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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

In crystallo organometallic chemistry

X-ray crystallography is an invaluable tool in design and development of organometallic catalysis, but application typically requires species to display sufficiently high solution concentrations and lifetimes for single crystalline samples to be obtained. In crystallo organometallic chemistry relies on chemical reactions that proceed within the single-crystal environment to access crystalline samples of reactive organometallic fragments that are unavailable by alternate means. Furthermore, this highlight describes approaches to in crystallo organometallic chemistry including (a) solid–gas reactions between transition metal complexes in molecular crystals and diffusing small molecules, (b) reactions of organometallic complexes within the extended lattices of metal–organic frameworks (MOFs), and (c) intracrystalline photochemical transformations to generate reactive organometallic fragments. Application of these methods has enabled characterization of catalytically important transient species, including σ-alkane adducts of transition metals, metal alkyl intermediates implicated in metal-catalyzed carbonylations, and reactive M–L multiply bonded species involved in C–H functionalization chemistry. Opportunities and challenges for in crystallo organometallic chemistry are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Organometallic complexes as preferred precursors to form molecular Ir(pyalk) coordination complexes for catalysis of oxygen evolution

Our previously reported ‘blue solution’ oxygen-evolution catalyst consists of an isomeric mixture of coordination complexes containing the (pyalk)Ir IV –O–Ir IV (pyalk) core unit and is thus entirely molecular but only when formed from organometallic precursors such as Cp*Ir(pyalk)Cl or Ir(pyalk)(CO) 2 (pyalk = (2-pyridyl)-2-propanolate). We now show that attempts to form it from such obvious coordination precursors as Na[Ir(pyalk)Cl 4 ] or Na[IrCl 2 (pyalk)(O 2 CPh) 2 ], under a variety of conditions, always fail in our hands, leading to a mixture of molecular ‘blue solution’ species and IrO x nanoparticles, rather than the purely homogeneous catalyst formed from organometallic precursors. The loss of the pyalk ligand during the oxidative activation is associated with the nanoparticle generation. External chelating ligands also failed to stop the nanoparticle formation. This work implies the paradoxical conclusion that organometallic complexes are effective as catalyst precursors, even when coordination complexes are the catalytically active species, since the inner-sphere organometallic ligands, although ultimately lost or degraded, may nevertheless have a stabilizing effect sufficient to suppress undesirable nanoparticle production pathways in the activation of the catalyst precursor. Finally, a key aspect of the present study is that organometallic complexes in general may be useful catalyst precursors even if the organometallic ligands are lost in the activation process.

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

Effects of surface acidity on the structure of organometallics supported on oxide surfaces

Well-defined organometallics supported on high surface area oxides are promising heterogeneous catalysts. An important design factor in these materials is how the metal interacts with the functionalities on an oxide support, commonly anionic X-type ligands derived from the reaction of an organometallic M–R with an –OH site on the oxide. The metal can either form a covalent M–O bond or form an electrostatic M + $\cdots$ – O ion-pair, which impacts how well-defined organometallics will interact with substrates in catalytic reactions. However, a less common reaction pathway involves the reaction of a Lewis site on the oxide with the organometallic, resulting in abstraction to form an ion-pair, which is relevant to industrial olefin polymerization catalysts. This Feature Article views the spectrum of reactivity between an organometallic and an oxide through the prism of Brønsted and/or Lewis acidity of surface sites and draws analogies to the molecular frame where Lewis and Brønsted acids are known to form reactive ion-pairs. Applications of the well-defined sites developed in this article are also discussed.

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

Nontraditional Catalyst Supports in Surface Organometallic Chemistry

The field of Surface Organometallic Chemistry (SOMC) aims to blend the positive attributes of homogeneous and heterogeneous catalysis. Significant insight into heterogeneous systems has been gained over the years through the synthesis, characterization, and application of well-defined surface organometallic catalysts, predominantly supported on silica and alumina. Considerable research efforts have focused on the application of homogeneous methods to the synthesis and characterization of these systems. Homogeneous catalysis has thrived on its ability to electronically and sterically tune ligands to yield desired reactivity and selectivity. Efforts in SOMC, however, have only recently turned to harnessing the stereoelectronic diversity of potential inorganic support materials beyond silica and alumina in order to exert similar control on the reactivity of the organometallic active site. The support material is intrinsically linked to electronic structure and reactivity of heterogeneous organometallic systems in the same way that ligands exert control over homogeneous catalyst systems. The ability to tune the reactivity of heterogeneous catalysts by changing the support is of great value, and it is anticipated that this will represent an area of significant growth in the field. In this Perspective, the use and future of nontraditional catalyst supports, such as sulfated metal oxides, modified silicas, and redox active supports are discussed.

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

C-Term magnetic circular dichroism (MCD) spectroscopy in paramagnetic transition metal and f-element organometallic chemistry

Magnetic circular dichroism (MCD) spectroscopy is a powerful experiment used to probe the electronic structure and bonding in paramagnetic metal-based complexes. While C-term MCD spectroscopy has been utilized in many areas of chemistry, it has been underutilized in studying paramagnetic organometallic transition metal and f-element complexes. From the analysis of isolated organometallic complexes to the study of in situ generated species, MCD can provide information regarding ligand interactions, oxidation and spin state, and geometry and coordination environment of paramagnetic species. The pratical aspects of this technique, such as air-free sample preparation and cryogenic experimental temperatures, allow for the study of highly unstable species, something that is often difficult with other spectroscopic techniques. This perspective highlights MCD studies of both transition metal and f-element organometallic complexes, including in situ generated reactive intermediates, to demonstrate the utility of this technique in probing electronic structure, bonding and mechanism in paramagnetic organometallic chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Tailoring electrophotonic capabilities of atomically thin GeS through controlled organometallic intercalation

The unique structure of van der Waals materials facilitates a robust mechanism for precise control of physical properties. In this study, we present a comprehensive analysis based on the intercalation of organometallics to modulate the optoelectronic behavior of two-dimensional germanium sulfide (GeS). Advanced computational exploration reveals significant and tunable features in the intercalated material. Additionally, the weak chemical interactions between organometallics and GeS support the electric-field-mediated drift and charge–discharge processes in intercalants. Controlling the concentration of organometallics in this manner enables the dynamic emergence of novel characteristics post-intercalation. These include flatbands near the Fermi level, significant enhancement of carrier mobility, and a magnetic ground state that is atypical for pristine GeS. Our findings demonstrate that organometallic intercalation offers a powerful strategy for tailoring the optoelectronic and magnetic characteristics of GeS, paving the way for harnessing emerging features for applications in next-generation devices.

Physics↗
DOE OSTI2024

Room‐Temperature Formate Ester Transfer Hydrogenation Enables an Electrochemical/Thermal Organometallic Cascade for Methanol Synthesis from CO 2

Abstract The reduction of CO 2 to synthetic fuels is a valuable strategy for energy storage. However, the formation of energy‐dense liquid fuels such as methanol remains rare, particularly under low‐temperature and low‐pressure conditions that can be coupled to renewable electricity sources via electrochemistry. Here, a multicatalyst system pairing an electrocatalyst with a thermal organometallic catalyst is introduced, which enables the reduction of CO 2 to methanol at ambient temperature and pressure. The cascade methanol synthesis proceeds via CO 2 reduction to formate by electrocatalyst [Cp*Ir(bpy)Cl] + (Cp*=pentamethylcyclopentadienyl, bpy=2,2′‐bipyridine), Fischer esterification of formate to isopropyl formate catalyzed by trifluoromethanesulfonic acid (HOTf), and thermal transfer hydrogenation of isopropyl formate to methanol facilitated by the organometallic catalyst (H‐PNP)Ir(H) 3 (H‐PNP=HN(C 2 H 4 P i Pr 2 ) 2 ). The isopropanol solvent plays several crucial roles: activating formate ion as isopropyl formate, donating hydrogen for the reduction of formate ester to methanol via transfer hydrogenation, and lowering the barrier for transfer hydrogenation through hydrogen bonding interactions. In addition to reporting a method for room‐temperature reduction of challenging ester substrates, this work provides a prototype for pairing electrochemical and thermal organometallic reactions that will guide the design and development of multicatalyst cascades.

Fernández, Sergio [Department of Chemistry Univers↗
DOE OSTI2024

Room-Temperature Formate Ester Transfer Hydrogenation Enables an Electrochemical/Thermal Organometallic Cascade for Methanol Synthesis from CO 2

The reduction of CO 2 to synthetic fuels is a valuable strategy for energy storage. However, the formation of energy-dense liquid fuels such as methanol remains rare, particularly under low-temperature and low-pressure conditions that can be coupled to renewable electricity sources via electrochemistry. Here, in this study, a multicatalyst system pairing an electrocatalyst with a thermal organometallic catalyst is introduced, which enables the reduction of CO 2 to methanol at ambient temperature and pressure. The cascade methanol synthesis proceeds via CO 2 reduction to formate by electrocatalyst [Cp*Ir(bpy)Cl] + (Cp*=pentamethylcyclopentadienyl, bpy=2,2'-bipyridine), Fischer esterification of formate to isopropyl formate catalyzed by trifluoromethanesulfonic acid (HOTf), and thermal transfer hydrogenation of isopropyl formate to methanol facilitated by the organometallic catalyst (H-PNP)Ir(H) 3 (H-PNP=HN(C 2 H 4 P i Pr 2 ) 2 ). The isopropanol solvent plays several crucial roles: activating formate ion as isopropyl formate, donating hydrogen for the reduction of formate ester to methanol via transfer hydrogenation, and lowering the barrier for transfer hydrogenation through hydrogen bonding interactions. In addition to reporting a method for room-temperature reduction of challenging ester substrates, this work provides a prototype for pairing electrochemical and thermal organometallic reactions that will guide the design and development of multicatalyst cascades.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Model for the Vaporization of Mixed Organometallic Compounds in the Metalorganic Chemical Vapor Deposition of High Temperature Superconducting Films

A model of the vaporization and mass transport of mixed organometallics from a single source for thin film metalorganic chemical vapor deposition is presented. A stoichiometric gas phase can be obtained from a mixture of the organometallics in the desired mole ratios, in spite of differences in the volatilities of the individual compounds. Proper film composition and growth rates are obtained by controlling the velocity of a carriage containing the organometallics through the heating zone of a vaporizer.

Meng, Guangyao↗
DOE OSTI2024

Formation of a Decanuclear Organometallic Dysprosium Complex via a Radical–Radical Cross–Coupling Reaction

Over the years, polynuclear cyclic or torus complexes have attracted increasing interest due to their unique metal topologies and properties. However, the isolation of polynuclear cyclic organometallic complexes is extremely challenging due to their inherent reactivity, which stems from the labile and reactive metal-carbon bonds. In this study, the pyrazine ligand undergoes a radical-radical cross-coupling reaction leading to the formation of a decanuclear [(Cp*) 20 Dy 10 (L1) 10 ] ⋅ 12(C 7 H 8 ) ( 1 ; where L1 = anion of 2-prop-2-enyl-2 H -pyrazine; Cp* = pentamethylcyclopentadienyl) complex, where all Dy III metal centres are bridged by the anionic L1 ligand. Amongst the family of polynuclear Ln organometallic complexes bearing Cp R 2 Ln x units (Cp R = substituted cyclopentadienyl), 1 features the highest nuclearity obtained to date. In-depth computational studies were conducted to elucidate the proposed reaction mechanism and formation of L1, while probing of the magnetic properties of 1 , revealed slow magnetic relaxation upon application of a static dc field.

cross-coupling↗
DOE OSTI2023

Oxidative Grafting for Catalyst Synthesis in Surface Organometallic Chemistry

The development of new methods of catalyst synthesis with the potential to generate active site structures orthogonal to those accessible by traditional protocols is of great importance for discovering new materials for addressing challenges in the evolving energy and chemical economy. Here, in this work, the generality of oxidative grafting of organometallic and well-defined molecular metal precursors onto redox-active surfaces such as manganese dioxide (MnO 2 ) and lithium manganese oxide (LiMn 2 O 4 ) is investigated. Nine molecular metal precursors are explored, spanning groups 4–11 and each of the three periods of the transition metal series. The byproducts of the oxidative grafting reaction, a mixture of protodemetalation and ligand homocoupling for several organometallic precursors, was found to provide insights into the mechanism of the grafting reaction, suggesting oxidation of both the metal d-orbitals, as well as the metal–carbon σ-bonds, resulting in ejection of the ligand radical fragment. Analysis of the supported structures and oxidation state by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) suggests that several of the chemisorbed metal ions are intercalated into interstitial vacancies of the surface structure while other complexes form intact molecular fragments on the surface. Proof of concept for the use of this metalation protocol to generate diverse, metal-dependent catalytic performance is demonstrated by the application of these materials in the conversion of cyclohexane to K/A oil (cyclohexanol and cyclohexanone) with tert-butyl hydroperoxide, as well as in the low-temperature (T ≤ 50 °C) oxidation of carbon monoxide to carbon dioxide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Propane Dehydrogenation Catalyzed by Supported Group IV (Ti, Zr, Hf) Organometallics on Silicon Nitride

Mesoporous silicon nitride (Si 3 N 4 ) enables access to chemisorbed group IV organometallics catalysts active for propane dehydrogenation (PDH) compared to the organometallic analogues on mesoporous silica under the same reaction conditions. The series of Si 3 N 4 -supported materials are active catalysts, (Zr > Hf > Ti k f = 290, 232, and 162 mol mol Metal -1 h -1 at 450 °C with 2% C 3 H 8 in Ar, respectively) with selectivity above 95%, demonstrating additional examples of Ti and Hf systems for PDH. However, the underlying mechanism of the improved performance relative to oxide supported homologues is not well-understood. Characterization of thermally treated samples (DRIFTS, XAS and SSNMR) and computational modeling of this catalyst series was utilized to differentiate between potential amido - (C-H activation along the M-N bond) and imido - (C-H activation along the M=N bond) mechanisms. Due to remaining mechanistic ambiguity, a Ga analogue was synthesized and evaluated for PDH activity as an indirect probe to experimentally differentiate pathways. An inversion of the oxide/nitride performance trend is observed for the Ga congener which does not form a Ga=N bond, most consistent with different mechanisms dictating the performance of the group IV/Si 3 N 4 catalysts vs Ga/Si 3 N 4 .

heterolytic cleavage↗
DOE OSTI2022

Broken-Symmetry Density Functional Theory Analysis of the Ω Intermediate in Radical S -Adenosyl- l -methionine Enzymes: Evidence for a Near-Attack Conformer over an Organometallic Species

Radical S-adenosyl-L-methionine (SAM) enzymes are found in all domains of life and catalyze a wide range of biochemical reactions. Recently, an organometallic intermediate, Ω, has been experimentally implicated in the 5'-deoxyadenosyl radical generation mechanism of the radical SAM superfamily. In this work, we employ broken-symmetry density functional theory to evaluate several structural models of Ω. The results show that the calculated hyperfine coupling constants (HFCCs) for the proposed organometallic structure of Ω are inconsistent with the experiment. In contrast, a near-attack conformer of SAM bound to the catalytic [4Fe–4S] cluster, in which the distance between the unique iron and SAM sulfur is ~3 Å, yields HFCCs that are all within 1 MHz of the experimental values. Furthermore, these results clarify the structure of the ubiquitous Ω intermediate and suggest a paradigm shift reversal regarding the mechanism of SAM cleavage by members of the radical SAM superfamily.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Computational Data Associated with the publication: Formation of a Decanuclear Organometallic Dysprosium Complex via a Radical–Radical Cross–Coupling Reaction

Over the years, polynuclear cyclic or torus complexes have attracted increasing interest due to their unique metal topologies and properties. However, the isolation of polynuclear cyclic organometallic complexes is extremely challenging due to their inherent reactivity, which stems from the labile and reactive metal‐carbon bonds. In this study, the pyrazine ligand undergoes a radical‐radical cross‐coupling reaction leading to the formation of a decanuclear [(Cp*)20Dy10(L1)10] ⋅ 12(C7H8) (1; where L1 = anion of 2‐prop‐2‐enyl‐2H‐pyrazine; Cp* = pentamethylcyclopentadienyl) complex, where all DyIII metal centres are bridged by the anionic L1 ligand. Amongst the family of polynuclear Ln organometallic complexes bearing CpR2Lnx units (CpR = substituted cyclopentadienyl), 1 features the highest nuclearity obtained to date. In‐depth computational studies were conducted to elucidate the proposed reaction mechanism and formation of L1, while probing of the magnetic properties of 1, revealed slow magnetic relaxation upon application of a static dc field.

Bajaj, Neha↗
NASA NTRS1977

Effectiveness of various organometallics as antiwear additives in mineral oil

Sliding friction experiments were conducted with 1045 steel contacting 302 stainless steel and lubricated with various organometallics in mineral oil. Auger emission spectroscopy was used to determine the element present in the wear contact zone. The results indicate that there are organometallics which are as effective an antiwear additives as the commonly used zinc dialkyl dithiophosphate. These include dimethyl cadmium, triphenyl lead thiomethoxide, and triphenyl tin chloride. The additives were examined in concentrations to 1 weight percent. With dimethyl cadmium at concentrations of 0.5 weight percent and above, cadmium was detected in the contact zone. Coincident with the detection of cadmium, a marked decrease in the friction coefficient was observed. All additives examined reduced friction, but only the aforementioned reduced wear to a level comparable to that observed with zinc dialkyl dithiophosphate.

Buckley, D. H.↗
NASA NTRS1987

Organometallic catalysts for primary phosphoric acid fuel cells

A continuing effort by the U.S. Department of Energy to improve the competitiveness of the phosphoric acid fuel cell by improving cell performance and/or reducing cell cost is discussed. Cathode improvement, both in performance and cost, available through the use of a class of organometallic cathode catalysts, the tetraazaannulenes (TAAs), was investigated. A new mixed catalyst was identified which provides improved cathode performance without the need for the use of a noble metal. This mixed catalyst was tested under load for 1000 hr. in full cell at 160 to 200 C in phosphoric acid H3PO4, and was shown to provide stable performance. The mixed catalyst contains an organometallic to catalyze electroreduction of oxygen to hydrogen peroxide and a metal to catalyze further electroreduction of the hydrogen peroxide to water. Cathodes containing an exemplar mixed catalyst (e.g., Co bisphenyl TAA/Mn) operate at approximately 650 mV vs DHE in 160 C, 85% H3PO4 with oxygen as reactant. In developing this mixed catalyst, a broad spectrum of TAAs were prepared, tested in half-cell and in a rotating ring-disk electrode system. TAAs found to facilitate the production of hydrogen peroxide in electroreduction were shown to be preferred TAAs for use in the mixed catalyst. Manganese (Mn) was identified as a preferred metal because it is capable of catalyzing hydrogen peroxide electroreduction, is lower in cost and is of less strategic importance than platinum, the cathode catalyst normally used in the fuel cell.

Walsh, Fraser↗
DOE OSTI2026

Rational design of heterogeneous single-site catalysts via surface organometallic chemistry

Single-site heterogeneous catalysts offer an attractive route to unite the molecular precision of homogeneous catalysis with the durability and practical advantages of solids. Surface organometallic chemistry (SOMC) provides a particularly powerful strategy for this purpose by grafting molecular precursors onto tailored surfaces and converting support functionalities into ligand environments for isolated metal centers. As a result, SOMC brings the language and logic of coordination chemistry to heterogeneous catalysis, where the support becomes an integral part of the active site coordination sphere. This Review surveys recent progress in the rational design of SOMC-derived single-site catalysts, with emphasis on synthetic routes, post synthetic transformations, and the deliberate tuning of catalytic behavior through metal-support interactions. Discussions are made on how support identity, hydroxyl topology, acidity, and redox activity shape the geometry, electronic structure, and oxidation state of supported metal sites, as well as how these factors determine activity, selectivity, and stability. We also examine a central limitation of these systems: despite their molecularly informed design, supported single sites often exist as structurally distributed ensembles rather than uniform species, particularly on amorphous supports. This site heterogeneity, along with catalyst dynamics under operating conditions, remains a major barrier to definitive structure-activity relationships. Therefore, emerging approaches that combine advanced characterization, first-principles modeling, ensemble kinetics, and machine learning to resolve active-site structure and guide catalyst development are highlighted. Together, these advances position SOMC as a versatile coordination chemistry framework for the predictive design of heterogeneous catalysts with well-defined molecularly tailored active sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗