Complexes of Rhenium(V) with Aminoacetopehenones and their Reactions with some Bidentate Ligands

Complexes of rhenium(V) with 2-, 3- and 4-aminoacetophenone (H2aap) have been synthesized. The reaction of trans-ReOCl3(PPh3)2 with 2-H2aap in benzene yielded the imido complex [Re(2-aap)Cl3(PPh3)], in which the oxo oxygen and one of the PPh3 groups were substituted by the dianionic imido nitrogen and the neutral ketonic oxygen, respectively. With 3- and 4-H2aap the imido complexes trans-[Re(aap)Cl3(PPh3)2] were isolated. The monodentate coordination mode of these latter two ligands was authenticated by the X-ray crystal structure of trans-[Re(3-aap)Cl3(PPh3)2]; crystals are triclinic, P1, with a = 10.567(5), b = 11.989(6), c = 18.739(8) Å, α= 74.82(4)º, β= 75.27(4)º, γ= 73.15(4)º, U = 2152(2) Å3, Z = 2, R = 0.0469. The further reaction of [Re(3-aap)Cl3(PPh3)2] with the bidentate ligands 2-aminophenol and 8-hydroxyquinoline (HL) led to the isolation of complexes of the type [Re(3-aap)Cl2(PPh3)(L)]. However, with 1,2-diaminobenzene (H2dab), the 3-aap imido moiety was displaced by the imido group {N(C6H4)NH2}, to give the complex trans-[Re(dab)Cl3(PPh3)2]. (Bulletin of The Chemical Society of Ethiopia: 2002 16 (2): 149-156

Synthesis, Stability Constant Determination, and Structural Study of Some Complexes of a Zinc Triad Containing Pyridyl-amine-quinoline and Pyridyl-thio-quinoline

The potentially fluorescent and terdentate ligands containing nitrogen or sulfur as coordinating atom were synthesized and used in the formation of perchlorate or chloride complexes of the metals of the Zn triad. The reaction of the ligands with metal perchlorate salts yields the corresponding bis-chelate derivatives, whereas the same ligands react with metal chloride salts to give monochelate complexes. All of these complexes undergo NMR-scale fast fluxional rearrangement in solution. Some structural X-ray diffractometric studies were also performed and the ensuing data confirm the surmised structures and the solution rearrangement in the case of monochelate substrates and of one Hg derivative, respectively. The equilibrium constants of formation in the case of monochelate derivatives were also determined in water by means of spectrophotometric titration of the studied ligand with the metal ions. The values of the equilibrium constants were confirmed by supplementary determination taking into account the exchange between two different metals and/or dissociation equilibria. The fluorescence activity of ligands and complexes was eventually studied and notably one fluorescent silent ligand gives rise to fluorescent zinc derivatives

Insertion of Substituted Alkynes into the Pd-C Bond of Methyl and Vinyl Palladium(II) Complexes Bearing Pyridylthioethers as Ancillary Ligands. The Influence of Ligand Substituents at Pyridine and Sulphur on the Rate of Insertion

The palladium(II) chloro methyl complexes bearing the bidentate 6-R-C5H3N-2-CH2SR' (RN-SR'; R = H, Me, Cl; R' = Me, t-Bu, Ph) and the potentially terdentate 2,6-(CH2SR')(2)-C5H3N (S-N-S(R'); R'= Me, t-Bu, Ph) pyridylthioethers as ancillary ligands were synthesized, characterized, and reacted with substituted alkynes ZC equivalent to CZ (Z = COOMe, Z' = COOt-Bu, Z" = COOEt). The reactions were followed under second-order conditions by H-1 NMR technique, and the reaction rates were determined. The corresponding vinyl derivatives were synthesized, and in the case of the complexes [PdCl(ZC=CZMe)(MeN-SPh)] and [PdCl(ZC= 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(ZC CZMe)(MeN-St-Bu)] (1) and the bis-inserted butadienyl [PdCl((ZC=CZ)(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

Synthesis, characterization and biological activity of novel Cu(II) complexes of 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehy de-4N-substituted thiosemicarbazones

Three new 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde-thiosemicarbazones-N-4-substituted pro-ligands and their Cu(II) complexes (1, -NH2; 2, -NHMe; 3, -NHEt) have been prepared and characterized. In both the X-ray structures of 1 and 3, two crystallographically independent complex molecules were found that differ either in the nature of weakly metal-binding species (water in 1a and nitrate in 1b) or in the co-ligand (water in 3a and methanol in 3b). Electron Paramagnetic Resonance (EPR) measurements carried out on complexes 1 and 3 confirmed the presence of such different species in the solution. The electrochemical behavior of the pro-ligands and of the complexes was investigated, as well as their biological activity. Complexes 2 and 3 exhibited a high cytotoxicity against human tumor cells and 3D spheroids derived from solid tumors, related to the high cellular uptake. Complexes 2 and 3 also showed a high selectivity towards cancerous cell lines with respect to non-cancerous cell lines and were able to circumvent cisplatin resistance. Via the Transmission Electron Microscopy (TEM) imaging technique, preliminary insights into the biological activity of copper complexes were obtained

New carboalkoxybis(triphenylphosphine)palladium(II) cationic complexes: Synthesis, characterization, reactivity and role in the catalytic hydrocarboalkoxylation of ethene. X-ray structure of trans-[Pd(COOMe)(TsO)(PPh3)2]·2CHCl3

The cationic complexes trans-[Pd(COOR)(H2O)(PPh3)2](TsO) have been synthesised by reacting cis-[Pd(H2O)2(PPh3)2](TsO)2·2H2O with CO in ROH (R = Me and Et), practically under room conditions, or by methathetical exchange of trans-[Pd(COOMe)Cl(PPh3)2] with Ag(TsO) (R = n-Pr, iso-Pr, n-Bu, iso-Bu, sec-Bu). They have been characterised by IR, 1H NMR and 31P NMR spectroscopies. The X-ray investigation of trans-[Pd(COOMe)(TsO)(PPh3)2] reveals that the palladium center is surrounded in a virtually square planar environment realized by two PPh3 trans to each other, the carbon atom of the carbomethoxy ligand and an oxygen atom of the p-toluensulfonate anion, with two crystallization molecules of CHCl3. The Pd–O–S angle, 151.9 (3)°, is very wide, probably due to the interaction of one CHCl3 molecule with the complex inner core. The carbomethoxy derivatives react with R′OH yielding the corresponding R′ carboalkoxy derivative (R′ = Et, n-Pr and iso-Pr); ethene does not insert into the Pd–COOMe bond; decarbomethoxylation occurs when treated with TsOH/H2O in MeOH at 50 °C. All the carboalkoxy are precursors for the catalytic carboalkoxylation of ethene if used in combination of PPh3 and TsOH, better in the presence of some water. Experimental evidences are more in favor of the so-called “hydride” mechanism rather than the “carbomethoxy” mechanism

Nitrido technetium-99m core in radiopharmaceutical applications: Four decades of research

The knowledge on element 43 (Tc) of the periodic table, built over the years through the contributions given by the close relationship between chemistry and nuclear medicine, allowed the development of new and increasingly effective radiopharmaceuticals useful both as perfusion and target specific imaging agents for SPECT (single photon emission tomography). Among the manifold Tc-compounds, Tc(V) nitrido complexes played a relevant role in the search for new technetium-99m radiopharmaceuticals, providing effcient labeling procedures that can be conveniently exploited for the design and synthesis of agents, also incorporating small organic molecules or peptides having defined structural features. With this work, we present an overview of four decades of research on the chemistry and on the nuclear medicine applications of Tc(V) nitrido complexes