4 research outputs found
Characterization of Structural and Electronic Transitions During Reduction and Oxidation of Ru(acac)3 Flow Battery Electrolytes by using Xāray 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 inā
situ Xāray 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 ā1.1ā
V versus Ag/Ag+. Inā
situ XAS and DFT indicate the formation of [Ru(acac)3]ā with RuāO 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 0.7ā
V. The initial product is likely [Ru(acac)3]+; however, this species is shortālived, converting to a product with a couple at ā0.2ā
V, a structure that is nearly identical to that of Ru(acac)3 within 3ā
Ć
of Ru, and approximately 70ā% of the charge extracted from Ru (balance from acetylacetone). This nonāinnocence 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 inā
situ Xāray 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 Ī³-Mo<sub>2</sub>N, are active and selective
for a variety of reactions, including
the hydrogenation of organics (e.g., hydrodeoxygenation), CO (e.g.,
FischerāTropsch synthesis), and CO<sub>2</sub>. 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 Ī³-Mo<sub>2</sub>N, with a particular
focus on characterizing the interactions of these hydrogens with crotonaldehyde.
Hydrogen was added to Ī³-Mo<sub>2</sub>N via exposure to gaseous
hydrogen at elevated temperatures, forming Ī³-Mo<sub>2</sub>NāH<sub><i>x</i></sub>, where 0.061< <i>x</i> <
0.082. Temperature-programmed desorption (TPD) experiments indicate
that Ī³-Mo<sub>2</sub>NāH<sub><i>x</i></sub> 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 (Īŗ<sup>1</sup>-NH<sub>surf</sub>), surface Mo-bound
(Īŗ<sup>1</sup>-MoH<sub>surf</sub>), and interstitial Mo-bound
(Ī¼<sub>6</sub>-Mo<sub>6</sub>H<sub>sub</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 Cī»O hydrogenation (i.e., formation of crotyl
alcohol). Collectively the results provide mechanistic insights regarding
the desorption and reactivity of hydrogen on and in Ī³-Mo<sub>2</sub>N. Hydrogen adsorption/desorption to Ī³-Mo<sub>2</sub>N is heterolytic; in particular, H<sub>2</sub> adds across a MoāN
bond. Because the surface MoāH 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 MoāH that is selective for hydrogenation of
the Cī»O bond. These insights will facilitate the design of
Ī³-Mo<sub>2</sub>N 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