Enol-functionalized N-heterocyclic carbene lanthanide amide complexes: Synthesis, molecular structures and catalytic activity for addition of amines to carbodiimides

Article abstract of DOI:10.1016/j.jorganchem.2012.04.006

Reaction of LnCl₃ (Ln = Y, Nd, Sm and Yb) with enol-functionalized imidazolium salt H₂LBr (L = 4-OMe-C ₆H₄COCH{C(NCHCHNⁱPr)}) and NaN(TMS)₂ at a molar ratio of 1:4:1 in THF at room temperature afforded the corresponding novel enol-functionalized N-heterocyclic carbene (NHC) lanthanide amides L ₂LnN(TMS)₂ (Ln = Y (1), Nd (2), Sm (3), Yb (4)) in 37-40% yields. Molecular structures of 1-4 were determined by X-ray structure analyses. All complexes adopt monomeric structures where each 5-coordinated metal is coordinated by two NHC ligands and one amido group.in distorted trigonal bipyramid geometry. All complexes, especially Yb complex (4), were found to be highly active precatalysts for the catalytic addition of amines to carbodiimides giving guanidines. The system with 4 shows good functional group tolerance and a wide scope of amines including primary and secondary cyclic amines.

Full text of DOI:10.1016/j.jorganchem.2012.04.006

Journal of Organometallic Chemistry 713 (2012) 27e34
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Enol-functionalized N-heterocyclic carbene lanthanide amide complexes:
Synthesis, molecular structures and catalytic activity for addition of amines
to carbodiimides
*
Zhi Li, Mingqiang Xue, Haisheng Yao, Hongmei Sun, Yong Zhang, Qi Shen
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Hengyi Road Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of LnCl3 (Ln ¼ Y, Nd, Sm and Yb) with enol-functionalized imidazolium salt H2LBr (L ¼ 4-OMe-
C6H4COCH{C(NCHCHNiPr)}) and NaN(TMS)2 at a molar ratio of 1:4:1 in THF at room temperature
afforded the corresponding novel enol-functionalized N-heterocyclic carbene (NHC) lanthanide amides
L2LnN(TMS)2 (Ln ¼ Y (1), Nd (2), Sm (3), Yb (4)) in 37e40% yields. Molecular structures of 1e4 were
determined by X-ray structure analyses. All complexes adopt monomeric structures where each 5-
coordinated metal is coordinated by two NHC ligands and one amido group.in distorted trigonal
bipyramid geometry. All complexes, especially Yb complex (4), were found to be highly active pre-
catalysts for the catalytic addition of amines to carbodiimides giving guanidines. The system with 4
shows good functional group tolerance and a wide scope of amines including primary and secondary
cyclic amines.
Received 17 January 2012
Received in revised form
27 March 2012
Accepted 5 April 2012
Keywords:
Enol-functionalized N-heterocyclic carbene
Lanthanide
Amide complex
Catalysis guanylation
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
polymerization of isoprene upon activation with AlR3 and [Ph3C]
[B(C6F5)4] [17].
N-heterocyclic carbene ligands (NHC)s with a pendant anionic
group have attracted increasing attention in organolanthanide
chemistry [1], as these ligands are hemilable and covalently bond to
metal with the tunable electronic and steric factors, which has
potential in homogeneous catalyzes. Several anionic-functionalized
NHC ligands were explored including alkoxo- [2,3], aryloxo- [4e7],
amido- [2,7e9], indenyl- [10], fluorenyl- [11], xylene- [12], salicy-
laldiminato- [13] and 2,4,6-trimethylphenyl- [14,15] functionalized
NHCs, and various lanthanide derivatives supported by these NHCs
ligands were successfully synthesized and characterized [2e15].
Moreover, the alkoxy-functionalized NHC yttrium amide complex
was reported to be a bifunctional catalyst of a combination of Lewis
acid and base functionalities for lactide polymerization [2]. The
lanthanide bis(alkyl)complexes bearing either fluorenyl- or
indenyl- functionalized NHC were found to be efficient catalysts for
syndiotactically enriched highly 3,4-selective polymerization of
isoprene in the presence of aluminum alkyls and organoborate [16]
and for the homo- and co-polymerization of ethylene and norbor-
nene [11], and the CCC-pincer 2,6-xylenyl bis(carbene) lanthanide
dibromides exhibited high activity and cis-1,4 selectivity in the
Enol-functionalized NHC ligands, which are another kind of O-
containing anionic-functionalized NHCs, have the advantages of
easy to prepare and enable enhance the stability of metal-NHC
bonding through the formation of six-membered metal-heterocy-
cles. These ligands have been successfully used in the syntheses of
NHC complexes of late-transition metals Pd [18,19], Ni [18,20,21]
and Fe [22]. In continuation of our work [4e7,13] we were inter-
ested in understanding the potential of this kind of NHC ligands in
the chemistry of organolanthanide metals. For this purpose, we
designed and synthesized lanthanide amide complexes bearing the
enol-functionalized NHC ligand
L
(L
¼
4-OMe-C6H4COCH
{C(NCHCHNiPr)}) and evaluated the catalytic activity of these new
amide complexes for catalytic addition of amines to carbodiimides.
Here we report details of the synthesis and molecular structures of
new complexes L2LnN(TMS)2 (Ln ¼ Y (1), Nd (2), Sm (3), Yb (4)) and
the catalytic behavior of 1e4.
2. Results and discussion
2.1. Synthesis and structural characterization of L2LnN(TMS)2
(Ln ¼ Y (1), Nd (2), Sm (3), Yb (4))
The enol-functionalized imidazolium salt H2LBr was synthe-
sized by a published method [22]. Reaction of YCl3 with 5
* Corresponding author. Tel.: þ86 512 65880306; fax: þ86 512 65880305.
E-mail address: qshen@suda.edu.cn (Q. Shen).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.04.006

28
Z. Li et al. / Journal of Organometallic Chemistry 713 (2012) 27e34
equivalents of NaN(TMS)2 in THF at room temperature, then
treatment with two equivalents of H2LBr did not allow to isolate the
target product as pure crystals, but the powders which were
insoluble even in THF. However, decreasing the molar ratio of YCl3/
NaN(TMS)2/H2LBr from 1:5:2 to 1:4:1 led to the isolation of pink
crystals in 37% yield easily upon crystallization from toluene.
Elemental analysis of the crystals is consistent with the formula of
L2YN(TMS)2 (1) (Scheme 1). The 13C NMR spectra of the crystals
revealed the characteristic signals of the ylidene carbons at 188.37
and 187.94 ppm, which are comparable to the values reported
previously for the NHC-containing
Y complexes [9,10]. The
appearance of the characteristic signals of the carbene carbon
indicates the formation of a direct Y-Ccarbene linkage. Complex 1 was
further confirmed by an X-ray crystal structure analysis.
The success in the preparation of complex 1 promoted us to
prepare the analogous complexes with other lanthanide metals.
Thus, the similar reactions with NdCl3, SmCl3 and YbCl3 were
conducted. All reactions went smoothly to give the corresponding
complexes L2LnN(TMS)2 (Ln ¼ Nd (2), Sm (3), Yb (4)) as blue
crystals for 2, light yellow and yellow crystals for 3 and 4 in the
yields similar to that for complex 1 (Scheme 1). The Ccarbene reso-
nate in 13C NMR spectroscopy of complexes 2e4 could not be
detected as the cases for the NHC complexes of the corresponding
lanthanide metals reported previously [7,9,10,12]. The confirmation
of complexes 2e4 were unequivocally established by X-ray crystal
structure analyses.
The low yield of complexes 1e4 might be attributed to the
shortage of the amount of NaN(TMS)2 and H2LBr used. Attempts to
improve the yield by use of the right molar ratio were unsuccessful.
All reactions, which were conducted at 60 ꢀC, 0 ꢀC and ꢁ78 ꢀC,
respectively, afforded the powders, which were insoluble in normal
solvents including THF. The poor solubility of the powders pre-
vented from the purification of the product, and from the full
characterization. The reason for it has not been clarified. Although
the yields of complexes 1e4 are somewhat low, the syntheses of
1e4 are reproducible.
Complexes 1e4 are very sensitive to air and moisture, but
thermal stable. They did not decompose up to 150 ꢀC. All complexes
are freely soluble in THF and toluene, but not soluble in hexane.
Single crystals of 1e4 suitable for X-ray diffraction were
obtained by crystallization from toluene. X-ray diffraction analyses
revealed 1e4 are isostructural and each of them being a monomer
as shown in Fig.1. The selected bond lengths and angles are listed in
Table 1.
Fig. 1. Molecular structures of complexes 1e4.
to 150.41(13)o for 1, 147.70(12)o for 2, 147.90(12)o for 3, and
152.87(11)o for 4. The average Ln-Ccarbene bond lengths (2.512(5) for
1, 2.621(4) for 2, 2.581(5) for 3, 2.463(4) for 4) in 1e4 are compared
to each other when the differences in ion radius among these
metals were considered. The values can also be comparable with
those found in the related lanthanide NHC complexes [7,12,13].
The LneO and LneN bond distances in each complex fall in the
range of the Ln-alkoxide and LneN bond distances found in Ln-
alkoxide [2,3] and Ln-amide complexes [9].
2.2. Catalytic activity of complexes 1e4 for addition of amines to
carbodiimides
Guanidines are important structural motifs found in many bio-
logically and pharmaceutically active compounds. An addition of
The central metal in each complex coordinates to two chelating
enol-functionalized NHC ligands and one eN(TMS)2 group. The
coordination geometry around each 5-coordinated metal can be
best described as a distorted trigonal bipyramid with the two car-
bene carbon atoms (C(3) and C(18)) and one nitrogen atom N(5)
occupying the apical positions and the two enolate oxygen atoms at
the axial sites. The sum of the angles in the plane of Ln-C(3)-C(18)-
N(5) is 359.97(14)o for 1, 359.88(13)o for 2, 359.99(13)o for 3, and
359.99(13)o for 4 and the angles of O(1)-Ln-O(3) deviate from 180ꢀ
amine to carbodiimide provides
economical approach to multisubstituted guanidines. However,
a convenient and atom-
Table 1
Selected bond distances (Å) and angles (deg) for complexes 1e4.
1
2
3
4
Ln(1)-O(3)
Ln(1)-O(1)
Ln(1)-N(5)
Ln(1)-C(3)
Ln(1)-C(18)
2.141(3)
2.160(3)
2.261(4)
2.512(5)
2.513(4)
2.220(3)
2.247(3)
2.356(4)
2.619(4)
2.624(4)
2.206(3)
2.219(3)
2.312(4)
2.579(4)
2.584(5)
2.116(3)
2.136(3)
2.212(3)
2.453(4)
2.473(4)
O(3)-Ln(1)-O(1)
O(3)-Ln(1)-N(5)
O(1)-Ln(1)-N(5)
O(3)-Ln(1)-C(3)
O(1)-Ln(1)-C(3)
N(5)-Ln(1)-C(3)
O(3)-Ln(1)-C(18)
O(1)-Ln(1)-C(18)
N(5)-Ln(1)-C(18)
C(3)-Ln(1)-C(18)
150.40(13)
103.06(13)
106.41(13)
93.17(14)
74.80(14)
108.83(13)
75.53(13)
92.49(13)
118.85(14)
132.29(14)
147.70(12)
103.61(12)
108.35(12)
93.78(12)
72.04(12)
108.30(13)
72.48(12)
94.09(12)
121.82(13)
129.76(13)
147.90(12)
106.97(12)
105.12(12)
74.15(13)
92.36(12)
116.69(14)
92.32(13)
73.21(13)
114.80(13)
128.50(13)
152.87(11)
101.99(11)
105.08(11)
93.41(12)
76.40(12)
108.40(13)
76.64(12)
92.02(12)
118.28(13)
133.31(13)
Scheme 1. Synthesis of complexes 1e4.

Z. Li et al. / Journal of Organometallic Chemistry 713 (2012) 27e34
29
the addition reaction without a catalyst requires harsh condition.
Thus, catalytic addition of amines to carbodiimides by metal
complexes under mild conditions has attracted increasing attention
[23e43]. Lanthanide amides are one of the most efficient pre-
catalysts for this transformation [29e31]. To assess the chemistry
behavior of complexes 1e4, catalytic addition of aniline to N,N0-
either electron-withdrawing or electron-donating substituents, or
the position of the substituents at the phenyl ring (Table 3, entries
1e11). The reaction with a steric bulky amine proceeded somewhat
slowly to yield the product 6t in 71% yield after 24 h (Table 3, entry
20), which is often observed with the other lanthanide complexes
i
[29,30]. Various cyclic secondary amines could react with PrN]
diisopropylcarbodiimide (iPrN]C]NiPr) by
4
was conducted
C]NiPr and CyN]C]NCy (N,N0-dicyclohexylcarbodiimide) at
60 ꢀC affording the corresponding tetrasubstituted guanidines in
excellent yields (Table 2, entries 12e17).
under various conditions. The results are listed in Table 2.
The catalytic addition of aniline to iPrN]C]NiPr with 0.5 mol%
of 4 can proceed either in toluene or in THF at 60 ꢀC to give the
guanidine 5 in almost quantitative yield. However, the reaction in
toluene is faster than that in THF (Table 2, entries 3 and 12). The
best result was obtained when the reaction proceeded under
solvent free condition (Table 2, entry 11). The addition reaction can
also proceed at 20 ꢀC although the reaction rate is lower (Table 2,
entries 3e5). The activity of 4 is extremely high. For example, the
yield of 5 can still reached to 97% at 60 ꢀC after 36 h, even the
catalyst loading decreased to 0.1 mol% (Table 2, entry 7).
Complexes 1e3 were also effective in this reaction. The activity
of Y complex (1) is almost equal to that of Yb complex (4), whilst
the activities of Sm (3) and Nd (2) complexes were somewhat lower
than that of 4 (Table 2, entries 3, 8, 9 and 10). The active sequence of
Nd < Sm < Y w Yb observed here is opposite to the trend reported
previously for half-sandwich lanthanide metal complexes [36] and
for lanthanide amides [29e31], but consistent with that found for
the Ln(OAr)3(THF)2 reported [43]. This may be because of the more
crowded coordination sphere around the metal compare to
complexes 2 and 3, which makes the reaction between 4 and an
amine easier.
A double catalytic addition reaction of diamines to two equiv-
alents of carbodiimides is a direct method to biguanidines. Thus,
the reaction of 1,4-diaminobenzene to two equivalents of iPrN]C]
NiPr was also tried. The reaction went smoothly to yield the
biguanidines 7a in 92% yield after 0.5 h (Scheme 2. (Eq. (1))). The
same reaction with 1,3-diaminobenzene yielded the biguanidine 7b
in 93% yield after 0.5 h (Scheme 2. (Eq. (2))).
A catalytic cycle which was suggested previously [29,30,35,36]
could be proposed for the present transformation. Complex 4
reacts with an amine to yield an amide species, which reacts further
with a carbodiimide to afford the guanidinate species. Protonolysis
of the guanidinate species by another amine molecule regenerates
the amide species and releases the guanidine.
3. Experimental section
3.1. General considerations
All manipulations were performed under pure argon with
rigorous exclusion of air and moisture using standard Schlenk
techniques. Solvents were distilled from Na/benzophenone ketyl
under pure argon prior to use. H2LBr (L ¼ 4-OMe-C6H4COCH
{C(NCHCHNiPr)}) [22] and NaN(TMS)2 [44] were synthesized
according to the literature methods. Elemental analysis was
Complex 4 was then chosen as a precatalyst for the addition
reaction of various amines including primary and secondary
amines to carbodiimides at 60 ꢀC under solvent free condition.
Representative results are summarized in Table 3.
Complex 4 is a very efficient precatalyst which showed good
functional group tolerance. The reaction was not influenced by
performed by direct combustion on
a Carlo-Erba EA-1110
instrument. IR spectra were recorded on
a
Magna-IR 550
Table 2
Catalytic addition of aniline to iPrN]C]NiPr by complexes 1e4
.
Entrya
Cat.
Catalyst loading (mol%)
Temp (ꢀC)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
4
4
4
4
4
4
4
1
2
3
4
4
0.5
0.5
0.5
0.5
0.5
0.25
0.1
0.5
0.5
0.5
0.5
0.5
60
60
60
20
20
60
60
60
60
60
60
60
0.5
1
3
79
82
98
60
>99
98
97
>99
23
35
98
4
12
24
36
3
3
3
9
10
11c
12d
0.25
24
>99
a
General condition: in 1 mL toluene.
Isolated yield.
b
c
Solvent free.
d
i
The concentration of PrN]C]NiPr is 1.9 mol/L in THF.

30
Z. Li et al. / Journal of Organometallic Chemistry 713 (2012) 27e34
Table 3
Catalytic addition of amines to carbodiimides by complex 4
.
Entrya
R
Amines
Time (h)
0.5
6
Product structure
Yield (%)b
1
iPr
6a
>99
2
3
Cy
iPr
0.5
6b
6c
94
97
2
4
5
Cy
iPr
2
6d
6e
>99
0.5
98
6
7
Cy
iPr
0.5
0.5
6f
96
95
6g
8
9
Cy
iPr
0.5
0.5
6h
6i
91
>99

Z. Li et al. / Journal of Organometallic Chemistry 713 (2012) 27e34
31
Table 3 (continued )
Entrya
R
Amines
Time (h)
6
Product structure
Yield (%)b
10
iPr
2
6j
96
11
12
iPr
12
12
6k
82
95
iPr
6l
13
14
Cy
iPr
12
12
6m
6n
96
93
15
16
17
18
Cy
iPr
Cy
iPr
12
12
12
4
6o
6p
6q
6r
94
96
92
98
19
Cy
6
6s
6t
97
71
20
iPr
24
a
General condition: solvent free, catalyst loading is 0.5 mol %.
Isolated yield.
b
spectrometer as KBr pellets. 1H NMR and 13C NMR were
measured on a VNMRS-300 and an INOVA-400 spectrometer in
d-C6D6. Melting points were measured in sealed Ar-filled capil-
lary tubes and are uncorrected.
3.2. Preparation of L2YN(TMS)2 (1)
The solution of NaN(TMS)2 (8.58 mL, 1.17 M, 10.04 mmol) in THF
was slowly added into the THF solution of anhydrous YCl3 (0.49 g,

32
Z. Li et al. / Journal of Organometallic Chemistry 713 (2012) 27e34
NaN(TMS)2 (8.58 mL, 1.17 M, 10.04 mmol) and H2LBr (0.85 g,
2.51 mmol) were used. Yellow crystals of complex 4 were isolated
(0.72 g, 40%). m.p.: 148e150 ꢀC. Anal. Calc. for C36H52N5O4Si2Yb: C,
50.99; H, 6.18; N, 8.26%. Found: C, 49.99; H, 6.08; N, 7.79%. IR (KBr,
cmꢁ1): 3490 (w), 2955 (m), 2835 (w), 1605 (s), 1508 (s), 1423 (m),
1252 (s), 1160 (s), 1097 (w), 1032 (m), 934 (m), 843 (s), 744 (m), 683
(m), 504 (s).
3.6. General procedure for the direct synthesis of guanidines from
the reaction of aromatic amines with carbodiimides catalyzed by
L2LnN(TMS)2 (Ln ¼ Y, Nd, Sm, Yb)
A 10.0 mL Schlenk tube under dried argon was charged with
L2LnN(TMS)2 (0.005 equiv.), aromatic amines (1.0 equiv.), and
toluene (1 mL). To the mixture was added carbodiimides (1.0
equiv.). The resulting mixture was stirred at 20 ꢀC or at 60 ꢀC for
a fixed interval, as shown in Tables 2or 3. Then the reaction mixture
was hydrolyzed by water (1 mL), extracted with dichloromethane
(3 ꢂ 10 mL), dried over anhydrous Na2SO4, and filtered. After the
solvent was removed under reduced pressure, the final products
were further purified by washing with diethyl ether or hexane.
Scheme 2. Catalytic addition of diamines to a carbodiimide.
2.51 mmol) at room temperature. The reaction mixture was stirred
over 12 h, then H2LBr (0.85 g, 2.51 mmol) was added and stirred for
additional 36 h. The suspension was centrifuged to remove the NaCl
and evaporated to dryness and extracted with about 15 mL of
toluene. Concentrating the toluene solution and cooling at 0 ꢀC led
to the isolation of pink crystals of 1 (0.71 g, 37%) after several days.
m.p.: 151e153 ꢀC. Anal. Calc. for C36H52N5O4Si2Y: C, 56.60; H, 6.86;
N, 9.17%. Found: C, 56.92; H, 6.89; N, 8.74%. 1H NMR (C6D6,
3.7. General procedure for the direct synthesis of guanidines from
the reaction of secondary amines with carbodiimides catalyzed by
L2YbN(TMS)2
400 MHz):
d
(ppm), 7.73 (d, 4H, J ¼ 8.4, 4 ꢂ PhH), 6.82 (d, 4H, J ¼ 8.4,
4 ꢂ PhH), 6.21 (s, 2H, 2 ꢂ C]CH), 6.18 (s, 2H, 2 ꢂ NCH), 6.10 (s, 2H,
2 ꢂ NCH), 5.49e5.34 (m, 2H, 2 ꢂ (CH3)2CH), 3.30 (s, 6H, 2 ꢂ CH3O),
1.15 (s, 12H, 2 ꢂ (CH3)2CH), 0.30 ppm (s, 18H, 2 ꢂ Si(CH3)3). 13C NMR
A 10.0 mL Schlenk tube under dried argon was charged with
complex 4 (0.005 equiv.) and secondary amines (1.0 equiv.). To this
mixture was added carbodiimides (1.0 equiv.). The resulting
mixture was stirred at 60 ꢀC for the desired time, as shown in
Table 3. The reaction mixture was then hydrolyzed with water
(0.5 mL), extracted with hot hexane (3 ꢂ 15 mL), dried over anhy-
drous Na2SO4, and filtered. After the solvent was removed under
vacuum, the final products were obtained.
(C6D6, 101 MHz): d (ppm), 188.37, 187.94 (Y-Ccarbene), 159.71 (OeC]
C), 151.90 (Ar), 151.88 (Ar), 134.11(Ar), 127.17(Ar), 120.14 (NC]CN),
113.61 (NC]CN), 101.78 (C]CN), 54.79 (OCH3), 52.02 (CH(CH3)2),
23.88 (CH(CH3)2), 5.29, 4.84, 2.58 (Si(CH3)3). IR (KBr, cmꢁ1): 3428
(w), 2955 (m), 2835 (w), 1605 (s), 1507 (s), 1423 (m), 1399 (m), 1247
(vs), 1157 (vs), 1099 (m), 1033 (s), 934 (s), 840 (s), 739 (m), 683 (w),
504 (w).
3.8. Synthesis of N,N0-1,4-phenylenebis (N,N0-diisopropyl-
guanidine) (7a)
3.3. Preparation of L2NdN(TMS)2 (2)
A 10 mL Schlenk tube was charged with complex 4 (0.0136 g,
0.016 mmol), N,N0-diisopropylcarbodiimide (1.0 mL, 6.42 mmol)
and 1,4-diaminobenzene (0.3469 g, 3.21 mol) under dried argon.
The resulting mixture was stirred at 60 ꢀC for 0.5 h. The reaction
mixture was extracted with ether and filtered to give a clean
solution. After removing the solvent under vacuum, the residue
was recrystallized in ether to provide a white solid 7a (1.0650 g,
Complex 2 was prepared by the procedure described for the
synthesis of complex 1, except NdCl3 (0.63 g, 2.51 mmol),
NaN(TMS)2 (8.58 mL, 1.17 M, 10.04 mmol) and H2LBr (0.85 g,
2.51 mmol) were used. Blue crystals of complex 2 were isolated
(0.72 g, 36%). m.p.: 154e156 ꢀC. Anal. Calc. for C36H52N5O4Si2Nd: C,
52.78; H, 6.40; N, 8.55%. Found: C, 52.69; H, 6.21; N, 8.38%. IR (KBr,
cmꢁ1): 3380 (w), 2955 (vs), 2894 (w), 1606 (w), 1446 (s), 1399 (m),
1250 (vs), 1181 (s), 1157(s), 1062 (m), 935 (s), 842 (s), 7784 (m), 685
(m), 504 (m).
92% yield). 1H NMR (300 MHz, CDCl3):
d (ppm), 6.76 (s, 4H), 3.75 (br,
4H),1.15e1.13 (d, 24H). 13C NMR (75 MHz, CDCl3):
d (ppm), 151.2,
143.9, 124.7, 43.4, 23.5.
3.9. Synthesis of N,N0-1,3-phenylenebis (N,N0-diisopropyl-
3.4. Preparation of L2SmN(TMS)2 (3)
guanidine) (7b)
Complex 3 was prepared by the procedure described for the
synthesis of complex 1, except SmCl3 (0.64 g, 2.49 mmol),
NaN(TMS)2 (8.51 mL, 1.17 M, 9.96 mmol) and H2LBr (0.85 g,
2.51 mmol) were used. Light yellow crystals of complex 3 were
isolated (0.72 g, 38%). m.p.: 151e153 ꢀC. Anal. Calc. for
C36H52N5O4Si2Sm: C, 52.39; H, 6.35; N, 8.49%. Found: C, 52.47; H,
6.32; N, 8.26%. IR (KBr, cmꢁ1): 3442 (w), 2955 (m), 2836 (w), 1604
(s), 1506 (s), 1423 (m), 1252 (s), 1160 (s), 1097 (w), 1032 (m), 934
(m), 843 (s), 744 (m), 683 (m), 504 (s).
Product 7b was obtained by the procedure described for the
synthesis of 7a, except complex 4 (0.0094 g, 0.011 mmol), N,N0-
diisopropylcarbodiimide (0.69 mL, 4.43 mmol) and 1,3-dia-
minobenzene (0.2398 g, 2.22 mol) were used. And a white solid 7b
was isolated (1.0764 g, 93% yield). 1H NMR (300 MHz, CDCl3):
d
(ppm), 7.15e7.10 (t, J ¼ 7.8 Hz, 1H), 6.46e6.43 (d, J ¼ 7.7 Hz, 2H),
6.38 (s, 1H), 3.73 (m, 4H), 1.15e1.13 (d, J ¼ 6.4 Hz, 24H). 13C NMR
(75 MHz, CDCl3): d (ppm), 151.4, 150.1, 129.9, 118.8, 117.3, 43.3, 23.4.
3.5. Preparation of L2YbN(TMS)2 (4)
3.10. X-ray crystallography
Complex 4 was prepared by the procedure described for the
synthesis of complex 1, except YbCl3 (0.70 g, 2.51 mmol),
A suitable single crystal was sealed in a thin-walled glass
capillary for X-ray structural analysis. Diffraction data were

Z. Li et al. / Journal of Organometallic Chemistry 713 (2012) 27e34
33
Table 4
X-ray crystallographic data for complexes 1e4.
1$C7H8
2$C7H8
3$1.5C7H8
4$C7H8
Formula
Mol wt
Temp (K)
C43H60N5O4Si2Y
856.05
223(2)
C43H60N5NdO4Si2
911.38
223(2)
C46.50H64N5O4Si2Sm
963.56
223(2)
C43H60N5O4Si2Yb
940.18
223(2)
l
(Å)
0.71075
0.71075
0.71075
0.71075
Cryst syst
Space group
a (Å)
b (Å)
c (Å)
Triclinic
ꢀ
Pı
Triclinic
ꢀ
Pı
Triclinic
ꢀ
Pı
Triclinic
ꢀ
Pı
13.4258(10)
14.3307(7)
14.4583(3)
61.918(8)
68.731(9)
85.954(12)
2270.1(2)
2, 1.252
13.3828(10)
14.4345(8)
14.4906(2)
61.855(8)
69.664(10)
85.900(12)
2299.9(2)
2, 1.316
13.9743(2)
14.6298(11)
15.5233(10)
85.391(11)
64.371(8)
61.799(8)
2490.8(2)
2, 1.285
13.4293(8)
14.2974(7)
14.401
61.923(6)
68.556(6)
86.069(8)
2252.73(17)
2, 1.386
2.173
a
b
g
(deg)
(deg)
(deg)
V (Å3)
Z (Å3), Dcalcd (g/mL)
m
(mmꢁ1
)
1.381
1.224
1.270
F(000)
Cryst size (mm)
range (deg)
Total no. of rflns
no. of indep rflns
Rint
904
946
1000
966
0.35 ꢂ 0.25 ꢂ 0.20
3.02e25.50
19,526
8403
0.0646
0.60 ꢂ 0.40 ꢂ 0.30
3.00e25.50
19,640
8500
0.0451
0.60 ꢂ 0.40 ꢂ 0.20
3.13e25.50
20,254
9201
0.0460
0.60 ꢂ 0.50 ꢂ 0.30
3.04e25.50
19,246
8334
0.0500
q
GOF
1.038
1.091
1.145
1.028
R1, wR2 (I > 2
R1, wR2 [all data]
s
(I))
0.0708, 0.1681
0.0992, 0.1854
0.0482, 0.1137
0.0570, 0.1195
0.0519, 0.1066
0.0597, 0.1107
0.0373, 0.0787
0.0420, 0.0806
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collected on a Rigaku Mercury CCD area detector at 223(2) K. The
structure was solved by direct methods and refined by full-matrix
least-squares procedures based on jFj2. All non-hydrogen atoms
were refined with anisotropic displacement coefficients. Hydrogen
atoms were treated as idealized contributions. The structures were
refined using SHELXTL-97 programs Crystal data, collection details
and main refinement parameters are given in Table 4.
4. Conclusion
The novel enol-functionalized NHC lanthanide amide
complexes L2LnN(TMS)2 (Ln ¼ Y (1), Nd (2), Sm (3), Yb (4)) were
synthesized and structurally characterized. Complex 4 was found to
be an excellent precatalyst for catalytic addition of primary and
secondary cyclic amines to carbodiimides, leading to efficient
formation of a series of guanidine derivatives. The catalytic system
has a wide scope of substrates.
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3193e3199.
Acknowledgements
We are grateful to the National Natural Science Foundation of
China (Grant Nos. 20972107, 21132002 and k110906111).
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Appendix A. Supplementary material
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CCDC 860025 (for 1), -860026 (for 2), -860027 (for 3) and
-860028 (for 4) contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[29] S. Zhou, S. Wang, G. Yang, Q. Li, L. Zhang, Z. Yao, Z. Zhou, H. Song, Organo-
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