A Bifunctional Iridium Catalyst Modified for Persistent Hydrogen Generation from Formic Acid: Understanding Deactivation via Cyclometalation of a 1,2-Diphenylethylenediamine Motif

Article abstract of DOI:10.1021/acscatal.7b01068

Thermal degradation of a bifunctional Ir complex with a 1,2-diphenylethylenediamine (DPEN) framework was investigated, which is relevant to catalyst deactivation in the acceptorless dehydrogenation of formic acid. The well-defined hydridoiridium complex 1b, derived from N-triflyl-1,2-diphenylethylenediamine (TfDPEN), proved to be solely transformed at the reflux temperature of 1,2-dimethoxyethane (DME) into two iridacycles (2 and 3) via C-H bond cleavage at the ortho carbon atoms of the phenyl substituents on the diamine backbone. These products were successfully isolated and characterized by NMR, elemental analysis, and X-ray crystallography. The iridacycle formation was significantly enhanced in the presence of water, possibly due to facile deprotonative orthometalation via a hydroxidoiridium intermediate. To prevent the deactivation process caused by the cyclometalation of the DPEN moiety, a hydridoiridium complex (5b) without phenyl substituents was synthesized from N-triflylethylenediamine (TfEN). The modified complex 5b showed a pronounced ability to catalyze hydrogen evolution from formic acid in a 1/1 mixed solvent of water and DME even in the absence of base additives. The initial rate was maintained for a longer time relative to 1b, and thus formic acid was mostly converted within 80 min under the conditions of a HCOOH/5b ratio of 15900 at 60°C. (Graph Presented).

Full text of DOI:10.1021/acscatal.7b01068

Subscriber access provided by Binghamton University | Libraries
Article
A Bifunctional Iridium Catalyst Modified for Persistent Hydrogen
Generation from Formic Acid: Understanding Deactivation
via Cyclometalation of a 1,2-Diphenylethylenediamine Motif
Asuka Matsunami, Shigeki Kuwata, and Yoshihito Kayaki
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 24 May 2017
Downloaded from http://pubs.acs.org on May 24, 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 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
A Bifunctional Iridium Catalyst Modified for Persistent
Hydrogen Generation from Formic Acid:
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Understanding Deactivation via Cyclometalation of a
1
,2-Diphenylethylenediamine Motif
†
†‡
†
Asuka Matsunami , Shigeki Kuwata , Yoshihito Kayaki*
†
Department of Chemical Science and Engineering, School of Materials and Chemical
Technology, Tokyo Institute of Technology, 2-12-1-E4-1 O-okayama, Meguro-ku, Tokyo
152-8552, Japan
‡
PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi,
Saitama 332-0012, Japan
ABSTRACT
Thermal degradation of a bifunctional Ir complex with a 1,2-diphenylethylenediamine
(DPEN) framework was investigated, which is relevant to catalyst deactivation in the
acceptorless dehydrogenation of formic acid. The well-defined hydridoiridium complex (1b),
derived from N-triflyl-1,2-diphenylethylenediamine (TfDPEN), proved to be solely
transformed at the reflux temperature of 1,2-dimethoxyethane (DME) into two iridacycles (2
and 3) via C-H bond cleavage at the ortho-carbon atoms of the phenyl substituents on the
ACS Paragon Plus Environment
1

ACS Catalysis
Page 2 of 20
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
diamine backbone. These products were successfully isolated and characterized by NMR,
elemental analysis, and X-ray crystallography. The iridacycle formation was significantly
enhanced in the presence of water, possibly due to facile deprotonative orthometalation via a
hydroxidoiridium intermediate. To prevent the deactivation process caused by the
cyclometalation of the DPEN moiety, a hydridoiridium complex (5b) without phenyl
substituents was synthesized from N-triflylethylenediamine (TfEN). The modified complex
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
5b showed a pronounced ability to catalyze hydrogen evolution from formic acid in a 1:1
mixed solvent of water and DME even in the absence of base additives. The initial rate was
maintained for a longer time relative to 1b, and thus formic acid was mostly converted within
80 min under the conditions of a HCOOH/5b ratio of 15,900 at 60 °C.
KEYWORDS: iridium, hydrogen generation, formic acid, cyclometalation, bifunctional
catalyst
INTRODUCTION
Hydrogen is a promising clean energy carrier in stationary and transportation power
1
applications for the future. However, the storage and transportation of large-scale production
2
pose a serious risk due to its highly flammable and explosive nature. Generating hydrogen
gas from other safe alternatives just before use has drawn much attention, as it is less
3
hazardous and potentially more cost effective. Formic acid is an attractive hydrogen carrier
4
because of its relatively high gravimetric hydrogen content (4.4 wt%). Various
5
5k,5o,6,7
5m,8
9
10
homogeneous catalysts, including Ru, Ir,
Rh,
Fe and other transition metal
complexes, have been reported to show the selective transformation of formic acid into
11
hydrogen and carbon dioxide without carbon monoxide contamination. Among them, Ir
ACS Paragon Plus Environment
2

Page 3 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
complexes with proton-responsive ligands achieved excellent results. For example, Himeda
-1
and Fujita reported a very high turnover frequency (TOF) of 228,000 h at 90 ºC using a
6d
binuclear Ir catalyst bearing a bipyrimidine ligand in the presence of sodium formate. Li
and co-workers developed a water-soluble iridium catalyst with an N,N’-diimine ligand,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
-
1
6j
which attained the best TOF of 487,500 h at 90 ºC without base additives. As a limited
example of exceptionally high turnover rates under mild conditions, Xiao’s bifunctional Ir
complex bearing a cyclometalated 2-aryl-imidazoline ligand demonstrated an excellent TOF
-
1
of 147,000 h for the initial 10 seconds at 40 ºC in an azeotropic mixture of formic acid and
6
f
triethylamine (5:2).
In our recent studies on bifunctional catalysts possessing a proton-responsive metal/NH
group, Cp*Ir complexes derived from N-sulfonylated DPEN proved to be effective for
7
catalyzing the evolution of hydrogen from formic acid. The substituted DPEN ligand has
12
been shown to facilitate Ru-, Rh-, and Ir-catalyzed asymmetric transfer hydrogenation,
13
14
+
-
H -hydrogenation of ketones, and oxidation of alcohols via a H /H delivery with the
2
15
interconversion between hydrido(amine) and amido complexes, as depicted in Scheme 1.
The function of the catalysts was found to be switchable from hydrogen transfer to
acceptorless dehydrogenation. In particular, TfDPEN-derived Ir catalysts 1a and 1b showed
-
1
an appreciably high activity with a TOF up to 6,090 h for the initial 5 min at 35 ºC without
base additives. The conversion of formic acid was accelerated by the NH moiety on the
ligand as well as an aqueous mixed solvent, possibly due to the effective protonation of the
metal hydride via a plausible proton-relay mechanism (Scheme 2).
For most of the catalysts used in the evolution of hydrogen from formic acid, it is difficult to
maintain their excellent initial efficiencies. The same was true for our catalysts 1a and 1b; for
example, the rate of hydrogen evolution at 35 °C decreased as time passed. On the other hand,
ACS Paragon Plus Environment
3

ACS Catalysis
Page 4 of 20
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
catalyst deterioration was suppressed at 0 °C and the highest turnover number (TON) of
6,780 was achieved after 53 h. Based on these results, we have shed light on the thermal
degradation pathway of the TfDPEN-Ir complexes toward making a more robust and reliable
dehydrogenation catalyst.
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 1. Efficient proton/hydride delivery system for bifunctional iridium complexes.
Scheme 2. Acceptorless dehydrogenation from formic acid using TfDPEN-derived iridium
catalysts 1a and 1b.
RESULTS AND DISCUSSION
ACS Paragon Plus Environment
4

Page 5 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
We initially investigated the temperature dependence of the catalytic activities of
dehydrogenation using the amidoiridium complex 1a. Formic acid (3 mL, 79.5 mmol) was
continuously introduced via a syringe pump at a rate of 0.3 mL/min to 1a (0.001 mmol) in a
7
mixed solvent of DME (6 mL) and water (6 mL), according to our reported procedure. The
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
rate of gas evolution was accurately estimated by a mass flowmeter for 1 h. As shown in
Figure 1, the initial catalytic efficiency was enhanced by increasing the reaction temperature.
-1
A very high TOF of 11,110 h was achieved at 60 ºC within the first 5 minutes of the
reaction, but the hydrogen generation decreased after 15 min and plateaued at a TON of
2,270 for 1 h. When the reaction was conducted at a lower temperature of 25 ºC, the TON for
-1
1 h was increased to 3,190. The initial TOF of 3,490 h was not as high as that at 35 ºC or 60
ºC but the TOF remained nearly the same for over 1 h. These results strongly indicate that
catalyst deactivation stemming from thermolysis of the catalytic species occurred during
dehydrogenation at higher temperatures.
3500
3000
2500
2000
1500
TON
1000
500
0
0
30
60
min
ACS Paragon Plus Environment
5

ACS Catalysis
Page 6 of 20
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
Figure 1. Time course of turnover numbers in the dehydrogenation of formic acid using the
iridium complex 1a at 25, 35, and 60 °C.
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
The thermal stability of the hydridoiridium complex 1b, which is a key intermediate in the
7
rate-determining hydrogen evolution step, was investigated by heating in refluxing DME for
1
38 h. The H NMR spectrum of the resulting mixture in CD
Cl
2 2
indicated that 1b was
transformed entirely into two new products, exhibiting two singlet signals centered at 1.83
and 1.84 ppm due to the methyl protons of the Cp* ligand at the ratio of 1:4.6. These
complexes were successfully separated by silica gel column chromatography eluted with
hexane-diethyl ether (1:2) and two isomeric iridacycles, 2 and 3, were identified, as depicted
1
19
13
1
in Scheme 3, from the result of H, F, and C{ H} NMR analyses and X-ray
crystallography. As shown in Figures 2 and 3, each iridacycle adopts a three-legged piano
stool structure around the Ir(III) atom with Cp*, amine, sulfonylamido, and phenyl ligands.
These iridacycles are dehydrogenative cyclometalation products where the ortho-carbon atom
of each phenyl substituent on the DPEN is attached to the Ir metal. Complex 2 was formed
via an intramolecular C-H bond cleavage of the phenyl group A proximal to the NTf moiety,
2
and complex 3 was the product metalated at the phenyl group B proximal to the NH moiety.
Both structures display similar bond lengths and bond angles around the Ir centers, as listed
in Table S1.
ACS Paragon Plus Environment
6

Page 7 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
H
Tf
N
A
B
–
H2
Ir
Ir
Ir
+
H
N
Tf
H
DME, reflux
38 h
N
H
2
N
N
Tf N
H
C H
C H
6 5
A
6
5
B
H H
H
100% conv
1
b
2
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4.6:1
Scheme 3. Thermal transformation of hydridoiridium complex 1b to iridacycles 2 and 3.
Figure 2. ORTEP structure of the iridacycle 2. The hydrogen atoms, except for the
coordinating amine protons are omitted for clarity. Thermal ellipsoids represent the 50%
probability level.
ACS Paragon Plus Environment
7

ACS Catalysis
Page 8 of 20
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
Figure 3. ORTEP structure of the iridacycle 3. The hydrogen atoms, except for the
coordinating amine protons are omitted for clarity. Thermal ellipsoids represent the 50%
probability level.
Although the underlying mechanism of the metalacycle formation is obscure, the release of
1
hydrogen gas could be confirmed by a H NMR monitoring experiment for the thermolysis of
1b in refluxing THF-d . Dehydrogenative cyclometalation was recently reported in a
8
rhodacycle system based on 2-(di-tert-butylphosphinomethyl)-6-phenylpyridine and utilized
8c
for the catalytic hydrogen evolution from formic acid. The cyclometalation of a
hydridorhodium intermediate with a bidentate PN coordination mode was proposed as a clue
2
to H elimination accompanied by formation of the PNC pincer structure. The reverse
decyclometalation was also demonstrated by treatment of the rhodacycle with formic acid to
give a formatorhodium complex with a premetalated aryl moiety. Differently from the
reversible nature of the PNC-pincer Rh complex conferred from the hemilabile aryl group,
8
the TfDPEN-derived iridacycles 2 and 3 kept intact in a THF-d solution at room temperature
after treatment with five molar amounts of formic acid.
ACS Paragon Plus Environment
8

Page 9 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
Interestingly, the cyclometalation was strongly influenced by water. The formation of the
iridacycles was accelerated in aqueous DME, which is the optimized reaction solvent for the
acceptorless dehydrogenation system. In contrast to the abovementioned cyclometalation in
DME that required 38 h (Scheme 3), thermolysis of 1b, in a 1:1 mixed solvent of DME and
water, was completed within 50 min to produce a mixture of 2 and 3 with a ratio of 6.3:1.
Koike and Ikariya reported a similar acceleration effect of phenols or acidic alcohols on the
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
16
cyclometalation of bifunctional Ru, Rh, and Ir complexes containing a TsDPEN ligand. In
addition to the products resulting from orthometalation of the Ts group, C-H bond metalation
on the phenyl group proximal to the NH moiety was exemplified by the reaction of the Ru
2
complex. Detailed kinetic and mechanistic studies revealed that orthometalation is promoted
via alkoxido intermediates accessible from the starting amido complexes with alcoholic
compounds. Analogously, the C-H activation of 1b should be facilitated by water via a
17
hydroxidoiridium intermediate, as shown in Scheme 4.
Scheme 4. A plausible cyclometalation mechanism of 1b via a hydroxidoiridium
intermediate.
ACS Paragon Plus Environment
9

ACS Catalysis
Page 10 of 20
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
Iridacycles 2 and 3 exhibited limited catalytic activity for the hydrogen evolution compared
with that of the amidoiridium complex 1a, suggesting that the cyclometalation is closely
related to the deterioration of the hydrogen generation. The reaction profile shown in Figure 4
illustrates a substantial decrease in the catalytic function of 2 and 3, especially at the initial
stage. The iridacycles catalyzed the dehydrogenation with the addition of excess formic acid
but with a lower performance compared with that of the parent complex 1a. The regeneration
of catalysis may involve the liberation of the NTf moiety from the iridacycles, as deduced
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
19
18
from the F NMR spectra of the reaction mixture displaying new signals around -78 ppm.
After approximately 20 minutes passed in the reaction, the sum of the signal intensities
ascribed to the free NTf was 9 times as much as the peak at -76 ppm of the remaining NTf
moiety of 3, whereas almost half of the starting iridacycle remained untouched in the case of
the less active 2. These results corroborate the catalytic behavior of 2 and 3. The NTf ligand
on the six-membered chelate ring of 3 would be susceptible to its dissociation relative to the
rigid five-membered ring of 2.
ACS Paragon Plus Environment
10

Page 11 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1500
1
000
5
00
0
0
5
10
15
20
Figure 4. Time versus TON plots for the catalytic hydrogen production from formic acid
using complexes 1a, 2, and 3.
To prevent the cyclometalation process of the DPEN moiety, we designed a new Ir system,
derived from N-triflylethylenediamine (TfEN). A precatalyst chloridoiridium complex 4 was
synthesized from [Cp*IrCl
2 2
] and the TfEN ligand in the presence of triethylamine with 58%
1
9
yield after recrystallization from dichloromethane/diethyl ether, as shown in Scheme 5a.
After transformation of 4 into an amidoiridium complex 5a in situ by treatment with aqueous
KOH at 0 ºC, subsequent addition of formic acid resulted in the hydridoiridium complex 5b
in an isolated yield of 69% (Scheme 5b). The amidoiridium complex 5a was not stable and
easily decomposed at room temperature. The chlorido complex and hydrido complex 5b were
1
19
13
characterized by H, F, and C NMR spectroscopies and X-ray crystallography. The
ORTEP structure of the hydridoiridium complex 5b clearly shows that the metal is bound to
ACS Paragon Plus Environment
11

ACS Catalysis
Page 12 of 20
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
Cp*, amine, and sulfonamide ligands in the typical three-legged piano stool coordination
environment, although the hydrido ligand is not located in the electron density map, as
depicted in Figure S4. The bond lengths and bond angles around the iridium centers of
complex 5b were similar to those of the hydridoiridium complex 1b derived from the
TfDPEN (see Table S3).
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 5. (a) Synthesis of a chloroiridium complex 4 derived from TfEN. (b) Synthesis of a
hydridoiridium complex 5b via a coordinately unsaturated amidoiridium 5a.
Finally, in order to assess the catalytic potential of the new hydridoiridium complex 5b
derived from TfEN, flow monitoring experiments of the hydrogen generation from formic
acid were performed at 35 and 60 °C. As shown in Figure 5, 5b showed excellent
-1
performance with the initial TOF of 5,590 h at 35 °C, on par with that of the Ir catalyst 1a
derived from TfDPEN. As expected, 5b kept its high performance for a far longer period
unlike the prototype 1a, achieving a TON of 6,850 (86% conversion) after 125 min.
Furthermore, the catalytic deactivation was evidently suppressed even at a higher temperature.
ACS Paragon Plus Environment
12

Page 13 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
When the reaction using 5b was carried out at 60 °C with a total substrate/catalyst molar ratio
of 15,900, 97% of the added formic acid was converted within 80 min, as depicted in Figure
S2.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
cat (0.013 mol%)
HCOOH
H2 + CO2
DME/H O, 35 °C
2
8000
8000
Tf
N
7
7
0
0
0
0
0
0
Ir
N
H
H
H
6000
6000
5b
5
5
0
0
0
00
0
TON125 min = 6,849
TON
4000
4000
Tf
C6H5
C6H5
N
3000
3000
Ir
N
H
2000
2000
1a
1000
1000
TON125 min = 3,010
0
0
0
0
5
5
0
0
100
100
min
Figure 5. Time versus TON plots for the catalytic acceptorless dehydrogenation from formic
acid using complexes 1a and 5b at 35 °C.
CONCLUSIONS
The well-defined bifunctional hydridoiridium complex, 1b, derived from TfDPEN was
thermally transformed into iridacycles 2 and 3, both of which were isolated and characterized.
The formation of iridacycle was markedly enhanced in an aqueous solvent identical to that
for the dehydrogenation. Judging from the catalytic behaviors of 2 and 3, the cyclometalation
ACS Paragon Plus Environment
13

ACS Catalysis
Page 14 of 20
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
process hampers the catalytic performance for the dehydrogenation from formic acid.
Actually, the rationally designed hydridoiridium complex 5b derived from
non-phenyl-substituted TfEN showed excellent catalytic activity in the absence of base
additives with no noticeable retardation even at elevated temperature. Formic acid was
mostly consumed at 60°C within 80 min to achieve a TON of 15,900. The findings on
thermal behavior of DPEN-based complexes should contribute to develop more efficient and
robust bifunctional catalysts for a range of asymmetric and non-asymmetric processes.
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
ASSOCIATED CONTENT
Supporting Information.
The Supporting Information is available free of charge on the ACS Publications website at
DOI:10.1021/.
Experimental procedures and characterization data including NMR spectra of new
compounds (PDF)
Single-crystal X-ray diffraction data for compounds 2, 3, 4·CH Cl , 5b (CIF)
2
2
AUTHOR INFORMATION
Corresponding Author
*E-mail: ykayaki@o.cc.titech.ac.jp (Y. Kayaki)
Author Contributions
The manuscript was written through contributions of all authors. All authors have given
approval to the final version of the manuscript.
Funding Sources
ACS Paragon Plus Environment
14

Page 15 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
Any funds used to support the research of the manuscript should be placed here (per journal
style).
Notes
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This study was financially supported by JSPS KAKENHI Grant Number 24350079 and
26621043 and in part by Grant for Engineering Research from Mizuho Foundation for the
Promotion of Sciences. A.M. is grateful to the Japan Society for the Promotion of Science
(JSPS) for a Research Fellowship for Young Scientists (No. 17J09484).
REFERENCES
(1) (a) Armaroli, N.; Balzani, V. Angew. Chem. Int. Ed. 2007, 46, 52-66. (b) Lubitz, W.;
Tumas, W. Chem. Rev. 2007, 107, 3900-3903.
(2) (a) Eberle, U.; Felderhoff, M.; Schüth, F. Angew. Chem. Int. Ed. 2009, 48, 6608-6630. (b)
Yadav, M.; Xu, Q. Energy Environ. Sci. 2012, 5, 9698-9725.
(3) (a) Fukuzumi, S. Eur. J. Inorg. Chem. 2008, 1351-1362. (b) Dalebrook, A. F.; Gan, W.;
Grasemann, M.; Moret, S.; Laurenczy, G. Chem. Commun. 2013, 49, 8735-8735. (c) Papp,
C.; Wasserscheid, P.; Libuda, J.; Steinrück, H.-P. Chem. Rec. 2014, 14, 879-896. (d) Zhu,
Q.-L.; Xu, Q. Energy Environ. Sci. 2015, 8, 478-512. (e) Preuster, P.; Papp, C.; Wasserscheid,
P. Acc. Chem. Res. 2017, 50, 74-85.
(4) a) Joó, F. ChemSusChem 2008, 1, 805-808. (b) Enthaler, S.; von Langermann, J.; Schmidt,
T. Energy Environ. Sci. 2010, 3, 1207-1217. (c) Grasemann, M.; Laurenczy, G. Energy
Environ. Sci. 2012, 5, 8171-8181. (d) Alsabeh, P. G.; Mellmann, D. Junge, H.; Beller, M.
Top. Organomet. Chem. 2014, 48, 45-80. (e) Mellmann, D.; Sponholz, P.; Junge, H.; Beller,
M. Chem. Soc. Rev. 2016, 45, 3954-3988. (f) Singh, A. K.; Singh, S.; Kumar, A. Catal. Sci.
Technol. 2016, 6, 12-40.
(
5) (a) Boddien, A.; Loges, B.; Junge, H.; Beller, M. ChemSusChem 2008, 1, 751-758. (b)
Loges, B.; Boddien, A.; Junge, H.; Beller, M. Angew. Chem. Int. Ed. 2008, 47, 3962-3965.
c) Fellay, C.; Dyson, P. J.; Laurenczy, G. Angew. Chem. Int. Ed. 2008, 47, 3966-3968. (d)
(
Junge, H.; Boddien, A.; Capitta, F.; Loges, B.; Noyes, J. R.; Gladiali, S.; Beller, M.
Tetrahedron Lett. 2009, 50, 1603-1606. (e) Fellay, C.; Yan, N.; Dyson, P. J.; Laurenczy, G.
Chem. Eur. J. 2009, 15, 3752-3760. (f) Loges, B.; Boddien, A.; Junge, H.; Noyes, J. R.;
Baumann, W.; Beller, M. Chem. Commun. 2009, 28, 4185-4187. (g) Boddien, A.; Loges, B.;
Junge, H.; Gärtner, F.; Noyes, J. R.; Beller, M. Adv. Synth. Catal. 2009, 351, 2517-2520. (h)
Scholten, J. D.; Prechtl, M. H. G.; Dupont, J. ChemCatChem 2010, 2, 1265-1270. (i)
ACS Paragon Plus Environment
15

ACS Catalysis
Page 16 of 20
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
Fukuzumi, S.; Kobayashi, T.; Suenobu, T. J. Am. Chem. Soc. 2010, 132, 1496-1497. (j) Gan,
W.; Fellay, C.; Dyson, P. J.; Laurenczy, G. J. Coord. Chem. 2010, 63, 2685-2694. (k)
Majewski, A.; Morris, D. J.; Kendall, K.; Wills, M. ChemSusChem 2010, 3, 431-434. (l)
Boddien, A.; Gärtner, F.; Federsel, C.; Sponholz, P.; Mellmann, D.; Jackstell, R.; Junge, H.;
Beller, M. Angew. Chem. Int. Ed. 2011, 50, 6411-6414. (m) Himeda, Y.; Miyazawa, S.;
Hirose, T. ChemSusChem 2011, 4, 487-493. (n) Czaun, M.; Goeppert, A.; May, R.; Haiges,
R.; Prakash, G. K. S.; Olah, G. A. ChemSusChem 2011, 4, 1241-1248. (o) Wang, W.-H.;
Hull, J. F.; Muckerman, J. T.; Fujita, E.; Hirose, T.; Himeda, Y. Chem. Eur. J. 2012, 18,
9397-9404. (p) Boddien, A.; Federsel, C.; Sponholz, P.; Mellmann, D.; Jackstell, R.; Junge,
H.; Laurenczy, G.; Beller, M. Energy Environ. Sci. 2012, 5, 8907-8911. (q) Gan, W.;
Snelders, D. J. M.; Dyson, P. J.; Laurenczy, G. ChemCatChem 2013, 5, 1126-1132. (r)
Czaun, M.; Goeppert, A.; Kothandaraman, J.; May, R. B.; Haiges, R.; Prakash, G. K. S.;
Olah, G. A. ACS Catal. 2014, 4, 311-320. (s) Filonenko, G. A.; van Putten, R.; Schulpen, E.
N.; Hensen, E. J. M.; Pidko, E. A. ChemCatChem 2014, 6, 1526-1530. (t) Guerriero, A.;
Bricout, H.; Sordakis, K.; Peruzzini, M.; Monflier, E.; Hapiot, F.; Laurenczy, G.; Gonsalvi,
L. ACS Catal. 2014, 4, 3002-3012. (u) Thevenon, A.; Frost-Pennington, E.; Weijia, G.;
Dalebrook, A. F.; Laurenczy, G. ChemCatChem 2014, 6, 3146-3152. (v) Pan, Y.; Pan, C.-L.;
Zhang, Y.; Li, H.; Min, S.; Guo, X.; Zheng, B.; Chen, H.; Anders, A.; Lai, Z.; Zheng, J.;
Huang, K.-W. Chem. Asian J. 2016, 11, 1357-1360. (w) Mellone, I.; Bertini, F.; Peruzzini,
M.; Gonsalvi, L. Catal. Sci. Technol. 2016, 6, 6504-6512. (x) Guan, C.; Zhang, D.-D.; Pan,
Y.; Iguchi, M.; Ajitha, M. J.; Hu, J.; Li, H.; Yao, C.; Huang, M.-H.; Min, S.; Zheng, J.;
Himeda, Y.; Kawanami, H.; Huang, K.-W. Inorg. Chem. 2017, 56, 438-445. (y) Siek, S.;
Burks, D. B.; Gerlach, D. L.; Liang, G.; Tesh, J. M.; Thompson, C. R.; Qu, F.; Shankwitz, J.
E.; Vasquez, R. M.; Chambers, N.; Szulczewski, G. J.; Grotjahn, D. B.; Webster, C. E.;
Papish, E. T. Organometallics 2017, 36, 1091-1106.
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) (a) Himeda, Y. Green Chem. 2009, 11, 2018-2022. (b) Himeda, Y.; Miyazawa, S.;
Onozawa-Komatsuzaki, N.; Hirose, T.; Kasuga, K. Dalton Trans. 2009, 32, 6286-6750. (c)
Tanaka, R.; Yamashita, M.; Chung, L. W.; Morokuma, K.; Nozaki, K. Organometallics 2011,
30, 6742-6750. (d) Hull, J. F.; Himeda, Y.; Wang, W.-H.; Hashiguchi, B.; Periana, R.;
Szalda, D. J.; Muckerman, J. T.; Fujita, E. Nature Chem. 2012, 4, 383-388. (e) Maenaka, Y.;
Suenobu, T.; Fukuzumi, S. Energy Environ. Sci. 2012, 5, 7360-7367. (f) Barnard, J. H.;
Wang, C.; Berry, N. G.; Xiao, J. Chem. Sci. 2013, 4, 1234-1244. (g) Oldenhof, S.; de Bruin,
B.; Lutz, M.; Siegler, M. A.; Patureau, F. W.; van der Vlugt, I. J. I.; Reek, J. N. H. Chem.
Eur. J. 2013, 19, 11507-11511. (h) Manaka, Y.; Wang, W.-H.; Suna, Y.; Kambayashi, H.;
Muckerman, J. T.; Fujita, E.; Himeda, Y. Catal. Sci. Technol. 2014, 4, 34-37. (i) Wang,
W.-H.; Xu, S.; Manaka, Y.; Suna, Y.; Kambayashi, H.; Muckerman, J. T.; Fujita, E.; Himeda,
Y. ChemSusChem 2014, 7, 1976-1983. (j) Wang, Z.; Lu, S.-M.; Li, J.; Wang, J.; Li, C. Chem.
Eur. J. 2015, 21, 12592-12595. (k) Barrett, S. M.; Slattery, S. A.; Miller, A. J. M. ACS Catal.
2015, 5, 6320-6327. (l) Onishi, N.; Ertem, M. Z.; Xu, S.; Tsurusaki, A.; Manaka, Y.;
Muckerman, J. T.; Fujita, E.; Himeda, Y. Catal. Sci. Technol. 2016, 6, 988-992. (m) Iguchi,
M.; Himeda, Y.; Manaka, Y.; Kawanami, H. ChemSusChem 2016, 9, 2749-2753. (n) Papp,
G.; Ölevti, G.; Horváth, H.; Kathó, Á.; Joó, F. Dalton Trans. 2016, 45, 14516-14519. (o) Li,
J.; Li, J.; Zhang, D.; Liu, C. ACS Catal. 2016, 6, 4746-4754. (p) Czaun, M.; Kothandaraman,
J.; Goeppert, A.; Yang, B.; Greenberg, S.; May, R. B.; Olah, G. A.; Prakash, G. K. S. ACS
Catal. 2016, 6, 7475-7484. (q) Celaje, J. J. A.; Lu, Z.; Kedzie, E. A.; Terrile, N. J.; Lo, J. N.;
Williams, T. J. Nat. Commun. 2016, 7, 11308-11313.
(7) Matsunami, A.; Kayaki, Y.; Ikariya, T. Chem. Eur. J. 2015, 21, 13513-13517.
ACS Paragon Plus Environment
16

Page 17 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
(8) (a) Fukuzumi, S.; Kobayashi, T.; Suenobu, T. ChemSusChem 2008, 1, 827-834. (b)
Wang, Z.; Lu, S.-M.; Wu, J.; Li, C.; Xiao, J. Eur. J. Inorg. Chesym. 2016, 490. (c) Jongbloed,
L. S.; de Bruin, B.; Reek, J. N. H.; Lutz, M.; van der Vlugt, J. I. Catal. Sci. Technol. 2016, 6,
1320-1327.
(9) (a) Boddien, A.; Loges, B.; Gärtner, F.; Torborg, C.; Fumino, K.; Junge, H.; Ludwig, R.;
Beller, M. J. Am. Chem. Soc. 2010, 132, 8924-8934. (b) Boddien, A.; Gärtner, F.; Jackstell,
R.; Junge, H.; Spannenberg, A.; Baumann, W.; Ludwig, R.; Beller, M. Angew. Chem. Int. Ed.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
010, 49, 8993-8996. (c) Boddien, A.; Mellmann, D.; Gärtner, F.; Jackstell, R.; Junge, H.;
Dyson, P. J.; Laurenczy, G.; Ludwig, R.; Beller, M. Science 2011, 333, 1733-1736. (d) Zell,
T.; Butschke, B.; Ben-Devid, Y.; Milstein, D. Chem. Eur. J. 2013, 19, 8068-8072. (e)
Mellmann, D.; Barsch, E.; Bauer, M.; Grabow, K.; Boddien, A.; Kammer, A.; Sponholz, P.;
Bentrup, U.; Jackstell, R.; Junge, H.; Laurenczy, G.; Ludwig, R.; Beller, M. Chem. Eur. J.
2
014, 20, 13589-13602. (f) Bielinski, E. A.; Lagaditis, P. O.; Zhang, Y.; Mercado, B. Q.;
Christian, W.; Bernskoetter, W. H.; Hazari, N.; Schneider, S. J. Am. Chem. Soc. 2014, 136,
1
0234-10237. (g) Bertini, F.; Mellone, I.; Ienco, A.; Peruzzini, M.; Gonsalvi, L. ACS Catal.
2015, 5, 1254-1265. (h) Mellone, I.; Gorgas, N.; Bertini, F.; Peruzzini, M.; Kirchner, K.;
Gonsalvi, L. Organometallics 2016, 35, 3344-3349.
(10) (a) Rieckborn, T. P.; Huber, E.; Karakoc, E.; Prosenc, M. H. Eur. J. Inorg. Chem. 2010,
30, 4757-4761. (b) Jeletic, M. S.; Helm, M. L.; Hulley, E. B.; Mock, M. T.; Appel, A. M.;
Linehan, J. C. ACS Catal. 2014, 4, 3755-3762. (c) Vogt, M.; Nerush, A.; Diskin-Posner, Y.;
Ben-Devid, Y.; Milstein, D. Chem. Sci. 2014, 5, 2043-2051. (d) Enthaler, S.; Brück, A.;
Kammer, A.; Junge, H.; Irran, E.; Gülak, S. ChemCatChem 2015, 7, 65-69. (e) Neary, M. C.;
Parkin, G. Chem, Sci. 2015, 6, 1859-1865.
(11) Review articles: (a) S. Enthaler, ChemSusChem 2008, 1, 801-804. (b) B. Loges, A.
Boddien, F. Gärtner, H. Junge, M. Beller, Top. Catal. 2010, 53, 902-914. (c) S. Enthaler, J.
Langermann, T. Schmidt, Energy Environ. Sci. 2010, 3, 1207-1217. (d) Johnson, T. C.;
Morris, D. J.; Wills, M. Chem. Soc. Rev. 2010, 39, 81-88. (e) Fukuzumi, S.; Suenobu, T.
Dalton Trans. 2013, 42, 18-28. (f) Fujita, E.; Muckerman, J. T.; Himeda, Y. Biochim.
Biophys. Acta 2013, 1827, 1031-1038.
(
12) (a) Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc.
995, 117, 7562-7563. (b) Fujii, A.; Hashiguchi, S.; Uematsu, N.; Ikariya, T.; Noyori, R. J.
Am. Chem. Soc. 1996, 118, 2521-2522. (c) Mashima, K.; Abe, T.; Tani, K. Chem. Lett. 1998,
199-1200. (d) Mashima, K.; Abe, T.; Tani, K. Chem. Lett. 1998, 1201-1202. (e) Murata, K.;
Ikariya, T. J. Org. Chem. 1999, 64, 2186-2187.
1
1
(13) (a) Ohkuma, T.; Utsumi, N.; Tsutsumi, K.; Murata, K.; Sandoval, C.; Noyori, R. J. Am.
Chem. Soc. 2006, 128, 8724-8725. (b) Moritani, J.; Kayaki, Y.; Ikariya, T. RSC Adv. 2014, 4,
61001-61004.
(14) (a) Haack, K.-J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R. Angew. Chem. Int. Ed.
1997, 36, 285-288. (b) Arita, S.; Koike, T.; Kayaki, Y.; Ikariya, T. Angew. Chem. Int. Ed.
2008, 47, 2447-2449. (c) Wills, M. Angew. Chem. Int. Ed. 2008, 47, 4264-4267. (d) Moritani,
J.; Hasegawa, Y.; Kayaki, Y.; Ikariya, T. Tetrahedron Lett. 2014, 55, 1188-1191.
(
15) (a) Muñiz, K Angew. Chem. Int. Ed. 2005, 44, 6622-6627. (b) Ikariya, T. Bull. Chem.
Soc. Jpn. 2011, 84, 1-16. (c) Zhao, B.; Han, Z.; Ding, K. Angew. Chem. Int. Ed. 2013, 52,
744-4788.
4
ACS Paragon Plus Environment
17

ACS Catalysis
Page 18 of 20
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
(16) Koike, T.; Ikariya, T. Organometallics 2005, 24, 724-730.
(17) (a) Kamezaki, S.; Akiyama, S.; Kayaki, Y.; Kuwata, S.; Ikariya, T. Tetrahedron Asymm.
2010, 21, 1169-1172. (b) Dub, P. A.; Wang, H.; Matsunami, A.; Gridnev, I. D.; Kuwata, S.;
Ikariya, T. Bull. Chem. Soc. Jpn. 2013, 86, 557-568.
(18) Ito, M.; Endo, Y.; Tejima, N.; Ikariya, T. Organometallics 2010, 29, 2397-2399.
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
(19) The ORTEP structure and crystallographic data and for 4 were shown in the Supporting
Information (Figure S3 and Table S3).
ACS Paragon Plus Environment
18

Page 19 of 20
ACS Catalysis
1
2
3
4
5
6
7
8
9
For Table of Contents Graphics
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
19

ACS Catalysis Page 20 of 20
1
2
3
4
5
6
7
8
ACS Paragon Plus Environment