UBC Theses and Dissertations
Intermolecular oxidative addition of aryl halides to Pt(II) and selective reductive elimination of alkyl-halides bond vs C-C bond from Pt(IV) complexes Zhang, Nan
This thesis examines the use of N-heterocyclic carbene ligands on Pt metal centers. Reactivity of chelated N-heterocyclic carbene ligands on Pt centers was studied in terms of oxidative addition, reductive elimination, isomerization, and ligand transfer reactions with an emphasis on carbon-halogen (C-X, X = Cl, Br, and I) bond reductive elimination. In Chapter 1, the research progress in the Love group in terms of carbon-halogen bond activation and methane functionalization is discussed. Chapter 2 describes the investigation of the mechanism of intermolecular oxidative addition of aryl halides to Pt(II) alkyl complexes. Pt(IV) phenyl complexes are successfully detected by 1H and NOESY NMR spectroscopy which provides experimental support for a concerted mechanism. Unusual selective reductive elimination of Csp³-I vs Csp²-Csp³ and Csp³-Csp³ bond is also observed. Computational methods support the experimental work. In Chapter 3, selective reductive elimination of Csp³-X (X = Cl, Br, and I) vs Csp³-Csp³ bond from isolated Pt(IV) complexes is discussed. Pt(IV) complexes are synthesized by oxidative addition of MeI, which exhibit an equilibrium with Pt(II) by oxidative addition and reductive elimination of MeI. Selective Csp³-I vs Csp³-Csp³ bond reductive elimination is observed in an (NHC)PtMe₂I₂ complex (NHC = N-heterocyclic carbene). Additionally, Csp³-Cl and Csp³-Br bond reductive elimination is observed in competitive with Csp³-I reductive elimination via initial isomerization. Computational methods are employed, that support the experimental work. In Chapter 4, reactivity of an anionic Pt(IV) complex is discussed in terms of imidazolium salt activation and NHC transfer. In an attempt to study the reactivity of cyclometalated Pt(IV) complexes, a cyclometalated (NHC)Pt(IV)Cl complex was synthesized by activation of imidazolium salt with a chloride arm, followed by oxidative addition of the Csp3-Cl bond. In contrast, the reaction occurs initially at the Csp³-Br position of the imidazolium salt in the reaction of Pt(II) with the Br analogous imidazolium salt. As a result, a novel anionic Pt(IV) complex stabilized by the bromide ion of imidazolium salt was isolated. Furthermore, intramolecular NHC transfer is observed from Pt(II) to Pt(IV) centers upon the reaction of the anionic Pt(IV) with additional Pt(II) precursor.
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