An Iron(II) Ylide Complex as a Masked Open-Shell Iron Alkylidene Species in Its Alkylidene-Transfer Reactions with Alkenes

Article abstract of DOI:10.1021/jacs.7b00484

Transition-metal alkylidenes are important reactive organometallic intermediates, and our current knowledge on them has been mainly restricted to those with closed-shell electronic configurations. In this study, we present an exploration on open-shell iron alkylidenes with a weak-field tripodal amido-phosphine-amido ligand. We found that a high-spin (amido-phosphine-amido)iron(II) complex can react with (p-tolyl)₂CN₂ to afford a high-spin (amido-ylide-amido)iron(II) complex, 2, which could transfer its alkylidene moiety to a variety of alkenes, either the electron-rich or electron-deficient ones, to form cyclopropane derivatives. The reaction of 2 with cis-β-deuterio-styrene gave deuterated cyclopropane derivatives with partial loss of the stereochemical integrity with respect to the cis-styrene. Kinetic study on the cyclopropanation reaction of 2 with 4-fluoro-styrene disclosed the activation parameters of ΔH^? = 23 ± 1 kcal/mol and ΔS^? = ?20 ± 3 cal/mol/K, which are comparable to those of the cyclopropanation reactions involving transition-metal alkylidenes. However, the cyclopropanation of para-substituted styrenes by 2 shows a nonlinear Hammett plot of log(k_X/k_H) vs σ_p. By introduction of a radical parameter, a linear plot of log(k_X/k_H) vs 0.59σ_p + 0.55σ_c^? was obtained, which suggests the “nucleophilic” radical nature of the transition state of the cyclopropanation step. In corroboration with the experimental observations, density functional theory calculation on the reaction of 2 with styrene suggests the involvement of an open-shell (amido-phosphine-amido)iron alkylidene intermediate that is higher in energy than its (amido-ylide-amido)iron(II) precursor and an “outer-sphere” radical-type mechanism for the cyclopropanation step. The negative charge distribution on the alkylidene carbon atoms of the open-shell states (S = 2 and 1) explains the high activity of the cyclopropanation reaction toward electron-deficient alkenes. The study demonstrates the unique activity of open-shell iron alkylidene species beyond its closed-shell analogues, thus pointing out their potential synthetic usage in catalysis.

Full text of DOI:10.1021/jacs.7b00484

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Article
An Iron(II) Ylide Complex as A Masked Open-Shell Iron Alkylidene
Species in Its Alkylidene-Transfer Reactions with Alkenes
Jian Liu, Lianrui Hu, Lei Wang, Hui Chen, and Liang Deng
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b00484 • Publication Date (Web): 21 Feb 2017
Downloaded from http://pubs.acs.org on February 21, 2017
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Journal of the American Chemical Society
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An Iron(II) Ylide Complex as A Masked Open-Shell Iron Alkyli-
dene Species in Its Alkylidene-Transfer Reactions with Al-
kenes
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Jian Liu,†,§ Lianrui Hu,‡,§ Lei Wang,† Hui Chen,*,‡ and Liang Deng*,†
†State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, University of Chinese Acadꢀ
emy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai, 200032, P. R. China. ‡Beijing National Laꢀ
boratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciꢀ
ences, Beijing, 100190, P. R. China.
ABSTRACT: Transitionꢀmetal alkylidenes are important reactive organometallic intermediates, and our current knowledge on
them has been mainly restricted to those with closedꢀshell electronic configurations. In this study, we present the exploration on
openꢀshell iron alkylidenes with a weakꢀfield tripodal amidoꢀphosphineꢀamido ligand. We found that a highꢀspin (amidoꢀ
phosphineꢀamido)iron(II) complex can react with (pꢀtolyl)2CN2 to afford a highꢀspin (amidoꢀylideꢀamido)iron(II) complex, 2,
which could transfer its alkylidene moiety to a variety of alkenes, either the electronꢀrich or electronꢀdeficient ones, to form cycloꢀ
propane derivatives. The reaction of 2 with cisꢀβꢀdeuterioꢀstyrene gave deuterated cyclopropane derivatives with partial loss of the
stereochemical integrity with respect to the cisꢀstyrene. Kinetic study on the cyclopropanation reaction of 2 with 4ꢀfluoroꢀstyrene
disclosed the activation parameters of ꢁH‡ = 23±1 kcal/mol and ꢁS‡ = ꢀ20±3 cal/mol/K, which are comparable to those of the
cyclopropanation reactions involving transitionꢀmetal alkylidenes. However, the cyclopropanation reaction of paraꢀsubstituted styꢀ
renes by 2 shows a nonꢀlinear Hammett plot of log(kX/kH) vs. σp. By the introduction of radical parameter, a linear plot of
log(kX/kH) vs. 0.59σp+0.55σc· was obtained, which suggests the “nucleophilic” radical nature of transitionꢀstate of the cyclopropaꢀ
nation step. In corroboration with the experimental observations, density functional theory calculation on the reaction of 2 with
styrene suggests the involvement of openꢀshell (amidoꢀphosphineꢀamido)iron alkylidene intermediate that is higher in energy than
its (amidoꢀylideꢀamido)iron(II) precursor and an “outerꢀsphere” radical type mechanism for the cyclopropanation step. The negative
charge distribution on the alkylidene carbon atoms of the openꢀshell states (S = 2 and 1) explains the high activity of the cycloproꢀ
panation reaction toward electronꢀdeficient alkenes. The study demonstrates the unique activity of openꢀshell iron alkylidene speꢀ
cies beyond its closedꢀshell analogs, thus pointing out their potential synthetic usage in catalysis.
Introduction
and some of them, the 18eꢀ cyclopentadienyliron and porphyꢀ
rin iron alkylidene complexes A and C, can react with alkenes
to form cyclopropanes.2b,5
Transitionꢀmetal alkylidene/carbene species1 in the form of
LnM(CR1R2) (R1, R2 = H, alkyl and aryl) are recognized as the
key intermediates of many important transitionꢀmetalꢀ
mediated organic transformations, e.g. alkene cyclopropanaꢀ
tion, CꢀH alkylation, and alkene metathesis.2 Therefore, with
the aim of developing new iron catalysts as alternatives to the
known precious metal catalysts, there has been great interest in
iron alkylidene complexes.3 Among the reported iron alkyliꢀ
dene complexes, the closedꢀshell diamagnetic complexes are
the best studied ones. Complexes of the type includes the cyꢀ
clopentadienyliron complexes [CpFeL2(CR1R2)]+ (R1, R2 = H,
alkyl and aryl; L = CO, phosphine, A in Chart 1),4 the porphyꢀ
rin iron complexes [(TPFPP)Fe(CPhR)] (R = Ph (B), CO2Et,
Chart 1. Examples of Isolable Iron Alkylidene Complexes
CO2CH2CH=CH2;
TPFPP
=
mesoꢀ
and
tetrakis(pentafluorophenyl)porphyrinato)5
[(TPFPP)Fe(ImMe)(CPh2)] (ImMe = Nꢀmethyl imidazole, C),5
the (tetrazaannulene)iron complex [(tmtaa)Fe(CPh2)] (tmtaa =
tetramethyldibenzotetrazaannulene, D),6 and also Wolczanꢀ
ski’s sixꢀcoordinate formal iron(IV) complexes bearing chelatꢀ
ing alkylidene ligands (E and F).7 Theoretical studies suggest
that these closedꢀshell alkylidene complexes are better to be
viewed as lowꢀspin iron(II) complexes featuring singlet carꢀ
bene ligands [:CR1R2]0.6ꢀ8 Therefore, they are electrophilic,
In contrast to plenty of studies on closedꢀshell iron alkyliꢀ
dene complexes, the chemistry of their openꢀshell congeners is
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rarely known. Floriani reported the preparation of the (caꢀ
lix[4]ꢀarene)iron alkylidene complexes [(calix[4]ꢀ
dfpN2P)Fe(THF)2] (1) was isolated as yellow crystals in 71%
yield (Scheme 1). A singleꢀcrystal Xꢀray diffraction study
1
2
3
4
5
6
7
8
arene)Fe(CPh2)] (G) from the reaction of the iron(II) precurꢀ
sors with Ph2CN2.9 Magnetic property studies indicated an S =
2 ground spinꢀstate for these complexes.9 Probably due to steꢀ
ric shielding by calix[4]ꢀarenes, they are highly thermal stable
and kinetically inert. Chirik synthesized fourꢀcoordinate iron
diphenylidene complexes [(PDI)Fe(CPh2)] (H) via the reacꢀ
tions of (bisimidopyridine)iron dinitrogen complexes with
Ph2CN2.10 Spectroscopic characterization and theoretical studꢀ
ies established the openꢀshell (S = 1) nature of these 16eꢀ iron
alkylidene complexes that contain a highꢀspin iron(II) center
antiꢀferromagnetically coupled with bis(imino)pyridine and
carbene radicals. The (bisiminopyridine)iron alkylidene comꢀ
plexes are unreactive toward alkenes.10 In addition, Shaik’s
recent theoretical study11 revealed the openꢀshell singlet
revealed the facial coordination mode of the dianionic amidoꢀ
phosphineꢀamido chelate [dfpN2P]2ꢀ to the iron center that is
further coordinating with two THF molecules to form a trigoꢀ
nal bipyramidal geometry (Figure S1). The long FeꢀP (2.424(2)
Å), FeꢀO (2.138(3) and 2.198(3) Å), and FeꢀN (2.030(2) Å)
separations observed in the structure are typical of highꢀspin
ferrous complexes. The measured solution magnetic moment
(ꢁeff = 4.4(1) ꢁB in C6D6) and zeroꢀfield 57Fe Mössbauer data
(isomer shift δ = 0.94 mm/s, quadrupole splitting |ꢁEQ| = 2.46
mm/s at 80 K, Figure S2) corroborate the highꢀspin (S = 2)
ground spinꢀstate for 1.
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Scheme 1. Synthesis of the Iron(II) Ylide Complex
THF
dfp
dfp
Ph
+ 0.5 equiv.
NH
HN
ground
state
of
the
iron
alkylidene
species
P
FeII THF
[Fe(N(TMS)2)2]2
[(por)Fe(SMe)(CHCO2Et)]ꢀ that has the two antiꢀ
ferromagnetically coupled electrons residing on the lowꢀspin
iron(III) center and the carbene ligand. NBO charge analysis
indicated the electrophilic nature of the carbene moiety in
[(por)Fe(SMe)(CHCO2Et)]ꢀ at its openꢀshell singlet state.11
P
THF, r.t.,
- HN(TMS)2
N
Ph
N
dfp
dfp
H2[dfpN2P]
1
dfp = 2,6-difluorophenyl
p-tolyl
tolyl-p
The limited knowledge on openꢀshell iron alkylidenes forms
a sharp contrast to the rich chemistry of openꢀshell iron imido
and oxo complexes,1c,12 and also that of openꢀshell cobalt alꢀ
kylidene complexes.13ꢀ15 Aiming to explore the chemistry of
openꢀshell iron alkylidenes, we envisioned the use of weakꢀ
field tripodal ligands to access openꢀshell iron alkylidene speꢀ
cies.16 In this context, we report herein the study with a tripoꢀ
Ph
THF
+ (p-tolyl)2CN2
FeII
P
THF, r.t.
- N2
N
N
dfp
dfp
2
dal
amidoꢀphosphineꢀamido
ligand,17
bis(Nꢀ(2,6ꢀ
difluorophenyl)ꢀoꢀaminophenyl)phenylphosphine
[dfpN2P]2ꢀ,
which led to the preparation of a “masked” iron alkylidene
complex, a highꢀspin (amidoꢀylideꢀamido)iron(II) complex,
from the reaction of an (amidoꢀphosphineꢀamido)iron(II)
complex with (pꢀtolyl)2CN2. Intriguingly, the “masked” iron
alkylidene complex effects alkylideneꢀtransfer to both elecꢀ
tronꢀrich and electronꢀdeficient alkenes to form cycloproꢀ
panes. Kinetic and theoretical studies on the cyclopropanation
reaction suggest the involvement of openꢀshell (amidoꢀ
phosphineꢀamido)iron alkylidene intermediate, and that the
openꢀshell iron alkylidene intermediate supported by the tripꢀ
odal amidoꢀphosphineꢀamido ligand shows “nucleophilic”
alkylidene radical character, showcasing a distinct reactivity of
openꢀshell iron alkylidene species over its closedꢀshell congeꢀ
ners that are usually electrophilic.2b,4ꢀ6
Results and Discussion
Figure 1. Molecular structure of 2, showing 30% probability elꢀ
lipsoids and the partial atom numbering scheme. Selected distancꢀ
es (Å) and angles (deg): Fe(1)ꢀC(55) 2.138(4), Fe(1)ꢀN(1)
2.002(4), Fe(1)ꢀN(2) 1.985(4), Fe(1)ꢀO(1) 2.011(4), P(1)ꢀC(55)
1.784(4), Fe(1)ꢀC(55)ꢀP(1) 90.9(2).
Preparation and Characterization of the “Masked” Iron
Alkylidene Complex. Previously, we found that the interacꢀ
tion of organic azides with the iron(II) complex [(κꢀN,N,Pꢀ
mesN2P)Fe(OEt2)] containing the tripodal ligand bis(Nꢀmesitylꢀ
oꢀaminophenyl)phenylphosphine led to facile CꢀH amination
reactions on the benzylic position of the ligand.16 To avoid
similar CꢀH activation reaction by the desired iron alkylidene
species, the new ligand incorporating Nꢀ2,6ꢀdifluorophenyl
Complex 1 can readily react with (pꢀtolyl)2CN2 at room
temperature to produce a yellow solution, from which the
iron(II) ylide complex [(κꢀN,N,CꢀdfpN2PC(tolylꢀp)2)Fe(THF)]
(2 in Scheme 1), rather than the desired alkylidene complex
(κꢀN,N,PꢀdfpN2P)Fe(C(tolylꢀp)2)(THF), was isolated as a yelꢀ
low crystalline solid in 81% yield. Complex 2 was characterꢀ
ized by 1H NMR spectroscopy (Figure S13), solution magnetic
susceptibility measurement, singleꢀcrystal Xꢀray diffraction
study, zeroꢀfield 57Fe Mössbauer spectroscopy, and elemental
analysis. The Mössbauer data (δ = 0.77 mm/s, |ꢁEQ|
substituents,
bis(Nꢀ(2,6ꢀdifluorophenyl)ꢀoꢀ
aminophenyl)phenylphosphine H2(dfpN2P), was prepared. As
shown below, this amidoꢀphosphineꢀamido ligand also funcꢀ
tions as a tripodal ligand when coordinating with iron.
Treatment of [Fe(N(SiMe3)2)2]2 with H2(dfpN2P) (2 equiv.) in
THF at room temperature gave a yellow suspension. After
workup and recrystallization, the iron(II) complex [(κꢀN,N,Pꢀ
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Table 1. Cyclopropanation Reactions of the Iron(II) Ylide Complex with Alkenes a
1
tolyl-p
tolyl-p
2
3
4
toluene or C6D6
r.t. or 80 oC
+
2
R
3
R
5
6
7
8
entry
1
substrate
temp.
r.t.
time
product
yield b
entry
substrate
temp.
time
product
yield b
tolyl-p
tolyl-p
3i
tolyl-p
88%
(39%)
(77%)
80 o
C
30 min
9
9 h
tolyl-p
Me2N
3a
9
Me2N
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
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58
59
60
tolyl-p
tolyl-p
tolyl-p
tolyl-p
91%
(79%)
80 o
80 o
80 o
C
C
C
(66%)
(76%)
(70%)
80 o
C
2
3
4
6 h
10
11
12
10 h
n-C6H13
n-C6H13
F
3j
3b
F
tolyl-p
tolyl-p
tolyl-p
94%
(67%)
80 o
C
6 h
8 h
tolyl-p
Cl
3k
3c
Cl
tolyl-p
tolyl-p
tolyl-p
90%
(66%)
80 o
C
12 h
4 h
Ph
tolyl-p
Ph
F3C
3l
3d
F3C
tolyl-p
tolyl-p
tolyl-p
90%
(81%)
80 o
80 o
80 o
80 o
C
C
C
C
80 o
80 o
80 o
80 o
C
(83%)
(97%)
5
6
7
8
14 h
14 h
10 h
11 h
13
14
15
16
30 min
Ph
tolyl-
p
3e
Ph
3m
tolyl-p
tolyl-p
tolyl-p
90%
(60%)
3 h
p-toly
C
C
C
tolyl-p
Ph
p-toly
Ph
3f
3n
tolyl-p
tolyl-p
tolyl-p
EtO
tolyl-p
89%
(57%)
88%
(61%)
7 h
EtO
O
MeO
3o
3g
O
MeO
tolyl-p
tolyl-p
tolyl-p
3p
tolyl-p
3h
96%
(72%)
22%
(16%)
9 h
NC
tBu
NC
tBu
a 2 with 3 equiv. of alkene. b NMR Yields (isolated yields) based on 2 with 1,3,5ꢀtrimethoxybenzene as the internal standard.
= 3.38 mm/s at 80 K, Figure S3) and magnetic moment (4.7(1)
ꢁB in C6D6 at room temperature) support the highꢀspin ferrous
nature of 2. As shown in Figure 1, the iron(II) center in 2 is
coordinating with a tripodal amidoꢀylideꢀamido ligand and a
THF molecule, forming a tetrahedral geometry with pyramidal
distortion (τ4 = 0.35).18 The newly formed ylide sideꢀarm has
the FeꢀC distance of 2.138(4) Å, being slightly longer than
those of the reported ylide complexes [Fe(CO)4(CH2PPh3)]
(2.122(3) Å)19 and [(Cp*)Fe(CO)2(CH2PPh3)][BF4] (2.11(1)
Å).20 Its PꢀCPh2 bond (1.784(4) Å) is longer than its congener
in CH2PPh3 (1.661(8) Å),21 and locates on the long end of the
PꢀC bonds of the reported phosphonium ylide metal complexꢀ
Å. The long PꢀC bond and acute FeꢀCꢀP angle reflect geomeꢀ
try constraint within the molecule.
The attainment of 2 from the reaction of 1 with the diazo
compound implicates the high reactivity of the iron alkylidene
intermediate (κꢀN,N,PꢀdfpN2P)Fe(C(tolylꢀp)2)(THF), which,
once formed, could undergo migratory insertion with the
phosphine ligand to form the iron ylide complex 2. The transꢀ
formation is reminiscent of the oneꢀelectron oxidationꢀ
triggered conversion of the nickel(II) alkylidene complex
[(dtbpe)Ni(CHdmp)] to the ylide complex [{κꢀP,Cꢀ
(But2PCH2CH2P(But)2CH(dmp))}Ni][BArF ].24 As the bulky
4
amineꢀphosphineꢀamine ligand H2(dfpN2P) proved unreactive
toward (pꢀtolyl)2CN2 at ambient conditions, the alternative
mechanism accounting for the formation of 2, which involves
the direct nucleophilic attack of the phosphine moiety to the
diazo compound, seems less likely.
es,
e.g.
[Co(PPh3)(CH2PPh3)Cl2]
(1.739
[{κꢀC,Cꢀ(NHCꢀ
Å),22
[Fe(CO)4(CH2PPh3)]
PPh2CH2)}Pd(C3H5)][OTf]
(1.755(3)
Å),19
(1.72(1)
Å),23
[(Cp*)Fe(CO)2(CH2PPh3)][BF4] (1.78(1) Å),20 [{κꢀP,Cꢀ
(But2PCH2CH2P(But)2CH(dmp))}Ni][BArF ] (1.811(4) Å).24
4
AlkylideneꢀTransfer Reactions of 2 with Alkenes. The
novel structure features of the iron(II) ylide complex, long PꢀC
separation, and acute FeꢀCꢀP angle, hint its potential to perꢀ
form alkylideneꢀtransfer reactions. Noted this, the reactions of
2 with alkenes were examined. Indeed, complex 2 can react
The FeꢀCꢀP angle (90.9(2)o) in 2 is acute and smaller than
those of the reported ylide complexes, which span in the range
100o to 140o.25 Alongside the small FeꢀCꢀP angle, the Fe···P
separation (2.81 Å) in 2 is merely longer than that of 1 by 0.42
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with various alkenes to produce cyclopropanation products 3 shows the change of yield versus time for the reaction employꢀ
1
2
3
4
5
6
7
8
in good to excellent yields (Table 1), along with 1 as the ironꢀ
containing product (Figure S4). An important feature of the
cyclopropanation reaction is its broad scope of alkenes as not
only electronꢀrich alkenes but also electronꢀdeficient alkenes
can be applied. The reactions of 2 with alkenes bearing alkyl
(entries 2ꢀ4, and 13), aryl (entries 5ꢀ12), alkenyl (entry 14),
ester (entry 15) groups gave the corresponding cyclopropanaꢀ
tion products in comparable yields despite of their differentiatꢀ
ed rates (vide infra). In spite of the coordinating nature of cyꢀ
ano group, the trial with 4ꢀcyanoꢀstyrene could still afford the
cyclopropanation product in 22% yield (entry 16). The cycloꢀ
propanation reaction is affected by the steric property of alꢀ
kenes. The interaction of 2 with the smallest alkene, ethylene,
took place at room temperature and completed in 0.5 h (entry
1). The reactions with substituted alkenes required higher
ing 35 equiv. of 4ꢀfluoroꢀstyrene. The linear dependence of the
observed pseudoꢀfirstꢀorder rate constants, kobs, on the alkene
concentration indicates that the reaction is also firstꢀorder in 4ꢀ
fluoroꢀstyrene (inset in Figure 2). The rate constants acquired
o
in the temperature range 45 to 85 C under the pseudoꢀfirstꢀ
order conditions using 20 equiv. of 4ꢀfluoroꢀstyrene are shown
in Table S2. The Eyring plot (Figure 3) gave the activation
parameters ꢁH‡ = 23±1 kcal/mol and ꢁS‡ = ꢀ20±3 cal/mol/K.
The large and negative entropy change indicates an associative
mechanism for the cyclopropanation reaction. These activation
parameters can be compared with those of cyclopropanation
reactions by transitionꢀmetal alkylidene species. For examples,
the reaction of the tungsten complex W(CO)5(CHC6H4ꢀOMeꢀp)
with vinyl acetate has ꢁH‡ = 10 kcal/mol and ꢁS‡ = ꢀ34
cal/mol/K,27 that of Warren’s copper alkylidene
[(nacnac)Cu(CPh2)] with styrene has ꢁH‡ = 10 kcal/mol and
ꢁS‡ = ꢀ32 cal/mol/K,28 and the copper(I) triflateꢀcatalyzed
cyclopropanation of 1ꢀhexene by ethyl diazoacetate has ꢁH‡ =
19 kcal/mol and ꢁS‡ = ꢀ9 cal/mol/K.29
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48
49
50
51
52
53
54
55
56
57
58
59
60
o
temperature (80 C) and longer reaction times (entries 2ꢀ16).
The internal alkenes, cyclohexene and cisꢀstilbene, are unreacꢀ
tive with 2 either at room temperature or 80 oC. For diꢀ
substituted alkenes, the only successful trial is the one with
norbornene, which gave the exoꢀaddition product in 83% yield
(entry 13). In contrast to these ironꢀmediated cyclopropanation
reactions, phosphonium ylides alone are known unreactive
toward nonꢀactivated alkenes.26
Scheme 2. Cyclopropanation of 4ꢀFluoroꢀStyrene by 2
tolyl-p
C6D6
tolyl-p
+ 2
45-85 o
C
F
3j
F
(10-35 equiv.)
Figure 3. Erying plot for the cyclopropanation of 4ꢀfluoroꢀstyrene
by 2 in C6D6 at the temperature range 45ꢀ85 oC.
Scheme 3. Competition Reactions
tolyl-p
tolyl-p
(3 equiv.)
+ 2
+
+
C6D6, 80 oC, 2 h
tolyl-p
tolyl-p
X
(3 equiv.)
X
Figure 2. Representative plot for the change of the yield of the
cyclopropanation product versus time for the reaction of 2 with 4ꢀ
fluoroꢀstyrene in C6D6 at 60 C. Inset: the linear dependence of
the observed pseudoꢀfirstꢀorder rate constants, kobs, versus alkene
concentration.
In order to probe the nature of the reactive species in the cyꢀ
clopropanation reaction, the relative rates of the cyclopropanaꢀ
tion of a series of paraꢀsubstituted styrenes by the ylide comꢀ
plex 2 were measured by competition experiments (Scheme 3).
As listed in Table 2, the styrene derivatives with either elecꢀ
tronꢀdonating or electronꢀwithdrawing substituents on the paꢀ
raꢀposition are found more reactive than styrene. Interestingly,
the electronꢀrich styrene derivatives only show slight rateꢀ
acceleration, whereas, the electronꢀwithdrawing substitutes
exhibit apparently rate acceleration. Plotting log(kX/kH) versus
σp gave a nonꢀlinear plot (Figure 4a) that is in striking differꢀ
ence to the linear plots of many of the reported transitionꢀ
metalꢀmediated or ꢀcatalyzed cyclopropanation reactions, e.g.
o
The cyclopropanation reaction of 2 shows a close resemꢀ
blance to those of transitionꢀmetal alkylidene complexes. Such
reactivity, however, is atypical for phosphonium yildes. Aimꢀ
ing to throw light on their reaction mechanisms, the reactions
of 2 with styrenes were examined in detail by kinetic studies.
Monitoring the increase of the 19F NMR signal of 2ꢀ(pꢀ
fluorophenyl)ꢀ1,1ꢀdi(pꢀtolyl)cyclopropane formed in the reacꢀ
tion of 2 with excess amount of 4ꢀfluoroꢀstyrene (10ꢀ35 equiv.)
o
in C6D6 at 60 C (Scheme 2) revealed the pseudoꢀfirstꢀorder
the
reaction
of
paraꢀsubstituted
styrenes
with
kinetics of the reaction. As a representative example, Figure 2
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[(TPFPP)Fe(CPhCOOEt)] (ρ = ꢀ0.41),5 the (TTP)Feꢀcatalyzed tion of substituted styrenes,35b alkene aziridation by
bis(tosylimido)ruthenium(VI) porphyrins,35c alkene aziridation
by organic azides catalyzed by ferrous dipyrrinato complexꢀ
es,35d and alkene aziridation by PhINTs catalyzed by copper(I)
tris(pyrazolyl)borate.32 The nonꢀlinearity was thought to hint
the existence of intermediates that have significant radical
character. Noted this, spinꢀdelocalization effect of the substitꢀ
uents was taken into account using the dual parameter equaꢀ
tion log(kX/kH) = ρXσX + ρ·σ·.36 While the multiple linear reꢀ
1
2
3
4
5
6
7
8
cyclopropanation of styrenes with ethyl diazoacetate (ρ = ꢀ
0.68),30 myoglobinꢀcatalyzed cyclopropanation of styrenes
with ethyl diazoacetate (ρ = ꢀ0.34),31 and Pérez’s copperꢀ
catalyzed cyclopropanation reaction (ρ = ꢀ0.85).32 In the latter
cases, the negative ρ values suggest the electrophilic nature of
the metal carbene intermediates.
Table 2. Relative Rates log(kX/kH) with σp and σc· Scales
for the Cyclopropanation of ParaꢀSubstituted Styrenes by
36
gression for the equation using Jiang’s σmb and σJJ· scales
2 a,b
9
gave poor linear correlation (R2 = 0.55), an appreciably better
linearity (R2 = 0.98) was achieved when the Hammett constant
σp 33 and Creary’s radical scale σc· 34 were applied, resulting in
ρp and ρc· values of 0.59 and 0.55, respectively (Figure 4b).
The positive ρp value implies that the attack toward the alkenes
is “nucleophilic”, being distinct from the reactions of the
aforementioned electrophilic metal carbene species with styꢀ
renes.2b,5,31,32 The positive ρp value, on the other hand, accounts
for the failure of using σmb and σJJ· scales to achieve good lineꢀ
ar fitting as these scales were obtained from reactions involvꢀ
ing electrophilic radicals.36 The ρp/ρc· ratio of 1.07 indicates
that both polar and spin effects are important in the ironꢀ
mediated cyclopropanation reaction. Notably, the scales σp and
σc· have proved successful for the dual parameter correlation
analysis of a bromoꢀabstraction reaction by a nucleophilic silyl
radical.37
10
11
12
13
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60
sub.
Me2N
MeO
But
kX/kH
1.28
1.24
1.18
1.16
1.25
1.88
3.12
log(kX/kH) σp
σc·
0.11
ꢀ0.83
0.90
0.24
0.13
0.11
ꢀ0.08
0.12
0.08
0.093
0.072
0.060
0.099
0.274
0.49
ꢀ0.27
ꢀ0.20
ꢀ0.17
0.06
0.23
0.54
CH3
F
Cl
CF3
a σp are Hammett constants measured on paraꢀsubstituented arꢀ
yl derivatives.33 b σc· are Creary’s constants.34
Scheme 4. Reaction of 2 with cisꢀβꢀDeuterioꢀStyrene
tolyl-p
tolyl-p
tolyl-p
tolyl-p
Hα
Hα
Hα
Hβ
2
+
+
Hβ
D
D
toluene
80 oC, 3h
Hβ
D
(3 equiv.)
cis-D-3e
trans-D-3e
JH β = 6.3 Hz
J
Hα−Hβ = 8.9 Hz
α−
H
cis : trans = 2.1 : 1
To gain insights into the stereochemistry of the cyclopropaꢀ
nation reaction, the reaction of 2 with the stereospecifically
labeled styrene cisꢀβꢀdeuterioꢀstyrene was tested. As seen in
Scheme 4 and Figures S48ꢀS50, the reaction yields a mixture
of cisꢀ and transꢀproducts with a ratio of 2.1 to 1 according to
2
1H and H NMR spectra. The partial loss of stereospecifity is
different from the cyclopropanation reactions by
[CpFeL2(CR1R2)]+ and [W(CO)5(CHPh)], which show high
stereochemical integrity,2b whereas, similar situation (loss of
stereospecifity) is known in alkene cyclopropanation, epoxidaꢀ
tion, and aziridation by certain porphyrinꢀmetal carbene,38a
oxo,38b and imido species.35c The scrambling of the deuterium
label implies the involvement of a stepwise pathway for the Cꢀ
C bond formation steps of the cyclopropanation reaction. The
low percentage of the transꢀproduct apparently suggests a
rapid ringꢀclosure step in a stepwise pathway. In addition to a
stepwise pathway, the high percentage of the cisꢀproduct sugꢀ
gests that the involvement of a concerted pathway in the cyꢀ
clopropanation step could not be excluded. Notably, these
understandings also provide explanation to the observation of
the absence of the ringꢀopening product in the reaction of 2
with the cyclopropyl ethene (entry 4 in Table 1).
Figure 4. Linearꢀfreeꢀenergy correlation of log(kX/kH) vs σp (a)
and vs 0.59σp+0.55σc· (b) for the cyclopropanation of paraꢀ
substituted styrene derivatives by 2.
In groupꢀtransfer reactions, nonꢀlinear Hammett plots have
been observed on the alkene epoxidation by transꢀ
dioxoruthenium(VI) porphyrins,35a amineꢀaccelerated osmylaꢀ
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tolyl-p
p-tolyl
p-tolyl
tolyl-p
THF
Ph
1
2
3
4
5
6
7
8
Quintet
Triplet
Singlet
Ph
p-tolyl
p-tolyl
P
N
Fe THF
N
Fe
ꢀH
P
(kcal/mol)
N
N
TS2-S
Ph
THF
Fe
N
P
TSS-T/S-L
42.6
40.7
27.2
17.2
N
P
[
dfpN2P]2-
TST-L
N
N
32.4
27.6
31.1
30.0
28.0
32.3
16.5
tolyl-p
Ph
9
26.5
p-tolyl
10
11
12
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59
60
17.3
0.0
THF
Fe
P
N
N
13.2
7.7
L
S
T
-1.5
p-tolyl tolyl-p
2
p-tolyl tolyl-p
Ph
p-tolyl
tolyl-p
THF
Fe
-10.2
P
P
Fe THF
N
THF
N
Fe
P
N
N
N
N
-22.1
Figure 5. Calculated pathways for the cyclopropanation reaction of 2 with styrene.
Theoretical Study on the Mechanism of the Reaction of
2 with Styrene. As the aforementioned results collectively
point out that the cyclopropanation reaction of 2 with the subꢀ
stituted styrenes probably involves the attack of a nucleophilic
iron alkylidene intermediate toward the alkenes with a spinꢀ
delocalized transitionꢀstate, DFT calculations on the reaction
of (dfpN2PC(tolylꢀp)2)Fe(THF) (2) with styrene were perꢀ
formed to evaluate the possibility.
mental stereochemical result of cisꢀβꢀdeuterioꢀstyrene
(Scheme 4). As a result, there could be a twoꢀstate reactivity
scenario operative in cyclopropanation reactions.39 Alternative
to “outerꢀsphere” mechanism, we also explored the correꢀ
sponding “innerꢀsphere” mechanism of cyclopropanation reacꢀ
tion between 2 and styrene (Figure S61). Compared to the
corresponding transition states (TSSꢀL and TSSꢀT) in “outerꢀ
sphere” mechanism, the higherꢀlying transition states of interꢀ
action between alkylidene moiety with the C=C double bond
of styrene in “innerꢀsphere” mechanism do not support this
mechanism for cyclopropanation reaction. These calculations,
along with the results of kinetic studies, suggest that “outerꢀ
sphere” pathway is more likely to be involved in the cycloproꢀ
panation reactions under study.
The computed reaction profiles show that the interaction of
the iron alkylidene intermediate (dfpN2P)Fe(C(tolylꢀp)2)(THF)
(S) with styrene in an “outerꢀsphere” manner indeed could be
responsible for the formation of the cyclopropanation product
(Figure 5). The transformation from the ylide complex 2 to the
iron alkylidene S on the quintet energy surface has to surꢀ
mount an activation barrier of 17.2 kcal/mol. The alkylidene
intermediate S has a triplet (S = 1) ground state that is higher
in energy than the reactant (dfpN2PC(tolylꢀp)2)Fe(THF) (2) in
its quintet (S = 2) ground spinꢀstate by 13.2 kcal/mol. The high
energy of S than 2 explains the failure of detecting the iron
alkylidene intermediate in our experimental studies. Followꢀ
ing the formation of the alkylidene intermediate, the interacꢀ
tion of its alkylidene moiety with the C=C double bond of
styrene via either a concerted manner (TSSꢀL) on the quintet
surface or a stepwise way (TSSꢀT) on the triplet or singlet surꢀ
face could result in the formation of the cyclopropanation
product. Along each surface, the transition state of the reaction
between S and styrene (TSSꢀL or TSSꢀT) lay the highest on the
energy surfaces, being 27.6, 32.4, and 42.6 kcal/mol higher
than the reactants (2 and styrene) on the quintet, triplet, and
singlet energy surfaces, respectively. Among these three barriꢀ
ers, the lower one (27.6 kcal/mol) on the quintet surface is
more comparable to the experimental activation enthalpy ꢁH‡
= 23±1 kcal/mol acquired from the cyclopropanation of 4ꢀ
Figure 6. The calculated structures of (dfpN2P)Fe(C(tolylꢀ
p)2)(THF) (S) (left), and the transition state TSSꢀL/SꢀT (right) at
their triplet and quintet states, respectively. Selected bond disꢀ
5
3
tances (Å) for S: FeꢀC1 2.001, FeꢀP 2.410, PꢀC1 2.928; for S:
5
FeꢀC1 1.935, FeꢀP 2.2620, PꢀC1 2.852; for TSSꢀL: FeꢀC1 2.197,
FeꢀP 2.423, PꢀC1 3.264, C1ꢀCβ 2.076, C1ꢀCα 2.791, CαꢀCβ 1.394;
and for 3TSSꢀT: FeꢀC1 2.053, FeꢀP 2.326, PꢀC1 3.093, C1ꢀCβ
2.109, C1ꢀCα 2.918, CαꢀCβ 1.406.
5
fluoroꢀstyrene. However, the relatively close energies of TSSꢀ
L (quintet) and TSSꢀT (triplet) imply that they can both be viaꢀ
ble in the cyclopropanation reaction, therefore indicating the
possibility of involving both the concerted and the stepwise
mechanisms of cyclopropanation, as inferred by the experiꢀ
3
Noting the limited knowledge on openꢀshell iron alkylidene
species, the openꢀshell nature of (dfpN2P)Fe(C(tolylꢀp)2)(THF)
(S) is noteworthy. Benefited from the weakꢀfield nature of the
tripodal amidoꢀphosphineꢀamido ligand, the alkylidene species
has a triplet ground state, with the quintet state lying slightly
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higher by only 3.3 kcal/mol, but being substantially lower in The interaction of the iron alkylidene intermediate S with
1
2
3
4
5
6
7
8
energy than the closedꢀshell singlet state by 19.1 kcal/mol.
The iron centers in the structures of both openꢀshell states
display trigonal bipyramidal geometry with the alkylidene
carbon atoms sitting on the equatorial position. Figure 6 shows
the structure of S at the triplet state. The FeꢀC(alkylidene)
distances (1.935 and 2.001 Å for that of the triplet and quintet
states, respectively) locate between its congeners in the lowꢀ
styrene gives rise to the cyclopropanation product. The spin
and charge distributions of the transition states (3TSSꢀT and
5TSSꢀL) give explanations to the linearꢀfreeꢀenergy correlation
of the relative rates of the cyclopropanation of paraꢀ
substituted styrenes by 2 versus the substituent constants (Figꢀ
ure 4). In the transition states, there are high spin density on
the αꢀcarbon of the styrene moiety (ꢀ0.546 and 0.364 in 3TSSꢀT
5
spin
iron
alkylidene
complexes,
(1.787(8)
e.g.
and TSSꢀL, respectively), revealing the radical addition charꢀ
[CpFe(dppe)(CHMe)][CF3SO3]
Å),4
acter of the CꢀC bond formation step (Table 3). Moreover,
negative charges are discerned on the alkylidene carbon atoms
9
[(TPFPP)Fe(CPh2)] (1.767(3) Å),5 and [(tmtaa)Fe(CPh2)]
(1.794(3) Å),6 and fiveꢀcoordinate highꢀspin iron(II)ꢀNꢀ
heterocyclic carbene complexes (ca. 2.10 Å),40 implying cerꢀ
tain multiple bond nature of FeꢀC(alkylidene) interaction, at
least in the triplet structure. Indeed, the FeꢀC(alkylidene)
bonds in the triplet and quintet structures have the Wiberg
bond orders of 0.96 and 0.80, respectively, which are higher
than those of the FeꢀN bonds (0.47 and 0.45) in the same molꢀ
ecules.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
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30
31
32
33
34
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40
41
42
43
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49
50
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53
54
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56
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59
60
(ꢀ0.163, ꢀ0.174, ꢀ0.258 and ꢀ0.260 in 3S, 5S, 3TSSꢀT, and 5TSSꢀL
,
respectively), as well as the αꢀcarbon of the styrene moiety (ꢀ
0.058 and ꢀ0.048 in 3TSSꢀT and 5TSSꢀL, respectively). The negaꢀ
tive charge distribution on the carbene atom resembles the
Schrock carbene species and differs from Fischer carbene speꢀ
cies that have positive charge on the carbene carbon,13g hinting
the “nucleophilic” character of the openꢀshell iron alkylidene
3
5
species S and S. Thus, while both electronꢀdonating and
electronꢀwithdrawing substituents on styrene could stabilize
the transitionꢀstates that have radical character on the αꢀcarbon
of the styrene moiety, the “nucleophilic” character of the
openꢀshell iron alkylidene species renders further stabilization
on the transitionꢀstate of the reaction with more electronꢀ
deficient alkenes, whereas, that of the reactions with the more
electronꢀrich alkenes might be destabilized. Consequently,
introduction of electronꢀwithdrawing substituents on styrene
could result in larger rate acceleration for the cyclopropananꢀ
tion reaction by 2, whereas, rate acceleration in the reactions
with styrene bearing electronꢀdonating substituents is modest.
Noted this, one could reason that the absence of the ringꢀ
openning product in the reaction of 2 with the cyclopropyl
ethene (entry 4 in Table 1) could suggest a concerted
mechanism for the formation of the cyclopropane (5S to 5L via
5TSSꢀL in Figure 5) or a fast rate of the second CꢀC bond
formation step (3T to 3L via 3TSTꢀL in Figure 5) exceeding that
of the ringꢀopenning of cyclopropylmethyl radical (8.6×107 s−1
at 298 K).41 The high activity of the openꢀshell iron alkylidene
species S toward electronꢀdeficient alkenes forms a sharp conꢀ
trast to many of the closedꢀshell metal carbene species that
usually exhibit high activity toward electronꢀrich alkenes.
While whether this is a common reactivity feature of openꢀ
shell transitionꢀmetal carbene species or not has to wait for
more studies, we note that Zhang and de Bruin’s cobalt porꢀ
phyrin carbene radicals [(por)Co(CRCO2Et)] indeed show
higher activity toward electronꢀdeficient alkenes,13 and that Uꢀ
shaped Hammett plots were observed in the catalytic cycloꢀ
propanation reaction of diazo compound with styrenes using
(terpyridine)iron(II)/cobalt(II) catalysts.42 On the other hand,
the failure of observing cyclopropanation products in the reacꢀ
Table 3. Selected Structure Parameters of the Calculated
Structures (dfpN2P)Fe(C(tolylꢀp)2)(THF) (S) and the Transiꢀ
tion States of the Cyclopropanation Step
S = 1
3S
S = 2
3TSSꢀT 5S
5TSSꢀL
Bond Order of
FeꢀC1
0.96
0.73
0.80
0.47
Spin Densitya on
Fe
2.926
3.129
3.678
3.593
ꢀ0.079
0.364
C1
ꢀ0.703 ꢀ0.543 0.059
ꢀ0.546
Cα
Chargeb on
Fe
0.465
0.522
0.587
0.612
C1
Cα
ꢀ0.163 ꢀ0.258 ꢀ0.174 ꢀ0.260
ꢀ0.058 ꢀ0.048
a Mulliken spin density. b Mulliken charge
Notably, in spite of the formal iron(IV) nature of S, the
compositions of the frontier molecular orbitals (Figures S62
and S63) indicate that S at the triplet state should be best deꢀ
scribed as an intermediateꢀspin iron(III) species bearing an
antiꢀferromagnetically coupled carbene radical [C(tolylꢀp)2]•ꢀ
with an overlap of 0.55 for the two corresponding orbitals
(implying certain πꢀbonding nature of the FeꢀC(alkylidene)
interaction), and that S at the quintet state could be described
as an highꢀspin iron(II) species bearing an singlet carbene
[C(tolylꢀp)2]0 ligand. This assignment is also reflected by the
spinꢀdensity distribution as the iron and the alkylidene carbon
atoms in the triplet structure have the corresponding spin denꢀ
sity population values of 2.926 and ꢀ0.703, whereas, the fourꢀ
unpaired spin in the quintet structure locate essentially on the
iron center (Table 3). The antiꢀferromagnetic coupling of iron
center with carbene radical in S at its triplet state shows remiꢀ
niscence to that of Chirik’s openꢀshell iron alkylidene species
7a
tions of Chirik’s iron complex [(PDI)Fe(CPh2)] and Groysꢀ
15
man’s cobalt complex [Co(OCBut2Ph)2(CPh2)] with alkenes
might be due to steric hindrance.
Conclusion
We found that the reaction of a highꢀspin iron(II) complex
supported by a tripodal amidoꢀphosphineꢀamido ligand with
the diazo compound (pꢀtolyl)2CN2 affords a highꢀspin (amidoꢀ
ylideꢀamido)iron(II) complex that displays alkylideneꢀtransfer
reactivity toward alkenes. The reactions of the iron(II) ylide
complex with alkenes furnish cyclopropane derivatives in
good to excellent yields. These alkylideneꢀtransfer reactions
[(PDI)Fe(CPh2)],7a
Shaik’s
iron
porphyrin
carbene
[(por)Fe(SMe)(CHCO2Et)]ꢀ,11 Zhang and de Bruin’s cobalt
porphyrin carbenes [(por)Co(CRCO2Et)],13 and Groysman’s
cobalt carbene complex [Co(OCBut2Ph)2(CPh2)].15
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are atypical for phosphonium ylides, but show similarity to
corrections were applied using SADABS.48 Space groups were
1
2
3
4
5
6
7
8
transitionꢀmetal alkylidene complexes. Notably, the cycloproꢀ
panation reaction by the ylide complex could be applied to
alkenes bearing either electronꢀdonating or electronꢀ
withdrawing groups, being different from the common cycloꢀ
propanation reactions by electrophilic transitionꢀmetal alkyliꢀ
dene complexes. The latter ones usually occur on electronꢀrich
alkenes.
assigned unambiguously by analysis of symmetry and systemꢀ
atic absences determined by XPREP. All structures were
solved and refined using SHELXTL.49 Metal and first coordiꢀ
nation sphere atoms were located from directꢀmethods Eꢀmaps.
Nonꢀhydrogen atoms were found in alternating difference
Fourier synthesis and leastꢀsquares refinement cycles and durꢀ
ing final cycles were refined anisotropically. Table S1 summaꢀ
rizes the crystal data and summary of data collection and reꢀ
finement for the complexes.
57Fe Mössbauer Spectroscopy. All solid samples for 57Fe
Mössbauer spectroscopy were run on nonꢀenriched samples of
the asꢀisolated complexes. Each sample was loaded into a Delꢀ
rin Mössbauer sample cup for measurements and loaded under
liquid nitrogen. Low temperature 57Fe Mössbauer measureꢀ
ments were performed using a See Co. MS4 Mössbauer specꢀ
trometer integrated with a Janis SVTꢀ400T He/N2 cryostat for
measurements at 80 K. Isomer shifts were determined relative
to αꢀFe at 298 K. All Mössbauer spectra were fitted using the
program WMoss (SeeCo).
The activation parameters obtained from the kinetic studies
on the reaction of the iron ylide complex with 4ꢀfluoroꢀstyrene
(ꢁH‡ = 23±1 kcal/mol and ꢁS‡ = ꢀ20±3 cal/mol/K) are comꢀ
parable to those of the cyclopropanation reactions catalyzed or
mediated by transitionꢀmetal alkylidene species. Competition
reactions of the cyclopropanation of paraꢀsubstituted styrenes
versus styrene, however, revealed a linear plot of log(kX/kH)
9
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48
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58
59
60
vs. 0.59σp+0.55σc·, hinting the “nucleophilic” radical characꢀ
ter of the cyclopropanation step. DFT calculation on the reacꢀ
tion of the iron(II) ylide complex with styrene indicated that
the conversion of the iron(II) ylide complex to openꢀshell iron
alkylidene intermediate is energetically feasible, and that the
cyclopropanation step occurs via an “outerꢀsphere” radical
type mechanism between the openꢀshell iron alkylidene interꢀ
mediates (S = 2 or 1) and styrene, corroborating the experiꢀ
mental observations. These results prove the capability of tripꢀ
odal ligands in supporting openꢀshell iron alkylidene species
and also point out the potential application of nonꢀheme iron
catalyst for new alkylideneꢀtransfer reactions, which might be
beyond those based on their closedꢀshell analogs.
Preparation of (2,6ꢀF2C6H3)(2ꢀBrC6H4)NH: To an ovenꢀ
dried Schlenk tube was added Pd2(dba)3 (2.20 g, 2.40 mmol, 6
mol%) and racꢀBINAP (2.99 g, 4.80 mmol, 12 mol%). The
tube was capped with a Teflon screw cap, evacuated, and
backfilled with dinitrogen. After the Teflon screw cap was
replaced with a rubber septum, toluene (50 mL) was added via
syringe under dinitrogen atmosphere. The suspension was
o
heated at 60 C with stirring for 30 minutes. After cooling to
room temperature, 2,6ꢀF2ꢀC6H3NH2 (5.40 g, 41.8 mmol, 1.1
equiv.), 2ꢀBrꢀC6H4I (11.02 g, 39.0 mmol, 1 equiv.), and
ButONa (4.61 g, 48.0 mmol, 1.2 equiv.) were added under
dinitrogen atmosphere. The reaction mixture was heated at
110 oC with stirring for 48 hours. After filtration and removal
of volatiles, the crude product was purified by flash column
chromatography (silica gel, nꢀhexane as elute) to give (2,6ꢀ
F2C6H3)(2ꢀBrC6H4)NH as a colorless oil (9.81 g, 89% yield).
1H NMR (400 MHz, CDCl3, 295 K): δ (ppm) 7.58ꢀ7.48 (m,
1H), 7.22ꢀ7.07 (m, 2H), 7.06ꢀ6.94 (m, 2H), 6.82ꢀ6.72 (m, 1H),
6.70ꢀ6.59 (m, 1H), 5.84 (br, 1H, NH). 13C NMR (101 MHz,
CDCl3, 295 K): δ (ppm) 157.40 (dd, JCꢀF = 248.6, 5.2 Hz),
141.20 (s), 132.64 (s), 128.21 (s), 124.93 (t, JCꢀF = 9.6 Hz),
121.09 (s), 118.26 (t, JCꢀF = 15.5 Hz), 114.56 (t, JCꢀF = 2.2 Hz),
112.14 (dd, JCꢀF = 17.9, 5.6 Hz), 111.29 (s). 19F NMR (376
MHz, CDCl3, 295 K): δ (ppm) ꢀ119.20 (s). IR (thin film, cmꢀ1):
υ = 3393 (w), 3068 (w), 1587 (m), 1509 (s), 1471 (s), 1422
(m), 1312 (m), 1236 (m), 1024 (m), 1000 (s), 887 (w), 774 (m),
738 (s), 699 (m), 665 (w). HRMS (EI) calcd for C12H8BrF2N
(M+): 282.9808. Found: 282.9809.
Experimental Section
General Procedures. All experiments were performed either
under an atmosphere of dry dinitrogen with the rigid exclusion
of air and moisture using standard Schlenk techniques or in a
glovebox. Organic solvents were dried with a solvent purificaꢀ
tion system (Innovative Technology) and bubbled with dry N2
gas prior to use. [Fe(N(TMS)2)2]2,43 (pꢀtolyl)2CN2,44 transꢀ1ꢀ
phenylꢀ2ꢀvinylꢀcyclopropane,45 and cisꢀβꢀdeuterioꢀstyrene46
were synthesized according to literature procedures. All other
chemicals were purchased from either Strem or J&K Chemical
1
2
Co. and used as received unless otherwise noted. H, H, 13C,
19F, and 31P NMR spectra were recorded on an Agilent 300,
400 or 600 MHz spectrometers. All chemical shifts were reꢀ
ported in units of ppm with references to the residue of the
deuterated solvents for proton and carbon chemical shifts, to
external 85% phosphoric acid solution for phosphorous chemꢀ
ical shifts, to CF3COOH for fluorine chemical shifts, and to
CDCl3 for deuterium chemical shifts. Elemental analysis was
performed by the Analytical Laboratory of Shanghai Institute
of Organic Chemistry (CAS). Magnetic moments were measꢀ
ured by the method originally described by Evans with stock
and experimental solutions containing a known amount of a
(CH3)3SiOSi(CH3)3 standard.47 Absorption spectra were recꢀ
orded with a Shimadzu UVꢀ3600 UVꢀvisꢀNIR spectrophotomꢀ
eter. IR spectra were recorded with a NICOLET AVATAR
330 FTꢀIR spectrophotometer.
Preparation of H2(dfpN2P): To an Et2O (20 mL) solution of
(2,6ꢀF2C6H3)(2ꢀBrC6H4)NH (4.54 g, 16.0 mmol, 1 equiv.) was
added BunLi (1.6 M in nꢀhexane, 20 mL, 32 mmol, 2 equiv.)
o
slowly at ꢀ78 C. The resulting mixture was allowed to warm
to room temperature and further stirred for 5 hours. To this
solution, an Et2O solution (10 mL) of PhPCl2 (1.42 g, 7.90
o
mmol, 0.5 equiv.) was added at ꢀ78 C. The resulting mixture
was allowed to warm to room temperature and further stirred
for 24 hours. The mixture was then quenched with a saturated
aqueous solution of NaHCO3, and extracted with CH2Cl2 (30
mL x 3). The combined organic phases were washed with a
saturated NaHCO3 aqueous solution, brine, and dried over
Na2SO4. After filtration and removal of volatiles, the crude
product was purified by flash column chromatography (silica
XꢀRay Structure Determination. Crystals were coated
with ParatoneꢀN oil and mounted on a Bruker APEX CCDꢀ
based diffractometer equipped with an Oxford lowꢀ
temperature apparatus. Cell parameters were retrieved with
SMART software and refined using SAINT software on all
reflections. Data integration was performed with SAINT,
which corrects for Lorentz polarization and decay. Absorption
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Journal of the American Chemical Society
gel, 8:1 nꢀhexanes/CH2Cl2 as elute) to give H2(dfpN2P) as a
white solid (2.87 g, 70% yield). H NMR (400 MHz, CDCl3,
Reaction of 2 with Ethylene: A red solution of 2 (129 mg,
0.15 mmol) in toluene (5 mL) was frozed with liquid N2, and
then ethylene gas (1 atm) was quickly introduced. The mixture
was allowed to warm to room temperature and stirred for 30
minutes, giving a red solution. Then the reaction mixture was
quenched with wet silica gel. Flash column chromatography
separation (silica gel, nꢀhexane as elute) gave 1,1ꢀdiꢀpꢀ
tolylcylopropane (3a) as a colorless oil (26 mg, 77% yield). 1H
NMR (400 MHz, CDCl3, 292 K): δ (ppm) 7.16 (d, J = 8.1 Hz,
4H), 7.11 (d, J = 8.0 Hz, 4H), 2.34 (s, 6H), 1.29 (s, 4H). 13C
NMR (101 MHz, CDCl3, 292 K): δ (ppm) 143.12, 135.51,
129.05, 128.38, 29.26, 21.11, 16.40. IR (thin film, cmꢀ1): υ =
3004 (w), 2920 (w), 1513 (m), 1452 (w), 1115 (w), 1019 (m),
923 (w), 809 (s), 723 (m). HRMS (EI) calcd for C17H18 (M+):
222.1409. Found: 222.1412.
1
1
2
3
4
5
6
7
8
295 K): δ (ppm) 7.54 ꢀ 7.45 (m, 2H), 7.45 ꢀ 7.40 (m, 3H), 7.32
ꢀ 7.26 (m, 2H), 7.05 ꢀ 6.95 (m, 4H), 6.95 ꢀ 6.86 (m, 6H), 6.78 ꢀ
6.70 (m, 2H), 6.06 (d, J = 3.7 Hz, 2H, NH). 13C NMR (75
MHz, CDCl3, 302 K): δ (ppm) 156.75 (dd, JCꢀF = 247.9, 5.6
Hz), 146.80 (d, JCꢀP = 17.4 Hz), 134.12 (d, JCꢀP = 3.2 Hz),
133.85 (d, JCꢀP = 18.8 Hz), 132.99 (d, JCꢀP = 4.1 Hz), 130.42 (s),
129.43 (s), 129.03 (d, JCꢀP = 7.3 Hz), 123.36 (t, JCꢀF = 9.5 Hz),
121.37 (d, JCꢀP = 2.4 Hz), 121.00 (d, JCꢀP = 6.2 Hz), 119.36 (t,
9
JCꢀF = 14.7 Hz), 114.92 (d, JCꢀP = 1.7 Hz), 111.89 (dd, JCꢀF
=
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16.5, 6.9 Hz). 19F NMR (376 MHz, CDCl3, 295 K): δ (ppm) ꢀ
120.08 (s). 31P NMR (162 MHz, CDCl3, 295 K): δ (ppm) ꢀ
30.56 (s). IR (thin film, cmꢀ1): υ = 3353 (w), 3066 (w), 2923
(w), 2853 (w), 1586 (m), 1569 (m), 1496 (s), 1469 (s), 1442
(m), 1300 (m), 1237 (m), 1159 (w), 1000 (s), 931 (w), 878 (w),
778 (s), 743 (s), 697 (s). HRMS (EI) calcd for C30H20F4N2P
[(M–H)+]: 515.1300. Found: 515.1303.
Reaction of 2 with 1ꢀOctene: To a toluene (5 mL) solution
of 2 (136 mg, 0.16 mmol) was added 1ꢀoctene (55 mg, 0.49
o
mmol). The resulting mixture was stirred at 80 C for 6 hours,
Preparation of [(κꢀN,N,PꢀdfpN2P)Fe(THF)2] (1): To a THF
(10 mL) solution of H2(dfpN2P) (266 mg, 0.51 mmol) was
added [Fe(N(TMS)2)2]2 (195 mg, 0.26 mmol). The resulting
mixture was stirred at room temperature for 2 hours to afford a
yellow suspension. After removal of the solvent under vacuum,
the yellow oily residue was washed by nꢀhexane (5 mL) and
Et2O (5 mL) to produce 1 as a yellow solid (259 mg, 71%).
Singleꢀcrystals of 1 suitable for Xꢀray diffraction study were
obtained by standing its saturated THF solution at room
providing a red solution. Then the reaction was quenched with
wet silica gel. Flash column chromatography separation (silica
gel, nꢀhexane as elute) gave the cyclopropanation product 2ꢀ
(nꢀhexyl)ꢀ1,1ꢀdi(pꢀtolyl)ꢀcyclopropane (3b) as a colorless oil
1
(33 mg, 66% yield). H NMR (400 MHz, CDCl3, 292 K): δ
(ppm) 7.22 (d, J = 7.8 Hz, 2H), 7.14 ꢀ 7.07 (m, 4H), 7.04 (d, J
= 8.1 Hz, 2H), 2.34 (s, 3H), 2.29 (s, 3H), 1.61 ꢀ 1.51 (m, 1H),
1.50 ꢀ 1.37 (m, 3H), 1.31ꢀ1.17 (m, 7H), 1.14 (t, J = 5.2 Hz,
1H), 0.88 (t, J = 6.8 Hz, 3H), 0.82 ꢀ 0.73 (m, 1H). 13C NMR
(101 MHz, CDCl3, 292 K): δ (ppm) 145.15, 139.31, 135.62,
135.04, 130.51, 128.93, 127.68, 34.57, 32.01, 31.07, 29.65,
29.33, 26.58, 22.77, 21.22, 21.03, 20.86, 14.24. IR (thin film,
cmꢀ1): υ = 2922 (s), 2854 (m), 1513 (s), 1451 (m), 1020 (w),
810 (s), 760 (w), 725 (m). HRMS (EI) calcd for C23H30 (M+):
306.2348. Found: 306.2346.
1
temperature for 2 days. H NMR (400 MHz, C6D6, 295 K): δ
(ppm) 43.92 (br), 36.53 (br), 34.43 (br), 31.48 (br), 16.45 (br),
12.36 (br), 3.81 (br), 2.18 (br), 1.09 (br), ꢀ2.90 (br), ꢀ27.95 (br),
ꢀ40.49 (br), ꢀ49.39 (br). Magnetic susceptibility (C6D6, 302 K):
ꢁeff = 4.4(1) ꢁB. Absorption spectrum (THF): λmax, nm (ε, Mꢀ1
cmꢀ1) = 279 (29600), 934 (70). IR (KBr, cmꢀ1): υ = 3049 (w),
2974 (w), 2876 (w), 1583 (m), 1463 (s), 1433 (m), 1303 (m),
1288 (m), 1233 (m), 1164 (w), 1039 (m), 997 (s), 867 (w), 778
(m), 743 (m), 727 (w), 694 (w). Anal. Calcd for
C38H35F4FeN2O2P: C 63.88, H 4.94, N 3.92; Found: C 63.34,
H 5.08, N 3.74.
Reaction of 2 with Heptaꢀ1,6ꢀDiene: To a toluene (5 mL)
solution of 2 (128 mg, 0.15 mmol) was added heptaꢀ1,6ꢀdiene
(43 mg, 0.60 mmol). The resulting mixture was stirred at 80
oC for 6 hours, providing a red solution. Then the reaction was
quenched with wet silica gel. Flash column chromatography
separation (silica gel, nꢀhexane as elute) gave the
cyclopropanation product 2ꢀ(4'ꢀpentenyl)ꢀ1,1ꢀdi(pꢀtolyl)ꢀ
Preparation of [(κꢀN,N,CꢀdfpN2PC(tolylꢀp)2)Fe(THF)] (2):
To a yellow suspension of 1 (735 mg, 1.0 mmol) in THF (20
mL) was added (pꢀtolyl)2CN2 (234 mg, 1.0 mmol). The color
of the suspension changed from yellow to dark brown
immediately. The reaction mixture was stirred at room
temperature for 12 hours, during which time the brown
suspension turned into a dark yellow solution. After removal
of the solvent under vacuum, the yellow oily residue was
washed by nꢀhexane (10 mL) and Et2O (5 mL) to produce 2 as
a yellow solid (695 mg, 81% yield). Singleꢀcrystals of 2
suitable for Xꢀray crystallography were obtained by vapor
1
cyclopropane (3c) as a colorless oil (33 mg, 76% yield). H
NMR (400 MHz, CDCl3, 292 K): δ (ppm) 7.24 (d, J = 8.0 Hz,
2H), 7.12 (dd, J = 7.8, 5.8 Hz, 4H), 7.07 (d, J = 6.0 Hz, 2H),
5.81 (ddt, J = 16.9, 10.2, 6.6 Hz, 1H), 5.05 ꢀ 4.91 (m, 2H),
2.36 (s, 3H), 2.31 (s, 3H), 2.10 ꢀ 2.02 (m, 2H), 1.64 ꢀ 1.46 (m,
4H), 1.25 ꢀ 1.20 (m, 1H), 1.19 ꢀ 1.15 (m, 1H), 0.88 ꢀ 0.78 (m,
1H). 13C NMR (101 MHz, CDCl3, 292 K): δ (ppm) 144.87,
139.05, 139.00, 135.51, 134.94, 130.31, 128.80, 128.76,
127.53, 114.15, 34.47, 33.57, 30.36, 28.83, 26.15, 21.05,
20.87, 20.62. IR (thin film, cmꢀ1): υ = 2996 (w), 2922 (m),
2855 (w), 1640 (w), 1513 (s), 1447 (m), 1113 (w), 1021 (w),
992 (w), 908 (m), 808 (s), 761 (w), 727 (m). HRMS (EI) calcd
for C22H26 (M+): 290.2035. Found: 290.2029.
1
diffusion of nꢀhexane into a benzene solution of 2. H NMR
(400 MHz, C6D6, 292 K): δ (ppm) 45.26 (br), 31.42 (br), 26.27
(br), 25.85 (br), 25.23 (br), 14.85 (br), 9.74 (br), 8.50 (br),
2.24 (br), ꢀ17.64 (br), ꢀ19.20 (br), ꢀ32.58 (br), ꢀ35.86 (br).
Magnetic susceptibility (C6D6, 292 K): ꢁeff = 4.7(1) ꢁB.
Absorption spectrum (THF): λmax, nm (ε, Mꢀ1 cmꢀ1) = 308
(21300), 1328 (180), 1462 (160). IR (KBr, cmꢀ1): υ = 2970 (w),
2916 (w), 2868 (w), 1583 (m), 1504 (m), 1468 (s), 1432 (s),
1330 (m), 1283 (m), 1236 (w), 1206 (w), 1022 (w), 999 (m),
866 (w), 816 (w), 781 (m), 747 (m), 697 (w). Anal. Calcd for
C49H41F4FeN2OP: C 70.34, H 4.94, N 3.35; Found: C 69.75, H
4.94, N 3.00.
Reaction of 2 with (2ꢀVinylcyclopropyl)benzene: To a
toluene (5 mL) solution of 2 (129 mg, 0.15 mmol) was added
1ꢀphenylꢀ2ꢀvinylꢀcyclopropane (46 mg, 0.32 mmol). The
resulting mixture was stirred at 80 oC for 12 hours, providing a
red solution. Then the reaction was quenched with wet silica
gel. Flash column chromatography separation (silica gel, nꢀ
hexane as elute) gave 2ꢀ(2'ꢀphenylcyclopropyl)ꢀ1,1ꢀdi(pꢀtolyl)ꢀ
cyclopropane (3d) as a colorless oil (36 mg, 70% yield). The
NMR data indicate the presence of both diastereoisomers of 2ꢀ
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Journal of the American Chemical Society
Page 10 of 15
o
(2‘ꢀphenylcyclopropyl)ꢀ1,1ꢀdi(pꢀtolyl)ꢀcyclopropane with the
was stirred at 80 C for 10 hours, providing a red solution.
1
2
3
ratio of 1:1.6 (denoted as A and B). The attempts to assign the
Then the reaction was quenched with wet silica gel. Flash
column chromatography separation (silica gel, nꢀhexane/ethyl
acetate (15:1) as elute) gave the cyclopropanation product 2ꢀ
identity of the isomers based on the NMR data were
1
unsuccessful. H NMR (400 MHz, CDCl3, 292 K): δ (ppm)
7.34 ꢀ 7.30 (m, 2H, HA), 7.29 ꢀ 7.25 (m, 2H, HB), 7.25 ꢀ 7.20
(m, 2H, HB), 7.18 ꢀ 7.12 (m, 3H, HA; 1H, HB), 7.11 ꢀ 7.04 (m,
6H, HA; 4H, HB), 7.00 – 6.96 (m, 2H, HB), 6.96 ꢀ 6.92 (m, 2H,
HB), 6.79 ꢀ 6.75 (m, 2H, HA), 2.34 (s, 3H, HA), 2.31 (s, 3H, HA;
3H, HB), 2.29 (s, 3H, HB), 1.91 ꢀ 1.85 (m, 1H, HB), 1.76 ꢀ 1.68
(m, 1H, HA), 1.57 ꢀ 1.50 (m, 1H, HB), 1.49 ꢀ 1.42 (m, 1H, HA),
1.36 ꢀ 1.27 (m, 3H, HA; 1H, HB ), 1.05 ꢀ 0.98 (m, 2H, HB), 0.96
ꢀ 0.90 (m, 1H, HA), 0.84 ꢀ 0.72 (m, 2H, HB), 0.68 ꢀ 0.60 (m, 1H,
HA). 13C NMR (101 MHz, CDCl3, 292 K): δ (ppm) 144.66,
144.60, 143.34, 143.07, 139.14, 139.07, 135.80, 135.70,
135.15, 130.80, 130.75, 129.10, 128.99, 128.91, 128.18,
127.99, 127.19, 127.16, 125.96, 125.76, 125.28, 125.26, 34.77,
34.75, 30.42, 30.25, 24.33, 23.98, 23.63, 22.98, 21.22, 21.18,
21.02, 20.05, 19.75, 15.73. IR (thin film, cmꢀ1): υ = 3023 (w),
2998 (w), 2920 (w), 1512 (m), 1447 (w), 1264 (w), 1113 (w),
1030 (w), 907 (w), 814 (m), 733 (s), 696 (s). HRMS (EI) calcd
for C26H26 (M+): 338.2035. Found: 338.2032.
(pꢀmethoxyphenyl)ꢀ1,1ꢀdi(pꢀtolyl)ꢀcyclopropane (3g) as a
4
5
6
7
8
9
1
colorless oil (28 mg, 57% yield). H NMR (400 MHz, CDCl3,
294 K): δ (ppm) 7.16 (d, J = 8.2 Hz, 2H), 7.07 (d, J = 8.0 Hz,
2H), 6.97 (d, J = 8.1 Hz, 2H), 6.92 (d, J = 8.0 Hz, 2H), 6.80 (d,
J = 8.6 Hz, 2H), 6.65 (d, J = 8.7 Hz, 2H), 3.73 (s, 3H), 2.74
(dd, J = 9.0, 6.7 Hz, 1H), 2.30 (s, 3H), 2.23 (s, 3H), 1.89 ꢀ 1.81
(m, 1H), 1.73 (dd, J = 9.0, 5.3 Hz, 1H). 13C NMR (101 MHz,
CDCl3, 294 K): δ (ppm) 157.61, 144.63, 137.63, 135.60,
135.40, 131.15, 131.04, 129.10, 129.01, 128.77, 127.36,
113.23, 55.26, 38.24, 31.84, 21.19, 21.05, 21.01. IR (thin film,
cmꢀ1): υ = 3021 (w), 2917 (w), 1512 (m), 1451 (m), 1112 (w),
1077 (w), 1019 (w), 966 (w), 812 (s), 779 (m), 738 (m), 693
(s). HRMS (EI) calcd for C24H24O (M+): 328.1827. Found:
328.1830.
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Reaction of 2 with 4ꢀtertꢀButylstyrene: To a toluene (5
mL) solution of 2 (54 mg, 0.07 mmol) was added 4ꢀtertꢀ
butylstyrene (31 mg, 0.19 mmol). The resulting mixture was
o
Reaction of 2 with Styrene: To a toluene (5 mL) solution
of 2 (117 mg, 0.14 mmol) was added styrene (44 mg, 0.42
mmol). The resulting mixture was stirred at 80 oC for 14 hours,
providing a red solution. Then the reaction was quenched with
wet silica gel. Flash column chromatography separation (silica
gel, nꢀhexane as elute) gave the cyclopropanation product 2ꢀ
phenylꢀ1,1ꢀdi(pꢀtolyl)ꢀcyclopropane (3e) as a white solid (34
mg, 81% yield). 1H NMR (400 MHz, CDCl3, 292 K): δ (ppm)
7.20 (d, J = 8.1 Hz, 2H), 7.15 ꢀ 7.04 (m, 5H), 6.99 (d, J = 8.1
Hz, 2H), 6.91 (dd, J = 14.4, 7.4 Hz, 4H), 2.82 (dd, J = 8.8, 6.7
Hz, 1H), 2.32 (s, 3H), 2.24 (s, 3H), 1.96 ꢀ 1.90 (m, 1H), 1.78
(dd, J = 8.9, 5.3 Hz, 1H). 13C NMR (101 MHz, CDCl3, 292 K):
δ (ppm) 144.54, 139.12, 137.47, 135.71, 135.51, 131.01,
129.13, 128.76, 128.08, 127.73, 127.38, 125.57, 38.81, 32.45,
21.19, 21.06, 21.03. IR (thin film, cmꢀ1): υ = 3021 (w), 2917
(w), 1512 (m), 1451 (m), 1112 (w), 1077 (w), 1019 (w), 966
(w), 812 (s), 779 (m), 738 (m), 693 (s). HRMS (EI) calcd for
C23H22 (M+): 298.1722. Found: 298.1719.
stirred at 80 C for 11 hours, providing a red solution. Then
the reaction was quenched with wet silica gel. Flash column
chromatography separation (silica gel, nꢀhexane as elute) gave
the cyclopropanation product 2ꢀ(pꢀtertꢀbutylphenyl)ꢀ1,1ꢀdi(pꢀ
tolyl)ꢀcyclopropane (3h) as a white solid (17 mg, 72% yield).
1H NMR (400 MHz, CDCl3, 294 K): δ (ppm) 7.17 (d, J = 8.0
Hz, 2H), 7.11 (d, J = 8.0 Hz, 2H), 7.07 (d, J = 7.9 Hz, 2H),
6.98 (d, J = 7.8 Hz, 2H), 6.91 (d, J = 7.7 Hz, 2H), 6.78 (d, J =
8.1 Hz, 2H), 2.81 ꢀ 2.65 (m, 1H), 2.29 (s, 3H), 2.23 (s, 3H),
1.82 ꢀ 1.87 (m, 1H), 1.76 (dd, J = 8.9, 5.2 Hz, 1H), 1.24 (s,
9H). 13C NMR (101 MHz, CDCl3, 294 K): δ (ppm) 148.33,
144.73, 137.67, 136.11, 135.61, 135.39, 131.11, 129.11,
128.73, 127.68, 127.35, 124.62, 38.58, 34.39, 32.22, 31.48,
21.43, 21.22, 21.06. IR (thin film, cmꢀ1): υ = 2963 (w), 2921
(w), 2867 (w), 1512 (m), 1450 (w), 1266 (w), 1108 (w), 1036
(w), 1019 (w), 940 (w), 848 (w), 828 (m), 805 (m), 765 (w),
728 (w), 625 (w), 552 (s), 536 (m). HRMS (EI) calcd for
C27H30 (M+): 354.2348. Found: 354.2347.
Reaction of 2 with 4ꢀMethylstyrene: To a toluene (5 mL)
solution of 2 (50 mg, 0.06 mmol) was added 4ꢀmethylstyrene
(21 mg, 0.18 mmol). The resulting mixture was stirred at 80
oC for 14 hours, providing a red solution. Then the reaction
was quenched with wet silica gel. Flash column
chromatography separation (silica gel, nꢀhexane as elute) gave
the cyclopropanation product 1,1,2ꢀtri(pꢀtolyl)ꢀcyclopropane
Reaction of 2 with N,NꢀDimethylꢀ4ꢀVinylaniline: To a
toluene (5 mL) solution of 2 (108 mg, 0.13mmol) was added
N,Nꢀdimethylꢀ4ꢀvinylaniline (57 mg, 0.39 mmol). The
o
resulting mixture was stirred at 80 C for 9 hours, providing a
red solution. Then the reaction was quenched wet with silica
gel. Flash column chromatography separation (silica gel, nꢀ
hexane/ethyl acetate (15:1) as elute) gave the
cyclopropanation product 2ꢀ(N,Nꢀdimethylꢀpꢀaminophenyl)ꢀ
1,1ꢀdi(pꢀtolyl)ꢀcyclopropane (3i) as a white solid (17 mg, 39%
yield). 1H NMR (400 MHz, CDCl3, 294 K): δ (ppm) 7.15 (d, J
= 8.2 Hz, 2H), 7.06 (d, J = 8.0 Hz, 2H), 6.98 (d, J = 7.8 Hz,
2H), 6.92 (d, J = 8.1 Hz, 2H), 6.74 (d, J = 8.3 Hz, 2H), 6.52 (d,
J = 8.2 Hz, 2H), 2.85 (s, 6H), 2.69 (dd, J = 8.6, 5.6 Hz, 1H),
2.29 (s, 3H), 2.22 (s, 3H), 1.75ꢀ1.84 (m, 1H), 1.70 (dd, J = 8.7,
5.2 Hz, 1H). 13C NMR (101 MHz, CDCl3, 294 K): δ (ppm)
148.82, 144.94, 137.94, 135.43, 135.22, 131.15, 129.05,
128.73, 127.33, 127.25, 112.52, 40.94, 38.00, 32.08, 21.22,
21.09, 21.05. IR (thin film, cmꢀ1): υ = 2963 (w), 1413 (w),
1259 (s), 1085 (s), 1016 (s), 865 (w), 796 (s), 701 (w). HRMS
(EI) calcd for C25H27N (M+): 341.2143. Found: 341.2146.
1
(3f) as a white solid (11 mg, 60% yield). H NMR (400 MHz,
CDCl3, 294 K): δ (ppm) 7.16 (d, J = 8.2 Hz, 2H), 7.06 (d, J =
8.0 Hz, 2H), 6.97 (d, J = 8.1 Hz, 2H), 6.94 ꢀ 6.86 (m, 4H),
6.75 (d, J = 8.1 Hz, 2H), 2.74 (dd, J = 9.0, 6.6 Hz, 1H), 2.29 (s,
3H), 2.23 (s, 3H), 2.22 (s, 3H), 1.89ꢀ1.83 (m, 1H), 1.73 (dd, J
= 9.0, 5.2 Hz, 1H). 13C NMR (101 MHz, CDCl3, 294 K): δ
(ppm) 144.69, 137.62, 136.00, 135.61, 135.41, 134.94, 131.04,
129.10, 128.77, 128.48, 127.94, 127.37, 38.54, 32.23, 21.21,
21.15, 21.12, 21.05. IR (thin film, cmꢀ1): υ = 3020 (w), 2919
(w), 2864 (w), 1513 (s), 1448 (m), 1261 (w), 1110 (w), 1040
(w), 1019 (m), 814 (s), 762 (w), 728 (m), 621 (w), 597 (w),
550 (s), 510 (m), 425 (w). HRMS (EI) calcd for C24H24 (M+):
312.1878. Found: 312.1884.
Reaction of 2 with 4ꢀMethoxystyrene: To a toluene (5 mL)
Reaction of 2 with 4ꢀFluorostyrene: To a toluene (5 mL)
solution of 2 (52 mg, 0.06 mmol) was added 4ꢀfluorostyrene
(23 mg, 0.18 mmol). The resulting mixture was stirred at 80
solution of
2 (125 mg, 0.15 mmol) was added 4ꢀ
methoxystyrene (60 mg, 0.45 mmol). The resulting mixture
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oC for 10 hours, providing a red solution. Then the reaction
Reaction of 2 with Norbornene: To a toluene (5 mL)
1
2
3
4
5
6
7
8
was quenched with wet silica gel. Flash column
chromatography separation (silica gel, nꢀhexane as elute) gave
the cyclopropanation product 2ꢀ(pꢀfluorophenyl)ꢀ1,1ꢀdi(pꢀ
tolyl)ꢀcyclopropane (3j) as a colorless oil (15 mg, 79% yield).
1H NMR (400 MHz, CDCl3, 294 K): δ (ppm) 7.21ꢀ7.14 (m,
2H), 7.08 (d, J = 8.0 Hz, 2H), 6.99 ꢀ 6.89 (m, 4H), 6.86 ꢀ 6.75
(m, 4H), 2.78 (dd, J = 9.0, 6.5 Hz, 1H), 2.31 (s, 3H), 2.23 (s,
3H), 1.85 ꢀ 1.90 (m, 1H), 1.75 (dd, J = 9.0, 5.4 Hz, 1H). 13C
solution of 2 (170 mg, 0.20 mmol) was added norbornene (56
mg, 0.60 mmol). The resulting mixture was stirred at 80 oC for
0.5 hour, providing a red solution. Then the reaction was
quenched with wet silica gel. Flash column chromatography
separation (silica gel, nꢀhexane as elute) gave the
cyclopropanation
product
3,3ꢀdiꢀpꢀ
tolyltricyclo[3.2.1.02,4]octane (3m) as a white solid (48 mg, 83%
yield). 1H NMR (400 MHz, CDCl3, 292 K): δ (ppm) 7.24 (d, J
= 8.0 Hz, 2H), 7.15 (d, J = 8.2 Hz, 2H), 7.10 (d, J = 7.8 Hz,
2H), 7.01 (d, J = 8.0 Hz, 2H), 2.52 (s, 2H), 2.32 (s, 3H), 2.26
(s, 3H), 1.52 ꢀ 1.47 (m, 2H), 1.46 (s, 2H), 1.36 ꢀ 1.31 (m, 2H),
0.63 ꢀ 0.56 (m, 1H), 0.47 ꢀ 0.41 (m, 1H). 13C NMR (101 MHz,
CDCl3, 292 K): δ (ppm) 145.83, 140.03, 135.33, 135.06,
129.67, 129.06, 128.99, 127.85, 36.71, 36.00, 31.87, 31.40,
30.37, 21.26, 20.98. IR (thin film, cmꢀ1): υ = 3005 (w), 2953
(s), 2923 (s), 2863 (m), 1507 (m), 1453 (w), 1109 (w), 1021
(w), 855 (m), 819 (s), 802 (s), 776 (m), 758 (m), 726 (m).
HRMS (EI) calcd for C22H24 (M+): 288.1878. Found: 288.1882.
NMR (101 MHz, CDCl3, 294 K): δ (ppm) 161.17 (d, JCꢀF
=
9
243.4 Hz), 144.28 (s), 137.26 (s), 135.84 (s), 135.60 (s),
134.75 (d, JCꢀF = 3.0 Hz), 130.96 (s), 129.35 (d, JCꢀF = 7.8 Hz),
129.16 (s), 128.84 (s), 127.37 (s), 114.56 (d, JCꢀF = 21.2 Hz),
38.56 (s), 31.62 (s), 21.17 (s), 21.05 (s). 19F NMR (376 MHz,
CDCl3, 294 K) δ (ppm) ꢀ117.86 (s). IR (thin film, cmꢀ1): υ =
3021 (w), 2921 (w), 2867 (w), 1605 (w), 1510 (s), 1448 (w),
1234 (m), 1159 (m), 1017 (w), 832 (m), 806 (m), 763 (w), 730
(m), 560 (w), 550 (m), 514 (w), 478 (w). HRMS (EI) calcd for
C23H21F (M+): 316.1627. Found: 316.1625.
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
Reaction of 2 with 4ꢀChlorostyrene: To a toluene (5 mL)
solution of 2 (50 mg, 0.06 mmol) was added 4ꢀchlorostyrene
(25 mg, 0.18 mmol). The resulting mixture was stirred at 80
oC for 8 hours, providing a red solution. Then the reaction was
quenched with wet silica gel. Flash column chromatography
separation (silica gel, nꢀhexane as elute) gave the
cyclopropanation product 2ꢀ(pꢀchlorophenyl)ꢀ1,1ꢀdi(pꢀtolyl)ꢀ
Reaction of 2 with 1ꢀPhenylꢀButeꢀ1,3ꢀDiene: To a toluene
(5 mL) solution of 2 (170 mg, 0.20 mmol) was added 1ꢀ
phenylꢀbuteꢀ1,3ꢀdiene (78 mg, 0.60 mmol). The resulting
o
mixture was stirred at 80 C for 3 hours, providing a red
solution. Then the reaction was quenched with wet silica gel.
Flash column chromatography separation (silica gel, nꢀhexane
as elute) gave the cyclopropanation product 2ꢀ(phenylvinyl)ꢀ
1,1ꢀdi(pꢀtolyl)ꢀcyclopropane (3n) as a white solid (63 mg, 97%
yield). 1H NMR (400 MHz, CDCl3, 292 K): δ (ppm) 7.31 (d, J
= 7.9 Hz, 2H), 7.26 (d, J = 7.3 Hz, 2H), 7.24 ꢀ 7.17 (m, 3H),
7.17 ꢀ 7.12 (m, 4H), 7.10 (d, J = 8.0 Hz, 2H), 6.60 (d, J = 15.8
Hz, 1H), 5.54 (dd, J = 15.8, 9.7 Hz, 1H), 2.44 ꢀ 2.38 (m, 1H),
2.37 (s, 3H), 2.33 (s, 3H), 1.74 (dd, J = 8.6, 4.9 Hz, 1H), 1.61 ꢀ
1.54 (m, 1H). 13C NMR (101 MHz, CDCl3, 292 K): δ (ppm)
143.94, 138.67, 137.87, 136.16, 135.48, 132.11, 130.85,
129.18, 129.11, 129.01, 128.54, 127.13, 126.73, 125.88, 37.09,
31.20, 22.96, 21.27, 21.04. IR (thin film, cmꢀ1): υ = 3022 (w),
2919 (w), 1643 (w), 1512 (m), 1446 (m), 1118 (w), 1022 (w),
957 (s), 807 (m), 744 (s), 692 (s). HRMS (EI) calcd for C25H24
(M+): 324.1878. Found: 324.1873.
1
cyclopropane (3k) as a colorless oil (13 mg, 67% yield). H
NMR (400 MHz, CDCl3, 294 K): δ (ppm) 7.16 (d, J = 8.1 Hz,
2H), 7.11 ꢀ 7.03 (m, 4H), 7.01 ꢀ 6.89 (m, 4H), 6.79 (d, J = 8.4
Hz, 2H), 2.76 (dd, J = 8.8, 6.6 Hz, 1H), 2.30 (s, 3H), 2.24 (s,
3H), 1.96 ꢀ 1.82 (m, 1H), 1.78 (dd, J = 8.9, 5.4 Hz, 1H). 13C
NMR (101 MHz, CDCl3, 294 K): δ (ppm) 144.16, 137.79,
137.05, 135.96, 135.66, 131.24, 130.95, 129.29, 129.17,
128.94, 127.84, 127.31, 38.97, 31.80, 21.27, 21.20, 21.06. IR
(thin film, cmꢀ1): υ = 3022 (w), 2920 (w), 1513 (m), 1494 (s),
1449 (w), 1093 (s), 1040 (w), 1014 (m), 828 (m), 814 (m), 550
(w), 535 (m), 511 (w). HRMS (EI) calcd for C23H21Cl (M+):
332.1332. Found: 332.1334.
Reaction of 2 with 4ꢀ(Trifluoromethyl)styrene: To a
toluene (5 mL) solution of 2 (170 mg, 0.20 mmol) was added
4ꢀ(trifluoromethyl)styrene (105 mg, 0.60 mmol). The resulting
Reaction of 2 with Ethyl Acrylate: To a toluene (5 mL)
solution of 2 (121 mg, 0.15 mmol) was added ethyl acrylate
(43 mg, 0.43 mmol). The resulting mixture was stirred at 80
oC for 7 hours, providing a red solution. Then the reaction was
quenched with wet silica gel. Flash column chromatography
separation (silica gel, nꢀhexane/CH2Cl2 (3:1) as elute) gave the
o
mixture was stirred at 80 C for 4 hours, providing a red
solution. Then the reaction was quenched with wet silica gel.
Flash column chromatography separation (silica gel, nꢀhexane
as elute) gave the cyclopropanation product 2ꢀ(pꢀ
trifluoromethylphenyl)ꢀ1,1ꢀdi(pꢀtolyl)ꢀcyclopropane (3l) as a
cyclopropanation
product
ethyl
2,2ꢀdi(pꢀ
1
colorless oil (49 mg, 66% yield). H NMR (400 MHz, CDCl3,
tolyl)cyclopropylcarboxylate (3o) as a colorless oil (26 mg, 61%
yield). 1H NMR (400 MHz, CDCl3, 294 K): δ (ppm) 7.22 (d, J
= 7.5 Hz, 2H), 7.15 (d, J = 7.6 Hz, 2H), 7.07 (s, 4H), 4.02 ꢀ
3.86 (m, 2H), 2.46 ꢀ 2.55 (m, 1H), 2.29 (s, 6H), 2.08 ꢀ 2.71 (m,
1H), 1.55 (dd, J = 7.2, 5.1 Hz, 1H), 1.06 (t, J = 6.9 Hz, 3H).
13C NMR (101 MHz, CDCl3, 294 K): δ (ppm) 170.99, 142.36,
137.53, 136.49, 136.19, 129.62, 129.21, 129.12, 127.53, 60.55,
39.44, 29.07, 21.27, 21.05, 20.31, 14.23. IR (thin film, cmꢀ1): υ
= 2922 (w), 1732 (s), 1514 (m), 1444 (w), 1396 (w), 1379 (m),
1261 (s), 1174 (s), 1090 (s), 1018 (s), 852 (w), 807 (s), 726
(w), 668 (w), 661 (w), 550 (m), 481 (w). HRMS (EI) calcd for
C2oH22O2 (M+): 294.1620. Found: 294.1617.
294 K): δ (ppm) 7.35 (d, J = 8.1 Hz, 2H), 7.18 (d, J = 8.1 Hz,
2H), 7.10 (d, J = 8.0 Hz, 2H), 7.03 ꢀ 6.88 (m, 6H), 2.83 (dd, J
= 8.6, 6.7 Hz, 1H), 2.31 (s, 3H), 2.25 (s, 3H), 1.92 ꢀ 1.99 (m,
1H), 1.85 (dd, J = 8.8, 5.4 Hz, 1H). 13C NMR (101 MHz,
CDCl3, 294 K): δ (ppm) 143.97 (s), 143.66 (s), 136.79 (s),
136.18 (s), 135.83 (s), 130.94 (s), 129.23 (s), 129.03 (s),
128.14 (s), 127.68 (q, JCꢀF = 32.2 Hz), 127.29 (s), 124.61 (q,
JCꢀF = 3.8 Hz), 124.53 (q, JCꢀF = 271.7 Hz), 39.68 (s), 32.18 (s),
21.70 (s), 21.19 (s), 21.06 (s). 19F NMR (376 MHz, CDCl3,
294 K) δ (ppm) ꢀ62.17 (s). IR (thin film, cmꢀ1): υ = 3023 (w),
2923 (w), 2867 (w), 1618 (w), 1513 (m), 1324 (m), 1191 (m),
1163 (s), 1120 (m), 1108 (m), 729 (w), 648 (w), 628 (w), 600
(w), 550 (w) HRMS (EI) calcd for C24H21F3 (M+): 366.1595.
Found: 366.1597.
Reaction of 2 with Acrylonitrile: To a toluene (5 mL)
solution of 2 (213 mg, 0.25 mmol) was added ethyl acrylate
(41 mg, 0.76 mmol). The resulting mixture was stirred at 80
oC for 9 hours, providing a red solution. Then the reaction was
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Page 12 of 15
quenched with wet silica gel. Flash column chromatography
separation (silica gel, nꢀhexane/CH2Cl2 (3:1) as elute) gave
the cyclopropanation product ethyl 2,2ꢀdi(pꢀ
functional with def2ꢀSVP basis set51 for all atoms, and
1
2
3
4
5
6
7
8
considering Grimme’s DFT empirical dispersion correction
DFTꢀD3.52 Optimized minima and transition states (TSs) were
verified by harmonic vibrational analysis to have no and one
proper imaginary frequency, respectively. To refine the
calculated energy, single point calculation with larger basis set
were then done based on these optimized structures, by using
B3LYP functional with def2ꢀTZVP basis set.51 Solvent effect
was modeled in these single point calculations by employing
continuum solvation model of SMD,53 with toluene as the
solvent. The reported enthalpies in this work were calculated
at the B3LYP/def2ꢀTZVP level, including the thermal
correction for enthalpy obtained from vibrational analysis in
gas phase at the reaction temperature, as well as Grimme’s
DFT empirical dispersion correction DFTꢀD3 with Grimme’s
original short range damping.52 All geometry optimizations
and single point calculations were performed with Gaussian 09
program.54
tolyl)cyclopropanecarbonitrile (3p) as a yellow oil (10 mg, 16%
yield). 1H NMR (400 MHz, CDCl3, 294 K): δ (ppm) 7.34 (d, J
= 8.0 Hz, 2H), 7.22 ꢀ 7.14 (m, 4H), 7.11 (d, J = 8.0 Hz, 2H),
2.34 (s, 3H), 2.32 (s, 3H), 2.19 (dd, J = 9.1, 5.7 Hz, 1H), 1.96 ꢀ
2.04 (m, 1H), 1.76 (dd, J = 9.1, 5.1 Hz, 1H). 13C NMR (101
MHz, CDCl3, 294 K): δ (ppm) 139.70, 137.61, 137.15, 136.26,
129.61, 129.49, 129.22, 127.68, 119.84, 37.78, 21.23, 21.15,
21.07, 12.26. IR (thin film, cmꢀ1): υ = 3025 (w), 2921 (w),
2237 (m), 1514 (s), 1444 (m), 1311 (w), 1260 (w), 1182 (w),
1112 (w), 1019 (m), 910 (w), 819 (s), 764 (m), 727 (s), 629
(w), 547 (s), 520 (w). HRMS (EI) calcd for C18H17N (M+):
247.1361. Found: 247.1364.
9
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
Reaction of 2 with cisꢀβꢀDeuterioꢀStyrene: To a toluene (5
mL) solution of 2 (150 mg, 0.18 mmol) was added cisꢀβꢀ
deuterioꢀstyrene (54 mg, 0.54 mmol). The resulting mixture
was stirred at 80 oC for 3 hours, providing a red solution. Then
the reaction was quenched with wet silica gel. Flash column
chromatography separation (silica gel, nꢀhexane as elute) gave
the deuterated cyclopropanation product 3ꢀDꢀ2ꢀphenylꢀ1,1ꢀ
di(pꢀtolyl)ꢀcyclopropane as a white solid. The NMR data
indicate the presence of both diastereoisomers of 3ꢀDꢀ2ꢀ
phenylꢀ1,1ꢀdi(pꢀtolyl)ꢀcyclopropane with the ratio of 2.1:1
ASSOCIATED CONTENT
Supporting Information. The Supporting Information is availaꢀ
ble free of charge on the ACS Publications website at DOI:
xxxxxxxxx.
Crystallographic data (CIF)
Molecular structure of 1, 57Fe Mössbauer spectra, NMR spectra,
other calculated reaction pathways, electronic configurations of
ironꢀalkylidene species S, Cartesian coordinates of the optimized
structures (PDF)
1
(cisꢀDꢀ3e and transꢀDꢀ3e). H NMR (400 MHz, CDCl3, 294
K): δ (ppm) 7.21 (d, J = 7.7 Hz, 2H), 7.17 ꢀ 7.07 (m, 5H), 7.00
(d, J = 7.7 Hz, 2H), 6.88 ꢀ 6.97 (m, 4H), 2.82 (d, J = 8.3 Hz,
1H), 2.33 (s, 3H), 2.25 (s, 3H), 1.94 (d, J = 6.3 Hz, 0.32H),
1.78 (d, J = 8.9 Hz, 0.68H). 13C NMR (101 MHz, CDCl3, 294
K): δ (ppm) 144.52 (s), 139.10 (s), 137.44 (s), 135.71 (s),
135.50 (s), 131.02 (s), 129.13 (s), 128.77 (s), 128.07 (s),
127.72 (s), 127.37 (s), 125.56 (s), 38.73 (s), 32.39 (s), 21.20
AUTHOR INFORMATION
Corresponding Author
* Eꢀmails: chenh@iccas.ac.cn (H.C.), deng@sioc.ac.cn (L.D.)
2
Author Contributions
§These authors contributed equally.
(s), 21.06 (s), 20.71 (t, JCꢀD = 23.5 Hz). H NMR (92 MHz,
CDCl3, 298 K): δ (ppm) 1.97, 1.82.
Kinetic Studies on the Reaction of
2 with 4ꢀ
Notes
Fluorostyrene at Various Temperatures: The kinetic studies
monitor the increase of the 19F NMR signal of 2,2ꢀdi(pꢀtolyl)ꢀ
1ꢀ(pꢀfluorophenyl)cyclopropane formed in the reaction of 2
with excess amount of 4ꢀfluorostyrene (10ꢀ35 equiv.) in C6D6
at certain temperature (85, 80, 75, 70, 65, 60, 55, 50, and 45
oC), using trifluoromethylbenzene as internal standard. These
reactions were conducted with general procedure as follow: To
a JꢀYoung tube was added 2 (0.025 M in C6D6, 400 ꢂL),
trifluoromethylbenzene (0.10 M in C6D6, 13 ꢂL) and certain 4ꢀ
fluoroꢀstyrene (100, 150, 200, 250, 300, and 350 ꢂmol). Then
the reaction mixture was diluted with C6D6 to 500 ꢂL. The
measured rate constants are compiled in Table S2, and the
plots of ln([P]1/([P]1ꢀ[P])) vs time are shown in Figure S51ꢀ
S59.
The authors declare no competing financial interests.
ACKNOWLEDGMENT
The work was supported by the National Key Research and
Development Program (2016YFA0202900), the National Natural
Science Foundation of China (Nos. 21690062, 21421091 and
21432001 to L.D., and Nos. 21290194, 21473215 and 21521062
to H.C.), and the Strategic Priority Research Program of the
Chinese Academy of Sciences (No. XDB20000000).
REFERENCES
(1) (a) Nugent, W. A.; Mayer, J. M. MetalꢀLigand Multiple
Bonds, The Chemistry of Transition Metal Complexes Conꢀ
taining Oxo, Nitrido, Imido, Alkylidyne Ligands; Wiley:
Canada, 1988. (b) Dörwald, F. Z. Metal Carbenes in Organic
Synthesis; WileyꢀVCH: Weinheim, 1999. (c) Che, C.ꢀM.;
Zhou, C.ꢀY.; Wong, E. L.ꢀM. Top. Organomet. Chem. 2011,
33, 111ꢀ138.
(2) (a) Doyle, M. P. Chem. Rev. 1986, 86, 919ꢀ939. (b)
Brookhart, M.; Studabaker, W. B. Chem. Rev. 1987, 87, 411ꢀ
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3747. (d) Schrock, R. R. Angew. Chem., Int. Ed. 2006, 45,
3748ꢀ3759. (e) Grubbs, R. H. Angew. Chem., Int. Ed. 2006,
45, 3760ꢀ3765. (f) Zhu, S.ꢀF.; Zhou, Q.ꢀL. Natl. Sci. Rev.
2014, 1, 580ꢀ603.
Competition Experiments. To a glass vessel was added 2
(42 mg, 0.05 mmol), styrene (16 mg, 0.15 mmol), a paraꢀ
substituted styrene (0.15 mmol), and 2.0 mL toluene. The
o
solution were stirred for 2 h at 80 C. Then the reaction was
quenched with wet silica gel and extracted by CH2Cl2 (20 mL).
After removal of volatiles under vacuum, the residue was reꢀ
1
dissolved in CDCl3 and analyzed by H NMR in CDCl3. The
ratio of the yield of the 2ꢀ(paraꢀsubstituted phenyl)ꢀ1,1ꢀdi(pꢀ
tolyl)ꢀcyclopropane to the yield of the 2ꢀphenylꢀ1,1ꢀdi(pꢀ
tolyl)ꢀcyclopropane is the relative rate kX/kH (Table 2).
(3) For examples, see: (a) VarelaꢀÁlvarez, A.; Musaev, D. G.
Chem. Sci. 2013, 4, 3758ꢀ3764. (b) Fallah, H.; Horng, F.;
Cundari, T. R. Organometallics 2016, 35, 950ꢀ958. (c) de
Computational Details. All molecular geometries were
optimized in gas phase, employing B3LYP50 density
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SYNOPSIS TOC
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(p-tolyl)2CN2
N2
in THF, r.t.
5
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p-tolyl
Ph
tolyl-p
THF
Ph
p-tolyl
THF
tolyl-p
P
FeII THF
FeII
P
via:
ꢀ
N
8
9
N
P
Fe THF
N
N
N
dfp
dfp
N
dfp
dfp
1
2
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p-tolyl
p-tolyl
in toluene,
r.t. or 80 o
R = alkyl, aryl,
CO2Et, CN
C
R
R
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