Stability and C-H Bond Activation Reactions of Palladium(I) and Platinum(I) Metalloradicals: Carbon-to-Metal H-Atom Transfer and an Organometallic Radical Rebound Mechanism.

One-electron oxidation of palladium(0) and platinum(0) bis(phosphine) complexes enables isolation of a homologous series of linear d metalloradicals of the form [M(PR)] (M = Pd, Pt; R = Bu, Ad), which are stable in 1,2-difluorobenzene (DFB) solution for >1 day at room temperature when partnered with the weakly coordinating [BAr] (Ar = 3,5-(CF)CH) counterion. The metalloradicals exhibit reduced stability in THF, decreasing in the order palladium(I) > platinum(I) and PAd > PBu, especially in the case of [Pt(PBu)], which is converted into a 1:1 mixture of the platinum(II) complexes [Pt(PBuCMeCH)(PBu)] and [Pt(PBu)H] upon dissolution at room temperature. Cyclometalation of [Pt(PBu)] can also be induced by reaction with the 2,4,6-tri-butylphenoxyl radical in DFB, and a common radical rebound mechanism involving carbon-to-metal H-atom transfer and formation of an intermediate platinum(III) hydride complex, [Pt(PBuCMeCH)H(PBu)], has been substantiated by computational analysis.

Demetallization of Sewage Sludge Using Low-Cost Ionic Liquids.

Sludge produced from wastewater treatment has little to no value and is typically treated through volume reduction techniques, such as dewatering, thickening, or digestion. However, these methods inherently increase heavy metal concentrations, which makes the sludge unsuitable for land spreading and difficult to dispose of, owing to strict legal requirements/regulations concerning these metals. We addressed this problem, for the first time, by using recyclable low-cost protic ionic liquids to complex these toxic metals through a chemical fractionation process.

Comparison of fast electron transfer kinetics at platinum, gold, glassy carbon and diamond electrodes using Fourier-transformed AC voltammetry and scanning electrochemical microscopy.

Heterogeneous electron transfer (ET) processes at electrode/electrolyte interfaces are of fundamental and applied importance and are extensively studied by a range of electrochemical techniques, all of which have various attributes but also limitations. The present study focuses on the one-electron oxidation of tetrathiafulvalene (TTF) and reduction of tetracyanoquinodimethane (TCNQ) in acetonitrile solution by two powerful electrochemical techniques: Fourier-transformed large amplitude alternating current voltammetry (FTACV); and scanning electrochemical microscopy (SECM), both of which are supported by detailed theoretical models. At conventional Pt, Au and glassy carbon (GC) electrode materials, the apparent (overall) charge transfer kinetic values determined by FTACV give standard ET rate constants, k, that are fast and close to the reversible limit.

Probing Electrode Heterogeneity Using Fourier-Transformed Alternating Current Voltammetry: Application to a Dual-Electrode Configuration.

Quantitative studies of electron transfer processes at electrode/electrolyte interfaces, originally developed for homogeneous liquid mercury or metallic electrodes, are difficult to adapt to the spatially heterogeneous nanostructured electrode materials that are now commonly used in modern electrochemistry. In this study, the impact of surface heterogeneity on Fourier-transformed alternating current voltammetry (FTACV) has been investigated theoretically under the simplest possible conditions where no overlap of diffusion layers occurs and where numerical simulations based on a 1D diffusion model are sufficient to describe the mass transport problem. Experimental data that meet these requirements can be obtained with the aqueous [Ru(NH)] redox process at a dual-electrode system comprised of electrically coupled but well-separated glassy carbon (GC) and boron-doped diamond (BDD) electrodes.

Electrochemistry of Fe at highly oriented pyrolytic graphite (HOPG) electrodes: kinetics, identification of major electroactive sites and time effects on the response.

The electrochemistry of the Fe redox couple has been studied on highly oriented pyrolytic graphite (HOPG) samples that differ in step edge density by 2 orders of magnitude, to elucidate the effect of surface structure on the electron transfer (ET) kinetics. Macroscopic cyclic voltammetry measurements in a droplet-cell arrangement, highlight that the Fe process is characterised by slow ET kinetics on HOPG and that step edge coverage has little effect on the electrochemistry of Fe. A standard heterogeneous ET rate constant of ∼5 × 10 cm s for freshly cleaved HOPG was derived from simulation of the experimental results, which fell into the range of the values reported for metal electrodes, e.

One-Electron Oxidation of [M(P(t) Bu3 )2 ] (M=Pd, Pt): Isolation of Monomeric [Pd(P(t) Bu3 )2 ](+) and Redox-Promoted C-H Bond Cyclometalation.

Oxidation of zero-valent phosphine complexes [M(P(t) Bu3 )2 ] (M=Pd, Pt) has been investigated in 1,2-difluorobenzene solution using cyclic voltammetry and subsequently using the ferrocenium cation as a chemical redox agent. In the case of palladium, a mononuclear paramagnetic Pd(I) derivative was readily isolated from solution and fully characterized (EPR, X-ray crystallography). While in situ electrochemical measurements are consistent with initial one-electron oxidation, the heavier congener undergoes C-H bond cyclometalation and ultimately affords the 14 valence-electron Pt(II) complex [Pt(κ(2) PC -P(t) Bu2 CMe2 CH2 )(P(t) Bu3 )](+) with concomitant formation of [Pt(P(t) Bu3 )2 H](+) .

Impact of Adsorption on Scanning Electrochemical Microscopy Voltammetry and Implications for Nanogap Measurements.

Scanning electrochemical microscopy (SECM) is a powerful tool that enables quantitative measurements of fast electron transfer (ET) kinetics when coupled with modeling predictions from finite-element simulations. However, the advent of nanoscale and nanogap electrode geometries that have an intrinsically high surface area-to-solution volume ratio realizes the need for more rigorous data analysis procedures, as surface effects such as adsorption may play an important role. The oxidation of ferrocenylmethyl trimethylammonium (FcTMA(+)) at highly oriented pyrolytic graphite (HOPG) is used as a model system to demonstrate the effects of reversible reactant adsorption on the SECM response.

Redox-dependent spatially resolved electrochemistry at graphene and graphite step edges.

The electrochemical (EC) behavior of mechanically exfoliated graphene and highly oriented pyrolytic graphite (HOPG) is studied at high spatial resolution in aqueous solutions using Ru(NH3)6(3+/2+) as a redox probe whose standard potential sits close to the intrinsic Fermi level of graphene and graphite. When scanning electrochemical cell microscopy (SECCM) data are coupled with that from complementary techniques (AFM, micro-Raman) applied to the same sample area, different time-dependent EC activity between the basal planes and step edges is revealed. In contrast, other redox couples (ferrocene derivatives) whose potential is further removed from the intrinsic Fermi level of graphene and graphite show uniform and high activity (close to diffusion-control).

Comparison and reappraisal of carbon electrodes for the voltammetric detection of dopamine.

The electro-oxidation of dopamine (DA) is investigated on the unmodified surfaces of five different classes of carbon electrodes: glassy carbon (GC), oxygen-terminated polycrystalline boron-doped diamond (pBDD), edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG), and the basal surface of highly oriented pyrolytic graphite (HOPG), encompassing five distinct grades with step edge density and coverage varying by more than 2 orders of magnitude. Surfaces were prepared carefully and characterized by a range of techniques, including atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and Raman spectroscopy. Although pBDD was found to be the least susceptible to surface fouling (even at relatively high DA concentrations), the reaction showed sluggish kinetics on this electrode.

Epinephrine electro-oxidation highlights fast electrochemistry at the graphite basal surface.

Macroscale and nanoscale measurements of epinephrine electro-oxidation at graphite electrodes, with different step edge densities, demonstrate unequivocally that the reaction occurs readily at the basal surface, and that step edges are not required for molecular electrocatalysis, in contrast to the current literature model.