Catalytic C?H Borylation Using Iron Complexes Bearing 4,5,6,7-Tetrahydroisoindol-2-ide-Based PNP-Type Pincer Ligand

Article abstract of DOI:10.1002/asia.201900501

Catalytic C?H borylation has been reported using newly designed iron complexes bearing a 4,5,6,7-tetrahydroisoindol-2-ide-based PNP pincer ligand. The reaction tolerated various five-membered heteroarenes, such as pyrrole derivatives, as well as six-membered aromatic compounds, such as toluene. Successful examples of the iron-catalyzed sp³ C?H borylation of anisole derivatives were also presented.

Full text of DOI:10.1002/asia.201900501

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Catalytic C-H Borylation Using Iron Complexes Bearing 4,5,6,7-
Tetrahydroisoindol-2-ide-Based PNP-Type Pincer Ligand
Authors: Takeru Kato, Shogo Kuriyama, Kazunari Nakajima, and
Yoshiaki Nishibayashi
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To be cited as: Chem. Asian J. 10.1002/asia.201900501
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Catalytic C-H Borylation Using Iron Complexes Bearing 4,5,6,7-
Tetrahydroisoindol-2-ide-Based PNP-Type Pincer Ligand
Takeru Kato,[a] Shogo Kuriyama,[a] Kazunari Nakajima,*[b] and Yoshiaki Nishibayashi*[a]
Abstract: We have newly designed the iron-catalyzed C-H borylation using
iron complexes bearing a 4,5,6,7-tetrahydroisoindol-2-ide-based PNP pincer
ligand, based on results of stoichiometric reactions of the iron complexes.
As a result, we can apply a variety of arenes, not only benzene derivatives
but also 5-membered heteroarenes such as pyrrole derivatives, to the C-H
borylation. We have also found the first successful example of the iron-
catalyzed sp3 C-H borylation in the reaction of 4-methylanisole.
iron complex (2) in 51% yield.
aromatic C-H bond prompted us to investigate further transformation of
2 with various reagents. However, 2 was inert toward various reagents
The successful activation of the
and further functionalization of the azobenzene was not successful.
Ph
N
N
Ph
PtBu2
Ph
N
N
P
1 equiv.
N
Fe
H
N
Fe
Et2O
rt, 1 h
P
PtBu2
Carbon-hydrogen (C-H) bond is the most fundamental and
plentiful chemical bond in organic chemistry. Direct functionalization
of C-H bonds based on metal-catalyzed C-H activation has attracted
broad interest in the last decades.[1] Although various metal species
have been used in a variety of C-H activation reactions to date, iron
species have provided outstanding utility because iron is the most
abundant and cheapest transition metal on earth.[2]
P = PtBu2
2, 51% yield
1-H
Scheme 1. C-H activation of azobenzene with iron-hydride complex 1.
To explore a novel reactivity of iron complexes bearing PNP-type
pincer ligand toward aromatic C-H functionalization, we have modified
the pyrrolide-based PNP ligand. We have designed and prepared 1,3-
bis(dicyclohexylphosphinomethyl)-4,5,6,7-tetrahydroisoindol-2-ide
ligand as a novel anionic PNP-type pincer ligand. We first prepared an
iron-chloride complex (3-Cl) from the reaction of [FeCl2(thf)1.5] with
To control reactivity of metal complexes, introduction of well-
defined supporting ligands plays a critical role. In the last decades,
pyridine-based
PNP
ligands
(2,6-
bis(dialkylphosphinomethyl)pyridines) have been typically utilized in
various transition metal complexes to achieve novel reactivities.[3] On
the other hand, pyrrolide-based PNP pincer ligands (2,5-
bis(dialkylphosphinomethyl)pyrrolide) have been recently studied as a
lithium
1,3-bis(dicyclohexylphosphinomethyl)-4,5,6,7-
tetrahydroisoindol-2-ide in the presence of 2 equiv of pyridine (Scheme
2a). Treatment of 3-Cl with 1.4 equiv of PhMgCl and MeMgCl gave
the corresponding phenyl- and methyl complexes (3-Ph and 3-Me) in
73% and 75% yields, respectively (Scheme 2b). The reaction of 3-Cl
with 1 equiv of KHBEt3 gave the corresponding hydride-bridged diiron
complex ([3-H]2) in 75% yield (Scheme 2b). A similar hydride-bridged
diiron complex bearing PNP pincer ligands was reported by Tonzetich
and co-workers.[4a] Detailed molecular structures of 3-Ph, 3-Me, and
[3-H]2 were confirmed by X-ray analysis. ORTEP drawings of 3-Ph,
new candidate.[4,5]
However, applications of pyrrolide-based PNP
pincer-iron complexes as catalysts for molecular transformations have
been limited.[6] Quite recently, our group has developed iron-catalyzed
conversion of dinitrogen into ammonia and hydrazine, where pyrrolide-
based PNP-iron complexes have been used as catalysts.[7] We have also
developed iron-catalyzed hydroboration of alkynes with the use of
similar PNP-iron complexes as catalysts.[8] To explore further utility of
these iron complexes in organic synthesis, we have newly designed the
iron-catalyzed C-H borylation using iron complexes bearing a 4,5,6,7-
tetrahydroisoindol-2-ide-based PNP pincer ligand.
3-Me, and [3-H]2 are shown in Figure 1.
(a)
PCy2
PCy2
Py
pyridine
2 equiv.
In the course of our previous study,[7,8] we found that an iron-
NLi
[FeCl2(thf)1.5
]
+
N
Fe Cl
hydride
complex
bearing
2,5-bis(di-tert-
THF
butylphosphinomethyl)pyrrolide ligand (1-H) reacted with azobenzene
via directing group-assisted C-H activation of the benzene ring (Scheme
rt, 20 h
PCy2
PCy2
1 equiv.
3-Cl, Py = pyridine
89% yield
1).
Treatment of 1-H with azobenzene in diethyl ether at room
temperature for 1 h afforded the corresponding penta-coordinate aryl-
(b)
PCy2
RMgCl
1.4 equiv.
N
Fe
R
THF
[a]
[b]
T. Kato, Dr. S. Kuriyama, Prof. Dr. Y. Nishibayashi
Department of Systems Innovation
School of Engineering
rt, 1 h
PCy2
3-Ph, R = Ph, 73% yield
3-Me, R = Me, 75% yield
3-Cl
The University of Tokyo
Cy2
P
Bunkyo-ku, Tokyo, 113-8656 (Japan)
E-mail: ynishiba@sys.t.u-tokyo.ac.jp
Dr. K. Nakajima
Frontier Research Center for Energy and Resources
School of Engineering
PCy2
Fe
H
H
N
KHBEt3
1 equiv.
N
Fe
P
Cy2P
THF
rt, 1 h
Cy2
The University of Tokyo
Bunkyo-ku, Tokyo, 113-8656 (Japan)
E-mail: nakajima@sys.t.u-tokyo.ac.jp
[3-H]2, 75% yield
Scheme 2. Preparation of PNP-iron complexes.
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/asia.201900501
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(a)
(b)
HBpin generated in situ from the reaction of 3-Bpin with benzene.
Similarly, PhBpin 4 was formed by the reaction of 3-Ph with HBpin. As
a result, only 4 (11%) was identified as a boron compound.
Based on the interconversion between 3-Ph and 3-Bpin shown in
Schemes 3a and 3b, we have envisaged a proposed catalytic cycle for
the iron-catalyzed C-H borylation[9-13] of benzene with B2pin2.
A
plausible reaction pathway is shown in Scheme 3c (Cycle A). The
reaction of 3-Ph with B2pin2 affords 3-Bpin and borylation product
PhBpin 4. Then, the reaction of 3-Bpin with benzene proceeds to
regenerate 3-Ph along with the presumable formation of pinacolborane
(HBpin). The generated HBpin may react with some iron species to
form [3-H]2 as a side product as observed in Scheme 3b. Separately,
we confirmed the regeneration of 3-Bpin through the reaction of [3-H]2
with B2pin2 (see Supporting Information for details).
(c)
With the assumption, we investigated the catalytic C-H borylation
(Table 1). Treatment of B2pin2 in the presence of 10 mol% of 3-Ph in
benzene (200 equiv) at 100 °C for 18 h gave PhBpin 4 in 80% yield
based on the mole of B2pin2 (Table 1, entry 1). The use of other iron
complexes 3-Bpin and [3-H]2 as catalysts gave PhBpin 4 in slightly
lower yields (Table 1, entries 2 and 3). When iron-methyl complex 3-
Me was used as a catalyst, a similar catalytic activity to 3-Ph was
observed (Table 1, entry 4). Separately, we confirmed that the reaction
of 3-Me with B2pin2 afforded the corresponding iron-boryl complex 3-
Bpin in quantitative yield (see Supporting Information for details). This
result indicates that 3-Me is also a candidate of catalyst precursors.
Figure 1. ORTEP drawings of PNP-iron complexes: (a) 3-Ph, (b) 3-Me, and (c) [3-H]2.
Hydrogen atoms except for H1 and H2 in (c) and cyclohexyl groups on phosphorous
atoms in (c) are omitted for clarity.
PCy2
(a)
Table 1. Catalytic C-H borylation reactions of benzene with B2pin2.[a]
N
Fe Bpin
3-Ph + B2pin2
+ PhBpin
benzene
100 °C, 10 min
1 equiv.
4
16%
PCy2
catalyst
10 mol%
3-Bpin
19%
+
Ph
H
B2pin2
Ph Bpin
temp., 18 h
(b)
(c)
200 equiv.
1 equiv.
4
3-Bpin
+
3-Ph + [3-H]2 + PhBpin
100 °C, 10 min
Cy2
P
PCy2
PR2
4
PCy2
500 equiv.
33%
30%
11%
N
Fe
X
N
Fe Me
PR2
R = Cy: 5-Me
iPr: 6-Me
Fe
H
N
N
H
Fe
B2pin2
Ph Bpin
PCy2
4
P
Cy2P
X = Ph: 3-Ph
Cy2
Bpin: 3-Bpin
Me: 3-Me
[3-H]2
tBu: 1-Me
PCy2
PCy2
entry
1
catalyst
3-Ph
temp. [C°]
100
yield [%][b]
N
Fe Ph
PCy2
N
Fe Bpin
80
72
64
PCy2
3-Ph
3-Bpin
2
3-Bpin
[3-H]2
3-Me
5-Me
6-Me
1-Me
3-Me
3-Me
100
cycle A
3[c]
4
100
100
79 (76[d]
)
H
Ph
HBpin
5
100
48
42
0
Scheme 3. Reactivity of iron-phenyl and iron-boryl complexes (3-Ph and 3-Bpin).
6
100
7
100
Next, we carried out a stoichiometric reaction of 3-Ph with 1
equiv of bis(pinacolato)diboron (B2pin2) in benzene at 100 °C for a short
reaction time such as 10 min to afford the corresponding iron-boryl
8[e]
9
100
10
23
80
complex
(3-Bpin)
and
2-phenyl-4,4,5,5-tetramethyl-1,3,2-
[a] Reactions of 20 mmol of benzene with 0.10 mmol of B2pin2 in the presence of
iron catalyst (0.01 mmol, 10 mol%) were carried out. The yields were determined
based on the mole of B2pin2. [b] NMR yield. [c] 5 mol% of [3-H2]. [d] Isolated
yield. [e] HBpin (0.10 mmol) was used instead of B2pin2.
dioxaborolane (PhBpin: 4) in 19% and 16% yields, respectively,
together with unreacted 3-Ph in 66% recovery (Scheme 3a). On the other
hand, 3-Bpin was heated in benzene at 100 °C for 10 min to give 3-Ph
in 33% yield together with [3-H]2 and PhBpin 4 in 30% and 11% yields,
respectively (Scheme 3b). This result indicates that 3-Ph and HBpin
were formed from the reaction of 3-Bpin with benzene. The iron-hydride
complex [3-H]2 was formed by the reaction of some iron species with
To examine the effect of substituents on the phosphorous atom in
the PNP ligand, we investigated the catalytic borylation with benzene
using
iron-methyl
complexes
bearing
(2,5-
bis(dicyclohexylphosphinomethyl)pyrrolide),
(2,5-bis(diisopropyl
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10.1002/asia.201900501
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phosphinomethyl)pyrrolide),
and
(2,5-bis(di-tert-butyl
The result of the C-H borylation of furans with B2pin2 shown in
Scheme 4d prompted us to investigate the borylation of furans in details.
The reaction of 2-methylfuran with HBpin in the presence of 10 mol%
of 3-Me at 100 °C for 18 h gave the corresponding borylated product in
61% yield (Scheme 5a). This result indicates that the C-H borylation of
furan derivatives with not only B2pin2 but also HBpin as boron sources
proceeds effectively, in sharp contrast to the C-H borylation of other
arenes.
phosphinomethyl)pyrrolide) as PNP-type pincer ligands (5-Me, 6-Me,
and 1-Me, respectively). Lower yields of 4 were obtained in the cases
using 5-Me and 6-Me as catalysts (Table 1, entries 5 and 6). However,
no catalytic activity was observed when 1-Me was used as a catalyst
(Table 1, entry 7).
When we used HBpin as a boron source instead of B2pin2, PhBpin
4 was obtained only in 10% yield (Table 1, entry 8). This result
indicates only B2pin2 is applicable as an effective boron source for the
present C-H borylation of benzene. We also confirmed that the reaction
at a lower temperature such as 80 °C gave only a lower yield of PhBpin
4 (Table 1, entry 9). Experimental results shown in Table 1 suggest that
3-Me worked as the best catalyst at 100 °C.
(a)
3-Me
O
O
10 mol%
Me
Me
Bpin
+
HBpin
100 °C, 18 h
200 equiv.
1 equiv.
61%, 5-/4- = 99/1
With the optimized conditions in hand, we investigated reactions
of various arenes at 100 °C using 3-Me as a catalyst.[14,15] The reaction
of toluene with B2pin2 gave the corresponding borylated products in
48% yield as a mixture of m- and p-isomers with the ratio of 75/25
PCy2
(b)
Me
O
O
Me
N
Fe
H2
+
[3-H]2
+
rt, 44 h
83% GC yield
400 equiv.
PCy2
3-Furyl
47% isolated yield
(Scheme 4a).
membered heteroarenes such as pyrrole, thiophen, and furan derivatives
were transformed successfully. When N-methylpyrrole, N-
Not only benzene derivatives but also other five-
(c)
(d)
O
Me
Bpin
(triisopropylsilyl)pyrrole, and thiophene were used as substrates, the
corresponding borylated products were obtained in 60%, 29% and 42%
yields, respectively (Schemes 4b and 4c). Interestingly, reactions with
furans (2-methylfuran and 2-ethylfuran) afforded the corresponding
borylated furans in 149% and 139% yields, respectively, where the yield
of borylated furan was estimated based on the mole of B2pin2 (Scheme
4d). Thus, the yields over 100% indicate that both two boron fragments
in B2pin2 were used as a boron source in the reactions with furans.
3-Furyl
+
HBpin
C6D6
rt, 17 h
10 equiv.
25%
O
O
Bpin
H2
B2pin2
PCy2
PCy2
PCy2
(a)
3-Me
10 mol%
O
Me
Me
N
Fe
H
N
Fe
N
Fe Bpin
+
Bpin
B2pin2
100 °C, 18 h
PCy2
PCy2
PCy2
3-Bpin
200 equiv.
1 equiv.
48%
o-/m-/p- = 0/75/25
cycle B
cycle A
(b)
R
N
R
N
3-Me
10 mol%
[3-H]2
+
B2pin2
100 °C, 18 h
O
O
HBpin
HBpin
Bpin
Bpin
200 equiv.
1 equiv.
R = Me, 60%, 2-/3- = 49/51
R = SiiPr3, 29%, 2-/3- = 0/100
(c)
(d)
Scheme 5. Reactivity of iron complexes toward furan derivatives.
3-Me
10 mol%
S
S
+
+
B2pin2
100 °C, 18 h
Bpin
To check the different reactivity of furans, we carried out the
following stoichiometric reactions. The reaction of hydride-bridged
diiron complex with an excess amount of 2-methylfuran at room
temperature for 44 h gave the corresponding iron-furyl complex (3-
Furyl) in 47% yield together with the formation of H2 in 83% GC yield
(Scheme 5b). On the other hand, the reaction of 3-Furyl with 10 equiv
of HBpin in C6D6 at room temperature for 17 h gave the corresponding
borylated furan in 25% yield together with a mixture of unidentified iron
complexes (Scheme 5c). Based on the results of the stoichiometric
reactions in Schemes 5b and 5c, we proposed a reaction pathway for the
C-H borylation of furan shown in Scheme 5d. In addition to the Cycle
A shown in Scheme 3c, the C-H borylation of furan with HBpin
proceeds via the Cycle B. In the Cycle B, 3-Furyl reacts with HBpin
to give the corresponding mononuclear iron-hydride complex, which is
presumably in equilibrium with [3-H]2, and the borylated furan. Then,
the resulting iron-hydride species may react with furan to give 3-Furyl
together with the formation of H2. Thus, the C-H borylation of furan
with B2pin2 proceeds via Cycle A and that with HBpin proceeds via
Cycle B.
200 equiv.
1 equiv.
42%, 2-/3- = 83/17
3-Me
10 mol%
O
O
R
R
B2pin2
100 °C, 18 h
Bpin
200 equiv.
1 equiv.
R = Me, 149%, 5-/4- = 91/9
R = Et, 139%, 5-/4- = 91/9
Scheme 4. C-H boryaltion reactions of various arenes with B2pin2.
Several research groups have already reported the iron-catalyzed
C-H borylation of arenes with B2pin2 and HBpin as boron sources.[10-13]
However, development of iron complexes which are applicable to not
only benzene derivatives but also five-membered heteroarenes such as
pyrroles and furans has not yet been reported until now. In sharp
contrast to the previous reports, we can apply the iron complexes bearing
a 4,5,6,7-tetrahydroisoindol-2-ide-based PNP pincer ligand to the
catalytic C-H borylation of a variety of arenes. Especially, we have
succeeded in the first successful examples of C-H borylation of pyrroles
using iron complexes as catalysts.
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[5]
Selected examples of other pyrrolide-based PNP complexes: a) N. Grüger, H.
Wadepohl, L. H. Gade, Dalton Trans. 2012, 41, 14028; b) J. A. Kessler, V. M.
Iluc, Inorg. Chem. 2014, 53, 12360; c) M. Kreye, M. Freytag, P. G. Jones, P. G.
Williard, W. H. Bernskoetter, M. D. Walter, Chem. Commun. 2015, 51, 2946;
d) D. S. Levine, T. D. Tilley, R. A. Andersen, Organometallics 2017, 36, 80; e)
B. Liu, S. Li, M. Wang, D. Cui, Angew. Chem. Int. Ed. 2017, 56, 4560; f) V. M.
Krishnan, I. Davis, T. M. Baker, D. J. Curran, H. D. Arman, M. L. Neidig, A.
Liu, Z. J. Tonzetich, Inorg. Chem. 2018, 57, 9544; g) H. Alawisi, K. F. Al-
Afyouni, H. D. Arman, Z. J. Tonzetich, Organometallics 2018, 37, 4128.
Selected examples on the use of pyrrolide-based PNP complexes as catalysts in
organic synthesis: a) G. T. Venkanna, S. Tammineni, H. D. Arman, Z. J.
Tonzetich, Organometallics 2013, 32, 4656; b) G. T. Venkanna, H. D. Arman,
Z. J. Tonzetich, ACS Catal. 2014, 4, 2941; c) D. S. Levine, T. D. Tilley, R. A.
Andersen, Organometallics 2015, 34, 4647; d) D. S. Levine, T. D. Tilley, R. A.
Andersen, Chem. Commun. 2017, 53, 11881; e) S. Nakayama, S. Morisako, M.
Yamashita, Organometallics 2018, 37, 1304.
Separately, we confirmed that no reaction of [3-H]2 with benzene
at room temperature for 44 h occurred at all. This result indicates that
iron-hydride species derived from [3-H]2 are reactive not toward
benzene but toward furan under the present reaction conditions. We
consider that this different reactivity is due to higher acidity of the C-H
bond of furan than that of benzene.[16,17]
During our investigation of the reactivity of the iron complexes,
we have found that the reaction of anisole with 1 equiv of B2pin2 in the
presence of 10 mol% of 3-Me at 100 °C for 18 h gave a mixture of the
sp2 C-H borylated products in 30% yield together with the sp3 C-H
borylated product in 13% yield (Scheme 6a). This result indicates the
superstoichiometric amount of the sp3 C-H borylation product was
produced. On the other hand, when 4-methylanisole was used to avoid
the sp2 C-H borylation of the benzene ring under the same reaction
conditions, the sp3 C-H borylation of methoxy group proceeded
selectively to give the sp3 C-H borylated product in 25% yield as a sole
product (Scheme 6b). To the best of our knowledge, this is the first
successful example of the iron-catalyzed sp3 C-H borylation.
[6]
[7]
a) S. Kuriyama, K. Arashiba, K. Nakajima, Y. Matsuo, H. Tanaka, K. Ishii, K.
Yoshizawa, Y. Nishibayashi, Nat. Commun. 2016, 7, 12181; b) Y. Sekiguchi, S.
Kuriyama, A. Eizawa, K. Arashiba, K. Nakajima, Y. Nishibayashi, Chem.
Commun. 2017, 53, 12040.
[8]
[9]
K. Nakajima, T. Kato, Y. Nishibayashi, Org. Lett., 2017, 19, 4323.
(a)
3-Me
10 mol%
OMe
OMe
O
Bpin
a) I. A. I. Mkhalid, J. H. Barnard, T. B. Marder, J. M. Murphy, J. F. Hartwig,
Chem. Rev. 2010, 110, 890; b) A. Ros, R. Fernández, J. M. Lassaletta, Chem.
Soc. Rev. 2014, 43, 3229; c) L. Xu, G. Wang, S. Zhang, H. Wang, L. Wang, L.
Liu, J. Jiao, P. Li, Tetrahedron 2017, 73, 7123.
+
+
B2pin2
100 °C, 18 h
Bpin
30%
o-/m-/p- = 10/75/15
200 equiv.
1 equiv.
13%
[10] T. Hatanaka, Y. Ohki, K. Tatsumi, Chem. Asian J. 2010, 5, 1657.
[11] G. Yan, Y. Jiang, C. Kuang, S. Wang, H. Liu, Y. Zhang, J. Wang, Chem.
Commun. 2010, 46, 3170.
(b)
3-Me
10 mol%
OMe
O
Bpin
+
B2pin2
[12] a) T. J. Mazzacano, N. P. Mankad, J. Am. Chem. Soc. 2013, 135, 17258; b) S.
R. Parmelee, T. J. Mazzacano, Y. Zhu, N. P. Mankad, J. A. Keith, ACS Catal.
2015, 5, 3689; c) T. Dombray, C. G. Werncke, S. Jiang, M. Grellier, L. Vendier,
S. Bontemps, J.-B. Sortais, S. Sabo-Etienne, C. Darcel, J. Am. Chem. Soc. 2015,
137, 4062.
100 °C, 18 h
Me
Me
200 equiv.
1 equiv.
25%
Scheme 6. sp3 C-H borylation of anisole derivatives.
[13] Y. Yoshigoe, Y. Kuninobu, Org. Lett. 2017, 19, 3450.
[14] In addition to the examples shown in Scheme 4, we examined ethylbenzene, m-
xylene, and fluorobenzene as substrates. However, the corresponding products
were obtained in low yields (15-30%).
In summary, we have newly designed the iron-catalyzed C-H
borylation using iron complexes bearing a 4,5,6,7-tetrahydroisoindol-2-
ide-based PNP pincer ligand, based on results of stoichiometric reactions
of the iron complexes. As a result, we can apply a variety of arenes, not
only benzene derivatives but also 5-membered heteroarenes such as
pyrrole derivatives, to the C-H borylation. We have also found the first
successful example of the iron-catalyzed sp3 C-H borylation in the
reaction of 4-methylanisole. Further work is currently in progress in
our laboratory.
[15] We investigated reactions of other heterocycles such as pyridine, 2,6-lutidine,
N-methylimidazole, N-methylindole, 1,3-oxazole. However, the corresponding
C-H borylation products were not observed in all cases.
[16] K. Shen, Y. Fu, J.-N. Li, L. Liu, Q.-X. Guo, Tetrahedron 2007, 63, 1568.
[17] In some C-H borylation reactions, correlates between reactivity and acidity of
C-H bonds were reported: a) B. A. Vanchura, II, S. M. Preshlock, P. C. Roosen,
V. A. Kallepalli, R. S. Staples, R. E. Maleczka, Jr., D. A. Singleton, M. R. Smith,
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Keywords: iron complex • pincer complex • C-H borylation •
heterocycles
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10.1002/asia.201900501
Chemistry - An Asian Journal
COMMUNICATION
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Takeru Kato, Shogo Kuriyama, Kazunari
Nakajima,* and Yoshiaki Nishibayashi*
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Catalytic C-H Borylation Using Iron
Complexes Bearing 4,5,6,7-
E = O, S, NR
Tetrahydroisoindol-2-ide-Based PNP-
Type Pincer Ligand
We have newly designed the iron-catalyzed C-H borylation using iron complexes bearing a
4,5,6,7-tetrahydroisoindol-2-ide-based PNP pincer ligand, based on results of stoichiometric
reactions of the iron complexes. As a result, we can apply a variety of arenes, not only
benzene derivatives but also 5-membered heteroarenes such as pyrrole derivatives, to the C-
H borylation. We have also found the first successful example of the iron-catalyzed sp3 C-
H borylation in the reaction of 4-methylanisole.
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