Aluminum ansa-indenyl compounds. Synthesis, structures, dynamic properties, and application in the synthesis of group 4 ansa-metallocenes

Article abstract of DOI:10.1021/om990381t

The synthesis, structures, dynamic properties, and indenyl transfer reactions of aluminum ansa-bis(indenyl) compounds are described. The reaction of 2 equiv of AlMe₂Cl with 1 equiv of Li₂[(1-indenyl)₂SiMe₂], Li₂[(2-Me-1-indenyl)₂SiMe₂], Li₂[(2-Me-4,5-benz-1-indenyl)₂SiMe₂]· Et₂O, Li₂[(2-Me-4-Ph-1-indenyl)₂SiMe₂]·Et ₂O, or Li₂[1,2-(3-indenyl)₂-C₂H₄] in Et₂O followed by treatment with the appropriate Lewis base (L) affords {AlMe₂(THF)(indenyl)}₂SiMe₂ (1), [{1-AlMe₂(1,4-dioxane)_0.5-2-Me-1-indenyl} ₂SiMe₂]_n (2a), {1-AlMe₂(Et₂O)-2-Me-4,5-benz-1-indenyl} ₂SiMe₂ (3), {1-AlMe₂(Et₂O)-2-Me-4-Ph-1-indenyl}₂SiMe ₂ (4a), {1-AlMe₂(THF)-2-Me-4-Ph-1-indenyl}₂SiMe₂ (4b), or 1,2-{3-AlMe₂(THF)-1-indenyl}₂-C₂H₄ (5), respectively, as colorless to pale yellow solids in 41-70percent isolated yields. Compounds 2a and 4b are isolated as the rac isomers, whereas 1 and 3 are isolated as rac/meso mixtures from which the rac isomer can be separated by recrystallization. Compound 5 was isolated as a single diastereomer of 1,2-{3-AlMe₂(THF)-1-indenyl}₂-C₂H₄. The molecular structures of rac-2a and rac-3 have been determined by X-ray crystallography. Low-temperature NMR studies establish that, in toluene-d₈, rac-1 exists as a 2/1 mixture of two isomers, ({1-AlMe₂(THF)-1-indenyl}{1-AlMe ₂(THF)-3-indenyl})SiMe₂ (rac-1a) and {1-AlMe₂(THF)-1-indenyl}₂SiMe₂ (rac-1b), which interconvert rapidly on the NMR time scale at room temperature. In contrast, similar studies establish that rac-2b (in THF-d₈) and rac-3 and rac-4b (in toluene-d₈) exist as the rac-{1-AlMe₂L-1-indenyl}₂SiMe₂ isomers; in these cases no other isomers are detected. rac-1, rac-3, and rac-4b isomerize to rac/meso mixtures slowly (days) at ambient temperature and more rapidly (minutes) at 70°C. Compounds 1 and 5 undergo slow partial disproportionation by ligand redistribution (e.g. 1: 28percent conversion, 2 days, 23°C, benzene); the more highly substituted indenyl compounds 3 and 4b are more resistant to this process. Compounds 1, 2, 3, 4a, and 5 react with Zr(NMe₂)₄ and Hf(NMe₂)₄ in benzene or toluene under mild conditions to yield the corresponding ansa-metallocenes {(1-indenyl)₂SiMe₂}-M(NMe₂)₂ (6, M = Zr, rac/meso = 4/1; 7, M = Hf, rac/meso = 10/1), {(2-Me-1-indenyl)₂SiMe₂}-Zr(NMe2)₂ (8, rac/meso = 3/4), {(2-Me-4,5-benz-1-indenyl)₂SiMe₂}Zr(NMe₂) ₂ (9, rac/meso = 9/10), {(2-Me-4-Ph-1-indenyl)₂SiMe₂}Zr(NMe₂) ₂ (10, rac/meso = 2/3) and {1,2-(3-indenyl)₂-C₂H₄}M(NMe2)₂ (11, M = Zr, rac/meso = 7.3/1; 12, M = Hf, rac/meso = 7/1) in 70-90percent NMR yields.

Full text of DOI:10.1021/om990381t

Organometallics 1999, 18, 5347-5359
5347
Alu m in u m a n sa -In d en yl Com p ou n d s. Syn th esis,
Str u ctu r es, Dyn a m ic P r op er ties, a n d Ap p lica tion in th e
Syn th esis of Gr ou p 4 a n sa -Meta llocen es
B. Thiyagarajan and Richard F. J ordan*
Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242
Victor G. Young, J r.
Department of Chemistry, The University of Minnesota, Minneapolis, Minnesota 55455
Received May 20, 1999
The synthesis, structures, dynamic properties, and indenyl transfer reactions of aluminum
ansa-bis(indenyl) compounds are described. The reaction of 2 equiv of AlMe2Cl with 1 equiv
of Li2[(1-indenyl)2SiMe2], Li2[(2-Me-1-indenyl)2SiMe2], Li2[(2-Me-4,5-benz-1-indenyl)2SiMe2]‚
Et2O, Li2[(2-Me-4-Ph-1-indenyl)2SiMe2]‚Et2O, or Li2[1,2-(3-indenyl)2-C2H4] in Et2O followed
by treatment with the appropriate Lewis base (L) affords {AlMe2(THF)(indenyl)}2SiMe2 (1),
[{1-AlMe2(1,4-dioxane)0.5-2-Me-1-indenyl}2SiMe2]n (2a ), {1-AlMe2(Et2O)-2-Me-4,5-benz-1-
indenyl}2SiMe2 (3), {1-AlMe2(Et2O)-2-Me-4-Ph-1-indenyl}2SiMe2 (4a ), {1-AlMe2(THF)-2-Me-
4-Ph-1-indenyl}2SiMe2 (4b), or 1,2-{3-AlMe2(THF)-1-indenyl}2-C2H4 (5), respectively, as
colorless to pale yellow solids in 41-70% isolated yields. Compounds 2a and 4b are isolated
as the rac isomers, whereas 1 and 3 are isolated as rac/meso mixtures from which the rac
isomer can be separated by recrystallization. Compound 5 was isolated as a single
diastereomer of 1,2-{3-AlMe2(THF)-1-indenyl}2-C2H4. The molecular structures of rac-2a and
rac-3 have been determined by X-ray crystallography. Low-temperature NMR studies
establish that, in toluene-d8, rac-1 exists as a 2/1 mixture of two isomers, ({1-AlMe2(THF)-
1-indenyl}{1-AlMe2(THF)-3-indenyl})SiMe2 (rac-1a ) and {1-AlMe2(THF)-1-indenyl}2SiMe2
(rac-1b), which interconvert rapidly on the NMR time scale at room temperature. In contrast,
similar studies establish that rac-2b (in THF-d8) and rac-3 and rac-4b (in toluene-d8) exist
as the rac-{1-AlMe2L-1-indenyl}2SiMe2 isomers; in these cases no other isomers are detected.
rac-1, rac-3, and rac-4b isomerize to rac/meso mixtures slowly (days) at ambient temperature
and more rapidly (minutes) at 70 °C. Compounds 1 and 5 undergo slow partial dispropor-
tionation by ligand redistribution (e.g. 1: 28% conversion, 2 days, 23 °C, benzene); the more
highly substituted indenyl compounds 3 and 4b are more resistant to this process.
Compounds 1, 2, 3, 4a , and 5 react with Zr(NMe2)4 and Hf(NMe2)4 in benzene or toluene
under mild conditions to yield the corresponding ansa-metallocenes {(1-indenyl)2SiMe2}-
M(NMe2)2 (6, M ) Zr, rac/meso ) 4/1; 7, M ) Hf, rac/meso ) 10/1), {(2-Me-1-indenyl)2SiMe2}-
Zr(NMe2)2 (8, rac/meso ) 3/4), {(2-Me-4,5-benz-1-indenyl)2SiMe2}Zr(NMe2)2 (9, rac/meso )
9/10), {(2-Me-4-Ph-1-indenyl)2SiMe2}Zr(NMe2)2 (10, rac/meso ) 2/3) and {1,2-(3-indenyl)2-
C2H4}M(NMe2)2 (11, M ) Zr, rac/meso ) 7.3/1; 12, M ) Hf, rac/meso ) 7/1) in 70-90% NMR
yields.
In tr od u ction
of stereoselectivity is difficult.2 We have described the
synthesis of rac-{(1-indenyl)2SiMe2}Zr(NMe2)2, rac-{1,2-
(1-indenyl)2-C2H4}Zr(NMe2)2, and other ansa-metal-
locenes by amine elimination reactions of M(NMe2)4
compounds and ansa-bis(indenes) or cyclopentadienes.3,4
However, this approach is less useful for the synthesis
of Ti or Hf ansa-metallocenes (order of reactivity: Zr >
Hf > Ti) and does not work well for crowded metal
amides or crowded or weakly acidic ansa-bis(indenes).5
Chiral group 4 ansa-metallocenes are important
because of their utility as stereoselective olefin poly-
merization catalysts and selective reagents or catalysts
for other reactions.1 ansa-Metallocenes are normally
prepared by the reaction of metal halides with alkali-
metal or alkaline-earth-metal ansa-cyclopentadienyl
reagents, but this method is often inefficient and control
Several groups have shown that silicon and tin
cyclopentadienyl derivatives can be used to synthesize
group 4 ansa-metallocene dichlorides.6 Nifant’ev syn-
thesized several ansa-metallocenes by the reaction of
MCl4 (M ) Zr, Hf) with distannylated bis(cyclopenta-
dienyl) or bis(indenyl) reagents; in particular, it was
* To whom correspondence should be addressed at The Department
of Chemistry, The University of Chicago, 5735 S. Ellis Ave., Chicago,
IL 60637.
(1) Reviews: (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.;
Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34,
1143. (b) Halterman, R. L. Chem. Rev. 1992, 92, 965. (c) Hoveyda, A.
H.; Morken, J . P. Angew. Chem., Int. Ed. Engl. 1996, 35, 1262.
10.1021/om990381t CCC: $18.00 © 1999 American Chemical Society
Publication on Web 11/10/1999

5348 Organometallics, Vol. 18, No. 25, 1999
Thiyagarajan et al.
shown that rac-1,2-(3-SiMe3-1-indenyl)2-ethane reacts
stereoselectively with ZrCl4 to yield rac-{1,2-(1-inde-
nyl)2-C2H4}ZrCl2.7 Brintzinger reported the synthesis of
the meso-Me2Si(3-tBu-C5H3)2ZrCl2 and meso-Me2Si(2,4-
Me2-C5H2)2ZrCl2 by the reaction of ZrCl4 with the
corresponding meso silastannatetrahydro-s-indacenes.8
Additionally, Resconi reported the diastereoselective
synthesis of rac- and meso-{1,2-(4,7-Me2-1-indenyl)2-
C2H4}ZrCl2 by the reaction of ZrCl4 with rac- and meso-
1,2-(4,7-Me2-1-SiMe3-3-indenyl)2-ethane, respectively.9
In these cases indenyl transfer is presumed to occur
with inversion of configuration via backside attack of
Zr at the Si-Cindenyl or Sn-Cindenyl center.10
rac-{1,2-(1-indenyl)2-C2H4}Zr(NMe2)2, rac-{(1-inden-
yl)2SiMe2}Zr(NMe2)2, and other ansa-zirconocene bis-
(amides) react quantitatively with AlMe3 to yield the
corresponding metallocene dialkyl derivatives and Al2-
Me5(µ-NMe2) as the major Al product (eq 1).11 These
facile alkyl/amide exchange reactions suggested that
aluminum ansa-bis(indenyl) compounds might undergo
analogous ansa-bis(indenyl)/NMe2 exchange reactions
with M(NMe2)4 compounds, which could be exploited in
the synthesis of group 4 ansa-metallocenes.
Cyclopentadienyl aluminum compounds are accessible
by halide displacement reactions of alkali-metal or
alkaline-earth-metal cyclopentadienyl reagents and alu-
minum halides or, less commonly, by alkane elimination
reactions of cyclopentadiene and aluminum alkyls.12,13
Electron-precise cyclopentadienyl aluminum compounds
(e.g. eight-electron CpAlX2L species) normally exhibit
η1 Cp-Al coordination. In contrast, electron-deficient
species (e.g. CpAlX2) often exhibit multihapto Cp-Al
bonding and η1, η2, η3, and η5 Cp-Al bonding modes
have all been observed in the solid state.12-14 Aluminum
cyclopentadienyl species are normally fluxional in solu-
tion and, like other Al compounds, may undergo ligand
redistribution and disproportionation reactions.15,16 The
use of cyclopentadienylaluminum compounds as cyclo-
pentadienyl transfer agents is very limited, one notable
example being the synthesis of Cp2TiCl2 by the reaction
of {(η1-C5H5)2Al(µ-OiPr}2 with TiCl4.17
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11.

Aluminum ansa-Indenyl Compounds
Organometallics, Vol. 18, No. 25, 1999 5349
Sch em e 1
Ta ble 1. Syn th esis of Alu m in u m a n sa -In d en yl Com p ou n d s
compd
isolated yield (%)
rac/meso ratio
{AlMe2(THF)-indenyl)}2SiMe2 (1)
54
41
70
6
62
54
1.2/1
rac
2/1
2/3
[{1-AlMe2(1,4-dioxane)0.5-2-Me-1-indenyl}2SiMe2]n (2a )
{1-AlMe2(Et2O)-2-Me-4,5-benz-1-indenyl}2SiMe2 (3)
{1-AlMe2(Et2O)-2-Me-4-Ph-1-indenyl}2SiMe2 (4a )
{1-AlMe2(THF)-2-Me-4-Ph-1-indenyl}2SiMe2 (4b)
1,2-{3-AlMe2(THF)-1-indenyl}2-C2H4 (5)
rac
single isomera
a
Stereochemistry not established.
of {(AlMe2L)-indenyl}2SiMe2 compounds that contain
indenyl or substituted-indenyl rings and are stabilized
by Lewis bases (L). In particular, Al derivatives of (2-
Me-4-Ph-1-indenyl)2SiMe2 and (2-Me-4,5-benz-1-inden-
yl)2SiMe2 have been investigated as possible reagents
for the synthesis of {(2-Me-4-Ph-indenyl)2SiMe2}MX2
and {(2-Me-4,5-benz-1-indenyl)2SiMe2}MX2 metallocenes,
which are precursors to high-performance olefin poly-
merization catalysts.2m,o,p Additionally, 1,2-{(AlMe2L)-
indenyl}2-ethane compounds have been investigated for
comparison to the SiMe2-bridged compounds. The in-
corporation of Lewis bases (L ) THF, dioxane, Et2O)
facilitates the isolation of these Al indenyl compounds
in solid form free of residual chloride and enforces η1-
indenyl-Al bonding, which simplifies the structural
chemistry.
Resu lts
Alu m in u m a n sa -Bis(in d en yl) Com p ou n d s. We
first discuss the synthesis, structures, and dynamic
properties of aluminum ansa-bis(indenyl) compounds.
The synthetic results are summarized in Table 1, and
specific details of each system are described in the
following sections.
r a c- a n d m eso-{AlMe2(THF )-in d en yl}2SiMe2 (1).
The synthesis and reactivity of {AlMe2(THF)-indenyl}2-
SiMe2 (1) have been described in a recent communica-
tion.18 The key properties of this system are summarized
here to provide a basis for the subsequent discussion of
more elaborate SiMe2-bridged and ethylene-bridged
aluminum ansa-bis(indenyl) compounds. The reaction
of Li2[(1-indenyl)2SiMe2] and 2 equiv of AlMe2Cl in Et2O,
followed by treatment with THF, yields {AlMe2(THF)-

5350 Organometallics, Vol. 18, No. 25, 1999
Thiyagarajan et al.
1
indenyl}2SiMe2 (1) as a ca. 1/1 mixture of rac and meso
isomers (eq 2 and Table 1), which differ in the relative
configurations of the Al-indenyl units.
position; e.g., H NMR monitoring of benzene-d6 solu-
tions of rac-1/meso-1 reveals that 1 is ca. 28% converted
to new Al-Me species after 2 days at 23 °C. A similar
but faster reaction is observed for 1 in THF-d8 (36%
conversion, 12 h, 23 °C); in this case one of the major
products is AlMe3(THF) (δ -0.99). These results suggest
that 1 undergoes partial disproportionation by ligand
redistribution in solution.20 Therefore, the rac-1/meso-1
isomerization may be more complicated than implied
by Scheme 1 and may involve intermolecular exchange
of -AlMe2L units between indenyl rings, as illustrated
schematically in eq 3. It was not possible to identify the
Recrystallization of the rac-1/meso-1 mixture from
toluene at -20 °C affords small quantities of pure rac-1
as colorless cubes. An X-ray crystallographic analysis
established that rac-1 crystallizes as a single isomer,
i.e., rac-{1-AlMe2(THF)-1-indenyl}{1-AlMe2(THF)-3-
indenyl}SiMe2 (rac-1a ; Scheme 1). However, low-tem-
1
perature H NMR studies (e-60 °C) show that rac-1
exists as a 2/1 mixture of rac-1a and rac-{1-AlMe2(THF)-
1-indenyl}2SiMe2 (rac-1b, Scheme 1) in toluene-d8. In
the -80 °C spectrum, the vinyl H2 and H3 resonances
of the 1-Al-1-Si-substituted indenyl rings of rac-1a and
rac-1b appear as doublets in the range δ 6.5-7.5 (J )
4 Hz), and the vinyl H2 and allylic H3 resonances of
the 1-Al-3-Si-substituted indenyl ring of rac-1a appear
as singlets at δ 6.49 and 4.10, respectively. Intercon-
version of these positional isomers is slow on the NMR
time scale at -60 °C but rapid at 23 °C in toluene-d8.
The rac-1a /rac-1b exchange likely occurs by sequential
suprafacial [1,5]-Al shifts via isoindene intermediates,
as illustrated in the horizontal processes in Scheme 1.
THF dissociation, which is not shown in Scheme 1,
accompanies and may be required for this process.15 The
rac-1a /rac-1b exchange could also occur by a combina-
tion of [1,5]-Si and [1,5]-H shifts (not shown), but these
processes are expected to be much slower than the
observed isomerization. For comparison, [1,5]-Si shifts
are slow on the NMR time scale and [1,5]-H shifts are
slow on the laboratory time scale below ca. 150 °C for
1-SiMe3-indene and related compounds.19
positional isomer(s) of meso-1 but is reasonable to
presume that, as for rac-1, both 1-Al-1-Si- and 1-Al-3-
Si-substituted isomers are possible.
[r a c-{1-AlMe2(1,4-d ioxa n e)0.5-2-Me-1-in d en yl}2-
SiMe2]n (r a c-2a ). The reaction of Li2[(2-Me-1-indenyl)2-
SiMe2] with 2 equiv of AlMe2Cl in Et2O at 23 °C,
followed by removal of the volatiles, extraction of the
product into hexanes to remove LiCl, and treatment
with 1,4-dioxane at 23 °C, affords the polymeric 1,4-
dioxane adduct [rac-{1-AlMe2(1,4-dioxane)0.5-2-Me-1-
indenyl}2SiMe2]n (2a , 41% isolated) as a colorless solid
(eq 4). Compound 2a is insoluble in benzene, toluene,
rac-1 isomerizes slowly (3 days) at 23 °C and rapidly
(minutes) at 70 °C to a 1/1 rac-1/meso-1 mixture in
benzene-d6. The interconversion of rac-1 and meso-1
requires inversion of configuration of one of the sp3
carbon centers of the indenyl rings. This process may
occur by combinations of [1,5]-Al or [1,5]-Si shifts and
[1,5]-H shifts, as illustrated in the vertical processes in
Scheme 1. However, it should be noted that the rac/meso
isomerization of 1 is accompanied by significant decom-
(17) (a) Kunicki, A.; Sadowski, R.; Zachara, J . J . Organomet. Chem.
1996, 508, 249. For other reactions of Al Cp compounds see: (b) Fiser,
J . D.; Shapiro, P. J .; Yap, G. P. A.; Rheingold, A. L. Inorg. Chem. 1996,
35, 272. (c) Shapiro, P. J .; Vij, A.; Yap, G. P. A.; Rheingold, A. L.
Polyhedron 1995, 1, 203. (d) Fisher, J . D.; Shapiro, P. J .; Budzelaar,
P. H. M.; Staples, R. J . Inorg. Chem. 1998, 37, 1295.
(18) Thiyagarajan, B.; J ordan, R. F.; Young, V. G., J r. Organome-
tallics 1998, 17, 281.
(19) (a) Rakita, P. E.; Davison, A. Inorg. Chem. 1969, 8, 1164. (b)
Ashe, A. J . III. Tetrahedron Lett. 1970, 24, 2105. (c) Larrabee, R. B.;
Dowden, B. F. Tetrahedron Lett. 1970, 12, 915. (d) Davison, A.; Rakita,
P. E. J . Organomet. Chem. 1970, 23, 407. (e) Rakita, P. E.; Taylor, G.
A. Inorg. Chem. 1972, 11, 2136. (f) Andrews, M. N.; Rakita, P. E.;
Taylor, G. A. Inorg. Chim. Acta 1975, 13, 191. (g) Rigby, S. S.; Girard,
L.; Bain, A. D.; McGlinchey, M. J . Organometallics 1995, 14, 3798.
See also: (h) Miller, L. L.; Boyer, R. F. J . Am. Chem. Soc. 1971, 93,
650.
and methylene chloride and dissolves in THF and
dioxane with decomposition. However, low-temperature
NMR spectra of freshly dissolved 2a in THF-d8 establish
that 2a undergoes ligand substitution by the solvent to
yield free 1,4-dioxane and rac-{1-AlMe2(THF-d8)-2-Me-

Aluminum ansa-Indenyl Compounds
Organometallics, Vol. 18, No. 25, 1999 5351
on the basis of electronegativity values.21 The Al-CH3
distances range from 1.960(4) to 1.980(4) Å and are
similar to the Al-CH3 distances in rac-1a (1.945(4)-
1.986(4) Å) and Al2Me6 (average Al-C(terminal) 1.97
Å).22 The Al-C(indenyl) bond distances in 2a (2.055-
(3), 2.047(4) Å) are similar to those in rac-1a (2.043(4),
2.067(4) Å) and the Al-Cp distances in (η1-Cp)3Al(NCt-
Bu) (2.067(6) Å) and {(η1-Cp)2AlOiPr}2 (2.003(2) Å).12l,17a
r a c- a n d m eso-{1-AlMe2(Et2O)-2-Me-4,5-ben z-1-
in d en yl}2SiMe2 (3). The reaction of Li2[(2-Me-4,5-benz-
1-indenyl)2SiMe2]‚Et2O with 2 equiv of AlMe2Cl in Et2O,
followed by removal of volatiles, extraction of the residue
with toluene, solvent removal, and hexane washing,
yields {1-AlMe2(Et2O)-2-Me-4,5-benz-1-indenyl}2SiMe2
(3) as a colorless solid (70% isolated, eq 5). The 1H NMR
F igu r e 1. Molecular structure of the monomeric unit of
[rac-{1-AlMe2(1,4-dioxane)0.5-2-Me-1-indenyl}2SiMe2]n (rac-
2a ).
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [r a c-{1-AlMe2(1,4-d ioxa n e)0.5-2-
Me-1-in d en yl}2SiMe2]n (r a c-2a )
Si(1)-C(1)
Si (1)-C(11)
Si(1)-C(21)
Si(1)-C(22)
Al(1)-O(1)
Al(2)-C(11)
1.889(3)
1.929(3)
1.880(4)
1.868(3)
1.973(3)
2.047(4)
Al(1)-C(23)
Al(1)-C(24)
Al(2)-C(25)
Al(2)-C(26)
Al(2)-O(2)
1.963(4)
1.960(4)
1.980(4)
1.970(4)
1.939(3)
C(1)-Si(1)-C(11)
113.8(1) C(23)-Al(1)-C(24)
116.3(2)
C(21)-Si(1)-C(22) 104.8 2) C(25)-Al (2)-C(26) 113.8(2)
C(23)-Al(1)-C(1)
C(23)-Al(1)-C(24) 116.3(2) C(25)-Al(2)-C(26)
116.1(2) C(25)-Al(2)-C(11)
119.9(2)
113.8(2)
119.9(2)
115.8(2)
99.3(1)
102.3(1)
101.0(1)
110.1(2)
C(23)-Al(1)-C(1)
C(24)-Al(1)-C(1)
O(1)-Al(1)-C(23)
O(1)-Al(1)-C(24)
O(1)-Al(1)-C(1)
Si(1)-C(11)-Al(2)
116.1(2) C(25)-Al(2)-C(11)
115.8(2) C(26)-Al(2)-C(11)
99.6(1) O(2)-Al(2)-C(25)
100.0(2) O(2)-Al(2)-C(26)
105.3(1) O(2)-Al(2)-C(11)
105.8(2) Si(1)-C(1)-Al(1)
spectrum of isolated 3 in benzene-d6 (23 °C) establishes
that this material is a 2/1 mixture of rac and meso
isomers. The spectrum of rac-3 contains one SiMe2
resonance and one broad AlMe2 resonance, whereas that
of meso-3 contains two SiMe2 resonances of equal
intensity and one broad AlMe2 resonance. The vinyl
hydrogen (H3) resonances for rac and meso 3 appear at
δ 6.46 and 6.15, respectively.
1-indenyl}2SiMe2 (2b), along with a small amount (ca.
10% at -90 °C) of other species. The H NMR spectrum
1
of rac-2b (generated in situ) in THF-d8 at -90 °C
contains two singlets (δ -0.72, -0.95; 6H each) for the
diastereotopic Al-Me groups, a singlet (δ 0.93, 6H) for
the two equivalent Si-Me groups, a singlet (δ 1.08, 6H)
for the two equivalent 2-Me groups, and a singlet at δ
6.09 ppm (2H) for the vinylic hydrogens (H3). As 2b is
derived from 2a by ligand substitution at Al, it is likely
that isolated 2a is structurally analogous to 2b. At-
tempts to isolate other {1-AlMe2(L)-2-Me-1-indenyl}2-
SiMe2 compounds (L ) THF, Et2O) yielded oily products
which could not be purified or characterized. 2b decom-
poses (ca. 24 h at 23 °C) in THF-d8, and consequently
possible isomerization processes could not be investi-
gated.
Recrystallization of the rac-3/meso-3 mixture from
toluene/hexanes (3:2) at 23 °C by slow evaporation yields
pure rac-3 as colorless blocks. An X-ray crystallographic
analysis of rac-3 (Figure 3, Table 3) confirms that the
-AlMe2(Et2O) units bind to the indenyl groups in an
η1 fashion at the 1-position. The Al atoms exhibit
distorted-tetrahedral geometry and the Al-CH3 dis-
tances (1.991(8), 1.988(3) Å) and Al-Cindenyl distance
(2.039(3) Å) are in the expected range.
1
The low-temperature (-20 °C) H NMR spectrum of
rac-3 in toluene-d8 is consistent with the solid-state
structure. There is no indication of the presence of other
isomers. This spectrum contains one Si-Me resonance,
two Al-Me resonances of equal intensity, one 2-Me
resonance, and a singlet at δ 6.46 (2H) for the H3 vinylic
hydrogens. The observation of two Al-Me resonances
indicates that Et2O exchange is slow on the NMR time
scale under those conditions; however, this exchange is
rapid at 23 °C. rac-3 isomerizes rapidly (<5 min) to a
1.2/1 equilibrium mixture of rac-3/meso-3 at 80 °C in
Crystallization of isolated 2a from 3/1 toluene/dioxane
at 23 °C by slow evaporation yields rac-2a as colorless
blocks. The solid-state structure of rac-2a was estab-
lished by X-ray crystallography (Figures 1 and 2; Table
2). rac-2a adopts a polymeric structure in which the
-AlMe2(dioxane) groups are bonded to the indenyl
groups in an η1-fashion at the 1-position, and the 1,4-
dioxane ligands bridge the monomer units. The alumi-
num atoms exhibit distorted-tetrahedral geometry. The
O-Al-C angles (average 101.3°) are ca. 15° smaller
than the C-Al-C angles (average 116.3°), as expected
(20) (a) Similar disproportionation processes have been reported for
other cyclopentadienylaluminum compounds; e.g., CpAlMe2(THF)
undergoes ca. 25% conversion to AlMe3(THF) and Cp2AlMe(THF) in
benzene-d6 at 23 °C.16 (b) However, other than AlMe3(THF), the
disproportionation products of 1 have not yet been identified.
(21) (a) Bent, H. A. J . Chem. Educ. 1960, 37, 616. (b) Bent, H. A.
Chem. Rev. 1961, 61, 275.
(22) Vranka, R. G.; Amma, E. L. J . Am. Chem. Soc. 1967, 89, 3121.

5352 Organometallics, Vol. 18, No. 25, 1999
Thiyagarajan et al.
F igu r e 2. Polymeric structure of rac-2a .
F igu r e 3. Molecular structure of rac-{1-AlMe2(Et2O)-2-
Me-4,5-benz-1-indenyl}2SiMe2 (rac-3).
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for r a c-{1-AlMe2(Et2O)-2-
Me-4,5-ben z-1-in d en yl}2SiMe2 (r a c-3)
Si(1)-C(1)
Al(1)-C(17)
Al(1)-O(1)
1.899(3)
1.988(3)
1.922(3)
Si(1)-C(15)
Al(1)-C(16)
Al(1)-C(1)
1.879(3)
1.991(4)
2.039(3)
for the H3 vinylic hydrogens. The observation of two
sharp Al-Me resonances indicates that THF exchange
is slow on the NMR time scale under these conditions;
however, the Al-Me resonances are significantly broad-
ened at 23 °C due to THF exchange. There is no
indication of the presence of other isomers even at -90
°C. rac-4b slowly isomerizes to a rac/meso mixture (3.5/1
rac/meso, 17 h, 23 °C; 1.7/1 rac/meso, 8 h, 75 °C). As for
3, no significant disproportionation of rac-4b is observed
during the isomerization under these conditions.
1,2-{3-AlMe2(THF )-1-in d en yl}2-C2H4 (5). The reac-
tion of Li2[1,2-(1-indenyl)2-ethane] with 2 equiv of
AlMe2Cl at 23 °C in Et2O, followed by treatment with
THF, affords 1,2-{3-AlMe2(THF)-1-indenyl}2-C2H4 (5) as
a colorless to pale yellow solid (54% isolated, eq 7). The
C1-Si(1)-C1A
111.0(2)
111.7(2)
103.6(2)
116.4(2)
102.8(1)
C(15)-Si1-C(15A)
C(16)-Al(1)-C(17)
O(1)-Al(1)-C(16)
C(17)-Al(1)-C(1)
102.8(2)
110.9(2)
103.7(2)
117.2(2)
Si(1)-C(1)-Al(1)
O(1)-Al(1)-C(17)
C(16)-Al(1)-C(1)
O(1)-Al(1)-C(1)
benzene-d6; however, this isomerization also occurs
slowly at 23 °C (2.5/1 rac-3/meso-3 mixture produced
after 27 h). In contrast to the case of 1, the rac-3/meso-3
isomerization is not accompanied by significant dispro-
portionation.
r a c- a n d m eso-{1-AlMe2(E t 2O)-2-Me-4-P h -1-in -
d en yl}2SiMe2 (4a ) a n d r a c-{1-AlMe2(THF )-2-Me-4-
P h -1-in d en yl}2SiMe2 (4b). The reaction of Li2[(2-Me-
4-Ph-1-indenyl)2SiMe2]‚Et2O with 2 equiv of AlMe2Cl in
Et2O, followed by removal of volatiles, extraction of the
residue with toluene, solvent removal, and hexane
washing yields {1-AlMe2(Et2O)-2-Me-4-Ph-1-indenyl}2-
SiMe2 (4a ) as a colorless solid. Compound 4a is isolated
in very low yield (6%, 2/3 mixture of rac and meso
isomers) by this method due to its high solubility in
hexanes. However, addition of THF to the hexane wash
obtained from the separation of 4a results in the
precipitation of rac-{1-AlMe2(THF)-2-Me-4-Ph-1-in-
denyl}2SiMe2 (4b) as a colorless solid (62% isolated, eq
6).
1
The low-temperature (-30 °C) H NMR spectrum of
1
rac-4b in toluene-d8 contains two singlets of equal
intensity (δ -0.44, -0.17; 6H each) for the diaste-
reotopic Al-Me groups, one singlet (δ 1.38, 6H) for the
two equivalent Si-Me groups, and a singlet (δ 6.58, 2H)
low-temperature (-90 °C) H NMR spectrum of 5 in
toluene-d8 establishes that only one isomer is present;
key resonances include a broad AlMe2 resonance (δ
-0.21, 6H), singlets for the H1 (δ 4.14, 2H) and H2 (δ

Aluminum ansa-Indenyl Compounds
Organometallics, Vol. 18, No. 25, 1999 5353
7.08, 2H) hydrogens of the indenyl C5 ring, and reso-
nances for the R- (δ 2.57, 1.92; each 4 H) and â-hydro-
gens (δ 0.44, 8H) of the coordinated THF. This isomer
is assigned as 1,2-{3-AlMe2(THF)-1-indenyl}2-C2H4 on
the basis of the chemical shifts of and lack of coupling
between the H1 and H2 resonances and the observation
of a 2D-COSY correlation between H1 and the ethylene
bridge hydrogens; however, the rac/meso stereochem-
istry could not be established. The 1,2-{1-AlMe2(THF)-
3-indenyl}2-C2H4 and 1,2-{1-AlMe2(THF)-1-indenyl}2-
C2H4 isomers were not detected. The 1H NMR spectrum
of 5 in C6D6 at 23 °C (freshly dissolved, vide infra) is
similar to the low-temperature spectrum, except that
the AlMe2 resonance is sharper and the R-THF reso-
nances are collapsed to a broad singlet (δ 2.78). These
observations indicate that THF exchange is rapid on the
NMR time scale at ambient temperature. Compound 5
undergoes ca. 50% isomerization/disproportionation af-
ter 2 days at 23 °C in benzene-d6.
Syn t h esis of a n sa -Met a llocen es. The aluminum
ansa-indenyl compounds 1-5 react with Zr(NMe2)4 and
Hf(NMe2)4 to yield the corresponding group 4 ansa-
metallocene bis-amide complexes and Al2Me4(µ-NMe2)2
as illustrated in eqs 8 and 9. The NMR yields and
stereoselectivities of these reactions are summarized in
eqs 8 and 9, and specific details of each case are
discussed in the following sections. In general, an excess
of 1-5 is required in these reactions because the
disproportionation/decomposition reactions of the Al
compounds discussed above are competitive with met-
allocene formation.
Rea ction of M(NMe2)4 (M ) Zr , Hf) w ith 1. The
reaction of Zr(NMe2)4 with 1.3 equiv of 1 (rac/meso )
1/1) in benzene-d6 (50 h, 23 °C) affords {(1-indenyl)2Si-
Me2}Zr(NMe2)2 (6, rac/meso ) 4/1) in 90% NMR yield
(vs Zr(NMe2)4), along with Al2Me4(µ-NMe2)2 (eq 8).
Complete removal of residual chloride (LiCl or AlCl
species) from 1 is important for selective indenyl
transfer. The reaction of Zr(NMe2)4 with samples of 1
containing residual chloride gave 6 in lower yield with
variable rac/ meso ratios, along with significant amounts
of rac-{(1-indenyl)2SiMe2}Zr(NMe2)Cl and rac- and meso-
{(1-indenyl)2SiMe2}ZrCl2. Similarly, the reaction of Hf-
(NMe2)4 with 1.3 equiv of 1 (rac/meso ) 1.3/1) in
benzene-d6 (70 °C, 21 h) affords {(1-indenyl)2SiMe2}Hf-
(NMe2)2 (7, rac/meso ) 10/1) in 70% NMR yield (vs Hf-
(NMe2)4) and Al2Me4(µ-NMe2)2. rac-7 was isolated as
pale orange needles in 61% yield by crystallization from
toluene/hexanes. Monitoring the reaction of Hf(NMe2)4
yellow (meso) crystals in 61% total yield. The crystals
1
were manually separated and characterized by H and
13C NMR and an X-ray crystal structure determination,
which confirmed the stereochemistry.23
Rea ction of Zr (NMe2)4 w ith 3. The reaction of Zr-
(NMe2)4 with 1.3 equiv of 3 (rac/meso ) 2.5/1) in
benzene-d6 (70 °C, 24 h) affords {(2-Me-4,5-benz-1-
indenyl)2SiMe2}Zr(NMe2)2 (9; 75% vs Zr(NMe2)4, rac/
meso ) 9/10, eq 8). Crystallization of the crude product
from toluene affords 9 (57%) as a 3/5 mixture of pale
orange (rac) and red (meso) crystals. The 1H NMR
spectrum of C2-symmetric rac-9 contains one SiMe2, one
NMe2, and one 2-Me resonance, while the spectrum of
Cs-symmetric meso-9 contains two SiMe2 and two NMe2
resonances and one 2-Me resonance. One of the NMe2
resonances for meso-9 is broad and appears at high field
(δ 0.93 at 23 °C). This feature is attributed to anisotropic
shielding and restricted rotation around the Zr-N bond
of the amide group that lies between the two benz-
indenyl groups on the crowded side of the meso struc-
ture. The high-field amide resonance splits into two
singlets of equal intensity at -53 °C (δ 1.72, 0.14; 3H
each) and collapses to a sharp singlet at 70 °C (δ 0.89).
Rea ction of Zr (NMe2)4 w ith 4a a n d 4b. The reac-
tion of Zr(NMe2)4 with 1.2 equiv of the Et2O adduct 4a
(2/3 rac/meso) in benzene-d6 (70 °C, 17 h) yields {(2-
Me-4-Ph-1-indenyl)2SiMe2}Zr(NMe2)2 (10; 75% vs Zr-
1
and 1 at 23 °C in benzene-d6 by H NMR revealed that
after 20 min the starting materials are completely
consumed and intermediate species with NMe2 reso-
nances in the range δ 2.7-2.9 (presumably mixed Hf/
Al indenyl compounds) are formed. After 24 h at 23 °C,
rac-7 is formed in 10% yield; after 24 h at 75 °C the
intermediates are converted to products.
Rea ction of Zr (NMe2)4 w ith 2a . The reaction of Zr-
(NMe2)4 with 1.3 equiv of 2a (rac) in benzene-d6 or
toluene (75 °C, 24 h) affords {(2-Me-1-indenyl)2SiMe2}-
Zr(NMe2)2 (8; 90% vs Zr(NMe2)4, rac/meso ) 3/4, eq 8).
Polymeric 2a is insoluble in benzene-d6 but dissolves
after a few minutes at 75 °C due to the reaction with
Zr(NMe2)4. Compound 8 was isolated by crystallization
from toluene at -20 °C as mixture of red (rac) and
(23) Structural studies of rac-8 and meso-8 will be published
separately.

5354 Organometallics, Vol. 18, No. 25, 1999
Thiyagarajan et al.
(NMe2)4, rac/meso ) 3/4, eq 8). In contrast, the reaction
of Zr(NMe2)4 with an excess of the THF adduct rac-4b
under similar conditions affords only a low yield (5%)
of 10 even after prolonged heating (>5 days, 75 °C).
Rea ction of M(NMe2)4 (M ) Zr , Hf) w ith 5. The
reaction of Zr(NMe2)4 with 1.2 equiv of 5a in benzene-
d6 (80 °C, 19 h) affords {1,2-(indenyl)2-C2H4}Zr(NMe2)2
(11; rac/meso ) 7/1) in 70% yield (vs Zr(NMe2)4) and
Al2Me4(µ-NMe2)2 (eq 9). Similarly, the reaction of Hf-
species and modify the solubility properties to facilitate
isolation in solid form.25 As summarized in Table 1, 2a
and 4b are isolated as pure rac isomers, while 1 and 3
are isolated as rac/meso mixtures; in the latter cases
the rac isomers may be obtained by selective crystal-
lization. The factors which control the rac/meso product
ratios in these reactions are not known.
Detailed structural assignments for the rac isomers
of 1, 2a ,b, 3, and 4b are available from NMR and X-ray
crystallographic studies. η1-Indenyl-Al bonding is ob-
served in all cases, as expected for 4-coordinate Al-
indenyl species. For the unsubstituted ansa-bis(indenyl)
compound rac-1, a 2/1 mixture of regioisomers is ob-
served in solution: the major isomer rac-1a contains
one 1-Al-3-Si-substituted and one 1-Al-1-Si-substituted
indenyl ring, while the minor isomer rac-1b contains
two 1-Al-1-Si-substituted indenyl rings (Scheme 1). The
rac-1a /rac-1b isomer ratio likely reflects a balance of
electronic and steric effects. The 1-Al-1-Si-substituted
indenyl structure allows electronic stabilization of the
Al-indenyl bond by the adjacent Si center26 but is
destabilized by steric interactions between the Al and
Si substituents. In contrast, the rac isomers of the 2-Me-
indenyl compounds 2a ,b, 3, and 4b all contain two 1-Al-
1-Si-substituted indenyl rings. In these cases the 1-Al-
3-Si-substituted indenyl unit would be destabilized by
steric interactions between the neighboring (and copla-
nar) 2-Me and 3-SiMe2(indenyl) groups.
rac-1a and rac-1b interconvert rapidly on the NMR
time scale at 23 °C. The most reasonable mechanism
for this exchange involves [1,5]-Al shifts, as illustrated
in Scheme 1. Similar [1,5]-Al shifts in the 2-Me-indenyl
compounds 2a ,b, 3, and 4b, would be undetectable in
the present experiments because the concentration of
1-Al-3-Si-substituted isomers is below the NMR detec-
tion limit.
Compounds 1, 3, and 4b undergo rac/meso isomer-
ization at 23 °C (days) and ca. 75 °C (minutes to hours).
For 1, this isomerization may occur by combinations of
[1,5]-Al or [1,5]-Si shifts and [1,5]-H shifts as illustrated
in Scheme 1. However, 3 and 4 cannot undergo rac/meso
isomerization by this mechanism, due to the presence
of the 2-Me-indenyl substituent, which precludes the
formation of indenyl or isoindenyl intermediates with
local Cs symmetry at a given indenyl ring. In these
cases, and probably in 1 as well, rac/meso isomerization
likely results from intermolecular exchange of -AlMe2L
units between indenyl rings, as illustrated in eq 3.
Intermolecular exchange also probably leads to the
decomposition/disproportionation observed for the two
least-crowded compounds 1 and 5.
(NMe2)4 with 1.3 equiv of 5 in benzene-d6 (80 °C, 27 h)
yields {1,2-(indenyl)2-C2H4}Hf(NMe2)2 (12; 80% vs Hf-
(NMe2)4, rac/meso ) 7/1).
Rea ction of Al a n sa -Bis(in d en yl) Rea gen ts w ith
Zir con iu m Ch lor id es. The reactions of several rac-
Al-ansa-bis(indenyl) reagents with simple Zr chlorides
were investigated briefly to determine whether stereo-
selective indenyl/chloride exchange occurs. The reaction
1 enriched in the rac isomer (rac/meso ) 4/1) with ZrCl4
in benzene-d6 proceeds readily (30 min) at 23 °C to yield
a 1/1 rac/meso mixture of {(1-indenyl)2SiMe2}ZrCl2 (74%
NMR).24 Similarly, rac-4b reacts with ZrCl4 in CD2Cl2
rapidly (<1 h) at 23 °C to yield a 1/1 rac/meso mixture
of {(2-Me-4-Ph-1-indenyl)SiMe2}ZrCl2 (84% isolated).
Additionally, rac-3 reacts with ZrCl4(SMe2)2 in benzene
(23 °C, 1 h) to yield a 1.2/1 rac/meso mixture of {(2-Me-
4,5-benz-1-indenyl)2SiMe2}ZrCl2 (73% isolated). In all
three cases, little rac/meso isomerization of the rac-Al-
indenyl reagent is expected under the reaction condi-
tions in the absence of the Zr chloride compound, on the
basis of the control experiments discussed above. There-
fore, while Al-indenyl reagents react readily with
simple Zr chlorides under mild conditions, these reac-
tions are not stereoselective.
The aluminum ansa-indenyl complexes react with
M(NMe2)4 (M ) Zr, Hf) under mild conditions (23-80
°C in aromatic solvents) to yield the corresponding ansa-
metallocene bis(amide) compounds in 70-90% NMR
yield along with Al2Me4(µ-NMe2)2 as the main Al
Discu ssion
Aluminum ansa-bis(indenyl) compounds, {(AlMe2L)-
indenyl}2SiMe2 and 1,2-{(AlMe2L)-indenyl}2-C2H4, which
contain unsubstituted or substituted indenyl rings, are
accessible by salt elimination reactions of the appropri-
ate Li ansa-bis(indenyl) reagents and AlMe2Cl. A key
feature of this synthesis is the use of Lewis bases (L )
THF, 1,4-dioxane, Et2O) to stabilize the Al-indenyl
(25) Attempts to prepare {(AlMe2)-indenyl}2SiMe2 or {(AlMe2L)-
indenyl}2SiMe2 compounds by alkane elimination reactions were
unsuccessful; e.g., no reaction was observed between AlMe3 and (1-
indenyl)2SiMe2 at 80 °C (neat, 12 h). Attempts to prepare AlR-
{(indenyl)2SiMe2} and AlR(L){(indenyl)2SiMe2} compounds by salt
elimination reactions were also unsuccessful.
(26) (a) Armitage, D. A. In Comprehensive Organometallic Chem-
istry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon:
Oxford, U.K., 1982; Vol. 2, Chapter 9.1. (b) Apeloig, Y.; Schleyer, P. v.
R.; Pople, J . A. J . Am. Chem. Soc. 1977, 99, 1291.
(24) The principal coproducts are tentatively identified as rac and
meso zirconocene methyl chloride compounds.

Aluminum ansa-Indenyl Compounds
Organometallics, Vol. 18, No. 25, 1999 5355
purification. (1-indenyl)2SiMe2,3b,29 {1,2-(3-indenyl)2}-C2H4,2c,l
and (2-Me-1-indenyl)2SiMe2 were prepared by literature
product. These reaction conditions are much milder than
those required to synthesize these metallocenes by
amine elimination. For example, the synthesis of 6 from
(1-indenyl)2SiMe2 and Zr(NMe2)4 requires efficient re-
moval of NMe2H, and the synthesis of 7, 11, and 12 from
the appropriate ansa-bis(indenes) and M(NMe2)4 com-
pounds requires elevated temperatures.3-5 The 2-Me-
substituted ansa-metallocenes 8-10 are not accessible
by amine elimination reactions.27 The high stability of
Al2Me4(µ-NMe2)2 and the strong three-center-four-
electron µ-NMe2 bridges in this species probably con-
tribute to the driving force for the facile indenyl/amide
exchange reactions observed here.
The rac/meso ratios for the metallocene products in
eqs 8 and 9 appear to be close to the thermodynamic
rac/meso ratios. The rac/ meso ratio of 4/1 observed for
metallocene 6 is identical with the thermodynamic rac/
meso ratio established for 6 in amine elimination
studies.3b The rac/meso ratio of 7/1 for 11 is somewhat
lower than the thermodynamic ratio (ca. >20/1) deter-
mined by studies of amine elimination reactions.3a The
2-Me-substituted metallocenes 8 and 9 are produced
with essentially no diastereoselectivity, even though the
starting Al ansa-bis(indenyl) reagents 2a (pure rac) and
3 (rac/meso ) 2.5/1) are enriched in the rac isomers. The
thermodynamic rac/meso ratios for 8 and 9 have not
been established but probably are close to 1/1. At
present, the factors that govern the stereoselectivity of
these indenyl/amide exchange reactions are unknown.
This issue is complicated by the fact that the Al indenyl
reagents undergo regioisomerization (e.g. rac-1a /rac-1b
exchange), rac/meso isomerization, and (for 1 and 5)
disproportionation/decomposition processes under the
reaction conditions.
2p
methods and converted to the corresponding dilithio salts by
reaction with nBuLi (2 equiv, 23 °C, overnight in hexanes,
followed by filtration, hexane washing, and vacuum drying).
2o
(2-Me-4,5-benz-1-indenyl)2SiMe2 and (2-Me-4-Ph-1-inden-
yl)2SiMe22p were prepared by literature methods and converted
to the corresponding dilithio salts (mono-Et2O adducts) by
n
reaction with BuLi (2 equiv, 23 °C, overnight in Et2O, followed
by filtration, hexane washing, and vacuum drying). Zr-
(NMe2)4,3a,30 Hf(NMe2)4,3c,31 and ZrCl4(SMe2)232 were prepared
by literature procedures. NMR spectra were recorded on a
Bruker AMX-360 spectrometer in Teflon-valved tubes at
ambient probe temperature (23 °C) unless indicated otherwise.
1H and 13C NMR chemical shifts are reported versus SiMe4
1
and were determined by reference to the residual H and 13C
solvent peaks. Coupling constants are reported in Hz. COSY
spectra were recorded in C6D6 with a 5 s delay, TD(F2) ) 2048,
TD(F1) ) 512, NS ) 16, and SW ) 9 ppm. Elemental analyses
were performed by Desert Analytics Laboratory (Tucson, AZ).
Low % C and % Si values (multiple analyses) were obtained
for the aluminum ansa-indenyl complexes, even for recrystal-
lized samples that were spectroscopically pure. However, %
H and % Al values were satisfactory. The origin of the low %
C and % Si values is not known.
r a c- a n d m eso-{AlMe2(THF )-in d en yl}2SiMe2 (1). A solu-
tion of AlMe2Cl (2.13 g, 23.0 mmol) in hexanes (10 mL) was
diluted with Et2O (50 mL). The colorless solution was slowly
added (10 min) to solid Li2[(1-indenyl)2SiMe2] (3.48 g, 11.5
mmol) via cannula. The yellow slurry was stirred overnight
at 23 °C. The volatiles were removed under vacuum, affording
a yellow-orange residue. The residue was taken up in hexanes
(50 mL), and the mixture was filtered to afford a pale yellow
filtrate and a white solid (LiCl, 0.95 g; 0.97 g expected). The
filtrate volume was reduced to ca. 10 mL under vacuum, THF
(10 mL) was added, and the solution was stirred for 5 min.
The volatiles were removed under vacuum. The red-orange
residue was taken up in hexanes (50 mL) and stirred for 3 h
at 23 °C, which resulted in the precipitation of an off-white
solid. The mixture was filtered, yielding a cream-colored solid
which was dried under vacuum (3.12 g). The filtrate was
concentrated to ca. 15 mL, cooled to -78 °C for 30 min, and
filtered cold to yield a second crop of white solid (0.28 g), which
was combined with the first crop. Total yield: 3.40 g (54%).
The 1H NMR spectrum (C6D6) established that this product
was a 1.2/1 mixture of rac- and meso-{AlMe2(THF)-indenyl}2-
SiMe2. Anal. Calcd for C32H46Al2O2Si: C, 70.55; H, 8.51; Al,
The results described here show that aluminum ansa-
bis(indenyl) compounds react readily with M(NMe2)4 (M
) Zr, Hf) and ZrCl4 compounds to afford ansa-metal-
locenes in high yield. However, the practical utility of
this approach to metallocene synthesis is limited by the
necessity of synthesizing the Al indenyl reagents (yields
40-70%), by the requirement of using excess Al indenyl
reagent to compensate for the disproportionation/
decomposition reactions, and in some cases by low rac/
meso ratios in the product metallocene. Conventional
salt elimination or amine elimination methods provide
more efficient routes to the specific metallocenes studied
here.28
1
9.90, Si, 5.15. Found: C, 69.65; H, 8.26; Al, 9.76, Si, 4.20. H
NMR (C6D6): δ 7.87 (d, J ) 6.3, 4H, indenyl), 7.60 (d, J ) 6.3,
4H, indenyl), 7.29 (d, 2H, H2 meso), 7.15 (overlapped with
solvent signal), 7.08 (br, 2H, H2 rac), 5.69 (br, 4H, H3 rac and
meso), 2.59 (br, 16H, THF), 0.96 (s, 3H, SiMe2 meso), 0.88(s,
6H, SiMe2 rac), 0.64 (s, 16H, THF), 0.53 (s, 3H, SiMe2 meso),
-0.44 (s, 12H, AlMe2 meso), -0.47 (s, 12H, AlMe2 rac). 1H
NMR (THF-d8, fast solvent exchange): δ 7.52 (m, 4H, indenyl),
7.37 (m, 4H, indenyl), 6.90 (m, 10H, indenyl), 6.78 (br, 2H,
H2 rac), 5.36 (br, 4H, H3 rac and meso). 0.59 (s, 3H, SiMe2
meso), 0.51 (s, 6H, SiMe2 rac), 0.22 (s, 3H, SiMe2 meso), -0.91
(s, 12H, AlMe2 rac), -0.94 (s, 12H, AlMe2 meso).
r a c-1. Recrystallization of a rac-1/meso-1 mixture from
above in toluene at -20 °C afforded pure rac-1 as colorless
cubes. 1H NMR (C6D6; rapid exchange of 1,3- and 1,1-
isomers): δ 7.89 (d, J ) 6.3, 2H, H4 or H7), 7.62 (d, J ) 6.3,
2H, H4 or H7), 7.15 (H5 and H6, partially obscured by solvent
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were carried out
under a purified nitrogen atmosphere. Solids were handled
in
a Vacuum Atmospheres glovebox filled with purified
nitrogen. Tetrahydrofuran, toluene, benzene, dioxane, and
ether were distilled under nitrogen from sodium/benzophenone
ketyl, and solutions were prepared and manipulated using
standard Schlenk techniques. ZrCl4 and HfCl4 were purchased
from CERAC Inc. and sublimed before use. LiNMe2 and AlMe2-
Cl were purchased from Aldrich and used without further
(27) Christopher, J . N. Ph.D. Thesis, The University of Iowa, 1997.
(28) For the best reported syntheses of rac-SiMe2- and rac-ethylene-
bridged bis(indenyl) metallocenes see refs 2o,p and 3a and: (a)
Strickler, J . R.; Power, J . M. U.S. Patent 5,847,175, 1998. (b) Rohr-
mann, J .; Ku¨ber, F. U.S. Patent 5,616,747, 1997. (c) Fischer, D.;
Schweier, G.; Brintzinger, H. H.; Damrau, H. R. H. Eur. Pat. Appl. 0
745 606 A2, 1996.
(29) (a) Marechal, E.; Tortal, J . P. C. R. Acad. Sci. Paris 1968, 267,
467. (b) Sommer, L. H.; Marans, N. S. J . Am. Chem. Soc. 1951, 73,
5135.
(30) (a) Bradley, D. C.; Thomas, I. M. Proc. Chem. Soc. 1959, 225.
(b) Bradley, D. C.; Thomas, I. M. J . Chem. Soc. 1960, 3857.
(31) Chandra, G.; Lappert, M. F. J . Chem. Soc. A 1968, 1940.
(32) Lund, E. C.; Livinghouse, T. Organometallics 1990, 9, 2426.

5356 Organometallics, Vol. 18, No. 25, 1999
Thiyagarajan et al.
signal), 7.08 (br, 2H, H2), 5.71 (br, 2H, H3), 2.64 (br, 4H, THF),
2.43 (br, 4H, THF), 0.88 (s, 6H, SiMe2), 0.54 (br, 8H, THF),
-0.47 (s, 12H, AlMe2). 1H NMR (toluene-d8, 193 K, 2/1 mixture
of slowly exchanging isomers): δ 8.11 (br, 2H, H4 or H7), 7.91
(d, J ) 7, 2H, H4 or H7), 7.85 (d, J ) 7, 2H, H4 or H7), 7.81
(d, J ) 7, 2H, H4 or H7), 7.75 (d, J ) 7, 2H, H4 or H7), 7.65
(d, J ) 7, 2H, H4 or H7), 7.51 (br d, 2H, vinylic H), 7.34 (br,
12H, H5 and H6), 7.0 (br, 2H, vinylic H, obscured by solvent),
6.82 (d, J ) 4, 2H, vinylic H), 6.61 (d, J ) 4, 2H, vinylic H),
6.49 (s, 2H, vinylic H), 4.10 (s, 2H, allylic H), 2.67 & 2.54 &
2.12 & 1.88 (br, 24H, THF), 1.20 (s, 6H, SiMe2), 1.08 (s, 6H,
SiMe2), 1.04 (s, 6H, SiMe2), 0.75 & 0.58 & 0.38 (br, 24H, THF),
-0.08 (s, 12H, AlMe2), -0.20 (s, 6H, AlMe2), -0.38 (s, 6H,
AlMe2), -0.54 (s, 12H, AlMe2).
[r a c-{1-AlMe2(d ioxa n e)0.5-2-Me-1-in d en yl}2SiMe2]n (2a ).
A solution of AlMe2Cl (1.66 g, 17.9 mmol) in hexanes (7.5 mL)
was diluted with Et2O (30 mL). The colorless solution was
slowly added to solid Li2[(2-Me-1-indenyl)2SiMe2] (2.97 g, 9.07
mmol) via cannula. The resulting red-brown slurry was stirred
at 23 °C for 1 h. The volatiles were removed under vacuum,
affording a red oily residue. The residue was taken up in
hexanes (40 mL), and the mixture was filtered to afford a red-
brown filtrate and a white solid (LiCl). The volatiles were
removed from the filtrate under vacuum, and the red oily
residue was dissolved in dioxane (10 mL) and stirred for 10
min. The volatiles were removed from the clear red solution
under vacuum, and the red-orange residue was dried overnight
under vacuum. The residue was taken up in hexanes (30 mL)
and stirred overnight at 23 °C, which resulted in the formation
of a solid. Additional hexanes (20 mL) were added, and the
mixture was stirred for 1 h and filtered, yielding a yellowish
white solid. The solid was washed thoroughly with hexanes
(30 mL) and dried under vacuum, yielding a cream-colored
solid (2.23 g, 41%). Anal. Calcd for C30H42Al2O2Si: C, 69.72;
H, 8.20; Al, 10.44; Si, 5.43. Found: C, 66.52; H, 7.79; Al, 10.32;
Si, 3.93. A sample of 2a in THF-d8 (which forms THF-d8 adduct
2b) was prepared at -196 °C and kept cold prior to NMR
analysis at -90 °C. 1H NMR (THF-d8, -90 °C): δ 7.64 (d, J )
7.2, 2H, H4 or H7), 7.23 (d, J ) 7.2, 2H, H4 or H7), 6.93 (m,
4H, H5 and H6), 6.09 (s, 2H, H3), 3.53 (m, dioxane, partially
obscured by solvent), 1.08 (s, 6H, 2-Me), 0.93 (s, 6H, SiMe2),
-0.67 (s, 6H, AlMe), -0.90 (s, 6H, AlMe). 13C{1H} NMR (THF-
d8, -50 °C): δ 151.5 (C), 148.0 (C), 144.0 (C), 123.7 (CH), 121.2
(CH), 119.8 (CH), 119.6 (CH), 119.3 (CH), 67.7 (dioxane,
partially obscured by solvent), 17.5 (2-Me), 6.1 (SiMe2), -6.5
(Al Me), -7.4 (Al Me). The C1 resonance was not observed due
to quadrupolar broadening by 27Al.
2H), 7.91 (d, J ) 7.2, 2H), 7.54 (d, J ) 7.2, 2H), 7.40 (t, J )
7.2, 2H), 7.34 (t, J ) 7.2, 2H), 6.46 (s, 2H, H3 on indenyl C5
ring), 2.47 (br, 8H, Et2O), 1.83 (s, 6H, 2-Me), 1.30 (s, 6H,
SiMe2), 0.00 (br, 12H, Et2O), -0.28 & -0.40 (two br s, 12H,
AlMe2). 1H NMR (toluene-d8, -20 °C): δ 8.17 (d, J ) 3.6, 2H),
8.15 (d, J ) 3.6, 2H), 7.91 (d, J ) 7.2, 2H), 7.54 (d, J ) 7.2,
2H), 7.45 (m, 2H), 7.37 (m, 2H), 6.64 (s, 2H, H3 on indenyl C5
ring), 2.36 (q, J ) 7.2, 4H, Et2O), 2.20 (q, J ) 7.2, 4H, Et2O),
1.66 (s, 6H, 2-Me), 1.39 (s, 6H, SiMe2), -0.08 (t, J ) 7.2, 12H,
Et2O), -0.24 (s, 6H, AlMe2), -0.44 (s, 6H, AlMe2). 13C{1H}
NMR (C6D6): δ 151.0 (C), 144.1 (C), 139.2 (C), 130.7 (C), 128.6
(2 CH), 128.4 (C), 124.6 (CH), 124.5 (CH), 124.1(CH), 124.0
(CH), 119.9 (CH), 109.9 (br, indenyl C1), 67.2 (Et2O), 18.3 (2-
Me), 12.8 (Et2O), 5.1 (SiMe2), -6.5 (br, AlMe2). Data for meso-3
(from rac/meso mixture) are as follows. 1H NMR (C6D6, 60
°C): δ 7.98 (d, J ) 7.2, 2H), 7.72 (d, J ) 7.2, 2H), 7.64 (d, J )
7.2, 2H), 7.30 (m, overlapped with rac resonance), 6.15 (s, 2H,
H3 on indenyl C5 ring), 2.56 (q, J ) 7.2, Et2O, overlapped with
rac resonance), 2.49 (s, 6H, 2-Me), 1.08 (s, 3H, SiMe2), 0.97 (s,
3H, SiMe2), 0.15 (t, J ) 7.2, Et2O, overlapped with rac
resonance), -0.47 (s, 12H, AlMe). 13C{1H} NMR (C6D6, 60 °C):
δ 151.8 (C), 144.2 (C), 139.6 (C), 130.7(C), 128.6 (C), 124.5 (CH),
124.1 (CH), 122.9 (CH), 124.5 (CH), 124.1 (CH), 120.1 (CH),
100.4 (indenyl C1), 67.5 (Et2O, overlapped with rac resonance),
19.5 (2-Me), 12.9 (Et2O, overlapped with rac resonance), 4.4
(SiMe2), 4.1 (SiMe2), -7.0 (br, Al-Me). One aromatic resonance
is obscured.
r a c- a n d m eso-{1-AlMe2(E t 2O)-2-Me-4-P h -1-in d en -
yl}2SiMe2 (4a ) a n d r a c-{1-AlMe2(THF )-2-Me-4-P h -1-in d en -
yl}2SiMe2 (4b). A solution of AlMe2Cl (0.68 g, 7.3 mmol) in
hexanes (4.0 mL) was diluted with Et2O (60 mL). The colorless
solution was slowly added to yellow solid Li2[(2-Me-4-Ph-1-
indenyl)2SiMe2]‚Et2O (2.00 g, 3.65 mmol) via cannula. The pale
yellow slurry was stirred at 23 °C for 2 h. The volatiles were
removed under vacuum, affording a pale brown foamy solid,
which was dried overnight. Toluene (40 mL) was added, and
the resulting slurry was filtered to afford a pale yellow filtrate
and a colorless solid (LiCl). The volatiles were removed from
the filtrate under vacuum, affording a pale brown foamy solid.
Hexanes (50 mL) were added to the solid, and the resulting
slurry was stirred for 30 min, concentrated to 10 mL, and
filtered to yield a colorless solid and a yellow filtrate. The solid
was dried under vacuum (0.16 g, 6.0%). 1H NMR analysis
(C6D6, 23 °C) established that the solid was a 2/3 mixture of
rac- and meso-{1-AlMe2(Et2O)-2-Me-4-Ph-1-indenyl}2SiMe2 (4a).
1
Data for 4a are as follows. H NMR (C6D6, 70 °C): δ 7.85 (d,
J ) 7.2, 2H, indenyl rac), 7.72 (d, J ) 7.2, 2H, indenyl rac),
7.66 (d, J ) 7.2, 2H, indenyl meso), 7.42 (m, indenyl rac and
meso), 7.31 (m, indenyl rac and meso), 7.05 (d, J ) 7.2, 2H,
indenyl meso), 6.86 (t, J ) 7.2, 2H, indenyl meso), 6.34 (s, 2H,
H3 of C5 indenyl ring, rac), 6.30 (s, 2H, H3 of C5 indenyl ring,
meso), 2.57 (br, 16H, Et2O rac and meso), 2.44 (s, 6H, 2-Me
meso), 1.76 (s, 6H, 2-Me rac), 1.22 (s, 3H, SiMe2 meso), 1.18
(s, 6H, SiMe2 rac), 1.04 (s, 3H, SiMe2 meso), 0.31 (br, 24H,
Et2O rac and meso), - 0.43 (s, 24H, AlMe rac), -0.47 (s, 24H,
AlMe meso). 13C{1H} NMR (C6D6): δ 151.1 (C), 150.0 (C), 148.5
(C), 147.7 (C), 143.9 (C), 143.8 (C), 142.1 (C), 141.4 (C), 133.0
(C), 132.2 (C), 129.5 (CH), 129.4 (2 CH), 128.6 (2 CH), 128.4
(CH), 126.5 (CH), 126.2 (CH), 123.1 (CH), 123.0 (CH), 121.9
(CH), 121.8 (CH), 120.3 (CH), 119.7 (CH), 118.7 (br, indenyl
C1 rac or meso), 115.5 (br, indenyl C1 rac or meso), 66.7 (Et2O),
19.4 (2-Me rac), 18.0 (2-Me meso), 12.8 (br, Et2O), 6.0 (SiMe2
meso), 5.4 (SiMe2 rac), 5.1 (SiMe2 meso), -6.1 (br, AlMe). THF
(10 mL) was added to the yellow filtrate, and the mixture was
stirred for 5 min. The volatiles were removed under vacuum
to give a colorless solid. Hexanes (70 mL) were added, and the
mixture was stirred overnight and filtered, yielding a colorless
solid which was washed with hexanes and dried under vacuum
(1.63 g, 61.7%). 1H NMR analysis (C6D6, 23 °C) established
that the solid was pure rac-{1-AlMe2(THF)-2-Me-4-Ph-1-
indenyl}2SiMe2 (rac-4b). Anal. Calcd for C46H58Al2O2Si: C,
r a c- a n d m eso-{1-AlMe2(Et2O)-2-Me-4,5-ben z-1-in d en -
yl}2SiMe2 (3). A solution of AlMe2Cl (1.46 g, 15.8 mmol) in
hexanes (4 mL) was diluted with Et2O (100 mL). The colorless
solution was slowly added to yellow solid Li2[(2-Me-4,5-benz-
1-indenyl)2SiMe2]‚Et2O (4.00 g, 7.83 mmol) via cannula. The
colorless slurry was stirred at 23 °C for 2 h. The volatiles were
removed under vacuum, affording a colorless solid which was
dried overnight. Toluene (90 mL) was added, and the colorless
slurry was stirred for 10 min and filtered to afford a pale yellow
filtrate and a colorless solid (LiCl). The LiCl was washed with
toluene (40 mL), and the wash was combined with the filtrate.
The volatiles were removed from the filtrate under vacuum,
affording a colorless solid. Hexanes (75 mL) were added to the
solid, and the resulting colorless slurry was stirred for 30 min,
cooled to 0 °C for 1 h, and filtered to yield a colorless solid
and a yellow filtrate. The solid was dried under vacuum (3.76
1
g, 70%). The H NMR spectrum in C6D6 at 23 °C established
that the solid was a 2/1 mixture of rac- and meso-{1-AlMe2-
(Et2O)-2-Me-4,5-benz-1-indenyl}2SiMe2 (3). This material was
recrystallized from toluene/hexanes (3/2 by volume) at 23 °C
by slow evaporation, yielding pure rac-3 as colorless blocks.
Data for rac-3: Anal. Calcd for C42H58Al2O2Si: C, 74.66; H,
8.63, Al, 7.96; Si, 4.14. Found: C, 72.21; H, 8.38; Al, 7.96; Si,
3.54. 1H NMR (C6D6): δ 8.15 (d, J ) 7.2, 2H), 8.11 (d, J ) 7.2,

Aluminum ansa-Indenyl Compounds
Organometallics, Vol. 18, No. 25, 1999 5357
76.19; H, 8.07, Al, 7.44; Si, 4.14. Found: C, 75.21; H, 8.19; Al,
7.41; Si, 4.53. Data for rac-4b are as follows. H NMR (C6D6):
meso ) 1/1, 0.16 g, 0.29 mmol), Zr(NMe2)4 (0.060 g, 0.22 mmol),
1
and C6D6 (0.5 mL). The tube was maintained at 23 °C and
1
δ 7.97 (d, J ) 7.2, 2H), 7.75 (d, J ) 7.2, 4H), 7.42 (t, J ) 7.2,
4H), 7.24 (m, 6H), 6.50 (s, 2H, H3 of C5 indenyl ring), 2.65 (br,
4H, THF), 2.26 (br, 4H, THF), 1.72 (s, 6H, 2-Me), 1.35 (s, 6H,
SiMe2), 0.54 (br, 8H, THF), -0.26 & -0.40 (two br s, 12H,
AlMe2). 1H NMR (toluene-d8, -30 °C): δ 8.01 (d, J ) 7.2, 2H),
7.80 (d, J ) 7.2, 4H), 7.46 (t, J ) 7.2, 4H), 7.27 (m, 6H), 6.58
(s, 2H, H3 of C5 indenyl ring), 2.57 (br, 4H, THF), 2.06 (br,
THF, partially obscured by solvent), 1.67 (s, 6H, 2-Me), 1.38
(s, 6H, SiMe2), 0.45 (br, 8H, THF), -0.17 (s, 6H, AlMe2), -0.44
(s, 6H, AlMe2). 13C{1H} NMR (C6D6): δ 152.2 (C), 148.9 (C),
144.3 (C), 142.1 (C), 133.1 (C), 129.6 (2 CH), 129.0 (CH), 126.6
(CH), 123.6 (CH), 121.9 (CH), 120.5 (CH), 119.2 (br, indenyl
C1), 71.9 (THF), 24.4 (THF), 18.1 (2-Me), 5.6 (SiMe2), -6.8 (br,
AlMe2). Data for meso-4b (from a rac/meso mixture generated
by thermolysis of rac-4b (toluene-d8, 75 °C, 8 h)) are as follows.
1H NMR (toluene-d8): δ 7.56 (d, J ) 7.2, 4H), 7.41 (d, J ) 7.2,
2H, partially overlapped with rac resonance), 7.24 (m, over-
lapped with rac resonance), 6.96 (t, J ) 7.2, 2H), 6.76 (t, J )
7.2, 2H), 6.43 (s, H3 of C5 indenyl ring, overlapped with rac
resonance), 2.68 (br, THF, overlapped with rac resonance), 2.48
(s, 6H, 2-Me), 2.29 (br, THF, overlapped with rac resonance),
1.33 (s, 3H, SiMe2), 1.12 (s, 3H, SiMe2), 0.64 (br, THF,
overlapped with rac resonance), -0.42 (br, AlMe2, overlapped
with rac resonance). 13C{1H} NMR (toluene-d8): δ 150.2 (C),
147.7 (C), 143.8 (C), 141.0 (C), 132.0 (C), 129.3 (2 CH), 128.3
(CH), 126.1(CH), 122.3 (CH), 120.0 (CH), 119.0 (CH), 117.4
(br, indenyl C1), 71.8 (THF, overlapped with rac resonance),
24.5 (THF, overlapped with rac resonance), 19.5 (2-Me), 6.3
(SiMe2), 5.2 (SiMe2), -6.8 (br, AlMe2, overlapped with rac
resonance).
monitored periodically by H NMR. The pale yellow solution
became dark orange. After 50 h at 23 °C, the 1H NMR
spectrum established that the starting materials were com-
pletely consumed and (SBI)Zr(NMe2)2 (90% vs Zr(NMe2)4 based
on total NMe2, rac/meso ) 4/1) and Al2Me4(µ-NMe2)2 were
present. The THF resonances had shifted to positions char-
1
acteristic of free THF (δ 3.60, 1.42). The H NMR data for the
products are consistent with literature data.
r a c-{(1-in d en yl)2SiMe2}Hf(NMe2)2 (7). (a ) NMR Sca le.
An NMR tube was charged with {AlMe2(THF)-indenyl}2SiMe2
(rac/ meso ) 1.3/1, 0.10 g, 0.18 mmol), Hf(NMe2)4 (0.048 g, 0.13
mmol), and C6D6 (0.5 mL). The tube was maintained at 70 °C
and monitored periodically by 1H NMR. The pale yellow
solution became orange. After 21 h at 70 °C, the 1H NMR
spectrum established that the starting materials were con-
sumed and {(1-indenyl)2SiMe2}Hf(NMe2)2 (70% vs Hf(NMe2)4
based on total NMe2, rac/ meso ) 10/1), Al2Me4(µ-NMe2)2, and
unidentified intermediates (δ NMe2 2.7-2.9) were present. The
1H NMR data for the reaction products are consistent with
literature data.
(b) P r ep a r a tive Sca le. A solution of Hf(NMe2)4 (1.24 g,
3.49 mmol) in benzene (35 mL) was added to solid {AlMe2(THF)-
indenyl}2SiMe2 (1; 2.50 g, 4.59 mmol). The pale yellow solution
was heated to 76 °C and stirred for 24 h. The volatiles were
removed under vacuum, affording an orange solid. The solid
was extracted with a mixture of toluene (15 mL) and hexanes
(110 mL). The extract was filtered, concentrated to ca. 30 mL,
and cooled to -38 °C. After 2 h, pale orange needles were
collected by filtration and dried under vacuum (1.19 g, 61%
1
based on Hf(NMe2)4). The H NMR spectrum established that
1,2-{3-AlMe2(THF )-1-in d en yl}2-eth a n e (5). A solution of
AlMe2Cl (3.86 g, 41.7 mmol) in hexanes (4 mL) was diluted
with Et2O (60 mL) at 10 °C. The colorless solution was slowly
added to pale yellow solid Li2[1,2-(indenyl)2-ethane] (5.39 g,
19.8 mmol) via cannula at 0 °C. The yellow slurry was stirred
at 23 °C for 2 h. The reaction mixture was filtered to afford a
pale orange filtrate and a white solid (LiCl). The filtrate was
concentrated to ca. 15 mL under vacuum, THF (8 mL) was
added at 0 °C, and the solution was stirred for 5 min at 0 °C.
The volatiles were removed under vacuum, affording an orange
oily residue. The residue was taken up in hexanes (40 mL)
and stirred overnight. Toluene (20 mL) was added, and the
mixture was stirred for 3 h. The resulting slurry was filtered,
yielding a cream-colored solid and a pale yellow filtrate.
Hexanes (40 mL) were added to the solid, and the mixture
was stirred for 2 h and filtered to yield an off-white solid and
a pale yellow filtrate. The solid was dried under vacuum (5.62
g). The filtrates were combined, and the volatiles were removed
under vacuum. The residue was taken up in hexanes (20 mL),
stirred for 10 h, and filtered to yield a white crystalline powder
(0.12 g), which was combined with the first crop. Total yield:
this product is pure rac-(SBI)Hf(NMe2)2.
{(2-Me-1-in d en yl)2SiMe2}Zr (NMe2)2 (8). (a ) NMR Sca le.
An NMR tube was charged with {1-AlMe2(dioxane)0.5-2-Me-
1-indenyl}2SiMe2 (0.038 g, 0.063 mmol), Zr(NMe2)4 (0.013 g,
0.048 mmol), and C6D6 (1 mL). The reaction mixture was a
pale yellow slurry, as {1-AlMe2(dioxane)0.5-2-Me-1-inden-
yl}2SiMe2 is insoluble in C6D6. The tube was heated to 75 °C.
A clear yellow solution formed within a few minutes and
1
turned orange after several hours. After 24 h at 75 °C, the H
NMR spectrum established that the starting materials were
completely consumed and {(2-Me-1-indenyl)SiMe2}Zr(NMe2)2
(>90% vs Zr(NMe2)4 based on total NMe2, rac/meso ) 3/4) and
Al2Me4(µ-NMe2)2 were present. The dioxane resonance had
shifted to δ 3.53, the position characteristic of free dioxane.
(b) P r ep a r a tive Sca le. Toluene (25 mL) was added to a
mixture of Zr(NMe2)4 (0.30 g, 1.1 mmol) and [{1-AlMe2-
(dioxane)0.5-2-Me-1-indenyl}2SiMe2]n (0.84 g, 1.4 mmol) at 23
°C. The mixture was heated to 77 °C for 21 h. The volatiles
were removed under vacuum, and the resulting red solid was
dried overnight, taken up in toluene (20 mL), and filtered. The
filtrate was concentrated to 15 mL and cooled to -20 °C to
afford a mixture of red and yellow crystals. The red and yellow
crystals were collected by filtration, dried under vacuum (0.21
g, 38%), manually separated, and identified as rac-{(2-Me-1-
indenyl)2SiMe2}Zr(NMe2)2 (rac-8) and meso-{(2-Me-1-inden-
yl)2SiMe2}Zr(NMe2)2 (meso-8), respectively, by X-ray crystal-
lography and 1H NMR. The rac-8/meso-8 ratio in the bulk
1
5.74 g (53.6%). The H NMR spectrum (C6D6) established that
this product is a single isomer of 1,2-{3-AlMe2(THF)-1-inde-
nyl}2-C2H4 (5). The solid was recrystallized from toluene at
-20 °C, affording a white crystalline solid. Anal. Calcd for
C
32H44Al2O2: C, 74.66; H, 8.63; Al, 10.48. Found: C, 73.65; H,
1
8.28; Al, 10.63. H NMR (C6D6): δ 7.73 (d, J ) 7.2, 2H, H4 or
H7), 7.70 (d, J ) 7.2, 2H, H4 or H7), 7.29 (m, 4H, H5 and H6),
7.00 (s, 2H, H2), 3.99 (s, 2H, H1), 3.29 (m, 4H, C2H4), 2.78 (br
1
sample was determined to be ca. 1/2 by H NMR. The mother
liquor was concentrated to 10 mL, pentane (5 mL) was added,
and the solution was cooled to -20 °C for 3 days. The yellow
precipitate was collected by filtration and dried under vacuum
(0.13 g, 23.5%). The 1H NMR spectrum established that the
yellow solid is enriched in the meso isomer (rac/meso ) 1/7.5).
Anal. Calcd for C26H34N2SiZr (1/2 rac/meso mixture): C, 63.22;
H, 6.95; N, 5.67. Found: C, 63.05; H, 7.09; N, 5.48. Data for
rac-{(2-Me-1-indenyl)2SiMe2}Zr(NMe2)2 are as follows. 1H
NMR (C6D6): δ 7.78 (d, J ) 7.2, 2H, H4 or H7), 7.50 (d, J )
7.2, 2H, H4 or H7), 6.92 (m, 2H, H5 or H6), 6.72 (m, 2H, H5
or H6), 6.56 (s, 2H, H3), 2.57 (s, 12H, NMe2), 2.40 (s, 6H, 2-Me),
1
s, 8H, THF), 0.70 (br s, 8H, THF), -0.46 (br, 12H, AlMe). H
NMR (toluene-d8, -90 °C): δ 7.83 (br s, 2H), 7.66 (br s, 2H),
7.35 (br s, 4H), 7.08 (br s, 2H, H2), 4.14 (s, 2H, H1), 3.28 (m,
4H, C2H4), 2.57 (br s, 4H, THF), 1.92 (br s, 4H, THF), 0.44 (br
s, 8 H, THF), -0.21 (br, 12H, AlMe). 13C{1H} NMR (C6D6): δ
147.9 (C), 141.9 (C), 132.5 (CH), 129.0 (br, C3), 122.1 (CH),
121.8 (CH), 121.5 (CH), 118.6 (CH), 71.3 (THF), 52.4 (C1), 28.4
(C2H4), 24.7 (THF), -9.5 (br AlMe).
{(1-in d en yl)2SiMe2}Zr (NMe2)2 (6). NMR Sca le. An NMR
tube was charged with {AlMe2(THF)-indenyl}2SiMe2 (1; rac/

5358 Organometallics, Vol. 18, No. 25, 1999
Thiyagarajan et al.
0.92 (s, 6H, SiMe2). 13C{1H} NMR (C6D6): δ 131.4 (C), 127.9
(C), 127.6 (C), 125.2 (CH), 123.6 (CH), 123.3 (CH), 123.1 (CH),
111.3 (CH), 96.5 (C1), 49.1 (NMe2), 18.4 (2-Me), 2.2 (SiMe2).
Data for meso-{(2-Me-1-indenyl)2SiMe2}Zr(NMe2)2 are as fol-
Ta ble 4. Su m m a r y of Cr ysta l Da ta for r a c-2a
a n d r a c-3
rac-2a
rac-3
formula
fw
C
30H42Al2O2Si
C21H29AlOSi0.50
338.47
1
lows. H NMR (C6D6): δ 8.08 (d, J ) 7.2, 2H, H4 or H7), 7.40
516.69
(d, J ) 7.2, 2H, H4 or H7), 6.89 (m, 2H, H5 or H6), 6.72 (m,
2H, H5 or H6), 6.47 (s, 2H, H3), 3.08 (s, 6H, NMe2), 2.16 (s,
6H, 2-Me), 1.76 (s, 6H, NMe2), 1.13 (s, 3H, SiMe), 0.72 (s, 3H,
SiMe). 13C{1H} NMR (C6D6): δ 134.7 (C), 132.1 (C), 129.6 (C),
125.5 (CH), 123.9 (CH), 123.0 (CH), 122.5 (CH), 107.7 (CH),
94.6 (C1), 49.1(NMe2), 44.7 (NMe2), 17.6 (2-Me), 2.5 (SiMe),
2.4 (SiMe).
cryst size, mm
color/shape
d(calcd), Mg/m3
cryst syst
space group
a, Å
0.20 × 0.20 × 0.12 0.40 × 0.35 × 0.15
colorless/block
1.192
colorless/block
1.150
monoclinic
C2/c
orthorhombic
Pbcn
32.701(2)
10.7556(6)
16.3851(8)
91.937(1)
5759.6(5)
8
14.4047(3)
11.9718(2)
22.6699(5)
b, Å
c, Å
{(2-Me-4,5-b en z-1-in d en yl)2SiMe2}Zr (NMe2)2 (9). (a )
NMR Sca le. A solution of {1-AlMe2(Et2O)-2-Me-4,5-benz-1-
indenyl}2SiMe2 (rac/meso ) 2/1, 0.16 g, 0.25 mmol) and Zr-
(NMe2)4 (0.051 g, 0.19 mmol) in C6D6 (1 mL) was heated to 70
°C and monitored periodically by 1H NMR. The pale yellow
â, deg
V, Å3
3909.43(14)
8
Z
temp, K
diffractometer
173(2)
173(2)
Siemens SMART
CCD
Siemens SMART
CCD
1
solution became dark orange. After 2.5 days at 70 °C, the H
radiation (λ), Å
θ range, deg
data collected: h;k;l
no. of rflns
no. of unique rflns
Rint
0.710 73
1.25-25.02
(38; 0-12; 0-19
13 811
0.710 73
1.80-25.04
0-17; 0-14; 0-26
18 905
NMR spectrum established that the starting materials were
completely consumed and {(2-Me-4,5-benz-1-indenyl)2SiMe2}-
Zr(NMe2)2 (>75% vs Zr(NMe2)4 based on total NMe2, rac/meso
) 0.90) and Al2Me4(µ-NMe2)2 were present. The Et2O reso-
nances had shifted to δ 1.10 and 3.25, which are characteristic
of free Et2O.
4993
3442
0.0358
0.0306
no. of obsd rflns
Ι >2σ(I), 3562
0.167
I >2σ(I), 2894
0.138
µ, mm-1
(b) P r ep a r a tive Sca le. Toluene (25 mL) was added to a
solid mixture of Zr(NMe2)4 (0.58 g, 2.2 mmol) and {1-AlMe2-
(Et2O)-2-Me-4,5-benz-1-indenyl}2SiMe2 (rac/meso ) 2/1, 1.85
g, 2.70 mmol) at 23 °C. The resulting clear solution was heated
for 24 h at 75 °C. The volatiles were removed under vacuum,
and the red-orange residue was taken up in pentane (120 mL)
and filtered to give an orange filtrate and a yellow solid. The
volatiles were removed from the filtrate under vacuum, and
the residue was heated to 62 °C for 3 h. The residue was
dissolved in toluene (10 mL) and filtered. The filtrate was
cooled to 0 °C for 3 h, affording yellow-orange crystals, which
were isolated by filtration and dried under vacuum (0.54 g).
The filtrate was concentrated to ca. 5 mL, cooled to 0 °C for 6
days, and filtered to yield a yellow-orange solid (0.19 g), which
was combined with the first fraction. Total yield: 0.73 g (57%).
transmissn range, %
no. of data/restraints/
params
82-100
4992/18/343
85 to 100
3421/21/232
structure soln
direct methods
1.040
direct methods
1.121
GOF on F2
R indices (I > 2σ(I))
R1 ) 0.0642,
wR2 ) 0.1262
R1 ) 0.0996,
wR2 ) 0.1404
R1 ) 0.0709,
wR2 ) 0.1789
R1 ) 0.0839,
wR2 ) 0.1889
0.568
R indices (all data)
max resid density, e/Å3 0.694
(µ-NMe2)2 were present. 1H NMR (C6D6): rac-10, δ 6.70 (s, 2H,
C5 indenyl), 2.24 (s, 12H, NMe2), 2.20 (s, 6H, 2-Me), 0.98 (s,
6H, SiMe2); meso-10, δ 6.81 (s, 2H, C5 indenyl), 3.12 (s, 6H,
NMe2), 2.12 (s, 6H, 2-Me),1.81 (s, 6H, NMe2), 1.21 (s, 3H,
SiMe2), 0.74 (s, 3H, SiMe2). The aromatic resonances of the
rac and meso isomers are extensively overlapped and could
not be assigned.
1
The H NMR spectrum established that the product consists
of a 3/5 mixture of rac (pale orange) and meso (red) {(2-Me-
4,5-benz-1-indenyl)2SiMe2}Zr(NMe2)2. Recrystallization of this
material from hexanes at -20 °C gave a mixture of pale orange
and red crystals which were manually separated in some trials.
Data for rac-{(2-Me-4,5-benz-1-indenyl)2SiMe2}Zr(NMe2)2 are
as follows. Anal. Calcd for C34H38N2SiZr: C, 68.74; H, 6.46;
{1,2-(in d en yl)2C2H4}Zr (NMe2)2 (11). An NMR tube was
charged with 1,2-{3-AlMe2(THF)-1-indenyl}2C2H4 (0.086 g,
0.16 mmol), Zr(NMe2)4 (0.034 g, 0.13 mmol), and C6D6 (∼0.5
mL). The tube was heated to 80 °C and monitored by 1H NMR.
The pale yellow solution became dark orange. After 19 h at
80 °C, the 1H NMR spectrum established that the starting
materials were completely consumed and {1,2-(indenyl)2C2H4}-
Zr(NMe2)2 (70% vs Zr(NMe2)4 based on total NMe2, rac/meso
) 7.3/1) and Al2Me4(µ-NMe2)2 were present. The THF reso-
nances had shifted to positions characteristic of free THF. The
1H NMR data for the reaction products are consistent with
literature data.3e
1
N, 4.71. Found: C, 68.39; H, 6.60; N, 4.43. H NMR (C6D6): δ
7.96 (d, J ) 7.2, 2H), 7.73 (d, J ) 10.8, 2H), 7.58 (d, J ) 7.2,
2H), 7.30 (m, 6H), 6.99 (s, 2H, H3), 2.42 (s, 6H, 2-Me), 2.00 (s,
12H, NMe2), 0.93 (s, 6H, SiMe2). 13C{1H} NMR (C6D6): δ 132.0
(C), 130.6 (C), 128.5 (CH), 127.6 (C), 127.3 (C), 126.3 (CH),
125.4 (CH), 124.6 (CH), 124.5 (CH), 123.0 (CH), 110.8 (CH),
101.7 (C1), 48.0 (NMe2), 18.0 (2-CH3), 2.03 (SiMe). One
aromatic resonance is obscured. Data for meso-{(2-Me-4,5-
benz-1-indenyl)2SiMe2}Zr(NMe2)2 are as follows. 1H NMR
(C6D6): δ 7.92 (d, J ) 7.2, 4H), 7.42 (m, 2H), 7.2 (m, 6H), 6.98
(s, 2H, H3), 3.13 (s, 6H, NMe2), 2.27 (s, 6H, 2-Me), 1.10 (s, 3H,
SiMe2), 0.93 (br, 6H, NMe2), 0.77 (s, 3H, SiMe2). 13C{1H} NMR
(C6D6): δ 132.0 (C), 130.1 (C), 129.7 (C), 128.8 (C), 128.7 9
(C), 126.0 (CH), 125.4 (CH), 123.9 (CH), 123.8 (CH), 107.6
(CH), 100.8 (C), 51.3 (NMe2), 44.8 (NMe2), 17.4 (2-Me), 2.1-
(SiMe2), 2.5 (SiMe2). Two aromatic resonances are obscured.
{(2-Me-4-P h -1-in d en yl)2SiMe2}Zr (NMe2)2 (10). A solution
of {1-AlMe2(Et2O)-2-Me-4-Ph-1-indenyl}2SiMe2 (rac/meso )
3/2, 0.12 g, 0.16 mmol) and Zr(NMe2)4 (0.035 g, 0.13 mmol) in
C6D6 (0.6 mL) in an NMR tube was heated to 75 °C and
{1,2-(in d en yl)2C2H4}Hf(NMe2)2 (12). An NMR tube was
charged with {1,2-{3-AlMe2(THF)-1-indenyl}2C2H4 (0.12 g, 0.24
mmol), Hf(NMe2)4 (0.064 g, 0.18 mmol), and C6D6 (0.5 mL).
The tube was heated to 80 °C and monitored by 1H NMR. The
pale yellow solution became dark orange. After 27 h at 80 °C,
1
the H NMR spectrum established that the starting materials
were completely consumed and {1,2-(indenyl)2C2H4}Hf(NMe2)2
(80% vs Hf(NMe2)4 based on total NMe2, rac/meso ) 7/1) and
Al2Me4(µ-NMe2)2 were present. The THF resonances had
shifted to positions characteristic of free THF. H NMR data
for the reaction products are consistent with literature data.3c
1
1
X-r a y Cr ysta llogr a p h ic An a lysis of r a c-2. Crystallo-
graphic details are summarized in Table 4. A crystal of the
compound was attached to a glass fiber and mounted on the
Siemens SMART system for data collection at 173(2) K. The
space group C2/c was determined on the basis of systematic
monitored periodically by H NMR. The pale yellow solution
became red. After 17 h at 75 °C, the 1H NMR spectrum
established that the starting materials were completely con-
sumed and {(2-Me-4-Ph-1-indenyl)2SiMe2}Zr(NMe2)2 (>75% vs
Zr(NMe2)4 based on total NMe2, rac/meso ) 3/4) and Al2Me4-

Aluminum ansa-Indenyl Compounds
Organometallics, Vol. 18, No. 25, 1999 5359
absences and intensity statistics.33 All non-hydrogen atoms
were refined with anisotropic displacement parameters, and
all hydrogen atoms were placed in ideal positions and refined
as riding atoms with relative isotropic displacement param-
eters. Individual monomers are linked in infinite chains
through dioxane bridges. Both dioxanes are centered over
inversion centers; therefore, only half of each is found in the
asymmetric unit. One dioxane is disordered in a 0.56:0.44 ratio
in two chair conformations, where the oxygen is mutual in both
fragments.
other by a crystallographic 2-fold axis. The diethyl ether ligand
is disordered.
Ack n ow led gm en t. This work was supported by the
National Science Foundation (Grant No. CHE-9413022)
and the Albemarle Corp.
Su p p or tin g In for m a tion Ava ila ble: For rac-2a and rac-
3, tables giving crystal data, data collection, and solution and
refinement details, atomic coordinates and isotropic displace-
ment parameters, bond lengths and angles, anisotropic dis-
placement parameters, and torsion angles and figures giving
additional views and the structure and atom-numbering
scheme. This material is available free of charge via the
Internet at http://pubs.acs.org.
X-r a y Cr ysta llogr a p h ic An a lysis of r a c-3. Crystallo-
graphic details are summarized in Table 4. The space group
Pbcn was determined on the basis of systematic absences and
intensity statistics.25 Halves of the molecule are related to each
(33) SHELXTL-Plus V5.0; Siemens Industrial Automation, Inc.,
Madison, WI.
OM990381T