Planar Mobius aromatic pentalenes incorporating 16 and 18 valence electron osmiums

Aromaticity, a highly stabilizing feature of molecules with delocalized electrons in closed circuits, is generally restricted to 'Huckel' systems with 4n + 2 mobile electrons. Although the Mobius concept extends the principle of aromaticity to 4n mobile electron species, the rare known examples have complex, twisted topologies whose extension is unlikely. Here we report the realization of osmapentalenes, the first planar Mobius aromatic complexes with 16 and 18 valence electron transition metals. The Mobius aromaticity of these osmapentalenes, documented by X-ray structural, magnetic and theoretical analyses, demonstrates the basis of the aromaticity of the parent osmapentalynes. All these osmapentalenes are formed by both electrophilic and nucleophilic reactions of the in-plane pi component of the same carbyne carbon, illustrating ambiphilic carbyne reactivity, which is seldom observed in transition metal chemistry. Our results widen the scope of Mobius aromaticity dramatically and open prospects for the generalization of planar Mobius aromatic chemistry.