Novel lanthanide amides incorporating neutral pyrrole ligand in a constrained geometry architecture: Synthesis, characterization, reaction, and catalytic activity

Article abstract of DOI:10.1021/om400409x

The first series of lanthanide amido complexes incorporating a neutral pyrrole ligand in a constrained geometry architecture were synthesized, and their bonding, reactions, and catalytic activities were studied. Treatment of [(Me₃Si)₂

Full text of DOI:10.1021/om400409x

Article
pubs.acs.org/Organometallics
Novel Lanthanide Amides Incorporating Neutral Pyrrole Ligand in a
Constrained Geometry Architecture: Synthesis, Characterization,
Reaction, and Catalytic Activity
Fenhua Wang,†,‡ Shaowu Wang,*,†,§ Xiancui Zhu,† Shuangliu Zhou,*,† Hui Miao,† Xiaoxia Gu,†
Yun Wei,† and Qingbing Yuan†
†Laboratory of Functionalized Molecular Solids, Ministry of Education, Anhui Laboratory of Molecule-Based Materials, Institute of
Organic Chemistry, School of Chemistry and Materials Science, Anhui Normal University, Wuhu, Anhui 241000, P. R. China
§State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, P. R. China
‡College of Biological and Chemical Engineering, Anhui Polytechnic University, Wuhu, Anhui 241000, P. R. China
S
* Supporting Information
ABSTRACT: The first series of lanthanide amido complexes
incorporating a neutral pyrrole ligand in a constrained
geometry architecture were synthesized, and their bonding,
reactions, and catalytic activities were studied. Treatment of
[(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 with 1 equiv of (N-
C6H5NHCH2CH2)(2,5-Me2C4H2N) (1) afforded the first
example of bisamido lanthanide complexes having the neutral
pyrrole η5-bonded to the metal formulated as [η5:η1-(N-
C6H5NCH2CH2)(2,5-Me2C4H2N)]Ln[N(SiMe3)2]2 (Ln = La (2) and Nd (3)). Reaction of [(Me3Si)2N]3Sm(μ-Cl)Li(THF)3
with 2 equiv of 1 produced the complex [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)][η1-(N-C6H5NCH2CH2)(2,5-
Me2C4H2N)]]SmN(SiMe3)2 (4). Treatment of 3 with 2 equiv of 1 gave the sandwich neodymium complex [η5:η1-(N-
C6H5NCH2CH2)(2,5-Me2C4H2N)]2Nd[η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)] (5), in which two neutral pyrroles bonded
with metal in an η5 mode. Complex 5 could also be prepared by reaction of [(Me3Si)2N]3Nd(μ-Cl)Li(THF)3 with 3 equiv of 1.
Reactivities of the lanthanide bisamido complexes were further investigated. Reaction of complex 2 with pyrrolyl-functionalized
imine [2-(2,6-iPr2C6H3NCH)C4H3NH] afforded a mixed η5-bonded neutral pyrrole and η1-bonded anionic pyrrolyl
lanthanum complex [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]{η1-2-[(2,6-iPr2C6H3)NCH]C4H3N}La[N(SiMe3)2] (6).
Reactions of complexes 2 and 3 with pyrrolyl-functionalized secondary amine afforded the mixed η5-bonded neutral pyrrole
and the η1-bonded anionic pyrrolyl lanthanide complexes [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)][(η1-2-tBuNCH)-
C4H3N]2Ln (Ln = La (7), Nd (8)) with dehydrogenation of the secondary amine. Investigation of the catalytic properties of
complexes 2−8 indicated that all complexes exhibited a high activity with a high chemo- and regioselectivity on the addition of
dialkyl phosphite to α,β-unsaturated carbonyl derivatives. An interesting result was found that 1,2-hydrophosphonylation
substrates could be catalytically converted to 1,4-hydrophosphinylation products when the substrates are the substituted
benzylideneacetones by controlling the reaction conditions.
anionic pyrrolyl (including poly pyrrolyl anions) ligands
bonded with rare-earth metals in η5 or η1 or η5:η1 capability
(B, Chart 1).11 As the isolobal analogues to cyclopentadienyl
anion,12 the π-bonded neutral benzenes13 or the π-bonded
neutral pyrrole rare-earth metal complexes are known. Among
the π-bonded neutral pyrrole rare-earth metal complexes, most
of them are supported by multipyrrolyl moiety or appended
with cyclopentadienyl anion.14 To the best of our knowledge,
lanthanide amides, alkyls, and hydrides containing a neutral
pyrrole in the constrained geometry architecture similar to
cyclopentadienyl and pyrrolyl anion supported analogues (C,
Chart 1) have not been developed.
INTRODUCTION
■
The introduction of cyclopentadienyl ligand or its derivatives to
rare-earth metals led to the development of a variety of
homogeneous precatalysts1 with findings of applications in
different unsaturated molecules transformations such as
polymerization of olefins,2 hydroamination of alkenes and
alkynes,3 hydrosilylation of unsaturated compounds,4,1b hydro-
phosphinylation or hydrophosphonylation of unsaturated
bonds,5 hydroboration,6 and the development of reagents for
activation of small molecules such as N2,7 CO,8 CO2,9 and so
on. Among the cyclopentadienyl supported rare-earth metal
complexes, the constrained geometry complexes (CGCs) have
been found to exhibit a high activity for the polymerization of
olefins (A, Chart 1).10 The reactivity of anionic pyrrolyl
supported complexes have been well developed, in which the
Received: May 9, 2013
Published: July 9, 2013
© 2013 American Chemical Society
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neodymium complex, [η5:η1-(N-C6H5NCH2CH2)(2,5-
Me2C4H2N)]2Nd[η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]
(5). This complex could also be prepared by treatment of
[(Me3Si)2N]3Nd(μ-Cl)Li(THF)3 with 3 equiv of 1 (Scheme
3). Reaction of complex 2 with 1 equiv of imino-functionalized
Chart 1
Scheme 3. Reactivities of the Neutral Pyrrole Incorporated
Lanthanide Amides
In this paper, we will for the first time report the synthesis of
lanthanide amides incorporating the neutral pyrrole ligand in
the constrained geometry architecture. Their bonding,
reactions, and catalytic activities for the addition of diethyl
phosphite to α,β-unsturated carbonyl compounds will also be
reported.
RESULTS AND DISCUSSION
■
Synthesis, Characterization, and Reactivity of Con-
strained Geometry Lanthanide Amides Incorporating
Neutral Pyrrole Ligand. Treatment of [(Me3Si)2N]3Ln(μ-
Cl)Li(THF)3 (Ln = La, Nd) with 1 equiv of (N-
C6H5NHCH2CH2)(2,5-Me2C4H2N) (1) in toluene at 70−80
°C for 12 h, after workup, afforded the first example of neutral
pyrrole incorporated constrained geometry lanthanide amides
[η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]Ln[N(SiMe3)2]2
(Ln = La (2), Nd (3)) (Scheme 1). Reaction of
Scheme 1. Synthesis of η5 Bonded Neutral Pyrrole
Lanthanide Amides
pyrrole [2-(2,6-iPr2C6H3NCH)C4H3NH] in toluene at 75
°C afforded the pyrrole deprotonated complex 6 in 80% yield.
When the complexes 2 and 3 were respectively reacted with 2
equiv of amino-functionalized pyrrole [2-(tBuNHCH2)-
C4H3NH] in toluene at 90 °C for 24 h, the mixed η5-bonded
neutral pyrrole and η1-bonded anionic pyrrolyl lanthanide
complexes [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]Ln-
[(η1-2-tBuNCH)C4H3N]2 (Ln = La (7), Nd (8)) were isolated
(Scheme 3). In the reaction, the dehydrogenation of the
pyrrolyl-functionalized secondary amines was found. The
results of the dehydrogenation were supported by X-ray
diffraction analyses and NMR spectral analyses. X-ray analyses
revealed that the bond distance of N(4)−C(19) 1.286(8) Å
and N(6)−C(28) 1.283(7) Å in 7, C−N distances of 1.286(6)
Å and 1.272(6) Å in 8 are in the range of normal CN double
bond, suggesting that the secondary amines were transformed
to imines.11n,p 1H NMR spectra of complexes 7 showed the
clear resonances of the protons of the imine (NCH) at about
8.10 and 8.01 ppm; the 13C NMR spectra also displayed the
resonances of the carbons of the imines (NCH) at about 155
and 154 ppm (see Supporting Information).
[(Me3Si)2N]3Sm(μ-Cl)Li(THF)3 with 2 equiv of 1 afforded
the complex [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]{η1-
[1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N]}SmN(SiMe3)2 (4)
(Scheme 2). Several attempts for the syntheses of La and Nd
complexes containing two neutral pyrrole ligands under the
same conditions were tested but failed. Attempts with other
ligands are still in progress.
Reactivities of complexes 2 and 3 were then investigated.
Treatment of 3 with 2 equiv of 1 produced the sandwich
Scheme 2. Synthesis of Samarium Complex 4
We have demonstrated that the lithium amide LiN(SiMe3)2
cannot promote the dehydrogenation of secondary amine to
imine.11n The dehydrogenation pathway is proposed as follows
(Scheme 4): Initial silylamine elimination of 2 gave the amido-
appended pyrrolyl intermediate D, and the amido-appended
intermediate underwent β-H elimination to give imine
intermediate E. The intermediate E reacted with HN(SiMe3)2
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Scheme 4. Proposed Pathway for the Dehydrogenation Process
through a fast acid−base exchange process to produce the new
amido intermediate, which then repeated the above processes
of silylamine elimination and β-H elimination to afford the final
products.
Structure and Bonding of the Complexes. The
structures of all the above complexes were determined by
single-crystal X-ray crystallographic analyses. X-ray analyses
revealed that complexes 2 and 3 were isostructural constrained
geometry organolanthanide bisamido complexes containing a
neutral pyrrole ligand. A representative structure diagram is
shown in Figure 1. In complexes 2 and 3, the rare-earth metal
Figure 2. Molecular structure of complex 4. Hydrogen atoms were
omitted for clarity.
Figure 1. Representative molecular structure of complexes 2 and 3.
Hydrogen atoms were omitted for clarity.
adopts a distorted pseudotetrahedral geometry, and the neutral
pyrrole appended amido ligand coordinated to rare-earth metal
in η5:η1 modes, which is similar to the constrained geometry
complexes having the cyclopentadienyl derivatives [(Bridge)-
Figure 3. Molecular structure of complex 5. Hydrogen atoms were
omitted for clarity. Selected bond lengths (Å): Nd−Pyrcent (1),
2.845(6) Å, Nd−Pyrcent (2), 3.012(7) Å. More bond distances and
angles can be found in Supporting Information.
t
(DR)(C5Me4)]2− (Bridge = Me2Si, CH2CH2, etc; R = Bu or
Ar, D = N, P; as shown in Chart 1) bonded with metal in η5:η1
modes.10 Different from the cyclopentadienyl supported CGCs
having the cyclopentadienyl anion as a π supporting ligand,
these series of complexes have the neutral pyrrole as the π
supporting ligand. Complex 4 (Figure 2) contains one
N(SiMe3)2, one neutral pyrrole appended amido ligand
coordinated to rare-earth metal in η5:η1 modes, and another
neutral pyrrole ligand serving as an amido ligand probably due
to steric effects. Complex 5 (Figure 3) has two neutral pyrrole
appended amido ligands bonded with metal in η5:η1 modes, and
another neutral pyrrole appended amido ligand serves as amido
ligand, thus forming a new kind of π-bonded neutral pyrrole
sandwich amido complex. In complexes 6 (Figure 4), 7, and 8
(complex 7 as a representative structure diagram in Figure 5),
the anionic iminopyrrolyl ligands serve as donor ligands σ-
bonded to the metal, suggesting the strong donating property
of the anionic pyrrolyl ligand.
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[2.850(2) Å] in 6 is longer than those found in 7 [2.794(6)
Å] and 8 [Nd−Pyrcent 2.747(5) Å].
Catalytic Addition of Diethyl Phosphite to α,β-
Unsaturated Carbonyl Derivatives. Various metal com-
plexes have been demonstrated to be the effective catalysts for
hydrophosphonylation of aldehydes, affording a direct and
atomic efficient way for the synthesis of α-hydroxy
phosphonates.17 Recently, our group has reported hydro-
phosphonylation of both aromatic and aliphatic aldehydes,
unactivated ketones, and substituted imines catalyzed by
lanthanide amides with high catalytic activities.5f,l,18 However,
a few catalytic strategies for the catalytic addition of dialkyl
phosphites to α,β-unsaturated carbonyl compounds have been
developed, and the reported methods require high catalyst
loadings (generally required 20 mol % catalyst loading) or
stoichiometric amount in the case of CaO as catalyst,19e and the
reported methods only focused on limited substrates (generally
with one or two series of α,β-unsaturated carbonyl
substrates).19 So, highly efficient catalysts with high chemo-
and regioselectivity suitable for catalytic addition of phosphites
to all α,β-unsaturated carbonyl compounds are highly required.
The addition reaction of diethyl phosphite to cinnamaldehyde
was first investigated in the presence of neutral pyrrole
supported lanthanide amido complexes, and the results are
summarized in Table 2. Results showed that the addition of
diethyl phosphite to cinnamaldehyde provided only 1,2-
regioselective addition product 9c in an excellent yield.
Lowering or elevating reaction temperature did not affect the
yield of product dramatically (compare the data in Table 2,
entries 2, 7, and 8). Studies on the catalytic activities of the
different lanthanide complexes revealed that complexes 2−8
exhibited high catalytic activities on the addition reaction,
Complexes 2 and 3 displayed an excellent catalytic activity due
to the leaving group of (Me3Si)2N. The differences in catalytic
activities of these complexes are probably due to different
amido groups, which displayed different reactivities in the
catalytic transformation. It is worth noting that
[(Me3Si)2N]3Nd(μ-Cl)Li(THF)3 as the catalyst displayed a
slightly lower catalytic activity under the same conditions
(Table 2, entry 15), suggesting the ligands’ and coordination
mode’s effects on the catalytic activities.
Under the optimized reaction conditions, we next examined
the substrate scope of the catalytic addition of diethyl phosphite
to different α,β-unsaturated carbonyl derivatives in the presence
of the neodymium amide 3 (Table 3). Results showed that only
1,2-addition products are isolated when the substrates are the
α,β-unsaturated aldehydes, and 2-cyclohexen-1-one.
Interestingly, 1,2-regioselectivity products could be obtained
when the benzylideneacetones were treated as substrates at
temperature 0 °C. The 1,4-hydrophosphinylation products
could be obtained when the catalytic reactions of benzylide-
neacetones with diethyl phosphite were carried out at a
temperature of 40 °C in the presence of 5 mol % catalyst
(Table 3, Scheme 5). It is also found that the 1,2-
hydrophosphonylation products could be transformed to the
1,4-hydrophosphinylation products in the presence of 3 mol %
catalyst at temperature of 40 °C.
Figure 4. Molecular structure of complex 6. Hydrogen atoms were
omitted for clarity. C(19)−N(4), 1.33(2) Å.
Figure 5. Molecular structure of complex 7. Hydrogen atoms were
omitted for clarity. Selected bond lengths (Å): N(4)−C(19), 1.286(8)
Å; N(6)−C(28), 1.283(7) Å; N(2)−C(8), 1.450(8) Å.
Complexes 2, 3, and 4 have the same coordination number,
but complex 4 has different amido ligands. The Sm−Pyrcent
distance of 2.704(3) Å in 4 is shorter than the Ln−Pyrcent
distances of 2.847(5) Å in 2 and 2.793(3) Å in 3, reflecting the
lanthanide contraction sequence (ionic radii values for six-
coordinate Ln3+: La3+ 1.032 Å, Nd3+ 0.983 Å, Sm3+ 0.958 Å).15
The Sm−Pyrcent distance in 4 is comparable with that found in
N,N′-dimethyl substituted porphyrinogen samarium complex
(2.69 Å),14b and is obviously longer than that found in the
lower coordination number silyl-linked amido cyclopentadienyl
complex [Me2Si(C5Me4)(tBuN)]SmN(SiMe3)2 (2.371 Å),16
indicating the labile nature of the π-coordinated neutral pyrrole
ring. The Pyrcent−Sm−N(1) bond angle in 4 [84.62(8)°] is
larger than the corresponding bond angle in 2 [79.97(6)°] and
3 [80.64(9)°].
The coordination geometry of complex 5 can be described as
a distorted trigonal bipyramid, the three anion nitrogens are
placed in the equatorial position, while centroids of two pyrrole
rings are in axial positons. The bond distances of Nd−Pyrcent(1)
[2.845(6) Å] and Nd−Pyrcent(2) [3.012(6) Å] (Table 1) with
an average of 2.928(6) Å are comparable to one neutral pyrrole
bonded with metal in η5 modes of 2, 3, and 4 (taking account
for iron radii of Nd3+ 0.983 Å for six coordinates, Nd3+ 1.163 Å
for nine coordinates).15
It was documented that the α-hydroxy phosphonates readily
underwent a retroreaction under basic conditions.20 In order to
understand the catalytic reaction, NMR technique was used to
probe the process of the catalytic transformation of the 1,2-
hydrophosphonylation product to the 1,4- hydrophosphinyla-
tion product. Upon addition of a catalytic amount of complex 2
In complexes 6, 7, and 8, the neutral pyrrole appended amido
ligand adopts η5:η1 bonding modes, and the anionic pyrrolyl
ring bonded with metal in an η1 fashion. The La−CPyr distances
in 6 fall in the same ranges of the η6 La−C(arene) of
[La(EtFormAlMe3)(AlMe4)2] (Form = ArNCHNAr)
(3.068(3)−3.144(4) Å).13c The distance of La−Pyrcent
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Table 1. Selected Bond Lengths (Å) and Bond Angles (deg)
2
3
4
5
6
7
8
Ln(1)−N(1)
Ln(1)−N(2)
Ln(1)−N(3)
Ln(1)−N(4)
Ln(1)−N(5)
Ln(1)−N(6)
C(10)−Ln(1), Ln−C(16)
C(11)−Ln(1), Ln−C(17)
C(12)−Ln(1), Ln−C(18)
C(13)−Ln(1), Ln−C(19)
C(19)−N(4), C(28)−N(6)
Ln(1)−Pyrav(1), Ln(1)−Pyrav(2)
2.384(18)
3.159(19)
2.396(18)
2.418(17)
2.330(2)
3.064(4)
2.339(2)
2.363(2)
2.295(2)
3.019(3)
2.293(18)
2.351(4)
3.143(4)
3.226(4)
2.372(5)
2.371(15) 2.414(5)
3.078(15) 3.025(4)
2.508(15) 2.519(5)
2.800(15) 2.711(5)
2.401(15) 2.522(5)
2.656(4)
2.367(4)
2.996(4)
2.459(4)
2.675(4)
2.675(4)
2.608(4)
2.937(5)
2.940(5)
3.014(5)
3.058(5)
2.280(2)
2.366(5)
3.079(2)
2.995(2)
3.026(2)
3.141(2)
3.031(3)
2.931(3)
2.958(3)
3.101(3)
2.998(3)
2.899(3)
2.872(3)
2.962(3)
3.125(6), 3.183(5)
3.026(6), 3.202(7)
3.009(6), 3.250(7)
3.082(6), 3.291(6)
3.15(2)
3.12(2)
3.05(2)
3.02(2)
1.33(3)
3.083(2)
2.850(2)
2.972(5)
2.876(6)
3.074(6)
3.100(5)
1.288(8), 1.283(7) 1.272(6), 1.286(6)
3.080(2)
2.847(5)
3.050(3)
2.793(3)
2.950(3)
2.704(3)
3.230(4), 3.077(6)
2.845(6), 3.012(6)
3.009(5)
2.794(6)
2.989(5)
2.747(5)
Ln(1)−Pyrcent(1), Ln(1)−
Pyrcent(2)
Pyrcent−Ln(1)−N(1)
Pyrcent−Ln(1)−N(3)
Pyrcent−Ln(1)−N(4)
Pyrcent−Ln(1)−N(5)
Pyrcent−Ln(1)−N(6)
Pyrcent(1)−Ln(1)−Pyrcent(2)
N(1)−Ln(1)−N(3)
N(1)−Ln(1)−N(4)
N(3)−Ln(1)−N(4)
N(1)−Ln(1)−N(5)
N(3)−Ln(1)−N(5)
N(1)−Ln(1)−N(6)
N(4)−Ln(1)−N(6)
N(5)−Ln(1)−N(6)
C(7)−N(1)−Ln(1)
79.97(6)
118.84(6)
112.38(6)
80.64(9)
118.33(9)
113.02(9)
84.62(8)
80.82(18), 94.81(17) 83.95(6)
98.36(15), 79.25(18) 95.47(5)
84.25(4)
97.98(16)
93.46(17)
85.35(14)
98.61(13)
93.84(13)
103.85(15)
172.32(14)
109.31(8)
128.21(8)
104.79(7)
109.65(6) 105.41(17)
172.33(16)
95.42(16), 89.67(17)
174.63(6)
112.98(6)
112.01(6)
115.54(6)
112.90(9)
111.47(9)
115.49(9)
91.14(17)
114.6(5)
91.82(14)
67.98(12)
65.0(5)
100.9(6)
84.5(5)
66.71(15)
114.55(8)
110.77(7)
125.74(16)
133.66 (13)
67.02(15)
68.56(13)
112.5(3)
107.68(14)
107.41(18)
106.68(15) 107.7(3)
111.5(13) 114.1(4)
(for the paramagnetic property of complex 3, so we used
complex 2 instead of complex 3 in the probing experiments) to
diethyl 2-hydroxy-4-phenylbut-3-en-2-ylphosphonate (9e) in
C6D6, the mixture was heated to 40 °C. The disappearance of
resonances of the protons on double bonds of 9e at 6.62 and
7.36 ppm and methyl (CH3CHOH−) at 2.0 ppm and
appearance of the protons of the methyl (CH3CO−) of diethyl
3-oxo-1-phenylbutylphosphonate (10a) at 1.60 ppm can be
recorded in 5 min. The transformation of 9e to 10a can be
finished in 2 h by comparison of the 1H NMR spectra with the
purified 10a. At the same time, we tested the temperature or
catalyst effects on this transformation. Compound 9e was
heated to 40 or 60 °C for 2 h, even 12 h, and no 1,4-
hydrophosphinylation product was found upon analysis of the
1H NMR spectra. However, 9e can be almost completely
transformed to 10a in the presence of a catalytic amount of
complex 2 at 10 °C, but it required 6 h (see Supporting
Information), indicating that catalyst played a key role in the
transformation of 1,2-addition products to 1,4-addition
products. On the basis of experimental results, the catalytic
transformation pathway of the 1,2-hydrophosphonylation
products to the 1,4-hydrophosphinylation products is proposed
involving acid−base interaction to give intermediate F, followed
by intramolecular addition of phosphorus to the CC to
produce the intermediate G similar to the retroaddition.20 This
intermediate reacted with amine to produce the final product
(Scheme 6).
regioselective addition products in good to high yields.
However, the catalytic reaction generally required 120 min
for the α,β-unsaturated chalcones and ester substrates to give
satisfactory yields of the products, suggesting these substrates
are relatively unactivated compared to other ones. It is found
that the electronic nature and steric hindrance of substituents
have an effect on the reactivity. For example, when electron-
donating substituents such as Me and OMe were used, good
yields of products 10k and 10l were isolated (entries 16 and
17), and the addition of diethyl phosphite to 4-nitrochalcone
produced the product in 80% yield, while the addition of
diethyl phosphite to 2-nitrochalcone gave the product in only
50% yield. For comparison, the catalytic activity of the
cyclopentadienyl-free neodymium amide [(Me3Si)2N]3Nd(μ-
Cl)Li(THF)3 was tested by running catalytic addition of diethyl
phosphite to some relatively unreactive substrates such as α,β-
unsaturated chalcones. Results (Table 3, entries 14, 16, 18, and
19) indicated the above neutral pyrrole incorporated con-
strained geometry lanthanide amido complexes generally
exhibited a higher activity than the [(Me3Si)2N]3Nd(μ-
Cl)Li(THF)3 did, indicating the advantage of the neutral
pyrrole incorporated constrained geometry lanthanide amido
complexes. High catalytic activity with a low catalyst loading (1
mol %) for the catalytic addition of phosphites to α,β-
unsaturated carbonyl derivatives is for the first time reported in
this field comparable to the literature’s results.19
CONCLUSIONS
It is found that the catalytic addition of diethyl phosphite to
2-cyclopenten-1-one, α,β-unsaturated chalcones, amides, and
esters in the presence of 1.0 mol % of 3 produced only 1,4-
■
In summary, we have for the first time synthesized and
characterized a series of rare-earth metal amides incorporating
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amides as catalysts. Further works on neutral pyrrole or indole
supported rare-earth metal complexes are in progress.
Table 2. Optimization of the Conditions on the Reaction of
Cinnamaldehyde with Diethyl Phosphite
a
EXPERIMENTAL SECTION
■
General Remarks. All syntheses and manipulations of air- and
moisture-sensitive materials were performed under dry argon and
oxygen-free atmosphere using standard Schlenk techniques or in a
glovebox. All solvents were refluxed and distilled over sodium
benzophenone ketyl under argon prior to use unless otherwise
noted. [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 (Ln = Nd, Sm, La),21 2-
[(2,6-iPr2C6H3)NCH]C4H3NH, and 2-(tBuNCH2)C4H3NH were
prepared according to literature methods.11p Acetonylacetone and
N-phenylethylenediamine were purchased and used without purifica-
tion. Solid α,β-unsaturated carbonyl derivatives were used directly, and
liquid derivatives were distilled before use. Elemental analysis data
were obtained on a Perkin-Elmer 2400 Series II elemental analyzer. 1H
NMR, 13C NMR, and 31P NMR spectra for analyses of compounds
were recorded on a Bruker AV-300 NMR spectrometer (300 MHz for
1H; 75.0 MHz for 13C; 121 MHz for 31P NMR) in C6D6 for lanthanide
complexes and in CDCl3 for organic compounds. Chemical shifts (δ)
were reported in ppm. J values are reported in Hz. IR spectra were
recorded on a Shimadzu FTIR-8400s spectrometer (KBr pellet). Mass
spectra were performed on a Micromass GCT-MS spectrometer.
Melting points were determined in capillaries and were uncorrected.
Preparation of N-Anilinoethyl-2,5-dimethylpyrrole (1). N-
Phenylethylenediamine (7.6 g, 0.05 mol), acetonylacetone (2.7 g, 0.05
mol), and sufficient toluene were placed in a round-bottom flask with a
water separator and heated at reflux overnight. The water produced
during the reaction was removed as a toluene azeotrope. The toluene
was removed in vacuo after the reaction was completed. Recrystalliza-
tion of crude product from hexane and ethyl acetate (1:3) gave the
temp
yield
b
entry
cat. (mol %)
3 (1 mol %)
solvent
(°C)
time
(%)
1
2
n-hexane
rt
rt
5 min
5 min
20 min
5 min
20 min
20 min
24 h
93
90
97
92
95
98
30
trace
95
97
95
85
98
80
95
88
92
93
88
95
3 (1 mol %)
toluene
3
3 (1 mol %)
THF
rt
4
3 (1 mol %)
3 (0.5 mol %)
3 (0.25 mol %)
3 (1 mol %)
3 (1 mol %)
2 (1 mol %)
4 (1 mol %)
solvent free
toluene
toluene
toluene
toluene
toluene
toluene
rt
rt
rt
0
5
6
24 h
7
20 min
20 min
20 min
20 min
2 h
8
40
rt
rt
10
11
12
5 (1 mol %)
toluene
rt
20 min
4 h
13
14
16
15
6 (1 mol %)
7 (1 mol %)
toluene
toluene
toluene
rt
rt
rt
rt
20 min
20 min
20 min
20 min
2 h
8 (1 mol %)
c
Nd[N]3 (1 mol %) toluene
a
Reaction conditions: cinnamaldehyde (2.0 mmol), diethyl phosphite
(2.4 mmol), solvent (2 mL) or solvent free, room temperature.
Isolated yields. Nd[N]3: [(Me3Si)2N]3Nd(μ-Cl)Li(THF)3.
1
product (1) (9.6 g, 90% yield). Mp: 74−76 °C. H NMR (300 MHz,
b
c
CDCl3, ppm,): δ 7.19−7.10 (m, 2H, C6H5), 6.67−6.55 (m, 1H,
C6H5), 6.53−6.52 (m, 2H, C6H5), 5.73 (s, 2H, pyr), 3.90 (t, J = 6.6
Hz, 2H, CH2), 3.33 (t, J = 6.6 Hz, 2H, CH2), 2.14 (s, 6H, CH3); 13C
NMR (75 MHz, CDCl3, ppm): δ 147.5, 129.6, 127.9, 117.8, 112.7,
105.7, 44.0, 42.9, 12.8. IR (KBr pellets, cm−1): ν 3435 (s), 3356 (s),
2974 (m), 2910 (w), 2580 (w), 1600 (s), 1508 (s), 1406 (s), 1325 (s),
1257 (w), 1114 (w), 881 (w), 752 (s), 690 (s). HRMS (ESI) calcd for
C14H19N2 (M + H+): 215.1548. Found: 215.1548.
neutral pyrrole appended amido ligand in the constrained
geometry architecture. X-ray diffraction analyses indicated the
neutral pyrrole bonded with rare-earth metal ions in an η5
mode. This work may open the chemistry of constrained
geometry organolanthanide complexes with π-bonded neutral
pyrrole ligands. Reactions of the neutral pyrrole supported
lanthanide bisamido complexes with imino and secondary
amine functionalized pyrroles were studied, and results
indicated that the neutral pyrrole still bonded with the rare-
earth metal ions in the η5 mode, while the anionic pyrrolyl
ligands bonded with the rare-earth metal ions as σ-donationg
ligands. Additionally, reactions of the neutral pyrrole supported
bisamido rare-earth complexes with secondary amine function-
alized pyrrole led to the dehydrogenation of secondary amine
to imine through the proposed β-H elimination process. The
neutral pyrrole supported rare-earth complexes exhibited a high
chemo- and regioselectivity in catalytic addition of diethyl
phosphite to α,β-unsaturated carbonyl derivatives. The catalytic
reactions provided only 1,4-regioselectivity addition for α,β-
unsaturated esters, amide, chalcones, and 2-cyclopenten-1-one,
and 1,2-addition for α,β-unsaturated aldehydes and 2-cyclo-
hexen-1-one. It is interesting to find that the reaction
conditions have a great effect on the regioselectivity for the
catalytic addition of diethyl phosphite to substituted
benzylideneacetones: the 1,2-regioselective addition products
were obtained when the reactions were run at 0 °C, while 1,4-
addition products could be separated when the reactions were
carried out at or above 40 °C, and the 1,2-addition products
could be transferred to the 1,4-addition products at or above 40
°C in the presence of the neutral pyrrole supported lanthanide
Preparation of [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]La[N-
(SiMe3)2]2 (2). To a toluene (20.0 mL) solution of [(Me3Si)2N]3La(μ-
Cl)Li(THF)3 (1.072 g, 1.2 mmol) was added a toluene (10.0 mL)
solution of ligand 1 (0.257 g, 1.2 mmol) at room temperature. After
the reaction mixture was stirred at room temperature for 2 h, the
mixture was stirred at 70 °C for 24 h. The solvent was evaporated
under reduced pressure. The residue was extracted with n-hexane (2 ×
10.0 mL). The extracts were combined and concentrated to about 10.0
mL. Pale yellow crystals were obtained by recrystallization from the
concentrated n-hexane solution at 0 °C (0.62 g, 77% yield). Mp: 178−
1
180 °C. H NMR (300 MHz, C6D6, ppm): δ 7.37−7.31 (m, 2H,
C6H5), 6.91−6.88 (m, 2H, C6H5), 6.75−6.70 (m, 1H, C6H5), 5.80 (s,
2H, pyr), 3.23 (t, J = 4.5 Hz, 2H, CH2), 2.91 (t, J = 4.8 Hz, 2H, CH2),
1.66 (s, 6H, CH3), 0.37 (s, 36H, CH3). 13C NMR (75.0 MHz, C6D6,
ppm): δ 153.3, 132.0, 128.8, 114.4, 112.9, 106.8, 46.6, 41.8, 11.3, 4.1.
IR (KBr pellets, cm−1): ν 2974 (w), 2910 (w), 1602 (s), 1498 (w),
1406 (w), 1327 (s), 1257 (m), 1178 (s), 1124 (s), 1001 (m), 937 (s),
831(m), 752 (s). Anal. Calcd for C26H53N4LaSi4 + (1/2)C6H14: C,
48.64; H, 8.45; N, 7.82. Found: C, 48.47; H, 8.58; N, 7.42.
Preparation of [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]Nd[N-
(SiMe3)2]2 (3). This compound was prepared as blue crystals in 85%
(0.616 g) yield by treatment of HL (1) (0.23 g, 1.07 mmol) with
[(Me3Si)2N]3NdIII(μ-Cl)Li(THF)3 (0.945 g, 1.07 mmol) using
procedures similar to those described above for preparation of 2.
Mp: 170−172 °C. IR (KBr pellet, cm−1): ν 2941 (s), 2902 (s), 2850
(s), 1602 (m), 1510 (m), 1406 (m), 1327 (s), 1273 (m), 1178 (s),
1124 (s), 1018 (s), 935 (s), 842 (s), 775(s), 690 (m). Anal. Calcd for
C26H53N4NdSi4: C, 46.04; H, 7.88; N, 8.26. Found: C, 45.84; H, 7.81;
N, 8.32.
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a
Table 3. Addition of Diethyl Phosphite to Various Unsaturated Carbonyl Compounds Catalyzed by Catalyst 3
3926
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Table 3. continued
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Table 3. continued
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Table 3. continued
a
Reaction conditions: substrate (2.0 mmol), diethyl phosphite (2.4 mmol), catalyst loading (1 mol %), toluene (2 mL) or solvent free, room
b
temperature or 0 °C. Isolated yields and the number in the parentheses refers to the yields of the reaction catalyzed by [(Me3Si)2N]3Nd(μ-
Cl)Li(THF)3 under the same conditions. Temperature: 40 °C, catalyst (5 mol %)
c
treated with 2 equiv of 1 following procedures similar to those used for
Scheme 5. Catalytic Addition of Diethyl Phosphite to
Benzylideneacetones and Transformation of 1,2-Addition
Products to 1,4-Addition Products
preparation of 2 to give the product 5 as blue crystals in 45% yield.
Mp: 182−184 °C. IR (KBr pellets, cm−1): ν 3356 (s), 2974 (m), 2852
(m), 1600 (s), 1510 (s), 1444 (m), 1325 (s), 1178 (m), 1124 (m),
1018 (m), 989 (w), 775 (m), 690 (m). Anal. Calcd for C42H51N6Nd:
C, 64.33; H, 6.56; N, 10.72. Found: C, 64.42; H, 6.46; N, 10.94.
Preparation of [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]La
{η1-2-[(2,6-iPr2C6H3)NCH]C4H3N}N(SiMe3)2 (6). To a toluene
(20.0 mL) solution of complex 2 (0.410 g, 0.61 mmol) was added a
toluene (10.0 mL) solution of 2-[(2,6-iPr2C6H3)NCH]C4H3NH
(0.155 g, 0.61 mmol) at room temperature. After the reaction mixture
was stirred for 24 h at 75 °C, the solvent was evaporated under
reduced pressure. The residue was extracted with hexane (2 × 10.0
mL). The extraction was combined and dried under vacuum to afford
complex 6 in 80% yield (0.729 g). Yellow crystals for X-ray analysis
were obtained from hexane at 0 °C for several days. Mp: 184−187 °C.
1H NMR (300 MHz, C6D6, ppm): δ 7.83 (d, J = 13.6, CHN, 1H),
7.17−7.05 (m, 6H, C6H5), 6.89 (s, 1H, Pyr), 6.60−6.53 (m, 2H,
C6H5), 6.29 (d, J = 7.9 Hz, 1H, Pyr), 6.05 (s, 1H, Pyr), 5.69 (s, 2H,
Pyr), 3.42 (s, 2H, CH2), 3.35 (t, J = 6.3 Hz, 1H, CHMe2), 2.97 (s, 1H,
Scheme 6. Proposed Mechanism for the Transformation of
the 1,2-Addition Products to the 1,4-Addition Products
CH2), 2.83 (t, J = 6.3 Hz, 1H, CHMe2), 1.64 (s, 6H, CH3), 1.05 (d, J =
6.5 Hz, 12H, 4CH3), 0.34 (s, 18H, 6CH3). 13C NMR (75.0 MHz,
C6D6, ppm): δ 162.3, 153.7, 149.4, 140.4, 139.8, 135.2, 129.2, 124.7,
122.6, 121.4, 116.6, 114.5, 111.5, 107.1, 50.3, 42.8, 27.5, 25.1, 20.9,
11.6, 4.1. IR (KBr pellets, cm−1): ν 2960 (m), 2866 (m), 1622 (m),
1602 (m), 1510 (s), 1406 (s), 1300 (s), 1255 (s), 1180 (s), 1134 (s),
1091 (m), 1033 (m), 933 (m), 860 (s), 746 (m). Anal. Calcd for
C37H56LaN5Si2: C, 58.02; H, 7.37; N, 9.14. Found: C, 58.15; H, 7.70;
N, 9.52.
Preparation of [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]La-
[(η1-2-tBuNCH)C4H3N]2 (7). To a toluene (20.0 mL) solution of
complex 2 (0.376 g, 0.56 mmol) was added a toluene (10.0 mL)
solution of 2-(tBuNCH2)C4H3NH (0.170 g, 1.12 mmol) at room
temperature. After the reaction mixture was stirred for 24 h at 90 °C,
the solvent was evaporated under reduced pressure. The residue was
extracted with hexane (2 × 10.0 mL). The extraction was combined
and dried under vacuum to afford complex 7 in 65% yield (0.237 g).
Yellow crystals for X-ray analyses were obtained from hexane at 0 °C
for several days. Mp: 184−185 °C. 1H NMR (300 MHz, C6D6, ppm):
δ 8.10 (s, CHN, 1H), 8.01 (s, CHN, 1H), 7.42 (s, 1H, Pyr), 7.35
(s, 1H, Pyr), 7.25−7.19 (m, 2H, C6H5), 7.03 (s, 1H, Pyr), 6.93 (s, 1H,
Pyr), 6.73−6.69 (m, 3H, C6H5), 6.67 (s, 1H, Pyr), 6.42 (s, 1H, Pyr),
6.18 (s, 1H, Pyr), 5.69 (s, 1H, Pyr), 3.93−3.85 (m, 1H, CH2), 3.59−
3.55 (m, 1H, CH2), 3.14−3.09 (m, 1H, CH2), 2.95−2.91 (m, 1H,
CH2), 1.89 (s, 3H, CH3), 1.43 (s, 3H, CH3), 0.95 (d, J = 13.2 Hz,
Preparation of [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]{η1-
[1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N]}SmN(SiMe3)2 (4). The com-
pound [(Me3Si)2N]3Sm(μ-Cl)Li(THF)3 was treated with 2 equiv of 1
following procedures similar to those used for preparation of 2 to give
the product 4 in 50% yield. Mp: 168−170 °C. IR (KBr pellets, cm−1):
ν 2974 (s), 2908 (s), 2850 (s), 2360 (s), 1602 (m), 1510 (m), 1406
(m), 1327 (s), 1271 (s), 1178 (s), 1124 (s), 1018 (s), 775 (s), 752 (s),
690 (m). Anal. Calcd for C34H52N5Si2Sm: C, 55.38; H, 7.11; N, 9.50.
Found: C, 55.68; H, 7.41; N, 9.30.
t
18H, Bu). 13C NMR (75.0 MHz, C6D6, ppm): δ 155.2, 154.3, 136.4,
Preparation of [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]2Nd-
[η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)] (5). The complex 3 was
134.9, 133.1, 132.6, 128.9, 119.2, 118.4, 113.8, 112.5, 110.4, 108.0,
3929
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Organometallics
Article
107.3, 48.7, 42.9, 28.8 (d, J = 53 Hz), 11.9, 9.35. IR (KBr pellets,
cm−1): ν 2966 (m), 2910 (w), 1633 (s), 1510 (s), 1406 (m), 1363 (s),
1325 (m), 1209 (s), 1095 (s), 1031 (s), 912 (s), 804 (m), 775 (m),
752 (m), 692 (s). Anal. Calcd for C32H43LaN6: C, 59.07; H, 6.66; N,
12.92. Found: C, 58.33; H, 6.74; N, 12.77.
ACKNOWLEDGMENTS
■
This work was cosupported by the National Natural Science
Foundation of China (Grants 20832001, 21172003,
21072004), the National Basic Research Program of China
(2012CB821600), and grants from the Ministry of Education
(20103424110001).
Preparation of [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]Nd
[(η1-2-tBuNCH)C4H3N]2 (8). Complex 8 was prepared as blue crystals
in 70% yield from the reaction of compound 3 (0.352 g, 0.52 mmol)
with 2 equiv of 2-(tBuNCH2)C4H3NH (0.158 g, 1.04 mmol) by
employing procedures similar to those used for the preparation of 7.
Mp: 180−182 °C. IR (KBr pellets, cm−1): ν 2742 (w), 2576 (m), 1936
(m), 1822 (s), 1631 (w), 1602 (w), 1510 (w), 1421 (w), 1363 (w),
1273 (m), 1209 (m), 1124 (m), 1095 (m), 958 (s), 912 (m), 866 (m).
Anal. Calcd for C32H43NdN6: C, 58.59; H, 6.61; N, 12.81. Found: C,
57.91; H, 6.72; N, 12.50.
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ASSOCIATED CONTENT
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AUTHOR INFORMATION
■
Corresponding Author
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Notes
The authors declare no competing financial interest.
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