[Sb(C₆F₅)₄][B(C₆F₅)₄]: An Air Stable, Lewis Acidic Stibonium Salt That Activates Strong Element-Fluorine Bonds

As part of our ongoing interest in main group Lewis acids for fluoride anion complexation and element-fluorine bond activation, we have synthesized the stibonium borate salt [Sb­(C₆F₅)₄]­[B­(C₆F₅)₄] (<b>3</b>). The perfluorinated stibonium cation [Sb­(C₆F₅)₄]⁺ present in this salt is a potent Lewis acid which abstracts a fluoride anion from [SbF₆]⁻ and [BF­(C₆F₅)₃]⁻ indicating that it is a stronger Lewis acid than SbF₅ and B­(C₆F₅)₃. The unusual Lewis acidic properties of <b>3</b> are further reflected by its ability to polymerize THF or to promote the hydrodefluorination of fluoroalkanes in the presence of Et₃SiH. While highly reactive in solution, <b>3</b> is a perfectly air stable salt, making it a convenient Lewis acidic reagent

Multimetallic Complexes Featuring a Bridging <i>N</i>‑heterocyclic Phosphido/Phosphenium Ligand: Synthesis, Structure, and Theoretical Investigation

By incorporating an N-heterocyclic phosphenium/phosphide (NHP) ligand into a chelating pincer ligand framework (PPP⁺/PPP^–), we have elucidated several different and unprecedented binding modes of NHP ligands in homobimetallic, heterobimetallic, and trimetallic metal complexes. One-electron reduction of the previously reported (PPP)⁻/M^II complexes (PPP)­M-Cl (M = Pd (<b>1</b>), Pt (<b>2</b>)) results in clean formation of the symmetric homobimetallic M^I/M^I complexes [(μ-PPP)­Pd]₂ (<b>5</b>) and [(μ-PPP)­Pt]₂ (<b>6</b>). The tridentate NHP ligand has also been utilized as a bridging linker in the M/Co heterobimetallic compounds (OC)₃Co­(u-PPP)­M­(CO) (M = Pd (<b>7</b>), Pt (<b>8</b>)), synthesized via salt elimination from mixtures of <b>1</b> and <b>2</b> and Na­[Co­(CO)₄]. Furthermore, an NHP-bridged trimetallic complex (PPP)₂Pd₃Cl₂ (<b>9</b>) can be synthesized in a manner similar to precursor <b>1</b> (Pd­(PPh₃)₄ + (PPP)­Cl) via careful adjustment of reaction stoichiometry. Examination of the interatomic distances and angles in complexes<b> 5</b>–<b>9</b>, in tandem with density functional theory calculations have been used to evaluate and characterize the bonding interactions in these complexes

N-Heterocyclic Phosphenium Ligands as Sterically and Electronically-Tunable Isolobal Analogues of Nitrosyls

The coordination chemistry of an N-heterocyclic phosphenium (NHP)-containing bis­(phosphine) pincer ligand has been explored with Pt⁰ and Pd⁰ precursors. Unlike previous compounds featuring monodentate NHP ligands, the resulting NHP Pt and Pd complexes feature pyramidal geometries about the central phosphorus atom, indicative of a stereochemically active lone pair. Structural, spectroscopic, and computational data suggest that the unusual pyramidal NHP geometry results from two-electron reduction of the phosphenium ligand to generate transition metal complexes in which the Pt or Pd centers have been formally oxidized by two electrons. Interconversion between planar and pyramidal NHP geometries can be affected by either coordination/dissociation of a two-electron donor ligand or two-electron redox processes, strongly supporting an isolobal analogy with the linear (NO⁺) and bent (NO^–) variations of nitrosyl ligands. In contrast to nitrosyls, however, these new main group noninnocent ligands are sterically and electronically tunable and are amenable to incorporation into chelating ligands, perhaps representing a new strategy for promoting redox transformations at transition metal complexes

N-Heterocyclic Phosphenium Ligands as Sterically and Electronically-Tunable Isolobal Analogues of Nitrosyls

The coordination chemistry of an N-heterocyclic phosphenium (NHP)-containing bis­(phosphine) pincer ligand has been explored with Pt⁰ and Pd⁰ precursors. Unlike previous compounds featuring monodentate NHP ligands, the resulting NHP Pt and Pd complexes feature pyramidal geometries about the central phosphorus atom, indicative of a stereochemically active lone pair. Structural, spectroscopic, and computational data suggest that the unusual pyramidal NHP geometry results from two-electron reduction of the phosphenium ligand to generate transition metal complexes in which the Pt or Pd centers have been formally oxidized by two electrons. Interconversion between planar and pyramidal NHP geometries can be affected by either coordination/dissociation of a two-electron donor ligand or two-electron redox processes, strongly supporting an isolobal analogy with the linear (NO⁺) and bent (NO^–) variations of nitrosyl ligands. In contrast to nitrosyls, however, these new main group noninnocent ligands are sterically and electronically tunable and are amenable to incorporation into chelating ligands, perhaps representing a new strategy for promoting redox transformations at transition metal complexes

Isolation of N‑Heterocyclic Alkyl Intermediates en Route to Transition Metal N‑Heterocyclic Carbene Complexes: Insight into a C–H Activation Mechanism

An imidazolinium cation has been incorporated into an arene-linked diphosphine pincer ligand, <b>[2]</b>^<b>+</b>, and the metalation of this ligand has been investigated via direct imidazolinium C–H activation to Pd⁰ and Pt⁰. The expected NHC-ligated metal-hydride species <b>[5]­PF</b>_<b>6</b> (M = Pt) and <b>6</b> (M = Pd) are obtained if the halide-free imidazolinium salt <b>[2]­PF</b>_<b>6</b> is used. In contrast, treatment of the imidazolinium chloride salt <b>[2]­Cl</b> with M­(PPh₃)₄ leads to isolation of N-heterocyclic alkyl M^II species <b>3</b> (M = Pd) and <b>4</b> (M = Pt), in which the imidazolinium C–H bond remains intact. Interestingly, there are no apparent agostic interactions between the imidazolinium protons and the metal centers in <b>3</b> and <b>4</b>, indicating that these species represent an unusual type of arrested C–H activation intermediate. While Pd complex <b>3</b> is thermally stable, Pt complex <b>4</b> undergoes C–H activation to afford the corresponding NHC-Pt^II-hydride species <b>[5]­Cl</b> upon heating. Additionally, both complexes <b>3</b> and <b>4</b> undergo rapid C–H activation upon abstraction of the metal-bound halide to form <b>6</b> and <b>[5]­PF</b>_<b>6</b>, respectively. The nature of the bonding in the unusual N-heterocyclic alkyl species is investigated computationally

Isolation of N‑Heterocyclic Alkyl Intermediates en Route to Transition Metal N‑Heterocyclic Carbene Complexes: Insight into a C–H Activation Mechanism

An imidazolinium cation has been incorporated into an arene-linked diphosphine pincer ligand, <b>[2]</b>^<b>+</b>, and the metalation of this ligand has been investigated via direct imidazolinium C–H activation to Pd⁰ and Pt⁰. The expected NHC-ligated metal-hydride species <b>[5]­PF</b>_<b>6</b> (M = Pt) and <b>6</b> (M = Pd) are obtained if the halide-free imidazolinium salt <b>[2]­PF</b>_<b>6</b> is used. In contrast, treatment of the imidazolinium chloride salt <b>[2]­Cl</b> with M­(PPh₃)₄ leads to isolation of N-heterocyclic alkyl M^II species <b>3</b> (M = Pd) and <b>4</b> (M = Pt), in which the imidazolinium C–H bond remains intact. Interestingly, there are no apparent agostic interactions between the imidazolinium protons and the metal centers in <b>3</b> and <b>4</b>, indicating that these species represent an unusual type of arrested C–H activation intermediate. While Pd complex <b>3</b> is thermally stable, Pt complex <b>4</b> undergoes C–H activation to afford the corresponding NHC-Pt^II-hydride species <b>[5]­Cl</b> upon heating. Additionally, both complexes <b>3</b> and <b>4</b> undergo rapid C–H activation upon abstraction of the metal-bound halide to form <b>6</b> and <b>[5]­PF</b>_<b>6</b>, respectively. The nature of the bonding in the unusual N-heterocyclic alkyl species is investigated computationally

Role of Chloride for a Simple, Non-Grignard Mg Electrolyte in Ether-Based Solvents

Mg battery operates with Chevrel phase (Mo₆S₈, ∼1.1 V vs Mg) cathodes that apply Grignard-based or derived electrolytes, which allow etching of the passivating oxide coating forms at the magnesium metal anode. Majority of Mg electrolytes studied to date are focused on developing new synthetic strategies to achieve a better reversible Mg deposition. While most of these electrolytes contain chloride as a component, and there is a lack of literature which investigates the fundamental role of chloride in Mg electrolytes. Further, ease of preparation and potential safety benefits have made simple design of magnesium electrolytes an attractive alternative to traditional air sensitive Grignard reagents-based electrolytes. Work presented here describes simple, non-Grignard magnesium electrolytes composed of magnesium bis­(trifluoromethane sulfonyl)­imide mixed with magnesium chloride (Mg­(TFSI)₂-MgCl₂) in tetrahydrofuran (THF) and diglyme (G2) that can reversibly plate and strip magnesium. Based on this discovery, the effect of chloride in the electrolyte complex was investigated. Electrochemical properties at different initial mixing ratios of Mg­(TFSI)₂ and MgCl₂ showed an increase of both current density and columbic efficiency for reversible Mg deposition as the fraction content of MgCl₂ increased. A decrease in overpotential was observed for rechargeable Mg batteries with electrolytes with increasing MgCl₂ concentration, evidenced by the coin cell performance. In this work, the fundamental understanding of the operation mechanisms of rechargeable Mg batteries with the role of chloride content from electrolyte could potentially bring rational design of simple Mg electrolytes for practical Mg battery

Role of Manganese Deposition on Graphite in the Capacity Fading of Lithium Ion Batteries

Lithium ion batteries utilizing manganese-based cathodes have received considerable interest in recent years for their lower cost and more favorable environmental friendliness relative to their cobalt counterparts. However, Li ion batteries using these cathodes combined with graphite anodes suffer from severe capacity fading at high operating temperatures. In this paper, we report on how the dissolution of manganese impacts the capacity fading within the Li ion batteries. Our investigation reveals that the manganese dissolves from the cathode, transports to the graphite electrode, and deposits onto the outer surface of the innermost solid-electrolyte interphase layer, which is known to be a mixture of inorganic salts (e.g., Li₂CO₃, LiF, and Li₂O). In this location, the manganese facilitates the reduction of the electrolyte and the subsequent formation of lithium-containing products on the graphite, which removes lithium ions from the normal operation of the cell and thereby induces the severe capacity fade

Origin of Electrochemical, Structural, and Transport Properties in Nonaqueous Zinc Electrolytes

Through coupled experimental analysis and computational techniques, we uncover the origin of anodic stability for a range of nonaqueous zinc electrolytes. By examination of electrochemical, structural, and transport properties of nonaqueous zinc electrolytes with varying concentrations, it is demonstrated that the acetonitrile–Zn­(TFSI)₂, acetonitrile–Zn­(CF₃SO₃)₂, and propylene carbonate–Zn­(TFSI)₂ electrolytes can not only support highly reversible Zn deposition behavior on a Zn metal anode (≥99% of Coulombic efficiency) but also provide high anodic stability (up to ∼3.8 V vs Zn/Zn²⁺). The predicted anodic stability from DFT calculations is well in accordance with experimental results, and elucidates that the solvents play an important role in anodic stability of most electrolytes. Molecular dynamics (MD) simulations were used to understand the solvation structure (e.g., ion solvation and ionic association) and its effect on dynamics and transport properties (e.g., diffusion coefficient and ionic conductivity) of the electrolytes. The combination of these techniques provides unprecedented insight into the origin of the electrochemical, structural, and transport properties in nonaqueous zinc electrolytes