Caught in the act: The first stable η4-diseleno-p-benzoquinone complex, [Cp*lr(η4-C6H4Se2)], has been isolated. The X-ray structure confirms the coordination of the elusive diselenobenzoquinone intermediate. The anticancer activity of this complex was compared to related oxygen and sulfur analogs; only the diseleno complex was cytotoxic, having a comparable activity to cisplatin.