Bis(imino)pyridine iron complexes for catalytic carbene transfer reactions

Article abstract of DOI:10.1039/c9sc02189b

The bis(imino)pyridine iron complex, for the first time, is developed as an effective metal carbene catalyst for carbene transfer reactions of donor-acceptor diazo compounds. Its broad catalytic capability is demonstrated by a range of metal carbene reactions, from cyclopropanation, cyclopropenation, epoxidation, and Doyle-Kirmse reaction to O-H insertion, N-H insertion, and C-H insertion reactions. The asymmetric cyclopropanation of styrene and methyl phenyldiazoacetate was successfully achieved by the new chiral bis(imino)pyridine iron catalyst, which delivers a new gateway for the development of chiral iron catalysis for metal carbene reactions.

Full text of DOI:10.1039/c9sc02189b

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DOI: 10.1039/C9SC02189B
ARTICLE
Bis(imino)pyridine Iron Complexes for Catalytic Carbene Transfer
Reactions
Ban Wang, Isaac G. Howard, Jackson W. Pope, Eric D. Conte and Yongming Deng*
Received 00th January 20xx,
Accepted 00th January 20xx
Bis(imino)pyridine iron complex, for the first time, is developed as an effective metal carbene catalyst for carbene transfer
reactions of donor-acceptor diazo compound. Its board catalytic capability is demonstrated by a range of metal carbene
reactions from cyclopropanation, cyclopropenation, epoxidation, Doyle–Kirmse reaction to O–H insertion, N–H insertion,
and C–H insertion reactions. The asymmetric cyclopropanation of styrene and methyl phenyldiazoacetate was successfully
achieved by a new chiral bis(imino)pyridine iron catalyst, which delivers a new gateway for the development of chiral iron
catalysis for metal carbene reactions.
DOI: 10.1039/x0xx00000x
Ar
a)
Introduction
O
L
R
N
N
N
N
+ FeX2
R
Ar
Fe
Ar
Transition-metal catalyzed carbene transfer reactions occurring
through the metal carbene intermediates encompass a vast
array of reactants and catalysts to achieve novel and selective
strategies for organic synthesis.1 The reactive carbenoid
intermediates can be catalytically generated from diazo
compounds by metal catalyzed dinitrogen extrusion,2 and their
reactions extend from addition and insertion to cycloaddition
and ylide formation.3 Dirhodium complexes have been
established as the most successful catalysts for carbene transfer
reactions of diazo compounds,4 great achievements have also
been accomplished recently by copper and other precious
metal catalysts (e.g. ruthenium, palladium, gold)5. Iron, the
second most abundant metal alone with its biological relevance,
is emerging as an important metal for catalytic metal carbene
reactions.6 However, iron catalysis is comparatively
underdeveloped than the enduring dominance of precious
metal catalysis in metal carbene chemistry.
Since the launching of iron porphyrin catalyzed
cyclopropanation by Woo,7 various carbene transfer processes
of diazo compounds, including cyclopropanation, heteroatom-
hydrogen bond insertions, and intramolecular C–H inversion,
have been achieved by porphyrin and related macrocyclic iron
complexes, however, generally occurred with active α-
hydrogen-diazocarbonyl compounds, diazoalkanes, or the
corresponding precursors.8 The spiro-bisoxazoline iron
complexes developed by Zhou group have exhibited high
catalytic activities and selectivities for heteroatom-hydrogen
bond insertions and intramolecular cyclopropanation reactions
of α-diazoesters.9 Despite these achievements, iron has not
N
N
O
Ar
iron porphyrin complexes
spiro-bisoxazoline iron complexes
This research
MeO2C
b)
R1
R2
R2
Ph
N
Ar
cyclopropanation
Ph
N
CO2Me
R1
Ar
CO2Me
Ph
C-H insertion
N2
+
Me2N
2+
O
Ph
O
Ph
Ph
CO2Me
PhNH2
Ar
N
iPr
-
N-H insertion
Ph
CO2Me
epoxidation
2SbF6
Fe
N
HN
Ph
NCMe
MeCN
iPr
S
Ph
O
CO2Me
R
[(iPrPDI) (CH3CN)2](SbF6)2
5 mol%
insertion
Ph
PhS
CO2Me
R-OH
Fe
Ph
O H
-
Doyle–Kirmse
reaction
Scheme 1 a) Selected iron catalysis for metal carbene reactions. b) This research:
bis(imino)pyridine iron catalyzed metal carbene reactions.
been developed as a catalyst to the same extent as other late
transition metals regarding usage in metal carbene reactions.
The advance of iron catalysis for general carbene transfer
reactions with broad substrate schemes, especially asymmetric
processes, and under mild reaction conditions remains a wide-
open field for discovery and innovation. We report here, for the
first time, the bis(imino)pyridine iron complexes serve as
effective catalysts for a range of metal carbene reactions under
mild reaction conditions (at room temperature or 40 °C),
including cyclopropanation/cycopropenation, epoxidation,
Doyle–Kirmse reaction, O–H insertion, N–H insertion, and C–H
insertion (Scheme 1). To the best of our knowledge, this
bis(imino)pyridine iron catalyst represents the most broad-
ranging catalytic activities towards metal carbene reactions of
diazo compounds than the previous reported iron catalysis
Chemistry Department, Western Kentucky University
1906 College Heights Boulevard, Bowling Green, Kentucky 42101
E-mail: yongming.deng@wku.edu
Electronic Supplementary Information (ESI) available: Experimental details and
copies of NMR spectra. See DOI: 10.1039/x0xx00000x
system.6
cyclopropanation proceeds on
aryldiazoacetates, vinyldiazoacetate, with styrenes and
The
bis(imino)pyridine
iron
catalyzed
a
wide range of
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phenylacetylene. Notably, a new chiral bis(imino)pyridine and sterically tune the bis(imino)pyridine iron (II) complexes to
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ligand derivatized from L-valine methyl ester has been achieve the carbene transfer reactions ofDdOoI:n1o0r.1-0a3c9c/eCp9tSoCr0d21ia89zoB
synthesized, and the corresponding enantiopure, C1-symmetric compound under mild reaction conditions.
iron catalyst enabled the asymmetric cyclopropanation of
styrene and phenyl diazoacetate.
Results and discussion
In the past decade, bis(imino)pyridine chelated iron
complexes have emerged as an effective class of catalysis for
ethylene polymerization, olefin hydrogenation, hydrosilation,
and [2π+2π]-cycloaddition reactions.10 Owing to its ease of
preparation, the bis(imino)pyridine ligand is easily modifiable
allowing versatility in ligand design, synthesis, and
screening.10a,b However, the catalytic metal carbene reactions
by bis(imino)pyridine iron complexes have not been achieved.
Recently, Chirik reported the formation of a bis(imino)pyridine
iron carbene complexes B from a stoichiometric amount of
As a starting point, we focused on the evaluation of a series of
bis(imino)pyridine iron(II) catalysts for the cyclopropanation
reaction of styrene 2a with methyl phenyldiazoacetate 1a
(Table 1). As proposed, in the presence of 5 mol% of
bis(arylimino)pyridine iron(II) dichloride complexes (entries 1
and 2), the reaction of 2a and phenyldiazoacetate 1a afforded
the cyclopropanation product 3a, however, in low yields with
predominately recovered starting material. To improve the
catalytic activity of iron complexes, the examination of
noncoordinating counterions was performed. The employment
o f m o r e e l e c t r o p h i l i c i r o n c o m p l e x e s w i t h
bis(imino)pyridine iron dinitrogen complex
A
and
diphenyldiazomethane by dinitrogen extrusion (Figure 1).11
While the attempts to metal carbene reactions, such as
cyclopropanation, and C–H insertion, were unsuccessful by this
bis(imino)pyridine iron carbene complex.11,12
-
hexafluoroantimonate (SbF6 ) as counterions (entries 3 and 4)
led to a marked increase in yield. The combination of
Table 1. Screening of Iron Catalysts for Cyclopropanation.a
Ph
N
CO2Me
catalyst (5 mol%)
DCE, 12h
CO2Me
Ph
R2
+
Ph
2a
Ph
N2
1a
R2
R1
N
R2
N
3a
Ar
N
N
Ph
Ph
Ar
N
R2
R1
N
N
Fe
N2
Ar
Ph
R2
2+
N2
N
N
Fe
Ar
N
N
-N2
R1
Fe
Ar
N
Fe
N2
N
-
N
2SbF6
Ph
Fe
N
R1
Ar
Cl
Cl
Ar
N
NCMe
MeCN
R1 = Me, Et
R2 = Me, Et
Ar
A
B
3, [(MePDI) (CH3CN)2](SbF6)2
Ar = 2,6-Me2C6H3, (MePDI) Cl2
Ar = 2,6-iPr2C6H3, (iPrPDI) Cl2
R2
Ar = 2,6-Me2C6H
Ar = 2,6-iPr2C6H
Fe
Fe
3, [(iPrPDI) (CH3CN)2](SbF6)2
Fe
Fe
Figure
1
Formation of
a
bis(imino)pyridine iron carbene from
bis(arylimino)pyridine iron dinitrogen complexes and diphenyldiazomethane.11
2+
O
N
O
O
N
R
N
N
-
We hypothesized that one reason for the lack of reactivity
for bis(imino)pyridine iron carbene complexes B in carbene
transfer process is due to the charge delocalization induced by
the diphenyl group. To address this issue, we predicted that
augmenting the electrophilicity of the disubstituted diazo
compound would increase the reactivity of the corresponding
iron carbene, thus it could more readily engage in carbene
transfer reactions.2b,c It has been documented that the donor-
acceptor metal carbene, which can be produced from donor-
acceptor diazo compound by metal catalyzed dinitrogen
extrusion, exhibited higher reactivity than the one from
diphenyldiazomethane due to its stronger electrophilicity.1c,3c,4a
Herein, donor-acceptor diazo compound, aryldiazoacetate, was
selected as the carbene precursor in this study to investigate
the bis(imino)pyridine iron catalyzed metal carbene reactions.
Additionally, recent computational studies of bis(imino)pyridine
iron complexes for C–H functionalization of donor-acceptor
diazo compound also suggests feasibility.13
The catalytic cycle for the conversion of a diazo compound
to a metal-stabilized carbene intermediate is initiated from the
metal catalyzed dinitrogen extrusion of nucleophilic diazo
compound. We predicted that, compared to the formally
iron(0) complex A, the more electrophilic bis(imino)pyridine
iron (II) complexes would exhibit higher reactivity towards the
nucleophilic diazo compound and facilitate the subsequent
metal carbene transfer. Therefore, we aimed to electronically
2SbF6
Fe
N
N
N
N
N
Ar
R
iPr
NCMe
MeCN
R
R
R = iPr
R = Cy
Fe
iPr
PyBOX I
Ar = 2,6-iPr2C6H3
i
, [( APDI) (CH3CN)2](SbF6)2
R = Pr,
R = Ph,
Cy
Fe
, [( APDI) (CH3CN)2](SbF6)2
OIP
oxazoline iminopyridine (
PyBOX II
)
Entry
Catalyst
MePDI)FeCl2
iPrPDI)FeCl2
T (°C)
50
50
rt
Yieldb
14
18
65
86
68
8
1
2
(
(
3
[(MePDI)Fe(CH3CN)2](SbF6)2
[(iPrPDI)Fe(CH3CN)2](SbF6)2
[(iPrPDI)Fe(CH3CN)2](SbF6)2
[(iPrAPDI)Fe(CH3CN)2](SbF6)2
[(CyAPDI)Fe(CH3CN)2](SbF6)2
FeCl2/PyBOX(I)/AgSbF6
FeCl2/PyBOX(II)/AgSbF6
FeCl2/OIP/ AgSbF6
4
rt
5c
6
rt
50
50
50
50
50
7
< 5
< 5
< 5
9
8
9
10
a Reaction condition unless otherwise noted: 1a (0.20 mmol, 1.0 equiv.) in dry DCE
(1.0 ml) was added to a 1.0 mL DCE solution of 2a (1.0 mmol, 5.0 equiv.), and
b
catalyst (0.01 mmol) under N2 within 1 hour. Yield of isolated product 3a based
on the limiting reagent 1a. cThe reaction was performed with 1a:2a = 1:1. (1,2-
dichloroethane = DCE).
2 | J. Name., 2012, 00, 1-3
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(iPrPDI)FeCl2 and NaBArF4 also delivered 3a with enhanced yield ortho-substituents on the aromatic ring resulted in lower yields
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(48%, Table S1). [(iPrPDI)Fe(CH3CN)2](SbF6)2 bearing bulky 2,6- (entries 7 and 8). We rationalize that sucDhOlIo: w10e.1r03re9/aCc9tSivCi0ty21c8a9nB
diisopropylphenyl substituents was identified as the best be attributed to a higher kinetic barrier for the generation of
catalyst,14 which catalyzed the cyclopropanation under room corresponding iron carbene intermediate, which is caused by
temperature generating 3a in 86% yield with excellent the increased steric hindrance between ortho-substituent and
diastereoselectivity (dr > 20:1). The lower yield of 3a (entry 5, the bulky bis(imino)pyridine ligand frame. The cyclopropanes
68%) was obtained when the reaction was performed with 3j-3l derived from styrene derivatives 2b-2d were obtained in
1a:2a = 1:1 in the presence of [(iPrPDI)Fe(CH3CN)2](SbF6)2. To yields ranging from 88 to 91%, whereas moderate yield (67%,
reveal the imino-substituents effect on the catalyst, iron entry 12) were obtained with 4-(trifluoromethyl)styrene 2e.
complexes containing N-alkyl substituents were examined. Disubstituted styrenes, including α-phenylstyrene 2f and trans-
However, they resulted in low catalytic activity with recovery of β-methylstyrene 2g, were also ideal reagents for this iron
starting material (entries 6 and 7), which could be due to catalyzed cyclopropanation, producing products 3n and 3o in
electronic and/or steric constraints from the imino-alkyl groups. good yields.
Additionally, neither iron complexes of pyridine bis(oxazoline)
In addition to the styrene derivatives, the reaction of 1,3-
ligands, nor oxazoline iminopyridine iron complexes were cyclohexadiene and 1a also effectively catalyzed by
effective catalysts for this transformation (entries 8 to 10). [(iPrPDI)Fe(CH3CN)2](SbF6)2 affording the cyclopropane product
These results demonstrate the indispensability of the imino-aryl 3p in 80% yield with dr > 20:1 (eq. 1). Furthermore, as shown in
substituent in the ligand frame to conduct active iron catalyst eq.
2,
the
[(iPrPDI)Fe(CH3CN)2](SbF6)2
catalyzed
for metal carbene reaction of donor-acceptor diazo compound. cyclopropanation of cyclohexene and 1a was also successfully
achieved affording the desired product 3q in 72% yield. To
further probe the diazo substrate generality, vinyl-diazoacetate
Table 2. Scope of Bis(imino)pyridine iron Catalyzed Cyclopropanation.a
[(iPrPDI) (CH3CN)2](SbF6)2
5 mol%
R2
1j was subjected to bis(imino)pyridine iron catalyzed
Fe
R1
Ar1
CO2Me
cyclopropanation with styrene (eq. 3). Gratifyingly, the
cyclopropane product 3r was obtained in 84% yield, which
demonstrates the catalytic capability of bis(imino)pyridine iron
for a broader scope of donor-acceptor diazo compounds.
Remarkably, [(iPrPDI)Fe(CH3CN)2](SbF6)2 was also capable to
catalyze the cylcopropenation of 1a and phenylacetylene
furnishing the product 3s in 61% yield at 40 °C (eq. 4), which has
not been achieved by other reported iron catalysis.
R1
CO2Me
Ar1
R2
+
Ar2
N2
Ar2
DCE, rt, 12 h
1
2
3
Entry
1
2
yieldb
1
2
1b, 4-MeC6H4
2a, Ph, H, H
2a, Ph, H, H
3b, 81
3c, 83
3d, 88
3e, 83
3f, 81
3g, <5
3h, 52
3i, 58
1c, 4-MeOC6H4
1d, 4-ClC6H4
1e, 4-BrC6H4
1f, 2-naphthyl
1g, 4-NO2C6H4
1h, 2-MeOC6H4
1i, 2-ClCH6H4
1a, Ph
3
2a, Ph, H, H
[(iPrPDI) (CH3CN)2](SbF6)2
Fe
MeO2C
4
2a, Ph, H, H
Ph
CO2Me
+
(1)
5 mol%
Ph
5
2a, Ph, H, H
N2
1a
DCE, rt, 12 h
2h
2i
3p
, 80%, dr > 20:1
6[c]
7
2a, Ph, H, H
H
[(iPrPDI) (CH3CN)2](SbF6)2
5 mol%
Fe
MeO2C
Ph
2a, Ph, H, H
Ph
CO2Me
+
(2)
8
2a, Ph, H, H
N2
1a
H
DCE, rt, 12 h
3q
, 72%, dr > 20:1
9
2b, 4-MeC6H4, H, H
2c, 4-MeOC6H4, H, H
2d, 4-ClC6H4, H, H
2e, 4-CF3C6H4, H, H
2f, Ph, Ph, H
3j, 91
10
11
12
13c
14c
1a, Ph
3k, 88
3l, 90
Ph
[(iPrPDI) (CH3CN)2](SbF6)2
Fe
CO2Me
1a, Ph
(3)
(4)
5 mol%
Ph
+
Ph
Ph
N2
Ph
Ph
1a, Ph
3m, 67
3n, 73
3o, 70
DCE, rt, 12 h
CO2Me
3r
, 84%, dr > 20:1
1j
2a
2i
1a, Ph
[(iPrPDI) (CH3CN)2](SbF6)2
1a, Ph
2g, Ph, H, CH3
Fe
MeO2C Ph
CO2Me
5 mol%
+
a For experimental details, see supporting information. b Isolated yield. c Reactions
were performed at 40°C.
N2
DCE, 40 C, 12 h
Ph
3s
, 61%
1a
With the accomplishment of achiral bis(arylimino)pyridine
iron catalyzed cyclopropanation, we have sought to modify the
ligand architecture to generate chiral iron catalyst for
asymmetric cyclopropanation. Our catalysts screening (Table 1)
indicated that the N-aryl substituent in bis(imino)pyridine
ligand is indispensable for the effective catalytic activity of iron
complexes. Guided by these experimental results and
Bianchini’s original design of chiral bis(imino)pyridine ligand,15
we synthesized an enantiopure, C1-symmetric chiral
bis(imino)pyridine ligand [(S)-VMEPDI] (Scheme 2), in which one
With the optimized condition, we investigated the scope of
this bis(arylimino)pyridine iron catalyzed cyclopropanation
across a range of aryldiazoacetates and styrene derivatives
(Table 2). As indicated by entries 1 to 5, aryldiazoacetates with
electron-rich, halogen para-substituents and 2-naphthyl group
all reacted smoothly with styrene, generating the
corresponding cyclopropanes in good yields (81−88%, 3b-3f)
with excellent diastereoselectivities (dr > 20:1). However, no
reaction occurred with the electron-deficient system even at 40
°C (1g, entry 6). Reactions of aryldiazoacetates 1h and 1j bearing
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J. Name., 2013, 00, 1-3 | 3
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reacted with 1a smoothly to form the Doyle–Kirmse product 5
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DOI: 10.1039/C9SC02189B
iPr
iPr
in 91% yield. [( PDI)Fe(CH3CN)2](SbF6)2 was also capable to
catalyze the N–H insertion of aniline and C–H insertion of N,N-
dimethylaniline, although higher reaction temperatures were
required (Scheme 3c and 3d). Furthermore, in the presence of
5 mol% [(iPrPDI)Fe(CH3CN)2](SbF6)2, O–H insertion reactions of
1a with methanol, n-butanol, and water were achieved
furnishing the corresponding products 8a-8c in good to
moderate yields (Scheme 3e).
As documented, bis(imino)pyridines have been recognized
as radical-based, redox non-innocent ligands, that can directly
participate in the electronic structure of metal complexes.10d,f,17
Chirik’s study demonstrated that a carbene radical is engaged in
bis(imino)pyridine iron carbene complexes A, which is obtained
from a formally iron(0) complex (Scheme 2).11 Therefore,
considering the redox activity of bis(imino)pyridine ligand,
radical tapping experiments were conducted to address
Chiral
element
N
N
iPr
OMe
N
O
iPr
(S)-VMEPDI
Activating element
FeCl2 (5 mol%)
(S)-VMEPDI
(6 mol%)
CO2Me
Ph
Ph
CO2Me
+
AgSbF6 (10 mol%)
Ph
Ph
2a
N2
DCE, rt, 12 hr
3a
, 78% yield
67% ee,
1a
dr > 20:1
Scheme 2. Chiral bis(imino)pyridine iron catalyzed cyclopropanation.
imine is “anchored” by 2,6-diisopropylphenyl group (Activating
element) and the other is prepared from L-valine methyl ester
(Chiral element). To our delight, the asymmetric
cyclopropanation reaction of 1a and styrene was successfully
achieved by in situ prepared chiral iron catalyst from (S)-VMEPDI,
FeCl2, and AgSbF6 at room temperature. The cyclopropane
product 1a was isolated in 78% yield with 67% enantiomeric
excess.16 Although with moderate enantioselectivity, the
success of this asymmetric cyclopropanation reaction provides
whether
a
radical
carbene
involved
in
this
bis(arylimino)pyridine iron(II) catalyzed carbene transfer
reactions.19 As shown in Scheme 4a, addition of the radical
scavenger TEMPO (2,2,6,6-tetramethylpiperidine N-oxide) did
not
harm
the
[(iPrPDI)Fe(CH3CN)2](SbF6)2
catalyzed
cyclopropanation reactions of 1a or vinyl-diazoacetate 1j, and
the corresponding products were isolated with similar yields to
that from the reactions in the absence of TEMPO. These results
reveal the unlikely involvement of the carbene radical
a
strong basis for the development of new chiral
bis(imino)pyridine iron catalysis for metal carbene reactions.
Encouraged by the success of bis(arylimino)pyridine iron(II)
catalyzed cyclopropanation, we then sought to examine the
generality of this iron catalyst for metal carbene reactions. As
depicted in Scheme 3, a range of metal carbene reactions of
phenyldiazoacetate 1a, including epoxidation, Doyle–Kirmse
reaction, N–H insertion, C–H insertion, and O–H insertion, were
all successfully catalyzed by [(iPrPDI)Fe(CH3CN)2](SbF6)2. The
bis(arylimino)pyridine iron catalyzed reaction of 1a and
benzaldehyde yielded epoxide product 4 in 80% yield with
excellent diastereoselectivity at room temperature (Scheme
3a). Under the same condition (Scheme 3b), allyl phenyl sulfide
intermediate
in
[(iPrPDI)Fe(CH3CN)2](SbF6)2
catalyzed
cyclopropanation reactions. Moreover, the achievement of C–H
insertion reaction of 1a with N,N-dimethylaniline (Scheme 3d)
imply the likely generation of donor-acceptor iron(II) carbene
intermediate.1c,6 Based on the obtained experimental results
and mechanism study, we propose that the donor-acceptor
diazo compound was decomposed by bis(arylimino)pyridine
iron(II) catalyst to generate an iron(II) carbene intermediate,
which readily undergo cyclopropanation of olefins to afford the
cyclopropane product (Scheme 4b).
4
, 80%
dr > 20:1
O
a)
(2.0 equiv)
Ph
O
[(iPrPDI) (CH3CN)2](SbF6)2
Ph
Fe
(a)
Ph
CO2Me
+
Ph
CO2Me
5 mol%
rt, DCE
S
Ph
CO2Me
CO2Me
Ph
TEMPO
Ph +
2a
N2
1a
Ph
Ph
N2
+
1a
DCE, rt, 12h
2.0 equiv.
Ph
3a
, 81%
1.0 equiv.
5.0 equiv.
Ph
CO2Me
(2.0 equiv)
5
, 91% (b)
PhS
2+
Ph
rt, DCE
[(iPrPDI) (CH3CN)2](SbF6)2
Fe
N
CO2Me
Ph
Ar
N
5 mol%
+
iPr
N2
Ph
TEMPO
+
Ph
CO2Me
Ph
(1.5 equiv)
-
PhNH2
2SbF6
Fe
N
6
, 68% (c)
CO2Me
1j
1.0 equiv.
DCE, rt, 12 h
2.0 equiv.
NCMe
3r, 79%
HN
MeCN
iPr
2a
5.0 equiv.
40 C, DCE
[(iPrPDI) (CH3CN)2](SbF6)2
CO2Me
Ph
Fe
N,N-dimethylaniline
b)
Ph
CO2Me
5 mol%
(1.5 equiv)
CO2Me
Ph
N2
(d)
(e)
Ph
7
, 71%
Fe(II)Ln
40 C, DCE
Me2N
[(iPrPDI) (CH3CN)2](SbF6)2
5 mol%
Ph
CO2Me
R
Fe
2+
Ph
CO2Me
O
+
R-OH
N
Ar
N
Ph
CO2Me
N2
Ph
rt, DCE
(5.0 equiv)
8a
, R = Me, 80%
, R = nBu, 74%
, R = H, 63%
N
Fe(II)
N2
R = H, Me, nBu
NCMe
-
8b
8c
Ar
MeCN
2SbF6
Scheme 3. Bis(arylimino)pyridine iron catalyzed a) Epoxidation; b) Doyle–
Kirmse reaction; c) N–H insertion; d) C–H insertion; and e) O–H insertion.
Scheme 4. a) Mechanism study. b) Proposed mechanism of
bis(arylimino)pyridine iron(II) catalyzed cyclopropanation.
4 | J. Name., 2012, 00, 1-3
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Chemical Science
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Journal Name
ARTICLE
Chem. Commun. 2016, 52, 7326; (c) X. Zhao, Y. Zhang, J. Wang,
Conclusions
Chem. Commun. 2012, 48, 10162; (d) Y. Zhang,VJie.wWAratinclge,OEnulinre.
DOI: 10.1039/C9SC02189B
J. Org. Chem. 2011, 2011, 1015; (e) C.-Y. Zhou, J.-S. Huang, C.-
M. Che, Synlett 2010, 2010, 2681; (f) H. M. L. Davies, S. J.
Hedley, Chem. Soc. Rev. 2007, 36, 1109.
In summary, the effective catalytic activity of
bis(arylimino)pyridine iron(II) complexes for carbene transfer
reactions of donor-acceptor diazo compounds has been
demonstrated by a range of metal carbene transformations
from cyclopropanation, insertions, to ylide formation. Notably,
asymmetric cyclopropanation of methyl phenyldiazoacetate
and styrene has been achieved by a new chiral iron catalyst
based on the bis(imino)pyridine ligand derivatized from L-valine
methyl ester. Future studies will be aimed at developing new
asymmetric bis(imino)pyridine iron catalysis for highly
enantioselective metal carbene reactions, as well as elucidating
the mechanism of such process and nature of the iron carbene
intermediate.
6
7
S.-F. Zhu, Q.-L. Zhou, Natl. Sci. Rev. 2014, 1, 580.
J. R. Wolf, C. G. Hamaker, J.-P. Djukic, T. Kodadek, L. K. Woo,
J. Am. Chem. Soc. 1995, 117, 9194.
8
For selected recent examples: (a) S. B. J. Kan, R. D. Lewis, K.
Chen, F. H. Arnold, Science 2016, 354, 1048; (b) J. Day, B.
McKeever-Abbas, J. Dowden, Angew. Chem. Int. Ed. 2016, 55,
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B. Morandi, E. M. Carreira, Science 2012, 335, 1471; (e) H. M.
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Phthalocyanines 2010, 14, 284; (f) L. K. Baumann, H. M. Mbuvi,
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7697; (c) J.-J. Shen, S.-F. Zhu, Y. Cai, H. Xu, X.-L. Xie, Q.-L. Zhou,
Angew. Chem. Int. Ed. 2014, 53, 13188; Angew. Chem. 2014,
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Conflicts of interest
There are no conflicts to declare.
9
Acknowledgements
Support for this research from Western Kentucky University and
the National Science Foundation under Cooperative Agreement
No. 1355438 (OIA-1355438, 3200000271-19-136) is gratefully
acknowledged.
10 For selected reviews: (a) P. J. Chirik, Acc. Chem. Res. 2015, 48,
1687; (b) V. C. Gibson, C. Redshaw, G. A. Solan, Chem. Rev.
2007, 107, 1745. For selected recent examples: (c) J. M. Hoyt,
V. A. Schmidt, A. M. Tondreau, P. J. Chirik, Science 2015, 349,
960; (d) M. Darmon, R. P. Yu, S. P. Semproni, Z. R. Turner, S. C.
E. Stieber, S. DeBeer, P. J. Chirik, Organometallics 2014, 33,
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J. Am. Chem. Soc. 2013, 135, 4862; (f) S. C. E. Stieber, C.
Milsmann, J. M. Hoyt, Z. R. Turner, K. D. Finkelstein, K.
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11 S. K. Russell, J. M. Hoyt, S. C. Bart, C. Milsmann, S. C. E. Stieber,
S. P. Semproni, S. DeBeer, P. J. Chirik, Chem. Sci. 2014, 5, 1168.
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13 Varela-Álvarez, D. G. Musaev, Chem. Sci. 2013, 4, 3758.
14 [(iPrPDI)Fe(CH3CN)2](SbF6)2 was prepared according to the
reported procedure: G. J. P. Britovsek, J. England, S. K.
Spitzmesser, A. J. P. White, Dalton Trans. 2005, 945.
15 C. Bianchini, G. Mantovani, A. Meli, F. Migliacci, F. Zanobini, F.
Laschi, A. Sommazzi, Eur. J. Inorg. Chem. 2003, 2003, 1620.
16 For further condition screening of the asymmetric
cyclopropanation, see: Table S2.
Notes and references
1
For selected books and reviews, see: (a) M. P. Doyle, M. A.
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For selected reviews of diazo compounds: (a) K. A. Mix, M. R.
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Ford, H. Miel, A. Ring, C. N. Slattery, A. R. Maguire, M. A.
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Chem. Int. Ed. 2009, 48, 8186; Angew. Chem. 2009, 121, 8332.
For selected reviews of insertions: (a) H. M. L. Davies, D.
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Davies, R. E. J. Beckwith, Chem. Rev. 2003, 103, 2861. For
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M. Lankelma, M. P. Doyle, Chem. Soc. Rev. 2017, 46, 5425; (g)
H. M. L. Davies, Y. Lian, Acc. Chem. Res. 2012, 45, 923; (h) H.-
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2
3
17 (a) P. J. Chirik, K. Wieghardt, Science 2010, 327, 794; (b) S. C.
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18 For the use of TEMPO to study metal carbene radical: (a) N. D.
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4
5
For selected reviews of dirhodium catalyzed metal carbene
reactions: (a) Y. Deng, H. Qiu, H. D.Srinivas, M. P. Doyle, Curr.
Org. Chem. 2015, 20, 61; (b) J. Hansen, H. M. L. Davies, Coord.
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