Thermodynamic and kinetic hydricity of transition metal hydrides.

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.

Bathochromic Shifts in Rhenium Carbonyl Dyes Induced through Destabilization of Occupied Orbitals.

A series of rhenium diimine carbonyl complexes was prepared and characterized in order to examine the influence of axial ligands on electronic structure. Systematic substitution of the axial carbonyl and acetonitrile ligands of [Re(deeb)(CO)(NCCH)] (deeb = 4,4'-diethylester-2,2'-bipyridine) with trimethylphosphine and chloride, respectively, gives rise to red-shifted absorbance features. These bathochromic shifts result from destabilization of the occupied d-orbitals involved in metal-to-ligand charge-transfer transitions.

Aqueous Hydricity from Calculations of Reduction Potential and Acidity in Water.

Hydricity, or hydride donating ability, is a thermodynamic value that helps define the reactivity of transition metal hydrides. To avoid some of the challenges of experimental hydricity measurements in water, a computational method for the determination of aqueous hydricity values has been developed. With a thermochemical cycle involving deprotonation of the metal hydride (pK), 2e oxidation of the metal (E°), and 2e reduction of the proton, hydricity values are provided along with other valuable thermodynamic information.

Solvent-Dependent Thermochemistry of an Iridium/Ruthenium H Evolution Catalyst.

The hydricity of the heterobimetallic iridium/ruthenium catalyst [Cp*Ir(H)(μ-bpm)Ru(bpy)] (1, where Cp* = η-pentamethylcyclopentadienyl, bpm = 2,2'-bipyrimidine, and bpy = 2,2'-bipyridine) has been determined in both acetonitrile (63.1 kcal mol) and water (29.7 kcal mol).

Aqueous Hydricity of Late Metal Catalysts as a Continuum Tuned by Ligands and the Medium.

Aqueous hydride transfer is a fundamental step in emerging alternative energy transformations such as H2 evolution and CO2 reduction. "Hydricity," the hydride donor ability of a species, is a key metric for understanding transition metal hydride reactivity, but comprehensive studies of aqueous hydricity are scarce. An extensive and self-consistent aqueous hydricity scale is constructed for a family of Ru and Ir hydrides that are key intermediates in aqueous catalysis.

Isolation of saccharides in dairy and soy products by solid-phase extraction coupled with analysis by ligand-exchange chromatography.

The present study reports an improved method to quickly and reproducibly isolate the saccharides from a variety of dairy and soy products utilizing reversed-phase solid-phase extraction to quantitatively remove fats, fatty acids, and lipids followed by desalination and deproteinization by ion-exchange solid-phase extraction with no loss of saccharides during extraction. Analysis of the isolated saccharides was performed by ligand-exchange HPLC. The method presented requires no prolonged heating (thus protecting the saccharides from hydrolysis or isomerization), uses benign reagents, and realizes a significant time savings over existing methods.