High-Spin Iron(II) Alkynyl Complexes with N-Heterocyclic Carbene Ligation: Synthesis, Characterization, and Reactivity Study

Article abstract of DOI:10.1021/acs.organomet.5b00028

High-spin iron(II) alkynyl complexes [(IPr₂Me₂)₂Fe(Ci≡CBu^t)₂] (1) and [(IPr₂Me₂)₂Fe(Ci≡CR)(NHMes)] (R = Bu^t 2, SiMe₃ 3) bearing a monodentate N-heterocyclic carbene ligand IPr₂Me₂ (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) have been prepared by salt metathesis and/or amine elimination methods and characterized by various spectroscopic methods. Complex 1 reacts with PMe₃ (4 equiv) and Bu^tNC (4 equiv) to form trans-[(PMe₃)₄Fe(Ci≡CBu^t)₂] (4) and [η³-{(Bu^tCi≡C)(Bu^t)CC(IPr₂Me₂)C(NBu^t)}Fe(NCBu^t)₃] (5), respectively. In contrast, the reactions of 1 with 4-Prⁱ-C₆H₄NCO and PrⁱNCNPrⁱ lead to the formation of the zwitterionic salts 4-Prⁱ-C₆H₄NC(O)(IPr₂Me₂) and (PrⁱN)₂C(IPr₂Me₂), respectively. The interaction of 1 with I₂ gives Bu^tCi≡CCi≡CBu^t and (IPr₂Me₂)₂FeI₂. The C(sp)-C(sp³) cross-coupling products n-C₈H₁₇Ci≡CBu^t and c-C₆H₁₁Ci≡CBu^t are formed in high yields when 1 is treated with the corresponding alkyl halides n-C₈H₁₇X and c-C₆H₁₁X (X = Br, Cl). The formation of the ring-opening product 7,7-dimethyloct-1-en-5-yne in the reaction of 1 with cyclopropylmethyl bromide supports the radical character of the cross-coupling reaction.

Full text of DOI:10.1021/acs.organomet.5b00028

Article
pubs.acs.org/Organometallics
High-Spin Iron(II) Alkynyl Complexes with N‑Heterocyclic Carbene
Ligation: Synthesis, Characterization, and Reactivity Study
Xiaojie Wang, Jia Zhang, Lei Wang, and Liang Deng*
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345
Lingling Road, Shanghai, People’s Republic of China, 200032
S
* Supporting Information
ABSTRACT: High-spin iron(II) alkynyl complexes [(IPr2Me2)2-
Fe(CCBut)2] (1) and [(IPr2Me2)2Fe(CCR)(NHMes)] (R =
But 2, SiMe3 3) bearing a monodentate N-heterocyclic carbene
ligand IPr2Me2 (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene)
have been prepared by salt metathesis and/or amine elimination
methods and characterized by various spectroscopic methods.
Complex 1 reacts with PMe3 (4 equiv) and ButNC (4 equiv) to
form trans-[(PMe3)4Fe(CCBut)2] (4) and [η3-{(ButCC)-
(But)CC(IPr2Me2)C(NBut)}Fe(NCBut)3] (5), respectively. In
contrast, the reactions of 1 with 4-Pri-C6H4NCO and PriNCNPri
lead to the formation of the zwitterionic salts 4-Pri-C6H4NC(O)(IPr2Me2) and (PriN)2C(IPr2Me2), respectively. The interaction
of 1 with I2 gives ButCCCCBut and (IPr2Me2)2FeI2. The C(sp)−C(sp3) cross-coupling products n-C8H17CCBut and c-
C6H11CCBut are formed in high yields when 1 is treated with the corresponding alkyl halides n-C8H17X and c-C6H11X (X = Br,
Cl). The formation of the ring-opening product 7,7-dimethyloct-1-en-5-yne in the reaction of 1 with cyclopropylmethyl bromide
supports the radical character of the cross-coupling reaction.
But, 2; SiMe3, 3), as well as the reactivity of 1 toward
unsaturated organic substrates, oxidants, and alkyl halides.
INTRODUCTION
■
The study of transition-metal alkynyl complexes represents a
research area of great interest due to the roles of these species
RESULTS AND DISCUSSION
as key intermediates in metal-catalyzed organic transformations
and their use as molecular wires and optoelectronic materials.1
Iron alkynyl compounds are representative examples, but
mostly involve ancillary ligands such as phosphine, cyclo-
pentadienyl, and CO.1b,2 With the strong field provided by
these ligands, iron alkynyl compounds are usually coordina-
tively saturated and in the low-spin states. As for coordinatively
unsaturated iron alkynyl complexes, there are only a handful of
examples, which include the cube-type compounds [(μ3-
Et3PN)4Fe4(CCSiMe3)4]3 and [(μ3-But3SiS)4Fe4(CCSi-
But3)4],4 three-coordinate complexes [(nacnac)Fe(CCR)]
(nacnac = (2,6-Pri2C6H3)NC(But)CHC(But)N(2,6-Pri2C6H3);
R = Ph, SiMe3)5 and [(2,6-(2′,6′-Pri2C6H3)2C6H3)Fe(C
CBut)2Li(THF)2],6 trisphosphine-supported complexes [(HB-
(C6H4-o-PPri2)3)Fe(CCAr)] (Ar = Ph, p-tolyl),7 and a bulky
alkynyl complex, [Fe(CCC6H3-2,6-(SiMe3)2)4Li2(THF)2].8
Given the scarcity of this type of complex, the chemistry of
coordinatively unsaturated iron alkynyl compounds remains
poorly understood. Recently, we and others have found that N-
heterocyclic carbenes (NHCs) can serve as excellent ancillary
ligands to support three- and four-coordinate iron(II) alkyl,
aryl, and amido complexes.9,10 The success then prompted us
to study iron(II) alkynyl complexes with NHC ligation. Herein,
we report the synthesis and characterization of the four-
coordinate iron(II) alkynyl complexes [(IPr2Me2)2Fe(C
CBut)2] (1) and [(IPr2Me2)2Fe(CCR)(NHMes)] (R =
■
Preparation and Characterization of Iron(II) Alkynyl
Complexes. Iron(II) dialkynyl complex [(IPr2Me2)2Fe(C
CBut)2] (1) can be prepared by a salt metathesis method.
Treatment of [(IPr2Me2)2FeCl2]10a with 2 equiv of LiCCBut
in THF gave a pale green solution. After workup, 1 was isolated
as green crystals in 82% yield (Scheme 1). Alternatively, 1 was
prepared in 41% isolated yield by elimination of MesNH2 from
[(IPr2Me2)2Fe(NHMes)2]10h in C6H6 using 8 equiv of HC
CBut. For the amine elimination method, the use of a large
excess of the alkyne is necessary, as the reaction with 2 equiv of
HCCBut resulted in a mixture of 1, the monoalkynyl
complex [(IPr2Me2)2Fe(CCBut)(NHMes)] (2), and the
unreacted [(IPr2Me2)2Fe(NHMes)2]. Attempts to prepare
(IPr2Me2)2Fe(CCSiMe3)2 via either salt metathesis or
amine elimination reaction were unsuccessful. However, the
amine elimination method produced the monoalkynyl complex
[(IPr2Me2)2Fe(CCSiMe3)(NHMes)] (3) as pale yellow
crystals in 18% yield (Scheme 1). Both methods were also
applied to the synthesis of (IPr2Me2)2Fe(CCPh)2. Unfortu-
nately, these attempts generally yielded intractable brown
mixtures.
Received: January 12, 2015
© XXXX American Chemical Society
A
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Scheme 1. Preparation of the Iron(II) Alkynyl Complexes
Table 1. Zero-Field 57Fe Mossbauer Data of Selected
Iron(II) Complexes Measured at 80 K
̈
complex
δ (mm/s)
ΔEQ (mm/s)
[(IPr2Me2)2Fe(CCBut)2]
[(IPr2Me2)2Fe(CCBut)(NHMes)]
[(IPr2Me2)2Fe (NHMes)2]
[(IPr2Me2)2FeI2]
0.52
0.61
0.72
0.71
0.47
0.49
2.44
2.55
2.54
2.98
2.38
2.53
a
[(IPr2Me2)2FePh2]
b
[(IEt2Me2)2Fe(CH2SiMe3)2]
a
b
Data from ref 10l. Data from ref 10m.
1
Complex 1 was characterized by H NMR spectroscopy,
solution magnetic susceptibility, IR spectroscopy, elemental
analysis, and single-crystal X-ray diffraction study. The 1H
NMR spectrum of 1 in THF-d8 shows three paramagnetically
shifted broad signals in the range +24 to +16 ppm. After
1
standing at room temperature for 24 h, the H NMR signals
corresponding to the free NHC ligand appear, indicating the
dissociation of IPr2Me2.11 The solution magnetic moment of 1
measured by Evans’ method is 5.1(1) μB, which corroborates a
Figure 2. Molecular structure of 1 showing 30% probability ellipsoids
and the partial atom-numbering scheme. Selected bond distances (Å)
and angles (deg): Fe(1)−C(1) 2.128(2), Fe(1)−C(2) 2.144(3),
Fe(1)−C(3) 2.049(3), Fe(1)−C(4) 2.052(3), C(3)−C(10) 1.223(4),
C(4)−C(5) 1.194(4); C(1)−Fe(1)−C(2) 108.22(10), C(3)−Fe(1)−
C(4) 118.39(11), Fe(1)−C(3)−C(10) 179.1(3), Fe(1)−C(4)−C(5)
175.6(2).
high-spin S = 2 electronic configuration.12 The 57Fe Mossbauer
̈
spectrum of 1 measured at 80 K features a quadrupole doublet
(Figure 1) with the fitting isomer shift (δ = 0.52 mm/s) and the
than those in the reported high-spin four-coordinate complexes
[(μ3-Et3PN)4Fe4(CCSiMe3)4] (1.99 Å),3 [(μ3-But3SiS)4-
Fe4(CCSiBut3)4] (2.00 Å),4 and [(HB(C6H4-o-PPri2)3)Fe-
(CCtolyl-p)] (1.92 Å).6 The long Fe−C(alkynyl) bonds
could be attributed to the strong σ-donating property of
NHCs.13 Compared to the Fe−C(Ph) bonds in [bis(NHC)-
FePh2] (2.08 Å on average)10k and the Fe−C(alkyl) bonds in
[(IEt2Me2)2Fe(CH2SiMe3)2] (2.11 Å on average),10a the Fe−
C(alkynyl) bonds in 1 are shorter. The C(alkynyl)−C(alkynyl)
distances (1.194(4) and 1.223(4) Å) in 1 are typical of C−C
triple bonds observed in the reported high-spin iron(II) alkynyl
complexes.3−7 The Fe−C(carbene) distances (2.128(2) and
2.144(3) Å) are comparable to those reported for iron(II) alkyl
complexes, e.g., 2.132(3) and 2.140(3) Å in [(IEt2Me2)2Fe-
(CH3)2] and 2.160(4) and 2.140(4) Å in [(IEt2Me2)2Fe-
(CH2SiMe3)2].10a
To probe the electronic structure of the alkynyl complex,
density functional theory14 calculation at the B3LYP level15
(TZVP/SVP,16 S = 2) based on the molecular structure of 1
established by X-ray diffraction (XRD) has been performed.17
The calculation revealed that its highest five occupied frontier
UHF natural orbitals (UNOs 160−156) are mainly composed
of the iron atom’s 3d orbitals, with four of them being singly
occupied (Figure S1). The dominant metal−ligand interaction
is the σ-type interaction between the lone pairs of alkynyl
ligands and the iron center’s 4s orbital (Figure S2). In addition,
a weak π-interaction that occurs between the filled π orbital of
the C−C triple bond and the iron atom’s 4p orbital is noticed
Figure 1. Zero-field 57Fe Mossbauer spectra of [(IPr Me ) Fe(C
̈
2
2 2
CBut)2] (1, a), [(IPr2Me2)2Fe(CCBut)(NHMes)] (2, b),
[(IPr2Me2)2Fe(NHMes)2] (c), and [(IEt2Me2)2Fe(CH2SiMe3)2]
(d),10m recorded at 80 K.
quadrupole splitting (ΔEQ = 2.44 mm/s), which are close to
those of the iron(II) dialkyl complex [(IPr2Me2)2FePh2]10l (δ =
0.47 mm/s, ΔEQ = 2.38 mm/s) and [(IEt2Me2)2Fe-
(CH2SiMe3)2]10m (δ = 0.49 mm/s, ΔEQ = 2.53 mm/s).
Table 1 compiles these data for comparison.
The molecular structure of 1 established by a single-crystal
X-ray diffraction study is shown in Figure 2. Its FeC4 core
displays distorted tetrahedral geometry, with the C−Fe−C
angles varying from 103.12(10)° to 118.39(11)°. The Fe−
C(alkynyl) distances (2.049(3) and 2.052(3) Å) are longer
B
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(Figure S3). The sum of these interactions leads to Mayer bond
orders of 0.60 and 0.83 for the Fe−C(carbene) and Fe−
C(alkynyl) bonds, respectively. The bond order of the Fe−
C(carbene) bonds (0.60) is smaller than that of their congeners
(0.85 and 0.88) in the cyclometalated square planar iron(II)-
NHC complex [(IMes′)Fe(IMes-Si)] with an S = 1 spin state
(IMes′ and IMes-Si denoting a cyclometalated IMes ligand and
a bidentate NHC-silyl ligand, respectively).10i Meanwhile, the
bond order of the Fe−C(alkynyl) bonds (0.83) is larger than
that of the Fe−C(benzyl) bond in [(IMes′)Fe(IMes-Si)]
(0.73). The difference in these bond orders suggests that the
NHC ligands can readily dissociate in the four-coordinate
alkynyl complex.
Reactions of 1 with PMe3 and ButNC. With the
dialkynyliron(II) complex [(IPr2Me2)2Fe(CCBut)2] in
hand, we subsequently examined its reactions with phosphines,
unsaturated organic substrates, and organic halides. Treatment
of 1 with 4 equiv of PMe3 in benzene yielded a pale yellow
solution immediately, from which the diamagnetic complex
[trans-(PMe3)4Fe(CCBut)2] (4) was isolated as a yellow
crystalline solid in 55% yield (Scheme 2). The 31P NMR
Scheme 2. Reactions of 1 with PMe3 and ButNC
Complexes 2 and 3 were characterized by 1H NMR
spectroscopy, solution magnetic susceptibility, IR spectroscopy,
and elemental analysis. The molecular structure of 3 was further
1
established by a single-crystal X-ray diffraction study. The H
NMR spectra of 2 and 3 in C6D6 show 12 paramagnetically
shifted broad signals, suggesting the restricted rotation of the
NHC ligands. Their solution magnetic moments (5.0(1) and
4.9(1) μB, respectively) are indicative of a high-spin nature.12
For comparison, the 57Fe Mossbauer spectrum of 2 was
̈
recorded (Figure 1). The isomer shift (δ = 0.61 mm/s) of its
quadrupole doublet is located between that of 1 (δ = 0.52 mm/
s) and the dianilido complex [(IPr2Me2)2Fe(NHMes)2] (δ =
0.72 mm/s) (Table 1). The gradual decreasing isomer shift
going from [(IPr2Me2)2Fe(NHMes)2] to 2 and to 1 reflects the
higher covalency of the Fe−C(alkynyl) bond versus the Fe−
N(anilido) bond.
spectrum of the reaction mixture shows only one signal at 22.11
ppm. The molecular structure established by XRD revealed a
trans-configuration for the two alkynyl groups (Figure S4),
which is similar to those of the reported six-coordinate iron(II)
alkynyl complexes with phosphine ligation, e.g., [trans-
(PMe3)4Fe(CCSiMe3)2]18 and [trans-(depe)2Fe(C
CPh)2] (depe = 1,2-bis(diethylphosphino)ethane).2a In con-
trast to the reaction with PMe3, complex 1 is inert toward PPh3.
Complex 1 can readily react with ButNC (4 equiv) to
produce yellow diamagnetic compound 5 (Scheme 2). Crystal
structure determination revealed its structure as an iron(0)
complex bearing three ButNC ligands and one zwitterionic
vinyliminacyl ligand η3-{(ButCC)(But)CC(IPr2Me2)CNBut}
with Fe−C(1), Fe−C(2), and Fe−C(3) distances of
2.1192(14), 2.0025(13), and 1.9364(14) Å, respectively
(Figure 4). The two C−C bonds in the allylic backbone have
similar bond distances (1.4648(19) and 1.4594(19) Å). The
terminal alkynyl moiety connected to C(1) has C(26)−C(27)
and C(26)−C(1) distances of 1.204(2) and 1.451(2) Å,
respectively, implying their localized triple- and single-bond
feature. The imidazolium moiety is bonded to the central
carbon atom C(2) of the allylic moiety, and its five-membered
plane forms a dihedral angle of 75.3° with the C(1)−C(2)−
C(3) plane. Both bent and linear geometries are observed for
the ButNC ligands, with the C−N bond distances in the two
bent ButNC ligands (1.1982(19) and 1.1934(19) Å) being
longer than that of the linear one (1.1682(19) Å). In accord
with these structure features, its infrared resonance spectrum
shows four resonances at 2161, 2112, 2040, and 1860 cm−1.
The molecular structure of 3 established by an X-ray
diffraction study is shown in Figure 3. The molecule has a
Figure 3. Molecular structure of 3, showing 30% probability ellipsoids
and the partial atom-numbering scheme. Selected bond distances (Å)
and angles (deg): Fe(1)−N(1) 1.979(2), Fe(1)−C(1) 2.153(2),
Fe(1)−C(2) 2.096(2), Fe(1)−C(3) 2.130(2), C(2)−C(33) 1.199(3);
N(1)−Fe(1)−C(2) 124.91(8), N(1)−Fe(1)−C(3) 113.72(8), C(2)−
Fe(1)−C(3) 104.01(8), N(1)−Fe(1)−C(1) 98.46(8), C(2)−Fe(1)−
C(1) 112.68(9), C(3)−Fe(1)−C(1) 100.65(8).
1
Complex 5 was characterized by H and 13C NMR spectros-
copy. Three 13C NMR signals appearing at +205.6, +206.5, and
+211.1 ppm further prove the presence of three ButNC ligands
in the complex. One possible route explaining the formation of
5 is shown in Scheme 3. Complex 1 might initially react with
four tert-butyl isocyanide molecules to afford cis-(ButNC)4Fe-
(CCBut)2 (A). While the attempts to isolate intermediate A
were unsuccessful, the analogous complex cis-[(ButNC)4Fe-
(CN)2] is known.19 Intermediate A undergoes migratory
insertion to produce iron vinylidene species B.20 This
severely distorted tetrahedral FeC3N core with the angles
around the iron center ranging from 98.46(8)° to 124.91(8)°
(Figure 3). The Fe−C(carbene) (2.153(2) and 2.130(2) Å),
Fe−N(anilido) (1.979(2) Å), and C(alkynyl)−C(alkynyl)
(1.199(3) Å) distances are typical of four-coordinate high-
spin iron(II) species, and its Fe−C(alkynyl) bond (2.096(2) Å)
is apparently longer than those of the aforementioned high-spin
iron(II) alkynyl complexes.3−7
C
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respectively, as colorless crystals in 47% and 54% yields,
respectively (Scheme 4).22 Compounds 6 and 7 were
Scheme 4. Reactions of 1 with 4-Pri-C6H4NCO and
PriNCNPri
1
characterized by H and 13C NMR spectroscopy and HRMS.
The formation of the NHC adducts is in stark contrast to that
of [(IPr2Me2)Fe(Mes)2] with PriNCNPri, wherein the insertion
of the carbodiimide into an Fe−C(aryl) bond took place to
afford [(IPr2Me2)Fe(PriNCMesNPri)(Mes)].10a The reactivity
difference described here, together with NHC-dissociation
behavior and the lower Fe−C(carbene) bond order, highlights
the lability of the Fe−C(carbene) bonds in 1. The reactions of
1 with a large excess of isocyanate and the carbodiimide
afforded ill-defined oily materials.
Figure 4. Molecular structure of 5, showing 30% probability ellipsoids
and the partial atom-numbering scheme. For simplicity, all the methyl
groups on the But moieties have been removed. Selected bond
distances (Å) and angles (deg): Fe(1)−C(1) 2.1192(14), Fe(1)−C(2)
2.0025(13), Fe(1)−C(3) 1.9364(14), Fe(1)−C(4) 1.7926(15),
Fe(1)−C(5) 1.8338(15), Fe(1)−C(6) 1.8245 (15), N(1)−C(3)
1.2726(18), N(2)−C(4) 1.1982(19), N(3)−C(5) 1.1682(19),
N(4)−C(6) 1.1934(19), C(26)−C(27) 1.204(2), C(1)−C(2)
1.4648(19), C(2)−C(3) 1.4594(19); C(1)−Fe(1)−C(6) 93.07(6),
C(1)−Fe(1)−C(2) 41.52(5), C(3)−Fe(1)−C(2) 43.45(6), C(3)−
Fe(1)−C(4) 94.60(6), C(6)−Fe(1)−C(5) 94.78(6), C(4)−Fe(1)−
C(5) 95.82(6), C(3)−N(1)−C(22) 122.15(12), C(4)−N(2)−C(32)
141.40(15), C(5)−N(3)−C(40) 178.21(16), C(6)−N(4)−C(36)
137.99(15).
Thermal- and Oxidation-Induced Decomposition of 1.
Carbon−carbon bond-forming reductive elimination is a well-
established reactivity for closed-shell diorganyl transition-metal
species,23 but has remained poorly understood for open-shell
complexes.10l To probe the potential of 1 to undergo
C(alkynyl)−C(alkynyl) reductive elimination, its thermal- and
oxidation-induced decomposition reactions were studied.
The C6D6 solution of 1 is stable at room temperature, but
decomposes slowly at 50 °C. Heating the solution at 80 °C for
5 h leads to the full decomposition. However, gas
chromatography−mass spectroscopy (GC-MS) analysis of the
hydrolyzed solution did not reveal the formation of the
coupling product ButCCCCBut, suggesting the difficulty
of 1 to undergo thermal-induced C(sp)−C(sp) reductive
elimination. Although no ButCCCCBut was detected in
Scheme 3. Possible Pathway for the Formation of 5
the reaction of 1 with [Cp2Fe][BArF ] (1 equiv), GC-MS
4
analysis indicated the formation of ferrocene. Attempts to
identify the resulting iron-containing products were unsuccess-
ful. The outcome of the oxidation reaction differs from that of
the one-electron oxidation reaction of [(bpy)2FeR2] (bpy =
2,2′-bipyridine; R = Et, Prn, Bun), where a small amount of
alkyl−alkyl coupling products was detected.23b However, it
should be mentioned that the observed difference does not
necessarily reflect the unique reactivity of high-spin iron alkynyl
species, as the system might be complicated by the redox
reaction of a ferrocenium cation with an NHC.24
intermediate can undergo further migratory insertion reaction
of the FeC bond toward the isocyanide to yield C.21 The
migration of the (ButCN)3Fe fragment along the cummulene
chain on C then gives D. One released NHC attacks the CC
bond of D to give E, which can isomerize to 5.
In contrast to the above reactions, the interaction of 1 with 1
equiv of iodine in THF affords ButCCCCBut and
(IPr2Me2)2FeI2 in high yields (Scheme 5). The composition
of (IPr2Me2)2FeI2 has been confirmed by elemental analysis,
and its fitting 57Fe Mossbauer parameters (δ = 0.71 mm/s, ΔE
̈
Q
Reactions of 1 with 4-Pri-C6H4NCO and PriNCNPri. To
further examine the reactivity of the Fe(II)−C(alkynyl) bonds
of 1, the reactions of 1 with other unsaturated organic
substrates were investigated. Complex 1 is inert toward
benzonitrile and 3-hexyne, whereas its reactions with 4-Pri-
C6H4NCO and PriNCNPri lead to the isolation of 4-Pri-
C6H4NC(O)(IPr2Me2) (6) and (PriN)2C(IPr2Me2) (7),
= 2.98 mm/s) (Figure S5) are found close to those of the
tetrahedral iron(II) diiodide supported by a methylene-bridged
bis(NHC) ligand (δ = 0.70 mm/s, ΔEQ = 3.74 mm/s).10c
Closely following the reaction by GC-MS indicates the
involvement of the alkynyl iodide ButCCI as an intermediate
in the early stage of the reaction. As the reaction proceeds, the
amount of ButCCI decreases, while that of ButCCC
D
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clock reagent cyclopropylmethylene bromide revealed the
radical character of the C−Br bond-cleavage step27 supported
by the formation of the ring-opening product 7,7-dimethyloct-
1-en-5-yne (Scheme 6).
Scheme 5. Reaction of 1 with Iodine and Its Possible Route
Scheme 6. Reaction of 1 with Cyclopropylmethyl Bromide
CBut increases. Figure S6 depicts the change in the amounts of
ButCCI and ButCCCCBut versus time. These observa-
tions point out a stepwise reaction mechanism for the
formation of ButCCCCBut (Scheme 5), in which the
reaction between the plausible intermediate (IPr2Me2)2Fe(C
CR)I and ButCCI accounts for, at least partially, the
formation of ButCCCCBut. Whether an oxidative
addition-reductive elimination mechanism, a radical-type
mechanism, or a σ-bond metathesis one is involved in the
conversion remains unknown to us at the moment.
Compared to the reactions with organic bromides, the
reactions of 1 with the alkyl chlorides n-C8H17Cl and c-C6H11Cl
proceeded more slowly at room temperature.28 The full
consumption of the organic chlorides was achieved after
heating the mixtures at 60 °C for 12 h, and the cross-coupling
products n-C8H17CCBut and c-C6H11CCBut were de-
tected in 83% and 74% GC yields, respectively (entries 3 and
4). These transformations thus established the capability of
high-spin iron(II) alkynyl species to promote cross-coupling
reactions with alkyl halides.
Reactions of 1 with Alkyl Halides. Iron alkynyl
complexes have been proposed as key intermediates in iron-
catalyzed cross-couplings of alkynyl Grignard reagents with
alkyl halides.25 However, the exact nature of iron-alkynyl
intermediates, e.g., the metal center’s oxidation state and the
reactivity of iron alkynyl species toward alkyl halides, has not
yet been fully established. To probe whether iron(II) alkynyl
species can promote the cross-coupling reaction, the stoichio-
metric reactivity of 1 toward alkyl halides was been examined.
Complex 1 can react with both alkyl bromides and chlorides
to afford cross-coupling products.26 The interaction of 1 with 1
equiv of n-C8H17Br or c-C6H11Br in benzene at room
temperature produced a brown solution. After 12 h, GC-MS
analysis of the quenched solution indicated the full
consumption of the organic halides and the formation of the
cross-coupling products n-C8H17CCBut and c-C6H11C
CBut in 95% and 96% yields, respectively (entries 1 and 2 in
CONCLUSION
■
In this study, we have accomplished the synthesis, character-
ization, and reactivity study of high-spin iron(II) alkynyl
complexes with NHC ligation. The salt metathesis reaction of
[(IPr2Me2)2FeCl2] with 2 equiv of LiCCBut leads to the
formation of the dialkynyl complex [(IPr2Me2)2Fe(CCBut)2]
in high yield. On the other hand, the amine elimination
reactions of [(IPr2Me2)2Fe(NHMes)2] with a large excess of
HCCBut or HCCSiMe3 produce the iron(II) monoalkynyl
complexes [(IPr2Me2)2Fe(CCR)(NHMes)] (R = But or
SiMe3). Characterization data obtained from solution magnetic
susceptibility measurement, 57Fe Mossbauer spectroscopy, and
̈
single-crystal X-ray diffraction studies confirm the high-spin
nature (S = 2) of the four-coordinate iron(II) complexes. DFT
calculation reveals both σ- and π-donating nature of the alkynyl
groups in the dialkynyl iron(II) species.
1
Table 2). Analyzing the H NMR spectrum of the resulting
a
Reactivity studies of [(IPr2Me2)2Fe(CCBut)2] have
disclosed its ligand-substitution reaction with PMe3 to form
trans-[(PMe3)4Fe(CCBut)2], its reaction with ButNC (4
equiv) to produce the iron(0) complex [η3-{(ButCC)(But)-
CC(IPr2Me2)C(NBut)}Fe(NCBut)3], the reactions with iso-
cyanate and carbodiimide to form the adducts of IPr2Me2 with
the polar unsaturated substrates as zwitterionic salts, and its
reactions with 1 equiv of iodine, n-C8H17X, and c-C6H11X (X =
Br, Cl) to furnish ButCC−CCBut, n-C8H17CCBut, and
c-C6H11CCBut, respectively, along with iron(II) species.
These conversions indicate (i) the tendency of the NHC ligand
to dissociate from the high-spin iron(II) center and (ii) the
capability of high-spin iron(II) alkynyl species to promote
cross-coupling with alkyl halides.
Table 2. Reactions of 1 with Alkyl Halides
GC yield of
b
entry
R-X
temp
rt
time (h)
E
F and G
1
2
3
4
n-C8H17Br
c-C6H11Br
n-C8H17Cl
c-C6H11Cl
12
12
12
12
95%
96%
83%
74%
5%
4%
rt
60 °C
60 °C
17%
22%
a
[(IPr2Me2)2Fe(CCBut)2] (1, 0.10 mmol) and halides (0.10 mmol) in
C6H6 (1 mL) at 30 °C with n-dodecane (0.10 mmol) as the internal
b
standard,. Time required for the full conversions of the halides.
EXPERIMENTAL SECTION
■
mixture (the reaction 1 with n-C8H17Br) indicates the
formation of a new paramagnetic species along with small
amounts of (IPr2Me2)2FeBr2 and 1. The 1H NMR peak pattern
of this unknown paramagnetic species is similar to that of
(IPr2Me2)2Fe(CCBut)I, suggesting it might be (IPr2Me2)2-
Fe(CCBut)Br (Figure S7). The reaction of 1 with the radical
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. Organic
solvents were freshly distilled from sodium benzophenone ketyl
immediately prior to use. [(IPr2Me2)2FeCl2]10a and [(IPr2Me2)2Fe-
(NHMes)2]10h were prepared according to our reported methods. All
E
DOI: 10.1021/acs.organomet.5b00028
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
chemicals were purchased from either Strem or J&K Chemical Co. and
used as received unless otherwise noted. NMR spectra were recorded
on a Varian Mercury 300 or 400 MHz spectrometer. Chemical shifts
were reported in δ units with references to the residual protons of the
deuterated solvents for proton chemical shifts, the 13C of deuterated
solvents for carbon chemical shifts, and the 31P of phosphoric acid
(85%) for phosphorus chemical shifts. GC-FID was performed on a
Shimadzu GC-2014 spectrometer. 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 29
°C by the method originally described by Evans with stock and
experimental solutions containing a known amount of a (CH3)3SiOSi-
(CH3)3 standard.12 IR spectra were recorded with a Nicolet Avatar 330
product shows an identical H NMR spectrum as that prepared via
method A.
Preparation of [(IPr2Me2)2Fe(CCBut)(NHMes)] (2). To a pale
yellow solution of [(IPr2Me2)2Fe(NHMes)2] (0.52 g, 0.76 mmol) in
C6H6 (5 mL) was slowly added a solution of HCCBut (0.13 g, 1.52
mmol) in C6H6 (5 mL) at room temperature in 10 min. The color of
the solution quickly turned yellow-brown. After stirring for 14 h and
the removal of the solvent, the residue was extracted with n-hexane (10
mL × 3) and filtered. The filtrate was concentrated to about 20 mL,
and hexamethyldisiloxane (3 mL) was added. Slow evaporation of n-
hexane afforded the product as yellow crystals. Yield: 0.11 g, 36%. The
1H NMR spectrum shows 12 peaks in the range +127 to +7 ppm, and
satisfactory integration for these peaks has not been obtained. 1H
NMR (400 MHz, C6D6): δ (ppm) 126.75, 91.21, 81.16, 53.04, 45.51,
17.30, 13.45, 13.02, 11.76, 11.18, 9.08, 7.84. Anal. Calcd for
C37H61FeN5: C, 70.34; H, 9.73; N, 11.09. Found: C, 70.26; H, 9.76;
N, 11.45. Magnetic susceptibility: μeff = 5.0(1) μB. IR (KBr, cm−1):
νCC 2058(w).
FT-IR spectrophotometer. The 57Fe Mossbauer for samples were
̈
measured with a constant acceleration spectrometer at 80 K. Low
temperature was maintained by a CCS-850 Mossbauer Cryostat
̈
system (Janis Research Company). Data were analyzed with
MossWinn 4.0Pre (Provider: Beijing Shengtianjiayuan Keji Company).
Isomer shifts are relative to iron metal at room temperature.
X-ray Structure Determinations. Crystallizations were per-
formed 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.29 Space groups were assigned
unambiguously by analysis of symmetry and systematic absences
determined by XPREP. All structures were solved and refined using
SHELXTL.30 Metal and first coordination sphere atoms were located
from direct-methods Emaps; other non-hydrogen atoms were found in
alternating difference Fourier synthesis and least-squares refinement
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
S1.
Preparation of [(IPr2Me2)2Fe(CCTMS)(NHMes)] (3). To a
pale yellow solution of [(IPr2Me2)2Fe(NHMes)2] (0.14 g, 0.20 mmol)
in C6H6 (5 mL) was slowly added a solution of HCCSiMe3 (0.039
g, 0.40 mmol) in C6H6 (5 mL) at room temperature in 10 min. The
color of the solution quickly turned yellow-brown. After stirring for 14
h and the removal of the solvent, the residue was extracted with n-
hexane (5 mL × 3) and filtered. Some yellow solid was left and was
extracted with diethyl ether (5 mL × 3) and filtered. n-Hexane (3 mL)
was added to the filtrate. Slow evaporation of diethyl ether afforded the
1
product as yellow crystals. Yield: 0.017 g, 18%. H NMR (400 MHz,
C6D6): δ (ppm) 131.67, 95.98, 81.26, 57.13, 45.59, 16.89, 12.82, 12.22,
10.22, 9.78, 9.14, 4.87. In addition to the peaks with their chemical
shifts paralleling with those of 2, three minor peaks at 92.34, 55.64,
and 17.47 ppm were also observed in the 1H NMR spectrum of 3. The
origin of these peaks is unknown yet. Even the sample that passed
elemenal analysis still exhibits these peaks. Anal. Calcd for
C36H61FeN5Si: C, 66.74; H, 9.49; N, 10.81. Found: C, 66.38; H,
9.35; N, 10.49. Magnetic susceptibility: μeff = 4.9(1) μB. IR (KBr,
cm−1): νCC 2005(m).
Computational Details. Density functional theory (DFT)14
studies have been performed with the ORCA 2.8 program17 using
the B3LYP15 method. The SVP basis set16a was used for the C, N, and
H atoms, and the TZVP basis set16b was used for the Fe atom. The
RIJCOSX approximation31 with matching auxiliary basis sets16a,32 was
employed to accelerate the calculation. TIGHTSCF was used for SCF
calculation.33 The single-point calculation on [(IPr2Me2)2Fe(C
CBut)2] (S = 2) was based on the coordinates obtained from an X-ray
diffraction study without optimization.
Preparation of [(PMe3)4Fe(CCBut)2] (4). To a solution of
[(IPr2Me2)2Fe(CCBut)2] (0.23 g, 0.40 mmol) in C6H6 (5 mL) was
added PMe3 (0.12 g, 1.60 mmol) at room temperature. The color of
the solution quickly turned pale yellow. After stirring for 14 h and
removal of the solvent, the residue was extracted with n-hexane (3 mL)
and filtered. Hexamethyldisiloxane (2 mL) was added to the filtrate.
Slow evaporation of n-hexane afforded the product as yellow crystals.
Yield: 0.11 g, 55%. Steric congestion renders the free rotation of the
Fe−P bonds and the chemical nonequivalence of the methyl groups on
Preparation of [(IPr2Me2)2Fe(CCBut)2] (1). Method A: To a
white suspension of [(IPr2Me2)FeCl2] (1.44 g, 2.96 mmol) in THF
(10 mL) was added a THF solution of LiCCBut, which was
prepared in situ by the reaction of HCCBut (694 mg, 8.44 mmol)
and n-BuLi (5.92 mmol) at −78 °C in THF and stirred for 12 h. The
color of the solution turned green during stirring. After removal of the
solvent, the residue was extracted with diethyl ether (20 mL × 3) and
filtered. The filtrate was concentrated to about 40 mL, and n-hexane (5
mL) was added. Slow evaporation of diethyl ether afforded the product
as green crystals. Yield: 1.40 g, 82%. 1H NMR (600 MHz, THF-d8): δ
(ppm) 23.49 (9H, CC(CH3)3), 18.84 (12H, NCH(CH3)2), 16.53
(6H, CCH3). Anal. Calcd for C34H58FeN4: C, 70.57; H, 10.10; N,
1
the phosphine ligands. H NMR (400 MHz, C6D6): δ (ppm) 1.52
(24H, P(CH3)3), 1.38 (12H, P(CH3)3), 1.36 (18H, CC(CH3)3).
13C NMR (100 MHz, C6D6): δ (ppm) 119.31, 109.91, 33.05, 29.89,
21.57, 16.51. 31P NMR (121.4 MHz, C6D6): δ (ppm) 22.11. Anal.
Calcd for C24H54FeP4: C, 55.18; H, 10.42. Found: C, 55.06; H, 10.16.
IR (KBr, cm−1): νCC 2056(m).
Preparation of [η3-{(ButCC)(But)CC(IPr2Me2)C(NBut)}Fe-
(NCBut)3] (5). To a solution of [(IPr2Me2)2Fe(CCBut)2] (0.23 g,
0.40 mmol) in C6H6 (5 mL) was added a solution of ButNC (0.14 g,
1.60 mmol) in C6H6 (5 mL) at room temperature. The color of the
solution quickly turned orange. After stirring for 16 h and the removal
of the solvent, the residue was extracted with n-hexane (3 mL) and
filtered. Hexamethyldisiloxane (2 mL) was added to the filtrate. Slow
evaporation of n-hexane afforded the product as orange crystals. Yield:
0.15 g, 57%. 1H NMR (400 MHz, C6D6): δ (ppm) 7.72 (sept, J = 6.8
Hz, 1H, NCH), 5.94 (sept, J = 6.8 Hz, 1H, NCH), 1.86 (d, J = 6.8 Hz,
3H, NCH(CH3)2), 1.76 (s, 9H, C(CH3)3), 1.69 (s, 9H, C(CH3)3),
1.66 (s, 3H, CCH3), 1.64 (d, J = 7.6 Hz, 3H, NCH(CH3)2), 1.63 (s,
3H, CCH3), 1.62 (s, 9H, CC(CH3)3), 1.54 (s, 9H, C(CH3)3), 1.49
(d, J = 7.2 Hz, 3H, NCH(CH3)2), 1.43 (s, 9H, C(CH3)3), 1.41 (d, J =
7.2 Hz, 3H, NCH(CH3)2), 1.36 (s, 9H, C(CH3)3). 13C NMR (100
MHz, C6D6): δ (ppm) 211.12, 206.49, 205.58, 186.89, 150.97, 122.99,
122.34, 110.0, 93.49, 89.07, 55.51, 55.05, 54.93, 53.68, 50.15, 46.59,
41.90, 41.50, 32.47, 32.34, 32.32, 32.27, 31.56, 31.27, 28.22, 24.00,
9.68. Found: C, 70.40; H, 10.19; N, 9.10. Magnetic susceptibility: μeff
=
5.1(1) μB. IR (KBr, cm−1): νCC 2060(w). Method B: To a pale
yellow solution of [(IPr2Me2)2Fe(NHMes)2] (0.44 g, 0.64 mmol) in
C6H6 (8 mL) was slowly added a solution of HCCBut (0.42 g, 5.12
mmol) in C6H6 (5 mL) at room temperature. The mixture was stirred
for 12 h. The color of the solution turned yellow-brown during
stirring. After removal of the solvent under vacuum, the residue was
extracted with n-hexane (10 mL × 3). After filtration, some light green
solid was left, which was then extracted with diethyl ether (10 mL × 3)
and filtered. The filtrate was concentrated to about 20 mL, and n-
hexane (5 mL) was added to the filtrate. Slow evaporation of diethyl
ether afforded the product as green crystals. Yield: 0.15 g, 41%. The
F
DOI: 10.1021/acs.organomet.5b00028
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
23.02, 22.56, 21.92, 9.68, 9.48. Anal. Calcd for C43H74FeN6: C, 70.66;
H, 10.20; N, 11.50. Found: C, 70.42; H, 10.39; N, 11.79. IR (KBr,
cm−1): νCC,CN 1886, 2040, 2113, 2161.
at room temperature. The reaction mixture was stirred and monitored
by GC. For the alkyl bromides, the reactions proceeded smoothly at
room temperature, and the color of the solution turned yellow-brown.
For the alkyl chlorides, the reactions were heated to 60 °C. When the
alkyl halides were consumed completely (determined by GC), part of
the solution was withdrawn and quenched with a saturated ammonium
chloride aqueous solution. The quenched mixture was extracted with
dichloromethane and separated. The organic phase was then dried
over MgSO4, analyzed by GC-MS to confirm the identity of the
products, and further analyzed by GC-FID to quantify the yields with
n-dodecane as the internal standard. For the unquenched solution, the
Reaction of 1 with 4-Pri-C6H4NCO. To a solution of
[(IPr2Me2)2Fe(CCBut)2] (0.18 g, 0.30 mmol) in C6H6 (5 mL)
was added 4-Pri-C6H4NCO (0.10 g, 0.60 mmol) at room temperature.
The color of the solution immediately turned red-brown and
eventually turned yellow-brown after stirring for 12 h. After the
removal of the solvent, the residue was extracted with diethyl ether (5
mL × 3). After filtration, some white solid was left, and then the white
solid was extracted with THF (5 mL × 3) and filtered. The filtrate was
concentrated to about 8 mL. Slow evaporation of THF afforded 4-Pri-
C6H4NC(O)(IPr2Me2) (6) as colorless crystals. Yield: 0.096 g, 47%.
1H NMR (400 MHz, C6D6): δ (ppm) 7.52 (d, J = 8.0 Hz, 2H, C6H4),
7.10 (d, J = 8.4 Hz, 2H, C6H4), 4.96 (sept, J = 6.8 Hz, 2H,
NCH(CH3)2), 2.82 (sept, J = 6.8 Hz, 1H, C6H4CH(CH3)2), 2.22 (s,
6H, CCH3), 1.58 (d, J = 7.2 Hz, 12H, NCH(CH3)2), 1.19 (d, J =
7.2 Hz, 6H, C6H4CH(CH3)2). 13C NMR (100 MHz, THF-d8): δ
(ppm) 158.72, 153.24, 150.93, 142.99, 128.40, 128.04, 126.11, 54.47,
37.38, 27.56 (overlapping with THF signal), 23.94, 12.08. HRMS:
calcd for [C21H31N3OH]+ 342.2545; found 342.2538. Attempts to
isolate the iron-containing species were unsuccessful.
1
solvent was removed and the residue was redissolved in C6D6. H
1
NMR analysis revealed the characteristic H NMR resonances for a
new paramagnetic product, but attempts to isolate this complex failed.
Table 1 tabulates the GC yields of the organic products. The identities
of the cross-coupling products n-C8H17CCBut, c-C6H11CCBut,
and CH2CHCH2CH2CCBut have been authenticated by
comparing their NMR spectra to the reported ones. For n-
C8H17CCBut:36 1H NMR (300 MHz, CDCl3): δ (ppm) 2.11 (t, J
= 6.9 Hz, 2H, CCH2), 1.50−1.22 (m, 12H, CCH2 (CH2)6), 1.18
(s, 9H, (CH3)3C), 0.87 (t, J = 6.9 Hz, 3H, CH3CH2). 13C NMR (75
MHz, CDCl3): δ (ppm) 88.79, 78.43, 31.77, 31.33, 29.14, 29.03, 28.70,
27.22, 22.60, 18.59, 14.04. For c-C6H11CCBut:37 1H NMR (400
MHz, CDCl3): δ (ppm) 2.33−2.28 (m, 1H, CH), 1.75−1.64 (m, 4H,
CH2), 1.51−1.25 (m, 6H, CH2), 1.19 (s, 9H, C(CH3)3). 13C NMR
(100 MHz, CDCl3): δ (ppm) 88.94, 82.73, 33.19, 31.51, 30.58, 28.91,
27.23, 26.01, 24.80. For CH2CHCH2CH2CCBut:38 1H NMR
(400 MHz, CDCl3): δ (ppm) 5.89−5.78 (m, 1H, H2CCH), 5.06−
5.97 (m, 2H, H2CCH), 2.20 (m, 4H, CHCH2CH2), 1.17 (s, 9H,
C(CH3)3). 13C NMR (100 MHz, CDCl3): δ (ppm) 137.25, 115.19,
89.43, 77.67, 33.52, 31.32, 27.27, 18.56. HRMS-EI: calcd for [C10H15]+
135.1174; found 135.1178.
Reaction of 1 with PriNCNPri. To a solution of [(IPr2Me2)2Fe-
(CCBut)2] (0.12 g, 0.20 mmol) in C6H6 (5 mL) was added a
solution of PriNCNPri (0.10 g, 0.80 mmol) in C6H6 (5 mL) at room
temperature. The color of the solution quickly turned brown. After
stirring for 12 h and removal of the solvent, the residue was extracted
with n-hexane (3 mL × 3). After filtration, some white solid was left,
which was extracted with diethyl ether (5 mL × 3) and filtered. The
filtrate was concentrated to about 6 mL, and n-hexane (2 mL) was
added. Slow evaporation of diethyl ether afforded (PriN)2C(IPr2Me2)
1
(7) as colorless crystals. Yield: 0.033 g, 54%. H NMR (400 MHz,
C6D6): δ (ppm) 5.08 (sept, J = 6.0 Hz, 1H, CH(CH3)2), 4.99 (sept, J
= 7.2 Hz, 2H, CH(CH3)2), 2.93 (sept, J = 6.0 Hz, 1H, CH(CH3)2),
1.80 (d, J = 6.0 Hz, 6H, CH(CH3)2), 1.52 (s, 6H, CCH3), 1.50 (d, J
= 7.2 Hz, 6H, CH(CH3)2), 1.25 (d, J = 6.8 Hz, 6H, CH(CH3)2), 1.07
(d, J = 7.2 Hz, 6H, CH(CH3)2). 13C NMR (100 MHz, C6D6): δ
(ppm) 149.69, 148.33, 122.27, 51.79, 50.63, 46.75, 28.33, 25.05, 24.45,
20.86, 20.58, 9.20. HRMS: calcd for [C18H34N4H]+ 307.2862; found
307.2861. The attempts to isolate the iron-containing species were
unsuccessful.
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic files in CIF format, molecular structure
of 4, the reaction profile of 1 with I2, 57Fe Mossbauer spectrum
̈
of (IPr2Me2)2FeI2, selected orbital graphs of (IPr2Me2)Fe(C
CBut)2, NMR spectra, and GC graphs of selected reactions.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00028.
Reaction of 1 with Iodine. To a solution of [(IPr2Me2)Fe(C
CBut)2] (0.174 g, 0.30 mmol) and n-dodecane (0.053 g, 0.31 mmol) in
THF (2 mL) was added iodine (0.082 g, 0.32 mmol) at −78 °C. The
mixture was allowed to warm to room temperature and stirred. A drop
of the solution was withdrawn once every hour in the first 7 h and then
every 2 h until 15 h. The aliquot was quenched by a saturated
ammonium chloride aqueous solution. The quenched mixture was
extracted with diethyl ether and separated. The organic phase was then
dried over MgSO4, analyzed by gas GC-MS to confirm the identity of
the organic products, and further analyzed by GC with a flame
ionization detector (GC-FID) to quantify the yields with n-dodecane
as the internal standard. Figure S6 shows the yield change of ButC
CCCBut and ButCC−I versus time. The identity of the two
organic products isolated from similar reaction without the addition of
n-dodecane was further confirmed by NMR spectroscopy. For ButC
CCCBut:34 1H NMR (400 MHz, CDCl3): δ (ppm) 1.21 (s, 9H).
13C NMR (100 MHz, CDCl3): δ (ppm) 86.21 (CCC(CH3)3),
63.62 (CCC(CH3)3), 30.56 (C(CH3)3), 27.92 (C(CH3)3). For
ButCC−I:35 1H NMR (300 MHz, CDCl3): δ (ppm) 1.23 (s, 9H).
13C NMR (75 MHz, CDCl3): δ (ppm) 102.85, 30.77, 29.75, −8.05.
The identity of the iron-containing product (IPr2Me2)2FeI2 was
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: deng@sioc.ac.cn.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work has been supported by the National Basic Research
Program of China (No. 2011CB808705), the National Natural
Science Foundation of China (Nos. 21222208, 21421091, and
21432001), and the Chinese Academy of Sciences. We thank
Prof. Hairong Guan at University of Cincinnati for his helpful
suggestions.
REFERENCES
supported by 57Fe Mossbauer spectroscopy characterization (Figure
■
̈
(1) (a) Rosenthal, U. In Acetylene Chemistry. Chemistry, Biology and
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Wiley-VCH: Weinheim, 2005; Chapter 4, p 139. (b) Long, N. J.;
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S5) and elemental analysis. For (IPr2Me2)2FeI2: Anal. Calcd for
C22H40FeI2N4: C, 39.42; H, 6.02; N, 8.36. Found: C, 39.49; H, 6.12;
N, 8.32.
General Procedure for Reactions of 1 with n-C8H17X and c-
C6H11X (X = Br, Cl) and Cyclopropylmethyl Bromide. A dried
Schlenk tube was charged with the alkyl halides (0.10 mmol), C6H6
(1.0 mL), n-dodecane (0.10 mmol), and 1 (0.10 mmol) in a glovebox
G
DOI: 10.1021/acs.organomet.5b00028
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Organometallics
Article
(2) (a) Field, L. D.; George, A. V.; Hambley, T. W. Inorg. Chem.
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H
DOI: 10.1021/acs.organomet.5b00028
Organometallics XXXX, XXX, XXX−XXX