Phenylene-bridged β-Ketoiminate Dilanthanide Aryloxides: Synthesis, Structure, and Catalytic Activity for Addition of Amines to Carbodiimides

Article abstract of DOI:10.1002/zaac.201500047

The synthesis and reactivity of a series of bimetallic lanthanide aryloxides stabilized by a p-phenylene-bridged bis(β-ketoiminate) ligand is presented. The reaction of 1,4-diaminobenzene with acetylacetone in a 1:2.5 molar ratio in absolute ethanol gave

Full text of DOI:10.1002/zaac.201500047

Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
DOI: 10.1002/zaac.201500047
Phenylene-bridged β-Ketoiminate Dilanthanide Aryloxides: Synthesis,
Structure, and Catalytic Activity for Addition of Amines to Carbodiimides
Yubiao Hong,[a] Yu Zheng,[a] Mingqiang Xue,*[a] Yingming Yao,[a] Yong Zhang,[a] and
Qi Shen*[a]
Keywords: Phenylene-bridged β-ketoiminate; Dilanthanide aryloxide; Catalytic activity; Guanidine
Abstract. The synthesis and reactivity of a series of bimetallic lantha-
nide aryloxides stabilized by a p-phenylene-bridged bis(β-ketoiminate)
ligand is presented. The reaction of 1,4-diaminobenzene with acetyl-
high isolated yields. Compound 1 and complexes 2–6 were fully char-
acterized, including X-ray crystal structure analyses for complexes 2,
3, 5, and 6. Complexes 2–6 can be used as efficient pre-catalysts for
acetone in a 1:2.5 molar ratio in absolute ethanol gave the compound catalytic addition of amines to carbodiimides, and the ionic radii of
1,4-bis(4-imino-2-pentanone)benzene (1) (LH2) in high yield. Com- the central metal atoms have significant effect on the
pound reacted with (ArO)3Ln(THF)2 (ArO 2,6-tBu2-4- catalytic activity with the increasing sequence of La (6) Ͻ Nd (5) ≈
a
1
=
MeC6H2O, THF = tetrahydrofuran) in a 1:2 molar ratio in THF, after
workup, to give the corresponding dilanthanide aryloxides
L[Ln(OAr)2(THF)]2 [Ln = Yb (2), Y (3), Sm (4), Nd (5), La (6)] in
Sm (4) Ͻ Y (3) ≈ Yb (2). The catalytic addition reaction with 2 showed
a good scope of substrates including primary and secondary amines.
a bulky substituent on one side but left the other side open,
thus resulting in ligand hemilability and potentially interesting
catalytic behavior.[6a,9] However, the application of ketoimin-
ate anions as ligands in organolanthanide chemistry has been
much less explored in comparison with their counterparts β-
diketiminate anions.[10] The first monomeric and solvent-free
homoleptic ytterbium tris(β-ketoiminate) complex was pre-
pared by Rees.[10i] Next, a series of (CH2)3-bridged lanthanide
β-ketoiminate complexes were intensively investigated by the
Belot group, including amido and aryloxo complexes,[10d,10e,10h]
and a drastical impact of lanthanide metal radii on the compo-
sition and molecular structure of the isolated complexes has
been pointed out.[10e,10h] In 2002, Edleman et al. developed
monomeric lanthanide complexes supported by β-ketoiminate
ligand. They demonstrated that these complexes could be used
as excellent MOCVD precursors.[10f] Our group presented the
synthesis and reactivity of lanthanide complexes supported by
N-aryloxo-functionalized β-ketoiminate ligand.[10a] Obviously,
further development of novel β-ketoiminate ligands and ex-
ploring their application in organolanthanide chemistry is cer-
tainly required.
Recently, a great attention has been paid to the construction
of C–N bonds, which is of great importance in organic synthe-
sis, by organometallic complexes as the catalysts or pre-cata-
lysts.[11] The catalytic formation of guanidine by addition of
amine and carbodiimide is especially an active arena as this
offers a straightforward and atom-economical route for the
preparation of multi-substituted guanidines, which play a vital
role in many biological and pharmaceutical compounds.[12]
Various organolanthanide complexes including alkyl and
amide derivatives were proven to be excellent catalysts for this
transformation.[13] We have recently addressed that homoleptic
Introduction
β-Diketiminate monoanions, as one of the significantly im-
portant non-cyclopentadienyl ancillary ligands, have received
increasing attention in organometallic chemistry of lanthanide
metals.[1] Various lanthanide complexes (alkyls, amides, alk-
oxides etc.) stabilized by β-diketiminate ligands have been
synthesized and structurally characterized.[2,3] Moreover, these
derivatives have been found to be efficient catalysts or pre-
catalysts in organic and polymerization reactions,[4] and also
exhibit versatile reactivity, such as activation of small
molecules, reduction by alkali metal, oxidation, deprotonation,
etc.[5] β-Ketoiminate anions can be viewed as the counterparts
of β-diketiminate anions. These monoanions, as ancillary li-
gands in organometallic chemistry, also own similar attractive
features: they can be facilely prepared with readily and inex-
pensive starting materials;[6] the steric and electric effects can
be easily modulated by adjusting the substituent on the nitro-
gen atom;[7] they display strong coordination ability to the cen-
tral metal as bidentate monoanionic ligands, which have been
viewed as excellent heteroatom analogues of pentadienyl li-
gands.[8] Besides, their binding to the metal center can lead to
a six-membered ring and cause the metal atom surrounded by
* Prof. Dr. M. Xue
E-Mail: xuemingqiang@suda.edu.cn
* Prof. Dr. Q. Shen
E-Mail: qshen@suda.edu.cn
[a] College of Chemistry
Chemical Engineering and Materials Science
Soochow University
Suzhou 215123, P. R. China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201500047 or from the au-
thor.
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lanthanide trisaryloxides could also serve as excellent pre-cata- tion with 1 was tried in order to explore an facile route for the
lysts.[14] The lanthanide aryloxides supported by a bridged- synthesis of lanthanide aryloxides stabilized by a p-phenylene-
amidinate[15] or by a β-diketiminate ligand[4a] are also efficient bridged bis(β-ketoiminate) ligand. The reaction of
pre-catalysts. Lanthanide aryloxides are robust and easier to be (ArO)3Yb(THF)2 [ArO = 2,6-tBu2-4-MeC6H2O] with 1 was
treated than lanthanide alkyl and amide complexes. Thus, fur- first conducted at a molar ratio of 2 to 1 in THF. The reaction
ther development of novel lanthanide aryloxide catalysts is of went smoothly at room temperature. Stirring 24 h afforded a
interest. To continue our study and to explore the application clear yellow solution, from which a bimetallic ytterbium
of β-ketoiminate ligands in lanthanide chemistry, we are inter- aryloxide bearing one L ligand L[Yb(OAr)2(THF)]2 (2) was
ested in development of novel β-ketoiminate ligands and lan- isolated in 76% yield. Further study demonstrated that this
thanide aryloxides with them, and exploit their potential cata- procedure is suitable for the synthesis of the lanthanide metal
lytic behavior. In this work, a novel phenylene-bridged bis(β- complexes including the early metals of La (6), Nd (5), middle
ketoiminate) ligand, 1,4-bis(4-imino-2-pentanone)benzene (1) metal of Sm (4), and the metal Y (3). All these complexes
(LH2) was developed and a series of bimetallic lanthanide were facilely isolated as crystals in high yields (Scheme 2).
aryloxides L[Ln(OAr)2(THF)]2 [Ln = Yb (2), Y (3), Sm (4), However, an attempt for the synthesis of a bimetallic lantha-
Nd (5), La (6)] were synthesized and fully characterized. The nide monoaryloxide bearing two L ligands by the reaction of
catalytic activity of these aryloxides as pre-catalyst towards [Yb(OAr)3)THF)2] with equiv. of L was unsuccessful. The re-
amines and carbodiimides addition giving guanidines and the action afforded a gel, which is difficult to be treated further.
possible reaction pathway are also addressed.
Complexes 2–6 are sensitive to air and moisture. They are
moderately soluble in THF and toluene, but poorly soluble in
hexane.
Results and Discussion
Synthesis and Characterization of Compound 1
The reaction of a mixture of 1,4-diaminobenzene with
2.5 equiv. of 2,4-pentanedione in absolute anhydrous ethanol
in the presence of catalytic amount of p-toluenesulfonic acid
under reflux condition afforded the novel p-phenylene-
bridged bis(β-ketoiminate) ligand LH2 (1) [L
=
Scheme 2. Synthesis of complexes 2–6.
p-OC(Me)CHC(Me)N-C6H4-p-NC(Me)CHC(Me)O] as a raw
product. After recrystallization from ethanol, pure 1 was ob-
tained in a satisfactory yield (85%) (Scheme 1). The merit of
this method is that the available and inexpensive 1,4-diami-
nobenzene was used as a starting material. Compound 1 was
comprehensively characterized by NMR spectroscopy, IR
All these novel aryloxide complexes were fully charac-
terized by elemental analysis and IR spectroscopy. The ele-
mental analyses of complexes 2–6 are consistent with their
formulae. Their IR spectra exhibit strong absorptions near
1622, 1609, 1605, 1566, 1559 cm–1, respectively, which are
consistent with the characteristic of partial C=N bond of the
β-ketoiminate ligands.[6,7a,10a] The 1H NMR spectra of the dia-
magnetic complexes 3 and 6 in C6D6 show the expected sets
of signals assigned to the L, ArO, and the coordinated THF
molecule.[14]
1
spectroscopy as well as elemental analysis. H NMR spectrum
of 1 reveals the methine proton of the ketoiminate backbone
at δ = 5.20 ppm, which is consistent with analogous bridged
bis(β-ketimine) ligand linked by 4,4Ј-methylene-bis(2–6-diiso-
propylaniline),[6b] and diaminocyclohexane.[6a,6c]
To provide comprehensively structural information com-
plexes 2, 3, 5, and 6 were further confirmed by a X-ray single-
crystal structure analysis (crystal structure of complex 4 was
not determined for its deterioration in the crystal quality). Suit-
able crystals were obtained by cooling a toluene solution at
0 °C for 2, 4, and 5, and by cooling a THF solution at 0 °C
for 3 and 6. Each complex has several free THF molecules in
its unit cell (5: toluene molecule in its unit cell), and these free
solvent molecules are entirely lost under vacuum. Therefore,
the elemental analysis data for each complex is well consistent
with the formula without the free solvent molecules.
Scheme 1. Synthesis of compound 1.
Complexes 2, 3, 5, and 6 are isostructural. Their molecular
structures are shown in Figure 1 and the selected bond lengths
and angles are listed in Table 1. Each complex is a THF-sol-
Synthesis and Characterization of Complexes 2–6
Ligand exchange is an effective strategy for the synthesis of vated monomer. They have a centrosymmetric structure with
various lanthanide complexes. Thus, the lanthanide triarylox- the symmetric center on phenyl ring of the bridge. Each
ide complex was used here as a starting material and its reac- molecule contains two metals and each metal atom coordinated
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Table 1. Selected bond lengths /Å and angles /° for complexes 2, 3, 5, and 6.
2
3
5
6
Ln(1)–O(1)
Ln(1)–O(2)
Ln(1)–O(3)
Ln(1)–O(4)
Ln(1)–N(1)
O(1)–C(2)
C(2)–C(3)
C(3)–C(4)
2.098(3)
2.075(3)
2.080(3)
2.340(3)
2.348(3)
1.303(5)
1.363(6)
1.420(6)
1.325(5)
108.01(12)
147.97(12)
103.20(12)
161.34(12)
2.137(3)
2.113(3)
2.125(3)
2.374(3)
2.396(3)
1.297(5)
1.358(6)
1.430(6)
1.308(5)
103.54(11)
147.03(10)
108.81(11)
159.49(11)
2.213(10)
2.190(9)
2.191(9)
2.520(11)
2.489(10)
1.286(17)
1.436(19)
1.428(18)
1.314(16)
106.8(4)
147.5(3)
105.0(4)
159.2(3)
2.291(2)
2.242(2)
2.253(2)
2.585(3)
2.561(3)
1.294(5)
1.362(5)
1.430(5)
1.314(4)
107.86(9)
142.38(8)
108.39(9)
151.59(10)
N(1)–C(4)
O(1)–Ln(1)–O(2)
O(2)–Ln(1)–O(3)
O(3)–Ln(1)–O(1)
N(1)–Ln(1)–O(4)
to one nitrogen atom and one oxygen atom from the L ligand,
The bond lengths of central metal atoms to the L ligand
two oxygen atoms from the two aryloxido groups and one oxy- including the bonds of Ln–O (alkoxo) and Ln–N {[2.098(3)
gen atom from the THF molecule. The coordination arrange- and 2.348(3) Å] (2), [2.137(3) and 2.396(3) Å] (3), [2.213(10)
ment surrounding each metal atom can be described as a dis- and 2.489(10) Å] (5), and [2.291(2) and 2.561(3) Å] (6),
torted trigonal bipyramid. The two oxygen atom of aryloxido, respectively} can be compared to those found in the
and the oxygen atom of the β-ketoiminate ligand form the ytterbium bidentate β-ketoiminate complex LЈ3Yb [LЈ =
equatorial vertices. The sum of three bond angles of tBuCOCHC(tBu)N(nPr)] (Yb–O
= 2.15, 2.15, 2.16 Å;
359.18(12), 359.38(11), 359.3(4), 358.63(9)° for 2, 3, 5, and Yb–N
=
2.38, 2.44, 2.44 Å),[10i] and the ytterbium
6, respectively, slightly deviates from ideal 360°. The nitrogen tridentate β-ketoiminate complex [LЈЈLnCl(DME)]2 (LЈЈ =
atom N(1) of the β-ketoiminate ligand and the oxygen atom [MeCOCHC(Me)NC6H4O(4-Me)]2–) [Yb–O = 2.140(4) Å,
O(4) of the THF occupy the apical positions with the angle of Yb–N = 2.399(4) Å],[10a] when the influences of the coordina-
N(1)–Ln–O(4) of 161.34(12)° (2), 159.49(11)° (3), 159.2(3)° tion number and the ion radium of the central metal atoms
(5), and 151.59(10)° (6), respectively, which significantly devi- were considered, revealing a similar π electron delocalization
ates from the ideal 180°. The two aryloxido groups located at present within (OCCCN) backbone in complexes 2, 3, 5, and
the opposite sites. This may be attributed to the steric hin- 6.
drance. The molecular structures of the present complexes are
The two Ln(1)–O(aryloxo) bond lengths are basically equiv-
quite similar to that of (CH2)3-bridged tetradentate bis(β-keto- alent [2.075(3) and 2.080(3) Å for 2; 2.113(3) and 2.125(3) Å
iminate) lanthanide complexes reported previously.[10d,10e]
for 3; 2.190(9) and 2.191(9) Å for 5; 2.242(2) and 2.253(2) Å
for 6], which reflect the coordination mode of metal to each
of the oxygen atom of aryloxido is same. All the bond param-
eters of complexes 2, 3, 5, and 6 including the bonds of metal
to L and to aryloxo groups are well comparable with each
other, when the differences in the ion radii among these metals
are considered.
Catalytic Activity of 2–6 for Additions of Amines to
Carbodiimides
Only one example regarding the catalytic behavior of lantha-
nide β-ketoiminate complex for polar monomer polymeriza-
tion has been reported to date.[10a] Thus, the catalytic activity
of complexes 2–6 for catalytic addition of amines to carbodi-
imides to guanidines was evaluated. The reaction of PhNH2
with N,NЈ-diisopropylcarbodiimide (iPrNCNiPr), as the model
reaction, was performed at 60 °C under solvent free condition
for 0.25 h in the presence and the absence of complex 2,
respectively. The results are listed in Table 2. It’s clear that the
reaction did not take place without the presence of complex 2
(Table 2, entry 1). In contrast, the reaction occurred immedi-
ately to yield the corresponding guanidine 7 in almost a quanti-
tative yield when 0.5 mol% of complex 2 was added (Table 2,
entry 2). Complexes 3–6 all can serve as catalyst precursors
Figure 1. ORTEP diagram of L[Ln(OAr)2(THF)]2 [Ln = Yb (2),
Y (3), Nd (5), La (6)] showing the atom-numbering scheme. Thermal
ellipsoids are drawn at the 20% probability level. Hydrogen atoms are
omitted for clarity.
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for this catalytic reaction to afford product 7. However, the
To see the generality of the present pre-catalysts for catalytic
yield of 7 varies greatly. For example, the reaction with com-
plexes 2 and 3 afforded 7 in 98% and 94% isolated yield,
respectively, whereas the yields were 51%, 49% and 20%,
respectively, when complexes 4, 5, and 6 were used (Table 2,
entries 2–6). The active sequence of La (6) Ͻ Nd (5) ≈ Sm
(4) Ͻ Y (3) ≈ Yb (2) found herein is in accordance with the
decrease of radii of the central metals. Such a dependence of
the activity on the metal size has also been found in the re-
ported systems with lanthanide aryloxide.[15] Complex 2 is a
highly active pre-catalyst and the reaction can still afford 7 in
33% yield after a short time period (0.25 h) even when the
amount of complex 2 decreased to 0.1 mol% (Table 2, entry
7).
syntheses of substituted guanidines, the catalytic addition of
various primary and secondary amines to carbodiimides was
then examined using complex 2. Representative results are
summarized in Table 3. As shown in Table 3, complex 2 is a
very robust and efficient pre-catalyst. The system is compati-
ble with a wide range of substituents at the phenyl ring of
the aromatic amines, regardless of the electron-withdrawing or
electron-donating groups. Primary and secondary amines both
could be used for this reaction. However, the reaction with a
bulky amine, 2,6-diisopropylaniline, is less efficient, affording
the guanidine in only a 64% yield, even prolong reaction
period to 24 h (Table 3, entry 14). This might be because of
the larger steric hindrance of the substrate. The similar situa-
tion was also documented in the published work.[4a,15,16] The
reaction with secondly aliphatic amines, such as pyrrolidine
and piperidine, also requires prolong the reaction time from
0.5 h to 24 h, to deliver the relevant guanidines (21 and 22) in
good yields (Table 3, entries 15 and 16). This may be attrib-
uted to their less active, compared to the primary aromatic
amines. Thus, the catalytic behavior of the present lanthanide
aryloxide complexes can be well comparable with the lantha-
nide aryloxide complexes including triaryloxides[14] and the
aryloxides stabilized by β-diketiminate[4a] and bridged amidin-
ate ligands reported previously.[15]
Table 2. Addition of PhNH2 to iPrNCNiPr by complexes 2–6.a)
b)
Entry
Cat.
Temp. /°C
Time /h
Yield /%
1
2
3
4
5
6
–
2
3
4
5
6
2
60
60
60
60
60
60
60
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0
To better understand the reaction pathway of the present
catalytic cycle, a NMR tube reaction with stoichiometric
amount of 3 and PhNH2 was measured. The slowly increasing
signal at δ = 4.79 ppm during the whole detection period was
observed. The new signal may be assigned to the OH proton
of the released 2,6-tBu2-4-MeC6H2OH. The appearance of free
2,6-tBu2-4-MeC6H2OH indicated that the protonation reaction
98
94
51
49
20
33
c)
7
a) Aniline (1.6 mmol), N,NЈ-diisopropylcarbodiimide (1.6 mmol).
b) Isolated yields. c) 0.1 mol% catalyst loading.
Table 3. Catalytic addition of amines to carbodiimides.a)
b)
Entry
R
R1R2NH
Catalyst loading /mol%
Time /h
Product
Yield /%
1
2
3
4
5
6
7
8
iPr
Cy
iPr
Cy
iPr
Cy
iPr
Cy
iPr
iPr
iPr
iPr
iPr
iPr
iPr
iPr
Ph-NH2
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.0
1.0
0.5
0.5
0.5
2
7
8
9
Ͼ99
96
Ͼ99
99
Ͼ99
90
93
93
95
Ͼ99
Ͼ99
98
p-F-Ph-NH2
o-Cl-Ph-NH2
o-Me-Ph-NH2
10
11
12
13
14
15
16
17
18
19
20
21
22
9
p-Me-Ph-NH2
p-Cl-Ph-NH2
p-Br-Ph-NH2
p-MeO-Ph-NH2
1-naPh-NH2
2,6-iPr2-Ph-NH2
cyclo-C4H8NH
cyclo-C5H10NH
10
11
12
13
14
15
16
24
24
24
24
94
64
83
95
a) The reaction was performed by treating 1 equiv. of amines with 1 equiv. of carbodiimides at 60 °C. b) Isolated yields.
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dium chips in the glovebox for NMR reactions. Carbodiimides and
of complex 3 with aniline occurred to form the intermediate
amines were purchased from TCI and were used as supplied. NaOAr
was prepared from the reaction of ArOH with Na in THF.
(ArO)3Ln(THF)2 was prepared according to a literature procedure.[17]
1H NMR and 13C NMR spectra were run with a Bruker DPX-300 or
a Unity Inova-400 spectrometer. Lanthanide analyses were performed
by EDTA titration with a xylenol orange indicator and a hexamine
buffer. Elemental analyses were performed by direct combustion with
a Carlo-Erba EA 1110 instrument. The Infrared spectra were recorded
with a Magna-IR 550 spectrometer as KBr pellets. The uncorrected
amido species. Also, the new signals at δ = 0.89 and 3.48 ppm,
which may be assigned to the corresponding Y-guanidinate
species formed, were detected, when an equiv. of iPrNCNiPr
was added. The formation of the Y-guanidinate species indi-
cates the nucleophilic addition of an Ln–N bond newly formed
to a carbodiimide compound then took place. The similar
transformations have been addressed in our recent work.[4a]
According to the NMR experimental data the possible catalytic
pathway is depicted in Scheme 3. At first, amination of com- melting points of crystalline samples in sealed capillaries (in argon)
are reported as ranges.
plex 3 by aniline afforded the intermediate A. Then, the nucle-
ophilic addition of A to a carbodiimide yielded the active spe-
cies B. The protonolysis of B by aniline gave the product guan-
idine and release A to complete the catalytic cycle. An attempt
to isolate the real active species A and B was unsuccessful.
Synthesis of the Proligand LH2 (1): To a solution of 2,4-pentane-
dione (45.0 mL, 0.44 mol) in absolute anhydrous ethanol (250 mL)
was added 1,4-diaminobenzene (19.5 g, 0.18 mol) and a catalytic
amount of p-toluenesulfonic acid at room temperature. After the reac-
tion mixture was stirred in oil bath and refluxed for 24 h under ambient
condition, a red-brown liquid and a pale yellow solid were formed.
This solid was separated by filtered, recrystallized from anhydrous eth-
anol and dried under vacuum. (41.6 g, 85%); m.p. 180.3–180.8 °C.
C16H20N2O2 (272.34): calcd. C 70.56; H 7.40; N 10.29%; found: C
1
70.31; H 7.41; N 10.42%. H NMR (400 MHz, CDCl3): δ = 12.47 (s,
2 H, NH), 7.08 (s, 4 H, ArH), 5.20 [s, 2 H, CH=C(CH3)N], 2.11 (s, 6
H, CH3), 2.01 (s, 6 H, CH3) ppm. 13C NMR (400 MHz, CDCl3): δ =
196.4 (C=O), 160.0 (C–N), 136.2 (Caryl), 125.2 (CHaryl), 98.0 [C(N)–
CH–C(N)], 29.3(CH3), 19.9(CH3) ppm. IR (KBr): ν˜ = 3643 (s), 3450
(s), 2956 (s), 2871 (m), 1613 (s), 1567 (vs), 1497 (s), 1436 (vs), 1358
(s), 1235 (s), 1158 (s), 1119(m), 1027 (m), 864 (m), 772 (m), 741 (m),
625 (m), 571 (m) cm–1.
L[Yb(OAr)2(THF)]2 (2): A THF (20 mL) solution of LH2 (0.60 g,
2.20 mmol) was added slowly to a (ArO)3Yb(THF)2 (4.40 mmol) in
THF (20 mL) at room temperature. After stirring for 24 h, the trans-
parent orange yellow solution was evaporated in vacuo, and the solid
residue extracted with toluene. After the undissolved portion was re-
moved by centrifugation, the yellow solution was concentrated.
Crystallization at 0 °C for a week afforded 2 as orange yellow crystals
(2.98 g, 76%); m.p. 125 °C (decomp.). C84H126N2O8Yb2 (1637.95):
calcd. C 61.60; H 7.75; N 1.71; Yb 21.13%; found C 61.43; H 7.88;
N 1.65; Yb 21.05%. IR (KBr): ν˜ = 3639 (m), 3432 (m), 2957 (s),
1609 (vs), 1518 (s), 1435 (vs), 1362 (s), 1310 (s), 1273 (vs), 1229 (s),
1157 (s), 1119 (m), 1026 (s), 921 (w), 861 (m), 770 (m), 624 (m), 503
(m) cm–1.
Scheme 3. Possible pathway of catalytic addition of amines to carbodi-
imides.
Conclusions
In this paper, we have developed a phenylene-bridged
bis(β-ketoiminate) proligand.
A
series of bridged
bis(β-ketoiminate) dilanthanide aryloxides stabilized by this
ligand was synthesized via ligand exchange reaction using
Ln(OAr)3(THF)2 as a synthon. Their structural features were
determined by X-ray diffraction experiments. These novel β-
ketoiminate lanthanide aryloxides exhibit good activity for
the catalytic addition of amines to N,NЈ-dialkylcarbodiimide
to substituted guanidines with the active sequence of
L[Y(OAr)2(THF)]2 (3): The synthesis of complex 3 was carried out
in the same way as that described for complex 2, but (ArO)3Y(THF)2
(4.22 mmol) was used instead of (ArO)3Yb(THF)2. Colorless crystals
were obtained from THF at 0 °C (2.79 g, 70%); m.p. 143 °C (de-
comp.). C84H126N2O8Y2 (1469.75): calcd. C 68.65; H 8.64; N 1.91; Y
12.10%; found: C 68.23; H 8.75; N 1.93; Y 12.02%. 1H NMR
(400MHz, C6D6): δ = 7.22 (s, 8 H, ArH), 7.12 (s, 4 H, ArH), 5.16 [s,
La (6) Ͻ Nd (5) ≈ Sm (4) Ͻ Y (3) ≈ Yb (2). Further study 2 H, CH=C(CH3)N], 2.39 (s, 12 H, ArCH3), 1.89 (s, 6 H, CH3), 1.65
(s, 6 H, CH3), 1.51 (s, 72 H, tBu) ppm. 13C NMR (400MHz, C6D6):
on design and synthesis of new bis(β-ketoiminate) lanthanide
δ = 177.9, 160.7, 143.8, 138.4, 126.2, 125.9, 124.2, 103.5, 67.7, 35.2,
31.6, 30.4, 26.2, 23.6, 23.1, 21.6, 14.4. IR (KBr): ν˜ = 3640 (m), 3439
derivatives are in process.
(s), 2960 (m), 1622 (vs), 1564 (s), 1505(m) 1450 (m), 1391 (vs), 1381
(vs), 1274 (m), 1224 (m), 1158 (s), 1123 (m), 998 (w), 880 (m), 773
(m), 624 (m), 421 (m) cm–1.
Experimental Section
General Procedures: All manipulations were performed in pure argon
atmosphere with rigorous exclusion of air and moisture using the stan-
dard Schlenk techniques. Solvents of THF, toluene and n-hexane were
L[Sm(OAr)2(THF)]2 (4): The synthesis of complex 4 was carried out
in the same way as that described for complex 1, but
dried and freed of oxygen by refluxing over sodium/benzophenone (ArO)3Sm(THF)2 (4.64 mmol) was used instead of (ArO)3Yb(THF)2.
ketyl and distilled prior to use. [D6]Benzene was dried with fresh so- Pale yellow crystals were obtained from toluene at 0 °C (2.84 g, 65%);
Z. Anorg. Allg. Chem. 2015, 1230–1237
1234
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
m.p. 152 °C (decomp.). C84H126N2O8Sm2 (1592.65): calcd. C 63.35; time, as shown in Table 3. After the reaction was completed, the reac-
H 7.97; N 1.76; Sm 18.88%; found: C 63.55; H 8.05; N 1.67; Sm,
18.89%. IR (KBr): ν˜ = 3621 (m), 3464 (m), 2958 (s), 1611 (s), 1566
(vs), 1470 (s), 1435 (s), 1309 (s), 1271 (s), 1232 (s), 1157 (s), 1119
(s), 1028 (s), 865 (m), 772 (m), 743 (m) cm–1.
tion mixture was hydrolyzed by water, extracted with dichloromethane
(3ϫ10 mL), dried with anhydrous Na2SO4, and filtered. The solvent
was removed under reduced pressure, and the final products were fur-
ther purified by crystallization from n-hexane (0.344 g, 98% yield).
L[Nd(OAr)2(THF)]2 (5): The synthesis of complex 5 was carried X-ray Crystallography: Crystals suitable for X-ray diffraction of
out in the same way as that described for complex 1, but complexes 2, 3, 5, and 6 were sealed, respectively, in a thin-walled
(ArO)3Nd(THF)2 (3.12 mmol) was used instead of (ArO)3Yb(THF)2. glass capillary filled with argon for structural analysis. Diffraction data
Pale green crystals were obtained from toluene at 0 °C (1.89 g, 72%); were collected with a Bruker APEX-II CCD area detector in the ω
m.p. 155 °C (decomp.). C84H126N2O8Nd2 (1580.41): calcd. C 63.84; scan mode using Mo-Kα radiation (λ = 0.71070 Å) for complexes 2
H 8.04; N 1.77; Nd 18.25%; found: C 64.12; H 8.20; N 1.75; Nd
18.32%. IR (KBr): ν˜ = 3643 (m), 3419 (s), 2964 (s), 2917 (m), 2871
(m), 1605 (s), 1566 (s), 1520 (s), 1436 (s), 1389 (s), 1312 (s), 1227
(vs), 1158 (vs), 1027 (m), 926 (w), 864 (m), 772 (m), 633 (m), 556
(m), 509 (m) cm–1.
and 6, with a Agilent Xcalibur CCD area detector in the ω scan mode
using Mo-Kα radiation (λ = 0.71073 Å) for complex 3, and with a
Rigaku Saturn CCD area detector in the ω scan mode using Mo-Kα
radiation (λ = 0.71075 Å) for complex 5. The diffracted intensities
were corrected for Lorentz-polarization effects and empirical absorp-
tion corrections. Details of the intensity data collection and crystal data
are given in Table 4. The structures were solved by direct methods and
refined by full-matrix least-squares procedures based on |F|2. All of
the non-hydrogen atoms were refined anisotropically. The hydrogen
atoms in these complexes were all generated geometrically, assigned
appropriate isotropic thermal parameters, and allowed to ride on their
parent carbon atoms. All of the hydrogen atoms were held stationary
and included in the structure factor calculations in the final stage of
full-matrix least-squares refinement. The structures were refined using
SHELEXL-97 programs.[18]
L[La(OAr)2(THF)]2 (6): The synthesis of complex 6 was carried
out in the same way as that described for complex 1, but
(ArO)3La(THF)2 (4.88 mmol) was used instead of (ArO)3Yb(THF)2.
Colorless crystals were obtained from THF at 0 °C (3.84 g, 85%); m.p.
173 °C (decomp.). C84H126N2O8La2 (1569.74): calcd. C 64.27; H 8.09;
1
N 1.78; La 17.70%; found: C 64.20; H 8.21; N 1.74; La 17.80%. H
NMR (400 MHz, C6D6): 7.18 (s, 12 H, ArH), 5.09 [s, 2 H,
CH=C(CH3)N], 2.43 (s, 12 H, ArCH3), 1.90 (s, 6 H, CH3), 1.63 (s, 6
H, CH3), 1.52 (s, 72 H, tBu) ppm. 13C NMR (400MHz, C6D6): δ =
178.4, 170.1, 162.2, 137.7, 136.0, 125.9, 125.7, 125.6, 123.7, 68.6,
34.8, 34.4, 31.2, 31.0, 30.5, 26.5, 25.6, 23.0, 21.8. IR (KBr): ν˜ = 2995 Crystallographic data (excluding structure factors) for the structures in
(s), 1945 (m), 1559 (vs), 1520 (vs), 1436 (s), 1358 (s), 1312 (vs), 1273
(vs), 1227 (s), 1189 (s), 1027 (s), 918 (s), 864 (s), 803 (2), 764 (s),
625 (s), 571 (m), 540 (m), 509 (m) cm–1.
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-1030495 (for 2), CCDC-1030496 (for 3), CCDC-
1030498 (for 5) and CCDC-1030499 (for 6) (Fax: +44-1223-336-033;
E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
General Procedure for the Reaction of Amines with Carbodiimides
Catalyzed by Complex 2: A 10 mL Schlenk tube in a dried argon
atmosphere was charged with 2 (14.2 mg, 0.008 mmol). To the flask
were added the aniline (PhNH2) (0.146 mL, 10.96 m, 1.60 mmol), Supporting Information (see footnote on the first page of this article):
N,NЈ-diisopropylcarbodiimide (iPrNCNiPr) (0.249 mL, 6.418 m, Spectroscopic data for the addition products of amines to carbodi-
1.60 mmol). The resulting mixture was stirred at 60 °C for the desired imides.
Table 4. Crystallographic data for complexes 2, 3, 5 and 6.
2·2thf
3·6thf
5·toluene
6·4thf
Empirical formula
Formula mass
T /K
C92H142N2O10Yb2
1782.16
193(2)
C108H174N2O14Y2
1902.31
223(2)
C91H134N2O8Nd2
1672.48
223(2)
C100H158N2O12La2
1858.10
153(2)
Crystal system
Space group
monoclinic
P21/n
triclinic
P1
monoclinic
P21/n
triclinic
P1
¯
¯
a /Å
b /Å
c /Å
α /°
16.8447(15)
16.6286(15)
17.1105(16)
90
102.498(3)
90
4679.1(7)
2
1.265
13.3209(8)
15.2897(7)
15.3594(11)
100.057(5)
107.043(6)
106.911(5)
2743.7(3)
1
17.768(6)
15.282(4)
18.636(5)
90
105.867(8)
90
4867(2)
2
1.141
12.7859(13)
13.1457(13)
15.6279(13)
75.040
76.787(4)
88.052(6)
2469.6(4)
1
β /°
γ /°
V /Å3
Z
Dcalcd. /g·cm–3
1.151
1.110
1.249
0.910
μ /mm–1
2.039
1.102
F(000)
1856
1026
1756
982
θ range /°
3.08–25.35
45675
7457
8542/12/490
1.138
0.0408
2.89–25.05
23444
6340
9725/6/584
0.993
0.0662
3.11–25.05
22197
3759
8520/325/490
1.032
0.1165
3.08–25.35
24269
8382
8990/10/527
1.090
0.0392
Reflns. collected
Reflns. observed [I Ͼ 2σ(I)]
Data/restraints/parameters
Goodness of fit on F2
Final R [I Ͼ 2σ(I)]
wR2 (all data)
0.0891
0.1320
0.3078
0.0947
Z. Anorg. Allg. Chem. 2015, 1230–1237
1235
© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
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ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
2010, 6426; c) F. Basuli, B. C. Bailey, J. C. Huffman, D. J. Mindi-
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We are grateful to the National Natural Science Foundation of China
(Grants 21132002 and 21372171), PAPD, and the Key Laboratory of
Organic Synthesis of Jiangsu Province (KJS1212) for financial sup-
port. The authors declare no competing financial interest.
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Received: January 29, 2015
Published Online: April 14, 2015
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