Imidazole-Fused Enediynes by Selective C5–C4 Alkynylations of 4,5-Dibromoimidazoles

An efficient synthesis of symmetrical 1,2-disubstituted 4,5-dialkynylimidazoles by Sonogashira alkynylation of the corresponding 4,5-dibromo derivatives was developed. Moreover, through a careful tuning of the palladium ligand, unsymmetrical 1,2-disusbtituted 4,5-dialkynylimidazoles were also prepared through a regioselective C5 alkynylation of 4,5-dibromoimidazoles, followed by a second alkynylation involving the 4-bromo derivatives so obtained. This interesting class of imidazole-fused enediynes is also able to give thermal Bergman cycloaromatization (BC), as proved by DSC experiments

A Specific Interaction between Ionic Liquids' Cations and Reichardt's Dye

Solvatochromic probes are often used to understand solvation environments at the molecular scale. In the case of ionic liquids constituted by an anion and a cation, which are designed and paired in order to obtain a low melting point and other desirable physicochemical properties, these two indivisible components can interact in a very different way with the probe. This is the case with one of the most common probes: Reichardt's Dye. In the cases where the positive charge of the cation is delocalized on an aromatic ring such as imidazolium, the antibonding orbitals of the positively charged aromatic system are very similar in nature and energy to the LUMO of Reichardt's Dye. This leads to an interesting, specific cation-probe interaction that can be used to elucidate the nature of the ionic liquids' cations. Parallel computational and experimental investigations have been conducted to elucidate the nature of this interaction with respect to the molecular structure of the cation

Expanding the Chemical Space of Benzimidazole Dicationic Ionic Liquids

Benzimidazole dicationic ionic liquids (BDILs) have not yet been widely explored in spite of their potential. Therefore, two structurally related families of BDILs, paired with either bromide or bistriflimide anions and bearing alkyl spacers ranging from C3 to C6, have been prepared. Their thermal properties have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), while their electrical properties have been assessed by cyclic voltammetry (CV). TG analysis confirmed the higher stability of the bistriflimide BDILs over the bromide BDILs, with minor variation within the two families. Conversely, DSC and CV allowed for ascertaining the role played by the spacer length. In particular, the thermal behavior changed dramatically among the members of the bistriflimide family, and all three possible thermal behavior types of ILs were observed. Furthermore, cyclic voltammetry showed different electrochemical window (C3(C1BenzIm)2/2Tf2N < C4(C1BenzIm)2/2Tf2N, C5(C1BenzIm)2/2Tf2N < C6(C1BenzIm)2/2Tf2N) as well as a reduction peak potential, shape, and intensity as a function of the spacer length. The results obtained highlight the benefit of accessing a more structurally diverse pool of compounds offered by dicationic ILs when compared to the parent monocationic ILs. In particular, gains are to be found in the ease of fine-tuning their properties, which translates in facilitating further investigations toward BDILs as designer solvents and catalysts

Systematic Synthesis and Properties Evaluation of Dicationic Ionic Liquids, and a Glance Into a Potential New Field

Dicationic ionic liquids (DILs), a subset of the ionic liquid (IL) family, have attracted growing interest in recent years, and the range of applications within which they are investigated is constantly expanding. However, data which allows structure to property correlation of a DIL is still limited, and thus selecting an appropriate salt to address a specific challenge can be problematic. In comparison to traditional ILs, DILs physico-chemical properties can be tuned by changing the length and type of spacer which connects the cationic heads as well as the type of cation. This in turn could give rise to symmetrical or asymmetrical DILs. In this work, a systematic study of a homogeneous class of 12 dibromide DILs and 12 di-carboxylate salts has been performed. The latter class of DILs were also compared to mono cation derivatives. The different traditional exchange methods to prepare carboxylate DILs have been evaluated and an insight into the drawbacks encountered is also presented. Prepared DILs were characterized (NMR, TGA, DSC) allowing the influence of the structure on their thermal stability to be understood. Most DILs were obtained as solid salts after careful drying. For some of these compounds, a new possible application was studied, namely their use as hydrogen bond acceptors (HBA) of deep eutectic mixtures, showing again some significant structural related effects

Synthesis, analysis and applications of novel dicationic ionic liquids

Sintesi e caratterizzazione di liquidi ionici dicationici e dianionici. Valutazione delle proprietà termiche e caratterizzazione FIR e THz. Applicazione e studio dell'attività catalitica nella addizione di CO2 a epossidi

Study, development and testing of innovative electrolytes for redox flow batteries

Durante questo dottorato è stata condotta una serie di studi incentrati sull’esplorazione di nuovi approcci per la risoluzione di alcune delle più tipiche problematiche delle batterie a flusso. Le attività di ricerca sono state indirizzate verso lo sviluppo di fluidi elettroattivi innovativi, rivolgendo una particolare attenzione allo studio di nuovi sistemi più performanti dal punto di vista della densità e dell'efficienza energetica, della stabilità e della riduzione dell'aggressività nei confronti delle altre componenti della batteria. Per la preparazione degli elettroliti oggetto dello studio, in ambiente sia acquoso che non acquoso, sono stati adottati due approcci principali: l’utilizzo di liquidi ionici come mezzo per modulare le caratteristiche di solubilità delle specie redox, e l’impiego di specifici agenti complessanti per incrementare la stabilità degli elettroliti. I risultati ottenuti da questo progetto di dottorato hanno certamente contribuito a confermare l’applicabilità dei nuovi approcci studiati come validi strumenti per il miglioramento delle prestazioni di elettroliti per batterie a flusso (sia acquosi che non acquosi) in termini sia di densità energetica che di stabilità. I metodi qui proposti possono quindi rappresentare un primo promettente passo verso la soluzione di alcune delle più importanti criticità delle batterie a flusso. During this PhD thesis a series of studies focused on the investigation and on the improvement of RFBs issues have been carried on. The research activities have been centered on the development of innovative redox-active fluids, with a particular attention on the study of novel approaches for the realization of systems characterized by improved energy density, efficiency, stability and a reduced aggressiveness toward the other battery components. Two main approaches have been followed for the preparation and the testing of innovative electrolyte systems, both in aqueous and in non-aqueous environments: the use of ionic liquid as a mean to tune the solubility properties of the redox active compounds, and the adoption of specific complexing agents for the enhancement of the electrolyte stability. The results obtained from of this PhD project have certainly contributed to assess the applicability of the investigated novel approaches for the realization of aqueous and non-aqueous RFB electrolytes with enhanced energy density and stability characteristics. The promising methods here proposed could therefore represent a first valuable step towards the solution of some of the most typical issues and limitations of redox flow battery technologies

Evaluation of the effect of the dicationic ionic liquid structure on the cycloaddition of CO2 to epoxides

The cycloaddition of CO2 to epoxides has attracted a great deal of interest in recent years as an atom efficient way to employ this greenhouse gas as a useful C1 building block. While several ionic liquids have been tested as catalysts for the reaction, little attention has been devoted to dicationic ionic liquids (DILs). Herein, the catalytic activity of a panel of structurally-related DILs has been evaluated in the cycloaddition of CO2 to epichlorohydrin, in order to study the influence of the DILs' structure on their activity. The solubilities of a series of bromide DILs in epichlorohydrin, featuring various linker lengths and imidazolium substituents, were investigated. The bromide Cn(MIM)2 series displayed a limited solubility in this medium, which particularly affected the performances of C3(MIM)2 2Br. However, the addition of 20※mol% of reaction product to the reactants was found to be an effective way to overcome this issue. This way, it was possible to compare the catalytic activity of both soluble and only partially soluble systems in epichlorohydrin. C6(MIM)2 2Br and C5(HIM)2 2Br were found to be the best performing DILs and have been tested, together with monocation C4MIM Br, also on less reactive epoxides. Mono and dicarboxylate (D)ILs instead proved to be less active than the bromide DILs and, when considering their synthesis, thermal stability and moisture sensitivity, ultimately less attractive for the development of future catalysts. Finally, a convenient and operationally simple way of recovering and reusing the bromide DILs at the end of the reaction was also evaluated

The Structure–Property Relationship of Pyrrolidinium and Piperidinium-Based Bromide Organic Materials

Two couples of dicationic ionic liquids, featuring pyrrolidinium and piperidinium cations and different linker chains, were prepared and characterized. 1,1′-(propane-1,3-diyl)bis(1-methylpyrrolidinium) bromide, 1,1′-(octane-1,8-diyl)bis(1-methylpyrrolidinium) bromide, 1,1′-(propane-1,3-diyl)bis(1-methylpiperidinium) bromide, and 1,1′-(octane-1,8-diyl)bis(1-methylpiperidinium) bromide were synthesized in quantitative yields and high purity and thermally characterized through TGA and DSC analysis. In this study, we propose a preliminary comparative evaluation of the effect of the linker chain length and of the size of the aliphatic ammonium ring on the thermal and solubility properties of bromide dicationic ionic liquids

Novel access to ionic liquids based on trivalent metal–EDTA complexes and their thermal and electrochemical characterization

Two series of ionic liquids (ILs) consisting in metal-EDTA complex anions ([MEDTA], with V, Cr, Mn, Fe and Co as metal center) and 1-butyl-3-methylimidazolium ([BMIM]) or trioctylmethylphosphonium ([TOMP]) cations have been prepared via a new synthetic approach based on the related acidic EDTA complexes (HMEDTA). A strong influence of both the coordinated metal and the cation type on the thermal behavior of the obtained ILs was assessed through DSC and TGA, while the solubility features were found to be primarily affected by the cation nature. The observed solubility results for [TOMP] series ILs in organic solvents showed the preparation of ILs as an effective way to solubilize metal-EDTA complexes into non-aqueous solutions, opening new investigation potential and applicative perspectives. The electrochemical properties of the synthesized ILs have been studied both in aqueous and non-aqueous environments, providing insights on the strong solvent effect on metal-EDTA complexes electrochemistry and, for many of the ILs, showing promising characteristics for electrochemical applications both in water and in organic solvents

An insight into the intermolecular vibrational modes of dicationic ionic liquids through far-infrared spectroscopy and DFT calculations

Dicationic ionic liquids (DILs) are a subclass of the ionic liquid (IL) family and are characterized by two cationic head groups linked by means of a spacer. While DILs are increasingly attracting interest due to their peculiar physico-chemical properties, there is still a lack of understanding of their intermolecular interactions. Herein, we report our investigations on the intermolecular vibrational modes of two bromide DILs and of a bistriflimide DIL. The minimal possible neutral cluster of ions was studied as a simplified model of these systems and was optimized at the DFT level. Normal modes of two sandwich-like conformers were then calculated using the harmonic approximation with analytical computation of the second derivatives of molecular energy with respect to the atomic coordinates. The calculated spectra were compared to far-infrared experimental spectra and two groups of peaks over three, for the two bromide DILs, and three over five, for the Tf2N- DIL, were described by the proposed neutral cluster model. Therefore, this model represents a reliable and computationally affordable model for the exploration of the intermolecular interactions of this kind of system