Carbon dioxide transformation in imidazolium salts: Hydroaminomethylation catalyzed by Ru-complexes

Article abstract of DOI:10.1002/cssc.201600385

The catalytic species generated by dissolving Ru₃(CO)₁₂ in the ionic liquids 1-n-butyl-3-methyl-imidazolium chloride or 1-n-butyl-2,3-dimethyl-imidazolium chloride are efficient multifunctional catalysts for: (a) reverse water-gas shift, (b) hydroformylation of alkenes, and (c) reductive amination of aldehydes. Thus the reaction of alkenes with primary or secondary amines (alkene/amine, 1:1) under CO₂/H₂ (1:1) affords the hydroamino-methylations products in high alkene conversions (up to 99%) and selectivities (up to 96%). The reaction proceeds under relatively mild reaction conditions (120 °C, 60 bar = 6 MPa) and affords selectively secondary and tertiary amines. The presence of amine strongly reduces the alkene hydrogenation competitive pathway usually observed in the hydroformylation of terminal alkenes by Ru complexes. The catalytic system is also highly active for the reductive amination of aldehydes and ketones yielding amines in high yields (> 90%).

Full text of DOI:10.1002/cssc.201600385

DOI: 10.1002/cssc.201600385
Full Papers
Carbon Dioxide Transformation in Imidazolium Salts:
Hydroaminomethylation Catalyzed by Ru-Complexes
Meher Ali,[a] Aitor Gual,[a, b] Gunter Ebeling,[a] and Jairton Dupont*[a, b]
The catalytic species generated by dissolving Ru3(CO)12 in the
ionic liquids 1-n-butyl-3-methyl-imidazolium chloride or 1-n-
butyl-2,3-dimethyl-imidazolium chloride are efficient multifunc-
tional catalysts for: (a) reverse water–gas shift, (b) hydroformy-
lation of alkenes, and (c) reductive amination of aldehydes.
Thus the reaction of alkenes with primary or secondary amines
(alkene/amine, 1:1) under CO2/H2 (1:1) affords the hydroamino-
methylations products in high alkene conversions (up to 99%)
and selectivities (up to 96%). The reaction proceeds under rel-
atively mild reaction conditions (1208C, 60 bar=6 MPa) and af-
fords selectively secondary and tertiary amines. The presence
of amine strongly reduces the alkene hydrogenation competi-
tive pathway usually observed in the hydroformylation of ter-
minal alkenes by Ru complexes. The catalytic system is also
highly active for the reductive amination of aldehydes and ke-
tones yielding amines in high yields (>90%).
Introduction
The abundance of CO2 and the impending shortage of fossil
building blocks, has led to the proposal that CO2 should be
the C1 building block of the future.[1–3] However, CO2 is very
unreactive, residing in a thermodynamic minimum, and its acti-
vation requires large amounts of energy. One of the key solu-
tions currently under intense investigation is the potential con-
version of CO2 into useful chemicals through the hydrogena-
tion reaction.[4–6] For example, the conversion of CO2 to syngas
(CO+H2), formic acid, methanol and dimethyl ether, hydrocar-
bons (via methane), and Fischer–Tropsch (FT) synthesis yields
fuels and chemicals.[7,8] Other important applications of CO2 as
a C1 building block in organic synthesis include the direct syn-
thesis of dimethylcarbonate, cyclic carbonates, urea and ure-
thane derivatives, carboxylic acids, esters and lactones, and iso-
cyanates.[9–13] The catalytic conversion of CO2 to CO through
the reverse water–gas shift (RWGS) reaction is the first step in
the production of hydrocarbons via FT synthesis or for carbon-
ylations using CO2. The RWGS is a well-established reaction
used to convert CO2 into CO and water.[14,15] However, it is an
equilibrium-limited endothermic reaction that is favored at
high temperatures. In some cases, the products must be re-
moved to shift the equilibrium toward the RWGS rather than
the forward water–gas shift (WGS) reaction. In addition, CH4 is
often formed as an undesired side product, particularly at low
temperatures (<6008C) when CH4 is the thermodynamically-
favored product.[16–22]
Recently, important breakthroughs in the activation and cat-
alytic transformation of CO2 have been reported using Ru and
Rh complexes in many carbonylation reactions.[23] These in-
clude the Ru-catalyzed reductive methylation of imines,[24,25]
amines,[26] and CÀH bonds,[27] as well as the Ru-[28–30] or Rh-
catalyzed carbonylation of alkenes, or even Au-promoted for-
mation of methyl formate.[31] In the Ru-catalyzed carbonyla-
tions, it has been proposed that the first step of the reaction
involves the presence of cationic Ru-hydrido ([Ru-H+]) com-
plexes and the addition of a proton source usually significantly
improves the catalytic activity.[32] These [Ru-H]+ species can
generate reactive metal-formate intermediates (Scheme 1,
path A) or CO (Scheme 1, RWGS, path B). Hence, by controlling
the reactivity of [Ru-H]+ species, the incorporation can either
use the formate intermediate to produce, for example, formic
acid or methanol, or the RWGS to generate carbonylation or
FT products.
Generally, sophisticated ligands are required to control the
reactivity of [Ru-H]+ species and to improve both catalytic ac-
tivity and selectivity.[24–26,29] However, it was reported that the
RWGS/hydroformylation path may be favored in the absence
of extra ligands if the reaction is performed in the presence of
imidazolium salt-based ionic liquids (IL)[30] that can generate
in situ abnormal Ru–carbene species (Scheme 2)[33] similar to
[a] M. Ali, Dr. A. Gual, Prof. G. Ebeling, Prof. J. Dupont
Institute of Chemistry
Universidade Federal do Rio Grande do Sul
Av. Bento GonÅalves, 9500 Porto Alegre 91501-970 RS (Brazil)
E-mail: Jairton.dupont@ufrgs.br
jairton.dupont@nottingham.ac.uk
[b] Dr. A. Gual, Prof. J. Dupont
School of Chemistry
University of Nottingham
NG7 2RD Nottingham (UK)
1
Supporting Information, including details about the H and 13C NMR
analysis, and the ORCID identification number(s) for the author(s) of this
article can be found under http://dx.doi.org/10.1002/cssc.201600385.
Scheme 1. Possible pathways involved in the hydrogenation of CO2.
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groups.[33] The beneficial effect of protic additives in
the hydroaminomethylation results was also previ-
ously ascribed to an increase in the imine hydroge-
nation activity.[42] This is another indication that the
reaction proceeds through RWGS, hydroformylation,
imine-enamine formation, and reduction (see
below). Other amines with distinct steric and elec-
tronic properties, such as benzylamine (2b), mor-
pholine (2c), pyrrolidine (2d), and diethylamine
Scheme 2. Abnormal NHC carbenes possibly formed in the reaction of [BMI]Cl and
[BMMI]Cl with Ru3(CO)12 under hydroformylation conditions using CO2 as a CO source.[33]
those species observed in the reaction of 1,3-di-tert-butylimi-
dazol-2-ylidene with Ru3(CO)12.[34] Note the formation of imida-
zolium-derived NHC carbenes in normal[35–38] and abnor-
mal[39–41] positions are usually observed in reactions involving
both 1,3- and 1,2,3-substituted imidazolium salts.
(2e), were also evaluated in the hydroaminomethylation of
1 (entries 7–9, Table 1).
Our reported procedure is more efficient in terms of activity
and productivity than those reported earlier for Ru-catalyzed
hydroaminomethylation of alkenes with secondary alkylic
amines employing LiCl-benzyl triethyl ammonium chloride
(BTAC) salts as additives, large amount of metal (6 mol% Ru)
under harsh reaction conditions (1608C, 80 bar=8 MPa) and
long reaction periods (5 days).[43] Furthermore, in general, the
main drawback of the hydroaminomethylation reaction is that
for primary amines the selectivity generally is low because of
over-alkylation.[44] Our catalytic system provided the formation
of secondary amines from primary amines (2a and 2b) with
no formation of over-alkylated amine. This selectivity is proba-
We also observed that the use of phosphines (i.e., PPh3) and
diphosphines
[e.g.,
1,1-bis(diphenylphosphino)methane
(dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(di-
phenylphosphino)propane (dppp), and 4,5-bis(diphenylphos-
phino)-9,9-dimethylxanthene (Xantphos)] as metal modifiers re-
sulted in poor selectivities for the formation of carbonylation
products with high selectivity for the hydrogenation of the al-
kenes. In contrast, phosphites [i.e., P(OEt)3] provided an im-
provement in both the catalytic activity and oxo-product selec-
tivity, as also observed by others.[28] However, 31P NMR experi-
ments revealed that this apparent ligand effect was caused by
the formation of phosphoric acid (H3PO4) under our reaction
conditions.[33] It is reasonable to assume, that even in the case
of reactions involving CO2/H2 in imidazolium salt IL media, it
will be possible to shift the selectivity towards the CO path by
fine-tuning the reaction conditions. We report herein that the
hydroaminomethylation can be easily performed with the
simple catalytic system (i.e., imidazolium chloride IL/Ru3CO2/
H3PO4).
Table 1. Ru-catalyzed hydroaminomethylation of cyclohexene (1) using
CO2 as a CO source.[a]
Entry Amine IL
Additive[b] Conv.[c]
[%]
1
Sel.[c]
[%]
3
Sel.[c]
[%]
4
Yield 5[c,d]
[%]
1
2
3
4
5
6
7
8
9
2a
2a
2a
2a
2a
2a
2b
2c
2d
2e
[BMI]Cl
[BMMI]Cl
[BMI]Cl
[BMMI]Cl P(OEt)3
[BMI]Cl H3PO4
[BMMI]Cl H3PO4
[BMMI]Cl H3PO4
[BMMI]Cl H3PO4
[BMMI]Cl H3PO4
[BMMI]Cl H3PO4
–
–
79
68
82
98
96
99
27
57
84
36
66
49
84
98
95
98
57
65
88
64
34
51
16
2
5
2
43
35
12
36
13
2
8
4
8
P(OEt)3
3
85
32
17
16
Results and Discussion
Hydroaminomethylation of alkenes
10
[a] Reaction conditions: 1 (20.0 mmol), 2a–e (20.0 mmol), imidazolium
salt IL (5.1 mmol), 0.5 mol% Ru3(CO)12 (1.5 mol% Ru), 60 bar=6 MPa CO2/
H2 (1:1), 1208C, 24 h. [b] Additive/Ru=3.0. [c] Conversion of 1 (%), yield
of 5 (%), and selectivity (%) determined by GC–MS and GC–FID. [d] Calcu-
lated from the conversion of 2.
The hydroaminomethylation of cyclohexene (1) with aniline
(2a) was carried out using CO2 as a CO source (entries 1–6,
Table 1) using the same reaction conditions developed earlier
for the hydroformylation of alkenes with CO2.[33] Conversions of
1 up to 99% after 17 h and selectivity up to 98% for product
(3) were achieved (Scheme 3). In all cases N-formylation (5) by-
products were also observed, indicating that both paths (A
and B, Scheme 1) are operative under these reaction condi-
tions. However, the RWGS pathway is predominant, as the
system is selective to the hydroaminomethylation reaction
rather than N-formylation.
The use of the additive H3PO4 or P(OEt)3 (that undergoes hy-
drolysis to yield acids under the reaction conditions used) pro-
duce an increase of the selectivity in the hydroaminoamina-
tions products (3). This behavior is similar to that previously
described in the Ru-catalyzed hydroformylation using CO2 as
a CO source, and it was attributed to the fact that the acid
likely facilitates hydride transfer and protonolysis, which are
key steps for the addition of hydrogen to carboxylate
Scheme 3. Hydroaminomethylation of cyclohexene (1) with primary [aniline
(2a) and benzylamine (2b)] and secondary amines [morpholine (2c), pyrroli-
dine (2d), and diethylamine (2e)] promoted by Ru3(CO)12 dissolved in
[BMI]Cl or [BMMI]Cl. Reaction conditions: cyclohexene (20.0 mmol), amine
(20.0 mmol), imidazolium salt IL (5.1 mmol), 0.5 mol% Ru3(CO)12 (1.5 mol%
Ru), 60 bar=6 MPa CO2/H2 (1:1), 1208C, 24 h.
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bly a result of removing the less soluble secondary amine from
the catalyst-containing imidazolium salt IL phase.[45]
11 with moderate-to-high conversions (88 to>99%) and selec-
tivities (60 to 96%), as shown in Table 2.
Under optimized reaction conditions, monosubstituted n-
terminal alkenes, such as 1-hexene, gave full conversion, with
the production of the corresponding amine (6) in high selectiv-
ity (up to 96%; see Table 2). Much lower selectivities for hepta-
It should be noted that in both cases (hydroformylatio-
n
[33]and hydroaminomethylation) the transformation of the 2,2-
di-substituted alkenes allowed the exclusive formation of linear
products.
In the case of carvone (Table 2, entry 7), the corresponding
di-amine 11 was obtained through a reductive amination step
of the carbonyl function of its cyclohexanone skeleton. For this
reason, the hydroaminomethylation of carvone was conducted
using a carvone/aniline (2a) ratio of 1:2. This is further evi-
dence that under the catalytic condition used, the carbonyl
groups present in the medium react with the amines to gener-
ate imines (from primary amines) and enamine salts (from sec-
ondary amines) that are further reduced to secondary and ter-
tiary amines, respectively.
Table 2. Conversion of alkene (%) and amine selectivity (%) obtained in
the Ru-catalyzed hydroformylation of alkenes using CO2 as a CO source.[a]
Entry
Alkene
Product
Conv.[b] [%]
Sel.[b] [%]
1
2
99
99
96
15
3
97
72
Mechanistic insights
4
5
6
97
91
88
96
87
93
The main reactions paths involved in the hydroaminomethyla-
tion of alkenes by the Ru3(CO)12/imidazolium salt IL catalytic
system is presented in Scheme 4. The first step is the RWGS re-
action (Path A, Scheme 4) that is well known to occur in many
processes that involve the use of CO2 and H2 mixtures and it is
the main step during the activation of CO2 for many carbony-
lation reactions.[47] However, the RWGS reaction is an endother-
mic reaction (DH298K =41.2 kJmolÀ1), and thus conventional
catalysts require high temperatures[48] to promote the forma-
tion of CO. Note that some noble metal catalysts (e.g., Pt, Ru,
and Rh) and promoters based in ionic additives (e.g., Li salts)
were revealed to be efficient catalysts for the RWGS at mild-to-
low temperatures.[48]
7[c]
99
60
[a] Reaction conditions: alkene (20.0 mmol), 2a (21.5 mmol), [BMMI]Cl
(5.1 mmol), 0.5 mol% Ru3(CO)12 (1.5 mol% Ru), H3PO4/Ru=3.0, 60 bar=
6 MPa CO2/H2 (1:1), 1208C, 36 h. [b] Conversion (%) and selectivity (%) de-
termined by GC–MS and GC–FID. [c] 2a (40.0 mmol).
nols (up to 38%) were previously obtained in the Ru-catalyzed
hydroformylation of 1-hexenes under similar reaction condi-
tions.[33] This is a clear indication that the amines are probably
acting also as modifiers, decreasing the C=C hydrogenation
competitive pathway akin to that was observed in the hydro-
formylation employing Ru-N-containing ligands catalysts in
molten salt media.[46]
It is worth nothing that in both cases (hydroformylation[33]
and hydroaminomethylation) the isomerization of the terminal
alkene to internal ones allowed the formation of mixtures of
products with similar amount of the linear and branched
isomer (i.e., linear/branched ratio of 0.9–1.2).
We already reported that Ru3(CO)12/imidazolium salt IL cata-
lytic system promote the RWGS at much lower temperatures
(1208C) than those observed using classical catalysts. There-
fore, the reported catalytic system is one of the most active to
allow the use of CO2 as a CO source as for example in hydro-
formylation of alkenes.[33] In these hydroformylation reactions,
preliminary spectroscopic (IR and NMR) investigations have re-
vealed the involvement of Ru-hydride-carbonyl-carbene com-
plexes as possible catalytic active species[33] akin to observed
in the hydroformylation using CO.[49] 1H and 13C HP NMR ex-
periments have been performed to investigate the nature and
structure of the species formed by dissolving Ru3(CO)12 either
in the 1-n-butyl-3-methyl-imidazolium chloride ([BMI]Cl) or 1-n-
butyl-2,3-dimethyl-imidazolium chloride ([BMMI]Cl). The main
results are summarized in Scheme 5 and a detailed discussion
Mono-substituted alkenes conjugated with aromatic groups
(i.e., styrene) gave full conversions with high-hydrogenated
product selectivity and low selectivity of the hydroaminome-
thylation product (7; Table 2). This behavior was ascribed to
the relatively faster hydrogenation rate of the C=C
bond of these types of substrates (terminal alkyl-
substituted alkenes and substrates with alkenes con-
jugated to aromatic groups) when compared to the
other two processes (RWGS and hydroformylation).
Cyclic di-substituted dienes (1,5-cyclooctadiene),
cyclic di-substituted conjugated dienes (1,3-cyclooc-
tadiene), and 2,2-di-substituted alkenes (methylsy-
trene, (R)-(+)-limonene and carvone) were easily hy-
droaminomethylated, thus leading to the amines 8–
Scheme 4. Main steps involved in the hydroaminomethylation of alkenes by Ru3(CO)12/
imidazolium salt IL catalytic system.
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1
Scheme 5. Main species detected by in situ H, 13C, and 13C{1H} NMR spectroscopy of the reaction of a solution of Ru3(CO)12 in [BMI]Cl and [BMMI]Cl.
and the NMR spectra are available in the Supporting Informa-
tion (Figure SI1–SI6). These new data corroborate the forma-
tion of Ru-hydride-carbonyl-carbene complexes by heating
Ru3(CO)12 in presence of [BMI]Cl under CO2/H2 or inert atmos-
phere, whereas the decomposition of the Ru3(CO)12 under H2
atmosphere that generates Ru nanoparticles akin to previously
reports in the literature.[50,51] In particular, the appearance of
a singlet at 160 ppm in the 13C NMR spectra (Figure SI2, SI4,
and SI6) of either [BMI]Cl or [BMMI]Cl indicate the formation of
“abnormal” type carbenes as usually observed under similar
conditions.[34] Most important, 13CO, formic acid (H13COOH),
and ethylene glycol (13CH2OH13CH2OH) have been observed in
the reaction employing 13CO2 (Figure SI2). Therefore, both
paths proposed in Scheme 1 are operative in these reaction
conditions, but the RWGS is the main path. The reaction kinet-
ics for the formation of the Ru-hydride-carbonyl-carbene com-
plexes under inert atmosphere was also monitored, and thus,
the initially formed main hydride species (d=19.3 ppm in the
1H NMR) evolved to generate a second hydride specie (d=
Therefore, it is reasonable to assume that the presence of
amine increases the RWGS path by increasing the solubility of
CO2 in the ionic phase and/or promoting the metal-formate in-
termediate reduction to CO. Note that no CÀN bond forming
reaction between cyclohexene (1) and morpholine (2c), and
thus the involvement of reductive amination of alkenes in the
reaction mechanism, can be excluded.[54]
The reaction of the formed carbonyl compounds with pri-
mary and secondary amines affords the imines and enamines,
respectively, that subsequently are reduced the amines.
Indeed, minor amounts of imines or enamines, derived from
aniline (2a) were detected by GC and GC–MS analysis of the
hydroaminomethylation reaction mixtures. This reaction path-
way is also supported by the observed reductive amination of
carvone (Table 2, entry 7). Furthermore, the reaction of benzal-
dehyde and amines under the same reaction conditions affords
the expected hydroaminomethylation product (Scheme 7) simi-
lar to other complexes reported in the literature.[44] Hence the
reductive amination of aldehydes and ketones probably occurs
under hydroaminomethylation conditions.
1
17.6 ppm and in the H NMR spectra, Figure SI3 and SI5). Final-
ly, by the addition of P(OEt)3, the high-field hydride signal
became predominant and no organometallic species associat-
ed with P-ligands were detected. Indeed, none of the signals
1
coupled with 13P by H, 13C, or 31P NMR spectroscopy, thus rein-
[52]
forcing the decomposition path of P(OEt)3 into H3PO4 (ob-
served by 31P NMR) that is an extra source of H+ necessary in
the protonation step.[32]
Scheme 7. Reductive amination of benzaldehyde (12) with aniline (2a) or
morpholine (2c) in the presence of CO2. Reaction conditions: 12
(20.0 mmol), 2a or 2c (20 mmol), [BMMI]Cl (5.1 mmol), 0.5 mol% Ru3(CO)12
(1.5 mol% Ru), 60 bar=6 MPa CO2/H2 (1:1), 1208C, 24 h.
We have also observed CO and water in the gas phase (by
GC) of the reaction of 60 bar=6 MPa CO2/H2 (1:1) at 1208C for
24 h, hence indicating the occurrence of RWGS reaction at this
relative low temperature. Consequently, it can be assumed
that the second step of the hydroaminomethylation reaction
will follow the same paths observed for the hydroaminomethy-
lation using CO (Scheme 4, paths B, C, and D).[53] The addition
of alkenes (in absence of amine) under these reaction condi-
tions affords alcohols resulting from the hydrogenation of the
hydroformylation products (paths B and C, Scheme 4). There-
fore, the amine is decreasing the rate of the simple hydrogena-
tion of the alkene. Indeed, the Ru3(CO)12/imidazolium salt IL
catalytic system displays very low cyclohexene hydrogenation
activity in the absence of CO2 (Scheme 6).
The possible involvement of amides in the reaction mecha-
nism can be in principle discarded as no catalytic activity for
the reduction of amide (14 was used as a model amide,
Scheme 8) was observed.
Moreover, the high selectivity for the alcohol (17), which is
formed by a hydroformylation–hydrogenation sequence, and
only moderate selectivity for the amine in the hydroformyla-
tion–hydroaminomethylation of alkenes using dimethylforma-
mides (15) as a CO source (Scheme 9), shows that the involve-
ment of N-formamides in the reaction mechanism as main
pathway can be also discarded.
Scheme 6. Reaction of cyclohexene (1) with H2 in the presence of morpho-
line (2c) and in the absence of CO2. Reaction conditions: 1 (20.0 mmol), 2c
(20 mmol), [BMMI]Cl (5.1 mmol), 0.5 mol% Ru3(CO)12 (1.5 mol% Ru),
60 bar=6 MPa H2, 1208C, 24 h.
Scheme 8. Attempt to hydrogenate amide by Ru3(CO)12/imidazolium salt IL.
Reaction conditions: 14 (20 mmol), [BMMI]Cl (5.1 mmol), 0.5 mol% Ru3(CO)12
(1.5 mol% Ru), 60 bar=6 MPa H2, 1208C, 24 h.
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program=10 min at 408C, 108CminÀ1 until 2508C, then
10 min at 2508C). GC–MS analyses were run with a Shi-
madzu GC System QP50 (column DB-17; T injector=
2508C; P=103 kPa;
T program=10 min at 408C,
108CminÀ1 until 2508C, then 10 min at 2508C; EI=
1
70 eV). H, 13C, COSY, and HSQC NMR analysis were per-
Scheme 9. Reaction of cyclohexene (1) with dimethyl formamide (15) under the same re-
action conditions used for the hydroaminomethylation protocol. Reaction conditions:
1 (20.0 mmol), 15 (20 mmol), [BMMI]Cl (5.1 mmol), 0.5 mol% Ru3(CO)12 (1.5 mol% Ru),
60 bar=6 MPa CO2/H2 (1:1), 1208C, 24 h.
formed on a Varian 400 MHz at the CNANO/UFRGS
using CDCl3 as a solvent. Chemical shifts (ppm) are
given relative to trimethylsilane (TMS) in 1H NMR and
CDCl3 in 13C NMR. The ESI–MS mass spectra (Figure S17
and S18) were acquired using a Q-Tof (Micromass) mass
spectrometer with an ESI capillary voltage of 3 kV and a cone volt-
age of 10 V. The sample (10 mL aliquots of reaction mixture added
to 1 mL of methanol) injection was performed using a syringe
Therefore, all the supporting studies indicated that the hy-
droaminomethylation reaction involves the sequential RWGS,
hydroformylation, and reductive amination pathways
(Scheme 4).
pump set to 5 mLminÀ1
.
General procedure for the hydroaminomethylation of alkenes
using CO2 as a CO source. In a typical experiment, the corre-
sponding substrate (20.0 mmol of alkenes) was mixed with the
amine (20.0 mmol), and they were added to a 100 mL reactor
vessel (Parr Micro-reactor 4590) containing 0.5 mol% Ru3(CO)12
(1.5% mol Ru) and the imidazolium salt IL (5.1 mmol). Then, the re-
actor was pressurized with CO2/H2 and warmed to the desired re-
action temperature and reaction time. After that, the reactor was
cooled and the reaction products were extracted with diethyl
ether (3ꢁ15 mL). The reaction products were analyzed by NMR
Conclusions
Ru3(CO)12/imidazolium salt ionic liquid (IL) is an efficient catalyt-
ic system for the hydroaminomethylation of both primary and
secondary amines using CO2 under mild reaction conditions
(1208C, 60 bar=6 MPa). This catalytic system provided the for-
mation of secondary amines from primary amines with no for-
mation of over-alkylated amine usually observed with other
catalytic systems. This procedure is much more efficient in
terms of activity and productivity than those reported earlier
for Ru-catalyzed hydroaminomethylation of alkenes with sec-
ondary alkylic amines using CO2 as a CO source that employs
higher Ru concentration and operates at 1608C. The reaction
proceeds through sequential RWGS and hydroformylation fol-
and GC–MS analysis (DB-17,
T injector=2508C, P=15 psi=
0.10 MPa, and T programme=10 min at 408C, 108CminÀ1 until
2508C, and 10 min at 2508C). Conversion, selectivity, and yield
were determined by GC–FID analysis using n-heptane as internal
standard.
lowed by imines/enamines reduction. The Ru3(CO)12/imidazoli- Acknowledgements
um salt IL is one of the most active systems to promote the
endothermic RWGS at temperature as lower as 1208C. We
have also demonstrated that the presence of amine dramati-
cally decreases the competitive alkene hydrogenation pathway
usually observed with terminal alkenes in hydroformylation re-
actions promoted by Ru precursors.
We would like to thank TWAS-CNPq, CNPq, CAPES, FAPERGS,
INCT-Catal., and Petrobras for providing financial support for this
work.
Keywords: carbon dioxide · hydroaminomethylation · ionic
liquid · reversed water–gas shift · ruthenium
Research details described herein are expected to contribute
to the development of new processes involving the use of CO2
as an abundant, cheap, easily accessible and green source of
CO for important industrial carbonylation processes under rela-
tive mild reactions conditions and the need of the use of so-
phisticated ligands.
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Received: March 22, 2016
Revised: May 4, 2016
Published online on && &&, 0000
&
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ÝÝ These are not the final page numbers!

FULL PAPERS
M. Ali, A. Gual, G. Ebeling, J. Dupont*
&& – &&
Carbon Dioxide Transformation in
Imidazolium Salts:
Hydroaminomethylation Catalyzed by
Ru-Complexes
VersatILe catalysis: The catalytic spe-
cies generated by dissolving Ru3(CO)12
in the ionic liquids 1-n-butyl-3-methyl-
imidazolium chloride or 1-n-butyl-2,3-di-
methyl-imidazolium chloride are effi-
cient multifunctional catalysts for:
mylation of alkenes, and (c) reductive
amination of aldehydes. The hydroami-
nomethylation using CO2 as CO source
proceeds under mild reaction conditions
(1208C, 60 bar=6 MPa) and affords
amines selectively.
(a) reverse water–gas shift, (b) hydrofor-
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ