Treatment of an areneruthenium dichloride dimer with thiols RSH to lead to cationic trithiolato complexes of the type [(arene)2Ru2(SR)3]+ was shown to proceed through the neutral thiolato complexes [(arene)2Ru2(SR)2Cl2], which have been isolated and characterized for arene = p-MeC6H4iPr and R = CH2Ph (1), CH2CH2Ph (2), CH2C6H4-p-tBu (3), and C6H11 (4). The single-crystal X-ray structure analysis of the p-tert-butylbenzyl derivative 3 reveals that the two ruthenium atoms are bridged by the two thiolato ligands without a metalmetal bond. The neutral dithiolato complexes[(arene)2Ru2(SR)2Cl2] (13) are intermediates in the formation of the cationic trithiolato complexes [(arene)2Ru2(SR)3]+ (57). Of the new [(arene)2Ru2(SR)2Cl2] complexes, derivative 2 is highly cytotoxic against human ovarian cancer cells, with IC50 values of 0.20 mu M for the A2780 cell line and 0.31 for the cisplatin-resistant cell line A2780cisR.