SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai.
Chemoselective transfer hydrogenation of α,β-unsaturated carbonyls using palladium
immobilized ionic liquid catalyst
Nilesh M. Patila, Takehiko Sasakib and Bhalchandra M. Bhanage a*
a
Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai-400019, India.
Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5,
Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
E-mail addresses: nileshpatil274@gmail.com, takehiko@k.u-tokyo.ac.jp, bm.bhanage@gmail.com
b
1. Introduction:
Recently, chemoselective hydrogenation of the olefinic bond of α,β-unsaturated carbonyl compounds has been paying great
attention due its broad application in pharmaceutical, agrochemicals and various valuable materials.The saturated carbonyl
moieties are useful key intermediates for the synthesis of various biologically active compounds such as HIV-I protease
inhibitors, in addition dihydrochalcone is useful in restraining the development of Molt-4 human leukemic cells.Selective
reduction of the olefinic bond of α,β-unsaturated carbonyl compounds without affecting carbonyl group is one of the significant
transformation, since both the olefinic double bond and carbonyl bonds are thermally susceptible for reduction. Often the use of
flammable hydrogen gas as a reducing agent was used and additionally it requires sophisticated instrument like high pressure
reactors .The use of transfer hydrogenation is more attractive and convenient alternative method for this conversion avoiding the
use of hydrogen gas and high pressure reactors.
The chemoselective olefin bond reduction in α,β-unsaturated carbonyl was studied using various transition metal catalysts such
as palladium, rhodium, iridium, ruthenium, and other metal catalysts. Recently, Zhang et al. reported chemoselective transfer
hydrogenation of α,β-unsaturated carbonyl compounds by using homogenous palladium pincer complexes. In 2012, Kantam and
co-workers explored the use of Pd/Mg-La mixed metal oxide as a catalyst for selective hydrogenation of α,β-unsaturated
carbonyl compounds using molecular hydrogen. However, in spite of their potential utility, previous reports associated with
some disadvantages e.g. less chemoselectivity, use of flammable hydrogen gas, use of hazardous metal hydride and use of
expensive metals/ligands in homogenous system, therefore, difficulties in catalyst product separation from the reaction mixture.
These restrict their applications in fine chemical industries. Hence, to overcome these drawbacks, the exploration of
heterogeneous catalytic system is still highly desirable.
Nowadays, Immobilization of transition metal on suitable supports solves the problem of contamination of product with
metal/ligand residue and also decreases the organic waste from the reaction work up, thus attains improvement of green
methodology. Recently, Milk et al. and Hermecz et al. reported the homogenous rhodium catalyst for transfer hydrogenation of
α,β-unsaturated carbonyls in ionic liquid. Hence, the development of heterogeneous immobilized metal ionic liquid on solid
support is highly desirable for organic transformation. Synthesis and characterization of immobilized metal ion-containing ionic
liquid (ImmM-IL) and its applications has been explored in various organic transformations. Recently, we reported ImmPd-IL as
an efficient catalyst for alkoxycarbonylation, aminocarbonylation and for carbonylative Suzuki coupling reaction. Continuing
our ongoing research on the development of efficient, heterogeneous catalysed chemoselective transfer hydrogenation,
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SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai.
herein we report ImmPd-IL as a versatile catalyst for chemoselectivity transfer hydrogenation of α,β-unsaturated carbonyls using
HCOONH4 as hydrogen donor (scheme 1).
2. Material and Methods:
All chemicals and reagents were procured from Aldrich and WAKO.The catalyst ImmPd-IL was prepared according to our
previous reports.All the products are well known in literature and were characterized and confirmed by GC, GCMS, 1H NMR
and 13C NMR spectra.
3. Significant Results and Discussion
The reaction parameters were optimized using ImmPd-IL catalyst and ammonium formate as a hydrogen source for
chemoselective transfer hydrogenation of benzylideneacetophenone as a model reaction.
3.1 Preparation of ImmPd-IL.
In a dry round bottom flask, 3-trimethoxysilylpropyl chloride (0.690 mol) and N-methylimidazole (0.690 mol) were added
under nitrogen atmosphere and resulting reaction mixture was refluxed for 48 h. After completion, the reaction mixture was
cooled to room temperature, washed with dry ethyl acetate. The obtained residue was dried at room temperature under reduced
pressure for 2 days and then stored at 253 K under dry nitrogen condition. In the next step, 1-methyl-3-(3trimethoxysilylpropyl) imidazolium chloride and silica (Aerosil 300, surface area 300 m2 g-1, calcined at 573 K for 1.5 h in air)
(weight ratio 1 : 1) were added in a round bottom flask containing dry toluene and were refluxed for 48 h under nitrogen
atmosphere. Thereafter, the reaction mixture was cooled at room temperature; the resulting mass was filtered by using glass
filter. The obtained residue was washed several times with dichloromethane to remove the excess ionic liquid. This obtained
residue was denoted as
Imm-IL. In the last step, PdCl2 and Imm-IL were added in acetonitrile and refluxed for 48 h. The
resulting suspension was filtered by using glass filter and washed with acetone till removal of excess metal chloride and
acetonitrile.
3.2 General procedure of chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds.
The round bottom flask containing α,β-unsaturated carbonyl (1 mmol), HCOONH4 (3 mmol ) and ImmPd-IL (2 mol%) was
added toluene (10 ml) and reaction mixture heated at 90 oC for 12 h. The progress of the reaction was monitored by using TLC
and GC analysis. After completion, the reaction mixture was cooled to room temperature and then filtered to separate catalyst.
The filtrate was then evaporated under high vacuum and obtained residue was purified by column chromatography using silica
gel (100-200 mesh size) with pet ether and ethyl acetate (95:5) to give the desired pure product.
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SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai.
3.3 Schemes, Tables and Figures
Scheme 1 Chemoselective transfer hydrogenation of α,β-unsaturated carbonyls.
Scheme 2 The Preparation of palladium metal-ion-containing immobilized ionic liquid.
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SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai.
Table 1 Effect of catalyst and catalyst loading on transfer hydrogenation of α,β-unsaturated carbonyl compound.a
Entry
Catalyst
Catalyst loading (mol%)
Conversion (%)b
Selectivity (2a:3a)
Catalyst screening
1
ImmPd-IL
2
99
99:01
2
Pd/C
2
39
40:60
3
Pd(OH)/C
2
35
46:54
4
PS-TPP-Pd
2
90
67:33
5
Pd(OAc)2
2
84
38:62
Catalyst loading
6
ImmPd-IL
1
43
99:01
7
ImmPd-IL
2
99
99:01
8
ImmPd-IL
5
99
98:02
a
Reaction condition:Benzylideneacetophenone(1 mmol), HCOONH4 (3 mmol), toluene (10 ml), temperature (90 oC),
time (12 h).
b
Conversion based on GC analysis.
Table 2 Effect of various types of hydrogen donar on transfer hydrogenation of α,β-unsaturated carbonyl compound.a
a
Entry
Hydrogen donar
Conversion (%)b
Selectivity (2a:3a)
1
HCOONH4
99
99:01
2
HCOONa
18
99:01
3
HCOOK
24
99:01
4
NH2-NH2.H2O
70
98:02
5
HCOOH+Et3N(1:1)
05
99:01
Reaction conditions: Benzylideneacetophenone (1mmol), ImmPd-IL (2 mol%), hydrogen donar (3 mmol), toluene (10 ml),
temperature (90 oC), time (12 h).
b
Conversion based on GC analysis.
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SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai.
Table 3 Effect of reaction parameter on transfer hydrogenation of benzylideneacetophenone.a
Entry
Solvent
HCOONH4(mmol)
Temp (oC)
Time (h)
Conversion(%)b
Selectivity(2a:3a)
(2a:3a)
(2a:3a)
Effect of solvent
1
DMF
3
100
12
72
98:02
2
Water
3
100
12
14
99:01
3
Ethanol
3
90
12
70
96:04
4
THF
3
100
12
30
99:01
5
DCM
3
90
12
05
99:01
6
Toluene
3
90
12
99
99:01
Effect of hydrogen donar concentration
7
Toluene
1
90
12
34
99:01
8
Toluene
2
90
12
78
99:01
9
Toluene
3
90
12
99
99:01
10
Toluene
5
90
12
99
98:02
Effect of temperature
11
Toluene
3
70
12
66
99:01
12
Toluene
3
90
12
99
99:01
Effect of Time
13
Toluene
3
90
6
48
99:01
14
Toluene
3
90
8
74
99:01
15
Toluene
3
90
12
99
99:01
Reaction condition: Benzylideneacetophenone (1 mmol), ImmPd-IL (2 mol%), HCOONH4 (3 mmol), solvent (10 ml),
temperature (90 oC), time (12 h).
b
Conversion based on GC analysis.
a
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Table 4 Chemoselective transfer hydrogenation of α,β-unsaturated carbonyl compounds.a
Conversion(%)b
Selectivity (2a:3a)
1
99
99:01
2
94
99:01
3
91
99:01
4
90
99:01
5
84
97:03
6
82
96:04
7
80
99:01
8
76
99:01
9
96
100:00
10
98
100:00
11
92
99:01
12
87
98:02
13
84
100:00
14
82
100:00
15
99
100:00
16c
97
99:01
17c
81
99:01
Entry
Substrate
Product
a
Reaction condition: Benzylideneacetophenone (1 mmol), ImmPd-IL (2 mol%), HCOONH4 (3 mmol), toluene (10 ml),
temperature (90 oC), time (12 h). b Conversion based on GC analysis.
c
6 mmol of HCOONH4 required for complete the reduction.
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SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai.
Figure 1 Recyclability study of the ImmPd-IL Catalyst.
Figure 2 XPS analysis of the ImmPd-IL catalyst (a) XPS survey spectrum (b) Pd3d region (c) Cl2p region.
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4. Conclusions:
In summary, the present protocol reports a simple, efficient, recyclable catalytic system for chemoselective transfer
hydrogenation of various α,β-unsaturated carbonyl compound by ImmPd-IL as a versatile heterogeneous catalyst. The present
methodology offers chemoselective 1,4-reduction of wide range of substrates with various functionalities such as ketones,
aldehydes, esters, amides and nitrile affording excellent yield and selectivity of the desired product. Also, the catalyst was reused
for four recycles without significant loss in the catalytic activity.
References
[1] N. M. Patil, T. Sasaki and B. M. Bhanage, Catal. Lett. 2014, 144, 1803-1809.
[2] D. B. Bagal, Z. S. Qureshi, K. P. Dhake, S. R. Khan and B. M. Bhanage, Green Chem. 2011, 13, 1490-1494.
[3] M. V. Khedkar, T. Sasaki, B. M. Bhanage, ACS Catal. 2013, 3, 287-293.
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