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Letter
Bimetallic Nickel Complexes for Aniline C#H Alkylations Debasish Ghorai, Lars H. Finger, Giuseppe Zanoni, and Lutz Ackermann ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b03770 • Publication Date (Web): 05 Nov 2018 Downloaded from http://pubs.acs.org on November 5, 2018
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ACS Catalysis
Bimetallic Nickel Complexes for Aniline C‒H Alkylations Debasish Ghorai,†,‡ Lars H. Finger,† Giuseppe Zanoni,‡ and Lutz Ackermann*†,‡ Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammanstraße 2, 37077 Göttingen (Germany) ‡ Department of Chemistry, University of Pavia, Viale Taramelli 10, 27100 Pavia, Italy †
ABSTRACT: A set of bimetallic nickel(II)/nickel(II) complexes featuring paddle-wheel structures was synthesized and fully characterized. These homobimetallic nickel complexes were identified as powerful catalysts for challenging aniline C‒H activations with primary and secondary β-hydrogen-containing alkyl halides. KEYWORDS: bimetallic • nickel • alkylation • C‒H activation • reaction mechanism
Transition metal-catalyzed C‒H activation has emerged as an increasingly powerful tool for molecular syntheses, with notable applications for the assembly of natural products as well as medicinal drugs and materials.1 Despite of numerous advances in site-selective arene C‒H functionalizations by chelation assistance, direct C‒H alkylations remain challenging, since undesired β-hydride elimination prevails. Thus, these transformations continue to be dominated by precious 4d transition metals.2 In contrast, recent focus has shifted towards earth abundant 3d transition metal-catalyzed C‒H functionalizations.3 In this regard, nickel complexes have been established as versatile catalysts for enabling C‒H functionalizations, with notable contributions by Chatani,4 Ge,5 Shi,6 and Ackermann,7 among others.8 Bimetallic catalysis has recently gained considerable momentum because of its remarkable metal-metal bonding and its unique ability towards substrate activation through multiple metal centers, which has been a long standing subject of fundamental interest.9 Disregarding bimetallic palladium catalysis,10 there is only limited knowledge on fundamental aspects of inexpensive bimetallic nickel catalysts. In this context, Uyeda disclosed the activation of small molecules by bimetallic nickel complexes of type A supported by the redox active naphthyridine-diimine ligand (Scheme 1a).11 In an elegant recent report, Diao presented N‒N bond formations proceeding through a bimetallic paddle-wheel complex of type B.12 Importantly, Diao fully characterized high valent nickel intermediates in C‒H functionalization by preparing several binuclear cyclometalated nickel(II) complexes of benzo[h]quinoline (type C). Here, the cautious treatment with selective oxidants led to the successful isolation of an one electron oxidized mixed-valent bimetallic intermediate, which upon further treatment with excess oxidant provided the C‒H functionalized product in a stoichiometric manner.13 Despite of this major progress, these studies were - with an elegant exception by Uyeda11c largely conducted in a stoichiometric fashion, with catalytic manifolds as of yet being scarce. In this context, Martin and co-workers very recently identified binuclear
nickel complexes of type D as key intermediates for C‒O cleavages (Scheme 1).14 Within our program on sustainable C‒H activation,15 we have now unravelled unprecedented paddle-wheel complexes as first homobimetallic nickel catalysts for C‒H activation (Scheme 1b). Scheme 1. Bimetallic nickel(II)/nickel(II) complexes. (a) previous work N
R
N
N
N
Ni
Ni
N
N
R
A, Ref 11 Uyeda primarily stoichiometric Si-H activation carbene transfer
N
N
Ni
N
N
B, Ref 12 Diao stoichiometric N-N formation N
(b) this work
Ni
N N
N
C, Ref 13 Diao stoichiometric C-X formation
Ni O
CMe3
Ni O PCy3 D, Ref 14 Martin catalytic C-O activation
N
H
N
HN
HN N
Ar
PCy3 Me Me
N Ni N N
N
N Ar
O O O Ni O Ni
N N Ni N N N
+ Br Alk
Ni
Ar
N Alk
Homobimetallic Nickel catalytic C–H activation key mechanistic insights challenging C–H alkylations kinetics and CV
We initiated our studies by probing the activation of aniline derivatives 1a-b with NiCl2(DME) in 1,4-dioxane at 120 °C. Thereby, we selectively obtained the novel binuclear nickel complexes 2a and 2b (Scheme 2).
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Scheme 2. Synthesis of bimetallic nickel(II) complexes 2ab. N
N
N NiCl2(DME) (0.5 equiv)
HN N
LiOt-Bu, 1,4-dioxane 120 oC, 16 h
Ar
Ni
Ar N Ar N N
N
N Ar N Ar
Ni N
N
N
N
Ar = Ph (2a): 20% Ar = 2-FC6H4 (2b): 28%
1
The single crystal X-ray structure of 2a revealed notable structural features, in which one substrate binds to the two metal centers in a bidentate chelating fashion to form five membered bimetallacycles. Overall, four bridging 2aminophenyl pyrimidine ligands coordinate to the two nickel(II) centres resulting in paddle-wheel9f, 10h, 16 bimetallic scaffolds (Figure 1a). This arrangement brings two metal centers into close proximity as to form strong intermetallic interactions, with the distance between the two nickel centers measuring 2.382 Å and 2.389 Å for 2a and 2b, respectively. The Ni‒Ni distances are within the range of known bimetallic nickel paddle-wheel complexes very recently reported by Diao.12, 13 To further interrogate the homobimetallic nature of complexes 2, we conducted cyclic voltammetry experiments. Thus, the homobimetallic compounds featured characteristic oxidation waves of E1/2 = 0.40 (2a) and 0.39 V (2b) (vs. Fc/Fc+; see Figure 1b), respectively, providing support for the formation of a nickel(II/III) intermediate. (a)
2a
2b
(b)
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N5-C15 1.386(4). (b) Cyclic voltammetric analysis of complex 2b in THF with 0.1 mol/l n-Bu4NPF6 at different scan rates, and of complexes 2a and 2b vs. decamethylferrocene.
With the connectivity and electrochemical behaviour of complexes 2 being established, we became intrigued to explore their potential in challenging C‒H alkylations with β-hydrogen-containing alkyl halides.17 Delightfully, when homobimetallic complex 2a was treated in a stoichiometric setting with n-butyl bromide (3a) in the presence of base, 40% of mono-alkylated product 4a was observed, along with its dialkylated analogue 4a’ (Scheme 3). Scheme 3. Stoichiometric Treatment of complex 2a with alkyl bromide 3a.
N
N Ni
Ph N Ph N N
N
N Ph N Ph
Ni N
N
N 2a
N
3a (4.0 equiv) LiOt-Bu (4.0 equiv) 1,4-dioxane 120 °C, 16 h
R
H N
2-pym
n-Bu
R = H (4a): R = n-Bu (4a'):
40% 25%
The homobimetallic complexes were not only competent in stoichiometric transformations. Indeed, catalytic C‒H alkylations of 2-aminophenyl pyrimidine (1a) with the well-defined homobinuclear complex 2a resulted in efficient formation of products 4 (Scheme 4a). Thus, the homobimetallic catalysts proved broadly applicable in C‒H alkylations with β-hydrogen-containing alkyl halides 3 with high site-selectivity. Hence, C−H alkylations with meta-substituted arenes 4n-p occurred at the sterically less hindered C−H bond with excellent levels of positional control, while the parent 2-fluoroaniline did not provide the desired product. Notably, the homobimetallic nickel catalyst also enabled more challenging secondary C‒H alkylation likewise. For instance, cyclic alkyl bromides 3f-h with different ring size selectively afforded the corresponding mono-substituted products 4h-k, including the cyclobutane derivative 4j being unambiguously characterized by single crystal X-ray diffraction analysis. Acyclic secondary alkyl bromides 3i-j were also found to be amenable substrates for the homobimetallic nickel-catalyzed C‒H functionalization without the formation of undesired isomerized byproducts. The pyrimidine group could be removed in a traceless fashion (Scheme 4b).7c
Figure 1. (a) Molecular structures of complexes 2a and 2b with anisotropic displacement parameters at the 50% probability level. All hydrogen atoms are omitted for clarity. Selected bond distances [Å]: For 2a: Ni1-Ni11 2.3817(4), Ni1-N1 1.8836(13), Ni1-N4 1.8916(13), N1-C1 1.3365(19), N2-C1 1.3769(19), N3C1 1.3591(19), N4-C11 1.3332(19), N5-C11 1.3819(19), N6-C11 1.3644(19). For 2b: Ni1-Ni11 2.3895(8), Ni1-N1 1.907(3), Ni1N4 1.902(3), N1-C1 1.340(4), N2-C1 1.384(4), N4-C15 1.332(4),
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ACS Catalysis Scheme 4. Scope of the nickel-catalyzed C‒H alkylations with alkyl halides 3. (a) Versatility N
N
N Ni
Ph N Ph N N H N
2-pym
Ar
H N
3
F 2-pym
n-Bu
H N
H N
a
2-pym
H N
H N
(a) Stoichiometric Reaction without Base 3a (4.0 equiv) DtBEDA (2.0 equiv) 2a 1,4-dioxane 120 °C, 16 h
Alk 4 H N
2-pym
2-pym
n-Pr
2-pym
H N
F
2-pym
Br
R = F (4h): 91% 93% (with 2b) b R = Me (4i): 89%
F 2-pym
H N
1b
2a (2.5 mol %) DtBEDA (10 mol %) LiOtBu, 1,4-dioxane 120 °C, 16 h
F
Me 4l: 92%
H N
2-pym Et
Me 4m: 61%
(b) Traceless Pyrimidine Removal H N Ar
2-pym
Alk 4
Ref. [7c] aq. HCl
W (40W), 3 h
H N
R
F
F
H N
2-pym
2-pym N
+ 4q': 30%
4q: 25%
Br
2-pym
2a (2.5 mol %) DtBEDA (10 mol %) LiOtBu, 1,4-dioxane 120 °C, 16 h
F
H N
F 2-pym
2-pym NH
+
4r: 37%
4k: 93%
2-pym n-Pr
No product formation
LiOt-Bu, 1,4-dioxane 120 °C, 16 h TEMPO (1.0 equiv)
Ph
4g: 78%
4j: 57%
H N
Br (2.0 equiv) 2a (5.0 mol %) DtBEDA (10 mol %)
(c) Radical rearrangement and cyclization
1b
F
H N
1b
2-pym
No product formation
(b) Radical Inhibition by TEMPO
4e: 38%
R
2
4f: 77%
2-pym
Ar
4d: 73%
F
Scheme 5. Key mechanistic findings.
H N
F
t-Bu
F
N
n-Oct
R = H (4a): 49% R = F (4b): 82% b 76% (with 2b) R = Me (4c): 50%
F
N
LiOt-Bu, 1,4-dioxane 120 °C, 16 h
H
R
Ni N
2a (2.5 mol%) DtBEDA (10 mol%)
Alk-Br
1
N N Ph N Ph
(Scheme 5c). Furthermore, it is important to note that electronwithdrawing substrates were preferentially converted under the standard conditions, as was evident from a competition experiment between substrates 1d and 1f (Scheme 5d). Finally, kinetic experiments revealed that the C‒H activation featured a first order dependence on the concentration of the bimetallic complex 2a (Scheme 5d).
4r': 33%
(d) Competition Experiment Br
2-pym H N
H3C/F3C
R = Me (4n): 59% R = OMe (4o): 46% R = CF3 (4p): 82%
NH2
2-pym
(0.8 equiv) 2a (5.0 mol %) F3C DtBEDA (10 mol %) LiOt-Bu, 1,4-dioxane 120 °C, 16 h
1d/1f
H N
2-pym
4p: 55% sole product
(e) Kinetic studies dependence on concentration of 2a
Ar Alk
a 4a’: 15%. b 2b (2.5 mol %) as the catalyst. DtBEDA = Ditert-butyl ethylenediamine.
Given the unique catalytic activity of the homobimetallic nickel complexes 2, we became attracted to unravelling the catalyst’s mode of action. In an attempt to detect further intermediates, treatment of bimetallic catalyst 2a with alkyl bromide and DtBEDA (Di-tert-butyl ethylenediamine) did not furnish the C‒H alkylation product in the absence of base (Scheme 5a). Along the same line, in the absence of alkyl halide C‒H activation was not observed on the nickel complex, being indicative of the C‒H activation occurring at a higher nickel oxidation state.18 Then, C‒H alkylation was attempted in the presence of stoichiometric amounts of the radical scavengers TEMPO and 9,10-dihydroanthracene, which inhibited the catalytic performance (Scheme 5b and the Supporting Information). In good agreement with these findings, radical probes provided strong support for a radical mechanism by radical rearrangement and radical cyclization
Based on our mechanistic studies, a plausible catalytic cycle initiates by alkyl radical generation on one of the nickel metal centers to form the nickel(III)/nickel(II) intermediate I, which thereby weakens the interaction between the two nickel centers (Scheme 6).12 Subsequently, alkyl radical rebound takes place to produce nickel(III)/nickel(III) intermediate II, while a radical chain mechanism can at this point not be excluded. At this stage, C‒H nickelation is proposed to occur to form nickel(III)/nickel(III) intermediate III which finally undergoes reductive elimination to furnish the alkylated product 4. Alternatively, reductive elimination from a single
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nickel center through a nickel(II)/nickel(IV) manifold is also viable.18a,b,d,e, 19 Scheme 6. Plausible mechanistic pathways. N N
4
N
N
N
R Br
R
H N
N
N
N NiII N N
N
1
N
NiII
N
R Ni
III
N
N
N
N Ni N N
N
III
III N LiBr DtBEDA HOt-Bu
N N LiOt-Bu DtBEDA
N
N
N
N
NiII
N
N NiIII N N Br H I
R NiIII
N R
N NiIII N N Br H II
In summary, we have prepared and fully characterized novel paddle-wheel homobimetallic nickel(II)/nickel(II) complexes. The homobimetallic nickel complexes were identified as being competent for challenging aniline C‒H alkylations under stoichiometric as well as catalytic20 settings. Detailed mechanistic studies, including cyclic voltammetry and kinetic experiments, provided support for an initial bimetallic nickel(II/III) single-electron-transfer (SET) oxidation, along with subsequent radical rebound and C‒H activation. Our findings substantiate the unique potential of bimetallic catalysis for earth abundant 3d metals in C‒H activation.
ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. Detailed experimental procedures, compound characterization data, and Crystallographic data for 2a, 2b and 4j (CCDC: 1863336-1863338).
AUTHOR INFORMATION Corresponding Author *E-mail:
[email protected] Notes The authors declare no competing financial interest.
ACKNOWLEDGMENT Generous support by the European Research Council under the European Community’s Seventh Framework Program (FP7 2007– 2013)/ERC Grant agreement no. 307535, the Regione Lombardia - Cariplo Foundation is gratefully acknowledged. We thank Dr. Christopher Golz (Georg-August-Universität Göttingen) for the X-ray diffraction analysis.
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ACS Catalysis with Secondary Alkyl Halides. J. Am. Chem. Soc. 2013, 135, 58775884. (m) Gao, K.; Yoshikai, N. Cobalt-Catalyzed ortho Alkylation of Aromatic Imines with Primary and Secondary Alkyl Halides. J. Am. Chem. Soc. 2013, 135, 9279-9282. (n) Song, G.; Wang, F.; Li, X. C–C, C–O and C–N Bond Formation via Rhodium(III)-Catalyzed Oxidative C–H Activation. Chem. Soc. Rev. 2012, 41, 3651-3678. (o) Ackermann, L.; Hofmann, N.; Vicente, R. Carboxylate-Assisted Ruthenium-Catalyzed Direct Alkylations of ketimines. Org. Lett. 2011, 13, 1875-1877. (p) Vechorkin, O.; Proust, V.; Hu, X. The Nickel/Copper-Catalyzed Direct Alkylation of Heterocyclic C–H Bonds. Angew. Chem. Int. Ed. 2010, 49, 3061-3064. (q) Shabashov, D.; Daugulis, O. Auxiliary-Assisted Palladium-Catalyzed Arylation and Alkylation of sp2 and sp3 Carbon-Hydrogen Bonds. J. Am. Chem. Soc. 2010, 132, 3965-3969. (r) Ackermann, L.; Novak, P.; Vicente, R.; Hofmann, N. Ruthenium-Catalyzed Regioselective Direct Alkylation of Arenes with Unactivated Alkyl Halides through C–H Bond Cleavage. Angew. Chem. Int. Ed. 2009, 48, 6045-6048. (3) For selected recent reviews, see: (a) Moselage, M.; Li, J.; Ackermann, L. Cobalt-Catalyzed C–H Activation. ACS Catal. 2016, 6, 498-525. (b) Liu, W.; Ackermann, L. Manganese-Catalyzed C–H Activation. ACS Catal. 2016, 6, 3743-3752. (c) Castro, L. C. M.; Chatani, N. Nickel Catalysts/N,N’-Bidentate Directing Groups: An Excellent Partnership in Directed C–H Activation Reactions. Chem. Lett. 2015, 44, 410-421. (d) Gao, K.; Yoshikai, N. Low-Valent Cobalt Catalysis: New Opportunities for C–H Functionalization. Acc. Chem. Res. 2014, 47, 1208-1219. (e) Ackermann, L. Cobalt-Catalyzed C–H Arylations, Benzylations, and Alkylations with Organic Electrophiles and Beyond. J. Org. Chem. 2014, 79, 8948-8954. (f) Yamaguchi, J.; Muto, K.; Itami, K. Recent Progress in Nickel-Catalyzed Biaryl Coupling. Eur. J. Org. Chem. 2013, 2013, 19-30. (g) Yoshikai, N. Cobalt-Catalyzed, Chelation-Assisted C–H Bond Functionalization. Synlett 2011, 2011, 1047-1051. (h) Nakao, Y. Hydroarylation of Alkynes Catalyzed by Nickel. Chem. Rec. 2011, 11, 242-251. (i) Daugulis, O.; Kulkarni, A. Direct Conversion of Carbon-Hydrogen into Carbon-Carbon Bonds by First-Row Transition-Metal Catalysis. Synthesis 2009, 4087–4109. (4) (a) Uemura, T.; Yamaguchi, M.; Chatani, N. Phenyltrimethylammonium Salts as Methylation Reagents in the Nickel-Catalyzed Methylation of C–H Bonds. Angew. Chem. Int. Ed. 2016, 55, 3162-3165. (b) Tobisu, M.; Zhao, J.; Kinuta, H.; Furukawa, T.; Igarashi, T.; Chatani, N. Nickel-Catalyzed Borylation of Aryl and Benzyl 2-Pyridyl Ethers: A Method for Converting a Robust orthoDirecting Group. Adv. Synth. Catal. 2016, 358, 2417-2421. (c) Misal Castro, L. C.; Obata, A.; Aihara, Y.; Chatani, N. Chelation-Assisted Nickel-Catalyzed Oxidative Annulation via Double C–H Activation/Alkyne Insertion Reaction. Chem. Eur. J. 2016, 22, 13621367. (d) Aihara, Y.; Chatani, N. Nickel-Catalyzed Reaction of C–H Bonds in Amides with I2: ortho-Iodination via the Cleavage of C(sp2)–H Bonds and Oxidative Cyclization to β-Lactams via the Cleavage of C(sp3)–H Bonds. ACS Catal. 2016, 6, 4323-4329. (e) Furukawa, T.; Tobisu, M.; Chatani, N. Nickel-Catalyzed Borylation of Arenes and Indoles via C–H Bond Cleavage. Chem. Commun. 2015, 51, 6508-6511. (f) Yokota, A.; Aihara, Y.; Chatani, N. Nickel(II)-Catalyzed Direct Arylation of C–H Bonds in Aromatic Amides Containing an 8-Aminoquinoline Moiety as a Directing Group. J. Org. Chem. 2014, 79, 11922-11932. (g) Iyanaga, M.; Aihara, Y.; Chatani, N. Direct Arylation of C(sp3)–H Bonds in Aliphatic Amides with Diaryliodonium Salts in the Presence of a Nickel Catalyst. J. Org. Chem. 2014, 79, 11933-11939. (h) Aihara, Y.; Chatani, N. Nickel-Catalyzed Direct Arylation of C(sp3)–H Bonds in Aliphatic Amides via Bidentate-Chelation Assistance. J. Am. Chem. Soc. 2014, 136, 898-901. (i) Aihara, Y.; Chatani, N. Nickel-Catalyzed Direct Alkylation of C-H Bonds in Benzamides and Acrylamides with Functionalized Alkyl Halides via BidentateChelation Assistance. J. Am. Chem. Soc. 2013, 135, 5308-5311. (j) Shiota, H.; Ano, Y.; Aihara, Y.; Fukumoto, Y.; Chatani, N. NickelCatalyzed Chelation-Assisted Transformations Involving ortho C–H Bond Activation: Regioselective Oxidative Cycloaddition of Aromatic Amides to Alkynes. J. Am. Chem. Soc. 2011, 133, 1495214955.
(5) (a) Wu, X.; Zhao, Y.; Ge, H. Direct Aerobic Carbonylation of C(sp(2))–H and C(sp(3))–H Bonds through Ni/Cu Synergistic Catalysis with DMF as the Carbonyl Source. J. Am. Chem. Soc. 2015, 137, 4924-4927. (b) Wu, X.; Zhao, Y.; Ge, H. Nickel-Catalyzed SiteSelective Alkylation of Unactivated C(sp3)–H Bonds. J. Am. Chem. Soc. 2014, 136, 1789-1792. (6) (a) Zhao, S.; Liu, B.; Zhan, B. B.; Zhang, W. D.; Shi, B. F. Nickel-Catalyzed ortho-Arylation of Unactivated (Hetero)aryl C‒H Bonds with Arylsilanes Using a Removable Auxiliary. Org. Lett. 2016, 18, 4586-4589. (b) Zhan, B. B.; Liu, Y. H.; Hu, F.; Shi, B. F. Nickel-Catalyzed ortho-Halogenation of Unactivated (hetero)Aryl C– H Bonds with Lithium Halides using a Removable Auxiliary. Chem. Commun. 2016, 52, 4934-4937. (c) Liu, B.; Zhang, Z.-Z.; Li, X.; Shi, B.-F. Nickel(II)-Catalyzed Direct Arylation of Aryl C–H Bonds with Aryl-Boron Reagents Directed by a Removable Bidentate Auxiliary. Org. Chem. Front. 2016, 3, 897-900. (d) Yan, S. Y.; Liu, Y. J.; Liu, B.; Liu, Y. H.; Zhang, Z. Z.; Shi, B. F. Nickel-Catalyzed Direct Thiolation of Unactivated C(sp(3))–H Bonds with Disulfides. Chem. Commun. 2015, 51, 7341-7344. (e) Liu, Y. J.; Zhang, Z. Z.; Yan, S. Y.; Liu, Y. H.; Shi, B. F. Ni(II)/BINOL-Catalyzed Alkenylation of Unactivated C(sp(3))–H Bonds. Chem. Commun. 2015, 51, 78997902. (f) Liu, Y. J.; Liu, Y. H.; Yan, S. Y.; Shi, B. F. A Sustainable and Simple Catalytic System for Direct Alkynylation of C(sp(2))–H Bonds with Low Nickel Loadings. Chem. Commun. 2015, 51, 63886391. (g) Liu, Y. H.; Liu, Y. J.; Yan, S. Y.; Shi, B. F. Ni(II)Catalyzed Dehydrative Alkynylation of Unactivated (Hetero)Aryl C– H Bonds using Oxygen: a User-Friendly Approach. Chem. Commun. 2015, 51, 11650-11653. (7) (a) Ruan, Z.; Ghorai, D.; Zanoni, G.; Ackermann, L. Nickel-Catalyzed C–H Activation of Purine Bases with Alkyl Halides. Chem. Commun. 2017, 53, 9113-9116. (b) Ruan, Z.; Lackner, S.; Ackermann, L. Nickel-Catalyzed C–H Alkynylation of Anilines: Expedient Access to Functionalized Indoles and Purine Nucleobases. ACS Catal. 2016, 6, 4690-4693. (c) Ruan, Z.; Lackner, S.; Ackermann, L. A General Strategy for the Nickel-Catalyzed C–H Alkylation of Anilines. Angew. Chem. Int. Ed. 2016, 55, 3153-3157. (d) Muller, T.; Ackermann, L. Nickel-Catalyzed C–H Chalcogenation of Anilines. Chem. Eur. J. 2016, 22, 14151-14154. (e) Song, W.; Lackner, S.; Ackermann, L. Nickel-Catalyzed C–H Alkylations: Direct Secondary Alkylations and Trifluoroethylations of Arenes. Angew. Chem. Int. Ed. 2014, 53, 2477-2480. (f) Song, W.; Ackermann, L. Nickel-Catalyzed Alkyne Annulation by Anilines: Versatile Indole Synthesis by C–H/N–H Functionalization. Chem. Commun. 2013, 49, 6638-6640. (g) Ackermann, L.; Punji, B.; Song, W. User-Friendly [(Diglyme)NiBr2]-Catalyzed Direct Alkylations of Heteroarenes with Unactivated Alkyl Halides through C–H Bond Cleavages. Adv. Synth. Catal. 2011, 353, 3325-3329. (8) Selected recent examples: (a) Patel, U. N.; Jain, S.; Pandey, D. K.; Gonnade, R. G.; Vanka, K.; Punji, B. Mechanistic Aspects of Pincer Nickel(II)-Catalyzed C–H Bond Alkylation of Azoles with Alkyl Halides. Organometallics 2018, 37, 1017-1025. (b) Soni, V.; Jagtap, R. A.; Gonnade, R. G.; Punji, B. Unified Strategy for Nickel-Catalyzed C-2 Alkylation of Indoles through Chelation Assistance. ACS Catal. 2016, 6, 5666-5672. (c) Muto, K.; Hatakeyama, T.; Yamaguchi, J.; Itami, K. C–H Arylation and Alkenylation of Imidazoles by Nickel Catalysis: Solvent-Accelerated Imidazole C–H Activation. Chem. Sci. 2015, 6, 6792-6798. (d) Meng, L.; Kamada, Y.; Muto, K.; Yamaguchi, J.; Itami, K. C–H Alkenylation of Azoles with Enols and Esters by Nickel Catalysis. Angew. Chem. Int. Ed. 2013, 52, 10048-10051. (e) Yao, T.; Hirano, K.; Satoh, T.; Miura, M. Nickel- and Cobalt-Catalyzed Direct Alkylation of Azoles with N-Tosylhydrazones Bearing Unactivated Alkyl Groups. Angew. Chem. Int. Ed. 2012, 51, 775-779. (f) Yao, T.; Hirano, K.; Satoh, T.; Miura, M. Palladium- and Nickel-Catalyzed Direct Alkylation of Azoles with Unactivated Alkyl Bromides and Chlorides. Chem. Eur. J. 2010, 16, 12307-12311, and cited references. (9) (a) Powers, I. G.; Uyeda, C. Metal–Metal Bonds in Catalysis. ACS Catal. 2017, 7, 936-958. (b) Brogden, D. W.; Turov, Y.; Nippe, M.; Li Manni, G.; Hillard, E. A.; Clerac, R.; Gagliardi, L.; Berry, J. F. Oxidative Stretching of Metal-Metal Bonds to their
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Limits. Inorg. Chem. 2014, 53, 4777-4790. (c) Beck, R.; Johnson, S. A. Dinuclear Ni(I)—Ni(I) Complexes with Syn-Facial Bridging Ligands from Ni(I) Precursors or Ni(II)/Ni(0) Comproportionation. Organometallics 2013, 32, 2944-2951. (d) Powers, D. C.; Ritter, T. Bimetallic Redox Synergy in Oxidative Palladium Catalysis. Acc. Chem. Res. 2011, 45, 840-850. (e) Berry, J. F.; Bothe, E.; Cotton, F. A.; Ibragimov, S. A.; Murillo, C. A.; Villagra, D.; Wang, X. Metal−Metal Bonding in Mixed Valence Ni25+ Complexes and Spectroscopic Evidence for a Ni26+ Species. Inorg. Chem. 2006, 45, 4396-4406. (f) Berry, J. F.; Cotton, F. A.; Daniels, L. M.; Murillo, C. A. A Trinickel Dipyridylamido Complex with Metal-Metal Bonding Interaction: Prelude to Polynickel Molecular Wires and Devices? J. Am. Chem. Soc. 2002, 124, 3212-3213. (10) (a) Haines, B. E.; Berry, J. F.; Yu, J.-Q.; Musaev, D. G. Factors Controlling Stability and Reactivity of Dimeric Pd(II) Complexes in C–H Functionalization Catalysis. ACS Catal. 2016, 6, 829-839. (b) Powers, D. C.; Ritter, T. A Transition State Analogue for the Oxidation of Binuclear Palladium(II) to Binuclear Palladium(III) Complexes. Organometallics 2013, 32, 2042-2045. (c) Nielsen, M. C.; Lyngvi, E.; Schoenebeck, F. Chemoselectivity in the Reductive Elimination from High Oxidation State Palladium Complexes-Scrambling Mechanism Uncovered. J. Am. Chem. Soc. 2013, 135, 1978-1985. (d) Chuang, G. J.; Wang, W.; Lee, E.; Ritter, T. A Dinuclear Palladium Catalyst for alpha-Hydroxylation of Carbonyls with O2. J. Am. Chem. Soc. 2011, 133, 1760-1762. (e) Powers, D. C.; Xiao, D. Y.; Geibel, M. A. L.; Ritter, T. On the Mechanism of Palladium-Catalyzed Aromatic C‒H Oxidation. J. Am. Chem. Soc. 2010, 132, 14530–14536. (f) Powers, D. C.; Ritter, T. Bimetallic Pd(III) Complexes in Palladium-Catalysed Carbon–Heteroatom Bond Formation. Nat. Chem. 2009, 1, 302-309. (g) Powers, D. C.; Geibel, M. A. L.; Klein, J. E. M. N.; Ritter, T. Bimetallic Palladium Catalysis: Direct Observation of Pd(III)-Pd(III) Intermediates. J. Am. Chem. Soc. 2009, 131, 17050-17051. (h) Cotton, F. A.; Gu, J.; Murillo, C. A.; Timmons, D. J. The First Dinuclear Complex of Palladium(III). J. Am. Chem. Soc. 1998, 120, 13280-13281. (11) (a) Maity, A. K.; Zeller, M.; Uyeda, C. Carbene Formation and Transfer at a Dinickel Active Site. Organometallics 2018, 37, 2437-2441. (b) Behlen, M. J.; Zhou, Y. Y.; Steiman, T. J.; Pal, S.; Hartline, D. R.; Zeller, M.; Uyeda, C. Dinuclear Oxidative Addition Reactions using an Isostructural Series of Ni2, Co2, and Fe2 Complexes. Dalton Trans. 2017, 46, 5493-5497. (c) Steiman, T. J.; Uyeda, C. Reversible Substrate Activation and Catalysis at an Intact Metal-Metal Bond using a Redox-Active Supporting Ligand. J. Am. Chem. Soc. 2015, 137, 6104-6110. (d) Zhou, Y. Y.; Hartline, D. R.; Steiman, T. J.; Fanwick, P. E.; Uyeda, C. Dinuclear Nickel Complexes in Five States of Oxidation using a Redox-Active Ligand. Inorg. Chem. 2014, 53, 11770-11777. (12) Diccianni, J. B.; Hu, C.; Diao, T. N–N Bond Forming Reductive Elimination via a Mixed-Valent Nickel(II)-Nickel(III) Intermediate. Angew. Chem. Int. Ed. 2016, 55, 7534-7538. (13) Diccianni, J. B.; Hu, C.; Diao, T. Binuclear, High-Valent Nickel Complexes: Ni–Ni Bonds in Aryl-Halogen Bond Formation. Angew. Chem. Int. Ed. 2017, 56, 3635-3639. (14) Somerville, R. J.; Hale, L. V. A.; Gomez-Bengoa, E.; Bures, J.; Martin, R. Intermediacy of Ni–Ni Species in sp(2) C–O
Bond Cleavage of Aryl Esters: Relevance in Catalytic C–Si Bond Formation. J. Am. Chem. Soc. 2018, 140, 8771-8780. (15) (a) Ackermann, L. Carboxylate-Assisted RutheniumCatalyzed Alkyne Annulations by C–H/Het–H Bond Functionalizations. Acc. Chem. Res. 2014, 47, 281-295. (b) Ackermann, L. Catalytic Arylations with Challenging Substrates: From Air-Stable HASPO Preligands to Indole Syntheses and C–HBond Functionalizations. Synlett 2007, 0507-0526. (16) (a) Lee, C.-M.; Chiou, T.-W.; Chen, H.-H.; Chiang, C.-Y.; Kuo, T.-S.; Liaw, W.-F. Mononuclear Ni(II)-Thiolate Complexes with Pendant Thiol and Dinuclear Ni(III/II)-Thiolate Complexes with Ni···Ni Interaction Regulated by the Oxidation Levels of Nickels and the Coordinated Ligands. Inorg. Chem. 2007, 46, 8913-8923. (b) Berry, J. F.; Cotton, F. A.; Daniels, L. M.; Murillo, C. A.; Wang, X. Oxidation of Ni3(dpa)4Cl2 and Cu3(dpa)4Cl2: Nickel−Nickel Bonding Interaction, but No Copper−Copper Bonds. Inorg. Chem. 2003, 42, 2418−2427. (c) Cotton, F. A.; Matusz, M.; Poli, R.; Feng, X. Dinuclear Formamidinato Complexes of Nickel and Palladium. J. Am. Chem. Soc. 1988, 110, 1144-1154. (17) Ackermann, L. Metal-Catalyzed Direct Alkylations of (Hetero)Arenes via C–H Bond Cleavages with Unactivated Alkyl Halides. Chem. Commun. 2010, 46, 4866–4877. (18) (a) D'Accriscio, F.; Borja, P.; Saffon-Merceron, N.; Fustier-Boutignon, M.; Mezailles, N.; Nebra, N. C–H Bond Trifluoromethylation of Arenes Enabled by a Robust, High-Valent Nickel(IV) Complex. Angew. Chem. Int. Ed. 2017, 56, 12898-12902. (b) Chong, E.; Kampf, J. W.; Ariafard, A.; Canty, A. J.; Sanford, M. S. Oxidatively Induced C–H Activation at High Valent Nickel. J. Am. Chem. Soc. 2017, 139, 6058-6061. (c) Xu, H.; Diccianni, J. B.; Katigbak, J.; Hu, C.; Zhang, Y.; Diao, T. Bimetallic C–C BondForming Reductive Elimination from Nickel. J. Am. Chem. Soc. 2016, 138, 4779-4786. (d) Camasso, N. M.; Sanford, M. S. Design, Synthesis, and Carbon-Heteroatom Coupling Reactions of Organometallic Nickel(IV) Complexes. Science 2015, 347, 12181220. (e) Bour, J. R.; Camasso, N. M.; Sanford, M. S. Oxidation of Ni(II) to Ni(IV) with Aryl Electrophiles Enables Ni-Mediated ArylCF3 Coupling. J. Am. Chem. Soc. 2015, 137, 8034-8037. (f) Zhang, C. P.; Wang, H.; Klein, A.; Biewer, C.; Stirnat, K.; Yamaguchi, Y.; Xu, L.; Gomez-Benitez, V.; Vicic, D. A. A Five-Coordinate Nickel(II) Fluoroalkyl Complex as a Precursor to a Spectroscopically Detectable Ni(III) Species. J. Am. Chem. Soc. 2013, 135, 8141-8144. (19) (a) Li, Y.; Zou, L.; Bai, R.; Lan, Y. Ni(I)–Ni(III) vs. Ni(II)–Ni(IV): Mechanistic Study of Ni-Catalyzed Alkylation of Benzamides with Alkyl Halides. Org. Chem. Front. 2018, 5, 615-622. (b) Omer, H. M.; Liu, P. Computational Study of Ni-Catalyzed C–H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways. J. Am. Chem. Soc. 2017, 139, 99099920. (20) When using [Ni(dppe)Cl2], [Ni(dppf)Cl2] or [Ni(PPh3)2Cl2] as the catalysts, the product 4h was isolated in the absence of DtBEDA with a conversion of 34%, 53% and 35%, respectively, as judged by 1H-NMR spectroscopy.
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ACS Catalysis
N
N
HN Ar
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+ Br Alk
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Homobimetallic Nickel Catalysts Challenging C–H Alkylations Kinetic Studies and CV analysis
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