Homogeneous Ethylene-Polymerization Catalysts Based on Alkyl Cations of the Rare-Earth Metals: Are Dicationic Mono(alkyl) Complexes the Active Species?

Article abstract of DOI:10.1002/anie.200352532

Easily accessible, the tris(alkyl) complexes of rare-earth elements [Ln(CH₂SiMe₃)₃(thf)₂] are activated by [NMe₂HPh] [B(C₆F₅)₄] in the presence of AliBu₃ to

Full text of DOI:10.1002/anie.200352532

Angewandte
Chemie
Efficient Ethylene Polymerization
Homogeneous Ethylene-Polymerization Catalysts
Based on Alkyl Cations of the Rare-Earth Metals:
Are Dicationic Mono(alkyl)Complexes the
Active Species?**
Stefan Arndt, Thomas P. Spaniol, and Jun Okuda*
Cationic alkyl complexes of Group 4 metals, for example,
alkyl zirconocenium ions, currently play a pivotal role as
single-site catalysts in homogeneous olefin-polymerization
reactions.[1] The first cationic alkyl rare earth metal complex
[La(h5-C5Me5){CH(SiMe3)2}(thf)x]+[BPh4]ꢀ (x = 0 or 3) was
reported in 1992,[2a] and since then, there has only been one
report with evidence that such a complex, a scandium
dimethyl cation, polymerizes ethylene.[2b] A number of
cationic alkyl complexes of the rare-earth metals [Ln(L)R]+
supported by monoanionic ancillary noncyclopentadienyl
ligands L, such as the amido-functionalized triazacyclono-
nane,[3] b-diketiminate,[4] or benzamidinate[5] were surmised to
also catalyze ethylene polymerization. We reported that the
thermally sensitive tris(trimethylsilylmethyl) complexes
[Ln(CH2SiMe3)3(thf)2] (L n= Lu, Y)[6] can be transformed
into robust monocationic bis(alkyl) complexes [Ln(CH2Si-
Me3)2(thf)x]+ by the reaction with BPh3.[7] Herein we report
that the tris(alkyl) complexes [Ln(CH2SiMe3)3(thf)2] without
any ancillary ligand Lcan act as precursors for highly active
catalysts for homogeneous ethylene polymerization. There is
evidence that the active species are the dications [Ln(CH2Si-
Me3)(solv)z]2+, which are formed by the protonolysis of
[Ln(CH2SiMe3)3(thf)2] via the dialkyl monocations
[Ln(CH2SiMe3)2(solv)y]+.
Toluene solutions of the alkyl complexes [Ln(CH2Si-
Me3)3(thf)2] (L n= Tm, Er, Y, Ho, Dy, Tb) efficiently catalyze
ethylene polymerization upon activation with the Brønsted
acid [NMe2HPh][B(C6F5)4] in the presence of AliBu3. After
short run times (10 min) at 5 bar of ethylene pressure, linear
¯
polyethylenes with molecular weights Mn = 3500–45000 and
¯
¯
polydispersities Mw/Mn = 2–6 were produced with activities
up to 899 kgmolꢀ1 hꢀ1 barꢀ1 (Table 1). As illustrated in
Figure 1, the catalyst performance can be adjusted by the
choice of the rare-earth metal as the activity is well correlated
[*] Prof. Dr. J. Okuda,+ Dipl.-Chem. S. Arndt, Dr. T. P. Spaniol
Institut für Anorganische Chemie und Analytische Chemie
JohannesGutenberg-Universität Mainz
Duesbergweg 10–14, 55099 Mainz (Germany)
Fax: (+49)6131-39-25605
E-mail: okuda@mail.uni-mainz.de
[+] New address:
Institute of Inorganic Chemistry
Aachen University of Technology (RWTH)
Prof.-Pirlet-Strasse 1, 52056 Aachen (Germany)
[**] Financial support by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie is gratefully acknowledged. We
thank Prof. Dr. U. Englert for recording the crystallographic data, Dr.
S. Matsui for GPC analysis, and Dipl.-Chem. K. Beckerle for DSC
analysis.
Angew. Chem. Int. Ed. 2003, 42, 5075 –5079
DOI: 10.1002/anie.200352532
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5075

Communications
Table 1: Ethylene polymerization with [Ln(CH2SiMe3)3(thf)2] ascatalyst
precursor.[a]
R[b] [Š] Yield [g] Activity
Mn
¯
¯ ¯
Mw/Mn Tm [8C]
Ln
[kgmolꢀ1 hꢀ1 barꢀ1
]
[gmolꢀ1
]
Sc[c] 0.89
Lu[c] 1.00
0.03
traces–
–
1
–
–
–
–
–
–
Yb
1.01
–
–
–
–
Tm 1.02
0.76
0.85
0.91
1.15
183
205
272
275
22033
13430
14150
44847
4.1
5.3
2.9
1.7
136.7
134.7
135.5
132.5
Er
1.03
Y[d] 1.04
Ho 1.04
3446[e] 1.8
Dy 1.05
3.51
3.74
842
899
3652
3816
3.6
2.9
126.3
126.3
Tb
1.06
[a] [NMe2HPh][B(C6F5)4] asactivator in the preesnce of Al iBu3. Con-
ditions: 5 mmol Ln; B:Ln=5:1, Al:Ln=200:1, T=258C, p=5 bar, t=
10 min, V=30 mL (toluene). [b] Effective ionic radiusof Ln 3+ for CN=6,
Scheme 1. Activation of [Y(CH2SiMe3)3(thf)2] with [NMe2HPh][B(C6F5)4]
in the presence of Al(CH2SiMe3)3; [a] isolated, [b] analogous complex
isolated as [Y(CH2SiMe3)2(thf)4]+[BPh4]ꢀ, [c] solv=toluene in polymeri-
zation experiments, the exchange of THF by toluene is postulated,[11]
[d] xs=excess, [e] analogous complex isolated as [Y(CH2Si-
see reference [8]
weight distribution.
. [c] t=60 min. [d] t=8 min. [e] Bimodal molecular
Me3)(thf)5]2+[BPh4]ꢀ
.
2
and NMR-tube experiments, the use of the polar solvents
pyridine or THF was required, as oils form from aromatic
hydrocarbons such as toluene, benzene, or bromobenzene. To
avoid ring opening polymerization of THF, the use of [BPh4]ꢀ
instead of [B(C6F5)4]ꢀ as the counter anion was required when
THF was used as solvent.
When a THF solution containing the yttrium tris(alkyl)
[Y(CH2SiMe3)3(thf)2] and three equivalents of [NMe2HPh]
[BPh4] was stirred for 24 h at 258C, colorless microcrystals of
the thermally robust dicationic alkyl complex [Y(CH2Si-
Me3)(thf)5]2+[BPh4]ꢀ were isolated in virtually quantitative
2
yield.[12] In [D5]pyridine, the methylene protons at yttrium
2
appear as a doublet at d = 0.73 ppm with J(Y,H) = 3.3 Hz in
the corresponding 1H NMR, while the 13C NMR spectrum
exhibits a doublet for the YCH2 group at d = 44.5 with
1J(Y,C) = 44.9 Hz. The 89Y NMR resonance of [Y(CH2Si-
Figure 1. Plot of the polymerization activity versus the effective ionic
radius R of the trivalent rare earth metal for coordination number
CN=6.
Me3)(thf)5]2+[BPh4]ꢀ in [D8]THF at d = 409.2 is shifted to a
2
significantly higher field compared with that for the corre-
sponding
monocations
[Y(CH2SiMe3)2(thf)4]+[Al(CH2-
with the effective ionic radius[8] of the rare-earth metal. For
the smaller elements scandium, lutetium, and ytterbium, no
significant activity was observed, whereas thulium produced
polyethylene with 183 kgmolꢀ1 hꢀ1 barꢀ1. For terbium, the
element with the largest radius within the series examined, an
activity of 899 kgmolꢀ1 hꢀ1 barꢀ1 was found, corroborating
that rare-earth metal alkyl cations are the active species.[9]
Although the active species initially appeared to be the
monocationic bis(alkyl) complex [Ln(CH2SiMe3)2(sol-
v)y]+[B(C6F5)4]ꢀ (Scheme 1), with aluminum alkyl acting as
scavenger for THF, two findings cast doubts on this hypoth-
esis. 1) Why is an excess of [NMe2HPh][B(C6F5)4] necessary
to activate the catalyst precursor?[10] 2) Why does the choice
of the aluminum alkyl have a significant influence on the
polymerization results?[11] We therefore studied the following
(Scheme 1) as model reactions for the activation steps: 1) The
reaction of [Y(CH2SiMe3)3(thf)2] with excess [NMe2HPh]
[BPh4]. 2) The reactivity of [Y(CH2SiMe3)3(thf)2] towards the
aluminum alkyl Al(CH2SiMe3)3. For these preparative-scale
SiMe3)4]ꢀ (d = 666.4,), [Y(CH2SiMe3)2(thf)4]+[BPh4]ꢀ (d =
660.0) or the neutral analogue [Y(CH2SiMe3)3(thf)2] (d =
882.7).
The reaction of [Y(CH2SiMe3)3(thf)2] in THF with more
than two equivalents [NMe2HPh][BPh4] to give the dication
[Y(CH2SiMe3)(thf)5]2+[BPh4]ꢀ as the exclusive yttrium-con-
2
taining species suggests that the activation of the tris(alkyl)
precursors [Ln(CH2SiMe3)3(thf)2] in toluene with [NMe2HPh]
[B(C6F5)4] generates dications [Ln(CH2SiMe3)(solv)z]2+ as the
active species.[13] When the tris(aluminate) [Y{(m-
Me2)(AlMe2)}3][14] was treated with excess [NEt3H][BPh4] in
THF, the ion triple [Y(CH3)(THF)6]2+[BPh4]ꢀ was obtained
2
in crystalline form [Eq. (1)].[15] The resonance of the methyl
2 ½NEt3HŠ½BPh4
3
Š
½Yfðm-Me ÞðAlMe Þg Š
ƒƒƒƒƒƒƒ!
2
2
THF
ð1Þ
½YðCH3ÞðthfÞ6Š ½BPh4Šꢀ þ 2 NEt3 þ 2 CH4 þ 3 AlMe3
2þ
2
group at the yttrium appears as a doublet in [D5]pyridine at
d = 0.69 with 2J(Y,H) = 2.1 Hz. The 13C NMR spectrum
5076
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2003, 42, 5075 –5079

Angewandte
Chemie
Table 2: Ethylene polymerization with yttrium catalyst precursors.[a]
exhibits a doublet for the YCH3 group at
d = 32.8 with 1J(Y,C) = 53.6 Hz, while the
89Y-NMR resonance appears at d = 433.2.
Precursor[b]
Aluminum
alkyl
Yield [g]
Activity
Mn
Mw/Mn
Tm [8C]
¯
¯
¯
[kgmolꢀ1 hꢀ1 barꢀ1
]
[gmolꢀ1
]
Single
crystals
of
[YR3(thf)2]
[YR3(thf)2]
[YR3(thf)2][c]
[YR3(thf)2]
AlEt3
AlnOct3
AliBu3
0.11
0.43
0.91
1.67
27
–
–
–
–
128.3
136.7
135.5
130.2
ꢀ
[Y(CH3)(thf)6]2+[BPh4]
suitable for X-
2
103
272
401
ray structure analysis were grown from a
14150
59730
2.9
1.7
2.3
2.9
2.4
–
supersaturated THF solution.[15b] The cati-
AliBu2H
3030[d]
110990
215599
–
onic
portion
of
the
ion
triple
[YR3(thf)2][e]
AlR3
AlR3
1.53
1.13
1.41
1840
1351
339
138.0
141.6
133.1
[Y(CH3)(thf)6]2+[BPh4]ꢀ
is shown in
2
[YR2(thf)4]+[AlR4]ꢀ[e,f]
[YR3(thf)2]
Figure 2, which illustrates the pentagonal
bipyramidal coordination geometry around
the yttrium center with the methyl group in
MAO[g]
[a] [NMe2HPh][B(C6F5)4] asactivator in the presence of aluminum alkyl. Conditions: 5 mmol Y, B:Y=5:1,
Al:Y=200:1, T=258C, p=5 bar, t=10 min, V=30 mL (toluene) [b] R=CH2SiMe3. [c] t=8 min.
[d] Bimodal molecular weight distribution. [e] t=2 min. [f] Al:Y=100:1. [g] Methylaluminoxane.
ꢀ
the apical position. The Y C bond length of
2.418(3) Š is comparable with those found
for the ion pair [Y(CH2SiMe3)2(th-
f)4]+[Al(CH2SiMe3)4]ꢀ
(2.384(6)
and
2.411(6) Š),[16] while the Y O bond lengths of
pair
[Y(CH2SiMe3)2(thf)4]+[Al(CH2SiMe3)4]ꢀ.
In
the
ꢀ
[Y(CH3)(thf)6]2+[BPh4]ꢀ (2.352(3)–2.427(3) Š) are similar
1H NMR spectrum of the product in [D8]THF, the resonance
of the methylene protons at the aluminate center was
recorded at d = ꢀ1.28 ppm as a broad multiplet owing to
2J(Al,H) coupling, whereas the methylene protons at the
cationic yttrium appear as a doublet at d = ꢀ0.73 with
2J(Y,H) = 3.1 Hz. The 13C NMR spectrum exhibits a doublet
2
ꢀ
to those found for Y O(THF) bond lengths at monocationic
yttrium centers.[17]
1
for the YCH2 group at d = 37.2 with J(Y,C) = 42.1 Hz.
Single crystals of [Y(CH2SiMe3)2(thf)4]+[Al(CH2-
SiMe3)4]ꢀ suitable for X-ray structure analysis were obtained
from pentane/THF.[15b] The cationic portion of the ion pair
[Y(CH2SiMe3)2(thf)4]+[Al(CH2SiMe3)4]ꢀ is shown in Figure 3,
which illustrates the distorted octahedral-coordination geom-
Figure 2. Molecular structure of the cationic portion of
[Y(CH3)(thf)6]2+[BPh4]ꢀ2. Thermal ellipsoids are drawn at the 30%
probability level, hydrogen atomsare omitted for clarity. Selected dis-
tances[Š] and angles[ 8]: Y-O1 2.352(3), Y-O2 2.426(3), Y-O3 2.355(3),
Y-O4 2.427(3), Y-O5 2.377(3), Y-O6 2.427(3), Y-C25 2.418(3); C25-Y-
O6 176.5(1).
The nature of the aluminum alkyl compounds was found
to have a remarkable influence on both the activity of the
catalyst system [Y(CH2SiMe3)3(thf)2]/[NMe2HPh][B(C6F5)4]
¯
as well as the molecular weight Mn. From Table 2 it is
apparent that the steric bulk of the alkyl group at the
aluminum center is critical with respect to the activity: only
traces of polyethylene were obtained with AlMe3, whereas
the use of Al(CH2SiMe3)3 gave high molecular weight poly-
¯
ethylene (Mn = 110990) with an outstanding activity of
Figure 3. Molecular structure of the cationic portion of [Y(CH2Si-
Me3)2(thf)4]+[Al(CH2SiMe3)4]ꢀ. Thermal ellipsoids are drawn at the
20% probability level, hydrogen atomsare omitted for clarity. Selected
distances [Šꢀ1] and angles[ 8]: Y-O1 2.448(4), Y-O2 2.354(4), Y-O3
2.354(4), Y-O4 2.479(4), Y-C1 2.384(6), Y-C5 2.411(6); O1-Y-C5
163.7(2), O2-Y-O3 165.3(1), O4-Y-C1 171.0 (2).
1840 kgmolꢀ1 hꢀ1 barꢀ1.[18]
Equimolar amounts of [Y(CH2SiMe3)3(thf)2] and Al(CH2-
[19]
SiMe3)3
were found to form the ion pair [Y(CH2Si-
Me3)2(thf)x]+[Al(CH2SiMe3)4]ꢀ in C6D6 and in [D8]THF,
which was isolated in 75% yield as the thermally stable ion
Angew. Chem. Int. Ed. 2003, 42, 5075 –5079
www.angewandte.org
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5077

Communications
etry around the yttrium center with the two alkyl groups
Keywords: alkyl ligands· aluminum · cations· polymerization ·
rare earth elements
.
arranged in a cis fashion.[20] The formation of alkyl aluminates
of the rare-earth metals as ion pairs is unprecedented. So far,
only complexes containing bridging alkyl groups such as
[Y{(m-Me2)(AlMe2)}3][14] were reported for the trivalent rare
earth metals. When [Y(CH2SiMe3)2(thf)4]+[Al(CH2SiMe3)4]ꢀ
was activated with [NMe2HPh][B(C6F5)4] for ethylene poly-
merization, similar results as for [Y(CH2SiMe3)3(thf)2] were
obtained (1351 versus 1840 kgmolꢀ1 hꢀ1 barꢀ1), thus indicating
that [Y(CH2SiMe3)2(thf)4]+[Al(CH2SiMe3)4]ꢀ is converted
into a dication (Table 2).[21]
[1] R. F. Jordan, Adv. Organomet. Chem. 1991, 32, 325 – 387.
[2] a) C. J. Schaverien, Organometallics 1992, 11, 3476 – 3478; a) S.
Hajela, W. P. Schaefer, J. E. Bercaw, J. Organomet. Chem. 1997,
532, 45 – 53.
[3] S. Bambirra, D. van Leusen, A. Meetsma, B. Hessen, J. H.
Teuben, Chem. Commun. 2001, 637 – 638.
[4] P. G. Hayes, W. E. Piers, R. McDonald, J. Am. Chem. Soc. 2002,
124, 2132 – 2133.
In conclusion, we have demonstrated that the easily
accessible tris(alkyl) complexes of the rare-earth metals
[Ln(CH2SiMe3)3(thf)2] are precursors for highly active cata-
lysts for ethylene polymerization and that an alkyl dication
[Ln(CH2SiMe3)(solv)z]2+, formed via the dialkyl monocation
[Ln(CH2SiMe3)2(solv)y]+, is most probably the active species.
[5] S. Bambirra, D. van Leusen, A. Meetsma, B. Hessen, J. H.
Teuben, Chem. Commun. 2003, 522 – 523.
[6] For the preparation by using a one-pot synthesis, see: M. F.
Lappert, R. Pearce, J. Chem. Soc. Chem. Commun. 1973, 126 –
127.
[7] For crystallographically characterized crown ether adducts
[Lu(CH2SiMe3)2(CE)(THF)x]+ (x = 1, CE = 12-crown-4; x = 0,
CE = 15-crown-5, 18-crown-6), see: S. Arndt, T. P. Spaniol, J.
Okuda, Chem. Commun. 2002, 896 – 897.
[8] R. D. Shannon, Acta Crystallogr. Sect. A 1976, 32, 751 – 767.
[9] In principle, cationic aluminum alkyls could be also considered
as ethylene polymerization catalyst, see: a) J. S. Kim, L. M.
Wojcinski II, S. Liu, J. C. Sworen, A. Sen, J. Am. Chem. Soc.
2000, 122, 5668 – 5669; b) K.-C. Kim, C. A. Reed, G. S. Long, A.
Sen, J. Am. Chem. Soc. 2002, 124, 7662 – 7663.
Experimental Section
[Y(CH2SiMe3)2(thf)4]+[BPh4]ꢀ:
A slurry of [Y(CH2SiMe3)3(thf)2]
(200 mg, 404 mmol) and [NEt3H][BPh4] (170 mg, 404 mmol) was
stirred in THF (20 mL) at ꢀ788C. The reaction mixture was allowed
to slowly warm up to ambient temperature and stirred for 24 h to give
a colorless clear solution. After the volatile fractions were removed
in vacuo, the resultant colorless solid was washed with Et2O (2 ”
20 mL) and dried under vacuum to give colorless microcrystals
(135 mg, 38%). 1H NMR (400 MHz, [D8]THF, 258C, TMS): d =
ꢀ0.78 (d, 2J(Y,H) = 3.3 Hz, 2 ” 2H; YCH2SiCH3), ꢀ0.06 (s, 2 ” 9H;
YCH2SiCH3), 1.76 (m, 4 ” 4H; b-CH2, THF), 3.60 (m, 4 ” 4H; a-CH2,
THF), 6.74 (t, 3J(H,H) = 7.0 Hz, 4H; 4-Ph), 6.87 (t, 3J(H,H) = 7.3 Hz,
2 ” 4H; 3-Ph), 7.28 ppm (br, 2 ” 4H; 2-Ph). 13C NMR (101 MHz,
[D5]pyridine, 258C, TMS): d = 4.5 (YCH2SiCH3), 25.8 (b-CH2, THF),
30.9 (dt, 1J(Y,C) = 36.5 Hz, 1J(C,H) = 97.2 Hz; YCH2SiCH3), 67.8 (a-
CH2, THF), 122.3 (4-Ph), 126.2 (3-Ph), 137.2 (2-Ph), 165.0 ppm (q,
1J(B,C) = 49.3 Hz; 1-Ph). 11B{1H} NMR (128 MHz, [D8]THF, 258C,
BF3·Et2O): d = ꢀ6.6 ppm. 89Y NMR (20 MHz, [D8]THF, 258C, YCl3):
d = 660.0 ppm. Elemental analysis calcd (%) for C48H74BO4Si2Y: C
66.19, H 8.56, Y 10.21; found: C 65.91, H 8.44, Y 9.74.
[10] In the presence of only one equivalent of [NMe2HPh][B(C6F5)4],
no polymerization of ethylene is observed.
[11] An excess of aluminum alkyl may activate the rare-earth metal
alkyl by removing THF under formation of [AlR3(thf)].
Furthermore, adduct formation between the (especially steri-
cally less demanding) aluminum alkyl and the cationic rare earth
metal catalyst may result in an inactive aluminate species. For a
cationic Zr aluminate [Zr{SiMe2(h5-C9H6)2}(m-Me)2(AlMe2)]
[B(C6F5)4] as dormant species, see: M. Bochmann, S. J. Lancas-
ter, Angew. Chem. 1994, 106, 1715 – 1718; Angew. Chem. Int. Ed.
Engl. 1994, 33,1634 – 1637.
[12] The third equivalent of [NMe2HPh][BPh4] did not lead to further
alkyl abstraction. Abstraction of two alkyl groups from a
scandium complex under formation of a contact ion pair was
reported in reference [4]; a) double alkyl abstraction by
=
B(C6F5)3 was observed for [Ti(N PtBu3)2Me2], see: F. Guerin,
J. C. Stewart, C. Beddie, D. W. Stephan, Organometallics 2000,
19, 2994 – 3000; b) double alkyl abstraction by Al(C6F5)3 was
observed for [Ti(h5:h1-C5Me4SiMe2NtBu)Me2], see: E. Y.-X.
Chen, W. J. Kruper, G. Roof, D. R. Wilson, J. Am. Chem. Soc.
2001, 123, 745 – 746.
[Y(CH2SiMe3)(thf)5]2+[BPh4]ꢀ
:
A
solution of [Y(CH2Si-
2
Me3)3(thf)2] (300 mg, 606 mmol) in THF (60 mL) was added to neat
[NMe2HPh][BPh4] (802 mg, 1818 mmol) at ꢀ788C. The reaction
mixture was stirred at ambient temperature for 24 h to give a
brownish solution. The solution was filtered, the volatile fractions
were removed by evaporation, and the residue was washed with
[13] An h6 coordinated arene adduct of a monocationic scandium
methyl complex was crystallographically characterized, see:
P. G. Hayes, W. E. Piers, M. Parvez, J. Am. Chem. Soc. 2003, 125,
5622 – 5623.
pentane (60 mL) gave
a
colorless powder of [Y(CH2Si-
Me3)(thf)5]2+[BPh4]ꢀ (661 mg, 99%). H NMR (400 MHz, [D5]pyri-
1
2
2
dine, 258C, TMS): d = 0.17 (s, 9H; YCH2SiCH3), 0.73 (d, J(Y,H) =
3.3 Hz, 2H; YCH2SiCH3), 1.62 (m, 5 ” 4H; b-CH2, THF), 3.66 (m, 5 ”
4H; a-CH2, THF), 7.10 (t, J(H,H) = 7.3 Hz, 2 ” 4H; 4-Ph), 7.27 (t,
[14] W. J. Evans, R. Anwander, J. W. Ziller, Organometallics 1995, 14,
1107 – 1109. We believe that a complex of this type is formed
when [Y(CH2SiMe3)3(thf)2] is treated with AlMe3.
3
3J(H,H) = 7.3 Hz, 2 ” 8H; 3-Ph), 8.06 ppm (br, 2 ” 8H; 2-Ph).
13C NMR (101 MHz, [D5]pyridine, 258C, TMS): d = 4.0 (YCH2-
SiCH3), 25.9 (b-CH2, THF), 44.5 (dt, 1J(Y,C) = 44.9 Hz, 1J(C,H) =
93.8 Hz; YCH2SiCH3), 67.9 (a-CH2, THF), 122.4 (4-Ph), 126.2 (3-
Ph), 137.1 (2-Ph), 165.0 ppm (q, 1J(B,C) = 49.2 Hz; 1-Ph).
11B{1H} NMR (128 MHz, [D8]THF, 258C, BF3·Et2O): d = ꢀ6.7 ppm.
89Y NMR (20 MHz, [D8]THF, 258C, YCl3): d = 409.2 ppm. Elemental
analysis calcd (%) for C72H91B2O5SiY: C, 73.59; H, 7.81; Y, 7.57;
found: C, 74.62; H, 8.37; Y, 7.16.
[15] a) NMR data for [Y(CH3)(thf)6]2+[BPh4]ꢀ2: 1H NMR (400 MHz,
[D5]pyridine, 258C, TMS): d = 0.69 (d, 2J(Y,H) = 2.1 Hz, 3H;
YCH3), 1.63 (m, 4 ” 4H; b-CH2, THF), 3.67 (m, 4 ” 4H; a-CH2,
THF), 7.10 (t, 3J(H,H) = 7.0 Hz, 2 ” 4H; 4-Ph), 7.26 (t, 3J(H,H) =
7.4 Hz, 2 ” 8H; 3-Ph), 8.04 ppm (br, 2 ” 8H; 2-Ph). 13C NMR
(101 MHz, [D5]pyridine, 258C, TMS): d = 27.6 (b-CH2, THF),
32.8 (dq, 1J(Y,C) = 53.6 Hz, 1J(C,H) = 105.5 Hz; YCH3), 69.7 (a-
CH2, THF), 124.2 (4-Ph), 128.0 (3-Ph), 139.0 (2-Ph), 166.8 ppm
(q, 1J(B,C) = 49.2 Hz; 1-Ph). 11B{1H}-NMR (128 MHz, [D8]THF,
258C, BF3·Et2O): d = ꢀ4.7 ppm. 89Y-NMR (20 MHz, [D5]pyri-
dine, 258C, YCl3): d = 433.2 ppm. Elemental analysis calcd (%)
for C77H99B2O7Y: C 74.16, H 8.00; found: C 73.27, H 7.22;
Received: July 31, 2003 [Z52532]
Published Online: October 8, 2003
5078
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
Angew. Chem. Int. Ed. 2003, 42, 5075 –5079

Angewandte
Chemie
b) CCDC-216055 ([Y(CH3)(THF)6]2+[BPh4]ꢀ2) CCDC-216054
([Y(CH2SiMe3)2(THF)4]+[Al(CH2SiMe3)4]ꢀ) contains the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrie-
ving.html (or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB21EZ, UK; fax: (+ 44)1223-336-
033; or deposit@ccdc.cam.ac.uk).
ꢀ
[16] For pertinent Y C bond lengths, see: K. C. Hultzsch, P. Voth, K.
Beckerle, T. P. Spaniol, J. Okuda, Organometallics 2000, 19, 228 –
243.
[17] Y-O(THF) bond distances at monocationic yttrium centers:
a) [YCl(OtBu)(thf)5]+[BPh4]ꢀ·THF: Y-O = 2.405(5), 2.411(5),
2.391(5), 2.422(5), 2.408(5) Š, see: W. J. Evans, J. M. Olofson,
J. W. Ziller, J. Am. Chem. Soc. 1990, 112, 2308 – 2314;
b) [YCl2(thf)5]+[YCl4(thf)2]ꢀ:
Y-O = 2.391(7),
2.368(5),
2.382(6) Š, see: P. Sobota, J. Utko, S. Szafert, Inorg. Chem.
1994, 33, 5203 – 5206; c) [YCl2(thf)5]+[C2B9H12]ꢀ: Y-O =
2.378(8), 2.377(7), 2.396(8), 2.401(7), 2.309(7) Š, see: K. Chiu,
Z. Zhang, T. C. W. Mak, Z. Xie, J. Organomet. Chem. 2000, 614,
107 – 112; d) [Y(CH2SiMe3)2(thf)4]+[Al(CH2SiMe3)4]ꢀ: Y-O =
2 ” 2.354(4), 2.448(4), 2.479(4) Š, this work.
[18] Not surprisingly, ethylene was also polymerized when methyl-
aluminoxane was used instead of aluminum trialkyl; see Table 2.
[19] Because of its inertness towards [NMe2HPh][B(C6F5)4], we
selected Al(CH2SiMe3)3 for our investigations. For Al(CH2-
SiMe3)3, neither formation of aluminum alkyl cation, see
reference [9], nor decomposition under ligand redistribution
was observed. AliBu3 was reported to react with [NMe2HPh]
[B(C6F5)4] in C6D6 under forcing conditions to produce a mixture
of BiBu3, Al(C6F5)3 and AliBu(C6F5)2, see: C. Gꢀtz, A. Rau, G.
Luft, J. Mol. Catal. A 2002, 184, 95 – 110.
[20] Higher coordination numbers 7 and 8 were reported for cationic
alkyl complexes of lutetium, see reference [7].
[21] The monocation [Y(CH2SiMe3)2(thf)x]+[Al(CH2SiMe3)4]ꢀ does
not polymerize ethylene unless activated with excess of
[NMe2HPh][B(C6F5)4]. In [D8]THF it reacts with one equivalent
of [NMe2HPh][BPh4], to form SiMe4, NMe2Ph, Al(CH2SiMe3)3,
and [Y(CH2SiMe3)2([D8]thf)x]+[BPh4]ꢀ.
A similar reaction
between [Sm(h5-C5Me5)2(AlMe4)]2 and [Ph3C][B(C6F5)4] was
reported to give [Sm(h5-C5Me5)2][B(C6F5)4], Ph3CMe, and
AlMe3, see: S. Kaita, Z. Hou, M. Nishiura, Y. Doi, J. Kurazumi,
A. C. Horiuchi, Y. Wakatsuki, Macromol. Rapid Commun. 2003,
24, 179 – 184.
Angew. Chem. Int. Ed. 2003, 42, 5075 –5079
www.angewandte.org
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5079