Phosphorescent PtIISystems Featuring Both 2,2′-Dipyridylamine and 1,3,5-Triazapentadiene Ligands

Equilibrium Studies on Pd(II)-Amine Complexes with Bio-Relevant Ligands in Reference to Their Antitumor Activity

This review article presents an overview of the equilibrium studies on Pd-amine complexes with bio-relevant ligands in reference to their antitumor activity. Pd(II) complexes with amines of different functional groups, were synthesized and characterized in many studies. The complex formation equilibria of Pd(amine)²⁺ complexes with amino acids, peptides, dicarboxylic acids and DNA constituents, were extensively investigated. Such systems may be considered as one of the models for the possible reactions occurring with antitumor drugs in biological systems. The stability of the formed complexes depends on the structural parameters of the amines and the bio-relevant ligands. The evaluated speciation curves can help to provide a pictorial presentation of the reactions in solutions of different pH values. The stability data of complexes with sulfur donor ligands compared with those of DNA constituents, can reveal information regarding the deactivation caused by sulfur donors. The formation equilibria of binuclear complexes of Pd(II) with DNA constituents was investigated to support the biological significance of this class of complexes. Most of the Pd(amine)²⁺ complexes investigated were studied in a low dielectric constant medium, resembling that of a biological medium. Investigations of the thermodynamic parameters reveal that the formation of the Pd(amine)²⁺ complex species is exothermic.

2,2'-Dipyridylamines: more than just sister members of the bipyridine family. Applications and achievements in homogeneous catalysis and photoluminescent materials

2,2'-Dipyridylamines (dpa) and related compounds belong to the family of polydentate nitrogen ligands. More than a century has passed since their first report but new complexes and applications have been emerging in recent years owing to the versatility of dpa-based architectures. This review aims to present and highlight the main achievements attained with dpa-containing metal complexes in the domains of homogeneous catalysis and luminescent materials.

Fluorinated triazapentadienyl ligand supported ethyl zinc(ii) complexes: reaction with dioxygen and catalytic applications in the Tishchenko reaction

Ethyl zinc complexes [N{(C3F7)C(Dipp)N}2]ZnEt, [N{(C3F7)C(Cy)N}2]ZnEt, [N{(CF3)C(2,4,6-Br3C6H2)N}2]ZnEt and [N{(C3F7)C(2,6-Cl2C6H3)N}2]ZnEt have been synthesized from the corresponding 1,3,5-triazapentadiene and diethyl zinc. X-ray data show that [N{(C3F7)C(Dipp)N}2]ZnEt has a distorted trigonal planar geometry at the zinc center. The triazapentadienyl ligand binds to zinc in a κ(2)-mode. The zinc-ethyl bonds of [N{(C3F7)C(Dipp)N}2]ZnEt, [N{(C3F7)C(Cy)N}2]ZnEt, [N{(CF3)C(2,4,6-Br3C6H2)N}2]ZnEt and [N{(C3F7)C(2,6-Cl2C6H3)N}2]ZnEt readily undergo oxygen insertion upon exposure to dry air to produce the corresponding zinc-ethoxy or zinc-ethylperoxy compounds. The ethoxy zinc adducts {[N{(CF3)C(2,4,6-Br3C6H2)N}2]ZnOEt}2 and {[N{(C3F7)C(2,6-Cl2C6H3)N}2]ZnOEt}2 as well as the ethylperoxy zinc adduct {[N{(C3F7)C(Cy)N}2]ZnOOEt}2 have been isolated and fully characterized by several methods including X-ray crystallography. They feature dinuclear structures with four-coordinate zinc sites and bridging-ethoxy or -ethylperoxy groups. The ethyl zinc complexes catalyze the Tishchenko reaction of benzaldehyde under solventless conditions affording benzyl benzoate. The reaction of ethyl zinc complexes with dioxygen and their catalytic behaviour in the Tishchenko reaction are affected by the electronic and steric factors of the triazapentadienyl ligand. {[N{(C3F7)C(Cy)N}2]ZnOOEt}2 is an excellent reagent for the epoxidation of trans-chalcone.

Bifunctional reactivity of amidoximes observed upon nucleophilic addition to metal-activated nitriles

Treatment of the aromatic nitrile complexes trans-[PtCl2(RC6H4CN)2] (R = p-CF3 NC1, H NC2, o-Cl NC3) with the aryl amidoximes p-R'C6H4C(NH2)=NOH (R' = Me AO1, H AO2, Br AO3, CF3 AO4, NO2 AO5) in all combinations, followed by addition of 1 equiv of AgOTf and then 5 equiv of Et3N, leads to the chelates [PtCl{HN=C(RC6H4)ON=C(C6H4R'-p)NC(RC6H4)═NH}] (1-15; 15 examples; yields 71-88% after column chromatography) derived from the platinum(II)-mediated coupling between metal-activated nitriles and amidoximes. The mechanism of this reaction was studied experimentally by trapping and identification of the reaction intermediates, and it was also investigated theoretically at the DFT level of theory. The combined experimental and theoretical results indicate that the coupling with the nitrile ligands involves both the HON and monodeprotonated NH2 groups of the amidoximes, whereas in the absence of the base, the NH2 functionality is inactive toward the coupling. The observed reaction represents the first example of bifunctional nucleophilic behavior of amidoximes. The complexes 1-16 were characterized by elemental analyses (C, H, N), high-resolution ESI(+)-MS, FTIR, and (1)H NMR techniques, whereas unstable 17 was characterized by HRESI(+)-MS and FTIR. In addition, 8·C4H8O2, 12, and 16·CHCl3 were studied by single-crystal X-ray diffraction.

Cyclic six-membered palladium complexes derived from palladium mediated C–N coupling of organonitrile and formamidine

Synthesis and structural characterizations of neutral, cationic and anionic six-membered palladium complexes obtained through palladium mediated C–N bond coupling between organonitrile and formamidinium salt are reported.