Bis-aryloxo-functionalized NHC complexes of ytterbium(III): Syntheses and structures of Yb[O-4,6-tBu2-C6H2-2-CH2{C(RNCHCHN)}]2N(iPr)2 (R = iPr, Me)

Article abstract of DOI:10.1016/j.jorganchem.2006.04.029

The transamination of anionic homoleptic amido ytterbium complex, LiYb[N(i-Pr)₂]₄ with aryloxo-functionalized N-heterocyclic carbene (NHC) precursor, HO-4,6-di-^tBu-C₆H₂-2-CH₂{CH[i-Pr-NCHCHN

Full text of DOI:10.1016/j.jorganchem.2006.04.029

Journal of Organometallic Chemistry 691 (2006) 3383–3390
www.elsevier.com/locate/jorganchem
Bis-aryloxo-functionalized NHC complexes of ytterbium(III):
Syntheses and structures of Yb[O-4,6-tBu2-C6H2-2-
CH2{C(RNCHCHN)}]2N(iPr)2 (R = iPr, Me)
a
a
a
a
Zhi-Guo Wang , Hong-Mei Sun , Hai-Sheng Yao , Ying-Ming Yao ,
a,b,
a
Qi Shen
*, Yong Zhang
a
College of Chemistry and Chemical Engineering, Suzhou University, Hengyi Road, Suzhou industrial Park, Suzhou 215123, PR China
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Science, Shanghai 200433, PR China
b
Received 15 March 2006; received in revised form 10 April 2006; accepted 20 April 2006
Available online 29 April 2006
Abstract
The transamination of anionic homoleptic amido ytterbium complex, LiYb[N(i-Pr)2]4 with aryloxo-functionalized N-heterocyclic
carbene (NHC) precursor, HO-4,6-di-tBu-C6H2-2-CH2{CH[i-Pr-NCHCHN]}Cl (H2LCl) 1 and HO-4,6-di-tBu-C6H2-2-CH2{CH[Me-
NCHCHN]}Cl (H2L0Cl) 2, and BuLi in 1:2:1 molar ratio in THF at 0 °C afforded the first bisaryloxo- NHC monoamido ytterbium com-
plexes, L2Yb[N(i-Pr)2] 3 and L02Yb½Nði-PrÞ2ꢀ 4, respectively. The same reactions in the molar ratio of 1:1 without BuLi yields also the
complex 3 and 4, not the bis-amido mono aryloxo-NHC complex {LYb[N(i-Pr)2]2} and {L0Yb[N(i-Pr)2]2}. The in situ low-temperature
reaction of 2 with two equivalents of BuLi, followed by addition of one equivalent of YbCl3 in THF does not afford the expected
LYbCl2, instead, [Li(DME)3][YbCl4(DME)] 5 and a dimeric imidazole-aryloxo lithium {[O-4,6-di-tBu-C6H2-2-CH2{CH(MeNC-
HCHNH)}]Li(THF)}2 6 which results from the 1,2-benzyl migration in N-heterocyclic carbene, are obtained. Complexes 3, 4, 5 and
6 have been characterized by elemental analysis and X-ray crystallography, and by NMR spectroscopy for 6.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Bis-aryloxo-functionalized; NHC complexes; Ytterbium(III)
1. Introduction
2001 [3]. The reason for it may be attributed to the lack
of NHC derivatives suitable for these f-block metals, as
the neutral ligands in these metals complexes are prone
to dissociation. Recently, a chelate NHC ligand that links
an anionic functionalized group has been developed and
shows the potential in the synthesis of lanthanide-NHC
complexes. The first amido-functionalized NHC complexes
of trivalent samarium(III), yttrium(III) [4a], cerium(III)
[4b] and neodymium [4c] were synthesized.
Aryloxo (alkoxo) groups, as alternatives to cyclopenta-
dienyl anions, have widely been used in organometallic
complexes of transition metals and lanthanides metals.
The aryloxo (alkoxo)-functionalized NHCs have been
found their applications in the complexes of copper [5a],
silver [5b], titanium [5c] and palladium [5d]. Recently, we
designed and synthesized two novel aryloxo-tethered
The application of N-heterocyclic carbenes (NHCs) as
ligands in organometallic chemistry has attracted increas-
ing attention, as their strong r-donating properties and
easy to tune their steric and electronic features by the sub-
stituents on the nitrogen atoms [1]. The vast majority of
NHC complexes of late transition metals have been
reported [1a,2], while the chemistry of NHC systems of lan-
thanides elements is considerably less developed. Only the
lanthanide NHC complexes in which the NHC coordinates
as a dative donor solvent molecule were synthesized until
*
Corresponding author. Tel.: +86 512 65880306; fax: +86 512
65880305.
E-mail address: qshen@suda.edu.cn (Q. Shen).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.04.029

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Z.-G. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 3383–3390
NHC precursors, (4,6-di-tert-butyl-2-hydroxybenzyl)N-iso-
propylimidazolium chloride (H2LCl) and 4,6-di-tert-butyl-
2-hydroxybenzyl)N-methylimidazolium chloride (H2L0Cl),
and successfully synthesized the corresponding NHC com-
plexes of Ni(II) [6a] and Fe(II) [6b]. However, no lantha-
nide complex with aryloxo (alkoxo)-functionalized NHC
ligand was found in the literature up to date. Moreover,
aryloxo lanthanides derivatives have shown good catalytic
activities in homogeneous catalysis including ethylene poly-
merization [7a], ring-opening polymerization of caprolac-
tones [7b], and organic synthesis as well [7c,7d]. Studying
on the synthesis and chemical behavior of the analogue
complexes of aryloxo-lanthanides with NHC should be
helpful for further understanding the effects of NHC in
homogeneous reactions catalyzed by organolanthanide
complexes. Accordingly, we put our attention to the chem-
istry of lanthanide complexes with aryloxo-functionalized
NHC systems. In this paper we report the synthesis of
the first bis-aryloxo-tethered NHC complex of ytterbium,
methyl-4,6-di-tert-butylphenol reacted with N-isopropy-
limidazole and N-methylimidazole, respectively, in THF
at room temperature for 0.5 h afforded the corresponding
1 and 2 in the yield of 84% and 98% (Scheme 1).
The transamination reaction was used here for the syn-
thesis of target complex to avoid the isolation of free NHC.
A neutral triamide complex of lanthanide Ln[(NSiMe3)2]3
has already shown to be the desired reagent [4]. However,
the synthesis of a neutral lanthanide triamides with other
amido groups, especially with less bulky amido groups, is
difficult because of the demand of high coordination num-
ber of lanthanide metals and an anionic complex
[MLn(NR2)4] (M = Li, Na) is often obtained instead. Con-
sidering the fact that the part of MNR2 in [MLn(NR2)4]
may be used as a reagent for the deprotonation of imidazo-
lium salt, an anionic amide complex was tried to use as a
starting material instead of a neutral one here. Thus, anio-
nic complex of ytterbium LiYb[N(i-Pr)2]4 was synthesized
by the reaction of YbCl3 with four equivalents of LiN(i-
Pr)2 [8], and used in sequential reaction. Based on the lack
of bis(NHC) complex of lanthanide in the literature, the
synthesis of bis-NHC complex of Yb was first tried. The
reaction of LiYb[N(i-Pr)2]4 with 1 and BuLi in the molar
ratio of 1:2:1 works cleanly in THF at 0 °C for 4 h, then
at room temperature for 36 h. After workup, the yellow
crystals are isolated in 70% yield, which are fully character-
ized to be the bis-phenoxo-NHC complex of Yb 3. The
same reaction with 2 affords the analogue complex 4 in
78% yield (Scheme 2). What we should emphasize is that
even the reaction proceeds at 0 °C, the desired NHC com-
plexes of Yb can still be prepared.
L2Yb[N(i-Pr)2] and L02Yb½Nði-PrÞ ꢀ, by the transamination
2
reaction of LiYb[N(i-Pr)2]4 with NHC precursors, H2LCl
and H2L0Cl, and LiBu and the 1,2-benzyl migration in aro-
matic carbene.
2. Results and discussion
2.1. Syntheses of L2Yb[N(i-Pr)2] 3 and L02Yb N i-Pr
4
2
The chelate NHC precursors, [HO-4,6-di-tBu-C6H2-2-
CH2{CH(RNCHCHN)}Cl] (R = i-Pr, 1, H2LCl; Me, 2,
H2L0Cl), are synthesized easily via nucleophilic attack of
a 1-alkylimidazole on an alkyl halide. Thus, 2-chloro-
An attempt to synthesize mono-carbene complexes of
Yb by the reaction of LiYb(Ni-Pr2)4 with 1 and 2, respec-
tively, in a 1:1 molar ratio without BuLi in THF at 0 °C
failed and the same bis-NHC complexes of 3 and 4 were
isolated in reasonable lower yield (27% for 3 and 32%,
for 4). It seems that the mono-NHC complex is not stable
enough in the present case, and prone to react further with
the second molecule of 1(2). The situation is different from
those for the reaction of Ln[(NSiMe3)2]3 with amido-func-
tionalized NHC published, where mono-NHC complex of
OH
Cl
OH
R
tBu
tBu
Cl
N
N
R
N
N
tBu
tBu
R=iPr(1), Me(2)
Scheme 1.
tBu
NiPr2
Yb NiPr2
O
N R
N
tBu
LiYb[NiPr2]4/THF
R=iPr.Me
Cl
OH
R
tBu
tBu
NiPr2
N
Yb
O
N
2
0¡æ
N R
tBu
N
tBu
R=iPr(3).Me(4)
1/2LiYb[NiPr2]4/THF
1/2n-BuLi
Scheme 2.

Z.-G. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 3383–3390
3385
lanthanide was obtained in high yield [4]. The reason for
the difference observed between this system and those
reported in Ref. [4] may be due to difference in steric hin-
drance of the ligand systems. The ligand combination in
Ref. [4] is apparently more sterically demanding, thus pre-
venting ligand redistribution.
Complexes 3 and 4 are very sensitive to air and mois-
ture. The paramagnetism of the complexes precludes 13C
NMR spectroscopic identification of the carbene carbon.
Yb–Ccarbene bond in solution is inferred from strongly
shifted CH backbone resonances of the heterocycle. The
same situation is also observed in the case of amido-func-
tionalized NHC complex of Sm [4a,4c]. The further confir-
mation of the syntheses of 3 and 4 was made by X-ray
crystal structure analysis.
The single crystals of 3 and 4 suitable for structural
analysis were obtained by recrystallization from toluene
at 0 °C. The details crystallographic data were collected
in Table 1. The molecular structures were shown in Figs.
1 and 2, respectively, and the selected bond lengths and
angles are listed in Table 2.
Complexes 3 and 4 are isostructural. The central metal is
coordinated to two O anions and two Ccarbene atoms (O(1,
2), C(8, 29) for 3 and O(1, 2), C(8, 27) for 4) of two phe-
noxo-NHC ligands and N(5) atom of N(i-Pr)2 group,
adopting a distorted trigonal-bipyramidal geometry in
which O(1), O(2) and N(5) occupy the equatorial sites,
while, two C atoms (C(8), C (29) for 3 and C(8), C(27)
for 4) axial. The equatorial angles of O(1)–Yb(1)–O(2),
O(1)–Yb(1)–N(5), and O(2)–Yb(1)–N(5) are 106.1(2)°,
130.1(2)°, and 123.8(2)° for 3, and 109.2(1)°, 124.6(1)°,
and 126.2(1)° for 4, respectively, which deviate from the
Fig. 1. ORTEP diagram of complex 3 showing atom numbering scheme.
Thermal ellipsoids are drawn at the 20% probability level. Hydrogen
atoms are omitted for clarity.
ideal angle of 120°. The axial angle C(8)–Yb(1)–C(29) in
complex
3 and C(8)–Yb(1)–C(27) in complex 4 is
162.3(2)° and 159.6(1)°, respectively, which is distinctly
non-linear. For both of 3 and 4, the two carbene ligands
bind to Yb asymmetrically, which distorted by the Yb–
C–N chelate angles 118.5(2)° and 138.1(5)° for one NHC
Table 1
Details of the crystallographic data and refinements for complexes 3, 4, 5, and 6
3 Æ toluene
55H84N5O2Yb
1020.3
193(2)
Orthorhombic
Pbca
4 Æ 1.5toluene Æ 0.5THF
5
6 Æ 4THF
Empirical formula
Fw
C
C56.50H84N5O2.50Yb
1046.33
193(2)
Monoclinic
C2/c
1 26.371(2)
21.438(2)
21.432(2)
90
111.418(2)
90
11279.4(17)
8
1.232
1.701
4384
C16H40Cl4LiO8Yb
682.26
193(2)
Monoclinic
P21/n
15.027(4)
13.867(3)
14.870(4)
90
113.161(7)
90
2848.9(12)
4
C58H94Li2N4O6
957.25
173(2)
Temperature
Crystal system
Space group
Triclinic
ꢀ
P1
˚
a (A)
8.652(2)
22.730(3)
25.989(4)
90
90
90
11018(3)
8
1.230
1.7391
4280
9.28(4)
10.286(3)
15.532(5)
76.15(2)
84.74(3)
86.45(3)
1425.8(9)
1
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
Density (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
1.591
0.898
1364
1.115
0.070
524
)
Reflections collected
Observed reflections
Unique reflections
Parameters refined
R [I > 2r(I)]
36474
7311
10004
566
0.0664
0.1135
1.144
55105
9253
10305
595
0.0382
0.0947
1.090
26677
4064
5196
13629
2700
5174
280
325
0.0718
0.1331
1.151
0.0757
0.1945
0.959
Rw
GOF on F2

3386
Z.-G. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 3383–3390
Fig. 2. ORTEP diagram of complex 4 showing atom numbering scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen and butyl
carbon atoms are omitted for clarity.
˚
˚
and 2.491(4) A (average Yb–Ccarbene distance of 2.487 A)
Table 2
˚
˚
˚
in 4 are shorter than 2.526(7) A and 2.543(7) A (average
Yb–Ccarbene distance of 2.535 A) found in 3. This may con-
Selected bond lengths (A) and angles (°) for 3 and 4
Complex 3
˚
tribute to the more bulky isopropyl group than methyl
group. The average Yb–Ccarbene distance of 2.487 A is
Yb–O(2)
Yb–N(5)
Yb–C(8)
O(2)–C(22)
N(1)–C(9)
N(2)–C(8)
2.094(4)
2.198(6)
2.543(7)
1.333(7)
1.394(8)
1.352(8)
Yb–O(1)
2.116(4)
2.526(7)
1.324(7)
1.357(9)
1.477(8)
1.373(9)
˚
Yb–C(29)
O(1)–C(1)
N(1)–C(8)
N(1)–C(7)
N(2)–C(10)
shorter than the monodentate Yb–Ccarbene distance of
˚
2.552(4) A [3b]. The values can compared with
˚
˚
˚
2.501(5) A, 2.588(2) A, 2.699(2) A [4,5], and 2.656(5) [4c]
for the complexes of Y, Sm, Ce(III), and Nd, respectively,
when the differences in ionic radii between Yb and each of
these metals are considered. The Yb–Nisopropyl bond dis-
O(2)–Yb–O(1)
O(1)–Yb–N(5)
O(1)–Yb–C(29)
O(2)–Yb–C(8)
N(5)–Yb–C(8)
N(1)–C(8)–Yb
106.10(18)
130.1(2)
87.26(19)
85.4(2)
100.0(2)
118.5(5)
O(2)–Yb–N(5)
O(2)–Yb–C(29)
N(5)–Yb–C(29)
O(1)–Yb–C(8)
C(29)–Yb–C(8)
N(2)–C(8)–Yb
123.8(2)
84.5(2)
97.8(2)
81.51(19)
162.3(2)
138.1(5)
˚
tance of 2.198(6) A in 3 is almost consistent with 2.206(3)
˚
A in 4. These values are comparable with the average value
˚
of 2.208 A, in anionic homoleptic ytterbium complex of
˚
LiYb[N(i-Pr)2]4 [8]. The Yb–O bond lengths of 2.116(4) A
(Yb–O(1)) and 2.094(4) A (Yb–O(2)), the average value
Complex 4
Yb–O(2)
Yb–N(5)
Yb–C(27)
O(2)–C(20)
N(1)–C(9)
N(2)–C(8)
˚
2.146(3)
2.206(3)
2.491(4)
1.331(5)
1.382(5)
1.361(5)
Yb–O(1)
Yb–C(8)
O(1)–C(1)
N(1)–C(8)
N(1)–C(7)
N(2)–C(10)
2.147(3)
2.483(4)
1.333(5)
1.355(5)
1.467(5)
1.375(6)
˚
˚
of 2.105 A, in3 is somewhat shorter than 2.146(3) and
˚
2.147(3) A, average distance of 2.146 A in 4. The Yb–O
˚
˚
bond length of 2.105 A for 3 is comparable with 2.08 A
found in five-coordinated complex of Yb(OC6H3Ph2-
˚
2,6)3(THF)2 [9], while 2.146(3) A for 4 is somewhat larger.
O(2)–Yb–O(1)
O(1)–Yb–N(5)
O(1)–Yb–C(8)
O(2)–Yb–C(27)
N(5)–Yb–C(27)
N(1)–C(8)–Yb
109.22(10)
126.15(12)
80.60(12)
80.44(12)
100.65(13)
117.5(3)
O(2)–Yb–N(5)
O(2)–Yb–C(8)
N(5)–Yb–C(8)
O(1)–Yb–C(27)
C(8)–Yb–C(27)
N(2)–C(8)–Yb
124.63(12)
87.15(11)
99.73(14)
88.23(11)
159.59(14)
138.0(3)
2.2. Metalation reaction of YbCl3 with the reaction solution
of 2 and BuLi
NHC lanthanide halides are the useful precursors for the
further transformations and metalation reaction of transi-
tion metal halides with the corresponding alkali metal salt
is the common synthetic pathway for theses complexes. So,
the synthesis of LYbCl2 is tried by the reaction of YbCl3
ligand and 120.9(5)° and 136.2(5)° for the other NHC
ligand in 3, and 117.3(3)°, 137.4(3)° and 117.5(3)°,
138.0(3)° in 4. The Yb–Ccarbene distances of 2.483(4) A
˚

Z.-G. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 3383–3390
3387
with in situ generated LLi. Thus, the in situ reaction of 2
with two equivalents of BuLi at ꢁ78 °C, followed by addi-
tion to one equivalent of YbCl3 in THF was carried out.
After workup, a red solution was obtained which yielded
the first crop of red crystals by crystallization from the mix-
ture of toluene/DME. The mother liquor was evaporated
to dry and the residue was extracted by THF. The THF
solution was crystallized at ꢁ10 °C to afford the second
crop of colorless crystals. The red crystals were character-
ized by X-ray crystal structure analysis to be an ion pair
complex of [YbCl4(DME)]ꢁ[Li(DME)3]+ 5, while the col-
orless crystals to be unexpected dimeric THF-solvated
imidazole-phenoxo lithium, {[O-4,6-di-tBu-C6H2-2-CH2-
{CH(i-PrNCHCHNH)}]Li(THF)}2 6 (Scheme 3). The fur-
ther study indicates that the reaction of BuLi with 2
without YbCl3 under the same conditions also yields 6.
The molecular structures of 5 and 6 are shown in Figs. 3
and 4. The selected bond lengths and angles are listed in
Table 3.
further reaction. In complex 6 two molecules of [O-4,6-
di-tBu-C6H2-2-CH2{CH(MeNCHCHNH)}]Li(THF) con-
nected asymmetrically by two bridged O atoms. Each Li
ion coordinates to two O atoms and one N atom from phe-
noxo-tethered imidazole and one O atom from a free THF
to form a tetrahedral geometry. The Li–O bond lengths of
˚
1.879(5) and 1.913(5) A, respectively, are comparable with
[(Ph2P(O)N(CH2Ph)CH3)LiOC6H2-2,6-{C(CH3)3}2-4-CH3]2
˚
[10]. The bond lengths of Li–N bonds are 2.048(6) A (Table
3), which lay in the range of dative Li–N bond lengths. It is
obvious that complex 6 results from the 1,2-migration of
the benzyl group from nitrogen to the carbene center of
the transient derivative. The 1,2-silyl migration from nitro-
gen to carbene center has already been reported [11]. Very
recently, the 1,2-benzyl migration was also mentioned in
the synthesis of titanium NHC complexes incorporating
an imidazolium-linked bis(phenol) [5c], however, the
details has not been presented. The failure in the synthesis
of NHC ytterbium chloride directly by the metalation reac-
tion might be supposed that the competition between two
reactions, reactions of YbCl3 with LiCl and with the tran-
sient lithium carbene, exists, and the former reaction
should be much favorable under the conditions used. The
The central metal Yb in complex 5 coordinates to four
Cl atoms and two oxygen atoms from solvated DME mol-
ecule to form a six-coordinated distorted octahedron
geometry. Such a stable structure of 5 may prevent it from
tBu
Cl
O
Yb Cl
N
N
iPr
tBu
Cl
OH
tBu
iPr
tBu
N
N
(1)-78oC, 2n-BuLi,YbCl3/THF,4h
t Bu
t Bu
Li
iPr
(2)36h,r.t
N
N
O
LiYb(DME)4Cl4
THF
+
O
N
Li
N
5
tBu
iPr
t Bu
THF
6
Scheme 3.
Fig. 3. ORTEP diagram of complex 5 showing atom numbering scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen atoms are
omitted for clarity.

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Z.-G. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 3383–3390
Fig. 4. ORTEP diagram of complex 6 showing atom numbering scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen atoms are
omitted for clarity.
Table 3
3. Conclusions
˚
Selected bond lengths (A) and angles (°) for 5 and 6
Complex 5
The first bis-aryloxo-functionalized NHC complexes of
monoamido ytterbium, L2YbN(i-Pr)2 3 and L02YbN-
ði-PrÞ2 4 were prepared by the transamination of anionic
homoleptic lanthanide amides, LiYb[N(i-Pr)2]4, with the
corresponding H2LCl and H2L0Cl and LiBu. The success
in the use of anionic lanthanide amide as a precursor may
provide a convenient way for the synthesis of a series of
amides complexes with Ln–NHC fragment. Attempt to syn-
thesize bis-amido ytterbium aryloxo-NHC complex resulted
in isolation of bis-aryloxo-NHC complexes of 3 and 4. The
in situ low-temperature reaction of 2 with two equivalents of
BuLi followed with one equivalent of YbCl3 in THF affords
[Li(DME)3][YbCl4(DME)] 5 and a dimeric imidazole-
aryloxo lithium {[O-4,6-di-tBu-C6H2-2-CH2{CH(MeNC-
HCHNH)}]Li(THF)}2 6, instead of the expected LYbCl2.
The isolation of 6 demonstrates 1,2-benzyl migration from
nitrogen to carbene center is easily occurred.
Yb–O(2)
Yb–Cl(1)
Yb–Cl(3)
O(3)–Li
2.364(7)
2.511(3)
2.564(3)
2.29(2)
Yb–O(1)
Yb–Cl(2)
Yb–Cl(4)
O(4)–C(6)
2.374(7)
2.554(3)
2.515(3)
1.416(15)
C(5)–C(6)
1.477(18)
O(2)–Yb–O(1)
O(1)–Yb–Cl(1)
O(1)–Yb–Cl(4)
O(2)–Yb–Cl(2)
Cl(1)–Yb–Cl(2)
O(4)–Li–O(7)
70.4(3)
90.56(19)
166.57(19)
82.1(2)
95.74(11)
164.0(12)
O(2)–Yb–Cl(1)
O(2)–Yb–Cl(4)
Cl(1)–Yb–Cl(4)
O(1)–Yb–Cl(2)
Cl(4)–Yb–Cl(2)
O(4)–Li–O(3)
160.9(2)
96.2(2)
102.86(12)
85.50(18)
92.80(11)
76.1(7)
Complex 6
O(1)–C(1)
N(1)–Li(1)
C(7)–C(8)
O(2)–Li(1)
1.310(3)
2.048(6)
1.500(4)
2.028(5)
O(1)–Li(1)
N(1)–C(8)
C(6)–C(7)
C(1)–C(6)
1.879(5)
1.328(4)
1.521(4)
1.416(4)
C(1)–O(1)–Li(1)
Li(1)–O(1)–Li(1A)
O(1)–Li(1)–O(2)
O(1A)–Li(1)–O(2)
133.5(2)
83.8(2)
126.1(3)
107.4(2)
C(1)–O(1)–Li(1A)
O(1)-Li(1)–O(1A)
C(8)–N(1)–Li(1)
128.7(2)
96.2(2)
119.2(2)
The study on the synthesis of aryloxo-NHC derivatives
of ytterbium and other lanthanide metals and the reactivity
of these complexes is proceeding in our laboratory.
isolation of 6 demonstrated unambiguously that the tran-
sient lithium carbene LLi is thermolabile, readily decom-
posing at even low temperature to the 2-alkylated
imidazole lithium derivative via 1,2-benzyl migration as
shown in Scheme 4.
4. Experimental section
4.1. General considerations
All of the manipulations were performed in a purified
argon atmosphere using standard Schlenk techniques. Tol-
uene, THF and DME were degassed and distilled from
sodium benzophenone ketyl under argon prior to use.
The compounds 1 and 2 were synthesized according to
the literature [6]. LiN(i-Pr)2 was synthesized by the reaction
of HN(i-Pr)2 with BuLi in hexane. Lanthanide analyses
were carried out by complexometric titration. Carbon,
hydrogen, and nitrogen analyses were performed by direct
combustion on a Carlo-Erba EA 1110 instrument. 1H
The unsuccessfulness in the synthesis of NHC ytterbium
chlorides is not special. The similar situation is also
observed for cerium complex, in that case the reaction of
the amine NHC t-BuNHCH2CH2[C{t-BuN(CHCH)N}]-
(HL*), KMe, and 1/2 equivalent of [CeI3THF4] does also
not afford [(L*)2CeI], but [CeI3THF4] and H2L* I [4b].
These results indicated that the synthesis of NHC lantha-
nide halides is much more difficult than that of the corre-
sponding amide complexes. The further study on the
synthesis of this kind of complex is proceeding.

Z.-G. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 3383–3390
3389
Cl
OLi
..
OH
tBu
iPr
iPr
tBu
tBu
2n-BuLi
N
N
N
N
2n-BuH
LiCl
+
+
tBu
YbCl3
t Bu
t Bu
Li
iPr
N
N
O
LiYb(DME)4Cl4
+
THF
O
5
N
Li
N
tBu
iPr
t Bu
THF
6
Scheme 4.
NMR spectrum was recorded on a Varian-400 spectrome-
ter. The uncorrected melting points were determined in
sealed Ar-filled capillary tubes.
solvent, the solid residue was extracted by toluene. For crys-
tallization a small amount of DME was added. The first
crop of red crystals suitable for X-ray diffraction study 5
was isolated (0.736 g, 54%). From the mother liquor at
10 °C, the second crop of colorless crystals suitable for X-
ray diffraction study, 6 was obtained (0.622 g, 65%). Anal.
Calc. for C16H40C14LiO8Yb: C, 52.76; H, 5.86; Yb, 25.35.
Found: C, 52.64; H, 5.83; Yb, 25.31. Anal. Calc. for
C58H94Li2N4O6: C, 72.70; H, 9.82; N, 5.85. Found: C,
4.2. Synthesis of L2YbN(i-Pr)2 3
A solution of LiYb[N(i-Pr)2]4 (12.5 ml, 4 mmol) in THF
was added dropwise to the suspension of 1 (3.48 g, 8 mmol)
under stirring, and then BuLi (3.8 ml, l.4 mmol) was intro-
duced at 0 °C for 4 h, then for 36 h at room temperature.
The solvent was removed in vacuum, and the residue was
exacted with toluene and centrifuged to remove precipita-
tion. The obtained solution was crystallized at room tem-
perature for a few days to afford light yellow crystals of 3
(2.85 g, 70%); m.p. 193–194 °C (dec.). Anal. Calc. for
C55H84N5O2Yb: C, 65.86; H, 8.23; N, 6.84; Yb, 14.06.
Found: C, 65.54; H, 8.34; N, 6.76: Yb, 14.26.
1
72.54; H, 9.67; N, 5.69. H NMR (CDCl3, d, ppm): 1.51
(s, 18H), 1.80 (s, 18H), 1.43 (d, 12H), 3.65 (m, 4H), 4.17
(brs, 2H), 6.19 (brs, 2H), 6.80 (d, brs, 2H), 6.99 (d, 2H).
4.5. X-ray crystallography
Suitable single crystals of complexes 3, 4, 5 and 6 were
sealed in a thin-walledglass capillary. Intensitydatawere col-
lected on a Rigaku Mercury CCD area detector in x scan
mode using graphite-monochromated Mo Ka radiation
4.3. Synthesis of L02YbN(i-Pr)2 4
˚
(k = 0.7107 A). Cell parameters were refined from the
Complex 4 was prepared by an analogous procedure
described as above, except 2 (3.37 g, 10 mmol) was used
instead of 1. Light yellow crystals obtained from toluene/
THF at ꢁ15 °C for a few days (4.08 g, 78%); m.p. 176–
177 °C (dec.). Anal. Calc. for C56.50H84N5O2Yb: C, 64.79;
H, 8.02; N, 6.69; Yb, 16.53. Found: C, 64.54; H, 8.12; N,
6.42; Yb, 16.48.
observed positions of all strong reflections in each data set.
The diffracted intensities were corrected for Lorentz-polari-
zation effects and empirical absorption corrections. The
structures were solved by heavy-atom and direct methods
and were refined by least-squares methods on all unique
2
jFj values. With anisotropic displacement parameters, pro-
grams used were SHELXS-97 and SHELXL-97 for structure solu-
tion, refinement, and molecular graphics. Details of the
intensity data collection and crystallographic data for 3, 4,
5 and 6 are given in Table 1, and further details of the struc-
ture determinations are given in the Supporting Information.
4.4. Metathesis of YbCl3 with 2 and BuLi
BuLi (3.42 ml, 4 mmol) was slowly added to a cold
(ꢁ78 °C) slurry of 2 (0.729 g, 2 mmol) in THF and stirred
for 4 h, during which time the color of solution changed
from yellow to red. The solution was then added to a slurry
of YbCl3 (0.2795 g, 2 mmol) in THF to give a yellow solu-
tion. The mixture was stirred for 4 h at ꢁ78 °C and then for
another 24 h at room temperature. After evaporation of the
Acknowledgement
We are grateful to National Natural Science Foundation
of China and PhD Foundation from Education Ministry of
China for the financial support.

3390
Z.-G. Wang et al. / Journal of Organometallic Chemistry 691 (2006) 3383–3390
(b) H. Shumann, M. Glanz, J. Winterfeld, H. Hemling, N. Kuhn, T.
Kratz, Angew. Chem. Int. Ed. 33 (1994) 1733;
Appendix A. Supplementary data
(c) W.J. Oldham Jr., S.M. Oldham, B.L. Scott, K.D. Abney, W.H.
Smith, D.A. Costa, Chem. Commun. (2001) 1348;
(d) W.A. Herrmann, F.C. Munck, G.R.J. Artus, O. Runte, R.
Anwander, Organometallics 16 (1997) 682;
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(f) H. Schumann, M. Glanz, J. Winterfeld, H. Hemling, N. Kuhn, T.
Kratz, Chem. Ber. 127 (1994) 2369.
Crystallographic data for the structural analysis have
been deposited with Cambridge Crystallographic Data
Centre, CCDC. Nos. 601689, 269256, 601701, 601702 for
3, 4, 5 and 6. Copies of this information may be free of
charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (fax: +44 1223 336033; e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk). Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.jorganchem.2006.04.029.
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