Enhanced Hydrogen Generation from Formic Acid by Half-Sandwich Iridium(III) Complexes with Metal/NH Bifunctionality: A Pronounced Switch from Transfer Hydrogenation

Article abstract of DOI:10.1002/chem.201502412

By switching the catalytic function from transfer hydrogenation based on the metal/NH bifunctionality, facile dehydrogenation of formic acid was achieved by amido- and hydrido(amine)-Ir complexes derived from N-triflyl-1,2-diphenylethylenediamine (TfDPEN)

Full text of DOI:10.1002/chem.201502412

DOI: 10.1002/chem.201502412
Communication
&
Homogeneous Catalysis
Enhanced Hydrogen Generation from Formic Acid by Half-
Sandwich Iridium(III) Complexes with Metal/NH Bifunctionality:
A Pronounced Switch from Transfer Hydrogenation
[
a]
Asuka Matsunami, Yoshihito Kayaki,* and Takao Ikariya*
Abstract: By switching the catalytic function from transfer
hydrogenation based on the metal/NH bifunctionality,
facile dehydrogenation of formic acid was achieved by
amido- and hydrido(amine)–Ir complexes derived from N-
triflyl-1,2-diphenylethylenediamine (TfDPEN) at ambient
temperature even in the absence of base additives. Fur-
ther acceleration was observed by the addition of water,
leading to
a maximum turnover frequency above
À1
6
000 h . A proton-relay mechanism guided by the protic
amine ligand and water is postulated for effective proto-
nation of metal hydrides.
Metal–ligand cooperating bifunctional catalysts, in which the
noninnocent ligands directly participate in substrate activation
and bond formation, have offered attractive and general strat-
Scheme 1. Metal/NH bifunctionality based on the interconversion between
the amido and amine complexes.
+
À
egies applicable to effective H and H delivery, facilitating
[1]
various redox transformations. A series of Group 8 and 9
metal complexes bearing N-sulfonylated 1,2-diphenylethylene-
diamine (DPEN) has been successfully utilized for efficient
À1
turnover frequency (TOF) of approximately 490 h . The addi-
tion of triethylamine proved to be indispensable, and the con-
version plateaued at approximately 20% due to the catalyst
deactivation. The direct hydrogen evolution conceptually de-
rived from the transfer hydrogenation using formic acid by the
metal/NH bifunctional catalysts remains scarcely explored.
As a feasible, potential transportable hydrogen storage ma-
terial, the utility of formic acid has been extensively studied
[
2]
asymmetric transfer hydrogenation of aromatic ketones, and
the interconversion between NH(amido) and NH (amine) li-
2
gands on the metal center has been confirmed as depicted in
Scheme 1A. In light of the smooth hydrogen transfer from the
bifunctional hydrido(amine) complexes to ketone substrates, it
is anticipated that the metal/NH bifunctionality will favor cata-
lytic hydrogen generation in the absence of appropriate hydro-
gen acceptors, as outlined in Scheme 1B. In the asymmetric
[
7]
with a range of transition metals. Recently, outstanding cata-
[
8]
[8i,l,9]
lytic performance was achieved with homogeneous Ru, Ir,
6
[8l,9b,10]
[11]
[12]
transfer hydrogenation catalyzed by the prototype [Ru(h -
Rh,
Fe, and other
catalysts, allowing the selective
arene)] complexes using a 5:2 mixture of formic acid and trie-
thylamine as a reaction medium and a hydrogen source,
transformation of formic acid into hydrogen and carbon diox-
ide. Himeda and co-workers recently reported that the highest
[
3]
[4]
À1
[9h]
À1
[9d]
Noyori and Xiao reported that hydrogen was detected in
TOFs (34000 h at 808C and 228000 h at 908C ) were
attained by half-sandwich Ir catalysts bearing chelate azoles
and bipyridine ligands. Among the limited examples of effec-
tive dehydrogenation conducted at ambient temperatures, the
[
5]
[6]
the reaction system. Wills and co-workers disclosed that the
related amine-tethered Rh and Ru catalysts can promote the
decomposition from the azeotropic mixture with a maximum
[
8a]
À1
phosphine–Ru complexes of Beller (TOF=3630 h at 408C)
[
9e]
À1
in addition to the Ir catalysts of Fukuzumi (TOF=1880 h at
[
a] A. Matsunami, Prof. Dr. Y. Kayaki, Prof. Dr. T. Ikariya
Department of Applied Chemistry
[
9f]
À1
2
58C) and Xiao (TOF=3080 h at 408C) have been demon-
Graduate School of Science and Engineering
Tokyo Institute of Technology, O-okayama 2-12-1-E4-1
Meguro-ku, Tokyo 152-8552 (Japan)
strated, although base additives, such as amines and formate
salts, are required for their catalytic activities. In the first report
of highly active homogeneous Fe catalysts with a tetradentate
E-mail: ykayaki@o.cc.titech.ac.jp
[
11c]
phosphine ligand by Beller’s group,
hydrogen was produced
tikariya@apc.titech.ac.jp
with a turnover number (TON) of 1942 after 3 h at 408C with-
out the addition of bases. Milstein reported that a well-defined
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502412.
Chem. Eur. J. 2015, 21, 13513 – 13517
13513
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
pincer-Fe catalyst had excellent activity at 408C in the pres-
ence of trialkylamines with a TON of up to 100000, but the
catalytic conversion was extremely diminished under base-free
[
11d]
conditions.
from formic acid using bifunctional [Cp*Ir] catalysts (Cp*=
,2,3,4,5-pentamethylcyclopentadienyl) at ambient tempera-
Herein, we report concise hydrogen generation
1
ture without base additives.
We initially investigated the catalytic performance of
a newly synthesized amidoiridium complex (1a) derived from
(
S,S)-TfDPEN (Tf=trifluoromethanesulfonyl) in formic acid/tri-
ethylamine azeotrope (1 mL) at 358C. In the presence of aceto-
phenone (2m) with a substrate/catalyst ratio of 200, transfer
hydrogenation proceeded smoothly to give (S)-1-phenyletha-
nol in 95% yield with 93% ee after 24 h in preference to hydro-
gen formation. In contrast, continuous gas evolution was ob-
served when the azeotrope was introduced into a solution of
Figure 2. Bifunctional amido and amine complexes used for hydrogen gen-
eration from formic acid.
Table 1. Comparison of the catalytic activity in the dehydrogenation of
formic acid.
1
a without the hydrogen acceptor, acetophenone, by a syringe
À1
pump at a rate of 0.3 mLmin . Formic acid was degraded to
hydrogen and carbon dioxide without contamination of
carbon monoxide, and the TON was determined as 33 after 1 h
by monitoring the amount of gaseous products with a flowme-
ter. The Ir–TfDPEN catalyst proved effective in the absence of
triethylamine, leading to a TON of up to 255 in 1,2-dimethoxy-
ethane (DME), unlike with most catalytic hydrogen generation
systems, in which amine additives or basic salts are required (A
in Figure 1). Further acceleration was observed by the addition
À1
[f]
Entry
1
Catalyst
TOF5 min [h
]
TON1 h
Yield [%]
1a
4990
0
1910
0
509
144
70
53
0
0
2570
240 (6780)
72
0
19
5
3
2
[a]
2
[
[IrCl(m-Cl)Cp*]
2
1b
1c
1d
3
4
1a
1a
2
a]
3
4
5
6
7
8
9
1
1720
1610
824
616
0
0
4110
48
[a]
0
0
[b,c]
32
[
b,d]
[e]
[e]
0
3 (85)
[
a] HCOONa (265 equiv/Ir) was added. [b] The reaction was conducted
with formic acid (3.0 mL, 79.5 mmol) and catalyst 1a (0.01 mmol) in DME
6 mL) and H O (6 mL). [c] At 358C or [d] at 08C. [e] The highest TON and
(
2
yield after 53 h in parenthesis. [f] The hydrogen yield based on formic
acid.
Cl)Cp*] , the chloroiridium complex (2), as a precursor of 1a,
2
promoted the hydrogen evolution in the presence of sodium
formate (265 equiv/Ir; see the Supporting Information) with
a TON of 509 (Table 1, entries 2 and 3). The positive effects of
the electron-deficient substituents on the sulfonyl group, such
as TfDPEN and p-CF C H SO DPEN, were confirmed in compari-
3
6
4
2
Figure 1. Time vs TON plots for the catalytic hydrogen generation from
formic acid (3.0 mL, 79.5 mmol) using 1a (0.03 mmol) at 358C in DME or in
a 1:1 mixture of DME and H O. The plots are the mean value of three meas-
2
son with the related amido–Ir complexes bearing widely used
MsDPEN (Ms=CH SO ) and TsDPEN (Ts=p-CH C H SO ) ligands
3
2
3
6
4
2
(
entries 1, 4–6). The [Cp*Rh] and [(p-cymeme)Ru] variants (3
urements and are displayed with error bars (~: A; *: B).
and 4) are characterized by a loss of the catalytic function
under the same conditions (entries 7 and 8). The preferable
catalyst 1a was allowed to reduce its loading amount to 1.0”
of water, whereas the reaction conducted in only water result-
ed in a lower catalytic performance, possibly due to the limited
solubility of 1a (see Supporting Information). A TON of 1910
À2
10 mmol (i.e., corresponding to a formic acid/Ir ratio of 7950)
and led to a TON of 2570 after 1 h at 358C (entry 9). Notably,
hydrogen was continuously produced even at a lower temper-
ature of 08C, and the highest TON of 6780 was achieved with
a prolonged reaction time of 53 h (entry 10).
À1
after 1 h and a TOF of 4990 h during the initial 5 min were
attained in a 1:1 mixed solvent of DME and water (B in
Figure 1).
Hydrogen generation was performed with a family of Ir, Rh,
In separate NMR experiments, treatment of the amido com-
À2
and Ru complexes (depicted in Figure 2; 3.0”10 mmol) in
plex 1a with 5.3 equivalents of formic acid in [D ]THF at
8
DME (3 mL) and water (3 mL) at 358C for 1 h with continuous
injection of HCOOH (3 mL, 79.5 mmol) for the initial 10 min.
The results in Table 1 indicate that the DPEN ligand is vital for
hydrogen formation from formic acid, as with the transfer hy-
drogenation. Although no reaction proceeded with [IrCl(m-
À808C resulted in addition across the amido–Ir bond to gener-
ate a formato(amine) complex displaying a formyl signal at d=
[
13]
8.73 ppm. The following decarboxylation took place above
À308C to afford the corresponding hydrido(amine) complex
5a, quantitatively, which is supported by the characteristic hy-
Chem. Eur. J. 2015, 21, 13513 – 13517
www.chemeurj.org
13514
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
superior to the Beller’s iron cata-
[
11c]
lyst
08C). A nearly full conversion
98.5%) of formic acid was
(TON=1942 after 3 h at
4
(
reached within 5 h, as confirmed
1
by H NMR spectroscopy. In
Scheme 2. Stoichiometric reaction of 1a and formic acid.
sharp contrast, an analogous Ir-
tertiary amine complex (5b) had
little contribution to the catalysis (Figure 4), which corrobo-
rates the crucial metal/NH cooperation in the hydrogen gener-
ation.
1
dride signal observed at d=À10.64 ppm in H NMR spectros-
copy (Scheme 2). Whereas the formation of hydrogen gas was
demonstrated by treatment of 5a with an excess (500 equiv)
amount of formic acid in [D ]1,4-dioxane at room temperature,
In view of these experimental results clarifying the impor-
tance of the metal/NH bifunctionality, as well as the remark-
able enhancement by the addition of water in hydrogen gen-
eration, a proton-relay mechanism guided by the protic amine
ligand and water is postulated for effective protonation of the
metal hydrides. As depicted in Figure 5A, the acidic amine
proton will facilitate locating a water molecule close to the hy-
drido ligand and accessing the hydrogen–hydrogen bond for-
mation by a six-membered transition state. The beneficial
effect of the Tf substituent on the DPEN ligand is probably ac-
countable for the increase in the acidity of the coordinating
NH group. A similar situation was achieved in asymmetric hy-
8
subsequent addition (730 equiv) of D O induced further accel-
2
eration and produced HD catalytically. The hydridoiridium 5a
persisted during the decomposition of formic acid, implying
that the protonation of hydrido-Ir species is likely a rate-deter-
mining step in the catalysis. Actually, the catalytic dehydrogen-
ation was considerably retarded by a factor of 1.5 when
HCOOH was replaced with DCOOH. A comparative experiment
using D O in place of H O resulted in a greater KIE value of 2.0,
2
2
+
implying that D is possibly involved in the rate-limiting pro-
cess.
The hydrido-Ir complex 5a bearing rac-TfDPEN was modest-
ly stable under an argon atmosphere, and the structure was
identified by X-ray crystallography (Figure 3) after recrystalliza-
Figure 3. X-ray structures of the hydrido(amine) complex 5a. The hydrogen
atoms, except for the coordinating amine protons and the hydride, are omit-
ted for clarity, and the thermal ellipsoids represent the 50% probability
level.
Figure 4. Time vs TON plots for the catalytic hydrogen generation from
formic acid (3.0 mL, 79.5 mmol) using 5a or 5b (0.03 mmol) at 358C in DME
or in a 1:1 mixture of DME and H
2
O (*: 5a; ~: 5b).
tion from methanol. From the result of the low-temperature
data collection, which enabled hydrogen atoms attached to
the amine nitrogen and Ir center in 5a to be located from the
Fourier difference map and refined isotropically, no marked in-
teractions in the NH···HIr motif were observed from the distan-
ces of 2.33(5) and 3.11(6) Š between the NH protons and the
[
14]
hydrido ligand.
The isolated hydrido complex 5a exhibited a comparable
catalytic activity to the amido complex 1a with a TOF (initial
Figure 5. Proton relay mechanisms in hydrogen formation mediated by
À1
5
min) of 6090 h and a TON of 2340 at 358C for 1 h, which is
H
2
O (A) and heterolysis of molecular hydrogen by alcohol (B).
Chem. Eur. J. 2015, 21, 13513 – 13517
www.chemeurj.org
13515
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
drogenation in which the heterolysis of molecular hydrogen
by bifunctional amido complexes can be driven with the help
Grace, A. Nova, R. N. Perutz, D. J. Taylor, A. C. Whitwood, Chem.
Commun. 2009, 6801.
[
[
6] D. J. Morris, G. J. Clarkson, M. Wills, Organometallics 2009, 28, 4133.
7] a) S. Enthaler, ChemSusChem 2008, 1, 801; b) B. Loges, A. Boddien, F.
Gärtner, H. Junge, M. Beller, Top. Catal. 2010, 53, 902; c) S. Enthaler, J.
Langermann, T. Schmidt, Energy Environ. Sci. 2010, 3, 1207; d) T. C. John-
son, D. J. Morris, M. Wills, Chem. Soc. Rev. 2010, 39, 81; e) M. Grasemann,
G. Laurenczy, Energy Environ. Sci. 2012, 5, 8171; f) S. Fukuzumi, T. Sueno-
bu, Dalton Trans. 2013, 42, 18; g) E. Fujita, J. T. Muckerman, Y. Himeda,
Biochim. Biophys. Acta Bioenerg. 2013, 1827, 1031; h) G. Laurenczy, P. J.
Dyson, J. Braz. Chem. Soc. 2014, 25, 2157.
[15]
of alcoholic solvents (Figure 5B). Within the context of the
formal reversibility of the hydrogen generation and hydrogen
activation processes, the pivotal roles of the protic reaction
media and the metal/NH moiety are ascertained in these trans-
[
9f]
[9i,16]
formations. Xiao and Himeda
recently proposed a related
mechanism involving formic acid or water in long-range
metal–proton bifunctional Ir catalyst systems.
[
8] a) A. Boddien, B. Loges, H. Junge, M. Beller, ChemSusChem 2008, 1, 751;
In conclusion, we achieved efficient catalytic hydrogen evo-
lution from formic acid by using the newly derived bifunctional
iridium complexes containing a TfDPEN ligand at ambient tem-
perature without controlling the pH by treatment of base addi-
tives. The hydrido-Ir complex was successfully isolated and
structurally determined as an important catalytic intermediate.
The proton-relay processes mediated by the NH proton and
water have great potential for accomplishing efficient hydro-
gen production, and thus, further modification of the bifunc-
tional catalysts is currently in progress in our laboratory.
b) B. Loges, A. Boddien, H. Junge, M. Beller, Angew. Chem. Int. Ed. 2008,
4
7, 3962; Angew. Chem. 2008, 120, 4026; c) C. Fellay, P. J. Dyson, G. Lau-
renczy, Angew. Chem. Int. Ed. 2008, 47, 3966; Angew. Chem. 2008, 120,
4030; d) H. Junge, A. Boddien, F. Capitta, B. Loges, J. R. Noyes, S. Gladia-
li, M. Beller, Tetrahedron Lett. 2009, 50, 1603; e) C. Fellay, N. Yan, P. J.
Dyson, G. Laurenczy, Chem. Eur. J. 2009, 15, 3752; f) B. Loges, A. Bod-
dien, H. Junge, J. R. Noyes, W. Baumann, M. Beller, Chem. Commun.
2009, 4185; g) A. Boddien, B. Loges, H. Junge, F. Gärtner, J. R. Noyes, M.
Beller, Adv. Synth. Catal. 2009, 351, 2517; h) J. D. Scholten, M. H. G.
Prechtl, J. Dupont, ChemCatChem 2010, 2, 1265; i) S. Fukuzumi, T. Ko-
bayashi, T. Suenobu, J. Am. Chem. Soc. 2010, 132, 1496; j) W. Gan, C.
Fellay, P. J. Dyson, G. Laurenczy, J. Coord. Chem. 2010, 63, 2685; k) A.
Boddien, F. Gärtner, C. Federsel, P. Sponholz, D. Mellmann, R. Jackstell,
H. Junge, M. Beller, Angew. Chem. Int. Ed. 2011, 50, 6411; Angew. Chem.
2011, 123, 6535; l) W.-H. Wang, J. F. Hull, J. T. Muckerman, E. Fujita, T.
Hirose, Y. Himeda, Chem. Eur. J. 2012, 18, 9397; m) A. Boddien, C. Feder-
sel, P. Sponholz, D. Mellmann, R. Jackstell, H. Junge, G. Laurenczy, M.
Beller, Energy Environ. Sci. 2012, 5, 8907; n) W. Gan, D. J. M. Snelders,
P. J. Dyson, G. Laurenczy, ChemCatChem 2013, 5, 1126; o) M. Czaun, A.
Goeppert, J. Kothandaraman, R. B. May, R. Haiges, G. K. S. Prakash, G. A.
Olah, ACS Catal. 2014, 4, 311; p) G. A. Filonenko, R. Putten, E. N. Schulp-
en, E. J. M. Hensen, E. A. Pidko, ChemCatChem 2014, 6, 1526; q) A. Guer-
riero, H. Bricout, K. Sordakis, M. Peruzzini, E. Monflier, F. Hapiot, G. Lau-
renczy, L. Gonsalvi, ACS Catal. 2014, 4, 3002; r) A. Thevenon, E. Frost-
Pennington, G. Weijia, A. F. Dalebrook, G. Laurenczy, ChemCatChem
Experimental Section
Typical procedure for the dehydrogenation from formic acid
Formic acid (3 mL, 79.5 mmol) was added to a solution of the cata-
lyst 1a (20.9 mg, 0.030 mmol) in DME (3 mL) and degassed water
(
0
3 mL) over 10 min by using a syringe pump (at a ratio of
.3 mLmin ). The rate of the gas evolution was measured by
À1
a flowmeter (wet gas meter W-NK-0.5, SHINAGAWA Co.). The ex-
perimental setup is shown in Figure S1 (Supporting Information).
2014, 6, 3146.
[
9] a) Y. Himeda, Green Chem. 2009, 11, 2018; b) Y. Himeda, S. Miyazawa, N.
Onozawa-Komatsuzaki, T. Hirose, K. Kasuga, Dalton Trans. 2009, 6286;
c) R. Tanaka, M. Yamashita, L. W. Chung, K. Morokuma, K. Nozaki, Orga-
nometallics 2011, 30, 6742; K. Nozaki, Organometallics 2011, 30, 6742;
d) J. F. Hull, Y. Himeda, W.-H. Wang, B. Hashiguchi, R. Periana, D. J.
Szalda, J. T. Muckerman, E. Fujita, Nat. Chem. 2012, 4, 383; e) Y. Maena-
ka, T. Suenobu, S. Fukuzumi, Energy Environ. Sci. 2012, 5, 7360; f) J. H.
Barnard, C. Wang, N. G. Berry, J. Xiao, Chem. Sci. 2013, 4, 1234; g) S. Old-
enhof, B. Bruin, M. Lutz, M. A. Siegler, F. W. Patureau, J. I. Vlugt, J. N. H.
Reek, Chem. Eur. J. 2013, 19, 11507; h) Y. Manaka, W.-H. Wang, Y. Suna,
H. Kambayashi, J. T. Muckerman, E. Fujita, Y. Himeda, Catal. Sci. Technol.
Acknowledgements
This work was financially supported by JSPS KAKENHI Grant
Numbers 24350079 and 26620143 and by Grant for Basic Sci-
ence Research Projects from The Sumitomo Foundation. The
authors acknowledge the Takasago International Corporation
for the generous gift of DPEN.
Keywords: cooperative
homogeneous catalysis · hydride ligands · iridium
effects
·
dehydrogenation
·
2
014, 4, 34; i) W.-H. Wang, S. Xu, Y. Manaka, Y. Suna, H. Kambayashi, J. T.
Muckerman, E. Fujita, Y. Himeda, ChemSusChem 2014, 7, 1976.
10] S. Fukuzumi, T. Kobayashi, T. Suenobu, ChemSusChem 2008, 1, 827.
[
[
[
1] a) T. Ikariya, Bull. Chem. Soc. Jpn. 2011, 84, 1; b) K. MuÇiz, Angew. Chem.
Int. Ed. 2005, 44, 6622; Angew. Chem. 2005, 117, 6780; c) B. Zhao, Z.
Han, K. Ding, Angew. Chem. Int. Ed. 2013, 52, 4744; Angew. Chem. 2013,
[11] a) A. Boddien, B. Loges, F. Gärtner, C. Torborg, K. Fumino, H. Junge, R.
Ludwig, M. Beller, J. Am. Chem. Soc. 2010, 132, 8924; b) A. Boddien, F.
Gärtner, R. Jackstell, H. Junge, A. Spannenberg, W. Baumann, R. Ludwig,
M. Beller, Angew. Chem. Int. Ed. 2010, 49, 8993; Angew. Chem. 2010, 122,
9177; c) A. Boddien, D. Mellmann, F. Gärtner, R. Jackstell, H. Junge, P.
Dyson, G. Laurenczy, R. Ludwig, M. Beller, Science 2011, 333, 1733; d) T.
Zell, B. Butschke, Y. Ben-Devid, D. Milstein, Chem. Eur. J. 2013, 19, 8068;
e) D. Mellmann, E. Barsch, M. Bauer, K. Grabow, A. Boddien, A. Kammer,
P. Sponholz, U. Bentrup, R. Jackstell, H. Junge, G. Laurenczy, R. Ludwig,
M. Beller, Chem. Eur. J. 2014, 20, 13589; f) E. A. Bielinski, P. O. Lagaditis, Y.
Zhang, B. Q. Mercado, W. Christian, W. H. Bernskoetter, N. Hazari, S.
Schneider, J. Am. Chem. Soc. 2014, 136, 10234.
[12] a) T. P. Rieckborn, E. Huber, E. Karakoc, M. H. Prosenc, Eur. J. Inorg. Chem.
2010, 4757; b) M. Vogt, A. Nerush, Y. Diskin-Posner, Y. Ben-Devid, D. Mil-
stein, Chem. Sci. 2014, 5, 2043; c) M. C. Neary, G. Parkin, Chem. Sci.
2015, 6, 1859.
[13] Related reports on the formation of formato species hydrogen-bonded
with a protic amine ligand: a) T. Koike, T. Ikariya, Adv. Synth. Catal. 2004,
346, 37; b) K. Abdur-Rashid, S. E. Clapham, A. Hadzovic, J. H. Harvey, A. J.
1
25, 4844.
2] a) S. Hashiguchi, A. Fujii, J. Takehara, T. Ikariya, R. Noyori, J. Am. Chem.
Soc. 1995, 117, 7562; b) K.-J. Haack, S. Hashiguchi, A. Fujii, T. Ikariya, R.
Noyori, Angew. Chem. Int. Ed. Engl. 1997, 36, 285; Angew. Chem. 1997,
1
09, 297; c) R. Noyori, S. Hashiguchi, Acc. Chem. Res. 1997, 30, 97; d) K.
Mashima, T. Abe, K. Tani, Chem. Lett. 1998, 1199; e) K. Mashima, T. Abe,
K. Tani, Chem. Lett. 1998, 1201; f) K. Murata, T. Ikariya, R. Noyori, J. Org.
Chem. 1999, 64, 2186.
3] a) A. Fujii, S. Hashiguchi, N. Uematsu, T. Ikariya, R. Noyori, J. Am. Chem.
Soc. 1996, 118, 2521; b) K. Murata, K. Okano, M. Miyagi, H. Iwane, R.
Noyori, T. Ikariya, Org. Lett. 1999, 1, 1119.
4] X. Wu, X. Li, F. King, J. Xiao, Angew. Chem. Int. Ed. 2005, 44, 3407;
Angew. Chem. 2005, 117, 3473.
5] Blacker also confirmed the formation of hydrogen in the asymmetric
transfer hydrogenation with the related [Cp*Rh]/N-tosyl-1,2-diamino-
benzene catalyst. A. J. Blacker, E. Clot, S. B. Duckett, O. Eisenstein, J.
[
[
[
Chem. Eur. J. 2015, 21, 13513 – 13517
www.chemeurj.org
13516
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Lough, R. H. Morris, J. Am. Chem. Soc. 2002, 124, 15104; c) T. J. Schmeier,
G. E. Dobereiner, R. H. Crabtree, N. Hazari, J. Am. Chem. Soc. 2011, 133,
[16] N. Onishi, S. Xu, Y. Manaka, Y. Suna, W.-H. Wang, J. T. Muckerman, E.
Fujita, Y. Himeda, Inorg. Chem. 2015, 54, 5114.
9
274.
14] a) A. J. Lough, S. Park, R. Ramachandran, R. H. Morris, J. Am. Chem. Soc.
994, 116, 8356; b) S. Park, R. Ramachandran, A. J. Lough, R. H. Morris, J.
Chem. Soc. Chem. Commun. 1994, 2201.
15] a) C. P. Casey, J. B. Johnson, S. W. Singer, Q. Cui, J. Am. Chem. Soc. 2005,
[
[
1
1
27, 3100; b) M. Ito, T. Ikariya, Chem. Commun. 2007, 5134; c) J. Morita-
Received: June 22, 2015
ni, Y. Kayaki, T. Ikariya, RSC Adv. 2014, 4, 61001.
Published online on August 13, 2015
Chem. Eur. J. 2015, 21, 13513 – 13517
www.chemeurj.org
13517
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim