Catalytic synthesis of silyl formates with 1 atm of CO2 and their utilization for synthesis of formyl compounds and formic acid

Article abstract of DOI:10.1016/j.molcata.2012.10.014

In the presence of simple Rh₂(OAc)₄ and K ₂CO₃, the hydrosilylation of CO₂ (1 atm) with various hydrosilanes efficiently proceeded to afford the corresponding silyl formates in moderate to high yields (53-90% yields). By using the dimethylphenylsilyl formate produced by the hydrosilylation, formamides, formic acid, and a secondary alcohol (via an aldehyde) could be synthesized by the reaction with various nucleophilic reagents such as amines, aniline, water, and the Grignard reagent.

Full text of DOI:10.1016/j.molcata.2012.10.014

Journal of Molecular Catalysis A: Chemical 366 (2013) 347–352
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Catalytic synthesis of silyl formates with 1 atm of CO2 and their utilization for
synthesis of formyl compounds and formic acid
Shintaro Itagaki, Kazuya Yamaguchi, Noritaka Mizuno∗
Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2012
Received in revised form 12 October 2012
Accepted 15 October 2012
Available online 24 October 2012
In the presence of simple Rh2(OAc)4 and K2CO3, the hydrosilylation of CO2 (1 atm) with various hydrosi-
lanes efficiently proceeded to afford the corresponding silyl formates in moderate to high yields (53–90%
yields). By using the dimethylphenylsilyl formate produced by the hydrosilylation, formamides, formic
acid, and a secondary alcohol (via an aldehyde) could be synthesized by the reaction with various nucleo-
philic reagents such as amines, aniline, water, and the Grignard reagent.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Carbon dioxide
Hydrosilane
Hydrosilylation
Silyl formate
Rhodium acetate
Bases
1. Introduction
of formamides from amines, hydrosilanes, and CO2 using nitrogen
bases or N-heterocyclic carbenes in 1 atm of CO2 [28,29]. In con-
Although energy from fossil fuels makes an invaluable con-
tribution to the quality of our lives, we are now facing serious
environmental problems, e.g., global warming caused by CO2 from
(over)use of fossil fuels. The increased concern for such serious
problems has put pressure on the society to reduce and reuse CO2.
The catalytic transformation of CO2 as a renewable C1 building
block is an attractive alternative [1–4]. To date, several procedures
for the transformation of CO2 have been reported. For example, (i)
chemical fixation of CO2 promoted by reactive substrates such as
epoxides, alcohols, amines, and alkynes to form new C O, C N,
and C C bonds has been achieved by using several transition
metal, acid, and/or base catalysts [5–8] and (ii) CO2 has chemically,
electrochemically, or photo-electrochemically been reduced to
useful C1 chemicals such as formic acid, formaldehyde, methanol,
methane, and CO [9–11].
Hydrosilanes are readily available, easy-to-handle, nontoxic,
and inexpensive reducing agents [12,13], and the reduction of CO2
with hydrosilanes to produce silyl formates [14–21], formaldehyde
[22], methoxysilanes [23–25], and methane [26,27] is thermo-
dynamically favorable. In particular, methoxysilanes [23–25] and
methane [26] have been obtained in 1 atm of CO2. Moreover, Can-
tat and co-workers have recently reported the direct synthesis
trast, conventional synthesis of formamides by the reduction of CO2
with H2 requires high temperatures (≥75 ◦C) and high pressures
(≥60 atm) [30–40].
Among the above-mentioned CO2 reduction products, silyl for-
mates are one of the most attractive compounds because they can
potentially be utilized as valuable synthons, which will provide
new routes for synthesis of a wide range of value-added chemi-
cals from CO2. For example, silyl formates can be converted into
formic acid by simple hydrolysis [41,42]. In addition, it is expected
that silyl formates can be regarded as “formyl synthons” due to
their strong Si O bonds and that various kinds of carbonyl com-
pounds can possibly be synthesized by the reaction with the
corresponding nucleophiles. However, the synthesis of silyl for-
mates from CO2 itself generally requires high pressure of CO2
(≥3 atm) (Table S1) [14–20]. In contrast, Sattler and Parkin quite
recently realized the hydrosilylation of 1 atm of CO2 using [Tris(2-
pyridylthio)methyl]zinc hydride [21]. In addition, Motokura et al.
recently reported that the in situ-prepared Cu(I)-hydride complex
can act as an efficient homogeneous catalyst for the reduction of
CO2 (1 atm) with hydrosilanes and that silyl formates are interme-
diates for the reduction [42].
In this paper, we report two important findings. Firstly, we
demonstrate that the hydrosilylation of CO2 can be realized in
1 atm of CO2 using simple Rh2(OAc)4 (OAc = acetate) and inor-
ganic bases (Scheme 1). Secondly, we report the utilization of
silyl formates for synthesis of various carbonyl compounds, that
∗
Corresponding author. Tel.: +81 3 5841 7272; fax: +81 3 5841 7220.
E-mail address: tmizuno@mail.ecc.u-tokyo.ac.jp (N. Mizuno).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.10.014

348
S. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 347–352
O
was completed, acetonitrile was removed by evaporation, followed
by addition of n-hexane (2 mL). Catalysts (Rh2(OAc)4 and K2CO3)
were insoluble in n-hexane and separated by filtration. Then, 4e
(1 mmol) was added to the filtrate, and the mixture was vigor-
ously stirred at 50 ◦C for 1 h. n-Hexane was evaporated, and white
precipitates obtained were washed with n-hexane and extracted
with toluene. Evaporation of toluene afforded analytically pure N-
benzylformamide (5e, 35% yield).
R2N
H
R2NH
O
O
O
OH
Ar
Rh2(OAc)4
ArMgBr
ArMgBr
R3Si−H + CO2
R3Si
O
H
Ar
Ar
H
H
1 atm
H2O
HO
Scheme 1. Synthesis of silyl formates and their utilization.
2.4. Procedure for synthesis of formic acid
After the hydrosilylation of CO2 with 1a was completed, water
(5 mmol) was added to the reaction solution of 2a and the reac-
tion mixture was vigorously stirred at room temperature for 0.5 h.
The conversion and the yield of the products were determined
by GC and 1H NMR analyses. Formic acid was confirmed by the
comparison of its HPLC retention time and 1H and 13C NMR spec-
tra. A procedure for isolation of formic acid is as follows: After
the hydrosilylation of CO2 with 1a was completed, acetonitrile
was removed by evaporation, followed by addition of n-hexane
(2 mL). Catalysts (Rh2(OAc)4 and K2CO3) were insoluble in n-
hexane and separated by filtration. Then, water (5 mmol) was
added to the filtrate, and the mixture was vigorously stirred at 50 ◦C
for 0.5 h. Formic acid was extracted with water (0.91 mL) and fur-
ther washed with n-hexane, affording an aqueous solution of formic
acid (0.66 M).
is, a one-pot synthesis of various carbonyl compounds from CO2
through hydrosilylation followed by reactions with various nucleo-
philes such as amines, water, and the Grignard reagent (Scheme 1).
2. Experimental
2.1. General
GC analyses were performed on Shimadzu GC-2014 with a
FID detector equipped with a TC-5 capillary column. Mass spec-
tra were recorded on Shimadzu GCMS-QP2010 equipped with
an InertCap 5 MS/Sil capillary column at an ionization voltage
of 70 eV. Liquid-state NMR spectra were recorded on JEOL JNM-
EX-270. HPLC analyses (for determination of formic acid) were
performed on a Shimadzu Prominence system with a RID detector
(Shimadzu RID 10A) equipped with a Shodex RSpak KC-811 column
(8.0 mm ID × 300 mm length). 1H and 13C NMR spectra were mea-
sured at 270 and 67.8 MHz, respectively. Rh2(OAc)4 was obtained
from Wako Pure Chemical Industries (Cat. No. 180-01151) and
used as received. Other metal salts and complexes, bases, and the
Grignard reagents of phenylmagnesium bromide (PhMgBr) were
obtained from Wako Pure Chemical Industries, Kanto Chemical, TCI,
or Aldrich (reagent grade) and used as received. Hydrosilanes and
amines were obtained from TCI and purified by distillation with
CaH2 before the use. Acetonitrile was purified by The Ultimate Sol-
vent System (Glass Contour Company) [43]. Other solvents were
obtained from Wako Pure Chemical Industries and Kanto Chemi-
cal. All hydrosilanes and solvents were stored over molecular sieve
3A 1/16 (Kanto Chemical), which was pretreated at 300 ◦C under
vacuum [44], and handled in a glove box under Ar (O2 < 1.0 ppm,
H2O < 1.0 ppm).
2.5. Procedure for synthesis of benzhydrol
The reaction mixture of 2a was evaporated, followed by the
addition of THF (1 mL) in a glove box under Ar. Then, the THF solu-
tion of PhMgBr (1.10 M, 2 mL) was added to the THF solution of 2a.
After being stirred at room temperature for 1 h, the resulting mix-
ture was quenched by the addition of H2O (0.5 mL). The conversion
and the yield of the products were determined by GC analysis. The
products were confirmed by the comparison of their GC retention
times and GC mass spectra. Benzhydrol was isolated by a similar
procedure to that for formamides.
3. Results and discussion
3.1. Effects of metal catalysts, bases, and solvents on the
hydrosilylation of CO2 with dimethylphenylsilane
2.2. Typical procedure for hydrosilylation of CO2
Initially, the hydrosilylation of CO2 with 1a was carried out
in the presence of catalytic amounts of various metal salts
(e.g., Rh2(OAc)4, AgOAc, Pd(OAc)2, Cu(OAc)2·H2O, Ru(acac)3
(acac = acetylacetonato), Pt(acac)2, AuBr3, IrCl3·H2O, 0.5 mol%)
and K2CO3 (0.5 mol%) (Table 1). No reaction proceeded in the
absence of metal salts. Among the metal salts examined, only
Rh2(OAc)4 showed the high catalytic activity and selectivity for the
hydrosilylation; for example, when the hydrosilylation was carried
out with Rh2(OAc)4 and K2CO3 under the conditions described in
Table 1, the corresponding silyl formate 2a was obtained in 90%
yield (Table 1, entry 1). In this case, the turnover frequency was
90 h−1, and the turnover number reached up to 180 (see Table S1
for comparison). Other rhodium complexes such as [RhCl2Cp*]2
(Cp* = pentamethylcyclopentadienyl), [Rh(cod)Cl]2 (cod = 1,5-
cyclooctadiene), and Rh(PPh3)3Cl (PPh3 = triphenylphosphine)
were almost inactive (Table 2), while these complexes are
reported to be active for dehydrosilylation of alcohols [45] and
hydrosilylation of alkenes and alkynes [46,47].
Into
a Schlenk tube (volume: 40 mL) were successively
placed Rh2(OAc)4 (0.25 mol%), K2CO3 (0.5 mol%), internal standard
(biphenyl), and a Teflon-coated magnetic stir bar. In a glove
box under Ar, dimethylphenylsilane (1a, 1 mmol) and acetoni-
trile (2 mL) were added. Then, the Ar gas in the Schlenk tube
was replaced with 1 atm of CO2, and the mixture was vigorously
stirred at 50 ◦C for 2 h. The conversion and the yield of the products
were determined by GC analysis. The silyl formates were identi-
fied by means of GC mass and 1H and 13C NMR (see the Supporting
Information).
2.3. Typical procedure for formylation of amines
After the hydrosilylation of CO2 with 1a was completed,
piperidine (4a, 1 mmol) was added to the reaction solution of
dimethylphenylsilyl formate (2a) and the reaction mixture was vig-
orously stirred at 50 ◦C for 1 h. The conversion and the yield of the
products were determined by GC and 1H NMR analyses. The for-
mamides were confirmed by the comparison of their GC retention
times and GC mass spectra. A typical procedure for isolation of for-
mamides is as follows: After the hydrosilylation of CO2 with 1a
As shown in Table 3, kinds of bases were also crucial for the
hydrosilylation of CO2 with 1a. Inorganic O-donor bases such as
K2CO3, Cs2CO3, K3PO4, and KOt-Bu (t-Bu = tert-butyl) were suit-
able for the present Rh2(OAc)4-catalyzed hydrosilylation, while

S. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 347–352
349
Table 1
Hydrosilylation of CO2 with 1a using various metal salts.a
Table 3
Hydrosilylation of CO2 with 1a using various bases.a
Entry
Catalyst
Conv. (%)
Yield (%)
Entry
Catalyst
Conv. (%)
Yield (%)
2a
3a
2a
3a
1
2
3
4
5
6
7
8
9
Rh2(OAc)4
AgOAc
>99
90
nd
<1
nd
<1
nd
nd
5
8
1
2
3
4
5
6
7
K2CO3
Cs2CO3
K3PO4
KOt-Bu
DBU
>99
90
90
77
81
4
8
8
23
13
11
3
1
22
6
4
12
6
nd
10
4
2
4
6
5
nd
>99
>99
94
15
3
Pd(OAc)2
Cu(OAc)2·H2O
Ru(acac)3
Pt(acac)2
AuBr3
Et3N
None
nd
nd
<1
nd
IrCl3·nH2O
18
1
a
Reaction conditions: Rh2(OAc)4 (0.25 mol%), base (0.5 mol%), 1a (1 mmol), CH3CN
(2 mL), CO2 (1 atm), 50 ◦C, 2 h. Conversions and yields were based on 1a and deter-
mined by GC analysis using biphenyl as an internal standard. nd = not detected.
3a = 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane.
None
nd
a
Reaction conditions: Catalyst (metal: 0.5 mol%), K2CO3 (0.5 mol%), 1a (1 mmol),
CH3CN (2 mL), CO2 (1 atm), 50 ◦C, 2 h. Conversions and yields were based on 1a and
determined by GC analysis using biphenyl as an internal standard. nd = not detected.
3a = 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane.
Table 4
Effect of solvents on the hydrosilylation of CO2 with 1a.a
Table 2
Entry
Solvent
Conv. (%)
Yield (%)
Hydrosilylation of CO2 with 1a using various Rh-based catalysts.a
2a
3a
Entry
Catalyst
Conv. (%)
Yield (%)
1
2
3
4
5
6
CH3CN
Acetone
1,4-Dioxane
THF
1,2-Dichloroethane
n-Hexane
>99
90
35
nd
nd
nd
nd
8
6
<1
<1
<1
nd
2a
3a
43b
<1
<1
<1
<1
1
2
3
4
5
6
7
Rh2(OAc)4
>99
90
<1
<1
nd
8
8
2
5
2
6
RhCl3·nH2O
[RhCl2Cp*]2
[Rh(cod)Cl]2
Rh(PPh3)3Cl
[Rh(CO)2Cl]2
Rh6(CO)16
7
10
5
16
3
a
Reaction conditions: Rh2(OAc)4 (0.25 mol%), K2CO3 (0.5 mol%), 1a (1 mmol), sol-
vent (2 mL), CO2 (1 atm), 50 ◦C, 2 h. Conversions and yields were based on 1a and
determined by GC analysis using biphenyl as an internal standard. nd = not detected.
3a = 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane.
nd
nd
<1
<1
2
a
Reaction conditions: Catalyst (metal: 0.5 mol%), base (0.5 mol%), 1a (1 mmol),
CH3CN (2 mL), CO2 (1 atm), 50 ◦C, 2 h. Conversions and yields were based on 1a and
determined by GC analysis using biphenyl as an internal standard. nd = not detected.
3a = 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane.
b
The hydrosilylation of acetone proceeded (2% yield).
obtained in moderate to high yields (53–90% yields, except for tri-
isopropylsilane, 1h). The transformation of dimethylphenylsilane
derivatives (1a–1d) with electron-donating as well as electron-
withdrawing para-substituents efficiently proceeded to attain high
yields of the corresponding substituted silyl formates for 2 h
(84–90% yields, Table 5, entries 1–4), though the reactivities were
slightly different. The catalytic activity of Rh2(OAc)4/K2CO3 for
the hydrosilylation of CO2 with dimethylphenylsilane derivatives
(1a–1c) increased in the order of 1b (p-OMe, 0.78) < 1a (p-H,
1.00) < 1c (p-Cl, 1.67), where the values in the parentheses are
the conversion ratios for competitive hydrosilylation (at 50 ◦C for
30 min), and the conversion of 1a is taken as unity. This order sug-
gests formation of a negatively charged transition state. The steric
effect of substrates was very significant. The hydrosilylation with
relatively bulky hydrosilanes such as diphenylmethylsilane (1e),
organic N-donor bases such as triethylamine (Et3N) and 1,8-
diazabicyclo[5.4.0]undec-7-ene (DBU) were not effective (Table 3).
Among the solvents examined, acetonitrile was the best solvent for
the present hydrosilylation (Table 4). Therefore, the hydrosilylation
reactions were hereafter carried out with Rh2(OAc)4 and K2CO3 in
acetonitrile.
3.2. Hydrosilylation of CO2 with various hydrosilanes
Next, the scope of the present Rh2(OAc)4-catalyzed hydrosily-
lation of CO2 (1 atm) was investigated for a range of structurally
diverse hydrosilanes (Table 5). The reaction efficiently proceeded
even in 1 atm of CO2, and the corresponding silyl formates were
Table 5
Transformation of various silanes to silyl formates using Rh2(OAc)4 and K2CO3.a
Rh2(OAc)4
K2CO3
O
R3SiH
+
CO2
+
R3SiOSiR3
R3Si
O
2
H
1 atm
1
3
Entry
Substrate
Temp. [◦C]
Time [h]
Conv. [%]
Yield [%]
2
3
1
2
3
4
5
6
7
8
X = H
X = OMe
X = Cl
1a
1b
1c
1d
1e
1f
50
50
50
50
50
70
70
80
2
2
2
>99
97
>99
>99
99
88
>94
<1
90
84
85
87
83
53
72
nd
8
Me
Si
Me
13
12
13
11
ndb
10
nd
X
H
X = CF3
2
Ph2MeSiH
Ph3SiH
Et3SiH
24
24
12
24
1g
1h
i-Pr3SiH
a
Reaction conditions: Rh2(OAc)4 (0.25 mol%), K2CO3 (0.5 mol%), silane (1 mmol), CH3CN (2 mL), CO2 (1 atm). Conversions and yields were based on silanes and determined
by GC analysis using biphenyl as an internal standard. nd = not detected.
b
The corresponding disiloxane (3f) was possibly formed but could not be detected by GC because of the low solubility in any solvents.

350
S. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 347–352
Table 6
One-pot synthesis of formamides from CO2, 1a, and nucleophiles (amines and aniline).a
O
i)
ii)
Products
PhMe2SiH
+
CO2
PhMe2Si
O
H
1 atm
1a
2a
Entry
1
Nucleophile
Time (h)
Products (yield (%))
O
H
N
O
N
H
HO
H
1
4
(43%)
4a
5a (43%)
O
O
n-Bu2N
H
HO
H
2
n-Bu2NH
4b
(50%)
5b (40%)
O
O
N
H
N
H
HO
H
3
4
5
1
1
1
4c
(40%)
5c (47%)
O
O
n-OctyINH2
OctylHN
H
HO
H
4d
(45%)
5d (46%)
O
O
NH2
N
H
H
HO
H
4e
(47%)
5e (41%)
O
Cl
O
Cl
NH2
N
H
H
HO
H
6
7
1
(45%)
4f
5f (43%)
O
NH2
O
N
H
H
MeO
HO
H
1.5
18
MeO
(47%)
4g
NH2
5g (40%)
H
O
N
H
HO
H
8
O
(33%)
4h
5h (34%)
a
Reaction conditions: (i) Rh2(OAc)4 (0.25 mol%), K2CO3 (0.5 mol%), 1a (1 mmol), CH3CN (2 mL), CO2 (1 atm), 50 ◦C, 2 h; (ii) nucleophile (1 mmol), 50 ◦C. Yields were based
on 1a and determined by GC and 1H NMR analyses. Consequently, 1a was quantitatively converted into 3a in all cases.
triphenylsilane (1f), and triethylsilane (1g) required longer reac-
tion times and/or a higher reaction temperature (70 ◦C) to attain the
corresponding silyl formates in moderate to high yields (84–90%
yields, Table 5, entries 5–7). The reaction with 1h hardly proceeded
likely due to the steric hindrance of the isopropyl groups (Table 5,
entry 8).
after the hydrosilylation of CO2 with 1a was completed. Various
kinds of nucleophilic reagents such as common amines, aniline,
water, and the Grignard reagent could be utilized to produce the
corresponding formyl compounds and/or formic acid.
In the case of common amines and aniline, a silyl formate 2a
could act as a “formyl synthon” to produce the corresponding
formamides with co-production of formic acid (Table 6). We con-
firmed that formic acid is co-produced through the reactions in
Scheme 2.
3.3. Reaction of dimethylphenylsilyl formate with various
nucleophilic reagents
It is noted that the reaction of amines with “methyl formate”
hardly proceeded under the conditions described in Table 6 [48].
Various kinds of amines could be utilized as nucleophiles, and
total yields of formamides (5a–5g) and formic acid based on 1a
were high in all cases (86–91% yields). Secondary amines including
aliphatic (4a and 4b) and benzylic (4c) ones could be converted
Finally, we turned out our attention to the reaction of the silyl
formate (2a, produced through the hydrosilylation of CO2) with
various nucleophilic reagents. The overall conversion of CO2 to car-
bonyl compounds was accomplished as a one-pot procedure by a
simple addition of nucleophilic reagents to the reaction solution

S. Itagaki et al. / Journal of Molecular Catalysis A: Chemical 366 (2013) 347–352
351
O
O
O
value-added products. The reaction of the silyl formate with amines
(including aniline) produced the corresponding formamides and
formic acid. Water and the Grignard reagent could also be utilized
as nucleophilic reagents to react with the silyl formate, produc-
ing formic acid and the corresponding secondary alcohol (via an
aldehyde), respectively.
PhMe2SiOH
PhMe2Si
+
+
+
RR’NH
O
O
H
H
RR'N
H
5
2a
4
O
PhMe2SiOH
+
(PhMe2Si)2O
3a
PhMe2Si
2a
HO
H
Acknowledgment
Scheme 2. The reaction of 2a with amines to produce formamides and formic acid.
This work was supported in part by Grants-in-Aid for Scientific
Researches from Ministry of Education, Culture, Sports, Science and
Technology.
O
O
water
PhMe2Si
PhMe2SiH
+
CO2
O
H
HO
H
1 atm
Appendix A. Supplementary data
1a
2a
90% yield
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.molcata.2012.10.014.
Scheme 3. Synthesis of formic acid from 1a, CO2, and water. After the hydrosily-
lation of CO2 with 1a under the conditions described in Table 1 was completed,
water (5 mmol) was added to the reaction solution, and then the mixture was
stirred at room temperature for 0.5 h. Consequently, 1a was mainly converted into
dimethylphenylsilanol (77% yield based on 1a).
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O
OH
Ph
77% yield
PhMgBr
PhMe2Si
PhMe2SiH
+
CO2
O
H
Ph
1 atm
1a
2a
Scheme 4. Synthesis of benzhydrol from 1a, CO2, and PhMgBr. After the hydrosily-
lation of CO2 with 1a under the conditions described in Table 1 was completed, the
solvent was removed by evaporation, followed by the addition of THF (1 mL). Then,
the THF solution of PhMgBr (1.10 M, 2 mL) was added to the reaction mixture and
stirred at room temperature for 1 h. Consequently, 1a was mainly converted into
dimethylphenylsilanol (84% yield based on 1a).
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1–3). An aliphatic primary amine (4d) also gave the corresponding
N-alkyl formamide (Table 6, entry 4). In the case of primary ben-
zylic amines (4e–4g), the electronic effect of substituents was not
significant, and the formylation efficiently proceeded, giving the
corresponding formamides (Table 6, entries 5–7). The formylation
of relatively less nucleophilic aniline (4h) also proceeded to give N-
phenylformamide, while a longer reaction time (18 h) was required
in comparison with common amines (1–4 h) (Table 6, entry 8).
Besides amines and aniline, water could act as a nucleophile
[41,42]; the addition of water to the solution containing 2a yielded
formic acid in 90% yield (Scheme 3). The reaction of 2a with the
Grignard reagent produced the corresponding secondary alcohol,
while the Grignard reaction of CO2 generally produces the cor-
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equivalents of the Grignard reagent of PhMgBr was carried out, ben-
zhydrol was obtained in 77% yield (Scheme 4). In this case, a silyl
formate 2a would also act as a formyl synthon to form benzalde-
hyde, and then the successive addition of PhMgBr to benzaldehyde
proceeds to give benzhydrol as a final product.
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