Development of New Ligand Scaffolds for the Preparation of Heterobimetallic Complexes

There is currently much interest in the development of methods to harness sustainable, CO2 neutral, non-fossil fuel based energy sources due to diminishing worldwide supply of fossil fuels and concerns over historically high levels of CO2 in the atmosphere, which may have a devastating impact on the world’s climate. One such avenue is through the conversion of atmospheric CO2 into useful, high-energy density, organic fuel sources. Photosynthesis is the biological process by which plants convert sunlight, water, and CO2 into the reduced organic materials that we extract from the earth and burn (completing the cycle back to CO2) to release the energy stored in the bonds of the molecules. The development of synthetic methods to mimic the enzymatic processes of photosynthesis in order to utilize CO2 as a carbon feedstock for organic fuels would be of tremendous benefit. The one electron reduction of CO2 to CO2- is a highly unfavorable process as evidenced by the relatively high reduction potential of -1.9V. The two electron reduction of CO2 via proton assisted electron transfers is a more favorable process. Noble metals are known to undergo 2 electron processes though they are generally quite rare, expensive, and toxic to work with. Efforts have been made to use the more abundant first row transition metals (base metals) to mediate 2 electron processes with little success as they are more likely to undergo 1 electron redox processes. One such approach that has shown some success in achieving 2 electron processes with base metals is through the use of bimetallic cooperativity where two separate metal centers, each involved in a 1 electron event, work in tandem to achieve a net 2 electron redox event. This thesis describes investigations into metal complexes of new ligand designs involving a hard-soft approach to preferentially bind different metals in a site specific manner intended for the production of heterobimetallic complexes. Two classes of ligands are explored and described: (1) a series of P2N3 pincer type ligands and (2) a series of N-confused Trispyrazolylmethane (Nc-Tpm’s) ligands

Accessing Spin-Crossover Behaviour In Iron(II) Complexes Of N-Confused Scorpionate Ligands

The first examples of a class of N-confused tris(pyrazolyl)methane ‘scorpionate’ ligands have been prepared. The magnetic properties of their iron(II) tetrafluoroborate complexes are dictated by changing one substituent per ligand rather than three as is typical for normal scorpionate ligands

Structural Classification of Metal Complexes with Three-Coordinate Centres

Attempts to describe the geometry about three-coordinate silver(I) complexes have proven difficult because interatomic angles generally vary wildly and there is no adequate or readily available classification system found in the literature. A search of the Cambridge Structural Database shows that complexes formed between any metal centre and three non-metal donors (18001 examples) usually adopt geometries that are quite different than ideal ‘textbook’ extremes of either trigonal planar (∼4% with α = β = γ = 120 ± 2°), T-shaped (∼0.05% with α = 180 ± 2°, β = γ = 90 ± 2°), or trigonal pyramidal (∼0.3% with α = β = γ = 110 ± 2°). Moreover, there are multiple variations of “Y-type” and “other” shapes that require elaboration. Thus, to assist in future structural descriptions, we developed a classification system that spans all known and yet-to-be-discovered three-coordinate geometries. A spreadsheet has also been constructed that utilizes the “shape-space” approach to extract the structural description from a user input of three angles about a tri-coordinate centre and the number of atoms in a plane. The structures of two silver(I) complexes of new N-donor ligands p-NH2C6H4C6H4CH(pz = pyrazol-1-yl)2, L1, and 2-ferrocenyl-4,5-di(2-pyridyl)imidazole, L2, illustrate the utility of this classification system