A New Family of Doubly Cyclopalladated Diimines. A Remarkable Effect of the Linker between the Metalated Units on Their Cytotoxicity

The cyclopalladation of a series
of symmetric diimines with the
formula (RC6H4CHNZ)2, where
Z = CH2 or (CH2)2OCH2 and
R = p-Cl, p-OMe, p-NO2, and o-Cl, is described. Optimal
conditions to obtain the dimetalated compounds were found to be palladium­(II)
acetate, in toluene, at 60 °C and with a reaction time of 2–4
h. The reactivity of the dimetalated compounds with monodentate, bidentate,
and bis­(monodentate) Lewis bases was also studied. The cytotoxic activity
of some selected compounds was evaluated against a panel of adenocarcinoma
cell lines (colon HCT116 and breast MCF7 and MDA-MB231). Compounds
containing the fragment NCH2CH2OCH2­CH2OCH2CH2N exhibited a remarkable
cytotoxic activity in the three cancer cells assayed, but complexes
containing the NCH2CH2N fragment showed no activity.
It seems that the length and flexibility of the central saturated
chain in the imine molecule, as well as its lipophilicity and hydrophilicity,
explain the different cytotoxicity of the two series of coordination
compounds here reported.