This thesis describes selected reactivity studies of group 15 Zintl anion [E7]3– (E = P, As) derived cages towards a series of unsaturated organic molecules. The synthesis and characterization of forty-two compounds derived from [E7]3– cages are detailed herein. A high yielding procedure for the synthesis of [HE7]2– (E = P, As) from the K3E7 Zintl phase has been developed. This solves prior issues with poor solubility and variable purity of the Zintl phases. The conditions required for the deprotonation of the phosphorus congener to [P7]3– are described. The reactivity of both [P7]3– and [HP7]2– towards carbon dioxide and isolobal isocyanates and carbodiimides was explored. This yielded a series of monofunctionalized [E7R]2– cages, via a net hydropnictination of a C=N double bond of the organic substrate. The protonation chemistry of these anions was further investigated, resulting in the formation of the protic [HP7C(NHDipp)(NDipp)]– cluster. This anion is capable of further hydrophosphination chemistry to give a series of difunctionalized heptaphosphide cages. The reaction of [E7]3– with alkynes results in the formation of the relatively unusual 1,2,3-tripnictolide anions. A series of such anions have been prepared, encompassing all of the previously reported anions and several novel species. Investigation of the coordination properties of these cyclopentadienyl analogues shows that they are superior π acceptor ligands. A synthetic route to [P5]– as a compositionally pure solid, and some initial studies on its protonation chemistry are also additionally presented.

This work was initially launched to study the synthesis of low-valent group 13 compounds bearing the bis(imino)pyridine ligand framework. Since its inception, this project has grown beyond the boundaries of group 13 to include low valent tin, silver, and rhenium. Alongside the reports of novel coordination compounds, we utilized computational chemistry to uncover unprecedented interactions which challenge conventional concepts of bonding. Synthesis, characterization, and complimentary computational studies are presented herein. Chapter 1 presents a historical overview of the bis(imino)pyridine ligand as well as our synthetic methodology and characterization of new ligand variants we have contributed to the literature. Chapter 2 presents the synthesis of a series of In(I) and In(III) bis(imino)pyridine complexes with varied sterics. Ligand-metal interaction and effect of ligand steric bulk on complex stability, as well as computational studies highlighting weak covalent interactions will be discussed. Chapter 3 presents the synthesis of Ga(III) bis(imino)pyridine complexes. Reactivity with “GaI” synthon as well as varied-stoichiometry one-pot synthesis attempts to generate low valent Ga-bis(imino)pyridine complexes will be discussed. Chapter 4 presents the synthesis of a series of Tl(I) bis(imino)pyridine complexes with varied sterics analogous to the approach taken with indium(I). Unprecedented weak ligand-metal as well as Tl-arene interactions will be discussed. Chapter 5 presents the synthesis of a series of Sn(II) bis(imino)pyridine complexes with varied sterics and halide substituents. Preferential cation-anion pair formation and attempted reactivity will be discussed. Chapter 6 presents the synthesis of a series of Ag(I) bis(imino)pyridine complexes with varied sterics. Resulting ligand-metal interactions as well as reactivity towards Lewis basic donor ligands will be discussed. Chapter 7 presents the synthesis of first crystallographically authenticated examples of rhenium(I) pincer complexes utilizing the bis(imino)pyridine ligand. Chapter 8 presents a general conclusion to the work.

Only within the last decade has supramolecular chemistry begun to adopt the Group 15 elements into its field of research. This dissertation presents a supramolecular approach to the self-assembly and reactivity of Group 15 metalloids, specifically arsenic and antimony, with organothiolate ligands. Investigating the self-assembly of pnictogen-based coordination complexes allows for in-depth characterization of the chemical behavior of arsenic, antimony and other Group 15 elements. Currently, the infiltration of arsenic into global groundwater systems has developed into a worldwide health concern. There are no chelating agents available for public use in the treatment of arsenic poisoning which are capable of binding arsenic (III) in its preferred coordination geometry thereby hindering the selectivity for rapid chelation. Chapter I is a review covering two important characteristics observed in the Group 15 elements: 1) a stabilizing, non-covalent cation-π interaction aiding in the formation of pnictogen-aryl thiolates, and 2) an observed lack of selectivity in environments containing multiple pnictogen ions which enables transmetalation of the complexes to occur or the generation of heterometallic assemblies. Based on the discovery of this new transmetalation reactivity, the remainder of the dissertation explores the effects of external additives during self-assembly in order to understand how they may affect the reactivity of these self-assembled complexes and provide insight into formation mechanisms. Chapter II identifies a catalyst for the acceleration of a slow self-assembly reaction between AsCl3 and a dithiolate ligand to give an As2L3 cryptand. Chapter III examines the oxidation of the arsenic cryptand using iodine, which leads to the self-assembly of a series of differently sized, discrete disulfide-bridged macrocycles. In Chapter IV, the self-assembly of the first trinuclear arsenic- and antimony-based coordination complexes was studied, revealing interesting solvent dependent conformational isomerism in solution. Chapter V applies the pnictogen-enhanced iodine oxidation to the synthesis of known and new cyclophanes using supramolecular chemistry, including the self-assembly and covalent capture of an unprecedented tetrahedral thiacyclophane. Additionally, an unusual trithioorthoformate capped tricyclophane cage was also synthesized and isolated by pnictogen-activated oxidation. Chapter VI includes the conclusion and future directions for the project. This dissertation includes co-authored material and previously published results. / 10000-01-01

This work was initially launched to study the synthesis of low-valent group 13 compounds bearing the bis(imino)pyridine ligand framework. Since its inception, this project has grown beyond the boundaries of group 13 to include low valent tin, silver, and rhenium. Alongside the reports of novel coordination compounds, we utilized computational chemistry to uncover unprecedented interactions which challenge conventional concepts of bonding. Synthesis, characterization, and complimentary computational studies are presented herein. Chapter 1 presents a historical overview of the bis(imino)pyridine ligand as well as our synthetic methodology and characterization of new ligand variants we have contributed to the literature. Chapter 2 presents the synthesis of a series of In(I) and In(III) bis(imino)pyridine complexes with varied sterics. Ligand-metal interaction and effect of ligand steric bulk on complex stability, as well as computational studies highlighting weak covalent interactions will be discussed. Chapter 3 presents the synthesis of Ga(III) bis(imino)pyridine complexes. Reactivity with “GaI” synthon as well as varied-stoichiometry one-pot synthesis attempts to generate low valent Ga-bis(imino)pyridine complexes will be discussed. Chapter 4 presents the synthesis of a series of Tl(I) bis(imino)pyridine complexes with varied sterics analogous to the approach taken with indium(I). Unprecedented weak ligand-metal as well as Tl-arene interactions will be discussed. Chapter 5 presents the synthesis of a series of Sn(II) bis(imino)pyridine complexes with varied sterics and halide substituents. Preferential cation-anion pair formation and attempted reactivity will be discussed. Chapter 6 presents the synthesis of a series of Ag(I) bis(imino)pyridine complexes with varied sterics. Resulting ligand-metal interactions as well as reactivity towards Lewis basic donor ligands will be discussed. Chapter 7 presents the synthesis of first crystallographically authenticated examples of rhenium(I) pincer complexes utilizing the bis(imino)pyridine ligand. Chapter 8 presents a general conclusion to the work.

Carbon and phosphorus have often been compared owing to their diagonal relationship on the periodic table. However, relative to carbon, there remains an enormous breadth of polyphosphorus chemistry that is unexplored, particularly in the area of cationic phosphorus. A key step in the systematic and rational development of larger catenated organo-polyphosphorus cations is a fundamental understanding of the reactivity of small cationic building blocks. The smallest catenated framework in this context is the phosphinophosphonium monocation [R3P-PR2]+ (or phosphine-stabilized phosphenium cation), which can be prepared with a variety of functional groups at either phosphorus centre. This dissertation explores the diverse reactivity of chloro-substituted phosphinophosphonium cations, with a particular focus on reductive coupling as a synthetic route to novel catena-phosphorus systems. The resulting cationic frameworks are comprehensively described in terms of their diasteroisomerism, solution dynamics, and solid-state structural features. Additionally, fundamental electrochemical investigations of these diphosphorus cations are outlined as a tool for understanding and quantifying the reactivity of phosphenium cations. Finally, extension of reductive coupling methodology to the first chlorostibinophosphonium cations presents a promising outlook towards the catenation of the heavier pnictogen cations.

The coordination chemistry of compounds featuring P-P and P—Sb bonds has been investigated to define the fundamental features of bonding in these systems. New reaction methodologies to form P—P bonds have been evolved based on careful consideration of bond strengths in the gas and condensed phase. Insights revealed from systematic studies of molecular structures have been used to augment and expand the scope of existing models for structural prediction (e.g. VSEPR theory). Unique classes of catena-antimony compounds have been discovered, illustrating a remarkable structural and electronic diversity for this heavy p-block metal. Detailed mechanistic examinations have revealed a previously unrecognized mode of ligand activation for phosphine complexes of very electrophilic acceptors. Stable sources of the hitherto unisolated and highly reactive tris-triflate reagents, E(OTf)3 (E = P, As, Sb, Bi), have been prepared and their coordination chemistry as Lewis acids and oxidizing agents has been mapped. Collectively, the findings described here span a range of coordination chemistry paradigms for p-block elements that may be broadly applicable across the periodic table. A robust plan has been proposed for applying these insights towards the preparation of fundamentally interesting molecular frameworks and towards new strategies for small molecule activation. / Graduate / 0488 / 0485

This work was initially launched to study the synthesis of low-valent group 13 compounds bearing the bis(imino)pyridine ligand framework. Since its inception, this project has grown beyond the boundaries of group 13 to include low valent tin, silver, and rhenium. Alongside the reports of novel coordination compounds, we utilized computational chemistry to uncover unprecedented interactions which challenge conventional concepts of bonding. Synthesis, characterization, and complimentary computational studies are presented herein. Chapter 1 presents a historical overview of the bis(imino)pyridine ligand as well as our synthetic methodology and characterization of new ligand variants we have contributed to the literature. Chapter 2 presents the synthesis of a series of In(I) and In(III) bis(imino)pyridine complexes with varied sterics. Ligand-metal interaction and effect of ligand steric bulk on complex stability, as well as computational studies highlighting weak covalent interactions will be discussed. Chapter 3 presents the synthesis of Ga(III) bis(imino)pyridine complexes. Reactivity with “GaI” synthon as well as varied-stoichiometry one-pot synthesis attempts to generate low valent Ga-bis(imino)pyridine complexes will be discussed. Chapter 4 presents the synthesis of a series of Tl(I) bis(imino)pyridine complexes with varied sterics analogous to the approach taken with indium(I). Unprecedented weak ligand-metal as well as Tl-arene interactions will be discussed. Chapter 5 presents the synthesis of a series of Sn(II) bis(imino)pyridine complexes with varied sterics and halide substituents. Preferential cation-anion pair formation and attempted reactivity will be discussed. Chapter 6 presents the synthesis of a series of Ag(I) bis(imino)pyridine complexes with varied sterics. Resulting ligand-metal interactions as well as reactivity towards Lewis basic donor ligands will be discussed. Chapter 7 presents the synthesis of first crystallographically authenticated examples of rhenium(I) pincer complexes utilizing the bis(imino)pyridine ligand. Chapter 8 presents a general conclusion to the work.

Previous studies of supramolecular association through chalcogen-centred secondary bonding interactions (SBIs) demonstrated the versatility of 1,2,5-telluradiazoles and their annulated congeners, the benzo-2,1,3-telluradiazoles, as supramolecular building blocks. Key to the properties of those compounds is their propensity to undergo auto-association through the [Te-N]2 supramolecular synthon leading to dimers or supramolecular ribbon polymers. Moderate steric repulsion induces structural distortions of [Te-N]2 without dissociation and, in doing so, enables properties of practical interest such as chromotropism and second-order non-linear optical responses. However, moisture sensitivity discourages wide-spread application of these compounds. While being more tolerant of the atmosphere, the analogous selenadiazoles form weaker intermolecular interactions. Using a combined experimental and computational approach, this thesis investigates methods by which the selenium-centred supramolecular interactions can be enhanced and applied in the construction of supramolecular architectures. The quantum mechanical description of the SBIs formed by 1,2,5-chalcogenadiazoles was updated with the application of modern dispersion corrections to relativistic density functional theory calculations (PBE-D3, ZORA). While in all cases the dispersion effect on optimized SBI distances is small (< 0.03 Å), the dispersion corrections to the calculated interaction energy range from 6 to 10 kJ mol-1 and increase with the weight of the chalcogen. The total interaction energy increases faster, however, therefore the relative weight of dispersion for the telluradiazole (10%) is significantly less than for the sulfur analogue (40%). The same dispersion-corrected functional was applied to the identification of the secondary ions observed in the Laser Desorption Ionization mass spectrum of benzotelluradiazoles. The most stable structure of the [2M+H]+ ion was shown to feature the [Te-N]2 supramolecular synthon and would be preferred over alternatives held by hydrogen bonding alone, one TeN SBI, a combination of the two or -stacking. The [2M]+ would also feature the [Te-N]2 supramolecular synthon. Shortening of the TeN distances in these ions implies that electron withdrawing groups strengthen the SBIs. The updated computational method was also applied to characterize the bonding in the adducts of a N-heterocyclic carbene with benzo-2,1,3-telluradiazole and 3,4-dicyano-2,1,5-telluradiazole recently prepared by the Zibarev group. The long TeC distances (2.53 and 2.34 Å) correspond to fractional bond orders (<0.6) but display a significant covalent character. Attachment of the carbene nearly erases the remaining σ-hole on tellurium, raises the LUMO energy and consequently prevents the dimerization of these adducts, in contrast to what has been observed with the pyridine and DMSO adducts of other telluradiazoles. Benzo-2,1,3-selenenadiazole reacted with boranes (BR3, R = Ph, F, Cl, Br) yielding 1:1 (R = Ph, F, Cl, Br) and 1:2 (R = Cl) adducts. The crystal structure the BPh3 adduct features molecules organized in pairs connected by long SeC SBIs but no SeN SBIs. The BF3 and BCl3 1:1 adducts dimerize forming the [Se-N]2 supramolecular synthon. In contrast, the BBr3 adduct does not dimerize although SeBr, BrBr SBIs are formed through the lattice. The 1:2 adduct displays SeCl SBIs accompanied by distortion of the N-B-Cl bond angle due to the enhanced electrophilicity of the chalcogen. DFT calculations were performed to evaluate the energies of dimerization of the 1:1 adducts, the calculated SBI energies are greater than those for the dimer of the parent heterocycle (benzo-2,1,3-selenadiazole, 3b). The products of the combination of benzo-2,1,3-selenenadiazole with chloride salts of divalent Mn, Fe, Co, Ni, and Cd crystallized from DMSO in two distinct structural types. While the smaller ions (FeII, CoII and NiII) form infinite chains of metal atoms N,N’-bridged by the heterocycle΄ the larger ions (MnII and CdII) stabilize infinite chains of metal atoms bridged by 2 halide ions. In the latter case, two heterocycle molecules cap each metal ion and are able to establish a link to the next chain in the lattice through the [Se‑N]2 supramolecular synthon. Despite the large (>9.2 Å) distance between [M(-Cl)2]∞ chains, the manganese derivative is only paramagnetic, not ferromagnetic. Symmetry-broken DFT calculations for small models were unable to quantitatively reproduce the measured couplings (J) but do indicate that the heterocycle acquires significant spin density in the MnII compound enabling paramagnetic coupling through the [Se‑N]2 supramolecular synthon. General methods for the synthesis of N-alkylated selenadiazolium cations were investigated. Methyl, iso-propyl and tert-butyl benzo-2,1,3-selenadiazolium cations were prepared by direct alkylation or cyclo-condensation of the alkyl-phenylenediamine with selenous acid. While the former reaction only proceeds with the primary and tertiary alkyl iodides, the latter is very efficient. Difficulties reported in earlier literature are attributable to the formation of adducts of benzoselenadiazole with its alkylated cations and side reactions initiated by aerobic oxidation of iodide. However, the cations themselves are resilient to oxidation and stable in acidic to neutral aqueous media. X-ray crystallography was used in the identification and characterization of the following compounds: [C6H4N2(R)Se]+X-, (R = CH(CH3)2, C(CH3)3; X = I-, I3-), [C6H4N2(CH3)Se]+I-, and [C6H4N2Se][C6H4N2(CH3)Se]2I2. Formation of SeN SBIs was only observed in the last structure because anion binding to selenium is stronger. The relative strengths of those forces and the structural preferences they enforce were assessed with DFT-D3 calculations supplemented by AIM analyses of the electron density. The methods developed for the preparation of N-alkyl benzoselenadiazolium cations were extended to the syntheses of dications intended for use as building blocks of supramolecular polymers. The structure of several salts was established by single-crystal X-ray diffraction. [H4C6NSeN-CH2-CH2-NSeNC6H4]Cl2 crystallized forming a macrocyclic structure in which two dications are bridged by SeCl SBIs; a third halide anion sits at the centre of the macrocycle. [1,2-(H4C6NSeN)2-C6H10]Cl2 features two selenadiazolium cations bridged by a 1‑(R),2‑(R)‑substituted cyclohexane and short SeCl SBIs. [1,4-(H4C6NSeN-CH2)2-C6H4](BF4)2, featuring a p-xylene bridge, crystallizes in two pseudopolymorphs; with dications in anti or syn conformations making SeF contacts. [H4C6NSeN-CH2-CH2-NSeNC6H4](CF3SO3)2 does dimerize though the [Se-N]2 supramolecular synthon, although SeO interactions with the anions cap the second selenium atom. In contrast, [H4C6NSeN-CH2-CH2-CH2-NSeNC6H4](CF3SO3)2 only displays SeO contacts. An oligonucleotide analogue containing N-substituted selenadiazolium cations was designed to create foldamers with structures controlled by main-group secondary bonding. The target structures take advantage of the methods developed in this thesis for the functionalization of selenadiazoles and is meant to be compatible with automated methods for oligonucleotide synthesis. The proposed synthesis begins with the preparation of 1-(α,β)-O-methyl-2-deoxy-D-ribose, which was chlorinated and treated with phenylenediamine. High-resolution mass spectrometry confirmed the attachment of the diamine to the ribose, however, the yield was too low to continue this synthetic project. A ground-breaking development in the application of secondary bonding in supramolecular chemistry is the discovery of the reversible auto-association of iso-tellurazole N-oxides through TeO SBIs into annular structures. These rings are persistent in solution and behave as actual macrocycles able to complex transition metal ions, form adducts with fullerenes, and host small molecules. Single-crystal X-ray diffraction was critical to the characterization of these structures and required careful disorder modelling for tetrahydrofuran molecules included in a macrocyclic hexamer and the occupational disorder of CH2Cl2 and BF4- anions due to metal depletion in the crystal of a PdII complex. / Thesis / Doctor of Philosophy (PhD) / Supramolecular chemistry is a prominent area of research that pursues the construction of large structures by the spontaneous assembly and organization of molecular building blocks. Its fundamental premise is that the judicious use of intermolecular forces allows the design of a structure and control of its properties. Most of the work in supramolecular chemistry has relied on hydrogen atoms bridging molecules and the bonding of metal ions to atoms rich in electrons. This thesis pursued the use of a different type of intermolecular force, termed “secondary bonding”, which is characteristic of the heaviest elements at the right of the periodic table (the “main-group” of elements). Previous work at McMaster demonstrated that cyclic molecules containing carbon, nitrogen and tellurium were particularly efficient as supramolecular building blocks. However, they are easily degraded by atmospheric water, this fact severely limits practical applications of these compounds. In this thesis, the tellurium atoms are replaced by selenium, a lighter element in the same family. The resulting molecules are more tolerant of atmospheric conditions but form weaker intermolecular links. Through a combination of quantum mechanical, synthetic, spectroscopic and structural studies, it is shown that certain modifications to the molecular structure increase the affinity of the selenium atoms for electrons. In this way, it is possible to strengthen the intermolecular interactions and promote the spontaneous assembly of supramolecular structures. These investigations eminently fall in the category of fundamental research but have broad-reaching implications for practical applications in optical and electronic technologies.

This thesis describes selected reactivity studies of the N-heterocyclic carbene, IPr, towards a range of main group compounds. The synthesis and characterisation of sixty-three compounds, all of which incorporate IPr as a ligand in one of three coordination modes, are detailed herein. The deprotonation of IPr allowed for the isolation of an anionic source of the aIPr: ligand which was synthesised as a novel potassium salt and along with the previously reported lithium salt, was employed in reactions with group 12 and 14 bis(trimethylsilyl)amides and tetrahalides. The further chemistry of such novel products was investigated towards both electrophilic and nucleophilic reagents making use of both the pendant nucleophilic carbene functionality and the electrophilic main group centre. An alternative route to such species was investigated by the spontaneous isomerisation of IPr in the coordination sphere of group 14 tetrabromides and group 15 tribromides. The scope of this reactivity was subsequently investigated and was found to provide a simpler route to access the abnormal coordination mode of IPr. The aIPr ligand which is generated may be deprotonated by additional IPr thereby affording aIPr: ligands. The addition of halide abstracting agents allowed for the synthesis of cationic species stabilised by the coordination of either IPr or aIPr ligands. A unique, spontaneous reductive coupling of two phosphorus centres was discovered to take place upon heating a THF solution of (IPr)PBr₃. This allowed for the isolation of a bromide bridged P–P bond with reduced phosphorus centres. This facile reduction chemistry was further explored by reaction with mild reducing agents which provide access to low oxidation state phosphorus compounds in high yields. This chemistry was found to be possible (and more effective) due to the presence of the weaker phosphorus bond to bromine relative to the commonly employed chlorine ligands.

No description available.