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Abstract

This thesis describes the synthesis of Pd(II) complexes that contain phosphine-sulfonate ligands (PO–) and their performances as catalysts for ethylene (E) homopolymerization and ethylene/vinyl-fluoride (VF) and ethylene/methyl-acrylate (MA) copolymerization. The objectives of this thesis were to identify new ways of modifying the (PO)Pd scaffold (i.e. incorporating a cyclopentane linker), to elucidate the effects of these modifications on polymerization performance, and to study the olefin polymerization and insertion behavior by new (PO)Pd alkyl and fluoride complexes. Chapter One introduces palladium(II) alkyl complexes that contain ancillary phosphine-arenesulfonate ligands (PO–). This class of catalysts is one of the few that catalyze the copolymerization of E and polar vinyl monomers to afford copolymers with the polar functionalities incorporated into a highly linear polyethylene (PE) backbone. The electronic asymmetry of the PO– ligand is believed to be important for the unique reactivity of (PO)Pd alkyl complexes. Importantly, the catalyst activity and the molecular weight (MW) of the PEs and copolymers produced by (PO)Pd alkyl catalysts can be significantly modified by changing the substituents on the phosphine. Chapter Two describes the synthesis and characterization of Pd(II) alkyl complexes that contain PAr2-cyclopentanesulfonate ligands (Ar = Ph, [PO-C5-Ph]–; Ar = 2-OMe-Ph, [PO-C5-OMe]–). Sulfonate-bridged, base-free {(PO-C5-OMe)PdMe}2 and borane-coordinated base-free [{(PO-C5-OMe)•B(C6F5)3}PdMe]2 were also prepared. The solution behavior and solid-state structures of these complexes are described. Chapter Three describes the olefin polymerization performance of complexes prepared in Chapter Two. (PO-C5-OMe)PdMe(py), {(PO-C5-OMe)PdMe}2, and [{(PO-C5-OMe)•B(C6F5)3}PdMe]2 polymerize E and copolymerize E with MA and VF to form linear PE and copolymers. The cyclopentane linker in the phosphine-sulfonate ligand strongly affects the activity of the catalysts and the PE MW. (PO-C5-OMe)PdMe(py) and {(PO-C5-OMe)PdMe}2 are much more stable and active in E polymerization than analogous (PAr2-CH2¬CH2SO3)PdR catalysts, and are less active but less inhibited by polar vinyl monomers than analogous (PAr2-arenesulfonate)PdR catalysts. Chapter Four describes experimental and computational investigations of the ethylene polymerization mechanism for complexes prepared in Chapter Two. Low temperature NMR studies show that {(PO-C5-OMe)PdMe}2 reacts with E below –10 °C to form ethylene adduct cis-P,R-(PO-C5-OMe)PdMe(ethylene), which undergoes insertion at 5 °C. DFT calculations for a model (PMe2-cyclopentanesulfonate)Pd(Pr)(ethylene) species show that E insertion proceeds by cis-P,R/trans-P,R isomerization followed by migratory insertion. The lower activity of {(PO-C5-OMe)PdMe}2 vis-à-vis analogous (PAr2-arenesulfonate)PdR catalysts results from a higher barrier for migratory insertion of the trans-P,R isomer. Chapter Five describes the synthesis and characterization of new (PO-OMe)PdX(lut) complexes (X= Br, F, FHF) bearing a P(2-OMe-Ph)2-4-Me-benzenesulfonate ligand. (PO-OMe)PdF(lut) exists as a mixture of cis/trans-P,F isomers in solution, with isomerization occurring both in the solid state and in CD2Cl2 solution at room temperature. The insertion reactions of cis/trans-P,F-(PO-OMe)PdF(lut) with VF, vinyl bromide, vinyl acetate, vinyl benzoate, and 1,4-hexadiene are described. (PO-OMe)Pd{CH2CH(C=O)H}(lut) and (PO-OMe)Pd(C6F5)(lut) were isolated from the reaction of (PO-OMe)PdF(lut) with vinyl-acetate/vinyl-benzoate and B(C6F5)3, respectively, and characterized by X-ray diffraction. Chapter Six describes the synthesis of (PO-Bp/PhOMe)PdMeL catalysts (L = py, lut) bearing a 2-{P(2-{2,6-(OMe)2-Ph}-Ph)(2-OMe-Ph))}-4-Me-benzenesulfonate ligand. The systematic process by which the NMR spectra for the proligand H[PO-Bp/PhOMe] and (PO-Bp/PhOMe)PdMe(lut) were assigned and how these assignments were exploited in NOESY studies to probe the solution structures of these compounds are described. The solid-state structure of one isomer of (PO-Bp/PhOMe)PdMe(py) was determined by X-ray diffraction. The solution-behavior of (PO-Bp/PhOMe)PdMe(py) is re-analyzed based on these structural studies.

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