Cyclopentadienyl-like ligand as a reactive site in half-sandwich bis(amidinato) rare-earth-metal complexes: An efficient application in catalytic addition of amines to carbodiimides

Article abstract of DOI:10.1021/om5002793

A series of mixed Cp′/bis(amidinato) (Cp′ = η⁵-C₅Me₄(SiMe₃)) lanthanide complexes were synthesized by the 1:2 acid-base reaction between Cp′Ln(CH₂SiMe₃)₂(THF) (Ln = Y, Dy, Er, Lu

Full text of DOI:10.1021/om5002793

Article
pubs.acs.org/Organometallics
Cyclopentadienyl-Like Ligand as a Reactive Site in Half-Sandwich
Bis(amidinato) Rare-Earth-Metal Complexes: An Efficient Application
in Catalytic Addition of Amines to Carbodiimides
Peng-Hui Wei,‡ Ling Xu,† Li-Cheng Song,*,‡ Wen-Xiong Zhang,*,†,‡ and Zhenfeng Xi*,†
†Beijing National Laboratory for Molecular Sciences, MOE Key Laboratory of Bioorganic Chemistry and Molecular Engineering,
College of Chemistry, Peking University, Beijing 100871, People’s Republic of China
‡Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry and Collaborative Innovation Center of Chemical
Science and Engineering, Nankai University, Tianjin 300071, People’s Republic of China
S
* Supporting Information
ABSTRACT: A series of mixed Cp′/bis(amidinato) (Cp′ = η5-
C5Me4(SiMe3)) lanthanide complexes were synthesized by the
1:2 acid−base reaction between Cp′Ln(CH2SiMe3)2(THF) (Ln
= Y, Dy, Er, Lu) and amidines. These Cp′/bis(amidinato)
complexes showed excellent catalytic activity for the addition of
amines to carbodiimides, yielding the corresponding guanidines.
Isolation, structural characterization, and catalytic application of
the binuclear lutetium amido complex showed clearly that the
catalytic cycle was initiated by the dissociation of Cp′. These
results demonstrated that Cp′, for the first time, acted as a
reactive site to yield the active Ln−N species.
rare-earth-metal catalyst precursors, the rare-earth-metal
complexes having Ln−C or Ln−N bonds usually serve as
precursors to yield the active Ln−N species. As far as we are
aware, this type of half-sandwich bis(amidinato) rare-earth-
metal complex is the first example of an η5-cyclopentadienyl-
like ligand acting as a reactive site to yield the active Ln−N
species.
INTRODUCTION
■
The study on the stabilizing ability of different types of
supporting ligands toward the same metal center in the
stoichiometric and catalytic process is of great importance in
the ligand design and elucidation of some reaction processes.1,2
Their stabilizing ability is significantly dependent on the acidity
and basicity of ligands, the steric hindrance, the coordination
environment, etc. Therefore, the design and synthesis of
organometallic complexes with mixed ligands, such as Cp/
amidinate, are in great demand in order to probe the difference
of their stabilizing ability. Hou et al. found the reaction of
terminal alkynes with half-sandwich yttrium complexes bearing
a silylene-linked Cp-amido ligand and propiolamidinate could
release propiolamidines at high temperatures, in which the Cp-
amido ligand remained bonded to yttrium.3 Very recently, we
communicated a comparative study on the stabilizing ability
between C5Me4(SiMe3) (Cp′ for short) and propiolamidinate
in half-sandwich bis(propiolamidinato) lanthanides, in which
Cp′ was found to dissociate from the rare-earth-metal center via
competition with a propiolamidinate.4 Herein we report the
synthesis and structural characterization of various half-
sandwich bis(amidinato) lanthanide complexes. Furthermore,
these lanthanide complexes can serve as excellent catalyst
precursors for the addition reaction of various amines to
carbodiimides (also known as guanylation reactions of amines
or hydroaminations of carbodiimides). Many catalysts including
transition-metal, main-group-metal, and rare-earth-metal com-
plexes are reported for the guanylation reaction because of the
atom-economical preparation of guanidines.5−9 In the case of
RESULTS AND DISCUSSION
■
Synthesis and Structure of Rare-Earth-Metal Com-
plexes Bearing Cp′/Bis(amidinates). The 1:2 acid−base
reaction between Cp′Y(CH2SiMe3)2(THF) (1-Y, Cp′ =
C5Me4(SiMe3)) and the amidine PhC(NPh)(NHPh) in
toluene at room temperature for 12 h yielded the mono-Cp′
bis(amidinato) yttrium complex Cp′Y{PhC(NPh)2}2 (2) in
94% isolated yield (Scheme 1). The analogous mono-Cp′
bis(amidinato) rare-earth-metal complexes Cp′Ln{PhC-
(NAr)2}2 (3, Ln = Y, Ar = 4-MeC6H4; 4, Ln = Dy, Ar = Ph;
5, Ln = Er, Ar = Ph; 6, Ln = Lu, Ar = Ph; 7, Ln = Lu, Ar = 4-
MeC6H4) were prepared similarly in high yields by the acid−
base reactions between Cp′Ln(CH2SiMe3)2(THF) (Ln = Y,
Dy, Er, Lu) and amidines PhC(NAr)(NHAr) (Scheme 1).
The diamagnetic complexes 2, 3, 6, and 7 were characterized by
1H NMR and 13C NMR spectroscopy.
All of these half-sandwich bis(amidinato) lanthanide
complexes 2−7 were structurally characterized by X-ray
Received: March 15, 2014
Published: May 27, 2014
© 2014 American Chemical Society
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Scheme 1. Synthesis of Rare-Earth-Metal Complexes Bearing
Mono-Cp′ and Bis(amidinates) via Acid−Base Reaction
Figure 1. ORTEP drawing of 3 with 30% thermal ellipsoids. Hydrogen
atoms are omitted for clarity.
diffraction analyses. Their selected bond lengths and angles are
summarized in Table 1, and only the ORTEP drawings of 3 and
7 are shown in Figures 1 and 2, respectively. In the case of the
bis(amidinate) complexes 2−7, the Ln3+ ion is bonded to one
η5-Cp′ and two η2-amidinate ligands; thus, the coordination
number of their metal centers is 6. These complexes 2−7,
which crystallize in the monoclinic P21/c space group, are
isostructural and isomorphous. The Y−N bond lengths
(2.341(3)−-2.471(4) Å) in 2 and 3 are comparable with
those of Cp′Y[(iPrN)2CCH2TMS]2 (2.376−2.411 Å).10
Catalytic Application in Addition of Amines to
Carbodiimides. Condition Screening. As a control experi-
ment, no reaction took place when a mixture of aniline and
N,N’-diisopropylcarbodiimide (iPrN=CNiPr, DIC) was
heated to 140 °C for 24 h in C6D5Cl (Table 2, entry 1). In
contrast, when 1 mol % of complexes 2−7 were involved, the
guanylation between aniline and DIC proceeded at 80 °C to
provide the corresponding guanidine 8a (Table 2, entries 2−7).
Among them, 3 shows the best catalytic activity, possibly owing
to the effect of the ionic radii and substitution effect on the
aromatic ring. The catalytic activity of 3 is comparable with that
of catalysts reported previously, including [{Me2Si(C5Me4)-
(NPh)}Y(CH2SiMe3)(thf)],8m [Cp4PrPhY(CH2SiMe3)3][Li-
(thf)3],8b and Zn(OTf)2.6b
Figure 2. ORTEP drawing of 7 with 30% thermal ellipsoids. Hydrogen
atoms are omitted for clarity.
group and whether electron-donating or electron-withdrawing
substituents were installed on the benzene ring. The reaction of
an aniline with the bulkier N,N’-di-tert-butylcarbodiimide
provided a relatively low yield of guanidine 8d, probably
owing to its steric hindrance. 5-Methylthiazol-2-amine was
tested to be a good substrate in this reaction as a representative
of heterocycle-substituted amines (8g). In addition, complex 3
Substrate Scope. Complex 3 was chosen as the catalyst
precursor for the guanylation process between various
substituted amines and carbodiimides. Representative results
are shown in Table 3. For most anilines, the processes could
afford excellent yields, whatever the position of the functional
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 2−7 and 10
2
3
4
5
6
7
10
Ln−N1
Ln−N2
Ln−N3
Ln−N4
2.352(3)
2.357(3)
2.364(3)
2.342(3)
2.380(3)
2.339(3)
2.351(3)
2.341(3)
2.366(2)
2.356(2)
2.361(2)
2.361(2)
2.337(4)
2.341(4)
2.324(4)
2.339(4)
2.307(3)
2.293(3)
2.309(3)
2.302(3)
2.321(7)
2.312(7)
2.272(8)
2.304(7)
2.273(7)
2.340(7)
2.346(6)
2.267(7)
2.339(8)
1.342(9)
1.340(11)
1.346(11)
1.345(10)
Ln−N5
N1−C(NCN)
N2−C(NCN)
N3−C(NCN)
N4−C(NCN)
Ln−Cp(centroid)
Ln−Cp(av)
∠N1−Ln−N2
∠N3−Ln−N4
∠N1−C−N2
∠N3−C−N4
1.332(4)
1.338(4)
1.334(4)
1.348(4)
2.372(30)
2.664(30)
56.87(10)
56.82(10)
114.3(3)
113.3(3)
1.336(5)
1.349(5)
1.341(5)
1.340(5)
2.336(4)
2.631(4)
57.06(11)
57.16(11)
114.2(3)
113.6(3)
1.333(3)
1.342(3)
1.339(3)
1.334(3)
2.293(10)
2.595(10)
56.82(6)
56.54(6)
114.2(2)
113.6(2)
1.341(6)
1.334(6)
1.349(6)
1.328(6)
2.311(5)
2.606(5)
57.21(13)
57.60(14)
113.7(4)
114.1(4)
1.342(5)
1.353(5)
1.335(5)
1.339(5)
2.276(4)
2.584(4)
58.36(11)
57.93(11)
112.6(3)
113.2(3)
1.337(10)
1.388(11)
1.325(11)
1.334(10)
2.286(9)
2.581(9)
58.5(3)
57.8(2)
58.2(2)
112.5(8)
113.1(7)
57.7(3)
112.3(8)
112.2(8)
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Table 2. Addition Reaction of an Aniline to N,N′-
Diisopropylcarbodiimide Catalyzed by the Mixed Cp′/
Scheme 2. Possible Mechanism of Catalytic Addition of
Amines to Carbodiimides
a
Bis(amidinato) Lanthanide Complexes
amt of catalyst
(mol %)
temp
(°C)
time
(h)
yield
b
entry
solvent
(%)
1
2
3
4
5
6
7
0
2
3
4
5
6
7
C6D5Cl
C6D6
C6D6
C6D6
C6D6
C6D6
C6D6
140
80
80
80
80
80
80
24
2
0
85
98
83
91
76
95
2
2
2
2
2
a
Conditions: aniline, 0.51 mmol; N,N′-diisopropylcarbodiimide, 0.50
b
1
mmol. Yields were determined by H NMR.
rearrange to the unsymmetrical guanidinate C as a more stable
intermediate.
a b
,
Table 3. Catalytic Addition of Amines to Carbodiimides
On the basis of the above catalytic cycle, the formation of the
amido species A should be the key point for the present
reaction. Thus, the isolation and structural characterization of
the intermediate A are of critical importance to elucidate the
initiation of the catalytic cycle. The reaction of 3 with aniline
1
was monitored by H NMR spectroscopy in [D6]benzene to
indicate the occurrence of the amination of 3 by the release of
Cp′. However, attempts to obtain suitable single crystals have
not yet been successful. Therefore, the analogous lutetium
complex 7 was chosen to react with aniline. The reaction of 7
with 1 equiv of aniline in [D6]benzene at 80 °C for 2 h yielded
the corresponding binuclear lutetium amido complex 10 in 70%
NMR yield. To make the transformation complete, we chose
toluene as the solvent. When the reaction was conducted at 110
°C for 12 h, complex 10 could be isolated in 77% yield
(Scheme 3). The complex 10 was structurally characterized by
Scheme 3. Isolation of Binuclear Lutetium Amido Complex
10
a
Conditions unless otherwise specified: amines, 0.51 mmol;
b
carbodiimides, 0.50 mmol; 3, 0.005 mmol; benzene, 0.5 mL. NMR
yield. Condition: 3 h. Condition: 12 h. Conditions: toluene, 24 h.
X-ray diffraction analyses. Its selected bond lengths and angles
are summarized in Table 1, and an ORTEP drawing of 10 is
shown in Figure 3. Furthermore, the reaction of aniline with
DIC in the presence of 1 mol % of 10 in [D6]benzene at 80 °C
for 2 h yielded the corresponding guanidine 8a in more than
95% NMR yield. This result shows clearly that the catalytic
cycle is initiated by the dissociation of Cp′ to yield the active
bis(amidinato) amido complexes.
c
d
e
was found to be a good catalyst to effect efficiently the
guanylation reaction of secondary amines (9a,b).
Mechanistic Aspects. A catalytic cycle for the addition of
amines to carbodiimides is shown in Scheme 2. The precursor
3 is thought to react with an amine to yield in situ the binuclear
yttrium amido species A. The active species A, having Y−N
bonds, brings about the catalytic cycle by two continuous steps:
the insertion of the carbodiimide into the Y−N bond and the
protonation of a guanidinate unit by an amine. In this process,
when primary aromatic amines were involved, B could
CONCLUSIONS
■
We have reported the synthesis of a series of mixed Cp′/
bis(amidinato) lanthanide complexes by the 1:2 acid−base
reaction between half-sandwich dialkyl complexes Cp′Ln-
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Preparation of 3. With 4-MeC6H4NHCPh(NC6H4Me-4)
(180.2 mg, 0.600 mmol) and Cp′Y(CH2SiMe3)2(thf) (158.6 mg,
0.300 mmol) as starting materials, 3 was obtained as a pale yellow solid
(214 mg, 0.243 mmol, 81% yield) in a manner analogous to that
described for the preparation of 2. Single crystals suitable for X-ray
analysis could be grown from toluene/hexane at room temperature. 1H
NMR (400 MHz, C6D6, Me4Si): δ 0.60 (s, 9H, SiMe3), 2.02 (s, 12H,
CH3C6H4), 2.23 (s, 6H, MeCp), 2.32 (s, 6H, MeCp), 6.58 (d, J = 7.6
Hz, 8H, Ar), 6.73 (br, 6H, Ar), 6.83 (d, J = 8.0 Hz, 8H, Ar), 7.08 (br,
4H, Ar). 13C NMR (100 MHz, C6D6, Me4Si): δ 2.8, 11.7, 14.2, 20.8,
115.4 (d, J = 2.3 Hz), 124.7, 125.2, 128.71, 128.74, 129.3, 130.5, 131.3,
133.1 (d, J = 2.7 Hz), 146.1, 173.6 (d, J = 2.8 Hz). Anal. Calcd for
C54H59N4SiY: C, 73.61; H, 6.75; N, 6.36. Found: C, 73.33; H, 6.78; N,
6.23. Single crystals of 3·0.5(hexane) suitable for X-ray analysis could
be grown from toluene/hexane at room temperature.
Preparation of 4. With PhNHCPh(NPh) (163.4 mg, 0.600
mmol) and Cp′Dy(CH2SiMe3)2(thf) (180.7 mg, 0.300 mmol) as
starting materials, 4 was obtained as a pale yellow solid (216 mg, 0.240
mmol, 80% yield) in a manner analogous to that described for the
preparation of 2. Single crystals suitable for X-ray analysis could be
grown from toluene/hexane at room temperature. Anal. Calcd for
C50H51N4SiDy: C, 66.83; H, 5.72; N, 6.24. Found: C, 66.73; H, 5.62;
N, 6.21.
Figure 3. ORTEP drawing of 10 with 30% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
(CH2SiMe3)2(THF) (Ln = Y, Dy, Er, Lu) and amidines. All
Cp′/bis(amidinato) complexes have been characterized un-
ambiguously by single-crystal X-ray diffraction analyses.
Excellent catalytic activity of these complexes was observed
for the addition of amines to carbodiimides, yielding the
corresponding guanidines. A mechanistic study showed that the
catalytic cycle was initiated by the dissociation of Cp′ to yield
the active bis(amidinato) amido complexes. These results
demonstrated that these half-sandwich bis(amidinato) rare-
earth-metal complexes served as the first example of an η5-
cyclopentadienyl-like ligand acting as a reactive site to yield the
active Ln−N species. A comparison between Cp′ and amidinate
in the reaction with amine suggested that the coordinative
ability of the chelate amidinate was stronger than that of η5-Cp′,
which will be useful for ligand design and mechanistic
elucidation in related stoichiometric and catalytic processes.
Preparation of 5. With PhNHCPh(NPh) (163.4 mg, 0.600
mmol) and Cp′Er(CH2SiMe3)2(thf) (182.2 mg, 0.300 mmol) as
starting materials, 5 was obtained as a pink solid (222 mg, 0.246 mmol,
82% yield) in a manner analogous to that described for the preparation
of 2. Single crystals suitable for X-ray analysis could be grown from
toluene/hexane at room temperature. Anal. Calcd for C50H51ErN4Si:
C, 66.48; H, 5.69; N, 6.20; Found: C, 66.32; H, 5.66; N, 6.13.
Preparation of 6. With PhNHCPh(NPh) (163.4 mg, 0.600
mmol) and Cp′Lu(CH2SiMe3)2(thf) (184.5 mg, 0.300 mmol) as
starting materials, 6 was obtained as a pale yellow solid (235 mg, 0.258
mmol, 86% yield) in a manner analogous to that described for the
1
preparation of 2. H NMR (400 MHz, [D8]THF): δ 0.36 (s, 9H;
SiMe3), 1.87 (s, 6H; MeCp), 2.12 (s, 6H; MeCp), 6.40 (d, J = 7.4 Hz,
8H; C6H5) 6.73 (t, J = 7.4 Hz, 4H; C6H5), 6.85−7.01 (m, 18H; C6H5).
13C NMR (100 MHz, [D8]THF): δ 2.8, 11.7, 14.2, 114.4, 122.8, 124.0,
126.1, 128.4, 128.7, 128.8, 129.4, 131.0, 133.3, 149.0, 173.6. Anal.
Calcd for C50H51LuN4Si: C, 65.92; H, 5.64; N, 6.15. Found: C, 65.78;
H, 5.53; N, 6.02. Single crystals of 6 suitable for X-ray analysis could
be grown from toluene/hexane at room temperature.
Preparation of 7. With 4-MeC6H4NHCPh(NC6H4Me-4)
(180.2 mg, 0.600 mmol) and Cp′Lu(CH2SiMe3)2(thf) (184.5 mg,
0.300 mmol) as starting materials, 7 was obtained as a pale yellow solid
(226 mg, 0.233 mmol, 78% yield) in a manner analogous to that
described for the preparation of 2. Single crystals of 7·0.5(hexane)
suitable for X-ray analysis could be grown from toluene/hexane/Et2O
at room temperature. The NMR data for 7·0.5(hexane) are as follows.
1H NMR (400 MHz, C6D6, Me4Si): δ 0.63 (s, 9H, SiMe3), 0.89 (t, J =
6.9 Hz, 3H; Me, hexane), 1.17−1.33 (m, 4H; CH2, hexane), 2.02 (s,
12H, CH3C6H4), 2.21 (s, 6H, MeCp), 2.35 (s, 6H, MeCp), 6.58 (s, 4H,
Ar), 6.60 (s, 4H, Ar), 6.73 (br, 5H, Ar), 6.82 (s, 4H, Ar), 6.84 (s, 4H,
Ar), 7.00−7.13 (m, 5H, Ar). 13C NMR (100 MHz, C6D6, Me4Si): δ
2.9, 11.8, 14.30 (hexane), 14.32, 20.8, 23.0 (hexane), 31.9 (hexane),
114.2, 123.8, 125.6, 128.5, 128.8, 129.2, 129.3, 130.6, 131.6, 133.2,
146.1, 173.0. It is noted that there is a residual ether peak in 7·
0.5(hexane). Anal. Calcd for C54H59LuN4Si: C, 67.06; H, 6.15; N,
5.79. Found: C, 67.29; H, 6.27; N, 5.55.
EXPERIMENTAL SECTION
■
General Methods. All reactions were conducted under a slightly
positive pressure of dry nitrogen using standard Schlenk line
techniques or under a nitrogen atmosphere in a glovebox. The
nitrogen in the glovebox was constantly circulated through a copper/
molecular sieves catalyst unit. The oxygen and moisture concen-
trations in the glovebox atmosphere were monitored by an O2/H2O
Combi-Analyzer to ensure both were always below 1 ppm. Unless
otherwise noted, all starting materials were commercially available and
were used without further purification. Solvents were purified by a
Solvent Purification System and dried over fresh Na chips in the
glovebox. Organometallic samples for NMR spectroscopic measure-
ments were prepared in the glovebox by use of J. Young valve NMR
tubes. 1H and 13C NMR spectra were recorded on a 400 M
spectrometer (FT, 400 MHz for 1H, 100 MHz for 13C) at room
temperature, unless otherwise noted.
Preparation of 2. A solution of PhNHCPh(NPh) (163.4 mg,
0.600 mmol) in toluene (ca. 3 mL) was added to a solution of
Cp′Y(CH2SiMe3)2(thf) (158.6 mg, 0.300 mmol) in toluene (ca. 3
mL). The reaction mixture was stirred for 12 h at room temperature.
Evaporation of toluene gave a yellow powder. When this powder was
washed with hexane (ca. 2 mL), 2 could be obtained as a pale yellow
Preparation of 10. In a glovebox, a solution of PhNH2 (17.7 mg,
0.180 mmol) in toluene (ca. 1 mL) and a solution of 7 (164 mg, 0.170
mmol) in toluene (ca. 2 mL) were placed in a Schlenk tube. Then the
Schlenk tube was taken outside the glovebox, and the mixture was
stirred at 110 °C for 12 h. Then the Schlenk tube was moved inside
the glovebox after cooling to room temperature. After the solvent was
removed under reduced pressure, the solid was washed with hexane (2
× 1 mL). 10 was obtained as a colorless solid (113 mg, 0.0653 mmol,
1
solid (233 mg, 0.282 mmol, 94% yield). H NMR (400 MHz, C6D6,
Me4Si): δ 0.56 (s, 9H; SiMe3), 2.16 (s, 6H; MeCp), 2.26 (s, 6H;
MeCp), 6.62−6.64 (m, 8H; C6H5) 6.70 (br, 6H; C6H5), 6.73−6.77 (m,
4H; C6H5), 6.96−7.00 (m, 12H; C6H5). 13C NMR (100 MHz, C6D6,
Me4Si): δ 2.7, 11.6, 14.0, 115.6 (d, J = 2.3 Hz), 122.4, 124.9 (d, J = 0.7
Hz), 125.3, 128.7, 128.9, 129.0 (d, J = 1.0 Hz), 129.3, 130.5, 132.7 (d, J
= 2.7 Hz), 148.5, 173.7 (d, J = 2.8 Hz). Anal. Calcd for C50H51N4SiY:
C, 72.80; H, 6.23; N, 6.79. Found: C, 72.78; H, 6.19; N, 6.75. Single
crystals of 2 suitable for X-ray analysis could be grown from toluene/
hexane at room temperature.
1
77% yield). H NMR (400 MHz, [D8]THF): δ 2.13 (s, 24H; Me),
4.14 (2H, NHC6H5), 6.12 (t, J = 7.1 Hz, 2H; NHC6H5), 6.43 (d, J =
8.1 Hz, 16H; C6H4CH3), 6.65 (d, J = 8.0 Hz, 4H; Ar), 6.72 (d, J = 8.1
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Hz, 16H; C6H4Me), 6.83−6.87 (m, 4H; Ar), 6.99−7.01 (m, 8H; Ar),
7.05−7.10 (m, 12H; Ar). 13C NMR (100 MHz, [D8]THF): δ 20.8,
111.7, 116.6, 125.5, 128.4, 128.8, 129.2, 129.3, 130.41, 130.44, 135.2,
147.5, 160.3, 172.7. Anal. Calcd for C96H88N10Lu2: C, 66.58; H, 5.12;
N, 8.09. Found: C, 66.35; H, 4.98; N, 7.93. Single crystals of 10
suitable for X-ray analysis could be grown from toluene/hexane at
room temperature.
Typical Procedures for the Catalytic Reaction between
Amines and Carbodiimides: NMR Tube Reaction. In the
glovebox, a J. Young valve NMR tube was charged with 3 (4.4 mg,
0.005 mmol), C6D6 (0.5 mL), aniline (48 mg, 0.51 mmol), and N,N′-
diisopropylcarbodiimide (63 mg, 0.50 mmol). The tube was taken out
of the glovebox and then heated to 80 °C in an oil bath for 1 h.
Formation of 8a−g and 9a,b was monitored by 1H NMR
spectroscopy. The NMR data of 8a−g and 9a,b were consistent
with those reported.8b
X-ray Crystallographic Studies. Single crystals of 2−7 and 10
suitable for X-ray analysis were grown as shown in the Experimental
Section. The crystals of 7 were manipulated under a nitrogen
atmosphere and were sealed in a thin-walled glass capillary. Data
collection for 2, 3, and 6 was performed at −100 °C on a Rigaku CCD
SATURN 724 diffractometer, using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). 7 was performed at 20 °C on a Rigaku
RAXIS RAPID IP diffractometer, using graphite-monochromated Mo
Kα radiation (λ = 0.71073 Å). Data collection for 4 and 10 was
performed at −173 °C and for 5 was performed at 20 °C on an Agilent
SuperNova Dual Atlas CCD diffractometer (CCD-2) using graphite-
monochromated Mo Kα radiation (α = 0.71073 Å).11 The
determination of crystal class and unit cell parameters was carried
out by the CrystalClear (Rigaku Inc., 2007) for 2, 3, and 6 or Rapid-
AUTO (Rigaku 2000) program package for 7. The raw frame data
were processed using Crystal Structure (Rigaku/MSC 2000) for 7 or
CrystalClear (Rigaku Inc., 2007) for 2, 3, and 6 to yield the reflection
data file. The structures of 2, 3, 6, and 7 were solved by use of the
SHELXTL program.12 Refinement was performed on F2 anisotropi-
cally for all the non-hydrogen atoms by the full-matrix least-squares
method. Using Olex2, the structure of 4 was solved with XS using
direct methods and refined with the ShelXL refinement package using
least-squares minimization.13 The structure of 5 was solved with
Superflip and refined with the XL refinement package using least-
squares minimization. The structure of 10 was solved with the
Superflip structure solution program using Charge Flipping and
refined with the XL refinement package using least-squares
minimization. The hydrogen atoms were placed at calculated positions
and were included in the structure calculation without further
refinement of the parameters. Crystal data, data collection, and
processing parameters for the rare-earth complexes 2−7 and 10 are
summarized in the Supporting Information. Crystallographic data
(excluding structure factors) have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication nos.
CCDC-972190 (2), CCDC-972191 (3·0.5(hexane)), CCDC-972192
(4), CCDC-972194 (5), CCDC-972195 (6), CCDC-972196 (7·
0.5(hexane)), and CCDC-972197 (10). Copies of these data can be
obtained free of charge from the Cambridge Crystallographic Data
Centre viawww.ccdc.cam.ac.uk/data_request/cif.
*E-mail for Z.X.: zfxi@pku.edu.cn.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the “973” program from National
Basic Research Program of China (2012CB821600,
2014CB845604) and the Natural Science Foundation of
China (NSFC).
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AUTHOR INFORMATION
Corresponding Authors
*E-mail for W.-X.Z.: wx_zhang@pku.edu.cn.
*E-mail for L.-C.S.: lcsong@nankai.edu.cn.
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