Radical Capture at Nickel(II) Complexes: C-C, C-N, and C-O Bond Formation

Article abstract of DOI:10.1021/acs.organomet.0c00021

The dinuclear β-diketiminato NiII tert-butoxide {[Me3NN]Ni}2(μ-OtBu)2 (2), synthesized from [Me3NN]Ni(2,4-lutidine) (1) and di-tert-butylperoxide, is a versatile precursor for the synthesis of a series of NiII complexes [Me3NN]Ni-FG (FG = functional group) to illustrate C-C, C-N, and C-O bond formation at NiII via radical capture. {[Me3NN]Ni}2(μ-OtBu)2 reacts with nitromethane, alkyl and aryl amines, acetophenone, benzamide, ammonia, and phenols to deliver the corresponding mono- or dinuclear [Me3NN]Ni-FG species (FG = O2NCH2, R-NH, ArNH, PhC(O)NH, PhC(O)CH2, NH2, and OAr). Many of these NiII complexes are capable of capturing the benzylic radical PhCH(?)CH3 to deliver the corresponding PhCH(FG)CH3 products featuring C-C, C-N, or C-O bonds. Density functional theory studies shed light on the mechanism of these transformations and suggest two competing pathways that depend on the nature of the functional groups. These radical capture reactions at [NiII]-FG complexes outline key C-C, C-N, and C-O bond forming steps, foreshadowing families of nickel radical relay catalysts.

Full text of DOI:10.1021/acs.organomet.0c00021

pubs.acs.org/Organometallics
Article
Radical Capture at Nickel(II) Complexes: C−C, C−N, and C−O Bond
Formation
Abolghasem Gus Bakhoda, Stefan Wiese, Christine Greene, Bryan C. Figula, Jeffery A. Bertke,
and Timothy H. Warren*
Cite This: https://dx.doi.org/10.1021/acs.organomet.0c00021
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: The dinuclear β-diketiminato NiII tert-butoxide {[Me3NN]Ni}2(μ-
OtBu)2 (2), synthesized from [Me3NN]Ni(2,4-lutidine) (1) and di-tert-butylperoxide,
is a versatile precursor for the synthesis of a series of NiII complexes [Me3NN]Ni−FG
(FG = functional group) to illustrate C−C, C−N, and C−O bond formation at NiII via
radical capture. {[Me3NN]Ni}2(μ-OtBu)2 reacts with nitromethane, alkyl and aryl
amines, acetophenone, benzamide, ammonia, and phenols to deliver the corresponding
mono- or dinuclear [Me3NN]Ni−FG species (FG = O2NCH2, R−NH, ArNH,
PhC(O)NH, PhC(O)CH2, NH2, and OAr). Many of these NiII complexes are capable
of capturing the benzylic radical PhCH(•)CH3 to deliver the corresponding
PhCH(FG)CH3 products featuring C−C, C−N, or C−O bonds. Density functional theory studies shed light on the mechanism
of these transformations and suggest two competing pathways that depend on the nature of the functional groups. These radical
capture reactions at [NiII]−FG complexes outline key C−C, C−N, and C−O bond forming steps, foreshadowing families of nickel
radical relay catalysts.
3
As Csp −H bonds are ubiquitous in organic molecules,
INTRODUCTION
■
3
discovering new methods to carry out Csp −H functionaliza-
tion opens new opportunities to modify existing molecules.
Nickel complexes serve as highly effective catalysts for cross-
coupling reactions.1 Alongside palladium, nickel has been used
extensively for both Suzuki−Miyaura and Negishi cross-
couplings.2 Over the past few decades, the scope of cross-
coupling reactions has improved well beyond more conven-
tional biaryl synthesis and now includes several types of
coupling partners. For instance, Ni-catalyzed protocols for
3
Several Csp −H functionalization protocols catalyzed by first-
row transition metals such as Mn,5 Fe,6 Co,7 Ni,8 and Cu9 are
proposed to proceed via capture of an organic C-based radical
(R•) by the metal center [M]−FG (where FG is the desired
functional group) to furnish the organic product R−FG. In
particular, several groups have successfully used nickel as an
3
3
Csp −Csp bond formation with alkyl halides and organic
nucleophiles bound to Mg, B, Si, Zn, Sn, and Zr can furnish
high yields along with high stereoselectivity in some cases
(Figure 1a).3
3
3
efficient catalyst for Csp −H functionalization to form Csp −C
8
3
and Csp −N bonds via a radical-relay mechanism (Figure 2).
For instance, Ni(acac)2 has been used as an effective catalyst in
Csp −Csp bond formation in the presence of BuOOtBu as an
external oxidant (Figure 2a,b).8 Similarly, Ni(acac)2 was shown
to be an effective catalyst for N-alkoxyamidation of simple
aliphatic hydrocarbons under oxidative conditions (Figure
2f).8f Recently, alkynylation of simple (cyclo)alkanes with
terminal alkynes has been reported via a multimetal catalyzed
t
3
2
Nickel catalysis also enables cross-electrophile coupling
between sp3 and sp2 as well as sp3 electrophiles (Figure 1b).4a−f
A commonly accepted mechanism involves the oxidative
addition of R−X that generates a X−[NiII]−R species followed
by attack of an alkyl radical R′• generated from R′−X′ under
reductive conditions to give the R−R′ coupled product. These
reactions can also proceed via metallaphotoredox conditions
that generate the alkyl radical R′• from carboxylic acids,
organoborate salts, alkylsilicates, and aryl halides, as well as
from sp3 C−H bonds via H atom abstraction (Figure 1c).4g−r
Attack of the alkyl radical R′• on X-[NiII]−R provides a NiIII
complex X−[NiIII](R)(R′) susceptible to reductive elimination
(Figure 1d). Alternatively, this NiIII intermediate can be
generated from a NiI organometallic [NiI]−R′ upon the
oxidative addition of R−X.4s−u In either case, the coupling
partners assemble to form a NiIII intermediate that enables R−
R′ bond formation.
3
reaction strategy in which Csp −Csp bond formation takes place
at Ni (Figure 2e).8a,c While these C−H functionalization
reactions are not as mechanistically well-defined, alkyl radicals
R• are thought to be involved en route to R−FG formation.
Received: January 11, 2020
https://dx.doi.org/10.1021/acs.organomet.0c00021
© XXXX American Chemical Society
Organometallics XXXX, XXX, XXX−XXX
A

Organometallics
pubs.acs.org/Organometallics
Article
Khasrasch−Sosnovky reaction.9 Seminal work by Kharasch and
Sosnovsky introduced Cu as an effective catalyst for the
formation of C−O bonds from a peroxyester.9j In the presence
of cuprous salts, tert-butyl perbenzoate (tBuO-OC(O)Ph)
3
reacts with various olefins to construct new Csp −O bonds in
the corresponding allylic benzoates.9j It is thought that a
radical R• generated via H atom abstraction of R−H from an
alkoxy radical reacts with a [CuII]−FG complex to deliver R−
FG products. Kochi demonstrated that a range of CuII
complexes containing the anions FG− (FG = O2CR, Cl, Br,
I, SCN, N3, and CN) lead to R−FG bond formation.10 More
recently, we have unequivocally demonstrated radical capture
by [CuII]−FG complexes (FG = anilide, phenoxide) formed by
acid−base reaction between [CuII]−OtBu and H−NHAr or
Ac−OAr enables C−H amination and etherification (Figure
3).11 Such radical-relay mechanisms have also been used for
C−C bond formation.12
Figure 1. Ni-catalyzed cross-coupling reactions.
Figure 3. Top: C−N and C−O bond formation by radical capture at
a copper(II) anilide and phenolate. Bottom: Radical capture at related
NiII complexes investigated in this work.
To expand the scope of functional groups that can be
installed via sp3 radicals, we were intrigued by the possibility of
related radical capture reactions at corresponding nickel
complexes [NiII]−FG (Figure 3). We hypothesized that such
nickel complexes could generally be more thermally stable than
corresponding [CuII]−FG complexes that can be prone to
reduction to [CuI], either via H atom abstraction to form H−
FG11c or via formation of FG−FG bonds (e.g., FG =
NHPh).11g This study outlines a general pathway for the
formation of a wide range of [NiII]−FG species from a
common [NiII]2(μ-OtBu)2 intermediate that features a basic
tert-butoxide group that enables facile acid−base reactions with
a range of H−FG species. Many of these [NiII]−FG species
undergo radical capture with the PhCH(•)Me radical,
foreshadowing new potential families of nickel catalysts for
radical relay reactions.
RESULTS AND DISCUSSION13
3
Figure 2. Csp −H functionalization catalyzed by Ni through alkyl
■
radical capture.
Synthesis and Characterization of Dinuclear Nickel(II)
tert-Butoxide 2. Since β-diketiminato [CuII]−OtBu com-
plexes allow for acid−base reactions with diverse H−FG
species to form [CuII]−FG intermediates that function in
The longest known system for catalytic C−H functionaliza-
tion that involves radical capture is the copper-catalyzed
B
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
radical relay catalysis,11 we sought the synthesis of the
plexes (FG = NO2CH2, CH2C(O)Ph, NHC(O)Ph, NHAr,
NHR, or OAr) as illustrated in Figure 5.
t
corresponding nickel analogue. Addition of excess BuOOtBu
Synthesis and Characterization of Mononuclear
Nickel(II) Nitromethanoate 3, Enolate 4, and Benza-
mide 5. {[Me3NN]Ni}2(μ-OtBu)2 (2) reacts with nitro-
methane to form mononuclear complex [Me3NN]Ni(κ2-
O2NCH2) (3) isolated as red crystals from ether in 78%
(Figure 6a). Complex 3 exhibits a somewhat unusual O,O′-
nitromethanoato coordination mode17 that gives rise to square
planar coordination at the NiII center. The Ni−O distances in
3 are 1.9064(13) and 1.9281(13) Å with O−N−O and O−
Ni−O angles of 110.03(14)° and 69.20(5)°, respectively
(Figure 6a). The CN distance is significantly shortened to
1.280(2) Å that indicates substantial CN double-bond
character as compared to a normal C−N single bond at 1.47 Å
(Figure 6a). This square planar complex is diamagnetic whose
NMR spectra in benzene-d6 exhibit effective C2v symmetry.
The IR spectrum of 3 shows νNO bands at 1608 and 1624 cm−1
along with νCN at 1529 cm−1 in accordance with reported
literature values.17
to a solution of nickel(I) complex [Me3NN]Ni(2,4-lutidine)
(1)14 in Et2O at RT results in the precipitation of the NiII
alkoxide {[Me3NN]Ni}2(μ-OtBu)2 (2) in 82% isolated yield as
Figure 4. Synthesis and crystal structure of complex 2.
Upon reaction with 2 equiv of acetophenone, complex 2
furnishes [Me3NN]Ni(η3-CH2C(O)Ph) (4) as yellow crystals
from ether in 60% isolated yield. While there are several early
transition-metal−enolate structures with either κ2- or η3-O-
binding coordination bonding modes,18 complex 4 is a
particularly rare, first-row transition-metal−enolate with both
O- and C-coordination, joined by only [NNN]Cu(κ1-OC(C
C(Me)Ph) recently reported by Tolman.18c The phenyl
enolate ligand binds to the nickel center through an η3-
interaction involving the O,C, and C atoms in the delocalized
a dark green solid (Figure 4). Slow vapor diffusion of
tBuOOtBu into a toluene solution of 1 forms dark green
crystals suitable for single-crystal X-ray diffraction. The solid-
state structure of dinuclear 2 consists of two monomeric
[Me3NN]NiII−OtBu units in which the two Ni centers are
related by an inversion center with a Ni···Ni separation of
3.058 Å (Figure 4). Complex 2 exhibits pseudotetrahedral
coordination at Ni with twist angles between N−Ni−N and
O−Ni−O planes of 83.01° and Ni−O distances of 1.9527(14)
and 1.9828(14) Å. Dinuclear 2 is structurally similar to
{[Me3NN]Ni}2(μ-OCy)2 (Cy = cyclohexyl) originally synthe-
sized by reaction of ONOCy with [Me3NN]NiI(lut).15 As
suggested by its tetrahedral geometry around the Ni center,
complex 2 is paramagnetic in solution with a μeff of 3.3(4) B.M.
in toluene-d8 by the Evans method,16 indicating some degree
of antiferromagnetic coupling.
π-system. The Ni−CCH and Ni−O bond distances in 4 are
2
2.0570(16) and 1.9055(11) Å, respectively, while the Ni−
Ccarbonyl bond length is 2.0400(16) Å (Figure 6b). The IR
spectrum of 4 shows a νCO band at 1651 cm−1. Similarly, 2
reacts with 2 equiv of benzamide to yield an analogous
[Me3NN]Ni(κ2-NHC(O)Ph) (5) complex isolated in 55%
yield as brown crystals. Benzamide complex 5 exhibits square
planar structure (Figure 6c) closely related to that of 4. The
Ni−Namide and Ni−O bond distances in 5 are 1.948(19) and
1.906(13) Å, respectively, while the Ni−Ccarbonyl bond length is
2.316(5) Å. Thus, 5 is best considered κ2-N,O with the Ni
center only 33.95° out of the benzamide O−C−N plane,
Despite the dinuclear nature that renders it rather insoluble
in common hydrocarbon solvents, 2 reacts readily with a
number of mildly acidic substrates H−FG to provide
mononuclear [NiII]−FG and dinuclear [NiII]2(μ-FG)2 com-
Figure 5. Synthetic pathways for the synthesis of NiII complexes 3−11.
C
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Figure 6. Crystal structures of complexes 3, 4, and 5. Ellipsoids are shown at 50% (3 and 4) and 30% (5) probability. H atoms have been omitted
for clarity with the exception of the C−H bonds in nitromethanoato and enolato ligands in 3 and 4, respectively, as well as the amido N−H bond in
5.
Figure 7. Crystal structures of complexes 6, 7, and 8. Ellipsoids are shown at 30% (6 and 7) and 50% (8) probability levels and hydrogen atoms
have been omitted for clarity with the exception of the N−H bonds in amido and anilido ligands.
Figure 8. Crystal structures of complexes 9 (left), 10 (middle), and 11 (right). Ellipsoids are shown at 30% (9) and 50% (10 and 11) probability
levels and hydrogen atoms have been omitted for clarity except the N−H bonds in the anilido ligand of 11.
whereas in η3-O,C,C-acetophenone enolate 4, the Ni center is
64.20° out of the enolate O−C−C plane.
benzamide 5 with ΔG⧧(288 K) = 13.9(4) kcal/mol and
ΔG⧧(207 K) = 10.3(2) kcal/mol, respectively (Figures S21
and S22).
1
Diamagnetic 4 and 5 exhibit fluxional H NMR spectra in
toluene-d8. At −80 °C, 4 and 5 each shows two sets of two
distinct β-diketiminato N-aryl ortho-Me, para-Me, and back-
bone Me resonances (Figures S21−S22) consistent with their
solid-state structure that possess two different donors in square
planar 4 and 5. Warming results in coalescence of these sets of
resonances indicating a symmetrization within the coordina-
tion wedge that may proceed via three-coordinate κ1-enolate
and κ1-benzamide intermediates or tetrahedral κ2-intermedi-
ates. The barrier is higher for enolate derivative 4 than for
Synthesis and Characterization of Dinuclear Nickel(II)
Alkylamide 6, Anilide 7, and Parent Amide 8. Both
phenethylamine and 3,5-dimethylaniline undergo an acid−base
reaction with 2 to provide dinuclear complexes {[Me3NN]-
Ni}2(μ-NHCH2CH2Ph)2 (6) and {[Me3NN]Ni}2(μ-
NHPh3,5‑Me2)2 (7) isolated as red crystals in 58 and 62%
yields, respectively (Figures 7a,b). X-ray structures of 6 and 7
reveal dinuclear, slightly distorted square planar structures
bridged by amide or anilide ligands to give Ni centers related
D
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
by inversion symmetry with Ni···Ni separations of 2.949 and
2.998 Å, respectively (Figures 7a,b). The Ni−Namido distances
in 6 are 1.918(3) and 1.922(3) Å, whereas 7 shows Ni−Namido
bond lengths of 1.9462(13) and 1.9551(13) Å. In both
complexes 6 and 7, the Ni centers adopt a twisted square
planar geometry with angles of 20.02 and 22.14° between the
Nβ‑dik−Ni−Nβ‑dik and opposing N3−Ni−N3′ planes, respec-
1
tively. In solution, 7 is diamagnetic and possesses a H NMR
spectrum in C6D6 at room temperature (Figure S15) that
features a β-diketiminato C−H backbone resonance at δ 4.51
ppm with two different signals for the β-diketiminato N-aryl
meta-Ar−H sites at δ 6.880 and 6.464 ppm. Thus, 7 maintains
its dimeric, square-planar structure in solution at room
temperature with one anilido NArMe2 group above and below
the N3−Ni−N3′ plane.
A particularly novel complex, the parent amido species
{[Me3NN]Ni}2(μ-NH2)2 (8), was isolated in 91% yield as
orange crystals by slow diffusion of NH3 into a solution of
{[Me3NN]Ni}2(μ-OtBu)2 (2) (Figure 8c). As compared to
dinuclear amido complexes 6 and 7, parent amide 8 possesses
the shortest Ni−Namide bond distances of 1.9001(11) and
1.9017(11) Å that result in a shortened Ni···Ni separation of
2.919 Å (Figure 7c). The twist angle between the Nβ‑dik−Ni−
Nβ‑dik and Namide−Ni−Namide planes of 18.42° deviates least
from idealized square planar geometry, likely a result of the
minimal steric demands of the amido ligands. Unfortunately, 8
is not soluble in organic solvents even at elevated temper-
atures, which hampers its solution characterization. FT-IR
spectrum of 8 shows two peaks at 3430 and 3413 cm−1 as a
result of two N−H stretching modes of the amido ligand.
Synthesis and Characterization of Dinuclear and
Mononuclear Nickel(II) Phenolates 9 and 10 and
Mononuclear Anilide 11. Nickel(II) complexes [NiII]−FG
that bear weaker donors give rise to dinuclear or mononuclear
species that are paramagnetic. For instance, addition of 2 equiv
of phenol to {[Me3NN]Ni}2(μ-OBut)2 (2) in ether at RT gives
the dinuclear phenoxide complex {[Me3NN]Ni}2(μ-OPh)2
(9) as dark green crystals (Figure 8a). The X-ray structure
of 9 reveals a distorted tetrahedral environment around the
NiII centers with Ni−O distances of 1.966(3) and 1.967(3) Å
along with a Ni···Ni separation of 3.115 Å, which is the longest
in the series of dinuclear complexes 6, 7, and 8 (Figures 8a−c).
This complex is paramagnetic in solution with a μeff of 2.7(2)
B.M. in benzene-d6 by the Evans method.16
Figure 9. PhCH(•)Me radical capture by [NiII]−FG complexes.
from the aliphatic azo compound (E/Z)-azobis(α-phenyl-
ethane) at 100 °C (Figure 9).19 Reaction of complexes 3−7
and 9 with (E/Z)-azobis(α-phenylethane) at 100 °C in
fluorobenzene solvent gave 25−67% yields of the correspond-
ing radical capture products PhCH(FG)Me. Thus, radical
capture at [NiII]−FG complexes results in the formation of C−
C (59% for 3 and 61% for 4), C−N (67% for 5, 55% for 6, and
25% for 7), and C−O (48% for 9) bonds. In the case of
complex 7, concomitant formation of diazene ArNNAr (Ar
= 3,5-Me2C6H3) was observed in 49% GC yield along with
25% yield of the amination product PhCH(NHAr)Me. For the
parent amide complex {[Me3NN]Ni}2(μ-NH2) (8) only a
trace amount of the C−H amination product PhCH(NH2)Me
was detected by GC-MS analysis, attributed to its poor
solubility, even at elevated temperatures.
In contrast, mononuclear complexes [Me3NN]Ni−FG with
bulky, electron-poor functional groups (FG = OArCl3 (10) or
NHArCl3 (11)) did not result in radical capture. Rather, only
erythro and threo isomers of the ethylbenzene radical dimer
PhCH(Me)−CH(Me)Ph are observed. In fact, this product of
PhCH(•)Me radical dimerization occurs in comparable
amounts across all reactions. Control experiments show no
radical capture at room temperature after overnight stirring of
the complexes with (E/Z)-azobis(α-phenylethane) in PhF.
Computational Analysis of Radical Capture Pathways
at Nickel(II) Nitromethanoate 3 and Benzamide 5. Most
mechanistic proposals for Ni-catalyzed Csp2-Csp3 bond
formation involve radical capture at NiII to form a NiIII
organometallic complex, followed by reductive elimination
(Figures 1d and 10, route a).4,20 A less prominent mechanism
involves concerted bond formation between the PhCH(•)Me
radical at the functional group (Figure 10, route b).21 When
radical capture at the functional group involves bond formation
with an atom that is bound to the metal center, both radical
capture at the metal center and functional group could be
competitive. To illustrate this competition between radical
capture pathways, we computationally considered capture of
Addition of the bulky, electron-poor 2,4,6-trichlorophenol or
2,4,6-trichloroaniline to 2 provided deep blue [Me3NN]Ni−
OPh2,4,6‑Cl (10) or teal [Me3NN]Ni−NHPh2,4,6‑Cl (11)
isolated in 49 and 40% yields, respectively (Figures 8b,c).
These structures feature much shorter Ni−N and Ni−O
distances to the anilido or phenoxy donors, 1.8765(19) and
1.8812(12) Å, respectively, than observed in the dinuclear
structures of 7 and 9. Interestingly, these structures are best
described as pseudotetrahedral due to coordination of one of
the ortho-Cl atoms with Ni−Cl distances of 2.4811(6) and
2.4595(5) Å in anilido 10 and phenoxy 11, respectively.
Accordingly, each is paramagnetic in solution with magnetic
susceptibilities (benzene-d6) of 2.8(1) and 2.6(2) B.M.,16
respectively. This is consistent with S = 1, high-spin d8
electronic structures.
3
3
Capture of the PhCH(•)Me Radical by [NiII]−FG
Complexes. We explored the radical capture ability of each
[Me3NN]Ni−FG complex 3−11 through the in situ
generation of the secondary benzylic radical PhCH(•)Me
E
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
center to form the NiIII organometallic species [Me3NN]-
NiIII(κ2-NHC(O)Ph)(CH(Ph)CH3) is slightly endergonic at
3.2 kcal/mol with a barrier of 8.8 kcal/mol. The overall barrier
for C−N bond formation comes from the reductive
elimination of [Me3NN]NiIII(κ2-NHC(O)Ph)(CH(Ph)CH3)
at 13.6 kcal/mol. We also considered the alternative pathway
with the formation of a [Me3NN]NiIII(κ1-NH(CH(Ph)CH3)-
C(O)Ph) intermediate via radical capture at the functional
group. We took into consideration the binding of the radical at
[Me3NN]NiIII(κ2-NHC(O)Ph) 5, but a relaxed potential
energy scan found that isomerization occurred prior to radical
binding. We propose that the [Me3NN]Ni(κ2-NHC(O)Ph)
will isomerize to form a [Me3NN]Ni(κ1NHC(O)Ph) complex
endergonically at +6.7 kcal/mol with a barrier of 9.4 kcal/mol
(at 298 K). While other isomers of [Me3NN]Ni(κ2-NHC(O)-
Ph) were considered, we found that the [Me3NN]Ni(κ1-
NHC(O)Ph) isomer was the most likely pathway (Scheme
S3). The calculated barrier for κ2 to κ1 isomerization is close to
the experimental value ΔG⧧(207 K) = 10.3(2) kcal/mol for
symmetrization determined by variable temperature NMR
(Figure S22). [Me3NN]Ni(κ1-NHC(O)Ph) can then undergo
direct radical capture at the functional group to form
Figure 10. Possible mechanistic routes for [NiII]−FG radical capture
in benzene.
the PhCH(•)Me radical at NiII nitromethanoate 3 and
benzamide 5.
DFT studies at the BP86+GD3BJ/6-311++G(d,p)/SMD-
benzene// BP86/6-31+G(d)/SMD-gas level of theory consid-
er both distinct pathways to form PhCH(FG)Me products
from 3 and 5 with PhCH(•)Me. In all cases, we consider the
NiI solvento species [Me3NN]Ni(η2-benzene) as the final
product to assess the overall thermodynamics of radical
capture. Accordingly, capture of the ethylbenzene radical by
nitroalkanoate [Me3NN]NiII(κ2-O2N = CH2) (3) and
benzamide [Me3NN]Ni(κ2-NHC(O)Ph) (5) is thermody-
namically favored with ΔGrxn = −18.2 and −8.1 kcal/mol,
respectively (Figure 11).
[Me3NN]Ni(NH(CH(CH3)C(O)Ph) complex (ΔGoverall
=
−6.4 kcal/mol) with an overall barrier of +14.9 which is
higher in energy than the barrier for the radical capture at the
metal center by 1.3 kcal/mol. While the barrier for radical
capture is slightly higher in energy at the metal center than at
the functional group, the difference between both pathways is
within the range of error suggesting that these pathways could
be competitive.
We considered in detail the interaction of the ethylbenzene
radical with nitroalkanoate 3 (Figure 11a). Radical capture at
the metal center to form the NiIII organometallic species
[Me3NN]NiIII(κ2-O2NCH2)(CH(Ph)CH3) is endergonic (ΔG
= +5.8 kcal/mol) and possesses a barrier of 11.3 kcal/mol.
However, direct capture of the radical at the C atom of the
nitroalkanoate ligand in [Me3NN]NiII(κ2-O2NCH2) (3) is
significantly exergonic to form [Me3NN]Ni(κ2-O2NCH2−
CH(CH3)Ph) with ΔG = −15.9 kcal/mol. Importantly, this
direct capture exhibits only a modest barrier of 7.5 kcal/mol,
which is lower in energy than the barrier for the formation of
the NiIII intermediate. Thus, direct C−C bond formation at the
nitromethanoate ligand is favored over initial radical capture at
the metal center.
For [Me3NN]NiII(κ2-O2NCH2) (3) radical capture at the
functional group is situated away from the metal center and
thus is the thermodynamically favored pathway. For radical
capture involving [Me3NN]Ni(κ2-NHC(O)Ph) (5), however,
a rearrangement is necessary for direct bond formation to
occur at the functional group. This barrier is within the same
thermodynamical range as radical capture at the metal center.
The results of this DFT study indicate that the mechanism is
highly dependent upon the functional group. This outlined
mechanism gives new insight into the importance of the
functional group in radical capture allowing for new variables
to be explored to improve catalytic function.
Examining the interaction of ethylbenzene radical (R•) with
benzamide 5 (Figure 11b), we find that capture at the metal
Figure 11. Possible mechanistic routes for radical capture at [Me3NN]NiII−FG complexes 3 and 5 in benzene at 298 K. Transition states that are
barriers for the pathway are bolded. All metal complexes are S = 1/2 species except 3,5-κ2-N,O, and 5-κ1-N. All values are in kcal/mol at 298 K.
F
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
CONCLUSIONS
AUTHOR INFORMATION
Corresponding Author
■
■
{[Me3NN]Ni}2(μ-OtBu)2 (2) serves as a versatile precursor
for the installation of a variety of functional groups onto the β-
diketiminato NiII center. H−FG reagents such as ammonia,
alkyl amines, anilines, nitromethane, acetophenone, benza-
mide, and phenols cleanly react with 2 to give mono- and
dinuclear β-diketiminato [NiII]−FG species that may be
isolated and fully characterized. Despite the considerably
higher pKa of many of the N−H and C−H bonds in substrates
used to install functional groups at NiII via {[Me3NN]Ni}2(μ-
OtBu)2 (2) as compared to the leaving H−OtBu, the
preference of later first row metals for somewhat softer donors
overcomes this unfavorable pKa difference, in some cases
assisted by chelation. Importantly, the mononuclear S = 0
[NiII]−FG complexes as well as the soluble dinuclear
[NiII]2(μ-FG)2 complexes capture the alkyl radical PhCH(•)-
CH3 to form PhCH(FG)CH3, clearly illustrating the ability of
a range of NiII complexes [NiII]−FG to mediate C−C, C−N,
Timothy H. Warren − Georgetown University, Department of
Chemistry, Washington, District of Columbia 20057-1227,
United States; orcid.org/0000-0001-9217-8890;
Email: thw@georgetown.edu
Authors
Abolghasem Gus Bakhoda − Georgetown University,
Department of Chemistry, Washington, District of Columbia
20057-1227, United States; orcid.org/0000-0002-3222-
8873
Stefan Wiese − Georgetown University, Department of
Chemistry, Washington, District of Columbia 20057-1227,
United States
Christine Greene − Georgetown University, Department of
Chemistry, Washington, District of Columbia 20057-1227,
United States
Bryan C. Figula − Georgetown University, Department of
Chemistry, Washington, District of Columbia 20057-1227,
United States
•
3
and C−O bond forming steps via Csp radicals R . Since nearly
all complexes of 3−7 and 9 that undergo radical capture are
reasonably stable at high temperatures required for PhCH(•)-
CH3 generation from the corresponding diazene RNNR
(Figures S23−S27), it is unlikely that alkyl radical capture
proceeds via ejection of a (•)FG radical from [NiII]−FG
complexes. Rather, alkyl radical capture occurs at somewhat
sterically shielded [NiII]−FG complexes, further supported by
the lack of radical capture when [NiII](κ2-NHC(O)Ph) (5) is
heated with with tBuNNtBu that readily generates the more
Jeffery A. Bertke − Georgetown University, Department of
Chemistry, Washington, District of Columbia 20057-1227,
United States; orcid.org/0000-0002-3419-5163
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00021
Notes
22
t
hindered Bu(•) radical.
The authors declare no competing financial interest.
Curiously, mononuclear S = 1 NiII phenolate 10 and anilide
11 did not provide radical capture products. This suggests that
their rates of radical capture are much slower than those of the
other complexes bearing more electron-rich functional groups.
Thus, there may be an electronic basis for the differential
radical capture behavior since these mononuclear complexes
do not have any obvious steric constraints against radical
capture. Moreover, computational studies identify competing
pathways for R−FG bond formation, indicating that radical
capture at NiII to give a NiIII intermediate is not always the
favored pathway as commonly assumed (Figure 1). Since
[NiII]−OtBu intermediates can be formed via interaction of
tBuOOtBu and [NiI] as well as undergo facile acid−base
reactions with H−FG to form key [NiII]−FG intermediates,
these [NiII]−FG species provide fresh insight into an array of
bond forming reactions that can be realized through C−H
functionalization utilizing new nickel radial relay catalysts.
ACKNOWLEDGMENTS
■
T.H.W. is grateful to the National Science Foundation (CHE-
1665348) and the Georgetown Environment Initiative for
support of this work.
REFERENCES
■
(1) (a) Hazari, N.; Melvin, P. R.; Beromi, M. M. Well-defined nickel
and palladium precatalysts for cross-coupling. Nat. Rev. Chem. 2017,
1, No. 0025. (b) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Recent
advances in homogeneous nickel catalysis. Nature 2014, 509, 299−
309. (c) Yamaguchi, J.; Muto, K.; Itami, K. Recent Progress in Nickel-
Catalyzed Biaryl Coupling. Eur. J. Org. Chem. 2013, 2013, 19−30.
(d) Rosen, B. M.; Quasdorf, K. W.; Wilson, D. A.; Zhang, N.;
Resmerita, A.-M.; Garg, N. K.; Percec, V. Nickel-Catalyzed Cross-
Couplings Involving Carbon−Oxygen Bonds. Chem. Rev. 2011, 111,
́
1346−1416. (e) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.;
Lemaire, M. Aryl−Aryl Bond Formation One Century after the
Discovery of the Ullmann Reaction. Chem. Rev. 2002, 102, 1359−
1469.
ASSOCIATED CONTENT
■
sı
* Supporting Information
(2) Han, F.-S. Transition-metal-catalyzed Suzuki−Miyaura cross-
coupling reactions: a remarkable advance from palladium to nickel
catalysts. Chem. Soc. Rev. 2013, 42, 5270−5298.
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00021.
(3) (a) Fu, G. C. Transition-Metal Catalysis of Nucleophilic
Substitution Reactions: A Radical Alternative to SN1 and SN2
Processes. ACS Cent. Sci. 2017, 3, 692−700. (b) Choi, J.; Fu, G. C.
Transition metal−catalyzed alkyl-alkyl bond formation: Another
dimension in cross-coupling chemistry. Science 2017, 356,
No. eaaf7230. (c) Lou, S.; Fu, G. C. Enantioselective Alkenylation
via Nickel-Catalyzed Cross-Coupling with Organozirconium Re-
agents. J. Am. Chem. Soc. 2010, 132, 5010−5011.
(4) (a) Weix, D. J. Methods and Mechanisms for Cross-Electrophile
Coupling of Csp2 Halides with Alkyl Electrophiles. Acc. Chem. Res.
2015, 48, 1767−1775. (b) Ackerman, L. K. G.; Anka-Lufford, L. L.;
Naodovic, M.; Weix, D. J. Cobalt co-catalysis for cross-electrophile
coupling: diarylmethanes from benzyl mesylates and aryl halides.
Synthesis and characterization of all the compounds in
this work and X-ray diffraction structures (PDF)
DFT calculated Cartesian coordinates for the optimized
structures (XYZ)
Accession Codes
CCDC 1861876−1861885 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
G
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Chem. Sci. 2015, 6, 1115−1119. (c) Everson, D. A.; Weix, D. J. Cross-
Electrophile Coupling: Principles of Reactivity and Selectivity. J. Org.
Chem. 2014, 79, 4793−4798. (d) Biswas, S.; Weix, D. J. Mechanism
and Selectivity in Nickel-Catalyzed Cross-Electrophile Coupling of
Aryl Halides with Alkyl Halides. J. Am. Chem. Soc. 2013, 135, 16192−
16197. (e) Everson, D. A.; Jones, B. A.; Weix, D. J. Replacing
Conventional Carbon Nucleophiles with Electrophiles: Nickel-
Catalyzed Reductive Alkylation of Aryl Bromides and Chlorides. J.
Am. Chem. Soc. 2012, 134, 6146−6159. (f) Everson, D. A.; Shrestha,
R.; Weix, D. J. Nickel-Catalyzed Reductive Cross-Coupling of Aryl
Halides with Alkyl Halides. J. Am. Chem. Soc. 2010, 132, 920−921.
(g) Twilton, J.; Le, C.; Zhang, p.; Shaw, M. H.; Evans, R. W.;
MacMillan, D. W. C. Earth-Abundant Transition Metal Catalysts for
Alkene Hydrosilylation and Hydroboration: Opportunities and
Assessments. Nat. Rev. Chem. 2017, 1, No. 0052. (h) Nielsen, M.
K.; Shields, B. J.; Liu, j.; Williams, M. J.; Zacuto, M. J.; Doyle, A. G.
Mild, Redox-Neutral Formylation of Aryl Chlorides through the
Photocatalytic Generation of Chlorine Radicals. Angew. Chem., Int. Ed.
2017, 56, 7191−7194. (i) Tellis, J. C.; Kelly, C. B.; Primer, D. N.;
Jouffroy, M.; Patel, N. R.; Molander, G. A. Single-Electron
Transmetalation via Photoredox/Nickel Dual Catalysis: Unlocking a
New Paradigm for sp3−sp2 Cross-Coupling. Acc. Chem. Res. 2016, 49,
1429−1439. (j) Oderinde, M. S.; Frenette, M. A.; Aquila, B.; Robbins,
D. W.; Johannes, J. W. Photoredox Mediated Nickel Catalyzed Cross-
Coupling of Thiols With Aryl and Heteroaryl Iodides via Thiyl
Radicals. J. Am. Chem. Soc. 2016, 138, 1760−1763. (k) Ahneman, D.
T.; Doyle, A. G. C−H functionalization of amines with aryl halides by
nickel-photoredox catalysis. Chem. Sci. 2016, 7, 7002−7006.
(l) Shields, B. J.; Doyle, A. G. Direct C(sp3)−H Cross Coupling
Enabled by Catalytic Generation of Chlorine Radicals. J. Am. Chem.
Soc. 2016, 138, 12719−12722. (m) Gutierrez, O.; Tellis, J. C.; Primer,
D. N.; Molander, G. A.; Kozlowski, M. C. Nickel-Catalyzed Cross-
Coupling of Photoredox-Generated Radicals: Uncovering a General
Manifold for Stereoconvergence in Nickel-Catalyzed Cross-Cou-
plings. J. Am. Chem. Soc. 2015, 137, 4896−4899. (n) Xuan, J.; Zeng,
T.-T.; Chen, J.-R.; Lu, L.-Q.; Xiao, W.-J. Room Temperature C-P
Bond Formation Enabled by Merging Nickel Catalysis and Visible-
Light-Induced Photoredox Catalysis. Chem. - Eur. J. 2015, 21, 4962−
4965. (o) Tellis, J. C.; Primer, D. N.; Molander, G. A. Single-electron
transmetalation in organoboron cross-coupling by photoredox/nickel
dual catalysis. Science 2014, 345, 433−436. (p) Skubi, K. L.; Blum, T.
R.; Yoon, T. P. Dual Catalysis Strategies in Photochemical Synthesis.
Chem. Rev. 2016, 116, 10035−10074. (q) Ni, S.; Li, C.-X.; Mao, Y.;
Han, J.; Wang, y.; Yan, H.; Pan, Y. Ni-catalyzed deaminative cross-
electrophile coupling of Katritzky salts with halides via C−N bond
activation. Sci. Adv. 2019, 5, No. eaaw9516. (r) Shen, Y.; Gu, Y.;
Martin, R. sp3 C−H Arylation and Alkylation Enabled by the Synergy
of Triplet Excited Ketones and Nickel Catalysts. J. Am. Chem. Soc.
2018, 140, 12200−12209. (s) García-Domínguez, A.; Mondal, R.;
Nevado, C. DualPhotoredox/Nickel-CatalyzedThree-Component
Carbofunctionalization of Alkenes. Angew. Chem., Int. Ed. 2019, 58,
12286−12290. (t) García-Domínguez, A.; Li, Z.; Nevado, C. Nickel-
Catalyzed Reductive Dicarbofunctionalization of Alkenes. J. Am.
Chem. Soc. 2017, 139, 6835−6838. (u) Li, Z.; García-Domínguez, A.;
Nevado, C. Nickel-Catalyzed Stereoselective Dicarbofunctionalization
of Alkynes. Angew. Chem., Int. Ed. 2016, 55, 6938−6941. (v) Luo, F.
X.; Cao, Z.-C.; Zhao, H.-W.; Wang, D.; Zhang, Y.-F.; Xu, X.; Shi, Z.-J.
Nickel-Catalyzed Oxidative Coupling of Unactivated C(sp3)−H
Bonds in Aliphatic Amides with Terminal Alkynes. Organometallics
2017, 36, 18−21.
751−759. (d) Liu, W.; Groves, J. T. Manganese Catalyzed C−H
Halogenation. Acc. Chem. Res. 2015, 48, 1727−1735.
(6) (a) Yamane, Y.; Yoshinaga, K.; Sumimoto, M.; Nishikata, T.
Iron-Enhanced Reactivity of Radicals Enables C−H Tertiary
Alkylations for Construction of Functionalized Quaternary Carbons.
ACS Catal. 2019, 9, 1757−1762. (b) Pangia, T. M.; Davies, C. G.;
Prendergast, J. R.; Gordon, J. B.; Siegler, M. A.; Jameson, G. N. L.;
Goldberg, D. P. Observation of Radical Rebound in a Mononuclear
Nonheme Iron Model Complex. J. Am. Chem. Soc. 2018, 140, 4191−
̈
4194. (c) Zaragoza, J. P. T.; Yosca, T. H.; Siegler, M. A.; Moenne-
Loccoz, P.; Green, M. T.; Goldberg, D. P. Direct Observation of
Oxygen Rebound with an Iron-Hydroxide Complex. J. Am. Chem. Soc.
2017, 139, 13640−13643. (d) Karimov, R. R.; Sharma, A.; Hartwig, J.
F. Late Stage Azidation of Complex Molecules. ACS Cent. Sci. 2016, 2,
715−724. (e) Sharma, A.; Hartwig, J. F. Metal-catalysed azidation of
tertiary C−H bonds suitable for late-stage functionalization. Nature
́
2015, 517, 600−604. (f) Krebs, C.; Galonic Fujimori, D.; Walsh, C.
T.; Bollinger, J. M., Jr. Non-Heme Fe(IV)−Oxo Intermediates. Acc.
Chem. Res. 2007, 40, 484−492.
(7) (a) Yoshino, T.; Matsunaga, S. Cobalt-Catalyzed C(sp3)−H
Functionalization Reactions. Asian J. Org. Chem. 2018, 7, 1193−1205.
(b) Lu, H.; Li, C.; Jiang, H.; Lizardi, C. L.; Zhang, X. P.
Chemoselective Amination of Propargylic C(sp3)-H Bonds by
Cobalt(II)-Based Metalloradical Catalysis. Angew. Chem., Int. Ed.
2014, 53, 7028−7032. (c) Belof, J. L.; Cioce, C. R.; Xu, X.; Zhang, X.
P.; Space, B.; Woodcock, H. L. Characterization of Tunable Radical
Metal−Carbenes: Key Intermediates in Catalytic Cyclopropanation.
Organometallics 2011, 30, 2739−2746. (d) Lyaskovskyy, V.; Suarez, A.
I. O.; Lu, H.; Jiang, H.; Zhang, X. P.; de Bruin, B. Mechanism of
Cobalt(II) Porphyrin-Catalyzed C−H Amination with Organic
Azides: Radical Nature and H-Atom Abstraction Ability of the Key
Cobalt(III)−Nitrene Intermediates. J. Am. Chem. Soc. 2011, 133,
12264−12273. (e) Caselli, A.; Gallo, E.; Fantauzzi, S.; Morlacchi, S.;
Ragaini, F.; Cenini, S. Allylic Amination and Aziridination of Olefins
by Aryl Azides Catalyzed by CoII(tpp): A Synthetic and Mechanistic
Study. Eur. J. Inorg. Chem. 2008, 2008, 3009−3019. (f) Harden, J. D.;
Ruppel, J. V.; Gao, G.-Y.; Zhang, X. P. Cobalt-catalyzed
intermolecular C−H amination with bromamine-T as nitrene source.
Chem. Commun. 2007, 4644−4646. (g) Ragaini, F.; Penoni, A.; Gallo,
E.; Tollari, S.; Li Gotti, C.; Lapadula, M.; Mangioni, E.; Cenini, S.
Amination of Benzylic C-H Bonds by Arylazides Catalyzed by CoII−
Porphyrin Complexes: A Synthetic and Mechanistic Study. Chem. -
Eur. J. 2003, 9, 249−259.
(8) (a) Tang, S.; Liu, Y.; Gao, X.; Wang, P.; Huang, P.; Lei, A. Multi-
Metal-Catalyzed Oxidative Radical Alkynylation with Terminal
Alkynes: A New Strategy for C(sp3)−C(sp) Bond Formation. J.
Am. Chem. Soc. 2018, 140, 6006−6013. (b) Li, Z.-L.; Sun, K.-K.; Cai,
C. Nickel-Catalyzed Cross-Dehydrogenative Coupling of α-C(sp3)−
H Bonds in N-Methylamides with C(sp3)−H Bonds in Cyclic
Alkanes. Org. Lett. 2018, 20, 6420−6424. (c) Tang, S.; Wang, P.; Li,
H.; Lei, A. Multimetallic catalysed radical oxidative C(sp3)−H/
C(sp)−H cross-coupling between unactivated alkanes and terminal
alkynes. Nat. Commun. 2016, 7, 11676. (d) Liu, D.; Li, Y.; Qi, X.; Liu,
C.; Lan, Y.; Lei, A. Nickel-Catalyzed Selective Oxidative Radical
Cross-Coupling: An Effective Strategy for Inert Csp3−H Function-
alization. Org. Lett. 2015, 17, 998−1001. (e) Li, K.; Wu, Q.; Lan, J.;
You, J. Coordinating activation strategy for C(sp3)−H/C(sp3)−H
cross-coupling to access β-aromatic α-amino acids. Nat. Commun.
2015, 6, 8404. (f) Zhou, L.; Tang, S.; Qi, X.; Lin, C.; Liu, K.; Liu, C.;
Lan, Y.; Lei, A. Transition-Metal-Assisted Radical/Radical Cross-
Coupling: A New Strategy to the Oxidative C(sp3)−H/N−H Cross-
Coupling. Org. Lett. 2014, 16, 3404−3407. (g) Liu, D.; Liu, C.; Li, H.;
Lei, A. Direct functionalization of tetrahydrofuran and 1,4-dioxane:
nickel-catalyzed oxidative C(sp3)-H arylation. Angew. Chem., Int. Ed.
2013, 52, 4453−4456.
(5) (a) Huang, X.; Zhuang, T.; Kates, P. A.; Gao, H.; Chen, X.;
Groves, J. T. Alkyl Isocyanates via Manganese-Catalyzed C−H
Activation for the Preparation of Substituted Ureas. J. Am. Chem. Soc.
2017, 139, 15407−15413. (b) Liu, W.; Cheng, M.-J.; Nielsen, R. J.;
Goddard, W. A., III; Groves, J. T. Probing the C−O Bond-Formation
Step in Metalloporphyrin-Catalyzed C−H Oxygenation Reactions.
ACS Catal. 2017, 7, 4182−4188. (c) Huang, X.; Groves, J. T. Taming
Azide Radicals for Catalytic C−H Azidation. ACS Catal. 2016, 6,
(9) (a) Zhang, Z.; Stateman, L. M.; Nagib, D. A. δ C−H
(hetero)arylation via Cu-catalyzed radical relay. Chem. Sci. 2019, 10,
1207−1211. (b) Stateman, L. M.; Wappes, E. A.; Nakafuku, K. M.;
Edwards, K. M.; Nagib, D. A. Catalytic β C−H amination via an
H
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
imidate radical relay. Chem. Sci. 2019, 10, 2693−2699. (c) Wang, F.;
Chen, P.; Liu, G. Copper-Catalyzed Radical Relay for Asymmetric
Radical Transformations. Acc. Chem. Res. 2018, 51, 2036−2046.
(d) Stateman, L. M.; Nakafuku, K. M.; Nagib, D. A. Remote C−H
Functionalization via Selective Hydrogen Atom Transfer. Synthesis
2018, 50, 1569−1586. (e) Kainz, Q. M.; Matier, C. D.; Bartoszewicz,
A.; Zultanski, S. L.; Peters, J. C.; Fu, G. C. Asymmetric copper-
catalyzed C-N cross-couplings induced by visible light. Science 2016,
351, 681−684. (f) Zhang, W.; Wang, F.; McCann, S. D.; Wang, D.;
Chen, P.; Stahl, S. S.; Liu, G. Enantioselective cyanation of benzylic
C−H bonds via copper-catalyzed radical relay. Science 2016, 353,
1014−1018. (g) Chikkade, P. K.; Kuninobu, Y.; Kanai, M. Copper-
catalyzed intermolecular C(sp3)−H bond functionalization towards
the synthesis of tertiary carbamates. Chem. Sci. 2015, 6, 3195−3200.
(h) Tran, B. L.; Li, B.; Driess, M.; Hartwig, J. F. Copper-Catalyzed
Intermolecular Amidation and Imidation of Unactivated Alkanes. J.
Am. Chem. Soc. 2014, 136, 2555−2563. (i) Gephart, R. T., III;
Warren, T. H. Copper-Catalyzed sp3 C−H Amination. Organo-
metallics 2012, 31, 7728−7752. (j) Kharasch, M. S.; Sosnovsky, G.
The Reactions of t-Butyl perbenzoate and Olefins-A stereospecific
Reaction. J. Am. Chem. Soc. 1958, 80, 756−756.
(14) (a) Wiese, S.; McAfee, J. L.; Pahls, D. R.; McMullin, C. L.;
Cundari, T. R.; Warren, T. H. C−H Functionalization Reactivity of a
Nickel−Imide. J. Am. Chem. Soc. 2012, 134, 10114−10121.
(b) Wiese, S.; Aguila, M. J. B.; Kogut, E.; Warren, T. H. β-
Diketiminato Nickel Imides in Catalytic Nitrene Transfer to
Isocyanides. Organometallics 2013, 32, 2300−2308.
(15) Melzer, M. M.; Jarchow-Choy, S.; Kogut, E.; Warren, T. H.
Reductive Cleavage of O-, S-, and N-Organonitroso Compounds by
Nickel(I) β-Diketiminates. Inorg. Chem. 2008, 47, 10187−10189.
(16) (a) Schubert, E. M. Utilizing the Evans method with a
superconducting NMR spectrometer in the undergraduate laboratory.
J. Chem. Educ. 1992, 69, 62. (b) Evans, D. F. The determination of the
paramagnetic susceptibility of substances in solution by nuclear
magnetic resonance. J. Chem. Soc. 1959, 2003.
(17) (a) Zhang, X.; Emge, T. J.; Ghosh, R.; Krogh-Jespersen, K.;
Goldman, A. S. Reaction of Nitromethane with an Iridium Pincer
Complex. Multiple Binding Modes of the Nitromethanate Anion.
Organometallics 2006, 25, 1303−1309. (b) Ito, H.; Ito, T. Syntheses,
Characterization, and Molecular Structures of Nitroalkanato Nickel-
(II), Zinc(II), and Cadmium(II) Complexes with Tetraazacycloal-
kanes. Chem. Lett. 1985, 14, 1251−1254.
(18) (a) Zabicky, J., Ed. The Chemistry of Metal Enolates; John Wiley
and Sons, Ltd.: West Sussex, 2009. (b) Knochel, P., Ed. Comprehensive
Organic Synthesis II; Elsevier Ltd.: Amsterdam, 2014. (c) Bailey, W.
D.; Gagnon, N. L.; Elwell, C. L.; Cramblitt, A. C.; Bouchey, C. J.;
Tolman, W. B. Revisiting the Synthesis and Nucleophilic Reactivity of
an Anionic Copper Superoxide Complex. Inorg. Chem. 2019, 58,
(10) (a) Jenkins, C. L.; Kochi, J. K. Homolytic and ionic
mechanisms in the ligand-transfer oxidation of alkyl radicals by
copper(II) halides and pseudohalides. J. Am. Chem. Soc. 1972, 94,
856−865. (b) Kochi, J. K.; Jenkins, C. L. Ligand transfer of halides
(chloride, bromide, iodide) and pseudohalides (thiocyanate, azide,
cyanide) from copper(II) to alkyl radicals. J. Org. Chem. 1971, 36,
3095−3102. (c) Kochi, J. K.; Jenkins, C. L. Kinetics of ligand transfer
oxidation of alkyl radicals. Evidence for carbonium ion intermediates.
J. Org. Chem. 1971, 36, 3103−3111. (d) Kochi, J. K.; Subramanian, R.
V. Studies of Ligand Transfer between Metal Halides and Free
Radicals from Peroxides. J. Am. Chem. Soc. 1965, 87, 1508−1514.
́
4706−4711. (d) Campora, J.; Maya, C. M.; Palma, P.; Carmona, E.;
́
Gutierrez-Puebla, E.; Ruiz, C. Synthesis and Aldol Reactivity of O-
and C-Enolate Complexes of Nickel. J. Am. Chem. Soc. 2003, 125,
1482−1483. (e) Burkhardt, E. R.; Bergman, R. G.; Heathcock, C. H.
Synthesis and reactions of nickel and palladium carbon-bound enolate
complexes. Organometallics 1990, 9, 30−44. (f) Belderraín, T. R.;
Knight, D. A.; Irvine, D. j.; Paneque, M.; Poveda, M. l.; Carmona, E.
Ethoxycarbonyl-, cyano- and methoxy-methyl complexes of nickel(II)
and their carbonylation reactions. J. Chem. Soc., Dalton Trans. 1992,
1491−1495. (g) Bonamico, M.; Dessy, G.; Fares, V.; Scaramuzza, L.
Structural studies of metal complexes with ω-nitroacetophenone.
Crystal structures of bis-(ω-nitroacetophenonato)copper(II), and of
its addition complexes with 2- and 4-methylpyridine (α-and γ-
picoline). J. Chem. Soc., Dalton Trans. 1972, 2477−2483.
̈
(11) (a) Jang, E. S.; McMullin, C. L.; Kaß, M.; Meyer, K.; Cundari,
T. R.; Warren, T. H. Copper(II) Anilides in sp3 C-H Amination. J.
Am. Chem. Soc. 2014, 136, 10930−10940. (b) Salvador, T. K.; Arnett,
C. H.; Kundu, S.; Sapiezynski, N. G.; Bertke, J. A.; Boroujeni, M. R.;
Warren, T. H. Copper Catalyzed sp3 C−H Etherification with Acyl
Protected Phenols. J. Am. Chem. Soc. 2016, 138, 16580−16583.
(c) Wiese, S.; Badiei, Y. M.; Gephart, R. T.; Mossin, S.; Varonka, M.
S.; Melzer, M. M.; Meyer, K.; Cundari, T. R.; Warren, T. H. Catalytic
C-H amination with unactivated amines through copper(II) amides.
Angew. Chem., Int. Ed. 2010, 49, 8850−8855. (d) Aguila, M. J. B.;
Badiei, Y. M.; Warren, T. H. Mechanistic Insights into C−H
Amination via Dicopper Nitrenes. J. Am. Chem. Soc. 2013, 135, 9399−
9406. (e) Gephart, R. T.; McMullin, C. L.; Sapiezynski, N. G.; Jang, E.
S.; Aguila, M. J. B.; Cundari, T. R.; Warren, T. H. Reaction of CuI
with Dialkyl Peroxides: CuII-Alkoxides, Alkoxy Radicals, and Catalytic
C−H Etherification. J. Am. Chem. Soc. 2012, 134, 17350−17353.
(f) Badiei, Y. M.; Dinescu, A.; Dai, X.; Palomino, R. M.; Heinemann,
F. W.; Cundari, T. R.; Warren, T. H. Copper-nitrene complexes in
catalytic C-H amination. Angew. Chem., Int. Ed. 2008, 47, 9961−9964.
(g) Gephart, R. T.; Huang, D. L.; Aguila, M. J. B.; Schmidt, G.; Shahu,
A.; Warren, T. H. Catalytic C-H Amination with Aromatic Amines.
Angew. Chem., Int. Ed. 2012, 51, 6488−6492.
(19) (a) Haidasz, E. A.; Meng, D. A.; Amorati, R.; Baschieri, A.;
Ingold, K. U.; Valgimigli, L.; Pratt, D. A. Acid Is Key to the Radical-
Trapping Antioxidant Activity of Nitroxides. J. Am. Chem. Soc. 2016,
138, 5290−5298. (b) Ross, S. D.; Finkelstein, M.; Petersen, R. C. The
Electrochemical Degradation of Quaternary Ammonium Salts. II. The
Mechanism of the Coupling Reaction. J. Am. Chem. Soc. 1960, 82,
1582−1585.
(20) (a) Khake, S. M.; Chatani, N. Chelation-Assisted Nickel-
Catalyzed C−H Functionalizations. Trends Chem. 2019, 1, 524−539.
(b) Liu, C.; Liu, D.; Lei, A. Recent Advances of Transition-Metal
Catalyzed Radical Oxidative Cross-Couplings. Acc. Chem. Res. 2014,
47, 3459−3470. (c) Gossage, R. A.; Van De Kuil, L. A.; Van Koten, G.
Diaminoarylnickel(II) “Pincer” Complexes: Mechanistic Consider-
ations in the Kharasch Addition Reaction, Controlled Polymerization,
and Dendrimeric Transition Metal Catalysts. Acc. Chem. Res. 1998,
31, 423−431.
(12) (a) Okoromoba, O. E.; Jang, E. S.; McMullin, C.; Cundari, T.;
Warren, T. H.Copper Catalyzed sp3 C-H α-Acetylation. 2019,
chemrxiv.11407116.v1. ChemRxiv Preprint. https://doi.org/10.
26434/chemrxiv.11407116.v1. (b) Vasilopoulos, A.; Zultanski, S. L.;
Stahl, S. S. Feedstocks to Pharmacophores: Cu-Catalyzed Oxidative
Arylation of Inexpensive Alkylarenes Enabling Direct Access to
Diarylalkanes. J. Am. Chem. Soc. 2017, 139, 7705−7708. (c) Zhang,
W.; Chen, P.; Liu, G. Copper-Catalyzed Arylation of Benzylic C−H
bonds with Alkylarenes as the Limiting Reagents. J. Am. Chem. Soc.
2017, 139, 7709−7712.
(13) A preprint of this manuscript has appeared on ChemRxiv:
Bakhoda, A.; Wiese, S.; Greene, C.; Figula, B. C.; Bertke, J. A.;
Warren, T. H. Radical Capture at Ni(II) Complexes: C-C, C-N, and
C-O Bond Formation. 2019, chemrxiv.8115860.v1. ChemRxiv
Preprint. https://doi.org/10.26434/chemrxiv.8115860.v1
(21) (a) Liu, S.; Qi, X.; Bai, R.; Lan, Y. Theoretical Study of Ni-
Catalyzed C-N Radical-Radical Cross-Coupling. J. Org. Chem. 2019,
84, 3321−3327. (b) Omer, H. M.; Liu, P. Computational Study of Ni-
Catalyzed C−H Functionalization: Factors That Control the
Competition of Oxidative Addition and Radical Pathways. J. Am.
Chem. Soc. 2017, 139, 9909−9920.
(22) Engel, P. S. Mechanism of the thermal and photochemical
decomposition of azoalkanes. Chem. Rev. 1980, 80, 99−150.
I
https://dx.doi.org/10.1021/acs.organomet.0c00021
Organometallics XXXX, XXX, XXX−XXX