Thermodynamic Hydricity of Transition Metal Hydrides

作者：Eric S. Wiedner, Matthew B. Chambers, Catherine L. Pitman, R. Morris Bullock, Alexander J. M. Miller, Aaron M. Appel · 发表于：Chemical Reviews · 年份：2016 · DOI：10.1021/acs.chemrev.6b00168 · 被引用次数：565 · 研究领域：Asymmetric Hydrogenation and Catalysis、Carbon dioxide utilization in catalysis、Ammonia Synthesis and Nitrogen Reduction

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.