Reactivity of a bis(amidinato)iron(II) complex [Fe(MesC(NPr i)2)2] toward some oxidizing reagents

Article abstract of DOI:10.1021/ic400053g

A diversified reactivity of the mononuclear bis(amidinato)iron(II) complex [Fe(MesC(NPrⁱ)₂)₂] (1) toward oxidizing reagents has been disclosed. The bis(amidinato)iron(II) complex was synthesized from the reaction of [Fe(Mes)₂]₂ with 4 equiv of diisopropyl carbodiimide in good yield. Treatment of 1 with 1 equiv of benzyl chloride gives the high-spin ferric complex [FeCl(MesC(NPrⁱ) ₂)₂] (2), with 0.25 equiv of S₈ affords the sulfur-insertion product [Fe(MesC(NPrⁱ)(NPrⁱS)) ₂] (3), with 1 equiv of 3,5-dimethylphenyl azide or phenyl azide yields nitrene-insertion product [Fe(MesC(NPrⁱ)₂)(Pr ⁱNC(Mes)N(Prⁱ)NAr)] (Ar = 3,5-dimethylphenyl, 4a; phenyl, 4b), and with 1 equiv of oxo-transfer reagent, trimethylamine oxide or 2,6-dichloropyridine oxide, generates the oxo-bridged diferric complex [(MesC(NPrⁱ)₂)₂FeOFe(MesC(NPrⁱ) ₂)₂] (5). Complexes 1-3, 4a, and 5 have been characterized by ¹H NMR, UV-vis, IR, elemental analysis, and single-crystal X-ray diffraction studies. The formations of these unusual sulfur- and nitrene-insertion products 3, 4a, and 4b, can be explained by the sequential redox reaction between 1 and the oxidants, followed by migratory insertion steps.

Full text of DOI:10.1021/ic400053g

Article
pubs.acs.org/IC
Reactivity of a Bis(amidinato)iron(II) Complex [Fe(MesC(NPri)2)2]
toward Some Oxidizing Reagents
Long Zhang,† Li Xiang,† Yihua Yu,‡ and Liang Deng*,†
†State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345
Lingling Road, Shanghai 200032, P.R. China
‡Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics, East China Normal University,
Shanghai 200062, P.R. China
S
* Supporting Information
ABSTRACT: A diversified reactivity of the mononuclear
bis(amidinato)iron(II) complex [Fe(MesC(NPri)2)2] (1)
toward oxidizing reagents has been disclosed. The bis-
(amidinato)iron(II) complex was synthesized from the
reaction of [Fe(Mes)2]2 with 4 equiv of diisopropyl
carbodiimide in good yield. Treatment of 1 with 1 equiv of
benzyl chloride gives the high-spin ferric complex [FeCl-
(MesC(NPri)2)2] (2), with 0.25 equiv of S8 affords the sulfur-
insertion product [Fe(MesC(NPri)(NPriS))2] (3), with 1
equiv of 3,5-dimethylphenyl azide or phenyl azide yields
nitrene-insertion product [Fe(MesC(NPri)2)(PriNC(Mes)N-
(Pri)NAr)] (Ar = 3,5-dimethylphenyl, 4a; phenyl, 4b), and
with 1 equiv of oxo-transfer reagent, trimethylamine oxide or
2,6-dichloropyridine oxide, generates the oxo-bridged diferric complex [(MesC(NPri)2)2FeOFe(MesC(NPri)2)2] (5).
1
Complexes 1−3, 4a, and 5 have been characterized by H NMR, UV−vis, IR, elemental analysis, and single-crystal X-ray
diffraction studies. The formations of these unusual sulfur- and nitrene-insertion products 3, 4a, and 4b, can be explained by the
sequential redox reaction between 1 and the oxidants, followed by migratory insertion steps.
(THF)]15e to afford carbamoyl compounds, the reduction of
INTRODUCTION
■
[FeBr(ButC(NDipp)2)]2 to produce iron(I) complexes [(ButC-
The relevance of nonheme type high valent iron-oxo and
-imido species to iron-mediated or -catalyzed organic trans-
formations has stimulated contemporary research studies on
their preparation, structure−reactivity relationship, as well as
(NDipp)2)Fe(toluene)] and [Fe2(N2)(DippNC(But)-
(NDipp))2],19 the oxidation of [Fe2(HC(NPh)2)3] with air
to yield [Fe4O(HC(NPh)2)6],13g and the use of bis-
(amidinato)iron(III) alkoxides [Fe(OR)(PhC(NSiMe3)2)2]
catalytic applications.1−3 Because of their oxidizing nature,
(R = Et, CHPh2) in polymerizations of ε-caprolactone and
these iron-oxo and -imido species are usually very reactive.
Hence, judicious design and selection of appropriate ligand
systems are necessary to ensure their isolation. While studies
lactides.20
This status quo warrants further exploration on the reactivity
have shown multidentate pyridine-,4 amine-,5 amide-,6
of amidinate iron(II) complexes. With regard to this, we report
pyrrolido-,7 phosphine-,8 and N-heterocyclic carbene-based9
ligands are among the privileged for this task, recent endeavors
herein the reactivity of a bis(amidinato)iron(II) complex
[Fe(MesC(NPri)2)2] toward a series of oxidizing reagents
including organic halides, elemental sulfur, aryl azides,
trimethylamine oxide, and 2,6-dichloropyridine oxide. While
revealed bidentate ligands, such as sterically encumbered β-
diketiminates10 and dipyrromethene anions,11 are also effective
no high-valent iron complex has yet been obtained, the
in stabilizing iron-imido species. Prompted by these pioneering
isolation of the iron(III) compounds [FeCl(MesC(NPri)2)2]
(2) and [(MesC(NPri)2)2FeOFe(MesC(NPri)2)2] (5), and the
iron(II) compounds of sulfur- and nitrene-insertion reaction
prodcuts [Fe(MesC(NPri)(NPriS))2] (3) and [Fe(MesC-
(NPri)2)(PriNC(Mes)N(Pri)NAr)] (Ar = 3,5-dimethylphenyl,
4a; phenyl, 4b) has revealed the distinct reactivity of
bis(amidinato)iron(II) complexes when compared with that
works, we are curious on the capability of amidinate ligands12 in
stabilizing high-valent iron-oxo, and -imido species.
In the recent years, elegant studies on the synthesis and
structural characterization of amidinate iron(II) complexes have
been reported.13−18 But the reactivity of these iron amidinate
compounds remains largely unknown. A few known explora-
tions on this aspect include the complexation of CO and Lewis
bases to [Fe(RC(NR′)2)2] (R = But, R′ = Cy, Pri),14b and
[Fe2(Me3SiNCPhN)2C6H10],16 the CO-insertion reactions of
[CpFe(FcC(NCy)2)(CO)]14a and [(PhC(NDipp)2)2Fe-
Received: January 8, 2013
Published: May 8, 2013
© 2013 American Chemical Society
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of other bis(amidinato) metal complexes or iron(II) complexes
bearing other nitrogen-based ligands.
pointing away from the mesityl group. This structural feature is
also present in the structures of 2−5 (vide infra).
Reactions of [Fe(MesC(NPri)2)2] with Organic Halides.
Complex 1 can readily react with benzyl chloride to afford the
iron(III) complex [FeCl(MesC(NPri)2)2] (2), but it is inert
toward common alkyl and aryl halides at ambient temperature,
such as dichloromethane, 1-bromooctane, and phenyl iodide.
Treatment of 1 with 1 equiv of PhCH2Cl in diethyl ether gives
a dark green solution, from which 2 has been isolated as blue
crystals in 68% yield, and 1,2-diphenylethane was identified as
the byproduct by GC-MS analysis (Scheme 2). Complex 2
RESULTS AND DISCUSSION
■
Synthesis and Characterization of [Fe(MesC(NPri)2)2].
Our previous study has shown the reaction of the three-
coordinate iron(II) complex [(IPr2Me2)Fe(Mes)2] (IPr2Me2:
2,5-diisopropyl-3,4-dimethylimidazol-1-ylidene, Mes: 2,4,6-tri-
methylphenyl) with 1 or 2 equiv of PriNCNPri gives the
mono(amidinato) complex [(IPr2Me2)Fe(Mes)(MesC-
(NPri)2)], irrespective of the reaction stoichiometry.21 In
contrast with this, [Fe(Mes)2]2 can react with 4 equiv of
PriNCNPri to yield the bis(amidinato)iron(II) complex
[Fe(MesC(NPri)2)2] (1) in good yield (Scheme 1). Similar
Scheme 2. Reaction of 1 with Benzyl Chloride
Scheme 1. Preparation of 1
shows good solubility in low polar solvent such as benzene and
diethyl ether, and solution magnetic moment measurement
(Evans’ method) has revealed its high-spin nature (μeff = 5.7(4)
μB), consistent with that (5.8 μB) of its analogues [FeX(PhC-
(NSiMe3)2)2] (X = OEt, OCHPh2).20
The molecular structure of 2 in solid state shows a close
resemblance to its congeners [FeX(PhC(NSiMe3)2)2] (X = Cl,
OEt, OCHPh2)13a,20 and [FeCl(PriHNC(NPri)2)2].24 As
shown in Figure 2, this mononuclear iron(III) complex has a
to its analogues [Fe(ButC(NR)2)2] (R = Pri, Cy),14b complex 1
is air-, moisture-, and light-sensitive. It is quite soluble in
benzene and diethyl ether, and slightly soluble in n-hexane. The
1H NMR spectra of 1 recorded in C6D6 and d8-THF are close
to each other.22 Solution magnetic moment measurement in
C6D6 revealed the iron(II) center in 1 has a high-spin electronic
configuration (μeff = 5.5(1) μB).23 The high sensitivity of this
complex toward adventitious water or [Bun N][PF4] made the
4
attempts to measure its voltammogram unsuccessful.
The molecular structure of 1 in solid state has been
established by a single-crystal X-ray diffraction study. As shown
in Figure 1, this molecule displays a crystallographically
Figure 2. Molecular structure of [FeCl(MesC(NPri)2)2] (2) showing
30% probability ellipsoids and the partial atom numbering schemes.
Selected distances (Å) and angles (deg): Fe1−N1 2.118(1), Fe1−N2
1.993(1), Fe1−N3 2.013(1), Fe1−N4 2.092(1), Fe1−Cl1 2.244(5),
C1−N1 1.324(2), C1−N2 1.344(2), C17−N3 1.336(2), C17−N4
1.326(2), N1−C1−N2 112.3(1), N3−C17−N4 111.8(1), N1−Fe1−
N2 65.1(5), N3−Fe1−N4 64.9(5), N2−Fe1−N3 118.3(6), N2−Fe1−
N4 108.3(6), N1−Fe1−Cl1 96.5(4), N3−Fe1−Cl1 124.7(4).
Figure 1. Molecular structure of [Fe(MesC(NPri)2)2] (1) showing
30% probability ellipsoids and the partial atom numbering schemes.
Selected distances (Å) and angles (deg): Fe1−N1 2.036(1), Fe1−N2
2.025(1), C1−N1 1.322(2), C1−N2 1.333(2), N1−C1−N2 112.4(1),
N1−Fe1−N2 65.8(5), N1−Fe1−N2′ 131.07(6).
penta-coordinate iron center that is coordinating with one
chloride and two chelating amidinates forming a distorted
trigonal bipyramidal geometry with the Addison parameter τ =
0.66. The bonding of the amidinato ligands to the iron center is
asymmetric as revealed by the different Fe−N bond distances
within the four-membered metallocycles (2.118(1) and
1.993(1) Å for Fe1−N1 and Fe1−N2, and 2.092(1) and
2.013(1) Å for Fe1−N4 and Fe1−N3).
approximate D2 symmetry in which two identical amidinato
anions are coordinating to the iron(II) center in chelating
fashion with the Fe−N distances of 2.025(1) and 2.036(1) Å,
the N−C(amidinato) distances of 1.322(2) and 1.333(2) Å,
and the dihedral angle between two chelating planes being
81.22 deg. These bond distances are found close to those of the
known mononuclear bis(amidinato)iron(II) complexes, such as
[Fe(FcC(NCy)2)2],14a [Fe(ButC(NCy)2)2],15a [Fe(PhC-
(NDipp)2)2],15b and [Fe(MeC(NBut)2)2]18a (Fc: ferrocenyl,
Cy: cyclohexyl, Dipp: 2,6-diisopropylphenyl). Besides these,
possibly because of steric congestion within the amidinato
ligands, the methyl groups on the iso-propyl moieties in 1 are all
Reactions of [Fe(MesC(NPri)2)2] with S8 and Se.
Treatment of 1 with 0.25 equiv of S8 in diethyl ether at −78
°C produced a yellow solution whose color slowly changed to
brown then raised to room temperature. After workup a yellow
complex [Fe(MesC(NPri)(NPriS))2] (3) has been isolated in
62% yield (Scheme 3). Complex 1 is unreactive toward Se in
C6D6 as suggested by NMR scale reactions at room
temperature and 70 °C. Complex 3 has been characterized by
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Scheme 3. Reaction of 1 with S8
Chart 1. Canonical Structures of Imidoyl Aminothiolato
Ligand
1H NMR, IR, elemental analysis, and single-crystal X-ray
diffraction study. The paramagnetic complex has a magnetic
moment of 4.5(1) μB (in C6D6 at room temperature) that is
slightly lower than the spin-only value expected for high-spin
ferrous complexes, but comparable to that of 4.4 μB observed
for the tetrahedral complexes (dmpe)Fe(Mes)2 and (depe)Fe-
(Mes)2 reported by Chirik.25 The unusual low magnetic
moment value spurred us to investigate the variable temper-
ature magnetic susceptibility of 3 in d8-THF which indicates its
solution magnetic moments varied in a narrow range (from 4.6
to 4.9 μB) when the temperature changed from 295 to 195 K
(II) complex when compared with other amidinates complexes
and iron(II) amides. For examples, the bis(amidinato)titanium-
(II) complex [{(PhC(NSiMe3)2)2Ti}2(N2)] is known to react
with S8 to yield disulfido complex [(PhC(NSiMe3)2)2Ti(S2)],28
the reaction of mono(amidinato)germanium(II) [(PhC-
(NBut)2)GeCl] with S8 and KC8 gives germanium sulfide
[(PhC(NBut)2)GeSGe(PhC(NBut)2)],29 and the interaction of
[Fe(N(SiMe3)2)2]2 or Fe(N(SiMe3)2)(NHBut) with S8 also
produces sulfide compound [Fe4S4(N(SiMe3)2)4],30 or [Fe2(μ-
S)(μ-NHBut)2(N(SiMe3)2)2],31 respectively. In light of these,
we propose the formation of 3 might entail transient iron
sulfide intermediates (MesC(NPri)2)2FeSFe(MesC(NPri)2)2,
(MesC(NPri)2)2Fe(S2), or (MesC(NPri)2)2Fe(S). But, because
of the nucleophilicity of the amidinato ligand (as demonstrated
by the aforementioned CO-insertion reactions of iron(II)
amidinates),14a,15e these intermediates might be unstable and
could convert to imidoyl aminothiolato complexes upon
migratory insertion steps.
1
(Supporting Information, Figure S4), meanwhile the H NMR
peaks showed peak-shifting phenomenon, but no peak-
coalescence (Supporting Information, Figure S3). These
observations suggest the low magnetic moment value might
not come from the geometry equilibrium between tetrahedral
and square planar geometry.
Single-crystal X-ray crystallography has revealed 3 is an
iron(II) compound featuring two unique bidentate imidoyl
aminothiolato ligands, [MesC(NPri)(NPriS)]− (Figure 3). The
Reactions of [Fe(MesC(NPri)2)2] with Aryl Azides. To
examining whether the bis(amidinato)iron scaffold can support
imido species, the reactions of 1 with aryl azides, 3,5-
dimethylphenyl azide, and phenyl azide, have been attempted.
Addition of 1 equiv of 3,5-dimethylphenyl azide, 3,5-
Me2C6H3N3, to a solution of 1 in benzene at room temperature
led to an instant color change from colorless to brown with
concomitant N2 gas evolution. 1H NMR analyses suggested the
formation of new paramagnetic species, and recrystallization on
the reaction mixture has led to the isolation of [Fe(MesC-
(NPri)(NPriNC6H3-3,5-Me2))(MesC(NPri)2)] (4a) as yellow
crystals in 47% yield (Scheme 4). Complex 4a has been fully
Figure 3. Molecular structure of [Fe(MesC(NPri)(NPriS))2] (3)
showing 30% probability ellipsoids and the partial atom numbering
schemes. Selected distances (Å) and angles (deg): Fe1−S1 2.283(8),
Fe1−S2 2.272(8), Fe1−N1 2.036(2), Fe1−N3 2.030(2), S1−N2
1.755(2), S2−N4 1.755(2), C1−N1 1.318(3), C1−N2 1.348(3),
C17−N3 1.321(3), C17−N4 1.344(3), S1−Fe1−S2 127.9(3), N1−
Fe1−N3 124.7(8), N1−Fe1−S1 84.8(6), N3−Fe1−S2 85.2(6), N1−
Fe1−S2 119.6(6), N3−Fe1−S1 119.6(6), N1−C1−N2 119.8(2),
N3−C17−N4 120.3(2).
Scheme 4. Reactions of 1 with the Aryl Azides
1
characterized by H NMR, IR, elemental analysis, and single-
coordination of these two chelates to the iron center renders it
a distorted tetrahedral geometry as the angles surrounding the
iron center spanning in a broad range from 84.8(6) to 127.9(3)
deg. The Fe−S distances (2.283(8) and 2.272(8) Å) and Fe−N
distances (2.036(2) and 2.030(2) Å) are consistent with the
corresponding ones in neutral iron(II) compounds containing
tetrahedral FeS2N2 units, such as [Fe(SDipp)2(1-MeIm)2] (1-
MeIm: 1-methylimidazole),26 and [Fe(STipp)2(btmgp)]
(Tipp: 2,4,6-trisiopropylphenyl, btmgp: 1,3-bis(N,N,N′N′-
tetramethylguanidino)propane).27 The structures of the two
imidoyl aminothiolato ligands, [MesC(NPri)(NPriS)]−, are
nearly identical, and both of them possess planar N−C−N-S
alignments, long S−N bonds (1.755(2) Å), and narrow N−C
distance distribution (1.318(3) to 1.348(3) Å), suggesting the
contributions of both canonical forms (Chart 1).
crystal X-ray diffraction study, and solution magnetic moment
measurement indicated its high spin nature (μeff = 5.1(1) μB).
The reaction of 1 with PhN3 gave new paramagnetic species
22
1
with similar H NMR spectrum as that of 4a. Though our
attempts to isolate the product upon recrystallization were
unsuccessful, column chromatographic separation on the
quenched reaction mixture yielded MesC(NPri)(NPriNHPh)
and MesC(NPri)(NPriH) in an 1:1 ratio. Thus, the para-
magnetic product can be formulated as [Fe(MesC(NPri)-
(NPriNPh))(MesC(NPri)2)] (4b). Notably, despite the
presence of the [Fe(MesC(NPri)2)] fragments in 4a and 4b,
they are found inert when treated with the second equivalent of
the corresponding azide.
As shown in Figure 4, complex 4a is a mono(amidinato)-
iron(II) complex bearing a bidentate imidoyl hydrazido ligand,
[MesC(NPri)(NPriNC6H3-3,5-Me2)]−. The chelation of the
imidoyl hydrazido ligand to the iron center gives a five-
The isolation of this imidoyl aminothiolato complex
demonstrates the distinct reactivity of the bis(amidinato)iron-
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(NPri)2)2Fe(N3Ar). While the terminal azide adduct might not
be amenable to eliminate N2, it could convert back to 1 upon
dissociation of the azide.2c,10b On the other hand, the internal
organic azide adduct could eliminate a N2 molecule to afford an
iron(IV)-imido or iron(II)-nitrene species (MesC(NPri)2)2Fe-
(NAr).34 A subsequent step of nitrene-insertion into an Fe−
N(amidinato) bond within the intermediate could then afford
the imidoyl hydrazido complex. The reactivity of nitrene-
insertion into an Fe−N(amidinato) bond is hitherto unknown.
However, it is apparent this conversion parallels that of the
aforementioned CO- and sulfur-insertion reactions, and also
the reported reactions of nitrene-insertion into metal-pyrrole
nitrogen bonds of metalloporphyrins.35
Figure 4. Molecular structure of [Fe(MesC(NPri)(NPriNC6H3-3,5-
Me2))(MesC(NPri)2)] (4a) showing 30% probability ellipsoids and
the partial atom numbering schemes. Selected distances (Å) and
angles (deg): Fe1−N1 2.038(2), Fe1−N2 2.059(2), Fe1−N3
2.044(2), Fe1−N5 2.004(2), C1−N1 1.338(3), C1−N2 1.326(3),
C17−N3 1.302(2), C17−N4 1.370(2), N4−N5 1.433(2), N1−Fe1−
N2 65.5(7), N3−Fe1−N5 80.3(6), N1−Fe1−N5 125.8(7), N2−Fe1−
N3 124.2(7), N1−C1−N2 112.6(2), N3−C17−N4 118.7(2), C17−
N4−N5 115.3(2).
Reactions of [Fe(MesC(NPri)2)2] with Oxo-Transfer
Reagents. Prompted by the imido/nitrene-insertion reactions,
we further investigated the reactions of 1 with 1 equiv of oxo-
transfer reagents, trimethylamine oxide, and 2,6-dichloropyr-
idine oxide in benzene, both of which, however, afforded a
dinuclear iron(III) complex [(MesC(NPri)2)2FeOFe(MesC-
(NPri)2)2] (5), rather than the oxygen-insertion analogue of 4a
(Scheme 6). The addition sequence of the reagents and the
membered Fe−N−N−C−N metallocylce with the sequential
N−N (1.433(2) Å), N−C (1.370(2) Å), and C−N (1.302(2)
Å) connections being single, single, and double bonds in
character. Consistent with this, both nitrogen atoms of the
hydrazido moiety, N5 and N4, display a trigonal pyramidal
geometry with the 3,5-dimethylphenyl and iso-propyl sub-
stituents on them being a transoid arrangement. The nonplanar
geometry observed for the two hydrazido nitrogen atoms,
which might be caused by steric congestion and the
stereochemically active property of N(sp3) atoms, signifies
the distinction of this imidoyl hydrazido ligand when compared
with those in [(p-cymene)Ru(PhC(NMe)(NHNMe2))Cl]Cl,32
and [Ti(PhC(NC6H3-2,6-Me2)(NMeO))2Cl2].33 In addition,
the Fe−N bond distances ranging from 2.004(2) to 2.059(2) Å
in 4a are found close to those of the aforementioned
bis(amidonato)iron(II) complexes,14a,15a,b,18a and the metric
data of the [Fe(MesC(NPri)2)] fragment are in line with those
observed in 1.
The evident formation of the imidoyl hydrazido ligand in the
structure of 4a points out iron(IV)-imido or iron(II)-nitrene
species might be involved in the reaction of 1 with the aryl
azide (Scheme 5), though other reaction mechanisms cannot
be excluded. As our control experiments showed the amidinato
anion Li[MesC(NPri)2)2] is inert toward 3,5-dimethylphenyl
azide, we propose the reaction should proceed by the
coordination of one azide molecule with the iron center in 1
to give terminal or internal organic azide adduct (MesC-
Scheme 6. Reactions of 1 with the Oxo-Transfer Reagents
reaction stoichiometry show no apparent effect on the reaction
outcome as either adding a solution of 1 (1 or 2 equiv) in
benzene to a solution of 2,6-dichloropyridine oxide, or with the
reversed addition sequence all afforded 5 in comparable yields.
Moreover, GC-MS analyses on the quenched reaction mixtures
indicated the absence of hydroxylamine MesC(NPri)-
(NPriOH).
Single-crystal X-ray diffraction study has shown the dinuclear
complex 5 possesses a μ2-oxo bridge that connects two
(MesC(NPri)2)2FeIII fragments with the Fe−O−Fe angle of
176.5(1) deg (Figure 5). The bond distances and angles of the
Scheme 5. Possible Mechanism for the Formations of 4a
Figure 5. Molecular structure of [(MesC(NPri)2)2FeOFe(MesC-
(NPri)2)2] (5) showing 30% probability ellipsoids and the partial atom
numbering schemes. For simplicity, the iso-propyl groups are omited.
Selected distances (Å) and angles (deg): Fe1−O1 1.795(2), Fe2−O1
1.797(2), Fe1−N5 2.127(3), Fe1−N6 2.137(3), Fe1−N7 2.129(3),
Fe1−N8 2.100(3), Fe2−N1 2.112(3), Fe2−N2 2.127(3), Fe2−N3
2.128(3), Fe2−N4 2.106(3), Fe1−O1−Fe2 176.5(1), N5−Fe1−N6
61.8(1), N7−Fe1−N8 62.7(1), N1−Fe2−N2 62.7(1), N3−Fe2−N4
62.7(1).
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(MesC(NPri)2)2Fe units are close to each other, and accord
well with those of the aforementioned high-spin bis-
(amidinato)iron(III) complexes.13a,20 Similar to many of the
known oxo-bridged dinuclear iron(III) complexes, 5 is
dented imidoyl aminothiolato ligand. The formation of this
imidoyl aminothiolato ligand is explained by migratory
insertion reactions of bis(amidinato)iron-sulfide or -disulfide
intermediate.
1
(3) The reactions of [Fe(MesC(NPri)2)2] with phenyl azides
give iron(II) complexes [Fe(MesC(NPri)(NPriNAr))(MesC-
(NPri)2)]. Iron(IV)-imido or iron(II)-nitrene intermediates are
proposed as the key intermediates for these reactions. In
contrast, the interactions of [Fe(MesC(NPri)2)2] with the oxo-
transfer reagents, trimethylamine oxide, and 2,6-dichloropyr-
idine oxide, give the diferric complex [(MesC(NPri)2)2FeOFe-
(MesC(NPri)2)2]. The different outcome of these two reactions
indicates the distinct property of the oxo- and imido-moieties
on the bis(amidinato)iron(IV) platform.
diamagnetic and its H NMR spectrum features resonances in
the range 1.0 to 8.0 ppm suggesting strong antiferromagnetic
coupling between the two iron(III) centers.36
Reactivity Patterns of [Fe(MesC(NPri)2)2] with the
Oxidizing Reagents. The current study has now revealed
two reactivity patterns of the bis(amidinato)iron(II) complex
toward oxidizing reagents: oxidation of the iron(II) center to
give bis(amidinato)iron(III) complex (2 and 5), and
“oxidation” of the ligand to give iron(II) complex (3 and 4a).
The latter type of reactivity can be viewed as the insertion of a
six-electron fragment, S or [NAr]0, into an Fe−N(amidinato)
bond. With the establishment of these distinct reactivity
patterns, it is now appropriate to discuss their underlying
causes.
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 or cannula techniques, or in a
glovebox. Organic solvents were dried with a solvent purification
system (Innovative Technology) and bubbled with dry N2 gas prior to
use. [Fe(Mes)2]239 and the phenyl azides40 were prepared according to
literature methods. All other chemicals were purchased from either
Strem or J&K Chemical Co. and used as received unless otherwise
noted. 1H and 13C NMR spectra were recorded on a VARIAN
Mercury 300 or 400 MHz spectrometer. Variable temperature NMR
study was performed on a VARIAN Mercury 500 MHz spectrometer.
All chemical shifts were reported in δ 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. IR
spectra were recorded with a NICOLET AVATAR 330 FT-IR
spectrophotometer. Absorption spectra were recorded with a
HITACHI U-3310 UV−vis spectrophotometer. Mass spectra were
recorded with a Waters Micromass GCT instruments for EI-MS, and
IonSpec 4.7 T FTMS for MALDI/DHB. GC/MS was performed on a
Shimadzu GCMS-QP2010 Plus spectrometer. Elemental analysis was
performed by the Analytical Laboratory of Shanghai Institute of
Organic Chemistry (CAS). Magnetic moments were measured at
room temperature by the method originally described by Evans with
stock and experimental solutions containing a known amount of a
(CH3)3SiOSi(CH3)3 standard.23
Among these oxidizing reagents, benzyl chloride is a well-
known single-electron oxidant for high-spin iron(II) com-
plexes,37 and the formation of 2 from the reaction of 1 with
benzyl chloride is straightforward and not unusual. Sulfur, N-
oxides, and organic azides are two-electron oxidants, and their
interaction with 1 should initially give iron(III)−sulfur species
[(MesC(NPri)2)2Fe]2S (or (MesC(NPri)2)2Fe(S2)) and the
formal iron(IV) intermediates (MesC(NPri)2)2FeX (X = S, O,
NAr) via two-electron redox processes. Once these formal
iron(III, IV) species are formed, the electronic properties of the
X groups should then affect their fates. The smaller
electronegativity values of sulfur and nitrogen atoms,38
compared with oxygen, might render the X (X = S, NAr)
moieties in [(MesC(NPri)2)2Fe]2S (or (MesC(NPri)2)2Fe(S2)
and (MesC(NPri)2)2Fe(S)) and (MesC(NPri)2)2FeNAr elec-
tron-deficient (or electrophilic), and trigger subsequent
migratory insertion reactions to produce the imidoyl amino-
thiolato and imidoyl hydrazido ligands in 3 and 4a. In contrast,
the largest electronegativity value of oxygen among these X
fragments would make the oxygen in (MesC(NPri)2)2FeO less
electron-deficient or even nucleophlic, facilitating its interaction
with another bis(amidinato)iron(II) molecule to afford the oxo-
bridged diferric complex 5. It should be mentioned, besides
these factors, the affinity of sulfur and nitrogen anions toward
iron(II) center and that of oxo toward iron(III) ion governed
by their hard/soft characters, as well as the thermodynamic
driving force of forming five-membered chelate rings from four-
membered rings should also play important roles for the
distinct reactivity patterns observed in these group-transfer
reactions. With these understanding, we are now modifying the
amidinato ligand aiming to reduce its nucleophilicity.
Preparation of [Fe(MesC(NPri)2)2] (1). To a solution of
Fe2(Mes)4 (588 mg, 1.00 mmol) in Et2O (10 mL) was added a
solution of N,N′-diisopropylcarbodiimide (505 mg, 4.00 mmol) in
Et2O (5 mL) at −78 °C. The color of solution changed to dark-brown
quickly, and the reaction mixture was warmed to room temperature
and further stirred for 8 h. After removal of the solvent under vacuum,
the brown residue was extracted with Et2O (20 mL) and filtered. Slow
evaporation of Et2O at room temperature afforded 1 as a colorless
1
crystalline solid. Yield: 837 mg, 76%. H NMR (300 MHz, C6D6, 298
K): δ (ppm) 14.54 (br, 2H, Mes-CH), 6.59 (br, 3H, p-Mes-CH3), 4.15
(br, 18H, o-Mes-CH3 + Pri-CH3), −130.3 (br, 2H, Pri-CH). 1H NMR
(300 MHz, d8-THF, 298 K): δ (ppm) 14.91 (s, 2H, Mes-CH), 7.00 (s,
3H, p-Mes-CH3), 4.70 (br, 6H, o-Mes-CH3), 3.18 (br, 12H, Pri-CH3),
CONCLUSION
The following are the principal results and conclusions of this
investigation.
■
1
−129.45 (br, 2H, Pri-CH). H NMR (400 MHz, C6D6, 298 K): δ
(ppm) 169.4 (br, 2H, Pri-CH), 14.51 (br, 2H, Mes-CH), 6.58 (br, 3H,
1
p-Mes-CH3), 4.16 (br, 18H, o-Mes-CH3 + Pri-CH3). H NMR (400
(1) The monomeric bis(amidinato)iron(II) complex [Fe-
(MesC(NPri)2)2] has been prepared in good yield by the
reaction of [Fe(Mes)2]2 with 4 equiv of PriNCNPri. The
ferrous complex has a high-spin electron configuration and has
been fully characterized by various spectroscopic methods.
(2) The bis(amidinato)iron(II) complex can react with
benzyl chloride via a single-electron redox process to afford the
mononuclear ferric compound [FeCl(MesC(NPri)2)2] and
diphenylethane. Its reaction with S8, however, gives the iron(II)
complex [Fe(MesC(NPri)(NPriS))2] featuring the unprece-
MHz, d8-THF, 298 K): δ (ppm) 172.28 (br, 2H, Pri-CH), 14.96 (s,
2H, Mes-CH), 7.04 (s, 3H, p-Mes-CH3), 4.76 (br, 6H, o-Mes-CH3),
3.22 (br, 12H, Pri-CH3). Anal. Calcd for C32H50FeN4: C 70.31, H 9.22,
N 10.25; Found: C 70.43, H 9.31, N 10.08. Magnetic susceptibility
(C6D6, 302 K): μeff = 5.5(1) μB. Absorption spectrum (C6H6): λmax
(εM) 267 (5700), 353(3000) nm. IR (KBr, cm−1): υ = 2963.6 (s),
2923.5 (s), 2864.8 (s), 1634.8 (s), 1612.8 (s), 1479.2 (s), 1451.0 (s),
1378.3 (m), 1358.7 (m), 1316.2 (m), 1267.5 (m), 1177.2 (s), 1140.2
(w), 1125.2 (w), 1012.4 (w), 852.3 (m), 764.5 (w), 690.0 (w), 482.5
(w).
5910
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Inorganic Chemistry
Article
Preparation of [FeCl(MesC(NPri)2)2] (2). To a solution of 1 (109
mg, 0.2 mmol) in Et2O (10 mL) was added a solution of benzyl
chloride (25.3 mg, 0.20 mmol) in Et2O (1.0 mL) at −78 °C. The color
of solution changed to green quickly, and the reaction mixture was
warmed to room temperature and further stirred for 8 h. After removal
of the solvent under vacuum, the green residue was extracted with
Et2O (5.0 mL) and filtered. Slow evaporation of Et2O at room
temperature afforded 2 as a green-blue crystalline solid. Yield: 79.2 mg,
Removal of all the volatiles under vacuum gave deep brownish oil.
Chromatographic separation (SiO2, 300−400 mesh, n-hexane/EtOAc
(1/1)) afforded the protonated ligand MesC(NPri)(NHPri) (59.1 mg,
48%) and the imidoyl hydrazine compound [(NPri)MesC-
(NPriNHPh)] (67.8 mg, 40%) both as colorless solid. For MesC-
1
(NPri)(NHPri): H NMR (300 MHz, CDCl3, 298 K): δ (ppm) 6.92
(s, 2H, Mes-CH), 3.05 (m, 2H, Pri-CH), 2.25 (s, 3H, p-Mes-CH3),
2.18 (s, 6H, o-Mes-CH3), 1.12 (d, 12H, Pri-CH3). The signal of NH
proton has not been observed. 13C NMR (100 MHz, CDCl3, 298 K):
δ (ppm) 163.85 (CN), 141.36, 134.36, 129.24, 122.55, 47.18 (CH-
Pri), 45.78 (CH-Pri), 23.10 (CH3-Mes), 21.07 (CH3-Mes), 19.13
(CH3-Pri), 8.62 (CH3-Pri). HRMS-TOF (m/z): [M+H]+ calcd for
C16H26N2, 247.2174; Found, 247.2177. IR (KBr, cm−1): υ = 2974.4
(s), 2925.2 (m), 2873.9 (m), 1613.5 (s), 1445.5 (m), 1395.9 (m),
1369.4 (m), 1327.7 (w), 11160.1 (m), 1131.3 (m), 1035.5 (w), 853.8
(m), 806.0 (w), 730.2 (m), 697.5 (w), 649.3 (w), 612.6 (w). The
streching resonance of N−H has not been observed. For (NPri)-
1
68%. H NMR (300 MHz, C6D6, 298 K): δ (ppm) 21.90 (br, 6H, p-
Mes-CH3), 13.63 (br, 12H, Pri-CH3). Anal. Calcd for C32H50ClFeN4:
C 66.03, H 8.66, N 9.63; Found: C 66.07, H 8.95, N 9.75. Magnetic
susceptibility (C6D6, 302 K): μeff = 5.7(4) μB. Absorption spectrum
(C6H6): λmax (εM) 397 (sh, 1700), 637(2800) nm. IR (KBr, cm−1): υ =
2964.0 (s), 2925.3 (s), 2868.8 (s), 1634.8 (s), 1612.3 (s), 1435.4 (s),
1379.4 (s), 1360.2 (s), 1333.1 (s), 1268.3 (w), 1222.3 (m), 1173.8
(m), 1138.8 (m), 1121.2 (m), 1013.6 (m), 942.4 (w), 850.6 (s), 761.5
(w), 727.5 (w), 692.2 (w), 552.8 (w), 489.9 (w), 425.9 (w), 404.9 (w).
Preparation of [Fe(MesC(NPri)(NPriS)2)2] (3). To a solution of 1
(109 mg, 0.20 mmol) in Et2O (10 mL) was added S8 (12.8 mg, 0.05
mmol) at −78 °C. The color of solution changed to brown slowly, and
the reaction mixture was warmed to room temperature and further
stirred for 8 h. After removal of the solvent under vacuum, the brown
residue was extracted with Et2O (10 mL) and filtered. Slow
evaporation of Et2O at room temperature afforded 3 as a yellow
1
MesC(NPriNHPh): H NMR (300 MHz, CDCl3, 298 K): δ (ppm)
7.27−7.21 (m, 2H, Ph−CH), 7.07 (br, 2H, Mes-CH), 6.91−6.87 (m,
3H, Ph−CH), 3.70 (br, NH), 2.99 (quintet, 1H, Pri-CH), 2.34 (s, 6H,
o-Mes-CH3), 2.28 (s, 3H, p-Mes-CH3), 1.21 (s, 6H, Pri-CH3), 1.09 (s,
3H, Pri-CH3), 0.69 (s, 3H, Pri-CH3). 13C NMR (100 MHz, CDCl3,
298 K): δ (ppm) 157.8 (CN), 151.0 (C-Mes), 137.4, 135.2, 130.4,
129.1, 128.1, 119.5, 115.3, 50.34, 49.79, 24.62, 22.19, 20.89, 20.20,
19.46. HRMS-TOF (m/z): [M+H]+ calcd for C22H31N3, 338.2596;
Found, 338.2583. IR (KBr, cm−1): υ = 3256.4 (w, NH), 2965.3 (s),
2925.8 (m), 2868.3 (w), 1612.9 (s), 1598.3 (s), 1494.2 (s), 1440.9
(w), 1377.6 (m), 1359.6 (m), 1340.4 (w), 1285.2 (s), 1245.1 (m),
1188.5 (w), 1154.6 (m), 1109.4 (m), 1080.9 (m), 1058.2 (m), 1025.2
(w), 980.4 (w), 945.8 (w), 884.9 (w), 852.6 (m), 752.6 (s), 692.5 (s),
664.0 (w), 622.9 (w).
1
crystalline solid. Yield: 71.6 mg, 62%. The H NMR spectrum of this
paramagnetic complex displayed four broad peaks in the range −150
1
to 150 ppm. Attempts to assign them have not been made. H NMR
(300 MHz, C6D6, 298 K): δ (ppm) 11.07 (br), 9.30 (br), 6.74 (br),
2.96 (br). 1H NMR (300 MHz, d8-THF, 298 K): δ (ppm) 11.32 (br),
8.25 (br), 6.79 (br), 2.31 (br). Anal. Calcd for C32H50FeN4S2: C 62.93,
H 8.25, N 9.17; Found: C 62.66, H 8.26, N 8.81. Magnetic
susceptibility (302 K): μeff = 4.5(1) μB in C6D6, 4.7(1) μB in THF-d8.
IR (KBr, cm−1): υ = 2967.3 (s), 2922.3 (s), 2866.5 (m), 1634.3 (m),
1611.4 (m), 1498.3 (s), 1478.8 (s), 1399.5 (m), 1379.3 (m), 1360.5
(m), 1336.0 (m), 1173.9 (m), 1127.4 (m), 1012.9 (m), 858.1 (m),
775.5 (w), 738.4 (w), 670.8 (w), 555.3 (w), 526.4 (w), 485.8 (w),
442.9 (w), 416.4 (w).
Preparation of [(MesC(NPri)2)2FeOFe(MesC(NPri)2)2] (5). To a
solution of 1 (109 mg, 0.20 mmol) in benzene (10 mL) was added
trimethylamine N-oxide (15.0 mg, 0.20 mmol) at −78 °C. The color
of solution changed to red quickly, and the reaction mixture was
warmed to room temperature and further stirred for 8 h. After removal
of the solvent under vacuum, the red residue was extracted with Et2O
(5 mL) and filtered. Slow evaporation of Et2O at room temperature
Preparation of [Fe(MesC(NPri)(NPriNC6H3-3,5-Me2)(MesC-
(NPri)2)] (4a). To a solution of 1 (164 mg, 0.30 mmol) in benzene
(10 mL) was added a solution of 3,5-dimethylphenyl azide (44.1 mg,
0.3 mmol) in benzene (5 mL) at room temperature. N2 bubbles were
released quickly, and the color of solution changed to dark brown. The
mixture was further stirred at room temperature for 8 h. After removal
of the solvent, the residue was extracted with Et2O (5.0 mL) and
filtered. Slow evaporation of Et2O at room temperature afforded 4a as
a yellow crystalline solid. Yield: 93.8 mg, 47%. The 1H NMR spectrum
of this paramagnetic complex displayed 15 characteristic peaks in the
range −150 to 150 ppm. Attempts to assign them have not been made.
1H NMR (300 MHz, C6D6, 298 K): δ (ppm) 53.11, 29.16, 28.80,
1
afforded 5 as a red crystalline solid. Yield: 34.3 mg, 31%. H NMR
(300 MHz, C6D6, 298 K): δ (ppm) 6.75 (s, 4H, Mes-CH), 4.43 (br,
2H, Pri-CH), 3.21 (br, 1H, Pri-CH), 3.02 (br, 1H, Pri-CH), 2.24 (s,
12H, o-Mes-CH3), 2.15 (s, 6H, p-Mes-CH3), 1.22 (d, 12H, Pri-CH3),
1.02 (d, 12H, Pri-CH3). Anal. Calcd for C64H100Fe2N8O: C 69.30, H
9.09, N 10.10; Found: C 70.02, H 9.25, N 10.01. IR (KBr, cm−1): ν =
2963.6 (s), 2925.6 (s), 2865.2 (s), 1635.4 (s), 1612.3 (s), 1480.4 (s),
1451.9 (s), 1378.4 (m), 1359.8 (m), 1316.7 (m), 1267.0 (m), 1177.1
(m), 1125.1 (w), 1033.7 (w), 977.4 (w), 852.6 (m), 802.6 (w), 742.7
(w). Alternatively, complex 5 can also be prepared from the reaction of
1 (109 mg, 0.20 mmol) with 2,6-dichloropyridine N-oxide (16.4 mg,
0.10 mmol) in benzene using similar procedures described above
(yield: 20.0 mg, 18%). The reaction of 1 with dioxygen in benzene
furnished 5 in trace amount.
X-ray Structure Determinations. The structures of the five
compounds were determined. Diffraction-quality crystals were
obtained as [Fe(MesC(NPri)2)2] (1), [FeCl(MesC(NPri)2)2] (2),
[Fe(MesC(NPri)(NPriS)2)2] (3), [Fe(MesC(NPri)(NPriNC6H3-3,5-
Me2)(MesC(NPri)2)] (4a), and [(MesC(NPri)2)2FeOFe(MesC-
(NPri)2)2] (5) in diethyl ether. Crystallizations were performed at
room temperature. Crystals were coated with Paratone-N oil and
mounted on a Bruker APEX CCD-based diffractometer equipped with
an Oxford low-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 corrections
were applied using SADABS.41 Space groups were assigned
unambiguously by analysis of symmetry and systematic absences
determined by XPREP. All structures were solved and refined using
SHELXTL.42 Metal and first coordination sphere atoms were located
from direct-methods E-maps; other non-hydrogen atoms were found
in alternating difference Fourier synthesis and least-squares refinement
26.28, 21.21, 16.83, 14.83, 11.99, 10.54, −9.74, −15.08, −22.38,
−35.97, −68.26, −95.86. Anal. Calcd for C40H59FeN5: C 72.16, H
8.93, N 10.52; Found: C 72.11, H 9.17, N 10.47. Magnetic
susceptibility (C6D6, 302 K): μeff = 5.1(1) μB. IR (KBr, cm−1): υ =
2954.8 (s), 2917.8 (s), 2864.4 (m), 1630.8 (m), 1611.6 (s), 1583.9 (s),
1534.4 (s), 1447.8 (s), 1378.2 (s), 1357.9 (s), 1327.7 (s), 1314.7 (s),
1232.2 (w), 1177.2 (m), 1156.9 (m), 1139.2 (m), 1121.7 (m), 1015.8
(m), 985.3 (w), 851.9, 817.0, 765.1 (w), 708.5 (w), 693.6 (w), 588.9
(w), 564.4 (w), 534.6 (w), 522.1 (w), 483.6 (w), 440.0 (w).
Reaction of [Fe(MesC(NPri)2)2] with PhN3. To a solution of 1
(273 mg, 0.50 mmol) in benzene (10 mL) was added a solution of
phenyl azide (60 mg, 0.50 mmol) in benzene (5 mL) at room
temperature. N2 bubbles were released quickly, and the color of
solution changed to dark brown. 1H NMR of this mixture displayed 14
characteristic peaks in the range −150 to 150 ppm. Attempts to assign
1
them have not been made. H NMR (300 MHz, C6D6, 298 K): δ
(ppm) 49.90, 28.09, 28.00, 23.65, 19.58, 16.32, 14.15, 11.16, 10.13,
−7.24, −12.40, −33.93, −69.08, −98.68. The mixture was further
stirred at room temperature for 8 h and then quenched with aq.
NH4Cl (6.8 M, 5 mL). After extraction with Et2O (2 × 10 mL), the
combined organic layers were dried over magnesium sulfate and filter.
5911
dx.doi.org/10.1021/ic400053g | Inorg. Chem. 2013, 52, 5906−5913

Inorganic Chemistry
Article
a
Table 1. Crystal Data and Summary of Data Collection and Refinement for 1−3, 4a, and 5
1
2
3
4a
5
formula
fw
C32H50FeN4
546.61
C32H50ClFeN4
582.06
C32H50FeN4S2
610.73
C40H59FeN5
665.77
C64H100Fe2N8O
1109.22
crystal system
space group
a, Å
orthorhombic
Pbcn
monoclinic
P2(1)/c
triclinic
triclinic
monoclinic
P2(1)/c
P1
̅
P1
̅
19.494(6)
7.970(3)
21.069(7)
90.00
12.070(1)
12.678(1)
22.399(2)
90.00
9.522(2)
11.688(2)
15.649(2)
98.99(3)
98.09(3)
101.00(3)
1662.2(4)/2
1.220
8.569(1)
12.400(2)
19.574(3)
101.18(2)
90.96(2)
108.06(2)
1933.4(5)/2
1.144
10.948(1)
27.900(1)
21.949(1)
90.00
b, Å
c, Å
α, deg
β, deg
γ, deg
90.00
104.87(2)
90.00
103.65(1)
90.00
90.00
V, Å3/Z
3273.1(2)/4
1.109
3312.9(6)/4
1.167
6514.8(3)/4
1.131
d
calcd, g/cm3
2θ range, deg
GOF (F2)
3.8−50.0
1.280
3.5−60.4
1.015
4.1−59.4
0.986
3.5−60.2
1.096
2.4−51.0
0.982
b
d
d
d
d
d
R1
0.0346,
0.0396,
0.0510,
0.0569,
0.0515,
e
e
e
e
e
0.0402
0.0663
0.1043
0.0761
0.0951
c
d
d
d
d
d
WR2
0.1329,
0.0948,
0.0978,
0.1699,
0.1277,
e
e
e
e
e
0.1453
0.1063
0.1164
0.1821
0.1589
a
b
c
d
e
2
2
Collected using Mo Kα radiation (λ = 0.71073 Å). R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = {∑[w(Fo − Fc2)2]/∑[w(Fo )2]]1/2. I > 2σ(I). All data.
cycles and during final cycles were refined anisotropically. Hydrogen
atoms were placed in calculated positions employing a riding model.
Final crystal parameters and agreement factors are reported in Table 1.
Tolman, W. B. Nature 2008, 455, 333−340. (b) Plietker, B. Iron
Catalysis in Organic Chemistry; Wiley-VCH: Weinheim, Germany,
2008; Chapter 3. (c) Gunay, A.; Theopold, K. H. Chem. Rev. 2010,
110, 1060−1081. (d) Che, C. M.; Zhou, C. Y.; Wong, E. L. M. Top.
Organomet. Chem. 2011, 33, 111−138. (e) Zhang, L.; Deng, L. Chin.
Sci. Bull. 2012, 19, 2352−2360.
ASSOCIATED CONTENT
* Supporting Information
■
S
(4) (a) Klinker, E. J.; Kaizer, J.; Brennessel, W. W.; Woodrum, N. L.;
Cramer, C. J.; Que, L., Jr. Angew. Chem., Int. Ed. 2005, 44, 3690−3694.
(b) Thibon, A.; England, J.; Martinho, M.; Young, V. J., Jr.; Frisch, J.
Crystallographic data in CIF format, UV−vis, and NMR spectra
for complexes 1−5. This material is available free of charge via
the Internet at http://pubs.acs.org.
R.; Guillot, R.; Girerd, J.-J.; Munck, E.; Que, L., Jr.; Banse, F. Angew.
̈
Chem., Int. Ed. 2008, 47, 7064−7067.
AUTHOR INFORMATION
Corresponding Author
*E-mail: deng@sioc.ac.cn.
(5) (a) Rohde, J. U.; In, J. H.; Lim, M. H.; Brennessel, W. W.;
■
Bukowski, M. R.; Stubna, A.; Munck, E.; Nam, W.; Que, L., Jr. Science
̈
2003, 299, 1037−1039. (b) Kotani, H.; Suenobu, T.; Lee, Y.-M.; Nam,
W.; Fukuzumi, S. J. Am. Chem. Soc. 2011, 133, 3249−3251.
(c) Morimoto, Y.; Kotani, H.; Park, J.; Lee, Y.-M.; Nam, W.;
Fukuzumi, S. J. Am. Chem. Soc. 2011, 133, 403−405.
Notes
The authors declare no competing financial interest.
(6) (a) MacBeth, C. E.; Golombek, A. P.; Young, V. G., Jr.; Yang, C.;
Kuczera, K.; Hendrich, M. P.; Borovik, A. S. Science 2000, 289, 938−
941. (b) Tiago de Oliveira, F.; Chanda, A.; Banerjee, D.; Shan, X.;
ACKNOWLEDGMENTS
■
We thank the financial support from the National Natural
Science Foundation of China (Nos. 20923005, 21121062, and
21222208) and the Science and Technology Commission of
Shanghai Municipality (No. 11PJ1412100).
Mondal, S.; Que, L., Jr.; Bominaar, E. L.; Munck, E.; Collins, T. J.
̈
Science 2007, 315, 835−838. (c) England, J.; Guo, Y.; Farquhar, E. R.;
Young, V. G., Jr.; Munck, E.; Que, L., Jr. J. Am. Chem. Soc. 2010, 132,
̈
8635−8644. (d) Lacy, D. C.; Gupta, R.; Stone, K. L.; Greaves, J.;
Ziller, J. W.; Hendrich, M. P.; Borovik, A. S. J. Am. Chem. Soc. 2010,
132, 12188−12190.
REFERENCES
■
(7) (a) Harman, W. H.; Chang, C. J. J. Am. Chem. Soc. 2007, 129,
15128−15129. (b) Bigi, J. P.; Harman, W. H.; Lassalle-Kaiser, B.;
Robles, D. M.; Stich, T. A.; Yano, J.; Britt, R. D.; Chang, C. J. J. Am.
Chem. Soc. 2012, 134, 1536−1542.
(8) (a) Brown, S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.
2003, 125, 322−323. (b) Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.
2003, 125, 10782−10783. (c) Brown, S. D.; Peters, J. C. J. Am. Chem.
Soc. 2005, 127, 1913−1923. (d) Thomas, C. M.; Mankad, N. P.;
Peters, J. C. J. Am. Chem. Soc. 2006, 128, 4956−4957. (e) Lu, C. C.;
Saouma, C. T.; Day, M. W.; Peters, J. C. J. Am. Chem. Soc. 2007, 129,
4−5. (f) Moret, M.-E.; Peters, J. C. Angew. Chem., Int. Ed. 2011, 50,
2063−2067.
(9) (a) Nieto, I.; Ding, F.; Bontchev, R. P.; Wang, H.; Smith, J. M. J.
Am. Chem. Soc. 2008, 130, 2716−2717. (b) Scepaniak, J. J.; Young, J.
A.; Bontchev, R. P.; Smith, J. M. Angew. Chem., Int. Ed. 2009, 48,
3158−3160.
(10) (a) Eckert, N. A.; Vaddadi, S.; Stoian, S.; Lachicotte, R. J.;
Cundari, T. R.; Holland, P. L. Angew. Chem., Int. Ed. 2006, 45, 6868−
(1) For recent reviews on nonheme type high-valent iron-oxo species,
see: (a) Costas, M.; Mehn, M. P.; Jensen, M. P.; Que, L., Jr. Chem.
Rev. 2004, 104, 939−986. (b) Tshuva, E. Y.; Lippard, S. J. Chem. Rev.
2004, 104, 987−1012. (c) Decker, A.; Solomon, E. I. Curr. Opin.
Chem. Biol. 2005, 9, 152−163. (d) Krebs, C.; Fujimori, D. G.; Walsh,
C. T.; Bollinger, J. M., Jr. Acc. Chem. Res. 2007, 40, 484−492. (e) Que,
L., Jr. Acc. Chem. Res. 2007, 40, 493−500. (f) Nam, W. Acc. Chem. Res.
2007, 40, 522−531. (g) Shaik, S.; Hirao, H.; Kumar, D. Acc. Chem. Res.
2007, 40, 532−542. (h) Ye, S.; Neese, F. Curr. Opin. Chem. Biol. 2009,
13, 89−98. (i) Solomon, E. I.; Wong, S. D.; Liu, L. V.; Decker, A.;
Chow, M. S. Curr. Opin. Chem. Biol. 2009, 13, 99−113.
(2) For recent reviews on iron-imido species with nonheme ligands,
see: (a) Mehn, M. P.; Peters, J. C. J. Inorg. Biochem. 2006, 100, 634−
643. (b) Berry, J. F. Comments Inorg. Chem. 2009, 30, 28−66.
(c) Saouma, C. T.; Peters, J. C. Coord. Chem. Rev. 2011, 255, 920−
937.
(3) For recent reviews on iron-catalyzed organic transformations
involving iron-oxo and -imido intermediates, see: (a) Que, L., Jr.;
5912
dx.doi.org/10.1021/ic400053g | Inorg. Chem. 2013, 52, 5906−5913

Inorganic Chemistry
Article
6871. (b) Cowley, R. E.; DeYonker, N. J.; Eckert, N. A.; Cundari, T.
R.; DeBeer, S.; Bill, E.; Ottenwaelder, X.; Flaschenriem, C.; Holland, P.
L. Inorg. Chem. 2010, 49, 6172−6187.
(31) Chen, X.-D.; Duncan, J. S.; Verma, A. K.; Lee, S. C. J. Am. Chem.
Soc. 2010, 132, 15884−15886.
(32) Crimmin, M. R.; Colby, D. A.; Ellman, J. A.; Bergman, R. G.
Dalton Trans. 2011, 40, 514−522.
(11) King, E. R.; Hennessy, E. T.; Betley, T. A. J. Am. Chem. Soc.
2011, 133, 4917−4923.
(33) Krajete, A.; Steiner, G.; Kopacka, H.; Ongania, K.-H.; Wurst, K.;
Kristen, M. O.; Preishuber-Pflugl, P.; Bildstein, B. Eur. J. Inorg. Chem.
̈
(12) For reviews on amidinato complexes, see: (a) Barker, J.; Kilner,
M. Coord. Chem. Rev. 1994, 133, 219−300. (b) Edelmann, F. T. Coord.
Chem. Rev. 1994, 137, 403−481. (c) Nagashima, H.; Kondo, H.;
Hayashida, T.; Yamaguchi, Y.; Gondo, M.; Masuda, S.; Miyazaki, K.;
Matsubara, K.; Kirchner, K. Coord. Chem. Rev. 2003, 245, 177−190.
(d) Edelmann, F. T. Adv. Organomet. Chem. 2008, 57, 183−352.
(e) Jones, C. Coord. Chem. Rev. 2010, 254, 1273−1289.
2004, 1740−1752.
(34) For examples of reactions of iron(II) complexes with aryl azides
giving iron-imido intermediates, see refs 3e, 11, and Cramer, S. A.;
Jenkins, D. M. J. Am. Chem. Soc. 2011, 133, 19342−19345.
(35) (a) Callot, H. J.; Chevrier, B.; Weiss, R. J. Am. Chem. Soc. 1978,
100, 4733−4741. (b) Mahy, J.-P.; Battioni, P.; Bedi, G.; Mansuy, D.;
Ficher, J.; Weiss, R.; Morgenstern-Badarau, I. Inorg. Chem. 1988, 27,
353−359.
(13) (a) Zinn, A.; von Arnim, H.; Massa, W.; Schafer, M.; Pebler, J.;
̈
Dehnicke, K. Z. Naturforsch., B: Chem. Sci. 1991, 46, 1300−1304.
(b) Cotton, F. A.; Daniels, L. M.; Falvello, L. R.; Murillo, C. A. Inorg.
Chim. Acta 1994, 219, 7−10. (c) Cotton, F. A.; Daniels, L. M.; Murillo,
C. A. Inorg. Chim. Acta 1994, 224, 5−9. (d) Cotton, F. A.; Daniels, L.
M.; Maloney, D. J.; Murillo, C. A. Inorg. Chim. Acta 1996, 242, 31−42.
(e) Cotton, F. A.; Daniels, L. M.; Maloney, D. J.; Murillo, C. A. Inorg.
Chim. Acta 1996, 252, 293−298. (f) Cotton, F. A.; Daniels, L. M.;
Matonic, J. H.; Murillo, C. A. Inorg. Chim. Acta 1997, 256, 277−282.
(g) Cotton, F. A.; Daniels, L. M.; Falvello, L. R.; Matonic, J. H.;
Murillo, C. A. Inorg. Chim. Acta 1997, 256, 269−275. (h) Cotton, F.
A.; Daniels, L. M.; Falvello, L. R.; Matonic, J. H.; Murillo, C. A.; Wang,
X.; Zhou, H. Inorg. Chim. Acta 1997, 266, 91−102.
(36) For examples, see: (a) Cheng, B.; J. Hobbs, J. D.; Debrunner, P.
G.; Erlebacher, J.; Shelnutt, J. A.; Scheidt, W. R. Inorg. Chem. 1995, 34,
102−110. (b) Vernik, I.; Stynes, D. V. Inorg. Chem. 1996, 35, 2006−
2010. (c) Patra, R.; Bhowmik, S.; Ghosh, S. K.; Rath, S. P. Eur. J. Inorg.
Chem. 2009, 654−665.
(37) Zhang, Q.; Xiang, L.; Deng, L. Organometallics 2012, 31, 4537−
4543.
(38) The electronegativity values of O, Cl, N, and S in the Pauling
scale are 3.44, 3.16, 3.04, and 2.58, respectively.
(39) Klose, A.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re,
N. J. Am. Chem. Soc. 1994, 116, 9123−9135.
(40) Pilyugina, T. S.; Schrock, R. R.; Hock, A. S.; Muller, P.
̈
(14) (a) Hagadorn, J. R.; Arnold, J. Inorg. Chem. 1997, 36, 132−133.
(b) Hagadorn, J. R.; Arnold, J. J. Organomet. Chem. 2001, 637−639,
521−530. (c) Schmidt, J. A. R.; Arnold, J. J. Chem. Soc.; Dalton Trans.
2002, 3454−3461.
Organometallics 2005, 24, 1928−1937.
(41) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray systems, Inc.:
Madison, WI, 1997.
(15) (a) Vendemiati, B.; Prini, G.; Meetsma, A.; Hessen, B.; Teuben,
J. H.; Traverso, O. Eur. J. Inorg. Chem. 2001, No. 31, 707−711.
(b) Nijhuis, C. A.; Jellema, E.; Sciarone, T. J. J.; Meetsma, A.;
Budzelaar, P. H. M.; Hessen, B. Eur. J. Inorg. Chem. 2005, 2089−2099.
(c) Sciarone, T. J. J.; Nijhuis, C. A.; Meetsma, A.; Hessen, B. Dalton
Trans. 2006, 4896−4904. (d) Sciarone, T. J. J.; Nijhuis, C. A.;
Meetsma, A.; Hessen, B. Organometallics 2008, 27, 2058−2065.
(e) Jellema, E.; Sciarone, T. J. J.; Navarrete, N. M.; Hettinga, M. J.;
Meetsma, A.; Hessen, B. Eur. J. Inorg. Chem. 2011, 91−100.
(16) Kawaguchi, H.; Matsuo, T. Chem. Commun. 2002, 958−959.
(17) Lee, H. K.; Lam, T. S.; Lam, C.-K.; Li, H.-W.; Fung, S. M. New J.
Chem. 2003, 27, 1310−1318.
(42) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure
Determination Software Programs; Bruker Analytical X-ray systems, Inc.:
Madison, WI, 1997.
(18) (a) Lim, B. S.; Rahtu, A.; Park, J.-S.; Gordon, R. G. Inorg. Chem.
2003, 42, 7951−7958. (b) Li, X.-G.; Li, Z.; Li, H.; Gordon, R. G. Eur.
J. Inorg. Chem. 2007, 1135−1142.
(19) (a) Rose, R. P.; Jones, C.; Schulten, C.; Aldridge, S.; Stasch, A.
Chem.Eur. J. 2008, 14, 8477−8480. (b) Fohlmeister, L.; Liu, S.;
Schulten, C.; Moubaraki, B.; Stasch, A.; Cashion, J. D.; Murray, K. S.;
Gagliardi, L.; Jones, C. Angew. Chem., Int. Ed. 2012, 51, 8294−8298.
(20) O’Keefe, B. J.; Breyfogle, L. E.; Hillmyer, M. A.; Tolman, W. B.
J. Am. Chem. Soc. 2002, 124, 4384−4393.
(21) Xiang, L.; Xiao, J.; Deng, L. Organometallics 2011, 30, 2018−
2025.
(22) For detailed information, please see Supporting Information.
(23) (a) Evans, D. F. J. Chem. Soc. 1959, 2003−2005. (b) Sur, S. K. J.
Magn. Reson. 1989, 82, 169−173.
(24) Foley, S. R.; Yap, G. P. A.; Richeson, D. S. Chem. Commun.
2000, 1515−1516.
(25) Hawrelak, E. J.; Bernskoetter, W. H.; Lobkovsky, E.; Yee, G. T.;
Bill, E.; Chirik, P. J. Inorg. Chem. 2005, 44, 3103−3111.
(26) Forde, C. E.; Lough, A. J.; Morris, R. H.; Ramachandran, R.
Inorg. Chem. 1996, 35, 2747−2751.
(27) Pohl, S.; Harmjanz, M.; Schneider, J.; Saak, W.; Henkel, G.
Inorg. Chim. Acta 2000, 311, 106−112.
(28) Hagadorn, J. R.; Arnold, J. Organometallics 1998, 17, 1355−
1368.
(29) Zhang, S.-H.; So, C.-W. Organometallics 2011, 30, 2059−2062.
(30) Ohki, Y.; Sunada, Y.; Tatsumi, K. Chem. Lett. 2005, 34, 172−
173.
5913
dx.doi.org/10.1021/ic400053g | Inorg. Chem. 2013, 52, 5906−5913