Three-Coordinate Iron(II) Dialkenyl Compound with NHC Ligation: Synthesis, Structure, and Reactivity

Article abstract of DOI:10.1021/acs.organomet.5b00632

The reaction of [(IPr₂Me₂)₂FePh₂] with PhC≡CPh furnished a three-coordinate iron(II) dialkenyl complex, [(IPr₂Me₂)Fe(σ-CPh=CPh₂)₂] (1, IPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene), that represents a rare example of isolable low-coordinate iron alkenyl complexes with a high-spin ground state. Complex 1 was characterized by ¹H NMR spectroscopy, solution magnetic susceptibility measurement, M?ssbauer spectroscopy, single-crystal X-ray diffraction study, and elemental analyses. A reactivity study revealed the reactions of 1 with PhCH₂Cl to produce cross-coupling product Ph₂C=CPhCH₂Ph (2), with [Cp₂Fe][BAr^F₄] to yield Ph₂C=CPh-CPh=CPh₂ (3), and with CO, 2,6-dimethylphenyl isocyanide, and phenyl azide to produce novel iron(0) and iron(II) complexes 4-6 bearing triphenylvinyl-derived ligands. These transformations demonstrated the high reactivity of the low-coordinate iron alkenyl complex.

Full text of DOI:10.1021/acs.organomet.5b00632

Article
pubs.acs.org/Organometallics
Three-Coordinate Iron(II) Dialkenyl Compound with NHC Ligation:
Synthesis, Structure, and Reactivity
Yuesheng Liu, Lei Wang, and Liang Deng*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345
Lingling Road, Shanghai 200032, People’s Republic of China
S
* Supporting Information
ABSTRACT: The reaction of [(IPr2Me2)2FePh2] with
PhCCPh furnished a three-coordinate iron(II) dialkenyl
complex, [(IPr2Me2)Fe(σ-CPhCPh2)2] (1, IPr2Me2 = 1,3-
diisopropyl-4,5-dimethylimidazol-2-ylidene), that represents a
rare example of isolable low-coordinate iron alkenyl complexes
with a high-spin ground state. Complex 1 was characterized by
1H NMR spectroscopy, solution magnetic susceptibility
measurement, Mossbauer spectroscopy, single-crystal X-ray
̈
diffraction study, and elemental analyses. A reactivity study
revealed the reactions of 1 with PhCH2Cl to produce cross-
coupling product Ph2CCPhCH2Ph (2), with [Cp2Fe]-
[BArF ] to yield Ph2CCPh−CPhCPh2 (3), and with
4
CO, 2,6-dimethylphenyl isocyanide, and phenyl azide to produce novel iron(0) and iron(II) complexes 4−6 bearing
triphenylvinyl-derived ligands. These transformations demonstrated the high reactivity of the low-coordinate iron alkenyl
complex.
iron(II) alkenyl complexes are high-spin and were characterized
by X-ray crystallographic studies. Power isolated a dinuclear
iron(I) alkenyl complex, [Fe2(ArCC(Ph)C(Ph)CAr] (Ar
= C6H3-2,6-(C6H3-2′,6′-Pri2)2, C in Chart 1), from the reaction
of [ArFe(μ-Br)]2 with PhCCLi (2 equiv).8 Magnetic
property studies indicated that the dinuclear complex contained
two antiferromaganetically coupled high-spin iron(I) centers. In
addition to these, Chirik found that [(PriPDI)Fe(N2)2] (PriPDI
= 2,6-(2,6-Pri2-C6H3NCMe)2C5H3N) can react with CH2
CHBr to produce (PriPDI)FeBr and (PriPDI)Fe(σ-CH
CH2).9 Unfortunately, the instability of the formal iron(I)
alkenyl species prevented detailed spectroscopic character-
ization.
In view of the wide use of N-heterocyclic carbene (NHC) in
iron-catalzyed organometallic transformations in recent years,10
we launched a project to study reactive organoiron species with
NHCs as supporting ligands. Our previous studies showed that,
with the selection of NHCs with appropriate steric property,
four-coordinate iron(II) alkyl, aryl, and alkynyl complexes in
the form of (NHC)2FeR2 were accessible (Chart 2).11,12
Reactivity studies enabled the establishment of versatile C−C
bond formation reactions of these open-shell iron(II)
dihydrocarbyl compounds with polar unsaturated organic
substrates, organic halides, and oxidants.11 In addition to
these, we wish to report herein the synthesis, characterization,
and reactivity study of a high-spin iron(II) alkenyl complex,
INTRODUCTION
■
The renaissance of iron catalysis1 in recent years urges deeper
knowledge of the chemistry of organoiron species beyond that
of the classical closed-shell complexes.2 Iron alkenyl species are
reactive intermediates proposed in iron-catalyzed cross-
couplings3 and the carbometalation4 and hydrosilylation5 of
alkynes. Peoples’ knowledge on them, however, has been
limited to the coordinatively saturated low-spin 18e− complexes
with cyclopentadienyl anion, carbonyl, and phosphines as
ancillary ligands.6 As for coordinatively unsaturated iron alkenyl
complexes, very limited examples were reported and their
reactivity is unknown. Holland et al. found that the iron(II)
hydride complexes (nacnac)Fe(H) (nacnac = β-diketiminate
ligand) can react with the alkynes PhCCPh and EtCCEt
to form the cis-addition products [(nacnac)Fe(σ-CRC(H)-
R)] (R = Ph, Et, A and B in Chart 1).7 The three-coordinate
Chart 1. Known Examples of Open-Shell Iron Alkenyl
Complexes
Received: July 22, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00632
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Chart 2. Examples of Four-Coordinate Organoiron(II)
Complexes with NHC Ligation
[(IPr2Me2)Fe(σ-CPhCPh2)2]. The iron(II) dialkenyl com-
plex, in addition to the alkyl, aryl, and alkynyl complexes,
completes the series of high-spin organoiron(II) species with
NHCs as ancillary ligands.
RESULTS AND DISCUSSION
■
Preparation and Characterization of the Iron(II)
Alkenyl Complex. Treatment of [(IPr2Me2)2FePh2]11d with
2 equiv of PhCCPh in THF produced a dark brown solution.
After workup, the iron(II) complex [(IPr2Me2)Fe(σ-CPh
CPh2)2] (1) was isolated as an orange crystalline solid in 41%
yield (Scheme 1). The synthetic method is reminiscent of
Figure 1. Molecular structure of 1 showing 30% probability ellipsoids
and partial atom schemes. Selected distances (Å) and angles (deg) for
1: Fe1−C1 2.096(2), Fe1−C2 2.061(2), Fe1−C3 2.066(2), C2−C4
1.362(2), C3−C5 1.363(2), C1−Fe1−C2 110.59(5), C1−Fe1−C3
111.45(5), C2−Fe1−C3 137.95(5).
on average),14 Ph2CCPh2 (1.34 Å),15 [CpFe(CO)2(CPh
CPh(C6H2-3,5-But2-4-OH))] (ca. 1.338 Å),13 and [(nacnac)-
Fe(σ-CPhC(H)Ph)] (1.347 Å),7b suggesting its double-bond
nature. The Fe−C(carbene) bond distance (2.096(2) Å) is
typical of three-coordinate high-spin iron(II)-NHC com-
plexes.11,12,16
Scheme 1. Preparation of the Iron(II) Alkenyl Complex
The zero-field 57Fe Mossbauer spectrum of 1 measured on
̈
Holland’s preparation of [(nacnac)Fe(σ-CRC(H)R)],
wherein alkynes were inserted into Fe−H bonds.7 The reaction
using 1 equiv of the alkyne, however, did not result in the
formation of the probable intermediate (IPr2Me2)FePh(σ-
CPhCPh2), but afforded a mixture of 1 and
[(IPr2Me2)2FePh2]. The establishment of the conversion of
[(IPr2Me2)2FePh2] to 1 implies that the reaction of open-shell
organo-iron(II) species with alkynes could be responsible for
the C−C bond-forming step in iron-catalyzed carbometalation
of alkynes.4
the polycrystalline sample at 200 K is shown in Figure 2. The
Complex 1 is air and moisture sensitive. It is insoluble in n-
hexane, slightly soluble in Et2O, and highly soluble in THF. Its
solution magnetic moment (5.3(1) μB) measured in C61D6
indicates its high-spin nature. Consistent with this, the H
NMR spectrum of 1 in C6D6 shows broad paramagnetically
shifted resonances in the range +65 to −55 ppm. The
molecular structure of 1 was established by X-ray crystallo-
graphic study. As shown in Figure 1, the iron center in 1
displays a trigonal planar coordination geometry via coordina-
tion with one IPr2Me2 ligand and two triphenylvinyl groups
with the sum of the three C−Fe−C angles around the iron
center being 360°. Likely due to steric repulsion between the
bulky triphenylvinyl ligands, the two vinyl groups are pointing
above and below the coordination plane, respectively, and the
C(alkenyl)−Fe−C(alkenyl) angle (137.95(5)o) is larger than
the C(carbene)−Fe−C(alkenyl) angles. The Fe−C(alkenyl)
distances of 2.061(2) and 2.066(2) Å are comparable to those
of the Fe−C(mesityl) bonds in [(IPr2Me2)Fe(Mes)2] (2.073
Å).11a As compared to the reported iron alkenyl complexes, the
Fe−C(alkenyl) distances in 1 are longer than those of its
congeners in the high-spin complex [(nacnac)Fe(σ-CPh
C(H)Ph)] (2.017 Å)7b and the low-spin complexes [cis-
Fe(PMe3)2(CO)2(CHCH2)2] (ca. 2.014 Å)6g and [CpFe-
(CO)2(CPhCPh(C6H2-3,5-But2-4-OH))] (ca. 2.043 Å).13
The C(alkenyl)−C(alkenyl) lengths in 1 (1.363 Å on average)
are comparable to those of [Sn(Bun)(σ-CPhCPh2)3] (1.34 Å
Figure 2. Zero-field 57Fe Mossbauer spectra measured on a
polycrystalline solid of 1 at 200 K.
̈
single quadrupole doublet has the fitting isomer shift δ = 0.33
mm/s and the quadruple splitting ΔEQ = 2.20 mm/s. These
data are comparable to those of the three-coordinate high-spin
iron(II) diaryl complex [(IPr2Me2)Fe(Mes)2] (δ = 0.30 mm/s,
ΔEQ = 1.38 mm/s)17 and [Fe(Mes)3]− (δ = 0.20 mm/s, ΔEQ =
1.44 mm/s),18 supporting its high-spin S = 2 ground state.
Reactivity of the Iron(II) Alkenyl Complex. The
attainment of 1 completed the series of high-spin organoiron-
(II)-NHC complexes with the hydrocarbyl groups ranging from
alkyl to phenyl to alkenyl and to alkynyl. With this iron(II)
dialkenyl complex in hand, we then studied its reactions with
various organic substrates and oxidants.
Testing the reactions of 1 with organic halides indicated that
it can react slowly with benzyl chloride (2 equiv) to afford the
cross-coupling product Ph2CCPhCH2Ph (2) in 48% yield
B
DOI: 10.1021/acs.organomet.5b00632
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
19
(Scheme 2). The iron(II) chloride species [(IPr2Me2)FeCl2]4
Scheme 3. Reactions of 1 with Unsaturated Organic
Substrates
was identified as the major iron-containing product based on
Scheme 2. C−C Bond Formation Reactions of 1
the 1H NMR spectrum of the resulting mixture. The reaction of
1 with 1-bromooctane required harsher conditions. At 50 °C,
the interaction of 1 with 2 equiv of 1-bromooctane in 36 h
produced Ph2CCPhC8H17-n in 69% GC yield (Figures S17
and S18). The coexistence of a large amount of Ph2CCPhH
in the quenched reaction mixture rendered the isolation of the
cross-coupling product via chromatographic separation on silica
gel difficult. The lower reactivity of the iron(II) alkenyl
complex toward the organic halides as reflected by the slow
rates versus those of the reactions with [(IPr2Me2)2FePh2] and
[(IPr2Me2)2Fe(CCBut)2]11d,f is likely due to steric factors, as
the bulky alkenyl groups in 1 might prevent the organic halide
from interacting with the iron center.
C(carbene) atoms appear at ca. 186 ppm. X-ray diffraction
studies have revealed 4 and 5 are five-coordinate iron(0)
complexes, and their iron centers are coordinating with one
IPr2Me2, two CO or isocyanide ligands, and one newly formed
η4-bound ligand (Figure 3). In the structure of 4, the η4-bound
hexaphenylpentadien-3-one ligand has the C4−C5−C6−O1
atoms coplanar to each other and the noncoordinated alkenyl
fragment positioning away from the plane with the torsion
angle C8−C7−C6−C5 being 56.2°. The C−C and C−O
distances of the C4−C5−C6-O1 fragment display enhanced
delocalization versus the free α,β-unsaturated ketone. This
pattern is consistent with that observed in other η4-(α,β-
unsaturated ketone)-iron(0) complexes, e.g., [(η4-PhCH
CHCHO)Fe(CO)3]21 and [(η4-PhCHCHCHO)Fe-
(CO)2(PPh3)].22 In the structure of 5, the indenimine ligand
is bonded with the iron center via the C5−C6−C7−C8
fragment. The C−N(imine) bond distance (1.297(2) Å) is
double-bond in character. The alternating short−long−short
C−C distances within the benzo fragment are suggestive of the
enhanced electron localization versus the free indenimines.23 In
both complexes 4 and 5, the Fe−C(carbene) distances
(2.012(2) and 2.032(2) Å, respectively) are close to that in
the low-spin complex [(IMes)Fe(CO)4] (2.00 Å).24
Similar to the iron(II) diphenyl and dialkynyl complex-
es,11a,d,f no C−C bond-forming reductive elimination reaction
occurred when the solution of 1 was kept at room temperature
or 60 °C. The interaction of 1 with 1 equiv of the one-electron
oxidant [Cp2Fe][BArF ] (ArF = 3,5-ditrifluoromethylphenyl),
4
however, led to the formation of the reductive elimination
product hexaphenyl-1,3-butadiene (3) in 70% isolated yield
(Scheme 2). The high yield of 3 suggests the occurrence of the
iron(III)/iron(I) reductive elimination process from
[(IPr2Me2)FeIII(σ-CPhCPh2)2]+. Probably due to their
instability, the efforts to isolate the iron(III) intermediate and
the iron(I) product were unfruitful. Indeed, only an irreversible
oxidation wave with an Ep = 0.48 V (vs SCE) was observed in
the cyclic voltammogram of 1 in THF (Figure S2).
Examining the reactions of 1 with unsaturated organic
substrates revealed the fascinating conversions of the
triphenylvinyl groups in 1 to versatile metal-bound unsaturated
organic molecules. As shown in Scheme 3, 1 can react with CO,
CNC6H3-2,6-Me2, and PhN3 at −78 °C or room temperature
to furnish the iron(0) complexes 4 and 5 and the iron(II)
complex 6, respectively, in moderate yields. The mild reaction
conditions form a sharp contrast to the harsh reaction
conditions required for the insertion reactions of coordinatively
saturated iron alkenyl complexes. For example, the intra-
molecular migratory insertion reaction of the 18e− species
[CpFe(CO)2(σ-CPhCPh2)] takes place at 190 °C.20
Accordingly, we propose that the readiness of 1 to react with
unsaturated substrates should be related to the low-coordinate
nature of 1, which enables the coordination of the substrates to
form transient coordinatively unsaturated species, presumably
the 14e− species (IPr2Me2)Fe(L)(σ-CPhCPh2)2, that could
undergo a facial migratory insertion reaction.
Complex 6 is a rare example of an iron complex bearing a
triazenido ligand.25 Its measured solution magnetic moment
(4.7(1) μB in C6D6) suggests its high-spin nature. As depicted
in Figure 4, the iron complex features an IPr2Me2 and two
chelating triphenylvinyltriazenido ligands. Its Fe−C(carbene)
bond distance (2.105(4) Å) is typical of high-spin iron(II)-
NHC compounds.11,12,16 The triphenylvinyltriazenido ligands
chelate to the iron center with the Fe−N(phenyl) separations
(2.062(4) and 2.088(3) Å) being much shorter than the Fe−
N(vinyl) ones (2.279(4) and 2.208(4) Å). Moreover, the two
N−N distances within each triazenido are close to each other.
The vinyl moieties are noncoplanar with the triazenido plane,
and the bond distances of C18−C25 and C44−C51 are
suggestive of their CC double-bond nature.
Both 4 and 5 are diamagnetic. Their 1H NMR spectra display
two characteristic heptetes (5.58 and 4.90 ppm for 4 and 6.14
and 5.16 ppm for 5) corresponding to the methine protons of
the IPr2Me2 ligand, indicating the restricted rotation of the
NHC ligands in 4 and 5. The 13C NMR signals of their
The formations of 4−6 demonstrate the unique reactivity of
the low-coordinate iron(II) alkenyl complex toward polar
unsaturated organic molecules beyond simple insertion
reactions. While the formation of 6 apparently resulted from
C
DOI: 10.1021/acs.organomet.5b00632
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
species with CO.11a,26 On the other hand, the evidence of the
indenimine ligand in 5 suggests the occurrence of a C−H bond
activation step in the reaction of 1 with the isocyanide. A
probable mechanism could be the insertion of one ArNC
molecule into one of the Fe−C(alkenyl) bonds to produce the
iminacyl intermediate A (Scheme 4).27 Intermediate A might
Scheme 4. Possible Pathway for the Formation of 5
eliminate Ph2CCPhH via an intramolecular C−H activation
step to furnish the iron(II) metallacycle B. The coordination of
ArNC to the iron center in B could induce C−C bond-forming
reductive elimination to produce the product 5. In this
proposed pathway, the formation of Ph2CCPhH was verified
by its isolation and characterizations from the reaction mixture,
and the C−H bond activation step might be reminiscent to the
C(arene)−H activation reaction of Tatsumi’s cyclometalated
high-spin iron(II)-NHC complexes.12a
Figure 3. Molecular structures of 4 (top) and 5 (bottom) showing
30% probability ellipsoids and partial atom-numbering schemes.
Selected distances (Å) for 4: Fe1−C1 2.012(2), Fe1−C2 1.806(2),
Fe1−C3 1.741(2), Fe1−C4 2.158(2), Fe1−C5 2.082(2), Fe1−C6
2.085(2), Fe1−O1 2.008(2), O2−C2 1.143(2), O3−C3 1.158(2),
O1−C6 1.304(2), C4−C5 1.470(2), C5−C6 1.434(2), C6−C7
1.505(2), C7−C8 1.345(2); for 5: Fe1−C1 2.032(2), Fe1−C2
1.803(2), Fe1−C3 1.772(2), Fe1−C4 2.490(2), Fe1−C5 2.195(2),
Fe1−C6 2.052(2), Fe1−C7 2.098(2), Fe1−C8 2.184(2), C4−C5
1.468(3), C5−C6 1.445(3), C6−C7 1.427(3), C7−C8 1.434(3), C4−
C8 1.485(3), N3−C2 1.178(2), N5−C3 1.177(2), N4−C4 1.297(2).
CONCLUSION
■
In this study, we achieved the synthesis, characterization, and
reactivity study of a three-coordinate iron(II) dialkenyl
complex, [(IPr2Me2)Fe(σ-CPhCPh2)2] (1). The preparation
route to 1, upon the interaction of [(IPr2Me2)2FePh2] with 2
equiv of diphenyl acetylene, proves the ability of the Fe−C
bond in open-shell organo-iron(II) species to undergo an
insertion reaction with alkyne, being relevant to the C−C
bond-forming step of iron-catalyzed carbometalation reactions.
Characterization data indicated a ground spin state of S = 2 for
1. Further study revealed the diversified reactivity of 1 toward
benzyl chloride, ferrocenium salt, and unsaturated polar organic
substrates, which enabled the buildup of versatile C−C and C−
N bond-forming transformations involving the triphenylvinyl
groups in the iron complex.
EXPERIMENTAL SECTION
■
General Procedures. All experiments were performed under an
atmosphere of dry dinitrogen with the rigid exclusion of air and
moisture using standard Schlenk techniques, or in a glovebox. Phenyl
azide was synthesized according to literature procedures.28 All other
chemicals were purchased from chemical vendors and used as received
unless otherwise noted. Organic solvents were dried with a solvent
purification system (Innovative Technology) and degassed prior to
Figure 4. Molecular structure of 6 showing 30% probability ellipsoids
and the partial atom-numbering scheme. Selected distances (Å): Fe1−
C1 2.105(4), Fe1−N3 2.062(4), Fe1−N5 2.279(4), Fe1−N6
2.088(3), Fe1−N8 2.208(4), N3−N4 1.297(6), N4−N5 1.304(5),
N6−N7 1.323(5), N7−N8 1.325(5), N5−C18 1.428(6), N8−C44
1.396(5), C18−C25 1.326(6), C44−C51 1.377(6).
1
use. H and 13C NMR spectra were recorded on Varian Mercury 300
and 400 MHz or Agilent 400 and 600 MHz spectrometers. Chemical
shifts were reported in units with references to the residual protons of
the deuterated solvents for proton chemical shifts and the 13C of
deuterated solvents for carbon chemical shifts. Elemental analyses were
performed by the Analytical Laboratory of Shanghai Institute of
Organic Chemistry (CAS). Magnetic moments were measured by the
method originally described by Evans with stock and experimental
solutions containing a known amount of a (CH3)3SiOSi(CH3)3
standard.29 Absorption spectra were recorded with a Shimadzu UV-
3600 UV−vis−NIR spectrophotometer. IR spectra were recorded with
a Nicolet Avatar 330 FT-IR spectrophotometer. Cyclic voltammetry
the direct insertion of the azide molecules into the Fe−
C(alkenyl) bonds in 1, the formation of the hexaphenylpenta-
dien-3-one ligand in 4 should involve a CO-coordination-
triggered reductive elimination step after the initial CO
insertion reaction. Similar mechanisms for the formation of
ketones were proposed in the reactions of other organoiron
D
DOI: 10.1021/acs.organomet.5b00632
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
measurements were made with a CHI 600D potentiostation in THF
solutions using a sweep rate of 100 mV/s, a glassy carbon working
electrode, 0.1 M (Bu4N)(PF6) supporting electrolyte, and a SCE
reference electrode. Under these conditions, E1/2 = 0.55 V for the
127.18, 126.57, 126.38, 125.89. The NMR spectra were identical to
those reported in the literature.32
Reaction of 1 with CO. A solution of 1 (150 mg, 0.20 mmol) in
THF (3 mL) was cooled with liquid N2, and then 1 atm of CO was
added via a CO balloon. The color of the mixture changed from
orange to light brown. After stirring for 30 min at room temperature,
the color of the solution turned to red. The reaction mixture was
further stirred for 1 h and was then subjected to vacuum to remove the
volatiles. The residue was washed with n-hexane (2 mL × 3) and then
dried under vacuum to afford 4 as an orange solid (117 mg, 71%).
Single crystals of 4 suitable for X-ray crystallography were obtained by
[Cp2Fe]0/+ couple. The 57Fe Mossbauer spectra were measured with a
̈
constant-acceleration spectrometer under zero-applied magnetic field.
Low temperature was maintained by a CCS-850 Mossbauer Cryostat
̈
system (Janis Research Company). Data were analyzed with
MossWinn 4.0 Pre (provider: Beijing Shengtianjiayuan Keji
Company). Isomer shifts are relative to iron metal at room
temperature.
1
X-ray Structure Determination. All single crystals were
immersed in Paraton-N oil and sealed under N2 in thin-walled glass
capillaries. Data were collected at 153 or 140 K on a Bruker AXSD8 X-
ray diffractometer using Mo K radiation. An empirical absorption
correction was applied using the SADABS program.30 All structures
were solved by direct methods and subsequent Fourier difference
techniques and refined anisotropically for all non-hydrogen atoms by
full-matrix least-squares calculations on F2 using the SHELXTL
program package.31 All hydrogen atoms were geometrically fixed using
the riding model. Crystal data and details of data collection and
structure refinements for 1 and 4−6 are given in Table S1.
slow evaporation of its Et2O solution at room temperature. H NMR
(400 MHz, C6D6, 294 K): δ (ppm) 8.55 (d, J = 7.6 Hz, 1H), 7.85 (br,
1H), 7.65 (br, 1H), 7.59 (t, J = 7.8 Hz, 1H), 7.28−7.18 (m, 4H),
7.13−7.07 (m, 1H), 7.05−6.86 (m, 10H), 6.86−6.79 (m, 5H), 6.77−
6.65 (m, 5H), 6.56 (d, J = 7.6 Hz, 1H), 5.58 (hept, J = 7.0 Hz, 1H,
CH(CH3)2), 4.90 (hept, J = 7.0 Hz, 1H, CH(CH3)2), 1.87 (s, 3H),
1.67 (s, 3H), 1.38 (d, J = 6.8 Hz, 3H), 1.30 (d, J = 7.2 Hz, 3H), 0.93
(d, J = 7.0 Hz, 3H), 0.78 (d, J = 6.9 Hz, 3H). 13C NMR (100 MHz,
C6D6, 294 K): δ (ppm) 214.10, 203.07, 184.96, 148.92, 147.99, 145.37,
143.39, 142.55, 142.09, 139.78, 138.32, 134.13, 134.05, 133.40, 133.23,
133.01, 129.82, 129.61, 127.67, 127.07, 126.88, 126.70, 126.64, 126.61,
126.57, 126.31, 126.16, 126.06, 125.96, 125.70, 125.68, 125.48, 125.05,
122.36, 100.17, 70.66, 52.48, 51.35, 21.55, 21.16, 20.59, 9.61, 9.39.
Absorption spectrum (C6H6): λmax, nm (ε, M−1 cm−1) = 370 (6810).
Anal. Calcd for C54H50FeN2O3: C 78.05, H 6.07, N 3.37. Found: C
78.05, H 6.22, N 3.11. IR (KBr, cm−1): ν = 3047 (w), 2973 (w), 1980
(s), 1909 (s), 1593 (w), 1574 (w), 1557 (w), 1489 (w), 1463 (w),
1455 (w), 1352 (w), 1288 (w), 770 (w), 748 (w), 738 (w), 697 (m),
602 (w), 556 (w).
Preparation of [(IPr2Me2)Fe(σ-CPhCPh2)2] (1). To a stirring
THF solution (15 mL) of [(IPr2Me2)2FePh2] (1.00 g, 1.75 mmol) was
added PhCCPh (640 mg, 3.59 mmol) at room temperature. The
color of the solution changed to dark brown immediately. After stirring
for 15 min, the solvent was removed under vacuum. The brown
residue was quickly washed with n-hexane (5 mL × 3) and diethyl
ether (2 mL × 3) to leave an orange solid. After drying under vacuum,
1 was obtained as an orange powder (530 mg, 41%). Single crystals of
1 suitable for X-ray crystallography were obtained by slow evaporation
Reaction of 1 with 2,6-Dimethyphenyl Isocyanide. To a
stirring THF solution (5 mL) of 1 (100 mg, 0.13 mmol) was added
2,6-dimethyphenyl isocyanide (53 mg, 0.40 mmol) at −78 °C. The
color of the solution changed immediately to dark red. The mixture
was allowed to warm to room temperature and stirred for 4 h, during
which time the color of the solution turned from red to dark brown.
After removal of the solvent, the residue was washed with n-hexane (2
mL) and then extracted with diethyl ether (3.0 mL) and filtered. Slow
evaporation of diethyl ether afforded 5 as dark brown crystals (43 mg,
1
of its Et2O solution at room temperature. H NMR (300 MHz, C6D6,
302 K): δ (ppm) 62.30 (br, 4H), 52.23 (br, 4H), 10.84 (br, 4H), 8.90
(br, 2H), 6.46 (br, 6H), −1.36 (br), −18.65 (br, 4H), −22.70 (br,
2H), −53.30 (br, 2H). Anal. Calcd for C51H50FeN2: C 82.02, H 6.75,
N 3.75. Found: C 81.46, H 7.03, N 3.47. Magnetic susceptibility
(C6D6, 302 K): μeff = 5.3(1) μB. Absorption spectrum (C6H6): λmax
,
nm (ε, M−1 cm−1) = 280 (61 500).
Reaction of 1 with PhCH2Cl. To a stirring THF solution (5 mL)
of 1 (150 mg, 0.20 mmol) was added PhCH2Cl (53 mg, 0.42 mmol) at
room temperature. After 36 h, GC analysis on the reaction mixture
indicated that the amount of PhCH2Cl was no longer decreasing.
During this time, the color of the solution gradually turned from
orange to light yellow. After removal of the solvent, the residue was
extracted with n-hexane (2 mL × 3) and filtered through Celite. The
filtrate was subjected to vacuum to remove the volatiles. Chromato-
graphic separation in silica gel with n-hexane as eluent led to the
isolation of 1,1,2,3-tetraphenyl-1-propene (Ph2CCPhCH2Ph, 2) as a
1
37%). H NMR (400 MHz, C6D6, 294 K): δ (ppm) 7.72 (br, 2H),
7.74 (br, 2H), 7.29−7.22 (m, 3H), 7.20−7.07 (m, 5H), 7.00 (t, J = 7.4
Hz, 1H), 6.80 (d, J = 8.7 Hz, 1H),6.75−6.65 (m, 7H), 6.29 (dd, J =
8.8, 6.0 Hz, 1H), 6.14 (hept, J = 7.0 Hz, 1H, CH(CH3)2), 5.16 (hept, J
= 7.0 Hz, 1H, CH(CH3)2), 2.12 (s, 3H), 2.05 (s, 6H), 1.99 (s, 6H),
1.87 (s, 3H), 1.82 (s, 3H), 1.65 (s, 3H), 1.29 (d, J = 7.2 Hz, 3H,
CH(CH3)2), 1.12 (d, J = 6.8 Hz, 3H, CH(CH3)2), 1.07 (d, J = 6.8 Hz,
3H, CH(CH3)2), 1.06 (d, J = 6.8 Hz, 3H, CH(CH3)2). 13C NMR (100
MHz, C6D6, 294 K): 194.54, 190.72, 186.02, 156.15, 154.52, 139.95,
137.98, 133.28, 132.69, 132.47, 131.98, 131.58, 131.19, 130.89, 129.64,
128.55, 128.28, 128.19, 127.89, 127.85, 127.61, 127.39, 127.27, 127.15,
126.59, 125.89, 125.70, 124.85, 124.73, 124.15, 123.65, 119.72, 119.15,
103.83, 87.42, 84.73, 68.89, 54.87, 52.01, 22.62, 22.47, 22.24, 21.34,
19.11, 18.44, 18.38, 18.05, 10.18, 10.00. Anal. Calcd for C58H61FeN5:
C 78.80, H 6.96, N 7.92. Found: C 78.57, H 6.91, N 7.78. Absorption
spectrum (THF): λmax, nm (ε, M−1 cm−1) = 327 (26 730), 414
(20 620), 515 (2730). IR (KBr, cm−1): ν = 3057 (w), 2968 (w), 2940
(w), 2047 (s), 1978 (s), 1560 (w), 1546 (s), 1495 (w), 1463 (w), 1356
(w), 1271 (w),1207 (w), 770 (w), 756 (w), 746 (w), 701 (w), 593
(w), 521 (w). On the other hand, the n-hexane solution and the
mother liquor of the ethereal solution were combined, quenched with
D2O (0.5 mL), and extracted with diethyl ether. After chromato-
graphic separation on silica gel with n-hexane as eluant, Ph2C
1
white solid in 48% yield. H NMR (400 MHz, CDCl3, 295 K): δ
(ppm) 7.35−7.27 (m, 5H), 7.22−7.16 (m, 2H), 7.14−7.11 (m, 3H),
7.08−7.01 (m, 8H), 6.98−6.94 (m, 2H), 3.92 (s, 2H). 13C NMR (100
MHz, CDCl3, 295 K): δ (ppm) 143.09, 142.81, 142.04, 141.59, 140.05,
137.90, 130.71, 129.91, 129.43, 128.70, 128.21, 128.11, 127.66, 127.43,
126.84, 126.19, 125.98, 125.69, 41.39. HRMS (EI): calcd for
1
[C27H22]+ 346.1722; found 346.1730. Further H NMR analysis on
the solid redidue indicated its identity as a mixture of [(IPr2Me2)-
FeCl2]4 and [(IPr2Me2)2FeCl2]11a (Figure S7).
19
Reaction of 1 with [Cp2Fe][BArF ]. To a stirring toluene solution
4
(5 mL) of 1 (75 mg, 0.10 mmol) was added [Cp2Fe][BArF ] (105 mg,
4
0.10 mmol) at −78 °C. The color of the solution quickly changed
from orange to brown. The reaction mixture was then warmed to
room temprature and further stirred for 2 h. After quenching by H2O,
extracting with Et2O, and drying over anhydrous MgSO4, the organic
phase was subjected to vacumm to remove the solvents. Chromoto-
graphic separation on silica gel with n-hexane as eluent afforded
hexaphenyl-1,3-butadiene (Ph2CCPhCPhCPh2, 3) as a white
1
C(H)Ph was isolated as a white solid (11 mg, 33%). H NMR (400
MHz, CDCl3, 294 K): δ (ppm) 7.37−7.28 (m, 8H), 7.24−7.20 (m,
2H), 7.15−7.10 (m, 3H), 7.07−7.02 (m, 2H), 6.98 (s, 1H). 13C NMR
(100 MHz, CDCl3, 294 K): δ (ppm) 143.41, 142.55, 140.33, 137.35,
130.37, 129.53, 128.62, 128.19, 128.15, 127.95, 127.60, 127.50, 127.40,
126.73. The NMR spectra were identical to those reported in the
literature.33 The isolation of Ph2CCHPh, rather than Ph2CCDPh,
1
solid (36 mg, 70%). H NMR (400 MHz, CDCl3, 292 K): δ (ppm)
7.22−7.17 (m, 4H), 7.02−6.93 (m, 12H), 6.90−6.81 (m, 12H), 6.90−
6.85 (m, 2H). 13C NMR (100 MHz, CDCl3, 292 K): δ (ppm) 143.95,
143.73, 142.93, 141.45, 140.48, 131.33, 131.27, 129.83, 127.44, 127.24,
E
DOI: 10.1021/acs.organomet.5b00632
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
indicates that Ph2CCHPh was formed before the quenching
experiment.
(6) (a) Reger, D. L.; McElligott, P. J.; Charles, N. G.; Griffith, E. A.
H.; Amma, E. L. Organometallics 1982, 1, 443−448. (b) Reger, D. L.;
Belmore, K. A. J. Am. Chem. Soc. 1983, 105, 5710−5711. (c) Reger, D.
L.; Belmore, K. A.; Mintz, E.; McElligott, P. J. Organometallics 1984, 3,
134−140. (d) Reger, D. L.; Swift, C. A. Organometallics 1984, 3, 876−
879. (e) Reger, D. L.; Belmore, K. A.; Mintz, E.; Charles, N. G.;
Griffith, E. A. H.; Amma, E. L. Organometallics 1983, 2, 101−105.
(f) Reger, D. L. Acc. Chem. Res. 1988, 21, 229−235. (g) Venturi, C.;
Bellachioma, G.; Cardaci, G.; Macchioni, A.; Zuccaccia, C. Inorg. Chim.
Acta 2005, 358, 3815−3823.
(7) (a) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. J. Am. Chem. Soc.
2003, 125, 15752−15753. (b) Yu, Y.; Sadique, A. R.; Smith, J. M.;
Dugan, T. R.; Cowley, R. E.; Brennessel, W. W.; Flaschenriem, C. J.;
Bill, E.; Cundari, T. R.; Holland, P. L. J. Am. Chem. Soc. 2008, 130,
6624−6638.
Reaction of 1 with Phenyl Azide. To a stirring THF solution (5
mL) of 1 (150 mg, 0.2 mmol) was added PhN3 (50 mg, 0.42 mmol) at
room temperature. The color of the solution immediately changed to
brown. After further stirring for 8 h, all the volatiles were removed
under vacuum. The residue was then extracted with diethyl ether (5.0
mL) and filtered. Slow evaporation of diethyl ether afforded 6 as a
1
brown, crystalline solid (121 mg, 65%). H NMR (300 MHz, C6D6,
302 K): δ (ppm) 22.77 (br), 14.74 (br), 11.46 (br), 10.50 (br), 8.99
(br), 8.75 (br), 8.56 (br), 8.09 (br), 6.84 (br), 6.52 (br), 5.64 (br),
4.09 (br), 3.56 (br), 2.68 (br), −4.06 (br), −5.50 (br), −10.51 (br),
−34.55 (br). The attempts to integrate the peaks did not result in a
reasonable integration set. Anal. Calcd for C63H60FeN8: C 76.82, H
6.14, N 11.38. Found: C 75.70, H 6.71, N 10.58. Magnetic
susceptibility (C6D6, 302 K): μeff = 4.7(1) μB. Absorption spectrum
(C6H6): λmax, nm (ε, M−1 cm−1) = 374 (59 500), 449 (19 900). IR
(KBr, cm−1): ν = 3055 (w), 3023 (w), 2969 (w), 2938 (w), 2869 (w),
1593 (m), 1484 (w), 1440 (w), 1400 (w), 1350 (w), 1296 (w), 1260
(s), 1106 (w), 1072 (w), 1027 (w), 906 (w), 804 (w), 781 (w), 759
(w), 696 (s), 661 (w), 554 (w).
(8) Ni, C.; Long, G. J.; Power, P. P. Organometallics 2009, 28, 5012−
5016.
(9) Trovitch, R. J.; Lobkovsky, E.; Bouwkamp, M. W.; Chirik, P. J.
Organometallics 2008, 27, 6264−6278.
(10) For reviews on NHC and iron catalysis, see: (a) Ingleson, M. J.;
Layfield, R. A. Chem. Commun. 2012, 48, 3579−3589. (b) Bez
́
ier, D.;
Sortais, J.-B.; Darcel, C. Adv. Synth. Catal. 2013, 355, 19−33.
ASSOCIATED CONTENT
* Supporting Information
(11) (a) Xiang, L.; Xiao, J.; Deng, L. Organometallics 2011, 30, 2018−
2025. (b) Ouyang, Z.; Deng, L. Organometallics 2013, 32, 7268−7271.
(c) Liu, Y.; Shi, M.; Deng, L. Organometallics 2014, 33, 5660−5669.
(d) Liu, Y.; Xiao, J.; Wang, L.; Song, Y.; Deng, L. Organometallics
2015, 34, 599−605. (e) Liu, Y.; Luo, L.; Xiao, J.; Wang, L.; Song, Y.;
Qu, J.; Luo, Y.; Deng, L. Inorg. Chem. 2015, 54, 4752−4760. (f) Wang,
X. J.; Zhang, J.; Wang, L.; Deng, L. Organometallics 2015, 34, 2775−
2782.
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00632.
Absorption, 57Fe Mossbauer, and NMR spectra (PDF)
̈
X-ray crystallographic files in CIF format (CIF)
(12) For studies on organoiron-NHC complexes from others, see:
(a) Ohki, Y.; Hatanaka, T.; Tatsumi, K. J. Am. Chem. Soc. 2008, 130,
17174−17186. (b) Hatanaka, T.; Ohki, Y.; Tatsumi, K. Chem. - Asian J.
2010, 5, 1657−1666. (c) Danopoulos, A. A.; Braunstein, P.; Wesolek,
M.; Monakhov, K. Y.; Rabu, P.; Robert, V. Organometallics 2012, 31,
4102−4105. (d) Hashimoto, T.; Urban, S.; Hoshino, R.; Ohki, Y.;
Tatsumi, K.; Glorius, F. Organometallics 2012, 31, 4474−4479.
(e) Danopoulos, A. A.; Monakhov, K. Y.; Braunstein, P. Chem. -
Eur. J. 2013, 19, 450−455. (f) Fillman, K. L.; Przyojski, J. A.; Al-
Afyouni, M. H.; Tonzetich, Z. J.; Neidig, M. L. Chem. Sci. 2015, 6,
1178−1188.
AUTHOR INFORMATION
Corresponding Author
*E-mail: deng@sioc.ac.cn.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The work was supported by the National Basic Research
Program of China (No. 2011CB808705) and the National
Natural Science Foundation of China (Nos. 21222208,
21421091, and 21432001).
(13) Akita, M.; Kakuta, S.; Sugimoto, S.; Terada, M.; Tanaka, M.;
Moro-oka, Y. Organometallics 2001, 20, 2736−2750.
(14) Cardin, C. J.; Cardin, D. J.; Norton, R. J.; Parge, H. E.; Muir, K.
W. J. Chem. Soc., Dalton Trans. 1983, 665−670.
(15) Ino, I.; Wu, L. P.; Munakata, M.; Kuroda-Sowa, T.; Maekawa,
M.; Suenaga, Y.; Sakai, R. Inorg. Chem. 2000, 39, 5430−5436.
(16) (a) Layfield, R. A.; McDouall, J. J. W.; Scheer, M.;
Schwarzmaier, C.; Tuna, F. Chem. Commun. 2011, 47, 10623−
10625. (b) Zlatogorsky, S.; Muryn, C. A.; Tuna, F.; Evans, D. J.;
Ingleson, M. J. Organometallics 2011, 30, 4974−4982. (c) Day, B. M.;
Pugh, T.; Hendriks, D.; Guerra, C. F.; Evans, D. J.; Bickelhaupt, F. M.;
Layfield, R. A. J. Am. Chem. Soc. 2013, 135, 13338−13341.
REFERENCES
■
(1) Plietker, B., Ed. Iron Catalysis in Organic Chemistry: Reaction and
Application; Wiley-VCH: Weinheim, 2008. (b) Sherry, B. D.; Furstner,
̈
A. Acc. Chem. Res. 2008, 41, 1500−1511. (c) Czaplik, W. M.; Mayer,
̌
M.; Cvengros, J.; von Wangelin, A. J. ChemSusChem 2009, 2, 396−417.
(d) Jegelka, M.; Plietker, B. Top. Organomet. Chem. 2011, 33, 177−
213. (e) Jahn, U. Top. Curr. Chem. 2011, 320, 191−322. (f) Bauer, I.;
(17) For the 57Fe Mossbauer spectrum of [(IPr Me )Fe(Mes) ],
̈
Knolker, H.-J. Chem. Rev. 2015, 115, 3170−3387.
̈
2
2
2
please see the Supporting Information.
(2) For reviews on open-shell organometallic chemistry, please see:
(18) Daifuku, S. L.; Al-Afyouni, M. H.; Snyder, B. E. R.; Kneebone, J.
L.; Neidig, M. L. J. Am. Chem. Soc. 2014, 136, 9132−9143.
(19) Dunsford, J. J.; Cade, I. A.; Fillman, K. L.; Neidig, M. L.;
Ingleson, M. J. Organometallics 2014, 33, 370−377.
(20) Butler, I. R.; Elliott, J. E.; Houde, J., Jr. Can. J. Chem. 1989, 67,
1308−1311.
(a) Poli, R. Chem. Rev. 1996, 96, 2135−2204. (b) Schroder, D.; Shaik,
̈
S.; Schwarz, H. Acc. Chem. Res. 2000, 33, 139−145. (c) Poli, R.;
Harvey, J. N. Chem. Soc. Rev. 2003, 32, 1−8.
́
(3) (a) Guerinot, A.; Reymond, S.; Cossy, J. Angew. Chem., Int. Ed.
2007, 46, 6521−6524. (b) Hashimoto, T.; Hatakeyama, T.; Nakamura,
M. J. Org. Chem. 2012, 77, 1168−1173.
(4) (a) Zhang, D.; Ready, J. M. J. Am. Chem. Soc. 2006, 128, 15050−
15051. (b) Yamagami, T.; Shintani, R.; Shirakawa, E.; Hayashi, T. Org.
Lett. 2007, 9, 1045−1048. (c) Shirakawa, E.; Masui, S.; Narui, R.;
Watabe, R.; Ikeda, D.; Hayashi, T. Chem. Commun. 2011, 47, 9714−
9716.
(21) De Cian, A.; Weiss, R. Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 1972, 28, 3273−3280.
(22) Sacerdoti, M.; Bertolasi, V.; Gilli, G. Acta Crystallogr., Sect. B:
Struct. Crystallogr. Cryst. Chem. 1980, 36, 1061−1065.
(23) Fukutani, T.; Umeda, N.; Hirano, K.; Satoh, T.; Miura, M.
Chem. Commun. 2009, 5141−5143.
(24) Warratz, S.; Postigo, L.; Royo, B. Organometallics 2013, 32,
893−897.
(5) (a) Bart, S. C.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2004,
126, 13794−13807. (b) Belger, C.; Plietker, B. Chem. Commun. 2012,
48, 5419−5421.
F
DOI: 10.1021/acs.organomet.5b00632
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(25) For examples of iron complexes bearing triazenido ligands, see
ref 7b and (a) Cotton, F. A.; Daniels, L. M.; Maloney, D. J.; Murillo, C.
A. Inorg. Chim. Acta 1996, 242, 31−42. (b) Schmid, R.; Strahle, J. Z.
Naturforsch., B: J. Chem. Sci. 1988, 43, 533−539. (c) Walstrom, A. N.;
Fullmer, B. C.; Fan, H.; Pink, M.; Buschhorn, D. T.; Caulton, K. G.
Inorg. Chem. 2008, 47, 9002−9009.
(26) (a) Bart, S. C.; Hawrelak, E. J.; Schmisseur, A. K.; Lobkovsky,
E.; Chirik, P. J. Organometallics 2004, 23, 237−246. (b) Hermes, A. R.;
Girolami, G. S. Organometallics 1988, 7, 394−401.
(27) The insertion of isocyanide into the Fe−C bond of high-spin
iron(II) complexes is well-known. For an early example, please see:
Klose, A.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N. J.
Am. Chem. Soc. 1994, 116, 9123−9135.
(28) Berger, O.; Kaniti, A.; van Ba, C. T.; Vial, H.; Ward, S. A.;
Biagini, G. A.; Bray, P. G.; O’Neill, P. M. ChemMedChem 2011, 6,
2094−2108.
(29) (a) Evans, D. F. J. Chem. Soc. 1959, 2003−2005. (b) Sur, S. K. J.
Magn. Reson. 1989, 82, 169−173.
(30) Sheldrick, G. M. SADABS: Program for Empirical Absorption
Correction of Area Detector Data; University of Gottingen: Germany,
̈
1996.
(31) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray Systems,
Inc.: Madison, WI, USA, 1997.
(32) Horiguchi, H.; Tsurugi, H.; Satoh, T.; Miura, M. Adv. Synth.
Catal. 2008, 350, 509−514.
(33) Xu, L.; Li, B.-J.; Wu, Z.-H.; Lu, X.-Y.; Guan, B.-T.; Wang, B.-Q.;
Zhao, K.-Q.; Shi, Z.-J. Org. Lett. 2010, 12, 884−887.
G
DOI: 10.1021/acs.organomet.5b00632
Organometallics XXXX, XXX, XXX−XXX