpholine (entries 9, 10).
While due to the weak nucleophilicity against the formation of
C-N bond, substrates with strong electron withdrawing groups,
e.g.
N-methyl-4-nitroaniline, are inert. Moreover, the reactivity
of diphenylamine is suppressed perhaps owing to the dual
effects of weak nucleophilicity and steric hindrance. In
addition, dimethylated products were obtained dominantly by
increasing the amount of PhSiH3 in the cases of primary
aromatic amines (entries 11-15).
electronic and steric effects.20 Moreover, both the
methylation and -formylation can still proceed efficiently with
N-
N
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 3 of 7
View Article Online
DOI: 10.1039/C7GC03416D
Journal Name
ARTICLE
Table 2 Substrate scope for the N-methylation.a
Table 3 Substrate scope for the N-formylation.a
Yield of 3/%b
Yield of
2/%b
Entry
Substrate
Product
Entry
Substrate
Product
1
2
3
4
X = H, 1a
X = Cl, 1b
X = H, 3a
X = Cl, 3b
94c
85
93
92
1
2
3
4
X = H, 1a
X = Cl, 1b
X = H, 2a
X = Cl, 2b
97c
90
97
92
X = CH3, 1c
X = OCH3, 1d
X = CH3, 3c
X = OCH3, 3d
X = CH3, 1c
X = OCH3, 1d
X = CH3, 2c
X = OCH3, 2d
5
6
7
8
R = Allyl, 1e
R = Et, 1f
R = iPr, 1g
R = Bn, 1h
R = Allyl, 2e
R = Et, 2f
R = iPr, 2g
R = Bn, 2h
94
89
92
99
5
6
7
8
9
R = Allyl, 1e
R = Et, 1f
R = Allyl, 3e
R = Et, 3f
81
90
R = iPr, 1g
R = Bn, 1h
R = Ph, 1p
R = iPr, 3g
R = Bn, 3h
R = Ph, 3p
76 (dr=31:5)
70
52
9
90
83
1i
10
2i
(dr=10.8:5)
1i
3i
10
90
1j
11
12
90
2j
1j
3j
98
(dr=4:3)
1q
3q
11d
12d
13d
14d
15d
X = H, 1k
X = Cl, 1l
X = H, 2a
X = Cl, 2b
41
63
42
45
45
a
Conditions: 1 (0.5 mmol), K2WO4 (0.0122 g, 7.5 mol%), PhSiH3 (186 ꢁL,
X = Br, 1m
X = CH3, 1n
X = OCH3, 1o
X = Br, 2m
X = CH3, 2c
X = OCH3, 2d
b
1.5 mmol ), 2 MPa CO2, CH3CN (2 mL), 70 K, 12 h. The yield was
determined by 1H NMR technique using 1,3,5-trimethyoxybenzene as an
internal standard. c Determined by GC using 1,3,5-trimethyoxybenzene as an
internal standard.
a
Unless otherwise specified, all of the reactions were performed with 1
(0.5 mmol), K2WO4 (0.0122 g, 7.5 mol%), PhSiH3 (186 ꢁL, 1.5 mmol ), 1
b
bar CO2, CH3CN (2 mL), 70 K, 12 h. The yield was determined by 1H
formate was obviously detected by NMR technique (Fig. S1,
ESI†), which is consistent with the reports by Liu22 and
Chung33. When 1a (0.5 mmol) was added into the above
reaction mixture, 3a was obtained in 90% yield with a reaction
time of 8 h. The above results confirmed that the CO2 is
reduced by PhSiH3 to silyl formate which subsequently reacts
with an amine to produce the formamide under 2 MPa CO2.
c
NMR technique using 1,3,5-trimethyoxybenzene as an internal standard.
Determined by GC using 1,3,5-trimethyoxybenzene as an internal
standard. d PhSiH3 (372 ꢁL, 3 mmol).
Subsequently, the utility of N-formylation was also explored by
tuning the pressure of CO2 to 2 MPa, as shown in Table 3. Most of
secondary aromatic amines were converted into the corresponding
formamides in good yields (entries 1-8). Unlike N-methylation,
diphenylamine can be formylated in 52% yield (entry 9), probably
because the intermediate of silyl formate in N-formylation has lower
steric hindrance than the N-methylation intermediate i.e.
bis(silyl)acetal (Scheme 2, intermediate II). Heterocyclic amines
1,2,3,4-tetrahydroquinoline and morpholine were transformed into
formamide derivatives efficiently as well (entries 10,11). N-benzyl-
N-methylformamide can also be obtained in 98% yield with aliphatic
N-methyl-1-phenylmethanamine as substrate (entry 12). However,
electron-deficient primary amines are not so nucleophilic enough to
trap the weak electrophilic silyl formate intermediate that the
primary amines become inert towards N-formylation.32c
That is to say, the
N-formylation undergoes a 2-electron
reduction of CO2 and then the C-N bond coupling, almost
simultaneously.
To gain insight into the mechanism of
N-methylation, the
reaction of atmospheric CO2 with 1a and PhSiH3 in deuterated
acetonitrile was studied by the 1H NMR technique. As shown in
Fig.1, in the first three hours of the reaction, a group of new
signals assigned to the intermediate emerged at
δ = 7.25, 6.84,
6.78, 4.77, 2.88 ppm (triangles in Fig. 1); meanwhile the signals
of 1a disappeared progressively. As the time went on, signals of
the intermediate gradually disappeared and 2a finally
generated. According to the analysis for the above 1H NMR
monitoring, we quenched the reaction after three hours with
large amount of acetonitrile, and then the intermediate was
To explore the reaction mechanism, a mixture of K2WO4
(0.0375 mmol), PhSiH3 (1.5 mmol) and CO2 (2 MPa) was
treated at 70 °C for 4 h in the absence of amine. The silyl
isolated by column chromatography, thus identified as
N,N'-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 7
View Article Online
DOI: 10.1039/C7GC03416D
ARTICLE
Journal Name
Scheme 2 Two possible pathways of aminal to methylamine.
dimethyl-
N
,
N'-diphenylmethanediamine
(aminal,
Fig.1,
compound III) by NMR and GC-MS (See the Supporting
Information).32c We used the aminal (0.5 mmol) replacing 1a to
CH3
N
a)
Ph
Ph
K2WO4 (7.5 mol%)
CH3
N
N
+
+
PhSiH3
CO2
2
CH3CN, 70 oC, 12 h
react with CO2 and PhSiH3 under the standard
conditions (Scheme 3, eq. a). As expected, 2a was obtained
quantitatively. As a result, the -methylation goes through the
formation of an aminal intermediate. It is also suggested that the
CO2 is reduced by hydrosilane in
-methylation to a C0 species, i.e.
bis(silyl)acetal which reacts with amine to generate the
aminal 31
N-methylation
CH3 CH3
Quantitative yield
N
b) Ph
c) Ph
Ph
K2WO4 (7.5 mol%)
CH3CN, 70 oC, 12 h
N
N
+
+
PhSiH3
PhSiH3
Ph3SiOH
+
N.R.
CH3 CH3
N
Ph
K2WO4 (7.5 mol%)
CH3CN, 70 oC, 12 h
N
N
N.R.
CH3 CH3
.
Furthermore, the transformation of aminal to methylamine
may occur via two possible pathways (Scheme 2). Path A: With
the silanol in situ formed as a proton donor, the aminal reacts
with hydrosilane to give methylamine and siloxane,
regenerating the amine substrate simultaneously. Path B: The
aminal is reduced by hydrosilane with the aid of bis(silyl)acetal,
giving methylamine, siloxane and aminosilylacetal derivative
(Scheme 2, intermediate IV) which is the precursor of aminal.
CHO
d)
e)
K2WO4 (7.5 mol%)
CH3CN, 70 oC, 12 h
N
PhSiH3
+
CO2
+
N.R.
CH3
3 equiv.
H
Ph2Si(OCH3)2
or
K2WO4(7.5 mol%)
CH3CN, 70 oC, 12 h
N
N.R.
CH3
+
+
CO2
CO2
+
PhSi(OCH3)3
3 equiv.
1
Because the H NMR peaks corresponding to the reactant 1a
O
f)
K2WO4(7.5 mol%)
CH3CN, 70 oC, 12 h
Ph
Ph
+
PhSiH3
3 equiv.
N
N
disappeared after 3 h (Fig. 1); and no reaction was observed for
aminal with PhSiH3 and triphenylsilanol catalyzed by K2WO4
(Scheme 3, eq. b), therefore the path A is ruled out. On the
other hand, there is no conversion of aminal and PhSiH3 in the
absence of CO2 (Scheme 3, eq. c), indicating that the reduction
of aminal to methylamine involves CO2 or the CO2 reductive
species, of which the bis(silyl)acetal is most likely. Accordingly,
the path B is reasonable. In addition, the formylamide,
N.R.
CH3 CH3
Scheme 3 Control experiments.
On basis of the above experimental results and previous
reports,28,30,31 a possible pathway for the present potassium
tungstate-promoted
functionalization of CO2 with amine and PhSiH3 was proposed,
as illustrated in Scheme 4. At 2 MPa CO2, the PhSiH3 is rapidly
and
pressure-switched
reductive
methoxysilanes and
N,N'-dimethyl-N,N'-diphenylurea can be
ruled out as the intermediate (Scheme 3, eq. d-f).
consumed up in the hydrosilylation of CO2 to form the silyl
30a
formate (
I
)
which reacts with amine to yield formamide.
While at atmospheric pressure of CO2, the rate of CO2
hydrosilation to silyl formate decreased and the silyl formate
can be further reduced by PhSiH3 to bis(silyl)acetal (II).30b The
further reduction of silyl formate to silylacetal has been also
demonstrated by Zhang in the research of N-heterocyclic carbene
catalyzed conversion of carbon dioxide with silanes.31 Subsequently,
nucleophilic attack of amine towards II delivers the
aminosilylacetal derivative
(
IV)
which is successively
converted into aminal (III). Then the aminal is further reduced
by PhSiH3 with the assistance of II, giving the methylated
product, siloxane and IV 28
The intermediate IV can be
.
regenerated to III. In the whole process, the tungstate may play
a vital role in the hydride transfer from hydrosilane to CO2 or
the reductive species via a nucleophilic interaction with the Si
atom of hydrosilane (Scheme S1). In short, the pressure of CO2
dominates the hierarchical reduction levels of CO2 i.e. the
formation of silyl formate at 2 MPa or bis(silyl)acetal at
atmospheric pressure, and successive generation of the aminal,
and thereby tunes the product selectivity i.e. formamide or
methylamine.
Fig. 1 1H NMR spectra for the methylation of 1a (0.0535 g, 0.5 mmol), PhSiH3 (186 ꢁL,
1.5 mmol) and CO2 (1 bar) in CD3CN.
R1R2NH
[SiOH]
H2
C
R1
[Si]O
O[Si]
R1
II
O
N
R2
O[Si]
+
N
+
[Si]
O
CH3
[Si]
[SiH]
R2
R1
R1
IV
path B
N
N
R2 R2
III
R1
N
R2
[SiH]
R1R2NH
CH3
+
[Si]
+
[Si]
[SiOH]
path A
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 5 of 7
View Article Online
DOI: 10.1039/C7GC03416D
Journal Name
ARTICLE
and yield were determined by GC or 1H NMR technique using
1,3,5-trimethyoxybenzene (40.0 mg) as an internal standard. The
reaction mixture was purified by column chromatography on silica
gel using petroleum ether/ethyl acetate as eluent to afford the
desired formylamide. All of the products were characterized by GC-
MS and NMR technique.
Conflicts of interest
The authors declare no conflicts of interest.
Scheme 4 Proposed pathways for the pressure-switched reductive functionalization of
CO2 with amine.
Acknowledgements
This work was financially supported by National Key Research
and Development Program (2016YFA0602900), National
Natural Science Foundation of China (21472103, 21421001,
21421062), and the Natural Science Foundation of Tianjin
(16JCZDJC39900).
Conclusions
In summary, we have found that tungstate, a kind of abundant
and environmentally benign inorganic salts, could efficiently
catalyze the reductive functionalization of CO2 with amine and
phenylsilane under mild conditions. Simply by tuning the
pressure of CO2, this protocol achieves the selective synthesis
References
1
Select examples and reviews on carbon dioxide as a C1
building block in organic synthesis: ( ) M. He, Y. Sun, B.
Han, Angew. Chem., Int. Ed., 2013, 52, 9620-9633; ( ) Q.
Liu, L. Wu, R. Jackstell and M. Beller, Nat. Commun., 2015,
6: 5933; ( ) K. Dong and X.-F. Wu, Angew. Chem., Int. Ed.
2017, 56, 5399-5401; ( ) M. Aresta, A. Dibenedetto and A.
Angelini, Chem. Rev., 2014, 114, 1709-1742; ( ) Q.-W. Song,
of formamides and methylamines. From
a mechanistic
a
standpoint, the pressure of CO2 controls the hierarchical
reduction levels of CO2, i.e. the formation of silyl formate at 20
bar or bis(silyl)acetal at atmospheric pressure, and successive
b
c
,
1
d
generation of the aminal. Through H NMR studies and control
e
experiments,
a
presumable pathway through the aminal
-methylation and the silyl formate for N-
Z.-H. Zhou and L.-N. He, Green Chem., 2017, 19, 3707-
3728.
intermediate for
N
formylation is demonstrated. Further studies on the reductive
functionalization of CO2 with amines, other nucleophiles and
various reductants are in progress in our laboratory.
2
For selected examples or reviews on chemical fixation of CO2
by forming C–C bond, see: (
Yoshino and M. W. Kanan, Nature, 2016, 531, 215-219; (
A.-H. Liu, B. Yu and L.-N. He, Greenhouse Gas Sci.
Technol., 2015, 5, 17-33. ( ) K. Sekine and T. Yamada,
Chem. Soc. Rev., 2016, 45, 4524-4532; for selected reviews
of chemical fixation of CO2 by forming C–N bond, see: (
Y. Li, X. Cui, K. Dong, K. Junge and M. Beller, ACS Catal.
2017, 7, 1077-1086; ( ) Z.-Z. Yang, L.-N. He, J. Gao, A.-H.
a) A. Banerjee, G. R. Dick, T.
b)
c
Experimental
d)
,
General procedure for the reductive functionalization of CO2
with amines to methylamines
Potassium tungstate (12.2 mg, 7.5 mol% relative to amine), amine
e
Liu and B. Yu, Energy Environ. Sci., 2012, 5, 6602-6639; for
selected examples and reviews on chemical fixation of CO2
(0.5 mmol), CH3CN (2 mL) and phenylsilane (186 ꢁL, 1.5 mmol)
by forming C–O bond, see: (
Fiorani, E. Martín, E. C. Escudero-Adán and A. W. Kleij,
Angew. Chem., Int. Ed., 2016, 55, 3972-3976; ( ) B.-H. Xu,
J.-Q. Wang, J. Sun, Y. Huang, J.-P. Zhang, X.-P. Zhang and
S.-J. Zhang, Green Chem., 2015, 17, 108-122; ( ) C. Martín,
G. Fiorani and A. W. Kleij, ACS Catal., 2015, 5, 1353-1370.
For selected reviews or examples on CO2 reduction, see: (
W. Wang, S. Wang, X. Ma and J. Gong, Chem. Soc. Rev.
2011, 40, 3703-3727; ( ) W.-H. Wang, Y. Himeda, J. T.
Muckerman, G. F. Manbeck and E. Fujita, Chem. Rev., 2015,
115, 12936-12973; ( ) S. Gao, Y. Lin, X. Jiao, Y. Sun, Q.
Luo, W. Zhang, D. Li, J. Yang and Y. Xie, Nature, 2015,
529, 68-71; ( ) J. Schneidewind, R. Adam, W. Baumann, R.
Jackstell and M. Beller, Angew. Chem., Int. Ed., 2017, 56,
1890-1893; ( ) A. Bordet, L.-M. Lacroix, P.-F. Fazzini, J.
Carrey, K. Soulantica and B. Chaudret, Angew. Chem., Int.
Ed., 2016, 55, 15894-15898; ( ) Y.-N. Li, R. Ma, L.-N. He
and Z.-F. Diao, Catal. Sci. Technol., 2014, 4, 1498-1512.
) C. Das Neves Gomes, O. Jacquet, C. Villiers, P. Thuéry,
M. Ephritikhine and T. Cantat, Angew. Chem., Int. Ed., 2012,
51, 187-190. ( ) A. Tlili, E. Blondiaux, X. Frogneux and T.
Cantat, Green Chem., 2015, 17, 157-168.
f) J. Rintjema, R. Epping, G.
was added successively into a 10 mL over-dried Schlenk tube
o
g
equipped with a stir-bar. The reaction mixture was stirred at 70 C
for 12 h under an atmosphere of CO2 (99.999%, balloon). Upon
h
1
completion, the conversion and yield were determined by GC or H
NMR technique using 1,3,5-trimethyoxybenzene (40.0 mg) as an
internal standard. The reaction mixture was purified by column
chromatography on silica gel using petroleum ether/ethyl acetate as
eluent to afford the corresponding methylamine. All of the products
were characterized by GC-MS and NMR technique.
General procedure for the reductive functionalization of CO2
with amines to formylamides
Potassium tungstate (12.2 mg, 7.5 mol% relative to amine), amine
3
a)
,
b
c
d
e
(0.5 mmol), CH3CN (2 mL) and phenylsilane (186 ꢁL, 1.5 mmol)
f
was added successively into a 10 mL (inner volumes) stainless steel
autoclave at room temperature. Then CO2 was charged into the
4
(a
o
reactor up to 2 MPa. The autoclave was heated at 70 C for 12 h.
o
b
Upon completion, the reactor was cooled to 0 C in ice-water bath
and carefully depressurized to atmospheric pressure. The conversion
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 7
View Article Online
DOI: 10.1039/C7GC03416D
ARTICLE
Journal Name
5
(
a
) S. Ding and N. Jiao, Angew. Chem., Int. Ed., 2012, 51,
9226-9237; ( ) D. K. Tosh, A. Janowsky, A. J. Eshleman, E.
Warnick, Z.-G. Gao, Z. Chen, E. Gizewski, J. A.
52, 2497-2500; (
Peng, Y.-H. Lin, Y.-P. Wang, W.-C. Shih, G. P. A. Yap and
T.-G. Ong, Angew. Chem., Int. Ed., 2015, 54, 15207-15212.
d
) W.-C. Chen, J.-S. Shen, T. Jurca, C.-J.
b
Auchampach, D. Salvemini and K. A. Jacobson, J. Med. 19 C. C. Chong and R. Kinjo, Angew. Chem., Int. Ed., 2015, 54,
Chem., 2017, 60, 3109-3123. 12116-12120.
) O. Krocher, R. A. Koppel and A. Baiker, Chem. 20 Z. Z. Yang, B. Yu, H. Y. Zhang, Y. F. Zhao, G. P. Ji, Z. S.
6
(a
Commun., 1997, 453-454; (
Junge and M. Beller, Angew. Chem., Int. Ed., 2013, 52,
12156-12160; (
and W. Leitner, Angew. Chem., Int. Ed., 2013, 52, 9554-
9557; ( ) Y. Li, X. Fang, K. Junge and M. Beller, Angew. 22 L. D. Hao, Y. F. Zhao, B. Yu, Z. Z. Yang, H. Y. Zhang, B. X.
Chem., Int. Ed., 2013, 52, 9568-9571; (
b) Y. Li, I. Sorribes, T. Yan, K.
Ma, X. Gao and Z. M. Liu, Green. Chem., 2015, 17, 4189-
4193.
c
) K. Beydoun, T. vom Stein, J. Klankermayer 21 X.-F. Liu, C. Qiao, X.-Y. Li and L.-N. He, Green Chem.
,
2017, 19, 1726-1731.
d
e
) L. Zhang, Z. Han,
Han, X. Gao and Z. M. Liu, ACS Catal., 2015, 5, 4989-4993.
23 J. Song, B. Zhou, H. Liu, C. Xie, Q. Meng, Z. Zhang and B.
Han, Green Chem., 2016, 18, 3956-3961.
X. Zhao, Z. Wang and K. Ding, Angew. Chem., Int. Ed.
2015, 54, 6186-6189.
,
7
8
(
a
) T. V. Q. Nguyen, W.-J. Yoo and S. Kobayashi, Angew. 24 H. Lv, Q. Xing, C. Yue, Z. Lei and F. Li, Chem. Commun.
Chem., Int. Ed., 2015, 54, 9209-9212; ( ) S. Itagaki, K. 2016, 52, 6545-6548.
) H. Niu, L. Lu, R. Shi, C.-W. Chiang, A. Lei, Chem.
Commun., 2017, 53, 1148-1151; ( ) T. X. Zhao, G. W. Zhai,
,
b
Yamaguchi and N. Mizuno, J. Mol. Catal. A: Chem., 2013, 25 (
366, 347-352.
a
b
(a
) D. S. Morris, C. Weetman, J. T. C. Wennmacher, M.
Cokoja, M. Drees, F. E. Kuhn and J. B. Love, Catal. Sci.
Technol, 2017, 7, 2838-2845. (
Siddiki, Y. Morita, T. Kamachi, A. S. Touchy, W. Onodera,
K. Kon, S. Furukawa, H. Ariga, K. Asakura, K. Yoshizawa 27 X.-F. Liu, R. Ma, C. Qiao, H. Cao and L.-N. He, Chem. Eur.
and K. Shimizu, Chem. Eur. J., 2017, 23, 14848-14859. J., 2016, 22, 16489-16493.
) Q.-Y. Bi, J.-D. Lin, Y.-M. Liu, S.-H. Xie, H.-Y. He and 28 X.-F. Liu, X.-Y. Li, C. Qiao, H.-C. Fu and L.-N. He, Angew.
Y. Cao, Chem. Commun., 2014, 50, 9138-9140. ( ) K. Park, Chem., Int. Ed., 2017, 56, 7425-7429.
G. H. Gunasekar , N. Prakash, K.-D. Jung and S. Yoon, 29 T. Kimura, K. Kamata and N. Mizuno, Angew. Chem., Int.
ChemSusChem, 2015, 8, 3410-3413. Ed., 2012, 51, 6700-6703.
10 ( ) C. Federsel, A. Boddien, R. Jackstell, R. Jennerjahn, P. J. 30 ( ) S. N. Riduan, J. Y. Ying and Y. Zhang, ChemCatChem
Dyson, R. Scopelliti, G. Laurenczy and M. Beller, Angew. 2013, 5, 1490-1496; ( ) Z. Z. Yang, B. Yu, H. Y. Zhang, Y.
Chem., Int. Ed., 2010, 49, 9777-9780; ( ) X. Frogneux, O.
Jacquet and T. Cantat, Catal. Sci. Technol., 2014, 4, 1529-
1533; (
J. Liang, P. Li, X. B. Hu and Y. T. Wu, Chem. Commun.
,
2017, 53, 8046-8049.
b
) T. Toyao, S. M. A. H. 26 C. Fang, C. Lu, M. Liu, Y. Zhu, Y. Fu and B.-L. Lin, ACS
Catal., 2016, 6, 7876-7881.
9
(a
b
a
a
,
b
b
F. Zhao, G. P. Ji and Z. M. Liu, RSC Adv., 2015, 5, 19613-
19619.
c
) U. Jayarathne, N. Hazari and W. H. Bernskoetter, 31 S. N. Riduan, Y. Zhang and J. Y. Ying, Angew. Chem., Int.
ACS Catal., 2018, 8, 1338-1345.
11 L. González-Sebastián, M. Flores-Alamo and J. J. García, 32 (
Organometallics, 2015, 34, 763-769.
Ed., 2009, 48, 3322-3325.
) G. Jin, C. G. Werncke, Y. Escudié, S. Sabo-Etienne and S.
Bontemps, J. Am. Chem. Soc., 2015, 137, 9563-9566; ( ) O.
Jacquet, C. Das Neves Gomes, M. Ephritikhine, T. Cantat,
ChemCatChem, 2013, 5, 117-120. ( ) X. Frogneux, E.
a
b
12 (
Yamaguchi, A. Miyaji and T. Baba, Cataly. Sci. Technol.
2013, 3, 2392-2396; R. Shintani and K. Nozaki,
Organometallics, 2013, 32, 2459-2462; ( ) S. Zhang, Q. Mei,
a) K. Motokura, N. Takahashi, D. Kashiwame, S.
,
c
(
b
)
Blondiaux, P. Thuery and T. Cantat, ACS Catal., 2015, 5,
3983-3987.
c
H. Liu, H. Liu, Z. Zhang and B. Han, RSC Adv., 2016, 6, 33 S. Chun, S. Yang and Y. K. Chung, Tetrahedron, 2017, 73,
32370-32373; ( ) O. Santoro, F. Lazreg, Y. Minenkov, L. 3438-3442.
Cavallo and C. S. J. Cazin, Dalton Trans., 2015, 44, 18138-
18144; ( ) X. Cui, X. Dai, Y. Zhang, Y. Deng and F. Shi,
Chem. Sci., 2014, 5, 649-655.
13 ( ) R. Luo, X. Lin, Y. Chen, W. Zhang, X. Zhou and H. Ji,
ChemSusChem, 2017, 10, 1224-1232; ( ) R. Luo, Y. Chen,
d
e
a
b
Q. He, X. Lin, Q. Xu, X. He, W. Zhang, X. Zhou and H. Ji,
ChemSusChem, 2017, 10, 1526-1533.
14 (
Bhaumik and S. M. Islam, ChemCatchem, 2017, 9, 1939-
1946; ( ) X. Cui, Y. Zhang, Y. Deng and F. Shi, Chem.
Commun., 2014, 50, 13521-13524.
15 ( ) X.-L. Du, G. Tang, H.-L. Bao, Z. Jiang, X.-H. Zhong, D.
S. Su and J.-Q. Wang, ChemSusChem, 2015, 8, 3489-3496;
) T. Mitsudome, T. Urayama, S. Fujita, Z. Maeno, T.
Mizugaki, K. Jitsukawa and K. Kaneda, ChemCatchem, 2017,
9, 3632-3636; ( ) G. Tang, H.-L. Bao, C. Jin, X.-H. Zhong
a) R. A. Molla, P. Bhanja, K. Ghosh, S. S. Islam, A.
b
a
(b
c
and X.-L. Du, RSC Advances, 2015, 5, 99678-99687.
16 K. Kon, S. M. A. H. Siddiki, W. Onodera and K.-i. Shimizu,
Chem. Eur. J., 2014, 20, 6264-6267.
17 E. Blondiaux, J. Pouessel and T. Cantat, Angew. Chem., Int.
Ed., 2014, 53, 12186-12190.
18 (
Cantat, J. Am. Chem. Soc., 2012, 134, 2934-2937; (
F. D. Bobbink, G. Laurenczy, P. J. Dyson, Angew. Chem., Int.
Ed., 2014, 53, 12876-12879; ( ) S. Das, F. D. Bobbink, S.
a
) O. Jacquet, C. Das Neves Gomes, M. Ephritikhine and T.
b
) S. Das,
c
Bulut, M. Soudani and P. J. Dyson, Chem. Commun., 2016,
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
Green Chemistry
View Article Online
DOI: 10.1039/C7GC03416D
TOC Graphic
A tungstate catalysis for reductive functionalization of CO2 with amines and phenylsilane is
successfully developed by simply varying the pressure to respectively form formamides and
methylamines.