Data di Pubblicazione:
2020
Citazione:
HYBRID CATALYSTS FOR CARBENE AND NITRENE TRANSFER REACTIONS / C. Damiano ; tutor: E. Gallo ; coordinatore: E. Licandro. DIPARTIMENTO DI CHIMICA, 2020 Jan 29. 32. ciclo, Anno Accademico 2019. [10.13130/damiano-caterina_phd2020-01-29].
Abstract:
The chemical industry is ever more focused on the development of sustainable and selective procedures for the synthesis of high-added value fine chemicals, in order to meet the demand in society for environment-friendly chemical processes. The metal-catalysed carbene and nitrene transfer reactions have proved to be an excellent strategy to achieve the goal, due to their ability to form C-C, C-N and C heteroatom bonds with high stereo- and regioselectivities. In addition, the good choice of the carbene and nitrene precursors can increase the reaction sustainability and the atom efficiency, as when diazo compounds and azides were used as starting materials thanks to the formation of molecular nitrogen as the only by product of the reaction. Among all the metal catalysed carbene and nitrene transfer reactions, the formation of three-membered ring compounds, such as cyclopropanes and aziridines, is a very attractive topic due to their use as building blocks in organic chemistry and their biological and/or pharmaceutical activity. Considering the catalytic activity of metal porphyrin complexes in promoting cyclopropanation and aziridination reactions of alkenes, the following PhD thesis aims to develop a new class of hybrid catalysts which are able to mediate carbene and nitrene transfer reactions under mild experimental conditions. In order to confer chiral recognition properties and modulate the catalyst properties, the conjugation of metal porphyrin complexes with bio scaffolds such as carbohydrates, amino acids, cellulose and β-lactoglobulins was studied. Carbohydrates are natural chiral, polyhydroxylated compounds which play critical roles in several biological processes, including the energy storage, cellular communications and recognitions, and the immune system maintenance. Glycoporphyrins, derived from the conjugation of porphyrin rings with sugar units, are efficient photosensitizers extensively used in photodynamic therapy (PDT) and they are desirable ligands for organometallic synthesis. To assess how different glycosylated porphyrin ligands can influence the catalytic activity of corresponding ruthenium and iron complexes, different meso glycosyl-conjugated porphyrins were synthesised. The number and position of carbohydrate units on the porphyrin skeleton play an important role in determining the ligand chemo-physical properties. Mono and tetra-glycosylated porphyrins were synthesized and the corresponding iron and ruthenium complexes were tested as catalysts of cyclopropanation and aziridination reactions. In the model cyclopropanation reaction between α-methylstyrene and EDA, Fe(III)(porphyrin)OMe complexes showed higher activity then Ru(II)(porphyrin)CO derivatives and obtained data indicated the strong dependence of the reaction diastereoselectivity on the ligand structure. Among all the iron complexes which were tested as cyclopropanation catalysts, Fe(15)OMe complex was chosen to study the reaction scope by testing different styrenes in view of the good compromise between the synthetic accessibility of synthesize it and reaction productivity (yields and diastereoselectivities). All the desired cyclopropanes were obtained in very good yields (up to 80%) and trans diastereoselectivities (up to 98:2). The obtained iron and ruthenium glycoporphyrin complexes were also tested in the model aziridination reaction between α-methylstyrene and 3,5-bis-(trifluoromethyl)phenylazide. Unfortunately, Fe(III)(porphyrin)OMe complexes didn’t catalyse the aziridination reaction but the desired product was obtained in a very good yield (83%) in the presence of Ru(15)CO. The latter catalyst was used to study the reactivity of α-methylstyrene towards different aryl azides and the obtained data indicated the ability of Ru(15)CO to p
Tipologia IRIS:
Tesi di dottorato
Keywords:
carbene transfer; nitrene transfer; hybrid catalysts; porphyrins; bio-scaffolds; sugars; aminoacids; cellulose; proteins; cyclopropanes; aziridines; CO2; cyclic carbonates; oxoazolidinones
Elenco autori:
C. Damiano
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