Radical metallacyclopropene: synthesis, structure and aromaticity.

Metallaaromatics are an important class of aromatic compounds, showing diverse and interesting aromatic properties. Radical rhenabenzofurans 1-3 with a fused metallacyclopropene unit are reported, containing d Re centers. Computational studies show that the three-membered rhenacyclopropene ring is σ-aromatic, while the rhenafuran ring is nonaromatic. These complexes represent the first radical metallacyclopropenes. α-Metallabenzofuran complexes 4-5 with d Re centers and 6 with a d Re center are also synthesized. α-Metallabenzofurans 1-6 have adjacent oxidation states (Re(III), Re(IV), and Re(V)). Both the structure and aromatic nature of these metallacycles are affected by the change of oxidation states of the metal center.