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We have recently reported a series of half-sandwich ruthenium(II) complexes with curcuminoid ligands showing excellent cytotoxic activities (particularly ionic derivatives containing PTA (PTA = 1,3,5-triaza-7-phosphaadamantane). In the present study, new members of this family of compounds have been prepared with the objective to investigate the effect of a long hydrophobic chain obtained by replacing the OH-groups, present in curcumin and bisdemethoxycurcumin, with the palmitic acid ester. We report the synthesis of ruthenium(II) and osmium(II) p-cymene derivatives containing palmitic acid curcumin ester ligands ((1E,3Z,6E)-3-hydroxy-5-oxohepta-1,3,6-triene-1,7-diyl)bis(2-methoxy-4,1-phenylene)dipalmitate (p-curcH) and ((1E,3Z,6E)-3-hydroxy-5-oxohepta-1,3,6-triene-1,7-diyl)bis(4,1-phenylene)dipalmitate (p-bdcurcH). Complexes [M(II)(cym)(p-curc)/(p-bdcurc)(Cl)] 1–4 (M = Ru or Os) are neutral, whereas [M(II)(cym)(p-curc)/(p-bdcurc)(PTA)][SO3CF3] 5–8 are salts obtained when the chloride ligand is replaced by the PTA ligand. Stability studies performed on 1–8 in DMSO-PBS under physiological conditions (pH = 7.4) indicate that the complexes remain intact. The complexes exhibit potent and selective cytotoxic activity against an ovarian carcinoma cell line and its cisplatin-resistant form (A2780 and A2780cis), and non-cancerous human embryonic kidney (HEK293T) cells. To define the structure–activity relationships (SAR), the compounds have been compared with other Ru(II) and Os(II) complexes with curcuminoid ligands previously reported. SAR data reveal that the bisdemethoxycurcumin complexes are generally more active and selective than analogous curcumin-containing complexes. [ABSTRACT FROM AUTHOR]

Two mononuclear Ru(II) complexes, i.e. [RuCl(κ3N-terpy)(κ2N-dpp)]PF6 ([1]PF6; terpy = 2,2′:6′,2′′-terpyridine; dpp = 2,3-bis(2′-pyridyl-pyrazine) and [RuCl(κ3N-tpm)(κ2N-dpp)]Cl ([2]Cl; tpm = tris(1-pyrazolyl)methane), and one dinuclear complex, i.e. [Ru2Cl(κ3N-tpm)(μ-κ2N:κ2N-dpp)Ru(κ2N-bpy)2][PF6]3 ([3][PF6]3; bpy = 2,2′-bipyridine), have been synthesized and their water oxidation catalytic properties have been investigated. A combined DFT and experimental (35Cl NMR and conductivity measurements) study aimed to elucidate the nature of [1]+ and [2]+ in aqueous solution has also been performed, indicating that one water molecule is allowed to enter the first coordination sphere of [2]+ in the ground state, replacing one tpm nitrogen. Conversely, in the case of [1]+, water coordination, assumed to be needed for the water oxidation process, presumably occurs following the oxidation of the metal. For all complexes, a catalytic wave has been detected in acetonitrile/water 1 : 1 (v/v) solution in the range 1.4–1.7 V vs. SCE. In all cases, water oxidation (investigated at pH < 8) takes place initially via a proton-coupled two-electron, two-proton process with the formation of an Ru(IV)＝O moiety, followed by one electron oxidation and water nucleophilic attack. The TON and TOF values (within the range of 16–33 and 1.3–2.2 h−1, respectively) of the complexes are higher than those of the benchmark [Ru(LLL)(LL)(OH2)]2+-type species (LLL and LL are tridentate and bidentate polypyridine ligands, respectively), which is [Ru(terpy)(bpm)(OH2)]2+. [ABSTRACT FROM AUTHOR]

A series of neutral ruthenium(ii)–arene complexes, [(arene)Ru(QR)Cl] (arene = p-cymene or hexamethylbenzene), containing 4-acyl-5-pyrazolonate (QR) ligands with aromatic substituents in the acyl moiety (a phenyl in QPh and a 1-naphthyl in Qnaph) and related ionic complexes [(arene)Ru(QR)(PTA)][PF6] (PTA = 1,3,5-triaza-7-phosphaadamantane) have been synthesized and characterized by IR, 1H, 13C and 31P NMR spectroscopy, elemental analysis and ESI mass spectrometry. The structures of five of these compounds were also determined by X-ray crystallography. DFT studies have been performed on all complexes and, in the case of two cationic [(arene)Ru(Qnaph)(PTA)][PF6], the existence of two conformers with a different relative orientation of the naphthyl group in the Qnaph ligand has been assessed, showing that they possess similar energies, in agreement with the experimentally observed NMR spectra in solution. The cytotoxicity of the 4-acyl-5-pyrazolonate proligands (HQR) and complexes was evaluated in vitro against human ovarian carcinoma cells (A2780 and A2780cisR) and non-tumorous human embryonic kidney (HEK293) cells. In general, each complex is about equally cytotoxic to all three cell lines and the PTA derivatives with the naphthyl-modified QR ligands are the most active of the series. [ABSTRACT FROM AUTHOR]

Esterification of (4-hydroxyphenyl)diphenylphosphine, coordinated to the [Ru(η6-p-cymene)Cl2] fragment, allows a series of bioactive carboxylic acids to be introduced directly into the organometallic molecule. Evaluation of the compounds on human ovarian cancer cells reveals synergistic enhancements in their antiproliferative activity relative to their bioactive organic and organometallic precursors. [ABSTRACT FROM AUTHOR]

The 1 : 1 molar reactions of niobium and tantalum pentahalides with the monodentate NHC ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (Ipr), in toluene (or benzene) at ca. 80 °C, afforded the complexes NbX5(Ipr) (X = F, 2; Br, 3) and TaX5(Ipr) (X = F, 4; Cl, 5; Br, 6), in generally good yields. Complexes 2–6 represent uncommon cases of stable NHC adducts of metal halides with the metal in an oxidation state higher than +4, and also rare examples of Nb–NHC and Ta–NHC bonding systems. In particular, the X-ray molecular structure determined for 6 provides the unprecedented crystallographic characterization of a tantalum compound with a monodentate NHC ligand. DFT results indicate that the metal–carbon bond in 2–6 is a purely σ one. According to NMR studies (1H, 13C, 93Nb), the formation of 3, 5, 6, as well as the previously communicated NbCl5(Ipr), 1, proceeded with the intermediacy of [MX6]− salts, presumably due to steric reasons. On the other hand, the intermediate formation of MF6− in the pathways to 2 and 4 was not observed, according to 19F (and 93Nb in the case of 2) NMR. DFT calculations were carried out in order to shed light on structural and mechanistic aspects, and allowed to trace possible reaction routes. [ABSTRACT FROM AUTHOR]

The reactivity of MoCl5 with α-amino acids was investigated for the first time by choosing CH2Cl2 as the reaction medium. The interaction of MoCl5 with l-proline proceeded with Cl/O interchange and led to the formation of [NH2(CH2)3CHC(O)Cl][MoOCl4], 1, in 63% yield. The reactions of MoCl5 with l-phenylalanine, sarcosine, N,N-dimethylglycine and N,N-dimethyl-l-phenylalanine afforded the α-amino-acylchloride complexes MoOCl3[O=C(Cl)CH(R)N(R′)(R′′)] (R = CH2Ph, R′ = R′′ = H, 2a; R = R′ = H, R′′ = Me, 2b; R = H, R′ = R′′ = Me, 2c; R = CH2Ph, R′ = R′′ = Me, 2d), in ca. 70% yields. According to DFT studies, 2a,d are mononuclear Mo(v) octahedral complexes bearing a N,O-coordinated α-amino-acylchloride ligand. The presumed species formed during the first stages of the MoCl5/l-phenylalanine interaction were DFT-elucidated, thus the calculated Gibbs free energy profile for the multi-step reaction of MoCl5 with l-phenylalanine was traced. [NH3CH(CH2Ph)C(O)Cl][MoOCl4], 3, acting as an intermediate in the course of the formation of 2a, was isolated by combination of [NH3CH(CH2Ph)C(O)Cl][Cl] with MoOCl3. [ABSTRACT FROM AUTHOR]

The 1 : 1 reaction of MoCl5 with 1,4-Me(SO3Me)C6H4 led to the isolation of crystalline Mo2O2Cl6[μ-κ2-1,4-Me(SO3Me)C6H4], 1, in low yields. Attempts to reproduce the synthesis of 1 from MoOCl3/1,4-Me (SO3Me)C6H4 resulted in the good-yield formation of [MoOCl2(μ-Cl)(κ¹-1,4-Me(SO3Me)C6H4)]2, 2. The 1 : 1 reaction of MoCl5 with 1,4-Me(SO3H)C6H4·H2O selectively yielded Mo4O4Cl8[μ3-1,4-Me(SO3)C6H4]4, 3. Compounds 1 and 3 were characterized by X-ray diffractometry; moreover DFT calculations were carried out on 1-3 in order to shed light on their thermodynamic and structural features. [ABSTRACT FROM AUTHOR]