This thesis focuses on the development of carbon-carbon/carbon-heteroatom bond forming reactions using strained ring systems under transition metal catalysis. The first chapter describes the use of bifunctional organoboron reagents with a rhodium catalyst to synthesize carbocycles through a cascade sequence. The reaction of norbornene derivatives gives vinylcyclopropane and cyclopentene products in moderate to good yield. The mechanistic proposal and insights into the reaction mechanism are presented. Preliminary results from studies toward an enantioselective sequential addition/cyclization process are described. The methodology is subsequently applied in the synthesis of a variety of polycyclic heteroaromatics using bifunctional heteroaryl boronate esters. The second chapter describes studies toward the formation of carbon-heteroatom bonds using cyclopropane derivatives. Under a recently developed Pd(OAc)2/PhI(OAc)2 catalytic system, methylenecyclopropanes are isomerized to substituted pyridines via a sequential fragmentation/cyclization process. Under same reaction conditions, allylic acetate products are obtained from the isomerization of cyclopropanes through a similar process.

Reaction of unsymmetrical allylic electrophiles with amines gives rise to regioisomeric allylamines. It was found that linear products result from the thermodynamically controlled isomerization of the corresponding branched products, which form initially. The isomerization was found to be promoted by the presence of acid and active palladium catalyst. The use of base shut down the isomerization pathway and allowed for the preparation and isolation of branched allylamines. This methodology provides a powerful control element, which allows for the installation of quaternary and chiral centres next to nitrogen. Later, the isomerization was combined with ring-closing metathesis to afford the synthesis of exocyclic allylamines from their thermodynamically less-stable endocyclic precursors. This rearrangement became feasible as a result of the electrophilic nature of a C – N bond in allylamines. When compared to the conventional intramolecular allylic amination, such approach escapes chemoselectivity issues, which makes it attractive attractive for late-stage synthetic modifications.

Chapter 1 details our investigation into the Diels-Alder reaction between arynes and chiral furans and pyrroles for the synthesis of unsymmetrical [2.2.1] oxabicyclic and azabicyclic scaffolds as single enantiomers. It was discovered that the diastereoselectivity of the aryne Diels-Alder reaction was sensitive to conformational effects that could be exploited to obtain both high yields and dr. Stereoselective synthesis using arynes is an overlooked field, and this contribution represents one of only three such examples in the literature. The desymmetrization of meso [2.2.1] oxabicyclic systems by intramolecular cyclization/ring- opening was studied, and a cationic Rh/t-Bu-Josiphos catalyst was developed that delivered polyclic dihydronaphthalene products in excellent yield and ee. These catalyst conditions were used for the ring-opening of an enantiomerically pure unsymmetrical oxabicyclic alkene, which led to the discovery that ring-opening proceeded with complete reagent control. A regiodivergent resolution was designed that gave pairs of enantiomerically enriched dihydronaphthalenes from unsymmetrical racemic starting materials. In chapter 3, the scope of the regiodivergent resolution was expanded to include the ring-opening of remotely-substituted oxabicyclic alkenes and furan-hetaryne Diels-Alder adducts. The utility ii of the method was demonstrated by using it to synthesize two important API molecules from a single racemic precursor. Finally, chapter 4 describes our lab’s efforts toward the total synthesis of the natural products phorbol and prostratin that features the ring-opening of an unsymmetrical [3.2.1] oxabicycle as the key step. Advanced intermediates (requiring >30 linear steps) were synthesized on gram- scale. The entire carbon framework was successfully installed, and our efforts to complete the synthesis are discussed.

This thesis focuses on the development of carbon-carbon/carbon-heteroatom bond forming reactions using strained ring systems under transition metal catalysis. The first chapter describes the use of bifunctional organoboron reagents with a rhodium catalyst to synthesize carbocycles through a cascade sequence. The reaction of norbornene derivatives gives vinylcyclopropane and cyclopentene products in moderate to good yield. The mechanistic proposal and insights into the reaction mechanism are presented. Preliminary results from studies toward an enantioselective sequential addition/cyclization process are described. The methodology is subsequently applied in the synthesis of a variety of polycyclic heteroaromatics using bifunctional heteroaryl boronate esters. The second chapter describes studies toward the formation of carbon-heteroatom bonds using cyclopropane derivatives. Under a recently developed Pd(OAc)2/PhI(OAc)2 catalytic system, methylenecyclopropanes are isomerized to substituted pyridines via a sequential fragmentation/cyclization process. Under same reaction conditions, allylic acetate products are obtained from the isomerization of cyclopropanes through a similar process.

Chapter 1 details our investigation into the Diels-Alder reaction between arynes and chiral furans and pyrroles for the synthesis of unsymmetrical [2.2.1] oxabicyclic and azabicyclic scaffolds as single enantiomers. It was discovered that the diastereoselectivity of the aryne Diels-Alder reaction was sensitive to conformational effects that could be exploited to obtain both high yields and dr. Stereoselective synthesis using arynes is an overlooked field, and this contribution represents one of only three such examples in the literature. The desymmetrization of meso [2.2.1] oxabicyclic systems by intramolecular cyclization/ring- opening was studied, and a cationic Rh/t-Bu-Josiphos catalyst was developed that delivered polyclic dihydronaphthalene products in excellent yield and ee. These catalyst conditions were used for the ring-opening of an enantiomerically pure unsymmetrical oxabicyclic alkene, which led to the discovery that ring-opening proceeded with complete reagent control. A regiodivergent resolution was designed that gave pairs of enantiomerically enriched dihydronaphthalenes from unsymmetrical racemic starting materials. In chapter 3, the scope of the regiodivergent resolution was expanded to include the ring-opening of remotely-substituted oxabicyclic alkenes and furan-hetaryne Diels-Alder adducts. The utility ii of the method was demonstrated by using it to synthesize two important API molecules from a single racemic precursor. Finally, chapter 4 describes our lab’s efforts toward the total synthesis of the natural products phorbol and prostratin that features the ring-opening of an unsymmetrical [3.2.1] oxabicycle as the key step. Advanced intermediates (requiring >30 linear steps) were synthesized on gram- scale. The entire carbon framework was successfully installed, and our efforts to complete the synthesis are discussed.

Nanomaterials have become a popular topic of research over the years because of their many important applications. It can be a challenge to stabilize the particles at a nanometer size, while having control over their surface features. Copper nanoparticles were synthesized photochemically using a photogenerated radical allowing spatial and temporal control over their formation. The synthesis was affected by the stabilizers used, which changed the size, dispersity, rate of formation, and oxidation rate. Copper nanoparticles suffer from their fast oxidation in air, so copper-silver bimetallic nanoparticles were synthesized in attempts to overcome the oxidation of copper nanoparticles. Bimetallic nanoparticles were synthesized, but preventing the oxidation of the copper nanoparticles proved difficult. One important application of nanoparticles that was explored here is in catalyzing organic reactions. Because of the fast oxidation of copper nanoparticles, silver nanoparticles were synthesized photochemically on different supports including TiO2 and hydrotalcite (HTC). Their catalytic efficiency was tested using alcohol oxidations. Different silver nanoparticle shapes (decahedra and plates) were compared with the spheres to see the different catalytic efficiencies.

Transition metal nanomaterials are used to catalyze many chemical reactions, including those key to environmental, medicinal, and petrochemical fields. Improving their catalytic properties and lifetime would have significant economic and environmental rewards. Potentially expedient options to make such advancements are to alter the shape, size, or composition of transition metal nanocatalysts. This work investigates the relationships between structure and catalytic properties of synthesized Au, Pd-on-Au, and Au-enzyme model transition metal nanocatalysts. Au and Pd-on-Au nanomaterials were studied due to their wide-spread application and structure-dependent electronic and geometric properties. The goal of this thesis is to contribute design procedures and synthesis methods that enable the preparation of more efficient transition metal nanocatalysts. The influence of the size and composition of Pd-on-Au nanoparticles (NPs) was systematically investigated and each was found to affect the catalyst’s surface structure and catalytic properties. The catalytic hydrodechlorination of trichloroethene and reduction of 4-nitrophenol by Pd-on-Au nanoparticles were investigated as these reactions are useful for environmental and pharmaceutical synthesis applications, respectively. Structural characterization revealed that the dispersion and oxidation state of surface Pd atoms are controlled by the Au particle size and concentration of Pd. These structural changes are correlated with observed Pd-on-Au NP activities for both probe reactions, providing new insight into the structure-activity relationships of bimetallic nanocatalysts. Using the structure-dependent electronic properties of Au NPs, a new type of light-triggered biocatalyst was prepared and used to remotely control a model biochemical reaction. This biocatalyst consists of a model thermophilic glucokinase enzyme covalently attached to the surface of Au nanorods. The rod-like shape of the Au nanoparticles made the thermophilic-enzyme complexes responsive to near infrared electromagnetic radiation, which is absorbed minimally by biological tissues. When enzyme-Au nanorod complexes are illuminated with a near-infrared laser, thermal energy is generated which activates the thermophilic enzyme. Enzyme-Au nanorod complexes encapsulated in calcium alginate are reusable and stable for several days, making them viable for industrial applications. Lastly, highly versatile Au nanoparticles with diameters of ~3-12 nm were prepared using carbon monoxide (CO) to reduce a Au salt precursor onto preformed catalytic Au particles. Compared to other reducing agents used to generate metallic NPs, CO can be used at room temperature and its oxidized form does not interfere with the colloidal stability of NPs suspended in water. Controlled synthesis of different sized particles was verified through detailed ultraviolet-visible spectroscopy, small angle X-ray scattering, and transmission electron microscopy measurements. This synthesis method should be extendable to other monometallic and multimetallic compositions and shapes, and can be improved by using preformed particles with a narrower size distribution.

No description available.

Monometallic and bimetallic model catalysts on either refractory metal singlecrystals as planar surfaces or oxide supports as nano-size clusters have been systematically studied using X-ray photoemission spectroscopy (XPS), low energy ion scattering spectroscopy (LEIS), low energy electron diffraction (LEED), infrared reflection absorption spectroscopy (IRAS), and temperature programmed desorption (TPD) under ultra-high vacuum (UHV) conditions. Of particular interest in this investigation is the characterization of the surface composition, morphology, and electronic/geometric structure of the following catalysts: Au/TiOx, Au-Pd/Mo(110), Au- Pd/SiO2, Cu-Pd/Mo(110), and Sn/Pd(100). Structure-reactivity correlations during surface-alloy formation and adsorption-desorption processes were explained in terms of ensemble and ligand effects. Prospects of translating the accumulated atomic-level information into more efficient 'real world' catalysts were discussed.

?The body of this work spans both fundamental organometallic chemistry and the application of previously studied catalyst systems to produce new polymeric materials. The cone angle of triphenylphosphite was estimated to be 128 degrees by Tolman in the late 70s; however, metal complexes bearing this ligand undergo cis/trans isomerization via a mechanism indicative of greater steric requirements. X-ray crystallographic studies coupled with data compiled from the Cambridge Crystallographic Database, were used to more accurately calculate the steric demand of this wieldy used ligand to be approximately 140 degrees. Additionally, in depth kinetic studies of the interaction of furan ligands with electron deficient manganese and chromium metal centers were performed. Data collected from timescales ranging from minutes to microseconds was utilized to calculate the bond dissociation energy of both 2,3-dihydrofuran (DHF) and furan. The aromatic furan ligand was found to bind to the both metals 7-10 kcal mol-1 weaker than DHF. Additionally, the more electron rich chromium center was found to bind both ligands ?weaker than the manganese center implying a minimization of the M-L pie -back bonding interaction. Solution studies coupled with DFT calculations were utilized to estimate the extent that the furan ligand is dearomatized by approximately 50% upon interaction with the metal center. Application-based studies of the separation of polymer catalyst mixtures were also undertaken. The addition of the 1000 Dalton poly(isobutylene) arms to the salen ligand in (salen)CrCl complexes yielded a catalyst that could be extracted from the reaction mixture containing poly(cyclohexene carbonate) via the addition of heptane. Another approach, not requiring catalyst modification, utilized a secondary amine to facilitate the purification of the polymer product. The reaction of an amine with CO2 to form an ionic liquid resulted in the precipitation of the polymer while the catalyst and byproducts remained in the liquid carbamate phase. Both approaches provided improvements over the long standing method of precipitating the polymer using methanol and strong acid. Lastly, the previous work of the Darensbourg group utilizing (salen)CrCl catalyst to produce polycarbonates from CO2 and epoxides was employed to synthesized sulfur rich poly(thiocarbonate)s. The effects of both CS2 loading and temperature on the copolymerization of CS2 and cyclohexene oxide were studied. Optimal conditions of 1 equivalent of CS2 and 50 degrees C were found to selectively produce the desired polymeric material. The observation of multiple thiocarbonate as well as carbonate functionalities, led to a detailed study of the reaction byproducts to gain insight into the copolymerization process.