A Highly Reduced Ni-Li-Olefin Complex for Catalytic Kumada-Corriu Cross-Couplings

Article abstract of DOI:10.1021/jacs.8b09849

The catalytic activity of a highly reduced Ni catalyst in the context of a Kumada-Corriu cross-coupling has been studied. This nickel complex is characterized by its high electron density, stabilized by simple olefin ligands in combination with two Li ions. Landmark reactivity has been found with this precatalyst which operates at cryogenic temperatures, thus allowing the presence of sensitive functionalities. Structural elucidation of oxidative addition intermediates and their reactivity suggest highly reduced species being operative in the C-C bond forming event.

Full text of DOI:10.1021/jacs.8b09849

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Communication
A Highly Reduced Ni#Li#Olefin Complex for
Catalytic Kumada-Corriu Cross-Couplings
Lukas Nattmann, Sigrid Lutz, Pascal Ortsack, Richard Goddard, and Josep Cornella
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 10 Oct 2018
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A Highly Reduced Ni-Li-Olefin Complex for Catalytic Kumada–
Corriu Cross-Couplings
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Lukas Nattmann, Sigrid Lutz, Pascal Ortsack, Richard Goddard and Josep Cornella*
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr, 45470, Germany.
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Supporting Information Placeholder
ture.10c,11 In the solid state, two Li atoms are bonded to the central
ABSTRACT: The catalytic activity of a highly reduced Ni cata-
Ni, but severely shifted from the central axis (1: Li1‒Ni1‒Li2
133.75(6) deg);12 The coordination of two molecules of THF and
the average Ni‒Li distance of 2.42 Å, suggest a metal-metal
bond.13 Importantly, complex 1 exhibits a significant elongation
of the three coordinated double bonds in the 1,5-cyclooctadiene
moiety (C1‒C2 1.4635(12), C5‒C6 1.4198(12), C9‒C10
1.4735(12) Å) compared to its Ni(0) congener Ni(COD)2
(1.391(2) Å)14 or the free COD (1.34(3) Å)15. The extreme elon-
gation of the bound olefins and the large rehybridization of the
C(sp2) atoms suggest a high electron density at the Ni center
which is in turn stabilized by a significant back-donation to the
empty π* orbitals of the double bonds.11 This experimental obser-
vations are in agreement with the Dewar-Chatt-Duncanson model,
in which the olefins can be described by the continuum from
metallacyclopropane to olefin (metal-olefin complex vs metal-
lacyclopropane).
lyst in the context of a Kumada–Corriu cross-coupling has been
studied. This nickel complex is characterized by its high electron-
density, stabilized by simple olefin ligands in combination with
two Li ions. Landmark reactivity has been found with this
precatalyst which operates at cryogenic temperatures, thus allow-
ing the presence of sensitive functionalities. Structural elucidation
of oxidative addition intermediates and their reactivity suggest
highly reduced species being operative in the C‒C bond forming
event.
In 1972 two seminal reports from Kumada and Corriu demon-
strated the ability of Ni salts to catalyze the formation of C(sp2)‒
C(sp2) bonds.1 Since then, the field of Ni-catalyzed cross-coupling
has grown exponentially finding applications across the chemical
sciences.2 In this sense, the ability of Ni catalysts to efficiently
maneuver across different oxidation states (Ni(0), Ni(I), Ni(II),
Ni(III) or Ni(IV) species) has proved efficient and versatile, thus
providing extremely powerful synthetic methodologies.2 While
other transition metals have been shown to efficiently catalyze
Kumada-Corriu cross-couplings,3-7 nickel salts have reign sover-
eign due to their efficiency with a variety of electrophiles and
nucleophiles. In particular, nickel salts have been widely em-
ployed in challenging transformations such as the coupling of
C(sp2) and C(sp3) with alkyl groups bearing β-hydrogen atoms,
due to their ability to suppress the commonly observed β-hydride
elimination/isomerization byproducts.8 In the particular case of
alkyl nucleophiles with C(sp2) electrophiles, the catalytic systems
are traditionally based on a nickel metal supported by highly elec-
tron-donating ligands such as phosphines or NHCs which serve a
double purpose: (i) stabilization of the metal center and (ii) dona-
tion of electron density into the Ni thereby increasing its nucleo-
philicity (Scheme 1A). In spite of comprehensive literature reports
in this area, fundamental investigations on the catalytic activity of
complexes with nickel in an extremely low-valent oxidation state
remain elusive. Herein we disclose the unprecedented catalytic
activity of a well-defined low-valent Ni precatalyst capable of
forging C‒C bonds at temperatures as low as ‒65 ºC (Scheme
1B). In contrast to the traditional catalyst designs, this catalytic
system features a highly electron-rich Ni center stabilized by sim-
ple olefin ligands, which outperforms its parent Ni(0) precatalyst
at low temperatures and tolerates the presence of functional
groups in a Kumada coupling.9
Scheme 1. Ligand features in Ni-catalyzed aryl-alkyl Kumada cross-
couplings.
With complex 1 in hand, we turned our attention to examining its
catalytic activity in the Kumada‒Corriu coupling. We subjected
complex
1
to
a
mixture of (E)-1-(2-bromovinyl)-4-
methoxybenzene (2) and hexMgBr (3) in MTBE. To our delight,
5 mol% of 1 effectively catalyzed the formation of coupling prod-
uct 4 in 76% yield at ‒65 ºC (Scheme 2). On the other hand, when
Ni(COD)2 was utilized instead, only traces of product were ob-
served. The addition of various lithium salts to the system did not
lead to conversion and starting material was recovered unreacted.
When the traditional NiCl2(dppe) was used instead, low yields of
4 were obtained. This highlights the high activity of 1 when com-
pared to highly nucleophilic phosphine-supported Ni(0) species.
Control experiments revealed no Mg-halogen exchange between 2
and 3.16 The intriguing reactivity posed by 1 led us to explore the
generality of this transformation to other organic halides. As
shown in Table 1, the electronics on the ring had minimal influ-
ence on the reaction outcome, as exemplified by 5. Interestingly,
no isomerization to the more stable E-isomer was observed when
Z-styrenyl was used instead (6), thus suggesting a non-radical
mechanism (vide infra). Non-conjugated vinyl bromides and 1,1-
disubstituted vinyl bromide could also smoothly couple to deliver
7 and 8 respectively. Vinyl triflates posed no problem and could
be readily activated (9). The presence of a sulfonate group prone
to oxidative addition under Ni catalysis was well accommodated
We began our investigations by synthesizing complex 1, from
the parent Ni(0) source Ni(COD)2 (Figure 1). This complex was
obtained by reduction with lithium sand in THF at 0 ºC, as de-
scribed by Jonas and Pörschke.10 After filtration and crystalliza-
tion with Et2O, compound 1 was isolated as a bright orange com-
plex. As depicted in the ORTEP in Figure 2, complex 1 has three
of the four olefins in the ancillary ligands coordinated to the Ni,
thus rendering an 18 electron complex configuration. In solution
however, the 1H NMR signals of the olefins in 1 indicate a coales-
cence event when increasing the temperature, thus suggesting a
fluxional behavior of the four olefinic ligands at this tempera-
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Table 1. Scope of the Kumada coupling catalyzed by 1.a
1
2
affording 61% of 10. Heterocyclic motifs bearing chlorides and
bromides, such as thiophene, isoquinoline and quinoline, also
3
4
5
6
performed well under the reaction conditions (11-13). Pleasingly,
a
moderate but relevant yield was obtained when 2-
fluoroquinoline was utilized. This result is of special importance
since C(sp2)‒F activation is traditionally restricted to the realm of
nickel catalysts bearing electron donating ligands.17
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Figure 1. Synthesis of complex 1.
Figure 2. Molecular structure of 1. Hydrogen atoms are omitted for clari-
ty. Selected bond distances (Å) and angles (deg): Li1‒Ni1 2.4171(17),
Li2‒Ni1 2.4184(17), C1‒C2 1.4635(12), C5‒C6 1.4198(12), C9‒C10
1.4735(12), C13‒C14 1.3311(17), C10‒Li2 2.2978(19), Li1‒Ni1‒Li2
133.75(6).
a Yields of isolated pure material. Reaction conditions: 1 (5 – 10 mol%),
aryl halide (1 equiv.), alkyl Grignard (1.5 equiv.), 0.1 M MTBE at the
indicated temperatures.
At this point, we questioned the stability of such Ni precatalyst
and we investigated the homogeneity of the system. Yet, the addi-
tion of an excess of Hg(0) to the reaction with 1 did not affect the
kinetic profile.20,21 Moreover, the use of freshly prepared Ni na-
noparticles did not lead to any catalytic activity at ‒65 °C, sug-
gesting a homogeneous catalytic process.20c,21 The interesting
reactivity observed for 1 led us to consider a possible oxidative
addition to the organic halide electrophile (Figure 3A, top). In-
deed, when 1 was reacted with 1 equiv. of bromostyrene, a change
in color was observed and a highly air- and temperature-sensitive
intermediate was obtained. Although speculative in structure, we
attributed this intermediate to nickelate compound 20 based on its
reactivity in solution. When 2 equiv. of hexMgBr (3) were added
to a solution of 20, a gratifying 32% of 5 was obtained. Moreover,
when this intermediate was quenched with H2O, styrene and COD
were the only products observed by GC-FID in 1:2 ratio respec-
tively. These results point out to the existence of rather polarized
C‒M bond in 20, formed upon C‒Br cleavage. In order to gather
additional evidence of the oxidative addition to 1, an alternative
route was devised to provide a more stable nickelate intermediate.
For this reason, we turned to the organometallic addition of PhLi
to Ni(0); this would result in a compound analogous to the postu-
lated oxidative addition species (Figure 3B, bottom). A mixture of
Ni(CDT) ((trans,trans,trans-1,5,9-cyclododecatriene)nickel(0))
and PhLi (solid) were reacted under ethylene atmosphere in a
mixture of Et2O and TMEDA.22 A yellow solid precipitated which
was characterized by NMR spectroscopy as the Ni(0) complex 21.
Following numerous attempts in Et2O, an extremely sensitive
crystal could be isolated and identified by X-ray spectroscopy as
compound 22 (Figure 4). The structure of 22 supports the charac-
terization of 21. This result also underscores the solvent-
dependent ionic character of Ni(0)-ate complexes, and their ability
to form stable Ni‒Li bonds. Albeit different from 20 in ligands,
Scheme 2. Catalytic activity of 1.
b
a Yields determined by GC-FID. Isolated yield. c 10 mol% NiCl2(dppe)
was used instead.
We speculated that the ability of 1 to perform well at such low
temperatures would enable compatibility with sensitive function-
alities. It is well established that ester or nitrile groups react im-
mediately with alkyl Grignards at low temperatures; however,
when substrates bearing nitrile (14) and ester (15) were subjected
to the reaction conditions, satisfactory yields of coupling were
obtained. This distinctive reactivity highlights the possibility of
adapting functional groups in Ni-catalyzed Kumada couplings
without observable side reactions at the electrophilic site.18 For
these sensitive substrates, the reactivity of 1 was compared with
NiCl2(dppe). Although comparable yields were obtained for com-
pound 14, no conversion was obtained towards 10 and 15. Im-
portantly, in all the aforementioned examples no isomerized by-
products from the alkyl Grignard were observed. Hence, we spec-
ulated that β-hydride elimination/isomerization events could be
suppressed with 1. Indeed, when secondary Grignard reagents
i
s
such as PrMgCl and BuMgCl were subjected to the reaction
conditions, good to excellent yields of the coupling product were
observed without isomerization of the alkyl chain (17 and 18).
Gratifyingly, a tertiary nucleophile such as tBuMgCl proved ame-
nable in the reaction; despite the low yield, 19 was obtained with-
out isomerization.19
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complex 21 provided an well-defined platform to study the reac-
bond product upon reductive elimination of intermediate IV
(Scheme 3B).
tivity of a putative oxidative addition of Ar‒X to a formal Ni(‒II).
The solid state structure of complex 22 features a Ni attached to a
phenyl ring, with two slightly elongated ethylene ligands acting as
π-acceptors. Judging by the elongation of the olefins, C7‒C8
1.411(2) and C9‒C10 1.397(2), the Ni center partially relocates its
electron density onto the ethylene ligands. The Li in the solid state
is faintly bridging both the ipso and ortho carbon on the Ph ring
and the Ni center. Simultaneously, the Li is also coordinated to a
carbon from the ethylene moiety.
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Figure 4. Molecular structure of complex [(C2H4)2NiPh]Li(TMEDA) (22).
Selected bond distances (Å) and angles (deg): C7‒C8 1.411(2), C9‒C10
1.397(2), Ni1‒C11 1.9634(12), Ni1‒Li1 2.500(2), Li1‒C11 2.197(3), Li1‒
C7 2.419(3), Li1‒C12 2.607(3); C11‒Ni1‒C7 99.14(5), C11‒Ni1‒Li1
57.46(7).
Scheme 3. Mechanistic investigations.
Figure 3. (A) Reaction of 1 with bromostyrene (B) Synthesis of nickelate
complexes 21 and 22. CDT: trans,trans,trans-1,5,9-cyclododecatriene.
With complex 21 in hand, we explored its reactivity with organ-
ometallic reagents in direct comparison to the equivalent catalytic
reaction with Ph‒Br. When Ph‒Br was reacted with hexMgBr (3),
18% yield of the cross-coupling product was obtained (Scheme
3A). It is important to point out that during our scope studies,
reaction of 1 with unactivated aryl bromides proved sluggish and
the presence of highly coordinating TMEDA was detrimental to
the reactivity.23 Nevertheless, the stoichiometric reaction of com-
plex 21 with hexMgBr (3) delivered a 10% yield of the direct C‒
C bond product, which compares well with the 18% yield ob-
tained under catalytic conditions.23 Similarly, the lower reactivity
is attributed to the effect of TMEDA, which renders the Ni(0)‒Ph
intermediate less electrophilic and hence, less able to accept more
negative charge from the nucleophile. The Ni(0) center would be
more electrophilic if THF, a weaker coordinating ligand, was the
ligand at the Li atom. Based on this hypothesis, we turned our
attention to the use of stronger organometallic nucleophiles, such
as organolithium reagents. When MeLi (24) was tested under
catalytic conditions, 87% yield of cross-coupling product was
obtained. Notably, when MeLi (24) is reacted with complex 21,
47% yield of C‒C bond formation was observed. Although still
preliminary, these results highlight the possibility of forging
C(sp2)-C(sp3) bonds from a Ni(0) complex with an organometallic
reagent.24 The mechanism of such transformation is unknown at
the present stage. However, previous observations by Pörschke on
the acidity of Ni(0) complexes revealed the ability of tris-olefin
Ni(0) complexes to accommodate two organolithium reagents
resulting in dilithiated adducts of Ni(0).10,25 Importantly, these
adducts were shown to undergo reductive elimination to afford the
C‒C bond product. In line with these observations, we believe
that such a C‒C forming event from putative intermediate II and
III could proceed via a similar mechanism, delivering the C‒C
In summary, this work has established the viability of highly
reduced Ni-Li-olefin complexes as competent precatalysts in Ku-
mada-Corriu cross-couplings between a series of aryl and vinyl
halides with alkyl Grignard reagents. The coupling proceeds at
extremely low temperatures, allowing the presence of sensitive
functional groups with Grignard reagents. The catalytic system
features a unique electronically congested Ni center stabilized by
olefin ligands. Stoichiometric experiments reveal a potential sce-
nario in which C‒C bonds can be forged from a nickelate Ni(0)‒
Ph complex and an organometallic reagent. Further investigations
to fully elucidate the operative mechanism as well as other syn-
thetic applications are currently under investigation.
ASSOCIATED CONTENT
Supporting Information. Experimental procedures and analyti-
cal data (1H and 13C NMR, HRMS) for all new compounds. This
material is available free of charge via the internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
E-mail: cornella@kofo.mpg.de
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
Financial support for this work was provided by Max-Planck-
Gesellschaft and Max-Planck-Institut für Kohlenforschung. We
thank Ms. J. Busch for synthesis of starting materials. We also
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2007, 13, 150; (c) Kumada Coupling of Aryl and Vinyl Tosylates
thank Prof. Dr. A. Fürstner, Prof. Dr. T. Ritter and Prof. Dr. K. R.
Pörschke for insightful discussions and generous support. We
thank Mr. A. Schlüter for TEM images.
under Mild Conditions, Limmert, M. E.; Roy, A. H.; Hartwig, J. F. J.
Org. Chem. 2005, 70, 9364; (d) Efficient Cross-Coupling of Aryl
Chlorides with Aryl Grignard Reagents (Kumada Reaction) Mediat-
ed by a Palladium/Imidazolium Chloride System, Huang, J.; Nolan,
S. P. J. Am. Chem. Soc. 1999, 121, 9889; (e) Dichloro[1,1'-
bis(diphenylphosphino)ferrocene]palladium(II): an effective catalyst
for cross-coupling of secondary and primary alkyl Grignard and al-
kylzinc reagents with organic halides, Hayashi, T.; Konishi, M.;
Kobori, Y.; Kumada, M.; Higuchi, T.; Hiritsu, K. J. Am. Chem. Soc.
1984, 106, 158.
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Zheng, B.; Rath, N. P.; Mirica, L. M. J. Am. Chem. Soc. 2016, 138,
12928; (i) Organometallic Nickel(III) Complexes Relevant to Cross-
Coupling and Carbon–Heteroatom Bond Formation Reactions,
Zheng, B.; Tang, F.; Luo, J.; Schultz, J. W.; Rath, N. P.; Mirica, L.
M. J. Am. Chem. Soc. 2014, 136, 6499; (j) Oxidative C–C Bond
Formation Reactivity of Organometallic Ni(II), Ni(III), and Ni(IV)
Complexes, Watson, M. B.; Rath, N. P.; Mirica, L. M. J. Am. Chem.
Soc. 2017, 139, 35; (k) Aromatic Methoxylation and Hydroxylation
by Organometallic High-Valent Nickel Complexes, Zhou, W.;
Schultz, J. W.; Rath, N. P.; Mirica, L. M. J. Am. Chem. Soc., 2015,
137, 7604; (l) Trifluoromethylation of a Well‐Defined Square‐
Planar Aryl‐NiII Complex involving NiIII/CF3. and NiIV−CF3 Inter-
mediate Species, Rovira, M.; Roldan-Gomez, S.; Martin-
Diaconescu, V.; Whiteoak, C. J.; Company, A.; Luis, J. M.; Ribas,
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(3) For selected references, see: (a) Iron-Catalyzed Cross-Coupling
Reactions, Fürstner, A.; Leitner, A.; Mendez, M.; Krause, H. J. Am.
Chem. Soc. 2002, 124, 13856; (b) Iron(III) salen-type catalysts for
the cross-coupling of aryl Grignards with alkyl halides bearing β-
hydrogens, Bedford, R. B.; Bruce, D. W.; Frost, R. M.; Goodby, J.
W.; Hird, M. Chem. Commun. 2004, 24, 2822; (c) Iron-Catalyzed
Cross-Coupling of Primary and Secondary Alkyl Halides with Aryl
Grignard Reagents, Nakamura, M.; Matsuo, K.; Ito, S.; Nakamura,
E. J. Am. Chem. Soc. 2004, 126, 3686; For recent reviews and full
articles on Fe-catalyzed cross-couplings, see: (d) Iron Catalysis in
Organic Synthesis: A Critical Assessment of What It Takes To Make
This Base Metal a Multitasking Champion, Fürstner, A. ACS Cent.
Sci. 2016, 2, 778; (e) Iron Catalysis in Organic Synthesis, Bauer, I.;
Knölker, H. –J.; Chem. Rev. 2015, 115, 3170; (f) Recent advances in
iron-catalysed cross coupling reactions and their mechanistic under-
pinning, Mako, T. L.; Byers, J. A. Inorg. Chem. Front. 2016, 3, 766;
(g) Active Species and Mechanistic Pathways in Iron-Catalyzed C–C
Bond-Forming Cross-Coupling Reactions, Cassani, C.; Bergonzini,
G.; Wallentin, C. –J. ACS Catal. 2016, 6, 1640.
Catalyzed Cross‐Coupling of Non‐activated and Functionalized
Alkyl Halides with Alkyl Grignard Reagents, Vechorkin, O.; Hu, X.
Angew. Chem. Int. Ed. 2009, 48, 2937; (d) Ligand Redox Effects in
the Synthesis, Electronic Structure, and Reactivity of an Alkyl-Alkyl
Cross-Coupling Catalyst, Jones, G. D.; Martin, J. L.; McFarland, C.;
Allen, O. R.; Hall, R. E.; Haley, A. D.; Brandon, J. R.; Konovalova,
(4) For selected examples, see: (a) Pd-Catalyzed Kumada−Corriu Cross-
Coupling Reactions at Low Temperatures Allow the Use of
Knochel-type Grignard Reagents, Martin, R.; Buchwald, S. L. J. Am.
Chem. Soc. 2007, 129, 3845; (b) Biaryls Made Easy: PEPPSI and the
Kumada–Tamao–Corriu Reaction, Organ, M. G.; Abdel-Hadi, M.;
Avola, S.; Hadei, N.; Nasielski, J.; O’Brien, C. J. Chem. –Eur. J.
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T.; Desrochers, P. J.; Pulay, P.; Vicic, D. A. J. Am. Chem. Soc. 2006,
Cl and C-F Bonds Using Nickel Complexes of Air-Stable Phosphine
Oxides, Ackermann, L.; Born, R.; Spatz, J. H.; Meyer, D. Angew.
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128, 13175; (e) Ni-Catalyzed Cascade Formation of C(sp3)-C(sp3)
Bonds by Cyclization and Cross-Coupling Reactions of Iodoalkanes
with Alkyl Zinc Halides, Phapale, V. B.; Buñuel, E.; Garcia-Iglesias,
M.; Cardenas, D. J. Angew. Chem. 2007, 119, 8946. For extensive
reviews, see: (f) Advances in Transition Metal (Pd,Ni,Fe)-Catalyzed
Cross-Coupling Reactions Using Alkyl-organometallics as Reaction
Partners, Jana, R.; Pathak, T. P.; Sigman, M. S. Chem. Rev. 2011,
111, 1417; (g) Transition metal–catalyzed alkyl-alkyl bond for-
mation: Another dimension in cross-coupling chemistry, Choi, J.;
Fu, G. C. Science, 2017, 356, 152 and references therein.
(18) For functional group tolerant Kumada: Pd catalysis with arylmagne-
sium reagents: Inherent vs Apparent Chemoselectivity in the Kuma-
da–Corriu Cross-Coupling Reaction, Hua, X.; Masson-Makdissi, J.;
Sullivan, R. J.; Newman, S. G. Org. Lett. 2016, 18, 5312. See also
ref 4a.
(19) For secondary and tertiary Grignards with vinyl nucleophiles, see:
(a) Nickel-Catalyzed Kumada Cross-Coupling Reactions of Tertiary
Alkylmagnesium Halides and Aryl Bromides/Triflates, Joshi-Pangu,
A.; Wang, C. –W.; Biscoe, M. R. J. Am. Chem. Soc. 2011, 133,
8478; (b) Stereoretentive Pd-Catalyzed Kumada–Corriu Couplings
of Alkenyl Halides at Room Temperature, Krasovskiy, A. L.; Haley,
S.; Voigtritter, K.; Lipshutz, B. H. Org. Lett. 2014, 16, 4066; (c)
Copper- and Nickel-Catalyzed Cross-Coupling Reaction of Mono-
fluoroalkenes with Tertiary, Secondary, and Primary Alkyl and Aryl
Grignard Reagents, Shi, H.; Dai, W.; Wang, B.; Cao, S. Organome-
tallics, 2018, 37, 459.
(20) (a) Suppression of unwanted heterogeneous platinum(0)-catalyzed
reactions by poisoning with mercury(0) in systems involving com-
peting homogeneous reactions of soluble organoplatinum com-
pounds: thermal decomposition of bis(triethylphosphine)-3,3,4,4-
tetramethylplatinacyclopentane, Whitesides, G. M. Hackett, M.;
Brainard, R. L.; Lavalleye, J. ‒P. P. M.; Sowinski, A. F.; Izumi, A.
N.; Moore, S. S.; Brown, D. W.; Staudt, E. M. Organometallics,
1985, 4, 1819; (b) Selective, Nickel-Catalyzed Hydrogenolysis of
Aryl Ethers, Sergeev, A. G.; Hartwig, J. F. Science, 2011, 332, 439;
(c) An Easily Accessed Nickel Nanoparticle Catalyst for Alkene
Hydrosilylation with Tertiary Silanes, Buslov, I.; Song, F.; Hu, X.
Angew. Chem. Int. Ed. 2016, 55, 12295.
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(9) For an extensive review on negative oxidation states, see: Adven-
tures with Substances Containing Metals in Negative Oxidation
States, Ellis, J. E. Inorg. Chem. 2006, 45, 3167 and references there-
in.
(10) (a) Dilithium‐Nickel‐Olefin‐Komplexe. Neuartige Bimetall-
komplexe aus einem Übergangsmetall und einem Hauptgruppenme-
tall, Jonas, K. Angew. Chem. 1975, 87, 809; (b) Über
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Bis(lithium)nickel-Olefin-
und
Lithium(monoorganyl)nickel-
bis(äthylen)-Komplexe Pörschke, K. ‒R. Dissertation, Universitӓt
Bochum, 1975; (c) Alkalimetall-Übergangsmetall-π-Komplexe, Jo-
nas, K.; Krüger, C. Angew. Chem. 1980, 92, 513; (d) Thermolabile
Hydridio- und Organonickel(0)-Verbindungen, Pörschke, K. ‒R.
Habilitationsschrift, Universitӓt Düsseldorf, 1988, p. 42.
(11) For a discussion on the fluxional behavior of complex 1 in solution
and structural details, see Supporting Information.
(12) For Li-olefin interaction in low-valent Ni complexes: (a) A New
Lithium-Nickel Polynuclear Complex: Ni(C12H17NiLi)2(THF)4, Jo-
nas, K.; Krüger, C.; Sekutowski, J. C. Angew. Chem. Int. Ed. 1979,
18, 487.
(13) Similar interactions have been previously observed for lithiated Fe
and Co complexes: (a) Simple Route to Li- or Zn-Metalated η5 Cy-
clopentadienyliron-Olefin Complexes, Jonas, K.; Schieferstein, L.;
Krüger, C.; Tsay, Y.-H. Angew. Chem. Int. Ed. 1979, 18, 550; (b)
Preparation, Structure, and Reactivity of Nonstabilized Organoiron
Compounds. Implications for Iron-Catalyzed Cross Coupling Reac-
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Lehmann, C. W. J. Am. Chem. Soc. 2008, 130, 8773; (c) A Cheap
Metal for a “Noble” Task:ꢀ Preparative and Mechanistic Aspects of
Cycloisomerization and Cycloaddition Reactions Catalyzed by Low-
Valent Iron Complexes, Fürstner, A.; Majima, K.; Martin, R.;
Krause, H.; Kattnig, E.; Goddard, R.; Lehmann, C. W. J. Am. Chem.
Soc. 2008, 130, 1992; (d) A Lithium-Cobalt Bimetal Complex, Bön-
nemann, H.; Krüger, C.; Tsay, Y. –H. Angew. Chem. Int. Ed. 1976,
15, 46.
(21) See Supporting Information for details.
(22) For a method on the synthesis of ionic salts, see: Jonas, K.; Pörsch-
ke, K. R.; Krüger, C. Tsay, Y. –H. Angew. Chem. Int. Ed. 1976, 15,
621.
(23) Large amounts of unreacted bromobenzene, together with benzene
and biphenyl were observed.
(24) For examples suggesting nickelate intermediates in C(sp3)‒C(sp3)
utilizing olefins as supporting ligands, see: (a) Nickel-Catalyzed
Cross-Coupling Reaction of Grignard Reagents with Alkyl Halides
and Tosylates:ꢀ Remarkable Effect of 1,3-Butadienes, Terao, J.;
Watanabe, H.; Ikumi, A.; Kuniyasu, H.; Kambe, N. J. Am. Chem.
Soc. 2002, 124, 4222; (b) Ni- or Cu-Catalyzed Cross-Coupling Reac-
tion of Alkyl Fluorides with Grignard Reagents, Terao, J.; Ikumi, A.;
Kuniyasu, H.; Kambe, N. J. Am. Chem. Soc. 2003, 125, 5646; (c)
Pd-Catalyzed Cross-Coupling Reaction of Alkyl Tosylates and Bro-
mides with Grignard Reagents in the Presence of 1,3-Butadiene,
Terao, J.; Naitoh, Y.; Kuniyasu, H.; Kambe, N. Chem. Lett. 2003,
32, 890; (d) Nickel‐Catalyzed Cross‐Coupling Reaction of Alkyl
Halides with Organozinc and Grignard Reagents with 1,3,8,10‐
Tetraenes as Additives, Terao, J.; Todo, H.; Watanabe, H.; Ikumi,
A.; Kambe, N. Angew. Chem. Int. Ed. 2004, 43, 6180. In these ex-
amples, a Ni(II)/Ni(IV) cycle was invoked.
(14) Proton Sandwiches: Nonclassical Carbocations with Tetracoordinate
Protons, Gutta, P.; Tantillo, D. J. Angew. Chem. Int. Ed. 2005, 44,
2719.
(15) The three-dimensional structure of trans.trans,trans-1,5,9-
cyclododecatrienenickel, Brauer, D. J.; Krüger, C. J. Organometal.
Chem. 1972, 44, 397.
(16) (a) Action des bromures α-éthyléniques sur les bromures organo-
magnésiens; résultats d´ensemble, Prevost, C. Bull. Soc. Chim. Fr.
1931, 49, 1372; (b) Highly Functionalized Organomagnesium Rea-
gents Prepared through Halogen–Metal Exchange, Knochel, P.; Doh-
le, W.; Gommermann, N.; Kneisel, F. F.; Kopp, F.; Korn, T.;
Sapountzis, I.; Ahn Vu, V. Angew. Chem., Int. Ed. 2003, 42, 4302;
(c) The Halogen/Magnesium-Exchange Using iPrMgCl·LiCl and
Related Exchange Reagents, Barl, N.; Werner, V.; Sämman, C.;
Knochel, P. Heterocycles, 2014, 88, 827.
(17) (a) Transition metal catalyzed cross-coupling of aryl Grignard rea-
gents with aryl fluorides via Pd- or Ni-activation of the C–F bond: an
efficient synthesis of unsymmetrical biaryls – application of micro-
wave technology in ligand and catalyst screening, Dankwardt, J. W.
J. Organomet. Chem. 2005, 690, 932; (b) Nickel-Catalyzed Cross-
Coupling Reaction of Aryl Fluorides and Chlorides with Grignard
Reagents under Nickel/Magnesium Bimetallic Cooperation, Yoshi-
kai, N.; Mashima, H.; Nakamura, E. J. Am. Chem. Soc. 2005, 127,
17978; (c) Efficient Aryl-(Hetero)Aryl Coupling by Activation of C-
(25) For Ni(0) complexes with organomagnesium, see: Zur Lewis ‐
Acidität von Nickel(0), X. Diorganylmagnesium‐Komplexe von
Nickel(0): (TMEDA)MgCH3(µ-CH3)Ni(C2H4)2 Kaschube, W.;
Pörschke, K. ‒R.; Angermund, K.; Krüger, C.; Wilke, G. Chem. Ber.
1988, 121, 1921. For Ni(0) complexes with organolithium, see: Zur
Lewis-Acidität von Nickel(O), IX. Alkyllithium- Komplexe von
Nickel(O), Pörschke, K. ‒R.; Jonas, K.; Wilke, G. Chem. Ber. 1988,
121, 1913; it was observed that butane could be formed from a Ni(0)
bearing two EtLi molecules:
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