UBC Theses and Dissertations
UBC Theses and Dissertations
1,3-N,O-Chelated complexes of rhodium and iridium : harnessing metal-ligand cooperativity for bond activation processes Drover, Marcus Walter
This thesis explores the use of 1,3-N,O chelating ligands, amidates and phosphoramidates as ligands for rhodium and iridium in the +1 and +3 oxidation states. Toward this end, a series of novel group 9 complexes were prepared, characterized, and employed for cooperative small molecule activation and element-hydrogen (E-H) bond cleavage reactions. In Chapter 1, amides and phosphoramides are introduced as ligands for late transition metals. In particular, it is highlighted that such ligands have traditionally been used to form early transition metal and lanthanide N,O-chelated complexes, with the late transition metal chemistry being highly underdeveloped. In Chapter 2, the fundamental reactivity of rhodium(I) complexes having amidate ancillary ligands is presented including catalytic oxygen atom transfer using O₂ – the products of such reactions: η²-O₂ complexes were characterized using NMR spectroscopy and density functional theory (DFT). Chapter 3 details the use of 1,3-N,O chelated complexes of monovalent Rh(I) and Ir(I) for the controlled capture of HBCy₂, providing six-membered genuine metallaheterocycles bearing a δ-B-H agostic interaction, which can be employed for chemoselective boron transfer reactions. In this chapter, the inclination of this ligand class to change the chemoselectivity of HBCy₂ hydroboration toward carbonyl-containing substrates (in the presence of an alkene) is provided. Chapter 4 examines the preparation of the first unsaturated Cp*Ir(III) (Cp* = C₅Me₅) phosphoramidate complex for use in element-hydrogen (E-H) bond activation (E = H, C, Si, B). The syntheses of coordinatively unsaturated (E)-vinyloxy Cp*Ir(III) complexes, which are prepared from regioselective 1-alkyne C-H bond activation and O-phosphoramidation is discussed. This regioselectivity is completely inverted from that of free phosphoramidates, which undergo preferential N-alkylation. Finally, we illustrate how aminoborane (H₂B=NR₂) B-N bond rotation can be accessed using joint metal-ligand stabilization between Ir and a phosphoramidate coligand. All complexes were rigorously characterized using NMR spectroscopy, X-ray diffraction, as well as by DFT. Chapter 5 surmises a new protocol for rhodium-mediated ethylene amination (nitrogen-carbon bond formation) using diazenes (RN=NR) as the N-atom source. This work provides a “proof-of-principle” for the functionalization of simple C₂-synthons using easily handled nitrogen-sources, providing rhoda(III)heterocycles, which undergo [Rh]-N bond protonolysis to provide ethyl-substituted hydrazine complexes.
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