Dihapto coordinated tungsten complexes: Synthesis, selectivity, and reactivity

Chapter 1 contains background information on the dearomatization of arenes and aromatic heterocycles. The chapter emphasizes pi-basic eta 2 chemistry previously explored by the Harman lab with the pentaammineosmium(II) fragment, as well as second generation dearomatization fragments.; Chapter 2 describes complexes of the form TpW(NO)(PMe3)(eta 2-thiophene) which have been synthesized in 31-40% yield by reduction of TpW(NO)(PMe3)(Br) in the presence of the thiophene ligand. The kinetics and thermodynamics of protonation/deprotonation have been studied. Sulfur-carbon, sulfur-oxygen, and carbon-carbon bond forming reactions have also been explored with these complexes.; Chapter 3 explores how pyridines bind to the {lcub}TpW(NO)(PMe3){rcub} fragment whether eta1 or eta2. We have determined what factors affect the binding selectivity, along with how to possibly control it. Kinetic and thermodynamic ratios of eta2 bound pyridines have been observed and protonation of eta2 pyridines is discussed.; Chapter 4 describes the formation of isoquinuclidines utilizing a Diels Alder reaction with TpW(NO)(PMe3)(eta2-pyridine) complexes. The Diels Alder reactions were accomplished with electron-deficient dienophiles under mild reaction conditions in good yields. Further more, inverse electron demand hetero Diels Alder reactions and Michael additions have been explored.; Chapter 5 describes a series of complexes of the form TpM(NO)(L')(eta 2-L) (where L is a nitrile, acetone, or alkene, M = W or Mo, L' = PMe3, MeIm). These complexes, are subjected to various electrophiles (e.g., alkyl halides, Bronsted acids, and trityl triflate) to systematically probe the ability of the pi-basic transition metal to affect the reactivity of the dihapto-coordinated ligand. Alkylation is observed at the heteroatom of the acetone and the nitrile, but depending on the reagent, alkylation of the nitrosyl also occurs. The structures of several nitrilium complexes and a rare example of an acetonium complex are also reported.