An Unprecedented Type of Linear Metallocene with an f-Element

The dication [(C5Me5)2U(NCMe)5]2+ was obtained by dissolving (C5Me5)2UI2 in acetonitrile or by treating (C5Me5)2UMe2 with HNEt3BPh4 in acetonitrile. The crystal structure revealed that the cyclopentadienyl rings are parallel and equidistant to the plane defined by the metal center and nitrogen atoms of the five MeCN ligands. Fifty years after the discovery of ferrocene, this compound represents a unique example of linear metallocene with auxiliary ligands in the equatorial girdle; it is also the first linear sandwich complex of an f-element.