116 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 textConstruction 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
A Sustainable Improvement of <em>ω</em>-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones
No full textOwing 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
Chemical routes to fine tuning the redox potential of monolayers covalently attached on H–Si(100)
No full textA closely related series of three ferrocene derivatives, bearing a short carbon-carbon tethering arm for covalent attachment to H-terminated Si(1 0 0). has been used to produce electroactive hybrid materials. Three different grafting procedures have been applied for the first time on this type of molecules in order to obtain the full series of possible unsaturations in the C-C lateral chain bound to Si: ethyl, vinyl and ethynyl group, respectively, associated with the surface species (eta(5)-C(5)H(5))Fe(2+)(eta(5)-C(5)H(4))-CH(2)-CH(2)-Si (EtFC/Si), (eta(5)-C(5)H(5))Fe(2+)(eta(5)-C(5)H(4))-CH=CH-Si (VFC/Si), and (eta(5)-C(5)H(5))Fe(2+)(eta(5)-C(5)H(4))-C C-Si (EFC/Si). The surface reactions here applied involve Grignard derivatization, Lewis acid catalysis and nucleophilic substitution by an acetylide anion. The redox potentials of the three molecule/surface hybrids, measured by cyclic voltammetry, are 0.059, 0.136 and 0.251 V vs. Ag/Ag(+), respectively, from EtFC/Si to EFC/Si and are supposedly following the increasing trend of the extent of unsaturation in the tethering arm. The above trend in redox potentials parallels the one experimentally found and theoretically reproduced for the corresponding isolated molecules, which shows that the adopted functionalization procedures may be used to control the number of residual unsaturations in the C-C arm. The presence and chemical nature of the redox species covalently attached to Si are strongly supported after evaluation of XPS spectra and electrochemical data. The formation of electroactive hybrids on Si with tuneable well-defined switching potentials can be highly beneficial to the development of Si-based memory devices. (C) 2010 Elsevier Ltd. All rights reserved
Bromination of tetrapyrrolic scaffolds: a sustainable approach
No full textA sustainable procedure developed for the bromination of organic substrates, such as olefins and small aromatic rings, has been applied to porphyrin derivatives. The synthetic method, based on a V(V) or Mo(VI) catalyzed reaction, occurs in a two-phase medium and uses cheap and environmental friendly reagents such as KBr and H2O2 as the bromine source and primary oxidant respectively. Compared to the classical protocols for porphyrinoid bromination, this approach is based on milder and safer reaction conditions. The selective formation of mono or polybrominated substrates has been achieved by accurate tuning of key parameters (H2O2 and KBr amount, catalyst). While with vanadium good results to obtain partially substituted porphyrins have been gained, full peripheral functionalization can be obtained with either vanadium or molybdenum catalysis depending on the metal ion coordinated to the inner cor
Sustainable Highly Selective Toluene Oxidation to Benzaldehyde
No full textThanks 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
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
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
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