Synthesis, structure, and reactivity of lanthanide complexes incorporating indolyl ligands in novel hapticities

Article abstract of DOI:10.1021/ic401515q

The chemistry of interactions of 2-(2,6-diisopropylphenylaminomethylene) indole ligand (1) with europium and ytterbium amides is described. Reaction of 2-(2,6-diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr₂C ₆H₃NHCH₂)C₈H₅NH (1) with europium amide [(Me₃Si)₂N]₃Eu ^III(μ-Cl)Li(THF)₃ afforded a novel europium(II) complex formulated as {[μ-η⁶:η¹:η¹-2- (2,6-i-Pr₂C₆H₃N=CH)C₈H ₅N]Eu[2-(2,6-i-Pr₂C₆H₃N=CH)C ₈H₅N]}₂ (2), having a bridged indolyl ligand in the novel μ-η⁶:η¹:η¹ hapticities with the reduction of europium(III) to europium(II) and the oxidation of amino to imino group. Reaction of 2-(2,6- diisopropylphenylaminomethylene)indole 2-(2,6-i-Pr₂C ₆H₃NHCH₂)C₈H₅NH (1) with ytterbium(III) amide [(Me₃Si)₂N]₃Yb ^III(μ-Cl)Li(THF)₃ produced the only deprotonated ytterbium(III) complex formulated as [2-(2,6-i-Pr₂C₆H ₃NCH₂)C₈H₅N]Yb[N(SiMe ₃)₂](THF)₂ (3), having an η¹ hapticity indolyl ligand. Reaction of 2 with formamidine [(2,6-Me ₂C₆H₃)NCHNH(C₆H₃Me ₂-2,6)] produced {[μ-η³:η¹: η¹-2-(2,6-i-Pr₂C₆H₃N=CH)C ₈H₅N]Eu[(2,6-Me₂C₆H ₃)NCHN(C₆H₃Me₂-2,6)](THF)} ₂ (4), which has a bridged indolyl ligand in the novel μ-η³:η¹:η¹ hapticities, whereas the reaction of 2 with the more sterically bulky formamidine [(2,6-i-Pr ₂C₆H₃)NCHNH(C₆H₃i-Pr ₂-2,6)] afforded complex {[μ-η²:η¹: η¹-2-(2,6-i-Pr₂C₆H₃N=CH)C ₈H₅N]Eu[(2,6-i-Pr₂C₆H ₃)N=CHN(C₆H₃i-Pr₂-2,6)](THF)} ₂ (5), having the indolyl ligand in the novel μ-η²: η¹:η¹ hapticities. The results represent the first example of organometallic complexes having indolyl ligands in the novel μ-η⁶:η¹:η¹, μ- η³:η¹:η¹, and μ- η²:η¹:η¹ bonding modes with metal.

Full text of DOI:10.1021/ic401515q

Article
pubs.acs.org/IC
Synthesis, Structure, and Reactivity of Lanthanide Complexes
Incorporating Indolyl Ligands in Novel Hapticities
Zhijun Feng,† Xiancui Zhu,† Shaoyin Wang,† Shaowu Wang,*,†,‡ Shuangliu Zhou,† Yun Wei,†
Guangchao Zhang,† Baojia Deng,† and Xiaolong Mu†
†Laboratory of Functionalized Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials,
College of Chemistry and Materials Science, Anhui Normal University, Wuhu, Anhui 241000, China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: The chemistry of interactions of 2-(2,6-diisopropyl-
phenylaminomethylene)indole ligand (1) with europium and ytterbium
amides is described. Reaction of 2-(2,6-diisopropylphenylamino-
methylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with euro-
pium amide [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 afforded a novel
europium(II) complex formulated as {[μ-η6:η1:η1-2-(2,6-
i-Pr2C6H3NCH)C8H5N]Eu[2-(2,6-i-Pr2C6H3NCH)C8H5N]}2
(2), having a bridged indolyl ligand in the novel μ-η6:η1:η1 hapticities
with the reduction of europium(III) to europium(II) and the oxidation
of amino to imino group. Reaction of 2-(2,6-diisopropylphenyl-
aminomethylene)indole 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1) with
ytterbium(III) amide [(Me3Si)2N]3YbIII(μ-Cl)Li(THF)3 produced the
only deprotonated ytterbium(III) complex formulated as [2-(2,6-
i-Pr2C6H3NCH2)C8H5N]Yb[N(SiMe3)2](THF)2 (3), having an η1
hapticity indolyl ligand. Reaction of 2 with formamidine [(2,6-Me2C6H3)NCHNH(C6H3Me2-2,6)] produced {[μ-η3:η1:η1-2-(2,6-
i-Pr2C6H3NCH)C8H5N]Eu[(2,6-Me2C6H3)NCHN(C6H3Me2-2,6)](THF)}2 (4), which has a bridged indolyl ligand in the novel
μ-η3:η1:η1 hapticities, whereas the reaction of 2 with the more sterically bulky formamidine [(2,6-i-Pr2C6H3)NCHNH(C6H3i-Pr2-2,6)]
afforded complex {[μ-η2:η1:η1-2-(2,6-i-Pr2C6H3NCH)C8H5N]Eu[(2,6-i-Pr2C6H3)NCHN(C6H3i-Pr2-2,6)](THF)}2 (5), having the
indolyl ligand in the novel μ-η2:η1:η1 hapticities. The results represent the first example of organometallic complexes having indolyl ligands
in the novel μ-η6:η1:η1, μ-η3:η1:η1, and μ-η2:η1:η1 bonding modes with metal.
Among the divalent lanthanides, the most accessible divalent
oxidation state is Eu2+. Pioneer works demonstrated that
europium(II) complexes displayed unique catalytic, photo-
physical, and magnetic properties of Eu2+ and spurred a great
deal of research with the findings of some novel bonding modes
and applications. For example, Deacon reported novel bonding
modes of the pyrazolate ligands to Eu(II) in complexes including
the η2, μ-η5:η2, and μ-η2:η2 fashions.9a Hitzbleck and co-workers
have also reported a μ-η5:η1 mode to Eu(II) with the bridging
3,5-diisopropylpyrazolate ligand.9b In addition, the π-arene
interactions of the phenyl-, biphenyl-, or terphenyl-containing
ligands bonded with Eu(II) via the benzo ring including the η1,
η3, η5, η4:η2:η1, η1:η6:η3, μ-η6:η1, and η6 fashion were also
reported.10a−g Recently, we have reported the indenyl ligand
bonded to the central metal europium through the benzo ring
with η4 hapticity.2f However, the μ-η6:η1:η1, μ-η3:η1:η1, and
μ-η2:η1:η1 coordination modes via both the benzo and five-
membered heterocyle rings of indolyl group with transition
metals remain scarce.
INTRODUCTION
■
Over the past decades, tremendous research efforts have been
devoted to the development of noncyclopentadienyl ancillary
ligand systems capable of stabilizing organometallic complexes
while provoking novel reactivity.1−6 Among those cyclo-
pentadienyl alternatives, many similar nitrogen-containing
systems such as various modified amido ligands,2 cyclic pyrrolyl,3
carbazolyl,4 pyrazolyl,5 and aromatic indolyl6 ligands have proved
to be versatile. It has been demonstrated that indole is an
electron-rich aromatic compound, and the indolyl compounds
widely used in transition metal chemistry7 are intriguing ligands
because they have a propensity to bind with metal in the η1 mode
ultilizing the electron-rich nitrogen atom,6a and they can also
bind in the η3 fashion via the nitrogen atom and the fused carbons
of indolyl ring,6a in the η5 manner through the five-membered
heterocyclic ring that is most common for cyclopentadienyl
ligands,8a in an η6 mode through the benzo ring,8b,c and in a
μ2-η1:η1 bonding mode with iron8d (see Chart 1). Recently, an
η1 and an unusual η1:(μ2-η1:η1) bonding mode of novel indolyl-
1,2-dianion ligand with rare-earth metals were reported by our
group8e,f (see Chart 1).
Received: May 18, 2013
© XXXX American Chemical Society
A
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Chart 1. Reported Bonding Modes of the Indolyl Ligand with Transition Metals
As part of our continuous work on the chemistry of lanthanide
complexes with functionalized indolyl ligand systems, we have
studied the reactivity of lanthanide amides [(Me3Si)2N]3LnIII(μ-
Cl)Li(THF)3 (Ln = Eu, Yb) with 2-(2,6-i-Pr2C6H3NHCH2)-
C8H5NH (1), resulting in the isolation and characterization of
lanthanide complexes having an indolyl ligand in novel μ-η6:η1:η1
hapticities. Furthermore, the reactivity of the novel europium(II)
complex was also examined. In this paper, we report the results.
spectroscopic and elemental analyses, and its structure was
elucidated by X-ray diffraction study.
The structure of 2 is displayed in Figure 1, and the selected
bond lengths and angles are given in Table 1. X-ray analyses
RESULTS AND DISCUSSION
■
Synthesis of 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1). Treat-
ment of 2-(2,6-i-Pr2C6H3NCH)C8H5NH with 3 equiv of
LiAlH4 in diethyl ether yielded, after workup, 2-(2,6-i-
Pr2C6H3NHCH2)C8H5NH (1) in 95% yield (Scheme 1). The
compound was fully characterized by NMR spectra.
Scheme 1. Synthesis of
2-(2,6-Diisopropylphenylaminomethylene)indole
Figure 1. ORTEP diagram of the molecular structure of complex 2
(ellipsoids at 15% probability level). All hydrogen atoms are omitted for
clarity.
Interactions of 2-(2,6-Diisopropylphenylaminomethylene)-
indole Ligand (1) with [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 and the
Synthesis and Characterization of Novel Indolyl Lanthanide
Complexes. Treatment of europium(III) amide [(Me3Si)2N]3-
Eu(μ-Cl)Li(THF)3 with 1 or 2 equiv of 2-(2,6-i-Pr2C6H3NHCH2)-
C8H5NH (1) in toluene at 80 °C produced a novel europium(II)
complex {[μ-η6:η1:η1-2-(2,6-i-Pr2C6H3NCH)C8H5N]Eu-
[2-(2,6-i-Pr2C6H3NCH)C8H5N]}2 (2) as deep red crystals in a
moderate yield (Scheme 2). Complex 2 is extremely sensitive to air
and moisture. It is readily soluble in common organic solvents such
as THF, toluene, and n-hexane. It was characterized by
revealed that complex 2 is a dinuclear europium(II) complex
having two indolyl ligands in bridged ways bonding with metals
in novel μ-η6:η1:η1 hapticities and two terminal indolyl ligands
bonding with metals in η1:η1 fashions. It represents the first
example of an organometallic complex that has the indolyl ligand
bonded with metal in μ-η6:η1:η1 modes.
The most important feature of complex 2 lies in the μ-η6:η1:η1
coordination of the indolyl ligand with the metal. The Eu(1)−C
(C6 ring, [C(3)−C(8)]) bond distances range from 2.921(3) to
Scheme 2. Synthesis of Complexes 2 and 3
B
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europium(III) to europium(II).3d Similarly, the reduction of
Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) of
Complexes 2−5
10f
−
Eu3+ to Eu2+ has been previously observed with C5Me5 ,
12
13
−
2−
C8H8
, and C9H6 .
2
4
5
3
Analogous reaction of [(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 with
1 equiv of 1 in toluene at 105 °C produced ytterbium(III) amido
complex [η1:η1-2-(2,6-i-Pr2C6H3NCH2)C8H5N]Yb[N-
(SiMe3)2](THF)2 (3) as dark red crystals (Scheme 2). A
difference from the above reaction for the preparation of complex
2 (the europium case) was observed; the N(2)−C(9) bond
distance of 1.471(5) Å found in complex 3 is normally observed
for a C−N single bond (see Table 1), indicating that no redox
reaction occurred even though the reaction was carried out at
elevated temperature. The difference in the reactivity between
europium(III) and ytterbium(III) amide with the same ligand
(1) can be ascribed to the difference in the reduction potentials
of the Eu3+/Eu2+ and Yb3+/Yb2+ couples, reported to be −0.35
and −1.15 V (versus NHE), respectively.14 This result is in
accordance with our previous report.3d X-ray diffraction showed
that compound 3 is a five-coordinate trivalent ytterbium complex
containing an amido-appended indolyl ligand bonding with Yb in
an η1:η1 fashion, two THF molecules, and an amido ligand
[N(SiMe3)2], adopting a distorted trigonal bipyramid geometry
(Figure 2) with three nitrogen atoms occuping the equatorial
Eu(1)−C(3)
Eu(1)−C(4)
Eu(1)−C(5)
Eu(1)−C(6)
Eu(1)−C(7)
Eu(1)−C(8)
C(9)−N(2)
Eu(1)−N(1)
Eu(1)−N(2)
Eu(1)−N(3)
Eu(1)−N(4)
Eu(1)−N(7)
Eu(1)−N(8)
Eu(1)−O(1)
Yb(1)−N(1)
Yb(1)−N(2)
Yb(1)−N(3)
Yb(1)−O(1)
Yb(1)−O(2)
3.132(3)
3.130(3)
3.063(3)
2.951(3)
2.921(3)
3.033(3)
1.276(4)
3.385(5)
3.377(5)
3.171(5)
3.037(5)
3.086(6)
3.273(5)
1.263(5)
3.530(8)
3.501(7)
3.273(8)
3.042(9)
3.081(10)
3.305(10)
1.250(11) 1.475(6)
2.512(6)
2.789(7)
2.581(3)
2.620(2)
2.508(3)
2.614(3)
2.544(4)
2.761(4)
2.612(4)
2.592(4)
2.593(4)
2.576(7)
2.671(7)
2.583(7)
2.279(5)
2.145(4)
2.249(4)
2.317(4)
2.330(4)
N(7)−Eu(1)−N(3) 142.84(8) 96.27(13)
N(8)−Eu(1)−N(4) 121.57(8) 152.12(13)
N(7)−Eu(1)−N(4) 92.25(8)
N(1)−Eu(1)−N(3)
N(4)−Eu(1)−N(2)
N(3)−Eu(1)−O(1)
O(1)−Eu(1)−N(4)
N(3)−Yb(1)−N(1)
N(3)−Yb(1)−O(1)
O(1)−Yb(1)−O(2)
99.60(12)
108.0(2)
99.70(19)
146.20(15) 102.2(3)
80.96(14) 95.5(2)
147.87(16)
89.25(15)
155.23(17)
3.132(3) Å (with an average Eu(1)−C distance of 3.038(3) Å) in
2 (Table 1). These values are considered to represent a
significant π-arene−Eu interaction that is entirely consistent with
the Eu−C distances in the complexes of Eu metals with neutral π
arenes, such as the average Eu−C distance of 3.002(18) Å found
in the η6-π-arene europium(II) complex [Eu(C6Me6)-
(AlCl4)2]4,10f the average Eu−C distance of 3.065(3) Å in
η6-π-arene complexes EuII(SAr*)2 (Ar* = 2,6-Trip2C6H3 with
Trip = 2,4,6-i-Pr3C6H2),10g and the average Eu−C distance of
3.105(3) Å for Eu−π-(μ-Ph2) in (C5Me5)Eu(μ-η6:
η1-Ph)2BPh2,10e when the differences in Eu2+ ionic radius with
different coordination numbers were taken into account.11
Therefore, the bonding of the indolyl ligand with the metal in 2 is
best described as the μ-η6:η1:η1 mode on the basis of these
structural parameters.
Furthermore, an X-ray diffraction study of the structure of 2
also indicates that the ligands in complex 2 are the imino-
functionalized indolyl ligands with a C(9)−N(2) bond distance
of 1.276(4) Å, which is normally observed for a CN double
bond. It is also found that the central europium metals are in the
oxidation state of +2. The facts suggest that a redox reaction
occurred in the interaction of 2-(2,6-i-Pr2C6H3NHCH2)-
C8H5NH (1) with [(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 resulting
in the isolation of the europium(II) and imino-functionalized
indolyl complex 2. This result is similar to our previous findings
of the redox chemistry between the europium(III) amide
[(Me3Si)2N]3Eu(μ-Cl)Li(THF)3 and the pyrrolyl-function-
alized secondary amines leading to oxidative dehydrogenation
of the secondary amines to imino groups and reduction of
Figure 2. ORTEP diagram of the molecular structure of complex 3
(ellipsoids at 15% probability level). All hydrogen atoms are omitted for
clarity.
positions and two oxygen atoms from the THF molecule situated
at the axial positions [O(1)−Yb−O(2) (155.23(17) °]. The Yb−N
distances in 3 are within the range 2.145(4)−2.279(5) Å (Table 1),
which are comparable to the range 2.152(6)−2.343(6) Å reported
in the related pyrrolyl complex [{(μ-η5:η1):η1-2-[(2,6-i-Pr2C6H3)-
NCH2]C4H3N}Yb{N(SiMe3)2}]2.3f The corresponding average
Yb−N distance of 2.221 Å found in 3 is also comparable to the value
2.232 Å found in [μ-{[η1:η1-3-(CyNHCH2)C8H5N]2Li(THF)}Yb-
[N(SiMe3)2]2],8f allowing for ionic radii difference.
Not only are different results obtained between the reactions
of europium amide and the ytterbium amide [(Me3Si)2N]3Ln(μ-
Cl)Li(THF)3 (Ln = Eu, Yb) with 2-amino-functionalized indole
[2-(2,6-i-Pr2C6H3NHCH2)C8H5NH] (1), but also the results
are different than those of reactions of 3-amino-functionalized
C
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Scheme 3. Proposed Pathway for the Formation of Complex 2
Scheme 4. Reaction of Complex 2 with Formamidines
indole with rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li-
(THF)3 (RE = different rare-earth metal), which produced the
only indole deprotonation complexes.8f The results are also
different than our previous finding that reactions of 3-imino-
functionalized indole with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3
(RE = Y, Yb) resulted in an unusual 1,2-dianionic indolyl
ligand.8e These results indicated that reactions of different
indoles having substituents at the 2- or 3-positions with rare-
earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 displayed
different reactivities and different bonding modes of the indolyl
ligands.
Isolation of complex 3 suggested that it may serve as an
intermediate in the formation of complex 2. This intermediate
underwent β-H elimination3d,f to produce the intermediate A,
D
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which has the imino-functionalized indolyl ligand, which then
reacted with amine HN(SiMe3)2 to give the diamido intermediate
B. The intermediate B underwent ligand redistribution followed by
homolysis of Eu−N bond2f,15 and dimerization to produce the final
novel europium(II) complex 2 (Scheme 3).
of 3.377(5) Å, and Eu(1)−C(8) of 3.273(5) Å. The average value
of 3.098(6) Å of the three Eu(1)−C distances can be compared
to the mean Eu−C distance of 3.038(3) Å found in complex 2,
indicating the bonding modes of the bridged indolyl ligands have
changed from the μ-η6:η1:η1 to the μ-η3:η1:η1 mode. A similar
change was found in complex 5 by comparing the distances of
Eu(1)−C(6) of 3.042(9) Å and Eu(1)−C(7) of 3.081(10) Å
with the other distances of Eu(1)−C(3) of 3.530(8) Å, Eu(1)−
C(4) of 3.501(7) Å, Eu(1)−C(5) of 3.273(8) Å, and Eu(1)−C(8)
of 3.305(10) Å, indicating that the bonding modes of the bridged
indolyl ligands were changed to the μ-η2:η1:η1 mode, suggesting
steric effects on the bonding for the different substituents (i-Pr and
Me) on the formamidinato ligands. Another reason for the
difference in bonding modes of the bridged indolyl ligands between
2 and 4 or 5 may be THF coordination.
Reactivity of Novel Indolyl Europium(II) Complex 2
with Formamidines (Form). Amidines are useful ligands and
important substrates for metal-based reactivity studies, and a
number of rare-earth metal amidinates have been reported.1,16
Although the bonding mode of amidines with lanthanides is
observed to be primarily η2, Hamidi and co-workers have recently
reported an example of [La{η1(N):η6(Ar)-Me2CH2FormAlMe3}-
(AlMe3)(AlMe4)][La(Me2CH2FormAlMe3)(AlMe3)(AlMe4)]-
(C6H14)1.5(AlMe4)2](C7H8)1.5 in which amidinato appended arene
ligand coordinated to the lanthanum center in η1(N):η6(arene)
manners.17 Given the coordination diversities of amidines and
indolyl ligands, the reactions of the novel europium(II) complex 2
with formamidines that have different substituents ArNCHNHAr
(Ar = 2,6-Me2C6H3; 2,6-i-Pr2C6H3) were examined to see if these
would make variations of the bonding mode of the indolyl or
amidine ligands to the central metal in complex 2.
As shown in Scheme 4, the reaction of 2 with 2 equiv of [(2,6-
Me2C6H3)NCHNH(C6H3Me2-2,6)] in toluene with the addi-
tion of a drop of THF produced a novel europium(II) complex
formulated as {[μ-η3:η1:η1-2-(2,6-i-Pr2C6H3NCH)C8H5N]-
Eu[(2,6-Me2C6H3)NCHN(C6H3Me2-2,6)](THF)}2 (4),
whereas treatment of complex 2 with 2 equiv of a sterically
bulky formamidine [(2,6-i-Pr2C6H3)NCHNH(C6H3i-Pr2-2,6)]
afforded a novel europium(II) complex formulated as {[μ-
η2:η1:η1-2-(2,6-i-Pr2C6H3NCH)C8H5N]Eu[(2,6-i-Pr2C6H3)-
NCHN(C6H3i-Pr2-2,6)](THF)}2 (5). The molecular structures
demonstrated that the bridged indolyl ligands in complex 2 still
remained in complexes 4 and 5 (Figures 3 and 4), but the bonding
CONCLUSIONS
■
Reactions of a 2-amino-functionalized indole with lanthanide
amides [(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3 (Ln = Eu, Yb) were
studied with the findings of different reactivity patterns and the
first example of a dinuclear Eu(II) complex incorporating
bridged indolyl ligand in novel μ-η6:η1:η1 hapticities. Reactivity
studies of the novel europium(II) complex led to the discovery of
bonding modes of the bridged indolyl ligands changing from the
novel μ-η6:η1:η1 to the μ-η3:η1:η1 or the μ-η2:η1:η1, depending on
the steric effects of the formamidinate ligands and coordination
of THF. The results represent the first report on the indolyl
ligands bonding with rare-earth metal in these ways. This work
together with previous works in this field implies that there
would be versatile reactivities of indolyl ligands with rare-earth
metals complexes, and also, there would be different bonding
modes of the indolyl ligands with rare-earth metals. Further
works on the chemistry of rare-earth metal complexes with
different indolyl ligands are now in progress.
EXPERIMENTAL SECTION
■
General Methods. All syntheses and manipulations of air- and
moisture-sensitive materials were performed under dry argon and in an
oxygen-free atmosphere using standard Schlenk techniques or in a
glovebox. All solvents were refluxed and distilled over sodium
benzophenone ketyl under argon prior to use unless otherwise noted.
[(Me3Si)2N]3LnIII(μ-Cl)Li(THF)3 (Ln = Eu, Yb),15d,18 2-(2,6-
i-Pr2C6H3NCH)C8H5NH,19 and formamidines 2,6-R2C6H3N
CHNHC6H3R2-2,6 (R = CH3, i-Pr)20 were prepared according to
literature methods. Elemental analyses data were obtained on a
PerkinElmer 2400 Series II elemental analyzer. 1H NMR and 13C
NMR spectra were run on a Bruker AV-300 NMR spectrometer (300
MHz for 1H; 75.0 MHz for 13C) with CDCl3 (for organic compounds)
as a solvent and internal standard. Chemical shifts (δ) were reported in
parts per millin (ppm). J values are reported in hertz (Hz). IR spectra
were run on a Shimadzu FTIR-8400s spectrometer (KBr pellets).
HRMS measurements were conducted with an Agilent 6220 ESI-TOF
mass spectrometer. Melting points were determined in sealed capillaries
and are uncorrected.
Figure 3. ORTEP diagram of the molecular structure of complex 4
(ellipsoids at 15% probability level). All hydrogen atoms are omitted for
clarity.
Preparation of 2-(2,6-i-Pr2C6H3NHCH2)C8H5NH (1). LiAlH4
(3.52 g, 90.0 mmol) was suspended in Et2O (30 mL), and a solution
of 2-(2,6-i-Pr2C6H3NCH)C8H5NH19 (9.12 g, 30.0 mmol) in Et2O
(30 mL) was added dropwise at 0 °C. The reaction mixture was stirred
overnight at room temperature; then it was hydrolyzed. The organic
layer was separated, and the white residue was extracted with diethyl
ether (3 × 20 mL). The combined organic layers were dried over
anhydrous MgSO4 followed by filtration. Removal of solvent under a
vacuum gave the objective compound as an off-white solid (8.72 g) in
95% yield. The product was subsequently recrystallized from the
mixture of hexane and ethyl acetate. Mp: 97−98 °C. 1H NMR
modes were changed, and the terminal indolyl ligands in complex 2
were replaced by the formamidinato ligands. Selected bond lengths
and angles of complexes 4 and 5 are given in Table 1.
X-ray analyses revealed that the Eu(1)−C distances in
complex 4 are in the range 3.037(5)−3.386(5) Å, and the
corresponding distances of Eu(1)−C(5) of 3.170(5) Å, Eu(1)−
C(6) of 3.037(5) Å, Eu(1)−C(7) of 3.086(6) Å (with an average
Eu(1)−C distance of 3.098(6) Å) are significantly shorter than
the other distances of Eu(1)−C(3) of 3.385(5) Å, Eu(1)−C(4)
E
dx.doi.org/10.1021/ic401515q | Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 4. ORTEP diagram of the molecular structure of complex 5 (ellipsoids at 15% probability level). All hydrogen atoms are omitted for clarity.
Table 2. Experimental Data for the X-ray Diffraction Studies of Complexes 2−5
2
3
4
5
formula
fw
C84H91Eu2N8
1516.58
C35H58N3O2Si2Yb
782.06
C84H100Eu2N8O2
1557.64
C100H132Eu2N8O2
1782.06
T (K)
293(2)
293(2)
293(2)
293(2)
λ (Å)
0.710 73
monoclinic
C2/c
0.710 73
monoclinic
P21/n
0.710 73
0.710 73
tetragonal
P43212
crystal system
space group
a (Å)
monoclinic
P21/c
40.057(6)
16.650(2)
26.106(4)
90
10.6005(8)
32.236(2)
11.9390(9)
90
17.1270(11)
15.5956(10)
35.030(2)
90
13.0633(6)
13.0633(6)
65.076(5)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
106.721(2)
90
109.7180(10)
90
99.5680(10)
90
90
90
16 675(4)
8
3840.6(5)
4
9226.7(10)
4
11 105.2(11)
4
D
calcd (mg m−3
)
1.209
1.353
1.121
1.066
μ (mm−1
)
1.534
2.529
1.389
1.162
F(000)
6224
1612
3208
3720
θ range (deg)
1.48−27.60
71 301/19 168
0.0370
1.92−27.64
33 049/8878
0.0256
1.43−25.00
64 835/16 255
0.0653
1.59−27.50
95 512/12 708
0.0727
reflections collected/unique
R (int)
goodness-of-fit on F2
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
1.009
1.000
1.039
1.022
0.0355, 0.0719
0.0642, 0.0786
+0.928 and −0.456
0.0438, 0.1603
0.0511, 0.1690
+0.637 and −2.715
0.0466, 0.0772
0.0994, 0.0843
+0.522 and −0.796
0.0720, 0.1714
0.0957, 0.1825
+1.031 and −1.228
largest diff. peak and hole (e Å−3
)
(300 MHz, CDCl3): δ 8.43 (s, 1H, NH), 7.60 (d, J = 7.47 Hz, 1H,
indoleArH), 7.38 (d, J = 7.68 Hz, 1H, indoleArH), 7.18−7.11
(m, 5H, ArH), 6.42 (s, 1H, NHCCH), 4.22 (s, 2H,
overnight at 80 °C. The solvent was removed under a vacuum, and the
dark red residue was extracted with n-hexane and filtered. The hexane
solution was cooled to 5 °C. Dark red crystals that were suitable for
X-ray diffraction were obtained from the solution after a few days
(0.18 g, 46%). Mp (sealed): 239−240 °C under Ar. Anal. Calcd for
C84H91Eu2N8: C, 66.52; H, 6.05; N, 7.39. Found: C, 65.64; H, 6.68; N,
6.77. IR (KBr pellet, cm−1) ν: 3048 (w), 2961 (m), 1632 (s), 1614 (s),
1587 (m), 1460 (m), 1435 (m), 1234 (w), 1178 (w), 1130 (m), 1098
(w), 933 (w), 816 (m), 802 (m), 770 (m), 739 (s), 660 (m).
CH2NH), 3.30 (t, 2H, CH(CH3)2), 1.21 (12H, CH3). 13
C
NMR (75.0 MHz, CDCl3): δ 142.8 (aromatic CNH), 142.4, 136.0,
100.1 (indole C of 2-pyrrole), 137.4, 128.4, 124.6, 123.8, 121.8, 120.4,
119.9, 110.8 (aromatic C), 49.3 (CH2NH), 27.9 (CH(CH3)2),
+
24.4 (CH3). HRMS (ESI) m/z: calcd for C21H25N2 , 305.2012; found,
305.2011. IR (KBr pellets, cm−1) ν: 3435 (s), 2955 (m), 1614 (s), 1589
(m), 1554 (m), 1456 (s), 1413 (m), 1286 (m), 1195 (m), 1064 (m),
1051 (m), 792 (s), 764 (m), 744 (s), 636 (s).
Preparation of [η1:η1-2-(2,6-i-Pr2C6H3NCH2)C8H5N]Yb[N-
(SiMe3)2](THF)2 (3). The complex 3 was prepared following procedures
similar to those used for the synthesis of 2 by running the reaction at 105
°C, using 0.31 g of 1 (1.00 mmol), 0.91 g of [(Me3Si)2N]3Yb(μ-
Cl)Li(THF)3 (1.00 mmol), and 30 mL of toluene. The reaction yielded
dark red crystals of 3 (0.62 g, 79%). Mp (sealed): 295 °C (decomp)
Preparation of {[μ-η6:η1:η1-2-(2,6-i-Pr2C6H3NCH)C8H5N]Eu-
[2-(2,6-i-Pr2C6H3NCH)C8H5N]}2 (2). A Schlenk flask was charged
with 1 (0.31 g, 1.00 mmol), [(Me3Si)2N]3EuIII(μ-Cl)Li(THF)3 (0.89 g,
1.00 mmol), and toluene (30 mL). The reaction mixture was stirred
F
dx.doi.org/10.1021/ic401515q | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
under Ar. Anal. Calcd for C35H58N3O2Si2Yb: C, 53.75; H, 7.48; N, 5.37.
Found: C, 53.64; H, 7.30; N, 5.25. IR (KBr pellet, cm−1) ν: 3024 (m),
2955 (s), 2870 (m), 2828 (m), 1925 (w), 1881 (w), 1456 (s), 1414 (m),
1383 (m), 1362 (m), 1319 (m), 1286 (m), 1196 (m), 1065 (m), 1051
(m), 993 (m), 793 (s), 748 (s), 630 (s).
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Preparation of {[μ-η2:η1:η1-2-(2,6-i-Pr2C6H3NCH)C8H5N]Eu-
[(2,6-i-Pr2C6H3)NCHN(C6H3i-Pr2-2,6)](THF)}2 (5). A Schlenk flask
was charged with 2 (1.51 g, 1.00 mmol), 2,6-i-Pr2C6H3NCHNH-
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1336 (m), 1319 (m), 1234 (m), 1178 (m), 1130 (m), 1097 (m), 1058
(w), 987 (w), 933 (m), 895 (w), 868 (m), 816 (m), 770 (m), 739 (s),
660 (m).
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CCD area detector diffractometer using graphite-monochromated Mo
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applied using the SADABS program.21 All structures were solved by
direct methods, completed by subsequent difference Fourier syntheses,
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least-squares calculations on F2 using the SHELXTL program package.22
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ASSOCIATED CONTENT
■
S
* Supporting Information
Characterization spectra for compound 1, crystallographic
information files (CIF), and selected bond distances (Å) and
angles (deg) of complexes 2−5. This material is available free of
charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
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Corresponding Author
*E-mail: swwang@mail.ahnu.edu.cn.
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science Foundation
of China (21172003, 20832001, 21172004, and 21202002), the Basic
Research Program of China (2012CB821600), the Ministry
of Education (20103424110001), and Anhui province
(11040606M36).
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