Synthesis, structure and catalytic activity of rare-earth metal amino complexes incorporating imino-functionalized indolyl ligand

Article abstract of DOI:10.1016/j.jorganchem.2020.121661

The reactions of the imino-functionalized indolyl ligand (HL, L = 3-(4-Me₂N-C₆H₄CH=N-CH₂CH₂)C₈H₅N) with the rare-earth metal amides [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ producing different types of rare-earth metal amido complexes were investigated. The reactions of HL with 1 equiv. of [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ generated a series of hetero-nuclear bimetallic rare-earth metal amino complexes {[η¹:μ-η²-3-(4-Me₂N-C₆H₄CH=N-CH₂CH₂)C₈H₅]RE[N(SiMe₃)₂]₂(μ-Cl)Li(THF)} (RE = Y(1), Sm(2), Gd(3), Er(4), Yb(5)). By extending the reaction time, only the reaction of HL with [(Me₃Si)₂N]₃Gd(μ-Cl)Li(THF)₃ gave an unexpected binuclear rare-earth metal complex {[(μ-η⁵:η¹):η¹:η¹-3-[(Me₂N)₂-C₁₄H₉]-(NCH₂CH₂-C₈H₅N)₂]Gd₂[N(SiMe₃)₂]₃} (6) incorporating a novel polycyclic ligand through C-C and C-N coupling. Treatment of HL with [(Me₃Si)₂N]₃Sm(μ-Cl)Li(THF)₃ in a 2:1 ratio generated the bis(indolyl) heteronuclear bimetallic rare-earth metal amino complex {(η¹:η¹-[μ-η²:η¹-3-(4-Me₂N-C₆H₄CH=N-CH₂CH₂)C₈H₅]Li[μ-η²:η¹-3-(4-Me₂N-C₆H₄CH=N-CH₂CH₂)C₈H₅])Sm[N(SiMe₃)₂]₂} (7) in low yield probably due to accompanying with the formation of the complex 2. The above results indicated that reaction conditions play important roles in the formation of different coordination modes of the imino-functionalized indolyl rare-earth metal amido complexes. All new complexes 1?7 are fully characterized including X-ray structural determination. The catalytic activity of complexes 1-7 for the addition of amines to carbodiimides was explored. The results showed that all complexes displayed an excellent activity towards the addition of amines to carbodiimides producing guanidine under solvent-free condition.

Full text of DOI:10.1016/j.jorganchem.2020.121661

Journal of Organometallic Chemistry 934 (2021) 121661
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, structure and catalytic activity of rare-earth metal amino
complexes incorporating imino-functionalized indolyl ligand
Lu Yu a, Fenhua Wang b, Hui Wang a, Shaoyin Wang a, Yunjun Wua, Xiaoxia Gua,∗
a Institute of Synthesis and Application of Medical Materials, Department of Pharmacy, Wannan Medical College, Wuhu, Anhui 241002, PR China
b College of Biological and Chemical Engineering, Anhui Polytechnic University, Wuhu, Anhui 241000, PR 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 the imino-functionalized indolyl ligand (HL, L = 3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5N)
with the rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 producing different types of rare-earth
Received 19 July 2020
Revised 10 December 2020
Accepted 17 December 2020
Available online 20 December 2020
metal amido complexes were investigated. The reactions of HL with
Cl)Li(THF)3 generated a series of hetero-nuclear bimetallic rare-earth metal amino complexes {[η1:μ-
η2-3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5]RE[N(SiMe3)2]2(μ-Cl)Li(THF)} (RE
1 equiv. of [(Me3Si)2N]3RE(μ-
=
Y(1), Sm(2), Gd(3), Er(4),
Yb(5)). By extending the reaction time, only the reaction of HL with [(Me3Si)2N]3Gd(μ-Cl)Li(THF)3
gave an unexpected binuclear rare-earth metal complex {[(μ-η5:η1):η1:η1-3-[(Me2N)2-C14 H9]-(NCH2CH2-
C8H5N)2]Gd2[N(SiMe3)2]3} (6) incorporating a novel polycyclic ligand through C-C and C-N coupling.
Treatment of HL with [(Me3Si)2N]3Sm(μ-Cl)Li(THF)3 in a 2:1 ratio generated the bis(indolyl) heteronuclear
bimetallic rare-earth metal amino complex {(η1:η1-[μ-η2:η1-3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5]Li[μ-
η2:η1-3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5])Sm[N(SiMe3)2]2} (7) in low yield probably due to accompa-
nying with the formation of the complex 2. The above results indicated that reaction conditions play
important roles in the formation of different coordination modes of the imino-functionalized indolyl rare-
earth metal amido complexes. All new complexes 1−7 are fully characterized including X-ray structural
determination. The catalytic activity of complexes 1-7 for the addition of amines to carbodiimides was
explored. The results showed that all complexes displayed an excellent activity towards the addition of
amines to carbodiimides producing guanidine under solvent-free condition.
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
explore the reactivity of imino-functionalized indolyl ligand with
rare-earth metal amides.
Functionalized indolyl ligands are used widely in organometal-
lic and coordination chemistry of rare-earth metals for their
strong electron-donating indolyl ring and the precise tailoring of
the metal coordination sphere, and enable the complexes to be
used as homogeneous catalysis [1]. Various rare-earth metal com-
plexes (alkyls, amides) stabilized by functionalized indolyl ligands
have been synthesized and structurally characterized [2]. More-
over, these complexes have been found to be efficient catalysts
Many substituted guanidines have biologically and pharmaceu-
tically activities [3], such as antimicrobial [4], anti-cancer agents
[5]. They are also widely used as ligands in organometallic and
coordination chemistry [6]. Meanwhile guanidine derivatives are
used in many kinds of base-catalyzed reactions [7]. As a result, var-
ious methods have been explored for the synthesis of guanidines
[8], among them, metal catalytic addition of amines to carbodi-
imides is a straightforward and atom-economic route to substi-
tuted guanidine [9]. Since Hou’s group employed the half-sandwich
lanthanide alkyl complexes as catalysts for this reaction [10a], the
development of rare-earth metal catalysts for the transformation
has attracted increasing attention [10]. Shen’s group found ytter-
bium triflate to be efficient catalyst for the reaction under solvent-
free condition [10c]. This finding aroused chemists’ enthusiasm and
many kinds of rare-earth metal complexes with different ancillary
ligands had been found for this reaction under solvent-free condi-
tion subsequently, such as β-diketiminate [10d, 10f], N-heterocyclic
carbene [10e], and bridged bis(amidate) [10g]. However, the draw-
–
or pre-catalysts for C C [2c-d, 2e, 2g] C-N [2h] and C-P [2a-b,
2i] bond construction. Among these work, the reactions of differ-
ent pyrrolyl-functionalized indoles with rare-earth metal amides
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 generated different kinds of rare-
earth metal amido complexes [2f-g]. The findings encouraged us to
∗
Corresponding author.
E-mail address: guxiaoxia@wnmc.edu.cn (X. Gu).
https://doi.org/10.1016/j.jorganchem.2020.121661
0022-328X/© 2020 Elsevier B.V. All rights reserved.

L. Yu, F. Wang, H. Wang et al.
Journal of Organometallic Chemistry 934 (2021) 121661
backs such as steric of ligands and the ionic radii of rare-earth
metals in most cases remain to be solved. Thus, searching for new
kinds of high efficiency catalysts to synthesis of substituted guani-
dine under solvent-free condition is still required.
We herein report the synthesis and structural characterization
of new rare-earth metal amides supported by imino-functionalized
indolyl ligand. The reaction of imino-functionalized indolyl lig-
and with rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3
obtained three kinds of rare-earth metal complexes under different
conditions. The structures of new complexes 1-7 are elucidated by
X-ray crystallography and spectrometry analysis. Their catalytic ad-
dition of arylamines to carbodiimides under solvent-free condition
was examined.
2. Results and discussion
2.1. Ligand synthesis
Fig. 1. Representative molecular structure of complex 1. Hydrogen atoms and the
The reaction of tryptamine with p-(N, N-dimethylamino) ben-
zaldehyde in ethanol at room temperature gave 4-(((2-(1H-indol-
3-yl)ethyl)imino)methyl)-N, N-dimethylaniline (HL) in high yield
(Scheme 1).
CH3 of N(SiMe3)2 group were omitted for clarity.
2.2. Synthesis and characterization of the hetero-nuclear bimetallic
rare-earth metal amino complexes
Treatments of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 1 equiv. of 4-
(((2-(1H-indol-3-yl)ethyl)imino)methyl)-N,N-dimethylaniline (HL)
at 80 °C in toluene for 24 h generated a series of hetero-nuclear
bimetallic rare-earth metal amido complexes{[η1:μ-η2-3-(4-Me2N-
C6H4CH=N-CH2CH2)C8H5]RE[N(SiMe3)2]2(μ-Cl)Li(THF)} (RE = Y(1),
Sm(2), Gd(3), Er(4), Yb(5)) in 23~41% yields (Scheme 2, route a).
Complexes 1-5 were readily crystallized from hexane at room
temperature, X-ray diffraction studies revealed that all the com-
plexes shared similar structural features. As shown in Fig. 1, the
rare-earth metal ion adopted a distorted tetrahedral geometry con-
sisting of one η1-bonded N atom of the indolyl ring, two N(SiMe3)2
groups, and an additional chloride ligand that also bridged the
lithium ion. The latter was ligated to the α- and β-carbon of in-
dolyl ring in an η2 fashion. Further coordination with the imine N
Fig. 2. Representative molecular structure of complex 4. Hydrogen atoms and CH3
of N(SiMe3)2 group were omitted for clarity.
atom from the pendant arm and one molecular of THF completed
its coordination sphere, leading to a distorted triangular pyramid
geometry. Interestingly, the crystal lattice of complex 4 contains
two independent molecules in which the arrangement of ligands
on the lithium ions led to two enantiomers. The representative
molecular structure of complexes 1 and 4 are shown in Figs. 1,2.
The selected bond lengths and angles of complexes 1-5 were listed
in Table 1.
The average distances between a rare-earth metal ion and an
N1 atom of an indolyl ring, gradually increased from 2.248(5)
˚
5 to 2.352(6) A in 2, are well consistent with the trend
in
of ionic radii of the corresponding lanthanide elements. For
Scheme 1. Preparation of the ligand HL.
˚
comparison, the bond lengths of Y-N1 (2.271(4) A) and Er-
˚
N1 (2.324(9) A) are closed to those of hetero-nuclear bimetal-
lic complexes {[(Me3Si)2N]2RE[η1:μ-η2-3-(2-(N-CH3)C4H3NCH=N-
˚
˚
CH2CH2)-C8H5](μ-Cl)Li(THF)} (RE = Y (2.280(3) A), Er (2.301(6)) A)
[2j]. However, the distances between a lithium ion and α-position
(or β-position) carbon atom of an indolyl ring are distinctly longer
than the reported hetero-nuclear bimetallic complexes [2g], which
might be attributed to differences steric of ligand.
When the reaction time was prolonged to 72 h, the reaction
of HL with 1 equiv. of [(Me3Si)2N]3Gd(μ-Cl)Li(THF)3 generated
the unexpected binuclear complex 6 {[(μ-η5:η1):η1:η1-3-[(Me2N)2-
C14 H9]-(NCH2CH2-C8H5N)2]Gd2[N(SiMe3)2]3} (Scheme 3, route b,
Fig. 3), which was isolated in 12% yield after crystallization from
hexane. However, the similar result was not observed in the re-
action of HL with other [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 under the
same conditions.
As shown in Fig. 3, the crystal structure of complex 6 contained
two Gd3+ ions that lie in distinct coordination sphere. One Gd3+
ion (Gd1), one indolyl ring ligated in an η5 mode, the tertiary
Scheme 2. Preparation of complexes 1-7.
2

L. Yu, F. Wang, H. Wang et al.
Journal of Organometallic Chemistry 934 (2021) 121661
Table 1
Selected bond lengths (A) and angles (°) for complexes 1-5.
˚
1
2
3
4
5
RE-N1
2.271(4)
2.352(6)
2.283(6)
2.265(5)
2.670(2)
2.351(14)
2.622(17)
2.643(18)
1.921(16)
2.008(17)
107.5(2)
120.7(2)
114.1(2)
125.13(16)
97.92(15)
87.11(17)
2.310(5)
2.324(9)
2.285(8)
2.295(8)
2.407(4)
2.39(2)
2.40(2)
2.58(3)
1.86(2)
2.07(2)
103.2(3)
126.4(3)
115.1(3)
124.2(2)
92.9(2)
90.0(2)
2.248(5)
RE-N4
2.211(3)
2.248(4)
2.178(5)
RE-N5
2.226(4)
2.256(5)
2.180(5)
RE-Cl
2.5932(14)
2.368(9)
2.6374(18)
2.353(12)
2.613(14)
2.632(15)
1.926(13)
2.001(13)
112.73(19)
120.50(19)
108.0(2)
2.5542(18)
2.374(13)
2.602(16)
2.637(17)
1.909(14)
2.031(14)
112.2(2)
Cl-Li
Li-C1
2.635(11)
2.635(12)
1.887(10)
2.029(10)
112.37(14)
121.52(14)
108.42(16)
99.89 (10)
122.15 (11)
87.56(11)
Li-C2
Li-O1
Li-N2
N1-RE-N4
N4-RE-N5
N1-RE-N5
N4-RE-Cl
N5-RE-Cl
N1-RE-Cl
121.8(2)
108.3(2)
99.57(13)
123.83(14)
87.72(14)
100.03(14)
121.59(16)
88.03(15)
Scheme 3. Proposed pathway for the formation of complex 6.
Gd1. For the other Gd3+ ion (Gd2) also possesses a distorted tetra-
hedral geometry consisting of two η1-bonded indolyl rings via the
N atoms, and two N(SiMe3)2 groups. The selected bond lengths
and angles of complex 6 are listed in Table 2.
–
The formation of complex 6 included a C H bond activation and
2
–
–
–
C C and C N bonds forming steps. The activation of sp C H bond
of pyridine [11], imidazole [12], indole [2j], or aromatic aldimines
[13] by rare-earth metal alkyl or amido complexes was well docu-
mented. On the basis of these works, a possible pathway of the for-
mation of complex 6 is proposed. The reaction was initiated by a
ligand redistribution of two molecules of complex 3 (intermediate
A), The intermediate A would go through a process involving the
activation of the ortho sp2 C−H bond of phenyl group in aldimine
to form intermediate B. Then, the Gd1-C bond was formed, the in-
dolyl ring subsequently changed its coordination centre from Gd1
to Gd2 to lead to Gd1 become cationic alkyl species (intermediate
C). The step reaction was similar to the diastereodivergent annu-
Fig. 3. Structure of complex 6. Hydrogen atoms and the CH3 of N(SiMe3)2 group
were omitted for clarity.
–
lations of aldimine with styrene via C H activation [13]. Then, the
resulted cationic Gd-phenyl-amido moiety then underwent a tan-
amino N atom (N3) and the secondary amino N atom (N-4) in an
η1 mode respectively. The coordination from the pendent amido
and N(SiMe3)2 group led to a distorted tetrahedral geometry on
dem insertion process to form C-C (intermediate D) [2j, 11b] and
3

L. Yu, F. Wang, H. Wang et al.
Journal of Organometallic Chemistry 934 (2021) 121661
Table 2
Table 3
˚
˚
Selected bond lengths (A) and angles (°) for complex 6.
Selected bond lengths (A) and angles (°) for complex 7.
˚
Bond lengths (A)
Angles (°)
Gd1-N3
Gd1-N4
Gd1-N5
Gd1-N6
Gd1-C1
Gd1-C2
Gd1-C3
Gd1-C4
Gd1-Inda
Gd2-N7
Gd2-N8
Gd2-N9
Gd2-N6
2.676(4)
2.261(4)
2.328(4)
2.859(4)
2.803(5)
2.914(5)
2.995(5)
2.953(5)
2.905(5)
2.371(4)
2.335(4)
2.306(4)
2.478(4)
N3-Gd1-N4
N5-Gd1-N3
N5-Gd1-N6
N5-Gd1-C1
N5-Gd1-C2
N5-Gd1-C3
N5-Gd1-C4
N6-Gd2-N7
57.06(13)
95.91(13)
121.94(14)
139.35(15)
118.29(16)
94.31(16)
96.43(15)
83.49(14)
˚
7
Bond length(A)
Angles (°)
Sm-N1
Sm-N2
Sm-N3
Sm-N4
Li-C1
2.290(5)
2.289(5)
2.349(6)
2.382(6)
2.830(14)
2.671(14)
2.562(13)
2.425(13)
2.064(13)
2.051(12)
N1-Sm-N2
N1-Sm-N3
N1-Sm-N4
N5-Li-N6
N5-Li-C1
N5-Li-C2
C1-Li-C2
120.98(18)
112.68(18)
109.06(19)
124.4(6)
131.0(6)
106.4(5)
28.4(2)
N6-Gd2-N8
N6-Gd2-N9
N7-Gd2-N8
N7-Gd2-N9
102.98(15)
126.12(16)
105.71(15)
107.63(15)
Li-C2
Li-C21
Li-C22
Li-N5
a
Gd1–Ind means the average bond distances between the
rare-earth metal ion and the five-membered heterocyclic ring of
the indolyl ligand.
C21-Li-C22
Cl-Li-C21
N6-Li-C21
32.9(2)
97.3(5)
Li-N6
154.6(6)
fluorescent properties of the complexes 1-5 were measured both in
solution and in the solid state. The absorption and emission spec-
tra of the ligand (HL) and the complexes 1-5 in acetonitrile are
shown in Figures S59-60 (see the SI). The solid-state photolumi-
nescence data for the complexes 1-5 are given in the figures S61-
S65 (see the SI). Unfortunately, all the characteristic transitions for
the RE3+ ions were not observed in the complexes 1-5. The reason
may be explained by the fact that the energy level of the ligand
is not well matched with the rare-earth ions in the complexes, re-
sulting in lower energy transfer efficiency [14].
–
2.4. Catalytic activities on addition of amines N H bond to
carbodiimides
The catalytic activities of the imino-functionalized indolyl lig-
and incorporating rare-earth metal amido complexes on amines
addition to carbodiimides were examined (Table 4).
Fig. 4. Structure of complex 7. Hydrogen atoms and the CH3 of N(SiMe3)2 group
were omitted for clarity.
Complex 1 was used as catalyst for the model reaction of the
aniline with N, N’-diisopropylcarbodiimide (DIC). The yields of the
C-N (intermediate E) bonds sequentially, leading to the formation
of 6.
When [(Me3Si)2N]3Sm(μ-Cl)Li(THF)3 was reacted with
equiv. of HL at 80 °C in toluene, the hetero-nuclear bimetal-
lic bis(indolyl) rare-earth metal complex
{(η1:η1-[μ-η2:η1-
3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5]Li[μ-η2:η1-3-(4-Me2N-
C6H4CH=NCH2CH2)C8H5])Sm[N(SiMe3)2]} was obtained alone
with complex 2 (Scheme 2, route c, Fig. 4).
2
Table 4
Optimization of the conditions on the catalytic addition of the aniline N-H bond
to N, N’-diisopropylcarbodiimide (DIC).
7
The X-Ray diffraction studies revealed that the Sm3+ ion
was ligated with two N atoms of two indolyl ligands and two
N(SiMe3)2 groups, forming a four-coordinated anionic Sm3+ cen-
ter. The Li+ ion lies in a distorted tetrahedral geometry, consisting
of two indolyl ring in an η2 fashion and two pendant imino
groups, where the coordination mode of indolyl ring is similar to
Entrya
Cat.(mol %)
Solv.
Temp. (°C)/Time (h)
Yield(%)b
1
1(0.5)
1(1.0)
1(2.0)
1(1.0)
1(1.0)
1(1.0)
1(1.0)
1(1.0)
1(1.0)
1(1.0)
1(1.0)
1(1.0)
2(1.0)
3(1.0)
4(1.0)
5(1.0)
6(1.0)
7(1.0)
THF
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
40/12
70/12
100/12
100/6
100/2
100/2
100/2
100/2
100/2
100/2
100/2
71
83
85
79
84
76
89
91
95
97
97
97
85
82
83
93
83
92
2
THF
3
THF
4
Hexane
˚
those in complexes 1-5. The Sm-Nindolyl (2.349(6) and 2.382(6)A)
5
Toluene
˚
˚
and Sm-Namido (2.290(5)A, 2.289(5)A) bond lengths in 7 are com-
6
CH2Cl2
˚
parable to those (Sm-Nindolyl = 2.352(6)A, Sm-Namido = 2.283(6)
7
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
8
˚
and 2.265(5)A) in complex 2, and both are comparable to the
9
reported hetero-nuclear bimetallic complexes {η1:η1-[η1-3-(2-(N-
CH3)C4H3N-CH=NCH2CH2)C8H5N]Li[μ-η2:η1-3-(2-(N-CH3-C4H3N-
CH=N-CH2CH2) C8H5N])RE[N(SiMe3)2]2} (RE = Yb, Dy) [2g], if the
difference of their ionic radii were considered.
10
11
12
13
14
15
16
17
18
2.3. Spectroscopic analysis
It is well-known that the rare-earth-metal complexes play an
important role in material chemistry, due to their distinctive and
excellent luminescent performance. In order to explore the fluo-
rescent properties of the complexes 1-5, the UV-vis absorption and
a
Reaction conditions: diisopropylcarbodiimide (1.0 mmol), phenylamine
(1.0 mmol), solvent (2 mL) or solvent-free.
b
Isolated yields.
4

L. Yu, F. Wang, H. Wang et al.
Journal of Organometallic Chemistry 934 (2021) 121661
Table 5
steric hindrance. The result was also consistent with the previous
reported works [9].
Results of reactions of different amines with carbodiimides catalyzed by com-
plex 1.
Entrya
R
Ar
Product
Yield(%)b
3. Conclusions
1
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
C6H5
8a
8b
8c
8d
8e
8f
97
97
77
78
76
78
80
81
78
78
2
In summary, the reaction of rare-earth metal amides
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with the imino-functionalized
indolyl ligand (HL) under different reaction conditions gener-
ated three kinds of novel rare-earth metal amido complexes,
including heteronuclear bimetallic monoindolyl complexes 1-5,
homonuclear bimetallic bis(indolyl) complex 6 and heteronuclear
bimetallic bis(indolyl) complex 7. The results indicated that the
imino-functionalized indolyl ligand had multiple reactivity with
rare-earth metal amides and diverse coordination modes with
rare-earth metal ions. The catalytic activity of complexes 1-7 in
the guanylation reaction was evaluated. All the complexes showed
good activity towards the addition of amine to carbodiimides
under solvent-free condition. Moreover, these complexes exhibited
a good catalytic efficiency on the substituted arylamines with
electron-withdrawing or small steric hindrance group on the
phenyl rings. Further studies on the coordination chemistry and
potential catalytic applications of the rare-earth metal complexes
incorporating imino-functionalized indolyl ligand are still in
progress.
3
4-MeC6H4
2-MeC6H4
2-OMeC6H4
4-OMeC6H4
4
5
6
7
8g
8h
8i
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
8j
2-tBuC6H4
8k
8l
40
c
c
c
46
c
c
2,6-Me2C6H3
2-NO2C6H4
4-NO2C6H4
4-BrC6H4
8m
8n
8o
8p
8q
8r
8s
8t
55
c
56
82
85
83
86
93
93
80
81
4-ClC6H4
8u
8v
a
Reaction conditions: carbodiimide (1.0 mmol), aromatic amine (1.0 mmol),
catalyst loading (1 mol %), solvent-free, 100 °C, reaction time 2 h.
b
Isolated yields.
c
4. Experimental
Reaction time 12 h.
4.1. Materials and procedures
catalytic guanylation reaction were raised along with an increase
of catalyst loading (Table 4, entries 1-3), but while the loading of
catalyst 1 was increased from 1 mol% to 2 mol%, the yield of guani-
dine 8a was raised slowly (Table 4, entries 2-3). It is indicated that
the effect on the reaction became less and less with the increase of
catalyst loading. The reaction was carried out under different sol-
vent conditions with 1mol % catalyst loading, toluene seemed to
be a better solvent than other solvents (THF, hexane or CH2Cl2) for
the reaction (Table 4, entries 3-6). Many previous works reported
that rare-earth metal complexes have excellent performance in the
guanylation reaction under solvent-free condition [10c-f]. On ac-
count of this, complex 1 on the addition reaction of aniline to DIC
was tested under solvent-free condition. The yield of the guanidine
under solvent-free condition was the best one than under other
solvents (Table 4, entry 7). Subsequent screening of reaction tem-
perature based on the complex 1 indicated that 100 °C was optimal
(Table 4, entries 8-10). When shorten the reaction time from 12 h
to 2 h, a 97% yield of product could be obtained (Table 4, entry 12).
The guanidine 8a was obtained in 85%, 82%, 83%, 93%, 83% and 92%
yields using the catalysts 2-6, 7 in 2 h (Table 4, entries 13-18) re-
spectively, indicating that the central metal ions of the complexes
had little influence on the catalytic activity. As a result, the reac-
tion should perform better in the presence of 1 mol % complex 1
at 100 °C for 2 h under solvent-free conditions.
All syntheses and manipulations of air- and moisture-sensitive
materials were performed under dry argon and an oxygen-free
atmosphere using standard Schlenk techniques or in a glovebox.
All solvents were refluxed and distilled over sodium benzophe-
none ketyl under argon prior to use unless otherwise noted. Other
reagents were used in their commercial form without further pu-
rification. [(Me3Si)2N]3RE(μ-Cl)Li(THF)3(RE = Y, Sm, Gd, Er, Yb)
were prepared according to literature methods [15]. Elemental
analyses were performed on a Perkin-Elmer 2400 CHN analyzer.
Melting points were determined in sealed capillaries without cor-
rection. 1H NMR and 13C NMR spectra for analyses of compounds
were recorded on a Bruker AV-500 NMR spectrometer (500 MHz
for 1H; 125 MHz for 13C) in CDCl3 or C6D6 or DMSO-d6 for com-
plexes. Chemical shifts (δ) were reported in ppm. J values are re-
ported in Hz. HRMS was performed on a Waters VEVO G2 Q-TOF.
The UV-vis absorption spectra were recorded on a UV-5900 PC.
The luminescence spectra were recorded on FL-4600 Spectropho-
tometer. IR spectra were recorded on Nicolet-470 spectrometer
(KBr pellet).
4.3. Synthesis of ligand and complexes
4.3.1. Synthesis of 3-(4-Me2N-C6H4CH=N-CH2CH2)C8H5NH (HL)
A 100 mL round bottom flask with a magnetic stirrer bar
was charged with (N, N-dimethylamino)benzaldehyde (1.492 g,
10.0 mmol) and tryptamine (1.602 g, 10.0 mmol), to which was
added ethanol. The reaction mixture was stirred at room tem-
perature for 4 h and during which time a yellow precipitate
formed. And was filtered with suction to obtain a crude prod-
uct, which was recrystallized from anhydrous methanol to ob-
tain pale yellow crystals. The final product is obtained as yellow
crystals (2.4153 g, 83% yield). mp: 144.9 °C. 1H NMR (500 MHZ,
DMSO-d6, 25 °C): δ 10.66 (s, 1H, NH), 7.98 (s, 1H, CH=N), 7.52
(d, J = 7.90 Hz, 1H, ArH), 7.48 (d, J = 8.60 Hz, 2H, ArH), 7.30
(t, J = 8.10 Hz, 1H, ArH), 7.02 (t, J = 7.50 Hz, 2H, ArH), 6.93 (t,
J = 7.40 Hz, 1H, ArH), 6.65 (d, J = 8.70 Hz, 2H, ArH), 3.70 (t,
J = 7.30 Hz, 2H, CH2), 2.95 (t, J = 7.30 Hz, 2H, CH2), 2.88 (s,
Next, different substrates of arylamines were tested under the
above optimized conditions (Table 5).
As shown in Table 5, the complex 1 displays a good catalytic
activity on guanylation reaction under solvent-free condition. The
substituents on phenyl ring of the arylamines can be electron-
withdrawing groups such as O2N, Br, Cl or electron-donating
groups such as CH3O, CH3. The reactions of amines with electron-
withdrawing substituted groups (Table 5, entries 15-22) afford
much more better results than those of amines with electron-
donating substituted groups with carbodiimides (Table 5, entries
3-10). However, the reaction with a steric bulky amine, such as
2, 6-dimethylaniline or 2-tert-butylaniline, proceeded slowly and
gave the corresponding guanidine in 40-56% yield, even prolonged
reaction period to 12 h (Table 5, entries 11-14), maybe due to the
5

L. Yu, F. Wang, H. Wang et al.
Journal of Organometallic Chemistry 934 (2021) 121661
6H, N(CH3)2). 13C NMR (125 MHz, CDCl3):δ 161.8 (C=N), 152.4
(C8H5N), 136.7 (C8H5N), 129.9 (2 C8H5N), 128.0 (C8H5N), 124.8
(C8H5N),122.6 (C8H5N), 122.2 (C8H5N), 119.5 (C8H5N), 119.4 (C6H4),
114.6 (C6H4), 112.1 (C6H4), 111.5 (C6H4), 62.4 (CH2), 41.3 (CH3),
40.6 (CH3), 27.6 (CH2). IR (KBr pellets, cm−1): ν3423(m), 3092(m,
C8H5N-H), 2918(m), 2861(m), 1636(m), 1608(s, C=N), 1556(m),
1534(m), 1431(m), 1370(m), 1344(m), 1310(m), 1228(m), 1181(m),
807(m), 730(m). Anal. Calcd for C19 H21N3: C, 78.32; H, 7.26; N,
14.42; Found: C, 78.28; H, 7.25; N, 14.44.
in toluene (10.0 mL) at 80 °C for 24 h in a 1:1 ratio. Color-
less crystals were obtained at room temperature after several days
from hexane solution (0.2042 g, 23%). mp: 189.9°C. IR (KBr pellets,
cm−1): ν 3442(m), 2960(m), 2861(m), 1637(m), 1607(s, -C=N-),
1556(m), 1533(m), 1443(m), 1431(m), 1370(m), 1344(m), 1309(m),
1260(m), 1227(m), 1181(m), 1109(m), 1070(m), 1043(m),1022(m),
842(m), 806(m), 729(m), 568(m), 524(m), 489(m), 419(m). Anal.
Calcd for C35H64ClLiN5OSi4Gd: C, 47.61; H, 7.31; N, 7.93; Found: C,
47.03; H, 7.25; N, 7.70.
4.3.5. Synthesis of {[η1:μ-η2-3-(4-Me2N-C6H4CH=
4.3.2. Synthesis of {[η1:μ-η2-3-(4-Me2N-C6H4CH=
N-CH2CH2)C8H5]Y[N(SiMe3)2](μ-Cl)Li(THF)} (1)
N-CH2CH2)C8H5]Er[N(SiMe3)2](μ-Cl)Li(THF)} (4)
The complex 4 following a procedure similar to that described
for the preparation of complex 1 by reaction of HL (0.2910 g,
1 mmol) with [(Me3Si)2N]3Er(μ-Cl)Li(THF)3 (0.9080 g, 1 mmol)
To
a
toluene (10.0 mL) solution of [(Me3Si)2N]3Y(μ-
Cl)Li(THF)3(0.8288 g, 1 mmol) was added 3-(4-Me2N-C6H4CH=N-
CH2CH2)C8H5NH (0.2910 g, 1 mmol) under 1:1 ratio. After the
solution was heated to 80 °C for 24 h, the color of the solution
gradually changed to yellow. The solvent was evaporated under
reduced pressure. The residue was extracted with hexane. Color-
less crystals were obtained at room temperature after several days
(0.2849 g, 35% yield). mp:186 °C. 1H NMR (500 MHz, C6D6, 25 °C):
δ 8.40 (d, J = 8.25 Hz, 1H, CH=N), 8.00 (s, 1H, ArH), 7.68 (s, 1H,
ArH), 7.48-7.53 (m, 3H, ArH), 7.33-7.36 (m, 1H, ArH), 7.14-7.16 (m,
1H, ArH), 6.40 (d, J = 8.95 Hz, 2H, ArH), 3.54 (t, J = 10.85 Hz, 2H,
C4H8O), 2.85 (t, J = 11.35 Hz, 2H, C4H8O), 2.69 (s, 4H, C4H8O),
2.20 (s, 6H, -N(CH3)2), 0.87 (t, J = 11.75 Hz, 4H, CH2), 0.57 (m,
36H, Si(CH3)3).13C NMR (125 MHz, C6D6, 25 °C): δ 165.8 (CH=N),
152.8 (C8H5N), 146.4 (C8H5N), 131.1 (C8H5N),130.5 (C8H5N), 130.2
(C8H5N), 122.1 (C8H5N), 121.3 (C8H5N), 119.8 (C8H5N), 118.4
(C6H4), 118.0 (C6H4), 111.8 (C6H4), 111.2 (C6H4), 67.8 (C4H8O), 61.6
(C4H8O), 39.6 (C4H8O), 39.3 (C4H8O), 27.5 (CH2), 24.9 (CH2), 5.6
(CH3), 5.5 (CH3), 5.2 (CH3). IR (KBr pellets, cm−1): ν 3423 (s), 2917
(m), 2861 (m), 1637 (m), 1607 (s, -C=N-), 1556 (m), 1533 (m),
1443 (m), 1431 (m), 1370 (m), 1344 (m), 1310 (m), 1228 (m), 1181
(m), 1111 (m), 1073 (m), 1044 (m), 807 (m), 730 (m), 595 (m), 523
(m), 489 (m), 424 (m). Anal. Calcd for C35H64ClLiN5OSi4Y: C, 51.51;
H, 7.92; N, 8.60; Found: C, 51.71; H, 7.61; N, 8.83.
in toluene (10.0 mL) at 80°C for 24
h in a 1:1 ratio. Pink
crystals were obtained at room temperature after several days
from hexane solution (0.2697g, 30%). mp: 188.3°C. IR (KBr pel-
lets, cm−1): ν 3443(m), 2918(m), 2861(m), 1636(m), 1608(s, -C=N-
), 1556(m), 1533(m), 1444(m), 1431(m), 1370(m), 1344(m), 1310(m)
1227(m), 1181(m), 1111(m), 1044(m), 807(m), 730(m), 608(m),
524(m), 489(m), 424(m). Anal. Calcd for C35H64ClLiN5OSi4Er: C,
47.08; H, 7.22; N, 7.84; Found:C, 46.95; H, 7.21; N, 7.94.
4.3.6. Synthesis of {[η1:μ-η2-3-(4-Me2N-C6H4CH=
N-CH2CH2)C8H5]Yb[N(SiMe3)2](μ-Cl)Li(THF)} (5)
The complex 5 following a procedure similar to that described
for the preparation of complex 1 by reaction of HL (0.2910 g,
1 mmol) with [(Me3Si)2N]3Yb(μ-Cl)Li(THF)3 (0.9129 g, 1 mmol) in
toluene (10.0 mL) at 80 °C for 24 h in a 1:1 ratio. Yellow crystals
were obtained at room temperature after several days from hexane
solution (0.3685g, 41% yield). mp: 191 °C. IR (KBr pellets, cm−1):
ν 3422(m), 2917(m), 2858(m), 1637(m), 1607(s, -C=N-,), 1555(m),
1532(m), 1443(m), 1431(m), 1369(m), 1310(m), 1228(m), 1180(m),
807(m), 730(m), 608(m), 525(m), 499(m), 423(m). Anal.Calcd for
C35H64ClLiN5OSi4Yb: C, 46.78; H, 7.18; N, 7.79; Found: C, 46.28; H,
7.29; N, 7.62.
4.3.3. Synthesis of {[η1:μ-η2-3-(4-Me2N-C6H4CH=
4.3.7. Synthesis of {[(μ-η5:η1):η1:η1-3-
[(Me2N)2C14 H9](NCH2CH2C8H5N)2]Gd2[N(Si-Me3)2]3} (6)
N-CH2CH2)C8H5]Sm[N(SiMe3)2](μ-Cl)Li(THF)} (2)
The complex 2 following a procedure similar to that described
for the preparation of complex 1 by reaction of HL (0.2910 g,
1 mmol) with [(Me3Si)2N]3Sm(μ-Cl)Li(THF)3 (0.890 g, 1 mmol)
in toluene (10.0 mL) at 80 °C for 24 h in a 1:1 ratio. Color-
less crystals were obtained at room temperature after several
days from hexane solution (0.2251 g, 25%). mp: 191.1°C;1H NMR
(500 MHz, C6D6): δ 14.77 (d, J = 6.6 Hz, 1H, CH=N), 12.55 (s,
1H, ArH), 8.97 (d, J = 6.5 Hz, 1H,ArH), 8.56 (d, J = 7.6 Hz, 1H,
ArH), 8.48 (s, 1H, ArH), 8.14 (t, J = 7.2 Hz, 1H, ArH), 8.09 (d,
J = 8.9 Hz, 2H, ArH), 6.27 (d, J = 9.0 Hz, 2H, ArH), 4.76 (m, 2H,
C4H8O), 3.82-3.74 (m, 2H, C4H8O), 3.53 (s, 4H, C4H8O), 2.04 (s,
6H, N(CH3)2), -1.24 (s, 4H, CH2), -1.49 (s, 36H, (Si(CH3)3). 13C NMR
(125 MHz, C6D6): δ 166.9 (CH=N), 152.9 (C8H5N), 130.9 (C8H5N),
123.6 (C8H5N), 122.8 (C8H5N), 120.3 (C8H5N), 119.4 (C6H4), 111.9
(C6H4), 68.6 (C4H8O), 62.8 (C4H8O), 39.8 (C4H8O), 39.2 (C4H8O),
29.1 (CH2), 25.4 (CH2), 3.5 (CH3), 3.0 (CH3), 2.7 (CH3). IR (KBr pel-
lets, cm−1): ν 3397(m), 2975(m), 2899(m), 1637(m), 1607(s, C=N),
1556(m), 1533(m), 1444(m), 1431(m), 1371(m), 1344(m), 1310(m),
1234(m), 1181(m), 1088(m), 1047(m), 880(m), 806(m), 729(m),
609(m), 500(m). Anal. Calcd for C35H64ClLiN5OSi4Sm: C, 47.99; H,
7.36; N, 7.99; Found:C, 47.26; H, 7.26; N, 7.73.
To
a
toluene (10.0 mL) solution of [(Me3Si)2N]3Gd(μ-
Cl)Li(THF)3(0.8973 g, 1 mmol) was added 3-(4-Me2N-C6H4CH=N-
CH2CH2)C8H5NH (0.2910 g, 1 mmol) in a 1:1 ratio. After the
reaction mixture was heated to 80 °C for 72 h and the color of the
solution gradually changed to yellow. The solvent was evaporated
under reduced pressure. The residue was extracted with hexane.
Yellow crystals were obtained at room temperature after several
days (0.1653 g, 12% yield). mp: 233 °C. IR (KBr pellets, cm−1): ν
3416(m), 3127(m), 3092(m), 3006(m), 2917(m), 2861(m), 1637(m),
1607(s, -C=N-), 1556(m), 1533(m), 1431(m), 1370(m), 1344(m),
1181(m), 807(m), 730(m). Anal. Calcd for C56H93Gd2N9Si6: C,
48.90; H, 6.82; N, 9.17; Found: C, 51.38; H, 5.86; N, 8.90.
4.3.8. Synthesis of {(η1:η1-[μ-η2:η1-3-(4-Me2N-C6H4CH=
N-CH2CH2)C8H5]Li-[μ-η2:η1-3-(4-Me2N-C6H4CH=
N-CH2CH2)C8H5])Sm[N(SiMe3)2]} (7)
To
a
toluene (10.0 mL) solution of [(Me3Si)2N]3Sm(μ-
Cl)Li(THF)3 (0.890 g, 1 mmol) was added 3-(4-Me2N-C6H4CH=N-
CH2CH2)C8H5NH (0.5820 g, 2 mmol) in a 1:2 ratio. After the
reaction mixture was heated to 80 °C for 48 h, the color of the
solution gradually changed to yellow. The solvent was evaporated
under reduced pressure. The residue was extracted with hexane.
Yellow crystals were obtained at room temperature after several
days (0.2214 g, 25% yield). mp: 160 °C. IR (KBr pellets, cm−1): ν
3414(m), 2916(m), 2848(m), 1636(m), 1604(s, -C=N-), 1527(m),
1482(m), 1456(m), 1361(m), 1312(m), 1259(m), 1179(m), 1097(m),
944(m), 816(m), 742(m), 594(m), 405(m).
4.3.4. Synthesis of {[η1:μ-η2-3-(4-Me2N-C6H4CH=
N-CH2CH2)C8H5]Gd[N(SiMe3)2](μ-Cl)Li(THF)} (3)
The complex 3 following a procedure similar to that described
for the preparation of complex 1 by reaction of HL (0.2910 g,
1 mmol) with [(Me3Si)2N]3Gd(μ-Cl)Li(THF)3 (0.8973 g, 1 mmol)
6

L. Yu, F. Wang, H. Wang et al.
Journal of Organometallic Chemistry 934 (2021) 121661
4.4. General experimental procedure for synthesis of guanidines
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Declaration of Competing Interest
The authors declare that they have no known competing finan-
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Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (grant No. 21602157), Anhui Provincial Natural Sci-
ence Foundation (grant No. 1908085QB50), Anhui Laboratory of
Molecule-Based Material (grant No. fzj19015), The Excellent Young
Talents Fund Program of Higher Education Institutions of Anhui
Province (grant No. gxyq2019041).
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