An efficient and recyclable ionic diphosphine-based Ir-catalyst for hydroaminomethylation of olefins with H2O as the hydrogen source

Article abstract of DOI:10.1039/c8cc03431a

Hydroaminomethylation of olefins with H₂O as the hydrogen source was accomplished over an Ir-catalyst with the involvement of an ionic diphosphine (L6). The use of H₂O as the hydrogen source could completely inhibit the hydrogenation

Full text of DOI:10.1039/c8cc03431a

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DOI: 10.1039/C8CC03431A
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Efficient and recyclable ionic diphosphine-based Ir-catalyst for
hydroaminomethylation of olefins with H2O as hydrogen source
Huan Liu,a Da Yang,a Dong-Liang Wang,a Peng Wang,a Yong Lu,a Giang VO-Thanh,b and Ye Liua*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Hydroaminomethylation of olefins with H2O as hydrogen source active catalysts for hydrogenation of olefins22 as well for
was accomplished over an Ir-catalyst with the involvement of an hydrogenation of imines23. In order to eliminate the undesired
ionic diphosphine (L6). The use of H2O as the hydrogen source could hydrogenation
of
olefins
in
the
course
of
completely inhibit the hydrogenation of olefins. The π-accepting hydroaminomethylation, the required H2 gas was generated in
ability and improved stability of L6 rendered the corresponding Ir- situ herein through water-gas shift reaction (WGSR, H2O + CO
catalyst high activity and good longevity for the cycling uses.
→ H2 + CO2) over the Ir-catalyst24,25. Compare to using H2 gas,
the use of water as hydrogen source is advantageous with
safety, low-cost, and environmental friendliness. In this
Amines and their derivatives were important compounds used synthesis protocol, the hydroaminomethylation of olefins
as agrochemicals, pharmaceutical intermediates, solvents, dyes, towards amines with H2O as the hydrogen source is a one-pot
monomers for polymerization, and functional materials1. A four-step tandem reaction including (1) WGSR, (2)
number of reactions for the synthesis of amines have been hydroformylation of olefins, (3) condensation of aldehydes and
extensively studied, such as hydroamination of olefins or amines26, and (4) hydrogenation of imines/iminiums (Scheme
alkynes2,3, hydrogenation of the respective nitriles4,5, amination 1). In principle, there are three basic requirements for the Ir-
of aryl halides6,7, the N-alkylation with alcohols8,9 and the catalyst applied in this tandem transformation. (1) It should
reductive amination with carbonyl compounds10,11. Despite all possess multiple catalytic functions which are compatible for
these known processes, there are still considerable interests in each step; (2) It should be moisture-insensitive to allow the
developing high atom-economic synthesis routes to such presence of water in the step of WGSR; (3) It should be stable
compounds. Hydroaminomethylation12,13, the one-pot tandem enough to fulfill recyclability, which fits the merits of
hydroformylation-reductive amination, is
a high atom- hydroaminomethylation as a high atom-economic process for
economic method for the synthesis of amines from olefins.
Since hydroaminomethylation discovered in 1949 by Reppe14,
a number of transition metal catalysts, including complexes of
the synthesis of amines from olefins.
rhodium15,16, ruthenium17–19 and even Rh/Ir dual-metals20,21
,
have been evaluated in this transformation. Anyway, the mono-
metallic Ir-catalyze hydroaminomethylation has never been
reported in the literature.
Herein we reported the first example of Ir-catalyzed
hydroaminomethylation of olefins with the involvement of a
novel ionic diphosphine (L6). However, Ir-complexes were
Scheme 1 Hydroaminomethylation of olefins towards amines including four-step
tandem WGSR-hydroformylation-condensation-hydrogenation with H2O as
hydrogen source
a.Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of
Chemistry & Molecular Engineering, East China Normal University, Shanghai
200062, PR China.
b.Institut de Chimie Moléculaire et des Matériaux d’Orsay, UMR 8182, Bat. 420,
Université Paris-Sud 91405, Orsay Cedex, France
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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1
31 77
Firstly, the hydroaminomethylation of 1-hexene with N- possessed much stronger

-acceptor ability with ViJew ArticolefO7nl8in1e
P- Se
1
31 77
methylaniline was investigated as a model reaction. For this reaction, Hz than L5 ( J Se = 735 Hz). Reasonably, DinOLI:61-0b.1a0s3e9d/CIr8-CcCa0ta34ly3s1tA,
P-
when H2O was applied as hydrogen source, atom economy was Ir-P bond was consolidated due to the intensive -backdonation
calculated as high as 70% with CO2 as the only released byproduct. interaction between Ir-center and the electron-deficient ligand
Under the optimal conditions (140 oC, Ir/P=1/1, 4.0 MPa CO, and of L6. Accordingly, the consilidated Ir-P bond did weaken the Ir-
NMP as the solvent) (see S. Table 1 in ESI), the ligand effect on the CO bond and favor the dissociation of CO ligand to form the
catalytic performance of [Ir(COD)Cl]2 was studied in Table 1, in which corresponding Ir-acyl complex. In addition, the TG/DTG analysis
the neutral and the corresponding ionic mono-/di-phosphines were confirmed that the ionic phosphines generally possessed better
selected. It was found that the ionic phosphines universally led to the stability against oxidative degradation than their neutral
much higher yields of the targeted products in comparison to those counterparts (see S. Fig. 1 in ESI). For example, in air flow, L6
over the neutral counterparts (Entry 2 vs 1; Entry 4 vs 3; Entry 6 vs 5). decomposed ca. 280 oC whereas L5 at 120 oC. Consequently, L6
-
Specifically, over the ionic diphosphine of L6, the yield of N-heptyl- based Ir-catalyst was oxygen-insensitive, which facilitated the
N-methylaniline reached 93% whereas its neutral counterpart of L5 process simplicity and manipulations in open air. These reasons
just corresponded to 32% yield (Entry 6 vs 5). Anyway, the neutral could account for the better catalytic performance over L6-base
phosphines without the electrostatic repulsive interaction all Ir catalyst than that of L5-based one (Entry 6 vs 5). Although the
resulted in the much higher regioselectivities to the linear products mono-phopshines of L2 and L4 also possessed the similar -
31 77
31 77
(Entries 1, 3 and 5).
acceptor ability like L6 (Fig. 1: L2, 1J Se = 780 Hz; L4, 1J Se = 786
P-
P-
Hz), the favourable chelation of L6 to Ir-center as a diphosphine
ligand with flexible butyl chain could protect Ir-catalyst against
deactivation, resulting in its better performance (Entry 6 vs 2
and 4). Notably, the use of H2O as the hydrogen source
dramatically inhibited the hydrogenation of 1-hexene (Entries
1-6 vs 7).
Table
1 Ir-catalyzed hydroaminomethylation of 1-hexene with N-
methylaniline over different ligandsa
J
= 781 Hz
18.96
Se-P
22.82
f
Selenide of L6
13.77
J
= 735 Hz
= 786Hz
17.40
Se-P
e
Selenide of L5
Selenide of L4
Selenide of L3
19.45
J
23.34
Se-P
d
c
Sel. (%)b
Amine
Conv.
(%)b
L/Bb
20.11
16.47
Entry Ligand
J
= 735 Hz
Se-P
Isomer
-
Hexane
<1
1
L1
L2
L3
L4
L5
L6
L6
L6
PPh3
-
32
86
33
85
32
93
92
99
55
10
>99
88:12
84:16
93:7
J
= 780 Hz
= 753 Hz
Se-P
24.01
20.15
2
>99
>99
>99
>99
>99
81
-
-
-
-
-
-
-
-
-
<1
<1
<1
<1
<1
19
15
<1
<1
b
a
Selenide of L2
3
J
17.30
21.03
Se-P
4
85:15
92:8
Selenide of L1
5
20
0
-20
6
84:16
85:15
-
Chemical Shift (ppm)
7c
8d
9
Fig. 1 The 31P NMR spectra of the selenides of L1-L6 (202 MHz) (reacting elemental
selenium with the ligand in CDCl3 at 50 oC for 24 h respectively)
-
>99
>99
87:13
88:12
Comparatively, when the syngas (4.0 MPa, CO/H2=3/1
volume ratio) was applied under the same conditions, 17% yield
of hexane was obtained due to the serious hydrogenation of 1-
hexene (Entry 7). Surprisingly, over L6-based Rh-catalyst, the
hydroaminomethylation completely stopped while the
competitive side reactions such as polymerization and
hydrogenation became predominant (Entry 8). By using PPh3 or
no ligand to repeat the reaction, the activities of Ir-catalyst
decreased obviously along with the dropped conversions of 1-
hexene (Entries 9 and 10).
10
a
[Ir(COD)Cl]2 0.025 mmol (Ir 1.0 mol %), mono-phosphine 0.05 mmol,
diphosphine 0.025 mmol (L5 and L6), P/Ir = 1 (molar ratio), 1-hexene 5.0
mmol, N-methylaniline 8.0 mmol, N-methyl pyrrolidone (NMP) 2 mL
(solvent), time 22 h, temperature 140 oC, H2O 0.3 mL, CO 4.0 MPa;
Determined by GC; c CO/H2 = 3/1 (4.0 MPa), time 8 h; d [Rh(COD)Cl]2.
b
1
31 77
The magnitude of
J
in the 77Se isotopomer of the
P- Se
corresponding phosphine-selenide in 31P NMR spectra has been
used to evaluate the

-acceptor ability of a phosphine 27,28. An
The reaction evolution profiles of hydroaminomethylation of
1-hexene with N-methylaniline over L6-base Ir-catalyst (Fig. 2)
indicated that, due to the relatively sluggish release of H2
1
31 77
increase of J
indicates an increase in the character of -
P- Se
acceptor ability (i.e., less 
-donor ability). The 31P NMR spectra
of the phosphine-selenides (Fig. 1) demonstrated that L6
2 | J. Name., 2012, 00, 1-3
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through WGSR, the hydroaminomethylation performed much
slower than that in syngas (CO/H2 4.0 MPa). Therefore, the efficient hydroaminomethylation evoked us to explore the formation
undesired hydrogenation of 1-hexene was completely and stability of the active Ir-H species, which was responsible for the
COMMUNICATION
The remarkable performance of L6-based Ir-catalyst for the
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DOI: 10.1039/C8CC03431A
depressed.
key step of hydroformylation, via the high pressure in situ FT-IR
spectroscopy 29. The in situ FT-IR spectra were presented in Fig. 3 and
Fig. 4. In syngas atmosphere, besides the strong characteristic
vibrations of gaseous CO at 2180 and 2115 cm-1, a weak absorption
peak at 2078 cm-1 gradually appeared as the temperature increasing
100
80
60
40
20
0
o
from 30 to 120 C, which was identified as the active Ir-H species
according to the previously reported work 30. Meanwhile, the
characteristic peak at 1362 cm-1 attributed to N-C vibration for the
targeted product of N-hepthyl-N-methylaniline (see S. Fig. 2 in ESI)
was concurrently observed. The accompanying peak at 1871 cm-1
was assigned to Ir-CO species which was the result of the
complexation of [Ir(COD)Cl]2 with CO. Similarly, in CO atmosphere
with H2O as the hydrogen source, the formation of Ir-H species (
2078 cm-1) was also observed while the temperature increased up to
140 oC over the L6-based system (Fig. 4). In contrast, over L5-based
Ir-catalyst, under CO/H2O condition, the vibration of Ir-H was
unobservable at all (see S. Fig. 3 in ESI). The in situ FT-IR analysis
indicated that only the presence of the ionic diphosphine of L6
facilitated the formation and stability of Ir-H active species while
using H2O as hydrogen source.
Yield of amine (CO/H2O)
Conv. of 1-hexene (CO/H2O)
Yield of amine (CO/H2)
Yield of n-hexane (CO/H2)
Conv. of 1-hexene (CO/H2)
2
4
6
8
10
12
14
16
18
20
22
24
Time (h)
Fig. 2 The evolution profiles of 1-hexene conversion and product yield vs
reaction time catalyzed by L6-based Ir-catalyst ([Ir(COD)Cl]2 0.025 mmol, L6
0.025 mmol, 1-hexene 5.0 mmol, N-methylaniline 8.0 mmol, NMP 2 mL, H2O
0.3 mL, CO 4.0 MPa (or CO/H2 4.0 MPa, CO/H2 =3/1 volume ratio),
temperature 140 oC).
30 oC, 1 min
110 oC, 1 min
120 oC, 1 min
120 oC, 10 min
120 oC, 20 min
120 oC, 30 min
1362
2078
2078
3000
2500
2000
1500
2300
2200
2100
2000
1900
Wavenumber (cm-1)
Fig. 3 The in situ high-pressure FT-IR spectra recorded from 30 to 120 oC after mixing [Ir(COD)Cl]2, L6, 1-hexene, N-methylaniline and NMP in CO/H2 (2.0 MPa;
vCO/vH = 3/1)
2
30 oC, 1 min
120 oC, 1 min
140 oC, 1 min
140 oC, 10 min
140 oC, 20 min
140 oC, 30 min
1362
2078
2000
2078
2100
2300
2200
2000
1900
3500
3000
2500
1500
Wavenumber (cm-1)
Fig. 4 The in situ high-pressure FT-IR spectra recorded from 30 to 140 oC after mixing [Ir(COD)Cl]2, L6, 1-hexene, N-methylaniline, H2O and NMP in CO (0.5
MPa)
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2
3
4
H. A. Wittcoff, B. G. Reuben and J. S. Plotkin, Industrial Organic
In addition, as an ionic ligand with high polarity, L6-based Ir-
catalyst could be precipitated by n-hexane upon completion to fulfil
the recovery and recycling uses of transition metal catalysts. As
demonstrated(see S. Fig. 4 in ESI), the catalyst could be recycled 7
runs. The ICP-OES analysis indicated that the leaching of Ir and P
elements in the combined extract was non-detectable (below the
detection limit of 0.1 g/g). The decreased activity of the catalyst in
the third run and afterwards was mainly due to the physical loss
during the transfer of the catalyst. The deactivation of the catalyst
was not observed since the reaction solution was always clear and
yellow without precipitation of metal blacks.
View Article Online
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5
6
The scope of hydroaminomethylation catalysed by L6-based
Ir-catalyst was explored (see S. Table 2 in ESI). It was found that,
as for the linear aliphatic -olefins, the increased carbon chains
7
8
9
led to the decreased reaction rate obviously. For example, 1-
heptene, 1-octene and 1-dodecene afforded 80~86% yields of
the products while 1-hexene corresponded to 93% yield (Entries
2-5 vs 1). The internal aliphatic olefins such as 2-octene and
cyclooctene led to very low yields of the amines due to the bulky
steric hindrance (Entries 6 and 7). When styrene and its
derivatives were applied to repeat the reactions at the
prolonged time of 48 h, styrene gave 80% yield of the
corresponding amines whereas styrene derivatives with para-
positioned substituents afforded the lower yields of the
products due to the obvious steric and electronic effects
(Entries 8-13). Unfortunately, the uses of the other amines
instead of N-methylaniline to perform hydroaminomethylation
of 1-hexene universally resulted in the drop of the product
yields (Entries 14 and 15).
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Conclusions
L6-based Ir-catalyst was proved highly efficient and recyclable
for hydroaminomethylation of different olefins by using H2O as
hydrogen source for the first time. In this protocol, the use of
H2O as the hydrogen source instead of H2 was advantageous to
depress the side-reaction of hydrogenation of olefins. L6, as an
ionic π-acceptor diphosphine with insensitivity to water and
oxygen, rendered the Ir-catalyst high activity towards
hydroaminomethylation and good longevity. The in situ high
pressure FT-IR analysis indicated that over L6-based Ir-catalyst,
the formation and stability of Ir-H active species (
2078 cm-1)
was favored, which was responsible for the key step of
hydorformylation in the hydroaminomethylation. In addition,
the high polarity of L6 as an ionic compound also facilitated the
recyclability of the homogeneous Ir-catalyst.
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This work was financially supported by the National Natural
Science Foundation of China (Nos. 21673077 and 21473058),
and the Science and Technology Commission of Shanghai
Municipality (18JC1412100).
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Conflicts of interest
There are no conflicts of interest to declare.
Notes and references
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