Heteroleptic diphenylamido complexes of ytterbium: Syntheses and molecular structures of (MeC5H4)2YbNPh2(THF) and (C5Me5)2YbNPh2

Article abstract of DOI:10.1016/S0022-328X(99)00735-4

Reaction of ytterbocene chloride with NaNPh₂ in THF or toluene-THF at 0°C yielded the neutral diphenylamido complexes (MeC₅H₄)₂YbNPh₂(THF) (1), (t-BuC₅H₄)₂YbNPh₂(THF) (2) and (C₅Me₅)₂YbNPh₂ (3) in good yields. The crystal structures of 1 and 3 were identified by X-ray diffraction analysis. Complex 1 has a distorted tetrahedral arrangement around ytterbium by two MeC₅H₄ groups, one oxygen atom and one nitrogen atom [orthorhombic, space group Pbca (no. 61); a=15.188(1), b=18.145(1), c=17.444(1) A?; V=4807.3(5) A?³, Z=8, D_calc.=1.579 g cm^-3]. The crystal structure of 3 [monoclinic, space group P2₁/n; a=15.834(2), b=9.992(2), c=18.504(3) A?; β=104.060(10)°, V=2839.9(8) A?³, Z=4, D_calc.=1.431 g cm^-3] shows a triangular array of two C₅Me₅ groups and one nitrogen atom surrounding ytterbium with additional intramolecular Yb-η²-Ph chelate interactions [Yb-C=2.986(6) and 3.053(6) A?]. The complexes 1 and 2 exhibit good catalytic activity for the polymerization of methyl methacrylate.

Full text of DOI:10.1016/S0022-328X(99)00735-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 598 (2000) 359–364
Heteroleptic diphenylamido complexes of ytterbium: syntheses and
molecular structures of (MeC5H4)2YbNPh2(THF) and
(C5Me5)2YbNPh2
Yaorong Wang a, Qi Shen a,*, Feng Xue b, Kaibei Yu c
a School of Chemistry and Chemical Engineering, Suzhou Uni6ersity, Suzhou 215006, PR China
b Department of Chemistry, The Chinese Uni6ersity of Hong Kong, Hong Kong, PR China
c Chengdu Institute of Organic Chemistry, Academia Sinica, Chengdu 610041, PR China
Received 26 August 1999; received in revised form 17 November 1999; accepted 22 November 1999
Abstract
Reaction of ytterbocene chloride with NaNPh2 in THF or toluene–THF at 0°C yielded the neutral diphenylamido complexes
(MeC5H4)2YbNPh2(THF) (1), (t-BuC5H4)2YbNPh2(THF) (2) and (C5Me5)2YbNPh2 (3) in good yields. The crystal structures of
1 and 3 were identified by X-ray diffraction analysis. Complex 1 has a distorted tetrahedral arrangement around ytterbium by two
MeC5H4 groups, one oxygen atom and one nitrogen atom [orthorhombic, space group Pbca (no. 61); a=15.188(1), b=18.145(1),
3
c=17.444(1) A; V=4807.3(5) A , Z=8, Dcalc. =1.579 g cm−3]. The crystal structure of 3 [monoclinic, space group P21/n;
,
,
a=15.834(2), b=9.992(2), c=18.504(3) A; i=104.060(10)°, V=2839.9(8) A , Z=4, Dcalc. =1.431 g cm−3] shows a triangular
3
,
,
array of two C5Me5 groups and one nitrogen atom surrounding ytterbium with additional intramolecular Ybꢀh2-Ph chelate
,
interactions [YbꢀC=2.986(6) and 3.053(6) A]. The complexes 1 and 2 exhibit good catalytic activity for the polymerization of
methyl methacrylate. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Synthesis; X-ray structure; Ytterbocene amides; Diphenylamide complex
HNC5H10 are highly effective initiators for the polymer-
ization of methyl methacrylate [4,5] and phenyl iso-
1. Introduction
cyanate [6]. Besides, they all show good catalytic
activity for ring-opening polymerization of o-caprolac-
In the last two decades, organolanthanide amides
have attracted much attention. This might be for the
tone [7]. These interesting results prompted us to inves-
two following reasons. First, anionic amides are the
tigate further the effect of amido ligands and p-ligands
suitable alternated ancillary ligands to replace the cy-
around central metals on the catalytic behavior. Here
clopentadienyl group usually used. Secondly, lan-
thanocene amides have been found to be the catalysts
we report the synthesis of ytterbocene diphenylamide
complexes, molecular structures and their catalytic be-
or precatalysts for important homogeneous processes,
havior for the polymerization of methyl methacrylate.
such as hydroamination/cyclization of aminoalkenes
[1], and polymerization of methyl methacrylate [2] and
o-caprolactone [3]. During our study on the chemistry
2. Results and discussion
of organolanthanide amides, we found that diisopropy-
lamido bis(methylcyclopentadienyl) lanthanides (MeC5-
H4)2LnN(i-Pr)2(THF) and piperidino bis(methylcy-
2.1. Synthesis
clopentadienyl) lanthanides (MeC5H4)2LnNC5H10-
The metathetical reaction of lanthanocene chloride
with alkali metal amides is a popular method for the
synthesis of organolanthanide amides [8]. For example,
the neutral lanthanocene amide complexes (MeC5H4)2-
* Corresponding author.
E-mail address: qshen@suda.edu.cn (Q. Shen)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00735-4

360
Y. Wang et al. / Journal of Organometallic Chemistry 598 (2000) 359–364
Table 1
LnN(i-Pr)2(THF) [6], (MeC5H4)2LnNC5H10(HNC5H10)
[5] were reported to be synthesized by the reaction of
lanthanocene chloride with corresponding lithium
amides (Eq. (1)).
,
Selected bond distances (A) and angles (°) for complex 1
Bond distances
YbꢀN
2.286(7)
2.642(9)
2.576(10)
2.641(10)
2.640(9)
2.639(10)
2.331
YbꢀO
2.329(6)
2.601(10)
2.613(9)
2.662(11)
2.609(9)
2.623(10)
2.354
YbꢀC13
YbꢀC15
YbꢀC17
YbꢀC20
YbꢀC22
YbꢀCent(1) a
YbꢀC14
YbꢀC16
YbꢀC19
YbꢀC21
YbꢀC23
YbꢀCent(2) b
(CH3C5H4)2LnCl(THF)+LiNR2
“(CH3C5H4)2LnNR2L+LiCl
Ln=Y, Er, Yb R=i-Pr
Ln=Y, Er, YbR2=C5H10
L=THF
L=HNC5H10
(1)
Bond angles
NꢀYbꢀO
NꢀYbꢀCent(2)
OꢀYbꢀCent(2)
C1ꢀNꢀC7
93.6(2)
111.9
102.8
115.1(6)
116.3(4)
NꢀYbꢀCent(1)
OꢀYbꢀCent(1)
Cent(1)ꢀYbꢀCent(2)
C1ꢀNꢀYb
111.4
105.1
126.0
128.0(5)
However, the reaction with lithium diphenylamide
gives anionic complexes containing lithium salt
[Li(DME)3][CH3C5H4Ln(NPh2)3](Ln=La, Pr, Nd) [9],
[Li(DME)3][(C5H5)2Nd(NPh2)2] [10], which have ion-
pair structure. Schumann et al. also isolated the anionic
C7ꢀNꢀYb
a Cent(1) is the centroid of the C(13)ꢀC(17) ring.
b Cent(2) is the centroid of the C(19)ꢀC(23) ring.
complex [Li(THF)4][(C5H5)2Ln(NPh2)2] (Ln=Lu, Sm)
from the reaction of methyl-bridged organolanthanide
alkyl (C5H5)2Ln(m-Me)2Li(tmed) with diphenylamine
[11]. It was reported that alkali metals often induced
structural changes in organolanthanide complexes
[8c,12]. We attempt to use NaNPh2 instead of LiNPh2
as a reagent to synthesize the neutral diphenylamido
complexes.
According to expectation, the reaction of lan-
thanocene chloride with sodium diphenylamide gives
the desired heteroleptic amide complexes in good yields.
No matter whether the p-ligands are methylcyclopenta-
dienyl, tert-butylcyclopentadienyl or pentamethylcy-
clopentadienyl groups, the products are all free of
sodium salt as shown in Eq. (2).
THF/toluene
Cp%YbCl(THF)+NaNPh2ꢀꢀꢀꢀꢀꢀꢀꢁCp%YbNPh2(THF)n
2
2
Fig. 1. Molecular structure of complex (MeC5H4)2YbNPh2(THF) (1)
with atomic numbering (hydrogen atoms have been omitted for
clarity).
+NaCl
Cp%=MeC5H4 (1), t-BuC5H4 (2)n=1
Cp%=C5Me5 (3)n=0
(2)
All these complexes are extremely sensitive to air and
moisture. Complexes 1 and 2 are highly soluble in THF
and DMF, moderately in diethyl ether and aromatic
solvents, and insoluble in aliphatic hydrocarbons. Com-
plex 3 has good solubility even in aliphatic hydrocar-
bons such as pentane, hexane etc.
2.2. X-ray crystal structures of 1 and 3
Complexes 1 and 3 were characterized by X-ray
diffraction to be monomers. The molecular structures
are shown in Figs. 1 and 2 and the important bond
lengths and angles are listed in Tables 1 and 2,
respectively.
Complex 1 is a THF-solvated complex as shown in
Fig. 1. The ytterbium metal is coordinated by two
Fig. 2. Molecular structure of complex (C5Me5)2YbNPh2 (3) with
atomic numbering (hydrogen atoms have been omitted for clarity).

Y. Wang et al. / Journal of Organometallic Chemistry 598 (2000) 359–364
361
Table 2
one nitrogen from diphenylamido group to form a
near-triangular arrangement. There is an additional
intramolecular Ybꢀh2-Ph interaction, due to p-bonding
of the phenyl group. Thus, the coordinated geometry
around ytterbium atom may be described to be a
distorted tetragonal pyramidal array composed of two
C5Me5 ring centroids, N, C(1) and C(6). The bond
angles C(7)ꢀNꢀYb and C(1)ꢀNꢀYb are 128.9(4) and
109.6(4)°, respectively. The difference of the two bond
angles (19.3°) is significantly larger than that of 1
(11.7°), which might result from the presence of the
chelate interaction. The bond distances of YbꢀC(1) and
YbꢀC(6) are in the range of h-PhꢀLn bonding values
,
Selected bond distances (A) and angles (°) for complex 3
Bond distances
YbꢀN
2.216(5)
2.619(6)
2.601(6)
2.593(6)
2.607(6)
2.578(6)
3.053(6)
2.306
YbꢀC13
YbꢀC15
YbꢀC17
YbꢀC24
YbꢀC26
YbꢀC1
2.605(6)
2.609(6)
2.619(6)
2.607(6)
2.612(6)
2.986(6)
2.318
YbꢀC14
YbꢀC16
YbꢀC23
YbꢀC25
YbꢀC27
YbꢀC6
YbꢀCent(1) a
YbꢀCent(2) b
Bond angles
NꢀYbꢀCent(1)
Cent(1)ꢀYbꢀCent(2)
C1ꢀNꢀYb
109.8
138.5
109.6(4)
117.3(6)
NꢀYbꢀCent(2)
C1ꢀNꢀC7
C7ꢀNꢀYb
110.6
120.9(5)
128.9(4)
,
published. The lengths 2.986(6) and 3.053(6) A for
NꢀC1ꢀC6
YbꢀC(1) and YbꢀC(6), respectively are similar to
2.739(35)–3.010(48)
MeC6H5 [21], 2.986(6), 3.180(9) A for bridging h -C5H5
in Yb(h6-C6Me6)(AlCl4)3-
,
A
a Cent(1) is the centroid of the C(13)ꢀC(17) ring.
b Cent(2) is the centroid of the C(23)ꢀC(27) ring.
2
,
bonding in (C5Me5)2Sm(m-C5H5)Sm(C5Me5)2 [22] and
2.814(4)–3.148(6) and 2.946(6)–3.158(9) A for chelat-
,
MeC5H4 rings, one oxygen atom of THF and one
nitrogen atom from the diphenylamido group to form a
distorted tetrahedral geometry, giving the central metal
a formal coordination number of eight. The bond an-
gles Cent(1)ꢀYbꢀCent(2) 126.0° and NꢀYbꢀO 93.6(2)°
are in good agreement with the corresponding values
Cent(1)ꢀErꢀCent(2) 126.3° and N(1)ꢀErꢀN(2) 93.0(2)°
in (MeC5H4)2ErNC5H10(HNC5H10) [5]. The two methyl
groups in the cyclopentadienyl rings are located at
opposite sides. Similar trans orientations have been
observed in (MeC5H4)2ErNC5H10(HNC5H10), [(MeC5-
H4)2YbCl]2 [13] and [(MeC5H4)2Yb(THF)2][BPh4] [14].
The metrical parameters in 1 are unexceptional. The
ing h6-, h1-PhꢀLn bonding in [Yb(Odpp)3] (Odpp−=
2,6-diphenylphenolate) [23] and in Nd(Odpp)3 [24],
respectively. To our best knowledge, this is the first
example of organolanthanide amide complexes with
intramolecular Ybꢀh2-Ph chelate interactions. The
YbꢀC(ring) distances range from 2.578(6) to 2.619(6)
,
,
A. The YbꢀC(ring) average distance of 2.605 A is
,
slightly shorter than 2.750(15) A SmꢀC(ring) average
distance in (C5Me5)2SmN(SiMe3)2 [25] and 2.682(4),
,
2.678(4) A YꢀC(ring) distances for the two independent
molecules in (C5Me5)2YN(SiMe3)2 [26], even if subtrac-
tion of the differences in ionic radii was carried out
,
[19]. The YbꢀN bond length 2.216(5) A is comparable
,
YbꢀO (THF) distance in 1, 2.329(6) A, is similar to the
,
to that in 1 and similar to the 2.301(3) A SmꢀN
YbꢀO (THF) distances in (t-BuC5H4)2YbCl(THF),
distance in (C5Me5)2SmN(SiMe3)2 and 2.274(5),
,
,
2.333(6) A [15] and (C5Me5)2YbCl(THF), 2.362 A [16].
,
2.253(5) A YꢀN distances in (C5Me5)2YN(SiMe3)2. The
The YbꢀC(ring) distances range from 2.576(10) to
bond angle Cent(1)ꢀYbꢀCent(2) of 138.5° is larger than
132.2 and 132.4° in (C5Me5)2YN(SiMe3)2 and 132.8° in
(C5Me5)2SmN(SiMe3)2, which reflects the smaller size of
NPh2 ligand set in 3.
,
2.662(11) A. The YbꢀC(ring) average distance of 2.625
,
A is in the range of values found in other ytterbocene
,
complexes: [(MeC5H4)2YbCl]2, 2.585 A [13]; [(C5H5)2-
,
,
YbCl]2, 2.58 A [17]; (t-BuC5H4)2YbCl(THF), 2.628 A;
(C5Me5)2YbCl(THF), 2.65 A.
The YbꢀN bond distance (2.286(7) A) compares well
with the distances found in other lanthanocene amide
,
2.3. Catalytic acti6ity
,
We tested the catalytic activity of complexes 1, 2 and
3 for the polymerization of methyl methacrylate and
the preliminary results show that complexes 1 and 2
have good catalytic activity. They give a conversion as
high as 95% for 1 and 100% for 2 at 0°C for 2 h in the
case of 0.2 mol% catalyst concentrations. The number-
average molecular weights and the molecular weight
distributions are 253×103, 133×103 and 1.67, 1.26,
respectively. The polymerization reaction can proceed
at a wide range of temperature from −40 to 40°C.
However, complex 3 has no activity at all under the
same polymerization conditions. This may be because
the two bulky pentamethylcyclopentadienyl groups and
amido group (NPh2) sterically crowd around the central
,
complexes: [(MeC5H4)2Yb(m-NH2)]2, 2.31
A
[18];
,
(C5H5)2Lu(NC4H2Me2)(THF), 2.289(4) A [8d]; [Li-
,
(THF)4][(C5H5)2Lu(NPh2)2], 2.290(7), 2.293(7) A [11];
[Li(DME)3][(C5H5)2Nd(NPh2)2], 2.421(7), 2.434(7) A
[10] when corrections are made for trivalent eight-coor-
dinate ionic radii [19]. However, the YbꢀN bond dis-
tance is larger than those found in (MeC5H4)2-
ErNC5H10(HNC5H10) (2.159(8) A) [5], (C5Me5)2La-
NHCH3(NH2CH3) (2.313(10) A) [20], even if the differ-
ences between Yb and La, Yb and Er in radii are
considered.
Complex 3 is an unsolvated complex (Fig. 2). The
ytterbium atom is coordinated by two C5Me5 rings and
,
,
,

362
Y. Wang et al. / Journal of Organometallic Chemistry 598 (2000) 359–364
ytterbium and make it difficult to initiate the insertion
of methyl methacrylate (MMA). Further study is in
progress on the relationship between the size of ligands
around the central metal and the polymerization
activity.
3.3. Preparation of (C5Me5)2YbNPh2 (3)
To a solution of (C5Me5)2YbCl(THF) [8c] in toluene
(53.5 ml, 4.37 mmol) was added to 7.8 ml of a THF
solution of NaNPh2 (4.37 mmol). The mixture was
stirred for 1 h at 0°C and then for another 48 h at room
temperature. After centrifugation, the solvent was com-
pletely removed and the oily residue was extracted with
hexane. The extracts were concentrated to about 5 ml
and cooled to −30°C for crystallization. Purple crys-
tals were isolated. Yield: 1.96 g (73.3%). m.p.=168–
174°C. Anal. Calc. for C32H40NYb: C, 62.84; H, 6.59;
N, 2.29; Yb, 28.28. Found: C, 62.45; H, 6.70; N, 2.35;
Yb, 27.80%. IR (KBr pellet, cm−1): 3048 w, 2967 m,
2920 s, 2855 m, 1636 m, 1593 s, 1508 s, 1443 w, 1377 w,
1312 s, 1084 m, 876 w, 748 s, 694 m.
3. Experimental
All manipulations were carried out under an argon
atmosphere using standard Schlenk techniques.Toluene,
THF and diethyl ether were dried over Na or sodium
benzophenone ketyl and distilled before use. MMA was
dried over calcium hydride powder for 4 days and
,
stored over 3 A molecular sieves under argon after
distillation. NaNPh2 was prepared as reported in the
literature [27].
Melting points were determined in a sealed argon-
filled capillary and uncorrected. Lanthanide metal
analyses were carried out by complexometric titration.
Carbon, hydrogen, and nitrogen analyses were per-
formed by direct combustion. The IR spectra were
obtained as KBr pellets on a Magna-550 spectrometer.
Table 3
Experimental data for the X-ray diffraction study of complexes 1 and
3
1
3
Formula
Formula weight
Temperature (K)
C28H32NOYb
571.59
293(2)
C32H40NYb
611.69
296(2)
3.1. Preparation of (MeC5H4)2YbNPh2(THF) (1)
,
To a solution of (MeC5H4)2YbCl [6] in THF (51.3
ml, 8.82 mmol) was added 15.8 ml of a THF solution of
NaNPh2 (8.82 mmol). The mixture was stirred for 1 h
at 0°C and then for another 48 h at room temperature.
After complete removal of THF, the residue was ex-
tracted with diethyl ether to remove NaCl. The extracts
were concentrated and cooled to −30°C for crystalliza-
tion. Dark red crystals were formed. Yield: 3.83 g
(76%). Single crystals suitable for X-ray diffraction
studies were obtained by recrystallization of 1 from
diethyl ether–toluene. m.p.=123–126°C. Anal. Calc.
for C28H32NOYb: C, 58.84; H, 5.64; N, 2.45; Yb, 30.27.
Found: C, 58.22; H, 5.36; N, 2.41; Yb, 30.53%. IR
(KBr pellet, cm−1): 3042 m, 2970 w, 2919 w, 2873 w,
1593 s, 1508 s, 1495 s, 1455 w, 1419 m, 1311 s, 1245 m,
1173 m, 1030 m, 881 m, 748 s, 692 s.
Wavelength (A)
Crystal system
Space group
0.71073
Orthorhombic
Pbca (no. 61)
15.188(1)
18.145(1)
17.444(1)
90
4807.3(5)
8
1.579
0.71073
Monoclinic
P21/n
15.834(2)
9.992(2)
18.504(3)
104.060(10)
2839.9(8)
4
,
a (A)
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
Dcalc. (Mg m−3
Absorption coefficient
(mm−1
F(000)
Crystal size (mm)
q range for data
collection (°)
)
1.431
3.312
3.910
)
2280
0.60×0.55×0.40
2.10–25.59
1236
0.60×0.40×0.16
2.33–25.00
Limiting indices
−185h518,
−215k521,
05l519
05h518,
−15k511,
−225l521
6367
Reflections collected
13 199
Independent reflections
4164
(Rint=0.1551)
4672
(Rint=0.0190)
0.6193 and 0.2412
3.2. Preparation of (t-BuC5H4)2YbNPh2(THF) (2)
Maximum and minimum 1.348 and 0.511
transmission
This complex was prepared from the reaction of
(t-BuC5H4)2YbCl(THF) [15] in toluene (50 ml, 5.62
mmol) with NaNPh2 in THF (10.1 ml, 5.62 mmol)
using a similar procedure to that described above. Dark
blue crystals were obtained. Yield: 2.08 g (56.4%).
m.p.=124–128°C. Anal. Calc. for C34H44NOYb: C,
62.28; H, 6.76; N, 2.14; Yb, 26.38. Found: C, 61.79; H,
6.67; N, 2.07; Yb, 25.93%. IR (KBr pellet, cm−1): 3080
w, 2963 s, 2910 w, 2870 w, 1593 s, 1506 m, 1497 s, 1462
w, 1365 w, 1312 m, 1219 s, 1157 s, 1026 w, 922 w, 748
s, 691 m, 629 m, 505 s.
Data/restraints/
parameters
4164/139/281
4672/0/318
Goodness-of-fit on F2
Final R indices
[I\2|(I)]
1.188
R1=0.0718
0.892
R1=0.0338
wR2=0.1697
R1=0.0813
wR2=0.1775
0.001
wR2=0.0753
R1=0.0508
wR2=0.0792
0.001
R indices (all data)
(D/|)max
Largest differnce peak
0.983 and −0.969 1.580 and −0.978
−3
,
and hole (e A
)

Y. Wang et al. / Journal of Organometallic Chemistry 598 (2000) 359–364
363
3.4. Polymerization of methyl methacrylate
Data Centre, CCDC nos. 136603 for complex 1 and
136604 for complex 3. Copies of this information may
be obtained 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).
To a toluene solution (10 ml) of MMA (1 ml, 9.35
mmol) was added at once the toluene solution (1 ml) of
(MeCp)2YbNPh2(THF) (10.7 mg, 0.019 mmol) with
vigorous magnetic stirring at the desired temperature.
The polymer was precipitated by ethanol after the
polymerization was held for 2 h and then washed with
ethanol and dried in vacuum.
Acknowledgements
We thank the Chinese National Foundation of Natu-
ral Science, Foundation of Natural Science of Jiangsu
and the Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, Academia
Sinica, for their financial support.
3.5. X-ray crystallographic analysis of 1
Suitable crystals were selected and mounted in thin-
walled glass capillaries for X-ray structure analysis. The
intensity data were collected at 294 K on a MSC/
Rigaku RAXIS IIc imaging-plate diffractometer using
,
graphite monochromated Mo–Ka (u=0.71073 A) radi-
ation. Unit cell dimension was determined from four
still frames, reflection data was collected by taking 45
oscillation frames in the range of 0–180°, D„=4°,
exposure 8 min per frame [28]. A self-consistent semi-
empirical absorption correction based on Fourier co-
efficient fitting of symmetry-equivalent reflections was
applied by using the ABSCOR program [29]. A summary
of crystallographic data is given in Table 3.
The crystal structure was solved by the direct
method, which yielded the positions of all non-hydro-
gen atoms. All the non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were located geomet-
rically and refined using a riding model. All computa-
tions were performed on an IBM compatible PC with
the SHELX-97 package [30].
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,
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