Mechanistic insight through factors controlling effective hydrogenation of CO2 catalyzed by bioinspired proton-responsive iridium(III) complexes

Article abstract of DOI:10.1021/cs400172j

Reversible H₂ storage near room temperature and pressure with pH as the switch for controlling the direction of the reaction has been demonstrated (Nat. Chem., 2012, 4, 383-388). Several bioinspired proton-responsive mononuclear Ir(III) catalysts for CO₂ hydrogenation were prepared to gain mechanistic insight through investigation of the factors that control the effective generation of formate. These factors include (1) kinetic isotope effects by water, hydrogen, and bicarbonate; (2) position and number of hydroxyl groups on bpy-type ligands; and (3) mono- vs dinuclear iridium complexes. We have, for the first time, obtained clear evidence from kinetic isotope effects and computational studies of the involvement of a water molecule in the rate-determining heterolysis of H ₂ and accelerated proton transfer by formation of a water bridge in CO₂ hydrogenation catalyzed by bioinspired complexes bearing a pendent base. Furthermore, contrary to expectations, a more significant enhancement of the catalytic activity was observed from electron donation by the ligand than on the number of the active metal centers.

Full text of DOI:10.1021/cs400172j

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Article
Mechanistic insight through factors controlling effective hydrogenation
of CO2 catalyzed by bio-inspired proton-responsive iridium(III) complexes
Wang Wan-Hui, James T. Muckerman, Etsuko Fujita, and Yuichiro Himeda
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/cs400172j • Publication Date (Web): 13 Mar 2013
Downloaded from http://pubs.acs.org on March 13, 2013
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Mechanistic insight through factors controlling effective
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hydrogenation of CO catalyzed by bio-inspired proton-
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responsive iridium(III) complexes
a,b
c,
c,
a,b,
WanꢀHui Wang, James T. Muckerman, * Etsuko Fujita, * and Yuichiro Himeda *
a
National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5ꢀ2, 1ꢀ1ꢀ1 Higashi, Tsukuba, Ibaraki,
305ꢀ8565 Japan.
b
Japan Science and Technology, ACTꢀC, 4ꢀ1ꢀ8 Honcho, Kawaguchi, Saitama, 332ꢀ0012 Japan.
c
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
KEYWORDS: proton-responsive iridium complexes, CO hydrogenation, formate, deuterium kinetic isotope effect, proton
2
relay
ABSTRACT: Reversible H storage near room temperature and pressure with pH as the ‘switch’ for controlling the direction of
2
the reaction has been demonstrated (Nat. Chem., 2012, 4, 383ꢀ388). Several bioꢀinspired ‘protonꢀresponsive’ mononuclear Ir(III)
catalysts for CO hydrogenation were prepared to gain mechanistic insight through investigation of the factors that control the efꢀ
2
fective generation of formate. These factors include: (1) kinetic isotope effects by water, hydrogen, and bicarbonate; (2) position
and number of hydroxyl groups on bpyꢀtype ligands; and (3) monoꢀ vs diꢀnuclear iridium complexes. We have, for the first time,
obtained clear evidence from kinetic isotope effects and computational studies of the involvement of a water molecule in the rateꢀ
determining heterolysis of H , and accelerated proton transfer by formation of a water bridge in CO hydrogenation catalyzed by
2
2
bioꢀinspired complexes bearing a pendent base. Furthermore, contrary to expectations, a more significant enhancement of the cataꢀ
lytic activity was observed from electron donation by the ligand than on the number of the active metal centers.
The investigation of proton transfer at the molecular level is
of great interest owing to its involvement in numerous
transformations involving hydrogen, especially in energyꢀ
related hydrogen storage. Enzymes such as hydrogenase use
proton channels, consisting of multiple proton relays, to
facilitate proton transfer between the active site and
Chart 1. Iridium complexes for hydrogenation of CO2.
2
+
2+
OH
HO
Ir
N
N
N
N
Cp*
Cp*
2
2
4
Ir
SO4
SO
H O
2
H O
2
1ꢀ3
surroundings.
FeNi] hydrogenase, DuBois et al. have made significant
Mimicking the active site of [FeFe] and
OH
HO
[
1
2
advances in developing synthetic complexes and
understanding the proton transfer mechanism assisted by
2+
2+
HO
Ir
OH
HO
Ir
N
N
OH
4ꢀ6
pendent amines. It has been demonstrated that the pendent
N
N
N
N
N
N
amines in the second coordination sphere act as proton relays
and help facile and precise transfer of protons between metal
Cp*
Cl
Cl
Cp*
2
Ir
SO4
Cp*
2
H O
7
ꢀ10
center and substrate.
the energy barrier for heterolysis or formation of H2.
Recently, a 2ꢀpyridonate unit has been discovered in a [Fe]ꢀ
hydrogenase that is known as H ꢀforming
methylenetetrahydromethanopterin dehydrogenase (Hmd).
Moreover, such an effect can reduce
11ꢀ13
2
Cl
HO
OH
HO
OH
3
4
2
14,15
deprotonation of the hydroxyl groups. Most recently, inspired
by the important role of the hydroxyl group adjacent to the
metal center in [Fe]ꢀhydrogenase, we modified our 4DHBP
Yang and Hall have demonstrated by DFT calculations that the
oxo group of 2ꢀpyridonate adjacent to the coordination site
16
can aid dihydrogen cleavage through hydrogen bonding. The
study of bioꢀinspired synthetic catalysts with a 2ꢀpyridonate or
bipyridonate unit by Yamaguchi et al. and Papish et al. have
identified experimentally the important role of the adjacent
catalyst 1 by changing the position of the hydroxyl groups
20,21
from para to ortho (complexes 2 and 3, Chart 1),
in a significant improvement in the CO
resulting
hydrogenation
2
catalytic activity in aqueous solution. While 3 is isolated as a Cl
coordinated species, the Cl ions readily dissociate in water to
form the aqua complex. The catalytic activity increases 4 times
and 10 times from 1 to 2 and 1 to 3, respectively. Our
theoretical studies have demonstrated that the adjacent
oxyanion can function as a pendent base and accelerate
17ꢀ19
hydroxyl group in proton transfer related reactions.
Our 4DHBP complex 1 (4DHBP = 4,4′ꢀdihydroxyꢀ2,2′ꢀ
bipyridine, Chart 1) has been demonstrated to be highly
efficient for CO hydrogenation in aqueous solution owing to
2
the strong electronꢀdonating ability of the oxyanions upon the
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Table 1. Hydrogenation of CO to formate with Ir catalysts.
2
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
b
−1 f
Entry
Cat./conc. (ꢁM)
1/50
Time (h)
Pressure (MPa)
Temp. (°C) Initial TOF (h )
TON
92
Final [formate] (M)
0.005
c
1
24
33
9
0.1
0.1
1.0
0.1
1.0
0.1
1.0
3.8
3.0
25
25
50
25
50
25
50
50
7
27
c
2
2/50
330
5150
0.016
c
3
2/20
1650
64
0.103
d
4
3/50
336
8
7200
0.360
d
5
3/20
4200
66
24,000
193
0.480
e
6
4/50
24
24
8
0.009
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
7
8
4/20
3060
11,100
33,300
28,000
38,400
34,300
0.560
4/10
0.384
e
9
4/20
8
80
0.687
a
b
c
The reaction was carried out in 1 M NaHCO unless otherwise noted. Total pressure of the gas mixture (H /CO = 1:1, v/v) used. ref.
0. ref. 21. The reaction was carried out in 2 M KHCO . Average rate over initial 1 h.
3
2
2
d
e
f
2
3
20
the rateꢀlimiting heterolysis of dihydrogen to produce Ir–H.
Herein, we report: (1) clear evidence from combined
experimental and computational studies of the involvement
A question arises upon further comparison of the activity of
complexes 2 and 3: Is the difference in catalytic activity
between 2 and 3 due to the presence of two active metal
centers or the stronger electronꢀdonation effect of the four
oxyanions in 3? To understand the factors controlling the
of a water molecule in the rateꢀdetermining heterolytic H
splitting, and enhancement of proton transfer by forming a
water bridge in CO hydrogenation catalyzed by bioꢀinspired
complexes bearing a pendent base; and (2) similar catalytic
activities of 3 and 4 toward CO hydrogenation owing to a
2
2
catalytic activity of CO hydrogenation, we have designed
2
2
and synthesized a new catalyst 4 that incorporates the
synergistic effect of electron donor and pendent base
activation while retaining a mononuclear Ir complex.
more significant enhancement from electron donation by the
ligand than on the number of the active metal centers.
Hydrogenation of CO2 with Ir complexes. The new
complex 4 was synthesized according to our previously
reported process (see SI). It was then utilized in the
homogeneous hydrogenation of CO in aqueous bicarbonate
solutions at relatively low temperatures and pressures. The
results are summarized in Table 1. Whether at ambient
conditions (25 °C, 0.1 MPa) or at higher pressure and
temperature, the initial TOF of complex 4 is double that of
complex 2 (entries 2 and 3 vs 6 and 7). Complex 4 bearing
four hydroxyl groups showed higher activity than 2 which
has only two hydroxyl substituents. The reaction rate of 4
(TOF: 66 h ) is comparable to the previously known most
effective complex 3 at ambient conditions (entries 4 and 6).
At 50 °C and 1 MPa of H /CO , the mononuclear complex 4
also showed similar activity (TOF: 3060 h ) to that of the
dinuclear complex 3 (TOF: 4200 h , entries 5 and 7).
Moreover, a high turnover of 28,000 and high concentration
of formate product (0.56 M) were obtained after 24 h. The
high activity of complex 4 indicates that it is among the most
effective catalysts of CO2 hydrogenation under mild
conditions. Temperature and pressure have a significant
impact on the reaction rate. When the pressure was increased
from 1 MPa to 3.8 MPa, the TOF was enhanced more than
3ꢀfold (entry 8). At elevated temperature and pressure (3
MPa, 80 °C), 4 achieved the highest initial TOF of 33,300
In addition, it is well recognized that proton transfer
through channels formed by water is the dominant pathway
21
2
2,23
in biological processes.
Our quest for a more detailed
2
mechanistic understanding has prompted us to investigate
the possible cooperation of solvent (i.e., water) in the proton
transfer process. Water has been recognized as an ideal
solvent for CO hydrogenation because it is abundant, cheap
and environmentally benign. The addition of a small amount
of water to benzene as an organic solvent was observed to
promote CO2 hydrogenation by Pd(diphos) (diphos =
Ph PCH CH PPh ) some time ago. The promoting effect of
water has been proposed to arise from the stabilizing effect
of an intramolecular hydrogen bond between the aqua ligand
2
2
2
4
−1
2
2
2
2
2
1
2
2
25,26
−1
and an oxygen of the approaching CO2.
Musashi and
−1
Sakaki demonstrated through calculations that the
acceleration stemmed from the trans effect of a coordinated
27
H O ligand, but was not caused by a hydrogen bond.
2
Hydrogen bonding of the incoming CO to external water
has also been proposed by Lau et al. Although several
mechanisms involving water have been proposed and
2
2
8
2
9,30
studied,
unambiguously understood. The role of water is also
unknown for the significantly accelerated H ꢀproduction rate
the rateꢀaccelerating effect of water is not yet
2
−
1
(
TOF above 100,000 s ) using hydrogenaseꢀmodel
complexes such as a synthetic Ni electrocatalyst by addition
water to the acetonitrile solution. Many reports on catalytic
CO hydrogenation in water using waterꢀsoluble catalysts
however, the involvement of a
water molecule to produce a protonꢀtransfer channel in the
rate determining step in CO hydrogenation has not been
−1
h
and gave a high concentration of formate of 0.687 M
6
after 8 h (entry 9) under the given conditions. In addition,
from Arrhenius plots, complexes 3 and 4 showed similar
activation energies of 49.5 and 49.9 KJ/mol, respectively
2
31ꢀ39
have been published,
(
see SI, Figure S1). These results clearly demonstrate that the
2
electron donating effect of the substituents is more important
for catalytic activity than the number of catalytically active
metal centers.
reported either experimentally or theoretically.
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Table 2. Isotope effect in the hydrogenation of CO catalyzed by Ir complexes.
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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
b
b
b
Entry
Gas (1/1,
MPa)
Reaction Sol.
(2 M)
Product
Complex 1
Complex 2
Complex 4
−1
c
−1
c
−1
c
1
TOF, h
KIE
ꢀ
TOF, h
KIE
TOF, h
KIE
ꢀ
1
2
3
H /CO
KHCO /H O
HCO K
683
697
572
570
1730
1520
1610
1360
ꢀ
2730
1800
1990
1190
2
2
2
2
2
3
2
2
H /CO
2
KDCO /D O
HCO K
0.98
1.19
1.20
1.14
1.07
1.27
1.51
1.37
2.29
3
2
2
D /CO
2
KHCO /H O
DCO K
3
2
2
4
a
D /CO
2
KDCO /D O
DCO K
3
2
2
The reaction was carried out with catalyst (0.2 ꢁmol) in 10 mL bicarbonate solution (2 M) under 1 MPa H /CO or D /CO (1/1) at 50 °C
for 1 h. Errors of TOFs and KIEs are typically less than 2 % and 4 %, respectively. KIE = TOF(entry 1)/TOF(entry n), (n = 2, 3, and 4).
2
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
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9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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9
0
1
2
3
4
5
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7
8
9
0
b
c
Mechanistic studies. As we previously reported, the CO2
hydrogenation first proceeds through the heterolysis of H2
determining step has been previously predicted by DFT
20
calculations to be the heterolytic cleavage of H
the heterolysis of D to contribute largely to the observed
KIE. Interestingly, we found a special effect of D O for
different complexes when D O was used in reaction with
/CO or D /CO . Heavy water has almost no effect on the
, we expect
2
(assisted by a pendent base in complexes 2 and 3) to form an
2
20,21
IrꢀH species.
This is followed by CO insertion into the
2
2
IrꢀH bond to give a formato complex. The dissociation of
formate is accompanied by the addition (via heterolysis) of
2
H
2
2
2
2
H to reinitiate the catalytic cycle. The IrꢀH species of 2 and
reaction rate when 4DHBP complex 1 was used (entries 1 vs
2, and entries 3 vs 4 for complex 1) In contrast, it showed a
remarkable influence on the reaction rate when complexes 2
and 4 were used. The reaction was significantly inhibited by
replacing H O with D O either in reaction using H /CO or
2
1
4 were detected with H NMR (δ = −10.56 and −10.32 ppm,
respectively) by adding high pressure H2 under a basic
condition (see SI, Figure S2). To gain further mechanistic
insight, we investigated the kinetic isotope effect with our
catalysts. To our knowledge, a deuterium kinetic isotope
effect in the hydrogenation has not yet been reported. This
may be due to the fact that the D /CO gas mixture is not
readily available. As our complexes not only serve as
catalysts for hydrogenation of CO to formate, but can also
catalyze the reverse reaction — the dehydrogenation of
formic acid (under slightly acidic conditions) — we have
recently reported a convenient method to obtain D /CO gas
mixtures from the decomposition of DCO D in D O with our
4DHBP catalyst 1. Consequently, this method of D /CO2
generation was employed to study the deuterium isotope
effect in the hydrogenation of CO . The D /CO (1/1)
mixture was generated from a degased DCO D/D O solution
of 4DHBP catalyst 1 in a stainless autoclave (see SI). The
pressure of the gas mixture was controlled by adjusting the
temperature to change the dehydrogenation rate. The
released gases were analyzed by GC, which indicated that
the ratio of D to CO is 1:1 and the purity of D is up to
2
2
2
2
D /CO (entries 1 vs 2, and entries 3 vs 4, for complexes 2
2
2
and 4, respectively). In addition, the reaction rate decreased
markedly with an increase in the D fraction in the reaction
solution (see SI, Figure S5). When the reaction was carried
out with D /CO in KDCO /D O, we obtained the lowest
TOF which indicates the dual effect of deuterated gas and
solvent. Comparing the KIE data for 1 with those for 2 and
4, we can conclude that heavy water is involved in the rateꢀ
limiting heterolysis of dihydrogen for complex 2 and 4 but
not for 4DHBP complex 1.
2
2
2
2
2
3
2
2
2
2
2
4
0
2
2
2
2
2
2
2
2
2
9
8% (2% HD, see SI, Figure S3). The gas generation system
Scheme 1. Proposed mechanism for H heterolysis assist-
2
was connected to a hydrogenation system in which the
pressure was adjusted by a backpressure regulator (1 MPa).
The hydrogenation was carried out in 2 M bicarbonate
solution (10 mL) with complexes 1, 2, and 4 (0.2 ꢁmol) at
50 °C for 1 h. The reaction results are listed in Table 2. The
product concentration was detected by HPLC and confirmed
ed by the pendent base and water molecule through a
proton relay. The green arrows indicate the movement of
protons via a proton relay. The open square indicates a
vacant coordination site.
The assistance of water on the splitting of H has been
predicted computationally.
2
4
1ꢀ44
1
Our previous studies have
by H NMR using DSS (sodium 3ꢀ(trimethylsilyl)ꢀ1ꢀ
demonstrated that the rateꢀdetermining step of the CO2
propanesulfonate) as an internal standard (see SI, Figure S4).
By comparing the concentration determined by H NMR and
HPLC, the main product was identified. DCO K in entry 2
and HCO K in entry 3 were found to be less than 5%.
1
hydrogenation is the heterolysis of H , and it was
significantly enhanced by the pendent base through a
secondꢀcoordinationꢀsphere effect. As our KIE experiments
described above suggest, the solvent effect of D O has a
remarkable influence on the reaction rate most likely through
participation in the rateꢀdetermining step. Accordingly, we
propose that solvent molecule (i.e., H O) may form hydrogen
bonds with the pendent base and the approaching H along
the reaction coordinate for heterolysis, and participate in the
proton transfer to the pendent base heterolysis (Scheme 1).
2
2
20
2
2
As shown in Table 2, when D /CO (entry 3) was used
instead of H /CO (entry 1), rate of the reaction in an
aqueous solution of KHCO decreased markedly (KIE =
2
2
2
2
3
2
1
.19, 1.07, 1.37 for complexes 1, 2, and 4, respectively;
2
Table 2, entry 3). The observed KIEs represent a composite
of the individual isotope effects for both heterolysis of D to
form Ir–D and CO insertion into Ir–D to generate Ir–ODCO.
Therefore, it is not possible to identify the rate determining
step by analysis of the KIE on the TOF alone. Since the rate
2
2
The participation of H O could stabilize the transition state
and facilitate the heterolysis of H2 which is further
demonstrated by DFT calculations.
2
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addnTS
heteroTS
Cp*Ir(H )(6,6’-ObpyO)0
2
relayTS
Cp*Ir(6,6’-ObpyO)0
Cp*IrH(6,6’-ObpyOH)0
Reaction Coordinate
Figure 1. The relative freeꢀenergy profiles for H addition to the Ir center to form a dihydrogen complex via the “addnTS” transition state,
H heterolysis to form the Cp*IrH(6,6′ꢀObpyOH) complex via the “heteroTS” transition state, and waterꢀassisted H heterolysis to form the
Cp*IrH(6,6′ꢀObpyOH) complex via the “relayTS” transition state. The hydrogen atoms corresponding to the reactant H are tinted green.
2
2
2
2
Larger pictures of the structures are presented in Figure S6 of the SI.
Theoretical Studies of the Reaction Mechanism. The
reactant H2 molecule was assigned a gasꢀphase standard
the pendent base (heteroTS) was found to be more
energetically favorable than the formation of a dihydrogen
adduct, having an activation free energy of 54.6 kJ mol and
a reaction free energy of −20.6 kJ mol . Moreover, the
calculations predicted the waterꢀassisted heterolysis pathway
shown in the first two panels of Scheme 1 (relayTS) to have
the even lower activation free energy (relative to Cp*Ir(6,6′ꢀ
−1
state, and the participating H O molecule was assigned the
2
−1
standard state of the pure liquid (see SI for details). Because
it is well known that the entropy in solution is overestimated
by gasꢀphase calculations, the gasꢀphase translational
entropy was omitted from the free energy of all species in
3
0
0
−1
solution and for the solvent H O. This consideration has a
ObpyO) , H
2
and H
2
O
(liq)) of 40.3 kJ mol . This result
2
negligible effect on the free energy of activation and reaction
supports the hypothesis that solvent water is involved in the
rateꢀdetermining step of H heterolysis. The energetics and
structures along these pathways are shown in Figure 1 (larger
structures are presented in Figure S1, and key geometric
parameters are listed in Table S1 of the SI). An animation of
the normal mode corresponding to the imaginary frequency
involving the addition of H to the active form of the catalyst
2
2
owing to cancellation of similar corrections, but it has a
substantial effect on the free energy of H O(liq), for which the
2
correction (correctly) removes most of its gasꢀphase entropy.
0
Using Cp*Ir(6,6′ꢀObpyO) as a prototype, we identified
−1
(981i cm ) of the relayTS is available as a pptx file in the
SI.
three different transition states and pathways to two reaction
intermediates resulting from the reaction of Cp*Ir(6,6′ꢀ
ObpyO) and H (and, as shown in the top two structures in
Scheme 1, H O). One of these corresponded to the formation
0
In summary, our experimental mechanistic studies with
2
D O, D , and KDCO have clearly demonstrated for the first
2
2 2 3
of a dihydrogen adduct to the Ir center via a dihydride
transition state (addnTS). This pathway had an activation
time that water is involved in the rateꢀlimiting step and
significantly accelerates heterolysis of H for complexes 2
and 4 that have pendent bases near the metal center, but not
for the 4DHBP complex 1. The theoretical studies also
predict that proton transfer proceeds through a hydrogenꢀ
bonding network involving a water molecule and the
2
−1
free energy of 59.3 kJ mol and a reaction free energy of
−
1
0
5
2.1 kJ mol relative to Cp*Ir(6,6′ꢀObpyO) and H gas. The
2
pathway for direct heterolysis of H to form Cp*IrH(6,6′ꢀ
2
0
ObpyOH) via a second coordination sphere interaction with
ACS Paragon Plus Environment

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pendent oxyanion, and can lower the barrier for H2
(12) Yang, J. Y.; Chen, S. T.; Dougherty, W. G.; Kassel, W. S.;
Bullock, R. M.; DuBois, D. L.; Raugei, S.; Rousseau, R.; Dupuis, M.;
Rakowski DuBois, M. Chem. Commun. 2010, 46, 8618ꢀ8620.
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heterolysis. Comparison between mononuclear and dinuclear
complexes with four hydroxyl groups (4 and 3, respectively)
shows that the catalytic activity is not significantly affected
by the number of metal centers. Comparison between
mononuclear complexes with two and four hydroxyl groups
(13) Jacobsen, G. M.; Yang, J. Y.; Twamley, B.; Wilson, A. D.;
Bullock, R. M.; Rakowski DuBois, M.; DuBois, D. L. Energy Environ.
Sci. 2008, 1, 167ꢀ174.
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Kahnt, J.; Thauer, R. K.; Steinbach, K.; Xie, X. L.; Verdier, L.;
Griesinger, C. Angew. Chem. Int. Ed. 2004, 43, 2547ꢀ2551.
(15) Wright, J. A.; Turrell, P. J.; Pickett, C. J. Organometallics
2010, 29, 6146ꢀ6156.
(2 and 4, respectively) demonstrates that more hydroxyl
groups in ortho and para positions to the coordinating N
atoms that donate electrons produce more effective catalysis
of CO hydrogenation.
2
(16) Yang, X. Z.; Hall, M. B. J. Am. Chem. Soc. 2009, 131,
1
0901ꢀ10908.
17) Kawahara, R.; Fujita, K.ꢀi.; Yamaguchi, R. J. Am. Chem.
0
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(
ACKNOWLEDGMENT
Soc. 2012, 134, 3643−3646.
(18) Nieto, I.; Livings, M. S.; Sacci, J. B.; Reuther, L. E.; Zeller,
M.; Papish, E. T. Organometallics 2011, 30, 6339ꢀ6342.
Y. H. and W.ꢀH. W. thank the Japan Science and
Technology Agency (JST), ACIꢀC for financial support. The
work at BNL was carried out under contract DEꢀAC02ꢀ
(19) Yamaguchi, R.; Ikeda, C.; Takahashi, Y.; Fujita, K. J. Am.
Chem. Soc. 2009, 131, 8410ꢀ8412.
9
8CH10886 with the U.S. Department of Energy and
(20) Wang, W.ꢀH.; Hull, J. F.; Muckerman, J. T.; Fujita, E.;
Himeda, Y. Energy Environ. Sci. 2012, 5, 7923ꢀ7926.
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ana, R.; Szalda, D. J.; Muckerman, J. T.; Fujita, E. Nat. Chem. 2012, 4,
supported by its Division of Chemical Sciences,
Geosciences, & Biosciences, Office of Basic Energy
Sciences.
3
83ꢀ388.
(22) Smedarchina, Z.; Siebrand, W.; FernandezꢀRamos, A.; Cui,
Supporting Information
Q. J. Am. Chem. Soc. 2003, 125, 243ꢀ251.
Experimental details including KIE measurements and syntheꢀ
sis, Arrhenius plot for hydrogenation of CO , H NMR charts of
Irꢀhydride for complexes 2 and 4, GC analysis of D gas generꢀ
ated from dehydrogenation of DCO D in D O, H NMR of hyꢀ
(23) Chen, P. T.; Wang, C. C.; Jiang, J. C.; Wang, H. K.;
Hayashi, M. J. Phys. Chem. B 2011, 115, 1485ꢀ90.
(24) Inoue, Y.; Izumida, H.; Sasaki, Y.; Hashimoto, H. Chem.
Lett. 1976, 863ꢀ864.
1
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25) Tsai, J. C.; Nicholas, K. M. J. Am. Chem. Soc. 1992, 114,
117ꢀ5124.
26) Jessop, P. G.; Hsiao, Y.; Ikariya, T.; Noyori, R. J. Am.
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27) Musashi, Y.; Sakaki, S. J. Am. Chem. Soc. 2002, 124, 7588ꢀ
drogenation products, plot for hydrogenation reaction rate vs D
fraction, computational details, calculated structures and
Cartesian coordinates of key intermediates, and animation of the
normal mode corresponding to the imaginary frequencies (981 i
5
(
(
−1
cm ) of the relay TS. This material is available free of charge
7
603.
(28) Yin, C. Q.; Xu, Z. T.; Yang, S. Y.; Ng, S. M.; Wong, K. Y.;
via the Internet at http://pubs.acs.org.
Lin, Z. Y.; Lau, C. P. Organometallics 2001, 20, 1216ꢀ1222.
(29) Ahlquist, M. S. G. J. Mol. Catal. A: Chem. 2010, 324, 3ꢀ8.
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Nozaki, K. Organometallics 2011, 30, 6742ꢀ6750.
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Soc. 2003, 125, 14266ꢀ14267.
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Corresponding Author
(
James T. Muckerman: muckerma@bnl.gov, Yuichiro Himeda:
himeda.y@aist.go.jp, Etsuko Fujita: fujita@bnl.gov.
(
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Table of Contents:
Pendent
Base
Water Bridge
PT
2
2
O
O
N
N
O
H
O
N
N
O
H
H
H
O
O
N
N
H
H
PT
H
H
Electronic
Effect
Ir
Ir
N
Cp*
Cp*
0
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2
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9
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3
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9
0
1
2
3
4
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9
0
1
2
3
4
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9
0
O
O
N
O
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