Treatment of bis(iminophosphorane)phosphane ligands 2a–2e with Li2PdCl4 gave a set of novel diphosphane-derived complexes bearing two metallacycle rings, each one enclosing a P=N double bond: the unprecedented bis(iminophosphorane)phosphane-[C,N,S] palladacycles. In the case of the ligand derived from bis(diphenylphosphino)methane, 2a, both the single and the double palladacycle complexes were obtained. Reaction of 3a with bis(diphenylphosphino)ethane did not yield the expected product with the diphosphane bonded to both palladium atoms, but rather the novel coordination compound 5. The crystal structures of 3c and 5 are described.
A theoretical and experimental study of tetradentate [C,N : C,N] iminophosphorane palladacycles was carried out for the purpose of elucidating their behavior as compared to the parent Schiff base analogues to determine the prospect of encountering new A-frame structures for the iminophosphor-ane derivatives. The DFT calculations were in agreement with the experimental results regarding the performance of these ligands. New insights into the chemistry of the related dinuclear species have been obtained.
Cyclometallated compounds have been extensively studied, in particular those with palladium and platinum. This is because of their possible applications in medicinal chemistry, as anticancer or antimicrobial agents; in some cases, with similar results as cisplatin, carboplatin or oxaliplatin. What is also remarkable is their use as homogeneous catalysts, for example, in cross coupling reactions such as Suzuki–Miyaura or Mizoroki–Heck. Herein, we report the synthesis of different thiosemicarbazone ligands, which will be reacted with a palladium or platinum salt, to give the corresponding cyclometallated compounds; in addition, their reactivity with bis(diphenylphosphino)methane (dppm) will be studied. Characterization has been carried out by elemental analysis, IR spectroscopy, 1H and 31P NMR spectroscopy. Additionally, 1c has been studied by X-ray diffraction.
Since the appearance of the term palladacycle, as coined by Trofimenko[1], one of the most salient groups is the one comprising thiosemicarbazones. Herein, the synthesis and characterization of several palladium cyclometallated compounds with thiosemicarbazone ligands is discussed. The ligands were synthesized by treatment of a ketone with four different thiosemicarbazides in acidified aqueous solution. Then, they were conveniently treated with a palladium salt to yield the corresponding palladacycle. All show a tetranuclear structure with [C, N, S] coordination of the ligands to the metal centers.
Herein we report on the synthesis and characterization of bisiminophosphoranes as potential tetradentate ligands. Treatment of the latter with palladium acetate gives tetranuclear structures with two ligand moieties linked by acetate-bridging ligands. The addition of ddpm (4 equivalents) provides doubly metallated structures where the phosphine acts as a bidentate chelating ligand.
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