Isolation of Cp*CoIII–Alkenyl Intermediate in Efficient Cobalt-Catalyzed C?H Alkenylation with Alkynes

Article abstract of DOI:10.1002/chem.201705183

A general and efficient procedure for C?H alkenylation of arenes with a broad substrate scope catalyzed by Cp*Co^III was demonstrated with alkynes. A highly selective mono-alkenylation and sequential bis-C?H bond functionalization was displayed to exemplify the versatility of the cobalt catalyst. Isolation of cationic Cp*Co^III–alkenyl intermediate was achieved under identical catalytic conditions to further establish the proposed pathway.

Full text of DOI:10.1002/chem.201705183

A Journal of
Accepted Article
Title: Isolation of Cp*Co(III)-Alkenyl Intermediate in Efficient Cobalt
Catalyzed C-H bond Alkenylation with Alkynes
Authors: malay sen, Nimmakuri Rajesh, balakumar Emayavaramban, J
Richard Premkumar, and Basker Sundararaju
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201705183
Link to VoR: http://dx.doi.org/10.1002/chem.201705183
Supported by

10.1002/chem.201705183
Chemistry - A European Journal
COMMUNICATION
Isolation of Cp*Co(III)-Alkenyl Intermediate in Efficient Cobalt
Catalyzed C-H bond Alkenylation with Alkynes
Malay Sen,[a] Nimmakuri Rajesh,[a] Balakumar Emayavaramban,[a] J. Richard Premkumar[b] and Basker
Sundararaju*[a]
Dedication ((optional))
Abstract: A general efficient, broad substrate scope for C-H bond
alkenylation of arene catalyzed by Cp*Co(III) was demonstrated with
alkynes. A highly selective mono-alkenylation and sequential bis-C-
H bond functionalization was displayed to exemplify the versatility of
the cobalt catalyst. Isolation of cationic Cp*Co(III)-alkenyl
intermediate was achieved under identical catalytic conditions to
further establish the proposed pathway.
Cp*Co(III) under mild conditions. Isolation of Co(III)-alkenyl
intermediate without addition of any external ligands
(e.g.CH3CN) in operative reaction conditions was achieved to
further ascertain the reaction mechanism.[9]
a) [M]-cationic unsaturated metal complex
[M]
R
Ar
+ H+
b) C-H activation with nucleophilic/electrophilic metal catalysts followed by insertion
H
R
R
R
R
R
Ar
[M]
H
C-H bond functionalization has received much attention in
the recent times and emerged as sustainable tool for modern
organic synthesis.[1] Functionalized stereoselective olefins can
be predictably achieved via hydroarylation (C-H bond addition to
alkyne) starting from arenes and alkynes.[2] Until recently, such
atom-economical transformations were dominated by noble
metals especially using [Pd], [Ru] and [Rh].[3] However, low cost,
earth abundant metal catalyst considered as an alternative to
noble metals.[4] Among them, Cp*Co(III) emerged as powerful
catalyst due to its unique reactivity,[5b] in addition to the
complimentary reactivity shown similar to Cp*Rh(III).[5],[6] There
were two different pathways proposed for hydroarylation with
alkynes (Scheme 1): a) activation of alkyne by coordinatively
unsaturated cationic metal complex followed by nucleophilic
attack of electron rich arene to the triple bond,[2] b) activation of
C-H bonds by nucleophilic or electrophilic metal catalyst
followed by migratory insertion of alkyne.[3], [5]
R
R
R
R
R
[M]
Ar
H
R
H
[M] = nucleophilic
[M]
Ar
H
Ar
O.A.
Ar
H
base
assisted
R
R
+ H+
R
[M]
Ar
R
R
[M] Ar
Ar
[M] = electrophilic
R
H
Scheme 1. Reaction pathways for intermolecular hydroarylation with alkynes
We began our optimization using 1-(m-tolyl)-1H-pyrazole 1a
and Tolane 2a as model substrates, Cp*Co(CO)I2 as catalyst
and metal carboxylate as additive/ligand in 2,2,2-trifluoroethanol
(TFE) (0.1 M) at 80 °C for 24 h (Table S1). Among the solvents
we screened, TFE gave quantitative C-H alkenylation product
(entries 1-4). Both Silver acetate and Silver pivalate provided
comparable isolated yield, but other carboxylate sources did not
provide satisfactory results (entries 5-8). Good to excellent
yields were obtained without addition of silver salt or with other
cobalt precursors (entries 9-11). Good yield of (E)-1-(2-(1,2-
diphenylvinyl)-6-methylphenyl)-1H-pyrazole (3aa) was obtained
when the reaction temperature lowered to 60 °C and room
temperature (entries 12-13). The reaction did not require an
excess of alkyne, as 1.1 equiv. of alkyne provide excellent yield
with complete atom efficiency (entry 14). Control experiments
revealed that [Co] and carboxylate were necessary for the
reaction to proceed towards the product 3aa (entries 15-16).
In this regard, Fagnou reported the intermolecular C-2
selective hydroarylation of indole with alkyne using Cp*Rh(III) as
electrophilic catalyst.[7] Later, Kanai and Matsunaga reported C-
H bond alkenylation/annulation with alkyne using low cost
Cp*Co(III) under different reaction conditions.[8a] Matsunaga
demonstrated the extension of such methodology to pyrrole but
the complimentary general arene C-H alkenylation is currently
unknown.[8b] Maji et al. reported the C-H bond alkenylation using
benzamide as directing group.[8c] However, such elusive
intermolecular reactivity neither well understood nor any Co(III)-
alkenyl intermediate was isolated after migratory insertion.[9] In
continuation of our effort on cobalt catalyzed C-H bond
functionalization,[10] we herein report, an efficient, general
intermolecular hydroarylation of arenes with alkyne using
With the best reaction conditions in hand, we next examined
the scope of arenes (Scheme 2). Me-, Ac-, Br-, CF3 and –CO2R
were well tolerated at C-2 position of arene and selective
alkenylation products were obtained in good yield (3ba-3ga).
The stereochemistry of olefin obtained after hydroarylation was
further confirmed by solid state structure of 3da.[12] Selective
C(3)-alkenylation was achieved when 1-(naphthalen-2-yl)-1H-
pyrazole was employed (3ha). Heterocycle such as thiophene
underwent smoothly for C(3)-H alkenylation in good yield (3ia).
Next, we undertook the challenge of selective mono-alkenylation
using simple phenylpyrazole (1j).
[a]
[b]
M. Sen, Dr. N. Rajesh, B. Emayavaramban, Prof. Dr. B. Sundararaju
Fine Chemical Laboratory, Department of Chemistry,
Indian Institute of Technology Kanpur,
Kanpur, Uttar Pradesh, India.
E-mail: basker@iitk.ac.in
Dr. J. Richard Premkumar,
Department of Chemistry, Bishop Heber College (Autonomous),
Tiruchirappalli, Tamilnadu, India.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
This article is protected by copyright. All rights reserved.

10.1002/chem.201705183
Chemistry - A European Journal
COMMUNICATION
Cp*Co(CO)I2 - 5 mol%
AgSbF6 - 10 mol%
NaOPiv - 20 mol%
Cp*Co(CO)I2 - 5 mol%
AgSbF6 - 10 mol%
NaOPiv - 20 mol%
Pyz
R
Pyz
DG
DG
R
R
R
R
H
H
+
R
+
R
H
R
TFE, 60 oC, 16 h
Me
Me
H
TFE, 60 oC, 16 h
2
1a
4
1
2
3
Br
OBn
H
R
Pyz
R
Pyz
Pyz
N
R
N
N
Ph
OBn
OTBDMS
N
Ph
H
H
R
Ph
Me
Me
Me
Ph
4ac; 93%
R = OTBDMS; 4ad; 48%
R = OH; 4ad' = 40%
4ae; 81% (R = CH2OH)
4af; 86% (R = nPr)
H
H
F
R = Me; 3ba; 97%;
R = Ac; 3ca; 89% (80 oC)
3da; 74% (X-ray)
(CCDC: 1567345)
N
F
Pyz
Pyz
Pyz
N
N
N
Ph
N
Ph
N
Ph
Ph
H
F3C
Ph
H
RO2C
Ph
H
4ah; 90%
Me
Me
Me
Me
H
4ag; 87%
4ai; 91%
H
H
R = Me; 3fa; 84%
R = Et; 3ga; 93%
3ea; 36%
Pyz Ph
Pyz Et
Pyz Ph
Pyz Me
3ha; 96%
Et
Ph
Me
Ph
+
+
N
N
N
H
H
H
H
N
Ph
N
N
Ph
N
Ph
Me
Me
Me
Ph
Ph
Ph
4aj; 54%
4aj'; 40%
4ak; 53%
4ak'; 30%
S
H
H
H
Pyz
Me
3ja; 97%a
3ka; 96%a
Pyz
Pyz
CO2Et
3ia; 98%
4
N
N
N
N
Ph
N
Ph
4jl; 31%
4jm; 64%
4jn; 62%
Ph
N
Ph
Ph
Ph
Ph
Ph
Scheme 3. Scope of alkynes
H
H
H
H
3la; 92%a
3ma; 83%a
nBu
nBu
3ja(bis); 95%b
tBu
The scope of alkyne was further explored as illustrated in
Scheme 3. Symmetrical, functionalized alkynes were well
tolerated and provided the resultant hydroarylated product in
good yield (4ac-4ai). Unsymmetrical alkyne gave the mixture of
two regio-isomers in almost 1:1 ratio (4aj-4ak). Subsequently,
we have examined the terminal alkynes, which indeed provide
the expected alkenylated product in moderate to good yield (4jl-
4jn).
Cl
nBu
nBu
Ph
Ph
N
N
N
Pym
Pym
Pym
3na; 33%c
3ob; 92%c
3pb; 44%c
O2N
nBu
Ph
MeO
nBu
nBu
nBu
N
N
N
nBu
nBu
Pym
Pym
Pym
3qb; 59%c
Pyz Ph
3sb; 40%c
3rb; 52%c
R1 = ph,R2 = Me (2l)
Me
Me
4hl; 99%
Scheme 2. Scope of arenes a4 equivalent of arene and 1 equiv. of 2a was
used. b1 equivalent of arene and 2 equiv. of 2a was used. creaction performed
using DCE (0.2 M) at 60 °C. TFE = 2,2,2-trifluoroethanol
Pyz
OH
R2
Cp*Co(CO)I2 - 5 mol%
AgSbF6 - 10 mol%
NaOPiv - 20 mol%
Solvent, 80 oC, 16 h
H
+
R2
R1
OH
Pyz
R1 = CH2OH, R2=H (2e)
OH
1h
2
H
After brief optimization, we found out that 4 equivalent of
arene is required to obtain mono-alkenylation product 3ja in
excellent yield. The reaction was further extended to other C-4
substituted arenes in good-to-excellent yield (3ka-3ma). On the
other hand, selective bis-alkenylation was also achieved using 2
equivalent of alkyne 2a and 1 equivalent of 1-phenylpyrazole 1j
in 95% yield (3ja-bis). We further extended the scope to indole
derivatives to achieve the generality of the reaction. Moderate to
good yields were obtained for C-2 selective alkenylation using
pyrimidine as directing group in DCE at 60 °C (3na-3sb) and no
satisfactory results were obtained using TFE as solvent. It is
necessary to note that lower yields were obtained with
diphenylacetylene compared to 5-decyne, probably due to steric
hindrance.
4he; 90%
Scheme 4. Switch in selectivity with propargyl alcohol
We next demonstrated alkenylation vs allenylation by
changing the internal alkyne with propargyl alcohol, where steric
at the α-position plays crucial role in the observed selectivity
(Scheme 4). For example, our recent report[8b] on the use of 2-
methyl-4-phenylbut-3-yn-2-ol as substrate under standard
conditions provides the tetra-substituted allene (scheme 4, top),
whereas but-2-yne-1,4-diol resulted in C-H alkenylation product
(Scheme 4, bottom) in good yield.
This article is protected by copyright. All rights reserved.

10.1002/chem.201705183
Chemistry - A European Journal
COMMUNICATION
Cp*Co(CO)I2 cat - 5 mol %
We next aimed to isolate the reactive intermediate in the
presence of stoichiometric amount of alkyne and 1-(4-
bromophenyl)-1H-pyrazole. 1 equivalent of arene 1t with 1.2
equiv. of diphenylacetylene 2a, along with 1 equiv. each of
Cp*Co(CO)I2 and AgSbF6 were added in TFE.
AgSbF6 - 12 mol %
AgOPiv - 20 mol %
R
R
Pyz
Pyz
OH
Prop alcohol - 150 mol%
H
1j
+
Ph
Ph
Ph
C6H5CF3, 80 oC, 24 h
Std conditions
1jk'
5
2
OH
OH
Ph
Pyz Ph
Pyz
Pyz
Ph
OH
(a) Intermolecular competitive experiments:
Pyz
Pyz Ph
(i)
5a; 62%
5b; 59%
standard conditions
5c; 66%
Ph
R
H
R
Ph
+
Ph
H
Scheme 5. Sequential functionalization with Cp*Co(III)
3ba/3ea = 89/11
R = CH3 (1b) / CF3 (1e)
2a
(3ba/3ea)
Pyz
(ii)
Pyz
R
standard conditions
Due to steric, syn-β-hydroxyelimination is faster in the former
case, where –hydroxyl group and cobalt are syn to each other
and in the later case protodemetallation is faster due to the
absence of methyl group at the α-position. This fundamental
reactivity switch was observed for the first time using the
Cp*Co(III) metal catalysts which resulted in different product
formation under the same reaction conditions. Subsequently, we
explored the sequential functionalization starting from
phenylpyrazole 1j. Initial mono C-H allenylation 1jk’ was
achieved with propargyl alcohol followed by second C-H bond
alkenylation with internal alkynes. Both symmetrical and
unsymmetrical alkynes were employed with excellent
regioselectivity in good yield (5a-5c, Scheme 5). The high
regioselectivity obtained with unsymmetrical alkyne in 5c largely
due to the geometry and steric nature of the substituents.
R
Me
H
Me
R
+
R
H
3ba/3bb = 7/93
1a
R = Ph (2a) / n-Bu (2b)
3ba (Ph) / 3bb (n-Bu)
(a) KIE Experiment (parallel):
Cp*Co(CO)I2 - 5 mol%
AgSbF6 - 10 mol%
NaOPiv - 20 mol%
2a - 100 mol%
(i)
Pyz
Pyz Ph
Ph
D5/H5
D5/H5
H/D
Solvent, 80 o
C
3ja
1j-H5/D5
kH/kD = 1.02 ± 0.1
Pyz Ph
Pyz
std conditions as above
Ph
H/D
D5/H5
H/D
kH/kD = 5.38 ± 0.3
1b-H/D
3ba
(c) Stoichiometric Experiment:
SbF6
To understand the reaction mechanism several experiments
were carried out. Intermolecular competitive experiments were
conducted and it is in favour of electron rich arenes with the ratio
of 89/11 (Scheme 6a (i)). Also, both electron rich and poor
alkyne were tested in one pot and the results are in favour of
electron rich alkyne with the ratio of 7/93 (Scheme 6a (ii)). These
results clearly indicate that electrophilic C-H activation may likely
operate in the reaction mechanism. H/D exchange experiments
were carried out to understand reversibility of cyclocobaltation.
Both 1a-H and 1a-D gave significant H/D exchange with and
without the presence of alkyne 2a (SI). This implies that the C-H
activation is reversible. Further, KIE experiments were
performed through parallel investigations starting from 1j-H5 and
1j-D5 under standard reaction conditions. KIE value of 1.02 ±
0.1 was obtained when TFE was used as solvent (Scheme 6b
(i)). On the other hand, KIE value of 5.38 ± 0.3 was observed
when sterically hindered 1b-H/D was used (Scheme 6b (ii)).
These experimental results suggest reversible C-H activation
and rate-limiting insertion for sterically unhindered substrate but
rate-limiting step (RLS) can shift from C-H activation due to
steric hindrance (Scheme 6).
Cp*Co(CO)I2 - 100 mol%
AgSbF6 - 100 mol%
NaOAc - 200 mol%
Pyz
H
Co CO
N
N
Ph
+
Ph
CF3CH2OH, 60 oC, 12 h
NMR
Br
1t
2a
(120 mol%)
[Co-Int]
(X-ray)
MS
Br
(100 mol%)
CCDC: 1551078
(c) Isolated [Co-Int] as catalyst:
[Co-Int] cat - 5 mol%
AgSbF6 - 10 mol%
PivOH - 20 mol%
N
N
Ph
N
Ph
N
+
Ph
H
Ph
TFE, 60 oC, 24 h
H
2a
3aa (94%)
1a
Scheme 6. Control experiments and isolation of [Co]-intermediate
To further confirm the RLS, we carried out DFT calculations
(Figure S2, SI).[12] These results showed that the transition state
(4TS,
-6.88 kcal/mol)
for concerted-metallation and
deprotonation is found to have a low energy barrier compared to
transition state (7TS, -1.52 kcal/mol) for C-C bond formation
during the alkyne insertion. In addition, cyclocobaltation in the
presence of ‘CO’ makes it highly energetic and hence it is not
preferred pathway. The re-coordination of CO molecule occurs
only after the alkyne insertion process.
This article is protected by copyright. All rights reserved.

10.1002/chem.201705183
Chemistry - A European Journal
COMMUNICATION
Figure 1. Solid-state structure of isolated cationic cobalt complex [Co-Int] (H
and SbF6 anion -omitted for clarity)
Acknowledgements
Financial support provided by SERB (EMR2016/000136) to
carry out this research work is gratefully acknowledged. BS
acknowledges IITK for (PK Kelkar) young faculty award. MS and
BE thanks to CSIR and IITK for their fellowship. NR thanks
SERB (PDF/2016/003710) for national post-doctoral fellowship.
J.R.P and B.S. acknowledge IIT Kanpur Computer Centre High
Performance Computing Facility.
Subsequently, 2 equiv. of NaOAc was added to the solution
and the resulting mixture was stirred at 60 °C for 12 h.
Evaporation of solvent followed by crystallization of crude
mixture gave the expected Cp*Co(III)-alkenyl intermediate,
which is confirmed by NMR, MS and X-ray (Figure 1).[13] Such
reactive intermediate was isolated under identical catalytic
reaction conditions. The isolated intermediate was used as
catalyst and hydroarylation product 3aa was obtained in 94%
yield after 24 h (Scheme 6c).
Keywords: Molecular Cp*Co catalyst • C-H bond alkenylation •
Hydroarylation • Reactive intermediate • Mechanism
Based on the control experiments, we propose the plausible
mechanism for C-H bond alkenylation as shown in Scheme 7.
[1]
[2]
P. H. Dixneuf, H. Doucet, C-H bond Activation and Catalytic
Functionalization II, Springer 2016, 1-207 and references therein.
For recent reviews on catalytic hydroarylation see: a) Y. Yamamoto,
Chem. Soc. Rev. 2014, 43, 1575-1600; b) T. Kitamura, Eur. J. Org.
Chem. 2009, 1111-1125; c) N. A. Foley, J. P. Lee, Z. Ke, T. B. Gunnoe,
T. R. Cundari, Acc. Chem. Res. 2009, 42, 585-597; d) F. Kakiuchi, T.
Kochi, Synthesis, 2008, 3013-3039; f) C. Nevado, A. M. Echavarren,
Synthesis, 2005, 167-182.
Electrophilic cationic Cp*Co(III)
A
undergoes reversible
cyclometallation with 1 (after initial displacement of ‘CO’) via
concerted metallation deprotonation.[14] Intermediate C will
undergo fast migratory insertion[9a] with alkyne lead to isolable
Co(III)-alkenyl intermediate E. This subsequently undergoes
protodemetallation to provide the hydroarylated product, along
with the regeneration of the active catalyst A.
[3]
For recent selected reviews see: a) G. E. M. Crisenza, J. F. Bower,
Chem. Lett. 2016, 45, 2-9; b) V. P. Boyarski, D. S. Ryabukhin, N. A.
Bokach, A. V. Vasilyev, Chem. Rev. 2016, 116, 5894-5986; c) L. Yang,
H. Huang, Chem. Rev. 2015, 115, 3468-3517; d) S. Pan, T. Shibata,
ACS Catal. 2013, 3, 704-712; e) D. A. Colby, R. G. Bergman, J. A.
Ellman, Chem. Rev. 2010, 110, 624-655; f) V. Ritleng, C. Sirlin, M.
Pfeffer, Chem. Rev. 2002, 102, 1731-1769; g) F. Kakiuchi, S. Murai,
Acc. Chem. Res. 2002, 35, 826-834.
1
3
[Cp*Co(CO)(k2-OPiv)]+ X-
CO
X = SbF6- & OPiv-
PivOH
Cp*
Reductive
elimination
Coordination
A
Cp*
[4]
For selected reviews on C-H bond functionalization using first row
transition metal catalysts see: a) G. Pototschnig, N. Maulide, M.
Schnürch, Chem. -Eur. J. 2017, 23, 9206-9232; b) Y. Liang, Y. –F.
Liang, N. Jiao, Org. Chem. Front. 2015, 2, 403-415; c) X. H. Cai, B. Xie,
ARKIVOC, 2015, 115, 184-211; d) N. Chatani, Top. Organomet. Chem.
2016, 56, 19-46; e) I. Bauer, H. J. Knölker, Chem. Rev. 2015, 115,
3170-3387; f) S. Z. Tasker, E. A. Standley, T. F. Jamison, Nature, 2014,
509, 299-309; g) K. Gao, N. Yoshikai, Acc. Chem. Res. 2014, 47, 1208-
1219; h) L. Ackermann, J. Org. Chem. 2014, 79, 8948-8954; i) J.
Yamaguchi, K. Muto, K. Itami, Eur. J. Org. Chem. 2013, 19-30; j) R. T.
Gephart, T. H. Warren, Organometallics, 2012, 31, 7728-7752; k) Y.
Nakao, Chem. Rec. 2011, 11, 242-251; l) E. Nakamura, N. Yoshikai, J.
Org. Chem. 2010, 75, 6061-6067; m) A. A. Kulkarni, O. Daugulis,
Synthesis, 2009, 4087-4109. Also see: n) K. Gao, P. –S. Lee, T. Fujita,
N. Yoshikai, J. Am. Chem. Soc. 2010, 132, 12249-12251; o) Z. Ding, N.
Yoshikai, Angew. Chem. Int. Ed. 2012, 51, 4698-4701; p) B. Zhou, H.
Chen, C. Wang, J. Am. Chem. Soc. 2013, 135, 1264-1267.
X
X
N
N
Co CO
Ph
o
C
N
O
N
H
O
CMe3
(X-ray)
B
Ph
Co
E
Cyclometallation
(CMD)
Alkyne
PivOH
Insertion
N
X
X
CO
N
Co Cp*
Cp*
N
N
Co
Ph
C
Alkyne
coordination
Ph
D
2
[5]
Reviews on Cp*Co(III)-catalyzed C-H bond functionalization see: a) P.
G. Chirila, C. J. Whiteoak, Dalton. Trans. 2017, 46, 9721-9739; b) T.
Yoshino, S. Matsunaga, Adv. Synth. Catal. 2017, 359, 1245-1262 and
references therein; c) S. Wang, S. –Y. Chen, X. –Q. Yu, Chem.
Commun. 2017, 53, 3165-3180; d) M. Usman, Z. –H. Ren, Y. –Y. Wang,
Z. H. Guan, Synthesis, 2017, 1419-1443; e) M. Moselage, J. Li, L.
Ackermann, ACS Catal. 2016, 6, 498-525; f) N. Yoshikai,
ChemCatChem. 2015, 7, 732-734; g) T. Hyster, Catal. Lett. 2015, 145,
458-467.
Scheme 7. Proposed mechanism
In conclusion, we have developed an efficient, cobalt-
catalyzed hydroarylation of arenes with alkyne under mild
conditions. The reaction can be performed even at room
temperature albeit in moderate yield. The reaction showed the
broad scope of arene with excellent functional group tolerance
and moderate-to-good regioselectivity. The switch in selectivity
between allenylation and alkenylation was observed, when
propargylic alcohols was used as coupling partner. We have
isolated Cp*Co(III)-alkenyl intermediate, which is active for
catalytic hydroarylation with excellent yield. We propose that the
electrophilic metal undergoes reversible C-H cobaltation first
followed by migratory insertion of alkyne led to Co(III)alkenyl
intermediate and subsequent protodemetallation provided the
hydroarylation product.
[6]
For selected examples see: a) T. Yoshino, H. Ikemoto, S. Matsunaga,
M. Kanai, Angew. Chem. Int. Ed. 2013, 52, 2207-2211; b) T. Yoshino,
H. Ikemoto, S. Matsunaga, M. Kanai, Chem. Eur. J. 2013, 19, 9142-
9146; c) B. Sun, T. Yoshino, S. Matsunaga, M. Kanai, Adv. Synth. Catal.
2014, 356, 1491-1495; d) Y. Suzuki, B. Sun, K. Sakata, T. Yoshino, S.
Matsunaga, M. Kanai, Angew. Chem. Int. Ed. 2015, 54, 9944-9947; e)
D. Zhao, J. H. Kim, L. Stegemann, C. A. Strassert, F. Glorius, Angew.
Chem. Int. Ed. 2015, 54, 4508-4511; f) A. Lerchen, T. Knecht, C. G.
Daniliuc, F. Glorius, Angew. Chem. Int. Ed. 2016, 55, 15166-15170; g)
J. Park, S. Chang, Angew. Chem. Int. Ed. 2015, 54, 14103-14107; h) H.
Wang, M. M. Lorion, L. Ackermann, Angew. Chem. Int. Ed. 2016, 55,
This article is protected by copyright. All rights reserved.

10.1002/chem.201705183
Chemistry - A European Journal
COMMUNICATION
10386-10390; i) J. A. Boerth, J. R. Hummel, J. A. Ellman, Angew.
Chem. Int. Ed. 2016, 55, 12650-12654.
[7]
[8]
D. J. Schipper, M. Hutchinson, K. Fagnou, J. Am. Chem. Soc. 2010,
132, 6910-6911.
a) H. Ikemoto, T. Yoshino, K. Sakata, S. Matsunaga, M. Kanai, J. Am.
Chem. Soc. 2014, 136, 5424-5431; b) R. Tanaka, H. Ikemoto, M. Kanai,
T. Yoshino, S. Matsunaga, Org. Lett. 2016, 18, 5732-5735; also see c)
S. S. Bera, S. Debbarma, A. K. Ghosh, S. Chand, M. S. Maji, J. Org.
Chem. 2017, 82, 420-430.
[9]
While our manuscript was in preparation similar Co(III)-alkenyl
intermediate was reported see: a) J. Sanjosé-Orduna, D. Gallego, A.
Garcia-Roca, E. Martin, J. Bennet-Buchholz, M. H. Pérez-Temprano,
Angew. Chem. Int. Ed. 2017, 56, 12137-12141; also see our recent
report on isolation of such Co(III) species, b) M. Sen, P. Dahiya, J.
Richard Premkumar, B. Sundararaju, Org. Lett. 2017, 19, 3699-3702.
[10] a) R. Mandal, B. Sundararaju, Org. Lett. 2017, 19, 2544-2547; b) D.
Kalsi, N. Barsu, P. Dahiya, B. Sundararaju, Synthesis, 2017, 3937-
3944; c) N. Barsu, S. K. Bolli, B. Sundararaju, Chem. Sci. 2017, 8,
2431−2435. d) N. Barsu, B. Emayavaramban, B. Sundararaju, Eur. J.
Org. Chem. 2017, 4370-4374; e) N. Barsu, Md. Atiur Rahman, M. Sen,
B. Sundararaju, Chem. Eur. J. 2016, 22, 9135-9138.
[11]
For calculations see, K. Sakata, M. Eda, Y. Kitaoka, T. Yoshino, S.
Matsunaga, J. Org. Chem. 2017, 82, 7379-7387.
[12] See the supporting information for more details.
[13] CCDC 1567345 (3da) & 1551078 (Co-Int) contains the supplementary
crystallographic data for this paper.
provides additional information.
The supporting information
[14] For carboxylate assisted CMD mechanism operated in C-H activation
see, a) D. Lapointe, K. Fagnou, Chem. Lett. 2010, 39, 1119-1126; b) E.
F. Flegeau, C. Bruneau, P. H. Dixneuf, A. Juttand, J. Am. Chem. Soc.
2011, 133, 10161-10170; c) L. Ackermann, Chem. Rev. 2011, 111,
1315-1345.
This article is protected by copyright. All rights reserved.

10.1002/chem.201705183
Chemistry - A European Journal
COMMUNICATION
COMMUNICATION
M. Sen, Dr. N. Rajesh, B.
Emayavaramban, Dr. J. Richard
Premkumar and Prof. Dr. B.
Sundararaju*
SbF6
Co CO
DG
DG Ph
N
Ph
Ph
N
+
Ph
H
Page No. – Page No.
Br
A general efficient, cobalt-catalyzed C-H bond alkenylation of arene was reported.
Broad substrate scope with excellent functional group tolerance was achieved using
various arenes and alkynes. Cp*Co-alkenyl intermediate isolated for the first time
under operative catalytic conditions to further validate the proposed mechanism.
Isolation of Co(III)-alkenyl
Intermediate in Efficient Cobalt-
Catalyzed C-H bond Alkenylation with
Alkynes
This article is protected by copyright. All rights reserved.