1,721,041 research outputs found
Peroxo-vanadium Complexes as Sustainable Catalysts in Oxidations, Halogenations and Other Organic Transformations
No full textVanadium in its high-oxidation state can activate hydrogen peroxide and other alkyl hydroperoxides, generating highly active oxidising species, namely vanadium peroxido-complexes. Several studies have been performed to deeply investigate structural features and reactivity of such species. In this chapter, the application of V-peroxido-complexes in oxidation and halogenation reactions will be discussed. Specifically, oxidation of different hydrocarbon substrates (i.e., alkanes, alkenes, aromatics), alcohols, phenols and sulphides, as well as the catalytic bromination reaction of diverse organic substrates will be addressed. Notably, vanadium peroxido-complexes result in effective catalysts to perform these transformations in very mild conditions. Importantly, the feasibility of the proposed procedures on a large scale allows their exploitation for appealing applicative purposes. Examples of lignin valorisation, fuel desulfurization, as well as clean synthetic methodologies for developing interesting building blocks for synthetic, industrial and pharmaceutic applications will be summarised
The effects of electronic delocalization and metal-metal coupling on the core levels of tetraferrocenylporphyrins
No full textQuinacridone dyes: versatile molecules and materials for photo- and photoelectrochemical processes
Full text linkThe renaissance of photochemistry and the explosion of photo- and photoelectro-catalysis open new opportunities in organic photocatalyst design and applications towards solar fuels and sustainable organic reactivity. In this perspective, we discuss the relevant case of quinacridone (QA) dyes: these have long been known to the scientific community, but their application in photocatalysis is recent and still explored in a limited way. This is somehow surprising given that QA is a cheap and readily available organic pigment, and in front of the appealing properties of QA derivatives, including intense absorption in the visible region, balanced redox properties making them suitable for both oxidative and reductive photochemistry, and versatility to several operative conditions. We will discuss recent examples of photo- and photoelectrochemical processes taking advantage of QA dyes, from solution photocatalysis to photoactive materials and devices (nanoparticles, covalent organic frameworks, photoelectrodes); the target applications include water splitting, carbon dioxide reduction, and organic transformations. We aim to show the potential of organic photocatalyst design and implementation, and to inspire the readers with new opportunities in this field.We discuss the versatility of quinacridone pigment in photocatalysis, embracing water splitting, carbon dioxide reduction and organic synthesis. Applications include homogeneous catalysis, nanoparticles, covalent organic frameworks, photoelectrodes
The crucial role of the supporting electrolyte in redox flow battery performances
No full text6 figures, 3 tables.Renewable energy sources are being adopted more widely around the world. This is due to increasing energy demands, the fact that countries have set targets to reduce carbon emissions, and that solar and wind energy are intermittent by nature. This means that reliable, large-scale storage solutions are needed urgently. Redox flow batteries (RFBs) are proving to be leading candidates in this field, as they decouple power and energy capacities, enabling highly scalable and modular installations. One of the key parameters of RFB performances relies on the supporting electrolyte. It can affect ionic conductivity (IC), redox stability, membrane selectivity and cycle life. In this review we present a comparison of the supporting electrolyte's role in both aqueous and non-aqueous RFBs. A comparison between traditional inorganic salts (e.g. H2SO4, Na2SO4, KCl) and novel neutral organic electrolytes such as ionic liquids (ILs) and deep eutectic solvents (DES) is assessed. Here we highlight how those latter are able to improve the properties of the electroactive solution in terms of increasing solubility, conductivity and thermal and electrochemical stability. In addition, a cost analysis of those novel organic electrolytes is presented, alongside future hybrid electrolytes.The authors are thankful for the Grant MUR Dipartimento di
Eccellenza 2023-27 X-CHEM project ‘‘eXpanding CHEMistry:
implementing excellence in research and teaching’’.Peer reviewe
Palladium-catalysed methylation of aryl halides in ionic liquids with stabilized AlMe3
No full textA new protocol for the methylation of aryl halides using the AlMe3 analogue DABAL-Me3 in a VOC/IL biphasic system is described. Very good isolated yields and chemoselectivities (methylation vs homocoupling), were observed in alkylmethylimidazolium and DABCO-based ILs, in presence of a bulky substituted phosphine (XPhos) and the structurally related sulfonated phosphine (XPhosSO3H). Recycling experiments of the IL-catalyst systems were satisfactory only in case of the butyldimethylimidazolium IL due to catalyst loss to the VOC phase. © 2010 Elsevier B.V. All rights reserved
Modulating electron transfer in ferrocene-naphthoquinone dyads: New insights in parameters influencing ET efficiency
No full textElectron transfer (ET) constitutes a key process for several biological transformations, including solar
energy conversion in bacteria and plants. Nowadays, numerous synthetic systems have been proposed to mimic such kind of natural occurring process. In this work, we elucidate the factors that mostly influence the electron transfer process in ferrocene-naphthoquinone dyads. In particular, the connection between the two redox units has been varied, in order to study the ET dependence from: i) the distance between donor-acceptor units and ii) the oxidation potential of the donor species. No interaction among the two moieties has been detected at the ground state, while efficient electron transfer process was observed following excitation of the naphthoquinone through UV-light, as well as upon the aid of a Lewis acid promoter in solution. Moreover, DFT calculations have been performed to support the experimental data
A Sustainable Improvement of <em>ω</em>-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones
Full text linkOwing to the attractiveness of organic phosphonic acids and esters in the pharmacological field and in the functionalization of conductive metal-oxides, the research of effective synthetic protocols is pivotal. Among the others, ω-bromoalkylphosphonates are gaining particular attention because they are useful building blocks for the tailored functionalization of complex organic molecules. Hence, in this work, the optimization of Michaelis–Arbuzov reaction conditions for ω-bromoalkylphosphonates has been performed, to improve process sustainability while maintaining good yields. Synthesized ω-bromoalkylphosphonates have been successfully adopted for the synthesis of new KuQuinone phosphonate esters and, by hydrolysis, phosphonic acid KuQuinone derivatives have been obtained for the first time. Considering the high affinity with metal-oxides, KuQuinones bearing phosphonic acid terminal groups are promising candidates for biomedical and photo(electro)chemical applications
Sustainable Highly Selective Toluene Oxidation to Benzaldehyde
Full text linkThanks to the well-recognized role of benzaldehyde in industry, nowadays the research of new and sustainable approaches to selectively synthesize such an interesting product is receiving great attention from the chemists’ community. In this paper, a V-based catalytic biphasic system is adopted to perform toluene oxidation to benzaldehyde. Importantly, to pursue sustainability, organic solvents have been avoided, so toluene is used as substrate and co-solvent, together with water. Also, the use of hydrophobic ionic liquids has been explored. To perform oxidation, NH4VO3 catalyst, H2O2, and a safe and inexpensive co-catalyst are used. Among the tested co-catalysts, KF and O2 were found to be the best choice, to guarantee good yields, in mild reaction conditions. In fact, with such a sustainable method, up to 30% of benzaldehyde can be obtained at 60 °C and, more interestingly, the oxidative system can be recharged, raising-up the yield. The entire process results highly selective, since no traces of benzyl alcohol or benzoic acid are detected. Hence, it constitutes a very appealing synthetic route, even suitable to be easily scaled-up at an industrial level
Construction of electron-active complex systems as model for artificial photosynthesis
No full textLa fotosintesi artificiale è un obiettivo ambizioso per la scienza moderna, che richiede una comprensione completa dei sistemi naturali. La comprensione di tutte le diverse reazioni del sistema è uno degli aspetti fondamentali nella ricerca chimica, fisica e biologica. Lo studio delle reazioni di trasferimento elettronico tra un accettore e un donatore è un punto cruciale, sia per lo sviluppo di sistemi artificiali sintetici, sia per possibili applicazioni nella costruzione di dispositivi elettronici e materiali fotosensibili. Lo scopo di questa tesi è stato quello di investigare reazioni di trasferimento elettronico e di energia, per avere informazioni riguardo le leggi che regolano questi sistemi complessi, usando diversi sistemi donatore-accettore, tra i quali particolare attenzione è stata rivolta al C60 come accettore e al ferrocene come donatore. Il lavoro sintetico è stato una parte importante della tesi, richiedendo tempo per ottimizzare le condizioni di reazione, le procedure di purificazione e per la completa caratterizzazione dei prodotti. Numerosi nuovi composti sono stati sintetizzati e sono state migliorate le rese per alcuni prodotti noti da letteratura. Un aspetto importante del lavoro ha riguardato lo studio dell’interazione tra donatore e l’accettore in alcune delle diadi ottenute, sia allo stato fondamentale, sia nello stato eccitato. Tra i vari risultati, i più interssanti possono essere riassunti nei seguenti punti. a) Un andamento peculiare emerge dagli esperimenti fotofisici e computazionali e dalle misure elettrochimiche e degli spettri di assorbimento nelle diadi fluorene-fullerene: cambia l’interazione, cambiando la posizione del fluorene che lega il fullerene. b) Risultati molto interessanti sono stati ottenuti quando ferrocene e fullerene sono uniti tramite legame spiro, dando una diade dalla geometria rigida. Difatti, confrontando le proprietà nello stato eccitato di questa diade con quelle della N-metil-2-ferrocenil-[3,4]-fulleropirrolidina, con maggiore libertà conformazionale, è stata osservata una reazione di trasferimento elettronico più veloce, indice di una maggiore interazione tra i due componenti. c) In diadi supramolecolari composte da ZnSalen e N-metil-2-piridil-[3,4]-fulleropirrolidina è stato osservato un efficiente trasferimento di energia. Questo sistema può essere usato come modello nei sistemi impiegati nella cattura della luce. d) Un efficiente trasferimento di elettroni avviene tra la tetraferrocenilporfirina di zinco e la N-metil-2piridil-[3,4]-fulleropirrolidina in una diade supramolecolare, come è stato osservato tramite la spettroscopia transiente, dove un tempo di vita di 800 ps della specie eccitata a separazione di carica è stato ottenuto in un solvente apolare come il toluene. In conclusione, sono stati ottenuti nuovi sistemi per lo studio delle reazioni di trasferimento di energia e di elettroni, che sono stati studiati usando diversi approcci sperimentali. I risultati possono essere di aiuto sia per una miglior comprensione dei fenomeni naturali, sia per lo sviluppo e la costruzione di dispositivi fotosensibili.Artificial photosynthesis is an ambitions target of modern science that obviously requires a complete understanding of natural photosynthesis. The understanding of all steps involved is one of the most important topic in chemical, biological, and physical research. The study of electron transfer reaction between donor and acceptor molecules is a crucial key point, both for development of artificial photosynthesis and for application in electronic devices and photosensible materials. The aim of this thesis was to investigate electron and energy transfer reactions, as source of information about the mechanisms that rule this complex reaction, using different donor-acceptor systems, among which attention have been focused at C60 as acceptor and ferrocene as donor. Synthetic work constituted a major task in this thesis, requiring several attempts in order to optimize reaction conditions, purification procedures and full characterization of products. A number of new compounds was obtained together with improved yields of known products. Another important aspect of the work involved investigation of donor-acceptor interaction in some of the dyads, both in ground and in excited states. Among all the results, the most significant ones may be summarized in the following points. a) A peculiar behaviour emerged from photophysical and computational experiments, electronic spectra and electrochemical measurements of fluorene-fullerene dyads. Different interaction was the result of changing the position through which the two moieties are connected. b) Very interesting results emerged when a frozen structure was obtained from connecting ferrocene and fullerene moieties in a rigid assembly. In fact, in comparison with a dyad with flexible connection, a faster electron transfer rate - and therefore an enhanced interaction - was observed in the excited state. c) Efficient energy transfer was observed with supramolecular (ZnSalen)-(N-methyl-2-pyridyl-[3,4]fulleropyrrolidine) dyads. This system can be used as a good model for light harvesting model. d) Very efficient electron transfer reaction occurred between zinctetraferrocenylporphyrin and pyridylfulleropyrrolidine in supramolecular (ZnFc4Porph)-(N-methyl-2-pyridyl-[3,4]-fulleropyrrolidine) dyad, as observed by transient spectroscopy, even in non polar solvent such as toluene. In conclusion, new good systems for energy an electron transfer were obtained and investigated by different approaches. They can be used to reach a deeper knowledge of complex phenomena that rule natural photosynthesis as well as to build photosensible devices
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