Ruthenocene 1,2-dicarboxylic acid, carboxylic anhydride, and acid chloride: A facile route to metallocene-fused acenequinones

The dehydration of 1′,2′,3′,4′,5′- pentamethylruthenocene-1,2-dicarboxylic acid with acetic anhydride gives 1′,2′,3′,4′,5′-pentamethylruthenocene-1, 2-dicarboxylic anhydride, the first crystallographically characterized, metallocene-fused carboxylic anhydride. Treatment of the diacid with oxalyl chloride/DMF produces its 1,2-diacyl chloride, which is an excellent precursor for AlCl₃-promoted double Friedel-Crafts acylation reactions with a variety of arenes, including benzene, toluene, o-xylene, p-dimethoxybenzene, and ferrocene. X-ray structural determinations of an acenequinone and a unique ferrocene/ruthenocene-fused benzoquinone show distortions attributed to strong electron donation from pentamethylruthenocene.