Bis(μ-(pentamethylcyclopentadienyl)aluminio)hexacarbonyldicobalt,
(μ-Cp*Al)2Co2(CO)6, is formed
in
the reaction between AlCp* (Cp* = C5Me5)
and Co2(CO)8
in toluene. The bonding description as a polyhedral
Al2Co2 cluster in which AlCp* has completely lost
its
originally carbene-like character is based on X-ray data
as well as on DFT calculations.
The orange precipitate obtained after the well-known preparation of fluorenyllithium was recrystallized from a solution of benzene or toluene in order to get orange-red crystals which were of sufficient quality for X-ray diffraction. By this procedure we succeeded in redetermining the molecular structure of a donor-free unsubstituted fluorenyllithium compound, which might be the smallest alkali-metal compound containing a donor-free cyclopentadienyl-like ligand within an annelated ring system to date. The description of the bonding situation is based on ab initio calculations as well as on a comparison with analogous compounds.
The co-condensation, by annealing from À 196 8C to room temperature, of the high-temperature species AlCl and 3-hexyne (EtCCEt) with an excess of toluene leads to the formation of the compound (AlCl´EtCCEt) 4 . Characterisation by X-ray analysis revealed the presence of two isomers in the same crystal: a dimeric 1,4-dialumina-2,5-cyclohexadiene and a 1,4,7,10-tetralumina-2,5,8,11-cyclododecatetraene. Both isomers exhibit aluminium ± olefin p-bonding, with the Al 4 entities present in a tetrahedral arrangement. The bonding in both isomers is discussed on the basis of ab initio calculations performed for model compounds.
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