Dehydrogenative oxidation of alcohols in aqueous media catalyzed by a water-soluble dicationic iridium complex bearing a functional N-heterocyclic carbene ligand without using base

Article abstract of DOI:10.1021/acscatal.7b02560

A dicationic iridium complex bearing a bidentate ligand that comprises N-heterocyclic carbene and α-hydroxypyridine moieties has been designed and synthesized. The complex exhibited high catalytic performance in aqueous media for the dehydrogenative oxidation of secondary alcohols to ketones accompanying the evolution of hydrogen. Furthermore, dehydrogenative transformation of primary alcohols to the carboxylic acids in aqueous media was also catalyzed by the complex without using base.

Full text of DOI:10.1021/acscatal.7b02560

Subscriber access provided by UNIVERSITY OF CALGARY
Letter
Dehydrogenative Oxidation of Alcohols in Aqueous Media
Catalyzed by a Water-Soluble Dicationic Iridium Complex Bearing
a Functional N-Heterocyclic Carbene Ligand without Using Base
Ken-ichi Fujita, Ryuichi Tamura, Yuhi Tanaka, Masato Yoshida, Mitsuki Onoda, and Ryohei Yamaguchi
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b02560 • Publication Date (Web): 15 Sep 2017
Downloaded from http://pubs.acs.org on September 15, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 6
ACS Catalysis
1
2
3
4
5
6
Dehydrogenative Oxidation of Alcohols in Aqueous Media Catalyzed
by a Water-Soluble Dicationic Iridium Complex Bearing a Function-
al N-Heterocyclic Carbene Ligand without Using Base
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Ken-ichi Fujita,* Ryuichi Tamura, Yuhi Tanaka, Masato Yoshida, Mitsuki Onoda, and Ryohei Yama-
guchi*
Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
ABSTRACT: A dicationic iridium complex bearing a bidentate ligand that comprises of N-heterocyclic carbene and α-
hydroxypyridine moieties has been designed and synthesized. The complex exhibited high catalytic performance in aqueous media
for the dehydrogenative oxidation of secondary alcohols to ketones accompanying the evolution of hydrogen. Furthermore, dehy-
drogenative transformation of primary alcohols to the carboxylic acids in aqueous media was also catalyzed by the complex without
using base.
KEYWORDS: dehydrogenation, iridium catalyst, functional ligand, N-heterocyclic carbene, alcohol, ketone, carboxylic acid
One of the greatest challenges in modern chemistry is to
perform efficient organic synthesis under environmentally
friendly conditions with the aid of catalyst. In the past few
decades, high performance catalysts have been designed for a
variety of organic transformations. By using an appropriate
catalyst, a number of reactions that would not usually proceed
have been accomplished and ingenious reaction selectivities
have been attained. These developments stimulated remarka-
To design a new catalyst that possesses a high capability for
dehydrogenative reactions of organic molecules in aqueous
media, three working hypotheses were considered: 1) the in-
troduction of a strongly electron-donating ligand would be
effective for dehydrogenation, which is based on our previous
9
computational study, 2) a chelating ligand that would form a
strong bond with the transition metal would be important to
avoid catalyst decomposition via dissociation of the ligand,
and 3) an ionic catalyst would be advantageous for solubility
in water. Based on these hypotheses, we designed a dicationic
catalyst having a chelating bidentate ligand that comprises
NHC and α-hydroxypyridine moieties because NHC is a very
1
ble progress in the field of catalytic organic synthesis. Con-
versely, it is generally difficult to perform an organic synthesis
in water which is the most environmentally benign solvent,
2
regardless of whether a catalyst is used. In particular, in the
10
case of reactions catalyzed by homogeneous transition metal
complexes, only very few aqueous reaction systems have been
developed because such complexes are either hardly soluble or
unstable in water.
strong σ-donor and forms a strong metal-carbene bond. As
shown in Scheme 1, starting from ligand precursor 1, iridium
Scheme 1. Preparation of Water-Soluble Dicationic Iridi-
um Complex 3 Bearing a Functional N-Heterocyclic Car-
bene Ligand
We have previously demonstrated the design and synthesis
of iridium catalysts bearing functional ligands and reported
their utilization as catalysts for the dehydrogenative reactions
3
4
of alcohols and amines. In the course of those studies, we
succeeded in the synthesis of homogeneous transition metal
catalysts that are readily soluble in water and stable over a
long period. However, in many cases, the activity of such cata-
lysts used in aqueous media is relatively low compared to
5
,6
those used in organic solvents. Therefore, it is necessary to
redesign functional ligands and synthesize new catalysts that
exhibit a high activity in aqueous media.
In this study, we designed a new functional ligand that
7
comprises N-heterocyclic carbene (NHC)
and α-
8
hydroxypyridine moieties. A new dicationic iridium catalyst
bearing the newly designed ligand was successfully synthe-
sized. Furthermore, it was revealed that the new iridium cata-
lyst showed high activity in the dehydrogenative reactions of
secondary and primary alcohols in aqueous media to give ke-
tones and carboxylic acids, respectively, accompanying the
evolution of hydrogen.
11
complex 2 was prepared by the carbene transfer method by
using Ag O followed by debenzylation under acidic condi-
tions. Then, the reaction of 2 with two equivalents of AgOTf
in water gave dicationic complex 3 with an aquo ligand in
2
ACS Paragon Plus Environment

ACS Catalysis
Page 2 of 6
9
6% yield. Complex 3 was highly soluble in water and stable tones, although a relatively large amount of the catalyst 3 (1.0
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
in air for months. The structure of 3 was elucidated by spec-
troscopic data, elemental analysis, and single-crystal X-ray
diffraction (see the supporting information).
or 2.0 mol%) was required (entries 13-15).
Table 2. Dehydrogenative Oxidation of Various Secondary
a
We next examined the dehydrogenative oxidation of 1-
phenylethanol to acetophenone in aqueous media in the pres-
ence of 0.50 mol% of various water-soluble iridium catalysts.
The results are summarized in Table 1. Iridium catalyst 3,
newly synthesized in this study, showed the highest activity,
giving acetophenone in 46% yield with complete selectivity
after 1 h reaction under reflux (entry 1). Catalyst 4, without
the α-hydroxy group in the ligand, and catalyst 5, with only
the NHC ligand, both exhibited very low catalytic activity
Alcohols under Reflux in Water Catalyzed by 3
OH
catalyst 3
O
+
H2
R1 R2
R1 R2
H O (5 mL), reflux, 20 h
2
1.0 mmol
entry
alcohol
cat. 3 (mol%)
conv. (%)b yield (%)b
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
OH
R'
(entries 2 and 3). With catalyst 6, which we have previously
5a
1
2
3
4
5
6
7
8
9
0
1
R' = H
0.25
0.10
1.0
99
99
95
98
97
100
92
98
99
87
96
99
reported for the dehydrogenative oxidation of alcohols, 15%
yield of acetophenone was obtained (entry 4), thus demon-
strating the superiority of the new catalyst 3. Catalyst 7, which
is also active for the dehydrogenative oxidation of alcohols in
aqueous media in combination with NaOH, also showed
lower activity than that of 3 (entry 5).
4-OMe
2-Me
3-Me
4-Me
4-F
97 (90)
85 (73)
98 (81)
97 (91)
86 (84)
89 (86)
98 (89)
99 (95)
87 (78)
96 (91)
0.25
0.25
1.0
5c
3-Cl
0.25
0.50
1.0
4-Cl
Table 1. Comparison of Catalytic Activities of Complexes
3
under Reflux in Water
4-Br
-7 for the Dehydrogenative Oxidation of 1-Phenylethanol
a
1
1
4-CF3
1.0
4-CO Me
0.25
2
OH
S
12
13
1.0
99
51 (34)
2.0
1.0
2.0
97
98
61
92
98
60
OH
OH
1
1
4
5
OH
a
The reaction was carried out with secondary alcohols (1.0
mmol) and catalyst 3 under reflux in water (5 mL) for 20 h.
b
1
Determined by GC (entries 1 and 13-15) and H NMR (en-
tries 2-12). Isolated yields are indicated in parentheses.
a
The reaction was carried out with 1-phenylethanol (1.0
mmol) and the catalyst (0.50 mol%) under reflux in water (5
b
c
mL) for 1 h. Determined by GC. NaOH (0.50 mol%) was al-
so added.
Note that catalyst 3 could be reused according to the follow-
ing simple procedure: After the dehydrogenation reaction
shown in Scheme 2, 30 mL of hexane was added to extract the
product and the remaining starting alcohol. The recovered
aqueous phase containing the catalyst could be used for the
second run of the catalytic dehydrogenation to give 93% yield
of ketone. Reuse of the catalyst was achieved at least three
times without the loss of activity.
Scheme 2. Reuse of the Catalyst 3 in the Dehydrogenative
Oxidation of 1-(4-Methylphenyl)ethanol in Water
To explore the scope of the new catalytic system employing
, reactions of various secondary alcohols were conducted.
3
OH
O
The results are summarized in Table 2. When the reaction of
-phenylethanol (1.0 mmol) was conducted in water (5 mL) in
Ir cat. 3 (0.50 mol%)
1
+
H2
H O (5 mL), reflux, 20 h
the presence of the catalyst 3 (0.25 mol%) under reflux for 20
h, acetophenone was obtained in 99% yield (entry 1). Reac-
tions of 1-arylethanols bearing electron-donating and electron-
withdrawing substituents in the aromatic ring proceeded
smoothly to give the corresponding acetophenone derivatives
in good to excellent yields (entries 2-12). Alkoxy, fluoro, chlo-
ro, bromo, trifluoromethyl, and methoxycarbonyl groups were
2
1.0 mmol
reuse
1
2
3
yield of ketone (%) 97 93 94
A possible mechanism for the present dehydrogenative oxi-
dation of secondary alcohols catalyzed by 3 is shown in
1
2
tolerated in this catalytic system. Aliphatic and cyclic sec-
ondary alcohols were also converted to the corresponding ke-
ACS Paragon Plus Environment

Page 3 of 6
ACS Catalysis
Scheme 3. The first step of the reaction would involve the
elimination of trifluoromethanesulfonic acid and the aquo
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Scheme 4. Additional Experiments Supporting the Pro-
posed Mechanism
ligand from dicationic catalyst 3 to afford the monocationic
unsaturated species A, which has an α-pyridonate moiety con-
nected to an NHC ligand. Then, activation of the alcohol
would occur via the concerted pathway through transition state
B to give a ketone product and hydrido iridium species C.
Finally, the protonolysis of the hydride on iridium by the hy-
droxy proton on the functional ligand would occur to release
hydrogen accompanying the regeneration of the catalytically
active unsaturated species A.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 3. Possible Mechanism for the Dehydrogenative
Oxidation of Secondary Alcohols Catalyzed by 3
into carboxylic acids. Although several efficient catalytic sys-
tems for such a transformation have been published, those
systems always require the addition of stoichiometric amounts
16
of a strong base. Conversely, our present system does not
require the addition of base and can be performed simply un-
der reflux in water in the presence of only catalyst 3. To the
best of our knowledge, this is the first example of the dehy-
drogenative (not employing any oxidant) transformation of
primary alcohols into the corresponding carboxylic acid with-
out using basic reagents.
To obtain information about the proposed mechanism, three
experiments were conducted (Scheme 4). The first experiment
addressed the formation of catalytically active species A (eq 1).
When dicationic catalyst 3 was treated with one equivalent of
sodium t-butoxide at room temperature for 1 h, a new mono-
cationic complex 8, having an α-pyridonate connected to NHC
ligand, which is closely related to species A in Scheme 3, was
formed and isolated in 51% yield. The structure of 8 was elu-
cidated by spectroscopic data, elemental analysis, and single-
crystal X-ray diffraction (see the supporting information).
Then, the catalytic activity of 8 was examined (eq 2). As we
expected, complex 8 exhibited high catalytic activity for the
dehydrogenative oxidation of 1-phenylethanol in aqueous me-
dia with a loading of 0.25 mol% to give acetophenone in ex-
Table 3. Dehydrogenative Oxidation of Primary Benzylic
Alcohols to Benzoic Acid Derivatives under Reflux in Wa-
a
ter Catalyzed by 3
13
cellent yield (99%). Quantitative analysis of the evolved
hydrogen gas was also conducted (eq 3). By running the dehy-
drogenative reaction on a larger scale (5 mmol scale), hydro-
gen was obtained in 89% yield, which was equimolar to the
14,15
ketone product.
The results of these three reactions strong-
ly support the proposed mechanism shown in Scheme 3.
After establishing a new and efficient catalytic system for
the dehydrogenative oxidation of secondary alcohols in aque-
ous media catalyzed by 3, we turned our attention to the reac-
tion of primary alcohols. We have previously reported the
dehydrogenative oxidation of primary alcohols catalyzed by
complex 6 in aqueous media, which resulted in the formation
a
The reaction was carried out with primary alcohols (1.0
mmol) and catalyst 3 under reflux in water (5 mL) for 20 h.
b
1
Determined by H NMR. Isolated yields are indicated in pa-
c
rentheses. Water (4.0 mL) and 1,4-dioxane (1.0 mL) were
used as solvent.
5a
of aldehydes. However, interestingly, the reaction of benzyl
alcohol under reflux in water for 20 h in the presence of cata-
lyst 3 (2.0 mol%) gave benzoic acid in 80% yield, as shown in
entry 1 of Table 3. Recently, much attention has been focused
on the dehydrogenative transformation of primary alcohols
In Table 3, results of the dehydrogenative oxidation of ben-
zylic primary alcohols in aqueous media to give benzoic acid
17,18
derivatives are summarized.
In addition to the methyl
ACS Paragon Plus Environment

ACS Catalysis
Page 4 of 6
group (entries 2 and 3), methoxy (entry 4), bromo (entry 5),
X-ray crystallographic data for 8 (CIF)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
and chloro (entry 6) substituents were tolerated in this catalyt-
ic system. The reaction of 2-naphthalenemethanol gave 2-
naphthoic acid in high yield (entry 7). In the case that the sol-
ubility of the substrates in water was extremely low, addition
of 1,4-dioxane as a co-solvent improved the yields of carbox-
ylic acids (entries 5-7).
AUTHOR INFORMATION
Corresponding Author
fujita.kenichi.6a@kyoto-u.ac.jp
yamaguchi.ryohei.75s@st.kyoto-u.ac.jp
A possible reaction pathway for the dehydrogenative oxida-
tion of primary alcohols to carboxylic acids in aqueous media
is illustrated in Scheme 5. The first step of the reaction would
be the dehydrogenation catalyzed by 3 to afford the aldehyde.
This step would proceed by a similar mechanism to that shown
in Scheme 3. Then, addition of water to the aldehyde would
occur to give a gem-diol. Finally, dehydrogenation of the gem-
diol catalyzed by 3 would proceed to give the carboxylic acid
product.
ACKNOWLEDGMENT
This work was supported by JSPS KAKENHI Grant Number
JP16H01018 in Precisely Designed Catalysts with Customized
Scaffolding and Grant-in-Aid for Scientific Research (B) Grant
Number 26288047.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
REFERENCES
(1) (a) Tsuji, J. Transition Metal Reagents and Catalysts: Innova-
tions in Organic Synthesis, John Wiley & Sons, Ltd., 2000. (b) Min-
gos, D. M. P.; Crabtree, R. H. (Eds), Comprehensive Organometallic
Chemistry III: From Fundamentals to Applications, vol. 10 (volume
editor: Ojima, I.), Elsevier, 2007. (c) Mingos, D. M. P.; Crabtree, R.
H. (Eds), Comprehensive Organometallic Chemistry III: From Fun-
damentals to Applications, vol. 11 (volume editor: Hiyama, T.), Else-
vier, 2007. (d) Hartwig, J. F. Organotransition Metal Chemistry:
From Bonding to Catalysis, University Science Books, 2010. (e)
Yamaguchi, R.; Fujita, K. Ligand Platforms in Homogenous Catalytic
Reaction with Metals, John Wiley & Sons, Ltd., 2015.
Scheme 5. Possible Reaction Pathway for the Dehydro-
genative Oxidation of Primary Benzylic Alcohols under
Reflux in Water Catalyzed by 3
(
2) (a) Lindström, U. M. Chem. Rev. 2002, 102, 2751-2772. (b)
Koba-yashi, S.; Manabe, K. Acc. Chem. Res. 2002, 35, 209-217. (c)
Manabe, K.; Kobayashi, S. Chem. Eur. J. 2002, 8, 4094-4101. (d) Li,
C.-J. Chem. Rev. 2005, 105, 3095-3165. (e) Chanda, A.; Fokin, V. V.
Chem. Rev. 2009, 109, 725-748. (f) Butler, R. N.; Coyne, A. G.
Chem. Rev. 2010, 110, 6302-6337. (g) Simon, M.-O.; Li, C.-J. Chem.
Soc. Rev. 2012, 41, 1415-1427. (h) Gawande, M. B.; Bonifácio, V. D.
B.; Luque, R.; Branco, P. S.; Varma, R. S. Chem. Soc. Rev. 2013, 42,
5522-5551.
Quantitative analysis of the evolved hydrogen gas in the de-
hydrogenative formation of the carboxylic acids from primary
alcohols was also conducted. The reaction of 4-methylbenzyl
alcohol on 2.5 mmol scale was conducted, as shown in eq 4.
Hydrogen (2 equiv.) evolved in 78% yield, which was the
corresponding amount expected because the carboxylic acid
product was also obtained in 78% yield.
(
3) (a) Fujita, K.; Tanino, N.; Yamaguchi, R. Org. Lett. 2007, 9,
109-111. (b) Fujita, K.; Yoshida, T.; Imori, Y.; Yamaguchi, R. Org.
Lett. 2011, 13, 2278-2281. (c) Kawahara, R.; Fujita, K.; Yamaguchi,
R. Angew. Chem. Int. Ed. 2012, 51, 12790-12794. (d) Yamaguchi, R.;
Kobayashi, D.; Shimizu, M.; Fujita, K. J. Organomet. Chem. 2017,
843, 14-19.
(
4) (a) Yamaguchi, R.; Ikeda, C.; Takahashi, Y.; Fujita, K. J. Am.
Chem. Soc. 2009, 131, 8410-8412. (b) Fujita, K.; Tanaka, Y.; Koba-
yashi, M.; Yamaguchi, R. J. Am. Chem. Soc. 2014, 136, 4829-4832.
(
5) (a) Kawahara, R.; Fujita, K.; Yamaguchi, R. J. Am. Chem. Soc.
012, 134, 3643-3646. (b) Fujita, K.; Ito, W.; Yamaguchi, R. Chem-
CatChem 2014, 6, 109-112. (c) Toyomura, K.; Fujita, K. Chem. Lett.
017, 46, 808-810.
6) Dehydrogenative oxidation of alcohols in aqueous media re-
2
2
(
ported by other research groups: (a) Feng, B.; Chen, C.; Yang, H.;
Zhao, X.; Hua, L.; Yu, Y.; Cao, T.; Shi, Y.; Hou, Z. Adv. Synth.
Catal. 2012, 354, 1559-1565. (b) Tang, L.; Sun, H.; Li, Y.; Zha, Z.;
Wang, Z. Green Chem. 2012, 14, 3423-3428. (c) Sawama, Y.; Morita,
K.; Yamada, T.; Nagata, S.; Yabe, Y.; Monguchi, Y.; Sajiki, H. Green
Chem. 2014, 16, 3439-3443. (d) Ngo, A. H.; Adams, M. J.; Do, L. H.
Organometallics 2014, 33, 6742-6745.
In summary, we have designed and prepared the new dica-
tionic iridium catalyst 3 bearing a chelating bidentate ligand
that comprises NHC and α-hydroxypyridine moieties. Catalyst
3 exhibited high activity in aqueous media for the dehydro-
genative oxidation of secondary alcohols to ketones accompa-
nying the evolution of hydrogen. Furthermore, the dehydro-
genative transformation of primary alcohols in aqueous media
to give carboxylic acids was also accomplished by employing
catalyst 3 without using base.
(
7) There are a few publications describing the dehydrogenative
oxidation of alcohols catalyzed by NHC-iridium based complexes: (a)
Prades, A.; Corberán, R.; Poyatos, M.; Peris, E. Chem. Eur. J. 2008,
14, 11474-11479; (b) Gülcemal, S.; Gülcemal, D.; Whitehead, G. F.
S.; Xiao, J. Chem. Eur. J. 2016, 22, 10513-10522.
(
8) During the present investigations and preparation of the manu-
script, Grotjahn, Webster, and Papish have very recently reported the
synthesis of the ligand comprises NHC and α-hydroxypyridine moie-
ties by a route different from our present study. They have also pre-
pared the monocationic iridium complex bearing this ligand and in-
vestigated its catalytic activity in hydrogenation of carbon dioxide and
dehydrogenation of formic acid. Siek, S.; Burks, D. B.; Gerlach, D.
L.; Liang, G.; Tesh, J. M.; Thompson, C. R.; Qu, F.; Shankwitz, J. E.;
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acscatal. *****.
Experimental details and characterization data (PDF)
X-ray crystallographic data for 3 (CIF)
ACS Paragon Plus Environment

Page 5 of 6
ACS Catalysis
Vasquez, R. M.; Chambers, N.; Szulczewski, G. J.; Grotjahn, D. B.;
Webster, C. E.; Papish, E. T. Organometallics 2017, 36, 1091-1106.
9) Zeng, G.; Sakaki, S.; Fujita, K.; Sano, H.; Yamaguchi, R. ACS
Catal. 2014, 4, 1010-1020.
10) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
(
1
2
309. (b) Peris, E.; Crabtree, R. H. Coord. Chem. Rev. 2004, 248,
239-2246. (c) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004,
248, 2247-2273. (d) Scott, N. M.; Nolan, S. P. Eur. J. Inorg. Chem.
005, 1815-1828. (e) Díez-González, S. (Eds), N-Heterocyclic Car-
2
benes, RSC Publishing, 2011. (f) Cazin, C. S. J. N-Heterocyclic Car-
benes in Transition Metal Catalysis and Organocatalysis, Springer,
2
011.
11) (a) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
972-975. (b) Chianese, A., R.; Li, X.; Janzen, M. C.; Faller, J. W.;
Crabtree, R. H. Organometallics 2003, 22, 1663-1667.
(
12) We have examined the reaction of a substrate having a pyri-
dine ring [1-(pyridin-2-yl)ethanol]. But the yield of dehydrogenated
product (2-acetylpyridine) was low (35%).
(
13) In order to carefully compare the catalytic activities of 3 and
8, we also carried out the reactions of 1-phenylethanol using a smaller
amount (0.10 mol%) of catalyst. The yields of acetophenone were
6
8% (with cat. 3) and 78% (with cat. 8), respectively. These results
indicate that the catalytic activity of 8 was higher than that of 3, sup-
porting the proposed mechanism.
(
14) The volume of evolved hydrogen gas was measured using a
gas burette. The molar amount of hydrogen was calculated using the
ideal gas law.
(
15) Purity of the evolved hydrogen gas was confirmed by GC
analysis. Details are shown in Figure S2 in the supporting infor-
mation.
(
16) (a) Balaraman, E.; Khaskin, E.; Leitus, G.; Milstein, D. Nat.
Chem. 2013, 5, 122-125. (b) Choi, J.-H.; Heim, L. E.; Ahrens, M.;
Prechtl, M. H. G. Dalton Trans. 2014, 43, 17248-17254. (c) Malineni,
J.; Keul, H.; Möller, M. Dalton Trans. 2015, 44, 17409-17414. (d)
Zhang, L.; Nguyen, D. H.; Raffa, G.; Trivelli, X.; Capet, F.; Desset,
S.; Paul, S.; Dumeignil, F.; Gauvin, R. M. ChemSusChem 2016, 9,
1
413-1423. (e) Wang, X.; Wang, C.; Liu, Y.; Xiao, J. Green Chem.
2016, 18, 4605-4610. (f) Sarbajna, A.; Dutta, I.; Daw, P.; Dinda, S.;
Rahaman, S. M. W.; Sarkar, A.; Bera, J. K. ACS Catal. 2017, 7, 2786-
2
790.
17) We have also conducted the reaction of benzyl alcohol cata-
(
lyzed by the complex 6 under the same reaction condition as Table 3.
However, the yield of benzoic acid was 21%, showing the high cata-
lytic performance of 3 for the dehydrogenative oxidation of primary
benzylic alcohols to benzoic acid derivatives.
(
18) We have also conducted the reaction of aliphatic primary al-
cohols (1-hexanol and 1-octanol) under the same conditions shown in
Table 3. However, the yields of carboxylic acids were very low (<
2
5%).
ACS Paragon Plus Environment

ACS Catalysis
Page 6 of 6
TOC Graphic
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
ACS Paragon Plus Environment