Transition metal-catalyzed hydrogen transfer processes

Sammanfattning: The first part describes the synthesis of new analogues of Bäckvall’s catalyst with varying electronic properties and their application in the racemization of sec-alcohols. The racemization involves two key steps: (i) β-hydride elimination (dehydrogenation of the alcohol) and (ii) hydride re-addition to the intermediate ketone. The obtained results confirmed our previous theory that the electronic properties of the substrate determine which of these two steps that is rate-determining. Furthermore, it was demonstrated that a dramatic increase in racemization rate could be obtained by matching the electronic properties of catalyst and substrate. The second part describes mechanistic studies done on Bäckvall’s catalyst, where the exchange of carbon monoxide was investigated. By monitoring the uptake of 13C-labeled CO by 13C NMR spectroscopy, we could observe that the CO-exchange was approximately 20 times faster in the catalytically active tBuO-species than in the chloride precatalyst. Furthermore, an inhibitory effect could be observed in the racemization reaction of (S)-1-phenylethanol upon addition of CO. These results provide strong experimental support for reversible CO dissociation as a key step in the racemization mechanism of sec-alcohols. The third part describes the synthesis and characterization of highly dispersed palladium nanoparticles immobilized on amino-functionalized siliceous mesocellular foam. The catalyst exhibited high activity in the aerobic oxidation of a wide range of primary and secondary alcohols, when using air as source of oxygen. Moreover, the catalyst exhibited excellent recyclability and negligible leaching, making it an environmentally friendly alternative for these transformations.