Synthesis, structure, and cyclic voltammetry of 4,6-bis(dimesitylboryl)dibenzofuran: Isolation of 4,6-dilithiobenzofuran and 4,5-dilithio-9,9-dimethylxanthene as tmeda adducts
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abstract
The reaction of dibenzofuran and 9,9-dimethylxanthene with sec-BuLi and n-BuLi, respectively, in the presence of N,N,N,N- tetramethylethylenediamine (tmeda) in hexane followed by storage at -20C results in the precipitation of 4,6-dilithiodibenzofuran-1.5-(tmeda) (1) and 4,5-dilithio-9,9-dimethylxanthene-1.5(tmeda) (2). Both of these adducts form tetranuclear dimers with the lithium atoms bridging the deprotonated aromatic ligands. The reaction of 1 with dimesitylboronfluoride affords 4,6-bis(dimesitylboryl)dibenzofuran (3), which has been fully characterized. Cyclic voltammetry of compound 3 shows two reduction waves at E 1/2 -2.45 and -2.81 V (vs Fc/Fc +), which substantiates significant electronic coupling of the two boron centers. Computational studies show that the p-orbital of the two boron centers participates equally to the LUMO, thus providing grounds for the observed electronic coupling. 2005 American Chemical Society.
