Multi-edge X-ray absorption near-edge spectroscopic analysis of palladium complexes in II, III and IV oxidation states
Barton, Rhonda Lee Hoffert
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Palladium-based complexes have profoundly impact on the synthetic tools of organic chemists due to their importance as catalysts in a myriad of chemical transformations. Palladium in the 0, II, III and IV oxidation states have all been experimentally observed to have catalytic activity in carbon-carbon bond coupling reactions. A common organometallic research aim is to improve catalytic activity of these complexes by designing and optimizing new ligand systems to access more difficult transformations. In order to understand the electronic effects that ligand systems have on reactivity, X-ray absorption spectroscopy is used to characterize the electronic structure of the ligand and metal components of pre-catalysts and palladium model complexes. The multi-edge X-ray absorption near-edge absorption spectroscopic technique (XANES) is an element specific technique that excites core electrons of the 1s (K-edge) and 2p (L-edge) orbitals to frontier unoccupied molecular orbitals, providing a ground state picture of a complex's ligand and metal electronic structure. This thisis will describe a comparative analysis between homoleptic chloropalladium complexes and interesting heteroleptic palladium based complexes of II, III and IV oxidation states to understand the stabilizing effects of a unique ligand environment. Furthermore, it will emphasize the benefits of using multi-edge XANES technique in rationalized catalyst design.