Ni(COD)(DQ): An Air-Stable 18-Electron Nickel(0)–Olefin Precatalyst

Article abstract of DOI:10.1002/anie.202000124

We report that Ni(COD)(DQ) (COD=1,5-cyclooctadiene, DQ=duroquinone), an air-stable 18-electron complex originally described by Schrauzer in 1962, is a competent precatalyst for a variety of nickel-catalyzed synthetic methods from the literature. Due to its apparent stability, use of Ni(COD)(DQ) as a precatalyst allows reactions to be conveniently performed without use of an inert-atmosphere glovebox, as demonstrated across several case studies.

Full text of DOI:10.1002/anie.202000124

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Accepted Article
Title: Ni(COD)(DQ): An Air-Stable 18-Electron Ni(0)–Olefin Precatalyst
Authors: Van Tran, Zi-Qi Li, Omar Apolinar, Joseph Derosa, Steven
Wisniewski, Matthew V. Joannou, Martin Eastgate, and Keary
Mark Engle
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202000124
Angew. Chem. 10.1002/ange.202000124
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Ni(COD)(DQ): An Air-Stable 18-Electron Ni(0)–Olefin Precatalyst
Van T. Tran[a], Zi-Qi Li[a], Omar Apolinar[a], Joseph Derosa[a], Matthew V. Joannou[b], Steven R.
Wisniewski[b], Martin D. Eastgate[b], and Keary M. Engle[a]*
first described by Schrauzer in 1962.[6,7] The structural
Abstract: We report that Ni(COD)(DQ) (COD
=
1,5-
properties[8] and fundamental organometallic reactivity[9] of
Ni(COD)(DQ) have been previously studied, but to our
knowledge its ability to serve as a precatalyst in organic
transformations has not been previously documented.
Ni(COD)(DQ) is isostructural and isoelectronic to Ni(COD)2,
both of which are 18-electron Ni(0)-olefin complexes.[10]
However, unlike Ni(COD)2, Ni(COD)(DQ) is unique in its high
air and moisture stability, in both solid and solution states,
along with high thermal stability (being stable to storage at
room temperature).
cyclooctadiene, DQ = duroquinone), an air-stable 18-electron
complex originally described by Schrauzer in 1962, is a
competent precatalyst for a variety of nickel-catalyzed synthetic
methods from the literature. Due to its apparent stability, use of
Ni(COD)(DQ) as
a precatalyst allows reactions to be
conveniently performed without use of an inert-atmosphere
glovebox, as demonstrated across several case studies.
The last decade has witnessed a renaissance in research
into homogeneous nickel catalysis.[1] Interest into the use of
nickel stems from its ability to serve as an inexpensive
alternative to precious metals in many catalytic
transformations, including palladium-catalyzed cross-
couplings, along with its capacity for facilitating unique types
of bond construction, ranging from C–H activation to alkene
functionalization.
Scheme 1. Overview of the growing nickel precatalyst toolkit.
The development of new synthetic methods leveraging
nickel as a catalytic species hinges on the development and
application of appropriate precatalysts; ones which are
stable to heat, air, and moisture, and can efficiently form the
catalytically active species under the desired reaction
conditions (Scheme 1A–D).[2] Prominent within the nickel
precatalyst toolkit are nickel(0)–olefin complexes, originally
pioneered by Wilke (Scheme 1D), including Ni(cdt) (cdt = all-
trans-1,5,9-cyclododecatriene) and Ni(COD)2 (COD = 1,5-
cyclooctadiene).[3,4] Ni(COD)2 in particular has found
extensive use as
a precatalyst and offers several
advantages in this context. These include its enhanced
stability as compared to Ni(cdt) by virtue of being a
coordinatively-saturated 18-electron complex, its ability to
efficiently associate various ancillary ligands in situ with
concomitant dissociation of a COD ligand, and its low-valent
nature, allowing it to directly engage in catalysis without
prerequisite reduction. Other attributes of Ni(COD)2,
however, are less desirable. Most notably it is sensitive to
air, which typically necessitates use of an inert atmosphere
glovebox for storage and reaction setup.[5] These limitations
have spurred the development of other families of nickel
precatalysts in recent years (Scheme 1B and C), which offer
advantages depending on the transformation of interest.
As part of an effort to broaden the portfolio of nickel(0)–
olefin precatalysts, herein we describe the catalytic reactivity
of Ni(COD)(DQ) (DQ = duroquinone), a complex that was
These practical features of Ni(COD)(DQ) when viewed
through the lens of the versatile reactivity described herein
make it a valuable addition to the growing repertoire of nickel
precatalysts. In parallel to this study, Cornella and
colleagues described a 16-electron nickel(0)-olefin complex,
[a]
V. T. Tran, Z-Q. Li, O. Apolinar, J. Derosa, Prof. K. M. Engle
Department of Chemistry, The Scripps Research Institute, 10550
North Torrey Pines Road, La Jolla, California 92037, United States
E-mail: keary@scripps.edu
Ni(Fstb)3
(Fstb
=
trans-1,2-bis(4-
(trifluoromethyl)phenyl)ethane) and documented its ability to
serve as a precatalyst for several different types of
reactions.[11]
[b]
Dr. Matthew V. Joannou, Dr. S. R. Wisniewski, Dr. Martin D.
Eastgate
Chemical & Synthetic Development, Bristol-Myers Squibb, 1 Squibb
Drive, New Brunswick, New Jersey 08903, United States
We initiated our study by first attempting to prepare a series
of nickel(0)–olefin complexes and testing their stability in air.
To this end, we treated Ni(COD)2 with various electron-
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.202000124
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deficient alkenes and dienes. Consistent with a previous
literature report,[12] well-defined 16-electron Ni(cod)(olefin)
complexes could be prepared in this manner, with olefins
such as dimethyl fumarate and maleic anhydride proving
capable of displacing a single COD ligand. However, in the
solid state these complexes proved to be unstable to air,
decomposing within 30 seconds of air exposure, as
evidenced by a color change from red to black. Analogously,
we found that using quinones as reaction partners, we could
obtain 18-electron Ni(COD)(quinone) complexes. Of the
quinones tested, duroquinone (DQ) was especially effective,
giving 79% yield on >8 g scale, of a red-colored, free-flowing
solid that exhibited remarkable stability in air in comparison
to Ni(COD)2 (Scheme 2). In an effort to develop a more user
friendly synthesis starting from air-stable Ni(II) precursors,
we found that Ni(COD)(DQ) can be generated from Ni(acac)2
in 60% yield using DIBAL-H as reductant or alternatively from
NiCl2(pyridine)4 in 28% yield using sodium as reductant.
Analytical data (X-ray) for material prepared by these routes
were identical to previously reported data for Ni(COD)(DQ)
(see Supporting Information), which was originally
synthesized from highly toxic Ni(CO)4 in the aforementioned
1962 report by Schrauzer.[7,13]
deposited in the CCDC (1972401). To briefly summarize the
key structural features noted in the original report,[9]
Ni(COD)(DQ) is monomeric in the solid state, possessing
two crystallographically inequivalent half-molecules with the
nickel center sandwiched between a DQ and COD ligand.
The COD ligand adopts the same boat-form as in Ni(COD)2.
The two pairs of olefin moieties in DQ and COD are
orthogonal to one another, with nickel in tetrahedral
geometry (the angle between COD olefins is 94°, and the
angle between DQ olefins is 72°). Complexation to nickel
distorts DQ, with the carbonyl groups puckering away from
the nickel center and the methyl groups puckering towards
the nickel center. The dihedral angle between the plane of
four central ring carbons and the carbonyl groups is 6°.
Significant π-back bonding from the nickel to the DQ ligand
is evident from the C=O stretching IR signal (1553 cm–1 in
the complex, versus 1687 cm–1 for free DQ).[6]
Surprisingly, we were unable to find any information in the
literature regarding the catalytic activity of Ni(COD)(DQ).
Nevertheless, its structural similarity to Ni(COD)2 led us to
believe that it too could be a competent precatalyst in various
reactions with in situ ligation from a phosphine, N-
heterocyclic carbene, or nitrogen-based ligand. To test this
idea, we evaluated the catalytic activity of Ni(COD)(DQ) in
reactions from the literature that have been reported to
proceed with different nickel precatalysts, with the hope of
establishing that Ni(COD)(DQ) could function in a myriad of
settings. For our initial experiments, we examined nickel-
catalyzed variants of two key transformations of direct
relevance to the pharmaceutical industry, Suzuki–Miyaura
coupling and Buchwald–Hartwig amination. All reactions
were set up outside of the glovebox using standard Schlenk
technique, following procedures using reaction conditions
that were otherwise identical to literature protocols, without
additional optimization or development.
Scheme 2. Gram-Scale Synthesis of Ni(COD)(DQ).
Scheme 3. Evaluation of Ni(COD)(DQ) as precatalyst in Suzuki–Miyaura
cross-coupling of aryl and heteroaryl coupling partners.[a–c]
0.5 mol% [Ni]
(0.5 mol% dppf)
Ar1/Het1–B(OH)2
Ar2/Het2–X
Ar1/Het1 Ar2/Het2
+
base, solvent
(X = Cl, Br)
N
O
MeO
MeO
1a (A)
1b (A)
1c (A)
Ni(COD)(DQ): >99%
[(dppf)Ni(cinnamyl)Cl]: 94%
Ni(COD)(DQ): 74%
[(dppf)Ni(cinnamyl)Cl]: 98%
Ni(COD)(DQ): >99%
[(dppf)Ni(cinnamyl)Cl]: 97%
N
S
N
N
S
O
N
1d (B)
1e (A)
1f (B)
Ni(COD)(DQ): 77%
[(dppf)Ni(cinnamyl)Cl]: 86%
Ni(COD)(DQ): 51%
[(dppf)Ni(cinnamyl)Cl]: 91%
Ni(COD)(DQ): 68%
[(dppf)Ni(cinnamyl)Cl]: 88%
Start
7 h
1 d
2 d
4 d
N
N
N
S
O
N
S
N
N
1g (A)
1h (A)
1i (A)
Ni(COD)(DQ): >99%
[(dppf)Ni(cinnamyl)Cl]: 94%
Ni(COD)(DQ): 85%
[(dppf)Ni(cinnamyl)Cl]: 92%
Ni(COD)(DQ): 98%
[(dppf)Ni(cinnamyl)Cl]: 92%
Ni(Fstb)3: >99%
[a] Reactions performed on 0.4 mmol scale. [b] Percentages represent
isolated yields. Yields with [(dppf)Ni(cinnamyl)Cl] and Ni(Fstb)3 are taken
from Refs. 2d and 11. [c] Method A: K3PO4 (1.5 equiv), dioxane (0.4 M),
80 °C, 8 h; Method B: K2CO3 (1.5 equiv), MeCN (0.4 M), 50 °C, 12 h; the
method is specified in parentheses after the compound number.
[a] Ellipsoids represent 50% probability; one of two inequivalent half-
molecules in the unit cell; hydrogen atoms omitted for clarity.
The structure and bonding of Ni(COD)(DQ) were first
elucidated in 1965 by X-ray crystallography.[9] During the
course of the present study, a new data set was collected on
a modern instrument, and the structure was solved and
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First we examined a nickel-catalyzed Suzuki–Miyaura
method from Ge and Hartwig, reported to proceed effectively
with 0.5 mol% [(dppf)Ni(cinnamyl)Cl] as the precatalyst.[2d]
By combining Ni(COD)(DQ) and dppf in equimolar ratio
under otherwise identical reaction conditions, we were able
halides[15,16], C–H activation[1e,17], alkene hydroarylation[18]
,
and decarboxylative cycloaddition[19] (Scheme 5). Indeed,
when we evaluated Ni(COD)(DQ) as a replacement for
NiCl2(dppp) in the catalytic coupling of HBpin and an aryl
chloride, we observed comparable yields to an original report
by Murata.[15] Analogously, Ni(COD)(DQ) performed similarly
to both Ni(COD)2 and Ni(Fstb)3 in a substrate-directed
C(aryl)–H activation/alkyne annulation developed by Chatani
and colleagues, in which PPh3 and the bidentate pyridyl
amide directing group presumably serve as ligands around
nickel.[11,17, 20] To evaluate the performance of Ni(COD)(DQ)
in alkene functionalization reactions, we implemented it in
the 8-aminoquinoline directed hydroarylation of an
unactivated alkene as reported originally by Zhao and
coworkers and found the yield to be comparable to that
reported using Ni(COD)2 as catalyst.[18] Lastly, we tested
Ni(COD)(DQ) in the synthesis of quinazolinediones via a
decarboxylative cycloaddition of isatoic anhydrides and
isocyanates as reported by Bristol-Myers Squibb.
Ni(COD)(DQ) as catalyst afforded the desired product in
good yield, albeit lower than that of the originally reported
Ni(COD)2 catalyst.[19]
to obtain comparable yields across
a representative
sampling of examples including simple aryl cases as well as
more challenging heteroaryl cases (Scheme 3). In a few
cases (1b, 1d, 1e, 1f, and 1i), the yields with Ni(COD)(DQ)
(while still in the synthetically useful range) were lower than
those of the original method, with the remaining material
balance accounted for by unreacted aryl halide starting
material. The origin of attenuated reactivity in these cases is
currently under investigation. In one case (1h), it was also
possible to make a direct comparison to Ni(Fstb)3,[11] and for
this product Ni(COD)(DQ) offered similarly high yield. Again,
noting that further optimization was not conducted, which
may be necessary for different precatalyst complexes to
optimize yield.
Next, we examined
a nickel-catalyzed aryl chloride
amination protocol originally reported by Wolfe and
Buchwald that was developed with Ni(COD)2 as precatalyst
(Scheme 4).[14a] In two representative examples from the
original publication, Ni(COD)(DQ) offered similar yields to
Ni(COD)2 (2a and 2b). Ni(COD)(DQ) can also be used to
synthesized 2c, an example not reported in Ref. 14a, under
the same conditions in comparable yield to Ni(COD)2. With
4-chlorobenzotrifluoride, an electrophile not included in the
original Buchwald paper, it has been reported that the use of
SIPr delivers high yields with morpholine as coupling
partner.[11,14b] Indeed, with in situ ligation of SIPr, Ni(COD)2
and Ni(COD)(DQ) both facilitated C–N coupling in
comparable yields (2d–f). Due to the sensitivity of reaction
components other than Ni(COD)(DQ)—presumably the
base, NaOtBu—slightly higher yields could be obtained when
reagents other than Ni(COD)(DQ) were handled in the
glovebox.
Scheme 5. Evaluation of Ni(COD)(DQ) as a precatalyst in (A) the
borylation of aryl halides[a], (B) C–H activation/alkyne annulation[a], (C)
directed hydroarylation of unactivated alkenes[b], and (D) decarboxylative
cycloaddition to form quinazolinediones[c] [d]
.
Scheme 4. Evaluation of Ni(COD)(DQ) as a precatalyst in the amination
of aryl chlorides. [a–c]
[a] Reactions performed on 0.5 mmol scale. Yield with NiCl2(dppp) was
taken from Ref. 15. Yields with Ni(COD)2 and Ni(Fstb)3 are taken from
Refs. 17 and 11, respectively. [b] Reactions performed on 0.2 mmol scale.
Yield with Ni(COD)2 was taken from Ref. 18. [c] Reaction performed on
0.85 mmol scale. Yield with Ni(COD)2 taken from Ref. 19. [d] Yield
obtained by 1H NMR using CH2Br2 as internal standard. Percentages
represent isolated yields unless otherwise indicated.
[a] Reactions performed on 0.1 mmol scale. [b] Percentages represent
isolated yields. For Ni(COD)(DQ) experiments, the values in parentheses
represent trials where the catalyst was massed outside of the glovebox
and brought into the glovebox for subsequent manipulations; the values
in brackets represent trials performed completely outside of the glovebox
using Schlenk technique. Yields with Ni(COD)2 for 2a and 2b are taken
from Ref. 14a; yields with Ni(COD)2 for 2c–f were obtained during the
course of this study. [c] Method A: dppf (10 mol%), NaOtBu (1.4 equiv),
PhMe (0.25 M), 100 °C, 24 h; Method B: SIPr•HCl (10 mol%), NaOtBu
(1.5 equiv), CPME (0.3 M), 100 °C, 24 h; the method is specified in
parentheses after the compound number.
To evaluate the solution-state stability of Ni(COD)(DQ)
upon long-term storage, we prepared a solution in non-
degassed, non-anhydrous methanol-d4. Periodic monitoring
of this solution over time revealed no detectable changes in
1
the H NMR spectrum after ~4 days. After longer times (1
week), we observed peak broadening, consistent with partial
decomposition (see Supporting Information). As mentioned
above, in the solid-state, Ni(COD)(DQ) is a red, free-flowing
solid that is indefinitely air stable. No detectable
decomposition (as observed by 1H NMR) could be observed
We next tested Ni(COD)(DQ) in four emerging types of
synthetic methodology with nickel: the borylation of aryl
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after storing this complex for 3 months in a capped vial under
air at room temperature (see Supporting Information).
deploy different nickel sources from the growing arsenal of
precatalysts.
Lastly, we performed a series of “stress tests” on
Ni(COD)(DQ), subjecting it to air, protic solvents, and heat
for several hours to examine if there was any impact on
catalytic activity (Table 1 and Supporting Information). In
particular, we found that dissolving Ni(COD)(DQ) in MeOH,
H2O, or a mixture of MeOH/H2O and allowing the solution to
stand open to air for 5 h did not lead to any detectable
changes in the 1H NMR spectrum or attenuation of catalytic
activity (as assayed by Suzuki–Miyaura cross-coupling to
form 1a) (entries 1–4). Similarly, heating solid Ni(COD)(DQ)
in the oven for 4 h did not have a measurable effect on its
Experimental Section
Synthesis of Ni(COD)(DQ): To a 350 mL bomb flask was
added
2,3,5,6-tetramethylcyclohexa-2,5-diene-1,4-dione
(duroquinone, DQ) (5.37 g, 32.7 mmol) and a stir bar. The
flask and contents were pumped into the glovebox and
Ni(cod)2 (9.00 g, 32.7 mmol) was added. Next, degassed
DCM (120 mL) was added, and the flask was capped,
removed from the glove box, and allowed to stir at 45 ˚C in
an oil bath for 17 h. All subsequent manipulations were
performed under air. The reaction was cooled to room
temperature, and the crude reaction mixture was filtered
through Celite with DCM as eluent to give a deep red
homogeneous mixture. This mixture was concentrated in
vacuo to give a dark red solid with residual COD liquid. To
the resulting crude mixture was added a small amount of
DCM (5 mL) followed by a large amount of pentanes (150
mL) resulting in the formation of a red precipitate. The mother
liquor was then removed by pipetting and the precipitate was
washed with DCM/pentanes (1:50) twice. Drying overnight
composition or ability to serve as
precatalyst (entry 5). Notably, heating solid Ni(COD)2 in the
oven under the same conditions for 1.5 lead to
a cross-coupling
h
decomposition (See Supporting Information), highlighting the
difference in thermal stability. Remarkably, we found
Ni(COD)(DQ) to be stable to silica gel chromatography using
MeOH/DCM as eluent, providing additional avenues for
purification (entry 6).
Table 1. Evaluation of the catalytic activity of Ni(COD)(DQ) after
different stress tests.
under reduced pressure yielded 8.52
g
(79%) of
Ni(COD)(DQ) as a dark red solid. Characterization data
match those reported in the literature.[12]
Entry
Conditions
(none)
Yield of 1a (%)
Acknowledgements
1
2
>99
94
This work was financially supported by Bristol-Myers Squibb,
the National Science Foundation (CHE-1800280), the Alfred
P. Sloan Fellowship Program, and the Camille Dreyfus
Teacher-Scholar Program. We further acknowledge the NSF
for a Graduate Research Fellowships (DGE-1346837, J.D.
and DGE-1842471, O.A), We thank Professor Phil S. Baran,
Dr. Michael A. Schmidt, and Professor Peng Liu for helpful
discussions. We further thank Prof. Arnold L. Rheingold
(UCSD) for X-ray crystallographic analysis.
MeOH, air, 5 h
3
H2O, air, 5 h
98
4
5
6
MeOH/H2O, air, 5 h
oven (90 °C), air, 4 h
silica gel, air
>99
98
95
Table 2. Photographs of a representative stress test (Table 1, Entry 4)
Keywords: nickel • homogeneous catalysis • cross-
coupling • precatalysts
Start (0 h)
in MeOH/H2O
5 h
5 h
dried
in MeOH/H2O
[1]
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In conclusion we have found that Ni(COD)(DQ) possesses
a previously underappreciated capacity to serve as a
precatalyst for a variety of mechanistically distinct catalytic
processes from the literature. In these cases in situ ligation
with a variety of ligands was possible to generate an active
catalyst without any additional reoptimization of the
published conditions. The profound stability of Ni(COD)(DQ)
makes it a promising new addition to the portfolio of nickel
precatalysts, particularly for handling situations where it is
not possible to completely exclude air and moisture, such as
in large-scale manufacturing. Our future research will seek
to elucidate the mechanism of catalyst initiation with
Ni(COD)(DQ) and cultivate an understanding of when to
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R. Longstreet, T. F. Jamison, Organometallics 2018, 37, 2716–
[13] For a preparation from di-π-allylnickel, see: A. N. Nesmeyanov, L.
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6054–6058. For the use of SIPr in nickel-catalyzed amination of
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[3]
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[4]
[5]
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Heterocycles 2010, 80, 213–218.
[16] For recent examples, see: a) G. A. Molander, L. N. Cavalcanti, C.
García-García, J. Org. Chem. 2013, 78, 6427–6439; b) J. R.
Coombs, R. A. Green, F. Roberts, E. M. Simmons, J. M. Stevens,
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[17] H. Shiota, Y. Ano, Y. Aihara, Y. Fukumoto, N. Chatani, J. Am.
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[6]
[7]
G. N. Schrauzer, H. Thyret, Z. Naturforsch. 1962, 17b, 73–76.
For related DQ-containing nickel complexes, see: a) G. N.
Schrauzer, H. Thyret, J. Am. Chem. Soc. 1960, 82, 6420–6421; b)
G. N. Schrauzer, H. Thyret, Z. Naturforsch. 1961, 16b, 353–356
M. D. Glick, L. F. Dahl, J. Organomet. Chem. 1965, 3, 200–221.
A. Pidock, G. G. Roberts, J. Chem. Soc. A 1970, 2922–2928.
[8]
[9]
[18] H. Lv, L.-J. Xiao, D. Zhao, Q.-L. Zhou, Chem. Sci. 2018, 9, 6839–
6843.
[10] Density functional theory calculations of these two complexes
showed a +0.09120 charge on Ni in the case of Ni(COD)2 and a
+0.21065 charge on Ni in the case of Ni(COD)(DQ) using natural
population analysis, consistent with increased π-backbonding and
more electron-poor nickel center in the latter complex. See SI for
additional information, including analysis of natural bonding
orbitals..
[19] G. L. Beutner, Y. Hsiao, T. Razler, E. M. Simmons, W. Wertjes,
Org. Lett. 2017, 19, 1052–1055.
[20] Although initiation mechanism and rates may differ per specific
reaction and substrate, evaluation of initial reaction rates of this
reaction showed no significant difference in initiation rates using
Ni(COD)(DQ) in comparison to Ni(COD)2 as catalyst (see
Supporting Information for details).
[11] L. Natmann, R. Saeb, N. Nöthling, J. Cornella, Nat. Catal. 2019,
DOI: 10.1038/s41929-41019-40392-41926.
[12] H. M. Buech, P. Binger, C. Krueger, Organometallics 1984, 3,
1504–1509.
This article is protected by copyright. All rights reserved.

10.1002/anie.202000124
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
O
• one-step synthesis • air-stable
• thermally stable • silica-stable
• stable in organic solvents
V. T. Tran, Z.-Q. Li, O. Apolinar, J.
Derosa, S. R. Wisniewski, M. V.
Joannou, M. D. Eastgate*, Keary M.
Engle*
Me
Ni0
Me
Me
Me
in H2O
under air
solid state
under air
Ni•Ln
O
• compatible w/ various ligands
• competent as precatalyst in
C–C, C–N, and C–B bond
formation
Ni(COD)(DQ)
(18-e– complex)
MilliporeSigma #912794
Page No. – Page No.
Ni(COD)(DQ): An Air-Stable 18-
Electron Ni(0)–Olefin Precatalyst
Old complex, new tricks: Ni(COD)(DQ) (COD = 1,5-cyclooctadiene, DQ =
duroquinone) is a remarkably stable Ni(0)–olefin complex first described in the
1960s. Herein, we demonstrate its ability to serve as a precatalyst for a variety of
nickel-catalyzed reactions.
This article is protected by copyright. All rights reserved.