title: Thermodynamic Hydricity of Transition Metal Hydrides.
abstract: Transition metal hydrides play a critical role in stoichiometric and catalytic transformations. Knowledge of free energies for cleaving metal hydride bonds enables the prediction of chemical reactivity, such as for the bond-forming and bond-breaking events that occur in a catalytic reaction. Thermodynamic hydricity is the free energy required to cleave an M-H bond to generate a hydride ion (H(-)). Three primary methods have been developed for hydricity determination: the hydride transfer method establishes hydride transfer equilibrium with a hydride donor/acceptor pair of known hydricity, the H2 heterolysis method involves measuring the equilibrium of heterolytic cleavage of H2 in the presence of a base, and the potential-pKa method considers stepwise transfer of a proton and two electrons to give a net hydride transfer. Using these methods, over 100 thermodynamic hydricity values for transition metal hydrides have been determined in acetonitrile or water. In acetonitrile, the hydricity of metal hydrides spans a range of more than 50 kcal/mol. Methods for using hydricity values to predict chemical reactivity are also discussed, including organic transformations, the reduction of CO2, and the production and oxidation of hydrogen.
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Eric S
authors.initials: ES
authors.lastname: Wiedner
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599-3290, United States.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Chambers
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599-3290, United States.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Pitman
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: R Morris
authors.initials: RM
authors.lastname: Bullock
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill , Chapel Hill, North Carolina 27599-3290, United States.
authors.forename: Alexander J M
authors.initials: AJ
authors.lastname: Miller
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Appel