Ambient-pressure highly active hydrogenation of ketones and aldehydes catalyzed by a metal-ligand bifunctional iridium catalyst under base-free conditions in water

Article abstract of DOI:10.1016/j.jcat.2021.04.023

A green, efficient, and high active catalytic system for the hydrogenation of ketones and aldehydes to produce corresponding alcohols under atmospheric-pressure H₂ gas and ambient temperature conditions was developed by a water-soluble metal–ligand bifunctional catalyst [Cp*Ir(2,2′-bpyO)(OH)][Na] in water without addition of a base. The catalyst exhibited high activity for the hydrogenation of ketones and aldehydes. Furthermore, it was worth noting that many readily reducible or labile functional groups in the same molecule, such as cyan, nitro, and ester groups, remained unchanged. Interestingly, the unsaturated aldehydes can be also selectively hydrogenated to give corresponding unsaturated alcohols with remaining C=C bond in good yields. In addition, this reaction could be extended to gram levels and has a large potential of wide application in future industrial.

Full text of DOI:10.1016/j.jcat.2021.04.023

Journal of Catalysis 399 (2021) 1–7
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Ambient-pressure highly active hydrogenation of ketones and aldehydes
catalyzed by a metal-ligand bifunctional iridium catalyst under base-free
conditions in water
Rongzhou Wang, Yuancheng Yue, Jipeng Qi, Shiyuan Liu, Ao Song, Shuping Zhuo, Ling-Bao Xing
School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo 255000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A green, efficient, and high active catalytic system for the hydrogenation of ketones and aldehydes to pro-
duce corresponding alcohols under atmospheric-pressure H2 gas and ambient temperature conditions
was developed by a water-soluble metal–ligand bifunctional catalyst [Cp*Ir(2,20-bpyO)(OH)][Na] in water
without addition of a base. The catalyst exhibited high activity for the hydrogenation of ketones and alde-
hydes. Furthermore, it was worth noting that many readily reducible or labile functional groups in the
same molecule, such as cyan, nitro, and ester groups, remained unchanged. Interestingly, the unsaturated
aldehydes can be also selectively hydrogenated to give corresponding unsaturated alcohols with remain-
ing C=C bond in good yields. In addition, this reaction could be extended to gram levels and has a large
potential of wide application in future industrial.
Received 7 February 2021
Revised 31 March 2021
Accepted 16 April 2021
Available online 28 April 2021
Keywords:
Catalytic hydrogenation
Catalysis in water
Iridium complex
Carbonyl reduction
High activity
Ó 2021 Elsevier Inc. All rights reserved.
1. Introduction
aldol side reactions unavoidably occurred, and the use of high-
pressure H2 gas needs specialized experimental setup for safety.
The reduction of the carbonyl moiety to an alcohol via hydro-
genation is a key step in the industrial synthesis of fine chemicals,
leading to molecules with hydroxyl functionalities [1]. Tradition-
ally, a stoichiometric amount of metal hydrides (e.g., NaBH4, bor-
More importantly, given that organic solvents are used in vast
quantities as compared to reactants, solvents have been the focus
of environmental concerns. Using green solvents is urgent because
of the toxicity and unfriendly environment of organic solvents.
Herein, water is attracting more and more interest from both
industrial and academic perspectives as a replacement for organic
solvents. Catalytic reactions in water mediated by aquo-soluble
coordination compounds could provide an interesting solution to
most of the problems found in the catalytic synthesis of organic
solvents [5].
But as far as we know, only two catalysts were reported, which
hydrogenate aldehydes or ketones under 1 atm H2 pressure and
base-free conditions. In 2014, Do and co-workers developed an
iridium catalyst for the hydrogenation of aldehydes and ketones
under 1 atm H2 without a base in mixed solvents of t-BuOH/H2O
(1:9), in which eight examples were reported with high yields for
24 h under room temperature (Scheme 1, a) [6]. Additionally,
Choudhury and co-workers reported an iridium-based catalyst
for hydrogenation of aldehydes for general applicability under
atmospheric-pressure H2 gas and base-free conditions in H2O or
ethanol/H2O (Scheme 1, b) [7]. The catalytic reaction can be uti-
lized only for the hydrogenation of aldehydes, but not for the
hydrogenation of ketones. Thus, developing a method for highly
efficient catalytic hydrogenation of aldehydes, as well as ketones,
anes, and LiAlH-(OR)3) were used to realize such
a
transformation with the generation of a large amount of undesir-
able waste [2]. Since several decades, transition metal-catalyzed
transfer hydrogenation reactions of ketones and aldehydes with
HCOOM (M = Na, NH4, H) or isopropanol have been developed
[3]. Nevertheless, either a certain pH range is necessary, or the gen-
eration of inorganic salt by-products is inevitable. Along with
increasing environmental awareness, the hydrogenation of C=O
bonds catalyzed with H2 gas as a clean and green reagent by tran-
sition metal complexes has been well explored and applied as the
most useful catalytic method of hydrogenation of ketones and
aldehydes for the production of alcohols due to the easy manipula-
tions, high reaction activities, and wide substrate scope. To date, a
number of transition metal catalysts (Ru, Rh, Ir, Fe, Co, and Mn)
have been developed for hydrogenation reactions of ketones and
aldehydes [4]. However, most systems are based on a base and
high-pressure H2 gas, and organic solvents are required for pro-
moting the reduction smoothly. In the presence of a base, self-
E-mail address: lbxing@sdut.edu.cn (L.-B. Xing)
https://doi.org/10.1016/j.jcat.2021.04.023
0021-9517/Ó 2021 Elsevier Inc. All rights reserved.

R. Wang, Y. Yue, J. Qi et al.
Journal of Catalysis 399 (2021) 1–7
Scheme 1. Recent catalytic hydrogenation of aldehydes or ketones under 1 atm H2 and the present approach.
without a base in pure water under ambient-pressure H2 gas is still
an issue with great challenge.
In recent years, Fujita, Yamaguchi, and co-workers have previ-
ously reported a series of metal–ligand bifunctional Cp*Ir com-
(Table 1). With a series of water-soluble catalysts in hand, we next
examined the catalytic activity for the hydrogenation reaction of
acetophenone (1a) in H2O for 12 h at 30 °C. Disappointingly, con-
ducting this reaction in the presence of [Cp*Ir(H2O)3][OTf]2 (cat.
1), [Cp*Ir(NH2)3]Cl2 (cat. 2), [Cp*Ir(bpy)(H2O)][OTf]2 (cat. 3),
plexes, which bear functional ligands with an
a-hydroxypyridine
or bipyridonate skeleton [8]. These catalysts exhibit high catalytic
[Cp*Ir(6,60-(OMe)2bpy)(H2O)][OTf]2
(cat.
4)
resulted
in
activity for borrowing-hydrogen reactions. On the basis of previous
only ꢀ 12% yield of the desired product. When [Cp*Ir(6,60-(OH)2–
2,20-bpy)(H2O)][OTf]2 (cat. 5) was texted bearing a functional bihy-
droxypyridine under same conditions, we obtained the 1-
phenylethanol (2a) in 80% yield. Interestingly, a higher yield of
1-phenylethanol (2a) was obtained when using [Cp*Ir(2,20-bpyO)
(OH)][Na] (cat. 6) with the bis-pyridonate ligand, and 95% yield
was obtained after filtration through a pad of silica gel. It was
apparent that the bis-hydroxypyridine or bis-pyridonate ligand is
indispensable for high catalytic performance. The catalytic activity
of cat. 6 with the bis-pyridonate ligand was higher than cat. 5 bear-
ing the bis-hydroxypyridine ligand under the same conditions. This
was probably because the cat. 5 must go through producing a
findings, we reported the synthesis of
dem acceptorless dehydrogenation/
a
-alkylated ketones via tan-
a
-alkylation from secondary
and primary alcohols [9a], the dehydrogenative cyclization for
the construction of quinazolinones from o-aminobenzyl alcohols
with ketones [9b], and the transfer hydrogenation of aldehydes
and ketones with isopropanol under neutral conditions [9c] by
using [Cp*Ir(2,20-bpyO)(H2O)] or [Cp*Ir(6,60-(OH)2–2,20-bpy)
(H2O)][OTf]2. More recently, we have developed the catalyst
[Cp*Ir(2,20-bpyO)(H2O)] for the hydrogenation of ketones and alde-
hydes under 1 atm H2 in tert-amyl alcohol [10]. As part of our
ongoing interest in hydrogenation of ketones and aldehydes, we
herein report a highly efficient and general catalyst for the hydro-
genation of ketones and aldehydes without a base under 1 atm H2
at 30 °C by a water-soluble Iridium complex [Cp*Ir(2,20-bpyO)(O
H)][Na] in water (Scheme 1, c).
monocationic unsaturated species intermediate having
a 2-
pyridonate-based ligand in the process of hydrogenation. However,
analogous water-soluble catalysts [Cp*Rh(6,60-(OH)2–2,20-bpy)
(H2O)][OTf]2 (cat. 7) and [(p-cymene)Ru(6,60-(OH)2–2,20-bpy)
(H2O)][OTf]2 (cat. 8) showed a lower activity than cat. 6. Addition-
ally, the hydrogenation reaction also proceeded with lower
amounts of the catalyst (0.50 mol %, cat. 6), giving a slightly lower
yield.
2. Results and discussion
Exploring the best reaction conditions for the hydrogenation
reaction, our initial catalytic investigations were carried out using
the hydrogenation of acetophenone (1a) as a benchmark reaction
After establishing optimal reaction parameters (1 mol% cat. 6,
1 atm H2, 1 mL H2O, 30 °C, 12 h), the hydrogenation of various
2

R. Wang, Y. Yue, J. Qi et al.
Journal of Catalysis 399 (2021) 1–7
Table 1
Hydrogenation of acetophenone (1a) in H2O under 1 atm H2 at 30 °C using a range of
catalysts.a,b
a
Reaction conditions: 1a (1 mmol), 1 atm H2 (balloon), catalyst (x mol %), H2O (1 mL),
30 °C, 12 h.
b
Catalyst structures.
Isolated yield.
c
ketones was studied (Table 2). The substituted 1-phenethyl alcohol
derivatives such as 1-(o-tolyl)ethanol (2b), 1-(p-tolyl)ethanol (2c),
1-(4-methoxyphenyl)ethanol (2d), and 1-(3,4-dimethoxyphenyl)
ethanol (2e), carrying electron-donating groups were isolated in
89–92% yields. Similarly, the presence of one or two halogen atoms
(fluorine, chlorine, or bromine) at the aromatic ring led to good
conversion, and the corresponding products (2f-2j) were obtained
with 86–96% yields. When 4-hydroxyacetophenone (1k) and
methyl-4-(1-hydroxyethyl)benzoate (1l) were used as the sub-
strates, the desired products 2k and 2l were obtained in 91% and
94% yields. Reactions with strong electron-withdrawing sub-
stituents, such as trifluoromethoxy, nitro, and cyan groups afforded
the desired products 2m-2o in 93–96% yields. When 2-
acetylpyridine (1p) and 2-acetonaphthone (2q) were examined,
the desired products were obtained in good yields. Interestingly,
when benzalacetone (1r) was subjected to the reaction under stan-
dard conditions, only the C=O bond was selectively hydrogenated
with retaining C=C bond and the desired product 2r was obtained
in 96% yield. In addition, nonmethyl ketone (1s) was proven to be a
suitable substrate, and the desired product 2s was obtained in 94%
yield. It was possible that due to the steric hinerance, the yields of
2-methyl-1-phenyl-1-propanol (2t) and 2,2-dimethyl-1-phenyl-1-
propanol (2u) were slowly depressed. Finally, aliphatic ketones,
including cyclohexanone (1v) and octanone (1w), were also evalu-
ated, which provided the corresponding products 2v and 2w in 92%
and 85% yields, respectively.
Next, we studied the general applicability of this procedure for
the hydrogenation of aldehydes, and the results were listed in
Table 3. Overall, cat. 6 was efficient for the hydrogenation of differ-
ently functionalized aromatic aldehydes, as well as heterocyclic
aromatic substrates and aliphatic aldehydes. Reactions of ben-
zaldehyde (3a) and the electron-donating aromatic aldehydes
afforded the desired products 4a-4d in 93–96% yields. Similarly,
the electron-poor (fluorine, chlorine, and bromine) benzaldehydes
were proved to be the ideal substrates to deliver products 4e-4h in
90–95% yields. 4-Hydroxybenzaldehyde (3i) and methyl-4-
formylbenzoate (3j) were proved suitable substrates, giving the
corresponding products 4i and 4j in 93% and 95% yields. When
benzaldehydes with a strong electron-withdrawing group, 4-
nitrobenzaldehyde (3k) and 4-cyanobenzaldehyde (3l) were used
as the substrates and the desired products were obtained in 93%
and 95% yields. For 2-pyridinecarboxaldehyde (3m) and 2-
naphthaldehyde (3n), the corresponding products 4m and 4n were
isolated in 94 and 95% yields, respectively. When benzenepropanal
(3o) was used, the desired alcohol 4o was obtained in 94%. It is
important to note that various aliphatic aldehydes (3p and 3q),
3

R. Wang, Y. Yue, J. Qi et al.
Journal of Catalysis 399 (2021) 1–7
Table 2
Hydrogenation of ketones in H2O under 1 atm H2 at 30 °C by cat. 6.a,b
a
Reaction conditions: 1 (1 mmol), 1 atm H2 (balloon), cat. 6 (1 mol %), H2O (1 mL), 30 °C, 12 h.
Isolated yield.
b
including cyclic and linear aliphatic aldehydes, were tolerated, giv-
ing 90% and 93% yields of the corresponding alcohols.
pared to the optimal benchmark reaction (Table, entry 6), which
proved to be a green and significant potential protocol with a wide
range of applications in industry.
Encouraged by the above result, we next sought to the hydro-
genation of a series of unsaturated aldehydes under standard con-
ditions (Table 4). As we expected, the reaction with cinnamyl
aldehyde (5a) afforded the desired product 6a in 97% yield. It
was found that parasubstituted substrates with incorporation of
electron-donating and electron-withdrawing substituents, such
as Me-, MeO-, and Cl-, reacted efficiently with H2 to produce the
desired products 6b-6d in 90–93% yields. High catalytic activities
were also observed when cinnamaldehydes bearing a substituent
Based on the previous reports by Fujita and Yamaguchi
[8d,8e,11,12a] as well as our works [9c,12b], a possible mechanism
for the hydrogenation reaction of acetophenone (1a) was shown in
Scheme 3. Initially, the anionic iridium hydride species A was gen-
erated via the reaction of cat. 6 with H2. Protonation of the bipyri-
donate ligand by water would give neutral hydride species B. Then,
the simultaneous transfer of the hydride on iridium with the
hydroxyl proton on the functional ligand in iridium species B to
C=O bond of acetophenone (1a), which would be subjected to the
formation of the corresponding alcohol 2a to generate the unsatu-
rated species C. Finally, cat. 6 would be regenerated by the reaction
of C with a hydroxide anion [13].
on the a-position were used, and the desired products 6e-6g were
obtained in good to excellent yields. Particularly, the industrially
important perillyl alcohol (6h) was also obtained in 91% yields.
Moreover, cyclohex-3-enecarbaldehyde (5i) was reduced to 3-
cyclohexene -1- methanol (6i), which was an important compound
for the fragrance industry, in good yield of 93%.
In order to test the utility of this strategy, a 10 mmol gram-scale
reaction was conducted (Scheme 2). The hydrogenation reaction of
acetophenone (1a) also performed very well in H2O with a smaller
amount of solvent and catalyst. To our delight, the product 2a was
obtained using a simple separation from the mixture without
another organic solvent, giving the product in a higher yield com-
3. Conclusions
In summary, we have demonstrated that the water-soluble Irid-
ium complex [Cp*Ir(2,20-bpyO)(OH)][Na] with a functional bipyri-
donate ligand is a highly active and general catalyst for the
hydrogenation of ketones, aldehydes, and unsaturated aldehydes
4

R. Wang, Y. Yue, J. Qi et al.
Table 3
Journal of Catalysis 399 (2021) 1–7
Hydrogenation of aldehydes in H2O under 1 atm H2 at 30 °C by cat. 6.a,b
a
Reaction conditions: 3 (1 mmol), 1 atm H2 (balloon), cat. 6 (1 mol %), H2O (1 mL),
30 °C, 12 h.
b
Isolated yield.
Table 4
Hydrogenation of unsaturated aldehydes in H2O under 1 atm H2 at 30 °C by cat. 6.a,b
a
Reaction conditions: 5 (1 mmol), 1 atm H2 (balloon), cat. 6 (1 mol %), H2O (1 mL),
30 °C, 12 h.
b
Isolated yield.
esters, and olefins. Moreover, high yields, up to 97%, were observed
under the optimal conditions. Overall, this water-soluble Iridium
complex represented a catalyst for the hydrogenation of ketones
and aldehydes with higher efficiency, higher activity, and more
environmental friendliness to date. Importantly, the gram-scale
experiment has been successfully conducted, which might indicate
that this strategy has more applications in the future.
Scheme 2. Large-Scale Hydrogenation of 1a with H2.
4. Experimental
with H2 gas at normal temperature and atmospheric pressure in
water. Of significant practical importance was that the catalyst tol-
erated aromatic, heteroaromatic, and aliphatic aldehydes or
ketones as well as a range of synthetically useful functional groups
including alkyl groups, alkoxy groups, halogens, nitro groups,
Melting points were measured on a RY-1 micro-melting appara-
tus. Proton nuclear magnetic resonance (1H NMR) spectra were
recorded at 400 MHz using a 400 spectrometer. Chemical shifts
are reported in delta (d) units, parts per million (ppm) downfield
5

R. Wang, Y. Yue, J. Qi et al.
Journal of Catalysis 399 (2021) 1–7
Scheme 3. Proposed hydrogenation mechanism.
from tetramethylsilane or ppm relative to the center of the singlet
at 7.26 ppm for CDCl3 and 2.50 ppm for DMSO d6. Coupling con-
stants J values are reported in Hertz (Hz), and the splitting patterns
were designated as follows: s, singlet; d, doublet; t, triplet; m, mul-
tiplet; b, broad. Analytical thin-layer chromatography (TLC) was
carried out using 0.2-mm commercial silica gel plates. [Cp*Ir
(H2O)3][OTf]2 (cat. 1) [14], [Cp*Ir(NH3)3][Cl]2 (cat. 2) [15], [Cp*Ir
(bpy)(H2O)][OTf]2 (cat. 3) [16], [Cp*Ir(6,60-(OMe)2bpy)(H2O)]
[OTf]2 (cat. 4) [17], [Cp*Ir(6,60-(OH)2–2,20-bpy)(H2O)][OTf]2 (cat.
5) [18], [Cp*Ir(2,20-bpyO)(OH)][Na] (cat. 6) [11], [Cp*Rh(6,60-
(OH)2–2,20-bpy)(H2O)][OTf]2 (cat. 7) [19], [(p-cymene)Ru(6,60-
(OH)2–2,20-bpy)(H2O)][OTf]2 (cat. 8) [20], were synthesized
according the previous reports.
stirrer. Next, vacuum was applied to the flask followed by filling
with H2 gas and keeping the flask attached to a balloon filled with
H2 gas. The mixture was heated at 30 °C for 12 h. After completion
of the reaction, the product 2a could be obtained through the sep-
aration of organic phase and aqueous phase. The conversion rate of
1a was proved to be 100% by 1H NMR. And finally, a minimum sup-
ply of water was removed under reduced pressure using a rotary to
give 2a (1.17 g) in 96% yield.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
4.1. General procedure for catalytic hydrogenation of ketones,
aldehydes or unsaturated aldehydes
Acknowledgments
We are grateful for the financial support from the National Nat-
ural Science Foundation of China (22005179), and Natural Science
Foundation of Shandong Province (ZR2020QB113 and
ZR2020MB018).
To an oven-dried 5 mL round-bottom flask were added ketones
or aldehydes or unsaturated aldehydes (1 mmol), cat. 6 (5.5 mg,
1 mol %) and H2O (1 mL). Next, vacuum was applied to the flask fol-
lowed by filling with H2 gas and keeping the flask attached to a bal-
loon filled with H2 gas. The mixture was heated at 30 °C for 12 h.
After completion of the reaction, the mixture was extracted with
ethyl acetate (5 mL ꢁ 3). Then, the ethyl acetate layers were com-
bined, dried with anhydrous sodium sulfate, filtered, and concen-
trated by evaporation under reduced pressure. The alcohols were
isolated and purified by filtering a hexanes/ethyl acetate (8:1)
solution of the crude product through a pad of silica gel. Then
the solvent was removed under reduced pressure to afford the cor-
responding products. The purity of alcohol products was assessed
using 1H NMR spectroscopy.
Appendix A. Supplementary material
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jcat.2021.04.023.
References
[1] (a) I. Dodgson, in: M. Guisnet et al. (Eds.), Heterogeneous catalysis and fine
chemicals III, Stud. Surf. Sci. Catal. 78 (1993) 6; (b) B. J. Arena, Deactivation of
ruthenium catalysts in continuous glucose hydrogenation, Appl. Catal. A. 87 (2)
(1992) 219–229.
[2] (a) H. C. Brown, H. I. Schlesinger, I. Sheft, D. M. Ritter, Addition compounds of
alkali metal hydrides. Sodium trimethoxyborohydride and related compounds,
J. Am. Chem. Soc. 75 (1) (1953) 192–195; (b) H. I. Schlesinger, H. C. Brown, A. E.
Finholt, The preparation of sodium borohydride by the high temperature
reaction of sodium hydride with borate esters, J. Am. Chem. Soc. 75 (1) (1953)
205–209; (c) H. C. Brown, S. Krishnamurthy, Forty years of hydride reductions,
4.2. Procedure for gram-scale synthesis of 2a [21]
1a (1.2 g, 10 mmol), cat. 6 (27.5 mg, 0.5 mol %) and H2O (5 mL)
were added into an oven-dried 10 mL round-bottom flask with a
6

R. Wang, Y. Yue, J. Qi et al.
Journal of Catalysis 399 (2021) 1–7
Tetrahedron 35 (5) (1979) 567–607; (d) N. Y. M. Fung, P. de Mayo, J. H.
Schauble, A. C. Weedon, Reduction by tributyltin hydride of carbonyl
compounds adsorbed on silica gel: selective reduction of aldehydes, J. Org.
Chem. 43 (20) (1978) 3977–3979; (e) J. Magano, J. R. Dunetz, Large-Scale
carbonyl reductions in the pharmaceutical industry, Org. Process Res. Dev. 16
(6) (2012) 1156–1184; (f) S. Krishnamurthy, Lithium tris (3-ethyl-3-
pentyloxy) aluminohydride. A new remarkably chemoselective reagent for
the reduction of aldehydes in the presence of ketones, J. Org. Chem. 46 (22)
(1981) 4628–4629; (g) Y. Kuroiwa, S. Matsumura, K. Toshima, Chemoselective
reduction of aldehydes over ketones with sodium tris (hexafluoroisopropoxy)
borohydride, Synlett. 2008 (16) (2008) 2523–2525; (h) M. V. N. de Souza, T. R.
A. Vasconcelos, Recent methodologies mediated by sodium borohydride in the
reduction of different classes of compounds, Appl. Organomet. Chem. 20 (11)
(2006) 798–810.
[7] S. Garhwal, B. Maji, S. Semwal, J. Choudhury, Ambient-pressure and base-free
aldehyde hydrogenation catalyst supported by a bifunctional abnormal NHC
ligand, Organometallics 37 (24) (2018) 4720–4725.
[8] (a) K. Fujita, T. Yoshida, Y. Imori, R. Yamaguchi, Dehydrogenative oxidation of
primary and secondary alcohols catalyzed by
a Cp*Ir complex having a
functional C, N-chelate ligand, Org. Lett. 13 (9) (2011) 2278–2281; (b) R.
Yamaguchi, C. Ikeda, Y. Takahashi, Homogeneous catalytic system for
reversible
dehydrogenationꢂhydrogenation
reactions
of
nitrogen
heterocycles with reversible interconversion of catalytic species, J. Am.
Chem. Soc. 131 (24) (2009) 8410–8412; (c) Y. Tanaka, M. Kobayashi, R.
Yamaguchi, Homogeneous perdehydrogenation and perhydrogenation of
fused bicyclic N-heterocycles catalyzed by iridium complexes bearing
a
functional bipyridonate ligand, J. Am. Chem. Soc. 136 (13) (2014) 4829–
4832; (d) K. Fujita, R. Yamaguch, Cooperative catalysis by iridium complexes
with a bipyridonate ligand: versatile dehydrogenative oxidation of alcohols
and reversible dehydrogenation–hydrogenation between 2-propanol and
acetone, Angew. Chem. Int. Ed. 51 (51) (2012) 12790–12794.(e) R. Kawahara,
K. Fujita, R. Yamaguchi, Multialkylation of aqueous ammonia with alcohols
catalyzed water-soluble Cp*Ir-Ammine complexes, J. Am. Chem. Soc. 132 (43)
(2010) 15108–15111.
[3] (a) F. Spindler, H. U. Blaser, Transition Metals for Organic Synthesis, Vol. 2
(Eds.: M. Beller, C. Bolm), Wiley-VCH, Weinheim, (2004) 113; (b) H. U. Blaser, F.
Spindler, Handbook of Homogeneous Hydrogenation, (Eds.: J. G. de Vires, C. J.
Elsevier), Wiley-VCH, Weinheim, 3 (2007) 1193; (c) S. Gladiali, E. Alberico,
Asymmetric transfer hydrogenation: chiral ligands and applications, Chem.
Soc. Rev. 35 (2006) 226-236; (d) X. Wu, J. Liu, X. Li, A. Zanotti-Gerosa, F.
Hancock, D. Vinci, J. Ruan, J. Xiao, On water and in air: fast and highly
chemoselective transfer hydrogenation of aldehydes with iridium catalysts,
Angew. Chem. Int. Ed. 45 (40) (2006) 6718ꢂ6722; (e) S. Fleischer, S. Zhou, K.
Junge, M. Beller, General and highly efficient iron-catalyzed hydrogenation of
[9] (a) R. Wang, J. Ma, F. Li, Synthesis of
a-alkylated ketones via tandem
acceptorless dehydrogenation/a-alkylation from secondary and primary
alcohols catalyzed by metal–ligand bifunctional iridium complex [Cp*Ir(2,20-
bpyO)(H2O)], J. Org. Chem. 80 (21) (2015) 10769–10776; (b) R. Wang, H. Fan,
W. Zhao, F. Li, Acceptorless dehydrogenative cyclization of o-aminobenzyl
alcohols with ketones to quinolines in water catalyzed by water-soluble
metal–ligand bifunctional catalyst [Cp*(6,60-(OH)2bpy)(H2O)][OTf]2, Org. Lett.
18 (15) (2016) 3558–3561; (c) R. Wang, Y. Tang, M. Xu, C. Meng, Transfer
hydrogenation of aldehydes and ketones with isopropanol under neutral
conditions catalyzed by a metal–ligand bifunctional catalyst [Cp*Ir(2,20-bpyO)
(H2O)], J. Org. Chem. 83 (4) (2018) 2274–2281.
aldehydes, ketones, and a,b-unsaturated aldehydes, Angew. Chem. Int. Ed. 52
(19) (2013) 5120ꢂ5124; (f) D. Talwar, X. Wu, O. Saidi, N. P. Salguero, J. Xiao,
Versatile iridicycle catalysts for highly efficient and chemoselective transfer
hydrogenation of carbonyl compounds in water, Chem. - Eur. J. 20 (40) (2014)
12835ꢂ12842; (g) X. S. Baldino, S. Facchetti, H. G. Nedden, A. Zanotti-Gerosa,
W. Baratta, Chemoselective transfer hydrogenation of aldehydes with
HCOONH4 catalyzed by RuCl(CNNPh)(PP) pincer complexes, ChemCatChem 8
(20) (2016) 3195ꢂ3198; (h) Z. Yang, Z. Zhu, R. Luo, X. Qiu, J. Liu, J. Yang, W.
Tang, Iridium-catalyzed highly efficient chemoselective reduction of aldehydes
in water using formic acid as the hydrogen source, Green Chem. 19 (14) (2017)
3296ꢂ3301; (i) M. Pandrala, A. Resendez, S. V. Malhotra, Polypyridyl iridium
(III) based catalysts for highly chemoselective hydrogenation of aldehydes, J.
Catal. 378 (2019) 283–288.
[10] R. Wang, J. Qi, Y. Yue, Z. Lian, H. Xiao, S. Zhuo, L. Xing, Ambient-pressure
hydrogenation of ketones and aldehydes by
a metal-ligand bifunctional
catalyst [Cp*Ir(2,2’-bpyO)(H2O)] without using base, Tetrahedron 75 (34)
(2019) 130463.
[11] K. Fujita, R. Kawahara, T. Aikawa, Hydrogen production from a methanol–
water solution catalyzed by an anionic iridium complex bearing a functional
bipyridonate ligand under weakly basic conditions, Angew. Chem. Int. Ed. 54
(31) (2015) 9057–9060.
[4] (a) S. Werkmeister, K. Junge, M. Beller, Catalytic hydrogenation of carboxylic
acid esters, amides, and nitriles with homogeneous catalysts, Org. Process Res.
Dev. 18 (2) (2014) 289–302; (b) Y. N. Duan, X. Y. Du, Z. K. Cui, Y. Q. Zeng, Y. F.
Liu, T. L. Yang, J. L. Wen, X. M. Zhang, Homogeneous hydrogenation with a
cobalt/tetraphosphine catalyst: a superior hydride donor for polar double
bonds and N–heteroarenes, J. Am. Chem. Soc. 141 (51) (2019) 20424ꢂ20433;
(c) M. Basauri-Molina, C. F. Riemersma, M. A. Würdemann, H. Kleijn, R. J. M.
Klein Gebbink, Lipase active site covalent anchoring of Rh(NHC) catalysts:
towards chemoselective artificial metalloenzymes, Chem. Commun. 51(31)
(2015) 6792-6795; (d) R. Sole, M. Bortoluzzi, A. Spannenberg, S. Tin, V.
Beghetto, J. G. de Vries, Synthesis, characterization and catalytic activity of
novel ruthenium complexes bearing NNN click based ligands, Dalton Trans. 48
(36) (2019) 13580–13588; (e) M. Garbe, Z. H. Wei, B. Tannert, A. Spannenberg,
H. J. Jiao, S. Bachmann, M. Scalone, K. Junge, M. Beller, Enantioselective
hydrogenation of ketones using different metal complexes with a chiral PNP
pincer ligand, Adv. Synth. Catal. 361 (18) (2019) 1913–1920; (f) P. Puylaert, R.
V. Heck, Y. T. Fan, A. Spannenberg, W. Baumann, M. Beller, J. Medlock, W.
[12] (a) R. Kawahara, K. Fujita, R. Yamaguchi, Dehydrogenative oxidation of
alcohols in aqueous media using water-soluble and reusable Cp*Ir catalysts
bearing a functional bipyridine ligand, J. Am. Chem. Soc. 134 (8) (2012), 3643–
3646; (b) R. Z. Wang, X. Y. Han, J. Xu, P. Liu, F. Li, Transfer hydrogenation of
ketones and imines with methanol under base-free conditions catalyzed by an
anionic metalꢂligand bifunctional Iridium catalyst, J. Org. Chem. 85 (4) 2020
2242ꢂ2249.
[13] The reaction of cat. 6 (2 mol%) with acetophenone (1 mmol) was performed
under 1 atm H2 in D2O at 30 °C for 20 min, and a peak (d ꢂ10.7) was observed
by the analysis of 1H NMR spectra. It was supposed to be a characteristic signal
of iridium hydride species, see Supplementary Material.
[14] S. Ogo, N. Makihara, Y. Watanabe, pH-dependent transfer hydrogenation of
water-soluble carbonyl compounds with [Cp*IrIII(H2O)3]2+ (Cp* =
g
5-C5Me5)
as
a catalyst precursor and HCOONa as a hydrogen donor in water,
Organometallics 18 (26) (1999) 5470–5474.
Bonrath, L. Lefort, S. Hinze, J. G. de Vries, Selective hydrogenation of
a
,b-
[15] R. Kawahara, K. Fujita, R. Yamaguchi, N-alkylation of amines with alcohols
catalyzed by a water-soluble Cp*Iridium complex: an efficient method for the
synthesis of amines in aqueous media, Adv. Synth. Catal. 353 (7) (2011) 1161–
1168.
[16] S. Ogo, N. Makihara, Y. Kaneko, Y. Watanabe, pH-dependent transfer
hydrogenation, reductive amination, and dehalogenation of water-soluble
carbonyl compounds and alkyl halides promoted by Cp*Ir complexes,
Organometallics 20 (23) (2001) 4903–4910.
[17] W. Wang, J.F. Hull, J.T. Muckerman, E. Fujita, Y. Himed, Second-coordination-
sphere and electronic effects enhance iridium(III)-catalyzed homogeneous
hydrogenation of carbon dioxide in water near ambient temperature and
pressure, Energy Environ. Sci. 5 (7) (2012) 7923–7926.
unsaturated aldehydes and ketones by air-stable ruthenium NNS complexes,
Chem. -Eur. J. 23 (25) (2017) 8473–8481; (g) D. Wang, T. Roisnel, C. Darcel, J.
Sortais, Hydrogenation of ketones with a manganese PN3P pincer pre-catalyst
antoine bruneau-voisine, Cataly. Commun. 92 (2017) 1–4; (h) S. R. Sler, J.
Obenauf, R. Kempe,
A highly active, easily accessible cobalt catalyst for
selective hydrogenation of C=O bonds, J. Am. Chem. Soc. 137 (25) (2015) 7998–
8001; (i) R. Buhaibeh, Oleg. A. Filippov, A. Bruneau-Voisine, J. Willot, C.
Duhayon, D. A. Valyaev, N. Lugan, Y. Canac, J. Sortais, Phosphine-NHC
manganese hydrogenation catalyst exhibiting a non-classical metal-ligand
cooperative H2 activation mode, Angew. Chem. Int. Ed. 58 (20) (2019) 6727–
6731.
[5] (a) F. Joó, Aqueous organometallic catalysis, Kluwer: Dordrecht, The
Netherlands, (2001); (b) D. J. Adams, P. J. Dyson, S. J. Tavener, Chemistry in
alternative reaction media; Wiley: Chichester, U.K. (2004); (c) B. Cornils, W. A.
Herrmann, Aqueous-phase organometallic catalysis, 2nd ed., Wiley-VCH:
Weinheim, Germany, (2004); (d) C. J. Li, L. Chen, Organic chemistry in water,
Chem. Soc. Rev. 35 (2006) 68–82; (e) T. Kitanosono, K. Masuda, P. Xu, S.
Kobayashi, Catalytic organic reactions in water toward sustainable society,
Chem. Rev. 118 (2) (2018) 679–746; (f) P. Lorenzo-Luis, A. Romerosa, M.
Serrano-ruiz, Catalytic isomerization of allylic alcohols in water, ACS Catal. 2
(6) (2012) 1079ꢂ1086; (g) A. Mehta, B. Saha, A. A. Koohang, M. S. Chorghade,
Arene ruthenium catalyst MCAT-53 for the synthesis of heterobiaryl
compounds in water through aromatic CꢂH bond activation, Org. Process
Res. Dev. 22 (9) (2018) 1119ꢂ1130.
[18] R. Kawahara, K. Fujita, R. Yamaguchi, Dehydrogenative oxidation of alcohols in
aqueous media using water-soluble and reusable Cp*Ir catalysts bearing a
functional bipyridine ligand, J. Am. Chem. Soc. 134 (8) (2012) 3643–3646.
[19] G. Zeng, S. Sakaki, K. Fujita, H. Sano, R. Yamaguchi, Efficient catalyst for
acceptorless alcohol dehydrogenation: interplay of theoretical and
experimental studies, ACS Catal. 4 (3) (2014) 1010–1020.
[20] M. Khanfar, N.J. Taylor, J.F. Britten, L. Harrington, Catalytic deoxygenation of
terminal-diols under acidic aqueous conditions by the ruthenium complexes
[(g
6-arene)Ru(X)(N \ N)](OTf)n, X = H2O, H, 6-arene = p-Me-iPr-C6H4, C6Me6,
g
N \ N = bipy, phen, 6,60-diamino-bipy, 2,9-diamino-phen, n = 1, 2): influence
of the ortho-amine substituents on catalytic activity, J. Mol. Catal. A-Chem. 277
(1–2) (2007) 233–251.
[21] Because the solubility of the reactant and the corresponding products were
limited in pure water, the stirring speed was very important for the
[6] A.H. Ngo, M.J. Adams, L.H. Do, Selective acceptorless dehydrogenation and
hydrogenation by iridium catalysts enabling facile interconversion of
glucocorticoids, Organometallics 33 (23) (2014) 6742–6745.
heterogeneous reaction. Hence,
required under standard reaction conditions.
a
high stirring speed (ꢃ 1500 rmp) was
7