Highly cytotoxic trithiolato-bridged dinuclear Rh(III) and Ir(III) complexes

Water soluble trithiolato-bridged cationic complexes of the type [(η5-C5Me5)2M2(μ–SC6H4–p-X)3]+ (M = Rh, X = H, 1; CH3, 3; OCH3, 5; Pri, 7; But, 9; M = Ir, X = H, 2; CH3, 4; OCH3, 6; Pri, 8; But, 10) were synthesized and isolated as their chloride salts by reacting pentamethylcyclopentadienyl rhodium and iridium dimers [(η5-C5Me5)2M2(μ-Cl)2Cl2] in ethanol with the corresponding thiophenol. All complexes were isolated in good yields and were fully characterized including single-crystal X-ray structure analysis on representative complexes. The complexes were found to have IC50 values in the nanomolar range in human ovarian A2780 cancer cells, but did not display selectivity with respect to noncancerous human HEK293 embryonic kidney cells.