Activation of carbodiimide and transformation with amine to guanidinate group by Ln(OAr)3(THF)2 (Ln: Lanthanide and yttrium) and Ln(OAr)3(THF)2 as a novel precatalyst for addition of amines to carbodiimides: Inf

Article abstract of DOI:10.1021/ic200091s

Reaction of Ln(OAr¹)₃(THF)₂ (Ar ¹= [2,6-(tBu)2- 4-MeC₆H₂] with carbodiimides (RNCNR) in toluene afforded the RNCNR coordinated complexes (Ar ¹O)₃Ln(NCNR) (R = iPr (iso

Full text of DOI:10.1021/ic200091s

ARTICLE
pubs.acs.org/IC
Activation of Carbodiimide and Transformation with Amine to
Guanidinate Group by Ln(OAr)3(THF)2 (Ln: Lanthanide and Yttrium)
and Ln(OAr)3(THF)2 as a Novel Precatalyst for Addition of Amines to
Carbodiimides: Influence of Aryloxide Group
Yang Cao,† Zhu Du,† Wenbo Li,† Junmei Li,† Yong Zhang,† Fan Xu,*,† and Qi Shen*,†,‡
†Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science,
Dushu Lake Campus, Soochow University, Suzhou 215123, People’s Republic of China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
S Supporting Information
b
ABSTRACT: Reaction of Ln(OAr1)3(THF)2 (Ar1= [2,6-(tBu)2-
4-MeC6H2] with carbodiimides (RNCNR) in toluene afforded
the RNCNR coordinated complexes (Ar1O)3Ln(NCNR) (R =
iPr (isopropyl), Ln = Y (1) and Yb (2); R = Cy (cyclohexyl), Ln =
Y (3)) in high yields. Treatment of 1 and 2 with 4-chloroaniline,
respectively, at a molar ratio of 1:1 yielded the corresponding
monoguanidinate complex (Ar1O)2Y[(4-Cl-C6H4N)C(NHiPr)
NiPr](THF) (4) and(Ar1O)2Yb[(4-Cl-C6H4N)C(NHiPr)NiPr]
(THF) (5). Complexes 4 and 5 can be prepared by the reaction of Ln(OAr1)3(THF)2 with RNCNR and amine in toluene at a 1:1:1
molar ratio in high yield directly. A remarkable influence of the aryloxide ligand on this transformation was observed. The similar
transformation using the less bulky yttrium complexes Y(OAr2)3(THF)2 (Ar2 = [2,6-(iPr)2C6H3]) or Y(OAr3)3(THF)2 (Ar3 = [2,6-
Me2C6H3]) did not occur. Complexes Ln(OAr1)3(THF)2 were found to be the novel precatalysts for addition of RNCNR with amines,
which represents the first example of catalytic guanylation by the lanthanide complexes with the Ln-O active group. The catalytic activity of
Y(OAr1)3(THF)2 was found to be the same as that of monoguanidinate complex 4, indicating 4 is one of the active intermediates in the
present process. The other intermediate, amide complex (Ar1O)2Ln[(2-OCH3-C6H4NH)(2-OCH3-C6H4NH2)] (6), was isolated by
protonolysis of 4 with 2-OCH3-C6H4NH2. All the complexes were structurally characterized by X-ray single crystal determination.
’ INTRODUCTION
the carbodiimides used. Similarly, a direct synthetic way to
guanidines or propiolamidine was also explored using divalent
lanthanide complexes as the precatalysts.3g
Activation and transformation of small molecules mediated by
lanthanide complexes are one of the most interesting topics in
organometallic chemistry and coordination chemistry of lantha-
nide metals.1 Carbodiimides, as one of the members of hetero-
cumulene family, have attracted increasing attention for lan-
thanide metal based reactivity studies.2 For example, insertion
reactions of carbodiimides into lanthanide metal Ln-C2b,3cor
Ln-N2cꢀg bonds have been explored to afford lanthanide(III)
complexes with a substituted propiolamidine group or a sub-
stituted guanidinate RNC(NHR0)NR ligand. More interestin-
gly, an atom economic method for the synthesis of substituted
guanudines or propiolamidine has been developed by the
combination of the insertion reaction and the following proton-
olysis.3 Recently, the activation and transformation of carbodii-
mides in different modes have been documented with divalent
lanthanide complexes by Deacon and Junks’ group, and our
group. These reduction reactions of carbodiimides by divalent
lanthanide complexes were found to afford an oxalamidinate,4a,c a
formamidinate, a linked formamidinate,4b or a diamidocarbene
species4d depending on the divalent lanthanide complex and/or
Lanthanide aryloxides are well-known to serve as catalysts in
many reactions, such as enantioselective alkylation of aldehydes,
asymmetric epoxidation of unsaturated ketones, decarboxylation
of carboxylic acids,5a,b intramolecular hydroalkoxylation,5c po-
lymerization of lactones and lactides,6aꢀd and copolymerization
of carbon dioxide with epoxides,6e and so forth. However, no
report concerning the activation and transformation of carbodii-
mides by a Ln-O active group has been found until now. In
continuation of our work, we studied the reactivity of Ln(OAr)3-
(THF)2 (Ln = lanthanide and yttrium metals) toward carbodii-
mides. It was found that the aryloxide ligand has a remarkable
influence on the reactivity. A carbodiimide coordinated complex
(Ar1O)3Ln(RNCNR) can be isolated when the aryloxide is a
bulky [2,6-(tBu)2-4-MeC6H2] (OAr1). In contrast, no carbodii-
mide-coordinated complexes could be isolated using the less bulky
Received: January 16, 2011
Published: March 22, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
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Scheme 1. Reaction of Ln(OAr)3(THF)2 with Carbodii-
mide: the Influence of Aryloxide Ligand
Scheme 2
Figure 1. ORTEP diagram of the molecular structures of complexes
1and 2 (Ln = Y (1), Yb (2)). Thermal ellipsoids are drawn at 30%
probability level. All hydrogen atoms are omitted for clarity.
lanthanide tris(aryloxides) complexes as Ln(OAr2)3(THF)2
(OAr2 = [2,6-(iPr)2C6H3]) or Ln(OAr3)3(THF)2 (OAr3 =
[2,6-Me2C6H3]). The carbodiimide-coordinated complex can
further react with an equivalent of amine to afford the correspond-
ing lanthanide bis(aryloxide) guanidinate, which reacts with amine
to yield the corresponding lanthanide bis(aryloxide) amide.
Complexes Ln(OAr1)3(THF)2 were found to serve as a novel
precatalysts for guanylation of amines with carbodiimides to
substituted guanidines. Here we report the results.
’ RESULTS AND DISCUSSION
i
Synthesis and Structures of (Ar1O)3Ln(RNCNR) R = Pr,
Ln = Y (1) and Yb (2); R = Cy, Ln = Y (3). A series of lanthanide
aryloxides were synthesized according to the literature meth-
od, including Ln(OAr1)3(THF)2 (Ar1 = [2,6-(tBu)2-4-
MeC6H2] Ln = Y and Yb), Y(OAr2)3(THF)2 (Ar2 = [2,6-(iPr)2-
C6H3]) and Y(OAr3)3(THF)2 (Ar3 = [2,6-Me2C6H3]).7 Treatment
of Y(OAr1)3(THF)2 with N,N0-diisopropylcarbodiimide (iPrNC-
NiPr) in a molar ratio of 1:2 at 60 °C in toluene gave a light
yellow solution from which the iPrNCNiPr coordinated complex
(Ar1O)3Y(iPrNCNiPr) (1) was isolated in a high yield
(Scheme 1). Following the same procedure, the analogous Yb
complex (Ar1O)3Yb(iPrNCNiPr) (2) can facilely be synthesized
via the replacement of the coordinated tetarhydrofuran (THF)
molecule by a PrNCNiPr molecule (Scheme 1). The similar
i
Figure 2. ORTEP diagram of the molecular structure of complex 3.
Thermal ellipsoids are drawn at 30% probability level. All hydrogen
atoms and lattice solvent molecules are omitted for clarity.
reaction of Y(OAr1)3(THF)2 with N,N0-dicyclohexylcarbodii-
mide (CyNCNCy) worked smoothly, and the corresponding
complex (Ar1O)3Y(CyNCNCy) (3) was also prepared in 80%
yield (Scheme 1).
However, the analogous reactions using the less bulky com-
plexes, Y(OAr2)3(THF)2 and Y(OAr3)3(THF)2, did not occur,
and the starting yttrium complexes were recovered. In both cases
no replacement of the coordinated THF molecules by a carbo-
diimide was observed (Scheme 1).
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ARTICLE
Complexes 1ꢀ3 are well soluble in toluene. They are thermo-
stable and do not decompose until 110 °C.
diimides moiety can only be compared with those in Cp3Y-
(iPrNCNiPr).2b The Ln-N bond distance is shorter than the
corresponding value found in Cp3Y(iPrNCNiPr) (2.547(6) Å).
A significant structural feature in these adducts is the apparent
elongation of the one CdN double bond in the carbodiimide
moiety (C(46)dN(1) 1.250(5) Å and C(46)dN(2) 1.182(5) Å).
The elongation of CdN double bond indicates clearly that the
coordinated carbodiimide has been activated. The bond param-
eters about the part of (Ar1O)3Ln compare well with those found
in Ln(OAr1)3(THF)2. The crystal structure of 3 is exactly similar
to those of 1 and 2.
As expected, the complexes 1ꢀ3 will completely convert to a
THF-solvate Y(OAr1)3(THF)2 via replacement of a carbodii-
mide by THF molecules, when putting them in a THF solution
and stirring for 12 h at room temperature (Scheme 2).
The molecular structures of 1ꢀ3 were determined and are
shown in Figures 1 and 2, respectively, as complexes 1 and 3 are
isostructural. X-ray structure determination shows that 1 and 2
i
featuring the donating coordinated PrNdCdNiPr moiety are
both solvent-free monomers with the central metal atom bonded
to three aryloxide groups and one carbodiimide molecule. The
coordination geometry around the each metal can be described
as a distorted-tetrahedral geometry. The Ln(1)ꢀN(1) distances
are 2.443(3) Å for 1 and 2.392(3) Å for 2, which are comparable
with each other when the difference in ion radius between Y and
Yb was considered and both are in the range of Ln-N donated
bonding (Table 1). Because no analogous complexes can be
found in the literature, the bond distances concerning carbo-
Reaction of 1 or 2 with 4-Chloroaniline: Synthesis and
Molecular Structures of the Monoguanidinate Complexes
(Ar1O)2Ln[(4-Cl-C6H4N)C(NHiPr)NiPr](THF) (Ln = Y (4); Yb
(5)). Heating 1 in a toluene solution did not lead to the product
(Ar1O)2Y[(iPrN)2C(OAr1)] via the insertion of iPrNCNiPr into
the Y-OAr1 bond as the case of the reaction of Ti(OiPr)4 with
carbodiimide,8 but the starting substrate recovered. However, 1
could react with 4-chloroaniline (4-Cl-C6H4NH2), at a molar
ratio of 1:1 clearly to give a light yellow solution. Evaporation and
crystallization from toluene solution resulted in the yellow
crystals of monoguanidinate complex (Ar1O)2Y[(4-Cl-C6H4N)
C(NHiPr)NiPr](THF) (4) (Scheme 3), which were fully char-
Table 1. Selected Bond Distances (Å) and Angles (deg) for
Complexes 1ꢀ3
1
2
3
1
acterized including elemental analysis, HNMR spectroscopy,
and X-ray single crystal structure determination. The analogous
Yb complex (Ar1O)2Yb[(4-Cl-C6H4N)C(NHiPr)NiPr](THF)
(5) could also be isolated by the same procedure in good yield as
dark red crystals (Scheme 3).
Bond Lengths
2.063(2)
2.098(2)
2.125(2)
2.443(3)
1.250(5)
1.182(5)
Ln (1)ꢀO (1)
Ln (1)ꢀO (2)
Ln (1)ꢀO (3)
Ln (1)ꢀN (1)
N (1)ꢀC (46)
N (2)ꢀC (46)
2.038(2)
2.062(2)
2.091(2)
2.392(3)
1.260(5)
1.172(5)
2.079(2)
2.091(2)
2.092(2)
2.462(3)
1.255(5)
1.191(5)
As is well-known, primary aromatic amines do not react with
carbodiimide to a guanidine without catalyst under mild con-
zditions.9 Consequently, the formation of guanidinate species
here should be attributed to the activation of carbodiimide via its
coordination to the metal of Ln(OAr1)3(THF)2 as confirmed by
the elongated CdN double bond distance in 1, followed by the
formation of an intermediate A via the coordination of amine. The
formation of A makes it favorable to realize the addition of amine
to the coordinated carbodiimide and to release a phenol via
protonolysis by in situ formed guanidine concomitantly in an
intramolecular transformation mode (Scheme 3). Further study
revealed that complex 4 can also be synthesized in high yield
Bond Angles
108.66(9)
116.16(8)
127.89(9)
110.0(2)
O (1)ꢀLn (1)ꢀO (2)
O (1)ꢀLn (1)ꢀO (3)
O (2)ꢀLn (1)ꢀO (3)
C (46)ꢀN (1)ꢀLn (1)
N (2)ꢀC (46)ꢀN (1)
C (46)ꢀN (1)ꢀC (47)
C (46)ꢀN (2)ꢀC (50)
108.74(9)
116.40(9)
127.92(10)
109.7(3)
170.5(5)
116.9(3)
149.0(5)
115.27(9)
114.42(10)
115.75(10)
112.6(3)
170.0(5)
172.5(4)
118.0(3)
118.2(7)
i
by the reaction of Y(OAr1)3(THF)2 with PrNCNiPr and
147.7(4)
136.9(4)
Scheme 3. Formation of 4 (5) by Reaction of 1 (2) with 4-Chloroaniline
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Inorganic Chemistry
ARTICLE
Scheme 4. Reaction of Ln(OAr)3(THF)2 with 4-Cl-C6H4N2 and iPrNCNiPr
Figure 3. ORTEP diagram of the molecular structure of complex 3. Thermal ellipsoids are drawn at 30% probability level. All hydrogen atoms and
lattice solvent molecules are omitted for clarity.
4-Cl-C6H4NH2 at a 1:1:1 molar ratio in toluene in one pot
synthesis (Scheme 4). Neither the less bulky aryloxides, Y-
(OAr2)3(THF)2, nor Y(OAr3)3(THF)2 could react with iPrNC-
NiPr and 4-Cl-C6H4NH2, only the starting materials were
recovered for both reactions (Scheme 4).
These results indicated that the formation of a carbodiimide
coordinated complex as the first step is crucial for the transfor-
mation of carbodiimide with amine to a guanidinate group, that
is, the activation of a carbodiimide molecule by Y(OAr1)3-
(THF)2 is the basis for its further transformation with amine.
Although the insertion of carbodiimide into the Ln-N bond to a
guanidinate group is well documented and becomes a general
method for synthesis of lanthanide guanidinate complexes.2cꢀh
To our best knowledge, this is the first example of activation of
carbodiimide and transformation with amine to a guanidinate
species mediated by an Ln-O active group.
Molecular structures of complexes 4 and 5 are depicted in
Figure 3. The crystal structure determination of complexes 4 and
5 revealed that they are isostructural, in which each center metal
is bonded to two aryloxide ligands and one guanidinate unit,
forming a distorted-tetragonal pyramidal geometry (Figure 3).
As expected, the coordinated guanidinate group forms essentially
a planar four-member ring with the metal atom within experi-
mental errors. The bond angles around C(37) are consistent with
sp2 hybridization. The C(37)ꢀN(1) bond distance (1.342(4) Å
in 4, 1.332(5) Å in 5) and C(37)ꢀN(2) bond distances
(1.342(4) Å in 4, 1.350(5) Å in 5) are almost equivalent and
significantly shorter than the CꢀN single-bond distance, indicat-
ing that the electrons are delocalized over the NꢀCꢀN unit
(Table 2). The bond distances of the YꢀN(1) (2.403(2) Å in 4)
and YbꢀN(1) (2.362(3) Å in 5) are significantly longer than that
of the Y(1)ꢀN(2) (2.299(2) Å in 4) and Yb(1)ꢀN(2)
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Inorganic Chemistry
ARTICLE
Table 2. Selected Bond Distances (Å) and Angles (deg) for Complexes 4ꢀ5
4
5
4
5
Bond Lengths
Ln (1)ꢀO (1)
Ln (1)ꢀO (2)
Ln (1)ꢀO (3)
N (2)ꢀC (37)
2.0859(19)
2.1024(19)
2.386(2)
2.058(3)
2.076(2)
2.347(2)
1.350(5)
Ln (1)ꢀN (1)
Ln (1)ꢀN (2)
N (1)ꢀC (37)
N (3)ꢀC (37)
2.403(2)
2.299(2)
1.342(4)
1.366(4)
2.362(3)
2.254(3)
1.332(5)
1.368(5)
1.342(4)
Bond Angles
O (2)ꢀLn (1)ꢀO (3)
O (2)ꢀLn (1)ꢀN (2)
N (2)ꢀLn (1)ꢀN (1)
O (3)ꢀLn (1)ꢀN (1)
86.97(8)
99.33(8)
57.08(8)
91.72(8)
86.89(9)
N (2)ꢀC (37)ꢀN (1)
N (2)ꢀC (37)ꢀN (3)
N (1)ꢀC (37)ꢀN (3)
113.8(2)
120.4(3)
125.6(3)
113.2(3)
120.9(3)
125.7(3)
98.89(11)
57.98(11)
91.63(10)
Table 3. Catalytic Guanylation of an Aniline with an N,N0-
Diisopropylcarbodiimidea
catalyst
loading
temp/ time/
entry
Cat.
(mol %)
R
°C
h
product yield(%)b
1
2
3
4
5
6
7
8
9
4
4
4
4
1
H
H
H
10
rt
0.5
1
7
7
7
8
7
7
7
7
7
7
7
95
87
99
96
63
98
58
13
50
67
85
0.5
0.5
0.5
1
60
0.5
0.5
0.5
0.5
4
Cl 60
Y(OAr1)3(THF)2
Y(OAr1)3(THF)2
Y(OAr2)3(THF)2
Y(OAr3)3(THF)2
Nd(OAr1)3(THF)2
H
H
H
H
H
H
H
10
60
60
60
60
60
60
0.5
0.5
0.5
0.5
0.5
0.5
24
0.5
0.5
0.5
Figure 4. ORTEP diagram of the molecular structures of complexes 6.
Thermal ellipsoids are drawn at 30% probability level. All hydrogen
atoms are omitted for clarity.
10 Sm(OAr1)3(THF)2
11 Yb(OAr1)3(THF)2
with iPrNCNiPr using 0.5 mol % of 4 at 60 °C worked well, and
the guanidine 8 was obtained in 96% yield (Table 3, entry 4).
These positive results prompted us to isolate the intermediate
amide complex by protonolysis of 4 with amines. The reaction of
4 with excess 2-OCH3-C6H4NH2 at room temperature in tol-
uene took place rapidly leading to a color change from light
yellow to darkish; the corresponding structurally characteri-
zable amide complex 6 (Figure 4) was isolated from the solution
(Scheme 5).
The isolation of 6 suggests that the catalytic formation of a
guanidine compound proceeds by the following pathways.
Complex 4 reacts with amine to afford the corresponding amide
intermediate, then nucleophilic addition of the amido species to
a carbodiimide, followed by amine protonolysis of the resultant
guanidinate species.
a 1 mmol of 4-chloroaniline or aniline, 1 mmol of N,N0-diisopropylcar-
bodiimide. b Isolated yields.
(2.254(3) Å in 5). This may be due to the steric hindrance of the
benzene group at N(1) stretching the Ln-N(1) bonds.
Catalytic Activity of 4 for Addition of Amines to RNCNR
and Isolation and Characterization of Amide Complex
(Ar1O)2Y[(2-OCH3-C6H4NH)(2-OCH3-C6H4NH2)] (6) via the
Protonolysis of 4 by 2-OCH3-C6H4NH2. As is well-known, an
amide and a guanidinate intermediates are the true catalyst spe-
cies for catalytic formation of a guanidine compound by lantha-
nide amide or alkyl complexes.3c Thus, the catalytic activity of 4
for addition of aniline to carbodiimide was tested. Addition of
1 mol % 4 into the mixture of iPrNCNiPr and PhNH2 at 10 °C
under solvent free condition led to rapid formation of the N,N0,
N00-trisubstitutedguanidine 7 in 95% yield after 0.5 h (Table 3,
entry 1). Even when the amount of 4 decreased to 0.5 mol %, the
reaction at room temperature can still afford 7 in 87% yield after
1 h (Table 3 entry 2). Raising the temperature to 60 °C led to
increasing the yield and shortening the reaction time (Table 3,
entry 3). Similarly, the reaction of 4-chloroaniline (4-Cl-C6H4NH2)
X-ray crystal structure analysis revealed that the center metal
ion of 6 is bonded to two aryloxide ligands and two oxygen atoms
and two nitrogen atoms from the two amido groups in a dis-
torted-octahedral geometry (Figure 4). The Y(1)ꢀN(1) bond
distance of 2.268(3) Å compares well with those found in the
yttrium amide complexes,10,11 while the bond distance of
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Inorganic Chemistry
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Scheme 5. Formation of 6 by Protonolysis of 4 with 2-OCH3-C6H4NH2
resultant guanidinate species by amine. The nucleophilic addi-
tion of an amido species formed to a carbodiimide3c to regenerate
the guanidinate species as shown in Scheme 6.
Table 4. Selected Bond Distances (Å) and Angles (deg) for
Complex 6
6
’ CONCLUSION
Bond Lengths
Y (1)ꢀO (1)
Y (1)ꢀO (2)
Y (1)ꢀO (3)
2.132(2)
2.118(2)
2.495(2)
Y (1)ꢀO (4)
Y (1)ꢀN (1)
Y (1)ꢀN (2)
2.553(3)
2.268(3)
2.483(3)
Activation of carbodiimide and transformation with amine
to guanidinate group was explored with the bulky complexes
Ln(OAr1)3(THF)2 (Ln = Y and Yb; Ar1 = [2,6-(tBu)2-4-
MeC6H2]), and the corresponding monoguanylate complexes
(Ar1O)2Ln[(4-Cl-C6H4N)C(NHiPr)NiPr] (Ln = Y (4); Yb
(5)) were isolated and structurally characterized. The analogous
transformation does not occur using the less bulky complexes
Y(OAr2)3(THF)2 (Ar2 = [2,6-(iPr)2C6H3]) or Y(OAr3)3-
(THF)2 (Ar3 = [2,6-Me2C6H3]). Thus, Ln(OAr1)3(THF)2 were
first found to be the efficient precatalysts for guanylation of amine
with carbodiimide under mild conditions, and the active species
in this process are the corresponding monoguanidinate com-
plexes 4 and the amide complex (Ar1O)2Y[(2-OCH3-C6H4
NH)(2-OCH3-C6H4NH2)] (6), which was formed by proto-
nolysis of 4 by 2-OCH3-C6H4NH2. The activity is greatly
influenced by aryloxide group with the sequence of [2,6-
(tBu)2-4-MeC6H2] > Ar2 = [2,6-(iPr)2C6H3] > Ar3 =[2,6-
Me2C6H3]. The results presented here indicate that the ro-
bust lanthanide tris(aryloxide) exhibits wide reactivity to small
molecules.
Bond Angles
O (2)ꢀY (1)ꢀO (1) 159.7(2)
O (2)ꢀY (1)ꢀO (3) 87.64(9)
O (1)ꢀY (1)ꢀO (3) 157.14(9)
O (3)ꢀY (1)ꢀO (4) 69.45(8)
N (1)ꢀY (1)ꢀN (2) 136.44(12)
Y(1)ꢀN(2) (2.483(3) Å) is much longer and falls into YꢀN
donating bonds (Table 4).11 The sum of the angles of O(1)ꢀ
Y(1)ꢀO(2), O(2)ꢀY(1)ꢀO(3), O(3)ꢀY(1)ꢀO(4), and O-
(4)ꢀY(1)ꢀO(1) is 360.8°, suggesting that the four oxygen
atoms are almost in a plane. The angle formed by two N atoms
and the central metal is 136.44°.
Ln(OAr1)3(THF)2 as an Efficient Precatalysts for Addition
of Amines to Carbodiimides. Given that 4 was synthesized
directly by the reaction of Y(OAr1)3(THF)2 with amine and
carbodiimide, the catalytic activity of Y(OAr1)3(THF)2 for
addition of aniline to carbodiimide was then tested under solvent
free conditions. As shown in Table 3, Y(OAr1)3(THF)2 exhibits
high activity for the addition of aniline to PrNCNiPr and the
i
’ EXPERIMENTAL SECTION
corresponding 7 was isolated in 97% yield with the amount of
0.5 mol % of Y(OAr1)3(THF)2 at 60 °C for 0.5 h (Table 3, entry
6). The activity of Y(OAr1)3(THF)2 is almost the same as that of
4, indicating 4 is the true active species. Aryloxide group has a
remarkable influence on the activity. The complexes with the less
bulky ligands Y(OAr2)3(THF)2 and Y(OAr3)3(THF)2 showed
very low activity (Table 3, entries 6ꢀ8). This is expected because
neither Y(OAr2)3(THF)2 nor Y(OAr3)3(THF)2 can react with a
mixture of amine and carbodiimide in a 1:1:1 molar ratio at 80 °C
to a guanidinate species as demonstrated above. The influence of
the central metals on the activity was clearly observed with the
increasing trend of Y > Yb > Sm > Nd (Table 3, entries 6, 9ꢀ11).
The complex Y(OAr1)3(THF)2 was then chosen as a precatalyst
for addition reaction of various aromatic primary amines with
carbodiimides. As shown in Table 5, a wide range of substituted
amines could be used for this reaction, including the amines with
either electron-withdrawing or electron-donating substituents
(Table 5, entries 1ꢀ11). The present catalytic guanylation was
suggested to proceed through the formation of guanidinate
species by reaction of Y(OAr1)3(THF)2 with amine and carbo-
diimide in a 1:1:1 molar ratio, followed by protonolysis of the
Materials and Methods. All operations involving air- and moist-
ure-sensitive compounds were carried out under an inert atmosphere of
purified argon or nitrogen using standard Schlenk techniques. The
solvents THF, toluene, and n-hexane were dried and distilled from
sodium benzophenone ketal under argon prior to use. Ln(OAr1)3-
(THF)2, Ln(OAr2)3(THF)2, and Ln(OAr3)3(THF)2 were prepared
according to the literature procedure.7 1H NMR and 13C NMR spectra
were recorded on a 300 MHz or 400 MHz instrument and processed
using MestReNova software. Elemental analyses were performed by
direct combustion using a Carlo-Erba EA 1110 instrument. The IR
spectra were recorded on a Magna-IR 550 spectrometer as KBr pellets.
All yields of lanthanide complexes were calculated based on ligands and
were crystallized yield only for the first time.
(Ar1O)3Y(iPrNCNiPr) (1). A certain amount of iPrNCNiPr (0.32 g, 2.57
mmol) was added to a solution of Y(OAr1)3(THF)2 (2.29 g, 2.57 mmol)
in toluene (20 mL) in a Schlenk tube. The mixture was stirred at 60 °C
for 12 h. After the solvent was removed under reduced pressure, the
residue was extracted with hexane to give a white powder: 1.9 g (85%),
and the white powder was dissolved in toluene and filtered to give a clean
solution. Single crystals of 1 suitable for X-ray analysis were obtained
from toluene at room temperature for about 1 day. 1H NMR (400 MHz,
3734
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Inorganic Chemistry
ARTICLE
Table 5. Catalytic Addition of Primary Aromatic Amines to Carbodiimidesa
a The reaction was performed by treating 1 equiv of amines with 1 equiv of carbodiimides at 60 °C. b Isolated yields.
OC6H2[C(CH3)3]2CH3), 0.91 (d, 12 H, CH(CH3)2); 13C NMR
(101 MHz, C6D6) 154.38, 132.03, 126.40, 122.73, 122.58, 122.34,
120.64, 119.50, 45.38, 30.03, 27.47, 18.46, 16.00; IR (KBr, cmꢀ1):
3648(m), 3359(w), 2957(s), 2915(s),2871(s), 2361(w), 2112(s),
1747(w), 1615(m),1418(s), 1386(m), 1360(m),1238(s), 1158(s),
1120(m), 922(w), 890(w), 861(m), 830(s), 640(w), 534(m), 504(w);
Anal. Calcd for C52H83N2O3Y (873.11): C, 71.53; H, 9.58; N, 3.21.
Found: C, 71.18; H, 9.78; N, 3.94.
Scheme 6. Mechanism for Addition of Amines to Carbodii-
mides Catalyzed by Y(OAr1)3(THF)2
i
(Ar1O)3Yb(iPrNCNiPr) (2). A certain amount of PrNCNiPr (0.28 g,
2.21 mmol) was added to a solution of Yb(OAr1)3(THF)2 (1.99 g, 2.21
mmol) in toluene (20 mL). The reaction mixture was subsequently
worked up by the method described above. Red crystals of 2 were
obtained in 78% yield (1.65 g). IR (KBr, cmꢀ1): 3652(m), 3345(w),
2945(s), 2909(s),2881(s), 2120(s), 1621(m), 1425(s), 1387(m), 1367-
(m),1239(s), 1155(s), 1123(m), 931(w), 893(w), 861(m), 838(s),
776(w), 646(w), 537(m); Anal. Calcd for C52H83N2O3Yb (957.24):
C, 65.24; H, 8.74; N, 2.93. Found: C, 65.86; H, 8.82; N, 2.79.
(Ar1O)3Y(CyNCNCy) (3). By the procedure described for 1, reaction of
Y(OAr1)3(THF)2 (2.54 g, 3.11 mmol) with CyNCNCy (0.64 g, 3.11
mmol) gave 3 as colorless crystals. Yield: 2.66 g (82%). 1H NMR (400
MHz, C6D6): δ 7.13 (s, 6H, OC6H2[C(CH3)3]2CH3), 3.04 (s, 2H, Cy),
2.29 (s, 9H, OC6H2[C(CH3)3]2CH3), 1.95ꢀ1.74 (m, 4H), 1.66 (d, 54H,
OC6H2[C(CH3)3]2CH3), 1.47 (d, 4H, Cy), 1.31 (d, 2H, Cy), 1.17 (d,
4H, Cy), 1.10ꢀ0.95 (m, 4H, Cy), 0.89 (dd, 2H, Cy). 13C NMR (101
MHz, C6D6): δ 159.94, 137.63, 131.24, 126.16, 124.94, 57.33, 35.48,
C6D6): δ 7.13 (s, 6 H, OC6H2[C(CH3)3]2CH3), 3.37 (s, 2 H, CH-
(CH3)2), 2.31 (s, 9 H, OC6H2[C(CH3)3]2CH3), 1.64 (s, 54 H,
3735
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Inorganic Chemistry
ARTICLE
Table 6. Crystallographic Data for Complexes 1ꢀ6
1
2
3
4
5
6
formula
C
52H83N2O3Y
C52H83N2O3Yb
957.24
C65H99N2O3Y
1045.37
C54H81ClN3O3Y
944.58
C54H81ClN3O3Yb
1028.71
C44H63N2O4Y
772.87
mol wt
873.11
λ (Å)
0.71075
0.71075
0.71075
0.71075
0.71075
0.71075
cryst syst
space group
cryst size (mm)
a (Å)
monoclinic
P21/c
monoclinic
P21/c
triclinic
triclinic
triclinic
monoclinic
P21/n
P1
P1
P1
0.80 ꢁ 0.40 ꢁ 0.15
15.5829(18)
17.9753(19)
18.564(2)
90
0.80 ꢁ 0.20 ꢁ 0.20
15.5373(12)
17.9224(13)
18.5630(15)
90
0.55 ꢁ 0.40 ꢁ 0.15
14.2961(4)
14.8441(5)
15.7236(6)
79.534(5)
75.579(5)
71.112(4)
3038.96(18)
2, 1.142
0.50 ꢁ 0.30 ꢁ 0.30
9.8439(7)
11.2519(9)
24.409(2)
83.406(7)
80.859(5)
76.620(6)
2588.3(4)
2, 1.212
0.60 ꢁ 0.18 ꢁ 0.12
9.8319(5)
11.2382(6)
24.3593(15)
83.370(4)
80.871(4)
76.612(4)
2576.5(2)
2, 1.326
0.70 ꢁ 0.30 ꢁ 0.20
14.7013(17)
17.9628(16)
16.8390(18)
90
b (Å)
c (Å)
R (deg)
β (deg)
103.940(3)
90
103.976(2)
90
110.551(3)
90
γ (deg)
V (Å3)
Z(Å3), Dcalcd (g/mL)
5046.8(10)
4, 1.149
5016.1(7)
4, 1.268
4163.8(8)
4, 1.233
μ (mmꢀ1
)
1.196
1.905
1.003
1.221
1.910
1.442
F (000)
1888
2012
1132
1012
1074
1648
θ range (deg)
total no. of rflns
no. of indep rflns
Rint
3.11ꢀ27.47
27663
3.00ꢀ25.50
25325
3.08ꢀ25.50
26299
3.10ꢀ25.50
22313
3.10ꢀ25.50
21011
3.01ꢀ25.50
20176
11447
9295
11250
9531
9482
7721
0.0530
0.0414
0.0594
0.0395
0.0340
0.0552
GOF
1.104
1.108
1.072
1.049
1.104
1.154
R1,wR2 (I > 2σ(I))
R1, wR2 (all data)
0.0695, 0.1462
0.0997, 0.1636
0.0399, 0.0748
0.0484, 0.0788
0.0702, 0.1513
0.0844, 0.1592
0.0520, 0.1230
0.0617, 0.1283
0.0377, 0.0781
0.0427, 0.0807
0.0681, 0.1122
0.0923, 0.1211
34.74, 33.03, 25.10, 21.53; IR (KBr, cmꢀ1): 3627(m), 3420(m), 2932(s),
2858(m), 2871(s), 2120(s), 1627(w), 1432(m), 1397(w), 1362(w),
1231(s), 1154(s), 1045(w), 922(w), 867(m), 774(w), 623(w), 503(w);
Anal. Calcd for C65H99N2O3Y (1045.37): C, 74.68; H, 9.55; N, 2.68.
Found: C, 73.97; H, 9.78; N, 2.86.
(Ar1O)2Y[(2-OCH3-C6H4NH)(2-OCH3-C6H4NH2)] (6).
A
certain
amount of 2-methoxyaniline (0.21 g, 1.7 mmol) was added to a solution
of 4 (1.57 g, 1.7 mmol) in toluene (20 mL) in a Schlenk tube. The mixture
was stirred at room temperature for 18 h. The volatiles were removed
under reduced pressure, and the residue was extracted with n-hexane.
Removing the n-hexane solution by centrifugation led to gray solids. Single
crystals of 6 suitable for X-ray analysis were grown in toluene and hexane
mixed solvent at room temperature for about 1 week. The crystallization of
6 was accompanied with guanidine generated by the amine protonolysis of
(Ar1O)2Y[(4-Cl-C6H4)NC(NHiPr)NiPr] (4). A certain amount of 4-chlor-
oaniline (0.38 g, 3 mmol) was added to a solution of Yb(OAr1)3(THF)2
(2.67 g, 3 mmol) in toluene (20 mL) in a Schlenk tube. Then iPrNCNiPr
(0.38 g, 3 mmol) was added to the mixture. The mixture was stirred at
60 °C for 12 h. After the solvent was removed under reduced pressure, the
residue was extracted with hexane to give a white powder, yield: 2.35 g
(83%), and the white powder was dissolved with toluene and filtered to
give a clean solution. Single crystals of 4 suitable for X-ray analysis were
4, so we could not obtain a pure sample of 6 suitable for the 1H NMR, 13
NMR, IR, and elemental analysis.
C
General Procedure for the Reaction of Amines with
Carbodiimides Catalyzed by 4 and Y(OAr1)3(THF)2. A 10 mL
Schlenk tube under dried argon was charged with the related catalysts
(0.01 equiv.), amines, and carbodiimides. The resulting mixture was
stirred at 10 or 60 °C for the desired time, as shown in Table 3 and
Table 5. After the reaction was completed, the reaction mixture was
hydrolyzed by water, extracted with dichloromethane (3 ꢁ 10 mL),
dried over anhydrous Na2SO4, and filtered. Then the solvent was
removed under reduced pressure, and the final products were further
purified by recrystallization from n-hexane.
X-ray Crystallography. Crystals suitable for X-ray diffraction of
complexes1ꢀ6 were sealedin a thin-walledglasscapillaryfilledwith argon
for structuralanalysis. Diffraction data were collected on a Rigaku Mercury
CCD area detector in the ω scan mode using Mo KR radiation (λ =
0.71075 Å); all data collection temperature is 223(2) K. The diffracted
intensities were corrected for Lorentz-polarization effects and empirical
absorption corrections. Details of the intensity data collection and crystal
data are given in Table 6. 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
1
grown in toluene at room temperature for about 1 day. H NMR (400
MHz, C6D6): 7.21 (s, 4 H, OC6H2[C(CH3)3]2CH3), 7.06 (d, 2 H,
ClC6H4N), 6.87 (d, 2 H, ClC6H4N), 3.61 (d, 4 H, OC4H8), 3.57 (s, 1 H,
CH(CH3)2NH), 3.26ꢀ3.04 (m, 2 H, CH(CH3)2), 2.35 (s, 6 H, OC6H2-
[C(CH3)3]2CH3), 1.61 (s, 36 H, OC6H2[C(CH3)3]2CH3), 1.27 (d, 6 H,
CH(CH3)2), 1.10 (s 4 H, OC4H8), 0.68 (d, 6 H, CH(CH3)2); 13C NMR
(101 MHz, C6D6): δ 164.51, 160.29, 149.15, 137.68, 129.33, 129.09,
128.57, 126.14, 125.62, 124.44, 45.98, 44.68, 35.31, 32.26, 30.49, 25.26,
24.85, 23.57, 21.57; IR (KBr, cmꢀ1): 3422(m), 2961(m), 2872(w),
2360(m), 1637(w), 1431(w), 1398(w), 1243(s), 1156(s), 1044.6(w),
861(w), 639(w), 555(w), 504(m); Anal. Calcd for C54H81ClN3O3Y
(944.58): C, 68.66; H, 8.64; N, 4.45. Found: C, 68.93; H, 8.71; N, 3.70.
(Ar1O)2Yb[(4-Cl-C6H4)NC(NHiPr)NiPr] (5). By the procedure de-
scribed for 4, reaction of Yb(OAr1)3(THF)2 (2.63 g, 2.7 mmol) with
iPrNCNiPr (0.34 g, 2.7 mmol) and 4-chloroaniline (0.34 g, 2.7 mmol)
gave 5 as dark red crystals. Yield: 1.82 g (72%). IR (KBr, cmꢀ1):
3428(m), 2957(m), 2879(w), 2364(m), 1632(w), 1438(w), 1396(w),
1245(s), 1151(s), 870(w), 644(w), 561(w), 507(m); Anal. Calcd for
C54H81ClN3O3Yb (1028.71): C, 63.05; H, 7.94; N, 4.08. Found: C,
62.02; H, 7.86; N, 4.21.
3736
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Inorganic Chemistry
ARTICLE
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 SHELXTL-97
programs.
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’ ASSOCIATED CONTENT
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Supporting Information. X-ray crystallographic data of
b
complexes 1ꢀ6. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
(10) Lu, M.; Yao, Y.; Zhang, Y.; Shen, Q. Dalton Trans. 2010,
39, 9530.
Corresponding Author
*E-mail: qshen@suda.edu.cn.
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’ ACKNOWLEDGMENT
We are grateful for financial support from the National Natural
Science Foundation of China (Grants 20632040, 20872106,
20972107).
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