10.1021/om030615f.s001 Ulrich Siemeling Ulrich Siemeling Imke Scheppelmann Imke Scheppelmann Beate Neumann Beate Neumann Hans-Georg Stammler Hans-Georg Stammler Wolfgang W. Schoeller Wolfgang W. Schoeller Cyclopentadienone-like Behavior of Fluorenone and 4,5-Diazafluoren-9-one American Chemical Society 2004 carbon monoxide complex compounds fluorenone η 2 cobaltocenium species Cp structure type acetyl chloride 2004-02-16 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Cyclopentadienone_like_Behavior_of_Fluorenone_and_4_5_Diazafluoren_9_one/3349933 The aromatic compounds fluorenone (<b>1</b>) and 4,5-diazafluoren-9-one (<b>2</b>) behave like cyclopentadienones in their reaction with [Cp*Co(C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>] (<b>3a</b>), affording the sandwich-type complexes [Cp*Co(η<sup>4</sup>-<b>1</b>)] (<b>4</b>) and [Cp*Co(η<sup>4</sup>-<b>2</b>)] (<b>5</b>), respectively, whose structures have been determined by X-ray diffraction. Both complexes show double-bond fixation in their η<sup>2</sup>-coordinated six-membered rings and belong to a new structure type of mononuclear organometallics. The cobalt-coordinated ligands <b>1</b> and <b>2</b> present in <b>4</b> and <b>5</b>, respectively, may be replaced by two molecules of carbon monoxide. In accord with their cyclopentadienone-like nature, they are nucleophilic and undergo O-acylation with acetyl chloride, affording cobaltocenium species.