Ruthenium-catalyzed selective hydroboronolysis of ethers

Article abstract of DOI:10.1021/acscatal.0c04269

A ruthenium-catalyzed reaction of HBpin with substituted organic ethers leads to the activation of C?O bonds, resulting in the formation of alkanes and boronate esters via hydroboronolysis. A ruthenium precatalyst, [Ru (p-cymene)Cl]₂Cl₂ (1), is employed, and the reactions proceed under neat conditions at 135 °C and atmospheric pressure (ca. 1.5 bar at 135 °C). Unsymmetrical dibenzyl ethers undergo selective hydroboronolysis on relatively electron-poor C?O bonds. In arylbenzyl or alkylbenzyl ethers, C?O bond cleavage occurs selectively on C_Bn?OR bonds (Bn = benzyl); in alkylmethyl ethers, selective deconstruction of C_Me?OR bonds leads to the formation of alkylboronate esters and methane. Cyclic ethers are also amenable to catalytic hydroboronolysis. Mechanistic studies indicated the immediate in situ formation of a mono-hydridobridged dinuclear ruthenium complex [{(η⁶-p-cymene)RuCl}₂(μ?H?μ?Cl)] (2), which is highly active for hydroboronolysis of ethers. Over time, the dinuclear species decompose to produce ruthenium nanoparticles that are also active for this transformation. Using this catalytic system, hydroboronolysis could be applied effectively to a very large scope of ethers, demonstrating its great potential to cleave C?O bonds in ethers as an alternative to traditional hydrogenolysis.

Full text of DOI:10.1021/acscatal.0c04269

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Research Article
Ruthenium-Catalyzed Selective Hydroboronolysis of Ethers
Akash Kaithal, Deepti Kalsi, Varadhan Krishnakumar, Sandip Pattanaik, Alexis Bordet, Walter Leitner,
and Chidambaram Gunanathan*
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ABSTRACT: A ruthenium-catalyzed reaction of HBpin with
substituted organic ethers leads to the activation of C−O bonds,
resulting in the formation of alkanes and boronate esters via
hydroboronolysis. A ruthenium precatalyst, [Ru (p-cymene)Cl]2Cl2
(1), is employed, and the reactions proceed under neat conditions
at 135 °C and atmospheric pressure (ca. 1.5 bar at 135 °C).
Unsymmetrical dibenzyl ethers undergo selective hydroboronolysis
on relatively electron-poor C−O bonds. In arylbenzyl or
alkylbenzyl ethers, C−O bond cleavage occurs selectively on
CBn−OR bonds (Bn = benzyl); in alkylmethyl ethers, selective
deconstruction of CMe−OR bonds leads to the formation of
alkylboronate esters and methane. Cyclic ethers are also amenable to catalytic hydroboronolysis. Mechanistic studies indicated the
immediate in situ formation of a mono-hydridobridged dinuclear ruthenium complex [{(η6-p-cymene)RuCl}2(μ−H−μ−Cl)] (2),
which is highly active for hydroboronolysis of ethers. Over time, the dinuclear species decompose to produce ruthenium nanoparticles
that are also active for this transformation. Using this catalytic system, hydroboronolysis could be applied effectively to a very large
scope of ethers, demonstrating its great potential to cleave C−O bonds in ethers as an alternative to traditional hydrogenolysis.
KEYWORDS: hydroboration, catalysis, hydroelementation, ethers, ruthenium
offset the thermodynamic barriers.17−19,21,22 Similar to C−O
INTRODUCTION
■
bond activation, Chatani and co-workers reported the nickel-
The catalytic reductive cleavage of C−O bonds in ethers is a
key transformation for the production of fuels and value-added
catalyzed C−N bond activation using HBpin under mild
conditions.27 While hydrogenolysis remains by far the most
investigated method to cleave ether bonds, the development of
alternative approaches recently gained increasing attention. In
particular, Martin and co-workers reported the ipso-borylation
of aryl methyl ethers via C−OMe bond cleavage.28 This
transformation involved a complex reaction medium contain-
ing a nickel catalyst, B2(nep)2, a base, a phosphine, and a
solvent, and was limited to only a few substrates.28 Recently,
Okuda and co-workers developed an aluminum-based catalyst
able to achieve the ring-opening of cyclic ethers (tetrahy-
drofuran and tetrahydropyran) through C−O bond cleavage
via hydroboration.29−31
chemicals from biomass.1−3 In particular, alkyl aryl ether
motifs are abundant in lignocellulosic biomass but possess a
relatively unreactive Caryl/alkyl−O bond.4−7 The development of
catalytic methods allowing their facile deconstruction is thus
essential for the valorization of biomass-derived feedstock.1−3
In this context, catalytic hydrogenolysis is the most common
approach to achieve C−O bond cleavage in ethers.8 However,
other than the palladium-catalyzed hydrogenolysis of benzyl
ethers,9 hydrogenolysis generally requires elevated temper-
atures, pressures, and specialized equipment. The deconstruc-
tion of ethers by conventional synthetic methods requires
harsh reaction conditions, including the use of strong acids10,11
or bases such as KOtBu along with stoichiometric amounts of
hydride reagents (e.g., Et3SiH, alkali-metal based hydrides). In
addition, such reactions also require high temperatures and
pressures.12,13
In this context, we show here that [Ru(p-cymene)Cl]2Cl2
(1) acts as an efficient precatalyst for hydroboronolysis of a
wide range of alkyl aryl ethers to the corresponding boronate
esters and alkanes. The nature of the active species was
As a result, extensive efforts have been dedicated to the
development of catalytic methods, allowing the activation of
ethers using H2.14−26 For example, Hartwig and co-workers
reported the selective activation of the Caryl−O bond of ethers
under mild conditions (1 bar H2) using nickel catalysts.15,16
The lanthanide triflates-catalyzed hydrogenolysis of ethers was
reported by Marks and co-workers in which the in situ formed
alkenols were hydrogenated using palladium nanoparticles to
Received: October 1, 2020
Revised: November 10, 2020
https://dx.doi.org/10.1021/acscatal.0c04269
© XXXX American Chemical Society
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a
Table 1. Reaction Optimization for Hydroboronolysis of Dibenzylether
entry
temp. (°C)
cat. (mol %)
time (h)
conv. (%)
PhCH2OBpin (%)
1
2
3
4
5
6
7
80
2
2
2
2
0.5
1
-
24
24
24
24
24
24
24
2
2
100
120
135
135
135
135
26
78
98
12
78
7
26
78
98
12
78
7
a
Reaction conditions: dibenzylether (1 mmol), HBpin (2 mmol), and [Ru(p-cymene)Cl]2Cl2 (1) (0.5−2.0 mol %) were heated in a closed vessel
1
for 24 h (Patm at r.t., ca. 1.5 bar at 135 °C). Conversion of dibenzylether and yield of boronoate ester were calculated using H NMR.
a
Table 2. Catalytic Selective Hydroboronolysis of Dibenzyl Ethers and Arylbenzyl Ethers
a
Reaction conditions: ether (1 mmol), HBpin (2 mmol), and [Ru(p-cymene)Cl]2Cl2 (1) (2 mol %) were heated at 135 °C in a closed vessel for 24
1
h (Patm at r.t., ca. 1.5 bar at 135 °C). Conversion of ethers was calculated using H NMR; conversion calculated by GC is given in parentheses.
b
1
Calculated based on H NMR analysis of the reaction mixture. n.d.: not determined.
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a
Table 3. Catalytic Selective Hydroboronolysis of Aliphatic Ethers
a
Reaction conditions: ether (1 mmol), HBpin (2 mmol), and [Ru(p-cymene)Cl]2Cl2 (1, 2 mol %) were heated at 135 °C in a closed vessel for 24
1
h (Patm at r.t., ca. 1.5 bar at 135 °C). Conversion of ethers was calculated using H NMR; Conversion calculated by GC is given in parentheses.
b
1
Calculated based on H NMR analysis of the reaction mixture.
investigated using a combination of control experiments and
characterization techniques, including NMR spectroscopy (in
situ reaction monitoring), kinetics, poisoning experiments, and
electron microscopy. The [Ru(p-cymene)Cl]2Cl2 complex was
converted into a mono-hydridobridged dinuclear species under
the reaction conditions used, in agreement with previous
observations.32−37 The resulting [{(η6-p-cymene)RuCl}2(μ−
H−μ−Cl)] (2) complex possesses high activity for hydro-
boronolysis of a wide range of ethers with various substituents
in solvent-free conditions. The complex decomposes with time,
forming Ru nanoparticles, which are moderately active for this
transformation by a reduced factor of ca.15-fold. The catalytic
system described provides an alternative approach for the
cleavage of ethers, operates through both homogeneous and
heterogeneous pathways, and may have possible application in
biomass valorization.
RESULTS AND DISCUSSION
■
Dibenzylether was selected as a model substrate and reacted
with pinacolborane (HBpin = 4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane) in the presence of the commercial [Ru(p-cymene)-
Cl]2Cl2 complex (1). After a parameter screening, the best
reaction conditions were found employing substrate (1 mmol),
HBpin (2 mmol), 1 (2 mol %), 135 °C, and 24 h reaction time
under neat conditions (Table 1, Entry 4). The pressure
remains in all cases very close to atmospheric pressure (ca. 1.5
bar at 135 °C). Using these parameters, the reaction resulted in
a 98% yield of benzyl boronate ester and toluene (Table 1,
Entry 4). In general, lowering the temperature (Table 1,
Entries 1−3) or decreasing the catalyst loading (Table 1,
Entries 5, 6) provided reduced conversions and yields. Control
experiments performed without the catalyst resulted in only
very low conversion (7%, Table 1, Entry 7).
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a
Table 4. Catalytic Selective Hydroboronolysis of Methylalkyl Ethers
a
Reaction conditions: ether (1 mmol), HBpin (2 mmol), and [Ru(p-cymene)Cl]2Cl2 (1, 5 mol %) were heated at 135 °C in a closed vessel for 36
b
1
1
h (Patm at r.t., ca. 1.5 bar at 135 °C). Conversion of ethers was calculated using H NMR. Calculated based on H NMR analysis of reaction
mixture.
Using the optimized conditions, hydroboronolysis of various
dibenzyl ethers and arylbenzyl ethers was explored (Table 2).
Symmetrical substrates were all converted into their corre-
sponding products in moderate to excellent yields (40−98%,
Entries 1−6). A particular focus was placed on unsymmetrical
substrates to understand the influence of substituents on the
selectivity. Using unsymmetrical dibenzyl ethers (Entries 7 and
8), the cleavage occurred preferentially on the relatively
electron-poor C−O bond, producing 4-methylbenzylpinacol
boronate ester and 4-tert-butylbenzyl boronate ester in high
selectivity. Considering unsymmetrical arylbenzyl ethers as
substrates (Entries 9−12), the corresponding arylboronate
esters were obtained in good to excellent yields (80−99%).
Selective hydroboronolysis of the CBn−O bond (Bn = benzyl)
in this case is attributed to the stronger bond strength of the
aryl-C−O bond. To confirm this hypothesis, DFT calculation
was performed for hydroboronolysis of (benzyloxy)benzene
(Table 2, Entry 9). The results from DFT calculation affirmed
toluene (40%) and benzylboronate ester (45%) were formed,
indicating a competing cleavage between the CBn−O and
Cmethyl−O bonds (Entry 1). ((Heptyloxy)methyl)benzene was
converted into heptylboronate ester in high yield (81%),
evidencing an excellent selectivity toward the cleavage of the
CBn−O bond (Entry 2). Similar observations were made using
sterically hindered alkyl benzyl ethers, with somewhat lower
yields (Entries 3−5). With the introduction of electron-
donating substituents on the para position of the phenyl ring, a
partial Calkyl−O bond cleavage was observed (8−11%), while
CBn−O bond cleavage remained predominant (Entries 6 and
7). (2-(Benzyloxy)ethyl)benzene was almost fully converted
(94%) to provide the 81% CBn−O activation product, while
Cphenethyl−O bond breaking yielded the corresponding
boronate ester in 13% yield (Entry 8). The CBn−O bond
was selectively cleaved in (4-(benzyloxy)butyl)benzene,
providing the corresponding 4-phenylbutyl boronate ester in
73% yield (Entry 9). Various alkyl chain tethered bis(benzyl)
diether derivatives were also considered. In all cases, the
cleavage occurred selectively on CBn−O bonds and the
corresponding dialkylboronate esters were obtained in
moderate to near quantitative yields (Entries 10−13).
However, when a sterically hindered ether such as (oxybis-
(ethane-1,1-diyl))dibenzene was used as the substrate,
complete consumption of the ether occurred and resulted in
the formation of unidentified products, perhaps due to the
sensitivity of secondary benzylic carbocation (Entry 14).
Then, the more challenging deconstruction of the CMe−O
bond in alkylmethyl ethers was investigated (Table 4). (4-
Methoxybutyl)benzene was initially subjected to 2 mol % of
the ruthenium precatalyst 1, resulting in only 42% conversion.
Under similar conditions, 1-methoxydecane and 1,8-dimethox-
yoctane reached conversions of 25 and 23%, respectively. To
enhance the substrate conversion and product yield, 5 mol %
of the precatalyst 1 and longer reaction time (36 h) were used
for hydroboronolysis of alkylmethyl ethers. Using these adapted
conditions, (2-methoxyethyl)benzene was quantitatively con-
verted into 2-phenethyloxy boronate ester and methane (Entry
1). Under similar conditions, various methyl ethers such as (4-
methoxybutyl)benzene, 1-methoxydecane, 1,8-dimethoxyoc-
tane, and 1,10-dimethoxydecane were used as substrates,
that the dissociation energy of the aryl-C−O bond (82.45
5
kcal·mol−1) is higher than that of the CBn−O bond (BDE =
38.74 5 kcal·mol−1) and the reaction favors the formation of
thermodynamically controlled products (see Supporting
Information, Table S1).
The scope of cyclic ethers was also explored. The reaction of
tetrahydropyran with HBpin confirmed the formation of
4,4,5,5-tetramethyl-2-(pentyloxy)-1,3,2-dioxaborolane with a
moderate yield of 21% but excellent selectivity (Entry 13).
Hydroboronolysis of tetrahydrofuran was not observed under
these conditions (Entry 14). Phthalan and isochromane
provided the corresponding ring-opening products 4,4,5,5-
tetramethyl-2-((2-methylbenzyl)oxy)-1,3,2-dioxaborolane and
4,4,5,5-tetramethyl-2-(2-methylphenethoxy)-1,3,2-dioxaboro-
lane, in moderate yields (64 and 58%, respectively; Entries 15
and 16). When a heterocyclic ether such as 2-((benzyloxy)-
methyl)pyridine was subjected to hydroboronolysis, the
formation of a complex product mixture was observed (Entry
17).
To investigate the versatility of the precatalyst 1 for
hydroboronolysis, more challenging substrates were considered,
that is, ethers containing various alkyl and benzyl substituents
(Table 3). When benzylmethyl ether was used as the substrate,
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Figure 1. Reaction of HBpin with Ru-precatalyst 1. Reaction conditions: [Ru(p-cymene)Cl]2Cl2 (1) (0.01 mmol), HBpin (0.022 mmol) and tol-d8
1
(0.5 mL) were heated at indicated reaction temperature, H NMR (400 MHz, tol-d8, T).
providing their corresponding boronate and diboronate esters
in 74 to 92% yields (Entries 2−5). Notably, excellent
selectivity was observed for all these substrates. Sanford and
Mindiola independently reported selective C−H borylation of
methane under pressurized conditions.38,39 Under our
experimental condition, no C−H borylation was observed.
Mechanistic Studies: Evidence for the Form of the
Ru-Based Catalyst. The efficiency and versatility of the
precatalyst 1 has now been demonstrated, but the exact nature
of the active species is not obvious. In particular, we have
previously shown that the use of complex 1 in the presence of
HBpin results in the immediate formation of a dinuclear
monohydrido bridged ruthenium complex [{(η6-p-cymene)-
RuCl}2(μ−H−μ−Cl)] (2).32−35 Since the hydroboronolysis
activity was observed at 120 °C and above [see Table 1, Entry
3], the in situ formation of 2 from the reaction of 1 with
HBpin was envisaged. To investigate this hypothesis, in situ
monitoring by 1H NMR of a stoichiometric reaction between 1
and HBpin was performed at different temperatures,
confirming the very quick formation of complex 2 (apparition
of a sharp singlet at δ − 10.26 ppm in 1H NMR characteristic
of the “bridged hydride” in 2) under the reaction conditions
used (Figure 1 and Figures S1,S2). Complex 2 was found
stable up to ca. 100 °C, but started decomposing above that
temperature, presumably reduced by HBpin or H2 elimination
to form ruthenium nanoparticles. At 135 °C, the signal
associated with complex 2 disappeared after ca. 50 min (Figure
S2). A comparable in situ NMR monitoring performed in the
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Figure 2. Time profiles for the conversion of dibenzylether to benzylboronate ester and toluene. (a) Without poison. (b) With 2 equiv. DCT
(dibenzo[a,e]cyclooctatetraene) as poison. Reaction conditions: dibenzylether (1 mmol), HBpin (2 mmol), and [Ru(p-cymene)Cl]2Cl2 (1, 2 mol
%) at 135 °C.
presence of dibenzyl ether also led to similar observations (see
Supporting Information, Figures S3-S6). In addition, in situ
formed mononuclear Ru−H species were previously found to
play a crucial role in the hydroelementation reactions of
unsaturated organic functionalities.32−35 The formation of such
ca. 2 h, some product formation was observed, evidencing the
presence of a heterogeneous catalyst.
Altogether, these observations are consistent with complex 2
being highly active for hydroboronolysis and responsible for the
very high reaction rate in the first 30 min (initial rate k = 0.90
mmol·h−1). After that, complex 2 is completely decomposed to
form Ru nanoparticles, which are also catalyzing this
transformation but with an apparent lower activity (initial
rate k′ = 0.06 mmol·h−1, meaning that 2 is ca. 15-fold more
active than the Ru NPs formed in situ). Interestingly, the slope
of product formation after 2 h is very similar in both cases
(with and without poison), strongly suggesting that after 2 h,
Ru NPs are the only species responsible for the activity
observed. TEM and EDX analyses were performed on the
black material collected after catalysis to confirm the formation
of small Ru nanoparticles (Figure 3 and see Supporting
Information, Figure S8).
1
Ru−H species was observed in H NMR analysis (δ = −13.6
ppm, Figure 1) of reaction mixtures up to 80 °C and found to
decompose at higher temperatures (Figure 1 and Figures
S4,S6). As hydroboronolysis of ethers is observed above 120 °C,
this is some evidence that mononuclear Ru-H species are not
involved in catalysis. In addition, the reaction performed at 135
°C in the absence of HBpin and only with dibenzyl ether failed
to produce any black precipitate and nanoparticles. The
resulting reaction mixture consisted of a homogeneous red
solution, indicating that the decomposition/reduction of
complex 2 indeed requires the presence of HBpin.
In addition, the solution after catalysis is black, suggesting
the decomposition of the Ru complex 2 to form clusters or
nanoparticles. Very recently, we investigated the hydrogenation
of heteroarenes and arenes employing complex 2. The
outcome from this study revealed that the hydrogenation of
heteroarenes proceeds via homogeneous catalysis and arenes
hydrogenation via heterogeneous catalysis, confirming that
dual catalysis is accessible starting from complex 2.40 To
determine whether the hydroboronolysis activity observed is
due to a homogeneous or heterogeneous catalyst, we started by
investigating the kinetics of the reaction using dibenzylether as
a model substrate. For that, a time profile was recorded under
the optimized conditions (Figure 2a). The profile shows a very
quick formation of benzylboronate ester (and toluene) in the
first 30 min (45% yield after 30 min), followed by a slow and
progressive increase of the yield to reach 100% after 18 h. This
indicates that active species are present in the reaction mixture
from the beginning. A second time profile was recorded, but
this time in the presence of two equivalents of DCT
(dibenzo[a,e]cyclooctatetraene), known to be a very efficient
poison for molecular catalysts (Figure 2b).41 The profile is, in
this case, completely different, with no product formation in
the first hour, followed by a slow and progressive increase of
the product yield in the next hours. These results are
consistent with a molecular complex being responsible for
the high activity in the initial times of the reaction. A molecular
catalyst is consistent with the kinetic data from Figures S2,S6,
which show that complex 2 is present in the reaction mixture
during the first 30−60 min. Then, after an induction period of
Figure 3. Characterization of the material obtained after catalysis.
Left: picture of the Schlenk tube after catalysis, showing a black
precipitate. Right: TEM analysis of the black precipitate.
Using the collected nanoparticles directly as catalysts for
hydroboronolysis of dibenzyl ether, 78% yield of benzylboro-
nate ester was obtained after 24 h. Additional poisoning
experiment on the recycled catalyst using mercury (50 mol %)
resulted in low conversion (18%) after 24 h, further supporting
the involvement of Ru NPs. Importantly, performing the
reaction without any precatalyst 1 results in a product yield of
7% (Table 1, Entry 7) after 24 h. 1,10-Phenanthroline was
previously shown to be a very good poison for Rh and Ru NPs
in hydrogenation reactions at 100 °C, allowing the differ-
entiation between clusters and NPs when performing
quantitative poisoning experiments.42−44 Interestingly, its use
was not successful in this particular case. The addition of 1,10-
phenanthroline to catalytic hydroboronolysis involving the
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recycled catalyst did not significantly affect the activity, even in
large excess (Figure S7). In this particular case, this can be due
to a combination of the neat substrate conditions and maybe
also the somewhat higher temperature (135 °C here vs 100 °C
in the literature15) that favor reversal of the exothermic
binding of 1,10-phenanthroline.42−44 This suggests that 1,10-
phenanthroline is not able to efficiently poison Ru NPs for this
particular transformation under these conditions. In addition,
preparing Ru nanoparticles on purpose in an ionic liquid45 and
using them as catalysts resulted as well in the production of
benzylboronate ester (52%), confirming that Ru NPs are active
in hydroboronolysis.
Deepti Kalsi − Max Planck Institute for Chemical Energy
Conversion, 45470 Mülheim an der Ruhr, Germany
Varadhan Krishnakumar − School of Chemical Sciences,
National Institute of Science Education and Research
(NISER), HBNI, Bhubaneswar 752050, India;
orcid.org/0000-0001-9400-3429
Sandip Pattanaik − School of Chemical Sciences, National
Institute of Science Education and Research (NISER), HBNI,
Bhubaneswar 752050, India
Alexis Bordet − Max Planck Institute for Chemical Energy
Conversion, 45470 Mülheim an der Ruhr, Germany;
orcid.org/0000-0003-0133-3416
Walter Leitner − Max Planck Institute for Chemical Energy
Conversion, 45470 Mülheim an der Ruhr, Germany; Institut
für Technische und Makromolekulare Chemie, RWTH
Aachen University, 52074 Aachen, Germany; orcid.org/
0000-0001-6100-9656
CONCLUSIONS
■
In summary, the first such report of catalytic hydroboronolysis
of ethers is described. Complex 1 is employed as simple
precatalyst, and the reactions are conducted under neat
conditions. In unsymmetrical ethers, hydroboronolysis occurs
selectively on electron-poor C−O bonds; thus, CBn−OR (R =
aryl or alkyl) bonds are selectively activated in arylbenzyl and
alkylbenzyl ethers to provide the corresponding boronate
esters and aryl alkanes. In alkylmethyl ethers, CMe−OR bonds
are activated. The cleavage of ethers is also applicable to cyclic
and other aliphatic ether compounds. Mechanistic studies
involving 1H NMR, time profile, quantitative poisoning
indicated the immediate formation of intermediate complex
2 from the precatalyst 1 in the presence of HBpin. In addition,
the in situ generation of Ru NPs from 2 was confirmed by
electron microscopy. Complex 2 is implicated as a highly active
catalyst for hydroboronolysis at the initial stage of the reactions.
However, over time, 2 decomposes and produces Ru NPs,
which also catalyze the hydroboronolysis activity albeit at an
apparent slower rate. The presented results highlight the
substantial scope of hydroboronolysis as a useful transformation
in organic synthesis and as an alternative approach to
hydrogenolysis. Applications including the deconstruction of
ether linkages in lignocellulosic biomass using this protocol can
be anticipated.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acscatal.0c04269
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank SERB New Delhi (EMR/2016/002517),
Department of Atomic Energy, India, and NISER for financial
support, and Dr. P. S. Subramanian for his kind help. V.K.
thanks SERB for the National Postdoctoral Fellowship. S.P.
thanks CSIR for a Fellowship. The authors also acknowledge
the financial support by the Max Planck Society and by the
Deutsche Forschungsgemeinschaft (DFG, German Research
Foundation) under Germany’s Excellence Strategy − Ex-
zellenzcluster 2186 “The Fuel Science Center” ID: 390919832.
̈
Furthermore, the authors would like to thank Norbert Pfander
(MPI for Chemical Energy Conversion, Mulheim an der
Ruhr), Adrian Schluter (MPI for Kohlenforschung, Mulheim
̈
̈
̈
an der Ruhr) for electron microscopy characterization.
DEDICATION
ASSOCIATED CONTENT
■
■
Dedicated to Prof. S. Chandrasekaran on the occasion of his
75th birthday.
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acscatal.0c04269.
REFERENCES
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AUTHOR INFORMATION
■
Corresponding Author
Chidambaram Gunanathan − School of Chemical Sciences,
National Institute of Science Education and Research
(NISER), HBNI, Bhubaneswar 752050, India;
orcid.org/0000-0002-9458-5198; Email: gunanathan@
niser.ac.in
Authors
Akash Kaithal − School of Chemical Sciences, National
Institute of Science Education and Research (NISER), HBNI,
Bhubaneswar 752050, India; Max Planck Institute for
Chemical Energy Conversion, 45470 Mülheim an der Ruhr,
Germany
14396
https://dx.doi.org/10.1021/acscatal.0c04269
ACS Catal. 2020, 10, 14390−14397

ACS Catalysis
pubs.acs.org/acscatalysis
Research Article
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14397
https://dx.doi.org/10.1021/acscatal.0c04269
ACS Catal. 2020, 10, 14390−14397