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The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1H-pyrazol-1-yl)methyl)pentane-2,4-dione (HLacPz) and 3-((3,5-dimethyl-1H-pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HLacPzMe), were synthesized and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae [Cu(HLacX)2(LacX)2] and [Cu(PPh3)2(HLacX)]PF6 (X = Pz (pyrazole) or PzMe (3,5-dimethylpyrazole)), respectively. In the syntheses of the Cu(I) complexes, the triphenylphosphine coligand (PPh3) was used to stabilize copper in the +1 oxidation state, avoiding oxidation to Cu(II). All compounds were characterized by CHN analysis, 1H-NMR, 13C-NMR, FT-IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The ligands HLacPz (1) and HLacPzMe (2) and the copper complex [Cu(PPh3)2(HLacPz)]PF6 (3) were also characterized by X-ray crystallography. The reactivity of these new compounds was investigated and the new compounds 4-phenyl-4-(1H-pyrazol-1-yl)butan-2-one (7) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-4-phenylbutan-2-one (8) were obtained in basic conditions via the retro-Claisen reaction of related 3-monosubstituted acetylacetone, providing efficient access to synthetically useful ketone compounds. Compound 8 was also characterized by X-ray crystallography.

A new dimeric copper(II) bromide complex, [Cu(LOHex)Br(μ-Br)]2 (1), was prepared by a reaction of CuBr2 with the hexyl bis(pyrazol-1-yl)acetate ligand (LOHex) in acetonitrile solution and fully characterized in the solid state and in solution. The crystal structure of 1 was also determined: the complex is interlinked by two bridging bromide ligands and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the Cu coordination sphere, resulting in a five-coordinated geometry—away from idealized trigonal bipyramidal and square pyramidal geometries—which can better be described as distorted square pyramidal, as measured by the τ and χ structural parameters. The pendant hexyloxy chain is disordered over two arrangements, with final site occupancies refined to 0.705 and 0.295. The newly synthesized complex was evaluated as a catalyst in copper-catalyzed C–H oxidation for allylic functionalization through a Kharasch–Sosnovsky reaction without any external reducing agent. Using 0.5 mol% of this catalyst, and tert-butyl peroxybenzoate (Luperox) as an oxidant, allylic benzoates were obtained with up to 90% yield. The general reaction time was only slightly decreased to 24 h but a very significant decrease in the alkene:Luperox ratio to 3:1 was achieved. These factors show relevant improvements with respect to classical Kharasch–Sosnovsky reactions in terms of rate and amount of reagents. The present study highlights the potential of copper(II) complexes containing functionalized bis(pyrazol-1-yl)acetate ligands as efficient catalysts for allylic oxidations.

In the previously reported [C2O4(SnPh3)2] complex [Diop et al. (2003). Appl. Organomet. Chem. 17, 881–882.], the SnIV atoms are able to formally complete their coordination by addition of dimethyl sulfoxide (DMSO) molecules provided by the reaction medium, affording the title complex, [Sn2(C6H5)6(C2O4)(C2H6OS)2]. The SnIV atoms are then pentacoordinated, with a common trans trigonal–bipyramidal arrangement. The asymmetric unit contains one half-molecule, which is completed by inversion symmetry in space group type C2/c. The inversion centre is placed at the mid-point of the central bis-monodentate oxalate dianion, C2O42−, which bridges the [(SnPh3)(DMSO)] moieties. The molecule crystallizes as a disordered system, with two phenyl rings disordered by rotation about their Sn—C bonds, while the DMSO molecule is split over two positions due to a tetrahedral inversion at the S atom. All disordered parts were refined with occupancies fixed of 0.5.

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.

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 efficient 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.

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)°, β = 75.27(4)°, γ= 73.15(4)°, 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].

The monooxo Re(V) core is conveniently stabilized by tripodal scorpionate ligands comprising carboxylate or sulfonate tails, giving a series of intermediate complexes of the type Re(O)(NNO)Cl(X) (X=Cl), whose structure depends on the type of NNO ligand and solvent utilized. The presence of 3,5-substituted pz in the NNO framework is crucial for further replacement of monodentate groups giving stable '3+2' mixed ligand groups.

A series of six-coordinate mono- and dioxo complexes is produced from ligand-exchange reactions of the bidentate hybrid ligand (o-hydroxyphenyl)diphenylphosphine, POH, onto labile pentavalent rhenium precursors. The mono-substituted (ReOCl3(PO))- was found to be the key intermediate for the syntheses of three more types of bis-substituted compounds. Two of these, the anionic dioxo (ReO2(PO)2)- and neutral monooxo mixed-ligand (ReOX(PO)(PNH)) complexes, are two uncommon examples of coordination around the metal center.