Transition metal hydrides are key intermediates in organometallic catalysis in a range of solvents, from non-polar aprotic, to polar aprotic, to protic and aqueous. The free energy required to release H– from these complexes, known as hydricity, can help rationalize and predict hydride transfer reactions. New insights into the influence of solvent on hydricity emerge from a study of iridium complexes [Cp*Ir(bpy-X)H]+ (bpy-X = 4,4'-X2-2,2'-bipyridine, X = H, Me, OMe, CO2Me, CF3, tBu). These studies illustrate how hydricity is equally influenced by bipyridine ligand electronic structure in both acetonitrile and water. Conversely, the addition of chloride ions that bind the metal center after hydride release has a dramatically different impact in the two solvents. In order to enhance the predictive power of hydricity, the data are used to develop an equation that accurately predicts changes in hydricity moving between solvents. With the aid of Density Functional Theory (DFT) and Natural Bond Orbital (NBO) analysis, we are able to draw a more complete picture of the influence of solvation on hydricity.

Thermodynamic hydricity across solvents: Subtle electronic effects and stark ligation effects in iridium hydrides

2019 Spring National Meeting

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