Rhodium olefin complexes : study of molecular motion in the solid state and characterization of Rhodium hybrid catalyst systems

This dissertation describes two studies that involve rhodium olefin complexes. The first is an investigation of solid-state motions of olefin ligands in such complexes and the second is an analysis of the structure and reactivity of rhodium hybrid catalyst systems. While reports of solid-state motions of asymmetrically shaped ligands in organometallic complexes have been rare thus far, it was found that the ethylene ligands in Rh(acac) (C₂H₄)2 (acac = 2,4- pentanedionate) and in [Rh(µ-Cl) (C₂H₄)₂]₂ undergo a rotational motion. This motion is analogous to ethylene rotation that is frequently observed in solution. It was found that the free energy of activation for ethylene rotation in solid Rh(acac) (C₂H₄)2 is not significantly higher than that for the same motion in solution. Thus, ethylene rotation in solid Rh(acac) (C₂H,sub>4)₂ appears to be under intramolecular control, and intermolecular interactions do not add significantly to this energy barrier. From structural information it was concluded that rotation of the ethylene ligands in these bisethylene complexes must be correlated.

An important application of rhodium olefin complexes is their use in catalysis. The second part of this dissertation describes the structure and reactivity of hybrid catalyst systems that were prepared by chemisorbing rhodium complexes [Rh(µ-X)L]₂ (X = Cl for L = (C₂H₄)₂, 1,5-cyclooctadiene (cod), (CO)₂ and X = OH, OMe for L = cod) onto &gamma:-alumina. It was found that the inter- actions of the rhodium with the surface functionalities are sensitive to the vii electronic nature of the terminal ligands L and that the chemisorbed species can undergo ligand exchange reactions.