Tridentate Phosphine Linkers for Immobilized Catalysts: Development and Characterization of Immobilized Rhodium Complexes and Solid-State NMR Studies of Polymers
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The major directions of this thesis involve (1) the synthesis, immobilization, and characterization of tridentate phosphine linkers on silica, (2) the study of unprecedented Si2C bond cleavage in Rh and Ir phosphine complexes, and (3) the study of performance polymers with solid2state NMR techniques. First a brief overview of solid2state NMR and its relevance to the various areas of chemistry covered in this thesis is given. Following the synthesis, immobilization, and characterization of tridentate phosphine ligands, EtOSi[(CH2)nPPh2]3 (n = 4, 7, 11) and [MeP((CH2)nPPh2)3]+I? (n = 4, 7, 11) on silica is detailed. Both, immobilization by electrostatic interactions and by a covalent siloxane bond to the support, is studied and compared. Ligand exchange with Wilkinson?s catalyst affords immobilized Rh complexes. These materials are applied to catalytic olefin hydrogenation. In either case active hydrogenation catalysts are obtained that can easily and efficiently be recycled up to 30 times. Detailed investigations reveal that irrespective of the linkage to the support the catalysts consist initially of well2defined molecular species that form supported Rh nanoparticles with a narrow size distribution in the course of the catalytic reaction. The nanoparticles are active hydrogenation catalysts as well, and no metal leaching into solution is detected. The reaction of the tridentate phosphine ligands EtOSi[(CH2)2PPh2]3 and MeSi[(CH2)2PPh2]3 with Rh and Ir complexes is investigated. This reaction does not lead to the anticipated Wilkinson2type complexes with the metal in the +I oxidation state, but instead to oxidative addition of the C(sp3)2Si bond to Rh or Ir centers to yield octahedral complexes with the metal in the +III oxidation state. These complexes are fully characterized by multinuclear NMR in solution and in the solid state. Preliminary density functional theory (DFT) calculations corroborate the preference for oxidative addition. Subsequently the study of performance thermoplastics which are important materials for the oil and gas industry is presented. The polymer morphology is studied by solid2state NMR techniques. Special attention is devoted to potential decomposition pathways at elevated temperatures for polyetheretherketone (PEEK) and polyphenylene sulfide (PPS) polymers. 13C CP/MAS (cross polarization with magic angle spinning) NMR and IR spectroscopy reveal that PEEK polymers show no detectable chemical change on the molecular level, while PPS polymers display signs of oxidation of the thioether group and branching via formation of ether, thioether, and biphenyl linkages. Furthermore, the water absorption of polybenzimidazole (PBI), polyetherketoneketone (PEKK), and their blend PEKK2PBI is studied. It is demonstrated that steam2treatment even at high temperatures and pressures does not cause chemical decomposition and that the changes, which are morphological in nature, are fully reversible.
Guenther, Johannes 1983- (2012). Tridentate Phosphine Linkers for Immobilized Catalysts: Development and Characterization of Immobilized Rhodium Complexes and Solid-State NMR Studies of Polymers. Doctoral dissertation, Texas A&M University. Available electronically from