Bridging the Gap: From Homogeneous to Heterogeneous Parahydrogen-induced Hyperpolarization and Beyond

Article abstract of DOI:10.1002/cphc.202001031

Demonstration of parahydrogen-induced polarization effects in hydrogenations catalyzed by heterogeneous catalysts instead of metal complexes in a homogeneous solution has opened an entirely new dimension for parahydrogen-based research, demonstrating its applicability not only for the production of catalyst-free hyperpolarized liquids and gases and long-lived non-equilibrium spin states for potential biomedical applications, but also for addressing challenges of modern fundamental and industrial catalysis including advanced mechanistic studies of catalytic reactions and operando NMR and MRI of reactors. This essay summarizes the progress achieved in this field by highlighting the research contributed to it by our colleague and friend Kirill V. Kovtunov whose scientific career ended unexpectedly and tragically at the age of 37. His role in this research was certainly crucial, further enhanced by a vast network of his contacts and collaborations at the national and international level.

Full text of DOI:10.1002/cphc.202001031

Essays
ChemPhysChem
doi.org/10.1002/cphc.202001031
Bridging the Gap: From Homogeneous to Heterogeneous
Parahydrogen-induced Hyperpolarization and Beyond
[a, b]
[c]
[d]
[e]
Eduard Y. Chekmenev,
Boyd M. Goodson, Valerii I. Bukhtiyarov, and Igor V. Koptyug*
In memoriam Kirill V. Kovtunov
Demonstration of parahydrogen-induced polarization effects in
hydrogenations catalyzed by heterogeneous catalysts instead of
metal complexes in a homogeneous solution has opened an
entirely new dimension for parahydrogen-based research,
demonstrating its applicability not only for the production of
catalyst-free hyperpolarized liquids and gases and long-lived
non-equilibrium spin states for potential biomedical applica-
tions, but also for addressing challenges of modern fundamen-
tal and industrial catalysis including advanced mechanistic
studies of catalytic reactions and operando NMR and MRI of
reactors. This essay summarizes the progress achieved in this
field by highlighting the research contributed to it by our
colleague and friend Kirill V. Kovtunov whose scientific career
ended unexpectedly and tragically at the age of 37. His role in
this research was certainly crucial, further enhanced by a vast
network of his contacts and collaborations at the national and
international level.
It is a curious coincidence that parahydrogen-induced polar-
Nowadays, parahydrogen-based research is mostly driven
by the incentive to develop novel contrast agents for
[1]
ization (PHIP) effects were reported – albeit not yet recognized
as such and interpreted as chemically induced dynamic nuclear
polarization (CIDNP) – in 1983, the same year that Kirill
Kovtunov (Figure 1) was born. The true meaning of the 1983
observations of Bryndza et al. became clear after the publication
[9,10]
biomedical MRI and MRS.
There is, however, another point
of entry to the field of PHIP – through chemical engineering
[2,3]
of the work of Bowers and Weitekamp
in 1986–1987. They
demonstrated, first theoretically and then experimentally, that if
parahydrogen is used in the hydrogenation of acrylonitrile to
propionitrile in a solution of Wilkinson’s organometallic catalyst,
this results in the enhancement of NMR signals. Since then, the
[4,5]
field of PHIP has grown tremendously,
and a number of
remarkable developments of this hyperpolarization technique
have emerged over the last 10 years or so, including PHIP by
[6]
side-arm hydrogenation (PHIP-SAH), signal amplification by
[7]
[8]
reversible exchange (SABRE), SABRE-RELAY, etc.
[
a] Prof. E. Y. Chekmenev
Department of Chemistry, Integrative Biosciences (Ibio)
Wayne State University
Karmanos Cancer Institute (KCI)
Detroit, MI 48202, USA
b] Prof. E. Y. Chekmenev
[
Russian Academy of Sciences
1
4 Leninskiy prospect, Moscow 119991, Russia
[
c] Prof. B. M. Goodson
Southern Illinois University
Department of Chemistry and Biochemistry
Materials Technology Center
Carbondale, IL 62901, USA
d] Prof. V. I. Bukhtiyarov
Boreskov Institute of Catalysis, SB RAS
[
[
Figure 1. Kirill V. Kovtunov (14.01.1983–19.05.2020) was born in Barnaul,
the Altai region of Russia. In 2000–2005 he was a student at the Novosibirsk
State University. After graduation in 2005, he joined the MR microimaging
laboratory at ITC SB RAS as a PhD student. He defended his PhD thesis
entitled “Parahydrogen-induced polarization of nuclear spins in heteroge-
neous catalytic hydrogenation reactions” on June 18, 2008. After that, he
continued to explore this research field further, and defended his
Habilitation thesis entitled “Parahydrogen-induced NMR signal enhancement
in heterogeneous catalysis” on December 25, 2019.
5
Acad. Lavrentiev pr., Novosibirsk 630090, Russia
e] Prof. I. V. Koptyug
ChemPhysChem 2021, 22, 710–715
710
© 2021 Wiley-VCH GmbH

Essays
ChemPhysChem
doi.org/10.1002/cphc.202001031
[3,11]
and catalysis. Already in the first publications on the subject
it was recognized that PHIP can be observed not only for the
reaction products but also for the short-lived intermediates
such as metal dihydride complexes, thereby holding the
potential to unveil the underlying sophistication of reaction
mechanisms. This has been explored later in the context of H
activation by transition metal complexes in solution.
2
[12]
During his undergraduate studies at Novosibirsk State
University (NSU), Kirill was involved in the pulsed-field-gradient
NMR and MRI studies of gas and liquid transport in various
geometries including porous media and microreactors at the
NMR microimaging group at ITC. Other research that was done
by group members included operando studies of catalytic
processes, with a setup designed to place a single catalyst
pellet or a catalyst bed in the probe of a microimaging
instrument to study dynamic redistribution of the liquid phase
in the catalyst and performing MR imaging and spatially
resolved NMR spectroscopy of the reaction progress. Hetero-
geneous hydrogenations, which are widely used in industrial
catalysis, were of primary interest in those studies, and not
surprisingly, the idea to use parahydrogen in these processes
was being entertained for some time. After graduating from
NSU in 2005, Kirill joined the group at ITC as a PhD student.
From then on, his research was about combining magnetic
resonance, catalysis, and parahydrogen.
1
Figure 2. a) H NMR spectra acquired after bubbling parahydrogen through
the C D solution of styrene at 7 T in the presence of polymer-supported
6 6
1
[13]
Wilkinson’s catalyst (top) or after catalyst removal (bottom). b) H NMR
spectrum acquired during gas-solid hydrogenation of propylene with
parahydrogen over silica-supported Wilkinson’s catalyst in the Earth’s
magnetic field. Adapted with permission from Ref. [15] Copyright (2007)
American Chemical Society.
catalyst (Figure 2b). Leaching of the metal complex is not
possible in such gas-solid hydrogenation processes performed
in the absence of any liquid phase. Successful demonstration of
both PASADENA and ALTADENA (Adiabatic Longitudinal Trans-
The main objective for his PhD thesis was to demonstrate
PHIP in heterogeneous hydrogenations, even though it has
[14]
[16]
been pronounced impossible earlier in the literature.
The
port After Dissociation Engenders Nuclear Alignment) effects
solution to this “impossible” problem was sought via the known
bridge between homogeneous and heterogeneous catalysis,
namely by immobilizing PHIP-active organometallic complexes
on a suitable solid support. Despite its deceptive conceptual
simplicity, this approach has proven difficult to implement.
Many unsuccessful attempts to immobilize various Rh and Ir
metal complexes and use them in PHIP experiments resulted in
no catalytic activity, or no PHIP effects, or metal complex
leaching into solution, or all of the above. The breakthrough
came in the end of 2006 when Kirill was visiting the Depart-
ment of Chemistry at UC Berkeley within the framework of a
joint project of the CRDF cooperative grants program imple-
mented by the ITC microimaging team and the group of Alex
Pines.
in those experiments provided an ultimate proof that those
experiments indeed resulted in the first demonstration of PHIP
in heterogeneous catalysis (HET-PHIP).
Coincidentally, this happened at the same location (Depart-
ment of Chemistry, UC Berkeley) where 23 years earlier
homogeneous PHIP effects were observed for the first time.
The PHIP studies with immobilized metal complexes
continue, and by now many other examples have been
demonstrated, for instance the cationic Au complex immobi-
[17]
lized on a metal-organic framework (MOF). Immobilized metal
complexes certainly represent a useful model system which can
provide a useful bridge between homogeneous and heteroge-
neous hydrogenations with parahydrogen and can help in
advancing our understanding of HET-PHIP in general.
The first successful experiments (Figure 2a) were performed
initially with the hydrogenation of styrene in solution using
At the same time, such immobilized metal complexes are
not very stable, particularly at high temperatures and in the
[15]
Wilkinson’s catalyst immobilized on silica or a polymer. In
these experiments, clear PASADENA (PArahydrogen and Syn-
presence of reducing agents such as H , and thus are not used
2
in industrial applications. Instead, much more robust catalysts
such as supported metal NPs are preferred for such reactions.
However, supported and bulk metals were not expected to be
able to achieve pairwise H2 addition to an unsaturated
substrate, which is a major prerequisite for efficient PHIP
[3]
thesis Allow Dramatically Enhanced Nuclear Alignment) effects
were observed for the reaction product ethylbenzene. Impor-
tantly, essentially no PHIP effects were detected once the
catalyst was removed from the slurry, which is very easy to
achieve with these solid materials. While these first successful
observations were encouraging, they were not completely
unambiguous. A more clear-cut proof was thus sought that
PHIP effects were observed in a heterogeneous reaction and
not as a result of metal complex leaching. This was achieved as
well, based on the hydrogenation of propylene into propane
over silica-immobilized cationic Rh complex or Wilkinson’s
production. Indeed, H chemisorption on metals is very efficient
2
but dissociative, and hydrogen atoms are known to be
extremely mobile on the metal surface. Therefore, hydro-
genation would be expected to inevitably involve random H
atoms, making pairwise addition of H impossible. But Kirill was
2
not quite convinced by this common knowledge, and in less
than a year demonstrated both PASADENA- and ALTADENA-
ChemPhysChem 2021, 22, 710–715
www.chemphyschem.org
711
© 2021 Wiley-VCH GmbH

Essays
ChemPhysChem
doi.org/10.1002/cphc.202001031
[
24]
type effects in hydrogenation of propylene to propane over
effects. It is also observed that introduction of a phosphine
ligand to the Cu NPs decreases the catalytic activity markedly
but at the same time NMR signal enhancements become larger.
[18]
supported Pt and Pd NPs. Remarkably, for the very first such
experiments he accidentally used a Pd/Al O catalyst which was
2
3
2
+
[23]
heavily doped with Mn for performing rapid MRI experiments
of hydrogenations and was certainly not intended for para-
hydrogen studies. Luckily, this experiment worked despite the
paramagnetic doping of the catalyst. Later studies also
confirmed that magnetic nature of a catalyst is not necessarily
an obstacle for observing PHIP effects, as demonstrated, for
instance for the catalyst comprising superparamagnetic Co
Observation of HET-PHIP effects with Mo sulfide catalysts
made it possible to study thiophene hydrodesulfurization
reaction, which is a model for industrial purification of fuels.
Other industrially important processes can certainly be ad-
dressed and their mechanisms and kinetics studied.
From the very beginning, a lot of PHIP work was performed
with gases with their rather short polarization lifetimes, usually
below 1 s for hydrocarbon gases at normal pressures. Many
efforts were thus directed at extending these lifetimes, partic-
ularly by exploring the properties of long-lived spin states
(LLSS) at low magnetic fields
hyperpolarized (HP) gases into a liquid state or dissolving them
in liquids, with up to tens of seconds of HP lifetime achieved
this way. Also, alternative ways were explored to produce HP
propane, for instance by hydrogenating cyclopropane with
[19]
nanoparticles on TiO support.
2
Observation of PHIP effects with supported metal NPs
contradicted the commonly accepted Horiuti-Polanyi mecha-
nism of hydrogenation by metals and required some explan-
ation. The one advanced originally was based on the fact that
under realistic conditions the surface of a catalytically active
metal is never clean during the reaction; it is covered with
various species and is thus possibly partitioned into smaller
clean patches of metal so that the reactants are forced to stay
together. This may prevent H atoms from separating freely on
the catalyst surface. However, this explanation has never been
experimentally tested, and recent results show that it may be
[25,26]
and also by condensing
[27]
[28]
parahydrogen. One very recent example of HET-PHIP with
gases is the production of HP diethylether,
[29,30]
an inhalable
anesthetic, by hydrogenation of an unsaturated precursor in
the liquid or in the gas phase, as well as exploring its LLSS in a
low magnetic field. HET-PHIP was also successfully used to
enhance MR imaging experiments, for instance to address gas
flow in various geometries (Figure 4), and to obtain 2D and 3D
[19,20]
incorrect.
Based on these innovative and exciting results, Kirill
defended his PhD thesis in 2008 with flying colors. But the work
certainly didn’t stop there. The scope of HET-PHIP has been
growing ever since, covering all sorts of different catalysts,
which now include various bulk and supported metals (Pt, Pd,
[
31]
maps of product distribution in a model catalytic reactor.
While supported metals do work in PHIP experiments, at
present the achieved polarizations normally do not exceed a
few percent in experiments where significant product yields
have been achieved. Therefore, an active search for better
heterogeneous catalysts continues. One of the current trends is
to explore the so-called single-atom and single site heteroge-
[
21]
Rh, Ir, Au, Ag, Co, Cu), metal oxides (Cr O , CeO , CaO, TiO ),
2
[23]
3
2
2
[22]
carbides (Mo C) and sulfides (MoS2), different particle sizes,
2
[19,20]
various solid supports, substrates, conditions, etc.
One
example is shown in Figure 3 for hydrogenation of propyne
over supported Cu NPs, demonstrating pronounced PHIP
[32,33]
neous catalysts.
PdÀ In NPs supported on Al O . In this system, individual Pd
This can be exemplified by intermetallic
[34]
2
3
atoms are essentially surrounded by inactive In atoms, provid-
ing a single metal atom configuration of the active catalytic
center. And indeed, this catalyst provides substantial polar-
ization levels and reaction yields and is able to enhance the
NMR signals significantly, thus facilitating the MR imaging of
gases (Figure 5).
The scope of the research Kirill was involved in is very
broad. Exploring the concept of PHIP-SAH introduced by Silvio
[
6,35,36]
Aime,
which involves hydrogenation of unsaturated pre-
1
3
cursors followed by hyperpolarization transfer to C nuclei, is
exemplified by the efforts to produce catalyst-free HP liquids or
solutions by hydrogenation of a substrate vapor and its
subsequent dissolution and hydrolysis, for instance, to yield HP
ethanol in solution which never contained any catalyst. In the
context of potential biomedical applications, aqueous hydro-
genations are very important and are being addressed. Other
remarkable achievements include the demonstration of the
unexpected spontaneous SABRE in high magnetic fields and
observation of HET-SABRE with an Ir complex immobilized on a
[
37]
[
38]
[
39]
Figure 3. The reaction scheme of 1-butyne hydrogenation over Cu/SiO
2
1
catalysts, and the H NMR spectra acquired during the reaction while the gas
was flowing (top) and after rapid interruption of the gas flow and
subsequent relaxation of nuclear spins to thermal equilibrium (bottom).
Adapted from Ref. [24] published by The Royal Society of Chemistry in
accordance with the term of the CC-BY 3.0 licence. Copyright (2017) The
Authors.
[40]
solid material. Another approach is to perform SABRE in a
traditional way in solution with subsequent removal of the
dissolved metal complex with a thiol-functionalized porous
[
41]
solid material to produce a clear catalyst-free HP solution.
ChemPhysChem 2021, 22, 710–715
www.chemphyschem.org
712
© 2021 Wiley-VCH GmbH

Essays
ChemPhysChem
doi.org/10.1002/cphc.202001031
Some notable work has been done on polarization transfer to
1
5
N nuclei to extend hyperpolarization lifetimes to many
[42–44]
minutes.
For instance, SABRE of nitrogen-containing drugs
is exemplified by HP fampridine which made it possible to
1
5
15
[45]
perform N MRI at natural abundance of the N isotope.
The joint CRDF project mentioned earlier, in addition to its
successfully achieved primary objective of demonstrating HET-
PHIP effects, encompassed numerous other objectives which
were rather challenging and ambitious. One of those was about
the use of ultralow field NMR to monitor catalytic processes in
metal containers. It has been finally achieved this year, in
collaboration between the Novosibirsk team and the group of
[
46]
Prof. D. Budker at Helmholtz Institute in Mainz. In that study,
unsaturated acetylenic compound was hydrogenated with
parahydrogen in a metal tube and the NMR spectra were
detected with an atomic magnetometer at zero magnetic field,
demonstrating that such approach is indeed promising for
studying heterogeneous systems and for applications in
heterogeneous catalysis. This was one of the last studies in
which Kirill was involved.
For many years now, one of the incentives was to think
outside the box and go beyond parahydrogen, and in particular
to introduce the use of nuclear spin isomers of molecules
(
NSIM) other than H and D for nuclear spin hyperpolarization.
2 2
One remarkable example is the successful chemical enrichment
of NSIM of ethylene by hydrogenation of acetylene with
[47]
parahydrogen.
Ethylene is a symmetric molecule, so to
demonstrate the NSIM enrichment of ethylene, a further
reaction is required to break its symmetry by producing a non-
symmetric product. And indeed, in such an experiment the
PHIP effects were clearly observable for the non-symmetric
product, proving that enrichment of NSIM of ethylene does
take place in acetylene hydrogenation with parahydrogen.
While a more direct experiment to confirm chemical synthesis
of NSIM would be a plus, these preliminary results provide a
clear glimpse into the bright and promising future of NSIM-
based hyperpolarization. Notably, NSIM of ethylene is also a
remarkable example of the molecular long-lived spin states
Figure 4. 3D gradient echo MRI of a spiral tube with continuously flowing
HP propane (a) and static water (b) acquired with 0.5 mm isotropic spatial
voxel resolution in 21.4 s at 4.7 T. A comparable SNR is obtained despite the
dramatic difference in gas and liquid spin densities. Adapted with permission
from Ref. [25]. Copyright (2014) Wiley-VCH Verlag GmbH & Co. KGaA,
Weinheim.
[48]
(LLSS), which are becoming increasingly popular for achieving
spin hyperpolarization storage times (TLLSS) that significantly
[
49]
exceed the conventional spin relaxation times (e.g., T1). In
particular, transferring the singlet spin state of a p-H molecule
2
to a reaction product is a natural way of producing such states,
and the chemical NSIM enrichment of ethylene convincingly
demonstrates such a possibility – the ratio TLLSS/T ~3500
1
measured for ethylene is likely the largest value reported so far
for any molecule except p-H itself.
2
While a lot has been already achieved in bridging the gap
between utilizing parahydrogen in homogeneous and hetero-
geneous processes, this is clearly just the tip of an iceberg.
Further progress in this field requires a much deeper under-
standing of the processes involved, particularly for nano-
particle-based catalysts, and further optimization of catalysts
and reaction conditions to implement these processes with
maximum possible efficiency. The extent of knowledge accu-
mulated to date is already adequate for developing mechanistic
models that are sufficiently realistic to guide further research
Figure 5. a) The reaction scheme for propyne hydrogenation over PdÀ In/
1
Al
2
O
3
catalyst. b) and c) H NMR spectra acquired during the reaction (b)
while the gas was flowing and (c) after an abrupt interruption of the gas
flow and the subsequent relaxation of nuclear spins to thermal equilibrium.
(
d) MR images of a 10 mm NMR tube filled with propylene in thermal
equilibrium (bottom) or hyperpolarized propylene (top). Adapted with
permission from Ref. [34]. Copyright (2018) Wiley-VCH Verlag GmbH & Co.
KGaA, Weinheim.
ChemPhysChem 2021, 22, 710–715
www.chemphyschem.org
713
© 2021 Wiley-VCH GmbH

Essays
ChemPhysChem
doi.org/10.1002/cphc.202001031
and applications in this field. In particular, as revealed by
previous studies, one clear possibility to improve the PHIP
efficiency of heterogeneous catalysts is a broader exploration of
single-site and single-atom catalyst structures. This parallels the
recent trend in fundamental catalysis, and can thus potentially
spearhead future research and applications toward multiple
goals, from producing highly polarized catalyst-free fluids for
advanced spectroscopic and imaging studies to exploring the
mechanistic details of important catalytic transformations.
Future advances in these directions will be the best possible
tribute to the efforts of Kirill Kovtunov to launch and promote
this field of research.
[16] M. G. Pravica, D. P. Weitekamp, Chem. Phys. Lett. 1988, 145, 255–258.
[
[
[
17] K. V. Kovtunov, V. V. Zhivonitko, A. Corma, I. V. Koptyug, J. Phys. Chem.
Lett. 2010, 1, 1705–1708.
18] K. V. Kovtunov, I. E. Beck, V. I. Bukhtiyarov, I. V. Koptyug, Angew. Chem.
Int. Ed. 2008, 47, 1492–1495; Angew. Chem. 2008, 120, 1514–1517.
19] K. V. Kovtunov, V. V. Zhivonitko, I. V. Skovpin, O. G. Salnikov, I. V.
Koptyug, in Magnetic nanomaterials: applications in catalysis and life
sciences (Eds: S. H. Bossmann, H. Wang), The Royal Society of Chemistry,
2017, pp. 142–171.
[
20] V. V. Zhivonitko, K. V. Kovtunov, I. V. Skovpin, D. A. Barskiy, O. G.
Salnikov, I. V. Koptyug, in Understanding organometallic reaction mecha-
nisms and catalysis (Eds: V. P. Ananikov), Wiley-VCH Verlag GmbH & Co.
KGaA, 2014, pp. 145–186.
[
21] K. V. Kovtunov, D. A. Barskiy, O. G. Salnikov, A. K. Khudorozhkov, V. I.
Bukhtiyarov, I. P. Prosvirin, I. V. Koptyug, Chem. Commun. 2014, 50, 875–
878.
[
22] D. B. Burueva, A. A. Smirnov, O. A. Bulavchenko, I. P. Prosvirin, E. Y.
Gerasimov, V. A. Yakovlev, K. V. Kovtunov, I. V. Koptyug, Top. Catal.
2
020, 63, 2–11.
Acknowledgements
[
[
[
[
23] O. G. Salnikov, D. B. Burueva, D. A. Barskiy, G. A. Bukhtiyarova, K. V.
Kovtunov, I. V. Koptyug, ChemCatChem 2015, 7, 3508–3512.
24] O. G. Salnikov, H.-J. Liu, A. Fedorov, D. Burueva, K. V. Kovtunov, C.
Coperet, I. V. Koptyug, Chem. Sci. 2017, 8, 2426–2430.
25] K. V. Kovtunov, M. L. Truong, D. A. Barskiy, I. V. Koptyug, A. M. Coffey,
K. W. Waddell, E. Y. Chekmenev, Chem. Eur. J. 2014, 20, 14629–14632.
26] K. V. Kovtunov, M. L. Truong, D. A. Barskiy, O. G. Salnikov, V. I. Bukhtiyar-
ov, A. M. Coffey, K. W. Waddell, I. V. Koptyug, E. Y. Chekmenev, J. Phys.
Chem. C 2014, 118, 28234–28243.
27] D. B. Burueva, A. S. Romanov, O. G. Salnikov, V. V. Zhivonitko, Y.-W.
Chen, D. A. Barskiy, E. Y. Chekmenev, D. W.-H. Hwang, K. V. Kovtunov,
I. V. Koptyug, J. Phys. Chem. C 2017, 121, 4481–4487.
28] O. Salnikov, K. Kovtunov, P. Nikolaou, L. Kovtunova, V. I. Bukhtiyarov,
I. V. Koptyug, E. Y. Chekmenev, ChemPhysChem 2018, 19, 2621–2626.
29] N. M. Ariyasingha, B. Joalland, H. R. Younes, O. G. Salnikov, N. V.
Chukanov, K. V. Kovtunov, L. M. Kovtunova, V. I. Bukhtiyarov, I. V.
Koptyug, J. G. Gelovani, E. Y. Chekmenev, Chem. Eur. J. 2020, 26, 13621–
I.V.K. thanks RFBR for supporting this research with a number of
grants over the years, including the ongoing grant # 19-29-10003.
B.M.G. and E.Y.C. thank NCI R21CA220137 and NIBIB
1
1
0
1
R01EB029829. E.Y.C. thanks NHLBI R21 HL154032, NSF CHE-
904780, DOD PRMRP W81XWH-15-1-0271 and W81XWH-20-1-
576. B.M.G. thanks NSF CHE-1905341, DOD PRMRP W81XWH-15-
-0272 and W81XWH-20-1-0578. We particularly thank those who
[
made a donation on the PERM 2020 meeting webpage to support
Kirill’s family.
[
[
Conflict of Interest
13626.
[
[
30] O. G. Salnikov, A. Svyatova, L. M. Kovtunova, N. V. Chukanov, V. I.
Bukhtiyarov, K. V. Kovtunov, E. Y. Chekmenev, I. V. Koptyug, Chem. Eur.
J. 2020, V3638, P3638.
31] K. V. Kovtunov, D. Lebedev, A. Svyatova, E. V. Pokochueva, I. P. Prosvirin,
E. Y. Gerasimov, V. I. Bukhtiyarov, C. R. Muller, A. Fedorov, I. V. Koptyug,
ChemCatChem 2019, 11, 969–973.
32] J. Liu, B. R. Bunes, L. Zang, C. Wang, Environ. Chem. Lett. 2018, 16, 477–
505.
33] M. K. Samantaray, V. D’Elia, E. Pump, L. Falivene, M. Harb, S. Ould Chikh,
The authors declare no conflict of interest.
Keywords: parahydrogen-induced hyperpolarization
signal enhancement heterogeneous hydrogenation
immobilized metal complexes · supported metal catalysts
· NMR
·
·
[
[
[
L. Cavallo, J.-M. Basset, Chem. Rev. 2020, 120, 734–813.
34] D. B. Burueva, K. V. Kovtunov, A. V. Bukhtiyarov, D. A. Barskiy, I. P.
Prosvirin, I. S. Mashkovsky, G. N. Baeva, V. I. Bukhtiyarov, A. Y. Stakheev,
I. V. Koptyug, Chem. Eur. J. 2018, 24, 2547–2553.
35] O. G. Salnikov, N. V. Chukanov, R. V. Shchepin, I. V. Manzanera Esteve,
K. V. Kovtunov, I. V. Koptyug, E. Y. Chekmenev, J. Phys. Chem. C 2019,
[
1] P. F. Seidler, H. E. Bryndza, J. E. Frommer, L. S. Stuhl, R. G. Bergman,
Organometallics 1983, 2, 1701–1705.
[
[
[2] C. R. Bowers, D. P. Weitekamp, Phys. Rev. Lett. 1986, 57, 2645–2648.
[3] C. R. Bowers, D. P. Weitekamp, J. Am. Chem. Soc. 1987, 109, 5541–5542.
[4] S. B. Duckett, R. E. Mewis, Acc. Chem. Res. 2012, 45, 1247–1257.
[5] R. A. Green, R. W. Adams, S. B. Duckett, R. E. Mewis, D. C. Williamson,
G. G. R. Green, Progr. NMR Spectr. 2012, 67, 1–48.
123, 12827–12840.
36] N. V. Chukanov, O. G. Salnikov, R. V. Shchepin, K. V. Kovtunov, I. V.
Koptyug, E. Y. Chekmenev, ACS Omega 2018, 3, 6673–6682.
37] O. G. Salnikov, K. V. Kovtunov, I. V. Koptyug, Sci. Rep. 2015, 5, 13930.
38] L. B. Bales, K. V. Kovtunov, D. A. Barskiy, R. V. Shchepin, A. M. Coffey,
L. M. Kovtunova, A. V. Bukhtiyarov, M. A. Feldman, V. I. Bukhtiyarov, E. Y.
Chekmenev, I. V. Koptyug, B. M. Goodson, J. Phys. Chem. C 2017, 121,
15304–15309.
[39] D. A. Barskiy, K. V. Kovtunov, I. V. Koptyug, P. He, K. A. Groome, Q. A.
Best, F. Shi, B. M. Goodson, R. V. Shchepin, A. M. Coffey, K. W. Waddell,
E. Y. Chekmenev, J. Am. Chem. Soc. 2014, 136, 3322–3325.
[40] K. V. Kovtunov, L. M. Kovtunova, M. E. Gemeinhardt, A. V. Bukhtiyarov, J.
Gesiorski, V. I. Bukhtiyarov, E. Y. Chekmenev, I. V. Koptyug, B. Goodson,
Angew. Chem. Int. Ed. 2017, 56, 10433–10437; Angew. Chem. 2017, 129,
10569–10573.
[41] B. E. Kidd, J. L. Gesiorski, M. E. Gemeinhardt, R. V. Shchepin, K. V.
Kovtunov, I. V. Koptyug, E. Y. Chekmenev, B. M. Goodson, J. Phys. Chem.
C 2018, 122, 16848–16852.
[
[
[
[
6] F. Reineri, T. Boi, S. Aime, Nat. Commun. 2015, 6, 5858.
7] R. W. Adams, J. A. Aguilar, K. D. Atkinson, M. J. Cowley, P. I. P. Elliott, S. B.
Duckett, G. G. R. Green, I. G. Khazal, J. Lopez-Serrano, D. C. Williamson,
Science 2009, 323, 1708–1711.
[
[
8] W. Iali, P. J. Rayner, S. B. Duckett, Sci. Adv. 2018, 4, eaao6250.
9] J. Hovener, A. N. Pravdivtsev, B. Kidd, C. R. Bowers, S. Gloggler, K. V.
Kovtunov, M. Plaumann, R. Katz-Brull, K. Buckenmaier, A. Jerschow, F.
Reineri, T. Theis, R. V. Shchepin, S. Wagner, N. M. M. Zacharias, P.
Bhattacharya, E. Y. Chekmenev, Angew. Chem. Int. Ed. 2018, 57, 11140–
1
1162; Angew. Chem. 2018, 130, 11310–11333.
[
[
[
[
10] E. Cavallari, C. Carrera, F. Reineri, Isr. J. Chem. 2017, 57, 833–842.
11] S. B. Duckett, C. J. Sleigh, Progr. NMR Spectr. 1999, 34, 71–92.
12] S. B. Duckett, N. J. Wood, Coord. Chem. Rev. 2008, 252, 2278–2291.
13] I. V. Koptyug, in Spectroscopic Properties of Inorganic and Organometallic
Compounds Vol. 45 (Eds: R. Douthwaite, S. Duckett, J. Yarwood), Royal
Society of Chemistry, Cambridge, 2014, pp. 1–42.
[42] J. R. Birchall, M. S. H. Kabir, O. G. Salnikov, N. V. Chukanov, A. Svyatova,
K. V. Kovtunov, I. V. Koptyug, J. G. Gelovani, B. M. Goodson, W. Pham,
E. Y. Chekmenev, Chem. Commun. 2020, 56, 9098–9101.
[
14] A. Eichhorn, A. Koch, J. Bargon, J. Molec. Catal. A Chem. 2001, 174, 293–
2
95.
[
15] I. V. Koptyug, K. V. Kovtunov, S. R. Burt, M. S. Anwar, C. Hilty, S. Han, A.
[43] R. V. Shchepin, J. R. Birchall, N. V. Chukanov, K. V. Kovtunov, I. V.
Koptyug, T. Theis, W. S. Warren, J. G. Gelovani, B. M. Goodson, S.
Pines, R. Z. Sagdeev, J. Am. Chem. Soc. 2007, 129, 5580–5586.
ChemPhysChem 2021, 22, 710–715
www.chemphyschem.org
714
© 2021 Wiley-VCH GmbH

Essays
ChemPhysChem
doi.org/10.1002/cphc.202001031
Shokouhi, M. S. Rosen, Y.-F. Yen, W. Pham, E. Y. Chekmenev, Chem. Eur.
J. 2019, 25, 8829–8836.
44] O. G. Salnikov, N. V. Chukanov, A. Svyatova, I. A. Trofimov, M. S. H. Kabir,
J. G. Gelovani, K. V. Kovtunov, I. V. Koptyug, E. Y. Chekmenev, Angew.
Chem. Int. Ed. 2021, 60, 2406–2413.
[47] V. V. Zhivonitko, K. V. Kovtunov, P. L. Chapovsky, I. V. Koptyug, Angew.
Chem. Int. Ed. 2013, 52, 13251–13255; Angew. Chem. 2013, 125, 13493–
13497.
[48] P. L. Chapovsky, Quantum Electron. 2019, 49, 623–627.
[49] M. H. Levitt, J. Magn. Reson. 2019, 306, 69–74.
[
[
45] I. V. Skovpin, A. Svyatova, N. V. Chukanov, E. Y. Chekmenev, K. V.
Kovtunov, I. V. Koptyug, Chem. Eur. J. 2019, 25, 12694–12697.
46] D. B. Burueva, J. Eills, J. W. Blanchard, A. Garcon, R. Picazo-Frutos, K. V.
Kovtunov, I. V. Koptyug, D. Budker, Angew. Chem. Int. Ed. 2020, 59,
[
Manuscript received: December 20, 2020
Revised manuscript received: February 19, 2021
Version of record online: April 6, 2021
1
7026–17032.
ChemPhysChem 2021, 22, 710–715
www.chemphyschem.org
715
© 2021 Wiley-VCH GmbH