Transition Metal Mediated Cycloaromatization of Dienyne and Enediyne Systems; Chromium Mediated Selective Terminal Alkene Hydrogenation; Chelated Zinc Lewis Acid Co-catalyzed Electrochemical Reduction of Carbon Dioxide by Mn Catalysts

This work started with a thorough review on current study in activating conjugate alkene or alkyne system with metal complexes. The insightful research on various metal coordinated η6, η4 and η2 complexes provided us with concrete references in resolving metal mediated electrocyclizations. With these studies we proposed many interesting hypotheses and investigated and produced novel research results.In chapter 2, we continued investigating the Cp*Ru+L3 triggered electrocyclization. We successfully isolated and characterized the first Cp*Ru(η6 -dienyne) complex, which was believed to be the crucial intermediate during the electrocyclization. Further study was carried out with a focus on phenyl substituted dienyne substrates. We confirmed the coordination priority and resolved an isomerization within its mechanism. We then ameliorated the ruthenium complex with a naphthalene ligand to achieve a control on the para-diradical formation with photon activation. Lastly, we presented an interesting and unexpected result when replacing the Ruthenium metal center with Iridium in reacting with dienyne substrate. In chapter 3, we report a chromium complex mediator, Cr(CO)3(η6-naphthalene), that mediates the traditional thermal dienyne cyclization at ambient temperature. Successful cycloaromatizations were observed to proceed to moderate yield in coordination. Further mechanistic study was undertaken by monitoring v(CO) stretching via infrared (IR) spectroscopy. A speculative Cr(CO)3(η6-dienyne) intermediate was observed using 2D-IR spectroscopic analysis and coanalysis. In chapter 4, we report a newly discovered alkene reduction reaction mediated by tris(acetonitrile)tricarbonylchromium in acetone. While attempting to effect chromium-mediated thermal cycloaromatization of dienynes, we discovered that, in a homogeneous tris(acetonitrile)tricarbonylchromium-acetone solution system, a highly selective reduction of a less hindered terminal alkene can be achieved without the source of hydrogen. A further mechanistic study has confirmed that hydrogen was provided by the solvent, acetone. Therefore, we present an attempt to elucidate its mechanism. In chapter 5 reports the use of a soluble Lewis acid complex, [Zn(cyclam)]2+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) as a co-catalyst coupled with Mn(Mesbpy)(CO)3Br (Mesbpy = 6,6’-dimesityl-2,2’-bipyridine) for the electrochemical reduction of CO2 to CO. Utilization of the soluble chelated Lewis acid avoids the use of sacrificial additives and prevents the formation of insoluble products such as MgCO3 or ZnCO3 that change the thermodynamics of the CO2 reduction. The use of soluble Lewis acids greatly improves catalysis compared to previously reported systems that used sacrificial anodes