Characterization of Structural and Electronic Transitions During Reduction and Oxidation of Ru(acac)3 Flow Battery Electrolytes by using X‐ray Absorption Spectroscopy

Metal acetylacetonates possess several very attractive electrochemical properties; however, their cyclabilities fall short of targets for use in nonaqueous redox flow batteries. This paper describes structural and compositional changes during the reduction and oxidation of ruthenium(III) acetylacetonate [Ru(acac)3], a representative acetylacetonate. Voltammetry, bulk electrolysis, and in situ X‐ray absorption spectroscopy (XAS) results are complemented by those from density functional theory (DFT) calculations. The reduction of Ru(acac)3 in acetonitrile is highly reversible, producing a couple at −1.1 V versus Ag/Ag+. In situ XAS and DFT indicate the formation of [Ru(acac)3]− with Ru−O bonds lengthened relative to Ru(acac)3, nearly all of the charge localized on Ru, and no ligand shedding. The oxidation of Ru(acac)3 is quasireversible, with a couple at 0.7 V. The initial product is likely [Ru(acac)3]+; however, this species is short‐lived, converting to a product with a couple at −0.2 V, a structure that is nearly identical to that of Ru(acac)3 within 3 Å of Ru, and approximately 70 % of the charge extracted from Ru (balance from acetylacetone). This non‐innocence likely contributes to the instability of [Ru(acac)3]+. Taken together, the results suggest that the stabilities and cyclabilities of acetylacetonates are determined by the degree of charge transfer to/from the metal.Track changes: The structural and electronic changes of Ru(acac)3 during oxidation and reduction are characterized using bulk electrolysis and in situ X‐ray absorption spectroscopy. Reduction is found to be reversible with minimal structural changes, and the electrons being stored entirely on the ruthenium. Oxidation results in a rapid side reaction as a result of electrons extracted from the ligand.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134821/1/celc201600360-sup-0001-misc_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134821/2/celc201600360_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134821/3/celc201600360.pd

Reactivity of Hydrogen on and in Nanostructured Molybdenum Nitride: Crotonaldehyde Hydrogenation

Early-transition-metal nitrides, including γ-Mo₂N, are active and selective for a variety of reactions, including the hydrogenation of organics (e.g., hydrodeoxygenation), CO (e.g., Fischer–Tropsch synthesis), and CO₂. In addition to adsorbing hydrogen onto the surface, some of these materials can incorporate hydrogen into subsurface, interstitial sites. Research described in this paper examined, experimentally and computationally, the nature of hydrogen on and in γ-Mo₂N, with a particular focus on characterizing the interactions of these hydrogens with crotonaldehyde. Hydrogen was added to γ-Mo₂N via exposure to gaseous hydrogen at elevated temperatures, forming γ-Mo₂N‑H_<i>x</i>, where 0.061< <i>x</i> < 0.082. Temperature-programmed desorption (TPD) experiments indicate that γ-Mo₂N‑H_<i>x</i> has at least two distinct hydrogen binding sites and that these sites can be selectively populated. Inelastic neutron scattering and density functional theory calculations indicate the presence of surface nitrogen-bound (κ¹-NH_surf), surface Mo-bound (κ¹-MoH_surf), and interstitial Mo-bound (μ₆-Mo₆H_sub) hydrogens. Selectivities for the hydrogenation of crotonaldehyde, a model of species in biomass-derived liquids, correlated with the populations at these sites. Importantly, materials with high densities of interstitial, hydridic hydrogen were selective for CO hydrogenation (i.e., formation of crotyl alcohol). Collectively the results provide mechanistic insights regarding the desorption and reactivity of hydrogen on and in γ-Mo₂N. Hydrogen adsorption/desorption to γ-Mo₂N is heterolytic; in particular, H₂ adds across a Mo–N bond. Because the surface Mo–H site is energetically unfavorable in comparison to the interstitial site, hydrogen migrates into interstitial sites once the surface NH sites are saturated. Crotonaldehyde adsorption facilitates migration of this interstitial hydrogen back to the surface, forming surface Mo–H that is selective for hydrogenation of the CO bond. These insights will facilitate the design of γ-Mo₂N and other early-transition-metal nitrides for catalytic applications

Development of an Efficient Route to 2-Ethynylglycerol for the Synthesis of Islatravir

The unnatural, alkyne-containing nucleoside analog islatravir (MK-8591) is synthetically accessed through a biocatalytic cascade starting from 2-ethynylglycerol as a building block. Herein, we describe the development of an efficient synthesis of this building block including the initial route, route scouting and final process development. Key challenges that have been overcome are the development of an efficient and safe acetylenic nucleophile addition to an appropriate ketone, and the identification of a 2-ethynylpropane-1,2,3-triol derivative with favorable physical properties. An acid-catalyzed cracking of commercially available 1,3-dihydroxyacetone dimer and subsequent 1,2-addition of an acetylenic nucleophile has been discovered and optimized into the manufacturing proces