Reduction of sterically hindered β-diketiminato europium(III) complexes by the β-diketiminato anion: A convenient route for the synthesis of β-diketiminato europium(II) complexes

Article abstract of DOI:10.1039/c2dt12176j

The metathesis reaction of anhydrous EuCl₃ with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4, 6- Me₃C₆H ₂)C(Me)]₂CH^-, L^{2, 4, 6-Me3}; [N(2,6-ⁱPr₂C

Full text of DOI:10.1039/c2dt12176j

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PAPER
Reduction of Sterically Hindered β-Diketiminato Europium(III) Complexes by
the β-Diketiminato Anion: A Convenient Route for the Synthesis of
β-Diketiminato Europium(II) Complexes†
Xiaodong Shen,a Yong Zhang,a Mingqiang Xuea and Qi Shen*a,b
Received 14th November 2011, Accepted 21st December 2011
DOI: 10.1039/c2dt12176j
The metathesis reaction of anhydrous EuCl3 with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4,
6- Me3C6H2)C(Me)]2CH−, L2, 4, 6-Me3; [N(2,6-iPr2C6H3)C(Me)]2CH−, L2, 6-ipr2 and [(2, 6-iPr2C6H3)NC
(Me)CHC(Me)N(C6H5)]−, L2, 6-ipr2Ph) in THF at 60 °C afforded the corresponding EuII complexes:
EuII(L2, 4, 6-Me3)2(THF) (1), EuII(L2, 6-ipr2)2 (2) and EuII(L2, 6-ipr2Ph)2 (5) with the formations of dimers
(L2, 4, 6-Me3)2 (3) and (L2, 6-ipr2)2 (4) for the former two reactions and proligand L2, 6-ipr2PhH (6) for the
latter one. Compounds 1–6 were confirmed by an X-ray crystal structure analysis. The central metal EuII
in 1 is coordinated by two monoanionic L2, 4, 6-Me3 ligands and one THF molecule in a trigonal
bipyramid. The EuII in each of 2 and 5 is ligated by two monoanionic ligands to form a tetrahedral
geometry. The BVS (Bond Valence Sum) calculation indicates the oxidation state of Eu in all the
three complexes is 2+ (2.12 for 1, 1.86 for 2 and 1.99 for 5). The isolation of dimers of (L2, 4, 6-Me3)2 and
L2, 6-ipr2)2 and proligand L2, 6-ipr2PhH demonstrates that the reducing agent in the present reduction of a
EuIII ion to a EuII ion might be the (L2, 4, 6-Me3)−, (L2, 6-ipr2)− and (L2, 6-ipr2Ph)−, respectively. The
possible mechanism for the reduction pathway is presented.
carbodiimides with high activity,1i,1k or an efficient
reducing agent in the case of Eu metal to reduce an Eu(III) ion to
Introduction
The application of β-diketiminates as monoanionic ancillary
ligands has attracted increasing attention in organometallic
chemistry of lanthanide metals because their electronic and steric
factors can be tuned by variation of the substituents on the nitro-
gen atoms or at their skeleton.1 However, recent results revealed
that β-diketiminato ligands themselves can participate in trans-
formations under certain conditions, including reduction by the
addition of a strong reducing agent,2 or an external strong base,3
and self-deprotonation by the elimination of a β-diketiminato
ligand induced from steric demand in a sterically hindered
lanthanide(III) complex.1f,1l
an Eu(II) ion by giving up an electron to Eu(III) ion. Thus,
6-Me2
the divalent Eu complex EuII(L2, 6-Me2)2(THF) (L2,
[N(2, 6- Me2C6H3)C-(Me)]2CH−) and the dimer (L2,
=
6-Me2
)
2
were isolated from the reaction of EuCl3 with three equivalents
of NaL2, 6-Me2 2
.
To assess the generality of reduction reaction of Eu(III)
by β-diketiminato anions in sterically hindered β-diketiminato
EuIII complexes, we continue to study the metathesis reaction
of EuCl3 with the sodium salts of the following three
β-diketiminato ligands: two symmetrical β-diketiminato ligands
L2, 4, 6-Me3H (L2,4,6-Me3 = [N(2, 4, 6- Me3C6H2)C(Me)]2CH−)
and L2, 6-ipr2H (L2, 6-ipr2 = [N(2,6-iPr2C6H3)C(Me)]2CH−) and
Very recently, we have found that the β-diketiminato ligand in
a sterically crowded tris(β-diketiminato) lanthanide complex
could serve as either an active species to catalyze ring
opening polymerization of lactones and addition of amines to
one asymmetrical β-diketiminato ligand L2, 6-ipr2PhH (L2, 6-ipr2
Ph
= [(2, 6-iPr2C6H3)-NC(Me)CHC(Me)N(C6H5)]−). Indeed, each
reaction afforded a Eu(II) complex plus either a dimer of a ligand
(for the reaction with the symmetrical ligand), or a proligand
(for the case with the asymmetrical ligand). Thus, three novel
aKey Laboratory of Organic Synthesis of Jiangsu Province, College of
Chemistry, Chemical Engineering and Materials Science, Soochow
University, Suzhou, 215123, People’s Republic of China. E-mail:
qshen@suda.edu.cn; Fax: +86-512-65880305
4,
6-ipr2
Eu(II) complexes, EuII(L2,
6-Me3)2(THF) (1), EuII(L2,
)
2
6-ipr2
(2) and EuII(L2,
) (5), were prepared by the sterically
Ph 2
induced reduction of Eu(III), which represents a new route
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 200032,
People’s Republic of China
for the synthesis of β-diketiminato Eu(II) complexes. The
dimers of (L2, 4, 6-Me3)2 (3) and (L2, 6-ipr2)2 (4) and the proligand
6-ipr2
L2,
PhH (6) were also fully characterized. In addition we
†Electronic supplementary information (ESI) available. CCDC reference
numbers 843447–843452. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt12176j
now report the possible mechanism for the sterically induced
reduction of Eu(III).
3668 | Dalton Trans., 2012, 41, 3668–3674
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isolated as red crystals in good yield upon crystallization
(Scheme 2).
Results and Discussion
Synthesis of L2, 4, 6-Me3H, L2, 6-ipr2H and L2,6-ipr2PhH
The elemental analysis of 1 is consistent with its formula. The
IR spectra of 1 exhibited strong absorptions near 1551 and
1528 cm−1, which were consistent with the partial CvN charac-
ter of the β-diketiminato ligands.6 However, a resolvable
1HNMR spectrum could not be measured owing to paramagnet-
ism. The identity of complex 1 was established by an X-ray
structure determination.
To further confirm the oxidation state of the central metal Eu
in 1, the BVS (Bond Valence Sum) calculation was made, as
BVS could be used as a convenient method to estimate the oxi-
dation state of a central metal in a complex.7 The BVS for 1
equals 2.12, indicating Eu metal being in the 2+ oxidation state.
Replacement of the NaL2, 4, 6-Me3 by the sodium salt of the
bulkier ligand NaL2, 6-ipr2 in the above reaction also led to a red
The following β-diketiminato ligands with varied substituents
on the nitrogen atoms were chosen including L2,
6-Me3H,
4,
L2, 6-ipr2H and L2, 6-ipr2PhH.
4,
The proligands L2,
6-Me3H and L2, 6-ipr2H were prepared
by the published method.4 The new asymmetrical proligand
L2, 6-iprPhH was synthesized by a similar procedure for the syn-
thesis of asymmetrically substituted diimines.5 The reaction of 2,
4-pentanedione with equivalent of 2, 6-diisopropyl-aniline in an
acidic toluene solvent, followed by treatment with an equivalent
of aniline hydrochloride in ethanol afforded the ligand
L2, 6-iprPhH as pale yellow crystals upon crystallization from the
n-hexane solution in 23% yield. (Scheme 1)
solution. Crystallization from the solution afforded the un-sol-
6-iPr2
vated complex EuII(L2,
) (2) as red crystals (Scheme 2).
2
Synthesis of EuII(L2, 4, 6-Me3)2(THF) (1) and
EuII(L2, 6-ipr2)2·CH3C6H5 (2), and the dimers of (L2, 4, 6-Me3
(3) and (L2, 6-ipr2)2 (4)
)
2
Complex 2 was characterized by satisfactory elemental analyses,
IR spectra and an X-ray structure determination. But no resolvable
1HNMR spectrum of 2 could be obtained as the in the case of 1.
BVS calculation for 2 gave the value of 1.86, demonstrating
the Eu metal in 2 being also 2+.
The reaction of anhydrous EuCl3 with NaL2, 4, 6-Me3 was con-
ducted first. Treatment of a suspension of EuCl3 in THF with a
THF solution of NaL2, 4, 6-Me3 in a molar ratio of 1 : 3 at 60 °C
gave a red suspension. Removing the NaCl by centrifugation led
to a red solution, from which EuII(L2,4,6-Me3)2(THF) (1) was
The formation of 1 and 2 indicates unequivocally that the
reduction of Eu(III) occurred in both reactions, and the efficient
reducing agent here might be the bulky anions of L2, 4, 6-Me3 and
L2, 6-iPr2, respectively, as mentioned previously.2 Thus, the dimer
of L2, 4, 6-Me3 for the former reaction and the dimer of L2, 6-iPr2
for the latter one could be isolated as the other product. After
the isolation of 1 or 2 was completed, the dimer of (L2, 4, 6-Me3
)
2
(3) and the dimer of (L2, 6-iPr2)2 (4) were indeed obtained upon
crystallization from each mother liquid (Scheme 2). However, the
isolation of 4 is more difficult than that of 3, as 4 is more soluble
in organic solvents compared to 3. Both 3 and 4 were identified
by a crystal structure analysis (see the supporting information†).
Complexes 1 and 2 are sensitive to air and moisture, but are
thermally stable up to their own melting point.
Scheme 1 Syntheses of L2, 6-iprPhH.
Scheme 2 Reaction of EuCl3 with the sodium derivatives of the ligands.
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Synthesis of [EuII(L2, 6-ipr2Ph)2] (5) and the proligand
L2,6-ipr2PhH (6)
The success in the syntheses of complexes 1 and 2 from the
above reactions encouraged us to further investigate the reaction
of EuCl3 with the sodium salt of asymmetrical β-diketiminato
NaL2, 6-ipr2 in a molar ratio of 1 : 3 at 60 °C in THF. The reac-
Ph
tion went smoothly to give a red solution. After workup, the cor-
responding EuII complex [EuII(L2, 6-ipr2Ph)2] (5) was prepared as
red crystals in reasonable yield (Scheme 2). The low yield of the
crystals of 5 may be attributed to its very high solubility in
organic solvents, even in n-hexane.
Complex 5 was fully characterized by elemental analysis, IR
spectrum and an X-ray structure analysis. The oxidation state of
the Eu metal in 5 was estimated by BVS calculation. The value
of BVS equals 1.99.
6-ipr2
It’s unexpected that no dimer of (L2,
) was isolated
Ph 2
from the mother liquid, but the proligand L2, 6-ipr2PhH (6) was
obtained instead (Scheme 2). The formation of 6 indicates oxi-
dation of a β-diketiminato anion under the present condition
could be realized in different ways (to a dimer or a proligand)
depending on the β-diketiminato anion used.
Fig. 2 ORTEP diagram of 2 showing the atom-numbering scheme.
Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
The proligand 6 was characterized by an X-ray crystal struc-
ture analysis (see the supporting information†).
Molecular structures of 1, 2 and 5
The molecular structures of 1, 2 and 5 are shown in Fig. 1, 2 and
3, respectively. Selected bond distances and angles are listed in
Table 2.
The Eu(II) ion in 1 is ligated by four nitrogen atoms and one
oxygen atom in a distorted trigonal bipyramid with the two nitro-
gen atoms of N1 and N3 and the three atoms of O1, N2 and N4,
occupying two axial sites (the angle of N1–Eu1–N3, 160.08
Fig. 3 ORTEP diagram of 5 showing the atom-numbering scheme.
Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
(14)°) and the equatorial positions, respectively. The molecular
structure of complex 1 is quite similar to that reported for
EuII(L2, 6-Me2)2(THF).2
Each of the Eu(II) ions in 2 and 5 coordinates to four nitrogen
atoms of the two ligands and the coordination geometry around
each Eu ion is a tetrahedron, which is similar to that of
YbII(LPh, Ph)2.8 There is no coordinated THF molecule in both
complexes. This might be because the coordination sphere
around each EuII ion in 2 or 5 is crowded by two bulkier ligands
L2, 6-ipr2 or L2, 6-ipr2Ph, compared to L2,4,6-Me3 in 1. There is a
Fig. 1 ORTEP diagram of 1 showing the atom-numbering scheme.
Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
3670 | Dalton Trans., 2012, 41, 3668–3674
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4,
(SiMe3)}2]).8 Whilst, each ligand in 1 (L2,
6-Me3) and 5
Table 1 Crystallographic data for complexes 1, 2, and 5
(L2, 6-ipr2Ph) coordinates to the Eu(II) ion in a κ2 mode, the dis-
tances of Eu(II) to C atoms (β-diketiminato) all are far from the
upper limit for significant intramolecular π-arene⋯Ln inter-
actions (Table 2). The dihedral angle between the N1–Eu–N2
and N1–C2–C4–N2 planes is 48.534° in 1 and 21.159° in 5
(10.8° in the κ2-bonded [Yb(L′)2]).8
1
2
5
Expirical
formula
C50 H66 Eu N4 O C58 H82N4Eu·C7H8 C46 H58 Eu N4
Formula weight 891.03
T/K 223(2)
Crystal system Orthorhombic
1079.37
223(2)
Orthorhombic
P 212121
−0.009(12)
818.92
223(2)
Triclinic
P 1
—
ˉ
Space group
Flack
parameters
a/Å
b/Å
c/Å
P 212121
0.013(11)
Possible mechanism for the reduction of a EuIII ion to a EuII ion
11.5227(15)
19.681(3)
20.917(3)
90
90
90
4743.5(12)
4
1.248
12.4327(8)
19.2691(12)
24.7480(16)
90
90
90
5928.8(7)
4
1.209
10.9466(15)
11.5259(16)
19.195(2)
101.515(2)
96.956(2)
115.923(2)
2073.8(5)
2
The reduction reaction of Ln(III) ions has not been observed in
the preparation of tris β-diketiminato Eu complexes with the less
bulky β-diketiminato ligand,2 although the reduction reaction of
Cp3Eu·THF or Cp2EuCl·THF with Li-naphthalene reagent was
reported,10 indicating the sodium salt of β-diketiminato, in
general, could not be used as an efficient reducing agent.
The reduction of Eu(III) here should result from sterically
induced reduction as in the cases with the formation of
EuII(L2, 6-Me2)2(THF) reported previously2 and the formation of
((4-nBu-C6H4)5C5)2Ln (Ln=Yb, Sm) from the reaction of
(2-Me2N-benzyl)3Ln with (4-nBu-C6H4)5C5H reported by
Harder11 The sterically induced reduction has been well docu-
mented by Evans12 in the reduction chemistry of the sterically
demanding (CpBIG)3Ln. A similar mechanism to that proposed
for the reduction reactivity of (CpBIG)3Ln (Ln = Yb, Sm) can be
used to explain the reduction of Eu(III) by β-diketiminato
anions in a overcrowded tris-β-diketiminato Eu(III) transient.
The reaction of EuCl3 with NaL (L = L2, 4, 6-Me3, L2, 6-ipr2 and
L2, 6-ipr2Ph) affords an unstable [LnL2…L] with a loose L farther
from the Eu(III) ion than their usual optimal distance. The loose
L anion in the transient is not electro-statically stabilized as
effectively as it is in conventional β-diketiminato complexes.
Thus, the unstable [LnL2…L] transfers to a stable Eu(II) complex
(1, 2 or 5) and a L radical(L2, 4, 6-Me3·, L2, 6-ipr2· or L2, 6-ipr2Ph·)
via giving up an electron by the loose L anion to the EuIII ion
(Scheme 3). The resulting radical dimerizes to a dimer or picks
up a H atom from the solvent to a proligand immediately. The
proposed pathway is confirmed by the isolation of dimers of 3
and 4 and proligand 6. The only difference in the mechanism
between our cases and the reduction reactivity of (C5Me5)3Ln is
that the ligand anion gives up an electron to the Eu(III) ion in our
cases and to the substrate in their cases. Efforts to isolate the
unstable intermediate have not been successful yet.
α (°)
β (°)
γ (°)
V/Å3
Z
Dcalcd.
1.311
(mg cm−3
)
Absorption
1.360
1.099
1.547
coefficient
(mm−1
)
F(000)
1860
3.10–25.50
15182/8384
2284
3.14–25.50
20443/10494
850
θ range (°)
Reflections
collected/
unique
3.04–25.50
17904/7668
[R(int) =
0.0576]
[R(int) = 0.0385] [R(int) = 0.0466]
Data/restraints/ 8384/10/516
parameters
Goodness-of-fit 1.033
10494/14/608
1.096
7668/0/419
1.121
on F2
Final R
[I > 2σ(I)]
wR2 (all data)
0.0416
0.0751
0.0468
0.0726
0.1458
0.0927
free toluene molecule in the unit cell of 2, but no toluene
molecule in 5.
The bond parameters in both Eu-β-diketiminato units of each
complex are almost constant. For example, each Eu–N bond dis-
tance and the angle of N–Eu–N in the two Eu–L units are 2.534
(4) Å, 2.542(4) Å and 75.44(13)°, 2.528(4) Å, 2.563(4) Å and
73.95(14)° for 1; 2.496(4) Å, 2.545(4) Å and 76.52(13)°, 2.499
(4) Å, 2.555(4) Å and 77.74(14)° for 2; 2.496(5) Å, 2.502(6) Å
and 75.39(18)°, 2.487(6) Å, 2. 506(5) Å and 74.53(18)° for 5,
respectively. This structural feature is the same as that found
Ph
Ph
in YbII(LPh,
)
(LPh,
= [N(SiMe3)C(Ph)C(H)C(Ph)N
2
(SiMe3)2])8 and EuII(L2, 6-Me2)2(THF).2 The average Eu–N dis-
tance in each complex (2.542(4) Å for 1; 2.524(4) Å for 2; 2.498
(6) Å for 5) is longer than the 2.467(9) Å found in the trivalent
complex Eu(L2-Me
)
(L2-Me = [N(2-MeC6H4)C(Me)]2CH),2 in
3
Conclusions
agreement with the difference in Eu3+ and Eu2+ ionic radii, but
can be compared with that found in EuII(L2, 6-Me2)2(THF) (2.557
(4) Å).2
Divalent complexes 1, 2 and 5 were synthesized in good yields
by the metathesis reaction of EuCl3 with three equivs of sodium
salt of bulky β-diketiminato NaL (L = L2, 4, 6-Me3, L2, 6-ipr2 and
However, the influence of the size of the β-diketiminato ligand
on the bonding mode of a β-diketiminato to a Eu(II) ion in 1, 2
and 5 is observed. Both L2, 6-ipr2 ligands in 2 coordinate to the
Eu(II) ion in a close η5 mode (Fig. 2). The distances of Eu–C
(β-diketiminato) bonds range from 3.044(5) Å to 3.131(57) Å,
which are within the upper limit for significant intramolecular
π-arene⋯Ln interactions.9 The dihedral angle between the N1–
Eu–N2 and N1–C2–C4–N2 planes is 69.984° in 2 (67.5° in the
η5-bonded [Yb{N(SiMe3)C-(C6H4Me-4)CHC-(adamantyl-1)N
6-ipr2
L2,
Ph). The reduction reaction proceeds mechanistically
through a sterically induced reduction pathway: the L anion in
the overcrowded L3Eu(III) transient gives up an electron to the
EuIII ion leading to the formation of the corresponding Eu(II)
complex and the L radical, which either dimerizes to a dimer or
picks up a H atom from solvent to a proligand. Further study on
the reactivity of β-diketiminato ligand in a sterically demanding
complex is now underway.
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Table 2 Selected bond lengths (Å) and angles (°) for complexes 1, 2, and 5
Bond lengths
1
5
Bond lengths
2
Ln(1)–N(1)
Ln(1)–N(2)
Ln(1)–N(3)
Ln(1)–N(4)
(Ln–N)av.
Ln(1)–O(1)
Ln(1)…C(2)
Ln(1)…C(3)
Ln(1)…C(4)
Ln(1)…C(25)
Ln(1)…C(26)
Ln(1)…C(27)
C(1)–C(2)
2.542(4)
2.534(4)
2.563(4)
2.528(4)
2.542(4)
2.542(3)
3.337(61)
3.524(59)
3.343(56)
3.426(60)
3.661(59)
3.436(59)
1.523(7)
1.331(7)
1.402(7)
1.392(9)
1.335(7)
1.538(7)
1.506(8)
1.325(7)
1.414(8)
1.375(9)
1.339(7)
1.528(7)
2.496(5)
2.502(6)
2.506(5)
2.487(6)
2.498(6)
—
Ln(1)–N(1)
Ln(1)–N(2)
Ln(1)–N(3)
Ln(1)–N(4)
(Ln–N)av.
Ln(1)–O(1)
Ln(1)…C(2)
Ln(1)…C(3)
Ln(1)…C(4)
Ln(1)…C(31)
Ln(1)…C(32)
Ln(1)…C(33)
C(1)–C(2)
2.496(4)
2.545(4)
2.499(4)
2.555(4)
2.524(4)
—
3.478(62)
3.783(59)
3.487(61)
3.507(50)
3.829(62)
3.520(74)
1.519(10)
1.319(8)
1.409(10)
1.389(10)
1.340(8)
1.503(10)
1.511(9)
1.309(8)
1.422(9)
1.399(10)
1.331(9)
1.510(9)
3.044(5)
3.131(57)
3.118(5)
3.053(4)
3.103(56)
3.086(6)
1.524(7)
1.312(7)
1.419(8)
1.410(7)
1.332(6)
1.508(7)
1.522(7)
1.310(7)
1.426(8)
1.425(8)
1.337(6)
1.520(7)
N(1)–C(2)
C(2)–C(3)
C(3)–C(4)
N(2)–C(4)
N(1)–C(2)
C(2)–C(3)
C(3)–C(4)
N(2)–C(4)
C(4)–C(5)
C(4)–C(5)
C(24)–C(25)
N(3)–C(25)
C(25)–C(26)
C(26)–C(27)
N(4)–C(27)
C(27)–C(28)
C(30)–C(31)
N(3)–C(31)
C(31)–C(32)
C(32)–C(33)
N(4)–C(33)
C(33)–C(34)
Bond angles
Bond angles
N(2)–Eu (1)–N(4)
N(2)–Eu(1)–N(1)
N(4)–Eu(1)–N(1)
N(2)–Eu(1)–N(3)
N(4)–Eu(1)–N(3)
N(1)–Eu(1)–N(3)
(N–Eu–N)av.
115.00(14)
75.44(13)
118.11(14)
115.33(14)
73.95(14)
160.08(13)
109.65(14)
105.64(18)
75.39(18)
121.35(19)
133.27(18)
74.53(18)
145.55(18)
109.29(18)
N(2)–Eu (1)–N(4)
N(2)–Eu(1)–N(1)
N(4)–Eu(1)–N(1)
N(2)–Eu(1)–N(3)
N(4)–Eu(1)–N(3)
N(1)–Eu(1)–N(3)
(N–Eu–N)av.
137.55(14)
76.52(13)
122.69(14)
122.41(13)
77.74(14)
128.37(14)
110.88(14)
Preparation
6-ipr
L2,
PhH. To a mixture of 2, 6-diisopropyl-aniline
(100 mmol) and acetylacetone (100 mmol) in toluene (150 mL)
was added p-toluenesulfonic acid (0.3 g). The reaction mixture
was refluxed for 24 h to remove water by the oil–water separator,
and then cooled to ambient temperature. Removing toluene led
to a precipitate and then PhNH3Cl (100 mol) and EtOH
(150 mL) were added. The resulting solution was refluxed for
24 h, and then cooled to ambient temperature. The undissolved
portion was removed by filtration and the yellow solution was
evaporated to dryness. The residue was treated with ether
(150 mL) and a saturated aqueous solution of Na2CO3. The
mixture was stirred for 4 h, and then extracted with ether
(30 mL) 3 times. The combined organic layers were dried with
MgSO4, and then the solvent was evaporated. The residue was
dissolved in a small amount of n-hexane to afford a yellow
Scheme 3 The possible mechanism for the reduction pathway.
Experimental Section
General Procedures
All manipulations were performed under a purified argon
atmosphere using standard Schlenk techniques. The proligands
4,
L2,
6-Me3H and L2, 6-ipr2H were prepared by the published
solution. Crystallization at −20 °C gave colorless crystals of
method.4 Anhydrous LnCl3 was prepared according to the litera-
ture procedure.13 Lanthanide analyses were performed by ethy-
lenediaminetetraacetic acid (EDTA) titration with a xylenol
orange indicator and a hexamine buffer.14 Solvents were
degassed and distilled from sodium benzophenone ketyl before
use. Element analyses were performed by direct combustion
using a CarloErba EA-1110 instrument. The IR spectra were
recorded with a Nicolet-550 FTIR spectrometer as KBr pellets.
The uncorrected melting points of crystalline samples were
determined in a sealed Ar-filled capillary.
6-ipr
L2,
PhH. Yield: 7.73 g (23.1%). m.p. 87.5–88.3 °C
1
(decomp.). HNMR (300 MHz, CDCl3) δ = 12.65 (1 H, s, NH),
7.21 (2 H, d, J 8.6, ArH), 7.08 (3 H, s, ArH), 6.97 (1H, t, J =
7.4 Hz, ArH), 6.89 (2 H, d, J = 7.4 Hz ArH), 4.83 (1 H, s, CH),
2.95 (2 H, dt, J 13.7, 6.9, CH-(CH3)2), 2.02 (3 H, s, CH3-
CvN), 1.65 (3 H, s, CH3-CvN), 1.12 (12 H, dd, J 22.1, 6.9,
CH-(CH3)2).13C NMR (101 MHz, CDCl3) δ = 163.37 (CvN),
157.87 (CvN), 145.31 (Ar), 143.01 (Ar), 141.66 (Ar), 129.48
(Ar), 125.25 (Ar), 123.64 (Ar), 123.19 (Ar), 120.52 (Ar), 96.53
(C(N)-CH-C(N)), 28.98 (CH-(CH3)2), 24.89 (CH3-CvN), 23.37
3672 | Dalton Trans., 2012, 41, 3668–3674
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(CH3-CvN), 21.72 (CH-(CH3)2), 21.48 (CH-(CH3)2).
C23H30N2 (334.49): calcd. C, 82.59; H, 9.04; N, 8.37; found C,
82.37; H, 9.17; N, 8.46. IR(KBr): 3059 (w), 2961 (w), 2919 (w),
2864 (w), 1937(w), 1870 (w), 1801(w),1738(w), 1629 (s), 1553
(s), 1485 (w), 1361 (m), 1273 (m), 1175 (m), 1175 (s), 1101
(w), 1022 (w), 801 (s), 791 (s), 751 (s), 696 (m), 597 (w), 507
concentrated and 3 mL n-hexane was added. Pale-yellow crystals
of 6 were obtained at −20 °C after several days.
X-ray Crystallography
Suitable single crystals of compounds 1–6 were sealed in a thin-
walled glass capillary, respectively, for determining the single-
crystal structure. Intensity data were collected with a Rigaku
Mercury CCD area detector in ω scan mode by using Mo-Kα
radiation (λ = 0.71075 Å). The diffracted intensities were cor-
rected for Lorentz polarization effects and empirical absorption.
Details of the intensity data collection and crystal data are given
in Table 1. The structures were solved by direct methods and
refined by full-matrix least-squares procedures based on |F|2. All
the non-hydrogen atoms were refined anisotropically. The hydro-
gen atoms in these complexes were all generated geometrically
(C–H bond lengths fixed at 0.95 Å), assigned appropriate iso-
tropic thermal parameters, and allowed to ride on their parent
carbon atoms. All the H atoms were held stationary and included
in the structure factor calculation in the final stage of full-matrix
least-squares refinement. The structures were solved and refined
by using SHELEXL-97 program. CCDC 843447 (for 1),
843448 (for 2), 843449 (for 3), 843450 (for 4), 843451 (for 5)
and 843452 (for 6) are contained in the supplementary crystallo-
graphic data for this paper.† These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_ request/cif
(w), 424(m) cm−1
.
4,
4, 6-Me3
Eu(L2,
6-Me3)2(THF) (1) and (L2,
) ·C6H14 (3). A
2
THF solution of NaL2, 4, 6-Me3 (26.6 mL, 0.489 M) which was
formed by reaction of L2, 4, 6-Me3H with NaH in THF was added
to a slurry of anhydrous EuCl3 (1.12 g, 4.34 mmol) in THF
(about 20 mL) at room temperature. The reaction mixture was
stirred at 60 °C for 24 h. After the undissolved portion was
removed by centrifugation, the red solution was concentrated to
dry then about 0.5 mL THF and 6 mL n-hexane were added.
Crystallization at room temperature afforded red crystals 1
(2.59 g, 67%). C50H66EuN4O (891.03): calcd. C 67.40, H 7.47,
N 6.29, Eu 17.05; found C 66.88, H 7.33, N 6.67, Eu 17.43. m.
p. 109.1–111.5 °C (decomp.). IR (KBr): 2916 (m), 2856 (w),
2727 (w), 1623 (s), 1552 (s), 1476 (s), 1433 (w), 1274 (m),
1187 (m), 1146 (m), 1027 (w), 853 (s), 795 (w), 598 (w), 563
(w), 492 (w) cm−1. After the isolation of complex 1 was com-
plete, the mother liquid of reaction was concentrated and 4 mL
n-hexane was added. Pale-yellow microcrystals of 3 were
obtained at −20 °C after several days.
6-ipr2
Eu(L2, 6-ipr2)2·CH3C6H5 (2) and (L2,
) (4). These were
2
obtained by the same procedure as that for complex 1, except
that EuCl3 (0.81 g, 3.14 mmol) and NaL2, 6-ipr2 (16.8 mL, 0.561
M), which was formed by reaction of L2, 6-ipr2H with NaH in
THF, were used. Complex 2 was first crystallized from a toluene
(3 mL) solution. However, no crystals could be obtained. Thus,
the toluene was evaporated to oil, into which was added a
mixture of 0.5 mL THF and 4 mL n-hexane. Crystallization at
room temperature afforded red crystals 2 (1.39 g, 41%).
C58H82N4Eu·C7H8 (1079.37): calcd. C 72.33, H 8.40, N 5.19,
Eu 14.08; found C 71.35, H 8.46, N 5.89, Eu 14.56. m.
p. 111.1–130.2 °C. IR (KBr): 3060 (w), 2961 (s), 2927 (m),
2868 (m), 1660 (m), 1622 (s), 1550 (s), 1462 (m), 1439 (m),
1381 (m), 1362 (m), 1276 (m), 1175 (m), 1057 (m), 934 (w),
788 (m), 759 (m), 696 (w), 599 (w), 429 (w) cm−1. After the iso-
lation of complex 2 was complete, the mother liquid of reaction
was concentrated and 10 mL n-hexane was added. Pale-yellow
microcrystals of 4 were obtained at −20 °C after several days.
Acknowledgements
We are grateful to the National Natural Science Foundation of
China (Grants 21132002 and 20972107) for financial support.
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