<p dir="ltr">The recently developed in this group, new method of generating cobalt and nickel vinylidene complexes in situ from 1,1-dichloroalkenes and their catalytic transfer reactions has proven to be a fertile ground for discovery of many useful transformations. In this dissertation, further studies of their reactivity and mechanisms are discussed based on the findings from several methodology projects. The use of chiral ligand enables asymmetric vinylidene transfer reactions and with symmetrical (Z)-alkenes as substrates, the products are methylenecyclopropanes with axial chirality (Chapter 2). DFT studies unveil the unique model of asymmetric induction where the substituent on the vinylidene substrate plays a crucial role. These products were intriguing due to their potential applications in many fields as well as their chirality transfer reactions that can provide diverse building blocks, but they were previously unobtainable. In Chapter 3, the finding of a new reducing condition for these general transformations was discussed in detail, followed by the uncovering of previously unknown effects of routinely used metallic Zn powder. This study provided a window to view the vulnerabilities in the general mechanism of this novel type of net-reductive reaction when ran under Zn reduction and explains some of the previously mysterious ligand effects. The new reduction condition runs under photoexcitation and is a Lewis acid free medium that can allow the discovery of new reactions. In Chapter 4, the above alternative reduction condition was applied to address the yield problem of a [2+2+1] cycloaddition reaction of vinylidenes with 1,6-enynes. This reaction was also found to work successfully in an intermolecular manner with excellent regioselectivity. Overall, this doctoral research work further expands this manifold towards the direction of asymmetric reactions and more complex cycloaddition reactions.</p>

This thesis deals with secondary interactions in asymmetric catalysis and their impact on the outcome of catalytic reactions. The first part revolves around the metal-catalyzed asymmetric allylic alkylation reaction and how interactions within the catalyst affect the stereochemistry. An OH–Pd hydrogen bond in Pd(0)–π-olefin complexes of hydroxy-containing oxazoline ligands was identified by density functional theory computations and helped to rationalize the contrasting results obtained employing hydroxy- and methoxy-containing ligands in the catalytic reaction. This type of hydrogen bond was further studied in phenanthroline metal complexes. As expected for a hydrogen bond, the strength of the bond was found to increase with increased electron density at the metal and with increased acidity of the hydroxy protons. The second part deals with the use of hydroxy- and methoxy-containing phosphinooxazoline ligands in the rhodium- and iridium-catalyzed asymmetric hydrosilylation reaction. The enantioselectivities obtained were profoundly enhanced upon the addition of silver salts. This phenomenon was explained by an oxygen–metal coordination in the catalytic complexes, which was confirmed by NMR studies of an iridium complex. Interestingly, the rhodium and iridium catalysts nearly serve as pseudo-enantiomers giving products with different absolute configurations. The final part deals with ditopic pyridinobisoxazoline ligands and the application of their metal complexes in asymmetric cyanation reactions. Upon complexation, these ligands provide catalysts with both Lewis acidic and Lewis basic sites, capable of activating both the substrate and the cyanation reagent. Lanthanide and aluminum complexes of these ligands were found to catalyze the addition of the fairly unreactive cyanation reagents ethyl cyanoformate and acetyl cyanide to benzaldehyde, whereas complexes of ligands lacking the Lewis basic coordination sites failed to do so. / QC 20100709