Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst [Cp*Ir(2,2′-bpyO)(H2O)] without using base

Article abstract of DOI:10.1016/j.tet.2019.07.021

An efficient catalytic system for hydrogenation of ketones and aldehydes using a Cp*Ir complex [Cp*Ir(2,2′-bpyO)(H₂O)] bearing a bipyridine-based functional ligand as catalyst has been developed. A wide variety of secondary and primary alcohols were synthesized by the catalyzed hydrogenation of ketones and aldehydes under facile atmospheric-pressure without a base. The catalyst also displays an excellent chemoselectivity towards other carbonyl functionalities and unsaturated motifs. This catalytic system exhibits high activity for hydrogenation of ketones and aldehydes with H₂ gas.

Full text of DOI:10.1016/j.tet.2019.07.021

Tetrahedron xxx (xxxx) xxx
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Ambient-pressure hydrogenation of ketones and aldehydes by a
0
metal-ligand bifunctional catalyst [Cp*Ir(2,2 -bpyO)(H O)] without
2
using base
a
,
b
,
*
a
a
a
a
Rongzhou Wang
, Jipeng Qi , Yuancheng Yue , Zhe Lian , Haibin Xiao ,
a
a, **
Shuping Zhuo , Lingbao Xing
School of Chemistry and Chemical Engineering, Shandong University of Technology, Zibo, 255000, PR China
a
b
Key Laboratory of Biobased Polymer Materials, Shandong Provincial Education Department, School of Polymer Science and Engineering, Qingdao
University of Science and Technology, Qingdao 266042, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 May 2019
Received in revised form
An efficient catalytic system for hydrogenation of ketones and aldehydes using a Cp*Ir complex
0
[
Cp*Ir(2,2 -bpyO)(H
2
O)] bearing a bipyridine-based functional ligand as catalyst has been developed. A
wide variety of secondary and primary alcohols were synthesized by the catalyzed hydrogenation of
ketones and aldehydes under facile atmospheric-pressure without a base. The catalyst also displays an
excellent chemoselectivity towards other carbonyl functionalities and unsaturated motifs. This catalytic
13 July 2019
Accepted 15 July 2019
Available online xxx
system exhibits high activity for hydrogenation of ketones and aldehydes with H
2
gas.
©
2019 Elsevier Ltd. All rights reserved.
Keywords:
Catalytic hydrogenation
Iridium complex
Carbonyl reduction
Chemoselective reduction
Homogeneous catalysis
1
. Introduction
self-aldol side reaction unavoidably occurred under the basic con-
ditions limits application of the catalytic hydrogenation. In addi-
tion, the specialized experimental setup was required for security
The reduction of ketones and aldehydes is of great relevance for
organic synthesis, as well as industrial application in the produc-
tion of flavours, fragrances, fine chemicals and pharmaceutical
compounds [1]. Typically, the stoichiometric amount of toxic
with the presence of high-pressure H
2
gas. Recently, Hanson [8] and
Do reported two catalysts for the hydrogenation of ketones and
aldehydes under 1 atm H pressure and base-free conditions.
However, only a few examples were reported in this condition, and
high-pressure H gas, higher reaction temperature and longer re-
5
b
2
4 3
reducing agents such as NaBH , boranes, and LiAlH-(OR) are used
for this transformation [2], and a large number of environmentally
unfriendly by-products are produced in these reactions. The cata-
lytic hydrogenation has been realized as an excellent method that
2
action time were required for aliphatic aldehydes. Thus, the
development of an efficient and general organometallic catalyst for
the hydrogenation of ketones and aldehydes at atmospheric pres-
resolves this problem by using H
A wide variety of highly productive catalysts based on metals ions
Ru [3], Rh [4], Ir [5], Fe [6], and Co [7]) have been developed for this
purpose. However, these hydrogenation reactions were achieved
using an inorganic/organic base and high-pressure H gas. A facile
2
gas as a clean and green reagent.
2
sure of H as well as under base-free conditions is highly desirable.
(
Recently, a series of metal-ligand bifunctional iridium com-
plexes containing a functional bipyridine or a bipyridonate ligand
were reported by Fujita and Yamaguchi [9]. It was demonstrated
that they are very active catalysts for acceptorless dehydrogenation
of alcohols and the dehydrogenative cyclization for the construc-
tion of quinazolinones [10a,10b]. More recently, we developed the
highly efficient transfer hydrogenation of aldehydes and chemo-
selective transfer hydrogenation of unsaturated aldehydes with
2
*
Corresponding author. School of Chemistry and Chemical Engineering, Shan-
dong University of Technology, Zibo, 255000, PR China.
* Corresponding author.
E-mail addresses: rongzhouwang@sdut.edu.cn (R. Wang), lbxing@sdut.edu.cn
L. Xing).
*
0
isopropyl alcohol under neutral conditions using [Cp*Ir(2,2 -
(
https://doi.org/10.1016/j.tet.2019.07.021
040-4020/© 2019 Elsevier Ltd. All rights reserved.
0
Please cite this article as: R. Wang et al., Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst
0
[
Cp*Ir(2,2 -bpyO)(H
2
O)] without using base, Tetrahedron, https://doi.org/10.1016/j.tet.2019.07.021

2
R. Wang et al. / Tetrahedron xxx (xxxx) xxx
bpyO)(H
2
O)] complexes [10c]. Within this context, to further
Table 2
at 30 C by cat. 7.a
ꢀ
Hydrogenation of ketones in tert-amyl alcohol under 1 atm H
2
explore the catalytic activity of the metal-ligand bifunctional
iridium complexes, we applied this kind of catalysts to catalytic
hydrogenation of ketones and aldehydes under 1 atm H
and base-free conditions.
2
pressure
2
. Results and discussion
Yield (%)b
Entry
1
Ketone
Product
95
The reaction conditions were optimized by using acetophenone
1a) as the model substrate (Table 1). Various catalysts were
initially evaluated in the model hydrogenation reaction of aceto-
(
ꢀ
phenone (1a) in tert-amyl alcohol for 12 h at 30 C. When
2
3
4
5
94
94
93
96
[
[
[
Cp*IrCl
Cp*Ir(H
Cp*Ir(6,6 -(OMe)
2
]
2
(Cp*
][OTf]
2
¼
pentamethylcyclopentadienyl) (cat. 1),
(cat. 2), [Cp*Ir(bpy)Cl)][Cl] (cat. 3) and
bpy)(H O)] [OTf] (cat. 4) were screened, the
2
O)
3
0
2
2
2
desired product 2a was only obtained in ꢁ20% yield. Interestingly, it
is clear from Table 1, that the yield of 2a could be obviously
increased with the presence of [Cp*Ir(2-(OH)py)]Cl
2
(cat. 5),
0
0
0
[Cp*Ir(6,6 e(OH)
2
e2,2 -bpy)(H
2
O)] [OTf]
2
(cat. 6) and [Cp*Ir(2,2 -
bpyO)(H
2
O)] (cat. 7) bearing a functional pyridine, bipyridine or
bipyridonate ligand. The yield of product 2a could reach up to 96%,
when the hydrogenation reaction was performed in the presence of
cat. 7. From the above results, it can be inferred that the functional
ligands play a crucial role in improving the activity of catalysts.
When the reaction was performed in the presence of [Cp*Rh(2,2 -
bpyO)(H
0
6
96
0
2
O)] (cat. 8) or [(p-cymene)Ru(2,2 -bpyO)(H
2
O)] (cat. 9) as
Table 1
7
8
92
96
ꢀ
Hydrogenation of acetophenone (1a) in tert-amyl alcohol under 1 atm H
using a range of catalysts.
2
at 30
C
a, b
9
94
entry
catalyst
x (mol %)
yield (%)c
1
2
3
4
5
6
7
8
9
cat. 1
cat. 2
cat. 3
cat. 4
cat. 5
cat. 6
cat. 7
cat. 8
cat. 9
cat. 7
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.2
20
12
n.d.
8
32
79
>98 (96 )
35
6
1
0
96
97
d
11
10
86
12
96
1
1
1
3
4
5
96
95
94
16
89
a
Reaction conditions: 1a (1 mmol), 1 atm H
2
(balloon), catalyst (x mol %), tert-
ꢀ
amyl alcohol (1 mL), 30 C, 12 h.
b
Catalyst structures.
c
Yield was determined on the basis of 1H NMR spectrum of the crude reaction.
Isolated yield.
d
Please cite this article as: R. Wang et al., Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst
0
[
Cp*Ir(2,2 -bpyO)(H
2
O)] without using base, Tetrahedron, https://doi.org/10.1016/j.tet.2019.07.021

R. Wang et al. / Tetrahedron xxx (xxxx) xxx
3
Table 2 (continued )
Table 3
at 30 C by cat. 7.a
ꢀ
Hydrogenation of aldehydes in tert-amyl alcohol under 1 atm H
2
Entry
Ketone
Product
Yield (%)b
87
17
a
Reaction conditions: 1 (1 mmol), 1 atm H
2
(balloon), cat. 7 (0.5 mol %), tert-amyl
ꢀ
Yield (%)b
96
alcohol (1 mL), 30 C, 12 h.
Entry
1
Aldehyde
Product
b
Isolated yield.
an alternative catalyst, we obtained only 35% and 6% yields of the
target product 2a, respectively. However, the yield of 2a is lower in
the presence of cat. 7 with a loading of 0.2 mol %.
2
3
4
94
92
96
The optimized condition (Table 1, entry 7) was then applied to
various ketones to extend the scope of the method. The results are
summarized in Table 2. The reactions with aromatic ketones
bearing electron-donating substituents at the aromatic ring, such
as methyl and methoxy, proceeded to give the corresponding
products (2b-2e) in good to excellent yields (entries 1e4). Halogen
atoms were well tolerated, as demonstrated by high yields of the
fluoro-, chloro-, bromo-substituted aromatic alcohols (2f-2k, en-
tries 5e10). Furthermore, the strong electron-withdrawing phenyl
rings in 1l and 1m survived from the reduction in 97% and 96%
yields (entries 11e12). 2-acetylpyridine (1n) and 2-acetonaphthone
5
6
93
94
(1o) also underwent hydrogenation readily and delivered excellent
yields of alcohols in 96% and 95% yields (entries 13e14). For the
reaction of butyrophenone (1p), the corresponding product 2p
could be obtained in high yield (entry 15). Fused aliphatic ketones
7
8
95
83
1
q and 1r also underwent the hydrogenation to yield the desired
products in 89% and 87% yields (entries 16e17), respectively.
Under the same conditions, hydrogenation of various aldehydes
was carried out using complex 7 as the catalyst (Table 3). In addi-
tion to benzaldehyde (3a), other electron-rich aldehydes such as 3-
methylbenzaldehyde (3b), 4-methylbenzaldehyde (3c), 3,4- dime-
thylbenzaldehyde (3d), 4-isopropylbenzaldehyde (3e), and 4-
methoxybenzaldehyde (3f), were readily reduced to correspond-
ing alcohols efficiently in 92e96% yields (entries 1e6). Similarly,
fluoro, chloro and bromo substituents were tolerant in this catalytic
system and the desired products 4g-4j were obtained in 83e97%
yield (entries 7e10). Strong electron-withdrawing substituents,
such as cyano and ester group, were also converted to the corre-
sponding primary alcohols (4k-4l) in 94% and 95% yields (entries
9
96
97
94
1
1
1
0
1
2
95
94
11e12). Other aromatic aldehydes such as 2-naphthaldehyde (3m)
and 2-pyridinecarboxaldehyde (3n) could be also used as suitable
substrates and the corresponding products 4m-4n were obtained
in 94% and 96% yields, respectively (entries 13e14). The present
catalytic system was also applicable to aliphatic aldehydes, such as
decanal (3o) and cyclohexanecarbaldehyde (3p), and the yields of
corresponding aliphatic alcohols were high (entries 15e16).
Furthermore, when the unsaturated aliphatic aldehyde 3q served
as a substrate, the C]C bond remained unreacted and the product
13
14
96
15
16
96
91
4
q was obtained in 92% yield (entry 17).
On the basis of the above results, chemoselectivity was inves-
tigated with aromatic substrates containing two ketone groups or
one aldehyde and one ketone group in the presence of cat. 7
17
92
(
Scheme 1). The hydrogenation of 4-acetylbenzaldehyde (5) was
accomplished, but only product 6 was obtained in 94% yield
Scheme 1, a). Both of aldehyde and ketone groups were hydroge-
nated to alcohols. Interestingly, while 1,3-diacetylbenzene (7) with
two ketone groups was tested, only one ketone group was selec-
tively hydrogenated and the corresponding product 8 was obtained
in 92% yield (Scheme 1, b).
Considering the above experimental results, a plausible mech-
anism was proposed for the present hydrogenation of ketones or
2
aldehydes with H catalyzed by cat. 7 (Scheme 2). This mechanism
a
(
Reaction conditions: 3 (1 mmol), 1 atm H2 (balloon), cat. 7 (0.5 mol %), tert-amyl
ꢀ
alcohol (1 mL), 30 C, 12 h.
b
Isolated yield.
is closely related to the proposed mechanism of the transfer hy-
drogenation of aldehydes with isopropyl alcohol [10c]. The initial
step of the reaction involves elimination of H
2
O from the catalyst
cat. 7 to afford an unsaturated species A bearing a 2-pyridonate-
Please cite this article as: R. Wang et al., Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst
0
[
Cp*Ir(2,2 -bpyO)(H
2
O)] without using base, Tetrahedron, https://doi.org/10.1016/j.tet.2019.07.021

4
R. Wang et al. / Tetrahedron xxx (xxxx) xxx
0.2-mm commercial silica gel plates. [Cp*IrCl
2
]
2
(cat. 1) [11],
[
[
Cl
Cp*Ir(H
Cp*Ir(6,6 -(OMe)2bpy)(H
2
O)
3 2
] [OTf] (cat. 2) [12], [Cp*Ir(bpy)Cl)] [Cl] (cat. 3) [13],
0
2
O)] [OTf]
2
(cat. 4) [14], [Cp*Ir(2-(OH)py)]
0
0
2
(cat. 5) [9e], [Cp*Ir(6,6 e(OH)
2
e2,2 -bpy)(H
2
O)] [OTf]
2
(cat. 6)
0
0
[9h], [Cp*Ir(2,2 -bpyO)(H
2
O)] (cat. 7) [15], [Cp*Rh(2,2 -bpyO)(H
2
O)]
0
(
cat. 8) [16], [(p-cymene)Ru(2,2 -bpyO)(H
2
O)] (cat. 9) [17] were
synthesized according the previous reports.
4.2. General procedure for catalytic hydrogenation of 2
To an oven-dried 5 mL round-bottom flask were added ketone
1 mmol), cat. 7 (2.7 mg, 0.5 mol %) and tert-amyl alcohol (1 mL).
Next, vacuum was applied to the flask followed by filling with H
Scheme 1. Chemoselective hydrogenation of ketones. Isolated yield.
(
2
gas and keeping the flask attached to a balloon filled with H
2
gas.
ꢀ
The mixture was heated at 30 C for 12 h. After completion of the
reaction, the solvent was removed by evaporation under reduced
pressure. The alcohols were isolated and purified by filtering a
hexanes/ethyl acetate (5:1) solution of the crude product through a
pad of silica gel, and then removing the solvent under reduced
pressure. The conversion and purity of the alcohol products was
assessed using NMR spectroscopy.
4
4
d
.3. Characterization date of 2
.3.1. 1-Phenylethanol (2a). [18]
Light yellow oil; 96% yield (117 mg); H NMR (400 MHz, CDCl
7.31e7.30 (m, 4H), 7.26e7.20 (m, 1H), 4.80 (q, J ¼ 6.5 Hz, 1H), 2.66
1
3
)
(br s, 1H), 1.43 (d, J ¼ 6.5 Hz, 3H).
Scheme 2. Proposed hydrogenation mechanism.
4
.3.2. 1-o-Tolylethanol (2b). [18]
Light yellow soil; 95% yield (129 mg); H NMR (400 MHz, CDCl
1
3
)
2
based ligand. Then, the reaction of H with the species A would
d
7.47 (d, J ¼ 7.6 Hz, 1H), 7.22e7.09 (m, 3H), 5.06 (q, J ¼ 6.4 Hz, 1H),
occur to afford iridium hydride species B. Finally, the simultaneous
transfer of the hydride on iridium with the hydroxyl proton on the
functional ligand to C]O bond of ketones or aldehydes would
occur to give the corresponding alcohols accompanied by the
regeneration of A.
2
.30 (s, 3H), 2.24 (br s, 1H), 1.42 (d, J ¼ 6.4 Hz, 3H).
4
.3.3. 1-(m-Tolyl)ethanol (2c). [18]
1
Light yellow oil; 94% yield (128 mg); H NMR (400 MHz, CDCl
3
)
d
7.21 (t, J ¼ 7.5 Hz, 1H), 7.16e7.12 (m, 2H), 7.08 (s, 1H), 4.81 (q,
J ¼ 6.5 Hz, 1H), 2.34 (s, 3H), 2.19 (br s, 1H), 1.46 (d, J ¼ 6.5 Hz, 3H).
3
. Conclusions
4
.3.4. 1-(p-Tolyl)ethanol (2d). [18]
Light yellow oil; 94% yield (128 mg); H NMR (400 MHz, CDCl
In conclusion, we have developed an efficient iridium catalyst
1
0
3
)
[
Cp*Ir(2,2 -bpyO)(H
2
O)] bearing a functional bipyridonate ligand
d
7.18 (d, J ¼ 8.0 Hz, 2H), 7.08 (d, J ¼ 7.9 Hz, 2H), 4.76 (q, J ¼ 6.4 Hz,
for the hydrogenation of ketones and aldehydes in tert-amyl
1
H), 2.26 (s, 3H), 1.97 (br s, 1H), 1.39 (d, J ¼ 6.5 Hz, 3H).
ꢀ
alcohol under 1 atm H
2
at 30 C. It does not require base or high-
pressure hydrogen condition, offering an operationally simple
and green procedure. Of significance is the good tolerance of a wide
variety of functional groups, such as electron-rich or deficient
groups, cyano, ester, and halide groups. Notably, the research ex-
hibits new potential of metal-ligand bifunctional catalysts for
hydrogenation.
4
.3.5. 1-(4-Methoxyphenyl)ethanol (2e). [18]
Light yellow oil; 93% yield (141 mg); H NMR (400 MHz, CDCl
1
3
)
d
7.28 (d, J ¼ 8.6 Hz, 2H), 6.87 (d, J ¼ 8.6 Hz, 2H), 4.82 (q, J ¼ 6.4 Hz,
1
H), 3.78 (s, 3H), 2.16 (br s, 1H), 1.46 (d, J ¼ 6.5 Hz, 3H).
4.3.6. 1-(4-Fluorophenyl)ethanol (2f). [18]
1
Light yellow oil; 96% yield (134 mg); H NMR (400 MHz, CDCl
3
)
4
. Experimental
d
7.30e7.26 (m, 2H), 7.62e6.98 (m, 2H), 4.82 (q, J ¼ 6.4 Hz, 1H), 2.61
(br s, 1H), 1.43 (d, J ¼ 6.5 Hz, 3H).
4.1. General
4
.3.7. 1-(2-Chlorophenyl)ethanol (2g). [18]
Light yellow oil; 96% yield (151 mg); H NMR (400 MHz, CDCl )
7.60 (d, J ¼ 7.3 Hz, 1H), 7.33e7.28 (m, 2H), 7.22e7.18 (m, 1H), 5.30
Authors Melting points were measured on a RY-1 micro-melting
apparatus. Proton nuclear magnetic resonance ( H NMR) spectra
were recorded at 400 MHz using a 400 spectrometer. Chemical
1
1
3
d
(q, J ¼ 6.3 Hz, 1H), 2.11 (br s, 1H), 1.49 (d, J ¼ 6.4 Hz, 3H).
shifts are reported in delta (
downfield from tetramethylsilane or ppm relative to the center of
the singlet at 7.26 ppm for CDCl . Coupling constants J values are
d) units, parts per million (ppm)
3
4.3.8. 1-(3-Chlorophenyl)ethanol (2h). [18]
1
reported in Hertz (Hz), and the splitting patterns were designated
as follows: s, singlet; d, doublet; t, triplet; m, multiplet; b, broad.
Analytical thin-layer chromatography (TLC) was carried out using
Light yellow oil; 92% yield (144 mg); H NMR (400 MHz, CDCl
3
)
d
7.38 (s, 1H), 7.27e7.23 (m, 3H), 4.88 (q, J ¼ 6.4 Hz, 1H), 1.93 (br s,
1H), 1.49 (d, J ¼ 4.5 Hz, 3H).
Please cite this article as: R. Wang et al., Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst
0
[
Cp*Ir(2,2 -bpyO)(H
2
O)] without using base, Tetrahedron, https://doi.org/10.1016/j.tet.2019.07.021

R. Wang et al. / Tetrahedron xxx (xxxx) xxx
5
4
.3.9. 1-(4-Chlorophenyl)ethanol (2i). [18]
Light yellow oil; 96% yield (151 mg); H NMR (400 MHz, CDCl
7.28 (m, 4H), 4.83 (q, J ¼ 6.4 Hz, 1H), 2.38 (br s, 1H), 1.44 (d,
4.5. Characterization date of 4
4.5.1. Phenylmethanol (4a) [21]
1
3
)
d
1
J ¼ 6.4 Hz, 3H).
Light yellow oil; 96% yield (104 mg); H NMR (400 MHz, CDCl
3
)
d
7.36e7.31 (m, 4H), 7.29e7.26 (m, 1H), 4.62 (s, 2H), 2.32 (br s, 1H).
4
.3.10. 1-(3,4-Dichlorophenyl)ethanol (2j). [19]
Light yellow oil; 94% yield (180 mg); H NMR (400 MHz, CDCl
1
3
)
4.5.2. m-Tolylmethanol (4b) [25]
1
d
7.42e7.36 (m, 2H), 7.14e7.12 (dd, 2.0 and 8.2 Hz, 1H), 4.80 (q,
Light yellow oil; 94% yield (115 mg); H NMR (400 MHz, CDCl )
3
J ¼ 6.5 Hz, 1H), 2.79 (br s, 1H), 1.42 (d, J ¼ 6.5 Hz, 3H).
d
7.24e7.20 (m, 1H), 7.14e7.07 (m, 3H), 4.58 (s, 2H), 2.43 (br s, 2H),
.33 (s, 3H).
2
4
.3.11. 1-(4-Bromophenyl)ethanol (2k). [18]
Light yellow oil; 96% yield (193 mg); H NMR (400 MHz, CDCl
1
3
)
4
.5.3. p-Tolylmethanol (4c). [21]
Yellow soil; 92% yield (112 mg); mp 59e61 C; 1H NMR
ꢀ
d
7.46 (d, J ¼ 8.4 Hz, 2H), 7.23 (d, J ¼ 8.3 Hz, 2H), 4.83 (q, J ¼ 6.4 Hz,
1
H), 2.23 (br s, 1H), 1.45 (d, J ¼ 6.5 Hz, 3H).
(
4
400 MHz, CDCl
.59 (s, 2H), 2.34 (s, 3H), 2.12 (br s, 1H).
3
)
d
7.23 (d, J ¼ 7.8 Hz, 2H), 7.16 (d, J ¼ 7.8 Hz, 2H),
4
.3.12. 1-(4-(Trifluoromethoxy)phenyl)ethanol (2l). [20]
Light yellow oil; 97% yield (200 mg); H NMR (400 MHz, CDCl
1
3
)
4
.5.4. (3,4-Dimethylphenyl)methanol (4d). [26]
Light yellow oil; 96% yield (131 mg); H NMR (400 MHz, CDCl
d
7.38 (d, J ¼ 8.6 Hz, 2H), 7.19 (d, J ¼ 8.1 Hz, 2H), 4.88 (q, J ¼ 6.4 Hz,
1
3
)
1
H), 2.34 (br s, 1H), 1.47 (d, J ¼ 6.5 Hz, 3H).
d
7.13e7.07 (m, 3H), 4.60 (s, 2H), 2.26 (s, 3H), 2.25 (s, 3H), 1.79 (br s,
1
H).
4
.3.13. 1-(4-(Trifluoromethyl)phenyl)ethanol (2m). [21]
1
Light yellow soil; 96% yield (183 mg); H NMR (400 MHz, CDCl
3
)
4
.5.5. (4-Isopropylphenyl)methanol (4e). [25]
d
7.57 (d, J ¼ 8.1 Hz, 2H), 7.42 (d, J ¼ 8.1 Hz, 2H), 4.87 (q, J ¼ 6.5 Hz,
1
Light yellow oil; 93% yield (140 mg); H NMR (400 MHz, CDCl
3
)
1
H), 2.95 (br s, 1H), 1.44 (d, J ¼ 6.6 Hz, 3H).
d
7.31 (d, J ¼ 8.0 Hz, 2H), 7.26 (d, J ¼ 6.0 Hz, 2H), 4.66 (s, 2H),
2
.96e2.86 (m, 1H), 1.26 (d, J ¼ 6.9 Hz, 6H).
4
.3.14. 1-(Pyridin-2-yl)ethanol (2n). [22]
Light yellow oil; 96% yield (118 mg); H NMR (400 MHz, CDCl
1
3
)
4
.5.6. (4-Methoxyphenyl)methanol (4f). [21]
d
8.50 (d, J ¼ 4.7 Hz, 1H), 7.70e7.66 (td, J ¼ 1.6 and 7.7 Hz, 1H), 7.34
1
Light yellow oil; 94% yield (130 mg); H NMR (400 MHz, CDCl
3
)
(
d, J ¼ 7.9 Hz, 1H), 7.19e7.16 (m, 1H), 4.90 (q, J ¼ 6.5 Hz, 1H), 4.71 (br
d
7.26 (d, J ¼ 8.6 Hz, 2H), 6.88 (d, J ¼ 8.6 Hz, 2H), 4.5 (s, 2H), 3.78 (s,
s, 1H), 1.51 (d, J ¼ 6.6 Hz, 3H).
3
H), 2.20 (br s, 1H).
4
.3.15. 1-(Naphthalen-2-yl)ethanol (2o). [18]
Light yellow solid; 95% yield (163 mg); mp 74e75 C; 1H NMR
400 MHz, CDCl 7.86e7.82 (m, 4H), 7.53e7.46 (m, 3H), 5.11e5.06
m, 1H), 1.89 (br s, 1H), 1.60 (d, J ¼ 6.4 Hz, 3H).
4
d
.5.7. (4-Fluorophenyl)methanol (4g). [21]
Light yellow oil; 95% yield (120 mg); H NMR (400 MHz, CDCl
7.34e7.26 (m, 4H), 4.66 (s, 2H), 1.97 (br s, 1H).
ꢀ
1
3
)
(
(
3
) d
4
.5.8. (2-Chlorophenyl)methanol (4h). [27]
4
.3.16. Phenylbutan-1-ol (2p). [23]
Light yellow oil; 94% yield (141 mg); H NMR (400 MHz, CDCl
7.36e7.33 (m, 4H), 7.28e7.25 (m, 1H), 4.66 (t, J ¼ 6.6 Hz, 1H), 1.96
Light yellow soil; 83% yield (118 mg); mp 71e72 C; 1H NMR
ꢀ
1
3
)
(400 MHz, CDCl
3
)
d
7.48 (d, J ¼ 7.3 Hz, 1H), 7.37 (d, J ¼ 8.6 Hz, 1H),
d
7.30e7.21 (m, 2H), 4.77 (s, 2H), 2.33 (br s, 1H).
(
3
br s, 1H), 1.83e1.62 (m, 2H), 1.49e1.23 (m, 2H), 0.92 (t, J ¼ 6.5 Hz,
H).
4
.5.9. (4-Chlorophenyl)methanol (4i). [21]
White soil; 96% yield (137 mg); mp 69e70 C; 1H NMR
7.33-.7.26 (m, 4H), 4.64 (s, 2H), 2.01 (br s, 1H).
ꢀ
4.3.17. Cyclohexanol (2q). [18]
Light yellow oil; 89% yield (89 mg); 1H NMR (400 MHz, CDCl
(400 MHz, CDCl
3
)
d
3
)
d
3.61e3.56 (m, 1H), 2.47 (br s, 1H), 1.90e1.88 (m, 2H), 1.75e1.72 (m,
H), 1.56e1.53 (m, 1H), 1.27e1.14 (m, 5H).
4
.5.10. (4-Bromophenyl)methanol (4j). [21]
Yellow soil; 97% yield (181 mg); mp 63e64 C; 1H NMR
400 MHz, CDCl
7.49 (d, J ¼ 8.2 Hz, 2H), 7.24 (d, J ¼ 8.2 Hz, 2H),
4.64 (s, 2H), 1.87 (br s, 1H).
2
ꢀ
(
3
) d
4
.3.18. 2-Octanol (2r). [24]
Light yellow oil; 87% yield (113 mg); H NMR (400 MHz, CDCl
1
3
)
d
3.82e3.74 (m, 1H), 1.46e1.29 (m, 10H), 1.21e1.17 (m, 4H), 0.89 (t,
4
.5.11. 4-(Hydroxymethyl)benzonitrile (4k). [21]
White soil; 94% yield (125 mg); mp 41e42 C; 1H NMR
400 MHz, CDCl
7.65 (d, J ¼ 8.2 Hz, 2H), 7.49 (d, J ¼ 8.1 Hz, 2H),
.78 (s, 2H), 2.16 (br s, 1H).
J ¼ 6.6 Hz, 1H).
ꢀ
(
4
3
) d
4.4. General procedure for catalytic hydrogenation of 4
To an oven-dried 5 mL round-bottom flask were added aldehyde
(
1 mmol), cat. 7 (2.7 mg, 0.5 mol %) and tert-amyl alcohol (1 mL).
Next, vacuum was applied to the flask followed by filling with H
gas and keeping the flask attached to a balloon filled with H gas.
4.5.12. Methyl-4-(hydroxymethyl)benzoate (4l). [25]
White solid; 95% yield (158 mg); mp 48e49 C; 1H NMR
(400 MHz, CDCl
ꢀ
2
3
)
d
8.04 (d, J ¼ 8.2 Hz, 2H), 7.45 (d, J ¼ 8.2 Hz, 2H),
2
ꢀ
The mixture was heated at 30 C for 12 h. After completion of the
reaction, the solvent was removed by evaporation under reduced
pressure. The alcohols were isolated and purified by filtering a
hexanes/ethyl acetate (5:1) solution of the crude product through a
pad of silica gel, and then removing the solvent under reduced
pressure. The conversion and purity of the alcohol products was
assessed using NMR spectroscopy.
4.78 (s, 2H), 3.92 (s, 3H), 1.88 (br s, 1H).
4.5.13. Naphthalen-1-ylmethanol (4m). [28]
Light yellow soil; 94% yield (149 mg); mp 58e59 C; 1H NMR
ꢀ
(400 MHz, CDCl
3
)
d
8.13 (d, J ¼ 8.2 Hz, 1H), 7.89 (d, J ¼ 7.6 Hz, 1H),
7.82 (d, J ¼ 8.1 Hz,1H), 7.57e7.49 (m, 3H), 7.44 (t, J ¼ 7.6 Hz,1H), 5.14
(s, 2H), 1.86 (br s, 1H).
Please cite this article as: R. Wang et al., Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst
0
[
Cp*Ir(2,2 -bpyO)(H
2
O)] without using base, Tetrahedron, https://doi.org/10.1016/j.tet.2019.07.021

6
R. Wang et al. / Tetrahedron xxx (xxxx) xxx
L.W. Chung, L.N. Zhang, X.-M. Zhang, Org. Lett. 18 (2016) 1518e1521;
4
.5.14. Pyridin-2-ylmethanol (4n). [21]
Light yellow oil; 96% yield (105 mg); H NMR (400 MHz, CDCl
8.52 (d, J ¼ 4.8 Hz, 1H), 7.68 (td, J ¼ 1.6 and 7.7 Hz, 1H), 7.33 (d,
1
c) P. Puylaert, R.V. Heck, Y.-T. Fan, A. Spannenberg, W. Baumann, M. Beller,
J. Medlock, W. Bonrath, L. Lefort, S. Hinze, J.G. Vries, Chem. Eur. J. 23 (2017)
3
)
d
8473e8481.
J ¼ 7.8 Hz, 1H), 7.19 (t, J ¼ 6.2 Hz, 1H), 4.80 (br s, 1H), 4.76 (s, 2H).
[4] a) V. Comte, C. Balan, P.L. Gendre, C. Moïse, Chem. Commun. (2007) 713e715;
b) Z.J. Yao, K. Li, J.-Y. Zhang, W. Deng, New J. Chem. 40 (2016) 8753e8759;
c) W.-H. Wang, Y. Suna, Y. Himeda, J.T. Muckerman, E. Fujita, Dalton Trans. 42
4
.5.15. Decan-1-ol (4o). [29]
Light yellow oil; 96% yield (152 mg); H NMR (400 MHz, CDCl
3.61 (t, J ¼ 6.7 Hz, 2H), 2.44 (br s, 1H), 1.59e1.52 (m, 2H), 1.31e1.27
(2013) 9628e9636.
1
3
)
[5] a) E.L. Roux, R. Malacea, E. Manoury, R. Poli, L. Gonsalvi, M. Peruzzinia, Adv.
Synth. Catal. 349 (2007) 309e313;
d
b) A.H. Ngo, M.J. Adams, L.H. Do, Organometallics 33 (2014) 6742e6745;
c) X.H. Chen, W.L. Jia, R.W. Guo, T.W. Graham, M.A. Gullons, K. Abdur-Rashid,
Dalton Trans. (2009) 1407e1410.
(
m, 14H), 0.88 (t, J ¼ 6.8 Hz, 3H).
[
6] a) G. Wienh o€ er, F.A. Westerhaus, K. Junge, R. Ludwig, M. Beller, Chem. Eur. J.
4
.5.16. Cyclohexylmethanol (4p). [30]
Light yellow oil; 91% yield (104 mg); H NMR (400 MHz, CDCl
3.43 (d, J ¼ 6.4 Hz, 2H), 2.32 (br s,1H),1.77e1.66 (m, 5H), 1.51e1.42
1
19 (2013) 7701e7707;
b) N. Gorgas, B. St o€ ger, L.F. Veiros, K. Kirchner, ACS Catal. 6 (2016) 2664e2672.
[7] S.R. Sler, J. Obenauf, R. Kempe, J. Am. Chem. Soc. 137 (2015) 7998e8001.
3
)
d
[
8] G.Q. Zhang, B.L. Scott, S.K. Hanson, Angew. Chem. Int. Ed. 51 (2012)
2102e12106.
(
m, 1H), 1.30e1.14 (m, 3H), 0.97e0.87 (m, 2H).
1
[
9] a) K. Fujita, R. Kawahara, T. Aikawa, R. Yamaguchi, Angew. Chem. Int. Ed. 54
(2015) 9057e9060;
4
.5.17. 3-Cyclohexene-1-methanol (4q). [31]
Light yellow soil; 92% yield (103 mg); H NMR (400 MHz, CDCl
5.71e5.65 (m, 2H), 3.55e3.50 (m, 2H), 2.31 (br s, 1H), 2.13e2.05
1
3
)
b) K. Fujita, R. Tamura, Y. Tanaka, M. Yoshida, M. Onoda, R. Yamaguchi, ACS
Catal. 7 (2017) 7226e7230;
c) M. Kuwahara, M. Nishioka, M. Yoshida, K. Fujita, ChemCatChem 10 (2018)
d
(
m, 3H), 1.84e1.73 (m, 3H), 1.29e1.23 (m, 1H).
3636e3640;
d) K. Fujita, W. Ito, R. Yamaguchi, ChemCatChem 6 (2014) 109e112;
e) K. Fujita, N. Tanino, R. Yamaguchi, Org. Lett. 9 (2007) 109e111;
f) R. Yamaguchi, C. Ikeda, Y. Takahashi, K. Fujita, J. Am. Chem. Soc. 131 (2009)
4
.5.18. 1-(4-(hydroxymethyl)phenyl)ethanol (6). [32]
Light yellow soil; 94% yield (143 mg); H NMR (400 MHz, CDCl
7.19 (m, 4H), 4.74 (q, J ¼ 6.4 Hz, 1H), 4.47 (s, 2H), 3.67 (br s, 2H),
1
3
)
8
410e8412;
g) K. Fujita, T. Yoshida, Y. Imori, R. Yamaguchi, Org. Lett. 13 (2011)
278e2281;
h) R. Kawahara, K. Fujita, R. Yamaguchi, J. Am. Chem. Soc. 134 (2012)
643e3646;
d
2
1.37 (d, J ¼ 6.5 Hz, 3H).
3
4
.5.19. 1-(3-(1-hydroxyethyl)phenyl)ethanone (8). [33]
Light yellow soil; 92% yield (151 mg); H NMR (400 MHz, CDCl
7.97 (s, 1H), 7.88 (d, J ¼ 7.7 Hz, 1H), 7.61 (d, J ¼ 7.7 Hz, 1H), 7.46 (t,
i) K. Fujita, Y. Tanaka, M. Kobayashi, R. Yamaguchi, J. Am. Chem. Soc. 136
(2014) 4829e4832.
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c) R.Z. Wang, Y.W. Tang, M. Xu, C. Meng, F. Li, J. Org. Chem. 83 (2018)
1
3
)
[
d
J ¼ 7.7 Hz,1H), 4.99 (q, J ¼ 6.5 Hz,1H), 2.62 (s, 3H),1.54 (d, J ¼ 6.4 Hz,
H).
2274e2281.
3
[
11] R.G. Ball, W.A.G. Graham, D.M. Heinekey, J.K. Hoyano, A.D. McMaster,
B.M. Mattson, S.T. Michel, Inorg. Chem. 29 (1990) 2023e2025.
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Acknowledgments
[
[
We are grateful for the financial support from the National
Natural Science Foundation of China (21402108 and 21576159), and
Natural Science Foundation of Shandong Province (ZR2014BQ036).
(2012) 7923e7926.
[
[
[
[
[
[
15] R. Kawahara, K. Fujita, R. Yamaguchi, Angew. Chem. Int. Ed. 51 (2012)
12790e12794.
16] G. Zeng, S. Sakaki, K. Fujita, H. Sano, R. Yamaguchi, ACS Catal. 4 (2014)
1
010e1020.
17] R. Zhu, B. Wang, M. Cui, J. Deng, X. Li, Y. Ma, Y. Fu, Green Chem. 18 (2016)
029e2036.
18] K. Li, J. Niu, M. Yang, Z. Li, L. Wu, X. Hao, M. Song, Organometallics 34 (2015)
170e1176.
19] J.L.N. Fernandes, M.C. Souza, E.C.S. Brenelli, J.A. Brenelli, Synthesis 23 (2009)
058e4062.
Appendix A. Supplementary data
2
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2019.07.021.
1
4
20] Shen, D. M.; Dwyer, M.; Sinz, C. J.; Wang, D. P.; Stachel, S.; Paone, D.; Nomland,
A.; Berger, R.; Shipe, W. D.; Chen, Y. L.; Qian, Y. M.; Xu, S. M.; Hu, C. M.; Fu, J.
M.; Guo, Z. G.; Li, H. T.; Bo, Y. J. WO 2016191935A1. 2016.
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Please cite this article as: R. Wang et al., Ambient-pressure hydrogenation of ketones and aldehydes by a metal-ligand bifunctional catalyst
0
[
Cp*Ir(2,2 -bpyO)(H
2
O)] without using base, Tetrahedron, https://doi.org/10.1016/j.tet.2019.07.021