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Ess, Daniel H.

Publications and source records attributed to Ess, Daniel H..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Coordination-induced O-H/N-H bond weakening by a redox non-innocent, aluminum-containing radical

Abstract Several renewable energy schemes aim to use the chemical bonds in abundant molecules like water and ammonia as energy reservoirs. Because the O-H and N-H bonds are quite strong (>100 kcal/mol), it is necessary to identify substances that dramatically weaken these bonds to facilitate proton-coupled electron transfer processes required for energy conversion. Usually this is accomplished through coordination-induced bond weakening by redox-active metals. However, coordination-induced bond weakening is difficult with earth’s most abundant metal, aluminum, because of its redox inertness under mild conditions. Here, we report a system that uses aluminum with a redox non-innocent ligand to achieve significant levels of coordination-induced bond weakening of O-H and N-H bonds. The multisite proton-coupled electron transfer manifold described here points to redox non-innocent ligands as a design element to open coordination-induced bond weakening chemistry to more elements in the periodic table.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

ReaLigands: A Ligand Library Cultivated from Experiment and Intended for Molecular Computational Catalyst Design

Computational catalyst design requires identification of a metal and ligand that together result in the desired reaction reactivity and/or selectivity. A major impediment to translating computational designs to experiments is evaluating ligands that are likely to be synthesized. Here we provide a solution to this impediment with our ReaLigands library that contains >30,000 monodentate, bidentate (didentate), tridentate, and larger ligands cultivated by dismantling experimentally reported crystal structures. Individual ligands from mononuclear crystal structures were identified using a modified depth-first search algorithm and charge was assigned using a machine learning model based on quantum-chemical calculated features. In the library ligands are sorted based on direct ligand-to-metal atomic connections and on denticity. Representative principal component analysis (PCA) and uniform manifold approximation and projection (UMAP) analyses were used to analyze several tridentate ligand categories, which revealed both the diversity of ligands and connections between ligand categories. Furthermore, we also demonstrated the utility of this library by implementing it with our building and optimization tools, which resulted in the very rapid generation of barriers for 750 bidentate ligands for Rh-hydride ethylene migratory insertion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Reactivity and Mechanisms of Methane, Ethane, and Benzene C–H Amination with an Iodine(III) Bistriflimide Complex

The iodine(III) bistriflamide complex (C 6 F 5 ) III I(NTf 2 ) 2 in HNTf 2 (bistriflimide acid; (CF 3 SO 2 ) 2 NH) selectively aminates methane and ethane. At a 100 °C reaction with methane after 3 h, it resulted in the exclusive formation of MeNTf 2 with a yield of approximately 40%. For ethane, at 100 °C in 2 h, a > 80% yield was found for a combination of monofunctionalized and difunctionalized amination products. In contrast to alkanes giving functionalized products, the reaction of (C 6 F 5 ) III I(NTf 2 ) 2 with benzene resulted in being stalled at (C 6 F 5 )I III (Ph)(NTf 2 ) with a <5% conversion to PhNTf 2 even at 120 °C. PWPB95-D3(BJ) density functional theory calculations indicate that C–H activation is the lowest energy pathway to break the hydrocarbon bonds and is lower in energy than radical, electron-transfer, proton-coupled electron-transfer, or hydride substitution pathways. For methane, from the (C 6 F 5 )I III (CH 3 )(NTf 2 ) intermediate, there is a one-step amine functionalization mechanism that avoids a carbocation intermediate. For ethane, from the (C 6 F 5 )I III (Et)(NTf 2 ) intermediate, dynamics simulations suggest the possibility of a competitive two-step functionalization pathway that involves a short-lived carbocation intermediate. As a result, a reaction coordinate strain analysis provides a straightforward model for understanding the relative reactivity rates for alkyl versus aryl functionalization.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Machine Learning Analysis of Direct Dynamics Trajectory Outcomes for Thermal Deazetization of 2,3-Diazabicyclo[2.2.1]hept-2-ene

Experimentally, the thermal gas-phase deazetization of 2,3-diazabicyclo[2.2.1]hept-2-ene (1) results in the loss of N2 and the formation of bicyclo products 3 (exo) and 4 (endo) in a nonstatistical ratio, with preference for the exo product. Here, we report unrestricted M06-2X quasiclassical trajectories initialized from the concerted N2 ejection transition state that were able to replicate the experimental preference to form 3. We found that the 3:4 ratio results from the relative amounts of very fast (ballistic) exotype trajectories versus trajectories that lead to the 1,3-diradical intermediate 2. These quasiclassical trajectories provided a set of transition-state vibrational, velocity, momenta, and geometric features for the machine learning analysis. Additionally, a selection of popular supervised classification algorithms (e.g., random forest) provided poor prediction of trajectory outcomes based on only transition-state vibrational quanta and energy features. However, these machine learning models provided more accurate predictions using atomic velocities and atomic positions, attaining ~70% accuracy using initial conditions and between 85 and 95% accuracy at later reaction time steps. This increased accuracy allowed the feature importance analysis to reveal that, at the later-time analysis, the methylene bridge out-of-plane bending is correlated with trajectory outcomes for the formation of either the exo product or toward the diradical intermediate. Possible reasons for the struggle of machine learning algorithms to classify trajectories based on transition-state features is the heavily overlapping feature values, the finite but very large possible vibrational mode combinations, and the possibility of chaos as trajectories propagate. We examined this chaos by comparing a set of nearly identical trajectories that differed by only a very small scaling of the kinetic energies resulting from the transition-state reaction coordinate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Supermetal: SbF 5 -mediated methane oxidation occurs by C–H activation and isobutane oxidation occurs by hydride transfer

Sb V F 5 is generally assumed to oxidize methane through a methanium-to-methyl cation mechanism. Yet, experimentally no H 2 is observed, and the mechanism of methane oxidation has remained unsolved for several decades. To solve this problem, density functional theory calculations with multiple chemical models (mononuclear and dinuclear) were used to examine methane oxidation by Sb V F 5 in the presence of CO leading to the methyl acylium cation ([CH 3 CO] + ). While there is a low barrier for methane protonation by [Sb V F 6 ] - [H] + (the combination of Sb V F 5 and HF) to give the [Sb V F 5 ] - [CH 5 ] + ion pair, H 2 dissociation is a relatively high energy process, even with CO assistance, and so this protonation pathway is reversible. While Sb-mediated hydride transfer has a reasonable barrier, the C–H activation/σ-bond metathesis mechanism with the formation of an Sb V –Me intermediate is lower in energy. This pathway leads to the acylium cation by functionalization of the Sb V –Me intermediate with CO and is consistent with no observation of H 2 . Because this C–H activation/metal-alkyl functionalization pathway is higher in energy than methane protonation, it is also consistent with the experimentally observed methane hydrogen-to-deuterium exchange. This is the first time that evidence is presented demonstrating that Sb V F 5 acts beyond a Bronsted superacid and involves C–H activation with an organometallic intermediate. In contrast to methane, due to the much lower carbocation hydride affinity, isobutane significantly favors hydride transfer to give the tert -butyl carbocation with concomitant Sb V to Sb III reduction. In this mechanism, the resulting highly acidic Sb V –H intermediate provides a route to H 2 through protonation of isobutane, which is constant with experiments and resolves the longstanding enigma of different experimental results for methane versus isobutane.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Selective C−H Functionalization of Methane and Ethane by a Molecular Sb V Complex

Abstract Owing to the strong nonpolar bonds involved, selective C−H functionalization of methane and ethane to esters remains a challenge for molecular homogeneous chemistry. We report that the computationally predicted main‐group p ‐block Sb V (TFA) 5 complex selectively functionalizes the C−H bonds of methane and ethane to the corresponding mono and/or diol trifluoroacetate esters at 110–180 °C with yields for ethane of up to 60 % with over 90 % selectivity. Experimental and computational studies support a unique mechanism that involves Sb V ‐mediated C−H activation followed by functionalization of a Sb V ‐alkyl intermediate.

Koppaka, Anjaneyulu↗
DOE OSTI2018

Selective C-H Functionalization of Methane and Ethane by a Molecular Sb V Complex

Owing to the strong nonpolar bonds involved, selective C-H functionalization of methane and ethane to esters remains a challenge for molecular homogeneous chemistry. Here, we report that the computationally predicted main-group p-block Sb V (TFA) 5 complex selectively functionalizes the C-H bonds of methane and ethane to the corresponding mono and/or diol trifluoroacetate esters at 110-180 °C with yields for ethane of up to 60 % with over 90 % selectivity. Additionally, experimental and computational studies support a unique mechanism that involves Sb V -mediated C-H activation followed by functionalization of a Sb V -alkyl intermediate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Why Two Metals Are Better Than One for Heterodinuclear Cobalt–Zirconium-Catalyzed Kumada Coupling

Heterodinuclear transition metal complexes with a direct metal–metal interaction offer the potential of unique reactivity compared with mononuclear catalysts. Heterodinuclear Co–Zr complexes with phosphinoamide ligands bridging Co and Zr metal centers are effective precatalysts for Kumada C–C bond coupling reactions between alkyl halides and alkyl Grignards. On the other hand, the analogous mononuclear Co tris(phosphinoamine) complex without Zr provides very inefficient catalysis. Here we describe density functional theory calculations that reveal the mechanistic and reactivity impact of the Co–Zr metal–metal interaction and phosphinoamide ligands on alkyl halide–alkyl Grignard Kumada coupling catalysis. The Co–Zr interaction enables two-electron reduction of the precatalyst to form an active catalyst, which then allows a low-energy electron-transfer alkyl halide oxidative addition mechanism. The Co–Zr interaction and the phosphinoamide ligands bridging the metal centers provide a dialkyl intermediate with a low-energy C–C bond forming reductive elimination route through a phosphine dissociation pathway, which is not viable for an analogous mononuclear Co complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Electrophilic Impact of High-Oxidation State Main-Group Metal and Ligands on Alkane C–H Activation and Functionalization Reactions

High-oxidation state main-group metal complexes are potential alternatives to transition metals for electrophilic alkane C–H functionalization reactions. Yet, there is little known about how selection of the p-block, main-group metal and ligand impact alkane C–H activation and functionalization thermodynamics and reactivity. This work reports density functional theory calculations used to determine qualitative and quantitative features of C–H activation and metal-methyl functionalization energy landscapes for reaction between high-oxidation state d 10 s 0 In III , Tl III , Sn IV , and Pb IV carboxylate complexes with methane. While the main-group metal influences the C–H activation barrier height in a periodic manner, the carboxylate ligand has a much larger quantitative impact on C–H activation with stabilized carboxylate anions inducing the lowest barriers. For metal-methyl reductive functionalization reactions, the main-group metal dramatically influences the barrier heights, which are correlated to reaction thermodynamics and bond heterolysis energies as a model for two-electron reduction energies. Generally, this work begins to outline which main-group metals and carboxylate ligands could be useful for alkane functionalization systems that utilize electrophilic C–H activation and metal-alkyl functionalization reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Mechanisms and Reactivity of Tl(III) Main-Group-Metal–Alkyl Functionalization in Water

Metal-mediated C–H activation reactions generate metal–alkyl intermediates that can be converted into carbon–oxygen bonds through functionalization reactions. Although the mechanisms and reactivity of C–H activation reactions have been well studied for transition-metal complexes, much less is known about functionalization reactions, especially for main-group-metal–alkyl complexes. Here we report density functional theory calculations on the reaction thermodynamics and kinetic pathways for main-group, p-block-metal Tl III –methyl functionalization reactions in water using a combination of continuum and explicit/continuum solvent models. Particularly, we examined the oxygen functionalization of (OAc)Tl III (CH 3 ) 2 and (OAc) 2 Tl III (CH 3 ) in water where in both cases functionalization gives methyl acetate and methanol. Our calculations suggest that (OAc)Tl III (CH 3 ) 2 is thermodynamically and kinetically stable against bond homolysis, heterolysis, protonolysis, and all reductive functionalization pathways. Functionalization is only possible after methyl anion group transfer to Tl III (OAc) 3 to give (OAc) 2 Tl III (CH 3 ). Our calculations indicate that this monomethyl structure is functionalized by acetate dissociation to give a Tl monocation and then a one-step nucleophilic functionalization where water and acetate have competitive transition states.

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