Pyridyl Phosphine Complexes in the Design of Hydration Catalysts

Recent advances in homogeneous catalysis have identified the importance of ligands able to participate in the catalytic cycle. Particularly relevant to making chemistry “greener” are those ligands that solubilise the catalyst in aqueous solution, and those that are able to activate water molecules towards reaction with the metal complex or substrate. This thesis describes the synthesis and coordination chemistry of a novel ligand bearing 2-pyridylphosphine substituents attached to a 2,6-pyridyl backbone (²⁻pyrPNP, [(C₅H₄N)₂PCH₂]₂C₅H₃N). These components were selected for their abilities to interact with water through dearomatisation processes, hydrogen bonding, and the basic pyridyl nitrogen atoms. The synthesis of pure ²⁻pyrPNP described here represents a much improved method for the synthesis of pyridylphosphines compared to those published in the literature. This is demonstrated by comparison with the original synthetic route, which produced many intractable impurities, as well as by the ability of the new method to provide PhPNP from an economical and air-stable starting material. Reactions of ²⁻pyrPNP with rhodium precursors show complicated reactivity, including the potential formation of paramagnetic species. Investigation into the reactivity of ²⁻pyrPNP with analogous iridium precursors resulted in the synthesis of [(²⁻pyrPNP)Ir(cod)]Cl. This is the first crystallographically characterised complex containing a facially coordinated PNP ligand. The cod ligand can be removed with ethene and hydrogen to form bis(ethene) and chloroiridium(III) bis(hydride) complexes [(²⁻pyrPNP)Ir(C₂H₄)₂]Cl and [(²⁻pyrPNP)Ir(H)₂Cl], respectively. Both complexes contain meridionally-coordinated ²⁻pyrPNP. Preliminary investigations reveal that the iridium complexes are fairly successful nitrile hydration catalysts under aqueous conditions. In addition, the cod and bis(ethene) complexes bearing ²⁻pyrPNP are more active than the cod complex of the pyridyl-free PhPNP ligand

SYNTHESIS, CHARACTERIZATION, AND REACTIVITY OF LATE TRANSITION METALALUMINUM HETEROBIMETALLICS

Heterobimetallic systems have seen an increase in development over the last several years. These bimetallic systems typically involve two transition metals with unique properties used in tandem to activate chemical bonds. Many of these systems use transition metals, consisting of a soft, electron rich (low valent) metal and a harder, electron deficient (high valent) metal. These types of heterobimetallics can be exploited as an intramolecular Lewis acidLewis Base pair, which allows access to reactivity that may not be accessible to one transition metal alone.Relatively unexplored is the use of a late transition metal (LTM) in tandem with a Lewis-acidic p-block (Group 13) metal. LTM-Lewis acid bimetallic complexes can be broadly categorized into two separate families, both capable of cooperative activation of a chemical bond. Among Group 13 Lewis acids specifically, aluminum is of particular interest to the Brewster laboratory due to it being earth-abundant and the most electropositive Group 13 element. Bimetallic complexes that contain an aluminum moiety are relatively unexplored compared to their boron analogs due to being highly reactive species and their synthetic difficulty. This has made their isolation and characterization quite challenging. The goal of the Brewster lab is to develop bimetallic systems that contain aluminum and an electron-rich transition metal and to exploit cooperative reactivity between both metal centers. In this dissertation, we describe the successfully completed syntheses of bi- or tridentate ligands for our bimetallic aluminum complexes and their respective transition metal complexes. We report the experimental reactivity of the LTM complexes that contain a docking group for alkylaluminum or haloaluminum. Syntheses of these complexes follow a ligand first approach, where the LTM complex is first synthesized and isolated, followed by the addition of the aluminum moiety. This synthetic route has been successful in the development of several bimetallicaluminum complexes synthesized by the Brewster lab. We report the reactivity of the aluminum complexes with small molecules (i.e. H2, CO2, etc.). Varying the docking substituent attached to the aluminum moiety provides different reactivity. Experimental and computational investigation of the activation of CO2 are reported

Towards the synthesis of imines and iminiums and their reactions in situ

Functionalised amines are important targets for organic chemists. Various methods are used to functionalise amines, however often these reactions will involve the use of toxic or expensive reagents and therefore must be controlled, especially when used as active pharmaceutical ingredients (API). These reagents could potentially increase the cost associated with API and fine chemical synthesis. There has been an impetus to directly activate the C-H bonds adjacent to amine groups, thus increasing the reactivity of the group. Metal complexes have been used to stoichiometrically activate amines, however catalytic methods would be more favourable due to potential cost reduction. Metal complexes are used widely for hydrogen transfer reaction, which have provided a new methodology to activate non-electrophilic substrates by forming their electrophilic analogues. This methodology has been used extensively with alcohols, however there remains the opportunity to form imines by amine activation. The research disclosed in this thesis discusses efforts toward the formation of imines or iminium ions from their amine precursors. Analysis of the N-alkylation of several amines has been carried out, with discussion of methods to inhibit N-alkylation to form more of the desired imine. Mechanistic analysis of the various species in the reactions has given information including a potential pathway for N-alkylation, amine iridium binding and a potential inhibition product. The optimisation of an indole cyclisation reaction has been probed, with different a range of conditions investigated. A discussion of an attempted telescoped reaction has been given as well, together with a study on the expansion of the methodology to include diverse structural motifs. The attempted incorporation of different nucleophiles has also been disclosed with a discussion of the results and potential improvements to these reactions. Finally, an overview of the future for this research has been presented with potential new avenues for exploitation