Transition metal hydrides are key intermediates in a variety of stoichiometric and catalytic transformations. The determination of metal-hydride bond energies, especially the energies required to cleave the M–H bond to form protons (acidity) or hydride ions (hydricity), is an essential element in the rational design of these catalysts. Knowledge of these parameters, and their relationship to the choice of metal and ligand, allows catalysts to be tuned to avoid energy mismatches that would otherwise impede catalysis. The hydricities and acidities of transition metal bis(diphosphine) complexes, for instance, have been extensively studied. The availability of this data has enabled these complexes to be developed as catalysts for a variety of important reactions, such as H2 production and oxidation, CO2 hydrogenation, and formic acid dehydrogenation. However, analogous thermodynamic data for the heteroleptic metal-(triphosphine)(monophosphine) systems, containing one tridentate ligand and one monophosphine ligand, have not been reported. This presentation will report results from combined theoretical and experimental studies of complexes with the formula [M(triphos)(PPh3)], where M = Group 9 or 10 metal. The results for these complexes show the same general Periodic trends previously observed for the analogous [M(diphosphine)2] complexes but indicate that the heteroleptic complexes are substantially weaker proton donors but substantially stronger hydride donors than their bis(diphosphine) analogues.

Thermodynamic hydricities and acidities of transition metal hydrides containing mixed triphosphine and monophosphine ligands

2019 Spring National Meeting

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