A new series of monoselenoquinone and diselenoquinone complexes, [((6)-p-cymene)Ru((4)-C6R4SeE)] (R=H, E=Se (6); R=CH3, E=Se (7); R=H, E=O (8)), as well as selenolate complexes [((6)-p-cymene)Ru((5)-C6H3R2Se)][SbF6] (R=H (9); R=CH3 (10)), stabilized by arene ruthenium moieties were prepared in good yields through nucleophilic substitution reactions from dichlorinated-arene and hydroxymonochlorinated-arene ruthenium complexes [((6)-p-cymene)Ru(C6R4XCl)]SbF6 (R=H, X=Cl (1); R=CH3, X=Cl (2); R=H, X=OH (3)) as well as the monochlorinated complexes [((6)-p-cymene)Ru((5)-C6H3R2Cl)]SbF6 (R=H (4); R=CH3 (5)). The X-ray crystallographic structures of two of the compounds, [((6)-p-cymene)Ru((4)-C6Me4Se2)] (7) and [((6)-p-cymene)Ru((4)-C6H4SeO)] (8), were determined. The structures confirm the identity of the target compounds and ascertain the coordination mode of these unprecedented ruthenium complexes of selenoquinones. Furthermore, these new compounds display relevant cytotoxic properties towards human ovarian cancer cells.