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Phosphorus-boron multiple-bonds are of interest because of their predicted reactivity with small molecules; their potential as reagents for the synthesis of molecules isosteric to carbon analogues which exhibit conjugation; and because they have potential as nucleation sites for the solution-phase synthesis of boron phosphide. Phosphaborenes (RP=BR') have not yet been reported due to their propensity to oligomerise to dimers or trimers, even with bulky and electronically-stabilising substituents upon phosphorus and boron. Base-stabilisation at boron allows the isolation of phosphaborenes by preventing oligomerisation, although this alters the reactivity of the phosphaborene unit. An alternative method of studying phosphaborenes free of base or acid coordination is via their thermal generation from a phosphaborene dimer and subsequent in situ reactions with suitable substrates. Chapter 1 examines the potential uses of phosphaborenes in the context of other low-valent main group molecules. The likely reactivity of phosphorus-boron multiple bonds is discussed in the context of the iminoboranes (RNBR') and the isoelectronic heavier group 14 alkyne and alkene analogues. The use of unsaturated main group fragments to build molecular clusters is considered along with the potential role that phosphorus boron multiple bonds could play in preparing boron phosphide fragments. The uses and methods of preparation of group 13/15 containing molecules exhibiting conjugation are discussed, along with the possibility that phosphaborenes would be useful reagents to prepare new P-B/C-C isosteres. Chapter 2 looks at how base-promoted trimethylsilylchloride elimination can be used to prepare base-stabilised phosphaborenes from suitable precursors (RP(SiMe₃)B(X)R' and the mechanism of these reactions. The reactivity of base-stabilised phosphaborenes with Lewis acids is also examined. Chapter 3 covers how base-promoted (L = base) trimethylsilyl halide abstraction from functionalised precursors ((Me₃Si)₃P·BBr₃) can be harnessed to prepare new functionalised phosphinoboranes ((Me₃Si)₂PB(L)Br₂) and phosphaborenes (Me₃SiP=B(L)Br). A 1-dihydro-2-dibromo functionalised phosphinoborane H₂PB(Br₂)L can be prepared from Me₃Si)₂PB(Br₂)L. A subsequent base-promoted dehydrohalogenation yields the hydro-bromo substituted phosphaborene HP=B(L)Br. Chapter 4 examines the in situ thermal generation of a phosphaborene generated from a phosphaborene dimer and its reactivity with bases and unsaturated organic molecules to prepare 1,2-phosphaboretes and 1,2-phosphaboretanes. Chapter 5 explores the diverse reactivity of the 1,2-phosphaboretes. 1,2- phosphaboretes are capable of FLP-like insertion reactions with an isonitrile and carbon monoxide. They are also ring-opened by the coordination of a Lewis acid or base to phosphorus or boron respectively to give P-B containing butadiene analogues. The reaction of the 1,2-phosphaborete with phenyl acetylene proceeds via an unusual carbon-carbon bond cleavage to generate the first example of a 1,3- phosphaborine benzene analogue, rather than the expected 1,4-phosphaborine.

The molecular recognition of fluoride and cyanide anions has become an increasingly pertinent objective in research due to the toxicity associated with these anions, as well as their widespread use. Fluoride is commonly added to drinking water and toothpastes to promote dental health, and often used in the treatment of osteoporosis, however, high doses can lead to skeletal fluorosis, an incurable condition. Cyanide is also an extremely toxic anion, which binds to and deactivates the cytochrome-c oxidase enzyme, often leading to fatality. The molecular recognition of these anions in water has proven to be challenging. For fluoride, the anion is small, and thus, efficiently hydrated (?H�hyd = -504 KJ/mol), making its complexation in aqueous environments particularly difficult. In addition to being small and efficiently hydrated like the fluoride anion, cyanide has a pKa(HCN) of 9.3 making its competing protonation in neutral water a further complication. Recent efforts to complex fluoride and cyanide have utilized triarylboranes, which covalently bind the anion. Monofunctional triarylboranes display a high affinity for fluoride with binding constants in the range of 105-106 M-1 in organic solvents, and chelating triarylboranes exhibit markedly higher anion affinities. These species, however, remain challenged in the presence of water. This dissertation focuses on the synthesis and properties of novel Lewis acids designed for the molecular recognition of fluoride or cyanide in aqueous environments. To this end, a group 15 element will be incorporated into a main group Lewis acidcontaining molecule for the purpose of: i) increasing the Lewis acidity of the molecule via incorporation of a cationic group, and ii) increasing the water compatibility of the host. Specifically, a pair of isomeric ammonium boranes has been synthesized. These boranes are selective sensors which selectively bind either fluoride or cyanide anions in water. The study of phosphonium boranes has revealed that the latent Lewis acidity of the phosphonium moiety is capable of aiding triarylboranes in the chelation of small anions. Finally, my research shows that Br�nsted acidic H-bond donors such as amides, when paired with triarylboranes, are capable of forming chelate complexes with fluoride.

Current industrial processes for the production of polycarbonates, a thermoplastic valued for commercial applications, leave much to be desired from an environmental viewpoint. Research into alternative methods for production of polycarbonates has focused on the copolymerization of carbon dioxide and epoxides for the benefits of eliminating phosgene as a reagent, and for the economic impact of incorporating CO2 as a low cost C1 feedstock. Early work in this field focused on the use of zinc-derived catalysts, but recent studies indicate that chromium complexes of the salen (N,N-bis-(salicylidene)-1,2-ethylene diimine) family of ligands are far superior to the zinc complexes in terms of reactivity and diminishing the formation of unwanted byproducts. Concomitant to the studies of chromium salen complexes, investigations of main-group salen metal complexes were carried out. Aluminum complexes were able to produce polycarbonate in the presence of tetrabutyl ammonium salts and neutral Lewis bases. Gallium complexes were essentially inactive for generating any product. Tin(IV) complexes were active for the production of polyether, the result of homopolymerization of epoxide without CO2 insertion. Tin(II) complexes generated the monomeric cyclic carbonate product but no copolymer. An additional aspect of research relative to this field of study is the development of polymeric materials from several different epoxide monomers. The complex [hydrotris(3-phenyl-pyrazol-1-yl)borate]Cd(II) acetate was used to study the thermodynamics of the binding of a series of potential epoxide monomers to a metal center via 113Cd NMR. Activation of the epoxide by a metal center was found to not play a significant role in the ability of the complex to be subsequently ring-opened for polymerization. A final relevant area of study involved the synthesis of cadmium analogues of Fe/Zn double metal cyanide (DMC) complexes. Heterogeneous DMCs are well known in patent literature as excellent catalysts for the production of polycarbonates and cyclic carbonates from CO2 and epoxides. Previous studies on homogeneous Fe/Zn DMCs have only provided cyclic carbonate. Cd analogues of these species provide a convenient NMR handle for studies on the activity of the metal centers in presence of an epoxide and by changes to the DMC structure.

Despite many drawn parallels between carbon and phosphorus, the development of catena-phosphorus chemistry is superficially explored when compared to carbon. This lack of progression is especially highlighted for cationic phosphorus frameworks, as neutral and anionic phosphorus frameworks have been studied to a much greater extent. This stresses cationic catena-phosphorus frameworks as important molecules for an improved understanding of fundamental phosphorus chemistry. Recent advancements in synthetic methods demonstrate that phosphorus frameworks of this type are viable target molecules. Furthermore, the precedence of a variety of new cationic catena-phosphorus frameworks by such methods exemplify their versatility. Here, novel 1,3-diphosphino-2-phosphonium [R2P-PR2-PR2]+, 2-phosphino-1,3-diphosphonium [R3P-PR-PR3]+ and cyclo-triphosphinophosphonium [R2P(RP)3]+ cations have been isolated and characterized in order to study the insertion of phosphenium cations into the phosphorus-phosphorus bonds of catena-phosphines.

This dissertation presents the synthesis and characterization of a variety of neutral and cationic complexes featuring Group 13-15 element centres stabilized by N-, P-, and O-based donors. Unique aluminum and gallium cationic complexes are obtained from equimolar reactions of the metal halide with the chelating alkyl phosphine dmpe. However, using the analogous amine donor tmeda, neutral adducts are preferred for aluminum as well as for GaCl3, while cations are obtained for GaBr3 and GaI3. New cations of Ge(II) and Sn(II) were also discovered, featuring the coordination of either bipyridine ligands or dmpe. Utilizing bipyridine led to the expected mono and dicationic chelate complexes, however, using dmpe led to the formation of unprecedented tetracationic molecules. The reactivities of the bipyridine complexes were investigated with a variety of substrates which showcased their Lewis acidity as well as their ability to be oxidized. Finally, a new series of high oxidation-state main group cations have been synthesized using a variety of ligands. The ligand choice was found to be an important role in compound isolation as ligand degradation occurred for some of the compounds due to their high electrophilicity. Additionally, the Lewis acidity of some of the complexes leads to interesting reaction chemistry including sp3 C-H activation. Overall, the results presented herein represent new coordination chemistry for the main group elements and opens the door towards new reactivity pathways including small molecule activation and catalysis. / Graduate

The evolution of the present work began with the syntheses of novel bis(alkylimino)acenaphthene (BIAN) ligands. At the outset of this research, despite the presence of dozens of aryl-BIAN ligands in the literature, there were as of yet no reported BIAN ligands bearing alkyl substituents. Given the nearly ubiquitous use of transition metal complexes of alkyl diazabutadiene (DAB) ligands for e.g. catalysis and as ligands for carbene chemistry, interest was generated in developing this emerging field of synthetic chemistry. Initial studies focused on the synthesis of alkyl-BIAN ligands since the traditional synthetic approaches that had been developed for aryl-BIAN ligands were unsuccessful for the alkyl analogues. As an alternate synthetic route, it was decided to employ amino- and imino-alane transfer reagents which had previously proved successful for the conversion of C=O into C=N-R functionalities. While this transfer route had proved successful to synthesize moderate yields of highly fluorinated DAB ligands, it was unknown how or whether this methodology would apply in the case of alkylated BIAN systems. Over the past decade, there has been a surge of interest regarding lanthanide complexes that are capable of undergoing spontaneous electron transfer processes. There are several reports in the literature that describe the ability of Ln(II) ions to undergo spontaneous oxidation, thereby causing one-electron reduction of the coordinated ligand and generally resulting in the corresponding Ln(III) complex. The present work focused on an enhanced understanding of the electronic communication between the lanthanide and the attached ligand. Particular emphasis was placed on defining the resulting oxidation states and the manner in which delocalized electrons of the radical anion species travel over a conjugated system. This fundamental information was gleaned from single-crystal X-ray diffraction studies and magnetic moment measurements that were obtained using the Evans method. Additional insights stemmed from the use of more classical techniques such as IR and NMR spectroscopy. In favorable cases, the presence or absence of spectral peaks can permit assignment of the lanthanide oxidation state. Accordingly, the research plan was to synthesize a series of BIAN-supported decamethyllanthanocene complexes with the goal of learning how to control the spontaneous charge transfer that had been reported in the literature. A longer term goal was to develop a bifunctional ligand of the BIAN type that was capable of accommodating two lanthanide or main group element moieties. Systems with tunable electronic interactions between lanthanide or main group elements are of interest because they offer the prospect of extended delocalization of electron density. Systems of this type have potential applications as e.g. molecular wires and single-molecule magnets. Indeed, such systems have been investigated by using bis(bipyridyl) and bis(terpyridyl) ligands to support two redox-active moieties. However, in the present work, it was recognized that a bifunctional BIAN-type ligand might be of considerable interest as the supporting structure for studying the communication between lanthanide or main group element moieties. A synthesis of variously substituted tetrakis(imino)pyracene (TIP) ligands was therefore undertaken. The flat, rigid nature of the TIP ligands rendered them ideal scaffolds for studying the redox behavior and electronic communication between lanthanide or main group element centers. The new TIP ligand class also proved to be useful for the assembly of the first example of a metallopolymer based on a BIAN-type ligand. / text

Investigation of catalytic main-group bond forming reactions is the basis of this dissertation. Coupling of group 14 and 15 elements by several different methods has been achieved. The influence of Si–N heterodehydrocoupling on the promotion of α-silylene elimination was realized. Efficient Si–N heterodehydrocoupling by a simple, earth abundant lanthanide catalyst was demonstrated. Significant advances in hydrophosphination by commercially available catalysts was achieved by photo-activation of a precious metal catalyst. Exploration of (N3N)ZrNMe2 (N3N = N(CH2CH2NSiMe3)33–) as a catalyst for the cross-dehydrocoupling or heterodehydrocoupling of silanes and amines suggested silylene reactivity. Further studies of the catalysis and stoichiometric modeling reactions hint at α-silylene elimination as the pivotal mechanistic step, which expands the 3p elements known to engage in this catalysis and provides a new strategy for the catalytic generation of low-valent fragments. In addition, silane dehydrocoupling by group 1 and 2 metal bis(trimethylsilyl)amide complexes was investigated. Catalytic silane redistribution was observed, which was previously unknown for d0 metal catalysts. La[N(SiMe3)2]3THF2 is an effective pre-catalyst for the heterodehydrocoupling of silanes and amines. Coupling of primary and secondary amines with aryl silanes was achieved with a loading of 0.8 mol % of La[N(SiMe3)2]3THF2. With primary amines, generation of tertiary and sometimes quaternary silamines was facile, often requiring only a few hours to reach completion, including new silamines Ph3Si(nPrNH) and Ph3Si(iPrNH). Secondary amines were also available for heterodehydrocoupling, though they generally required longer reaction times and, in some instances, higher reaction temperatures. By utilizing a diamine, dehydropolymerization was achieved. The resulting polymer was studied by MS and TGA. This work expands upon the utility of f-block complexes in heterodehydrocoupling catalysis. Stoichiometric and catalytic P–E bond forming reactions were explored with ruthenium complexes. Hydrophosphination of primary phosphines and activated alkenes was achieved with 0.1 mol % bis(cyclopentadienylruthenium dicarbonyl) dimer, [CpRu(CO)2]2. Photo-activation of [CpRu(CO)2]2 was achieved with a commercially available UV-A 9W lamp. Preliminary results indicate that secondary phosphines as well as internal alkynes may be viable substrates with this catalyst. Attempts to synthesize ruthenium phosphinidene complexes for stoichiometric P–E formation have been met with synthetic challenges. Ongoing efforts to synthesize a ruthenium phosphinidene are discussed. The work in this dissertation has expanded the utility of metal-catalyzed main-group bond forming reactions. A potential avenue for catalytic generation low-valent silicon fragments has been discovered. Rapid Si–N heterodehydrocoupling by an easily obtained catalyst has been demonstrated. Hydrophosphination with primary phosphines has been achieved with a commercially available photocatalyst catalyst, requiring only low intensity UV light.

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The coordination chemistry of antimony(III) and antimony(V) have been investigated to reveal fundamental structural and electronic features. The limited scope of known cationic antimony(V) complexes was greatly expanded, including the first examples of pnictogen(V) trications. The systematic nature of these investigations led to the observation of redox chemistry, determined to be the result of reductive elimination of chlorobenzene and biphenyl from an antimony center. The reactivity of [Ph2Sb(OPyrMe)4][OTf]3 was investigated and it was found that the OPyrMe ligands are sufficiently labile to perform ligand substitution chemistry. However, when exposed to phosphines, ligand-centered reactivity prevails and phosphonium salts of the form [R3P(2-4-methylpyridine)][OTf] which may be useful reagents in the field of medicinal chemistry and drug design. While attempts were made to synthesise antimony(V) tetra- and penta- cations have been unsuccessful, the methodologies reported here will serve as a foundation to future endeavors. / Graduate / 2019-08-31