Electro-Oxidative C-C Alkenylation by Rhodium(III) Catalysis

Article abstract of DOI:10.1021/jacs.8b13692

Electrochemical C-C activations were accomplished by expedient oxidative rhodium(III) catalysis. Thus, oxidative C-C alkenylations proved viable with the aid of electricity, avoiding the use of toxic and/or expensive transition-metal oxidants. The chelation-assisted C-C functionalizations proceeded with ample scope and excellent levels of chemo- and position selectivities within an organometallic C-C activation manifold. Detailed mechanistic studies provided support for a kinetically relevant C-C scission, and a well-defined organometallic rhodium(III) complex was identified as a catalytically competent intermediate. The electrochemical C-C functionalization was devoid of additional electrolytes, could be conducted on a gram scale, and provided position-selective access to densely 1,2,3-substituted arenes, which are not viable by C-H activation.

Full text of DOI:10.1021/jacs.8b13692

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Article
Electrooxidative C–C Alkenylation by Rhodium(III) Catalysis
Youai Qiu, Alexej Scheremetjew, and Lutz Ackermann
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b13692 • Publication Date (Web): 12 Jan 2019
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Electrooxidative C–C Alkenylation by Rhodium(III) Catalysis
Youai Qiu,† Alexej Scheremetjew,† and Lutz Ackermann*
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Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstrasse 2,
37077, Göttingen, Germany.
Supporting Information
ABSTRACT: Electrochemical C–C activations were accomplished by expedient oxidative rhodium(III) catalysis. Thus,
oxidative C–C alkenylations proved viable with the aid of electricity, avoiding the use of toxic and/or expensive transition
metal oxidants. The chelation-assisted C–C functionalizations proceeded with ample scope and excellent levels of chemo-
and position-selectivities within an organometallic C–C activation manifold. Detailed mechanistic studies provided
support for a kinetically-relevant C–C scission, and a well-defined organometallic rhodium(III) complex was identified as
catalytically competent intermediate. The electrochemical C–C functionalization was devoid of additional electrolytes,
could be conducted on gram scale, and provided position-selective access to densely-1,2,3-subtituted arenes, which are
not viable by C–H activation.
1.
INTRODUCTION
(d) and mechanistic insights into electrooxidative C–C
functionalizations, including detailed cyclovoltammetric
analysis. It is furthermore noteworthy that the C–C
activation strategy provided unique access to challenging
densely-1,2,3-trisubtituted arenes, which cannot be
prepared by any C–H functionalization method.
C–H activation has emerged as a powerful platform for
molecular sciences, with transformative applications to
inter alia medicinal chemistry, crop protection and
material sciences.1 In sharp contrast, methods for the
catalytic activation of strong C–C bonds continue to be
scarce,2 with great, yet largely untapped potential for
molecular assembly and late-stage diversification. In
recent years, considerable progress in C–C activation
catalysis has been realized by Murakami,3 Bower,4 Dong,5
and Shi,6 among others.7 Despite these major advances,
oxidative C–C activations continue to heavily depend
upon expensive and/or toxic transition metals as the
sacrificial oxidants, prominently featuring copper(II) and
silver(I). In the meantime, electrocatalysis has been
identified as an increasingly viable approach for
preventing stoichiometric redox-reagents in organic
synthesis.8 Hence, this approach has recently proven
instrumental for establishing alkene functionalizations,9
direct oxygenations,10 reductive and oxidative couplings,11
polymerizations,12 as well as C–H activations13 with
palladium,14 cobalt,15 ruthenium,16 rhodium,17 iridium,18
copper,19a and nickel19b complexes. In sharp contrast to
this very recent progress in electrochemical C–H
activation, organometallic C–C functionalizations by
electrocatalysis has thus far proven elusive. Within our
program on sustainable C–C activation,20 we have now
Scheme 1. Electrooxidative C–C functionalization
Electrochemical C–C Activation
H
rDG
O
Pt
rDG
RVC
R3
H
R2
O
R1
+
H2
+
R
R
+
Rh
R3
R1 R2
1
2
3
4
electrocatalytic C–C activation
rhodium catalysis
no Cu(II), or Ag(I)
mechanistic insights
electricity as green oxidant
2.
RESULTS AND DISCUSSION
Optimization Studies
We initiated our studies by exploring various reaction
conditions for the envisioned electrooxidative C–C
functionalization of tertiary benzylic alcohol 1a in a user-
friendly undivided cell set-up. Orienting experiments
indicated [Cp*RhCl2]2 as a viable catalyst, particularly in
combination with a platinum plate cathode and a
reticulated vitreous carbon (RVC) anode, along with
KOAc as additive in H2O at 100 °C (Scheme 2). To our
developed
the
first
electrochemically-enabled,
organometallic C–C activation, on which we report
herein. Notable features of our strategy include (a)
unprecedented electrooxidative C–C activations by
versatile rhodium(III) catalysis, (b) chemical oxidant-free
C–C alkenylations avoiding stoichiometric copper and
silver byproducts, (c) electricity as a user-friendly oxidant,
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delight, the desired C–C activation product 3aa was
Page 2 of 10
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obtained in 35% yield. To the best of our knowledge,
efficient electrooxidative C–C activation by transition
metal catalysis had, as of yet, not been reported.
Table 1. Optimization of rhodium-catalyzed
electrochemical C–C activationa
RVC
Pt
N
N
Scheme
electrochemical C–C activation
2.
Preliminary
observation
of
N
OH
Me
Me
N
catalyst (2.5 mol %)
H
+
Ph
Ph
additives, solvent
100 °C, 8 h
Me
Me
8
9
CCE at 4.0 mA
1a
2a
3aa
N
RVC
Pt
N
N
N
OH
[Cp*RhCl2]2 (2.5 mol %)
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Me
Me
Ph
+
Ph
KOAc, H2O
100 °C, 8 h,
CCE at 4.0 mA
Me
Me
Entry
catalyst
additive solvent
3aa (%)b
1a
2a
3aa
: 35%
1
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*IrCl2]2
[Ru]
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
K2CO3
NaOPiv
KPF6
H2O
35
10
18c
2
t-AmOH
TFE
Based on these exciting initial results, we further
interrogated the electrochemical C–C/C–H
functionalization regime (Table 1; Table S-1 in the
Supporting After considerable
Information).21
3
d
4
toluene
–
5
t-AmOH/H2O (3:1)
t-AmOH/H2O (3:1)
t-AmOH/H2O (1:1)
t-AmOH/H2O (7:1)
t-AmOH/H2O (3:1)
t-AmOH/H2O (3:1)
t-AmOH/H2O (3:1)
t-AmOH/H2O (3:1)
t-AmOH/H2O (3:1)
t-AmOH/H2O (3:1)
t-AmOH/H2O (3:1)
82
9e
experimentation, we were pleased to find that the desired
transformation was best realized with a solvent mixture of
t-AmOH and H2O, and KOAc as the additive in an
operationally simple undivided cell (entries 1-5). It is
noteworthy that these findings highlight the water-
tolerant nature of the electrochemical C–C alkenylation,
which, moreover, did not require an additional
electrolyte. Control experiments confirmed the essential
role of the electricity, the carboxylate additive22 and the
rhodium-catalyst for the electrooxidative C–C/C–H
functionalization (entries 6-15). While iridium catalysis
was not a viable option (entry 9), electrooxidative
ruthenium-catalyzed C–C activation was observed, albeit
with somewhat reduced efficacy under otherwise
identical reaction conditions (entry 10).
6
7
69
51
8
9
10
11
12
13
14
–
34 f
g
–
–
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
46
61
8
15
–
22
a
Undivided cell, RVC anode, Pt cathode, constant current at
4.0 mA, 1a (0.25 mmol), 2a (0.5 mmol), catalyst (2.5 mol %),
b
additive (2.0 equiv), solvent (4.0 mL), 100 °C, under N2, 8 h.
Isolated yield. c 70 °C. d n-Bu4NBF4 (0.1 M) was added. e Without
electricity. f [RuCl2(p-cymene)]2 (5.0 mol %) was used. g Without
[Rh] catalyst.
Thereafter, we probed the effect exerted by the
substitution pattern of the leaving group in substrates 1
(Scheme 3). Hence, a variety of alcohols was subjected to
the optimized reaction conditions of the electrochemical
C–C activation. Interestingly, tertiary and secondary
alcohols bearing either aryl or alkyl groups smoothly
underwent the C–C alkenylation process. Contrarily, a
primary alcohol or an ether fell short in delivering the
desired products 3, illustrating the importance of the
acidic functionality for inducing the C–C cleavage event.
It is furthermore noteworthy that an attempted
electrooxidative C–H alkenylation gave the product 3aa in
a significantly diminished yield of only 16% under
otherwise identical reaction conditions, reflecting the
complementary potential of electrochemical C–C
activation. To our delight, the desired product 3da was
obtained in 50% yield with imine as the leaving group.
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Scheme 3. Examination of leaving group substitution
pattern
Scheme 4. Electrochemical C–C alkenylation of
arenes 1
1
2
3
4
5
6
RVC
Pt
RVC
N
N
Pt
DG OH
R2
DG
N
OH
R2
N
[Cp*RhCl2]2 (2.5 mol %)
[Cp*RhCl2]2 (2.5 mol %)
O
R1 R2
4
Ph
O
R1 R2
4
Ph
+
+
+
+
Ph
R1
KOAc
R
Ph
R1
KOAc
t-AmOH/H2O (3/1)
100 °C, 6-8 h
R
R
R
t-AmOH/H2O (3/1)
100 °C, 4-12 h
CCE at 4.0 mA
1
2a
3
1
2a
3
7
CCE at 4.0 mA
8
9
N
N
N
N
N
N
R1 = Me, R2 = Me (3aa): 82%
N
H
N
N
OH
R2
N
R1 = Ph, R2 = H
R1 = Me, R2 = H (
(
): 84%
): 46%
---
Ph
Ph
3aa
Ph
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3aa
R1
R1 = H, R2 = H (
):
3aa
Me
Me
Me
CF3
3ca
Me
3ba
3aa
: 16%
OMe
3aa
: 84%
: 71%
: 32%
Me
Me
N
N
N
OH
3da
(
R
=
H
(
): 72%
3da
): 35%
48%
N
N
R = CH3
R = CF3
R = F (
): 69%
N
N
N
Me
Me
Me
N
N
3da
(
Ph
Ph
3da
):
Ph
R
3da
: ---
Me
3da
3ea
3fa
: 65%
: 72%
: 62%
N
N
N
N
Ph
N
HN
N
O
N
N
N
N
Me
Ph
Ph
Ph
Me
3da
: 50%
3da
3da
: ---
: ---
3ga
3ha
3ia
: 78%
: 58%
: 75%
N
N
N
OH
N
OH
N
Me
N
N
Ph
Me
Ph
MeO
Ph
1af
1ag
: ---
: ---
OMe
3ja
3ka
3la
: 81%
: 78%
: 68%
Next, we turned our attention to probing the scope of
amenable olefins 2 (Scheme 5). Thus, styrenes 2 bearing
electron-withdrawing or electron-donating substituents
afforded the corresponding products 3 with high catalytic
efficacy. Notably, halogen substituents were fully
tolerated, which should prove invaluable for orthogonal
late-stage diversification. We were also pleased to observe
that the sensitive cyano group remained chemo-
selectively untouched by the electrochemical C–C
functionalization manifold. Useful olefinic substrates,
such as the acrylate 2p and vinyl phosphonate 2q, were
also found to react effectively to afford the corresponding
products 3ap and 3aq, respectively.
Versatility and Scope
With the thus optimized reaction conditions for the
electrooxidative C–C activation established, we explored
its versatility with a set of representative arenes 1 (Scheme
4). Differently substituted substrates 1 bearing para-,
meta-, and ortho-substituents were thereby well accepted.
In addition to pyrazolyl arenes 1a-1f, we were delighted to
observe that indazolyl and pyridinyl-substituted arenes 1g
and 1h-1l likewise underwent the C–C alkenylation with
high levels of chemo- and position-selectivity.
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Scheme 5. Electrooxidative C–C activation using at a reduced catalyst loading without compromising the
1
2
alkenes 2
catalyst’s efficacy (Scheme 7b).
3
4
5
6
RVC
N
N
N
Pt
OH
N
[Cp*RhCl2]2 (2.5 mol %)
O
R
+
+
Me
R
KOAc
Scheme 7. Traceless removal and gram scale
electrocatalytic C–C activation
Me
Me
Me
t-AmOH/H2O (3/1)
100 °C, 5-12 h
CCE at 4.0 mA
Me
Me
1a
2
3
4a
7
8
9
(a) Removal of Pyrazole Group
N
N
R
3ab
3af
R = Ph ( ):
R = Me (
R = CF3
):
3ac
71%
76%
73%
58%
72%
3ag
R = Cl (
(
):
3ad
R = F (
):
3ah
62%
68%
66%
R = t-Bu (
R = OMe (
):
3ae
):
3ai
R = Br ( ):
):
NH2
N
1) TMSCl, TMPMgCl LiCl,
0 °C, 38 h
N
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Me
Ph
Ph
2) aq. HCl, MeOH,
40 °C, 2 h
Me
N
N
N
N
N
N
CN
Me
3aa
5a
: 75%
Me
Br
Me
Me
Me
(b) Gram scale transformation
3aj
3ak
3al
: 93%
: 71%
: 62%
RVC
Pt
N
N
N
N
OH
[Cp*RhCl2]2 (1.5 mol %)
N
N
N
N
Ph
+
Ph
N
N
Me
Me
KOAc
t-AmOH/H2O (3/1)
100 °C, 12 h, 30 mA
Me
3aa
Me
Me
N
Br
Me
Me
Me
1a
2a
1.17 g
: 75%,
: 6 mmol
3am
3an
3ao
: 85%
: 51%
: 64%
N
N
N
O
Mechanistic Studies
CO2n-Bu
P
OEt
OEt
Given the efficiency of the unprecedented
electrocatalytic C–C activation, we became attracted to
delineating its modus operandi. To this end, three
Me
Me
3ap
3aq
: 66%
: 43%
competition
reactions
between
electronically
The unique power of the C–C functionalization
approach was clearly highlighted by the position-selective
synthesis of 1,2,3-tri-substituted arenes 3ma-3me (Scheme
6). These findings demonstrate the beneficial assets of the
C–C activation strategy, while structural motifs of 1,2,3-
tri-substituted arenes cannot be accessed by C–H
activation.
differentiated substrates 1 and 2 were performed under
the optimized conditions, as depicted in Scheme 8a. Here,
the more electron-rich arenes 1 were preferentially
converted, which can be rationalized by the more
nucleophilic nature of an rhodium(III) organometallic
intermediate (vide infra). Furthermore, the more electron-
rich styrene 2 reacted predominantly, which is in line
with a kinetically-relevant migratory olefin insertion. An
additional competition experiment was conducted to test
the relative efficacies of the C–C and the C–H
functionalizations. Counterintuitively, we found that the
C–C activation occurred significantly faster as compared
to the corresponding C–H activation (Scheme 8b). When
the C–C alkenylation was conducted in the presence of
the isotopically labelled cosolvent D2O, we did not
observe a notable deuterium incorporation (Scheme 8c),
thus being indicative of a slow C–C scission, accompanied
Scheme 6. Position-selective rhodium-catalyzed C–C
activation
RVC
N
N
Pt
N
OH
N
[Cp*RhCl2]2 (2.5 mol %)
H
H
R
+
Me
R
Me
Me
KOAc
t-AmOH/H2O (3/1)
100 °C, 8 h
Me
1
2
3
CCE at 4.0 mA
by
a fast subsequent migratory insertion of the
coordinated alkene. In addition, this observation
highlights the preferential C–C over C–H cleavage.
Furthermore, gas-chromatographic headspace analysis
confirmed the formation of molecular hydrogen as the
byproduct (Scheme 8d).21 To probe the organometallic
nature of the electrooxidative C–C alkenylation, we
independently prepared the well-defined complex 6a and
6b,23 which proved to be a competent catalyst likewise
(Scheme 8e).
N
N
N
Me
OMe
N
N
N
H
Ph
H
H
Me
Me
3mb
Me
3me
3ma
: 68%
: 62%
: 55%
The practical utility of the thus established
electrooxidative rhodium-catalyzed C–C activation was
next substantiated by the traceless removal of the
pyrazolyl motif,7a thereby furnishing synthetically
meaningful anilines
electrochemical rhodium-catalyzed C–C transformation
could be easily conducted on gram scale (6.0 mmol), even
5 (Scheme 7a). Notably, the
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Scheme 8. Summary of key mechanistic studies on
Scheme 9. Electrochemical versus chemical C–C
2
electrochemical C–C activation
alkenylation
3
4
(a) competition experiment
(a) electrochemical oxidation
5
6
7
8
RVC
Pt
N
N
RVC
N
N
Pt
N
OH
N
N
OH
Ph
N
[Cp*RhCl2
]
2 (2.5 mol %)
[Cp*RhCl2]2 (2.5 mol %)
Ph
+
Ph
Ph
Me
Me
+
KOAc
Ph
KOAc
t-AmOH/H2O (3/1)
100 °C, 8 h
t-AmOH/H2O (3/1)
100 °C, 5 h
CCE at 4.0 mA
R
R
Me
Me
1a
3aa
R = CH3
(
)
R = CH3
R = H (
(
): 52%
3da
): 22%
1ab
2a
3aa
: 84%
2a
1d
CCE at 4.0 mA
R = H (
)
3aa 3da
/
= 2.4/1
9
(b) chemical oxidation
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RVC
Pt
N
N
N
OH
N
R
[Cp*RhCl2]2 (2.5 mol %)
N
N
N
OH
Ph
N
Me
Me
Ph
+
Ph
[Cp*RhCl2]2 (2.5 mol %)
KOAc
t-AmOH/H2O (3/1)
100 °C, 5 h
Ph
+
Ph
oxidant (1.2 equiv), KOAc
t-AmOH/H2O (3/1)
100 °C, 8 h, N2
CH3/CF3
CCE at 4.0 mA
Me
Me
Ag2CO3
1b/1c
2a
3ba
3ba 3ca
/
R = CH3
R = CF3
(
): 48%
): 17%
= 2.8/1
1ab
2a
3ca
(
3aa
(
): 64%
3aa
): 66%
Cu(OAc)2
(
RVC
Pt
N
N
OH
N
N
R
[Cp*RhCl2]2 (2.5 mol %)
Me
Me
+
KOAc
t-AmOH/H2O (3/1)
100 °C, 5 h
Finally, we performed detailed mechanistic studies by
means of cyclic voltammetry (Figure 1).24 The starting
materials 1 and 2 were found to be electrochemically inert
within the investigated redox window, whereas product
Me
Me
CH3/CF3
CCE at 4.0 mA
R = CH3 (3ab): 32%
1a
2b/2c
3ac
R = CF3
(
): 28%
3ab 3ac
/
= 1.1/1
(b) C–C activation versus C–H activation
3aa exhibited
a distinct oxidation peak at Ep =
RVC
[Cp*RhCl2
Pt
2 (2.5 mol %)
N
N
N
N
0.93 V versus Fc+/0 (Figure 1a), which is in line with our
observation that extended reaction times led to
decomposition of the product. Upon addition of KOAc to
[Cp*RhCl2]2 the cyclic voltammogram clearly indicated a
ligand exchange, forming [Cp*Rh(OAc)2]2 (Figure 1b). The
proposed re-oxidation of the rhodium(I) species to
regenerate the catalytically competent rhodium(III)
intermediate was explored with the well-defined Cp*Rh(I)
complex [Cp*Rh(cod)] (Figure 1c). This complex was thus
N
OH
Ph
N
]
H
+
+
Ph
KOAc
t-AmOH/H2O (3/1)
100 °C, 6 h
CCE at 4.0 mA
Me
R
3aa
R = CH3
R = H (
(
): 52%
): 10%
1ab
1a'
2a
3da
3aa 3da
/
= 5.2/1
(c) D2O as cosolvent
< 5% D
< 5% D
RVC
Pt
< 5% D
N
N
N
tBu
N
OH
N
H
N
OD
[Cp*RhCl2
]2 (2.5 mol %)
H
H
+
H
+
Me
Me
Me
KOAc
Me
D
O
(3/1)
t-AmOD/
H
2
tBu
100 °C, 2 h
CCE at 4.0 mA
Me
Me
[D]n
Me
1b
< 5% D
: 22%
shown to be easily oxidized at Ep = -0.16 V versus Fc+/0
.
3bd
-
[D]n
-
: 51%
1b
2d
Notably, the process was found to be facilitated by the
presence of HOAc, which is being formed during the
reductive elimination step. We did not observe any
indication for the coordination of the product 3aa after its
release via β-H-elimination (Figure 1d).
(d) headspace H2-analysis
RVC
Pt
]2 (2.5 mol %)
N
N
N
OH
Ph
N
[Cp*RhCl2
Ph
H2
+
Ph
+
KOAc, MeOH
45 °C, 5 h
CCE at 4.0 mA
confirmed by
headspace
GC-analysis
Me
Me
1ab
2a
3aa
(e) well-defined complex 6
Me
Me
Me
Me
Me
Me
Me
Me
N
Me
RVC
6a 6b
Me
Pt
N
N
OH
Ph
N
or
(5.0 mol %)
N
Rh
N Rh
OAc
Cl
Ph
+
Ph
N
N
KOAc
t-AmOH/H2O (3/1)
100 °C, 5 h
3da
6a
6b
: 67% (
70% (
)
)
6a
6b
1d
2a
CCE at 4.0 mA
Thereafter, we compared the efficacy of the
electrochemical C–C activation with the one observed
when employing chemical oxidants (Scheme 9).
Interestingly, typically used chemical oxidants, such as
copper(II) acetate or silver(I) acetate, furnished the
desired product 3aa in significantly inferior yields under
otherwise identical reaction conditions.
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Page 6 of 10
subsequently affords the rhodium(I) intermediate 11
1
2
3
4
through hydride elimination and reductive elimination.
Finally, an anodic oxidation of the rhodium(I)
intermediate 11 regenerates the catalytically active
rhodium(III) complex.
5
6
7
Scheme 10. Proposed catalytic cycle
8
9
N
RVC
Pt
N
OH
[Cp*RhCl2]2
Me cathodic reduction
Me
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
RVC
Pt
2 HOAc
H2
1
[Cp*Rh(OAc)2]2
anodic oxidation
HOAc
Me
Me
N
Me
Me
Cp*RhL2
N
Me
N
11
Rh
O
R
+
N
OAc
HOAc
Me
Me
3
electrocatalytic C–C activation
no Cu(II), no Ag(I)
electricity as green oxidant
H2 as sole byproduct
7
-hydride elimination
reductive elimination
C–C activation
O
Me
Me
Me
Me
Me
Me
Rh
Me
4
Me
Me
Me
Me
Me
Rh
N
OAc
R
N
N
OAc
N
Me
Me
Me
Me
Me
8
10
R
R
N
Rh
N
OAc
OAc
2
migratory insertion
9
3. CONCLUSIONS
In conclusion, we have reported on the first
electrochemical C−C activation by expedient rhodium
catalysis. Thus, oxidative C−C alkenylations were
achieved by electricity, which avoided the formation of
metal-containing stoichiometric byproducts. The versatile
rhodium catalysis manifold occurred with excellent levels
of chemo- and position-selectivities, generating H2 as the
sole byproduct. Mechanistic studies provided support for
a slow C−C cleavage within an organometallic regime.
Our findings highlight the unique synthetic utility of
electrocatalysis for sustainable C−C functionalizations.
The power of the C–C activation strategy was likewise
substantiated by providing position-selective access to
densely-1,2,3-substituted arenes, which cannot be
obtained by any of the existing C–H functionalization
method.
Figure 1. Cyclic voltammetry. Conditions: a), b) and d):
MeOH, 0.1 M [n-Bu4N][PF6], 1 mM substrates, 100 mV/s;
c): MeOH, 0.1 M KOAc, 4 mM [Cp*Rh(cod)], 100 mV/s.
ASSOCIATED CONTENT
Supporting Information
Proposed Catalytic Cycle
Experimental procedures and compound characterization
Based on our mechanistic studies, a plausible catalytic
cycle for the rhodium-electrocatalyzed C–C alkenylation
was proposed, as depicted in Scheme 10. Coordination of
substrate 1 through its nitrogen and oxygen to the
rhodium(III) catalyst generates intermediate 7, and
thereby set the stage for a the key C–C cleavage.
Thereafter, migratory alkene insertion occurs to furnish
data, including the H/13C NMR spectra. This material is
1
available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
the
seven-membered
rhoda(III)cycle
10,
which
*Lutz.Ackermann@chemie.uni-goettingen.de
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Journal of the American Chemical Society
Allylglyoxylamides. Angew. Chem. Int. Ed. 2015, 54, 7418-7421; (c)
Author Contributions
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Reactions. J. Am. Chem. Soc. 1996, 118, 8285-8290; (f) Murakami,
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Bonds Next to a Carbonyl Group. Nature 1994, 370, 540-541.
(4) (a) Wang, G. W.; McCreanor, N. G.; Shaw, M. H.;
Whittingham, W. G.; Bower, J. F., New Initiation Modes for
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1
2
3
4
5
6
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8
†These authors contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
Generous support by the DFG (Gottfried-Wilhelm-Leibniz
award to LA) is gratefully acknowledged.
9
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Electrochemical C–C Activation
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H
rDG
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rDG
RVC
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electrocatalytic C C activation
–
rhodium catalysis
no Cu(II), or Ag(I)
mechanistic insights
electricity as green oxidant
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