Aminopyridinate-stabilized lanthanoid complexes: Synthesis, structure and polymerization of ethylene and isoprene

Article abstract of DOI:10.1002/ejic.201000097

A series of aminopyridinate-stabilized dialkyl-lanthanoid complexes has been synthesized and characterized. The complexes were prepared by alkane elimination reacting [Ln(CH₂SiMe₃)₃(thf) ₂] (Ln = Er, Yb, Lu) or

Full text of DOI:10.1002/ejic.201000097

FULL PAPER
DOI: 10.1002/ejic.201000097
Aminopyridinate-Stabilized Lanthanoid Complexes: Synthesis, Structure and
Polymerization of Ethylene and Isoprene
Christian Döring,[a] Winfried P. Kretschmer,[a] and Rhett Kempe*[a]
Keywords: Polymerization / Ethylene / Isoprene / Lanthanoids / Aminopyridinato ligands
A series of aminopyridinate-stabilized dialkyl-lanthanoid
complexes has been synthesized and characterized. The
complexes were prepared by alkane elimination reacting
[Ln(CH2SiMe3)3(thf)2] (Ln = Er, Yb, Lu) or [Ln(CH2Ph)3(thf)3]
(Ln = Y, Er, Lu) with one equivalent of the bulky aminopyr-
idine (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-
pyridin-2-yl]amine. Single-crystal X-ray analyses were car-
ried out for all of the benzyl derivatives. The reaction of these
compounds with ammonium borate leads to the elimination
of one of the two alkyl functions and affords organolan-
thanoid cations. The aminopyridinate-stabilized dialkyl-lan-
thanoid compounds can initiate the polymerization of iso-
prene after activation with perfluorinated tetraphenyl bo-
rates. The obtained polymers have a 3,4-content of 60–95%.
The metal ion size as well as the addition of alkylaluminium
compounds influences the microstructure of the obtained
polymer. Aminopyridinate-stabilized organolanthanoid cat-
ions of Sc, Lu, Er and Y can polymerize ethylene in the pres-
ence of alkylaluminium compounds. The Lu, Er and Y com-
plexes act as a CCTP catalyst and the erbium compound ex-
hibits the highest activity.
CCTP is an excellent tool to polymerize ethylene and α-
olefins in a highly controlled and efficient fashion. A variety
of systems are described which are capable of catalyzing
this type of chain growing at main group metals or Zn.[16]
Introduction
Cationic rare earth metal alkyl compounds (mainly gen-
erated by the reaction of neutral di- or trialkyl complexes
with perfluorinated borate compounds) are known to be
useful initiators/catalysts for the polymerization of olefins
or 1,3-dienes.[1] One advantage of rare earth catalysts in
comparison to other (for instance, group 4) metal alkyl cat-
ion catalysts is the fine tuning of the catalysts activity and/
or selectivity by varying the size of the rare earth atom. For
instance, Bambirra et al.[2] as well as Okuda and co-
workers[3] imposingly demonstrated the relation between
polymerization activity and the metal ion size.
Results and Discussion
Metal Complex Synthesis
As we reported recently, a series of aminopyridinate-sta-
bilized bis(trimethylsilylmethyl)scandium complexes were
synthesized via alkane elimination (Scheme 1).[8] Similarly
the reaction of the trialkyl precursor compounds
Herein we report the synthesis and structure of bis(tri-
methylsilylmethyl) and dibenzyl rare earth complexes stabi-
lized by bulky aminopyridinato[4–8] (Ap) ligands. In ad-
dition, the performance of these compounds as precatalysts
for the polymerization of ethylene and isoprene will be dis-
cussed. The focus will be put on the influence of the ionic
radius of the rare earth atom on the activity and selectivity
of the polymerization reactions as well as the ability of
these compounds to mediate coordinative chain-transfer
polymerisation (CCTP)[9] of ethylene.
[Ln(CH2SiMe3)3(thf)2] (Ln
= Y, Er, Yb, Lu) and
[Ln(CH2Ph)3(thf)3] (Ln = Y, Er, Lu) with the aminopyr-
idine ligand 1a yield after alkane/toluene elimination selec-
tively the corresponding dialkyl compounds 3–10
(Scheme 2). Efforts to obtain monoaminopyridinate com-
plexes with larger lanthanoids (ϾEr) led to a mixture of
mono- and bis(aminopyridinato) complexes. The com-
pounds 3, 6 and 10 were already described in earlier re-
ports.[7j,8,16l] The erbium and ytterbium analogues, com-
pounds 4 and 5 (Scheme 2, left side) were synthesized in
moderate and very good yield (64% and 93%), respectively.
The aminopyridinate-stabilized dibenzyl complexes 7, 8,
and 9 (Scheme 2, right side) were obtained in 63, 85 and
56% yield, respectively. The proton NMR spectra of 7 and
9 exhibit the characteristic splitting pattern of the amino-
pyridinato ligand. In contrast to the scandium analogue
10[8] where the methylene groups from the two benzyl li-
gands exhibit an AB-system only one signal is observed in
Isoprene polymerisation using cationic rare earth initia-
tors has become an intensively investigated area[10–13] after
the initiating reports of Okuda and co-workers[14] as well as
Hou and co-workers.[15]
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Fax: +49-921-55-2157
E-mail: kempe@uni-bayreuth.de
Eur. J. Inorg. Chem. 2010, 2853–2860
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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C. Döring, W. P. Kretschmer, R. Kempe
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Scheme 1. Synthesis of aminopyridinate-stabilized dialkylscandium compounds 2a–c.
Scheme 2. Synthesis of aminopyridinate-stabilized dialkyl-lanthanoid compounds 3–10.
1
the H NMR spectra of 7 and 9, whereas the signal of 9
appears as a broad singlet. The 13C NMR spectra show
only one resonance for the methylene groups of the benzyl
ligands at 54.1 (doublet, 1J(Y,C) = 28.6 Hz) for 7 and
59.1 ppm for compound 9, respectively.
The compounds 7–9 were also characterized by X-ray
structure analysis. Suitable crystals were obtained by cool-
ing a saturated pentane or hexane solution to 0 °C. The
complexes 7–9 are isostructural and crystallize in the mono-
clinic space group C2/c. The structures are depicted in Fig-
ures 1 and 2, crystallographic details are summarized in
Table 4. The metal atoms are five-coordinate by one amino-
pyridinato ligand, one thf ligand and two benzyl ligands
which show (in the solid state) different coordination
modes.
Figure 1. Molecular structure of 7 (ellipsoids set at 40% probability
level). H atoms have been omitted for clarity.
Similar to the scandium derivative 10[8] one of the two trium [N1–Ln1–N2: 57.25(12) (7), 57.69(15) (8), 58.33(15)
benzyl ligands has a η1-coordination [Ln1–C1–C2: 116.0(3) (9) and 61.31(7)° (10)]. Another significant effect of similar
(7), 116.2(4) (8), 119.5(5) (9) and 121.88(16)° (10)], whereas nature is the decreasing Ln1–C8–C9 angle of the η2-coordi-
the other ligand exhibits an η2-coordination which is indi- nated benzyl ligand with increasing ionic radius (Table 1).
cated by the decreased Ln1–C8–C9 angles of 83.2(3) (7),
The dialkyl complexes 2a, 3 and 7–10 react with one
84.4(4) (8), 85.4(4) (9) and 88.50(15)° (10) and a shortened equivalent of ammonium borate in thf to afford after alk-
distance of the lanthanoid atom to the ipso-carbon atom of ane elimination the thf stabilized organolanthanoid cations
this ligand [Ln1–C9: 2.675(4) (7), 2.677(6) (8) and 2.668(6) 11–14 respectively (Scheme 3). The alkyl complexes 11, 12
(9) Å]. Within the series 7–10 the N1–Ln1–N2 bite angle of and 14 have been already characterized in our previous re-
the aminopyridinato ligand decreases with an increasing ports.[8,16l] The organoerbium cation 13 was characterized
ionic radius of the metal centre[17] from scandium to yt- by an X-ray structure analysis. Suitable single crystals were
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Aminopyridinate-Stabilized Lanthanoid Complexes
Figure 2. Molecular structure of 8 (left) and 9 (right) (ellipsoids set at 40% probability level). H atoms and solvent molecules have been
omitted for clarity.
Table 1. Selected bond lengths [Å] and angles [°] for the complexes
[Ap*Ln(CH2Ph)2(thf)] (Ln = Y, Er, Lu, Sc).
Ln = Y (7) Ln = Er (8) Ln = Lu (9) Ln = Sc (10)[a]
Bond length
Ln1–N1
Ln1–N2
Ln1–O1
Ln1–C1
Ln1–C8
Ln1–C9
2.423(4)
2.303(3)
2.328(3)
2.414(5)
2.436(5)
2.675(4)
2.403(4)
2.287(4)
2.310(4)
2.411(7)
2.414(7)
2.677(6)
2.381(4)
2.244(4)
2.294(4)
2.351(7)
2.365(7)
2.668(6)
2.286(2)
2.129(2)
2.1728(17)
2.245(3)
2.256(3)
2.657(2)
Bond angle
Ln1–C1–C2
Ln1–C8–C9
N1–Ln1–N2 57.25(12)
[a] From ref.[8]
116.0(3)
83.2(3)
116.2(4)
84.4(4)
57.69(15)
119.5(5)
85.4(4)
58.33(15)
121.88(16)
88.50(15)
61.31(7)
Figure 3. ORTEP diagram of the molecular structure of 13 in the
solid state (ellipsoids set to 40% probability level). H atoms, solvent
molecule and anion have been omitted for clarity. Selected bond
lengths [Å] and angles [°]: Er1–C1 2.418(8), Er1–N1 2.462(6), Er1–
N2 2.325(6), Er1–O1 2.348(5), Er1–O2 2.317(5), Er1–O3 2.302(5),
Er1–C1–C2 117.4(6), O1–Er1–C1 96.9(2), O2–Er1–C1 94.8(2), O3–
Er1–C1 90.1(2).
obtained by slow diffusion of pentane into a thf solution of
13. The compound crystallizes in the triclinic space group
¯
P1, crystallographic details are summarized in Table 4 and
Polymerization of Ethylene
the molecular structure is presented in Figure 3. The cation
of 13 shows a distorted octahedral coordination of the er-
We have recently demonstrated, that aminopyridinate-
bium atom indicated by O–Er–Cbenzyl angles of 90.1(2) and stabilized organoyttrium cations show attractive activities
94.8(2)°. The metal atom is coordinated by three thf, one in the polymerization of ethylene in the presence of small
benzyl [η1-coordination, Er1–C1–C2 117.4(6)°] and one amounts of alkylaluminium compounds.[16l] We could also
aminopyridinato ligand. The thf ligands show a meridonal show the influence of the steric bulk of the aminopyridinato
arrangement and the methylene group of the benzyl ligand ligand on the polymerization activity for this yttrium-based
is in trans-position to the pyridine nitrogen atom of the system. Therefore, we wanted to investigate the polymeriza-
aminopyridinato ligand.
tion activities for other aminopyridinate-stabilized lan-
Scheme 3. Synthesis of organolanthanoid cations 11–14.
Eur. J. Inorg. Chem. 2010, 2853–2860
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C. Döring, W. P. Kretschmer, R. Kempe
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Table 2. Polymerization of ethylene catalyzed by 2–4 under various conditions.[a]
Run
Cat.
Alkyl-Al
(equiv.)
mpol
[g]
Mn
Mw/Mn
Activity
[gmol–1]
[kgPE molcat–1 h–1 bar–1]
1[b]
2[b]
3
4
5
6
7
8
9
10
11
12
13
3
TIBAO (20)
TIBAO (50)
TIBAO (20)
TIBAO (50)
TIBAO (20)
TIBAO (50)
TIBAO (20)
TIBAO (50)
TIBAO (20)
TIBAO (50)
TIBA (25)
13.4
4.7
20.2
13.6
0.03
0.03
1.6
0.5
6.7
6
3.9
20800[c]
3610
29600
14500
n.d.
n.d.
6000
n.d.
3.2
1.09
2.0
1072
376
1616
1088
2
2
128
40
536
480
312
384
312
3
4
4
1.6
5
n.d.
n.d.
1.5
5
6
6
n.d.
2a
2a
2a
2b
2c
607100[c] (13100)[d]
610900[c] (13000)[d]
5150
3.33 (1.62)
4.71 (1.77)
2.71
16.1 (1.56)
2.56
TIBAO (50)
TIBAO (50)
4.8
3.9
373500[c] (4280)[e]
39600
[a] Conditions: for dialkyl (2–6): 10 µmol, ammonium borate [R2N(CH3)H]+[B(C6F5)4]– (R = C16H33–C18H37), Y/B = 1:1.1, 260 mL of
toluene, time 15 min, temperature: 80 [°C], pressure: 5 bar. [b] From ref.[8] [c] Bimodal distribution. [d] Mw of the main fraction (98%).
[e] Mw of the main fraction (83%).
thanoid complexes. The compounds 2a,b,c and 4–6 were obtained polymer revealed a bimodal distribution, but the
investigated as precatalysts for the controlled ethylene poly- main fraction has a content of 98% (Mn = 13100, Mw/Mn
merization (CCTP). All of these dialkyl compounds except = 1.62). In contrast to the ethylene polymerization catalysts
for the ytterbium derivative 5 showed low to very good ac- 3, 4 and 6, the scandium compound 2a did not show a
tivities.[18] The erbium (4) and the lutetium (6) compounds significant dependency of the TIBAO concentration on the
revealed a similar dependency on the TIBAO concentration activity and the molecular weight (Table 2, run 9, 10). We
like it was already observed for the yttrium system. On the suppose that the ion radius of the scandium metal is too
basis of this observation we suggest these compounds to be small for the coordination of alkylaluminium compounds,
coordinative chain transfer polymerization catalysts. which is necessary for the polyethylene chain transfer. Re-
Whereas the lutetium compound 6 showed only low activi- duction of the steric demand of the aminopyridinato ligand
ties (Table 2, run 7, 8), the dialkylerbium compound 4 leads to a decreased activity (Table 2, run 10, 12, 13), the
revealed the highest activities up to 1616 kgPE same effect was observed for the yttrium compound, and
molcat–1 h–1 bar–1. This polymerization activity is compar- can be explained by ligand redistribution (Figure 4).[16l]
able with that of other efficient CCTP catalysts, for example
a [Cp*2SmCl2Li(OEt2)2]/BuMgEt catalyst from Mortreux
et. al (activities from 400–3070 kgPE molcat–1 h–1 bar–1)[16c]
and a bis(iminopyridine)-iron(II)/ZnEt2/MAO catalyst sys-
tem described by Britovsek et al.[16i] with activities from
1404–1944 kgPE molcat–1 h–1 bar–1.
Because of the related ionic radii of erbium and yttrium
(0.89 vs. 0.90 Å, for coordination number 6),[17] both show
high ethylene polymerization activities (Table 2, run 1–4).
The activity of the erbium compound is slightly higher due
to a smaller ionic radius which leads to a hampered coordi-
nation to aluminium and thus to an increased concentra-
tion of the chain growing state.[9a] The average number mo-
lecular weight (Mn) of the polymer obtained with the er-
Figure 4. Influence of the metal ion size and the Al concentration
on the ethylene polymerization activity.
bium compound 4 is higher than the polymer obtained with
the yttrium derivative 3 (29600 and 14500 gmol–1 for 4 vs.
20800 and 3610 gmol–1for 3), whereas the molecular weight
distribution remains narrow (2.0 and 1.6, Table 2, run 3, 4).
Polymerization of Isoprene
When the ionic radius is decreased to 0.86 Å (coordination
As we have described very recently, the aminopyridinate-
number 6), in the case of lutetium, the polymerization ac- stabilized dialkyl compounds of scandium (2a–c and 10) are
tivity significantly decreased and the obtained polymer active and selective catalysts for the controlled 3,4-selective
show a molecular weight of 6000 gmol–1 and a relatively polymerization of isoprene.[8] In order to investigate the in-
narrow molecular weight distribution of 1.5 (Table 2, run fluence of the metal centre on the selectivity of the isoprene
7). When the scandium compound 2a was used as a precat- polymerization we also tested the complexes 3–9 as precata-
alyst, which comply with an ionic radius of 0.74 Å, a good lysts for the isoprene polymerization. The microstructure of
1
activity for the polymerization of ethylene is observed. The the obtained polyisoprene was determined by H and 13C
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Aminopyridinate-Stabilized Lanthanoid Complexes
NMR spectroscopy. The results of the polymerization ex-
periments are summarized in Table 3. The bis(trimethylsilyl-
methyl)lanthanoid compounds 3, 4 and 6 polymerize iso-
prene after activation with perfluorinated ammonium bo-
rate in chlorobenzene or toluene (Table 3, run 1, 2 and 4).
Only the ytterbium derivative in this series is unable to initi-
ate the polymerization of isoprene after activation (Table 3,
run 3). Presumably a reduction of the ytterbium metal is an
issue as indicated by a colour change of the dialkyl during
the formation of the cation. The polymerization activities
are comparable with that of 2a.[8] The thf-stabilized organ-
oerbium cation 13 does not polymerize isoprene, even not
in the presence of 10 equiv. of AliBu3. The microstructure
of the polymer obtained with 2–4 and 6 as precatalysts de-
pends significantly on the metal size: with an increasing
ionic radii of the metal centre the cis-1,4-polyisoprene con-
tent is increasing and the 3,4-polyisoprene content is
decreasing respectively [3,4-content: 60% (Y) Ͻ 80% (Er)
Ͻ 86% (Lu) Ͻ 93% (Sc)]. The same influence of the ionic
radius of the central metal atom on the 3,4-selectivity was
also observed by Cui and co-workers [the 3,4-content de-
creases from 88.5% (Sc) to 43.8% (Y)].[10l] GPC analyses of
these polymers show bimodal molecular weight distribu-
tions. When the new dibenzyl complexes 7–9 are used as
precatalysts for the polymerization of isoprene the same re-
lation between the ionic radii and the microstructure, as it
was described above for the bis(trimethylsilylmethyl)lan-
thanoid compounds, is observed (Figure 5).
Figure 5. Influence of the metal centre on the microstructure of the
obtained polyisoprene (Table 3, run 13, 11, 8, 6).
tion is observed when triisobutylaluminium (10 equiv.) was
mixed with the polymerization catalyst (Table 3, see runs 7,
9 and 12). For complex 8 the polymerization was also car-
ried out in the presence of trimethylaluminium to obtain a
high cis-1,4-polyisoprene (92%). This effect of the alkylalu-
minium compounds on the microstructure of the polyiso-
prene was also observed for the scandium derivative 10 and
an amidinato-yttrium isoprene polymerization catalyst de-
scribed by Hou and co-workers.[13]
Conclusions
Table 3. Effect of Ln size and alkyl ligand on the polymerization[a]
of isoprene.
Mono(aminopyridinate)lanthanoid
bis(trimethylsilyl-
[b]
methyl) and dibenzyl complexes have been synthesized and
characterized. These dialkyl-lanthanoid compounds with
exception of the ytterbium compound are active catalysts
for the polymerization of isoprene after activation with bo-
rates. The obtained polyisoprenes have an enriched 3,4-con-
tent. The ionic radius of the lanthanoid metal is in relation
to the cis-1,4- to 3,4-content ratio. Smaller metals, like scan-
dium or lutetium predominantly afford polyisoprene with
high 3,4-content (Ͼ90%). The 3,4-content decreases to
68% when yttrium is used as a precatalyst. Addition of tri-
methylaluminium to the erbium catalyst system leads to a
drastical change of the microstructure. The aminopyrid-
inate-stabilized lanthanoid bis(trimethylsilylmethyl) com-
pounds show very high ethylene polymerization activities
in the presence of Al compounds (trialkyl compounds and
aluminoxanes) and perfluorinated tetraphenyl borate. The
activity is strongly influenced by the ionic radius of the lan-
thanoid metal. The highest activity was observed for the
erbium compound. The dialkyl-ytterbium is inactive under
the same conditions.
Run Cat. Cocatalyst Yield Mnϫ10–3 Mw/Mn
Microstructure[c]
cis-1,4:trans-1,4/3,4
[%]
[gmol–1][b]
1
2
3
4
3
4
5
6
2a
7
7
8
8
8
9
9
A
A
A
A
A
B
100
100
–
100
94
97
99
100
92
92
86
34
–
3.82[d]
3.52[d]
–
37:3:60
13:7:80
–
104
135
157
86
222
57
112
168
24
2.98[d]
1.26
2.45
2.66
1.80
2.57
2.90
1.65
2.43
1.68
4:10:86
7:0:93
32:0:68
42:0:58
13:3:84
40:0:60
92:0:8
7:0:93
23:5:72
5:0:95
5[e]
6
7
8
9
10
11
12
B/AliBu3
B
B/AliBu3
B/AlMe3
B
96
100
97
B/AliBu3
B
13[e] 10
130
[a] Conditions: 10 mL of C6H5Cl, catalyst: 10 µmol, cocatalyst: A
= [C6H5NH(CH3)2][B(C6F5)4], B = [Ph3C][B(C6F5)4], [cat]/[cocat]
1:1, [Al]/[cat] = 10, isoprene: 10 mmol, reaction time: 20 h, T =
20 °C. [b] Determined by GPC against polystyrene standards. [c]
Determined by 1H and 13C NMR spectroscopy. [d] Bimodal distri-
bution. [e] From ref.[8]
The molecular weight distribution of polyisoprene pro-
duced with the dibenzyl complexes 7–10 is narrow and
monodisperse, compared with the molecular weight distri-
bution of the polyisoprene produced with the bis(trimethyl-
silylmethyl) complexes 3–6, but become broader with an in-
creasing ionic radius of the lanthanoid metal [1.68 (Sc) to
2.45 Å (Y)]. A marked decrease of the 3,4-polyisoprene
Experimental Section
General Procedures Synthesis and Structure: All reactions and ma-
nipulations involving air-sensitive compounds were performed un-
der dry argon by using standard Schlenk and glovebox techniques.
content and broadening of the molecular weight distribu- Non-halogenated solvents were dried with sodium/benzophenone
Eur. J. Inorg. Chem. 2010, 2853–2860
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C. Döring, W. P. Kretschmer, R. Kempe
FULL PAPER
Table 4. Details of the X-ray crystal structure analyses.
Compound
7
8
9
13
Formula
C50H65N2OY
monoclinic
C2/c
36.7280(10)
13.0360(6)
24.1120(9)
90
118.307(4)
90
8
C50H65ErN2O·C5H12
monoclinic
C2/c
36.7240(15)
13.0460(9)
24.1000(13)
90
118.352(5)
90
8
C50H65LuN2O·C6H14
monoclinic
C2/c
36.8040(10)
13.0430(6)
24.0810(9)
90
118.511(3)
90
8
C73H90BErN2O3·OC4H8
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
triclinic
¯
P1
13.6250(12)
15.2430(13)
19.1560(17)
101.422(7)
99.138(6)
112.884(7)
2
Z
µ [mm–1]
1.180
1.689
1.982
1.258
Cell volume [Å3]
Crystal size [mm3]
T [K]
10164.0(7)
0.36ϫ0.13ϫ0.09
133(2)
10161.3(10)
0.25ϫ0.15ϫ0.08
133(2)
10157.8(7)
0.32ϫ0.16ϫ0.11
133(2)
3468.0(5)
0.58ϫ0.32ϫ0.14
133(2)
θ range [°]
Refl. unique
Refl. obsd. [IϾ2σ(I)]
Parameters
wR2 (all data)
R value [IϾ2σ(I)]
1.26–26.08
8666
6447
487
0.150
1.68–26.04
9423
6556
572
0.105
1.68–25.74
9588
5852
548
0.087
1.51–25.72
13035
7669
785
0.154
0.075
0.053
0.041
0.058
ketyl and halogenated solvents with CaH2. Deuterated solvents
were obtained from Cambridge Isotope Laboratories, degassed,
dried with molecular sieves and distilled prior to use. Starting mate-
rials 1a–c,[7a,16l] tetraisobutylaluminoxane ([iBu2Al]2O, TIBAO),[19]
[Ln(CH2SiMe3)3(thf)2],[20] [Ln(CH2Ph)3(thf)3],[21] [LScR2(thf)] (L =
After stirring the mixture for two hours it was filtered. After the
evaporation of all volatile components 4 was yielded as an orange
powder (280 mg, 64%). C44H73ErN2OSi2 (869.5): calcd. C 60.78,
H 8.46, N 3.22; found C 61.17, H 8.42, N 3.61.
Synthesis of 5: The compounds [Yb(CH2SiMe3)3(thf)2] (289 mg,
0.50 mmol) and 1a (228 mg, 0.50 mmol) were dissolved in hexane
(20 mL). The mixture was stirred for two hours, subsequent fil-
tration and removal of all volatile components yielded 5 as a red
powder (405 mg, 93%). C44H73N2OSi2Yb (875.3): calcd. C 60.38,
H 8.41, N 3.20; found C 60.07, H 8.14, N 3.22.
1,
R =
CH2SiMe3, CH2Ph),[8] [Ap*Y(CH2SiMe3)2(thf)],[16l]
[Ap*Lu(CH2SiMe3)2(thf)],[7j] [C6H5NH(CH3)2][B(C6H5)4][22] were
synthesized according to literature methods. All other chemicals
were purchased from commercial sources in purities Ͼ97% and
used without further purification, if not otherwise stated. NMR
spectra were obtained with either a Varian INOVA 300 or a Varian
INOVA 400 spectrometer. Chemical shifts are reported in ppm rela-
tive to the deuterated solvent. Elemental analyses were carried out
with a Vario elementar EL III apparatus. The molecular weights
(Mw/Mn) of the isoprene polymers were determined by gel permea-
tion chromatography (GPC) on an Agilent 1200 series (column:
PLgel Mixed-C) at 30 °C using thf as eluent and a flow rate of
1 mL/min against polystyrene standards. The molecular weights
(Mw/Mn) of the ethylene polymers were determined by gel permea-
tion chromatography on a Polymer Laboratories Ltd. (PL-GPC210
or PL-GPC220) chromatograph at 150 °C using 1,2,4-trichloroben-
zene as the mobile phase. The samples were prepared by dissolving
the polymer (0.1% weight/volume) in the mobile phase solvent in
an external oven and were run without filtration. The molecular
weight was referenced to polyethylene (Mw = 50000 gmol–1) and
polystyrene (Mw = 100000–500000 gmol–1) standards. The reported
values are the average of at least two independent determinations.
X-ray crystal structure analyses were performed with a STOE-
IPDS II equipped with an Oxford Cryostream low-temperature
unit. Structure solution and refinement were accomplished using
SIR97,[23] SHELXL-97[24] and WinGX.[25] Crystallographic details
are summarized in Table 4.
Synthesis of 7: The compounds [Y(CH2Ph)3(thf)3] (463 mg,
0.80 mmol) and 1a (365 mg, 0.80 mmol) were dissolved in thf
(20 mL) and the mixture was stirred for two hours. After removal
of all volatile components the residue was extracted with hexane
(40 mL). The solvent was removed under reduced pressure to yield
7 as a yellow powder (400 mg, 63%). C50H65N2OY (799.0): calcd.
1
C 75.16, H 8.20, N 3.51; found C 75.00, H 8.63, N 3.42. H NMR
(400 MHz, C6D6, 298 K): δ = 1.03 (br., 4 H, β-CH2, THF), 1.15
3
3
(d, J(H,H) = 6.7 Hz, 6 H, CH(CH3)2), 1.18 [d, J(H,H) = 6.9 Hz,
3
6 H, CH(CH3)2], 1.22 [d, J(H,H) = 6.8 Hz, 6 H, CH(CH3)2], 1.29
3
3
[d, J(H,H) = 6.9 Hz, 6 H, CH(CH3)2], 1.49 [d, J(H,H) = 6.8 Hz,
6 H, CH(CH3)2], 1.76 (s, 4 H, CH2Ph), 2.86 [sept, 3J(H,H) =
6.9 Hz, 1 H, 15-H], 3.13 [sept, 3J(H,H) = 6.7 Hz, 2 H, 13,14/22,23-
H], 3.25 (br, 4 H, α-CH2, THF), 3.53 [sept, 3J(H,H) = 6.8 Hz, 2 H,
13,14/22,23-H], 5.76 [d, 3J(H,H) = 8.4 Hz, 1 H, 3-H], 6.16 [d,
3J(H,H) = 7.0 Hz, 1 H, 5-H], 6.40 [d, 3J(H,H) = 7.5 Hz, 4 H, o-
3
3
H], 6.65 [t, J(H,H) = 7.3 Hz, 2 H, p-H], 6.84 [dd, J(H,H) = 8.4,
3J(H,H) = 7.0 Hz, 1 H, 4-H], 7.02 [t, 3J(H,H) = 7.6 Hz, m-H], 7.11–
7.23 (m, 3 H, 18,19,20-H), 7.27 (s, 2 H, 9,11-H) ppm. 13C NMR
(100 MHz, C6D6, 298 K): δ = 22.7, 22.9, 24.1, 24.3, 24.7, 28.6, 30.9,
31.8, 34.9, 54.1 [d, 1J(Y,C) = 28.6 Hz], 70.0, 106.7, 117.5, 121.1,
121.9, 124.0, 124.9, 129.2, 131.0, 135.8, 139.2, 144.1, 144.2, 147.0,
149.9, 151.1, 155.7, 170.2 ppm.
CCDC-763799 (for 7), -763800 (for 8), -763801 (for 9), -763802 (for
13) contain 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.
Synthesis of 8:
A mixture of [Er(CH2Ph)3(thf)3] (394 mg,
0.60 mmol) and 1a (274 mg, 0.60 mmol) were dissolved in thf
(20 mL). The resulting red solution was stirred for two hours. All
volatile components were removed under reduced pressure and the
residue was extracted with hexane (20 mL). Removal of the solvent
yield 8 as an orange crystalline compound (447 mg, 85%).
Synthesis of the Complexes
Synthesis of 4: Hexane (20 mL) was added to mixture of [Er(CH2-
SiMe3)3(thf)2] (287 mg, 0.50 mmol) and 1a (228 mg, 0.50 mmol).
2858
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Eur. J. Inorg. Chem. 2010, 2853–2860

Aminopyridinate-Stabilized Lanthanoid Complexes
C50H65ErN2O (877.3): calcd. C 68.45, H 7.47, N 3.19; found C
68.14, H 7.53, N 3.42.
the reactor was vented and the residual alkylaluminium com-
pounds were destroyed by addition of 2-propanol (100 mL). The
precipitated polymer was decanted and washed with acidified 2-
propanol and again with 2-propanol, then dried at 80 °C to a con-
stant weight to afford 6.5 g of polyethylene.
Synthesis of 9: [Lu(CH2Ph)3(thf)3] (532 mg, 0.80 mmol) and 1a
(365 mg, 0.80 mmol) were dissolved in thf (20 mL) and stirred over-
night. All volatile components were removed under reduced pres-
sure and the residue was extracted with hexane (30 mL). Removal
of the solvent affords 9 as a yellow spectroscopically pure com-
pound (400 mg, 56%). C50H65LuN2O (884.0): calcd. C 67.85, H
Polymerization of Isoprene: A detailed polymerization procedure
(Table 3, run 8) is described as a typical example: in a glove box
the complex 3 (8 mg, 10 µmol) was dissolved in C6H5Cl (8 mL) and
isoprene (680 mg, 1 mL, 10 mmol) was added. The mixture was
1
7.40, N 3.17; found C 67.63, H 7.74, N 3.33. H NMR (400 MHz,
3
C6D6, 298 K): δ = 0.87 (br., 4 H, β-CH2, THF), 1.15 [d, J(H,H) placed in a water bath (20 °C). Then AlMe3 (100 µmol, 50 µL,
= 6.8 Hz, 12 H, CH(CH3)2], 1.21 [d, 3J(H,H) = 6.8 Hz, 6 H,
CH(CH3)2], 1.30 [d, 3J(H,H) = 6.9 Hz, 6 H, CH(CH3)2], 1.52 [d, (8 mg, 10 µmol) in C6H5Cl (2 mL) were added. After stirring for
3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2], 1.64 (br. s, 4 H, CH2Ph), 2.87
20 h at room temperature the mixture was poured into a large
2.0  in hexane) and a solution of [C6H5NH(CH3)2][B(C6F5)4]
3
3
[sept, J(H,H) = 6.9 Hz, 1 H, 15-H], 3.17 [sept, J(H,H) = 6.8 Hz, quantity of acidified 2-propanol containing 0.1% (w/w) 2,6-di-tert-
2 H, 13,14/22,23-H], 3.19 (br., 4 H, α-CH2, THF), 3.48 [sept, butyl-4-methylphenol as a stabilizing agent. The precipitated poly-
3
3J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-H], 5.74 [d, J(H,H) = 8.7 Hz,
mer was decanted, washed with 2-propanol and dried in vacuo at
60 °C to a constant weight to afford 626 mg of polyisoprene (92%).
3
3
1 H, 3-H], 6.22 [d, J(H,H) = 7.1 Hz, 1 H, 5-H], 6.47 [d, J(H,H)
= 7.8 Hz, 4 H, o-H], 6.69 [t, J(H,H) = 7.3 Hz, 2 H, p-H], 6.85 [t, The microstructure of the polymer was examined by 13C NMR
3
3J(H,H) = 7.8 Hz, 1 H, 4-H], 7.02 [t, 3J(H,H) = 7.6 Hz, m-H], 7.10–
7.19 (m, 3 H, 18,19,20-H), 7.29 (s, 2 H, 9,11-H) ppm. 13C NMR
(100 MHz, C6D6, 298 K): δ = 22.8, 24.2, 24.4, 24.9, 25.0, 27.0, 28.7,
31.1, 35.0, 59.1, 70.5, 106.8, 111.9, 118.2, 121.2, 123.4, 124.1, 125.3,
130.0, 135.8, 139.7, 144.0, 144.5, 147.1, 150.0, 151.3, 155.9,
169.0 ppm.
spectroscopy in CDCl3.
Acknowledgments
Financial support from the Deutsche Forschungsgemeinschaft
(DFG) (SPP 1166 “Lanthanoid specific functionalities in molecules
and materials“). We thank A. M. Dietel and T. Bauer for labora-
tory assistance.
Synthesis of 13: To a mixture of 8 (132 mg, 0.15 mmol) and
[C6H5NH(CH3)2][B(C6H5)4] (64 mg, 0.15 mmol) were added thf
(2.0 mL) and toluene (1.0 mL). The reaction mixture was stirred
for 5 min to obtain a clear solution. Slowly diffusion of pentane
into this solution over a period of 4 d affords 13·(OC4H8) as yellow
crystalline plates which were separated by decanting off the solu-
tion and washed twice with pentane (2ϫ10 mL); yield 84 mg
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(Table 2, run 1) is described as a typical example. The catalytic
ethylene polymerization reactions were performed in a stainless
steel 1-L autoclave, equipped with a mechanical stirrer. In a typical
experiment, the autoclave was evacuated and heated for 2 h at
100 °C prior to use. The reactor was then brought to 80 °C, and
charged with toluene (250 mL) together with trialkylammonium
tetrakis(pentafluorophenyl)borate (11 mmol, 0.12 g) and the re-
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ethylene to reach the desired pressure, the autoclave was equili-
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jected together with toluene (10 mL) to start the reaction. During
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Eur. J. Inorg. Chem. 2010, 2853–2860
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C. Döring, W. P. Kretschmer, R. Kempe
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Received: January 29, 2010
Published Online: April 6, 2010
2860
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Eur. J. Inorg. Chem. 2010, 2853–2860