Ni-Catalyzed Carboxylation of C(sp2)-S Bonds with CO2: Evidence for the Multifaceted Role of Zn

Article abstract of DOI:10.1021/acscatal.9b05141

Nickel-catalyzed reductive carboxylation reactions of aryl electrophiles typically require the use of metallic reducing agents. At present, the prevailing perception is that these serve as both a source of electrons and as a source of Lewis acids that may aid CO₂ insertion into the Ni-C bond. Herein, we provide evidence for the in situ formation of organometallic species from the metallic reductant, a step that has either been ruled out or has been unexplored in catalytic carboxylation reactions with metal powder reductants. Specifically, we demonstrate that Zn(0) acts as a reductant and that Zn(II) generates arylzinc species that might play a role in the C(sp²)-S carboxylation of arylsulfonium salts. Overall, the reductive Ni-catalyzed C(sp²)-S carboxylation reaction proceeds under mild conditions in a non-amide solvent, displays a wide substrate scope, and can be applied to the formal para C-H carboxylation of arenes.

Full text of DOI:10.1021/acscatal.9b05141

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Letter
Ni-Catalyzed Carboxylation of C(sp2)–S bonds
with CO2: Evidence for the Multifaceted Role of Zn
Tomoyuki Yanagi, Rosie J. Somerville, Keisuke Nogi, Ruben Martin, and Hideki Yorimitsu
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b05141 • Publication Date (Web): 15 Jan 2020
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ACS Catalysis
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Ni-Catalyzed Carboxylation of C(sp2)–S bonds with CO2: Evidence
for the Multifaceted Role of Zn
Tomoyuki Yanagi,†⊥ Rosie J. Somerville,‡§⊥ Keisuke Nogi,† Ruben Martin*‡‖ and Hideki
Yorimitsu*†
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†Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
‡Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, Av. Països Catalans 16, 43007
Tarragona, Spain
§Universitat Rovira i Virgili, Departament de Química Analítica i Química Orgànica, c/Marcel·lí Domingo, 1, 43007 Tarragona, Spain.
‖ICREA, Passeig Lluís Companys, 23, 08010 Barcelona, Spain
KEYWORDS: Carboxylation, Nickel, C–S cleavage, Carbon dioxide, Zinc.
ABSTRACT: Nickel-catalyzed reductive carboxylation reactions of aryl electrophiles typically require the use of metallic reducing
agents. At present, the prevailing perception is that these serve as both a source of electrons and as sources of Lewis acids that may
aid CO2 insertion into the Ni–C bond. Herein, we provide evidence for the in situ formation of organometallic species from the
metallic reductant, a step that has either been ruled out or has been unexplored in catalytic carboxylation reactions with metal powder
reductants. Specifically, we demonstrate that Zn(0) acts as a reductant and that Zn(II) generates arylzinc species that might play a
role in the C(sp2)–S carboxylation of arylsulfonium salts. Overall, the reductive Ni-catalyzed C(sp2)–S carboxylation reaction
proceeds under mild conditions in a non-amide solvent, displays a wide substrate scope, and can be applied to a formal para C–H
carboxylation of arenes.
Nickel-catalyzed reductive carboxylation reactions of organic
(pseudo)halides with CO2 have recently gained considerable
Scheme 2. Carboxylation of arylsulfonium salts.
momentum as routes to carboxylic acids, privileged molecules
in a myriad of biologically relevant scaffolds (Scheme 1).1,2
Despite the advances realized, the intricacies of these reactions
still remain speculative, probably due to the difficulty in
accessing well-defined catalytically relevant species and the
non-trivial roles exerted by the ligands and/or additives.3
Although Zn(0) and Mn(0) are typically employed in these
endeavors as a source of electrons in order to access Ni(0)Ln
and Ni(I)Ln species within the catalytic cycle,2 Hazari has
recently shown that Mn(II) salts derived from these reductions
might also play a beneficial role in the carboxylation of aryl
chlorides.3d,4 Overall, these observations underscore our limited
mechanistic knowledge of carboxylation processes and suggest
that a better understanding of the roles of the metallic reductants
may in turn lay the foundation for improving these reactions.
Driven by the ready availability and synthetic versatility of
organosulfur compounds, we wondered whether it would be
possible to develop a Ni-catalyzed reductive carboxylation of
arylsulfonium salts via C(sp2)–S cleavage (Scheme 2).5-8 The
choice of this electrophile is not arbitrary.9 First, arylsulfonium
salts are bench-stable compounds that are easily accessed on a
large scale from simple aryl sulfides upon treatment with an
appropriate electrophilic partner. Second, the neutral R2S
leaving group of the sulfonium moiety should not compete for
binding at the nickel center.10,11 Furthermore, the electron-
deficient nature of the arylsulfonium salt should facilitate
oxidative addition at Ni(0)Ln.12 If successful, we recognized
that such a reaction would not only provide an unrealized
opportunity to enable a catalytic C–S functionalization/CO2
fixation, but would also offer the possibility to study
mechanistic aspects of the reaction, such as the role of the metal
reductant in the targeted carboxylation event. As part of our
ongoing interest in catalytic carboxylations13,14 and C–S bond
functionalization,7d,11b,f,g we report herein the successful
realization of a mild catalytic carboxylation of arylsulfonium
salts. Importantly, we provide evidence for the intermediacy of
a Ni(I) species and the involvement of organozinc species, thus
Scheme 1. Metallic reductants in carboxylation reactions.
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ACS Catalysis
revealing a multifaceted role played by Zn that may have
Page 2 of 7
did not undergo carboxylation, ruling out the requirement for
aryl sulfide intermediates during the carboxylation of
arylsulfonium salts.
1
2
implications in related reductive cross-coupling endeavors.
Our investigations began by evaluating the catalytic
carboxylation of 2a, which is readily obtained on a multigram
scale from the corresponding aryl sulfide 1a by treatment with
MeOTf. After some experimentation, we found that 2a
underwent carboxylation with CO2 (1 atm) in the presence of a
Ni(II) precatalyst bearing L1 and Zn powder to give 3a in 84%
isolated yield at room temperature (Table 1, entry 1). Of
particular note was the use of DMSO as the solvent (entries 8
and 9): our protocol is therefore a rare example of a Ni-
catalyzed reductive carboxylation that avoids toxic amide
solvents such as DMF, DMA, or NMP.3d,15 As anticipated, the
nature of the ligand was critical to success, with phenanthroline
ligands possessing substituents adjacent to the nitrogen atoms
providing the best results (entries 2-6). Strikingly, Zn (E° = –
0.76 V vs SCE)16 was uniquely suited for the carboxylation of
2a and no acid was obtained with stronger reductant Mn (E° =
3
4
5
6
7
8
9
Table 1. Optimization of the Reaction Conditions.
L1
NiBr2 (2.5 mol %)
CO2H
SMe2
OTf
L1
(3.5 mol %)
CO
Zn (3 equiv),
2 (1 atm)
Me
Me
2a
3a
DMSO, rt, 16 h
b
3
(%)
entry
deviation from standard conditions
none
87 (84)c
1
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N
N
2
L2
L3
L4
L5
L1
L1
L1
L1
instead of
instead of
instead of
instead of
48
33
R1
R2
1
2
3
L1
L2
L3
(R =R =Me)
1
2
4
(R =Me; R =H)
56
1
2
(R =R =H)
5
47
6
L1 L1
/
NiCl2(dppf) instead of NiBr2
3
7
L1
L1
Ni(COD)2/ instead of NiBr2
DMA (DMF) instead of DMSO
NMP as solvent
86
N
N
R3
R3
3
8
13 (28)
15
L4
(R =Me)
3
9
L5
(R =H)
–1.32 V vs SCE, entry 11).17 Likewise, the use of homogeneous
10
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12
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15
1a
2a
p-C6H4SMe ( ) instead of
0
reductants such as tetrakis(dimethylamino)ethylene (TDAE; E°
= –0.62 V vs SCE)16, DMAP-OED (E° = –1.24 V vs SCE)18, or
CoCp2 (E° = –0.87 V vs SCE)19,20 did not deliver 3a (entries 12-
14). Importantly, direct reduction of 2g by Zn only gave a 3%
yield of aryl sulfide 1g, while reaction between DMAP-OED
N
Mn instead of Zn
N
0
0d
0d,e
TDAE (3 equiv) instead of Zn
DMAP-OED (3 equiv) instead of Zn
CoCp2 (3 equiv) instead of Zn
Me2N
NMe2
0
0
DMAP-OED
L1
no Zn or no Ni/
and 2f gave a 60% yield of 1f.21 The use of Mn did not result in
a 2a (0.30 mmol), NiBr2L1 (2.5 mol %), L1 (3.5 mol %), Zn powder
(0.90 mmol), CO2 (1 atm), DMSO (1.5 mL) at rt for 16 h followed
by acidic workup. b NMR yields using 1,1,2,2-tetrabromoethane as
internal standard c Isolated yield. d A similar result was found with
the addition of 1 equiv Zn(OTf)2. e THF solvent.
the formation of 1a. Together, these experiments suggest that
Zn does not solely act as a reductant during the catalytic cycle
and that other scenarios might come into play. Control
experiments revealed that both Ni and Zn were critical for
success (entry 15). In particular, we observed that p-tolylSMe
Scheme 3. Scope of the Catalytic Carboxylation of Arylsulfonium Salts.
one-pot carboxylationa
OTf
L1
NiBr2 (2.5 mol %)
SMe
SMe2
CO
2H
L1
(3.5 mol %)
MeOTf (1.1 equiv)
R
R
R
CO
Zn (3 equiv),
2 (1 atm)
CH2Cl2, rt
DMSO, rt, 16 h
then remove volatiles
1a-y
2a-y
3a-y
Scope of aryl substituents
X
SMe2
OTf
SMe2
OTf
SMe2
OTf
SMe2
OTf
SMe2
OTf
SMe2
R
Me
2a-OTf
R
RO
(EtO)2OPO
PivO
2m
2b
2c
2d
2e
2f
2g
2h
: 84% (84%)
4: 78%b
(R = H), 80% (79%)
(R = Me), 83% (78%)
(R = Hex), 84%
2i
2j
2l
66%
(R = Me), 84% (76%)
85% (73%)
c
2a-BF
2a-PF
(R = tBu), 86%
(R = CF3), 81%
(R = CF3), 54%
6: 85%b
(R = TIPS), (68%)
2k
c
c
(R = CO2Me), 58%
6: 84%b
2a-SbF
(R = F), 74% (72%)
OTf
SMe2
OTf
SMe2
OTf
Me
OTf
SMe2
OTf
SMe2
OTf
SMe2
SMe2
Me
O
Bu3Sn
MeS
Cl
O
O
c,d
c
e
c
2n
2q
76%
75%
2o
2p
2r
2s
73%
73%
56%
Cy
(58%)
Scope of leaving sulfide
Scope of other classes of sulfonium salts
Me
Me
Me
Me
Et
OTf
OTf
OTf
OTf
OTf
OTf
C12H25
OTf
S
S
S
S
S
SMe2
S
Et
C12H25
Ph
C12H25
Me
MeO
Me
CF3
OMe
c
c
b
2u
2v
68%
(63%)
with 5% CyCO2H
2t
2w
2x
2y
2z
<10%
(71%)
58%
47%
36%
with 12% C12H25CO2H
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ACS Catalysis
a Isolated yield from arylsulfonium salts. Yields in one-pot carboxylation of aryl sulfides are shown in parentheses. b Yield was
determined by NMR using 1,1,2,2-tetrabromoethane as an internal standard. c 5.0 mol % NiBr2L1 and 7.0 mol % L1 was used.
d 5% of 2b was also formed. e Obtained as 4-acetylbenzoic acid after acidic workup.
1
2
3
4
With optimized conditions in hand, we investigated the
generality of the reaction (Scheme 3). Overall, electron-neutral
or electron-rich arylsulfonium salts showed good-to-excellent
reactivity regardless of the counterion.21,22 Likewise, groups
that are also reactive in Ni-catalyzed reactions – esters (2k, 2m),
aryl fluorides (2e), phosphonates (2l), ethers (2f, 2g, 2h and 2q)
and alkyl chlorides (2q) – were all well tolerated. We note that
reactions of electron-deficient substrates (2d, 2j and 2k) were
carried out with higher catalyst loadings due to competitive
reductive demethylation by Zn.21 As expected, a substrate
possessing an aryl methyl sulfide group was selectively
carboxylated at the sulfonium moiety (2o). Surprisingly, the
carboxylation reaction could be conducted in the presence of an
organotin group (2p), providing ample room for further
derivatization via orthogonal Stille-Migita-Kosugi cross-
coupling reactions. Unfortunately, pyridyl sulfides could not be
transformed to sulfonium salts with MeOTf due to preferential
N-methylation. As shown for 2n, the use of an ortho-substituted
arylsulfonium salts did not hinder the reaction.22 Similar results
were also obtained regardless of the alkyl substituents on the
sulfonium moiety (2t-2v). Note, however, that non-negligible
amounts of alkyl carboxylic acids were sometimes obtained via
C(sp3)–S bond cleavage. Interestingly, the reaction can also be
extended to diarylsulfonium salts (2w). For unsymmetrically
substituted analogues (2x), carboxylation occurred
preferentially at the most electron-deficient C–S bond. As
demonstrated by the successful carboxylation of β -
styrylsulfonium 2y, C(sp2)–S carboxylation is not limited to
arylsulfonium salts. Unfortunately, the reaction could not be
extended to trialkylsulfonium salts (2z). Particularly
noteworthy was the observation that the catalytic carboxylation
of a variety of arylsulfonium salts can be carried out in a one-
pot procedure from the parent aryl sulfide after simply
removing volatiles upon completion of the reaction with
MeOTf. The versatility and synthetic applicability of our
protocol is further illustrated in Scheme 4. As shown, 6 can
easily be obtained from 4 by telescoping the formation of the
arylsulfonium salt 5 without isolation. Indeed, the successful
preparation of 6 indicates that sulfonium salts might be used as
linchpins in formal para-C(sp2)–H carboxylation reactions.23
This is particularly important, as it might lead to new
knowledge in synthetic design for incorporating CO2 at remote
C(sp2)–H bonds.
incorporation (Scheme 5, top). This suggested a build-up of
basic aryl organometallic species in solution.24 Considering that
the Ni catalyst is required for the carboxylation to occur, the
formation of 3 suggests that a Ni-to-Zn transmetalation might
occur prior to CO2 insertion.25,26 This notion was investigated
by attempting the carboxylation of phenylzinc triflate with CO2
in order to determine whether arylzinc species were competent
reaction intermediates (Scheme 5, bottom). Low conversions to
3b were observed in the absence of Ni(II) or Zn(0), and a high
yield was only observed in the presence of both the Ni catalyst
and Zn(0). Although Zn(OTf)2 may promote carboxylation of
PhZnOTf as a Lewis acid,27 its addition did not result in an
increased yield of 3b. These results provide evidence that the
carboxylation event is assisted by the Ni catalyst regardless of
whether or not arylzinc species are formed.15a,27
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Scheme 5. Intermediacy of Arylzinc Species.
buildup of organozinc species
plausible intermediate
L1
NiBr2 (2.5 mol %)
L1
D
(3.5 mol %)
ZnX
Zn (3 equiv), DMSO
2g
then
HexO
HexO
X = OTf, aryl
D2O
7
, 56% (>90%D)
0% with no Ni/L1
carboxylation of well-defined arylzinc triflate
L1
NiBr2 (x mol %)
CO
ZnOTf
2H
L1
41% (x=2.5; y=3.5; z=3)
7% (x=2.5; y=3.5; z=0)
11% (x=y=z=0)
(y mol %)
CO
Zn (z equiv),
2 (1 atm)
3b
DMSO, rt
3%* (x=y=z=0)
*with 1 equiv Zn(OTf)2
Aiming at shedding light on the origin of C(sp2)–S cleavage,
we next turned our attention to investigating the formation of
Ni(0)Ln from Ni(II)Ln prior to oxidative addition. In order to
mimic the optimized catalytic carboxylation conditions, we
monitored the reduction of NiBr2L1 with Zn(0) using 1H NMR
spectroscopy. The formation of DMSO-ligated Ni(II) species
was observed upon dissolving NiBr2L1 in DMSO-d6 and the
formation of a DMSO adduct was confirmed by X-ray
crystallography.28 In the presence of Zn(0), NiBr2L1 was
transformed within 10 minutes into a deep blue paramagnetic
Ni(I) complex in 74% yield (Scheme 6). X-ray crystallography
identified this complex as [Ni(I)(L1)2]Br, with the halide anion
being outer-sphere.29,30 After longer reaction times, we
observed that the yield [Ni(I)(L1)2]Br had reduced to only 16%,
suggesting the formation of further reduced Ni(0)L1 species.
Unfortunately, these Ni(0) species could not be quantified,
probably due to the very poor solubility of Ni(L1)2 in DMSO.31
However, evidence for the presence of Ni(0) was obtained by
addition of Ph2S2 or 1,5-cyclooctadiene to the reaction mixture,
leading to the observation of oxidized products and COD-
bearing complexes, respectively.32 These experiments provided
indirect evidence for the formation of Ni(0) species from the
overall reaction between NiBr2L1 and Zn. This contrasts with a
recent report by Diao where the formation of Ni(0) from a
related Ni(bipyridine)/Zn system was ruled out.33
Scheme 4. Formal para-C(sp2)–H carboxylation of arenes.
Encouraged by the preparative aspects of our catalytic
carboxylation reaction, we turned our attention to studying the
mechanistic intricacies of the reaction. Interestingly, exposing
2g to the optimized conditions in the absence of CO2 followed
by a D2O quench led to 7 in 55% yield and with >90% D
Scheme 6. Formation of a Ni(I) Complex.
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prior to reduction.3d,25 Given that carboxylation of PhZnOTf
Page 4 of 7
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2
3
4
5
6
7
8
required the presence of both Ni and Zn for yields to surpass
ca. 10%, we suggest that ArZnX species may serve as a
reservoir of the aryl group rather than as species at which
significant amounts of carboxylation occurs. This observation
is particularly relevant in the context of Ni-catalyzed cross-
electrophile coupling reactions mediated by Zn, because these
results contribute to the perception that the role of the metallic
reductant in these endeavors might not be as straightforward as
one might initially anticipate and that further investigations
might be required to unravel the intricacies of these processes.38
Prompted by the results shown in Scheme 6, we investigated
the catalytic relevance of [Ni(I)(L1)2]+ complexes in the
carboxylation of arylsulfonium salts. Indeed, analyzing the
catalytic carboxylation of 2f by both NMR and EPR
spectroscopy allowed us to detect the presence of
[Ni(I)(L1)2]OTf during catalysis. An aliquot removed after 1 h
of reaction showed that of the initial catalyst loading (5 mol %),
60% of the Ni existed as [Ni(I)(L1)2]OTf. After 3.5 h this was
44%.30 This finding is particularly relevant as it suggests that
[Ni(L1)2]OTf may be a catalyst resting state. With evidence for
both Ni(I) and Ni(0) intermediates in hand, stoichiometric
experiments were carried out with Ni(L1)2 in order to study
oxidative addition of the C(sp2)–S bond (Scheme 7). First,
reaction of 2f with Ni(L1)2 and Zn(OTf)2 – produced during
every turnover of the catalyst – resulted in 50% conversion of
2f and a 44% yield of Me2S, with [Ni(L1)2]OTf (70%) being
the only Ni species detected by 1H NMR spectroscopy.34
Interestingly, the presence of Zn(0) led to full conversion of 2f
and an 80% yield of Me2S, indicating that Zn could generate
Ni(0) species from [Ni(L1)2]OTf.
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Scheme 8. Proposed Mechanistic Rationale.
In conclusion, we have developed a mild Ni-catalyzed
reductive carboxylation of arylsulfonium salts that is mediated
by Zn and offers reactivity complementary to that observed with
aryl (pseudo)halides. Our studies have provided evidence for
the formation of organozinc intermediates during the reaction,
suggesting that Ni-to-Zn transmetalation is plausible and that a
greater variety of mechanistic pathways may need to be studied
depending on the aryl electrophile.
Overall, these experiments provide further evidence that the
targeted C(sp2)–S bond cleavage occurs at Ni(0). Although the
isolation of an oxidative addition complex of an arylsulfonium
salt to Ni(L1)2 proved to be elusive, we were able to track the
fate of the aryl group after C(sp2)–S cleavage. Specifically,
reactions between 2f and Ni(L1)2 carried out in the presence of
Zn(OTf)2 revealed new 1H NMR signals that were assigned to
1
arylzinc species based on the identical H NMR data obtained
upon reaction of ZnAr2 with Zn(OTf)2/L1 (Scheme 7).35 Putting
everything into perspective, we believe these experiments
provide a strong argument for the formation of arylzinc species
after C(sp2)–S cleavage by Ni(0)Ln.26
AUTHOR INFORMATION
Corresponding Author
*rmartinromo@iciq.es
*yori@kuchem.kyoto-u.ac.jp
Scheme 7. Stoichiometric Experiments with Ni(L1)2.
Note
Stoichiometric reactions (Ar = p-MeOC6H4)
In situ arylzinc species
⊥T.Y and R.J.S. contributed equally
Zn(OTf)2 (2 equiv)
Zn (x equiv)
2f
+
L1
Zn(OTf)2,
2f
Ar2Zn
+
Me2S + “ArZn+”
Supporting Information
DMSO-d6
L1
Ni(
)
2
x = 0
x = 3 traces
50%
44%
85%
40%
90%
Experimental procedures, crystallographic data and spectral data
(PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
In light of our results, we propose the mechanistic scenario
depicted in Scheme 8, which includes Ni-to-Zn transmetalation
steps. At this stage, it is unclear whether the product of C(sp2)–
ACKNOWLEDGMENT
H.Y. thanks JSPS KAKENHI Grant Numbers JP16H04109,
JP18H04254, JP18H04409, and JP19H00895. K.N. thanks JSPS
KAKENHI Grand Number JP18K14212. T.Y. acknowledges a
JSPS Predoctoral Fellowship and JSPS Overseas Challenge
Program for Young Researchers. This work was partly supported
by JST CREST Grant Number JPMJCR19R4, Japan. R.M. and
R.J.S. thank ICIQ, FEDER/MICIU − AEI/PGC2018- 096839-B-
100, and funding from “la Caixa” Foundation (ID 100010434)
under the agreement LCF/BQ/SO15/52260010 for financial
support. We also acknowledge the X-ray diffraction Research
Support Area at ICIQ and Dr. Georgiana Stoica for her help with
+
SMe2 oxidative addition (I) undergoes transmetalation with
Zn(II) to give Ni(II) complex II or whether I is first reduced to
Ar–Ni(I) species III prior to transmetalation en route to IV and
ArZnX. The latter may be more feasible when comparing the
nucleophilicities of the nickel centers of I and III.3a,35 Whether
IV indeed corresponds to [Ni(L1)2]OTf – identified in the
catalytic carboxylation reaction
–
requires further
investigations.36,37 After CO2 insertion to Ar–Ni(I) species III,
the resulting carboxylate complex V is either directly reduced
to Ni(0)Ln or undergoes anion exchange with ZnX2 to form IV
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(8) Reviews: (a) Modha, S. G.; Mehta, V. P.; Van der Eycken, E. V.
EPR studies. R.J.S. sincerely thanks “la Caixa” for a predoctoral
fellowship.
Transition metal-catalyzed C–C bond formation via C–S bond
cleavage. Chem. Soc. Rev. 2013, 42, 5042–5055. (b) Pan, F.; Shi, Z. J.
Recent Advance in Transition-Metal-Catalyzed C–S Activation: From
Thioester to (Hetero)aryl Thioether. ACS Catal. 2014, 4, 280–288. (c)
Gao, K.; Otsuka, S.; Baralle, A.; Nogi, K.; Yorimitsu, H.; Osuka, A.
Cross-coupling of Aryl Sulfides Powered by N-Heterocyclic Carbene
Ligands. J. Synth. Org. Chem., Jpn. 2016, 74, 1119−1127. (d) Otsuka,
S.; Nogi, K.; Yorimitsu, H. C−S Bond Activation. Top. Curr. Chem.
2018, 376, 13.
(9) Pioneering report: Srogl, J.; Allred, G. D.; Liebeskind, L. S.
Sulfonium Salts. Participants par Excellence in Metal-Catalyzed
Carbon–Carbon Bond-Forming Reactions. J. Am. Chem. Soc. 1997,
119, 12376–12377.
(10) Reviews on cross-coupling reactions of arylsulfonium salts: (a)
Tian, Z.-Y.; Hu, Y.-T.; Teng, H.-B.; Zhang, C.-P. Application of
arylsulfonium salts as arylation reagents. Tetrahedron Lett. 2018, 59,
299–309. (b) Kaiser, D.; Klose, I.; Oost, R.; Neuhaus, J.; Maulide, N.
Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides,
Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts. Chem. Rev. 2019,
119, 8701–8780.
(11) Selected recent examples: (a) Cowper, P.; Jin, Y.; Turton, M. D.;
Kociok-Köhn, G.; Lewis, S. E. Azulenesulfonium Salts: Accessible,
Stable, and Versatile Reagents for Cross-Coupling. Angew. Chem. Int.
Ed. 2016, 55, 2564–2568. (b) Kawashima, H.; Yanagi, T.; Wu, C.-C.;
Nogi, K.; Yorimitsu, H. Regioselective C–H Sulfanylation of Aryl
Sulfoxides by Means of Pummerer-Type Activation. Org. Lett. 2017,
19, 4552–4555. (c) Tian, Z.-Y.; Wang, S.-M.; Jia, S.-J.; Song, H.-X.;
Zhang, C.-P. Sonogashira Reaction Using Arylsulfonium Salts as
Cross-Coupling Partners. Org. Lett. 2017, 19, 5454–5457. (d) Hock, K.
J.; Hommelsheim, R.; Mertens, L.; Ho, J.; Nguyem, T. V.; Koening, R.
M. Corey-Chaykovsky Reactions of Nitro Styrenes Enable cis-
Configured Trifluoromethyl Cyclopropanes. J. Org. Chem. 2017, 82,
8220–8227. (e) Aukland, M. H.; Talbot, F. J. T.; Fernández-Salas, J.
A.; Ball, M.; Pulis, A. P.; Procter, D. J. An Interrupted
Pummerer/Nickel-Catalyzed Cross-Coupling Sequence. Angew. Chem.
Int. Ed. 2018, 57, 9785–9789. (f) Uno, D.; Minami, H.; Otsuka, S.;
Nogi, K.; Yorimitsu, H. Palladium-Catalyzed Mizoroki-Heck-Type
Alkenylation of Monoaryldialkylsulfoniums. Chem. Asian J. 2018, 13,
2397–2400. (g) Minami, H.; Otsuka, S.; Nogi, K.; Yorimitsu, H.
Palladium-Catalyzed Borylation of Arylsulfoniums with Diborons.
ACS Catal. 2018, 8, 579–583. (h) Tian, Z.-Y.; Zhang, C.-P. Ullmann-
type N-arylation of anilines with alkyl(aryl)sulfonium salts. Chem.
Commun. 2019, 55, 11936–11939.
(12) We reported the carboxylation of benzylamines via inert C–N
bond activation by conversion to the corresponding ammonium salts:
Moragas, T.; Gaydou, M.; Martin, R. Nickel-Catalyzed Carboxylation
of Benzylic C–N bond with CO2. Angew. Chem. Int. Ed. 2016, 55,
5053–5057.
(13) Selected examples: (a) Correa, A.; Martin, R. Palladium-
Catalyzed Direct Carboxylation of Aryl Bromides with Carbon
Dioxide. J. Am. Chem. Soc. 2009, 131, 15974–15975. (b) Börjesson,
M.; Moragas, T.; Martin, R. Ni-Catalyzed Carboxylation of
Unactivated Alkyl Chlorides with CO2. J. Am. Soc. Chem. 2016, 138,
7504–7507. (c) Juliá-Hernández, F.; Moragas, T.; Cornella, J.; Martin,
R. Remote Carboxylation of Halogenated Aliphatic Hydrocarbons with
Carbon Dioxide. Nature 2017, 545, 84–88.
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5
6
7
8
REFERENCES
(1) (a) Carbon Dioxide as Chemical Feedstock; Aresta, M., Ed.; Wiley-
VCH: Weinheim, 2010. (b) Sakakura, T.; Choi, J.-C.; Yasuda, H.
Transformation of Carbon Dioxide. Chem. Rev. 2007, 107, 2365–2387.
(c) Artz, J.; Müller, T. E.; Thenert, K.; Kleinekorte, J.; Meys, R.;
Sternberg, A.; Bardow, A.; Leitner, W. Sustainable Conversion of
Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle
Assessment. Chem. Rev. 2018, 118, 434–504.
(2) Selected reviews: (a) Cokoja, M.; Bruckmeier, D.-C. C.; Rieger, B.;
Herrmannn, W. A.; Kühn, F. E. Transformation of Carbon Dioxide
with Homogeneous Transition-Metal Catalysts: A Molecular Solution
to a Global Challenge? Angew. Chem. Int. Ed. 2011, 50, 8510–8537.
(b) Huang, K.; Sun, C.-L.; Shi, Z.-J. Transition-metal-catalyzed C–C
bond formation through the fixation of carbon dioxide. Chem. Soc. Rev.
2011, 40, 2435–2452. (c) Tortajada, A.; Juliá-Hernández, F.;
Börjesson, M.; Moragas, T.; Martin, R. Transition Metal-Catalyzed
Carboxylation Reactions with Carbon Dioxide. Angew. Chem. Int. Ed.
2018, 57, 15948–15982. (d) Burkart, M. D.; Hazari, N.; Tway, C. L.;
Zeitler, E. L. Opportunities and Challenges for Catalysis in Carbon
Dioxide Utilization. ACS Catal. 2019, 9, 7937–7956.
(3) (a) Sayyed, F. B.; Tsuji, Y.; Sakaki, S. The Crucial Role of a Ni(I)
Intermediate in Ni-Catalyzed Carboxylation of Aryl Chloride with
CO2: A Theoretical Study. Chem. Commun. 2013, 49, 10715. (b)
Sayyed, F. B.; Sakaki, S. The Crucial Roles of MgCl₂ as a Non-
Innocent Additive in the Ni-Catalyzed Carboxylation of Benzyl Halide
with CO₂. Chem. Commun. 2014, 50, 13026–13029. (c) Obst, M.;
Pavlovic, L.; Hopmann, K. H. Carbon-Carbon Bonds with CO2:
Insights from Computational Studies. J. Organomet. Chem. 2018, 864,
115–127. (d) Charboneau, D. J.; Brudvig, G. W.; Hazari, N.; Lant, H.
M. C.; Saydjari, A. K. Development of an Improved System for the
Carboxylation of Aryl Halides through Mechanistic Studies. ACS
Catal. 2019, 9, 3228–3241. (e) Mohadjer Beromi, M.; Brudvig, G. W.;
Hazari, N.; Lant, H. M. C.; Mercado, B. Q. Synthesis and Reactivity of
Paramagnetic Nickel Polypyridyl Complexes Relevant to C(sp2)–
C(sp3) Coupling Reactions. Angew. Chem. Int. Ed. 2019, 58, 6094–
6098.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(4) See ref. 3 and, for a specific focus on metallic reducing agents, see:
Richmond, E.; Moran, J. Recent Advances in Nickel Catalysis Enabled
by Stoichiometric Metallic Reducing Agents. Synthesis 2018, 50, 499–
513.
(5) (a) Ruano, J. L. G.; de la Plata, B. C. In Organosulfur Chemistry I;
Page, P. C. B., Ed.; Springer: Heidelberg, 1999; p 1. (b) Furukara, N.;
Sato, S. In Organosulfur Chemistry II; Page, P. C. B., Ed.; Springer:
Heidelberg, 1999; p 89. (c) Rayner, C. M.; Advances in Sulfur
Chemistry; JAI Press: Greenwich, 2000, Vol.2. (d) Sulfur Compounds:
Advances in Research and Application; Acton, A. Q., Ed.; Scholarly
Eds.: Atlanta, GA, 2012. (e) Feng, M.; Tang, B.; Liang, S. H.; Jiang,
X. Sulfur Containing Scaffolds in Drugs: Synthesis and Application in
Medicinal Chemistry. Curr. Top. Med. Chem. 2016, 16, 1200–1216.
(6) Sun, S.; Yu, J.-T.; Cheng. J. Copper(I)-Catalyzed Desulfinative
Carboxylation of Sodium Sulfinate using Carbon Dioxide. Adv. Synth.
Catal. 2015, 357, 2022–2026.
(7) Related carbonylation with CO gas via aromatic C–S bond
cleavage: (a) Shim, S. C.; Alper, H. Desulfurization and carbonylation
of mercaptans. J. Org. Chem. 1985, 50, 147–149. (b) Kamigata, N.;
Satoh, A.; Yoshida, M.; Kameyama, M. The Reaction of Arylazo Aryl
Sulfones with Carbon Monoxide and Nucleophiles Catalyzed by the
Palladium(0) Complex. Bull. Chem. Soc. Jpn. 1989, 62, 605–607. (c)
Li, X.; Liang, D.; Huang, W.; Zhou, H.; Li, Z.; Wang, B.; Ma, Y.;
Wang, H. Visible light-induced carbonylation of indoles with
arylsulfonyl chlorides and CO. Tetrahedron 2016, 72, 8442–8448. (d)
Minami, H.; Nogi, K.; Yorimitsu, H. Palladium-Catalyzed
Alkoxycarbonylation of Arylsulfoniums. Org. Lett. 2019, 21, 2518–
2522.
(14) Selected examples from other groups: (a) Fujihara, T.; Nogi, K.;
Xu, T.; Terao, J.; Tsuji, Y. Nickel-Catalyzed Carboxylation of Aryl and
Vinyl Chlorides Employing Carbon Dioxide. J. Am. Chem. Soc. 2012,
134, 9106–9109. (b) Meng, Q.-Y.; Wang, S.; König, B. Carboxylation
of Aromatic and Aliphatic Bromides and Triflates with CO2 by Dual
Visible ‐ Light–Nickel Catalysis. Angew. Chem. Int. Ed. 2017, 56,
13426–13430. (c) Gui, Y.-Y.; Hu, N.; Chen, X.-W.; Liao, L.-L.; Ju, T.;
Ye, J.-H.; Zang, Z.; Li, J.; Yu, D.-G. Highly Regio- and
Enantioselective Copper-Catalyzed Reductive Hydroxymethylation of
Styrenes and 1,3-Dienes with CO2. J. Am. Chem. Soc. 2017, 139,
17011–17014. (d) Hou, J.; Ee, A.; Cao, H.; Ong, H.-W.; Xu, J.-H.; Wu,
J. Visible-Light-Mediated Metal‐Free Difunctionalization of Alkenes
with CO2 and Silanes or C(sp3)-H Alkanes. Angew. Chem. Int. Ed.
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2018, 57, 17220–17224. (e) Ma, C.; Zhao, C.-Q.; Xu, X.-T.; Li, Z.-M.;
(26) For Ni-catalyzed carbozincation, see: (a) Stüdemann. T.; Knochel,
P. New Nickel-Catalyzed Carbozincation of Alkynes: A Short
Synthesis of (Z)-Tamoxifen. Angew. Chem. Int. Ed. Engl. 1997, 36,
93–95. (b) Stüdemann. T.; Ibrahim-Ouali, M.; Knochel, P. A Nickel-
Catalyzed Carbozincation of Aryl-Substituted Alkynes. Tetrahedron
1998, 54, 1299–1316. For reviews of carbozincation, see: Murakami,
K.; Yorimitsu, Y. Recent Advances in Transition-Metal-Catalyzed
Intermolecular Carbomagnesiation and Carbozincation. Beilstein J,
Org, Chem. 2013, 9, 278–302.
(27) (a) Yeung, C. S.; Dong, Vy. M. Beyond Aresta’s Complex: Ni-
and Pd-Catalyzed Organozinc Coupling with CO2. J. Am. Chem. Soc.
2008, 130, 7826–7827. (b) Ochiai, H.; Jang, M.; Hirano, K.; Yorimitsu,
H.; Oshima, K. Nickel-Catalyzed Carboxylation of Organozinc
Reagents with CO2. Org. Lett. 2008, 10, 2681–2683. (c) Kobayashi, K.;
Kondo, Y. Transition-Metal-Free Carboxylation of Organozinc
Reagents Using CO2 in DMF Solvent. Org. Lett. 2009, 11, 2035–2037.
(d) Metzger, A.; Bernhardt, S.; Manolikakes, G.; Knochel, P. MgCl2-
Accelerated Addition of Functionalized Organozinc Reagents to
Aldehydes, Ketones, and Carbon Dioxide. Angew. Chem. Int. Ed. 2010,
49, 4665–4668.
(28) For similar reactivity in an NiCl2(L3) complex, see: Brewer, B.;
Brooks, N. R.; Sykes, A. G. Characterization of an Asymmetric
M(chelate)2(µ-Cl)2 MCl2 Dimer and Isolation of Corresponding DMSO
Adducts: X-Ray Crystal Structures of Co(phen)2(µ-Cl)2CoCl2·C4H8O
and M(chelate)Cl2(DMSO)x(Co, X = 1ꢀ; Ni, X = 2) Complexes. J.
Chem. Crystallogr. 2003, 33 (9), 663–668.
(29) Bond distances between the cationic Ni(I) centre and L1 and
spectroscopic features (NMR, EPR) were comparable to those of
analogous complexes previously reported in the literature: ref. 3(e) and:
Powers, D. C.; Anderson, B. L.; Nocera, D. G. Two-Electron HCl to
H2 Photocycle Promoted by Ni(II) Polypyridyl Halide Complexes. J.
Am. Chem. Soc. 2013, 135, 18876–18883.
Wang, X.-Y.; Zhang, K.; Mei, T. S. Nickel-Catalyzed Carboxylation of
Aryl and Heteroaryl Fluorosulfates Using Carbon Dioxide. Org. Lett.
2019, 21, 2464–2467.
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(15) (a) Williams, C. M.; Johnson, J. B.; Rovis, T. Nickel-Catalyzed
Reductive Carboxylation of Styrenes Using CO2. J. Am. Chem. Soc.
2008, 130, 14936–14937. (b) See ref. 23a-b for Ni-catalyzed
carboxylation reactions of organozinc species in THF and DME. (c)
For a Cu-catalyzed carboxylation reaction carried out in DMSO, see:
Tran-Vu, H.; Daugulis, O. Copper-Catalyzed Carboxylation of Aryl
Iodides with Carbon Dioxide. ACS Catal. 2013, 3, 2417–2420. (d) For
an example of a Pd-catalyzed carboxylation conducted in diglyme:
Sasano, K.; Takaya, J.; Iwasawa, N. Palladium(II)-Catalyzed Direct
Carboxylation of Alkenyl C–H Bonds with CO2. J. Am. Chem. Soc.
2013, 135, 10954–10957. (e) For an example of a redox-neutral Rh-
catalyzed carboxylation in dioxane: Ukai, K.; Aoki, M.; Takaya, J.;
Iwasawa, N. Rhodium(I)-Catalyzed Carboxylation of Aryl- and
Alkenylboronic Esters with CO2. J. Am. Chem. Soc. 2006, 128, 8706–
8707.
(16) (a) Wiberg, N. Tetraaminoäthylene Als Starke Elektronendonoren.
Angew. Chem. 1968, 80, 809–856. (b) Broggi, J.; Terme, T.; Vanelle,
P. Organic Electron Donors as Powerful Single-Electron Reducing
Agents in Organic Synthesis. Angew. Chem. Int. Ed. 2014, 53, 384–
413.
(17) Birbilis, N.; Buchheit, R. G. Electrochemical Characteristics of
Intermetallic Phases in Aluminum Alloysꢀ: An Experimental Survey
and Discussion. J. Electrochem. Soc. 2005, 152, 140–151.
(18) (a) Murphy, J. A.; Gamier, J.; Park, S. R.; Schoenebeck, F.; Zhou,
S. Z.; Turner, A. T. Super-Electron Donors: Bis-Pyridinylidene
Formation by Base Treatment of Pyridinium Salts. Org. Lett. 2008, 10,
1227–1230. (b) Garnier, J.; Kennedy, A. R.; Berlouis, L. E. A.; Turner,
A. T.; Murphy, J. A. Structure and Reactivity in Neutral Organic
Electron Donors Derived from 4-Dimethylaminopyridine. Beilstein J.
Org. Chem. 2010, 6, 4–11.
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(30) The Ni(I) complexes [Ni(I)(L1)2]Br and [Ni(I)(L1)2]OTf were
synthesized by oxidation of Ni(L1)2 with the corresponding AgX salt
as reported in ref. 29
(31) Oxidation states in NiL2 complexes have been studied in: Wang,
M.; England, J.; Weyhermüller, T.; Wieghardt, K. Electronic Structures
of “Low-Valent” Neutral Complexes [NiL2]0(S = 0; L = bpy, phen, tpy)
- An Experimental and DFT Computational Study. Eur. J. Inorg. Chem.
2015, 1511–1523.
(19) Organometallics and Catalysis: An Introduction; Bochmann, M.,
Ed.; Oxford University Press: Oxford, 2015; p 189.
(20) Use of 3.0 equiv CoCp2 with 1.0 equiv Zn(OTf)2 in the
carboxylation of sulfonium salt 2g gave 3g in 18% yield. See the
Supporting Information for further information.
(21) For single electron reduction of dialkylarylsuflonium salts, see:
Beak, P.; Sullivan, T. A. One-electron chemical reductions of
phenylalkylsulfonium salts. J. Am. Chem. Soc. 1982, 104, 4450.
(22) For unsuccessful and low-yielding substrates, see the Supporting
Information Scheme S2.
(32) See Supporting Information for details.
(33) Lin, Q.; Diao, T. Mechanism of Ni-Catalyzed Reductive 1,2-
Dicarbofunctionalization of Alkenes. J. Am. Chem. Soc. 2019, 141,
17937–17948.
(23) Selected examples of catalytic C−H carboxylation: (a) Mizuno,
H.; Takaya, J.; Iwasawa, N. Rhodium(I)-Catalyzed Direct
Carboxylation of Arenes with CO2 via Chelation-Assisted C−H Bond
Activation. J. Am. Chem. Soc. 2011, 133, 1251–1253. (b) Boogaerts, I.
I. F., Nolan, S. P. Carboxylation of C−H Bonds Using N-Heterocyclic
Carbene Gold(I) Complexes. J. Am. Chem. Soc. 2010, 132, 8858–8859.
(c) Luo, J.; Larrosa, I. C−H Bond Carboxylation with Carbon Dioxide.
ChemSusChem 2017, 10, 3317–3332.
(24) For deuterium or acidic quenching experiments in the context of
reductive carboxylations involving organozinc reagents, see ref. 15
and: (a) Nogi, K.; Fujihara, T.; Terao, J.; Tsuji, Y. Carboxyzincation
Employing Carbon Dioxide and Zinc Powder: Cobalt-Catalyzed
Multicomponent Coupling Reactions with Alkynes. J. Am. Chem. Soc.
2016, 138, 5547–5550. For activation of C–SMe bonds by Zn: (b)
Begouin, J.-M., Rivard, M.; Gosmini, C. Cobalt-Catalyzed C–SMe
Bond Activation of Heteroaromatic Thioethers. Chem. Commun. 2010,
46, 5972–5974.
(25) (a) Conan, A.; Sibille, S.; Périchon, J. Metal Exchange between an
Electrogenerated Organonickel Species and Zinc Halideꢀ: Application
to an Electrochemical, Nickel-Catalyzed Reformatsky Reaction J.
Org. Chem. 1991, 56, 2018–2024. (b) Sibille, S.; Ratovelomanana, V.;
Périchon, J. Electrochemical Conversion of Functionalised Aryl
Chlorides and Bromides to Arylzinc Species. J. Chem. Soc., Chem.
Commun. 1992, 283–284.
(34) In the absence of Zn and Zn(II), this reaction gave a very low
conversion of 2f (9%) to 1f (6%), Me2S (5%), biaryl (2%), and
[Ni(L1)2]OTf (8%).
(35) In the electrochemical zincation of aryl halides under cobalt
catalysis, one-electron reduction of ArCo(III) to ArCo(II) prior to Co-
to-Zn transmetalation was proposed. See: Seka, S.; Buriez, O.;
Nédélec, J.-Y.; Périchon, J. Mechanism of the Electrochemical
Conversion of Aryl Halides to Arylzinc Compounds by Cobalt
Catalysis in DMF/Pyridine. Chem. Eur. J. 2002, 8, 2534–2538.
(36) The majority of Ni(I) halide complexes bearing phenanthroline
ligands have been found to have an outer sphere counteranion and a
[NiL2]X formula. See references 3(e) and 29. Diao recently reported a
Ni(I) complex LNiBr where only one ligand is coordinated to Ni and
the bromide ligand is bound directly to Ni (ref. 33).
(37) Recent work by Diao has shown that insertion into a Ni(I)-alkyl
bond is more rapid than insertion into the analogous Ni(II)-alkyl bond:
Diccianni, J. B.; Hu, C. T.; Diao, T. Insertion of CO2 Mediated by a
(Xantphos)NiI-Alkyl Species. Angew. Chem. Int. Ed. 2019, 58, 13865–
13868.
(38) For example, see the following reference for a discussion of Zn
insertion during a cross-electrophile coupling between aryl bromides
and aryl chlorides with alkyl bromides: 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.
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CO2
CO2H
X
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Ni
Zn
R
R
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Wide scope & mild conditions
evidence for Ni(I) resting state
X = SMe
X = SMe2OTf
LnNiI
LnNiII
LnNi0
LnNiAr
Zn
ArZnX
multifaceted role of Zn
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