Cyclopentadienone-like Behavior of Fluorenone and 4,5-Diazafluoren-9-one

Abstract

The aromatic compounds fluorenone ( 1 ) and 4,5-diazafluoren-9-one ( 2 ) behave like cyclopentadienones in their reaction with [Cp*Co(C 2 H 4 ) 2 ] ( 3a ), affording the sandwich-type complexes [Cp*Co(η 4 - 1 )] ( 4 ) and [Cp*Co(η 4 - 2 )] ( 5 ), respectively, whose structures have been determined by X-ray diffraction. Both complexes show double-bond fixation in their η 2 -coordinated six-membered rings and belong to a new structure type of mononuclear organometallics. The cobalt-coordinated ligands 1 and 2 present in 4 and 5, 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.