Chiral Cyclopentadienyl Cobalt(III) Complexes Enable Highly Enantioselective 3d-Metal-Catalyzed C-H Functionalizations

Article abstract of DOI:10.1021/jacs.9b02569

The synthesis of a set of cobalt(III)-complexes equipped with trisubstituted chiral cyclopentadienyl ligands is reported, and their steric and electronic parameters are mapped. The application potential of these complexes for asymmetric C-H functionalizations with 3d-metals is shown by the synthesis of dihydroisoquinolones from N-chlorobenzamides with a broad range of alkenes. The transformation proceeds with excellent enantioselectivities of up to 99.5:0.5 er and high regioselectivities. The observed values outperform the best rhodium(III)-based methods for this reaction type. Moreover, challenging substrates such as alkyl alkenes also react with high regio- and enantioselectivities.

Full text of DOI:10.1021/jacs.9b02569

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Communication
Chiral Cyclopentadienyl Cobalt(III) Complexes Enable Highly
Enantioselective 3d-Metal-Catalyzed C-H Functionalizations
Kristers Ozols, Yun-Suk Jang, and Nicolai Cramer
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 22 Mar 2019
Downloaded from http://pubs.acs.org on March 22, 2019
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Chiral Cyclopentadienyl Cobalt(III) Complexes Enable Highly
Enantioselective 3d-Metal-Catalyzed C-H Functionalizations
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Kristers Ozols, Yun-Suk Jang and Nicolai Cramer*
Laboratory of Asymmetric Catalysis and Synthesis, Institute of Chemical Sciences and Engineering, Ecole Polytechnique
Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
Supporting Information Placeholder
for corresponding tasks with cobalt(III) remains elusive. One might
speculate that this void is linked to a low reactivity and unknown
stability of CpxCoIII species. Complementary low-valent chiral
indenyl CoI complexes have been reported in 2004 for asymmetric
[2+2+2]-cyclotrimerizations.16 Herein, we report a trisubstituted
chiral CpxCoIII complex and show its superior performance for the
asymmetric C-H bond functionalization of N-chlorobenzamides
providing access to a broad range of dihydroisoquinolones in
excellent enantioselectivities.
ABSTRACT: The synthesis of a set of cobalt(III)-complexes
equipped with trisubstituted chiral cyclopentadienyl ligands is
reported and their steric and electronic parameters are mapped. The
application potential of these complexes for asymmetric C-H
functionalizations with 3d-metals is shown by the synthesis of
dihydroisoquinolones from N-chlorobenzamides with a broad range
of alkenes. The transformation proceeds with excellent
enantioselectivities of up to 99.5:0.5 er and high regioselectivities.
The observed values outperform the best rhodium(III)-based
methods for this reaction type. Moreover, challenging substrates
such as alkyl alkenes also react with high regio- and
enantioselectivities.
The cobalt(III) complexes were designed based upon our robust Cpx
backbones14b,14f and one additional variable substitution on the Cp
core14c,17 (Scheme 1). In contrast to the complexation with precious
metals,10,14a,15a-b the targeted complexes Co1-Co7 were obtained by
simply mixing CpxH with Co2CO8, followed by oxidation with I2.18
To boost the yields with respect to the Cpx-ligands, one equivalent of
Co2CO8 under a CO atmosphere was employed, significantly
improving the previous procedure (see SI). All CoIII complexes are
air- and moisture-stable solids and voluntarely crystallize to provide
important structural information.
The rise of catalytic C-H functionalization has contributed to
substantial changes in synthesis design and increases in synthetic
efficiency.1 Besides advances in chemo- and regioselectivity,2
asymmetric reactions have been devised.3 Most frequently, the
underlying are catalyst systems precious-metal complexes and
specifically tailored chiral ligands.4 In recent years, a shift to more
abundant 3d-metals as C-H functionalization catalysts is occuring.5
While largely fueled by the price argument, it also creates new
reactivity opportunities. 3d-Metal complexes often follow other
mechanisms and offer complementary transformations and
selectivities with respect to their heavier noble congeners.6 However,
enantioselective C-H functionalizations with abundant 3d-metals
remain a highly challenging and underdeveloped research area.5,7
Since the seminal work of Kanai/Matsunaga,8 Cp*CoIII-catalyzed
transformations emerged as a very versatile tool to complement
Cp*RhIII processes.6,9 Despite the availability of chiral Cpx-ligand
bound CoIII complexes,10 no application in asymmetric catalysis has
been reported. Very recently, Ackermann reported an
enantioselective indole alkylation with up to 93:7 er, using the
achiral Cp*CoIII complex in conjunction with a chiral carboxylic
acid, responsible for the enantioselective protonation.11
Independently, Matsunaga/Yoshino disclosed an asymmetric
thioamide-directed amidation with a bulky achiral Cp*CoIII catalyst,
again together with a chiral carboxylic acid responsible for the
enantiodetermining C-H activation with up to 94:6 er.12 The
seemingly most logical and straightforward strategy of using chiral
Cpx ligands13,14 that have a proven performance with other metals15
Scheme 1: Synthesis of the chiral CpxCoIII complexes.
R
Co2(CO)8, 1 atm. CO
CH2Cl2, 40 °C, 6 h
*
R
*
Co
then I2, Et2O
I
OC
CpxH
I
Co
1
2
3
4
Co2
Co3
(91 %, R =OMe, R =R =R =H)
Ph
Ph
1
2
3
4
R1
R1
R3
(75 %, R =OiPr, R =R =R =H)
1
2
3
4
Co4
Co5
Co6
Co7
(44 %, R =OMe, R =R =R =Me)
R2
1
3
2
4
Co
(22 %, R =OMe, R =TMS, R =R =H)
R4
I
OC
1
2
3
4
(41 %, R =OMe, R =iPr, R =R =H)
I
Co
1
2
3
4
(80 %, R =OMe, R =tBu, R =R =H)
Co1
(42 %)
OC
I
I
The synthesized CoIII complexes were exploited as catalysts for
enantioselective C-H functionalizations of chlorobenzamides to
provide dihydroisoquinolones. Besides the synthetic relevance of
them,19 this reaction type became a benchmark transformation for
chiral CpRhIII-catalysts.14a,14d,14g,14h,17 Moreover, it is reported with
achiral Cp*Co-catalysts20 allowing to collect valuable data on
reactivity/selectivity differences between CpxCo and Cp*Co, as well
as between CpxCo and CpxRh complexes. N-Chlorobenzamide (1a)
and styrene (2a) were selected as model substrates (Table 1). While
exposure to Co1 complex did not yield desired product 3aa, Co2
with binaphthyl-derived Cpx-ligand provided 3aa in a modest yield
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and poor enantioselectivity of 44:56 (entry 2). Co3 having larger R1 selectively at the least hindered ortho-C-H group, giving 3da as a
sidewalls (iPrO instead of MeO) resulted in 31.5:68.5 er (entry 3). A single regioisomer (entry 4).
1
2
3
4
5
6
7
8
switch to Co4 with
a
penta-substituted Cpx reversed the
Table 2. Scope of the CpxCoIII-catalyzed functionalization
enantioselectivity to 66:34 er (entry 4). Complex Co5 with a
trisubstituted Cp-ring (R3=TMS) slightly improved the selectivity to
79:21 er (entry 5). Notably, Co6, having a isopropyl group as third
substituent, gave superior reactivity and a massively improved
enantioselectivity of 97:3 er (entry 6). Increasing the size of R2 to a
tert-butyl group (Co7) lowered the reactivity but simultaneously
boosted the selectivity even further (entry 7), giving 3aa in 99.5:0.5
er. Such an impressive selectivity level is uncommon for asymmetric
C-H functionalizations. For comparison, the highest selectivity for
3aa obtained by RhIII-catalysis is 96:4 er.17 Replacing TFE by HFIP
and KOAc by CsOPiv substantially improved the reactivity, giving
3aa in 90% yield and maintaining the outstanding enantioselectivity
(entries 7-10). Lowering the catalyst loading to 5 mol% had no
influence on the reaction performance (entry 11). In the absence of
Co7, chloroamide 1a is completely consumed by Hofmann-
rearrangement leading to hexafluoropropan-2-yl phenylcarbamate
(entry 12). Notably, silver triflate is not mandatory for the generation
of the active catalyst (entry 13), although its omission slightly
reduces the yield.
with respect to N-chlorobenzamides and styrenesa
O
O
Co7
5.0 mol%
Cl
10 mol% AgOTf, CsOPiv
N
NH
Ar
+
H
Ar
HFIP, 40 °C, 18 h
R
R
3xy
1x
2y
R
H
% yieldb
87
erc
99.5:0.5
9
Entry 3xy
Ar
Ph
10
11
12
13
14
15
16
17
18
19
20
21
22
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34
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42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
2d
3aa
3ba
3ca
3da
3ea
3fa
3ga
3ab
3ac
3ad
3ae
3af
61 99.0:1.0
63 98.5:1.5
73 99.5:0.5
89 98.5:1.5
82 99.5:0.5
87 99.5:0.5
4-OMe
4-Me
3-Me
4-Br
4-Cl
4-F
H
Ph
3
Ph
4
Ph
5
Ph
6
Ph
7
Ph
87
81
88
88
85
8
4-MeO-C6H4
4-tBu-C6H4
4-Me-C6H4
3-Me-C6H4
4-F-C6H4
99.5:0.5
98.0:2.0
99.5:0.5
99.5:0.5
99.5:0.5
9
H
Table 1. Screen of CpxCoIII complexes and optimizationa
10
11
12
H
O
O
Co
10 mol%
H
Cl
20 mol% AgOTf, 1.2 equiv. base
NH
Ph
N
Ph
2a
H
solvent, 40 °C, 18 h
H
3aa
1a
a
0.20 mmol 1x, 0.30 mmol 2y, 10 µmol Co7, 20 µmol AgOTf,
Entry Co
solvent base
% conv.b % yieldb
erc
-
b
0.24 mmol CsOPiv, 0.10 M in HFIP at 40 °C for 18 h; isolated
yield; c determined by chiral HPLC; d 20 µmol Co7, 40 µmol AgOTf.
1
2
3
4
5
6
7
8
9
Co1 TFE
Co2 TFE
Co3 TFE
Co4 TFE
Co5 TFE
Co6 TFE
Co7 TFE
Co7 HFIP
Co7 HFIP
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOPiv
CsOPiv
CsOPiv
CsOPiv
CsOPiv
49
70
-
27
28
29
33
51
26
51
88
90
96
0
44: 56
Next, more challenging olefin acceptors that are problematic for
CpxRhIII catalysis were tested (Scheme 2). These suffer from at least
one shortcoming such as poor enantioselectivity,14a,14g limited regio-
control,21 as well as low reactivity and scope limitations.14g,14h
Pleasingly, acrylates reacted very well. For tert-butyl acrylate,
product 3ah was generated in 75% yield and 99:1 er. Hindered acryl
amide 2i reacted and yielded 3ai in 99.5:0.5 er. Alternatively, less
congested Co6 provides an increased yield. Noteworthy, vinyl
phthalimide as an example for a hetero atom-substituted olefin23
provides access to 3aj with an aminal stereogenic center as single
regioisomer in 99:1 er. Simple olefins such as 1-hexene and 1-octene
yield single regioisomers of 3ak and 3al with 95.5:4.5 er. These
olefins react under RhIII-catalysis in a notoriously low regio- and
enantioselectivity. Noteworthy, bulky achiral CpRhIII catalysts favor
the opposite regioisomer.21,22 The introduction of an oxygen atom in
coordination distance influenced the enantioselectivity (3am) as well
as the regioselectivity (3an). Allyl acetate delivered
dihydroisoquinolone product 3ao as a single regioisomer in 96:4 er.
A linear conjugated diene (2p), as well as myrcene (2q) were suitable
substrates giving excellent levels of enantioselectivity. Myrcene (2q)
did not react under Cp*RhIII catalysis.22 Cyclohexadiene and
cyclooctadiene were competent, albeit with attenuated reactivity and
selectivity.The excellent enantioselectivity was restored in strained
bicyclic systems to afford products 3at and 3au as single
diastereomers.
58
31.5:68.5
66:34
70
70
79:21
80
97:3
72
99.5:0.5
99.5:0.5
99.5:0.5
99.5:0.5
99.5:0.5
-
100
100
100
100
100
100
10 Co7 HFIP
11d Co7 HFIP
12d
13d,e Co7 HFIP
-
HFIP
73
99.5:0.5
a
50 μmol 1a, 75 μmol 2a, 5.0 μmol Co, 10 μmol AgOTf, 60 μmol
base, 0.10 M at 40 °C for 18 h; determined by 1H-NMR;
b
c
d
e
determined by chiral HPLC; 2.5 μmol Co, 5.0 μmol AgOTf; no
AgOTf.
With the optimized conditions, the scope of the reaction was
investigated. The initial focus was set on variations of the
chloroamide and the styrene acceptor. Both electron-deficient and
electron-rich aryl groups on both reactants reliably delivered desired
products 3. Without any exception, the outstanding
enantioselectivities were maintained and were largely independent of
the substituents on both aryl groups. The parasitic Hofmann
rearrangement is slightly more pronounced with N-chlorobenzamides
bearing electron-donating substituents such as 1b-1d, causing a slight
reduction in yield (entries 2-4). The functionalization proceeded
2
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Scheme 2: Scope for miscellaneous olefinsa
Table 3. Comparison of key analytical data of selected
cyclopentadienyl Co(CO)I2 complexesa
1
2
3
4
5
6
7
8
O
O
Cl
Co7
, 10 mol% AgOTf
5 mol%
N
R
NH
dihedral
angle θ
+
H
[Co]
ν(CO) (cm-1)a Co-CO (Å) Co-Cp (Å)
CsOPiv, HFIP, 40 °C, 18 h
R'
R
2y
1a
R'
3ay
-
CpCo(CO)I2 2060
1.76b
1.79
1.79
1.79
1.80
1.86
1.68b
1.69
1.70
1.71
1.72
1.72
O
O
O
O
69.6
70.0
76.5
72.0
-
Co2
Co6
Co7
Co4
2061
2054
2054
2047
NH
O
NH
NH
NH
O
N
O
O
N
O
OMe
3ai
OtBu
3agb
9
44 % 99.5:0.5 erb
74 % 93:7 erc,d
O
3ah
3aj
68 %, 91:9 er
75 %, 99:1 er
68 %, 99:1 er
10
11
12
13
14
15
O
Cp*Co(CO)I2 2026
NH OH
O
O
O
a ATR measurement; b reported values.24
3anb,e
49 %, 98:2 er
NH
NH
NH OBn
O
Me
Me
( )5
( )3
NH
3amb
3ak
3al
3an'b,e
21 %, 78:22 er
86 %, 95.5:4.5 er
74 %, 94.5:5.5 er 78 %, 92.5:7.5 er
OMe
=69.6°
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
OH
O
O
O
OMe
Co
NH
NH
NH
greater -angle
opens backwall
OC
I
OAc
Co2
Ph
Me
Me
( )3
I
3ao
77 %, 96:4 er
3aqb,d,f
73 %, 99.5:0.5 er
3ap
76 %, 98.5:1.5 er
OMe
OMe
Me
Me
Me
O
O
O
=76.5°
O
NH
H
NH
NH
H
Co
NH
H
H
O
I
I
Co7
O
H
N
H
OC
H
OPh
H
CO ligand position swapped
3ar
3at
3au
85 %, 96.5:3.5 er
3as
Figure 1. Comparison of Co2 (grey C-atoms) and Co7 (black C-
atoms) by X-ray crystal structure overlay.
74 %, 86.5:13.5 er
53 %, 87.5:12.5 er
91 %, 98:2 er
a
0.20 mmol 1a, 0.30 mmol 2y, 10 µmol Co7, 20 µmol AgOTf, 0.24
b
mmol CsOPiv in HFIP (0.10 M) at 40 °C for 18 h; 20 µmol Co7,
To foster further understanding of the ligand geometry/selectivity
relationship, steric maps of the binding pocket were generated with
the SambVca 2 tool (Figure 2).27 The buried volume increase from
48.2% VBur of Co2 (disubstituted Cpx) to 52.0% VBur of Co4
(pentasubstituted Cpx). Co6 and Co7 (both trisubsituted Cpx) range
within 50.3% and 50.2% VBur. The steric maps along the Z-axis (Co-
Cp) provide information of the chiral binding pockets around the
metal. Comparing the steric heatmaps of Co2 and Co4 to Co6 and
Co7, the common feature is the naphthyl backbone, the
„backwall“,13a generating significant bulk in the SW quadrant. For
Co2 and Co4, the remaining three quadrants are rather indifferent in
their sterics. In contrast, the map for Co7 reveals the massive bulk of
the tert-butyl group. This diminishes access to the southern
hemisphere, thus making the nothern trajectory most accessible. The
present enantioselection falls into the double facial selectivity
category. The backwall is responsible for the orientation and
alignment of the metallocycle. The tert-butyl group then forces a
specific orientation of the olefin, minimizing the steric interaction.
The poor enantioselectivity of Co2 can be attributed to a lack of this
guiding interaction, leading to several possible approaches of the
olefin.
40 µmol AgOTf; c 20 µmol Co6, 40 µmol AgOTf d with 0.60 mmol
alkene; 0.36 mmol CsOPiv; f with 0.10 mmol Cs2CO3 additive in
e
HFIP/DCE 2:1.
To gain insights into the dramatic performance difference between
the cobalt complexes, X-ray and IR data were obtained for Co2, Co4,
18c
Co6, Co7 along with CpCo(CO)I224 and Cp*Co(CO)I2 (Table 3).
Despite its frequent use, no X-ray crystal structure data was available
for Cp*Co(CO)I2. The CO-stretching frequencies decrease with the
number of donating alkyl substituents on the Cp.25 The best
performing tri-substituted Cpx are between Cp (2060 cm-1) and Cp*
(2026 cm-1). The Co-C bond length increases from 1.76 Å in
CpCo(CO)I2 to 1.80 Å in Co4 (respective 1.86 Å in Cp*Co(CO)I2).
The distance of the cobalt atom from the Cp-plane increases
incrementally with the number and size of the Cp substituents and
ranges from 1.68-1.72 Å. An important difference between the
complexes is the influence of the remote substituents on the dihedral
angle θ of the biaryl backbone of the Cpx. For chiral biaryl
phosphines, θ is well known for its influence on the chiral
discrimination of catalysts.26 The consequences of the change in the
dihedral angle θ for the Cpx complexes can be visualized
straightforwardly by an overlay of the X-ray crystal structure of Co2
and Co7 (Figure 1). A larger dihedral angle slightly opens up the
methoxy naphthyl portion of the pocket. A noteworthy feature setting
the most selective complex Co7 apart from the others, is the
orientation of the CO ligand with respect to the chiral Cpx backbone.
For Co2, Co4 and even Co6, the direction of CO bond is virtually
completely parallel with the plane of the lower naphthyl ring. In
contrast, the CO ligand of Co7 swapped position with an iodide,
indicating the significantly modulated chiral environment of this
particular Cpx ligand.
3
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ASSOCIATED CONTENT
Page 4 of 6
Co2
Co4
1
2
3
4
Supporting Information
Synthetic procedures, characterization data for all new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
5
6
7
8
9
AUTHOR INFORMATION
Corresponding Author
nicolai.cramer@epfl.ch
48.2 %VBur
N
52.0 %VBur
N
10
11
12
13
14
15
16
17
18
19
20
21
22
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60
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
E
E
W
W
Co
S
Co
S
This work is supported by the SNF (no 157741). We thank Dr. R.
Scopelliti and Dr. F. Fadaei Tirani for the X-ray crystallographic
analysis.
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Co6
Co7
50.3 %VBur
N
50.2 %VBur
N
E
E
W
Co
S
W
Co
S
(8) Yoshino, T.; Ikemoto, H.; Matsunaga, S.; Kanai, M. A Cationic High-
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[Å]
-3.00 -2.25 -1.50 -0.75 0.00 0.75 1.50 2.25 3.00
Figure 2: X-ray crystal structures of Co2, Co4, Co628 and Co7,
buried volumes and corresponding steric maps.27 Bondi radii
scaled by 1.17, sphere radius: 3.5 Å, mesh spacing: 0.1 Å.
(9) For reviews, see: (a) Loginov, D. A.; Shul'pina, L. S.; Muratov, D. V.;
Shul'pin, G. B. Cyclopentadienyl cobalt(III) complexes: Synthetic and
catalytic chemistry Coord. Chem. Rev. 2019, 387, 1; (b) Yoshino, T.;
Matsunaga, S. Cobalt-Catalyzed C(sp3)−H Functionalization Reactions
Asian J. Org. Chem. 2018, 7, 1193; (c) Prakash, S.; Kuppusamy, R.; Cheng,
C.-H. Cobalt-Catalyzed Annulation Reactions via C−H Bond Activation
ChemCatChem 2018, 10, 683; (d) Usman, M.; Ren, Z.-H.; Wang, Y.-Y.;
Guan, Z.-H. Recent Developments in Cobalt Catalyzed Carbon–Carbon and
Carbon–Heteroatom Bond Formation via C–H Bond Functionalization
Synthesis 2017, 49, 1419; (e) Wang, S.; Chen, S.-Y.; Yu, X.-Q. C–H
Functionalization by high-valent Cp*Co(III) catalysis Chem. Commun.
2017, 53, 3165; (f) Pototschnig, G.; Maulide, N.; Schnürch, M. Direct
Functionalization of C−H Bonds by Iron, Nickel, and Cobalt Catalysis
Chem. − Eur. J. 2017, 23, 9206; (g) Chirila, P. G.; Whiteoak, C. J. Recent
advances using [Cp*Co(CO)I2] catalysts as a powerful tool for C–H
functionalisation Dalton Trans. 2017, 46, 9721; (h) Moselage, M.; Li, J.;
Ackermann, L. Cobalt-Catalyzed C–H Activation ACS Catal. 2016, 6, 498;
(i) Wei, D.; Zhu, X.; Niu, J.-L.; Song, M.-P. High-Valent-Cobalt-Catalyzed
C−H Functionalization Based on Concerted Metalation−Deprotonation and
In summary, we disclosed CoIII-complexes equipped with
trisubstituted chiral cyclopentadienyl ligands. Their catalytic
potential for asymmetric C-H functionalizations was showcased with
the synthesis of dihydroisoquinolones from N-chlorobenzamides and
a
large set of alkenes. Excellent enantioselectivities and
regioselectivities were obtained, outperforming the corresponding
RhIII-catalyzed processes. Particularly noteworthy is the observed
opposite regioselectivity of cobalt vs rhodium complexes alkyl
alkenes. This makes the CpxCo complexes not just a cheaper and
more abundant version of rhodium but a truly unique set of catalysts
with complementary behavior and a bright future potential. Enlarging
the application scope of this CpxCoIII complex class with further
valuable transformations is currently being investigated in our
laboratory.
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Single-Electron-Transfer Mechanisms ChemCatChem 2016, 8, 1242; (j)
Gao, K.; Yoshikai, N. Low-Valent Cobalt Catalysis: New Opportunities for
C–H Functionalization Acc. Chem. Res. 2014, 47, 1208.
(17) Audic, B.; Wodrich, M. D.; Cramer, N. Mild complexation protocol for
chiral CpxRh and Ir complexes suitable for in situ catalysis Chem. Sci. 2019,
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(10) Smits, G.; Audic, B.; Wodrich, M. D.; Corminboeuf, C.; Cramer, N. A
β-Carbon elimination strategy for convenient in situ access to
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(11) Pesciaioli, F.; Dhawa, U.; Oliveira, J. C. A.; Yin, R.; John, M.;
Ackermann, L. Enantioselective Cobalt(III)-Catalyzed C−H Activation
Enabled by Chiral Carboxylic Acid Cooperation Angew. Chem., Int. Ed.
2018, 57, 15425.
(12) (a) Fukagawa, S.; Kato, Y.; Tanaka, R.; Kojima, M.; Yoshino, T.;
Matsunaga, S. Enantioselective C(sp3)–H Amidation of Thioamides
Catalyzed by a CobaltIII/Chiral Carboxylic Acid Hybrid System Angew.
Chem., Int. Ed. 2019, 58, 1153. During manuscript drafting a related report
appeared: (b) Liu, Y.-H.; Li, P.-X.; Yao, Q.-J.; Zhang, Z.-Z.; Huang, D.-Y.;
Le, M. D.; Song, H.; Liu, L.; Shi, B.-F. Cp*Co(III)/MPAA-Catalyzed
Enantioselective Amidation of Ferrocenes Directed by Thioamides under
Mild Conditions Org. Lett. 2019, 21, 1895.
(13) For reviews, see: (a) Newton, C. G.; Kossler, D.; Cramer, N.
Asymmetric Catalysis Powered by Chiral Cyclopentadienyl Ligands J. Am.
Chem. Soc. 2016, 138, 3935; (b) Ye, B.; Cramer, N. Chiral
Cyclopentadienyls: Enabling Ligands for Asymmetric Rh(III)-Catalyzed C–
H Functionalizations Acc. Chem. Res. 2015, 48, 1308.
(18) (a) Heck, R. F. Dihalocarbonylcyclopentadienylcobalt Complexes
Inorg. Chem. 1965, 4, 855; (b) King, R. B. Organometallic Chemistry of the
Transition Metals. XI. Some New Cyclopentadienyl Derivatives of Cobalt
and Rhodium Inorg. Chem. 1966, 5, 82; (c) Sun, B.; Yoshino, T.;
Matsunaga,
S.;
Kanai,
M.
Air‐Stable
Carbonyl(pentamethylcyclopentadienyl)cobalt Diiodide Complex as
a
Precursor for Cationic (Pentamethylcyclopentadienyl)cobalt(III) Catalysis:
Application for Directed C-2 Selective C–H Amidation of Indoles Adv.
Synth. Catal. 2014, 356, 1491.
(19) (a) Amer, M. M.; Carrasco, A. C.; Leonard, D. J.; Ward, J. W.;
Clayden, J. Substituted Dihydroisoquinolinones by Iodide-Promoted
Cyclocarbonylation of Aromatic α-Amino Acids Org. Lett. 2018, 20, 7977;
(b) Palmer, N.; Peakman, T. M.; Norton, D.; Rees, D. C. Design and
synthesis of dihydroisoquinolones for fragment-based drug discovery
(FBDD) Org. Biomol. Chem. 2016, 14, 1599.
(20) (a) Yu, X.; Chen, K.; Wang, Q.; Zhang, W.; Zhu, J. Co(III)-Catalyzed
N-chloroamide-directed C–H activation for 3,4-dihydroisoquinolone
synthesis Org. Chem. Front. 2018, 5, 994; (b) Muniraj, N.; Prabhu, K. R.
Cobalt(III)-Catalyzed [4 + 2] Annulation of N-Chlorobenzamides with
Maleimides Org. Lett. 2019, 21, 1068; (c) Yu, X.; Chen, K.; Guo, S.; Shi, P.;
Song, C.; Zhu, J. Direct Access to Cobaltacycles via C–H Activation: N-
Chloroamide-Enabled Room-Temperature Synthesis of Heterocycles Org.
Lett. 2017, 19, 5348.
(21) (a) Hyster, T. K.; Dalton, D. M.; Rovis, T. Correction: Ligand design
for Rh(III)-catalyzed C–H activation: an unsymmetrical cyclopentadienyl
group enables a regioselective synthesis of dihydroisoquinolones Chem. Sci.
2018, 9, 8024; (b) Hyster, T. K.; Dalton, D. M.; Rovis, T. Ligand design for
Rh(III)-catalyzed C–H activation: an unsymmetrical cyclopentadienyl group
enables a regioselective synthesis of dihydroisoquinolones Chem. Sci. 2015,
6, 254.
(22) Trifonova, E. A.; Ankudinov, N. M.; Kozlov, M. V.; Sharipov, M. Y.;
Nelyubina, Y. V.; Perekalin, D. S. Rhodium(III) Complex with a Bulky
Cyclopentadienyl Ligand as a Catalyst for Regioselective Synthesis of
Dihydroisoquinolones through C−H Activation of Arylhydroxamic Acids
Chem. − Eur. J. 2018, 24, 16570.
(23) (a) Webb, N. J.; Marsden, S. P.; Raw, S. A. Rhodium(III)-Catalyzed C–
H Activation/Annulation with Vinyl Esters as an Acetylene Equivalent Org.
Lett. 2014, 16, 4718; (b) Sun, R.; Yang, X.; Chen, X.; Zhang, C.; Zhao, X.;
Wang, X.; Zheng, X.; Yuan, M.; Fu, H.; Li, R.; Chen, H. Rh(III)-Catalyzed
[4 + 2] Self-Annulation of N-Vinylarylamides Org. Lett. 2018, 20, 6755.
(24) Avilés, T.; Dinis, A.; Gonçalves, J. O.; Félix, V.; Calhorda, M. J.;
Prazeres, Â.; Drew, M. G. B.; Alves, H.; Henriques, R. T.; da Gama, V.;
Zanello, P.; Fontani, M. Synthesis, X-ray structures, electrochemistry,
magnetic properties, and theoretical studies of the novel monomeric
[CoI2(dppfO2)] and polymeric chain [CoI2(μ-dppfO2)n] J. Chem. Soc.,
Dalton Trans. 2002, 4595.
(25) Piou, T.; Romanov-Michailidis, F.; Romanova-Michaelides, M.;
Jackson, K. E.; Semakul, N.; Taggart, T. D.; Newell, B. S.; Rithner, C. D.;
Paton, R. S.; Rovis, T. Correlating Reactivity and Selectivity to
Cyclopentadienyl Ligand Properties in Rh(III)-Catalyzed C–H Activation
Reactions: An Experimental and Computational Study J. Am. Chem. Soc.
2017, 139, 1296.
(26) (a) Jeulin, S.; de Paule, S. D.; Ratovelomanana-Vidal, V.; Genêt, J.-P.;
Champion, N.; Dellis, P. Chiral biphenyl diphosphines for asymmetric
catalysis: Stereoelectronic design and industrial perspectives Proc. Natl.
Acad. Sci. U. S. A. 2004, 101, 5799; (b) Dierkes, P.; W. N. M. van Leeuwen,
P. The bite angle makes the difference: a practical ligand parameter for
diphosphine ligands J. Chem. Soc., Dalton Trans. 1999, 1519.
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(14) For seminal reports of Cpx ligand families, see: (a) Trifonova, E. A.;
Ankudinov, N. M.; Mikhaylov, A. A.; Chusov, D. A.; Nelyubina, Y. V.;
Perekalin, D. S. A Planar-Chiral Rhodium(III) Catalyst with a Sterically
Demanding Cyclopentadienyl Ligand and Its Application in the
Enantioselective Synthesis of Dihydroisoquinolones Angew. Chem., Int. Ed.
2018, 57, 7714; (b) Wang, S.-G.; Park, S. H.; Cramer, N. A Readily
Accessible Class of Chiral Cp Ligands and their Application in RuII-
Catalyzed Enantioselective Syntheses of Dihydrobenzoindoles Angew.
Chem., Int. Ed. 2018, 57, 5459; (c) Sun, Y.; Cramer, N. Tailored
trisubstituted chiral CpxRhIII catalysts for kinetic resolutions of phosphinic
amides Chem. Sci. 2018, 9, 2981; (d) Jia, Z.-J.; Merten, C.; Gontla, R.;
Daniliuc, C. G.; Antonchick, A. P.; Waldmann, H. General Enantioselective
C−H Activation with Efficiently Tunable Cyclopentadienyl Ligands Angew.
Chem., Int. Ed. 2017, 56, 2429; (e) Zheng, J.; Cui, W.-J.; Zheng, C.; You,
S.-L. Synthesis and Application of Chiral Spiro Cp Ligands in Rhodium-
Catalyzed Asymmetric Oxidative Coupling of Biaryl Compounds with
Alkenes J. Am. Chem. Soc. 2016, 138, 5242; (f) Ye, B.; Cramer, N. A
Tunable Class of Chiral Cp Ligands for Enantioselective Rhodium(III)-
Catalyzed C–H Allylations of Benzamides J. Am. Chem. Soc. 2013, 135,
636; (g) Ye, B.; Cramer, N. Chiral Cyclopentadienyl Ligands as
Stereocontrolling Element in Asymmetric C–H Functionalization Science
2012, 338, 504; (h) Hyster, T. K.; Knörr, L.; Ward, T. R.; Rovis, T.
Biotinylated Rh(III) Complexes in Engineered Streptavidin for Accelerated
Asymmetric C–H Activation Science 2012, 338, 500.
(15) For seminal reports of catalytic enantioselective applications with
additional metals, see: with Ir (a) Dieckmann, M.; Jang, Y.-S.; Cramer, N.
Chiral Cyclopentadienyl Iridium(III) Complexes Promote Enantioselective
Cycloisomerizations Giving Fused Cyclopropanes Angew. Chem., Int. Ed.
2015, 54, 12149; with Ru (b) Kossler, D.; Cramer, N. Chiral Cationic
CpxRu(II) Complexes for Enantioselective Yne-Enone Cyclizations J. Am.
Chem. Soc. 2015, 137, 12478; with Fe (c) Gajewski, P.; Renom-Carrasco,
M.; Facchini, S. V.; Pignataro, L.; Lefort, L.; de Vries, J. G.; Ferraccioli, R.;
Piarulli,
U.;
Gennari,
C.
Synthesis
of
(R)-BINOL-Derived
(Cyclopentadienone)iron Complexes and Their Application in the Catalytic
Asymmetric Hydrogenation of Ketones Eur. J. Org. Chem. 2015, 2015,
5526; with rare-earth metals and Sc (d) Song, G.; O, W. W. N.; Hou, Z.
Enantioselective C–H Bond Addition of Pyridines to Alkenes Catalyzed by
Chiral Half-Sandwich Rare-Earth Complexes J. Am. Chem. Soc. 2014, 136,
12209; (e) Teng, H.-L.; Luo, Y.; Wang, B.; Zhang, L.; Nishiura, M.; Hou, Z.
Synthesis of Chiral Aminocyclopropanes by Rare-Earth-Metal-Catalyzed
Cyclopropene Hydroamination Angew. Chem., Int. Ed. 2016, 55, 15406.
(16) (a) Gutnov, A.; Heller, B.; Fischer, C.; Drexler, H.-J.; Spannenberg, A.;
Sundermann, B.; Sundermann, C. Cobalt(I)-Catalyzed Asymmetric [2+2+2]
Cycloaddition of Alkynes and Nitriles: Synthesis of Enantiomerically
Enriched Atropoisomers of 2-Arylpyridines Angew. Chem., Int. Ed. 2004,
43, 3795; (b) Gutnov, A.; Drexler, H.-J.; Spannenberg, A.; Oehme, G.;
Heller, B. Syntheses of Chiral Nonracemic Half-Sandwich Cobalt
Complexes with Menthyl-Derived Cyclopentadienyl, Indenyl, and Fluorenyl
Ligands Organometallics 2004, 23, 1002.
(27) (a) Poater, A.; Ragone, F.; Mariz, R.; Dorta, R.; Cavallo, L. Comparing
the Enantioselective Power of Steric and Electrostatic Effects in Transition-
Metal-Catalyzed Asymmetric Synthesis Chem. − Eur. J. 2010, 16, 14348;
(b) Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.; Scarano,
V.; Cavallo, L. SambVca: A Web Application for the Calculation of the
Buried Volume of N-Heterocyclic Carbene Ligands Eur. J. Inorg. Chem.
2009, 2009, 1759; (c) Poater, A.; Ragone, F.; Giudice, S.; Costabile, C.;
Dorta, R.; Nolan, S. P.; Cavallo, L. Thermodynamics of N-Heterocyclic
Carbene Dimerization: The Balance of Sterics and Electronics
Organometallics 2008, 27, 2679.
(28) The iPr group of Co6 may rotate free in solution and adopt a different
conformation than in the solid state.
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OMe
Me
Me
Me
OMe
O
Co
O
Cl
I
I
N
5 mol%
OC
6
H
NH
*
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*
+
10 mol% AgOTf
CsOPiv, HFIP, 40 °C, 18 h
R
R'
R
up to 96 % yield & up to 99.5:0.5 er
R'
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