Electrochemical promotion (EP) is a new way of controlling catalytic performance. It is implemented by depositing porous thin film metal catalysts on solid electrolyte supports where they act as both a catalyst and a working electrode of an electrochemical cell. The technique entails electrochemical pumping of ions from the solid electrolyte to the surface of the catalytically active metal film with which it is in contact. In short, controlling the potential difference of the electrochemical cell controls the coverage of promoters on the catalyst while a catalytic reaction is taken place. Thus, it provides a unique method for studying promotion in heterogeneous catalysis. My research has focused on elucidating the phenomena that underlie the EP effect. The resulting advances in fundamental understanding have been used to exploit EP as a tool to study alkali promotion in new applications in heterogeneous catalysis and to diversify the catalytic chemistry that can be addressed by EP. Thus, we have used conventional and spatially resolved in situ photoelectron spectroscopic data to demonstrate that EP of thin film metal catalysts deposited on solid electrolyte supports is the result of the spillover phenomena at the three phase boundary between the electrolyte, the catalyst and the gas phase. Ions from the electrolyte are discharged at the catalyst/ electrolyte interface and migrate to cover the catalyst surface whose properties are thereby strongly altered. This is the first time that such advanced spectroscopic techniques have been brought to bear on this fascinating and complex problem. Reactor measurements along with post-reaction photoelectron spectroscopies were used in order to: (i) establish the mechanism of reaction, (ii) determine the mode of promoter action and (iii) identify the chemical state of the promoter phase, in the Na-promoted catalytic control of toxic emissions. Very large increases both in activity and in selectivity of the catalysts were achieved and point the way towards further developments and possible applications. Finally, the use of EP as a mechanistic probe in surface catalysed polymerisation reactions has been demonstrated for the first time, broadening the range of utility of the extraordinary phenomenon of EP.

The regioselectivity in Pd(0)-catalyzed direct arylation of pyrrole, thiophene, and indole can be improved by blocking some of the reactive sites with a chloride group, leading to increased yields of the desired regioisomers. Competition experiments and computational studies show that the blocking group also activates the substrates toward arylation. Due to the activated nature of chlorinated heteroaromatics, rare and sought after regioisomers, such as 3-arylthiophenes, can be obtained under mild conditions in good yields. Chlorine-bearing thiophenes arylated at C3 and C4 have the potential to undergo controlled regioregular polymerization under conditions developed in the field of polythiophene chemistry. Mechanistic studies support the hypothesis that the arylation of the substrates under investigation likely proceeds via the CMD transition state.

Fluorocarbons (FCs) and their derivatives (FCDs) are heavily relied on due to their wide range of uses (e.g. solvents, surfactants, refrigerants, and pharmaceuticals). Currently, FCs and FCDs are produced on an industrial scale via energy-intensive processes, using hazardous materials. Hence, new catalytic chemical technologies are required to provide cleaner and greener synthetic routes to partially fluorinated materials. The exploration of fundamental organofluorometallic chemistry of base metals, such as nickel, has potential to advance the development of novel catalytic processes towards this end. It has been established previously that zero-valent nickel complexes have the ability to efficiently catalyze the hydrodimerization of polyfluoroalkenes. The reactivity of the intermediate polyfluoronickelacycles was found to be influenced by modifications in the ligand sphere. Furthermore, an increase in oxidation state of the central metal atom was proposed as an additional strategy to increase the reactivity of the M-RF bond. In this thesis, through variation of the ligand environment and oxidation state of nickel, we have further developed the chemistry of high-valent polyfluoronickelacycles. Synthesis and characterization (NMR, EPR, UV/Vis, IR spectroscopy and electrochemistry) of new trivalent polyfluoronickelacycles are described as well as attempts to generate the corresponding tetravalent cations. Attempts to induce nucleophilic insertion of acetonitrile into the Ni-RF bond were also investigated herein. Challenges were encountered with the isolation of the tetravalent cations due to decomposition to the corresponding divalent nickelacycle.

The ever-worsening environmental crisis has stimulated development of less wasteful “green” technologies. To this end, tandem catalysis enables multiple catalytic cycles to be performed within a single reaction vessel, thereby eliminating intermediate processing steps and reducing solvent waste. Assisted tandem catalysis employs suitable chemical triggers to transform the initial catalyst into new species, thereby providing a mechanism for “switching on” secondary catalytic activity. This thesis demonstrates the importance of highly productive secondary catalysts through a comparative hydrogenation study involving prominent hydrogenation catalysts of tandem ring-opening metathesis polymerization (ROMP)-hydrogenation, of which hydridocarbonyl species were proved superior. This thesis illuminates optimal routes to hydridocarbonyls under conditions relevant to our ROMP-hydrogenation protocol, using Grubbs benzylidenes as isolable proxies for ROMP-propagating alkylidene species. Analogous studies of ruthenium methylidenes and ethoxylidenes illuminate optimal routes to hydridocarbonyls following ring-closing metathesis (RCM) and metathesis quenching, respectively. The formation of unexpected side products using aggressive chemical triggers is also discussed, and emphasizes the need for cautious design of the post-metathesis trigger phase.

Over the past 15 years, ruthenium-catalyzed olefin metathesis has emerged as a cornerstone synthetic methodology in academia. Applications in fine-chemicals and pharmaceutical manufacturing, however, are just beginning to come on stream. Industrial uptake has been impeded by economic constraints associated with catalyst costs. These are due both to direct costs (exacerbated by intellectual property issues), and to further pressure exerted by the low turnover numbers attainable, and the need for extensive purification to remove ruthenium residues. From another perspective, however, these difficulties can be seen as arising from our rudimentary understanding of the fundamental organometallic chemistry of the Ru=CHR bond. In particular, we know little about the nature and reaction pathways of the Ru-methylidene unit present in the active species that propagates metathesis, and in the catalyst resting state. We know slightly more about the ruthenacyclobutane species, but still too little to guide us as to their non-metathetical reaction pathways, their contribution to deactivation relative to the methylidene species, and potential work-arounds. This thesis work was aimed at improving our understanding of the reactivity, speciation, and decomposition of key ruthenium intermediates in olefin metathesis. A major focus was the behaviour and deactivation of species formed from the second-generation Grubbs catalyst RuCl2(H2IMes)(PCy3)(=CHPh) (S-GII), which dominates ring-closing metathesis. Also studied were derivatives of the corresponding IMes catalyst A-GIIm, containing an unsaturated Nheterocyclic carbene (NHC) ligand. The methylidene complexes RuCl2(NHC)(PCy3)(=CH2) (GIIm) represent the resting state of the catalyst during ring-closing and cross-metathesis reactions: that is, the majority Ru species present during catalysis. Mechanistic studies of these key intermediates have been restricted, however, by the low yields and purity with which they could be accessed. Initial work therefore focused on designing a clean, high-yield route to the second-generation Grubbs methylidene complexes S-GIIm and A-GIIm. These routes were subsequently expanded to develop access to isotopically-labelled derivatives. Locating a 13C-label at the key alkylidene site, in particular, offers a powerful means of tracking the fate of the methylidene moiety during catalyst deactivation. Access to GIIm enabled detailed studies of the behaviour and decomposition of the Grubbs catalysts. First, the long-standing question of the impact of saturation of the NHC backbone (i.e. IMes vs. H2IMes) was examined. Dramatic differences in the behaviour of the two complexes were traced to profound differences in PCy3 lability arising from the diminished π-acidity of the IMes ligand. Secondly, the vulnerability of GIIm to nucleophiles was examined. This is an important issue from the perspective of decomposition by adventitious nucleophiles in the reaction medium during catalysis, but also reflects on substrate scope. For amine additives, the dominant deactivation pathway was shown to typically involve attack on the resting-state methylidene complex, not the metallacyclobutane, which has often been regarded as the most vulnerable intermediate. In addition, the sigma-alkyl intermediate formed by nucleophilic attack of displaced phosphine at the methylidene carbon was trapped by moving to the first-generation complex, and using a nitrogen donor (pyridine) that cannot promote decomposition via N–H activation pathways. Interception of this long-suspected species led to the proposal of “donorinduced” deactivation as a general decomposition pathway for Grubbs-class catalysts. Finally, the capacity of phosphine-free catalysts to overcome the shortcomings of the secondgeneration Grubbs catalysts was demonstrated, in a case study involving application of crossmetathesis (CM) to the synthesis of a high-value antioxidant. An efficient CM methodology was developed for the reaction of renewable essential-oil phenylpropenoids with vinyl acrylates. This work illustrates a new paradigm in sustainable metathesis. Rather than degrading unsaturated feedstocks via metathesis (a process that can be termed “metathe[LY]sis”), it demonstrates how metathesis with directly-functionalized olefins can be used to augment structure and function. From the perspective of organometallic chemistry and catalyst design, key comparisons built into this thesis are the effect of the NHC ligand (IMes vs. H2IMes) and its trans ancillary ligand on the efficient entry into catalysis; the susceptibility to nucleophilic attack of the alkylidene ligand (benzylidene vs. methylidene) vs. the metallacyclobutane; and the effect of replacing a phosphine ancillary ligand with a non-nucleophilic donor. From a practical standpoint, Chapter 2 brings new life to metathesis with the high-yield synthesis of the resting state species, Chapters 3 and 4 examine the deactivation, or death, of the methylidene complexes, and Chapter 5 establishes a new paradigm for olefin metathesis within the context of sustainable synthesis.

Olefin metathesis is the most powerful, versatile reaction in current use for the formation of new carbon-carbon bonds. While metathesis has been known for over 60 years, it has only recently been implemented into pharmaceutical and specialty chemical manufacturing. The slow uptake of olefin metathesis can be attributed in part to low catalyst productivity, a consequence of short catalyst lifetime. Improving catalyst activity is critical for the advancement of metathesis. This improvement can be achieved through greater understanding of the catalysts and their limitations. The ability to perform metathesis in aqueous media is desirable, but as yet largely unrealized, for the modification of water-soluble, biologically-relevant substrates. At present, high catalyst loadings are necessary even for less demanding metathesis reactions in water. The limited mutual solubility of the catalyst and substrate in water are one limitation. Examined in this thesis are more fundamental challenges associated with catalyst deactivation by water. The impact of water on catalyst productivity was assessed for both the second-generation Grubbs catalyst GII, and the phosphine-free Hoveyda catalyst HII, in ring-closing and cross-metathesis reactions. Water was shown to have a negative impact on metathesis productivity, owing to catalyst decomposition. The decomposition pathway was catalyst-dependent: GII was found to decompose through a pathway in which water accelerated abstraction of the methylidene ligand by dissociated phosphine. For HII, water was found to decompose the metallacyclobutane intermediate. A β-hydride transfer mechanism was proposed, to account for the organic decomposition products observed. Chapter 4 focuses on problems encountered during the synthesis of ruthenium catalysts, and presents improved methods. An updated method was developed for the synthesis of phenyldiazomethane, the principal source of the alkylidene ligand required in synthesis of GI. Challenges in use of the phosphine-scavenging resin Amberlyst-15 resin are discussed. Improving synthetic routes to the important first- and second-generation Grubbs catalysts will aid in expansion of olefin metathesis methodologies, particularly in the industrial context, in which batch-to-batch reproducibility is paramount.

Transglutaminases (protein-glutamine:amine y-glutamyl- transferase, EC 2.3.2.13) are a family of calcium-dependent enzymes which catalyze an acyl transfer between glutamine residues and a wide variety of primary amines. When lysine acts as the acyl-acceptor substrate, α-glutamyl lysine isopeptide bond is formed. Isopeptide catalyzation results in protein cross-linkage which is prevalent throughout biological processes. Microbial transglutaminase (mTG) is a bacterial variant of the transglutaminase family, distinct by virtue of its calcium-independent catalysis of the isopeptidic bond. Furthermore, mTGs promiscuity in donor substrate preference highlights its biocatalytic potential. To realize the potential of the enzyme, a high-reactivity tag was necessary for protein labelling. To address this, an enzyme-coupled assay was developed to characterize peptides in the hopes of developing orthogonal substrates to facilitate mTG-mediated labelling and biocatalysis. The discovery of high-reactivity peptide tags allowed the realization of in vitro protein labelling- facilitated by mTG. The 7M48 peptide was fused to a test protein, where it was subsequently propargylated with propargyl amine to fluorescently label or immobilize a test protein. Although there are endless possibilities for in vitro bio-conjugation through mTG, proteolytic activation limits any in-cell labelling strategies with this enzyme. To circumvent this issue, development of an alternative bacterial enzyme, Bacillus subtilis transglutaminase (bTG), was chosen to replace mTG. bTG maintains the advantages associated with mTG but is expressed in its active form. Unlike mTG, there is limited preliminary research associated with the enzyme or its substrate scope. To better understanding substrate reactivity, a FRET-based assay was developed allows for the discovery of new high-reactivity peptides for bTG. These peptides were then used in labelling strategies to demonstrate the potential bTG-mediated bioconjugation. This strategy includes the added advantage of potential for in-cellulo labelling.

Over the past decade, the field of photoredox catalysis has garnered increasing amounts of attention in the organic chemistry community due to its wide applicability in sustainable free radical-mediated processes. Several examples have demonstrated that under carefully optimized conditions, efficient and highly selective processes can be developed through excitation of a photosensitizer using inexpensive, readily available light sources. Furthermore, these reactions can generally be performed under milder conditions than thermal reactions, as all the energy required to overcome the reaction barrier is supplied by light. Despite all these recent advancements in the field, many of these discoveries often lack in depth investigations into the excited state kinetics and underlying mechanisms. Furthermore, the vast majority of these transformations are photocatalyzed by ruthenium and iridium polypyridyl complexes. Not only are these precious metal catalysts extremely costly, but these metals are also known to be toxic, limiting their potential use in the development of pharmaceutical protocols. Herein, we present our solutions to these shortcomings, which involve a three-prong approach in the development of novel protocols, understanding the underlying mechanisms through detailed kinetic analysis, and by the development of new tools to facilitate mechanistic investigation for practitioners who may not possess specialized photochemical equipment. In this work, we were the first to demonstrate that radicals derived from amines, commonly employed as “sacrificial” electron-donors, can also act as reducing agents in photoredox transformations. We also present examples in which Methylene Blue, an inexpensive, non-toxic organic dye, can be employed as a viable alternative to ruthenium complexes for photoredox transformations. By employing a photosensitizer with more favourable excited state kinetics for electron-transfer, we successfully demonstrated that Methylene Blue could be used to increase the efficiency of a previously developed photoredox transformation. While employing organic dyes is an excellent strategy to lowering the cost of photoredox transformations, another viable strategy is to employ heterogeneous semiconductors. Titanium dioxide is an example of a semiconductor which is often employed in photocatalytic applications due to its low cost, desirable redox properties, and high chemical stability which allows for continued use. However, titanium dioxide has seen limited use in organic synthesis due to the requirement of UV irradiation for excitation. Herein, we present a process which led to the discovery of visible light photochemistry with titanium dioxide, generated through the adsorption of indole substrates creating a new, visible light absorbing complex. Employing this strategy, we were able to promote the photocatalytic Diels–Alder reaction of indoles with electron-rich dienes, giving access to valuable tetrahydrocarbazole scaffolds. Finally, in order to facilitate the characterization of chain processes in photoredox catalysis, we have successfully developed a visible light actinometer based on the ubiquitous photocatalyst, Ru(bpy)3Cl2. This actinometer offers many advantages compared to other visible light actinometers, such as completely eliminating the need for spectral matching, as the actinometer is also the photocatalyst. This technique should provide researchers with a mechanistic tool to properly characterize chain propagation in the transformation of interest.

Fluorinated organic compounds play important roles in our society, as these products range from life-saving pharmaceuticals and agrochemicals, to fluoropolymers with extremely high thermal and chemical stability. Although elemental fluorine (F2) is the most reactive element, some fluoro-organic compounds are chemically inert. As such, controlled reactivity of fluorine or highly-fluorinated organic fragments is a considerable, yet important challenge for synthetic chemists. Fluoro-organometallic chemistry has been studied for decades, as researchers attempt to maximize the potential of metal mediated/catalyzed processes for the synthesis of fluorinated organic molecules. Within this framework, metal fluorocarbene complexes are particularly interesting because of their highly tunable reactivity, and are proposed for use in important metathesis/polymerization reactions of perfluorinated alkenes. While considerable work is still needed to make these proposed reactions a reality, this thesis outlines contributions from our research group. We showed that cobalt fluorocarbene complexes CpCo(=CFRF)(PPh2Me) (RF = F, CF3) undergo [2+2] cycloaddition reactions with tetrafluoroethylene (TFE) and phenylacetylene to form perfluorometallacyclobutane and partially fluorinated metallacyclobutene products, respectively. For both reactions, computational studies reveal a stepwise ring-closing mechanism, which proceeds through a singlet 1,4-diradical intermediate. Next, the formation of CpCo(=CF2)(L) complexes is achieved via the direct addition of difluorocarbene, generated in situ, to a cobalt(I) precursor. Subsequent addition of CF2 to cobalt fluorocarbene complexes results in [2+1] cycloaddition and formation of perfluorinated alkene complexes. The [2+1] addition is highly favored as the cobalt fluorocarbenes readily react with electrophilic CF2. A series of experiments provide evidence for the stepwise nature of fluoroalkene complex formation. From Co(I) fluorocarbene complexes, the focus shifts to preparing metal fluorocarbenes with electrophilic-type reactivity. The synthesis of bis(perfluoroalkyl) complexes serve as precursors for preparation of perfluoroalkyl cobalt(III) fluorocarbenes, which undergo migratory insertion reactions of the fluorocarbene into the perfluoroalkyl ligand. Using a similar synthetic approach, nickel(II) and palladium(II) difluorocarbene complexes are prepared from their corresponding trifluoromethyl precursors. The synthesis, characterization and reactivity of cobalt(III) fluoride complexes is also described, including the catalytic fluorination of acyl chlorides, demonstrating the first example of a cobalt(III) catalyzed fluorination reaction. The effects of the various ancillary ligands on these cobalt catalysts are investigated using high-throughput experimentation technology, and the scope of the reaction is expanded to include the synthesis of a variety of acyl fluoride compounds. Finally, the results and learnings from this work will be summarized and highlighted. The future directions and novel research which could result from the continuation of these projects is discussed, with an emphasis placed on the areas believed to have the highest potential impact.

This thesis is a dissertation to support the development of new domino pericyclic oxy-Cope/ene/Claisen/Diels-Alder reaction, diversity oriented synthesis of PPAPs scaffold via sequential one pot cascade reaction and ethyl aluminum sesquichloride catalyzed highly hindered Diels-Alder reaction. The first part concentrates on the domino pericyclic oxy-Cope/ene/Claisen/Diels-Alder reaction. As a result of this study, we have developed a general methodology for rapidly constructing complex diterpenes and discovered a thermal oxy-Cope/ene/Claisen/Claisen rearrangement, applied to the synthesis of trans decalin benzofurans. The second part involved the development of an efficient synthetic approach towards bicyclo[3.3.1]nonenone core found in many natural products, via a sequential Diels-Alder/gold(I)-catalyzed 6-endo-dig cyclization and its application to the synthesis of a diversified library of PPAPs. Finally, we have developed an efficient synthetic methodology for the formation of cyclohexene rings bearing quaternary carbon centers via an ethyl aluminum sesquichloride mediated highly hindered Diels-Alder reaction. This method solved an important problem encountered in the synthesis of many natural products including PPAPs. This methodology opened new opportunities in the total synthesis of PPAPs.