Synthesis and Reactivity of η5-Silolyl, η5-Germolyl, and η5-Germole Dianion Complexes of Zirconium and Hafnium

Article abstract of DOI:10.1021/ja993563n

Reaction of 2 equiv of Li[C₄Me₄GeSiMe₃] with Cp*HfMe₂Cl produced the first transition metal complex of a germole dianion, [Cp*(η⁵-C₄Me₄Ge)HfMe ₂Li(THF)]₂ (1), via the apparent elimination of Me₃-SiCl, along with C₄Me₄Ge(SiMB₃)₂ as the final Me₃Si-containing product. Compound 1 adopts a dimeric structure in which one Li atom is sandwiched in an η⁵-fashion between two germole rings, while the other Li atom is coordinated by both germanium atoms. Reaction of 1 with an excess of Me₃SiCl resulted in loss of the germole ligand as C₄Me₄Ge(SiMe₃)₂, while 2 equiv of Me₃SiOSO₂CF₃ reacted with 1 to give the new germolyl complex Cp*[η⁵-C₄Me₄GeSiMe ₃]HfMe₂ (2). Yet a different process results from treatment of 1 with CH₃CH₂OSO₂-CF₃, involving migration of a methyl group from hafnium to germanium to produce Cp*(η⁴-C₄Me₄GeMeEt)-HfMe (3). Reaction of 2 with H₂ gave CH₄ and Me₃SiH as the result of σ-bond metathesis involving the germole-bound trimethylsilyl group and (presumably) an intermediate hafnium hydride species. Similarly, the reaction of 2 with PhSiH₃ gave PhMeSiH₂ and Me₃SiH. Compound 2 also reacted with MeI to produce C₄-Me₄Ge(Me)SiMe₃, while the reaction with (Et₂O)LiCH₂Ph gave 1 and Me₃SiCH₂Ph. Compound 2 did not react cleanly with various small molecules (CO, CN(2,6-Me₂C₆H₃), trimethylsilylacetylene, and benzophenone), nor with the methide abstraction reagents B(C₆F₅)₃ and [Ph₃C][B(C₆F₅)₄]. In addition, reaction of 2 with these abstraction reagents in the presence of 1-hexene or cyclohexene did not result in the formation of a polymer. The germole C₄Me₄Ge(H)CMe₃ was prepared via reaction of C₄Me₄GeCl₂ with 1.5 equiv of Me₃CLi, followed by treatment with LiAlH₄. This germole was cleanly deprotonated by ⁿBuLi in THF to give the new germole anion Li[C₄Me₄GeCMe₃] as a THF solvate. This anion reacted with Cp*HfMe₂Cl to give the product of methyl migration from hafnium to germanium, Cp*[η4-C₄Me₄Ge(Me)CMe₃]HfMe (4). Analogously, Li[C₄Me₄GePh] reacted with Cp*HfMe₂Cl to give Cp*[η⁴-C₄Me₄Ge(Me)Ph]HfMe (5). Treatment of MgBr₂(Et₂O) with 2 equiv of K[C₄Me₄SiSiMe₃] in THF resulted in formation of Mg[η¹-C₄Me₄SiSiMe₃] ₂(THF) (6). Reaction of 6 with Cp*ZrCl₃ gave quantitative formation of Cp*[η⁵-C₄Me₄SiSiMe ₃]ZrCl₂ (7), while the reaction of 6 with Cp*HfCl₃ provided the previously reported complex Cp*[η⁵-C₄Me₄SiSiMe ₃]HfCl₂ (8) in quantitative yield.

Full text of DOI:10.1021/ja993563n

J. Am. Chem. Soc. 2000, 122, 3097-3105
3097
Synthesis and Reactivity of η5-Silolyl, η5-Germolyl, and η5-Germole
Dianion Complexes of Zirconium and Hafnium
Jeffrey M. Dysard and T. Don Tilley*
Contribution from the Department of Chemistry, UniVersity of California at Berkeley,
Berkeley, California 94720-1460
ReceiVed October 4, 1999
Abstract: Reaction of 2 equiv of Li[C4Me4GeSiMe3] with Cp*HfMe2Cl produced the first transition metal
complex of a germole dianion, [Cp*(η5-C4Me4Ge)HfMe2Li(THF)]2 (1), via the apparent elimination of Me3-
SiCl, along with C4Me4Ge(SiMe3)2 as the final Me3Si-containing product. Compound 1 adopts a dimeric structure
in which one Li atom is sandwiched in an η5-fashion between two germole rings, while the other Li atom is
coordinated by both germanium atoms. Reaction of 1 with an excess of Me3SiCl resulted in loss of the germole
ligand as C4Me4Ge(SiMe3)2, while 2 equiv of Me3SiOSO2CF3 reacted with 1 to give the new germolyl complex
Cp*[η5-C4Me4GeSiMe3]HfMe2 (2). Yet a different process results from treatment of 1 with CH3CH2OSO2-
CF3, involving migration of a methyl group from hafnium to germanium to produce Cp*(η4-C4Me4GeMeEt)-
HfMe (3). Reaction of 2 with H2 gave CH4 and Me3SiH as the result of σ-bond metathesis involving the
germole-bound trimethylsilyl group and (presumably) an intermediate hafnium hydride species. Similarly, the
reaction of 2 with PhSiH3 gave PhMeSiH2 and Me3SiH. Compound 2 also reacted with MeI to produce C4-
Me4Ge(Me)SiMe3, while the reaction with (Et2O)LiCH2Ph gave 1 and Me3SiCH2Ph. Compound 2 did not
react cleanly with various small molecules (CO, CN(2,6-Me2C6H3), trimethylsilylacetylene, and benzophenone),
nor with the methide abstraction reagents B(C6F5)3 and [Ph3C][B(C6F5)4]. In addition, reaction of 2 with these
abstraction reagents in the presence of 1-hexene or cyclohexene did not result in the formation of a polymer.
The germole C4Me4Ge(H)CMe3 was prepared via reaction of C4Me4GeCl2 with 1.5 equiv of Me3CLi, followed
by treatment with LiAlH4. This germole was cleanly deprotonated by nBuLi in THF to give the new germole
anion Li[C4Me4GeCMe3] as a THF solvate. This anion reacted with Cp*HfMe2Cl to give the product of methyl
migration from hafnium to germanium, Cp*[η4-C4Me4Ge(Me)CMe3]HfMe (4). Analogously, Li[C4Me4GePh]
reacted with Cp*HfMe2Cl to give Cp*[η4-C4Me4Ge(Me)Ph]HfMe (5). Treatment of MgBr2(Et2O) with 2 equiv
of K[C4Me4SiSiMe3] in THF resulted in formation of Mg[η1-C4Me4SiSiMe3]2(THF) (6). Reaction of 6 with
Cp*ZrCl3 gave quantitative formation of Cp*[η5-C4Me4SiSiMe3]ZrCl2 (7), while the reaction of 6 with Cp*HfCl3
provided the previously reported complex Cp*[η5-C4Me4SiSiMe3]HfCl2 (8) in quantitative yield.
Recent interest in cyclic π-systems containing silicon and
germanium has led to an enhanced understanding of the
electronic properties of these species.1,2 For example, we have
characterized free silolyl and germolyl anions of the type [C4-
Me4E-R]- (E ) Si or Ge) as possessing pyramidal E centers
and bond-localized structures.2 Interestingly, however, coordina-
tion of these π-systems to electron-rich or electron-poor d0
transition metal fragments promotes delocalization of electron
density in the five-membered heterole ring and planarization
of the E center.3 Thus, silolyl and germolyl anions represent
interesting new ligands in transition metal chemistry which are
expected to possess novel electronic properties. In fact, elec-
trochemical studies on Cp*Ru[η5-C4Me4GeSi(SiMe3)3] (Cp* )
η5-C5Me5) suggest that the germolyl ligand might be signifi-
cantly more electron donating than Cp*.3a Furthermore, it has
been shown that free silole and germole dianions [C4R4E]2-
possess a high degree of aromatic character.4 Such species
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1997, 16, 1543. (r) Tokitoh, N.; Wakita, K.; Okazaki, R.; Nagase, S.;
Schleyer, P. v. R.; Jiao, H. J. Am. Chem. Soc. 1997, 119, 6951.
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Angew. Chem., Int. Ed. Engl. 1993, 32, 1744. (b) Freeman, W. P.; Tilley,
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10.1021/ja993563n CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/18/2000

3098 J. Am. Chem. Soc., Vol. 122, No. 13, 2000
Dysard and Tilley
represent an additional class of novel, 6-electron π-systems that
could function as ligands for transition metals. These consid-
erations have compelled us to investigate silolyl and germolyl
anions, and the corresponding silole and germole dianions, as
ancillary ligands in early transition metal chemistry.
Scheme 1
Group 4, d0 transition metal complexes have attracted much
attention in recent years, particularly as alkene polymerization
catalysts, dehydropolymerization catalysts, and reagents for
organic synthesis.5 Because of this, considerable effort has been
devoted to controlling the chemical properties of the metal-
locenes by manipulation of the electronic and steric properties
of the cyclopentadienyl ligands. Part of this effort has focused
on metallocenes featuring main group-containing heterocycles
as ancillary ligands.6 Given the novel electronic properties for
π-systems containing silicon and germanium, we became
interested in examining d0 metallocene complexes that incor-
porate silolyl and germolyl ligands. A related issue concerns
the degree to which d0 metal centers might induce delocalization
of charge in such rings and stabilize η5-bonding, in the absence
of dπ-π* back-bonding. Here we report investigations into the
synthesis, characterization, and reactivity of germolyl and silolyl
complexes of d0 group 4 metals, including the remarkable
formation and isolation of a complex containing the germole
ride Cp*HfMe2Cl7 does not give the anticipated metallocene
derivative Cp*[η5-C4Me4GeSiMe3]HfMe2 (2) upon reaction with
Li[C4Me4GeSiMe3]. Rather than proceed via LiCl elimination
to give 2, the reaction of Li[C4Me4GeSiMe3] and Cp*HfMe2Cl
in a 2:1 molar ratio gave the germole dianion complex 1 in
86% isolated yield (eq 1). In tetrahydrofuran-d8, this reaction
produced 1 and C4Me4Ge(SiMe3)2 as the only identifiable
products. We believe that the reaction of eq 1 proceeds via loss
of Me3SiCl (Scheme 1), which is not observed as a product
because of its rapid reaction with the germolyl anion (and/or 1,
see below) to afford C4Me4Ge(SiMe3)2.
dianion [C4Me4Ge]2-
.
Results and Discussion
Synthesis and Reactivity of a Germole Dianion Complex.
We have previously described a method for preparing the d0
hafnium germolyl complex Cp*[η5-C4Me4GeSiMe3]HfCl2, in-
volving reaction of the salt Li[C4Me4GeSiMe3] with Cp*HfCl3
at low temperatures.3c Unfortunately, this reaction produced the
desired η5-germolyl complex in low and variable yields. We
postulated that complications with this reaction may arise from
the presence of more than one reactive site on the hafnium metal
center, which could allow the germolyl nucleophile to react with
more than one chloride of Cp*HfCl3. However, the monochlo-
(5) (a) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.;
Waymouth, R. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b) Jordan,
R. F. AdV. Organomet. Chem. 1991, 32, 325. (c) Kaminsky, W. Catal. Today
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H.; Morken, J. P. Angew. Chem., Int. Ed. Engl. 1996, 35, 1262. (f) Ivin, K.
J. Olefin Metathesis Polymerization; Academic Press: San Diego, 1997.
(g) Grubbs, R. H.; Tumas, W. Science 1989, 243, 907. (h) Schrock, R. R.
Acc. Chem. Res. 1990, 23, 158. (i) Schrock R. R. Tetrahedron 1999, 55,
8141. (j) Schuster, M.; Blechert, S. Angew. Chem., Int. Ed. Engl. 1997, 36,
2036. (k) Lin, Z.; Marks, T. J. J. Am. Chem. Soc. 1987, 109, 7979. (l) Lee,
N. E.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116, 5985. (m) Fu, P.-F.;
Brard, L.; Li, Y.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 7157. (n)
Molander, G. A.; Julius, M. J. Org. Chem. 1992, 57, 6347. (o) Molander,
G. A.; Dowdy, E. D.; Noll, B. C. Organometallics 1998, 17, 3754. (p)
Carter, M. B.; Schiott, B.; Gutierrez, A.; Buchwald, S. L. J. Am. Chem.
Soc. 1994, 116, 11667. (q) Gauvin, F.; Harrod, J. F.; Woo, H. G. AdV.
Organomet. Chem. 1998, 42, 363. (r) Tilley, T. D. Acc. Chem. Res. 1993,
26, 22. (s) Corey, J. In AdVances in Silicon Chemistry; Larson, G., Ed.;
JAI Press: Greenwich, CT, 1991; Vol. 1, p 327.
(6) (a) Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. J. Am. Chem.
Soc. 1991, 113, 1455. (b) Kreuder, C.; Jordan, R. F.; Zhang, H. Organo-
metallics 1995, 14, 2993. (c) Quan, R. W.; Bazan, G. C.; Kiely, A. F.;
Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4459. (d)
Bazan, G. C.; Donnelly, S. J.; Rodriguez, G. J. Am. Chem. Soc. 1995, 117,
2671. (e) Kowal, C. M.; Bazan, G. C. J. Am. Chem. Soc. 1996, 118, 10317.
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Bazan, G. C.; Rodriguez, G.; Ashe, A. J., III; Al-Ahmand, S.; Mu¨ller, C.
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A. J., III; Al-Ahmad, S.; Kampf, J. W. Organometallics 1997, 16, 2492.
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1999, 18, 1363.
On the basis of thermodynamic considerations, the elimination
of Me3SiCl, rather than LiCl, in the reaction of eq 1 initially
seemed unlikely. We therefore considered an alternative mech-
anism involving the initial formation of 2, which would be
converted to 1 via nucleophilic cleavage of the Ge-Si bond
with another equivalent of Li[C4Me4GeSiMe3] (Scheme 1).
Indeed, the reaction of 2 (the synthesis of which is described
below) with Li[C4Me4GeSiMe3] in tetrahydrofuran-d8 quanti-
tatively forms 1 and C4Me4Ge(SiMe3)2 (in a 1:1 molar ratio,
by 1H NMR spectroscopy). However, the reaction of Cp*HfMe2-
Cl with Li[C4Me4GeSiMe3] in a 1:1 ratio (in tetrahydrofuran-
d8, with the germolyl anion as limiting reagent) did not produce
2, and the only products that could be identified were 1 and
1
C4Me4Ge(SiMe3)2 (in 39 and 41% yields, respectively, by H
NMR spectroscopy). Note that according to the mechanism
proceeding via LiCl elimination and intermediate 2 (Scheme
1), the 1:1 reaction of Cp*HfMe2Cl with Li[C4Me4GeSiMe3]
should produce an equimolar mixture of 1, C4Me4Ge(SiMe3)2,
and unreacted Cp*HfMe2Cl (which was not observed in the
(7) Roddick, D. M. Ph.D. Thesis, California Institute of Technology,
1984

Synthesis of Dianion Complexes of Zr and Hf
J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3099
to the corresponding ones in Cp*(C4Me4GeSiMe3)HfCl2 (2.33
Å, 2.22 Å, 136.1°).3c The C4Gecentroid-Li(1) distance of 1.98 Å
is somewhat longer than the corresponding distance in [Li(THF)-
(TMEDA)][2,3,4,5-Et4-Ge,Ge-{Li(2,3,4,5-Et4C4Ge)2}C4Ge] (1.918
Å),8 but is fully consistent with the Li-C5 centroid distance of
2.008 Å in the lithocene anion [Cp2Li]-.9
At room temperature, the 7Li NMR spectrum of 1 contains a
single broad resonance, which splits into two resonances at 1.70
and -4.60 ppm upon cooling to -40 °C. These values are
comparable to corresponding shifts for the σ- and π-bound
lithium atoms in [Li(THF)(TMEDA)][2,3,4,5-Et4-Ge,Ge-{Li-
(2,3,4,5-Et4C4Ge)2}C4Ge] (-0.93 and -4.98 ppm, respectively),
which are decoalesced at -50 °C.8 Thus, the dimeric structure
of 1 appears to be preserved at low temperature, but in solution
at room temperature the Li ions undergo exchange on the NMR
time scale.
Initial reactivity studies with 1 focused on its possible
conversion to the neutral species Cp*[η5-C4Me4Ge]HfMe upon
abstraction of a Me group. Unfortunately, reaction of 1 with
B(C6F5)3 produced only complex mixtures in both benzene-d6
and tetrahydrofuran-d8, and use of the methide abstraction
reagent [Ph3C][B(C6F5)4] also yielded numerous unidentified
products. These attempted abstraction reactions were not cleaner
in the presence of the Li-atom sequestering reagents TMEDA
and 12-crown-4. Finally, 1 did not react with PhSiH3 or H2 in
benzene solution at room temperature over 1 week.
Figure 1. ORTEP diagram of [Cp*(η5-C4Me4Ge)HfMe2Li(THF)]2 (1).
product mixture). However, since 1 and Cp*HfMe2Cl react
quantitatively (to give a mixture of uncharacterized products,
1
by H NMR spectroscopy), the 1:1 reaction of Cp*HfMe2Cl
and Li[C4Me4GeSiMe3] would not have produced 1 via the LiCl-
elimination process of Scheme 1.
Based on the experiments described above, we favor the
mechanism involving Me3SiCl elimination. Trimethylsilyl chlo-
ride is not observed as a product in this process, since it reacts
rapidly with either the germolyl anion or the product 1. The
latter possibility was demonstrated by the observed reaction of
1 with Me3SiCl (excess) in tetrahydrofuran-d8 solution, which
gave only C4Me4Ge(SiMe3)2 and unidentified Cp*Hf-containing
species.
Highly air- and moisture-sensitive 1 was purified by washing
with pentane, in which it is completely insoluble, and then
crystallization from a toluene/THF mixture. X-ray quality
crystals of 1 as a THF solvate were isolated after slow cooling
of a toluene solution to -35 °C for several days. The germole
ring containing Ge(2) is conformationally disordered about the
Hf(1)-Li(1) axis, and Hf(2) was also disordered (see Experi-
mental Section for details). The molecular structure of 1 (Figure
1) may be described as a dimer of Li[Cp*(η5-C4Me4Ge)HfMe2]
in which the germole dianion rings are bridged by two lithium
atoms. One lithium atom is “sandwiched” in an η5-fashion
between the two germole rings, while the other lithium atom is
coordinated in an η1 mode by both germanium atoms. This
coordination geometry for the germole dianions of 1 is
reminiscent of that seen in Boudjouk’s germole dianion [Li-
(THF)(TMEDA)][2,3,4,5-Et4-Ge,Ge-{Li(2,3,4,5-Et4C4Ge)2}C4-
Ge], in which one lithium atom is sandwiched between two
germole rings while the (THF)(TMEDA)Li group is bound in
an η1-fashion by one Ge atom.8
Reaction of a tetrahydrofuran solution of 1 with 2 equiv of
MeI immediately produced a deep red solution, which gave a
deep red powder after removal of solvent. Inspection of the 1H
NMR spectrum (benzene-d6) of this solid revealed the quantita-
tive formation of Li[C4Me4GeMe]2 along with unidentified
Cp*Hf-containing materials. In contrast, 1 reacted cleanly with
ethyl triflate in benzene to produce the η4-germole complex 3,
the product of methyl group migration from hafnium to
1
germanium (eq 2). Complex 3 is formed in 90% yield by H
NMR spectroscopy, but its isolation was prohibited by its oily
nature and high solubility in all solvents employed (toluene,
pentane, ether, and hexamethyldisiloxane). The characterization
1
of 3 follows from the interpretation of its H and 13C NMR
The C-C bond lengths within the nondisordered germole ring
are equal within experimental error (1.42(2), 1.40(2), and 1.43-
(2) Å), and the Ge-C bond lengths are also equivalent (1.96-
(1) Å) and similar to those in the free germolyl dianion [K4(18-
crown-6)3][C4Me4Ge]2(THF) (1.846(9) and 1.959(8) Å).2 The
Hf(2) atom lies 2.27 Å from the centroid of the planar germole
ring and 2.25 Å from the Cp* centroid, and the centroid-
hafnium-centroid angle is 136.4°. These values are comparable
spectra, which was aided by comparisons to reported spectra
for analogous hafnium diene complexes of the type Cp′HfMe-
(diene) [Cp′ ) Cp or substituted Cp].10 Compounds of the latter
type display solubility properties similar to those of 3. The single
methyl group bound to hafnium exhibits a resonance at δ -0.83,
whereas the migrated methyl group exhibits a resonance
consistent with a Ge-Me group, at δ 0.26.2 In addition, the
two ring carbons of the germole unit resonate at δ 130.0 and
97.16, which corresponds to a separation consistent with η4-
coordination of the germole ring to hafnium in a σ2,π-
metallacyclopentene fashion.10 Finally, resonances for the two
methyl groups (δ 49.27 for HfMe and δ 1.40 for GeMe) are
consistent with analogous chemical shifts for Cp*[η4-C4Me4-
Ge(Me)CMe3]HfMe (vide infra).
(8) Hong, J. H.; Pan, Y.; Boudjouk, P. Angew. Chem., Int. Ed. Engl.
1996, 35, 186.
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J. H. Organometallics 1987, 6, 459. (b) Pindada, G. J.; Thornton-Pett, M.;
Bochmann, M. J. Chem. Soc., Dalton Trans. 1997, 3115. (c) Note that
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without the assistance of a co-activator: Hessen, B.; van der Heijden, H. J.
Am. Chem. Soc. 1996, 118, 11670.
Synthesis and Reactivity of Neutral Hafnium η5-Germolyl
Complex 2. Recently, much attention has been devoted to the

3100 J. Am. Chem. Soc., Vol. 122, No. 13, 2000
Dysard and Tilley
use of cationic group 4 bent metallocene complexes for the
polymerization of olefins.5a-d,11 These complexes are formed
upon abstraction of a methyl anion from the group 4 metal
center, usually by a Lewis acid (e.g., B(C6F5)3). Therefore, we
targeted dialkyl complexes of the type Cp*[η5-C4Me4GeR]-
HfMe2 to study the effects of incorporation of an η5-germolyl
ligand on this chemistry. Unfortunately, alkylation of Cp*[η5-
C4Me4GeSiMe3]HfCl2 is not a viable route to these complexes
due to the low and variable yields of this compound. In addition,
the direct reaction of Cp*HfMe2Cl with Li[C4Me4GeSiMe3] did
not lead to a neutral species, but instead gave the dianion
complex 1 as described above. Furthermore, the reaction of 1
with an alkyl triflate did not lead to a neutral η5-ligand but rather
to an η4-germole complex (eq 2).
Scheme 2
Reaction of 1 with 2 equiv of Me3SiOTf in benzene produced
the desired neutral η5-germolyl complex 2 as yellow crystals
in 87% isolated yield (eq 3). Assignment of the structure of 2
formed is apparently not stable and decomposes to unidentified
products. This transformation is analogous to that seen in the
reaction of (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3](CH2CMe3) with H2,
which also transiently forms a silyl hydride complex that
decomposes via the elimination of Me3SiH.15 Unfortunately,
attempts to trap the neutral germole dianion complex (C) with
various reagents (PPh3, PMe3, 2,2′-bipyridine, diphenylacety-
lene) were unsuccessful.
Initial reactivity studies therefore suggest that the germolyl
ligand in 2 is quite reactive. This is perhaps also reflected in
the observed thermal decomposition of 2 in toluene solution at
100 °C, which occurred over several hours to give an array of
unidentified products. It is worth noting that 2 did not
decompose via a σ-bond metathesis pathway analogous to that
in Scheme 2, as Me4Si is not a decomposition product. For
comparison, the dichloride Cp*[η5-C4Me4GeSiMe3]HfCl2 is
stable in toluene solution at 100 °C for several weeks.3c
Reactions involving the germolyl ligand may also account for
the complex mixtures observed when 2 was exposed to various
small molecules (CO, CN(2,6-Me2C6H3), trimethylsilylacety-
lene, and benzophenone). In addition, reaction of 2 with MeI
in tetrahydrofuran-d8 resulted in quantitative loss of the germolyl
ligand as C4Me4Ge(Me)SiMe3 (characterized by comparison of
its NMR spectra with those for an independently synthesized
sample), with generation of unidentified hafnium-containing
species (eq 4). Compound 2 did not react at room temperature
in benzene-d6 with an excess of either Me3SiCl or Me3SiOTf.
as an η5-germolyl complex is based on NMR spectroscopic data.
The hafnium methyl protons in 2 resonate at δ -0.58, a shift
typical for hafnium methyl protons in a bent metallocene
complex,12 and the 13C NMR shifts for the germole ring carbon
atoms (δ 139.4 and 129.4) are similar to those found for Cp*-
[η5-C4Me4GeSiMe3]HfCl2 (δ 146.0 and 135.8).3c
The hafnium-methyl bonds in 2 are active toward σ-bond
metathesis. Exposure of 2 to an excess of H2 at 25 °C in
benzene-d6 resulted in formation of CH4 (1.0 equiv) and Me3-
SiH (0.4 equiv) after several hours as the only characterizable
products by 1H NMR spectroscopy. Likewise, the reaction of 2
with PhSiH3 at room temperature in benzene-d6 proceeded over
24 h to PhMeSiH2 (1.0 equiv) and Me3SiH (0.63 equiv), along
with unidentified organometallic species. It is interesting to note
that the complex CpCp*HfMe2 does not react with PhSiH3 at
room temperature over several weeks, or after 12 h at 90 °C.13
Also for comparison, Cp2ZrMe2 requires greater than 86 h at
room temperature to completely react with hydrogen at 1 atm,14a
and Cp*2ZrMe2 reacts with H2 (1 atm) to give the corresponding
dihydride only after heating to 70 °C for 1 week.14b These
comparisons imply that the germolyl ring imparts significant
enhancement of reactivity to the hafnium-methyl bonds, despite
the greater steric demands for this ligand as compared to those
for unsubstituted Cp. Presumably, the first step in both reactions
is formation of a hafnium hydride (A) via σ-bond metathesis
with H2 or PhSiH3 (Scheme 2). The Me3SiH formed in both
reactions appears to result from abstraction of the hydride ligand
by the germole-bound -SiMe3 group. This is also suggested
by the reaction of 2 with D2, which resulted only in formation
The reaction of 2 with (Et2O)LiCH2Ph in tetrahydrofuran-d8
rapidly produced Me3SiCH2Ph and 1 quantitatively (eq 5). This
result seems to reflect favorable bonding between hafnium and
the aromatic germole dianion, as Li[C4Me4GeSiMe3] did not
react with (Et2O)LiCH2Ph in THF solution under the same
conditions.
1
of Me3SiD (by H NMR spectroscopy; no evidence for the
formation of Me3SiH). The germole dianion complex thus
(11) (a) Jia, L.; Yang, X. M.; Stern, C. L.; Marks, T. J. Organometallics
1997, 16, 842. (b) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 225.
(c) Mohring, R. C.; Coville, N. J. J. Organomet. Chem. 1994, 479, 1. (d)
Marks, T. J. Acc. Chem. Res. 1992, 25, 57.
(12) Cardin, D. J.; Lappert, M. F.; Raston, C. L. Chemistry of Organo-
Zirconium and -Hafnium Compounds; Ellis Horwood Limited: West Sussex,
England, 1986; p 126.
(13) Aitken, C.; Barry, J.-P.; Gauvin, F.; Harrod, J. F.; Malek, A.;
Rousseau, D. Organometallics 1989, 8, 1732.
Initial attempts to use complex 2 as a catalyst for the
polymerization of olefins focused on generation of a cationic

Synthesis of Dianion Complexes of Zr and Hf
J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3101
species of the type [Cp*(η5-C4Me4GeSiMe3)HfMe][BR4] by
abstraction of a methyl group. Reaction of 2 with the neutral
borane B(C6F5)3 or [Ph3C][B(C6F5)4] did not result in the clean
1
generation of a characterizable cationic complex (by H NMR
spectroscopy). Furthermore, reaction of 2 with either of these
abstraction reagents in the presence of 1-hexene or cyclohexene
did not result in the formation of a polymer. These results,
coupled with the observed reactivity of the Ge-SiMe3 bond in
2, prompted us to focus attention on the synthesis of η5-germolyl
complexes containing a more robust germanium-alkyl linkage,
which were expected to produce more stable metallocene
derivatives exhibiting cleaner reaction chemistry.
Reactions of Germolyl Anions with Cp*HfMe2Cl. In an
effort to simplify the ligand-substitution chemistry for introduc-
tion of a germolyl ligand, we focused on the hafnium starting
material Cp*HfMe2Cl, which possesses only one chloride
leaving group. For this strategy, we also preferred germolyl
anion reagents possessing an alkyl substituent at germanium,
in the hope of avoiding elimination processes of the type
described in Scheme 2. Initial attempts focused on generation
of Li[C4Me4GeCMe3], via deprotonation of C4Me4Ge(H)CMe3.
This approach required synthesis of the latter germole com-
pound, which was unknown.
Figure 2. ORTEP diagram of Cp*[η4-C4Me4Ge(Me)CMe3]HfMe (4).
the Ge-Me and Hf-Me groups, at -1.69 and 49.8 ppm,
respectively. In addition, two distinct resonances for the germole
ring carbons (at δ 96.0 and 131.1) are characteristic for early
transition metal complexes in which a diene is bound in a σ2,π-
metallocyclopentene fashion to the metal center.10 In contrast,
the analogous separation of resonances in the η5-germolyl
complex Cp*[η5-C4Me4GeSiMe3]HfMe2 (δ 129.4 and 139.4)
is only 10 ppm. X-ray quality crystals of 4 were grown by slow
cooling of a concentrated pentane solution to -35 °C over
several days, and the molecular structure is shown in Figure 2.
Due to a poor data set, only the two heavy atoms were refined
anisotropically. Thus, a detailed analysis of bond lengths and
angles is not possible.
A reaction analogous to that in eq 6, of Cp*HfMe2Cl with
Li[C4Me4GePh], also resulted in migration of a methyl group
from hafnium to germanium to give Cp*[η4-C4Me4Ge(Me)Ph]-
HfMe (5). Although complex 5 formed in high yield (90% based
on 1H NMR spectroscopy) it could not be isolated in pure form.
The characterization of 5 as an η4-germole complex is therefore
based on its 1H NMR spectrum, which contains a characteristic
Hf-Me resonance at δ -0.71 and a peak for the Ge-Me group
at δ 0.54. In addition, the 13C NMR spectrum of 5 exhibits
resonances at δ 131.4 and 95.18 for the germole ring carbons,
and at δ 50.25 (HfMe) and 2.87 (GeMe) for the methyl groups.
Convenient Syntheses of η5-Silolyl Complexes of d0
Hafnium and Zirconium. We have recently reported the first
synthesis and structural characterization of a transition metal
silolyl complex, Cp*[η5-C4Me4SiSiMe3)HfCl2, obtained from
the reaction of Li[C4Me4SiSiMe3] with Cp*HfCl3.3c However,
because the yield of this reaction is rather low, we have sought
a more reliable and general route to complexes of this type.
Recent results suggest that magnesium silyl derivatives may
be useful in preparing early transition metal silyl derivatives,
especially in circumstances where the corresponding lithium
reagents fail.16 To employ this strategy in the preparation of
silolyl complexes, we prepared the magnesium bis(silolyl)
compound Mg[η1-C4Me4SiSiMe3]2(THF) (6) via reaction of 2
equiv of K[C4Me4SiSiMe3] with MgBr2(Et2O) in THF at -80
°C. Compound 6 was isolated in 70% yield as a crystalline white
Reaction of C4Me4GeCl2 with Me3CLi in Et2O at -78 °C,
followed by warming to room temperature and addition of
LiAlH4 at 0 °C, produced a 2:1 mixture containing C4Me4Ge-
1
(H)CMe3 and C4Me4Ge(CMe3)2 (by H NMR spectroscopy).
Unfortunately, the desired monoalkylated species could not be
separated from this mixture by distillation. In addition, the
germole dichloride did not react with Me3CMgCl in refluxing
diethyl ether, and addition of tetrahydrofuran to the reaction
mixture, followed by further heating to 65 °C, produced only
an unidentified mixture of products. However, reaction of C4-
Me4GeCl2 with 1.5 equiv of Me3CLi in benzene at room
temperature resulted in clean monoalkylation of the starting
germole, which, upon treatment with LiAlH4 in Et2O at 0 °C,
gave the desired product C4Me4Ge(H)CMe3 as a clear, colorless
liquid in 70% yield after distillation. Interestingly, the 1.5 molar
excess of the alkyllithium species is required to drive this
reaction to completion, and inspection of the reaction mixture
by 1H NMR spectroscopy (benzene-d6) revealed clean formation
of C4Me4Ge(Cl)CMe3 along with isobutane (0.25 equiv) and
isobutylene (0.25 equiv), suggesting that this reaction proceeds
at least in part via a radical pathway. The germole C4Me4Ge-
(H)CMe3 was cleanly deprotonated in tetrahydrofuran to give
solutions of Li[C4Me4GeCMe3], from which Li(THF)[C4Me4-
GeCMe3] was isolated as a yellow solid in 72% yield.
Reaction of Li(THF)[C4Me4GeCMe3] with 1 equiv of
Cp*HfMe2Cl in benzene did not produce the desired η5-germolyl
species, but rather the migrated species Cp*[η4-C4Me4Ge(Me)-
CMe3]HfMe (4) in 40% isolated yield. This reaction (eq 6) is
quantitative by 1H NMR spectroscopy, and the low isolated yield
of 4 is due to its high solubility in all solvents employed
(pentane, hexamethyldisiloxane, ether, and toluene).
(14) (a) Jordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.
Organometallics 1987, 6, 1041. (b) Schock, L. E.; Marks, T. J. J. Am. Chem.
Soc. 1988, 110, 7701.
(15) Casty, G. L.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1997, 16, 4746.
The 1H NMR spectrum of deep red 4 contains separate
resonances for the Hf-Me (δ -0.72) and Ge-Me protons (δ
0.30), suggesting its formulation as the η4-germole complex.
The 13C NMR spectrum contains two separate resonances for
(16) Marschner, C.; Tilley, T. D. Unpublished results.

3102 J. Am. Chem. Soc., Vol. 122, No. 13, 2000
Dysard and Tilley
Å) suggesting σ2,π-coordination of the C4 fragment to hafnium.
The magnesium reagent 6 also reacted with 0.5 equiv of
Cp*HfCl3 in benzene to give the previously reported complex
8 in 68% overall yield, in a one-pot synthesis starting from C4-
Me4Si(SiMe3)2. However, the corresponding reaction of 6 with
0.5 equiv of Cp*HfMe2Cl did not produce the desired η5-silolyl
complex, but instead gave an array of products which could
not be identified. In addition, reactions of 8 with MeMgBr or
MeLi did not produce the desired dimethyl species, and attempts
to alkylate 7 and 8 (with various reagents including MeMgBr,
MeLi, PhCH2Li(Et2O), Me3CCH2MgCl, (Me3CCH2)2Mg, Me3-
Al, and Me2Zn) produced highly colored solutions (purple or
green) and no isolable metal-containing products.
Conclusions
Here we have described synthetic routes to neutral η5-silolyl
and η5-germolyl complexes of zirconium and hafnium, and to
an anionic hafnium complex of the germole dianion C4Me4Ge2-
.
Figure 3. ORTEP diagram of Cp*[η5-C4Me4SiSiMe3]ZrCl2 (7).
In particular, the magnesium compound Mg[η1-C4Me4SiSiMe3]2-
(THF) (6) has proven to be a useful silolyl-transfer reagent for
the synthesis of η5-silolyl complexes of hafnium and zirconium.
The germole dianion complex, [Cp*(η5-C4Me4Ge)HfMe2Li-
(THF)]2 (1), has been observed to form in various reactions,
for which the driving force would seem to be formation of the
delocalized germole dianion ligand. Compound 1 is reactive,
and loses the germole ligand upon reaction with trimethylsilyl
chloride. Attempts to alkylate at the germanium center result
in hafnium-to-germanium migration of the methyl group.
However, 1 provides an excellent route to the neutral η5-
germolyl complex Cp*[η5-C4Me4GeSiMe3]HfMe2 (2), via a
silylation reaction that converts the germole dianion ring to a
germolyl ligand.
powder. The characterization of this compound as an η1-silolyl
derivative is based on the 29Si NMR shift (δ -40.9), which is
consistent with a pyramidal silicon center σ-bound to an
electropositive metal.2
Reaction of 6 with 0.5 equiv of Cp*ZrCl3 in benzene
produced Cp*[η5-C4Me4SiSiMe3]ZrCl2 (7) in quantitative yield
(by 1H NMR spectroscopy). A more convenient synthesis of 7
is illustrated in eq 7, which describes the generation of K[C4-
Reactivity studies with d0 complexes of silolyl and germolyl
groups have so far characterized these ligands as being non-
innocent, in that they are readily lost under fairly mild reaction
conditions. In some cases, germolyl complexes have been seen
to participate in metal-to-germanium migration reactions which
produce η4-germole complexes (eqs 2 and 6). This process
appears to be promoted by alkyl substituents at the germanium
of the germolyl ligand, as the analogous silyl derivatives do
not undergo such reactions. The fact that silyl substitution at
the germanium atom stabilizes η5-coordination of the germolyl
ligand and guards against methyl anion migration may be related
to the well-known ability of silyl groups to stabilize anions via
π-bonding. Alternatively, the greater σ-donating ability of the
silyl (vs alkyl) group may render the germanium center less
susceptible to nucleophilic attack by a migrating carbanion.17
For 2, we have also observed participation of the germolyl
ligand in Me3SiH-elimination reactions. While these reactions
are not yet understood in detail, it seems clear that the germolyl
ligand activates the Hf-Me bonds toward σ-bond metathesis
reactions with H2 and PhSiH3 (compared to Cp and Cp* ligands
in analogous complexes). This result would seem to have
important implications for the development of new σ-bond
metathesis chemistry, and we are therefore continuing to explore
this area in search of novel chemical transformations.
Me4SiSiMe3] in tetrahydrofuran solution, followed by its in situ
reaction with MgBr2(Et2O) to give 6, which was then treated
with Cp*ZrCl3 to provide the η5-silolyl complex 7 in an overall
yield of 65%. The 29Si NMR shift of the ring silicon in this
complex is δ 48.9, which is comparable to that in the previously
reported hafnium analogue (δ 49.7).3c The molecular structure
of 7 (Figure 3) is analogous to that for previously reported Cp*-
[η5-C4Me4SiSiMe3]HfCl2 (8).3c The zirconium atom in 7 lies
2.30 Å from the C4Si centroid and 2.24 Å from the Cp* centroid,
and the centroid-zirconium-centroid angle is 136.6°. As in
the case of the hafnium analogue, the ring silicon atom adopts
a nearly planar geometry as evidenced by the summation of
bond angles about Si (353.9°). Furthermore, this silicon atom
deviates by only 0.002(1) Å from the C4Si least-squares plane.
The Si-C bond distances in the ring (1.816(4) and 1.794(4)
Å) are short relative to those for the sp3 silicon-carbon bonds
in the free anion [K(18-crown-6)][C4Me4SiSiMe3] (1.890(4) and
1.880(3) Å) and are comparable to the corresponding values
for Cp*[η5-C4Me4SiSiMe3]HfCl2 (1.798(7) and 1.780(1) Å).3c
However, the C-C bond lengths in the silolyl ring of 7 are
roughly equivalent (1.418(6), 1.419(5), and 1.400(6) Å), in
contrast to the situation for the hafnium analogue in which these
distances vary according to a pattern (1.42(1), 1.37(2), and 1.46
Experimental Section
All manipulations were performed under an argon atmosphere using
standard Schlenk techniques or a nitrogen-filled glovebox. Dry, oxygen-
free solvents were employed throughout. Pentane, THF, toluene, and
(17) Bassindale, A. R.; Taylor, P. G. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley and Sons: New
York, 1989; p 893.

Synthesis of Dianion Complexes of Zr and Hf
J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3103
diethyl ether were distilled from sodium/benzophenone, whereas
benzene-d6 and toluene-d8 were distilled from Na/K alloy. The
compounds KCH2Ph,18 (Et2O)LiCH2Ph,18 Cp*HfMe2Cl,7 Cp*ZrCl3,19
Cp*HfCl3,20 C4Me4GeCl2,21 C4Me4Ge(SiMe3)2,2 C4Me4SiCl2,4d C4Me4-
Si(SiMe3)2,4d C4Me4Ge(H)Ph,22 Li[C4Me4GePh],22 and [C4Me4GeSiMe3]22
were prepared according to literature procedures. Me3SiCl, Me3SiOTf,
EtOTf, and MeI were purchased from Aldrich chemical company and
distilled prior to use. MgBr2(Et2O) was purchased from Aldrich
chemical company and used as received. NMR spectra were recorded
at 300 or 500 MHz (1H) with Bruker AMX-300 and DRX-500
spectrometers, at 125 MHz (13C{1H}) with a DRX-500 spectrometer,
or at 99 MHz (29Si{1H}), at ambient temperature unless otherwise noted.
Elemental analyses were performed by the microanalytical laboratory
at the University of California, Berkeley. IR samples of solid materials
were prepared as KBr pellets, while IR spectra of oils were obtained
with neat samples between CsI plates. All IR absorptions are reported
in cm-1 and were recorded with a Mattson Infinity 60 MI FTIR
spectrometer.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Compound 1
Hf(1)-Ge(2)
Hf(1)-C4Ge(2)plane
Hf(1)-Cp*centroid
Hf(1)-C(41)
Hf(1)-C(42)
Li(1)-C4Ge(2)plane
Ge(2)-Li(2)
Ge(2)-C(1)
2.903(2) Hf(2)-Ge(1)
2.878(1)
2.274
2.2492(5)
2.30(1)
2.27(1)
1.984
2.69(2)
1.96(1)
1.96(1)
1.42(2)
1.40(2)
1.43(2)
2.256
Hf(2)-C4Ge(1)plane
2.2408(4) Hf(2)-Cp*centroid
2.29(1)
2.26(1)
1.953
2.80(2)
2.10(2)
1.72(2)
1.34(2)
1.39(2)
1.41(2)
Hf(2)-C(43)
Hf(2)-C(44)
Li(1)-C4Ge(1)plane
Ge(1)-Li(2)
Ge(1)-C(13)
Ge(1)-C(16)
C(13)-C(14)
C(14)-C(15)
C(15)-C(16)
Ge(2)-C(4)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(41)-Hf(1)-C(42) 90.1(5)
Cp*-Hf(1)-C4Ge(2) 136.4
Ge(2)-Li(2)-Ge(1) 86.3(6)
C(43)-Hf(2)-C(44) 87.5(6)
Cp*-Hf(2)-C4Ge(1) 136.5
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compound 7
[Cp*(η5-C4Me4Ge)HfMe2Li(OC4H8)]2 (1). A 100 mL Schlenk tube
was charged with C4Me4Ge(SiMe3)2 (0.207 g, 0.633 mmol), (Et2O)LiCH2-
Ph (0.109 g, 0.633 mmol), and 50 mL of THF, and the contents were
stirred for 30 min. The resulting orange solution was then added to a
250 mL round-bottom Schlenk flask containing Cp*HfMe2Cl (0.120
g, 0.317 mmol) in 100 mL of THF. This reaction mixture was stirred
for 30 min before the volatile materials were removed under dynamic
vacuum. The remaining orange residue was washed with pentane (3 ×
30 mL) leaving a yellow solid. This solid was extracted with toluene
(3 × 20 mL) and the toluene was removed via dynamic vacuum to
give 1 as yellow-orange crystals in 86% yield (0.330 g, 0.274 mmol).
1H NMR (benzene-d6, 500 MHz, 25 °C) δ 3.61 (m, 4 H, OC4H8), 2.40
(s, 6 H, C4Me4Ge), 2.13 (s, 6 H, C4Me4Ge), 2.08 (s, 15 H, C5Me5),
1.40 (m, 4 H, OC4H8), -0.660 (s, 6 H, HfMe2). 13C{1H} NMR (500
MHz, benzene-d6, 25 °C) δ 129.6 (s, C4Me4Ge),116.6 (s, C5Me5), 69.54
(s, OC4H8), 42.95 (s, HfMe2), 25.95 (s, OC4H8), 20.32, 16.73 (s, C4Me4-
Zr(1)-Si(1)
Zr(1)-C4Si(1)
Si(1)-C(4)
C(2)-C(3)
2.844(1) Zr(1)-Cp*centroid
2.301
2.24
Si(1)-C(1)
1.816(4)
1.418(6)
1.400(6)
1.794(4) C(1)-C(2)
1.419(5) C(3)-C(4)
Si(1)-Si(2)
2.352(1) Cl(1)-Zr(1)-Cl(1) 96.51(4)
Cp*-Zr(1)-C4Si(1) 134.6
C(1)-Si(1)-Si(2)
C(1)-Si(1)-C(4)
92.5(2)
129.5(2)
131.9(1) C(4)-Si(1)-Si(2)
Me4Ge), 117.9 (s, C5Me5), 49.27 (s, HfMe), 15.58, 15.08 (s, C4Me4-
Ge), 12.08 (C5Me5), 11.91 (s, CH2CH3), 8.170 (s, CH2CH3), 1.398 (s,
GeMe).
C4Me4Ge(Me)SiMe3. A 200 mL Schlenk tube was charged with
[C4Me4GeSiMe3]2 (2.00 g, 3.94 mmol) and K metal (0.320 g, 8.18
mmol), and 100 mL of THF was added to generate a light orange
solution. This solution was stirred for 1 week, after which time all of
the potassium had been consumed and the solution had turned to a
deep red color. The flask was placed in an ice bath and the solution
was cooled to 0 °C. MeI (0.520 mL, 8.27 mmol) was then added to
the flask resulting in formation of a white cloudy suspension. This
suspension was allowed to warm to room temperature and was then
stirred for 1 h. The volatile materials were removed under dynamic
vacuum, and the resulting residue was extracted with pentane (3 × 30
mL). Pentane was removed from the extracts to give the product as a
colorless oil in 80% yield (1.69 g, 6.30 mmol). This oil was purified
by a short-path distillation (bp 48 °C, 1 × 10-3 Torr). 1H NMR
(benzene-d6, 300 MHz, 25 °C) δ 2.03 (s, 6 H, C4Me4Ge), 1.82 (s, 6 H,
C4Me4Ge), 0.427 (s, 3 H, GeMe), 0.161 (s, 9 H, GeSiMe3). 13C{1H}
NMR (125 MHz, benzene-d6, 25 °C) δ 146, 135 (s, C4Me4Ge), 16.7,
14.9 (s, C4Me4Ge), -0.300 (s, GeSiMe3), -7.30 (s, GeMe). Anal. Calcd
7
Ge), 13.58 (s, C5Me5). Li (194.4 MHz, toluene-d8, -40 °C) δ 1.70
(m, η1-Li), -4.60 (m, η5-Li). Anal. Calcd for C24H41GeHfLiO: C,
47.76; H, 6.85. Found: C, 47.76; H, 6.52. IR (cm-1) 2907 s, 2361 w,
1448 m, 1376 m, 1136 w, 1041 m, 446 m. Mp 155-158 °C dec.
Cp*(η5-C4Me4GeSiMe3)HfMe2 (2). To a solution of 1 (0.21 g, 0.17
mmol) in benzene (50 mL) was added Me3SiOTf (0.07 g, 0.34 mmol,
in 30 mL of benzene). The resulting solution was stirred at room
temperature for 30 min, after which time the volatile materials were
removed under dynamic vacuum. The remaining orange residue was
extracted with pentane (3 × 10 mL). The combined extracts were
concentrated to 10 mL and cooled to -80 °C to give 3 as orange crystals
1
in 87% yield (0.18 g, 0.30 mmol). H NMR (benzene-d6, 500 MHz,
25 °C) δ 2.17 (s, 6 H, C4Me4Ge), 2.16 (s, 6 H, C4Me4Ge), 1.99 (s, 15
H, C5Me5), 0.440 (s, 9 H, SiMe3), -0.580 (s, 6 H, HfMe2). 13C{1H}
NMR (125 MHz, benzene-d6, 25 °C) δ 139.4, 129.4 (s, C4Me4Ge),
117.2 (s, C5Me5), 43.32 (s, HfMe2), 19.18, 15.96 (s, C4Me4Ge), 13.23
(s, C5Me5), 3.130 (s, SiMe3). Anal. Calcd for C23H42GeHfSi: C, 46.22;
H, 7.08. Found: C, 46.30; H, 7.08. IR (cm-1) 2948 s, 2905 s br, 1436
m, 1375 m, 1246 m, 1129 w, 1020 w, 841 s, 753 w, 701 w, 628 w,
464 w. Mp 125-128 °C.
for C12H24GeSi: C, 53.58; H, 8.99. Found: C, 52.66; H, 9.26. IR (cm-1
)
2951 s br, 2905 s br, 2851 s br, 1551 w, 1441 m, 1399 sh, 1245 s,
1058 m, 839 s, 785 s, 741 m, 693 m, 622 m, 578 m, 484 m.
C4Me4Ge(H)CMe3. To a solution of C4Me4GeCl2 (1.00 g, 3.97
mmol) in 100 mL of benzene was added a benzene (100 mL) solution
of LiCMe3 (0.381 g, 5.96 mmol) to generate a cloudy yellow solution
that was allowed to stir at room temperature for 60 min. This solution
was then added to LiAlH4 (0.181 g, 4.77 mmol) in 100 mL of diethyl
ether. The resulting yellowish suspension was allowed to stir at room
temperature for 60 min after which time the volatile materials were
removed under dynamic vacuum. The resulting yellow residue was
extracted with pentane (3 × 25 mL). The combined pentane extracts
were removed in vacuo to leave a yellow oil. This yellow oil was
distilled (37 °C; 1 × 10-3 Torr) to give the pure colorless product in
70% yield (0.664 g, 2.78 mmol). 1H NMR (benzene-d6, 300 MHz, 25
°C) δ 4.88 (s, 1 H, GeH), 1.97 (s, 6 H, C4Me4Ge), 1.73 (s, 6 H, C4Me4-
Ge), 1.15 (s, 9 H, CMe3). 13C{1H} NMR (125 MHz, benzene-d6, 25
°C) δ 148.2, 129.2 (s, C4Me4Ge), 29.56 (s, CMe3), 24.41 (s, CMe3),
17.15, 14.71 (s, C4Me4Ge). Anal. Calcd for C12H22Ge: C, 60.33; H,
9.28. Found: C, 60.57; H, 9.86. IR (cm-1) 2950 s, 2923 s, 2853 s,
2009 s (GeH), 1458 m, 1363 m, 1059 w, 1017 w, 800 w, 702 m, 665
w.
Cp*(η4-C4Me4GeMeEt)HfMe (3). In the glovebox, a vial was
charged with 1 (0.025 g, 0.040 mmol) and 0.5 mL of benzene-d6 was
added, generating a deep yellow solution. To this was added CH3CH2-
OTf (0.007 g, 0.040 mmol) generating a deep orange solution of 2. 1H
NMR (500 MHz, benzene-d6, 25 °C) δ 2.05 (s, 6 H, C4Me4Ge), 2.00
(s, 15 H, C5Me5), 1.86 (s, 6 H, C4Me4Ge), 1.28 (m, 3 H, CH3CH2Ge),
1.26 (m, 2 H, CH3CH2Ge), 0.257 (s, 3 H, GeMe), -0.833 (s, HfMe).
13C{1H} NMR (125 MHz, benzene-d6, 25 °C) δ 130.0, 97.16 (s, C4-
(18) Hartmann, J.; Schlosser, M. Angew. Chem., Int. Ed. Engl. 1973,
12, 508.
(19) Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982, 1, 793.
(20) Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hillhouse, G. L.;
Bercaw, J. E. Organometallics 1985, 4, 97.
(21) (a) Fagan, P. J.; Nugent, W. A.; Calabrese, J. C. J. Am. Chem. Soc.
1994, 116, 1880. (b) Fagan, P. J.; Nugent, W. A. J. Am. Chem. Soc. 1988,
110, 2310.
(22) Dufour, P.; Dubac, J.; Dartiguenave, M.; Dartiguenave, Y. Orga-
nometallics 1990, 9, 3001.

3104 J. Am. Chem. Soc., Vol. 122, No. 13, 2000
Table 3. Crystallographic Data for Compounds 1, 4, and 7
Dysard and Tilley
1
4
7
(a) Crystal Parameters
Hf2Li2O2C48H82Ge2
1207.22
formula
formula weight
size mm
crystal system
space group
a (Å)
HfGeC24H42
581.68
ZrC25Cl2Si2H36
554.86
0.2 × 0.18 × 0.05
monoclinic
P21/c(No. 14)
15.0143(1)
20.1799(2)
17.1168(1)
90, 97.408, 90
5142.88(6)
4
0.045 × 0.05 × 0.01
monoclinic
P21/m(No. 11)
9.2701(5)
13.3564(7)
10.5768(5)
90, 112.399, 90
1236.80(1)
2
0.35 × 0.18 × 0.04
monoclinic
Cc(No. 9)
18.6163(4)
9.0536(2)
17.2578(4)
90, 122.47, 90
2454.00(1)
2
b (Å)
c (Å)
R, â, γ (deg)
V (Å3)
Z
D
calc (g cm-3
)
1.559
1.562
3.003
F000
2400.00
580.00
2304.00
(b) Data Collection
-158.0
9367/24375
0.056
temp (°C)
unique/total
Rint
-127.0
1858/5047
0.131
-104.0
3867/5912
0.028
empirical absorption corr
max/Tmin
0.07
0.992/0.593
0.10
0.953/0.639
none
T
(c) Refinement
5706
496
observations [I > 3σ(I)]
no. of variables
888
67
3657
233
reflection/parameter ratio
R ) ∑||Fo| - |Fc||/∑|Fo|
11.50
0.043
0.054
1.71
13.25
0.065
0.072
1.19
15.70
0.033
0.051
2.33
Rw ) [∑ω(|Fo| - |Fc|)2/∑ωFo )]1/2
2
goodness of fit ([∑ω(|Fo| - |Fc|)2/(No - Nv)]1/2
)
max and min peaks in final diff map (e-/Å3)
1.12/-1.04
1.62/-2.81
0.67/-0.60
n
1
Li(THF)[C4Me4GeCMe3]. BuLi (1.57 mL, 2.51 mmol, 1.6 M in
hexanes) was added via syringe to C4Me4Ge(H)CMe3 (0.600 g, 2.51
mmol) in 50 mL of THF. The resulting reaction solution was stirred
for 30 min after which time the volatile materials were removed under
dynamic vacuum. The resulting oily yellow/orange residue was
extracted into 30 mL of pentane, and the resulting pentane solution
was concentrated to 10 mL. Cooling to -80 °C gave the product as
yellow crystals, which contained 1.2 THF molecules per lithium atom,
deep orange solution of 5. H NMR (300 MHz, benzene-d6, 25 °C) δ
7.65-7.20 (m, 5 H, GePh), 2.08 (s, 6 H, C4Me4Ge), 2.01 (s, 15 H,
C5Me5), 1.86 (s, 6 H, C4Me4Ge), 0.540 (s, 3 H, GeMe), -0.710 (s,
HfMe). δ 131.4, 95.18 (s, C4Me4Ge), 144.0, 135.9, 135.6, 129.2 (s,
GePh), 118.3 (s, C5Me5), 50.25 (s, HfMe), 15.77, 14.49 (s, C4Me4Ge),
12.10 (C5Me5), 2.870 (s, GeMe).
Mg[C4Me4SiSiMe3]2(THF) (6). A 250 mL round-bottom Schlenk
flask was charged with C4Me4Si(SiMe3)2 (2.30 g, 8.14 mmol), KCH2-
Ph (1.13 g, 8.14 mmol), and 50 mL of THF. The resulting solution
was cooled to -80 °C, and then MgBr2(Et2O) (1.05 g, 4.07 mmol) in
100 mL of THF was added to give a bright red solution. The solution
was allowed to stir at -80 °C for 15 min, and then the cooling bath
was removed and the solution was allowed to warm to room
temperature. After this time the solution turned blue-green in color.
The volatile materials were removed under dynamic vacuum leaving a
tan oily residue. This oily residue was extracted with pentane (3 × 30
mL). The pentane was removed from the combined extracts leaving
an oily tan residue. Me3SiOSiMe3 (25 mL) was added to the flask to
wash the residue. After filtration, a white powder remained which was
recrystallized from pentane (-35 °C) to give 6 in 70% yield (1.47 g,
2.85 mmol) as colorless, blocklike crystals. 1H NMR (benzene-d6, 500
MHz, 25 °C) δ 3.39 (m, 4 H, OC4H8), 2.30 (s, 6 H, C4Me4Si), 2.09 (s,
6 H, C4Me4Si), 1.22 (m, 4 H, OC4H8), 0.351 (s, SiSiMe3). 13C{1H}
NMR (125 MHz, benzene-d6, 25 °C) δ 143.7, 139.9 (s, C4Me4Si), 69.49
(s, OC4H8), 25.17 (s, OC4H8), 17.00, 15.01 (s, C4Me4Ge), 0.9100 (s,
SiMe3). 29Si{1H} (99.4 MHz, benzene-d6, 25 °C) δ -40.9 (s, C4Me4Si),
-12.0 (s, SiMe3). Anal. Calcd For C26H50MgOSi4: C, 60.60; H, 9.78.
Found: C, 59.93; H, 9.77. IR (cm-1) 2954 s br, 2913 s br, 1444 m,
1246 m, 1057 m br, 839 s, 757 w, 701 w, 509 w. Mp 180-185 °C
dec.
1
in 72% yield (0.599 g, 1.81 mmol). H NMR (benzene-d6, 500 MHz,
25 °C) δ 3.66 (m, 4.6 H, OC4H8), 2.20 (s, 6 H, C4Me4Ge), 1.95 (s, 6
H, C4Me4Ge), 1.41 (m, 4.6 H, OC4H8), 1.35 (s, 9 H, CMe3). 13C{1H}
NMR (125 MHz, benzene-d6, 25 °C) δ 157.7, 128.8 (s, C4Me4Ge),
69.51 (s, OC4H8), 32.68 (s, CMe3), 29.01 (s, CMe3), 26.04 (s, OC4H8),
19.16, 15.35 (s, C4Me4Ge). Anal. Calcd for C16.8H30.8GeO1.2Li: C, 60.90;
H, 9.31. Found: C, 61.34; H, 9.52. IR (cm-1) 2950 s, 2947 s, 2912 s,
2842 s, 1457 m, 1352 w, 1158 w, 1050 m, 893 w, 811 w, 665 w, 452
w. Mp 251 °C dec.
Cp*[η4-C4Me4Ge(Me)CMe3]HfMe (4). To a solution of Cp*HfMe2-
Cl (0.500 g, 1.32 mmol) in 100 mL of THF was added a THF (50 mL)
solution of Li(THF)[C4Me4GeCMe3] (0.437 g, 1.32 mmol) to give a
deep orange solution. The reaction solution was allowed to stir for 60
min, and then the volatile materials were removed by vacuum transfer.
The resulting oily orange residue was extracted with pentane (3 × 25
mL). The combined extracts were concentrated to 5 mL and cooled to
-80 °C to give 4 as red needles in 40% yield (0.308 g, 0.530 mmol).
1H NMR (benzene-d6, 300 MHz, 25 °C) δ 2.07 (s, 6 H, C4Me4Ge),
1.99 (s, 15 H, CMe5), 1.85 (s, 6 H, C4Me4Ge), 1.28 (s, 9 H, CMe3),
0.300 (s, 3 H, GeMe), -0.730 (s, 3 H, HfMe). 13C{1H} NMR (125
MHz, benzene-d6, 25 °C) δ 131.1, 96.02 (s, C4Me4Ge), 118.2 (s, CMe5),
49.82 (s, HfMe), 35.42 (s, CMe3), 31.69 (s, CMe3), 15.47, 14.94 (s,
C4Me4Ge), 12.19 (s, C5Me5), -1.686 (s, GeMe). Anal. Calcd for C24H42-
HfGe: C, 49.56; H, 7.28. Found: C, 49.61; H, 7.31. IR (cm-1) 2914
s br, 2839 s br, 1456 m, 1377 w, 1141 w, 1018 w, 769 m, 702 w, 416
w. Mp 115-117 °C.
Cp*(η5-C4Me4SiSiMe3)ZrCl2 (7). A 100 mL Schlenk tube was
charged with C4Me4Si(SiMe3)2 (1.10 g, 3.90 mmol), KCH2Ph (0.508
g, 3.90 mmol), and 50 mL of THF. The resulting solution was cooled
to -80 °C, and then MgBr2(Et2O) (0.503 g, 1.95 mmol) in THF (100
mL) was added via cannula. This solution was allowed to stir at -80
°C for 15 min after which time the cooling bath was removed and the
solution was allowed to warm to room temperature. After this time the
solution turned blue-green in color. The volatile materials were removed
under dynamic vacuum leaving a tan oily residue of the magnesium
reagent, which was dissolved in 50 mL of benzene. The latter solution
Cp*[η4-C4Me4Ge(Me)Ph]HfMe (5). In the glovebox, a vial was
charged with Cp*HfMe2Cl (0.020 g, 0.053 mmol), and 0.5 mL of
benzene-d6 was added to generate a colorless solution. Li[C4Me4GePh]
(0.014 g, 0.053 mmol) was weighed into a separate vial and dissolved
in 0.5 mL of benzene-d6 to give a yellow solution. This solution was
added to the vial containing Cp*HfMe2Cl to immediately generate a

Synthesis of Dianion Complexes of Zr and Hf
J. Am. Chem. Soc., Vol. 122, No. 13, 2000 3105
was then added to Cp*ZrCl3 (1.30 g, 3.90 mmol) in 100 mL of benzene
to give a light orange solution. This solution was stirred at room
temperature for 30 min, and then the volatile components were removed
by vacuum transfer. The remaining orange residue was extracted into
pentane (3 × 50 mL). The combined extracts were concentrated to 40
mL and cooled to -80 °C to give 7 as orange crystals in 65% yield
were included in calculated positions but not refined. The function
minimized in the full-matrix least-squares refinement was ∑w(|Fo| -
|Fc|)2. The weighting scheme was based on counting statistics and
included a p-factor to downweight the intense reflections. Crystal-
lographic data are summarized in Table 3.
For 1: Crystals were grown from a 50:1 toluene/THF solution at
-35 °C. The non-hydrogen atoms that displayed no disorder were
refined anisotropically except for Li(1) and Li(2), which were refined
isotropically. Hydrogen atoms were included but not refined. The two
THF molecules displayed large “thermal parameters” indicative of
probable disorder. This disorder was modeled with the anisotropic
displacement parameters. Hf(2) and Hf(3) showed disorder and were
refined anisotropically and isotropically with occupancies of 92 and
8%, respectively. In addition the germole ring containing Ge(2) showed
disorder in which the ring appeared to have two orientations, twisted
about the Li(1) to Hf(1) vector. The ring carbons were modeled with
anisotropic displacement parameters but the Ge atoms and methyl
carbons were modeled with partial occupancy isotropic atoms. The
occupancy of Ge(3) was constrained to be equal to the difference of
one and the occupancy of Ge(2), as were carbons 6, 8, 10, and 12.
Carbons 5, 7, 9, and 11 were constrained to have the same occupancy
as Ge(2). The occupancy factor was refined to 55% for Ge(2) and
carbons 5, 7, 9, and 11 and occupancies of 45% for Ge(3) and carbons
6, 8, 10, and 12. See the Supporting Information for a full ORTEP
view of 1, including all of the disordered atoms.
1
(1.29 g, 2.54 mmol). H NMR (400 MHz, benzene-d6, 25 °C) δ 2.36
(s, 6 H, C4Me4Si), 2.02 (s, 15 H, C5Me5), 1.96 (s, 6 H, C4Me4Si), 0.262
(s, 9 H, SiMe3). 13C{1H} NMR (125 MHz, benzene-d6, 25 °C) δ 138.2,
131.9 (s, C4Me4Si), 123.2 (s, C5Me5), 16.67, 16.01 (s, C4Me4Si), 13.59
(s, C5Me5), 1.490 (s, SiMe3). 29Si{1H} (99.4 MHz, benzene-d6, 25 °C)
δ 48.9 (s, C4Me4Si), -9.42 (s, SiMe3). Anal. Calcd for C21H36Cl2-
ZrSi2: C, 49.77; H, 7.16. Found: C, 49.43; H, 7.19. IR (cm-1) 2950
br s, 2901 br s, 1601 w, 1454 m, 1375 m, 1248 m, 1075 w, 1016 m,
843 s, 801 sh, 698 w. Mp 199-202 °C dec.
Cp*(η5-C4Me4SiSiMe3)HfCl2 (8). A procedure analogous to that
used to prepare 7 was employed using C4Me4Si(SiMe3)2 (0.675 g, 2.39
mmol), KCH2Ph (0.311 g, 2.39 mmol), MgBr2(Et2O) (0.309 g, 1.20
mmol), and Cp*HfCl3 (1.00 g, 2.39 mmol). The product was isolated
after crystallization from Et2O to provide 8 as orange blocks in 68%
1
yield (0.965 g, 1.63 mmol). 8 was characterized by comparison of H
NMR data with that previously reported.3c 1H NMR (benzene-d6, 300
MHz, 25 °C) δ 2.25 (s, 12 H, C4Me4Ge), 2.05 (s, 15 H, C5Me5), 0.33
(s, 9 H, SiMe3).
X-ray Structure Determinations. X-ray diffraction measurements
were made on a Siemens SMART diffractometer with a CCD area
detector, using graphite monochromated Mo KR radiation. The crystal
was mounted on a glass fiber using Paratone N hydrocarbon oil. A
hemisphere of data was collected using ω scans of 0.3°. Cell constants
and an orientation matrix for data collection were obtained from a least-
squares refinement using the measured positions of reflections in the
range 4 < 2Θ < 45°. The frame data were integrated using the program
SAINT (SAX Area-Detector Integration Program; V4.024; Siemens
Industrial Automation, Inc.: Madison, WI, 1995). An empirical
absorption correction based on measurements of multiply redundant
data was performed using the programs XPREP (part of the SHELXTL
Crystal Structure Determination Package; Siemens Industrial Automa-
tion, Inc.: Madison, WI, 1995) or SADABS. Equivalent reflections
were merged. The data were corrected for Lorentz and polarization
effects. A secondary extinction correction was applied if appropriate.
The structures were solved using the teXsan crystallographic software
package of the Molecular Structure Corporation, using direct methods,
and expanded with Fourier techniques. All non-hydrogen atoms were
refined anisotropically unless otherwise noted and the hydrogen atoms
For 4: Crystals were grown from a concentrated pentane solution
at -35 °C. Due to poor data only the heavy atoms Hf(1) and Ge(1)
were refined anisotropically. All of the carbon atoms were refined
isotropically. Hydrogen atoms were calculated but not refined.
For 7: Crystals were grown from a concentrated ether solution at
-35 °C.
Acknowledgment is made to the National Science Founda-
tion of their generous support of this work. We thank Dr. Fred
Hollander for assistance with the X-ray structure determinations.
Supporting Information Available: Tables of crystal, data
collection, and refinement parameters, bond distances and
angles, and anisotropic displacement parameters for 1, 4, and 7
(PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
JA993563N