Stoichiometric Routes Research Articles

Mechanism of Nitrous Oxide Activation in C(sp2)-O Bond Formation Reactions Catalyzed by Nickel Complexes.

Recent groundbreaking experimental reports demonstrated that Ni complexes bearing a bidentate- or tridentate-bipyridine-based ligand can be used to activate N2O for use as an O-transfer agent in C(sp2)-O bond formation reactions under mild experimental conditions. In this work, quantum chemical calculations are used to shed light on the mechanism through which such metal complexes catalytically activate nitrous oxide, providing new fundamental insights into the development of novel catalysts for N2O revalorization. As a case study, we consider the recent work by Cornella and co-workers (Nature, 2022, 604, 677) concerning the synthesis of phenols from aryl halides at room temperature, which requires the use of an external reducing agent. Our results suggest that the metal center remains in its Ni(II) oxidation state throughout the whole catalytic cycle, despite the presence of various redox steps in the mechanism and the Ni ability to maneuver between a number of oxidation states. This counterintuitive behavior is made possible by the ligand redox activity in the catalytic process, which involves accepting electrons from the reducing agent. Several possible pathways are systematically investigated, each associated with distinct activation modes, kinetics, and reaction outcomes. The governing factors in dictating the preferred path lie in the electronic nature of the ligand (strong vs weak field) and its geometric structure (specifically, the number of coordinating arms). These characteristics play a pivotal role in determining whether the process follows a catalytic or stoichiometric route and can be in principle modulated for the design of new metal complexes with tailored redox properties and reactivity.

A transient kinetic analysis of the evolution of a reducible metal oxide towards catalyzing nonoxidative alkanol dehydrogenation

Quantitative analyses of four sets of aerobic/anaerobic ethanol conversion transients point to the evolution of a native high-surface-area cerium oxide surface that effects the reduction half of the ethanol oxidation turnover to catalyzing, exclusively, nonoxidative ethanol dehydrogenation upon complete surface reduction. Aerobic–anaerobic switches at 498 K lead to new steady state dehydrogenation rates, rather than termination of catalytic acetaldehyde formation. Concurrent termination of oxygen imbalances (reflecting ceria reduction) and induction periods (reflecting active site creation) in anaerobic experiments point to ethanol dehydrogenation turnovers owing their provenance to surface reduction. Implausibly high vacancy densities obtained from analysis of oxygen imbalances when using acetaldehyde and CO2 formation rates, unlike those obtained when using water and CO2 formation rates, point to the catalytic origin of at least part of the acetaldehyde formed during both aerobic–anaerobic switches and anaerobic induction periods. Normalized water molar flow rates, used as a measure of the relative contributions of catalytic and stoichiometric routes to acetaldehyde formation, evince a transition from stoichiometric ethanol oxidation to catalytic ethanol dehydrogenation upon progressive surface reduction. High-temperature hydrogen pretreatments can be used to manipulate both the initial contribution of ethanol dehydrogenation to overall acetaldehyde formation as well as the fractional surface reduction that ethanol, rather than molecular hydrogen, effectuates. Alpha hydrogen-free titrants such as phenol, on the other hand, can be used to titrate sites contributing to catalytic alkanol dehydrogenation without altering the prevalence of stoichiometric routes responsible for site creation in the first place. The combination of transient experiments used herein capture, with clarity, the evolution in catalytic function of high-surface-area cerium oxide toward ethanol upon progressive reduction that originates from its stoichiometric conversion over a native, fully oxidized surface. Not unimportantly, the results also point to an avenue for the water-free synthesis of alkanals over reducible metal oxides.

Ce0.9Zr0.1O2 nanocatalyst: Influence of synthesis conditions in the reducibility and catalytic activity

This paper analyzes the influence of synthesis conditions on the reducibility and catalytic behavior of Ce0.9Zr0.1O2 mixed oxide synthesized by α-amino acid/metallic nitrate combustion processes, through stoichiometric and non-stoichiometric routes. We concluded that the α-amino acid selected and the α-amino acid/nitrate molar ratio strongly influence the reducibility and catalytic activity in the total combustion of methane. Thus, the Ce0.9Zr0.1O2 catalyst synthesized by the stoichiometric route with glycine showed the higher catalytic activity, which, in conjunction with the well-known ionic and electronic conductivities of ceria-based oxides under reducing conditions, positions this solid as an appropriate anode material for methane-fuelled solid oxide fuel cells.

Lanthanide-transition metal chalcogenido cluster materials.

[(THF)3Sm(SePh)2Zn(SePh)2]n decomposes to give a variety of products, including [(THF)8Sm4Se(SePh)8](2+)[Zn8Se(SePh)16](2-), an ionic cluster that can also be prepared in more than 60% yield by stoichiometric addition of Se to a mixture of Sm(SePh)3 and Zn(SePh)2. The isostructural Nd compound [(THF)8Nd4Se(SePh)8](2+)[Zn8Se(SePh)16](2-) was also prepared by the stoichiometric route to establish the viability of this cluster type with redox-inactive Ln. In addition, the salt [Yb(THF)6](3+)[Fe4Se4(SePh)4](3-) was isolated and structurally characterized. These ionic cluster materials illustrate the difficulties associated with doping Ln ions into covalent metal chalcogenido matrixes.

ChemInform Abstract: Palladium‐Assisted Formation of Carbon‐Carbon Bonds. Part 3. Reactions of Bis(η2‐(2,3,4‐trimethoxy‐6‐acetylphenyl‐C,O))bis(μ‐chloro) dipalladium(II) with Symmetrical and Unsymmetrical Internal Alkynes. A Stoichiometric Route to Highly Functionalized Spirocyclic and Benzofulvene Compounds. Isolation of a π‐Allylic Palladium Intermediate. X‐Ray Structure of 10‐(1‐Hydroxyethyl)‐6,7‐dimethoxy‐1,2, 3,4‐tetraphenylspiro(4.5)1,3,6,9‐decatetraen‐8‐one.

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Palladium-Assisted Formation of Carbon-Carbon Bonds. 3. Study of Reactions of Bis{.eta.2-(2,3,4-trimethoxy-6- acetylphenyl-C,O)}di(.mu.-chloro)dipalladium(II) with Symmetrical and Unsymmetrical Internal Alkynes. A Stoichiometric Route to Highly Functionalized Spirocyclic and Benzofulvene Compounds. Isolation of a .pi.-Allylic Palladium Intermediate. X-ray Structure of 10-(1-Hydroxyethyl)-6,7-dimethoxy-1,2,3,4-tetraphenylspiro[4.5]1,3,6,9-decatetraen-8-one

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPalladium-Assisted Formation of Carbon-Carbon Bonds. 3. Study of Reactions of Bis{.eta.2-(2,3,4-trimethoxy-6- acetylphenyl-C,O)}di(.mu.-chloro)dipalladium(II) with Symmetrical and Unsymmetrical Internal Alkynes. A Stoichiometric Route to Highly Functionalized Spirocyclic and Benzofulvene Compounds. Isolation of a .pi.-Allylic Palladium Intermediate. X-ray Structure of 10-(1-Hydroxyethyl)-6,7-dimethoxy-1,2,3,4-tetraphenylspiro[4.5]1,3,6,9-decatetraen-8-oneJose Vicente, Jose-Antonio Abad, Juan Gil-Rubio, and Peter G. JonesCite this: Organometallics 1995, 14, 6, 2677–2688Publication Date (Print):June 1, 1995Publication History Published online1 May 2002Published inissue 1 June 1995https://doi.org/10.1021/om00006a014RIGHTS & PERMISSIONSArticle Views236Altmetric-Citations58LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

The methanation reaction on a nickel catalyst: CO, H 2 competition for dissociated oxygen

The methanation reaction on a nickel catalyst has been investigated in a plug flow reactor using temperature programmed synthesis (TPS). It is clear from the results that methanation can proceed via two mechanistic pathways, firstly, classical methanation with water formation (CO + 3H 2 → CH 4 + H 2O) and secondly, with CO 2 formation (2CO + 2H 2 → CH 4 + CO 2). The proceeds exclusively with low CO levels in the feed while the latter predominates at high CO levels. It is inferred that the high propensity of the catalyst for CO 2 production may be the result of reactivity modification by the presence of atoms such as Ca which are present in the catalyst preparation. The data lend support to the dissociative mechanism for methanation and the two different stoichiometric routes outlined above result from CO/H 2 competition for adsorbed, dissociated oxygen atoms.