Aqueous Organometallic Catalysis: Nitrile Hydration Catalyzed by Ruthenium(II) 1,3,5-triaza-7-phosphaadamantane (PTA) Derived Complexes
AuthorOunkham, Whalmany Linglee
AdvisorFrost, Brian J.
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This dissertation investigates the synthesis and characterization of ruthenium complexes containing water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA) and PTA derived ligands for the application of aqueous phase nitrile hydration. A series of PTA and PTA derivatives were characterized via solid-state NMR (SSNMR) and compared to their corresponding solution NMR spectra. Highly water-soluble β-phosphino alcohols (PTA-CR1R2OH) were prepared by reacting lithiated PTA with pyridiniecarboxaldehyde (e.g. 2-, 3-, or 4-pyridinecarboxaldehyde). A series of ruthenium arene β-phosphino alcohol (PTA-CR1R2OH) complexes were prepared by reacting highly water-soluble 2-, 3-, or 4- pyridyl PTA derivatives with the corresponding Ru arene (arene = toluene, p-cymene, or benzene) dimer [(arene)RuCl2]2. Ruthenium arene complexes containing PTA-CH-(2py)OH (20) resulted in monodentate κ1-P and bidentate κ2-P,N coordination modes. Complexes containing PTA-CH-(3py)OH (21) displayed predominately κ1-P coordination mode with a minor impurity (possibly a bridging species). The PTA-CH-(4py)OH (22) yielded a mixture of κ1-P and bridging coordination modes. All compounds were characterized by 1H, 13C, and 31P NMR spectroscopy and ESI-MS. The air-stable and water-soluble ruthenium complexes are active in catalytic hydration of nitriles to amides in water under air at 100°C. Our group previously reported RuCl2PTA4 as a highly active catalyst for aqueous phase nitrile hydration with tolerance for a wide substrate scope (e.g. ether, hydroxyl, nitro, bromo, pyridyl, and alkyl). The in situ generated catalyst (RuCl33H2O + 6 equivalents PTA) was found to be comparably active for nitrile hydration in water. In situ catalyzed nitrile hydration was evaluated in pH 6.8 buffer solution at 100°C under air and demonstrated higher activity than what was observed when conducted in water. Similar substrate tolerance, easy product separation (e.g. decantation), and recyclability was observed. Mechanistic studies (e.g. inhibition experiments, salt effects, and cyanide poisoning experiments) were conducted for this system. The final portion of this dissertation focuses on chemical education and active/inquiry-based learning (IBL) projects developed during an NSF GK-12 E-Fellowship for an Advanced Placement (AP) chemistry class. A combination of materials (e.g. brain teasers and class discussions) was used for curriculum development with inquiry-based experiments as a primary tool. The development of skills (e.g. critical thinking, problem-solving, and communication skills) through the exposure of IBL was empirically assessed.