Platinum Diolefin Complexes – Synthesis, Structures, and Cytotoxicity

Abstract

AbstractThe synthesis, spectroscopy, structures and chemical reactivity of platinum(II) diolefin complexescis‐[(∥∧∥)PtCl2],cis‐[(∥∧∥)PtCl(R)] andcis‐[(∥∧∥)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 thecis‐[(∥∧∥)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]2undergoes 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]2with the very labile coligandsN‐methyl‐4,4′‐bipyridinium (MQ+) andN‐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.