Inorg. Chem. 2005, 44, 4906−4908
Ferrocenylalanes: Solid-State and Solution Structures of Some New
Aluminum-Bridged ansa-Ferrocenes
Holger Braunschweig,* Christian Burschka, Guy K. B. Clentsmith, Thomas Kupfer, and
Krzysztof Radacki
Institut fu¨r Anorganische Chemie, Bayerische Julius-Maximilians UniVersita¨t der Wu¨rzburg, Am
Hubland, Wu¨rzburg D-97074, Germany
Received February 4, 2005
κ
2-C,NNMe2-
Chart 1
Addition of dilithiated ferrocene to AlEt2Cl and Al(
CH2C6H4)Cl2 yields the trimeric ferrocenyl derivative 1 and the
dimeric [1,1 ]-ferrocenophane 2, respectively. Solution spectroscopy
′
is consistent with the solid-state structures, which reveal unusual
and unprecedented bonding around the aluminum centers.
Substitution of the ferrocene unit by main group elements
has recently been the subject of considerable attention.1 Such
systems are prized both as precursors to polymeric materials
with ferrocenyl repeat units and as frameworks for new
ferrocene-based ligands capable of important catalytic trans-
formations when bound to a suitable transition metal.2
Depending on the Lewis acidity of the main group element,
“E”, such systems can give rise to multinuclear metallo-
cenophanes in which E bridges across the cyclopentadienyl
ring to another ferrocene or spans the cyclopentadienyl rings
bound to the same iron center to give an ansa bridge.
Monomers, dimers, and trimers, with respect to ferrocene,
are all possible outcomes and representative examples (A-
C) incorporating group 13 elements are shown in Chart 1.
substituted metallocenophanes are conspicuously absent for
iron and, indeed, for any other transition metal. From the
point of view of reactivity, this is reasonable in that the
Lewis-acidic aluminum center would be expected to draw
any electron density toward itself and undergo exhaustive
substitution to give oligomeric or intractable material. In fact,
although a few examples of aluminum directly bound to a
ferrocenyl group have been isolated,8 in none of these cases
is any degree of structural complexity exhibited. In this
Communication, the isolation and structure of a multinuclear
ferrocene derivative with aluminum substitution is reported
by way of reaction between dilithiated ferrocene and the
simple aluminum reagent AlEt2Cl. In addition, an unprec-
edented and authentic [1,1′]-ferrocenophane is presented in
which a based-stabilized aluminum is the bridging element.
Slow addition of stoichiometric AlEt2Cl (2 equiv) in
hexanes to a slurry of [Fe(η5-C5H4)2]Li2‚TMEDA (TMEDA
) N,N,N,N-tetramethylethylenediamine) in toluene at
-78 °C results in rapid dissolution of the starting material
and the deposition of an insoluble white precipitate. Upon
The examples shown incorporate either boron or gallium
centers;3-6 except for a very recent, rare exception,7 aluminum-
* To whom correspondence should be addressed. E-mail:
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4906 Inorganic Chemistry, Vol. 44, No. 14, 2005
10.1021/ic0501925 CCC: $30.25
© 2005 American Chemical Society
Published on Web 06/15/2005