"This is the peer reviewed version of the following article: Weakly Coordinated Cobaltacycles: Trapping Catalytically Competent
Intermediates in Cp*CoIII Catalysis, which has been published in final form at https://doi.org/10.1002/anie.201916387. This
article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."

Weakly Coordinated Cobaltacycles: Trapping
Competent Intermediates in Cp*CoIII Catalysis

Catalytically

Sara Martínez de Salinas,[a] Jesús Sanjosé-Orduna,[a] Carlota Odena,[a] Sergio Barranco,[a] Jordi BenetBuchholz,[a] Mónica H. Pérez-Temprano*[a]
Abstract: Herein, we disclose the synthesis of metallacyclic Cp*CoIII
complexes containing weakly-chelating functional groups. We have
employed these compounds not only as an exceptional platform for
accessing some of the most widely invoked transient intermediates
in C–H functionalization processes but also as competent catalysts
in different Cp*Co-catalyzed transformations, including a benchmark
coupling reaction.

Over the past several decades, C–H functionalization reactions
directed by weakly-coordinated functional groups have emerged
as powerful strategies for forming carbon–carbon and carbon–
heteroatom bonds.1 A key advantage of this approach is that the
directing substrates contain common moieties found in
synthetically relevant organic compounds (e.g., ketones,
aldehydes, amides or esters). Therefore, extra synthetic steps for
their installation/removal are often not necessary.2 Usually, the
weaker coordination of these directing groups to the metal center
affords highly reactive metallacyclic intermediates towards
subsequent functionalization. However, this entails a major
obstacle, even when employing noble metals:3 the low
thermodynamic stability of the resulting transient species hinders
their detection and/or isolation (Figure 1a). The inherent lack of
stability has shown to be even more problematic with first-row
metals systems, such as cobalt-based platforms.4 While
important synthetic advances have been made in the field of
Cp*CoIII catalysis,5 characterizing the putative cobalt
intermediates in these transformations remains challenging.5f
This profound lack of fundamental understanding at the
molecular level precludes the rational design and development
of novel and more efficient Cp*Co-catalyzed processes. As part
of our ongoing interest in uncovering the mechanistic “black box”
of Cp*CoIII-catalyzed C–H functionalization reactions,6 we have
recently reported the synthesis of well-defined cobaltacycles
stabilized by strong -donor moieties such as pyridine or
pyrimidine. In the present study (Figure 1b), we describe the
synthesis of metallacyclic Cp*CoIII complexes (A) supported by
weakly chelating ligands commonly used in Cp*Co-catalyzed C–
H functionalizations, via an alternative oxidative addition route.
We have leveraged these compounds to explore the access to
direct analogues of long-sought-after cationic transient cobalt
species (A+) that have been widely proposed as key reactive
intermediates. Moreover, we demonstrate the intermediacy of
the A-type compounds in selected Cp*CoIII-catalyzed C–H

[a]

Sara Martínez de Salinas,[a] Jesús Sanjosé-Orduna,[a] Carlota
Odena,[a] Sergio Barranco,[a] Jordi Benet-Buchholz,[a] Mónica H.
Pérez-Temprano*[a]
Institute of Chemical Research of Catalonia (ICIQ)
Avgda. Països Catalans 16, 43007 Tarragona (Spain)
E-mail: mperez@iciq.es

functionalizations, as well as their potential participation in the
functionalization of aryl halides, using a benchmark reaction.

Figure 1. (a) State-of-the-art of C–H functionalization reactions assisted by
weakly-coordinated directing groups; (b) the present work.

Initial studies were focused on designing a suitable platform for
interrogating the accessibility to isolable Cp*CoIII complexes
containing weakly-coordinated scaffolds. We explored an
oxidative addition route to access complex A, which would
circumvent the proposed reversibility of the Cp*CoIII-mediated C–
H metalation.4,5,6 We selected 2-iodobenzaldehyde (1ald-I) as the
ideal substrate for this oxidative addition given its synthetic
relevance, widespread availability, and the opportunity to utilize
the aldehydic proton as a spectroscopic handle in 1H NMR
analyses. Moreover, reported examples of Cp*CoI aldehyde
complexes support the feasible coordination of this carbonyl
group to a cobalt metal center.7
The treatment of 1ald-I with [Cp*CoI(VTMS)2] (2-VTMS) in THF
at room temperature for 15 minutes afforded the oxidative
addition product 3ald-I as a greenish-black solid in 91% isolated
yield (Figure 2).8 The metallacyclic compound was fully
characterized by 1D (1H, 13C) and 2D NMR spectroscopy, MSESI and single-crystal X-ray diffraction, showing the coordination
of the aldehyde group in a -fashion.9 1H NMR spectroscopy
revealed an upfield shift of the aldehydic proton in 3ald-I ( = 9.04
ppm) compared to 1ald-I ( = 10.03 ppm) due to its interaction
with the cobalt center.

O
H
I
1ald-I
(1 equiv)

Me3Si
CoI

2-VTMS
(1 equiv)

SiMe3

H

O
CoIII

THF, 25 ºC
15 min, Ar

I
3ald-I
91 %

3ald-I

3ald-I

Figure 2. Synthesis and Characterization of 3ald-I via Oxidative Addition.
ORTEP Diagram of 3ald-I is shown at 50% of probability (H atoms have been
omitted for clarity).

by NMR spectroscopy at 25 ºC, whereas 3CONH2-I and 3CONHtBu-I
were characterized at –35 ºC due to their comparatively lower
stability. The nature of the synthesized compounds was
confirmed by X-ray diffraction (Figure 4). The solid-state
structures of 3DG-I containing amide groups show its coordination
to the cobalt metal center by the oxygen atom, which is the most
basic site for neutral amides. The isolation and characterization
of 3acetanilide-I is particularly interesting since access to a sixmembered Cp*CoIII cobaltacycle had not previously been
reported in the literature.
Table 1. Scope of 3DG-I Containing Different Weakly Chelating Functional
Groupsa

We next explored the influence of the (pseudo)halide in the
formation of 3ald-X (X = I, Br, Cl, OMe) (Figure 3). As expected,
the nature of X affects the oxidative addition event,10 as 1ald-Br
reacted more slowly than the iodide derivative (Figure 3).11 3aldBr was fully characterized by NMR spectroscopy and X-ray
diffraction. Under the same reaction conditions, 1ald-Cl and 1aldOMe did not oxidatively add to the metal center, leading to
decomposition of 2-VTMS over time.
(a)

O

X = Cl, OMe

CoI

+

X
1ald-X
(1 equiv)

2-VTMS
(1 equiv)

SiMe3

X = Br

THF, 25 ºC
1 h, Ar

THF, 25 ºC
time , Ar

decomposition

O

X
1ald-X

+

H3C

EtO

O
CoIII

tBuHN

H2N

O

O
CoIII

I
3ester-I (50%)

O

I
3CONH2-I (84%)b

NH

O

CoIII
I

3acetanilide-I (87%)b

yields. bReaction Conditions: 5 minutes

Br

3ald-Br

H
CoI

I
3DG-I

CoIII

a Isolated

CoIII

SiMe3

CoIII

THF, 25 ºC
15 min, Ar

Weakly-Coordinated DGs Scope

3CONHtBu-I (80%)

Me3Si
H

2-VTMS

1DG-I

DG

CoI

CoIII

3ald-Br
80 %
O

+

I
H

(b)

Me3Si
I

I
3ket-I (78%)

Me3Si
H

DG

X = I, Br

THF, 25 ºC, Ar
SiMe3 reaction trend
2-VTMS
I > Br

O
CoIII
X
3ald-X

3ald-I
3ald-Br

Figure 4. ORTEP Diagrams of 3DG-I. Thermal ellipsoids drawn at 50% of
probability (H atoms have been omitted for clarity).

Figure 3. (a) Addition of 1ald-X to [Cp*CoI(VTMS)2]. ORTEP Diagram of 3ald-Br
is shown at 50% of probability (H atoms have been omitted for clarity). (b)
Reaction Profile for the formation of 3ald-X (X = I, Br) at 25 ºC in THF-d8.

Having confirmed the accessibility and stability of 3ald-I/Br, we
next aimed to expand the scope of chelating groups involved in
the formation of these CoIII compounds. The oxidative addition
approach used to access 3ald-I proved to be general for a range
of substrates, such as ketones, esters and amides, enabling the
synthesis of various 3DG-I-type complexes shown in Table 1.12
3DG-I (DG = ketone, ester, acetanilide) were fully characterized

After demonstrating the accessibility and stability of various
CoIII complexes supported by catalytically relevant scaffolds, we
next pursued detecting the direct analogues of the reactive
species formed after the C–H metalation step (Figure 5).5b, 5d, 5gh, 13
In this context, we have previously described the employment
of coordinating ligands to access otherwise highly reactive
cationic metallacyclic Cp*CoIII species. Following the same
approach14 and using 3ald-I as our initial platform, we were able
to provide the first experimental evidence of a five-membered
cationic cyclometalated Cp*CoIII complex bearing weakly
coordinated functional groups. The reaction of 3ald-I with AgBF4
in THF-d8 afforded the in situ formation of 3ald-THF in full
conversion by 1H NMR spectroscopy. Although this complex was

O

too unstable for isolation,15 its structure could be characterized
by multinuclear NMR spectroscopy and X-ray diffraction. After
some optimization, the remaining 3DG-THF analogues could be
detected in the crude 1H NMR spectra by treatment with AgNTf2.
3keto-THF and 3acetanilide-THF were fully characterized by 1D and
2D NMR spectroscopy, whereas 3CONH2-THF and 3CONHtBu-THF
were only characterized by 1H NMR spectroscopic analyses due
to their greater instabilities.

4
97% yield

O

Bn
N

O
N
Bn

O

10 mol% [3ket-I]
AgSbF6 (20 mol%)
PivOH (50 mol%)
TFE, 120 ºC, 24 h

O

(1.5 equiv)

DG

DG

1.1 equiv AgBF4

CoIII

H

BF4−

O

CoIII

THF-d8, Ar
25 ºC, 3 min

I
3DG-I

3ald-THF
95%

1.1 equiv AgNTf2

O

d8
NTf2−

CoIII

tBuHN

NTf2−

3ket-THF
80%

d8

O

d8

H2N

3CONtBu-THF
86%

O

d8

NTf2−

O

NH

CoIII

O

NTf2−
CoIII

O
3CONH2-THF
91%

O

d8

1DG-H

Ph
5
44% yield

6
Ph
quantitative

NTf2−

O
CoIII

CoIII

Ph

5 mol% [3CONHtBu-I]
AgSbF6 (10 mol%)
PivOH (25 mol%)
HFIP, 80 ºC, 24 h
O
OH
(3 equiv)
NHtBu

Figure 6. Catalytic competence of 3DG-I. Reported yields were determined via
1
H NMR spectroscopic analysis of the crude reaction mixture versus an internal
standard using the substrate as the limiting reagent.

O
3DG-THF

O

Cation of
3ald-THF

H

Ph
(1.2 equiv)

N

DG

THF-d8, Ar
25 ºC, 3 min

H3C

12 mol% [3acetanilide-I]
AgNTf2 (1 equiv)
DCE, 130 ºC, 16 h

3acetanilide-THF
100%

d8

Figure 5. Conversion of 3DG-I to 3DG-THF. Reported yields were determined
by the 1H NMR spectroscopic analysis of the crude reaction mixture. ORTEP
plot of 3ald-THF. Thermal ellipsoids drawn at 50% of probability, and the
hydrogen/deuterium atoms and BF4 anion are omitted for clarity.

Having
established
the
synthesis,
isolation
and
characterization of different 3DG-I complexes and the accessibility
of their cationic analogues, we next sought to explore the
reactivity of 3DG-I in Cp*CoIII-catalyzed C–H functionalization
reactions (Figure 6). As mentioned above, these complexes are
precursors of the putative intermediates involved in these
transformations. However, their inaccessibility had previously
hampered investigations of their catalytic competence. We
therefore sought to utilize 3ket-I, 3CONHtBu-I and 3acetanilide-I as a
platform for determining the intermediacy of these species in
representative catalytic reactions. Importantly, these directing
groups have been utilized in Cp*Co-catalyzed C–H
functionalizations.5h,13a-b As shown in Figure 6, these
cyclometalated complexes proved to be suitable catalysts for
representative C–C coupling reactions, supporting the feasibility
of the corresponding cationic intermediates in these
transformations.16

Finally, inspired by the facile formation of 3DG-I complexes
through oxidative addition, we wondered whether these Cp*Co
species could promote cross-coupling reactions of aryl halides
containing this type of auxiliary ligands. Different types of cobalt
species, normally generated by the combination of cobalt salts
and Grignard reagents, have shown to be effective catalysts in
aryl halide cross coupling reactions. However, the involvement of
Cp*Co intermediates in these types of transformations remains
practically unexplored.17,18 Guided by our previous studies on
Cp*CoIII-catalyzed C–H functionalizations,6 we selected alkyne
annulations as a benchmark reaction. In the context of C–H
functionalization reactions, these transformations proceed via
CoI/III catalytic cycles and involve a re-oxidation step after product
formation to regenerate the active Cp*CoIII species that
subsequently participates in C–H bond cleavage. When using
aryl halides as starting materials, we envisioned a similar
catalytic cycle to the one proposed for the C–H activation but with
an oxidative addition/halide abstraction sequence (Figure 7).
R

DG

R

reductive
elimination

reductive
elimination

DG CoIII

[Cp*Co I]

novel
proposed cycle:
C−X functionalization
[Cp*Co I]

DG
I

R
oxidation

R

oxidative
addition

R

[Ox]

1DG-I

R
[Cp*Co III]

reversible
C−H metalation

DG
CoIII

halide
abstraction

DG
CoIII
I

DG
H

H+

AgX

previous work:
1DG-H C−H functionalization

Figure 7. Proposed mechanism for known C–H oxidative alkyne annulation vs
new pathway involving the activation of aryl halides.

To test our working hypothesis, we chose the reaction between
2-iodobenzamide and diphenylacetylene as the representative
system (Table 2). It should be noted that the formation of the
desired product by Cp*Co-catalyzed C–H functionalization using
benzamide as a coupling partner is currently unprecedented in
the literature.19 To our delight, after some experimentation, we
found that the desired annulated product (7) was obtained in 75%
yield in the presence of catalytic quantities of 2-VTMS in DCE at
100 ºC for 24 hours, using AgSbF6 and K2CO3 as additives. While
not anticipated, the choice of silver salt and base had an
important effect on the reactivity (entries 4 and 7). 3CONH2-I is a
competent catalyst in the annulation reaction, although we
observed the desired product in a slightly lower yield (66%) than
with 2-VTMS. These preliminary results provide experimental
evidence for the functionalization of 1DG-type substrates by
Cp*Co systems. We anticipate this type of cross-coupling
reactions can be potentially applied to other Cp*Co-catalyzed
transformations involving oxidative addition and reductive
elimination steps.
Table 2. Optimization of the Reaction Conditions a
O

Ph
NH2

I
1CONH2-I

+

[Cp*CoI(VTMS)2] (10 mol%)
AgSbF6 (1 equiv)
K2CO3 (2 equiv)

O
NH

DCE, 100º C, 24 h, Ar
Ph

Ph

75 (66)[c]

DCE (0.1 M), AgBF4, 40 ºC

In summary, we have developed a promising strategy that
enables entry to catalytically relevant metallacyclic Cp*CoIII
complexes supported by synthetically relevant scaffolds. We
have demonstrated the competence of these 3DG-I-type
complexes, not only in select C–H functionalization reactions but
also in a benchmark coupling reaction with aryl halides. This
fundamental work is expected to open new avenues for
accessing previously elusive reactive intermediates in Cp*Co
catalysis and designing novel catalytic systems.

Acknowledgements
We thank the CERCA Programme/Generalitat de Catalunya and
the Spanish Ministry of Economy, Industry and Competitiveness
(MINECO: CTQ2016-79942-P, AIE/FEDER, EU) for the financial
support. J.S.-O. thanks Severo Ochoa Excellence Accreditation
for a predoctoral contract. S. B. thanks ICIQ Summer Fellowship
Programme funded by Fundació “la Caixa”. We also thank the
Research Support Areas of ICIQ.

0

3

DCE (0.1 M), AgBF4

53

4

DCE (0.1 M), AgBF4, KOAc

0

5

Dioxane (0.1 M), AgBF4

38

6

DCE (0.1 M)

70

7

[4]

66

7 [%][b]

none

2

[3]

Deviation from standard conditions

1

[2]

3CONH2-I (10 mol%)

Reaction conditions: 1CONH2-I (0.05 mmol), diphenylacetylene (0.15 mmol), 2VTMS (10 mol%), AgSbF6 (0.05 mmol), K2CO3 (0.1 mmol) in DCE (0.5 M) at
100 ºC under Ar. bNMR yields using an internal standard. cIsolated yield.

Ph

7

Entry

[1]

8
a

AgBF4

67

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Conflict of interest
The authors declare no conflict of interest.
Keywords: cobalt • C–H activation • homogeneous catalysis •
structural elucidation • weak coordination

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[15]

[9]

[10]
[11]

[12]

[13]

[14]

to [C5Me5Co(L)] during the hydroacylation of olefins with aromatic
aldehydes (ref. 7a). Under our reaction conditions, we only observed the
oxidative addition of the Csp2–I bond.
CCDC 1971411 (3ald-I), CCDC 1971412 (3ald-Br), CCDC 1971413 (3ketI), CCDC 1971414 (3ester-I), CCDC 1971415 (3CONH2-I), CCDC 1971416
(3CONHtBu-I), CCDC 1971417 (3acetanilide-I), CCDC 1971418 (3ald-THF),
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could not be confirmed or excluded, since the reaction of 2-VTMS with
1ald-I, in the presence of TEMPO, afforded the formation of other
unknown species. See SI for further details.
Our attempts for synthesizing the corresponding 3DG-I complexes when
using as starting material 2-iodobenzoic acid, 2-iodobenzyl alcohol, 2iodonitrobenzene
2-iodophenol,
2-iodoaniline
and
2iodomethoxybenzoate led to the decomposition of 2-VTMS.
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89:11 ratio, respectively. The amount of [Cp*Co(MeCN) 3][BF4]2
increases along time in solution. See SI for further details.

[16]

[17]

[18]

[19]

When the solvent was removed on a rotary evaporator and the resulting
precipitate was re-dissolved in CD2Cl2 we observed decomposition.
Although the employment of 3CONHtBu-I resulted in moderate yields of 5,
this experimental result is comparable to the one described by
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1435−1462.
Joshi and co-workers have reported the Cp*CoIII-catalyzed coupling
between alkenes and aryl halides in the absence of directing groups,
see: A. K. Srivastava, N. Satrawala, M. Ali, C. Sharma, R. K. Joshi,
Tetrahedron Lett. 2019, 60, 151283. Our attempts to synthesize
different cobaltacycles using Cp*Co(VTMS) 2 (2-VTMS) and PhI in the
presence and abscence of external stabilizing ligands led to a complex
mixture of products. See SI for further details.
The formation of 7 by Cp*Co-catalyzed C–H functionalization reactions
has been reported using as starting material N-methoxy or N-chloro
benzamides, see: a) G. Sivakumar, A. Vijeta, M. Jeganmohan, Chem.
Eur. J. 2016, 22, 5899−5903; b) X. Yu, K. Chen, S. Guo, P. Shi, C. Song,
J. Zhu, Org. Lett. 2017, 19, 5348−5351.

Layout 1:

COMMUNICATION
Reported here is a versatile platform
for capturing thermodynamically
unfavoured cobaltacyclic species
which
contain
weakly-chelating
moieties. This strategy offers the
opportunity to not only fully
characterize direct analogues of key
transient reactive species but also
interrogate their efficient reactivity
and intermediacy in different Cp*Cocatalyzed processes.
Twitter: @Perez_Temprano

Sara Martínez de Salinas,[a] Jesús
Sanjosé-Orduna,[a] Carlota Odena,[a]
Sergio Barranco,[a] Jordi BenetBuchholz,[a]
Mónica
H.
PérezTemprano*[a]
Page No. – Page No.
Weakly Coordinated Cobaltacycles:
Trapping Catalytically Competent
Intermediates in Cp*CoIII Catalysis