Effects of Structurally Different Tertiary Amines on the Properties of Quaternized Anionic Exchange Membranes Potentially Applicable for Water Electrolysis.

In this work, two structurally different monoamines (trimethylamine [TMA] and N-methylpiperidine [N-MPip]) are used for the amination of a g-VBC-15 graft copolymer, obtained by the functionalization of a mechanically robust, commercially available styrene-butadiene block copolymer (SB) with vinylbenzyl chloride (VBC) via solution free-radical polymerization. Results demonstrate that g-VBC-15-based membranes quaternized with TMA have superior electrochemical performance than N-MPip counterparts; while, the mechanical properties are good and only slightly inferior to those of N-MPip. Therefore, TMA is the selected monoamine to be alternatively mixed with two polyamines (tetramethyl-1,3-propanediamine [TMPDA] and N,N,N',N'',N''-pentamethyldiethylenetriamine [PMDETA]) into different proportions, in order to modulate the average functionality of the amination mixture in terms of number of amine functional groups available for the quaternization reaction of the membranes. g-VBC-15-based membranes derived therefrom are extensively characterized to assess their thermal, mechanical, and ex situ electrochemical properties. Results indicate that membranes quaternized with a TMA/PMDETA mixture (90:10 in mole) display the highest conductivity among all the investigated membranes aminated with polyamine-based mixtures. Moreover, they have comparable mechanical and electrochemical properties to those quaternized with TMA, while exhibiting a reduced water uptake.

Luminescent Au(III)-M(I) (M = Cu, Ag) Aggregates Based on Dicyclometalated Bis(alkynyl) Gold Anions†.

The syntheses and structures of a series of complexes based on the C∧C-chelated Au(III) unit (C∧C = 4,4'-bis(t-butyl) 2,2'-biphenyl-1,1'-diyl) are reported, namely, [{(C∧C)Au(C≡CtBu)2}2M2], (C∧C)Au(C≡CR)(C≡NXyl), and [{(C∧C)Au(C≡CR)2}{M(C≡NXyl)}] (M = Ag, Cu; R = tBu, C6H4tBu-4, C6H4OMe-4; Xyl = 3,5-Me2C6H3). The X-ray structures reveal a broad range of dispositions determined by the different coordination modes of Ag(I) or Cu(I). The complexes are bright photoemitters in the solid state and in poly(methyl methacrylate) (PMMA) films. The photoluminescence is dominated by 3IL(C∧C) transitions, with indirect effects from the rest of the molecules, as supported by theoretical calculations. This work opens up the possibility of accessing Au(III) carbon-rich anions to construct photoluminescent aggregates.

Vinylbenzyl Chloride/Styrene-Grafted SBS Copolymers via TEMPO-Mediated Polymerization for the Fabrication of Anion Exchange Membranes for Water Electrolysis.

In this work, a commercial SBS was functionalized with the 2,2,6,6-tetramethylpiperidin-N-oxyl stable radical (TEMPO) via free-radical activation initiated with benzoyl peroxide (BPO). The obtained macroinitiator was used to graft both vinylbenzyl chloride (VBC) and styrene/VBC random copolymer chains from SBS to create g-VBC-x and g-VBC-x-co-Sty-z graft copolymers, respectively. The controlled nature of the polymerization as well as the use of a solvent allowed us to reduce the extent of the formation of the unwanted, non-grafted (co)polymer, thereby facilitating the graft copolymer's purification. The obtained graft copolymers were used to prepare films via solution casting using chloroform. The -CH2Cl functional groups of the VBC grafts were then quantitatively converted to -CH2(CH3)3N+ quaternary ammonium groups via reaction with trimethylamine directly on the films, and the films, therefore, were investigated as anion exchange membranes (AEMs) for potential application in a water electrolyzer (WE). The membranes were extensively characterized to assess their thermal, mechanical, and ex situ electrochemical properties. They generally presented ionic conductivity comparable to or higher than that of a commercial benchmark as well as higher water uptake and hydrogen permeability. Interestingly, the styrene/VBC-grafted copolymer was found to be more mechanically resistant than the corresponding graft copolymer not containing the styrene component. For this reason, the copolymer g-VBC-5-co-Sty-16-Q with the best balance of mechanical, water uptake, and electrochemical properties was selected for a single-cell test in an AEM-WE.

Mono-, Di- and Tetra-iron Complexes with Selenium or Sulphur Functionalized Vinyliminium Ligands: Synthesis, Structural Characterization and Antiproliferative Activity.

A series of diiron/tetrairon compounds containing a S- or a Se-function (2a-d, 4a-d, 5a-b, 6), and the monoiron [FeCp(CO){SeC1(NMe2)C2HC3(Me)}] (3) were prepared from the diiron µ-vinyliminium precursors [Fe2Cp2(CO)( µ-CO){ µ-η1: η3-C3(R')C2HC1N(Me)(R)}]CF3SO3 (R = R' = Me, 1a; R = 2,6-C6H3Me2 = Xyl, R' = Ph, 1b; R = Xyl, R' = CH2OH, 1c), via treatment with S8 or gray selenium. The new compounds were characterized by elemental analysis, IR and multinuclear NMR spectroscopy, and structural aspects were further elucidated by DFT calculations. The unprecedented metallacyclic structure of 3 was ascertained by single crystal X-ray diffraction. The air-stable compounds (3, 4a-d, 5a-b, 6) display fair to good stability in aqueous media, and thus were assessed for their cytotoxic activity towards A2780, A2780cisR, and HEK-293 cell lines. Cyclic voltammetry, ROS production and NADH oxidation studies were carried out on selected compounds to give insights into their mode of action.

Anticancer Potential of Diiron Vinyliminium Complexes.

Invited for the cover of this issue is the group of Fabio Marchetti at the Università di Pisa and Paul J. Dyson at Ecole Polytechnique Fédérale de Lausanne (EPFL). Read the full text of the article at 10.1002/chem.201902885.

Anticancer Potential of Diiron Vinyliminium Complexes.

Although ferrocene derivatives have attracted considerable attention as possible anticancer agents, the medicinal potential of diiron complexes has remained largely unexplored. Herein, we describe the straightforward multigram-scale synthesis and the antiproliferative activity of a series of diiron cyclopentadienyl complexes containing bridging vinyliminium ligands. IC50 values in the low-to-mid micromolar range were determined against cisplatin sensitive and resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines. Notable selectivity towards the cancerous cells lines compared to the non-tumoral human embryonic kidney (HEK-293) cell line was observed for selected compounds. The activity seems to be multimodal, involving reactive oxygen species (ROS) generation and, in some cases, a fragmentation process to afford monoiron derivatives. The large structural variability, amphiphilic character and good stability in aqueous media of the diiron vinyliminium complexes provide favorable properties compared to other widely studied classes of iron-based anticancer candidates.

Controlled Dissociation of Iron and Cyclopentadienyl from a Diiron Complex with a Bridging C3 Ligand Triggered by One-Electron Reduction.

The one-electron reduction of a diiron cationic complex revealed unique features: cleavage of the diiron structure occurred despite a multidentate bridging C3 ligand and was accompanied by the clean dissociation of one η5-cyclopentadienyl ring and one iron as isolated units. Thus, the iron(II)-iron(II) µ-vinyliminium complex [Fe2Cp2(CO)(µ-CO){µ-η1:η3-C3(Et)C2HC1N(Me)(Xyl)}][SO3CF3] ([1a]SO3CF3) reacted with cobaltocene in tetrahydrofuran (THF), affording the iron(II) vinylaminoalkylidene [FeCp(CO){C1N(Me)(Xyl)C2HC3(Et)C(═O)}] (2a) in 77% yield relative to the C3 ligand. Analogously, [FeCp(CO){C1N(Me)(Xyl)C2HC3(CH2OH)C(═O)}] (2b) was obtained in 64% yield from the appropriate diiron precursor and CoCp2. The formation of 2a is initiated by the one-electron reduction of [1a]+, followed by a reversible intramolecular rearrangement terminating with the irreversible release of CpH (NMR and gas chromatography-mass spectrometry) and Fe [electron paramagnetic resonance (EPR) and magnetometry]. The key intermediate iron(I) ferraferrocene (3) was detected by EPR and IR spectroelectrochemistry, while the related species 3-H-3 was isolated after the addition of a hydrogen source and then identified by X-ray diffraction. A plausible mechanism for the route from [1a]+ to 3 was ascertained by density functional theory calculations. The dication [1a]2+, displaying both carbonyl ligands in terminal positions, and the anion [3]- were electrochemically generated. The functionalized diiron compounds 4 (52% yield) and 5 (62%) were afforded through the activation of O2 and S8 by a radical intermediate along the reductive pathway of [1a]+. The reaction of [Fe2Cp2(CO)(µ-CO){µ-η1:η3-C(SiMe3)CHCN(Me)(Xyl)}][SO3CF3] ([1c]SO3CF3) with CoCp2 in THF afforded [Fe2Cp2(C≡CSiMe3)(CO)(µ-CO){µ-CNMe(Xyl)}] (6) in 65% yield.

Gold(III) Alkyne Complexes: Bonding and Reaction Pathways.

The synthesis and characterization of hitherto hypothetical AuIII π-alkyne complexes is reported. Bonding and stability depend strongly on the trans effect and steric factors. Bonding characteristics shed light on the reasons for the very different stabilities between the classical alkyne complexes of PtII and their drastically more reactive AuIII congeners. Lack of back-bonding facilitates alkyne slippage, which is energetically less costly for gold than for platinum and explains the propensity of gold to facilitate C-C bond formation. Cycloaddition followed by aryl migration and reductive deprotonation is presented as a new reaction sequence in gold chemistry.

Synthesis and Antiproliferative Activity of New Ruthenium Complexes with Ethacrynic-Acid-Modified Pyridine and Triphenylphosphine Ligands.

Pyridine- and phosphine-based ligands modified with ethacrynic acid (a broad acting glutathione transferase inhibitor) were prepared and coordinated to ruthenium(II)-arene complexes and to a ruthenium(III) NAMI-A type complex. All the compounds (ligands and complexes) were fully characterized by analytical and spectroscopic methods and, in one case, by single-crystal X-ray diffraction. The in vitro anticancer activity of the compounds was studied, with the compounds displaying moderate cytotoxicity toward the human ovarian cancer cell lines. All the complexes led to similar levels of residual GST activity in the different cell lines, irrespective of the stability of the Ru-ligand bond.