COBALT AND NICKEL CATALYZED VINYLIDENE TRANSFER REACTIONS AND THEIR APPLICATIONS

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.