Fused Aromatic and Antiaromatic Smaragdyrin Dimers

Singly-linked aromatic [22]smaragdyrin BF₂ complex dimer was synthesized by the reductive coupling of 16-brominated [22]smaragdyrin BF₂ complex, which was oxidized to a stable diradical with PbO₂. As the first example of fused smaragdyrin dimer, a fused [22]smaragdyrin BF₂ complex dimer was synthesized by the oxidation of a CuCl-BF₂ complex dimer with FeCl₃ and subsequent reduction with NaBH₄. After removal of the BF₂ 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.