Hydrofunctionalization Through Electrophilic Alkene Activation Using Carbodicarbene Ligands

Alkenes and related π-systems serve as versatile and readily available feedstocks for the synthesis of a plethora of natural products and fine chemicals. The benefits of using these ubiquitous structures has fueled industrial research into alkene functionalization and related catalysis. Industrially relevant examples include the Tsuji-Wacker oxidation, the Mizoroki-Heck reaction, and asymmetric epoxidation. Successive improvements to alkene functionalization have been accomplished through iterative design of new ligands that form increasingly active metal complexes. These organometallic complexes are particularly effective at binding alkenes in order to activate stable π-systems. One mode of activation is to bind the alkene to an electron poor metal, which withdraws electron density from the alkene, making it susceptible to attack from an external nucleophile. Known as electrophilic activation, this mechanism can be generalized for a variety of nucleophiles that allow for C-C (hydroalkylation), C-N (hydroamination), and C-O (hydroetherification) bond formation. The mechanism begins with the binding of an alkene to the electrophilic metal center. The properties of the metal center are tuned by the ligand framework, which can be used to control the reactivity of the bound alkene. Alkene binding is followed by external addition of the nucleophile to generate a metal-alkyl intermediate. The metal-alkyl bond is then protonated to form a C-H σ-bond and the product. Dissociation of the product regenerates the electrophilic metal center and closes the catalytic cycle. The following studies will relate efforts to design organometallic catalysts for electrophilic alkene activation with the goal of promoting hydrofunctionalization reactions. Hydrofunctionalization is formally defined as a class of alkene reactions where the π-bond of the alkene is transformed into two new σ-bonds including a carbon-hydrogen bond. Such transformations have received considerable attention for their utility in forming desirable bonds with complete atom economy. The following chapters will document research into electrophilic hydrofunctionalization catalyzed by a series of new cationic metal complexes employing carbodicarbene ligands. Carbodicarbenes were not previously known as catalytically active ligands, but their unique reactivity has proved beneficial for stabilizing cationic Rh complexes.Doctor of Philosoph