Azaruthena(II)-bicyclo[3.2.0]heptadiene: Key Intermediate for Ruthenaelectro(II/III/I)-catalyzed Alkyne Annulations

Article abstract of DOI:10.1002/anie.202000762

A ruthenium-catalyzed electrochemical dehydrogenative annulation reaction of imidazoles with alkynes has been established, enabling the preparation of various bridgehead N-fused [5,6]-bicyclic heteroarenes through regioselective electrochemical C?H/N?H annulation without chemical metal oxidants. Novel azaruthenabicyclo[3.2.0]heptadienes were fully characterized and identified as key intermediates. Mechanistic studies are suggestive of an oxidatively induced reductive elimination pathway within a ruthenium(II/III) regime.

Full text of DOI:10.1002/anie.202000762

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Accepted Article
Title: Aza-Ruthena(II)-Bicyclo-[3.2.0]-Heptadiene: Key Intermediate for
Ruthenaelectro(II/III/I)-Catalyzed Alkyne Annulations
Authors: Long Yang, Ralf Steinbock, Alexej Scheremetjew, Rositha
Kuniyil, Lars H. Finger, Antonis M. Messinis, and Lutz
Ackermann
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202000762
Angew. Chem. 10.1002/ange.202000762
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http://dx.doi.org/10.1002/ange.202000762

10.1002/anie.202000762
Angewandte Chemie International Edition
RESEARCH ARTICLE
Aza-Ruthena(II)-Bicyclo-[3.2.0]-Heptadiene: Key Intermediate for
Ruthenaelectro(II/III/I)-Catalyzed Alkyne Annulations
Long Yang, Ralf Steinbock, Alexej Scheremetjew, Rositha Kuniyil, Lars H. Finger, Antonis M. Messinis,
and Lutz Ackermann*
Dedication
[a]
Long Yang, Ralf Steinbock, Alexej Scheremetjew, Dr. Rositha Kuniyil, Dr. Lars H. Finger, Dr. Antonis Messinis, Prof. Dr. Lutz Ackermann
Institut für Organische und Biomolekulare Chemie and Wöhler Research Institute for Sustainable Chemistry
Georg-August-Universität Göttingen
Tammannstrasse 2, 37077 Göttingen (Germany)
E-mail: Lutz.Ackermann@chemie.uni-goettingen.de
Homepage: http://www.ackermann.chemie.uni-goettingen.de/ and http://wisch.chemie.uni-goettingen.de//
Supporting information for this article is given via a link at the end of the document.
Abstract: A ruthenium-catalyzed electrochemical dehydrogenative
annulation reaction of imidazoles with alkynes has been established,
enabling the preparation of various bridgehead N−fused [5,6]-bicyclic
heteroarenes through regioselective electrochemical C−H/N−H
annulation without chemical metal oxidants. Novel aza-ruthena-
bicyclo-[3.2.0]-heptadienes were fully characterized and identified
as key intermediates. Mechanistic studies are suggestive of an
provides first structural proof for an unprecedented mechanistic
manifold for annulations – even beyond the generally accepted
metallalkenyl, metallacyclopropene, and recently proposed
metallallylcarbenoid intermediates.[12] Salient features of our
findings include 1) ruthenaelectro-catalytic alkenylic[8c] and aryl
C–H functionalization, 2) alkyne annulations for N−fused [5,6]-
bicyclic heteroarenes, 3) isolation and full characterization of a
oxidatively-induced reductive elimination pathway within
ruthenium(II/III) regime.
a
novel
mechanistic
aza-ruthena(II)-bicyclo-[3.2.0]-heptadiene
and
reductive
4)
insights
into
oxidation-induced
elimination[13] at ruthenium(II) by experiments and calculation.
Introduction
Transition metal-catalyzed C–H activations have emerged as a
transformative platform,[1] with enabling applications to drug
design,[2] natural product synthesis,[3] and material sciences.[4] As
a consequence, a plethora of transition metal-catalyzed C–
H/Het–H activation/alkyne annulations has emerged as a useful
tool for the preparation of heterocycles.[5] However, these
methods generally require a stoichiometric amount of organic or
metal-based oxidant, such as toxic and/or expensive copper(II) or
silver(I) salts. In recent years, the use of electricity as a formal
redox agent to empower chemical reactions has been recognized
as an increasingly viable, environmentally-friendly strategy.[6]
Significant recent impetus was gained by the merger of
electrocatalysis with oxidative C–H activation, thus avoiding the
use of toxic and expensive metal oxidants.[7]
Figure 1. Novel mechanism for electrooxidative C–H activation by aza-
ruthena(II)-bicyclo-[3.2.0]-heptadienes.
Despite considerable progress,[8] the development of new
catalytic manifolds is hampered by a lack of mechanistic
Results and Discussion
understanding.
This
holds
especially
true
for
At the outset of our studies, we explored various reaction
conditions for the envisioned ruthenium-catalyzed electro-
oxidative C–H/N–H activation of alkenyl imidazole 1a with alkyne
2a in an operationally simple undivided cell setup equipped with
a GF (graphite felt) anode and a Pt cathode (Table 1 and see
Table S-1 in the Supporting Information).[14] After considerable
preliminary experimentation, we observed that the desired
product 3aa was indeed obtained by catalytic amounts of
[RuCl2(p-cymene)]2, along with KPF6 as the optimal catalytic
additive, while among various solvents, the best results were
ruthenaelectrocatalysis, which continues to be underdeveloped.
Thus, a plethora of ruthenium-catalyzed C–H activations with
chemical oxidants[9] is contrasted by only a few examples of
ruthenaelectrocatalysis.[10] Within our program on electrochemical
C–H activation,[11] we have now developed a ruthenium-catalyzed
electrochemical dehydrogenative alkyne annulation by imidazoles
that assembles a variety of bridgehead N−fused [5,6]-bicyclic
heteroarenes (Figure 1). Notably, a novel aza-ruthena(II)-bicyclo-
[3.2.0]-heptadiene was identified as the key intermediate, which
undergoes oxidation induced reductive elimination. This motif
1
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10.1002/anie.202000762
Angewandte Chemie International Edition
RESEARCH ARTICLE
observed in DMF (entries 1–5). The yield was reduced when
sodium salts were used, such as NaCl and NaPF6 (entries 6–7).
Gratifyingly, reducing the reaction time to 8 h led to the same yield
of product 3aa (entry 8). A reaction conducted with a Pt anode
instead of GF resulted in a sharp drop in yield (entry 10). The
addition of the redox mediator of BQ did not improve the
performance of the ruthenium catalyst (entries 11–12). Control
experiments verified the essential role of the electricity, the
additive and the ruthenium catalyst (entries 13–15). A set of
otherwise typical transition metal catalysts were also probed, but
gave none or significantly reduced amounts of product 3aa
(entries 16–20).
Having identified the optimal reaction conditions, we explored the
versatility of our electrochemical annulation with diversely
decorated alkynes 2 (Scheme 1). Electron-rich as well as
electron-deficient aromatic moieties at the alkynes 2 were
amenable to the ruthenaelectro-catalyzed C–H functionalizations.
Thereby, a variety of synthetically useful electrophilic functional
groups, such as chloro (3af), cyano (3ag) and bromo (3al)
substituents, were fully tolerated, which should prove invaluable
for late-stage manipulation.
Table 1. Optimization of ruthenaelectro-catalyzed annulation.[a]
Entry
1
Catalyst
Additive
KPF6
KPF6
KPF6
KPF6
KPF6
NaCl
NaPF6
KPF6
KPF6
KPF6
KPF6
KPF6
KPF6
---
Solvent
MeOH
t-AmOH/H2O
DMA
Yield [%][b]
10%c
12%d
33%
10%
75%
50%
66%
75%e
56%f
46%g
33%h
28%i
10%j
50%
---
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2
---
2
3
4
NMP
5
DMF
6
DMF
7
DMF
8
DMF
9
DMF
10
11
12
13
14
15
16
17
18
19
20
DMF
Scheme 1. Electrochemical C–H/N–H activation with alkynes 2.
DMF
DMF
We next turned our attention to diversified alkenyl imidazoles 1
(Scheme 2). Imidazoles 1b–f bearing a range of substituents at
different sites on the alkene or the imidazole were effectively
transferable to deliver products 3ba–3fa. In addition,
benzimidazole substrates with a β-methyl group (1g) and without
a β-substituent on the alkene (1h) were effective for C–H/N–H
activation. Notably, thiophenyl substituted benzimidazole 1i also
was a competent substrate, giving the corresponding annulation
product 3ia with high efficacy.
DMF
DMF
KPF6
KPF6
KPF6
KPF6
KPF6
KPF6
DMF
Ru(p-cymene)(OAc)2
DMF
53%
---
Co(OAc)2 4H2O
DMF
·
[Cp*RhCl2]2
[Cp*IrCl2]2
Pd(OAc)2
DMF
36%
10%
---
The ruthenaelectro-catalyzed dehydrogenative alkyne annulation
regime was not restricted to alkenyl imidazoles 1. Indeed, we next
investigated the generality of the metallaelectrocataylsis by the
assembly of the benzimidazoisoquinoline skeleton 5 (see Table
S2 for optimization) through annulation of alkynes 2 by 2-
arylimidazoles 4 (Scheme 3). Substitution at the 2-aryl group (4b–
4i) and the benzimidazole (4l–4m) gave the desired benzimidazo-
isoquinolines. Likewise, 2-naphthylbenzimidazole (4j) and 2-
phenylnaphthoimidazole (4k) also afforded the corresponding
products. The unsymmetrical 1-phenyl-1-propyne 2m gave the
product 5am with high levels of regioselectivity. Importantly,
DMF
DMF
[a] Reaction conditions: Undivided cell, 1a (0.40 mmol), 2a (0.80 mmol),
catalyst (5.0 mol %), additive (20 mol %), solvent (4.0 mL), 140 °C, 16
h,constant current at 4.0 mA, GF anode, Pt-plate cathode. [b] Yields of isolated
product. [c] 60 °C. [d] t-AmOH/H2O = 1/1, 100 °C. [e] 8 h. [f] 5 h. [g] Pt-plate as
anode. [h] BQ (10 mol %). [i] BQ (10 mol %), 100 °C. [j] no electricity. DMF =
N,N-Dimethylformamide, BQ = 1,4-Benzoquinone.
2
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10.1002/anie.202000762
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RESEARCH ARTICLE
chloro, bromo, ester, amide and enolizable ketone substituents
were thereby fully tolerated.
Intrigued
by
the
ruthenaelectro-catalyzed
C–H/N–H
functionalization, we became attracted to delineating the
catalyst’s mode of action. To this end, reactions with isotopically
labeled solvent were suggestive of a fast C–H cleavage, occurring
by an organometallic C–Ru bond formation (Scheme 4a).
Intermolecular competition experiments revealed
a
slight
preference for electron-poor alkynes 2 and electron-rich arenes 4
(Scheme 4b). Molecular H2 is generated as the by-product
through cathodic proton reduction, which was confirmed by head-
space GC analysis.[14]
Scheme 2. Electrochemical alkyne annulation by alkenyl imidazoles 1.
Scheme 4. Summary of key mechanistic experiments.
Next, we probed the isolation of intermediates by stoichiometric
experimentation. Thus, we first selectively prepared the
ruthenacycle Ru-II (Scheme 5a). Second, the ruthenacycle Ru-II
delivered upon stoichiometric reaction with alkynes 2 the
unprecedented aza-ruthena(II)-bicyclo-[3.2.0]-heptadienes Ru-
IVa and Ru-IVb, which were unambiguously characterized by X-
ray diffraction analysis. Notably, the metallacyles Ru-II and Ru-IV
proved to be competent under catalytic reaction conditions also
(Scheme 5b). It is noteworthy that the aza-ruthena(II)-bicyclo-
[3.2.0]-heptadiene Ru-IVa was stable, but gave the product 3aa
upon electrolysis, being suggestive of an oxidation-induced
reductive elimination within a ruthenium(II/III) manifold.
Scheme 3. Electrooxidative C–H activation of benzimidazoles 4.
3
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Furthermore, we probed the electrochemical C–H activation by
means of cyclovoltammetric analysis of the well-defined
ruthenacycles (Figure 2). Thus, we observed at ambient
temperature an irreversible oxidation of the ruthenium(II) complex
Ru-II at Ep = 0.60 V vs. SCE. The aza-ruthena(II)-bicyclo-[3.2.0]-
heptadiene Ru-IVa featured a considerably higher oxidation wave
at Ep = 1.20 V vs. SCE, both of which could be rationalized by an
oxidation-induced reductive elimination within a ruthenium(II/III)
regime.
30
20
Ru-II
Ru-IV
10
0
-0.5
0.0
0.5
1.0
1.5
2.0
Potential vs. SCE (V)
Figure 2. Cyclic voltammetry in DMF with 100 mM KPF6 under N2 at RT with
100 mV/s of Ru-II (5 mM) and Ru-V (5 mM).
Scheme 5. X-ray crystal structure analysis and applications. Selected bond
lengths [Å]: Ru-II: Ru1-N1: 2.086(3), Ru1-C3: 2.083(3), N1-C1: 1.340(4), C1-
C2: 1.446(4), C2-C3: 1.356(4); Ru-IVa: Ru1-N1: 2.101(2), Ru1-C14: 2.172(3),
Ru1-C15: 2.171(3), Ru1-C16: 2.222(3), N1-C13: 1.326(4), C12-C13: 1.481(4),
C12-C14: 1.577(4), C12-C16: 1.564(4), C14-C15: 1.442(4), C15-C16: 1.449(4);
Ru-IVb: Ru1-N1: 2.094(3), Ru1-C13: 2.220(3), Ru1-C14: 2.185(3), Ru1-C15:
2.174(3), N1-C11: 1.333(4), C11-C12: 1.477(4), C12-C13: 1.557(4), C12-C15:
1.587(4), C13-C14: 1.446(5), C14-C15: 1.449(5).
4
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10.1002/anie.202000762
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RESEARCH ARTICLE
Figure 3. Relative Gibbs free energy profile in kcal∙mol–1 comparing the direct reductive elimination and oxidatively induced reductive elimination pathways at the
PBE0-D3(BJ)/6-311++G(d,p),def2-TZVP(Ru),SDD(Ru)+SMD(DMF)//TPSS-D3(BJ)/6-31G(d),def2-SVP(Ru),SDD(Ru) level of theory. Non-participating hydrogen
atoms were omitted for clarity. The bond distances in the transition states are given in angstrom.
Based on our mechanistic studies, we propose a plausible
catalytic cycle to commence by a fast organometallic C–H
activation (Scheme 6). Thereby, ruthena(II)cycle Ru-II is
generated.[15] Thereafter, alkyne coordination and migratory
insertion furnish the aza-ruthena-bicyclo-[3.2.0]-heptadiene Ru-
IV, which undergoes anodic oxidation to deliver the ruthenium(III)
complex Ru-V. Subsequent pericyclic ring opening yields
ruthenium(III) complex Ru-VI. Oxidation-induced reductive
elimination forms ruthenium(I) complex Ru-VII, which is
anodically reoxidized.
Conclusion
In conclusion, we have reported on the electrocatalytic
organometallic C–H/N–H functionalization of imidazoles. Novel
aza-ruthena-bicyclo-[3.2.0]-heptadienes were identified as the
key intermediate, setting the stage for alkyne annulations from
synthetically meaningful alkenyl and aryl imidazoles with ample
scope. The C–H activation employed electricity as the only
oxidant and generated molecular hydrogen as the sole byproduct.
Scheme 6. Proposed catalytic cycle.
Mechanistic studies by experiment and DFT provided strong
support for an oxidation-induced reductive elimination of aza-
ruthena-bicyclo-[3.2.0]-heptadienes by environmentally-benign
electricity. These findings should prove instrumental for the
mechanistic understanding and catalyst design of ruthenium(II)-
catalyzed oxidative C–H activations.
Further, we have compared the direct reductive elimination at
the
aza-ruthena(II)-bicyclo-[3.2.0]-heptadiene
with
the
oxidatively-induced reductive elimination at ruthenium(III) Ru-IV
and Ru-V at the PBE0-D3(BJ)/6-311++G(d,p),def2-TZVP(Ru),
SDD(Ru)+SMD(DMF)//TPSS-D3(BJ)/6-31G(d),def2-SVP(Ru),
SDD(Ru) level of theory (Figure 3). Thus, our computational
findings confirmed the preferential reductive elimination at
ruthenium(III), being indicative of a ruthenium(II/III/I) manifold.
Acknowledgements
5
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10.1002/anie.202000762
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RESEARCH ARTICLE
Ackermann, Angew. Chem. Int. Ed. 2018, 57, 2383-2387; h) S. Tang, D.
Wang, Y. Liu, L. Zeng, A. Lei, Nat. Commun. 2018, 9, 798; i) N.
Sauermann, R. Mei, L. Ackermann, Angew. Chem. Int. Ed. 2018, 57,
5090-5094; j) R. Mei, N. Sauermann, J. C. A. Oliveira, L. Ackermann, J.
Am. Chem. Soc. 2018, 140, 7913- 7921; k) X. Gao, P.Wang, L. Zeng, S.
Tang, A. Lei, J. Am. Chem. Soc. 2018, 140, 4195-4199; k) Y. Qiu, M.
Stangier, T. H. Meyer, J. C. A. Oliveira, L. Ackermann, Angew. Chem. Int.
Ed. 2018, 57, 14179-14183; m) S.-K. Zhang, R. C. Samanta, N.
Sauermann, L. Ackermann, Chem. Eur. J. 2018, 24, 19166-19170; n) Q.-
L. Yang, X.-Y. Wang, J.-Y. Lu, L.-P. Zhang, P. Fang, T.-S. Mei, J. Am.
Chem. Soc. 2018, 140,11487- 11494; o) N. Sauermann, T. H. Meyer, C.
Tian, L. Ackermann, J. Am. Chem. Soc. 2017, 139, 18452-18455; p) Q.-
L. Yang, Y.-Q. Li, C. Ma, P. Fang, X.-J. Zhang, T.-S. Mei, J. Am. Chem.
Soc. 2017, 139, 3293-3298; q) Y.-Q. Li, Q.-L.Yang, P. Fang, T.-S. Mei,
D. Zhang, Org. Lett. 2017, 19, 2905-2908; r) C. Ma, C.-Q. Zhao, Y.-Q. Li,
L.-P. Zhang, X.-T. Xu, K. Zhang, T.-S. Mei, Chem. Commun. 2017, 53,
12189-12192; sF. Kakiuchi, T. Kochi, H. Mutsutani, N. Kobayashi, S.
Urano, M. Sato, S. Nishiyama, T. Tanabe, J. Am. Chem. Soc. 2009, 131,
11310-11311; t) C. Amatore, C. Cammoun, A. Jutand, Adv. Synth. Catal.
2007, 349, 292-296. A review: u) N. Sauermann, T. H. Meyer, Y. Qiu, L.
Ackermann, ACS Catal. 2018, 8, 7086-7103.
Generous support by the DFG (Gottfried-Wilhelm-Leibniz award
to LA), the CSC (LY) is gratefully acknowledged. We thank Dr.
Christopher Golz (Göttingen University) for assistance with the X-
ray diffraction analysis.
Keywords: ruthenium • C–H activation • dehydrogenation •
electrochemistry • N–heterocycles
[1]
a) S. Rej, Y. Ano, N. Chatani, Chem. Rev. 2020,
DOI:10.1021/acs.chemrev.9b00495; b) A. Dey, S. K. Sinha, T. K. Achar,
D. Maiti, Angew. Chem. Int. Ed. 2019, 58, 10820-10843; c) P.
Gandeepan, T. Müller, D. Zell, G. Cera, S. Warratz, L. Ackermann, Chem.
Rev. 2019, 119, 2192-2452; d) Y. Park, Y. Kim, S. Chang, Chem. Rev.
2017, 117, 9247-9301; e) J. He, M. Wasa, K. S. L. Chan, Q. Shao, J.-Q.
Yu, Chem. Rev. 2017, 117, 8754-8786; f) B. Ye, N. Cramer, Acc. Chem.
Res. 2015, 48, 1308-1318; g) O. Daugulis, J. Roane, L. D. Tran, Acc.
Chem. Res. 2015, 48, 1053-1064; h) B. Li, P. H. Dixneuf, Chem. Soc.
Rev. 2013, 42, 5744-5767; i) D. A. Colby, A. S. Tsai, R. G. Bergman, J.
A. Ellman, Acc. Chem. Res. 2012, 45, 814-825, and cited references.
a) T. Cernak, K. D. Dykstra, S. Tyagarajan, P. Vachal, S. W. Krska, Chem.
Soc. Rev. 2016, 45, 546-576; b) L. Ackermann, Org. Process Res. Dev.
2015, 19, 260-269.
[2]
[9]
a) G. Duarah, P. P. Kaishap, T. Begum, S. Gogoi, Adv. Syn. Catal. 2019,
361, 654-672; b) P. Nareddy, F. Jordan, S. E. Brenner-Moyer, M. Szostak,
ACS Catal. 2016, 6, 4755-4759; c) C. Bruneau, P. H. Dixneuf, Top. Curr.
Chem. 2016, 137-188; d) L. Ackermann, Acc. Chem. Res. 2014, 47, 281-
295; e) P. B. Arockiam, C. Bruneau, P. H. Dixneuf, Chem. Rev. 2012,
112, 5879-5918.
[3]
[4]
J. Wencel-Delord, F. Glorius, Nat. Chem. 2013, 5, 369-375.
J.-R. Pouliot, F. Grenier, J. T. Blaskovits, S. Beaupré, M. Leclerc, Chem.
Rev. 2016, 116, 14225-14274.
[5]
For select references, see: a) A. Obata, A. Sasagawa, K. Yamazaki, Y.
Ano, N. Chatani, Chem. Sci. 2019, 10, 3242-3248; b) T. Wezeman, R.
Scopelliti, F. F. Tirani, K. Severin, Adv. Synth. Catal. 2019, 361, 1383-
1388; c) T. Yoshino, S. Matsunaga, Adv. Synth. Catal. 2017, 359, 1245-
1262; d) K. S. Halskov, H. S. Roth, J. A. Ellman, Angew. Chem. Int. Ed.
2017, 56, 9183-9187; e) M. Gulías, J. L. Mascareꢀas, Angew. Chem. Int.
Ed. 2016, 55, 11000-11019; f) N. Kavitha, G. Sukumar, V. P. Kumar, P.
S. Mainkar, S. Chandrasekhar, Tetrahedron Lett. 2013, 54, 4198-42001;
g) W. Ma, K. Graczyk, L. Ackermann, Org. Lett. 2012, 14, 6318-6321; h)
B. Li, H. Feng, N. Wang, J. Ma, H. Song, S. Xu, B. Wang, Chem. Eur. J.
2012, 18, 12873-12879; i) L. Ackermann, A. V. Lygin, N. Hofmann,
Angew. Chem. Int. Ed. 2011, 50, 6379-6382; j) K. Morimoto, K. Hirano,
T. Satoh, M. Miura, Org. Lett. 2010, 12, 2068-2071; k) T. K. Hyster, T.
Rovis, J. Am. Chem. Soc. 2010, 132, 10565-10569; l) K. Morimoto, K.
Hirano, T. Satoh, M. Miura, Org. Lett. 2010, 12, 2068-2071; m) N. Umeda,
H. Tsurugi, T. Satoh, M. Miura, Angew. Chem. Int. Ed. 2008, 47, 4019-
4022, and cited references.
[10] a) L. Massignan, X. Tan, T. H. Meyer, R. Kuniyil, A. M. Messinis, L.
Ackermann, Angew. Chem. Int. Ed. 2020, DOI:10.1002/anie.201914226;
b) M. J. Luo, M. Hu, R. J. Song, D. L. He, J. H. Li, Chem. Comun. 2019,
55, 1124-1127; c) M.-J. Luo, T.-T. Zhang, F.-J. Cai, J.-H. Li, D.-L. He,
Chem. Commun. 2019, 55, 7251-7254; d) Z.-Q. Wang, C. Hou, Y.-F.
Zhong, Y.-X. Lu, Z.-Y. Mo, Y.-M. Pan, H.-T. Tang, Org. Lett. 2019, 21,
9841-9845; e) R. Mei, J. Koeller, L. Ackermann, Chem. Commun. 2018,
54, 12879-12882; f) F. Xu, Y.-J. Li, C. Huang, H.-C. Xu, ACS Catal. 2018,
8, 3820-3824; g) Y. Qiu, C. Tian, L. Massignan, T. Rogge, L. Ackermann,
Angew. Chem. Int. Ed. 2018, 57, 5818-5822.
[11] a)
L.
Ackermann,
Acc.
Chem.
Res.
2020,
53, DOI:
10.1021/acs.accounts.9b00510; b) Y. Qiu, J. Struwe, L. Ackermann,
Synlett 2019, 30, 1164-1173.
[12] J. Jiang, H. Liu, L. Cao, C. Zhao, Y. Liu, L. Ackermann, Z. Ke, ACS Catal.
2019, 9, 9387-9392.
[13] a) W.-J. Kong, L. H. Finger, A. M. Messinis, R. Kuniyil, J. C. A. Oliveira,
L. Ackermann, J. Am. Chem. Soc. 2019, 141, 17198-17206; b) K. Shin,
Y. Park, M.-H. Baik, S. Chang, Nat. Chem. 2018, 10, 218-224; c) L. Li,
W. W. Brennessel, W. D. Jones, J. Am. Chem. Soc. 2008, 130, 12414-
12419.
[6]
a) M. Elsherbini, T. Wirth, Acc. Chem. Res. 2019, 52, 3287-3296; b) P.
Xiong, H.-C. Xu, Acc. Chem. Res. 2019, 52, 3339-3350; c) Y. Yuan, A.
Lei, Acc. Chem. Res. 2019, 52, 3309-3324; d) S. R. Waldvogel, S. Lips,
M. Selt, B. Riehl, C. J. Kampf, Chem. Rev. 2018, 118, 6706-6765; e) S.
Tang, Y. Liu, A. Lei, Chem 2018, 4, 27-45; f) J. E. Nutting, M. Rafiee, S.
S. Stahl, Chem. Rev. 2018, 118, 4834-4885; g) G. S. Sauer, S. Lin, ACS
Catal. 2018, 8, 5175-5187; h) R. Feng, J. A. Smith, K.D. Moeller, Acc.
Chem. Res. 2017, 50, 2346-2352; i) M. Yan, Y. Kawamata, P. S. Baran,
Chem. Rev. 2017, 117, 13230-13319; j) R. Francke, R. D. Little, Chem.
Soc. Rev. 2014, 43, 2492-2521; k) A. Jutand, Chem. Rev. 2008, 108,
2300-2347.
[14] For detailed information, see the Supporting Information.
[15] a) I. Fabre, N. von Wolff, G. Le Duc, E. Ferrer Flegeau, C. Bruneau, P.
H. Dixneuf, A. Jutand, Chem. Eur. J. 2013, 19, 7595-7604; b) E. F.
Flegeau, C. Bruneau, P. H. Dixneuf, A. Jutand, J. Am. Chem. Soc. 2011,
133, 10161-10170; c) L. Ackermann, R. Vicente, H. K. Potukuchi, V.
Pirovano, Org. Lett. 2010, 12, 5032-5035; d) L. Ackermann, R. Vicente,
A. Althammer, Org. Lett. 2008, 10, 2299- 2302; e) D. L. Davies, S. A.
Macgregor, C. L. McMullin, Chem. Rev. 2017, 117, 8649-8709; f) L.
Ackermann, Chem. Rev. 2011, 111,1315-1345; g) see also:
Naksomboon, K.; Poater, J.; Bickelhaupt, F. M.; Fernández-Ibáñez, M.
Á., J. Am. Chem. Soc. 2019, 141, 6719-6725.
[7]
[8]
a) T. H. Meyer, L. H. Finger, P. Gandeepan, L. Ackermann, Trends Chem.
2019, 1, 63-76; b) Q.-L. Yang, P. Fang, T.-S. Mei, Chin. J. Chem. 2018,
36, 338-352; c) C. Ma, P. Fang, T.-S. Mei, ACS Catal. 2018, 8, 7179-
7189; d) N. Sauermann, T. H. Meyer, L. Ackermann, Chem. Eur. J. 2018,
24, 16209-16217.
Selected examples: a) Z.-J. Wu, F. Su, W. Lin, J. Song, T.-B. Wen, H.-J.
Zhang, H.-C. Xu, Angew. Chem. Int. Ed. 2019, 58, 16770-16774; b) W.-
J. Kong, L. H. Finger, J. C. A. Oliveira, L. Ackermann, Angew. Chem. Int.
Ed. 2019, 58, 6342-6346; c) Q. L. Yang, Y. K. Xing, X. Y. Wang, H. X.
Ma, X. J. Weng, X. Yang, H. M. Guo, T. S. Mei, J. Am. Chem. Soc.
2019,141,18970-18976; d) C. Tian, U. Dhawa, A. Scheremetjew, L.
Ackermann, ACS Catal. 2019, 9, 7690-7696; e) C. Zhu, M. Stangier, J.
C. A. Oliveira, L. Massignan, L. Ackermann, Chem. Eur. J. 2019,
25,16382-16389; f) A. Shrestha, M. Lee, A. L. Dunn, M. S. Sanford, Org.
Lett. 2018, 20, 204-207; g) C. Tian, L. Massignan, T. H. Meyer, L.
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10.1002/anie.202000762
Angewandte Chemie International Edition
RESEARCH ARTICLE
Entry for the Table of Contents
New mechanism: Aza-ruthena-bicyclo-[3,2,0]-heptadienes as key intermediates for ruthena(II/III)electro-catalyzed C–H activation.
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