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Tris(pyrazolyl)methane (tpm), 2,2,2-tris(pyrazolyl)ethanol (tpmOH) and its esterification derivatives with ibuprofen and flurbiprofen (tpmIBU and tpmFLU) were used as ligands to obtain complexes of the type [Fe(tpmX)2]Cl2 (1–4). The tpmIBU and tpmFLU ligands and corresponding complexes 3 and 4 were characterized by IR and multinuclear NMR spectroscopy, and the structure of tpmIBU was elucidated by single crystal X-ray diffraction. Complexes 1–4 were also assessed for their behaviour in aqueous media (solubility in D2O, octanol/water partition coefficient, stability in physiological-like conditions). The antiproliferative activity of ligands and complexes was determined on A2780, A2780cis and A549 cancer cell lines and the non-cancerous HEK 293T and BJ cell lines. The ligands and complexes were investigated for their ability to inhibit COX-2 (cyclooxygenase) and HNE (4-hydroxynonenal) enzymes. Complexes 3 and 4 exhibited cytotoxicity that may be attributed predominantly to their bioactive fragments, while DNA binding and enhancement of ROS production do not appear to play any significant role. [ABSTRACT FROM AUTHOR]

We present a new synthetic strategy for obtaining mixed-valence triiron complexes where the metal centers are bridged by a novel, highly functionalized hydrocarbyl ligand. The alkynyl–vinyliminium complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(X–C≡CH)CHCNMe2}]CF3SO3 (X = 4-C6H4, [2a1]CF3SO3; X = (CH2)3, [2a2]CF3SO3) were synthesized in almost quantitative yields from the aminocarbyne precursor [Fe2Cp2(CO)2(μ-CO){μ-CNMe2}]CF3SO3, [1a]CF3SO3, and the di-alkynes HC≡C–X–C≡CH. Then, the ferracycle [Fe(Cp)(CO){C(NMe2)CH＝C(4-C6H4C≡CH)C(O)}], 4a1, was produced in 47% yield from the cleavage of [2a1]CF3SO3 promoted by pyrrolidine. Subsequent reactions of the acetonitrile adducts [Fe2Cp2(CO)(μ-CO)(NCMe){μ-CNMe(R)}]CF3SO3 (R = Me, [1aACN]CF3SO3; R = Xyl, [1bACN]CF3SO3) ([FeIFeI]) with 4a1 ([FeII]) at room temperature resulted in the formation of [FeIFeIFeII] complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(X–C＝CHC(NMe2)＝FeCp(CO)C＝O)CHCNMe(R)}]CF3SO3 (R = Me, [5a1]CF3SO3; R = Xyl, [5b1]CF3SO3) in yields ranging from 56% to 64%. The new products were characterized by IR and multinuclear NMR spectroscopy, and the structures of [2a2]CF3SO3 and 4a1 were confirmed by single crystal X-ray diffraction. Cyclic voltammetry and spectroelectrochemical studies on [5a1]+ have revealed that reduction and oxidation events occur almost independently at the [FeIFeI] and [FeII] units, respectively. This observation underscores a minimal electronic interaction between the two fragments within the triiron complex. Accordingly, DFT studies pointed out that the HOMO and LUMO orbitals are predominantly localized in the two distinct compartments of [5a1]+. [ABSTRACT FROM AUTHOR]

To reduce the costs of proton exchange membrane fuel cells, the amount of Pt necessary to drive efficient oxygen reduction reaction (ORR) should be minimized. Particle nanostructuring, (nano‐)alloying, and metal‐doping can yield higher activities per Pt mass through tailoring catalysts owning a high number of active sites and precise electronic properties. In this work, the atom‐precise [NBnMe3]2[Co8Pt4C2(CO)24] (Co8Pt4) cluster is encapsulated and activated in a zeolitic imidazolate framework (ZIF)‐8, which unlocks the access to defined, bare Pt−Co nanoclusters, Co8±xPt4±yNC@ZIF‐8, for the fabrication of highly active ORR catalysts. Upon controlled C‐interfacing and ZIF‐8‐digestion, Co‐doped Pt NPs (Pt27Co1) with a homogenous and narrow size distribution of (1.1±0.4) nm are produced on Vulcan® carbon. Restructuring of the Pt27Co1/C catalyst throughout the ORR measurement was monitored via high‐angle annular dark field‐scanning transmission electron microscopy and X‐ray photoelectron spectroscopy. The measured ORR mass activity of (0.42±0.07) A mgPt−1 and the specific activity of (0.67±0.06) mA cmECSA−2 compare favourably with the catalyst obtained by direct C‐interfacing the pristine Co8Pt4 cluster and with state‐of‐the‐art Pt/C reference catalysts. Our results demonstrate the potential of ZIF‐8‐mediated Pt−Co NP synthesis toward devising ORR catalysts with high Pt‐mass activity. [ABSTRACT FROM AUTHOR]

Iron(II) can show a very rich coordination chemistry with concomitant modulation of its properties as promising functional materials. Metalation of the neutral tridentate nitrogen-donor mer-coordinating ligand 2,6-bis(2-(methyl)-2H-tetrazol-5-yl)pyridine (Me2btp) with Fe(ClO4)2·6H2O through accurate solvent polarity control enables the selective crystallization of [FeHS/LS(Me2btp)2](ClO4)2·MeCN·2.75H2O (2HS/LS·MeCN·2.75H2O) as red rods, where half of the iron(II) centres resides in the low spin (LS, S = 0) state and the other half is in the high spin (HS, S = 2) state. The red rods spontaneously convert into yellow crystals once removed from the mother liquor and exposed to air due to solvent rearrangement within the crystal packing; these new crystals can be assigned to [FeHS(Me2btp)2](ClO4)2·solvent (2HS·solvent) where all the iron(II) centres are now blocked in the HS state, as confirmed by magnetic measurements. The polarity of the crystallization solvent, together with the maintenance of the crystals within the mother liquor, are pivotal for the reactivity and interconversion of different species. Indeed, upon long standing in solution, 2HS/LS·MeCN·2.75H2O converts to another form of red crystals belonging to [FeLS(Me2btp)2][FeHS(Me2btp)(MeCN)2(H2O)](ClO4)4·MeCN (2LS·3HS·MeCN), as confirmed by single crystal X-ray diffraction data. In this co-crystal, the iron(II) in 2 resides in the LS state at all temperatures while the iron(II) in 3 is blocked in the HS state. Well-formed yellow crystals could be also isolated among the red crystals of 2HS/LS·MeCN·2.75H2O, and they could be identified as the unprecedented octacoordinated species [Fe(Me2btp)2(MeCN)(H2O)](ClO4)2·H2O (1·H2O) by single-crystal X-ray diffraction. These yellow crystals are stable in the air, but slowly convert into 2LS·3HS·MeCN if kept in the mother liquor for about one week. 1·H2O can be considered the trapped intermediate in the solid state during the conversion of [FeHS(Me2btp)2]2+ into [FeHS(Me2btp)(MeCN)2(H2O)]2+ in solution, where the two tridentate ligands in the starting species can unfold to accommodate coordinated MeCN and H2O molecules, as confirmed by theoretical calculations, and eventually one of the two Me2btp is completely replaced by the solvent. [ABSTRACT FROM AUTHOR]

Reaction of [HRu3(CO)11]− (1) with [Ir(COD)Cl]2 in CH2Cl2 under a H2 atmosphere afforded dihydride [H2Ru3Ir(CO)12]− (2), which was quantitatively protonated to H3Ru3Ir(CO)12 (3) by strong acids such as HBF4·Et2O. The related mono-hydride [HRu3Ir(CO)12]2− (4) was obtained by deprotonation of 2 with a strong base such as KOtBu, or by the reaction of 1 with [Ir(CO)4]− in refluxing THF. Hydride carbonyl clusters 2–4 were fully characterized by IR and 1H NMR spectroscopies, and the molecular structures of 2 and 3 were determined by single-crystal X-ray diffraction (SC-XRD). The location of the hydride ligands within the tetrahedral cages of these clusters was further corroborated by computational studies employing DFT methods. Clusters 2–4 were tested as catalyst precursors for transfer hydrogenation on the model substrate 4-fluoroacetophenone, using iPrOH as a solvent and a hydrogen source. The results obtained using these heterometallic Ru–Ir clusters were compared to those using homometallic 1, evidencing a significant difference, particularly regarding the effect of the base on catalysis. Heterometallic cluster 2 was also tested in the hydrogenation of trans-cinnamaldehyde in iPrOH at refluxing temperature both under N2 and H2 atmospheres, and H2 pressure. [ABSTRACT FROM AUTHOR]

In this paper, we present a comparative study of the redox properties of the icosahedral [Rh12E(CO)27]n− (n = 4 when E = Ge or Sn and n = 3 when E = Sb or Bi) family of clusters through in situ infrared spectroelectrochemistry experiments and density functional theory computational studies. These clusters show shared characteristics in terms of molecular structure, being all E-centered icosahedral species, and electron counting, possessing 170 valence electrons as predicted by the electron-counting rules, based on the cluster-borane analogy, for compounds with such metal geometry. However, in some cases, clusters of similar nuclearity, and beyond, may show multivalence behavior and may be stable with a different electron counting, at least on the time scale of the electrochemical analyses. The experimental results, confirmed by theoretical calculations, showed a remarkable electron-sponge behavior for [Rh12Ge(CO)27]4− (1), [Rh12Sb(CO)27]3− (3), and [Rh12Bi(CO)27]3− (4), with a cluster charge going from −2 to −6 for 1 and 3 and from −2 to −7 for cluster 4, making them examples of molecular electron reservoirs. The [Rh12Sn(CO)27]4− (2) derivative, conversely, presents a limited ability to exist in separable reduced cluster species, at least within the experimental conditions, while in the gas phase it appears to be stable both as a penta- and hexa-anion, therefore showing a similar redox activity as its congeners. As a fallout of those studies, during the preparation of [Rh12Sb(CO)27]3−, we were able to isolate a new species, namely, [Rh11Sb(CO)26]2−, which presents a Sb-centered nido-icosahedral metal structure possessing 158 cluster valence electrons, in perfect agreement with the polyhedral skeletal electron pair theory. [ABSTRACT FROM AUTHOR]