Ln(AlMe4)3 as new synthetic precursors in organolanthanide chemistry: Efficient access to half-sandwich hydrocarbyl complexes

Article abstract of DOI:10.1021/om0506163

The homoleptic complexes Ln(AlMe₄)₃ (Ln = Y, La, Nd, Lu) were reacted with pentamethylcyclopentadiene to yield the corresponding half-sandwich complexes (C₅Me₅)Ln-(AlMe₄) ₂ in high yield and purity. NMR spectroscopic investigations revealed a highly dynamic nature of the bridging and terminal alkyl groups, even at -85°C. In the solid state, the tetramethylaluminato ligands coordinate differently to the metal center, as shown by an X-ray structure analysis of the lanthanum derivative. Due to the steric unsaturation of the large lanthanum metal center, one of the aluminate ligands adopts an unusual distorted μ:η³ coordination mode, while the second ligand bonds in a routine μ:η² fashion. An alcoholysis reaction of (C ₅Me₅)Y(AlMe₄)₂ with HOCHtBu ₂ gave the heteroleptic complex (C₅Me₅) Y(OCHtBu₂)(AlMe₄). (C₅Me₅) Nd(AlMe₄)₂ was reacted with dehydrated periodic mesoporous silica MCM-41, affording surface-grafted (C₅Me₅) Nd(AlMe₄)₂@MCM-41. The half-metallocene bis(aluminate) complexes were converted into donor-free [(C₅Me₅)LnMe ₂l₃ (Ln = Y, Lu) via stoichiometric THF-induced cleavage and reversibly regenerated by addition of trimethylaluminum. The organolanthanide complexes were fully characterized by NMR and FTIR spectroscopy and elemental analysis. The organometallic-inorganic hybrid materials were characterized by FTIR spectroscopy, elemental analysis, and nitrogen physisorption.

Full text of DOI:10.1021/om0506163

Organometallics 2005, 24, 5767-5771
5767
Ln(AlMe4)3 as New Synthetic Precursors in
Organolanthanide Chemistry: Efficient Access to
Half-Sandwich Hydrocarbyl Complexes
H. Martin Dietrich,† Clemens Zapilko,† Eberhardt Herdtweck,‡ and
Reiner Anwander*,†
Department of Chemistry, University of Bergen, Alle´gaten 41, N-5007, Bergen, Norway, and
Anorganisch-chemisches Institut, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4,
D-85747 Garching, Germany
Received July 22, 2005
The homoleptic complexes Ln(AlMe4)3 (Ln ) Y, La, Nd, Lu) were reacted with penta-
methylcyclopentadiene to yield the corresponding half-sandwich complexes (C5Me5)Ln-
(AlMe4)2 in high yield and purity. NMR spectroscopic investigations revealed a highly
dynamic nature of the bridging and terminal alkyl groups, even at -85 °C. In the solid
state, the tetramethylaluminato ligands coordinate differently to the metal center, as shown
by an X-ray structure analysis of the lanthanum derivative. Due to the steric unsaturation
of the large lanthanum metal center, one of the aluminate ligands adopts an unusual
distorted µ:η3 coordination mode, while the second ligand bonds in a routine µ:η2 fashion.
An alcoholysis reaction of (C5Me5)Y(AlMe4)2 with HOCHtBu2 gave the heteroleptic complex
(C5Me5)Y(OCHtBu2)(AlMe4). (C5Me5)Nd(AlMe4)2 was reacted with dehydrated periodic
mesoporous silica MCM-41, affording surface-grafted (C5Me5)Nd(AlMe4)2@MCM-41. The half-
metallocene bis(aluminate) complexes were converted into donor-free [(C5Me5)LnMe2]3 (Ln
) Y, Lu) via stoichiometric THF-induced cleavage and reversibly regenerated by addition
of trimethylaluminum. The organolanthanide complexes were fully characterized by NMR
and FTIR spectroscopy and elemental analysis. The organometallic-inorganic hybrid
materials were characterized by FTIR spectroscopy, elemental analysis, and nitrogen
physisorption.
Introduction
dependent ligand redistribution reactions.2,4-10 Re-
cently, we described the synthesis of mono(tetra-
methylcyclopentadienyl) bis(silylamide) complexes ac-
cording to our previously established extended silyl-
amide route. A trialkylaluminum-mediated silylamide
f alkyl transformation afforded donor-free half-sand-
wich complexes of the type CpLn[(µ-R)2AlR2]2 of the
smaller rare-earth metals yttrium and lutetium.11 Herein
we describe a highly efficient synthetic route to mono-
(cyclopentadienyl) complexes of both smaller and larger
lanthanide(III) centers. Note that the synthetic ap-
proaches toward half-lanthanidocene bis(hydocarbyl)
complexes reported so far were applicable only for either
smaller or larger Ln metal centers using Ln(CH2SiMe3)3-
(THF)x (x ) 2, 3) and Ln[CH(SiMe3)2]3 as synthetic
precursors, respectively.2,7,12,13
Organolanthanide complexes supported by only one
cyclopentadienyl-type ancillary ligand are ascribed a
high potential in homogeneously catalyzed reactions
such as the polymerization of styrene or acrylonitrile.1,2
Moreover, an intrinsic stereoelectronic unsaturation is
anticipated to impart unprecedented structural chem-
istry.3,4 A very limited number of catalytically relevant
bis(amide) and bis(hydrocarbyl) half-sandwich com-
plexes has been structurally examined, disclosing un-
desirable features such as (i) Lewis base (solvent)
complexation, (ii) ate complexation, and (iii) metal-size-
* To whom correspondence should be addressed. Fax: +47 555
89490. E-mail: reiner.anwander@kj.uib.no.
† University of Bergen.
‡ Technische Universita¨t Mu¨nchen.
(5) Arndt, S.; Okuda, J. Chem. Rev. 2002, 102, 1953.
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Acta 1985, 110, 145.
(7) (a) van der Heijden, H.; Schaverien, C. J.; Orpen, A. G. Orga-
nometallics 1989, 8, 255. (b) van der Heijden, H.; Pasman, P.; de Boer,
E. J. M.; Schaverien, C. J.; Orpen, A. G. Organometallics 1989, 8, 1459.
(c) Klooster, W. T.; Brammer, V.; Schaverien, C. J.; Budzelaar, P. H.
M. J. Am. Chem. Soc. 1999, 121, 1381.
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(9) (a) Taube, R.; Maiwald, S.; Sieler, J. J. Organomet. Chem. 1996,
513, 37. (b) Taube, R.; Maiwald, S.; Sieler, J. J. Organomet. Chem.
2001, 621, 327.
(1) (a) Yasuda, H.; Ihara, E. Bull. Chem. Soc. Jpn. 1997, 70, 1745.
(b) Yasuda, H. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 1955.
(2) For recent successful applications of the derivatives Cp′Ln(CH2-
SiMe3)2(THF) (Ln ) Sc, Y, Gd, Lu; Cp′ ) C5Me5, C5Me4SiMe3, C5Me3-
(SiMe3)2-1,3) in styrene polymerization and styrene-ethylene and
styrene-norbornene copolymerization catalysis, see: (a) Luo, Y.;
Baldamus, J.; Hou, Z. J. Am. Chem. Soc. 2004, 126, 13910. (b) Li, X.;
Baldamus, J.; Hou, Z. Angew. Chem., Int. Ed. 2005, 44, 962.
(3) (a) Kretschmer, W. P.; Teuben, J. H.; Troyanov, S. I. Angew.
Chem., Int. Ed. 1998, 37, 88. (b) Anwander, R. Angew. Chem., Int. Ed.
1998, 37, 599.
(4) (a) Hou, Z.; Zhang, Y.; Tardif, O.; Wakatzuki, Y. J. Am. Chem.
Soc. 2001, 123, 9216. (b) Tardif, O.; Nishiura, M.; Hou, Z. Organome-
tallics 2003, 22, 1171. (c) Hultzsch, K. C.; Voth, P.; Spaniol, T. P.;
Okuda, J. Z. Anorg. Allg. Chem. 2003, 629, 1272.
(10) Evans, W. J.; Brady, J. C.; Ziller, J. W. J. Am. Chem. Soc. 2001,
123, 7711.
(11) Anwander, R.; Klimpel, M. G.; Dietrich, H. M.; Shorokhov, D.
J.; Scherer, W. Chem. Commun. 2003, 1008.
10.1021/om0506163 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/05/2005

5768 Organometallics, Vol. 24, No. 23, 2005
Dietrich et al.
Scheme 1. Synthesis of Half-Sandwich
Rare-Earth Metal Tetraalkylaluminate Complexes
2 (Ln ) Y (a), La (b), Nd (c), Lu (d)) According to
an Alkane Elimination and Secondary
Tetraalkylaluminate Ligand Exchange
Figure 1. Molecular structure of 2b (ORTEP drawing).
Atoms are represented by atomic displacement ellipsoids
at the 50% level. Selected bond lengths (Å) and angles
(deg): La- - -Al1 ) 3.0141(9), La- - -Al2 ) 3.2687(9), La-
C(C5Me5) ) 2.753(2)-2.801(3), La-C1 ) 2.794(3), La-C2
) 2.802(4), La- - -C4 ) 3.140(3), La-C5 ) 2.694(3), La-
C6 ) 2.707(3), La-H12 ) 2.88(4), La-H13 ) 2.75(4), La-
H21 ) 2.51(5), La-H22 ) 3.06(5), La-H41 ) 2.83(4), La-
H51 ) 2.60(3), La-H52 ) 2.68(3), La-H61 ) 2.70(3), La-
H62 ) 2.62(3), Al1-C1 ) 2.058(3), Al1-C2 ) 2.058(3),
Al1-C3 ) 1.960(4), Al1-C4 ) 1.994(3), Al2-C5 ) 2.077-
(3), Al2-C6 ) 2.074(3), Al2-C7 ) 1.969(4), Al2-C8 )
1.968(4); Al1-La-Al2 ) 117.23(2), C1-La-C2 ) 73.0(1),
C5-La-C6 ) 78.5(1), C1-La-C6 ) 94.3(1), C2-La-C5
) 94.4(1), La-C1-Al1 ) 75.1(1), La-C2-Al1 ) 74.9(1),
La-C5-Al2 ) 85.5(1), La-C6-Al2 ) 85.2(1), La-C1-H11
) 169(3), La-C1-H12 ) 85(2), La-C1-H13 ) 77(2), La-
C2-H21 ) 62(3), La-C2-H22 ) 98(4), La-C2-H23 )
150(3), La-C5-H51 ) 74(2), La-C5-H52 ) 79(2), La-
C5-H53 ) 174(2), La-C6-H61 ) 80(2), La-C6-H62 )
74(2), La-C6-H63 ) 174(2), La-C4-H41 ) 62(3), La-
C4-H42 ) 129(2), La-C4-H43 ) 134(3). Bond lengths
and angles involving hydrogen atoms should be discussed
carefully, due to their location close to heavy atoms.
Results and Discussion
Synthesis and Characterization of Half-Lan-
thanidocene Bis(tetramethylaluminato) Com-
plexes. Homoleptic tetramethylaluminates Ln[(µ-
Me)2AlMe2]3 (1: Ln ) Y(a), La (b), Nd (c), Lu (d)) were
synthesized according to the literature method and are
readily available on a 10 g scale by the reaction of LnCl3-
(THF)x (x ) 3.5 (Y), 1.25 (La), 1.75 (Nd), 3 (Lu)) with 3
equiv of freshly prepared LiNMe2 and a subsequent
AlMe3-mediated [NMe2] f [AlMe4] transformation.14-17
We found that such peralkylated rare-earth metal
complexes 1 are ideal precursors for mono(C5Me5)-bis-
(alkyl) complexes via a protonolysis reaction. Accord-
ingly, (C5Me5)Ln[(µ-Me)2AlMe2]2 (2: Ln ) Y(a), La (b),
Nd (c), Lu (d)) were obtained from 1 and 1,2,3,4,5-
pentamethylcyclopentadiene (Scheme 1).18 The volatile
byproducts trimethylaluminum and methane can easily
be removed under vacuum to afford the pure compounds
in high yield (Y (86%), La (93%), Nd (91%), Lu (91%)).
Caution! The evaporated hexane fractions containing
AlMe3 react violently when exposed to air; deactivation
by addition of anhydrous 2-propanol is recommended.
1H NMR spectroscopic investigations of complexes 2
at 25 °C showed one signal in the metal alkyl region.
In comparison to the homoleptic precursors 1 the methyl
resonances of the diamagnetic derivatives 2a (-0.33 vs
-0.27), 2b (-0.29 vs -0.20), and 2d (-0.18 vs 0.35) are
shifted slightly to higher field. The corresponding broad
signal of the paramagnetic neodymium complex 2c
appeared at 4.2 ppm compared to the 10.7 ppm in 1c.
As evidenced for the yttrium derivative 2a by variable-
temperature NMR spectroscopy, the aluminate moieties
are highly fluxional, even at -85 °C. This clearly
revealed a rapid exchange of bridging and terminal
aluminate methyl groups.11 The spectrum of complex
2a also showed the characteristic doublet (2JY,H ) 2.0
-
Hz) for the AlMe4 ligands.19,20
Decisively, the formation of lanthanidocene complexes
(C5Me5)2Ln(AlMe4) via ligand redistribution was not
observed. We have recently reported the solid-state
structure of lutetium derivative 2d obtained according
to a different synthetic route.11 The present X-ray
structure analysis of lanthanum complex 2b featuring
the largest Ln(III) metal center gives further evidence
of differently coordinated tetramethylaluminate ligands
-
(Figure 1).11 One AlMe4 ligand coordinates in an η2
(12) Complexes Ln(CH2SiMe3)3(THF)x (x ) 2, 3) are important
precursors to heteroleptic hydrocarbyl complexes; however, isolable
derivatives are limited to samarium and smaller Ln(III): Schumann,
H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg. Chem. 2002, 628,
2422.
(13) Booij, M.; Kiers, N. H.; Heeres, H. J.; Teuben, J. H. J.
Organomet. Chem., 1989, 364, 79.
(14) Evans, W. J.; Anwander, R.; Ziller, J. W. Organometallics 1995,
14, 1107.
fashion with an almost planar heterobimetallic
[La(µ-CH3)2Al] moiety (torsion angle C5-La-C6-Al2
) -2.2(1)°). The second AlMe4- ligand shows structural
features similar to those previously found for the
lutetium complex 2d, including (i) an atypically bent
heterobimetallic [La(µ-CH3)2Al] moiety ( C1-La-C2-
Al1 ) 32.5(1)°, interplanar angle LaC1C2-Al1C1C2 )
(15) Anwander, R. Top. Organomet. Chem. 1999, 2, 1.
(16) Fischbach, A.; Klimpel, M. G.; Widenmeyer, M.; Herdtweck, E.;
Scherer, W.; Anwander, R. Angew. Chem., Int. Ed. 2004, 43, 2234.
(17) Dietrich, H. M.; Klimpel, Raudaschl-Sieber, G.; Anwander, R.
Angew. Chem., Int. Ed. 2005, 44, 5202.
(19) Klimpel, M. G.; Eppinger, J.; Sirsch, P.; Scherer W.; Anwander,
R. Organometallics 2002, 21, 4021.
(20) Fischbach, A.; Herdtweck, E.; Anwander, R.; Eickerling, G.;
Scherer, W. Organometallics 2003, 22, 499.
(18) Recently, we reported the first successful derivatization of Ln-
(AlMe4)3 by a tetramethylaluminate f siloxide transformation.16

Ln(AlMe4)3 as New Synthetic Precursors
Organometallics, Vol. 24, No. 23, 2005 5769
Table 1. Analytical Data, Pore Volume, Surface Area, and Effective Mean Pore Diameter of Supported
Neodymium Tetraalkylaluminate Complexes
b
c
d
C/
wt %
Nd loading/
mmol g-1
as
/
Vp
/
dp /
materiala
m2 g-1
cm3 g-1
nm
MCM-41 (4)e
1040
650
570
1.06
0.54
0.42
3.3
2.8
2.5
Nd[(µ-Me)2AlMe2]3@MCM-41 (5c)
10.84
16.71
1.73
1.49
Cp*Nd[(µ-Me)2AlMe2]2@MCM-41 (6c)
a Pretreatment temperature: 280 °C, 4 h, 10-3 Torr for 4; 25 °C, 5 h, 10-3 Torr for 5c and 6c. Cp* ) C5Me5. b Specific BET surface
area. c BJH desorption cumulative pore volume of pores between 1.5 and 6.5 nm diameter. d Pore diameter according to the maximum of
the BJH pore size distribution. e A pore-expanded sample of 4 was synthesized by using the divalent surfactant C16-3-1 and hydrothermal
restructuring; the silanol population was derived as 3.45 mmol g-1 from the functionalized material HN(SiHMe2)2@MCM-41.23b
118.0(2)°), (ii) elongated La-(µ-CH3) bond lengths (∆La-C
) ca. 0.10 Å), and (iii) a shortened La- - -Al distance
(∆La- - -Al ) ca. 0.255 Å). However, due to an enhanced
steric unsaturation of the larger lanthanum center, an
even shorter additional La-(µ-CH3) contact of 3.140(3)
Å is observed (cf. 2d, Lu- - -(µ-CH3) ) 3.447 Å). This
pronounced La- - -C4 contact is also evidenced by dif-
ferent bond angles La-Al-Cterminal of the bent ( La-
Al1-C3/4 ) 168.8(2), 74.6(1)) compared to the η2-bonded
aluminate ligands ( La-Al2-C7/8 ) 120.9(1), 122.5-
-
(1)°). Hence, the bent AlMe4 ligand accomplishes a
distorted η3 coordination mode comparable to that of the
[Yb(µ-Et)3AlEt]+ moiety in the homoleptic complex [Yb-
(AlEt4)2]n, involving the even larger Yb(II) center.21 For
comparison, the La-C(µ) bond lengths in six-coordinate
La(NMe2)2(GaMe3)2(GaMe4) and seven-coordinate Ln-
[OSi(OtBu)3](AlMe4)2(AlMe3) are in the ranges of 2.742-
(2)-2.992(5) and 2.668(5)-2.798(3) Å, respectively.16,22
The bridging five-coordinate carbon atoms of the η2-
-
coordinating AlMe4 ligand display distorted-trigonal-
Figure 2. Nitrogen adsorption/desorption isotherms at
77.4 K and the corresponding BJH pore size distributions
of the parent and modified MCM-41 materials 4, 5c, and
6c (cf. Table 1).
bipyramidal geometries with one hydrogen atom and the
lanthanum metal in the apical positions ( La-C5-H53,
La-C6-H63 ) 174(2)°). Two of the equatorial hydro-
gen atoms each form a close contact to the lanthanum
center (2.60(3)-2.70(3) Å) involving La-C-H angles
as acute as 74(2)°. It is worth noting that the η3-
coordinating AlMe4- ligand features the shortest La- - -
H contact (2.51(5) Å) and the most acute angles La-
C-H (62(3)°).
A dehydrated sample of pore-enlarged MCM-41 (4)
was treated with an excess of each of the tetraalkyl-
aluminate complexes to give a blue reaction mixture,
from which after several hexane washings blue-green
materials 5c and 6c were isolated. The enhanced steric
bulk of the C5Me5 ligand implies a significantly lower
Nd loading of 6c, while the high carbon content of 6c
suggests the presence of surface-confined half-metal-
locene species (proposed surface species for material 6c
are shown in Scheme 1).25,26 Also, the nitrogen adsorp-
tion/desorption isotherms of the materials 4, 5c, and 6c
(Figure 2) clearly indicate a distinct filling of the
mesopores depending on the ligand environment of the
neodymium surface centers. The mesoporosity of the
hybrid materials was retained; however, analysis of the
Barret-Joyner-Halenda (BJH) pore size distributions
shows drastically reduced pore diameters.27
Ligand Exchange at Half-Lanthanidocene Bis-
(tetramethylaluminato) Complexes. The feasibility
of secondary ligand exchange reactions for complexes 2
was initially examined for a simple alcoholysis reaction.
A tetramethylaluminate f alkoxide transformation
could be achieved by reacting 2a with di-tert-butyl-
carbinol. The heteroleptic complex (C5Me5)Y(OCHtBu2)-
(AlMe4) (3a), featuring three different monoanionic
ligands, was formed as the main product after crystal-
lization from hexane solution. This tetramethylalumi-
nate/alkoxide exchange implicates a stronger bonding
of the remaining [La(µ-CH3)2Al(CH3)2] moiety, as evi-
2
denced by an increased coupling constant JY,H of 3.2
Hz. In another preliminary study, Nd(AlMe4)3 (1c) and
(C5Me5)Nd(AlMe4)2 (2c) were grafted onto a high-
surface-area periodic mesoporous silica material, i.e.,
MCM-41 (4) of hexagonal topology with a two-dimen-
sional mesopore system.23-25 The resulting organome-
tallic-inorganic hybrid materials were characterized by
FTIR spectroscopy, elemental analysis, and nitrogen
physisorption (Table 1).
(23) (a) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.;
Kresge, C. T.; Schmitt, K. D.; Chu, C. T.-W.; Olson, D. H.; Sheppard,
E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem.
Soc. 1992, 114, 10834. (b) Anwander, R.; Nagl, I.; Widenmeyer, M.;
Engelhardt, G.; Groeger, O.; Palm, C.; Ro¨ser, T. J. Phys. Chem B 2000,
104, 3532. (c) Widenmeyer, M. Ph.D. Thesis, Technische Universita¨t
Mu¨nchen, 2001.
(24) For a review on surface organometallic chemistry at periodic
mesoporous silica, see: Anwander, R. Chem. Mater. 2001, 13, 4419.
(25) For an in situ DRIFT study of supported neodymium allyl
complexes of the composition (C5Me5)Nd(C3H5)2/2,3-dimethylbutadiene/
MAO/MAO-SiO2, see: Berndt, H.; Landmesser, H. J. Mol. Catal. A
2003, 197, 245.
(26) For group 4 half-metallocene complexes on periodic mesoporous
silica MCM-41, see: Maschmeyer, T.; Rey, F.; Sankar, G.; Thomas, J.
M. Nature 1995, 378, 159.
(21) Klimpel, M. G.; Anwander, R.; Tafipolsky, M.; Scherer, W.
Organometallics 2001, 20, 3983.
(22) Evans, W. J.; Anwander, R.; Doedens, R. J.; Ziller, J. W. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1641.

5770 Organometallics, Vol. 24, No. 23, 2005
Dietrich et al.
methylammonium dibromide, [CH3(CH2)15N(CH3)2(CH2)3N-
Lappert’s Donor-Induced Aluminate Cleavage at
Half-Lanthanidocene Bis(tetramethylaluminato)
Complexes. The applicability of Lappert’s concept of a
donor (THF)-induced aluminate cleavage revealed com-
plexes 2 to exhibit true masked bis(hydrocarbyl) com-
plexes. Lappert and co-workers showed that lanthani-
docene deriviatives (C5H5)2Ln(AlMe4) (Ln ) Y, Dy, Ho,
Er, Tm, Yb) can be converted into alkyl-bridged com-
plexes [(C5H5)2Ln(µ-Me)]2 by addition of equimolar
amounts of pyridine and separation of AlMe3(Py).28
Correspondingly, addition of 2 equiv of THF as a Lewis
base to a solution of complexes 2a and 2d in hexane
instantly formed [(C5Me5)LnMe2]3 (7a, Ln ) Y; 7d, Ln
) Lu) as a white precipitate (Scheme 1). Microanalytical
and 1H NMR spectroscopic data are consistent with the
molecular compositions of 7a and 7d. The 1H NMR
spectrum of complex 2a revealed a quartet for the
Y-bonded methyl groups with a small 2JY,H coupling of
1.2 Hz.29 Interestingly, as previously found for lanthani-
docene complexes rac-[Me2Si(2-Me-C9H5)2]YR (R ) Me,
AlMe4) and [(C5H5)2Ln(µ-Me)]2 this donor-induced alu-
minate cleavage is a reversible process.18,28 Treatment
of complexes 7 suspended in hexane with 2 equiv of
AlMe3 quantitatively redissolved 7 as 2a and 2d (Scheme
1).
(CH3)3]2+Br- (C16-3-1), as a structure-directing agent (SDA),
2
and hydrothermal posttreatment methods.23c C16-3-1 was
synthesized according to the literature by reacting C16NMe2
with (3-bromopropyl)trimethylammonium bromide.23c,30 The
tetramethyldisilazane-mediated surface silylation was per-
formed according to the literature method.23b 1H and 13C NMR
data were obtained in C6D6 solution at 25 °C on FT-JEOL-
JNM-GX-400 (1H, 399.80 MHz; 13C, 100.51 MHz) and FT-
JEOL-JNM-GX-270 instruments (1H, 270 MHz; 13C, 67.5
MHz). 1H and 13C shifts are referenced to internal solvent
resonances and reported relative to TMS. IR spectra were
recorded on a Perkin-Elmer 1650-FTIR spectrometer as Nujol
mulls. Elemental analyses were performed in the microana-
lytical laboratory at TUM. Nitrogen adsorption-desorption
isotherms were measured with an ASAP 2010 volumetric
adsorption apparatus (Micromeritics) at 77.4 K for relative
pressures from 10-2 to 0.99 (am(N2, 77 K) ) 0.162 nm2). The
samples were outgassed in the degas port of the adsorption
analyzer, as indicated in Table 1. The BET specific surface
area was obtained from the nitrogen adsorption data in the
relative pressure range from 0.04 to 0.2. The pore size
distributions were derived from the desorption branches using
the BJH method.
General Procedure for the Preparation of Half-
Sandwich Bis(aluminato) Complexes 2a-d. In a glovebox,
Ln(AlMe4)3 was dissolved in hexane. 1,2,3,4,5-Pentamethyl-
cyclopentadiene (1 equiv) in 5 mL of hexane was added under
vigorous stirring to the alkylaluminate solution. Instant gas
formation was observed. After the reaction mixture was stirred
for 5 min, the solvent was removed in vacuo. After they were
dried for 1 h, the products were obtained in pure crystalline
form and in high yields.
Conclusions
Homoleptic Ln(AlMe4)3 complexes are efficient syn-
thetic precursors for highly soluble, mononuclear bis-
(tetraalkylaluminate) half-sandwich complexes of large
(La, Nd), medium (Y), and small (Lu) Ln(III) centers.
Given the accessibility of (C5Me5)Ln(AlMe4)2 to various
ligand exchange reactions, including a Lewis base-
mediated “reversible” [AlMe4] f [Me] transformation
and a silanolysis-driven [Cp*Ln] surface attachment,
applications in polymerization catalysis can be antici-
pated.
(1,2,3,4,5-Pentamethylcyclopentadienyl)bis(tetramethyl-
aluminato)yttrium(III) (2a). Following the procedure de-
scribed above, Y(AlMe4)3 (350 mg, 1.00 mmol) and 1,2,3,4,5-
pentamethylcyclopentadiene (136 mg, 1.00 mmol) yielded 2a
(343 mg, 86%) as a colorless crystalline solid. IR (Nujol, cm-1):
1462 vs, 1377 vs, 1258 w, 1233 w, 1193 m, 1022 w, 916 m, 857
1
m, 720 s, 580 m, 506 m, 469 w. H NMR (400 MHz, C6D6, 25
°C): δ 1.72 (s, 15H, CpCH3); -0.33 (s, 24H, AlCH3) ppm. 13C-
{1H} NMR (100 MHz, C6D6, 25 °C): δ 122.3 (CpC), 11.8
(CpCH3), 0.13 (br s, AlCH3) ppm. Anal. Calcd for C18H39Al2Y
(398.376): C, 54.27; H, 9.87. Found: C, 53.96; H, 9.66.
(1,2,3,4,5-Pentamethylcyclopentadiene)bis(tetramethyl-
aluminato)lanthanum(III) (2b). Following the procedure
described above, La(AlMe4)3 (400 mg, 1.00 mmol) and 1,2,3,4,5-
pentamethylcyclopentadiene (136 mg, 1.00 mmol) yielded 2b
Experimental Details
General Procedures. All operations were performed with
rigorous exclusion of air and water, using standard Schlenk,
high-vacuum, and glovebox techniques (MB Braun MB150B-
G-II; <1 ppm O2, <1 ppm H2O). Hexane was purified by using
Grubbs columns. Toluene and THF were predried and distilled
from Na/K alloy (benzophenone ketyl) under argon. C6D6 was
obtained from Deutero GmbH, degassed, dried over Na/K alloy
for 24 h, and filtered. Trimethylaluminum and 1,2,3,4,5-penta-
methylcyclopentadiene were purchased from Aldrich and used
as received. Lithium dimethylamide was synthesized via
1
(417 mg, 93%) as a colorless crystalline solid. H NMR (400
MHz, C6D6, 25 °C): δ 1.81 (s, 15H, CpCH3); -0.29 (s, 24H,
AlCH3) ppm. 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ 125.0
(CpC), 11.6 (CpCH3), 2.4 (br s, AlCH3) ppm. Anal. Calcd for
C18H39Al2La (448.36): C, 48.22; H, 8.77. Found: C, 47.94; H,
8.53.
(1,2,3,4,5-Pentamethylcyclopentadienyl)bis(tetramethyl-
aluminato)neodymium(III) (2c). Following the procedure
described above, Nd(AlMe4)3 (406 mg, 1.00 mmol) and 1,2,3,4,5-
pentamethylcyclopentadiene (136 mg, 1.00 mmol) yielded 2c
(413 mg, 91%) as a blue-green crystalline solid. 1H NMR (400
MHz, C6D6, 25 °C): δ 12.08 (s, 15H, CpCH3); 4.21 (s, 24H,
AlCH3) ppm. 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ 258.1
(CpC), 229.3 (br s, AlCH3), -21.0 (CpCH3) ppm. Anal. Calcd
for C18H39Al2Nd (453.711): C, 47.65; H, 8.66. Found: C, 47.43;
H, 8.35.
n
deprotonation of dimethylamine with BuLi. Homoleptic Ln-
(AlMe4)3 (Ln ) Lu, Y, Nd, La) were synthesized according to
the literature method.14 Hexadecyldimethylamine (C16NMe2)
and (3-bromopropyl)trimethylammonium bromide were pur-
chased from Aldrich. Pore-expanded MCM-41 (4) was prepared
according to slightly changed literature procedures using the
divalent surfactant (3-(trimethylammonio)propyl)hexadecyldi-
(27) Barret, E. P.; Joyner, L. G.; Halenda, P. P. J. Am. Chem. Soc.
1951, 73, 373.
(28) Holton, J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood,
J. L.; Hunter, W. E. J. Chem. Soc., Dalton Trans. 1979, 54.
(29) Complex 7a was previously obtained by reacting (C5Me5)Y-
(OC6H3tBu2-2,6)2 with 1.6 equiv of MeLi in hexane/ether. The hexane-
insoluble products [(C5Me5)Y(µ-Me)2]3 and Li(OC6H3tBu2-2,6) were
separated by benzene washings and the trinuclear structure proposed
from the quartet 1H resonance of fluxional methyl groups, which
experience coupling to a Y3 framework: Schaverien, C. J. Organome-
tallics 1994, 13, 69.
(1,2,3,4,5-Pentamethylcyclopentadienyl)bis(tetramethyl-
aluminato)lutetium(III) (2d). Following the procedure de-
scribed above, Lu(AlMe4)3 (436 mg, 1.00 mmol) and 1,2,3,4,5-
pentamethylcyclopentadiene (136 mg, 1.00 mmol) yielded 2d
(441 mg, 91%) as a colorless crystalline solid. IR (Nujol, cm-1):
(30) Zana, R.; Benrraou, M.; Rueff, R. Langmuir 1991, 7, 1072.

Ln(AlMe4)3 as New Synthetic Precursors
Organometallics, Vol. 24, No. 23, 2005 5771
Table 2. Crystal Data and Data Collection
Parameters of Complex 2b
1462 vs, 1377 vs, 1258 w, 1237 w, 1193 m, 1023 w, 913 m, 855
m, 721 s, 579 m, 499 m, 458 w. H NMR (400 MHz, C6D6, 25
1
°C): δ 1.75 (s, 15H, CpCH3), -0.18 (s, 24H, AlCH3) ppm. 13C-
{1H} NMR (100 MHz, C6D6, 25 °C): δ 120.9 (CpC), 11.8
(CpCH3), 1.5 (br s, AlCH3) ppm. Anal. Calcd for C18H39Al2Lu
(484.440): C, 42.36; H, 6.22. Found: C, 41.29; H, 6.12.
(Di-tert-butylmethoxy)(1,2,3,4,5-pentamethylcyclopen-
tadienyl)(tetramethylaluminato)yttrium(III) (3a). In a
glovebox, (C5Me5)Y(AlMe4)2 (199 mg, 0.50 mmol) was dissolved
in hexane and cooled to -35 °C. A solution of di-tert-butyl-
methanol (144 mg, 1.00 mmol) was added under vigorous
stirring at -35 °C. After the mixture was stirred for 1 h at
ambient temperature, the solvent was removed in vacuo. The
product was crystallized from the crude reaction mixture at
-35 °C, which yielded 93 mg (41%) of colorless crystals. 1H
NMR (400 MHz, C6D6, 25 °C): δ 3.32 (s, 1H, OCHtBu2), 1.92
(s, 15H, CpCH3), 0.97 (s, 18H, tBuCH3), -0.26 (d, 12H, AlCH3)
ppm. Anal. Calcd for C23H46AlOY (454.504): C, 60.78; H, 10.20.
Found: C, 60.54; H, 10.03.
chem formula
fw
C18H39Al2La
448.36
color/shape
cryst size (mm)
cryst syst
space group
a (Å)
colorless/fragment
0.64 × 0.43 × 0.38
orthorhombic
Pbca (No. 61)
14.6850(1)
18.1332(1)
17.2624(1
4596.74(5)
8
b (Å)
c (Å)
V (Å3)
Z
T (K)
143(1)
F
calcd (g cm-3
)
1.296
µ (mm-1
F000
θ range (deg)
)
1.930
1840
2.14-25.38
(17, (21, (20
88226
data collected (h,k,l)
no. of rflns collected
no. of indep rflns/Rint
no. of obsd rflns (I >2σ (I))
no. of params refined
R1 (obsd/all)
4219 (all)/0.057
3487 (obsd)
347
0.0222/0.0317
0.0504/0.0537
1.059/1.059
+0.855/-0.399
Nd[(µ-Me)2AlMe2]3@MCM-41 (5c). Dehydrated MCM-41
(4; 250 mg) was suspended in hexane, and a solution of 1c
(512 mg, 1.26 mmol) in hexane was added. The blue mixture
was stirred for 3 h at ambient temperature. After centrifuga-
tion and several hexane washings 5c was dried to constant
weight, yielding 360 mg of a light green material. Anal.
Found: C, 10.84; H, 2.98. The amount of recovered 1c was
determined to be 340 mg (0.84 mmol, 66%). IR (Nujol, cm-1):
the sharp signal at 3695 cm-1 attributed to isolated SiO-H
completely disappeared.
(C5Me5)Nd[(µ-Me)2AlMe2]2@MCM-41 (6c). Dehydrated
MCM-41 (4; 125 mg) was suspended in hexane, and a solution
of 2c (297 mg, 0.65 mmol) in hexane was added. The blue
mixture was stirred for 3 h at ambient temperature. After
centrifugation and several hexane washings, separated light
blue-green material 6c was dried to constant weight. Yield:
280 mg. Anal. Found: C, 16.71; H, 3.07. The amount of
recovered 2c was determined as 211 mg (0.46 mmol, 71%).
Note that ligand redistribution via formation of homoleptic 1c
and metallocene (C5Me5)2Nd(AlMe4) did not occur during the
solution grafting reaction. IR (Nujol, cm-1): the sharp signal
at 3695 cm-1 attributed to isolated SiO-H completely disap-
peared and a weak broad band centered at 3650 cm-1 ap-
peared.
wR2 (obsd/all)
GOF (obsd/all)
max/min ∆F (e Å-3
)
X-ray Crystallography and Crystal Structure Deter-
mination of 2b. Crystals suitable for diffraction experiments
were selected in a glovebox, coated with perfluorinated ether,
and fixed in a capillary. Preliminary examination of the crystal
quality and data collection were carried out on a Nonius
KappaCCD diffractometer in combination with a rotating
anode X-ray generator and graphite-monochromated Mo KR
radiation (λ ) 0.710 73 Å) employing the COLLECT software
package.31 A total of 1092 collected images were processed
using Denzo.32 Absorption and/or decay effects were corrected
during the scaling procedure.32 The structures were solved by
direct methods33 and refined with standard difference Fourier
techniques.34 All non-hydrogen atoms of the asymmetric unit
were refined with anisotropic thermal displacement param-
eters. All hydrogen atoms were found in the difference Fourier
maps and refined freely with individual isotropic thermal
displacement. Full-matrix least-squares refinements were
carried out by minimizing ∑w(Fo - Fc2)2 employing the
2
General Procedure for the Preparation of Half-
Sandwich Dimethyl Complexes 7a,b. In a glovebox, (C5-
Me5)Ln(AlMe4)2 was dissolved in hexane. Tetrahydrofurane (2
equiv) in 5 mL of hexane was added with vigorous stirring to
the aluminate solution. Instantly, the formation of a white
precipitate was observed. After the reaction mixture was
stirred for 5 min, the product had precipitated completely and
was separated by centrifugation and washed three times with
hexane. Drying in vacuo produced analytically pure complexes
7 as white powders in almost quantitative yields. Due to the
low solubility of complexes 7 in benzene, useful solution 13C
NMR spectra could not be obtained. For a solid-state 13C NMR
spectrum of 7a, see ref 17.
SHELXL-97 weighting scheme and stopped at maximum shift/
error of <0.002. In the final model, 347 parameters were
refined to wR2 ) 0.0537 based on all 4219 data. For details
see Table 2.
Acknowledgment. We thank the Deutsche Fors-
chungsgemeinschaft (SPP 1166) and the Fonds der
Chemischen Industrie for generous support. E. H.
thanks Tim Bartels for his help with the X-ray deter-
mination of complex 2b.
Supporting Information Available: A CIF file giving
crystallographic data for 2b. This material is available free of
charge via the Internet at http://pubs.acs.org.
(1,2,3,4,5-Pentamethylcyclopentadienyl)dimethyl-
yttrium(III) (7a). Following the procedure described above,
(C5Me5)Y(AlMe4)2 (199 mg, 0.50 mmol) and tetrahydrofurane
(72 mg, 1.00 mmol) yielded 7a (123 mg, 97%) as a white
OM0506163
1
powder. H NMR (400 MHz, C6D6, 25 °C): δ 2.00 (s, 15H, Cp
(31) Hooft, R. COLLECT, Data Collection Software for Nonius
KappaCCD Devices; Nonius BV, Delft, The Netherlands, 2001.
(32) Otwinowski, Z.; Minor, W. In Processing of X-ray Diffraction
Data Collected in Oscillation Mode; Carter, C. W., Jr., Sweet, R. M.,
Eds.; Academic Press: New York, 1997; Vol. 276, p 307.
(33) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27,
435.
(34) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen, Go¨ttingen,
Germany, 1998.
(35) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University, Utrecht, The Netherlands, 2001.
CH3), -0.41 (q, 6H, YCH3) ppm. Anal. Calcd for C12H21Y
(484.440): C, 56.70; H, 8.33. Found: C, 57.03; H, 8.45.
(1,2,3,4,5-Pentamethylcyclopentadienyl)dimethyl-
lutetium(III) (7b). Following the procedure described above,
(C5Me5)Lu(AlMe4)2 (242 mg, 0.50 mmol) and tetrahydrofurane
(72 mg, 1.00 mmol) yielded 7b (164 mg, 96%) as a white
powder. 1H NMR (400 MHz, C6D6, 25 °C): δ 2.00 (s, 15H,
CpCH3), 0.04 (s, 6H, LuCH3) ppm. Anal. Calcd for C12H21Lu
(340.269): C, 42.36; H, 6.22. Found: C, 42.81; H, 6.57.