The molybdenum tetraphenylcyclopentadienone complex (C5Ph4O)­Mo­(CO)3­(CH3CN) 1a is an effective precatalyst for the transfer hydrogenation of aldehydes, allylic alcohols, ketones, and imines under mild conditions with either 2-propanol or formic acid as reducing reagent. Mechanistic studies suggest that these molybdenum cyclopentadienone complexes can be reduced to the corresponding hydroxycyclopentadienyl Mo hydrides. These complexes, by virtue of the hydroxyl group on the cyclopentadienyl ligand, are more reactive and chemoselective than the analogous cyclopentadienyl molybdenum complexes for the reduction of ketones, aldehydes, and imines.

Pentamethylcyclopentadienyl (Cp*) iridium-(III) chloride catalyzed acceptorless dehydrogenation of αtetralone is reported. Cp* iridium chloride showed higher activity in comparison to other Cp* iridium complexes having bromide, iodide, or hydride or complexes without a Cp ring. The desired product, naphthol, was obtained in up to 71% yield from α-tetralone. The dehydrogenation by Cp* iridium catalyst could be applied to not only α-tetralone but also dihydrocoumarin, dihydroquinolinone, dimethylcyclohexanone, dihydrobenzofuran and 1-isochromanone, although the conversion stayed moderate. The catalytic turnover was not limited by the increased concentration of the product but by catalyst decomposition.

The reaction of tetraphenylcyclopentadienone with Co2­(CO)8 generates the mixed-valence tricobalt complex [Ph4C4­CO]­Co­(CO)2]2­[μ-Co­(MeCN)2]. In contrast to the conventional Pauson–Khand reaction to generate cyclopentadienone-ligated cobalt complexes, this method benefits from both mild reaction conditions and high yields. Treatment of this tricobalt complex with proton sources such as water or alcohols yields the monomeric hydroxytetraphenylcyclopentadienyl cobalt complex [Ph4­Cp­OH]­Co­(CO)2. Phosphite substituted monomeric cobalt complexes [Ph4­CpOH]­Co­(CO)­[P­(OR)3] were also synthesized, and protonation of these complexes transiently formed cobalt hydride species.