Combining [Arene-Ru] with Azocarboxamide to Generate a Complex with Cytotoxic Properties

Designing Homogeneous Copper-Free Sonogashira Reaction through a Prism of Pd-Pd Transmetalation

Simultaneous introduction of two different palladium (pre)catalysts, one tuned to promote oxidative addition to (hetero)aryl bromide and another to activate terminal alkyne substrate, leads to productive Pd–Pd transmetalation, subsequent reductive elimination, and formation of disubstituted alkyne. This conceptually novel rational design of copper-free Sonogashira reaction enabled facile identification of the reaction conditions, suitable for the synthesis of alkyl, aryl, and heteroaryl substituted alkynes at room temperature with as low as 0.125 mol % total Pd loading.

Mononuclear Ru(II) Complexes of an Arene and Asymmetrically Substituted 2,2'-Bipyridine Ligands: Photophysics, Computation, and NLO Properties

By using monosubstituted 2,2'-bipyridine asymmetric ancillary ligands with different electron donor moieties and an arene ligand (p-cymene), we successfully designed and synthesized six Ru(II) compounds (RuBPY1-6) that belong to a piano-stool-type system. The NLO properties of the synthesized complexes have been studied in both solution and the solid state. The electronic spectra of these compounds show a broad feature with two absorption bands in the visible window (350-650 nm). RuBPY1-6 complexes exhibit NIR emission spectra in the solution state (at >720 nm), the maxima of which are bathochromically shifted in comparison to those of the concerned ligands. Interestingly, compounds RuBPY1-6 show NIR emission in their solid state too. Title compounds RuBPY1-6 have lifetimes in the range of 0.2 to 0.9 ns. An important feature of this work is the π-association of the p-cymene ligand to Ru(II) in the synthesized complexes; the π complex is formed by breaking the symmetry of p-cymene, found in the starting precursor (Ru₂ dimer). This has been established by NMR spectral studies along with DFT calculations on the ¹H NMR spectra. We could derive the molecular structure of the cationic part of this system by density functional theory (DFT), associated with ¹H NMR spectral studies. The minimum energy structures for RuBPY1 and RuBPY2 have been optimized at DFT/B3LYP along with the LANL2DZ basis set for ruthenium atoms. These optimized structures are further considered to calculate the excited state properties using the TDDFT method. The electrochemical studies of the complexes, investigated in acetonitrile solution, show that this system is associated with a well-defined Ru(III)/Ru(II) reversible couple, rarely observed for a Ru(II) piano-stool-type compound, along with a feature of irreversible ligand oxidation. The absorption cross-section values, obtained from the two-photon absorption studies of title compounds RuBPY1-6, are worth reporting and lie in the range of 3-28 GM (in the femtosecond case).

Versatile Coordination of Azocarboxamides: Redox-Triggered Change of the Chelating Binding Pocket in Ruthenium Complexes

Azocarboxamides occupy a special place among azo ligands owing to their versatility for metal coordination. Herein ruthenium complexes with two different azocarboxamide ligands that differ in the presence (or not) of a coordinating pyridyl heterocycle are presented. By making full use of the O,N(amide), N(azo), and N(pyridyl) coordinating sites, the first diruthenium complex that is bridged by an azo ligand containing two different binding pockets was obtained. Moreover, it was conclusively proven that, in the mononuclear complexes, oxidation at the ruthenium center leads to a complete change of coordination at the chelating binding pocket. The complexes were characterized by NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Additionally, the mechanism of the aforementioned redox-triggered change in the chelating binding pocket and the electronic structures of all the complexes were investigated by a combination of electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations. This is first instance in which a redox-driven change in the complete chelating binding pocket has been observed in a ruthenium complex as well as with azo-based ligands. These results thus show the potential of these versatile azocarboxamide ligands to act as redox-driven switches with possible relevance to electrocatalysis.

α-Diimines as Versatile, Derivatizable Ligands in Ruthenium(II) p-Cymene Anticancer Complexes

α-Diimines are among the most robust and versatile ligands available in synthetic coordination chemistry, possessing finely tunable steric and electronic properties. A series of novel cationic ruthenium(II) p-cymene complexes bearing simple α-diimine ligands, [(η⁶- p-cymene)RuCl{κ² N-(HCNR)₂}]NO₃ (R = Cy, [1]NO₃; R = 4-C₆H₁₀OH, [2]NO₃; R = 4-C₆H₄OH, [3]NO₃), were prepared in near-quantitative yields as their nitrate salts. [2]NO₃ displays high water solubility. The potential of the α-diimine ligand in [3]NO₃ as a carrier of bioactive molecules was investigated via esterification reactions with the hydroxyl groups. Thus, the double-functionalized derivatives [(η⁶- p-cymene)RuCl{κ² N-(HCN(4-C₆H₄OCO-R))₂}]NO₃ (R = aspirinate, [5]NO₃; valproate, [6]NO₃) and also [4]Cl (R = Me) were obtained in good-to-high yields. UV-vis and multinuclear NMR spectroscopy and cyclic voltammetric studies in aqueous solution revealed only minor ruthenium chloride hydrolytic cleavage, biologically accessible reduction potentials, and pH-dependent behavior of [3]NO₃. Density functional theory analysis was performed in order to compare the Ru-Cl bond strength in [1]⁺ with the analogous ethylenediamine complex, showing that the higher stability observed in the former is related to the electron-withdrawing properties of the α-diimine ligand. In vitro cytotoxicity studies were performed against tumorigenic (A2780 and A2780cisR) and nontumorigenic (HEK-293) cell lines, with the complexes bearing simple α-diimine ligands ranging from inactive to IC₅₀ values in the low micromolar range. The complexes functionalized with bioactive components, i.e., [5]NO₃ and [6]NO₃, exhibited a marked increase in the cytotoxicity with respect to the precursor [3]NO₃.

Versatile coordination of acetazolamide to ruthenium(ii) p-cymene complexes and preliminary cytotoxicity studies

The bioactive molecule acetazolamide was incorporated in Ru(ii)-p-cymene complexes with different coordination modes. Two of the resulting complexes were non cytotoxic towards A2780, A2780cisR and HEK-293 cell lines.

Hydrogen bonding and anticancer properties of water-soluble chiral p-cymene Ru(II) compounds with amino-oxime ligands

The investigation of the hydrogen-bonding effect on the aggregation tendency of ruthenium compounds [(η⁶-p-cymene)Ru(κNHR,κNOH)Cl]Cl (R = Ph (1a), Bn (1b)) and [(η⁶-p-cymene)Ru(κ²NH(2-pic),κNOH)][PF₆]₂ (1c), [(η⁶-p-cymene)Ru(κNHBn,κNO)Cl] (2b) and [(η⁶-p-cymene)Ru(κNBn,κ²NO)] (3b), has been performed by means of concentration dependence ¹H NMR chemical shifts and DOSY experiments. The synthesis and full characterization of new compounds 1c, [(η⁶-p-cymene)Ru(κNPh,κ²NO)] (3a) and 3b are also reported. The effect of the water soluble ruthenium complexes 1a-1c on cytotoxicity, cell adhesion and cell migration of the androgen-independent prostate cancer PC3 cells have been assessed by MTT, adhesion to type-I-collagen and recovery of monolayer wounds assays, respectively. Interactions of 1a-1c with DNA and human serum albumin have also been studied. Altogether, the properties reported herein suggest that ruthenium compounds 1a-1c have considerable potential as anticancer agents against advanced prostate cancer.