Transition Metal Catalysis for Selective Synthesis and Sustainable Chemistry
Abstract: This thesis discusses the preparation and use of transition-metal catalysts for selective organic chemical reactions. Specifically, two different matters have been studied; the asymmetric hydrogenation of carbon-carbon double bonds using N,P-ligated iridium catalysts and the metal-catalyzed transfer of small molecules from biomass to synthetic intermediates.In the first part of this thesis, chiral N,P-ligands were synthesized and evaluated in iridium catalysts for the asymmetric hydrogenation of non- and weakly functionalized alkenes (Papers I & II). The new catalysts were prepared via chiral-pool strategies and exhibited superior properties for the reduction of certain types of alkenes. In particular, some of the catalysts showed excellent activity and selectivity in the enantioselective reduction of terminal alkenes, and the preparation of a modular catalyst library allowed the asymmetric hydrogenation of a wide range of 1,1-disubstituted alkenes with unprecedented efficiency and enantioselectivity (Paper III). Methods for the selective preparation of chiral hetero- and carbocyclic fragments using iridium-catalyzed asymmetric hydrogenation as an enantiodetermining key step were also developed. A range of elusive chiral building blocks that have applications in pharmaceutical and natural-product chemistry could thus be conveniently prepared (Papers IV & V).The second part of this thesis deals with the catalytic decomposition of polysaccharides into sugar alcohols and the incorporation of their decomposition products into alkene substrates. Iridium-catalyzed dehydrogenative decarbonylation was found to decompose polyols into CO:H2 mixtures that could be used immediately in the ex situ low-pressure hydroformylation of styrene (Paper VI). The net process was thus the hydroformylation of alkenes with biomass-derived synthesis gas.
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