Fused Aromatic and Antiaromatic Smaragdyrin Dimers.

Singly-linked aromatic [22]smaragdyrin BF 2 complex dimer was synthesized by the reductive coupling of 16-brominated [22]smaragdyrin BF 2 complex, which was oxidized to a stable diradical with PbO 2 . As the first example of fused smaragdyrin dimer, a fused [22]smaragdyrin BF 2 complex dimer was synthesized by the oxidation of a CuCl-BF 2 complex dimer with FeCl 3 and subsequent reduction with NaBH 4 . After removal of the BF 2 group, the singly-linked and fused aromatic dimers were oxidized to the corresponding antiaromatic [20]smaragdyrin free base dimers. The first oxidation and reduction potentials of these dimers are split depending upon the intramolecular electronic interactions, which are larger for the fused dimers. Despite the large electronic interactions, the aromatic and antiaromatic characters are well preserved in the fused dimers.