Ten complexes of general formula [Ru(η⁶-arene)Cl₂(L)], [Ru(η⁶-arene)Cl(L)₂][X], and [Ru(η⁶-arene)(L)₃][X]₂ (η⁶-arene = benzene, p-cymene; L = imidazole, benzimidazole, N-methylimidazole, N-butylimidazole, N-vinylimidazole, N-benzoylimidazole; X = Cl, BF₄, BPh₄) have been prepd. and characterized by spectroscopy. The structures of five representative compds. have been established in the solid state by single-crystal X-ray diffraction. All the new compds. were assessed by the same in vitro screening assays applied to [imidazole-H][trans-RuCl₄(DMSO)(imidazole)] (NAMI-A) and [Ru(η⁶-arene)Cl₂(1,3,5-triaza-7-phosphaadamantane)] (RAPTA) compds. It was found that the new compds. show essentially the same order of cytotoxicity as the RAPTA compds. toward cancer cells. Several of the compds. were selective toward cancer cells in that they were less (or not) cytotoxic toward nontumorigenic cells that are used to model healthy human cells. Thus, two of the compds., [Ru(η⁶-p-cymene)Cl(vinylimid)₂][Cl] (vinylimid = N-vinylimidazole) and [Ru(η⁶-benzene)(mimid)₃][BF₄]₂ (mimid = N-methylimidazole), have been selected for a more detailed in vivo evaluation.