Synthesis and Reactivity of NNNNN-Pincer Multidentate Pyrrolyl Rare-Earth-Metal Amido-Chloride or Dialkyl Complexes

Article abstract of DOI:10.1021/acs.organomet.0c00606

The NNNNN-pincer multidentate pyrrolyl rare-earth-metal amido-chloride complexes {η1:κ3-2,5-[CH3N(CH2CH2)2NCH2]2C4H2N}RECl[N(SiMe3)2] (RE = Y (2a), Sm (2b), Dy (2c), Er (2d), Yb (2e)) were synthesized by one step from reactions of [(Me3Si)2N]3RE(μ-Cl)Li(T

Full text of DOI:10.1021/acs.organomet.0c00606

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Synthesis and Reactivity of NNNNN-Pincer Multidentate Pyrrolyl
Rare-Earth-Metal Amido-Chloride or Dialkyl Complexes
Weiming Sheng,§ Xiaolong Xu,§ Shuangliu Zhou,* Xiuli Zhang, Zeming Huang, Jun Du, Lijun Zhang,
Yun Wei, Xiancui Zhu, Peng Cui, and Shaowu Wang*
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ABSTRACT: The NNNNN-pincer multidentate pyrrolyl rare-earth-metal amido-chloride complexes {η1:κ3-2,5-[CH3N-
(CH2CH2)2NCH2]2C4H2N}RECl[N(SiMe3)2] (RE = Y (2a), Sm (2b), Dy (2c), Er (2d), Yb (2e)) were synthesized by one
step from reactions of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with {2,5-[CH3N(CH2CH2)2NCH2]2}C4H2NH (1). Reactions of
compound 1 with RE(CH2SiMe3)3(THF)2 gave the rare-earth-metal dialkyl complexes {η1:κ2-2,5-[CH3N-
(CH2CH2)2NCH2]2C4H2N}Sc(CH2SiMe3)2 (3a) and {η1:κ3-2,5-[CH3N(CH2CH2)2NCH2]2C4H2N}RE(CH2SiMe3)2 (RE = Y
(3b), Dy (3c), Er (3d), Yb (3e), Lu (3f)). Further reactions of complexes 3 with dimethylaniline afforded rare-earth-metal diamido
complexes bearing an NNNNN-pincer multidentate pyrrolyl ligand, but not rare-earth-metal imido complexes even under the
condition of additional DMAP. All complexes were characterized by spectroscopic methods, elemental analyses, and single-crystal X-
ray diffraction. The pincer multidentate pyrrolyl rare-earth-metal dialkyl complexes showed high catalytic activities for the addition
of amines to carbodiimides or isothiocyanate to afford the substituted guanidines and thioureas.
or dialkyl complexes have generally been more difficult to
synthesize due to their facile ligand redistribution. Therefore, it
is very important to develop new ancillary ligands to support
the rare-earth diamido or dialkyl complexes.
Pincer-type ligands have attracted increasing attention in
modern coordination chemistry, because they possess a
controlled balance of stability and reactivity through
modifications of the ligand.4 Many typical pincer ligands
have been widely applied in the synthesis of rare-earth-metal
complexes due to their stability with the rare-earth metal.5
Rare-earth-metal dialkyl complexes containing PNP-, NNN-,
and CPC-pincer ligands have displayed a high catalytic activity
INTRODUCTION
■
Rare-earth-metal diamido or dialkyl complexes are potential
precursors with the treatment of an appropriate borate
compound such as [Ph3C][B(C6F5)4] or [PhNMe2H][B-
(C6F5)4] to generate cationic monoamido or monoalkyl
species, which have been demonstrated to be excellent catalysts
of polymerization and copolymerization, as well as other
catalytic transformations such as alkylative alumination and
C−H alkylations.1 Additionally, hydrogenolysis of the rare-
earth dialkyl complexes with H2 will result in the formation of
rare-earth polyhydride complexes showing novel features in
both structure and reactivity.2 Moreover, rare-earth dialkyl
complexes have been demonstrated to afford elusive rare-earth
terminal imido [REN] complexes through a subsequent
intramolecular alkane elimination reaction of hybrid alkyl/
amido species, which were obtained via the elimination of an
alkyl group when rare-earth dialkyl complexes were reacted
with a primary amine.3 In comparison with rare-earth-metal
monoamido or monoalkyl complexes, rare-earth-metal diamido
Received: September 14, 2020
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toward the polymerization and copolymerization of olefins and
dienes.6 The CNC-pincer rare-earth-metal diamido complexes
have displayed a high catalytic activity toward the C−H/P−H
bond addition of terminal alkynes or a phosphine to give
heterocumulenes.7 Mindiola and his co-workers demonstrated
the existence of a scandium terminal imido complex with a
PNP-pincer ancillary ligand by applying a combination of
isotopic labeling and reactivity studies of scandium terminal
imido intermediates that could promote intermolecular C−H
bond activation.8 Chen reported groundbreaking studies in this
field on the isolation and structural characterization of the first
rare-earth-metal terminal imido complex bearing an NNN-
tridentate β-diketiminato ligand.9 Further, they developed the
synthesis of a rare-earth-metal terminal imido complex with an
NNNN-tetradentate β-diketiminato ligand without additional
DMAP.10 Moreover, they revealed the predicted very rich and
diverse reactivity of the highly polarized ScN functionality.11
Cui and co-workers have also successfully isolated a scandium
terminal imido complex with an NPNPN-pincer ancillary
ligand by use of a scandium alkyl amide precursor in the
presence of DMAP, which was derived from the reaction of a
scandium dialkyl complex with 2,6-diisopropylaniline.12
Pyrrole-based NNN-pincer ligands have also been applied in
syntheses of rare-earth dialkyl complexes to exhibit specific
selective living polymerization of isoprene and intramolecular
C−H activation.13 Attempting to increase the coordination
atoms of pyrrole-based pincer ligands, we herein report the
synthesis of NNNNN-pincer multidentate pyrrolyl rare-earth-
metal amido-chloride and dialkyl complexes and further
reactions of rare-earth-metal dialkyl complexes with dimethy-
laniline, and their catalytic activities toward the addition of
amines to carbodiimides or isothiocyanate have been
examined.
inequivalent SiMe3 groups was due to the steric crowding
that suppressed the rotation of the Y−N bond. The reaction of
[(Me3Si)2N]3Y(μ-Cl)Li(THF)3 with compound 1 in d8-
1
toluene was followed by H NMR spectroscopy, and one
singlet (0.22 ppm) was observed in about 2 h, probably owing
to the leaving of (Me3Si)2NLi (Figure S1 in the Supporting
Information).
X-ray analyses revealed that complexes 2a−e had isostruc-
tural octahedral configurations, and a representative structure
diagram of complex 2d is shown in Figure 1. In complexes 2a−
Figure 1. Representative molecular structure of complex 2d. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms are
omitted for clarity.
2e, the rare-earth-metal ion adopted a six-coordinate heavily
distorted tetragonal bipyramidal geometry in which the rare-
earth-metal ion was coordinated by four nitrogen atoms of the
NNNNN-pincer multidentate pyrrolyl ligand in η1:κ3 fashions,
chlorine, and the nitrogen atom of silylamine; however, one of
the nitrogen atoms of the pincer ligand is uncoordinated to the
rare-earth metal. The bond angles N(3)−RE(1)−N(4) (124−
131°) and N(6)−RE(1)−Cl(1) (164−169°) in complexes
2a−e reflect the heavily distorted tetragonal bipyramidal
geometry.
RESULTS AND DISCUSSION
■
Synthesis of Pincer Multidentate Pyrrolyl Rare-Earth
A m i d o - C h l o r i d e C o m p l e x e s . R e a c t io n s o f
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with compound 1 in toluene
afforded the unexpected pincer pyrrolyl rare-earth-metal
amido-chloride complexes {η1 :κ3 -2, 5-[CH3 N-
(CH2CH2)2NCH2]2C4H2N}RECl[N(SiMe3)2] (RE = Y (2a),
Sm (2b), Dy (2c), Er (2d), Yb (2e)) in one step (Scheme 1).
The selected bond lengths and angles of complexes 2a−e are
given in Table 1. In the rare-earth amido-chloride complexes
2a−e, the average bond lengths RE−N (2.470(2) Å for Y (2a),
2.519(2) Å for Sm (2b), 2.478(2) Å for Dy (2c), 2.452(3) Å
for Er (2d), 2.438(3) Å for Yb (2e)) were consistent with the
order of ionic radii of the rare-earth metal. Meanwhile, the
bond length RE−N(1) was shorter than those of RE−N(2),
−N(3), and −N(4) in complexes 2a−e, as expected due to the
donation from the anionic pyrrolide being stronger than those
from the neutral amino donors in the molecules.
Synthesis of Pincer Multidentate Pyrrolyl Rare-Earth
Metal Dialkyl Complexes. Reactions of RE-
(CH2SiMe3)3(THF)2 with compound 1 gave the rare-earth-
m e t a l d i a l k y l c o m p l e x e s { η 1 : κ 2 - 2 , 5 - [ C H 3 N -
(CH2CH2)2NCH2]2C4H2N}Sc(CH2SiMe3)2 (3a) and {η1:κ3-
2,5-[CH3N(CH2CH2)2NCH2]2C4H2N}RE(CH2SiMe3)2 (RE
= Y (3b), Dy (3c), Er (3d), Yb (3e), Lu (3f)) (Scheme 2).
Complexes 3a−f are extremely sensitive to air and moisture.
They are soluble in THF, toluene, and n-hexane. All complexes
were characterized by spectroscopic methods, elemental
analyses, and single-crystal X-ray diffraction.
Scheme 1. Synthesis of Complexes 2a−e
These types of rare-earth-metal amido-chloride complexes
could also be prepared through reaction of ligands with
Ln[N(SiMe3)2]2Cl(THF).14 Complexes 2a−e are extremely
sensitive to air and moisture, and they are soluble in THF,
toluene, and n-hexane. All complexes were characterized by
spectroscopic methods, elemental analyses, and single-crystal
X-ray diffraction. Interestingly, the 1H NMR spectrum of
complex 2a exhibited two singlets (0.53 and 0.16 ppm) of the
N(SiMe3)2 group, integrating to 9 H each, and the 13C{1H}
NMR spectrum of complex 2a exhibited two singlets (6.2 and
5.3 ppm) of the N(SiMe3)2 group; the observation of
B
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Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) of Complexes 2a−e
2a (Y)
2b (Sm)
2c (Dy)
2d (Er)
2e (Yb)
RE(1)−N(1)
RE(1)−N(2)
RE(1)−N(3)
RE(1)−N(4)
RE(1)−N(6)
RE(1)−Cl(1)
RE(1)−Nav
N(1)−RE(1)−N(2)
N(2)−RE(1)−N(3)
N(3)−RE(1)−N(4)
N(1)−RE(1)−N(4)
N(6)−RE(1)−Cl(1)
2.269(2)
2.584(2)
2.571(2)
2.663(2)
2.261(2)
2.5769(8)
2.470(2)
65.57(8)
58.38(8)
167.34(7)
65.98(8)
125.90(6)
2.3003(13)
2.641(2)
2.633(2)
2.707(2)
2.314(2)
2.6481(8)
2.519(2)
64.44(8)
57.44(8)
169.49(7)
64.92(7)
127.02(6)
2.281(3)
2.597(3)
2.582(3)
2.667(3)
2.265(3)
2.5863(10)
2.478(2)
65.36(11)
58.15(11)
167.64(10)
65.99(10)
125.45(7)
2.240(2)
2.548(3)
2.552(3)
2.674(2)
2.248(2)
2.5567(9)
2.452(3)
66.03(8)
59.06(11)
164.79(10)
67.06(7)
131.26(6)
2.237(3)
2.554(3)
2.538(3)
2.631(3)
2.231(2)
2.5411(9)
2.438(3)
66.25(10)
59.02(10)
165.92(10)
66.57(10)
124.46(7)
Scheme 2. Synthesis of Complexes 3a−f
X-ray diffraction revealed that the rare-earth-metal ion in
complex 3a (Figure 2) adopted a five-coordinate trigonal-
bipyramidal geometry. The NNNNN-pincer multidentate
pyrrolyl ligand coordinated to the rare-earth metal in η1:κ3
modes; one of the nitrogen atoms was uncoordinated to the
rare-earth metal. Different from NNN-tridentate pyrrolyl rare-
eart-metal complexes, the coordination mode of the tridentate
ligand could stabilize the Sc3+ ion but could not afford
satisfactory steric shielding for the Ln3+ ion; thus two
molecules combined and redistributed into a dimer.13 The
selected bond distances and angles of complexes 3a−f are
given in Table 2. The average lengths RE(1)−C of 2.407(4) Å
in 3b, 2.419(3) Å in 3c, 2.383(8) Å in 3d, 2.364(8) Å in 3e,
and 2.363(7) Å in 3f fell in a reasonable range when the
difference in ionic radii of the rare-earth metals was considered.
The average lengths RE(1)−C were comparable to those of
NNN-tridentate pyrrolyl rare-earth complexes13 and β-
diketiminato scandium complexes.16
Reactivity of Pincer Multidentate Pyrrolyl Rare-Earth
Metal Dialkyl Complexes with Arylamine. In order to
further explore the reactivity of pincer multidentate pyrrolyl
rare-earth metal dialkyl complexes, reactions of complexes 3
with arylamine were studied. Reactions of complexes 3 with 1
equiv of 2,6-Me2C6H3NH2 afforded the rare-earth-metal
diarylamido complexes 4a,b,d,f bearing an NNNNN-pincer
multidentate pyrrolyl ligand (Scheme 3). Different from the
case for a β-diketiminato ligand,9−11 no rare-earth-metal imido
complexes were obtained through proton abstraction even with
additional DMAP as a Lewis base, although there was still an
uncoordinated nitrogen of one piperazidine. Especially, there
were still two uncoordinated nitrogens of one piperazidine in
scandium complex 4a. In order to further determine the yields,
complexes 4a,b,d,f as catalysts were synthesized by reactions of
complexes 3 with 2 equiv of 2,6-Me2C6H3NH2 to afford the
complexes in 76−88% yields. Complexes 4a,b,d,f were
extremely sensitive to air and moisture. They were soluble in
THF, slightly soluble in toluene, and insoluble in hexane. All
complexes were characterized by spectroscopic methods,
elemental analyses, and single-crystal X-ray diffraction.
Figure 2. Molecular structure of complex 3a. Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms are omitted for
clarity.
bipyramidal geometry and the NNNNN-pincer multidentate
pyrrolyl ligand coordinated to the rare-earth metal in η1:κ2
modes; the two nitrogen atoms of another N-methylpiperazine
were uncoordinated to the rare-earth metal. The average bond
length Sc(1)−σ-C of 2.218(3) Å in complex 3a (Table 2) was
comparable to those in NNN-tridentate pyrrolyl scandium
complexes (2.222(5) and 2.225(5) Å).13 The bond length
Sc−σ-N(1) (2.138(3) Å) in complex 3a was slightly longer
than those of 2.087(4) and 2.079(2) Å in NNN-tridentate
pyrrolyl scandium complexes13 and was slightly shorter than
that of 2.219 Å in pyrrolylaldiminato scandium complexes.15
However, in complexes 3b−f (a representative structure
diagram of complex 3b is given in Figure 3), the rare-earth-
metal ion adopted a six-coordinate distorted-tetragonal-
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Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) of Complexes 3a−e
3a (Sc)
3b (Y)
3c (Dy)
3d (Er)
3e (Yb)
3f (Lu)
RE(1)−N(1)
RE(1)−N(2)
RE(1)−N(3)
RE(1)−N(4)
RE(1)−C(17)
RE(1)−C(21)
RE(1)−Nav
N(1)−RE(1)−N(2)
N(2)-RE(1)-N(3)
N(3)−RE(1)−N(4)
N(1)−RE(1)−N(4)
N(3)−RE(1)−C(21)
N(1)−RE(1)−C(21)
N(1)−RE(1)−C(17)
N(2)-RE(1)-C(17)
N(3)−RE(1)−C(17)
C(21)−RE(1)−C(17)
2.138(3)
2.306(3)
2.363(3)
2.274(4)
2.565(4)
2.532(3)
2.690(3)
2.404(4)
2.407(5)
2.5153(4)
66.46(14)
58.81(12)
169.93(12)
64.93(13)
90.24(15)
127.27(15)
101.57(14)
113.08(15)
80.80(14)
121.70(16)
2.289(3)
2.579(3)
2.551(2)
2.701(2)
2.416(3)
2.422(3)
2.53(3)
66.42(10)
58.67(9)
170.26(9)
64.68(9)
90.55(10)
128.03(11)
101.21(11)
112.64(10)
86.74(10)
121.00(12)
2.263(7)
2.537(7)
2.525(6)
2.679(6)
2.376(8)
2.390(7)
2.501(7)
66.8(3)
2.241(7)
2.522(7)
2.503(6)
2.673(7)
2.360(8)
2.364(8)
2.4848(7)
67.5(2)
2.238(6)
2.522(7)
2.499(7)
2.675(7)
2.358(7)
2.367(8)
2.4835(6)
67.4(3)
2.200(3)
2.216(3)
2.269(3)
74.96(11)
63.42(11)
59.3(2)
169.3(2)
64.8(3)
58.9(2)
168.8(2)
65.5(2)
59.4(2)
168.3(2)
65.7(2)
91.68(10)
86.5(3)
86.6(3)
90.2(3)
103.50(10)
112.88(10)
112.07(11)
100.34(11)
111.84(11)
101.8(3)
127.1(2)
114.3(3)
90.2(3)
127.5(3)
101.3(3)
113.7(3)
89.6(3)
126.5(3)
101.9(3)
113.9(3)
86.8(3)
121.5(3)
121.6(3)
121.3(3)
Figure 3. Representative structure diagram of complex 3b. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms are
omitted for clarity.
Figure 4. Molecular structure of complex 4a. Thermal ellipsoids are
drawn at the 30% probability level. Hydrogen atoms are omitted for
clarity.
Scheme 3. Synthesis of Complexes 4a,b,d,f
NNNNN- pincer multidentate pyrrolyl ligand coordinated to
the rare-earth metal in η1:κ2 modes, leaving one piperazidine
dangling without coordination. Complexes 4b,d,f had iso-
structural six-coordinate distorted-tetragonal-bipyramidal geo-
metries, and a representative structure diagram of complex 4b
is shown in Figure 5. X-ray analyses showed that RE3+ was
bound to four nitrogen atoms of the pyrrolyl ligand and two
nitrogen atoms of the anilido fragments in complexes 4b,d,f,
and the NNNNN-pincer multidentate pyrrolyl ligand coordi-
nated to the rare-earth metal in η1:κ3 modes. Selected bond
lengths and angles of complexes 4a,b,d,f are given in Table 3.
Catalytic Hydroamination of Heterocumulenes. The
catalytic addition of an amide to carbodiimides or
isothiocyanate has provided a straightforward and atom-
economical route to synthesis of guanidines and thioureas.17
Rare-earth-metal complexes as catalysts for the hydroamination
of heterocumulenes have been developed in recent years.18
The previous studies showed that the reaction of the amines
with rare-earth-metal amidates or alkylates gave the rare-earth-
metal amido as an intermediate, which further went through an
insertion of carbodiimide to intermediate to afford a metal
X-ray analyses revealed that complex 4a (Figure 4) adopted
a five-coordinate trigonal-bipyramidal geometry, and the
D
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Table 4. Optimization of the Catalytic Addition of Aniline
a
to CyNCNCy
b
entry catalyst loading (mol %) time (h)
solvent
toluene
THF
yield (%)
1
2
3
4
5
6
7
8
3a
3a
3a
3b
3c
3d
3e
3f
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
99
99
99
99
99
99
99
99
83
87
81
83
86
95
70
99
99
99
hexane
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
solvent-free
9
2a
2b
2c
2d
2e
3b
3b
3b
3b
3b
1
1
1
1
6
6
6
6
6
2
2
1
10
11
12
13
14
15
16
17
18
Figure 5. Representative molecular structure of complex 4b. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms are
omitted for clarity.
1
0.5
0.1
1
1
1
guanidinate species.19 Therefore, NNNNN-pincer pyrrolyl
rare-earth-metal dialkyl complexes were reacted with an
amide to afford the corresponding rare-earth-metal diamido
complexes, which should also be able to serve as intermediates.
The additions of aniline to N,N′-dicyclohexylcarbodiimide
were first examined using 1 mol % of complex 3a in different
solvents to afford the product in almost quantitative yields
(entries 1−3, Table 4), indicating the solvent compatibility of
the catalyst. It was found that complexes 3b−f could all highly
catalyze the addition of aniline to N,N′-dicyclohexylcarbodii-
mide (entries 4−8, Table 4). However, rare-earth amido-
chloride complexes 2a−e catalyzed the addition of aniline to
N,N′-dicyclohexylcarbodiimide to give the product 7a in 81−
85% yields over 6 h (entries 9−13, Table 4). Further
optimizations for the guanylation of aniline were accomplished,
affording the product 7a in 95% yield with 0.5 mol % of
catalyst 3b under solvent-free conditions (entry 18, Table 4).
Complex 4a as catalyst for the a guanylation of aniline
provided the product 7a in a yield similar to that of complex 3a
as the catalyst, indicating that the rare-earth-metal diamido
complex was probably an intermediate of the catalytic reaction.
0.5
0.5
a
Reaction conditions: aniline (1.0 mmol), CyNCNCy (1.0
b
mmol), solvent (2.0 mL). Isolated yield.
Thus, complex 3b was selected as the catalyst for the
following experiments to examine the addition of various
amines to heterocumulene under solvent-free conditions or in
toluene (2.0 mL, to increase the solubility for solid amines),
and the results are presented in Table 5. The results showed
that the additions afforded the guanylation products 7b−j in
excellent yields of 96−99% for various aromatic amines with
electron-donating or electron-withdrawing groups (entries 2−
10, Table 5). The catalytic system also worked excellently for
addition of aliphatic amines to afford the corresponding
compounds 7k−n (entries 11−14, Table 5). The addition of
amines to N,N′-diisopropylcarbodiimide also gave the
corresponding compounds 7o−r in high yields (entries 15−
18, Table 5). Further expansion of the addition of amines to
isothiocyanate also worked well to afford the substituted
Table 3. Selected Bond Lengths (Å) and Bond Angles (deg) of Complexes 4a,b,d,f
4a (Sc)
4b (Y)
4d (Er)
4f (Lu)
RE(1)−N(1)
RE(1)−N(2)
RE(1)−N(3)
RE(1)−N(4)
RE(1)−N(6)
RE(1)−N(7)
RE(1)−Nav
N(1)−RE(1)−N(2)
N(2)−RE(1)−N(3)
N(3)−RE(1)−N(4)
N(1)−RE(1)−N(3)
N(1)−RE(1)−N(4)
N(6)−RE(1)−N(7)
N(2)−RE(1)−N(6)
N(2)−RE(1)−N(7)
2.1535(17)
2.4098(18)
2.4327(19)
2.2933(16)
2.5776(16)
2.5668(17)
2.8058(16)
2.2457(16)
2.2244(15)
2.4523(17)
65.24(6)
2.276(3)
2.556(3)
2.548(3)
2.802(3)
2.216(2)
2.234(2)
2.4387(3)
65.54(9)
58.67(9)
167.82(8)
120.03(9)
65.26(9)
122.21(10)
115.91(10)
107.92(9)
2.246(2)
2.523(2)
2.519(2)
2.806(2)
2.180(2)
2.202(2)
2.4127(2)
66.34(8)
59.37(7)
166.95(7)
121.45(8)
65.49(7)
121.93(9)
116.79(8)
107.70(8)
2.0729(19)
2.0562(17)
2.2250(19)
69.50(7)
61.46(7)
58.28(5)
168.29(5)
119.43(6)
65.06(5)
122.32(6)
115.54(6)
107.96(6)
126.22(7)
121.05(8)
120.02(8)
107.86(7)
E
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Organometallics XXXX, XXX, XXX−XXX

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Article
(THF)320 and RE(CH2SiMe3)3(THF)221 were prepared according to
the literature procedures. 1H NMR and 13C NMR spectra for analyses
of compounds were recorded on a Bruker AV-400 or 500 NMR
spectrometer in C6D6 for lanthanide complexes and in CDCl3 for
organic compounds. IR spectra were recorded on a Shimadzu FTIR-
8400S spectrometer.
Table 5. Catalytic Addition of Various Amines to
Heterocumulenes by Complex 3b
a
Synthesis of Compound 1. To a solution of 1-methylpiperazine
(5.0 mL, 45.0 mmol), 37% formaldehyde solution (3.65 mL, 45.0
mmol), and pyrrole (1.58 mL, 22.5 mmol) in ethanol (20.0 mL) was
added dropwise glacial acetic acid. The reaction mixture was stirred at
room temperature for 12 h. The reaction mixture was extracted with
dichloromethane (50.0 mL × 3), and the extracts were dried over
anhydrous Mg2SO4 and filtered. The organic layer was concentrated
under reduced pressure to provide the white solid 1 (5.64 g, 86%
yield). Mp: 131−133 °C. 1H NMR (300 MHz, CDCl3, ppm): δ 8.57
(s, 1H), 5.89 (s, 2H), 3.44 (s, 4H), 2.44 (br, 16H), 2.27 (s, 6H). 13C
NMR (75 MHz, CDCl3, ppm): δ 128.2, 107.4, 55.5, 55.1, 53.0, 46.0.
HRMS (ESI): calcd for C16H29N5 [M + H+] 292.2496, found
292.2494.
General Synthesis of Complexes 2a−e. Under an argon
atmosphere, an oven-dried 250.0 mL Schlenk flask equipped with a
magnetic stir bar was charged with compound 1 (0.29 g, 1.00 mmol),
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 (1.00 mmol), and toluene (20.0
mL) at room temperature. The reaction mixture was stirred at 90 °C
for 12 h, and the solvent was evaporated under reduced pressure. The
residue was extracted with n-hexane/toluene (1/1), and crystals were
obtained by cooling the solution to 0 °C for several days.
Complex 2a. Colorless crystals (0.50 g, 89% yield). Mp: 227−229
°C. IR (KBr pellets, cm−1): ν 2935(s), 2850(s), 2809(s), 1452(w),
1339(s), 1282(m), 1157(s), 1012(s), 937(s), 449(m). 1H NMR (400
MHz, C6D6): δ 6.30 (s, 2H), 4.12 (s, 4H), 3.72−2.68 (m, 10H),
2.38−1.95 (m, 12H), 0.53 (s, 9H), 0.16 (s, 9H). 13C NMR (101
MHz, C6D6): δ 134.6, 103.1, 59.7, 53.3, 49.2, 46.1, 6.2, 5.3. Anal.
Calcd for C22H46ClN6Si2Y·C6H14: C, 50.85; H, 9.14; N, 12.71.
Found: C, 50.41; H, 8.98; N, 12.89.
Complex 2b. Pale yellow crystals (0.58 g, 81% yield). Mp: 235−
237 °C. IR (KBr pellets, cm−1): ν 2945(s), 2846(s), 2814(s),
1452(w), 1342(s), 1286(m), 1168(s), 1015(s), 924(s), 808(s). Anal.
Calcd for C22H46ClN6Si2Sm: C, 41.51; H, 7.28; N, 13.20. Found: C,
41.33; H, 6.91; N, 13.12.
Complex 2c. Colorless crystals (0.62 g, 84% yield). Mp: 231−233
°C. IR (KBr pellets, cm−1): ν 2945(s), 2852(s), 2810(s), 1638(w),
1455(s), 1352(m), 1282(s), 1245(s), 1154(s), 1012(s), 927(m).
Anal. Calcd for C22H46ClDyN6Si2: C, 40.73; H, 7.15; N, 12.95.
Found: C, 40.33; H, 7.04; N, 13.01.
Complex 2d. Pink crystals (0.48 g, 75% yield). Mp: 227−229 °C.
IR (KBr pellets, cm−1): ν 2952(s), 2839(s), 2811(s), 1455(w),
1345(s), 1295(m), 1248(s), 1147(s), 1009(s), 921(s), 826(m). Anal.
Calcd for C22H46ClErN6Si2: C, 40.43; H, 7.09; N, 12.86. Found: C,
40.07; H, 7.22; N, 12.41.
Complex 2e. Yellow crystals (0.59 g, 79% yield). Mp: 224−226 °C.
IR (KBr pellets, cm−1): ν 2942(s), 2815(s), 1455(w), 1345(s),
1279(m), 1147(s), 1053(s), 1006(s), 924(s), 804(m). Anal. Calcd for
C22H46ClN6Si2Yb: C, 40.08; H, 7.03; N, 12.75. Found: C, 40.16; H,
7.08; N, 12.73.
b
entry
R1R2NH
PhNH2
R3/X
product
yield (%)
1
2
3
4
5
6
7
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
Cy/NCy
iPr2/NiPr2
iPr2/NiPr2
iPr2/NiPr2
4-MePh/S
4-MePh/S
4-MePh/S
4-MePh/S
tBu/S
7a
7b
7c
7d
7e
7f
7g
7h
7i
99
99
99
98
99
99
99
96
99
99
99
99
97
94
99
98
98
95
96
93
99
98
2-MeC6H4NH2
3-MeC6H4NH2
2,6-Me2C6H3NH2
2,6-iPr2C6H3NH2
2-ClC6H4NH2
3-ClC6H4NH2
2,6-Cl2C6H3NH2
2-BrC6H4NH2
3,5-(CF3)2C6H3NH2
PhCH2NH2
c
8
c
9
10
11
12
13
14
7j
7k
7l
CyNH2
pyrrolidine
CH2(CH2CH2)2NH
PhNH2
c
7m
7n
7o
7p
7q
7r
7s
7t
c
15
16
17
18
19
20
21
22
2-MeC6H4NH2
2-ClC6H4NH2
PhNH2
2-MeC6H4NH2
2-ClC6H4NH2
CyNH2
7u
7v
CyNH2
a
Reaction conditions: complex 3b (0.005 mmol), amine (1.0 mmol),
heterocumulene (1.0 mmol), room temperature. Isolated yields.
Reaction was run in toluene (2.0 mL) to increase the solubility for
b
c
solid amines.
thioureas 7s−v in almost quantitative yields (entries 19−22,
Table 5).
CONCLUSION
■
A series of rare-earth-metal complexes bearing an NNNNN-
pincer multidentate pyrrolyl ligand were synthesized and well-
defined. Pincer multidentate pyrrolyl rare-earth-metal amido-
chloride complexes were synthesized via one-step reactions of
[(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with the NNNNN-pincer
multidentate pyrrolyl ligand. Pincer multidentate pyrrolyl
rare-earth-metal dialkyl complexes were synthesized through
reactions of RE(CH2SiMe3)3(THF)2 with the NNNNN-pincer
multidentate pyrrolyl ligand, and their reactivities with 2,6-
Me2C6H3NH2 were examined to afford rare-earth-metal
diarylamido complexes. No rare-earth-metal imido complexes
were obtained even under the condition of additional DMAP,
although there still were uncoordinated nitrogens in the ligand
of rare-earth-metal complexes. Further, the NNNNN-pincer
multidentate pyrrolyl rare-earth-metal dialkyl complexes
exhibited high catalytic activities toward the addition of
amines to carbodiimides or isothiocyanate for synthesis of the
substituted guanidines and thioureas in quantitative yields.
General Synthesis of Complexes 3a−f. Under an argon
atmosphere, an oven-dried 50.0 mL Schlenk flask equipped with a
magnetic stir bar was charged with compound 1 (0.29 g, 1.00 mmol),
RE(CH2SiMe3)3(THF)2 (1.00 mmol), and THF (20.0 mL) at room
temperature. The reaction mixture was stirred at room temperature
for 12 h, and the solvent was evaporated under reduced pressure. The
residue was extracted with n-hexane (10.0 mL), and the crystals were
obtained by cooling the solution to 0 °C for several days.
Complex 3a. Colorless crystals (0.31 g, 60% yield). Mp: 98−99
°C. IR (KBr pellets, cm−1): ν 2941 (s), 2798 (s), 1455 (s), 1345(m),
1287 (w), 1110(m), 1011 (s), 813(s). 1H NMR (500 MHz, C6D6): δ
6.25 (s, 2H), 3.69 (br, 4H), 3.08−2.51 (m, 16H), 2.17 (s, 6H), 0.22
(s, 18H), 0.20 (s, 4H). 13C NMR (126 MHz, C6D6): δ 137.5, 107.9,
57.9, 53.0, 52.5, 46.2, 41.9, 4.4. Anal. Calcd for C24H50N5ScSi2: C,
56.54; H, 9.89; N, 13.74. Found: C, 56.63; H, 9.88; N, 13.27.
EXPERIMENTAL SECTION
■
General Remarks. 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. Solvents were refluxed and distilled over sodium/
benzophenone under argon prior to use. [(Me3Si)2N]3RE(μ-Cl)Li-
F
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Organometallics XXXX, XXX, XXX−XXX

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Article
Complex 3b. Pale yellow crystals (0.35 g, 63% yield). Mp: 169−
171 °C. IR (KBr pellets, cm−1): ν 2938 (s), 2797 (s), 1452 (s), 1345
C32H48LuN7: C, 54.46; H, 6.86; N, 13.89. Found: C, 54.12; H, 6.62;
N, 13.76.
1
(m), 1279 (w), 1106 (m), 1015 (s), 811(s). H NMR (400 MHz,
X-ray Crystallography. Suitable crystals of complexes 2a−e, 3a−
f, and 4a,b,d,f were each mounted in a sealed capillary. Diffraction was
performed on a Burker SMART CCD area detector diffractometer
using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). An
empirical absorption correction was applied by using the SADABS
program. All structures were solved by direct methods, completed by
subsequent difference Fourier syntheses, and refined anisotropically
for all non-hydrogen atoms by full-matrix least-squares calculations on
F2 using the SHELXTL program package. All hydrogen atoms were
refined using a riding model. See the Supporting Information for
crystallographic parameters and data collection and refinement
information.
General Procedure for the Catalytic Addition of Amine to
Carbodiimide. Under an argon atmosphere, an oven-dried 25.0 mL
Schlenk flask equipped with a magnetic stir bar was charged with
complex 2b (3.20 mg, 0.005 mmol), the aniline (98.0 μL, 1.0 mmol),
and N,N’-dicyclohexylcarbodiimide (206.30 mg, 1.0 mmol) and the
resulting mixture was stirred either under solvent-free conditions or in
toluene (2.0 mL) for 2 h. The reaction mixture was then hydrolyzed
with water (0.5 mL) and extracted with dichloromethane (10.0 mL ×
3), and the extracts were dried over anhydrous MgSO4 and filtered.
After the solvent was removed under reduced pressure, the final
product could be obtained by washing the crude product with 10.0
mL of diethyl ether.
General Procedure for the Catalytic Addition of Amines to
Isothiocyanate. Under an argon atmosphere, an oven-dried 25.0 mL
Schlenk flask equipped with a magnetic stir bar was charged with
complex 2b (3.20 mg, 0.005 mmol), the aniline (98.0 μL, 1.0 mmol),
and 4-methylphenyl isothiocyanate (146.0 μL, 1.0 mmol) and the
resulting mixture was stirred under solvent-free conditions for 2 h.
The reaction mixture was then hydrolyzed with water (0.5 mL) and
extracted with dichloromethane (10.0 mL × 3), and the extracts were
dried over anhydrous MgSO4 and filtered. The solvent was removed
under reduced pressure, and the final product was obtained.
C6D6): δ 6.28 (s, 2H), 3.76 (s, 4H), 3.24 (s, 4H), 2.63−2.26 (m, 8H),
2.09 (s, 6H), 1.82 (s, 4H), 0.26 (s, 18H), −0.64 (d, J = 2.8 Hz, 4H).
13C NMR (101 MHz, C6D6): δ 134.1, 104.3, 56.4, 50.9, 50.3, 45.6,
32.1 (JY−C = 47.5 Hz), 5.2. Anal. Calcd for C24H50N5Si2Y: C, 52.05;
H, 9.10; N, 12.65. Found: C, 52.06; H, 9.02; N, 12.38.
Complex 3c. Pale yellow crystals (0.41 g, 66% yield). Mp: 177−
179 °C. IR (KBr pellets, cm−1): ν 2937(s), 2800(s), 1459(s),
1345(m), 1286(w), 1160 (m),1009(s), 921(s), 814(s). Anal. Calcd
for C24H50DyN5Si2: C, 45.95; H, 8.03; N, 11.16. Found: C, 45.59; H,
8.10; N, 11.16.
Complex 3d. Pink crystals (0.38 g, 60% yield). Mp: 172−174 °C.
IR (KBr pellets, cm−1): ν 2945(s), 2807(s), 1455(s), 1345(m),
1260(w), 1150 (m), 1015(s), 808(s). Anal. Calcd for C24H50ErN5Si2:
C, 45.60; H, 7.97; N, 11.08. Found: C, 45.71; H, 7.58; N, 10.92.
Complex 3e. Yellow crystals (0.36 g, 56% yield). Mp: 165−167 °C.
IR (KBr pellets, cm−1): ν 2954(s), 2786(s), 1588(s), 1449(m),
1339(w), 1260(m), 921(s), 792(s). Anal. Calcd for C24H50N5Si2Yb:
C, 45.19; H, 7.90; N, 10.98. Found: C, 44.88; H, 8.18; N, 10.81.
Complex 3f. Colorless crystals (0.45 g, 70% yield). Mp: 102−104
°C. IR (KBr pellets, cm−1): ν 2937(s), 2797(s), 1455(s), 1345(m),
1
1285(w), 1102(m), 1010(s), 810(s). H NMR (500 MHz, C6D6): δ
6.28 (s, 2H), 3.79 (s, 4H), 3.32−2.26 (m, 16H), 2.09 (s, 6H), 0.24 (s,
18H), −0.85 (s, 4H). 13C NMR (126 MHz, C6D6): δ 134.7, 104.6,
55.8, 50.8, 50.1, 45.5, 38.1, 5.4. Anal. Calcd for C24H50N5Si2Lu: C,
45.05; H, 7.88; N, 10.95. Found: C, 45.15; H, 7.77; N, 10.94.
General Synthesis of Complexes 4a,b,d,f. Under an argon
atmosphere, an oven-dried 50.0 mL Schlenk flask equipped with a
magnetic stir bar was charged with complex 3a (0.25 g, 0.50 mmol),
3b (0.28 g, 0.50 mmol), 3d (0.32g, 0.50 mmol), or 3f (0.32 g, 0.50
mmol) in toluene (2.0 mL) was added dropwise into a solution of 2,6-
Me2C6H4NH2 (123.0 μL, 1.00 mmol) in toluene (3.0 mL) at room
temperature. The reaction mixture was stirred at room temperature
for 6 h, and solvent was evaporated under reduced pressure. The
residue was extracted with THF/n-hexane (1/1), and the crystals
were obtained by cooling the solution to 0 °C for several days. The
yields of complexes 4a,b,d,f were based on the corresponding
complexes 3 with 2 equiv of 2,6-Me2C6H4NH2.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00606.
■
sı
Complex 4a. Colorless crystals (0.21 g, 76% yield). Mp: 123−125
°C. IR (KBr pellets, cm−1): ν 3385(s), 2936(s), 2796(s), 1591(s),
1
Full experimental details, characterization data for
compounds 7a−v, and crystallographic data and refine-
ments for complexes 2a−e, 3a−f, and 4a,b,d,f (PDF)
1455(s), 1284(w), 1146(m), 1010(s), 808(s). H NMR (500 MHz,
C6D6): δ 7.14−7.09 (m, 4H), 6.29 (t, J = 7.2, 2H), 6.31 (s, 2H), 4.41
(s, 2H), 3.63 (s, 4H), 3.05 (s, 4H), 2.11−2.39 (m, 24 H), 1.83 (s,
6H). 13C NMR (126 MHz, C6D6): δ 153.9, 135.4, 128.9, 122.0,
115.5, 104.3, 57.5, 55.3, 52.3, 45.1, 20.0. Anal. Calcd for C32H48ScN7·
C4H8O: C, 66.74; H, 8.71; N, 15.13. Found: C, 66.83; H, 8.37; N,
15.75.
Accession Codes
CCDC 2025788−2025802 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Complex 4b. Colorless crystals (0.26 g, 87% yield). Mp: 141−143
°C. IR (KBr pellets, cm−1): ν 3386(s), 2937(s), 2797(s), 1591(s),
1
1456(s), 1269(w), 1125(m), 1011(s), 806(s). H NMR (500 MHz,
C6D6): δ 7.13-7.10 (m, 4H), 6.68 (t, J = 7.0 Hz, 2H), 6.31 (s, 2H),
4.41 (s, 2H), 3.63 (s, 4H), 3.04 (s, 4H), 2.38−1.88 (m, 21H), 1.88 (s,
3H), 1.83 (s, 6H). 13C NMR (101 MHz, C6D6): δ 143.3, 128.8,
128.6, 121.4, 118.2, 107.6, 56.0, 55.6, 53.5, 46.2, 17.6. Anal. Calcd for
C32H48YN7: C, 62.02; H, 7.81; N, 15.82. Found: C, 61.63; H, 7.84; N,
15.78.
Complex 4d. Pink crystals (0.30 g, 88% yield). Mp: 121−123 °C.
IR (KBr pellets, cm−1): ν 3386(s), 2937(s), 2796(s), 1590(s),
1456(s), 1278(w), 1125(m), 1011(s), 805(s). Anal. Calcd for
C32H48ErN7: C, 55.06; H, 6.93; N, 14.05. Found: C, 54.83; H,
7.16; N, 13.63.
AUTHOR INFORMATION
Corresponding Authors
■
Shuangliu Zhou − Laboratory of Functionalized Molecular
Solids, Ministry of Education, Anhui Laboratory of Molecule-
Based Materials, College of Chemistry and Materials Science,
Anhui Normal University, Wuhu, Anhui 241000, People’s
Republic of China; orcid.org/0000-0002-0103-294X;
Email: slzhou@ahnu.edu.cn
Complex 4f. Colorless crystals (0.28 g, 81% yield). Mp: 123−125
Shaowu Wang − Laboratory of Functionalized Molecular
Solids, Ministry of Education, Anhui Laboratory of Molecule-
Based Materials, College of Chemistry and Materials Science,
Anhui Normal University, Wuhu, Anhui 241000, People’s
Republic of China; Anhui Laboratory of Functional
Complexes for Materials Chemistry and Application, College
°C. IR (KBr pellets, cm−1): ν 3385(s), 2937(s), 2796(s), 1591(s),
1
1456(s), 1278(w), 1126(m), 1010(s), 806(s). H NMR (500 MHz,
C6D6): δ 7.14−7.11 (m, 4H), 6.69 (t, J = 7.5 Hz, 2H), 6.34 (s, 2H),
4.01 (s, 2H), 3.66 (s, 4H), 3.06 (s, 4H), 2.55−1.90 (m, br, 24H), 1.83
(s, 6H). 13C NMR (126 MHz, C6D6): δ 155.9, 135.3, 128.3, 121.5,
114.4, 104.9, 55.6, 53.5, 52.0, 46.2, 44.9, 20.1, 17.7. Anal. Calcd for
G
https://dx.doi.org/10.1021/acs.organomet.0c00606
Organometallics XXXX, XXX, XXX−XXX

Organometallics
of Chemical and Environmental Engineering, Anhui
pubs.acs.org/Organometallics
Article
ACKNOWLEDGMENTS
■
Polytechnic University, Wuhu, Anhui 241000, People’s
Republic of China; orcid.org/0000-0003-1083-1468;
Email: swwang@ahnu.edu.cn
This work was supported by the National Natural Science
Foundation of China (21672004, 21702004, 21861162009,
22031001, 21871004).
ABBREVIATIONS
Cy, cyclohexane
Authors
■
Weiming Sheng − Laboratory of Functionalized Molecular
Solids, Ministry of Education, Anhui Laboratory of Molecule-
Based Materials, College of Chemistry and Materials Science,
Anhui Normal University, Wuhu, Anhui 241000, People’s
Republic of China
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Xiaolong Xu − Laboratory of Functionalized Molecular Solids,
Ministry of Education, Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and Materials Science, Anhui
Normal University, Wuhu, Anhui 241000, People’s Republic
of China
Xiuli Zhang − Laboratory of Functionalized Molecular Solids,
Ministry of Education, Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and Materials Science, Anhui
Normal University, Wuhu, Anhui 241000, People’s Republic
of China
Zeming Huang − Laboratory of Functionalized Molecular
Solids, Ministry of Education, Anhui Laboratory of Molecule-
Based Materials, College of Chemistry and Materials Science,
Anhui Normal University, Wuhu, Anhui 241000, People’s
Republic of China
Jun Du − Laboratory of Functionalized Molecular Solids,
Ministry of Education, Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and Materials Science, Anhui
Normal University, Wuhu, Anhui 241000, People’s Republic
of China
Lijun Zhang − Laboratory of Functionalized Molecular Solids,
Ministry of Education, Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and Materials Science, Anhui
Normal University, Wuhu, Anhui 241000, People’s Republic
of China
Yun Wei − Laboratory of Functionalized Molecular Solids,
Ministry of Education, Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and Materials Science, Anhui
Normal University, Wuhu, Anhui 241000, People’s Republic
of China
Xiancui Zhu − Laboratory of Functionalized Molecular Solids,
Ministry of Education, Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and Materials Science, Anhui
Normal University, Wuhu, Anhui 241000, People’s Republic
of China; orcid.org/0000-0001-7354-3573
Peng Cui − Laboratory of Functionalized Molecular Solids,
Ministry of Education, Anhui Laboratory of Molecule-Based
Materials, College of Chemistry and Materials Science, Anhui
Normal University, Wuhu, Anhui 241000, People’s Republic
of China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00606
Author Contributions
§W.S. and X.X. contributed equally.
(4) (a) Arevalo, R.; Chirik, P. J. Enabling Two-Electron Pathways
with Iron and Cobalt: From Ligand Design to Catalytic Applications.
J. Am. Chem. Soc. 2019, 141, 9106−9123. (b) Rummelt, S. M.;
Darmon, J. M.; Yu, R. P.; Viereck, P.; Pabst, T. P.; Turner, Z. R.;
Notes
The authors declare no competing financial interest.
H
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