Unexpected C-H bond activation promoted by bimetallic lanthanide amido complexes bearing a META-phenylene-bridged Bis(β-diketiminate) ligand

Article abstract of DOI:10.1021/om400018b

Treatment of META-[Na(THF)₂]₂ (1; META = {[2,6- ⁱPr₂C₆H₃NC(Me)C(H)C(Me)N] ^-}₂-(m-phenylene)] with 1 equiv of {Ln[N(SiMe ₃)₂]₂(μ-Cl)(THF)}₂ (Ln = Y, Yb) in toluene at 110 C afforded bimetallic lanthanide amido complexes bridged by a chloride and a phenyl group, {Ln[N(SiMe₃)₂]} ₂(META′)(μ-Cl) (Ln = Y (2), Yb (3)), which formed via unexpected C-H bond activation of the arene ring. However, the same reactions carried out in both THF and toluene at room temperature gave the bimetallic lanthanide amido-chloro complexes {Ln[N(SiMe₃)₂] ₂}META{Ln[N(SiMe₃)₂]Cl(THF)} (Ln = Y (4), Yb (5)). When they were heated to 110 C in toluene, complexes 4 and 5 were converted to complexes 2 and 3 via amine elimination. All of these complexes were confirmed by elemental analysis, FT-IR, and X-ray structure analysis and by NMR analysis in the cases of complexes 1, 2, and 4.

Full text of DOI:10.1021/om400018b

Article
pubs.acs.org/Organometallics
Unexpected C−H Bond Activation Promoted by Bimetallic
Lanthanide Amido Complexes Bearing a META-Phenylene-Bridged
Bis(β-diketiminate) Ligand
Song Sun,† Qiu Sun,† Bei Zhao,*,† Yong Zhang,† Qi Shen,† and Yingming Yao*,†,‡
†Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Dushu
Lake Campus, Soochow University, Suzhou 215123, People’s Republic of China
‡The Institute of Low Carbon Economy, Suzhou 215123, People’s Republic of China
S
* Supporting Information
ABSTRACT: Treatment of META-[Na(THF)2]2 (1; META =
{[2,6-iPr2C6H3NC(Me)C(H)C(Me)N]−}2-(m-phenylene)] with
1 equiv of {Ln[N(SiMe3)2]2(μ-Cl)(THF)}2 (Ln = Y, Yb) in
toluene at 110 °C afforded bimetallic lanthanide amido complexes
bridged by a chloride and a phenyl group, {Ln[N-
(SiMe3)2]}2(META′)(μ-Cl) (Ln = Y (2), Yb (3)), which formed
via unexpected C−H bond activation of the arene ring. However,
the same reactions carried out in both THF and toluene at room
temperature gave the bimetallic lanthanide amido−chloro
complexes {Ln[N(SiMe3)2]2}META{Ln[N(SiMe3)2]Cl(THF)}
(Ln = Y (4), Yb (5)). When they were heated to 110 °C in
toluene, complexes 4 and 5 were converted to complexes 2 and 3
via amine elimination. All of these complexes were confirmed by
elemental analysis, FT-IR, and X-ray structure analysis and by NMR analysis in the cases of complexes 1, 2, and 4.
properties are tunable.5 Numerous organolanthanide β-
diketiminate complexes have been prepared, and some of
INTRODUCTION
■
In recent years, the design and synthesis of bimetallic
them have exhibited exciting catalytic activities and/or
selectivities for the polymerization of lactones and lactides6
and conjugated dienes.7 Phenylene-bridged bis(β-diketiminate)
groups, as one type of β-diketiminate ligand, are useful
dinucleating ligands to stabilize bimetallic organometallic
complexes. Recently, Harder et al. reported that the bimetallic
calcium and zinc phenylene-bridged bis(β-diketiminate)
complexes are efficient catalysts for the copolymerization of
cyclohexene oxide and CO2. Moreover, the META-phenylene-
bridged zinc complexes are superior to the PARA-phenylene-
bridged analogues for this copolymerization, which was
attributed to the cooperative effects in these binuclear
catalysts.8 However, the phenylene-bridged bis(β-diketiminate)
ligands have not been used in organolanthanide chemistry to
our knowledge. Herein, we introduce such ligands into this
area. During the synthesis of lanthanide amido complexes
stabilized by a META-phenylene-bridged bis(β-diketiminate)
ligand, we found an unexpected C−H bond activation of the
arene ring promoted by the bimetallic complexes.
complexes supported by binucleating ligands have received
considerable attention, due to their wide application in
homogeneous catalysis. Such chemistry has been developed
on the basis of the notion of the presence of cooperative effects
between the two metal centers and/or nuclearity effects.1 To
date, a number of bimetallic complexes of main-group and
transition metals supported by well-defined binucleating ligands
have been reported.2 In comparison with their monometallic
analogues, these complexes indeed have demonstrated
promising catalytic activities and/or selectivities in the
polymerization of olefins,2g,h,j−l,o the copolymerization of
epoxide with CO2,2a,e,f,m and a series of organic trans-
formations.2c,d,n For example, Marks et al. reported that a
series of bimetallic titanium (Ti2) and zirconium (Zr2)
complexes supported by “constrained geometry” ligands have
shown obvious bimetallic cooperative effects in olefin polymer-
ization.1b,3 However, the cooperative effects of bimetallic
lanthanide complexes in organolanthanide chemistry remains
largely unexplored, due to the fact that the synthesis of
covalently linked binuclear lanthanide complexes is more
challenging.4
During the past 10 years, β-diketiminate ligands have been
widely used in organolanthanide and organolanthanoid
chemistry to stabilize lanthanide complexes, because these
ligand systems are easily available and their steric and electronic
Received: January 10, 2013
Published: March 12, 2013
© 2013 American Chemical Society
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Article
(0.77 g, 60%). Mp: 221−223 °C dec. IR (KBr, cm−1): 3055 (m), 2962
(s), 2860 (m), 1625 (s), 1593 (s), 1550 (s), 1493 (s), 1434 (s), 1380
(s), 1367 (m), 1267 (s), 1176 (m), 1024 (w), 843 (w), 769 (m). Anal.
Calcd for C52H87ClN6Si4Yb2: C, 48.41; H, 6.80; N, 6.51. Found: C,
48.73; H, 6.35; N, 6.76.
EXPERIMENTAL SECTION
■
General Procedures. All of the manipulations were performed
under an argon atmosphere, using standard Schlenk techniques.
Anhydrous LnCl3, HN(TMS)2, and NaH are commercially available.
HN(SiMe3)2 was dried over CaH2 for 4 days and distilled before use.
Tetrahydrofuran (THF), toluene, and hexane were dried and freed of
oxygen by refluxing over sodium/benzophenone ketyl and distilled
prior to use. The ligand META-H2 (=[2,6-iPr2C6H3NHC(Me)C(H)-
C(Me)N]2-(m-phenylene),8 NaN(TMS)2, and {Ln[N(SiMe3)2]2(μ-
Cl)(THF)}2 (Ln = Y, Yb)9 were prepared according to the published
procedures. Carbon, hydrogen, and nitrogen analyses were performed
by direct combustion with a Carlo-Erba EA-1110 instrument. The FT-
IR spectra were recorded with a Nicolet-550 FT-IR spectrometer as
KBr pellets. The 1H NMR spectra were recorded in a C6D6 or d8-THF
solution for complexes 1, 2, and 4 with a Unity Varian-300 or Unity
Varian-400 spectrometer. Because of their paramagnetism, no
resolvable NMR spectra for complexes 3 and 5 were obtained. The
uncorrected melting points of crystalline samples in sealed capillaries
(under argon) are reported as ranges.
Synthesis of {Y[N(SiMe3)2]2}META{Y[N(SiMe3)2]Cl(THF)} (4).
To a THF solution of {Y[N(SiMe3)2]2(μ-Cl)(THF)}2 (1.03 g, 1.00
mmol) was added a THF solution of META-[Na(THF)2]2 (6.10 mL,
1.00 mmol). The mixture was stirred overnight at 25 °C. The
precipitate that formed was removed by centrifugation, and the solvent
was evaporated completely under reduced pressure. Hexane (3 × 3
mL) was added to precipitate the product. Colorless crystals were
obtained from a mixture of hexane and toluene (6/1 v/v) at 25 °C
overnight (0.63 g, 46%). Mp: 253−257 °C dec. IR (KBr, cm−1): 3060
(m), 2960 (s), 2866 (m), 1625 (s), 1593 (m), 1552 (s), 1492 (m),
1435 (s), 1380 (s), 1363 (m), 1278 (m), 1178 (w), 933 (s), 841 (m),
757 (m). 1H NMR (d8-THF, 400 MHz): 7.34 (m, 1H, CHN‑aryl), 7.20
(m, 8H, CHN‑aryl), 6.68 (s, 1H, CHN‑aryl), 5.40 (s, 1H, CH3CNCH),
5.09 (s, 1H, CH3CNCH), 3.62 (m, 4H, THF-α-CH2), 3.25−2.91 (m,
4H, CH(CH3)2), 2.14 (s, 3H, CH3CN), 1.96 (s, 3H, CH3CN), 1.79−
1.77 (m, 7H, CH3CN+THF-β-CH2), 1.66 (s, 3H, CH3CN CH-
(CH3)2), 1.34 (d, 12H, CH(CH3)2), 1.14 (d, 12H, CH(CH3)2), 0.25
(m, 54H, SiMe3). 13C NMR (d8-THF, 100 MHz): δ 5.48 (SiMe3),
25.08 (THF-β-CH2), 26.06 (CH(CH3)2), 26.14 (CH(CH3)2), 26.29
(CH3CN), 26.55 (CH3CN), 26.75 (CH(CH3)2), 68.39 (THF-α-CH2),
96.46 (CH3CNCH), 99.83 (CH3CNCH), 123.13 (CHN‑aryl), 125.06
(CHN‑aryl), 125.58 (CHNaryl), 126.68 (CHNaryl), 127.02 (CHNaryl),
129.82 (CHNaryl), 143.03 (CHN‑aryl), 146.22 (CHN‑aryl), 146.54
(CHNaryl), 150.21 (CN), 151.61 (CN), 167.89 (CN), 168.87
(CN). Anal. Calcd for C62H114ClN7OSi6Y2: C, 54.94; H, 8.48; N,
7.23. Found: C, 54.65; H, 8.57; N, 7.06.
Synthesis of META-[Na(THF)2]2 (1). A THF solution of META-
H2 (50 mL, 14.77 g, 25.00 mmol) was added to a suspension of NaH
(1.20 g, 50.00 mmol) in 20 mL of THF. The resulting mixture was
heated to reflux for about 6 h. The dissolved portion was removed by
centrifugation, the solvent was removed under vacuum, and hexane
was added to extract the product. Red crystals were obtained from the
concentrated hexane solution at room temperature (20.78 g, 90%).
Mp: 157−159 °C. IR (KBr, cm−1): 3063 (m), 2960 (s), 2867 (s), 1626
(s), 1588 (s), 1553 (s), 1440 (s), 1382 (s), 1325 (m), 1278 (s), 1178
1
(s), 1100 (w), 865 (s), 758 (s). H NMR (C6D6, 400 MHz): 7.15−
7.17 (m, 8H, CHN‑aryl, overlapped with C6D6), 7.08−7.11 (m, 3H,
CHN‑aryl), 6.65 (s, 1H, CHN‑aryl), 4.60 (s, 1H, CH3CNCH), 3.45 (m,
16H, THF-α-CH2), 3.13 (s, 4H, CH(CH3)2), 1.38 (s, 16H, THF-β-
CH2), 1.24−1.28 (m, 36H, CH3CN + CH(CH3)2). 13C NMR (C6D6,
100 MHz): δ 23.93 (CH3CN), 24.13 (CH(CH3)2), 25.43 (THF-β-
CH2), 26.06 (CH(CH3)2), 67.79 (THF-α-CH2), 93.56 (CH3CNCH),
117.86 (CHN‑aryl), 122.28 (CHN‑aryl), 123.22 (CHNaryl), 129.12
(CHNaryl), 139.51 (CHNaryl), 147.52 (CN), 150.31 (CN),
155.98 (CN), 161.71 (CN). Anal. Calcd for C56H84N4Na2O4:
C, 72.85; H, 9.17; N, 6.07. Found: C, 72.52; H, 9.43; N, 5.88.
Synthesis of {Y[N(SiMe3)2]}2(META′)(μ-Cl) (2). To a toluene
solution of {Y[N(SiMe3)2]2(μ-Cl)(THF)}2 (1.03 g, 1.00 mmol) was
added a toluene solution of META-[Na(THF)2]2 (6.10 mL, 1.00
mmol). The mixture was stirred at 110 °C for about 48 h. The
precipitate that formed was removed by centrifugation, and the solvent
was evaporated completely under reduced pressure. Hexane (1 × 3
mL) was added to precipitate the product. Colorless crystals were
obtained from a mixture of hexane and toluene (6/4 v/v) at 25 °C
overnight (0.59 g, 53%). Mp: 219−222 °C dec. IR (KBr, cm−1): 3054
(m), 2960 (s), 2862 (m), 1625 (s), 1595 (s), 1553 (s), 1492 (s), 1434
(s), 1381 (s), 1368 (m), 1277 (s), 1178 (m), 1026 (w), 842 (w), 758
(m). 1H NMR (C6D6, 300 MHz): 7.43 (m, 2H, CHN‑aryl), 7.16 (s, 5H,
CHN‑aryl + overlapped with C6D6), 6.77 (d, 2H, CHN‑aryl), 4.95 (s, 2H,
CH3CNCH), 3.28−3.37 (m, 4H, CH(CH3)2), 2.27 (s, 6H, CH3CN),
1.61 (s, 6H, CH3CN), 1.39−1.48 (d, 12H, CH(CH3)2), 1.05−1.12 (d,
12H, CH(CH3)2), 0.02 (s, 36H, SiMe3). 13C NMR (d8-THF, 100
MHz): δ 5.14 (Si(CH3)3), 5.59 (Si(CH3)3), 23.56 (CH(CH3)2), 25.07
(CH(CH3)2), 25.60 (CH(CH3)2), 25.87 (CH(CH3)2), 27.07
(CH3CN), 28.99 (CH(CH3)2), 29.59 (CH(CH3)2), 101.99
(CH3CNCH), 118.08 (CHN‑aryl), 125.20 (CHN‑aryl), 125.61 (CHNaryl),
126.94 (CHNaryl), 133.51 (CHNaryl), 143.90 (CHNaryl), 144.44
(CHNaryl), 146.81 (CHNaryl), 154.27 (CHNaryl), 158.83 (CN),
168.07 (CN). Anal. Calcd for C52H87ClN6Si4Y2: C, 55.67; H,
7.82; N, 7.49. Found: C, 55.93; H, 7.98; N, 7.35.
Synthesis of {Yb[N(SiMe3)2]2}META{Yb[N(SiMe3)2]Cl(THF)}
(5). The synthesis of complex 5 was carried out in the same way as
that described for complex 4, but {Yb[N(SiMe3)2]2(μ-Cl)(THF)}2
(1.20 g, 1.00 mmol) was used instead of {Y[N(SiMe3)2]2(μ-
Cl)(THF)}2. Red crystals were obtained from a mixture of hexane
and toluene (7/2 v/v) at 25 °C in a few days (0.61 g, 40%). Mp: 249−
252 °C dec. IR (KBr, cm−1): 3058 (m), 2963 (s), 2876 (m), 1627 (s),
1595 (m), 1552 (s), 1489 (m), 1436 (s), 1380 (s), 1364 (m), 1276
(m), 1178 (w), 928 (s), 843 (m), 756 (m). Anal. Calcd for
C62H114ClN7OSi6Yb2: C, 48.87; H, 7.54; N, 6.43. Found: C, 48.51 ; H,
7.69; N, 6.21.
X-ray Crystallography. Suitable single crystals of complexes 2−5
were sealed in a thin-walled glass capillary for the determination of
single-crystal structures. Intensity data were collected with a Rigaku
Mercury CCD area detector in ω scan mode using Mo Kα radiation (λ
= 0.71070 Å). The diffracted intensities were corrected for Lorentz/
polarization effects and empirical absorption corrections. Details of the
intensity data collection and crystal data are given in STable 1
(Supporting Information).
The structures were solved by direct methods and refined by full-
matrix least-squares procedures on the basis of |F|2. All of the non-
hydrogen atoms were refined anisotropically. The hydrogen atoms in
these complexes were all generated geometrically, assigned appropriate
isotropic thermal parameters, and allowed to ride on their parent
carbon atoms. All of the hydrogen 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 using SHELXL-97 programs.
RESULTS AND DISCUSSION
■
The amine elimination reaction of lanthanide amido complexes
with a preligand is a popular method for the synthesis of new
lanthanide complexes. However, a 1H NMR monitoring
reaction between Y[N(SiMe3)2]3 and m-phenylene-bridged
bis(β-diketimine) (META-H2) revealed that this reaction did
not occur in C6D6 at 70 °C, as the methyl signal of the free
HN(SiMe3)2 at δ 0.10 ppm is very weak, even after the reaction
time was elongated to 72 h (SFigures 2−5, Supporting
Synthesis of {Yb[N(SiMe3)2]}2(META′)(μ-Cl) (3). The synthesis
of complex 3 was carried out in the same way as that described for
complex 2, but {Yb[N(SiMe3)2]2(μ-Cl)(THF)}2 (1.20 g, 1.00 mmol)
was used instead of {Y[N(SiMe3)2]2(μ-Cl)(THF)}2. Hexane (2 × 3
mL) was added to precipitate the product. Red crystals were obtained
from a solution of hexane and toluene (5/5 v/v) at 25 °C overnight
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Information). Therefore, we attempted to synthesize the
desired lanthanide amido complexes via a metathesis reaction.
The preligand META-H2 reacted with NaH in THF under
reflux, after workup, to give red crystals from hexane in a good
isolated yield. Elemental analysis and NMR characterization
revealed that the formula of this compound is META-
[Na(THF)2]2. X-ray diffraction analysis confirmed that the
product is the bimetallic sodium bis(β-diketiminate) complex
META-[Na(THF)2]2 (1), as shown in Scheme 1. However, the
crystal data of compound 1 are relatively poor, and only the
framework was obtained.
yttrium amido complex META-{Y[N(SiMe3)2]2}2 (SFigure 8,
Supporting Information). Further X-ray structure determina-
tion confirmed that complexes 4 and 5 were the bimetallic
lanthanide amido−chloro complexes {Ln[N(SiMe3)2]2}-
META{Ln[N(SiMe3)2]Cl(THF)}, (Ln = Y (4), Yb (5))
(Scheme 2). It was found that the reaction media do not
influence these reactions at room temperature. Complexes 4
and 5 can also be obtained in toluene at room temperature. It
seems that the ionic radii play a key role on the formation of a
bimetallic lanthanide bis(amido) complex, because the complex
META-{Nd[N(SiMe3)2]2}2 can be isolated.10
A further study revealed that complexes 4 and 5 can be
converted to complexes 2 and 3 under suitable conditions, and
the reaction media and temperature have a significant influence
on this transformation. An NMR monitoring reaction revealed
Scheme 1
1
that the H NMR spectrum had no obvious change when
complex 4 was dissolved in d8-THF in a J. Young valve NMR
tube, even after the sample was heated to 70 °C for about 3
days (SFigure 9, Supporting Information). However, part of
complex 4 was converted to complex 2 when complex 4 in
C6D6 was heated to 70 °C for about 3 days, as evidenced by a
new resonance at 0.02 ppm assignable to the amido groups in
complex 2 (SFigure 10, Supporting Information). After the
toluene solution of complex 4 was heated to 110 °C for 12 h,
toluene was evaporated completely under reduced pressure,
and C6D6 was added. The 1H NMR spectrum revealed that the
transformation was complete, and only one singlet appeared at
δ 4.95 ppm for the two protons of CH3CNCH, in comparison
with the two singlets at δ 5.40 and 5.09 ppm in complex 4,
indicating that the chemical environments of the two protons of
CH3CNCH in the two β-diketiminate units of complex 2 are
the same. Furthermore, the broad multiplet at δ 0.09−0.25 ppm
almost disappeared, and a doublet appeared at 0.01 and 0.03
ppm, which is similar to that of complex 2 (SFigure 11,
Supporting Information). These results indicated that com-
plexes 4 and 5 were the intermediates and that complexes 2 and
3 formed from complexes 4 and 5 via an unexpected C−H
bond activation of the arene ring along with the release of
HN(TMS2)2 at high reaction temperature.
Treatment of {Ln[N(SiMe3)2]2(μ-Cl)(THF)}2 (Ln = Y, Yb)
with 1 equiv of compound 1 in toluene at 110 °C, after workup,
gave colorless (for Y, 2) and red (for Yb, 3) crystals in good
1
isolated yields. In the H NMR spectrum of complex 2 (in
C6D6), in addition to the signals for the m-phenylene-bridged
bis(β-diketiminate) ligand, there is a slightly broad singlet at δ
0.02 ppm, which can be assigned to the amido groups
−N(SiMe3)2. Its integration amounts to only 36 H, which is
less than the 72 H in the desired complex META-{Y[N-
(SiMe3)2]2}2 (SFigure 6, Supporting Information). Further X-
ray structure determination confirmed that complexes 2 and 3
were not the desired lanthanide bisamido complexes but the
novel bimetallic lanthanide amido complexes bridged by a
chloride and a phenyl group {Ln[N(SiMe3)2]}2(META′)(μ-
Cl) (Ln = Y (2), Yb (3)), in which an unexpected C−H bond
activation of the phenyl group occurred, as shown in Scheme 2.
Scheme 2
The possible pathway for the formation of the C−H bond
activation product is postulated in Scheme 3. Although the two
central metals in complexes 4 and 5 are located at opposite
sides of the bridge plane to avoid steric congestion, the two
metals could adjust to be on the same side at raised
temperature, which is favorable for elimination of HN(SiMe3)2,
and to form a bridged chloride bond. It is noteworthy that the
C−H bond activation cannot occur in the monometallic
complex 6 (see the Supporting Information for details for the
synthesis of complex 6) (Chart 1) under the same conditions.
These results demonstrate that the bimetallic structure plays a
key role in the C−H bond activation reaction in these
complexes and provide experimental evidence for cooperative
effects in a bimetallic system.
The definitive molecular structures of complexes 2−5 were
provided by single-crystal X-ray structure diffraction. Com-
plexes 2 and 3 are isostructural, and the molecular structure of
complex 2 is shown in Figure 1, along with selected bond
lengths and angles. Complex 2 has a C2-symmetric bimetallic
structure, and the two yttrium atoms are connected by one
chlorine atom and a phenyl group. The bridging phenyl ring
adopts an η3 coordination mode, which is different from the η1
coordination mode in the monometallic lanthanide β-
diketiminate complexes obtained via C−H bond activation
When the same reactions were conducted in THF at room
temperature, colorless (for Y, 4) and red (for Yb, 5) crystals
were isolated from concentrated toluene/hexane solutions in
1
46% and 40% isolated yields, respectively. In the H NMR
spectrum of complex 4 (in d8-THF), the signal of the amido
groups −N(SiMe3)2 appeared at δ 0.09−0.25 ppm as a broad
multiplet, which is different from that in complex 2. In addition,
the integration of this peak revealed that there are 54 H for the
amido group, which was also less than the 72 H in the desired
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Scheme 3
complexes 2 and 3 adopts an η3 coordination mode, the
C(35)−C(36) and C(36)−C(37) bond lengths are 1.414(8)
and 1.389(8) Å, respectively, which are in the range for normal
benzene rings. The Y1−Cl1 and Y2−Cl1 bond lengths are
2.6285(18) and 2.6359(18) Å, respectively, which are also
similar to the bridged Ln−Cl bond lengths reported in the
literature.4c Additionally, the distance between the two yttrium
atoms is 3.8248(12) Å, which falls in the range of two metal
centers in close proximity (3.5−6.0 Å) that may in some cases
lead to enhanced substrate activation or to a more stabilized
reaction center.2n The Cl(1), Y(1), C(36), and Y(2) atoms are
coplanar, and the dihedral angle between this plane and the
bridging phenylene plane defined by C(35)−C(40) is
45.19(1)°.
Chart 1
Complexes 4 and 5 are also isostructural, and the molecular
structure of complex 4 is shown in Figure 2, along with selected
Figure 1. ORTEP diagram of complex 2 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 30% probability level, and
hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
angles (deg): Y1−N1 = 2.350(5), Y1−N2 = 2.272(4), Y1−N5 =
2.232(5), Y1−C36 = 2.589(5), Y1−Cl1 = 2.6359(18), Y1−Y2 =
3.8248(12), Y2−N6 = 2.237(5), Y2−N4 = 2.281(5), Y2−N3 =
2.352(5), Y2−C36 = 2.560(5), Y2−Cl1 = 2.6285(18); C36−Y1−Cl1
= 85.03(12), C36−Y2−Cl1 = 85.77(13).
Figure 2. ORTEP diagram of complex 4 showing the atom-numbering
scheme. Thermal ellipsoids are drawn at the 30% probability level, and
hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and
angles (deg): Y1−N1 = 2.306(4), Y1−N2 = 2.344(4), Y1−N5 =
2.260(4), Y1−N6 = 2.233(4), Y2−N3 = 2.373(4), Y2−N4 = 2.343(4),
Y2−N7 = 2.228(4), Y2−O1 = 2.389(3), Y2−Cl1 = 2.5363(14); N7−
Y2−O1 = 89.14(14), N7−Y2−Cl1 = 120.56(11), O1−Y2−Cl1 =
87.99(9), N3−Y2−Cl1 = 110.75(10).
reported by Chen et al. and Cui et al., respectively.11a,b In
complex 2, each of the yttrium atoms is six-coordinated with
two nitrogen atoms from the N,N-chelating β-diketiminate
unit, a −N(SiMe3)2 group, two carbon atoms from the bridged
phenyl, and a chlorine atom. The coordination geometry can be
best described as a distorted trigonal bipyramid. The bond
lengths of Y1−C36 and Y2−C36 are 2.589(5) and 2.560(5) Å,
respectively, which are obviously shorter than that of 2.798(2)
bond lengths and angles. In complex 4, two yttrium atoms are
situated at opposite sides of the bridging phenyl plane to reduce
steric repulsion. The coordination environments around the
two yttrium atoms are inequivalent. One is four-coordinated
with two nitrogen atoms from the N,N-chelating β-diketiminate
unit and two nitrogen atoms from two (Me3Si)2N− groups,
and the coordination geometry can be described as a distorted
tetrahedron. The other yttrium atom is five-coordinated with
two nitrogen atoms from the N,N-chelating β-diketiminate
unit, one nitrogen atom from the (Me3Si)2N− group, one
Å
i n [ Y b { η 5 - C 1 3 H 8 C (  N [ 2 , 6 - i P r 2 C 6 H 3 ] ) -
CH2NHC6H3(2,6-iPr2C6H3)}2(THF)] reported by Trifonov
et al..12 However, these bond lengths are apparently longer than
the values in the lanthanide alkyl complexes supported by a
pyridyl-1-azaallyl dianionic ligand (2.396(3) Å)11b and anilido
phosphinimine ligands (2.435(5) Å).11a Although one carbon
atom (C(36)) is anionic and the bridging phenylene group in
1879
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Organometallics
Article
Morimoto, H.; Kumagai, N.; Shibasaki, M. J. Am. Chem. Soc. 2004,
126, 8777. (e) Lee, B. Y.; Kwon, H. Y.; Lee, S. Y.; Na, S. J.; Han, S.;
Yun, H.; Lee, H.; Park, Y. W. J. Am. Chem. Soc. 2005, 127, 3031.
(f) Xiao, Y. L.; Wang, Z.; Ding, K. L. Macromolecules 2006, 39, 128.
(g) Amin, S. B.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 2938.
(h) Rodriguez, B. A.; Delferro, M.; Marks, T. J. Organometallics 2008,
27, 2166. (i) Arbaoui, A.; Redshaw, C.; Hughes, D. L. Chem. Commun.
2008, 4717. (j) Guo, N. C.; Stern, L.; Marks, T. J. J. Am. Chem. Soc.
chlorine atom, and one oxygen atom from a THF molecule to
form a distorted square pyramid. The distance between the two
yttrium atoms is 8.2143(14) Å, which is decidely longer than
that in complex 2.
Further attempts to elucidate the reactivity of complexes 2
and 3 were carried out but were unsuccessful. For example, we
recently reported that the dianionic lanthanide β-diketiminate
complexes can react with borate to give cationic lanthanide
amido complexes.13 Zhou et al. found that the insertion of
carbodiimide into the Ln−C bond of the lanthanide γ-
alkylamide chelate formed via C−H activation can occur
smoothly.14 However, no cationic species were detected from
the reaction of complex 2 with borate ([Ph3C][[B(C6F5)4] or
[PhNMe2H][[B(C6F5)4]). The insertion reactions of complex
2 with a series of unsaturated molecules, such as carbodiimines,
were also carried out, but no reaction was observed. These
results indicated that complexes 2 and 3 are rather inert.
̀
2008, 130, 2246. (k) Motta, A.; Fragala, I. L.; Marks, T. J. J. Am. Chem.
Soc. 2009, 131, 3974. (l) Rodriguez, A.; Delferro, M.; Marks, T. J. J.
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Organometallics 2011, 30, 5978. (o) Weberski, M. P.; Chen, C.;
Delferro, M.; Zuccaccia, C.; Macchioni, A.; Marks, T. J. Organo-
metallics 2012, 31, 3773. (p) Li, W. Y.; Wu, W. T.; Wang, Y. R.; Yao, Y.
M.; Zhang, Y.; Shen, Q. Dalton Trans. 2011, 40, 11378. (q) Li, W. Y.;
Yao, Y. M.; Zhang, Y.; Shen,, Q. Chin. J. Chem. 2012, 30, 609.
(3) (a) Li, H.; Li, L.; Marks, T. J. Angew. Chem., Int. Ed. 2004, 43,
4937. (b) Li, H.; Li, L.; Schwartz, D. J.; Stern, C. L.; Marks, T. J. J. Am.
Chem. Soc. 2005, 127, 14756. (c) Li, H.; Stern, C. L.; Marks, T. J.
Macromolecules 2005, 38, 9015.
CONCLUSION
■
In conclusion, an unexpected C−H bond activation of an arene
ring was observed in a bimetallic system, and the novel
bimetallic lanthanide amido complexes bridged by a chloride
and a phenyl group {Ln[N(SiMe3)2]}2(META′)(μ-Cl) (Ln =
Y (2), Yb (3)) were isolated and characterized. Moreover, the
bimetallic lanthanide amido−chloro complexes supported by a
META-phenylene-bridged bis(β-diketiminate) ligand {Ln[N-
(SiMe3)2]2}META{Ln[N(SiMe3)2]Cl(THF)} (Ln = Y (4), Yb
(5)) were synthesized at room temperature, which have been
proven to be the intermediates in the formation of complexes 2
and 3. These results provided experimental evidence for
cooperative effects in a bimetallic system. The investigation of
the reactivity of complexes 2 and 3 is still ongoing in our
laboratory.
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ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files and a table giving crystallographic data for 2−5, text
giving experimental details for 6, and figures giving NMR
spectra and an ORTEP diagram for 1. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Y.Y.: fax, (86)512-65880305; tel, (86)512-65882806; e-mail,
yaoym@suda.edu.cn.
■
(6) (a) Xue, M. Q.; Yao, Y. M.; Shen, Q.; Zhang, Y. J. Organomet.
Chem. 2005, 690, 4685. (b) Yao, Y. M.; Zhang, Z. Q.; Peng, H. M.;
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Zhang, Y.; Yao, Y. M.; Shen, Q. Dalton Trans. 2010, 39, 6877.
(7) Li, D. F.; Li, S. H.; Cui, D. M.; Zhang, X. Q. Organometallics
2010, 29, 2186.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the National Natural Science
Foundation of China (Grants 21174095, 21172165, and
21132002), the PAPD, and the Qing Lan Project is gratefully
acknowledged.
(8) Piesik, D. F. J.; Range, S.; Harder, S. Organometallics 2008, 27,
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