Ir(III)-PC(sp3)P Bifunctional Catalysts for Production of H2 by Dehydrogenation of Formic Acid: Experimental and Theoretical Study

Article abstract of DOI:10.1021/acscatal.7b02482

Reversible storage of hydrogen in the form of stable and relatively harmless chemical substances such as formic acid (FA) is one of the cornerstones of a fossil-fuel-free economy. Recently, Ru(III)-PC(sp³)P (where PC(sp³)P = modular dibenzobarrelene-based pincer ligand possessing a pendant functional group) complex 1 has been reported as a mild and E-selective catalyst in semihydrogenation of alkynes with stoichiometric neat formic acid. Discovery of the additive-free protocol for dehydrogenation of FA launched further studies aiming at the rational design of highly efficient catalysts for this reaction operating under neutral conditions. We now report the results of our investigation on a series of bifunctionl PC(sp³)P complexes equipped with different outer-sphere auxiliaries, that allowed us to identify an amine-functionalized Ir(III)-PC(sp³)P complex 3, as a clean and efficient catalyst for the FA dehydrogenation. The catalyst is suitable for fuel-cell applications demonstrating a TON up to 5 × 10⁵ and TOF up to 2 × 10⁴ h^-1 (3.8 × 10⁵ and 1.2 × 10⁴ h^-1 with no additives). In addition to the practical value of the catalyst, experimental and computational mechanistic studies provide rationale for the design of improved next-generation catalysts.

Full text of DOI:10.1021/acscatal.7b02482

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Article
Ir(III)-PC(sp3)P Bifunctional Catalysts for Production of H2 by
Dehydrogenation of Formic Acid: Experimental and Theoretical Study
Shirel Cohen, Veniamin Borin, Igor Schapiro, Sanaa Musa,
Sophie De-Botton, Natalia V. Belkova, and Dmitri Gelman
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b02482 • Publication Date (Web): 20 Oct 2017
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Ir(III)ꢀPC(sp3)P Bifunctional Catalysts for
Production of H2 by Dehydrogenation of Formic
Acid: Experimental and Theoretical Study
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Shirel Cohen,a‡ Veniamin Borin,b‡ Igor Schapiro,*b Sanaa Musa,a Sophie De-Botton,a Natalia V.
Belkova,c and Dmitri Gelman*a.
aInstitute of Chemistry, The Hebrew University, Edmond Safra Campus, Givat Ram, 91904
b
Jerusalem, Israel. Fax: (+) 972ꢀ2ꢀ6585279. Institute of Chemistry, Fritz Haber Center for
Molecular Dynamics Research, The Hebrew University, Edmond Safra Campus, Givat Ram,
c
91904 Jerusalem, Israel. Fax: (+) 972ꢀ2ꢀ6585679. A.N.Nesmeyanov Institute of Organoelement
Compound RAS, 28 Vavilov str., 119991 Moscow, Russia.
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ABSTRACT Reversible storage of hydrogen in the form of stable and relatively harmless
chemical substances such as formic acid (FA) is one of the cornerꢀstones of fossil fuelsꢀfree
economy. Recently, Ru(III)ꢀPC(sp3)P (where PC(sp3)P = modular dibenzobarreleneꢀbased pincer
ligand possesing a pendant functional group) complex 1 has been reported as a mild and Eꢀ
selective catalyst in semihydrogenation of alkynes with stoichiometric neat formic acid.
Discovery of the additiveꢀfree protocol for dehydrogenation of FA launched further studies
aiming at the rational design of highly efficient catalysts for this reaction operating under neutral
conditions. We now report the results of our investigation on a series of bifunctionl PC(sp3)P
complexes equipped with different outerꢀsphere auxiliaries, that allowed to identify an amineꢀ
functionalized Ir(III)ꢀPC(sp3)P complex 3, as a clean and efficient catalyst for the FA
dehydrogenation. The catalyst is suitable for fuel cells applications demonstrating TON up to
5*105 and TOF up to 2*104 hꢀ1 (3.8*105 and 1.2*104 hꢀ1 with no additives). In addition to the
practical value of the catalyst, experimental and computational mechanistic studies provide
rationale for the design of improved nextꢀgeneration catalysts.
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KEYWORDS. ligandꢀmetal cooperation, dehydrogenation, formic acid, hydrogen, pincer
complexes.
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Introduction
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Efficient hydrogenꢀbased fuel technology is an important concept for the development
of future global energy markets. However, successful realization of the environmentally
benign fuel solutions is conditioned upon finding a way to reversibly store hydrogen
under ambient conditions. Dehydrogenation of formic acid (FA) is among the favorites on
the list of potential hydrogen storageꢀrelease systems, especially, for fuel cell applications
because formic acid is sustainable (as it maybe produced chemically or biotechnologically
from naturals stocks on million tonnes/year scale on demand),1 it is stable in
transportation and relatively harmless in storage. Finally yet importantly, FA is
technologically convenient for engineering fuel cells, as only one gaseous byꢀproduct
(CO2) is coꢀproduced upon hydrogen liberation.
Dehydrogenation of neat FA under relatively harsh reaction temperatures using either
heterogeneous or heterogenized catalysts was known for a long time.2 However,
dehydration of FA leading to the formation of carbon monoxide often accompanies highꢀ
temperature processes, which complicates any fuel cell applications.3 Homogeneous
catalysis brought a significant progress in the COꢀfree dehydrogenation. The most
efficient catalytic systems based on Ir, Ru, Au, Ag, Pd and Fe complexes have been
reported to dehydrogenate FA selectively to H2 and CO2.4 Some of these catalysts
demonstrate exceptionally high stability (TONs up to 5*106), high conversion rates
(TOFs up to 5*105 hꢀ1), but some require the presence of overꢀ or slightly
substoichiometric bases. For example, FA/amine azeotropes are often employed to
achieve the desired conversions;4c, 4m, 4q, 5 iodide ions were found to enhance the rate of
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the dehydrogenation even further.6 However, such mixtures are less attractive for the fuel
cell applications because they are characterized by a lower hydrogen content, on the one
hand, and because of the complicated waste treatment, on the other.
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More recently, iridium complexes bearing hydroxypyridine ligands were spotted as
efficient catalysts for the dehydrogenation of FA to H2 and CO2 in aqueous medium
without amine additives. However, pH adjustment with buffers might be needed to
achieve highest performance.7 In addition, hydrogen production in water poses
engineering problems in the design of fuel cells. New Feꢀbased catalysts demonstrate
good TONs under additiveꢀfree conditions (although, an excess of the ligand is
required),4p while excellent performance is achieved when catalytic Lewis acids are
added.8 Although these recent developments are encouraging and exciting, the TON and
TOF characteristics of the truly additiveꢀfree systems4a, 9 still require improvement that
may come only from new catalysts operating via less traditional mechanistic schemes.4h,
10
We previously reported several iridium, rhodium, palladium and platinum bifunctional
catalysts mimicking naturally occurring [FeFe]ꢀhydrogenase enzymes capable of
promoting reversible activation and fixation of small molecules in outer coordination
sphere with the aid of the pendant sidearm (Scheme 1).11
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Scheme 1. Previously reported bifunctional catalysts.
With the hypothesis that these polyfunctional complexes are also capable of catalyzing
hydrogen transfer from formic acid via outerꢀsphere mechanism, we have investigated FA
dehydrogenation cycle coupled with hydrogenation of unsaturated hydrocarbons. Their
catalytic performances have been tested under a variety of conditions. We discovered that
the carbometalated Ru complex (
1
) equipped with a pendant hydroxyl arm in the
ꢀselective catalyst in
secondary coordination sphere acts as a mild and
E
semihydrogenation of alkynes with formic acid.12 In this rutheniumꢀcatalyzed reaction,
the FA dehydrogenation and the alkyne hydrogenation steps are wellꢀsynchronized
driving the reaction to completion under nearly stoichiometric FA/alkyne ratio (Scheme
2).
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Scheme 2. Previously reported bifunctional catalysts.
Our brief mechanistic studies revealed that the presence of the OH group in the outer
coordination sphere was crucial for the described catalytic activity. Even more
importantly, the reaction proceeded in neat FA obviating employment of additives of any
kind, which also can be attributed to the assistance of the pendant functionality spotting
this class of compounds as attractive candidates for the development of efficient and
“clean” catalysts for the FA dehydrogenation suitable for fuel cells applications.
Obviously, structural modification of the ligands at the secondary coordination sphere
will likely affect their catalytic performance. This prompted us to study the potential
influence of the pendent functionality on the mechanism and efficiency of FA
dehydrogenation with these multifunctional complexes.
Here, we present studies on new and known iridium pincerꢀtype compounds possessing
different functional groups and their use as catalysts for the dehydrogenation of FA under
neutral conditions including an example without external additives.
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Results and discussion
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After preliminary optimization studies (for details, please, see SI), we decided to focus
on a series of iridiumꢀbased complexes bearing ligands with different pendant groups: a
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neutral OHꢀcontaining 2, a basic NH2ꢀcontaining 3 and an acidic CO2Hꢀcontaining 4.
The compounds are easily accessed in a threeꢀstep protocol in good yields from
common and readily available precursors: i) quantitative DielsꢀAlder cycloaddition of
1,8ꢀbisꢀ(diphenylphosphino)anthracene and a dienophile of choice (dimethyl fumarate or
fumaronitrile, correspondingly); ii) hydrogenation or hydrolysis, correspondingly, and iii)
metalation with [IrCl(COE)]2 (Scheme 3).
Scheme 3. Synthesis of the ligands used in this study.
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was depicted by us in the past.11f Complexation of the aminoꢀ and
3
4
The compound
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carboxylic acidꢀcontaining ligands with [IrCl(COE)]2 led to the formation of bright, airꢀ
and moistureꢀstable solids and that were identified as the corresponding
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carbometalated pincer complexes.
31P{1H} and 1HꢀNMR patterns of the new complexes were quite similar and showed an
expected set of doublets (14.4 and 14.9 ppm with
with = 14 Hz for ) due to the presence of two different phosphine groups, while the
hydride signals appeared as virtual double doublet or triplet (ꢀ9.6 ppm with = 28 Hz for
and ꢀ18.3 ppm = 14 Hz for ) indicating nonꢀequivalence of the phosphine groups.
J = 12 Hz for 3 and 21.8 and 28.8 ppm
J
4
J
3
J
4
Remarkably, the hydride signals of the complexes
complexes left in solution.13
2 and 4 gradually disappear if the
The decomposition of 211d and
4 proceeds via stoichiometric extrusion of the molecular
hydrogen which apparently originates from intramolecular iridium hydride–
carboxylic/hydroxyl proton interactions (Scheme 4). We cannot completely rule out an
intermolecular pathway,14 however, isolation and full structural assignment of the
suggested intermediates ꢀ the alkoxideꢀiridium species 2’11d and of the carboxylateꢀ
iridium species 4’ strongly support this hypothesis.
Hydrogen formation, however, proceeds in a different rate according to 1H NMR: while
o
hydride signals of
2
disappear after 30 min heating to 60 C, this process with
4
occurs at
room temperature. This reactivity trend is most likely dictated by the acidity of the
corresponding protons in and , as well as thermodynamic stability of the resultant 2’
2
4
and 4’. Expectedly, a reversed process followed the opposite trend: when 2’ and 4’ were
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pressurized with 500 kPa of hydrogen at 100 C in CDCl3 side by side, the parent
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compound
2 was regenerated after 3 hours, while only ca. 5% of 4 reꢀformed.
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Scheme 4. Hydrogen formation step in 2ꢀ4.
On the other hand, the amineꢀcontaining
3
is stable in solution and no hydrogen
ꢀtoluenesulfonic, acetic or formic
formation was observed unless external acids (e.g.
p
acid) are added. In this case, the hydride signal quickly disappears followed by hydrogen
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liberation independently of the strength of the acid.15 We, therefore, assume that H2
originates from intramolecular (rather than intermolecular) protonolysis of the IrꢀH bond
with the aid of the protonated sidearm in 3’ leading to the formation of a cationic
intermediate stabilized by the amine chelation (3” in the Scheme 4, bottom). Expectedly,
utilization of DCO2D results in the formation of HD as was detected by IRꢀMS.16 The
presumed formation of 3” is supported by a significant lowꢀfield P NMR shift
characteristic of the formation of cationic species of this type observed in the
3
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stoichiometric reaction between
3
and FA.17
With these compounds in hand (2-4), we performed a new series of structureꢀreactivity
relationship studies of decomposition of formic acid in different formulations:
HCO2H/TEA, HCO2H/Na2CO3 and HCO2H/HCO2Na in DME (1,2ꢀdimethoxyethane) at
o
70 C using the constant 1:2000 catalyst:FA ratio. Formic acid degrades to hydrogen and
carbon dioxide without contamination of carbon monoxide as was monitored by GCꢀ
TCD, and the TON was determined by monitoring the amount of gaseous products using
the standard gas burette measurements (please, see ESI). The results are listed in the
Table 1.
Table 1. Representative results of FA dehydrogenation using the catalysts 2ꢀ4.
N
1
Cat
2
Conditionsa
TONb
TOF (hꢀ1)c
HCO2H/TEA(5:3), DME, 70 oC
HCO2H/TEA (5:3) , DME, 70 oC
HCO2H/TEA (5:3) , DME, 70 oC
318500 13710
2
35080
1452
1200
ND
3
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2
HCO2H/Na2CO3 (1:0.3) , DME, 70 oC
258800 9380
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HCO2H/Na2CO3 (1:0.3) , DME, 70 oC
468690 18630
1660 ND
HCO2H/Na2CO3 (1:0.3) , DME, 70 oC
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7
HCO2H/HCO2Na (1:0.3) , DME, 70 oC
HCO2H/HCO2Na (1:0.3) , DME, 70 oC
HCO2H/HCO2Na (1:0.05) , DME, 70 oC
HCO2H, neat, 70 oC
189500 9460
2
3
3
3
4
8
498190 18390
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18890d
473950
383000 11760
560 ND
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HCO2H/HCO2Na (1:0.3) , DME, 70 oC
aCatalyst:FA = 1:2000, 70 C under air. Maximal TON. Initial TOF (average of 2 runs). After repetitious
injections of FA.
o
b
c
d
We found that the carboxylic acidꢀfunctionalyzed
4 was the least active catalyst under
all sets of conditions (Table 1, entries 3, 6 and 11). Decomposition of FA catalyzed by
o
this compound was negligible at 30ꢀ100 C, although some activity (TONs up to 2000)
o
was observed at 140 C after replacing DME with analogous diglyme. On the contrary,
complexes
2 and 3 decomposed FA in different formulations, albeit with different
efficacy and in opposite reactivity trends.18
Thus, when the reaction was performed in 5M DME solution of HCO2H/TEA (5:3) at
70 oC, the initial TOF of 13710 hꢀ1 (Table 1, entry 1) was achieved by the OHꢀmodified
showing 3.18*105 turnovers (after repetitious injections of FA). Under the same
2
conditions,
3 was about one order of magnitude less reactive (Table 1, entry 2).
Azeotropes with other amines (trioctylamine or TMEDA) did not lead to a significant
improvement.
An opposite reactivity trend was observed under the amineꢀfree conditions. Thus, using
the complex
2, 1:0.2 mixture of HCO2H/Na2CO3 (5M in DME) can be completely
dehydrogenated, giving an initial TOF of 9380 hꢀ1 and 2.58*105 turnovers (Table 1, entry
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4). Under the same conditions, the reaction with the amineꢀcontaining
3 provides a
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significantly higher TOF of 18390 hꢀ1 and TON of 4.68*105 (Table 1, entry 5). A
practically similar reactivity was obtained when sodium carbonate was replaced with 30
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mol% of sodium formate: the amineꢀcontaining
3
was superior over the hydroxylꢀ
with almost doubled TON and TOF ꢀ 4.98*105 ( ) versus 1.89*105 (
) versus 9460 hꢀ1 ( ), correspondingly.19 Furthermore, we found that
containing
18390 hꢀ1 (
2
3
3
2
) and
was
2
3
equally active in the presence of only 5 mol% of sodium formate (Table 1, entry 9) and
even in neat formic acid (Table 1, entry 10). This performance in neat FA is comparable
to or exceeding the stateꢀofꢀtheꢀart catalysts operating under amineꢀfree conditions and in
the absence of exotic additives.4i, 4p, 5d, 8, 10a, 20 Noteworthy, our attempts to employ
2 under
the solventꢀless and baseꢀfree conditions failed, emphasizing the difference between the
catalysts. Obveously, protonation of the amine groups facilitates solubilization of the
catalyst. A relatively short induction period of ca. 2ꢀ3 minutes was typically observed. To
rule out a possibility that the induction is due to decomposition of the homogenous
catalysts and that the FA cleavage is practically catalyzed by the metal particles, we
carried out a catalytic experiment in the presence of mercury – no diminished catalytic
performance was detected.
We further evaluated the performance of the catalyst under highꢀpressure conditions.
The experiment was performed in the sealed 100 mL Parr bomb in the presence of 0.05
1
mol% of the catalyst
3
(conversion of FA was determined by HꢀNMR using DMF as an
internal standard). Full conversion of 130 mmol of formic acid free of additives to the 1:1
mixture of CO2 and H2 was obtained within 14 h corresponding to the total pressure of
978 kPa.4r, 21
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On the basis of the stoichiometric and catalytic studies, we suggested a plausible
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sequence of mechanistic events for the decomposition of FA by
3
(Scheme 5). As the first
takes place in the
step, we propose that immediate protonation of the preꢀcatalyst
3
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presence of diluted or neat formic acid forming actual catalytic species 3’. Next, the
activated 3’ starts a turnover by releasing dihydrogen via intramolecular protonolysis of
the IrꢀH bond with the subsequent formation of a cationic 16ꢀelectron intermediate 3”
.
Unlike the traditional and generally accepted mechanism, where protonolysis of such
metalꢀhydride intermediates by FA may be mediated intermolecularly by water or
external amines,4b, 4f, 4i, 4n, 7b, 10l we believe that the intramolecular interaction with a highly
acidic pendant ammonium group greatly facilitates hydrogen liberation from 3’
.
Formation of a coordinatively saturated iridium formate complex 3”’ proceeds via 1,2ꢀ
addition a molecule of formic acid across coordination IrꢀN bond of 3”. Finally, extrusion
of CO2 from 3”’and regeneration of 3’ locks the catalytic cycle.
Taking into account the steric hindrance of the iridium center in 3”’, the last step may
be rateꢀdetermining because βꢀH elimination from coordinatively saturated complexes
requires either additional ligand dissociation step or coordination switch from an Oꢀbound
formate to an Hꢀbound formate prior to CO2 elimination. Since the dissociation of, for
example, a chloride ligand from the protonated 3” is highly unlikely, rearrangement of the
Oꢀbound formate intermediate is hypothesized, despite that such reorganization is usually
energetically disfavoured5a and/or requires assistance of external agents.8
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Scheme 5. Plausible mechanism of the FA dehydrogenation using 3.
To confirm this assumption and to validate the suggested mechanism, we performed
quantum chemical calculations. Figure 1 represents the free energy profile for the
catalytic cycle. The computations confirmed that the first step in the cycle proceeds via
polar 1,2ꢀIrꢀH…. HNꢀelimination of dihydrogen from 3’ via a TS3-I located only 10.8
3
kcal molꢀ1 above 3’ resulting in the formation of the cationic iridium intermediate 3”. This
step is chelationꢀassisted, which makes it exergonic by 11.9 kcal molꢀ1. The next step of
the catalytic cycle is the concert 1,2ꢀaddition of FA across the NꢀIr coordination bond of
3” toward the formation of the Oꢀbound iridium formate intermediate 3”’ with a
protonated ligand sideꢀarm. Finally, we concentrated on the most questionable and apparently
rateꢀdetermining step – the βꢀH elimination of carbon dioxide from the coordinatively saturated
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3”’ to regenerate catalytically active 3’. The identified TS3ꢀII is located 34.0 kcal molꢀ1 above
3
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6
–
the Ir-formate intermediate 3”’ with the cleaved IrꢀO bond and nonꢀclassical O2C…H…Ir
7
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9
contact. Clearly, the stabilizing interactions between the positively charged ammonium site and
the negatively charged carboxylate make the βꢀH elimination of CO2 at the coordinatively
saturated metal center possible via intramolecular outerꢀsphere mechanism (see also Scheme 5).
In order to verify the obtained TS, we have computed the frequencies and we calculated
the Intrinsic Reaction Coordinate (IRC) pathway using Damped VelocityꢀVerlet
integrator22 forward, to the product, and backward, to the reactant species. The normal
mode analysis yielded one imaginary frequency confirming the transition state nature of
TS3ꢀII. Further, the IRC connected 3”’ and 3’ via TS3ꢀII providing additional evidence
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for βꢀH elimination of CO2 (the animation of the IRC can be found in the ESI).
This arguable point was experimentally probed by the KIE experiments. Thus, when
HCO2H was replaced with fully deuterated DCO2D, the initial reaction rate measured
over the first 6 min decreased strongly showing the KIE of 2.5. Less expectedly,
employment of both partially deuterated HCO2D and DCO2H demonstrated a lower KIE
(1.7 and 2.1, correspondingly). This observation, consistent with a scenario when both
proton and hydride participate in a single bottleneck step, also supports relevance of the
transition state TS3ꢀII.
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Figure 1. Calculated mechanism (BP86/def2ꢀTZVP/W06) of the FA dehydrogenation using 3
(left) and 2 (right). The free energy values are given below in kcal/mol.
To stress differences between the catalysts equipped with different functional groups,
we attempted evaluation of the free energy profiles for
2 (Figure 1, right). It turned out
that hydrogen formation step for a less acidic OHꢀcontaining catalyst is highly endergonic
by 15.6 kcal molꢀ1 with a more significant barrier of 18.6 kcal molꢀ1 (Figure 1, right). This
is consistent with experimentally observed spontaneous H2 extrusion from
3 in contrast to
2
(pls, see Scheme 4). We also attempted to compute a free energy profile of the
decarboxylation step via Oꢀbound/Hꢀbound formate switch for this catalyst. We failed to
locate the corresponding transition state using various techniques. The lack of this TS may
indicate a different decarboxylation mechanism, for example, the one that proceeds via
dissociation of the chloride ligand to provide a vacant coordination site essential for a more
conventional βꢀH elimination of carbon dioxide.
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Conclusions
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In conclusion, we have described a highly efficient Ir catalyst for the selective
decomposition of formic acid to hydrogen and carbon dioxide operating under amineꢀfree
conditions and in the absence of exotic additives. According to our studies, dihydrogen
liberation proceeds via intramolecular protonolysis of the Irꢀhydride species with the aid
of acidic remote functionality. Regeneration of the active hydride catalyst is also achieved
via nonꢀclassical outerꢀsphere intramolecular βꢀH elimination of CO2, as we deduced
from the experimental studies and quantum chemical calculations. Nevertheless, the most
important ramification of this work is that unique topology of this family of compounds
and flexibility in their synthesis offer essentially unlimited opportunities for the fineꢀ
tuning of the catalytic activity in many classical reaction schemes, as well as render new
reactivity to many classical organometallic catalysts. Further mechanistic and catalytic
studies are under way.
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AUTHOR INFORMATION
Corresponding Author
*Eꢀmail to DG (experiment): dmitri.gelman@mail.huji.ac.il *Eꢀmail to IS (calculations):
igor.schapiro@mail.huji.ac.il
Author Contributions
All authors have given approval to the final version of the manuscript. ‡SC performed all
experimental work; VB performed all theoretical investigations.
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ASSOCIATED CONTENT
5
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Computational details
9
All geometries were optimized using the BP86 functional23 in conjunction with the def2ꢀ
TZVP basis set24 and W06 auxiliary basis set for density fitting25 in Gaussian 0926
program package. In addition we have benchmarked three different density functionals
using a smaller basis set def2ꢀSVP (see Figure S35 in the ESI). To account for the longꢀ
range dispersion interaction, Grimme’s dispersion with BeckeꢀJohnson damping (GD3BJ)
was included.27 To simulate the solvent effects, the conductorꢀlike continuum model (Cꢀ
PCM)28 was used. The transition states (TSs) were obtained using the QST3 algorithm.
The initial guess for the TSꢀII was obtained by interpolation of the geometries of the
product and reactant. All transition states we confirmed by a normal mode analysis that
showed a single imaginary frequency in all cases. The Intrinsic Reaction Coordinate
(IRC) calculation was carried out starting from the transition state (TS3ꢀII) towards the
reactant (backward) and the product (forward). The Damped Velocity Verlet22 (DVV)
algorithm was utilized for the IRC computation.
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Supporting Information
The Supporting Information including spectral data, experimental protocols and computational
details, is available free of charge on the ACS Publications website at DOI:
ACKNOWLEDGMENT
The studies were supported by ISF (Israel Science Foundation) Grants N 917/15 and 1384/13.
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References
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8
9
10
11
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13
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15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
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1.
(a) Bernskoetter, W. H.; Hazari, N., Acc. Chem. Res. 2017, 50, 1049ꢀ1058; (b) Joo, F.,
ChemSusChem 2008, 1, 805ꢀ808; (c) Walspurger, S.; Haije, W. G.; Louis, B., Isr. J. Chem. 2014,
54, 1432ꢀ1442; (d) Muiuane, V. P.; Ferreira, M.; Bignet, P.; Bettencourt, A. P.; Parpot, P., J.
Environ. Chem. Eng. 2013, 1, 1237ꢀ1244; (e) Moret, S.; Dyson, P. J.; Laurenczy, G., Nat.
Commun. 2014, 5, 4017ꢀ4023; (f) Laurenczy, G., Chem. - Eur. J. 2016, 22, 15605ꢀ15608; (g)
Omae, I., Coord. Chem. Rev. 2012, 256, 1384ꢀ1405; (h) Chow, M. C.; Jackson, W. R.; Chaffee,
A. L.; Marshall, M., Energy Fuels 2013, 27, 1926ꢀ1950; (i) Jones, J.ꢀP.; Prakash, G. K. S.; Olah,
G. A., Isr. J. Chem. 2014, 54, 1451ꢀ1466; (j) Wang, W.ꢀH.; Himeda, Y.; Muckerman, J. T.;
Manbeck, G. F.; Fujita, E., Chem. Rev. 2015, 115, 12936ꢀ12973; (k) Mellmann, D.; Sponholz,
P.; Junge, H.; Beller, M., Chem. Soc. Rev. 2016, 45, 3954ꢀ3988; (l) Taheri, A.; Berben, L. A.,
Chem. Commun. 2016, 52, 1768ꢀ1777.
2.
(a) Trillo, J. M.; Munuera, G.; Criado, J. M., Catal. Rev. 1972, 7, 51ꢀ86; (b) Schwab, G.ꢀ
M., Trans. Faraday Soc. 1946, 42, 689ꢀ697; (c) Szabo, Z. G.; Solymosi, F., Acta Chim. Acad.
Sci. Hung. 1960, 25, 145ꢀ160; (d) Noto, Y.; Fukuda, K.; Onishi, T.; Tamaru, K., Trans. Faraday
Soc. 1967, 63, 3081ꢀ3087; (e) Willhoft, E. M. A., Chem. Commun. 1968, 146ꢀ147; (f)
Yurchenko, E. N., Kinet. Katal. 1973, 14, 515ꢀ518; (g) Solymosi, F.; Erdohelyi, A., J. Catal.
1985, 91, 327ꢀ337.
3.
(a) Grasemann, M.; Laurenczy, G., Energy Environ. Sci. 2012, 5, 8171ꢀ8181; (b) An, L.;
Chen, R., J. Power Sources 2016, 320, 127ꢀ139; (c) Meng, H.; Zeng, D.; Xie, F., Catalysts 2015,
5, 1221ꢀ1274; (d) Singh, A. K.; Xu, Q., ChemCatChem 2013, 5, 652ꢀ676; (e) Yu, X.; Pickup, P.
G., J. Power Sources 2008, 182, 124ꢀ132.
4.
(a) Fink, C.; Laurenczy, G., Dalton Trans. 2017, 46, 1670ꢀ1676; (b) Xu, C.; Zhang, L.;
Dong, C.; Xu, J.; Pan, Y.; Li, Y.; Zhang, H.; Li, H.; Yu, Z.; Xu, L., Adv. Synth. Catal. 2016, 358,
567ꢀ572; (c) Mellone, I.; Gorgas, N.; Bertini, F.; Peruzzini, M.; Kirchner, K.; Gonsalvi, L.,
Organometallics 2016, 35, 3344ꢀ3349; (d) Ertem, M. Z.; Himeda, Y.; Fujita, E.; Muckerman, J.
T., ACS Catal. 2016, 6, 600ꢀ609; (e) Celaje, J. J. A.; Lu, Z.; Kedzie, E. A.; Terrile, N. J.; Lo, J.
N.; Williams, T. J., Nat. Commun. 2016, 7, 11308ꢀ11313; (f) Wang, W.ꢀH.; Ertem, M. Z.; Xu,
S.; Onishi, N.; Manaka, Y.; Suna, Y.; Kambayashi, H.; Muckerman, J. T.; Fujita, E.; Himeda, Y.,
ACS Catal. 2015, 5, 5496ꢀ5504; (g) RosasꢀHernandez, A.; Junge, H.; Beller, M., ChemCatChem
2015, 7, 3316ꢀ3321; (h) Oldenhof, S.; Lutz, M.; de Bruin, B.; van der Vlugt, J. I.; Reek, J. N. H.,
Chem. Sci. 2015, 6, 1027ꢀ1034; (i) Matsunami, A.; Kayaki, Y.; Ikariya, T., Chem. - Eur. J. 2015,
21, 13513ꢀ13517; (j) Bertini, F.; Mellone, I.; Ienco, A.; Peruzzini, M.; Gonsalvi, L., ACS Catal.
2015, 5, 1254ꢀ1265; (k) Vogt, M.; Nerush, A.; DiskinꢀPosner, Y.; BenꢀDavid, Y.; Milstein, D.,
Chem. Sci. 2014, 5, 2043ꢀ2051; (l) Thevenon, A.; FrostꢀPennington, E.; Weijia, G.; Dalebrook,
A. F.; Laurenczy, G., ChemCatChem 2014, 6, 3146ꢀ3152; (m) Hsu, S.ꢀF.; Rommel, S.;
Eversfield, P.; Muller, K.; Klemm, E.; Thiel, W. R.; Plietker, B., Angew. Chem., Int. Ed. 2014,
53, 7074ꢀ7078; (n) Manca, G.; Mellone, I.; Bertini, F.; Peruzzini, M.; Rosi, L.; Mellmann, D.;
Junge, H.; Beller, M.; Ienco, A.; Gonsalvi, L., Organometallics 2013, 32, 7053ꢀ7064; (o) Czaun,
M.; Goeppert, A.; May, R.; Haiges, R.; Prakash, G. K. S.; Olah, G. A., ChemSusChem 2011, 4,
1241ꢀ1248; (p) Boddien, A.; Mellmann, D.; Gaertner, F.; Jackstell, R.; Junge, H.; Dyson, P. J.;
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Page 20 of 22
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2
3
4
5
6
7
8
9
Laurenczy, G.; Ludwig, R.; Beller, M., Science 2011, 333, 1733ꢀ1736; (q) Loges, B.; Boddien,
A.; Gaertner, F.; Junge, H.; Beller, M., Top. Catal. 2010, 53, 902ꢀ914; (r) Iguchi, M.; Himeda,
Y.; Manaka, Y.; Kawanami, H., ChemSusChem 2016, 9, 2749ꢀ2753; (s) Wang, Z.; Lu, S.ꢀM.; Li,
J.; Wang, J.; Li, C., Chemistry – Eur. J. 2015, 21, 12592ꢀ12595.
5.
(a) Zell, T.; Butschke, B.; BenꢀDavid, Y.; Milstein, D., Chem. - Eur. J. 2013, 19, 8068ꢀ
8072; (b) Mellone, I.; Peruzzini, M.; Rosi, L.; Mellmann, D.; Junge, H.; Beller, M.; Gonsalvi, L.,
Dalton Trans. 2013, 42, 2495ꢀ2501; (c) Boddien, A.; Loges, B.; Junge, H.; Gaertner, F.; Noyes,
J. R.; Beller, M., Adv. Synth. Catal. 2009, 351, 2517ꢀ2520; (d) Guerriero, A.; Bricout, H.;
Sordakis, K.; Peruzzini, M.; Monflier, E.; Hapiot, F.; Laurenczy, G.; Gonsalvi, L., ACS Catal.
2014, 4, 3002ꢀ3012.
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
6.
7.
Wang, Z.; Lu, S.ꢀM.; Wu, J.; Li, C.; Xiao, J., Eur. J. Inorg. Chem. 2016, 2016, 490ꢀ496.
(a) Onishi, N.; Xu, S.; Manaka, Y.; Suna, Y.; Wang, W.ꢀH.; Muckerman, J. T.; Fujita, E.;
Himeda, Y., Inorg. Chem. 2015, 54, 5114ꢀ5123; (b) Wang, W.ꢀH.; Himeda, Y.; Muckerman, J.
T.; Fujita, E., Adv. Inorg. Chem. 2014, 66, 189ꢀ222; (c) Wang, L.; Onishi, N.; Murata, K.;
Hirose, T.; Muckerman, J. T.; Fujita, E.; Himeda, Y., ChemSusChem 2017, 10, 1071ꢀ1075; (d)
Suna, Y.; Ertem, M. Z.; Wang, W.ꢀH.; Kambayashi, H.; Manaka, Y.; Muckerman, J. T.; Fujita,
E.; Himeda, Y., Organometallics 2014, 33, 6519ꢀ6530; (e) 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,
1091ꢀ1106; (f) Papp, G.; Ölveti, G.; Horváth, H.; Kathób, Á.; Joó F., Dalton Trans., 2016, 45,
14516–14519; (g) MontandonꢀClerc, M.; Dalebrook, A. F.; Laurenczy, G., J. Catal., 2016, 343,
62ꢀ67.
8.
W. H.; Hazari, N.; Schneider, S., J. Am. Chem. Soc. 2014, 136, 10234ꢀ10237.
9. Guan, C.; Zhang, D.ꢀD.; Pan, Y.; Iguchi, M.; Ajitha, M. J.; Hu, J.; Li, H.; Yao, C.;
Bielinski, E. A.; Lagaditis, P. O.; Zhang, Y.; Mercado, B. Q.; Würtele, C.; Bernskoetter,
Huang, M.ꢀH.; Min, S.; Zheng, J.; Himeda, Y.; Kawanami, H.; Huang, K.ꢀW., Inorg. Chem.
2017, 56, 438ꢀ445.
10.
(a) Oldenhof, S.; de Bruin, B.; Lutz, M.; Siegler, M. A.; Patureau, F. W.; van der Vlugt,
J. I.; Reek, J. N. H., Chem. - Eur. J. 2013, 19, 11507ꢀ11511; (b) Tan, C.; Wang, P.; Liu, H.;
Zhao, X.ꢀL.; Lu, Y.; Liu, Y., Chem. Commun. 2015, 51, 10871ꢀ10874; (c) Saha, B.; Wahidur
Rahaman, S. M.; Daw, P.; Sengupta, G.; Bera, J. K., Chem. - Eur. J. 2014, 20, 6542ꢀ6551; (d)
Musina, E. I.; Khrizanforova, V. V.; Strelnik, I. D.; Valitov, M. I.; Spiridonova, Y. S.;
Krivolapov, D. B.; Litvinov, I. A.; Kadirov, M. K.; Loennecke, P.; HeyꢀHawkins, E.; Budnikova,
Y. H.; Karasik, A. A.; Sinyashin, O. G., Chem. - Eur. J. 2014, 20, 3169ꢀ3182; (e) Schneider, S.;
Meiners, J.; Askevold, B., Eur. J. Inorg. Chem. 2012, 2012, 412ꢀ429; (f) Wylie, W. N. O.;
Lough, A. J.; Morris, R. H., Organometallics 2012, 31, 2152ꢀ2165; (g) Burford, R. J.; Piers, W.
E.; Parvez, M., Organometallics 2012, 31, 2949ꢀ2952; (h) Schwartsburd, L.; Iron, M. A.;
Konstantinovski, L.; BenꢀAri, E.; Milstein, D., Organometallics 2011, 30, 2721ꢀ2729; (i) Li, B.;
Darcel, C.; Dixneuf, P. H., Chem. Commun. 2014, 50, 5970ꢀ5972; (j) Masoud, S. M.; Mailyan,
A. K.; Dorcet, V.; Roisnel, T.; Dixneuf, P. H.; Bruneau, C.; Osipov, S. N., Organometallics
2015, 34, 2305ꢀ2313; (k) Hayes, J. M.; Deydier, E.; Ujaque, G.; Lledos, A.; MalaceaꢀKabbara,
R.; Manoury, E.; Vincendeau, S.; Poli, R., ACS Catal. 2015, 5, 4368ꢀ4376; (l) Hayes, J. M.;
Deydier, E.; Ujaque, G.; Lledós, A.; MalaceaꢀKabbara, R.; Manoury, E.; Vincendeau, S.; Poli,
R., ACS Catalysis 2015, 5, 4368ꢀ4376; (m) Kleinhans, G.; Hansmann, M. M.; GuisadoꢀBarrios,
G.; Liles, D. C.; Bertrand, G.; Bezuidenhout, D. I., J. Am. Chem. Soc. 2016, 138, 15873ꢀ15876.
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11.
(a) Musa, S.; Fronton, S.; Vaccaro, L.; Gelman, D., Organometallics 2013, 32, 3069ꢀ
3073; (b) Musa, S.; Ackermann, L.; Gelman, D., Adv. Synth. Catal. 2013, 355, 3077ꢀ3080; (c)
Oded, K.; Musa, S.; Gelman, D.; Blum, J., Catal. Commun. 2012, 20, 68ꢀ70; (d) Musa, S.;
Shaposhnikov, I.; Cohen, S.; Gelman, D., Angew.Chem., Int. Ed. 2011, 50, 3533ꢀ3537; (e) Deꢀ
Botton, S.; Romm, R.; Bensoussan, G.; Hitrik, M.; Musa, S.; Gelman, D., Dalton Trans. 2016,
45, 16040ꢀ16046; (f) Musa, S.; Filippov, O. A.; Belkova, N. V.; Shubina, E. S.; Silantyev, G. A.;
Ackermann, L.; Gelman, D., Chem. - Eur. J. 2013, 19, 16906ꢀ16909.
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12.
Musa, S.; Ghosh, A.; Vaccaro, L.; Ackermann, L.; Gelman, D., Adv. Synth. Catal. 2015,
357, 2351ꢀ2357.
13.
A suitable crystal of 2 can only be obtained in the CO atmosphere; otherwise it loses
hydrogen to form the previously observed 2’. Attempts to crystallize 4 failed even in the
presence of CO and the crystal of 4’ was analyzed (please see ESI for details).
14.
A crossover experiment staring from the stoichiometric mixture of 2 and a fully
deuterated 2 (ESI), resulted in the formation of statistically distributed H2, D2 and HD according
to IRꢀMS analysis. However, the HꢀD exchange may also originate from the presence of a
spectator hydroxyl group.
15.
In principle, intramolecular protonolysis of transition metal hydrides with strong acids is
well known (e.g. Dobson, A.; Robinson, S. D. J. Organomet. Chem., 1975, 87, C52ꢀ53).
Therefore, we tested a similar reaction with 2. Fast decomposition of 2 along with the formation
of H2 was observed after one hour heating with pꢀtoluenesulfonic acid in CDCl3. The same
experiment with formic acid, revealed decomposition only after 24 hours, showing a clear acid
strength dependence in contrast to 3.
16.
Gelman, F.; Kotlyar, A.; Chiguala, D.; Ronen, Z., Int. J. Environ. Anal. Chem. 2011, 91,
1392ꢀ1400.
17.
18.
Musa, S.; Shpruhman, A.; Gelman, D., J. Organomet. Chem. 2012, 699, 92ꢀ95.
The FA/TEA (5:3) decomposition rate in the presence of 1ꢀ7 was evaluated at
o
temperatures between 30 and 100 C showing the expected temperature dependence. In both of
the cases, an activation period of ca. 3ꢀ5 minutes was required for the catalysts to initiate gas
evolution at temperatures below 70 oC, while essentially immediate reaction took place when the
o
reactor was immersed into the preheated oil bath at the temperatures above 70 C (See
supporting information).
19.
stressing out the robustness of the catalytic systems.
20. (a) Yang, X.; Pachfule, P.; Chen, Y.; Tsumori, N.; Xu, Q., Chem. Commun. 2016, 52,
Remarkably, all catalyst manipulations and the experiments were performed in air
4171ꢀ4174; (b) Onishi, N.; Ertem, M. Z.; Xu, S.; Tsurusaki, A.; Manaka, Y.; Muckerman, J. T.;
Fujita, E.; Himeda, Y., Catal. Sci. Technol. 2016, 6, 988ꢀ992; (c) Liu, Q.; Yang, X.; Huang, Y.;
Xu, S.; Su, X.; Pan, X.; Xu, J.; Wang, A.; Liang, C.; Wang, X.; Zhang, T., Energy Environ. Sci.
2015, 8, 3204ꢀ3207; (d) Manaka, Y.; Wang, W.ꢀH.; Suna, Y.; Kambayashi, H.; Muckerman, J.
T.; Fujita, E.; Himeda, Y., Catal. Sci. Technol. 2014, 4, 34ꢀ37; (e) Gan, W.; Snelders, D. J. M.;
Dyson, P. J.; Laurenczy, G., ChemCatChem 2013, 5, 1126ꢀ1132; (f) Fellay, C.; Dyson, P. J.;
Laurenczy, G., Angew. Chem., Int. Ed. 2008, 47, 3966ꢀ3968.
21.
22.
23.
Fellay, C.; Yan, N.; Dyson, P. J.; Laurenczy, G., Chem. - Eur. J. 2009, 15, 3752ꢀ3760.
Hratchian H. P.; Schlegel, H. B., J. Phys. Chem. A, 2002, 106, 165ꢀ169.
(a) Becke, A. D. Phys. Rev. A 1988, 38, 3098– 3100, (b) Perdew, J. P. Phys. Rev. B 1986,
33, 8822– 8824.
24. Schafer, A.; Huber, C.; Ahlrichs, R. J. Chem. Phys. 1994, 100, 5829– 5835.
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Page 22 of 22
1
2
3
4
5
6
7
8
9
25.
26.
27.
28.
Weigend, F. Phys. Chem. Chem. Phys. 2006, 8, 1057– 1065.
Frisch, M. J. Gaussian 09, revision B.01; Gaussian, Inc.: Wallingford, CT, 2010.
Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem. 2011, 32, 1456– 1465.
(a) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105, 2999– 3093, (b)
Scalmani, G.; Frisch, M. J. J. Chem. Phys. 2010, 132, 114110ꢀ114115.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
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