Scandium aminopyridinates: Synthesis, structure and isoprene polymerization

Article abstract of DOI:10.1002/ejic.200900504

Alkane elimination reactions of [Sc(CH₂SiMe₃) ₃(thf)₂] or [Sc(CH₂Ph)₃(thf) ₃] with aminopyridines (1a = (2,6-diisopropylphenyl.)-[6-(2,4,6- triisopropylphenyl)pyridin-2-yl]amine, 1b = [6-(2,4,6-triisopropylphenyl) pyridin-2-yl]-(2,4,6-trimethylphenyl)amine, 1c = (2,6-diisopropylphenyl)-[6-(2, 6-dimethylphenyl)pyridin-2-yl]amine) led to selective formation of dialkyl complexes of scandium, stabilized by one amlnopyridinato (Ap) ligand, The reaction of these compounds with anilinium borate leads to the elimination of one of the two alkyl functions and affords organoscandium cations, The amine elimination reaction of [Sc[N(SiHMe₂)₂]₃(thf)] with the aminopyridine 1a yields the corresponding mono(aminopyridinato) complex, Single-crystal X-ray analyses were carried out for [Ap*Sc(CH ₂Ph)₂(IhI)] (3a), [Ap*Sc(CH₂Ph)(thf) ₃][B(C₆H5)₄] (4a) and [Ap*Sc{N(SiHMe ₂)₂}₂] (6a) (Ap^*-H = 1a), The aminopyridinato-stabilized dialkylscandium complexes [ApScR₂(thf)] (R = CH₂SiMe₃, CH₂Ph) are initiators for controlled 3,4-selective isoprene polymerization after activation with perfluorinated tetraphenyl borates. Variation of the polymerization temperature as well as the addition of different alkylaluminium compounds influence the microstructure of the obtained polymer, Bis(dimethylsilyl)amides of scandium polymerize isoprene in the presence of aniliniuni borate and alkylaluminium compounds with high cis-1,4-selectivity. Wiley-VCH Verlag GmbH & Co. KGaA,.

Full text of DOI:10.1002/ejic.200900504

FULL PAPER
DOI: 10.1002/ejic.200900504
Scandium Aminopyridinates: Synthesis, Structure and Isoprene Polymerization
Christian Döring,[a] Winfried P. Kretschmer,[a] Tobias Bauer,[a] and Rhett Kempe*[a]
Keywords: Isoprene / N ligands / Organocations / Polymerization / Scandium
Alkane elimination reactions of [Sc(CH2SiMe3)3(thf)2] or
[Sc(CH2Ph)3(thf)3] with aminopyridines (1a = (2,6-diisopro-
pylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine,
1b = [6-(2,4,6-triisopropylphenyl)pyridin-2-yl]-(2,4,6-trimeth-
out for [Ap*Sc(CH2Ph)2(thf)] (3a), [Ap*Sc(CH2Ph)(thf)3][B-
(C6H5)4] (4a) and [Ap*Sc{N(SiHMe2)2}2] (6a) (Ap*-H = 1a).
The aminopyridinato-stabilized dialkylscandium complexes
[ApScR2(thf)] (R = CH2SiMe3, CH2Ph) are initiators for con-
ylphenyl)amine, 1c = (2,6-diisopropylphenyl)-[6-(2,6-dimeth- trolled 3,4-selective isoprene polymerization after activation
ylphenyl)pyridin-2-yl]amine) led to selective formation of di-
alkyl complexes of scandium stabilized by one aminopyr-
idinato (Ap) ligand. The reaction of these compounds with
anilinium borate leads to the elimination of one of the two
alkyl functions and affords organoscandium cations. The
amine elimination reaction of [Sc{N(SiHMe2)2}3(thf)] with the
aminopyridine 1a yields the corresponding mono(aminopyr-
idinato) complex. Single-crystal X-ray analyses were carried
with perfluorinated tetraphenyl borates. Variation of the po-
lymerization temperature as well as the addition of different
alkylaluminium compounds influence the microstructure of
the obtained polymer. Bis(dimethylsilyl)amides of scandium
polymerize isoprene in the presence of anilinium borate and
alkylaluminium compounds with high cis-1,4-selectivity.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
1,4-polyisoprene (natural rubber),[2d,3e,4,7,8] most likely since
isoprene prefers to coordinate in most of the catalytically
active systems in the thermodynamically more stable cis-
1,4-mode.[3a,9]
Herein we report the synthesis and the structure of di-
alkyl and bis(dimethylsilylamide) complexes of scandium
stabilized by aminopyridinato (Ap) ligands[10,11] and their
catalytic properties in the isoprene polymerization in the
presence of borates. Furthermore, the influence of the ami-
nopyridinato ligand, the polymerization temperature, the
catalyst concentration and various alkylaluminium com-
pounds on the polymerization will be discussed.
Introduction
Isoprene polymerization catalyzed by organolanthanoid
cations has gained a lot of attention recently after the initial
reports published by Okuda and co-worker as well as Hou
and co-worker simultaneously.[1] Rare earth metal-alkyl(ha-
lide) complexes of the type [(L)LnR2(D)] (R = CH2SiMe3,
AlMe4, o-CH2C6H4NMe2, µ3-C3H5, Cl, D = thf) where L
is a cyclopentadienyl[2] or an anionic N-ligand,[3,4] are
known to catalyse or initiate isoprene polymerization.[5]
Very interesting in terms of stereoselectivity are the precur-
sors [{Me2Si(C5Me4)-(PHCy)}YCH2SiMe3]2 (Cy = cyclo-
hexyl)[1b]
or
[(PhC(NC6H4iPr2-2,6)2)Y(o-CH2C6H4-
NMe2)2][4] which show, in the combination with
[Ph3C][B(C6F5)4], very high regio- and stereoselectivities
(3,4-selectivity: Ͼ99%, mmmm Ͼ 99%). Furthermore, the
yttrium amidinate complex switches the stereoselectivity
drastically from 3,4-isospecific to cis-1,4-selective by ad-
dition of AlMe3. Recently Zimmermann et al. described
half-sandwich complexes of the type [(C5Me5)Ln(AlMe4)2]
(Ln = Y, La, Nd) which, upon activation with fluorinated
borates or boranes, are highly active catalysts for the living
trans-1,4-selective (up to 99.5%) polymerization of iso-
prene.[2b] Although 3,4-polyisoprene is used as an impor-
tant component of high-performance rubber, for example
in tires,[6] the number of 3,4-selective catalyst systems is
smaller in contrast to systems which preferably yield cis-
Results and Discussion
Metal Complex Synthesis and Structure
Similarly to the synthesis of aminopyridinato-dialkylyt-
trium complexes [ApY(CH2SiMe3)2(thf)][12] the corre-
sponding scandium complexes were successfully prepared
(Scheme 1). Only very recently the first (homoleptic) ami-
nopyridinato-scandium complex was described.[13] The re-
action of the aminopyridines 1a–c with one equivalent of
[Sc(CH2SiMe3)3(thf)2] yielded after tetramethylsilane elimi-
nation the corresponding scandium compounds 2a–c
(Scheme 1, left) which were characterized by H and 13C
NMR spectroscopy and elemental analysis. The H NMR
1
1
spectra of the compounds 2a–c exhibit the characteristic
splitting pattern of each aminopyridinato ligand as it was
observed for the already described analogous yttrium com-
pounds. In contrast to the yttrium derivatives the methylene
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Fax: +49-921-55-2157
E-mail: kempe@uni-bayreth.de
Eur. J. Inorg. Chem. 2009, 4255–4264
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4255

C. Döring, W. P. Kretschmer, T. Bauer, R. Kempe
FULL PAPER
Scheme 1. Synthesis of Ap-stabilized dialkyl compounds 2a, 2b, 2c and 3a.
groups of the alkyl ligand exhibit an AB-system (doublets
at δ = 0.01 and 0.09 ppm for 2a; –0.01 and 0.07 ppm for 2b
1
and 0.01 and 0.07 ppm for 2c) in the H NMR spectrum.
This effect can be attributed to the smaller coordination
sphere of the scandium ion and hindered rotation of the
aminopyridinato ligands therewith. The aminopyridine 1a
reacts also with one equivalent of the tribenzyl complex
[Sc(CH2Ph)3(thf)3] to afford after toluene elimination the
aminopyridinato-stabilized dibenzyl complex 3a. Suitable
single crystals for X-ray structure analysis of this com-
pound were obtained by cooling a saturated pentane solu-
tion to 0 °C. The compound 3a crystallizes in the mono-
clinic space group C2/c. The molecular structure is depicted
in Figure 1, the crystallographic details are summarized in
Table 5. The metal centre has a coordination number of five
and is coordinated by one aminopyridinato ligand, one thf
ligand and two benzyl ligands which show different coordi-
nation modes in the solid state. One of the two benzyl li-
gands has an η1-coordination [Sc1–C1–C2 121.88(16)°],
while the other ligand exhibits η2-coordination indicated by
the Sc1–C8–C9 angle of 88.50(15)° and a shortened dis-
Figure 1. ORTEP diagram of the molecular structure of 3a in the
solid state (ellipsoids set at 50% probability level). H Atoms and
solvent molecules have been omitted for clarity. Selected bond
lengths [Å] and angles [°]: Sc1–N1 2.286(2), Sc1–N2 2.1290(19),
Sc1–C1 2.245(3), Sc1–C8 2.256(3), Sc1–C9 2.657(2), N1–Sc1–N2
61.31(7), Sc1–C1–C2 121.88(16), Sc1–C8–C9 88.50(15).
tance of the scandium atom to the ipso-carbon atom of this troscopy and elemental analyses. Furthermore, compound
ligand [Sc1–C9 2.657(2) Å]. 4a was characterized by an X-ray structure analysis. Suit-
The dialkyl complexes 2a and 3a react with one equiva- able single crystals were obtained by slow diffusion of pen-
lent of anilinium borate to afford after alkane elimination tane into a thf/toluene (1:1) solution of 4a. The compound
¯
the organoscandium cations 4a and 5a respectively which crystallizes in the triclinic space group P1 as yellow plates.
were isolated in the presence of thf (Scheme 2). The compo- Crystallographic details are summarized in Table 5 and the
sition of the compounds was determined by NMR spec- molecular structure of 4a is presented in Figure 2.
Scheme 2. Synthesis of organoscandium cations 4a and 5a.
4256
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4255–4264

Scandium Aminopyridinates for Isoprene Polymerization
atoms [N1–Sc–N4 116.33(5)°, N3–Sc–N4 107.36(6)°, N2–
Sc–N3 109.49(6)°] [two from the aminopyridinato and two
from the bis(dimethylsilyl)amido ligand respectively]. Both
scandium to nitrogen bond lengths between the
{N(SiHMe2)2} groups and the scandium atom of 6a
[2.0573(15) and 2.0409(14) Å] are only marginally shorter
than the average of Sc–N bond lengths of 2.069(2) Å in
[Sc{N(SiHMe2)2}3(thf)].[15] Both {N(SiHMe2)2} ligands ex-
hibit an asymmetrical coordination to the metal centre
which is caused by a Sc···(Si–H) interaction of both bis(di-
methylsilyl)amido ligands respectively. As a result, the Sc–
N–Si angles within each of amido ligands are different [Sc–
N3–Si1 100.93(7)° vs. Sc–N3–Si2 129.36(9)° and Sc–N4–Si3
99.40(7)° vs. Sc–N4–Si4 131.32(8)°]. This bending towards
the scandium centre also results in different Sc–Si distances
of each {N(SiHMe2)2} ligand [Sc–Si1 2.9003(6) and Sc–Si3
2.8642(6) Å vs. Sc–Si2 3.4117(6) and Sc–Si4 3.4208(6) Å].
The very short Sc–Si3 distance of 2.8642(6) Å is the short-
est observed up to now for an agostic Sc–Si interaction and
is very close to the known distance of Sc–Si σ-bonds in
Figure 2. ORTEP diagram of the molecular structure of 4a in the
solid state (ellipsoids set at 50% probability level). H Atoms have
been omitted for clarity. Selected bond lengths [Å] and angles [°]:
Sc1–C1 2.234(6), Sc1–N1 2.188(4), Sc1–N2 2.358(4), Sc1–O1
2.177(3), Sc1–O2 2.192(3), Sc1–O3 2.217(3), Sc1–C1–C2 121.2(4),
O1–Sc1–C1 95.15(17), O2–Sc1–C1 89.51(17), O3–Sc1–C1
95.94(18).
[(C5H5)2Sc{Si(SiMe3)3}thf][16]
with
2.863(2) Å
and
[(C5Me5)2Sc(SiH2SiPh3)][17] with 2.797(1) Å. Proton NMR
spectra of 6a were recorded in [D8]toluene in the tempera-
ture range of 23 to 100 °C (Figure 4). The room tempera-
ture 1H NMR spectrum reveals two doublets for the methyl
groups of the silylamide group but only one septet for the
SiH protons. The same splitting pattern was observed at
–80 °C. Above 20 °C, the signals for the SiMe groups begin
to broaden and at 100 °C only one doublet is observed.
The cation of 4a shows a distorted octahedral coordina-
tion of the scandium atom indicated by O–Sc–Cbenzyl angles
of 89.51(17) and 95.94(18)°. The metal atom is coordinated
by three thf, one benzyl [η1-coordination, Sc1–C1–C2
121.2(4)°] and one aminopyridinato ligand. The thf ligands
show a meridonal arrangement and the methylene group of
the benzyl ligand is in trans-position to the pyridine nitro-
gen atom of the aminopyridinato ligand.
As we reported recently, the bulky aminopyridines 1a,b
react with triamide precursors, namely [Ln{N(SiHMe2)2}3-
(thf)2] (Ln
=
Y, La).[14] Similarly the compound
[Sc{N(SiHMe2)2}3(thf)] reacts with the aminopyridine 1a in
toluene at 60 °C within four days to afford the diamide 6a
(Scheme 3).
Figure 3. ORTEP diagram of the molecular structure of 6a in the
solid state (ellipsoids set at 50% probability level). H Atoms have
been omitted for clarity. Selected bond lengths [Å] and angles [°]:
Sc–N1 2.2548(14), Sc–N2 2.1320(14), Sc–N3 2.0573(15), Sc–N4
2.0409(14), Sc–Si1 2.9003(6), Sc–Si2 3.4117(6), Sc–Si3 2.8642(6),
Sc–Si4 3.4208(6), Si1–N3–Si2 129.45(9), Sc–N3–Si1 100.93(7), Sc–
N3–Si2 129.36(9), Si3–N4–Si4 128.64(9), Sc–N4–Si3 99.40(7), Sc–
N4–Si4 131.32(8), N1–Sc–N4 116.33(5), N3–Sc–N4 107.36(6), N2–
Sc–N3 109.49(6).
Scheme 3. Synthesis of the aminopyridinato-stabilized diamide 6a.
The rate constants for this exchange were determined by
Figure 3 depicts the molecular structure of 6a, crystallo- NMR simulation using the program DNMR3.[18] From the
graphic details are summarized in Table 5. The structure of Eyring equation, the activation parameters for this process
6a demonstrates that the thf ligand present in the starting were calculated (∆G‡
=
73.9Ϯ0.9 kJmol–1; ∆H‡
=
=
=
compound was eliminated due to steric demand of the ami- 49.2Ϯ0.3 kJmol–1; ∆S‡ = 71.9Ϯ1.0 Jmol–1 K–1, Tc
nopyridinato ligand. The metal atom displays a distorted 348 K; Figure 5). The activation energy of ∆G‡
tetrahedral geometry and is coordinated by four nitrogen 73.9 kJmol–1 for this process is similar to that found in
Eur. J. Inorg. Chem. 2009, 4255–4264
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4257

C. Döring, W. P. Kretschmer, T. Bauer, R. Kempe
FULL PAPER
1
Figure 4. H NMR spectra of 6a in [D8]toluene at different temperatures.
[(etbmp)Sc{N(SiHMe2)2}(thf)] (etbmp = 1,4-dithiabutane- zene or toluene. A narrow molecular weight distribution of
diyl-bis(6-tert-butyl-4-methylphenol)
with
∆G‡
=
1.26 to 1.33 is observed (Table 1, run 1–3). A marked de-
crease of the 3,4-polyisoprene content and broadening of
the molecular weight distribution is observed when triiso-
butylaluminium (10 equiv.) was mixed with the polymeriza-
tion catalyst. (Table 1, run 5–7). Detailed investigations of
the influence of different alkylaluminium compounds or
TIBAO (tetraisobutylalumoxane) on the microstructure of
the obtained polymer were performed (Table 1, run 8–10).
Switching from AliBu3 to the short-chain aluminium com-
pounds AlEt3 and AlMe3 results in a decrease of 3,4-poly-
isoprene content and increase of cis-1,4-polyisoprene con-
tent in the direct relation to the size of the alkyl groups at
the aluminium metal; the molecular weight distributions are
very broad due to a bimodal distribution. A similar influ-
ence of the aluminium alkyls on the microstructure of the
polymer was also reported by Zhang et al. for an yttrium-
amidinate isoprene polymerization catalyst.[4] When the po-
lymerization temperature was increased to 40 °C for the sys-
tem 2a/[C6H5NH(CH3)2][B(C6F5)4]/AliBu3 a decrease of
the 3,4-polyisoprene content to 62% together with a broad-
ening of the molecular weight distribution were observed
69.79 kJmol–1 and Tc = 330 K).[19]
Figure 5. Eyring plot (–Rln(kh/kBT) = –∆S‡ + ∆H‡/T) for the co-
alescence of the SiMe signals.
Polymerization of Isoprene
The complexes 2, 3a and 6a were tested as precatalysts (Table 1, run 11). Decrease of the polymerization tempera-
for the polymerization of isoprene. The microstructure of ture (0 °C) for this system leads to an increased 3,4-polyiso-
1
the obtained polyisoprene was determined by H and 13C prene content going along with an isotactically enrichment
NMR spectroscopy. The results of the polymerization ex- (mm ≈ 100%, mmmm ≈ 30% and 35%, Table 1, run 12,
periments are summarized in Tables 1, 2, 3, and 4. The bis- 13). At a lower temperature (–14 °C) a relatively narrow
(trimethylsilylmethyl)scandium compounds 2a–c polymer- molecular weight distribution was observed, indicative of
ize isoprene in a 3,4-selective fashion (Ͼ93%) after acti- the deactivation of other polymerization-active species or
vation with perfluorinated anilinium borate in chloroben- absence of such species at low temperature.
4258
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4255–4264

Scandium Aminopyridinates for Isoprene Polymerization
Table 1. Polymerization of isoprene with complexes 2 under various conditions.[a]
[b]
Run
Cat.
Alkyl-Al
T [°C]
Yield [%]
Mn ϫ10–3[b]
Mw/Mn
Microstructure [%][c]
3,4:cis-1,4
1[d]
2
2a
2b
2c
2a
2a
2b
2c
2a
2a
2a
2a
2a
2a
2a
–
–
–
–
–
20
20
20
20
20
20
20
20
20
20
40
0
94
100
94
135
141
192
58
137
144
144
104
32
25
31
147
225
80
1.26
1.27
1.33
4.47
3.84
3.08
2.59
2.00
93:7
97:3
96:4
83:17
80:20
91:9
89:11
96:4
81:19
33:67
62:38
96[h]:4
96[i]:4
96:4
3
4[e]
5
81
AliBu3
AliBu3
AliBu3
TIBAO
AlEt3
AlMe3
AliBu3
AliBu3
AliBu3
–
100[f]
98
6
7
8
9
10
11
12
13
14
15
100
100
96
6.84[g]
6.10[g]
6.10[g]
3.54
1.75
2.35
–
90
100
100
100
99
–14
0
20
AliBu3
–
–
–
[a] Conditions: 10 mL C6H5Cl, dialkyl compounds 2a–c: 10 µmol, anilinium borate: [C6H5NH(CH3)2][B(C6F5)4] 10 µmol, isoprene:
1
10 mmol, [Al]/[complex] = 10, reaction time: 20 h. [b] Determined by GPC against polystyrene standards. [c] Determined by H and 13C
spectroscopy, no trans-1,4-polyisoprene was found. [d] 10 mL toluene used as solvent. [e] [Ph3C][B(C6F5)4] was used as the activator,
polymerization time 2 h. [f] 98% conversion after 30 min. [g] Bimodal distribution. [h] mm = 100%, mmmm = 30%. [i] mm = 100%,
mmmm = 35%.
Table 2. Polymerization of isoprene with complex 2a with different catalyst/monomer ratios.[a]
[b]
Run
Concentration
Mn ϫ10–3[b]
Mw/Mn
Microstructure [%][c]
2a [µmol]
3,4:cis-1,4
1
2
3
5
10
15
157
115
75
1.96
1.55
1.30
96:4
94:6
94:6
[a] Conditions: 10 mL C6H5Cl, anilinium borate: [C6H5NH(CH3)2][B(C6F5)4], [2a]/[B] = 1, isoprene: 10 mmol, reaction time: 20 h. [b]
1
Determined by GPC against polystyrene standards. [c] Determined by H and 13C spectroscopy, no trans-1,4-polyisoprene was found.
Table 3. Polymerization of isoprene with complex 3a under various conditions.[a]
[b]
Run
Alkyl-Al (equiv.)
T [°C]
Yield [%]
Mn ϫ10–3[b]
Mw/Mn
Microstructure [%][c]
3,4:cis-1,4
1
–
–
–
20
20
20
20
20
20
20
20
20
20
0
–
–
97
100
98
–
–
130
33
78
–
–
–
–
2[d]
3[e]
4[e]
5
1.68
9.48
5.32[g]
2.85
2.10
1.76
3.86[g]
4.51[g]
3.43[g]
2.40
95[f]:5
81:19
76:24
73:27
77:23
81:19
37:63
10:90
Ͼ99:0
Ͼ99:0
AliBu3 (10)
AliBu3 (10)
AliBu3 (5)
AliBu3 (2)
AliBu3 (1)
AlEt3 (10)
AlMe3 (10)
AliBu3 (10)
AliBu3 (10)
6
7
8
9
10
11
12
99
73
100
100
99
96
100
100
139
119
63
67
153
129
–14
[a] Conditions: 10 mL C6H5Cl, 3a 10 µmol, anilinium borate: [C6H5NH(CH3)2][B(C6F5)4] 10 µmol, isoprene: 10 mmol, reaction time:
1
20 h. [b] Determined by GPC against polystyrene standards. [c] Determined by H and 13C spectroscopy, no trans-1,4-polyisoprene were
found. [d] B(C6F5)3 was used as the activator. [e] [Ph3C][B(C6F5)4] was used as the activator, 20 mL C6H5Cl. [f] mm = 100%, mmmm =
35%. [g] Bimodal distribution.
To investigate the isoprene polymerization catalyzed by
The aminopyridinato-stabilized dibenzyl complex 3a
2a in more detail, the polymerizations were carried out at showed no activity in the polymerization of isoprene in the
different monomer to catalyst ratios. The results are sum- presence of anilinium borate or tris(pentafluorophenyl)-
marized in Table 2. A plot of the concentration of 2a borane (Table 3, run 1–2). However, if [Ph3C][B(C6F5)4] is
against the average number molecular weight (Mn) affords used as an activator a high stereo- and regioselectivity (95%
a linear dependence, indicative of controlled polymerization 3,4-isoprene, mm = 100%, mmmm = 35%, Table 3, run 3)
(Figure 6).
and a narrow molecular weight distribution of 1.68 is ob-
Eur. J. Inorg. Chem. 2009, 4255–4264
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4259

C. Döring, W. P. Kretschmer, T. Bauer, R. Kempe
FULL PAPER
Table 4. Polymerization of isoprene with bis(dimethylsilylamide)scandium complexes.[a]
[b]
Run
Cat.
Yield [%]
Mn ϫ10–3[b]
Mw/Mn
Microstructure [%][c]
3,4:cis-1,4
1[d]
2[e]
3[d]
4[e]
[Sc{N(SiHMe2)2}3(thf)]
[Sc{N(SiHMe2)2}3(thf)]
97
91
100
100
183
64
206
241
2.73
2.81
2.22
2.32
6:94
7:93
22:78
4:96
6a
6a
[a] Conditions: 10 mL C6H5Cl, Cat. 10 µmol, anilinium borate: [C6H5NH(CH3)2][B(C6F5)4] 10 µmol, isoprene: 10 mmol, reaction time:
1
20 h. [b] Determined by GPC against polystyrene standards. [c] Determined by H and 13C spectroscopy, no trans-1,4-polyisoprene was
found. [d] AliBu3 (10 equiv.) used for alkylation/activation. [e] AlMe3 (10 equiv.) used for alkylation/activation.
The diamide 6a is also an effective precatalyst for the
polymerization of isoprene. After alkylation with 10 equiv.
of alkylaluminium compounds (AlMe3 or AliBu3) the com-
pound 6a yields cis-1,4-enriched polyisoprene in the pres-
ence of [C6H5NH(CH3)2][B(C6F5)4] (Table 4, run 3, 4).
Aminopyridinato-stabilized yttrium- or lanthanum di-
amides react with alkylaluminium compounds by transfer
of the aminopyridinato ligand from the rare earth metal to
the aluminium atom.[14] 1H NMR spectroscopic investi-
gations of the reaction of 6a with an excess of trimethylalu-
minium (6 equiv.) reveal that the diamide 6a react immedi-
Figure 6. Plot of concentration of 2a vs. average number molecular
weight (Mn) of the obtained polyisoprene.
ately with the alkylaluminium compound. The proton
NMR spectrum showed the formation of a new aminopyr-
idinato ligand containing species and one equivalent of
[Me2Al{µ-N(SiHMe2)2}]2. Furthermore, two equivalents of
served for the polymer. Isotactically enriched 3,4-polymeri-
zation of isoprene has been rarely described.[1b,4,8g] Ad-
dition of alkylaluminium compounds (Table 3, run 4–13) to
the system 3a/[C6H5NH(CH3)2][B(C6F5)4] also leads to a
polymerization active system with the same trend as it was
observed for 2 as a precatalysts (the use of [Ph3C][B-
(C6F5)4] as an activator leads to a similar selectivity like it
was observed for the system 3a/[C6H5NH(CH3)2][B(C6F5)4]/
AlR3, but it highly increases the molecular weight distribu-
tion, Table 3, run 4). The influence on the cis-1,4-selectivity
in the presence of AlMe3 is even more pronounced (67%
cis-1,4-polyisoprene with 2a vs. 90% with 3a). If less than
10 equiv. of AliBu3 were used a significantly narrower mo-
lecular weight distribution was observed. The presence of
bimodal distributions for the system 3a/[C6H5NH(CH3)2]-
[B(C6F5)4]/AlR3 (R = Me, Et, iBu) suggests also the pres-
ence of several polymerization-active species; because of its
close relation to the amidinato-yttrium system used by
Zhang et al.[4] (addition of AlMe3 switches the regio- and
stereoselectivity), where a heterotrinuclear Y/Al complex is
formed, it is suggested that a similar species might be one
of these active species in our system (Table 3, run 4, 9–11).
The thf-stabilized organoscandium cation 4a does not poly-
unreacted AlMe3 were detected. This led to the conclusion
that a bis(aluminate)scandium species of the type [Ap-
Sc(AlMe4)2] had been formed. A similar formation of a bis-
(aluminate) complex was described by Anwander et al. in
the reaction of [Cp*Ln{N(SiHMe2)2}2] (Cp* = pentameth-
ylcyclopentadienyl, Ln = Y, Lu) with AlMe3.[20] Unfortu-
nately, we did not succeed to separate these species from
the byproduct [Me2Al{µ-N(SiHMe2)2}]2 in order to prove
clearly the existence of the aminopyridinato-bis(aluminate)
complex. The NMR tube reaction of 6a with trimethylalu-
minium also displayed the formation of [ApAlMe2] by li-
gand transfer[11g,14] (11% after 3.5 h, 40% after 10 d).
Further investigations revealed that the triamide
[Sc{N(SiHMe2)2}3(thf)] showed similar cis-1,4-selectivity
under the same conditions for the polymerization of poly-
isoprene (Table 4, runs 1, 2). A similar system ([Nd{N(Si-
Me3)2}3]/[C6H5NH(CH3)2][B(C6F5)4]/AliBu3) also showed
1,4-cis-selectivity for the polymerization of butadiene.[21]
Conclusions
Mono(aminopyridinato)scandium complexes of the type
merize isoprene, even not in the presence of 10 equiv. of [ApScR2(thf)x] (R = CH2SiMe3, CH2Ph, x = 1; R =
AliBu3. N(SiHMe2)2, x = 0) were synthesized and characterized.
We cannot completely rule out the formation of amino- The dialkyl complexes are active and selective catalysts for
pyridinato-aluminium complexes under the polymerization the controlled 3,4-selective polymerization of isoprene after
conditions, but aminopyridinato ligand transfer from the activation by borates. Addition of alkylaluminium com-
lanthanide to the aluminium atom is usually observed in pounds to the catalyst system leads to drastical changes in
significant rates for neutral rare earth complexes and not the microstructure of the polymer which are depending
for cations.[12,14]
from the steric demand of the alkyl ligand of the aluminium
4260
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4255–4264

Scandium Aminopyridinates for Isoprene Polymerization
CCDC-734318 (for 6a), -734319 (for 3a), -734320 (for 4a) contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
and the polymerization temperature. The stereo- and re-
gioselectivity can be improved by polymerization at low
temperatures. The highest stereo- and regioselectivity was
observed for the catalyst/activator system 3a/[Ph3C]-
[B(C6F5)4] (3,4-content 95%, mm = 100%, mmmm = 35%,
Mw/Mn = 1.68), whereas the system 2a/[C6H5NH(CH3)2]-
[B(C6F5)4] shows the narrowest molecular weight distribu-
tion (3,4-content 93%, Mw/Mn = 1.26). The ternary systems
Crystallographic
data_request/cif.
Data
Centre
via
www.ccdc.cam.ac.uk/
Synthesis of the Complexes
Synthesis of 2a: To a mixture of [Sc(CH2SiMe3)3(thf)2] (451 mg,
1.00 mmol) and 1a (457 mg, 1.00 mmol) was added hexane (20 mL)
at room temperature. The reaction mixture was stirred for 1 h and
filtered. Removal of all volatiles under vacuum yielded 610 mg
(80%) of 2a as a yellow crystalline material. C44H67N2OScSi2
(747.2): calcd. C 70.73, H 9.85, N 3.75; found C 70.57, H 10.12, N
6a/AlR3/[C6H5NH(CH3)2][B(C6F5)4]
and
[Sc{N(SiH-
Me2)2}3(thf)]/AlR3/[C6H5NH(CH3)2][B(C6F5)4] (R = Me,
iBu) polymerize isoprene cis-1,4-selective.
2
3.48. 1H NMR (300 MHz, C6D6, 298 K): δ = 0.01 (d, J(H,H) =
11 Hz, 2 H, CHAHBSiMe3), 0.09 (d, 2J(H,H) = 11 Hz, 2 H,
CHAHBSiMe3), 0.14 (s, 18 H, CH2SiMe3), 1.08 (br., 4 H, β-CH2,
THF), 1.16 (d, 3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.20 (d,
Experimental Section
General Procedures Synthesis and Structure: All reactions and ma-
nipulations involving air-sensitive compounds were performed un-
der dry and oxygen free argon by using standard Schlenk and
glovebox techniques. Non-halogenated solvents were dried with so-
dium/benzophenone 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 materials 1a–c,[12,22] tetraisobutylaluminoxane
([iBu2Al]2O, TIBAO),[23] [Sc(CH2SiMe3)3(thf)2],[24] [Sc(CH2Ph)3-
3
3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.23 (d, J(H,H) = 6.8 Hz, 6
3
H, CH(CH3)2), 1.36 (d, J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.61
(d, 3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 2.93 (sept, 3J(H,H) =
6.8 Hz, 1 H, 15-H), 3.16 (sept, 3J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-
3
H), 3.44 (sept, J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-H), 3.81 (br., 4
H, α-CH2, THF), 5.63 (d, 3J(H,H) = 8.5 Hz, 1 H, 3-H), 6.16 (d,
3
3
3J(H,H) = 7.1 Hz, 1 H, 5-H), 6.74 (dd, J(H,H) = 8.5, J(H,H) =
7.1 Hz, 1 H, 4-H), 7.16–7.30 (m, 5 H, 9,11,18,19,20-H) ppm. 13C
NMR (75 MHz, C6D6, 298 K): δ = 3.7, 23.3, 24.1, 24.5, 24.7, 25.3,
27.0, 28.6, 31.0, 35.1, 45.3, 71.5, 106.4, 112.3, 121.2, 124.3, 125.2,
(thf)3],[25]
[Sc{N(SiHMe2)2}3(thf)],[15]
[C6H5NH(CH3)2][B-
(C6H5)4][26] were synthesized according to literature methods. All
other chemicals were purchased from commercial sources in purit-
ies 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 re-
ported in ppm relative to the deuterated solvent. Elemental analy-
ses were carried out with a Vario elementar EL III apparatus. The
molecular weights (Mw/Mn) of the polymers were determined by
gel-permeation 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. X-ray crystal struc-
ture analyses were performed with a STOE-IPDS II equipped with
an Oxford Cryostream low-temperature unit. Structure solution
and refinement were accomplished using SIR97,[27] SHELXL-97[28]
and WinGX.[29] Crystallographic details are summarized in Table 5.
Table 5. Details of the X-ray crystal structure analyses.
Compound
3a
4a
6a
Formula
C50H65N2OScϫC5H12
monoclinic
C2/c
36.4750(12)
12.9730(6)
23.8620(9)
90
118.169(4)
90
4
C75H94BN2O3Sc
triclinic
P1
13.6470(11)
15.2080(13)
19.1700(15)
101.638(6)
98.954(6)
113.099(6)
2
C40H71N4Si4Sc
monoclinic
P21/n
11.6110(5)
18.8400(8)
21.6160(9)
90
103.936(3)
90
4
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
¯
Z
µ [mm–1]
0.186
0.152
0.295
Cell volume [Å3]
Crystal size [mm3]
T [K]
9953.9(7)
0.55ϫ0.29ϫ0.21
133(2)
3460.5(5)
0.35ϫ0.35ϫ0.11
133(2)
4589.3(3)
0.24ϫ0.13ϫ0.12
133(2)
θ range [°]
Reflections unique
Reflections obsd. [IϾ2σ(I)]
Parameters
wR2 (all data)
R value [IϾ2σ(I)]
1.79–26.05
9361
5866
532
0.123
1.52–24.00
10851
5776
742
0.206
1.45–26.19
8654
7552
458
0.109
0.052
0.088
0.040
Eur. J. Inorg. Chem. 2009, 4255–4264
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4261

C. Döring, W. P. Kretschmer, T. Bauer, R. Kempe
FULL PAPER
135.8, 139.6, 144.3, 144.4, 146.7, 149.6, 156.0, 170.0 ppm. 29Si
NMR (60 MHz, C6D6, 298 K): δ = –4.9 ppm.
THF), 5.58 (d, 3J(H,H) = 8.6 Hz, 1 H, 3-H), 5.86 (d, 3J(H,H) =
7.1 Hz, 1 H, 5-H), 6.80 (dd, 3J(H,H) = 8.6, 3J(H,H) = 7.1 Hz, 1
H, 4-H), 7.03–7.20 (m, 6 H, 9,10,11,17,18,19-H) ppm. 13C NMR
(75 MHz, C6D6, 298 K): δ = 3.8, 20.9, 24.1, 24.7, 25.2, 28.4, 44.5,
71.5, 105.6, 109.2, 124.2, 125.3, 127.8, 128.7, 135.9, 139.9, 140.8,
143.9, 144.3, 156.0, 169.5 ppm. 29Si NMR (60 MHz, C6D6, 298 K):
δ = –5.0 ppm.
Synthesis of 2b: The compounds [Sc(CH2SiMe3)3(thf)2] (451 mg,
1.00 mmol) and 1b (415 mg, 1.00 mmol) were dissolved in hexane
(20 mL). The resulting mixture was stirred for 1 h and filtered. The
solvent was removed in vacuo to yield 2b as a yellow crystalline
compound (420 mg, 60%). C41H67N2OScSi2 (705.1): calcd. C
69.84, H 9.58, N 3.97; found C 69.44, H 9.56, N 3.92. 1H NMR
(300 MHz, C6D6, 298 K): δ = –0.01 (d, 2J(H,H) = 11 Hz, 2 H,
CHAHBSiMe3), 0.07 (d, 2J(H,H) = 11 Hz, 2 H, CHAHBSiMe3),
0.16 (s, 18 H, CH2SiMe3), 1.03 (br., 4 H, β-CH2, THF), 1.19 (d,
Synthesis of 3a: [Sc(CH2Ph)3(thf)3] (428 mg, 0.80 mmol) and 1a
(365 mg, 0.80 mmol) were dissolved in thf (20 mL) and stirred at
room temperature for about 1 h. All volatiles were removed under
reduced pressure and the residue was extracted with hexane
(40 mL). Removal of the solvent affords 3a as a yellow spectroscop-
ically pure compound (364 mg, 60%). C50H65N2OSc (755.0): calcd.
3
3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.35 (d, J(H,H) = 6.8 Hz, 6
3
H, CH(CH3)2), 1.59 (d, J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 2.18
(s, 6 H, 28,29-H), 2.21 (s, 3 H, 30-H), 2.92 (sept, 3J(H,H) = 6.8 Hz,
1
C 79.54, H 8.68, N 3.71; found C 79.07, H 9.06, N 3.75. H NMR
3
1 H, 19-H), 3.15 (sept, J(H,H) = 6.8 Hz, 2 H, 13,16-H), 3.74 (br.,
(300 MHz, C6D6, 298 K): δ = 0.79 (br., 4 H, β-CH2, THF), 1.13
3
3
3
4 H, α-CH2, THF), 5.64 (d, J(H,H) = 8.5 Hz, 1 H, 3-H), 6.20 (d,
(d, J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.19 (d, J(H,H) = 6.5 Hz,
12 H, CH(CH3)2), 1.32 (d, 3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.52
(d, 3J(H,H) = 6.7 Hz, 6 H, CH(CH3)2), 2.02 (dd, 3J(H,H) = 8.8 Hz,
4 H, CH2Ph), 2.90 (sept, 3J(H,H) = 6.8 Hz, 1 H, 15-H), 3.23 (sept,
3J(H,H) = 6.7 Hz, 2 H, 13,14/22,23-H), 3.31 (br., 4 H, α-CH2,
3J(H,H) = 7.1 Hz, 1 H, 5-H), 6.84 (m, 3 H, 4-H, 9,11/24,26-H), 7.29
(s. 2 H, 9,11/24,26-H) ppm. 13C NMR (75 MHz, C6D6, 298 K): δ
= 3.9, 19.0, 21.0, 23.3, 24.5, 24.6, 27.1, 31.0, 35.1, 45.3, 71.2, 104.2,
112.0, 121.1, 129.5, 133.0, 133.3, 135.8, 140.0, 143.7, 146.7, 149.6,
156.1, 167.9 ppm. 29Si NMR (79 MHz, C6D6, 298 K):
δ =
3
THF), 3.39 (sept, J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-H), 5.74 (d,
3J(H,H) = 8.5 Hz, 1 H, 3-H), 6.28 (d, 3J(H,H) = 7.1 Hz, 1 H, 5-
H), 6.58 (d, 3J(H,H) = 7.5 Hz, 4 H, o-H), 6.76 (t, 3J(H,H) = 7.1 Hz,
–4.8 ppm.
3
3
2 H, p-H), 6.88 (t, J(H,H) = 7.8 Hz, 1 H, 4-H), 7.05 (t, J(H,H)
= 7.4 Hz, m-H), 7.16 (m, 3 H, 18,19,20-H), 7.33 (s, 2 H, 9,11-H).
13C NMR (100 MHz, C6D6, 298 K): δ = 22.6, 24.0, 24.4, 24.7, 24.9,
27.2, 28.6, 31.3, 34.0, 60.1, 71.5, 105.8, 112.3, 119.1, 121.2, 124.2,
124.6, 125.5, 129.0, 135.5, 139.9, 143.5, 144.4, 147.2, 150.1, 150.2,
155.7, 169.3 ppm.
Synthesis of 4a: To a mixture of 3a (76 mg, 0.10 mmol) and
[C6H5NH(CH3)2][B(C6H5)4] (44 mg, 0.10 mmol) were added thf
(1.0 mL) and toluene (1.0 mL). The reaction mixture was shaken
for 5 min to obtain a clear solution. Slowly diffusion of pentane
into this solution over a period of 3 d affords 4a·(OC4H8) as yellow
crystalline plates which where decanted and washed twice with hex-
ane (2ϫ10 mL); yield 54 mg (40%). [C51H74N2O3Sc][C24H20B]
(OC4H8) (1199.4): calcd. C 79.11, H 8.57, N 2.34; found C 79.10,
H 8.39, N 2.50. 1H NMR (400 MHz, C6D5Br, 298 K): δ = 1.12–
1.16 (m, 12 H, CH(CH3)2), 1.22 (br., 12 H, β-CH2, THF), 1.31–1.35
(m, 12 H, CH(CH3)2), 1.40 (d, 3J(H,H) = 6.9 Hz, 6 H, CH(CH3)2),
Synthesis of 2c: [Sc(CH2SiMe3)3(thf)2] (270 mg, 0.60 mmol) and 1c
(215 mg, 0.60 mg) were dissolved in hexane (20 mL). The mixture
was stirred for 1 h and filtered. All volatiles were removed under
reduced pressure yielding 2c (196 mg, 51%) as a yellow crystalline
material. C37H55N2OScSi2 (649.0): calcd. C 68.47, H 9.16, N 4.32;
found C 68.30, H 9.00, N 4.40. 1H NMR (300 MHz, C6D6, 298 K):
δ = 0.01 (d, 2J(H,H) = 11 Hz, 2 H, CHAHBSiMe3), 0.07 (d, 2J(H,H)
= 11 Hz, 2 H, CHAHBSiMe3), 0.17 (s, 18 H, CH2SiMe3), 1.09 (br.,
4 H, β-CH2, THF), 1.16 (d, 3J(H,H) = 6.9 Hz, 6 H, CH(CH3)2),
1.21 (d, 3J(H,H) = 6.9 Hz, 6 H, CH(CH3)2), 2.40 (s, 6 H, 13,14-H),
3.42 (sept, 3J(H,H) = 6.9 Hz, 2 H, 21,24-H), 3.82 (br., 4 H, α-CH2,
3
2.11 (br., 2 H, CH2Ph), 2.85 (sept, J(H,H) = 6.7 Hz, 2 H, 13,14/
3
22,23-H), 3.02 (sept, J(H,H) = 6.9 Hz, 1 H, 15-H), 3.24 (br., 2 H,
3
13,14/22,23-H), 3.47 (br., 12 H, α-CH2, THF), 5.85 (d, J(H,H) =
3
8.7 Hz, 1 H, 3-H), 6.37 (d, J(H,H) = 7.1 Hz, 1 H, 5-H), 6.53 (d,
3
3J(H,H) = 7.6 Hz, 2 H, o-Benzyl), 6.86 (t, J(H,H) = 7.3 Hz, 1 H,
p-Benzyl), 7.07–7.37 (m, 20 H, m-Benzyl, 4,9,11,18,19,20-H,
BC6H5), 7.83 (br., 8 H, o-BC6H5) ppm. 13C NMR (100 MHz,
C6D5Br, 298 K): δ = 22.9, 24.1, 24.6, 25.7, 26.3, 27.8, 30.5, 34.5,
40.3, 67.4, 68.1, 108.1, 112.7, 113.5, 116.7, 121.2, 125.0, 125.0,
129.1, 134.3, 135.3, 137.2, 137.8, 139.8, 142.2, 143.6, 146.6, 147.3,
1
150.8, 154.2, 164.5 (q, J(C,B) = 49.3 Hz, BC6H5), 169.6 ppm.
Synthesis of 5a: The compounds 2a (75 mg, 0.10 mmol) and
[C6H5NH(CH3)2][B(C6H5)4] (44 mg, 0.10 mmol) were dissolved in
thf (5 mL). The mixture was stirred for 20 min. After removal of
all volatiles the mixture was washed twice with hexane (2ϫ10 mL)
and the remaining yellow solid was dried in vacuo to yield 5a as a
yellow powder (74 mg, 70%). [C44H70N2O2ScSi][C24H20B] (1051.3):
1
calcd. C 77.69, H 8.63, N 2.66; found C 78.05, H 8.95, N 2.31. H
NMR (400 MHz, C6D6, 298 K): δ = 0.02 (s, 9 H, CH2SiMe3), 0.36
(br.,
2 H, CH2SiMe3), 1.00–1.22 (m, 38 H, β-CH2, THF,
CH(CH3)2), 2.66 (br., 2 H, 13,14/22,23-H), 2.79 (sept, 3J(H,H) =
6.9 Hz, 1 H, 15-H), 3.00 (br., 2 H, 13,14/22,23-H), 3.30 (br., 8 H,
4262
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4255–4264

Scandium Aminopyridinates for Isoprene Polymerization
α-CH2, THF), 5.59 (d, 3J(H,H) = 8.6 Hz, 1 H, 3-H), 6.06 (d, valve in C6D6 (0.5 mL). After the addition of 6 equiv. trimethylalu-
3J(H,H) = 7.1 Hz, 1 H, 5-H), 7.05–7.28 (m, 18 H, 4,9,11,18,19,20- minium (19 µL, 0.2 mmol) the tube was sealed and shaken. 1H
H, BC6H5), 7.95 (br., 8 H, o-BC6H5) ppm. 13C NMR (100 MHz,
C6D6, 298 K): δ = 3.4, 23.7, 24.6, 24.7, 25.5, 25.6, 26.5, 29.2, 31.2,
35.1, 40.6, 72.7, 108.5, 113.4, 121.7, 122.6, 125.4, 126.5, 127.3,
NMR (400 MHz, C6D6, 298 K): δ = –0.34 (s, 24 H, AlMe4), –0.13–
0.07 (br., 30 H, AlMe3, NAlMe2), 0.19 (d, 3J(H,H) = 3.0 Hz, 24
3
H, Si(CH3)2), 1.08 (d, J(H,H) = 6.7 Hz, 6 H, CH(CH3)2), 1.12 (d,
3
129.7, 137.4, 139.3, 141.7, 142.5, 147.2, 151.4, 154.9, 165.4 (q, 3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.26 (d, J(H,H) = 6.9 Hz, 6
1J(C,B) = 49.5 Hz, BC6H5), 169.7 ppm.
H, CH(CH3)2), 1.31 (d, J(H,H) = 6.7 Hz, 6 H, CH(CH3)2), 1.32
3
3
(d, J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 2.76–2.95 (m, 3 H, 13,14/
Synthesis of 6a: The compounds [Sc{N(SiHMe2)2}3(thf)] (797 mg,
1.55 mmol) and 1a (708 mg, 1.55 mmol) were dissolved in toluene
(20 mL). The reaction mixture was stirred at 60 °C for 4 d. All vola-
tiles were removed and the residue was extracted with hexane
(40 mL). The solvent was removed in vacuo to yield 925 mg (78%)
of a yellow crystalline compound. C40H71N4ScSi4 (765.3): calcd. C
62.78, H 9.35, N 7.32; found C 62.26, H 9.49, N 7.02. 1H NMR
(400 MHz, C6D6, 298 K): δ = 0.17 (d, 3J(H,H) = 2.3 Hz, 12 H,
Si(CH3)2), 0.23 (d, 3J(H,H) = 2.2 Hz, 12 H, Si(CH3)2), 1.11–1.15
(m, 12 H, CH(CH3)2), 1.27 (d, 3J(H,H) = 6.9 Hz, 6 H, 30,31-H),
1.40–1.42 (m, 12 H, CH(CH3)2), 2.83 (sept, 3J(H,H) = 6.9 Hz, 1
22,23-H, 15-H), 3.37 (sept, 3J(H,H) = 6.7 Hz, 2 H, 13,14/22,23-H),
4.74 (sept, 1J(Si,H) = 211, 3J(H,H) = 3 Hz, 4 H, SiH), 5.68 (d,
3J(H,H) = 8.6 Hz, 1 H, 3-H), 6.13 (d, 3J(H,H) = 7.1 Hz, 1 H, 5-
3
3
H), 6.80 (dd, J(H,H) = 7.1, J(H,H) = 8.6 Hz, 1 H, 4-H), 7.17 (s,
2 H, 9,11-H), 7.23 (s, 3 H, 18,19,20-H) ppm.
Polymerization of Isoprene: A detailed polymerization procedure
(Table 1, run 4) is described as a typical example. In a glove box
the complex 2a (8 mg, 10 µmol) was dissolved in C6H5Cl (8 mL)
and isoprene (680 mg, 1 mL, 10 mmol) was added. The mixture
was placed in a water bath (20 C). Then AlMe3 (100 µmol, 50 µL,
2.0  in hexane) and a solution of [C6H5NH(CH3)2][B(C6F5)4]
(8 mg, 10 µmol) in C6H5Cl (2 mL) were added. After stirring for
20 h at room temperature the mixture was poured into a large
quantity of acidified 2-propanol containing 0.1% (w/w) 2,6-di-tert-
butyl-4-methylphenol as a stabilizing agent. The precipitated poly-
mer was decanted, washed with 2-propanol and dried in vacuo at
60 °C to a constant weight to afford 680 mg of polyisoprene
(100%). The microstructure of the polymer was examined by 13C
NMR spectroscopy in CDCl3.
3
H, 15-H), 2.95 (sept, J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-H), 3.60
3
1
(sept, J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-H), 4.92 (br., J(Si,H) =
3
162 Hz, 4 H, SiH), 5.63 (d, J(H,H) = 8.6 Hz, 1 H, 3-H), 6.02 (d,
3J(H,H) = 7.0 Hz, 1 H, 5-H), 6.67 (t, 3J(H,H) = 7.8 Hz, 1 H, 4-H),
7.14–7.28 (m, 5 H, 9,11,18,19,20-H) ppm. 1H NMR (300 MHz,
[D8]toluene, 373 K): δ = 0.15 (d, 3J(H,H) = 2.8 Hz, 24 H,
Si(CH3)2) 1.09 (d, 3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.11 (d,
3
3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.26 (d, J(H,H) = 6.9 Hz, 6
3
H, 30,31-H), 1.34 (d, J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 1.38 (d,
3
3J(H,H) = 6.8 Hz, 6 H, CH(CH3)2), 2.85 (sept, J(H,H) = 6.9 Hz,
1 H, 15-H), 2.94 (sept, 3J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-H), 3.52
3
3
(sept, J(H,H) = 6.8 Hz, 2 H, 13,14/22,23-H), 4.86 (sept, J(H,H)
Acknowledgments
= 2.8, 1J(Si,H) = 164 Hz, 4 H, SiH), 5.66 (dd, 3J(H,H) = 8.6,
1J(H,H) = 0.9 Hz, 1 H, 3-H), 6.01 (dd, J(H,H) = 7.0, J(H,H) =
0.9 Hz, 1 H, 5-H), 6.80 (dd, 3J(H,H) = 7.0, 3J(H,H) = 8.6 Hz, 1 H,
4-H), 6.96–7.22 (m, 5 H, 9,11,18,19,20-H) ppm. 13C NMR
(100 MHz, C6D6, 298 K): δ = 2.1, 2.8, 24.1, 24.2, 24.3, 25.4, 25.7,
28.3, 30.9, 34.7, 107.2, 111.5, 121.0, 124.3, 125.6, 135.3, 139.3,
142.7, 144.1, 146.4, 149.3, 156.3 168.6; ppm. 29Si NMR (60 MHz,
[D8]toluene, 298 K): δ = –19.3 ppm.
3
1
Financial support from the Deutsche Forschungsgemeinschaft
(DFG) (SPP 1166 “Lanthanide-specific functionalities in molecules
and materials“) and the Fonds der Chemischen Industrie is ac-
knowledged. We thank A. M. Dietel and H. Maisel for lab assist-
ance.
NMR Tube Reaction of 2a with [C6H5NH(CH3)2][B(C6F5)4]: The
compounds 2a (15 mg, 20 µmol) and [C6H5NH(CH3)2][B(C6F5)4]
(16 mg, 20 µmol) were dissolved in deuterated bromobenzene
(0.5 mL) and thf (30 µL) was added. After 5 min the solution was
transferred into a NMR tube equipped with a young valve. 1H
NMR (400 MHz, C6D5Br, 298 K): δ = 0.00 (s, 12 H, SiMe4), 0.11
(s, 9 H, CH2SiMe3), 0.31 (br., 2 H, CH2SiMe3), 1.10–1.13 (m, 12
[1] a) S. Arndt, K. Beckerle, P. M. Zeimentz, T. P. Spaniol, J.
Okuda, Angew. Chem. 2005, 117, 7640–7644; Angew. Chem.
Int. Ed. 2005, 44, 7473–7477; b) L. Zhang, Y. Luo, Z. Hou, J.
Am. Chem. Soc. 2005, 127, 14562–14563.
[2] a) E. Le Roux, F. Nief, F. Jaroschik, K. W. Törnroos, R. An-
wander, Dalton Trans. 2007, 4866; b) M. Zimmermann, K. W.
Törnroos, R. Anwander, Angew. Chem. 2008, 120, 787–790;
Angew. Chem. Int. Ed. 2008, 47, 775–778; c) M. Zimmermann,
K. W. Törnroos, H. Sitzmann, R. Anwander, Chem. Eur. J.
2008, 14, 7266–7277; d) B. Wang, D. Cui, K. Lv, Macromole-
cules 2008, 41, 1983–1988; e) N. Yu, M. Nishiura, X. Li, Z. Xi,
Z. Hou, Chem. Asian J. 2008, 3, 1406–1414; f) H. Zhang, Y.
Luo, Z. Hou, Macromolecules 2008, 41, 1064–1066; g) A.-S.
Rodriguesa, E. Kirillova, B. Vuilleminb, A. Razavic, J.-F. Carp-
entier, Polymer 2008, 49, 2039–2045.
[3] a) L. Zhang, T. Suzuki, Y. Luo, M. Nishiura, Z. Hou, Angew.
Chem. 2007, 119, 1941–1945; Angew. Chem. Int. Ed. 2007, 46,
1909–1913; b) Y. Luo, M. Nishiura, Z. Hou, J. Organomet.
Chem. 2007, 692, 536–544; c) Y. Yang, B. Liu, K. Lv, W. Gao,
D. Cui, X. Chen, X. Jing, Organometallics 2007, 26, 4575–4584;
d) Y. Yang, Q. Wang, D. Cui, J. Polym. Sci., Part A 2008, 46,
5251–5262; e) S. Li, W. Miao, T. Tang, W. Dong, X. Zhang, D.
Cui, Organometallics 2008, 27, 718–725; f) W. Gao, D. Cui, J.
Am. Chem. Soc. 2008, 130, 4984–4991.
3
H, CH(CH3)2), 1.30–1.34 (m, 12 H, CH(CH3)2), 1.36 (d, J(H,H)
= 6.9 Hz, 6 H, CH(CH3)2), 1.64 (br., β-CH2, THF), 2.78 (s, 6 H,
NMe2), 2.88 (br., 2 H, 13,14/22,23-H), 2.98 (sept, 3J(H,H) =
6.9 Hz, 1 H, 15-H), 3.22 (br., 2 H, 13,14/22,23-H), 3.67 (br., α-CH2,
THF), 5.78 (d, 3J(H,H) = 8.6 Hz, 1 H, 3-H), 6.32 (d, 3J(H,H) =
3
7.1 Hz, 1 H, 5-H), 6.72 (d, J(H,H) = 8.1 Hz, 2 H, o-C6H5NMe2),
3
3
6.83 (t, J(H,H) = 7.3 Hz, 1 H, p-C6H5NMe2), 7.11 (dd, J(H,H)
= 8.6, 3J(H,H) = 7.1 Hz, 1 H, 4-H), 7.23 (s, 2 H, 9,11-H), 7.27–7.33
(m, 5 H, 18,19,20-H, m-C6H5NMe2) ppm. 13C NMR (100 MHz,
C6D5Br, 298 K): δ = 0.0, 3.6, 23.0, 24.2, 24.5, 24.7, 25.8, 26.4, 27.9,
30.6, 34.6, 40.4, 67.5, 108.2, 112.8, 113.6, 116.8, 121.3, 125.1, 129.2,
134.4, 135.4, 137.2, 137.8, 139.7, 139.9, 142.3, 143.7, 146.7, 147.5,
149.9, 150.9, 154.3, 169.7 ppm. 19F NMR (376 MHz, C6D5Br,
298 K): δ = –132.4 (br. d, 3J(F,F) = 12.0 Hz, o-F), –162.7 (t, 3J(F,F)
3
= 21.0 Hz, p-F), –166.7 (t, J(F,F) = 18.9 Hz, m-F) ppm.
[4] L. Zhang, M. Nishiura, M. Yuki, Y. Luo, Z. Hou, Angew.
Chem. 2008, 120, 2682–2685; Angew. Chem. Int. Ed. 2008, 47,
2642–2645.
NMR Tube Reaction of 6a with AlMe3: The complex 6a (25 mg,
33 µmol) was dissolved in a NMR tube equipped with a young
Eur. J. Inorg. Chem. 2009, 4255–4264
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4263

C. Döring, W. P. Kretschmer, T. Bauer, R. Kempe
FULL PAPER
[5] For an example of a stoichiometric reaction of a yttrium alkyl
complex with isoprene see: B. Liu, X. Liu, D. Cui, L. Liu,
Organometallics 2009, 28, 1453–1460.
[6] a) J. Wolpers, H. B. Fuchs, C. Herrmann, W. Hellermann,
K. H. Nordsiek, Eur. Pat. Appl. EP 456902 A1, 1991; b) J. D.
Massie, W. Hsu, A. F. Halasa, P. H. Sandstrom, US Pat. US
5356997, 1994; c) A. F. Halasa, W. Hsu, D. J. Zanzig, G. L.
Allen, L. E. Austin, US Patent US 5627237 A, 1997.
[7] Selected reviews on isoprene polymerization: a) L. Porri, A.
Giarrusso, in: Comprehensive Polymer Science, vol. 4 (Eds.:
G. C. Eastmond, A. Ledwith, S. Russo, P. Sigwalt), Pergamon,
Oxford, 1989, pp. 74–79; b) R. Taube, G. Sylvester, in: Applied
Homogeneous Catalysis with Organometallic Compounds, vol. 2
(Eds.: B. Cornils, W. A. Herrmann), Wiley-VCH, Weinheim,
1996, pp. 285–315; c) L. Friebe, O. Nuyken, W. Obrecht, Adv.
Polym. Sci. 2006, 204, 82–83; d) A. Fischbach, R. Anwander,
Adv. Polym. Sci. 2006, 204, 155–191.
Kempe, Eur. J. Inorg. Chem. 2008, 2377–2381; i) D. M. Lyubov,
C. Döring, G. K. Fukin, A. V. Cherkasov, A. V. Shavyrin, R.
Kempe, A. A. Trifonov, Organometallics 2008, 27, 2905–2907;
j) A. Noor, F. R. Wagner, R. Kempe, Angew. Chem. 2008, 120,
7356–7359; Angew. Chem. Int. Ed. 2008, 47, 7246–7259; k) A.
Noor, W. P. Kretschmer, G. Glatz, A. Meetsma, R. Kempe, Eur.
J. Inorg. Chem. 2008, 5088–5098; l) A. Noor, G. Glatz, R.
Müller, M. Kaup, S. Demeshko, R. Kempe, Nature Chem.
2009, 1, 322–325.
W. P. Kretschmer, A. Meetsma, B. Hessen, T. Schmalz, S.
Qayyum, R. Kempe, Chem. Eur. J. 2006, 12, 8969–8978.
G. Glatz, S. Demeshko, G. Motz, R. Kempe, Eur. J. Inorg.
Chem. 2009, 1385–1392.
[12]
[13]
[14]
[15]
C. Döring, R. Kempe, Eur. J. Inorg. Chem. 2009, 412–418.
R. Anwander, O. Runte, J. Eppinger, G. Gerstberger, E.
Herdtweck, M. Spiegler, J. Chem. Soc., Dalton Trans. 1998,
847–858.
[8] For examples of 3,4-polymerization of isoprene please see: a)
G. Natta, L. Porri, A. Carbonaro, Makromol. Chem. 1964, 77,
126–138; b) W. Gronski, N. Murayama, H. J. Cantow, T. Miya-
moto, Polymer 1976, 17, 358–360; c) G. Ricci, M. Battistella,
L. Porri, Macromolecules 2001, 34, 5766–5769; d) C. Bazzini,
A. Giarrusso, L. Porri, Macromol. Rapid Commun. 2002, 23,
922–927; e) Y. Nakayama, Y. Baba, H. Yasuda, K. Kawakita,
N. Ueyama, Macromolecules 2003, 36, 7953–7958; f) C. Baz-
zini, A. Giarrusso, L. Porri, B. Pirozzi, R. Napolitano, Polymer
2004, 45, 2871–2875; g) Z. Hou, Y. Luo, X. Li, J. Organomet.
Chem. 2006, 691, 3114–3121.
[16]
[17]
B. K. Campion, R. H. Heyn, T. D. Tilley, Organometallics
1993, 12, 2584–2590.
A. D. Sadow, T. D. Tilley, J. Am. Chem. Soc. 2005, 127, 643–
656.
D. A. Kleier, G. Binsch, J. Magn. Reson. 1970, 3, 146–160.
H. Ma, T. P. Spaniol, J. Okuda, Dalton Trans. 2003, 4770–4780.
R. Anwander, M. G. Klimpel, H. M. Dietrich, D. J. Shorokhov,
W. Scherer, Chem. Commun. 2003, 1008–1009.
[18]
[19]
[20]
[21] V. Monteil, R. Spitz, C. Boisson, Polym. Int. 2004, 53, 576–
581.
[9] For a theoretical review on butadiene polymerization with
transition metals, see: S. Tobisch, THEOCHEM 2006, 771,
171–179.
[22] N. M. Scott, T. Schareina, O. Tok, R. Kempe, Eur. J. Inorg.
Chem. 2004, 3297–3304.
[23] World Pat. Appl. WO 2000035974 A1, J. F. van Baar, P. A.
Schut, A. D. Horton, O. T. Dall, G. M. M. van Kassel, Montell
Techn. Co., June 22, 2000.
[24] M. F. Lappert, R. J. Pearce, J. Chem. Soc., Chem. Commun.
1973, 126–127.
[10] For review articles on aminopyridinato ligands see: a) R.
Kempe, H. Noss, T. Irrgang, J. Organomet. Chem. 2002, 647,
12–20; b) R. Kempe, Eur. J. Inorg. Chem. 2003, 791–803.
[11] For selected work with very bulky aminopyridinato ligands ple-
ase see: a) N. M. Scott, R. Kempe, Eur. J. Inorg. Chem. 2005,
1319–1324; b) W. P. Kretschmer, A. Meetsma, B. Hessen, N. M.
Scott, S. Qayyum, R. Kempe, Z. Anorg. Allg. Chem. 2006, 632,
1936–1938; c) S. M. Guillaume, M. Schappacher, N. M. Scott,
R. Kempe, J. Polym. Sci., Part A 2007, 45, 3611–3619; d) A. M.
Dietel, O. Tok, R. Kempe, Eur. J. Inorg. Chem. 2007, 4583–
4586; e) S. Qayyum, K. Haberland, C. M. Forsyth, P. C. Junk,
G. B. Deacon, R. Kempe, Eur. J. Inorg. Chem. 2008, 557–562;
f) G. G. Skvortsov, G. K. Fukin, A. A. Trifonov, A. Noor, C.
Döring, R. Kempe, Organometallics 2007, 26, 5770–5773; g)
W. P. Kretschmer, B. Hessen, A. Noor, N. M. Scott, R. Kempe,
J. Organomet. Chem. 2007, 692, 4569–4579; h) A. Noor, R.
[25] N. Meyer, P. W. Roesky, S. Bambirra, A. Meetsma, B. Hessen,
K. Saliu, J. Takats, Organometallics 2008, 27, 1501–1505.
[26] F. E. Crane, Anal. Chem. 1956, 28, 1794–1797.
[27] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C.
Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Crystallogr. 1999, 32, 115–119.
[28] G. M. Sheldrick, SHELX-97, Program for Crystal Structure
Analysis (rel. 97-2), Institut für Anorganische Chemie der Uni-
versität, Göttingen, Germany, 1998.
[29] L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837–838.
Received: June 5, 2009
Published Online: August 19, 2009
4264
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 4255–4264