B(C6F5)3-catalyzed methylation of amines using CO2 as a C1 building block

Article abstract of DOI:10.1039/c5gc01386k

B(C₆F₅)₃ was proven to be an efficient metal-free catalyst for the methylation of amines using CO₂ as a C1 building block in the presence of hydrosilanes under easy-handling conditions. A broad range of N-alkylanilines, dialkylamines and primary anilines all proceeded well under the catalytic conditions.

Full text of DOI:10.1039/c5gc01386k

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B(C6F5)3-catalyzed methylation of amines using
CO2 as a C1 building block
Cite this: DOI: 10.1039/x0xx00000x
Zhenzhen Yang, Bo Yu, Hongye Zhang, Yanfei Zhao, GuipengJi,
Zhishuang Ma, Xiang Gao and Zhimin Liu*
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
B(C6F5)3 was proved to be an efficient metal-free catalyst for However, these catalytic systems all needed to be manipulated
the methylation of amines using CO2 as a C1 building block under inert atmosphere. Hence, the development of new efficient
in the presence of hydrosilanes under easy-handling and chemoselective catalysts, especially metalꢀfree systems for
conditions. A broad scope of N-alkylanilines, dialkylamines the methylation of amines employing CO2 as a C1 source under
and primary anilines all proceeded well under the catalytic easyꢀhandling reaction conditions still remains desirable.
conditions.
Reduction with SiꢀH compounds is an important method in
synthetic organic chemistry because of the mild reaction
conditions compared to established classic methods.12 The
activation of silanes by boron Lewis acids, especially B(C6F5)3
and its derivatives, is developed as a powerful metalꢀfree
approach for the hydrosilylation of various carbonyl compounds13
and later imine functions.14 B(C6F5)3 and related electrophilic
boranes feature the ability to activate not only SiꢀH bonds (90
kcal/mol), but also the stronger HꢀH bond (108 kcal/mol)
heterolytically together with electronꢀdonors of high steric
hindrance (now referred to as frustrated Lewis pair (FLP)
chemistry), thereby allowing for metalꢀfree hydrogenation.2c, 14 As
one component of FLP, B(C6F5)3 together with bulk
phosphines/amines were shown to catalyze stoichiometric or
catalytic reduction of CO2 in the presence of H2 or hydrosilanes
for the production of CO or methanol.2c
CO2 is an abundant, safe and renewable carbon source and
therefore an attractive C1 building block for the formation of
organic molecules via the construction of CꢀC, CꢀH, CꢀO or CꢀN
bond.1 In these years, increasing research efforts have been
devoted to promoting the reduction of CO2 by hydrosilanes,
hydroboranes or H2 to CO, formic acid, methanol or methane,
which can be served as H2 carriers or directly as fuels.2 First
unveiled in 2013,3 the catalytic reduction of CO2 by hydrosilanes
to methylamines is a promising new method for recycling CO2 to
valueꢀadded chemicals, to byꢀpass the use of formaldehyde or
toxic methylating reagents such as methyl iodide, dimethyl
sulfate or diazomethane.4 The product Nꢀmethylated compounds
are important solvents and functionality in platform chemicals
such as medicines, agrochemicals, dyes and perfumes.5 Later on,
using CO2 and H2 as sources for the methyl group, Beller et al.
and Leitner et al. described rutheniumꢀbased catalysts that
mediated the Nꢀmethylation of amines/imines.6 Subsequently,
Shi et al. reported heterogeneous catalytic systems such as
CuAlOx,7 Pd/ZrCuOx,8 and PtꢀMoOx/TiO2.9 However, elevated
pressure and limited substrate scope generally appeared owing
to the high thermal stabilities of these two gas molecules. While
other reducing agents, such as hydrosilanes, together with
homogeneous Nꢀheterocyclic carbenes (NHCs) zinc complex,3
ruthenium complex,10 NHCs11 catalysts, afforded Nꢀmethylated
compounds under comparatively mild reaction conditions.
On the other hand, incorporation of strongly polar CꢀF bonds
was favourable for CO2 activation through electrostatic
interactions (Scheme 1, species II). For example, perfluorinated
covalent triazineꢀbased framework exhibited high CO2 uptake
capacity especially at low pressures (77 mg gꢀ1 at 273 K and 0.1
bar).15 Fluoroꢀfunctionalized polymeric ionic liquids (FꢀPILs)
showed three times higher activity for cycloaddition reactions of
CO2 with epoxides than the corresponding nonꢀfluorous one.16
Fluorinated microporous organic polymers (FꢀMOPs) exhibited
twice higher CO2 adsorption capacity than corresponding nonꢀ
fluorous MOPs and displayed high efficiency for CO2 reacting
with propargyl alcohols to αꢀalkylidene cyclic carbonates at 25 oC.
Beijing National Laboratory for Molecular Sciences, Key Laboratory of
Colloid, Interface and Thermodynamics, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, China
E-mail: liuzm@iccas.ac.cn
Electronic Supplementary Information (ESI) available: For experimental
details and spectral data,See DOI:10.1039/b000000x/
As mentioned above, B(C6F5)3 could activate R3SiꢀH via species
I
through reversible η1 coordination (Scheme 1), with subsequent
transfer of R3Si+ to a nucleophile.13a, 17 On the other hand, as a
highly electronꢀdeficient species, B(C6F5)3 could undoubtedly
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DOI: 10.1039/C5GC01386K
activate the substrate amine through strong electrostatic
interaction (Scheme 1, species III), as proved by NMR technique
(Figure S1, ESI). In addition, B(C6F5)3 is air stable and could be
handled conveniently. Thus, we envisioned that the fluorinated
B(C6F5)3 could act as an efficient metalꢀfree catalyst for the
methylation of amines using CO2 as C1 building block under
easyꢀhandling conditions.
Indeed, B(C6F5)3 was found to be highly efficient catalyst for
the methylation of amines in the presence of PhSiH3 under 0.5
MPa CO2 pressure. Methylation of primary and secondary
amines, aromatic and aliphatic amines with electronꢀdonating
and electronꢀwithdrawing groups at oꢀ, mꢀ, pꢀpositions was
realized with high reactivity. Therefore, the excellent synergistic
effect of B and F atom centre of B(C6F5)3 for the activation of
hydrosilanes (by B centre), CO2 (by F centre) and amines (by B
centre) has ensured the efficient catalytic activity for the
methylation of amines using CO2 as a C1 building block.
O
O
N
H
C
R
R
Si
H
B(C6F5)3
B(C6F5)3
B(C6F5)3
R
I
II
III
Scheme 1 Interaction of B(C6F5)3 with hydrosilane, CO2 and amines.
As shown in Figure 1, NMR technique was employed to
identify the interaction of Nꢀmethylaniline (1a) with B(C6F5)3. It
was found that the proton signal of the methyl group of 1a (Hꢀ1)
showed a downfield shift from 2.85 to 2.91 ppm after addition of
B(C6F5)3, and the proton on the benzene ring also shifted from
6.64 (Hꢀ2), 6.74 (Hꢀ3) and 7.22 ppm (Hꢀ4) to 7.12 (Hꢀ2) and 7.43
(Hꢀ3, Hꢀ4) obviously owing to the strong electrostatic interaction
between the electronꢀdonating N atom of1a and the strong
electronꢀwithdrawing B atom of B(C6F5)3. Correspondingly, the B
signal showed an upfield shift from 15.05 (for B(C6F5)3) to ꢀ3.48
ppm after interaction with 1a. Moreover, upfield shift of the F
signal in B(C6F5)3 after addition of 1a also proved the
electrostatic interaction: from ꢀ163.5, ꢀ152.6, ꢀ122.6 ppm to ꢀ
164.5, ꢀ159.5, ꢀ136.1 ppm, respectively for Fꢀ1, Fꢀ2 and Fꢀ3.
The reaction of 1a with PhSiH3 was taken as a model
system to identify and optimize the key reaction parameters
under 0.5 MPa CO2 pressure at 140 oC. As shown in Table 1, 82%
yield of N,Nꢀdimethylaniline (2a) was obtained catalyzed by 5
mol% of B(C6F5)3 (entry 2), while almost no reaction occurred in
the absence of any catalyst (entry 1). In contrast, B(C6H5)3
without strong electronꢀwithdrawing fluorine atoms showed low
catalytic activity (2a yield: 13%, entry 3), due to diminished Lewis
acidic characterization of the boron center, and is also for
diethyl(3ꢀpyridyl)borane (BEt2Py) containing electronꢀdonating
groups (2a yield: 12%, entry 4). Interestingly, tetraꢀsubstituted
LiB(C6F5)4 without unoccupied molecular orbital with the boron
center, thus no Lewis acidity, produced 2a in 39% yield, probably
owing to the CO2 activation by the polar CꢀF bonds. For other
Figure 1 1H, 11B and 19F NMR in CDCl3 of N-methylaniline (1a) before and after
mixing with B(C6F5)3 (molar ratio 1: 1).
Lewis acidic nature and the CO2ꢀphilic fluorine atoms. As
reported, super acidic Al(C6F5)3 could react with hydrosilanes and
the elusive silaneꢀalane complex has been isolated and
characterized.18 However, it performed worse (2a yield: 45%)
compared with B(C6F5)3 for the methylation of amines (entry 2 vs.
8). Previously, methylation of amines with CO2 proceeded in the
presence
of
hydroboranes
(reductant)
catalyzed
by
proazaphosphatrane super bases.19 Actually, hydroborane such
as 9ꢀborabicyclo(3.3.1)nonane (9ꢀBBN) could act as catalyst in
the presence of hydrosilane, giving 2a in 39% yield (entry 9).
Hence, among various boron derivatives investigated, B(C6F5)3
showed the best performance and was taken as optimal catalyst
for further study.
The catalytic activity of B(C6F5)3 was greatly influenced by
the solvents. It was demonstrated that the polar solvents were
more favourable to the methylation reaction. For example, lower
yield of 2a (44%) was obtained taking toluene as the reaction
medium, while 2a yield was 60%, 69% and 82% obtained in DMF,
THF and CH3CN, respectively (entries 2, 10, 11 vs. 12). Notably,
catalytic activity almost remained unchanged by decreasing
PhSiH3 to 1 mmol (2a yield: 82%, entry 2 vs. 13), and
overwhelmed PhSiH3 (4 mmol) failed to further increase the yield
of 2a (83%, entry 14), while inadequate amount of PhSiH3 (0.5
mmol) caused tremendous decrease of 2a yield (43%, entry 15),
along with production of the formamide intermediate PhNHCHO
(yield: 38%) (Scheme 3, 3a). Another byproduct being detected
Lewis acidic boronꢀcontaining derivatives, e.g., BF3 (2a yield:
26%) and BCl3 (2a yield: 10%) (entry 6 vs. 7), BF3 revealed a
little higher catalytic activity, which was benefitted from stronger
2 | J. Name., 2012, 00, 1-3
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in the system was N,N'ꢀdiphenylꢀN,N'ꢀdimethylurea (4a), which not for triethoxysilane ((EtO)3SiH) (2a yield: 34%), triethylsilane
could be quantitatively reduced to give 1a and 2a in the presence (Et3SiH) (2a yield: 3%) and poly(methylhydrosiloxane) (PMHS)
of PhSiH3 catalyzed by [RuCl2(dmso)4].10 However, only 2% yield
(2a yield: 13%), while in the case of di(SiꢀH) containing
of 2a was obtained catalyzed by B(C6F5)3 (Scheme 2), hydrosilanes such as diphenylsilane (Ph2SiH2), diethylsilane
supporting the formamide intermediate formation pathway. This (Et2SiH2) very low 2a yield of 12% and 7% was obtained. Hence,
was also demonstrated the constant yield of 2a by increasing the PhSiH3 was the most befitting reductant in this catalytic system.
amount of hydrosilane PhSiH3.
The possible reason for discriminatory activity of various
hydrosilanes was different electronic and steric effect derived
from the substituted groups. Further increasing of 2a yield was
not observed by screening of the reaction conditions such as
catalyst loading, CO2 pressure, and reaction temperature (entries
23ꢀ26). It was reported that formamide was detected as an
intermediate for the methylation of amines,10 which was also
present in our system. As shown in Figure 2, 66% yield of 2a
was reached within 1 h taking PhNHCHO (3a) as the starting
material in the absence of CO2. Then the yield further increased
to 83% within 5 h and kept constant within 15 h. While at least 24
h was needed reaching a similar yield of 83% for 2a starting from
1a, thus the formation of formamide PhNHCHO was the rateꢀ
determining step for the methylation reaction under low CO2
pressure (0.5 MPa).
Table 1 Methylation of N-methylaniline (1a) by CO2 and hydrosilanesa
Entry
1
2
3
4
5
6
7
8
Catalyst
-
B(C6F5)3
B(C6H5)3
BEt2Py
LiB(C6F5)4
BF3
BCl3
Solvent
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
THF
Silane
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
Yield/%b
<1
82
13
12
39
26
10
45
39
69
60
44
82
83
43
75
75
34
3
Al(C6F5)3
9-BBN
9
10
11
12
13c
14c
15c
16d
17d
18d
19d
20d
21d
22d
23e
24f
25g
26g
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
B(C6F5)3
DMF
Toluene
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
80
60
40
Me(EtO)2SiH
Me(MeO)2SiH
(EtO)3SiH
Et3SiH
PMHS
13
12
7
75
83
70
83
20
PhNHCHO as substrate
Ph2SiH2
Et2SiH2
PhSiH3
PhSiH3
PhSiH3
PhNHMe as substrate
0
0
5
10
15
20
25
30
Reaction time/h
Figure 2 Production of 2a taking PhNHCHO or PhNHMe as substrate. Reaction
conditions: 1a or PhNHCHO 0.5 mmol, PhSiH3 1 mmol, B(C6F5)3 5 mol%, CO2
pressure 0.5MPa for 1a as substrate, no CO2 was added for PhNHCHO as
substrate, CH3CN 2 mL, 140 oC, 24 h. Yield of 2a was determined by GC using
dodecane as an internal standard.
PhSiH3
a Reaction conditions:1a 0.5 mmol, PhSiH3 2 mmol, catalyst loading 5 mol%
based on 1a, CO2 pressure 0.5MPa, solvent 2 mL, 140 oC, 24 h. b Determined
by GC using dodecane as an internal standard.c 1mmol, 4 mmol and 0.5
d
mmol PhSiH3 was added for entry 13-15, respectively. 3 mmol Si-H was
added for different hydrosilanes. e 2.5 mol% B(C6F5)3 was added for entry 23.
f
g
o
o
CO2 pressure was 1 MPa or 3 MPa. Temperature was 120 C and 160 C
The methylation of NꢀH bonds in a variety of amines was then
undertaken to explore the scope of active substrates. As shown
in Table 2, paraꢀsubstituted Nꢀmethylanilines with either electron
donating or electron withdrawing groups are active substrates in
the methylation reaction and the corresponding N,Nꢀ
dimethylanilines were obtained in yields ranging from 80~93%.
Generally, the unsubstituted derivate 1a showed similar activity
(entry 1) with electron donating groups such as methylꢀ and
for entry 25 and 26, respectively.
Scheme 2 Synthesis of N,N-dimethylaniline (2a) using N,N'-diphenyl-N,N'-
dimethylurea (4a) as substrate.
methoxyꢀsubstituted Nꢀmethylanilines (entries
4
and 5).
Comparatively, electron withdrawing groups such as Fꢀ, Brꢀ and
Clꢀ substituted Nꢀmethylanilines exisbited relatively higher
reactivity (entries 6ꢀ8). Notably, orthoꢀ or metaꢀsubstituted aryl
ring set back the reactivity for the methylation reaction (entries 2,
3, 9 and 10), especially for Clꢀsubstituted Nꢀmethylanilines,
probably due to electronic and steric effects. Increasing the steric
hindrance of the Nꢀsubstituted group led to weakened reactivity,
with the product yield of 72% for Nꢀethylaniline (entry 11). In
Various hydrosilanes were also examined for the methylation
of 1a (entries 13 and 16ꢀ22). It was found that the reaction also
proceeded well in the presence of mono (SiꢀH) containing
hydrosilanes such as diethoxymethylsilane (Me(EtO)2SiH) and
methyldimethoxysilane (Me(MeO)2SiH) with 2a yield of 75%, but
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addition, dialkylamines also showed moderate reactivity under between the electronꢀdonating N atom of 1a and the strong
our catalytic systems (entries 12). However, diphenyl groupꢀ electronꢀwithdrawing B atom of B(C6F5)3 (Figure S1, ESI); (3)
substituted aromatic amines only gave 26% yield of the activating CO2 through CO2ꢀphilic fluorine atom. These
methylation product (entry 13), possibly owing to the decreased interactions may work together to make the reaction proceed
electrophilic nature of the substrate. Primary aniline could also through formylation of the NꢀH bond with CO2 and the
be converted to 2a in 50% yield (entry 14).
hydrosilane, and then hydrosilylation of the formamide 3a gave
the methylamine product.
a
Table 2 Substrate scope for the methylation of amines catalysed by B(C6F5)3
In summary, B(C6F5)3 was proved to be an efficient metalꢀfree
catalyst for the methylation of amines using CO2 as a C1 building
block in the presence of hydrosilanes under easyꢀhandling
conditions. Nꢀmethylanilines with both electron donating and
electron withdrawing groups on orthoꢀ, metaꢀ and paraꢀpositions
of the benzene ring showed good reactivity. Methylation of other
Nꢀalkylanilines with steric hindrance groups, dialkylamines,
diphenylꢀsubstituted aromatic amine and primary aniline all
proceeded well under the experimental conditions.
Entry
1
Substrate
Product
Yield/%b
80
2
3
71
75
The authors thank the National Natural Science Foundation of
China (No. 21125314, 21321063, 21402208) for the financial
support.
4
5
6
7
8
82
80
89
82
93
9
41
10
11
12
59
72
52
Scheme 3 Possible reaction mechanism for methylation of amines catalysed by
B(C6F5)3.
13
26
50
References and notes
1 (a) M. He, Y. Sun and B. Han, Angew. Chem. Int. Ed., 2013, 52, 9620-
14c
9633; (b) M. Aresta, A. Dibenedetto and A. Angelini, Chem. Rev.
,
2014, 114, 1709-1742.
aReaction conditions: amine 0.5 mmol, PhSiH31mmol, B(C6F5)3 5 mol%, CO2
pressure 0.5MPa, CH3CN 2 mL, 140 oC, 24 h. b Isolated yield.c 2 mmol
PhSiH3 was added.
2 (a) A. Goeppert, M. Czaun, J.-P. Jones, G. K. Surya Prakash and G. A.
Olah, Chem. Soc. Rev., 2014, 43, 7995-8048; (b) C. Lescot, D. U.
Nielsen, I. S. Makarov, A. T. Lindhardt, K. Daasbjerg and T.
Skrydstrup, J. Am. Chem. Soc., 2014, 136, 6142-6147; (c) D. W.
Stephan, Acc. Chem. Res., 2015, 48, 306-316.
As a strong Lewis acidic catalytic centre, B(C6F5)3 showed
somewhat electronꢀdeficient characterization as transition metal
centre for the activation of SiꢀH bond.18 Hence, the possible
reaction mechanism for the B(C6F5)3ꢀcatalyzed methylation of
amines was proposed in accordance with that reported in the
literature (Scheme 3).10 Herein, B(C6F5)3 worked in three aspects:
3 O. Jacquet, X. Frogneux, C. Das Neves Gomes and T. Cantat, Chem.
Sci., 2013, 4, 2127-2131.
4 (a) H. T. Clarke, H. B. Gillespie and S. Z. Weisshaus, J. Am. Chem.
Soc., 1933, 55, 4571-4587; (b) A. Tlili, X. Frogneux, E. Blondiaux and
T. Cantat, Angew. Chem. Int. Ed., 2014, 53, 2543-2545.
(1) activating SiꢀH through reversible η1 coordination (I
);18b (2)
5 M. F. Ali, M. F. Ali and J. G. Speight, Handbook of Industrial
Chemistry: Organic Chemicals, McGraw-Hill Education, 2005.
activating the amine substrate via strong electrostatic interaction
4 | J. Name., 2012, 00, 1-3
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6 (a) K. Beydoun, T. vom Stein, J. Klankermayer and W. Leitner, Angew.
Chem. Int. Ed., 2013, 52, 9554-9557; (b) Y. Li, I. Sorribes, T. Yan, K.
Junge and M. Beller, Angew. Chem. Int. Ed., 2013, 52, 12156-12160;
(c) K. Beydoun, G. Ghattas, K. Thenert, J. Klankermayer and W.
Leitner, Angew. Chem. Int. Ed., 2014, 53, 11010-11014.
7 X. Cui, X. Dai, Y. Zhang, Y. Deng and F. Shi, Chem. Sci., 2014,
5,
649-655.
8 X. Cui, Y. Zhang, Y. Deng and F. Shi, Chem. Commun., 2014, 50
,
13521-13524.
9 K. Kon, S. M. A. H. Siddiki, W. Onodera and K.-i. Shimizu, Chem.
Eur. J., 2014, 20, 6264-6267.
10 Y. Li, X. Fang, K. Junge and M. Beller, Angew. Chem. Int. Ed., 2013,
52, 9568-9571.
11 S. Das, F. D. Bobbink, G. Laurenczy and P. J. Dyson, Angew. Chem.
Int. Ed., 2014, 53, 12876-12879.
12 (a) Modern Reduction Methods (Eds.: P. G. Andersson, I. J.
Munslow), Wiley-VCH, Weinheim, 2008; (b) Hydrosilylation: A
Comprehensive Review on Recent Advances(Ed.: B. Marciniec),
Springer, New York, 2009.
13 (a) D. J. Parks and W. E. Piers, J. Am. Chem. Soc., 1996, 118, 9440-
9441; (b) D. J. Parks, J. M. Blackwell and W. E. Piers, J. Org. Chem.
,
2000, 65, 3090-3098.
14 J. Hermeke, M. Mewald and M. Oestreich, J. Am. Chem. Soc., 2013,
135, 17537-17546.
15 Y. Zhao, K. X. Yao, B. Teng, T. Zhang and Y. Han, Energy Environ.
Sci., 2013, 6, 3684-3692.
16 Z.-Z. Yang, Y. Zhao, G. Ji, H. Zhang, B. Yu, X. Gao and Z. Liu,
Green Chem., 2014, 16, 3724-3728.
17 S. Rendler and M. Oestreich, Angew. Chem. Int. Ed., 2008, 47, 5997-
6000.
18 (a) T. Robert and M. Oestreich, Angew. Chem. Int. Ed., 2013, 52
,
5216-5218; (b) M. Oestreich, J. Hermeke and J. Mohr, Chem. Soc.
Rev., 2015, 44, 2202-2220.
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B(C6F5)3 was proved to be an efficient metal-free catalyst for the methylation of amines using CO2
as a C1 building block in the presence of hydrosilanes under easy-handling conditions.