Synthesis of dianionic β-diketiminate lanthanide amides L′LnN(SiMe3)2THF by deprotonation of the β-diketiminate ligand L (L = {[(2,6- i Pr2C6H 3)NC(CH3)]2CH}-) and the transformation with [HNEt3][BPh4] to the cationic samarium amide [LSmN(SiMe3)2][BPh4]

Article abstract of DOI:10.1021/om2010904

Reaction of β-diketiminate lanthanide dichlorides LLnCl ₂(THF)₂ (L = {[(2,6-iPr₂C₆H ₃)NC(CH₃)]₂CH}^-) with 2 equiv of NaN(SiMe₃)₂ in toluene afforded lanthanide amide complexes supported by a dianionic β-diketiminate ligand L′, L′LnN(SiMe₃)₂(THF) (L′ ={(2,6-iPr ₂C₆H₃)NC(CH₂)CHC(CH ₃)N(2,6-iPr₂C₆H₃)}^2-, Ln = Yb (1), Y (2), Gd (3), Sm (4)), in moderate yields via deprotonation of L. Addition of a small amount of THF led to an increase of the yields of 1-4. Lanthanide metals have a great influence on the deprotonation of L. The same reaction with LNdCl₂(THF)₂ did not afford the analogous complex L′NdN(SiMe₃)₂(THF), but the normal diamide complex LNd[N(SiMe₃)₂]₂ (5) was isolated instead. The metathesis reaction of the triply bridged dichlorides of Sm, LSmCl(μ-Cl)₃SmL(THF), with 2 equiv of NaN(SiMe₃) ₂ yielded the diamide complexes LSm[N(SiMe₃) ₂]₂ in toluene, while complex 4 was formed instead in a mixture of toluene and THF. In contrast, the same reactions with LYbCl(μ-Cl)₃YbL(THF) either in toluene or in a mixture of toluene and THF both afforded 1. Treatment of 4 with [HNEt₃][BPh₄] in THF at room temperature gave the novel cationic Sm β-diketiminate amide complex [LSmN(SiMe₃)₂(THF)₂][BPh₄] (7) in good yield. Complexes 1-5 and 7 have been confirmed by single-crystal X-ray structural analyses. The mechanism of deprotonation of L was discussed.

Full text of DOI:10.1021/om2010904

Article
pubs.acs.org/Organometallics
Synthesis of Dianionic β-Diketiminate Lanthanide Amides
L′LnN(SiMe3)2(THF) by Deprotonation of the β-Diketiminate Ligand L
(L = {[(2,6-iPr2C6H3)NC(CH3)]2CH}−) and the Transformation with
[HNEt3][BPh4] to the Cationic Samarium Amide [LSmN(SiMe3)2][BPh4]
Peng Liu,† Yong Zhang,† Yingming Yao,† and Qi Shen*,†,‡
†Key Laboratory of Organic Synthesis of Jiangsu Province, Department of Chemistry and Chemical Engineering, Dushu Lake
Campus, Soochow University, Suzhou 215123, People’s Republic of China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
S
* Supporting Information
ABSTRACT: Reaction of β-diketiminate lanthanide dichlor-
ides LLnCl2(THF)2 (L = {[(2,6-iPr2C6H3)NC(CH3)]2CH}−)
with 2 equiv of NaN(SiMe3)2 in toluene afforded lanthanide
amide complexes supported by a dianionic β-diketiminate
ligand L′, L′LnN(SiMe3)2(THF) (L′ ={(2,6-iPr2C6H3)NC-
(CH2)CHC(CH3)N(2,6-iPr2C6H3)}2−, Ln = Yb (1), Y (2),
Gd (3), Sm (4)), in moderate yields via deprotonation of L.
Addition of a small amount of THF led to an increase of the
yields of 1−4. Lanthanide metals have a great influence on the
deprotonation of L. The same reaction with LNdCl2(THF)2
did not afford the analogous complex L′NdN(SiMe3)2(THF),
but the normal diamide complex LNd[N(SiMe3)2]2 (5) was isolated instead. The metathesis reaction of the triply bridged
dichlorides of Sm, LSmCl(μ-Cl)3SmL(THF), with 2 equiv of NaN(SiMe3)2 yielded the diamide complexes LSm[N(SiMe3)2]2 in
toluene, while complex 4 was formed instead in a mixture of toluene and THF. In contrast, the same reactions with LYbCl(μ-
Cl)3YbL(THF) either in toluene or in a mixture of toluene and THF both afforded 1. Treatment of 4 with [HNEt3][BPh4] in
THF at room temperature gave the novel cationic Sm β-diketiminate amide complex [LSmN(SiMe3)2(THF)2][BPh4] (7) in
good yield. Complexes 1−5 and 7 have been confirmed by single-crystal X-ray structural analyses. The mechanism of
deprotonation of L was discussed.
synthetic pathways.6 However, the syntheses of cationic
lanthanide amide complexes are still limited. The cationic
INTRODUCTION
Monoanionic β-diketiminates have been widely used in
■
species of lanthanide amides have been mentioned by
organolanthanide chemistry as versatile spectator ligands,
abstraction of the amido ligand using ammonium borate7a
stabilizing various Ln-active groups due to their strong binding
and trityl borate,7b but no molecular structures were reported.
to the lanthanide metals and tunable electronic and steric
factors.1 However, these monoanionic β-diketiminate ligands
Recently, the first structurally characterized cationic Sc amide
complexes of (2-Me-Ind)Sc{N(SiMe3)2}(PhNMe2)]+[B-
themselves can participate in transformations under certain
(C6F5)4]− and [(2-Me-Ind)Sc{N(SiMe3)2}(THF)2]+[B-
(C6F5)4]− were formed via the unexpected abstraction of an
indenyl group.7c Therefore, we attempted to synthesize isolable
cationic lanthanide amides by protonation of a dianionic β-
diketiminate lanthanide amide complex by ammonium borate
with the aim of searching for a convenient route for the
preparation of cationic β-diketiminate lanthanide amides.
The deprotonation of monoanionic β-diketiminate ligand by
the highly hindered base NaN(SiMe3)2 was first described in
2001.2a In that case the dianionic β-diketiminate Sc amide
formed was unstable and transferred immediately to a binuclear
conditions, including deprotonation via an amine2a or an alkane
elimination2b−f or an β-diketiminate elimination to a dianionic
ligand,3a,b reduction to a di- or trianionic ligand,4a−e and
oxidation to a dimer or a proligand.4f In particular, the dianionic
β-diketiminate ligands formed are highly reactive.3a,5 The
reactivity of L′TmL toward ammonium borate led to the direct
preparation of cationic β-diketiminate Tm complexes [TmL2]-
[BPh4] and [TmL2][B(C6F5)4] in good yields via protonation
of L′.3a
Cationic organometallic complexes of lanthanide have
attracted increasing attention, as the reactivity of these
complexes in catalytic and stoichiometric reactions has often
led to improved activity with respect to their neutral analogues
and in some cases allowed the development of completely new
Received: November 7, 2011
Published: February 2, 2012
© 2012 American Chemical Society
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Scheme 1. Reaction of LLnCl2(THF)2 with NaN(SiMe3)2: Influence of Lanthanide Metals
Scheme 2. Reaction of LLnCl(μ-Cl)3LnL(THF) with NaN(SiMe3)2: Influence of the Lanthanide Metals
Sc amide complex via dimerization of the newly formed highly
reactive dianionic β-diketiminate ligand.2a Thus, no dianionic β-
diketiminate lanthanide amide complex could be used to date.
In a continuation of our study on the reactivity of β-
diketiminate ligands in a sterically demanding complex,4e,8 we
found that the dianionic β-diketiminate lanthanide amide
complexes L′LnN(SiMe3)2(THF) (L′ = {(2,6-iPr2C6H3)NC-
(CH2)CHC(CH3)N(2,6-iPr2C6H3)}2−, Ln = Yb (1), Y (2), Gd
(3), Sm (4)) could be synthesized by the reaction of LLnCl2
(THF)2 with 2 equiv of NaN(SiMe3)2, via deprotonation of the
L ligand (L = {(2,6-iPr2C6H3)NC(CH2)CHC(CH3)N(2,6-
iPr2C6H3)} by the −N(SiMe3)2 group. The deprotonation
reaction is greatly influenced by the size of the central metals.
For the large Nd metal the deprotonation of L did not occur in
any cases. In contrast, the deprotonation product 1 was isolated
as the only product in all the cases with the small Yb metal. For
the medium-sized Sm metal, the presence of THF molecules is
crucial for the occurrence of a deprotonation reaction. The
cationic amide complex [LSmN(SiMe3)2(THF)2]+[BPh4]− (7)
could be synthesized in high yield by the reaction of 4 with
[HNEt3][BPh4]. Here we wish to report the results, and the
pathway for the deprotonation of L is also discussed.
(2,6-iPr2C6H3)}2−; Ln = Yb (1), Y (2), Gd (3), Sm (4)):
Influence of the Lanthanide Metals. The reaction of
LYbCl2(THF)2 (L = {[(2,6-iPr2C6H3)NC(CH3)]2CH}−) with
2 equiv of NaN(SiMe3)2 at room temperature was first tried in
toluene solution. The solution changed gradually from red to
dark green during the reaction period. After workup dark green
crystals were isolated in 40% yield. Elemental analysis of the
crystals is consistent with the formula of L′YbN(SiMe3)2(THF)
(1) (Scheme 1). Complex 1 was further confirmed by an X-ray
crystal structure analysis. The formation of 1 indicates that the
reaction proceeds with the elimination of a hydrogen atom
from a methyl group of the ligand backbone by a −N(SiMe3)2
group and formation of a methylene moiety.
Further study revealed that an addition of a small amount of
THF could result in an increase in the yield up to 70%.
To see the generality of the deprotonation reaction, the same
reactions with the dichlorides of lanthanide metals of Y, Gd,
and Sm were conducted in a mixture of toluene and THF. All
reactions went smoothly and a color change for all the cases
was observed (from yellow to orange for Y and Gd and yellow
to red for Sm). After workup, the analogous complexes
L′LnN(SiMe3)2(THF) were prepared as pale yellow crystals for
Y (2), orange crystals for Gd (3), and red crystals for Sm (4) in
moderate yields (54% for 2, 48% for 3, and 43% for 4)
(Scheme 1).
RESULTS AND DISCUSSION
■
Synthesis and Molecular Structures of Dianionic β-
Diketiminate Lanthanide Amide Complexes L′LnN-
(SiMe3)2(THF) (L′ = {(2,6-iPr2C6H3)NC(CH2)CHC(CH3)N-
Complexes 2−4 were further confirmed by single-crystal X-
ray structural analyses.
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Scheme 3. Proposed Mechanism for the Deprotonation of L
However, replacing the above dichlorides by the large Nd
metal complex LNdCl2(THF)2 did not afford the analogous
complex L′NdN(SiMe3)2 whether the solvent was toluene or a
mixture of toluene and THF; the normal diamide complex
LNd[N(SiMe3)2]2 (5) was isolated instead (Scheme 1).
Complex 5 was confirmed by elemental analysis, IR, and an
X-ray structure analysis. Obviously, in the present case
deprotonation of L could not occur. This might be because
the ionic radius of Nd metal is the largest in comparison to the
above metals, which makes the coordination environment
around the Nd metal less crowded and the coordination of the
second −N(SiMe3)2 group to the Nd metal is allowed.
Therefore, a crowded coordination environment around the
central metal might be required for the occurrence of
deprotonation of L.
The formation of 4 is somewhat surprising, as a similar
reaction with the triply bridged dichloride LSmCl(μ-Cl)3SmL-
(THF) in toluene was reported to give the normal diamide
complex LSm[N(SiMe3)2]2.9 Therefore, the metathesis reac-
tion of LSmCl(μ-Cl)3SmL(THF), which was prepared as
yellow crystals according to the published procedure,9 with 2
equiv of NaN(SiMe3)2 was carried out again in toluene. Indeed,
only the diamide complex LSm[N(SiMe3)2]2 was isolated in
48% yield and no complex 4 was detected (Scheme 2).
However, addition of a small amount of THF into the above
reaction solution led to the occurrence of deprotonation of L
with the formation of 4 (Scheme 2), indicating that the
presence of THF is the key point for the formation of 4.
In contrast, a similar reaction with the small Yb metal
analogue LYbCl(μ-Cl)3YbL(THF) in toluene gave the
deprotonation product 1 only. In this case the presence of
THF is not necessary. The difference in outcome between the
two reactions should be attributed to the smaller ionic radius of
Yb metal, in comparison to the Sm metal, which makes the
coordination sphere around the Yb metal more crowded, and
the entrance of the second hindered −N(SiMe3)2 group
becomes impossible even without the presence of a THF
molecule.
LLnCl2(THF)2 to form a monoamide with a loose THF
molecule A (Scheme 3). The intermediate A reacts with
another NaN(SiMe3)2 immediately by C−H bond breaking due
to the steric congestion around the metal center, which favors
the base-assisted dehydrochlorination via monodeprotonation
of a methyl group on the backbone of L instead of a
nucleophilic Cl/N(SiMe3)2 substitution (Scheme 3). The
existence of the loosely coordinated THF molecule in the
coordination sphere certainly makes the intermediate (A) more
crowded in comparison with that without the THF, thereby
favoring the occurrence of deprotonation. For the small Yb
metal the presence of a loose coordinated THF in the
intermediate might be not necessary.
To further confirm the assumption, monoamide complexes
LLn[N(SiMe3)2]Cl (Ln = Sm, Yb (6)) were synthesized by the
reaction of LLnCl2(THF)2 with 1 equiv of NaN(SiMe3)2 and
complex 6 was fully characterized including an X-ray diffraction
as it is a novel one. Treatment of 6 with 1 equiv of
NaN(SiMe3)2 either in toluene or in a mixture of toluene and
THF at room temperature both afforded 1 as the only product
(Scheme 4). In contrast, the reaction of LSm[N(SiMe3)2]Cl
Scheme 4. Reactions of LLn[N(SiMe3)2]Cl with
NaN(SiMe3)2
with 1 equiv of NaN(SiMe3)2 yielded different outcomes
depending on the reaction solvent used: the normal diamide
complex LSm[N(SiMe3)2]2 for toluene but complex 4 for a
mixture of toluene and THF (Scheme 4).
Deprotonation of a β-diketiminate ligand by an alkyl or
amide group in a thermally unstable complex is well
documented.2a,d However, the diamide complexes LNd[N-
(SiMe3)2]2 (5) and LSm[N(SiMe3)2]2 are thermally stable.
Heating a solution of LSm[N(SiMe3)2]2 in THF at 60 °C for
72 h did not lead to deprotonation of L, and LSm[N(SiMe3)2]2
was recovered completely, indicating complex 4 is formed by an
intermolecular deprotonation process, not an intramolecular
pathway.
Molecular Structures of 1−6. Single crystals of complexes
1−4 suitable for X-ray diffraction analysis were obtained by
recrystallization from a mixture of toluene and n-hexane at −10
°C. All the complexes crystallize in the orthorhombic space
group P21/n with a toluene molecule in the unit cell. The
molecular structure of complexes 1−4 are shown in Figure 1 as
they are isostructural. Selected bond lengths and angles are
given in Table 1. All the complexes are THF-solvated
monomers. The coordination of a THF molecule is not
surprising, because of the low coordination number of 4 (see
Thus, the deprotonation of L in the present case proceeds by
the following steps, as described previously.2a The first step is
monosubstitution of one of the chlorine atoms in
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(6) and 2.334(3) Å in [LSmN(SiMe3)2(Cl)]9) but very close
to the corresponding Ln−Namide distances. The bond
parameters feature the dianionic nature of L′ in complexes
1−4. Each Ln(L′) moiety in 1−4 is best described as η3-1-
azaallyl (C3−C4−N2) and amido (N1) centered bonds to the
Ln atom. Thus, the Ln···C3 (2.899(12) Å for 1, 2.857(6) Å for
2, 2.887(9) Å for 3, and 2.890(6) Å for 4) and Ln···C4 contacts
(2.780(11) Å for 1, 2.771(5) Å for 2, 2.775(8) Å for 3, and
2.800(5) Å for 4) are near the upper range of LnCp3 distances
(2.62(1)−2.79(1) Å, average 2.69 Å for Cp3Yb(NC4H4N)-
YbCp3;10a 2.614(11)−2.859(14) Å, average 2.73 Å for
[YCp3];10b 2.766(2)−2.897(4) Å, average 2.80 Å for
[GdCp3];10c 2.78(2)−2.91(3) Å, average 2.82 Å for
[SmCp3]10d), whereas the Ln···C3 contact is longer
(2.899(12) Å for 1, 2.857(6) Å for 2, 2.887(9) Å for 3, and
2.890(6) Å for 4). The bite angle for L′ (N(1)−Ln−N(2) =
94.6(4)° for 1 and 88.59(17)° for 4) is larger than those found
for L (N(1)−Ln−N(2) = 85.9(2)° in 6 and 81.6(1)° in
[LSmN(SiMe3)2(Cl)]9). The wider ligand bite angle leads to
facilitating the Ln···C(3,4) close contacts in theLn(L′) moiety.
Most notably, deprotonation of the methyl on the β-carbon
is evident from shortening of the sp3 H3C−C bond to an sp2
H2CC bond (1.518(16) Å (1), 1.526(8) Å (2), 1.522(11) Å
(3), 1.520(8) Å (4) for an sp3 CH3−C bond vs 1.373(16) Å
(1), 1.364(8) Å (2), 1.333(11) Å (3), 1.359(9) Å (4) for the
sp2 CH2C bond).
Figure 1. ORTEP diagram of L′LnN(SiMe3)2(THF) (Ln = Yb (1), Y
(2), Gd (3), Sm (4)), showing the atom-numbering scheme. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms are
omitted for clarity.
Table 1. Selected Bond Lengths (Å) and Bond Angles (deg)
for Complexes 1−4
The molecular structures of 5 and 6 are shown in Figures 2
and 3, respectively. Both complexes are solvent-free monomers,
1
2
3
4
Bond Lengths
2.177(4)
2.241(5)
2.227(5)
2.337(4)
2.294(9)
2.857(6)
2.771(5)
1.381(8)
1.382(7)
1.364(8)
1.489(9)
1.380(8)
1.526(8)
Bond Angles
93.15(17)
Ln(1)−N(1)
Ln(1)−N(2)
Ln(1)−N(3)
Ln(1)−O(1)
Ln(1)−C(2)
Ln(1)−C(3)
Ln(1)−C(4)
N(1)−C(2)
N(2)−C(4)
C(1)−C(2)
C(2)−C(3)
C(3)−C(4)
C(4)−C(5)
2.151(9)
2.196(9)
2.179(9)
2.273(8)
2.874(12)
2.899(12)
2.780(11)
1.382(15)
1.407(13)
1.373(16)
1.474(17)
1.390(16)
1.518(16)
2.223(7)
2.283(7)
2.262(7)
2.412(7)
2.922(9)
2.887(9)
2.775(8)
1.386(11)
1.355(10)
1.333(11)
1.493(12)
1.411(12)
1.522(11)
2.239(4)
2.294(5)
2.291(5)
2.443(4)
2.933(6)
2.889(6)
2.799(5)
1.388(8)
1.371(7)
1.359(9)
1.472(8)
1.393(8)
1.520(8)
N(1)−Ln(1)−
94.6(4)
90.8(3)
88.59(17)
114.54(18)
128.33(17)
N(2)
N(1)−Ln(1)−
116.6(4)
131.6(4)
116.07(19)
130.37(17)
114.5(3)
128.5(3)
N(3)
N(2)−Ln(1)−
N(3)
Figure 2. ORTEP diagram of LNd[N(SiMe3)2] (5) showing the atom-
numbering scheme. Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Nd(1)−N(1) = 2.163(3), Nd(1)−
N(2) = 2.471(2), Nd(1)−N(3) = 2.327(2), Nd(1)−N(4) = 2.342(3),
N(1)−C(2) = 1.344(4), C(2)−C(3) = 1.390(4), C(3)−C(4) =
1.403(4), C(4)−N(2) = 1.343(4); N(1)−Nd(1)−N(2) = 77.36(7).
below). Each Ln metal ion in 1−4 is four-coordinate and is
bound to the two nitrogen atoms of the chelating β-
diketiminate dianion (L′), one −N(SiMe3)2 ligand, and one
coordinated THF molecule. The coordination geometry can be
described as a distorted tetrahedron. The of Ln−N bond
distances (Ln−N(1) and Ln−N(2) bonds) are 2.151(9) and
2.196(9) Å for 1, 2.177(4) and 2.241(5) Å for 2, 2.223(7) and
2.283(7) Å for 3, 2.239(4) and 2.294(5) Å for 4, which are
quite comparable with each other, when the differences in ionic
radii among the lanthanide metals are considered. The values
are 0.058−0.103 Å (for 1) and 0.040−0.095 Å (for 4) shorter
than those found in the corresponding lanthanide monoanionic
β-diketiminate derivatives (2.254(6) Å in [LYbN(SiMe3)2(Cl)]
but there is 0.5 toluene molecule in the unit cell for 5. The four-
coordinated central Nd atom in 5 is ligated by four nitrogen
atoms from the L ligand and the two −N(SiMe3)2 groups,
while the four-coordinated central Yb atom in 6 is ligated by
two nitrogen atoms from the L ligand, one −N(SiMe3)2 group,
and one chlorine atom. The coordination geometry around
each metal can be described as a distorted tetrahedron. The
solid-state structures of 5 and 6 are quite similar to those of
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Figure 3. ORTEP diagram of LYb[N(SiMe3)2]Cl (6) showing the
atom-numbering scheme. Thermal ellipsoids are drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Yb(1)−N(1) = 2.225(6), Yb(1)−
N(2) = 2.254(6), Yb(1)−N(3) = 2.174(6), Yb(1)−Cl(1) = 2.489(2),
N(1)−C(2) = 1.341(9), C(2)−C(3) = 1.417(9), C(3)−C(4) =
1.411(10), C(4)−N(2) = 1.333(9); N(1)−Yb(1)−N(2) = 85.9(2).
Figure 4. ORTEP diagram of [LSmN(SiMe3)2(THF)2]+[BPh4]− (7)
showing the atom-numbering scheme. Thermal ellipsoids are drawn at
the 30% probability level. Hydrogen atoms, iPr substituent of L and
BPh4 are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Sm(1)−N(1) = 2.380(3), Sm(1)−N(2) = 2.384(3), Sm(1)−
N(3) = 2.280(3), Sm(1)−O(1) = 2.490(3), Sm(1)−O(2) = 2.506(3),
Sm(1)−C(2) = 3.087(4), Sm(1)−C(3) = 3.274(4), Sm(1)−C(4) =
3.162(4), N(1)−C(2) = 1.343(5), N(2)−C(4) = 1.326(5), C(1)−
C(2) = 1.528(6), C(2)−C(3) = 1.385(6), C(3)−C(4) = 1.420(6);
their analogous Sm complexes LSm[N(SiMe3)2]2 and LSm[N-
(SiMe3)2]Cl9 reported previously. The bond distances N(1)−
C(2), C(2)−C(3), C(3)−C(4), C(4)−N(2) (1.344(4),
1.390(4), 1.403(4), 1.343(4) Å for 5; 1.341(9), 1.417(9),
1.411(10), 1.333(9) Å for 6) suggest significant delocalization
within the π- ystem of the β-diketiminate ligand.
O(1)−Sm(1)−N(2)
= 112.99(11), O(1)−Sm(1)−N(3) =
137.65(11), O(2)−Sm(1)−N(1) = 144.02(11), N(2)−Sm(1)−N(3)
= 109.34(12).
Synthesis and Characterization of the Cationic
S a m a r i u m A m i d e C o m p l e x [ L S m N -
(SiMe3)2(THF)2]+[BPh4]− (7). The reaction of complex 4
with [HNEt3][BPh4] was tried with the aim of developing a
useful route for the synthesis of cationic lanthanide amide
complexes. Treatment of 4 with 1 equiv of [HNEt3][BPh4] in
THF at room temperature resulted in an immediate color
change of the reaction solution from red to yellow. Removing
the volatiles, washing with hexane, and extracting with THF
gave yellow crystals in 85% yield upon crystallization.
two nitrogen atoms from the L ligand, one nitrogen atom of the
−N(SiMe3)2 group, and two oxygen atoms from the two THF
molecules in a distorted-trigonal-bipyramidal geometry. The
nitrogen N(1) of the β-diketiminate ligand and the O(2) of one
THF ligand occupy the apical positions with the angle of
N(1)−Sm−O(2) being 144.02(11)°, which deviates greatly
from 180°. The nitrogen atom N(2), oxygen atom O(1), and
the nitrogen N(3) of the amido group are located at the
equatorial vertices, with the sum of these bond angles around
the Sm atom of 359.98°. The bond distances N(1)−C(2)
(1.343(5) Å), C(1)−C(2) (1.528(6) Å), C(2)−C(3)
(1.385(6) Å), and N(2)−C(4) (1.420(6) Å) suggest significant
delocalization within the π system of the β-diketiminate ligand.
The Sm−C(2,3,4) distances are quite long, indicating a
negligible π contribution to the β-diketiminate−Sm bonding
in this complex. The bond parameters in the LSm part are quite
comparable with those found in the cationic thulium β-
diketiminate.3a The bond distance Sm−N(amide) = 2.280(3) Å
can be compared to 2.005(2) Å found in the cationic amide
complex,7c when the difference in ionic radii between Sm and
Sc metals is considered.
The elemental analysis of the crystals is consistent with the
formula of the cationic amide complex [LSmN-
(SiMe3)2(THF)2]+[BPh4]− (7) (Scheme 5). The IR spectra
Scheme 5. Synthesis of Complex 7
of complex 7 exhibited strong absorptions near 1551 cm−1,
indicating partial CN double-bond character.11 Complex 7
was further confirmed by an X-ray crystal structure analysis.
Complex 7 is soluble in THF but not in nonpolar solvents
such as hexane and toluene.
The molecular structure of 7 is shown in Figure 4. Complex
7 consists of separated ion pairs of the THF-solvated cationic
species [LSmN(SiMe3)2(THF)2]+ and the anion of [BPh4]−.
The five-coordinated central Sm atom in the cation is ligated by
CONCLUSION
■
A series of dianionic β-diketiminate lanthanide monoamide
complexes, L′LnN(SiMe3)2(THF) (Ln = Yb (1), Y (2), Gd (3),
Sm (4)), were prepared via deprotonation of L by an
−N(SiMe3)2 group, which represents the first examples of
lanthanide amides supported by a dianionic β-diketiminate
ligand. The size of the lanthanide metal has a profound
influence on the deprotonation reaction of L, indicating that an
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Article
123.8, 83.5, 63.6, 36.4, 35.3, 30.7, 29.8, 28.4, 27.3, 27.1, 26.1, 25.7,
25.2, 24.2, 21.8, 20.9. Anal. Calcd for C46H74N3OSi2Sm (891.61): C,
61.97; H, 8.37; N, 4.71. Found: C, 61.52; H, 8.12; N, 4.88. IR (KBr,
cm−1): 3062 (w), 2962 (m), 2869 (w), 1623 (s), 1550(vs), 1378 (s),
1233 (s), 1065 (m), 1058 (m), 633 (m), 505 (s).
Method 2. A solution of NaN(SiMe3)2 in toluene (20.0 mL, 6.00
mmol) was added to a slurry of LSmCl(μ-Cl)3SmL(THF) (1.54 g,
1.50 mmol) in about 25 mL of toluene as soon as possible, and about 5
mL of THF was added to the reaction mixture. The reaction mixture
was stirred at room temperature for 24 h, and the undissolved portion
was then removed by centrifugation. The red solution obtained was
concentrated to about 2 mL, and 4 mL n-hexane was then added. The
solution was cooled to −10 °C for crystallization to give red crystals of
4 in 45% yield (1.20 g).
overcrowded coordination environment around the central
metal is necessary for deprotonation of L. By virtue of the high
reactivity of the dianionic β-diketiminate ligand, the corre-
sponding cationic Sm amide complex [LSmN-
(SiMe3)2(THF)2]+[BPh4]− (7) was synthesized in high yield
by the reaction of 4 with [HNEt3][BPh4] and structurally
characterized. The reactivity of dianionic β-diketiminate ligands
in lanthanide derivatives toward small molecules is ongoing in
our laboratory.
EXPERIMENTAL SECTION
■
Materials and Methods. All manipulations were performed under
a purified argon atmosphere using standard Schlenk techniques.
Solvents were degassed and distilled from sodium benzophenone ketyl
before use. Anhydrous LnCl3 was prepared according to the literature
procedure.12 The proligand LH (L = {[(2,6-iPr2C6H3)NC-
(CH3)]2CH}−)13 and the complexes LLnCl2(THF)2 (Ln = Yb, Y,
Gd, Sm),14 LLnCl(μ-Cl)3LnL(THF) (Ln = Yb,14 Sm9), and
LSm[N(SiMe3)2]Cl9 were prepared by the methods reported.
[HNEt3][BPh4] was prepared according to the literature method.15
1H NMR and 13C NMR spectra were recorded on a 400 MHz
instrument and processed using MestReNova software. Elemental
analyses were performed by direct combustion using a Carlo-Erba EA
1110 instrument. The IR spectra were recorded on a Nicolet-550 FT-
IR spectrometer as KBr pellets. The uncorrected melting points of
crystalline samples were determined in sealed Ar-filled capillaries.
L′YbN(SiMe3)2(THF)·(toluene) (1). To a slurry of LYbCl2(THF)2
(2.19 g, 3.00 mmol) in about 30 mL of toluene was added a solution of
NaN(SiMe3)2 in toluene (20.0 mL, 6.00 mmol) as soon as possible,
and about 5 mL of THF was added to the reaction mixture. The
reaction mixture was stirred at room temperature for 24 h, and the
undissolved portion was then removed by centrifugation. The dark
green solution obtained was concentrated to about 2 mL, and 4 mL of
n-hexane was then added. The solution was cooled to −10 °C for
crystallization to give dark green crystals of 1 in 70% yield (1.92 g).
Mp: 145−148 °C dec. Anal. Calcd for C46H74N3OSi2Yb (914.3): C,
60.43; H, 8.16; N, 4.60. Found: C, 59.98; H, 8.02; N, 5.42. IR (KBr,
cm−1): 3064 (w), 2962 (s), 2868 (m), 2318 (w), 1622 (s), 1550 (s),
1252 (s), 1156 (m), 935 (m), 840 (m), 503 (m).
LNd[N(SiMe3)2]2·0.5(toluene) (5). To a slurry of LNdCl2(THF)2
(2.19 g, 3.00 mmol) in about 30 mL of toluene was added a solution of
NaN(SiMe3)2 in toluene (20.0 mL, 6.00 mmol). The reaction mixture
was stirred at room temperature for 24 h, and the undissolved portion
was then removed by centrifugation. The yellow-green solution
obtained was concentrated to about 5 mL. The solution was cooled to
−10 °C for crystallization to give yellow-green crystals of 7 in 52%
yield (1.45 g). Mp: 263−266 °C. Anal. Calcd for C44.50H81N4NdSi4
(928.73): C, 57.55; H, 8.79; N, 6.03. Found: C, 57.83; H, 8.62; N,
5.85. IR (KBr, cm−1): 3064 (w), 2360 (m), 2340 (m), 1622 (s), 1550
(s), 1306 (s), 1252 (s), 1156 (m), 935 (m), 924 (s), 840 (m), 790
(m), 771 (m), 731 (m), 665 (s), 605 (m).
LYb[N(SiMe3)2]Cl (6). A solution of NaN(SiMe3)2 in toluene (10.0
mL, 3.00 mmol) was added dropwise to a slurry of LYbCl2(THF)2
(2.41 g, 3.00 mmol) in about 20 mL of toluene. The reaction mixture
was stirred at room temperature for 12 h. The undissolved portion was
then removed by centrifugation. The red solution was concentrated to
about 5 mL. The solution was cooled at −10 °C for crystallization to
give red crystals of 6 in 45% yield (1.06 g). Mp: 225−228 °C dec.
Anal. Calcd for C35H59Cl N3Si2Yb (786.52): C, 53.45; H, 7.56; N,
5.34. Found: C, 53.18; H, 7.65; N, 5.42. IR (KBr, cm−1): 3053 (w),
2961 (s), 2926 (w), 2673 (m), 1621 (s), 1551(vs), 1488 (m), 1367
(m), 1324 (m), 1220 (m), 789 (m), 759 (m), 611 (w).
Reaction of LYb[N(SiMe3)2]Cl (6) with NaN(SiMe3)2. To a
slurry of LYb[N(SiMe3)2]Cl (2.36 g, 3.00 mmol) in about 30 mL of
toluene was added a solution of NaN(SiMe3)2 in toluene (10.0 mL,
3.00 mmol), and about 4 mL of THF was added to the reaction
mixture. The reaction mixture was stirred at room temperature for 24
h. The undissolved portion was then removed by centrifugation. The
dark green solution was concentrated to about 2 mL, and 4 mL of n-
hexane was then added. The solution was cooled to −10 °C for
crystallization to give dark green crystals of 1 in 73% yield (2.00 g).
Reaction of LSm[N(SiMe3)2]Cl with NaN(SiMe3)2 in Toluene.
To a slurry of LSm[N(SiMe3)2]Cl (2.29 g, 3.00 mmol) in about 30
mL of toluene was added a solution of NaN(SiMe3)2 in toluene (10.0
mL, 3.00 mmol). The reaction mixture was stirred at room
temperature for 24 h. The undissolved portion was removed by
centrifugation. The yellow solution was concentrated to about 6 mL
and then cooled to −10 °C for crystallization to give yellow crystals of
LSm[N(SiMe3)2]2 in 46% yield (1.68 g).
Reaction of LSm[N(SiMe3)2]Cl with NaN(SiMe3)2 in a
Toluene/THF Mixture. To a slurry of LSm[N(SiMe3)2]Cl (2.29 g,
3.00 mmol) in about 30 mL of toluene were added a solution of
NaN(SiMe3)2 in toluene (10.0 mL, 3.00 mmol) and about 4 mL of
THF. The reaction mixture was stirred at room temperature for 24 h.
The undissolved portion was removed by centrifugation. The red
solution was concentrated to about 2 mL, and 4 mL of n-hexane was
then added. The solution was cooled to −10 °C for crystallization to
give red crystals of 4 in 50% yield (0.89 g).
L′YN(SiMe3)2(THF)·(toluene) (2). The synthesis of complex 2 was
carried out in the same way as that described for complex 1; pale
yellow crystals of 2 suitable for X-ray crystal structure analysis were
1
obtained (1.34 g, 54%). Mp: 155−158 °C dec. H NMR (400 MHz,
C6D6): δ 7.16−6.99 (m, 6 H), 5.09 (s, 1 H), 3.74 (m, 4 H), 3.09 (s, 2
H), 1.57 (d, 3 H), 1.49 (m, 4 H), 1.41 (d, 3 H), 1.33 (d, 18 H), 1.06
(m, 4 H), 0.00 (s, 18 H); 13C NMR (101 MHz, C6D6): 168.2, 153.9,
147.8, 147.4, 145.1, 144.7, 143.9, 142.7, 142.1, 141.8, 138.1, 129.5,
128.7, 124.7, 123.1, 98.0, 32.1, 30.8, 30.7, 28.6, 28.3, 27.3, 26.8, 26.4,
26.3, 26.0, 25.8, 25.5, 25.2, 24.9, 24.5, 24.3, 23.2, 21.6. Anal. Calcd for
C46H74N3OSi2Y (830.17): C, 66.55; H, 8.98; N, 5.06. Found: C, 66.13;
H, 8.64; N, 4.89. IR (KBr, cm−1): 3062 (w), 2961 (s), 2868 (m), 2361
(w), 1623 (s), 1551 (s), 1252 (s), 935 (m), 788 (m), 758 (s).
L′GdN(SiMe3)2(THF)·(toluene) (3). The synthesis of complex 3
was carried out in the same way as that described for complex 1;
orange crystals of 3 suitable for X-ray crystal structure analysis were
obtained (1.29 g, 48%), Mp: 158−160 °C dec. Anal. Calcd for
C46H74N3OSi2Gd (898.51): C, 61.49; H, 8.30; N, 4.68. Found: C,
61.12; H, 8.21; N, 4.42. IR (KBr, cm−1): 3062 (w), 2961 (s), 2868
(m), 2356 (w), 1623 (s), 1552 (s), 1252 (s), 935 (m), 844 (m), 758
(s), 504 (m).
L′SmN(SiMe3)2(THF)·(toluene) (4). Method 1. The synthesis of
complex 4 was carried out in the same way as that described for
complex 1, red crystals 4 suitable for X-ray crystal structure analysis
[LSmN(SiMe3)2(THF)2]+[BPh4]− (7). Into a red solution of 4 (0.89
g, 1.00 mmol) in THF (20 mL) was added dropwise a THF (10 mL)
solution of [HNEt3][BPh4] (0.42 g, 1.00 mmol) at room temperature
with stirring. During this period, the reaction mixture was changed
color from red to yellow. The reaction mixture was stirred for another
4 h. The volatiles were removed under reduced pressure, and the
residues were washed three times with about 10 mL portions of n-
1
were obtained (1.15 g, 43%), Mp: 160−162 °C dec. H NMR (400
MHz, C6D6): δ 7.45−6.96 (m, 6 H), 5.64 (s, 1 H), 3.87 (s, 3 H), 3.05
(s, 2 H), 2.68−2.62 (d, 9 H), 2.11 (s, 3 H), 1.27 (s, 3 H), 0.89−0.79
(d, 6 H), −0.22 (s, 3 H), −1.78 (s, 18 H). 13C NMR (101 MHz,
C6D6): 153.2, 152.0, 140.7, 139.2, 138.2, 137.7, 126.0, 125.4, 124.2,
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Table 2. Crystallographic Data for Complexes 1−4
1
2
3
4
empirical formula
formula wt
temp (K)
cryst syst
space group
cryst size (mm)
a (Å)
C46H74N3OSi2Yb
914.3
C46H74N3OSi2Y
830.17
C46H74N3OSi2Gd
898.51
C46H74N3OSi2Sm
891.61
223(2)
223(2)
223(2)
223(2)
orthorhombic
P21/n
orthorhombic
P21/n
orthorhombic
P21/n
orthorhombic
P21/n
0.50 × 0.10 × 0.10
11.7551(13)
18.556(2)
21.673(3)
90
0.60 × 0.25 × 0.20
11.7778(8)
18.5593(12)
21.6903(15)
90
0.55 × 0.15 × 0.10
11.7938(11)
18.5139(18)
21.713(2)
90
0.30 × 0.30 × 0.20
11.7896(12)
18.507(2)
21.740(3)
90
b (Å)
c (Å)
α (deg)
β (deg)
90
90
90
90
γ (deg)
90
90
90
90
V (Å3)
4727.48(90)
4
4741.2(6)
4
4741.0(8)
4
4743.6(9)
4
Z
Dcalcd (mg cm−3)
1.285
1.163
1.259
1.248
−1
abs coeff (mm )
2.063
1.315
1.484
1.323
F(000)
1908
1784
1884
1876
θ range (deg)
3.03−25.50
19 628/8629
0.0824
3.02−25.50
24 485/8798
0.0678
3.02−25.50
14 324/8365
0.0646
3.02−25.50
17 378/8477
0.0380
no. of collected/unique rflns
R(int)
no. of data/restraints/params
goodness of fit on F2
final R1 (I > 2σ(I))
wR2 (all data)
8629/27/432
1.106
8798/27/432
1.079
8365/49/444
1.105
8477/28/445
1.084
0.0791
0.0936
0.0745
0.0542
0.1483
0.1713
0.1229
0.1118
Table 3. Crystallographic Data for Complexes 5−7
5
6
7
empirical formula
formula wt
temp (K)
cryst syst
space group
cryst size (mm)
a (Å)
C44.50H81N4NdSi4
928.73
C35H59ClN3Si2Yb
786.52
C67H95BN3O2Si2Sm
1191.80
223(2)
223(2)
223(2)
triclinic
monoclinic
P21/n
triclinic
P1
̅
P1
̅
0.60 × 0.60 × 0.50
11.7324(3)
11.7814(2)
20.5952(6)
75.163(3)
79.407(3)
68.293(3)
2544.08(11)
2
0.25 × 0.20 × 0.07
17.156(5)
18.248(5)
13.096(4)
90
0.40 × 0.40 × 0.20
12.9937(18)
13.2278(19)
18.722(3)
87.865(7)
84.872(6)
82.374(7)
3175.6(8)
2
b (Å)
c (Å)
α (deg)
β (deg)
104.166(4)
90
γ (deg)
V (Å3)
3975.3(18)
4
Z
−3
Dcalcd (mg cm )
1.212
1.314
1.246
−1
abs coeff (mm )
1.146
2.505
1.006
F(000)
984
1620
1258
θ range (deg)
3.08−25.50
12 138/8630
0.0678
3.14−25.50
17 901/7373
0.0824
3.15−25.50
27 301/11 741
0.0563
no. of collected/unique rflns
R(int)
no. of data/restraints/params
goodness of fit on F2
final R1 (I > 2σ(I))
wR2 (all data)
8630/8/496
1.064
7373/0/396
1.164
11 741/22/672
1.120
0.0303
0.0767
0.0529
0.0764
0.1046
0.1127
hexane. The solids were dissolved in THF, and the solution was kept
at −10 °C for crystallization. Complex 7 was isolated as yellow crystals
after several days. Yield: 1.01 g (85%). Mp: 168−170 °C dec. Anal.
Calcd for C67H95BN3O2Si2Sm (1191.80): C, 67.52; H, 8.03; N, 3.53.
Found: C, 67.28; H, 7.84; N, 3.65. IR (KBr, cm−1): 3215 (m), 3057
(m), 2960 (s), 2867 (m), 1621 (s), 1551(vs), 1383 (m), 1276 (m),
1254 (m), 1058 (m), 743 (s), 714 (s), 601 (m).
X-ray Crystallography. Suitable single crystals of complexes 1−7
were sealed in thin-walled glass capillaries, to determine the single-
crystal structures. Intensity data were collected with a Rigaku Mercury
CCD area detector in ω scan mode using Mo Kα radiation (λ = 0.710
70 Å). The diffracted intensities were corrected for Lorentz−
polarization effects and empirical absorption corrections. Details of
the data collection and crystal data for complexes 1−7 are given in
Tables 2 and 3. The structures were solved by direct methods and
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Article
refined by full-matrix least-squares procedures based on |F|2. All the
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms in these complexes were all generated geometrically (C−H
bond lengths fixed at 0.95 Å), assigned appropriate isotropic 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 the SHELXL-97
program. CCDC-820930 (for 1), -820929 (for 2), -835065 (for 3),
-820927 (for 4), -846319 (for 5), -846318 (for 6), and -835064 (for 7)
contain supplementary crystallographic 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.
(9) Cui, C. M.; Shafir, A.; Schmidt, J. A. R.; Olivera, A. G.; Arnold, J.
Dalton Trans. 2005, 1387.
(10) (a) Baker, E. C.; Raymond, K. N. Inorg. Chem. 1977, 16, 2710.
(b) Roger, R. D.; Atwood, J. L.; Emad, A.; Sikora, D. J.; Rausch, M. D.
J. Organomet. Chem. 1981, 216, 383. (c) Roger, R. D.; Bynum, R. V;
Atwood, J. L. J. Organomet. Chem. 1980, 192, 65. (d) Evans, M. J.;
Gonzales, S. L.; Ziller, J. W. J. Am. Chem. Soc. 1991, 113, 7423.
(11) Yao, Y. M.; Xue, M. Q.; Luo, Y. J.; Zhang, Z. Q.; Jiao, R.; Zhang,
Y.; Shen, Q.; Wong, W. J. Organomet. Chem. 2003, 678, 108.
(12) Taylor, M. D.; Carter, C. P. J. Inorg. Nucl. Chem. 1962, 387.
(13) Feldman, J.; Mclain, S. T.; Parthasarathy, A.; Marshall, W. J.;
Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16, 1514.
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ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving X-ray crystallographic data of complexes 1−7.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the National Natural Science Foundation of
China (Grant No. 20972107, 21132002) for financial support.
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