Activation of Aryl Halides by Nickel(I) Pincer Complexes: Reaction Pathways of Stoichiometric and Catalytic Dehalogenations

Article abstract of DOI:10.1021/acs.inorgchem.6b01448

Homolytic C-X bond cleavage of organohalides by the T-shaped nickel(I) complexes [LigNi^I] 1 bearing the iso-PyrrMeBox ligand had been found previously to be the crucial activation step in the asymmetric hydrodehalogenation of geminal dihalides. Here, this mechanistic investigation is extended to aryl halides, which allowed a systematic study of the activation process by a combination of experimental data and density functional theory modeling. While the activation of both aryl chlorides and geminal dichlorides appears to proceed via an analogous transition state, the generation of a highly stabile nickel(II)aryl species in the reaction of the aryl chlorides for the former represents a major difference in the reactive behavior. This difference was found to have a crucial impact on the activity of these nickel pincer systems as catalysts in the dehalogenation of aryl chlorides compared to geminal dichlorides and highlights the importance of the regulatory pathways controlling the nickel(I) concentration throughout the catalysis. These results along with the identification and characterization of novel nickel(II)aryl species are presented.

Full text of DOI:10.1021/acs.inorgchem.6b01448

Article
pubs.acs.org/IC
Activation of Aryl Halides by Nickel(I) Pincer Complexes: Reaction
Pathways of Stoichiometric and Catalytic Dehalogenations
Christoph A. Rettenmeier, Jan Wenz, Hubert Wadepohl, and Lutz H. Gade*
Anorganisch-Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: Homolytic C−X bond cleavage of organo-
halides by the T-shaped nickel(I) complexes [LigNiI] 1
bearing the iso-PyrrMeBox ligand had been found previously
to be the crucial activation step in the asymmetric hydro-
dehalogenation of geminal dihalides. Here, this mechanistic
investigation is extended to aryl halides, which allowed a
systematic study of the activation process by a combination of
experimental data and density functional theory modeling.
While the activation of both aryl chlorides and geminal
dichlorides appears to proceed via an analogous transition
state, the generation of a highly stabile nickel(II)aryl species in the reaction of the aryl chlorides for the former represents a major
difference in the reactive behavior. This difference was found to have a crucial impact on the activity of these nickel pincer
systems as catalysts in the dehalogenation of aryl chlorides compared to geminal dichlorides and highlights the importance of the
regulatory pathways controlling the nickel(I) concentration throughout the catalysis. These results along with the identification
and characterization of novel nickel(II)aryl species are presented.
corresponding nickel(I) complexes and thus allows the
systematic investigation of their reactivity.
INTRODUCTION
■
The activation of organic halogen compounds by low-valent
metal complexes presents one of the most fundamental reaction
steps in organometallic chemistry and has been investigated
extensively.1 Reactions with molecular nickel(0) and nickel(I)
species have been studied in great detail in pioneering work by
Cassar,2 Kochi,3 and Espenson,4 which has shaped our
understanding of such reaction steps. These feature in more
sophisticated reaction sequences of nickel-catalyzed trans-
formations such as dehalogenations5 or C−C cross-coupling
reactions.6
The aim of this study was to further our understanding of the
activation of organohalides by the T-shaped nickel(I) complex
1. This had previously been found to be the key activation step
in the asymmetric hydrodehalogenation of geminal dihalides
(Scheme 1).8 However, the high rates of reaction between
these dihalide substrates and the nickel(I) complex led us to
extend our investigation to aryl halides, allowing us to gain a
more complete picture of these transformations. In this work,
we report a combined experimental and computational study of
In comparison to its heavier homologue palladium, nickel has
shown a greater variety of accessible oxidation states, frequently
favoring one-electron redox processes in the activation of
halogen compounds over concerted two-electron steps.7 This
greater diversity in the reactive behavior of nickel may lead to a
change in the reaction mechanism of a given type of
transformation upon going from one catalyst to another.
Detailed insight into such reaction pathways is thus essential for
the development of more effective catalysts.
Scheme 1. Proposed Mechanism for the Catalytic Cycle of
the Hydrodehalogenation of Geminal Dihalogenides
Recently, we reported the asymmetric hydrodehalogenation
of geminal dihalides8 catalyzed by nickel(I)/nickel(II) hydride
complexes bearing the iso-PyrrMeBox ligand.9 This ligand
system combines the advantageous sterical features of a chiral
bisoxazoline pincer ligand with a delocalized electronic π-
system almost identical to that of hydrocorphins found in
cofactor F430 of methyl coenzyme M reductase.10 In contrast
to most ligand systems with isolated hard nitrogen donor
atoms, the delocalized π-electron system stabilizes the
Received: June 15, 2016
© XXXX American Chemical Society
A
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these reactions along with the synthesis and characterization of
novel nickel(II) aryl species.
coordination plane spanned by the three nitrogens and the aryl
carbon donors, thus reducing the extent of steric repulsion of
the two Ph substituents and the aryl ligand. The latter is
oriented in a near-perpendicular manner with respect to the
coordination plane to allow efficient π-back-bonding and
minimal interligand repulsion [N−Ni−C−C torsion angles of
−84.0° (4-F), −77.3° (4-H), and −84.6° (4-OMe)]. In all
three cases, the aryl ligand is slightly tilted out of the
coordination plane [176.5° (4-F), 174.3° (4-H), and 166.6°
(4-OMe)]. The presence of neither the electron-withdrawing
fluoro nor the electron-donating methoxy para substituent at
the phenyl ligand causes significant differences in the Ni−C
bond lengths.
In all three complexes, the protons in α-position to the
oxazolines’ substituents are located in close proximity of the
face of the aryl ligand. The corresponding chemical shifts of the
1H nuclear magnetic resonance (NMR) spectra were found to
be strongly affected by the electronic nature of the different aryl
ligands, which proved useful for their identification and
quantification in mixtures.
RESULTS AND DISCUSSION
■
This study focuses first on the preparation and characterization
of arylnickel(II) complexes via substitution of the correspond-
ing halide precursors, followed by a mechanistic study of their
generation via the stoichiometric reaction of NiI complexes
with aryl halides. This is followed by an investigation into the
corresponding catalytic conversion and the way in which the
accumulation of aryl−nickel species may be developed into a
preparative method. Finally computational modeling of
reaction pathways governing the hydrodehalogenation of
geminal alkyl dihalides provides additional mechanistic insight
into this previously reported reaction.
Synthesis and Structural Characterization of iso-
PyrrMeBox−Nickel−Aryl Complexes. Nickel(I) complex 1
reacted with aryl halides in a formal bimolecular oxidative
addition giving the corresponding nickel(II)halogenido and aryl
complexes in equimolar quantities (Scheme 2).11
Stoichiometric and Catalytic C−X Bond Activation
Using iso-PyrrMeBox−Nickel(I) Complex 1. The nature of
the halide had a strong influence on the reaction rate of the
stoichiometric transformation depicted in Scheme 2, the
general trend being the following: I > Br > Cl > F. In fact,
C−F activation could be observed only for the reactive
hexafluorobenzene, while monofluorobenzene was stable even
at elevated temperatures.13b Among the para-substituted phenyl
chlorides, those bearing electron-withdrawing groups reacted
faster than the derivatives with electron-donating groups (OMe
< Me < H < F < CF3). A Hammett correlation of this series of
reactions gave a ρ value of 3.0 (Figure 2a). The value is lower
than that obtained by Kochi et al. in the case of nickel(0)
complexes (ρ = 5.4)3 but is similarly interpreted to reflect the
feasibility of accepting electron density from the electron rich
nickel(I) complex during the transition state (see below). Initial
rate kinetics for the reaction of p-chlorofluorobenzene and
nickel(I) complex 1 showed a linear dependency on both the
complex and chloroaryl concentrations [k = (5.0 0.5) × 10−3
M−1 s−1 (Figure 2b,c)]. The Eyring plot based on the reaction
in the temperature range from 10 to 50 °C gave values for the
activation barrier of 20.4 kcal mol−1 for ΔG⧧295 K and 14.2 kcal
mol−1 for ΔH (Figure 2d). Upon reaction of 2,4,6-tri-tert-butyl-
1-bromobenzene with nickel(I) complex 1, isomerization was
observed,8 consistent with an intermediate formation of the
organo radical, and the alkyl species 5 was the organometallic
product formed as reported previously (Scheme 4).8
Scheme 2. Bimolecular Oxidative Addition of Aryl Halides to
Two Independent Nickel(I) Centers
As will be discussed below, this type of transformation not
only models a key step in the catalytic hydrodehalogenation of
halocarbons but also may be developed into an efficient
synthetic protocol for the preparation of aryl−nickel complexes
that are difficult to access via conventional substitution of the
halide compounds using aryllithium, Grignard, or related aryl
transfer reagents.
The nickel halogenido complexes 2 and 3 described
previously8 represent a convenient starting point for the
synthesis of aryl and alkyl12 nickel(II) complexes via reaction
with the corresponding Grignard reagents as shown in Scheme
3. Accordingly, a series of diamagnetic para-substituted
Scheme 3. Synthetic Route to Nickel(II)aryl Complexes
These results are consistent with the observations made by
Kochi et al.3 and Espenson et al.4a on low-valent nickel
complexes and strongly support the idea of a C−X bond
activation process involving a partial electron transfer to the
aryl halides resulting in the formation of organic radical
intermediates (vide infra). However, a key aspect of whether
nickel(III) species are involved in the activation process
remained unclear. To shed light on this issue, a computational
study [density functional theory (DFT), ub3lyp/6-311G(d,p)]
of this initial reaction step was performed. A transition state was
nickel(II)phenyl complexes 4-OMe, 4-Ph, and 4-F as well as
pentafluorophenyl species 4-F5 were synthesized and charac-
terized. The molecular structures of complexes 4-OMe, 4-Ph,
and 4-F were determined by X-ray structure analysis and are
shown in Figure 1. The molecular structures show the typical
characteristics of nickel(II) complexes of the iso-PyrrMeBox
ligand13 and of other nickel(II)aryl pincer complexes.14 The
backbone of the pincer is slightly twisted relative to the
1
found (S = /2) for the activation of p-chlorofluorobenzene
(Figure 4) analogous to that described by Budzelaar et al.15 for
cobalt(I) complexes in which the nickel(I) complex attacks the
halogen atom with an almost linear Ni···Cl···C atom arrange-
ment (Ni···Cl, 2.309 Å; C···Cl, 2.289 Å; Ni···Cl···C, 154.4°).
The elongation of the C···Cl bond indicates that a significant
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Figure 1. Molecular structures of aryl complexes 4-F, 4-H, and 4-OMe. Only one of the independent molecules is shown for 4-F and 4-H. Hydrogen
atoms have been omitted for the sake of clarity. Footnote a denotes that the averages over values of all the independent molecules in the unit cell are
given and that standard uncertainties are those of the individual values.
electron transfer from the nickel(I) center to the antibonding
orbital has occurred (Figure 3).
organoradical generated in the initial step. Therefore, the
catalytic hydrodehalogenation of geminal dihalides occurs
efficiently only at a relatively high concentration of hydrido
complex 6 and a very low concentration of nickel(I) complex 1,
which is continuously regenerated through the elimination of
H2 from two nickel hydrido complexes 6.8 In the case of
geminal dihalides, the nickel(I) concentration is decreased by
the reaction of the organoradical with the nickel(I) complex
itself. The reaction of 2,2-dichlorotetrahydronaphthalene with
two molecules of nickel(I) complex 1 gives almost
quantitatively chlorido complex 2, which is part of the actual
catalytic cycle of the hydrodehalogenation.8
On the other hand, the aryl chlorides react with the nickel(I)
complex in the bimolecular oxidative addition described above
leading to nickel(II)aryl complexes that were found to be stable
under the reaction conditions [no reaction was observed when
complex 4-F was exposed to H2 (5 bar), nickel hydrido
complex 6 (in the presence of 5 bar of H2), or LiEt3BH even at
100 °C]. In the course of the catalysis, these aryl complexes
accumulate at the expense of the catalytically active nickel
species and thereby lead to the experimentally observed low
level of conversion in the actual hydrodehalogenation (Figure
5).
In fact, a near-quantitative formation of the aryl species from
the nickel halogenido complex can be achieved under these
conditions. For simple aryl halides that lead to complexes that
are often directly accessible by the reaction of the
corresponding Grignard reagent with a nickel halogenido
complex (Scheme 2), this methodology is of little synthetic use.
However, we were able to apply the bimolecular oxidative
addition to obtain more sophisticated target molecules, whose
synthesis proved to be difficult using organomagnesium species.
The di- and tetrametalated aryl compounds 7 and 8 were
synthesized using the corresponding aryl bromides and
nickel(I) complex 1 (Figure 6).
In the case of the latter, suitable single crystals for a single-
crystal X-ray structure analysis were obtained (Figure 7).
Besides minor deviations, all four LigNi fragments are
equivalent and are tilted with respect to the central
tetraazaperopyrene plane. The homochiral centers at the
oxazoline ring of the pincers generate the overall D2 symmetry
of the molecule with a broken local C2 symmetry in the LigNi
fragments that is reflected in the NMR spectra of 8.
After the homolytic cleavage of the C−Cl bond, the initial
products formed are the chlorido complex and the p-
fluorophenyl radical. Interestingly, the addition of the latter
to the nickel(II)halogenido complex giving a nickel(III) species
(Scheme 5) is energetically favored {Δ(ΔG) = 16 kcal mol−1 [S
= 1/2 (Figure 3)]} and appears to proceed in an almost barrier-
free manner (see the Supporting Information). However,
attempts to locate a transition state that directly links the NiI
species to such a nickel(III) complex were not successful.
Given these results, a stabilization of the organoradical
formed in the initial activation by coordination to the
simultaneously generated nickel(II) chlorido complex appears
to be likely to occur (Scheme 5).
Possibly, the capture of the phenyl radical by the nickel(II)
complex competes with its diffusion out of the solvent cage
immediately after the C−Cl bond activation step. This would
be analogous to the scenario described by Kochi et al., who
observed the partial formation of nickel(I) species in the
reaction of aryl halides with the tetrakis(triethylphosphine)-
nickel(0) complex.3 Nevertheless, in both cases, diffusion or
capture of the phenyl radical, the subsequent reaction with the
second molecule of the nickel(I) complex is expected to give
the bimolecular oxidative addition products observed exper-
imentally (see above). DFT modeling generally overestimates
the energy barriers for the activation of aryl chlorides [ΔG⧧
298 K
= 27.0 kcal/mol (DFT) compared to ΔG⧧295 K = 20.4 kcal/mol
(Eyring analysis)] for chlorofluorobenzene; however, the
relative reaction rates (krel, Hammett plot) correlate well with
the calculated values (Figure 4).
Catalytic Dehalogenation of Aryl Halides: Accumu-
lation of Aryl−Nickel Species. The hydrodehalogenation of
the aryl chlorides can be performed catalyically using LiEt3BH
as a reductant and the nickel(I) complex as catalyst; however,
the activity of the catalyst for this class of substrates is poor
compared to the previously reported hydrodehalogenation of
geminal dichlorides (Scheme 1).8 The main reason for the
decrease in activity becomes apparent only when considering
the regulating pathways that control the concentration of the
active nickel(I) species in the hydrodehalogenation of geminal
dihalides (Scheme 6). The latter not only is crucial for the
activation of the substrate itself but also competes very
effectively with the nickel hydrido species to react with the
C
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Scheme 4. Isomerization during the Bimolecular Oxidative
Addition of the Sterically Very Demanding 2,4,6-Tri-tert-
butyl-1-bromobenzene to Nickel(I) Complexes 18
Figure 3. Results of the DFT modeling [UB3LYP/6-311G(d,p)] on
the activation of p-chlorofluorobenzene by nickel(I) complex 1: (top)
geometry and SOMO (natural orbital) of the transition state and
(bottom) energy profile of the total activation process (brackets
indicate a close association of both molecules). The organoradical
formed may either diffuse into solution or be captured to form a
corresponding nickel(III) species.
Scheme 5. Proposed Reversible Coordination of the Aryl
Radical to the Nickel Chlorido Complex To Give a
Nickel(III) Intermediate
Figure 2. (a) Hammett plot using the relative rates (krel) of the
reaction of nickel(I) complex 1 with the para-substituted chlor-
ophenyls (-CF3, -F, -H, -Me, and -OMe) in C6D6 at 295 K. (b and c)
Initial rate kinetics on the activation of chlorofluorobenzene by varying
the p-chlorofluorobenzene and complex concentrations, respectively.
(d) Eyring plot of the reaction over the temperature range of 10−50
°C.
D
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Figure 4. Correlation between relative reaction rates krel and the
activation energies of the rate-determining step obtained from the
modeling.
Figure 5. Course of the catalytic hydrodehalogenation of p-
chlorofluorobenzene with LiEt3BH and chlorido complex 2 as a
catalyst (10 mol %) monitored by 19F NMR spectroscopy. After an
induction period, in which the nickel(I) complex is generated via the
elimination of H2, the catalytic hydrodehalogenation takes place,
during which nickel(II)aryl complex 4-F accumulates.
Scheme 6. Regulatory Pathways for the Concentration of the
Nickel(I) Species in the Case of (A) Geminal Dichlorides
and (B) Aryl Chlorides
Figure 6. Dimetalated biphenyl 7 and tetrametalated tetraazaperopyr-
ene 8 synthesized via the direct reaction of nickel(I) complex 1 with
the corresponding aryl bromides.
obenzene], reflecting the experimentally observed rapid
reaction of geminal dichlorides with the nickel(I) complex.
Notably, the corresponding transition states for the activation
of 2-chlorotetrahydronaphthalene (both enantiomers) were
disfavored by roughly 5−7 kcal/mol [21.8 kcal/mol (S) and
21.4 kcal/mol (R) (see the Supporting Information)], which is
in agreement with the relatively slow reaction of 2-
chlorotetrahydronaphthalene with 1 and high selectivity for
the monohydrodehalogenation during the catalytic reduction of
geminal dihalides observed experimentally.8
Besides the differences in the activation energies for the aryl
and alkyl chlorides, additional insights, which concern the
subsequent H-transfer as it occurs during the catalytic
hydrodehalogenation of geminal dichlorides, were gained by
the DFT study. While the coordination of the aryl radical to
nickel(II)chlorido complex 2 forming the nickel(III) species
leads to a large stabilization (Figure 3), in the case of the alkyl
radical, on the other hand, only a relatively small energy gain
results from its coordination to the metal center (Figures 9 and
10).
Computational Modeling of the Hydrodehalogena-
tion of Geminal Alkyl Dihalides. The computational studies
were extended to the activation of 2,2-dichlorotetrahydronaph-
thalene by nickel(I) complex 1, which was found to react
rapidly to a mixture of 1,2-dihydronaphthalene and 1,4-
dihydronaphthalene as well as the nickel(II)chlorido complex8
to establish whether similar initial activation paths exist in both
cases. Indeed, two diastereomeric transition states analogous to
those described above were found (Figure 8). For both, the
activation barrier was calculated to be significantly lower than
for the aryl chlorides [17.0 kcal/mol (pro-R) and 15.3 kcal/mol
(pro-S) compared to 27.0 kcal/mol for the p-fluorochlor-
Assuming a low barrier for the homolytic Ni−C bond
dissociation [as found in the case of Ni3−Cl-dia_r (see the
E
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Figure 9. DFT-modeled geometries of nickel(III) species Ni3−Cl-
dia_r and Ni3−H-dia_r (one of two diastereomeric structures is
depicted).
The consequences of the significant difference in the stability
between aryl and alkyl nickel(III) complexes toward homolytic
cleavage of the Ni−C bond for the hydrodehalogenation are
not yet fully understood. A reversible addition of the
corresponding organic radicals to the nickel(II) halogenido
complexes may be accessible in both cases; however, the degree
to which such a stabilizing interaction actually occurs may
determine the mechanism subsequent to the activation step of
the halogen compound.
In the case of the aryl chlorides, the possibility that the
relatively high stability of the nickel(III) species allows a
chloride/hydride exchange at the nickel(III) center by LiEt3BH
followed by a subsequent elimination of the corresponding
benzene cannot be ruled out [attempts to optimize the
modeled structure of a nickel(III) species with a hydride and p-
fluorophenyl ligand led directly to the elimination of
fluorobenzene].
Figure 7. Molecular structure of tetrametalated tetraazaperopyrene 8.
Only one of two independent molecules is shown. Hydrogen atoms
have been omitted for the sake of clarity. Selected bond lengths
(angstroms) and angles (degrees): Ni−C, 1.881(5)−1.940(5); Ni−
N(pyr), 1.916(5)−1.982(5); Ni−N(oxaz), 1.857(6)−1.912(5); C−
Ni−N(pyr), 158.8(2)−174.4(2); C−Ni−N(oxaz), 86.3(2)−91.6(2).
CONCLUSION
■
The experimental and computational investigation of the
activation of aryl halides by nickel(I) complex 1 provided
insight into the basic steps involved in this transformation.
Furthermore, by extending the DFT investigation to geminal
dichlorides that appear to react via an analogous activation step,
we were able to model a complete catalytic cycle for the
enantioselective hydrodehalogenation of geminal dihalides that
is consistent with the previous experimental study. Besides the
main reaction cycle, other regulatory pathways that control the
crucial ratio between the nickel(I)- and nickel(II)hydrido
species 1 and 6 during the reaction exist. In the case of the aryl
halides, this regulation is dysfunctional, and instead of the
nickel(I) species being transformed to the hydrido complex, a
stable nickel(II)aryl complex is formed that accumulates and
does not re-enter the catalytic cycle, leading to the eventual halt
of the catalytic conversion.
Figure 8. DFT-modeled transtion states for the C−Cl bond activation
and the subsequent H-transfer (one of two diastereomeric transition
states is depicted).
Supporting Information)], a rapid diffusion of the alkyl radical
into solution would be expected to occur. These findings are in
accordance with the experimental investigation into the
reversible addition of alkyl radicals to (1,4,8,11-
tetraazacyclotetradecan)nickel(II) complexes by Espenson et
al.16 and by Meyerstein et al.17 as well as the theoretical
investigation by Kozlowski et al. on bipyridine nickel complexes
as catalysts in photoredox cross-coupling reactions.18 Attempts
to synthesize aryl or alkyl nickel(III) species of this type were
not successful;19 however, the potential involvement of
nickel(III) intermediates was indicated by the in situ
observation of EPR resonances in frozen tetrahydrofuran
(THF) of the ongoing hydrodehalogenation of 2,2-dichlorote-
trahydronaphthalene with LiEt3BH and nickel(I) complex 1 as
a catalyst (Supporting Information), although the actual nature
of the EPR active species as well as its role in the catalysis
remains elusive.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations of air- and moisture-
sensitive materials were performed under an inert atmosphere of dry
argon (Argon 5.0 purchased from Messer Group GmbH and dried
over Granusic phosphorpentoxide granulate) using standard Schlenk
techniques or by working in a glovebox. The solvents were dried over
sodium (toluene), potassium (hexane), or a sodium/potassium alloy
(pentane and diethyl ether), distilled, and degassed prior to being
used.20 Deuterated solvents were purchased from Deutero GmbH and
F
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Figure 10. Energy and free energy profiles of the activation of 2,2-dichlorotetrahydronaphthalene by nickel(I) complex LigNiI (1) and the
subsequent H-transfer by hydrido complex LigNiH (6) to give 2-chlorotetrahydronaphthalene. The geometries of the crucial steps of the reaction
path marked in blue are depicted (representing only one of the two diastereomeric geometries in each case; brackets indicate a close association of
both molecules).
or from Euriso-Top GmbH, dried over potassium (C6D6, toluene-d8,
and THF-d8), vacuum distilled, degassed, and stored in Teflon valve
ampules under argon. Hydrogen 5.0 (Messer Group GmbH) was used
as purchased without further purification. The phenyl-substituted 2,5-
bis(oxazolinylmethyl)pyrrole protioligands9a as well as complexes
LigNiI (1),8 LigNiCl (2),8 and LigNiBr (3)8 were synthesized
according to literature procedures. All other reagents were obtained
from commercial sources and used as received unless explicitly stated
otherwise. Air-sensitive samples for NMR spectroscopy were prepared
under argon in 5 mm Wilmad tubes equipped with J. Young Teflon
by the analytical service of the Heidelberg Chemistry Department
using the vario EL and vario MIKRO cube analytical devices. Mass
spectra were recorded on Bruker ApexQe hybrid 9.4 T FT-IVR (HR-
ESI, HR-DART) and JEOL JMS-700 magnetic sector (HR-FAB, HR-
EI, LIFDI) spectrometers at the mass spectrometry facility of the
Organic Department at the University of Heidelberg. Either 3-
nitrobenzyl alcohol (NBA) or o-nitrophenyloctyl ether (NPOE) was
used as the matrix in the FAB-MS measurements. X-ray diffraction
analysis was performed at the laboratory for structural analysis of the
Inorganic Chemistry Department at the University of Heidelberg
under the supervision of Prof. Dr. Wadepohl. An Agilent Technologies
Supernova-E CCD (Cu Kα or Mo Kα X-radiation, microfocus tube,
and multilayer mirror optics) and a Bruker AXS Smart 1000 CCD
diffractometer (Mo Kα radiation, graphite monochromator, and λ =
0.71073 Å) were used for data acquisition. UV/vis spectra were
recorded on a Varian Cary 5000 UV/vis/NIR spectrometer.
Preparation of Complex LigNiC6F5 (4-F5). A solution of
bromido complex 3 (69 mg, 0.13 mmol), chloropentafluorobenzene
(0.70 mmol, 5.3 equiv), and magnesium (0.82 mmol, 6.2 equiv) in 5
mL of THF was stirred at room temperature for 30 min. After removal
of the solvents, a toluene/pentane mixture (1/15) was added, and the
reaction mixture was stirred for 4 h and subsequently filtered. After
removal of the solvents, the crude was recrystallized from a THF/
pentane mixture at −40 °C to give a yellow crystalline solid in 84%
yield (68 mg). The synthesis of 4-F5 was also performed using
previously prepared Grignard reagent BrMgC6F5 in THF instead of
1
valves. H and 13C NMR spectra were recorded on Bruker Avance
(200 MHz), Bruker Avance II (400 MHz), and Bruker Avance III (600
MHz, equipped with a CryoProbe) NMR spectrometers and were
referenced internally using the residual protio solvent (1H) or solvent
(13C).21 The appearance of the signals was described using the
following abbreviations: s, singlet; d, doublet; dd, doublet of doublet;
ddd, doublet of doublet of doublet; dt, doublet of triplets; t, triplet; q,
quartet; m, multiplet; b, broad signal. Continuous-wave X-band (∼9
GHz) EPR spectra were recorded using a Bruker Biospin Elexsys E500
EPR spectrometer fitted with a super high Q cavity. The magnetic field
and the microwave frequency were calibrated with a Bruker ER 041XK
Teslameter and a Bruker microwave frequency counter. The
temperature of the sample was adjusted using a flow-through cryostat
in conjunction with a Eurotherm (B-VT-2000) variable-temperature
controller. EPR spectral simulations were conducted using the XSophe
software (Bruker, version 1.1.4). Elemental analyses were performed
G
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1
the one-pot methodology described above: H NMR (C6D6, 600.130
4 H, H1,1′); 13C NMR (C6D6, 150.903 MHz, 295 K) δ 171.4 (C2),
165.0 (C4), 157.2 (C14), 144.7 (C7), 144.6 (C11), 137.3 (C12), 128.3
(C9), 127.1 (C10), 126.2 (C8), 111.7 (C13), 81.3 (C3), 73.4 (C5), 69.4
(C6), 54.8 (C15), 31.0 (C1); HR-MS (FAB+) calcd for
C31H29N358NiO2 m/z 549.1562, found m/z 549.1541. Elemental
Anal. Calcd for C31H29N3NiO2: C, 67.66%; H, 5.31%; N, 7.64%.
Found: C, 67.68%; H, 5.20%; N, 7.65.
MHz, 295 K) δ 7.10 (m, 4 H, H9), 7.05 (m, 2 H, H10), 6.65 (m, 4 H,
H8), 5.03 (s, 2 H, H3), 3.70 (dd, J = 9.0 Hz, J = 3.0 Hz, 2 H, H6),
3.45 (dd, 2J = 8.3 Hz, 3J = 8.5 Hz, 2 H, H5), 3.45 (dd, 2J = 8.3 Hz, 3J =
3.0 Hz, 2 H, H5′), 2.14−2.00 (m, 4 H, H1,1′); 13C NMR (C6D6,
3
3
150.903 MHz, 295 K) δ 172.2 (C2), 166.0 (C4), 149.1 (C12/13/14, JCF
1
1
= 231.3 Hz), 142.9 (C7), 138.4 (C12/13/14, JCF = 231.3 Hz), 135.3
(C12/13/14, 1JCF = 231.3 Hz), 128.8 (C9), 127.9 (C10), 125.2 (C8), 116.1
(C11), 81.6 (C3), 73.4 (C5), 69.9 (C6), 30.7 (C1); 19F NMR (C6D6,
376.273 MHz, 295 K) δ −116.6 (m, 2 F, F12/13), −161.2 (m, 1 F, F14),
−163.9 (m, 2 F, F12/13); HR-MS (FAB+) calcd for C30H22F5N358NiO2
m/z 609.0986, found m/z 609.1052. Elemental Anal. Calculated for
C30H22F5N3NiO2: C, 59.05%; H, 3.63%; N, 6.89%. Found: C, 59.05%;
H, 3.78%; N, 6.96%.
Preparation of Dinuclear Complex 4,4′-[LigNi]2biphenyl (7).
To a solution of 4,4′-dibromobiphenyl (15 mg, 0.048 mmol) and 3 mL
of THF was added a solution of nickel(I) complex 1 (0.202 mmol, 4.2
equiv in 2 mL of THF) at room temperature. After 1 h, LiEt3BH (0.1
mmol, 2.1 equiv) was added and the solution was concentrated and
stirred at 60 °C for 30 min to convert generated nickel hydrido species
6 into nickel(I) complex 1. Additional 4,4′-dibromobiphenyl (6.4 mg,
0.02 mmol, 0.42 equiv) was added, and the reaction mixture was
stirred at room temperature for 30 min. Again, LiEt3BH was added
(0.07 mmol), and the solvents were removed. The residue was treated
with a toluene/pentane mixture (2/1), and the solution was filtered.
After removal of the solvents, the residue was dissolved in toluene and
the product was precipitated with pentane at −40 °C to give a yellow
solid in 50% yield (52 mg): 1H NMR (C6D6, 600.130 MHz, 295 K) δ
7.44 (d, 3J = 7.7 Hz, 4 H, H12), 7.21 (d, 3J = 7.6 Hz, 4 H, H13), 7.11−
7.02 (m, 12 H, H9,10), 6.90 (d, 3J = 7.8 Hz, 8 H, H8), 5.21 (s, 4 H, H3),
4.16 (dd, 3J = 8.2 Hz, 3J = 8.5 Hz, 4 H, H6), 3.57 (dd, 2J = 8.4 Hz, 3J =
Preparation of p-Fluorphenyl Complex LigNiC6H4F (4-F). To
a solution of chlorido complex 2 (192 mg, 0.40 mmol) in 20 mL of
THF was added p-fluorophenylmagnesium bromide (0.48 mmol, 1.2
equiv) at 0 °C. After 10 min, the cooling bath was removed and the
reaction mixture was stirred for an additional 5 min. After removal of
the solvents, the residue was treated with a toluene/pentane mixture
(1/15) and the solution was filtered. After removal of the solvents, the
crude was recrystallized from a toluene/pentane mixture at −40 °C to
give a yellow crystalline solid in 77% yield (165 mg): 1H NMR (C6D6,
3
3
600.130 MHz, 295 K) δ 7.10 (dd, J = 8.2 Hz, JFH = 6.8 Hz, 2 H,
H12), 7.08−7.00 (m, 6 H, H9,10), 6.79 (d, J = 6.7 Hz, 4 H, H8), 6.54
3
2
3
8.4 Hz, 4 H, H5), 3.43 (dd, J = 8.2 Hz, J = 2.3 Hz, 4 H, H5′), 2.19
(m, 8 H, H1′1); 13C NMR (C6D6, 150.903 MHz, 295 K) δ 171.6 (C2),
166.0 (C4), 156.5 (C14), 144.7 (d, C7), 138.0 (C12), 136.5 (C11), 128.4
(C9), 127.2 (C10), 126.3 (C8), 123.2 (C13), 81.3 (C3), 73.4 (C5), 69.4
(C6), 31.0 (C1); HR-MS (FAB+) calcd for C60H52N658Ni2O4 m/z
1036.2757, found m/z 1036.2710. Elemental Anal. Calcd for
C60H52N6Ni2O4: C, 69.39%; H, 5.05%; N, 8.09%. Found: C,
68.92%; H, 5.03%; N, 7.98.
(dd, 3J = 8.2 Hz, 4JFH = 9.9 Hz, 2 H, H13), 5.17 (s, 2 H, H3), 3.84 (dd,
3J = 8.5 Hz, 3J = 2.0 Hz, 2 H, H6), 3.55 (dd, 3J = 8.5 Hz, 2J = 8.1 Hz, 2
H, H5), 3.43 (dd, 2J = 8.1 Hz, 3J = 2.3 Hz, 2 H, H5′), 2.34−2.10 (m, 4
H, H1,1′); 13C NMR (C6D6, 150.903 MHz, 295 K) δ 171.5 (C2), 166.1
(C4), 161.6 (d, JCF = 238.6 Hz, C14), 149.7 (d, JCF = 2.9 Hz, C11),
1
4
144.4 (C7), 137.5 (d, JCF = 5.0 Hz, C12), 128.4 (C9), 127.3 (C10),
2
126.1 (C8), 111.8 (d, JCF = 17.8 Hz, C13), 81.3 (C3), 73.4 (C5), 69.3
3
(C6), 31.0 (C1); 19F NMR (C6D6, 376.273 MHz, 295 K) δ 123.9 (m);
HR-MS (FAB+) calcd for C30H26FN358NiO2 m/z 537.1363, found m/
z 537.1350. Elemental Anal. Calcd for C30H26FN3NiO2: C, 66.94%; H,
4.87%; N, 7.81%. Found: C, 66.43%; H, 4.53%; N, 7.68.
Preparation of Tetranuclear Complex 4,7,11,14-[Lig-
Ni]4TAPP (8). To a solution of 9-bisperfluoropropyl 4,7,11,14-
tetrabromo-1,3,8,10-tetraazaperopyrene (29 mg, 0.030 mmol) in 30
mL of THF was added a solution of nickel(I) complex 1 (132 mg,
0.298 mmol, 8.9 equiv) at 0 °C, and the mixture was stirred for 10 h.
After removal of the solvents, the residue was treated with toluene and
stirred and pentane was added to precipitate the product. After
filtration, the crude was recrystallized from a THF/Et2O/pentane
mixture at room temperature to give a red crystalline solid in 38% yield
Preparation of Phenyl Complex LigNiPh (4-H). To a solution
of chlorido complex 2 (113 mg, 0.24 mmol) in 5 mL of THF was
added PhMgCl (0.31 mmol, 1.3 equiv) at 0 °C. After 5 min, the
cooling bath was removed and the reaction mixture was stirred for an
additional 5 min. After removal of the solvents, the residue was treated
with a toluene/pentane mixture (1/20) and the solution was filtered.
After removal of the solvents, the crude was recrystallized from a
toluene/pentane mixture (1/30) at −40 °C to give a yellow crystalline
solid in 41% yield (50 mg): 1H NMR (C6D6, 600.130 MHz, 295 K) δ
7.35 (m, 2 H, H12), 7.11−7.01 (m, 6 H, H9,10), 6.90−6.84 (m, 5 H,
1
(28 mg): H NMR (C6D6, 600.130 MHz, 295 K) δ 9.44 (s, 4 H,
H
TAPP), 7.83 (d, 3J = 7.5 Hz, 8 H, H8), 7.58 (dd, 3J = 7.4 Hz, 3J = 7.3
Hz, 8 H, H9), 7.42 (t, 3J = 7.3 Hz, 4 H, H10), 6.49 (t, 3J = 7.2 Hz, 4 H,
H20), 6.37 (dd, 3J = 7.4 Hz, 3J = 7.3 Hz, 8 H, H19), 5.72 (d, 3J = 7.4 Hz,
8 H, H18), 5.39 (s, 4 H, H3/13), 5.31 (s, 4 H, H3/13), 4.57 (dd, 3J = 8.5
Hz, 3J = 2.5 Hz, 4 H, H6), 4.18 (dd, 2J = 8.2 Hz, 3J = 8.6 Hz, 4 H, H5),
3.87 (dd, 2J = 8.2 Hz, 3J = 8.6 Hz, 4 H, H5′), 3.60 (dd, 3J = 8.0 Hz, 3J =
H
8,14), 6.74 (m, 2 H, H13), 5.19 (s, 2 H, H3), 4.00 (dd, 3J = 8.6 Hz, 3J =
2.1 Hz, 2 H, H6), 3.56 (dd, 3J = 8.6 Hz, 2J = 8.0 Hz, 2 H, H5), 3.45 (dd,
2J = 8.0 Hz, J = 2.2 Hz, 2 H, H5′), 2.18 (m, 4 H, H1,1′); 13C NMR
3
2
3
1.6 Hz, 4 H, H16), 3.45 (dd, J = 8.2 Hz, J = 8.3 Hz, 4 H, H15), 2.98
(dd, 2J = 8.0 Hz, 3J = 1.9 Hz, 4 H, H15′), 2.53−2.29 (m, 16 H,
H1,1′,11,11′); 13C NMR (C6D6, 150.903 MHz, 295 K) δ 172.5 (C2/1212),
172.4 (C2/12), 166.1 (C14), 165.7 (C4), 160.7 (CTAPP), 160.4 (CTAPP),
144.9 (C7), 142.2 (C17), 138.2 (CHTAPP), 129.4 (C9), 127.8 (C10),
127.6 (CTAPP), 127.3 (C19), 126.7 (C8), 126.4 (C20), 124.7 (C18),
122.1 (CTAPP), 119.0 (CTAPP), 112.7 (CTAPP), 81.8 (C3/13), 80.8
(C3/13), 73.8 (C5), 73.6 (C15), 69.4 (C6,16), 31.1 (C1,11); 19F NMR
(C6D6, 376.273 MHz, 295 K) δ −79.7 (t, 3J = 10.6 Hz, 6 F), −106.2 to
−110.3 (m, 4 F), −123.5 (m, 4 H); HR-MS (ESI+) calcd for
C124H92F14N1658Ni4O8 m/z 2430.4474, found m/z 2430.4484.
Elemental Anal. Calcd for C124H92F14N16Ni4O8: C, 61.17%; H,
3.81%; N, 9.20. Found: C, 61.38%; H, 4.17%; N, 9.30.
(C6D6, 150.903 MHz, 295 K) δ 171.4 (C2), 166.1 (C4), 158.9 (C14),
144.7 (C7), 137.8 (C12), 128.4 (C9), 127.2 (C10), 126.2 (C8), 125.1
(C13), 122.4 (C11), 81.3 (C3), 73.4 (C5), 69.4 (C6), 54.8 (C15), 31.0
(C1); HR-MS (FAB+) calcd for C30H27N358NiO2 m/z 519.1457,
found m/z 519.1465. Elemental Anal. Calcd for C30H27N3NiO2: C,
69.26%; H, 5.23%; N, 8.08%. Found: C, 69.09%; H, 5.24%; N, 7.94.
Preparation of p-Methoxyphenyl Complex LigNiC6H4OMe
(4-OMe). To a solution of chlorido complex 2 (100 mg, 0.21 mmol)
in 10 mL of Et2O and 5 mL of toluene was added p-
methoxyphenylmagnesium bromide (0.25 mmol, 1.2 equiv) at −78
°C. After 5 min, the cooling bath was removed and the reaction
mixture was stirred for an additional 30 min. After removal of the
solvents, the residue was treated with a toluene/pentane mixture (1/6)
and the solution was filtered. After removal of the solvents, the crude
was recrystallized from a toluene/Et2O/pentane mixture at −40 °C to
give a yellow crystalline solid in 88% yield (101 mg): 1H NMR (C6D6,
600.130 MHz, 295 K) δ 7.15 (d, 3J = 8.6 Hz, 2 H, H12), 7.10−7.05 (m,
4 H, H9), 7.05−7.02 (m, 2 H, H10), 6.88 (d, 3J = 7.2 Hz, 4 H, H8), 6.49
(d, 3J = 8.6 Hz, 2 H, H13), 5.20 (s, 2 H, H3), 4.04 (dd, 3J = 8.5 Hz, 3J =
2.1 Hz, 2 H, H6), 3.60 (dd, 2J = 8.1 Hz, 3J = 8.5 Hz, 2 H, H5), 3.49 (s,
3 H, H15), 3.47 (dd, 2J = 8.1 Hz, 3J = 2.1 Hz, 2 H, H5′), 2.26−2.12 (m,
Catalytic Hydrodehalogenation of p-Chlorofluorobenzene
(NMR experiment). A NMR sample was prepared using p-
chlorofluorobenzene (13.1 mg, 0.1 mmol), LiEt3BH (0.21 mmol),
complex 2 (4.8 mg, 0.01 mmol, 10 mol %), and 1,4-bis-
(trifluoromethyl)benzene as an internal standard in 0.5 mL of THF-
d8, and the reaction was monitored by 19F NMR spectroscopy.
Initial Rate Determination of the Reaction of Nickel(I)
Complex 1 with p-Chlorofluorobenzene. The order of the
reaction of 1 with p-chlorofluorobenzene was determined by initial
H
DOI: 10.1021/acs.inorgchem.6b01448
Inorg. Chem. XXXX, XXX, XXX−XXX

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Article
rate measurements in a series of kinetic experiments using 19F NMR
spectroscopy. Therefore, the concentration of 1 and later of p-
chlorofluorobenzene was varied in two series of NMR measurements
at 295 K in C6D6.
In the first series, a solution of p-chlorofluorobenzene (5 mg) and
1,4-dimethoxybenzene as an internal standard in 0.2 mL of C6D6 was
added to a solution of nickel(I) complex 1 (1.25, 2.5, 5.0, 7.5, 10.0,
12.5, and 15.0 mg) in 0.4 mL of C6D6, respectively, and the reaction
was monitored by 19F NMR spectroscopy. In a second series, a
solution of nickel(I) complex 1 (5.0 mg) in 0.2 mL of C6D6 was added
to a solution of p-chlorofluorobenzene (2.5, 5, 7.5, 10, 12.5, and 15
mg) and 1,4-dimethoxybenzene in 0.4 mL of C6D6, respectively.
Additionally, the temperature dependence of the initial rate was
probed using 5 mg of 1 and 5 mg of p-chlorofluorobenzene (0.6 mL of
C6D6) at 283, 303, 313, and 333 K. The initial rate of each run was
determined by fitting (least-squares, no constraints) the general
function of a second-order reaction (reaction 1) to the data obtained
from the NMR measurements (intensity of the 19F NMR signal
corresponding to aryl complex 4-F vs time). The value of the first
derivative of the fitted function at y = 0 was used as the initial rate that
was plotted versus the concentration of 1 or p-chlorofluorobenzene.
a − {a(a − b) exp[k(a − b)(x − c)]}
/{a × exp[k(a − b)(x − c)] − b}
Figure 11. Observed diffraction patterns (simulated precession
pictures) of 8·xTHF: (a) (h0l), a* horizontal, c* vertical; (b) (hk0);
(c) (hk1); and (d) (hk2). Intensities in panels c and d are multiplied
by 23 with respect to those in panel b. The overall intensity
distribution of (hk3) in panel c is similar to that of (hk4) in panel b.
No background or LP corrections were applied.
(1)
Determining the Relative Rates of Reaction of Differently
Substituted Chlorobenzenes with the Nickel(I) Complex and
the Hammett Correlation. The relative rates of the reaction of para-
substituted chlorobenzenes (R = MeO, CH3, H, F, or CF3) with
nickel(I) complex 1 under pseudo-first-order conditions were
determined in three separately performed competition experiments
(A, F and MeO; B, F, H, and CH3; C, F and CF3). Therefore, an
excess of the corresponding p-chlorobenzenes (0.339 mmol each, 10
equiv each) was dissolved in 12 mL of THF and the mixture held at
295 K. A solution of the nickel(I) complex (15.0 mg, 0.034 mmol) in 2
mL of THF was added, and the reaction mixture was stirred for 16 h.
The solvent was removed, and the residue was analyzed by NMR
spectroscopy in C6D6. The ratio of the integrals of the H6 proton
signals [for R = MeO, H, and F, see above; the complexes with R = Me
(H6 = 4.07 ppm) and CF3 (H6 = 3.75 ppm) were not separately
prepared and isolated] was used for a Hammett plot (Figure 2a).
Crystallographic Data. Crystal data and details of the structure
determinations are listed in Table S1 (Supporting Information). Full
shells of intensity data were collected at low temperatures with an
Agilent Technologies Supernova-E CCD diffractometer (Cu Kα
radiation, microfocus X-ray tube, multilayer mirror optics). Detector
frames (typically ω-scans, occasionally φ-scans, scan width of 1°) were
integrated by profile fitting.22,23 Data were corrected for air and
detector absorption and Lorentz and polarization effects23 and scaled
essentially by application of appropriate spherical harmonic
functions.24,25 Absorption by the crystal was treated with a
semiempirical multiscan method (as part of the scaling process) and
augmented by a spherical correction,25 analytically23,26 or numerically
(Gaussian grid).23,27 The structures were determined by intrinsic
phasing28 (complex 8) or by the charge flip procedure29 (all others)
and refined by full-matrix least-squares methods based on F2 against all
unique reflections.30 All non-hydrogen atoms were given anisotropic
displacement parameters. Hydrogen atoms were input at calculated
positions and refined with a riding model.30
Although lower-symmetry space group P31 could not be ruled out, we
chose to refine the structure with the higher symmetry (space group
P3121 with two independent complex molecules). This choice of space
group was made in view of the large amount of disorder, very obvious
with the C3F7 groups and numerous THF solvent molecules, and
considerably reduced complexity without imposing too much bias on
the molecular structure of 8. In particular, the resolution of the C3F7
and phenyl groups did not improve with the lower symmetry.
The tetranickelated tetraazaperopyrene core was well-defined [some
residual electron density (maximum of 1.79 e Å−3), very close to some
of the Ni atoms, may indicate that the lower symmetry of the solvent
environment has a minor effect on the effective symmetry of the
nonsolvent part of the structure]. Some rotational disorder (or
libration) of the phenyl substituents on the iso-PyrrMeBox ligand
could be battled by suitable geometry constraints. However, the
apparent extensive multisite disorder of the perfluorinated propyl
substituents could not be modeled satisfactorily with a split-atom
approach. We therefore resorted to a rigid group refinement of a single
C3F7 moiety each, the site occupation factor of which was refined (to
values below 1.0) to achieve reasonable Ueq values. Hence, the refined
orientations of these substituents resemble the most populated
conformations only. Rigid body restraints were applied throughout.
The electronic contribution of the THF solvent molecules was finally
removed from the Fobs with the smtbx solvent masking procedure.31−33
Final refinement was then performed against appropriately modified
Fobs. A satisfactory final absolute structure parameter34 of 0.012(5), in
line with what was expected from the configuration of 1 used for the
synthesis, further confirms the validity of our approach.
The diffraction pattern of complex 8·xTHF clearly showed weak
superstructure reflections in the c* direction (Figure 11). The
structure could be determined nevertheless in both the sub- and
supercells (with c quadrupled) in space groups P3121 (or P3221) and
P31 (or P32), to reveal the molecular core of 8 with the C3F7 groups
completely or partially missing and many of the phenyl substituents
badly resolved. In any case, difference Fourier syntheses showed much
rather diffuse additional electron density not associated with the
complex molecules, apparently from heavily disordered THF solvent.
Final integration of the diffraction intensities and all further
calculations were then performed in the large supercell (Table S1).
Computational Data. DFT calculations were performed using
Gaussian 09, revision D.01,35 on the bwforcluster JUSTUS. Geometry
optimization and the harmonic frequency analysis were conducted at
the unrestricted B3LYP/6-311G(d,p)36 level of theory, including
Grimme D3 dispersion correction37 and SMD polarizable continuum
model38 using the “tight” convergence criteria for SCF calculations.
The connection between the transition states and minimum
geometries was verified by two separate optimizations starting from
the transition state geometry with a slight distortion along either
direction of the negative vibrational mode.
I
DOI: 10.1021/acs.inorgchem.6b01448
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b01448.
■
S
(8) Rettenmeier, C.; Wadepohl, H.; Gade, L. H. Chem. - Eur. J. 2014,
20, 9657.
Complete experimental procedures and characterization
data of complexes 1−8, including their atom labeling
schemes; listings of the crystal data and structural
parameters of all compounds characterized by X-ray
diffraction; and additional computational details (PDF)
Cartesian coordinates of all relevant minimum structures
of this study (XYZ)
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and 8 (CIF)
AUTHOR INFORMATION
Corresponding Author
■
(b) Mayr, S.; Latkoczy, C.; Kruger, M.; Gunther, D.; Shima, S.;
̈
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Thauer, R. K.; Widdel, F.; Jaun, B. J. Am. Chem. Soc. 2008, 130, 10758.
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Nickel Corphin Coenzyme F430 in Methanogenic Archaea. In Nickel
and Its Surprising Impact in Nature; John Wiley & Sons, Ltd.: New
York, 2007; pp 323.
*Anorganisch-Chemisches Institut, Universitat of Heidelberg,
̈
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany. E-
mail: lutz.gade@uni-heidelberg.de.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
(12) Rettenmeier, C. A.; Wadepohl, H.; Gade, L. H. Chem. Sci. 2016,
7, 3533.
■
We thank Prof. Julio Lloret-Fillol (ICIQ, Tarragona, Spain) for
his support of the computational study and Lena Hahn for the
Tapp-Br synthesis and experimental support. We acknowledge
funding by the Deutsche Forschungsgemeinschaft (DFG, Ga
488/9-1). The computational studies were supported in part by
bwGRiD, a member of the German D-Grid initiative, funded by
the Ministry for Education and Research and the Ministry for
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Science, Research and Arts Baden-Wurttemberg and in part by
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the bwHPC initiative and the bwHPC-C5 project provided
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facility at the University of Ulm. bwHPC and bwHPC-C5
(http://www.bwhpc-c5.de) are funded by the Ministry of
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and the Germany Research Foundation (DFG).
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