Synthesis of rare earth metal complexes incorporating amido and enolate mixed ligands: Characterization and reactivity

Article abstract of DOI:10.1016/j.poly.2008.05.030

The reactions of 2,6-(R)₂C₆H₃NHSiMe₃ (R = iPr or Et) with excess nBuLi in THF or n-hexane, followed by treatment with LnCl₃, produced different kinds of rare earth metal complexes. Complexes incorporating amido and enolate mixed ligands having the general formula (CH₂{double bond, long}CHO)Ln[2,6-(iPr)₂C₆H₃NSiMe₃]₂(μ-Cl)Li(THF)₃ (Ln = Y(1), Yb(2)) were prepared by the reaction of N-trimethylsilyl-2,6-diisopropylaniline 2,6-(iPr)₂C₆H₃NHSiMe₃ with excess nBuLi in THF, followed by treatment with LnCl₃. Complexes with the formula [2,6-(Et)₂C₆H₃NSiMe₃]₂Y(THF)(μ-Cl)₂Li(THF)₂ (3) and {[2,6-(Et)₂C₆H₃NSiMe₃]₃YCl}[Li(THF)₄] (4) were isolated when 2,6-(Et)₂C₆H₃NHSiMe₃ was treated with nBuLi in n-hexane, followed by treatment with 1/2 or 1/3 equiv. of YCl₃ in THF, respectively. All the structures of the complexes were determined by single-crystal X-ray analyses. Investigation on the reactivity of complexes 1 and 2 towards aromatic aldehydes indicated that the amido ligand of complexes 1 and 2 could selectively react with aromatic aldehydes to afford the disproportionation products of amides and alcohols. The reaction of the lithium amide {[2,6-(iPr)₂C₆H₃](Me₃Si)N}Li with aromatic aldehydes in the presence of a catalytic amount of YCl₃ was also studied.

Full text of DOI:10.1016/j.poly.2008.05.030

Polyhedron 27 (2008) 2757–2764
Contents lists available at ScienceDirect
Polyhedron
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Synthesis of rare earth metal complexes incorporating amido and enolate mixed
ligands: Characterization and reactivity
a
a
a
a
a
Shao-wu Wang a,b, , Hui-min Qian , Wei Yao , Li-jun Zhang , Shuang-liu Zhou , Gao-sheng Yang ,
*
Xian-cui Zhu a, Jia-xi Fan a, Yu-yu Liu a, Guo-dong Chen a, Hai-bin Song c
a Anhui Key Laboratory of Functional Molecular Solids, Institute of Organic Chemistry, College of Chemistry and Materials Science, Anhui Normal University, Wuhu,
Anhui 241000, People’s Republic of China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of China
c State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactions of 2,6-(R)2C6H3NHSiMe3 (R = iPr or Et) with excess nBuLi in THF or n-hexane, followed by
treatment with LnCl3, produced different kinds of rare earth metal complexes. Complexes incorporating
amido and enolate mixed ligands having the general formula (CH2@CHO)Ln[2,6-(iPr)2C6H3NSiMe3]2(l-
Cl)Li(THF)3 (Ln = Y(1), Yb(2)) were prepared by the reaction of N-trimethylsilyl-2,6-diisopropylaniline
Received 17 April 2008
Accepted 22 May 2008
Available online 7 July 2008
2,6-(iPr)2C6H3NHSiMe3 with excess nBuLi in THF, followed by treatment with LnCl3. Complexes with
the formula [2,6-(Et)2C6H3NSiMe3]2Y(THF)(l-Cl)2Li(THF)2 (3) and {[2,6-(Et)2C6H3NSiMe3]3YCl}[Li(THF)4]
Keywords:
Rare earth metals
Complexes
Synthesis
Reactivity
(4) were isolated when 2,6-(Et)2C6H3NHSiMe3 was treated with nBuLi in n-hexane, followed by treatment
with 1/2 or 1/3 equiv. of YCl3 in THF, respectively. All the structures of the complexes were determined by
single-crystal X-ray analyses. Investigation on the reactivity of complexes 1 and 2 towards aromatic alde-
hydes indicated that the amido ligand of complexes 1 and 2 could selectively react with aromatic alde-
hydes to afford the disproportionation products of amides and alcohols. The reaction of the lithium amide
{[2,6-(iPr)2C6H3](Me3Si)N}Li with aromatic aldehydes in the presence of a catalytic amount of YCl3 was
also studied.
Enolate ligand
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
do rare earth metal clusters through a proposed enolate intermedi-
ate, based on the experimental spectroscopic evidences [6].
Recently, rare earth metal complexes have attracted much
attention for their potential applications in catalysis [1,2]. Lantha-
nide complexes incorporating substituted enolate ligands of the
general formula O-CR = CR0R00 are generally derived from CO activa-
tion. For example, the reaction of the samarium(II) complex
Organolanthanide complexes having both cyclopentadienyl (Cp
or MeCp) and a simple enolate ligand (O–CH@CH2) have been re-
ported to be prepared by the direct metallation of the organolanth-
anide chloride, by thermolysis of the organolanthanide alkyl
complexes in THF [7a] or by thermolysis of the corresponding
organolanthanide alkoxides [7b,c]. The synthesis of cyclopentadi-
enyl-free lanthanide complexes incorporating enolate ligands is
far less reported [2].
*
Cp 2Sm(THF)2 with 1,2-di(2-pyrdinyl)ethylene, followed by treat-
ment with CO afforded a novel samarium(III) complex incorporat-
*
ing
a
substituted enolate ligand Cp2 Sm[
*
l-g
4-(C5H4N)CH@
C(O)C(O)@CH(C5H4N)]SmCp2 [3]. Reaction of the samarium(II)
complex Cp 2Sm(THF)2 with CO or reaction of the samarium(II)
complex Cp 2Sm(THF)2 with unsaturated hydrocarbons followed
Given that the Aldol reaction goes through an enolate as an
intermediate when the reaction is carried out in an inorganic base
medium [8], and the lanthanide amides [(Me3Si)2N]3Ln(l-
*
*
by treatment with CO also gave novel lanthanide complexes incor-
porating enolate-like ligands [4,5]. More recently, Hou and his
coworkers reported the reaction of CO with the tetranuclear yt-
Cl)Li(THF)3 can initiate disproportionation of aromatic aldehydes
to amides and alcohols [9a], and the lanthanide amides [(Me3-
Si)2N]3Ln can be the catalysts for amidation of aldehydes with
amines [9b] and the Tishchenko reaction [9c] through the addition
of the amido group (Me3Si)2Nꢀ or (R1R2)Nꢀ to the aldehydes, lan-
thanide complexes incorporating both amido and enolate ligands
would possess two competitive reactive groups towards alde-
hydes. The reactivity of this kind of complex incorporating both
amido and enolate ligands with aldehydes has scarcely been
investigated.
trium and lutetium polyhydrido complexes {Cp0Ln(
l-H)2}4(THF)
(Cp0 = C5Me4SiMe3, Ln = Y, Lu), which leads to selective formation
of ethylene and structurally characterized polyoxo and oxo/hydri-
* Corresponding author. Tel.: +86 553 3937137; fax: +86 553 3883517.
E-mail address: swwang@mail.ahnu.edu.cn (S.-w. Wang).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.05.030

2758
S.-w. Wang et al. / Polyhedron 27 (2008) 2757–2764
Recently, Steiner et al. reported that the reaction of hexaprotic
phosphazene {2-(MeO)(C6H4NH)}6P3N3 with excess (12 equiv.)
nBuLi in THF produced a monomeric dodecanuclear complex incor-
porating six enolate ligands [10]. We report here the synthesis of
novel lanthanide complexes incorporating amido and enolate li-
gands
having
the
general
formula
(CH2@CHO)Ln[2,6-
(iPr)2C6H3NSiMe3]2(
l
-Cl)Li(THF)3, by the one-pot reaction of N-tri-
methylsilyl-2,6-diisopropylaniline 2,6-(iPr)2C6H3NHSiMe3 with ex-
cess nBuLi in THF, followed by treatment with 1 equiv. of LnCl3.
The reactivity of this kind of complexes with aromatic aldehydes
is also reported.
2. Results and discussion
The structurally characterized rare earth metal complexes
incorporating
amido
and
enolate
mixed
ligands
(CH2@CHO)Ln[2,6-(iPr)2C6H3NSiMe3]2(l-Cl)Li(THF)3
(Ln = Y(1),
Yb(2)) were synthesized for the first time by the one-pot reaction
of N-trimethylsilyl-2,6-diisopropylaniline 2,6-(iPr)2C6H3NHSiMe3
with 1.5 equiv. of nBuLi in THF, followed by treatment with LnCl3
in good yields (Scheme 1). The complexes are soluble in toluene,
benzene, THF and CH2Cl2, but only slightly soluble in n-hexane.
These complexes were well characterized by spectroscopic meth-
ods and elemental analyses. Their structures were additionally
determined by X-ray diffraction study (Figs. 1 and 2).
Fig. 2. Molecular structure of complex 2, hydrogen atoms are omitted for clarity.
can be compared with those of the enolate ligand in
(Cp0Y)4(OCH@CH2)(
l-O)(l-H)5(THF) [6], [(C5H5)2Y(l-OCH@CH2)]2
or [(CH3C5H4)2Y(
l-OCH@CH2)]2 [7], and LiOCH = CH2 [11]. Each
IR spectrum of complex 1 or 2 contains a very broad strong band
around 1650 cmꢀ1, which can be attributable to the C@C bond of
the enolate and the phenyl ring stretch.
In order to search for the origination of the enolate ligand of
the above complexes, 2,6-(Et)2C6H3NHSiMe3 was treated with
nBuLi in n-hexane at first, followed by treatment with 1/2 or 1/
3 equiv. of YCl3 in THF respectively, and complexes with the
The 1H NMR spectrum of complex 1 exhibited resonances at
6.90, 4.24 and 4.20 ppm, which can be attributed to the corre-
sponding proton resonances of the enolate ligand OCH@CH2 in
the complex. The resonances of the enolate ligand exhibited cou-
pling. The proton resonances of the enolate ligand of the complex
formula [2,6-(Et)2C6H3NSiMe3]2Y(THF)(l-Cl)2Li(THF)2 (3) and
{[2,6-(Et)2C6H3NSiMe3]3YCl}[Li(THF)4] (4) were isolated (Scheme
2). The complexes were well characterized by spectroscopic meth-
ods and elemental analyses. The elemental analyses data are in
agreement with the loss of THF molecules, which is common in
lanthanide chemistry. The structures of complexes 3 and 4 were
determined by single crystal X-ray analyses. These results suggested
that (1) the produced lithium amide Li(2,6-(iPr)2C6H3NSiMe3) is
not responsible for the resulting enolate ligand in complexes 1
and 2; (2) YCl3 cannot react with THF leading to the formation of
the enolate ligand. Evidence that nBuLi can react with THF leading
to the cleavage of the THF ring to produce a lithium enolate and
ethylene is reported, and this process has been monitored by
NMR spectroscopy [11]. Thus, the enolate ligand in complexes 1
and 2 is believed to have come from the cleavage of the THF
molecule by nBuLi. To further prove the above conclusion, the
SiMe3
HN
N
O
Me3Si
n-BuLi
LnCl3
r. t.
Ln
THF. -78 οC
Cl Li(THF)3
N
SiMe3
Ln = Y(1), Yb(2)
Scheme 1.
SiMe3
N
Cl
thf
thf
Y
Li
Me3Si
1/2 YCl3
thf
Cl
N
Me3Si
NH
nBuLi
THF
3
nhexane
1/3 YCl3
SiMe3
THF
N
Cl
Y
Li(thf)4
Me3Si
N
N
Me3Si
4
Fig. 1. Molecular structure of complex 1, hydrogen atoms are omitted for clarity.
Scheme 2.

S.-w. Wang et al. / Polyhedron 27 (2008) 2757–2764
2759
Table 1
product of the reaction of N-trimethylsilyl-2,6-diethylaniline with
1.5 equiv. of nBuLi was analyzed by 1H NMR spectroscopy. The
spectra clearly indicated the formation of Li[2,6-(Et)2C6H3NSiMe3)]
and LiOCH = CH2, and the existence of three coordinated THF
molecules.
Selected bond distances (Å) and angles (°) for 1, 2, 3 and 4
1
2
Y(1)–O(4)
Y(1)–O(40)
Y(1)–N(1)
Y(1)–N(2)
Y(1)–Cl(1)
Cl(1)–Li(1)
Li(1)–O(1)
Li(1)–O(2)
2.103(7)
2.104(2)
2.229(5)
2.254(6)
2.603(2)
2.394(2)
1.93(2)
1.90(2)
1.89(2)
1.351(10)
107.1(3)
102.7(3)
126.9(2)
105.4(3)
105.98(2)
107.08(15)
136.3(4)
Yb(1)–O(4)
Yb(1)–O(40)
Yb(1)–N(1)
Yb(1)–N(2)
Yb(1)–Cl(1)
Cl(1)–Li(1)
Li(1)–O(1)
Li(1)–O(2)
2.070(6)
2.067(9)
2.188(5)
2.201(5)
2.552(2)
2.401(2)
1.92(2)
1.86(2)
1.90(2)
1.344(9)
106.1(3)
102.3(3)
127.61(2)
105.2(3)
106.01(2)
107.70(2)
136.1(3)
X-ray analyses confirmed that complexes 1 and 2 consisted of
two amido ligands, an enolate ligand and a bridged chlorine atom
connected with a lithium atom coordinated by three THF mole-
cules. The central rare earth metal of each complex is coordinated
by two nitrogen atoms of the amido ligand, an oxygen atom of the
enolate ligand and a chlorine atom. The central yttrium atom in
complex 3 is coordinated by two nitrogen atoms of the amido li-
gand, one oxygen atom of a THF molecule and two chlorine atoms
(Fig. 3). The central yttrium atom in complex 4 is coordinated by
three nitrogen atoms of the amido ligand and one chlorine atom
Li(1)–O(3)
Li(1)–O(3)
C(43)–C(44)
C(43)–C(44)
O(4)–Y(1)–N(1)
O(4)–Y(1)–N(2)
N(1)–Y(1)–N(2)
O(4)–Y(1)–Cl(1)
N(1)–Y(1)–Cl(1)
N(2)–Y(1)–Cl(1)
Li(1)–Cl(1)–Y(1)
O(4)–Yb(1)–N(1)
O(4)–Yb(1)–N(2)
N(1)–Yb(1)–N(2)
O(4)–Yb(1)–Cl(1)
N(2)–Yb(1)-Cl(1)
N(1)–Yb(1)–Cl(1)
Li(1)–Cl(1)–Yb(1)
3
4
Y(1)–N(1)
Y(1)–N(2)
Y(1)–O(1)
Y(1)–Cl(1)
Y(1)–Cl(2)
Cl(2)–Li(1)
Cl(1)–Li(1)
O(2)–Li(1)
2.228(3)
2.252(4)
2.404(3)
2.657(2)
2.638(2)
2.370(2)
2.331(2)
1.90(2)
Y(1)–N(1)
Y(1)–N(2)
Y(1)–N(3)
Y(1)–Cl(1)
Li(1)–O(1)
Li(1)–O(2)
Li(1)–O(3)
Li(1)–O(4)
2.302(5)
2.292(5)
2.289(5)
2.621(2)
1.97(2)
1.95(2)
1.89(2)
1.89(2)
O(3)–Li(1)
1.92(2)
N(2)–Y(1)–N(1)
N(3)–Y(1)–N(1)
N(3)–Y(1)–N(2)
N(3)–Y(1)–Cl(1)
N(2)–Y(1)–Cl(1)
N(1)–Y(1)–Cl(1)
118.04(18)
115.39(18)
116.58(19)
98.5(2)
99.04(18)
104.35(19)
N(1)–Y(1)–N(2)
N(1)–Y(1)–O(1)
N(2)–Y(1)–O(1)
N(1)–Y(1)–Cl(2)
N(2)–Y(1)–Cl(2)
O(1)–Y(1)–Cl(2)
O(1)–Y(1)–Cl(1)
N(1)–Y(1)–Cl(1)
N(2)–Y(1)–Cl(1)
Cl(2)–Y(1)–Cl(1)
Cl(1)–Li(1)–Cl(2)
O(2)–Li(1)–O(3)
120.22(14)
101.27(12)
92.57(13)
93.10(9)
91.91(10)
160.16(10)
80.87(10)
111.46(10)
128.16(11)
81.17(5)
94.3(4)
105.5(5)
(Fig. 4). The bond angles of N–Ln–N, Cl–Ln–O, N–Ln–Cl, O–Ln–N
(Ln = Y, Yb), in the range 102.7(3)–126.9(2)° (Table 1) for complex
1, 102.3(3)–127.61(19)° (Table 1) for complex 2, and 98.5(2)–
118.04(18)° for complex 4, are deviated from the ideal tetrahedral
angle. Thus the coordination geometry around the central metal of
complexes 1, 2 and 4 can be described as a distorted tetrahedral.
The bond angles of O(1)–Y(1)–Cl(2), N(1)–Y(1)–N(2), N(1)–Y(1)–
Cl(1) and N(2)–Y(1)–Cl(1) are 160.16(10), 120.22(14), 111.46(10)
and 128.16(11)° (Table 1), respectively in complex 3, largely devi-
ated from the ideal trigonal bipyramidal bond angles, so the coor-
dination geometry of the central yttrium in complex 3 can be
described as pseudo-trigonal bipyramidal with O(1) and Cl(2) at
the axial positions.
Fig. 3. Molecular structure of complex 3, hydrogen atoms are omitted for clarity.
The Y–N distances are 2.229(5) and 2.254(6) Å, with an average
of 2.242(6) Å, in 1, which is comparable to the average distance of
2.194(5) Å found in 2, and that of 2.240(4) Å in 3 and 2.294(5) Å in
4, if the ionic radii difference between the central metal is taken
into account. The average Y–N distance of 2.242(6) Å in 1 is similar
to that of 2.243(4) Å found in [
But the average Yb–N bond distance of 2.194(5) Å found in 2 is
slightly longer than that of 2.162(5) Å found in
g
5-(CH2)2(C9H6)2]YN(SiMe3)2 [12].
[
g5
-
(CH2)2(C9H6)2]YbN(SiMe3)2 [13], this difference can be attributable
to ionic and steric effects [14]. The Yb–Cl distance of 2.552(2) Å
found in 2 is equal to that of 2.552(2) Å found in [(Me3Si)2-
N]3Yb(l-Cl)Li(THF)3 [13a]. The Y–Cl distance of 2.603(2) Å found
in 1 is longer than the Yb–Cl distance of 2.552(2) Å found in 2
due to the ionic radii difference. The Y–Cl distance of 2.603(2) Å
found in 1 is shorter than those of 2.648(2) Å in 3 and 2.621(2) Å
Fig. 4. The structure of the anion in 4, hydrogen atoms are omitted for clarity.

2760
S.-w. Wang et al. / Polyhedron 27 (2008) 2757–2764
Table 2
in 4, probably due to steric effects. The Ln–Cl bond distances found
Conditions and results of the reaction of 4-bromobenzyl aldehyde with a stoichiom-
in the above complexes are comparable to those found in
etric amount of yttrium complex 1a
Ln{N[Si(Me)2CH2CH2Si(Me)2]}(
yttrium–oxygen distance of 2.104(10) Å is shorter than those of
2.275(3) and 2.290(3) Å found in [(CH3C5H4)2Y( -OCH@CH2)]2 [7]
The Li(1)–Cl(1)–Y(1) angle of 136.3(4)° in 1 is comparable to that
of 136.1(3)° found in 2, but these angles are significantly smaller
than the corresponding Li–Cl–Ln angles of 175 1° found in [(Me3-
μ-Cl)Li(L)3
(L = THF or Et2O) [15]. The
Entry
Temperature (°C)
Solvent
Time (d)
Yield of amideb
1
2
3
4
5
r. t.
r. t.
r. t.
50
Toluene
CH2Cl2
THF
CH2Cl2
THF
2
2
2
2
2
49
68
35
41
23
l
80
Si)2N]3Ln(l-Cl)Li(THF)3 (Ln = Yb, Sm, Eu) [16], and those of 170 2°
a
Aldehyde:yttrium complex = 4:1 (mol ratio).
Isolated yield based on the yttrium complex.
b
found in Ln{N[Si(Me)2CH2CH2Si(Me)2]}(
μ-Cl)Li(L)3 (L = THF or Et2O)
[15].
The C@C double bond distances of the enolate, 1.351(10) Å in 1
and 1.344(4) Å in 2, are slightly longer than the standard 1.34 Å ex-
pected for the C@C bond in ethylene, they are also longer than that
of 1.287(8) Å for the C@C double bond of the enolate found in
decomposed to aldehydes during workup. Thus, the conditions
for doing the following experiments were fixed as room tempera-
ture reaction, employing CH2Cl2 as the solvent.
[(CH3C5H4)2Y(
l
-OCH@CH2)]2 [7].
A series of aromatic aldehydes can selectively react with the
amido group of the lanthanide complexes 1 and 2 to produce the
corresponding disproportionation products of amides and alcohols
(Scheme 5, Table 3), and no Aldol reaction products were found to
any detectable degree, indicating that the electron-deficient lan-
thanide metal has a great influence on the reactivity of the enolate
group. The substituents on the aromatic aldehydes could be either
electron-donating groups such as CH3ꢀ, CH3Oꢀ and Me2Nꢀ or elec-
tron-withdrawing ones such as Clꢀ, Brꢀ, O2Nꢀ and F3Cꢀ. However,
the electronic effects of the substituent groups have an influence
on the output of the reactions. When the substituents are elec-
tron-donating groups such as CH3ꢀ, CH3Oꢀ and Me2Nꢀ or elec-
tron-withdrawing ones such as Clꢀ and Brꢀ, the main products of
amides and alcohols (>50% yield based on the lanthanide com-
plexes) could be isolated, and only a trace or a very small amount
of the corresponding imines could be detected from the reaction
mixture. When the substituents are O2Nꢀ and F3Cꢀ, the output of
the imines increased as the output of the amides and alcohols de-
creased. The corresponding imines could be isolated under the
workup conditions, and they were well characterized (Fig. 5), how-
ever, in all other cases the imine products could not be isolated un-
der the workup conditions. These results are different to our
previous work on the reaction of lanthanide amides [(Me3-
It has been well documented that the Aldol reaction proceeds
through an enolate intermediate when the reaction is carried out
in an inorganic base medium [8]. We have found that lanthanide
amides [(Me3Si)2N]3Ln(l-Cl)Li(THF)3 can initiate the dispropor-
tionation reaction of aromatic aldehydes to give the corresponding
amides and alcohols [9]. In order to search for the influence of the
rare earth metals on the reactivity or selectivity of the amido and
enolate ligands with aromatic aldehydes (Scheme 3), the reactivity
of the lanthanide complexes 1 and 2 with aromatic aldehydes was
explored.
First, a model reaction of 4-bromobenzyl aldehyde with a stoi-
chiometric amount of the yttrium complex 1 was tested (Scheme 4,
Table 2). It was found that the reaction can proceed in different sol-
vents such as toluene, CH2Cl2 and THF (Table 2, entries 1–3), but
the outputs of the reaction products are higher in CH2Cl2 than for
reactions carried out in other solvents such as THF and toluene.
It was found that only the disproportionation products of the cor-
responding amide and alcohol instead of the Aldol reaction product
could be isolated, suggesting that the amido ligand could selec-
tively react with aromatic aldehydes. The outputs of the reaction
products were influenced by the reaction temperatures. Low yields
of the products could be obtained when the reaction was carried
out at moderately higher temperatures. It should be noted that a
small amount of imines could be detected when the reaction was
carried out at moderately higher temperatures, but the imines is
Si)2N]3Ln(l-Cl)Li(THF)3 with aromatic aldehydes, producing the
corresponding amides and alcohols as the only products [9a], with
no imine products being found to any detectable degree.
a
OH
CH
N
O
Me3Si
CH2CHO
Ar
Ln
+ ArCHO
O
Cl Li(THF)3
SiMe3
N
Ar
+
ArCH2OH
6
N
H
5
b
Scheme 3.
O
CHO
Br
CH2OH
N
O
Me3Si
N
H
+
+
Y
Br
Cl Li(THF)3
SiMe3
N
Br
5d
6d
Scheme 4.

S.-w. Wang et al. / Polyhedron 27 (2008) 2757–2764
2761
CHO
R
O
CH2OH
N
O
Me3Si
H
+
N
+
Ln
C
N
+
H
Cl Li(THF)3
SiMe3
R
R
N
R
5
5'
6
Scheme 5.
ferences between the stoichiometric reactions of the lanthanide
complexes 1 or 2 with aldehydes and the catalytic reaction of lith-
ium amide with the aldehydes are: (1) no imine products have
been detected in all cases (Table 4); and (2) the output of the cor-
responding amides and alcohols are improved significantly when
the substituents on the aromatic aldehydes are electron-withdraw-
ing ones such as O2Nꢀ and F3Cꢀ (Table 4, entries 5 and 6) under al-
most the same reaction conditions. These results are somewhat
different to our previous work, which may be due to the coordi-
nated enolate ligand’s effect on the reactions. We have proposed
that the reaction of lithium amide (Me3Si)2NLi with aromatic alde-
hydes in the presence of LnCl3 goes through lanthanide amides
Table 3
Results of the reaction of aromatic aldehydes with
lanthanide complex 1 and 2a
a stoichiometric amount of
Entry Ar-
Time Product Yield of
Product Yield of Yield of
of 6
6 (%)b product 50
of 5
5 (%)b
1
2
3
4
5
4-CH3C6H4–
2
2
2
2
2
5a
5b
5c
5d
5e
88c (87)d 6a
73 (75) 6b
74 (67) 6c
68 (49) 6d
54 (59) 6e
85 (83) Trace
67 (69) Trace
69 (65) Trace
65 (47) Trace
51 (57) Trace
4-CH3OC6H4–
4-ClC6H4–
4-BrC6H4–
4-
Me2NC6H4–
4-O2NC6H4–
4-F3CC6H4–
C6H5–
6
7
8
2
2
3
5f
5g
5h
51 (55) 6f
53 (49) 6g
49 (47) 6h
49 (52) 32 (39)
47 (44) 38 (37)
47 (45) Trace
[(Me3Si)2N]3Ln(l-Cl)Li(THF)3 as intermediates. It is reported that
Conditions: aCH2Cl2 as a solvent, room temperature. bisolated yield based on lan-
thanide complex. cData are obtained from the reaction of the aldehydes with
yttrium complex 1. dData in the parenthesis are obtained from the reaction of the
aldehydes with ytterbium complex 2.
the reaction of lithium amides {[2,6-(iPr)2C6H3](Me3Si)N}Li with
lanthanide chlorides LnCl3 produced the lanthanide amides {[2,6-
(iPr)2C6H3](Me3Si)N}3Ln [17]. On the basis of these results, we
can conclude that the reaction of lithium amide {[2,6-(iPr)2C6H3]-
(Me3Si)N}Li with aldehydes in the presence of YCl3 may go through
a similar mechanism as in our previous work, which has been dem-
onstrated as a Cannizzaro type disproportionation [9a]. The reac-
tion involves the addition of the amido group from the
lanthanide metal center to one molecule of aldehyde to give the
intermediate {ArCH(O)N(SiMe3)[C6H3-2,6-(iPr)2]}ꢀ (A), which
leads to the oxidation of the aldehyde by transferring the hydride
from the intermediate (A) to another molecule of aldehyde to pro-
duce the amide precursor, leading to the reduction of the aldehyde,
ArCH2Oꢀ. The final products of amide and alcohols could be iso-
lated after workup. The formation of imine products in the stoichi-
ometric reactions of lanthanide complex 1 or 2 with aromatic
aldehydes may be due to the influence of the coordinated enolate
ligand in the complexes. However, further work on this detail
should be carried out.
We have found that the reaction of lithium amide (Me3Si)2NLi
with aromatic aldehydes in the presence of LnCl3, or the stoichiom-
etric reaction of [(Me3Si)2N]3Ln(l-Cl)Li(THF)3 with aromatic alde-
hydes, yielded the corresponding disproportionation products of
amides and alcohols. No imine product has been detected in the
reaction [9a]. For comparison, the reaction of the lithium amide
{[2,6-(iPr)2C6H3](Me3Si)N}Li with some selected aromatic alde-
hydes catalyzed by YCl3 was investigated (Scheme 6). The reaction
goes smoothly producing the disproportionation products of
amides and alcohols in the presence of 5 mol% YCl3 (Table 4) in sat-
isfactory yields. The substituents on the aromꢀatic aldehydes can be
either electron-donating groups such as CH3 and CH3Oꢀ or elec-
tron-withdrawing ones such as Clꢀ, Brꢀ and O2Nꢀ. The major dif-
Fig. 5. Molecular structure of 5f0, hydrogen atoms are omitted for clarity.

2762
S.-w. Wang et al. / Polyhedron 27 (2008) 2757–2764
crystal plate, Nujol and Fluoroble mulls). Melting points were
O
CH2OH
Li
CHO
determined in sealed capillaries and are reported without correc-
tion. 1H NMR and 13C NMR spectra for analyses of compounds were
recorded on a Bruker Avance-300 NMR spectrometer in benzene-d6
for the lanthanide complexes, and in CDCl3 for organic compounds,
and chemical shifts for 1H and 13C NMR spectra were referenced to
the internal solvent resonances.
N
YCl3, 5 mol %
N
+
+
SiMe3
H
R
6
R
R
5
Scheme 6.
4.2. Preparation of (CH2@CHO)Y[2,6-(iPr)2C6H3NSiMe3]2(
l-
Cl)Li(THF)3 (1)
Table 4
Reaction of lithium amide {[2,6-(iPr)2C6H3](Me3Si)N}Li with aromatic aldehydes
catalyzed by YCl3
a
To a THF solution of 2,6-(iPr)2C6H3NHSiMe3 (5.90 g, 23.6 mmol)
at ꢀ78 °C was slowly added an n-hexane solution of nBuLi
(20.6 mL, 35.8 mmol). The temperature of the reaction mixture
was then gradually raised to room temperature after the addition.
The mixture was stirred at room temperature for another 12 h. The
reaction mixture was then transferred to a suspension of YCl3
(2.31 g, 11.8 mmol) in THF. The reaction mixture was stirred at
room temperature for 6 h, and then at 60 °C overnight. The solvent
was pumped off. The residue was washed with 15 mL of n-hexane.
The solid was extracted with a mixture of toluene and n-hexane
(2:3, v/v) at 50 °C. Colorless crystals were obtained upon cooling
the extracts at ꢀ10 °C for several days (6.27 g, 60%). M.p.: 82–
84 °C (dec.). 1H NMR (300 MHz, C6D6, d in ppm): 7.32–7.16 (m,
6H, C6H3), 6.90 (dd, 1H, J = 12.9 Hz, J = 5.4 Hz, CH@CH2), 4.24 (dd,
1H, J = 12.9 Hz, J = 1.2 Hz, CH@CH2), 4.20 (dd, 1H, J = 5.4 Hz,
J = 1.2 Hz, CH@CH2), 3.12 (m, 4H, CH(CH3)2), 3.50 (m, 12H,
OC4H8), 1.46 (m, 12H, OC4H8), 1.25–1.23 (m, 24H, CH(CH3)2), 0.50
Entry Ar–
Solvent
Time Product Yield of Product Yield of
of 5
5 (%)b
of 6
6 (%)b
1
2
3
4
4-CH3C6H4–
4-CH3OC6H4– Toluene
Toluene
3
3
2
2
2
2
3
5a
5b
5c
5d
5f
76
70
75
72
81
83
86
6a
6b
6c
6d
6f
73
65
74
70
75
79
79
4-ClC6H4–
4-BrC6H4–
4-O2NC6H4–
4-F3CC6H4–
C6H5–
Toluene
Toluene
CH2Cl2
CH2Cl2
Toluene
5c
6c
7
5g
5h
6g
6h
Conditions: a5 mol% YCl3, 80 °C; bisolated yield based on the lithium amide; croom
temperature reaction.
3. Conclusion
We have for the first time rationally synthesized novel rare
earth metal complexes incorporating amido and enolate mixed li-
gands by a one-pot reaction. The experimental results suggest that
this method may be applied to the synthesis of complexes incorpo-
rating amido and enolate mixed ligands. Investigation on the reac-
tivity of this kind of lanthanide complex indicates that the amido
ligand of the complex can selectively react with aromatic alde-
hydes to afford the disproportionation products of amides and
alcohols, suggesting that the Lewis acid property of the rare earth
metals have a great influence on the reactivity of the enolate li-
gand. When the enolate is coordinated with the rare earth metals;
it showed no reactivity with aromatic aldehydes. This kind of com-
plex has compatibility for substituents on the aromatic aldehyde
ring such as Clꢀ, Brꢀ, F3Cꢀ, O2Nꢀ and other electron-donating
groups. The outputs of the reaction were influenced by the substit-
uents on the aromatic aldehydes ring, the solvents and the ligands
of the lanthanide complexes. The results of the reaction of the lith-
ium amide {[2,6-(iPr)2C6H3](Me3Si)N}Li with aromatic aldehydes
in the presence of a catalytic amount of YCl3 suggested that the
method for the preparation of the amides from aldehydes by a
one step reaction may be extended to reaction of other lithium
amides with aldehydes. Further investigation on the reactivity of
other lithium amides with aldehydes in the presence of lanthanide
compounds is now in progress in our laboratory.
(s, 18H, Si(CH3)3). IR (Nujol and Fluoroble mulls, cmꢀ1):
m 2961
(w), 2870 (s), 1651 (vs), 1441 (m), 1383 (m), 1327 (w), 1252 (vs),
1196 (w), 1044 (w), 907 (s), 843(s). Anal. Calc. for C44H79ClLiN2O4-
Si2Y: C, 59.54; H, 8.97; N, 3.16. Found: C, 59.26; H, 9.13; N, 3.00%.
4.3. Preparation of (CH2@CHO)Yb[2,6-(iPr)2C6H3NSiMe3]2(
l-
Cl)Li(THF)3 (2)
This complex was prepared as yellow crystals in 61% yield from
the reaction of 2,6-(iPr)2C6H3NHSiMe3 (4.45 g, 17.8 mmol) with
nBuLi (15.5 mL, 26.9 mmol) in THF, followed by treatment with
YbCl3 (2.49 g, 8.9 mmol) by applying the procedures similar to
those used for the preparation of 1. M.p.: 86–88 °C (dec.). IR (Nujol
and Fluoroble mulls, cmꢀ1): 2960 (s), 2870 (w), 1632 (vs), 1462
(m), 1363 (m), 1263 (w), 1092 (w), 1057 (w), 745 (w). Anal. Calc.
for C44H79ClLiN2O4Si2Yb (971.70): C, 54.39; H, 8.19; N, 2.88. Found:
C, 54.12; H, 8.03; N, 2.98%.
4.4. Preparation of [2,6-(Et)2C6H3NSiMe3]2Y(THF)(l-Cl)2Li(THF)2 (3)
To a Schlenk flask containing an n-hexane solution of 2,6-
(Et)2C6H3NHSiMe3 (2.78 g, 12.6 mmol) was added nBuLi (10.6 mL,
13.0 mmol) at ꢀ78 °C. The reaction mixture temperature was
slowly raised to room temperature, and it was stirred for another
12 h at room temperature. The excess nBuLi was filtered off and
washed with n-hexane, then 30 mL of THF was added. To the
THF solution of the resulting lithium amide Li[2,6-(Et)2C6H3NSiM-
e3], was added YCl3 (1.23 g, 6.3 mmol). The reaction mixture was
stirred at room temperature overnight, and then at 60 °C for an-
other 24 h. The solvent was evaporated under reduced pressure.
The residue was extracted with toluene and n-hexane mixed sol-
vents (1:1, v/v, 2 ꢁ 10 mL), the extraction was combined and con-
centrated. Colorless crystals were obtained upon standing the
concentrated solution at ꢀ20 °C for several days (3.54 g, 83%).
M.p.: 86–88 °C. 1H NMR (300 MHz, C6D6, d in ppm): 7.20–6.94
(m, 6H), 3.37–3.26 (m, 4H), 2.97–2.88 (m, 8H), 1.46–1.33 (m,
4H), 1.24–1.19 (m, 12H), 0.46–0.34 (m, 18H). IR (KBr, cmꢀ1):
3406 (w), 2966 (s), 2874 (w), 1624 (s), 1454 (s), 1253 (vs), 1107
4. Experimental
4.1. Materials and methods
All syntheses and manipulations of air and moisture-sensitive
materials were carried out in flamed dried Schlenk-type glassware
on a Schlenk line. All solvents were refluxed and distilled over
either finely divided LiAlH4 or sodium benzophenone ketyl under
argon prior to use unless otherwise noted. 2,6-(iPr)2C6H3NHSiMe3
2,6-(Et)2C6H3NHSiMe3 [17] and LnCl3 [18] (Ln = Yb, Y) were pre-
pared according to the literature procedures. CDCl3 was dried over
activated 4 Å molecular sieves. Elemental analysis data were ob-
tained on a Perkin–Elmer 2400 Series II elemental analyzer. IR
spectra were recorded on a BIO-RAD FTS-40 spectrometer (CsI

S.-w. Wang et al. / Polyhedron 27 (2008) 2757–2764
2763
(m), 1060 (w), 902 (m), 840 (w), 748 (w). Anal. Calc. for
30H52Cl2LiN2OSi2Y (3-2THF) (679.67): C, 53.01; H, 7.71; N, 4.12.
4.7. Reaction of complexes 1 or 2 with aromatic aldehydes
C
Found C, 52.81; H, 7.36; N, 3.75%.
A 30 mL Schlenk tube was charged with the complex (1 mmol)
under dried argon. To the flask were added CH2Cl2 (3 mL) and the
aromatic aldehydes (4 mmol). The reaction mixture was stirred at
room temperature for 2–3 days; the mixture was then quenched
with diluted HCl (0.1 M, 1. 0 mL). The mixture was extracted with
acetyl acetate, and the extracts were dried over MgSO4 and filtered.
The solvent was removed by rotary evaporation. The residue was
4.5. Preparation of {[2,6-(Et)2C6H3NSiMe3]3YCl}[Li(THF)4] (4)
This complex was prepared as colorless crystals in 75% yield
from the reaction of 2,6-(Et)2C6H3NHSiMe3 (4.59 g, 20.8 mmol)
with nBuLi (17.4 mL, 21.4 mmol) in n-hexane, followed by treat-
ment with YCl3 (1.35 g, 6.9 mmol) in THF, by employing proce-
dures similar to those used for the preparation of complex 3. 1H
NMR (300 MHz, C6D6, d in ppm): 7.19–6.92 (m, 6H), 3.35–3.25
(m, 4H), 2.95–2.88 (m, 8H), 1.45–1.30 (m, 4H), 1.24–1.19 (m,
12H), 0.46–0.34 (m, 18H). IR (KBr, cmꢀ1): 2962 (s), 2874 (m),
2330 (w), 1631 (s), 1454 (s), 1373 (w), 1253 (vs), 1111 (s), 1057
(m), 906 (s), 840 (m), 748 (w). Anal. Calc. for C43H74ClLiN3OSi3Y
(4-3THF) (864.62): C, 59.73; H, 8.63; N, 4.86. Found: C, 59.49; H,
8.63; N 4.97%.
purified with
a flash chromatography column (10:1 n-hex-
ane:acetyl acetate, v/v) to give the corresponding products. In the
case of the reactions of aromatic aldehydes having strong elec-
tron-withdrawing groups, such as O2Nꢀ and F3Cꢀ, with stoichiom-
etric amounts of complexes 1 or 2, the imine products could be
isolated and characterized under the experimental conditions.
4.8. Reaction of lithium amide {[2,6-(iPr)2C6H3](Me3Si)N}Li with
aromatic aldehydes catalyzed by YCl3
4.6. Reaction of N-trimethylsilyl-2, 6-diethylaniline with nBuLi
A 30 mL Schlenk tube was charged with YCl3 (5 mol%). To the
tube were added solvent (toluene, or CH2Cl2, 3 mL), lithium amide
[2,6-(iPr)2C6H3NSiMe3]Li (1 mmol) and the aromatic aldehyde
(2 mmol). The reaction mixture was stirred at a certain tempera-
ture for a fixed interval; the mixture was then quenched with
diluted HCl (0.1 M, 1. 0 mL). The mixture was extracted with acetyl
acetate, and the extracts were dried over MgSO4 and filtered. The
solvent was removed by rotary evaporation. The residue was
purified with flash chromatography column (10:1 n-hexane:acetyl
acetate, v/v) to give the corresponding products.
To a Schlenk flask containing a tetrahydrofuran (THF) solution
of 2,6-(Et)2C6H3NHSiMe3 (0.278 g, 1.26 mmol) was added nBuLi
(1.60 mL, 2.0 mmol) at ꢀ78 °C. The reaction mixture temperature
was slowly raised to room temperature after the addition, and it
was stirred for another 12 h at room temperature. The excess nBuLi
was filtered off and washed with n-hexane. The solvents were
pumped off, and the solid product was dried under vacuum. 1H
NMR (300 MHz, C6D6, d in ppm): 7.08–7.06 (m, 6 H), 6.69 (dd,
1H, J = 12.5 Hz, J = 6.9 Hz, CH@CH2), 3.99 (dd, 1H, J = 12.5 Hz,
J = 1.2 Hz, CH@CH2), 3.72 (dd, 1H, J = 6.9 Hz, J = 1.2 Hz, CH@CH2),
3.43 (m, 12H, OC4H8), 2.94 (t, 8H, J = 7.2 Hz, CH2CH3), 1.45
(m, 12H, OC4H8), 1.32 (t, J = 7.2 Hz, 12H, CH2CH3), 0.24 (s,
18H, Si(CH3)3). This clearly shows the formation of Li[2,
6-(Et)2C6H3NSiMe3], LiOCH = CH2 and the existence of three
coordinated THF molecules.
4.9. X-ray crystallography
A suitable crystal of each of the complexes 1, 2, 3, 4 and 5f0 was
mounted in a sealed capillary. Diffraction was performed on a Sie-
mens SMART CCD-area detector diffractometer using graphite-
monochromated Mo Ka radiation (k = 0.71073 Å); temperature
Table 5
Crystallographic data and structure refinement details for 1, 2, 3, 4 and and 50
1
2
3
4
5f0
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C44H79ClLiN2O4Si2Y
887.57
C44H79ClLiN2O4Si2Yb
971.70
C38H68Cl2LiN2O3Si2Y
823.87
orthorhombic
Pna21
37.272(2)
12.2901(8)
10.0790(7)
90
90
90
4617.0(5)
293(2)
1.175
C55H98ClLiN3O4Si3Y
1080.93
monoclinic
P21/n
18.494(2)
17.872(2)
19.879(3)
90
97.657(2)
90
6511.9(14)
293(2)
C19H22N2O2
310.39
monoclinic
P21/c
8.4963(2)
28.2166(7)
8.1526(2)
90
117.122(2)
90
1739.56(7)
293(2)
1.185
triclinic
triclinic
ꢀ
ꢀ
P1
P1
13.123(2)
13.266(2)
16.606(3)
85.256(3)
84.929(3)
66.722(3)
2641.7(7)
294(2)
13.041(2)
13.246(2)
16.579(3)
85.127(2)
84.736(3)
66.766(2)
2616.7(7)
294(2)
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
T (K)
qcalc. (g/cm3)
Z
1.116
2
1.233
2
1.103
4
4
4
F(000)
952
1014
1724
2328
664
Reflections collected
Unique reflections
Rint
13552
9282
0.056
13397
9185
0.036
38934
9993
0.050
55588
15001
0.111
9238
3051
0.031
Parameters refined
538
538
453
629
213
k (Å); Mo K
(mmꢀ1
h Range (°)
Goodness-of-fit (GOF) on F2
R [I > 2 (I)]
a
0.71073
1.236
1.67–25.02
0.984
0.71073
1.920
1.68–25.02
1.027
0.71073
1.463
1.74–27.52
1.016
0.71073
1.032
1.41–27.60
0.960
0.71073
0.077
1.44–25.00
1.031
l
)
r
0.070
0.053
0.053
0.088
0.045
wR2 (all data)
0.229
0.459 and ꢀ0.377
0.138
1.875 and ꢀ1.763
0.143
0.401 and ꢀ0.335
0.318
2.433 and ꢀ1.502
0.121
0.142 and ꢀ0.135
Largest difference in peak and hole (e Åꢀ3
)

2764
S.-w. Wang et al. / Polyhedron 27 (2008) 2757–2764
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were solved by direct methods (SHELXS-97) [19], completed by sub-
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least-square calculations based on F2
(SHELXS-97) [19]. See Table 5
for crystallographic data.
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Acknowledgments
This work was co-supported by the National Natural Science
Foundation of China (Grant Nos. 20672002 and 20702001), the
program for the NCET (Grant No. NCET-04-0590). The Grant from
Anhui Province and Anhui Education Department (Grant Nos.
2007Z016, TD200707). We are also grateful for the assistance of
Prof. Bao-hui Du and Ji-ping Hu in running IR and NMR spectra.
Appendix A. Supplementary data
CCDC 684085, 684086, 684087, 684088 and 684089 contain the
supplementary crystallographic data for 1, 2, 3, 4 and 5f0. These
data can be obtained free of charge via www.ccdc.ac.uk/conts/
retrieving.html or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data
associated with this article can be found, in the online version, at
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