One to Find Them All: A General Route to Ni(I)-Phenolate Species

Article abstract of DOI:10.1021/jacs.1c03763

The past 20 years have seen an extensive implementation of nickel in homogeneous catalysis through the development of unique reactivity not easily achievable by using noble transition metals. Many catalytic cycles propose Ni(I) complexes as potential reac

Full text of DOI:10.1021/jacs.1c03763

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One to Find Them All: A General Route to Ni(I)−Phenolate Species
̈
Alessandro Bismuto, Patrick Muller, Patrick Finkelstein, Nils Trapp, Gunnar Jeschke,* and Bill Morandi*
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ABSTRACT: The past 20 years have seen an extensive
implementation of nickel in homogeneous catalysis through the
development of unique reactivity not easily achievable by using
noble transition metals. Many catalytic cycles propose Ni(I)
complexes as potential reactive intermediates, yet the scarcity of
nickel(I) precursors and the lack of a general, non-ligand-specific
protocol for their synthesis have hampered progress in this field of
research. This has in turn also limited the access to novel, well-
defined Ni(I) species for the development of new catalytic
reactions. Herein, we report a simple, general route to access a wide variety of Ni(I)−phenolate complexes via an unusual
example of an olefinic Ni(I) complex, [Ni(COD)(OPh*)] (COD = 1,5-cyclooctadiene, OPh* = O(tBu)3C6H2). This route has
proven to be highly efficient for several coordination numbers and ligand classes enabling access to the following complexes:
[Ni(IPr)(OPh*)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), [Ni(dcype)(OPh*)] (dcype = 1,2-bis(dicyclohexyl-
phosphino)ethane), [Ni(dppe)(OPh*)] (dppe = 1,2-bis(diphenylphosphino)ethane), and [Ni(terpy)(OPh*)] (terpy = 2,2′:6′,2″-
terpyridine). Moreover, reacting [Ni(dcype)(OPh*)] with trimethylsilyl triflate has led to the isolation of a unique example of a
cationic binuclear Ni(I)−arene complex. All these complexes have been characterized by single-crystal X-ray, DFT, and EPR
analyses, thus providing crucial experimental and theoretical information about their coordination environment and confirming a d9
electronic structure for all complexes involved. Overall, this new synthetic approach offers exciting opportunities for the discovery of
new stoichiometric and catalytic reactivity as well as the mechanistic elucidation of Ni-based catalytic cycles.
The synthesis of the first Ni(I) compound was reported at
the beginning of the past century by Bellucci and co-workers,
but only structurally characterized many years later.38,39 This
pioneer report has subsequently inspired many research
groups, including Sigman,40 Tilley,41 Johnson,42 and
others,43−54 to develop new protocols for the preparation of
Ni(I) compounds (Scheme 1B). Interestingly, only in 2011,
the first example of a fully characterized olefinic Ni(I) complex
INTRODUCTION
■
The field of catalysis has traditionally been dominated by late-
transition metals such as Pd, Ru, Rh, and Ir, which have
unlocked the development of many catalytic reactions that
have changed everyday life.1−4 For instance, cross-coupling
chemistry has been continually serving as a platform for the
discovery of new drugs and fine chemicals.5−8 Recently, there
has been a drive to explore more abundant elements for
catalysis due to the limited availability of noble metals.9−11
Among others, nickel has shown potential to not only act as a
more sustainable alternative to palladium but also enable
access to new mechanistic manifolds proceeding through less
common oxidation states.12−21 Nickel-catalyzed C−C and C−
N cross-couplings have often been proposed to operate under
a Ni(0)−Ni(II) pathway, usually with the oxidative addition of
the halide or pseudo-halide as a starting point.22−25 However,
recently, Ni(I)−Ni(III) cycles have been increasingly
proposed as alternative pathways (Scheme 1A).26−32 Because
of the limited availability of simple, well-defined Ni(I) sources,
those compounds are usually accessed in situ starting from a
Ni(II) species and an external reductant.33−36 Unfortunately,
the efficiency of this approach is highly dependent on the
ligand used, thus hindering access to optimal catalytic systems
and the discovery of new reactivity. Aside from the synthetic
challenge, Ni(I) complexes also feature a low stability due to
facile disproportionation reactions.37
was reported by Trincado and Gru
̈
tzmacher.55 This complex
has demonstrated remarkable efficiency in catalytic dehydro-
genation. Importantly, a chelating amino-olefin ligand was
crucial to stabilize this otherwise unstable class of complexes.
In 2015, Krossing and co-workers reported the synthesis and
+
characterization of a cationic Ni(COD)2 complex (Scheme
1B).56
Despite this recent progress, the field of nickel(I) chemistry
is still in its infancy when compared to that of more common
oxidation states. We believe the lack of a simple, versatile Ni(I)
precursor that could be easily converted to a wide variety of
Received: April 9, 2021
Published: July 12, 2021
© 2021 The Authors. Published by
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phenoxy radical (1) led to an immediate color change from
blue to red with complete conversion within 2 h (Figure 1a).
Scheme 1. Context of the Work: (A) State-of-the-Art for
Nickel Catalysis; (B) Previous Examples of Nickel(I)
Species; (C) This Work
Figure 1. Synthesis and characterization of complex 2. (a) Synthesis
and X-ray structure of complex 2. (b) Continuous-wave (cw) EPR
spectrum of a frozen solution of complex 2 in toluene at X-band (9.74
GHz) at a temperature of 20 K (black) and simulation (red) with gx =
2.0195, gy = 2.0389, gz = 2.4363. Experimental parameters: Microwave
power 0.02 mW; modulation amplitude: 0.1 mT (100 kHz
modulation frequency); time constant 1.28 ms. (c) Field-swept
echo-detected EPR spectrum recorded at 9.73 GHz, 10 K (black) and
its simulation (red) revealing a majority component (64%) with large
gz strain (0.12) and with gx = 2.0255, gy = 2.0449, gz = 2.3100 together
with the component (36%) that dominates the derivative-type cw
EPR spectrum.
well-defined Ni(I) catalysts has hampered reaction discovery in
this area. Aside from this aspect, a general route to Ni(I)
complexes could also help shed light on the often-debated
mechanisms in nickel catalysis. The discovery of a universal
and simple route to a variety of Ni(I) species bearing a diverse
set of catalytically relevant ligands would thus greatly impact
organonickel chemistry and the field of catalysis.
Herein, we report the first general protocol that can mediate
the formation of Ni(I)−L species in good to high yields in a
single step (Scheme 1C). Key to the success of this was the
isolation and full characterization of a rare example of an
olefinic Ni(I) complex.55,56 This protocol can serve as a
platform for synthesizing a plethora of well-defined nickel(I)
complexes in a modular manner, thus promoting new research
avenues in nickel chemistry.
Single-crystal X-ray structure analysis unambiguously con-
firmed the identity of this Ni(I) phenolate species. The nickel
center presents a pseudo-trigonal-planar geometry with slightly
elongated Ni−C bonds compared to those of zerovalent
LNi(COD) species. The strong donation of the phenolate
moiety results in one of the shortest Ni−O single bonds
reported (Ni−O, 1.804(1) Å). Interestingly, despite the
expected sp2-hybridization around the oxygen, the Ni−O−
CAr angle is nearly linear, 179.60(9)°. This unusual behavior
has been previously observed in other complexes and explained
as a combination of electronic and crystal packing effects.41
However, we cannot rule out any distortion related to a Ni−
COD orbital interaction.41
To gain more insights into the electronic structure of this
rare example of Ni(I)−olefin complex, we performed density
functional theory (DFT) analysis. Single-point energy
calculations were run at the PBE0 def2-QZVPP(Ni,P)/def2-
TZVPP(other atoms) level of theory by using optimized
structures computed at the PBE0 def2-TZVP(Ni)/def2-SVP
(other atoms) level.59 The optimized geometry reveals a
similar angle (Ni−O−CAr, 168.5°) in the gas phase when
RESULTS AND DISCUSSION
■
In light of the widespread use and versatility of Ni(COD)2
complexes as Ni(0) precursors, we reasoned that the synthesis
of a stable Ni(I) olefin complex would be key to the
development of a new platform for Ni(I) chemistry.55
Accordingly, we started our investigation through single-
electron oxidation of a Ni(0) precursor with heteroatom
centered radicals.57 Because of the ease of undesirable
overoxidation to a stable Ni(II) species, the choice of the
oxidant was crucial. For instance, the reaction of Ni(COD)2
with TEMPO leads to a nickel(II) compound with a η2-
coordinate NO fragment.58 In contrast, a bulkier radical such
as 2,4,6-tris-tert-butylphenoxy should efficiently avoid over-
oxidation due to the increased steric bulk of the resulting Ni(I)
complex.57 Indeed, the reaction between Ni(COD)2 and the
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compared to the solid-state structure, hinting at a more
complicated effect than crystal packing (see the Supporting
Information, Table S1). The Mulliken spin population analysis
showed 90% of the spin population localized on Ni, mainly in
the d orbitals (see Table S6). This is similar to that of cationic
Scheme 2. Syntheses of Ni(I) Complexes
+
Ni(COD)2 and in line with previously reported metal-
centered radicals.60 The Ni−CCOD distances, experimental
+
and calculated, were compared to those of Ni(COD)2 ,
showing on average shortened bonds (see Table S1).56 This is
presumably due to the higher back-donation compared to the
cationic complex.
To confirm the d9 configuration of complex 2, we performed
EPR spectroscopy (Figure 1). The continuous-wave (cw) EPR
spectrum of complex 2 (Figure 1b), recorded in toluene at 20
K, revealed a slightly rhombic g tensor with gx, gy < gz, in line
with an approximate |x2−y2⟩ ground state of a 3d9 species with
S = 1/2. The fitted principal values of the g tensor (gx = 2.020,
gx = 2.039, and gz = 2.44) are surprisingly similar to those of
Ni(COD)2 (2.047, 2.061, and 2.390).56 Schwab et al.
+
reported a minor second component with smaller gz and
larger gz strain both in frozen solution and in a powder.60,61
Because signals with large g strain may go unnoticed in the
derivative-mode CW EPR spectra and are better seen in
absorption spectra, we acquired a field-swept echo-detected
EPR spectrum at 10 K. This spectrum (Figure 1c) showed
similar values of the g tensor to those of the frozen solution.62
It did, however, indeed contain a second component with
smaller gz and larger gz strain that in our case turned out to be
the majority component (64%).
All the complexes were structurally characterized by single-
crystal X-ray analysis (Figure 2). Complexes 3 and 4 feature a
It is worth noting that complex 2 is a rare example of a
structurally characterized Ni(I)−olefin species, which have
long been sought after.55,56 Interestingly, complex 2 shows
higher stability both in solution and in solid phase when
compared to that of halido analogues, which decompose within
minutes in the absence of free COD.51 This makes complex 2
an ideal candidate to become a general source of Ni(I) in
organonickel chemistry.
Once we had fully characterized complex 2, bearing a labile
alkene fragment, we wondered whether this complex could be
used as a central platform for the synthesis of both established
and new Ni(I) complexes bearing a broad diversity of ligands
and coordination numbers. To demonstrate its versatility, we
evaluated three general classes of ligands that are widely
employed in catalysis: phosphine, N-heterocyclic carbene
(NHC), and pyridine. In situ generated complex 2 smoothly
reacted with each ligand to generate the corresponding
products in good to excellent yields (Scheme 2). Both
bidentate phosphines, dcype (1,2-bis(dicyclohexylphosphino)-
ethane) and dppe (1,2-bis(diphenylphosphino)ethane), gave
the corresponding nickel(I) species, 3 and 4, in 81% and 89%
isolated yield regardless of the change in electronics. The
reaction with a monodentate NHC ligand also resulted in good
yield (complex 5, 80%), giving access to a two-coordinate 13-
electron compound. This unusually low coordination number
is of great interest due to the high propensity of such species to
undergo oxidative addition reactions.45 This class of complexes
has been previously only accessed via reduction with KC8 or
other strong reductants of the nickel(II) halo precursor in a
multistep synthesis, clearly highlighting the unique modularity
of our new synthetic approach.27,41,64 Finally, the efficiency of
this protocol was also tested on a tridentate nitrogen-based
ligand, terpy (2,2′:6′,2″-terpyridine), allowing the isolation of
complex 6 in 51% yield.
Figure 2. Molecular structures of 3 and 4 (A and B, respectively, top)
and 5 and 6 (C and D, respectively, bottom) in the solid state.
Ellipsoids are drawn at 50% probability; hydrogen atoms are omitted
for clarity. Selected bonds and angles (four independent moieties in
5): Ni−O[Å]: 3, 1.834(4); 4, 1.808(2); 5, 1.805(2), 1.818(3),
1.800(2), 1.820(3); 6, 1.915(3). C(1)−O−Ni [deg]: 3, 164.2(9); 4,
172.1(2); 5, 140.8(2), 140.9(2), 142.2(2), 138.6(2); 6, 129.7(3).
three-coordinate planar geometry with similar Ni−O bond
length (1.834(4) Å for complex 3, 1.808(2) Å for complex 4)
with, however, a different C(1)−O−Ni angle (164.2(9)° for
complex 3 vs 172.1(2)° for complex 4). The P−Ni bond
distance and angles are in agreement with previously reported
ones.65 The solid-state structure of complex 5 shows four
symmetry-independent molecules in the asymmetric unit
arranged in a pseudo-linear two-coordinate geometry, with an
average Ni−O bond distance of 1.81 Å and an average O−Ni−
C(2) angle of 168.0°. The C(1)−O−Ni angle has an average
of 140.6°, which is consistent with an sp2-hybridized oxygen
atom and the previous example reported by Tilley and co-
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workers.41 Complex 6 displays a distorted square-planar
geometry with the phenolate ligand pointing out of the plane
by 8.5(2)°. The Ni−O bond length is 1.915(3) Å, which is
elongated compared to those of complexes 3, 4, and 5. This
has been previously explained by the noninnocent behavior of
the terpyridine moiety.21
In contrast, complex 6 gave a cw EPR spectrum with the
expected intensity (Figure 4a) and with principal values of the
Next, the geometries of the complexes were optimized, and
single-point energies were calculated by DFT.59 The Mulliken
spin density analysis suggested that all complexes are best
described as Ni(I) species with metal-centered radicals. The
smallest values were obtained for complexes 3 and 4 (both
0.81), possibly due to delocalization over the phosphorus
atoms (see Tables S7 and S8). Complexes 5 and 6 instead
showed a higher localization with predicted values of 0.93 and
1.29, respectively (see Tables S9 and S10).
Figure 4. (a) Continuous-wave (cw) EPR spectrum of complex 6
obtained at X-band frequency (9.68 GHz) at 78 K. (b) HYSCORE
spectrum obtained at 9.69 GHz, 15 K, and a field of 331.7 mT of a
frozen solution of complex 6 in toluene.
The cw EPR spectra of complexes 3 and 4 (Figure 3, a and
b, respectively) showed very similar features. The g tensor
g tensor (gx = 2.052, gy = 2.090, and gz = 2.207) quite similar to
the ones in complexes 3 and 4 and to previously reported
analogues.66 The large line width in this spectrum is mainly
due to unresolved hyperfine coupling on the order of 25−40
MHz to the three directly coordinated 14N nuclei. However, g
strain appears to contribute significantly, especially at gz, also
explaining the only moderate quality of the line shape fit. The g
tensor principal values are surprisingly similar to the ones
found for [Cu(tpy-d2)2Cl2] in ethanol-d6 (gx = 2.028, gy =
2.096, and gz = 2.260).67
The HYSCORE spectrum (Figure 4b) does not reveal the
14N hyperfine couplings that would contribute in the negative
quadrant (not shown). The isotropic deuterium hyperfine
coupling of 0.72 MHz determined by W-band ENDOR and X-
band HYSCORE for the most strongly coupled o-deuterons in
the [Cu(tpy-d2)2Cl2] complex in 1:1 ethanol/dichloromethane
translates to a proton coupling of 4.7 MHz, whereas a coupling
of 5.6 MHz can be read off the spectrum in Figure 3b.67 Taken
together, the cw EPR and HYSCORE spectrum indicate a
rather similar electronic structure and spin density distribution
in complex 6 and [Cu(tpy-d2)2Cl2], which are both 3d9 species
with an approximate |x2−y2⟩ ground state.
Figure 3. Continuous-wave (cw) EPR spectra of frozen solutions of
complexes 3 (a) and 4 (b) in toluene at X-band frequencies (9.39
GHz) at 78 K (black) and simulations (red) assuming a rhombic g
tensor and anisotropic hyperfine couplings to two 31P nuclei (for
parameters, see Table S12). Experimental parameters: microwave
power 1.616 mW (a), 0.6325 mW (b); modulation amplitude: 0.2 mT
(100 kHz modulation frequency); time constant 1.28 ms.
principal values agree within experimental uncertainty (gx ≈
2.053, gy ≈ 2.075, and gz ≈ 2.215; see Table S12) and again
reveal a 3d9 species with S = 1/2 and an approximate |x2−y2⟩
ground state. The difference is in the 31P hyperfine tensors,
which are nearly axial and rather similar for the two
phosphorus atoms in 3 and rhombic and rather dissimilar for
the two phosphorus atoms in complex 4. This stronger
deviation from a symmetric distribution around the two
phosphorus atoms can be seen directly in the line shape. The
symmetry breaking arises from a torsion of the P−Ni−P plane
with respect to the phenyl plane of the phenolate ligand (∼85°
for dcype, ∼80° for dppe) together with a tilt of the P−Ni−P
angle bisector with respect to the Ni−O bond that leads to a
difference between the two O−Ni−P angles by about 7° in
both cases. We assign the stronger influence on the 31P
hyperfine couplings in the dppe case to the more facile
distribution of spin density into the phenyl substituents as
compared to the cyclohexyl substituents.
Once we had established a synthetic route for these nickel(I)
species, we investigated their reactivity in catalysis. Taking
inspiration from a recent work of Matsubara,31 we decided to
undertake a Buchwald−Hartwig amination using 4-
bromobenzophenone and diphenylaniline as benchmark
substrates (Scheme 3). After a preliminary optimization of
Scheme 3. Catalytic Buchwald−Hartwig Amination with
Complexes 3, 4, 5, and 6
Unfortunately, despite repeated attempts, we were unable to
obtain an EPR spectrum of complex 5 in frozen solution. We
did observe weak signals of paramagnetic species in line with a
Ni(I) 3d9 species, but the spectra proved to be poorly
reproducible, even when preparing the solution with freshly
distilled toluene and sealing the sample tube immediately.
However, the paramagnetic NMR was in agreement with a
previously reported analogue,41 and we obtained an EPR
spectrum with the expected amplitude from the microcrystal-
line powder in a sealed tube (see Figure S2).
the reaction conditions, we were able to successfully perform
this transformation obtaining the product in 77% isolated yield
using complex 3 as the catalyst. To select the best catalytic
system, we then evaluated the performance of the other
complexes. Most of the complexes gave moderate to good
yields with the exception of complex 6. Future work will
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evaluate the mechanism, the functional group tolerance, and
versatility of this protocol.
and toluene (equal volume fractions) at 80 K corresponds to a
3d9 S = 1/2 species with rhombic g tensor and an approximate
|x2−y2⟩ ground state (see Figure S4). However, a HYSCORE
spectrum reveals substantial 14N hyperfine couplings, strongly
suggesting that acetonitrile replaced toluene as a ligand (see
Figure S4), leading to a paramagnetic, potentially mononuclear
species.
We then wondered about the lability of the phenolate
fragment, particularly whether it would be possible to extrude
it to open a free coordination site and generate a highly
reactive Ni(I) species. We decided to use complex 3 as a
benchmark complex. Addition of Me3SiOTf to this compound
in toluene gave formation of complex 7 as a red powder in
more than 90% yield (Figure 5). Surprisingly, in contrast to
CONCLUSIONS
■
In summary, we have developed a new general protocol for the
synthesis of challenging and novel Ni(I) compounds starting
from a simple and rare example of an olefinic Ni(I) complex.
Reaction of this precursor with a variety of mono-, bi-, and
tridentate ligands has led to the isolation of the corresponding
Ni(I) complexes. All the compounds were structurally
characterized by single-crystal X-ray analysis, DFT calculations,
and EPR spectroscopy to confirm a d9 electronic structure for
all complexes involved. In addition, the first example of a Ni(I)
̈
analogue of Porschke’s complex has been reported. In a
broader context, we anticipate that this new, versatile platform
to access Ni(I) complexes will open new research avenues in
nickel catalysis and will play an important role in elucidating
the mechanistic relevance of Ni(I) species in catalysis.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c03763.
■
sı
Figure 5. Synthesis and characterization of complex 7.
what has been reported by Hillhouse using 1,2-bis(di-tert-
butylphosphino)ethane as ligand, we did not obtain a
mononuclear nickel complex with triflate in the inner
coordination sphere.68 Single-crystal X-ray analysis revealed
instead this compound to be a binuclear nickel complex held
together by a central coordinating toluene fragment. The two
[(dcype)Ni] moieties are antifacial, with the toluene fragment
plane almost perpendicular to the P−Ni−P plane. Because of
disorder of the toluene fragment on a special position, precise
information about the aromatic bond lengths cannot be
recovered, and thus the mode of coordination remains unclear.
The very short Ni−CAr distances, observed between 2.0 and
2.5 Å (without further interpretation or assignment of
connectivity within the disorder), hint to a potential activation
of the toluene. Although a similar complex with a guanidinato
ligand has been reported, this type of Ni(I)−arene complex
has been rarely isolated with phosphine ligands.69 We believe
that this complex could be considered as a Ni(I) analogue of
Details of experimental and computational procedures
and spectroscopic data and copies of EPR/NMR spectra
(PDF)
Cartesian coordinates of the optimized structures (XYZ)
Accession Codes
CCDC 2075543−2075548 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Gunnar Jeschke − Laboratorium fu
̈
r Physikalische Chemie,
ETH Zurich, 8093 Zurich, Switzerland; orcid.org/0000-
̈
̈
0001-6853-8585; Email: gunnar.jeschke@
phys.chem.ethz.ch
Porschke’s Ni(0) complex.70 The solid-state structures show in
̈
Bill Morandi − Laboratorium fu
Zurich, 8093 Zurich, Switzerland; orcid.org/0000-0003-
3968-1424; Email: bill.morandi@org.chem.ethz.ch
̈
r Organische Chemie, ETH
fact nearly identical geometry and Ni−CAr bond lengths,
suggesting an analogous η2-coordination of the aromatic
fragment.
̈
̈
In the interest of understanding the electronic nature of this
compound, we pursued DFT and EPR studies. Computational
analysis revealed that the two Ni(I) centers are antiferromag-
netically coupled with the broken-symmetry solution being
lower in energy than the triplet state by 57 kJ/mol.59 To
further investigate, we performed solid-state EPR spectroscopy
which showed only weak intensity (see Figure S3). Because of
this and the absence of the expected zero-field splitting, we
cannot assign this spectrum to complex 7, which is in line with
a predominant, antiferromagnetic singlet nickel(I) dimer. To
gain more insight into the properties of this species, we
performed EPR measurements in a frozen solution. The EPR
spectrum of a shock-frozen solution in a mixture of acetonitrile
Authors
Alessandro Bismuto − Laboratorium fu
ETH Zurich, 8093 Zurich, Switzerland; orcid.org/0000-
0002-5840-1144
Patrick Muller − Laboratorium fu
Zurich, 8093 Zurich, Switzerland
Patrick Finkelstein − Laboratorium fu
ETH Zurich, 8093 Zurich, Switzerland
Nils Trapp − Laboratorium fur Organische Chemie, ETH
Zurich, 8093 Zurich, Switzerland
̈
r Organische Chemie,
̈
̈
̈
̈
r Organische Chemie, ETH
̈
̈
̈
r Organische Chemie,
̈
̈
̈
̈
̈
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c03763
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(18) Meucci, E. A.; Ariafard, A.; Canty, A. J.; Kampf, J. W.; Sanford,
M. S. Aryl−Fluoride Bond-Forming Reductive Elimination from
Nickel(IV) Centers. J. Am. Chem. Soc. 2019, 141 (33), 13261−13267.
(19) Camasso, N. M.; Sanford, M. S. Design, synthesis, and carbon-
heteroatom coupling reactions of organometallic nickel(IV) com-
plexes. Science 2015, 347 (6227), 1218−1220.
Author Contributions
A.B. and P.M. contributed equally to this work.
Funding
The Swiss National Science Foundation (SNSF 184658) and
̈
ETH Zurich are acknowledged for financial support.
(20) Maher, A. G.; Liu, M.; Nocera, D. G. Ligand Noninnocence in
Nickel Porphyrins: Nickel Isobacteriochlorin Formation under
Hydrogen Evolution Conditions. Inorg. Chem. 2019, 58 (12),
7958−7968.
(21) Wagner, C. L.; Herrera, G.; Lin, Q.; Hu, C. T.; Diao, T. Redox
Activity of Pyridine-Oxazoline Ligands in the Stabilization of Low-
Valent Organonickel Radical Complexes. J. Am. Chem. Soc. 2021, 143
(14), 5295−5300.
(22) Zell, T.; Fischer, P.; Schmidt, D.; Radius, U. C-Br Activation of
Aryl Bromides at Ni0(NHC)2: Stoichiometric Reactions, Catalytic
Application in Suzuki-Miyaura Cross-Coupling, and Catalyst Degra-
dation. Organometallics 2012, 31 (14), 5065−5073.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the NMR and X-ray departments of ETH Zu
̈
rich for
technical assistance. All the authors thank Dr. Michael J.
Cowley for fruitful discussions. We also thank the Morandi
group for proofreading.
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