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The synthesis, spectroscopy, structures and chemical reactivity of platinum(II) diolefin complexes cis‐[(∥∧∥)PtCl2], cis‐[(∥∧∥)PtCl(R)] and cis‐[(∥∧∥)Pt(R)2] [∥∧∥ = chelate diolefin ligand: 1,5‐cyclooctadiene (COD), 1,5‐dimethylocta‐1,5‐diene (Me2COD), norbornadiene (NBD), 1,5‐hexadiene (HEX), 3‐allyloxypropene (All2O, diallyl ether), diallylamine (All2NH); R = Me, Bn, C6F5, C6F4H‐4 (or ‐5), or C≡C(4‐Me)Ph] have been explored. The relative exchange rates of the cis‐[(∥∧∥)PtCl2] complexes towards the diimine ligand diisopropyl‐1,4‐diazabutadiene (iPr‐DAB) increased along the series COD < Me2COD < NBD < HEX < All2O by a factor of 4. The presumably dimeric complex [(All2NH)PtCl2]2 undergoes a unique rearrangement process in dimethyl sulfoxide (DMSO) solution to yield the dimeric piperazine complex [PtCl(dmso)(C6H10N)]2, which has been characterised by single‐crystal XRD. For selected platinum complexes, cytotoxic effects in HT‐29 colon carcinoma and MCF‐7 breast cancer cell lines were evaluated. For comparison, the dicationic complexes [(COD)Pt(Bn)(L)][PF6]2 with the very labile coligands N‐methyl‐4,4′‐bipyridinium (MQ+) and N‐methyl‐1,4‐pyrazinium (Mpz+) were added to the study. Although the hexadiene complexes [(HEX)Pt(C6F4H‐4)2] and [(HEX)Pt(C6F4H‐5)2] show strong cytotoxicity, the introduction of labile diolefin ligands or the labile cationic MQ+ or Mpz+ coligands does not generally lead to markedly increased cytotoxicity.

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The reaction of HSC6F4H‐4 or KSC6F4H‐4 with the palladium(II) complexes [(NN)PdCl2] [NN = 2,2′‐bipyridine (bpy) or 1,10‐phenanthroline (phen)] leads to the mononuclear palladium complexes [(NN)Pd(SC6F4H‐4)2] or [(NN)PdCl(SC6F4H‐4)], whereas the reaction with [(COD)PdCl2] (COD = 1,5‐cyclooctadiene) results in the loss of COD and the formation of the oligonuclear species [Pd(SC6F4H‐4)2]m. For NN = phen, the compound [(phen)2K(μ‐phen)2K(phen)2][(4‐HC6F4S)2Pd(μ‐SC6F4H‐4)2Pd(SC6F4H‐4)2] containing a homoleptic dimeric dianionic Pd complex was also obtained. The reaction of KSC6F4H‐4 with PdCl2 yielded K2[Pd(SC6F4H‐4)4]. The new compounds were analysed and characterised by single‐crystal XRD, 1H and 19F NMR spectroscopy and IR spectroscopy. The UV/Vis absorption spectroscopy and electrochemistry of [(bpy)Pd(SC6F4H‐4)2] have been investigated and are compared to those of the related Pt derivative [(bpy)Pt(SC6F5)2].

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