Direct Insertion Mechanism Research Articles

Fluoride shuttle batteries: On the performance of the BiF3 electrode in organic liquid electrolytes containing a mixture of lithium bis(oxalato)borate and triphenylboroxin

In a typical organic liquid electrolyte-based fluoride shuttle battery (FSB), a high concentration of a boron-based anion acceptor (AA) capable of binding specific anions is required to provide a sufficient amount of dissolved fluoride salt. In this study, and a mixture of lithium bis(oxalato)borate (LiBOB) and an AA, triphenylboroxin (TPhBX), was used as an organic liquid electrolyte. The tetraglyme (G4)-based electrolyte system (LiBOB0.25/TPhBX0.25/sat_CsF/G4) containing equal concentrations of LiBOB, TPhBX, and saturated cesium fluoride (CsF) was prepared. The potential effects of reducing the amount of the AA and using a mixture of LiBOB and TPhBX on the electrochemical compatibility of the BiF3 electrode were investigated through cyclic voltammetry, charge–discharge tests, and alternating current impedance measurements. The potential advantages of using the LiBOB/TPhBX mixture as an electrolyte additive include the fact that it increases ionic conductivity, widens the cathodic and anodic stability window, and enhances the electrochemical performance of the BiF3 positive electrode. Moreover, according to Raman microscopy, the direct insertion mechanism was found to be predominant for the FSB reaction mechanism of BiF3 microparticles in LiBOB0.25/TPhBX 0.25/sat_CsF/G4. These improvements can be attributed to the increase in fluorine anion mobility, which occurs when the cesium cation mobility is reduced; this, in turn, is a result of the stabilization of the cesium cation due to the interaction between LiBOB and TPhBX. Therefore, mixing equal concentrations of LiBOB and TPhBX can be a promising alternative method to ensure electrolyte stability and prevent the potential loss of active materials during the redox reactions.

Mechanistic Study and Ligand Design for the Formation of Zinc Formate Complexes from Zinc Hydride Complexes and Carbon Dioxide

Density functional theory (DFT) study of the reactions of mononuclear phenolate diamine zinc hydride complexes and CO2 reveals a direct insertion mechanism with a rate-determining C–H bond formation step. A total of 16 zinc hydride complexes with various functional groups, including 3 experimental structures and 13 newly proposed complexes, have been optimized. The influences of various substituents at different positions, the ring size of nitrogen bidentate ligands, and the ortho groups of nitrogen on the reaction rate are investigated. Computational results indicate that the ortho effect of nitrogen is the most effective factor in reducing the reaction energy barrier, and the complex with isopropyls as the ortho groups of the nitrogen atom has the lowest barrier of 10.9 kcal/mol.

Reactions of Laser-Ablated Zirconium Atoms within a Supersonic Expansion: Insertion versus Radical Mechanism

In a laser ablation type microreactor followed by supersonic expansion, zirconium atoms have been reacted with methyl fluoride, CH(3)F (MeF), and mixtures of MeF and dimethylether, CH(3)-O-CH(3) (DME) seeded in He. With both mixtures, only a number of simple fluorinated products are formed, and they have been identified by one-photon ionization. All products can be linked to radical reactions either with F atoms, CH(3), or ZrF(1, 2, 3) radicals. No insertion products of the Grignard reagent type, F -Zr-CH(3) could be identified with or in the absence of DME. On the other hand, evidence has been found for the presence of organometallic compounds of the type ZrC(2)H(n=2, 4, 6), which could result from radical attack. Thus, even in conditions where intense solvation is at work, induced by clustering with polar DME molecules, which can act as stabilizing agents, a direct insertion mechanism into the C-F bond involving barrier suppression is not at work in our conditions. The reactivity due to radicals is very effective in this type of reactor, and the products that are efficiently formed can be quickly stabilized in the expansion. The radical attack supersedes, in the case of zirconium solvated by DME, the metastable mechanism with Zr(4d)(3)(5s)(1), that is certainly energetically impossible in the absence of strong reaction barrier suppression by a solvent. High level ab initio calculations performed at the CASPT2 level of theory are used for characterizing the electronic and geometric structure of the inserted products. They also reveal striking features of the reaction mechanism that support the absence of observation of inserted products within solvated clusters of zirconium.

Pd-Mediated Activation of Molecular Oxygen: Pd(0) versus Direct Insertion

In developing environmentally benign chemistries, it is most important to use dioxygen directly in lieu of toxic and/or corrosive stoichiometric oxidants. Unfortunately, for many processes such direct oxidations have not yet become practical. To help develop such processes, we elucidate here the mechanism for the reaction of molecular oxygen with toluene-solvated palladium-hydride complex using quantum mechanics (B3LYP/LACVP** with the PBF polarizable continuum solvent model) for Pd(II-)((-)sparteine)(H)(Cl) in the presence of base, specifically focusing on the pathways proceeding through Pd(0). The lowest barrier Pd(0) pathway proceeds through a rate-determining base-assisted deprotonation of the palladium, followed by the association of molecular oxygen and the subsequent loss of chloride, forming the corresponding eta(2)-peroxo-palladium complex. We also examine the spin transition and the completion of the reaction to form PdCl(2) and H2O2. Together with our previously published Pd-H/O2 direct insertion mechanism, these reports provide a complete mapping of the possible pathways for reoxidation of palladium hydride with molecular oxygen. For this particular system, we conclude that direct insertion is preferred (DeltaDeltaH++ = 6.2 kcal/mol, DeltaDeltaG++ = 7.5 kcal/mol) and trace this preference to the bidentate character of sparteine and the lack of pi-accepting ligands. Suggestions are included for how this preference can be switched.

Effect of the geometric phase on the dynamics of the hydrogen-exchange reaction

A recent puzzle in nonadiabatic quantum dynamics is that geometric phase (GP) effects are present in the state-to-state opacity functions of the hydrogen-exchange reaction, but cancel out in the state-to-state integral cross sections (ICSs). Here the authors explain this result by using topology to separate the scattering amplitudes into contributions from Feynman paths that loop in opposite senses around the conical intersection. The clockwise-looping paths pass over one transition state (1-TS) and scatter into positive deflection angles; the counterclockwise-looping paths pass over two transition states (2-TS) and scatter into negative deflection angles. The interference between the 1-TS and 2-TS paths thus integrates to a very small value, which cancels the GP effects in the ICS. Quasiclassical trajectory (QCT) calculations reproduce the scattering of the 1-TS and 2-TS paths into positive and negative deflection angles and show that the 2-TS paths describe a direct insertion mechanism. The inserting atom follows a highly constrained "S-bend" path, which allows it to avoid both the other atoms and the conical intersection and forces the product diatom to scatter into high rotational states. By contrast, the quantum 2-TS paths scatter into a mainly statistical distribution of rotational states, so that the quantum 2-TS total ICS is roughly twice the QCT ICS at 2.3 eV total energy. This suggests that the S-bend constraint is relaxed by tunneling in the quantum system. These findings on H+H(2) suggest that similar cancellations or reductions in GP effects are likely in many other reactions.

Direct ab initio molecular dynamics study of [formula omitted

An ab initio direct molecular dynamics study of the reaction of CH 3 + with benzene has been performed and the mechanism of reaction examined. Ab initio energy and gradient evaluations were done at the QCISD/6-31+G** and MP2/6-31+G** levels. The primary products of reaction were several isomeric forms of arenium ion (σ complex). The reaction proceeds through a single channel, a direct barrierless insertion of a methyl cation into benzene to form a σ complex. The direct insertion mechanism supports a recent quantum chemical study but differs from that posited in earlier experimental and theoretical studies of the reaction, which have assumed formation of a stable π complex. The molecular dynamics simulation shows that product arenium ions are internally energetic enough for a hydrogen to shift about the benzenium ring to form several isomers.

Hydrogen insertion reaction with restricted diffusion. Part 1. Potential step—EIS theory and review for the direct insertion mechanism

Electrochemical impedance spectroscopy (EIS) theory is presented for the direct hydrogen insertion reaction with restricted diffusion. The limiting shapes of the Nyquist impedance plots are given and the changes in the impedance diagrams due to the double-layer capacitance are presented. The responses to small potential steps are also considered. All the limiting expressions for the current transients are given and a kinetic zone diagram is plotted in the time domain to determine the conditions of validity of these expressions. The correspondences between EIS diagrams and current transients due to small potential steps are shown. The results obtained for small potential steps are finally generalized to large steps when a Langmuir insertion isotherm is considered and the hydrogen diffusion coefficient is assumed to be constant.

The direct insertion mechanism in Ziegler-Natta polymerization: a theoretical study of Cp2TiCH3+ + C2H4 .fwdarw. Cp2TiC3H7+

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe direct insertion mechanism in Ziegler-Natta polymerization: a theoretical study of Cp2TiCH3+ + C2H4 .fwdarw. Cp2TiC3H7+Cynthia A. Jolly and Dennis S. MarynickCite this: J. Am. Chem. Soc. 1989, 111, 20, 7968–7974Publication Date (Print):September 1, 1989Publication History Published online1 May 2002Published inissue 1 September 1989https://doi.org/10.1021/ja00202a043RIGHTS & PERMISSIONSArticle Views350Altmetric-Citations112LEARN 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 (847 KB) Get e-Alerts Get e-Alerts

Evidence against an abstraction or direct insertion mechanism for cytochrome P-450 catalysed meta hydroxylations

Warfarin, specifically labeled with deuterium in the 7 position, was incubated with liver microsomes from untreated rats or rats which were pretreated with either phenobarbital of β-napthoflavone. The four phenolic metabolites (6-, 7-, 8- and 4′-hydroxywarfarin) were isolated and quantitated by GC MS and the percent deuterium retention calculated. In all induction states the 7-hydroxy metabolite of (7, 2H)warfarin retained greater than 77% of the deuterium. These results suggest that hydroxylation at the 7 position (meta hydroxylation) cannot proceed by either a direct insertion or abstraction mechanism.