Triple para-Functionalized Cations and Neutral Radicals of Enantiopure Diaza[4]helicenes.

Modulation of absorbance and emission is key for the design of chiral chromophores. Accessing a series of compounds absorbing and emitting (circularly polarized) light over a wide spectral window and often toward near-infrared is of practical value in (chir)optical applications. Herein, by late-stage functionalization on derivatives bridging triaryl methyl and helicene domains, we have achieved the regioselective triple introduction of para electron-donating or electron-withdrawing substituents. Extended tuning of electronic (e.g., E1/2red -1.50 V → -0.68 V) and optical (e.g., emission covering from 550 to 850 nm) properties is achieved for the cations and neutral radicals; the latter compounds being easily prepared by mono electron reductions under electrochemical or chemical conditions. While luminescence quantum yields can be increased up to 70% in the cationic series, strong Cotton effects are obtained for certain radicals at low energies (λabs ∼ 700-900 nm) with gabs values above 10-3. The open-shell electronic nature of the radicals was further characterized by electron paramagnetic resonance revealing an important spin density delocalization that contributes to their persistence.

Mixed valence triiron complexes from the conjugation of [FeIFeI] and [FeII] complexes via intermolecular carbyne/alkyne coupling.

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]+.

Oxaliplatin(IV) Prodrugs Functionalized with Gemcitabine and Capecitabine Induce Blockage of Colorectal Cancer Cell Growth-An Investigation of the Activation Mechanism and Their Nanoformulation.

The use of platinum-based anticancer drugs, such as cisplatin, oxaliplatin, and carboplatin, is a common frontline option in cancer management, but they have debilitating side effects and can lead to drug resistance. Combination therapy with other chemotherapeutic agents, such as capecitabine and gemcitabine, has been explored. One approach to overcome these limitations is the modification of traditional Pt(II) drugs to obtain new molecules with an improved pharmacological profile, such as Pt(IV) prodrugs. The design, synthesis, and characterization of two novel Pt(IV) prodrugs based on oxaliplatin bearing the anticancer drugs gemcitabine or capecitabine in the axial positions have been reported. These complexes were able to dissociate into their constituents to promote cell death and induce apoptosis and cell cycle blockade in a representative colorectal cancer cell model. Specifically, the complex bearing gemcitabine resulted in being the most active on the HCT116 colorectal cancer cell line with an IC50 value of 0.49 ± 0.04. A pilot study on the encapsulation of these complexes in biocompatible PLGA-PEG nanoparticles is also included to confirm the retention of the pharmacological properties and cellular drug uptake, opening up to the possible delivery of the studied complexes through their nanoformulation.

Triiron Complex with N-Ferrocenyl Aminocarbyne Ligand Bridging a Diiron Core: DFT, Electrochemical, and Biological Insights.

The first N-ferrocenyl aminocarbyne complex, [Fe2Cp2(CO)2(µ-CO){µ-CN(Me)(Fc)}]CF3SO3 ([2]CF3SO3), was synthesized with an 88% yield from [Fe2Cp2(CO)4], isocyanoferrocene (CNFc), and methyl triflate. The synthesis proceeded through the intermediate formation of [Fe2Cp2(CO)3(CNFc)], 1. Multinuclear NMR experiments revealed the presence of cis and trans isomers for [2]CF3SO3 in organic solvents, in agreement with DFT outcomes. Electrochemical and spectroelectrochemical studies demonstrated one reduction process occurring prevalently at the diiron core and one oxidation involving the ferrocenyl substituent. The oxidation process is expected to favor the redox activation of [2]+ in a biological environment. Both [2]CF3SO3 and its phenyl analogue [Fe2Cp2(CO)2(µ-CO){µ-CN(Me)(Ph)}]CF3SO3 ([3]CF3SO3), prepared for comparison, exerted moderate antiproliferative activity against the human cancer cell lines A431, HCT-15, PSN-1, 2008, and U1285. However, [2]CF3SO3 exhibited a higher cytotoxicity than [3]CF3SO3, showed a substantial ability to induce intracellular ROS production, and outperformed cisplatin in a three-dimensional SCLC cell model.

Anticancer Potential of Diruthenium Complexes with Bridging Hydrocarbyl Ligands from Bioactive Alkynols.

Diruthenacyclopentenone complexes of the general composition [Ru2Cp2(CO)2{µ-η1:η3-CH═C(C(OH)(R))C(═O)}] (2a-c; Cp = η5-C5H5) were synthesized in 94-96% yields from the reactions of [Ru2Cp2(CO)2{µ-η1:η3-C(Ph)═C(Ph)C(═O)}] (1) with 1-ethynylcyclopentanol, 17α-ethynylestradiol, and 17-ethynyltestosterone, respectively, in toluene at reflux. Protonation of 2a-c by HBF4 afforded the corresponding allenyl derivatives [Ru2Cp2(CO)3{µ-η1:η2-CH═C═R}]BF4 (3a-c) in 85-93% yields. All products were thoroughly characterized by elemental analysis, mass spectrometry, and IR, UV-vis, and nuclear magnetic resonance spectroscopy. Additionally, 2a and 3a were investigated by cyclic voltammetry, and the single-crystal diffraction method was employed to establish the X-ray structures of 2b and 3a. The cytotoxicity in vitro of 2b and 3a-c was evaluated against nine human cancer cell lines (A2780, A2780R, MCF-7, HOS, A549, PANC-1, Caco-2, PC-3, and HeLa), while the selectivity was assessed on normal human lung fibroblast (MRC-5). Overall, complexes exert stronger cytotoxicity than cisplatin, and 3b (comprising 17α-estradiol derived ligand) emerged as the best-performing complex. Inductively coupled plasma mass spectrometry cellular uptake studies in A2780 cells revealed a higher level of internalization for 3b and 3c compared to 2b, 3a, and the reference compound RAPTA-C. Experiments conducted on A2780 cells demonstrated a noteworthy impact of 3a and 3b on the cell cycle, leading to the majority of the cells being arrested in the G0/G1 phase. Moreover, 3a moderately induced apoptosis and oxidative stress, while 3b triggered autophagy and mitochondrial membrane potential depletion.

Highly Reduced Ruthenium Carbide Carbonyl Clusters: Synthesis, Molecular Structure, Reactivity, Electrochemistry, and Computational Investigation of [Ru6C(CO)15]4.

The reaction of [Ru6C(CO)16]2- (1) with NaOH in DMSO resulted in the formation of a highly reduced [Ru6C(CO)15]4- (2), which was readily protonated by acids, such as HBF4·Et2O, to [HRu6C(CO)15]3- (3). Oxidation of 2 with [Cp2Fe][PF6] or [C7H7][BF4] in CH3CN resulted in [Ru6C(CO)15(CH3CN)]2- (5), which was quantitatively converted into 1 after exposure to CO atmosphere. The reaction of 2 with a mild methylating agent such as CH3,I afforded the purported [Ru6C(CO)14(COCH3)]3- (6). By employing a stronger reagent, that is, CF3SO3CH3, a mixture of [HRu6C(CO)16]- (4), [H3Ru6C(CO)15]- (7), and [Ru6C(CO)15(CH3CNCH3)]- (8) was obtained. The molecular structures of 2-5, 7, and 8 were determined by single-crystal X-ray diffraction as their [NEt4]4[2]·CH3CN, [NEt4]3[3], [NEt4][4], [NEt4]2[5], [NEt4][7], and [NEt4][8]·solv salts. The carbyne-carbide cluster 6 was partially characterized by IR spectroscopy and ESI-MS, and its structure was computationally predicted using DFT methods. The redox behavior of 2 and 3 was investigated by electrochemical and IR spectroelectrochemical methods. Computational studies were performed in order to unravel structural and thermodynamic aspects of these octahedral Ru-carbide carbonyl clusters displaying miscellaneous ligands and charges in comparison with related iron derivatives.

Adding Diversity to a Diruthenium Biscyclopentadienyl Scaffold via Alkyne Incorporation: Synthesis and Biological Studies.

We report the synthesis and the assessment of the anticancer potential of two series of diruthenium biscyclopentadienyl carbonyl complexes. Novel dimetallacyclopentenone compounds (2-4) were obtained (45-92% yields) from the thermal reaction (PhCCPh exchange) of [Ru2Cp2(CO)(µ-CO){µ-η1:η3-C(Ph)═C(Ph)C(═O)}], 1, with alkynes HCCR [R = C5H4FeCp (Fc), 3-C6H4(Asp), 2-naphthyl; Cp = η5-C5H5, Asp = OC(O)-2-C6H4C(O)Me]. Protonation of 1-3 by HBF4 afforded the corresponding µ-alkenyl derivatives 5-7, in 40-86% yields. All products were characterized by IR and NMR spectroscopy; moreover, cyclic voltammetry (1, 2, 5, 7) and single-crystal X-ray diffraction (5, 7) analyses were performed on representative compounds. Complexes 5-7 revealed a cytotoxic activity comparable to that of cisplatin in A549 (lung adenocarcinoma), SW480 (colon adenocarcinoma), and ovarian (A2780) cancer cell lines, and 2, 5, 6, and 7 overcame cisplatin resistance in A2780cis cells. Complexes 2, 5, and 7 (but not the aspirin derivative 6) induced an increase in intracellular ROS levels. Otherwise, 6 strongly stabilizes and elongates natural DNA (from calf thymus, CT-DNA), suggesting a possible intercalation binding mode, whereas 5 is less effective in binding CT-DNA, and 7 is ineffective. This trend is reversed concerning RNA, and in particular, 7 is able to bind poly(rA)poly(rU) showing selectivity for this nucleic acid. Complexes 5-7 can interact with the albumin protein with a thermodynamic signature dominated by hydrophobic interactions. Overall, we show that organometallic species based on the Ru2Cp2(CO)x scaffold (x = 2, 3) are active against cancer cells, with different incorporated fragments influencing the interactions with nucleic acids and the production of ROS.

From M6 to M12, M19 and M38 molecular alloy Pt-Ni carbonyl nanoclusters: selective growth of atomically precise heterometallic nanoclusters.

Heterometallic Chini-type clusters [Pt6-xNix(CO)12]2- (x = 0-6) were obtained by reactions of [Pt6(CO)12]2- with Ni-clusters such as [Ni6(CO)12]2-, [Ni9(CO)18]2- and [H2Ni12(CO)21]2-, or from [Pt9(CO)18]2- and [Ni6(CO)12]2-. The Pt/Ni composition of [Pt6-xNix(CO)12]2- (x = 0-6) depended on the nature of the reagents employed and their stoichiometry. Reactions of [Pt9(CO)18]2- with [Ni9(CO)18]2- and [H2Ni12(CO)21]2-, as well as reactions of [Pt12(CO)24]2- with [Ni6(CO)12]2-, [Ni9(CO)18]2- and [H2Ni12(CO)21]2-, afforded [Pt9-xNix(CO)18]2- (x = 0-9) species. [Pt6-xNix(CO)12]2- (x = 1-5) were converted into [Pt12-xNix(CO)21]4- (x = 2-10) upon heating in CH3CN at 80 °C, with almost complete retention of the Pt/Ni composition. Reaction of [Pt12-xNix(CO)21]4- (x ≈ 8) with HBF4·Et2O afforded the [HPt14+xNi24-x(CO)44]5- (x ≈ 0.7) nanocluster. Finally, [Pt19-xNix(CO)22]4- (x = 2-6) could be obtained by heating [Pt9-xNix(CO)18]2- (x = 1-3) in CH3CN at 80 °C, or [Pt6-xNix(CO)12]2- (2-4) in DMSO at 130 °C. The molecular structures of these new alloy nanoclusters have been determined by single crystal X-ray diffraction. The site preference of Pt and Ni within their metal cages has been computationally investigated. The electrochemical and IR spectroelectrochemical behavior of [Pt19-xNix(CO)22]4- (x = 3.11) has been studied and compared to the isostructural homometallic nanocluster [Pt19(CO)22]4-.

Synthesis, Characterization and Photoactivation Studies on the Novel Pt(IV)-Based [Pt(OCOCH3)3(phterpy)] Complex.

Photoactivatable Pt(IV) prodrugs represent nowadays an intriguing class of potential metal-based drugs, endowed with more chemical inertness in their oxidized form and better selectivity for the target with respect to the clinically established Pt(II) compounds. In fact, they have the possibility to be reduced by light irradiation directly at the site of interest. For this reason, we synthesized a new Pt(IV) complex, [Pt(OCOCH3)3(4'-phenyl-2,2':6',2''-terpyridine)][CF3SO3] (1), that is well soluble in aqueous medium and totally unreactive towards selected model biomolecules until its reduction. The highlight of this work is the rapid and efficient photoreduction of 1 with visible light (460 nm), which leads to its reactive Pt(II) analogue. This behavior was made possible by taking advantage of an efficient catalytic system based on flavin and NADH, which is naturally present in the cellular environment. As a comparison, the reduction of 1 was also studied with simple UV irradiation, but both UV-Vis spectrophotometry and 1H-NMR spectrometry showed that the flavin-catalyzed reduction with visible light was faster. Lastly, the reactivity against two representative biological targets, i.e., human serum albumin and one monofilament oligonucleotide fragment, was evaluated by high-resolution mass spectrometry. The results clearly pointed out that the prodrug 1 did not interact with these targets until its photoreduction to the Pt(II) analogue.

Atomically Precise Platinum Carbonyl Nanoclusters: Synthesis, Total Structure, and Electrochemical Investigation of [Pt27(CO)31]4- Displaying a Defective Structure.

The molecular Pt nanocluster [Pt27(CO)31]4- (14-) was obtained by thermal decomposition of [Pt15(CO)30]2- in tetrahydrofuran under a H2 atmosphere. The reaction of 14- with increasing amounts of HBF4·Et2O afforded the previously reported [Pt26(CO)32]2- (32-) and [Pt26(CO)32]- (3-). The new nanocluster 14- was characterized by IR and UV-visible spectroscopy, single-crystal X-ray diffraction, direct-current superconducting quantum interference device magnetometry, cyclic voltammetry, IR spectroelectrochemistry (IR SEC), and electrochemical impedance spectroscopy. The cluster displays a cubic-close-packed Pt27 framework generated by the overlapping of four ABCA layers, composed of 3, 7, 11, and 6 atoms, respectively, that encapsulates a fully interstitial Pt4 tetrahedron. One Pt atom is missing within layer 3, and this defect (vacancy) generates local deformations within layers 2 and 3. These local deformations tend to repair the defect (missing atom) and increase the number of Pt-Pt bonding contacts, minimizing the total energy. The cluster 14- is perfectly diamagnetic and displays a rich electrochemical behavior. Indeed, six different oxidation states have been characterized by IR SEC, unraveling the series of 1n- (n = 3-8) isostructural nanoclusters. Computational studies have been carried out to further support the interpretation of the experimental data.

Atomically Precise Ni-Pd Alloy Carbonyl Nanoclusters: Synthesis, Total Structure, Electrochemistry, Spectroelectrochemistry, and Electrochemical Impedance Spectroscopy.

The molecular nanocluster [Ni36-xPd5+x(CO)46]6- (x = 0.41) (16-) was obtained from the reaction of [NMe3(CH2Ph)]2[Ni6(CO)12] with 0.8 molar equivalent of [Pd(CH3CN)4][BF4]2 in tetrahydrofuran (thf). In contrast, [Ni37-xPd7+x(CO)48]6- (x = 0.69) (26-) and [HNi37-xPd7+x(CO)48]5- (x = 0.53) (35-) were obtained from the reactions of [NBu4]2[Ni6(CO)12] with 0.9-1.0 molar equivalent of [Pd(CH3CN)4][BF4]2 in thf. After workup, 35- was extracted in acetone, whereas 26- was soluble in CH3CN. The total structures of 16-, 26-, and 35- were determined with atomic precision by single-crystal X-ray diffraction. Their metal cores adopted cubic close packed structures and displayed both substitutional and compositional disorder, in light of the fact that some positions could be occupied by either Ni or Pd. The redox behavior of these new Ni-Pd molecular alloy nanoclusters was investigated by cyclic voltammetry and in situ infrared spectroelectrochemistry. All three compounds 16-, 26-, and 35- displayed several reversible redox processes and behaved as electron sinks and molecular nanocapacitors. Moreover, to gain insight into the factors that affect the current-potential profiles, cyclic voltammograms were recorded at both Pt and glassy carbon working electrodes and electrochemical impedance spectroscopy experiments performed for the first time on molecular carbonyl nanoclusters.

Heterometallic rhodium clusters as electron reservoirs: Chemical, electrochemical, and theoretical studies of the centered-icosahedral [Rh12E(CO)27]n- atomically precise carbonyl compounds.

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.

Tetrasubstituted Selenophenes from the Stepwise Assembly of Molecular Fragments on a Diiron Frame and Final Cleavage of a Bridging Alkylidene.

A series of 2,3-dicarboxylato-5-acetyl-4-aminoselenophenes, 5a-j, was obtained via the uncommon assembly of building blocks on a diiron platform, starting from commercial [Fe2Cp2(CO)4] through the stepwise formation of diiron complexes [2a-d]CF3SO3, 3a-d, and 4a-j. The selenophene-substituted bridging alkylidene ligand in 4a-j is removed from coordination upon treatment with water in air under mild conditions (ambient temperature in most cases), affording 5a-j in good to excellent yields. This process is highly selective and is accompanied by the disruption of the organometallic scaffold: cyclopentadiene (CpH) and lepidocrocite (γ-FeO(OH)) were identified by NMR and Raman analyses at the end of one representative reaction. The straightforward cleavage of the linkage between a bridging Fischer alkylidene and two (or more) metal centers, as observed here, is an unprecedented reaction in organometallic chemistry: in the present case, the carbene function is converted to a ketone which is incorporated into the organic product. DFT calculations and electrochemical experiments were carried out to give insight into the release of the selenophene-alkylidene ligand. Compounds 5a-j were fully characterized by elemental analysis, mass spectrometry, IR, and multinuclear NMR spectroscopy and by X-ray diffraction and cyclic voltammetry in one case.

Redox active Ni-Pd carbonyl alloy nanoclusters: syntheses, molecular structures and electrochemistry of [Ni22-xPd20+x(CO)48]6- (x = 0.62), [Ni29-xPd6+x(CO)42]6- (x = 0.09) and [Ni29+xPd6-x(CO)42]6- (x = 0.27).

A redox active Ni-Pd alloy nanocluster [Ni22-xPd20+x(CO)48]6- (x = 0.62) ([1]6-) was obtained from the redox condensation of [NBu4]2[Ni6(CO)12] with 0.7-0.8 equivalents of Pd(Et2S)2Cl2 in CH2Cl2. Conversely, [Ni29-xPd6+x(CO)42]6- (x = 0.09) ([2]6-) and [Ni29+xPd6-x(CO)42]6- (x = 0.27) ([3]6-) were obtained by employing [NEt4]2[Ni6(CO)12] and 0.6-0.7 equivalents of Pd(Et2S)2Cl2 in CH3CN. The molecular structures of these high nuclearity Ni-Pd carbonyl clusters were determined by single-crystal X-ray diffraction (SC-XRD). [1]6- adopted an M40ccp structure comprising five close-packed ABCAB layers capped by two additional Ni atoms. Conversely, [2]6- and [3]6- displayed an hcp M35 metal core composed of three compact ABA layers. [1]6-, [2]6- and [3]6- showed nanometric sizes, with the maximum lengths of their metal cores being 1.3 nm ([1]6-) and 1.0 nm ([2]6- and [3]6-), which increased up to 1.9 and 1.5 nm, after including also the CO ligands. Ni-Pd distribution within their metal cores was achieved by avoiding terminal Pd-CO bonding and minimizing Pd-CO coordination. As a consequence, site preference and partial metal segregation were observed, as well as some substitutional and compositional disorders. Electrochemical and spectroelectrochemical studies revealed that [1]6- and [2]6- were redox active and displayed four and three stable oxidation states, respectively. Even though several redox active high nuclearity metal carbonyl clusters have been previously reported, the nanoclusters described herein represent the first examples of redox active Ni-Pd carbonyl alloy nanoclusters.

Rh-Sb Nanoclusters: Synthesis, Structure, and Electrochemical Studies of the Atomically Precise [Rh20Sb3(CO)36]3- and [Rh21Sb2(CO)38]5- Carbonyl Compounds.

The reactivity of [Rh7(CO)16]3- with SbCl3 has been deeply investigated with the aim of finding a new approach to prepare atomically precise metalloid clusters. In particular, by varying the stoichiometric ratios, the reaction atmosphere (carbon monoxide or nitrogen), the solvent, and by working at room temperature and low pressure, we were able to prepare two large carbonyl clusters of nanometer size, namely, [Rh20Sb3(CO)36]3- and [Rh21Sb2(CO)38]5-. A third large species composed of 28 metal atoms was isolated, but its exact formulation in terms of metal stoichiometry could not be incontrovertibly confirmed. We also adopted an alternative approach to synthesize nanoclusters, by decomposing the already known [Rh12Sb(CO)27]3- species with PPh3, willing to generate unsaturated fragments that could condense to larger species. This strategy resulted in the formation of the lower-nuclearity [Rh10Sb(CO)21PPh3]3- heteroleptic cluster instead. All three new compounds were characterized by IR spectroscopy, and their molecular structures were fully established by single-crystal X-ray diffraction studies. These showed a distinct propensity for such clusters to adopt an icosahedral-based geometry. Their characterization was completed by ESI-MS and NMR studies. The electronic properties of the high-yield [Rh21Sb2(CO)38]5- cluster were studied through cyclic voltammetry and in situ infrared spectroelectrochemistry, and the obtained results indicate a multivalent nature.

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.

Photocytotoxic Pt(iv) complexes as prospective anticancer agents.

The use of Pt(iv) complexes as potential anticancer drugs is attractive, because they have higher stability and less side effects than Pt(ii) compounds. Moreover, some Pt(iv) complexes can also be activated with light, opening an avenue to photochemotherapy. Our purpose is to widen the library of photoactivatable Pt(iv)-based prodrugs and here we report on the oxidation of the Pt(ii) compound [PtCl(4'-phenyl-2,2':6',2''-terpyridine)][CF3SO3] (1) with PhICl2 or H2O2. The synthetic procedure avoids the formation of multiple species: the treatment with PhICl2 produces the Pt(iv) complex with axial chlorides, [PtCl3(4'-phenyl-2,2':6',2''-terpyridine)][CF3SO3] (2), while H2O2 oxidation and post-synthesis carboxylation produce [Pt(OCOCH3)2Cl(4'-phenyl-2,2':6',2''-terpyridine)][CF3SO3] (3), bearing acetates in the axial positions. 2 and 3 are stable in physiological-like buffers and in DMSO in the dark, but undergo photoreduction to 1 upon irradiation at 365 nm. Their stability toward reduction is a fundamental parameter to consider: cyclic voltammetry experiments show that the 2 electron reduction Pt(iv) → Pt(ii) occurs at a more negative potential for 3, because of the greater stabilization provided by the acetate axial groups; noteworthily, 3 is stable for hours also in the presence of mM concentration of glutathione. The cytotoxicity of 2 and 3 toward A2780 and A2780cis cell lines reveals that 3 is the least toxic in the dark, but is able to produce cytotoxic effects far higher than cisplatin when irradiated. To shed light on the mechanistic aspects, the interaction with protein and DNA models has been explored through high-resolution mass spectrometry revealing that 2 and 3 behave as prodrugs, but are able to bind to biological targets only after irradiation.

Circularly-Polarized Electrochemiluminescence from a Chiral Bispyrene Organic Macrocycle.

The first observation of circular polarization of electrochemiluminescence (ECL) from a purely organic derivative is reported. A bispyrene scaffold mounted on a constrained polyether macrocycle displaying intense excimer fluorescence and highly circularly-polarized (CP) photoluminescence has been selected for this purpose. The compound displays an ECL dissymmetry factor of about |8×10-3 |, which is in good agreement with the corresponding photoluminescence value. This observation is the first step towards the molecular engineering of tailored dyes that can act as both ECL and CP-ECL reporters for (bio)analysis by bringing a new level of information when dealing with chiral environments. Additionally, it provides an extra dimension to the ECL phenomenon and opens the way to chiral detection and discrimination.

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.