Facile synthesis of dibenzopentalene dianions and their application as new π-extended ligands.

Reduction of phenyl(silyl)ethynes with potassium followed by quenching with iodine gave dibenzopentalenes in moderate yields. The intermediates of the reactions, dipotassium dibenzopentalenides, were isolated. The first dibenzopentalene-transition-metal complex was successfully synthesized. The ruthenium atoms are located above the six-membered rings. However, X-ray diffraction analysis and theoretical calculations revealed that the aromatic nature of the five-membered rings was retained. The cyclic voltammetry of the Ru complex revealed two oxidation waves with relatively large separation.