A Tale of Two Metals: Come to Cobalt: Synthesis and Characterization of Novel Cobalt-SNS Complexes for H2 Fuel Catalysis [AND] Degradation of Organophosphonates: Study and Characterization of a Novel Fusion Diiron Oxygenase from F. multimorphosa.
Creators: name: Koob, Jeremy
Publisher: name: Brandeis University
Year: 2019
Subjects: Ammonia borane
Dehydrogenation
Cobalt(III)
Co(N2S2)
SNS ligand
Organophosphonates
2-aminoethylphosphonate
FeOf
PhnY/Z
HD-domain
Diiron oxygenase

description: Chapter 1: Come to Cobalt: Synthesis and Characterization of Novel Cobalt-SNS Complexes for H2 Fuel Catalysis.\r \r Catalyst development for acceptorless dehydrogenation of H2-dense solids such as ammonia borane (NH3BH3) moves toward a future using H2 fuel. Initial synthesis of a novel family of CoI catalysts using sulfur-nitrogen-sulfur (SNS) ligands proposes several complexes useful for future catalytic cycles due to the hemi-labile and inner-sphere base character of the SNS ligand. One such complex, proposed to be Co(SNSMe)(dmpe), was successful in complete ammonia borane dehydrogenation, but showed signs of catalyst decomposition. We report here the synthesis of the precursor to this successful catalyst, and show the efficient and clean synthesis of a new paramagnetic CoIII(N2S2) complex.\r Synthesis of a thiol SNHSMe heterocyclic ligand is shown with its subsequent ring-opening deprotonation that yields a lithium-THF dimer, characterized by X-ray crystallography and NMR spectroscopy. Coordination of this anionic ligand to cobalt results in an internal ligand imine coupling to produce a cobalt(III) square planar complex: [Co(SNSMe)2][(THF)3Li]2(µ-Cl)]. This paramagnetic complex is characterized by NMR spectroscopy, X-ray crystallography, Evans’ method NMR, and cyclic voltammetry, and relevant data are discussed herein. This work provides one of the first cobalt-SNS precatalysts for NH3BH3 dehydrogenation, and opens the door for new cobalt-SNS complexes as potential precatalysts for reductive processes.\r \r Chapter 2: Degradation of Organophosphonates: Study and Characterization of a Novel Fusion Diiron Oxygenase from F. multimorphosa.\r \r The HD-domain superfamily describes enzymes that are designated as phosphohydrolases; however, recent discoveries have shown that two HD-domain proteins, myo-inositol oxygenase (MIOX) and PhnZ, function as oxygenases. Both MIOX and PhnZ contain a diiron cluster that performs a novel 4 electron oxidative cleavage of, respectively, carbon-carbon or carbon-phosphorous bonds via incorporation of O2. In conjunction with the enzyme PhnY, the HD-domain protein PhnZ catalyzes the degradation of 2-aminoethylphosphonate to glycine and inorganic phosphate, showing us a new strategy to cleave an ‘old’ bond. \r This work confirms a third known example of an HD-domain diiron oxygenase, and shows that the fusion oxygenase obtained from F. multimorphosa roughly resembles the catalytic action of the PhnY/Z system. The fusion oxygenase has a wider range of phosphonate substrates than the PhnY/Z system and a wider range of pH stability, as perhaps expected for a pathogenic fungus that must be adaptable to environmental niches. We have now defined and assigned function to a novel fusion protein, and in the process showed that the fusion protein is perhaps a strategy to chemically diversify and expand the functional repertoire of these enzymes.