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

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 −20 °C 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 E1/2 −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.