Radical-Polar Crossover in Bismuth LMCT PhotocatalysisKermelj, Vid (Avtor) Iskra, Jernej (Mentor) König, Burkhard (Komentor) bismuthLMCTphotocatalysisradical-polar crossoverdecarboxylationLigand to metal charge transfer (LMCT) has emerged as a promising photochemical activation process for facilitating organic transformations. Recently, the LMCT properties of bismuth – an element renowned for its minimal toxicity and environmental sustainability – have garnered significant interest. Given bismuth's ability to adopt multiple oxidation states, the radical-polar crossover represents a viable alternative reaction pathway. This pathway is explored in this master's thesis, aiming to potentially unlock novel reactivity and explore its applications in green chemistry. The ability of bismuth to mediate ligand to metal charge transfer (LMCT) decarboxylation of benzylic carboxylic acids has been confirmed. The observed results corroborate existing literature on the radical-radical rebound of bismuth(II) species and carbon radicals. The ionic nature of this system was confirmed by successful trapping of the resultant carbocations using electron-deficient nitrogen nucleophiles. Bismuth(III) triflate was identified as the optimal bismuth source due to its superior facilitation of oxidation to a carbocation-like intermediate. The findings suggest that coordination of the nucleophile to the bismuth center is essential, leading to product formation through a reductive elimination mechanism. A significant competing reaction within the system is the radical-radical homocoupling of the formed carbon radicals. The pH of the system plays a pivotal role, with an excess of a base enhancing the formation of homocoupling products. This is attributed to multiple carboxylic acids coordinated to the bismuth’s center, which facilitates rapid homocoupling and impedes nucleophile coordination. Conversely, the release of protons during oxidative coupling decelerates the reaction. Dichloromethane was identified as the optimal solvent due to its high polarity and non-coordinating nature. The system has been rendered catalytic, with persulfate salts proving to be the most effective external oxidants. DFT calculations have been performed for a series of bismuth complexes with aryl acetic acids. The visualizations of molecular orbitals suggest that the HOMO orbital of LMCT-active complexes is centered on the π-orbital system of the pendant aryl residue. DFT-derived UV-Vis predictions show absorption variance for different ligand environments. UV-Vis measurements have shown a shift of LMCT towards longer wavelengths with increasing electron richness of the pendant aryl ring for a series of aryl acetic acid complexes with bismuth(III) triflate.20242024-08-23 09:15:00Magistrsko delo/naloga160211VisID: 22978COBISS_ID: 205911299sl