Synthesis of Naphthoquinone-Fused Cyclobutadiene Ruthenium Complexes

A coordinatively unsaturated ruthenacycle, which was formed from Cp*RuCl(cod) and 1,2-bis(phenylpropiolyl)benzene, was isomerized to a new sandwich complex consisting of a Cp* and a naphthoquinone-fused cyclobutadiene ligand at ambient temperature. On the other hand, the treatment of the same ruthenacycle with excess AgBF4 at room temperature produced a tetramethylfulvene cyclobutadiene complex. In contrast, a cationic cyclobutadiene complex was formed from the isolated Cp*RuCl(cyclobutadiene) with excess AgBF4.