Synthesis and cytotoxicity against tumor cells of pincer N-heterocyclic ligands and their transition metal complexes

The complexes: [CoL₂](ClO₄)₂ (1), [FeL₂](ClO₄)₂ (2), [NiL₂](ClO₄)₂ (3) and [MnLCl₂] (4), with L = diethyl-1,1′-(pyridine-2,6-diyl)bis(5-methyl-1H-pyrazole-3-carboxylate), were synthesized and fully characterized. Structural analysis revealed two distinct patterns influenced by the counter ions where L acts as a tridentate chelating ligand. The in vitro antitumor activity of L and L′ (diethyl 2,2′-(pyridine-2,6-diylbis(5-methyl-1H-pyrazole-3,1-diyl)) diacetate) as well as their metal complexes, was tested by the measurement of their cytostatic and cytotoxic properties towards the blood cancer mastocytoma cell line P815. We have also investigated their interactions with the antioxidant enzyme system. As a result, [MnL′Cl₂] (1′) exhibited the strongest activity compared to reference cis-platin with no cytotoxicity towards normal cells PBMCs (Peripheral Blood Mononuclear Cells). On the other hand, the antioxidant enzyme activity showed that the efficiency of metal complex 1′ against P815 tumor cells was via the rise in the SOD activity and inhibition of CAT enzyme activity. This proof of concept study allows disclosure of a new class of molecules in cancer therapeutics.

The complexes: [CoL₂](ClO₄)₂ (1), [FeL₂](ClO₄)₂ (2), [NiL₂](ClO₄)₂ (3) and [MnLCl₂] (4), with L = diethyl-1,1′-(pyridine-2,6-diyl)bis(5-methyl-1H-pyrazole-3-carboxylate), were synthesized and fully characterized.

N3-Ligated nickel(ii) diketonate complexes: synthesis, characterization and evaluation of O2 reactivity

Interest in O2-dependent aliphatic carbon-carbon (C-C) bond cleavage reactions of first row divalent metal diketonate complexes stems from the desire to further understand the reaction pathways of enzymes such as DKE1 and to extract information to develop applications in organic synthesis. A recent report of O2-dependent aliphatic C-C bond cleavage at ambient temperature in Ni(ii) diketonate complexes supported by a tridentate nitrogen donor ligand [(MBBP)Ni(PhC(O)CHC(O)Ph)]Cl (7-Cl; MBBP = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine) in the presence of NEt3 spurred our interest in further examining the chemistry of such complexes. A series of new TERPY-ligated Ni(ii) diketonate complexes of the general formula [(TERPY)Ni(R2-1,3-diketonate)]ClO4 (1: R = CH3; 2: R = C(CH3)3; 3: R = Ph) was prepared under air and characterized using single crystal X-ray crystallography, elemental analysis, 1H NMR, ESI-MS, FTIR, and UV-vis. Analysis of the reaction mixtures in which these complexes were generated using 1H NMR and ESI-MS revealed the presence of both the desired diketonate complex and the bis-TERPY derivative [(TERPY)2Ni](ClO4)2 (4). Through selective crystallization 1-3 were isolated in analytically pure form. Analysis of reaction mixtures leading to the formation of the MBBP analogs [(MBBP)Ni(R2-1,3-diketonate)]X (X = ClO4: 5: R = CH3; 6: R = C(CH3)3; 7-ClO4: R = Ph; X = Cl: 7-Cl: R = Ph) using 1H NMR and ESI-MS revealed the presence of [(MBBP)2Ni](ClO4)2 (8). Analysis of aerobic acetonitrile solutions of analytically pure 1-3, 5 and 6 containing NEt3 and in some cases H2O using 1H NMR and UV-vis revealed evidence for the formation of additional bis-ligand complexes (4 and 8) but suggested no oxidative diketonate cleavage reactivity. Analysis of the organic products generated from 3, 7-ClO4 and 7-Cl revealed unaltered dibenzoylmethane. Our results therefore indicate that N3-ligated Ni(ii) complexes of unsubstituted diketonate ligands do not exhibit O2-dependent aliphatic C-C bond clevage at room temperature, including in the presence of NEt3 and/or H2O.

Bis(2,2′:6′,2′′-terpyridine-κ3N,N′,N′′)nickel(II) bis(perchlorate) hemihydrate

In the title compound, [Ni(C15H11N3)2](ClO4)2·0.5H2O, the Ni2+cation is coordinated by two terpyridine ligands to form a discrete complex and the coordination polyhedron can be described as a slightly distorted octahedron. It crystallizes as a hemihydrate with two perchlorate anions to compensate the charges. In the crystal, one of the two crystallographically independent perchlorate anions is involved in O—H...O hydrogen bonding to the water molecules, where two inversion-related water molecules link two inversion-related perchlorate anions into a ring with anR42(12) loop. The O-atom position of the water molecule is only half occupied,i.e.only half of the anions are involved in hydrogen bonding. A similar arrangement of two anions is also observed for the second crystallographically independent perchlorate anion but no water molecules are located between the anions. The cationic complex and the perchlorate anions are additionally linked by a number of weak C—H...O hydrogen bonds, forming a three-dimensional supramolecular structure. The crystal structure of the monohydrate of the same complex has been reported [Bakeret al.(1995).Aust. J. Chem.48, 1373–1378].

Homoleptic nickel(II) complexes of redox-tunable pincer-type ligands

Different synthetic methods have been developed to prepare eight new redox-active pincer-type ligands, H(X,Y), that have pyrazol-1-yl flanking donors attached to an ortho-position of each ring of a diarylamine anchor and that have different groups, X and Y, at the para-aryl positions. Together with four previously known H(X,Y) ligands, a series of 12 Ni(X,Y)2 complexes were prepared in high yields by a simple one-pot reaction. Six of the 12 derivatives were characterized by single-crystal X-ray diffraction, which showed tetragonally distorted hexacoordinate nickel(II) centers. The nickel(II) complexes exhibit two quasi-reversible one-electron oxidation waves in their cyclic voltammograms, with half-wave potentials that varied over a remarkable 700 mV range with the average of the Hammett σ(p) parameters of the para-aryl X, Y groups. The one- and two-electron oxidized derivatives [Ni(Me,Me)2](BF4)n (n = 1, 2) were prepared synthetically, were characterized by X-band EPR, electronic spectroscopy, and single-crystal X-ray diffraction (for n = 2), and were studied computationally by DFT methods. The dioxidized complex, [Ni(Me,Me)2](BF4)2, is an S = 2 species, with nickel(II) bound to two ligand radicals. The mono-oxidized complex [Ni(Me,Me)2](BF4), prepared by comproportionation, is best described as nickel(II) with one ligand centered radical. Neither the mono- nor the dioxidized derivative shows any substantial electronic coupling between the metal and their bound ligand radicals because of the orthogonal nature of their magnetic orbitals. On the other hand, weak electronic communication occurs between ligands in the mono-oxidized complex as evident from the intervalence charge transfer (IVCT) transition found in the near-IR absorption spectrum. Band shape analysis of the IVCT transition allowed comparisons of the strength of the electronic interaction with that in the related, previously known, Robin-Day class II mixed valence complex, [Ga(Me,Me)2](2+).

catena-Poly[[(2,2':6',2''-terpyridine-κN,N',N'')(tricyano-methanido-κN)nickel(II)]-μ-tricyano-methanido]

In the title complex, [Ni(C₄N₃)₂(C₁₅H₁₁N₃)]_n, each of the two different Ni^II atoms is coordinated by one 2,2′:6′2′′-terpyridine (terpy) and three tricyano­methanide ligands in a distorted octa­hedral geometry. The Ni^II atoms are linked to each other, forming an infinite chain parallel to (10). π–π Stacking inter­actions of terpy mol­ecules between adjacent chains (centroid–centroid distance = 3.785 Å), along with weak inter­molecular C—H⋯N hydrogen bonds involving the uncoordinated terminal N atoms of the tricyanomethanide ions and the terpyridine H atoms, result in the formation of a three-dimensional network structure.