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The palladium(II) chloro methyl complexes bearing the bidentate 6-R-C 5 H 3 N-2-CH 2 SR′ (RN-SR′; R ) H, Me, Cl; R′ ) Me, t-Bu, Ph) and the potentially terdentate 2,6-(CH 2 SR′) 2 -C 5 H 3 N (S-N-S(R′); R′ ) Me, t-Bu, Ph) pyridylthioethers as ancillary ligands were synthesized, characterized, and reacted with substituted alkynes ZCtCZ (Z ) COOMe, Z′ ) COOt-Bu, Z′′ ) COOEt). The reactions were followed under second-order conditions by 1 H NMR technique, and the reaction rates were determined. The corresponding vinyl derivatives were synthesized, and in the case of the complexes [PdCl(ZCdCZMe)(MeN-SPh)] and [PdCl(ZCd CZMe)(C1N-St-Bu)] (Z ) COOMe) reaction rates for alkyne insertion yielding the corresponding butadienyl complexes were also determined. The rate of insertion of the second alkyne on the vinyl complex is more than 3 orders of magnitude lower than the first insertion rate in both the studied complexes, thereby allowing easy separation between vinyl and butadienyl derivatives and an easy preparation of mixed butadienyl esters. Furthermore, the reaction rates are strongly dependent on the steric and electronic features of the ancillary ligands. In particular, the distortion of the complex main coordination plane, induced by the substituent in position 6 of the pyridine ring, was found to significantly influence the substrate reactivity. The structures of the mono-inserted vinyl [PdCl(ZCdCZMe)(MeN-St-Bu)] (1) and the bis-inserted butadienyl [PdCl((ZCdCZ) 2 Me)(MeN-St-Bu)] (2) complexes were determined by X-ray diffraction, and the persistence of a structural distortion of the complex skeleton was observed. Moreover, the distortion may be related to facile ancillary ligand displacement, a feature that can be exploited for the synthesis of substrates that would not be easily obtained otherwise.

A series of new palladium allyl complexes bearing purine-based carbenes derived from caffeine, theophylline and theobromine have been prepared and characterized by NMR spectroscopy, and elemental analysis and in two cases by single crystal X-ray diffraction. The cytotoxic and proapoptotic activities of compounds have been determined in vitro on human ovarian cancer A2780 and SKOV-3 cell lines. These experiments have shown that the palladium-allyl fragment induces a general cytotoxicity, but the choice of the supporting ligands is of paramount importance for achieving the best results. In particular complexes 4c, 4d and 5d exhibit a higher antiproliferative effect (IC50: 0.09, 0.81 and 0.85 μM respectively) than cisplatin (IC50: 1.5 μM) on A2780 cells, and 4d (IC50: 1.7 μM vs. 5.94 μM) on SKOV-3 cell line. Moreover in many cases it has been proved that the cytotoxicity of our complexes is associated with the induction of apoptosis.

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