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

Abstract

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. Potassium is effective! Reduction of phenyl(silyl)ethynes with potassium gave dipotassium dibenzopentalenides in 35-89 % yield. The first dibenzopentalene- transition-metal complex was successfully synthesized and characterized. X-ray diffraction analysis revealed an unexpected coordination mode, in which the two ruthenium atoms are not coordinated by the five-membered rings, but rather by the six-membered rings (see scheme). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.