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1. Thermodynamic and kinetic hydricity of transition metal hydrides

   https://doi.org/10.1039/D0CS00405G  

   Brereton, Kelsey R.; Smith, Nicholas E.; Hazari, Nilay; Miller, Alexander J. (November 2020, Chemical Society Reviews)

   null (Ed.)

   The prevalence of transition metal-mediated hydride transfer reactions in chemical synthesis, catalysis, and biology has inspired the development of methods for characterizing the reactivity of transition metal hydride complexes. Thermodynamic hydricity represents the free energy required for heterolytic cleavage of the metal–hydride bond to release a free hydride ion, H − , as determined through equilibrium measurements and thermochemical cycles. Kinetic hydricity represents the rate of hydride transfer from one species to another, as measured through kinetic analysis. This tutorial review describes the common methods for experimental and computational determination of thermodynamic and kinetic hydricity, including advice on best practices and precautions to help avoid pitfalls. The influence of solvation on hydricity is emphasized, including opportunities and challenges arising from comparisons across several different solvents. Connections between thermodynamic and kinetic hydricity are discussed, and opportunities for utilizing these connections to rationally improve catalytic processes involving hydride transfer are highlighted. 

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2. Toggling the Z-type interaction off-on in nickel-boron dihydrogen and anionic hydride complexes

   https://doi.org/10.1039/D2CC03219H  

   Prat, Jacob R.; Cammarota, Ryan C.; Graziano, Brendan J.; Moore, James T.; Lu, Connie C. (January 2022, Chemical Communications)

   Completing a series of nickel-group 13 complexes, a coordinatively unsaturated nickel-boron complex and its derivatives with a H 2 , N 2 , or hydride ligand were synthesized and characterized. The toggling “on” of a Ni(0)–B( iii ) inverse-dative bond enabled the stabilization of a nickel-bound anionic hydride with a remarkably low thermodynamic hydricity of kcal mol −1 in THF. The flexible topology of the boron metalloligand confers both favorable hydrogen binding affinity and strong hydride donicity, albeit at the cost of high H 2 basicity during deprotonation to form the hydride. 

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3. Accessing Reactive Metal Hydrides through Designed Heterometallic Bridges

   https://doi.org/10.1055/a-2264-9040  

   Gonzalez, Fernando; De_Leon, Edgardo; Shoshani, Manar M (February 2024, Synlett)

   Abstract A methodology to access reactive hydride moieties is highly desirable, yet limited. Multimetallic hydride fragments are notable for their heightened reactivity and catalysis, but deliberate access to these species is lacking. In this highlight, we discuss recent developments by our group in the design of a new heterometallic complex that invokes an architecture designed to provide modular access to reactive hydride moieties by leveraging metal hydrides in combination with pendent donors to a model heterotrimetallic Ni–(Al–H)2 complex. An amplification of insertion-based reactivity has been examined in the hydrofunctionalization of quinolines, and our complex substantially outperformed the parent aluminum hydride LAlH (L = ligand). A potential rationale for the dramatically increased reactivity, and a further examination of these motifs and methodology in catalysis are also discussed. 1. Introduction 2. Heterometallic Hydride Design and Characterization 3. Amplification in Catalysis 4. Summary and Outlook 

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4. Ruthenium hydrides encapsulated in sol–gel glasses exhibit new ultrafast vibrational dynamics

   https://doi.org/10.1063/5.0082752  

   Pyles, Cynthia G.; Patrow, Joel G.; Cheng, Yukun; Tonks, Ian A.; Massari, Aaron M. (March 2022, The Journal of Chemical Physics)

   Vibrational dynamics were measured by IR pump–probe spectroscopy and two-dimensional IR spectroscopy for triruthenium dodecacarbonyl and the undecacarbonyl hydride that forms when it is encapsulated in an alumina sol–gel glass. For comparison, a triruthenium undecacarbonyl hydride salt was also synthesized and studied in neat solution to identify the potential influence of the confined solvent environment on the dynamics experienced by carbon monoxide ligands. The vibrational lifetime was found to be significantly decreased for both hydride species relative to the dodecacarbonyl compound. Conversely, spectral diffusion of the CO vibrations was measured to be faster for the parent compound. The most significant dynamic changes occurred upon transformation from the starting compound to the hydride, while only minor differences were observed between the dynamics of the freely dissolved and sol–gel encapsulated hydrides. The results suggest that the structural change to the hydride has the largest impact on the dynamics and that its improved catalytic properties likely do not originate from confined solvent effects. 

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5. Identification, classification and characterisation of hydrides in Zr alloys

   https://doi.org/10.1016/j.scriptamat.2023.115768  

   Maric, Mia; Thomas, Rhys; Davis, Alec; Lunt, David; Donoghue, Jack; Gholinia, Ali; De_Graef, Marc; Ungar, Tamas; Barberis, Pierre; Bourlier, Florent; et al (January 2024, Scripta Materialia)

   Hydride precipitation in zirconium alloys leads to embrittlement, making it essential to understand their prevalence and stability in the microstructure. Dictionary indexing of Kikuchi patterns, along with orientation relationship analysis and x-ray diffraction, confirmed the presence of both delta and gamma hydride phases in Zircaloy-4. Both phases were found to be stable in recrystallised zirconium, with the gamma phase exhibiting a distinct orientation relationship with the matrix. Delta hydride morphology and orientation were influenced by local stresses, resulting in a change in orientation during precipitation. By analysing the orientation relationships, the evolution of hydride phases could be visualised, providing insights into the room temperature stability of both delta and gamma hydrides. 

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