Syntheses, Structures, and Catalytic Activities of the Anionic Heterobimetallic Rare-Earth Metal Complexes Supported by Pyrrolyl-Substituted 1,2-Diimino Ligands

Article abstract of DOI:10.1021/acs.inorgchem.8b01556

A series of the anionic heterobimetallic rare-earth metal complexes supported by trans- or chiral pyrrolyl-substituted 1,2-diimino ligands were synthesized in good yields via reactions of [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)_3<

Full text of DOI:10.1021/acs.inorgchem.8b01556

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Syntheses, Structures, and Catalytic Activities of the Anionic
Heterobimetallic Rare-Earth Metal Complexes Supported by
Pyrrolyl-Substituted 1,2-Diimino Ligands
Wei Wang,† Xiaojia Wang,† Shuangliu Zhou,*,† Xiaolong Xu,† Jun Du,† Lijun Zhang,† Xiaolong Mu,†
Yun Wei,† Xiancui Zhu,† and Shaowu Wang*,†,‡
†Laboratory of Functionalized Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials (State Key
Laboratory Cultivation Base), 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: A series of the anionic heterobimetallic rare-earth metal complexes supported by trans- or chiral pyrrolyl-
substituted 1,2-diimino ligands were synthesized in good yields via reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with the
corresponding 1,2-diimino proligands. Reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 2 equiv of trans-1,2-bis(pyrrol-2-
ylmethylene)-1,2-diphenylethanediamine (H2L1) afforded the discrete ion-pair rare-earth metal complexes [Li-
(THF)4]+[(L1)2RE]− (RE = Sm(5), Dy(6), Er(7)). Reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 2 equiv of (R,R)-
1,2-bis(pyrrol-2-ylmethylene)-1,2-diphenylethanediamine (H2L2) gave the heterobimetallic rare-earth metal complexes
(L2)2RELi(THF)2 (RE = Sm(8), Y(9)). When the rare-earth metal is Er, the chiral linear rare-earth coordination polymer
{(L2)2ErLi}n (10) was obtained. Reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 2 equiv of trans-1,2-bis(pyrrol-2-
ylmethyleneamino)cyclohexane (H2L3) gave the heterobimetallic rare-earth metal complexes (L3)2RELi(THF)2 (RE = Pr (11),
Sm(12), Eu(13)). Reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 2 equiv of (R,R)-1,2-bis(pyrrol-2-ylmethyleneamino)-
cyclohexane (H2L4) also gave the heterobimetallic rare-earth metal complexes (L4)2RELi(THF)2 (Ln = Pr(14), Sm(15)). All
complexes were characterized by spectroscopic methods and elemental analyses, and complexes 5−11, 13, and 14 were further
determined by single-crystal X-ray diffraction. The catalytic properties of racemic rare-earth metal complexes on cyanosilylation
of ketones were examined, and results showed that the above complexes could effectively catalyze the cyanosilylation of ketones.
Chiral rare-earth metal complexes as catalysts for the enantioselective epoxidation of α,β-unsaturated ketones were also
examined to afford the chiral epoxides in high yields with moderate enantioselectivities.
ligands,6 bisphenolate and binaphtholates,7 binaphthylamido
ligands,8 phenoxy-amidinate ligands,9 etc. have proved to be
INTRODUCTION
■
Heterobimetallic rare-earth metal alkylaluminate complexes
have attracted wide attention as the efficient olefin polymer-
ization catalysts due to their similarity to Ziegler−Natta
systems.1 Though rare-earth metal heterobimetallic complexes
bearing Group 1 metals such as lithium and potassium have
also been developed for various transformation,2 the system-
atically synthetic method for this type of heterobimetallic
complexes needs to be developed. Dianionic ligands, such as
the chelating diamido ligands,3 boraamidinate,4 bis(allyl)-
silane,5 linked amido-cyclopentadienyl or indenyl-pyrrolyl
particularly useful in the formation of heterobimetallic
lanthanide complexes. Salen-type Schiff-base ligands also
have a tendency to form the heterobimetallic lanthanide
complexes, especially, when the backbone of Salen ligand was
chiral diamine, the resulting chiral rare-earth metal complexes
Received: June 10, 2018
© XXXX American Chemical Society
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DOI: 10.1021/acs.inorgchem.8b01556
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Scheme 1. Synthesis of Complexes 5−7
Scheme 2. Synthesis of Complexes 8−10
Scheme 3. Synthesis of Complexes 11−13
exhibited the good catalytic activities for asymmetric trans-
formation or stereoselective polymerization.10
complexes containing pyrrolyl-substituted diimino ligands, as
expected, the anionic heterobimetallic rare-earth metal
complexes were obtained. Their catalytic activities in the
cyanosilylation of ketones and the enantioselective epoxidation
of chalcones will also be reported.
Pyrrolyl-substituted Schiff-base ligands have widely been
applied to organolanthanide chemistry;11 however, hetero-
bimetallic rare-earth metal complexes containing pyrrolyl-
substituted diimino ligands still needs to be developed.12
Pyrrolyl-substituted 1,1′-bi-2-naphthylamino rare-earth metal
complexes have been studied as catalysts for asymmetric
hydroamination of alkenes.12a The heterobimetallic rare-earth
metal and uranium complexes bearing a binucleating
polypyrrole Schiff-base ligand showed magnetic bistability at
3 K, a property required for the development of single-
molecule magnets.12d Anionic heterobimetallic rare-earth metal
complexes supported by a pyrrole-based substituted diimino
ligand have been demonstrated as catalysts toward the
polymerization of ε-caprolactone.12c Herein, we will report
the preparation and characterization of the rare-earth metal
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The trans- or chiral
pyrrolyl-substituted 1,2-diimines H2L1−H2L4 were synthesized
through condensation of pyrrole-2-carboxyaldehyde with the
corresponding trans- or chiral 1,2-diamino ligands under a
catalytic amount of TsOH according to the published
procedure.13 Reaction of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3
with 2 equiv of H2L1 afforded the discrete ion-pair
heterobimetallic rare-earth metal complexes [Li-
(THF)4]+[(L1)2RE]− (RE = Sm(5), Dy(6), Er(7)) (Scheme
1). However, reaction of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3
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DOI: 10.1021/acs.inorgchem.8b01556
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Scheme 4. Synthesis of Complexes 14 and 15
with 2 equiv of H2L2 gave the chiral heterobimetallic rare-earth
metal complexes (L2)2RELi(THF)2 (RE = Sm(8), Y(9))
(Scheme 2). It is noteworthy that the chiral linear rare-earth
coordination polymer {(L2)2ErLi}n (10) was obtained when
rare-earth metal is Er (Scheme 2). Reactions of
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 2 equiv of H2L3,
different from pyrrolyl-substituted trans-1,2-diphenylethylene-
diamine, gave the heterobimetallic rare-earth metal complexes
(L3)2RELi(THF)2 (RE = Pr(11), Sm(12), Eu(13)) (Scheme
3). Reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 2 equiv
of H2L4 gave the chiral heterobimetallic rare-earth complexes
(L4)2RELi(THF)2 (RE = Pr(14), Sm(15)) (Scheme 4).
Complexes 5−15 are extremely sensitive to air and moisture.
They are soluble in THF and toluene and slightly soluble in n-
hexane. All complexes were fully characterized by spectro-
scopic methods and elemental analyses. The structures of
complexes 5−11, 13, and 14 were further determined by
single-crystal X-ray analyses.
The molecular structures of complexes 5−11, 13, and 14
were determined by the single-crystal X-ray diffraction. As
expected, a series of the anionic heterobimetallic rare-earth
metal complexes were obtained. X-ray analyses revealed that
complexes 5−7 were isostructural discrete ion-pair rare-earth
metal complexes, and a representative structure diagram of
complex 6 is shown in Figure 1. Chiral complexes 8 and 9 were
heterobimetallic rare-earth metal complexes, and a representa-
tive structure diagram of complex 9 is shown in Figure 2.
Complex 10 was the chiral linear rare-earth metal coordination
Figure 2. Representative molecular structure of complex 9. Hydrogen
atoms are omitted for clarity.
polymer, and the structure diagram is shown in Figure 3. Rare-
earth metal complexes 11 and 13 containing trans-1,2-
bis(pyrrol-2-ylmethyleneamino)cyclohexane were isostructural
heterobimetallic rare-earth metal complexes, and a representa-
tive structure diagram of complex 11 is shown in Figure 4. The
corresponding chiral complex 14 (Figure 5) was also
heterobimetallic rare-earth metal complex. The selected bond
distances and angles are listed in Tables 1 and 2.
X-ray analyses revealed that each RE3+ is bound to four
nitrogen atoms from the two ligands which are perpendicular
to each other, and the Li ion adopts tetrahedral geometry.
From Tables 1 and 2, the average RE(1)−N bond distances
are also consistent with the trend in ionic radius of the
corresponding elements. The average RE(1)−N bond length
in discrete ion-pair rare-earth metal complexes was slightly
shorter than those in the heterobimetallic rare-earth metal
complexes, for example, Sm(1)−Nav of 2.529(5) Å in complex
5 vs 2.537(4) Å in complex 8 and Er(1)−Nav of 2.466(8) Å in
complex 7 vs 2.473(4) Å in complex 10. These RE−N bond
lengths are also comparable with the RE−N bond length in the
reported (R)-bis(pyrrol-2-ylmethyleneamino)-1,1′-binaphthyl
rare-earth metal complexes.12a,b
X-ray analyses revealed that the coordination modes
between lithium and pyrrolyl group were affected by different
rare-earth metals and ligands. In complexes 8 and 9, two
pyrrolyl groups coordinated to lithium in η2-modes. In
complex 10, one pyrrolyl group coordinated to lithium in η2-
Figure 1. Representative molecular structure of complex 6. Hydrogen
atoms are omitted for clarity.
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DOI: 10.1021/acs.inorgchem.8b01556
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Figure 3. Molecular structure of complex 10. Hydrogen atoms are omitted for clarity.
Figure 5. Molecular structure of complex 14. Hydrogen atoms are
omitted for clarity.
Figure 4. Representative molecular structure of complex 11.
Hydrogen atoms are omitted for clarity.
These differences may be owing to the different coordination
modes caused by the direct incorporation of Li ions in the
latter.
modes, and the other coordinated to lithium in η5-modes. In
complexes 11, 13, and 14, two pyrrolyl groups coordinated to
lithium in η1-modes. From bond angles of complexes in Tables
1 and 2, the sums of N(1)−RE(1)−N(2), N(2)−RE(1)−
N(3), N(3)−RE(1)−N(4), and N(1)−RE(1)−N(4) in
discrete ion-pair complexes 5−7 were 359.71°−360.14°,
indicating that the atoms of Er(1) and N(1)−N(4) are nearly
planar, which were further demonstrated by rms deviation of
fitted atoms of Er(1) and N(1)−N(4) from the corresponding
least-squares planes being less than 0.070 as are the atoms of
Er(1) and N(5)−N(8). However, in heterobimetallic com-
plexes 8−11, 13, and 14, the sums of N(1)−RE(1)−N(2),
N(2)−RE(1)−N(3), N(3)−RE(1)−N(4), and N(1)−
RE(1)−N(4) deviate farther from 360° degrees, indicating
that the atoms of N(1)−N(4) or N(5)−N(8) were slightly
distorted in the heterobimetallic rare-earth metal complexes.
Catalytic Additions of Trimethylsilyl Cyanide to
Ketones. Rare-earth metal complexes as catalysts for the
addition or enantioselective addition of Me3SiCN to carbonyl
compounds have been developed.14 Recently, rare-earth-
polyoxometalates as Lewis acid−base catalysts have also
showed great potential for cyanosilylation of carbonyl
compounds.15 Herein, the above heterobimetallic complexes
supported by trans- or chiral pyrrolyl-substituted 1,2-diimino
ligands were examined for the addition or enantioselective
addition of Me3SiCN to ketones. The enantioselective addition
of Me3SiCN to acetophenone was first investigated as the
template reaction in the presence of 1 mol % of rare-earth
metal complexes supported by chiral pyrrolyl-substituted 1,2-
diimino ligands. The reactions underwent rapidly to provide
D
DOI: 10.1021/acs.inorgchem.8b01556
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Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) of Complexes 5−10
5 (Sm)
6 (Dy)
7 (Er)
8 (Sm)
9 (Y)
10 (Er)
RE(1)−N(1)
RE(1)−N(2)
RE(1)−N(3)
RE(1)−N(4)
RE(1)−N(5)
RE(1)−N(6)
RE(1)−N(7)
RE(1)−N(8)
RE(1)−Nav
Li(1)−N(3)
Li(1)−N(8)
Li(1)−C(16)
Li(1)−C(17)
Li(1)−C(18)
Li(1)−C(19)
Li(1)−C(48)
Li(1)−C(45)
Li(1)−C(22)#A
Li(1)−C(23)#A
Li(1)−O(1)
Li(1)−O(2)
Li(1)−O(3)
Li(1)−O(4)
2.541(5)
2.541(4)
2.503(5)
2.509(5)
2.555(5)
2.561(5)
2.512(5)
2.509(5)
2.529(5)
2.506(6)
2.509(6)
2.462(6)
2.452(5)
2.508(7)
2.499(6)
2.472(7)
2.474(7)
2.485(7)
2.500(7)
2.506(6)
2.427(6)
2.429(5)
2.487(7)
2.500(6)
2.442(7)
2.436(7)
2.466(7)
2.530(4)
2.525(4)
2.570(5)
2.490(4)
2.537(5)
2.549(4)
2.484(5)
2.607(4)
2.537(5)
2.171(9)
2.138(8)
2.511(10)
2.530(12)
2.578(11)
2.504(11)
2.511(10)
2.516(10)
2.474(12)
2.526(12)
2.519(12)
2.15(3)
2.492(4)
2.518(4)
2.442(4)
2.465(4)
2.499(4)
2.466(4)
2.395(4)
2.506(4)
2.473(4)
2.152(11)
2.231(12)
2.302(12)
2.549(12)
2.532(12)
2.292(12)
2.20(3)
2.776(12)
2.754(11)
2.71(3)
2.80(3)
2.765(13)
2.338(11)
2.623(12)
1.88(2)
1.90(2)
1.89(2)
1.94(2)
1.85(3)
1.97(3)
1.89(3)
1.87(3)
1.92(3)
1.84(3)
1.85(3)
1.93(3)
1.968(12)
1.987(12)
2.01(3)
1.91(3)
N(1)−RE(1)−N(2)
N(2)−RE(1)−N(3)
N(3)−RE(1)−N(4)
N(4)−RE(1)−N(1)
N(5)−RE(1)−N(6)
N(6)−RE(1)−N(7)
N(7)−RE(1)−N(8)
N(5)−RE(1)−N(8)
62.19(15)
66.76(15)
164.32(16)
66.44(16)
62.45(16)
66.22(14)
165.34(16)
66.13(17)
63.3(2)
66.3(2)
163.8(2)
66.7(2)
62.5(2)
67.8(2)
162.9(2)
66.6(2)
63.6(3)
67.5(2)
162.0(3)
67.0(3)
63.2(2)
67.5(3)
162.3(3)
67.0(3)
63.19(14)
65.68(14)
166.27(14)
66.62(14)
63.24(17)
66.90(17)
159.50(16)
65.50(15)
63.1(4)
66.7(4)
158.9(4)
67.0(4)
62.7(3)
67.2(3)
165.1(4)
66.4(3)
63.61(13)
67.54(14)
161.91(14)
67.50(13)
64.27(13)
69.92(14)
157.80(14)
66.04(14)
the cyanosilylation products in high yields, but unfortunately,
the products are almost racemic. Next, we examined rare-earth
metal complexes supported by trans-pyrrolyl-substituted 1,2-
diimino ligands, and optimizations of the catalytic activity were
listed in Table 3. The cyanosilylation of acetophenone could
be accomplished in various solvents at room temperature
within 4 h, affording the product in >90% yields with a 0.01
mol % catalyst loading (Table 3, entries 6−8). It was further
found that a high yield of product 17a could be also obtained
under solvent-free conditions using rare-earth metal complexes
5−7 and 11−13 as catalysts (Table 3, entries 9−14). Results
also showed that both the discrete ion-pair and hetero-
bimetallic rare-earth metal complexes are capable of catalyzing
the cyanosilylation of ketone under the mild conditions with
low catalyst loadings.
So, complex 5 or 12 was selected as the catalyst for the
following experiments to examine the scope of the
cyanosilylation reaction of ketones, and the results are
presented in Table 4. Results showed that various aromatic
ketones bearing either electron-donating (CH3, OMe) or
electron-withdrawing groups (Cl, Br, NO2) underwent
cyanosilylation to produce the expected products in good to
excellent yield (86−99%). It seems that the sterics of the
substrates have neglectable effect on the reaction (entries 2−3,
5−6, 8−10, and 11), further indicating the high efficiency of
the catalysts. Notably, aliphatic ketones, either cyclic or acyclic,
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg)
of Complexes 11, 13, and 14
11 (Pr)
13 (Eu)
14 (Pr)
RE(1)−N(1)
RE(1)−N(2)
RE(1)−N(3)
RE(1)−N(4)
RE(1)−N(5)
RE(1)−N(6)
RE(1)−N(7)
RE(1)−N(8)
RE(1)−Nav
Li(1)−N(4)
Li(1)−N(8)
Li(1)−O(1)
Li(1)−O(2)
2.548(3)
2.579(3)
2.623(3)
2.593(3)
2.538(3)
2.555(2)
2.619(2)
2.597(3)
2.582(3)
2.113(7)
2.111(7)
1.958(7)
1.989(7)
2.491(9)
2.532(9)
2.572(10)
2.530(9)
2.493(9)
2.496(9)
2.558(9)
2.534(9)
2.526(10)
2.14(2)
2.518(6)
2.575(5)
2.597(5)
2.623(6)
2.511(5)
2.589(5)
2.608(4)
2.653(5)
2.584(6)
2.109(13)
2.168(17)
1.963(12)
1.962(14)
2.11(2)
2.00(2)
1.97(2)
N(1)−RE(1)−N(2)
N(2)−RE(1)−N(3)
N(3)−RE(1)−N(4)
N(1)−RE(1)−N(4)
N(5)−RE(1)−N(6)
N(6)−RE(1)−N(7)
N(7)−RE(1)−N(8)
N(5)−RE(1)−N(8)
65.84(9)
61.79(9)
64.95(9)
157.29(9)
66.34(8)
62.27(8)
64.91(8)
158.41(9)
67.1(3)
63.0(3)
65.7(3)
156.0(3)
67.5(3)
63.2(3)
65.5(3)
157.1(3)
66.19(17)
62.70(17)
64.20(17)
167.35(17)
66.47(17)
61.89(15)
63.43(14)
162.79(18)
E
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a
enantioselective epoxidation of α,β-unsaturated ketones
afforded the chiral epoxides in good yields with moderate
enantioselectivities.
Table 3. Optimization of Cyanosilylation of Acetophenone
EXPERIMENTAL SECTION
■
General Remarks. All syntheses and manipulations of air- and
moisture-sensitive materials were performed under dry argon and
oxygen-free atmosphere using standard Schlenk techniques or in a
glovebox. Solvents were refluxed and distilled over sodium/
benzophenone under argon prior to use. [(Me3Si)2N]3RE(μ-Cl)Li-
(THF)3 (RE = Sm, Eu, Dy, Y, Er),17 trans-1,2-bis(pyrrol-2-
ylmethyleneamino)cyclohexane,13 and (R,R)-1,2-bis(pyrrol-2-
ylmethyleneamino)cyclohexane18 were prepared according to liter-
ature methods. IR spectra were recorded on a SHIMADZU FTIR-
b
entry catalyst loading (mol %) time (h)
solvent
toluene
toluene
toluene
toluene
toluene
toluene
Et2O
THF
solvent free
solvent free
solvent free
solvent free
solvent free
solvent free
yield (%)
1
2
7
7
1
1
0.5
1
74
85
92
97
95
95
92
97
97
99
98
97
99
96
3
7
1
2
4
7
0.1
4
5
6
7
8
7
7
7
7
7
5
6
11
12
13
0.05
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
4
4
4
4
4
4
4
3
1
8400S spectrometer. H NMR and 13C NMR spectra for analyses of
compounds were recorded on a Bruker AV-300 NMR or AV-500
NMR spectrometer in C6D6 for rare-earth complexes and in CDCl3
for organic compounds.
9
10
11
12
13
14
Synthesis of Compounds H2L1 or H2L2. Pyrrole-2-carbaldehyde
(1.90 g, 20 mmol) and either trans- or (R,R)-1,2-diphenylethylenedi-
amine (2.12 g, 10.0 mmol) were dissolved in ethanol (30.0 mL). The
mixture was stirred, and then a few drops of TsOH were added. After
the reaction mixture was stirred for 3 h, the precipitate obtained from
filtration was washed with hexane, dried in vacuum, and crystallized
from CH3CH2OH. Compound H21L1 (3.08 g, 84% yield) or H2L2
(2.93 g, 80% yield) was obtained. H NMR (500 MHz, CDCl3): δ
7.92 (s, 2H), 7.21−7.08 (m, 10H), 6.83 (s, 2H), 6.35−6.33 (m, 2H),
6.17−6.14 (m, 2H), 4.64 (s, 2H). 13C NMR (125 MHz, CDCl3): δ
152.5, 141.8, 130.3, 128.0, 126.9, 121.7, 114.5, 109.6, 80.3. HR-MS
(ESI) Calcd for C24H22N4 [M + H+]: 367.1917, found: 367.1913.
General Synthesis of [Li(THF)4]+[(L1)2RE]− (RE = Sm(5),
Dy(6), Er(7)). Under an argon atmosphere, an oven-dried 50.0 mL
Schlenk flask equipped with a magnetic stir bar was charged with the
compound H2L1 (0.44 g, 1.20 mmol), [(Me3Si)2N]3RE(μ-Cl)Li-
(THF)3 (0.60 mmol), and THF (30.0 mL) at room temperature.
After the reaction mixture was stirred at 60 °C for 12 h, the solvent
was evaporated under reduced pressure. The residue was washed with
n-hexane (10.0 mL), and the resulting solid was extracted with
toluene (2 × 15.0 mL). The extractions were combined and
concentrated to about 15.0 mL. The crystals were obtained by
cooling the concentrated solution at 0 °C for several days.
Complex 5. Pale yellow crystals (0.46 g, 65% yield). Mp 216−218
°C. IR (KBr pellets, cm−1): ν 3028 (w), 2976 (m), 2868 (m), 1631
(s), 1597 (m), 1489 (m), 1452 (m), 1392 (s), 1311 (s), 1267 (s),
1031 (s), 974 (s), 810 (m), 740 (s), 700 (s), 604 (m). Anal. Calcd for
C64H72N8O4SmLi: C, 65.44; H, 6.18; N, 9.54; Found: C, 65.78; H,
5.88; N, 9.66.
Complex 6. Colorless crystals (0.41 g, 58% yield). Mp 211−213
°C. IR (KBr pellets, cm−1): ν 3028 (w), 2968 (m), 2876 (m), 2360
(m), 2330 (m), 1629 (s), 1597 (s), 1497 (s), 1448 (s), 1390 (s),
1311 (m), 1031 (m), 974 (m), 889 (m), 806 (m), 738 (w), 700 (m),
613 (m). Anal. Calcd for C64H72N8O4DyLi: C, 64.77; H, 6.12; N,
9.44; Found: C, 64.98; H, 5.95; N, 9.56.
Complex 7. Pale yellow crystals (0.42 g, 59% yield). Mp 216−218
°C. IR (KBr pellets, cm−1): ν 3024 (w), 2968 (m), 2875 (m), 1631
(s), 1597 (s), 1489 (s), 1452 (s), 1433 (s), 1392 (s), 1311 (m), 1267
(m), 1180 (m), 1031 (s), 974 (m), 889 (m), 810 (m), 740 (m), 700
(m), 613 (m). Anal. Calcd for C64H72N8O4ErLi: C, 64.51; H, 6.09; N,
9.40; Found: C, 64.15; H, 5.78; N, 9.58.
General Synthesis of (L2)2RELi(THF)2 (RE = Sm(8), Y(9)).
Under an argon atmosphere, an oven-dried 50.0 mL Schlenk flask
equipped with a magnetic stir bar was charged with the compound
H2L2 (0.44 g, 1.20 mmol), [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (0.60
mmol), and THF (30.0 mL) at room temperature. After the reaction
mixture was stirred at 60 °C for 12 h, the solvent was evaporated
under reduced pressure. The residue was washed with n-hexane (10.0
mL), and the resulting solid was extracted with toluene (2 × 15.0
mL). The extractions were combined and concentrated to about 15.0
3
3
a
Conditions: acetophenone (5.0 mmol), Me3SiCN (6.0 mmol),
b
solvent (2.0 mL) or solvent free, room temperature. Isolated yields.
also afforded the cyanosilylation products in nearly quantitative
yields (entries 12−14).
Enantioselective Epoxidation of α,β-Unsaturated
Ketones. Despite the wealth of catalytic enantioselective
epoxidations of α,β-unsaturated ketones, rare-earth complexes
as catalysts still need to be further developed.7a Very recently, a
strategy for the enantioselective epoxidation of α,β-unsaturated
ketones employing a heterobimetallic rare-earth-lithium
complex bearing a phenoxy-functionalized diphenylprolinolate
ligand has been developed.16 So, we tested the heterobimetallic
rare-earth metal complexes for the enantioselective epoxidation
of chalcones, and results are listed in Table 5. Results showed
that the heterobimetallic rare-earth metal complexes supported
by a chiral pyrrolyl-substituted 1,2-diphenyldiimino ligand
were superior to those bearing a chiral pyrrolyl-substituted 1,2-
cyclohexanyl diimino ligand (entries 1−5, Table 5). The
moderate enantioselectivity of 57% ee was obtained by
employing complex 9 as catalyst (entry 2, Table 5). Further
optimizations revealed that lowering the temperature slightly
improved the enantioselectivity to 63% ee (entry 9, Table 5).
Next, complex 9 was selected as the catalyst for the
enantioselective epoxidation of α,β-unsaturated ketones
bearing halide, methyl, and methoxy groups, and the
corresponding products 19a−19e were obtained in moderate
enantioselectivities of 57−65% ee with good yields (entries 1−
5, Table 6).
CONCLUSION
■
In conclusion, a series of the anionic heterobimetallic rare-
earth metal complexes supported by trans- or chiral pyrrolyl-
substituted 1,2-diimino ligands were systematically synthesized
via reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with the
corresponding 1,2-diimino ligands. X-ray diffraction revealed
that they separately belonged to the two types of the discrete
ion-pair or heterobimetallic rare-earth metal complexes. The
racemic heterobimetallic rare-earth metal complexes showed
high catalytic activity for the cyanosilylation of ketones. Chiral
heterobimetallic rare-earth metal complexes as catalysts for the
F
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Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 4. Cyanosilylation of Various Ketones Catalyzed by Complex 5
a
b
c
Conditions: catalyst (0.0005 mmol), ketone (5.0 mmol), Me3SiCN (6.0 mmol), room temperature. Isolated yields. The yields were obtained
using complex 12 as catalyst, time: 3 h.
mL. The crystals were obtained by cooling the concentrated solution
at 0 °C for several days.
NMR (125 MHz, C6D6): δ 160.4, 158.4, 140.4, 136.9, 129.9, 127.6,
125.7, 119.6, 119.1, 111.9, 76.0, 74.3, 68.2, 25.4, 21.5. IR (KBr pellets,
cm−1): ν 3080 (w), 3028 (w), 2976 (m), 2876 (m), 2360 (w), 1616
(s), 1595 (m), 1431 (s), 1388 (s), 1267 (m), 1160 (m), 1031 (m),
972 (m), 893 (w), 806 (m), 700 (s), 609 (s). Anal. Calcd for
C56H56N8O2YLi: C, 69.42; H, 5.83; N, 11.56. Found: C, 69.92 ; H,
5.65; N, 11.08.
Complex 8. Pale yellow crystals (0.34 g, 55% yield). Mp 227−229
°C. IR (KBr pellets, cm−1): ν 3080 (w), 3021 (w), 2961 (m), 2876
(m), 2364 (w), 1624 (s), 1595 (m), 1497 (m), 1456 (m), 1433 (m),
1388 (s), 1118 (m), 1095 (m), 1033 (m), 1029 (m), 970 (m), 806
(m), 698 (s), 609 (s). Anal. Calcd for C56H56N8O2SmLi: C, 65.28; H,
5.48; N, 10.87; Found: C, 64.95; H, 5.95; N, 10.56.
Synthesis of {(L2)2ErLi}n (10). Complex 10 was prepared as pale
yellow crystals in a 52% yield from reaction of [(Me3Si)2N]3Er(μ-
Cl)Li(THF)3 (0.55 g, 0.60 mmol) with the compound H2L2 (0.44 g,
1.20 mmol) by employing the procedures similar to those used for
Complex 9. Colorless crystals (0.37 g, 64% yield). Mp 236−238
1
°C. H NMR (500 MHz, C6D6): δ 7.86 (m, 8H), 7.27−6.87 (m,
20H), 6.58 (m, 8H), 5.70 (m, 4H), 3.05 (m, 8H), 1.10 (m, 8H). 13C
G
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Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
concentrated to about 15.0 mL. The crystals were obtained by
cooling the concentrated solution at 0 °C for several days.
Complex 11. Colorless crystals (0.46 g, 76%). Mp 214−216 °C. IR
(KBr pellets, cm−1): ν 2933 (w), 1583 (s), 1416 (m), 1313 (m), 1043
(m), 885 (s), 838 (w), 745 (m), 625 (s). Anal. Calcd for
C40H52N8O2PrLi·0.5C7H8: C, 60.00; H, 6.48; N, 12.87. Found: C,
60.35; H, 6.47; N, 12.52.
Table 5. Optimization of the Enantioselective Epoxidation
of α,β-Unsaturated Ketone
a
Complex 12. Colorless crystals (0.61 g, 83%). Mp 222−223 °C. IR
(KBr pellets, cm−1): ν 2849 (w), 1629 (s), 1425 (m), 1388 (m), 1304
(w), 1072 (m), 1043 (s), 745 (m), 606 (m). Anal. Calcd for
C40H52N8O2SmLi·C7H8: C, 60.94; H, 6.53; N, 12.11. Found: C,
61.01; H, 6.77; N, 12.36.
c
entry catalyst temp (°C)
solvent
time (h) yield (%) ee (%)
1
2
3
4
5
6
7
8
9
8
9
10
14
15
9
9
9
9
0
0
0
0
0
0
0
−20
−40
THF
THF
THF
THF
6
6
6
10
4
10
10
6
87
89
84
88
95
85
70
74
65
53
57
39
11
13
8
6
61
63
Complex 13. Pale yellow crystals (0.73 g, 78%). Mp 215−217 °C.
IR (KBr pellets, cm−1): ν 2849 (w), 1593 (s), 1416 (s), 1304 (s),
1136 (m), 1034 (m), 745 (m), 615 (m). Anal. Calcd for
C40H52N8O2EuLi·C7H8: C, 60.83; H, 6.52; N, 12.08. Found: C,
60.91; H, 6.68; N, 12.05.
THF
toluene
CH3CN
THF
General Synthesis of (L4)2RE−Li+(THF)2 (RE = Pr(14), Sm(15)).
Complexes 14 and 15 were prepared from reactions of
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (0.60 mmol) with the compound
H2L4 (0.32 g, 1.20 mmol) by employing the procedures similar to
those used for preparation of complexes 11−13.
THF
6
a
Conditions: catalyst (0.1 mmol), chalcone (1.0 mmol), TBHP (tert-
butyl hydroperoxide) (1.2 mmol), solvent (2.0 mL). Isolated yields.
Enantiomeric excess was determined by the HPLC analysis by using
b
c
Complex 14. Colorless crystals (0.66 g, 63% yield). Mp 202−204
°C. IR (KBr pellets, cm−1): ν 2867 (w), 1651 (s), 1414 (s), 1370 (m),
1028 (m), 761 (m), 584 (m). Anal. Calcd for C40H52N8O2PrLi: C,
58.25; H, 6.36; N, 13.59. Found: C, 57.85; H, 6.08; N, 13.35.
Complex 15. Colorless crystals (0.34 g, 46% yield). Mp 211−214
°C. IR (KBr pellets, cm−1): ν 2845 (s), 1616 (s), 1304 (m), 1417
(m), 1035 (m), 725 (s), 612 (m). Anal. Calcd for C40H52LiN8O2Sm:
C, 57.59; H, 6.28; N, 13.43. Found: C, 57.28; H, 6.31; N, 13.23.
Crystal Structure Determinations. A suitable crystal of
complexes 5−11, 13, and 14 was each mounted in a sealed capillary.
Diffraction was performed on a Bruker SMART CCD area detector
diffractometer using graphite-monochromated Mo−Kα radiation (λ =
0.71073 Å). An empirical absorption correction was applied using the
SADABS program. All structures were solved by direct methods,
completed by subsequent difference Fourier syntheses and refined
anisotropically for all non-hydrogen atoms by full-matrix least-squares
calculations on F2 using the SHELXTL program package. All
the chiral column.
preparation of complexes 8 and 9. Mp 215−217 °C. IR (KBr pellets,
cm−1): ν 3088 (m), 3028 (m), 2968 (m), 2884 (m), 2360 (w), 1620
(s), 1598 (s), 1493 (m), 1452 (m), 1437 (m), 1390 (s), 1311 (s),
1029 (m), 893 (m), 810 (m), 700 (s), 609 (s). Anal. Calcd for
C48H40N8ErLi: C, 64.52; H, 5.41; N, 11.15; Found: C, 64.17; H, 5.47;
N, 10.85.
General Synthesis of (L3)2RELi(THF)2 (RE = Pr(11), Sm(12),
Eu(13)). Under an argon atmosphere, an oven-dried 50.0 mL Schlenk
flask equipped with a magnetic stir bar was charged with the
compound H2L3 (0.32 g, 1.20 mmol), [(Me3Si)2N]3RE(μ-Cl)Li-
(THF)3 (0.60 mmol), and THF (30.0 mL) at room temperature.
After the reaction mixture was stirred at 60 °C for 12 h, the solvent
was evaporated under reduced pressure. The residue was washed with
n-hexane (10.0 mL), and the resulting solid was extracted with
toluene (2 × 15.0 mL). The extractions were combined and
a
Table 6. Epoxidation of α,β-Unsaturated Ketones Catalyzed by Complex 9
a
b
c
Conditions: complex 9 (0.1 mmol), chalcone (1.0 mmol), TBHP (1.2 mmol), THF (2.0 mL). Isolated yields. Enantiomeric excess was
determined by the HPLC analysis by using the chiral column.
H
DOI: 10.1021/acs.inorgchem.8b01556
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
hydrogen atoms were refined using a riding model. See the
Supporting Information for crystallographic parameters and data
collection and refinement information.
J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood, J. L.; Hunter,
W. E. Alkyl-bridged complexes of the D- and F-block elements. Part 2.
Bis[bis(η-cyclopentadienyl)methylmetal(III)] complexes, and the
crystal and molecular structure of the yttrium and ytterbium species.
J. Chem. Soc., Dalton Trans. 1979, 45−53. (c) Evans, W. J.;
Chamberlain, L. R.; Ziller, J. W. Reactivity of trimethylaluminum
with (C5Me5)2Sm(THF)2: synthesis, structure, and reactivity of the
samarium methyl complexes (C5Me5)2Sm[(μ-Me)AlMe2(μ-
Me)]2Sm(C5Me5)2 and (C5Me5)2SmMe(THF). J. Am. Chem. Soc.
1988, 110, 6423−6432. (d) Klimpel, M. G.; Eppinger, J.; Sirsch, P.;
Scherer, W.; Anwander, R. The Lanthanide Ziegler-Natta Model:
Aluminum-Mediated Chain Transfer. Organometallics 2002, 21,
4021−4023. (e) Fischbach, A.; Perdih, F.; Sirsch, P.; Scherer, W.;
Anwander, R. Rare-Earth Ziegler-Natta Catalysts: Carboxylate-Alkyl
Interchange. Organometallics 2002, 21, 4569−4571. (f) Dietrich, H.
General Experimental Procedure for Cyanosilylation of
Ketones. Under an argon atmosphere, an oven-dried 20.0 mL
Schlenk flask equipped with a magnetic stir bar was charged with
complex 9 (3.86 mg, 0.0005 mmol), acetophenone (0.58 mL, 5
mmol), and Me3SiCN (0.75 mL, 6 mmol), and the resulting mixture
was stirred under solvent-free conditions for 4 h. At completion, the
crude product was purified by column chromatography on silica gel
using ethyl acetate/petroleum ether (1/20, V/V) as the eluent. The
desired 2-trimethylsilyloxy-2-phenylpropanenitrile was obtained as a
colorless oil (1.08 g, 99% yield).
General Procedure for the Catalytic Asymmetric Epoxida-
tion of α,β-Unsaturated Ketones. Under an argon atmosphere, an
oven-dried 20.0 mL Schlenk flask equipped with a magnetic stir bar
was charged with catalyst (0.1 mmol), α,β-unsaturated ketone (1.0
mmol), and THF (2.0 mL). The mixture was stirred at room
temperature for 5 min, and then the TBHP (1.2 mmol, 0.22 mL) was
added in the above solution. The reaction system was stirred for a
further 6 h at room temperature and quenched by a Na2SO3 aqueous
solution. The crude product was purified by column chromatography
(ethyl acetate/hexane, 1:10) to obtain the final epoxide product. The
enantiomeric excess of epoxides was determined by chiral HPLC
analysis.
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M.; Grove, H.; Tornroos, K. W.; Anwander, R. Multiple C−H Bond
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ASSOCIATED CONTENT
* Supporting Information
■
S
̈
Tornroos, K. W.; Anwander, R. Bis(tetramethylaluminate) Complexes
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01556.
of Yttrium and Lanthanum Supported by a Quinolyl-Substituted
Cyclopentadienyl Ligand: Synthesis and Performance in Isoprene
Polymerization. Organometallics 2010, 29, 2588−2595. (k) Hamidi,
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S.; Jende, L. N.; Dietrich, H. M.; Maichle-Mossmer, C.; Tornroos, K.
W.; Deacon, G. B.; Junk, P. C.; Anwander, R. C−H Bond Activation
and Isoprene Polymerization by Rare-Earth-Metal Tetramethylalumi-
nate Complexes Bearing Formamidinato N-Ancillary Ligands.
Organometallics 2013, 32, 1209−1223. (l) Dettenrieder, N.;
Full experimental details, characterization data for
compounds 17 and 19, crystallographic data and
refinements for complexes 5−11, 13, and 14 (PDF)
Accession Codes
̈
Hollfelder, C. O.; Jende, L. N.; Maichle-Mossmer, C.; Anwander, R.
CCDC 1846325−1846333 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Half-Sandwich Rare-Earth-Metal Alkylaluminate Complexes Bearing
Peripheral Boryl Ligands. Organometallics 2014, 33, 1528−1531.
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Muller, J.; Bruncks, N.; Lauke, H.; Pickardt, J.; Schwarz, H.; Eckart, K.
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[(tetramethylethylenediamine)lithium] hexamethyl derivatives of the
rare earths. Organometallics 1984, 3, 69−74. (c) Clark, D. L.; Gordon,
J. C.; Huffman, J. C.; Vincent-Hollis, R. L.; Watkin, J. G.; Zwick, B. D.
Preparation and X-ray Structures of K[Ln(O-2,6-i-Pr2C6H3)4] (Ln =
La, Nd, Er). Extended Chain Structures of Lanthanide Tetrakis-
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: slzhou@ahnu.edu.cn (S.Z.).
*E-mail: swwang@ahnu.edu.cn (S.W.).
ORCID
Shuangliu Zhou: 0000-0002-0103-294X
Shaowu Wang: 0000-0003-1083-1468
Notes
■
37, 832. (e) Noss, H.; Oberthur, M.; Fischer, C.; Kretschmer, W. P.;
̈
The authors declare no competing financial interest.
Kempe, R. Complexes of group 3 metals and lanthanides that contain
siloxane-bridged bisaminopyridinato ligands: Synthesis, structure, and
application in the ring-opening polymerization of lactones. Eur. J.
Inorg. Chem. 1999, 1999, 2283. (f) Kempe, R.; Noss, H.; Irrgang, T.
Towards f and d electron interactions in amido metal complexes. J.
Organomet. Chem. 2002, 647, 12−20. (g) Collin, J.; Daran, J. C.;
Schulz, E.; Trifonov, A. Lanthanide complexes derived from (R)-1,1’-
binaphthyl-2,2’-bis(neopentylamine)-{Li(THF)4}{Ln[(R)-
C20H12N2(C10H22)]2} (Ln = Sm, Yb)-novel catalysts for enantiose-
lective intramolecular hydroamination. Chem. Commun. 2003, 3048−
3049. (h) Zhou, L.; Wang, J.; Zhang, Y.; Yao, Y.; Shen, Q. Synthesis
and Structural Characterization of a Series of Lanthanide(II) Amides:
Steric Effect of Amido Ligand. Inorg. Chem. 2007, 46, 5763−5772.
(i) Pan, C.-L.; Chen, W.; Song, J. Lanthanide(II)-Alkali Sandwich
Complexes with Cation-Arene π Interactions: Synthesis, Structure,
ACKNOWLEDGMENTS
■
This work is supported by the National Natural Science
Foundation of China (21672004, 21432001, 21372009) and
the Special and Excellent Research Fund of Anhui Normal
University.
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