Subscriber access provided by FORDHAM UNIVERSITY
Communication
Iron-Catalyzed Aromatic Amination for Nonsymmetrical Triarylamine Synthesis Takuji Hatakeyama, Ryuji Imayoshi, Yuya Yoshimoto, Sujit Kumar Ghorai, Masayoshi Jin, Hikaru Takaya, Kazuhiro Norisuye, Yoshiki Sohrin, and Masaharu Nakamura J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja309845k • Publication Date (Web): 26 Nov 2012 Downloaded from http://pubs.acs.org on November 30, 2012
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Journal of the American Chemical Society
Iron-Catalyzed Aromatic Amination for Nonsymmetrical Triarylamine Synthesis Takuji Hatakeyama,†,‡ Ryuji Imayoshi,† Yuya Yoshimoto,† Sujit K. Ghorai,† Masayoshi Jin,†,§ Hikaru Takaya†, Kazuhiro Norisuye,† Yoshiki Sohrin,† and Masaharu Nakamura*,† †
International Research Center for Elements Science (IRCELS), Institute for Chemical Research (ICR), Kyoto University, Uji, Kyoto, 611-0011, Japan, ‡PRESTO, Japan Science and Technology Agency (JST), 5, Sanbancho, Chiyoda-ku, Tokyo, 102-0075, Japan Supporting Information Placeholder Scheme 1. Iron-catalyzed amination reaction between pABSTRACT: Novel iron-catalyzed amination reactions of various bromoanisole 1 and magnesium diphenylamide 2 aryl bromides have been developed for the synthesis of diaryl- and triarylamines. The key to the success of this protocol is the use of in situ generated magnesium amides in the presence of a lithium halide, which dramatically increases the product yield. The present method is simple and free of precious and expensive metals and ligands, thus providing a facile route to triarylamines, a recurrent core unit in organic electronic materials as well as pharmaceuticals.
Ph Br
N MgBr
OMe + Ph 1 (1.0 equiv)
catalyst (X mol %) additive (Y equiv)
Ph
xylene, 140 ºC, time
Ph
Since the standard conditions for Pd- or Cu-catalyzed aromatic amination3 were not effective for iron catalysis, our study began with an extensive screening of bases and additives. We eventually found that the combination of a Grignard reagent (base) and a lithium bromide (additive) dramatically promoted the amination of aryl bromides with arylamines. 8 The reaction between pbromoanisole 1 and magnesium diphenylamide 2, prepared in situ from diphenylamine and an ethyl Grignard reagent, was carried out in xylene at 140 °C for 12–48 h, using a variety of catalysts and additives (Scheme 1). Table 1 summarizes the results of this initial
OMe 3
2 (2.0 equiv) OMe + MeO
+ 4
Transition-metal-catalyzed aromatic amination is widely used for the synthesis of arylamines, which are of particular interest in the fields of organic electronics and bioactive compounds.1,2 Despite recent improvements to Pd- and Cu-catalyzed amination methodologies such as the Buchwald–Hartwig and catalytic Ullmann reactions,3 new methods that do not require hazardous and expensive transition metals and ligands are highly desired for the efficient production of functional arylamines. Although considerable effort has been devoted to the development of iron-catalyzed amination reactions in the last decade,4 they have limited substrate scope and are unsuited for the synthesis of triarylamines,5,6 which are among the most prevailing hole-transport materials.1 In addition, Buchwald and Bolm reported that the product yields of the reported iron-catalyzed amination reactions are sensitive even to trace quantities of copper contaminants, especially in the presence of N,N'dimethylethylenediamine (DMEDA). 7 Hence, further investigation of suitable routes to triarylamines is needed from synthetic and mechanistic perspectives. Herein, we report a facile and environmentally benign method based on iron-catalyzed aromatic amination for synthesizing diaryl- and triarylamines and provide mechanistic insights obtained through experimental and computational studies on the iron amide species.
N
OMe 5
Table 1. Screening of catalysts and additivesa entry 1 2 3 4 5 6 7 8 9 10 11
yield (%)b additive time (h) 3 (Y equiv) 4 5 24 10 0 0 none 24 26 0 0 LiBr (0.2) 12 51 0 0 LiBr (2.0) 24 95 0 0 12 >99 0 0 FeCl2 (5.0) LiBr (4.0) 48 99 0 0 FeCl2 (0.5) LiBr (4.0) 48 6 4 0 PdCl2 (0.5) LiBr (4.0) 48 2 0 0 CuCl2 (0.5) LiBr (4.0) 48 27 4 0 CoCl2 (0.5) LiBr (4.0) 48 88 4 6 NiCl2 (0.5) LiBr (4.0) 48 80 3 8 Ni(acac)2 (0.5) LiBr (4.0) 48 8 0 0 Ni(acac)2 (0.0005) LiBr (4.0) catalyst (X mol%) FeCl2 (5.0) FeCl2 (5.0) FeCl2 (5.0)
recovery of 1 (%)b 89 67 41 0 0 0 80 92 47 0 0 90
a Reactions were carried out on a 1.0 mmol scale. bThe yield was determined by GC analysis using undecane as an internal standard.
screening of catalyst systems based on iron and other transition metals. The reaction between 1 and 2 in the presence of 5 mol % FeCl2 gave the desired product 3 in 10% yield (entry 1), while the reaction between 1 and diphenylamine in the presence of conventional inorganic bases (K3PO4, Cs2CO3, NaHCO3, t-BuOK) did not give any coupling product. The addition of LiBr accelerated the reaction and the optimum yield (99%) was achieved when using 4.0 equiv of LiBr (entries 2–4).9 The increased yield is probably due to the deaggregation of magnesium amide by the lithium salt to facilitate transmetallation of the amide ligand from magnesium to iron.10 Notably, magnesium diphenylamide, prepared from lithium diphenylamide and MgBr2, gave good yield (95%), while lithium diphenylamide gave a very poor yield (2%) under the same conditions. 11 Complete conversion could be achieved even with 0.5 mol % FeCl2 when the reaction was done in 48 h (entry 5).12
ACS Paragon Plus Environment
Journal of the American Chemical Society
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
To clarify the effects of the metal contaminants, the iron salts were analyzed by inductively coupled plasma-mass spectrometry and atomic emission spectroscopy (ICP-MS and ICP-AES). Since ppm-order amounts of Pd, Cu, Co and Ni were found in some iron salts, we performed the amination reaction in the presence of these transition-metal catalysts. As in entries 6–8, PdCl2, CuCl2, and CoCl2 showed poor catalytic activities under the same reaction conditions. As reported by Yang,13 NiCl2 and Ni(acac)2 showed catalytic activity comparable to that of the iron catalysts but gave lower product yields owing to the competing homocoupling of pbromoanisole (entries 9 and 10). Since the amount of nickel Table 2. Substrate scopea entry 1 2 3 4 5
amine
aryl halide
Ph N H
Br
R
N Ph
Ph
6
N H Ph
Ph Ph Ph
Br
N H
Ph
Ph
Ph
p-Tol
p-Tol Br
N H
61
96
N
p-Tol
contaminant in FeCl2 was determined to be 12.9 ppm by the above mentioned analysis, 14 we examined the use of 5 × 10–4 mol % Ni(acac)2 (1000 ppm of 0.5 mol %) as the catalyst to confirm the low reactivity, and hence, concluded that nickel contamination does not play an important role in the present iron-catalyzed amination reaction (entry 11). Table 2 summarizes the substrate scope of the aromatic amination. As shown in entries 1–10, a variety of aryl- and heteroaryl bromides could be coupled with diarylamines to give the corresponding triarylamines in good yields. Although anilines did not participate in the reaction, a protected aniline, N-(trimethylsilyl) aniline, coupled with the aryl bromides to give, upon hydrolysis, the corresponding diarylamines in excellent yields (entries 11–14).15 The reactions with N-(trimethylsilyl)aniline proceeded more smoothly in dibutyl ether than in xylene. As shown in entries 15 and 16, the hole-transport material, N,N'-diphenyl-N,N'-di(mtolyl)benzidine (TPD), and its precursor could be prepared from 4,4'-dibromo-1,1'-biphenyl in 82% and 87% yields, respectively. Aryl bromides possessing an ester or nitrile group underwent the addition of magnesium amides to the electrophilic functional groups and desired amination products were not obtained. Ketone and nitro groups were not tolerated under the reaction conditions and gave complex mixtures (data not shown). The relatively narrow functional-group compatibility compared to the standard Pdand Cu-catalyzed aminations5,6 is due to the high reactivity of the magnesium amides and further effort to find suitable combinations of a base and a neutral amine is needed to overcome this limitation. Scheme 2. Preparation of iron(II) diamide complex A and the stoichiometric reaction
p-Tol
p-FC6H4 N H Ph
Ph
p-FC6H4 OMe N Ph
Br
Ph
11c
S
N
Ph
9
10
N
Ph
S
Br
N H
82
N
N
Ph
8
90
N
Br
Ph
7
92 (R = Me) 90 (R = OMe) R 88 (R = NMe2) 59 (R = Cl) 77 (R = F)
Ph
Ph
yield (%)b
product
OMe
Br
OMe
Me3Si Ph
13c
FeCl2 (1.0 equiv)
THF, rt, 3 h
rt, 15 h
(2.0 equiv)
N H
OMe
96
N H Me
Me
76
OMe
Br
N H
N H
Me3Si
Si1'
Br
N H
N H
N
98
N
N2
Fe1
m-Tol
m-Tol N H
Br
Ph
a
2
N Ph Ph
Ph N H Me3Si
Br
Br
Br 2
N H
Si2'
m-Tol N 82 2 Ph Ph N 2 H
87
Reactions were carried out on a 1.00 mmol scale according to the procedure described in Table 1 (entry 4), unless otherwise noted. bIsolated yield. cThe reaction was carried out in dibutyl ether. dThe reaction was carried out on a 0.50 mmol scale using 4.0 equiv of amine.
N1' Fe1'
N2'
C10'
Si2 Si1
C1'
OMe
N H
X, Y = 0.10, 1 X, Y = 0.10, 6 X, Y = 0.20, 1 X, Y = 0.20, 6
C10
N1
16c, d
dibutyl ether 140 ºC, Y h
97
Ph
Ph Me3Si
15c, d
A (X mmol)
1 (0.40 mmol)
C1
14c
+
Ph
Ph
Me3Si Ph N SiMe3 N FeII FeII N Ph Me3Si N Ph SiMe3 A 25% yield Ph
Ph
Ph
Br
N H Me3Si
NaN(SiMe3)2 (2.0 equiv)
Me3Si
Ph N H
N H
82
Br
12c
Page 2 of 5
47% yield 53% yield 81% yield 93% yield
Selected bond lengths Fe1–N2 1.9147(18) Å Fe1–N1 2.0702(18) Å Fe1–N1' 2.0348(16) Å Fe1–Fe1' 2.7408(7) Å Selected angles N2–Fe1–N1 130.88(7)º N2–Fe1–N1' 132.89(8)º N1–Fe1–N1' 96.23(6)º Fe1–N1–Fe1' 83.77(6)º Fe1–N2–C1 114.04(13)º Fe1–N2–Si2 128.45(10)º C1–N2–Si2 117.46(14)º C10–N1–Si1 115.22(13)º
Figure 1. ORTEP drawing of A. Thermal ellipsoids are shown at 50% probability; hydrogen atoms are omitted for clarity. To gain further insights into the mechanism, we prepared an iron(II) diamide complex A according to Power’s method16 and conducted a stoichiometric reaction (Scheme 2). Deprotonation of N-(trimethylsilyl)aniline with sodium bis(trimethylsilyl)amide
ACS Paragon Plus Environment
Page 3 of 5
(NaHMDS), followed by treatment with FeCl2, gave a dimer complex of iron(II) diamide A in 25% yield. X-ray crystallography analysis showed that A was dimeric, with each trigonal-planar iron bound to one terminal and two bridging amide groups (Figure 1).16 Aromatic amination of 1 in Bu2O at 140 °C for 6 h gave the desired product in 53% and 93% yields in the presence of 0.25 and 0.50 equiv of A, respectively. This result clearly show that the iron(II) diamide can be a reactive intermediate in which one of two amide groups (per iron) takes part in the amination. Ar2
Br–Ar2
Ar1
FeIICl2 +
N R
Br
FeIV
R N Ar1
2 Ar1RNMgBr!LiBr
Ar1 N Ar2 R
Ar1 R N FeII N R Ar1
R = aryl or SiMe3
R Ar1 N Ar1 R 1/2 N FeII FeII N R Ar1 N Ar1 R A
Ar1 N FeII Br R
MgBr2!LiBr Ar1RNMgBr!LiBr
Figure 2. Possible catalytic cycle of iron-catalyzed aromatic amination. Figure 2 shows a plausible mechanism on the basis of the stoichiometric studies. The precatalyst, FeCl2, reacts with 2.0 equiv of magnesium amide to form monomeric and dimeric iron(II) diamide complexes, which are in monomer–dimer equilibrium. 17,18 The coordinatively unsaturated monomer may undergo oxidative addition with an aryl bromide to form a formal iron(IV) intermediate. Successive reductive elimination of the coupling product affords iron(II) monoamide complex. Regeneration of the active species completes the catalytic cycle via the LiBr-assisted transmetallation with magnesium amide. Ph
Ph + Ph–Br
N FeII N
SiMe3
Me3Si
N
FeII
N
Me3Si
Ph SiMe3
!G‡ = +14.2
FeIV 1.8 N 9
N SiMe3
Ph Br Ph
Ph SiMe3
N Fe N Ph SiMe3 SiMe3
TSCD (+26.7)
D (+11.2)
Ph 2.34 Br – Ph2NSiMe3 Ph Ph N FeII N FeII Br N Me3Si Ph Me3Si SiMe3 E (–11.8) F (–8.3)
‡
2.55
Ph
2.20
Ph Br
2.40
2.08
!G‡ = +8.7
2.15
TSDE (+19.9)
‡
1
Ph2.10 Br Fe Ph 5 Ph N 1.9 N SiMe 3 SiMe3
In summary, we have developed an efficient iron-catalyzed aromatic amination between diaryl- or arylsilyl amines and aryl bromides, which affords high product yields and selectivity, in the presence of a simple catalyst system. The key to the success of the reaction is the combined use of magnesium amide and lithium salt additives, which promotes the catalyst turnover. A stoichiometric reaction involving a newly synthesized iron(II) diamide complex and DFT studies on the reaction pathway reveal that the present reaction proceeds via a nonconventional Fe(II)–Fe(IV) mechanism. These mechanistic insights will aid the design of new carbon– nitrogen and other carbon–heteroatom bond formations in the future.
ASSOCIATED CONTENT Supporting Information. Experimental procedure, characterization, photophysical data, electrochemical data, crystallographic data, and a CIF file for the products, as well as computational method and data. This material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
[email protected] Present Address
C (+12.5)
B (+5.4)
kcal/mol higher in energy than dimer A, undergoes oxidative addition with bromobenzene (Ph–Br) through the formation of σcomplex (C) to give the iron(IV) intermediate D. The overall activation energy from A to D via TSCD is 26.7 kcal/mol, which is in fair agreement with the experimental finding that the reaction proceeds smoothly at 140 °C. Although oxidative addition is an endothermic process, rapid reductive elimination of the coupling product from D gives the stable σ-complex E, which can drive the C–N coupling reaction forward. Dissociation of the coupling product (E to F) and subsequent transmetalation with magnesium amide regenerates the iron diamide B to complete the catalytic cycle, or alternatively, the dimer formation from F to G22 and the transmetalation regenerate the starting dimer A, the experimentally determined reactive intermediate.
Corresponding Author
Ph Br Ph
2.80
Me3Si Ph SiMe3 N Ph 1/2 N FeII FeII N Me3Si Ph N Ph SiMe3 A (0)
2.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Journal of the American Chemical Society
Br SiMe3 N FeII FeII N Me3Si Ph Br
Ph
1/2
G (–28.4)
Figure 3. Reaction pathways for oxidative addition and reductive elimination. Gibbs free energies (ΔG, calculated at the B3LYP/631G(d) level) relative to A are given in kcal/mol in parentheses.
To evaluate the nonconventional Fe(II)–Fe(IV) mechanism,19,20 we performed a set of density functional theory (DFT) calculations and have located an energetically reasonable reaction coordinates, starting from monomer B (Figure 3).21 Monomer B, which is 5.4
§
Process Technology Research Laboratories, Pharmaceutical Technology Division, Daiichi Sankyo Co., Ltd., 1-12-1, Shinomiya, Hiratsuka, Kanagawa 254-0014, Japan
ACKNOWLEDGMENT This research was supported by the Japan Society for the Promotion of Science (JSPS) through the “Funding Program for Next Generation World-Leading Researchers (NEXT Program),” initiated by the Council for Science and Technology Policy (CSTP) and the Japan Science and Technology Agency (JST), the Core Research for Evolutional Science and Technology (CREST) Program. We are grateful to Professor Kazuyuki Tatsumi (Nagoya University), Associate Professor Yasuhiro Ohki (Nagoya University), Mr. Takayoshi Hashimoto (Nagoya University), and Mr. Genki Kawase (Nagoya University) for their experimental guidance on the synthesis of iron amides. We also thank Mr. Sigma Hashimoto (Kyoto University) and Mr. Yoshihiro Okada (Kyoto University) for the experimental support. The synchrotron Xray absorption measurements were performed at BL14B2 (2011B1945,
ACS Paragon Plus Environment
Journal of the American Chemical Society
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 5
2012A1595) and BL27SU (2011B1418, 2012A1636) in SPring-8 with the approval of JASRI.
REFERENCES
(1) (a) Shirota, Y. J. Mater. Chem. 2000, 10, 1–25. (b) Shirota, Y. J. Mater. Chem. 2005, 15, 75–93. (c) Ning, Z.; Tian, H. Chem. Commun. 2009, 5483–5495. (d) Duan, L.; Hou, L.; Lee, T.-W.; Qiao, J.; Zhang, D.; Dong, G.; Wang, L.; Qiu, Y. J. Mater. Chem. 2010, 20, 6392–6407. (2) (a) Leroux, F.; Jeschke, P.; Schlosser, M. Chem. Rev. 2005, 105, 827–856. (b) Tasler, S.; Mies, J.; Lang, M. Adv. Synth. Catal. 2007, 349, 2286–2300. (c) Bikker, J. A.; Brooijmans, N.; Wissner, A.; Mansour, T. S. J. Med. Chem. 2009, 52, 1493–1509. (3) Reviews: (a) Ley, S. V.; Thomas, A. W. Angew. Chem., Int. Ed. 2003, 42, 5400–5449. (b) Schlummer, B.; Scholz, U. Adv. Synth. Catal. 2004, 346, 1599–1626. (c) Hartwig, J. F. Synlett 2006, 9, 1283–1294. (d) Surry, D. S.; Buchwald, S. L. Angew. Chem., Int. Ed. 2008, 47, 6338–6361. (e) Evano, G.; Blanchard, N.; Toumi, M. Chem. Rev. 2008, 108, 3054–3131. (f) Monnier, F.; Taillefer, M. Angew. Chem., Int. Ed. 2009, 48, 6954–6971. (g) Surry, D. S.; Buchwald, S. L. Chem. Sci. 2010, 1, 13–31. (h) Sadig, J. E. R.; Willis, M. C. Synthesis 2011, 1–22. (i) Surry, D. S.; Buchwald, S. L. Chem. Sci. 2011, 2, 27–50. (j) Rauws, T. R. M.; Maes B. U. W. Chem. Soc. Rev. 2012, 41, 2463– 2497. (4) Review: (a) Correa, A.; Mancheño, O. G.; Bolm, C. Chem. Soc. Rev. 2008, 37, 1108–1280. Recent reports: (b) Nakamura, Y.; Ilies, L.; Nakamura, E. Org. Lett. 2011, 13, 5998–6001. (c) Liu, X. Zhang, S. Synlett. 2011, 8, 1137–1142. (5) Selected examples for triarylamine synthesis based on palladium catalysis: (a) Thayumanavan, S.; Barlow, S.; Marder, S. R. Chem. Mater. 1997, 9, 3231–3235. (b) Louie, J.; Hartwig, J. F. J. Am. Chem. Soc. 1997, 119, 11695–11696. (c) Yamamoto, T.; Nishiyama, M.; Koie, Y. Tetrahedron Lett. 1998, 39, 2367–2370. (d) Harris, M. C.; Buchwald, S. L. J. Org. Chem. 2000, 65, 5327–5333. (e) Hooper, M. W.; Utsunomiya, M.; Hartwig, J. F. J. Org. Chem. 2003, 68, 2861–2873. (f) Surry, D. S.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 10354–10355. (h) Suzuki, K.; Hori, Y.; Kobayashi, T. Adv. Synth. Catal. 2008, 350, 652–656. (i) Monguchi, Y.; Kitamoto, K.; Ikawa, T.; Maegawa, T.; Sajiki, H. Adv. Synth. Catal. 2008, 350, 2767–2777. (j) Hirai, Y.; Uozumi, Y. Chem. Asian J. 2010, 5, 1788–1795. (6) Selected examples for triarylamine synthesis based on copper catalysis: (a) Goodbrand, H. B.; Hu, N.-X. J. Org. Chem. 1999, 64, 670–674. (b) Gujadhur, R. K.; Bates, C. G.; Venkataraman, D. Org. Lett. 2001, 3, 4315– 4317. (c) Kelkar, A. A.; Patil, N. M.; Chaudhari, R. V. Tetrahedron Lett. 2002, 43, 7143–7146. (d) Patil, N. M.; Kelkar, A. A.; Chaudhari, R. V. J. Mol. Catal. A 2004, 223, 45–50. (e) Liu, Y.-H.; Chen, C.; Yang, L.-M. Tetrahedron Lett. 2006, 47, 9275–9278. (f) Zhao, Y.; Wang, Y.; Sun, H.; Li, L.; Zhang, H. Chem. Commun. 2007, 3186–3188. (g) Nandurkar, N. S.; Bhanushali, M. J.; Bhor, M. D.; Bhanage, B. M. Tetrahedron Lett. 2007, 48, 6573–6576. (h) Sawant, S. K.; Gaikwad, G. A.; Sawant, V. A.; Yamgar, B. A.; Chavan, S. S. Inorg. Chem. Commun. 2009, 12, 632–635. (i) Tlili, A.; Monnier, F.; Taillefer, M. Chem. Commun. 2012, 48, 6408–6410. (7) Buchwald, S. L.; Bolm, C. Angew. Chem., Int. Ed. 2009, 48, 5586– 5587 and references cited therein. (8 ) Lithium salts accelerate the iron-catalyzed cross-coupling of alkenyl bromides and triflates with alkynyl Grignard reagents: Hatakeyama, T.; Yoshimoto, Y; Toma, G.: Nakamura, M. Org. Lett. 2008, 10, 5541–5544. (9) Other lithium salts (LiCl, LiI, LiOMe, LiOH) and NaBr also improved the product yield but were not as effective as LiBr. See the supporting information for details.
(10) Lithium chloride deaggregates TMPMgCl resulting in the formation of a highly active deprotonation reagent (Knochel–Hauser base): (a) Krasovskiy, A.; Krasovskaya, V.; Knochel, P. Angew. Chem. Int. Ed. 2006, 45, 2958–2961. X-ray crystallographic and NMR spectroscopic studies: (b) García-Álvarez, P.; Graham, D. V.; Hevia, E.; Kennedy, A. R.; Klett, J.; Mulvey, R. E. O'Hara, C. T., Weatherstone, S. Angew. Chem., Int. Ed. 2008, 47, 8079–8081. (c) Armstrong D. R.; García-Álvarez, P.; Kennedy, A. R.; Mulvey, R. E.; Parkinson, J. A. Angew. Chem., Int. Ed. 2010, 49, 3185–3188. (11) Lithum bis(trimethylsilylamide) (LiHMDS) is as effective as BuLi and gave 92% yield of 3 in the presence of MgBr2. See the supporting information for details. (12) The other iron salts, FeCl3, Fe(acac)2, and Fe(acac)3, showed comparable catalytic activities, although a small amount (2–3%) of anisole was formed as a side product. See the supporting information for details. (13) Nickel phosphine complexes are reported to be suitable for the aromatic amination of aryl halides, including the inert chlorides.: (a) Yang L.M.; Chen, C. Org. Lett. 2005, 7, 2209–2211. (b) Yang L.-M.; Chen, C. J. Org. Chem. 2007, 72, 6324–6327. (14) ICP-MS analysis of FeCl2 showed the presence of < 0.1, 35.8, 26.9, and 12.9 ppm Pd, Cu, Co, and Ni, respectively. See the supporting information for ICP-MS analysis of the other iron salts. (15) The reaction with magnesium bis(trimethylsilylamide) prepared from LiHMDS and MgBr2 gave less than 5% yield of the corresponding amination product under the same conditions. (16) Bond lengths and angles are similar to those reported for the related iron(II) diamide complexes, [Fe{N(SiMe3)2}2]2 and [Fe(NPh2)2]2. Olmstead, M. M.; Power, P. P.; Shoner, S. C. Inorg. Chem. 1991, 30, 2547– 2551. (17) The dimer form is stable in the solid and solution states. See the supporting information and reference 16. (18) Preliminary synchrotron X-ray absorption measurements have shown that the oxidation state of the iron diamides was not lower than +II state. Details will be reported in a separate paper. (19) The Fe(II)–Fe(III) mechanism was proposed for iron-catalyzed cross coupling of alkyl halides. (a) Noda, D.; Sunada, Y.; Hatakeyama, T.; Nakamura, M.; Nagashima, H. J. Am. Chem. Soc. 2009, 131, 6078–6079. (b) Hatakeyama, T.; Hashimoto, T.; Kondo, Y.; Fujiwara, Y.; Seike, H.; Takaya, H.; Tamada, Y.; Ono, T.; Nakamura, M. J. Am. Chem. Soc. 2010, 132, 10674–10676. (c) Kawamura, S.; Ishizuka, K.; Takaya. H.; Nakamura, M. Chem. Commun. 2010, 46, 6054–6056. (d) Hatakeyama, T.; Okada, Y.; Yoshimoto, Y.; Nakamura, M. Angew. Chem., Int. Ed. 2011, 50, 10973– 10976. (d) Hatakeyama, T.; Fujiwara, Y.; Okada, Y.; Itoh, T.; Hashimoto, T.; Kawamura, S.; Ogata, K.; Takaya, H.; Nakamura, M. Chem. Lett. 2011, 40, 1030–1032. (e) Ghorai, S. K.; Jin, M.; Hatakeyama, T.; Nakamura, M. Org. Lett. 2012, 14, 1066–1069. (f) Hatakeyama, T.; Hashimoto, T.; Kathriarachchi, K. K. A. D. S.; Zenmyo, T.; Seike, H.; Nakamura, M. Angew. Chem., Int. Ed. 2012, 51, 8834–8837. (20) The Fe(II)–Fe(IV) mechanism was proposed for iron-catalyzed biaryl coupling. (a) Hatakeyama, T.; Nakamura, M. J. Am. Chem. Soc. 2007, 129, 9844–9845. (b) Hatakeyama, T.; Hashimoto, S.; Ishizuka, K.; Nakamura, M. J. Am. Chem. Soc. 2009, 131, 11949–11963. (21) The reaction coordinate was investigated for the high-spin state (A: S = 4, others: S = 2) because A and B in the high-spin state are stable by more than 20 kcal/mol as compared to those in the low- and intermediatespin states. See the supporting information for details. (22) The nitrogen-bridged dimer was less stable by 1.9 kcal/mol (Gibbs free energy) than G. See the supporting information for details.
ACS Paragon Plus Environment
Page 5 of 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Journal of the American Chemical Society
Ar NMgBr
+
R R = aryl or Me3Si
Ar'–Br
cat. FeCl2 LiBr
Ar
xylene or Bu2O 140 ºC
R
N Ar'
16 examples, 59–98% yield
ACS Paragon Plus Environment
5
