Reductive transformation of CO2: Fluoride-catalyzed reactions with waste silicon-based reducing agents

Article abstract of DOI:10.1016/S1872-2067(17)62800-6

CO₂ is one of the most important “renewable” carbon sources. To transform CO₂ to useful organic compounds, we examined the reactivity of two model silicon-based “waste” materials, disilanes and metallic Si powder, as reducing agents. In these reactions, fluoride salts were found to be active catalysts: CO₂ was converted to formic acid at atmospheric pressure in the presence of H₂O as a proton source and the silicon-based reducing reagents. Based on in-situ NMR and kinetics analyses, a hydrosilane and penta-coordinate Si species are proposed as the reaction intermediate and active species, respectively.

Full text of DOI:10.1016/S1872-2067(17)62800-6

Chinese Journal of Catalysis 38 (2017) 434–439
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article (Special Column on Novel Catalysts for Energy and Environmental Issues)
Reductive transformation of CO2: Fluoride‐catalyzed reactions with
waste silicon‐based reducing agents
Ken Motokura, Masaki Naijo, Sho Yamaguchi, Akimitsu Miyaji, Toshihide Baba*
Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta‐cho,
Midori‐ku, Yokohama, 226‐8502, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
CO2 is one of the most important “renewable” carbon sources. To transform CO2 to useful organic
compounds, we examined the reactivity of two model silicon‐based “waste” materials, disilanes and
metallic Si powder, as reducing agents. In these reactions, fluoride salts were found to be active
catalysts: CO2 was converted to formic acid at atmospheric pressure in the presence of H2O as a
proton source and the silicon‐based reducing reagents. Based on in‐situ NMR and kinetics analyses,
a hydrosilane and penta‐coordinate Si species are proposed as the reaction intermediate and active
species, respectively.
Received 27 September 2016
Accepted 20 October 2016
Published 5 March 2017
Keywords:
Carbon dioxide
Fluoride
Homogeneous catalysis
Formic acid
Disilane
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
polydimethylsiloxane (PDMS), is produced from metallic sili‐
con, along with several byproducts containing Si–Si bonds, in‐
The reductive transformation of CO2 to useful compounds
represents a chemical process that would be ideal, and quite
desirable from an environmental perspective [1–4]. However,
because of its strong C–O bonds, this task is always energeti‐
cally “uphill” and requires the input of energy to proceed [5].
Consequently, in the transformation of CO2 to derivative chem‐
icals and/or fuels, significantly more energy and/or fuel is
consumed to promote the reductive reaction. To overcome this
problem and balance the process economics, we considered
lowering the cost of the reducing agents by using “waste” ma‐
terials based on silicon, as shown on the right side of Fig. 1.
The “waste” reducing agents can be obtained as byproducts
from the silicone process or from used solar cells (Fig. 1). In the
silicone process, the most widely used silicon‐based polymer,
cluding disilanes and polysilanes [6]. These “waste” compounds
contain Si–Si chemical bonds which can potentially act as re‐
ducing agents in chemical reactions. Similarly, versatile solar
cells can usually contain as much as 2 wt% metallic silicon that
can also act as a reductant [7], therefore, used solar panels con‐
stitute another possible source of a “waste” reducing agent.
Further, because of the increasing demand of solar cells, the
projected generation rate of waste solar panels in Japan in
2036 is 800000 tons/year [7].
We envisaged that a general solution for the “uphill task” of
CO2 transformation could be realized by the use of such waste
silicon‐based reducing agents. Our preliminary results indicat‐
ed that the fluoride‐catalyzed reaction of a model disilane with
H2O afforded a hydrosilane which reacted with CO2 to give for‐
* Corresponding author. E‐mail: tbaba@chemenv.titech.ac.jp
This work was supported by JSPS KAKENHI (15H04182), JSPS Grant‐in‐Aid for Scientific Research on Innovative Areas “3D Active‐Site Science
(26105003)”, “Precisely Designed Catalysts with Customized Scaffolding (16H01010)”, and Grant for Challenging Research Award, Tokyo Institute of
Technology.
DOI: 10.1016/S1872‐2067(17)62800‐6 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 3, March 2017

Ken Motokura et al. / Chinese Journal of Catalysis 38 (2017) 434–439
435
To a glass reactor equipped with a CO2 balloon was added
TBAF‐3H2O (0.05 mmol), Si powder (0.50 mmol), water (10
mmol), and DMA (2 mL). The resulting reaction mixture was
stirred vigorously at 95 °C for 24 h. The reaction residue was
filtered, and the residue was analyzed by X‐ray photoelectron
spectroscopy (XPS, vide infra) after vacuum drying at room
temperature. The reaction products in the filtrate were con‐
firmed by the comparison of their GC‐MS spectra and 1H NMR
spectra with those of authentic samples. The yields were de‐
termined by the internal standard technique using a CDCl3 so‐
lution of the reaction mixture and mesitylene or triiso‐
propylbenzene as the internal standard.
Fig. 1. CO2 transformation process using “waste” silicon‐based reducing
agents.
mic acid [8–11]. In this case, the fluoride anion was effective for
both Si–Si bond breaking and the activation of the Si–H bond
for the reduction of CO2, because fluoride anion has a high af‐
finity for Si [12,13]. In this paper, we fully investigate the reac‐
tions between CO2 and a disilane or metallic Si as model silicon
waste compounds and potential CO2 reducing agents.
2.4. Characterization
To a glass reactor equipped with an Ar balloon was added
KF (0.50 mmol), dimethyltetraphenyldisilane (0.55 mmol),
2.2.2‐cryptand (0.50 mmol), and DMSO‐d6 (1.5 mL). The re‐
sulting reaction mixture was stirred at room temperature for
10 min, and then transferred to an NMR tube under Ar. After
2. Experimental
1
the H and 19F NMR measurements (Fig. 4(a) and (b)), 13CO2
was introduced into the NMR tube. Then, further 1H NMR
measurements were acquired (Fig. 4(c)).
2.1. General methods
XPS analyses were performed on an ESCA1700R system
equipped with a dual Mg/Al X‐ray source and a hemispherical
analyzer operating in the fixed analyzer transmission mode.
Spectra were obtained using a pass energy of 58.7 eV, and the
Al Kα X‐ray source was operated at 350 W and 14 kV. Excess
charges on the samples were neutralized by argon ion sputter‐
ing. The analysis area was 0.8 × 2 mm2. The working pressure
in the analysis chamber was less than 1 × 10−7 Pa. Spectra were
acquired in the O 1s, C 1s, and Si 2p regions. The C 1s peak at a
binding energy (BE) of 285 eV was taken as an internal refer‐
ence.
1
The H, 13C, and 19F NMR spectra were recorded in CDCl3
using a Bruker AVANCE 400 spectrometer operating at 400,
100.61, and 376.5 MHz, respectively. A Shimadzu QP2010 in‐
strument equipped with a DB‐1 column was used for the GC‐MS
analyses.
Tetrabutylammonium fluoride trihydrate (TBAF‐3H2O,
>99%) was purchased from Arcos Organics. 13CO2 (13C 99%,
18O <1%) was purchased from Cambridge Isotope Laboratories.
CDCl3 (>99.8%) was purchased from Kanto Kagaku Co. Dime‐
thylacetamide (DMA, dehydrated, >99%) was purchased from
Kanto Kagaku Co. and used without further purification. Si
powder was purchased from Wako Chemicals (Si, 99.9%). Un‐
less otherwise noted, all the other materials were purchased
from Wako Pure Chemicals, Tokyo Kasei Co., Kanto Kagaku Co.,
and Aldrich Inc. Fluoride salts were used without any further
pretreatment such as dehydration. Catalytic experiments were
set up under an oxygen‐free atmosphere using standard
Schlenk techniques.
3. Results and discussion
3.1. Optimization of reaction conditions
We began our investigation of this reductive transformation
of CO2 by using tetrabutylammonium fluoride trihydrate
(TBAF‐3H2O), 1,2‐dimethyl‐1,1,2,2‐tetraphenyldisilane (dis‐
ilane), and DMSO as the catalyst, disilane, and solvent, respec‐
tively. Combining these reagents and H2O under a balloon of
CO2 at 80 °C overnight afforded 0.13 mmol formate per 0.5
mmol disilane used, an 92% conversion of the disilane and
26% yield overall (Table 1, entry 1). Other fluoride salts, such
as KHF2 and KF, also showed catalytic activity for the reaction
of disilane, however, the product yields were lower than TBAF
as a catalyst (Table 1, entries 2 and 3) [8]. The product was not
obtained without fluoride salt (Table 1, entry 5).
2.2. Typical procedure for formic acid synthesis form CO2, H2O,
and disilane
To a glass reactor equipped with a CO2 balloon was added
TBAF‐3H2O (0.05 mmol), dimethyltetraphenyldisilane (0.50
mmol), water (2.4 mmol), and DMA (1 mL). The resulting reac‐
tion mixture was stirred vigorously at 80 °C for 24 h. The
products were confirmed by the comparison of their GC‐MS
1
spectra and H NMR spectra with those of authentic samples.
As shown in Table 1, entry 6, no formate product was ob‐
tained without disilane, indicating that disilane is necessary for
the reductive transformation. To confirm the conversion of CO2
and H2O to the formic acid product, isotopic experiments were
conducted [8]. The use of 13CO2 instead of 12CO2 afforded formic
acid with >99% 13C incorporation (Scheme 1) [8]. This fact
The yields were determined by the internal standard technique
using a CDCl3 solution of the reaction mixture and mesitylene
or triisopropylbenzene as the internal standard.
2.3. Typical procedure for formic acid synthesis form CO2, H2O,
and Si powder

436
Ken Motokura et al. / Chinese Journal of Catalysis 38 (2017) 434–439
Table 1
Formic acid synthesis from CO2 and H2O with (Ph2MeSi)2 with various
fluorides.
0.2
0.1
Conversion
Entry Fluoride Salt of disilane
(%)
HCOOH
produceda
(mmol)
0.13
0.11
0.07
0.04
<0.00
<0.00
HCOOH yield based
on disilane a
(%)
26
22
15
8
1
TBAF‐3H2O
KHF2
92
94
91
93
2
2
3
KF
0
2
4
6
8
10
4
CsF
H2O / mmol
5
6 b
None
<1
<1
TBAF‐3H2O
<1
Fig. 2. Optimization of the amount of H2O. Reaction conditions: dime‐
thyltetraphenyldisilane (0.50 mmol), CO2 (1 atm, balloon), H2O (2.35
mmol), TBAF·3H2O (0.05 mmol), DMA (1.0 mL), 80 °C, 24 h.
Reaction conditions: 1,2‐dimethyl‐1,1,2,2‐tetraphenyldisilane (0.50
mmol), CO2 (1 atm, balloon), H2O (0.50 mmol), fluoride salt (0.05 mmol),
DMSO (1.0 mL), 80 °C, 24 h.
a This value contains formic acid salt. b Without disilane.
solvents, such as DMF and DMSO, show good results compared
with nonpolar solvents. In the case of alcohol solvents, the
strong interaction between hydroxyl group and fluoride anion
may inhibit the catalytic reaction.
clearly indicates the transformation of CO2 to formic acid and
the formate salt. The use of D2O instead of H2O gave deuterated
formic acid, as shown in Scheme 2 [8]. No deuterium incorpo‐
ration into the co‐produced disiloxane was observed. These
results strongly support that the atoms in the formic acid
product were originated from CO2 and H2O. The relatively low‐
er content of deuterium (80%) compared with 13C may be due
to hydrated water of TBAF and proton release from DMSO sol‐
vent under acidic conditions [14].
Since H2O is the key substrate molecule for the fomic acid
production, the amount of H2O was optimized. The amount of
formate products were plotted against the amount of H2O, as
shown in Fig. 2. Addition of 2.4 mmol of H2O to the reaction
mixture containing 0.50 and 0.05 mmol of the disilane and
TBAF afforded the highest amount of product. Further increas‐
ing of H2O did not give good results, and this may be due to the
decreasing solubility of the organic disilane compound.
3.2. Reaction mechanism and active species
To elucidate the reaction pathway, the transformation of
CO2 was monitored over time, as shown in Fig. 3. After 5 min,
similar amounts of hydrosilane and fluorosilane are obtained;
thereafter, the amount of hydrosilane decreases with increas‐
ing formic acid formation. These results indicate the following
two phenomena. First, the reaction of the disilane, H2O, and the
fluoride salt affords a hydrosilane, fluorosilane, and hydroxide
anion (Eq. (1)). The detection of deuterated hydrosilane
(PhMe2Si‐D) during the reaction using D2O (Scheme 2) also
indicate the reaction step (Eq. (1)). Second, the hydrosilane
intermediate is converted into a silanol (or disiloxane) and
Table 2
Next, the effect of solvent on the yield of formic acid was in‐
vestigated. The results are summarized in Table 2. In the case
of the reaction using 2.4 mmol of H2O and 1.0 mL of DMA, the
highest product yield of 44% was achieved (Table 2, entry 1).
Formate products are also obtained in other aprotic polar sol‐
vents such as 1,4‐dioxane and acetonitrile (Table 2, entries 3
and 4), although the products are scarcely formed in nonpolar
solvents or alcohols (Table 2, entries 7–10). It can be consid‐
ered that due to the high solubility of CO2, the aprotic nonpolar
Formic acid synthesis from CO2 and H2O with (Ph2MeSi)2 in various
solvents.
Temper‐ Conversion
HCOOH
HCOOH yield
based on
disilane a (%)
Entry Solvent
ature
(°C)
80
of disilane produced a
(%)
80
>99
96
54
88
14
18
10
<1
2
(mmol)
0.22
0.17
0.07
0.05
0.03
0.03
<0.01
<0.01
<0.01
<0.01
1
2
3
4
5
6
7
8
9
10
DMA
DMSO
44
33
14
10
6
80
80
1,4‐dioxane
Acetonitrile
THF
80
60
Acetone
Hexane
50
50
6
Scheme 1. Transformation of 13CO2 to formic acid.
<1
<1
<1
<1
Chloroform
Ethanol
1‐propanol
60
70
80
Reaction conditions: 1,2‐dimethyl‐1,1,2,2‐tetraphenyldisilane (0.50
mmol), CO2 (1 atm, balloon), H2O (2.4 mmol), TBAF·3H2O (0.05 mmol),
solvent (1.0 mL), 24 h.
Scheme 2. Transformation of CO2 to formic acid in the presence of D2O.
a This value contains formic acid salt.

Ken Motokura et al. / Chinese Journal of Catalysis 38 (2017) 434–439
437
▲:
●:
0.2
0.1
▼:
◆:
Scheme 4. Proposed reaction pathway for fluoride‐catalyzed formic
acid formation.
0
100
200
Time / min.
Ph
Ph
Si Si
Ph
Fig. 3. Time course of the transformation of CO2 to formic acid with
disilane. (Red) Formic acid; (green) disiloxane; (black) fluorosilane ;
(blue) hydrosilane. Reaction conditions: dimethyltetraphenyldisilane
(0.50 mmol), CO2 (1 atm, balloon), H2O (2.50 mmol), TBAF‐3H2O (0.05
mmol), DMA (2.0 mL), 80 °C.
[2.2.2] cryptand
+
KF
+
+
H2O
Ph
(0.50 mmol) (0.50 mmol)
(0.50 mmol)
Ph
F Si
Ph
(i)
Ph
F
+
Si H
Ph
(ca. 0.03 mmol)
formic acid in the presence of CO2 (Eq. (2)) [15]. It should be
noted that the silyl formate, i.e., the hydrosilylation product of
CO2, was not detected during formic acid formation. This sug‐
gests that the formate salt directly reacts with H2O to give the
formic acid product.
CH3
[K [2.2.2] cryptand]
(ca. 0.02 mmol)
(ii) 13CO2, H2O
O
13C
+
disiloxane
H
OK
(ca. 0.02 mmol)
Scheme 5. Stepwise experiments for (i) penta‐coordinate silicate for‐
mation and (ii) reduction of CO2 to formic acid salt.
To investigate the regeneration pathway of the fluoride cat‐
alyst, the reaction of the disilane, fluorosilane, and cesium hy‐
droxide under CO2 atmosphere was examined. In this case, the
formate product was obtained, although no product was
formed in the absence of cesium hydroxide (Scheme 3) [8]. The
results indicate that the fluoride anion is regenerated by the
reaction between the fluorosilane and hydroxide anion. A pro‐
posed overall catalytic reaction pathway is shown in Scheme 4.
We next conducted an in‐situ NMR study to determine the
catalytically active fluoride species. To increase the concentra‐
tion of the active species, KF and 2.2.2‐cryptand were reacted
with dimethyltetraphenyldisilane (Scheme 5). In the absence of
CO2, the formation of a penta‐coordinate silicate with two fluo‐
1
rides was detected by 19F and H NMR, along with a similar
amount of hydrosilane (Fig. 4(a) and (b), Scheme 5(i)) [16]. The
hydrosilane might be formed from a small quantity of adventi‐
tious H2O. The structure of the penta‐coordinate silicate was
also confirmed by 1H‐19F HOESY NMR (Fig. 5). Then, 13CO2 and
Ph
Ph
Si Si
Ph
O
C
Reagent(s)
disiloxane
+
+
+
CO2
H2O
H
OX
DMSO (2 mL)
80 oC, 24 h
Ph
(1 atm)
(2.5 mmol)
(0.50 mmol)
Yield
Yield (%)
18
Reagent (s)
Ph
F
Si
Ph
CsOH-H2O
+
<1
<1
Ph
Si
Ph
F
Fig. 4. 19F (a) and 1H NMR (b) spectra of penta‐coordinate silicate spe‐
cies and 1H NMR spectrum (c) after the treatment with 13CO2 and H2O.
(a): Ph2SiMeF2 (−82.9 ppm, q, J1H‐19F = 9.5 Hz); (b) a: Ph2SiMeF2 (0 ppm,
t, J1H‐19F = 9.5Hz, 3H), b: Ph2SiMeF2 (7.7 ppm, m, 2H), c, d: Ph2SiMeF2
(7.0 ppm, m, 3H), Ph2MeSiH (4.8 ppm, q, J = 3.9Hz, 1H); (c) H13C(O)OK
(8.4 ppm, d, J1H‐13C = 181Hz, 1H).
CsOH‐H2O
Fluorosilane (0.06 mmol), CsOH‐H2O (0.06 mmol).


Scheme 3. Control experiments using fluorosilane and/or cesium hy‐
droxide.

438
Ken Motokura et al. / Chinese Journal of Catalysis 38 (2017) 434–439
Table 3
Formic acid synthesis from CO2 and H2O with Me6Si2.
Conversion
HCOOH
HCOOH yield
Entry
Catalyst
of disilane produced *
based on
(%)
67
35
(mmol)
0.06
0.01
disilane * (%)
1
2
3
TBAF‐3H2O
KF
KF + [2.2.2] cryptand
12
2
7
57
0.04
Reaction conditions: hexamethyldisilane (0.50 mmol), CO2 (1 atm, bal‐
loon), H2O (2.5 mmol), fluoride salt (0.05 mmol), DMSO (1.0 mL), 80 °C,
24 h. *This value contains formic acid salt.
Table 4
Formic acid synthesis from CO2 and H2O using Si powder.
Fig. 5. 1H‐19F HOESY spectrum of the reaction mixture after the reaction
of KF, [2.2.2] cryptand, and disilane. Reaction conditions: dimethyl‐
tetraphenyldisilane (0.55 mmol), KF (0.50 mmol), [2.2.2] cryptand
(0.50 mmol), DMSO‐d6 (1.5 mL), room temperature, 10 min.
H2Oa
(mmol)
10
5.0
2.5
2.5
2.5
10
10
2.5
110 b
Temp. HCOOH produced a
Entry
Catalyst
(°C)
95
95
95
80
50
95
95
80
95
(mmol)
0.10
0.08
0.08
0.06
<0.01
<0.01
0.03
<0.01
0.008
1
2
3
4
5
6
7
8
9
TBAF‐3H2O
TBAF‐3H2O
TBAF‐3H2O
TBAF‐3H2O
TBAF‐3H2O
KF
1
H2O were added to the NMR sample tube. H NMR analysis
revealed that the hydrosilane signal disappeared, with the for‐
mation of a doublet at 8.4 ppm corresponding to the 13C‐labeled
formic acid salt (J = 181 Hz) (Fig. 4(c), Scheme 5(ii)). These
results strongly support not only a reaction pathway that in‐
cludes the formation of the hydrosilane, as mentioned above
(Scheme 4), but also the possible active species: the pen‐
ta‐coordinate silicate.
KF + [2.2.2] cryptand
none
TBAF‐3H2O
Reaction conditions: silicon powder (0.5 mmol), CO2 (1 atm, balloon),
H2O, catalyst (0.05 mmol), DMA (2 mL), 24 h. a This value contains hy‐
drated water in TBAF‐3H2O. b H2O was used as solvent instead of DMA.
3.3. Application for reaction using hexamethydisilane and
metallic silicon
sents the Si 2p XPS spectra of fresh Si powder and the reaction
residue after the reaction with CO2. After the reaction, the sur‐
face of the metallic Si was nearly completely oxidized to SiO2,
The reductive transformation of CO2 with hexamethyl‐
disilane, a possibly produced disilane as a waste compound
from silicone industry [5], was examined using DMA solvent
and fluoride salts. The results are summarized in Table 3. The
reaction with TBAF catalyst, the 14% yield of formic acid was
obtained (Table 3, entry 1). The reaction scarcely proceeded
with KF, however, the addition of [2.2.2] cryptand enhanced
product yield to 7% (Table 3, entry 3).
The good catalytic activity of the fluoride salt for the reduc‐
tive transformation of CO2 with the disilane encouraged us to
examine the reduction of CO2 with metallic Si powder as a re‐
ducing agent. The optimization of the reaction conditions is
shown in Table 4. Interestingly, the reaction of 0.50 mmol Si
powder with 10 mmol H2O under the action of the TBAF cata‐
lyst afforded 0.10 mmol formic acid and its salt (Table 4, entry
1). Decreases in the amount of H2O or reaction temperature
resulted in decreased product yields (Table 4, entries 2–5). The
combination of KF and [2.2.2] cryptand induced slightly better
results (Table 4, entry 7) compared with KF alone (Table 4,
entry 6), whereas the TBAF produced much better yields. The
use of H2O as solvent instead of DMA also afforded a small
amount of formic acid product (Table 4, entry 9). Fig. 6 pre‐
Si0
Si4+
Fig. 6. XPS spectra of Si powder (a) and reaction residue (b).

Ken Motokura et al. / Chinese Journal of Catalysis 38 (2017) 434–439
439
Graphical Abstract
Chin. J. Catal., 2017, 38: 434–439 doi: 10.1016/S1872‐2067(17)62800‐6
Reductive transformation of CO2: Fluoride‐catalyzed reactions
with waste silicon‐based reducing agents
Ken Motokura, Masaki Naijo, Sho Yamaguchi, Akimitsu Miyaji,
Toshihide Baba*
Tokyo Institute of Technology, Japan
Fluoride‐catalyzed transformation of CO2 to formic acid was ex‐
amined using “waste” Si‐based materials, disilane and metallic Si
powder, as reducing agents.
[5] X. Z. Lim, Nature, 2015, 526, 628–630.
suggesting that metallic Si also acts as an effective reducing
agent toward CO2 in the presence of a fluoride catalyst.
[6] W. Kalchauer, B. Pachaly, in: G. Ertl, H. Knozinger, F. Schuth, J.
Weitkamp eds., Handbook of Heterogeneous Catalysis, 2nd Ed.,
Wiley‐VCH, Weinheim, 2008, 2635–2647.
[7] Website of the Ministry of the Environment, Government of Japan:
http://www.env.go.jp/press/101130.html; http://www.env.go.jp
/press/files/jp/27519s.pdf (page 25 and 31) (accessed April
2016).
[8] K. Motokura, M. Naijo, S. Yamaguchi, A. Miyaji, T. Baba, Chem. Lett.,
2015, 44, 1464–1466.
[9] E. Shirakawa, H. Otsuka, T. Hayashi, Chem. Commun., 2005,
5885–5886.
[10] E. Shirakawa, K. Hironaka, H. Otsuka, T. Hayashi, Chem. Commun.,
2006, 3927–3929.
[11] C. Gryparis, M. Stratakis, Chem. Commun., 2012, 48, 10751–10753.
[12] T. Hiyama, M. Obayashi, I. Mori, H. Nozaki, J. Org. Chem., 1983, 48,
912–914.
4. Conclusions
Model compounds of silicon waste, disilane and metallic Si,
were found to be effective reducing agents for CO2 in the pres‐
ence of fluoride catalysts. In the case of disilane, the yield of
formic acid was as high 44% based on the disilane used.
Time‐course and in‐situ NMR experiments revealed the reac‐
tion pathway and possible active species. A catalytic CO2 recy‐
cling process using waste silicon‐based reducing agents has the
potential to be one of the most effective solutions toward envi‐
ronmentally‐friendly society.
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