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Facile Benzene Reduction by a Ca2+ /AlI Lewis Acid/Base Combination
Steffen Brand1, Holger Elsen1, Jens Langer1
1Chair of Inorganic and Organometallic Chemistry, Universität Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany.
Abstract:
Attempted synthesis of the donor-acceptor complex (BDI)Ca+ ←AlI (BDI) complex by reaction of (BDI)Ca+ in the form of its B(C6 F5 )4 - salt with (BDI)AlI in benzene led to dearomatization of the solvent and formation of (BDI)Ca+ (C6 H6 )AlIII (BDI) (BDI=CH[C(CH3 )N-Dipp]2 , Dipp=2,6-diisopropylphenyl). The C6 H6 2- anion is strongly puckered and its boat form features four long (ca. 1.50 Å) and two short (ca. 1.34 Å) C-C bond distances. The flagpole positions of the C6 H6 2- anion chelate an AlIII cation giving a norbornadiene-like fragment with Al in the 7-position. The C=C double bonds of this alumina-norbornadiene strongly coordinate to the Ca2+ metal ion. The complex is stable in solution up to 80 °C. Several mechanisms for its formation are discussed including a highly likely frustrated Lewis pair type mechanism in which benzene is activated by the Lewis acid (BDI)Ca+ followed by nucleophilic attack by the Lewis base (BDI)AlI .
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