Tetrakis(cyclopentadienyl)uranium(IV)
Tetrakisuranium, U4, abbreviated U4, is an organouranium compound composed of a uranium atom sandwiched between four cyclopentadienide rings.Tetrakisuranium was first prepared in 1962 by Ernst Otto Fischer, who reacted uranium tetrachloride with excess potassium cyclopentadienide in benzene and obtained the complex as red crystals at 6% yield:
Solid crystals of U4 are air-stable, but the benzene solution is extremely air-sensitive.
Reduction of U4 with uranium metal yields trisuranium, U3.
