Synthesis of Functionalized (η5-Indenyl)rhodium(III) Complexes and Their Application to C?H Bond Functionalization

Article abstract of DOI:10.1002/asia.201701716

It has been established that reductive complexation of functionalized benzofulvenes, which are readily prepared from commercially available indene and 2-methylindene, with RhCl₃ in ethanol affords the corresponding indenyl–rhodium(III) dichlorides bearing substituents at the 1- (H or CO₂Et), 2- (H or Me), and 3- [CH₂Ph or CH₂(2-MeOC₆H₄)] positions. The indenyl–rhodium(III) complexes bearing one ethoxycarbonyl group showed higher thermal stability and regioselectivity than our previously reported Cp^ERh^III complex toward the oxidative [3+2] annulation of acetanilides with internal alkynes.

Full text of DOI:10.1002/asia.201701716

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Synthesis of Functionalized (η5-Indenyl)rhodium(III) Complexes
and Their Application to C-H Bond Functionalization
Authors: Jyunichi Terasawa, Yu Shibata, Yuki Kimura, and Ken
Tanaka
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Synthesis of Functionalized (η5-Indenyl)rhodium(III) Complexes
and Their Application to C–H Bond Functionalization
Jyunichi Terasawa, Yu Shibata,* Yuki Kimura, and Ken Tanaka*
Abstract: It has been established that reductive complexation of
functionalized benzofulvenes, which are readily prepared from
commercially available indene and 2-methylindene, with RhCl3 in
ethanol affords the corresponding indenyl-rhodium(III) dichlorides
bearing substituents at the 1- (H or CO2Et), 2- (H or Me), and 3-
[CH2Ph or CH2(2-MeOC6H4)] positions. The thus obtained indenyl-
rhodium(III) complexes bearing one ethoxycarbonyl group showed
higher thermal stability and regioselectivity than our previously
reported CpERhIII complex toward the oxidative [3+2] annulation of
acetanilides with internal alkynes.
We found that reductive complexation of functionalized fulvenes,
which are readily prepared by our previously reported
rhodium(I)-catalyzed [2+2+1] cycloadditions,[3a,3n] with RhCl3
using ethanol as a reducing agent affords functionalized CpRhIII
complexes bearing the esters (CpE)[3a] or the pendant amides
(CpA) (Scheme 1, top).[3n] We anticipated that this strategy would
be applicable to the synthesis of functionalized indenyl-
rhodium(III) complexes from the corresponding benzofulvenes
and RhCl3 in ethanol. As such, Honzíček reported the synthesis
of an indenyl-molybdenum complex from the benzofulvene and
a
molybdenum chloride,[9] while strongly basic lithium
triethylborohydride was employed as a reducing agent, and the
synthesis of catalytically active complexes has not been
reported. In this paper, we have established the facile synthesis
of functionalized benzofulvenes (Scheme 1, middle) and their
reductive complexation with RhCl3 in ethanol, leading to
functionalized IndRhIII complexes (Scheme 1, bottom). Their
catalytic activity toward the oxidative [3+2] annulation of
acetanilides with internal alkynes is also disclosed.
It has long been known that η5-cyclopentadienyl-rhodium(III)
(CpRhIII) complexes are highly active catalysts for C–H bond
functionalization.[1] Especially,
a
commercially available
pentamethylcyclopentadienyl (Cp*)-rhodium(III) complex is the
most frequently used catalysts for this purpose. In order to
improve catalytic activity and selectivity, rhodium(III) complexes
with several sterically and electronically tuned Cp ligands were
developed recently (Scheme 1, top).[2,3] On the other hand, it
would be interesting to use substituted η5-indenyl (Ind)-
transition-metal complexes in place of the substituted Cp-
transition-metal complexes due to their characteristic steric
environment and ability of ring slippage to η3-coordination.[4]
However, the reactions catalyzed by sterically and/or
electronically tuned indenyl-transition-metal complexes have not
been well examined due to difficulty of their synthesis.[5] In the
C–H bond functionalization, only a single example of the
indenyl-rhodium(III) complex-catalyzed reaction has been
Cyclopentadienyl Ligands (Cp)
Sterically Tuned Cp
Me
tBu
tBu
R
Me
Me
Me
Me
Me
Me
Me
Me
Rh
CptRh
Rh
CpCyRh
Rh
Cp*tBuRh (R = tBu)
Cp*CyRh (R = Cy)
CpPhRh (R = Ph)
Rh
Cp*Rh
Electronically Tuned Cp
Pendant Amide-Armed Cp
Me
Me
Ph
CO2Et
Me
R
NR1R2
EtO2C
Me
Me
Me
O
Me
Ph
O
Rh
CpERh
Rh
Rh
CpARh
reported.[6] Rovis reported that the use of
a
η5-
Cp*CF3Rh (R = CF3)
[R = 3,5-(CF3)2C6H3]
heptamethylindenyl-rhodium(III) [Ind*RhIII] complex, which is
synthesized by anion exchange (Scheme 1, middle and bottom),
improves diastereoselectivity of the [4+2] annulation of
benzamides with 3,3-disubstituted cyclopropenes.[6,7] Cramer
reported the synthesis of unsubstituted indenyl- and 1,2,3-
trimethylindenyl-rhodium(III) complexes by β-carbon elimination
(Scheme 1, bottom), but their catalytic activity toward the C–H
bond functionalization was not demonstrated.[8] Thus, structural
diversity of IndRhIII complexes is very limited, especially, an
electronically tuned one has not been reported to date.
Indenyl Ligands (Ind)
Sterically Tuned Ind
Sterically and Electronically
Tuned Ind (this work)
Me
Me
Me
Me
R3
Me
R1 = H, CO2Et
R
R2 = H, Me
Me
Me
R3 = Ph, 2-MeOC6H4
R1
R2
Rh
R
R
Rh
R = H, Me
Rh
Ind*Rh
R3
Anion Exchange
(many precedents)
H
R2
M–X
R3
R3
R1
–HX
M–H
R2
On the other hand, our research group developed the novel
method for the synthesis of functionalized CpRhIII complexes.
R3
OH
R2
R1
M–OH
Me
Me
R2
M
R1
Reductive Complexation
Cp: our previous works (M = Rh, using EtOH)
Ind: Honzícek (M = Mo, using Li[Et3BH])
this work (M = Rh, using EtOH)
–H2O, Me2CO
!-Elimination
R1
[a]
J. Terasawa, Dr. Y. Shibata, Y. Kimura, Prof. Dr. K. Tanaka
Department of Chemical Science and Engineering, Tokyo Institute
of Technology
Scheme 1. Functionalized η5-cyclopentadienyl- and η5-indenyl-rhodium(III)
complexes.
O-okayama, Meguro-ku, Tokyo 152-8550 (Japan)
E-mail: ktanaka@apc.titech.ac.jp
E-mail: yshibata@apc.titech.ac.jp
http://www.apc.titech.ac.jp/~ktanaka/
Supporting information for this article is given via a link at the end
of the document.
During our investigation into the CpERhIII complex-catalyzed
C–H bond functionalization, we have experienced that thermal
stability of the cationic CpERhIII complex is lower than the
cationic Cp*RhIII complex, presumably due to the presence of
two electron-withdrawing ethoxycarbonyl groups, which
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10.1002/asia.201701716
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O
R3
and 6bb. On the other hand, 2-methyl substituted indenyl
complexes 4ca, 4da, and 4db, obtained from 3ca, 3da, and 3db,
could be characterized as the corresponding chloro-bridged
dimers. This dimer 4da could also be converted to the
corresponding mono-nuclear PPh3 complex 5da and iodo-
bridged dimer 6da.
H
R3
2a (R3 = H)
2b (R3 = OMe)
pyrroridine (1.1 equiv)
R2
R2
MeOH or CH2Cl2, reflux
then HCl
R1
R1
3aa / 75%
3ba / 89% 3bb / 67%
3ca / 57%
1a (R1 = H, R2 = H)
The structures of four mono-nuclear PPh3 complexes 5aa,
5ba, 5bb, and 5da were confirmed by X-ray single crystal
analyses (Figure 1). In all the solid-state structures, the
phosphine ligand with the grater trans influence than Cl located
at the trans-position to the fused benzene ring (C4–C5). The
benzyl groups were located at the opposite side to the rhodium
centre regardless of the substituents on the benzene rings.
1b (R1 = CO2Et, R2 = H)
1c (R1 = H, R2 = Me)
66%
83%
NaH (1 equiv)
(EtO)2CO (1.1 equiv)
THF, 0 °C to reflux
1d (R1 = CO2Et, R2 = Me)
3da / 84% 3db / 55%
RhCl3•nH2O
(1 equiv)
EtOH, 80 °C
1–16 h
R3
PPh3
(1 equiv)
R2
R1
CH2Cl2, RT
1 h
Rh
R3
Cl
Cl
PPh3
5
R2
R1
Rh
R3
Cl
Cl
NaI
(10 equiv)
n
R2
R1
Rh
I
4
acetone
40 °C
16 h
I
2
6
OMe
EtO2C
EtO2C
[Rh]
[Rh]
[Rh]
4aa / –[a]
4ba / –[a]
4bb / –[a]
5aa / 79% (2 steps)
6aa / 32% (2 steps)
5ba / 48% (2 steps)
6ba / 38% (2 steps)
5bb / 74% (2 steps)
6bb / 31% (2 steps)
OMe
Me
EtO2C
Me
EtO2C
Me
[Rh]
[Rh]
[Rh]
4ca / 46% (n = 2)
4da / 50% (n = 2)
5da / 96%[b]
4db / 75% (n = 2)
6da / 66%[b]
Scheme 2. Synthesis of functionalized (η5-indenyl)rhodium(III) complexes 4–6.
The cited yields are of the isolated complexes from 3. [a] The products could
not be characterized presumably due to the presence of mixtures of oligomers.
[b] The cited yields are of the isolated complexes from 4da.
stabilizes the non-coordinating cyclopentadienyl anion.
Additionally, the use of the CpERhIII catalyst did not improve the
regioselectivity presumably due to its close steric environment to
the Cp*RhIII catalyst. Thus, we focused our attention into the
synthesis and catalysis of η5-indenyl-rhodium(III) complexes with
one ethoxycarbonyl group. We expected that their modest
electron negativity and bulky steric environment would realize
high thermal stability and regioselectivity, respectively, with
Figure 1. Molecular structures of complexes (a) 5aa, (b) 5ba, (c) 5bb, and (d)
5da, with 30% thermal ellipsoids. All hydrogen atoms are omitted for clarity.
Table 1. Slippage parameters of 5.
7a
1
3a
2
3
Rh
retaining
good
catalytic
activity.
The
synthesis
of
! = (Rh"C3a,7a)"(Rh"C1,3
)
ethoxycarbonyl-substituted η5-indenyl-rhodium(III) complexes is
Δ (Å)[d]
shown in Scheme 2. Introduction of the ethoxycarbonyl group to
Complex
indene
(1a)
and
2-methylindene
(1c)
afforded
1-
5aa
5ba
5bb
5da
0.187 (8)
0.185 (8)
0.150 (5)
0.156 (4)
0.155 (6)
ethoxycarbonylindenes 1b and 1d, respectively. Condensation
of 1b and 1d with benzaldehyde (2a) and 2-
methoxybenzaldehyde (2b) in the presence of pyrrolidine
furnished benzofulvenes 3ba, 3bb, 3da, and 3db in good yields.
Additionally, the corresponding benzofulvenes 3aa and 3ca with
no ethoxycarbonyl group were also synthesized for comparison.
We were pleased to find that the reductive complexation of the
thus obtained benzofulvenes 3 with RhCl3•nH2O in ethanol
proceeded to give the corresponding indenyl complexes 4.
However, 4aa, 4ba, and 4bb[11] could not be characterized due
to the presence of oligomers. Thus, these products were
characterized as the corresponding mono-nuclear PPh3
complexes 5aa, 5ba, and 5bb or iodo-bridged dimers 6aa, 6ba,
Ind*RhCl2(PMe2Ph)[b]
[a] Δ = (Rh-C3a,7a)–(Rh-C1,3). [b] Ref 13.
To see the effect of substituents on the indenyl ring of 5
toward the indenyl ring-slippage, which indicates stability of the
complexes,[2k] their slippage parameters (Δ)[12] were determined
as shown in Table 1. Introduction of the ester moiety on the Ind
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10.1002/asia.201701716
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ring slightly decreased the Δ value (5aa vs. 5ba). The presence
of the methoxy group or the 2-methyl group further decreased
the Δ value (5ba vs. 5bb and 5da), which were close to the Δ
value of the highly stable Ind* complex.[13,14] This feature predicts
acetone (entries 1 and 2).[3e] Pleasingly, screening of our newly
developed indenyl-rhodium(III) complexes (entries 3–8) revealed
that trisubstituted IndRhIII complex 4da with one ethoxycarbonyl
group efficiently catalyzes the reaction to give 9aa in high yield
high stability of the indenyl complexes derived from 3bb and 3da. (entry 7). The yield of 9aa using diiodide complex 6da was lower
than that using dichloride complex 4da presumably due to the
Table 2. Catalytic activity of functionalized IndRhIII complexes in oxidative
incomplete generation of the corresponding cationic complex
from 4da (entries 7 vs. 9). Complex 4da also catalyzed the
reaction of 7a and diphenylacetylene (8b), although the yield
was moderate (entry 10). Increasing the amount of catalyst
loading (5 mol % Rh2) resulted in the almost quantitative yield of
9aa (entry 11), which was comparable to that using the CpERhIII
catalyst under the previously employed conditions.[3e] In contrast,
the use of the CpERh catalyst resulted in low yields under the
current conditions (entry 12). For the reaction of dialkylacetylene
8c, 4da showed almost the same high catalytic activity as the
CpERh catalyst (entries 13 vs 14). The reaction of unsymmetric
alkyne 8d bearing phenyl and t-butyl groups afforded the
corresponding indole 9ad accompanied with deacetylated 9ad-H
and regioisomer 9’ad (entries 15–17). Interestingly, the use of
6bb showed the opposite regioselectivity compared to those of
4da and CpERh,[3e] although the yield and regioselectivity were
moderate.
[3+2] annulation of 7a with 8a–c.[a]
2.5 mol % [Rh2]
10 mol % AgSbF6
20 mol % Cu(OAc)2•H2O
R1 (R2)
R1
Ac
+
R2 (R1)
N
H
CH2Cl2, 40 °C, 16 h
under O2
N
Ac
R2
9aa (R1 = Me, R2 = Ph)
9ab (R1 = R2 = Ph)
9ac (R1 = R2 = nPr)
9ad (9'ad)
7a
(1.1 equiv)
8a (R1 = Me, R2 = Ph)
8b (R1 = R2 = Ph)
8c (R1 = R2 = nPr)
8d (R1 = tBu, R2 = Ph)
(R1 = tBu, R2 = Ph)
Entry
1
Alkyne
8a
[Rh2]
[CpERhCl2]2
[CpERhCl2]2
6aa
Yield [%][b]
39
R.r.
>20:1
>20:1
>20:1
>20:1
>20:1
>20:1
>20:1
>20:1
>20:1
–
2[c]
3
8a
34
8a
2
4
8a
6ba
19
5
8a
6bb
25
Reaction profiles of 7a and 8a in CH2Cl2 at 40 °C using
IndRhIII (6ba and 4da) and CpERhIII complexes were shown in
Figure 2. For convenient monitoring, the reactions were
conducted under air. At the initial stage (1–2 h), the use of 4da
produced 9aa in higher yield than that of 6ba and the CpERhIII
complex. Furthermore, the reaction using 4da continuously
generated 9aa even at the late stage (2–18 h). In sharp contrast,
6ba and the CpERhIII complex were deactivated under the above
conditions, while the CpERhIII complex was continuously active in
acetone at RT. These facts suggest that the moderately
electron-deficient trisubstituted IndRhIII complex 4da is thermally
more stable than the highly electron-deficient CpERhIII complex.
6
8a
4ca
8
7
8a
4da
84
8
8a
4db
60
9
8a
6da
74
10
11[d]
12
13
14
15
16
17
8b
8b
8b
8c
4da
31
4da
98
–
[CpERhCl2]2
4da
24
–
89
–
8c
[CpERhCl2]2
6bb
88
–
8d
8d
8d
50[e]
31[e]
96[e]
(15+46[e]):39
(32+7[e]):61
(28+11[e]):61
4da
[CpERhCl2]2
[a] [Rh2] (0.0050 mmol), AgSbF6 (0.020 mmol), Cu(OAc)2•H2O (0.040 mmol),
7a (0.200 mmol), 8 (0.220 mmol), and CH2Cl2 (2.0 mL) were used. [b] Isolated
yield. [c] Acetone was used as a solvent at room temperature under air. [d]
[Rh2] (0.010 mmol), AgSbF6 (0.040 mmol), Cu(OAc)2•H2O (0.080 mmol), 7a
(0.200 mmol), 8 (0.220 mmol), and CH2Cl2 (2.0 mL) were used. For 72 h. [e]
Including deacetylated 9ad-H. See the supporting information.
tBu
Ph
N
9ad-H
H
Figure 2. Reaction profiles for oxidative [3+2] annulation of 7a with 8a in
CH2Cl2 at 40 °C under air. [a] In acetone at RT.
We investigated the catalytic activity of the thus obtained
functionalized indenyl-rhodium(III) iodide (6) and chloride (4)
complexes toward the oxidative [3+2] annulation of acetanilide
(7a) with alkyl- and/or phenyl-substituted internal alkynes 8a–c
as shown in Table 2.[3e] Preliminary screening of reaction
conditions revealed that the IndRhIII catalysts showed better
performance in CH2Cl2 at 40 °C than previously employed
conditions for the CpERhIII catalyst (in acetone at RT)[3e] (Table
S1). In the CpERh catalysis, reactivity of methyl- and phenyl-
substituted alkyne 8a was significantly low in both CH2Cl2 and
We next investigated the regioselectivity of the oxidative
[3+2] annulation of 3-methoxyacetanilide (7b) with 8b as shown
in Table 3.[3e] In the CpERhIII catalysis, 9bb and 10bb were
obtained with moderate yield and regioselectivity (entry 1). The
use of the most active indenyl complexes 4da and 4db
significantly improved the product yield, while the regioselectivity
improvement was small (entries 2 and 3). Gratifyingly, the use of
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10.1002/asia.201701716
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diiodide complex 6bb, bearing hydrogen and the 2-
methoxybenzyl group at the 2- and 3-positions, respectively,
significantly improved the regioselectivity, but decreased the
product yield (entry 4). Fortunately, increasing the amount of
AgSbF6 facilitated the generation of the cationic complex, and
thus the product yield increased (entry 5). Although dichloride
complex 4bb was isolated as an uncharacterizable mixture of
oligomers, the use of 4bb afforded the products with comparable
yield and regioselectivity without using an excess amount of
AgSbF6 (entry 4). Prolonged reaction time further increased the
product yield with retaining the high regioselectivity (entry 6).
Keywords: C-H Bond Functionalization • Benzofulvenes •
Indenyl Complexes • Reductive Complexation • Rhodium
[1]
For selected reviews, see: a) J. Wencel-Delord, F. W. Patureau, F.
Glorius, in C-H Bond Activation and Catalytic Functionalization I (Eds.:
H. P. Dixneuf, H. Doucet), Springer International Publishing, Cham,
Switzerland, 2016, p. 1; b) C. G. Newton, D. Kossler, N. Cramer, J. Am.
Chem. Soc. 2016, 138, 3935; c) T. Gensch, M. N. Hopkinson, F.
Glorius, J. Wencel-Delord, Chem. Soc. Rev. 2016, 45, 2900; d) G.
Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651; e) S. Chiba,
Chem. Lett. 2012, 41, 1554; f) J. Wencel-Delord, T. Droege, F. Liu, F.
Glorius, Chem. Soc. Rev. 2011, 40, 4740; g) T. Satoh, M. Miura, Chem.
Eur. J. 2010, 16, 11212. For a review of Cp*Co(III) catalysis, see: h) T.
Yoshino, S. Matsunaga, Adv. Synth. Catal. 2017, 359, 1245.
Table 3. Catalytic activity and regioselectivity of functionalized IndRhIII
complexes in oxidative [3+2] annulation of 7b with 8b.[a]
[2]
For selected examples using sterically tuned CpRh catalysts, see: a) M.
Shimizu, H. Tsurugi, T. Satoh, M. Miura, Chem. Asian J. 2008, 3, 881;
b) T. K. Hyster, T. Rovis, Chem. Sci. 2011, 2, 1606; c) R. Zeng, J. Ye,
C. Fu, S. Ma, Adv. Synth. Catal. 2013, 355, 1963; d) J. M. Neely, T.
Rovis, J. Am. Chem. Soc. 2014, 136, 2735; e) T. Piou, T. Rovis, J. Am.
Chem. Soc. 2014, 136, 11292; f) M. D. Wodrich, B. Ye, J. F. Gonthier,
C. Corminboeuf, N. Cramer, Chem. Eur. J. 2014, 20, 15409; g) T. A.
Davis, C. Wang, T. Rovis, Synlett 2015, 26, 1520; h) B. Li, J. Yang, H.
Xu, H. Song, B. Wang, J. Org. Chem. 2015, 80, 12397; i) T. Piou, T.
Rovis, Nature 2015, 527, 86; j) F. Romanov-Michailidis, K. F. Sedillo, J.
M. Neely, T. Rovis, J. Am. Chem. Soc. 2015, 137, 8892; k) T. Piou, F.
Romanov-Michailidis, M. Romanova-Michaelides, K. E. Jackson, N.
Semakul, T. D. Taggart, B. S. Newell, C. D. Rithner, R. S. Paton, T.
Rovis, J. Am. Chem. Soc. 2017, 139, 1296.
2.5 mol % [Rh2]
10 mol % AgSbF6
20 mol % Cu(OAc)2•H2O
Ph
+
Ac
CH2Cl2, 40 °C, 16 h
under O2
MeO
N
H
Ph
OMe
Ph
Ph
7b
8b (1.1 equiv)
Ph
+
Ph
N
N
MeO
Ac
Ac
10bb
9bb
Yield [%][b]
regioselectivity
Entry
[Rh2]
(9bb+10bb)
(9bb/10bb)
1
2
[CpERhCl2]2
4da
50
94
70:30
74:26
[3]
For selected examples using electronically tuned CpRh catalysts, see:
a) Y. Shibata, K. Tanaka, Angew. Chem. 2011, 123, 11109; Angew.
Chem. Int. Ed. 2011, 50, 10917; b) K. Morimoto, M. Itoh, K. Hirano, T.
Satoh, Y. Shibata, K. Tanaka, M. Miura, Angew. Chem. 2012, 124,
5455; Angew. Chem. Int. Ed. 2012, 51, 5359; c) M. Itoh, K. Hirano, T.
Satoh, Y. Shibata, K. Tanaka, M. Miura, J. Org. Chem. 2013, 78, 1365;
d) M. Fukui, Y. Hoshino, T. Satoh, M. Miura, K. Tanaka, Adv. Synth.
Catal. 2014, 356, 1638; e) Y. Hoshino, Y. Shibata, K. Tanaka, Adv.
Synth. Catal. 2014, 356, 1577; f) B. Zhou, Y. Yang, H. Tang, J. Du, H.
Feng, Y. Li, Org. Lett. 2014, 16, 3900; g) Y. Takahama, Y. Shibata, K.
Tanaka, Chem. Eur. J. 2015, 21, 9053; h) M. Fukui, Y. Shibata, Y.
Hoshino, H. Sugiyama, K. Teraoka, H. Uekusa, K. Noguchi, K. Tanaka,
Chem. Asian J. 2016, 11, 2260; i) E. Kudo, Y. Shibata, M. Yamazaki, K.
Masutomi, Y. Miyauchi, M. Fukui, H. Sugiyama, H. Uekusa, T. Satoh, M.
Miura, K. Tanaka, Chem. Eur. J. 2016, 22, 14190; j) Y. Shibata, E.
Kudo, H. Sugiyama, H. Uekusa, K. Tanaka, Organometallics 2016, 35,
1547; k) Y. Takahama, Y. Shibata, K. Tanaka, Org. Lett. 2016, 18,
2934; l) S. Y. Hong, J. Jeong, S. Chang, Angew. Chem. 2017, 129,
2448; Angew. Chem. Int. Ed. 2017, 56, 2408; m) S. Yoshizaki, Y.
Shibata, K. Tanaka, Angew. Chem. 2017, 129, 3644; Angew. Chem. Int.
Ed. 2017, 56, 3590.
3
4db
92
71:29
4
6bb (4bb)
6bb
40 (63)
67
90:10 (92:8)
92:8
5[c]
6[c,d]
6bb
93
92:8
[a] [Rh2] (0.0050 mmol), AgSbF6 (0.020 mmol), Cu(OAc)2•H2O (0.040 mmol),
7b (0.200 mmol), 8b (0.220 mmol), and CH2Cl2 (2.0 mL) were used. [b]
Isolated yield. [c] 20 mol % AgSbF6 was used. [d] For 72 h.
In conclusion, we have established that reductive
complexation of functionalized benzofulvenes, which are readily
prepared from commercially available indene and 2-
methylindene, with RhCl3•nH2O affords the corresponding
indenyl-rhodium(III) dichlorides bearing substituents at the 1- (H
or CO2Et), 2- (H or Me), and 3- [CH2Ph or CH2(2-MeOC6H4)]
positions. The thus obtained indenyl-rhodium(III) complexes with
one ethoxycarbonyl group showed higher thermal stability and
regioselectivity than our previously reported CpERhIII complex
toward the oxidative [3+2] annulation of acetanilides with internal
alkynes. Future works will focus on further modification of the
indenyl ligands and their application to the catalysis including the
C–H bond functionalization.
[4]
[5]
M. J. Calhorda, C. C. Romao, L. F. Veiros, Chem. - Eur. J. 2002, 8, 868.
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2017, 129, 2906; Angew. Chem. Int. Ed. 2017, 56, 2862. For selected
examples see: b) B. M. Trost, R. C. Livingston, J. Am. Chem. Soc.
1995, 117, 9586; c) C. E. Garrett, G. C. Fu, J. Org. Chem. 1998, 63,
1370; d) Y. Yamamoto, H. Kitahara, R. Ogawa, H. Kawaguchi, K.
Tatsumi, K. Itoh, J. Am. Chem. Soc. 2000, 122, 4310; e) B. M. Trost, R.
C. Livingston, J. Am. Chem. Soc. 2008, 130, 11970.
Acknowledgements
This work was supported partly by ACT-C (No.
JPMJCR1122YR) from JST (Japan) and Grants-in-Aid for
Scientific Research (No. JP26102004), Research Activity Start-
up (No. 15H06201), and Young Scientists (No. 17K14481) from
JSPS (Japan). We thank Umicore for generous support in
supplying RhCl3•nH2O.
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N. Semakul, K. E. Jackson, R. S. Paton, T. Rovis, Chem. Sci. 2017, 8,
1015.
As a stoichiometric reaction, the highly stereoselective C–H bond
cleavage with a sulfinyl-substituted indenyl-rhodium(III) complex was
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G. Smits, B. Audic, M. D. Wodrich, C. Corminboeuf, N. Cramer, Chem.
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10.1002/asia.201701716
Chemistry - An Asian Journal
COMMUNICATION
[9]
J. Honzíček, J. Vinklarek, Z. Padělková, L. Šebestová, K. Foltánová, M.
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[14] Their values were significantly larger than the values of
Cp*RhCl2(PPh3) and CpERhCl2(PPh3) (11) complexes. For the slippage
parameters (Δ) of the Cp*RhCl2(PPh3) complex, see: Y.-F. Lau, C.-M.
Chan, Z. Zhou, W.-Y. Yu, Org. Biomol. Chem. 2016, 14, 6821. For that
of the complex 11, see the supporting information
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10.1002/asia.201701716
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COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
COMMUNICATION
H
O
H
R3
R2
Jyunichi Terasawa, Yu Shibata,* Yuki
Kimura, Ken Tanaka*
Sterically and
H
R3
R3 Electronically Tuned
Indenyl-Rhodium(III)
Complexes
RhCl3
EtOH
R2
R1
R2
Rh
Cl
Cl
R1
R1
n
R5
R5
R6
R6
+
Ac
R4
N
H
Page No. – Page No.
cat. AgI+/CuII
R4
N
Ac
Synthesis of Functionalized (η5-
Indenyl)rhodium(III) Complexes and
Their Application to C–H Bond
Functionalization
high yield and regioselectivity
It has been established that reductive complexation of functionalized
benzofulvenes, prepared from commercially available indene derivatives, with
RhCl3 in ethanol affords the corresponding indenyl-rhodium(III) dichlorides with
various combination of substituents. The thus obtained indenyl-rhodium(III)
complexes with one ethoxycarbonyl group showed high thermal stability and
regioselectivity toward the oxidative [3+2] annulation of acetanilides with alkynes.
This article is protected by copyright. All rights reserved.