Bio-inspired transition metal complexes and actinide-selective extractants using triphenoxymethane-based C3-symmetric ligand systems

Various classic metal ligand moieties were secured to a triphenoxymethane platform to generate pre-organized C₃-symmetric ligand systems with new metal coordination properties. One series of these systems, formed by attaching three triamine ligands such as 2,2′ -dipicolylamine and 1,4-dimethyl-1,4,7-triazacyclononane to the platform via ethylene linkers, was used to explore the rather rare chemistry of three pre-arranged metal centers, especially in the context of modelling the tricopper active sites of multi-copper oxidase and particulate methane mono-oxygenase enzymes shown to bind and reduce dioxygen at an active site containing three proximate histidine-coordinated copper ions. The synthesis of these ligands and their copper complexes, the structural characterization of these complexes, and the reactivity of these complexes with dioxygen with its implication towards understanding the biological system is presented and discussed, as is the potential for these systems to model other trinuclear enzyme active sites such as those found in zinc phosphodiesterases. A failed synthetic pathway in the development of these trinuclear ligand systems resulted in a modified triphenoxymethane platform to which the heavy metal extractant ligand carbamoylmethylphosphine oxide (CMPO) could easily be attached. Extractions of simulated nuclear waste streams with the resulting tris-CMPO compound resulted in the selective removal of actinides over lanthanides from these streams, an intractable problem not yet overcome with existing nuclear waste treatment technologies. A thorough solution and solid state analysis of the lanthanide and actinide coordination complexes formed with this ligand system suggests a possible mechanism for this selectivity that can be tested and applied to create new extractants with increased actinide affinities. The synthesis and characterization of these complexes and the extraction experiments with the ligand are presented and discussed in light of this mechanism and its implications to nuclear waste treatment.