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[Fe(tpyPY2Me)]2+ ([Fe]2+) is a homogeneous electrocatalyst for converting CO2 into CO featuring low overpotentials of <100 mV, near-unity selectivity, and high activity with turnover frequencies faster than 100,000 s–1. To identify the origins of its exceptional performance and inform future catalyst design, we report a combined computational and experimental study that establishes two distinct mechanistic pathways for electrochemical CO2 reduction catalyzed by [Fe]2+ as a function of applied overpotential. Electrochemical data shows the formation of two catalytic regimes at low (hTOF/2 of 160 mV) and high (hTOF/2 of 590 mV) overpotential plateaus. We propose that at low overpotentials [Fe]2+ undergoes a two-electron reduction, two-proton transfer mechanism (electrochemical-electrochemical-chemical-chemical, EECC), where turnover occurs through the dicationic iron complex, [Fe]2+. Computational analysis supports the importance of the singlet ground state electronic structure for CO2 binding and that the rate-limiting step is the second protonation in this low-overpotential regime. When more negative potentials are applied, an additional electron transfer event occurs through either a stepwise or proton-coupled electron transfer (PCET) pathway, enabling catalytic turnover from the monocationic iron complex ([Fe]+) via an electrochemical-chemical-electrochemical-chemical (ECEC) mechanism. Comparison of experimental kinetic data obtained from variable controlled potential electrolysis (CPE) experiments with direct product detection with calculated rates obtained from the energetic span model support the PCET pathway as the most likely mechanism. Moreover, we build upon this mechanistic understanding to propose the design of an improved ligand framework that is predicted to stabilize the key transition states identified from our study and explore their electronic structures using an energy decomposition analysis. Taken together, this work highlights the value of synergistic computational/experimental approaches to decipher mechanisms of new electrocatalysts and direct the rational design of improved platforms

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTPalladium-Catalyzed Intermolecular Hydroamination of Vinylarenes Using ArylaminesMotoi Kawatsura and John F. HartwigView Author Information Department of Chemistry, Yale University P.O. Box 208107, New Haven, Connecticut 06520-8107 Cite this: J. Am. Chem. Soc. 2000, 122, 39, 9546–9547Publication Date (Web):September 15, 2000Publication History Received26 June 2000Published online15 September 2000Published inissue 1 October 2000https://pubs.acs.org/doi/10.1021/ja002284thttps://doi.org/10.1021/ja002284trapid-communicationACS PublicationsCopyright © 2000 American Chemical SocietyRequest reuse permissionsArticle Views9172Altmetric-Citations327LEARN 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 InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Addition reactions,Catalysts,Hydrocarbons,Organic reactions,Styrenes Get e-Alerts

Abstract We present six epochs of optical spectropolarimetry of the Type II supernova (SN) 2023ixf ranging from ∼2 to 15 days after the explosion. Polarimetry was obtained with the Kast double spectrograph on the Shane 3 m telescope at Lick Observatory, representing the earliest such observations ever captured for an SN. We observe a high continuum polarization p cont ≈ 1% on days +1.4 and +2.5 before dropping to 0.5% on day +3.5, persisting at that level up to day +14.5. Remarkably, this change coincides temporally with the disappearance of highly ionized “flash” features. The decrease of the continuum polarization is accompanied by a ∼70° rotation of the polarization position angle (PA) as seen across the continuum. The early evolution of the polarization may indicate different geometric configurations of the electron-scattering atmosphere as seen before and after the disappearance of the emission lines associated with highly ionized species (e.g., He ii , C iv , and N iii ), which are likely produced by elevated mass loss shortly prior to the SN explosion. We interpret the rapid change of polarization and PA from days +2.5 to +4.5 as the time when the SN ejecta emerge from the dense asymmetric circumstellar material (CSM). The temporal evolution of the continuum polarization and the PA is consistent with an aspherical SN explosion that exhibits a distinct geometry compared to the CSM. The rapid follow-up spectropolarimetry of SN 2023ixf during the shock ionization phase reveals an exceptionally asymmetric mass-loss process leading up to the explosion.

Computational methods were utilized to study the formation of a dimeric neopentylpalladium(II) amido complex (D). The dimeric core of D contains asymmetric bridging of the anilide groups. Electron density analyses indicate that each palladium center of D forms a dative bond to the nitrogen trans to the coordinated phosphine, while the bond to the nitrogen cis to the phosphine lies closer to the covalent regime. Analysis of the structure of D was corroborated by study of the frontier orbitals and the energetics of dimerization. D was likely generated by the monomers with cis P,N configuration rather than those with trans P,N configuration, which is an important side reaction that inhibits the desired C–N bond coupling. Calculations further revealed the critical importance of dispersion interactions upon dimerization and suggested one possible dimeric isomer Q.

This paper is a complete report on both the experimental and theoretical aspects of the recently discovered self-phase modulation in laser-breakdown plasmas. Mainly responsible for these effects is the sudden index change which accompanies the ionization of the gaseous medium. Two theoretical models are introduced for the phase and amplitude modulation induced by the plasma. These effects are applied to the problem of short-optical-pulse generation, with emphasis on the prospects for producing a pulse consisting of only a few optical cycles. The techniques described here have the unique advantage that the generation mechanism is linear, resulting in particularly clean, reproducible and predictable optical transients. Methods are suggested for raising the plasma nucleation intensity by further cleaning up the gas. It is shown that index dispersion of the optical components may place a lower limit on pulse duration.