10.1002/anie.201916387
Angewandte Chemie International Edition
COMMUNICATION
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.
8
3CONH2-I (10 mol%)
66
aReaction conditions: 1CONH2-I (0.05 mmol), diphenylacetylene (0.15 mmol), 2-
VTMS (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.
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.
Table 2. Optimization of the Reaction Conditionsa
[Cp*CoI(VTMS)2] (10 mol%)
O
O
AgSbF6 (1 equiv)
K2CO3 (2 equiv)
Ph
NH2
NH
Ph
+
DCE, 100º C, 24 h, Ar
I
Ph
1CONH2-I
Entry
1
7
Ph
Deviation from standard conditions
none
7 [%][b]
75 (66)[c]
Conflict of interest
2
3
4
5
6
7
DCE (0.1 M), AgBF4, 40 ºC
DCE (0.1 M), AgBF4
DCE (0.1 M), AgBF4, KOAc
Dioxane (0.1 M), AgBF4
DCE (0.1 M)
0
53
0
The authors declare no conflict of interest.
38
70
67
Keywords: cobalt • C–H activation • homogeneous catalysis •
structural elucidation • weak coordination
AgBF4
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