New half sandwich-type Ru(II) coordination compounds characterized by the fac-Ru(dmso-S)3 fragment: influence of the face-capping group on the chemical behavior and in vitro anticancer activity.

The Ru(II) complex fac-[RuCl(dmso-S)3(dmso-O)2][PF6] (P2) was found to be an excellent precursor for the facile preparation in high yield of half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)3(N)2][PF6] (e.g. (N)2 = 1,2-diaminoethane (en, 4), trans-1,2-diaminocyclohexane (dach, 5), or 2 NH3 (6)). Neutral half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)3(N–O)] where N–O is an anionic chelating ligand (e.g. N–O = picolinate (pic, 7)) are best prepared from the universal Ru(II)-dmso precursor cis-[RuCl2(dmso)4] (P1). These complexes, that were fully characterized in solution and in the solid state, are structurally similar to the anticancer organometallic compounds [Ru(h6-arene)(chel)Cl][PF6]n but, in place of a face-capping arene, have the fac-Ru(dmso-S)3 fragment. In contrast to what observed for the corresponding arene compounds, that rapidly hydrolyze the Cl ligand upon dissolution in water, compounds 4–6 are very stable and inert in aqueous solution. Probably their inertness is the reason why they showed no significant cytotoxicity against the MDA-MB-231 cancer cell line