Cyclopentadienyl Molybdenum(II) Compounds Bearing Ether and Thioether Functions in the Side Chain: Synthesis, Characterization, and Cytotoxic/Cytostatic Studies

A series of molybdenum(II) compounds [(η 5 ‐Cp’)Mo(CO) 2 (L 2 )][BF 4 ] (Cp’=C 5 H 4 (CH 2 ) 2 SPh, C 9 H 6 (CH 2 ) 2 OMe, L 2= N,N ‐chelating ligand) have been synthesized and characterized by spectroscopic and analytical methods including X‐ray crystallography. The in vitro assay on human leukemia cells MOLT‐4 has shown that the substitution in the π‐ligand in combination with suitable N,N ‐chelating ligand can lead to species with cytotoxicity considerably higher than reported to cisplatin. Unusually high activity was observed for compounds bearing phenanthroline ligands [{η 5 ‐C 9 H 6 (CH 2 ) 2 OMe}Mo(CO) 2 (3,4,7,8‐Me 4 phen)][BF 4 ] (IC 50 =0.7±0.3 μM) and [{η 5 ‐C 9 H 6 (CH 2 ) 2 OMe}Mo(CO) 2 (4,7‐Ph 2 phen)][BF 4 ] (IC 50 values 0.8±0.4 μM).