Group 4 Metallocene Complexes
A R T I C L E S
dichlorides to obtain metallacyclotrisilanes.10 In an elegant study,
they could show that switching the electron count at palladium,
by removal or addition of a phosphane ligand, changes the
character of the compound from a metallacycle to a
π-complex.10b Kira and co-workers have also reported the first
example of a complex of a chlorine substituted disilene from
the reaction of tetracarbonylpotassium ferrate with the respective
2,2,3,3-tetrachlorotetrasilane.11 While all the mentioned ex-
amples concern disilene complexes of late transition metals, the
only example of coordination of a disilene to an early metal
has been reported for hafnocene.12 Reaction of a 1,2-dipotas-
siodisilane with hafnocene dichloride gave a hafnocene disilene
complex, which was attributed to have some disilylene character.
Adduct formation of this complex with trimethylphosphane
changed the character of the compound to a more conventional
metallacyclotrisilane.
Most of what was said above for disilenes is also true for
digermenes. Compared to silicon, germanium chemistry in
general has received less attention and so have digermene
transition metal complexes. The only known examples concern
digermene platinum complexes reported by Satge´ and co-
workers,13 which have utilized both the double oxidative
addition strategy of 1,2-dihydrodigermanes13b as well as the
reaction of a 1,2-dilithiodigermane with a platinum chloride
complex.13a The number of theoretical studies concerning
disilene and digermene complexes14 is also very small with an
emphasis on palladium and platinum complexes. No distannene
complexes of transition metals are known so far to the best of
our knowledge.
Scheme 1
dichloride involves the reduction of titanium and subsequently
the formation of silylated titanates.18
In principle, a simple access to 1,2-dipotassiodisilanes,19 1,2-
dipotassiodigermanes20 and 1,2-dipotassiodistannanes21 should
provide a convenient way to transition metal complexes of
disilenes, digermenes and distannenes.
Transmetalation of 1,2-dipotassiotetrakis(trimethylsilyl)disilane19
(1) with magnesium bromide22 and subsequent reaction with
hafnocene dichloride gave the hafnocene disilene complex 2
(Scheme 1), which exhibits a characteristic 29Si NMR spectrum
with the metalated silicon atoms resonating at +132.8 ppm.12
Isolation of this compound in the solid state was not possible.
However, upon addition of trimethylphosphane, the PMe3 adduct
3 was formed, which could be isolated and subjected to crystal
structure analysis (Scheme 1).12 Repeating the reaction of 1 with
zirconocene dichloride was possible but accompanied by the
formation of approximately 10% byproducts, which seemed to
be only monosilylated. Nevertheless, formation of the zir-
conocene disilene complex 4 could be observed by NMR
spectroscopy. Again, isolation in the solid phase was not
possible, but also in this case the PMe3 adduct (5) could be
obtained (Scheme 1) (discussion of NMR and X-ray data follows
the synthetic section). For the reaction of the 1,2-dimagnesium-
disilane with titanocene dichloride, it was expected that the
reaction products would exhibit titanium in the oxidation state
+3.18 However, much to our delight, the neutral titanocene
disilene complex 6 was formed in some 30% yield along with
some paramagnetic material. In this case, even isolation in solid
phase was possible, and the structure assignment was confirmed
by crystal structure analysis (Figure 3).
Results and Discussion
Synthesis. Reactions of oligosilanyl anions in general and in
particular of tris(trimethylsilyl)silanides with group 4 metal-
locene dichlorides are well established for zirconocene and
hafnocene.15,16 In the course of studies concerning the synthesis
and reactivity of oligosilanyl dianions we have also investigated
their behavior with zirconocene and hafnocene dichlorides. 1,3-
and 1,4-dipotassio -tri- and tetrasilanes were found to react
cleanly to the respective metallocyclotetra- and -pentasilanes,
respectively.17 The situation for reactions with titanocene
During the numerous attempts to obtain single crystals of
zirconocene PMe3 adduct 5, some crystals of a related compound
(5a) were isolated. Upon structure analysis, it became evident
that the compound was a derivative of 5, where one of the
trimethylsilyl groups was replaced by a hydrogen atom. It is
likely that the formation of this compound can be associated
with the presence of an excess potassium tert-butoxide and some
partial hydrolysis. Intermediately formed K(Me3Si)2SiSi(SiMe3)2H
might have been converted to K(Me3Si)2SiSi(SiMe3)(H)K,
which eventually could react with Cp2ZrCl2 and PMe3 to 5a
(Scheme 2). The compound is interesting, as it represents the
first example of a disilene metal complex with a hydrogen
substituent at a formal disilene silicon atom.
(11) Hashimoto, H.; Suzuki, K.; Setaka, W.; Kabuto, C.; Kira, M. J. Am.
Chem. Soc. 2004, 126, 13628–13629.
(12) Fischer, R.; Zirngast, M.; Flock, M.; Baumgartner, J.; Marschner, C.
J. Am. Chem. Soc. 2005, 127, 70–71.
(13) (a) Castel, A.; Rivie`re, P.; Satge´, J.; Desor, D.; Ahbala, M.;
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461–467.
(14) (a) Cundari, T. R.; Gordon, M. S. THEOCHEM 1994, 313, 47–54.
(b) Sakaki, S.; Yamaguchi, S.; Musashi, Y.; Sugimoto, M. J.
Organomet. Chem. 2001, 635, 173–186. (c) Sakaki, S.; Ieki, M. Inorg.
Chem. 1991, 30, 4218–4224.
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(21) Fischer, R.; Baumgartner, J.; Marschner, C.; Uhlig, F. Inorg. Chim.
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(22) For references on the transmetallation of oligosilyl potassium and
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